Simplified Description of Instrument Features All probe microscopes have two common features: (1) a sharp, tiny probe which gets very close to the sample and feels the surface by monitoring an interaction, sensitive to distance, between the probe and the surface; and (2) the sample or the probe is scanned in a raster fashion with near atomic accuracy and the variation in the interaction is translated to a topographic map of the surface.    Among the family of SPM's the two most commonly used are Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM).