1
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Aravind I, Wang YY, Wang Y, Li R, Cai Z, Zhao B, Zhang B, Weng S, Shahriar R, Cronin SB. Photoexcited Hot Electron Catalysis in Plasmon-Resonant Grating Structures with Platinum, Nickel, and Ruthenium Coatings. ACS Appl Mater Interfaces 2024; 16:17393-17400. [PMID: 38563348 DOI: 10.1021/acsami.3c16462] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
We report the electrochemical potential dependence of photocatalysis produced by hot electrons in plasmon-resonant grating structures. Here, corrugated metal surfaces with a period of 520 nm are illuminated with 785 nm wavelength laser light swept as a function of incident angle. At incident angles corresponding to plasmon-resonant excitation, we observe sharp peaks in the electrochemical photocurrent and dips in the photoreflectance consistent with the conditions under which there is wavevector matching between the incident light and the spacing between the lines in the grating. In addition to the bare plasmonic metal surface (i.e., Au), which is catalytically inert, we have measured grating structures with a thin layer of Pt, Ru, and Ni catalyst coatings. For the bare Au grating, we observe that the plasmon-resonant photocurrent remains relatively featureless over the applied potential range from -0.8 to +1.2 V vs NHE. For the Pt-coated grating, we observe a sharp peak around -0.3 V vs NHE, three times larger than the bare Au grating, and near complete suppression of the oxidation half-reaction, reflecting the reducing nature of Pt as a good hydrogen evolution reaction catalyst. The photocurrent associated with the Pt-coated grating is less noisy and produces higher photocurrents than the bare Au grating due to the faster kinetics (i.e., charge transfer) associated with the Pt-coated surface. The plasmon-resonant grating structures enable us to compare plasmon-resonant excitation with that of bulk metal interband absorption simply by rotating the polarization of the light while leaving all other parameters of the experiment fixed (i.e., wavelength, potential, electrochemical solution, sample surface, etc.). A 64X plasmon-resonant enhancement (i.e., p-to-s polarized photocurrent ratio) is observed for the Pt-coated grating compared to 28X for the bare grating. The nickel-coated grating shows an increase in the hot-electron photocurrent enhancement in both oxidation and reduction half-reactions. Similarly, Ru-coated gratings show an increase in hot-electron photocurrents in the oxidation half-reaction compared to the bare Au grating. Plasmon-resonant enhancement factors of 36X and 15X are observed in the p-to-s polarized photocurrent ratio for the Ni and Ru gratings, respectively.
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Affiliation(s)
- Indu Aravind
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
| | - Yu Yun Wang
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Yu Wang
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Ruoxi Li
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Zhi Cai
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Bofan Zhao
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Boxin Zhang
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Sizhe Weng
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Rifat Shahriar
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Stephen B Cronin
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California 90089, United States
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
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2
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Li R, Yoc-Bautista MG, Weng S, Cai Z, Zhao B, Cronin SB. Voltage-Induced Inversion of Band Bending and Photovoltages at Semiconductor/Liquid Interfaces. ACS Appl Mater Interfaces 2024; 16:9355-9361. [PMID: 38319802 DOI: 10.1021/acsami.3c14116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2024]
Abstract
At semiconductor/liquid interfaces, the surface potential and photovoltages are produced by a combination of band bending and quasi-Fermi-level splitting at the semiconductor surface, which are usually treated in a qualitative fashion. As such, it is important to develop quantitative metrics for the band energies and photovoltaics at these interfaces. Here, we present a spectroscopic method for monitoring the photovoltages produced at semiconductor/liquid junctions. The surface reporter molecule mercaptobenzonitrile (MBN) is functionalized on the photoelectrode surface (p-type silicon) and is measured using in situ surface-enhanced Raman scattering (SERS) spectroscopy with a water immersion lens under electrochemical working conditions. In particular, the vibrational frequency of the C≡N stretch mode (ωCN) around 2225 cm-1 is sensitive to the local electric field in solution at the electrode/electrolyte interface via the vibrational Stark effect. Over the applied potential range from -0.8 to 0.6 V vs Ag/AgCl, we observe ωCN to increase from 2220 to 2229 cm-1 (at low laser power). As the incident laser power is increased from 83.5 μW to 13.3 mW, we observe additional shifts of ΔωCN = ±1 cm-1, corresponding to photovoltages produced at the semiconductor/liquid interface ΔV = ±0.2 V. Based on Mott-Schottky measurements, the flat band potential (FBP) occurs at -0.39 V vs Ag/AgCl. For applied potentials above the FBP, we observe ΔωCN > 0 (i.e., blue-shifts ∼1 cm-1) corresponding to positive photovoltages, whereas for applied potentials below the flat band potential, we observe ΔωCN < 0 (i.e., red-shifts ∼1 cm-1) corresponding to negative photovoltages. These spectroscopic observations reveal voltage-induced changes in the band bending at the semiconductor/liquid junction that, thus far, have been difficult to measure.
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3
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Wang YY, Shi H, Gong Y, Zhang B, Zhao B, Li R, Cronin SB. Measuring Local p Ka and pH Using Surface Enhanced Raman Spectroscopy of 4-Mercaptobenzoic Acid. Langmuir 2023; 39:16807-16811. [PMID: 37956213 DOI: 10.1021/acs.langmuir.3c02073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
We report spectroscopic measurements of the local pH and pKa at an electrode/electrolyte interface using surface enhanced Raman scattering (SERS) spectroscopy of 4-mercaptobenzoic acid (4-MBA). In acidic and basic solutions, the protonated and deprotonated carboxyl functional groups at the electrode surface exist in the solution as -COOH and -COO-, which have different Raman active vibrational features at around 1697 and 1414 cm-1, respectively. In pH neutral water, as the applied electrochemical potential is varied from negative to positive, the acidic form of the 4-MBA (i.e., -COOH) decreases in Raman intensity and the basic form (i.e., -COO-) increases in Raman intensity. The change in local ion concentration is due to the application of electrochemical potentials and the accumulation of ions near the electrode surface. Under various applied potentials, the ratio of 1697 and 1587 cm-1 (pH-independent) peak areas spans the range between 0.7 and 0, and the ratio of the 1414 and 1587 cm-1 peak areas ranges from 0 to 0.3. By fitting these data to a normalized sigmoid function, we obtain the percentage of surface protonation/deprotonation, which can be related to the pKa and pH of the system. Thus, we can measure the local pKa at the electrode surface using the surface enhanced Raman signal of the 4-MBA.
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Affiliation(s)
- Yu Yun Wang
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Haotian Shi
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Yichen Gong
- Department of Chemical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Boxin Zhang
- Department of Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Bofan Zhao
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Ruoxi Li
- Department of Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Stephen B Cronin
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
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4
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Cai Z, Weinstein H, Aravind I, Li R, Weng S, Zhang B, Habif JL, Cronin SB. Dynamic Study of Intercalation/Deintercalation of Ionic Liquids in Multilayer Graphene Using an Alternating Current Raman Spectroscopy Technique. J Phys Chem Lett 2023; 14:7223-7228. [PMID: 37552573 PMCID: PMC10440811 DOI: 10.1021/acs.jpclett.3c01686] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2023] [Accepted: 07/31/2023] [Indexed: 08/10/2023]
Abstract
We report Raman spectra and infrared (IR) imaging collected during the intercalation-deintercalation half cycles in a multilayer graphene (MLG) device (∼100 layers) operating at 0.2-10 Hz. The device consists of a MLG/alumina membrane/copper stack, in which the alumina membrane is filled with ionic liquid [DEME][TFSI], forming an electrochemical cell. Upon the application of a positive voltage, the TFSI- anions intercalate into the interstitial spaces in the MLG. The incident laser light is modulated using an optical chopper wheel that is synchronized with (and delayed with respect to) a 0.2-10 Hz alternating current (AC) voltage signal. Raman spectra taken just 200 ms apart show the emergence and disappearance of the intercalated G band mode at around 1610 cm-1. By integration of over hundreds of cycles, a significant Raman signal can be obtained. The intercalation/deintercalation is also monitored with thermal imaging via voltage-induced changes in the carrier density, complex dielectric function ε(ω), and thermal emissivity of the device.
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Affiliation(s)
- Zhi Cai
- Mork
Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Haley Weinstein
- Ming
Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Indu Aravind
- Department
of Physics and Astronomy, University of
Southern California, Los Angeles, California 90089, United States
| | - Ruoxi Li
- Mork
Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Sizhe Weng
- Ming
Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Boxin Zhang
- Mork
Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Jonathan L. Habif
- Ming
Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Stephen B. Cronin
- Department
of Physics and Astronomy, University of
Southern California, Los Angeles, California 90089, United States
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089, United States
- Ming
Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
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5
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Ou TH, Hu P, Liu Z, Wang Y, Hossain S, Meng D, Shi Y, Zhang S, Zhang B, Song B, Liu F, Cronin SB, Wu W. Plasmon-Enhanced Photocatalytic CO 2 Reduction for Higher-Order Hydrocarbon Generation Using Plasmonic Nano-Finger Arrays. Nanomaterials (Basel) 2023; 13:nano13111753. [PMID: 37299656 DOI: 10.3390/nano13111753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Revised: 05/18/2023] [Accepted: 05/26/2023] [Indexed: 06/12/2023]
Abstract
The carbon dioxide reduction reaction (CO2RR) is a promising method to both reduce greenhouse gas carbon dioxide (CO2) concentrations and provide an alternative to fossil fuel by converting water and CO2 into high-energy-density chemicals. Nevertheless, the CO2RR suffers from high chemical reaction barriers and low selectivity. Here we demonstrate that 4 nm gap plasmonic nano-finger arrays provide a reliable and repeatable plasmon-resonant photocatalyst for multiple-electrons reactions: the CO2RR to generate higher-order hydrocarbons. Electromagnetics simulation shows that hot spots with 10,000 light intensity enhancement can be achieved using nano-gap fingers under a resonant wavelength of 638 nm. From cryogenic 1H-NMR spectra, formic acid and acetic acid productions are observed with a nano-fingers array sample. After 1 h laser irradiation, we only observe the generation of formic acid in the liquid solution. While increasing the laser irradiation period, we observe both formic and acetic acid in the liquid solution. We also observe that laser irradiation at different wavelengths significantly affected the generation of formic acid and acetic acid. The ratio, 2.29, of the product concentration generated at the resonant wavelength 638 nm and the non-resonant wavelength 405 nm is close to the ratio, 4.93, of the generated hot electrons inside the TiO2 layer at different wavelengths from the electromagnetics simulation. This shows that product generation is related to the strength of localized electric fields.
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Affiliation(s)
- Tse-Hsien Ou
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Pan Hu
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Zerui Liu
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Yunxiang Wang
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Sushmit Hossain
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Deming Meng
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Yudi Shi
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Sonia Zhang
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Boxin Zhang
- Mork Family Department of Chemical Engineering and Material Science, University of Southern California, Los Angeles, CA 90089, USA
| | - Boxiang Song
- Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Fanxin Liu
- Department of Applied Physics, Zhejiang University of Technology, Hangzhou 310023, China
| | - Stephen B Cronin
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089, USA
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
| | - Wei Wu
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089, USA
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6
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Xu Z, Hou B, Zhao F, Suo S, Liu Y, Shi H, Cai Z, Hill CL, Musaev DG, Mecklenburg M, Cronin SB, Lian T. Direct In Situ Measurement of Quantum Efficiencies of Charge Separation and Proton Reduction at TiO 2-Protected GaP Photocathodes. J Am Chem Soc 2023; 145:2860-2869. [PMID: 36715560 PMCID: PMC9912250 DOI: 10.1021/jacs.2c10578] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Photoelectrochemical solar fuel generation at the semiconductor/liquid interface consists of multiple elementary steps, including charge separation, recombination, and catalytic reactions. While the overall incident light-to-current conversion efficiency (IPCE) can be readily measured, identifying the microscopic efficiency loss processes remains difficult. Here, we report simultaneous in situ transient photocurrent and transient reflectance spectroscopy (TRS) measurements of titanium dioxide-protected gallium phosphide photocathodes for water reduction in photoelectrochemical cells. Transient reflectance spectroscopy enables the direct probe of the separated charge carriers responsible for water reduction to follow their kinetics. Comparison with transient photocurrent measurement allows the direct probe of the initial charge separation quantum efficiency (ϕCS) and provides support for a transient photocurrent model that divides IPCE into the product of quantum efficiencies of light absorption (ϕabs), charge separation (ϕCS), and photoreduction (ϕred), i.e., IPCE = ϕabsϕCSϕred. Our study shows that there are two general key loss pathways: recombination within the bulk GaP that reduces ϕCS and interfacial recombination at the junction that decreases ϕred. Although both loss pathways can be reduced at a more negative applied bias, for GaP/TiO2, the initial charge separation loss is the key efficiency limiting factor. Our combined transient reflectance and photocurrent study provides a time-resolved view of microscopic steps involved in the overall light-to-current conversion process and provides detailed insights into the main loss pathways of the photoelectrochemical system.
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Affiliation(s)
- Zihao Xu
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States,ZJU-Hangzhou
Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, Zhejiang310014, China
| | - Bingya Hou
- Department
of Electrical Engineering, University of
South California, 3710 McClintock Ave, Los Angeles, California90089, United States
| | - Fengyi Zhao
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States
| | - Sa Suo
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States
| | - Yawei Liu
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States
| | - Haotian Shi
- Department
of Chemistry, University of South California, 3710 McClintock Ave, Los Angeles, California90089, United States
| | - Zhi Cai
- Department
of Electrical Engineering, University of
South California, 3710 McClintock Ave, Los Angeles, California90089, United States
| | - Craig L. Hill
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States
| | - Djamaladdin G. Musaev
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States,Cherry
L. Emerson Centre for Scientific Computation, Emory University, 1515 Dickey Drive, Atlanta, Georgia30322, United
States
| | - Matthew Mecklenburg
- Core Center
of Excellence in Nano Imaging (CNI), University
of South California, 814 Bloom Walk, Los Angeles, California90089, United States
| | - Stephen B. Cronin
- Department
of Electrical Engineering, University of
South California, 3710 McClintock Ave, Los Angeles, California90089, United States,Department
of Chemistry, University of South California, 3710 McClintock Ave, Los Angeles, California90089, United States,
| | - Tianquan Lian
- Department
of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, Georgia30322, United States,
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7
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Zhang B, Aravind I, Yang S, Weng S, Zhao B, Schroeder C, Schroeder W, Thomas M, Umstattd R, Singleton D, Sanders J, Jung H, Cronin SB. Plasma-enhanced electrostatic precipitation of diesel exhaust particulates using nanosecond high voltage pulse discharge for mobile source emission control. Sci Total Environ 2022; 851:158181. [PMID: 35988598 DOI: 10.1016/j.scitotenv.2022.158181] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 07/31/2022] [Accepted: 08/17/2022] [Indexed: 06/15/2023]
Abstract
This study reports enhancement in the electrostatic precipitation (ESP) of diesel engine exhaust particulates using high voltage nanosecond pulse discharge in conjunction with a negative direct current (DC) bias voltage. The high voltage (20 kV) nanosecond pulses produce ion densities that are several orders of magnitude higher than those in the corona produced by a standard DC-only ESP. This plasma-enhanced electrostatic precipitator (PE-ESP) demonstrated 95 % remediation of PM and consumes less than 1 % of the engine power (i.e., 37 kW diesel engine at 75 % load). While the DC-only ESP remediation increases linearly with applied voltage, the plasma-enhanced ESP remains approximately constant over the applied range of negative DC biases. Numerical simulations of the PE-ESP process agree with the DC-only experimental results and enable us to verify the charge-based mechanism of enhancement provided by the nanosecond high voltage pulse plasma. Two different reactor configurations with different flow rates yielded the same remediation values despite one having half the flow rate of the other. This indicates that the reactor can be made even smaller without sacrificing performance. Here, this study finds that the plasma enhancement enables high remediation values at low DC voltages and smaller ESP reactors to be made with high remediation.
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Affiliation(s)
- Boxin Zhang
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089, USA
| | - Indu Aravind
- Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA
| | - Sisi Yang
- Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA
| | - Sizhe Weng
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Bofan Zhao
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Christi Schroeder
- Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA
| | - William Schroeder
- Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA
| | - Mark Thomas
- Transient Plasma Systems, Inc., Torrance, CA 90501, USA
| | - Ryan Umstattd
- Transient Plasma Systems, Inc., Torrance, CA 90501, USA
| | - Dan Singleton
- Transient Plasma Systems, Inc., Torrance, CA 90501, USA
| | - Jason Sanders
- Transient Plasma Systems, Inc., Torrance, CA 90501, USA
| | - Heejung Jung
- Department of Mechanical Engineering, University of California, Riverside, Riverside, CA 92507, USA; College of Engineering-Center for Environmental Research and Technology (CE-CERT), University of California, Riverside, Riverside, CA 92507, USA
| | - Stephen B Cronin
- Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA; Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089, USA; Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA.
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8
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Weinstein HA, Cai Z, Cronin SB, Habif JL. Harvesting Planck radiation for free-space optical communications in the long-wave infrared band. Opt Lett 2022; 47:6225-6228. [PMID: 37219212 DOI: 10.1364/ol.476394] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Accepted: 10/28/2022] [Indexed: 05/24/2023]
Abstract
We demonstrate a free-space optical communication link with an optical transmitter that harvests naturally occurring Planck radiation from a warm body and modulates the emitted intensity. The transmitter exploits an electro-thermo-optic effect in a multilayer graphene device that electrically controls the surface emissivity of the device resulting in control of the intensity of the emitted Planck radiation. We design an amplitude-modulated optical communication scheme and provide a link budget for communications data rate and range based on our experimental electro-optic characterization of the transmitter. Finally, we present an experimental demonstration achieving error-free communications at 100 bits per second over laboratory scales.
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9
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Xu Z, Hou B, Zhao F, Cai Z, Liu Y, Hill CL, Musaev DG, Mecklenburg M, Cronin SB, Lian T. Correction to Nanoscale TiO 2 Protection Layer Enhances the Built-In Field and Charge Separation Performance of GaP Photoelectrodes. Nano Lett 2022; 22:3173. [PMID: 35357168 DOI: 10.1021/acs.nanolett.2c01063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
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10
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Wang Y, Wang Y, Aravind I, Cai Z, Shen L, Zhang B, Wang B, Chen J, Zhao B, Shi H, Dawlaty JM, Cronin SB. In Situ Investigation of Ultrafast Dynamics of Hot Electron-Driven Photocatalysis in Plasmon-Resonant Grating Structures. J Am Chem Soc 2022; 144:3517-3526. [PMID: 35188777 DOI: 10.1021/jacs.1c12069] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Understanding the relaxation and injection dynamics of hot electrons is crucial to utilizing them in photocatalytic applications. While most studies have focused on hot carrier dynamics at metal/semiconductor interfaces, we study the in situ dynamics of direct hot electron injection from metal to adsorbates. Here, we report a hot electron-driven hydrogen evolution reaction (HER) by exciting the localized surface plasmon resonance (LSPR) in Au grating photoelectrodes. In situ ultrafast transient absorption (TA) measurements show a depletion peak resulting from hot electrons. When the sample is immersed in solution under -1 V applied potential, the extracted electron-phonon interaction time decreases from 0.94 to 0.67 ps because of additional energy dissipation channels. The LSPR TA signal is redshifted with delay time because of charge transfer and subsequent change in the dielectric constant of nearby solution. Plateau-like photocurrent peaks appear when exciting a 266 nm linewidth grating with p-polarized (on resonance) light, accompanied by a similar profile in the measured absorptance. Double peaks in the photocurrent measurement are observed when irradiating a 300 nm linewidth grating. The enhancement factor (i.e., reaction rate) is 15.6× between p-polarized and s-polarized light for the 300 nm linewidth grating and 4.4× for the 266 nm linewidth grating. Finite-difference time domain (FDTD) simulations show two resonant modes for both grating structures, corresponding to dipolar LSPR modes at the metal/fused silica and metal/water interfaces. To our knowledge, this is the first work in which LSPR-induced hot electron-driven photochemistry and in situ photoexcited carrier dynamics are studied on the same plasmon resonance structure with and without adsorbates.
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Affiliation(s)
- Yu Wang
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Yi Wang
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Indu Aravind
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
| | - Zhi Cai
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Lang Shen
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Boxin Zhang
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Bo Wang
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
| | - Jihan Chen
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Bofan Zhao
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Haotian Shi
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Jahan M Dawlaty
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Stephen B Cronin
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.,Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.,Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
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11
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Xu Z, Hou B, Zhao F, Cai Z, Shi H, Liu Y, Hill CL, Musaev DG, Mecklenburg M, Cronin SB, Lian T. Nanoscale TiO 2 Protection Layer Enhances the Built-In Field and Charge Separation Performance of GaP Photoelectrodes. Nano Lett 2021; 21:8017-8024. [PMID: 34569798 DOI: 10.1021/acs.nanolett.1c02257] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Nanoscale oxide layer protected semiconductor photoelectrodes show enhanced stability and performance for solar fuels generation, although the mechanism for the performance enhancement remains unclear due to a lack of understanding of the microscopic interfacial field and its effects. Here, we directly probe the interfacial fields at p-GaP electrodes protected by n-TiO2 and its effect on charge carriers by transient reflectance spectroscopy. Increasing the TiO2 layer thickness from 0 to 35 nm increases the field in the GaP depletion region, enhancing the rate and efficiency of interfacial electron transfer from the GaP to TiO2 on the ps time scale as well as retarding interfacial recombination on the microsecond time scale. This study demonstrates a general method for providing a microscopic view of the photogenerated charge carrier's pathway and loss mechanisms from the bulk of the electrode to the long-lived separated charge at the interface that ultimately drives the photoelectrochemical reactions.
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Affiliation(s)
- Zihao Xu
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| | - Bingya Hou
- Departments of Electrical Engineering and Chemistry, University of South California, 3710 McClintock Avenue, Los Angeles, California 90089, United States
| | - Fengyi Zhao
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| | - Zhi Cai
- Departments of Electrical Engineering and Chemistry, University of South California, 3710 McClintock Avenue, Los Angeles, California 90089, United States
| | - Haotian Shi
- Departments of Electrical Engineering and Chemistry, University of South California, 3710 McClintock Avenue, Los Angeles, California 90089, United States
| | - Yawei Liu
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| | - Craig L Hill
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| | - Djamaladdin G Musaev
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States
- Cherry L. Emerson Centre for Scientific Computation, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| | - Matthew Mecklenburg
- Core Center of Excellence in Nano Imaging (CNI), University of South California, 814 Bloom Walk, Los Angeles, California 90089, United States
| | - Stephen B Cronin
- Departments of Electrical Engineering and Chemistry, University of South California, 3710 McClintock Avenue, Los Angeles, California 90089, United States
| | - Tianquan Lian
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States
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12
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Montenegro A, Dutta C, Mammetkuliev M, Shi H, Hou B, Bhattacharyya D, Zhao B, Cronin SB, Benderskii AV. Asymmetric response of interfacial water to applied electric fields. Nature 2021; 594:62-65. [PMID: 34079138 DOI: 10.1038/s41586-021-03504-4] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2019] [Accepted: 03/29/2021] [Indexed: 11/09/2022]
Abstract
Our understanding of the dielectric response of interfacial water, which underlies the solvation properties and reaction rates at aqueous interfaces, relies on the linear response approximation: an external electric field induces a linearly proportional polarization. This implies antisymmetry with respect to the sign of the field. Atomistic simulations have suggested, however, that the polarization of interfacial water may deviate considerably from the linear response. Here we present an experimental study addressing this issue. We measured vibrational sum-frequency generation spectra of heavy water (D2O) near a monolayer graphene electrode, to study its response to an external electric field under controlled electrochemical conditions. The spectra of the OD stretch show a pronounced asymmetry for positive versus negative electrode charge. At negative charge below 5 × 1012 electrons per square centimetre, a peak of the non-hydrogen-bonded OD groups pointing towards the graphene surface is observed at a frequency of 2,700 per centimetre. At neutral or positive electrode potentials, this 'free-OD' peak disappears abruptly, and the spectra display broad peaks of hydrogen-bonded OD species (at 2,300-2,650 per centimetre). Miller's rule1 connects the vibrational sum-frequency generation response to the dielectric constant. The observed deviation from the linear response for electric fields of about ±3 × 108 volts per metre calls into question the validity of treating interfacial water as a simple dielectric medium.
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Affiliation(s)
- Angelo Montenegro
- Department of Chemistry, University of Southern California, Los Angeles, CA, USA
| | - Chayan Dutta
- Department of Chemistry, University of Southern California, Los Angeles, CA, USA
| | | | - Haotian Shi
- Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA
| | - Bingya Hou
- Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA
| | | | - Bofan Zhao
- Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA
| | - Stephen B Cronin
- Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA
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13
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Li S, Zhao B, Aguirre A, Wang Y, Li R, Yang S, Aravind I, Cai Z, Chen R, Jensen L, Cronin SB. Monitoring Reaction Intermediates in Plasma-Driven SO 2, NO, and NO 2 Remediation Chemistry Using In Situ SERS Spectroscopy. Anal Chem 2021; 93:6421-6427. [PMID: 33855854 DOI: 10.1021/acs.analchem.0c05413] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In situ surface-enhanced Raman scattering (SERS) spectroscopy is used to identify the key reaction intermediates during the plasma-based removal of NO and SO2 under dry and wet conditions on Ag nanoparticles. Density functional theory (DFT) calculations are used to confirm the experimental observations by calculating the vibrational modes of the surface-bound intermediate species. Here, we provide spectroscopic evidence that the wet plasma increases the SO2 and the NOx removal through the formation of highly reactive OH radicals, driving the reactions to H2SO4 and HNO3, respectively. We observed the formation of SO3 and SO4 species in the SO2 wet-plasma-driven remediation, while in the dry plasma, we only identified SO3 adsorbed on the Ag surface. During the removal of NO in the dry and wet plasma, both NO2 and NO3 species were observed on the Ag surface; however, the concentration of NO3 species was enhanced under wet-plasma conditions. By closing the loop between the experimental and DFT-calculated spectra, we identified not only the adsorbed species associated with each peak in the SERS spectra but also their orientation and adsorption site, providing a detailed atomistic picture of the chemical reaction pathway and surface interaction chemistry.
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Affiliation(s)
- Shujin Li
- Mork Family Department of Chemical Engineering and Materials Science and Daniel J. Epstein Department of Industrial & System Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Bofan Zhao
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Alejo Aguirre
- Instituto de Desarrollo Tecnológico para la Industria Química (INTEC), Universidad Nacional del Litoral, CONICET, Güemes 3450, S3000GLN Santa Fe, Argentina
| | - Yu Wang
- Mork Family Department of Chemical Engineering and Materials Science and Daniel J. Epstein Department of Industrial & System Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Ruoxi Li
- Mork Family Department of Chemical Engineering and Materials Science and Daniel J. Epstein Department of Industrial & System Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Sisi Yang
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
| | - Indu Aravind
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
| | - Zhi Cai
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Ran Chen
- Department of Chemistry Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Lasse Jensen
- Department of Chemistry Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Stephen B Cronin
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States.,Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
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14
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Edwards PJ, Wang B, Cronin SB, Bushmaker AW. Direct Measurement of Water-Assisted Ion Desorption and Solvation on Isolated Carbon Nanotubes. ACS Nano 2020; 14:16854-16863. [PMID: 33202132 DOI: 10.1021/acsnano.0c05638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We have investigated the change in mean residence time of gaseous ions adsorbed on the surface of suspended carbon nanotube field-effect transistors (CNT-FETs) with and without native surface water layers that exists in atmospheric conditions. Devices were characterized electrically before and after dehydration by thermal, dry gas, and vacuum desiccation and in each scenario were found to have substantially higher mean ion residence times. It is proposed that water molecules native to the CNT surface in ambient conditions provide a reduction pathway for incoming gaseous ions, yielding hydronium ions (H3O+). This is supported by the appearance of frequent clustered readsorption events in the presence of surface water, caused by the rapid hopping of H+ between the device surface and the lowest water layer, which are not present in data collected from desiccated devices. After desiccation of the device, a thermal trial was conducted to determine the adsorption energy of N2+ ions on the CNT surface. This work has profound implications for our understanding of wetting in one-dimensional systems and the chemistry of ion chemisorption and solvation on the surfaces of materials in general.
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Affiliation(s)
- Patrick J Edwards
- Department of Physics, The University of Southern California, 825 Bloom Walk, Los Angeles, California 90089, United States
- Physical Sciences Laboratories, The Aerospace Corporation, 355 S. Douglas Street, El Segundo, California 90245, United States
| | - Bo Wang
- Department of Physics, The University of Southern California, 825 Bloom Walk, Los Angeles, California 90089, United States
| | - Stephen B Cronin
- Department of Electrical Engineering, The University of Southern California, 3601 W. Way, Los Angeles, California 90089, United States
| | - Adam W Bushmaker
- Physical Sciences Laboratories, The Aerospace Corporation, 355 S. Douglas Street, El Segundo, California 90245, United States
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15
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Song B, Jiang Z, Liu Z, Wang Y, Liu F, Cronin SB, Yang H, Meng D, Chen B, Hu P, Schwartzberg AM, Cabrini S, Haas S, Wu W. Probing the Mechanisms of Strong Fluorescence Enhancement in Plasmonic Nanogaps with Sub-nanometer Precision. ACS Nano 2020; 14:14769-14778. [PMID: 33095557 DOI: 10.1021/acsnano.0c01973] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Plasmon-enhanced fluorescence is demonstrated in the vicinity of metal surfaces due to strong local field enhancement. Meanwhile, fluorescence quenching is observed as the spacing between fluorophore molecules and the adjacent metal is reduced below a threshold of a few nanometers. Here, we introduce a technology, placing the fluorophore molecules in plasmonic hotspots between pairs of collapsible nanofingers with tunable gap sizes at sub-nanometer precision. Optimal gap sizes with maximum plasmon enhanced fluorescence are experimentally identified for different dielectric spacer materials. The ultrastrong local field enhancement enables simultaneous detection and characterization of sharp Raman fingerprints in the fluorescence spectra. This platform thus enables in situ monitoring of competing excitation enhancement and emission quenching processes. We systematically investigate the mechanisms behind fluorescence quenching. A quantum mechanical model is developed which explains the experimental data and will guide the future design of plasmon enhanced spectroscopy applications.
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Affiliation(s)
- Boxiang Song
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Zhihao Jiang
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
| | - Zerui Liu
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Yunxiang Wang
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Fanxin Liu
- Department of Applied Physics, Zhejiang University of Technology, Hangzhou, Zhejiang, China 310023
| | - Stephen B Cronin
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Hao Yang
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Deming Meng
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Buyun Chen
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Pan Hu
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Adam M Schwartzberg
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Stefano Cabrini
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Stephan Haas
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
| | - Wei Wu
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
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16
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Wang Y, Hamann DM, Cordova DLM, Chen J, Wang B, Shen L, Cai Z, Shi H, Karapetrova E, Aravind I, Shi L, Johnson DC, Cronin SB. Enhanced Low-Temperature Thermoelectric Performance in (PbSe) 1+δ(VSe 2) 1 Heterostructures due to Highly Correlated Electrons in Charge Density Waves. Nano Lett 2020; 20:8008-8014. [PMID: 33095023 DOI: 10.1021/acs.nanolett.0c02882] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We explore the effect of charge density wave (CDW) on the in-plane thermoelectric transport properties of (PbSe)1+δ(VSe2)1 and (PbSe)1+δ(VSe2)2 heterostructures. In (PbSe)1+δ(VSe2)1 we observe an abrupt 86% increase in the Seebeck coefficient, 245% increase in the power factor, and a slight decrease in resistivity over the CDW transition. This behavior is not observed in (PbSe)1+δ(VSe2)2 and is rather unusual compared to the general trend observed in other materials. The abrupt transition causes a deviation from the Mott relationship through correlated electron states. Raman spectra of the (PbSe)1+δ(VSe2)1 material show the emergence of additional peaks below the CDW transition temperature associated with VSe2 material. Temperature-dependent in-plane X-ray diffraction (XRD) spectra show a change in the in-plane thermal expansion of VSe2 in (PbSe)1+δ(VSe2)1 due to lattice distortion. The increase in the power factor and decrease in the resistivity due to CDW suggest a potential mechanism for enhancing the thermoelectric performance at the low temperature region.
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Affiliation(s)
| | - Danielle M Hamann
- Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1253, United States
| | - Dmitri Leo M Cordova
- Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1253, United States
| | | | | | | | | | | | - Evguenia Karapetrova
- Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | | | - Li Shi
- Department of Mechanical Engineering and Texas Materials Institute, University of Texas at Austin, Austin, Texas 78712, United States
| | - David C Johnson
- Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1253, United States
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17
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Wang B, Yang S, Wang Y, Kim Y, Htoon H, Doorn SK, Foran BJ, Bushmaker AW, Baker DR, Forcherio GT, Cronin SB. Formation of Brightly Luminescent MoS 2 Nanoislands from Multilayer Flakes via Plasma Treatment and Laser Exposure. ACS Omega 2020; 5:20543-20547. [PMID: 32832807 PMCID: PMC7439701 DOI: 10.1021/acsomega.0c02753] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Accepted: 07/23/2020] [Indexed: 06/11/2023]
Abstract
A robust and reliable method for enhancing the photoluminescence (PL) of multilayer MoS2 is demonstrated using an oxygen plasma treatment process followed by laser exposure. Here, the plasma and laser treatments result in an indirect-to-direct band gap transition. The oxygen plasma creates a slight decoupling of the layers and converts some of the MoS2 to MoO3. Subsequent laser irradiation further oxidizes the MoS2 to MoO3, as confirmed via X-ray photoelectron spectroscopy, and results in localized regions of brightly luminescent MoS2 monolayer triangular islands as seen in high-resolution transmission electron microscopy images. The PL lifetimes are found to decrease from 494 to 190 ps after plasma and laser treatment, reflecting the smaller size of the MoS2 grains/regions. Atomic force microscopic imaging shows a 2 nm increase in thickness of the laser-irradiated regions, which provides further evidence of the MoS2 being converted to MoO3.
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Affiliation(s)
- Bo Wang
- Department
of Physics and Astronomy, University of
Southern California, Los Angeles, California 90089, United States
| | - Sisi Yang
- Department
of Physics and Astronomy, University of
Southern California, Los Angeles, California 90089, United States
| | - Yu Wang
- Mork
Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Younghee Kim
- Center
for Integrated Nanotechnologies, Materials Physics and Applications
Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Han Htoon
- Center
for Integrated Nanotechnologies, Materials Physics and Applications
Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Stephen K. Doorn
- Center
for Integrated Nanotechnologies, Materials Physics and Applications
Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Brendan J. Foran
- The
Aerospace Corporation, El Segundo, California 90245, United States
| | - Adam W. Bushmaker
- The
Aerospace Corporation, El Segundo, California 90245, United States
| | - David R. Baker
- Sensors and
Electron Devices Directorate, U.S. Army
Research Laboratory, Adelphi, Maryland 20783, United States
| | - Gregory T. Forcherio
- Sensors and
Electron Devices Directorate, U.S. Army
Research Laboratory, Adelphi, Maryland 20783, United States
- Electro-Optic
Technology Division, Naval Surface Warfare
Center, Crane, Indiana 47522, United
States
| | - Stephen B. Cronin
- Department
of Physics and Astronomy, University of
Southern California, Los Angeles, California 90089, United States
- Ming
Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States
- Mork
Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
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18
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Wang Y, Aravind I, Cai Z, Shen L, Gibson GN, Chen J, Wang B, Shi H, Song B, Guignon E, Cady NC, Page WD, Pilar A, Cronin SB. Hot Electron Driven Photocatalysis on Plasmon-Resonant Grating Nanostructures. ACS Appl Mater Interfaces 2020; 12:17459-17465. [PMID: 32212673 DOI: 10.1021/acsami.0c00066] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We demonstrate the hot electron injection of photoexcited carriers in an Ag-based plasmon resonant grating structure. By varying the incident angle of irradiation, sharp dips are observed in the reflectance with p-polarized light (electric field perpendicular to grating lines) when there is wavevector matching between the incident light and the plasmon resonant modes of the grating and no angle dependence is observed with s-polarized light. This configuration enables us to compare photoelectrochemical current produced by plasmon resonant excitation with that of bulk metal interband absorption simply by rotating the polarization of the incident light while keeping all other parameters of the measurement fixed. With 633 nm light, we observed a 12-fold enhancement in the photocurrent (i.e., reaction rate) between resonant and nonresonant polarizations at incident angles of ±7.6° from normal. At 785 nm irradiation, we observed similar resonant profiles to those obtained with 633 nm wavelength light but with a 44-fold enhancement factor. Using 532 nm light, we observed two resonant peaks (with approximately 10× enhancement) in the photocurrent at 19.4° and 28.0° incident angles, each corresponding to higher order modes in the grating with more nodes per period. The lower enhancement factors observed at shorter wavelengths are attributed to interband transitions, which provide a damping mechanism for the plasmon resonance. Finite difference time domain (FDTD) simulations of these grating structures confirm the resonant profiles observed in the angle-dependent spectra of these gratings and provide a detailed picture of the electric field profiles on and off resonance.
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Affiliation(s)
| | | | | | | | - George N Gibson
- Department of Physics, University of Connecticut, Storrs, Connecticut 06269, United States
- Ciencia Inc., East Hartford, Connecticut 06108, United States
| | | | | | | | | | - Ernest Guignon
- Ciencia Inc., East Hartford, Connecticut 06108, United States
| | - Nathaniel C Cady
- Colleges of Nanoscale Science & Engineering, SUNY Polytechnic Institute, Albany, New York 12203, United States
| | - William D Page
- Ciencia Inc., East Hartford, Connecticut 06108, United States
| | - Arturo Pilar
- Ciencia Inc., East Hartford, Connecticut 06108, United States
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19
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Wang B, Yang S, Wang Y, Ahsan R, He X, Kim Y, Htoon H, Kapadia R, John DD, Thibeault B, Doorn SK, Cronin SB. Auger Suppression of Incandescence in Individual Suspended Carbon Nanotube pn-Junctions. ACS Appl Mater Interfaces 2020; 12:11907-11912. [PMID: 32083460 DOI: 10.1021/acsami.9b17519] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
There are various mechanisms of light emission in carbon nanotubes (CNTs), which give rise to a wide range of spectral characteristics that provide important information. Here we report suppression of incandescence via Auger recombination in suspended carbon nanotube pn-junctions generated from dual-gate CNT field-effect transistor (FET) devices. By applying equal and opposite voltages to the gate electrodes (i.e., Vg1 = -Vg2), we create a pn-junction within the CNT. Under these gating conditions, we observe a sharp peak in the incandescence intensity around zero applied gate voltage, where the intrinsic region has the largest spatial extent. Here, the emission occurs under high electrical power densities of around 0.1 MW/cm2 (or 6 μW) and arises from thermal emission at elevated temperatures above 800 K (i.e., incandescence). It is somewhat surprising that this thermal emission intensity is so sensitive to the gating conditions, and we observe a 1000-fold suppression of light emission between Vg1 = 0 and 15 V, over a range in which the electrical power dissipated in the nanotube is roughly constant. This behavior is understood on the basis of Auger recombination, which suppresses light emission by the excitation of free carriers. Based on the calculated carrier density and band profiles, the length of the intrinsic region drops by a factor of 7-25× over the range from |Vg| = 0 to 15 V. We, therefore, conclude that the light emission intensity is significantly dependent on the free carrier density profile and the size of the intrinsic region in these CNT devices.
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Affiliation(s)
| | | | | | | | - Xiaowei He
- Center for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Younghee Kim
- Center for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Han Htoon
- Center for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | | | - Demis D John
- Nanotech, Department of Electrical and Computer Engineering, University of California Santa Barbara, Santa Barbara, California 93106, United States
| | - Brian Thibeault
- Nanotech, Department of Electrical and Computer Engineering, University of California Santa Barbara, Santa Barbara, California 93106, United States
| | - Stephen K Doorn
- Center for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
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20
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Abstract
Here, we show that the turn-on voltage for the hydrogen evolution reaction on a graphene surface can be tuned in a semiconductor-insulator-graphene (SIG) device immersed in a solution. Specifically, it is shown that the hydrogen evolution reaction (HER) onset for the graphene can shift by >0.8 V by application of a voltage across a graphene-Al2O3-silicon junction. We show that this shift occurs due to the creation of a hot electron population in graphene due to tunneling from the Si to graphene. Through control experiments, we show that the presence of the graphene is necessary for this behavior. By analyzing the silicon, graphene, and solution current components individually, we find an increase in the silicon current despite a fixed graphene-silicon voltage, corresponding to an increase in the HER current. This additional silicon current appears to directly drive the electrochemical reaction, without modifying the graphene current. We term this current "direct injection current" and hypothesize that this current occurs due to electrons injected from the silicon into graphene that drives the HER before any electron-electron scattering occurs in the graphene. To further determine whether hot electrons injected at different energies could explain the observed total solution current, the nonequilibrium electron dynamics was studied using a 2D ensemble Monte Carlo Boltzmann transport equation (MCBTE) solver. By rigorously considering the key scattering mechanisms, we show that the injected hot electrons can significantly increase the available electron flux at high energies. These results show that semiconductor-insulator-graphene devices are a platform which can tune the electrochemical reaction rate via multiple mechanisms.
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Affiliation(s)
- Hyun Uk Chae
- Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Ragib Ahsan
- Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Jun Tao
- Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Stephen B Cronin
- Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California 90089, United States
| | - Rehan Kapadia
- Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California 90089, United States
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21
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Affiliation(s)
- Ji-Yuan Liu
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
- Key Laboratory for Advanced Materials, Center for Computational Chemistry and Research Institute of Industrial Catalysis, School of Chemistry and Molecular Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, People’s Republic of China
| | - Xue-Qing Gong
- Key Laboratory for Advanced Materials, Center for Computational Chemistry and Research Institute of Industrial Catalysis, School of Chemistry and Molecular Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, People’s Republic of China
| | | | | | | | - Anastassia N. Alexandrova
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
- California NanoSystems Institute, Los Angeles, California 90095, United States
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22
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Hou W, Liu Z, Hsuan W, Pavaskar P, Cronin SB. Plasmon Resonant Enhancement of Photocatalytic Solar Fuel Production. ACTA ACUST UNITED AC 2019. [DOI: 10.1149/1.3629967] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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23
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Yang S, Subramanian S, Singleton D, Schroeder C, Schroeder W, Gundersen MA, Cronin SB. First results on transient plasma-based remediation of nanoscale particulate matter in restaurant smoke emissions. Environ Res 2019; 178:108635. [PMID: 31514016 DOI: 10.1016/j.envres.2019.108635] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2019] [Revised: 08/06/2019] [Accepted: 08/06/2019] [Indexed: 06/10/2023]
Abstract
Recent studies have shown that nanoscale particulate matter produced in commercial charbroiling processes represents a serious health hazard and has been linked to various forms of cancer and cardiopulmonary disease. In this study, we propose a highly effective method for treating restaurant smoke emissions using a transient pulsed plasma reactor produced by nanosecond high voltage pulses. We measure the size and relative mass distributions of particulate matter (PM) produced in commercial charbroiling processes (e.g., cooking of hamburger meat) both with and without the plasma treatment. Here, the plasma discharge is produced in a 3" diameter cylindrical reactor with a 5-10 ns high voltage (17 kV) pulse generator. The distribution of untreated nanoparticle sizes is peaked around 125-150 nm in diameter, as measured using a scanning mobility particle sizer (SMPS) spectrometer. With plasma treatment, we observe up to a 55-fold reduction in relative particle mass and a significant reduction in the nanoparticle size distribution using this method. The effectiveness of the nanoscale PM remediation increases with both the pulse repetition rate and pulse voltage, demonstrating the scalability of this approach for treating particulate matter at higher flow rates and larger diameter reactors.
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Affiliation(s)
- Sisi Yang
- Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA
| | - Sriram Subramanian
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Dan Singleton
- Transient Plasma Systems, Inc., Torrance, CA 90501, USA
| | - Christi Schroeder
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - William Schroeder
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Martin A Gundersen
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA; Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA
| | - Stephen B Cronin
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA; Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA.
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24
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Shi H, Zhao B, Ma J, Bronson MJ, Cai Z, Chen J, Wang Y, Cronin M, Jensen L, Cronin SB. Measuring Local Electric Fields and Local Charge Densities at Electrode Surfaces Using Graphene-Enhanced Raman Spectroscopy (GERS)-Based Stark-Shifts. ACS Appl Mater Interfaces 2019; 11:36252-36258. [PMID: 31498591 DOI: 10.1021/acsami.9b11892] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We report spectroscopic measurements of the local electric fields and local charge densities at electrode surfaces using graphene-enhanced Raman spectroscopy (GERS) based on the Stark-shifts of surface-bound molecules and the G band frequency shift in graphene. Here, monolayer graphene is used as the working electrode in a three-terminal potentiostat while Raman spectra are collected in situ under applied electrochemical potentials using a water immersion lens. First, a thin layer (1 Å) of copper(II) phthalocyanine (CuPc) molecules are deposited on monolayer graphene by thermal evaporation. GERS spectra are then taken in an aqueous solution as a function of the applied electrochemical potential. The shifts in vibrational frequencies of the graphene G band and CuPc are obtained simultaneously and correlated. The upshifts in the G band Raman mode are used to determine the free carrier density in the graphene sheet under these applied potentials. Of the three dominant peaks in the Raman spectra of CuPc (i.e., 1531, 1450, and 1340 cm-1), only the 1531 cm-1 peak exhibits Stark-shifts and can, thus, be used to report the local electric field strength at the electrode surface under electrochemical working conditions. Between applied electrochemical potentials from -0.8 V to 0.8 V vs NHE, the free carrier density in the graphene electrode spans a range from -4 × 1012 cm-2 to 2 × 1012 cm-2. Corresponding Stark-shifts in the CuPc peak around 1531 cm-1 are observed up to 1.0 cm-1 over a range of electric field strengths between -3.78 × 106 and 1.85 × 106 V/cm. Slightly larger Stark-shifts are observed in a 1 M KCl solution, compared to those observed in DI water, as expected based on the higher ion concentration of the electrolyte. Based on our data, we determine the Stark shift tuning rate to be 0.178 cm-1/ (106 V/cm), which is relatively small due to the planar nature of the CuPc molecule, which largely lies perpendicular to the electric field at this electrode surface. Computational simulations using density functional theory (DFT) predict similar Stark shifts and provide a detailed atomistic picture of the electric field-induced perturbations to the surface-bound CuPc molecules.
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Affiliation(s)
| | | | | | - Mark J Bronson
- Department of Chemistry , Pennsylvania State University , University Park , Pennsylvania 16802 , United States
| | | | | | | | | | - Lasse Jensen
- Department of Chemistry , Pennsylvania State University , University Park , Pennsylvania 16802 , United States
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25
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Abstract
Using hot electrons to drive electrochemical reactions has drawn considerable interest in driving high-barrier reactions and enabling efficient solar to fuel conversion. However, the conversion efficiency from hot electrons to electrochemical products is typically low due to high hot electron scattering rates. Here, it is shown that the hydrogen evolution reaction (HER) in an acidic solution can be efficiently modulated by hot electrons injected into a thin gold film by an Au-Al2O3-Si metal-insulator-semiconductor (MIS) junction. Despite the large scattering rates in gold, it is shown that the hot electron driven HER can reach quantum efficiencies as high as ∼85% with a shift in the onset of hydrogen evolution by ∼0.6 V. By simultaneously measuring the currents from the solution, gold, and silicon terminals during the experiments, we find that the HER rate can be decomposed into three components: (i) thermal electron, corresponding to the thermal electron distribution in gold; (ii) hot electron, corresponding to electrons injected from silicon into gold which drive the HER before fully thermalizing; and (iii) silicon direct injection, corresponding to electrons injected from Si into gold that drive the HER before electron-electron scattering occurs. Through a series of control experiments, we eliminate the possibility of the observed HER rate modulation coming from lateral resistivity of the thin gold film, pinholes in the gold, oxidation of the MIS device, and measurement circuit artifacts. Next, we theoretically evaluate the feasibility of hot electron injection modifying the available supply of electrons. Considering electron-electron and electron-phonon scattering, we track how hot electrons injected at different energies interact with the gold-solution interface as they scatter and thermalize. The simulator is first used to reproduce other published experimental pump-probe hot electron measurements, and then simulate the experimental conditions used here. These simulations predict that hot electron injection first increases the supply of electrons to the gold-solution interface at higher energies by several orders of magnitude and causes a peaked electron interaction with the gold-solution interface at the electron injection energy. The first prediction corresponds to the observed hot electron electrochemical current, while the second prediction corresponds to the observed silicon direct injection current. These results indicate that MIS devices offer a versatile platform for hot electron sources that can efficiently drive electrochemical reactions.
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Affiliation(s)
- Hyun Uk Chae
- Department of Electrical and Computer Engineering , University of Southern California , Los Angeles , California 90089 , United States
| | - Ragib Ahsan
- Department of Electrical and Computer Engineering , University of Southern California , Los Angeles , California 90089 , United States
| | - Qingfeng Lin
- Department of Electrical and Computer Engineering , University of Southern California , Los Angeles , California 90089 , United States
| | - Debarghya Sarkar
- Department of Electrical and Computer Engineering , University of Southern California , Los Angeles , California 90089 , United States
| | - Fatemeh Rezaeifar
- Department of Electrical and Computer Engineering , University of Southern California , Los Angeles , California 90089 , United States
| | - Stephen B Cronin
- Department of Electrical and Computer Engineering , University of Southern California , Los Angeles , California 90089 , United States
| | - Rehan Kapadia
- Department of Electrical and Computer Engineering , University of Southern California , Los Angeles , California 90089 , United States
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26
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Aizpurua J, Baumberg J, Boltasseva A, Christopher P, Cortes E, Cronin SB, Dadhich BK, de Nijs B, Deshpande P, Diaz Fernandez Y, Fabris L, Gawinkowski S, Govorov A, Halas N, Huang J, Jankiewicz B, Kamarudheen R, Khurgin J, Lee TK, Mahin J, Marini A, Maurer RJ, Mueller NS, Park JY, Rahaman M, Schlücker S, Schultz Z, Sivan Y, Tagliabue G, Thangamuthu M, Xu H, Zayats A. New materials for hot electron generation: general discussion. Faraday Discuss 2019; 214:365-386. [PMID: 31090770 DOI: 10.1039/c9fd90013f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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27
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Hou B, Shen L, Shi H, Chen J, Zhao B, Li K, Wang Y, Shen G, Ha MA, Liu F, Alexandrova AN, Hung WH, Dawlaty J, Christopher P, Cronin SB. Resonant and Selective Excitation of Photocatalytically Active Defect Sites in TiO 2. ACS Appl Mater Interfaces 2019; 11:10351-10355. [PMID: 30768239 DOI: 10.1021/acsami.8b12621] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
It has been known for several decades that defects are largely responsible for the catalytically active sites on metal and semiconductor surfaces. However, it is difficult to directly probe these active sites because the defects associated with them are often relatively rare with respect to the stoichiometric crystalline surface. In the work presented here, we demonstrate a method to selectively probe defect-mediated photocatalysis through differential alternating current (ac) photocurrent (PC) measurements. In this approach, electrons are photoexcited from the valence band to a relatively narrow distribution of subband gap states in TiO2 and then subsequently to the ions in solution. Because of their limited number, these defect states fill up quickly, resulting in Pauli blocking, and are thereby undetectable under direct current or continuous wave excitation. In the method demonstrated here, the incident light is modulated with an optical chopper, whereas the PC is measured with a lock-in amplifier. Thin (5 nm) films of TiO2 deposited by atomic layer deposition on various metal films, including Au, Cu, and Al, exhibit the same wavelength-dependent PC spectra, with a broad peak centered around 2.0 eV corresponding to the band-to-defect transition associated with the hydrogen evolution reaction (HER). While the UV-vis absorption spectra of these films show no features at 2.0 eV, photoluminescence (PL) spectra of these photoelectrodes show a similar wavelength dependence with a peak of around 2.0 eV, corresponding to the subband gap emission associated with these defect sites. As a control, alumina (Al2O3) films exhibit no PL or PC over the visible wavelength range. The ac PC plotted as a function of electrode potential shows a peak of around -0.4 to -0.1 V versus normal hydrogen electrode, as the monoenergetic defect states are tuned through a resonance with the HER potential. This approach enables the direct photoexcitation of catalytically active defect sites to be studied selectively without the interference of the continuum interband transitions or the effects of Pauli blocking, which is limited by the slow turnover time of the catalytically active sites, typically on the order of 1 μs. We believe that this general approach provides an important new way to study the role of defects in catalysis in an area where selective spectroscopic studies of these are few.
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Affiliation(s)
| | | | | | | | | | - Kun Li
- Department of Chemical Engineering , University of California, Santa Barbara , Santa Barbara , California 93106-5080 , United States
| | | | - Guozhen Shen
- State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors , Chinese Academy of Science , Beijing 100083 , P. R. China
| | - Mai-Anh Ha
- Department of Chemistry and Biochemistry, California NanoSystems Institute , University of California, Los Angeles , Los Angeles , California 90025 , United States
| | - Fanxi Liu
- Collaborative Innovation Center for Information Technology in Biological and Medical Physics, and College of Science , Zhejiang University of Technology , Hangzhou 310023 , P. R. China
| | - Anastassia N Alexandrova
- Department of Chemistry and Biochemistry, California NanoSystems Institute , University of California, Los Angeles , Los Angeles , California 90025 , United States
- Materials Sciences Division , Lawrence National Laboratory , Berkeley , California 94720 , United States
| | - Wei Hsuan Hung
- Department of Materials Science and Engineering , Feng Chia University , Taichung 407, 40724 , Taiwan
| | | | - Phillip Christopher
- Department of Chemical Engineering , University of California, Santa Barbara , Santa Barbara , California 93106-5080 , United States
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28
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Wang Y, Shen L, Wang Y, Hou B, Gibson G, Poudel N, Chen J, Shi H, Guignon E, Cady NC, Page WD, Pilar A, Dawlaty J, Cronin SB. Hot electron-driven photocatalysis and transient absorption spectroscopy in plasmon resonant grating structures. Faraday Discuss 2019; 214:325-339. [DOI: 10.1039/c8fd00141c] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
We have developed a method to measure photocurrents produced by photoexcited hot electrons and holes in bulk metal films.
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29
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Shi H, Cai Z, Patrow J, Zhao B, Wang Y, Wang Y, Benderskii A, Dawlaty J, Cronin SB. Monitoring Local Electric Fields at Electrode Surfaces Using Surface Enhanced Raman Scattering-Based Stark-Shift Spectroscopy during Hydrogen Evolution Reactions. ACS Appl Mater Interfaces 2018; 10:33678-33683. [PMID: 30187745 DOI: 10.1021/acsami.8b11961] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
We report the use of surface-enhanced Raman scattering (SERS) to measure the vibrational Stark shifts of surface-bound thiolated-benzonitrile molecules bound to an electrode surface during hydrogen evolution reactions (HERs). Here, the electrode surface consists of Au nanoislands deposited both with and without an underlying layer of monolayer graphene on a glass substrate. The Stark shifts observed in the nitrile (C-N) stretch frequency (around 2225 cm-1) are used to report the local electric field strength at the electrode surface under electrochemical working conditions. Under positive (i.e., oxidative) applied potentials [vs normal hydrogen electrode (NHE)], we observe blue shifts of up to 7.6 cm-1, which correspond to local electric fields of 22 mV/cm. Under negative applied potentials (vs NHE), the C-N stretch frequency is red-shifted by only about 1 cm-1. This corresponds to a regime in which the electrochemical current increases exponentially in the hydrogen evolution process. Under these finite electrochemical currents, we estimate the voltage drop across the solution ( V = IR). Correcting for this voltage drop results in a highly linear electric field versus applied electrochemical voltage relation. Here, the onset potential for the HER lies around 0.2 V versus NHE and the point of zero charge (PZC) occurs at 0.04 V versus NHE, based on the capacitance-voltage ( C- V) profile. The solution field is obtained by comparing the C-N stretch frequency in solution with that obtained in air. By evaluating the local electric field strength at the PZC and the onset potential, we can separate the solution field from the reaction field (i.e., electrode field), respectively. At the onset of HER, the solution field is -0.8 mV/cm and the electrode field is -1.2 mV/cm. At higher ion concentrations, we observe similar electric field strengths and more linear E-field versus applied potential behavior because of the relatively low resistance of the solution, which results in negligible voltage drops ( V = IR).
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30
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Sarkar D, Wang W, Mecklenburg M, Clough AJ, Yeung M, Ren C, Lin Q, Blankemeier L, Niu S, Zhao H, Shi H, Wang H, Cronin SB, Ravichandran J, Luhar M, Kapadia R. Confined Liquid-Phase Growth of Crystalline Compound Semiconductors on Any Substrate. ACS Nano 2018; 12:5158-5167. [PMID: 29775282 DOI: 10.1021/acsnano.8b01819] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The growth of crystalline compound semiconductors on amorphous and non-epitaxial substrates is a fundamental challenge for state-of-the-art thin-film epitaxial growth techniques. Direct growth of materials on technologically relevant amorphous surfaces, such as nitrides or oxides results in nanocrystalline thin films or nanowire-type structures, preventing growth and integration of high-performance devices and circuits on these surfaces. Here, we show crystalline compound semiconductors grown directly on technologically relevant amorphous and non-epitaxial substrates in geometries compatible with standard microfabrication technology. Furthermore, by removing the traditional epitaxial constraint, we demonstrate an atomically sharp lateral heterojunction between indium phosphide and tin phosphide, two materials with vastly different crystal structures, a structure that cannot be grown with standard vapor-phase growth approaches. Critically, this approach enables the growth and manufacturing of crystalline materials without requiring a nearly lattice-matched substrate, potentially impacting a wide range of fields, including electronics, photonics, and energy devices.
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Affiliation(s)
| | | | | | | | - Matthew Yeung
- Molecular Foundry, Lawrence Berkeley National Laboratory , One Cyclotron Road , Berkeley , California 94720 , United States
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31
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Abate Y, Akinwande D, Gamage S, Wang H, Snure M, Poudel N, Cronin SB. Recent Progress on Stability and Passivation of Black Phosphorus. Adv Mater 2018; 30:e1704749. [PMID: 29749007 DOI: 10.1002/adma.201704749] [Citation(s) in RCA: 119] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2017] [Revised: 12/29/2017] [Indexed: 05/08/2023]
Abstract
From a fundamental science perspective, black phosphorus (BP) is a canonical example of a material that possesses fascinating surface and electronic properties. It has extraordinary in-plane anisotropic electrical, optical, and vibrational states, as well as a tunable band gap. However, instability of the surface due to chemical degradation in ambient conditions remains a major impediment to its prospective applications. Early studies were limited by the degradation of black phosphorous surfaces in air. Recently, several robust strategies have been developed to mitigate these issues, and these novel developments can potentially allow researchers to exploit the extraordinary properties of this material and devices made out of it. Here, the fundamental chemistry of BP degradation and the tremendous progress made to address this issue are extensively reviewed. Device performances of encapsulated BP are also compared with nonencapsulated BP. In addition, BP possesses sensitive anisotropic photophysical surface properties such as excitons, surface plasmons/phonons, and topologically protected and Dirac semi-metallic surface states. Ambient degradation as well as any passivation method used to protect the surface could affect the intrinsic surface properties of BP. These properties and the extent of their modifications by both the degradation and passivation are reviewed.
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Affiliation(s)
- Yohannes Abate
- Department of Physics and Astronomy, University of Georgia, Athens, GA, 30602, USA
| | - Deji Akinwande
- Department of Electrical and Computer Engineering, University of Texas at Austin, Austin, TX, 78758, USA
| | - Sampath Gamage
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, 30303, USA
| | - Han Wang
- Viterbi School of Engineering University of Southern California, Los Angeles, CA, 90089, USA
| | - Michael Snure
- Air Force Research Laboratory, Wright Patterson Air Force Base, OH, 45433, USA
| | - Nirakar Poudel
- Viterbi School of Engineering University of Southern California, Los Angeles, CA, 90089, USA
| | - Stephen B Cronin
- Viterbi School of Engineering University of Southern California, Los Angeles, CA, 90089, USA
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32
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Shi H, Poudel N, Hou B, Shen L, Chen J, Benderskii AV, Cronin SB. Sensing local pH and ion concentration at graphene electrode surfaces using in situ Raman spectroscopy. Nanoscale 2018; 10:2398-2403. [PMID: 29334114 DOI: 10.1039/c7nr08294k] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We report a novel approach to probe the local ion concentration at graphene/water interfaces using in situ Raman spectroscopy. Here, the upshifts observed in the G band Raman mode under applied electrochemical potentials are used to determine the charge density in the graphene sheet. For voltages up to ±0.8 V vs. NHE, we observe substantial upshifts in the G band Raman mode by as much as 19 cm-1, which corresponds to electron and hole carrier densities of 1.4 × 1013 cm-2 and Fermi energy shifts of ±430 meV. The charge density in the graphene electrode is also measured independently using the capacitance-voltage characteristics (i.e., Q = CV), and is found to be consistent with those measured by Raman spectroscopy. From charge neutrality requirements, the ion concentration in solution per unit area must be equal and opposite to the charge density in the graphene electrode. Based on these charge densities, we estimate the local ion concentration as a function of electrochemical potential in both pure DI water and 1 M KCl solutions, which span a pH range from 3.8 to 10.4 for pure DI water and net ion concentrations of ±0.7 mol L-1 for KCl under these applied voltages.
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Affiliation(s)
- Haotian Shi
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA.
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33
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Song B, Yao Y, Groenewald RE, Wang Y, Liu H, Wang Y, Li Y, Liu F, Cronin SB, Schwartzberg AM, Cabrini S, Haas S, Wu W. Probing Gap Plasmons Down to Subnanometer Scales Using Collapsible Nanofingers. ACS Nano 2017; 11:5836-5843. [PMID: 28599108 DOI: 10.1021/acsnano.7b01468] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Gap plasmonic nanostructures are of great interest due to their ability to concentrate light into small volumes. Theoretical studies, considering quantum mechanical effects, have predicted the optimal spatial gap between adjacent nanoparticles to be in the subnanometer regime in order to achieve the strongest possible field enhancement. Here, we present a technology to fabricate gap plasmonic structures with subnanometer resolution, high reliability, and high throughput using collapsible nanofingers. This approach enables us to systematically investigate the effects of gap size and tunneling barrier height. The experimental results are consistent with previous findings as well as with a straightforward theoretical model that is presented here.
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Affiliation(s)
- Boxiang Song
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
| | - Yuhan Yao
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
| | - Roelof E Groenewald
- Department of Physics and Astronomy, University of Southern California , Los Angeles, California 90089, United States
| | - Yunxiang Wang
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
| | - He Liu
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
| | - Yifei Wang
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
| | - Yuanrui Li
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
| | - Fanxin Liu
- Department of Applied Physics, Zhejiang University of Technology , Hangzhou, Zhejiang 310023, China
| | - Stephen B Cronin
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
| | - Adam M Schwartzberg
- Molecular Foundry, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Stefano Cabrini
- Molecular Foundry, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Stephan Haas
- Department of Physics and Astronomy, University of Southern California , Los Angeles, California 90089, United States
| | - Wei Wu
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
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34
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Li Z, Bauers SR, Poudel N, Hamann D, Wang X, Choi DS, Esfarjani K, Shi L, Johnson DC, Cronin SB. Cross-Plane Seebeck Coefficient Measurement of Misfit Layered Compounds (SnSe) n(TiSe 2) n (n = 1,3,4,5). Nano Lett 2017; 17:1978-1986. [PMID: 28177640 DOI: 10.1021/acs.nanolett.6b05402] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
We report cross-plane thermoelectric measurements of misfit layered compounds (SnSe)n(TiSe2)n (n = 1,3,4,5), approximately 50 nm thick. Metal resistance thermometers are fabricated on the top and bottom of the (SnSe)n(TiSe2)n material to measure the temperature difference and heat transport through the material directly. By varying the number of layers in a supercell, n, we vary the interface density while maintaining a constant global stoichiometry. The Seebeck coefficient measured across the (SnSe)n(TiSe2)n samples was found to depend strongly on the number of layers in the supercell (n). When n decreases from 5 to 1, the cross-plane Seebeck coefficient decreases from -31 to -2.5 μV/K, while the cross-plane effective thermal conductivity decreases by a factor of 2, due to increased interfacial phonon scattering. The cross-plane Seebeck coefficients of the (SnSe)n(TiSe2)n are very different from the in-plane Seebeck coefficients, which are higher in magnitude and less sensitive to the number of layers in a supercell, n. We believe this difference is due to the different carrier types in the n-SnSe and p-TiSe2 layers and the effect of tunneling on the cross-plane transport.
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Affiliation(s)
| | - Sage R Bauers
- Department of Chemistry, University of Oregon , Eugene, Oregon 97403-1253, United States
| | | | - Danielle Hamann
- Department of Chemistry, University of Oregon , Eugene, Oregon 97403-1253, United States
| | - Xiaoming Wang
- Department of Physics and Astronomy University of Toledo , Toledo, Ohio 43606-3390, United States
- Institute for Advanced Materials, Devices and Nanotechnology, Rutgers University , Piscataway, New Jersey 08854, United States
| | - David S Choi
- Department of Mechanical Engineering, The University of Texas at Austin , Austin, Texas 78712-0292, United States
| | - Keivan Esfarjani
- Department of Mechanical and Aerospace Engineering, University of Virginia , Charlottesville, Virginia 22904-4746, United States
| | - Li Shi
- Department of Mechanical Engineering, The University of Texas at Austin , Austin, Texas 78712-0292, United States
| | - David C Johnson
- Department of Chemistry, University of Oregon , Eugene, Oregon 97403-1253, United States
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35
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Chatzakis I, Li Z, Benderskii AV, Cronin SB. Broadband terahertz modulation in electrostatically-doped artificial trilayer graphene. Nanoscale 2017; 9:1721-1726. [PMID: 28091664 DOI: 10.1039/c6nr07054j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We report a terahertz optical modulator consisting of randomly stacked trilayer graphene (TLG) deposited on an oxidized silicon substrate by means of THz-Time Domain Spectroscopy (THz-TDS). Here, the gate tuning of the Fermi level of the TLG provides the fundamental basis for the modulation of THz transmission. We measured a 15% change in the THz transmission of this device over a broad frequency range (0.6-1.6 THz). We also observed a strong absorption >80% in the time-domain signals and a frequency independence of the conductivity. Furthermore, unlike previous studies, we find that the underlying silicon substrate, which serves as a gate electrode for the graphene, also exhibits substantial modulation of the transmitted THz radiation under applied voltage biases.
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Affiliation(s)
- Ioannis Chatzakis
- Department of Electrical Engineering, University of Southern California, Los Angeles, California, CA 90089, USA.
| | - Zhen Li
- Department of Electrical Engineering, University of Southern California, Los Angeles, California, CA 90089, USA.
| | - Alexander V Benderskii
- Department of Chemistry, University of Southern California, Los Angeles, California, CA 90089, USA
| | - Stephen B Cronin
- Department of Electrical Engineering, University of Southern California, Los Angeles, California, CA 90089, USA. and Department of Chemistry, University of Southern California, Los Angeles, California, CA 90089, USA and Department of Physics, University of Southern California, Los Angeles, California, CA 90089, USA
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36
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Abstract
We report measurements of photocatalytic water splitting using Au films with and without TiO2 coatings.
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Affiliation(s)
- Bingya Hou
- Department of Electrical Engineering
- University of Southern California
- Los Angeles
- USA
| | - Lang Shen
- Department of Material Science
- University of Southern California
- Los Angeles
- USA
| | - Haotian Shi
- Department of Chemistry
- University of Southern California
- Los Angeles
- USA
| | - Rehan Kapadia
- Department of Electrical Engineering
- University of Southern California
- Los Angeles
- USA
| | - Stephen B. Cronin
- Department of Electrical Engineering
- University of Southern California
- Los Angeles
- USA
- Department of Chemistry
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37
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Abate Y, Gamage S, Li Z, Babicheva V, Javani MH, Wang H, Cronin SB, Stockman MI. Nanoscopy reveals surface-metallic black phosphorus. Light Sci Appl 2016; 5:e16162. [PMID: 30167125 PMCID: PMC6059827 DOI: 10.1038/lsa.2016.162] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Revised: 04/22/2016] [Accepted: 05/06/2016] [Indexed: 05/24/2023]
Abstract
Black phosphorus (BP) is an emerging two-dimensional material with intriguing physical properties. It is highly anisotropic and highly tunable by means of both the number of monolayers and surface doping. Here, we experimentally investigate and theoretically interpret the near-field properties of a-few-atomic-monolayer nanoflakes of BP. We discover near-field patterns of bright outside fringes and a high surface polarizability of nanofilm BP consistent with its surface-metallic, plasmonic behavior at mid-infrared frequencies <1176 cm-1. We conclude that these fringes are caused by the formation of a highly polarizable layer at the BP surface. This layer has a thickness of ~1 nm and exhibits plasmonic behavior. We estimate that it contains free carriers in a concentration of n≈1.1 × 1020 cm-3. Surface plasmonic behavior is observed for 10-40 nm BP thicknesses but absent for a 4-nm BP thickness. This discovery opens up a new field of research and potential applications in nanoelectronics, plasmonics and optoelectronics.
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Affiliation(s)
- Yohannes Abate
- Center for Nano-Optics, Georgia State University, Atlanta, GA 30303, USA
- Department of Physics and Astronomy, Center for Nano-Optics, Georgia State University, Atlanta, GA 30303, USA
| | - Sampath Gamage
- Department of Physics and Astronomy, Center for Nano-Optics, Georgia State University, Atlanta, GA 30303, USA
| | - Zhen Li
- Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Viktoriia Babicheva
- Center for Nano-Optics, Georgia State University, Atlanta, GA 30303, USA
- Department of Physics and Astronomy, Center for Nano-Optics, Georgia State University, Atlanta, GA 30303, USA
| | - Mohammad H Javani
- Center for Nano-Optics, Georgia State University, Atlanta, GA 30303, USA
- Department of Physics and Astronomy, Center for Nano-Optics, Georgia State University, Atlanta, GA 30303, USA
| | - Han Wang
- Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Stephen B Cronin
- Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Mark I Stockman
- Center for Nano-Optics, Georgia State University, Atlanta, GA 30303, USA
- Department of Physics and Astronomy, Center for Nano-Optics, Georgia State University, Atlanta, GA 30303, USA
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38
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Abstract
We report Raman and photoluminescence spectra of mono- and few-layer WSe2 and MoSe2 taken before and after exposure to a remote oxygen plasma. For bilayer and trilayer WSe2, we observe an increase in the photoluminescence intensity and a blue shift of the photoluminescence peak positions after oxygen plasma treatment. The photoluminescence spectra of trilayer WSe2 exhibit features of a bilayer after oxygen plasma treatment. Bilayer WSe2 exhibits features of a monolayer, and the photoluminescence of monolayer WSe2 is completely absent after the oxygen plasma treatment. These changes are observed consistently in more than 20 flakes. The mechanism of the changes observed in the photoluminescence spectra of WSe2 is due to the selective oxidation of the topmost layer. As a result, N-layer WSe2 is reduced to N-1 layers. Raman spectra and AFM images taken from the WSe2 flakes before and after the oxygen treatment corroborate these findings. Because of the low kinetic energy of the oxygen radicals in the remote oxygen plasma, the oxidation is self-limiting. By varying the process duration from 1 to 10 min, we confirmed that the oxidation will only affect the topmost layer of the WSe2 flakes. X-ray photoelectron spectroscopy shows that the surface layer WOx of the sample can be removed by a quick dip in KOH solution. Therefore, this technique provides a promising way of controlling the thickness of WSe2 layer by layer.
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Affiliation(s)
| | | | | | - Ewa Kosmowska
- XEI Scientific , Redwood City, California 94063, United States
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39
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Qiu J, Zeng G, Ge M, Arab S, Mecklenburg M, Hou B, Shen C, Benderskii AV, Cronin SB. Correlation of Ti3+ states with photocatalytic enhancement in TiO2-passivated p-GaAs. J Catal 2016. [DOI: 10.1016/j.jcat.2016.02.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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40
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Qiu J, Zeng G, Ha MA, Ge M, Lin Y, Hettick M, Hou B, Alexandrova AN, Javey A, Cronin SB. Correction to Artificial Photosynthesis on TiO2-Passivated InP Nanopillars. Nano Lett 2016; 16:824. [PMID: 26689351 DOI: 10.1021/acs.nanolett.5b05117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
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41
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Chang SW, Hazra J, Amer M, Kapadia R, Cronin SB. A Comparison of Photocurrent Mechanisms in Quasi-Metallic and Semiconducting Carbon Nanotube pn-Junctions. ACS Nano 2015; 9:11551-11556. [PMID: 26498635 DOI: 10.1021/acsnano.5b03873] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We present a comparative study of quasi-metallic (Eg ∼ 100 meV) and semiconducting (Eg ∼ 1 eV) suspended carbon nanotube pn-junctions introduced by electrostatic gating. While the built-in fields of the quasi-metallic carbon nanotubes (CNTs) are 1-2 orders of magnitude smaller than those of the semiconducting CNTs, their photocurrent is 2 orders of magnitude higher than the corresponding semiconducting CNT devices under the same experimental conditions. Here, the large exciton binding energy in semiconducting nanotubes (∼400 meV) makes it difficult for excitons to dissociate into free carriers that can contribute to an externally measured photocurent. As such, semiconducting nanotubes require a phonon to assist in the exciton dissociation process, in order to produce a finite photocurrent, while quasi-metallic nanotubes do not. The quasi-metallic nanotubes have much lower exciton binding energies (∼50 meV) as well as a continuum of electronic states to decay into and, therefore, do not require the absorption of a phonon in order to dissociate, making it much easier for these excitons to produce a photocurrent. We performed detailed simulations of the band energies in quasi-metallic and semiconducting nanotube devices in order to obtain the electric field profiles along the lengths of the nanotubes. These simulations predict maximum built-in electric field strengths of 2.3 V/μm for semiconducting and 0.032-0.22 V/μm for quasi-metallic nanotubes under the applied gate voltages used in this study.
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Affiliation(s)
| | | | - Moh Amer
- Department of Electrical Engineering University of California , Los Angeles, California 90095, United States
- King Abdulaziz City for Science and Technology , Riyadh 12612, Saudi Arabia
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42
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Shen L, He C, Qiu J, Lee SM, Kalita A, Cronin SB, Stoykovich MP, Yoon J. Nanostructured Silicon Photocathodes for Solar Water Splitting Patterned by the Self-Assembly of Lamellar Block Copolymers. ACS Appl Mater Interfaces 2015; 7:26043-26049. [PMID: 26575400 DOI: 10.1021/acsami.5b08661] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We studied a type of nanostructured silicon photocathode for solar water splitting, where one-dimensionally periodic lamellar nanopatterns derived from the self-assembly of symmetric poly(styrene-block-methyl methacrylate) block copolymers were incorporated on the surface of single-crystalline silicon in configurations with and without a buried metallurgical junction. The resulting nanostructured silicon photocathodes with the characteristic lamellar morphology provided suppressed front-surface reflection and increased surface area, which collectively contributed to the enhanced photocatalytic performance in the hydrogen evolution reaction. The augmented light absorption in the nanostructured silicon directly translated to the increase of the saturation current density, while the onset potential decreased with the etching depth because of the increased levels of surface recombination. The pp(+)-silicon photocathodes, compared to the n(+)pp(+)-silicon with a buried solid-state junction, exhibited a more pronounced shift of the current density-potential curves upon the introduction of the nanostructured surface owing to the corresponding increase in the liquid/silicon junction area. Systematic studies on the morphology, optical properties, and photoelectrochemical characteristics of nanostructured silicon photocathodes, in conjunction with optical modeling based on the finite-difference time-domain method, provide quantitative description and optimal design rules of lamellar-patterned silicon photocathodes for solar water splitting.
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Affiliation(s)
| | - Chunlin He
- Department of Chemical and Biological Engineering, University of Colorado Boulder , Boulder, Colorado 80309, United States
| | | | | | | | | | - Mark P Stoykovich
- Department of Chemical and Biological Engineering, University of Colorado Boulder , Boulder, Colorado 80309, United States
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43
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White ER, Kerelsky A, Hubbard WA, Dhall R, Cronin SB, Mecklenburg M, Regan BC. Imaging interfacial electrical transport in graphene-MoS 2 heterostructures with electron-beam-induced-currents. Appl Phys Lett 2015; 107:223104. [PMID: 26648594 PMCID: PMC4670446 DOI: 10.1063/1.4936763] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Accepted: 11/17/2015] [Indexed: 06/05/2023]
Abstract
Heterostructure devices with specific and extraordinary properties can be fabricated by stacking two-dimensional crystals. Cleanliness at the inter-crystal interfaces within a heterostructure is crucial for maximizing device performance. However, because these interfaces are buried, characterizing their impact on device function is challenging. Here, we show that electron-beam induced current (EBIC) mapping can be used to image interfacial contamination and to characterize the quality of buried heterostructure interfaces with nanometer-scale spatial resolution. We applied EBIC and photocurrent imaging to map photo-sensitive graphene-MoS2 heterostructures. The EBIC maps, together with concurrently acquired scanning transmission electron microscopy images, reveal how a device's photocurrent collection efficiency is adversely affected by nanoscale debris invisible to optical-resolution photocurrent mapping.
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Affiliation(s)
- E R White
- Department of Physics and Astronomy and California NanoSystems Institute, University of California , Los Angeles, California 90095, USA
| | - Alexander Kerelsky
- Department of Physics and Astronomy and California NanoSystems Institute, University of California , Los Angeles, California 90095, USA
| | - William A Hubbard
- Department of Physics and Astronomy and California NanoSystems Institute, University of California , Los Angeles, California 90095, USA
| | - Rohan Dhall
- Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, USA
| | - Stephen B Cronin
- Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, USA
| | - Matthew Mecklenburg
- Center for Electron Microscopy and Microanalysis, University of Southern California , Los Angeles, California 90089, USA
| | - B C Regan
- Department of Physics and Astronomy and California NanoSystems Institute, University of California , Los Angeles, California 90095, USA
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44
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Yao M, Cong S, Arab S, Huang N, Povinelli ML, Cronin SB, Dapkus PD, Zhou C. Tandem Solar Cells Using GaAs Nanowires on Si: Design, Fabrication, and Observation of Voltage Addition. Nano Lett 2015; 15:7217-7224. [PMID: 26502060 DOI: 10.1021/acs.nanolett.5b03890] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Multijunction solar cells provide us a viable approach to achieve efficiencies higher than the Shockley-Queisser limit. Due to their unique optical, electrical, and crystallographic features, semiconductor nanowires are good candidates to achieve monolithic integration of solar cell materials that are not lattice-matched. Here, we report the first realization of nanowire-on-Si tandem cells with the observation of voltage addition of the GaAs nanowire top cell and the Si bottom cell with an open circuit voltage of 0.956 V and an efficiency of 11.4%. Our simulation showed that the current-matching condition plays an important role in the overall efficiency. Furthermore, we characterized GaAs nanowire arrays grown on lattice-mismatched Si substrates and estimated the carrier density using photoluminescence. A low-resistance connecting junction was obtained using n(+)-GaAs/p(+)-Si heterojunction. Finally, we demonstrated tandem solar cells based on top GaAs nanowire array solar cells grown on bottom planar Si solar cells. The reported nanowire-on-Si tandem cell opens up great opportunities for high-efficiency, low-cost multijunction solar cells.
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Affiliation(s)
- Maoqing Yao
- Ming Hsieh Department of Electrical Engineering, ‡Center for Energy Nanoscience, University of Southern California , Los Angeles, California 90089, United States
| | - Sen Cong
- Ming Hsieh Department of Electrical Engineering, ‡Center for Energy Nanoscience, University of Southern California , Los Angeles, California 90089, United States
| | - Shermin Arab
- Ming Hsieh Department of Electrical Engineering, ‡Center for Energy Nanoscience, University of Southern California , Los Angeles, California 90089, United States
| | - Ningfeng Huang
- Ming Hsieh Department of Electrical Engineering, ‡Center for Energy Nanoscience, University of Southern California , Los Angeles, California 90089, United States
| | - Michelle L Povinelli
- Ming Hsieh Department of Electrical Engineering, ‡Center for Energy Nanoscience, University of Southern California , Los Angeles, California 90089, United States
| | - Stephen B Cronin
- Ming Hsieh Department of Electrical Engineering, ‡Center for Energy Nanoscience, University of Southern California , Los Angeles, California 90089, United States
| | - P Daniel Dapkus
- Ming Hsieh Department of Electrical Engineering, ‡Center for Energy Nanoscience, University of Southern California , Los Angeles, California 90089, United States
| | - Chongwu Zhou
- Ming Hsieh Department of Electrical Engineering, ‡Center for Energy Nanoscience, University of Southern California , Los Angeles, California 90089, United States
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45
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Zeng G, Qiu J, Hou B, Shi H, Lin Y, Hettick M, Javey A, Cronin SB. Frontispiece: Enhanced Photocatalytic Reduction of CO 2to CO through TiO 2Passivation of InP in Ionic Liquids. Chemistry 2015. [DOI: 10.1002/chem.201583961] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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46
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Qiu J, Zeng G, Ha MA, Ge M, Lin Y, Hettick M, Hou B, Alexandrova AN, Javey A, Cronin SB. Artificial Photosynthesis on TiO2-Passivated InP Nanopillars. Nano Lett 2015; 15:6177-6181. [PMID: 26267352 DOI: 10.1021/acs.nanolett.5b02511] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Here, we report photocatalytic CO2 reduction with water to produce methanol using TiO2-passivated InP nanopillar photocathodes under 532 nm wavelength illumination. In addition to providing a stable photocatalytic surface, the TiO2-passivation layer provides substantial enhancement in the photoconversion efficiency through the introduction of O vacancies associated with the nonstoichiometric growth of TiO2 by atomic layer deposition. Plane wave-density functional theory (PW-DFT) calculations confirm the role of oxygen vacancies in the TiO2 surface, which serve as catalytically active sites in the CO2 reduction process. PW-DFT shows that CO2 binds stably to these oxygen vacancies and CO2 gains an electron (-0.897e) spontaneously from the TiO2 support. This calculation indicates that the O vacancies provide active sites for CO2 absorption, and no overpotential is required to form the CO2(-) intermediate. The TiO2 film increases the Faraday efficiency of methanol production by 5.7× to 4.79% under an applied potential of -0.6 V vs NHE, which is 1.3 V below the E(o)(CO2/CO2(-)) = -1.9 eV standard redox potential. Copper nanoparticles deposited on the TiO2 act as a cocatalyst and further improve the selectivity and yield of methanol production by up to 8-fold with a Faraday efficiency of 8.7%.
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Affiliation(s)
| | | | | | | | | | | | | | | | - Ali Javey
- Material Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
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47
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Liu B, Köpf M, Abbas AN, Wang X, Guo Q, Jia Y, Xia F, Weihrich R, Bachhuber F, Pielnhofer F, Wang H, Dhall R, Cronin SB, Ge M, Fang X, Nilges T, Zhou C. Black Arsenic-Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties. Adv Mater 2015; 27:4423-4429. [PMID: 26112061 DOI: 10.1002/adma.201501758] [Citation(s) in RCA: 152] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Revised: 05/12/2015] [Indexed: 06/04/2023]
Abstract
New layered anisotropic infrared semiconductors, black arsenic-phosphorus (b-AsP), with highly tunable chemical compositions and electronic and optical properties are introduced. Transport and infrared absorption studies demonstrate the semiconducting nature of b-AsP with tunable bandgaps, ranging from 0.3 to 0.15 eV. These bandgaps fall into the long-wavelength infrared regime and cannot be readily reached by other layered materials.
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Affiliation(s)
- Bilu Liu
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Marianne Köpf
- Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, Garching b, München, 485748, Germany
| | - Ahmad N Abbas
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Xiaomu Wang
- Department of Electrical Engineering, Yale University, New Haven, CT, 06511, USA
| | - Qiushi Guo
- Department of Electrical Engineering, Yale University, New Haven, CT, 06511, USA
| | - Yichen Jia
- Department of Electrical Engineering, Yale University, New Haven, CT, 06511, USA
| | - Fengnian Xia
- Department of Electrical Engineering, Yale University, New Haven, CT, 06511, USA
| | - Richard Weihrich
- Institut für Anorganische Chemie, Universität Regensburg, Universitätsstraße 31, Regensburg, 93040, Germany
| | - Frederik Bachhuber
- Institut für Anorganische Chemie, Universität Regensburg, Universitätsstraße 31, Regensburg, 93040, Germany
| | - Florian Pielnhofer
- Institut für Anorganische Chemie, Universität Regensburg, Universitätsstraße 31, Regensburg, 93040, Germany
| | - Han Wang
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Rohan Dhall
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Stephen B Cronin
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Mingyuan Ge
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Xin Fang
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Tom Nilges
- Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, Garching b, München, 485748, Germany
| | - Chongwu Zhou
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
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48
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Zeng G, Qiu J, Hou B, Shi H, Lin Y, Hettick M, Javey A, Cronin SB. Enhanced Photocatalytic Reduction of CO2to CO through TiO2Passivation of InP in Ionic Liquids. Chemistry 2015. [DOI: 10.1002/chem.201501671] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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49
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Amer MR, Chang SW, Cronin SB. Competing Photocurrent Mechanisms in Quasi-Metallic Carbon Nanotube pn Devices. Small 2015; 11:3119-3123. [PMID: 25767070 DOI: 10.1002/smll.201403413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2014] [Revised: 02/07/2015] [Indexed: 06/04/2023]
Abstract
Photodetectors based on quasi-metallic carbon nanotubes exhibit unique optoelectronic properties. Due to their small bandgap, photocurrent generation is possible at room temperature. The origin of this photocurrent is investigated to determine the underlying mechanism, which can be photothermoelectric effect or photovoltaic effect, depending on the bandgap magnitude of the quasi-metallic nanotube.
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Affiliation(s)
- Moh R Amer
- Center of Excellence for Green Nanotechnologies, University of California Los Angeles, CA 90095, USA and King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia
| | - Shun-Wen Chang
- Department of Physics and Astronomy, University of Southern California, Los Angeles, CA, 90089, USA
| | - Stephen B Cronin
- Department of Physics and Astronomy, University of Southern California, Los Angeles, CA, 90089, USA
- Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
- Department of Material Science, University of Southern California, Los Angeles, CA, 90089, USA
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50
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Li Z, Ezhilarasu G, Chatzakis I, Dhall R, Chen CC, Cronin SB. Indirect Band Gap Emission by Hot Electron Injection in Metal/MoS₂ and Metal/WSe₂ Heterojunctions. Nano Lett 2015; 15:3977-82. [PMID: 25993397 DOI: 10.1021/acs.nanolett.5b00885] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Transition metal dichalcogenides (TMDCs), such as MoS2 and WSe2, are free of dangling bonds and therefore make more "ideal" Schottky junctions than bulk semiconductors, which produce Fermi energy pinning and recombination centers at the interface with bulk metals, inhibiting charge transfer. Here, we observe a more than 10× enhancement in the indirect band gap photoluminescence of transition metal dichalcogenides (TMDCs) deposited on various metals (e.g., Cu, Au, Ag), while the direct band gap emission remains unchanged. We believe the main mechanism of light emission arises from photoexcited hot electrons in the metal that are injected into the conduction band of MoS2 and WSe2 and subsequently recombine radiatively with minority holes in the TMDC. Since the conduction band at the K-point is 0.5 eV higher than at the Σ-point, a lower Schottky barrier exists for the Σ-point band, making electron injection more favorable. Also, the Σ band consists of the sulfur pz orbital, which overlaps more significantly with the electron wave functions in the metal. This enhancement in the indirect emission only occurs for thick flakes of MoS2 and WSe2 (≥100 nm) and is completely absent in monolayer and few-layer (∼10 nm) flakes. Here, the flake thickness must exceed the depletion width of the Schottky junction, in order for efficient radiative recombination to occur in the TMDC. The intensity of this indirect peak decreases at low temperatures, which is consistent with the hot electron injection model.
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Affiliation(s)
| | - Goutham Ezhilarasu
- ‡Department of Electrical and Electronics Engineering, College of Engineering Guindy, Anna University, Chennai Tamil Nadu 600026, India
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