Electric Force Microscope (EFM)

MFM image of a textured hard diskDomains in Garnet Film. 2Electric Force Microscopy is analogous to standard MFM, except that gradients being sensed are due to electrostatic forces. In this method the cantilever is vibrated by a small piezoelectric element near its resonant frequency. The cantilever's resonant frequency changes in response to any additional force gradient. 1

Attractive forces make the cantilever effectively "softer", reducing the cantilever resonant frequency. Conversely, repulsive forces make the cantilever effectively "stiffer", increasing the resonant frequency.1

References
  1. Scanning Probe Microscopy Training Notebook, Digital Instruments, Veeco Metrology Group
  2. http://www.digitalinstruments.com/