Browsing by Author "Swearer, Dayne F."

Now showing 1 - 7 of 7
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    Communicating Science Concepts to Individuals with Visual Impairments Using Short Learning Modules
    (American Chemical Society, 2016) Stender, Anthony S.; Newell, Ryan; Villarreal, Eduardo; Swearer, Dayne F.; Bianco, Elisabeth; Ringe, Emilie
    Of the 6.7 million individuals in the United States who are visually impaired, 63% are unemployed, and 59% have not attained an education beyond a high school diploma. Providing a basic science education to children and adults with visual disabilities can be challenging because most scientific learning relies on visual demonstrations. Creating resources to help teachers and service organizations better communicate science is thus critical both to the education of sighted students as well as to the continuing education of individuals with blindness or low vision (BLV). Here, 4 new scientific learning activities that last 5–15 min each are described. These simple exercises are designed to educate the general public, including both those who are sighted and those with BLV. The modules use tactile and auditory approaches to convey basic concepts including the metric system, material strength and deformation, transparency, and the electromagnetic spectrum. These modules were tested on 20 adults with BLV during a science outreach event. Answers to learning assessment questions indicate that the modules conveyed information about the scientific concepts presented and increased an interest in science for most participants.
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    From tunable core-shell nanoparticles to plasmonic drawbridges: Active control of nanoparticle optical properties
    (AAAS, 2015) Byers, Chad P.; Zhang, Hui; Swearer, Dayne F.; Yorulmaz, Mustafa; Hoener, Benjamin S.; Huang, Da; Hoggard, Anneli; Chang, Wei-Shun; Mulvaney, Paul; Ringe, Emilie; Halas, Naomi J.; Nordlander, Peter; Link, Stephan; Landes, Christy F.
    The optical properties of metallic nanoparticles are highly sensitive to interparticle distance, giving rise to dramatic but frequently irreversible color changes. By electrochemical modification of individual nanoparticles and nanoparticle pairs, we induced equally dramatic, yet reversible, changes in their optical properties. We achieved plasmon tuning by oxidation-reduction chemistry of Ag-AgCl shells on the surfaces of both individual and strongly coupled Au nanoparticle pairs, resulting in extreme but reversible changes in scattering line shape. We demonstrated reversible formation of the charge transfer plasmon mode by switching between capacitive and conductive electronic coupling mechanisms. Dynamic single-particle spectroelectrochemistry also gave an insight into the reaction kinetics and evolution of the charge transfer plasmon mode in an electrochemically tunable structure. Our study represents a highly useful approach to the precise tuning of the morphology of narrow interparticle gaps and will be of value for controlling and activating a range of properties such as extreme plasmon modulation, nanoscopic plasmon switching, and subnanometer tunable gap applications.
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    Metal-organic frameworks tailor the properties of aluminum nanocrystals
    (AAAS, 2019) Robatjazi, Hossein; Weinberg, Daniel; Swearer, Dayne F.; Jacobson, Christian; Zhang, Ming; Tian, Shu; Zhou, Linan; Nordlander, Peter; Halas, Naomi J.
    Metal-organic frameworks (MOFs) and metal nanoparticles are two classes of materials that have received considerable recent attention, each for controlling chemical reactivities, albeit in very different ways. Here, we report the growth of MOF shell layers surrounding aluminum nanocrystals (Al NCs), an Earth-abundant metal with energetic, plasmonic, and photocatalytic properties. The MOF shell growth proceeds by means of dissolution-and-growth chemistry that uses the intrinsic surface oxide of the NC to obtain the Al3+ ions accommodated into the MOF nodes. Changes in the Al NC plasmon resonance provide an intrinsic optical probe of its dissolution and growth kinetics. This same chemistry enables a highly controlled oxidation of the Al NCs, providing a precise method for reducing NC size in a shape-preserving manner. The MOF shell encapsulation of the Al NCs results in increased efficiencies for plasmon-enhanced photocatalysis, which is observed for the hydrogen-deuterium exchange and reverse water-gas shift reactions.
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    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.
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    Plasmonic Photocatalysis of Nitrous Oxide into N2 and O2 Using Aluminum–Iridium Antenna–Reactor Nanoparticles
    (American Chemical Society, 2019) Swearer, Dayne F.; Robatjazi, Hossein; Martirez, John Mark P.; Zhang, Ming; Zhou, Linan; Carter, Emily A.; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
    Photocatalysis with optically active “plasmonic” nanoparticles is a growing field in heterogeneous catalysis, with the potential for substantially increasing efficiencies and selectivities of chemical reactions. Here, the decomposition of nitrous oxide (N2O), a potent anthropogenic greenhouse gas, on illuminated aluminum–iridium (Al–Ir) antenna–reactor plasmonic photocatalysts is reported. Under resonant illumination conditions, N2 and O2 are the only observable decomposition products, avoiding the problematic generation of NOx species observed using other approaches. Because no appreciable change to the apparent activation energy was observed under illumination, the primary reaction enhancement mechanism for Al–Ir is likely due to photothermal heating rather than plasmon-induced hot-carrier contributions. This light-based approach can induce autocatalysis for rapid N2O conversion, a process with highly promising potential for applications in N2O abatement technologies, satellite propulsion, or emergency life-support systems in space stations and submarines.
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    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 Nanophotonics
    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.
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    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.