Confined Friedel oscillations on Au(111) terraces probed by thermovoltage scanning tunneling microscopy

The spatial dependence of the local density of states at the Fermi level of a stepped Au(111) surface is studied by thermovoltage scanning tunneling microscopy. The periodicity of the standing waves is not given by λF/2=1.8 nm, as expected based on the band diagram of Au(111), but rather varies between 1.5 and 2.1 nm depending on the exact width of the terraces. This counterintuitive result can be understood by considering the superposition of incident and reflected electron waves, which have a periodicity of λF/2. The change in periodicity is a direct consequence of the decaying nature of the Friedel oscillations.