Date of Award

7-1-2014

Degree Type

Thesis

University or Center

Clark Atlanta University(CAU)

Degree Name

M.S.

Department

Physics

First Advisor

Dr. Xiao-Oian Wang

Second Advisor

Dr. Alfred Z. Msezane

Third Advisor

Dr. Zhifan Chen

Abstract

We employ a global optimization method to predict two-dimensional (2D) nanostructures through the particle swarm optimization (PSO) algorithm. By performing PSO simulations, we predict new stable structures of boron monolayer sheets for a wide range of boron concentrations. We present a new class of boron sheets, composed of triangular and hexagonal motifs, which are more likely to be the precursors of boron nanotubes. We describe a simple and clear picture of electronic bonding in boron sheets and highlight the importance of three-center bonding and its competition with two-center bonding, which can also explain the stability of recently discovered boron monolayer sheets.

The graphene-based electronics is an intriguing prospective for replacing silicon for next-generation of transistors. Practical application of graphene based materials requests a band gap. We present results from first-principles density-function calculation for semiconducting graphene based on nitrogen-seeded epitaxial graphene. A small fraction of covalently-bonded nitrogen leads to a band gap opening in epitaxial graphene and a transition from a semi metallic to a semiconducting state. The induced gap is shown to be attributed to the modification of the 1t conjugation of epitaxial graphene. The resulting nitrogen-seeded graphene opens a band gap about 0.8 eV, in good agreement with experimental observations.

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