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On the Contrast in Eddy Current Microscopy using Atomic Force Microscopes

: Hirsekorn, S.; Rabe, U.; Boub, A.; Arnold, W.


Surface and Interface Analysis 27 (1999), Nr.5/6, S.474-481
ISSN: 0142-2421
SXM-3 Conference <1998, Basel>
Fraunhofer IZFP ()
atomic force microscopy; dynamic mode; eddy current; magnetic probe; materials characterization; vibration analysis

A magnetic probe of an atomic force microscope oscillating above a sample induces eddy currents within conducting materials. The resulting electrodynamic interaction between sample and probe influences the probe vibrations so that local variations in conductivity of a sample might be imaged with an atomic force microscope by phase shifts and/or amplitude changes of the probe vibrations. A quantitative evaluation of this effect allows one to judge wheter the local conductivity can be measured. This paper presents the calculation of attainable contrast in phase and in amplitude images by measuring the high-frequency flexural vibrations of a rectangular beam cantilever. For the sensor tip dimsensions of available contilevers, the dipole approximation turned out not to be valid but the monopole appoximation yields a reasonable estimation of the contrast. Calculations based on the monopole approximation show that the amplitude and the phase changes of the cantilever vibration ensuing from s amples with conductivity changes of 20 MS m-1 are below the thermal noise level.