Scanning capacitance microscopy using a relaxation oscillator
  We have performed scanning capacitance microscopy using a relaxation oscillator. Precision calibrations indicate a sensitivity on the order of 0.05 pF. Surface topography of metallic structures, such as machined grooves and coins, can be readily obtained either in the constant-height (non-contact) or tapping (contact) mode. Spatial resolution of sub-50 $\mu$m has been achieved. 
Marie Pahlmeyer, Andrew Hankins, Sam Tuppan, and Woo-Joong Kim
cond-mat.mtrl-sci physics.ins-det