The origins of tetrahedral coordination in molten and glassy ZnCl2 and other group-2B metal dihalides

We report the results of first-principles calculations carried out within a relativistic density-functional method, on the molecular trimers of the MX₂ compounds (with M = Zn or Cd and X = Cl, Br, or I), showing how a distorted tetrahedral coordination of a group-2B metal atom by halogens first arises. The trimers of HgX₂ are also discussed, both in unstable and in stable configurations.     

Soft x-ray absorption and high-resolution powder x-ray diffraction study of superconducting CaxLa1−xBa1.75−xLa0.25+xCu3Oy system

We have studied the electronic structure of unoccupied states measured by O K-edge and Cu L-edge x-ray absorption spectroscopy (XAS), combined with crystal structure studied by high resolution powder x-ray diffraction (HRPXRD), of charge-compensated layered superconducting Ca_xLa_1−xBa_1.75−xLa_0.25+xCu₃O_y (0≤x≤0.4 and 6.4≤y≤7.3) cuprate. A detailed analysis shows that, apart from hole doping, chemical pressure on the electronically active CuO₂ plane due to the lattice mismatch with the spacer layers greatly influences the superconducting properties of this system. The results suggest chemical pressure to be the most plausible parameter to control the maximum critical temperatures (T_c^max) in different cuprate families at optimum hole density.     

Quantum imaging and spatio-temporal correlations

We report on recent progress for two topics in the field of Quantum Imaging. The first is the detection of faint amplitude objects with a sensitivity which surpasses the standard quantum limit. The second is the theoretical/numerical analysis of spatio-temporal entanglement in optical parametric down-conversion.     

Instabilities for a coherently driven Fabry-Perot cavity with a very thin absorber

We study the multi-longitudinal mode instability in purely absorptive optical bistability in the limit of nonlinear absorber much thinner than one wavelength. Under that assumption the dynamical equations are space-independent difference-differential equations which allow for an analysis as simple as for the ring cavity, with two additional parameters related to the position of the absorber in the cavity. Different instability scenarios are found as the relative position varies.     

CuO/ZnO Nanocomposite Gas Sensors Developed by a Plasma‐Assisted Route

CuO/ZnO nanocomposites were synthesized on Al₂O₃ substrates by a hybrid plasma‐assisted approach, combining the initial growth of ZnO columnar arrays by plasma‐enhanced chemical vapor deposition (PE‐CVD) and subsequent radio frequency (RF) sputtering of copper, followed by final annealing in air. Chemical, morphological, and structural analyses revealed the formation of high‐purity nanosystems, characterized by a controllable dispersion of CuO particles into ZnO matrices. The high surface‐to‐volume ratio of the obtained materials, along with intimate CuO/ZnO intermixing, resulted in the efficient detection of various oxidizing and reducing gases (such as O₃, CH₃CH₂OH, and H₂). The obtained data are critically discussed and interrelated with the chemical and physical properties of the nanocomposites.     

A review of catalyst-enhanced magnesium hydride as a hydrogen storage material

Magnesium hydride remains an attractive hydrogen storage material due to the high hydrogen capacity and low cost of production. A high activation energy and poor kinetics at practical temperatures for the pure material have driven research into different additives to improve the sorption properties. This review details the development of catalytic additives and their effect on the activation energy, kinetics and thermodynamic properties of magnesium hydride.     

Electronic structure of single crystal UPd3, UGe2, and USb2 from hard X-ray and angle-resolved photoelectron spectroscopy

Electronic structure of single crystal UPd₃, UGe₂, and USb₂ has been measured from hard X-ray photoelectron spectroscopy (HAXPES) with 7.6 keV photons at the European Synchrotron Radiation Facility (ESRF). Lower photon energy angle-resolved photoelectron spectroscopy (ARPES) was also performed at the Synchrotron Radiation Center (SRC). Herein the following results are presented: (i) ARPES results demonstrate hybridization between the U 5f and Pd 4d electrons within UPd₃. (ii) The greatly reduced surface sensitivity of HAXPES enabled observation of the bulk core levels in spite of surface oxidation. Photoelectron mean-free-path versus oxide layer thickness considerations were used to model the effectiveness of HAXPES for probing bulk features of in-air cleaved samples. (iii) Two distinct features separated by 800 meV were observed for the Sb 3d core level. These two features are attributed to manifestations of two distinct Sb sites within the USb₂ single crystal as supported by consideration of interatomic distances and enthalpy-of-formation. (iv) Doniach–Sunjic line shape analysis of core level spectral features revealed correlations between asymmetry coefficients and 5f localization.