Table of contents

The 5th Biennial Conference on High Resolution X-ray Diffraction and Topography (XTOP2000) was held in Ustron-Jaszowiec, Poland from 13-15 September 2000. It was organised jointly by the Institute of Experimental Physics of University of Warsaw and the Institute of Physics of Polish Academy of Sciences (PAS) in Warsaw, and a couple of colleagues from several other scientific institutions in Poland (High Pressure Research Center of PAS, Institute of Physical Chemistry of PAS, Institute of Atomic Energy, Institute of Electronic Materials Technology —all in Warsaw, Mining and Metallurgy Academy in Cracow, and Institute of Structure and Low Temperature Research of PAS in Wroclaw) were also active in the Organising Committee. We were supported by the International Programme Committee which — apart from two of us (Jadwiga Bak-Misiuk and Maria Lefeld-Sosnowska)— included Václav Holý (Czech Republic), José Baruchel and Cécile Malgrange (France), Rolf Köhler and Ullrich Pietsch (Germany), Emil Zolotoyabko (Israel), Stefano Lagomarsino and Leander Tapfer (Italy), Anatoli V Andreev (Russia), Paul Fewster and Brian K Tanner (UK), and Richard J Matyi (USA). Their helpful suggestions of invited speakers are acknowledged. The conference was sponsored in part by the Polish Ministry of National Education, the State Committee for Scientific Research and the Committee for Physics of PAS.

The choice of the small resort of Jaszowiec in the Beskidy mountains had been decided at the previous XTOP meeting in Durham in 1998. It had seemed a good idea then, to change the entourage from the 11th century castle of University College, overlooking the famous Durham Cathedral, to a relaxing view of some 900-metre-high spruce-covered mountains, fresh air and seclusion. In the opinion of a vast majority of delegates the idea has proved excellent. The personnel of the two hotels housing the conference, `Gwarek' and `Kolejarz', took every care to satisfy the needs of the participants. In spite of a rather intense scientific programme and the short duration of the conference, we even managed to reserve one afternoon for a walking tour in the mountains, which perfectly coincided with a spell of fair weather.

There were 118 delegates from 22 countries, mostly European, but also from Asia, North America and Australia. The scientific programme of the conference was divided into 9 oral sessions and 2 poster sessions. In all, 165 papers were accepted; of these, 9 were 30-minute-long plenary or invited talks, 32 were qualified as 15-minute orals, and 124 as posters. There were relatively few withdrawals (4 orals and about 20 posters). The invited speakers included Jürgen Härtwig, Petra Pernot-Rejmánková, Wolfgang Ludwig and Peter Cloetens (all ESRF, Grenoble), Cinzia Giannini (PASTIS-CNRSM, Brindisi), Václav Holý (Masaryk University, Brno), Brian K Tanner (University of Durham), Mike Leszczynski (UNIPRESS, Warsaw) and Justin S Wark (University of Oxford). The full list of papers can be found on the conference Internet page at http://info.ifpan.edu.pl/XTOP2000.html.

The present special issue of Journal of Physics D: Applied Physics is a collection of 44 original papers from those presented at XTOP2000. However, they are not conference proceedings — all of them have been subjected to the normal, stringent standards of the host journal. I would like to express my thanks to all the referees for their work and to my graduate student Ilona Frymark for her help with the administration of the refereeing process.

Contrary to the previous conference in Durham where the emphasis had been on phase contrast imaging [1], at XTOP2000 the tone was set by several other techniques. In high resolution diffraction, several studies of quantum dots and wires were prominent, represented in this issue by the works, among others, of Holý et al, Roch et al, Grenzer etal and Ulyanenkov et al. Interesting and novel were papers on epitaxial layers, both for gallium arsenide (Vasyukov et al) and gallium nitride (Heinke et al, Ratnikov et al). Also worthy of note is Matyi et al's work on defects in protein. In topography, further advancements in studies of real structure of quasicrystals performed at ESRF by Klein etal as well as Härtwig etal should be emphasized. The fundamental and clearly written paper on the use of topography to measure the critical thickness of InGaAs epitaxial layers on GaAs by Tanner etal was certainly one of the highlights of the conference. New perspectives of topographic techniques with synchrotron radiation were explored by Baruchel etal for `exotic' magnetic domains and Heyroth etal in the three-beam case. It should be noted that x-ray topography is still going strong not only on synchrotron sources (e.g. Pernot et al) but also in laboratories, which is proved, for example, by Feichtinger et al's excellent work. Finally, reflectivity techniques are still in bloom for various systems, as evidenced by Aspelmeyer etal for ferroelectric devices, Meduna etal for Ge/Si superlattices or Mikulík etal for W/Si gratings. The same applies to grazing incidence diffraction (see the elegant and sound studies of InGaAs quantum wells by Zeimer etal as well as of silicon oxide stripes by Daniel et al).

Estimating the scientific level of the conference in general terms, I observe a very reassuring fact: there was a rather prominent group of young and very talented colleagues who presented brilliant papers, done with refined techniques and in large co-operations. This observation applies not only to people centred around synchrotron radiation facilities (notably ESRF) but also in conventional x-ray laboratories. Therefore, the prospects for the field are bright, and we all look forward to the next XTOP conference which will be organised by José Baruchel and his group in Grenoble, in 2002.

Reference

[1] Tanner B K 1999 Special issue on high resolution x-ray diffraction and topography J. Phys. D: Appl. Phys.32 A1-A2

Dr J Gronkowski, Guest Editor

Institute of Experimental Physics, University of Warsaw, Hoza 69, 00-681 Warsaw, Poland

May 2001

High-resolution x-ray diffraction and grazing-incidence small-angle x-ray scattering are used for the investigation of the morphology of free-standing and buried self-assembled PbSe quantum dots in PbSe/PbEuTe superlattices. The measured data are simulated by means of kinematical and semikinematical scattering theories, and linear elasticity theory. The differences in the parameters of free-standing and buried dots yield a direct evidence of structure changes of self-assembled dots during their overgrowth.

The step-bunching process during the growth on vicinal Si substrates provides a template both for improved lateral ordering and size control of the resulting Ge-rich self-assembled quantum dots or wires. We have investigated a 20 period SiGe/Si wire multilayer grown by molecular beam epitaxy on a misorientated Si(001) substrate with a large miscut of 3.5° towards the [100] direction. Parallel to the steps, i.e. along the [010] direction, Ge-rich wires are formed spontaneously. Their surface morphology was studied with atomic force microscopy. In order to get information on the shape and the lateral correlation not only of the wires on the top surface but also of the buried ones, we employed grazing incidence small-angle x-ray scattering (GISAXS). The GISAXS data were taken for different information depths in two orthogonal azimuths. Side maxima in coplanar high-angle diffraction and GISAXS data indicate the presence of Ge-rich self-organized wires at the buried heterointerfaces.

We report on the strain analysis of a vertically stacked GaAs/Ga_0.97In_0.03As/[GaAs/Al_0.2Ga_0.8As]₉/GaAs [001] multiquantum well structure which was laterally patterned by a focused Ga⁺ ion beam implantation of 5×10¹³ cm^-2 ions. We studied the strain distribution in the samples before and after a rapid thermal annealing for 60 s at 650 and 800 °C by means of x-ray grazing incidence diffraction. In the as-implanted sample we found a nearly constant strain distribution of about 4×10^-3 up to a maximum information depth of approximately 500 nm. Annealing at 650 °C led to a reduced strain within the sample. After annealing at 800 °C the strain disappeared almost completely but a significant increase of the multilayer interface width could be observed, indicating an intermixing of Ga and Al atoms across the interfaces.

Sb-doped and Sb-free GaAs films were grown by molecular beam epitaxy (MBE) at low temperature (LT) and were annealed in the MBE set-up at various temperatures within the range of 500-900 °C. The concentrations of arsenic antisites in as-grown samples obtained using near-infra-red optical absorption were found to be as high as 6×10¹⁹ and 7×10¹⁹ cm^-3 in Sb-doped and Sb-free samples, respectively. Samples were studied by high-resolution x-ray diffractometry (HRXRD) and transmission electron microscopy (TEM). Despite the high concentration of intrinsic point defects, x-ray rocking curves demonstrated perfect crystalline quality in as-grown samples. After annealing at temperatures of 500-700 °C, the lattice mismatch decreased in both Sb-doped and Sb-free samples, but in Sb-doped samples the reduction was much higher than would be expected for the antisite defect concentration determined from optical measurements. The segregation of isovalent Sb impurity into the As clusters was suggested. Upon annealing at temperatures higher than 700 °C, Sb-doped samples manifested a strong broadening of the diffraction maximum related to the LT GaAs:Sb layer. The TEM and HRXRD studies revealed that high-temperature annealing resulted in formation of dislocation loops attached to the large As clusters.

A strained superlattice composed of five bilayers of In_0.2Ga_0.8As/GaAs grown on a (001) GaAs substrate was studied via comparison of the measured high-resolution reciprocal space maps near to the various substrate Bragg peaks with the theoretically modelled intensity distributions. Fourier synthesis was used to describe the strain field and the morphology of the nucleated islands. Modelling, which explains the presence of the side intensity maxima, shows that the lateral compositional variation produces domains with enriched In concentration surrounded by In depleted regions. The distribution of the strain field in both substrate and the multilayer suggests that the compositional modulation promotes nucleation of the islands with a skew vertical correlation on the subsequent interfaces.

GaN(0001) epitaxial layers were grown by molecular beam epitaxy on a few-nanometres thick low-temperature GaN nucleation layers on c-plane sapphire. Despite extremely high densities of extended defects, the layers show a narrow (002) x-ray diffraction peak, superimposed by broad diffuse scattering. Triple-axis transverse and radial scans were measured for (00l) reflections of different orders and for various GaN layer thicknesses. The results can be described by an interfacial displacement-difference correlation function. Its microscopic origin is assigned to either inversion domain boundaries or edge-type threading dislocations in the GaN layers, in agreement with findings of transmission electron microscopy. These defects are associated with an only weak rotational disorder perpendicular to the growth plane as proven by the x-ray scattering characteristics.

The dislocation structure of hydride vapour phase epitaxial thick GaN layers grown on sapphire is studied by analysis of the microdistortion tensor components. Symmetrical reflections (including reflections from planes forming large angles with the basal plane) with two modes of scanning (θ and θ-2θ) in two geometries (Bragg and Laue) are used to obtain the tensor components. The instant connections between the tensor components and major dislocation types are specified. Different types of dislocation distributions have been identified in the thick GaN films grown on sapphire without and with undoped and Si-doped metal-organic chemical vapour deposited templates.

On the basis of high-resolution x-ray diffraction measurements, the strain-stress analysis of GaN/(00.1)α-Al₂O₃ heteroepitaxial structures grown by molecular beam epitaxy is performed. The deformation state of the heteroepitaxial structures is investigated depending on the relative content of N in the Ga_1-xN_x buffer layer with the given thickness (=4 nm) and growth conditions. Using the extrapolating technique, the a- and c-lattice parameters, as well as the in-plane and out-of-plane strains (of the order of -10^-3 and 10^-4, respectively) are determined for GaN epilayers from θ-2θ x-ray diffraction spectra. For GaN epilayers, both the biaxial in-plane and in-depth strains (of the order of -10^-3 and 10^-3, respectively) and the hydrostatic strain component (of the order of -10^-4) are extracted from the measured strains. It is supposed that the hydrostatic strain in the epilayers is caused by native point defects. The maximal level for the biaxial stress in the GaN epilayer, -1.3 GPa, is achieved for the sample with a relative content, x = 0.377, of N in the Ga_1-xN_x buffer layer.

In this work we present the results of a residual strain analysis performed on LOCOS processed films by means of x-ray reciprocal space mapping. Our findings demonstrate the possibility of achieving a sub-micrometre spatial resolution by using an x-ray waveguide as an innovative optical element in the measurement configuration. The entire set-up, working as a projection microscope, can be schematically described as waveguide, sample and CCD camera. In order to derive a quantitative description of the strain field induced in the Si wafer by the 1 µm wide SiO₂ stripes, we performed data analysis by dynamical simulation of the x-ray diffraction profiles based on an analytical treatment of the elastic field.

The availability of high-precision diffractometers enables one to study in detail the reciprocal space surrounding chosen Bragg reflections from small crystals. Here we have applied three-dimensional reciprocal-space mapping to study individual grains in polycrystalline chemical vapour deposited diamond grown on W and Mo substrates. Correlations between (a) the strain within grains and (b) the crystallite size and/or orientation (microtexture) have been investigated. The high angular resolution of the instrument has enabled us to isolate individual crystallites in reciprocal space. The reduction of the axial divergence reduces the size of the probe and hence partially eliminates the projection effect.

For several years the ESRF, the University of the Witwatersrand and De Beers Industrial Diamonds (PTY) Ltd through their Diamond Research Laboratories have pursued a development programme to improve the quality of synthetic diamond crystals. Recently, in an effort to study the influence of nitrogen impurities on the defect structure, x-ray excited optical luminescence and spatially resolved double-crystal diffractometry were employed as new techniques. Finally, the impurity concentration distribution obtained by optical spectroscopy was superimposed on the defect structure determined by x-ray diffraction. The correlation between nitrogen impurities and the raw defect structure was clearly visible. It was confirmed that concentration variations are related to lattice imperfections, where tilts are much superior to lattice parameter variations.

Inline characterization of SiGe and SiGe:C heterobipolar transistors places stringent requirements on x-ray diffraction set-ups: (i) precise mounting and positioning of 8 inch wafers for single position scans and area mapping; (ii) high beam intensity in a small spot; and (iii) low background to realize a dynamic range better than five orders of magnitude for precise rocking curve simulation. The Bede QC200 x-ray diffractometer, which applies a novel micro-focus x-ray source and a novel beam conditioning optics to a double-crystal x-ray diffraction system, meets these requirements. Data collected on SiGe structures with the QC200 are compared with data collected at a synchrotron source. We demonstrate that reliable depth profiles of Ge content can be obtained in structures of 500×500 µm² size in an automatic operation mode at different positions over an 8 inch wafer in a well defined grid. Two automatic fitting programs, one involving a genetic algorithm, are used to extract material information from simulation of the high-resolution diffraction scans. Rapid, reliable convergence on the global minimum gives objective fitting, suitable for quality control in a SiGe technology. Finally, we show how the lateral distribution of Ge content and layer thickness can be mapped over an 8 inch wafer.

Simulated intensity maps from perfect crystals are compared with experimental ones collected with high-resolution Philips MRD and Bede D³ diffractometers employing a four-reflection Bartels monochromator and two-reflection analyser optics with the sample set in dispersive and non-dispersive configurations, respectively. The patterns resulting from the instrumental monochromator and analyser optical elements, as well as from the wavelength dispersion of the conventional x-ray source, are elaborated. The convolution of the intensity maps with the instrumental function based on two-dimensional integration and on the interactive graphical method are discussed. The latter approach is convenient and facilitates the convolution of the model simulations for comparison with experiment.

We have used high-resolution triple-axis x-ray diffraction analyses to monitor the defect structure in tetragonal crystals of hen egg-white lysozyme as a function of x-ray irradiation time. At long irradiation times we observed the expected decrease in peak intensity and increase in the angular extent of the peak breadth. In contrast, the initial stages of irradiation showed relatively complex changes in both the peak breadth and the intensity; in fact, during the period from 25 to 45 h of irradiation the angular breadth of the intensity (both the full-width at half-maximum and the full-width at 1% of the maximum intensity) decreased to a minimum value. We have found that the unambiguous analysis of defects at high angular resolution is complicated by the fact that the diffraction characteristics of protein crystals apparently lie at the confluence of the kinematic (ideally imperfect) and dynamic (ideally perfect) treatments of diffraction.

The most important variants of the dynamical theory for perfect and deformed crystals are derived from one general form of the basic equation of dynamical diffraction theory for deformed crystals. The approximations necessary to be applied and the limits of these variants of the dynamical theory with respect to the allowed deformation are given.

The Green's function formalism is applied to the analysis of the surface contribution to the inelastic scattering of x-rays by acoustic modes of thermal excitations in a crystal. It is shown that the surface contribution to thermal diffuse scattering (TDS) near the surface can become comparable to and can even exceed the volume contribution. The same formalism is applied to the investigation of TDS in the case of dynamical diffraction, when an x-ray standing wave is generated in a crystal. TDS yield curves calculated according to this model show good agreement with the experimental results.

The known method of the `integral' diffuse scattering has been generalized in the Bragg case of x-ray diffraction for crystals, which contain large microdefects commensurable with the extinction length. In the framework of the developed statistical dynamical theory, relatively simple analytical expressions have been derived for coherent and diffuse components of reflectivity of single crystals with randomly distributed microdefects.

To test the characterization possibilities of the proposed method, the rocking curves (RCs) of Czochralski-grown silicon single crystal annealed at 1080 °C for 6 h have been measured for 111 and 333 reflections of Cu K_α1 radiation using a high-resolution double-crystal x-ray diffractometer. The fitting results for the two RCs are in good mutual agreement and demonstrate the high information ability of the method.

Two-dimensional maps of x-ray diffuse scattering (DS) in a reciprocal space for a real crystal containing Coulomb deformation centres (clusters or dislocation loops) were calculated using a new dynamical theory developed for a crystalline media with homogeneously distributed defects. Such maps were calculated for both the fundamental, 400, as well as the quasi-forbidden, 200, reflections of x-rays (CuKα₁ radiation) for a binary crystal (GaAs). They were also discovered experimentally in the GaAs films heavily doped with Si (up to 10²⁰ cm^-3) by means of a Philips three-crystal diffractometer. The procedure for fitting calculated values of differential DS to the experimental data enabled not only the integral characteristics of the structure's perfection (Debye-Waller static factor, L_H, and coefficient of extinction of radiation due to additional energy losses on defects, µ_d) but also the average radius, , and concentration, , of microdefects (precipitates to be obtained).

The influence of one-dimensional distortions on the multiple effect of enhancement of anomalous x-ray transmission in a Ge crystal is considered. The distributions of intensity in transmitted and diffracted beams on an exit surface are obtained by numerical solution of the Takagi equations for three-, four- and six-beam diffraction. The correlations between the degree of blur, displacement, enhancement or decay of multiple scattering areas, on the one hand, and the type, one-dimensional strain magnitude and its direction, on the other hand, are studied.

We carried out a systematic study of typical defect contrasts in various single grains of icosahedral Al-Pd-Mn quasicrystals. White-beam topographs with different sample-to-detector distances and multiple-crystal topographs with different sample-to-detector distances, different working points on the rocking curve and different harmonic reflections have been recorded. Despite the extreme geometrical resolution at the ID19 topography beamline of the ESRF, white-beam topography showed reasonable (not blurred) contrast only for very short sample-to-detector distances ({<}4 cm). Depending on the defect type, in synchrotron multiple-crystal topography the defect contrast changes considerably as a function of the position of the working point on the rocking curve. Under the special conditions chosen, the dependence of contrast shape and size on the harmonic reflection used was rather weak.

The perfection of one of the quasicrystal grains with the highest degrees of perfection was checked by means of x-ray diffractometry and x-ray topography. Full widths at half maximum of de-convoluted reflectivity curves were close to the theoretical values and a partial Borrmann effect was clearly visible in the measured reflection and transmission curves, whereas the topographs still showed rather strong intricate contrast, which means that strong deformations (defects) still exist in the grain. Consequently, dynamical effects like anomalous transmission were confirmed to exist in selected quasicrystalline grains, but even then the structural quality is still far from being `highly perfect'.

In situ high-resolution double-axis x-ray topography measurements have been made of the critical thickness at which misfit dislocations form in strained layers of In_xG_1-xAs grown epitaxially on (001) GaAs substrates. The critical thickness for formation of the initial fast B(g) misfit dislocations was found to be close to, but larger than the predictions of the Matthews-Blakeslee model. The discrepancy and the variation of the critical thickness with silicon doping have been modelled by inclusion of a Peierls stress in the force balance equation of misfit dislocation motion. Only a very small change was observed in the critical thickness as a function of growth temperature. Inclusion of a temperature-dependent term in the Matthews-Blakeslee model enabled an activation energy 0.3±0.2 eV to be determined.

Synchrotron radiation topography on modern sources, coupled with adequate CCD detectors, is producing (in a shorter time and with better resolution) results which could only be obtained, up to now, by using neutron topography. This is shown by two examples, carried out at the ESRF, on `exotic' antiferromagnetic domains: (1) the imaging of 180° antiferromagnetic domains in cobalt fluoride is performed using the inverse piezomagnetic effect: the action of a magnetic field while cooling and `memory' effects are investigated in this way, and (2) the spin density wave domains in chromium are observed using their associated, weak, charge density wave peaks: the importance of the surface effects to determine the domain type is evidenced.

For the first time, we have obtained the real-time observation, by x-ray topography, of the laser degradation due to the formation of misfit dislocations. We drive the laser diode under a high-energy, high-flux synchrotron micro-x-ray beam. We simultaneously obtain both the laser characteristic curve and the structural characteristics during operation, i.e. the presence of misfit dislocations, laser diode curvature and strain status. From the strain we measure the temperature increase in the epilayer due to the injection current. In other lasers device degradation occurred without the formation of misfit dislocations, but by mass transport, and in other lasers no structural degradation was observed.

Simultaneous analysis of strain modulation fringes in synchrotron Bragg-case section patterns and rocking curves recorded with a very narrow probe beam was used for the determination of strain profiles in GaAs implanted with high doses of 1.5 MeV Se ions. The existence of two components of the strain was revealed: the first is due to the introduced interstitial defects of the matrix crystal and the second is directly connected with introduced Se ions. These two components significantly differed in their depth profiles and their behaviour upon thermal annealing.

We studied the propagation and interaction of individual misfit dislocations in strained p/p⁺ Si wafers. Relaxation of misfit strain occurs at the wafer edge during high-temperature epitaxial growth. The thick epitaxial layer (about five times the critical thickness) and low misfit dislocation densities (~100 cm^-1) are highly compatible with a non-destructive study via x-ray topography. We determined that as a gliding 60° misfit dislocation encounters a strain field in its path, it cross-slips to a specific lattice direction. Misfit dislocation segments with either an orthogonal or quasi-parallel (in the case of the off-oriented substrate) glide direction of the Burger's vector were determined to act as cross-slip initiation sites. This interaction happens during layer growth as well as post-growth annealing cycles. We did not find a case of misfit dislocation blocking during sample annealing. No occurrence of annihilation or multiplication reaction of crossing dislocations was detected during our studies. We show that, due to geometry, a distribution of tilt across the wafer surface results from preferential cross-slipping events. Our results are applicable to early stages of strain relaxation in other strained systems, like graded buffer layers.

X-ray diffraction topographs of extremely pure and perfect silicon single crystals are made using low-energy undulator radiation from a positron storage ring. Typical defect images observed are rather large round images having a black-white contrast and a diameter of about 40 µm. Applying the dynamical theory of x-ray diffraction, the defect contrast is explained by tensile strain in the lattice around voids close to the exit surface. This discovery of void-like microdefects explains, at least in part, the reduced density of the crystal intended to be used for a redefinition of the unit of mass, the kilogram.

4H silicon carbide as-grown ingots were investigated by diffraction imaging using synchrotron radiation. The white beam section topographs obtained for various sample geometries allowed us to reveal structural imperfections before slicing the bulky ingots to the thin wafers used as electronic device substrates. The systematic investigation indicated that the observed inclusions of different polytypes in 4H-SiC ingots are correlated with the 8° off-axis orientation of the seed. These inclusions, formed at the beginning of the crystal growth, provoke planar defects that propagate along the main vertical axis of the cylindrical crystal. New findings permitted us to understand the inclusion formation with the aim to increase the useful volume.

Microchannel (macroporous) silicon obtained by photoelectrochemical etching of cylindrical pores with high aspect ratio of the pore length to the diameter has been studied by x-ray diffractometry and topography. It is shown that the crystal lattice of microchannel silicon is practically not distorted. The channels induce additional diffuse scattering of x-rays. However, thermal oxidation leads to strong distortion of planes, both parallel and normal to the crystal surface, and also to the generation of dislocations. It is shown that x-ray topography allows one to obtain the image of an inner boundary between microchannel silicon and the substrate, to estimate its quality and to define its position in the sample non-destructively.

X-ray topographic and chemical etching examination of Si:Ge single crystals containing 1.2 at% and 3.0 at% Ge, together with precise lattice parameter measurements, was performed. Diffraction contrasts in the form of concentric `quasi-circles' (striations), probably due to the non-uniform distribution of Ge atoms, were observed in projection topographs. The etching patterns revealed bands corresponding to striations and dislocations as etch pits. The central `core' crystal region (striation-free) exhibited a crystal lattice strongly disturbed by microdefects, as was concluded from the section topography analysis. The lattice parameter measurements have shown the non-uniformity of the distribution of Ge atoms across the samples.

GaN single crystals grown by the high-pressure/high-temperature method were investigated by x-ray diffractometry and projection topography methods. The grown-in extended defects - low-angle grain boundary, straight dislocations of directions correlated to the growing lattice planes and large defects (probably inclusions) - were for the first time observed and investigated by x-ray projection topography.

Series of experimental pinhole topographs are presented, which were taken by exciting a perfect, plane-parallel crystal plate in the three-beam case of diffraction. These images depict the energy flow inside the crystal. Therefore, modifications of the energy flow in the three-beam cases can be made visible directly. In this paper we investigate the effects of changing the coupling strength or the triplet phase between the two primary reflections. The experimental results are compared with simulations of the recorded intensity distributions and discussed with reference to the course of the dispersion surface.

Two topography experimental stations are presently available at SPring-8. The first, constructed at the short-length bending magnet beam line BL28, is designed to perform white- and selected wide-energy-range x-ray topography. The other is a high-resolution diffraction topography station located on the medium-length bending magnet beam line BL20, where the incoming beam displays a large cross section and high degree of parallelism. This allows us to observe fine structures of three-dimensionally large crystals used in industry if high energy is employed. The construction concepts, as well as first, selected experimental results are presented.

A real-time investigation of the light-induced deformation on Fe:LiNbO₃ crystals was performed by taking advantage of both the high flux and the detector system (FRELON CCD camera) available at a modern synchrotron radiation source like the ESRF. The observed contrast and effective misorientation after illumination of a Z-cut crystal are mainly due to (00l) lattice planes tilts. Considering the coupling of the bulk photovoltaic field and the converse piezoelectric effect, we develop a `parallel plate condenser'-like macroscopic model of the distortion generated by the visible light beam. Calculation of the effective misorientation at the edges of the illuminated region gives values of the order of ±20 arcsec which are consistent with our experimental data.} \setlength\abswidth{32pc

In this paper we describe a regularization approach to diffraction enhanced tomography. This approach represents an improvement over methods based on a geometrical optics approximation. Reconstructed images of the attenuation coefficients and refractive indices of computer generated phantoms are presented. An experimental scheme is also discussed, which utilizes a first-generation tomography set-up, in conjunction with an analyser crystal.

The structural interface properties of layered Pt/Ti/SiO₂/Si electrodes have been investigated using high-resolution specular and diffuse x-ray reflectivity under grazing angles. Currently this multilayer system represents a technological standard as bottom electrodes for ferroelectric thin-film applications. For the electronic and ferroelectric properties of integrated devices, the film-electrode interface is of crucial importance. We focused on Pt 1000 Å/Ti 100 Å/SiO₂/Si electrodes prepared under annealing conditions as employed in industrial processing, prior to the deposition of ferroelectric films. The comparison between annealed and non-annealed electrodes clearly revealed strong interfacial effects due to interdiffusion and oxidation of Ti, especially at the Pt-Ti interface. Migration of Ti into the Pt layer results in a shift of the critical angle due to the enclosure of TiO_2-x within the Pt layer. The heterogeneous distribution of TiO_2-x suggests a diffusion mechanism mainly along the Pt grain boundaries. At the SiO₂ interface a relatively weakly oxidized Ti layer of 20 Å remained, which is most probably correlated with the remaining adhesion to the substrate.

Combined x-ray diffraction and reflectivity experiments have been performed on free-standing trapezoidal GaAs/InGaAs quantum wires using a conventional x-ray tube. Interpreting the intensity distribution around (004) by curve simulation of the extracted coherent grating truncation rods on the basis of a semikinematical diffraction theory (DWBA) the shape and geometric parameters as well as the strain within the wires could be determined taking the results of a finite element calculation of the atomic displacements into account. The map of the coplanar x-ray reflectivity around (000), as well as the intensity profiles of the coherent grating truncation rods, located equidistantly around the specularly reflected beam, have been recorded in order to estimate the roughness properties of the sample interfaces as well as the wire shape and layer set-up without the influence of strain. All small-angle as well as wide-angle scattering experimental results went in to the mutually consistent estimate of the sample properties. The experiments performed for a conventional x-ray tube supply a parameter set comparable in completeness and precision to that obtained from similar samples by interpreting synchrotron experiments.

A strain-induced lateral periodic charge carrier confinement is achieved within an InGaAs single quantum well (SQW) by lateral patterning of an InGaP stressor layer. The one-dimensional periodicity of the long-range strain field is obtained by etching a lateral surface grating into the initially pseudomorphicly strained InGaP layer, while the SQW itself remains unaffected by etching.

Grazing incidence x-ray diffraction was applied to analyse the depth variation of the in-plane strain field within the nanostucture. The measured intensity profiles are discussed in terms of a strain distribution model, created by finite-element calculations using a linear elasticity theory approach. By photoluminescence a strain-induced shift of the SQW electronic band levels was verified. In particular a splitting of the SQW emission line was found, caused by the differently strained parts of the SQW. The photoluminescence results are compared to band structure calculations using a deformation potential ansatz.

Structural characterization of a fully etched amorphous W/Si multilayer grating with a lateral periodicity of 800 nm is performed by x-ray reflectivity in the coplanar and non-coplanar modes using a scintillation detector and a two-dimensional gas-filled detector, respectively. Three-dimensional reciprocal space constructions were used to explain the scattering features recorded in both geometries. Coplanar coherent grating truncation rods were fitted by a dynamical theory for rough gratings. Comparison of the reflectivity from the reference planar multilayer completes the study.

We have investigated the structural properties of one-dimensional self-organized patterns in strained Ge/Si superlattices epitactically grown on vicinal Si(001) substrates. The orientation of the patterns with respect to the miscut was studied by non-specular x-ray reflectivity under grazing incidence and by atomic force microscopy. The unusual orientation of the structure was explained by the zigzag alignment of the monoatomic steps on 2×1 reconstruction surfaces.

Lateral strain modulations in a Si substrate arising from laterally patterned periodic SiO₂ stripes were investigated by x-ray grazing incidence diffraction. In this diffraction geometry a depth dependent in-plane strain analysis was performed. Using finite element calculations the displacement field in the non-patterned Si substrate was calculated, which served as an input for the simulation of the diffracted intensities based on the distorted-wave Born approximation. By varying the lattice mismatch between the SiO₂ stripes and the Si substrate, a good agreement between simulations and experimental diffraction data could be achieved.

The ability to distinguish between roughness and mosaic defect types in (001) and (111) oriented Fe/Au multilayers has been studied using synchrotron radiation. For the (001) orientation structures, the full-width at half-maximum of scans taken transverse to the 002 reciprocal lattice vector through the satellite diffraction peaks exhibit a parabolic dependence on the satellite order, which we interpret as arising from interfacial roughness. An additional contribution, constant with satellite order, is identified with mosaic defects within the system. The observations are not fully consistent with an established theoretical defect model: the minimum in the parabolic fit not occurring at the zero-order peak although the actual experimental minima were found at this position. For the (111) oriented Fe/Au multilayers, no variation in the transverse width was found with satellite order. This was attributed to the lower roughness, measured independently by grazing incidence scattering.

Structural properties of Co/Gd multilayers grown by MBE on Si substrates with and without a Si-N buffer are compared. The x-ray and TEM investigation revealed a strong dependency of the structure on the existence of the buffer layer. The multilayers deposited on pure Si substrate show polycrystalline microstructure with significant correlation with respect to the distinct crystallographic orientation related to the Si substrate. The structure deposited on the Si-N buffer can be described as amorphous. A strong mixing of Co and Gd sublayers in samples deposited on Si-N can be concluded while the multilayer on Si seems to be formed with rather low intermixing. The structural difference between the studied samples was clearly reflected in their respective magnetic properties.

The thermal stability of [Nb(6.0 nm)/Si(2.0 nm)]×50(×100) multilayers with a partially crystalline Nb sublayer deposited onto an (001) oxidized Si wafer has been studied by in situ x-ray reflectivity, ex situ x-ray diffraction, transmission electron microscopy and measurement of low-temperature resistivity on annealing in the temperature range up to 450 °C. It has been shown that the annealing leads to interface shift without any significant change of interface roughness, which was explained by the diffusion of Si atoms into the Nb sublayer. The densification of the multilayer was attributed to the creation of a Nb₃Si phase at the Nb/Si interface; the presence of this phase was proved by electron diffraction. Annealing up to 250 °C has practically no influence on superconductivity of the system although the structure changes are clearly detectable.