Table of contents

High-resolution studies of the transmitted divergent-beam diffraction pattern of a perfect diamond are reported. The specimen has damage-free polished surfaces, and is dislocation-free. A 2 mu m thick copper film evaporated on to one surface acts as source of Cu K alpha X-rays, being irradiated by a focused electron beam while the specimen is inside a scanning electron microscope. The X-ray source diameter is <10 mu m, the camera length is 700 mm, nuclear emulsions are used for pattern recording and specimen temperature is well controlled. Fine structures on an angular scale of a few arcseconds are revealed within the much larger areas of overlap of intersecting wavelength-dispersion-broadened Kossel lines, both within accidental intersections of a pair of lines (in the three-beam case, 0, g₁ and g₂) and in systematic intersections, for the n-beam case, n>or=4. Observations were made under conditions of moderate absorption, mu t=1.7. The fine structures delineate loci of coherent multiple diffraction within the overlap areas. They impose "markers' on an otherwise relatively diffuse diffraction pattern and are demonstrated to be usable in diamond lattice parameter measurements. Their further exploitability is examined.

The early experimental proofs of the dynamical theory can roughly be subdivided into the periods 1914-35, 1935-40 and 1940-65. Experiments mostly performed with calcite crystals in the Bragg case in the first of these periods confirmed Darwin's theory from 1914. Later observations, however, such as the Renninger effect, Pendellosung fringes and others, needed Ewald's 1917 theory for their interpretation, founding a second period, After 1940 Borrmann's experiments and their interaction with von Laue's expansions of his 1931 form of the theory initiated a third period of deeper understanding of the properties of Ewald's wavefields, finally smoothing the way to a true 'crystal optics of X-rays' with the help of artificially grown crystals of high perfection.

We report results from a novel facility constructed to enable in situ X-ray diffraction studies during the molecular beam epitaxy growth of Ill-V strained layer device structures on 50 mm diameter substrates. This new facility, used in conjunction with the Daresbury synchrotron source, permits X-ray topographic imaging of individual misfit dislocations formed during the molecular beam epitaxy growth process. The misfit dislocation growth and interactions can be imaged as a function of layer thickness, strain, growth and post-growth conditions. Our recent results show that the nature and distribution of dislocations threading up from the substrate are crucial in determining the initial pattern of epilayer relaxation. Under certain growth conditions and substrate dislocation distributions, large areas of the epilayer remain free of misfit dislocations at epilayer thicknesses significantly higher than the measured initial critical thickness t_c1. We have observed in situ for the first time a second critical thickness t_c2 (under certain conditions t_c2>2t_c1) at which there is a rapid increase in misfit dislocation density as a second misfit dislocation source(s) becomes active.

The utility of synchrotron radiation white-beam X-ray topography using real-time imaging as a probe for characterizing the structural nature of solid-solid phase transitions is demonstrated through a study of the paraelectric-to-ferroelectric phase transition in ammonium sulphate at 223 K.

Images of precipitates in X-ray section topographs have been modelled by use of a spherically symmetric strain field in numerical solution of Takagi's equations. The critical distance from the surface at which relaxation effects become negligible has been examined, and the effect of long-range wafer curvature on the images investigated. Simulations have been made corresponding to precipitate densities and distributions such as exist in intrinsically 'gettered' silicon. The effect of dynamical and intermediary images on the measurement of the denuded zone width has been studied. From studies of pairs of precipitates displaced normal to the dispersion plane, the minimum separation at which individual defects are resolved is found to vary logarithmically with the deformation parameter.

The numerical integration of Takagi-Taupin equations was used for the simulation of double-crystal topographic images of threading dislocations, misfit dislocation crossings and point-like precipitates in silicon and gallium arsenide. The simulations took account of lattice parameter profiles and the finite divergence of the beam. It was found that the images of dislocations, especially those outcropping on the surface, are dominated by a dilation-orientation contrast. Stronger interference effects were present in the images of point-like defects. A similarity was observed between the images of threading dislocations computed for equivalent positions in the layer and substrate maxima. A reasonable correspondence between simulated and experimental images was confirmed in several cases.

Dislocations emitted at crack tips in silicon are characterized by X-ray topography. It is shown that a controlled mixed mode of loading can be achieved in double-cantilever-beam samples thanks to warping of the crack and that activated slip systems are different when a mode III component is superimposed on the usual mode I component.

A variety of oxygen-related micro-defects (spherical and octahedral precipitates, their agglomerations, dislocations and dislocation loops) with dimensions in the range 0.1-100 mu m were revealed using X-ray topography and transmission electron microscopy after two-step annealing of Czochralski-grown silicon. The defects are distributed in a non-uniform way across the samples with the gradient of their density normal to the crystal surface.

X-ray projection reflection topography has been applied to a number of strongly absorbing crystals in order to find general rules for rendering dislocations visible. Single- and double-crystal schemes have been utilized. Considering direct images of dislocations and calculating the ratio of extinction to the absorption depth, we have established a quantitative criterion for detecting individual dislocations. It is shown that ordered dislocation arrangements are less sensitive to the restriction due to the absorption.

By means of X-ray double-crystal topography we have investigated silicon-on-insulator lamellae grown by liquid-phase epitaxy upon thermally oxidized silicon. The majority of the lamellae were free of extended defects. It is shown that the topographic contrasts of these lamellae are mainly due to vertical stress exerted by the lamellae onto the substrate. This is surprising because the aspect ratio (thickness/lateral dimension) is of the order of 10^-2. Our first calculations lead us to estimate the stress to be around 10 N cm^-2. A simple model, which may be assumed to apply in general for crystal growth on amorphous substrates, is described here. It relates the stress to an adhesive force, which acts during growth.

White-beam synchrotron topographic analysis of SiC device configurations of various polytypes has been carried out. The devices, p-n junctions of area 1 mm², were fabricated via chemical vapour deposition epilayer growth of nominally 3C- or 6H-SiC, on 6H-SiC substrates grown by either the physical vapour transport or the Lely technique. Detailed analysis of diffracted intensities from the different device areas in grazing reflection geometry, using a specially developed computer program, is presented. Depth profiling carried out using variable penetration depth, grazing-incidence geometries reveals both the polytype configuration and the defect structure as a function of depth in these multi-polytype epilayers.

Synchrotron white-beam X-ray topography studies, in conjunction with Nomarski optical microscopy, have been carried out on 6H-SiC single crystals grown by the sublimation physical vapour transport technique. Two kinds of dislocations were observed using topography: dislocations exhibiting bimodal images of various widths and with line directions approximately parallel to the (0001) axis and dislocations confined to the basal plane, which appear to have emanated from the former dislocations. The larger bimodal image width dislocations were found to have hollow cores, known as 'micropipes'. Detailed contrast analysis of topographic images obtained in transmission and back-reflection geometries establishes that 'micropipes' are Frank-type hollow-core screw dislocations with Burgers vectors typically equal to 3-7 times the c lattice parameter. X-ray topography also revealed many line defects approximately parallel to the (0001) axis that were determined to be screw dislocations with Burgers vectors equal to the c lattice parameter and there were no discernible 'micropipes' associated with these latter screw dislocations.

The changes in the light, neutron and X-ray diffracted intensities observed when an electric field is applied to crystals of alpha -LiIO₃ are not yet fully understood. In the present paper, after summarizing the already known diffraction topographic experimental results, we present new ones obtained mainly by the use of section topographs. The discussion tries to establish connections between these data, and considers their origins. In particular, the present investigation shows that the majority of the enhanced diffracted intensity originates from small areas, which seem to correspond to growth bands. The influence of the nature and inhomogeneities of the electrodes is also considered. Finally, we describe the results of topographic experiments and conductivity measurements under an alternating electric field.

2 mm thick silicon wafers, implanted with 4.8 MeV alpha -particles are studied by means of transmission section topography and additionally by Lang and double-crystal methods. It was found that all three methods produced a negligible contrast in the symmetric transmission reflection apart from some fragments of the implanted area's boundaries. The interference fringes were observed in the case of asymmetric reflections. The asymmetric section topographs revealed distinct interference fringes, which cannot be explained in terms of simple bicrystal models. In particular, the curvature of these fringes may be interpreted as being due to the change in the implanted ion dose along the beam intersecting the crystal. Some features of the fringe pattern were reproduced by numerical integration of Takagi-Taupin equations.

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 OOL reflections is mainly explained in terms of 'primary extinction' and 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.

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.

A high-resolution two-dimensional position-sensitive detector was used to investigate the spatial intensity distribution in output coherent beams of thermal neutrons behind the neutron interferometer. In the case of sufficiently wide neutron beams passing through the interferometer, the neutron 'topographic' experiment can be performed when putting a sample into one of the coherent beams inside the interferometer. The intensity modulation of coherent beams depends on the relative neutron phase shift introduced by passing the neutron through the sample. The resulting topographs thus exhibit the contrast that is sensitive to the phase of the neutron, depending on local variations in both thickness and scattering length density of a tested sample. Some computer-processed topographs of a wedge-shaped Ge wafer and an isotopically enriched sample of ²⁰⁸Pb are presented.

X-ray diffuse scattering in (001) InGaAs/(AlGa)As transistor structures of high electron mobility was observed for structures whose InGaAs channel thickness substantially exceeded the critical thickness for misfit dislocation formation. The diffuse scattering was determined to originate from misfit dislocations, as confirmed by plan-view transmission electron microscopy. Diffuse scattering was measured using triple-axis X-ray diffraction, which showed that the diffuse scattering was sensitive to the density and direction of the misfit dislocations. Using transmission electron microscopy for calibration, we determined that the diffuse scattered intensity was directly proportional to the dislocation density. For samples with misfit dislocations along only (110), diffuse scattering was confined to a crystallographic direction that was perpendicular to the misfit segments, but for samples with thicker InGaAs layers (and with misfit segments in both (110) directions) diffuse scattering extended along all azimuthal directions. We also determined that observation of directional diffuse scattering provided a more sensitive means of detecting misfit segments than other commonly used techniques.

The elucidation of the structure of semiconductor multilayers can be adequately determined by X-ray methods but the interpretation is not always straightforward. In this paper we introduce the idea of full three-dimensional diffraction-space mapping to obtain information on the three-dimensional structure of imperfect materials. We also stress the importance of this method for the interpretation of the data from high-resolution X-ray diffractometry. The presence of defects and diffraction effects can create significant changes to the diffraction pattern that require a more complete analysis than that obtained from simple profiles. These subtle influences can in general only be understood by diffraction-space mapping. Interpretation of diffraction-space maps from the high-resolution multiple-crystal multiple-reflection diffractometer permits the use of three extra very powerful tools. The first is multiple-crystal topography so that the diffraction-space intensity features can be related to lateral contrast on the photographic emulsion, the second is the accurate determination of lattice parameters and the third is the simulation of the diffraction shapes using dynamical theory.

Reciprocal space mapping by high-resolution X-ray diffraction is a powerful method for detailed structural characterization of imperfect crystalline layers. The application of a relaxation line model for the interpretation of reciprocal space maps will be demonstrated for epitaxially grown Il-VI heterostructures. This model enables one to distinguish between a gradient of the strain and of the chemical composition in epitaxial layers. In addition, the use of a relaxation line model in describing thermoelastic strain in heterostructures is shown for HgSe layers on ZnTe buffers grown on GaAs(001) substrates. The degree of thermoelastic strain can be influenced by either the growth temperature or by the temperature during characterization. The former was investigated.

Pseudomorphic Si_1-xGe_x (0.15<x<0.35) and Si_1-yC_y (0.008<y<0.016) thin epilayers on Si(100) substrate, grown by rapid thermal chemical vapour deposition and molecular beam epitaxy, were investigated at annealing temperatures up to 1000 degrees C. To measure in situ the variation of the epilayer lattice constant, a conventional X-ray powder diffractometer with high-temperature attachment in combination with a high-power X-ray generator was used. From the decrease in the angular distance between substrate and epilayer reflection, the strain state of the system can be obtained. In the compressive strained Si_1-xGe_x/Si system, strain relaxation could be observed, which is explicable in terms of the introduction of misfit dislocations at the interface. At temperatures of about 1000 degrees C an additional effect, the interdiffusion of Si and Ge and thus the decrease in the Ge concentration inside the layer, enhances the relief of the strain. Both effects were separately measurable and the diffusion coefficient was determined in its dependence on the Ge content. On the other hand, in the tensile strained Si_1-yC_y/Si system the nucleation and diffusion-controlled growth of SiC nanocrystals was found to be the dominant mechanism at temperatures above 800 degrees C, decreasing the amount of C atoms on substitutional sites and thus relieving the strain in the layer.

An approach for the determination of dislocation densities in epilayers is presented, which is based on the analysis of the two-dimensional intensity distribution of diffuse X-ray scattering measured by triple-axis X-ray reciprocal-space mapping. A new formalism for the simulation of experimental iso-intensity contours is used, which assumes a defect model based on random elastic deformation due to the strain fields of dislocations. The simulation of the two-dimensional intensity contours yields the random strain field from which the energy density stored in the epilayer due to the presence of dislocations is calculated. On the other hand, the self-energy of threading dislocations is calculated assuming 60 degrees (for diamond or zincblende structure) or screw-type dislocations. The threading dislocation density is obtained by dividing the energy density by this self-energy. The method was applied for the analysis of SiGe layers grown on compositionally graded SiGe alloy buffer layers. The diffuse X-ray scattering analysis reproduces the increase in the dislocation densities in the buffer with higher Ge grading rates and yields upper limits for the threading dislocation densities.

Single-crystalline ZnSe layers were grown by metal-organic vapour phase and molecular beam epitaxy on (001) oriented GaAs substrates. The lattice mismatch between layer and substrate at growth temperature causes a strain in the layer material, which is relaxed by the nucleation of misfit dislocations. The relaxation process starts at the critical thickness, which depends on the growth conditions. The crystalline quality and the residual strain of the epilayers were investigated with a high-resolution X-ray diffractometer. Additionally, the intensity distribution of the scattered X-rays in the directions perpendicular and parallel to the reciprocal lattice vector (004) was observed by a two-reflection analyser crystal. For the system ZnSe/GaAs, this intensity distribution depends on the degree of strain relaxation, which is dependent on the layer thickness. The results are compared with transmission electron microscopy results.

In this work, ZnS epitaxial layers grown by vapour phase epitaxy on (100)-oriented GaAs substrates are investigated by X-ray diffraction. The residual strain status of the as-grown samples was determined by high-resolution double-crystal X-ray diffraction measurements. Eleven diffraction curves were recorded in the vicinity of the (400), (422) and (531) Bragg reflections in different diffraction geometries and for several azimuth angles. The analysis of the experimental data was performed by using a general model, which relates the angular distances between diffraction peaks and strain tensor components in the second-order approximation. This model considers the lowest crystallographic symmetry (triclinic) for the lattice distortion of a cubic unit cell. Our results indicate that the crystallographic symmetry of the distorted ZnS unit cell is orthorhombic. In order to determine the strain contribution due to the different thermal expansion coefficients of ZnS and GaAs (thermal strain) the temperature variation of the residual strain was measured between 25 degrees C and the growth temperature (650 degrees C) by using a single-crystal X-ray diffractometer. From our temperature-dependent measurements we determined the thermal misfit between ZnS and GaAs and the linear thermal expansion coefficient of ZnS.

GaAs/Ge heterostructures were grown by metal-organic vapour phase epitaxy with different V/III flow ratios; the layer thickness was always much larger than the critical threshold for the elastic strain relaxation. The structural properties of the specimens were investigated by both X-ray topography and high-resolution X-ray diffractometry. It has been found that, at high V/III ratios, the layers are affected by a high density of stacking faults, whereas misfit dislocations are completely absent; the fault density decreases on decreasing the V/III value. A small, but significant strain relaxation has also been observed, thus demonstrating the effectiveness of the partial dislocations bordering the faults in relaxing the strain. At lower V/III ratios the dominant defects are the misfit dislocations to which the strain relaxation can be attributed.

We have studied the profiles of the Bragg peaks and diffuse scattering in reciprocal space along both the plane perpendicular (q_{perpendicular to} ) and plane parallel (q/sub ///) directions for sample structures consisting of layers of In_0.1Ga_0.9As grown by molecular beam epitaxy on (001) oriented GaAs substrates. The samples have different layer thicknesses and different dislocation distributions. We have measured the dislocation distributions in the interfaces using plan view transmission electron microscopy. We find that, for thin layers with low dislocation densities, the diffraction profiles in both the plane perpendicular (q_{perpendicular to} ) and plane parallel (q/sub ///) can be modelled by considering two components of the diffraction profile, namely, dynamical scattering from the coherently coupled regions of perfect layer between dislocations and diffuse scattering from decoupled regions around the dislocations. From the q/sub /// profile a lateral dimension can be associated with the regions that give rise to the diffuse scattering, and we show that this dimension scales with the layer thickness. For thicker layers with higher dislocation densities, the strain fields of the dislocations overlap. In this case the diffraction profiles in (q_{perpendicular to} ) are modelled by considering the ratio of the depth of coherently scattering decoupled crystal, above the dislocation array, with the total depth of the layer, assuming that scattering from the greatly distorted crystal close to the array is lost. Along q/sub /// the diffuse scattering is discussed on the basis of a statistical distribution of finite correlation lengths and microscopic tilts.

High-resolution X-ray diffraction methods have been used to characterize the structural characteristics of GaAs grown by molecular beam epitaxy at low substrate temperatures. Triple-crystal X-ray diffraction scans demonstrate that, as the As₄/Ga incorporation ratio was increased, there occurred increases in the magnitude of diffuse scattering as well as an anisotropy in the scattering. A degradation of the crystal truncation rod is also observed. Differences have also been observed in the diffuse scattering from n- and p-doped GaAs samples grown in this way; we attribute this to changes in the kinetics of arsenic incorporation due to the electrical characteristics of the material. Analysis of the annealed GaAs layers has shown the development of long-range strain fields from distortions generated by the growth of the arsenic precipitates. The diffuse scattering has been used to develop estimates of the average size of the arsenic precipitates.

High-resolution X-ray diffraction is a non-destructive method with an extremely high strain sensitivity. It is shown that its sensitivity is high enough to detect the influence of very small degrees of contamination by oxygen at the interface and the influence of H₂ incorporation. Interference fringes due to the strain induced by 0.01 monolayer of oxygen between the substrate and epilayer can be observed and distinguished from the H₂ incorporation. Depending on the sample preparation, the fit of the X-ray rocking curve measurements is different. Therefore, it is possible to distinguish between interface contamination, which leads to a well-defined strain at the interface, and the strain induced by H₂ incorporation, which is smeared out over a large region. Secondary-ion mass spectrometry as well as the cross section transmission electron microscopy measurements were correlated with the high-resolution X-ray diffraction measurements. Additional Rutherford backscattering channelling measurements also confirmed these results.

High-resolution X-ray diffraction measurements can be performed at variable temperatures and pressures. The usefulness of such experiments is shown when taking gallium nitride, which is a wide-band semiconductor, as an example. The GaN samples were grown at high pressures (bulk crystals) and as epitaxial layers on silicon carbide and sapphire. The X-ray examinations were done at temperatures of 293-750 K and at pressures of up to 8 kbar. The results served for an evaluation of the basic physical properties of gallium nitride; namely lattice constants, thermal expansion and compressibility. The comparison of monocrystals with epitaxial layers grown on highly mismatched substrates provided important information about the influence of the substrate on the crystallographic perfection of the layers.

Aluminium delta-barriers grown in GaAs at 400 degrees C by molecular beam epitaxy have been studied using high-resolution X-ray diffractometry. Superlattice structures of up to 100 periods enabled measurement of layers containing fractions of a monolayer of Al. It was also possible to determine the period variation and interface roughness or grading to a depth resolution of about a monolayer by measuring the weak, high-order satellites around the 002 Bragg reflection. Dynamical simulations showed that there was no interface roughness or grading beyond two monolayers depth. The results were compared with those from Si delta -doped GaAs, in order to provide an understanding of Si delta -doping, which has a wide range of device applications.

We investigate the structural properties of (311) (In,Ga)As/GaAs-heterostructures by means of high-resolution X-ray diffractometry and topography. The low symmetry of the (311) orientation is shown to introduce shear strain. Furthermore, we observe strongly anisotropic diffraction patterns caused by the onset of strain relaxation in heavily strained (311) structures.

A new method based on X-ray interference for the characterization of extremely thin buried single layers by means of high-resolution X-ray diffraction is presented. The independent determination of layer composition and thickness is obtained by comparing measurements performed in at least two different settings, one of which in the asymmetric grazing emergence geometry. The method is applied to study In segregation in InAs/GaAs monolayers grown by molecular beam epitaxy. In segregation lengths of nearly 6 A are measured.

Nearly lattice-matched InGaAs/InP superlattices have been grown on (001) InP substrates by metal-organic vapour phase epitaxy. The number of periods has been kept fixed at 30, whereas barrier and well thicknesses have been changed over a wide range. The samples have been investigated by high-resolution X-ray diffraction and the experimental curves analysed by means of a simulation procedure. The superlattices exhibit a good structural quality when the barrier is much thicker than the well, but the quality is worsened by decreasing the barrier thickness. When the well is much thicker than the barrier, the structural quality is satisfactory, but not as good as in the reverse case; moreover, it is worsened by decreasing the well thickness. For very short periods, the superlattice ordering tends to disappear.

X-ray diffraction studies were performed on different Ill-V heterostuctures grown by planar and embedded selective area epitaxy (SAE) using metal-organic vapour phase epitaxy (MOVPE) and metal-organic molecular beam epitaxy (MOMBE). In order to characterize the heterostructures at the boundaries of masked areas, a convergent-beam double-crystal X-ray diffractometer for laboratory X-ray sources was developed, allowing rocking curve measurements with high lateral resolution. The X-ray beam was focused onto the sample as a line focus by means of a cylindrically curved mirror. A position-sensitive proportional counter was used for the parallel recording of rocking curves along the line focus, resulting in a spatial resolution of 20 mu m*50 mu m. With this set-up rocking curve measurements across the growth/non-growth boundaries of selectively grown heterostructures were performed. These measurements indicate compositional changes in a region of 100 mu m at the boundaries of layers grown by SAE using MOVPE. The changes for MOMBE grown SAE are on a scale of only a few micrometres and are not resolved with this system.

In this work we show the potential of high-resolution X-ray diffractometry for the non-destructive investigation of nanostructures and low-dimensional semiconductor systems. A characterization of the geometrical and structural properties of corrugated semiconductor surfaces (crystalline surface gratings) and semiconductor quantum wires is presented. Double-crystal and triple-crystal X-ray diffraction measurements and reciprocal-space mapping are used in order to determine the geometrical parameters such as the wire periodicity, width and height and the corrugation profile as well as the strain status of quantum wires.

Using the statistical approach to dynamical X-ray diffraction, we found the exact analytical solutions for coherently and incoherently scattered intensity from a damaged epitaxial layer with a constant strain gradient. These solutions and numerical methods were applied to simulations of rocking curves and scattered intensity distributions with depth. It is shown that rocking curves and X-ray intensity depth distributions have oscillatory structure due to the interference of scattered waves from different regions of a graded layer.

A high-resolution triple-axis diffractometer has been used for the structural characterization of periodically domain-inverted nonlinear optical crystals of KTiOPO₄ and LiNbO₃. Striations have been revealed in high-strain-sensitivity multiple-crystal topographs of the domain-inverted regions of both these samples and these are dominated by orientation contrast. The combination of high-resolution reciprocal-space mapping and topography has shown that the extended diffraction streak in the q₍₂₁₀₎ direction for the domain-inverted LiNbO₃ originates from the 'minutely misoriented structure' which is related to the original configuration of dislocations. The reason for the generation of the structural imperfections via the domain-inversion processing is interpreted in terms of the converse piezoelectric effect.

We have investigated periodic arrays of dry etched 150 nm and 175 nm wide, (110) oriented GaAs/AlAs quantum wires and quantum dots by means of reciprocal-space mapping using triple-axis X-ray diffractometry. From the X-ray data the lateral periodicity of wires and dots, the etch depth and the angle of misorientation of the wires with respect to the (110) direction are extracted. The reciprocal-space maps reveal that, after the fabrication process the lattice constant along the growth direction increases slightly for the wires and even more so for the dots.

Some Ill-V heterostructures grown by selective area MOMBE and MOVPE were investigated by double-crystal diffractometry with high spatial resolution. The high spatial resolution was achieved using synchrotron radiation focused by one-dimensional Bragg-Fresnel X-ray optics to a line focus of 2 mu m width. The lattice mismatch close to growth/non-growth boundaries was investigated by performing rocking curve scans with micrometre step width across the lateral transition zones. The rocking curves reveal material variations at the boundaries in the range of 100 mu m for MOVPE to below 6 mu m for MOMBE.

X-ray diffraction has been extended by simultaneously measuring inelastic signals excited internally by the X-ray standing wave field. As the inelastic X-ray standing wave signal we recorded the photoelectron current from an (AlAs)_m(GaAs)_n short-period superlattice on a GaAs(001) substrate. It shows clear modulations due to the GaAs(004) substrate reflection, the (AlAs)(GaAs)(004; 0) superlattice main reflection and the thickness fringes. The modulation at the (AlAs)(GaAs)(004; 0) reflection is related to the content of atoms in lattice plane positions. This is of technological interest, since the coherent fraction offers a new parameter for the characterization of the quality of short-period superlattices. The X-ray diffraction measurement in a wide angular range gives the complete set of satellites between two neighbouring substrate reflections. For some of the samples investigated, a non-coincidence of the (AlAs)(GaAs) satellite groups belonging to GaAs(002) and GaAs(004) is observed, which can be shown to be due to an incommensurate modulation of the superlattice. From the satellite intensities, the Fourier coefficients of the modulation can be determined by comparison with kinematical diffraction theory. This gives a description of the (AlAs)_m(GaAs)_n superlattice unit cell and its interface widths.

YBa₂Cu₃O_7-x thin layers grown with a magnetron sputtering technique have been thoroughly investigated by using various X-ray diffractometry schemes. High-resolution triple-crystal setting has proved to be a powerful tool for identifying basic types of damage: out-of-plane grain misorientations, microstrain and grain size. By using double-axis modes, layer thickness and composition were extracted. The lattice parameter c of the layer was measured and discussed in comparison with that of bulk high-temperature superconductor crystals. The results obtained have promoted an essential extension of the range of the YBaCuO layer structural characteristics.

Multilayers from fatty acid salts, such as Pb or Cd stearate, exhibit a perfect lamellar stacking along the surface normal but a powder-like behaviour in the plane. The amphiphilic molecules are arranged into single-crystalline domains, which are randomly distributed around the surface normal. Using X-ray scattering methods, our films show strong resonant as well as non-resonant diffuse scattering in non-specular directions. The off-specular scattering of lamellar systems is usually described by Sinha's model, which considers the diffuse scattering from rough interfaces as the main process. We present an alternative model, which takes the two-dimensional small-angle scattering of randomly distributed domains into account.

X-ray reflection, strongly asymmetric X-ray diffraction and grazing incidence X-ray diffraction are extremely sensitive to the state of interfaces of a layered sample. Random structural defects at the interfaces give rise to diffuse X-ray scattering. In this paper, the diffuse X-ray scattering in all three arrangements has been described within a uniform formalism by means of a distorted-wave Born approximation that includes dynamical phenomena influencing the scattering process. The theory has been used for calculating the diffuse scattering from randomly rough multilayers in all these experimental arrangements. In the case of X-ray reflectivity, the results have been compared with experiments and good agreement has been achieved.

The possibilities for the investigation of thin-layered samples by specular and non-specular X-ray reflectivity and angle-dependent X-ray fluorescence are shown. As an example, measurements on an oxidic multilayer are discussed. Layer thickness, interface roughness and conformality, as well as compound formation at the interfaces, are found in an unambiguous way. Also, the lateral structure of the interface roughness can be described and is tentatively interpreted in terms of terrace widths.

In this work X-ray diffraction measurements on thin polystyrene films deposited on laterally structured surfaces are reported. The experiments were performed in the region of small incidence and exit angles. The X-ray data are compared with the results of atomic force microscopy investigations, both being performed to obtain the morphology of the polymer film on top of the surface grating. Our results do not confirm existing theoretical predictions assuming pure van der Waals interactions between the substrate and the film.

We present measurements of non-specular X-ray scattering from rough interfaces at a dedicated small-angle scattering beamline that allows for very low divergence of the incident beam and therefore for high resolution close to the specularly reflected beam. A two-dimensional detector is used to measure the non-specular intensity both in and out of the plane of reflection. The method is exemplified by an Au single layer, an amorphous Nb/Al₂O₃ multilayer and an epitaxial GaAs/AlAs superlattice sample.

X-ray reflectivity and diffuse scattering measurements at grazing incidence including 2 theta and omega scans were done using Cu K alpha ₁ radiation on W/Si multilayers deposited obliquely at different angles and on W_1-xSi_x/Si multilayers of different compositions. The reflectivity and omega scans were simulated by the Fresnel optical computational code and within the distorted-wave Born approximation, taking the vertical roughness correlation into account, respectively. The root-mean-square interface roughness increases by about 15% while lateral correlation length decreases by nearly one order of magnitude on increasing deposition angle of the W/Si multilayers up to 47 degrees . Simultaneously the vertical roughness correlation decreases, which is shown also by 2 theta scans. Thus rougher, less correlated interfaces and an increased tendency for agglomeration appear. No root-mean-square interface roughness change was detected for W_1-xSi_x/Si multilayers with x up to x=0.67 while the lateral correlation length decreased by one order of magnitude, interfaces being more correlated vertically. The interfaces do not exhibit the fractal behaviour in either type of multilayer.

InAs single quantum wells were grown by means of a low-pressure metal-organic chemical vapour deposition technique on GaAs(001). Their nominal thickness was varied among 0.7, 2, 3 and 4 monolayers and they were buried under a thick GaAs top layer. The samples were investigated by means of the grazing incidence X-ray diffraction using the weak (200) in-plane reflection. Depth resolution was obtained setting the angle of incidence and exit alpha _i and alpha _f, respectively, smaller or larger than the critical angle of total external reflection alpha _c. Owing to the high sensitivity near the surface the collected rod scans show pronounced thickness oscillations for alpha _i> alpha _c. The thickness and the In-content, which control the scattering power of the single quantum wells were evaluated via simulation using the kinematic approach to X-ray diffraction. Partial relaxation occurs whenever the single quantum wells' thickness exceeds one monolayer. It is explained by the appearance of strain-reduced and non-tetragonally deformed islands built after the two- to three-dimensional transition of the growing mode.

The source characteristics of third-generation synchrotron radiation machines lead to enhanced possibilities for diffraction topographic techniques: real-time observations, high-resolution experiments, investigation of heavy or bulky materials using short wavelengths and the possibility of using large sample environments. We describe the instrumentation of the ESRF ID19 'Topography and High Resolution Diffraction Beamline', which has been designed to take advantage of these new experimental possibilities. Experiments performed, in white and monochromatic beam, on two other beamlines of the ESRF illustrate these new possibilities. They show that (i) typical exposure times for white-beam topography (down to about 10^-2 s) are about 10²-10³ times shorter than at other synchrotron radiation topographic set-ups, (ii) the divergence of the diffracted beam is small enough to retain good spatial resolution when placing the film far (up to 1 m) from the sample, (iii) with short wavelengths (about 10 pm and less) it is possible to carry out topographical investigations of bulky or heavy samples or to detect weak long-range deformation fields of defects and (iv) 'low-divergent wave' or 'weak-beam' monochromatic beam topographs can be recorded in a few seconds. Sample-heating effects are observed in white-beam topography even for materials that are not highly absorbing or thermally insulating. A simple criterion for observation of these effects is presented and tested.

Novel high-resolution X-ray optics for the use of the extremely high brilliance of the undulator X-radiation from the third-generation synchrotron light sources are presented. These include plane-wave X-ray optics to produce a 40 nrad collimated beam, multiple flat-crystal monochromators with milli-electron-volt and sub-milli-electron-volt resolution, a nuclear Doppler monochromator with 50 neV resolution and interface-selective X-ray topography with 30 nm depth resolution.

A perfect silicon crystal is used at the ESRF as monochromator for monochromatic synchrotron diffraction topography. This monochromator produces a beam with a narrow range of energy, which is not suitable for some experiments. Moreover, the diffracted energy varies spatially on the monochromatic beam section. A solution to overcome the narrow energy range and the wavelength dispersion is the use of a vibrating monochromator. We present in this paper the three-pole electromagnet device used to vibrate, at about 100 Hz, the perfect (110) Si crystal, the results on the homogeneity of the vibrations and the X-ray topographs recorded using this method.

The principle of the double-crystal technique with curvable monochromator-collimator crystal is applied using synchrotron radiation. In this technique the curvature of the monochromator-collimator crystal is adapted to the sample curvature during the experiment, thereby obtaining large area double crystal topographs. This technique is well suited for the investigation of homogeneously bent samples like heteroepitaxial layer systems, especially when it is applied in reflection geometry. It is shown to have the full sensitivity of the double-crystal technique for topography, and allows very short exposure times. Topographs obtained using adapted monochromator-collimator crystal curvature are compared with those using a plane crystal. The suitably curved monochromator-collimator crystal reflects the wave corresponding to the local Bragg condition in the sample by selecting appropriate wavelengths resulting in the increase of the sample area investigated. As an example for a typical heteroepitaxial system a distributed Bragg reflector structure on a GaAs substrate is investigated. The diffractometer curve of this structure has a large number of superstructure diffraction peaks. The defect contrasts in satellite reflection topographs differ from those in the corresponding substrate reflection topograph. On the slope of the substrate reflection a new type of small defect contrast is detected, probably originating from small dislocation half loops. The effects of additional monochromatization by a silicon double-crystal monochromator are studied. The level of radiation background is considerably reduced.

Parabolically bent multilayers with laterally graded period were applied as condensing reflectors to convert divergent X-rays from laboratory X-ray sources into a parallel beam. Two different modes of coupling such a collimated beam into multi-reflection channel-cut monochromators for high-resolution X-ray diffractometry were tested. (i) Parallel coupling (the scattering vector of the mirror reflection is in the plane of the scattering vectors of the monochromator and the sample) enables one to exploit a wider solid angle range of the X-ray source and to gain nearly two orders of magnitude in intensity. (ii) Crossed coupling (the scattering vector of the mirror reflection is perpendicular to the scattering vectors of the monochromator and the sample) delivers a beam with much reduced vertical divergence. This eliminates the line broadening in rocking curve measurements even for strongly tilted samples.

Strong X-ray resonant magnetic scattering near the M absorption edges of rare earth elements results in a drastic decrease in the magnetic extinction length, which becomes comparable to the absorption length. Under such conditions it may be possible to observe dynamical effects in direct X-ray diffraction on spiral magnetic structures in rare earth magnets. A dynamical theory of X-ray diffraction on a simple magnetic spiral is presented. Diffraction properties of spiral magnets are shown to be similar to the well-known unique properties of liquid crystals (such as cholesterics), but the magnetic nature of the spiral leads to more complex diffraction phenomena. Diffraction on spiral magnets shows both 'cholesteric' and 'gyrotropic' (magnetic) features: two types of reflections with different polarization properties at different Bragg angles may be observed. The region of magnetic reflection is shown to have a complex angular and polarization structure. Specific 'elliptical' standing waves are formed in a magnetic crystal over this region.

Theoretical, experimental and numerical analysis of the effect of acoustic vibrations on the X-ray diffraction in a slightly deformed single crystal is presented. We have found for the first time that the sensitivity of the diffraction with respect to small static deformation is highest for the case of X-ray acoustic resonance.

Dynamical X-ray diffraction in the Bragg geometry, under surface acoustic wave excitation, was found to be sensitive to small static and dynamic strains in almost perfect single crystals. An acoustic wave stimulates X-ray scattering processes that lead to various modifications in the shape of rocking curves, depending on the strain level of the sample and on the amplitude, w, of the acoustic wave. These modifications in strained Si crystals are studied by means of double-crystal diffractometry. A new strain analysis is proposed on the basis of the observed anomalous behaviour of the rocking curves width as a function of w.

First results of an X-ray diffraction study of a newly found substantial reduction in radiation damage by permanent magnetic fields in InSb single crystals during implantation with In⁺ ions are discussed. The data indicate that, in the presence of a permanent magnetic field, there is a decrease in formation of point defects, and in their trend to form clusters. These observations are supported by Rutherford backscattering measurements. A scheme to perform grazing-incidence measurements using a diffractometer equipped with parallel beam optics is presented.

Sputter-deposited films and multilayers are used for a wide variety of applications including protective coatings on turbine engine blades, magnetic recording heads, optical elements, electronic packaging, X-ray filters and monochromator components to name a few examples. This wide range of interest requires growth thicknesses from a few nanometres to tens of micrometres depending on the product. In many applications, specific film textures in the growth direction as well as in the plane of growth are required. The control and manipulation of these textures can be accomplished by using advanced characterization techniques to select particular processing conditions. A variety of X-ray methods including grazing-incidence X-ray scattering, conventional pole figure studies and synchrotron white-beam transmission Laue scattering were used to study texture evolution for the thinnest films up to the thickest multilayer coatings.