Scanning tunneling microscopy and (scanning) tunneling spectroscopy on stepped Ni(111)/H

Abstract

Topographic and electronic properties of both the (111) flat surface and atomic steps of nickel have been measured with scanning tunneling microscopy (STM) and (scanning) tunneling spectroscopy in UHV. Micrographs of the (111) plane show a hexagonal pattern with a dimension of two times the unit structure and a corrugation of 1 Å which increases towards a step. This suggests a p(2 × 2)2H monolayer, induced by the high partial pressure of hydrogen. Micrographs of atomic steps show protrusions of 1–3 Å at the corners of the steps. Several explanations are discussed. Spectroscopic images of these areas show the same hexagonal pattern on the (111) surface and indicate an increase in the density of states at the adsorption sites and at the step edges. dI dV versus V spectra were also recorded. Various peaks in the density of states, at different energies below 1 eV above E F showed up, their intensity strongly dependent on the lateral position of the tip. These local changes in the density of states might indicate the presence of adsorbate-induced surface states.