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 liquidsolid 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.

Scanning Tunneling Microscopy Images of Alkane Derivatives on Graphite: Role of Electronic Effects

“…A survey of papers shows that the image of the arms is often asymmetric. 1,[15][16][17][18][19][20][21][22][23][24][25][26] Two examples from our experiments illustrate this effect in Figure 1. The alternating rows of bright and dark spots evidently correspond Image has dimensions of 7.5 nm × 7.5 nm and was recorded at a bias of -1.5 V, setpoint current of 300 pA, and a scan rate of 6.78 Hz.…”

Ultra-high vacuum scanning tunneling microscopy and theoretical studies of 1-halohexane monolayers on graphite

“…However, many subtle modifications of the self-assembled structures have been observed, depending on alkane functionalization and chain length (3, 6, 10-12, 15, 17-19, 28, 35, 36, 41, 46). Specific headgroup interactions (e.g., hydrogen bonding and electrostatic forces) (11,12,17,19,28,41) and geometric subtleties (e.g., odd vs. even chain length) (31, 32, 36) also can have a profound influence on the self-assembly. The resulting set of interactions creates competing constraints, which are evident in the calculated and measured adsorption energies (47).…”

Biomimetic polymers of plant cutin: an approach from molecular modeling

“…This fact allows us to assume reasonably that the adsorption occurs preferentially by the carboxylic group. Furthermore, previous STM studies on selfassembly of fatty hydroxyl acids on HPOG have shown that -COOH•••HOOC-interaction is stronger than -COOH•••HO- [17][18]. This observation may cause competition between head to head (-COOH•••HOOC-) and head to mica bonding and reverse orientation (bonded to mica through the hydroxyl group) of a fraction of molecules in the self-assembled system.…”