STM Investigations of Organic Molecules Physisorbed at the Liquid−Solid Interface

Abstract

Investigations of long-chain hydrocarbon and substituted hydrocarbon materials physisorbed at the liquid−solid interface have provided a particularly fruitful area of investigation for the scanning tunneling microscope (STM). Studies of this kind provide considerable information concerning surface−adsorbate interactions, the nature of the STM contrast mechanism for molecules adsorbed on surfaces, the effect of the chemical nature of the liquid solvent on the rearrangement and bonding of adsorbates, and the role played by the underlying structure of the surface itself (defects, domains, etc.) in determining the molecular arrangement of these adsorbates. All of these studies are aimed at the elucidation and control of surface and adsorbate structures and their relationship to the electronic and chemical properties of materials. The successful imaging of numerous physisorbed organic films at the solution−solid interface has demonstrated that the STM is sensitive enough to differentiate chemical functional groups within these films, but participation of molecular states in the tunneling process for many organic thin-film insulators remains a topic of vigorous discussion. Simulations of the self-assembly of long-chain molecules at the liquid−solid interface provide a microscopic, molecular scale view of the dynamic processes that lead to the kinds of structures observed in STM studies of interfaces. These model molecular dynamics simulations offer useful clues to the physical and chemical driving forces that control molecular assembly. This paper reviews the progress and interconnections among the areas of interfacial adsorbate images, imaging mechanisms, and dynamical processes at the liquid−solid interface.