Scanning Tunneling Spectroscopy (STS)

STS studies the local electronic structure of a sample's surface, depending upon its atomic species  and also upon its local chemical environment .
STS can be implemented in many methods:

taking "topographic" (constant-current) images using different bias voltages and comparing them;

taking current (constant-height) images at different heights;

ramping the bias voltage with the tip positioned over a feature of interest while recording the tunneling current.
The last example results in current vs. voltage (I-V) curves characteristic of the electronic structure at a specific x,y location on the sample surface. STMs can be set up to collect I-V curves at every point in a data set, providing a three-dimensional map of electronic structure.
With a lock-in amplifier, dI/dV (conductivity) or dI/dz (work function) vs. V curves can be collected directly. 

Go to SPM Basic