Scanning tunneling microscopy (STM) employs a biased sharp metal probe in close proximity to a surface. When the tip-sample separation is small, there is a finite probability that electrons will tunnel across this gap. As the tip is scanned across the sample the tunneling current is utilized as a feedback signal in order to maintain the tip-sample separation. STM can be used to measure properties of metals, semiconductors and other materials having medium to high conductivities.