EMPTY STATES OF THE NI/SI(111)7X7 INTERFACE

Up to now, the evolution of the empty states of the metal/silicon interface has received only little attention. It is however necessary to investigate both occupied and unoccupied states in order to get a complete picture of the interface electronic structure. We present a combined X-ray photoemission (XPS)/bremstrahlung isochromat spectroscopy (BIS) study of the Ni/Si(111)7 x 7 interface formation at room temperature. Valence and conduction band densities of states, as well as metal and Si core levels, were recorded for coverages (theta) ranging from 1 to 100 ML. Above 1 ML, the data reveal an intermixed phase. Its composition is close to Ni2Si at low coverage (theta = 3-6 ML), as testified by both XPS and BIS spectra. (For higher coverages, we found evidence for composition changes induced by the e-beam.) In the 1 ML range the situation seems to be more complex, with possible specific empty interface states.