DEFECT PINNING IN MONOLAYER FILMS BY HIGHLY CONTROLLED GRAPHITE DEFECTS - MOLECULE CORRALS

Domain boundaries in a self-assembled molecular film are immobilized o r ''pinned'' for study with scanning tunneling microscopy using monola yer 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 mot ions involving small groups of molecules. A model for grain boundary m otion is developed and used to analyze two types of boundaries: those separating molecular domains with identical structures and those separ ating domains with different structures. When the structures are diffe rent, a ''one-dimensional pressure'' is exerted on the boundary by the structure with the lower free energy, causing it to distort. By measu ring the dependence of this distortion on the distance between pinning centers, we extract quantitative information about certain energetic properties of the film.