Ballistic electron emission microscopy (BEEM) measurements have been made,
as a function of Au thickness, of Au(111)/Si(111) and Au(111)/Si(100) inter
faces, fabricated and studied in ultrahigh vacuum. The measured ballistic e
lectron attenuation length for Au is in excess of 230 Angstrom for both Si
orientations. In accord with metal band-structure considerations, the BEEM
current is consistently more than 50% higher for Si(111) than for Si(100) s
ubstrates. Surface electron states have been observed on atomically flat su
rfaces of the Au grains, and their presence correlated with a spatially var
ying BEEM current. [S0163-1829(99)51304-0].