Electronic structure and tunneling current for chemisorbed atoms

We discuss the tunneling current density in the vacuum region between two planar metal electrodes, one of which has an atom chemisorbed on its surface. The relation of this current distribution to the electronic structure of the adatom is analyzed. The study of this model problem leads to a better understanding of important aspects of the current flow in the scanning tunneling microscope. The emphasis of this work is not so much on the question of resolution discussed in other theoretical studies as on the characteristic signatures of chemically different atoms.