BALLISTIC-ELECTRON-EMISSION MICROSCOPY STUDY OF THE AU SI(111)7X7 ANDAU/CAF2/SI(111)7X7 INTERFACES/

Ballistic-electron emission microscopy (BEEM) has been performed on Au /n-Si(111)7 x 7 and Au/CaF2/n-Si(111)7 x 7 in UHV. In both cases, the topography of the Au surface is characterized by almost-equal-to 2.5 a ngstrom height terraces, stacked in several stages, with rounded shape s for Au/Si, and hexagonal shapes for Au/CaF2/Si. BEEM up to tip volta ges of 8 V on Au/Si is not altering the ballistic transmissivity, in c ontrast to previous work on Au/Si interfaces which involved chemical p reparations of the Si surfaces. The shape of the BEEM spectra on Au/Ca F2/Si depends on spectral features of the density of states of the CaF 2 thin film.