How the down step edges influence formation of the 7x7 structure of Si(111)

A surface that has wide terraces was fabricated by utilizing the step bunching phenomenon to study the effect of the down step edges on the formation of the 7x7 reconstruction. The surface with wide terraces was quenched through the 1x1-7x7 phase transition, freezing the formation process of the 7x7 reconstruction. On this surface, it became possible to investigate the influence of the down step edges on the formation of the 7x7 reconstruction because the influence of the upper step edge, which is located at the other side of the terrace, did not reach to the down step edge. A considerable decrease in the existence probability of the 7x7 reconstruction was observed near the down step edges. This decrease cannot explained by electromigration and steps advancement caused by the difference in adatom density between the 7x7 and disordered structure. Instead, we propose that the decrease in existence probability at down step edges is well explained by a simple topographic model assuming corner holes as the growth nuclei of the 7x7 domains.