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Niu G, Zoellner MH, Schroeder T, Schaefer A, Jhang JH, Zielasek V,Bäumer M, Wilkens H, Wollschläger J, Olbrich R, Lammers C and Reichling M (2015), Controlling the physics and chemistry of binary and ternary praseodymium and cerium oxide systems, Phys. Chem. Chem. Phys. 17, 24513
Abstract: Rare earth praseodymium and cerium oxides have attracted intense research interest in the last few decades, due to their intriguing chemical and physical characteristics. An understanding of the correlation between structure and properties, in particular the surface chemistry, is urgently required for their application in microelectronics, catalysis, optics and other fields. Such an understanding is, however, hampered by the complexity of rare earth oxide materials and experimental methods for their characterisation. Here, we report recent progress in studying high-quality, single crystalline, praseodymium and cerium oxide films as well as ternary alloys grown on Si(111) substrates. Using these well-defined systems and based on a systematic multitechnique surface science approach, the corresponding physical and chemical properties, such as the surface structure, the surface morphology, the bulk-surface interaction and the oxygen storage/release capability, are explored in detail. We show that specifically the crystalline structure and the oxygen stoichiometry of the oxide thin films can be well controlled by the film preparation method. This work leads to a comprehensive understanding of the properties of rare earth oxides and highlights the applications of these versatile materials. Furthermore, methanol adsorption studies are performed on binary and ternary rare earth oxide thin films, demonstrating the feasibility of employing such systems for model catalytic studies. Specifically for ceria systems, we find considerable stability against normal environmental conditions so that they can be considered as a "materials bridge" between surface science models and real catalysts.
BibTeX:
@article{PhysChemChemPhys17p24513(2015)_Niu,
  author = {G. Niu, M. H. Zoellner, T. Schroeder, A. Schaefer, J. H. Jhang, V. Zielasek, M. Bäumer, H. Wilkens, J. Wollschläger, R. Olbrich, C. Lammers, and M. Reichling},
  title = {Controlling the physics and chemistry of binary and ternary praseodymium and cerium oxide systems},
  journal = {Phys. Chem. Chem. Phys.},
  year = {2015},
  volume = {17},
  pages = {24513},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysChemChemPhys17p24513(2015)_Niu.pdf},
  doi = {10.1039/c5cp02283e}
}
Schmidsfeld A von and Reichling M (2015), Controlling the opto-mechanics of a cantilever in an interferometer via cavity loss, Appl. Phys. Lett. 107, 123111
Abstract: In a non-contact atomic force microscope, based on interferometric cantilever displacement detection, the optical return loss of the system is tunable via the distance between the fiber end and the cantilever. We utilize this for tuning the interferometer from a predominant Michelson to a predominant Fabry-Perot characteristics and introduce the Fabry-Perot enhancement factor as a quantitative measure for multibeam interference in the cavity. This experimentally easily accessible and adjustable parameter provides a control of the opto-mechanical interaction between the cavity light field and the cantilever. The quantitative assessment of the light pressure acting on the cantilever oscillating in the cavity via the frequency shift allows an in-situ measurement of the cantilever stiffness with remarkable precision.
BibTeX:
@article{ApplPhysLett107p123111(2015)_Schmidsfeld,
  author = {Schmidsfeld, Alexander von and Reichling, Michael},
  title = {Controlling the opto-mechanics of a cantilever in an interferometer via cavity loss},
  journal = {Appl. Phys. Lett.},
  year = {2015},
  volume = {107},
  pages = {123111},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ChemPhysLett640p72(2015)_Dyachenko.pdf},
  doi = {10.1063/1.4931702}
}
Dyachenko O, Diek N, Shapiro Y, Tamang R, Harneit W, Reichling M and Borodin A (2015), A diamond (1 0 0) surface with perfect phase purity, Chem. Phys. Lett. 640, pp. 72-76
Abstract: Diamond surfaces with (1 0 0) orientation and perfect phase purity regarding the coexistence of sp3 and sp2 bonding as well as near surface nitrogen implanted layers are repeatedly produced from onesample by a cycle of nitrogen implantation, etching in oxygen and wet chemical etching. Comprehensivesurface studies carried out by X-ray photoelectron spectroscopy (XPS) involving a deconvolution of theC 1s peak into contributions of C sp3, C sp2 and C sp3(N) reveal the surface and near-surface phase andstoichiometry. It is demonstrated that efficient etching of nitrogen implanted diamond occurs by hightemperature annealing in oxygen and a wet chemical treatment.
BibTeX:
@article{ChemPhysLett640p72(2015)_Dyachenko,
  author = {Dyachenko, Oleksiy and Diek, Nadine and Shapiro, Yevgeniy and Tamang, Rajesh  and Harneit, Wolfgang and Reichling, Michael and Borodin, Andriy},
  title = {A diamond (1 0 0) surface with perfect phase purity},
  journal = {Chem. Phys. Lett.},
  year = {2015},
  volume = {640},
  pages = {72-76},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ChemPhysLett640p72(2015)_Dyachenko.pdf},
  doi = {10.1016/j.cplett.2015.10.015}
}
Bollmann TRJ, Antipina LY, Temmen M, Reichling M, Sorokin PB (2015), Hole doping of mechanically exfoliated graphene by confined hydration layers, Nano Res. Vol. 63, pp. 1.
Abstract: By the use of non-contact Atomic Force Microscopy (NC-AFM) and Kelvin Probe Force Microscopy (KPFM), we measure the local surface potential of graphene mechanically exfoliated on CaF2(111) as a prototype insulating surface. The hydration layers confined between graphene and substrate, resulting from preparation under ambient conditions on the hydrophilic surface are found to electronically modify the graphene as electron-density is transferred from graphene to the hydration layer. Density Functional Theory (DFT) calculations predict that the first 2 to 3 water layers adjacent to the graphene hole dope graphene by several percent of a unit charge per unit cell.
BibTeX:
@article{NanoRes63p1(2015)_Bollmann,
  author = {Bollmann, Tjeerd R. J. and Antipina, Liubov Yu. and Temmen, Matthias and Reichling, Michael and Sorokin, Pavel B.},
  title = {Hole doping of mechanically exfoliated graphene by confined hydration layers},
  journal = {Nano Res.},
  year = {2015},
  volume = {63},
  pages = {1-9},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=NanoRes63p1(2015)_Bollmann.pdf},
  doi = {10.1007/s12274-015-0807-x}
}
Temmen M, Ochedowski O, Schleberger M, Reichling M and Bollmann TRJ (2014), Hydration layers trapped between graphene and a hydrophilic substrate, New J. Phys. Vol. 16, pp. 053039.
Abstract: Graphene is mechanically exfoliated on CaF2(111) under ambient conditions. We demonstrate the formation of a several monolayer thick hydration layer on the hydrophilic substrate and its response to annealing at temperatures up to 750 K in an ultra-high vacuum environment. Upon heating, water is released, however, it is impossible to remove the first layer. The initially homogeneous film separates into water-containing and water-free domains by two-dimensional Ostwald ripening. Upon severe heating, thick graphene multilayers undergo rupture, while nanoblisters confining sealed water appear on thinner sheets, capable of the storage and release of material. From modeling the dimensions of the nanoblisters, we estimate the graphene/CaF2(111) interfacial adhesion energy to be 0.33 ± 0.13 J m-2, thereby viable for polymer-assisted transfer printing.
BibTeX:
@article{NJP16p053039(2014)_Temmen,
  author = {M. Temmen and O. Ochedowski and and M. Schleberger and M. Reichling and T.R.J. Bollmann},
  title = {Hydration layers trapped between graphene and a hydrophilic substrate},
  journal = {New J. Phys.},
  year = {2014},
  volume = {16},
  pages = {053039},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=NJP16p053039(2014)_Temmen.pdf},
  doi = {10.1088/1367-2630/16/5/053039}
}
Olbrich R, Pieper HH, Oelke R, Wilkens H, Wollschläger J, Zoellner MH, Schroeder T and Reichling M (2014), A well-structured metastable ceria surface, Appl. Phys. Lett. Vol. 104, pp. 081910.
Abstract: By the growth of a 180 nm thick film on Si(111), we produce a metastable ceria surface with a morphology dominated by terraced pyramids with an oriented triangular base. Changes in the nanoscale surface morphology and local surface potential due to annealing at temperatures ranging from 300K to 1150K in the ultra-high vacuum are studied with non-contact atomic force microscopy and Kelvin probe force microscopy. As the surface is stable in the temperature range of 300K to 850 K, it is most interesting for applications requiring regular steps with a height of one O-Ce-O triple layer.
BibTeX:
@article{ApplPhysLett104p081910(2014)_Olbrich,
  author = {R. Olbrich and H.H. Pieper and R. Oelke and H. Wilkens and J. Wollschläger and M.H. Zoellner and T. Schroeder and M. Reichling},
  title = {A well-structured metastable ceria surface},
  journal = {Appl. Phys. Lett.},
  year = {2013},
  volume = {104},
  pages = {081910},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysLett104p081910(2014)_Olbrich.pdf},
  doi = {10.1063/1.4866667}
}
Tröger L, Pieper HH, and Reichling M (2013), Concept for support and heating of plate-like samples in the ultra-high vacuum, Rev. Sci. Instrum. Vol. 84, pp. 013703.
Abstract: We present the concept for a sample holder designed for mounting and heating of plate-like samples that is based on a clamping mechanism for easy handling. The clamping mechanism consists of a U-shaped bracket encompassing the sample support plate from the rear. Two spring wires are fixed in the walls of the bracket spanning the sample to secure it with only two point contacts. This enables the sample to freely expand or contract during heating and cooling. To accommodate for a large variety in sample size, shape, and quality, we introduce two designs differing in the generation of the clamping force: One pressing the sample against the spring wires, the other one pulling the spring wires onto the sample. Both designs yield an automatically even alignment of the sample during the mounting process to achieve an even load distribution and reliable fixation specifically for brittle samples. For high temperature treatment, the sample holders are enhanced by a resistive heating plate. As only the sample and a small fraction of the sample holder are heated, temperatures of 1300° C are reached with only 8 W heating power. The sample support and heating components are mounted on a 11 mm x 13 mm base plate with a handle that can be transferred between the sample entry stage, the preparation stage, and surface science experiments in the ultra-high vacuum system.
BibTeX:
@article{RevSciInstrum84p013703(2013)_Tröger,
  author = {L. Tröger and H.H. Pieper and M. Reichling},
  title = {Concept for support and heating of plate-like samples in the ultra-high vacuum},
  journal = {Rev. Sci. Instrum.},
  year = {2013},
  volume = {84},
  pages = {013703},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=RevSciInstrum84p013703(2013)_Troger.pdf},
  doi = {10.1063/1.4769994}
}
Lübbe J, Temmen M, Rahe P, Kühnle A and Reichling M (2013), Determining cantilever stiffness from thermal noise, Beilstein J. Nanotech. Vol. 4, pp. 227-233.
Abstract: We critically discuss the extraction of intrinsic cantilever properties, namely eigenfrequency f(n), quality factor Q(n) and specifically the stiffness k(n) of the nth cantilever oscillation mode from thermal noise by an analysis of the power spectral density of displacement fluctuations of the cantilever in contact with a thermal bath. The practical applicability of this approach is demonstrated for several cantilevers with eigenfrequencies ranging from 50 kHz to 2 MHz. As such an analysis requires a sophisticated spectral analysis, we introduce a new method to determine kn from a spectral analysis of the demodulated oscillation signal of the excited cantilever that can be performed in the frequency range of 10 Hz to 1 kHz regardless of the eigenfrequency of the cantilever. We demonstrate that the latter method is in particular useful for noncontact atomic force microscopy (NC-AFM) where the required simple instrumentation for spectral analysis is available in most experimental systems.
BibTeX:
@article{BeilsteinJNanotech4p227(2013)_Luebbe,
  author = {J. Lübbe and M. Temmen and and P. Rahe and A. Kühnle and M. Reichling},
  title = {Determining cantilever stiffness from thermal noise},
  journal = {Beilstein J. Nanotech.},
  year = {2013},
  volume = {4},
  pages = {227-233},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=BeilsteinJNanotech4p227(2013)_Luebbe.pdf},
  doi = {10.3762/Bjnano.4.23}
}
Temmen M, Ochedowski O, Bussmann BK, Schleberger M, Reichling M and Bollmann TRJ (2013), Routes to rupture and folding of graphene on rough 6H-SiC(0001) and their identification, Beilstein J. Nanotech. Vol. 4, pp. 625-631.
Abstract: Twisted few layer graphene (FLG) is highly attractive from an application point of view, due to its extraordinary electronic properties. In order to study its properties, we demonstrate and discuss three different routes to in situ create and identify (twisted) FLG. Single layer graphene (SLG) sheets mechanically exfoliated under ambient conditions on 6H-SiC(0001) are modified by (i) swift heavy ion (SHI) irradiation, (ii) by a force microscope tip and (iii) by severe heating. The resulting surface topography and the surface potential are investigated with non-contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM). SHI irradiation results in rupture of the SLG sheets, thereby creating foldings and bilayer graphene (BLG). Applying the other modification methods creates enlarged (twisted) graphene foldings that show rupture along preferential edges of zigzag and armchair type. Peeling at a folding over an edge different from a low index crystallographic direction can result in twisted BLG, showing a similar height as Bernal (or AA-stacked) BLG in NC-AFM images. The rotational stacking can be identified by a significant contrast in the local contact potential difference (LCPD) measured by KPFM.
BibTeX:
@article{BeilsteinJNanotech4p625(2013)_Temmen,
  author = {M. Temmen and O. Ochedowski and B.K. Bussmann and M. Schleberger and M. Reichling and T.R.J. Bollmann},
  title = {Routes to rupture and folding of graphene on rough 6H-SiC(0001) and their identification},
  journal = {Beilstein J. Nanotech.},
  year = {2013},
  volume = {4},
  pages = {625-631},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=BeilsteinJNanotech4p625(2013)_Temmen.pdf},
  doi = {10.3762/bjnano.4.69}
}
Wilkens H, Schuckmann O, Oelke R, Gevers S, Reichling M, Schaefer A, Bäumer M, Zoellner MH, Niu G, Schroeder T and Wollschläger J (2013), Structural transitions of epitaxial ceria films on Si(111), Phys. Chem. Chem. Phys. Vol. 15, pp. 18589-18599.
Abstract: The structural changes of a (111) oriented CeO2 film grown on a Si(111) substrate covered with a hex-Pr2O3(0001) interface layer due to post deposition annealing are investigated. X-ray photoelectron spectroscopy measurements revealing the near surface stoichiometry show that the film reduces continuously upon extended heat treatment. The film is not homogeneously reduced since several coexisting crystalline ceria phases are stabilized due to subsequent annealing at different temperatures as revealed by high resolution low energy electron diffraction and X-ray diffraction. The electron diffraction measurements show that after annealing at 660° C the l-phase (Ce7O12) is formed at the surface which exhibits a (v7 x v7)R19.1° surface structure. Furthermore, a v27 x v27)R30° with a stoichiometry close to Ce2O3 is stabilized after annealing at 860° C which cannot be attributed to any bulk phase of ceria stable at room temperature. In addition, it is shown that the fully reduced ceria (Ce2O3) film exhibits a bixbyite structure. Polycrystalline silicate (CeSixOy) and crystalline silicide (CeSi1.67) are formed at 850° C and detected at the surface after annealing above 900° C.
BibTeX:
@article{ApplPhysChemChemPhys15p18589(2013)_Wilkens,
  author = {H. Wilkens and O. Schuckmann and R. Oelke and S. Gevers and M. Reichling and A. Schaefer and M. Bäumer and M.H. Zoellner and G. Niu and T. Schroeder and J. Wollschläger},
  title = {Structural transitions of epitaxial ceria films on Si(111)},
  journal = {Physical Chemistry Chemical Physics},
  publisher = {Phys. Chem. Chem. Phys.},
  year = {2013},
  volume = {15},
  pages = {18589-18599},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysChemChemPhys15p18589(2013)_Wilkens.pdf},
  doi = {10.1039/c3cp52688g}
}
Rahe P, Kittelmann M, Neff JL, Nimmrich M, Reichling M, Maass P and Kühnle A (2013), Tuning molecular self-assembly on bulk insulator surfaces by anchoring of the organic building blocks, Adv. Mater. Vol. 25, pp. 3948–3956.
Abstract: Molecular self-assembly constitutes a versatile strategy for creating functional structures on surfaces. Tuning the subtle balance between intermolecular and molecule-surface interactions allows structure formation to be tailored at the single-molecule level. While metal surfaces usually exhibit interaction strengths in an energy range that favors molecular self-assembly, dielectric surfaces having low surface energies often lack sufficient interactions with adsorbed molecules. As a consequence, application-relevant, bulk insulating materials pose significant challenges when considering them as supporting substrates for molecular self-assembly. Here, the current status of molecular self-assembly on surfaces of wide-bandgap dielectric crystals, investigated under ultrahigh vacuum conditions at room temperature, is reviewed. To address the major issues currently limiting the applicability of molecular self-assembly principles in the case of dielectric surfaces, a systematic discussion of general strategies is provided for anchoring organic molecules to bulk insulating materials.
BibTeX:
@article{AdvMater25p3948(2013)_Rahe,
  author = {P. Rahe and M. Kittelmann and J. L. Neff and M. Nimmrich and M. Reichling and P. Maass and A. Kühnle},
  title = {Tuning molecular self-assembly on bulk insulator surfaces by anchoring of the organic building blocks},
  journal = {Adv. Mater.},
  year = {2013},
  volume = {25},
  pages = {3948–3956},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=AdvMater25p3948(2013)_Rahe.pdf},
  doi = {10.1002/adma.201300604}
}
Lübbe J, Temmen M, Rode S, Rahe P, Kühnle A and Reichling M (2013), Thermal noise limit for ultra-high vacuum noncontact atomic force microscopy, Beilstein J. Nanotech. Vol. 4, pp. 32-44.
Abstract: The noise of the frequency-shift signal ?f in noncontact atomic force microscopy (NC-AFM) consists of cantilever thermal noise, tip-surface-interaction noise and instrumental noise from the detection and signal processing systems. We investigate how the displacement-noise spectral density dz at the input of the frequency demodulator propagates to the frequency-shift-noise spectral density d?f at the demodulator output in dependence of cantilever properties and settings of the signal processing electronics in the limit of a negligible tip-surface interaction and a measurement under ultrahigh-vacuum conditions. For a quantification of the noise figures, we calibrate the cantilever displacement signal and determine the transfer function of the signal-processing electronics. From the transfer function and the measured dz, we predict d?f for specific filter settings, a given level of detection-system noise spectral density dzds and the cantilever-thermal-noise spectral density dzth. We find an excellent agreement between the calculated and measured values for d?f. Furthermore, we demonstrate that thermal noise in d?f, defining the ultimate limit in NC-AFM signal detection, can be kept low by a proper choice of the cantilever whereby its Q-factor should be given most attention. A system with a low-noise signal detection and a suitable cantilever, operated with appropriate filter and feedback-loop settings allows room temperature NC-AFM measurements at a low thermal-noise limit with a significant bandwidth.
BibTeX:
@article{BeilsteinJNanotech4p32(2013)_Lubbe,
  author = {J. Lübbe and M. Temmen and S. Rode and P. Rahe and A. Kühnle and M. Reichling},
  title = {Thermal noise limit for ultra-high vacuum noncontact atomic force microscopy},
  journal = {Beilstein J. Nanotech.},
  year = {2013},
  volume = {4},
  pages = {32-44},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=BeilsteinJNanotech4p32(2013)_Lubbe.pdf},
  doi = {10.3762/bjnano.4.4}
}
Thomas L, Diek N, Beginn U and Reichling M (2012), Dimer/tetramer motifs determine amphiphilic hydrazine fibril structures on graphite, Beilstein J. Nanotech. Vol. 3, pp. 658-666.
Abstract: Fibril structures are produced at a solvent-graphite interface by self-assembly of custom-designed symmetric and asymmetric amphiphilic benzamide derivatives bearing C10 aliphatic chains. Scanning tunnelling microscopy (STM) studies reveal geometry-dependent internal structures for the elementary fibrils of the two molecules that are distinctly different from known mesophase bulk structures. The structures are described by building-block models based on hydrogen-bonded dimer and tetramer precursors of hydrazines. The closure and growth in length of building units into fibrils takes place through van der Waals forces acting between the dangling alkyl chains. The nanoscale morphology is a consequence of the basic molecular geometry, where it follows that a closure to form a fibril is not always likely for the doubly substituted hydrazine. Therefore, we also observe crystallite formation.
BibTeX:
@article{BeilsteinJNanotech3p658(2012)_Thomas,
  author = {L. Thomas and N. Diek and U. Beginn and M. Reichling},
  title = {Dimer/tetramer motifs determine amphiphilic hydrazine fibril structures on graphite},
  journal = {Beilstein J. Nanotech.},
  year = {2012},
  volume = {3},
  pages = {658-666},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=BeilsteinJNanotech3p658(2012)_Thomas.pdf},
  doi = {10.3762/Bjnano.3.75}
}
Pieper HH, Barth C and Reichling M (2012), Characterization of atomic step structures on CaF2(111) by their electric potential, Applied Physics Letters Vol. 101(5), pp. 051601. AIP.
BibTeX:
@article{ApplPhysLett101p051501(2012)_Pieper,
  author = {H. H. Pieper and C. Barth and M. Reichling},
  title = {Characterization of atomic step structures on CaF2(111) by their electric potential},
  journal = {Applied Physics Letters},
  publisher = {AIP},
  year = {2012},
  volume = {101},
  number = {5},
  pages = {051601},
  url = {http://link.aip.org/link/?APL/101/051601/1},
  doi = {10.1063/1.4739944}
}
Bollmann T (2012), Dwars door de 2de dimensie: Opzienbarende groei van dunne metaalfilms, Nederlands Tijdschrift voor Natuurkunde, Aug, 2012. Vol. 78(8)
BibTeX:
@article{Bollmann2012-2,
  author = {Bollmann, T.R.J.},
  title = {Dwars door de 2de dimensie: Opzienbarende groei van dunne metaalfilms},
  journal = {Nederlands Tijdschrift voor Natuurkunde},
  year = {2012},
  volume = {78},
  number = {8}
}
Torbrügge S, Custance O, Morita S and Reichling M (2012), Manipulation of individual water molecules on CeO2(111), J. Phys.: Condens. Matter Vol. 24, pp. 084010.
Abstract: Water molecules adsorbed on the CeO2(111) surface are investigated by non-contact atomic force microscopy (NC-AFM) at several tip?sample temperatures ranging between 10 and 300 K. Depending on the strength of the tip?surface interaction, they appear as triangular protrusions extended over three surface oxygen atoms or as small pits at hollow sites. During NC-AFM imaging with the tip being close to the surface, occasionally the transfer of molecules between tip and surface or the tip-induced lateral displacement of water molecules to equivalent surface lattice sites is observed. We report how this situation can be exploited to produce controlled lateral manipulations. A protocol to manipulate the water molecules between pre-de?ned neighbouring equivalent adsorption sites of the regular lattice as well as across a surface oxygen vacancy is demonstrated.
BibTeX:
@article{JPhysCM24p084010(2012)_Torbrugge,
  author = {S. Torbrügge and O. Custance and S. Morita and M. Reichling},
  title = {Manipulation of individual water molecules on CeO2(111)},
  journal = {J. Phys.: Condens. Matter},
  year = {2012},
  volume = {24},
  pages = {084010},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysCM24p084010(2012)_Torbrugge.pdf },
  doi = {10.1088/0953-8984/24/8/084010}
}
Lübbe J, Doering L and Reichling M (2012), Precise determination of force microscopy cantilever stiffness from dimensions and eigenfrequencies, Meas. Sci. Technol. Vol. 23(4), pp. 045401.
Abstract: We demonstrate the non-destructive measurement of the stiffness of single-beam, monocrystalline silicon cantilevers with a trapezoidal cross-section and tips as used for atomic force microscopy from the knowledge of cantilever dimensions, eigenfrequencies and material parameters. This yields stiffness values with an uncertainty of ±25% as the result critically depends on the thickness of the cantilever that is experimentally difficult to determine. The uncertainty is reduced to ±7% when the measured fundamental eigenfrequency is included in the calculation and a tip mass correction is applied. The tip mass correction can be determined from the eigenfrequencies of the fundamental and first harmonic modes. Results are verified by tip destructive measurements of the stiffness with a precision instrument recording a force?bending curve yielding an uncertainty better than ±5%.
BibTeX:
@article{MeasSciTechnol23p045401(2012)_Lubbe,
  author = {J. Lübbe and L. Doering and M. Reichling},
  title = {Precise determination of force microscopy cantilever stiffness from dimensions and eigenfrequencies},
  journal = {Meas. Sci. Technol.},
  year = {2012},
  volume = {23},
  number = {4},
  pages = {045401},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=MeasSciTechnol23p045401(2012)_Lubbe.pdf
}, doi = {10.1088/0957-0233/23/4/045401} }
Venkataramani K, Jensen TN, Helveg S, Reichling M, Besenbacher F and Lauritsen JV (2012), Al2O3(11-20) surface as a template for the ordered growth of Ni and Co nanostructures, Phys. Chem. Chem. Phys. Vol. 14, pp. 2092-2098.
Abstract: The morphology and thermal stability of Ni and Co nanoclusters grown by physical vapour deposition on a reconstructed (1120) surface of ?-Al2O3 is investigated using non-contact atomic force microscopy (NC-AFM). NC-AFM images reveal that the clean ?-Al2O3(1120) substrate adopts a characteristic (12 x 4) reconstruction when prepared in vacuum at high temperature. Subsequent deposition of Ni and Co onto this substrate at room temperature facilitates the growth of well-ordered metal nanocluster arrays with a preferred inter-cluster distance determined by the (12 x 4) periodicity of the substrate surface. The order in the cluster arrangement remains intact even upon annealing the system to temperatures up to 500 oC indicating a high resistance against sintering. The reconstructed ?-Al2O3(1120) surface can, therefore, serve as an appropriate insulating template for studies of size-dependent magnetic or catalytic effects in a well-defined ensemble of metallic nanoclusters.
BibTeX:
@article{PhysChemChemPhys14p2092(2012)_Venkataramani,
  author = {K. Venkataramani and T. N. Jensen and S. Helveg and M. Reichling and F. Besenbacher and J. V. Lauritsen},
  title = {Al2O3(11-20) surface as a template for the ordered growth of Ni and Co nanostructures},
  journal = {Phys. Chem. Chem. Phys.},
  year = {2012},
  volume = {14},
  pages = {2092-2098},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysChemChemPhys14p2092(2012)_Venkataramani.pdf},
  doi = {10.1039/c2cp22712f}
}
Zoellner MH, Dabrowski J, Zaumseil P, Giussani A, Schubert MA, Lupina G, Wilkens H, Wollschläger J, Reichling M, Bäumer M and Schroeder T (2012), Stacking behavior of twin-free type-B oriented CeO2(111) films on hexagonal Pr2O3(0001)/Si(111) systems, Phys. Rev. B Vol. 85(85), pp. 035302.
Abstract: Tailored CeO2/Pr2O3 thin-film oxide heterostructures are of interest for model catalysis studies by surface science techniques. For this purpose, thin CeO2(111) films were grown by molecular beam epitaxy on hex-Pr2O3(0001)/Si(111) as well as on cub-Pr2O3(111)/Si(111) support systems. A comparative, rigorous structure investigation by reflection high-energy electron diffraction transmission electron microscopy and laboratory and synchrotron based x-ray diffraction is reported. It is found that twin-free, exclusively type-B oriented CeO2(111) films are obtained on both oxide supports. CeO2(111) films adopt the stacking sequence from the cub-Pr2O3(111) buffer, but the transfer of the stacking information is less evident in the case of hex-Pr2O3(0001) films. Ab initio calculations are applied to understand the unusual stacking behavior of the CeO2(111) on the hex-Pr2O3Pr2O3(0001)/Si(111) system. It is revealed that the type-B stacking configuration is the more favorable configuration by 8 eV/nm2 due to electronic and crystallographic factors.
BibTeX:
@article{PhysRevB85p035302(2012)_Zoellner,
  author = {M. H. Zoellner and J. Dabrowski and P. Zaumseil and A. Giussani and M. A. Schubert and G. Lupina and H. Wilkens and J. Wollschläger and M. Reichling and M. Bäumer and T. Schroeder},
  title = {Stacking behavior of twin-free type-B oriented CeO2(111) films on hexagonal Pr2O3(0001)/Si(111) systems},
  journal = {Phys. Rev. B},
  year = {2012},
  volume = {85},
  number = {85},
  pages = {035302},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB85p035302(2012)_Zoellner.pdf},
  doi = {10.1103/PhysRevB.85.035302}
}
Bollmann TRJ, van Gastel R, Wormeester H, Zandvliet HJW and Poelsema B (2012), Growth and decay of hcp-like Cu hut-shaped structures on W(100), Phys. Rev. B, Mar, 2012. Vol. 85, pp. 125417. American Physical Society.
Abstract: We have studied both the morphology and structure of thin Cu deposits on W(100) during growth and desorption, using low-energy electron microscopy (LEEM) and selective area low-energy electron diffraction (uLEED). During growth at 674 K hut-shaped Cu crystallites with steep facets (> 54 degrees) coexist with a pseudomorphic Cu monolayer. The uLEED data suggest that these crystallites predominantly have a hcp structure with a high density of stacking faults and the (11-2 0) plane parallel to W(100). The boundaries run along the [-1 50] azimuth on W(100), which is explained by cancellation of shear stress exerted by Cu on the W(100) surface. Upon slow heating, Cu desorbs and the pseudomorphic wetting layer is transformed into coexisting surface alloy patches, with respectively, a Cu-rich p(2×2) and p(2×1) structure at 815 K. At about 950 K the islands are fully desorbed, leaving p(2×1) footprints behind. The p(2×2) patches disappear at about 1020 K, resulting in a homogeneous p(2×1) surface. Upon continued Cu desorption this surface transforms into small c(2×2) domains until all Cu has been desorbed at 1150 K.
BibTeX:
@article{PhysRevB85p125417(2012)_Bollmann,
  author = {Bollmann, Tjeerd R. J. and van Gastel, Raoul and Wormeester, Herbert and Zandvliet, Harold J. W. and Poelsema, Bene},
  title = {Growth and decay of hcp-like Cu hut-shaped structures on W(100)},
  journal = {Phys. Rev. B},
  publisher = {American Physical Society},
  year = {2012},
  volume = {85},
  pages = {125417},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB85p125417(2012)_Bollmann.pdf},
  doi = {10.1103/PhysRevB.85.125417}
}
Pieper HH, Lammers C, Tröger L, Bahr S and Reichling M (2012), Versatile system for the temperature-controlled preparation of oxide crystal surfaces, Review of Scientific Instruments Vol. 83, pp. 055110.
Abstract: We present a versatile system for the preparation of oxide crystal surfaces in the ultra-high vacuum (UHV) at temperatures up to 1300 K. Thermal treatment is accomplished by direct current heating of a tantalum foil in contact with the oxide sample. The sample temperature is measured by a thermocouple at a position close to the crystal and its reading is calibrated against the surface temperature determined by a second thermocouple temporarily attached to the surface. The design of the sample holder is based on a transferable plate originally developed for a commercial UHV scanning probe microscope. The system is, however, also suitable for the use with electron spectroscopy or electron diffraction based surface analytical techniques. We present results for the high-temperature preparation of CeO2 (111) surfaces with atomically ?at terraces exhibiting perfect atomic order and cleanliness as revealed by non-contact atomic force microscopy (NC-AFM) imaging. NC-AFM imaging is, furthermore, used to demonstrate the temperature-controlled aggregation of gold atoms on the CeO2 (111) surface and their evaporation at high temperatures.
BibTeX:
@article{RevSciInstrum83p055110(2012)_Pieper,
  author = {H. H. Pieper and C. Lammers and L. Tröger and S. Bahr and M. Reichling},
  title = {Versatile system for the temperature-controlled preparation of oxide crystal surfaces},
  journal = {Review of Scientific Instruments},
  year = {2012},
  volume = {83},
  pages = {055110},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=RevSciInstrum83p055110(2012)_Pieper.pdf},
  doi = {10.1063/1.4717674}
}
Rix S, Natura U, Loske F, Letz M, Felser C and Reichling M (2011), Formation of metallic colloids in CaF2 by intense ultraviolet light, Appl. Phys. Lett. Vol. 99(99), pp. 261909.
Abstract: Highest purity CaF2 single crystals are irreversibly modified when irradiated with millions of pulses of 193 nm light at fluences of 120 mJ/cm2. Mie theory explains the observed haze by attributing the wavelength dependent extinction and the ratio between absorption and scattering to metallic colloids with radii in the range of 20 to 30 nm and a fractional volume of up to 2.8 x 10-7. Non-contact scanning force microscopy (NC-AFM) measurements performed on a surface produced by in-vacuo cleavage reveals that laser irradiation additionally produces a 104 times higher volume density of colloids with a radius of 1 to 2 nm.
BibTeX:
@article{ApplPhysLett99p261909(2011)_Rix,
  author = {S. Rix and U. Natura and F. Loske and M. Letz and C. Felser and M. Reichling},
  title = {Formation of metallic colloids in CaF2 by intense ultraviolet light},
  journal = {Appl. Phys. Lett.},
  year = {2011},
  volume = {99},
  number = {99},
  pages = {261909},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysLett99p261909(2011)_Rix.pdf},
  doi = {10.1063/1.3673301}
}
Loske F, Reichling M and Kühnle A (2011), Steering molecular island morphology on an insulator surface by exploiting sequential deposition, Chem. Comm. Vol. 47(37), pp. 10386-10388.
Abstract: Depending on the deposition order in coadsorption of C60 and SubPc molecules on CaF2(111), distinctly different island morphologies can be obtained. We demonstrate that non-equilibrium processes can play a significant role in molecular structure formation and constitute a new route for complex molecular patterning of an insulating surface.
BibTeX:
@article{ChemComm47p10386(2011)_Loske,
  author = {F. Loske and M. Reichling and A. Kühnle},
  title = {Steering molecular island morphology on an insulator surface by exploiting sequential deposition},
  journal = {Chem. Comm.},
  year = {2011},
  volume = {47},
  number = {37},
  pages = {10386-10388},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ChemComm47p10386(2011)_Loske.pdf
}, doi = {10.1039/C1cc12996a} }
Loske F, Reichling M and Kühnle A (2011), Deposition Sequence Determines Morphology of C60 and 3,4,9,10-Perylenetetracarboxylic Diimide Islands on CaF2(111), Jpn. J. Appl. Phys. Vol. 50(8), pp. 08LB07.
Abstract: The coadsorption of C60 and 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) molecules on atomically flat terraces of the CaF2(111) surface is studied under ultra-high vacuum conditions using non-contact atomic force microscopy (NC-AFM). Deposition of PTCDI molecules on CaF2(111) yields needle-shaped, molecularly well-ordered crystals. Upon following deposition of C(60) molecules, the PTCDI islands are completely covered by C60. For the opposite deposition order, the initially grown C60 islands are not covered by PTCDI molecules, instead, most of the PTCDI molecules condense in pure islands, while only few PTCDI molecules nucleate at the edges of previously grown C60 islands. Simultaneous deposition of both molecules results in an intermixed phase with yet another island morphology. The observed fundamental differences in island morphology suggest that different dewetting barriers are involved in the formation process.
BibTeX:
@article{JpnJApplPhys50p08LB07(2011)_Loske,
  author = {F. Loske and M. Reichling and A. Kühnle},
  title = {Deposition Sequence Determines Morphology of C60 and 3,4,9,10-Perylenetetracarboxylic Diimide Islands on CaF2(111)},
  journal = {Jpn. J. Appl. Phys.},
  year = {2011},
  volume = {50},
  number = {8},
  pages = {08LB07},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JpnJApplPhys50p08LB07(2011)_Loske.pdf
}, doi = {Doi 10.1143/Jjap.50.08lb07} }
Lübbe J, Temmen M, Schnieder H and Reichling M (2011), Measurement and modelling of non-contact atomic force microscope cantilever properties from ultra-high vacuum to normal pressure conditions, Meas. Sci. Technol. Vol. 22, pp. 055501.
Abstract: The resonance frequency and Q-factor of cantilevers typically used for non-contact atomic force microscopy (NC-AFM) are measured as a function of the ambient pressure varied from 10?8 mbar to normal pressure. The Q-factor is found to be almost constant up to a pressure in the range of 10?2?10?1 mbar and then decreases by about three orders of magnitude when increasing the pressure further to normal pressure. The decrease in the resonance frequency measured over the same pressure range amounts to less than 1% where a significant change is observed in the range of 10?103 mbar. The pressure dependence of the effective Q-factor and resonance frequency is approximated by analytical models accounting for different processes in the molecular and viscous flow regimes. By introducing a heuristic approach for describing the pressure dependence in the transition regime, we are able to well approximate the cantilever properties over the entire pressure range.
BibTeX:
@article{MeasSciTechnol22p055501(2011)_Lubbe,
  author = {J. Lübbe and M. Temmen and H. Schnieder and M. Reichling},
  title = {Measurement and modelling of non-contact atomic force microscope cantilever properties from ultra-high vacuum to normal pressure conditions},
  journal = {Meas. Sci. Technol.},
  year = {2011},
  volume = {22},
  pages = {055501},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=MeasSciTechnol22p055501(2011)_Lubbe.pdf},
  doi = {10.1088/0957-0233/22/5/055501}
}
Borodin A and Reichling M (2011), Characterizing TiO2(110) surface states by their work function, Phys. Chem. Chem. Phys. Vol. 13(34), pp. 15442-15447.
Abstract: The unreconstructed TiO2(110) surface is prepared in well-defined states having different characteristic stoichiometries, namely reduced (r-TiO2, 6 to 9% surface vacancies), hydroxylated (h-TiO2, vacancies filled with OH), oxygen covered (ox-TiO2, oxygen adatoms on a stoichiometric surface) and quasi-stoichiometric (qs-TiO2, a stoichiometric surface with very few defects). The electronic structure and work function of these surfaces and transition states between them are investigated by ultraviolet photoelectron spectroscopy (UPS) and metastable impact electron spectroscopy (MIES). The character of the surface is associated with a specific value of the work function that varies from 4.9 eV for h-TiO2, 5.2 eV for r-TiO2, 5.35 eV for ox-TiO2 to 5.5 eV for qs-TiO2. We establish the method for an unambiguous characterization of TiO2(110) surface states solely based on the secondary electron emission characteristics. This is facilitated by analysing a weak electron emission below the nominal work function energy. The emission in the low energy cut-off region appears correlated with band gap emission found in UPS spectra and is attributed to localised electron emission through Ti3+(3d) states.
BibTeX:
@article{PhysChemChemPhys13p15442(2011)_Borodin,
  author = {A. Borodin and M. Reichling},
  title = {Characterizing TiO2(110) surface states by their work function},
  journal = {Phys. Chem. Chem. Phys.},
  year = {2011},
  volume = {13},
  number = {34},
  pages = {15442-15447},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysChemChemPhys13p15442(2011)_Borodin.pdf
}, doi = {10.1039/C0cp02835e} }
Mysovsky AS, Sushko PV, Radzhabov EA, Reichling M and Shluger AL (2011), Structure and properties of oxygen centers in CaF2 crystals from ab initio embedded cluster calculations, Phys. Rev. B Vol. 84(6), pp. 064133.
Abstract: We present the results of ab initio calculations of several intrinsic and oxygen-containing defects in CaF2 including an F center, a substitutional O- ion, an O2--vacancy dipole, and FA(O2-) and F2A+(O2-) centers. The calculations have been performed using a hybrid density functional and an embedded cluster method. The calculated optical absorption (OA) spectra and magnetic properties are in a very good agreement with available experimental data. It is suggested that isolated substitutional O- ions induce an OA band in the vacuum ultraviolet region at about 7 eV. The nature of the OA bands associated with O2--vacancy dipoles and other, more complex, defects is clarified and corresponding luminescence mechanisms are discussed.
BibTeX:
@article{PhysRevB84p064133(2011)_Mysovsky,
  author = {A. S. Mysovsky and P. V. Sushko and E. A. Radzhabov and M. Reichling and A. L. Shluger},
  title = {Structure and properties of oxygen centers in CaF2 crystals from ab initio embedded cluster calculations},
  journal = {Phys. Rev. B},
  year = {2011},
  volume = {84},
  number = {6},
  pages = {064133},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB84p064133(2011)_Mysovsky.pdf
}, doi = {10.1103/Physrevb.84.064133} }
Körner M, Loske F, Einax M, Kühnle A, Reichling M and Maass P (2011), Second-Layer Induced Island Morphologies in Thin-Film Growth of Fullerenes, Phys. Rev. Lett. Vol. 107(1), pp. 016101.
Abstract: Deposition of fullerenes on the CaF2(111) surface yields peculiar island morphologies with close similarities to previous findings for (100) surfaces of other ionic crystals. By means of noncontact atomic force microscopy we find a smooth transition from compact, triangular islands to branched hexagonal islands upon lowering the temperature. While triangular islands are two monolayers high, hexagonal islands have a base of one monolayer and exhibit a complicated structure with a second-layer outer rim and trenches oriented towards the interior. By developing a kinetic growth model we unravel the microscopic mechanisms of the structure formation.
BibTeX:
@article{PhysRevLett107p016101(2011)_Korner,
  author = {M. Körner and F. Loske and M. Einax and A. Kühnle and M. Reichling and P. Maass},
  title = {Second-Layer Induced Island Morphologies in Thin-Film Growth of Fullerenes},
  journal = {Phys. Rev. Lett.},
  year = {2011},
  volume = {107},
  number = {1},
  pages = {016101},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevLett107p016101(2011)_Korner.pdf
}, doi = {10.1103/Physrevlett.107.016101} }
Rahe P, Schütte J, Schniederberend W, Reichling M, Abe M, Sugimoto Y and Kühnle A (2011), Flexible drift-compensation system for precise 3D force mapping in severe drift environments, Rev. Sci. Instrum. Vol. 82(6), pp. 063704.
Abstract: The acquisition of dense 3D data sets is of great importance, but also a challenge for scanning probe microscopy (SPM). Thermal drift often induces severe distortions in the data, which usually constrains the acquisition of dense data sets to experiments under ultra-high vacuum and low-temperature conditions. Atom tracking is an elegant approach to compensate for thermal drift and to position the microscope tip with highest precision. Here, we present a flexible drift compensation system which can easily be connected to existing SPM hardware. Furthermore, we describe a 3D data acquisition and position correction protocol, which is capable of handling large and non-linear drift as typically present in room temperature measurements. This protocol is based on atom-tracking for precise positioning of the tip and we are able to acquire dense 3D data sets over several hours at room temperature. The performance of the protocol is demonstrated by presenting 3D data taken on a CaCO3(1014) surface with the data density being as large as 85×85×500 pixel.
BibTeX:
@article{RevSciInstrum82p063704(2011)_Rahe,
  author = {P. Rahe and J. Schütte and W. Schniederberend and M. Reichling and M. Abe and Y. Sugimoto and A. Kühnle},
  title = {Flexible drift-compensation system for precise 3D force mapping in severe drift environments},
  journal = {Rev. Sci. Instrum.},
  year = {2011},
  volume = {82},
  number = {6},
  pages = {063704},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=RevSciInstrum82p063704(2011)_Rahe.pdf},
  doi = {10.1063/1.3600453}
}
Tröger L and Reichling M (2010), Quantification of antagonistic optomechanical forces in an interferometric detection system for dynamic force microscopy, Appl. Phys. Lett. Vol. 97(21), pp. 213105.
Abstract: In fiber-optic interferometer systems detecting oscillatory cantilever motion, the intensity distribution of the light field in the interferometric cavity generates an optomechanical coupling determining the effective properties of the oscillating system. For a low finesse cavity established by an uncoated cantilever and the fiber end, the resonance frequency and spring constant are shifted mainly due to radiation pressure whereas the Q-factor is varied due to photothermal forces under typical conditions. We find, that radiation pressure and photothermal force act in opposite directions and discuss the retardation times governing the antagonistic effects differing by orders of magnitude.
BibTeX:
@article{ApplPhysLett97p213105(2010)_Troger,
  author = {L. Tröger and M. Reichling},
  title = {Quantification of antagonistic optomechanical forces in an interferometric detection system for dynamic force microscopy},
  journal = {Appl. Phys. Lett.},
  year = {2010},
  volume = {97},
  number = {21},
  pages = {213105},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysLett97p213105(2010)_Troger.pdf},
  doi = {10.1063/1.3509412}
}
Motzer C and Reichling M (2010), Morphological classification and quantitative analysis of etch pits, J. Appl. Phys. Vol. 108(11), pp. 113523.
Abstract: Etch pits created by hydrochloric and phosphoric acid on cleaved CaF2(111) are investigated by scanning force microscopy (SFM). A geometric and dimensional analysis of the etch pits reveals two distinctly different types. Type-I etch pits evolve at dislocation defects, are pointed and their size and eccentricity is related to the angle between the dislocation and the surface. Type-II etch pits result from defects below the surface, are flat-bottomed for longer etching times and exhibit a characteristic ratio of depth and edge length depending on the type of etchant. An analysis of etch pit morphology allows an identification of the origin of an etch pit and a characterization of the associated defect structure.
BibTeX:
@article{JApplPhys108p113523(2010)_Motzer,
  author = {C. Motzer and M. Reichling},
  title = {Morphological classification and quantitative analysis of etch pits},
  journal = {J. Appl. Phys.},
  year = {2010},
  volume = {108},
  number = {11},
  pages = {113523},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JApplPhys108p113523(2010)_Motzer.pdf},
  doi = {10.1063/1.3510535}
}
Thomas LK, Kühnle A, Rode S, Beginn U and Reichling M (2010), Monolayer Structure of Arachidic Acid on Graphite, J. Phys. Chem. C Vol. 114(44), pp. 18919-18924.
Abstract: The self-assembly of arachidic acid (C19H39COOH) at the liquid?solid interface between 1-phenyloctane (C6H5(CH2)7CH3) and highly oriented pyrolytic graphite (HOPG) is studied by scanning tunneling microscopy (STM) to identify the structure of the monomolecular film. We observe the formation of highly ordered domains with molecules oriented in three different orientations compatible with the symmetry of the HOPG substrate, a spontaneous enantiomeric separation of the pro-chiral molecules, and reveal structural details with submolecular resolution. To determine the surface unit cell with an intrinsic calibration to the substrate atomic structure, the intermolecular distance is precisely determined from the analysis of a STM image exhibiting a moir pattern created by the superposition of current contributions from the molecular structure with contributions from the graphite atomic lattice. The dimensions of the unit cell accommodating two molecules are |a| = 0.94 nm and |b| = 2.83 nm with an angle of 85° between unit cell vectors a and b. The respective molecular arrangement allows hydrogen bonding between carboxylic groups with an unrelaxed O?O bond distance of 0.31 nm.
BibTeX:
@article{JPhysChemC114p18919(2010)_Thomas,
  author = {L. K. Thomas and A. Kühnle and S. Rode and U. Beginn and M. Reichling},
  title = {Monolayer Structure of Arachidic Acid on Graphite},
  journal = {J. Phys. Chem. C},
  year = {2010},
  volume = {114},
  number = {44},
  pages = {18919-18924},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysChemC114p18919(2010)_Thomas.pdf},
  doi = {10.1021/jp105205y}
}
Lauritsen JV and Reichling M (2010), Atomic resolution non-contact atomic force microscopy of clean metal oxide surfaces, J. Phys.: Condens. Matter Vol. 22(26), pp. 263001.
Abstract: In the last two decades the atomic force microscope (AFM) has become the premier tool for topographical analysis of surface structures at the nanometre scale. In its ultimately sensitive implementation, namely dynamic scanning force microscopy (SFM) operated in the so-called non-contact mode (NC-AFM), this technique yields genuine atomic resolution and offers a unique tool for real space atomic-scale studies of surfaces, nanoparticles as well as thin films, single atoms and molecules on surfaces irrespective of the substrate being electrically conducting or non-conducting. Recent advances in NC-AFM have paved the way for groundbreaking atomic level insight into insulator surfaces, specifically in the most important field of metal oxides. NC-AFM imaging now strongly contributes to our understanding of the surface structure, chemical composition, defects, polarity and reactivity of metal oxide surfaces and related physical and chemical surface processes. Here we review the latest advancements in the field of NC-AFM applied to the fundamental atomic resolution studies of clean single crystal metal oxide surfaces with special focus on the representative materials Al2O3(0001), TiO2(110), ZnO(1000) and CeO2(111).
BibTeX:
@article{JPhysCondensMatter22p263001(2010)_Lauritsen,
  author = {J. V. Lauritsen and M. Reichling},
  title = {Atomic resolution non-contact atomic force microscopy of clean metal oxide surfaces},
  journal = {J. Phys.: Condens. Matter},
  year = {2010},
  volume = {22},
  number = {26},
  pages = {263001},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysCM22p263001(2010)_Lauritsen.pdf},
  doi = {10.1088/0953-8984/22/26/263001}
}
Arai T, Gritschneder S, Tröger L and Reichling M (2010), Atomic resolution force microscopy imaging on a strongly ionic surface with differently functionalized tips, J. Vac. Sci. Technol. B Vol. 28(6), pp. 1279-1283.
Abstract: Three types of tips for noncontact atomic force microscopy imaging, namely, a silicon nanopillar tip, a carbon nanopillar tip, and a fluoride cluster tip, are prepared for atomic resolution imaging on the CaF2(111) surface. The most enhanced atomic corrugation is obtained with the fluoride cluster tip prepared by gently touching the fluorite surface. Atom resolved images are much harder to obtain with the other tips. This demonstrates the importance of having a polar tip for atomic resolution imaging of an ionic surface and supports the general notion that a surface is best imaged with a tip of the same material.
BibTeX:
@article{JVacSciTechnolB28p1279(2010)_Arai,
  author = {T. Arai and S. Gritschneder and L. Tröger and M. Reichling},
  title = {Atomic resolution force microscopy imaging on a strongly ionic surface with differently functionalized tips},
  journal = {J. Vac. Sci. Technol. B},
  year = {2010},
  volume = {28},
  number = {6},
  pages = {1279-1283},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JVacSciTechnolB28p1279(2010)_Arai.pdf},
  doi = {DOI: 10.1116/1.3511505}
}
Schütte J, Rahe P, Tröger L, Rode S, Bechstein R, Reichling M and Kühnle A (2010), Clear signature of the (2x1) reconstruction of calcite (10-14), Langmuir Vol. 26(11), pp. 8295?8300.
Abstract: Calcite is a mineral of fundamental importance that plays a crucial role in many fields of research such as biomineralization, biomolecule adsorption, and reactivity as well as industrial and daily life applications. Consequently, the most stable cleavage plane of calcite has been studied extensively using both direct imaging techniques such as atomic force microscopy as well as spectroscopic and diffraction techniques. Several surface structures have been reported for the (10-14) cleavage plane of calcite differing from the simple bulk-truncated structure and an ongoing controversy exists in literature whether the cleavage plane exhibits a (2 x 1) reconstruction or not. We study the (10-14) cleavage plane using high-resolution noncontact atomic force microscopy (NC-AFM) under ultrahigh vacuum conditions and obtain a clear signature of the (2 x 1) reconstruction. This reconstruction is observed in very narrow tip-surface distance ranges only, explaining why in some experiments the reconstruction has been observed and in others not. Moreover, as all sample preparation is performed in ultrahigh vacuum, the possibility of the (2 x 1) reconstruction being adsorbate-induced appears rather unlikely. Additionally, tip-induced surface changes are ruled out as origin for the observed reconstruction either. In conclusion, our study suggests that the (2 x1) reconstruction is a true surface property of the (10-14) cleavage plane of calcite.
BibTeX:
@article{Langmuir26p8295(2010)_Schutte,
  author = {J. Schütte and P. Rahe and L. Tröger and S. Rode and R. Bechstein and M. Reichling and A. Kühnle},
  title = {Clear signature of the (2x1) reconstruction of calcite (10-14)},
  journal = {Langmuir},
  year = {2010},
  volume = {26},
  number = {11},
  pages = {8295?8300},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Langmuir26p8295(2010)_Schutte.pdf},
  doi = {10.1021/la904706p}
}
Lübbe J, Tröger L, Torbrügge S, Bechstein R, Richter C, Kühnle A and Reichling M (2010), Achieving high effective Q-factors in ultra-high vacuum dynamic force microscopy, Meas. Sci. Technol. Vol. 21(10), pp. 125501.
Abstract: The effective Q-factor of the cantilever is one of the most important figures-of-merit for a non-contact atomic force microscope (NC-AFM) operated in ultra-high vacuum (UHV). We provide a comprehensive discussion of all effects influencing the Q-factor and compare measured Q-factors to results from simulations based on the dimensions of the cantilevers. We introduce a methodology to investigate in detail how the effective Q-factor depends on the fixation technique of the cantilever. Fixation loss is identified as a most important contribution in addition to the hitherto discussed effects and we describe a strategy for avoiding fixation loss and obtaining high effective Q-factors in the force microscope. We demonstrate for room temperature operation, that an optimum fixation yields an effective Q-factor for the NC-AFM measurement in UHV that is equal to the intrinsic value of the cantilever.
BibTeX:
@article{MeasSciTechnol21p125501(2010)_Luebbe,
  author = {J. Lübbe and L. Tröger and S. Torbrügge and R. Bechstein and C. Richter and A. Kühnle and M. Reichling},
  title = {Achieving high effective Q-factors in ultra-high vacuum dynamic force microscopy},
  journal = {Meas. Sci. Technol.},
  year = {2010},
  volume = {21},
  number = {10},
  pages = {125501},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=MeasSciTechnol21p125501(2010)_Luebbe.pdf},
  doi = {10.1088/0957-0233/21/12/125501}
}
Venkataramani K, Helveg S, Hinnemann B, Reichling M, Besenbacher F and Lauritsen JV (2010), Ordering of monodisperse Ni nanoclusters by templating on high-temperature reconstructed a-Al2O3(0001), Nanotechnology Vol. 21(26), pp. 265602.
Abstract: We demonstrate that the characteristic ?31 x?31 R9° reconstructed surface of ?-alumina (Al2O3) acts as a nanotemplate for the growth of well-ordered monodisperse arrays of Ni nanoclusters. Due to the insulating nature of the substrate we use dynamic scanning force microscopy operated in the non-contact mode (NC-AFM) to characterize the nanotemplate, to examine the size and distribution of metallic clusters on the surface and to investigate their position with respect to the surface atomic structure. The present NC-AFM results for the interaction of Ni with ?-Al2O3 are supported by density functional theory (DFT) calculations. The ability of ?-Al2O3(0001) to act as a nanotemplate is attributed to a spatially modulated affinity towards the accommodation of Ni into the top layer by substituting the surface Al atoms at certain sites on the?31 x ?31 R9° degrees reconstructed surface formed by high-temperature annealing. The insulating template, demonstrated for Al2O3, may be a generally attractive system for the study of nanostructures which need to be isolated from a conducting bulk.
BibTeX:
@article{Nanotechnology21p265602(2010)_Venkataramani,
  author = {K. Venkataramani and S. Helveg and B. Hinnemann and M. Reichling and F. Besenbacher and J. V. Lauritsen},
  title = {Ordering of monodisperse Ni nanoclusters by templating on high-temperature reconstructed a-Al2O3(0001)},
  journal = {Nanotechnology},
  year = {2010},
  volume = {21},
  number = {26},
  pages = {265602},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nanotechnology21p265602(2010)_Venkataramani.pdf
}, doi = {10.1088/0957-4484/21/26/265602} }
Pieper HH, Venkataramani K, Torbrügge S, Bahr S, Lauritsen JV, Besenbacher F, Kühnle A and Reichling M (2010), Unravelling the atomic structure of cross-linked (1 x 2 ) TiO2(110), Phys. Chem. Chem. Phys. Vol. 12(36), pp. 12436?12441.
Abstract: The cross-linked (1 x 2) reconstruction of TiO2(110) is a frequently observed phase reflecting the surface structure of titania in a significantly reduced state. Here we resolve the atomic scale structure of the cross-linked (1 x 2) phase with dynamic scanning force microscopy operated in the non-contact mode (NC-AFM). From an analysis of the atomic-scale contrast patterns of the titanium and oxygen sub-structures obtained by imaging the surface with AFM tips having different tip apex termination, we infer the hitherto most accurate model of the atomic structure of the cross-linked (1 x 2 ) phase. Our findings suggest that the reconstruction is based on added rows in [001] direction built up of Ti3O6 units with an uninterrupted central string of oxygen atoms accompanied by a regular sequence of cross-links consisting of linear triples of additional oxygen atoms in between the rows. The new insight obtained from NC-AFM solves previous controversy about the cross-linked TiO2(110) surface structure, since previously proposed models based on cross-links with a lower O content do not appear to be consistent with the atom-resolved data presented here. Instead, our measurements strongly support the Ti3O6 motif to be the structural base of the cross-linked (1 x 2) reconstruction of TiO2(110).
BibTeX:
@article{PhysChemChemPhys12p12436(2010)_Pieper,
  author = {H. H. Pieper and K. Venkataramani and S. Torbrügge and S. Bahr and J. V. Lauritsen and F. Besenbacher and A. Kühnle and M. Reichling},
  title = {Unravelling the atomic structure of cross-linked (1 x 2 ) TiO2(110)},
  journal = {Phys. Chem. Chem. Phys.},
  year = {2010},
  volume = {12},
  number = {36},
  pages = {12436?12441},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysChemChemPhys12p12436(2010)_Pieper.pdf},
  doi = {10.1039/c0cp00160k}
}
Nimmrich M, Kittelmann M, Rahe P, Mayne AJ, Dujardin G, v. Schmidsfeld A, Reichling M, Harneit W and Kühnle A (2010), Atomic-resolution imaging of clean and hydrogen-terminated C(100)-(2 x 1) diamond surfaces using noncontact AFM, Phys. Rev. B Vol. 81(20), pp. 201403R.
Abstract: High-purity, type IIa diamond is investigated by noncontact atomic force microscopy (NC-AFM). We present atomic-resolution images of both the electrically conducting hydrogen-terminated C(100)-(2 x 1):H surface and the insulating C(100)-(2 x 1) surface. For the hydrogen-terminated surface, a nearly square unit cell is imaged. In contrast to previous scanning tunneling microscopy experiments, NC-AFM imaging allows both hydrogen atoms within the unit cell to be resolved individually, indicating a symmetric dimer alignment. Upon removing the surface hydrogen, the diamond sample becomes insulating. We present atomic-resolution images, revealing individual C-C dimers. Our results provide real-space experimental evidence for a (2 x 1) dimer reconstruction of the truly insulating C(100) surface.
BibTeX:
@article{PhysRevB81p201403R(2010)_Nimmrich,
  author = {M. Nimmrich and M. Kittelmann and P. Rahe and A. J. Mayne and G. Dujardin and A. v. Schmidsfeld and M. Reichling and W. Harneit and A. Kühnle},
  title = {Atomic-resolution imaging of clean and hydrogen-terminated C(100)-(2 x 1) diamond surfaces using noncontact AFM},
  journal = {Phys. Rev. B},
  year = {2010},
  volume = {81},
  number = {20},
  pages = {201403R},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB81p201403R(2010)_Nimmrich.pdf},
  doi = {10.1103/PhysRevB.81.201403}
}
Loske F, Lübbe J, Schütte J, Reichling M and Kühnle A (2010), Quantitative description of C60 diffusion on an insulating surface, Phys. Rev. B Vol. 82(15), pp. 155428.
Abstract: The diffusion of C60 molecules on large, atomically flat terraces of the CaF2(111) surface is studied under ultrahigh vacuum conditions at various substrate temperatures below room temperature. The weak molecule-substrate interaction on this insulating surface makes a direct observation of hopping events difficult. Therefore, to determine a quantitative value of the diffusion barrier, we employ the so-called onset method. This method is based on the analysis of spatial properties of islands created by nucleation of diffusing C60 molecules, as measured by noncontact atomic force microscopy. We first determine the critical cluster size to be i* = 1 from coverage-dependent island size distributions prepared at a fixed substrate temperature. The diffusion barrier of Ed = (214±16) meV and an attempt frequency of ?0 = 1.4 × 10(12±0.6) s?1 are then obtained by analyzing the island densities at different substrate temperatures.
BibTeX:
@article{PhysRevB82p155428(2010)_Loske,
  author = {F. Loske and J. Lübbe and J. Schütte and M. Reichling and A. Kühnle},
  title = {Quantitative description of C60 diffusion on an insulating surface},
  journal = {Phys. Rev. B},
  year = {2010},
  volume = {82},
  number = {15},
  pages = {155428},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB82p155428(2010)_Loske.pdf},
  doi = {10.1103/PhysRevB.82.155428}
}
Motzer C and Reichling M (2009), High resolution study of etch figures on CaF2(111), J. Appl. Phys. Vol. 105(6), pp. 064309.
Abstract: Calcium difluoride crystals cleaved along the (111) direction are etched with the dislocation site selective etchants HNO3, HCl, H2SO4, and H3PO4 and their surfaces are inspected ex situ with scanning force microscopy (AFM). Force microscopy yields characteristic features of the etch pits at the nanometer scale such as terracing and ditrigonal patterns. The method enables direct quantitative measurements of etch pit structures to derive kinetic data revealing details of the dissolution mechanism. Orthophosphoric acid is found to yield the best scaleable etching figures at ambient and elevated temperatures, as for this etchant, the dissolution is reaction-rate controlled. The scanning tip can induce a precipitationlike process by adherent traces of sulfuric or phosphoric acid that can be removed by a treatment with nitric acid following the regular etching procedure.
BibTeX:
@article{JApplPhys105p064309(2009)_Motzer,
  author = {C. Motzer and M. Reichling},
  title = {High resolution study of etch figures on CaF2(111)},
  journal = {J. Appl. Phys.},
  year = {2009},
  volume = {105},
  number = {6},
  pages = {064309},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JApplPhys105p064309(2009)_Motzer.pdf},
  doi = {10.1063/1.3078774}
}
Sils J, Hausfeld S, Clauß W, Pahl U, Lindner R and Reichling M (2009), Impurities in synthetic fluorite for deep ultraviolet optical applications, J. Appl. Phys. Vol. 106(6), pp. 063109.
Abstract: The impurity content of synthetic calciumdifluoride fluorite, CaF2 single crystals produced for optical applications in the deep ultraviolet DUV and infrared IR spectral regions are investigated by luminescence and absorption spectroscopy. Lead, oxygen, and rare earth RE ions, namely, trivalent Ce3+, Pr3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, and Yb3+ and divalent Eu2+ are identified as common impurities. RE ions are dominating impurities in the IR grade sample and the impurity concentration for this sample is found to be about 100 times higher than the one for DUV samples. Due to the strongly reduced RE luminescence background, we additionally identify lead and oxygen in DUV grade crystals. Remarkable differences in the luminescence spectra are found when comparing DUV grade crystals from different sources.
BibTeX:
@article{JApplPhys106p063109(2009)_Sils,
  author = {J. Sils and S. Hausfeld and W. Clauß and U. Pahl and R. Lindner and M. Reichling},
  title = {Impurities in synthetic fluorite for deep ultraviolet optical applications},
  journal = {J. Appl. Phys.},
  year = {2009},
  volume = {106},
  number = {6},
  pages = {063109},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JApplPhys106p063109(2009)_Sils.pdf},
  doi = {10.1063/1.3224879}
}
Torbrügge S, Ostendorf F and Reichling M (2009), Stabilization of Zinc-Terminated ZnO(0001) by a Modified Surface Stoichiometry, J. Phys. Chem. C Vol. 113(12), pp. 4909-4914.
Abstract: The stabilization of polar oxide surfaces is of fundamental interest for understanding many processes in surface chemistry. We study the zinc-terminated Zn?ZnO(0001), a surface important in heterogeneous catalysis, by highest resolution scanning force microscopy (SFM) operated in the noncontact mode (NC-AFM). While most of the surface morphology is dominated by a phase consisting of triangular shaped nanostructures, we observe a coexisting (1 × 3) reconstructed phase where the reconstruction is ascribed to the formation of missing Zn-rows. Our findings provide evidence that the electrostatic instability of the polar Zn?ZnO(0001) surface can be canceled by a reduction of the surface charge by 1/3 which is considerably larger than the value of 1/4 derived from a simple ionic model for polar stabilization. Within the presented model for the (1 × 3) reconstruction, the role of point defects tentatively ascribed to hydrogen adsorbed on top of double Zn-rows forming zinc-hydride is discussed.
BibTeX:
@article{JPhysChemC113p4909(2009)_Torbrugge,
  author = {S. Torbrügge and F. Ostendorf and M. Reichling},
  title = {Stabilization of Zinc-Terminated ZnO(0001) by a Modified Surface Stoichiometry},
  journal = {J. Phys. Chem. C},
  year = {2009},
  volume = {113},
  number = {12},
  pages = {4909-4914},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysChemC113p4909(2009)_Torbrugge.pdf},
  doi = {10.1021/jp804026v}
}
Ostendorf F, Schmitz C, Hirth S, Kühnle A, Kolodziej JJ and Reichling M (2009), Evidence for Potassium Carbonate Crystallites on Air-Cleaved Mica Surfaces, Langmuir Vol. 25(18), pp. 10764?10767.
Abstract: Air-cleaved mica surfaces exhibit a high density of nanometer or micrometer size particles that have been ascribed to potassium carbonate formed as a reaction product of carbonaceous gases with potassium ions. Unambiguous evidence for this assignment has, however, never been presented. We study air-cleaved mica surfaces by high-resolution noncontact atomic force microscopy (NC-AFM) in ultrahigh vacuum to reveal the detailed structure of such precipitates on the surface. Among a large number of irregularly shaped surface structures, we find f lat, hexagonally shaped islands exhibiting two different patterns on their surfaces, namely a rectangular atomic corrugation pattern and a hexagonal moiré structure. The unit cell of the rectangular pattern corresponds to the dimensions of the potassium carbonate bulk structure and is found on high crystallites. The moiré structure solely appears on very f lat islands and is caused by the interference of the potassium carbonate lattice periodicity and the lattice periodicity of the underlying mica substrate. Both results strongly point to the presence of potassium carbonate crystallites on air-cleaved mica surfaces.
BibTeX:
@article{Langmuir25p10764(2009)_Ostendorf,
  author = {F. Ostendorf and C. Schmitz and S. Hirth and A. Kühnle and J. J. Kolodziej and M. Reichling},
  title = {Evidence for Potassium Carbonate Crystallites on Air-Cleaved Mica Surfaces},
  journal = {Langmuir},
  year = {2009},
  volume = {25},
  number = {18},
  pages = {10764?10767},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Langmuir25p10764(2009)_Ostendorf.pdf},
  doi = {10.1021/la901311k}
}
Loske F, Bechstein R, Schütte J, Ostendorf F, Reichling M and Kühnle A (2009), Growth of ordered C60 islands on TiO2(110), Nanotechnology Vol. 20(6), pp. 065606.
Abstract: Non-contact atomic force microscopy is used to study C60 molecules deposited on the rutile TiO2(110) surface in situ at room temperature. At submonolayer coverages, molecules adsorb preferentially at substrate step edges. Upon increasing coverage, ordered islands grow from the decorated step edges onto the lower terraces. Simultaneous imaging of bridging oxygen rows of the substrate and the C60 island structure reveals that the C60 molecules arrange themselves in a centered rectangular superstructure, with the molecules lying centered in the troughs formed by the bridging oxygen rows. Although the TiO2(110) surface exhibits a high density of surface defects, the observed C60 islands are of high order. This indicates that the C60 intermolecular interaction dominates over the molecule?substrate interactions that may cause structural perturbations on a defective surface. Slightly protruding C60 strands on the islands are attributed to anti-phase boundaries due to stacking faults resulting from two islands growing together.
BibTeX:
@article{Nanotechnology20p065606(2009)_Loske,
  author = {F. Loske and R. Bechstein and J. Schütte and F. Ostendorf and M. Reichling and A. Kühnle},
  title = {Growth of ordered C60 islands on TiO2(110)},
  journal = {Nanotechnology},
  year = {2009},
  volume = {20},
  number = {6},
  pages = {065606},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nanotechnology20p065606(2009)_Loske.pdf},
  doi = {10.1088/0957-4484/20/6/065606}
}
Schütte J, Bechstein R, Rohlfing M, Reichling M and Kühnle A (2009), Cooperative mechanism for anchoring highly polar molecules at an ionic surface, Phys. Rev. B Vol. 80(20), pp. 205421.
Abstract: Structure formation of the highly polar molecule cytosine on the (111) cleavage plane of calcium fluoride is investigated in ultrahigh vacuum using noncontact atomic force microscopy at room temperature. Molecules form well-defined trimer structures, covering the surface as homogeneously distributed stable structures. Density-functional theory calculations yield a diffusion barrier of about 0.5 eV for individual molecules suggesting that they are mobile at room temperature. Furthermore, it is predicted that the molecules can form trimers in a configuration allowing all molecules to attain their optimum adsorption position on the substrate. As the trimer geometry facilitates hydrogen bonding between the molecules within the trimer, we conclude that the stabilization of individual diffusing molecules into stable trimers is due to a cooperative mechanism involving polar interactions between molecules and substrate as well as hydrogen bonding between molecules.
BibTeX:
@article{PhysRevB80p205421(2009)_Schutte,
  author = {J. Schütte and R. Bechstein and M. Rohlfing and M. Reichling and A. Kühnle},
  title = {Cooperative mechanism for anchoring highly polar molecules at an ionic surface},
  journal = {Phys. Rev. B},
  year = {2009},
  volume = {80},
  number = {20},
  pages = {205421},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB80p205421(2009)_Schutte.pdf},
  doi = {10.1103/PhysRevB.80.205421}
}
Tröger L, Schütte J, Ostendorf F, Kühnle A and Reichling M (2009), Concept for support and cleavage of brittle crystals, Rev. Sci. Instrum. Vol. 80(6), pp. 063703.
Abstract: We report on sample holders for crystals to be cleaved for the preparation of surfaces with large atomically flat terraces. The concept for mounting sample crystals is based on a vicelike clamping mechanism to securely hold the crystal in position while reducing the risk of fragmentation. Sample holders based on this concept and made of suitable materials allow preparation and cleavage of crystals in the ultrahigh vacuum at high or low temperatures. To cleave the crystal, we employ a scalpel blade mounted on a wobble stick to generate a highly localized stress field initiating the cleavage process. The sample holders are used for experiments of highest resolution scanning force microscopy, however, the concept can be transferred to any other system where cleavage faces of crystals are of interest. Exemplarily, scanning force microscopy results demonstrate that (111) cleavage faces of CaF2 crystals can be prepared with steps only a few F?Ca?F triple-layers high and atomically flat terraces extending over areas of several ?m2.
BibTeX:
@article{RevSciInstrum80p063703(2009)_Troger,
  author = {L. Tröger and J. Schütte and F. Ostendorf and A. Kühnle and M. Reichling},
  title = {Concept for support and cleavage of brittle crystals},
  journal = {Rev. Sci. Instrum.},
  year = {2009},
  volume = {80},
  number = {6},
  pages = {063703},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=RevSciInstrum80p063703(2009)_Troger.pdf},
  doi = {10.1063/1.3152367}
}
Torbrügge S, Cranney M and Reichling M (2008), Morphology of step structures on CeO2(111), Appl. Phys. Lett. Vol. 93(7), pp. 073112.
Abstract: The morphology of step structures on the CeO2(111) surface is studied by dynamic scanning force microscopy (SFM) operated in the noncontact mode. The surface exhibits hexagonal islands and pits of O?Ce?O triple layer height with steps mostly enclosing an angle of 120°. Atomically resolved images reveal that the (111) surface almost exclusively exhibits alternating steps having (110) and (001) facets. Kink sites and missing oxygen atoms at step edges are identified to be the dominating defective sites at step edges. It is demonstrated that low coordinated oxygen atoms at step edges can be removed by the scanning SFM tip.
BibTeX:
@article{ApplPhysLett93p073112(2008)_Torbrugge,
  author = {S. Torbrügge and M. Cranney and M. Reichling},
  title = {Morphology of step structures on CeO2(111)},
  journal = {Appl. Phys. Lett.},
  year = {2008},
  volume = {93},
  number = {7},
  pages = {073112},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysLett93p073112(2008)_Torbrugge.pdf
}, doi = {10.1063/1.2969790} }
Jensen MCR, Venkataramani K, Helveg S, Clausen BS, Reichling M, Besenbacher F and Lauritsen JV (2008), Morphology, Dispersion, and Stability of Cu Nanoclusters on Clean and Hydroxylated a-Al2O3(0001) Substrates, J. Phys. Chem. C Vol. 112(43), pp. 16953-16960.
Abstract: Using high-resoln. dynamic scanning force microscopy (SFM) operated in the noncontact mode, the authors study here the detailed morphol., dispersion, and thermal stability of nanometer-sized three-dimensional Cu clusters on an ?-Al2O3(0001) substrate. The authors systematically study the effect of surface hydroxylation by depositing metallic Cu either on an ultrahigh vacuum prepd. Al-terminated alumina surface or on surfaces prehydroxylated/hydrated by exposure to varying doses of H2O. Three-dimensional growth of Cu nanoclusters dispersed evenly on the surface is observed independent of surface preparation. As the top facet of the nanoclusters appears hexagonal in SFM images, they are regular Cu crystallites in the equilibrium form. For strongly hydroxylated surfaces, however, a reduced aspect ratio (height-to-width) of the nanoclusters indicates an increased wetting of the Cu. Probably Cu bonding to the hydroxylated surface is enhanced by the formation of Cu-O-Al bonds. Surprisingly when heating the surface, Cu remains dispersed on the surface, but the total coverage of Cu on the surface is rapidly reduced when the sample is heated to temperatures above 450°C for clean and 550 °C for hydroxylated surfaces. The results unexpectedly show that Cu is desorbed from the ~3 nm wide Cu nanoclusters at temperatures well-below the melting temperature of bulk Cu, and the sublimation is completed before the onset of sintering or ripening of the Cu nanoclusters under the conditions of the experiment. The observations thus reveal significant changes in the cohesive energies of nanometer-sized Cu clusters, which is an effect that should be taken into account when modeling the stability of Cu crystallites, for example, with regard to sintering of Cu-based catalysts.
BibTeX:
@article{J,
  author = {M. C. R. Jensen and K. Venkataramani and S. Helveg and B. S. Clausen and M. Reichling and F. Besenbacher and J. V. Lauritsen},
  title = {Morphology, Dispersion, and Stability of Cu Nanoclusters on Clean and Hydroxylated a-Al2O3(0001) Substrates},
  journal = {J. Phys. Chem. C},
  year = {2008},
  volume = {112},
  number = {43},
  pages = {16953-16960},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysChemC112p16953(2008)_Jensen.pdf},
  doi = {10.1021/jp804492h}
}
Ostendorf F, Schmitz C, Hirth S, Kühnle A, Kolodziej JJ and Reichling M (2008), How flat is an air-cleaved mica surface?, Nanotechnology Vol. 19(30), pp. 305705.
Abstract: Muscovite mica is an important mineral that has become a standard substrate, due to its easy cleavage along the 001 planes, revealing a very flat surface that is compatible with many biological materials. Here we study mica surfaces by dynamic atomic force microscopy (AFM) operated in the non-contact mode (NC-AFM) under ultra-high vacuum (UHV) conditions. Surfaces produced by cleaving in UHV cannot be imaged with NC-AFM due to large surface charges; however, cleavage in air yields much less surface charge and allows for NC-AFM imaging. We present highly resolved NC-AFM images of air-cleaved mica surfaces revealing a rough morphology originating from a high density of nanometre-sized particles. Among these particles, we find regularly shaped structures indicating the growth of crystallites on the surface. The contamination layer cannot be removed by degassing in UHV; even prolonged heating at a temperature of 560 K under UHV conditions does not yield an atomically flat surface.
BibTeX:
@article{Nanotechnology19p305705(2008)_Ostendorf,
  author = {F. Ostendorf and C. Schmitz and S. Hirth and A. Kühnle and J. J. Kolodziej and M. Reichling},
  title = {How flat is an air-cleaved mica surface?},
  journal = {Nanotechnology},
  year = {2008},
  volume = {19},
  number = {30},
  pages = {305705},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nanotechnology19p305705(2008)_Ostendorf.pdf},
  doi = {10.1088/0957-4484/19/30/305705}
}
Ostendorf F, Torbrügge S and Reichling M (2008), Atomic scale evidence for faceting stabilization of a polar oxide surface, Phys. Rev. B Vol. 77(4), pp. 041405.
Abstract: By highest-resolution dynamic scanning force microscopy operated in the non-contact mode, we reveal the complex stabilization mechanism of polar zinc-terminated ZnO(0001). The nanoscopic and atomic structures unveiled corroborate a model of stabilization via triangular structures. High-temperature preparation (T > 1300 K) yields a phase with an additional stabilization by faceting in the form of highly ordered step arrays. The terraces between steps are partly covered with triangular reconstructions exhibiting exclusively 101-10 nanofacets on step edges. Both mechanisms together allow a complete stabilization of the surface without the involvement of adsorbates.
BibTeX:
@article{PhysRevB77p041405(2008)_Ostendorf,
  author = {F. Ostendorf and S. Torbrügge and M. Reichling},
  title = {Atomic scale evidence for faceting stabilization of a polar oxide surface},
  journal = {Phys. Rev. B},
  year = {2008},
  volume = {77},
  number = {4},
  pages = {041405},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB77p041405(2008)_Ostendorf.pdf},
  doi = {10.1103/PhysRevB.77.041405}
}
Enevoldsen GH, Pinto HP, Foster AS, Jensen MCR, Kühnle A, Reichling M, Hofer WA, Lauritsen JV and Besenbacher F (2008), Detailed scanning probe microscopy tip models determined from simultaneous atom-resolved AFM and STM studies of the TiO2(110) surface, Phys. Rev. B Vol. 78(4), pp. 045416.
Abstract: The atomic-scale contrast in noncontact atomic force microscopy (nc-AFM) images is determined by the geometry and exact atomic structure of the tip apex. However, the tip state is an experimentally unknown parameter, and the lack of insight into the tip apex often limits the possibilities of extracting precise quantitative and qualitative atomistic information on the surface under inspection. From an interplay between simultaneously recorded nc-AFM and scanning tunneling microscopy (STM) data, and atomistic STM simulations based on multiple scattering theory, we demonstrate how the state of the scanning probe microscopy (SPM) tip in the experiments may be determined. The analysis of a large number of experimental SPM images recorded with different tips reveals that no general correlation exists between the contrast observed in the nc-AFM and the tunneling current (It) images on TiO2(110) surface. The exact state of the SPM tip must, therefore, be determined for each specific case, which is normally a very difficult endeavor. However, our analysis of the AFM contrast on TiO2(110) surface allows us to considerably reduce the number of tips to be considered in a full simulation. By carefully evaluating the contrast of a handpicked library of SPM tips, we manage to determine a very accurate model of the SPM tip used in an experiment for the first time. It is envisioned that the approach presented here may eventually be used in future studies to screen for and select a SPM tip with a special functionalization prior to imaging an unknown sample, and in that way facilitate precise modeling and chemical identification of surface species.
BibTeX:
@article{PhysRevB78p045416(2008)_Enevoldsen,
  author = {G. H. Enevoldsen and H. P. Pinto and A. S. Foster and M. C. R. Jensen and A. Kühnle and M. Reichling and W. A. Hofer and J. V. Lauritsen and F. Besenbacher},
  title = {Detailed scanning probe microscopy tip models determined from simultaneous atom-resolved AFM and STM studies of the TiO2(110) surface},
  journal = {Phys. Rev. B},
  year = {2008},
  volume = {78},
  number = {4},
  pages = {045416},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB78p045416(2008)_Enevoldsen.pdf
}, doi = {10.1103/PhysRevB.78.045416} }
Torbrügge S, Lübbe J, Tröger L, Cranney M, Eguchi T, Hasegawa Y and Reichling M (2008), Improvement of a dynamic scanning force microscope for highest resolution imaging in ultrahigh vacuum, Rev. Sci. Instrum. Vol. 79(8), pp. 083701.
Abstract: We report on a modification of a commercial scanning force microscope (Omicron UHV AFM/STM) operated in noncontact mode (NC-AFM) at room temperature in ultrahigh vacuum yielding a decrease in the spectral noise density from 2757 to 272 fm/?Hz. The major part of the noise reduction is achieved by an exchange of the originally installed light emitting diode by a laser diode placed outside the vacuum, where the light is coupled into the ultrahigh vacuum chamber via an optical fiber. The setup is further improved by the use of preamplifiers having a bandpass characteristics tailored to the cantilever resonance frequency. The enhanced signal to noise ratio is demonstrated by a comparison of atomic resolution images on CeO2(111) obtained before and after the modification.
BibTeX:
@article{RevSciInstrum79p083701(2008)_Torbrugge,
  author = {S. Torbrügge and J. Lübbe and L. Tröger and M. Cranney and T. Eguchi and Y. Hasegawa and M. Reichling},
  title = {Improvement of a dynamic scanning force microscope for highest resolution imaging in ultrahigh vacuum},
  journal = {Rev. Sci. Instrum.},
  year = {2008},
  volume = {79},
  number = {8},
  pages = {083701},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=RevSciInstrum79p083701(2008)_Torbrugge.pdf
}, doi = {10.1063/1.2964119} }
Gritschneder S, Becker C, Wandelt K and Reichling M (2007), Disorder or Complexity? Understanding a Nanoscale Template Structure on Alumina, J. Am. Chem. Soc. Vol. 129(16), pp. 4925-4928.
Abstract: One strategy in creating functional nanostructures is templating where active nanoparticles are arranged on a regular nanoscale array of anchor sites on an inert substrate. An extraordinarily well ordered substrate with a 4.2 nm template periodicity is an alumina (aluminum oxide) film grown on a Ni3Al(111) metallic alloy support. Templating on the alumina film is facilitated by a dot and a network superstructure that can readily be prepd. but has not yet been understood at the at. scale. By imaging the alumina surface with dynamic scanning force microscopy (SFM) operated in the noncontact mode (NC-AFM), we reveal that the main structural element of the oxide film is a lattice of hexagons with a 0.29 nm side length that is pinned to the 0.51 nm periodicity of the substrate. The surface unit cell is defined by distinguished sites forming the dot structure. Pinning the oxide film to the substrate furthermore results in a honeycomb-like topog. modulation referred to as the network structure. These findings demonstrate how long range order is generated by the superposition of complex structures that locally exhibit apparent atomic disorder.
BibTeX:
@article{JAmChemSoc129p4925(2007)_Gritschneder,
  author = {S. Gritschneder and C. Becker and K. Wandelt and M. Reichling},
  title = {Disorder or Complexity? Understanding a Nanoscale Template Structure on Alumina},
  journal = {J. Am. Chem. Soc.},
  year = {2007},
  volume = {129},
  number = {16},
  pages = {4925-4928},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JAmChemSoc129p4925(2007)_Gritschneder.pdf},
  doi = {10.1021/ja065118f}
}
Sils J, Radzhabov E and Reichling M (2007), Characterisation of oxygen defects in calciumdifluoride, J. Phys. Chem. Solids Vol. 68(3), pp. 420-425.
Abstract: We study the aggregation of oxygen dipoles well dispersed in a CaF2 crystal upon annealing at temps. ranging from 370 to 420 K. The concn. of oxygen dipoles is monitored by measuring the intensity of the ionic thermocurrent peak as well as by absorption and luminescence spectroscopies. Results from three methods agree within experimental error and yield an activation energy of (1.2 ±0.1) eV for the diffusion of isolated oxygen centers in the crystal.
BibTeX:
@article{JPhysChemSolids68p420(2007)_Sils,
  author = {J. Sils and E. Radzhabov and M. Reichling},
  title = {Characterisation of oxygen defects in calciumdifluoride},
  journal = {J. Phys. Chem. Solids},
  year = {2007},
  volume = {68},
  number = {3},
  pages = {420-425},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysChemSolids68p420(2007)_Sils.pdf},
  doi = {10.1016/j.jpcs.2006.12.003}
}
Gritschneder S and Reichling M (2007), Structural elements of CeO2(111) surfaces, Nanotechnology Vol. 18, pp. 044024.
Abstract: The atomic structure of the CeO2(111) surface in different states of cleanliness and reduction is studied in an ultra-high vacuum with high resolution dynamic scanning force microscopy operated in the non-contact mode (nc-AFM) and its structural elements are described by their characteristic contrast patterns. From a synopsis of results we develop a self-consistent interpretation of contrast features that is cross-checked by a systematic variation of experimental conditions and a comparison to previously obtained results. The most common deviations from the regular structure of the stoichiometric surface are surface oxygen vacancies, water adsorbed on top of cerium ions and hydroxide substituting surface oxygen. All of the species are found as single defects as well as in the form of structures composed of several similar defects. We find that water readily adsorbs on the surface and forms hydroxide if oxygen vacancies are present, while both the clean and defective surfaces are rather inert against exposure to molecular oxygen.
BibTeX:
@article{Nanotechnology18p044024(2007)_Gritschneder,
  author = {S. Gritschneder and M. Reichling},
  title = {Structural elements of CeO2(111) surfaces},
  journal = {Nanotechnology},
  year = {2007},
  volume = {18},
  pages = {044024},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nanotechnology18p044024(2007)_Gritschneder.pdf},
  doi = {10.1088/0957-4484/18/4/044024}
}
Gritschneder S, Iwasawa Y and Reichling M (2007), Strong adhesion of water to CeO2(111), Nanotechnology Vol. 18, pp. 044025.
Abstract: The adsorption of water molecules on a stoichiometric CeO2(111) surface at room temperature is studied with dynamic scanning force microscopy. Atomic resolution imaging reveals spontaneous adsorption as well as deposition of molecules by the tip of the force microscope. Water molecules localize exclusively on one type of site that is associated with the cerium ion sub-lattice and stick to the surface with an estimated surface diffusion barrier of 1 eV. Occasionally adsorbates are moved laterally across the cerium sub-lattice by the action of the scanning tip.
BibTeX:
@article{Nanotechnology18p044025(2007)_Gritschneder,
  author = {S. Gritschneder and Y. Iwasawa and M. Reichling},
  title = {Strong adhesion of water to CeO2(111)},
  journal = {Nanotechnology},
  year = {2007},
  volume = {18},
  pages = {044025},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nanotechnology18p044025(2007)_Gritschneder.pdf},
  doi = {10.1088/0957-4484/18/4/044025}
}
Gritschneder S, Degen S, Becker C, Wandelt K and Reichling M (2007), Atomic structure of a stripe phase on Al2O3/Ni3Al(111) revealed by scanning force microscopy, Phys. Rev. B Vol. 76(1), pp. 014123.
Abstract: The most remarkable feature of the ultrathin aluminum oxide film grown on Ni3Al(111) as reported in the literature is its surface reconstruction resulting in a dot structure with a large rhombic surface unit cell. Here, we demonstrate that this is the reconstruction of the dominant phase of the oxide film, while 5% ? 20% of the surface area may be covered by another reconstruction that is characterized by zigzag features arranged in parallel stripes. When investigated with scanning tunneling microscopy, this stripe phase appears to be very different from the dominant phase; however, highest resolution dynamic scanning force microscopy operated in the noncontact mode reveals great similarity of the atomic structures. Both phases consist of a modulated hexagonal lattice with 0.51 nm periodicity resembling the aluminum sublattice of the Ni3Al(111) substrate.
BibTeX:
@article{PhysRevB76p014123(2007)_Gritschneder,
  author = {S. Gritschneder and S. Degen and C. Becker and K. Wandelt and M. Reichling},
  title = {Atomic structure of a stripe phase on Al2O3/Ni3Al(111) revealed by scanning force microscopy},
  journal = {Phys. Rev. B},
  year = {2007},
  volume = {76},
  number = {1},
  pages = {014123},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB76p014123(2007)_Gritschneder.pdf},
  doi = {10.1103/PhysRevB.76.014123}
}
Kolodziej JJ, Goryl M, Konior J, Reichling M and Szymonski M (2007), Direct real-space imaging of the c(2 x 8)/(2 x 4) GaAs (001) surface structure, Phys. Rev. B Vol. 76(24), pp. 245314-245316.
Abstract: We have performed frequency-modulated atomic-force microscopy (FM-AFM) on the c(2×8)/(2×4) GaAs (001) surface obtained from the c(8×2)/(4×6) surface by exposing it to As2 gas and annealing. Highly resolved interaction patterns reflect prevailing surface dimer pairs consistent with a so-called ?2 structure, but more rare motifs characteristic of ?2 and ? structures are also seen. Atoms of the dimers interact with the atomic force microscope tip repulsively and appear as sharp features on a smooth background when imaged in constant-height mode. An analysis of the interaction decay length and lateral size of the atomic features indicates that the surface atoms are visualized through a core-core repulsion mechanism. In this imaging mode, the FM-AFM can be regarded as a true surface structure tool, since the observed features are, in the absence of significant lateral relaxation, associated with surface atoms directly.
BibTeX:
@article{PhysRevB76p245314(2007)_Kolodziej,
  author = {J. J. Kolodziej and M. Goryl and J. Konior and M. Reichling and M. Szymonski},
  title = {Direct real-space imaging of the c(2 x 8)/(2 x 4) GaAs (001) surface structure},
  journal = {Phys. Rev. B},
  year = {2007},
  volume = {76},
  number = {24},
  pages = {245314-245316},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB76p245314(2007)_Kolodziej.pdf},
  doi = {10.1103/PhysRevB.76.245314}
}
Torbrügge S, Reichling M, Ishiyama A, Morita S and Custance O (2007), Evidence of Subsurface Oxygen Vacancy Ordering on Reduced CeO2(111), Phys. Rev. Lett. Vol. 99(5), pp. 056101.
Abstract: Surface and subsurface oxygen vacancies on the slightly reduced CeO2(111) surface have been studied by atomic resolution dynamic force microscopy at 80 K. Both types of defect are clearly identified by the comparison of the observed topographic features with the corresponding structures predicted from recent first-principles calculations. By combining two simultaneously acquired signals (the topography and the energy dissipated from the cantilever oscillation), we are able to unambiguously locate subsurface oxygen vacancies buried at the third surface atomic layer. We report evidence of local ordering of these subsurface defects that suggests the existence of a delicate balance between subtle interactions among adjacent subsurface oxygen vacancy structures.
BibTeX:
@article{PhysRevLett99p056101(2007)_Torbrugge,
  author = {S. Torbrügge and M. Reichling and A. Ishiyama and S. Morita and O. Custance},
  title = {Evidence of Subsurface Oxygen Vacancy Ordering on Reduced CeO2(111)},
  journal = {Phys. Rev. Lett.},
  year = {2007},
  volume = {99},
  number = {5},
  pages = {056101},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevLett99p056101(2007)_Torbrugge.pdf},
  doi = {10.1103/PhysRevLett.99.056101}
}
Schmid M, Kresse G, Buchsbaum A, Napetschnig E, Gritschneder S, Reichling M and Varga P (2007), Nanotemplate with Holes: Ultrathin Alumina on Ni3Al(111), Phys. Rev. Lett. Vol. 99(19), pp. 196104-196104.
Abstract: We have determined the structure of the ultrathin (?67 × ?67)R12.2° aluminum oxide on Ni3Al(111) by a combination of scanning tunneling microscopy and density functional theory. In addition to other local defects, the main structural feature of the unit cell is a 0.4-nm-diameter hole reaching down to the metal substrate. Understanding the structure and metal growth on this oxide allows us to use it as a template for growing highly regular arrays of nanoparticles.
BibTeX:
@article{PhysRevLett99p196104(2007)_Schmid,
  author = {M. Schmid and G. Kresse and A. Buchsbaum and E. Napetschnig and S. Gritschneder and M. Reichling and P. Varga},
  title = {Nanotemplate with Holes: Ultrathin Alumina on Ni3Al(111)},
  journal = {Phys. Rev. Lett.},
  year = {2007},
  volume = {99},
  number = {19},
  pages = {196104-196104},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevLett99p196104(2007)_Schmid.pdf},
  doi = {10.1103/PhysRevLett.99.196104}
}
Lauritsen JV, Foster AS, Olesen GH, Christensen MC, Kühnle A, Helveg S, Rostrup-Nielsen JR, Clausen BS, Reichling M and Besenbacher F (2006), Chemical identification of point defects and adsorbates on a metal oxide surface by atomic force microscopy, Nanotechnology Vol. 17(14), pp. 3436-3441.
Abstract: Atomic force microscopy in the non-contact mode (nc-AFM) can provide atom-resolved images of the surface of, in principle, any material independent of its conductivity. Due to the complex mechanisms involved in the contrast formation in nc-AFM imaging, it is, however, far from trivial to identify individual surface atoms or adsorbates from AFM images. In this work, we successfully demonstrate how to extract detailed information about defects and the chemical identity of adsorbates on a metal oxide surface from nc-AFM images. We make use of the observation that the apex of the AFM tip can be altered to expose either a positive or negative tip termination. The complementary set of images recorded with the two tip terminations unambiguously define the ionic sub-lattices and reveal the exact positions of oxygen vacancies and hydroxyl (OH) defects on a TiO2 surface. Chemical specificity is extracted by comparing the characteristic contrast patterns of the defects with results from comprehensive AFM simulations. Our methodology of analysis is generally applicable and may be pivotal for uncovering surface defects and adsorbates on other transition metal oxides designed for heterogeneous catalysis, photo-electrolysis or biocompatibility.
BibTeX:
@article{Nanotechnology17p3436(2006)_Lauritsen,
  author = {J. V. Lauritsen and A. S. Foster and G. H. Olesen and M. C. Christensen and A. Kühnle and S. Helveg and J. R. Rostrup-Nielsen and B. S. Clausen and M. Reichling and F. Besenbacher},
  title = {Chemical identification of point defects and adsorbates on a metal oxide surface by atomic force microscopy},
  journal = {Nanotechnology},
  year = {2006},
  volume = {17},
  number = {14},
  pages = {3436-3441},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nanotechnology17p3436(2006)_Lauritsen.pdf},
  doi = {10.1088/0957-4484/17/14/015}
}
Hirth S, Ostendorf F and Reichling M (2006), Lateral manipulation of atomic size defects on the CaF2(111) surface, Nanotechnology Vol. 17(7), pp. S148-S154.
Abstract: Atomic scale manipulation on insulating surfaces is one of the great challenges of non-contact atomic force microscopy. Here we demonstrate lateral manipulation of defects occupying single ionic sites on a calcium fluoride (111)-surface. Defects stem from the interaction of the residual gas with the surface. The process of surface degradation is briefly discussed. Manipulation is performed over a wide range of path lengths ranging from tens of nanometres down to a few lattice constants. We introduce a simple manipulation protocol based on line-by-line scanning of a surface region containing defects to be manipulated, and record tip-surface distance and cantilever resonance frequency detuning as a function of the manipulation pathway in real time. We suggest a hopping model to describe manipulation where the tip-defect interaction is governed by repulsive forces.
BibTeX:
@article{Nanotechnology17pS148(2006)_Hirth,
  author = {S. Hirth and F. Ostendorf and M. Reichling},
  title = {Lateral manipulation of atomic size defects on the CaF2(111) surface},
  journal = {Nanotechnology},
  year = {2006},
  volume = {17},
  number = {7},
  pages = {S148-S154},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nanotechnology17pS148(2006)_Hirth.pdf},
  doi = {10.1088/0957-4484/17/7/S08}
}
Hoffmann R, Barth C, Foster AS, Shluger AL, Hug HJ, Güntherodt H-J, Nieminen RM and Reichling M (2005), Measuring Site-Specific Cluster-Surface Bond Formation, J. Am. Chem. Soc. Vol. 127(50), pp. 17863-17866.
Abstract: Recent advances in dynamic force microscopy show that it is possible to measure the forces between atomically sharp tips and particular at. positions on surfaces as a function of distance. However, on most ionic surfaces, the pos. and neg. ions can so far not be distinguished. In this paper, we use the CaF2(111) surface, where at. resoln. force microscopy has allowed identification of the positions of the Ca2+ and F- ions in the obtained images, to demonstrate that short-range interaction forces can be measured selectively above chem. identified surface sites. Combining exptl. and theor. results allows a quantification of the strength and distance dependence of the interaction of a tip-terminating cluster with particular surface ions and reveals details of cluster and surface relaxation. Further development of this approach will provide new insight into mechanisms of chem. bond formation between clusters, cluster deposition at surfaces, processes in adhesion and tribol., and single atom manipulation with the force microscope.
BibTeX:
@article{JAmChemSoc127p17863(2005)_Hoffmann,
  author = {R. Hoffmann and C. Barth and A. S. Foster and A. L. Shluger and H. J. Hug and H.-J. Güntherodt and R. M. Nieminen and M. Reichling},
  title = {Measuring Site-Specific Cluster-Surface Bond Formation},
  journal = {J. Am. Chem. Soc.},
  year = {2005},
  volume = {127},
  number = {50},
  pages = {17863-17866},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JAmChemSoc127p17863(2005)_Hoffmann.pdf},
  doi = {10.1021/ja055267i}
}
Gritschneder S, Namba Y and Reichling M (2005), Nanoscale structures on ultra-precision machined fluorite surfaces, Nanotechnology Vol. 16(6), pp. 883-887.
Abstract: Highest purity calcium difluoride crystals having a roughness below 1nm over large areas were prepared by ultra-precision machining to create technical surfaces for optical applications. High resolution dynamic scanning force microscopy reveals surfaces with close to atomic flatness over areas larger than 10 ?m2. The residual roughness is due to a high density of pits and protrusions with a height of 0.32 nm corresponding to an F-Ca-F triple-layer that is the smallest possible unit on stoichiometric CaF2(111). Additionally, imperfections of the machining process may appear as protrusions of typically 1 nm height or a high density of aligned triple-layer steps for surfaces that were apparently slightly inclined with respect to the machining plane. A terraced structure also appears in the vicinity of nanometre-sized defects found for one sample. Machining may also cause a fracture in the form of branched channels of some tens of nanometres in width and some micrometers in length.
BibTeX:
@article{Nanotechnology16p883(2005)_Gritschneder,
  author = {S. Gritschneder and Y. Namba and M. Reichling},
  title = {Nanoscale structures on ultra-precision machined fluorite surfaces},
  journal = {Nanotechnology},
  year = {2005},
  volume = {16},
  number = {6},
  pages = {883-887},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nanotechnology16p883(2005)_Gritschneder.pdf},
  doi = {10.1088/0957-4484/16/6/044}
}
Giessibl FJ and Reichling M (2005), Investigating atomic details of the CaF2(111) surface with a qPlus sensor, Nanotechnology Vol. 16(3), pp. S118-S124.
Abstract: The (111) surface of CaF2 has been intensively studied with large-amplitude frequency-modulation at. force microscopy, and the at. contrast formation is now well understood. It has been shown that the apparent contrast patterns obtained with a polar tip strongly depend on the tip terminating ion, and three sub-lattices of anions and cations can be imaged. Here, we study the details of at. contrast formation on CaF2(111) with small-amplitude force microscopy utilizing the qPlus sensor that has been shown to provide the utmost resoln. at high scanning stability. Step edges resulting from cleaving crystals in situ in the ultra-high vacuum appear as very sharp structures, and on flat terraces the at. corrugation is seen in high clarity even for large area scans. The at. structure is also not lost when scanning across triple layer step edges. High-resoln. scans of small surface areas yield contrast features of anion- and cation sub-lattices with unprecedented resoln. These contrast patterns are related to previously reported theor. results.
BibTeX:
@article{Nanotechnology16pS118(2005)_Giessibl,
  author = {F. J. Giessibl and M. Reichling},
  title = {Investigating atomic details of the CaF2(111) surface with a qPlus sensor},
  journal = {Nanotechnology},
  year = {2005},
  volume = {16},
  number = {3},
  pages = {S118-S124},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nanotechnology16pS118(2005)_Giessibl.pdf},
  doi = {10.1088/0957-4484/16/3/022}
}
Gritschneder S, Namai Y, Iwasawa Y and Reichling M (2005), Structural features of CeO2(111) revealed by dynamic SFM, Nanotechnology Vol. 16(3), pp. S41-S48.
Abstract: Cerium dioxide is an insulating material that is important in various fields of catalysis and often used as an oxygen reservoir. The (111) surface of CeO2 is catalytically active and we study this surface in its various oxidation states by dynamic force microscopy, an analysis that may eventually help to establish structure–function relationships for catalysis. We present highly resolved images and atomic details of surface features on CeO2(111) like terrace structures, step edges, kinks and hexagonally shaped pits that are naturally formed during surface preparation by sputtering and annealing cycles. We find that such structures can be well imaged with atomic resolution and that they exhibit morphological characteristics that are significantly different in details from those of cleaved CaF2(111), a surface with exactly the same crystallographic structure and very similar lattice constants and ionic radii. In this study, we continuously monitor the shape of the tip apex and demonstrate that high quality atomic resolution imaging is possible with one tip, although the tip apex is drastically changed by wear during 45 h of scanning.
BibTeX:
@article{Nanotechnology16pS41(2005)_Gritschneder,
  author = {S. Gritschneder and Y. Namai and Y. Iwasawa and M. Reichling},
  title = {Structural features of CeO2(111) revealed by dynamic SFM},
  journal = {Nanotechnology},
  year = {2005},
  volume = {16},
  number = {3},
  pages = {S41-S48},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nanotechnology16pS41(2005)_Gritschneder.pdf},
  doi = {10.1088/0957-4484/16/3/008}
}
Mysovsky AS, Radzhabov EA, Reichling M, Shluger AL and Sushko PV (2005), Optical properties and transformation mechanism of oxygen centres and their aggregates in CaF2 crystals, Phys. Status Solidi C Vol. 2(1), pp. 392-396.
Abstract: Oxygen vacancy dipoles and dimers in CaF2 crystals have been studied ab-initio at DFT level and with the shell model using pair potentials. The calculated dipole reorientation barrier is 0.64 eV and the activation energy for diffusion of the dipoles is 1.61 eV. Optical absorption of O2--VA dipole have been calcd. with TD DFT and identified with exptl. absorption bands, which appeared to have complex structure. The photodissocn. mechanism of the dipole is discussed. Several configurations of the dimer (O2--VA)2 were calculated. The association. energy for the most favorable one is 0.48 eV.
BibTeX:
@article{PhysStatusSolidiC2p392(2005)_Mysovsky,
  author = {A. S. Mysovsky and E. A. Radzhabov and M. Reichling and A. L. Shluger and P. V. Sushko},
  title = {Optical properties and transformation mechanism of oxygen centres and their aggregates in CaF2 crystals},
  journal = {Phys. Status Solidi C},
  year = {2005},
  volume = {2},
  number = {1},
  pages = {392-396},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysStatusSolidiC2p392(2005)_Mysovsky.pdf},
  doi = {10.1002/pssc.200460191}
}
Cecco C, Barth C, Gille P, Feuerbacher M, Krausch G and Reichling M (2004), Cleaved surfaces of d-AlNiCo and x'-AlPdMn, J.Non-Cryst. Solids Vol. 334-335, pp. 491-494.
Abstract: Decagonal Al-Ni-Co quasicrystals were cleaved in ultrahigh-vacuum and the resulting surfaces were investigated by dynamic scanning force microscopy. The samples were cleaved perpendicular to the tenfold axis and perpendicular to one of the twofold axes. Both surfaces show a rough structure with lateral features on the nanometer scale and height differences of angstroms to nanometers. While the corrugation of the tenfold surface does not show any correlation to the quasiperiodic bulk structure, the twofold surface exhibits row-like corrugations, which indicate the existence of columnar structure motifs along the direction of the tenfold axis as expected from structure models. Images from surface regions tilted with respect to the twofold plane strongly indicate the existence of inclined net-planes. In addn., surfaces of an x'-(Al-Pd-Mn) quasicrystal approximant were studied which was cleaved perpendicular to the pseudo-tenfold b-axis. These surfaces show a corrugated structure as well, similar to the results obtained from the decagonal Al-Ni-Co surfaces. There is no indication of a correlation to the periodicity or other structural features of this orthorhombic, crystalline material.
BibTeX:
@article{JournalofNon-CrystallineSolids334-335p491(2004)_Cecco,
  author = {C. Cecco and C. Barth and P. Gille and M. Feuerbacher and G. Krausch and M. Reichling},
  title = {Cleaved surfaces of d-AlNiCo and x'-AlPdMn},
  journal = {J.Non-Cryst. Solids},
  year = {2004},
  volume = {334-335},
  pages = {491-494},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JournalofNon-CrystallineSolids334-335p491(2004)_Cecco.pdf},
  doi = {10.1016/j.jnoncrysol.2003.12.019}
}
Arai T, Gritschneder S, Tröger L and Reichling M (2004), Carbon tips as sensitive detectors for nanoscale surface and sub-surface charge, Nanotechnology Vol. 15, pp. 1302-1306.
Abstract: Electrically insulating tips prepared by carbon deposition are used as sensitive detectors of nanoscale charge patterns on cleaved insulating surfaces. Dynamic scanning force microscopy images recorded with a neutral carbon tip reveal the surface topography and strong local charging at step edges while images taken with a charged tip exhibit subtle contrast features resulting from charges located at or beneath the surface of flat terraces. Analysing dynamic phenomena during imaging allows a determination of charge polarity and identifies sub-surface charges as trapping centres for charges exchanged between the tip and the surface. A density of a few hundred charged sub-surface defects per ?m2 is determined on CaCO3(10-14) while the defect density is one order of magnitude smaller on CaF2(111). The method allows the detection of elementary charges at room temperature.
BibTeX:
@article{Nanotechnology15p1302(2004)_Arai,
  author = {T. Arai and S. Gritschneder and L. Tröger and M. Reichling},
  title = {Carbon tips as sensitive detectors for nanoscale surface and sub-surface charge},
  journal = {Nanotechnology},
  year = {2004},
  volume = {15},
  pages = {1302-1306},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nanotechnology15p1302(2004)_Arai.pdf},
  doi = {10.1088/0957-4484/15/9/032}
}
Foster AS, Barth C, Shluger AL, Nieminen RM and Reichling M (2002), Role of tip structure and surface relaxation in atomic resolution dynamic force microscopy. CaF2(111) as a reference surface, Phys. Rev. B Vol. 66(23), pp. 235417.
Abstract: By combining exptl. dynamic scanning force microscope (SFM) images of the CaF2(111) surface with an extensive theor. modeling, we demonstrate that the two different contrast patterns obtained reproducible on this surface can be clearly explained in terms of the change of the sign of the electrostatic potential at the tip end. We also present direct theor. simulations of exptl. dynamic SFM images of an ionic surface at different tip-surface distances. Exptl. results demonstrate a qual. transformation of the image pattern, which is fully reproduced by the theor. modeling and is related to the character of tip-induced displacements of the surface atoms. The modeling of the image transformation upon a systematic redn. of the tip-surface distance with ionic tips allows an est. of the tip-surface distance present in expt., where 0.28-0.40 nm is found to be optimal for stable imaging with well-defined at. contrast. We also compare the modeling with ionic tips to results for a pure Si tip. This comparison demonstrates that a Si tip can yield only one type of image contrast and that the tip-surface interaction is not strong enough to explain the image contrast obsd. exptl. The proposed interpretation of two types of images for the CaF2(111) surface can also be used to det. the chem. identity of imaged features on other surfaces with similar structure.
BibTeX:
@article{PhysRevB66p235417(2002)_Foster,
  author = {A. S. Foster and C. Barth and A. L. Shluger and R. M. Nieminen and M. Reichling},
  title = {Role of tip structure and surface relaxation in atomic resolution dynamic force microscopy. CaF2(111) as a reference surface},
  journal = {Phys. Rev. B},
  year = {2002},
  volume = {66},
  number = {23},
  pages = {235417},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB66p235417(2002)_Foster.pdf},
  doi = {10.1103/PhysRevB.66.235417}
}
Puchin VE, Puchina AV, Huisinga M and Reichling M (2001), Theoretical modelling of steps on the CaF2(111) surface, J. Phys.: Condens. Matter Vol. 13(10), pp. 2081-2094.
Abstract: The atomic and electronic structure and relaxation of the perfect (111) surface and several low-index surfaces of CaF2 are calculated using an ab initio Hartree-Fock method. We find marked differences between the bulk and surface valence band structures; however, the band gap is reduced by only 0.5 eV for the stepped surface. The (111) surface is found to exhibit no significant relaxation and we obtain a surface energy of 0.47 J m-2. The atomic structure of two types of stepped surface both having 0.32 nm high steps aligned along the [110] crystallographic direction is determined and the step energies are found to be 0.25 and 0.35 nJ m-1, respectively. Step energies for configurations involving other orientations of steps are considerably higher. The formation of double-height steps along [110], however, is found to be energetically favourable. A considerable amount of relaxation is found for stepped surfaces and we explain qualitatively why it results in a roughening of the surface in some cases. The energetic position of gap electronic states induced by steps on the (111) surface is found to be very similar to that for surface states of the perfect (111) surface; i.e. such states do not yield a significant density of states more than 0.5 eV above the bulk valence band maximum. We discuss how the step formation energies found here might explain surface topographical features found on cleaved and grown CaF2(111) surfaces.
BibTeX:
@article{JPhysCM13p2081(2001)_Puchin,
  author = {V. E. Puchin and A. V. Puchina and M. Huisinga and M. Reichling},
  title = {Theoretical modelling of steps on the CaF2(111) surface},
  journal = {J. Phys.: Condens. Matter},
  year = {2001},
  volume = {13},
  number = {10},
  pages = {2081-2094},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysCM13p2081(2001)_Puchin.pdf},
  doi = {10.1088/0953-8984/13/10/304}
}
Barth C, Foster AS, Reichling M and Shluger AL (2001), Contrast formation in atomic resolution scanning force microscopy on CaF2(111): experiment and theory, J. Phys.: Condens. Matter Vol. 13(10), pp. 2061-2079.
Abstract: We investigate mechanisms of contrast formation in atomic resolution imaging of flat terraces on the CaF2(111) surface with scanning force microscopy operated in the dynamic mode. Experimental results are interpreted with a theory based on atomistic modelling. Experiments reveal characteristic contrast features in the form of triangles that can be explained by theory as being due to the interaction of a positively terminated tip with fluorine ions from two different sublattices. Results for a tip with negative termination are found not to be compatible with experiments. We demonstrate that theory correctly predicts the trend in contrast changes when varying the tip-surface distance but is also limited in quantitative agreement due to the non-ideal atomic structure of real tips, In a distance range where such peculiarities do not play a major role, however, we find good quantitative agreement between theoretical predictions and experimental results, The validity of the comparison between theory and experimental scan lines is discussed in detail using an extensive statistical image analysis.
BibTeX:
@article{JPhysCondensMatter13p2061(2001)_Barth,
  author = {C. Barth and A. S. Foster and M. Reichling and A. L. Shluger},
  title = {Contrast formation in atomic resolution scanning force microscopy on CaF2(111): experiment and theory},
  journal = {J. Phys.: Condens. Matter},
  year = {2001},
  volume = {13},
  number = {10},
  pages = {2061-2079},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysCM13p2061(2001)_Barth.pdf},
  doi = {10.1088/0953-8984/13/10/303}
}
Lindner R, Reichling M, Williams RT and Matthias E (2001), Femtosecond laser pulse excitation of electrons and excitons in CaF2 and SrF2, J. Phys.: Condens. Matter Vol. 13(10), pp. 2339-2346.
Abstract: Conduction band electrons, valence holes and subsequently self-trapped excitons (STEs) are created in CaF2 and SrF2 by two-photon absorption of 5.9 eV photons. Transient absorption after femtosecond pulse excitation is measured at probe wavelengths of 3.0 eV and 4.4 eV, respectively. Transient absorption of 3.0 eV photons yields a fast initial response in SrF2 due to absorption by conduction band electrons, while in CaF2 we sample the F centre part of the STE at 3.0 eV and determine its formation time constant to be 690 fs. Excitation at 3.0 eV also yields a reduction in STE luminescence sampled nanoseconds after STE creation that is attributed to a forced recombination of the nearest-neighbour defect pair. Probing with 4.4 eV photons yields much weaker absorption but confirms results for 3.0 eV photons. Additionally we observe stronger absorption due to the formation of long living defects.
BibTeX:
@article{JPhysCondensMatter13p2339(2001)_Lindner,
  author = {R. Lindner and M. Reichling and R. T. Williams and E. Matthias},
  title = {Femtosecond laser pulse excitation of electrons and excitons in CaF2 and SrF2},
  journal = {J. Phys.: Condens. Matter},
  year = {2001},
  volume = {13},
  number = {10},
  pages = {2339-2346},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysCM13p2339(2001)_Lindner.pdf},
  doi = {10.1088/0953-8984/13/10/324}
}
Barth C and Reichling M (2001), Imaging the atomic arrangements on the high-temperature reconstructed a-Al2O3(0001) surface, Nature Vol. 414, pp. 54-57.
Abstract: Alumina is a technologically important oxide crystal because of its use as a catalyst and as a substrate for microelectronic applications. A precise knowledge of its surface atomic structure is a prerequisite for understanding and controlling the physical processes involved in many of its applications. Here we use a dynamic scanning force microscopy technique to image directly the atomic structure of the high-temperature phase of the ?-Al2O3(0001) surface. Evidence for a surface reconstruction appears as a grid of protrusions that represent a rhombic unit cell, and we confirm that the arrangement of atoms is in the form of surface domains with hexagonal atomic order at the centre and disorder at the periphery. We show that, on exposing the surface to water and hydrogen, this surface structure is important in the formation of hydroxide clusters. These clusters appear as a regular pattern of rings that can be explained by self-organization processes involving cluster?surface and cluster?cluster interactions. Alumina has long been regarded as the definitive test for atomic-resolution force microscopy of insulators so the whole class of insulating oxides should now open for direct atomic-scale surface investigations.
BibTeX:
@article{Nature414p54(2001)_Barth,
  author = {C. Barth and M. Reichling},
  title = {Imaging the atomic arrangements on the high-temperature reconstructed a-Al2O3(0001) surface},
  journal = {Nature},
  year = {2001},
  volume = {414},
  pages = {54-57},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Nature414p54(2001)_Barth.pdf},
  doi = {10.1038/35102031}
}
Lindner R, Williams RT and Reichling M (2001), Time-dependent luminescence of self-trapped excitons in alkaline-earth fluorides excited by femtosecond laser pulses, Phys. Rev. B Vol. 63(07), pp. 075110.
Abstract: We studied the decay of self-trapped excitons (STE's) in BaF2, SrF2, and CaF2 excited at room temperature by two-photon absorption of femtosecond laser pulses by recording time-resolved triplet-luminescence spectra. For BaF2 we detected significant spectral changes as a function of decay time but this effect was much less pronounced for SrF2 and barely to be identified in CaF2. A careful analysis of BaF2 data revealed two principal decay times of 0.6 mus and approximately 4 ?s, respectively, where the latter is actually a range of decay times correlating with photon energy within the luminescence band. We attribute this spectral characteristic to a superposition of contributions from several relaxed STE configurations while the two principal decay times are believed to result from the zero-field splitting of the 3?+u state of the STE.
BibTeX:
@article{PhysRevB63p075110(2001)_Lindner,
  author = {R. Lindner and R. T. Williams and M. Reichling},
  title = {Time-dependent luminescence of self-trapped excitons in alkaline-earth fluorides excited by femtosecond laser pulses},
  journal = {Phys. Rev. B},
  year = {2001},
  volume = {63},
  number = {07},
  pages = {075110},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB63p075110(2001)_Lindner.pdf},
  doi = {10.1103/PhysRevB.63.075110}
}
Foster AS, Barth C, Shluger AL and Reichling M (2001), Unambiguous interpretation of atomically resolved force microscopy images of an insulator, Phys. Rev. Lett. Vol. 86(11), pp. 2373-2376.
Abstract: The (111) surface of CaF2 was imaged with dynamic mode scanning force microscopy and modeled using atomistic simulation. Both experiment and theory showed a clear triangular contrast pattern in images, and theory demonstrated that the contrast pattern is due to the interaction of a positive electrostatic potential tip with fluorine ions in the two topmost surface layers. We find a good agreement of position and relative height of scan line features between theory and experiment and thus establish for the first time an unambiguous identification of sublattices of an insulator imaged by force microscopy.
BibTeX:
@article{PhysRevLett86p2373(2001)_Foster,
  author = {A. S. Foster and C. Barth and A. L. Shluger and M. Reichling},
  title = {Unambiguous interpretation of atomically resolved force microscopy images of an insulator},
  journal = {Phys. Rev. Lett.},
  year = {2001},
  volume = {86},
  number = {11},
  pages = {2373-2376},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevLett86p2373(2001)_Foster.pdf},
  doi = {10.1103/PhysRevLett.86.2373}
}
Moritz W, Roth U, Heyde M, Rademann K, Reichling M and Hartmann J (2001), Submicrosecond range surface heating and temperature measurement for efficient sensor reactivation, Thin Solid Films Vol. 391(1), pp. 143-148.
Abstract: A method for submicrosecond heating of sensor surfaces and simultaneous detection of the surface temperature was developed enabling accurate and fast reactivation of a semiconductor based oxygen sensor. High power electrical pulses with current densities of more than 10(7) A/cm(2) were applied to the 60-nm-thick Pt layer of a chemical semiconductor sensor structure resulting in surface temperatures as high as 700 K maintained in the nanosecond to microsecond range. Temperature measurement was carried out using the temperature dependent electrical resistance of the Pt film. Electrical power pulses of defined shape allowed accurate control of the surface temperature with ns time resolution. The high reactivation surface temperatures required high current densities, eventually leading to fatal destruction of the sensor structure. Comparative numerical simulations of the thermal impact as well as photo thermal and scanning force microscopy measurements were performed to optimize the heating process and to investigate the destruction mechanism. (C) 2001 Elsevier Science B.V. All rights reserved.
BibTeX:
@article{ThinSolFilms391p143(2001)_Moritz,
  author = {W. Moritz and U. Roth and M. Heyde and K. Rademann and M. Reichling and J. Hartmann},
  title = {Submicrosecond range surface heating and temperature measurement for efficient sensor reactivation},
  journal = {Thin Solid Films},
  year = {2001},
  volume = {391},
  number = {1},
  pages = {143-148},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ThinSolFilms391p143(2001)_Moritz.pdf},
  doi = {10.1016/S0040-6090(01)00967-1}
}
Barth C and Reichling M (2000), Resolving ions and vacancies at step edges on insulating surfaces, Surf. Sci. Vol. 470(1-2), pp. L99-L103.
Abstract: Surfaces of BaF2 and SrF2 prepared by cleavage along (111) planes in ultra-high vacuum were investigated with a dynamic scanning force microscope operated in the constant frequency detuning mode. We observe an atomic corrugation of some 10 pm on terraces and demonstrate that individual ions and vacancies can be resolved at step edges. Step edges do not necessarily follow low index crystallographic directions but may exhibit significant roughness on the atomic scale.
BibTeX:
@article{SurfSci470pL99(2000)_Barth,
  author = {C. Barth and M. Reichling},
  title = {Resolving ions and vacancies at step edges on insulating surfaces},
  journal = {Surf. Sci.},
  year = {2000},
  volume = {470},
  number = {1-2},
  pages = {L99-L103},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=SurfSci470pL99(2000)_Barth.pdf},
  doi = {10.1016/S0039-6028(00)00916-X}
}
Reichling M, Sils J, Johansen H and Matthias E (1999), Nanosecond UV laser damage and ablation from fluoride crystals polished by different techniques, Appl. Phys. A Vol. 69, pp. S743-S747.
Abstract: Ablation thresholds and damage behavior of cleaved and polished surfaces of CaF2, BaF2, LiF and MgF2 subjected to single-shot irradiation with 248 nm/14 ns laser pulses have been investigated using the photoacoustic mirage technique and scanning electron microscopy. For CaF2, standard polishing yields an ablation threshold of typically 20 J/cm2. When the surface is polished chemo-mechanically, the threshold can be raised to 43 J/cm2, while polishing by diamond turning leads to intermediate values around 30 J/cm2 Cleaved surfaces possess no well-defined damage threshold. When comparing different fluoride surfaces prepared by diamond turning it is found that the damage resistivity roughly scales with the band gap. We find an ablation threshold of 40 J/cm2 for diamond turned LiF while the MgF2 surface can withstand a fluence of more than 60 J/cm2 without damage. The damage topography of conventionally polished surfaces shows flaky ablation across the laser-heated area with cracks along the cleavage planes. No ablation is observed in the case of chemo- mechanical polishing; only a few cracks appear. Diamond turned surfaces show small optical absorption but mostly cracks and ablation of flakes and, in some cases, severe damage in the form of craters larger than the irradiated area. The origin of such different damage behavior is discussed.
BibTeX:
@article{ApplPhysA69pS743(1999)_Reichling,
  author = {M. Reichling and J. Sils and H. Johansen and E. Matthias},
  title = {Nanosecond UV laser damage and ablation from fluoride crystals polished by different techniques},
  journal = {Appl. Phys. A},
  year = {1999},
  volume = {69},
  pages = {S743-S747},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysA69pS743(1999)_Reichling.pdf},
  doi = {10.1007/s003399900369}
}
Lindner R, Reichling M, Matthias E and Johansen H (1999), Luminescence and damage thresholds of cerium-doped LaF3 for ns-pulsed laser excitation at 248 nm, Appl. Phys. B Vol. 68(2), pp. 233-241.
Abstract: We have studied time-resolved luminescence spectra and laser damage thresholds of Ce:LaF3 following excitation with 248 nm/14 ns laser pulses at room temperature for the two Ce concentrations 0.03 and 1 mol %. The relative intensities of the 5d-4f bands emitted from Ce3+ at regular and at perturbed lattice sites were found to vary linearly with time for the higher concentration and quadratically for the lower one. This can be explained by radiative energy transfer between the two sites and generation of new perturbed sites at a rate that only shows up for the low Ce concentration. Lifetimes of the respective emission bands were determined to be about 18 ns and 41 ns. Despite resonant absorption of the 5 eV photons, surprisingly high ablation thresholds - 16 J/cm2 for 0.03% Ce, and 10 J/cm2 for 1% Ce - were observed by the probe-beam deflection technique. The reason is the strong energy loss due to intense fluorescence and deposition of the nonradiative energy fraction in the bulk rather than at the surface. The depth of energy deposition was revealed by scanning electron microscopy in the form of distinctly different ablation morphologies for the two Ce concentrations.
BibTeX:
@article{ApplPhysB68p233(1999)_Lindner,
  author = {R. Lindner and M. Reichling and E. Matthias and H. Johansen},
  title = {Luminescence and damage thresholds of cerium-doped LaF3 for ns-pulsed laser excitation at 248 nm},
  journal = {Appl. Phys. B},
  year = {1999},
  volume = {68},
  number = {2},
  pages = {233-241},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysB68p233(1999)_Lindner.pdf},
  doi = {10.1007/s003400050612}
}
Sils J, Reichling M, Matthias E and Johansen H (1999), Laser damage and ablation of differently prepared CaF2(111) surfaces, Czech. J. Phys. Vol. 49(12), pp. 1737-1742.
Abstract: Ablation thresholds and damage behavior of cleaved and polished CaF2(111) surfaces produced by single shot irradiation with 248 nm/14 ns laser pulses have been investigated using the photoacoustic mirage technique and scanning electron microscopy. The standard polishing yields an ablation threshold of typically 20 J/cm2. When surfaces are polished chemo-mechanically the threshold is raised to 43 J/cm2. Polishing by diamond turning leads to intermediate values around 30 J/cm2. Cleaved surfaces possess no well-defined damage threshold. The damage topography of conventionally polished surfaces shows ablation of flakes across the laser heated area with cracks along the cleavage planes. In the case of chemo-mechanical polishing only a few cracks appear. Diamond turned surfaces show small optical absorption, but cracks and ablation of tiles. The origin of such different damage behavior is discussed.
BibTeX:
@article{CzechJPhys49p1737(1999)_Sils,
  author = {J. Sils and M. Reichling and E. Matthias and H. Johansen},
  title = {Laser damage and ablation of differently prepared CaF2(111) surfaces},
  journal = {Czech. J. Phys.},
  year = {1999},
  volume = {49},
  number = {12},
  pages = {1737-1742},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=CzechJPhys49p1737(1999)_Sils.pdf},
  doi = {10.1023/A:1022836104646}
}
Bennewitz R, Smith D and Reichling M (1999), Bulk and surface processes in low-energy-electron-induced decomposition of CaF2, Phys. Rev. B Vol. 59(12), pp. 8237-8246.
Abstract: The irradiation of CaF2, with low-energy (typically 1 keV) electrons results in a decomposition of the crystal and the formation of metallic clusters on its surface, and in a near-surface layer. In this paper we describe the formation of surface clusters and their typical shapes and transformations they undergo in an ultrahigh-vacuum environment. From the evidence found in a variety of experiments, we conclude that surface metallization is strongly related to diffusive transport of irradiation-induced defects. We can coherently explain experimental results presented here, and earlier observations, by assuming that both the conversion of primarily created F and H center defects into charged Vk and I centers, as well as their electric-field-induced diffusion, are controlled by the electron irradiation. Fluorine diffusion into the bulk leads to the formation of subsurface fluorine gas bubbles appearing as micron-sized surface elevations in scanning force microscopy images. For the initial stages of metal cluster formation on the (111) surface, we observe ordering phenomena indicating an epitaxial growth. Due to oxidation the surface topography changes when metal clusters are subjected to a residual gas atmosphere of 1 x 10-9 mbar for more than one day.
BibTeX:
@article{PhysRevB59p8237(1999)_Bennewitz,
  author = {R. Bennewitz and D. Smith and M. Reichling},
  title = {Bulk and surface processes in low-energy-electron-induced decomposition of CaF2},
  journal = {Phys. Rev. B},
  year = {1999},
  volume = {59},
  number = {12},
  pages = {8237-8246},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB59p8237(1999)_Bennewitz.pdf},
  doi = {10.1103/PhysRevB.59.8237}
}
Reichling M and Barth C (1999), Scanning force imaging of atomic size defects on the CaF2 (111) surface, Phys. Rev. Lett. Vol. 83(4), pp. 768-771.
Abstract: Cleaved (111) surfaces on CaF2 were imaged with scanning force microscopy operated in the dynamic mode in ultrahigh vacuum. Imaging the pristine surface reveals an atomic scale contrast with the structure expected For the fluorine terminated surface. We always reproduced the perfect surface periodicity never observing stable defects. However, after exposing the surface to 280 L of oxygen while constantly scanning, we detected,stable atomically resolved defects that are assigned to OH- groups incorporated into the surface. We could identify a jump of one of the groups from one atomic cell to the next. The observed contrast at regular lattice sites as well as at defects is discussed and qualitatively explained.
BibTeX:
@article{PhysRevLett83p768(1999)_Reichling,
  author = {M. Reichling and C. Barth},
  title = {Scanning force imaging of atomic size defects on the CaF2 (111) surface},
  journal = {Phys. Rev. Lett.},
  year = {1999},
  volume = {83},
  number = {4},
  pages = {768-771},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevLett83p768(1999)_Reichling.pdf},
  doi = {10.1103/PhysRevLett.83.768}
}
Reichling M, Huisinga M, Gogoll S and Barth C (1999), Degradation of the CaF2(111) surface by air exposure, Surf. Sci. Vol. 439(1-3), pp. 181-190.
Abstract: We investigate the electronic and geometric structure of CaF2(111) surfaces produced by cleavage in air in comparison to surfaces cleaved in an ultra-high vacuum. An analysis with ultraviolet photoelectron spectroscopy reveals a broadening of the fluorine 2p valence band peak, the formation of a broad band of occupied electronic states extending into the band gap and an increase in electron scattering after the surface has been exposed to air. We attribute these effects to the incorporation of gas molecules into the crystal and chemical reactions at the surface. Surface modifications appear as stable, nanometer-sized patches of reactants that can be directly observed by scanning force microscopy. These patches are found to be randomly distributed over the surface and have a height never exceeding the minimum possible step height on the CaF2(111) surface. Furthermore, it is demonstrated that oxygen in the crystal can be transformed into CaO when metallising the surface and near surface bulk by low-energy electron irradiation. Oxidation is strongly enhanced by electron-stimulated diffusion of oxygen. By monitoring oxidation in a shallow surface layer with X-ray photoelectron spectroscopy, we also monitor thermally activated diffusion of oxygen to the surface after electron irradiation.
BibTeX:
@article{SurfSci439p181(1999)_Reichling,
  author = {M. Reichling and M. Huisinga and S. Gogoll and C. Barth},
  title = {Degradation of the CaF2(111) surface by air exposure},
  journal = {Surf. Sci.},
  year = {1999},
  volume = {439},
  number = {1-3},
  pages = {181-190},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=SurfSci439p181(1999)_Reichling.pdf},
  doi = {10.1016/S0039-6028(99)00760-8}
}
Reichling M, Klotzbücher T and Hartmann J (1998), Local variation of room-temperature thermal conductivity in high-quality polycrystalline diamond, Appl. Phys. Lett. Vol. 73(6), pp. 756-758.
Abstract: Local thermal conductivity inside grains of high-quality polycrystalline diamond grown by chemical vapor deposition is measured at room temperature with micrometer spatial resolution. An effective conductivity is determined by choosing experimental conditions where the measured heat flow extends over adjacent grains. It is found that the effective conductivity may vary by a factor of 2, depending on the averaged volume and position on the sample. These variations an attributed to different grain structures present at the investigated locations. Local conductivity within a single grain varies by ±30% and a maximum value of 2350 W/mK is found. Local thermal conductivity data are related to the crystalline quality and impurity content determined by micro-Raman measurements.
BibTeX:
@article{ApplPhysLett73p756(1998)_Reichling,
  author = {M. Reichling and T. Klotzbücher and J. Hartmann},
  title = {Local variation of room-temperature thermal conductivity in high-quality polycrystalline diamond},
  journal = {Appl. Phys. Lett.},
  year = {1998},
  volume = {73},
  number = {6},
  pages = {756-758},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysLett73p756(1998)_Reichling.pdf},
  doi = {10.1063/1.121991}
}
Huisinga M, Puchin VE and Reichling M (1998), Photoemission from pure and electron irradiated CaF2, Nucl. Instrum. Meth. B Vol. 141(1-4), pp. 528-532.
Abstract: We describe changes of the electronic structure of CaF2 (111) surfaces caused by electron irradiation. with an emphasis on radiation stimulated oxidation. CaF2 crystals cleaved in air and in ultra high vacuum (UHV) were investigated with ultraviolet photoelectron spectroscopy using HeI light (21.2 eV). Surfaces produced by cleavage in air show a large density of states in the band gap region, in contrast to those cleaved in UHV. When irradiating the air cleaved crystals with low energy electrons, we observed the formation of a new peak in the band gap region that is attributed to oxygen. From the electron dosage dependence of this new peak, we conclude that it is mainly formed during irradiation by oxygen already present at the crystal surface. For crystals cleaved in UHV, no new features are observed following irradiation. although a metallic film on the crystal surface is visible with the bare eye. However, dosage with oxygen also yields the band gap peak. The oxidized surface is modeled by ab-initio calculations, based on the Hartree-Fock method. Results are compatible with experimental observations.
BibTeX:
@article{NuclInstrumMethPhysResB141p528(1998)_Huisinga,
  author = {M. Huisinga and V. E. Puchin and M. Reichling},
  title = {Photoemission from pure and electron irradiated CaF2},
  journal = {Nucl. Instrum. Meth. B},
  year = {1998},
  volume = {141},
  number = {1-4},
  pages = {528-532},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=NuclInstrumMethPhysResB141p528(1998)_Huisinga.pdf
}, doi = {10.1016/S0168-583X(98)00044-5} }
Huisinga M, Bouchaala N, Bennewitz R, Kotomin EA, Reichling M, Kuzovkov VN and von Niessen W (1998), The kinetics of CaF2 metallization induced by low-energy electron irradiation, Nucl. Instrum. Meth. B Vol. 141(1-4), pp. 79-84.
Abstract: Results of experimental and theoretical studies on metal colloid growth after irradiation and subsequent heating of CaF2 are presented. Samples at a temperature of 200 K were irradiated in UHV for 30 min with 2.5 keV electrons. After irradiation samples were heated at a rate of about 1 K/min and colloid formation was investigated by optical extinction spectroscopy. Colloid radii as well as the amount of metal were determined from a Mie scattering analysis. A steep rise in colloid size was observed between 260 and 270 K, The concentration off centers not aggregated into colloids was below the detection limit for all temperatures. A microscopic theory of F and H center aggregation taking into account defect creation, interaction, diffusion, and annihilation of dissimilar defects is presented. Theory successfully reproduces the main experimental observations of small colloid formation at low temperatures during irradiation and the onset of colloid growth at a temperature where F centers become mobile.
BibTeX:
@article{NuclInstrumMethPhysResB141p79(1998)_Huisinga,
  author = {M. Huisinga and N. Bouchaala and R. Bennewitz and E. A. Kotomin and M. Reichling and V. N. Kuzovkov and W. von Niessen},
  title = {The kinetics of CaF2 metallization induced by low-energy electron irradiation},
  journal = {Nucl. Instrum. Meth. B},
  year = {1998},
  volume = {141},
  number = {1-4},
  pages = {79-84},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=NuclInstrumMethPhysResB141p79(1998)_Huisinga.pdf
}, doi = {10.1016/S0168-583X(98)00065-2} }
Hartmann J, Costello M and Reichling M (1998), Influence of thermal barriers on heat flow in high quality chemical vapor deposited diamond, Phys. Rev. Lett. Vol. 80(1), pp. 117-120.
Abstract: Thermal barriers in high quality chemical vapor deposited (CVD) diamond were investigated by photothermal microscopy. High resolution measurements confirm that the in-plane heat transport is strongly limited by the presence of thermal barriers. Thermal resistances in the range of 10-9 to 10-8 m2K/W located at grain boundaries are extracted from photothermal line scans. Recently published data on macroscopic one-dimensional thermal transport in CVD diamond are well explained by the microscopic measurements in connection with a simple one-dimensional heat flow model.
BibTeX:
@article{PhysRevLett80p117(1998)_Hartmann,
  author = {J. Hartmann and M. Costello and M. Reichling},
  title = {Influence of thermal barriers on heat flow in high quality chemical vapor deposited diamond},
  journal = {Phys. Rev. Lett.},
  year = {1998},
  volume = {80},
  number = {1},
  pages = {117-120},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevLett80p117(1998)_Hartmann.pdf},
  doi = {10.1103/PhysRevLett.80.117}
}
Puchina AV, Puchin VE, Kotomin EA and Reichling M (1998), Ab initio study of the F centers in CaF2: Calculations of the optical absorption, diffusion and binding energies, Solid State Commun. Vol. 106(5), pp. 285-288.
Abstract: The ground electronic state of the F center in CaF2 crystal, its optical absorption energy, the activation energy of thermal diffusion and M center dissociation to pair of F centers are calculated using the Hartree-Fock embedded molecular cluster method. Different pseudopotentials, basis sets, boundary conditions and two computer codes, EMBED96 and Gaussian94, are employed and their results compared.
BibTeX:
@article{SolidStateComm106p285(1998)_Puchina,
  author = {A. V. Puchina and V. E. Puchin and E. A. Kotomin and M. Reichling},
  title = {Ab initio study of the F centers in CaF2: Calculations of the optical absorption, diffusion and binding energies},
  journal = {Solid State Commun.},
  year = {1998},
  volume = {106},
  number = {5},
  pages = {285-288},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=SolidStateComm106p285(1998)_Puchina.pdf
}, doi = {10.1016/S0038-1098(98)00027-1} }
Bouchaala N, Kotomin EA, Kuzovkov VN and Reichling M (1998), F center aggregation kinetics in low-energy electron irradiated LiF, Solid State Commun. Vol. 108(9), pp. 629-633.
Abstract: Results of experimental and theoretical studies describing aggregation of F centers after irradiation and subsequent heating of LiF are presented and analysed. Samples were irradiated in UHV for 30 min with 2.5 keV electrons at a temperature of 300 K and then heated at a rate of 1.5 K min-1. The evolution of F centers from single defects into metal colloids was monitored by optical extinction spectroscopy. The concentration of F centers is found to decrease monotonously for temperatures above 360 K and to fall below the limit of detectability at about 450 K. Experimental data are compared to results of a microscopic theory of F and H center interaction and aggregation. This theory predicts the activation energy for single F center diffusion to be around 1.5 eV and demonstrates the key role of defect mutual attraction for the aggregation kinetics.
BibTeX:
@article{SolidStateComm108p629(1998)_Bouchaala,
  author = {N. Bouchaala and E. A. Kotomin and V. N. Kuzovkov and M. Reichling},
  title = {F center aggregation kinetics in low-energy electron irradiated LiF},
  journal = {Solid State Commun.},
  year = {1998},
  volume = {108},
  number = {9},
  pages = {629-633},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=SolidStateComm108p629(1998)_Bouchaala.pdf
}, doi = {10.1016/S0038-1098(98)00438-4} }
Reichling M, Huisinga M, Ochs D and Kempter V (1998), Electron- and photon-stimulated metallization and oxidation of the CaF2(111) surface, Surf. Sci. Vol. 402-404(1-3), pp. 145-149.
Abstract: Calcium difluoride bulk crystals cleaved along (111) planes in air and in ultra-high vacuum have been irradiated with 2.5 keV electrons and 1486 eV photons. Radiation induced changes in the surface electronic structure were monitored as a function of irradiation dosage with ultraviolet photoelectron spectroscopy (UPS) and metastable impact electron spectroscopy (MIES). The radiation induced decomposition of the surface is directly evidenced in MIES spectra where upon increased dosage a continuous band appears at the Fermi energy while UPS performed with 21.2 eV photons is found not to be sensitive for the detection of metallized areas at the surface. For crystals cleaved in air after irradiation an additional structure 3 eV above the fluorine 2p valence band edge is found in UPS and MIES spectra that is attributed to oxidized metal patches at the surface. This assignment is confirmed by spectroscopy on Ca films on silicon surfaces dosed with oxygen.
BibTeX:
@article{SurfSci402-404p145(1998)_Reichling,
  author = {M. Reichling and M. Huisinga and D. Ochs and V. Kempter},
  title = {Electron- and photon-stimulated metallization and oxidation of the CaF2(111) surface},
  journal = {Surf. Sci.},
  year = {1998},
  volume = {402-404},
  number = {1-3},
  pages = {145-149},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=SurfSci402-404p145(1998)_Reichling.pdf
}, doi = {10.1016/S0039-6028(97)00949-7} }
Puchina AV, Puchin VE, Huisinga M, Bennewitz R and Reichling M (1998), Theoretical modelling of steps and surface oxidation on CaF2(111), Surf. Sci. Vol. 402-404(1-3), pp. 687-691.
Abstract: The atomic and electronic structure of several low index surfaces of CaF2 were calculated using the Hartree-Fock method, a slab model and the CRYSTAL-95 computer code. The calculated value of the (111) surface energy is 0.47 Jm-2. Two types of stepped surfaces have been considered, namely the (331) and (211) surface. These surfaces have 3.2 Å high steps with different atomic configuration. The step energy was found to be different for these two types of steps. The structure of the CaF2(111)/CaO(111) interface was calculated using the same method. The O(2p) band of CaO was found 2.7 eV above the F(2p) band edge of CaF2.
BibTeX:
@article{SurfSci404p687(1998)_Puchina,
  author = {A. V. Puchina and V. E. Puchin and M. Huisinga and R. Bennewitz and M. Reichling},
  title = {Theoretical modelling of steps and surface oxidation on CaF2(111)},
  journal = {Surf. Sci.},
  year = {1998},
  volume = {402-404},
  number = {1-3},
  pages = {687-691},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=SurfSci402-404p687(1998)_Puchina.pdf},
  doi = {10.1016/S0039-6028(97)00950-3}
}
Reichling M, Bodemann A and Kaiser N (1998), Defect induced laser damage in oxide multilayer coatings for 248 nm, Thin Solid Films Vol. 320(2), pp. 264-279.
Abstract: Photothermal displacement microscopy is used for the detection of mu m-sized defects in Al2O3/SiO2 multilayer coatings highly retlective for 248 nm. Tt is shown that fur high quality coatings the global (averaged over several cm2) laser-induced damage threshold for coatings of different quality is determined by the density and absorption strength of the light absorbing defects. This is confirmed by a measurement of local (averaged over 0.02 mm2) damage thresholds with the pulsed photoacoustic mirage technique allowing a direct correlation of local damage with photothermally detected thin film defects. An analysis of laser-damaged spots reveals damage-craters of 13 ?m diameter at the onset of detrimental irradiation effects. The formation of these craters is explained by a thermoelastic model describing the tensile stress in the film system resulting from evaporation of a defect located at the interface between thin film and substrate.
BibTeX:
@article{ThinSolFilms320p264(1998)_Reichling,
  author = {M. Reichling and A. Bodemann and N. Kaiser},
  title = {Defect induced laser damage in oxide multilayer coatings for 248 nm},
  journal = {Thin Solid Films},
  year = {1998},
  volume = {320},
  number = {2},
  pages = {264-279},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ThinSolFilms320p264(1998)_Reichling.pdf
}, doi = {10.1016/S0040-6090(97)00399-4} }
Stenzel E, Gogoll S, Sils J, Huisinga M, Johansen H, Kastner G, Reichling M and Matthias E (1997), Laser damage of alkaline-earth fluorides at 248 nm and the influence of polishing grades, Appl. Surf. Sci. Vol. 110, pp. 162-167.
Abstract: Damage behaviour and thresholds for single 248 nm/14 ns excimer laser pulses have been investigated for single crystals of CaF2 and BaF2 with (111) surface orientation. The probe beam deflection technique was applied as a sensitive tool for detecting the onset of single-shot damage. Below the plasma threshold, we observed one- and two-photon absorption for CaF2 and BaF2, respectively, When testing the influence of different polishing techniques, we found the lowest thresholds for conventional hard-polish. Advanced methods as ductile machining or chemical polishing lead to a distinct increase in damage threshold up to and even better than what is observed for cleaved surfaces, SEM investigations of irradiated areas show that damage preferably takes place at residual steps or other structural defects.
BibTeX:
@article{ApplSurfSci110p162(1997)_Stenzel,
  author = {E. Stenzel and S. Gogoll and J. Sils and M. Huisinga and H. Johansen and G. Kastner and M. Reichling and E. Matthias},
  title = {Laser damage of alkaline-earth fluorides at 248 nm and the influence of polishing grades},
  journal = {Appl. Surf. Sci.},
  year = {1997},
  volume = {110},
  pages = {162-167},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplSurfSci110p162(1997)_Stenzel.pdf},
  doi = {10.1016/S0169-4332(96)00653-8}
}
Hartmann J, Voigt P and Reichling M (1997), Measuring local thermal conductivity in polycrystalline diamond with a high resolution photothermal microscope, J. Appl. Phys. Vol. 81(7), pp. 2966-2972.
Abstract: A photothermal microscope that provides micrometer lateral and submicrometer depth resolution was designed. Thermal conductivity measurements with modulation frequencies up to 12 MHz on single grains in polycrystalline diamond demonstrate its lateral resolution power even for a highly conducting material. Measured conductivities strongly depend on the averaged volume and values up to 2200 W/mK are found in the high frequency limit where: the properties inside a grain are sampled. The capability of the instrument to measure thermal parameters on thin films is demonstrated for gold films evaporated on quartz with a thickness ranging from 20 to 1500 nm. Measurements reveal a strong thickness dependence for both thin film conductivity and the contact resistance between film and substrate. Thermal conductivity decreases monotonically from 230 to 30 W/mK whereas the contact resistance rises from 2 x 10(-7) to 8 x 10(-6) m(2)K/W with decreasing film thickness. (C) 1997 American Institute of Physics.
BibTeX:
@article{JApplPhys81p2966(1997)_Hartmann,
  author = {J. Hartmann and P. Voigt and M. Reichling},
  title = {Measuring local thermal conductivity in polycrystalline diamond with a high resolution photothermal microscope},
  journal = {J. Appl. Phys.},
  year = {1997},
  volume = {81},
  number = {7},
  pages = {2966-2972},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JApplPhys81p2966(1997)_Hartmann.pdf}
}
Leblans M, Thoma RKR, LoPresti JL, Reichling M and Williams RT (1997), Femtosecond time-resolved photoelectron spectroscopy of annealed and sputtered GaP(110), J. Lumin. Vol. 72-74, pp. 108-109.
Abstract: The relaxation of photoexcited electrons and holes at surfaces of GaP(110) was studied by means of two- and three-photon photoelectron emission under 3.16 eV photon excitation. With 200 fs time resolution, only the relaxation of surface states within the bulk band gap could be resolved occurring with time constants of 0.3 and 2.5 ps.
BibTeX:
@article{JLumin72-74p108(1997)_Leblans,
  author = {M. Leblans and R. K. R. Thoma and J. L. LoPresti and M. Reichling and R. T. Williams},
  title = {Femtosecond time-resolved photoelectron spectroscopy of annealed and sputtered GaP(110)},
  journal = {J. Lumin.},
  year = {1997},
  volume = {72-74},
  pages = {108-109},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JLumin72-74p108(1997)_Leblans.pdf
}, doi = {10.1016/S0022-2313(96)00294-3} }
Reichling M and Bennewitz R (1997), Scanning force imaging of colloids on CaF2 (111) in the ultra-high vacuum, Mater. Sci. Forum Vol. 239, pp. 657-662.
Abstract: Scanning force imaging of dielectric surfaces in the ultra-high vacuum is a well established technique yielding images with a lateral resolution down to the atomic level. In contrast, scanning force images of metallic particles on dielectric surfaces are often obscured by artifacts resulting from strong metal/tip interactions. For the system Ca/CaF2(111) prepared by electron-induced metallization it is shown that imaging in the contact mode is strongly influenced by electrostatic and adhesive forces while the non-contact mode reveals differences in the van der Waals interaction of the tip with the metal and the dielectric surface. Both modes of operation are applied to study electron beam induced effects on the CaF2(111) surface ranging from the onset of erosion at step edges to the formation of nm-sized colloids.
BibTeX:
@article{MatSciFor239p657(1997)_Reichling,
  author = {M. Reichling and R. Bennewitz},
  title = {Scanning force imaging of colloids on CaF2 (111) in the ultra-high vacuum},
  journal = {Mater. Sci. Forum},
  year = {1997},
  volume = {239},
  pages = {657-662},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=MatSciFor239p657(1997)_Reichling.pdf
}, doi = {10.4028/www.scientific.net/MSF.239-241.657} }
Huisinga M, Reichling M and Matthias E (1997), Ultraviolet photoelectron spectroscopy and photoconductivity of CaF2, Phys. Rev. B Vol. 55(12), pp. 7600-7605.
Abstract: Vacuum ultraviolet photoelectron spectroscopy and a systematic study of charging during irradiation with 21.2-eV photons was carried out on cleaved (111) surfaces of CaF2 crystals. The goal was twofold: (1) to find ways of suppressing charging effects and (2) to use surface charging for monitoring photoconductivity. Attempts to reduce charging included crystal heating, use of negatively charged grids at the rear of the sample, and flooding with low-energy electrons. At crystal temperatures between 220 and 350 degrees C both the negative grid and the flood-gun technique produce charge-free surfaces. The enhanced photoconductivity during UV irradiation is explained by thermally activated diffusion of V-k centers. The observed temperature dependence yields an activation energy of 0.30+/-0.06 eV.
BibTeX:
@article{PhysRevB55p7600(1997)_Huisinga,
  author = {M. Huisinga and M. Reichling and E. Matthias},
  title = {Ultraviolet photoelectron spectroscopy and photoconductivity of CaF2},
  journal = {Phys. Rev. B},
  year = {1997},
  volume = {55},
  number = {12},
  pages = {7600-7605},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysRevB55p7600(1997)_Huisinga.pdf
}, doi = {10.1103/PhysRevB.55.7600} }
Langer G, Hartmann J and Reichling M (1997), Thermal conductivity of thin metallic films measured by photothermal profile analysis, Rev. Sci. Instrum. Vol. 68(3), pp. 1510-1513.
Abstract: Thermal conductivity of nickel and gold films on quartz (thickness 0.4-8 mu m) was measured by a modulated thermoreflectance technique recording the surface temperature profile. Model calculations predict an optimum frequency for measuring thermal transport within the film. Measurements on films with various thicknesses reveal a thermal conductivity close to the bulk value for nickel while gold films exhibit a reduced conductivity with decreasing film thickness. (C) 1997 American Institute of Physics.
BibTeX:
@article{RevSciInstrum68p1510(1997)_Langer,
  author = {G. Langer and J. Hartmann and M. Reichling},
  title = {Thermal conductivity of thin metallic films measured by photothermal profile analysis},
  journal = {Rev. Sci. Instrum.},
  year = {1997},
  volume = {68},
  number = {3},
  pages = {1510-1513},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=RevSciInstrum68p1510(1997)_Langer.pdf
}, doi = {10.1063/1.1147638} }
Johansen H, Erfurth W, Gogoll S, Stenzel E, Reichling M and Mattias E (1997), Scanning electron microscopy imaging of microcracks and charging phenomena on a laser-damaged CaF2 surface, Scanning Vol. 19(6), pp. 416-425.
Abstract: Systematic scanning electron microscopy (SEM) investigations of charging phenomena on a laser-damaged CaF2 surface have been carried out as a function of primary electron energy. To this purpose, we imaged an uncoated trapezoidal area of about 400 mu m(2) surrounded by a carbon-covered surface at ground potential. It was located at the periphery of a laser-fractured spot and contained microcracks that served to define the local contrast. Areal surface charging was inspected by comparing the brightness of the uncovered area with that of its surrounding. Microcracks were imaged using backscattered (BSE) and secondary (SE) electrons, and optimal imaging conditions were established for both techniques. The best contrast of the fracture pattern was obtained with 20 keV primary electrons in BSE composition mode. In SE mode, the microstructure was more or less blurred, except for 5 keV and 25 degrees surface inclination where the cracks showed an enhanced SE emission, which might originate from occupied defect states in the band gap.
BibTeX:
@article{Scanning19p416(1997)_Johansen,
  author = {H. Johansen and W. Erfurth and S. Gogoll and E. Stenzel and M. Reichling and E. Mattias},
  title = {Scanning electron microscopy imaging of microcracks and charging phenomena on a laser-damaged CaF2 surface},
  journal = {Scanning},
  year = {1997},
  volume = {19},
  number = {6},
  pages = {416-425},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=Scanning19p416(1997)_Johansen.pdf
} }
Bennewitz R, Reichling M and Matthias E (1997), Force microscopy of cleaved and electron-irradiated CaF2(111) surfaces in ultra-high vacuum, Surf. Sci. Vol. 387(1-3), pp. 69-77.
Abstract: We present scanning force micrographs of as-cleaved and electron-irradiated CaF2(lll) surfaces taken in ultra-high vacuum at room temperature. Among the forces acting on the tip, the electrostatic force was found to make an important contribution. This allows us to study the ionic conductivity of the crystals. Freshly cleaved surfaces can be imaged in contact mode with high resolution exhibiting the hexagonal structure of the (lll) surface. For electron-irradiated surfaces, noncontact mode is required for imaging radiation-induced stoichiometric changes. Strong adhesive forces between the tip and metal-enriched areas are found to be a severe obstacle for contact mode imaging. Weak irradiation with 850 eV electrons results in the formation of 10 nm-wide holes with surrounding elevations as the first stages of metallization. (C) 1997 Elsevier Science B.V.
BibTeX:
@article{SurfSci387p69(1997)_Bennewitz,
  author = {R. Bennewitz and M. Reichling and E. Matthias},
  title = {Force microscopy of cleaved and electron-irradiated CaF2(111) surfaces in ultra-high vacuum},
  journal = {Surf. Sci.},
  year = {1997},
  volume = {387},
  number = {1-3},
  pages = {69-77},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=SurfSci387p69(1997)_Bennewitz.pdf}
}
Hartmann J, Voigt P, Reichling M and Matthias E (1996), Photothermal measurement of thermal anisotropy in pyrolytic graphite, Appl. Phys. B Vol. 62(5), pp. 493-497.
Abstract: We investigated the anisotropic thermal conductivity in pyrolytic graphite by thermoreflectance. A laser-heated circular spot on a surface perpendicular to the planes developed into an elliptical temperature distribution which was recorded by a raster scanning technique at modulation frequencies ranging from 600 Hz to 100 kHz. The ratio of in-plane and perpendicular thermal conductivity was determined by fitting the phase of the temperature data with an analytical model, and was found to decrease with increasing modulation frequency. Highest conductivity values were considerably smaller than previously published data based on steady-state measurements. The frequency dependence and additional features in the phase profiles at high frequencies are discussed in view of sample surface preparation and the local nature of the thermoreflectance measurement.
BibTeX:
@article{ApplPhysB62p493(1996)_Hartmann,
  author = {J. Hartmann and P. Voigt and M. Reichling and E. Matthias},
  title = {Photothermal measurement of thermal anisotropy in pyrolytic graphite},
  journal = {Appl. Phys. B},
  year = {1996},
  volume = {62},
  number = {5},
  pages = {493-497},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysB62p493(1996)_Hartmann.pdf
} }
Gogoll S, Stenzel E, Reichling M, Johansen H and Matthias E (1996), Laser damage of CaF2(111) surfaces at 248nm, Appl. Surf. Sci. Vol. 96-8, pp. 332-340.
Abstract: Single-shot laser damage of polished and cleaved CaF2(111) surfaces induced by (248 nm)/(14 ns) pulses was studied by electron microscopy and probe beam deflection, It is shown that the onset of laser damage is fracturing rather than melting. The fragment thickness is found to increase with fluence which points to an enhanced near surface absorption of about 0.4 mu m characteristic depth. Bending of the fragments with typical curvature radii around 100 mu m indicates that within this fragment thickness a transition to plasticity has taken place.
BibTeX:
@article{ApplSurfSci96-8p332(1996)_Gogoll,
  author = {S. Gogoll and E. Stenzel and M. Reichling and H. Johansen and E. Matthias},
  title = {Laser damage of CaF2(111) surfaces at 248nm},
  journal = {Appl. Surf. Sci.},
  year = {1996},
  volume = {96-8},
  pages = {332-340},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplSurfSci96-8p332(1996)_Gogoll.pdf}
}
Verhoeven H, Hartmann J, Reichling M, Mueller-Sebert W and Zachai R (1996), Structural limitations to local thermal diffusivities of diamond films, Diam. Relat. Mater. Vol. 5(9), pp. 1012-1016.
Abstract: The photothermal displacement technique at transient thermal gratings and photothermal microscopy, both providing a spatial resolution on a micrometer scale, were used to investigate the thermal properties of crystallites and regions located between crystallites of diamond grown by microwave plasma chemical vapour deposition. The thermal properties are related to the structural properties by micro-Raman/photoluminescence spectroscopy and infrared spectroscopy. In the vicinity of a highly defective region located between crystallites, which exhibits a preferential incorporation of non-diamond carbon, silicon-vacancy complexes and hydrogen, a reduction of the thermal diffusivity by about 35% was observed. Depending upon whether this region is a grain boundary or a defect-filled microcrack, the decrease in the thermal diffusivity is caused by enhanced phonon scattering from these defects accumulated at the boundary or by a vanishing transmission probability of phonons across the crack. High thermal conductivities between 1500 W m(-1)K(-1) and 1700 W m(-1)K(-1) were determined within the crystallites at room temperature.
BibTeX:
@article{DiamRelMat5p1012(1996)_Verhoeven,
  author = {H. Verhoeven and J. Hartmann and M. Reichling and W. Mueller-Sebert and R. Zachai},
  title = {Structural limitations to local thermal diffusivities of diamond films},
  journal = {Diam. Relat. Mater.},
  year = {1996},
  volume = {5},
  number = {9},
  pages = {1012-1016},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=DiamRelMat5p1012(1996)_Verhoeven.pdf}
}
Voigt P, Hartmann J and Reichling M (1996), Thermal wave imaging of electrically heated microstructures, J. Appl. Phys. Vol. 80(4), pp. 2013-2018.
Abstract: The thermoreflectance technique is applied for imaging electric current distributions and thermal transfer in a temperature reference resistor heated by an alternating current. High-frequency scans (30 kHz) allow imaging of the current density distribution in conducting strips of the resistor while scans of amplitude and phase of the surface temperature variation at lower frequencies reveal plane, cylindrical, and spherical thermal waves. We investigate wave dimensionality as a function of heating geometry and thermal length, and present a simple method allowing a quantitative thermal analysis by exploiting the phase profile of cylindrical thermal waves. (C) 1996 American Institute of Physics.
BibTeX:
@article{JApplPhys80p2013(1996)_Voigt,
  author = {P. Voigt and J. Hartmann and M. Reichling},
  title = {Thermal wave imaging of electrically heated microstructures},
  journal = {J. Appl. Phys.},
  year = {1996},
  volume = {80},
  number = {4},
  pages = {2013-2018},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JApplPhys80p2013(1996)_Voigt.pdf
}, doi = {10.1063/1.363094} }
Johansen H, Gogoll S, Stenzel E, Reichling M and Matthias E (1996), Charging phenomena in low-voltage electron microscopy of laser-fractured fluoride surfaces, J. Appl. Phys. Vol. 80(9), pp. 4928-4933.
Abstract: Surfaces of fluoride crystals, fractured by a single excimer laser pulse and then covered by a thin conductive layer, are imaged by scanning electron microscopy in the low-voltage secondary electron mode. As a result of charging, at lower primary electron energies a contrast enhancement can be obtained for surface fragments that are no longer tightly attached to the crystal. This differs from high-energy (>10 keV) imaging which only yields topographic contrasts and allows the analysis of the fractured structure by edge and shadowing effects. Even contrast inversion from positive to negative charging of an entire fragment can be achieved, depending on the primary electron energy. It is shown that this effect can be utilized to discriminate between fragments with a good mechanical contact to the bulk and partially detached ones by systematically studying the contrast as a function of electron energy and specimen inclination. (C) 1996 American Institute of Physics.
BibTeX:
@article{JApplPhys80p4928(1996)_Johansen,
  author = {H. Johansen and S. Gogoll and E. Stenzel and M. Reichling and E. Matthias},
  title = {Charging phenomena in low-voltage electron microscopy of laser-fractured fluoride surfaces},
  journal = {J. Appl. Phys.},
  year = {1996},
  volume = {80},
  number = {9},
  pages = {4928-4933},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JApplPhys80p4928(1996)_Johansen.pdf
}, doi = {10.1063/1.363463} }
Gogoll S, Stenzel E, Johansen H, Reichling M and Matthias E (1996), Laser-damage of cleaved and polished CaF2 at 248 nm, Nucl. Instrum. Meth. B Vol. 116(1-4), pp. 279-283.
Abstract: We investigated the surface damage of CaF2 induced by irradiation with 248 nm/14 ns laser pulses. Experiments were carried out in single shot mode in air. The photoacoustic deflection technique was utilized for in situ damage detection and irradiated spots were inspected by scanning electron microscopy. Fracture along the natural cleavage planes was observed. Comparison of cleaved and polished samples in connection with modelling the thermoelastic response of the crystal during damage reveals that polishing causes enhanced surface absorption, Damage topography at the periphery of the irradiated spots was used to obtain a rough estimate of the temperature rise leading to fracture. Electron microscopy shows surface modifications of weakly irradiated spots where no ablation or cracking could be detected.
BibTeX:
@article{NuclInstrumMethPhysResB116p279(1996)_Gogoll,
  author = {S. Gogoll and E. Stenzel and H. Johansen and M. Reichling and E. Matthias},
  title = {Laser-damage of cleaved and polished CaF2 at 248 nm},
  journal = {Nucl. Instrum. Meth. B},
  year = {1996},
  volume = {116},
  number = {1-4},
  pages = {279-283},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=NuclInstrumMethPhysResB116p279(1996)_Gogoll.pdf
} }
Hartmann J, Reichling M and Matthias E (1996), Thermal resistance of thermal barriers in polycrystalline diamond, Prog. Nat. Sci. Vol. 6, pp. S297-S300.
Abstract: Micrometer resolved photothermal measurements on chemical vapour deposited (CVD) diamond are presented. It is shown that the thermal conductivity inside the grains is as high as that of natural IIa diamond. Using two different approaches we measure the thermal resistance of thermal barriers like grain boundaries or microcracks and obtain values of the order of 10(-9) m(2)K/W. A simple model is presented, relating the overall thermal conductivity for one-dimensional heat flow to the thermal resistance at barriers and the average size of the grains. Good agreement between predictions and literature data is found.
BibTeX:
@article{ProgNatSci6pS297(1996)_Hartmann,
  author = {J. Hartmann and M. Reichling and E. Matthias},
  title = {Thermal resistance of thermal barriers in polycrystalline diamond},
  journal = {Prog. Nat. Sci.},
  year = {1996},
  volume = {6},
  pages = {S297-S300},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ProgNatSci6pS297(1996)_Hartmann.pdf}
}
Reichling M, Voigt P and Hartmann J (1996), Quantitative thermal imaging of current densities and heat flow in electronic microstructures, Prog. Nat. Sci. Vol. 6, pp. S519-S523.
Abstract: The thermoreflectance technique is applied for imaging electric current distributions and thermal transfer in a temperature reference resistor heated by an alternating current and a high power transistor tested for its internal thermal management. High frequency scans allow imaging of the current density distribution in conducting strips of the resistor while scans of amplitude and phase of the surface temperature variation at lower frequencies reveal plane, cylindrical and spherical thermal waves. We investigate wave dimensionality as a function of heating geometry and thermal length, and present a method allowing a quantitative thermal analysis by exploiting the phase profile of cylindrical thermal waves.
BibTeX:
@article{ProgNatSci6pS519(1996)_Reichling,
  author = {M. Reichling and P. Voigt and J. Hartmann},
  title = {Quantitative thermal imaging of current densities and heat flow in electronic microstructures},
  journal = {Prog. Nat. Sci.},
  year = {1996},
  volume = {6},
  pages = {S519-S523},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ProgNatSci6pS519(1996)_Reichling.pdf
} }
Reichling M, Wilson RM, Bennewitz R, Williams RT, Gogoll S, Stenzel E and Matthias E (1996), Surface colloid evolution during low-energy electron irradiation of CaF2(111), Surf. Sci. Vol. 366(3), pp. 531-544.
Abstract: The effects of 1 keV electron irradiation (current density typically 40 mu A cm(-2)) on the surface structure of CaF2 (111) are studied by scanning force microscopy (SFM) to investigate the role of diffusion in the process of electron-induced surface metal colloid Formation. Systematic variation of beam voltage, irradiation time, intensity and dosage is investigated in regard to metal formation on CaF2 surfaces. The main features observed in an experiment with constant irradiation intensity are colloids on the surface growing from an average size of 50 nm at a dosage density of 0.66 mC cm(-2) to 200 nm at 85 mC cm(-2). The surface metal volume first increases quadratically in time and saturates at dosage densities above 6 mC cm(-2) due to the increasing coverage of the surface by metal. Such a quadratic dependence confirms that surface metal is created by electron-stimulated F-center diffusion from the bulk. By varying current density we also find a saturation in F-centers arriving at the surface. A competing mechanism of metal creation directly at the surface becomes dominant for current densities above 50 mu A cm(-2). In this intensity regime we find dosage-dependent metallization features showing a transition from metallic clusters of 30 nm diameter to larger aggregates and formation of mu m-sized blisters with increasing dosage. For highest irradiation dosages, the main features are large irregularly shaped metal platelets with folded ridges of approximately 150 nm elevation. We propose that these result from the collapse of blisters that were previously filled with fluorine gas resulting from the radiolysis of the halide crystal. Furthermore, the CaF2 surface is investigated after removal of the metallic deposits by water treatment. SFM images reveal the existence of holes about 30 nm in diameter, which grow into a random network of larger grooves at higher dosages.
BibTeX:
@article{SurfSci366p531(1996)_Reichling,
  author = {M. Reichling and R. M. Wilson and R. Bennewitz and R. T. Williams and S. Gogoll and E. Stenzel and E. Matthias},
  title = {Surface colloid evolution during low-energy electron irradiation of CaF2(111)},
  journal = {Surf. Sci.},
  year = {1996},
  volume = {366},
  number = {3},
  pages = {531-544},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=SurfSci366p531(1996)_Reichling.pdf
} }
Bennewitz R, Günther C, Reichling M, Matthias E, Vijayalakshmi S, Barnes AV and Tolk NH (1995), Size Evolution of Low-Energy-Electron Generated Ca Colloids in CaF2, Appl. Phys. Lett. Vol. 66(3), pp. 320-322.
BibTeX:
@article{ApplPhysLett66p320(1995)_Bennewitz,
  author = {R. Bennewitz and C. Günther and M. Reichling and E. Matthias and S. Vijayalakshmi and A. V. Barnes and N. H. Tolk},
  title = {Size Evolution of Low-Energy-Electron Generated Ca Colloids in CaF2},
  journal = {Appl. Phys. Lett.},
  year = {1995},
  volume = {66},
  number = {3},
  pages = {320-322},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysLett66p320(1995)_Bennewitz.pdf
}, doi = {10.1063/1.113531} }
Maznev AA, Hartmann J and Reichling M (1995), Thermal-Wave Propagation in Thin-Films on Substrates, J. Appl. Phys. Vol. 78(9), pp. 5266-5269.
Abstract: A simple dispersion equation for surface thermal waves propagating along a solid surface covered with a thin film of higher thermal conductivity is presented. It is shown to describe well phase measurements with a photothermal microscope carried out on metal films on glass substrates. (C) 1995 American Institute of Physics.
BibTeX:
@article{JApplPhys78p5266(1995)_Maznev,
  author = {A. A. Maznev and J. Hartmann and M. Reichling},
  title = {Thermal-Wave Propagation in Thin-Films on Substrates},
  journal = {J. Appl. Phys.},
  year = {1995},
  volume = {78},
  number = {9},
  pages = {5266-5269},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JApplPhys78p5266(1995)_Maznev.pdf
}, doi = {10.1063/1.359702} }
Grönbeck H and Reichling M (1995), Harmonic Heat-Flow in Anisotropic Thin-Films, J. Appl. Phys. Vol. 78(11), pp. 6408-6413.
Abstract: The three-dimensional equation of heat conduction is solved to obtain the time-dependent (harmonic) temperature field in an opaque, thermally anisotropic layer on a thermally thick and isotropic substrate when the system is heated by a modulated Gaussian laser beam. The influence of the anisotropy on the amplitude and phase response of the temperature variation as a function of the position on the surface and depth in the layer is studied. The limiting case of one-dimensional heat diffusion in highly anisotropic media is discussed. For one example the influence of thermal anisotropy on the frequency dependence of the surface temperature distribution is studied. (C) 1995 American Institute of Physics.
BibTeX:
@article{JApplPhys78p6408(1995)_Gronbeck,
  author = {H. Grönbeck and M. Reichling},
  title = {Harmonic Heat-Flow in Anisotropic Thin-Films},
  journal = {J. Appl. Phys.},
  year = {1995},
  volume = {78},
  number = {11},
  pages = {6408-6413},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JApplPhys78p6408(1995)_Gronbeck.pdf}
}
Reichling M (1995), The Role of Defect Diffusion and Metallization for Electron-Stimulated Desorption from CaF2, Nucl. Instrum. Meth. B Vol. 101(1-2), pp. 108-114.
Abstract: The desorption of neutral and ionized anion and cation species from CaF2 and LiF was studied for 1 keV electron irradiation. Experiments were performed for temperatures ranging from room temperature to 400 degrees C at dosage levels resulting in a notable metallization of bulk and surface at elevated temperatures. There we found desorption of neutrals as well as ions from both crystals except calcium ions from the CaF2 surface in contrast to LiF where Li+ was the predominant ionic desorbant. For CaF2 the F+ desorption yield was investigated in more detail. It was found that this yield increases as a function of temperature and is strongly dependent on dosage and irradiation intensity. Furthermore F+ desorption is most efficient at the lowest beam intensity and a peaked structure in the dosage-dependent yield indicates a limiting process and/or depletion of a surface layer from fluorine. Results for emission of F+ are explained by a model including the precipitation and growth of Ca colloids from F-centers as well as halogen formation from H-centers and halogen transport to the surface.
BibTeX:
@article{NuclInstrumMethPhysResB101p108(1995)_Reichling,
  author = {M. Reichling},
  title = {The Role of Defect Diffusion and Metallization for Electron-Stimulated Desorption from CaF2},
  journal = {Nucl. Instrum. Meth. B},
  year = {1995},
  volume = {101},
  number = {1-2},
  pages = {108-114},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=NuclInstrumMethPhysResB101p108(1995)_Reichling.pdf
} }
Bennewitz R, Smith D, Reichling M, Matthias E and Itoh N (1995), Electron-Stimulated Desorption from CaF2 - Penetration Depth of Electrons and Sample Charging, Nucl. Instrum. Meth. B Vol. 101(1-2), pp. 118-121.
Abstract: Two aspects of electron stimulated desorption experiments are covered in this contribution, namely the energy deposition of low energy electrons in CaF2 and the charging of the surface during irradiation. The stopping power for electron energies in the range from 50 eV to 5 keV is calculated using optical absorption data. Energy deposition curves and penetration depth vs. electron energy curves are given based on stopping power values and a Monte Carlo simulation of elastic scattering. Charging of the surface is described by means of an equilibrium between primary and secondary electrons. The sensitivity of the surface charging to stoichiometric changes is shown by monitoring the kinetic energy of desorbing F+ ions during metallization of the surface.
BibTeX:
@article{NuclInstrumMethPhysResB101p118(1995)_Bennewitz,
  author = {R. Bennewitz and D. Smith and M. Reichling and E. Matthias and N. Itoh},
  title = {Electron-Stimulated Desorption from CaF2 - Penetration Depth of Electrons and Sample Charging},
  journal = {Nucl. Instrum. Meth. B},
  year = {1995},
  volume = {101},
  number = {1-2},
  pages = {118-121},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=NuclInstrumMethPhysResB101p118(1995)_Bennewitz.pdf
} }
Johansen H, Gogoll S, Stenzel E and Reichling M (1995), Scanning Electron-Microscopic Inspection of Uncoated CaF2 Single-Crystals, Phys. Status Solidi A Vol. 150(2), pp. 613-624.
Abstract: Cleaved and mechanically polished surfaces of CaF2 single crystals in the uncoated stale are investigated by means of secondary (SE) and backscattered (BE) electron imaging in the scanning electron microscope with respect to their strongly different charge-up properties. There is a relationship between the density of preparation-induced defects and the amount of surface charge detectable by characteristic image disturbances. Different electrical contacting techniques of the crystals are tested to obtain imaging free of charge. For the cleavage face the relatively low electrical resistance of the bulk material of Q approximate to 10(13) Ohm cm controls the imaging conditions rather than the electron trapping by cleavage-induced surface defects. On mechanically polished surfaces already during the first slow scan with E(p) < 5 keV an equipotential surface is formed leading to a pronounced electron mirror effect detectable by SE and BE. However, also in this case Imaging of selected crystal areas free of disturbances succeeds if they are located within an electrical deceleration field.
BibTeX:
@article{PhysStatusSolidi150p613(1995)_Johansen,
  author = {H. Johansen and S. Gogoll and E. Stenzel and M. Reichling},
  title = {Scanning Electron-Microscopic Inspection of Uncoated CaF2 Single-Crystals},
  journal = {Phys. Status Solidi A},
  year = {1995},
  volume = {150},
  number = {2},
  pages = {613-624},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=PhysStatusSolidi150p613(1995)_Johansen.pdf
}, doi = {10.1002/pssa.2211500205} }
Johansen H, Gogoll S, Stenzel E, Reichling M and Matthias E (1995), SEM-analysis of fracture features formed in excimer-laser induced surface damage of CaF2, Radiat. Eff. Defect. Solid. Vol. 136(1-4), pp. 1061-1066.
Abstract: The fracture damage of bulk (111)-CaF2 crystals induced by pulsed irradiation in single shot mode with 248 nn laser light in air is investigated. The irradiated spots are studied with a scanning electron microscope (SEM) using different operational modes. An analysis of the fracture features yields evidence for defect induced absorption, thermal stress and shock wave generation as the main cause of damage. Fracturing is preferentially aligned along the (111)-directions resulting in a triangular shape for the file fragments. The thickness of the fragments shows a clear dependence on incident laser fluence, what can be explained assuming an enhanced surface absorption in the CaF2 crystal.
BibTeX:
@article{RadEffDefSol136p1061(1995)_Johansen,
  author = {H. Johansen and S. Gogoll and E. Stenzel and M. Reichling and E. Matthias},
  title = {SEM-analysis of fracture features formed in excimer-laser induced surface damage of CaF2},
  journal = {Radiat. Eff. Defect. Solid.},
  year = {1995},
  volume = {136},
  number = {1-4},
  pages = {1061-1066},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=RadEffDefSol136p1061(1995)_Johansen.pdf
}, doi = {10.1080/10420159508218812} }
Bennewitz R, Gunther C, Reichling M, Matthias E, Wilson RM and Williams RT (1995), Bulk and surface metallization of CaF2 under low energy electron irradiation, Radiat. Eff. Defect. Solid. Vol. 137(1-4), pp. 1245-1250.
Abstract: Electron irradiation of CaF2 with 2 keV electrons causes metallization of the surface and near surface layers by the formation of colloids. Colloids on the surface are significantly larger than those in the bulk indicating a higher mobility of defects on the surface. Optical spectroscopy on extinction bands of bulk colloids reveals Ostwald ripening as the driving force for aggregation, while scanning force microscopy results suggest that similar processes dominate the early stages of surface colloid formation.
BibTeX:
@article{RadEffDefSol137p1245(1995)_Bennewitz,
  author = {R. Bennewitz and C. Gunther and M. Reichling and E. Matthias and R. M. Wilson and R. T. Williams},
  title = {Bulk and surface metallization of CaF2 under low energy electron irradiation},
  journal = {Radiat. Eff. Defect. Solid.},
  year = {1995},
  volume = {137},
  number = {1-4},
  pages = {1245-1250},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=RadEffDefSol137p1245(1995)_Bennewitz.pdf
}, doi = {10.1080/10420159508222686} }
Matthias E, Siegel J, Petzoldt S, Reichling M, Skurk H, Käding O and Neske E (1995), In-Situ Investigation of Laser-Ablation of Thin-Films, Thin Solid Films Vol. 254(1-2), pp. 139-146.
Abstract: The probe beam deflection technique, based on the mirage effect, has been applied to monitor laser processing of polymer and metal films and to measure damage thresholds of optical coatings. The technique is described and it will be shown that its sensitivity permits distinguishing between surface effects like heating and cracking, causing normal sound waves, and plasma formation outside the surface, giving rise to shockwaves. Examples are presented for single-shot ablation with 14 ns laser pulses of 248 nm wavelength. In particular, ablation studies of Ni films of varying thicknesses disclose a quantitative correlation between threshold fluences and thermal properties like heat diffusion, melting, and evaporation. In contrast, for Cr films a simple thermodynamic model fails because the films crack before melting and vaporizing.
BibTeX:
@article{ThinSolFilms254p139(1995)_Matthias,
  author = {E. Matthias and J. Siegel and S. Petzoldt and M. Reichling and H. Skurk and O. Käding and E. Neske},
  title = {In-Situ Investigation of Laser-Ablation of Thin-Films},
  journal = {Thin Solid Films},
  year = {1995},
  volume = {254},
  number = {1-2},
  pages = {139-146},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ThinSolFilms254p139(1995)_Matthias.pdf
}, doi = {10.1016/0040-6090(94)06242-D} }
Matthias E, Reichling M, Siegel J, Käding OW, Petzoldt S, Skurk H, Bizenberger P and Neske E (1994), The Influence of Thermal-Diffusion on Laser-Ablation of Metal-Films, Appl. Phys. A Vol. 58(2), pp. 129-136.
Abstract: Single-shot ablation thresholds of nickel and gold films in the thickness range from 50 nm to 7 mu m have been measured for 14ns laser pulses at 248 nm, using photoacoustic shock wave detection in air. The metal films were deposited on fused silica substrates. The ablation threshold was found to increase linearly with film thickness up to the thermal diffusion length of the film. Beyond this point it remains independent of film thickness. The proportionality between threshold fluence and thickness allows the prediction of ablation thresholds of metal films from the knowledge of their optical properties, evaporation enthalpies and thermal diffusivities. Physically it proves that ablation is driven by the energy density determined by the thermal diffusion length. A simple thermodynamic model describes the data well. Thermal diffusivities, an essential input for this model, were measured using the technique of transient thermal gratings. In addition, the substrate dependence of the ablation threshold was investigated for 150 nm Ni films.
BibTeX:
@article{ApplPhysA58p129(1994)_Matthias,
  author = {E. Matthias and M. Reichling and J. Siegel and O. W. Käding and S. Petzoldt and H. Skurk and P. Bizenberger and E. Neske},
  title = {The Influence of Thermal-Diffusion on Laser-Ablation of Metal-Films},
  journal = {Appl. Phys. A},
  year = {1994},
  volume = {58},
  number = {2},
  pages = {129-136},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysA58p129(1994)_Matthias.pdf
}, doi = {10.1007/BF00332169} }
Reichling M and Grönbeck H (1994), Harmonic Heat-Flow in Isotropic Layered Systems and Its Use for Thin-Film Thermal-Conductivity Measurements, J. Appl. Phys. Vol. 75(4), pp. 1914-1922.
Abstract: A theoretical model is presented describing harmonic heat flow in a two layer system heated by a modulated Gaussian laser beam. Amplitude and phase of the modulated temperature rise in the layers, as well as in the backing substrate and adjacent atmosphere, are calculated by solving the three-dimensional heat conduction equation with a source term including exponential absorption of the laser light in one or two layers. Heat conduction is assumed to be isotropic throughout the system, however, a thermal contact resistance between the two layers can be taken into account. Results are presented for single and double layer systems of gold and various dielectric thin film materials on glass substrates. Amplitude and phase of the harmonic temperature variation are calculated either as a function of position in the sample system or at the surface as a function of the laser beam modulation frequency. It is found that both amplitude and phase of the calculated temperature rise exhibit typical thin film features in their frequency dependence, however, the phase is more sensitive to thin film phenomena than the amplitude. The phase shows typical extrema in that frequency region, where the thermal diffusion length in the film is equal to the film thickness. Based on these findings, we demonstrate how these calculations can be utilized for the interpretation of thin film thermal parameter measurements. The influence of thermal wave interference is demonstrated, and it is discussed how the main thermal parameters like conductivity, effusivity, and thermal contact resistance of the thin film system can be extracted from measurements by a fit of theoretical curves to experimental data. Applying a simple one-dimensional thermal expansion model, surface displacements for thin film systems are calculated and the applicability of photothermal surface displacement for thin film conductivity measurements is discussed.
BibTeX:
@article{JApplPhys75p1914(1994)_Reichling,
  author = {M. Reichling and H. Grönbeck},
  title = {Harmonic Heat-Flow in Isotropic Layered Systems and Its Use for Thin-Film Thermal-Conductivity Measurements},
  journal = {J. Appl. Phys.},
  year = {1994},
  volume = {75},
  number = {4},
  pages = {1914-1922},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JApplPhys75p1914(1994)_Reichling.pdf
}, doi = {10.1063/1.356338} }
Reichling M, Bennewitz R and Matthias E (1994), Probing Electron-Induced Defects in CaF2 by Photothermal Displacement, J. Phys. IV France Vol. 4(C7), pp. 191-194.
Abstract: The surface displacement technique is used to measure the temperature and frequency dependence of the periodic expansion of a CaF2-surface subject to a modulated focused beam of 1keV electrons. Theoretical models are presented for a prediction of the observed phenomena based on thermal transport and defect lifetime effects. The use of such investigations for the study of thermal and non-thermal transport phenomena in alkaline-earth halides is discussed.
BibTeX:
@article{JPhysIVFrance4p191(1994)_Reichling,
  author = {M. Reichling and R. Bennewitz and E. Matthias},
  title = {Probing Electron-Induced Defects in CaF2 by Photothermal Displacement},
  journal = {J. Phys. IV France},
  year = {1994},
  volume = {4},
  number = {C7},
  pages = {191-194},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysIVFrance4p191(1994)_Reichling.pdf
} }
Bodemann A, Kaiser N, Reichling M and Welsch E (1994), Micrometer Resolved Inspection of Defects and Laser Damage Sites in Uv High-Reflecting Coatings by Photothermal Displacement Microscopy, J. Phys. IV France Vol. 4(C7), pp. 611-614.
Abstract: Characteristic features of defects in dielectric multilayer UV-mirrors are determined by photothermal displacement imaging. A large number of micron sized absorbing defects are detected, however, their size and absorption strength distribution strongly depends on thin film preparation conditions. It is found that all features well correlate with thin film damage thresholds at 248nm. An enhanced photothermal amplitude in a halo around ablation spots damaged by high fluence UV light indicates thin film delamination resulting from thermoelastic stress during laser irradiation.
BibTeX:
@article{JPhysIVFrance4p611(1994)_Bodemann,
  author = {A. Bodemann and N. Kaiser and M. Reichling and E. Welsch},
  title = {Micrometer Resolved Inspection of Defects and Laser Damage Sites in Uv High-Reflecting Coatings by Photothermal Displacement Microscopy},
  journal = {J. Phys. IV France},
  year = {1994},
  volume = {4},
  number = {C7},
  pages = {611-614},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysIVFrance4p611(1994)_Bodemann.pdf
} }
Zimmermann P, Ristau D, Welsch E, Langer G and Reichling M (1994), Potentiality of the Photothermal Surface Displacement Technique for Precisely Performed Absorption Measurement of Optical Coatings, J. Phys. IV France Vol. 4(C7), pp. 623-626.
Abstract: The absolute and comparative determination of the absorption of optical films by the Photothermal-Surface-Displacement-Technqiue (PTD) is only possible if the sample configuration is in agreement with the limits of the theoretical model. Carrying out simultaneous absorption measurements in the IR-region at lambda=10,6 mu m by using lasercalorimetry as well as the surface displacement technique, it can be demonstrated that the thermophysical properties of the film contribute to the probed surface displacgment. The results of PTD measurements at a wavelength of 488 nm show, that there is a similar influence of the film properties on the PTD signal.
BibTeX:
@article{JPhysIVFrance4p623(1994)_Zimmermann,
  author = {P. Zimmermann and D. Ristau and E. Welsch and G. Langer and M. Reichling},
  title = {Potentiality of the Photothermal Surface Displacement Technique for Precisely Performed Absorption Measurement of Optical Coatings},
  journal = {J. Phys. IV France},
  year = {1994},
  volume = {4},
  number = {C7},
  pages = {623-626},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysIVFrance4p623(1994)_Zimmermann.pdf
} }
Siegel J, Reichling M, Matthias E, Hacker E and Lauth H (1994), Investigation of Laser-Induced Damage at 248-Nm in Oxide Thin-Films with a Pulsed Photoacoustic Mirage Technique, J. Phys. IV France Vol. 4(C7), pp. 745-748.
Abstract: Laser damage thresholds at 248nm of TiO2, ZrO2 and HfO2 thin films of lambda optical thickness on SQ1 quartz glass substrates are determined by the photoacoustic mirage technique. Damage thresholds correlate with the band gap energy of these materials, as determined by optical spectroscopy. It is demonstrated that the damage resistance can be raised by an additional lambda/2 SiO2 overlayer. Damage thresholds are identical for polycrystalline and amorphous film structure and not influenced by a change of substrate material from quartz to BK7 glass.
BibTeX:
@article{JPhysIVFrance4p745(1994)_Siegel,
  author = {J. Siegel and M. Reichling and E. Matthias and E. Hacker and H. Lauth},
  title = {Investigation of Laser-Induced Damage at 248-Nm in Oxide Thin-Films with a Pulsed Photoacoustic Mirage Technique},
  journal = {J. Phys. IV France},
  year = {1994},
  volume = {4},
  number = {C7},
  pages = {745-748},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JPhysIVFrance4p745(1994)_Siegel.pdf
} }
Bennewitz R, Reichling M, Wilson RM, Williams RT, Holldack K, Grunze M and Matthias E (1994), Characterization of Ca Aggregates on CaF2 (111)-Surfaces by Atomic-Force, Xps, and Fluorescence Microscopy, Nucl. Instrum. Meth. B Vol. 91(1-4), pp. 623-627.
Abstract: In this contribution we report on the metallization of (111)-surfaces of CaF2 single crystals as a result of low energy electron irradiation. An in-situ control of the spatial distribution of the metal coverage was obtained by rapidly scanning a low intensity electron beam across the irradiated area and monitoring the STE luminescence radiation. Metallized spots are identified by a reduced luminescence intensity. Surface stoichiometry was tested by XPS-microscopy. The spatially resolved observation of line intensities as well as line shifts revealed an effective metallization and oxidation of the surface. Using atomic force microscopy we found evidence for a 3-dimensional island-like formation of Ca aggregates with a size up to 12 mum diameter. Results for cluster formation in the center of the irradiating beam are compared to those from outer regions. The size distribution of the aggregates reproduces the different levels of electron dosage across the beam profile.
BibTeX:
@article{NuclInstrumMethPhysResB91p623(1994)_Bennewitz,
  author = {R. Bennewitz and M. Reichling and R. M. Wilson and R. T. Williams and K. Holldack and M. Grunze and E. Matthias},
  title = {Characterization of Ca Aggregates on CaF2 (111)-Surfaces by Atomic-Force, Xps, and Fluorescence Microscopy},
  journal = {Nucl. Instrum. Meth. B},
  year = {1994},
  volume = {91},
  number = {1-4},
  pages = {623-627},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=NuclInstrumMethPhysResB91p623(1994)_Bennewitz.pdf
}, doi = {10.1016/0168-583X(94)96298-7} }
Reichling M, Johansen H, Gogoll S, Stenzel E and Matthias E (1994), Laser-Stimulated Desorption and Damage at Polished CaF2 Surfaces Irradiated with 532-Nm Laser-Light, Nucl. Instrum. Meth. B Vol. 91(1-4), pp. 628-633.
Abstract: Laser-stimulated emission of Ca neutrals from polished CaF2 (111)-surfaces was studied with a quadrupole mass filter system under UHV conditions. For intensity dependent measurements performed at various spots of the crystal surface a threshold pulse energy could be determined where a sharp decrease in transmitted light intensity occurred. Only for a few measurements this threshold coincided with the ablation threshold (type 1 spots). In most cases, however, the transmission breakdown threshold was found to be distinctly lower than the ablation threshold (type 2 spots). For type 2 spots a weak emission of delayed calcium atoms was observed at the transmission breakdown threshold. Irradiated spots have been examined by optical and scanning electron microscopy. Damage phenomena observed included coloration, cracking along crystal axes, surface erosion and surface melting depending on incident laser intensity. Pronounced differences between type 1 and type 2 spots with respect to laser light entrance and exit surface damage morphology were found.
BibTeX:
@article{NuclInstrumMethPhysResB91p628(1994)_Reichling,
  author = {M. Reichling and H. Johansen and S. Gogoll and E. Stenzel and E. Matthias},
  title = {Laser-Stimulated Desorption and Damage at Polished CaF2 Surfaces Irradiated with 532-Nm Laser-Light},
  journal = {Nucl. Instrum. Meth. B},
  year = {1994},
  volume = {91},
  number = {1-4},
  pages = {628-633},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=NuclInstrumMethPhysResB91p628(1994)_Reichling.pdf
} }
Reichling M, Welsch E, Duparre A and Matthias E (1994), Photothermal Absorption Microscopy of Defects in ZrO2 and MgF2 Single-Layer Films, Opt. Eng. Vol. 33(4), pp. 1334-1342.
Abstract: Photothermal displacement microscopy has been used for the characterization of ZrO2 and MgF2 single-layer thin films to detect absorption inhomogeneities at X = 514 nm. Images are presented for films of lambda/2, lambda, and 2lambda optical thickness deposited on BK7 glass and SQ1 quartz substrates. Applying modulation frequencies ranging from 1 to 100 kHz a lateral resolution of several micrometers was obtained. We found that the size and density of the absorption inhomogeneities as well as absorptance depend strongly on the deposition process and weakly on the substrate material. No dependence on thin film thickness was found. The apparent defect density varies with the modulation frequency demonstrating the capability of the photothermal method to localize absorption in various depths of the thin film. Defect densities derived from the photothermal measurements are compared with results from total integrated light scattering (TIS) experiments performed on various samples at lambda = 632 nm. TIS intensities for MgF2 films on glass substrates were about one order of magnitude smaller than those from films on quartz. The latter revealed strong long-range (1-mm) variations of the light scattering intensity. This finding is in accordance with the absorption measurements.
BibTeX:
@article{OptEng33p1334(1994)_Reichling,
  author = {M. Reichling and E. Welsch and A. Duparre and E. Matthias},
  title = {Photothermal Absorption Microscopy of Defects in ZrO2 and MgF2 Single-Layer Films},
  journal = {Opt. Eng.},
  year = {1994},
  volume = {33},
  number = {4},
  pages = {1334-1342},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=OptEng33p1334(1994)_Reichling.pdf
} }
Reichling M, Kaiser N and Bodemann A (1994), Photothermische Mikroskopie zeigt verborgene Defekte in UV-Hochleistungsoptiken, Phys. Bl. Vol. 50(3), pp. 247-249.
BibTeX:
@article{R,
  author = {M. Reichling and N. Kaiser and A. Bodemann},
  title = {Photothermische Mikroskopie zeigt verborgene Defekte in UV-Hochleistungsoptiken},
  journal = {Phys. Bl.},
  year = {1994},
  volume = {50},
  number = {3},
  pages = {247-249}
}
Reichling M (1994), Electron-Surface Interaction and Metallization of the CaF2 (111)-Surface Studied by Photothermal Techniques, Radiat. Eff. Defect. Solid. Vol. 128(1-2), pp. 55-66.
Abstract: The interaction of low energy electrons with the surface of alkaline-earth halides results in a variety of microscopical physical phenomena commonly described in terms of defect formation and diffusion, surface metallization and desorption of neutral- and charged particles. These processes are accompanied by local changes in the electronic and geometrical structure of bulk and surface and result in a variation of macroscopically measurable parameters like modulated optical reflectance and a deformation of the crystal lattice. In this paper it will be shown that photothermal analysis, that so far has mostly been used for the determination of optical and thermophysical properties of materials, is also capable of measuring defect related nonthermal phenomena apparent during election irradiation of insulator surfaces. Experiments were performed with an intensity modulated electron beam of typically 1 mu A at 1 keV focused into a spot of 1 mm(2) on the (111)-surface of a polished CaF2 single crystal under ultra-high vacuum conditions. Measurements revealed that modulated reflectance is sensitive to changes in optical properties induced by electron irradiation induced defects at low electron dosages. At a dosage level where metallization starts, a dramatic change in the modulated reflectance signal was observed indicating changes in electronic structure due to metal clustering at the surface. The photothermal displacement technique has been utilized to monitor surface deformations induced by electron bombardment. It was found that results cannot be explained by a thermo-elastic expansion model that works well for metal surfaces. Therefore, this technique can be used for the measurement of nonthermal contributions to lattice expansion resulting from volume changes of created defects.
BibTeX:
@article{RadEffDefSol128p55(1994)_Reichling,
  author = {M. Reichling},
  title = {Electron-Surface Interaction and Metallization of the CaF2 (111)-Surface Studied by Photothermal Techniques},
  journal = {Radiat. Eff. Defect. Solid.},
  year = {1994},
  volume = {128},
  number = {1-2},
  pages = {55-66},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=RadEffDefSol128p55(1994)_Reichling.pdf
}, doi = {10.1080/10420159408218856} }
Matthias E, Gogoll S, Stenzel E and Reichling M (1994), Laser-Stimulated Desorption from CaF2 Crystals, Radiat. Eff. Defect. Solid. Vol. 128(1-2), pp. 67-78.
Abstract: Optical transmission and laser-induced desorption (LID) of neutral particles and positive ions from optical-grade CaF2 has been studied, using nanosecond laser pulses of 532 nm. Two different emission characteristics were found: one for which the breakdown of transmission coincides with the onset of ablation; and another for which the transmission breakdown occurs at about 20-30% lower fluences compared to the ablation threshold. In the latter case the transmission breakdown is accompanied by delayed (tenths of seconds) particle emission. We propose that the particle emission below the ablation threshold is defect-assisted LID, in the sense that light absorption by preexisting defects leads to local heating and thermal expansion, causing microcracks from which particles are ejected.
BibTeX:
@article{RadEffDefSol128p67(1994)_Matthias,
  author = {E. Matthias and S. Gogoll and E. Stenzel and M. Reichling},
  title = {Laser-Stimulated Desorption from CaF2 Crystals},
  journal = {Radiat. Eff. Defect. Solid.},
  year = {1994},
  volume = {128},
  number = {1-2},
  pages = {67-78},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=RadEffDefSol128p67(1994)_Matthias.pdf
}, doi = {10.1080/10420159408218857} }
Reichling M, Siegel J, Matthias E, Lauth H and Hacker E (1994), Photoacoustic Studies of Laser Damage in Oxide Thin-Films, Thin Solid Films Vol. 253(1-2), pp. 333-338.
Abstract: Laser damage thresholds of ZrO2, TiO2 and HfO2 films of optical thickness lambda, (lambda = 248 nm) evaporated on quartz glass substrates were investigated with the photoacoustic probe beam deflection technique in a 1-on-1 irradiation mode for a range of fluences from below to above the thin-film laser damage threshold. In addition, irradiated spots were investigated systematically by a video imaging difference technique. It is demonstrated that the photoacoustic technique allows a more sensitive and precise determination than optical inspection of the onset of damage. An exponential dependence of damage thresholds on the apparent band gap of the respective thin-film material, as determined by optical absorption spectroscopy, was found. Results for amorphous and polycrystalline films on BK7 glass and SQ1 quartz substrates are compared and the influence of a SiO2 protective coating on the laser-damage threshold is investigated.
BibTeX:
@article{ThinSolFilms253p333(1994)_Reichling,
  author = {M. Reichling and J. Siegel and E. Matthias and H. Lauth and E. Hacker},
  title = {Photoacoustic Studies of Laser Damage in Oxide Thin-Films},
  journal = {Thin Solid Films},
  year = {1994},
  volume = {253},
  number = {1-2},
  pages = {333-338},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ThinSolFilms253p333(1994)_Reichling.pdf
}, doi = {10.1016/0040-6090(94)90343-3} }
Wu ZL, Reichling M, Hu XQ, Balasubramanian K and Guenther KH (1993), Absorption and Thermal-Conductivity of Oxide Thin-Films Measured by Photothermal Displacement and Reflectance Methods, Appl. Opt. Vol. 32(28), pp. 5660-5665.
Abstract: Photothermal reflectance and photothermal displacement measurements of optical absorption and thermal conductivity are reported for electron-beam- (EB) deposited and ion-plated (IP) thin films of TiO2, Ta2O5, and ZrO2. Of the particular set of samples investigated, the EB films have higher absorption than the IP films. The absorption of the EB samples decreases over a period of approximately 90 min on irradiations with an Ar-ion laser of 488-nm wavelength. By contrast, the absorption of the IP samples changes insignificantly or not at all. Photothermal displacement area scans of coating surfaces yield lower defect densities for the IP samples compared with the EB samples for al three oxide materials. The feasibility and limitations of photothermal measurements for thin-film optical and thermal characterizations are discussed.
BibTeX:
@article{ApplOptics32p5660(1993)_Wu,
  author = {Z. L. Wu and M. Reichling and X. Q. Hu and K. Balasubramanian and K. H. Guenther},
  title = {Absorption and Thermal-Conductivity of Oxide Thin-Films Measured by Photothermal Displacement and Reflectance Methods},
  journal = {Appl. Opt.},
  year = {1993},
  volume = {32},
  number = {28},
  pages = {5660-5665},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplOptics32p5660(1993)_Wu.pdf
} }
Welsch E and Reichling M (1993), Micrometer Resolved Photothermal Displacement Inspection of Optical Coatings, J. Mod. Optic. Vol. 40(8), pp. 1455-1475.
Abstract: Two-dimensional c.w. photothermal surface displacement (PTD) scans with high spatial resolution provide a new quality for thin-film characterization. This is demonstrated for optical single-layer films of ZrO2 and MgF2 on various substrates. Inhomogeneities of the films were detected with a lateral resolution <2 mum. Variation of the modulated frequency was employed for depth-profiling. The resolving power has been investigated experimentally and a model for signal generation by absorbing inhomogeneities is presented. A calculation of the photothermal thin-film response for thermally thick coatings is carried out to obtain a better understanding of the PTD images with respect to film absorption and thermophysical sample properties.
BibTeX:
@article{JModOptic40p1455(1993)_Welsch,
  author = {E. Welsch and M. Reichling},
  title = {Micrometer Resolved Photothermal Displacement Inspection of Optical Coatings},
  journal = {J. Mod. Optic.},
  year = {1993},
  volume = {40},
  number = {8},
  pages = {1455-1475},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JModOptic40p1455(1993)_Welsch.pdf
}, doi = {10.1080/09500349314551531} }
Welsch E, Reichling M, Göbel C, Schäfer D and Matthias E (1992), Modulated Thermoreflectance Imaging of Hidden Electric-Current Distributions in Thin-Film Layered Structures, Appl. Phys. Lett. Vol. 61(8), pp. 916-918.
Abstract: Thermal imaging of hidden electric current distributions with a resolution of several ten micrometers is demonstrated. It is shown that the thermoreflectance technique is capable of monitoring current-induced temperature variations on as well as beneath the surface of thin layered structures. A temperature pattern was generated by Joule heating using an ac current in a 2.5-mu-m thick structured gold film that was evaporated on a glass substrate and covered by a TiOx layer. The current density distribution in the gold film is revealed by the measured photothermal pattern, provided that both laser beam diameter and thermal diffusion length are smaller than the desired lateral resolution.
BibTeX:
@article{ApplPhysLett61p916(1992)_Welsch,
  author = {E. Welsch and M. Reichling and C. Göbel and D. Schäfer and E. Matthias},
  title = {Modulated Thermoreflectance Imaging of Hidden Electric-Current Distributions in Thin-Film Layered Structures},
  journal = {Appl. Phys. Lett.},
  year = {1992},
  volume = {61},
  number = {8},
  pages = {916-918},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysLett61p916(1992)_Welsch.pdf
}, doi = {10.1063/1.107727} }
Cronberg H, Reichling M, Broberg E, Nielsen HB, Matthias E and Tolk N (1991), Effects of Inverse Bremsstrahlung in Laser-Induced Plasmas from a Graphite Surface, Appl. Phys. B Vol. 52(3), pp. 155-157.
Abstract: The kinetic energy of electrons emitted due to laser interaction with a graphite surface was studied with a time-of-flight spectrometer. In addition the yields of carbon atomic and molecular ions were measured as a function of laser pulse energy. Pulse energy thresholds for ion emission are observed to correlate with the observed maximum electron energies. Furthermore, the data suggest that ionic carbon clusters can be dissociated by energetic electrons or photons created in the plasma. We believe that initially photoemitted electrons are accelerated by inverse bremsstrahlung to the energies required for electron impact ionization and dissociation
BibTeX:
@article{ApplPhysB52p155(1991)_Cronberg,
  author = {H. Cronberg and M. Reichling and E. Broberg and H. B. Nielsen and E. Matthias and N. Tolk},
  title = {Effects of Inverse Bremsstrahlung in Laser-Induced Plasmas from a Graphite Surface},
  journal = {Appl. Phys. B},
  year = {1991},
  volume = {52},
  number = {3},
  pages = {155-157},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysB52p155(1991)_Cronberg.pdf
}, doi = {10.1007/BF00750943} }
Reichling M, Masujima T, Shiwaku H, Kawata H, Ando M and Matthias E (1989), Photoacoustic X-Ray Absorption Fine-Structure Spectroscopy of the Ni K-Edge, Appl. Phys. A Vol. 49(6), pp. 707-710.
BibTeX:
@article{ApplPhysA49p707(1989)_Reichling,
  author = {M. Reichling and T. Masujima and H. Shiwaku and H. Kawata and M. Ando and E. Matthias},
  title = {Photoacoustic X-Ray Absorption Fine-Structure Spectroscopy of the Ni K-Edge},
  journal = {Appl. Phys. A},
  year = {1989},
  volume = {49},
  number = {6},
  pages = {707-710},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysA49p707(1989)_Reichling.pdf
} }
Masujima T, Shiwaku H, Yoshida H, Kataoka M, Reichling M, Imai H, Kawata H, Iida A, Koyama A and Ando M (1989), Photoacoustic EXAFS of Solid-Phase, Jpn. J. Appl. Phys. Vol. 28(3), pp. L513-L514.
Abstract: Fine structures observed in X-ray photoacoustic spectra of various solids were compared with those in the absorption spectra. For a precise comparison, the photoacoustic spectra were corrected for energy-depending X-ray absorption of gas existing in the optical path. Finally corrected photoacoustic spectra showed a leveled or decreasing trend with increasing photon energy. Good correspondence between the X-ray photoacoustic spectra and the absorption spectra further confirmed that the fine structures in the photoacoustic spectra are identical with the extended X-ray absorption fine structures (EXAFS).
BibTeX:
@article{JpnJApplPhys28pL513(1989)_Masujima,
  author = {T. Masujima and H. Shiwaku and H. Yoshida and M. Kataoka and M. Reichling and H. Imai and H. Kawata and A. Iida and A. Koyama and M. Ando},
  title = {Photoacoustic EXAFS of Solid-Phase},
  journal = {Jpn. J. Appl. Phys. },
  year = {1989},
  volume = {28},
  number = {3},
  pages = {L513-L514},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=JpnJApplPhys28pL513(1989)_Masujima.pdf
}, doi = {10.1143/JJAP.28.L513} }
Petzoldt S, Elg AP, Reichling M, Reif J and Matthias E (1988), Surface Laser Damage Thresholds Determined by Photoacoustic Deflection, Appl. Phys. Lett. Vol. 53(21), pp. 2005-2007.
Abstract: The technique of intensity-dependent photoacoustic probe beam deflection was applied to the detn. of surface damage thresholds. Advantage is taken of an unambiguous correlation between the degree of laser damage and the energy in the generated acoustic pulse. The high sensitivity of this method, cross checked by measuring scatter losses in reflection, is independent of any surface optical properties. As an example for optical materials, damage thresholds for MgF2 and CaF2 were detd. to be .apprx.1.4 GW/cm2, and for LiF to be .apprx.0.2 GW/cm2.
BibTeX:
@article{ApplPhysLett53p2005(1988)_Petzoldt,
  author = {S. Petzoldt and A. P. Elg and M. Reichling and J. Reif and E. Matthias},
  title = {Surface Laser Damage Thresholds Determined by Photoacoustic Deflection},
  journal = {Appl. Phys. Lett.},
  year = {1988},
  volume = {53},
  number = {21},
  pages = {2005-2007},
  url = {http://reichling.physik.uos.de/download_paper.php?paper=ApplPhysLett53p2005(1988)_Petzoldt.pdf
}, doi = {10.1063/1.100491} }
Last update on 11/01/2015.