Browsing by Author "Everitt, Henry O."
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Item Aluminum Nanocrystals(American Chemical Society, 2015) McClain, Michael J.; Schlather, Andrea E.; Ringe, Emilie; King, Nicholas S.; Liu, Lifei; Manjavacas, Alejandro; Knight, Mark W.; Kumar, Ish; Whitmire, Kenton; Everitt, Henry O.; Nordlander, Peter; Halas, Naomi J.; Laboratory for NanophotonicsWe demonstrate the facile synthesis of high purity aluminum nanocrystals over a range of controlled sizes from 70 to 220 nm diameter with size control achieved through a simple modification of solvent ratios in the reaction solution. The monodisperse, icosahedral, and trigonal bipyramidal nanocrystals are air-stable for weeks, due to the formation of a 2-4 nm thick passivating oxide layer on their surfaces. We show that the nanocrystals support size-dependent ultraviolet and visible plasmon modes, providing a far more sustainable alternative to gold and silver nanoparticles currently in widespread use.Item Carbon nanotube fiber terahertz polarizer(AIP Publishing, 2016) Zubair, Ahmed; Tsentalovich, Dmitri E.; Young, Colin C.; Heimbeck, Martin S.; Everitt, Henry O.; Pasquali, Matteo; Kono, JunichiroConventional, commercially available terahertz (THz) polarizers are made of uniformly and precisely spaced metallic wires. They are fragile and expensive, with performance characteristics highly reliant on wire diameters and spacings. Here, we report a simple and highly error-tolerant method for fabricating a freestanding THz polarizer with nearly ideal performance, reliant on the intrinsically one-dimensional character of conduction electrons in well-aligned carbon nanotubes(CNTs). The polarizer was constructed on a mechanical frame over which we manually wound acid-doped CNT fibers with ultrahigh electrical conductivity. We demonstrated that the polarizer has an extinction ratio of ∼−30 dB with a low insertion loss (<0.5 dB) throughout a frequency range of 0.2–1.1 THz. In addition, we used a THzellipsometer to measure the Müller matrix of the CNT-fiber polarizer and found comparable attenuation to a commercial metallic wire-grid polarizer. Furthermore, based on the classical theory of light transmission through an array of metallic wires, we demonstrated the most striking difference between the CNT-fiber and metallic wire-grid polarizers: the latter fails to work in the zero-spacing limit, where it acts as a simple mirror, while the former continues to work as an excellent polarizer even in that limit due to the one-dimensional conductivity of individual CNTs.Item Monitoring Chemical Reactions with Terahertz Rotational Spectroscopy(American Chemical Society, 2018) Swearer, Dayne F.; Gottheim, Samuel; Simmons, Jay G.; Phillips, Dane J.; Kale, Matthew J.; McClain, Michael J.; Christopher, Phillip; Halas, Naomi J.; Everitt, Henry O.Rotational spectroscopy is introduced as a new in situ method for monitoring gas-phase reactants and products during chemical reactions. Exploiting its unambiguous molecular recognition specificity and extraordinary detection sensitivity, rotational spectroscopy at terahertz frequencies was used to monitor the decomposition of carbonyl sulfide (OCS) over an aluminum nanocrystal (AlNC) plasmonic photocatalyst. The intrinsic surface oxide on AlNCs is discovered to have a large number of strongly basic sites that are effective for mediating OCS decomposition. Spectroscopic monitoring revealed two different photothermal decomposition pathways for OCS, depending on the absence or presence of H2O. The strength of rotational spectroscopy is witnessed through its ability to detect and distinguish isotopologues of the same mass from an unlabeled OCS precursor at concentrations of <1 nanomolar or partial pressures of <10 μTorr. These attributes recommend rotational spectroscopy as a compelling alternative for monitoring gas-phase chemical reactants and products in real time.Item Non-Hermitian metasurface with non-trivial topology(De Gruyter, 2022) Yang, Frank; Prasad, Ciril S.; Li, Weijian; Lach, Rosemary; Everitt, Henry O.; Naik, Gururaj V.The synergy between topology and non-Hermiticity in photonics holds immense potential for next-generation optical devices that are robust against defects. However, most demonstrations of non-Hermitian and topological photonics have been limited to super-wavelength scales due to increased radiative losses at the deep-subwavelength scale. By carefully designing radiative losses at the nanoscale, we demonstrate a non-Hermitian plasmonic–dielectric metasurface in the visible with non-trivial topology. The metasurface is based on a fourth order passive parity-time symmetric system. The designed device exhibits an exceptional concentric ring in its momentum space and is described by a Hamiltonian with a non-Hermitian Z 3 ${\mathbb{Z}}_{3}$ topological invariant of V = −1. Fabricated devices are characterized using Fourier-space imaging for single-shot k -space measurements. Our results demonstrate a way to combine topology and non-Hermitian nanophotonics for designing robust devices with novel functionalities.Item Plasmonic nanoparticle-based epoxy photocuring: A deeper look(Elsevier, 2019) Roberts, Adam T.; Yang, Jian; Reish, Matthew E.; Alabastri, Alessandro; Halas, Naomi J.; Nordlander, Peter; Everitt, Henry O.Many epoxyﾠadhesivesﾠrequire high temperatures to bondﾠcomposite materials. However, oven heating severely restricts what may be attached or enclosed within composite material-based structures and greatly limits the possibilities for repair. Inspired by initial reports of photothermal epoxy curing usingﾠplasmonicnanoparticles, we examine how laser-illuminated Au nanoparticles embedded within high-temperature epoxy films convert the conventional thermal curing process into a photothermally driven one. Our theoretical investigations reveal that plasmonic nanoparticle-based epoxy photocuring proceeds through a four-stage process: a rapid, plasmon-induced temperature increase, a slow localizedﾠinitializationﾠof the curing chemistry that increases theﾠoptical absorptionﾠof the epoxy film, a subsequent temperature increase as the epoxy absorbs theﾠlaser radiationﾠdirectly, and a final stage that completes theﾠchemical transformationﾠof the epoxy film to its cured state. Our experimental studies validate this model, and also reveal that highly local photocuring can create a stronger bond between composite materials than thermal curing without nanoparticles, at times even stronger than the composite material itself, substantially reducing the time needed for the curing process. Our findings support key advances in our understanding of this approach to the rapid, highly efficient bonding and repair of composite materials.Item Quantitative analysis of gas phase molecular constituents using frequency-modulated rotational spectroscopy(AIP Publishing LLC, 2019) Lou, Minghe; Swearer, Dayne F.; Gottheim, Samuel; Phillips, Dane J.; Simmons, Jay G. Jr.; Halas, Naomi J.; Everitt, Henry O.; Laboratory for NanophotonicsRotational spectroscopy has been used for decades for virtually unambiguous identification of gas phase molecular species, but it has rarely been used for the quantitative analysis of molecular concentrations. Challenges have included the nontrivial reconstruction of integrated line strengths from modulated spectra, the correlation of pressure-dependent line shape and strength with partial pressure, and the multiple standing wave interferences and modulation-induced line shape asymmetries that sensitively depend on source-chamber-detector alignment. Here, we introduce a quantitative analysis methodology that overcomes these challenges, reproducibly and accurately recovering gas molecule concentrations using a calibration procedure with a reference gas and a conversion based on calculated line strengths. The technique uses frequency-modulated rotational spectroscopy and recovers the integrated line strength from a Voigt line shape that spans the Doppler- and pressure-broadened regimes. Gas concentrations were accurately quantified to within the experimental error over more than three orders of magnitude, as confirmed by the cross calibration between CO and N2O and by the accurate recovery of the natural abundances of four N2O isotopologues. With this methodology, concentrations of hundreds of molecular species may be quantitatively measured down to the femtomolar regime using only a single calibration curve and the readily available libraries of calculated integrated line strengths, demonstrating the power of this technique for the quantitative gas-phase detection, identification, and quantification.Item Quantitative analysis of gas phase molecular constituents using frequency-modulated rotational spectroscopy(AIP Publishing LLC, 2019) Lou, Minghe; Swearer, Dayne F.; Gottheim, Samuel; Phillips, Dane J.; Simmons, Jay G.; Halas, Naomi J.; Everitt, Henry O.Rotational spectroscopy has been used for decades for virtually unambiguous identification of gas phase molecular species, but it has rarely been used for the quantitative analysis of molecular concentrations. Challenges have included the nontrivial reconstruction of integrated line strengths from modulated spectra, the correlation of pressure-dependent line shape and strength with partial pressure, and the multiple standing wave interferences and modulation-induced line shape asymmetries that sensitively depend on source-chamber-detector alignment. Here, we introduce a quantitative analysis methodology that overcomes these challenges, reproducibly and accurately recovering gas molecule concentrations using a calibration procedure with a reference gas and a conversion based on calculated line strengths. The technique uses frequency-modulated rotational spectroscopy and recovers the integrated line strength from a Voigt line shape that spans the Doppler- and pressure-broadened regimes. Gas concentrations were accurately quantified to within the experimental error over more than three orders of magnitude, as confirmed by the cross calibration between CO and N2O and by the accurate recovery of the natural abundances of four N2O isotopologues. With this methodology, concentrations of hundreds of molecular species may be quantitatively measured down to the femtomolar regime using only a single calibration curve and the readily available libraries of calculated integrated line strengths, demonstrating the power of this technique for the quantitative gas-phase detection, identification, and quantification.