Self-assembly of polystyrene spheres guided by pattered InP substrates has been studied using atomic force microscopy (AFM). Using photoresist stripes and posts, 1-D and 2-D colloidal particle structures were found to preferentially nucleate at the step edges of the photoresist. The dangling bonds created by photocleavage of molecular bonds at the steps are identified as playing a major role in attracting the colloidal suspension.