Degree Type

Dissertation

Date of Award

2012

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Patricia A. Thiel

Abstract

Electronegative adsorbates such as sulfur, oxygen, and chlorine can strongly affect metal transport on surfaces of coinage metals. Hence, they can affect processes of self-assembly (including nucleation and growth) and coarsening of metal nanostructures. These processes are important to many applications that exploit nanoscale particles of these metals, such as surface enhanced Raman scattering and catalysis. To understand how and why the adsorbate affects metal transport, it is necessary to first understand the basic interaction of the adsorbate with the metal surface.

Both adsorbed oxygen and sulfur reconstruct coinage metal surfaces and enhance metal island coarsening, under certain conditions. We have found that atomic S interacts strongly with Ag, inducing surface reconstruction and accelerating Ag island coarsening or sintering. In other words, S destabilizes the Ag surface and nanostructures. On the other hand, molecular H2S interacts weakly with the Ag surface at low temperature, forming only adsorbate structures. The relative effect of O or S depends on the geometry of the substrate, in terms of the structures that appear and the rate of metal island coarsening. Sulfur reconstructs both the Ag(111) and Ag(100) surfaces resulting in long-range ordered phases composed of both S and Ag. Sulfur accelerates Ag island coarsening by 1 order of magnitude on Ag(100) and by 3 or more orders of magnitude on Ag(111). Low coverages of oxygen enhance Ag island coarsening on Ag(100), but has no effect on Ag islands on Ag(110). In addition, the nature of the chalcogen (O vs S) seems to have larger influence on surface structures than does the nature of the metal (Cu vs Ag).

In this thesis, we describe work in which we have expanded the understanding of fundamental processes that govern nanostructure formation and dynamics by employing single crystals in ultra-high vacuum (UHV) and surface analytical techniques, including variable and low temperature scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED), in addition to density functional theory (DFT) calculations. This research may identify a commonality in chalcogen induced mass transport on the coinage metal surfaces and ultimately lead to controlled production of nanoclusters.

Copyright Owner

Selena M Russell

Language

en

File Format

application/pdf

File Size

418 pages

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