Browsing by Author "Yuan, Lin"

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    Impact of chemical interface damping on surface plasmon dephasing
    (Royal Society of Chemistry, 2019) Therrien, Andrew J.; Kale, Matthew J.; Yuan, Lin; Zhang, Chao; Halas, Naomi J.; Christopher, Phillip; Laboratory for Nanophotonics; Smalley-Curl Institute
    The excellent light harvesting ability of plasmonic nanoparticles makes them promising materials for a variety of technologies that rely on the conversion of photons to energetic charge carriers. In such applications, including photovoltaics and photocatalysis, the excitation of surface plasmons must induce charge transfer across the metal–adsorbate or metal–semiconductor interface. However, there is currently a lack of molecular level understanding of how the presence of a chemical interface impacts surface plasmon dephasing pathways. Here, we report an approach to quantitatively measure the influence of molecular adsorption on the spectral shape and intensity of the extinction, scattering, and absorption cross-sections for nanostructured plasmonic surfaces. This is demonstrated for the case of thiophenol adsorption on lithographically patterned gold nanodisk arrays. The results show that the formation of a chemical interface between thiophenol and Au causes surface plasmons to decay more prominently through photon absorption rather than photon scattering, as compared to the bare metal. We propose that this effect is a result of the introduction of adsorbate-induced allowable electronic transitions at the interface, which facilitate surface plasmon dephasing via photon absorption. The results suggest that designed chemical interfaces with well-defined electronic structures may enable engineering of hot electron distributions, which could be important for understanding and controlling plasmon-mediated photocatalysis and, more generally, hot carrier transfer processes.
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    Plasmonically Enhanced Hydrogen Evolution with an Al–TiO2-Based Photoelectrode
    (American Chemical Society, 2022) Yuan, Lin; Kuriakose, Anvy; Zhou, Jingyi; Robatjazi, Hossein; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
    Photoelectrochemical water splitting, as a method for producing clean hydrogen, could benefit from both plasmon-enhanced processes and the incorporation of earth-abundant materials in photoelectrode design. Here we report a n-TiO2/aluminum (Al) nanodisk/p-GaN photoelectrode sandwich device that exhibits enhanced H2 generation efficiencies due to a combination of plasmon-enhanced processes. Hot electrons generated in the illuminated Al nanodisk are injected into the conduction band of the TiO2 layer, subsequently transferring into water molecules adsorbed on the TiO2 surface, driving H2 evolution. The photocurrent densities we observe are nearly an order of magnitude higher than in an equivalent device with the Al nanodisk replaced with a Au nanodisk of the same size and are on par or better than previous reports of plasmonic photoelectrodes using Au nanoparticles in combination with cocatalyst species.
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    Tailoring Plasmonic Photocatalysis by Nanostructure Design
    (2022-04-19) Yuan, Lin; Halas, Naomi J
    Plasmonic photocatalysis utilizing strong light-matter interaction originated from localized surface plasmon resonance (LSPR), the collective oscillations of conduction band electrons on the metal surface to convert the light energy into chemical energy. “Antenna-reactor” complexes take the advantage of both plasmonic antenna and the catalytic favorable active sites to achieve chemical transformations at mild conditions with high efficiency and selectivity. The size, shape, materials composition, dielectric environment, and plasmon coupling can be utilized the knob to tune the optical properties, cooperated with the catalytic surface design, the nanostructure can therefore tailor the plasmonic photocatalysis. In this thesis, I present 4 types of nanostructure design for distinct plasmonic photocatalysis, and they can be divided into two parts based on the mechanism governing the chemical transformation. The first part shows examples of utilizing both plasmon-mediated hot carriers and the hydrogen spillover effect on the Pd surface. In chapter 2, I will present the design of tilted Pd plasmonic nanocone, the standalone Pd nanocones can be photocatalyst by focusing the light on its tip to facilitate the hot-electron mediated hydrogen desorption on Pd, and it can be utilized to hydrogenate the adjacent graphene layer, turning it from a metal to semiconductor. And in chapter 3, I will present a planar Al nanodisk antenna-dual reactor complex with two chemically distinct and spatially separated reactors in the form of Pd and Fe nanodisks. The photocatalytic NH3-D2 and H2-D2 exchange reactions together with the hot carrier and quantum mechanical reaction pathway calculations suggest the hot electron on the surface of Fe and the hydrogen spillover from Pd to Fe synergistically and mutually optimize the N-H bond activation process. The second part presents the exploration of using Al plasmonics for photocatalysis. As the most abundant metallic element in the earth’s crust, aluminum has been considered a promising future sustainable plasmonic material with superior optical properties. In chapter 4, 3 morphology-dependent aluminum nanocrystals with similar plasmon resonance frequencies show the morphological trend for photocatalytic hydrogen dissociation reaction: the more cuspate nanocrystals show higher reactivity and lower apparent activation energy under visible light illumination, but the trend disappears with the light turning off. The semi-classic model assigned this trend originating from the interband transition of aluminum nanocrystals. In chapter 5, I will present a design of n-TiO2/Al nanodisks/p-GaN photocathode for photoelectrochemical hydrogen evolution reaction under visible light irradiation. Our device shows 10 times higher photocurrent densities compared to the same structural design utilizing Au nanodisks as light-harvester. By simply engineering the diameter of Al nanodisks, we found the 80 nm diameter Al nanodisks in n-TiO2/Al nanodisks/p-GaN device show the highest reactivity due to the interplay of local light absorption and hot electrons in TiO2 film. The photocurrent density measurement and hydrogen production measurement show that our device achieves one of the best performances compared to the device utilizing Au plasmonic previously reported. This thesis contributes to the knowledge of the effective nanostructure design for plasmon-mediated chemical transformations and paves the way for future applications of plasmonic photocatalysis.