1
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Mantilla ABC, Wang CF, Krayev A, Gu Y, Schultz ZD, El-Khoury PZ. Classical vs. quantum plasmon-induced molecular transformations at metallic nanojunctions. Proc Natl Acad Sci U S A 2024; 121:e2319233121. [PMID: 38547064 PMCID: PMC10998572 DOI: 10.1073/pnas.2319233121] [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] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Accepted: 02/12/2024] [Indexed: 04/08/2024] Open
Abstract
Chemical transformations near plasmonic metals have attracted increasing attention in the past few years. Specifically, reactions occurring within plasmonic nanojunctions that can be detected via surface and tip-enhanced Raman (SER and TER) scattering were the focus of numerous reports. In this context, even though the transition between localized and nonlocal (quantum) plasmons at nanojunctions is documented, its implications on plasmonic chemistry remain poorly understood. We explore the latter through AFM-TER-current measurements. We use two molecules: i) 4-mercaptobenzonitrile (MBN) that reports on the (non)local fields and ii) 4-nitrothiophenol (NTP) that features defined signatures of its neutral/anionic forms and dimer product, 4,4'-dimercaptoazobenzene (DMAB). The transition from classical to quantum plasmons is established through our optical measurements: It is marked by molecular charging and optical rectification. Simultaneously recorded force and current measurements support our assignments. In the case of NTP, we observe the parent and DMAB product beneath the probe in the classical regime. Further reducing the gap leads to the collapse of DMAB to form NTP anions. The process is reversible: Anions subsequently recombine into DMAB. Our results have significant implications for AFM-based TER measurements and their analysis, beyond the scope of this work. In effect, when precise control over the junction is not possible (e.g., in SER and ambient TER), both classical and quantum plasmons need to be considered in the analysis of plasmonic reactions.
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Affiliation(s)
| | - Chih-Feng Wang
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA99352
| | | | - Yi Gu
- Department of Physics and Astronomy, Washington State University, Pullman, WA99164
| | - Zachary D. Schultz
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH43210
| | - Patrick Z. El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA99352
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2
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Wang CF, Mantilla ABC, Krayev A, Gu Y, El-Khoury PZ. Probing Local Optical Fields via Ultralow Frequency Raman Scattering from a Corrugated Probe. J Phys Chem Lett 2023; 14:8334-8338. [PMID: 37698921 DOI: 10.1021/acs.jpclett.3c02122] [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] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/14/2023]
Abstract
We revisit nanoscale local optical field imaging via tip-enhanced Raman scattering (TERS). Rather than taking advantage of molecular reporters to probe different aspects of the local fields, we show how ultralow frequency Raman (ULF) scattering from the (nanocorrugated) metallic probe itself can be used for the same purpose. The bright ULF-TERS response we record allows non-invasive (tapping mode feedback) local field imaging, enables visualization of the local fields of small (≥20 nm) isolated plasmonic particles, and can also be exploited to distinguish between Si and SiO2 domains with 5 nm spatial resolution. We describe our approach and its limitations, particularly when it comes to using all-metallic versus molecular reporters.
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Affiliation(s)
- Chih-Feng Wang
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Alexander B C Mantilla
- Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, United States
| | - Andrey Krayev
- Horiba Instruments, Inc., 359 Bel Marin Keys Boulevard, Suite 18, Novato, California 94949, United States
| | - Yi Gu
- Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, United States
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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3
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Zhang T, Liu M, Fujisawa K, Lucking M, Beach K, Zhang F, Shanmugasundaram M, Krayev A, Murray W, Lei Y, Yu Z, Sanchez D, Liu Z, Terrones H, Elías AL, Terrones M. Spatial Control of Substitutional Dopants in Hexagonal Monolayer WS 2 : The Effect of Edge Termination. Small 2023; 19:e2205800. [PMID: 36587989 DOI: 10.1002/smll.202205800] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Revised: 11/20/2022] [Indexed: 06/17/2023]
Abstract
The ability to control the density and spatial distribution of substitutional dopants in semiconductors is crucial for achieving desired physicochemical properties. Substitutional doping with adjustable doping levels has been previously demonstrated in 2D transition metal dichalcogenides (TMDs); however, the spatial control of dopant distribution remains an open field. In this work, edge termination is demonstrated as an important characteristic of 2D TMD monocrystals that affects the distribution of substitutional dopants. Particularly, in chemical vapor deposition (CVD)-grown monolayer WS2 , it is found that a higher density of transition metal dopants is always incorporated in sulfur-terminated domains when compared to tungsten-terminated domains. Two representative examples demonstrate this spatial distribution control, including hexagonal iron- and vanadium-doped WS2 monolayers. Density functional theory (DFT) calculations are further performed, indicating that the edge-dependent dopant distribution is due to a strong binding of tungsten atoms at tungsten-zigzag edges, resulting in the formation of open sites at sulfur-zigzag edges that enable preferential dopant incorporation. Based on these results, it is envisioned that edge termination in crystalline TMD monolayers can be utilized as a novel and effective knob for engineering the spatial distribution of substitutional dopants, leading to in-plane hetero-/multi-junctions that display fascinating electronic, optoelectronic, and magnetic properties.
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Affiliation(s)
- Tianyi Zhang
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, 16802, USA
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Mingzu Liu
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, 16802, USA
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Kazunori Fujisawa
- Research Initiative for Supra-Materials, Shinshu University, Nagano, 380-8553, Japan
| | - Michael Lucking
- Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY, 12180, USA
| | - Kory Beach
- Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY, 12180, USA
- Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA, 94550, USA
| | - Fu Zhang
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, 16802, USA
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, 16802, USA
| | | | | | - William Murray
- Department of Electrical Engineering, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Yu Lei
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, 16802, USA
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
- Institute of Materials Research, Tsinghua Shenzhen International Graduate School, Shenzhen, 518055, China
| | - Zhuohang Yu
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, 16802, USA
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, 16802, USA
| | - David Sanchez
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, 16802, USA
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Zhiwen Liu
- Department of Electrical Engineering, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Humberto Terrones
- Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY, 12180, USA
| | - Ana Laura Elías
- Department of Physics, Binghamton University, Binghamton, NY, 13902, USA
| | - Mauricio Terrones
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, 16802, USA
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, 16802, USA
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
- Department of Chemistry, The Pennsylvania State University, University Park, PA, 16802, USA
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4
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Shang B, Rooney CL, Gallagher DJ, Wang BT, Krayev A, Shema H, Leitner O, Harmon NJ, Xiao L, Sheehan C, Bottum SR, Gross E, Cahoon JF, Mallouk TE, Wang H. Aqueous Photoelectrochemical CO 2 Reduction to CO and Methanol over a Silicon Photocathode Functionalized with a Cobalt Phthalocyanine Molecular Catalyst. Angew Chem Int Ed Engl 2023; 62:e202215213. [PMID: 36445830 DOI: 10.1002/anie.202215213] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Revised: 11/28/2022] [Accepted: 11/29/2022] [Indexed: 11/30/2022]
Abstract
We report a precious-metal-free molecular catalyst-based photocathode that is active for aqueous CO2 reduction to CO and methanol. The photoelectrode is composed of cobalt phthalocyanine molecules anchored on graphene oxide which is integrated via a (3-aminopropyl)triethoxysilane linker to p-type silicon protected by a thin film of titanium dioxide. The photocathode reduces CO2 to CO with high selectivity at potentials as mild as 0 V versus the reversible hydrogen electrode (vs RHE). Methanol production is observed at an onset potential of -0.36 V vs RHE, and reaches a peak turnover frequency of 0.18 s-1 . To date, this is the only molecular catalyst-based photoelectrode that is active for the six-electron reduction of CO2 to methanol. This work puts forth a strategy for interfacing molecular catalysts to p-type semiconductors and demonstrates state-of-the-art performance for photoelectrochemical CO2 reduction to CO and methanol.
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Affiliation(s)
- Bo Shang
- Department of Chemistry, Yale University, New Haven, CT 06520, USA.,Energy Sciences Institute, Yale University, West Haven, CT 06516, USA
| | - Conor L Rooney
- Department of Chemistry, Yale University, New Haven, CT 06520, USA.,Energy Sciences Institute, Yale University, West Haven, CT 06516, USA
| | - David J Gallagher
- Department of Chemistry, Yale University, New Haven, CT 06520, USA.,Energy Sciences Institute, Yale University, West Haven, CT 06516, USA
| | - Bernie T Wang
- Department of Chemistry, Yale University, New Haven, CT 06520, USA.,Energy Sciences Institute, Yale University, West Haven, CT 06516, USA
| | - Andrey Krayev
- HORIBA Instruments Inc., 359 Bel Marin Keys Blvd, Suite 18, Novato, CA 94949, USA
| | - Hadar Shema
- Institute of Chemistry and Center for Nanoscience and Nanotechnology, Hebrew University of Jerusalem, Jerusalem, 91904, Israel
| | - Oliver Leitner
- Department of Chemistry, Yale University, New Haven, CT 06520, USA.,Energy Sciences Institute, Yale University, West Haven, CT 06516, USA
| | - Nia J Harmon
- Department of Chemistry, Yale University, New Haven, CT 06520, USA.,Energy Sciences Institute, Yale University, West Haven, CT 06516, USA
| | - Langqiu Xiao
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Colton Sheehan
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Samuel R Bottum
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA
| | - Elad Gross
- Institute of Chemistry and Center for Nanoscience and Nanotechnology, Hebrew University of Jerusalem, Jerusalem, 91904, Israel
| | - James F Cahoon
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA
| | - Thomas E Mallouk
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Hailiang Wang
- Department of Chemistry, Yale University, New Haven, CT 06520, USA.,Energy Sciences Institute, Yale University, West Haven, CT 06516, USA
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5
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Shang B, Rooney CL, Gallagher DJ, Wang B, Krayev A, Shema H, Leitner O, Harmon NJ, Xiao L, Sheehan C, Bottum SR, Gross E, Cahoon JF, Mallouk TE, Wang H. Aqueous Photoelectrochemical CO2 Reduction to CO and Methanol over a Silicon Photocathode Functionalized with a Cobalt Phthalocyanine Molecular Catalyst. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202215213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Bo Shang
- Yale University chemistry UNITED STATES
| | | | | | | | - Andrey Krayev
- HORIBA Jobin-Yvon Inc: HORIBA Scientific NA UNITED STATES
| | - Hadar Shema
- Hebrew University of Jerusalem chemistry ISRAEL
| | | | | | - Langqiu Xiao
- University of Pennsylvania Department of Chemistry chemistry UNITED STATES
| | - Colton Sheehan
- Upenn: University of Pennsylvania chemistry UNITED STATES
| | - Samuel R. Bottum
- UNC-Chapel Hill: The University of North Carolina at Chapel Hill chemistry UNITED STATES
| | - Elad Gross
- Hebrew University of Jerusalem chemistry ISRAEL
| | - James F. Cahoon
- UNC-Chapel Hill: The University of North Carolina at Chapel Hill chemistry UNITED STATES
| | | | - Hailiang Wang
- Yale University Chemistry 810 West Campus Dr 06516 West Haven UNITED STATES
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6
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Rodriguez A, Krayev A, Velický M, Frank O, El-Khoury PZ. Nano-optical Visualization of Interlayer Interactions in WSe 2/WS 2 Heterostructures. J Phys Chem Lett 2022; 13:5854-5859. [PMID: 35727212 PMCID: PMC9335877 DOI: 10.1021/acs.jpclett.2c01250] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The interplay between excitons and phonons governs the optical and electronic properties of transition metal dichalcogenides (TMDs). Even though a number of linear and nonlinear optical-, electron-, and photoelectron-based approaches have been developed and/or adopted to characterize excitons and phonons in single/few-layer TMDs and their heterostructures, no existing method is capable of directly probing ultralow-frequency and interlayer phonons on the nanoscale. To this end, we developed ultralow-frequency tip-enhanced Raman spectroscopy, which allows spectrally and spatially resolved chemical and structural nanoimaging of WSe2/WS2 heterostructures. In this work, we apply this method to analyze phonons in nanobubbles that are sustained in these heterobilayers. Our method is capable of directly probing interlayer (de)coupling using our novel structurally sensitive nano-optical probe and the interplay between excitons and interlayer/intralayer phonons through correlation analysis of the recorded spectral images.
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Affiliation(s)
- Alvaro Rodriguez
- J.
Heyrovský Institute of Physical Chemistry, Czech Academy of
Sciences, Dolejškova 2155/3, 182 23 Prague, Czech Republic
| | - Andrey Krayev
- Horiba
Instruments, Inc., 359 Bel Marin Keys Boulevard, Suite 18, Novato, California 94949, United States
| | - Matěj Velický
- J.
Heyrovský Institute of Physical Chemistry, Czech Academy of
Sciences, Dolejškova 2155/3, 182 23 Prague, Czech Republic
| | - Otakar Frank
- J.
Heyrovský Institute of Physical Chemistry, Czech Academy of
Sciences, Dolejškova 2155/3, 182 23 Prague, Czech Republic
| | - Patrick Z. El-Khoury
- Physical
Sciences Division, Pacific Northwest National
Laboratory, P.O. Box 999, Richland, Washington 99352, United States
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7
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Sarycheva A, Shanmugasundaram M, Krayev A, Gogotsi Y. Tip-Enhanced Raman Scattering Imaging of Single- to Few-Layer Ti 3C 2T x MXene. ACS Nano 2022; 16:6858-6865. [PMID: 35404582 DOI: 10.1021/acsnano.2c01868] [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: 06/14/2023]
Abstract
MXenes are among the most widely researched materials due to a unique combination of high electronic conductivity and hydrophilic surface, confined in a 2D structure. Therefore, comprehensive characterization of individual MXene flakes is of great importance. Here we report on nanoscale Raman imaging of single-layer and few-layer flakes of Ti3C2Tx MXene deposited on a gold substrate using tip-enhanced Raman scattering (TERS). TERS spectra of MXene monolayers are dominated by an intense peak at around 201 cm-1 and two well-defined peaks at around 126 and 725 cm-1. Absolute intensities of these peaks decrease with increasing number of layers, though the relative intensity of the 126 and 725 cm-1 bands as compared to the 201 cm-1 band increases. The peak positions of the main MXene bands do not significantly change in flakes of different number of layers, suggesting weak coupling between the MXene layers. In addition, we observed stiffening of the 201 cm-1 vibration over the wrinkles in MXene flakes. Using TERS for nanoscale spectroscopic characterization of Ti3C2Tx allows fast Raman mapping with deep subdiffraction resolution at the laser power density on the sample about an order of magnitude lower as compared to confocal Raman measurements. Finally, we demonstrate very high environmental stability of stoichiometric single-layer MXenes and show that the intensity of TERS response from the single- and few-layer flakes of Ti3C2Tx can be used to track early stages of degradation, well before significant morphological changes appear.
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Affiliation(s)
- Asia Sarycheva
- A. J. Drexel Nanomaterials Institute, and Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, United States
| | | | - Andrey Krayev
- HORIBA Scientific 20 Knightsbridge Road, Piscataway, New Jersey 08854, United States
| | - Yury Gogotsi
- A. J. Drexel Nanomaterials Institute, and Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, United States
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8
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Kargar F, Krayev A, Wurch M, Ghafouri Y, Debnath T, Wickramaratne D, Salguero TT, Lake RK, Bartels L, Balandin AA. Metallic vs. semiconducting properties of quasi-one-dimensional tantalum selenide van der Waals nanoribbons. Nanoscale 2022; 14:6133-6143. [PMID: 35388816 DOI: 10.1039/d1nr07772d] [Citation(s) in RCA: 2] [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: 06/14/2023]
Abstract
We conducted a tip-enhanced Raman scattering spectroscopy (TERS) and photoluminescence (PL) study of quasi-1D TaSe3-δ nanoribbons exfoliated onto gold substrates. At a selenium deficiency of δ ∼ 0.25 (Se/Ta = 2.75), the nanoribbons exhibit a strong, broad PL peak centered around ∼920 nm (1.35 eV), suggesting their semiconducting behavior. Such nanoribbons revealed a strong TERS response under 785 nm (1.58 eV) laser excitation, allowing for their nanoscale spectroscopic imaging. Nanoribbons with a smaller selenium deficiency (Se/Ta = 2.85, δ ∼ 0.15) did not show any PL or TERS response. The confocal Raman spectra of these samples agree with the previously-reported spectra of metallic TaSe3. The differences in the optical response of the nanoribbons examined in this study suggest that even small variations in Se content can induce changes in electronic band structure, causing samples to exhibit either metallic or semiconducting character. The temperature-dependent electrical measurements of devices fabricated with both types of materials corroborate these observations. The density-functional-theory calculations revealed that substitution of an oxygen atom in a Se vacancy can result in band gap opening and thus enable the transition from a metal to a semiconductor. However, the predicted band gap is substantially smaller than that derived from the PL data. These results indicate that the properties of van der Waals materials can vary significantly depending on stoichiometry, defect types and concentration, and possibly environmental and substrate effects. In view of this finding, local probing of nanoribbon properties with TERS becomes essential to understanding such low-dimensional systems.
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Affiliation(s)
- Fariborz Kargar
- Nano-Device Laboratory (NDL) and Phonon Optimized Engineered Materials (POEM) Center, Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA.
| | | | - Michelle Wurch
- Nano-Device Laboratory (NDL) and Phonon Optimized Engineered Materials (POEM) Center, Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA.
- Department of Chemistry and Material Science and Engineering Program, University of California, Riverside, California 92521, USA
| | - Yassamin Ghafouri
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
| | - Topojit Debnath
- Laboratory for Terahertz and Terascale Electronics, Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA
| | - Darshana Wickramaratne
- Center for Computational Materials Science, U.S. Naval Research Laboratory, Washington, DC 20375, USA
| | - Tina T Salguero
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
| | - Roger K Lake
- Laboratory for Terahertz and Terascale Electronics, Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA
| | - Ludwig Bartels
- Department of Chemistry and Material Science and Engineering Program, University of California, Riverside, California 92521, USA
| | - Alexander A Balandin
- Nano-Device Laboratory (NDL) and Phonon Optimized Engineered Materials (POEM) Center, Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA.
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9
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Wong J, Davoyan A, Liao B, Krayev A, Jo K, Rotenberg E, Bostwick A, Jozwiak CM, Jariwala D, Zewail AH, Atwater HA. Spatiotemporal Imaging of Thickness-Induced Band-Bending Junctions. Nano Lett 2021; 21:5745-5753. [PMID: 34152777 DOI: 10.1021/acs.nanolett.1c01481] [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] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
van der Waals materials exhibit naturally passivated surfaces and an ability to form versatile heterostructures to enable an examination of carrier transport mechanisms not seen in traditional materials. Here, we report a new type of homojunction termed a "band-bending junction" whose potential landscape depends solely on the difference in thickness between the two sides of the junction. Using MoS2 on Au as a prototypical example, we find that surface potential differences can arise from the degree of vertical band bending in thin and thick regions. Furthermore, by using scanning ultrafast electron microscopy, we examine the spatiotemporal dynamics of charge carriers generated at this junction and find that lateral carrier separation is enabled by differences in the band bending in the vertical direction, which we verify with simulations. Band-bending junctions may therefore enable new optoelectronic devices that rely solely on band bending arising from thickness variations to separate charge carriers.
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Affiliation(s)
| | - Artur Davoyan
- Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, California 90095 United States
| | - Bolin Liao
- Department of Mechanical Engineering, University of California, Santa Barbara, California 93106, United States
| | - Andrey Krayev
- Horiba Scientific, Novato, California 94949, United States
| | - Kiyoung Jo
- Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Eli Rotenberg
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720,United States
| | - Aaron Bostwick
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720,United States
| | - Chris M Jozwiak
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720,United States
| | - Deep Jariwala
- Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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10
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Abstract
We combine nanoindentation, herein achieved using atomic force microscopy-based pulsed-force lithography, with tip-enhanced Raman spectroscopy (TERS) and imaging. Our approach entails indentation and multimodal characterization of otherwise flat Au substrates, followed by chemical functionalization and TERS spectral imaging of the indented nanostructures. We find that the resulting structures, which vary in shape and size depending on the tip used to produce them, may sustain nano-confined and significantly enhanced local fields. We take advantage of the latter and illustrate TERS-based ultrasensitive detection/chemical fingerprinting as well as chemical reaction imaging-all using a single platform for nano-lithography, topographic imaging, hyperspectral dark field optical microscopy, and TERS.
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Affiliation(s)
- Chih-Feng Wang
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Brian T O'Callahan
- Earth and Biological Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Andrey Krayev
- Horiba Instruments, Inc., 359 Bel Marin Keys Blvd., Suite 18, Novato, California 94949, USA
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
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11
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Darlington TP, Carmesin C, Florian M, Yanev E, Ajayi O, Ardelean J, Rhodes DA, Ghiotto A, Krayev A, Watanabe K, Taniguchi T, Kysar JW, Pasupathy AN, Hone JC, Jahnke F, Borys NJ, Schuck PJ. Imaging strain-localized excitons in nanoscale bubbles of monolayer WSe 2 at room temperature. Nat Nanotechnol 2020; 15:854-860. [PMID: 32661371 DOI: 10.1038/s41565-020-0730-5] [Citation(s) in RCA: 68] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Accepted: 06/03/2020] [Indexed: 05/23/2023]
Abstract
In monolayer transition-metal dichalcogenides, localized strain can be used to design nanoarrays of single photon sources. Despite strong empirical correlation, the nanoscale interplay between excitons and local crystalline structure that gives rise to these quantum emitters is poorly understood. Here, we combine room-temperature nano-optical imaging and spectroscopic analysis of excitons in nanobubbles of monolayer WSe2 with atomistic models to study how strain induces nanoscale confinement potentials and localized exciton states. The imaging of nanobubbles in monolayers with low defect concentrations reveals localized excitons on length scales of around 10 nm at multiple sites around the periphery of individual nanobubbles, in stark contrast to predictions of continuum models of strain. These results agree with theoretical confinement potentials atomistically derived from the measured topographies of nanobubbles. Our results provide experimental and theoretical insights into strain-induced exciton localization on length scales commensurate with exciton size, realizing key nanoscale structure-property information on quantum emitters in monolayer WSe2.
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Affiliation(s)
| | - Christian Carmesin
- Institute for Theoretical Physics, University of Bremen, Bremen, Germany
| | - Matthias Florian
- Institute for Theoretical Physics, University of Bremen, Bremen, Germany
| | - Emanuil Yanev
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Obafunso Ajayi
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Jenny Ardelean
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Daniel A Rhodes
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Augusto Ghiotto
- Department of Physics, Columbia University, New York, NY, USA
| | | | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | | | - Jeffrey W Kysar
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | | | - James C Hone
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Frank Jahnke
- Institute for Theoretical Physics, University of Bremen, Bremen, Germany.
| | - Nicholas J Borys
- Department of Physics, Montana State University, Bozeman, MT, USA.
| | - P James Schuck
- Department of Mechanical Engineering, Columbia University, New York, NY, USA.
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12
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Wang CF, O'Callahan BT, Kurouski D, Krayev A, Schultz ZD, El-Khoury PZ. Suppressing Molecular Charging, Nanochemistry, and Optical Rectification in the Tip-Enhanced Raman Geometry. J Phys Chem Lett 2020; 11:5890-5895. [PMID: 32619091 DOI: 10.1021/acs.jpclett.0c01413] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Classical versus quantum plasmons are responsible for the recorded signals in non-contact-mode versus contact-mode tip-enhanced Raman spectroscopy (TERS) and lead to distinct observables. Under otherwise identical experimental conditions, we illustrate the concept through tapping- and contact-mode TERS mapping of chemically functionalized silver nanocubes. Whereas molecular charging, chemical transformations, and optical rectification are prominent observables in contact-mode TERS, the same effects are suppressed using tapping-mode feedback. In effect, this work demonstrates that nanoscale physical and chemical processes can be accessed and/or suppressed on demand in the TERS geometry. The advantages of tapping-mode TERS are otherwise highlighted with the latter in mind.
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Affiliation(s)
| | | | - Dmitry Kurouski
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843, United States
| | - Andrey Krayev
- Horiba Instruments Inc., 359 Bel Marin Keys Boulevard, Suite 18, Novato, California 94949, United States
| | - Zachary D Schultz
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
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13
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Darlington TP, Krayev A, Venkatesh V, Saxena R, Kysar JW, Borys NJ, Jariwala D, Schuck PJ. Facile and quantitative estimation of strain in nanobubbles with arbitrary symmetry in 2D semiconductors verified using hyperspectral nano-optical imaging. J Chem Phys 2020; 153:024702. [DOI: 10.1063/5.0012817] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Affiliation(s)
- Thomas P. Darlington
- Department of Physics, University of California, Berkeley, California 94720, USA
| | | | - Vishal Venkatesh
- Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Ravindra Saxena
- Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Jeffrey W. Kysar
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA
| | - Nicholas J. Borys
- Department of Physics, Montana State University, Bozeman, Montana 59717, USA
| | - Deep Jariwala
- Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - P. James Schuck
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA
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14
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Wang CF, O'Callahan BT, Kurouski D, Krayev A, El-Khoury PZ. The Prevalence of Anions at Plasmonic Nanojunctions: A Closer Look at p-Nitrothiophenol. J Phys Chem Lett 2020; 11:3809-3814. [PMID: 32340455 DOI: 10.1021/acs.jpclett.0c01006] [Citation(s) in RCA: 5] [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: 06/11/2023]
Abstract
We revisit the reductive coupling of p-nitrothiophenol (NTP) to form dimercaptoazobenzene (DMAB), herein monitored through gap-mode tip-enhanced Raman spectroscopy (TERS) and nanoimaging. We employ a plasmonic Au probe (100 nm diameter at its apex) illuminated with a 633 nm laser source (50 μW/μm2 at the sample position) to image an NTP-coated faceted silver nanoparticle (∼70 nm diameter). A detailed analysis of the recorded spectra reveals that anionic NTP species contribute to the recorded spectral images, in addition to the more thoroughly described DMAB product. Notably, the signatures of the anions are more pronounced than those of the DMAB product under our present experimental conditions. Our results thus demonstrate that anions and their spectral signatures must be considered in the analysis of plasmon-enhanced optical spectra and images.
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Affiliation(s)
- Chih-Feng Wang
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Brian T O'Callahan
- Earth and Biological Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Dmitry Kurouski
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843, United States
| | - Andrey Krayev
- Horiba Instruments Inc., 359 Bel Marin Keys Blvd, Suite 18, Novato, California 94949, United States
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
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15
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Krayev A, Krylyuk S, Ilic R, Hight Walker AR, Bhattarai A, Joly AG, Velický M, Davydov AV, El-Khoury PZ. Comparable Enhancement of TERS Signals from WSe 2 on Chromium and Gold. J Phys Chem C Nanomater Interfaces 2020; 124:https://doi.org/10.1021/acs.jpcc.0c01298. [PMID: 33093932 PMCID: PMC7574560] [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] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Plasmonic tip-sample junctions, at which the incident and scattered optical fields are localized and optimally enhanced, are often exploited to achieve ultrasensitive and highly spatially localized tip-enhanced Raman scattering (TERS). Recent work has demonstrated that the sensitivity and spatial resolution that are required to probe single molecules are attainable in such platforms. In this work, we observe and rationalize comparable TERS from few-layer WSe2 single crystals exfoliated onto Au- and Cr-coated Si substrates, using a plasmonic TERS probe excited with a 638 nm laser. Our experimental observations are supported by finite-difference time-domain simulations that illustrate that the attainable field enhancement factors at the Au-Au and Au-Cr tip-sample junctions are comparable in magnitude. Through a combined experimental and theoretical analysis, we propose that besides Au/Ag, several metallic substrates may be used to record bright TERS spectral images.
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Affiliation(s)
- Andrey Krayev
- Horiba Instruments Inc., Novato, California 94949, United States
| | - Sergiy Krylyuk
- Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States; Theiss Research, Inc., La Jolla, California 92037, United States
| | - Robert Ilic
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Angela R Hight Walker
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Ashish Bhattarai
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Alan G Joly
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Matěj Velický
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States; School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
| | - Albert V Davydov
- Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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16
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Krayev A, Bailey CS, Jo K, Wang S, Singh A, Darlington T, Liu GY, Gradecak S, Schuck PJ, Pop E, Jariwala D. Dry Transfer of van der Waals Crystals to Noble Metal Surfaces To Enable Characterization of Buried Interfaces. ACS Appl Mater Interfaces 2019; 11:38218-38225. [PMID: 31512847 DOI: 10.1021/acsami.9b09798] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have been explored for many optoelectronic applications. Most of these applications require them to be on insulating substrates. However, for many fundamental property characterizations, such as mapping surface potential or conductance, insulating substrates are nonideal as they lead to charging and doping effects or impose the inhomogeneity of their charge environment on the atomically thin 2D layers. Here, we report a simple method of residue-free dry transfer of 2D TMDC crystal layers. This method is enabled via noble-metal (gold, silver) thin films and allows comprehensive nanoscale characterization of transferred TMDC crystals with multiple scanning probe microscopy techniques. In particular, intimate contact with underlying metal allows efficient tip-enhanced Raman scattering characterization, providing high spatial resolution (<20 nm) for Raman spectroscopy. Further, scanning Kelvin probe force microscopy allows high-resolution mapping of surface potential on transferred crystals, revealing their spatially varying structural and electronic properties. The layer-dependent contact potential difference is clearly observed and explained by charge transfer from contacts with Au and Ag. The demonstrated sample preparation technique can be generalized to probe many different 2D material surfaces and has broad implications in understanding of the metal contacts and buried interfaces in 2D material-based devices.
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Affiliation(s)
- Andrey Krayev
- Horiba Scientific , Novato , California 94949 , United States
| | - Connor S Bailey
- Department of Electrical Engineering , Stanford University , Stanford , California 94305 , United States
| | - Kiyoung Jo
- Department of Electrical and Systems Engineering , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States
| | - Shuo Wang
- Department of Chemistry , University of California , Davis , California 95616 , United States
| | - Akshay Singh
- Department of Materials Science and Engineering , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
| | - Thomas Darlington
- Department of Mechanical Engineering , Columbia University , New York , New York 10027 , United States
| | - Gang-Yu Liu
- Department of Chemistry , University of California , Davis , California 95616 , United States
| | - Silvija Gradecak
- Department of Materials Science and Engineering , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
| | - P James Schuck
- Department of Mechanical Engineering , Columbia University , New York , New York 10027 , United States
| | - Eric Pop
- Department of Electrical Engineering , Stanford University , Stanford , California 94305 , United States
| | - Deep Jariwala
- Department of Electrical and Systems Engineering , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States
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17
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Su W, Kumar N, Krayev A, Chaigneau M. In situ topographical chemical and electrical imaging of carboxyl graphene oxide at the nanoscale. Nat Commun 2018; 9:2891. [PMID: 30038358 PMCID: PMC6056528 DOI: 10.1038/s41467-018-05307-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2017] [Accepted: 06/20/2018] [Indexed: 11/30/2022] Open
Abstract
Visualising the distribution of structural defects and functional groups present on the surface of two-dimensional (2D) materials such as graphene oxide challenges the sensitivity and spatial resolution of the most advanced analytical techniques. Here we demonstrate mapping of functional groups on a carboxyl-modified graphene oxide (GO–COOH) surface with a spatial resolution of ≈10 nm using tip-enhanced Raman spectroscopy (TERS). Furthermore, we extend the capability of TERS by measuring local electronic properties in situ, in addition to the surface topography and chemical composition. Our results reveal that the Fermi level at the GO–COOH surface decreases as the ID/IG ratio increases, correlating the local defect density with the Fermi level at nanometre length-scales. The in situ multi-parameter microscopy demonstrated in this work significantly improves the accuracy of nanoscale surface characterisation, eliminates measurement artefacts, and opens up the possibilities for characterising optoelectronic devices based on 2D materials under operational conditions. Mapping the distribution of functional groups on 2D materials with high resolution remains challenging. Here, the authors combine tip-enhanced Raman spectroscopy and Kelvin probe force microscopy to simultaneously examine the topography, chemical composition and electronic nature of graphene oxide surfaces with nanoscale spatial resolution.
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Affiliation(s)
- Weitao Su
- College of Materials and Environmental Engineering, Hangzhou Dianzi University, 310018, Hangzhou, China. .,Key Laboratory of RF Circuits and Systems (Hangzhou Dianzi University), Ministry of Education, Hangzhou, 310018, China.
| | - Naresh Kumar
- National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, UK. .,Inorganic Chemistry and Catalysis group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG, Utrecht, The Netherlands.
| | - Andrey Krayev
- HORIBA Instruments Incorporated, Novato, CA, 94949, USA
| | - Marc Chaigneau
- HORIBA France, Avenue de la Vauve, Passage Jobin Yvon, 91120, Palaiseau, France.
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18
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Bhattarai A, Krayev A, Temiryazev A, Evplov D, Crampton KT, Hess WP, El-Khoury PZ. Tip-Enhanced Raman Scattering from Nanopatterned Graphene and Graphene Oxide. Nano Lett 2018; 18:4029-4033. [PMID: 29791800 DOI: 10.1021/acs.nanolett.8b01690] [Citation(s) in RCA: 14] [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: 06/08/2023]
Abstract
Tip-enhanced Raman spectroscopy (TERS) is particularly sensitive to analytes residing at plasmonic tip-sample nanojunctions, where the incident and scattered optical fields may be localized and optimally enhanced. However, the enhanced local electric fields in this so-called gap-mode TERS configuration are nominally orthogonal to the sample plane. As such, any given Raman active vibrational eigenstate needs to have projections (of its polarizability derivative tensor elements) along the sample normal to be detectable via TERS. The faint TERS signals observed from two prototypical systems, namely, pristine graphene and graphene oxide are a classical example of the aforementioned rather restrictive TERS selection rules in this context. In this study, we demonstrate that nanoindentation, herein achieved using pulsed-force lithography with a sharp single-crystal diamond atomic force microscope probe, may be used to locally enhance TERS signals from graphene and graphene oxide flakes on gold. Nanoindentation locally perturbs the otherwise flat graphene structure and introduces out-of-plane protrusions that generate enhanced TERS. Although our approach is nominally invasive, we illustrate that the introduced nanodefects are highly localized, as evidenced by TERS nanoscale chemical mapping. As such, the described protocol may be used to extend and generalize the applicability of TERS for the rapid identification of two-dimensional material systems on the nanoscale.
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Affiliation(s)
- Ashish Bhattarai
- Physical Sciences Division , Pacific Northwest National Laboratory , P.O. Box 999, Richland , Washington 99352 , United States
| | - Andrey Krayev
- Horiba Instruments Inc. , 359 Bel Marin Keys Boulevard, Suite 20 , Novato , California 94949 , United States
| | - Alexey Temiryazev
- Kotel'nikov Institute of Radioengineering and Electronics of RAS, Fryazino Branch , Vvedensky Square 1 , Fryazino 141190 , Russia
| | - Dmitry Evplov
- Horiba Instruments Inc. , 359 Bel Marin Keys Boulevard, Suite 20 , Novato , California 94949 , United States
| | - Kevin T Crampton
- Physical Sciences Division , Pacific Northwest National Laboratory , P.O. Box 999, Richland , Washington 99352 , United States
| | - Wayne P Hess
- Physical Sciences Division , Pacific Northwest National Laboratory , P.O. Box 999, Richland , Washington 99352 , United States
| | - Patrick Z El-Khoury
- Physical Sciences Division , Pacific Northwest National Laboratory , P.O. Box 999, Richland , Washington 99352 , United States
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19
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Plathier J, Krayev A, Gavrilyuk V, Pignolet A, Ruediger A. Permittivity imaged at the nanoscale using tip-enhanced Raman spectroscopy. Nanoscale Horiz 2017; 2:365-369. [PMID: 32260667 DOI: 10.1039/c7nh00075h] [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] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Localized surface plasmon resonances are the dominating contribution to the optical enhancement and the lateral resolution in tip-enhanced Raman spectroscopy. This well studied phenomenon may give access to more information about the sample than the enhanced Raman spectra alone due to its sensitivity to the permittivity of the tip environment. In this work, the effects of the permittivity of the sample on the properties of localized surface plasmon resonance are studied through the amplified signal of the luminescence of gold tips.
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Affiliation(s)
- Julien Plathier
- INRS-EMT, 1650 Boul. Lionel-Boulet, Varennes, Québec, J3X1S2, Canada.
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20
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Nicklaus M, Nauenheim C, Krayev A, Gavrilyuk V, Belyaev A, Ruediger A. Note: tip enhanced Raman spectroscopy with objective scanner on opaque samples. Rev Sci Instrum 2012; 83:066102. [PMID: 22755668 DOI: 10.1063/1.4725528] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We report on 14 nm lateral resolution in tip-enhanced Raman spectroscopy mapping of carbon nanotubes with an experimental setup that has been designed for the analysis of opaque samples in confocal side-access through a novel piezo-driven objective scanner. The objective scanner allows for fast and stable laser-to-tip alignment and for the adjustment of the focus position with sub-wavelength precision to optimize the excitation of surface plasmons. It also offers the additional benefit of imaging the near-field generated Raman scattering at the gap between tip and sample as direct control of the tip enhancement.
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Affiliation(s)
- Mischa Nicklaus
- Laboratory of Ferroelectric Nanoelectronics, INRS-EMT, 1650 Boul. Lionel-Boulet, Varennes J3X1S2 Québec, Canada.
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