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 104–105 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〈 Rg〉≈ 0. 9 obtained from an analysis of the bulk resistivity data taken over the temperature range 4. 2 K< T< 300 K.

Charge transport in thin metal films is not uniform on the nanometer scale and is accompanied by strong inhomogeneities in the field and current density near localized scatterers such as grain boundaries (GBs) and defects. Conventional theories of transport ignore these spatial variations and consider the averaged field. In this average picture all details of the charge transport in the conductor are parameterized by a single parameter, namely the mean free path of the charge carrier. This describes the correct picture in a bulk system but as the sample dimension decreases it becomes necessary to measure the relevant quantities on a nanometer scale and the deviations of the local fields and potentials from the average values become significant. The significance of the influence of localized scatterers was first recognized and investigated theoretically by Landauer [1]. He pointed out that the microscopic dipole field that results from the asymmetry of the electron scattering at a point defect is the ultimate source of the residual resistivity. Work of Landauer and subsequent developments [2, 3] showed the equivalence of the residual resistivity dipole approach and the more conventional Boltzmann transport approach. Understanding the exact microscopic nature of the scattering process is important in order to gain insight into fundamental questions like