Scanning-tunneling-microscopy observation of adsorbate-induced two-dimensional step faceting on the S/Cu(11 1 1) surface

Two superstructures of adsorbed sulfur coexisting on the stepped Cu(11 1 1) surface are identified by scanning tunneling microscopy. A p(2×{}2) and a c(4×{}2) structures are atomically resolved and their interaction with the steps investigated. The direction taken by a step edge is found to be strongly correlated with the sulfur arrangement on the adjacent terraces. The origin of this two-dimensional faceting phenomenon is discussed.