Density functional theory based screening of ternary alkali-transition metal borohydrides: A computational material design project

The dissociation of molecules, even the most simple hydrogen molecule, cannot be described accurately within density functional theory because none of the currently available functionals accounts for strong on-site correlation. This problem led to a discussion of properties that the local Kohn-Sham potential has to satisfy in order to correctly describe strongly correlated systems. We derive an analytic expression for the nontrivial form of the Kohn-Sham potential in between the two fragments for the dissociation of a single bond. We show that the numerical calculations for a one-dimensional two-electron model system indeed approach and reach this limit. It is shown that the functional form of the potential is universal, i.e., independent of the details of the two fragments.We acknowledge funding by the Spanish MEC (Grant No. FIS2007-65702-C02-01), “Grupos Consolidados UPV/EHU del Gobierno Vasco” (Grant No. IT-319-07), and the European Community through e-I3 ETSF project (Grant Agreement No. 211956).Peer reviewe

Dioxins in Food and Feed - Reference Methods and New Certified Reference Materials (DIFFERENCE)

The European research project DIFFERENCE (“Dioxins in Food and Feed – Reference methods and New Certified Reference Materials”) was focussed on the development of an alternative methods for analysis of polychlorinated dibenzodioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) using comprehensive multi-dimensional gas chromatography (GC×GC), gas chromatography combined with low resolution ion-trap mass spectrometry (GCLRMS/ MS), the CALUX bioassay and an Ah-PCR technique. GC combined with high resolution mass spectrometry (HRMS) was used as a reference method in all comparisons

Synchrotron area diffractometry as a tool for spatial high-resolution three-dimensional lattice misorientation mapping

We have developed a high-resolution diffraction imaging method for determination of the complete three-dimensional rotational local lattice misorientation of crystalline samples. The method, called synchrotron area diffractometry, is based on recording double-crystal diffraction rocking scans in three mutually non-coplanar scattering planes with a two-dimensional area detector. The subsequent multiple-peak analysis of the rocking curve image series for all pixels and their backprojection to the wafer surface provides local misorientation angles (Euler angles) with spatial resolution up to micrometre range over the wafer surface. We applied this technique to determine the distribution of tilt and twist angles of the lattice misorientation of a macroscopic defect localized in a 6 inch semi-insulating GaAs(001) wafer

Laboratory-based multi-modal X-ray microscopy and micro-CT with Bragg magnifiers

We report on the successful demonstration of X-ray phase contrast microscopy and micro computed tomography (CT) with a Bragg magnifier microscope (BMM) in a laboratory setup. The Bragg magnifiers, constituted by two channel-cut crystals in asymmetric diffraction, produced a 15X magnification of the X-ray beam, thus enabling high resolution imaging to be attained. The angular sensitivity of the crystals was used to implement analyzer-based phase contrast imaging: acquiring images at different angular positions and the three parametric images (apparent absorption, differential phase and scattering) have been obtained. Micro-CT, with resolution of about 5 μm is demonstrated with the same system. The main limitations, as well as the ways to mitigate them, are discussed with the aid of the experimental data. The technique demonstrated herein extends high-resolution, multi-modal, x-ray imaging and micro-CT to compact laboratory setups, with the potential of broadening the reach of these techniques outside the community of synchrotron users

In-line Bragg magnifier based on v-shaped germanium crystals

In this work an X-ray imaging system based on a recently developed in-line two-dimensional Bragg magnifier composed of two monolithic V-shaped crystals made of dislocation-free germanium is presented. The channel-cut crystals were used in one-dimensional and in two-dimensional (crossed) configurations in imaging applications and allowed measurement of phase-contrast radiograms both in the edge-enhanced and in the holographic regimes. The measurement of the phase gradient in two orthogonal directions is demonstrated. The effective pixel size attained was 0.17 mu m in the one-dimensional configuration and 0.5 mu m in the two-dimensional setting, offering a twofold improvement in spatial resolution over devices based on silicon. These results show the potential for applying Bragg magnifiers to imaging soft matter at high resolution with reduced dose owing to the higher efficiency of Ge compared with Si

On the physical parameters and crystal defects of bulk semi-insulating InP for radiation detector fabrication

Semi-insulating (SI) InP substrates from various producers have been studied by the Hall technique, X-ray diffraction, laser scattering tomography and photoluminescence. The detection performances of radiation detectors fabricated from selected materials were tested using a 60 keV photon source (241Am). High Hall mobility, low dislocation and precipitation density have been observed in the substrate with low Fe content, which also gave the best detector performances. Its SI properties seem to be controlled by native defects