Scanning tunneling potentiometry: The power of STM applied to electrical transport

The introduction of scanning tunneling microscopy (STM) followed by scanning tunneling spectroscopy (STS) opened experimental access to the geometric and electronic structure of materials on an atomic scale and essentially ushered in the modern field of nanoscience. The goal of scanning tunneling potentiometry (STP) is to adapt the scanning tunneling probe to measure electrical transport on the same length scale. The approach is to establish a current laterally in the sample, then to map the voltage locally by determining the tip bias that produces no tunneling at each point. The technique is similar to the macroscopic four-probe method commonly adopted for measuring electrical transport, with the inner two probes replaced by a scanning tunneling tip. This chapter describes principles, reviews approaches, and illustrates capabilities of STP.