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19 Jul 1999

Volume 75, Issue 3, pp. 307-435

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Electric-field-induced ion migration in polymer-dispersed liquid- crystal films observed by near-field scanning optical microscopy

Erwen Mei and Daniel A. Higgins

Appl. Phys. Lett. 75, 430 (1999); http://dx.doi.org/10.1063/1.124398 (3 pages) | Cited 5 times

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Near-field scanning optical microscopy (NSOM) is used to study electric-field-induced ion migration in polymer-dispersed liquid-crystal (PDLC) films. An electric field is applied between the aluminum-coated NSOM probe and an optically transparent, conductive glass substrate, upon which the film is supported. Electric-field-induced reorientation of the liquid crystal beneath the probe is observed optically. PDLC films doped with tetraalkylammonium tetrafluoroborate salts show dramatically different reorientation dynamics than those prepared without ionic dopants. The behavior observed is attributed to the charging of double layers at the polymer/liquid-crystal interface that cancel the field within the “bulk” of the liquid crystal in time. Observation of subsequent liquid-crystal relaxation yields a measure of the local ion migration rate. © 1999 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
68.15.+e Liquid thin films
66.10.C- Diffusion and thermal diffusion

Relations between interaction force and frequency shift in large-amplitude dynamic force microscopy

U. Dürig

Appl. Phys. Lett. 75, 433 (1999); http://dx.doi.org/10.1063/1.124399 (3 pages) | Cited 86 times

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Large-amplitude dynamic force microscopy based on measuring shifts of the resonance frequency of the force sensor has proved to be a powerful imaging tool. General expressions relating arbitrary interaction forces to resonance frequency shifts are derived using variational methods and Fourier expansion of the tip motion. For interactions with a range much shorter than the vibration amplitude, the frequency shift can be expressed in terms of a convolution product involving the interaction force and a weakly divergent kernel. The convolution can be inverted, thus enabling one to recover unequivocally interaction potentials and forces from measured frequency shift data. © 1999 American Institute of Physics.
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07.79.Lh Atomic force microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
02.30.Nw Fourier analysis
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