Residual stress relaxation in sputtered ZnO films has been studied in-situ by synchrotron x-ray diffraction. The films deposited on (001) Si substrates were thermally treated from 25°C to 700°C. X-ray diffraction 2D patterns were captured continuously during the heating, plateau and cooling ramps. The corrections carried out for compensating the furnace drift are discussed. We first observe an increase of the intrinsic compressive stresses before stress relaxation starts to operate around 370°C. Then, thermal contraction upon cooling dominates so that overall, the large initial compressive film stresses turn to tensile after thermal treatment. The overall behaviour is discussed in terms of structural changes induced by the heat treatment.

Ce travail concerne l'analyse microstructurale par diffraction des rayons X de couches epitaxiees d'oxydes. Dans cet objectif, nous avons mis en œuvre differentes techniques de diffraction des rayons X a la fois sur montage de laboratoire et au synchrotron. Un modele combinant a la fois une description microscopique des effets de forme et de taille des cristaux constituant les couches et une description phenomenologique des effets de distorsions de reseaux a ete developpe afin de rendre compte des effets dus aux defauts microstructuraux les plus couramment rencontres dans les couches epitaxiees. Deux systemes oxydes ont ete etudies. Le premier est le systeme a fort desaccord de reseau ZrO2/MgO dont l'analyse a montre l'existence de deux sous-reseaux de dislocations d'interface. Le premier, presentant une symetrie carree, est constitue de dislocations aleatoirement distribuees et se caracterise par une faible densite de dislocations. Le second responsable de l'accommodation des reseaux cristallins entre ZrO2 et MgO est constitue de dislocations periodiques dont la densite est elevee. Le second systeme etudie, SmNiO3/SrTiO3, se caracterise par un faible desaccord de reseau. L'analyse des cartographies de l'espace reciproque a permis de separer la relaxation des contraintes d'origine mecanique de celle d'origine chimique. Les mecanismes associes, la formation de dislocations d'interface et de lacunes d'oxygene ont ete mis en evidence par l'examen des profils transversaux d'intensite diffractee des couches et par le calcul de la valence du nickel. Finalement, une correlation entre la relaxation des contraintes et les proprietes de transport electronique des couches a clairement ete etablie.

Residual stresses in sputtered ZnO films on Si are determined and discussed. By means of X-ray diffraction, we show that as-deposited ZnO films are highly compressively stressed. Moreover, a transition of stress is observed as a function of the post-deposition annealing temperature. After an 800°C annealing, ZnO films are tensily stressed while ZnO films encapsulated by Si3N4 are stress-free. With the aid of in-situ X-ray diffraction under ambient and argon atmosphere, we argue that this thermally activated stress relaxation may be attributed to a variation of the stoichiometry of the ZnO films.

X-ray diffraction stress analyses have been performed on two different thin films deposited onto silicon substrate: ZnO and ZnO encapsulated into Si3N4 layers. We showed that both as-deposited ZnO films are in a high compressive stress state. In situ X-ray diffraction measurements inside a furnace revealed a relaxation of the as-grown stresses at temperatures which vary with the atmosphere in the furnace and change with Si3N4 encapsulation. The observations show that Si3N4 films lying on both sides of the ZnO film play an important role in the mechanisms responsible for the stress relaxation during heat treatment The different temperatures observed for relaxation in ambient and argon atmospheres suggest that the thermally activated stress relaxation may be attributed to a variation of the stoichiometry of the ZnO films. The present observations pave the way to fine tuning of the residual stresses through thermal treatment parameters. (C) 2010 Elsevier B.V. All rights reserved.

A simple least-squares fitting-based method is described for the determination of strain profiles in epitaxial films using high-resolution X-ray diffraction. The method is model-independent, i.e. it does not require any 'guess' model for the shape of the strain profile. The shape of the vertical displacement profile is modelled using the versatile cubic B-spline functions, which puts smoothness and curvature constraints on the fitting procedure. The effect of a coherently diffracting substrate is taken into account as well as the effects of film thickness fluctuations. The model is applied to the determination of strain profiles in SmNiO3 films epitaxically grown on SrTiO3(001) substrates. The shape of the retrieved strain profile is discussed in terms of oxygen vacancies.

Residual stresses in sputtered ZnO films on Si are investigated and discussed. By means of X-ray diffraction, we show that as-deposited ZnO films encapsulated or not by Si3N4 protective coatings are highly compressively stressed. Moreover, a transition of stress is observed as a function of the post-deposition annealing temperature. After a heat treatment at 800°C, ZnO films are tensily stressed while ZnO films encapsulated by Si3N4 are stress-free. With the aid of in-situ X-ray diffraction, we argue that this thermally-activated stress relaxation can be attributed to a variation of the chemical composition of the ZnO films.

The present work is devoted to explaining the role of epitaxial strain in the structure and the metal-insulator (MI) transition in SmNiO3 (SNO) films deposited on LaAlO3 (LAO) and SrTiO3 (STO) substrates. X-ray reciprocal space mapping and valence bond calculations allow us to show that in-plane compressive strain (for SNO/LAO) stabilizes Ni3+ in the orthorhombically distorted structure with the result that films exhibit a sharp MI transition at 120 degrees C, whereas in-plane tensile strain (for SNO/STO) stabilizes Ni2+, implying the creation of oxygen vacancies, which is accompanied by a 'flattening' of the resistivity curves together with a huge increase of the overall resistivity. As SNO films are deposited on STO, we demonstrate that strain relaxation acts like the temperature or the rare-earth size, increasing the Ni-O-Ni bond angles. Hence in-plane tensile strain shifts the MI transition towards high temperatures. The flattening of the resistivity curve observed for SNO/STO can be understood by taking into account the inhomogeneous strain distribution across the film thickness (strain gradient) while the increase in resistivity has been ascribed to the homogeneous part of the strain.

This article deals with strain relaxation in SmNiO3 epitaxial films deposited by chemical vapor deposition on SrTiO3 substrates. Thanks to x-ray reciprocal space mapping, we demonstrate that the strain relaxation is driven both “chemically” and “mechanically” by the formation of oxygen vacancies and misfit dislocations, respectively. Besides, a careful interpretation of the resistivity measurements allows us to highlight a correlation between the formation of oxygen vacancies, the stabilization of Ni3+, and the metal-insulator transition in the SmNiO3 films. Furthermore, using coplanar and grazing incidence diffraction, the shape of the strain gradient within the films is retrieved. This latter is calculated using a versatile scattering model involving B-spline functions. Finally, particular planar faults (Ruddlesden–Popper faults) that give rise to extended diffuse scattering on transverse scans are analyzed using a recent phenomenological model.

A novel non-destructive method to characterize stacking faults (SFs) in 3C-SiC crystals is presented. This method is based on fast X-ray diffraction reciprocal space mapping and can be used qualitatively for routine analysis of 3C-SiC as SFs give rise to a characteristic star-like pattern in reciprocal space whose intensity depends on the SF density. The simulation of the diffusely scattered intensity streaks with an appropriate model also enables one to obtain quantitative results such as SF densities, mosaic domain size and mosaicity. The model is tested with a commercial (001) 3C-SiC crystal from HAST corporation, and then it is used to analyze SFs in (111) 3C-SiC crystals grown by continuous feed-physical vapor transport.

Despite outstanding properties, the development of 3C-SiC electronics continues to suffer from the lack of good quality bulk 3C-SiC substrates. Up to now, there is no real seed and/or optimized growth processes. In this work, we address these two different issues. A two-step approach is shown, which couples the advantage of vapour–liquid–solid hetero-epitaxial growth of 3C-SiC on a 6H-SiC substrate for the seed formation and the ones of the continuous feed physical vapour transport method for the growth of the bulk material at reasonably high rate. Using such an approach, we could combine the elimination of the twin boundaries which systematically form in the 3C/6H-SiC epitaxial system, with getting a growth rate of about 0.2mm/h for the bulk material. An evaluation of results is done, with respect to the change in growth conditions.

The epitaxial stabilization of SmNiO3 (SNO) films grown by an injection MO-CVD process on ( 0 0 1) SrTiO3 (STO) substrates is discussed. By means of high-resolution x-ray diffraction, we show for the first time that SNO can be stabilized on STO with a minor amount of secondary phases and with a layer thickness reaching several hundreds of nanometres. It is argued that this stabilization is achieved because the lattice mismatch between these two perovskites is not as high as expected (1.8% instead of 2.8%). Moreover, the well-known dissociation of the SNO phase into NiO and Sm2O3 has been clearly correlated with the relaxation of epitaxial strain which is driven by the formation of misfit dislocations.

SmNiO3 thin films have been prepared by liquid injection Metal Organic Chemical Vapour Deposition on SrTiO3 (100) and LaAlO3 (100) single crystalline substrates. The influence of the film thickness on the epitaxial stabilisation has been studied for both substrates by X-ray diffraction and Atomic Force Microscopy (AFM). In the case of SmNiO3 on LaAlO3, the nickelate is obtained as a single phase up to a thickness of 200 nm; the surface remains smooth in agreement with the small lattice mismatch between film and substrate. In the case of the SrTiO3 substrate, SmNiO3 is never stabilised as single phase: NiO and Sm2O3 single oxides both appear beside the perovskite. We show that the strain state is driven by the choice of the substrate and the thickness of the film. Two different relaxation mechanisms of the film are evidenced depending on the substrate used. For LaAlO3, the good in-plane lattice match leads to a relaxation only in the growth direction. On the contrary, in the case of SrTiO3 which presents a strong lattice mismatch with the film, the out-of plane lattice parameter remains constant and constraints are relaxed through the chemical dissociation of SmNiO3 into single oxides.

Thick 3C‐SiC single crystals grown by continuous‐feed physical vapor transport (CF‐PVT) are studied by high‐resolution X‐ray reciprocal space mapping. These crystals contain Shockley‐type stacking faults (SFs) lying in the {111} planes, which give rise to diffuse intensity streaks along the 〈111〉 directions. An approach is presented that allows to determine, in combination with the simulation of transverse scans, the SF density from the simulation of the diffuse intensity streaks. SF densities as low as 0.4 × 103 cm–1 could be detected in high‐quality CF‐PVT grown crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We present here a detailed study describing the strain relaxation mechanisms occurring in the highly mismatched ZrO2/MgO system. Especially, we show using reciprocal space mapping that the ZrO, islands epitaxially grown on the MgO substrate are fully relaxed implying the formation of misfit dislocations at the interface. Furthermore, an analysis of transverse scans performed through symmetrical ZrO, reflections for several azimuthal positions of the sample lets us conclude that dislocations form a square network parallel to ZrO2, cell axes. Finally, an accurate analysis of the diffraction data evidences the existence of two subsets of misfit dislocations.

The structural stabilization of SmNiO3 (SNO) films epitaxially grown by an injection MO-CVD process on (001) SrTiO3 (STO) substrates is investigated. Using high-resolution X-ray diffraction (XRD), we show that SNO can be stabilized on STO with a minor amount of secondary phases and with a layer thickness reaching several hundreds of nanometers. The film quality is discussed by means of the simulation of X-ray reflectivity and XRD profiles that evidence smooth surfaces and interfaces. The actual lattice parameter of bulk (i.e. strain free) SNO is calculated as a function of the deposited thickness. It turns out firstly that the stabilization of SNO is achieved because the lattice mismatch between STO and SNO is not as high as expected (1.6% instead of 2.8%) and secondly the layer chemical composition varies with the film thickness. Finally, the well-known dissociation of the SNO phase into NiO and Sm2O3 is clearly correlated to the relaxation of epitaxial strain.

Stacking faults in thick (001)- and (111)-oriented 3C-SiC single crystals are studied by high resolution x-ray diffraction. The authors demonstrate that the analysis of the diffuse scattering intensity distribution can be used as a nondestructive means to accurately determine the densities of Shockley-type stacking faults. The diffuse scattering intensity is simulated with a scattering model based on a difference-equation description of faulting in fcc materials. It is shown that the (001) SiC crystals exhibit an anisotropic fault distribution, whereas the (111) SiC crystals exhibit an isotropic fault distribution, in excellent quantitative agreement with transmission electron microscopy observations.

The investigation of nanostructured oxide thin films using high-resolution X-ray diffraction (XRD) is considered. Because of the small amount of matter deposited and significant defect densities, such oxide thin film structures can be considered as imperfect materials that require specific data acquisition and data analysis methods. Fast reciprocal space mapping is carried out using a diffractometer based on an 18kW X-ray source, a four-reflection monochromator and a curved position sensitive detector. In order to extract quantitative information concerning the microstructure of the films, an approach is developed that combines a microscopic modelling of dimensional effects (crystallite or island shape, size and size distribution) with a phenomenological description of lattice disorder. Within this approach, simple analytical expressions or expressions implying a simple Fourier transform, can be derived for the XRD intensity distribution in the direction perpendicular to the film surface and parallel to it. Profiles exhibiting damped and/or broadened fringes and profiles exhibiting a two-component line shape can be simulated. Parameters of primary interest, such as the island thickness, thickness distribution function, island in-plane dimensions and the distribution function of the dimensions, the level of disorder, the disorder correlation length and the spatial distribution of disorder, can be extracted. The applicability of the model is illustrated with yttria stabilized zirconia films epitaxially grown on sapphire by sol–gel dip-coating.

A development is presented that allows the simulation of reciprocal-space maps (RSMs) of epitaxic thin films exhibiting fluctuations in the size and shape of the crystalline domains over which diffraction is coherent (crystallites). Three different crystallite shapes are studied, namely parallelepipeds, trigonal prisms and hexagonal prisms. For each shape, two cases are considered. Firstly, the overall size is allowed to vary but with a fixed thickness/width ratio. Secondly, the thickness and width are allowed to vary independently. The calculations are performed assuming three different size probability density functions: the normal distribution, the lognormal distribution and a general histogram distribution. In all cases considered, the computation of the RSM only requires a two-dimensional Fourier integral and the integrand has a simple analytical expression, i.e. there is no significant increase in computing times by taking size and shape fluctuations into account. The approach presented is compatible with most lattice disorder models (dislocations, inclusions, mosaicity, ...) and allows a straightforward account of the instrumental resolution. The applicability of the model is illustrated with the case of an yttria-stabilized zirconia film grown on sapphire.