"Only reading tells how much can be left un-read"
Wilhelm Raabe (1831-1910)

Diese sind meine wissenschaftlichen Veröffentlichungen. Ich lasse Titel und Zusammenfassung im englischen Original.

X-ray diffraction topography using a difractometer with a bendable monochromator at a synchrotron radiation source

D. Altin, J. Härtwig, R. Köhler, W. Ludwig, M. Ohler, H. Klein, Journal of Synchrotron Radidation 9 (2002), 282-286.

The different properties of laboratory and synchrotron-based double-crystal setups for X-ray topographic applications are discussed as a basis for the realisation of a versatile instrument allowing the investigation of all kinds of crystals with high strain sensitivity and without any reduction in image size. It appears that the use of a benable highly perfect monochromator (silicon) achieves this goal, through the local adaptiation of Bragg angles, to compensate either dispersion or a bending of the sample.

X-ray diffraction topography at a synchrotron radition source applied to the study of bonded silicon on insulator material

Härtwig J, Köhler S, Ludwig L, Moriceau H, Ohler M, Prieur E, Crystal Research and Technology 37 (2002), 707-715.

New possibilities of X-ray diffraction topography offered by the modern sycnhrotron radiation sources for the investigation o fwafer-bonded material are demonstrated. They allowed detecting defects and long-range strain fields at and close to the bonding interface. A quantiative estimation of teh deformation of the region near to the bonding interface was possible eg by investigating focussing distances and dominant spatial frequencies of the contrast patterns (often in the oder of 200 µm). In typical wafer bonded material the maximum bonding-indiced inclination of the lattice planes was in the order of 10 arcsec and the approximate amplitude of the deformation in the oder of 1.5 nm. The sensitivity of the presented methods to characterise the influence of various prcess parameters was demonstrated.

Applied Microtechnology

Ed. by Rainer Brück, Nadeem Rizvi and Andreas Schmidt: Applied Microtechnology, w. CD-ROM. 2001. XIV, 269 p. w. 150 figs. (mostly col.). 24 cm. Hanser Fachbuchverlag ISBN-Nr. 3446214720.

This book provides an introductory review of the physical and technical fundamentals of the three basic micro-structuring technologies: LIGA technique, laser micromachining, and micro precision engineering. In addition, production processes and examples of applications from the fields of telecommunications, drive technology, medicine and actuators are also discussed. The book is primarily aimed at students of the technical faculties of higher education institutions and universities but is also aimed at providing engineers with practical knowledge of the important aspects of the three technologies. The concept of the book is that of a fundamental introduction and a first step to an in-depth treatment of these technologies. The enclosed CD-ROM offers the reader access to a more detailed internet course, which enlarges upon the topics dealt within the book and provides a multi-media presentation together with additional information and interaction with related experts. This course can be accessed via http://www-ttec.rs.uni-siegen.de

High-resolution high energy X-ray diffraction studies of charge ordering in CMR manganites and nickelates

Wilkins SB, Hatton PD, Liss KD, Ohler M, Katsufuji T, Cheong SW, International Journal for Modern Physics B14 (2000), 3753-3758

High-resolution, high-energy, X-ray diffraction results are presented for the study of weak charge ordering phenomenon. By utilizing X-rays in the 100 keV region the dramatic increase in the penetration depth allows for both bulk-sensitive and high- resolution measurements to be made. The strontium doped La2NiO4 system is a prototypical system in the understanding of strong electron-phonon coupling, and the resultant effects on material properties. At doping levels of 1/3 and (1)/(2) commensurate charge modulations are observed indicating real-space charge stripes. We have measured the correlation lengths of these charge stripes using both 100 keV X-rays and 8.3 keV X-rays. In comparing our results we have observed that the charge stripes appear to be well correlated in the near-surface region with correlation lengths xi approximate to 2400 Angstrom. However, our bulk sensitive measurements show that the charge stripes appear in a possible stripe glass phase with a correlation length of only xi approximate to 300 Angstrom. Our measurements on the 3D charge order manganite system Nd0.5Sr0.5MnO3 show that the charge ordering appears to be well correlated in the bulk of the sample in contrast to our nickelate results.

X-ray topographic determination of the granular structure in a graphite mosaic crystal: a three-dimensional reconstruction

Ohler M, del Rio MS, Tuffanelli A, Gambaccini M, Taibi A, Fantini A, Pareschi G, Journal of Applied Crystallography 33 (2000) 1023-1030

Section topographs recorded at different spatial locations and at different rocking angles of a highly oriented pyrolytic graphite (HOPG) crystal allow three-dimensional maps of the local angular-dependent scattering power to be obtained. This is performed with a direct reconstruction from the intensity distribution on such topographs. The maps allow the extraction of information on local structural parameters such as size, form and internal mosaic spread of crystalline domains. This data analysis leads to a new method for the characterization of mosaic crystals. Perspectives and limits of applicability of this method are discussed.

A conical slit for three-dimensional XRD mapping

Nielsen SF, Wolf A, Poulsen HF, Ohler M, Lienert U, Owen RA, Journal of Synchrotron Radiation 7 (2000), 103-109

Traditionally, depth resolution in diffraction experiments is obtained by inserting pinholes in both the incoming and diffracted beam. For materials science investigations of local strain and texture properties this leads to very slow data-acquisition rates, especially when characterization is performed on the level of the individual grains. To circumvent this problem a conical slit has been manufactured by wire-electrodischarge machining. The conical slit has six 25 mu m-thick conically shaped openings matching six of the Debye-Scherrer cones from a face-centred-cubic powder. By combining the slit with a microfocused incoming beam of hard X-rays, an embedded gauge volume is defined. Using a two-dimensional detector, fast and complete information can be obtained regarding the texture and strain properties of the material within this particular gauge volume. The average machining and assemblage errors of the conical slit are found both to be of the order of 5 mu m. An algorithm for alignment of the slit is established, and the potential of the technique is illustrated with an example of grain mapping in a 4.5 mm-thick Cu sample.

TRANSTEC - A new tool for online educational multimedia training on innovative high aspect ratio microtechnologies

Schmidt A, Bruck R, Hahn K, Labeque A, Popovic G, Ohler M, Riedel H, Rizvi N, Stange T, Microsystem Technologies 6 (2000), 109-112.

Microtechnology is regarded as one of the key technologies of the 21st century that will decisively influence nearly all fields of daily life. The demand for vocational education in this discipline is growing rapidly. This education must be a continuous life long learning process since microtechnology is characterised by frequent improvements of the fabrication processes and facilities. The use of Internet-resources offers new chances in teaching and training, especially for design, production or application of products from high aspect ratio micro-engineering technologies. The present paper reports on the development of a novel concept of interactive Internet-based training entities in the field of High Aspect Ratio Technologies. The training topics are dedicated towards innovative engineering technologies, particularly the LIGA technique, laser-based microtechnologies and microengineering related aspects of precision engineering. This training is addressed to graduate students, design engineers and executives mainly in small and medium sized enterprises. http://www-ttec.rs.uni-siegen.de

Reduction of elastic strains in directly-bonded silicon structures

Argunova TS, Vitman RF, Grekhov IV, Kostina LS, Kudryavtseva TV, Gutkin MY, Shturbin AV, Härtwig J, Ohler M, Kim ED, Kim SC, Physics of the solid state 41 (1999), 1790-1798.

The elastically strained state of the interface in directly-bonded silicon structures has been studied by x-ray diffraction topography and IR spectrometry. The pattern of the contrast observed in the x-ray topographs and the intensity oscillations in the IR spectra indicate a periodic strain distribution caused by the long-period surface microroughness on the plates to be bonded. The local microroughness did not exceed 2 Angstrom, and it did not noticeably affect the interface structure. Two types of the structure were subjected to a comparative analysis, (i) with a smooth interface prepared by standard direct-bonding technology, and (ii) with an interface displaying a regular relief. The strain level in type-II structures was found to be lower by more than an order of magnitude. A model is proposed to account for the observed reduction of elastic strains at the bonded sections of the interface in terms of elastic relaxation of the free surfaces in the relief voids through their deflection and displacement.

Theory of moire fringes on X-ray diffraction topographs of bicrystals

Ohler M, Härtwig J, Acta Crystallographica A55 (1999), 413-422

The theory of moire fringes on X-ray diffraction topographs of bicrystals is derived from the dynamical theory of X-ray diffraction for the reflection (Bragg) and the transmission (Laue) case. The influence on the moire fringes of the diffraction geometry, of the geometry of the sample, of its optical properties and of the topographic method is investigated. The perfect-crystal theory is also expanded to weakly deformed bicrystals.

X-ray diffraction moire topography as a means to reconstruct relative displacement fields in weakly deformed bicrystals

Ohler M, Köhler S, Härtwig J, Acta Crystallographica A55 (1999), 423-432

X-ray diffraction topographs of wafers produced by separation by implanted oxygen (SIMOX) show moire fringes in both reflection and transmission geometry. These fringes reveal deformations of the order of 10-6 to 10-8 between the layer and the substrate of the SIMOX material. A new method for a quantitative analysis of moire fringes is developed and allows reconstruction with a high sensitivity of the three components of the relative displacement field between layer and substrate directly from a set of topographs. This method is used for the interpretation of moire topographs of entire 4 in SIMOX wafers and of regions around crystal defects. Finally, the capabilities of an analysis of moire fringes are compared with those of the usual diffraction topography.

High-resolution x-ray diffraction and high-resolution scanning electron microscopy studies of Si-based structures with a buried amorphous layer

Ahilea T, Zolotoyabko E, Härtwig J, Ohler M, Prieur E, Journal of Applied Physics 84 (1998), 6076-6082

Structural and geometrical parameters of Si samples with buried amorphous layers, produced by oxygen implantation and high-temperature annealings, were measured by high-resolution x-ray diffraction and high-resolution scanning electron microscopy. By using a newly developed simulation procedure precise fittings of x-ray diffraction spectra were made and important parameters were derived, such as the averaged fluctuations of the thickness of the amorphous layer ("interface roughness'') and of the interplanar spacing in the Si top layer. The data obtained revealed a reduction in interface roughness, i.e., an improvement of the samples' quality after additional high-temperature annealing. This conclusion was supported by electron microscopy images demonstrating a more complete dissolution of SiO2 precipitates as a result of additional heat treatment. The importance of more sophisticated annealing was also confirmed by the Moire x-ray diffraction topographs taken on the topography beamline of the European Synchrotron Radiation Facility.

Direct observation of mosaic blocks in highly oriented pyrolytic graphite

Ohler M, Baruchel J, Moore AW, Galez P, Freund A, Nuclear Instruments and Methods in Physics Research B129 (1997), 257-260

Section topographs have been recorded on Highly Oriented Pyrolytic Graphite (HOPG) samples utilizing a highly collimated monochromatic X-ray beam. Both the spatial and the angular

Enhanced possibilities of section topography at a third-generation synchrotron radiation facility

Medrano C, Rejmankova P, Ohler M, Matsouli I, Nuovo Cimento della Societa Italiana di Fisica D19 (1997), 195-203

We show the new possibilities of section topography techniques at a third-generation synchrotron radiation facility, taking advantage of the high performances of this machine. Examples of the 1) so-called multiple sections, 2) visibility of weakly misoriented regions, 3) study of thick samples, 4) monochromatic and 5) real-time sections ape presented.

Effect of doping on Ga1-xAlxAs structural properties

BakMisiuk J, Domagala J, Paszkowicz W, Trela J, Zytkiewicz ZR, Leszczynski M, Reginski K, Muszalski J, Härtwig J, Ohler M, Acta Physica Polonica A91 (1997), 911-915

The microstructure of Ga1-xAlxAs layers was studied using methods of high resolution diffractometry and topography. Mapping out the reciprocal space in the vicinity of 004 reciprocal lattice points shows a difference in diffuse scattering between doped and undoped layers. This result is attributed to a difference in a point-defect density. From the measurements of lattice parameters at different temperature it was found that the thermal expansion coefficients for the doped layers are higher than for the undoped ones. This phenomenon is attributed to the change of the anharmonic part of lattice vibrations by free electrons or/and point defects.

X-ray characterization of GaAs:Zn gas-transport grown whiskers using conventional and synchrotron sources

Paszkowicz W, Gorecka J, Domagala J, Dmitruk N, Varshava SS, Härtwig J, Ohler M, Pietraszko A, Acta Physica Polonica A91 (1997), 997-1002

GaAs:Zn whiskers grown by the gas-transport method are characterized by diffraction methods using white and monochromatic radiation. The methods applied include the white-beam topography at ESRF synchrotron source and Laue patterns, 4-circle Bond diffractometry and high-resolution diffractometry at conventional X-ray sources. The results obtained concern the growth morphology and defect structure. It is found that GaAs:Zn whiskers grown by the described method have the form of long needles and blades of the morphologies represented by growth direction and largest lateral face [112]{111} and [111]{112}, respectively, with a single exception of a blade of uncommon morphology [111]{110}.

Moire fringes and/or translation-fault fringes?

Ohler M, Härtwig J, Prieur E, Acta Crystallographica A53 (1997), 199-201

Interference fringes on transmission topographs of crystals with an implanted amorphous layer are, among others, attributed to the moire or the translation-fault effect. This discussion is reconsidered in the frame of the theory of a perfect bicrystal extended to a deformed one. It is shown that translation-fault fringes have the same properties as moire fringes and that it is not necessary to introduce translation-fault fringes as a new diffraction phenomenon.

X-ray topographic contrast of threading dislocations in silicon on insulator structures

Prieur E, Ohler M, Härtwig J, Physica Status Solidi A158 (1996), 19-34

Threading dislocations in a thin silicon layer of SIMOX (Separation by IMplanted OXygen) samples were studied by white and monochromatic beam X-ray diffraction topography in transmission and reflection geometry. The symmetrical transmission geometry appeared to be most suitable for the present study. The dislocation images were visible on topographs even though the Si layer thickness was very small compared to the pendellosung distance. The dislocation contrast could coherently be explained by an 'interferometer like'' and a ''double crystal diffractometric like'' formation mechanism. The first is controlled by local variations of the reciprocal lattice vector difference between the two parts of a bicrystal and the second by variations of the effective misorientation. The contrast analysis revealed that dislocations occurred in pairs with antiparallel Burgers vectors. The dislocation contrast dependence on the layer thickness, X-ray wavelength, working point on the rocking curve, position on the moire fringe pattern, and measurement geometry were also investigated.

Synchrotron white beam topographic investigation of crystalline defects in silicon on insulator materials

Prieur E, Härtwig J, Garcia A, Ohler M, Baruchel J, Aspar B, Rolland G, Journal of Crystal Growth 166 (1996), 329-333

Samples prepared by separation by implantation of oxygen (SIMOX) with dislocation densities of about 105 cm-2 have been studied by synchrotron white beam X-ray diffraction topography (WET) in transmission geometry. The threading dislocations in the top Si layer were detected and found to have Burgers vectors parallel to the [011] and to the [01(1) over bar] directions. From moire fringes the lattice parameter difference between the top Si layer and the substrate was found to be about 6 x 10-8 in the surface plane.

X-ray Moire topography on SIMOX structures

Ohler M, Prieur E, Härtwig J, Journal of Applied Crystallography 29 (1996), 568-573

Moire fringes are observed on X-ray diffraction topographs of silicon on insulator structures produced by different SIMOX (separation by implantation of oxygen) processes. The parameters that can be extracted from a diffraction Moire experiment are discussed. A Moire experiment is sensitive to the relative strain between the two parts of a bicrystal system. The sign of the relative strain and its components perpendicular to the sample surface cannot be determined from the geometry of the Moire fringes. The influence of sample curvature on Moire fringes is considered. Different deformation models are discussed to interpret the experimental findings. It is found that a triclinic relative deformation explains the observed symmetries between Moire topographs from different reflections, the spacings of the Moire fringes and their angles to a reference direction. Both the dilational and the shear components of the relative strain tensor are found to be in the order of 10-7. Significant differences in relative strain are observed on SIMOX samples produced by different processes.

Threading dislocations in silicon layer produced by separation by implanted oxygen process

Prieur E, Guilhalmenc C, Härtwig J, Ohler M, Garcia A, Aspar B, Journal of Applied Physics 80 (1996), 2113-2120

Threading dislocations in the silicon layer in three different types of the silicon on insulator samples produced by standard and improved separation by implanted oxygen (SIMOX) processes were investigated by synchrotron x-ray topography, scanning electron microscopy (SEM), and optical microscopy. The densities and Burgers vectors of the dislocations were first determined. nondestructively by synchrotron x-ray topography. Then the line directions of the same dislocations were determined by SEM after chemical Secco etching. Some of these results were compared with results obtained from optical microscopy of Secco etched samples. The threading dislocations in the Si layer were found to occur mainly in pairs with densities of the order of 105 cm-2 in standard SIMOX samples and of the order of 104 cm-2 in improved SIMOX samples. These dislocations have an edge character. Other features of these dislocations, such as the distances between two dislocations forming a pair, orientations of these pairs, and dislocations that change their line direction, are also discussed.

An X-ray diffraction topographic study of highly oriented pyrolytic graphite

Ohler M, Baruchel J, Galez P, Journal of Physics D28 (1995), A78-A83

Highly oriented pyrolytic graphite is a very efficient and well-known x-ray and neutron monochromator that is obtained by thermal cracking of a hydrocarbon gas and a subsequent graphitization treatment. Its microstructure is still, however, a matter of controversy. Several samples of different quality were extensively studied by x-ray diffraction topography. The contrast obtained on 00l reflections is mainly explained in terms of 'primary extinction' acid orientation contrast. This implies that the interlayer spacing of the graphite lattice planes remains constant over distances of several tens of micrometres. Graphitization mechanisms are discussed in the light of this interpretation. A microstructural model, closely related to that of as-deposited pyrolytic carbon, is proposed.

Observation of defects in crystal-surface layers by grazing-incidence diffraction X-ray topography

Novikov DV, Ohler M, Köhler R, Materlik G, Journal of Physics D28 (1995), A84-A87

Threading dislocations in gallium arsenide and point defects in silicon were observed for the first time by x-ray topography under grazing-incidence diffraction conditions. A new type of contrast on polished surfaces has been resolved for single crystals with defects. The characteristics of grazing-incidence diffraction topography are discussed.

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