[en] This work illustrates the potential of Dark-Field X-ray microscopy (DFXM), a three dimensional imaging technique of nanostructures, in characterizing novel epitaxial structures of gallium nitride (GaN) on top of GaN/AlN/Si/SiO₂ nanopillars for optoelectronic applications. The nano-pillars are intended to allow independent GaN nanostructures to coalesce into a highly-oriented film due to the SiO₂ layer becoming soft at GaN growth temperature. Dark-Field X-ray microscopy is demonstrated on different types of samples at the nano scale and the results show that extremely well oriented lines of GaN (standard deviation of 0.04 degrees) as well as highly oriented material for zones up to 10 x 10 nm² in area are achieved with this growth approach. At a macro scale, high intensity X-ray diffraction as used to show that the coalescence of GaN pyramids causes disorientation of the silicon in the nano-pillars, implying that the growth occurs as intended (i.e. that pillars rotate during coalescence). Our model for coalescence of GaN pyramids on nano-pillars suggested that the SiO₂ layers in the nano-pillars would become soft at GaN growth temperature, and allow the GaN pyramids to auto-orient themselves, thus reducing dislocations. Our observations using high intensity X-ray diffraction show that during coalescence, the silicon layers in the nano-pillars become significantly less well oriented, suggesting that the auto-orientation of the GaN pyramids is disaligning the silicon layers. These two diffraction methods demonstrate the enormous promise of this growth approach for micro-displays and micro-LEDs, which require small islands of high quality GaN material and offer a new way to enlarge the fundamental understanding of optoelectronic relevant materials at the highest spatial resolution

[en] After a keynote address on climate history, and presentations of rewarded thesis on various topics (imogolite nano-tubes, phage recognition, 1D polymer materials with spin transition), the contributions and posters are grouped in thematic sessions which addressed the following issues: Instrumentation in laboratory and on synchrotron sources; Solid chemistry and material chemistry; Microstructure, texture and stresses; In situ studies; Natural complex systems; Small angle scattering; Nano-structures, microelectronics and optronics; Heritage materials; Tomography; Composition analysis, speciation, fluorescence and spectroscopy

[en] X-ray diffraction was recognized from the early days as highly sensitive to atomic displacements. Indeed structural crystallography has been very successful in locating with great precision the position of atoms within an individual unit cell. In disordered systems, it is the average structure and fluctuations about it that may be determined. In the field of mechanics, diffraction may thus be used to evaluate elastic displacement fields. In this short overview, we give examples from recent work where X-ray diffraction has been used to investigate average strains in lines, films or multilayers. In small objects, the proximity of surfaces or interfaces may create very inhomogeneous displacement fields. X-ray scattering is again one of the best methods to determine such distributions. The need to characterize displacement fields in nano-structures together with the advent of third generation synchrotron radiation sources has generated new and powerful methods (anomalous diffraction, coherent diffraction, micro-diffraction, etc.). We review some of the recent and promising results in the field of strain measurements in small dimensions via X-ray diffraction

[en] To fabricate and qualify nanodevices, characterization tools must be developed to provide a large panel of information over spatial scales spanning from the millimeter down to the nanometer. Synchrotron x-ray-based tomography techniques are getting increasing interest since they can provide fully three-dimensional (3D) images of morphology, elemental distribution, and crystallinity of a sample. Here we show that by combining suitable scanning schemes together with high brilliance x-ray nanobeams, such multispectral 3D volumes can be obtained during a single analysis in a very efficient and nondestructive way. We also show that, unlike other techniques, hard x-ray nanotomography allows reconstructing the elemental distribution over a wide range of atomic number and offers truly depth resolution capabilities. The sensitivity, 3D resolution, and complementarity of our approach make hard x-ray nanotomography an essential characterization tool for a large panel of scientific domains.

[en] Ultrathin compressively strained SiGe layers is one of the most promising materials for high mobility channels of p-type metal oxide semiconductor field effect transistors (pMOSFETs). Fabrication of such layers by SiGe thermal oxidation processes need to be well controlled, which then require well-controlled oxidation kinetics and oxide properties for use in an industrial environment. In the present paper, we address oxidation kinetics of Si, Si_0.9Ge_0.1 and Si_0.7Ge_0.3 by means of dry furnace oxidation and dry rapid thermal oxidation (RTO). We showed in a previous paper that oxidation of SiGe by means of either dry furnace oxidation or dry RTO is limited by diffusion of the oxidizing species through the growing oxide and that the oxidation rate of SiGe is significantly higher than the one of Si. In the present paper we focus on the influence of the oxide density measured by Soft x-ray Reflectivity on oxidation kinetics. It is shown that the lower the density of the oxide is, the higher the oxidation rate is, in agreement with an oxidation regime that is governed by diffusion of O₂ through the growing oxide. Finally, we propose a model of O₂ diffusivity that depends on the oxide density through the modulation of the diffusion barrier. The modulation of the diffusion barrier is found to be linearly dependent on the oxide density. (paper)

[en] In sample-scanning Laue micro diffraction, the local crystal orientation and local deviatoric strain tensor are obtained by illuminating the polycrystalline sample with a broadband 'white' (5-30 keV) X-ray microbeam and analyzing the spot positions in the resulting local Laue pattern. Mapping local hydrostatic strain is usually slower, owing to the need to alternate between white and tunable-energy monochromatic microbeams. A technique has been developed to measure hydrostatic strain while keeping the white beam. The energy of one of the Laue spots of the grain of interest is measured using an energy-dispersive point detector, while simultaneously recording the Laue pattern on the two-dimensional detector. The experimental spot energy, E(exp), is therefore measured at the same time as Etheor, the theoretical spot energy for zero hydrostatic strain, which is derived from the analysis of the Laue pattern. The performance of the technique was compared with that of the monochromatic beam technique in two test cases: a Ge single crystal and a micrometre-sized UO₂ grain in a polycrystal. Accuracies on the hydrostatic strain Δa/a of ±0.4*10^-4 and ±1.3*10^--4 were obtained for Ge and UO₂, respectively. Measurement strategies to limit the remaining uncertainties on Etheor are discussed. (authors)

[en] We propose a new approach to follow stress development during solid state reaction between a Ni thin film and Si (0 0 1). Substrate curvature measurements were performed simultaneously with X-ray diffraction at LURE synchrotron radiation facility. The measured curvature yields the average force whereas X-ray diffraction yields the different phases that form as well as the strain variation undergone by these phases. During annealing with a constant heating rate of 2 deg. C/min, Ni grain growth is first observed, followed by the formation of Ni₂Si, Ni₃Si₂ and then NiSi. The Ni₂Si formation is correlated with a rapid increase in compressive force. At the end of Ni consumption, the force evolves in tension until NiSi formation, which is accompanied by an additional increase in compressive force and then a final force relaxation at higher temperature. It is interesting to note that the NiSi phase appears at the expense of Ni₃Si₂, and surprisingly, at the benefit of Ni₂Si until the Ni₃Si₂ is completely consumed. Strain buildup during Ni₂Si and Ni₃Si₂ formation exhibit clear differences. Both Ni₃Si₂ and Ni₂Si phases exhibit a bell shape behavior of the strain evolution versus temperature at variance with predictions from the Zhang and d'Heurle model [Thin Solid Films. 213, 1992, 34]

[en] Here, white X-ray μ-beam Laue diffraction is developed and applied to investigate elastic strain distributions in three-dimensional (3D) materials, more specifically, for the study of strain in Cu 10 μm diameter–80 μm deep through-silicon vias (TSVs). Two different approaches have been applied: (i) two-dimensional μ-Laue scanning and (ii) μ-beam Laue tomography. 2D μ-Laue scans provided the maps of the deviatoric strain tensor integrated along the via length over an array of TSVs in a 100 μm thick sample prepared by Focused Ion Beam. The μ-beam Laue tomography analysis enabled to obtain the 3D grain and elemental distribution of both Cu and Si. The position, size (about 3 μm), shape, and orientation of Cu grains were obtained. Radial profiles of the equivalent deviatoric strain around the TSVs have been derived through both approaches. The results from both methods are compared and discussed.

[en] Reactive diffusion in the Ni/Si system has been studied by annealing nickel thin films deposited on a (1 0 0)silicon crystal. A curvature measurement technique was used to study the stress build up during nickel silicidation. The first silicide to grow is Ni₂Si. Its occurrence creates compressive stresses, which relax according to time and temperature of annealing. A new model which takes into account relaxation activated by temperature and thermal expansion of layers during growth is proposed. This approach introduces the material parameters for the viscoplastic constitutive equation and phase change characteristics like activation energy for Ni₂Si growth and Ni grain growth. The agreement between experiment and numerical simulation is rather good

[en] The germanium fraction dependence of the Solid Phase Epitaxial Regrowth (SPER) rate in SiGe alloys has been investigated using a lattice kinetic Monte Carlo (LKMC) approach. Experiments show that the SPER rate is monotonically increasing with the addition of germanium. However, the extracted activation energy exhibits a non-linear evolution with the increase of germanium content. To investigate the influence of germanium in SiGe alloys, a comprehensive atomistic model is presented. The model focuses on the chemical bond types between the amorphous and the crystalline phases. As several recrystallization configurations exist at the amorphous–crystalline interface, a competition between them arises during SPER. This competition, implemented into a LKMC simulator, is able to reproduce several phenomena observed during SPER experiments on SiGe alloys: the monotonically increasing SPER rate and the non linear activation energy behavior regarding the germanium content as well as the temperature dependence on the extracted activation energy. The presented model is in close agreement with experimental data from literature.