Core-level photoemission investigations of the CDTE(100) and INSB(100) surface and interfacial structures

Photoemission techniques, utilizing a synchrotron light source, were used to analyze the clean (100) surfaces of the zinc-blende semiconductor materials CdTe and InSb. Several interfacial systems involving the surfaces of these materials were also studied, including the CdTe(lOO)-Ag interface, the CdTe(lOO)-Sb system, and the InSb(lOO)-Sn interface. High-energy electron diffraction was also employed to acquire information about of surface structure. A one-domain (2xl) structure was observed for the CdTe(lOO) surface. Analysis of photoemission spectra of the Cd 4d core level for this surface structure revealed two components resulting from Cd surface atoms. The total intensity of these components accounts for a full monolayer of Cd atoms on the surface. A structural model is discussed commensurate with these results. Photoemission spectra of the Cd and Te 4d core levels indicate that Ag or Sb deposited on the CdTe(l00)-(2xl) surface at room temperature do not bound strongly to the surface Cd atoms. The room temperature growth characteristics for these two elements on the CdTe(lOO)-(2xl) are discussed. The growth at elevated substrate temperatures was also studied for Sb deposition. The InSb(lOO) surface differed from the CdTe(lOO) surface. Using molecular beam epitaxy, several structures could be generated for the InSb(lOO) surface, including a c(8x2), a c(4x4), an asymmetric (lx3), a symmetric (lx3), and a (lxl). Analysis of photoemission intensities and line shapes indicates that the c(4x4) surface is terminated with 1-3/4 monolayers of Sb atoms. The c(8x2) surface is found to be terminated with 3/4 monolayer of In atoms. Structural models for both of these surfaces are proposed based upon the photoemission results and upon models of the similar GaAs(lOO) structures. The room temperature growth characteristics of grey Sn on the lnSb(lOO)-c(4x4) and InSb(l00)-c(8x2) surfaces were studied with photoemission. The discontinuity in the valence band maximum for this semiconductor heterojunction system is measured to be 0.40 eV, independent of the starting surface structure and stoichiometry. This result is reconciled with theoretical predictions for heterostructure behavior.

Carbon-carbon bond formation methods for the preparation of shape-persistent architectures

Carbon-rich, conjugated organic scaffolding is a popular basis for functional materials, especially for electronic and photonic applications. However, synthetic methods for generating these types of materials lack diversity and, in many cases, efficiency; the insistence of investigators focusing on the properties of the end product, rather than the process in which it was created, has led to the current state of the relatively homogeneous synthetic chemistry of functional organic materials. Because of this, there is plenty of room for improvement at the most basic level. Problems endemic to the preparation of carbon-rich scaffolding can, in many cases, be solved with modern advances in synthetic methodology. We seek to apply this synthesis-focused paradigm to solve problems in the preparation of carbon-rich scaffolds. Herein, the development and utilization of three methodologies: iridium-catalyzed arene C-H borylation; zinc- mediated alkynylations; and Lewis acid promoted Mo nitride-alkyne metathesis, are presented as improvements for the preparation of carbon-rich architectures. In addition, X-ray crystallographic analysis of two classes of compounds are presented. First, an analysis of carbazole-containing arylene ethynylene macrocycles showcases the significance of alkyl chain identity on solid-state morphology. Second, a class of rigid zwitterionic metal-organic compounds display an unusual propensity to crystallize in the absence of inversion symmetry. Hirshfeld surface analysis of these crystalline materials demonstrates that subtle intermolecular interactions are responsible for the overall packing motifs in this class of compounds.