A study of the spatial variation of electric field in highly resistivemetal films by scanning tunneling potentiometry

Electronic transport in highly resistive (but metallic) thin platinum films (≈ 10 nm) deposited by electronbeam evaporation has been studied by scanning tunneling microscopy and scanning tunneling potentiometry (STP). The films have an average grain size of ≈ 10 nm. On this scale transport through the film is very inhomogeneous. Scattering from grain boundaries (GBs) results in large variations in the local potential resulting in fields as high as 10 ⁴-10⁵ V/cm located near the GB. The reflection coefficient Rg of electrons at a GB has values between 0.5-0.7 as determined from the STP data. This can be compared to an average [R_g ]≈ 0:9 obtained from an analysis of the bulk resistivity data taken over the temperature range 4:2K<T<300 K.