On the contrast in eddy current microscopy using atomic force microscopes

✍ Scribed by Hirsekorn, S.; Rabe, U.; Boub, A.; Arnold, W.

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 133 KB
• Volume: 27
• Category: Article
• ISSN: 0142-2421
• DOI: 10.1002/(sici)1096-9918(199905/06)27:5/6<474::aid-sia528>3.0.co;2-h

✦ Synopsis

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 inÑuences 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 e †ect allows one to judge whether 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 Ñexural vibrations of a rectangular beam cantilever. For the sensor tip dimensions of available cantilevers, the dipole approximation turned out not to be valid but the monopole approximation 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 samples with conductivity changes of 20 MS m-1 are below the thermal noise level.