Theoretical investigations of gold nanostructures

Toto, Nicola (2007). Theoretical investigations of gold nanostructures. University of Birmingham. Ph.D.

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Abstract

The research described in this thesis has focused on the properties of some nanometre scale systems mainly composed of gold. These systems have attracted a considerable amount of attention within the scientific community due to their vast range of applicability and their profound physical interest. Throughout this work, a semiempirical many-body potential has been used to model the atomic interaction in gold.

The first part of the thesis reports a study carried out on gold nanoclusters of between 53 and 80 atoms. The structures of the clusters have been globally optimised by using a genetic algorithm. The potential energy surface generated by the semiempirical potential has thus been sampled by the algorithm in a search for the global minimum. Decahedral structures have been found to predominate in the size range investigated.

The second part of the thesis is concerned with the study of the nanoscale finger pattern induced on a stepped Au(111) surface when scanning with a scanning tunneling microscope. An atomistic model of the system implemented by a Kinetic Monte Carlo algorithm has been set up which proved that the phenomenon is a diffusion kinetic instability triggered by the effect of the scanning tunneling microscope tip.

A thorough study of the kinetics of diffusion on Au(111) has made it possible to improve the model, thus reaching a satisfactory agreement between the experimental and simulated data. It has been found that the diffusion barriers for certain processes, such as step, corner, and kink diffusion, are important in determining the shape of the fingers. In particular it has been observed that the finger width can be finely tuned simply by varying the height of the barrier for diffusion on the bare surface. Finally, the model has been further refined by introducing the effect of the microscope tip on the surface. This is the most realistic atomistic simulation of such a system performed so far.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):