Non-invasive dielectric measurements with the scanning potential microscope

Abstract

The scanning potential microscope (SPM) is a new form of scanning microscope, which maps distributions of spatial potential by direct measurement. The SPM may be used to study, non-invasively, the electrical properties of samples through the potential distribution created near the sample in response to an applied electric field. Spatial resolution and sample to SPM spacing are both close to 1 mu m at the present stage of development of the instrument. We present an SPM study of a test sample comprising three dielectric layers with differing relative permittivities: a 35 mu m film of cellulose acetate (CA, epsilon r approximately=5); a 25 mu m film of polyvinylidenefluoride (PVDF, epsilon r approximately=8.4); and a 50 mu m film of polytetrafluoroethylene (PTFE, epsilon r approximately=2-2.1). In the experimental set-up a small, audio-frequency electric displacement was applied through the sample. SPM mapping of the resultant potential distribution close to the sample yielded values of relative permittivity that were within 2% of the material specifications.