Transport properties of photoexcitations in stretchedtrans-polyacetylene.
Item
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Title
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Transport properties of photoexcitations in stretchedtrans-polyacetylene.
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Identifier
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AAI9119688
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identifier
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9119688
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Creator
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Walser, Ardie Darnel.
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Contributor
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Advisers: Robert R. Alfano | Roger Dorsinville
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Date
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1991
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Electronics and Electrical
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Abstract
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The temperature, sample orientation (1D and 3D), intensity, and optical field polarization dependence of the picosecond photoconductive response of highly oriented stretched trans-polyacetylene has been measured. The results of these experiments strongly suggest that solitons and polarons are the main mobile charged carriers in this quasi one-dimensional organic semiconductor.;The main results are summarized as follows: (i) The fast component of the photoconductivity parallel to the polymer chains (1D configuration) is temperature independent for both above- and below-gap photoexcitation. (ii) The fast component of the photoconductivity perpendicular to the chains (3D configuration) decreases exponentially with 1/T for both above- and below-gap excitation each with an activation energy E{dollar}\sb{lcub}\rm A{rcub}{dollar} of 48 meV and 63 meV respectively. (iii) The 1D and 3D cw photoconductivity decreases with 1/T exhibiting approximately the same activation energy of E{dollar}\sb{lcub}\rm A{rcub}{dollar} = 0.15 eV. (iv) The fast component of the photoresponse is roughly three orders of magnitude higher than the cw response with a decay time of about 400 ps. The transient mobility {dollar}\mu{dollar} is approximately 0.04 cm{dollar}\sp2{dollar}/V-s along the chain. The mean drift distance of the photogenerated charge carriers {dollar}\langle{dollar}x{dollar}\rangle{dollar} along the chain is estimated at 13 angstroms. (v) The I-V characteristic curve of the 1D picosecond photoconductive response is superlinear for both above- and below-gap excitation, while the I-V characteristic curve for the 3D picosecond photoconductive response is linear. (vi) The intensity dependence of the picosecond 1D and 3D photocurrent varied linearly with the laser intensity, independent of the polarization and wavelength (0.53 {dollar}\mu{dollar}m and 1.06 {dollar}\mu{dollar}m) of the incident beam. (vii) The anisotropy with below gap excitation is constant at 2.4, while with above gap excitation it decreases from 7.4 to 4.5 as the laser intensity increases. It has also been found, that the photoconductive response is greatest for below gap excitation independent of the optical field polarization.;These results were accounted for by a combination of a direct interchain generation model, which was derived from an extended tight binding model, laser heating and bimolecular recombination. Solitons dominant the 1D picosecond photocurrent and polarons dominant the 3D picosecond photocurrent.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
