Multi-frequency, repulsive-mode amplitude-modulated atomic force microscopy imaging mode

Keywords:
atomic force microscopy, AFM, scanning probe microscopy, SPM, imaging mode, cantilever

Abstract:
We will present a new SPM imaging mode that goes beyond traditional phase imaging in measuring mechanical and chemical properties. In this new imaging mode, Dual AC™, a cantilever is driven at or near two of its flexural resonant eigenmodes. For most cantilevers, these eigenmodes are non-harmonic. Most of the work we have done to date makes use of the first and second resonant modes of the cantilever. The amplitude and phase signals for these two modes show interesting contrast on a variety of samples. In particular, the second mode amplitude and phase exhibit contrast not visible in the first mode. In one example, the cantilever and imaging parameters are chosen such that the tip-sample interactions are repulsive. The driven second eigenmode amplitude and phase shows strikingly different contrast from those same fundamental eigenmode signals on graphite samples imaged in air and other material samples. As illustrated below, “A” is height, “B” is fundamental amplitude, “C” is fundamental phase, and “D” is the second mode amplitude image (Dual AC). These results can be partially explained in forms of energy dissipation and the topographic feedback scheme.

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Nanotech 2007 Conference Program Abstract