Thermovoltage in scanning tunneling microscopy

If the sample and the tip of a scanning tunneling microscope are at different temperatures a `thermovoltageʹ arises which is superposed on the external bias. Although it is small it can be measured with high accuracy applying scanning tunneling potentiometry. Since it depends on the details of the electronic states contributing to the tunneling process it provides useful information, e.g. on interference patterns of electronic surface states, on the distribution of different chemical elements on a surface etc. Results on homogeneous as well as on inhomogeneous metallic surfaces will be shown. The correlation between the thermovoltage and the electronic states will be discussed for the Si(111) 7×7 surface.