Synchrotron X-ray Diffraction Measurements Research Articles

Enhanced magnetocaloric effect accompanying successive magnetic transitions in TbMn2Si2-xGex compounds

The lack of magnetic refrigeration (MR) materials with high magnetocaloric effect (MCE) and large relative cooling power (RCP) in the temperature range required for hydrogen liquefaction (20 K–77 K) is a bottleneck for practical applications of MR cooling systems. The present investigation of TbMn2Si2-xGex compounds (x = 0.1, 0.2) by variable temperature neutron and synchrotron X-ray diffraction, magnetization and heat capacity measurements, establish that substitution of Si with Ge in TbMn2Si2 leads to a significant enlargement of the unit cell and modification of the magnetic properties. Two consecutive ferromagnetic first-order transitions occur below 77 K with the third transition from paramagnetism to a collinear antiferromagnetic state being determined around 500 K. The resultant plateau-like MCE with large RCP below 77 K in these designed compounds offers scope for application for hydrogen liquefaction. Detailed neutron investigation confirm that four magnetic states exist within the temperature range 5 K to 500 K, with two successive first-order magnetic transitions below 77 K responsible for the large MCE. Our specific heat studies provide evidence of strong contributions from the nuclear specific heat and the corresponding nuclear specific heat coefficients of A = 430 ± 50 mJ mol−1 K and A = 418 ± 60 mJ mol−1 K have been determined for TbMn2Si2-xGex with x = 0.1 and x = 0.2, respectively. The overlapping entropy curves near these successive transitions lead to a plateau-like magnetothermal effect as well as a large reversible MCE for both samples (e.g. ΔSMmax = 14.0 J/kg K and ΔTmax = 7.6 K; RCP = 379 J/kg for TbMn2Si1.9Ge0.1 for an applied field of 5 T) indicating that the material can operate over a wide temperature range – particularly for hydrogen liquefaction.

Li2s-PI3 Cathode for High-Energy-Density All-Solid-State Lithium-Sulfur Batteries

1.Introduction All-solid-state lithium-sulfur batteries (ASSLSBs) are one of the most promising next-generation large scale energy storage devices due to their remarkably high theoretical energy density, which is generated by high capacity of both cathodes, like element S or Li2S and Li metal anode. However, due to insufficient electronic and/or ionic conductivities of element S and Li2S, the low sulfur utilization and correspondingly unsatisfied practical energy density hinder the application of ASSLSBs largely. By heterovalent doping, vacancies in Li2S could be created, leading to higher ionic conductivity [1-2]. In this study, we developed different proportion of PI3-doping Li2S as active material to improve the sulfur utilization. Mixing with CNovel as electronic additive, Li2S-PI3-CNovel as cathode material shows good electrochemical performance. In order to clarify the effect of doping PI3, a detailed analysis of the point defect structure was performed using pair distribution function analysis using high-energy X-ray diffraction, synchrotron X-ray diffraction measurements, and X-ray absorption measurements to correlate with the electrochemical properties. 2. Experimental Li2S-PI3 as active material was synthesized by mixing Li2S and PI3 as raw materials with ball milling method and the proportion of raw materials has been optimized. The characterization of the prepared Li2S-PI3 was conducted by Synchrotron XRD coupled with pair Distribution Function analysis. The ionic conductivities were measured by AC impedance. The cathode materials were prepared based on active materials (90 wt%) and CNovel (10 wt%) as electronic conductor. The batteries composed of Li2S-PI3-CNovel as cathode, Li3PS4 as SSE and Li-In alloy as anode were assembled in the glove box filled with Ar atmosphere. The charge-discharge curves were obtained by galvanostatic measurement. The electronic structure and morphology of the Li2S-PI3-CNovel after electrochemical measurements were examined by X-ray Absorption Spectroscopy (XAS) for S K-edge, P K-edge, and I K-edge. 3.Results and Discussion Pair distribution function (PDF) analysis revealed that with PI3 doping, iodine atoms would occupy sulfur sites and phosphorous atoms would occupy lithium sites, creating lithium vacancies in the antifluorite structure. Figure 1 shows the charge/discharge curves of the Li2S-PI3-CNovel as cathode. The Li2S-PI3-CNovel cathode shows a charge capacity of 440 mAh g-1 and a discharge capacity of 494 mAh g-1 in the first cycle. And the capacities increase to 538 mAh g-1 during the subsequent cycles, with an average voltage of 1.81 V (vs Li/Li+). Even at 1 C (1 C=626 mAh g-1), the cathode without solid-state electrolyte could deliver 207 mAh g-1, corresponding to 38 % capacity retention of that at 0.05 C, which demonstrates good rate performance (Figure 2). The charge compensation is attributed to S, suggesting the conversion reaction between Li2S and element S, which was confirmed by XAS for S K-edge and P K-edge. References H Gamo.et al., Adv. 2022, 3, 2488-2494.NHH Phuc. et al., Energy Res., 2021, 8, 606023. Acknowledgement This research was financially supported by JST ALCA-SPRING Project. Figure 1

Effect of Deposition Time on the Properties of Cu<sub>x</sub>Zn<sub>y</sub>S Thin Films Synthesized by Ultrasonic Spray Pyrolysis

Copper Zinc Sulfide CuxZnyS (CZS) thin films with different thicknesses were prepared by the ultrasonic spray pyrolysis method (USP). The influence of deposition time on the structural, morphological, and optical properties of the thin films has been investigated. XRD styles revealed the formation of ternary CZS films. Synchrotron X-ray diffraction measurements confirmed the presence of the two phases CuS and ZnS, which form the ternary compound CZS. Crystallite size increases from 75.29 nm to 105.46 nm as deposition time increases whereas the strain parameter decreases from 6.27*10-4 to 3.28*10-4. The obtained SEM images show that CZS thin films have a dense and rough surface topography. Spectrometric analysis of the deposited films confirmed the alloy nature of the elaborated films, whereas the corresponding values of band gaps were in the range of 3.28 to 3.17 eV. Results show that increasing the deposition time enhances the optical properties. Furthermore, the electrical properties of CZS films are influenced by the deposition time and phase transition. Significant improvements on these properties were obtained when the thin film thickness increased: the resistivity decreased from 95.10 to 0.12 Ω cm the carrier centration increased from 4.03×1021 to 14.07×1021 cm−3 and the mobility varied from 0.83 to 18.75 cm2 V−1 S−1.

Observation of superconductivity and enhanced upper critical field of η-carbide-type oxide Zr4Pd2O

We report the first observation of bulk superconductivity of a η-carbide-type oxide Zr4Pd2O. The crystal structure and the superconducting properties were studied through synchrotron X-ray diffraction, magnetization, electrical resistivity, and specific heat measurement. The superconducting transition was observed at Tc = 2.73 K. Our measurement revealed that the η-carbide-type oxide superconductor Zr4Pd2O shows an enhanced upper critical field μ0Hc2(0) = 6.72 T, which violates the Pauli-Clogston limit μ0HP = 5.29 T. On the other hand, we found that the enhanced upper critical field is absent in a Rh analogue Zr4Rh2O. The large μ0Hc2(0) of Zr4Pd2O would be raised from strong spin–orbit coupling with Pd-4d electrons. The discovery of new superconducting properties for Zr4Pd2O would shed light on the further development of η-carbide-type oxide superconductors.

Adaptive Pore Opening to Form Tailored Adsorption Sites in a Cooperatively Flexible Framework Enables Record Inverse Propane/Propylene Separation.

A proposed low-energy alternative to the separation of alkanes from alkenes by energy-intensive cryogenic distillation is separation by porous adsorbents. Unfortunately, most adsorbents preferentially take up the desired, high-value major component alkene, requiring frequent regeneration. Adsorbents with inverse selectivity for the minor component alkane would enable the direct production of purified, reagent-grade alkene, greatly reducing global energy consumption. However, such materials are exceedingly rare, especially for propane/propylene separation. Here, we report that through adaptive and spontaneous pore size and shape adaptation to optimize an ensemble of weak noncovalent interactions, the structurally responsive metal-organic framework CdIF-13 (sod-Cd(benzimidazolate)2) exhibits inverse selectivity for propane over propylene with record-setting separation performance under industrially relevant temperature, pressure, and mixture conditions. Powder synchrotron X-ray diffraction measurements combined with first-principles calculations yield atomic-scale insight and reveal the induced fit mechanism of adsorbate-specific pore adaptation and ensemble interactions between ligands and adsorbates. Dynamic column breakthrough measurements confirm that CdIF-13 displays selectivity under mixed-component conditions of varying ratios, with a record measured selectivity factor of α ≈ 3 at 95:5 propylene:propane at 298 K and 1 bar. When sequenced with a low-cost rigid adsorbent, we demonstrated the direct purification of propylene under ambient conditions. This combined atomic-level structural characterization and performance testing firmly establishes how cooperatively flexible materials can be capable of unprecedented separation factors.

Characterization of Biogenic PbS Quantum Dots.

Heavy metals in a polluted environment are toxic to life. However, some microorganisms can remove or immobilize heavy metals through biomineralization. These bacteria also form minerals with compositions similar to those of semiconductors. Here, this bioprocess was used to fabricate semiconductors with low energy consumption and cost. Bacteria that form lead sulfide (PbS) nanoparticles were screened, and the crystallinity and semiconductor properties of the resulting nanoparticles were characterized. Bacterial consortia that formed PbS nanoparticles were obtained. Extracellular particle size ranged from 3.9 to 5.5 nm, and lattice fringes were observed. The lattice fringes and electron diffraction spectra corresponded to crystalline PbS. The X-ray diffraction (XRD) patterns of bacterial PbS exhibited clear diffraction peaks. The experimental and theoretical data of the diffraction angles on each crystal plane of polycrystalline PbS were in good agreement. Synchrotron XRD measurements showed no crystalline impurity-derived peaks. Thus, bacterial biomineralization can form ultrafine crystalline PbS nanoparticles. Optical absorption and current-voltage measurements of PbS were obtained to characterize the semiconductor properties; the results showed semiconductor quantum dot behavior. Moreover, the current increased under light irradiation when PbS nanoparticles were used. These results suggest that biogenic PbS has band gaps and exhibits the general fundamental characteristics of a semiconductor.

Coupled magnetic and structural transition in topological antiferromagnet EuAgAs under high pressure

Recently, EuAgAs and its derivatives have emerged as a promising platform for studying the interplay of transports, magnetism and topology. Herein, we report construction of a temperature-pressure phase diagram for antiferromagnetic Dirac semimetal EuAgAs, through electrical transport, synchrotron x-ray diffraction and Raman spectroscopy measurements in diamond anvil cells at high pressures up to 48.6 GPa. At Pc1∼3–5 GPa, we found a pressure-induced magnetic phase transition with accompanying a structural P63/mmc→Pnma transition. In the pristine antiferromagnetic phase, negative colossal magnetoresistance is observed mainly below the Néel temperature TN along with a field-induced metamagnetic transition; in the emergent magnetic phase, however, it is evident both above and below the magnetic critical temperature TC yet with no field-induced metamagnetic transition. These distinct features lead us to argue a ferromagnetic-like state for EuAgAs above Pc1, which is further supported by observation of a T5/3 temperature dependence of low-temperature resistance, a characteristic of marginal Fermi-liquid state expected to exist close to a ferromagnetic instability by spin fluctuations in metallic ferromagnets. At Pc2∼20 GPa, a possible phase transition of electronic origin may take place, which is revealed jointly by change of a T5/3→T5/2 temperature dependence of low-temperature resistance and change in slope of linear-in-T resistance at high temperatures.

Facile and Scalable Development of High-Performance Carbon-Free Tin-Based Anodes for Sodium-Ion Batteries.

Tin (Sn)-based anodes for sodium (Na)-ion batteries possess higher Na-storage capacity and better safety aspects compared to hard carbon -based anodes but suffer from poor cyclic stability due to volume expansion/contraction and concomitant loss in mechanical integrity during sodiation/desodiation. To address this, the usage of nanoscaled electrode-active particles and nanoscaled-carbon-based buffers has been explored, but with compromises with the tap density, accrued irreversible surface reactions, overall capacity (for "inactive" carbon), and adoption of non-scalable/complex preparation routes. Against this backdrop, anode-active "layered" bismuth (Bi) has been incorporated with Sn via a facile-cum-scalable mechanical-milling approach, leading to individual electrode-active particles being composed of well-dispersed Sn and Bi phases. The optimized carbon-free Sn-Bi compositions, benefiting from the combined effects of "buffering" action and faster Na transport of Bi, to go with the greater Na-storage capacity and lower operating potential of Sn, exhibit excellent cyclic stability (viz., ∼83-92% capacity retention after 200 cycles at 1C) and rate capability (viz., no capacity drop from C/5 to 2C, with only ∼25% drop at 5C), despite having fairly coarse particles (∼5-10 μm). As proven by operando synchrotron X-ray diffraction and stress measurements, the sequential sodiation/desodiation of the components and, concomitantly, stress build-ups at different potentials provide "buffering" action even for such "active-active" Sn-Bi compositions. Furthermore, the overall stress development upon sodiation of Bi has been found to be significantly lower than that of Sn (by a factor of ∼3.8), which renders Bi promising as a "buffer" material, in general. Dissemination of such complex interplay between electrode-active components during electrochemical cycling also paves the way for the development of high-performance, safe, and scalable "alloying-reaction"-based anode materials for Na-ion batteries and beyond, sans the need for ultrafine/nanoscaled electrode particles or "inactive" nanoscaled-carbon-based "buffer" materials.

Effect of grain size on amorphization mechanism and kinetics of bridgmanite in shocked meteorites

Bridgmanite formation and amorphization in shocked meteorites constrain the pressure and temperature conditions during planetary impact. However, the effect of the bridgmanite grain size on its amorphization kinetics is still unclear. Here, the amorphization mechanism and kinetics of fine-grained polycrystalline bridgmanite were studied at high temperatures up to 1080 K. High-temperature time-resolved synchrotron X-ray diffraction measurements showed that significant volume expansion due to temperature-induced amorphization caused static stress, which then hindered amorphization progress. Further, the temperature required for the amorphization of fine-grained bridgmanite (~ 1 μm) was found to be approximately 100 K higher than that required for the amorphization of coarse-grained samples (> 10 μm). We also noted that amorphization preferentially commenced at the twin planes and subgrain boundaries of bridgmanite grains, resulting in lower amorphization temperatures for the coarse-grained samples. The limited number of such specific locations in fine-grained natural bridgmanite suggested that grain boundary amorphization may be the dominant mechanism for bridgmanite amorphization in shocked meteorites. This unique amorphization kinetics would support the preservation of bridgmanite during the post-shock annealing in the shocked meteorite. Although bridgmanite amorphization starts easily at temperatures above ~ 420 K, a small amount of bridgmanite grains can survive at temperatures above 800 K by the effect of amorphization-induced stress.

Selective Synthesis of Perovskite Oxyhydrides Using a High-Pressure Flux Method.

Oxyhydrides with multi-anions (O2- and H-) are a recently developed material family and have attracted attention as catalysts and hydride ion conductors. High-pressure and high-temperature reactions are effective in synthesizing oxyhydrides, but the reactions sometimes result in inhomogeneous products due to insufficient diffusion of the solid components. Here, we synthesized new perovskite oxyhydrides SrVO2.4H0.6 and Sr3V2O6.2H0.8. We demonstrated that the addition of SrCl2 flux promotes diffusion during high-pressure and high-temperature reactions, and can be used for selective synthesis of the oxyhydride phases. We conducted in-situ synchrotron X-ray diffraction measurements to reveal the role of this flux and reaction pathways. We also demonstrated the electronic and magnetic properties of the newly synthesized oxyhydrides and that they work as anode materials for Li-ion batteries with excellent reversibility and high-rate characteristics, the first case with an oxyhydride. Our synthesis approach would also be effective in synthesizing various types of multi-component systems.

Combining synchrotron X-ray diffraction, mechanistic modeling and machine learning for in situ subsurface temperature quantification during laser melting.

Laser melting, such as that encountered during additive manufacturing, produces extreme gradients of temperature in both space and time, which in turn influence microstructural development in the material. Qualification and model validation of the process itself and the resulting material necessitate the ability to characterize these temperature fields. However, well established means to directly probe the material temperature below the surface of an alloy while it is being processed are limited. To address this gap in characterization capabilities, a novel means is presented to extract subsurface temperature-distribution metrics, with uncertainty, from in situ synchrotron X-ray diffraction measurements to provide quantitative temperature evolution data during laser melting. Temperature-distribution metrics are determined using Gaussian process regression supervised machine-learning surrogate models trained with a combination of mechanistic modeling (heat transfer and fluid flow) and X-ray diffraction simulation. The trained surrogate model uncertainties are found to range from 5 to 15% depending on the metric and current temperature. The surrogate models are then applied to experimental data to extract temperature metrics from an Inconel 625 nickel superalloy wall specimen during laser melting. The maximum temperatures of the solid phase in the diffraction volume through melting and cooling are found to reach the solidus temperature as expected, with the mean and minimum temperatures found to be several hundred degrees less. The extracted temperature metrics near melting are determined to be more accurate because of the lower relative levels of mechanical elastic strains. However, uncertainties for temperature metrics during cooling are increased due to the effects of thermomechanical stress.

Space-Group Determination of Superlattice Structure Due to Electric Toroidal Ordering in Ca5Ir3O12

Synchrotron X-ray diffraction measurements on a single crystal of Ca5Ir3O12 were performed to clarify the details of the superlattice reflections characterized by \(\mathbf{q} = (1/3,1/3,1/3)\). A search for superlattice reflections in a wide reciprocal space was performed using an imaging plate, and it was confirmed that there were no superlattice reflections at other than \(\mathbf{q} = (1/3,1/3,1/3)\). From the extinction rule of the superlattice reflections, the space group of the crystal structure below 105 K was found to be R3. The details of the superlattice reflections at specific q were investigated using a four-circle diffractometer. The temperature dependence of the integrated intensity at several q confirms that the order parameter of the phase transition of Ca5Ir3O12 at 105 K belongs to an A2 irreducible representation in the point group C3v from the discussion based on the Landau theory of phase transitions. The basis function of the A2 irreducible representation, which is a rotation around the c-axis, corresponds to an electric toroidal dipole.

Absence of magnetostriction and transition from rapid positive thermal expansion to negative thermal expansion at high temperatures in Sm0.5Y0.5Fe0.58Mn0.42O3 – A synchrotron X-ray diffraction study

X-ray photoemission spectroscopic (XPS) studies and temperature dependent synchrotron X-ray diffraction (SXRD) investigation have been conducted on polycrystalline samples of Sm0.5Y0.5Fe0.58Mn0.42O3 [SYFM (58-42)]. Room temperature XPS measurements revealed the mixed valance of the Fe and Mn ions along with the traces of oxygen vacancies in the material. The room temperature synchrotron X-ray diffraction (SXRD) of specimen shows the monophasic nature of the prepared composition, without the presence of any magnetic or non-magnetic impurity phases. SXRD measurements at variable temperatures between 298 and 873 K, indicates the absence of magnetostriction in the specimen at the magnetic transition temperatures TSR1 ≈ 348 K, TSR2 ≈ 300 K and TN ≈ 361 K. At much higher temperatures above TN, an anisotropic rapid positive thermal expansion (RPTE) to negative thermal expansion (NTE) of the a lattice parameter of the unit cell is further revealed for T > 573 K. The anomalous variation of phonons, are suggested to give rise to anomalous thermal variation in a lattice parameter of the specimen.

Long-and short-range structure of SnO2 nanoparticles: Synthesis and photo(electro)catalytic activity

We report herein a detailed study on the influence of hydrothermal treatment temperature on both long- and short-range structures of SnO2 nanoparticles (NPs) applied as photocatalysts for the discoloration of organic pollutants and as photoanodes for water splitting. Synchrotron X-ray diffraction and X-ray absorption near-edge spectroscopy measurements confirmed the enhancement of the structural order of SnO2 NPs as a function of hydrothermal temperature. Fourier transform infrared spectroscopy revealed that the hydrothermal treatment increased the amount of hydroxyl groups on the SnO2 NPs surface. Regarding the photocatalytic activity, the NPs were able to promote the discoloration of different dyes that can act as potential organic pollutants. The photoelectrocatalytic performance of the samples depended on the hydrothermal treatment temperature, with the degree of crystallinity and surface hydroxyl groups playing a significant role in their performance as photoanodes. In particular, the NPs treated at a higher temperature presented a better degree of crystallinity, in addition to many hydroxyls on their surface, leading to increased mobility of the photogenerated charge carriers and improving the interaction between the molecules degraded and the material surface. The results demonstrated that the hydroxyls adsorbed on the SnO2 surface favor the formation of hydroxyl radicals, a species that indirectly participate in the photocatalytic oxidation of rhodamine B dye. The photoelectrocatalytic tests showed that the NPs treated at 200 °C increased oxygen evolution reaction performance.

Impact of Ti and Zn Dual-Substitution in P2 Type Na2/3 Ni1/3 Mn2/3 O2 on Ni-Mn and Na-Vacancy Ordering and Electrochemical Properties.

High-entropy layered oxide materials containing various metals that exhibit smooth voltage curves and excellent electrochemical performances have attracted attention in the development of positive electrode materials for sodium-ion batteries. However, a smooth voltage curve can be obtained by suppression of the Na+ -vacancy ordering, and therefore, transition metal slabs do not need to be more multi-element than necessary. Here, the Na+ -vacancy ordering is found to be disturbed by dual substitution of TiIV for MnIV and ZnII for NiII in P2-Na2/3 [Ni1/3 Mn2/3 ]O2 . Dual-substituted Na2/3 [Ni1/4 Mn1/2 Ti1/6 Zn1/12 ]O2 demonstrates almost non-step voltage curves with a reversible capacity of 114mAhg-1 and less structural changes with a high crystalline structure maintained during charging and discharging. Synchrotron X-ray, neutron, and electron diffraction measurements reveal that dual-substitution with TiIV and ZnII uniquely promotes in-plane NiII -MnIV ordering, which is quite different from the disordered mixing in conventional multiple metal substitution.

Fading analyses of commercial lithium-ion batteries with blended cathodes using synchrotron X-ray diffraction measurement and discharge curve analysis

We investigated the fading behavior of commercial lithium-ion batteries with blended cathodes. Synchrotron X-ray diffraction measurements revealed the constituent materials of the blended cathode and the degradation state of the cathode due to particle cracking. A particle model was newly introduced to the discharge curve analysis in order to explain the voltage change due to particle cracking, which is not considered in the conventional discharge curve analyses. Herein, blended cathode and particle models to advance the conventional discharge curve analyses have been presented. We have implemented these models besides basic model within our discharge curve analysis code called VOLCALO (VOLtage CALculation and Optimization). The blended cathode model could reproduce the measured values of the discharge curve of cycled batteries better than the conventional method and obtain a change in blend weight ratio due to degradation. The particle model analysis revealed that considering the particle size change due to particle cracking, changes in the discharge curves near the discharge end could be explained by the increase of surface sites.

In Situ Synchrotron XRD Characterization of Piezoelectric Al1−xScxN Thin Films for MEMS Applications

Aluminum scandium nitride (Al1-xScxN) film has drawn considerable attention owing to its enhanced piezoelectric response for micro-electromechanical system (MEMS) applications. Understanding the fundamentals of piezoelectricity would require a precise characterization of the piezoelectric coefficient, which is also crucial for MEMS device design. In this study, we proposed an in situ method based on a synchrotron X-ray diffraction (XRD) system to characterize the longitudinal piezoelectric constant d33 of Al1-xScxN film. The measurement results quantitatively demonstrated the piezoelectric effect of Al1-xScxN films by lattice spacing variation upon applied external voltage. The as-extracted d33 had a reasonable accuracy compared with the conventional high over-tone bulk acoustic resonators (HBAR) devices and Berlincourt methods. It was also found that the substrate clamping effect, leading to underestimation of d33 from in situ synchrotron XRD measurement while overestimation using Berlincourt method, should be thoroughly corrected in the data extraction process. The d33 of AlN and Al0.9Sc0.1N obtained by synchronous XRD method were 4.76 pC/N and 7.79 pC/N, respectively, matching well with traditional HBAR and Berlincourt methods. Our findings prove the in situ synchrotron XRD measurement as an effective method for precise piezoelectric coefficient d33 characterization.

In Situ Study of the Interface-Mediated Solid-State Reactions during Growth and Postgrowth Annealing of Pd/a-Ge Bilayers.

Ohmic or Schottky contacts in micro- and nanoelectronic devices are formed by metal-semiconductor bilayer systems, based on elemental metals or thermally more stable metallic compounds (germanides, silicides). The control of their electronic properties remains challenging as their structure formation is not yet fully understood. We have studied the phase and microstructure evolution during sputter deposition and postgrowth annealing of Pd/a-Ge bilayer systems with different Pd/Ge ratios (Pd:Ge, 2Pd:Ge, and 4Pd:Ge). The room-temperature deposition of up to 30 nm Pd was monitored by simultaneous, in situ synchrotron X-ray diffraction, X-ray reflectivity, and optical stress measurements. With this portfolio of complementary real-time methods, we could identify the microstructural origins of the resistivity evolution during contact formation: Real-time X-ray diffraction measurements indicate a coherent, epitaxial growth of Pd(111) on the individual crystallites of the initially forming, polycrystalline Pd2Ge[111] layer. The crystallization of the Pd2Ge interfacial layer causes a characteristic change in the real-time wafer curvature (tensile peak), and a significant drop of the resistivity after 1.5 nm Pd deposition. In addition, we could confirm the isostructural interface formation of Pd/a-Ge and Pd/a-Si. Subtle differences between both interfaces originate from the lattice mismatch at the interface between compound and metal. The solid-state reaction during subsequent annealing was studied by real-time X-ray diffraction and complementary UHV surface analysis. We could establish the link between phase and microstructure formation during deposition and annealing-induced solid-state reaction: The thermally induced reaction between Pd and a-Ge proceeds via diffusion-controlled growth of the Pd2Ge seed crystallites. The second-phase (PdGe) formation is nucleation-controlled and takes place only when a sufficient Ge reservoir exists. The real-time access to structure and electronic properties on the nanoscale opens new paths for the knowledge-based formation of ultrathin metal/semiconductor contacts.

Fabrication and Properties of Epitaxial VO2 Thin Film on m-Al2O3 Substrate

A thin film of thermochromic VO2 was prepared on m-Al2O3 substrate using a radio frequency (RF) magnetron sputtering technique. The epitaxial growth of the monoclinic M1 phase of VO2 on the m-Al2O3 substrate was confirmed through synchrotron X-ray diffraction (XRD) measurements. The transformation of this monoclinic M1 phase into a rutile phase at ~68 °C was reflected in the temperature-dependent XRD measurements of the VO2 thin film. The temperature-dependent electrical resistance measurements of this sample also revealed an abrupt metal-to-insulator transition at ~68 °C, which is reversible in nature. Temperature-dependent X-ray absorption (XAS) measurements at V L-edge and O K-edge were performed to study the electronic structure of the epitaxial VO2/m-Al2O3 thin film during the metal-to-insulator (MIT) transition.

In-Situ X-ray Diffraction Analysis of Metastable Austenite Containing Steels Under Mechanical Loading at a Wide Strain Rate Range

This paper presents and discusses the methodology and technical aspects of mechanical tests carried out at a wide strain rate range with simultaneous synchrotron X-ray diffraction measurements. The motivation for the study was to develop capabilities for in-situ characterization of the loading rate dependency of mechanically induced phase transformations in steels containing metastable austenite. The experiments were carried out at the DanMAX beamline of the MAX IV Laboratory, into which a custom-made tensile loading device was incorporated. The test setup was supplemented with in-situ optical imaging of the specimen, which allowed digital image correlation-based deformation analysis. All the measurement channels were synchronized to a common time basis with trigger signals between the devices as well as post-test fine tuning based on diffraction ring shape analysis. This facilitated precise correlation between the mechanical and diffraction data at strain rates up to 1 s−1 corresponding to test duration of less than one second. Diffraction data were collected at an acquisition rate of 250 Hz, which provided excellent temporal resolution. The feasibility of the methodology is demonstrated by providing novel data on the kinetics of the martensitic phase transformation in EN 1.4318-alloy following a rapid increase in strain rate (a so-called jump test).