Crystal defects in Seeded Chemical Vapour Transport (SCVT) and hydrothermal ZnO substrates were characterised mainly by X-ray topography and diffraction. Zn1−xMxO (M=Co, Mn) epilayers were grown on hydrothermal ZnO(00.1¯) substrate by Pulsed Laser Deposition (PLD). It is shown that the epitaxy strains are partially relaxed through dislocations in the {10.0} glide planes. The crystal perfection of the epilayers was analysed by high-resolution X-ray diffraction. Almost intrinsic rocking curves were observed for Zn1−xCoxO epilayers and the c-axis parameter increases proportionally with the Co content. This suggests that Co atoms are well located at substitutional sites in the ZnO matrix. A larger distortion of the ZnO matrix is induced by the insertion of Mn atoms. A paramagnetic behaviour was observed in Zn1−xCoxO epilayers with a low proportion of active Co atoms. A weak ferromagnetic behaviour was observed only for Zn1−xCoxO epilayers when a few Al atoms (1.6%) were incorporated.

X-ray standing waves (XSW) in a thin epitaxic film are treated in the framework of the dynamical theory. It is demonstrated that the fluorescence yield around the main peak of the rocking curve has essentially the same characteristics as that of the usual XSW on a bulk crystal surface. Thus, XSW provide a direct method to probe the atom position in a thin film. The method was applied to an epilayer of the diluted magnetic semiconductor Zn0.94Co0.06O, in order to determine the Co-atom position. The XSW established that Co atoms occupy the substitutional Zn site in the ZnO matrix, although their coherent fraction, which measures the degree of order, is rather low. Moreover, the measurement of the Zn fluorescence in the film gives approximately the same value for the coherent fraction of the Zn atoms. Besides, by using the substrate rocking curve, it is shown that the XSW signal of the Zn atoms in the substrate can be detected through the film. This interesting approach allows the coherent fraction of an element of a substrate below an interface to be probed in situ. For the Zn fluorescence, the coherent fraction is lower near the interface than in the bulk. These results should relate to strains and defects on both sides of the interface.

X-ray standing waves (XSW) in a thin epitaxic film are treated in the framework of the dynamical theory. It is demonstrated that the fluorescence yield around the main peak of the rocking curve has essentially the same characteristics as that of the usual XSW on a bulk crystal surface. Thus, XSW provide a direct method to probe the atom position in a thin film. The method was applied to an epilayer of the diluted magnetic semiconductor Zn0.94Co0.06O, in order to determine the Co-atom position. The XSW established that Co atoms occupy the substitutional Zn site in the ZnO matrix, although their coherent fraction, which measures the degree of order, is rather low. Moreover, the measurement of the Zn fluorescence in the film gives approximately the same value for the coherent fraction of the Zn atoms. Besides, by using the substrate rocking curve, it is shown that the XSW signal of the Zn atoms in the substrate can be detected through the film. This interesting approach allows the coherent fraction of an element of a substrate below an interface to be probed in situ. For the Zn fluorescence, the coherent fraction is lower near the interface than in the bulk. These results should relate to strains and defects on both sides of the interface.

The epitaxial growth of very thin GaSe films on H-Si(111), 7 x 7-Si(111), and root 3 x root 3 Ga-Si(111) has been investigated using the x-ray standing-wave technique. The interface structure was found to be identical whatever the Si(111) surface preparation used and consists of a GaSe half-layer. Ga atoms are covalently bonded with Si top atoms and are located in T sites. Beyond the interface, the growth proceeds layer by layer and not atomic plane by atomic plane. Moreover, the first complete layer above the interface is almost completely relaxed with respect to the Si substrate.

The epitaxial growth of the layered compound GaSe on three-dimensional materials (GaAs and Si) has already been achieved by several research groups and is often referred to as “Van der Waals epitaxy”. To check this assumption very thin films (approximately half a layer) of GaSe were grown, by molecular beam epitaxy, on HSi(111) substrates. The X-ray standing waves technique was used to determine the structure of the interface. The Ga atoms are located in T sites, straight above top Si atoms, with a SiGa bond length of 2.37 Å. The position of Se atoms was found to be in agreement with the one calculated from GaSe bulk structure. Therefore, and at least for HSi(111) substrates, the GaSeSi(111) heteroepitaxy is in fact a “classical” pseudomorphic epitaxy. Half a GaSe layer is firstly bonded to Si by covalent bonds and Van der Waals growth of GaSe layers occurs in a second stage.

Very thin GaSe films, about 100 Angstrom thick, have been epitaxially grown by molecular beam epitaxy on differently ordered Si(lll) substrates, namely: the clean 7 x 7 reconstructed surface with its dangling bonds, the H-passivated 1 x 1 surface and the Ga-passivated root 3 x root 3 R30 degrees reconstructed one. For each substrate, the GaSe layer and its interface with Si have been studied by low energy electron diffraction, Auger electron spectroscopy and photoemission yield spectroscopy. Upon sequential removal of the GaSe film by Joule heating in ultrahigh vacuum, it is shown that, (i) the band offsets are not sensitive to the initial surface structure of the substrate, (ii) the uniformity of the GaSe layer and of the Fermi level position is questionable on Si(111) root-Ga, (iii) the density of gap states in the GaSe layer increases upon ageing in air.

Thin films of the lamellar semiconductor GaSe, grown on different silicon surfaces SeSi(111), Si(111)-7 × 7, Ga√3 × √3 Si(111) and HSi(111) -have been investigated using transmission electron microscopy (TEM). Cross-sectional observations indicate a well-defined epitaxy: GaSe(001) ‖ Si(111) and GaSe[100] ‖ Si[11¯0]. The GaSe γ phase is often encountered in the films, but stacking faults occur in GaSe basal planes. Planar view images exhibit three moirépatterns at 120° involving Si22¯0* and GaSe110* type spots. The moiréfringe spacing (∼ 85Å) indicates a GaSe lattice relaxed with respect to the silicon one. A residual lattice extension of about 0.4% remains in the GaSe film in comparison with bulk GaSe and might be due to stacking faults. Electron diffraction in planar view setting revealed the existence of GaSe100* type spots forbidden for the γ phase. These spots are not related to the presence of β or ε phases, but to stacking faults. Based on all these observations, the GaSe/Si interface structure is discussed and a model of the earliest stage of the growth is proposed.

Iron silicide thin films (∈-FeSi, α-FeSi2 and β-FeSi2) were grown on silicon (111) substrates using the metalorganic vapour phase epitaxy (MOVPE) process with iron pentacarbonyl (Fe(CO)5) and disilane (Si2H6) precursors. Attention was mainly paid to the β-FeSi2 phase. Transmission electron microscopy (TEM) and X-ray diffraction measurements allowed optimization of the growth process and revealed the nature and structure of the layers grown on the silicon substrate. A growth model is discussed and the action of the thermal annealing, which leads to the coalescence of the dendrites to form a continuous film of β-FeSi2 up to about 1000 Å thick, is described. Finally a photoluminescence signal has been detected in the range of the expected direct band gap value of β-FeSi2.

Thin films of beta-FeSi2, grown on Si(111) by the technique of solid-phase epitaxy (SPE) in ultra-high vacuum (UHV) conditions, were analysed by transmission electron microscopy (TEM). The expected epitaxies, beta-FeSi2(101)/Si(111) and beta-FeSi2(110)/Si(111), were detected for film thicknesses smaller than approximately 250 angstrom. The present analysis reveals an unusual microstructure: the films are composed of very thin lamellae (5-30 angstrom) of both orientations induced by planar defects. Such lamellar films are strained, with a parameter shift estimated to be about 0.4%. For these films, grain sizes in the mum range were obtained and the interface roughness increased with increasing film thickness. An unexpected film orientation, beta-FeSi2(100)/Si(111), was also found.

The structure of an iron film, deposited at low temperature (50-degrees-C) upon a silicon (111) substrate, has been determined by means of X-ray Standing Wave experiments performed at LURE (Orsay, France). Experimental results are coherent with the model of an abrupt interface between the adsorbate and the surface: the first site of adsorption terminates the bulk silicon and a body-centred iron layer epitaxially grows on the substrate with a preferential growth orientation.

Microplanar defects were observed in β -iron disilicide by transmission electron microscopy. They were identified as (100)[011]/2 intrinsic stacking faults by means of electron diffraction patterns and observed in high-resolution lattice images. A structural model of the faults is proposed here in setting the defect position at x = ¼ within the cell.

Growth imperfections in (Ga1−xAlxAs)n1–(GaAs)n2/ GaAs superlattices, grown on GaAs(001) substrates, have been investigated by X-ray diffraction techniques coupling image and rocking-curve recording. The use of a synchrotron radiation source has enabled topographic images formed with very weak superlattice reflections to be obtained. The intensity distribution across the sample surface observed in such images has revealed two different types of superlattice defects: either overall gradients of both the average composition and period or islands showing different composition and period from the surrounding material. Since these parameters control the optoelectronic properties and particularly the gap value it is of primary importance to grow homogeneous samples and to have a technique able to detect inhomogeneities such as the ones described in the present work.

Single crystals of KDP and DKDP give a strong electro-optical effect at temperatures close to their Curie point. This property is the basis for the use of DKDP as a solid-state light modular for large-screen display devices. However, electrical conductivity hetegeneities in these crystals eventually impair the performances of the devices. The paper reports on a remarkable differentiation in electrical conductivity in polyhedral-shaped regions which result from the interaction of a dislocation line with the boundary between pyramid sectors. A close correlation is established between the lattice dilation and the electrical conductivity differentiation in these polyhedral regions as estimated by plane-wave X-ray topography and electroding decoration techniques. A phenomenological interpretation for both the genesis of the polyhedral and their physical properties is proposed.

The specific rotation of NaBrO 3 single crystals has been measured with an X-ray beam extracted from the white synchrotron radiation spectrum by a specially designed silicon monochromator–polarizer. A detailed description of the monochromator principle and expected performance is given and the characteristics of the output beam are as follows: extremely narrow angular and wavelength spread ( Δθ = 7 μrad, Δλ = 8 × 10 –6 Å), nearly pure linear polarization (polarization ratio 2.5 × 10 8 ). The wavelength has been chosen very close to the bromine K edge ( λ − λ K = 2 × 10 –3 Å) in order to take advantage of possible resonant effects. The experimental set-up is of the crossed-polarizer type, the analyzer being a GaAs crystal adjusted for the 555 reflection with a Bragg angle θ A equal to 44.95°. The specific rotation measured in these conditions has been found to be 0.35 ± 0.31° cm −1 . An explanation is proposed for this small value.

Nearly screw dislocations perpendicular to the crystal surfaces of KDP have been studied by the Lang X-ray topography technique in the case of reflections where the bulk strain tensor gives no contrast. Stress-relaxation deformations at the intersections with the crystal surfaces give images which have been studied in both reflected and refracted beams on section topography. The interpretation of the contrast is based on dynamical theory for slightly distorted crystals and leads to the determination of the sign of the Burgers vector. The formulation adopted here (after Malgrange 1975) leads to a convenient interpretation (both qualitative and semi-quantitative) of the contrast. In particular, the interpretation of the shape and size of the stress-relaxation-deformation images is a good example of what can be done on the basis of results of dynamical theory and without any computer calculation.

A computer program based on the Takagi-Taupin differential equations for X-ray propagation in distorted crystals has been developed in order to simulate dislocation images in the Bragg case. The program is valid both for thin and thick crystals. Simulated images of misfit dislocations formed either in a thin epilayer or in a thick substrate are compared with experimental images obtained by synchrotron-radiation plane-wave topography. The influence of the various strain components on the image features is discussed.