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By an extensive investigation of the principal growth parameters on the deposition process, we realized the epitaxial growth of crystalline wurtzite GaN thin films on single crystal (001) diamond substrates by metal organic chemical vapor deposition. From the influence of pressure, V/III ratio, and temperature, it was deduced that the growth process is determined by the mass-transport of gallium precursor material toward the substrate. The highest temperature yielded an improved epitaxial relationship between grown layer and substrate. X ray diffraction (XRD) pole figure analysis established the presence of two domains of epitaxial layers, namely (0001) < 101 0> GaN∥ (001)[110] diamond and (0001) < 101 0> GaN∥ (001) [110] diamond, which are 90° rotated with respect to each other. The presence of these domains is explained by the occurrence of areas of (2×1) and (1×2) surface reconstruction of the diamond substrate. When applying highly misoriented diamond substrates toward the [110] diamond direction, one of the growth domains is suppressed and highly epitaxial GaN on (001) diamond is realized. [ABSTRACT FROM AUTHOR]

Upon cooling, condensed-matter systems typically transition into states of lower symmetry. The converse—i.e., the emergence of higher symmetry at lower temperatures—is extremely rare. In this work, we show how an unusually isotropic magnetoresistance in the highly anisotropic, one-dimensional conductor Li0.9Mo6O17 and its temperature dependence can be interpreted as a renormalization group (RG) flow toward a so-called separatrix. This approach is equivalent to an emergent symmetry in the system. The existence of two distinct ground states, Mott insulator and superconductor, can then be traced back to two opposing RG trajectories. By establishing a direct link between quantum field theory and an experimentally measurable quantity, we uncover a path through which emergent symmetry might be identified in other candidate materials. [ABSTRACT FROM AUTHOR]

Here we report two new crystal structures of the amino acid quasiracemate d-2-aminobutyric acid:l-norvaline, as well as the fully reversible solid-state phase transition which connects the two forms. The room temperature form II is obtained by co-crystallisation through slow evaporation from an equimolar aqueous solution. Form I is obtained through cooling of form II below 150 K. The crystal structures of forms I and II have been determined using single crystal X-ray diffraction at 100 and 150 K, respectively. Both forms consist of 2D hydrogen bonded bilayers with an ld–ld hydrogen bonding pattern. The room temperature form II shows two conformations for the l-norvaline side chain in a disordered 50/50 occupancy distribution. The solid-state phase transition between the two polymorphic forms involves a displacement of the bilayers and conformational changes in all molecules. It has been further characterised using differential scanning calorimetry and thermal polarisation microscopy. These crystal structures and the single-crystal-to-single-crystal phase transition are similar to other quasiracemates and racemates of linear chain aliphatic amino acids. [ABSTRACT FROM AUTHOR]

[Display omitted] • Versatile atmospheric furnace for CIGS manufacturing, based on industrial setup. • Allows process parameters tuning for Ga/(Ga + In) (GGI) profile control. • Ga/In interdiffusion during selenisation of Cu-In-Ga is studied by in-situ XRD. • Lower Se crucible temperature yields faster but incomplete Ga/In interdiffusion. • Higher sample temperature yields much faster interdiffusion than 580 °C. The selenisation of Cu-Ga-In metallic precursors is investigated by in-situ X-Ray Diffraction (XRD) in a selenisation tool which mimics at the laboratory scale an industrial tool (thus fully scalable) and allows fine control over the selenisation parameters and reproducibility. In this setup, the interdiffusion of Ga and In was significantly accelerated by decreasing the Se crucible temperature or increasing the sample temperature. Applying a lower Se crucible temperature yielded a very fast initial interdiffusion that quickly reached a steady-state, non-flat Ga/(Ga + In) (GGI) depth profile. On the other hand, the higher crucible temperature tested led to a slower interdiffusion which kept evolving to a flatter GGI profile after a sufficiently long dwell time at the maximum temperature. Strategies to gain better control over the GGI profile, and hence bandgap profile, are discussed. The results indicate that the versatility of the setup is key to achieving fine control over the GGI depth profile, which is particularly relevant today, when new alkali doping strategies are being introduced. [ABSTRACT FROM AUTHOR]

The article discusess a study examining emergence of a real-space symmetry axis in the magnetoresistance of the one-dimensional conductor Li0.9Mo6O17. It mentions that unusual negative magnetoresistance is consistent with the melting of dark excitons, composed of previously omitted orbitals within the t2g manifold that order below temperature.

The solid-state phase transition between the low temperature β and the high temperature α forms of dl-methionine was characterised in detail using DSC, SCXRD, thermal stage polarisation microscopy and solid-state NMR. The thermodynamic transition point of the α↑β transition of dl-methionine was determined to fall between 306 and 317 K. The transition is kinetically hindered, as is indicated by a large hysteresis. Moreover, the transition rate during cooling is significantly lower than during heating and there is a large temperature region of coexistence. The kinetic barriers involved are lower for single crystals than for powders. dl-Methionine crystals consist of 2D hydrogen-bonded bilayers interconnected by weak Van der Waals interactions. The crystals transform layer-wise, without complete delamination or deterioration, and with a transition front that propagates perpendicular to the layers and a relatively fast transition within one layer. The fast kinetics within the plane of the layers, combined with the faster kinetics in single crystals, indicate that cooperative motion could play a role in this single-crystal-to-single-crystal phase transition. [ABSTRACT FROM AUTHOR]

We have studied the polar surface of singly terminated DyScO3 (110) crystals by reflective high-energy electron diffraction, surface x-ray diffraction and angle-resolved mass spectroscopy of recoiled ions. These techniques show that the surfaces are (1 × 1) reconstructed, which points to the absence of ordered cation vacancies at the surface. The best surfaces were obtained after a selective chemical wet etch. We suggest that for ScO2 terminated surfaces, adsorbates, or oxygen vacancies are most likely to occur in order to overcome the polarity difference between stoichiometric bulk crystal and vacuum. [ABSTRACT FROM AUTHOR]

Abstract: We present a surface X-ray diffraction determination of the silicon (111)-liquid interface structure during alkaline etching. Preparation of an atomically smooth surface was realized by an in-situ procedure using an aqueous NH4F solution devoid of oxygen. Using diluted aqueous potassium hydroxide (KOH) and ammonium fluoride (NH4F) etchant, we have observed that the crystal surface is hydrogen terminated and is not reconstructed at open circuit potential. In addition, a partial liquid ordering of two water layers on top of the crystal surface was found, indicating a weak interaction with the hydrophobic, hydrogen terminated surface. We have followed in-situ the development of the oxide layer by a birth and spread mechanism during anodic passivation of the silicon surface. [Copyright &y& Elsevier]