Defect Pinning in Monolayer Films by Highly Controlled Graphite Defects: Molecule Corrals

Abstract

Domain boundaries in a self-assembled molecular film are immobilized or pinned for study with scanning tunneling microscopy using monolayer deep etch pits in the basal plane of graphite (molecule corrals). Molecule corrals are shown to provide a highly controllable method of generating substrate defects to study pinning in monolayer films. Diffusion of pinned boundaries is found to take place via discreet motions involving small groups of molecules. A model for grain boundary motion is developed and used to analyze two types ofboundaries : those separating molecular domains with identical structures and those separating domains with different structures. When the structures are different, a one-dimensional pressure is exerted on the boundary by the structure with the lower free energy, causing it to distort. By measuring the dependence of this distortion on the distance between pinning centers, we extract quantitative information about certain energetic properties of the film.