Scanning tunneling microscopy study of the Re(0001) surface passivated by one-half a monolayer of sulfur in an atmospheric environment

The Re(0001) surface can be passivated by the adsorption of 50% of a monolayer of sulfur. The structure is ordered as shown by a 2((3)1/2×(3)1/2)R30° low-energy electron diffraction pattern. Exposure to air does not modify the surface composition nor the structure. We have obtained STM images of this surface in an atmospheric environment. Large and atomically flat domains have been observed, together with areas composed of multiple steps of various heights. Images of the local barrier height show a significant decrease near the steps, as expected. Higher resolution images recorded in this mode exhibit atomiclike features which are tentatively assigned to sulfur atoms. Short-range order with distances of the order of the superlattice parameter could be detected. No long-range order, however, has been observed.