Table of contents

The name of the X-TOP conferences originates from the first x-ray topography-related meeting, held in Grenoble in 1990, which aimed to define the ESRF beamline devoted to diffraction topography. X-TOP conferences took place in Marseille (France) 1992, Berlin (Germany) 1994, Palermo (Italy) 1996, Durham (UK) 1998 and Ustron-Jaszowiec (Poland) 2000. These conferences extended the topics well beyond `topography' and incorporated other imaging and diffraction techniques (high resolution and grazing incidence diffraction, reflectometry, microtomography, phase contrast imaging), which emerged or developed in strong connection with the availability of SR sources.

We wish to dedicate the X-TOP 2002 conference to the memory of Professor Norio Kato (1923-2002). Professor Kato brought about outstanding developments of the dynamical theory of x-ray diffraction in perfect and deformed crystals. He established, in addition, many of the basic concepts necessary for the interpretation of x-ray topographs. Professor A Authier was invited to review Norio Kato's career and scientific contributions (first paper of this special issue).

The X-TOP conferences are now a well-established scientific exchange opportunity for the community concerned. More than 170 participants coming from 21 countries attended X-TOP 2002 (Grenoble-Aussois). An original feature of this meeting were the four `basic' courses on (1) high resolution diffraction (2) grazing incidence diffraction (3) x-ray imaging techniques (absorption, phase contrast, Bragg diffraction) and (4) standing waves, which initiated the conference. Their aim was to give all participants (and more particularly the youngest) the background required to take full advantage of the scientific contributions using the various diffraction and imaging techniques which are used by this scientific community. These basic courses were followed by 40 oral contributions (invited reviews or original contributions) and more than 100 posters. The general scientific and presentation standard of these contributions was very high, and very lively discussions followed most of the talks, or were held in front of the posters.

A special issue of Journal of Physics D: Applied Physics has been published after each X-TOP meeting. The present one is, in the tradition of the X-TOP conferences, not the `Conference Proceedings': it only includes high-level original contributions and invited review papers. The refereeing process has maintained the same standard as for regular contributions to this journal. The rejection rate (not far from 30%) indicates our clear will to retain only the best scientific quality contributions.

The conference covered a wide range of topics such as:

New developments in methods and instrumentation (imaging and diffraction methods, mainly using synchrotron radiation, x-ray optics with special emphasis on the microfocusing and magnifying devices, data recording and processing)

Applications to physical studies (defects, deformation, phase transitions, etc)

Characterization of interesting materials (bulk crystals including biological crystals, layers and super-lattices, nanostructures, quantum dots)

Theoretical aspects such as the predictions of dynamical theory when using ultrashort pulses (new x-ray sources) or how valid usual approximations of this theory are when considering the new, layered or nanostructured, materials.

Most of these topics can be found in the contributions to the current issue. While there is of course considerable overlap, these contributions have been grouped into four main areas: (1) diffraction theory and techniques (2) x-ray imaging and coherence (3) high angle, high resolution, diffraction and (4) grazing incidence diffraction and reflectivity.

I would like to thank Claudine Brun and Myriam Dhez for the outstanding work they performed organizing the conference and the administration of the refereeing process. I would also like to thank the 130 referees for their cooperation. In many cases, their work led to a significant improvement of these papers.

Norio Kato's contributions to the dynamical theory of diffraction are briefly reviewed along with some brief bibliographical notes. A few points are developed with more detail such as the diffraction of electrons by polyhedral crystals, the propagation of wavefields in crystals, the dynamical diffraction of spherical waves and the diffraction of x-rays by deformed crystals.

We present two-beam and three-beam dynamical diffraction theories for strained multilayers, where no other approximations are used. We compare the resulting diffraction curves with the calculations using the conventional two-beam dynamical theory and by a kinematical approach. We show that between the diffraction maxima all the dynamical approaches used do not yield correct results and a two-dimensional formulation of the dynamical theory must be used.

A dispersion analysis is carried out for low asymmetric x-ray Bragg diffraction in the case of one-dimensional bending. The cases of strong and weak deformations are examined in detail. Considering the asymmetric Bragg cases of steep incidence and steep exit, the new effect is established for the integrated intensity of the diffracted wave. An interpretation of this effect, based on the `quasi-block' model of a bent crystal, is presented.

Production of He isotopes in surface rocks enables one to study their origin. Quartz is a widespread mineral; understanding He mobility in it will be valuable to helium studies in many environments. Measurements of the He diffusivity in quartz demonstrated that a perfect crystalline quartz lattice was virtually impermeable for He. In this paper, we show that lattice dislocations serve as the high diffusivity paths for helium in quartz. Synthetic crystals were grown to contain a certain amount of helium, which was then degassed under heating. Synchrotron imaging was applied to characterize and map grown-in defects. Samples for desorption were prepared from the chosen growth zones where the average dislocation densities were evaluated. From the highly dislocated samples helium appeared to release more rapidly and to have a lower activation energy. The gain in diffusivity was interpreted due to a smaller amount of energy required to permit the passage of a He atom through an increased `doorway' provided by a dislocation pipe.

X-ray topography (XRT) is recognized as being a powerful tool for directly imaging defects in single crystals, semiconductor wafers and epitaxially grown layers. The timely identification of defects can lead to increased yields and significant cost savings in wafer processing. The primary limitation to its general usage within the semiconductor community has been the difficulty in system use and difficulty in integration into an in-line analytical tool. We have developed a novel, high-speed digital XRT method that can be implemented on a standard high-resolution x-ray diffraction (HRXRD) system equipped with a wafer translation stage and a microfocus tube (or a small aperture in front of a standard point source). It is also appropriate for an in-line fab tool with robot loading and automated operation. In this paper, we discuss the theory and present examples from work undertaken on a variety of materials, including: silicon, compound semiconductors and ionic crystals. Reflection and transmission methods are illustrated. Data were collected on a HRXRD system with a microfocus source and a CCD detector, and an innovative software integration and processing algorithm. Algorithms for full automation of the alignment, exposure and data collection processes have been worked out. It is estimated that the dedicated XRT tool now in prototype form will be capable of scanning a full 300 mm wafer in reflection in under two hours at 50 μm resolution and can achieve < 15 μm resolution.

Besides attenuation, x-ray refraction occurs in an x-ray beam passing through an object containing details of different refractive indices or of non-uniform thicknesses. The emerging x-rays present characteristic angular deflections, which are on the microradian scale. Different refraction directions can be resolved by using an angular analyser, for instance a perfect crystal, which can then be revealed by a detector placed behind it. By varying the alignment of the analyser with regard to the incoming x-ray beam, the unrefracted x-rays can either be recorded on a detector or rejected, thus, either contributing or not contributing to the image contrast.

The x-ray refraction contrast can greatly exceed the absorption contrast, for instance in imaging low Z materials, where the potentialities of the technique have been exploited from the beginning. An analyser-based imaging technique has been presented in various versions also assuming different names.

An important variation, based on an algorithm that differentiates the separation of the refraction contrast from the absorption contrast in an image, has been introduced with the name `diffraction enhanced imaging' (DEI).

The interest in the potential medical application of the diffraction imaging technique has given origin to many projects utilizing analyser-based refraction imaging. Initiated with conventional x-ray generators, it has been rapidly developed in synchrotron radiation sites thanks to the highly intense collimated beams available that permit fast projection and tomographic imaging. Mammographic in vitro protocols and cartilage characterization are the most exploited applications of DEI. The potential medical application has refocused the interest towards the utilization of presently available conventional high-power x-ray generators that can open the doors to large-scale utilization. The aim of this paper is to present a review of the technique in its theoretical and practical aspects; an abundant bibliography, highlights the most significant and recent results.

A short review is presented of the various synchrotron white beam x-ray topography (SWBXT) imaging techniques developed for characterization of silicon carbide (SiC) crystals and thin films. These techniques, including back-reflection topography, reticulography, transmission topography, and a set of section topography techniques, are demonstrated to be particularly powerful for imaging hollow-core screw dislocations (micropipes) and closed-core threading screw dislocations, as well as other defects, in SiC. The geometrical diffraction mechanism commonly underlying these imaging processes is emphasized for understanding the nature and origins of these defects. Also introduced is the application of SWBXT combined with high-resolution x-ray diffraction techniques to complete characterization of 3C/4H or 3C/6H SiC heterostructures, including polytype identification, 3C variant mapping, and accurate lattice mismatch measurements.

We propose a three-dimensional and high-resolution quantitative image analysis technique for the investigation of the internal microstructure of polymer foams. Microscopy, which is the conventional method of investigation of foams, images only the surface of samples, though, three-dimensional x-ray computed microtomography (μCT) enables the non-destructive imaging of multiple slices of a sample. It is a powerful technique for the examination of porous and multiphase materials. In this paper, we present the application of three-dimensional synchrotron radiation μCT for the characterization of foam samples. After a brief description of the imaging system, we present three-dimensional image-processing tools developed to extract structural parameters quantifying the internal structure of foams. Results of this three-dimensional quantitative image analysis on various types of plasticized poly vinyl chloride foams are presented. This approach provides a tool to study the relationships between the foam microstructures and their physical properties.

In x-ray topographs of Si/Ge_xSi_1−x/Si(001) heterosystems, the intensity variations, which are associated with inhomogeneous GeSi thickness, are observed. The layers of GeSi and Si were grown by molecular beam epitaxy. The growth conditions preserving the pseudomorphic state of the intermediate SiGe layer from misfit dislocation appearance were kept. The topographs were recorded using a spherically bent monochromator as well as a flat one. The observed contrast peculiarities are established to be Moiré (translation fault) fringes. The displacement of interference fringes due to the crystal angular position variation is observed. For Pendellösung maxima, the dependence of their angular positions on nondiffracted layer thickness is established. The image simulated in the framework of semikinematical approach demonstrates the main contrast peculiarities observed in the topograph.

Snow, from its fall until its full melting, undergoes a structure metamorphism governed by temperature and humidity fields. Among the many possible mechanisms that contribute to snow metamorphism, those that depend only on curvature are the most accessible to modelling. The isothermal metamorphism of a dry snow sample near 0°C is addressed in this paper. Near 0°C, the vapour pressure of water is high: the metamorphism can be considered, in first approximation, as fully curvature-driven. This corresponds to neglect crystallographic orientation and diffusion-limited effects.

Based on Kelvin's and Langmuir–Knudsen equations, a growth law of the ice phase can be analytically obtained. In this law, the variation of the local volume fraction is proportional to the difference between integral and local curvatures. A simple numerical model was implemented in three dimensions and applied on real tomographic images.

The mechanisms of the x-ray Moiré images formation was investigated for the strain fields created by point forces in the analyser plate of a three-crystal LLL-interferometer. The size of the area of the effective interaction between two series of Moiré fringes—the Moiré fringes caused by a stationary phase shift of the interfering waves and strain Moiré fringes—depends on the crystal thickness and on the force. The largest transformations of Moiré patterns are observed in the case of a force acting on the crystal-analyser entrance (with respect to the incident x-ray beam) surface.

White beam synchrotron x-ray topography (WBSXRT) is a non-destructive technique, which is capable of analysing the strain and/or dislocation distribution in single crystal materials. This paper discusses the application of WBSXRT to the analysis of strain fields due to the microelectronic packaging of integrated circuits. A ball grid array package containing an Intel^® Pentium^® III microprocessor was employed to investigate the spatial extent of strain fields imposed on the underlying silicon substrate due to the reflow process for lead–tin solder bumps.

Large area and section back-reflection SXRT images were taken before and after the reflow process at 350°C in atmosphere. The effects of strain imposed by the overlying bump structures in these x-ray topographs have been observed principally via orientational contrast. This was also the situation after the reflow process due to severe stresses in the underlying silicon beneath the lead bumps. The estimated magnitudes of shear stress, |τ_xy|, imposed on the underlying silicon were calculated to be of the order of 100 MPa. A simulation of the orientational contrast at the edge of bump was performed based on the kinematical theory of x-ray diffraction (Rantamäki R et al 1999 J. Appl. Phys.86 4298). The degree of lattice distortion is well fitted to the topographs of the post-reflow sample. The spatial strain in the underlying silicon was relieved dramatically after the lead bumps were removed from the wafer, which confirms that the solder bump formation is indeed a major source of strain in the underlying Si. Finite element modelling was performed in two-dimensional plane strain mode. The magnitudes and spatial distribution of the stresses after the reflow process are in good agreement with the SXRT results.

In x-ray imaging and beam conditioning it is useful to magnify or demagnify the x-ray beam, or an image, approaching (sub)micrometre resolution or the (sub)micrometre illuminated region. Using an asymmetric diffractor it is possible to expand or compress the x-ray beam in one direction. Combining two such diffractors with mutually perpendicular planes of diffraction even two-dimensional beam expansion or compression can be obtained and, for suitable wavelengths, it is even possible to design and cut a single crystal in such a way that it works as a monolithic device expanding or compressing the x-ray beam in two directions. In this paper, a new magnifying monolithic optical device for a two-dimensional magnification of 25 at 10 keV, based on two noncoplanar asymmetrically inclined {311} diffractors, was designed and made from a single silicon crystal. A ray-tracing image has been simulated to check the functionality of the device. The experimental testing of this device was performed at Optics beamline BM5 at ESRF Grenoble. An undistorted image magnification of about 15 was achieved at a photon beam energy of 9.6 keV. When the photon energy was increased, a higher magnification and increased distortion were observed (horizontal magnification of 39, vertical magnification of 20) at an energy of 10.045 keV. The advantages and disadvantages of the device, as well as further steps to improve it are briefly discussed.

Two stroboscopic shutters, adapted for the study of periodic phenomena in the 1–400 Hz range, were developed and tested. The principle, advantages and drawbacks of these devices are pointed out. Results obtained by x-ray diffraction imaging (topography) on a vibrating silicon crystal, and on the investigation of defects produced in KTiOPO₄ by the application of an electric field, illustrate the possibilities of this stroboscopic imaging technique at low frequencies.

We have developed a high-resolution diffraction imaging method for determination of the complete three-dimensional rotational local lattice misorientation of crystalline samples. The method, called synchrotron area diffractometry, is based on recording double-crystal diffraction rocking scans in three mutually non-coplanar scattering planes with a two-dimensional area detector. The subsequent multiple-peak analysis of the rocking curve image series for all pixels and their backprojection to the wafer surface provides local misorientation angles (Euler angles) with spatial resolution up to micrometre range over the wafer surface. We applied this technique to determine the distribution of tilt and twist angles of the lattice misorientation of a macroscopic defect localized in a 6 inch semi-insulating GaAs(001) wafer.

We report on x-ray microscopy of advanced microelectronic devices imaged in Zernike-type phase contrast mode at 4 keV photon energy. Fresnel zone plates were used as high resolution x-ray objectives providing 60 nm spatial resolution. Integrated circuit copper interconnect structures were imaged in positive as well as negative phase contrast. In both cases the phase contrast in the x-ray images is about five times higher than the pure absorption contrast.

During directional solidification of a binary alloy, the solid–liquid interface exhibits a variety of patterns that are due to the Mullins–Sekerka instability and governed by the growth conditions. It is well known that properties of the grown material are largely controlled by the microstructures left in the solid during processing. Thus, a precise mastering of the solidification is essential to tailor products in a reproducible fashion to a specified quality. One major difficulty for this study is the real-time and in situ observation of the interface, especially for metallic alloys. A possibility is to use an intense and coherent third generation x-ray beam. By combining different x-ray imaging techniques (absorption/phase contrast radiography and diffraction topography), we have studied the directional melting and solidification of aluminium-based alloys. The preliminary results show the great potential of these techniques for the study of the coupling between stress effects and microstructure formation in solidification processing.

A significant enhancement of the anomalous transmission in the multiple-beam diffraction geometry 008/404/04/044/04 was experimentally examined using synchrotron radiation. The experiment was performed on the 1 km beamline BL29XU at the SPring-8 facility in Japan. High resolution rocking curves of the directly transmitted beam were measured in the vicinity of the exact backscattering position. A collimation effect in the transmitted beam was observed in a slit image. The experimental results were compared with theoretical simulations based on x-ray dynamical theory, and they were found to be in agreement with experimental ones.

Fraunhofer patterns of a 5 μm entrance pinhole were detected at the white-beam bending-magnet beamline at BESSY II. Using an energy-dispersive detector the Fraunhofer fringes could be recorded simultaneously between 5<E<15 keV. At the present apparative conditions the intensity is sufficient to resolve Fraunhofer fringes of more than five orders. After the successful investigation of the Fraunhofer diffraction over a large energy band pass static speckle pattern were measured from the optical components of the set-up. The proposed technique seems to be suitable for a fast characterization of coherent properties over a wide energy range.

The application of in situ synchrotron radiation (SR) transmission topography to the study of grain boundary migration in bicrystals of an Fe–6 at.%Si alloy is described. The details on experimental arrangement of the high-temperature in situ observations of dynamic processes in material are given. The pertinence of this method is documented by comparison of the data on migration of {130} grain boundary measured this way and by optical method after heating and cooling cycles.

This study addressed how defects in SiC substrates influence the crystallographic properties of AlGaN/GaN layers deposited by metallorganic vapour phase epitaxy and by molecular beam epitaxy. We employed double crystal reflection x-ray topography using symmetric (0008) and (00012) reflections with CuKα radiation (λ = 1.54 Å) to image dislocations, micropipes, and low angle boundaries in SiC substrates. Lattice strain near the core of a micropipe defect was estimated to be of the order of 10⁻⁷. The substrates investigated exhibited radial patterns of strain and, primarily, of tilt of the order of tens of arcsec.

After deposition of the AlGaN and GaN layers, DCXRT images were generated from the substrate (0008) or (00012) and GaN epitaxial layer (0004) reflections. Full-width at half-maximum values ranging from ∼100 to 300 arcsec were typical of the GaN reflections, while those of the 4H–SiC reflections were ∼20–70 arcsec. Micropipes, tilt boundaries, and inclusions in the SiC were shown to produce structural defects in the GaN layers. A clear correlation between SiC substrate defects and GaN defects has been established.

Diffraction enhanced imaging (DEI) is a phase-sensitive x-ray imaging technique based on the use of an analyser crystal placed between the sample and the detector. In the recent years, DEI has proven outstanding image quality both in material science and medical imaging, as well as the capability to provide quantitative information. However, in the case of objects featuring a fine refractive structure, which is not resolved by the spatial resolution of the detector, the fundamental requirements for the applicability of the DEI algorithm are not fulfilled. Herein a new algorithm is presented that takes into account this particular case. Formally similar to DEI, it allows obtaining quantitative information on the absorption and refraction properties of the object. Thus, structures in the sub-pixel length scale can be imaged and analysed quantitatively.

Often detector resolution limits the spatial resolution of x-ray imaging close to 1 μm. Image magnification is one of the solutions of this problem. Among several approaches magnification by asymmetric Bragg reflection is a promising way to achieve magnification around or above a factor of 100. This technique is well known for many years but not yet established. Therefore this paper will discuss the implications regarding experimental set-up, resolution and efficiency. This will be done mainly from the experimental point of view by means of experiments which were done at the beamline ID11 of the European synchrotron radiation facility. It is shown that submicrometre resolution can be achieved at high magnification in two dimensions. This even holds in case of objects with low contrast. The technique is well suited for an energy range around 10 keV at highly brilliant sources. Some effects related with beam optics, Fresnel and Bragg reflection are observed, which might be critical for further image evaluation.

Phase coexistence during the spin-reorientation Morin transition in haematite (α-Fe₂O₃) was investigated by observing phase boundary movements under the influence of temperature and of a magnetic field, using synchrotron radiation white beam section topography. The sample was a high quality (111) platelet shaped crystal, 1.1 mm thick. The phase boundaries are observed to move while remaining nearly parallel to (111). Nucleation of the weak ferromagnetic phase and pinning of interphase boundaries on defects located in the bulk of the crystal were observed. The observed behaviour patterns are discussed in terms of the elastic and magnetostatic energies involved.

In this paper the capabilities of stroboscopic x-ray topography to visualize the propagation of short (<10 μm) surface acoustic waves (SAW) in single crystals are analysed. Experiments with LiNbO₃ crystals under SAW excitation were carried out at the ID19 beam line of the European synchrotron radiation facility. The developed theoretical analysis of the SAW-induced contrast in Bragg scattering geometry helped to optimize experimental conditions and receive high quality images with well-resolved individual acoustic wave fronts. The basic contrast mechanism is related to the SAW-induced corrugation of atomic planes that causes the focusing of x-rays. The focal distance is directly proportional to the SAW wavelength and inversely proportional to the deformation amplitude at the crystal surface. Simulations of diffraction contrast allowed us to conclude that the best contrast is achieved when the acoustic wave vector is perpendicular to the x-ray scattering plane and the sample/film distance equals 2–4 focal distances.

We have performed x-ray topography experiments in a new configuration using a Fresnel zone plate to form a magnified image of the sample intensity distribution on the detector plane. The main difference from the x-ray topography techniques where no optics is used between the sample and the detector, is the absence of free space propagation effects in the image and the possibility to form a magnified image. Other advantages include large working distance around the sample and low background radiation on the detector. As a first application, we recorded x-ray topographs of an Al interconnect structure as a function of time in an in situ electromigration experiment. The contrast in the images is explained in terms of lattice deformations caused by the stress in the metal films. The results show the evolution of stress due to the electromigration process. The technique should make it possible to obtain best possible spatial resolution allowed by the sample in x-ray topography.

The samples cut out from Si : Ge crystals with 3% and 1.2% of germanium were studied by means of synchrotron white beam Bragg-case section and projection topography as well as conventional transmission Lang topography. The obtained topographs revealed dominant contrast coming from the segregation of germanium. The use of Bragg-case section topography made possible to follow the shape of growth surfaces inside the crystal. The formation of contrast in Bragg-case section topographs for different orientation of growth surfaces with respect to the incident beam is discussed. The applied methods enabled also revealing growth surface instabilities occurring in some regions of Si : Ge crystals.

The origin of the opalescence observed at the α–β transition of quartz remains an open question. This intense light scattering occurs during the coexistence, at the first order transition, of the α and incommensurate (inc) phases, in the vicinity of the phase interface. New hard x-ray diffraction experiment shows that the large angle light scattering is mainly in the α-phase region of the crystal and reveals the existence of an intermediate structure between the α-phase and the 3q inc phase.

The influence of in situ photoexcitation on the defect structure generation in GaAs crystals implanted by Ar⁺ ions with energy of 200 keV and doses of 1×10¹³, 3×10¹³ and 5×10¹³ cm⁻² was studied by high-resolution x-ray diffraction and Rutherford backscattering spectroscopy. The in situ photoexcitation is found to provide for annihilation of Frenkel pairs that decrease a residual concentration of radiation-induced point defects. The amorphization of the damaged layer is assumed to proceed by a generation and a growth of radiation-induced point defect clusters. The vacancy- and interstitial-type clusters are spatially separated: the former are located closer to the surface than the latter ones. The in situ photoexcitation is shown to hinder the cluster growth and to stimulate diffusion of interstitials towards undamaged substrate.

A reciprocal space map recorded by means of a high-resolution diffractometer is a function of two angular variables: ω and 2θ defined as angular position of the studied crystal and position of an analyser, respectively. For comparative investigations of different samples the inter-planar spacing distribution function and the lattice reflecting plane orientation distribution function are more useful. In this paper we present the integral equations, which allow one to obtain these functions through the integration of the reciprocal space map matrix. An example of the mathematical analysis of the reciprocal space map for GaAs single crystal recorded by means of a Philips MRD high-resolution diffractometer is described and well-defined analytical formulae for the apparatus functions are given.

Three-dimensional reciprocal-space mapping was performed to determine the true microstrain: that is, the distribution of strain within individual grains: and to calculate the precise lattice parameters and deviation from near-perfect samples. In order to accomplish this, Bragg reflections from individual grains were isolated (Fewster P F 1997 Crit. Rev. Solid State Mater. Sci.22 69–110; Golshan M, Fewster P F, Andrew N L, Kidd P, Moore M and Butler J E 2001 J. Phys. D: Appl. Phys.34 A44–6). This was achieved by increasing the 2θ resolution and by reducing the axial divergence of the beam, resulting in a smaller probe and partially eliminating the effect of projection on to the diffraction plane along the perpendicular direction. A suitable divergence was achieved by using two pairs of slits, placed after the monochromator and before the detector, respectively. The incident beam size was reduced to 50 μm² to ensure that only a small part of the sample was illuminated. The experiments were carried out at Daresbury Laboratory, Stations 16.3 (Collins S P, Cernik R J, Fell B, Tang C C, Harris N W, Miller M C and Oszlanyi G 1998 J. Synchrotron Radiat.5 1263–9) and at ESRF, ID10B. The results obtained from three different grades of CVD diamond films were compared. Nitrogen incorporated in one diamond during growth appeared to relieve the strain and give a sharper texture to the film.

Many transition metal oxides display strongly correlated charge, spin, or orbital ordering resulting in varied phenomena such as colossal magnetoresistance, high temperature superconductivity, metal–insulator transitions etc. X-ray scattering is one of the principle techniques for probing the structural response to such effects. In this paper, we discuss and review the use of synchrotron radiation high energy x-rays (50–200 keV) for the study of transition metal oxides such as nickelates (La_2−xSr_xNiO₄) and manganites (La_2−2xSr_1+2xMn₂O₇). High energy x-rays have sufficient penetration to allow us to study large flux-grown single crystals. The huge increase in sample scattering volume means that extremely weak peaks can be observed. This allows us to study very weak charge ordering. Measurements of the intensity, width and position of the charge ordering satellites as a function of temperature provide us with quantitative measures of the charge amplitude, inverse correlation length and wavevector of the charge ordering.

Some GaAs reflections (002 and 006 for instance) are very weak due to the small difference in scattering factors between gallium and arsenic. The integral intensity of these reflections is very sensitive to the composition and hardly sensitive to the large crystal lattice defects like dislocations. The use of these `very weak' reflections is the basis of a method that compares the integrated intensities for the investigated crystal with the reference, quasi-ideal crystal. Experimental data obtained with this method is compared with theoretical models of lattice point defects and local distortions. The main goal of this investigation was to find how the Be atoms are incorporated into the Be doped GaAs layers lattice, and to study the local microscopic structures around them. We can conclude that Be atoms substitute Ga in the lattice and there are also some lattice distortions in the first and second nearest neighbour shells.

Structural study of CdSe/BeTe superlattices (SLs) grown by molecular beam epitaxy on GaAs substrate was performed by using double and triple crystal x-ray diffractometry. The period of the studied structures was about 5 nm, while the thickness of thin CdSe insertions varied from 0.4 to 1.5 monolayer. It is shown that new Be–Se bonds arise at the BeTe–CdSe interfaces in addition to the Be–Se bonds expected at the CdSe–BeTe interfaces. From the analysis of the diffraction curves of 002-reflection the complex composition of interfaces and thin insertions has been determined and contribution of all types of bonds in each SL period calculated. The diffraction curves of 004-reflection were used for the specification of the fine structure of the interfaces.

The paper examines the kinetics of the electric field induced, first-order transition from the commensurate to the ferro-electric phase in thiourea (SC(NH₂)₂) at 170 K. The satellite reflection from the modulated phase, locked in with a wave vector q = 1/9b* disappears when the phase transition is induced by a static electric field E_c along the a-axis. In order to study the kinetics of the phase transition, an oscillating electric voltage of rectangular shape was applied to the sample and photon events were acquired separately for ON- and OFF-field half-periods. Results received in a series of measurements at different amplitudes between 0 and 500 V and frequencies between 0.125 and 512 Hz lead to the conclusion that a slow and a fast relaxation time play a role for the OFF → ON and the ON → OFF transitions, respectively. Further, the highest frequency at which the phase transformation still follows the switching of the electric field depends linearly on the applied field amplitude. A qualitative explanation of the experimental results is given in terms of nucleation and growth of specific ferro-electric domains.

The structural changes that accommodate wafer splitting after hydrogen implantation of silicon and the transfer of split layers to a handle substrate were investigated using triple axis x-ray diffraction, to monitor the strain in the implanted layer, and atomic force microscopy. Silicon substrates (004) were implanted with a hydrogen dose that ranged from 5×10¹⁵ cm⁻² to 8×10¹⁶ cm⁻² and energies of either 30 kV or 140 kV. The changes in the implanted layer properties were investigated after annealing at 150–300°C for short times. For annealing temperatures up to 150°C, the strain-induced implant profile did not change appreciably nor did the surface roughness increase, indicating that, for these implant conditions, the implant is stable. Annealing at 200°C or higher for 10 min or more led to increased surface roughness and a change to the implant profile, although blister formation did not occur. Higher surface roughness is not conducive to successful wafer bonding, so these measurements helped to determine the annealing sequence that is appropriate for bonding. In this case, hydrophobic bonded wafers were successfully fabricated with the transferred layer showing similar structural properties as a thin epitaxial film of the same thickness. The use of x-ray scattering for this technique can be easily transferred to other materials for which other techniques, such as infrared absorption, have not been developed.

Reciprocal space mapping in non-coplanar diffraction geometry using a triple-crystal diffractometer is applied to study strained In_0.2Ga_0.8As/GaAs multilayer. The modelling accounts for the measured integrated intensities of the satellites in the simulation of the reciprocal space map to provide compositional profile of In distribution in the nucleated islands on the interfaces. Theoretical approach to calculate the intensity in this unconventional geometry is discussed.

Thin uncoalesced gallium nitride (GaN) layers grown on Si(111) by maskless cantilever epitaxy (CE) have been investigated using high resolution x-ray diffraction at variable temperatures. The crystallographic tilt of the free-hanging wings relative to the stripe regions of the samples was determined for different temperatures. With increased temperature the wing tilt decreased non-linearly and seemed to approach a constant value at higher temperatures. The wing tilts of two samples differing at room temperature by one order of magnitude were found to vary by less than 20% between 300 and 1020 K. This suggests that the main part of the crystallographic wing tilt is not thermally induced for samples grown with the CE technique.

We investigated by using high resolution x-ray diffraction and glancing incidence x-ray reflectivity In_xGa_1−xN/GaN and Al_xGa_1−xN/GaN multiple quantum wells (MQWs) grown by plasma-assisted molecular beam epitaxy on (0001) 6H–SiC substrates covered by a GaN buffer layer. In particular, the macrostrain field is investigated by using a theoretical approach based on the exact calculation of the incidence parameter and an arbitrary strain field and it is directly assessed by measuring the angular separation between the heterostructure and substrate Bragg peaks for several reflections and diffraction geometries. The experimental results reveal non-zero off-diagonal strain components for all the investigated samples, indicating a triclinic deformation of the buffer and the superlattices unit cells. Moreover, we found a coherent interface between the buffer and the Al_xGa_1−xN/GaN MQW, and a partial relaxation between the GaN buffer and the In_xGa_1−xN/GaN MQWs. The chemical composition of the ternary alloys has been determined from the strain components by assuming Vegard's law and applying the equilibrium conditions of the elasticity theory. We found a pronounced In-segregation if the MQW was grown under metal-stable flux conditions; in contrast no appreciable segregation effect was observed under nitrogen-stable flux condition. A cumulative interface roughness was found for the samples grown on nitrogen-stable flux condition, exhibiting a strong increase of the rms interface roughness towards the MQW surface.

The relaxation of Si-doped In_0.04Ga_0.96As epitaxial layers on (001) GaAs has been studied by in situ high-resolution x-ray diffraction during molecular beam epitaxy growth. By use of a novel technique to measure the wafer curvature with very high sensitivity, we have identified three regions in the relaxation process as a function of epilayer thickness. For thickness below that for multiplication of the slow A(g) misfit dislocations, the behaviour is effectively elastic, there being no detectable change in curvature at the critical thickness for dislocation nucleation. Beyond the thickness at which the A(g) dislocations multiply there is total or substantial relaxation, with very little increase in elastic strain as a function of thickness in this region corresponding to stage 1 of work-hardening in cubic materials. At much greater thickness, corresponding to stage 2 of bulk work-hardening, only partial relaxation occurs as the lattice hardens to the creation of misfit dislocations. Substantial elastic strain is observed to be locked into highly mismatched epilayers many times thicker than the critical thickness.

An x-ray study which reveals diffraction peaks from an additional polycrystalline phase in a single crystal matrix, is reported. The recording of these lines was possible due to the lowering of the diffractometer background through the use of a bent monochromator and Soller slits, as well as by rotating the single crystal sample out of Bragg condition. As an example of the use of the proposed experimental strategy, the results for the silicon single crystal, in which an additional phase in the form of silicon polycrystalline grains was created by ion implantation process, are presented.

The non-conventional technique of high-energy x-ray reflectivity is used to investigate buried Si|Si interface obtained by hydrophobic wafer bonding. In this experiment the well-collimated beam is transmitted through the sample and is reflected by the bonding interface described by its density and width. Transmission x-ray reflectivity curves are fitted using this two-parameter model with a Gaussian or exponential profile to analyse the evolution of the bonding interface as a function of temperature from 250°C to 1100°C.

Grazing incidence specular and diffuse x-ray scattering have been used to measure the thickness and roughness of indium tin oxide thin films deposited on glass. The techniques have been used to calibrate the etching rate, determine the variation of the top surface roughness changes with etching time and measure non-destructively the period and atomic-scale roughness of 400 nm period gratings produced by etching after laser interferometric patterning of a photoresistive layer. The propagation of the roughness through the polymer light emitting layer has also been examined.

The conventional x-ray standing wave (XSW) technique [1, 2] is a phase sensitive and element specific Fourier technique, which is commonly used to analyse single crystals on the millimetre to centimetre scale. Here, we present an advanced microprobe technique based on the XSW method demonstrating that structural analysis can be achieved with chemical sensitivity on a microscopic scale. We apply the XSW microscopy technique to study the crystallographic polarity from inversion domains in GaN-based lateral polarity heterostructures. We focus the x-ray beam by a refractive lens [3] into a micrometre slice and generate the XSW field by Bragg-reflection from the (0002) diffraction planes recording the GaK_α fluorescence as a function of the incidence angle. In this first demonstration of microscopic polarity determination with x-rays, we analyse the reversion of polarity across a inversion domain boundary with a spatial resolution of 1.5 μm. The new micro-XSW technique will permit microscopic examinations of the crystalline structure of modern semiconductor devices with chemical sensitivity and structural resolution on the picometre scale.

The diffuse x-ray scattering from a single buried layer of quantum dots has been observed and interpreted to estimate the composition and shape of the dots. The diffuse scattering is measured on a modified laboratory diffractometer in very high-resolution mode, using the in-plane scattering geometry. The resultant reciprocal space maps were interpreted based on the distorted Born wave approximation. In-plane scattering removes all the influences except those associated with lateral inhomogeneities, i.e. the strain fields of the dots. This sample was also analysed by transmission electron microscopy, to extract the shape and by energy dispersive x-ray analysis to determine the composition. Despite the very different averaging volumes of the two approaches the results are in general agreement and suggest that this x-ray scattering method for this extreme case (very weak scattering from a single layer of dots) gives a useful estimate of the composition and shape of these structures.

The strain distribution of a lateral nanostructure containing an InGaAs single quantum well (SQW) is studied by depth-resolved high-resolution x-ray grazing-incidence diffraction. The lateral strain variation is realized by patterning of an initially tensily strained InGaP stressor grown on top of the compressively strained SQW. The finite element method (FEM) is applied to the analysis of the strain distribution within the SQW induced by strain relaxation of the stressor layer. In particular, it is shown that the strain field reaches a maximum beneath the valleys and varies with the valley width. Based on the distorted wave Born approximation the experimental x-ray scattering curves were simulated using the displacements calculated by FEM as an input. We found a rather good agreement between simulation and experiment.

We have investigated the x-ray intensity distribution around 220 reciprocal lattice point in case of grazing incidence diffraction at SiGe nanoscale free-standing islands grown on Si(001) substrate by LPE. Experiments and computer simulations based on the distorted wave Born approximation utilizing the results of elasticity theory obtained by FEM modelling have been carried out. The data reveal fine structure in the distribution of scattered radiation with well-pronounced maxima and complicated fringe pattern. Explanation of the observed diffraction phenomena in their relation to structure and morphology of the island is given. An optimal island model including its shape, size and Ge spatial distribution was elaborated.

Grazing incidence x-ray scattering and cross-sectional high-resolution electron microscopy (HREM) have been applied to the study of thin trilayers of the miscible system Co–Cr–Co grown by ultra-high vacuum evaporation on silicon. Good agreement was found between numerical values for layer thickness deduced by the two techniques. The Co–Cr interface roughness was found to be low with substantial interdiffusion, significantly greater than the roughness amplitude. HREM images confirmed the diffuseness of the interfaces. The roughness had a lateral correlation length of typically 150 Å and a very low fractal parameter h of 0.15. The correlation length was always found to correspond to the lateral grain size observed in the HREM images.

X-ray scattering techniques were employed to study the processing and materials issues that are important for III–V semiconductor wafer bonding. To demonstrate the feasibility of creating wafer-bonded III–V on insulator structures, InP and GaAs wafers were bonded to GaAs wafers using silicon nitride (SiN) intermediate layers. A key process parameter is the SiN intermediate layer that is deposited by either sputtering or by plasma-enhanced chemical vapour deposition. We demonstrate that x-ray reflectivity is uniquely able to determine thin film density as well as surface roughness of the nitride; both of which are critical for successful bonding and layer transfer. The strain in the InP layer after transfer to a GaAs substrate was assessed using high resolution x-ray reciprocal space mapping. Annealing the bonded pairs at low temperatures (⩽300°C) produced a strong bond with no strain in the InP layer. After subsequent higher temperature (500°C) annealing, approximately 0.1% tensile strain appeared in the InP layer as well as a reduction in the crystalline quality. X-ray topography confirmed that this strain was accompanied by the introduction of dislocations. Topographic measurements of other samples also showed the presence of void-induced defects. X-ray scattering techniques proved to be very valuable in the evaluation of wafer-bonded structures.

The development of light-induced polymer surface relief gratings (SRGs) inscribed onto polymer films containing photosensitive moieties is probed in situ by x-ray and visible (VIS) light scattering techniques. Both methods are complementary due to the different momentum transfer probed. The SRG appears with nearly perfect sinusoidal shape and amplitudes and is accompanied by a density grating (DG) below the surface. The time development of grating peak intensities for continuous and pulse like exposure is interpreted in terms of a new approach of kinematic scattering theory. The simulations demonstrate the extraordinary sensitivity of x-ray reflectivity for very small grating amplitudes (h<5 nm), i.e. for the initial state of grating formation. VIS light scattering becomes sensitive if the grating amplitudes exceed about h = 10 nm. In particular, we find that the DG develops prior to SRG formation under actinic light.

Direct measurements of the mosaic twist in GaN films have been carried out using grazing incidence in-plane x-ray diffraction (GIIXD) on a commercially-available diffractometer in the laboratory. The GaN 11.0 in-plane diffraction was measured to obtain the twist mosaic directly, while the GaN 00.2 surface-symmetric rocking curve was used to measure the tilt mosaic. For GaN growth temperatures between 1002°C and 1062°C, the tilt mosaic decreased monotonically with increased temperature, while the twist mosaic showed a minimum at 1022°C, a temperature previously selected empirically as giving the best device yield and optimum optical domain size. A substantial fall in twist and tilt mosaic was observed on annealing of the nucleation layers, the lowest twist mosaic occurring at an annealing temperature of 1002°C, where it was almost equal to the tilt mosaic. A weak minimum in the tilt mosaic variation was seen at an annealing temperature of 1023°C.

Structural and chemical properties of self-assembled InAs islands grown on GaAs(001) were studied using x-ray scattering. Two measurements performed under grazing incidence geometry were correlated to obtain the three-dimensional strain and chemical status of InGaAs coherent islands. Grazing incidence diffraction was employed to reveal the in-plane strain-size interplay. Mapping out the reciprocal space near the GaAs(022) reflection and correlating the in-plane and out-of-plane strain information, we have been able to quantify the tetragonal distortion of the unit cells at any position inside the islands. Simple theory of elasticity of alloys enabled us to analyse the elastic deformation of the unit cells. Any variation in the expected tetragonal distortion of the unit cell was associated to the presence of Ga atoms inside the islands. Using this method, the Ga content in our islands was shown to vary linearly from 25% (island bottom) to 8% (island top).