In order to determine how the sample density of states is reflected in topographic images obtained in the scanning tunneling microscope, the apparent size of an adsorbed atom is studied as a function of bias voltage for several different atoms. This quantity is found to reflect state-density features that lie well above the Fermi level, but it shows a striking absence of any trace of $d$-state peaks below the Fermi level.

• Received 23 October 1986

DOI:https://doi.org/10.1103/PhysRevLett.58.45