Tn situ ballistic-electron-emission microscopy (BEEM) and scanning tun
neling spectroscopy have been performed at 77 K on CoSi2/Si(111) films
grown by molecular beam epitaxy. Different atomic surface structures
induce significant variations of the BEEM current. For the first time
periodic surface structures could be imaged at atomic resolution by BE
EM. This surface effect is explained by the energy distribution of the
injected electrons, which is influenced by surface-induced variations
of the tunneling barrier height. Quantum size effects in the local de
nsity of states can be correlated with subtle features in the BEEM spe
ctra.