Possible many-body effects in scanning tunneling microscopy of molecular adsorbates

The imaging of nonconducting adsorbates has been reported for a variety of materials using scanning tunneling microscopy. These results are unexpected because of the low densities of states these adsorbates have near the Fermi level. We discuss how screening effects could couple the adsorbate states with the substrate electronic states in the vicinity of the Fermi surface and enhance the local density of states of the adsorbate states near the Fermi level.