A Thin-Film Infrared Absorber using CNT/Nanodiamond Nanocomposite
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A Thin-Film Infrared Absorber using CNT/Nanodiamond Nanocomposite Yu Sui1, Vikrant J. Gokhale1, Olga A. Shenderova2, Gary E. McGuire2, and Mina Rais-Zadeh1 1
Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48105, USA 2
International Technology Center, Raleigh, NC, 27617, USA
ABSTRACT This paper reports on the fabrication and characterization of thin-film nanocomposites comprised of tangled carbon nanotubes in a polymer matrix. The concentration of nanotubes in the polymer was significantly increased using detonation nanodiamonds. Nanodiamonds reduce the surface forces between the polymer and the nanotubes and mitigate the agglomeration problem of nanotubes in polymer. This resulted in thinner and more uniform networks that are efficient absorbers of infrared energy over a broad spectrum, ranging from the visible to the midwavelength infrared. An infrared absorbance of 97% was achieved for a 1.6 µm thick nanocomposite film across the spectral range of 714 nm to 5 µm. The films are mechanically and thermally stable up to 300 ˚C, and can be integrated with microbolometers to enhance their responsivity. INTRODUCTION Broadband infrared (IR) detectors enable night vision, imaging, and non-destructive testing of objects and thus can be used in many applications. Infrared detectors are either uncooled or cooled. Generally, uncooled (or thermal) detectors offer a much wider bandwidth and work at higher temperatures as compared to cooled IR detectors [1]. The working principle of thermal detectors is that the absorption of incident radiation as heat causes a physical change in the sensor, such as a resistivity change or a frequency shift. This change is transduced into an electrical signal proportional to the radiated IR power. The IR absorption efficiency and thus the sensitivity of thermal detectors can be improved by the addition of a thin-film IR absorber. This paper presents carbon nanotube (CNT) based polymer composites that exhibit high IR absorptivity even at film thicknesses less than 2 µm. Charged detonation nanodiamond particles (DND), produced from carbon-containing explosives are used to enhance the dispersion of CNTs in the polymer matrix. The CNT/DND polymer films are electrically insulating, mechanically robust, and thermally stable, making them ideal candidates for thin-film infrared absorbers. THEORY Various approaches have been taken for implementing IR absorbers. These include metallic thin films [2], quarter wavelength resonant cavities [3], metal blacks [4]-[6], carbon or graphite blacks [7], [8], and nanostructured metamaterials [9]. While good IR absorption characteristics have been obtained following these approaches, the reported IR absorbers are either temperature unstable, have a narrow absorption spectrum, or need to be deposited in a thick film to achieve high absorption. Specifically, quarter-wavelength cavities are too thick and wavelength specific.
Metal alloy films, porous metals, and metal blacks have issues with aging and film stability
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