AN STM STUDY OF CARBON-INDUCED STRUCTURES ON NI(111) - EVIDENCE FOR A CARBIDIC-PHASE CLOCK RECONSTRUCTION

The interaction of carbon with Ni(111) has been studied by scanning tunnelling microscopy. In the carbidic phase, formed by exposing the surface to ethylene at similar to 500 K, the surface atoms are found to rearrange into an almost square surface mesh with a ''clock'' reconstruction which is quite similar to that observed for carbon on the Ni(100) surface. The square surface mesh is argued to be incommensurate although a \(7)(2) (2)(7)\ cell is close to coincidence. The implications of the observed clock reconstruction for a possible structure sensitivity of the methanation reaction on Ni are discussed. Exposure of the Ni(111) surface to ethylene at higher temperatures leads to formation of single or multiple layers of graphite.