Employing the Au(111) surface as substrate for the synthesis of two-dimensional metal oxide and metal sulfide structures

Abstract

Novel properties of a material arise by reducing the length scale from macroscopic to the nanometer scale. This effect can be exploited to engineer materials with unique electronic, catalytic, optical and mechanical properties. The goal is to develop materials with unique properties that meet the design requirements for a particular technology. In this thesis, I will demonstrate that we are able to synthesize novel, nanocrystalline monolayer structures of MoO3, TiS2, MoS2 and AuS on Au(111). In the course of this thesis I will demonstrate that the Au(111) surface is anything but a static, inert surface. I will discuss various levels of interaction between the Au(111) surface and various adsorbates and adsorbed monolayer structures. Specifically, I will discuss the role of surface stress, the enhanced reactivity of under-coordinated Au atoms such as step edge atoms or surface atoms, and surface alloying. We will see that: the surface stress of Au(111) is modified by small amounts of adsorbed sulfur causing a lifting of the herringbone reconstruction; high sulfur coverages lead to the corrosion of Au(111) surfaces and formation of a 2D AuS phase; the step edges of Au(111) are reactive sites for decomposition of Mo(CO)6; place exchange with physical vapour deposited Mo occurs at the elbow sites of the herringbone reconstruction; Mo deposited on Au(111) at elevated temperatures leads to formation of a substitutional surface alloy; bond lengths and bond angles within nanocrystalline MoO3 structures on Au(111) are distorted to fit the symmetry of the underlying gold substrate; the orientation of triangular TiS2 nanocrystals on Au(111) is affected by a strain field interaction; Au clusters exhibit a high reactivity towards SO2 decomposition. This list of examples demonstrates that the Au(111) surface can be a very dynamic rather than a static substrate.