Scanning-tunneling-microscopy investigation of the Ni(100)-p(2×2)C surface

Abstract

The scanning-tunneling-microscopy (STM) image of the Ni(100)-p(2×2)C surface has been investigated both experimentally and theoretically. The well-known p4g reconstruction of this surface could not be observed in the STM. Atomic resolution could be achieved only for positive or very small negative sample bias voltage, and even then the Ni atoms were not visible. Surprisingly, for a metallic surface, the corrugation could be observed for a bias voltage of up to +2 V. These observations are explained theoretically by the presence of a surface band gap above the Fermi energy, which causes the tip to come closer for positive voltage than for negative voltage. A model calculation reproduces most of the observations: the absence of the p4g reconstruction in the image, the asymmetry in the I(V) spectrum, and the fact that the corrugation is small, only present at positive voltage and observable up to large voltage. However, the calculated STM image show the C atoms as depressions while in the experiment, a small protrusion is observed. A more elaborate investigation would be necessary to resolve this discrepancy.