Schematic of STM tip above a sample.
Scanning Tunnelling Microscopy
A Scanning tunnelling microscope relies on the quantum mechanical tunnelling of electrons between a sharp conducting tip and a flat conducting sample. By applying a bias voltage (Vb) between tip and sample, a current will flow, and this current can be measured as a function of (x, y) location. By varying the bias voltage the occupied and unoccupied states can be probed with sub-nanometer precision allowing individual atoms to be resolved. This is illustrated schematically here.
