Charge carrier dynamics and interactions in electric force microscopy

In electric force microscopy, a charged atomic force microscope tip in vacuum senses a fluctuating electrical force generated by the sample. Such measurements can in principle probe electrical noise generated by moving charge carriers in an organic semiconductor. We present a theory of cantilever fr...

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Bibliographic Details
Published in:The Journal of chemical physics 2012-09, Vol.137 (12), p.124701-124701
Main Authors: Lekkala, Swapna, Hoepker, Nikolas, Marohn, John A, Loring, Roger F
Format: Article
Language:English
Subjects:
Carrier transport
Charge carriers
Diffusion
Dynamics
Fluctuation
Mathematical models
Microscopy
Noise
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Summary:In electric force microscopy, a charged atomic force microscope tip in vacuum senses a fluctuating electrical force generated by the sample. Such measurements can in principle probe electrical noise generated by moving charge carriers in an organic semiconductor. We present a theory of cantilever frequency fluctuations in electric force microscopy, driven by coupled charge carrier dynamics and dielectric fluctuations. The connection between observable frequency fluctuations in electric force microscopy and the Casimir-Lifshitz force is described. This classical electrodynamic calculation is based on Maxwell's equations coupled to diffusive carrier transport. The effects of carrier transport and inter-carrier interactions on the spectrum of cantilever frequency noise are elucidated. We find that a simplified model of freely diffusing carriers can overestimate cantilever frequency noise by several orders of magnitude because of the neglect of interactions. Electric force microscopy measurements on an organic field effect transistor are reported and qualitatively interpreted in terms of the suppression of electrical noise from charge carriers by Coulomb interactions.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.4754602