Browsing by Author "Wang, Yumin"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Chiral and Achiral Nanodumbbell Dimers: The Effect of Geometry on Plasmonic Properties
    (American Chemical Society, 2016) Smith, Kyle W.; Zhao, Hangqi; Zhang, Hui; Sánchez -Iglesias, Ana; Grzelczak, Marek; Wang, Yumin; Chang, Wei-Shun; Nordlander, Peter; Liz-Marzán, Luis; Link, Stephan; Laboratory for Nanophotonics
    Metal nanoparticles with a dumbbell-like geometry have plasmonic properties similar to those of their nanorod counterparts, but the unique steric constraints induced by their enlarged tips result in distinct geometries when self-assembled. Here, we investigate gold dumbbells that are assembled into dimers within polymeric micelles. A single-particle approach with correlated scanning electron microscopy and dark-field scattering spectroscopy reveals the effects of dimer geometry variation on the scattering properties. The dimers are prepared using exclusively achiral reagents, and the resulting dimer solution produces no detectable ensemble circular dichroism response. However, single-particle circular differential scattering measurements uncover that this dimer sample is a racemic mixture of individual nanostructures with significant positive and negative chiroptical signals. These measurements are complemented with detailed simulations that confirm the influence of various symmetry elements on the overall peak resonance energy, spectral line shape, and circular differential scattering response. This work expands the current understanding of the influence self-assembled geometries have on plasmonic properties, particularly with regard to chiral and/or racemic samples which may have significant optical activity that may be overlooked when using exclusively ensemble characterization techniques.
  • Thumbnail Image
    Item
    Fully integrated CMOS-compatible photodetector with color selectivity and intrinsic gain
    (2017-10-31) Zheng, Bob Yi; Wang, Yumin; Halas, Nancy J.; Nordlander, Peter; Rice University; United States Patent and Trademark Office
    A metal-semiconductor-metal photodetecting device and method of manufacturing a metal-semiconductor-metal photodetecting device that includes a p-type silicon substrate with an oxide layer disposed on the p-type silicon substrate. Schotty junctions are disposed adjacent to the oxide layer on the p-type silicon substrate and a plasmonic grating disposed on the oxide layer. The plasmonic grating provides wavelength range selectability for the photodetecting device.
  • Thumbnail Image
    Item
    Implementation of Hot Electrons in Hybrid Antenna-Graphene Structures
    (2013-09-16) Wang, Yumin; Nordlander, Peter J.; Halas, Naomi; Link, Stephan
    Graphene, a one-atom-thick sheet of hexagonally packed carbon atoms, is a novel material with high electron mobility due to its unique linear and gapless electronic band structure. Its broadband absorption and unusual doping properties, along with superb mechanical flexibility make graphene of promising application in optoeletronic devices such as solar cell, ultrafast photodetectors, and terahertz modulators. How- ever, the current performance of graphene-based devices is quite unacceptable owning to serious limitations by its inherently small absorption cross section and low quan- tum efficiency. Fortunately, nanoscale optical antennas, consisting of closely spaced, coupled metallic nanoparticles, have fascinating optical response since the collective oscillation of electrons in them, namely surface plasmons, can concentrate light into a subwavelength regime close to the antennas and enhance the corresponding field considerably. Given that optical antenna have been applied in various areas such as subwavelength optics, surface enhanced spectroscopies, and sensing, they are also able to assist graphene to harvest visible and near-infrared light with high efficiency. Moreover, the efficient production of hot electrons due to the decay of the surface plasmons can be further implemented to modulate the properties of graphene. Here we choose plasmonic oligomers to serve as optical antenna since they pos- sess tunable Fano resonances, consisting of a transparency window where scattering is strongly suppressed but absorption is greatly enhanced. By placing them in di- rect contact with graphene sheet, we find the internal quantum efficiency of hybrid antenna-graphene devices achieves up to 20%. Meanwhile, doping effect due to hot electron is also observed in this device, which can be used to optically tune the elec- tronic properties of graphene.
  • Thumbnail Image
    Item
    Plasmon Resonances in Metallic Nanostructures for Photodetection and Signal Modulation
    (2014-08-15) Wang, Yumin; Nordlander, Peter J.; Halas, Naomi J; Link, Stephan
    Metallic nanostructures can strongly interact with the light and exhibit fascinating optical properties due to inherent collective oscillations of electrons in metals, also known as plasmon resonances. Since the plasmons are capable of confining light into a small regime and meanwhile significantly enhancing its field intensity, the metallic nanostructures can be widely used for light harvesting and manipulation. By placing gold gratings on top of a silicon substrate, hot electrons created from plasmon decay can efficiently go across the Schottky barrier and be harvested by the silicon, leading to a substantial photocurrent. This yields a good photodetector which not only possesses a narrowband photoresponse due to the plasmon resonances but also has the ability to work at wide frequency range even below the bandgap of the silicon. Moreover, instead of the top-gratings structures, embedding gold nanostructures into the semiconductors will effectively increase the photoresponsivity. Theoretical calculation shows that the embedment can lead to an increase in the surface area of the Schottky barrier and at the meantime broaden the directional range of the emitted hot electrons able to transport across the Schottky barrier. More importantly, the vertical Schottky barrier is found to be the predominant area where photoemission take places. Aside from creating hot electrons, the plasmons can also influence the performance of the photodetection by facilitating the generation of electron-hole pairs directly in the semiconductors. Here, the aluminum gratings are demonstrated to serve as good color filters when they are integrated with metal-semiconductor-metal photodiodes. The interference of plasmon near-field and incident field could either block or assist the light going through the aluminum gratings to hit the photodiodes. As for light manipulation, the metallic nanostructures act just like optical nanoantennas whose photoresponse can be modulated by loading optical materials in them. The corresponding modulation process can be described in terms of optical nanocircuitry in which various materials are represented by capacitors, inductors, and resistors. With the help of the optical nanocircuitry theory, optical nanofilters become convenient and straightforward to design and build. In addition, substrate also can strongly modify the optical response of the nanoantenna. It has been proven that a conductive substrate will blueshift and reduce the original plasmon resonances and meanwhile bring in a new charge transfer mode appearing at low energy level. Given that plasmon resonances can effectively harvest light and modulate optical signal, they may have promising applications in sensing, imaging and communication systems in the near future.