Browsing by Author "McCarthy, Lauren A."

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Chiral Plasmonic Pinwheels Exhibit Orientation-Independent Linear Differential Scattering under Asymmetric Illumination
    (American Chemical Society, 2023) McCarthy, Lauren A.; Verma, Ojasvi; Naidu, Gopal Narmada; Bursi, Luca; Alabastri, Alessandro; Nordlander, Peter; Link, Stephan
    Plasmonic nanoantennas have considerably stronger polarization-dependent optical properties than their molecular counterparts, inspiring photonic platforms for enhancing molecular dichroism and providing fundamental insight into light-matter interactions. One such insight is that even achiral nanoparticles can yield strong optical activity when they are asymmetrically illuminated from a single oblique angle instead of evenly illuminated. This effect, called extrinsic chirality, results from the overall chirality of the experimental geometry and strongly depends on the orientation of the incident light. Although extrinsic chirality has been well-characterized, an analogous effect involving linear polarization sensitivity has not yet been discussed. In this study, we investigate the differential scattering of rotationally symmetric chiral plasmonic pinwheels when asymmetrically irradiated with linearly polarized light. Despite their high rotational symmetry, we observe substantial linear differential scattering that is maintained over all pinwheel orientations. We demonstrate that this orientation-independent linear differential scattering arises from the broken mirror and rotational symmetries of our overall experimental geometry. Our results underscore the necessity of considering both the rotational symmetry of the nanoantenna and the experimental setup, including illumination direction and angle, when performing plasmon-enhanced chiroptical characterizations. Our results demonstrate spectroscopic signatures of an effect analogous to extrinsic chirality for linear polarizations.
  • Thumbnail Image
    Item
    Enhanced control of plasmonic properties of silver–gold hollow nanoparticles via a reduction-assisted galvanic replacement approach
    (Royal Society of Chemistry, 2019) Daniel, Josée R.; McCarthy, Lauren A.; Ringe, Emilie; Boudreau, Denis
    Hollow noble metal nanoparticles are of growing interest due to their localized surface plasmon resonance (LSPR) tunability. A popular synthetic approach is galvanic replacement which can be coupled with a co-reducer. Here, we describe the control over morphology, and therefore over plasmonic properties including energy, bandwidth, extinction and scattering intensity, offered by co-reduction galvanic replacement. This study indicates that whereas the variation of atomic stoichiometry using the co-reduction method described in this work offers a rather modest tuning range of LSPR energy when compared to traditional galvanic replacement, it nevertheless has a profound effect on shell thickness, which imparts a degree of control over scattering intensity and sensitivity to changes in the dielectric constant of the surrounding environment. Therefore, in this context particle size and gold content become two design parameters that can be used to independently tune LSPR energy and intensity.
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Single-particle scattering spectroscopy: fundamentals and applications
    (De Gruyter, 2021) Al-Zubeidi, Alexander; McCarthy, Lauren A.; Rafiei-Miandashti, Ali; Heiderscheit, Thomas S.; Link, Stephan
    Metallic nanoparticles supporting a localized surface plasmon resonance have emerged as promising platforms for nanoscopic labels, sensors, and (photo-) catalysts. To use nanoparticles in these capacities, and to gain mechanistic insight into the reactivity of inherently heterogeneous nanoparticles, single-particle characterization approaches are needed. Single-particle scattering spectroscopy has become an important, highly sensitive tool for localizing single plasmonic nanoparticles and studying their optical properties, local environment, and reactivity. In this review, we discuss approaches taken for collecting the scattered light from single particles, their advantages and disadvantages, and present some recent applications. We introduce techniques for the excitation and detection of single-particle scattering such as high-angle dark-field excitation, total internal reflection dark-field excitation, scanning near-field microscopy, and interferometric scattering. We also describe methods to achieve polarization-resolved excitation and detection. We then discuss different approaches for scanning, ratiometric, snapshot, and interferometric hyperspectral imaging techniques used to extract spectral information. Finally, we provide a brief overview of specialized setups for in situ measurements of nanoparticles in liquid systems and setups coupled to scanning tip microscopes.