The origin of native selenium microparticles during the oxidation of sideritic mudstones in the Veřovice Formation (Outer Western Carpathians)

Microparticles of native selenium were detected in weathered sideritic mudstones of the Veřovice Formation (Aptian) of the Silesian Unit (Outer Western Carpatians, NE part of the Czech Republic). This mineral forms small needle-like crystals with lengths of up to 20 μm, and is confined to fissures in sideritic mudstones covered by goethite or rarely also by hydrated Mn-oxide minerals. The oxidized sideritic mudstones show zonal structure and resemble the initial stage of the formation of the so-called rattle stones. From the superposition of phase diagrams of selenium and Fe-oxyhydroxides, Fe apparently occupies a large field in which Se(0) and FeOOH and/or Fe(OH)3 can co-exist. The reduction of selenites or selenates by pyrite or by any other phase, capable of charge transfer, is likely to have been responsible for the formation of microparticles of native selenium. The crucial factor controlling the origin of these particles is the extremely low solubility of Se(0). The source of Se is not obvious. It can be released in trace concentrations during the weathering of pyrite. Sediments of the Veřovice Formation correspond to the anoxic event OAE1b and accumulation of siderophile elements in similar sediments is very probable. A probable mechanism for the origin of Se microcrystals is gradual crystallization from solution.

Native selenium as a byproduct of microbial oxidation of distorted pyrite crystals: the first occurrence in the Carpathians

Acicular crystals of native selenium up to 30 μm long occur together with barite on the surface of goethite partial pseudomorphs after millimeter-sized pseudotetragonal-prismatic pyrite crystals in calcite veins that cross-cut Senonian sandstones of the Silesian Nappe in the western Polish Outer Carpathians. Native selenium originated from selenium apparently released during bacteria-induced oxidation of pyrite at neutral or near-neutral pH conditions. Oxidizing bacteria preferentially colonized {100} faces of pyrite relative {111} faces.

Synthesis, Characterization and Evaluation of Zinc-Amides as Potential Dopant Sources for ZnSe OMVPE

ABSTRACTCompounds of the general forms Zn[N(R)2]2, Zn(N(R)(R')2] and Zn{[N(R)2][N(R')2]} have been prepared, these new compositions have been characterized by multinuclear NMR, GC/MS, FTIR, elemental analysis and single crystal x-ray diffraction, and they have been evaluated for their potentialto serve as “designer dopants” in the epitaxial growth of p-type ZnSe. Retention of the Zn-N bond during deposition should insure selective location of the nitrogen atom on the native selenium lattice site. Precursor vapor pressures, vapor phase decomposition mechanisms, and thin film properties are presented. Results from materials characterization by XRD, SIMS, PL, Raman and SEM are presented in the context of evaluating dopantlevel.