1
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Jo K, Stevens CE, Choi B, El-Khoury PZ, Hendrickson JR, Jariwala D. Core/Shell-Like Localized Emission at Atomically Thin Semiconductor-Au Interface. Nano Lett 2024. [PMID: 38593418 DOI: 10.1021/acs.nanolett.3c03790] [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: 04/11/2024]
Abstract
Localized emission in atomically thin semiconductors has sparked significant interest as single-photon sources. Despite comprehensive studies into the correlation between localized strain and exciton emission, the impacts of charge transfer on nanobubble emission remains elusive. Here, we report the observation of core/shell-like localized emission from monolayer WSe2 nanobubbles at room temperature through near-field studies. By altering the electronic junction between monolayer WSe2 and the Au substrate, one can effectively adjust the semiconductor to metal junction from a Schottky to an Ohmic junction. Through concurrent analysis of topography, potential, tip-enhanced photoluminescence, and a piezo response force microscope, we attribute the core/shell-like emissions to strong piezoelectric potential aided by induced polarity at the WSe2-Au Schottky interface which results in spatial confinement of the excitons. Our findings present a new approach for manipulating charge confinement and engineering localized emission within atomically thin semiconductor nanobubbles. These insights hold implications for advancing the nano and quantum photonics with low-dimensional semiconductors.
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Affiliation(s)
- Kiyoung Jo
- Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Christopher E Stevens
- KBR Inc., Beavercreek, Ohio 45431, United States
- Sensors Directorate, Air Force Research Laboratory, Wright-Patterson AFB Ohio 45433, United States
| | - Bongjun Choi
- Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Joshua R Hendrickson
- Sensors Directorate, Air Force Research Laboratory, Wright-Patterson AFB Ohio 45433, United States
| | - Deep Jariwala
- Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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2
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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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3
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Primera-Pedrozo OM, Mantilla ABC, Myers TL, Gu Y, El-Khoury PZ. Controlling the Fluctuating Tip-Enhanced Raman Spectra of Chloramben on Silver Nanocubes. Anal Chem 2024. [PMID: 38315807 DOI: 10.1021/acs.analchem.3c05542] [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: 02/07/2024]
Abstract
Tip-enhanced Raman (TER) scattering from molecules residing at plasmonic junctions can be used to detect, identify, and image single molecules. This is most evident for flat molecules interrogated under conditions of extreme temperatures and pressure. It is also the case for (bio)molecular systems that feature preferred orientations/conformations under ambient laboratory conditions. More complex molecules that can adopt multiple conformations and/or feature different protonation or charge states give rise to complex TER spectra. We illustrate how the latter can be controlled in the case of chloramben molecules coated onto plasmonic silver nanocubes. We show that characteristic molecular Raman spectra cannot be obtained when tunneling plasmons are operative, i.e., when the tip is in direct contact with the chemically functionalized plasmonic nanoparticles. We rationalize these observations and propose an approach to less invasive and hence more analytical TER spectral imaging.
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Affiliation(s)
- Oliva M Primera-Pedrozo
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Alexander B C Mantilla
- Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, United States
| | - Tanya L Myers
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, 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, P.O. Box 999, Richland, Washington 99352, United States
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4
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Peterson BN, Morales AC, Tomlin JM, Gorman CGW, Christ PE, Sharpe SAL, Huston SM, Rivera-Adorno FA, O'Callahan BT, Fraund M, Noh Y, Pahari P, Whelton AJ, El-Khoury PZ, Moffet RC, Zelenyuk A, Laskin A. Chemical characterization of microplastic particles formed in airborne waste discharged from sewer pipe repairs. Environ Sci Process Impacts 2023; 25:1718-1731. [PMID: 37781874 DOI: 10.1039/d3em00193h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/03/2023]
Abstract
Microplastic particles are of increasing environmental concern due to the widespread uncontrolled degradation of various commercial products made of plastic and their associated waste disposal. Recently, common technology used to repair sewer pipes was reported as one of the emission sources of airborne microplastics in urban areas. This research presents results of the multi-modal comprehensive chemical characterization of the microplastic particles related to waste discharged in the pipe repair process and compares particle composition with the components of uncured resin and cured plastic composite used in the process. Analysis of these materials employs complementary use of surface-enhanced Raman spectroscopy, scanning transmission X-ray spectro-microscopy, single particle mass spectrometry, and direct analysis in real-time high-resolution mass spectrometry. It is shown that the composition of the relatively large (100 μm) microplastic particles resembles components of plastic material used in the process. In contrast, the composition of the smaller (micrometer and sub-micrometer) particles is significantly different, suggesting their formation from unintended polymerization of water-soluble components occurring in drying droplets of the air-discharged waste. In addition, resin material type influences the composition of released microplastic particles. Results are further discussed to guide the detection and advanced characterization of airborne microplastics in future field and laboratory studies pertaining to sewer pipe repair technology.
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Affiliation(s)
| | - Ana C Morales
- Department of Chemistry, Purdue University, West Lafayette, IN, USA.
| | - Jay M Tomlin
- Department of Chemistry, Purdue University, West Lafayette, IN, USA.
| | - Carrie G W Gorman
- Department of Chemistry, Purdue University, West Lafayette, IN, USA.
| | - Peter E Christ
- Department of Chemistry, Purdue University, West Lafayette, IN, USA.
| | - Steven A L Sharpe
- Department of Chemistry, Purdue University, West Lafayette, IN, USA.
| | - Shelby M Huston
- Department of Chemistry, Purdue University, West Lafayette, IN, USA.
| | | | - Brian T O'Callahan
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, USA
| | | | - Yoorae Noh
- Lyles School of Civil Engineering, Purdue University, West Lafayette, IN, USA
- Department of Environmental and Ecological Engineering, Purdue University, West Lafayette, IN, USA
| | - Pritee Pahari
- Lyles School of Civil Engineering, Purdue University, West Lafayette, IN, USA
- Department of Environmental and Ecological Engineering, Purdue University, West Lafayette, IN, USA
| | - Andrew J Whelton
- Lyles School of Civil Engineering, Purdue University, West Lafayette, IN, USA
- Department of Environmental and Ecological Engineering, Purdue University, West Lafayette, IN, USA
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA
- Chemical Physics & Analysis, Pacific Northwest National Laboratory, Richland, WA, USA
| | | | - Alla Zelenyuk
- Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Alexander Laskin
- Department of Chemistry, Purdue University, West Lafayette, IN, USA.
- Department of Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, IN, USA
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5
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Wang CF, Krayev AV, El-Khoury PZ. Subnanometer Visualization of Spatially Varying Local Field Resonances that Drive Tip-Enhanced Optical Spectroscopy. Nano Lett 2023; 23:9114-9118. [PMID: 37751571 DOI: 10.1021/acs.nanolett.3c03028] [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: 09/28/2023]
Abstract
Our knowledge of the electromagnetic fields that power modern nanoscale optical measurements, including (non)linear tip-enhanced Raman and photoluminescence, chiefly stems from numerical simulations. Aside from idealized in silico vs heterogeneous (nano)structures in the laboratory, challenges in quantitative descriptions of nanoscale light-matter interactions more generally stem from the very nature of the problem, which lies at the interface of classical and quantum theories. This is particularly the case in ultrahigh spatial resolution measurements that are sensitive to local optical field variations that take place on subnanometer length scales. This work approaches this challenge through extinction-based spectral nanoimaging experiments. We demonstrate <1 nm spatial resolution in hyperspectral extinction measurements that track spatially varying plasmon resonances. We describe the principles behind our experiments and highlight more general implications of our observations.
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Affiliation(s)
- Chih-Feng Wang
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Andrey V 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, Richland, Washington 99352, United States
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6
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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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7
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Primera-Pedrozo OM, Tan S, Zhang D, O'Callahan BT, Cao W, Baxter ET, Wang XB, El-Khoury PZ, Prabhakaran V, Glezakou VA, Johnson GE. Influence of surface and intermolecular interactions on the properties of supported polyoxometalates. Nanoscale 2023; 15:5786-5797. [PMID: 36857667 DOI: 10.1039/d2nr06148a] [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: 06/18/2023]
Abstract
Polyoxometalates (POMs) with localized radical or open-shell metal sites have the potential to be used as transformative electronic spin based molecular qubits (MQs) for quantum computing (QC). For practical applications, MQs have to be immobilized in electronically or optically addressable arrays which introduces interactions with supports as well as neighboring POMs. Herein, we synthesized Keggin POMs with both tungsten (W) and vanadium (V) addenda atoms. Ion soft landing, a highly-controlled surface modification technique, was used to deliver mass-selected V-doped POMs to different self-assembled monolayer surfaces on gold (SAMs) without the solvent, counterions, and contaminants that normally accompany deposition from solution. Alkylthiol, perfluorinated, and carboxylic-acid terminated monolayers were employed as representative model supports on which different POM-surface and POM-POM interactions were characterized. We obtained insights into the vibrational properties of supported V-doped POMs and how they are perturbed by interactions with specific surface functional groups using infrared reflection absorption and scattering-type scanning near-field optical microscopy, as well as tip enhanced Raman spectroscopy. Different functional groups on SAMs and nanoscale heterogeneity are both shown to modulate the observed spectroscopic signatures. Spectral shifts are also found to be dependent on POM-POM interactions. The electronic structure of the V-doped POMs was determined in the gas phase using negative ion photoelectron spectroscopy and on surfaces with scanning Kelvin probe microscopy. The chemical functionality and charge transfer properties of the SAMs are demonstrated to exert an influence on the charge state and electronic configuration of supported V-doped POMs. The geometric and electronic structure of the POMs were also calculated using density functional theory. Our joint experimental and theoretical findings provide insight into how V substitution as well as POM-surface and POM-POM interactions influence the vibrational properties of POMs.
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Affiliation(s)
- Oliva M Primera-Pedrozo
- Pacific Northwest National Laboratory, Physical Sciences Division, P.O. Box 999, MSIN J7-10, Richland, Washington 99352, USA.
| | - Shuai Tan
- Pacific Northwest National Laboratory, Physical Sciences Division, P.O. Box 999, MSIN J7-10, Richland, Washington 99352, USA.
| | - Difan Zhang
- Pacific Northwest National Laboratory, Physical Sciences Division, P.O. Box 999, MSIN J7-10, Richland, Washington 99352, USA.
| | - Brian T O'Callahan
- Pacific Northwest National Laboratory, Earth and Biological Sciences Division, P.O. Box 999, MSIN K8-88, Richland, Washington 99352, USA
| | - Wenjin Cao
- Pacific Northwest National Laboratory, Physical Sciences Division, P.O. Box 999, MSIN J7-10, Richland, Washington 99352, USA.
| | - Eric T Baxter
- Pacific Northwest National Laboratory, Physical Sciences Division, P.O. Box 999, MSIN J7-10, Richland, Washington 99352, USA.
| | - Xue-Bin Wang
- Pacific Northwest National Laboratory, Physical Sciences Division, P.O. Box 999, MSIN J7-10, Richland, Washington 99352, USA.
| | - Patrick Z El-Khoury
- Pacific Northwest National Laboratory, Physical Sciences Division, P.O. Box 999, MSIN J7-10, Richland, Washington 99352, USA.
| | - Venkateshkumar Prabhakaran
- Pacific Northwest National Laboratory, Physical Sciences Division, P.O. Box 999, MSIN J7-10, Richland, Washington 99352, USA.
| | | | - Grant E Johnson
- Pacific Northwest National Laboratory, Physical Sciences Division, P.O. Box 999, MSIN J7-10, Richland, Washington 99352, USA.
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8
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El-Khoury PZ. High spatial resolution ambient tip-enhanced (multipolar) Raman scattering. Chem Commun (Camb) 2023; 59:3536-3541. [PMID: 36852462 DOI: 10.1039/d3cc00434a] [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: 03/01/2023]
Abstract
This article summarizes lessons learnt from ambient tip-enhanced Raman (TER) mapping of molecules interacting with plasmonic nanostructures. It is shown that numerous physical and chemical phenomena contribute to high-resolution TER spectral images. As a result, selectively tracking interfacial chemical transformations via TERS is more challenging than currently appreciated.
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Affiliation(s)
- Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA, 99352, USA.
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9
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El-Khoury PZ. Tip-Enhanced Raman Chemical and Chemical Reaction Imaging in H 2O with Sub-3-nm Spatial Resolution. J Am Chem Soc 2023; 145:6639-6642. [PMID: 36919918 DOI: 10.1021/jacs.3c01626] [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: 03/16/2023]
Abstract
Reproducible chemical and chemical reaction nanoimaging at solid-liquid interfaces remains challenging, particularly when resolutions on the order of a few nanometers are sought. In this work, we demonstrate the latter through liquid-tip-enhanced Raman (TER) measurements that target gold nanoplates functionalized with 4-mercaptobenzonitrile (MBN). In addition to chemical imaging and local optical field nanovisualization with high spatial resolution, we observe the signatures of 4-mercaptobenzoic acid, which forms as a result of plasmon-induced hydrolysis of MBN. Evidently, the solvent leads to distinct plasmon-induced/enhanced chemical reaction pathways that have not been documented. This work shows that such reactions that take place at solid-liquid interfaces can be tracked with a record sub-3-nm spatial resolution via TER spectral nanoimaging in liquids.
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Affiliation(s)
- Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
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10
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Wang CF, Mantilla ABC, Gu Y, El-Khoury PZ. Ambient Tip-Enhanced Two Photon Photoluminescence from CdSe/ZnS Quantum Dots. J Phys Chem A 2023; 127:1081-1084. [PMID: 36689268 DOI: 10.1021/acs.jpca.2c07750] [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: 01/24/2023]
Abstract
Nonlinear nano-optical measurements that combine ultrafast spectroscopy with tools of scanning probe microscopy are scarce. This is particularly the case when high spatial resolution on the order of a few nanometers is sought after in experiments performed under ambient laboratory conditions. In this work, we demonstrate the latter through measurements that track two-photon photoluminescence from aggregates of CdSe/ZnS quantum dots with sub-5 nm spatial resolution. Our proof-of-principle measurements that only take advantage of a plasmonic probe (as opposed to a gap mode) pave the way for nonlinear photoluminescence-based spectral nanoimaging of realistic/heterogeneous (bio) molecular and (bio) material systems.
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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
| | - 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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11
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Obloy LM, El-Khoury PZ, Tarnovsky AN. Excited-State-Selective Ultrafast Relaxation Dynamics and Photoisomerization of trans-4,4'-Azopyridine. J Phys Chem Lett 2022; 13:10863-10870. [PMID: 36384033 DOI: 10.1021/acs.jpclett.2c02523] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Excited-state dynamics of trans-4,4'-azopyridine in ethanol is studied using femtosecond transient absorption with 30 fs temporal resolution. Exciting the system at three different wavelengths, 460 and 290 (275) nm, to access the S1 nπ* and S2 ππ* electronic states, respectively, reveals a 195 cm-1 vibrational coherence, which suggests that the same mode is active in both nπ* and ππ* relaxation channels. Following S1-excitation, relaxation proceeds via a nonrotational pathway, where a fraction of the nπ* population is trapped in a planar minimum (lifetime, 2.1 ps), while the remaining population travels further to a second shallow minimum (lifetime, 300 fs) prior to decay into the ground state. Population of the S2 state leads to 30 fs nonrotational relaxation with a concurrent buildup of nπ* population and nearly simultaneous formation of hot ground-state species. An increase in the cis-isomer quantum yield upon ππ* versus nπ* excitation is observed, which is opposite to trans-azobenzene.
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Affiliation(s)
- Laura M Obloy
- Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, United States
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | - Alexander N Tarnovsky
- Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, United States
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12
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Mantilla ABC, Wang CF, Gu Y, Schultz ZD, El-Khoury PZ. Multipolar Raman Scattering vs Interfacial Nanochemistry: Case of 4-Mercaptopyridine on Gold. J Am Chem Soc 2022; 144:20561-20565. [PMID: 36343210 PMCID: PMC10193591 DOI: 10.1021/jacs.2c10132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Caution needs to be exercised in associating changes in plasmon-enhanced Raman spectra with chemical transformations. This is demonstrated through a detailed analysis of tip-enhanced Raman (TER) scattering from 4-mercaptopyridine (MPY) on gold. The substrate used consists of gold nanoplates atop a gold surface featuring heterogeneous grooves, all coated with a monolayer of MPY. The brightest spectra across the substrate exhibit features that can only be recovered by considering the generalized polarizability of oriented MPY molecules. The complex TER spectra we observe do not mark interfacial chemistry but rather multipolar TER scattering driven by local field gradients.
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Affiliation(s)
- Alexander B. C. Mantilla
- Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, USA
| | - Chih-Feng Wang
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA
| | - Yi Gu
- Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, USA
| | - Zachary D. Schultz
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA
| | - Patrick Z. El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA
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13
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Morales AC, Tomlin JM, West CP, Rivera-Adorno FA, Peterson BN, Sharpe SAL, Noh Y, Sendesi SMT, Boor BE, Howarter JA, Moffet RC, China S, O'Callahan BT, El-Khoury PZ, Whelton AJ, Laskin A. Atmospheric emission of nanoplastics from sewer pipe repairs. Nat Nanotechnol 2022; 17:1171-1177. [PMID: 36203091 DOI: 10.1038/s41565-022-01219-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Accepted: 08/22/2022] [Indexed: 06/16/2023]
Abstract
Nanoplastic particles are inadequately characterized environmental pollutants that have adverse effects on aquatic and atmospheric systems, causing detrimental effects to human health through inhalation, ingestion and skin penetration1-3. At present, it is explicitly assumed that environmental nanoplastics (EnvNPs) are weathering fragments of microplastic or larger plastic debris that have been discharged into terrestrial and aquatic environments, while atmospheric EnvNPs are attributed solely to aerosolization by wind and other mechanical forces. However, the sources and emissions of unintended EnvNPs are poorly understood and are therefore largely unaccounted for in various risk assessments4. Here we show that large quantities of EnvNPs may be directly emitted into the atmosphere as steam-laden waste components discharged from a technology commonly used to repair sewer pipes in urban areas. A comprehensive chemical analysis of the discharged waste condensate has revealed the abundant presence of insoluble colloids, which after drying form solid organic particles with a composition and viscosity consistent with EnvNPs. We suggest that airborne emissions of EnvNPs from these globally used sewer repair practices may be prevalent in highly populated urban areas5, and may have important implications for air quality and toxicological levels that need to be mitigated.
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Affiliation(s)
- Ana C Morales
- Department of Chemistry, Purdue University, West Lafayette, IN, USA
| | - Jay M Tomlin
- Department of Chemistry, Purdue University, West Lafayette, IN, USA
| | | | | | | | | | - Yoorae Noh
- Lyles School of Civil Engineering, Purdue University, West Lafayette, IN, USA
| | - Seyedeh M T Sendesi
- Lyles School of Civil Engineering, Purdue University, West Lafayette, IN, USA
| | - Brandon E Boor
- Lyles School of Civil Engineering, Purdue University, West Lafayette, IN, USA
| | - John A Howarter
- School of Materials Engineering, Purdue University, West Lafayette, IN, USA
| | | | - Swarup China
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Brian T O'Callahan
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Andrew J Whelton
- Lyles School of Civil Engineering, Purdue University, West Lafayette, IN, USA
- Department of Environmental and Ecological Engineering, Purdue University, West Lafayette, IN, USA
| | - Alexander Laskin
- Department of Chemistry, Purdue University, West Lafayette, IN, USA.
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14
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Wang CF, El-Khoury PZ. Resonant Coherent Raman Scattering from WSe 2. J Phys Chem A 2022; 126:5832-5836. [PMID: 35976736 DOI: 10.1021/acs.jpca.2c04120] [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: 11/29/2022]
Abstract
Low-dimensional transition-metal dichalcogenides (TMDs) continue to comprise a subject of intense research because of their unique optical and electronic properties that may be harnessed in modern devices. Intense photoluminescence (PL) from few-/monolayer TMDs rendered PL-based micro- and nanospectroscopic characterization ideal in the quest to understand the correlation between structure and function in these materials. Nonlinear optical methods are by comparison far less utilized for this purpose. In this work, we describe an approach based on electronically resonant four-wave-mixing that allows spatio-spectral characterization of excitons in monolayer WSe2. Due to the coherent nature of the response that we exploit to trace exciton resonances, and recent demonstrations of electronic four-wave-mixing-based nanoimaging and nanospectroscopy, our present work is an important step toward characterizing TMDs on the nano-femto scale using light.
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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
| | - 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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Abstract
This Perspective highlights recent advances in linear and nonlinear spectral nanoimaging. The described developments are motivated by the need to characterize molecular and material systems noninvasively with nanometer spatial and femtosecond temporal resolution. Indeed, the ability to image and chemically characterize heterogeneous interfaces with joint nano-femto resolution is a prerequisite to advancing our fundamental understanding of processes as diverse as heterogeneous catalysis, microbial communication, and energy flow in pristine/defect-containing low-dimensional quantum materials, to name a few. We describe pioneering work and recent demonstrations of (non)linear optical nanoimaging and nanospectroscopy, with an emphasis on high spatial resolution measurements conducted under ambient laboratory conditions.
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Affiliation(s)
- Chih-Feng Wang
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, 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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Prabhakaran V, Romo J, Bhattarai A, George K, Norberg ZM, Kalb D, Aprà E, Kottke PA, Fedorov AG, El-Khoury PZ, Johnson GE, Laskin J. Integrated photoelectrochemical energy storage cells prepared by benchtop ion soft landing. Chem Commun (Camb) 2022; 58:9060-9063. [PMID: 35899861 PMCID: PMC9367248 DOI: 10.1039/d2cc02595g] [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: 11/24/2022]
Abstract
The exceptional photochromic and redox properties of polyoxometalate anions, PW12O403−, have been exploited to develop an integrated photoelectrochemical energy storage cell for conversion and storage of solar energy. Elimination of strongly coordinating cations using benchtop ion soft landing leads to a ∼370% increase in the maximum power output of the device. Additionally, the photocathode displayed a pronounced color change from clear to blue upon irradiation, which warrants the potential application of the IPES cell in advanced smart windows and photochromic lenses. Soft landing eliminates counter cations from Keggin polyoxometalate-based photocathodes, resulting in a ∼370% increase in maximum power output from a novel device that simultaneously harvests and stores solar energy.![]()
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Affiliation(s)
| | - Joelle Romo
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
| | - Ashish Bhattarai
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
| | - Kyle George
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
| | - Zachary M Norberg
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
| | - David Kalb
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
| | - Edoardo Aprà
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352, USA
| | - Peter A Kottke
- School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - Andrei G Fedorov
- School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
| | - Grant E Johnson
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
| | - Julia Laskin
- Department of Chemistry, Purdue University, West Lafayette, IN, 47907, USA.
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17
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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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18
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Abstract
Tip-enhanced Raman spectroscopy (TERS) is a powerful technique that enables ultrahigh spatial resolution and ultrasensitive chemical imaging. This technique's ability to track plasmon-induced/enhanced chemical reactions in real space has gained increasing popularity in recent years. In this study, we expose inherent difficulties associated with assigning TERS signatures that accompany chemical transformations. Namely, distinct selection rules as well as the possibility of multiple physical processes/chemical reaction pathways complicate spectral assignments and necessitate caution in assigning the experimental observables. We illustrate the latter using 4,4'-dimercaptostilbene-functionalized plasmonic silver nanocubes, wherein we identify the TERS signatures of product formation, molecular charging, multipolar Raman scattering, and preferred molecular orientations that all lead to distinct and assignable spectral patterns.
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Affiliation(s)
- Brian T O'Callahan
- Earth and Biological 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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Abstract
Historically, molecular spectroscopists have focused their attention to the right-hand side of the Schrödinger equation. Our major goal had and still has to do with determining a (bio)molecular system's Hamiltonian operator. From a theoretical spectroscopist's perspective, this entails varying the parameters of a model Hamiltonian until the predicted observables agree with their experimental analogues. In this context, less emphasis has been put on the left-hand side of the equation, where the interplay between a system and its immediate local environment is described. The latter is particularly meaningful and informative in modern applications of optical microscopy and spectroscopy that take advantage of surface plasmons to enhance molecular scattering cross-sections and to increase the attainable spatial resolution that is classically limited by diffraction. Indeed, the manipulation of light near the apex of a metallic nanotip has enabled single molecule detection, identification, and imaging. The distinct advantages of the so-called tip-enhanced optical nanospectroscopy/nanoimaging approaches are self-evident: ultrahigh spatial resolution (nanometer or better) and ultimate sensitivity (down to yoctomolar) are both attainable, all while retaining the ability to chemically fingerprint one molecule at a time (e.g., through Raman scattering). An equally interesting aspect of the same approach stems from using the properties of a single molecule to characterize the local environment in which it resides. This concept of single molecule spectroscopy on the left-hand side of the Schrödinger equation is certainly not novel and has been discussed in pioneering single molecule studies that ultimately led to a Nobel prize in chemistry. That said, local environment mapping through ultrasensitive optical spectroscopy acquires a unique flavor when executed using tip-enhanced Raman scattering (TERS). This is the subject of this Account.In a series of recent reports, our group utilized TERS to characterize different properties of nanolocalized and enhanced optical fields. The platforms that were used to this end consist of chemically functionalized plasmonic nanostructures and nanoparticles imaged using visible-light-irradiated gold- or silver-coated probes of an atomic force microscope. Through a detailed analysis of the recorded spectral nanoimages, we found that molecular Raman spectra may be used to track the magnitudes, resonances, spatiotemporal gradients, and even vector components of optical fields with nanometer spatial resolution under ambient conditions. On the other side of the equation, understanding how spatially varying optical fields modulate molecular nano-Raman spectra is of utmost importance to emerging areas of nanophotonics. For instance, tracking plasmon-enhanced chemical transformations via TERS necessitates a deeper fundamental understanding of the optical signatures of molecular reorientation and multipolar Raman scattering, both of which may be driven by local optical field gradients that are operative in TERS. We illustrate these concepts and introduce the readers to the generally less appreciated and equally exciting world of TERS on the left-hand side of the Schrödinger equation.
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Affiliation(s)
- Patrick Z. El-Khoury
- Chemical Physics and Analysis Group, Physical Sciences Division, Pacific Northwest National Laboratory; Richland, Washington 99352, United States
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20
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Abstract
Optical field localization at plasmonic tip-sample nanojunctions has enabled high-spatial-resolution chemical analysis through tip-enhanced linear optical spectroscopies, including Raman scattering and photoluminescence. Here, we illustrate that nonlinear optical processes, including parametric four-wave mixing (4WM), second-harmonic/sum-frequency generation (SHG and SFG), and two-photon photoluminescence (TPPL), can be enhanced at plasmonic junctions and spatiospectrally resolved simultaneously with few-nm spatial resolution under ambient conditions. Through a detailed analysis of our spectral nanoimages, we find that the efficiencies of the local nonlinear signals are determined by sharp tip-sample junction resonances that vary over the few-nanometer length scale. Namely, plasmon resonances centered at or around the different nonlinear signals are tracked through TPPL, and they are found to selectively enhance nonlinear signals with closely matched optical resonances.
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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
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
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21
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Abstract
Exciton localization in transition-metal dichalcogenide monolayers is behind a variety of interesting phenomena and applications, including broad-spectrum solar cells and single-photon emissions. Strain fields at the periphery of topographically distinct features such as nanoscopic bubbles were recently associated with localized charge-neutral excitons. Here, we use tip-enhanced photoluminescence (PL) to visualize excitons in WSe2/MoSe2 heterobilayers (HBL). We find strong optical emission from charged excitons, particularly positively charged trions, in HBL supported by interlayer charge transfer. Our results reveal strong trion confinement, with a localization length scale comparable to the trion size, at the apex region inside individual nanoscopic bubbles. Nano-PL mapping also shows sub-10-nm spatial variations in the localized trion emission spectra, which stem from atomic-scale potential energy fluctuations. These findings demonstrate the possibility of confining charged exciton complexes that are electrically tunable, opening up further opportunities to probe many-body exciton physics and to explore additional possible sites for strong exciton localization that can lead to quantum emission.
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Affiliation(s)
- Matthew Gabel
- 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
| | - Yi Gu
- Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, United States
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22
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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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23
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Zhao X, Campbell S, El-Khoury PZ, Jia Y, Wallace GQ, Claing A, Bazuin CG, Masson JF. Surface-Enhanced Raman Scattering Optophysiology Nanofibers for the Detection of Heavy Metals in Single Breast Cancer Cells. ACS Sens 2021; 6:1649-1662. [PMID: 33847111 DOI: 10.1021/acssensors.1c00332] [Citation(s) in RCA: 16] [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] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Mercury(II) ions (Hg2+) and silver ions (Ag+) are two of the most hazardous pollutants causing serious damage to human health. Here, we constructed surface-enhanced Raman scattering (SERS)-active nanofibers covered with 4-mercaptopyridine (4-Mpy)-modified gold nanoparticles to detect Hg2+ and Ag+. Experimental evidence suggests that the observed spectral changes originate from the combined effect of (i) the coordination between the nitrogen on 4-Mpy and the metal ions and (ii) the 4-Mpy molecular orientation (from flatter to more perpendicular with respect to the metal surface). The relative intensity of a pair of characteristic Raman peaks (at ∼428 and ∼708 cm-1) was used to quantify the metal ion concentration, greatly increasing the reproducibility of the measurement compared to signal-on or signal-off detection based on a single SERS peak. The detection limit of this method for Hg2+ is lower than that for the Ag+ (5 vs 100 nM), which can be explained by the stronger interaction energy between Hg2+ and N compared to Ag+ and N, as demonstrated by density functional theory calculations. The Hg2+ and Ag+ ions can be masked by adding ethylenediaminetetraacetate and Cl-, respectively, to the Hg2+ and Ag+ samples. The good sensitivity, high reproducibility, and excellent selectivity of these nanosensors were also demonstrated. Furthermore, detection of Hg2+ in living breast cancer cells at the subcellular level is possible, thanks to the nanometric size of the herein described SERS nanosensors, allowing high spatial resolution and minimal cell damage.
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Affiliation(s)
- Xingjuan Zhao
- Département de chimie, Centre québécois des matériaux fonctionnels (CQMF) and ⊥Regroupement québécois des matériaux de pointe (RQMP), Université de Montréal, C.P. 6128 Succ. Centre-Ville, Montréal, Quebec H3C 3J7, Canada
| | - Shirley Campbell
- Département de pharmacologie et physiologie, Université de Montréal, C.P. 6128 Succ. Centre-Ville, Montreal, Quebec H3C 3J7, Canada
| | - Patrick Z. El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Yuechen Jia
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
| | - Gregory Q. Wallace
- Département de chimie, Centre québécois des matériaux fonctionnels (CQMF) and ⊥Regroupement québécois des matériaux de pointe (RQMP), Université de Montréal, C.P. 6128 Succ. Centre-Ville, Montréal, Quebec H3C 3J7, Canada
| | - Audrey Claing
- Département de pharmacologie et physiologie, Université de Montréal, C.P. 6128 Succ. Centre-Ville, Montreal, Quebec H3C 3J7, Canada
| | - C. Geraldine Bazuin
- Département de chimie, Centre québécois des matériaux fonctionnels (CQMF) and ⊥Regroupement québécois des matériaux de pointe (RQMP), Université de Montréal, C.P. 6128 Succ. Centre-Ville, Montréal, Quebec H3C 3J7, Canada
| | - Jean-Francois Masson
- Département de chimie, Centre québécois des matériaux fonctionnels (CQMF) and ⊥Regroupement québécois des matériaux de pointe (RQMP), Université de Montréal, C.P. 6128 Succ. Centre-Ville, Montréal, Quebec H3C 3J7, Canada
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24
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Gabel M, O'Callahan BT, Groome C, Wang CF, Ragan R, Gu Y, El-Khoury PZ. Mapping Molecular Adsorption Configurations with <5 nm Spatial Resolution through Ambient Tip-Enhanced Raman Imaging. J Phys Chem Lett 2021; 12:3586-3590. [PMID: 33819047 DOI: 10.1021/acs.jpclett.1c00661] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We interrogate para-mercaptobenzoic acid (MBA) molecules chemisorbed onto plasmonic silver nanocubes through tip-enhanced Raman (TER) spectral nanoimaging. Through a detailed examination of the spectra, aided by correlation analysis and density functional theory calculations, we find that MBA chemisorbs onto the plasmonic particles with at least two distinct configurations: S- and CO2-bound. High spatial resolution TER mapping allows us to distinguish between the distinct adsorption geometries with a pixel-limited (<5 nm) spatial resolution under ambient laboratory conditions.
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Affiliation(s)
- Matthew Gabel
- Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, United States
| | - Brian T O'Callahan
- Earth and Biological Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Chloe Groome
- Department of Materials Science and Engineering, University of California, Irvine, Irvine, California 92697-2575, United States
| | - Chih-Feng Wang
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Regina Ragan
- Department of Materials Science and Engineering, University of California, Irvine, Irvine, California 92697-2575, 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, P.O. Box 999, Richland, Washington 99352, United States
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25
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Abstract
Four-wave mixing at plasmonic tip-sample nanojunctions may be used to visualize plasmonic fields with sub-2 nm spatial resolution under ambient laboratory conditions. We illustrate the latter using a gold-coated atomic force microscopy probe irradiated with a pair of near-infrared femtosecond laser pulses and used to image plasmonic gold nanoplates and silver nanocubes. Through diagnostic polarization-dependent tip-only measurements, we illustrate that the four-wave mixing signal is localized to the tip apex. The apex-bound signal is further enhanced when the tip is located at specific locations near plasmonic nanoparticles. Overall, this work paves the way for visualizing chemical transformations as well as coherent electronic and vibrational dynamics with joint femtosecond temporal and few-nanometer spatial resolution under ambient conditions.
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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
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
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26
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Li Z, El-Khoury PZ, Kurouski D. Tip-enhanced Raman imaging of photocatalytic reactions on thermally-reshaped gold and gold–palladium microplates. Chem Commun (Camb) 2021; 57:891-894. [DOI: 10.1039/d0cc07060b] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The plasmonic/photocatalytic properties of thermally-reshaped walled gold–palladium microplates (WAu@PdMPs) have been explored by TERS.
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Affiliation(s)
- Zhandong Li
- Department of Biochemistry and Biophysics
- Texas A&M University
- College Station
- USA
| | | | - Dmitry Kurouski
- Department of Biochemistry and Biophysics
- Texas A&M University
- College Station
- USA
- The Institute for Quantum Science and Engineering
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27
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El-Khoury PZ, Schultz ZD. From SERS to TERS and Beyond: Molecules as Probes of Nanoscopic Optical Fields. J Phys Chem C Nanomater Interfaces 2020; 124:27267-27275. [PMID: 34306295 PMCID: PMC8297906 DOI: 10.1021/acs.jpcc.0c08337] [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] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
A detailed understanding of the interaction between molecules and plasmonic nanostructures is important for several exciting developments in (bio)molecular sensing and imaging, catalysis, as well as energy conversion. While much of the focus has been on the nanostructures that generate enhanced and nano-confined optical fields, we herein highlight recent work from our groups that uses the molecular response in surface and tip enhanced Raman scattering (SERS and TERS, respectively) to investigate different aspects of the local fields. TERS provides access to ultra-confined volumes, and as a result can further explore and explain ensemble-averaged SERS measurements. Exciting and distinct molecular behaviors are observed in the quantum limit of plasmons, including molecular charging, chemical conversion, and optical rectification. Evidence of multipolar Raman scattering from molecules additionally provides insights into the inhomogeneous electric fields that drive SERS and TERS and their spatial and temporal gradients. The time scales of these processes show evidence of cooperative nanoscale phenomena that altogether contribute to SERS and TERS.
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Affiliation(s)
- Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA
| | - Zachary D Schultz
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
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28
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Aprà E, Bhattarai A, Baxter E, Wang S, Johnson GE, Govind N, El-Khoury PZ. Simplified Ab Initio Molecular Dynamics-Based Raman Spectral Simulations. Appl Spectrosc 2020; 74:1350-1357. [PMID: 32285679 DOI: 10.1177/0003702820923392] [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] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We describe a simplified approach to simulating Raman spectra from ab initio molecular dynamics (AIMD) calculations. The protocol relies on on-the-fly calculations of approximate molecular polarizabilities using the well-known sum over orbitals (as opposed to states) method. This approach bypasses the more accurate but computationally expensive approach to calculating molecular polarizabilities along AIMD trajectories, i.e., solving the coupled perturbed Hartree-Fock/Kohn-Sham equations. We demonstrate the advantages and limitations of our method through a few case studies targeting molecular systems of interest to surface- and/or tip-enhanced Raman spectroscopy practitioners.
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Affiliation(s)
- Edoardo Aprà
- Environmental and Molecular Sciences Laboratory, 6865Pacific Northwest National Laboratory, Richland, USA
| | - Ashish Bhattarai
- Physical Sciences Division, 6865Pacific Northwest National Laboratory, Richland, USA
| | - Eric Baxter
- Physical Sciences Division, 6865Pacific Northwest National Laboratory, Richland, USA
| | - ShanYi Wang
- Physical Sciences Division, 6865Pacific Northwest National Laboratory, Richland, USA
| | - Grant E Johnson
- Physical Sciences Division, 6865Pacific Northwest National Laboratory, Richland, USA
| | - Niranjan Govind
- Environmental and Molecular Sciences Laboratory, 6865Pacific Northwest National Laboratory, Richland, USA
| | - Patrick Z El-Khoury
- Physical Sciences Division, 6865Pacific Northwest National Laboratory, Richland, USA
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29
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Edgecomb J, Xie X, Shao Y, El-Khoury PZ, Johnson GE, Prabhakaran V. Mapping Localized Peroxyl Radical Generation on a PEM Fuel Cell Catalyst Using Integrated Scanning Electrochemical Cell Microspectroscopy. Front Chem 2020; 8:572563. [PMID: 33195059 PMCID: PMC7609508 DOI: 10.3389/fchem.2020.572563] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2020] [Accepted: 09/11/2020] [Indexed: 11/13/2022] Open
Abstract
Understanding molecular-level transformations resulting from electrochemical reactions is important in designing efficient and reliable energy technologies. In this work, a novel integrated scanning electrochemical cell microspectroscopy (iSECCMS) capability is developed by combining a high spatial resolution electrochemical scanning probe with in situ fluorescence spectroscopy. Using 6-carboxyfluorescein as a fluorescent probe, the iSECCMS platform is employed to measure the effect of the detrimental generation of reactive oxygen species (ROS) formed at the active sites of oxygen reduction reaction (ORR) catalysts. Carbon-supported tantalum-doped titanium oxide (TaTiOx) catalysts, a potential Pt-group-metal-free (PGM-free) cathode material explored for low temperature polymer electrolyte fuel cells (PEFCs), is used as a representative model ORR system, where generation of intermediate H2O2 instead of fully oxidized H2O is a major concern. We establish that the iSECCMS platform provides a novel and versatile capability for spatially resolved mapping of in situ ROS generation and activity during the kinetically-limited ORR and may, therefore, aid the future characterization and development of high-performance PGM-free PEFC cathodes.
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Affiliation(s)
| | | | | | | | - Grant E. Johnson
- Pacific Northwest National Laboratory, Richland, WA, United States
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30
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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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31
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O'Callahan BT, Park KD, Novikova IV, Jian T, Chen CL, Muller EA, El-Khoury PZ, Raschke MB, Lea AS. In Liquid Infrared Scattering Scanning Near-Field Optical Microscopy for Chemical and Biological Nanoimaging. Nano Lett 2020; 20:4497-4504. [PMID: 32356991 DOI: 10.1021/acs.nanolett.0c01291] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [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: 05/27/2023]
Abstract
Imaging biological systems with simultaneous intrinsic chemical specificity and nanometer spatial resolution in their typical native liquid environment has remained a long-standing challenge. Here, we demonstrate a general approach of chemical nanoimaging in liquid based on infrared scattering scanning near-field optical microscopy (IR s-SNOM). It is enabled by combining AFM operation in a fluid cell with evanescent IR illumination via total internal reflection, which provides spatially confined excitation for minimized IR water absorption, reduced far-field background, and enhanced directional signal emission and sensitivity. We demonstrate in-liquid IR s-SNOM vibrational nanoimaging and conformational identification of catalase nanocrystals and spatio-spectral analysis of biomimetic peptoid sheets with monolayer sensitivity and chemical specificity at the few zeptomole level. This work establishes the principles of in-liquid and in situ IR s-SNOM spectroscopic chemical nanoimaging and its general applicability to biomolecular, cellular, catalytic, electrochemical, or other interfaces and nanosystems in liquids or solutions.
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Affiliation(s)
| | - Kyoung-Duck Park
- Department of Physics, School of Natural Science, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea
| | | | | | | | - Eric A Muller
- Department of Physics, Department of Chemistry, and JILA, University of Colorado at Boulder, Boulder, Colorado 80309, United States
| | | | - Markus B Raschke
- Department of Physics, Department of Chemistry, and JILA, University of Colorado at Boulder, Boulder, Colorado 80309, United States
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32
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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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33
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Sloan-Dennison S, Zoltowski CM, El-Khoury PZ, Schultz ZD. Surface Enhanced Raman Scattering Selectivity in Proteins Arises from Electron Capture and Resonant Enhancement of Radical Species. J Phys Chem C Nanomater Interfaces 2020; 124:9548-9558. [PMID: 32542105 PMCID: PMC7295139 DOI: 10.1021/acs.jpcc.0c01436] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Plasmon-enhanced Raman scattering is a powerful approach to detecting and characterizing proteins in live and dynamic biological systems. However, the selective detection/enhancement of specific residues as well as spectral diffusion and fluctuations have complicated the interpretation of enhanced Raman spectra and images of biological matter. In this work, we demonstrate that the amino acid tryptophan (Trp) can capture an electron from an excited plasmon, which generates a radical anion that is resonantly enhanced: a visible excited electronic state slides into resonance upon charging. This surface enhanced resonance Raman scattering (SERRS) mechanism explains the persistence of Trp signatures in the SERS and TERS spectra of proteins. Evidence for this picture includes the observation of visible resonances in the UV-Vis extinction spectrum, changes in the ground state vibrational spectrum, and plasmon-resonance dependent behavior. DFT calculations support the experimental observations. The behavior observed from the free Trp molecule is shown to explain the SERS spectrum of the Trp-cage protein. In effect, resonant Raman scattering from radicals formed through plasmonic excitation represents an under-investigated mechanism that may be exploited for chemical sensing applications.
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Affiliation(s)
- Sian Sloan-Dennison
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210
| | - Chelsea M. Zoltowski
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210
| | - Patrick Z. El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA
| | - Zachary D. Schultz
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210
- corresponding author
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Bhattarai A, O'Callahan BT, Wang CF, Wang S, El-Khoury PZ. Spatio-Spectral Characterization of Multipolar Plasmonic Modes of Au Nanorods via Tip-Enhanced Raman Scattering. J Phys Chem Lett 2020; 11:2870-2874. [PMID: 32208725 DOI: 10.1021/acs.jpclett.0c00485] [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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Tip-enhanced Raman (TER) spectral images of 4-thiobenzonitrile-coated Au nanorods map the spatial profiles and trace the resonances of dipolar and multipolar plasmonic modes that are characteristic of the imaged particles. For any particular rod, we observe sequential transitions between high-order modes at low frequency shifts and lower-order modes at higher frequencies. We also notice that higher-order modes (up to m = 4) are generally observed for long rods as compared to their shorter analogues, where longitudinal dipolar resonances (m = 1) are observable. In effect, this work adds a new dimension to local optical field mapping via TERS, which we have previously explored. Not only can the magnitudes, vector components, local/nonlocal characters of local optical fields be imaged through molecular TERS, but spatially varying local optical resonances are also direct observables.
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Affiliation(s)
- Ashish Bhattarai
- 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
| | - Chih-Feng Wang
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - ShanYi Wang
- 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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35
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Abstract
We record nanoscale chemical images of thiobenzonitrile (TBN)-functionalized plasmonic gold nanocubes via tip-enhanced Raman spectroscopy (TERS). The spatially averaged optical response is dominated by conventional (dipolar) TERS scattering from TBN but also contains weaker spectral signatures in the 1225-1500 cm-1 region. The weak optical signatures dominate several of the recorded single-pixel TERS spectra. We can uniquely assign these Raman-forbidden transitions to multipolar Raman scattering, which implicates spatially varying enhanced electric field gradients at plasmonic tip-sample nanojunctions. Specifically, we can assign observations of tip-enhanced electric dipole-magnetic dipole as well as electric dipole-electric quadrupole driven transitions. Multipolar Raman scattering and local optical field gradients both need to be understood and accounted for in the interpretation of TERS spectral images, particularly in ongoing quests aimed at chemical reaction mapping via TERS.
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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
| | - Zhihua Cheng
- Department of Chemistry, Department of Materials Science & Nanoengineering, Rice University, 6100 Main Street, Houston, Texas 77005, United States
| | - Brian T O'Callahan
- Environmental and Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Kevin T Crampton
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Matthew R Jones
- Department of Chemistry, Department of Materials Science & Nanoengineering, Rice University, 6100 Main Street, Houston, Texas 77005, 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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36
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Bhattarai A, Cheng Z, Joly AG, Novikova IV, Evans JE, Schultz ZD, Jones MR, El-Khoury PZ. Tip-Enhanced Raman Nanospectroscopy of Smooth Spherical Gold Nanoparticles. J Phys Chem Lett 2020; 11:1795-1801. [PMID: 32069408 DOI: 10.1021/acs.jpclett.0c00217] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We record nanoscale-resolved chemical images of thiobenzonitrile (TBN)-functionalized smooth gold nanospheres on silicon via tip-enhanced Raman (TER) nanospectroscopy. The recorded images trace the nascence of the familiar doughnut-shaped scattering profile of nanoparticles on silicon at its origin (the particle surface), which appears as a horseshoe-shaped scattering pattern under our experimental conditions. The local optical field maps are in agreement with their simulated finite-difference time-domain analogues. Analysis of the recorded spectra with the aid of ab-initio-molecular-dynamics-based Raman spectral simulations further suggests that optical rectification and molecular charging take place throughout the course of atomic-force-microscopy-based TER nanoscale chemical imaging.
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Affiliation(s)
- Ashish Bhattarai
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Zhihua Cheng
- Department of Chemistry, Department of Materials Science & Nanoengineering, Rice University, 6100 Main Street, Houston, Texas 77005, United States
| | - Alan G Joly
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Irina V Novikova
- Environmental and Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - James E Evans
- Environmental and Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Zachary D Schultz
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Matthew R Jones
- Department of Chemistry, Department of Materials Science & Nanoengineering, Rice University, 6100 Main Street, Houston, Texas 77005, 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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37
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Abstract
A series of optical and electron microscopies are utilized in concert to unravel the properties of corrugated metallic tips. While the overall microscopic shapes of the tips dictate their optical resonances and plasmonic field enhancement factors, nanometric structural details govern their tip-enhanced Raman (TER) spectra and images. Using 4-thiobenzonitrile (TBN) as a molecular reporter, spatially resolved TER spectra reveal that optical rectification and molecular charging are among the prominent observables in the tip-tip TER geometry. We show the spurious appearance of anions is driven by highly localized resonances that appear as a result of surface corrugation and their manifestation throughout the course of TER nanospectroscopy complicates spectral assignments. Overall, nanoscale spatial variations in the TERS spectra suggest that the tip-tip geometry sustains junction plasmons that appear very different from what may be expected from the hybridization of the bulk tip resonances.
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Affiliation(s)
- Ashish Bhattarai
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Kevin T Crampton
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Alan G Joly
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Chih-Feng Wang
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Zachary D Schultz
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, 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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38
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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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Abstract
We deploy two-dimensional nanohole arrays as resonant surface plasmon polariton (SPP) couplers that enable counter-propagation and excitation field interference-free imaging of SPP wave packets. We monitor the spatiotemporal evolution of the resulting SPPs using two-color photoemission electron microscopy. The measurements track the electric field envelope of the SPP in real space and time and enable direct characterization of their spatiotemporal properties in a regime where the SPP wave packet is the principal observable. We provide an analysis of the observables for both the co- and counter-propagating directions via SPP trajectories that are recorded in tandem. Our results highlight the advantages of isolating SPPs through counter-propagation, where excitation field-SPP interactions are suppressed.
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Affiliation(s)
- Kevin T Crampton
- Physical Sciences Division , Pacific Northwest National Laboratory , P.O. Box 999, Richland , Washington 99352 , United States
| | - Alan G Joly
- 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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40
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Aprà E, Bhattarai A, El-Khoury PZ. Gauging Molecular Orientation through Time Domain Simulations of Surface-Enhanced Raman Scattering. J Phys Chem A 2019; 123:7142-7147. [DOI: 10.1021/acs.jpca.9b06182] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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41
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Abstract
Not all regions of optical field nanolocalization and enhancement are suitable sites for chemical transformations on plasmonic metals. We illustrate the concept using chemically functionalized monocrystalline gold platelets in aqueous solution imaged using a Au-coated tip-enhanced Raman scattering (TERS) probe. For our proof-of-principle study, we select a model plasmon-driven chemical process, namely, the dimerization of p-nitrothiophenol (NTP) to dimercaptoazobenzene. Consistent with recent observations from our group, we find that TERS maps at vibrational resonances corresponding to NTP trace the optical fields that are maximally enhanced toward the edges of the platelets. Conversely, simultaneously recorded product maps reveal that the dimerization process occurs only at specific sites on our substrate. Given the uniformity of the structures and local optical fields at the edges of the gold platelets, our results suggest that molecular crowding and steric effects play a key role in our case of plasmon-driven NTP dimerization at the gold-water interface.
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Affiliation(s)
- Ashish Bhattarai
- 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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42
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Bhattarai A, Crampton KT, Joly AG, Kovarik L, Hess WP, El-Khoury PZ. Imaging the Optical Fields of Functionalized Silver Nanowires through Molecular TERS. J Phys Chem Lett 2018; 9:7105-7109. [PMID: 30517015 DOI: 10.1021/acs.jpclett.8b03324] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We image 4-mercaptobenzonitrile-functionalized silver nanowires (∼20 nm diameter) through tip-enhanced Raman scattering (TERS). The enhanced local optical field-molecular interactions that govern the recorded hyperspectral TERS images are dissected through hybrid finite-difference time-domain density functional theory simulations. Our forward simulations illustrate that the recorded spatiospectral profiles of the chemically functionalized nanowires may be reproduced by accounting for the interaction between orientationally averaged molecular polarizability derivative tensors and enhanced incident/scattered local fields polarized along the tip axis. In effect, we directly map the enhanced optical fields of the nanowire in real space through TERS. The simultaneously recorded atomic force microscopy (AFM) images allow a direct comparison between our attainable spatial resolution in topographic (13 nm) and TERS (5 nm) imaging measurements performed under ambient conditions. Overall, our described protocol enables local electric field imaging with few nm precision through molecular TERS, and it is therefore generally applicable to a variety of plasmonic nanostructures.
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43
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Abstract
Surface plasmon polaritons (SPPs) launched from a protruded silver spherical cap structure using s-polarized femtosecond laser excitation are investigated using photoemission electron microscopy. The resulting SPP is comparable in intensity to SPPs launched with p-polarized excitation but propagates with a distinct spatial profile. The spatial and temporal properties of the nascent SPP are determined by splitting the femtosecond pulse into a spatially separated pump-probe pair of orthogonal polarizations. The s-polarized pump pulse initiates the SPP, which is then visualized by the photoelectron emission induced by a spatially and temporally separated p-polarized probe pulse. The s-polarization launched SPP displays a bifurcated spatial structure with an antisymmetric mirror plane and may be regarded as two spatially distinct, temporally phase-locked wave packets. Significantly, the wave packets are one-half period out of phase with each other governed by the phase of the driving laser field. Finite difference time domain calculations corroborate the experimental results. The resulting SPP can be utilized for either polarization multiplexing or as a pulse splitter in nanophotonic circuits.
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Affiliation(s)
- Alan G Joly
- Physical Sciences Division , Pacific Northwest National Laboratory , P.O. Box 999, Richland , Washington 99352 , United States
| | - Yu Gong
- 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
| | - Wayne P Hess
- Physical Sciences Division , Pacific Northwest National Laboratory , P.O. Box 999, Richland , Washington 99352 , United States
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44
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Aprà E, Bhattarai A, Crampton KT, Bylaska EJ, Govind N, Hess WP, El-Khoury PZ. Time Domain Simulations of Single Molecule Raman Scattering. J Phys Chem A 2018; 122:7437-7442. [PMID: 30148635 DOI: 10.1021/acs.jpca.8b05912] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Nonequilibrium chemical phenomena are known to play an important role in single molecule microscopy and spectroscopy. Herein, we explore these effects through ab initio molecular dynamics (AIMD)-based Raman spectral simulations. We target an isolated aromatic thiol (thiobenzonitrile, TBN) as a prototypical molecular system. We first show that the essential features contained in the ensemble-averaged Raman spectrum of TBN can be reproduced by averaging over 18 short AIMD trajectories spanning a total simulation time of ∼60 ps. This involved more than 90 000 polarizability calculations at the B3LYP/def2-TZVP level of theory. We then illustrate that the short trajectories (∼3.3 ps total simulation time), where the accessible phase space is not fully sampled, provide a starting point for understanding key features that are often observed in measurements targeting single molecules. Our results suggest that a complete understanding of single molecule Raman scattering needs to account for molecular conformational flexibility and nonequilibrium chemical phenomena in addition to local optical fields and modified selection rules. The former effects are well-captured using the described AIMD-based single molecule Raman spectral simulations.
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45
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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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46
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Mishra K, Zheng J, Patel R, Estevez L, Jia H, Luo L, El-Khoury PZ, Li X, Zhou XD, Zhang JG. High performance porous Si@C anodes synthesized by low temperature aluminothermic reaction. Electrochim Acta 2018. [DOI: 10.1016/j.electacta.2018.02.166] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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47
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Abellan P, El-Khoury PZ, Ramasse QM. Mapping VIS-terahertz (≤17 THz) surface plasmons sustained on native and chemically functionalized percolated gold thin films using EELS. Microscopy (Oxf) 2018; 67:i30-i39. [PMID: 29136197 DOI: 10.1093/jmicro/dfx092] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Accepted: 10/08/2017] [Indexed: 01/25/2023] Open
Abstract
Heterogeneous assemblies of molecules (Rhodamine B) adsorbed onto a nano-corrugated metallic surface (a percolated Au network) are investigated using electron energy loss spectroscopy in the scanning transmission electron microscope (STEM-EELS). Our first measurements target the native metallic substrate, which consists of a commercial Au thin film atop an ultrathin carbon membrane. The Au film displays a percolated morphology with nanostructures of estimated thickness ≤10 nm approximately. We observe a rich plasmonic response from the metallic substrate; one which varies nanometrically and spans the VIS-terahertz region. Multiple localized plasmons are detected at individual nanometric integrated areas, while an analysis of their spatial distribution reveals that for each integrated energy range (50 meV integration window) resonances are simultaneously supported at different locations within the film. We record subsequent EEL spectrum images of the hybrid molecular-metallic construct after deposition of Rhodamine B molecules onto the substrate, where plasmons, molecular vibrations and electronic excitations might all be simultaneously detected. A comparison of average signals for both systems is performed and spectral variations within the three spectral regions where molecular signatures may be observed are discussed. Our measurements and their analysis, if applied to the same location before and after molecular deposition, may be used to rationalize optical microscopic and spectroscopic measurements that take advantage of the interplay between molecules and plasmons.
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Affiliation(s)
- Patricia Abellan
- SuperSTEM Laboratory, SciTech Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, UK
| | - Patrick Z El-Khoury
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA
| | - Quentin M Ramasse
- SuperSTEM Laboratory, SciTech Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, UK
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Borin VA, Matveev SM, Budkina DS, El-Khoury PZ, Tarnovsky AN. Direct photoisomerization of CH 2I 2vs. CHBr 3 in the gas phase: a joint 50 fs experimental and multireference resonance-theoretical study. Phys Chem Chem Phys 2018; 18:28883-28892. [PMID: 27722308 DOI: 10.1039/c6cp05129d] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Femtosecond transient absorption measurements powered by 40 fs laser pulses reveal that ultrafast isomerization takes place upon S1 excitation of both CH2I2 and CHBr3 in the gas phase. The photochemical conversion process is direct and intramolecular, i.e., it proceeds without caging media that have long been implicated in the photo-induced isomerization of polyhalogenated alkanes in condensed phases. Using multistate complete active space second order perturbation theory (MS-CASPT2) calculations, we investigate the structure of the photochemical reaction paths connecting the photoexcited species to their corresponding isomeric forms. Unconstrained minimum energy paths computed starting from the S1 Franck-Condon points lead to S1/S0 conical intersections, which directly connect the parent CHBr3 and CH2I2 molecules to their isomeric forms. Changes in the chemical bonding picture along the S1/S0 isomerization reaction path are described using multireference average coupled pair functional (MRACPF) calculations in conjunction with natural resonance theory (NRT) analysis. These calculations reveal a complex interplay between covalent, radical, ylidic, and ion-pair dominant resonance structures throughout the nonadiabatic photochemical isomerization processes described in this work.
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Affiliation(s)
- Veniamin A Borin
- Center for Photochemical Sciences, Department of Chemistry, Bowling Green State University, Bowling Green, Ohio, USA.
| | - Sergey M Matveev
- Center for Photochemical Sciences, Department of Chemistry, Bowling Green State University, Bowling Green, Ohio, USA.
| | - Darya S Budkina
- Center for Photochemical Sciences, Department of Chemistry, Bowling Green State University, Bowling Green, Ohio, USA.
| | - Patrick Z El-Khoury
- Physical Sciences Division, Pacific Northwest National Laboratory, P. O. Box 999, Richland, WA 99352, USA
| | - Alexander N Tarnovsky
- Center for Photochemical Sciences, Department of Chemistry, Bowling Green State University, Bowling Green, Ohio, USA.
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Abstract
Tip-enhanced Raman scattering (TERS) can be used to image plasmon-enhanced local electric fields on the nanoscale. This is illustrated through ambient TERS measurements recorded using silver atomic force microscope tips coated with 4-mercaptobenzonitrile molecules and used to image step edges on an Au(111) surface. The observed two-dimensional TERS images uniquely map electric fields localized at Au(111) step edges following 671 nm excitation. We establish that our measurements are not only sensitive to spatial variations in the enhanced electric fields but also to their vector components. We also experimentally demonstrate that (i) few nanometer precision is attainable in TERS nanoscopy using corrugated tips with nominal radii on the order of 100-200 nm, and (ii) TERS signals do not necessarily exhibit the expected E4 dependence. Overall, we illustrate the concept of electric field imaging via TERS and establish the connections between our observations and conventional TERS chemical imaging measurements.
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Affiliation(s)
- Ashish Bhattarai
- Physical Sciences Division, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99352, United States
| | - Alan G Joly
- 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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50
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Novikova IV, Smallwood CR, Gong Y, Hu D, Hendricks L, Evans JE, Bhattarai A, Hess WP, El-Khoury PZ. Multimodal hyperspectral optical microscopy. Chem Phys 2017. [DOI: 10.1016/j.chemphys.2017.08.011] [Citation(s) in RCA: 3] [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: 12/16/2022]
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