Browsing by Author "Robatjazi, Hossein"
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Item Broadband Absorption Engineering to Enhance Light Absorption in Monolayer MoS2(American Chemical Society, 2016) Bahauddin, Shah Mohammad; Robatjazi, Hossein; Thomann, Isabell; Laboratory for Nanophotonics; Rice Quantum InstituteHere we take a first step toward tackling the challenge of incomplete optical absorption in monolayers of transition metal dichalcogenides for conversion of photon energy, including solar, into other forms of energy. We present a monolayer MoS2-based photoelectrode architecture that exploits nanophotonic light management strategies to enhance absorption within the monolayer of MoS2, while simultaneously integrating an efficient charge carrier separation mechanism facilitated by a MoS2/NiOx heterojunction. Specifically, we demonstrate two extremely thin photoelectrode architectures for solar-fuel generation: (i) a planar optical cavity architecture, MoS2/NiOx/Al, that improves optical impedance matching and (ii) an architecture employing plasmonic silver nanoparticles (Ag NPs), MoS2/Ag NPs/NiOx/Al, that further improves light absorption within the monolayer. We used a combination of numerical simulations, analytical models, and experimental optical characterizations to gain insights into the contributions of optical impedance matching versus plasmonic near-field enhancement effects in our plasmonic photoelectrode structures. By performing three-dimensional electromagnetic simulations, we predict structures that can absorb 37% of the incident light integrated from 400 to 700 nm within a monolayer of MoS2, a 5.9× enhanced absorption compared to that of MoS2 on a sapphire (Al2O3) substrate. Experimentally, a 3.9× absorption enhancement is observed in the total structure compared to that of MoS2/Al2O3, and photoluminescence measurements suggest this enhancement largely arises from absorption enhancements within the MoS2 layer alone. The results of these measurements also confirm that our MoS2/NiOx/Al structures do indeed facilitate efficient charge separation, as required for a photoelectrode. To rapidly explore the parameter space of plasmonic photoelectrode architectures, we also developed an analytical model based on an effective medium model that is in excellent agreement with results from numerical FDTD simulations.Item Direct plasmon-driven photoelectrocatalysis(2016-05-18) Robatjazi, Hossein; Thomann, IsabellHarnessing the energy from hot charge carriers is an emerging research area with the potential to improve energy conversion technologies. This thesis present a novel plasmonic photoelectrode architecture carefully designed to drive photocatalytic reactions by efficient, non-radiative 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 with heterogeneous particle size distribution to adsorbed water molecules. Also, the quantum efficiency of hot electron injection for different particle diameters has been investigated to elucidate potential quantum effects while keeping the plasmon resonance frequency unchanged. This thesis also present a simple strategy to prepare free-standing through-hole ultrathin alumina membranes (UTAMs) for efficient sub-100 nm nanoarray fabrication that, in contrast to past works, can be generalized to any substrate and material. The potential of developed strategy for nanoarray fabrication has been demonstrated through fabrication of centimeter-scale of dense plasmonic nanoarray of sub-100 nm nanodots on very susceptible and rough substrates. Subsequently, the fabricated nanoarray has been employed for direct plasmon-driven photoelectrocatalysis of water.Item Direct Plasmon-Driven Photoelectrocatalysis(American Chemical Society, 2015) Robatjazi, Hossein; Bahauddin, Shah Mohammad; Doiron, Chloe; Thomann, Isabell; Laboratory for Nanophotonics (LANP); Rice Quantum InstituteHarnessing 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.Item Metal-organic frameworks tailor the properties of aluminum nanocrystals(AAAS, 2019) Robatjazi, Hossein; Weinberg, Daniel; Swearer, Dayne F.; Jacobson, Christian; Zhang, Ming; Tian, Shu; Zhou, Linan; Nordlander, Peter; Halas, Naomi J.Metal-organic frameworks (MOFs) and metal nanoparticles are two classes of materials that have received considerable recent attention, each for controlling chemical reactivities, albeit in very different ways. Here, we report the growth of MOF shell layers surrounding aluminum nanocrystals (Al NCs), an Earth-abundant metal with energetic, plasmonic, and photocatalytic properties. The MOF shell growth proceeds by means of dissolution-and-growth chemistry that uses the intrinsic surface oxide of the NC to obtain the Al3+ ions accommodated into the MOF nodes. Changes in the Al NC plasmon resonance provide an intrinsic optical probe of its dissolution and growth kinetics. This same chemistry enables a highly controlled oxidation of the Al NCs, providing a precise method for reducing NC size in a shape-preserving manner. The MOF shell encapsulation of the Al NCs results in increased efficiencies for plasmon-enhanced photocatalysis, which is observed for the hydrogen-deuterium exchange and reverse water-gas shift reactions.Item 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 OfficeA 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.Item 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 OfficeA 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.Item Plasmonic Photocatalysis of Nitrous Oxide into N2 and O2 Using Aluminum–Iridium Antenna–Reactor Nanoparticles(American Chemical Society, 2019) Swearer, Dayne F.; Robatjazi, Hossein; Martirez, John Mark P.; Zhang, Ming; Zhou, Linan; Carter, Emily A.; Nordlander, Peter; Halas, Naomi J.; Laboratory for NanophotonicsPhotocatalysis with optically active “plasmonic” nanoparticles is a growing field in heterogeneous catalysis, with the potential for substantially increasing efficiencies and selectivities of chemical reactions. Here, the decomposition of nitrous oxide (N2O), a potent anthropogenic greenhouse gas, on illuminated aluminum–iridium (Al–Ir) antenna–reactor plasmonic photocatalysts is reported. Under resonant illumination conditions, N2 and O2 are the only observable decomposition products, avoiding the problematic generation of NOx species observed using other approaches. Because no appreciable change to the apparent activation energy was observed under illumination, the primary reaction enhancement mechanism for Al–Ir is likely due to photothermal heating rather than plasmon-induced hot-carrier contributions. This light-based approach can induce autocatalysis for rapid N2O conversion, a process with highly promising potential for applications in N2O abatement technologies, satellite propulsion, or emergency life-support systems in space stations and submarines.Item 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 NanophotonicsPhotoelectrochemical 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.Item Tailoring the Surface Chemistry of Aluminum Nanocrystals for Plasmon-mediated Catalysis(2019-04-05) Robatjazi, Hossein; Halas, Naomi J.Light-driven chemical transformation with optically active plasmonic nanoparticles is a new paradigm in heterogeneous photocatalysis that may offer an ultimately sustainable alternative to traditional thermal-driven catalytic reactions. However, plasmonic metals nanostructures, despite strong coupling of their electron density with electromagnetic radiation, are not universally good catalytic materials, which limits the type of chemical reactions that can be induced directly on their surface. Recently, we introduced multicomponent plasmonic photocatalysts by rationally coupling of plasmonic nanoantennas directly to active catalytic reactors. This combination leverages and combines the light-harvesting abilities of plasmonic nanoparticles with high-efficiency catalysts to drive chemical reactions under milder operating conditions in contrast to traditional energy-intensive heat/pressure-driven chemical conversions. The modularity in ‘antenna-reactor’ design to create tailored catalysts holds promise to expand the scope and enhances the efficiencies of chemical reactions enabled by plasmonic photocatalysis. This thesis reports on utilizing aluminum nanocrystals (Al NCs), an earth-abundant metal with energetic and plasmonic properties, for developing novel light-activated photocatalysts, where chemically synthesized Al NCs were used as optical nanoantennas and the reactor was chosen among the semiconductor layer, active transition metal (TM) nanoparticles, and porous organic framework shells. Rational design and independent control over the catalytic and light-harvesting components in aluminum-cuprous oxide (Al-Cu2O) and aluminum-iridium (Al-Ir) ‘antenna-reactor’ nanoparticles results in light-driven mitigation of anthropogenic carbon dioxide and nitrous oxide, respectively. The mechanistic pathways of plasmonic photocatalysis for those reactions were investigated through the rigorous combination of the experimental and theoretical studies. Furthermore, the surface modification of Al NCs via bottom-up encapsulation within metal-organic frameworks (MOFs) shell layer was investigated. MOF growth around Al NCs provides a new level of controlling the growth and surface chemistry and plasmonic characteristics of Al NCs. The enhanced reactant uptake near the plasmonic center afforded by the porous nature of MOF shell results in increased photocatalytic activity of Al NCs, which is observed for the hydrogen-deuterium exchange and reverse water-gas shift reactions. The transition from noble metals to aluminum-based antenna-reactor heterostructures in plasmonic photocatalysis provides a sustainable route to high-value chemicals and reaffirms the practical potential of plasmon-mediated chemical transformations.Item Ultrathin AAO Membrane as a Generic Template for Sub-100 nm Nanostructure Fabrication(American Chemical Society, 2016) Robatjazi, Hossein; Bahauddin, Shah Mohammad; Macfarlan, Luke H.; Fu, Sidan; Thomann, Isabell; Laboratory for Nanophotonics; Rice Quantum Institute; Rice Center for Quantum MaterialsAnodic aluminum oxide (AAO) templates are emerging as a platform for simple, cost-effective, high-throughput top-down nanofabrication of regular arrays of nanostructures. Thus far, however, AAO pattern transfer has largely been restricted to smooth and chemically inert surfaces, mostly Silicon substrates. Here, we present a more generalizable strategy for preparing free-standing through-hole ultrathin alumina membranes (UTAMs) and transferring them to both smooth and rough substrates, thereby enabling the fabrication of centimeter-scale arrays of nanostructures with sub-100 nm feature diameters on almost arbitrary substrates. To validate the utility of our procedures, we transferred UTAMs to surfaces relevant for photocatalytic applications and prepared plasmonic photocathodes consisting of dense arrays of size-controlled sub-100 nm Au and Ni nanodots on top of chemically noninert NiOx thin films. To demonstrate the functionality of the fabricated structures, we used a plasmonic photocathode consisting of an array of sub-50 nm Au nanodots on NiOx/Al substrates to drive direct, plasmon-enhanced photoelectrocatalysis and found excellent device performance. We also successfully decorated very rough fluorine-doped tin oxide substrates with an array of high-density sub-100 nm nanodots. Our results extend the opportunities for AAO masks to serve as generic templates for novel applications that were previously prohibited by lack of methods to transfer to the required substrate.