How to measure energy dissipation in dynamic mode atomic force microscopy

When studying a mechanical system like an atomic force microscope (AFM) in dynamic mode it is intuitive and instructive to analyse the forces involved in tip-sample interaction. A different but complementary approach is based on analysing the energy that is dissipated when the tip periodically inter acts with the sample surface. This method does not require solving the diff erential equation of motion for the oscillating cantilever, but is based en tirely on the analysis of the energy flow in and out of the dynamic system. Therefore the problem of finding a realistic model to describe the tip-sam ple interaction in terms of non-linear force-distance dependencies and damp ing effects is omitted. Instead, it is possible to determine the energy dis sipated by the tip-sample interaction directly by measuring such quantities as oscillation amplitude, frequency, phase shift and drive amplitude. The method proved to be important when interpreting phase data obtained in tapp ing mode, but is also applicable to a variety of scanning probe microscopes operating in different dynamic modes. Additional electronics were designed to allow a direct mapping of local energy dissipation while scanning a sam ple surface. By applying this technique to the cross-section of a polymer b lend a material specific contrast was observed. (C) 1999 Elsevier Science B .V. All rights reserved.