Carla Eichler

Different substrates for gallium nitride growth are discussed. The commercially relevant substrates, silicon carbide and sapphire, and the two most promising alternatives, silicon and gallium nitride, are compared in terms of suitability for epitaxial processes and in their effects on devices. An estimation on future market success is given.

The most recent volcanism in the Valles caldera is represented by the El Cajete Pyroclastic Beds (ECPB), Battleship Rock Ignimbrite (BRI), and Banco Bonito Flow (BBF) as well as the VC-1 rhyolite, which are collectively known as the East Fork Member (EFM) of the Valles Rhyolite. The EFM was erupted at approximately 55 ka and 40 ka after an approximate 460 ka lull in volcanism. Previous studies suggested a mafic intrusion at depth triggered the eruptions. This thesis represents the first detailed study of the EFM. Crystal assemblages consist of plagioclase, biotite, clinopyroxene, orthopyroxene, amphibole, sanidine, quartz, and oxides. Electron probe microanalysis and detailed petrography indicates that two distinct crystal populations are present in the ECPB, BRI, and BBF. Large (1 mm), typically resorbed or subhedral crystals represent one population, and small (0.5 mm), generally euhedral crystals represent the other. The large resorbed plagioclase crystals typically have rim over...

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non-H atoms missing; R factor = 0.026; wR factor = 0.061; data-to-parameter ratio = 19.5. Safflorite, a naturally occurring cobalt-nickel-iron diarsenide (Co,Ni,Fe)As2, possesses the marcasite-type structure, with cations (M = Co + Ni + Fe) at site symmetry 2/m and As anions at m. TheMAs6 octahedra share two edges, forming chains parallel to c. The chemical formula for safflorite should be expressed as (Co,Ni,Fe)As2, rather than the end-member format CoAs2, as its structure stabilization requires the simultaneous interaction of the electronic states of Co, Ni,

This study presents the first structural report of iranite, ideally CuPb10(CrO4)6(SiO4)2(OH)2 [copper decalead hexachromate bis(orthosilicate) dihydroxide], based on single-crystal X-ray diffraction data. Iranite is isomorphous with hemihedrite, with substitution of Cu for Zn and OH for F. The Cu atom is situated at the special position with site symmetry 1. The CrO4 and SiO4 tetrahedra and CuO4(OH)2 octahedra form layers that are parallel to (120) and are linked together by five symmetrically independent Pb cations displaying a rather wide range of bond distances. The CuO4(OH)2 octahedra are corner-linked to two CrO4 and two SiO4 groups, while two additional CrO4 groups are isolated. The mean Cr—O distances for the three nonequivalent CrO4 tetrahedra are all slightly shorter than the corresponding distances in hemihedrite, whereas the CuO4(OH)2 octahedron is more distorted than the ZnO4F2 octahedron in hemihedrite in terms of octahedral quadratic elongation.

The land-sea interface is considered as a threatening environment due to anthropogenic development activities. Unplanned developments can cause effects on important ecosystems, water and human health as well. In this study, the influence of rapid regional development on the accumulation of trace elements to the sediments of an important ecosystem, Batticaloa lagoon, Sri Lanka was examined. Surface sediment pollution status and ecological risk was compared with that of the recent sedimentary history of about 1 m depth. Sediment core samples were collected and analyzed for grain size, organic matter and carbonate contents and trace elements (As, Pb, Zn, Cu, Ni and Cr) by the X-Ray Fluorescence (XRF) technique. The chemical results of core samples and recently published data of surface sediments of the same project were evaluated by pollution load index (PLI), potential ecological risk index (PERI) and sediment quality guidelines (SQG). Except for Cr, all other elements in cores show l...