Laboratory-based X-ray Diffraction Research Articles

Deciphering the Roles of Chemistry and Structure in Iridium Oxide Oxygen Evolution Catalysts through the Study of Annealed Iridium Oxide Nanoparticles

The development of proton exchange membrane (PEM) water electrolysis, which enables the production of de-carbonized hydrogen, is hindered by the low efficiency of the oxygen evolution reaction (OER). This is especially true in acidic environment where only noble metals (mainly Ru and Ir) can be used as electrocatalysts. Iridium oxide nanocatalysts (IrOx) are promising due to their high OER activity and good resistance to acidic and oxidative conditions. However, finding a compromise between their electrocatalytic activity and stability remains challenging. Moreover, it is not yet clear which parameter (the material structure1 or the initial iridium oxidation state2) controls these two properties.To address these challenges, we synthesized IrOx nanoparticles (NPs) supported on carbon (IrOx/C), through a modified polyol process, and annealed them under air, at temperatures ranging from 200◦C to 850◦C. This allows us to deconvolute the effects of the oxidation state, the structure and the size of IrOx NPs and to tune their activity and stability3. To analyze the structure, morphology, and oxidation state of Ir in these catalysts, we used transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and both laboratory-based and synchrotron-based X-ray diffraction (XRD) techniques.We observed in situ the crystallization of IrOx NPs, leading to crystallite size growth and change in Ir electronic state (see Figure 1a). Additionally, we investigated the morphological changes of IrOx NPs with respect to annealing temperature (refer to Figure 1b-f). We assessed their electrocatalytic activity towards the OER and determined their stability number4 (S-number) using inductively coupled plasma mass spectrometry and electrochemistry. We observed that increasing the annealing temperature led to an increase in particle size and degree of crystallinity, but did not result in significant changes in the iridium oxidation state (refer to Figure 1g). We observed the evolution of the electrochemical activity of the nanoparticles with the annealing temperature (see Figure 1h). Our results show a correlation between the changes in electronic structure, morphology, and size, and the evolution of OER activity and stability of the IrOx NPs. Specifically, we identified certain conditions that achieved an optimal balance between activity and stability.(1) Elmaalouf, M.; Odziomek, M.; Duran, S.; Gayrard, M.; Bahri, M.; Tard, C.; Zitolo, A.; Lassalle-Kaiser, B.; Piquemal, J.-Y.; Ersen, O.; Boissière, C.; Sanchez, C.; Giraud, M.; Faustini, M.; Peron, J. Nat. Commun. 2021, 12 (1), 3935. https://doi.org/10.1038/s41467-021-24181-x.(2) Claudel, F.; Dubau, L.; Berthomé, G.; Sola-Hernandez, L.; Beauger, C.; Piccolo, L.; Maillard, F. ACS Catal. 2019, 9 (5), 4688–4698. https://doi.org/10.1021/acscatal.9b00280.(3) Geiger, S.; Kasian, O.; Shrestha, B. R.; Mingers, A. M.; Mayrhofer, K. J. J.; Cherevko, S. J. Electrochem. Soc. 2016, 163 (11), F3132. https://doi.org/10.1149/2.0181611jes.(4) Geiger, S.; Kasian, O.; Ledendecker, M.; Pizzutilo, E.; Mingers, A. M.; Fu, W. T.; Diaz-Morales, O.; Li, Z.; Oellers, T.; Fruchter, L.; Ludwig, A.; Mayrhofer, K. J. J.; Koper, M. T. M.; Cherevko, S. Nat. Catal. 2018, 1 (7), 508–515. https://doi.org/10.1038/s41929-018-0085-6.Acknowledgments: This work was supported by the French National Research Agency in the frame of the MATHYLDE project (grant number n° ANR-22-PEHY-0001).Figure 1 – a. X-ray diffractograms obtained on IrOx/C annealed at 290, 340, 380, 420, 470, 520, 570, 620, 670 and 850°C under air. Each measurement lasted 13 minutes. The hashes correspond to tetragonal IrO2 (PDF card 00-043-1019) and the stars to metallic Ir (PDF card 00-006-0598). b-f. TEM images of IrOx/C NPs as-synthesized and calcined at 290, 380, 420, 570 and 850 °C. g. X-ray photoelectron spectra showing the Ir 4f levels of IrOx/C NPs as-synthesized and calcined at 380, 420, 520 and 850 °C. The dotted lines indicates the theoretical position of the peaks for Ir(IV) and Ir(III). h. Cyclic voltammograms measured in 0.1 M HClO4 at 50 mV s−1 indicating the change in electrochemical properties of IrOx/C NPs with annealing temperature. Figure 1

Influence of sulfur addition on the glass formation, phase transformation and mechanical properties of Cu50Zr50 alloy

In this work, a thorough study on the effects of sulfur-addition in the Cu50Zr50 glass-forming system was conducted using laboratory-based X-ray diffraction (XRD), synchrotron-based high-energy XRD (HESXRD), differential scanning calorimetry, and uniaxial compression testing. We report that the glass-forming ability (GFA), thermal stability, phase transformation sequence during heating and cooling, as well as the mechanical properties of the Cu50Zr50 system are highly sensitive to the sulfur concentration. Proper addition of sulfur can not only stabilize the B2-CuZr phase, but also enhances the GFA of the system. This enables the formation of BMG composites that solely contain a B2 phase, which results in a combination of high strength and substantial plastic strain under compressive loading. The total strains of the newly developed BMG composites with sulfur contents of 0.5 and 1.0 at.% are as large as ∼10 at.%, exceeding the previously reported strains of the Cu50Zr50 BMG by far. These superior properties make the Cu-Zr-S BMG composites a promising candidate material for industrial applications. In addition, it is found that excessive addition of sulfur leads to the precipitation of the Cu10Zr7 phase upon cooling from the alloy melt and a sulfide phase during heating from the glassy state. HESXRD experiments suggest that the preferential bonding between Zr and S atoms could be the determining structural mechanism on the atomic scale, leading to the changing primary crystallization sequence for heating and cooling. The findings in this work further strengthen the high relevance of sulfur in alloy development and tuning of properties in BMGs, especially considering the low cost, good availability, and non-toxicity of sulfur in the relevant modifications.

Percolation of grain boundaries and triple junctions in three-dimensions: A test of theory

Percolation is a fundamental property of grain boundary (GB) networks that has so far been analyzed through synthetic three-dimensional (3D) microstructures alone. In this work, we visualize an unprecedented 10,265 GBs in a 3D Al-Cu sample using laboratory-based X-ray diffraction tomography (LabDCT). By applying finite-size scaling with the critical exponents from standard percolation theory, we determine from our experimental data a percolation threshold of 0.236 ± 0.039 for the GBs in the thermodynamic limit. We compare our results to those from past simulations, which model the 3D microstructure using space-filling polyhedra; the thresholds show good agreement when they are normalized by the topological characteristics of the GB network. We further investigate the percolation threshold of triple junction (TJ) lines, which we show to be necessarily lower than that of the GBs. The percolation behavior of TJs is also different from that of the theoretical diamond lattice due to two factors: a surprisingly higher coordination of nodes (6.184 vs. 4) and also a spatial clustering of TJs in the microstructure. The insights obtained herein can help inform the design of failure-resistant materials via GB engineering.

Tracking the high-temperature synthesis of LiNiO2 under oxygen gas flow by laboratory-based X-ray diffraction

Tracking the high-temperature synthesis of LiNiO₂ under oxygen gas flow by laboratory-based X-ray diffraction

Tracing Low Amounts of Mg in the Doped Cathode Active Material LiNiO2

The resurgence of electromobility drives the need for high energy density cathode materials. LiNiO2 (LNO) meets this demand, based on its high specific capacity in a narrow voltage range and without relying on scare elements. Yet, it has been plagued by various issues, such as poor cycling performance and thermal instability. Adding dopants, such as widely available Mg2+, is a common strategy to balance cycling performance and energy density. Most prior studies focused on large Mg content ranges and were based on laboratory X-ray diffraction. Hence, the influence of Mg2+ addition on the crystal structure remains ambiguous, especially when small amounts are used (≤ 5 mol%; particularly interesting for industrial applications). Here, we present a systematic study of LiNi1−y Mg y O2 (0 ≤ y ≤ 0.05) investigated by high-resolution synchrotron-based X-ray diffraction combined with elemental analysis, electron microscopy and electrochemical testing. The synthetic route relies on the addition of 10 nm Mg(OH)2 nanoparticles prior to the final calcination, as well as on co-precipitation. It is found that Mg2+ mostly occupies the Ni site until saturating at ∼1.7%, then the Li site becomes preferred. This trend in the site occupancies influences the lattice parameters, oxygen coordinate within the unit cell and Ni–O bond distances. Doping also modifies the electrochemical behavior as a cathode material, stabilizing the capacity retention during cycling but sacrificing specific discharge capacity. Laboratory-based operando X-ray diffraction reveals that the increase in capacity retention is due to the suppression of the H2-H3 phase transition and interlayer distance collapse already in 3% Mg-doped LNO. The combination of structural and electrochemical characterization of doped LNO provides useful insights into the structural chemistry of the Mg2+ dopant and can serve as a starting point to understand Mg as a component in multiple dopant strategies for cathode material design and application.

Multi-Technique Analytical Approach to Quantitative Analysis of Spodumene

The aim of this study was to establish the capability of X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) methods to determine different spodumene forms (α-, β- and γ-spodumene) occurring during heat treatment of lithium spodumene. It is essential to correctly identify and quantify the presence of different forms of spodumene after heat treatment to ensure optimum lithium extraction. A sample from the Haapaluoma lithium-pegmatite (western Finland) was used for this study. An experimental programme was initiated to model the progression of the mineral transformation at different stages through heat treatment. The specimen was broken down and split into five portions. One of the splits was analysed unheated with XRD, FTIR, XRF and ICP; the other four splits were analysed with XRD and FTIR after heat treatment at different temperatures from 850 to 1100 °C. In this study, we show that both laboratory-based XRD and portable FTIR methods are effective in identifying and quantifying α-, β- and γ-spodumene as well as impurities. The accuracy of the quantification of the minerals with XRD was established by using a mass balance calculation and was compared with the actual chemistry of the sample measured with ICP analysis. Fully quantitative XRD analysis of heat-treated spodumene is considered a challenge due to peak overlaps between the β-, and γ-spodumene forms, particularly when gangue minerals and amorphous content are present. The novelty of this study consists of the use of the XRD technique complemented by the Rietveld method to fully quantify the different forms of spodumene from one another: α-, β- and γ-spodumene, along with the gangue minerals and the amorphous content. It is also shown that reproducible systematic changes occur in the FTIR spectra that track the spodumene transformation during heat treatment. With more samples and cross-validation between the XRD results, the FTIR methodology could be developed further to provide semi-quantitative information on the different spodumene forms in the future. This would permit the use of a fast, cost-effective and portable technique for quality control of the spodumene forms, which would open opportunities across the Li value chain.

The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO4 (M = Ce, U).

Orthosilicates adopt the zircon structure types (I41/amd), consisting of isolated SiO4 tetrahedra joined by A-site metal cations, such as Ce and U. They are of significant interest in the fields of geochemistry, mineralogy, nuclear waste form development, and material science. Stetindite (CeSiO4) and coffinite (USiO4) can be formed under hydrothermal conditions despite both being thermodynamically metastable. Water has been hypothesized to play a significant role in stabilizing and forming these orthosilicate phases, though little experimental evidence exists. To understand the effects of hydration or hydroxylation on these orthosilicates, in situ high-temperature synchrotron and laboratory-based X-ray diffraction was conducted from 25 to ∼850 °C. Stetindite maintains its I41/amd symmetry with increasing temperature but exhibits a discontinuous expansion along the a-axis during heating, presumably due to the removal of water confined in the [001] channels, which shrink against thermal expansion along the a-axis. Additional in situ high-temperature Raman and Fourier transform infrared spectroscopy also confirmed the presence of the confined water. Coffinite was also found to expand nonlinearly up to 600 °C and then thermally decompose into a mixture of UO2 and SiO2. A combination of dehydration and dehydroxylation is proposed for explaining the thermal behavior of coffinite synthesized hydrothermally. Additionally, we investigated high-temperature structures of two coffinite-thorite solid solutions, uranothorite (UxTh1-xSiO4), which displayed complex variations in composition during heating that was attributed to the negative enthalpy of mixing. Lastly, for the first time, the coefficients of thermal expansion of CeSiO4, USiO4, U0.46Th0.54SiO4, and U0.9Th0.1SiO4 were determined to be αV = 14.49 × 10-6, 14.29 × 10-6, 17.21 × 10-6, and 17.23 × 10-6 °C-1, respectively.

Tracking polycrystal evolution non-destructively in 3D by laboratory X-ray diffraction contrast tomography

The ability to accurately map crystal grain morphology and grain boundaries in polycrystalline materials, non-destructively and in three-dimensions is required for detailed investigations into many aspects of polycrystalline deformation, as well as many other properties. Previously, the laboratory-based X-ray diffraction contrast tomography technique (LabDCT) has been shown to be capable of reconstructing crystallographic orientations and grain centres in 3D. Here we demonstrate the extension of the method to the reconstruction of the individual 3D grain shapes. Firstly, the grain boundaries are mapped by DCT in a beta‑titanium alloy (Ti-β21S) sample and validated by independent measurements of the grain shapes obtained from phase contrast tomography. The independent validation measurements show that the boundaries can be located with a mean accuracy of 4.4 μm. Secondly, the grain locations and orientations in a copper powder sample sintered at 1050 °C are tracked over time in a time-lapse manner by LabDCT and then the final state compared and validated against destructive serial sectioning EBSD (3D-EBSD) post-mortem. In this case we are able to follow the recrystallisation and competitive grain growth over time, by visualising the migration of selected grain boundaries. In particular the shrinkage and dissolution of grains in the immediate vicinity of a fast-growing grain are observed and quantified in the light of changes in misorientation relationships with the growing grain. More generally, LabDCT can be used to characterise, track or establish realistic 3D image-based models of polycrystalline microstructures across a range of crystal structures.

X-ray diffraction study of strain relaxation, spontaneous compositional gradient, and dislocation density in GeSn/Ge/Si(100) heterostructures

The strain relaxation, depth profiles of composition and density of dislocations in GeSn epilayers were studied by using the x-ray diffraction. Regions with uniform and graded composition, different levels of strain relaxation, and dislocation density were found in the GeSn layers grown at fixed growth conditions. At the initial stage of growth, the GeSn layer is under ∼8 × 10–3 compressive strain, and the Sn composition is close to the target value of 6.6%. With increasing layer thickness, the Sn content is enhanced by 0.85 ± 0.12% due to the relief of compressive strain down to ∼5.0 × 10–4. The plastic strain relaxation is dominated by 60° misfit dislocations at the GeSn/Ge interface, where their density is 3 × 105 cm−1. The relaxed GeSn layer serves as a buffer for the high-quality GeSn overlayer with uniform and enhanced Sn composition. The laboratory-based x-ray diffraction is shown as a non-destructive reliable technique for strain, composition, and defects characterization, as an alternative to secondary ion mass spectrometry and transmission electron microscope techniques.

Applying a combination of laboratory X-Ray diffraction and digital image correlation for recording uniaxial stress-strain curves in thin surface layers

By combining laboratory-based x-ray diffraction stress analysis with optical digital image correlation recorded in-situ during tensile loading, a new methodology has been developed to obtain for surface specific stress-strain curves. This novel methodology has been validated by comparing the reconstructed stress-strain curves from the x-ray diffraction/optical digital image correlation approach with stress-strain curves recorded using standard methods. The validated methodology enables now the recording of standard mechanical test data of altered surface layers, such as shot peened and machined surfaces or from proton-irradiated samples where the irradiated layer is limited to a depth of 10 s of microns.

Chemical ordering and relaxor properties in a novel solid solution of (1-x)Pb(Mg1/3Nb2/3)O3-xPb(Cd1/3Nb2/3)O3

A novel relaxor solid solution of (1-x)Pb(Mg1/3Nb2/3)O3-xPb(Cd1/3Nb2/3)O3 [(1-x)PMN-xPCN] is synthesized by the solid-state reaction method. The crystal structure, electric properties and relaxor behavior are investigated. This system exhibits an average cubic perovskite structure at room temperature. The cation ordering, which is hardly detectable in the canonical PMN by laboratory-based high-resolution X-ray diffraction, is clearly evidenced in this solid solution. The relaxor behavior of the solid solution is found to be enhanced in the (1-x)PMN-xPCN solid solution compared with PMN. The enhanced relaxor behavior is attributed to be formation of complex ordered and disordered structures, which leads to a broader distribution of the size and dynamics of local polar heterogeneities.

3D grain reconstruction from laboratory diffraction contrast tomography.

A method for reconstructing the three-dimensional grain structure from data collected with a recently introduced laboratory-based X-ray diffraction contrast tomography system is presented. Diffraction contrast patterns are recorded in Laue-focusing geometry. The diffraction geometry exposes shape information within recorded diffraction spots. In order to yield the three-dimensional crystallographic microstructure, diffraction spots are extracted and fed into a reconstruction scheme. The scheme successively traverses and refines solution space until a reasonable reconstruction is reached. This unique reconstruction approach produces results efficiently and fast for well suited samples.

Field-based accounting of CO2sequestration in ultramafic mine wastes using portable X-ray diffraction

Carbon mineralization, the sequestration of carbon within minerals, presents one method through which we could control rising levels of anthropogenic carbon dioxide (CO) emissions. The mineral wastes produced by some ultramafic-hosted mines have the ability to sequester atmospheric CO via passive carbonation reactions. Carbon accounting in mine tailings is typically performed using laboratory-based quantitative X-ray diffraction (XRD) or thermogravimetric methods, which are used to measure the abundances of carbonate-bearing minerals such as hydromagnesite [Mg(CO)(OH)·4HO] and pyroaurite [Mg Fe23+ $\text{Fe}^{3+}-{2}$ (CO)(OH)·4HO]. The recent development of portable XRD instruments now allows for the characterization and quantification of minerals in the field. Here we assess the feasibility of using a portable XRD instrument for field-based carbon accounting in tailings from the Woodsreef Chrysotile Mine, New South Wales, Australia. Modal mineralogy was obtained by Rietveld refinements of data collected with an inXitu Terra portable XRD. The Partial Or No Known Crystal Structures (PONKCS) method was used to account for turbostratic stacking disorder in serpentine minerals, which are the dominant phases in tailings from Woodsreef. Weighed mixtures of synthetic tailings were made to evaluate the precision and accuracy of quantitative phase analysis using the portable instrument. An average absolute deviation (bias) of 8.2 wt% from the actual composition of the synthetic tailings was found using the portable instrument. This is comparable to the bias obtained using a laboratory-based diffractometer (9.6 wt% absolute) and to the results from previous quantitative XRD studies involving serpentine minerals. The methodology developed using the synthetic tailings was then applied to natural tailings samples from Woodsreef. Surface crusts forming on the tailings pile were found to contain hydromagnesite (∼5.8 wt%) and pyroaurite (∼2.1 wt%). Comparable results were obtained using the laboratory-based instrument and these results are expected to have similar biases to the analyses of the synthetic tailings. These findings demonstrate that portable XRD instruments may be used for field-based measurement of carbon sequestration in minerals in engineered and natural environments.

In-situ X-ray diffraction studies of slip and twinning in the presence of precipitates in AZ91 alloy

The effect of basal plate precipitates on the hardening of basal slip and {101¯2} twinning modes was investigated for a non-aged and aged AZ91 alloy in the twin dominated strain paths. Exploiting in-situ synchrotron and laboratory based X-ray diffraction methodologies, we quantified the critical resolved shear stress (CRSS) for basal slip and twinning modes. The twin volume fraction changes were quantified from the intensity changes with applied load. We observed that the twin volume fraction changes with plastic strain is sensitive to the initial texture, while the relative hardening of different deformation modes are considered as a secondary effect. We also found that the twin interior stresses were significantly smaller and consistent with the high twin back stresses in the presence of precipitates. We propose, based on a simple analytical equation, that the leading edge of the propagating twin have a Burgers vector equivalent to 100 twinning dislocations and when the propagating twin is blocked by a precipitate, relatively high resolved stress is required for bowing the twin dislocation and hence the propagation of the twin occurs by the dissociation of the leading edge of the twinning dislocation.

A laboratory-based Laue X-ray diffraction system for enhanced imaging range and surface grain mapping.

Although CCD X-ray detectors can be faster to use, their large-area versions can be much more expensive than similarly sized photographic plate detectors. When indexing X-ray diffraction patterns, large-area detectors can prove very advantageous as they provide more spots, which makes fitting an orientation easier. On the other hand, when looking for single crystals in a polycrystalline sample, the speed of CCD detectors is more useful. A new setup is described here which overcomes some of the limitations of limited-range CCD detectors to make them more useful for indexing, whilst at the same time making it much quicker to find single crystals within a larger polycrystalline structure. This was done by combining a CCD detector with a six-axis goniometer, allowing the compilation of images from different angles into a wide-angled image. Automated scans along the sample were coupled with image processing techniques to produce grain maps, which can then be used to provide a strategy to extract single crystals from a polycrystal.

Development of a laboratory-based transmission diffraction technique forin situdeformation studies of Mg alloys

A laboratory-based transmission X-ray diffraction technique was developed to measure elastic lattice strains parallel to the loading direction duringin situtensile deformation. High-quality transmission X-ray diffraction data were acquired in a time frame suitable forin situloading experiments by application of a polycapillary X-ray optic with a conventional laboratory Cu X-ray source. Based on the measurement of two standard reference materials [lanthanum hexaboride (NIST SRM 660b) and silicon (NIST SRM 640c)], precise instrumental alignment and calibration of the transmission diffraction geometry were realized. These results were also confirmed by the equivalent data acquired using the standard Bragg–Brentano measurement geometry. An empirical Caglioti function was employed to describe the instrumental broadening, while an axis of rotation correction was used to measure and correct the specimen displacement from the centre of the goniometer axis. For precise Bragg peak position andhkilintensity information, a line profile fitting methodology was implemented, with Pawley refinement used to measure the sample reference lattice spacings (do(hkil)). It is shown that the relatively large X-ray probe size available (7 × 7 mm) provides a relatively straightforward approach for improving the grain statistics for the study of metal alloys, where grain sizes in excess of 1 µm can become problematic for synchrotron-based measurements. This new laboratory-based capability was applied to study the lattice strain evolution during the elastic–plastic transition in extruded and rolled magnesium alloys. A strain resolution of 2 × 10−4at relatively low 2θ angles (20–65° 2θ) was achieved for thein situtensile deformation studies.In situmeasurement of the elastic lattice strain accommodation with applied stress in the magnesium alloys indicated the activation of dislocation slip and twin deformation mechanisms. Furthermore, measurement of the relative change in the intensity of 0002 and 10\overline 13 was used to quantify {10\overline 12}〈\overline 1011〉 tensile twin onset and growth with applied load.

Non-destructive laboratory-based X-ray diffraction mapping of warpage in Si die embedded in IC packages

Reliability issues as a consequence of thermal/mechanical stresses created during packaging processes have been the main obstacle towards the realisation of high volume 3D Integrated Circuit (IC) integration technology for future microelectronics. However, there is no compelling laboratory-based metrology that can non-destructively measure or image stress/strain or warpage inside packaged chips, System-on-Chip (SoC) or System-in-Package (SiP), which is identified as a requirement by the International Technology Roadmap for Semiconductors (ITRS). In the work presented here, a triple-axis Jordan Valley Bede D1 X-ray diffractometer is used to develop a novel lab-based technique called X-ray diffraction 3-dimensional surface modelling (XRD/3DSM) for non-destructive analysis of manufacturing process-induced stress/warpage inside completely encapsulated packaged chips. The technique is demonstrated at room temperature and at elevated temperatures up to 115°C by in situ XRD annealing experiments. The feasibility of this technique is confirmed through the characterisation of die stress inside encapsulated commercially available ultra-thin Quad Flat Non-lead (QFN) packages, as well as die stress in embedded QFN packages at various stages of the chip manufacturing process.

Stress Evolution during Tensile Twinning in MgAZ31 Alloy Processed by Extrusion

An in-situ laboratory based X-ray diffraction technique has been developed to directly measure lattice strain and stress evolution associated with {10.2} < 10.1 > twin nucleation and growth in rolled and extruded Mg alloys during tensile loading. A transmission diffraction geometry was utilised to measure peak position and intensity for the (10.0), (00.2) and (10.1) lattice planes while the sample was loaded in uni-axial tension. Lattice re-orientation arising from deformation twinning is utilizedto estimate the twin volume fraction by measuring the increase in the (10.0) peak intensity along with a simultaneous decrease in the (00.2) peak intensity as a function of applied load. From observation of the lattice strain plotted against applied stress for different orientations it was found that the (10.1) orientation displayed the anticipated linear behaviour within the whole stress range. Yielding in the (10.2) and (10.3) orientations was identified at around 75 and 90 MPa respectively, indicating theonset of basal slip. Twin nucleation was observed at at a stress of approximately 110 MPa.

Temperature-Dependent Reduction of Epitaxial Ce1–xPrxO2−δ (x = 0–1) Thin Films on Si(111): A Combined Temperature-Programmed Desorption, X-ray Diffraction, X-ray Photoelectron Spectroscopy, and Raman Study

The inherent properties of epitaxial oxide thin-film layers have attracted the intense interest of different research fields, such as catalysis and microelectronics. The focus of this work is the temperature-dependent oxygen release, oxygen vacancy formation, and lattice rearrangement of Ce1–xPrxO2−δ thin films with systematic stoichiometry variation (x = 0–1) and oxygen deficiency (δ > 0) on Si(111). The mixed oxide layers were heteroepitaxially grown by coevaporating molecular beam epitaxy. To observe the oxygen release, temperature-programmed desorption was performed. Furthermore, laboratory-based X-ray diffraction measurements were carried out after several annealing steps to investigate the crystal structure rearrangement. The contribution of Ce4+/Ce3+ and Pr4+/Pr3+ redox systems to the oxygen release and lattice rearrangement was clarified by X-ray photoelectron spectroscopy. Finally, Raman spectroscopy was performed to detect structural defects in the oxide lattice (i.e., oxygen vacancies and MO8-c...

Reduction of Structural Defects in Ge Epitaxially Grown on Nano-Structured Si Islands on SOI Substrate

One way to further increase performance and/or functionality of Si micro-and nanoelectronics is the integration of alternative semiconductors on silicon (Si). We studied the Ge/Si heterosystem with the aim to realize a Ge deposition free of misfit dislocations and with low content of other structural defects. Ge nanostructures were selectively grown by chemical vapor deposition on periodic Si nanoislands (dots and lines) on SOI substrate either directly or with a thin (about 10 nm) SiGe buffer layer. The strain state of the structures was measured by different laboratory-based x-ray diffraction techniques. It was found that a suited SiGe buffer improves the compliance of the Si compared to direct Ge deposition; plastic relaxation during growth can be prevented, and fully elastic relaxation of the structure can be achieved. Transmission electron microscopy confirms that the epitaxial growth of Ge on nanostructured Si is free of misfit dislocations.