Recursos de colección

Caltech Authors (160.918 recursos)

Repository of works by Caltech published authors.

Group = JCAP

Mostrando recursos 1 - 20 de 125

  1. Predictive simulation of non-steady-state transport of gases through rubbery polymer membranes

    Soniat, Marielle; Tesfaye, Meron; Brooks, Daniel; Merinov, Boris; Goddard, William A., III; Weber, Adam Z.; Houle, Frances A.
    A multiscale, physically-based, reaction-diffusion kinetics model is developed for non-steady-state transport of simple gases through a rubbery polymer. Experimental data from the literature, new measurements of non-steady-state permeation and a molecular dynamics simulation of a gas-polymer sticking probability for a typical system are used to construct and validate the model framework. Using no adjustable parameters, the model successfully reproduces time-dependent experimental data for two distinct systems: (1) O_2 quenching of a phosphorescent dye embedded in poly(n-butyl(amino) thionylphosphazene), and (2) O_2, N_2, CH_4 and CO_2 transport through poly(dimethyl siloxane). The calculations show that in the pre-steady-state regime, permeation is only correctly...

  2. Dynamically controlled Purcell enhancement of visible spontaneous emission in a gated plasmonic heterostructure

    Lu, Yu-Jung; Sokhoyan, Ruzan; Cheng, Wen-Hui; Shirmanesh, Ghazaleh Kafaie; Davoyan, Artur R.; Pala, Ragip A.; Thyagarajan, Krishnan; Atwater, Harry A.
    Emission control of colloidal quantum dots (QDs) is a cornerstone of modern high-quality lighting and display technologies. Dynamic emission control of colloidal QDs in an optoelectronic device is usually achieved by changing the optical pump intensity or injection current density. Here we propose and demonstrate a distinctly different mechanism for the temporal modulation of QD emission intensity at constant optical pumping rate. Our mechanism is based on the electrically controlled modulation of the local density of optical states (LDOS) at the position of the QDs, resulting in the modulation of the QD spontaneous emission rate, far-field emission intensity, and quantum...

  3. Dynamically controlled Purcell enhancement of visible spontaneous emission in a gated plasmonic heterostructure

    Lu, Yu-Jung; Sokhoyan, Ruzan; Cheng, Wen-Hui; Shirmanesh, Ghazaleh Kafaie; Davoyan, Artur R.; Pala, Ragip A.; Thyagarajan, Krishnan; Atwater, Harry A.
    Emission control of colloidal quantum dots (QDs) is a cornerstone of modern high-quality lighting and display technologies. Dynamic emission control of colloidal QDs in an optoelectronic device is usually achieved by changing the optical pump intensity or injection current density. Here we propose and demonstrate a distinctly different mechanism for the temporal modulation of QD emission intensity at constant optical pumping rate. Our mechanism is based on the electrically controlled modulation of the local density of optical states (LDOS) at the position of the QDs, resulting in the modulation of the QD spontaneous emission rate, far-field emission intensity, and quantum...

  4. Discovery and Characterization of a Pourbaix Stable, 1.8 eV Direct Gap Bismuth Manganate Photoanode

    Newhouse, Paul F.; Reyes-Lillo, Sebastian E.; Li, Guo; Zhou, Lan; Shinde, Aniketa; Guevarra, Dan; Suram, Santosh K.; Soedarmadji, Edwin; Richter, Matthias H.; Qu, Xiaohui; Persson, Kristin; Neaton, Jeffrey B.; Gregoire, John M.
    Solar-driven oxygen evolution is a critical technology for renewably synthesizing hydrogen and carbon-containing fuels in solar fuels generators. New photoanode materials are needed to meet efficiency and stability requirements, motivating materials explorations for semiconductors with (i) band gap energy in the visible spectrum and (ii) stable operation in aqueous electrolyte at the electrochemical potential needed to evolve oxygen from water. Motivated by the oxygen evolution competency of many Mn-based oxides, the existence of several Bi-containing ternary oxide photoanode materials, and the variety of known oxide materials combining these elements with Sm, we explore the Bi-Mn-Sm oxide system for new photoanodes....

  5. Ultralight Angstrom-Scale Optimal Optical Reflectors

    Papadakis, Georgia T.; Narang, Prineha; Sundararaman, Ravishankar; Rivera, Nicholas; Buljan, Hrvoje; Engheta, Nader; Soljačić, Marin
    High reflectance in many state-of-the-art optical devices is achieved with noble metals. However, metals are limited by losses and, for certain applications, by their high mass density. Using a combination of ab initio and optical transfer matrix calculations, we evaluate the behavior of graphene-based angstrom-scale metamaterials and find that they could act as nearly perfect reflectors in the mid–long-wave infrared (IR) range. The low density of states for electron–phonon scattering and interband excitations leads to unprecedented optical properties for graphene heterostructures, especially alternating atomic layers of graphene and hexagonal boron nitride, at wavelengths greater than 10 μm. At these wavelengths,...

  6. Effects of surface condition on the work function and valence-band position of ZnSnN_2

    Shing, Amanda M.; Tolstova, Yulia; Lewis, Nathan S.; Atwater, Harry A.
    ZnSnN_2 is an emerging wide band gap earth-abundant semiconductor with potential applications in photonic devices such as solar cells, LEDs, and optical sensors. We report the characterization by ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy of reactively radio-frequency sputtered II–IV-nitride ZnSnN_2 thin films. For samples transferred in high vacuum, the ZnSnN2 surface work function was 4.0 ± 0.1 eV below the vacuum level, with a valence-band onset of 1.2 ± 0.1 eV below the Fermi level. The resulting band diagram indicates that the degenerate bulk Fermi level position in ZnSnN_2 shifts to mid-gap at the surface due to band bending that results from equilibration...

  7. Electrochemical Stability of Metastable Materials

    Singh, Arunima K.; Zhou, Lan; Shinde, Aniketa; Suram, Santosh K.; Montoya, Joseph H.; Winston, Donald; Gregoire, John M.; Persson, Kristin A.
    We present a first-principles based formalism to provide a quantitative measure of the thermodynamic instability and propensity for electrochemical stabilization, passivation or corrosion of metastable materials in aqueous media. We demonstrate that this formalism can assess the relative Gibbs free energy of candidate materials in aqueous media as well as their decomposition products, combining solid and aqueous phases, as a function of pH and potential. Based on benchmarking against 20 stable as well as metastable materials reported in the literature and also our experimental characterization of metastable triclinic-FeVO_4 we present quantitative estimates for the relative Gibbs free energy and corresponding...

  8. Hot Carrier Dynamics in Photoexcited Gold Nanostructures: Role of Interband Excitations and Evidence for Ballistic Transport

    Tagliabue, Giulia; Jermyn, Adam S.; Sundararaman, Ravishankar; Welch, Alex J.; DuChene, Joseph S.; Davoyan, Artur R.; Narang, Prineha; Atwater, Harry A.
    Harnessing short-lived photoexcited electron-hole pairs in metal nanostructures has the potential to define a new phase of optoelectronics, enabling control of athermal mechanisms for light harvesting, photodetection and photocatalysis. To date, however, the spatiotemporal dynamics and transport of these photoexcited carriers have been only qualitatively characterized. Plasmon excitation has been widely viewed as an efficient mechanism for generating non-thermal hot carriers. Despite numerous experiments, conclusive evidence elucidating and quantifying the full dynamics of hot carrier generation, transport, and injection has not been reported. Here, we combine experimental measurements with coupled first-principles electronic structure theory and Boltzmann transport calculations to provide...

  9. Hot Carrier Dynamics in Photoexcited Gold Nanostructures: Role of Interband Excitations and Evidence for Ballistic Transport

    Tagliabue, Giulia; Jermyn, Adam S.; Sundararaman, Ravishankar; Welch, Alex J.; DuChene, Joseph S.; Davoyan, Artur R.; Narang, Prineha; Atwater, Harry A.
    Harnessing short-lived photoexcited electron-hole pairs in metal nanostructures has the potential to define a new phase of optoelectronics, enabling control of athermal mechanisms for light harvesting, photodetection and photocatalysis. To date, however, the spatiotemporal dynamics and transport of these photoexcited carriers have been only qualitatively characterized. Plasmon excitation has been widely viewed as an efficient mechanism for generating non-thermal hot carriers. Despite numerous experiments, conclusive evidence elucidating and quantifying the full dynamics of hot carrier generation, transport, and injection has not been reported. Here, we combine experimental measurements with coupled first-principles electronic structure theory and Boltzmann transport calculations to provide...

  10. Hot Carrier Dynamics in Photoexcited Gold Nanostructures: Role of Interband Excitations and Evidence for Ballistic Transport

    Tagliabue, Giulia; Jermyn, Adam S.; Sundararaman, Ravishankar; Welch, Alex J.; DuChene, Joseph S.; Davoyan, Artur R.; Narang, Prineha; Atwater, Harry A.
    Harnessing short-lived photoexcited electron-hole pairs in metal nanostructures has the potential to define a new phase of optoelectronics, enabling control of athermal mechanisms for light harvesting, photodetection and photocatalysis. To date, however, the spatiotemporal dynamics and transport of these photoexcited carriers have been only qualitatively characterized. Plasmon excitation has been widely viewed as an efficient mechanism for generating non-thermal hot carriers. Despite numerous experiments, conclusive evidence elucidating and quantifying the full dynamics of hot carrier generation, transport, and injection has not been reported. Here, we combine experimental measurements with coupled first-principles electronic structure theory and Boltzmann transport calculations to provide...

  11. Ultrahigh Mass Activity for Carbon Dioxide Reduction Enabled by Gold-iron Core-shell Nanoparticles

    Sun, Kun; Cheng, Tao; Wu, Lina; Hu, Yongfeng; Zhou, Jigang; MacLennan, Aimee; Jiang, Zhaohua; Gao, Yunzhi; Goddard, William A., III; Wang, Zhijiang
    Wide application of carbon dioxide (CO_2) electrochemical energy storage requires catalysts with high mass activity. Alloy catalysts can achieve superior performance to single metals while reducing the cost by finely-tuning the composition and morphology. We used in silico Quantum Mechanics Rapid Screening to identify Au-Fe as a candidate improving CO_2 reduction, and then synthesized and tested it experimentally. The synthesized Au-Fe alloy catalyst evolves quickly into a stable Au-Fe core-shell nanoparticle (AuFe-CSNP) after leaching out surface Fe. This AuFe-CSNP exhibits exclusive CO selectivity, long-term stability, nearly a hundred-fold increase in mass activity towards CO_2 reduction compared with Au NP, and...

  12. Ultrahigh Mass Activity for Carbon Dioxide Reduction Enabled by Gold-iron Core-shell Nanoparticles

    Sun, Kun; Cheng, Tao; Wu, Lina; Hu, Yongfeng; Zhou, Jigang; MacLennan, Aimee; Jiang, Zhaohua; Gao, Yunzhi; Goddard, William A., III; Wang, Zhijiang
    Wide application of carbon dioxide (CO_2) electrochemical energy storage requires catalysts with high mass activity. Alloy catalysts can achieve superior performance to single metals while reducing the cost by finely tuning the composition and morphology. We used in silico quantum mechanics rapid screening to identify Au–Fe as a candidate improving CO_2 reduction and then synthesized and tested it experimentally. The synthesized Au–Fe alloy catalyst evolves quickly into a stable Au–Fe core–shell nanoparticle (AuFe-CSNP) after leaching out surface Fe. This AuFe-CSNP exhibits exclusive CO selectivity, long-term stability, nearly a 100-fold increase in mass activity toward CO_2 reduction compared with Au NP,...

  13. Ultrahigh Mass Activity for Carbon Dioxide Reduction Enabled by Gold-iron Core-shell Nanoparticles

    Sun, Kun; Cheng, Tao; Wu, Lina; Hu, Yongfeng; Zhou, Jigang; MacLennan, Aimee; Jiang, Zhaohua; Gao, Yunzhi; Goddard, William A., III; Wang, Zhijiang
    Wide application of carbon dioxide (CO_2) electrochemical energy storage requires catalysts with high mass activity. Alloy catalysts can achieve superior performance to single metals while reducing the cost by finely tuning the composition and morphology. We used in silico quantum mechanics rapid screening to identify Au–Fe as a candidate improving CO_2 reduction and then synthesized and tested it experimentally. The synthesized Au–Fe alloy catalyst evolves quickly into a stable Au–Fe core–shell nanoparticle (AuFe-CSNP) after leaching out surface Fe. This AuFe-CSNP exhibits exclusive CO selectivity, long-term stability, nearly a 100-fold increase in mass activity toward CO_2 reduction compared with Au NP,...

  14. Reprint of: Surface reconstruction of pure-Cu single-crystal electrodes under CO-reduction potentials in alkaline solutions: A study by seriatim ECSTM-DEMS

    Kim, Youn-Geun; Javier, Alnald; Baricuatro, Jack H.; Torelli, Daniel; Cummins, Kyle D.; Tsang, Chu F.; Hemminger, John C.; Soriaga, Manuel P.
    Quasi-operando electrochemical scanning tunneling microscopy (ECSTM) recently showed that a polycrystalline Cu electrode kept in 0.1 M KOH at − 0.9 V (SHE), a potential very close to that for electrochemical CO reduction, underwent a two-step surface reconstruction, initially to Cu(111), or Cu(pc)-[Cu(111)], and terminally to Cu(100), or Cu(pc)-[Cu(100)]. When subjected to monolayer-limited Cu_((s)) ↔ Cu2O_((s))oxidation-reduction cycles (ORC), the Cu(pc)-[Cu(100)] surface was further transformed to Cu(pc)-[Cu(511)] that produced C_2H_5OH exclusively, as detected by differential electrochemical mass spectrometry, at an overvoltage lower by 645 mV relative to that for the formation of hydrocarbons. In this paper, results are presented from studies...

  15. Tunable optical response and purcell enhancement of gated plasmonic structures

    Sokhoyan, Ruzan; Shirmanesh, Ghazaleh Kafaie; Lu, Yu-Jung; Thyagarajan, Krishnan; Pala, Ragip A.; Atwater, Harry A.
    We experimentally demonstrate plasmonic nanostructures that enable dynamic electrical control of the phase and/or amplitude of the plane wave reflected from the nanostructures. We also demonstrate dynamically controlled Purcell enhancement of spontaneous emission of InP quantum dots (QDs) coupled to plasmonic heterostructures.

  16. Tunable optical response and purcell enhancement of gated plasmonic structures

    Sokhoyan, Ruzan; Shirmanesh, Ghazaleh Kafaie; Lu, Yu-Jung; Thyagarajan, Krishnan; Pala, Ragip A.; Atwater, Harry A.
    We experimentally demonstrate plasmonic nanostructures that enable dynamic electrical control of the phase and/or amplitude of the plane wave reflected from the nanostructures. We also demonstrate dynamically controlled Purcell enhancement of spontaneous emission of InP quantum dots (QDs) coupled to plasmonic heterostructures.

  17. General Thermal Texturization Process of MoS_2 for Efficient Electrocatalytic Hydrogen Evolution Reaction

    Kiriya, Daisuke; Lobaccaro, Peter; Nyein, Hnin Yin Yin; Taheri, Peyman; Hettick, Mark; Shiraki, Hiroshi; Sutter-Fella, Carolin M.; Zhao, Peida; Gao, Wei; Maboudian, Roya; Ager, Joel W.; Javey, Ali
    Molybdenum disulfide (MoS_2) has been widely examined as a catalyst containing no precious metals for the hydrogen evolution reaction (HER); however, these examinations have utilized synthesized MoS_2 because the pristine MoS_2 mineral is known to be a poor catalyst. The fundamental challenge with pristine MoS_2 is the inert HER activity of the predominant (0001) basal surface plane. In order to achieve high HER performance with pristine MoS_2, it is essential to activate the basal plane. Here, we report a general thermal process in which the basal plane is texturized to increase the density of HER-active edge sites. This texturization is...

  18. Layer-by-Layer Degradation of Methylammonium Lead Tri-iodide Perovskite Microplates

    Fan, Zheng; Xiao, Hai; Wang, Yiliu; Zhao, Zipeng; Lin, Zhaoyang; Cheng, Hung-Chieh; Lee, Sung-Joon; Wang, Gongming; Feng, Ziying; Goddard, William A., III; Huang, Yu; Duan, Xiangfeng
    The methylammonium lead iodide (MAPbI3) perovskite has attracted considerable interest for its high-efficiency, low-cost solar cells, but is currently plagued by its poor environmental and thermal stability. To aid the development of robust devices, we investigate here the microscopic degradation pathways of MAPbI3 microplates. Using in situ transmission electron microscopy to follow the thermal degradation process, we find that under moderate heating at 85°C the crystalline structure shows a gradual evolution from tetragonal MAPbI3 to trigonal lead iodide layered crystals with a fixed crystallographic direction. Our solid-state nudged elastic band calculations confirm that the surface-initiated layer-by-layer degradation path exhibits the...

  19. Discovery of Manganese-Based Solar Fuel Photoanodes via Integration of Electronic Structure Calculations, Pourbaix Stability Modeling, and High-Throughput Experiments

    Shinde, Aniketa; Suram, Santosh K.; Yan, Qimin; Zhou, Lan; Singh, Arunima K.; Yu, Jie; Persson, Kristin A.; Neaton, Jeffrey B.; Gregoire, John M.
    The solar photoelectrochemical generation of hydrogen and carbon-containing fuels comprises a critical energy technology for establishing sustainable energy resources. The photoanode, which is responsible for solar-driven oxygen evolution, has persistently limited technology advancement due to the lack of materials that exhibit both the requisite electronic properties and operational stability. Efforts to extend the lifetime of solar fuel devices increasingly focus on mitigating corrosion in the highly oxidizing oxygen evolution environment, motivating our development of a photoanode discovery pipeline that combines electronic structure calculations, Pourbaix stability screening, and high-throughput experiments. By applying the pipeline to ternary metal oxides containing manganese, we...

  20. Discovery of Manganese-Based Solar Fuel Photoanodes via Integration of Electronic Structure Calculations, Pourbaix Stability Modeling, and High-Throughput Experiments

    Shinde, Aniketa; Suram, Santosh K.; Yan, Qimin; Zhou, Lan; Singh, Arunima K.; Yu, Jie; Persson, Kristin A.; Neaton, Jeffrey B.; Gregoire, John M.
    The solar photoelectrochemical generation of hydrogen and carbon-containing fuels comprises a critical energy technology for establishing sustainable energy resources. The photoanode, which is responsible for solar-driven oxygen evolution, has persistently limited technology advancement due to the lack of materials that exhibit both the requisite electronic properties and operational stability. Efforts to extend the lifetime of solar fuel devices increasingly focus on mitigating corrosion in the highly oxidizing oxygen evolution environment, motivating our development of a photoanode discovery pipeline that combines electronic structure calculations, Pourbaix stability screening, and high-throughput experiments. By applying the pipeline to ternary metal oxides containing manganese, we...

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