An electret microphone as a force sensor for combined scanning probe microscopy

The operation of an electret microphone as a sensitive force sensor in scanning probe microscopy is described. The behavior of the electret microphone used as a capacitive force sensor is characterized and the experimental setup for a combined STM/SFM is described. First applications of this hybrid microscope to biological objects are presented. Unlike in conventional force microscopy, the sample can be placed on the top of the force sensor. This allows for a free choice of the near-field probe. Hence, the electret microphone is well suited for combined scanning microscopies where the probe-to-sample distance is kept constant by force gradient measurement while the near-field probe measures some local properties of the specimen.