Browsing by Author "Zhang, Chao"

Now showing 1 - 7 of 7
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    Aluminum Nanocrystals as a Plasmonic Photocatalyst for Hydrogen Dissociation
    (2016-03-31) Zhang, Chao; Halas, Naomi J
    Hydrogen dissociation is a critical step in many hydrogenation reactions central to industrial chemical production and pollutant removal. This step typically utilizes the favorable band structure of precious metal catalysts like platinum and palladium to achieve high efficiency under mild conditions. Here we demonstrate that aluminum nanocrystals (Al NCs), when illuminated, can be used as a photocatalyst for hydrogen dissociation at room temperature and atmospheric pressure, despite the high activation barrier toward hydrogen adsorption and dissociation. We show that hot electron transfer from Al NCs to the antibonding orbitals of hydrogen molecules facilitates their dissociation. Hot electrons generated from surface plasmon decay and from direct photoexcitation of the interband transitions of Al both contribute to this process. Our results pave the way for the use of aluminum, an earth-abundant, nonprecious metal, for photocatalysis.
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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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    Multicomponent plasmonic photocatalysts consisting of a plasmonic antenna and a reactive catalytic surface: the antenna-reactor effect
    (2020-09-08) Halas, Nancy Jean; Nordlander, Peter; Robatjazi, Hossein; Swearer, Dayne Francis; Zhang, Chao; Zhao, Hangqi; Zhou, Linan; Rice University; United States Patent and Trademark Office
    A multicomponent photocatalyst includes a reactive component optically, electronically, or thermally coupled to a plasmonic material. A method of performing a catalytic reaction includes loading a multicomponent photocatalyst including a reactive component optically, electronically, or thermally coupled to a plasmonic material into a reaction chamber, introducing molecular reactants into the reaction chamber, and illuminating the reaction chamber with a light source.
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    Multicomponent plasmonic photocatalysts consisting of a plasmonic antenna and a reactive catalytic surface: the antenna-reactor effect
    (2024-04-16) Halas, Nancy Jean; Nordlander, Peter; Robatjazi, Hossein; Swearer, Dayne Francis; Zhang, Chao; Zhao, Hangqi; Zhou, Linan; Rice University; United States Patent and Trademark Office
    A method of making a multicomponent photocatalyst, includes inducing precipitation from a pre-cursor solution comprising a pre-cursor of a plasmonic material and a pre-cursor of a reactive component to form co-precipitated particles; collecting the co-precipitated particles; and annealing the co-precipitated particles to form the multicomponent photocatalyst comprising a reactive component optically, thermally, or electronically coupled to a plasmonic material.
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    Multicomponent plasmonic photocatalysts consisting of a plasmonic antenna and a reactive catalytic surface: the antenna-reactor effect
    (2024-10-08) Halas, Nancy Jean; Nordlander, Peter; Robatjazi, Hossein; Swearer, Dayne Francis; Zhang, Chao; Zhao, Hangqi; Zhou, Linan; Rice University; United States Patent and Trademark Office
    A multicomponent photocatalyst includes a reactive component optically, electronically, or thermally coupled to a plasmonic material. A method of performing a catalytic reaction includes loading a multicomponent photocatalyst including a reactive component optically, electronically, or thermally coupled to a plasmonic material into a reaction chamber; introducing molecular reactants into the reaction chamber; and illuminating the reaction chamber with a light source.
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    Plasmonic Heterodimers: Antenna-Reactor Effect and Optical Forces
    (2018-08-31) Zhang, Chao; Halas, Naomi J
    Surface plasmon is the collective oscillation of free electrons in metallic nanoparticles. When two plasmonic nanoparticles are brought close together as a plasmonic dimer, their near field can interact with each other to generate new hybridized resonances. In particular, pairing nanoparticles with different optical, chemical, electrical, or mechanical properties as a heterodimer allows one to customize nanophotonic systems that utilize the desired features of individual components simultaneously. In this thesis, I present two examples to show the flexibility and modularity of such plasmonic heterodimers. In the first example, I demonstrate the use of Al-Pd nanodisk heterodimers as an antenna-reactor photocatalyst. A photocatalyst harvests energy from light to drive chemical reactions. Conventional catalysts are made of transition metal nanoparticles, which only interact weakly with light. On the contrary, plasmonic metals such as Al, Au, and Ag interact strongly with light, but are far poorer catalysts. By combining plasmonic and catalytic metal nanoparticles in one entity, the plasmonic antenna can drive a polarization in the catalytic reactor, creating a forced plasmon. This process dramatically enhances the optical response of the reactor, making it an efficient photocatalyst. Precisely defined, self-aligned, and strongly coupled Al-Pd nanodisk heterodimers can be prepared at the wafer scale using hole-mask colloidal lithography. Light-induced hydrogen dissociation reaction was performed as a model reaction to evaluate the performance of this photocatalyst. The wavelength- and polarization-dependent reaction rate closely follows the Al-mediated optical absorption of the Pd nanodisk. The high structural uniformity of the heterodimers also enables microscopic quantification of reaction rates and quantum efficiencies at single nanostructure level. In the second example, I investigate the optical properties of Al-Au nanodisk heterodimers. Both components of this heterodimer support surface plasmon resonances, but in different wavelength ranges. Forced plasmon can be created when the on-resonance nanodisk drives the off-resonance nanodisk through near field coupling. The hybridized resonances are not only observed with far field extinction spectroscopy, but also probed in the near field by photo-induced force microscopy. Moreover, when the interdisk spacing is very small and the near field interaction extremely strong, the Au nanodisk of the heterodimer can be repositioned and reshaped under laser illumination. This is attributed to a joint effect of photothermal softening of the Au lattice and the optical forces applied to the Au nanodisk. This thesis paves the way of designing and utilizing plasmonic heterodimers for a rich abundance of applications including photocatalysis, solar energy harvesting, sensing, and optically-induced nanomanufacturing.
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    Role of the 245 phase in alkaline iron selenide superconductors revealed by high-pressure studies
    (American Physical Society, 2014) Gao, Peiwen; Yu, Rong; Sun, Liling; Wang, Hangdong; Wang, Zhen; Wu, Qi; Fang, Minghu; Chen, Genfu; Guo, Jing; Zhang, Chao; Gu, Dachun; Tian, Huanfang; Li, Jianqi; Liu, Jing; Li, Yanchun; Li, Xiaodong; Jiang, Sheng; Yang, Ke; Li, Aiguo; Si, Qimiao; Zhao, Zhongxian
    There is considerable interest in uncovering the physics of iron-based superconductivity from the alkaline iron selenides, a materials class containing an insulating phase (245 phase) and a superconducting (SC) phase. Due to the microstructural complexity of these superconductors, the role of the 245 phase in the development of the superconductivity has been a puzzle. Here we demonstrate a comprehensive high-pressure study on the insulating samples with pure 245 phase and biphasic SC samples. We find that the insulating behavior can be completely suppressed by pressure in the insulating samples and also identify an intermediate metallic (M′) state. The Mott insulating (MI) state of the 245 phase and the M′ state coexist over a significant range of pressure up to ∼10 GPa, the same pressure at which the superconductivity of the SC samples vanishes. Our results reveal the M′ state as a pathway that connects the insulating and SC phases of the alkaline iron selenides and indicate that the coexistence and interplay between the MI and M′ states is a necessary condition for superconductivity. Finally, we interpret the M′ state in terms of an orbital selectivity of the correlated 3d electrons.