Shevlin, Stephen Andrew; (2001) A theoretical study of the atomic and electronic structures of three prospective atomic scale wire system. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

The structural and electronic properties of several candidate atomic scale wires are analysed. Three candidates are studied: the trans-polyacetylene molecule, the silicon line on the (001) face of cubic silicon carbide (the (nx2) series of reconstructions) and the indium chain on the (111) face of silicon carbide (the (4x1) reconstruction). We use the polyacetylene molecule as a test-bed for the techniques that we use to calculate transport properties in an empirically based tight-binding Hamiltonian (the SSH Hamiltonian). We calculate the transport properties of wires that show evidence of a strong coupling of the electronic degrees of freedom to the phonon degrees of freedom (Peierls distorted wires). The structure of the (nx2) series of silicon lines (composed of the (3x2) reconstruction which forms the line and the c(4x2) reconstruction which forms the surface the line resides on) axe modelled in a supercell geometry using ab initio plane-wave calculations in the Local-Density-Approximation and an ab initio Density Functional Theory based tight-binding technique. We found that the thermodynamically favoured model for the (3x2) reconstruction was the Two-Adlayer-Asymmetric-Dimer Model (with IML of Si adatoms) and the favoured model for the c(4x2) reconstruction is the Additional-Dimer- Row-Model (with 0.5ML of Si adatoms). In the tight-binding approximation the line was found to undergo a Peierls-like transition and holes are observed to form polaron-like defects. The transport properties of the line are also calculated. Finally we find which of the two models of the Si(111)-(4x1)-In reconstruction is thermodynamically favoured in a supercell geometry. We use ab initio plane wave techniques in the Local-Density-Approximation, and calculate and compare the electronic structure of the two models with respect to the characteristic energies for electron dispersion along and across the chain structures. We also consider the effects of electronic structure on the in-plane transport properties of the indium lines.

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