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Title: Electric force microscopy of semiconductors: Theory of cantilever frequency fluctuations and noncontact friction

An electric force microscope employs a charged atomic force microscope probe in vacuum to measure fluctuating electric forces above the sample surface generated by dynamics of molecules and charge carriers. We present a theoretical description of two observables in electric force microscopy of a semiconductor: the spectral density of cantilever frequency fluctuations (jitter), which are associated with low-frequency dynamics in the sample, and the coefficient of noncontact friction, induced by higher-frequency motions. The treatment is classical-mechanical, based on linear response theory and classical electrodynamics of diffusing charges in a dielectric continuum. Calculations of frequency jitter explain the absence of contributions from carrier dynamics to previous measurements of an organic field effect transistor. Calculations of noncontact friction predict decreasing friction with increasing carrier density through the suppression of carrier density fluctuations by intercarrier Coulomb interactions. The predicted carrier density dependence of the friction coefficient is consistent with measurements of the dopant density dependence of noncontact friction over Si. Our calculations predict that in contrast to the measurement of cantilever frequency jitter, a noncontact friction measurement over an organic semiconductor could show appreciable contributions from charge carriers.
Authors:
; ;  [1]
  1. Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853 (United States)
Publication Date:
OSTI Identifier:
22251503
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 139; Journal Issue: 18; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ATOMIC FORCE MICROSCOPY; CARRIER DENSITY; CHARGE CARRIERS; DENSITY; DIELECTRIC MATERIALS; ELECTRODYNAMICS; FIELD EFFECT TRANSISTORS; FLUCTUATIONS; FRICTION; FRICTION FACTOR; INTERACTIONS; MICROSCOPES; ORGANIC SEMICONDUCTORS; SPECTRAL DENSITY