Teflon AF/Ag nanocomposites with tailored optical properties
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T.D. Pounds and M. Grant Norton School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington 99164
M. Elbahri Chair for Multicomponent Materials, Faculty of Engineering, Christian Albrechts University, D-24143, Kiel, Germany (Received 13 February 2006; accepted 5 May 2006)
Teflon AF/Ag nanocomposites with various metal concentrations were fabricated by an evaporation process. Transmission electron microscopy examination showed that for low metal concentrations, the silver formed isolated individual nanoparticles. At higher metal concentrations, percolating metallic networks within the polymer matrix were formed. Optical absorption measurements showed a transition from individual plasmon absorption peaks for individual Ag nanoparticles to broadband optical absorption for the metallic networks. The absorption profile closely matches the solar radiation spectrum for an intermediate metal concentration of 45%. Thus, these novel polymer-metal nanocomposites have significant potential for photovoltaic applications.
The desire to create new materials with improved optical properties has led many researchers to synthesize nanometer-scale composites. As an example, polymer– metal nanocomposites, consisting of metallic nanoparticles embedded in various polymer matrices, have been evaluated for their novel functional properties, including optical, electronic, magnetic, and chemical.1,2 Polymer–metal nanocomposites can absorb light by the excitation of surface plasmons (oscillations of the electron gas) in the nanometer-sized metal particles. The resonance frequency of this oscillation depends on the size of the metal particles, their shape, and the type of metal.3 When the frequency of the incoming light is close to the resonance frequency of the surface plasmon, strong absorption can occur.4 Surface plasmon resonance (SPR) occurs normally in the visible part of the electromagnetic spectrum; the typical resonance frequency for spherical Ag nanoparticles is at about 400 nm.3,4 However, nanostructures with specific shapes and structures can exhibit SPRs at longer wavelengths into the infrared (IR) region. Surface plasmons have been investigated by many authors5,6 for various applications, including surfaceenhanced Raman scattering (SERS) in which a roughened Address all correspondence to these authors. e-mail: [email protected] b) Present address: Office of Electronic Miniaturization, University of Alaska-Fairbanks, Fairbanks, AK 99709 e-mail: [email protected] DOI: 10.1557/JMR.2006.0267 a)
2168 J. Mater. Res., Vol. 21, No. 9, Sep 2006 http://journals.cambridge.org Downloaded: 13 Mar 2015
metal layer on a dielectric is used to enhance the Raman scattering signal from an absorbed sample species.4 The strongly enhanced signal allows for single-molecule detection. Surface plasmons are also used in the form of dielectric nanoparticles capped with a metallic layer.7 The spectral response of such a capped nanoparticle depends on the size of the nanoparticles and the thickness of the shell. By varying
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