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Title: Frequency-dependent photothermal measurement of transverse thermal diffusivity of organic semiconductors

We have used a photothermal technique, in which chopped light heats the front surface of a small (∼1 mm{sup 2}) sample and the chopping frequency dependence of thermal radiation from the back surface is measured with a liquid-nitrogen-cooled infrared detector. In our system, the sample is placed directly in front of the detector within its dewar. Because the detector is also sensitive to some of the incident light, which leaks around or through the sample, measurements are made for the detector signal that is in quadrature with the chopped light. Results are presented for layered crystals of semiconducting 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pn) and for papers of cellulose nanofibrils coated with semiconducting poly(3,4-ethylene-dioxythiophene):poly(styrene-sulfonate) (NFC-PEDOT). For NFC-PEDOT, we have found that the transverse diffusivity, smaller than the in-plane value, varies inversely with thickness, suggesting that texturing of the papers varies with thickness. For TIPS-pn, we have found that the interlayer diffusivity is an order of magnitude larger than the in-plane value, consistent with previous estimates, suggesting that low-frequency optical phonons, presumably associated with librations in the TIPS side groups, carry most of the heat.
Authors:
; ;  [1] ; ;  [2] ; ;  [3]
  1. Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506-0055 (United States)
  2. Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055 (United States)
  3. Department of Science and Technology, Organic Electronics, Linköping University, SE-601 74 Norrköping (Sweden)
Publication Date:
OSTI Identifier:
22493075
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 23; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CELLULOSE; CRYSTALS; DEWARS; FREQUENCY DEPENDENCE; INFRARED THERMOGRAPHY; NANOFIBERS; ORGANIC SEMICONDUCTORS; PENTACENE; PHONONS; SIGNALS; STYRENE; THERMAL DIFFUSIVITY; THERMAL RADIATION; VISIBLE RADIATION