ATOMIC-SCALE VARIATIONS OF THE STM TUNNELING DISTRIBUTION OBSERVED BYBALLISTIC-ELECTRON-EMISSION MICROSCOPY

In this work we present an experimental method which allows to investi gate experimentally the energy and momentum distribution of the carrie rs which are injected by an STM lip into a metallic sample. We perform in situ ballistic-electron-emission microscopy (BEEM) and spectroscop y (8EES) simultaneously with atomic-resolution STM. The experiments ar e done at 77K on epitaxial CoSi2 films on Si(111) and Si(100). The pot ential of the method to improve on our understanding of tunneling on a n atomic scale will be illustrated by two important findings: For the first time we have directly observed variations of the tunneling distr ibution on an atomic scale. The BEEM data also give evidence for a pro nounced forward focussing of the angular distribution of the tunneling electrons.