Variation of the thermovoltage across a vacuum tunneling barrier: Copper islands on Ag(111)

If there is a temperature difference between tip and sample of a scanning tunneling microscope a thermovoltage is generated which is very sensitive to the electronic states involved in the tunneling process. This has been used, e.g., to distinguish between different metals of a heterogeneous metallic surface. To demonstrate the capability of this method it has been applied to copper islands on a Ag(111) surface. Knowing the thermopower for chemically homogeneous silver and copper surfaces of −45 and −15 μV/K, respectively, islands of copper on the silver substrate can be well identified with a lateral resolution of 1 nm.