Broadband Local Dielectric Spectroscopy

A route to extend the measurement bandwidth of local dielectric spectroscopy up to the MHz range has been devised. The method is based on a slow amplitude modulation at a frequency X of the excitation field oscillating at a frequency x and the coherent detection of the modulated average electric force or force gradient at X. The cantilever mechanical response does not affect the measurement if X is well below its resonant frequency; therefore, limitations on the excitation field frequency are strongly reduced. Demonstration on a thin poly(vinyl acetate) film is provided, showing its structural relaxation spectrum on the local scale up to 45 C higher than glass temperature, and nanoscale resolution dielectric relaxation imaging near conductive nanowires embedded in the polymer matrix was obtained up to 5MHz frequency, with no physical reason to hinder further bandwidth extension.