Atomic-Scale Variations of the Tunneling Distribution in a Scanning Tunneling Microscope Observed by Ballistic-Electron-Emission Microscopy

In situ ballistic-electron-emission microscopy (BEEM) and spectroscopy (BEES) have been performed at 77 K on epitaxial CoS${\mathrm{i}}_2$/Si (100) and (111). BEEM images reflect the atomic-scale periodicity of the surface topography. Atomically resolved BEES is correlated with tunneling spectroscopy and the apparent tunneling barrier height. The effect is due to variations of the energy distribution of the tunneling electrons on an atomic scale.