Theoretical Investigations for Molecular Electronic Devices: Metal⁄Semiconductor Interfaces, Capacitance of atomic scale wires, and Organics on Diamond Surfaces

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Title: Theoretical Investigations for Molecular Electronic Devices: Metal⁄Semiconductor Interfaces, Capacitance of atomic scale wires, and Organics on Diamond Surfaces
Author: Odbadrakh, Khorgolkhuu
Advisors: Christopher Roland, Committee Chair
Donald W. Brenner, Committee Member
Lubos Mitas, Committee Member
Celeste Sagui, Committee Member
Abstract: This thesis presents three different investigations of materials systems, with possible applications in the area of molecular electronics. Specifically, the binding of glycine, the simplest amino acid, to diamond surfaces, and the quantum transport characteristics of two prototypical metal/semiconductor interfaces are investigated. With density functional theory based simulations, we have investigated the binding of the amino acid glycine on two of the most prominent diamond surfaces, i.e. C(100) and C(111) (2x1)- with a focus on the associated energetics, charge transfer, electronic, and structural characteristics. With regards to the dimerized C(100) surface, interaction is mostly via the amide group of the glycine molecule (both with and without H-atom abstraction) and via a cycloaddition reaction whose activation barrier has been estimated via quantum chemistry methods. In contrast, the C(111) (2x1) surface was found to be mostly inert with respect to interactions with the glycine molecule. Second part of this thesis presents theoretical investigations of electronic transport devices at atomic scale. One such device is a capacitance made of atomic wires, for which we present the results of ab initio investigation of the capacitance of Al nanowires. The systems considered include cross sectional areas for the wires: Al(100)(3x3), Al(100)(5x5), and Al(100)(7x7). First principles estimates of capacitance matrix coefficients for the systems are provided. In the second part of this thesis, we have characterized the fully self-consistent electronic properties of a prototypical metal/nanotube interface using a combined nonequilibrium Greens function and density functional theory based formalism, under different conditions of gate and bias voltages. Both carbon and boron nitride nanotubes between Al electrodes, were considered. The electronic properties of the interface are dominated both by a dipole and by metal induced gap states (MIGS) formed through the transfer of charge between the metal and the nanotube. In addition, first principles estimates - within the local density approximation - of the Schottky barrier heights are given.
Date: 2007-05-02
Degree: PhD
Discipline: Physics
URI: http://www.lib.ncsu.edu/resolver/1840.16/2982


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