Single-electron tunneling to insulator surfaces detected by electrostatic force microscopy

A short overview of the main Scanning Probe Microscopy techniques is presented. The high charge sensitivity of Electrostatic Force Microscopy is used to detect single electron tunneling events between a specially fabricated probe and a graphite sample. The probe is an oxidized silicon atomic force microscope tip with an electrically isolated metallic dot at its apex. The fabrication method is described. A probe with a metallic dot at its end is brought into tunneling range of the surface. Abrupt variation in the amplitude and the phase of the oscillating cantilever are detected due to single electron tunneling from the dot to the sample. The same measurements are performed with metallic tips above thin SiO2 films. Local probing of the localized electronic states on SiO2 films shows that mostly single electrons tunnel from the tip to the surface. The cantilever motion in proximity to the sample is solved analytically and numerically. A good agreement is achieved between experimental data and a theoretical model of electron tunneling events. Instability of cantilever motion is observed. Tunneling to insulator surfaces will provide for atomic scale characterization of the electronic properties of insulators.