Scanning tunneling microscopy (STM) studies have demonstrated that mon
olayer-deep, flat-bottomed, circular etch pits can be grown on highly
ordered pyrolytic graphite by high-temperature etching in the presence
of oxygen. In this work, these graphite etch pits are used as ''molec
ule corrals'' to isolate ensembles of molecules for study by STM. The
nucleation of self-assembled molecular films in the corrals took place
by nucleation events separate from those leading to self-assembly on
the surrounding terrace and allowed the measurement of the nucleation
rate constant in the corrals. The dependence of the nucleation rate fo
r self-assembly on pit size shows that nucleation occurs at open terra
ce sites and that step edges (that is, the corral's perimeter) and con
finement inhibit film growth.