THERMOVOLTAGE ACROSS A VACUUM BARRIER INVESTIGATED BY SCANNING-TUNNELING-MICROSCOPY - IMAGING OF STANDING ELECTRON WAVES

The thermovoltage of a vacuum barrier has been studied by heating the tip of a scanning tunneling microscope. It is extremely sensitive to m inor variations of the electronic structure of the sample. As an examp le an electronic surface state on Cu(lll) has been investigated. The r eflection at step edges and other defects leads to an interference pat tern modulating the thermovoltage by up to 2 mu V/K. The findings are well described by a numerical calculation which confirms that the latt er differs from a map of the electronic density of states.