Concurrent X-ray Diffraction Research Articles

Impact of radiation induced crystallization on programmable metallization cell electrical characteristics and reliability

Chalcogenide-based, programmable metallization cells (PMC) cells have been characterized after exposure to increasing levels of absorbed dose (i.e., ionizing radiation exposure). We found, and show here for the first time, that total absorbed dose effects induce a slight modification of the switching phenomena with a moderate increase of the programmable low resistance state (LRS) of the PMCs after repeated switching depending on the processing conditions, while it does not impact the state programmed before exposure. We also show that an increase of the programmable high resistance state (HRS) occurs with irradiation. Such observations are discussed through correlation with crystallization observed in the concurrent X-ray diffraction (XRD) characterization of representative thin-film stacks of the PMCs. These new results are compared to previous results obtained on chalcogenide-based PMCs that did not identify/observe such effects.

Thermal Gradients in Solid Oxide Fuel Cell Anodes: X-Ray Diffraction, Thermal Imaging and Model Prediction

Thermal gradients can be induced within solid oxide fuel cells (SOFC) due to a range of design and operational considerations. These gradients coupled with the mismatched coefficient of thermal expansion between the anode and electrolyte layer can advance cell degradation and lead to cell failure. In this study a combined experimental and modelling approach is taken to investigate the effect of thermal gradients on the stresses within SOFC anodes. Experimental results obtained from investigations performed at Diamond Light Source using a concurrent X-ray diffraction and infrared thermal imaging approach are coupled with finite element analysis modelling to assess the impact of various parameters upon the cell. Operational considerations including cell polarisation and fuel flow configurations are examined to demonstrate the importance of optimization in minimising thermal gradients and subsequent stresses within the anode to prolong the lifetime of the cell whilst also maintaining the performance of the cell.

Porosity and phase fraction evolution with aging in lithium iron phosphate battery cathodes

Rechargeable Lithium-ion batteries designed for electric vehicles operate under different charge and discharge rates, state of charge and temperature . However, aging of these batteries due to disruption of ionic or electronic conductivity while operating under these different cycling conditions has been a concern. In this research, we measured statistical distribution of porosity in the cathode as a function of aging and location within the cylindrical battery, using X-Ray micro-computed tomography. A change in porosity (∼20%) of the sample is noticed between aged and unaged samples. Concurrent X-Ray diffraction studies in these samples showed an increase (∼34%) in FePO4 phase fraction. Structural breakdown of the composite cathode material during charge and discharge cycling is proposed as a possible mechanism to rationalize the above results.

Characterization of room temperature recrystallization kinetics in electroplated copper thin films with concurrent x-ray diffraction and electrical resistivity measurements

Concurrent in-situ four-point probe resistivity and high resolution synchrotron x-ray diffraction measurements were used to characterize room temperature recrystallization in electroplated Cu thin films. The x-ray data were used to obtain the variation with time of the integrated intensities and the peak-breadth from the Cu 111 and 200 reflections of the transforming grains. The variation of the integrated intensity and resistivity data with time was analyzed using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. For both 111-textured and non-textured electroplated Cu films, four-point probe resistivity measurements yielded shorter transformation times than the values obtained from the integrated intensities of the corresponding Cu 111 reflections. In addition, the JMAK exponents fitted to the resistivity data were significantly smaller. These discrepancies could be explained by considering the different material volumes from which resistivity and diffraction signals originated, and the physical processes which linked these signals to the changes in the evolving microstructure. Based on these issues, calibration of the resistivity analysis with direct structural characterization techniques is recommended.

Fabrication and thermoelectricity of La_{1-x}(Ca, RE)_{x}VO_{3}(⩽ x ⩽ 1) composition-spread films

La _{1-x} (Ca, RE) _x VO _3 (0⩽ x ⩽ 1) composition-spread films were fabricated successfully by Combinatorial Pulsed Laser Deposition (CPLD). The structures and thermoelectric (TE) properties of the films were evaluated paralelly by Concurrent X-ray Diffraction (CXRD) and Multi-channel Thermoelectric Measurement systems respectively. The CXRD (200) peaks of the composition-spread films changed linearly, which indicated that the composition-spread films formed solid solution in the whole composition range (0 ⩽ x ⩽ 1). The effects of oxygen content and the substitutions of Ca and rare earth (RE: Ce, Nd, Eu) ions on TE properties of LaVO _3 were also analysed respectively. There was little change in the Seebeck coefficients of LaVO _3 films grown at different growth temperatures, while the resistivity decreased with the enhance of the growth temperatures. The largest power factor (0.7 μW/cm K ^2 ) of LaVO _3 film was obtained at 800°C, while the valence of vanadium ion changed from 3+ to 2+ because of the lack of oxygen. With the increase of the content of Ca ^{2+} ions, the valence of vanadium ion changed from 3+ to 4+, which was responsible for the decrease of TE properties in La1-xCaxVO _3 system. The substitution of RE (Ce, Nd, Eu) ions for La ions changed not only Seebeck coefficient but also resistivity, but power factor (α) was not increased obviously. In La1-xCexVO _3 system, La ion took 3+, and Ce ion took 3+ although Ce ^{4+} was stable in theory, which caused the valence of V ion not changed as expected from 3+ to 2+. The reason may be that the size of Ce ^{3+} ion is similar to that of La ^{3+} ion, so Ce takes the valence of 3+ easily in LaVO _3 .

High-throughput Analysis for Combinatorial Epitaxial Thin Films by Concurrent X-Ray Diffraction

In order to rapid structural characterization of combinatorial epitaxial thin films, we developed a new x-ray diffraction system. A convergent x-ray beam from a curved crystal monochromator is focused on sample surface about 0.1 mm x 10 mm in size. Diffraction patterns of this area are observed on the two-dimensional detector. Rocking curve profile for each irradiated position can be measured within a few tens seconds, concurrently. We applied the present method to characterization of combinatorial [(SrTiO3)n/(BaTiO3)n]30 (n=12 to 30) superlattice and composition spread SrxBa1−xTiO3 on SrTiO3 substrate grown by laser molecular beam epitaxy (laser MBE). We could see the film diffraction peaks together with substrate peaks. Changes in superlattice periods and in composition of each position for the samples (combinatorial library) are clearly characterized only at one time rapid measurement.

High-pressure X-ray diffraction and X-ray emission studies on iron-bearing silicate perovskite under high pressures

Iron-bearing silicate perovskite is believed to be the most abundant mineral of the Earth's lower mantle. Recent studies have shown that Fe2+ exists predominantly in the intermediate-spin state with a total spin number of 1 in silicate perovskite in the lower part of the lower mantle. Here we have measured the spin states of iron and the pressure–volume relation in silicate perovskite [(Mg0.6,Fe0.4)SiO3] at pressure conditions relevant to the lowermost mantle using in situ X-ray emission and X-ray diffraction in a diamond cell. Our results showed that the intermediate-spin Fe2+ is stable in the silicate perovskite up to ∼ 125 GPa but starts to transition to the low-spin state at approximately 135 GPa. Concurrent X-ray diffraction measurements showed a decrease of approximately 1% in the unit cell volume in the silicate perovskite [(Mg0.6,Fe0.4)SiO3], which is attributed to the intermediate-spin to the low-spin transition. The transition pressure coincides with the pressure conditions of the lowermost mantle, raising the possibility of the existence of the silicate perovskite phase with the low-spin Fe2+ across the transition from the post-perovskite to the perovskite phases in the bottom of the D″ layer.

Crystallization and shear modulus of a forming biopolymer film determined by in situ x-ray diffraction and ultrasound reflection methods

The structure and the rigidity of a forming biopolymer film were determined using concurrent x-ray diffraction and ultrasonic reflection measurements. Film formation of a xylan solution (de-ionized water, 10g∕l xylan, 4g∕l glycerol) was studied during water evaporation at 24(±2)°C, 37(±5)%RH. X-ray diffraction (XRD) data showed the crystallization and ultrasonic data the increase of the shear modulus (G) during water evaporation. Xylan crystallized into small xylan dihydrate crystallites, the number of which increased as water evaporated. Crystallization began earlier than the increase in G during film formation. The increase in G also continued after the crystallites were fully formed, indicating still ongoing structural changes in the amorphous parts. The maximum value of G was 0.1–0.5GPa. XRD measurements performed ex situ showed a crystallinity of 16%–19% (±5%) and a fairly isotropic crystallite orientation in the surface plane of the films.

Combinatorial exploration of flux material for Bi 4Ti 3O 12 single crystal film growth

The combinatorial approach to materials synthesis was employed for the quick screening of a flux material for liquid phase-mediated epitaxy of Bi 4Ti 3O 12 single crystal film. A series of ternary flux libraries composed of two self-fluxes (Bi 2O 3 and Bi 4Ti 3O 12) and an impurity flux (VO x , WO x , CuO x , BiPO x , BaO, MoO x ) were fabricated on the SrTiO 3 (0 0 1) substrates. Then, stoichiometric Bi 4Ti 3O 12 was grown on each one of these flux libraries at a temperature presumed to melt the flux. High-throughput characterization with the concurrent X-ray diffraction (XRD) method resulted in the discovery of a novel flux material, CuO, containing Bi 2O 3, for Bi 4Ti 3O 12 single crystal film.

High throughput oxide lattice engineering by parallel laser molecular-beam epitaxy and concurrent x-ray diffraction

A laser molecular-beam epitaxy (LMBE) system for the fabrication of atomically controlled oxides superlattices and an x-ray diffractometer that measures spatially resolved x-ray diffraction spectra have been developed based on the concept of combinatorial methodology. The LMBE chamber has two moving masks, an automated target stage, a substrate heating laser, and an in situ scanning reflection high-energy electron diffraction system. The x-ray diffractometer with a curved monochromator and two-dimensional detector is used for rapid concurrent x-ray diffraction intensity mapping with the two axes of the detector corresponding to the diffraction angle and a position in the sample.

Fabrication of spin-frustrated Sm2Mo2O7 epitaxial films: High throughput optimization using a temperature gradient method

Epitaxial thin films of pyrochlore-type ferromagnetic molybdates Sm2Mo2O7, as a geometrically spin-frustrated system, were fabricated by a pulsed-laser deposition. The temperature gradient method combined with the concurrent x-ray diffraction method was exploited for high throughput optimization of the film quality. The excess supply of Mo for compensating the volatile Mo-related species improved the crystallinity. The resistivity and magnetization of the optimized film were 3 mΩ cm and 0.8 μB/Mo at 10 K, respectively, being similar to those of a single crystal. The observed finite anomalous Hall term that persists down to the lowest temperature reflects an appearance of spin chirality in this spin-frustrated system.

Synthesis of epitaxial Y-type magnetoplumbite thin films by quick optimization with combinatorial pulsed laser deposition

Y-type magnetoplumbite (Ba 2Co 2Fe 12O 22:Co 2Y) epitaxial thin films with such a huge lattice parameter as 43.5 Å have been synthesized for the first time. Combinatorial thin film technology was successfully employed to eliminate an impurity phase in the film by quickly optimizing such reaction parameters as the deposition temperature and the thickness of pre-deposition of CoO layer. The coupling of combinatorial pulsed laser deposition and subsequent concurrent X-ray diffraction, both of which we have developed, is a promising way to high throughput optimization of thin film growth and properties.

Combinatorial fabrication and cathodoluminescence properties of composition spread MHfO 3:Tm 3+(M = Ca, Sr and Ba) films

A series of MHfO 3:Tm 3+ (M=Ca, Sr and Ba) films were fabricated on SrTiO 3 (0 0 1) substrate by using combinatorial pulsed laser deposition (PLD) technique. Their crystal structures and luminescence properties were characterized by the concurrent X-ray diffraction (CXRD) and by the cathodoluminescence (CL) using 5 kV electron beam, respectively. By monitoring the reflection high energy electron diffraction (RHEED) intensity oscillation, the growth of MHfO 3:Tm 3+ films were optimized to proceed in a epitaxial layer-by-layer fashion. Different from bulk powders, which had the highest CL intensity in SrHfO 3:Tm 3+, the composition spread film of Sr 1− x Ca x HfO 3:Tm 3+ ( x=0–1) exhibited the highest CL intensity at x=0.7 rather than SrHfO 3:Tm 3+ ( x=0). This anomalous behavior in the films is discussed in view of the stress effect from the substrate.

Quick optimization of Y-type magnetoplumbite thin films growth by combinatorial pulsed laser deposition technique

Quick growth optimization of complex oxide, Y-type magnetoplumbite (Ba 2Co 2Fe 12O 22 (Co 2Y)) thin films is demonstrated by using combinatorial thin film technology. Planning a CoO buffer layer on MgAl 2O 4(1 1 1) substrate was found to be very effective for preventing the phase separation of Co deficient impurity (BaFe 2O 4) and forming the desired Co 2Y phase. The combinatorial pulsed laser deposition and subsequent concurrent X-ray diffraction facilitate the production of Y-type magnetoplumbite thin film in a single phase.

High Throughput X-ray Diffractometer for Combinatorial Epitaxial Thin Films

AbstractWe report on the development of a high throughput x-ray diffractometer that concurrently measures spatially resolved x-ray diffraction (XRD) spectra of epitaxial thin films integrated on a substrate. A convergent x-ray is focused into a stripe on a substrate and the diffracted beam is detected with a two-dimensional x-ray detector, so that the snapshot image represents a mapping of XRD intensity with the axes of the diffraction angle and the position in the sample. High throughput characterization of crystalline structure is carried out for a BaxSr1-xTiO3 composition-spread film on a SrTiO3 substrate. Not only the continuous spread of the composition (x), but also the continuous spread of the growth temperature (T) are given to the film by employing a special heating method. The boundary between the strained lattice and relaxed lattice is visualized by the concurrent XRD as functions of x and T in a high throughput fashion.

Low-temperature interdiffusion in titanium–permalloy thin-film diffusion couples

Interdiffusion in thin-film Ti–Permalloy (nominally 81 at. % Ni+19 at. % Fe) diffusion couples has been investigated in the temperature range 200°–350°C. These diffusion couples were isothermally annealed in vacuum for times up to 6×105 s, and their magnetic properties such as the coercivity, the anisotropy field, the saturation magnetization, and electrical properties such as the sheet resistance and the sheet magnetoresistance were monitored as functions of time. From the observed changes in these properties and from concurrent x-ray diffraction measurements, it may be concluded that the dominant mechanism in this interdiffusion process is the volume diffusion of Ti in Permalloy; the activation energy for this process is estimated to be 1.9 eV.