Heterodyne Force-Detection for High Frequency Local Dielectric Spectroscopy by Scanning Maxwell Stress Microscopy

The scanning Maxwell stress microscope (SMM) is a type of non-contact scanning force microscope, capable of imaging a variety of electrical and topographical features of surfaces solely based on harmonic analysis of the electric field-induced oscillations of the cantilever. We propose here a heterodyne force-detection scheme which enables the SMM to perform local dielectric spectroscopy up to high frequencies beyond the mechanical resonance of the cantilever. The method exploits the nonlinear dependence of the Maxwell stress on the field strength, which acts as a mechanical frequency mixer to create a low frequency beat force on the tip from closely separated high frequency electric-field components. The amplitude and the phase of the beat force carry information on the dielectric constant and loss at the high frequencies.