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(1 00) surface itself, have been imaged in an ultrahigh-vacuum scanning t unneling microscope and topographic and spectroscopic information was obtained from all three surfaces. These data are compared to theoretic al calculations of the surfaces derived using the Green's-function met hod of Pendry, Pretre, and Krutzen, where the sample Green's function is calculated in a multiple-scattering formalism based on the layer Ko rringa-Kohn-Rostoker method. Our simple model has proved reasonably su ccessful in predicting the corrugation heights observed on the sulfate d nickel surfaces, and confirmed the fact that the difference in heigh t 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 presenc e of a magnetic surface state immediately below the Fermi energy. Atte mpts to model the I-V and dI/dV spectroscopy curves proved less succes sful but it is believed that this was largely attributable to the appr oximations used in the present calculation.