Browsing by Author "Manjavacas, Alejandro"

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    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 Nanophotonics
    We 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.
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    Distinguishing between plasmon-induced and photoexcited carriers in a device geometry
    (Macmillan Publishers Limited, 2015) Zheng, Bob Y.; Zhao, Hangqi; Manjavacas, Alejandro; McClain, Michael; Nordlander, Peter; Laboratory for Nanophotonics (LANP)
    The use of surface plasmons, charge density oscillations of conduction electrons of metallic nanostructures, to boost the efficiency of light-harvesting devices through increased light-matter interactions could drastically alter how sunlight is converted into electricity or fuels. These excitations can decay directly into energetic electron-hole pairs, useful for photocurrent generation or photocatalysis. However, the mechanisms behind plasmonic carrier generation remain poorly understood. Here we use nanowire-based hot-carrier devices on a wide-bandgap semiconductor to show that plasmonic carrier generation is proportional to internal field-intensity enhancement and occurs independently of bulk absorption. We also show that plasmon-induced hot electrons have higher energies than carriers generated by direct excitation and that reducing the barrier height allows for the collection of carriers from plasmons and direct photoexcitation. Our results provide a route to increasing the efficiency of plasmonic hot-carrier devices, which could lead to more efficient devices for converting sunlight into usable energy.
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    High Chromaticity Aluminum Plasmonic Pixels for Active Liquid Crystal Displays
    (American Chemical Society, 2016) Olson, Jana; Manjavacas, Alejandro; Basu, Tiyash; Huang, Da; Schlather, Andrea E.; Zheng, Bob; Halas, Naomi; Nordlander, Peter; Link, Stephan; Laboratory for Nanophotonics
    Chromatic devices such as flat panel displays could, in principle, be substantially improved by incorporating aluminum plasmonic nanostructures instead of conventional chromophores that are susceptible to photobleaching. In nanostructure form, aluminum is capable of producing colors that span the visible region of the spectrum while contributing exceptional robustness, low cost, and streamlined manufacturability compatible with semiconductor manufacturing technology. However, individual aluminum nanostructures alone lack the vivid chromaticity of currently available chromophores because of the strong damping of the aluminum plasmon resonance in the visible region of the spectrum. In recent work, we showed that pixels formed by periodic arrays of Al nanostructures yield far more vivid coloration than the individual nanostructures. This progress was achieved by exploiting far-field diffractive coupling, which significantly suppresses the scattering response on the long-wavelength side of plasmonic pixel resonances. In the present work, we show that by utilizing another collective coupling effect, Fano interference, it is possible to substantially narrow theﾠshort-wavelengthﾠside of the pixel spectral response. Together, these two complementary effects provide unprecedented control of plasmonic pixel spectral line shape, resulting in aluminum pixels with far more vivid, monochromatic coloration across the entire RGB color gamut than previously attainable. We further demonstrate that pixels designed in this manner can be used directly as switchable elements in liquid crystal displays and determine the minimum and optimal numbers of nanorods required in an array to achieve good color quality and intensity.