Atomic Force Microscopy
We analyze the nonlinear oscillations of an AFM cantilever to reveal the forces between the tip and the surface. The cantilever is driven with two pure tones and the nonlinear tip-surface force gives rise to frequency mixing, or intermodulation of the drive tones. Here is a link to a movie which demonstrates intermodulation as the AFM probe approaches a surface. With a multifrequency intermodulation lockin we capture in real-time the amplitude and phase at many intermodulation products as we scan. The method gives multiple amplitude and phase images in one scan, with each image showing rich and varying contrast. We have several different algorithms for interpreting the intermodulation spectra at each image pixel in terms of the conservative and dissipative forces between the tip and surface. We have also developed multifrequency methods to quickly extract current-voltage characteristics in conducting AFM and STM.
We are coordinating an EU project Q-AFM , part of the FET-Open program, with the goal of developing the next generation of quantum-limited resonant mechanical force sensors for the low-temperatute AFM community.