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.