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Interpretation of atomic force microscope (AFM) signals from surface charge on insulators

: Wintle, H.J.


Measurement Science and Technology 8 (1997), Nr.5, S.508-13
ISSN: 0957-0233
Fraunhofer HHI ()
atomic force microscopy; insulating materials; signal resolution; space charge; surface charging; afm signals; surface charge on insulators; stored charge; charge spreading dynamics; surface conduction; self-repulsion; bulk space charge motion; decay curves; surface-charge-perturbed cases; time constant

Charge stored on the surface of an insulator at the sub-micron length scale can be observed with an atomic force microscope (AFM). The dynamics of the charge spreading due to three mechanisms are calculated: (a) surface conduction; (b) surface charge spreading due to self-repulsion; and (c) bulk space charge motion, which is necessarily coupled to a surface charge. Self-similar motion occurs in all three cases. The AFM signals decay with time, and the shapes of the decay curves are similar. We show that the surface-charge-perturbed cases can be identified because the time constant depends on the magnitude of the initial charge, but that separating the pure surface spreading from the bulk process may prove difficult.