Browsing by Author "Doiron, Chloe"

Now showing 1 - 4 of 4
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    Alternative Materials for Harnessing Symmetry and Topology in Thermal Light Sources for Thermophotovoltaics
    (2020-11-30) Doiron, Chloe; Naik, Gururaj V.
    Selective thermal emitters emit thermal radiation in a narrow frequency range enabling applications in sensing, waste heat energy conversion, and radiative cooling. Waste heat energy recovery through thermophotovoltaics requires high performance selective thermal emitters. To date, the achieved conversion efficiency values fall well below thermodynamic limits. The primary factors limiting device performance arise from material limitations of commonly used optical materials. In this dissertation, I will demonstrate the need for alternative material platforms and show how these new platforms enable unconventional thermal light sources using the principles of phase, symmetry, and topology. First, I will discuss physical modeling to predict the optical properties of doped semiconductors at high temperatures. This analysis will demonstrate the role loss engineering plays in designing selective thermal emitters. Next, I will present experimental results of loss engineering in hybrid plasmonic-photonic resonators resulting in passive parity-time (PT) symmetry in thermal emission. Using the principles of non-Hermitian physics in such a loss asymmetric system provides a pathway for overcoming the trade-off between spectral linewidth and peak emissivity. Furthermore, controlling the coupling between horizontal and vertical modes in such a hybrid system allows for the observation of higher-order non-Hermitian phenomena. This control permits the creation of exceptional concentric rings and thermal emitters with non-trivial topology. Additionally, I will present an experimental demonstration of iron pyrite (FeS$_2$) as an ultrahigh index dielectric material for mid-infrared metamaterials. Iron pyrite has a very large refractive index, up to 4.4, with an optical band gap close to 1 eV far surpassing performance estimates using the Moss rule's common form. Finally, I will conclude with an experimental demonstration of a hyperbolic metamaterial using aligned films of single-walled carbon nanotubes. The optical anisotropy of the aligned films facilitates the creation of ultra-small thermal emitters with volumes below ~$\frac{\lambda^3}{700}$.
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    Direct Plasmon-Driven Photoelectrocatalysis
    (American Chemical Society, 2015) Robatjazi, Hossein; Bahauddin, Shah Mohammad; Doiron, Chloe; Thomann, Isabell; Laboratory for Nanophotonics (LANP); Rice Quantum Institute
    Harnessing the energy from hot charge carriers is an emerging research area with the potential to improve energy conversion technologies. Here we present a novel plasmonic photoelectrode architecture carefully designed to drive photocatalytic reactions by efficient, nonradiative plasmon decay into hot carriers. In contrast to past work, our architecture does not utilize a Schottky junction, the commonly used building block to collect hot carriers. Instead, we observed large photocurrents from a Schottky-free junction due to direct hot electron injection from plasmonic gold nanoparticles into the reactant species upon plasmon decay. The key ingredients of our approach are (i) an architecture for increased light absorption inspired by optical impedance matching concepts, (ii) carrier separation by a selective transport layer, and (iii) efficient hot-carrier generation and injection from small plasmonic Au nanoparticles to adsorbed water molecules. We also investigated the quantum efficiency of hot electron injection for different particle diameters to elucidate potential quantum effects while keeping the plasmon resonance frequency unchanged. Interestingly, our studies did not reveal differences in the hot-electron generation and injection efficiencies for the investigated particle dimensions and plasmon resonances.
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    Femtosecond Carrier Dynamics in Metal/Quasi-2D MoS2 Nanostructures
    (2016-04-25) Doiron, Chloe; Thomann, Isabell
    Plasmonic nanoparticles and quasi-2D (Q2D) transition metal dichalcogenides (TMDs) have been identified as promising materials for solar-to-fuel energy conversion. Plasmonically active materials are interesting because large absorption cross-sections and non-radiative decay of plasmons that can excite hot electrons for injection into semiconducting materials. Q2D MoS$_2$ is known to be highly catalytically active for driving the hydrogen evolution reaction (HER). Combined together plasmonically active particles and MoS$_2$ can act as a hybrid antenna/catalyst nanostructures with both high absorption and catalytic activity. We performed femtosecond transient absorption spectroscopy measurements of Au/MoS$_2$ hybrid nanostructures finding ultrafast signatures of hot electron generation in the form of "anomalous" sub-100 fs lifetime signals indicative of electron-electron scattering. Coherent generation of acoustic phonon modes was also observed allowing for estimation of the peak electron temperature during excitation. Near field scanning probe microscopy measurements showed the presence of hot spots that may be responsible for hot electron generation observed in Au/MoS$_2$ hybrid nanostructures.
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    Non-Hermitian metasurfaces for the best of plasmonics and dielectrics
    (Optical Society of America, 2021) Yang, Frank; Hwang, Alexander; Doiron, Chloe; Naik, Gururaj V.
    Materials and their geometry make up the tools for designing nanophotonic devices. In the past, the real part of the refractive index of materials has remained the focus for designing novel devices. The absorption, or imaginary index, was tolerated as an undesirable effect. However, a clever distribution of imaginary index of materials offers an additional degree of freedom for designing nanophotonic devices. Non-Hermitian optics provides a unique opportunity to take advantage of absorption losses in materials to enable unconventional physical effects. Typically occurring near energy degeneracies called exceptional points, these effects include enhanced sensitivity, unidirectional invisibility, and non-trivial topology. In this work, we leverage plasmonic absorption losses (or imaginary index) as a design parameter for non-Hermitian, passive parity-time symmetric metasurfaces. We show that coupled plasmonic-photonic resonator pairs, possessing a large asymmetry in absorptive losses but balanced radiative losses, exhibit an optical phase transition at an exceptional point and directional scattering. These systems enable new pathways for metasurface design using phase, symmetry, and topology as powerful tools.