Scanning Tunneling Microscopy Observation of Electron Standing Waves on Au(111) Film with a Superconducting Tip

Using low-temperature scanning tunneling microscopy (LT-STM) with normal metal tungsten tips and superconducting niobium tips, we have observed in real space the formation of electron standing waves by the scattering of surface state electrons at surface defects and step edges on a Au (111) surface. From constant-current STM images of the Au(111) surface observed at low temperature with both tips, we have observed the strong effects of tip materials on the interference of the two-dimensional (2D) electron waves. Compared with using tungsten tips, enhanced electron standing waves have been clearly observed using niobium tips at 4.2 K. A simple model has been proposed to explain these observed effects.