STM-Scanning Tunneling Microscope

 STM is a powerful instrument for imaging surfaces at the atomic level.   Individual atoms within materials are routinely imaged and manipulated.   It provides a three-dimensional profile of the surface which is very useful for characterizing surface roughness, observing surface defects, and determining the size and conformation of molecules and aggregates on the surface.  For the electron tunneling to take place, both the sample and the tip must be conductive.

Using a conducting tip that applies a voltage between sample and the tip, electrons can “tunnel” through the narrow gap either from the sample to the tip or from the tip to the sample, depending on the sign of the voltage. The tunneling current changes with tip-to-sample distance, decaying exponentially as distance increases, allowing to make  high precision measurments in positioning the tip sub-angstrom vertically and atomic resolution laterally.