Browsing by Author "Smith, Kyle W."

Now showing 1 - 5 of 5
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    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.
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    Chiral templating of self-assembling nanostructures by circularly polarized light
    (Nature Publishing Group, 2015) Yeom, Jihyeon; Yeom, Bongjun; Chan, Henry; Smith, Kyle W.; Dominguez-Medina, Sergio; Bahng, Joong Hwan; Zhao, Gongpu; Chang, Wei-Shun; Chang, Sung Jin; Chuvilin, Andrey; Melnikau, Dzmitry; Rogach, Andrey L.; Zhang, Peijun; Link, Stephan; Král, Petr; Kotov, Nicholas A.
    The high optical and chemical activity of nanoparticles (NPs) signifies the possibility of converting the spin angular momenta of photons into structural changes in matter. Here, we demonstrate that illumination of dispersions of racemic CdTe NPs with right- (left-)handed circularly polarized light (CPL) induces the formation of right- (left-)handed twisted nanoribbons with an enantiomeric excess exceeding 30%, which is ∼10 times higher than that of typical CPL-induced reactions. Linearly polarized light or dark conditions led instead to straight nanoribbons. CPL 'templating' of NP assemblies is based on the enantio-selective photoactivation of chiral NPs and clusters, followed by their photooxidation and self-assembly into nanoribbons with specific helicity as a result of chirality-sensitive interactions between the NPs. The ability of NPs to retain the polarization information of incident photons should open pathways for the synthesis of chiral photonic materials and allow a better understanding of the origins of biomolecular homochirality.
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    Circular Differential Scattering of Single Chiral Self-Assembled Gold Nanorod Dimers
    (American Chemical Society, 2015) Wang, Lin-Yung; Smith, Kyle W.; Dominiquez-Medina, Sergio; Moody, Nicole; Olson, Jana M.; Zhang, Huanan; Chang, Wei-Shun; Kotov, Nicholas; Link, Stephan; Laboratory for Nanophotonics
    Circular dichroism spectroscopy is essential for structural characterization of proteins and chiral nanomaterials. Chiral structures from plasmonic materials have extraordinary strong circular dichroism effects compared to their molecular counterparts. While being extensively investigated, the comprehensive account of circular dichroism effects consistent with other plasmonic phenomena is still missing. Here we investigated the circular differential scattering of a simple chiral plasmonic system, a twisted side-by-side Au nanorod dimer, using single-particle circular dichroism spectroscopy complimented with electromagnetic simulations. This approach enabled us to quantify the effects of structural symmetry breaking, namely, size-mismatch between the constituent Au nanorods and large twist angles on the resulting circular differential scattering spectrum. Our results demonstrate that, if only scattering is considered as measured by dark-field spectroscopy, a homodimer of Au nanorods with similar sizes produces a circular differential scattering line shape that is different from the bisignate response of the corresponding conventional CD spectrum, which measures extinction, that is, the sum of scattering and absorption. On the other hand, symmetry breaking in a heterodimer with Au nanorods with different sizes yields a bisignate circular differential scattering line shape. In addition, we provide a general method for correcting linear dichroism artifacts arising from slightly elliptically polarized light in a typical dark-field microscope, as is necessary especially when measuring highly anisotropic nanostructures, such as side-by-side nanorods. This work lays the foundation for understanding absorption and scattering contributions to the CD line shape of single chiroplasmonic nanostructures free from ensemble-averaging, especially important for self-assembled chiral nanostructures that usually exist as both enantiomers.
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    Polarized evanescent waves reveal trochoidal dichroism
    (National Academy of Sciences, 2020) McCarthy, Lauren A.; Smith, Kyle W.; Lan, Xiang; Jebeli, Seyyed Ali Hosseini; Bursi, Luca; Alabastri, Alessandro; Chang, Wei-Shun; Nordlander, Peter; Link, Stephan; Laboratory for Nanoscale Spectroscopic Imaging at Rice; Laboratory for Nanophotonics
    Matter’s sensitivity to light polarization is characterized by linear and circular polarization effects, corresponding to the system’s anisotropy and handedness, respectively. Recent investigations into the near-field properties of evanescent waves have revealed polarization states with out-of-phase transverse and longitudinal oscillations, resulting in trochoidal, or cartwheeling, field motion. Here, we demonstrate matter’s inherent sensitivity to the direction of the trochoidal field and name this property trochoidal dichroism. We observe trochoidal dichroism in the differential excitation of bonding and antibonding plasmon modes for a system composed of two coupled dipole scatterers. Trochoidal dichroism constitutes the observation of a geometric basis for polarization sensitivity that fundamentally differs from linear and circular dichroism. It could also be used to characterize molecular systems, such as certain light-harvesting antennas, with cartwheeling charge motion upon excitation.
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    Snapshot Hyperspectral Imaging (SHI) for Revealing Irreversible and Heterogeneous Plasmonic Processes
    (American Chemical Society, 2018) Kirchner, Silke R.; Smith, Kyle W.; Hoener, Benjamin S.; Collins, Sean S.E.; Wang, Wenxiao; Cai, Yi-Yu; Kinnear, Calum; Zhang, Heyou; Chang, Wei-Shun; Mulvaney, Paul; Landes, Christy F.; Link, Stephan
    Plasmon-mediated processes provide unique opportunities for selective photocatalysis, photovoltaics, and electrochemistry. Determining the influence of particle heterogeneity is an unsolved problem because often such processes introduce irreversible changes to the nanocatalysts and/or their surroundings. The challenge lies in monitoring heterogeneous nonequilibrium dynamics via the slow, serial methods that are intrinsic to almost all spectral acquisition methods with suitable spatial and/or spectral resolution. Here, we present a new metrology, snapshot hyperspectral imaging (SHI), that facilitates in situ readout of the tube lens image and first-order diffraction image of the dark-field scattering from many individual plasmonic nanoparticles to extract their respective spectra simultaneously. Evanescent wave excitation with a supercontinuum laser enabled signal-to-noise ratios greater than 100 with a time resolution of only 1 ms. Throughput of ∼100 simultaneous spectra was achieved with a highly ordered nanoparticle array, yielding a spectral resolution of 0.21 nm/pixel. Additionally, an alternative dark-field excitation geometry utilized a combination of a supercontinuum laser and a reflecting objective for polarization-controlled SHI. Using a simplified version of SHI, we temporally resolve on the millisecond time scale the heterogeneous kinetics of an electrochemical surface redox reaction for many individual gold nanoparticles simultaneously.