The STM intrinsically images electronic properties rather than atomic structure of surfaces. Scanning Tunneling Spectroscopy is a method that uses
the information contained in the I(V) curve of the tunneling contact to derive specific electronic states or excitations at surfaces. Examples are the scattering of electrons that become apparent
in standing electron waves or the excitation of phonons by the tunneling electrons.
The method still needs a lot of fundamental work to be done. When applied to unknown systems it is sometimes hard to extract reliable information. This is mainly due to the specific properties of the tunneling tips but can also be due to special unexpected line shapes arising from the tunneling effect itself. With our experiments conducted on a large variety of surfaces we collect a large data base with the aim of controlling most if not all relevant parameters.