Single-electron tunneling to insulator surfaces measured by frequency detection electrostatic force microscopy

A frequency detection electrostatic force microscopy (EFM) technique was used for measurements of single-electron tunneling events between a metallic probe and an insulator surface. In the process, the probe was positioned above the insulator surface and scanned up and down perpendicular to the surface by a few nanometers. The 300 kHz resonance frequency was shifted 1-10 Hz of the oscillating force probe. It was observed that the frequency shifts appeared only within a sub-2 nm tip-sample gap.