SCANNING-TUNNELING-MICROSCOPY INVESTIGATION OF THE P(2X2) AND C(2X2) OVERLAYERS OF S ON NI(100)

The p(2X2) and c(2X2) sulfur overlayers on Ni(100), and the clean Ni(100) surface itself, have been imaged in an ultrahigh-vacuum scanning tunneling microscope and topographic and spectroscopic information was obtained from all three surfaces. These data are compared to theoretical calculations of the surfaces derived using the Green's-function method of Pendry, Pretre, and Krutzen, where the sample Green's function is calculated in a multiple-scattering formalism based on the layer Korringa-Kohn-Rostoker method. Our simple model has proved reasonably successful in predicting the corrugation heights observed on the sulfated nickel surfaces, and confirmed the fact that the difference in height observed between the p(2 X 2) and the c(2 X 2) phases is electronic in origin. It is also proposed that the enhanced corrugation observed on the clean nickel surface may in part be attributable to the presence of a magnetic surface state immediately below the Fermi energy. Attempts to model the I-V and dI/dV spectroscopy curves proved less successful but it is believed that this was largely attributable to the approximations used in the present calculation.