Browsing by Author "Simin, Nicholas"

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    Enhanced nanoplasmonic heating in standoff sensing of explosive residues with infrared reflection-absorption spectroscopy
    (2020-03-10) Simin, Nicholas; Park, Yangkyu; Lee, Dongkyu; Thundat, Thomas; Kim, Seonghwan
    Various standoff sensing techniques employing optical spectroscopy have been developed to address challenges in safely identifying trace amounts of explosives at a distance. A flexible anodic aluminum oxide (AAO) microcantilever and a high-power quantum cascade laser utilized as the infrared (IR) source are used for standoff IR reflection-absorption spectroscopy to detect explosive residues on a metal surface. Standoff sensing of trinitrotoluene (TNT) is demonstrated by exploiting the high thermomechanical sensitivity of a bimetallic AAO microcantilever. Moreover, sputtering gold onto the fabricated AAO nanowells generates a strong scattering and absorption of IR light in the wavelength range of 5.18 μm to 5.85 μm resulting in enhanced nanoplasmonic heating. Utilizing the IR absorption enhancement in this wavelength range, the plasmonic AAO cantilever could detect TNT molecules 7 times better than the bimetallic AAO cantilever.
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    Nanoporous Microcantilevers with Plasmonic Absorbers for Photothermal Infrared Spectroscopy
    (2019-05-13) Simin, Nicholas; Kim, Seonghwan; Kim, Seonghwan; Dalton, Colin; Sanati-Nezhad, Amir; Park, Simon S.
    A nanoporous anodic aluminum oxide (AAO) bimetallic cantilever enhanced by a gold coating on the nanopores creates a plasmonic crystal structure. The fabricated sensor is used for photothermal cantilever deflection spectroscopy (PCDS). Explosive compounds tested, showed spectra identifying explosive compounds by their characteristic wavelengths. Through a two-step anodization process, photolithography, and bimetallic and plasmonic coatings, a sensitive photothermal microcantilever was fabricated. The bimetallic layer thickness was optimized through analytical calculations. The ideal plasmonic layer thickness was found through experimentation. Molecules adsorbed onto the cantilever surface had their mass quantified through a measured change in 2nd mode resonant frequency. Simultaneously, the molecules were identified by high power infrared (IR) spectroscopy. For standoff spectroscopy, a plasmonic enhanced AAO cantilever was shown to improve characteristic peak depth 10-fold and 7-fold compared to silicon and AAO bimetallic cantilevers, respectively. The limit of detection (LOD) of the plasmonic AAO cantilever was determined to be 63.42 ng/cm2.