Thesis (Ph. D.)--University of Oregon, 2003. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 153-163). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (Ph. D.)--University of Delaware, 2009. / Principal faculty advisor: Svilen Bobev, Dept. of Chemistry and Biochemistry. Includes bibliographical references.

Thesis (Ph. D.)--University of North Texas, Dec., 2009. / Title from title page display. Includes bibliographical references.

Thesis (Ph. D.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on June 29, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Chemistry, University of Alberta." Includes bibliographical references.

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This thesis focuses on the synthesis, structures, and physical properties of ternary rare-earth antimonides and germanides. These ternary compounds exhibit diverse polyanionic substructures with classical and non-classical Sb–Sb bonding, Ge–Ge bonding, or both. The Zintl-Klemm concept and band structure calculations were applied to understand their structures and bonding. Electrical resistivities and magnetic properties were measured for these compounds. The compounds RE2Ti7Sb12 (RE = La–Nd) and RE2Ti11–xSb14+x (RE = Sm, Gd, Tb, Yb), which were synthesized by arc-melting, adopt different structures depending on the size of the RE atoms. Both consist of a complex arrangement of TiSbn polyhedra, linked to form a 3D framework with large cavities in which the RE atoms reside. Hypervalent Sb–Sb bonds are manifested in disordered Sb fragments in RE2Ti7Sb12, and 1D linear chains, zig-zag chains, and pairs in RE2Ti11–xSb14+x. A series of compounds, RECrGe3 (RE = La–Nd, Sm), was synthesized by the Sn-flux method. They adopt a hexagonal perovskite structure type, in which chains of face-sharing Cr-centred octahedra are linked by triangular Ge3 clusters. These unusual single-bonded Ge3 substructures can be rationalized simply by the Zintl-Klemm concept. Electrical resistivity measurements show metallic behaviour with prominent transitions coincident with ferromagnetic transitions (Tc ranging from 62 to 155 K) found in magnetic measurements. Band structure calculations show the presence of a narrow, partially filled band with high DOS at Ef, in agreement with the observation that LaCrSb3 is an itinerant ferromagnet. With a different number of d-electrons in the M site, the isostructural REVGe3 compounds exhibit antiferromagnetic behaviour. The doped quaternary compounds LaCr1-xVxGe3 and LaCr1-xMnxGe3 exhibit depressed Curie temperatures. The structures of RECrxGe2 compounds (RE = Sm, Gd–Er) are built up by inserting transition-metal atoms into the square pyramidal sites of a hypothetical “REGe2” host structure (ZrSi2-type). The presence of extensive anionic Ge substructures in the form of 1D zigzag chains and 2D square sheets can be explained by the Zintl-Klemm concept. Magnetic measurements indicated antiferromagnetic ordering with low TN ranging from 3 to 17 K. Compounds involving a p-block element as the second component were prepared. In RE12Ge7–xSb21 (RE = La–Pr), a complex 3D polyanionic framework with Ge pairs, five-atom-wide Sb ribbons, and 2D Ge/Sb layers is present. The bonding exemplifies the competition of valence electron transfer from the RE atoms to metalloids with similar electronegativities. Full electron transfer from the RE atoms to the anionic substructure cannot be assumed. Magnetic measurements on Ce12Ge6.5Sb21 indicate antiferromagnetic coupling. The metal-rich compounds RE5TtxSb3–x (Tt = Si, Ge) adopt the orthorhombic beta-Yb5Sb3-type structure with a range of solid solubility between 0.9 and 1.6. They are not electron-precise and do not obey the Zintl-Klemm concept.

We present a theoretical study of the electronic structure, surface energies and work functions of orthorhombic Pt monosilicide and germanides of Pt, Ni, Y and Hf within the framework of density functional theory (DFT). Calculated work functions for the (001) surfaces of PtSi, NiGe and PtGe suggest that these metals and their alloys can be used as self-aligned contacts to p-type silicon and germanium. In addition, we also study electronic structure and calculate the Schottky-barrier height at Si(001)/PtSi(001) interface and GaAs(001)/NiPtGe(001) interfaces with different GaAs(001) and NiPtGe (001) terminations. The p-type Schottky barrier height of 0.28 eV at Si/PtSi interface is found in good agreement with predictions of a simple metal induced gap states (MIGS) theory and available experiment. This low barrier suggests PtSi as a low contact resistance junction metal for silicon CMOS technology. We identify the growth conditions necessary to stabilize this orientation. The calculated p-type Schottky barrier heights (SBH) at different GaAs/NiPtGe interfaces vary by as much as 0.18 eV around the average value of 0.5 eV. We further identify and discuss factors responsible for strong Fermi level pinning resulting in small variation in the p-SBH. We also present a theoretical study of magnetic state of [beta]-MaAs and show that it is antiferromagnetic and explain the lack of observed long-range order.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

The semiconducting silicides offer significant potential for use in optoelectronic devices. Full implementation of the materials, however, requires the ability to tailor the energy gap and band structure to permit the synthesis of heterojunctions. One promising approach is to alloy the silicides with Ge. As part of an investigation into the synthesis of semiconducting silicide heterostructures, a series of β-Fe(Si1−xGex)2 epilayer samples, with nominal alloy content in the range 0 < x < 0.15, have been prepared by molecular beam epitaxy on Si(100). I present results of the epitaxial and crystalline quality of the films, as determined by reflection high-energy electron diffraction, Rutherford backscattering spectroscopy, and double crystal x-ray diffraction, and of the band gap dependence on the alloy composition, as determined by Fourier transform infrared spectroscopy. A reduction in band gap was observed with increasing Ge content, in agreement with previous theoretical predictions. However Ge segregation was also observed in β-Fe(Si1−xGex)2 epilayers when x > 0.04. Osmium silicide films have been grown by molecular beam epitaxy on Si(100). The silicides have been grown using e-beam evaporation sources for both Os and Si onto Si(100) substrates at varying growth rates and temperatures ranging from 600-700ºC. The resulting films have been analyzed using reflection high-energy electron diffraction, Raman spectroscopy, reflectivity measurements, in-plane and out of plane X-ray diffraction and temperature dependent magnetotransport. A change in crystalline quality is observed with an increase in Si overpressure. For a lower silicon to osmium flux ration (JSi/JOs=1.5) both OsSi2 and Os2Si3 occur, whereas with a much larger Si overpressure (JSi/JOs>4), crystalline quality is greatly increased and only a single phase, Os2Si3, is present. The out-of-plane X-ray diffraction data show that the film grows along its [4 0 2] direction, with a good crystal quality as evidenced by the small FWHM in the rocking curve. The in-plane X-ray diffraction data show growth twins with perpendicular orientation to each other.

The main focus of the present work was the Ge-rich part of the binary Ba – Ge system, in which by inspecting the behavior of the clathrate-I Ba8Ge43 under pressure, several new phases were found. The new phases in this system have the following compositions: BaGe3 (with two modifications), BaGe5, BaGe5.5 and BaGe6, therefore they are quite close in composition range: 75% - ~85% at. Ge. Concerning the conditions required for the synthesis of each phase, several combinations of temperature and pressure were employed in order to find a stability range. It was possible to establish such a formation range for all phases. In some cases two phases were found for a given conditions and in many other cases three or more phases were found to coexist. Thus, the stability range of pressure and temperature for single phase formation turned out to be very narrow. By inspecting of some structural features, for instance the interatomic distances, it is found that the average of the Ge – Ge distances change in line with the composition, i.e. the shorter contacts belong to BaGe6 while the longer distances are present in BaGe3 (both modification). An opposite trend is observed for the calculated density of each phase (neglecting the tI32 form of BaGe3): the lower density is found for BaGe3 and the denser compound is found to be BaGe6. Of course this is not coincidence, since due to the Ge content, BaGe6 has the largest molar mass. Similarly, by examining the density as a function of the interatomic distance. In such case, the denser compound is characterized by shorter Ge – Ge contacts, while the less dense phase holds the longest Ge – Ge contacts. This is in agreement with the building motifs within each crystal structure: columns in BaGe3 (open framework) passing through layers in BaGe5, ending in a three-dimensional network (closed framework) in BaGe6.