As-deposited and unencapsulated GeTe1-xSex (x = 0, 0.5) 3-μm-thick amorphous films on Si(001) were obtained via the thermal co-evaporation technique. The crystallization and the structure of these phase change materials were examined using in situ temperature-dependent X-ray diffraction (XRD) and grazing-incidence fluorescence X-ray Absorption Near Edge Structure (XANES) in isochronal annealing conditions under nitrogen flow. The results show that the onset temperature of crystallization is highly sensitive to the substitution of the Te atoms by the Se ones and that the rhombohedral structure, with the space group R3m, is the one that crystallized for both samples without Ge or Te rejection. Moreover, the local order around the Ge and Se atoms, probed by Ge and Se K-edge XANES analyses, presents clear modifications from the amorphous state to the crystalline one expecting a Ge four-fold and a Se two-fold coordination in the amorphous state, with an increase of the local disorder with the Se substitution (x = 0.5).

In the context of the heat treatment optimisation of steels used for nuclear reactor pressure vessel, the carbide precipitations in three model alloys: Fe-0.2 %C-1 %Mn, Fe-0.2 %C-1.5 %Mo and Fe-0.2 %C-1 %Mn-1.5 %Mo have been experimentally investigated and modelled. The precipitation sequences for times up to 2 months at 650 and 700 degrees C have been determined Fe-0.2 C-1.5Mn: cementite only Fe-0.2 C-1 Mo: cementite -> cementite + M2C -> M2C + xi carbide Fe-0.2 C-1 Mo-1.5 Mn: cementite -> cementite + M2C + xi carbide The volume fractions in carbide were determined by Rietveld refinement of synchrotron X-ray diffractograms. This characterisation has confirmed the tendency for cementite dissolution in favour of other Mo rich carbides in Mo containing alloys. Similarly, PRISMA modelling of the carbide volume fractions predicts a tendency for cementite dissolution in Mo containing alloys. It has also enabled the relative contribution of some of the factors affecting xi carbide precipitation to be understood.

Crystallization in unencapsulated GeTe(0.2)6Se(0.74) amorphous 3 mu m-thick films produced by thermal co-evaporation technique was studied by in situ temperature-dependent synchrotron powder X-ray diffraction from room temperature up to 418 degrees C and back to 30 degrees C. The experimental results obtained with a continuous heating rate of 2 degrees C/min under a protective nitrogen atmosphere showed that the crystallization process took place in several steps i) total crystallization of the amorphous phase to an intermediate crystallized phase, (ii) total transformation of the intermediate phase to a second crystallized phase. The intermediate phase corresponds to a solid solution with a metastable alpha-GeTe-like rhombohedral polar structure (R3m) presenting a uniaxial negative thermal ex-pansion along the c-axis. The onset of crystallization to the polar structure is around 270 degrees C. The high-temperature phase has a stable hexagonal structure with a P6(3)mc space group. When cooling, until back to room temperature, the hexagonal structure is conserved. The effect of a changing heating rate from 2 degrees to 0.1 degrees C/min was also investigated. In this context, the crystallization scheme is modified. (c) 2023 Elsevier B.V. All rights reserved.

Ge-rich and N-doped Ge-Sb-Te thin films and patterned structures for memory applications are investigated in situ during annealing up to 500 degrees C with a heating rate of 2 degrees C/min using synchrotron x-ray diffraction. The initial material is amorphous. Under these annealing conditions, Ge crystallization occurs at 340 degrees C and precedes the one of cubic Ge2Sb2Te5 by about 15 degrees C. In situ monitoring of diffraction allows for a quantification of crystallized quantity, grain size and elastic strain during the material transformation. Increasing N doping reduces the amount of crystallized Ge and Ge grain size. These results bring important insights into the multiphase crystallization of Ge-rich GST phase change materials for memory applications.

Thin film architectures with brittle and ductile material layers are often combined for functionality. Easy to fracture brittle films are often necessary due to their function as diffusion barriers, adhesion or protective layers. Especially in the field of flexible and wearable electronics brittle materials may cause short lifetimes. Direct current magnetron sputtered bilayers on a polyimide substrate containing brittle Mo and ductile Al layers (Al/Mo/PI and Mo/Al/PI) as well as Al films (Al/PI) were subjected to equi-biaxial loading with in-situ X-ray diffraction measurements. The setup enabled the extraction of the stress and full width at half-maximum as a function of the strain. The data yields deeper insights into underlying deformation and fracture mechanisms and the significance of the layer arrangement. It will be demonstrated that for stretchable applications the position of the Mo layer affects the fracture strain of the bilayers and the individual layers.

fast and reliable data storage is and Computing being is the global next-generation data an annual of non-volatile data their properties, p hase change materials (PCMs) can the PCMs can be reversibly switched between an amorphous and a crystalline phase through controlled (local) heating, e,g, by lasers or by an electrical current PCMs the to Phase Change Random Access Memories (PCRAM), very alternative to replace flash technology In this contribution investigations on the PCM GST-theta a Ge-rich material within the Ge-Sb-Te ternary system GST-theta crystallization temperatures above 350°C , is in automotive applications In a previous study on 50 nm thick of GST-theta we that the

Many mechanical systems are submitted to stresses repeated for a very large number of cycles during their lifespan and can break under stress amplitudes lower than their ultimate tensile stress (fatigue of materials).Materials fatigue design is thus crucial in engineering and requires the accurate characterization of mechanical behavior of materials under cyclic stress to ensure the safety and reliability of the structures throughout their life service.Mechanical properties in crystalline materials depends on their microstructure, e.g.density of dislocations present.Several techniques, including transmission electron microscopy (TEM), synchrotron x-ray diffraction and neutron diffraction techniques, and electron backscattered diffraction (EBSD), were used to evaluate the dislocation density in plastically deformed materials.However, all these techniques are affected from several limitations in distinguishing the influences of domain size and dislocation density.During the last two decades, Groma et al. developed a new method, the so-called variance method, for the evaluation of the dislocation density and its fluctuation in plastically deformed specimens with the only limitation of the coherent domain size that should be larger than 1m.This method is based on the asymptotic behavior of the secondand fourth-order restricted moment in the tail portion of the x-ray diffraction peak.The present research aims to use the variance method for estimating dislocation density when a very large number (~10 9 ) cyclic loadings is applied on the single crystal with an applied stress significantly lower than the yield stress so that deformation is almost entirely elastic.The monocrystalline copper specimen was loaded using a 20 kHz ultrasonic fatigue machine mounted on the sixcircle diffractometer available at the DiffAbs beamline on the SOLEIL synchrotron facility (France).Since we are interested to investigate the very high cycle fatigue domain, the amplitudes of the cyclic stresses range from 7 to 91 MPa.The diffraction patterns were acquired with a 2D hybrid pixel X-ray detector (XPAD S140) which integration time has been synchronized with the fatigue rig.The diffraction data are evaluated by the restricted moments method of the tail portions of individual Bragg peaks, for estimating the microstructure evolution in terms of dislocation density and spatial distribution of the dislocations.The results of these experimental data will be presented and discussed.

Nanometric laminar two-dimensional artificial multiferroic oxide thin films can be elaborated using spinel ferrites and perovskite ferroelectrics like CoFe2O4 and BaTiO3. Such materials can retain their individual ferromagnetic or ferroelectric properties. In the thin epitaxial film regime a cross coupling of these properties is possible thanks to strain engineering. After introducing the concepts supporting artificial multiferroic laminar structures, the growth of strained BaTiO3 thin films and the growth of subsequent Co-ferrites layers will be detailed. With respect to the relative film thickness, a detailed understanding of the elastic behavior of these films will be proposed based on the characterization using several synchrotron radiation techniques including x-ray specular and off-specular diffraction, x-ray absorption spectroscopy, as well as x-ray magnetic circular dichroism.

Piezo-electric ultrasonic fatigue machines are used to carry out fatigue tests more rapidly than what is possible using other technologies, at a frequency of 20kHz. The very high cycle fatigue (VHCF) domain can be studied with these machines as 109 cycles are reached within 14 h when specimens are loaded at stress amplitudes below the yield stress or conventional fatigue strength. The estimation of stress in specimens fatigued at high frequency is a current challenge when adopting this technology. This paper discusses the accuracy and reliability of three methods used to estimate stress amplitudes in specimens subjected to VHCF tests at a high loading frequency. Two historically used methods using strain gauges and a laser vibrometer are discussed and compared with a third, recently developed method based on time-resolved in situ X-ray diffraction (XRD). The three methods are applied to estimate the stress amplitude in a pearlitic steel specimen. The experimental artifacts and uncertainties are evaluated quantitatively to compare the benefits and limits of the methods. The experimental results show that the three methods correctly estimate the stress amplitudes applied to fatigued specimens.

We report on the growth of thin NiSi films via the thermal reaction of Ni layers (13-35 nm) with Si(100) substrates modified by ion implantation. By introducing substrate damage or nitrogen impurities prior to the solid-phase reaction, several properties of the NiSi films can be modified: the formation temperature, texture, diffusion-limited growth rate and morphological stability. As some of the modifications to the NiSi films are rooted in the early silicide phases preceding the NiSi phase, particularly its formation temperature, special attention is devoted to the growth of the amorphous Ni-Si alloy and the crystalline delta-Ni2Si and -Ni2Si phases. We employed a number of experimental techniques, including in situ synchrotron x-ray diffraction (XRD), in situ Rutherford backscattering spectrometry (RBS), in situ sheet resistance measurements, ex situ ion beam channelling and ex situ pole figure measurements. We show that both the formation temperature of the NiSi films and the intensity of epitaxial and axiotaxial components of the NiSi texture can be either lowered or raised by selecting appropriate implantation conditions. Agglomeration of the NiSi films at high temperature (> 700 degrees C) can be slowed down, either by slowing down the mobility of the Ni and Si atoms, or by removing the morphologically destabilizing axiotaxial texture. Our results emphasize the strong interwoven nature of phase formation, texture and morphological degradation. We illustrate that the kinetics of the early stages of thin film reactions consist of more than just diffusion, i.e. nucleation can also play a crucial role.

Wide-bandgap nitride semiconductors are currently in development for high-power electronic applications. Compositional layered heterostructures of such nitrides result in a high polarization field at the interface, enabling a higher electron mobility, a higher power density, and a higher conversion efficiency. Further optimization of such GaN-based high-electron-mobility transistors can be achieved by evolving from a top AlxGa1−xN barrier toward AlN or even InyAl1−yN. An ongoing challenge in using such hexagonal nitride semiconductors is the formation of a low-resistive, Au-free, ohmic contact far below 1Ωmm. In this paper, we investigate the formation of ohmic contacts by Ti–Al–TiN-based metalization as a function of different annealing temperatures (up to 950°C), Ti–Al ratios (from 15 up to 35 at. %) and nitride barrier composition (AlxGa1−xN, GaN, AlN, and InyAl1−yN). Contacts processed on AlxGa1–x/GaN, and AlN/GaN heterostructures result in low contact resistance of, respectively, 0.30 and 0.55Ωmm, whereas the same contact stack on InyAl1−yN results in resistance values of 1.7Ωmm. The observed solid-phase reaction of such Ti–Al–TiN stacks were found to be identical for all investigated barrier compositions (e.g., AlxGa1−xN , GaN, AlN, and InyAl1−yN), including the preferential grain alignment to the epitaxial nitride layer. The best performing ohmic contacts are formed when the bottom Ti-layer is totally consumed and when an epitaxially-aligned metal layer is present, either epitaxial Al (for a contact which is relatively Al-rich and annealed to a temperature below 660°C) or ternary Ti2AlN (for a relatively Ti-rich contact annealed up to 850°C). The observation that the solid-phase reaction is identical on all investigated nitrides suggests that a further decrease of the contact resistance will be largely dependent on an optimization of the nitride barriers themselves.

The achievement of high growth rates in YBa 2 Cu 3 O 7 epitaxial high-temperature superconducting films has become strategic to enable high-throughput manufacturing of long length coated conductors for energy and large magnet applications. We report on a transient liquid assisted growth process capable of achieving ultrafast growth rates (100 nm s −1 ) and high critical current densities (5 MA cm −2 at 77 K). This is based on the kinetic preference of Ba-Cu-O to form transient liquids prior to crystalline thermodynamic equilibrium phases, and as such is a non-equilibrium approach. The transient liquid-assisted growth process is combined with chemical solution deposition, proposing a scalable method for superconducting tapes manufacturing. Additionally, using colloidal solutions, the growth process is extended towards fabrication of nanocomposite films for enhanced superconducting properties at high magnetic fields. Fast acquisition in situ synchrotron X-ray diffraction and high resolution scanning transmission electron microscopy (STEM) become crucial measurements in disentangling key aspects of the growth process.

The formation of GaN nanocrystals in SiO2/Si and SiNx/Si dielectric layers implanted with Ga + and N + ions, followed by annealing at 950 degrees C for 60-120 min in N-2, has been studied by high resolution transmission electron microscopy (HRTEM), synchrotron radiation X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) technique at the Ga K-edge, as well as by Rutherford Backscattering spectrometry (RBS), X-Ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS) and Scanning electron microscopy (SEM). The effect of the dielectric matrix, of the gas annealing environment (N-2) and of the annealing time at 950 degrees C have been inves-tigated. GaN nanocrystals implanted near the surface are observed in SiO2/Si only. The hexagonal wurtzite crystalline structure was confirmed by HRTEM, XRD and Raman spectroscopy. However, the synthesis process is multiphasic as elemental Ga-0 nanoparticles at larger depths and Ga2O3 rods (similar to 200-300 nm) on the surface were formed in addition to implanted h-GaN, as shown by TEM, XAFS, SEM, XPS and Raman spectroscopy. Moreover, Ga atoms are always remaining on some vacant Si sites in the SiO2 matrix. The local environment around Ga is quite different in the SiNx matrix, as seen by XAFS. This difference can be explained by the gallium and nitrogen diffusions which are much faster in the case of the SiO2 matrix, as shown by RBS profiles. Results are discussed in close comparison with existing literature.

We present an experimental and k⋅p theoretical study on the origin of the strong in-plane uniaxial magnetic anisotropy in (Ga,Mn)As layers, unexpected from the cubic crystalline structure. The symmetry lowering can be accounted for by structural or effective shear strains. We find theoretically out-of-plane and in-plane magnetic anisotropy constants being linear with the shear strain. Searching for a real shear strain arising from lattice relaxation, we perform two types of measurements: anomalous x-ray diffraction and strain-induced optical birefringence, at room temperature. Working on a strongly anisotropic (Ga,Mn)As layer, the estimated ϵxy=10−4 was not found although it lied an order of magnitude above the detection threshold. This ensemble of results indicates as unlikely a relaxation-driven uniaxial anisotropy. As previously suggested theoretically, the magnetic symmetry-lowering could instead originate from the anisotropic incorporation of Mn atoms during growth. This would yield a perfectly in-plane matched lattice, with an anisotropy that could nevertheless be modeled as an effective shear strain and modified by an external shear stress, in agreement with the existing experimental literature.

We propose a method for detecting a Guttman effect in a complete disjunctive table U with Q questions. Since such an investigation is a nonsense when the Q variables are independent, we reuse a previous unpublished work about the chi-squared independence test for Burt's tables. Then, we introduce a two-steps method consisting in plugging the first singular vector from a preliminary Correspondence Analysis (CA) of U as a score x into a subsequent singly-ordered Ordinal Correspondence Analysis (OCA) of U. OCA mainly consists in completing x by a sequence of orthogonal polynomials superseding the classical factors of CA. As a consequence, in presence of a pure Guttman effect, we should in principle have that the second singular vector coincide with the polynomial of degree 2, etc. The hybrid decomposition of the Pearson chi-squared statistics (resulting from OCA) used in association with permutation tests makes possible to reveal such relationships, i.e. the presence of a Guttman effect in the structure of U, and to determine its degree - with an accuracy depending on the signal to noise ratio. The proposed method is successively tested on artificial data (more or less noisy), a well-known benchmark, and synchrotron X-ray diffraction data of soil samples.

In situ synchrotron X-ray diffraction experiments were conducted to extract strain distributions in Ni-30W (wt%) alloy processed by Spark Plasma Sintering and loaded in tension. The alloy was designed for a strength-ductility tradeoff. It has a microstructure made of multi-crystalline W clusters embedded in Ni(W) solid solution matrix. Lattice strain analysis made it possible to separate the respective behavior of the two phases. Indeed, stress (590 MPa) and strain thresholds (2%) at which cracks initiate and propagate inside the W were detected. Further hardening observed between 2% and 10% is attributable to the Ni(W) solid solution. (C) 2018 Elsevier B.V. All rights reserved.

A new method based on time-resolved X-ray diffraction is proposed in order to measure the elastic strain and stress during ultrasonic fatigue loading experiments. Pure Cu was chosen as an example material for the experiments using a 20 kHz ultrasonic fatigue machine mounted on the six-circle diffractometer available at the DiffAbs beamline on the SOLEIL synchrotron facility in France. A two-dimensional hybrid pixel X-ray detector (XPAD3.2) was triggered by the strain gage signal in a synchronous data acquisition scheme (pump–probe-like). The method enables studying loading cycles with a period of 50 µs, achieving a temporal resolution of 1 µs. This allows a precise reconstruction of the diffraction patterns during the loading cycles. From the diffraction patterns, the position of the peaks, their shifts and their respective broadening can be deduced. The diffraction peak shift allows the elastic lattice strain to be estimated with a resolution of ∼10−5. Stress is calculated by the self-consistent scale-transition model through which the elastic response of the material is estimated. The amplitudes of the cyclic stresses range from 40 to 120 MPa and vary linearly with respect to the displacement applied by the ultrasonic machine. Moreover, the experimental results highlight an increase of the diffraction peak broadening with the number of applied cycles.

In this paper, in situ measurements of synchrotron x-ray pole figure have been performed during incremental uniaxial deformation test on a single-crystal gold foil. The 50 nm thick Au thin film was elaborated by ion sputtering at 400 degrees C on NaCl single crystal as a template. The resulting film consists of a single-crystal gold foil containing a small density of thin and small {111} growth twins (few nm thick and few tens of nm long) revealed by x-ray pole figure measurement. The as-deposited gold single crystal was then transferred onto flexible polyimide substrates for deformation test. This work focuses on the relative evolution of the diffracting volume related to growth twins during a loading-unloading tensile test. Macroscopic applied deformations and x-ray pole figures were measured in situ during a uniaxial tensile test in the Au [110] direction. X-ray pole figures clearly evidenced the relative evolution of the diffracting volumes related to the (111) and ((1) over bar(1) over bar1) twins which exhibit a huge increase of about 450% at a uniaxial applied true strain of about 4%. The concomitant variation of diffracting volumes related to the two other twin variants (namely ((1) over bar 11) and (1 (1) over bar1) twins) shows a relatively low decrease of 25%. The results open out onto a true strain-twinning volume hysteresis curve, indicative of the deformation mechanisms of gold thin films that can be interpreted as a twinning-detwinning mechanism.

The controlled formation of silicide materials is an ongoing challenge to facilitate the electrical contact of Si-based transistors. Due to the ongoing miniaturisation of the transistor, the silicide is trending to ever-thinner thickness's. The corresponding increase in surface-to-volume ratio emphasises the importance of low-energetic interfaces. Intriguingly, the thickness reduction of nickel silicides results in an abrupt change in phase sequence. This paper investigates the sequence of the silicides phases and their preferential orientation with respect to the Si(001) substrate, for both “thin” (i.e., 9 nm) and “ultra-thin” (i.e., 3 nm) Ni films. Furthermore, as the addition of ternary elements is often considered in order to tailor the silicides' properties, additives of Al, Co, and Pt are also included in this study. Our results show that the first silicide formed is epitaxial θ-Ni2Si, regardless of initial thickness or alloyed composition. The transformations towards subsequent silicides are changed through the additive elements, which can be understood through solubility arguments and classical nucleation theory. The crystalline alignment of the formed silicides with the substrate significantly differs through alloying. The observed textures of sequential silicides could be linked through texture inheritance. Our study illustrates the nucleation of a new phase drive to reduce the interfacial energy at the silicide-substrate interface as well as at the interface with the silicide which is being consumed for these sub-10 nm thin films.

Stress changes in GeTe thin films on silicon have been studied in situ as a function of temperature by optical curvature measurements. Crystallization of the initially amorphous layers is evidenced by a steep tensile stress buildup. The crystallization temperature is shown to be thickness-dependent for the thinner films. Various annealing conditions, such as cooling/re-heating steps and isothermal stages, allow exploring the thermo-mechanical behavior of the films. A non-thermoelastic temperature-dependent behavior is observed in the amorphous phase before crystallization.