Theoretical calculations of STM data on Ni(100)-C for various concentrations of carbon

Abstract

The presence of adsorbed carbon on a Ni(100) surface in the carbidic phase leads to a reduction of the local density of states at the surrounding Ni atoms, for energies around the Fermi energy. This effect influences the way in which this surface is imaged in scanning tunneling microscopy (STM). We study theoretically how the tip distance changes as the carbon coverage increases from virtually single carbon atoms to the saturated 1/2 monolayer case. As the concentration of carbon in the surface grows, the number of available states for tunneling decreases and the STM tip comes closer. At low coverage, the effect of the C on the surrounding electronic structure is restricted to the nearest neighbour Ni atoms. These results are in qualitative agreement with recent observations by Schmid et al. [Surface Science Letters 294 (1993) L952].