
NSF Org: |
CHE Division Of Chemistry |
Recipient: |
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Initial Amendment Date: | July 11, 2017 |
Latest Amendment Date: | July 19, 2017 |
Award Number: | 1708581 |
Award Instrument: | Continuing Grant |
Program Manager: |
Christopher Elles
CHE Division Of Chemistry MPS Directorate for Mathematical and Physical Sciences |
Start Date: | July 15, 2017 |
End Date: | August 31, 2021 (Estimated) |
Total Intended Award Amount: | $265,192.00 |
Total Awarded Amount to Date: | $265,192.00 |
Funds Obligated to Date: |
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History of Investigator: |
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Recipient Sponsored Research Office: |
3720 S FLOWER ST FL 3 LOS ANGELES CA US 90033 (213)740-7762 |
Sponsor Congressional District: |
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Primary Place of Performance: |
3720 S Flower St Los Angeles CA US 90089-0001 |
Primary Place of
Performance Congressional District: |
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Unique Entity Identifier (UEI): |
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Parent UEI: |
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NSF Program(s): | Chemical Measurement & Imaging |
Primary Program Source: |
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Program Reference Code(s): |
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Program Element Code(s): |
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Award Agency Code: | 4900 |
Fund Agency Code: | 4900 |
Assistance Listing Number(s): | 47.049 |
ABSTRACT
With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Cronin at University of Southern California and Professor Jensen at Pennsylvania State University investigate the use of Raman spectroscopy as a powerful tool that measures the energies of specific bond stretches. This technique provide the unique fingerprint for chemical identification. As such, Raman spectroscopy is extremely useful for a number of applications in chemical, environmental and threat detection monitoring. While a highly useful technique, the Raman scattering cross-section of most molecules is extremely small, and this generally limits its potential uses. Surface Enhanced Raman Scattering (SERS) and Graphene Enhanced Raman Scattering (GERS), the techniques investigated in this research project, can be used to improve the small signal intensities, thus making Raman spectroscopy-related applications more practical. In terms of broader impacts Dr. Cronin creates workshops for Los Angeles high school chemistry teachers. He leverages existing relationships between USC and its neighboring high schools (e.g., USC's Good Neighbors Campaign, Joint Education Project, and the Service Learning Program) to increase the attendance from disadvantaged schools (i.e., central Los Angeles inner city schools) serving underrepresented minority groups. The content of the workshop is reformulated to expose underrepresented students to the results and, more importantly, the excitement of research. Research projects for undergraduate students introduce them to fundamental scientific research and give them confidence to pursue careers in science and engineering. A new module devoted to SERS is developed for a new course at USC on nanoscience and nanotechnology, and their research accomplishments are discussed in class and integrated into the curriculum. Professor Jansen uses a website, nanoHub.org, to share their computational tools with scientists outside of his labs.
In this collaboration, Professors Cronin and Jensen investigate the mechanism behind the strong spectroscopic responses observed in two surface-based spectroscopic techniques: Surface Enhanced Raman Scattering (SERS) and Graphene Enhanced Raman Scattering (GERS). They use both experimental and computational tools to carefully isolate the enhanced Raman signals caused by Chemical Enhancement (CE) from those signals caused by ElectroMagnetic Enhancement (EM) in order to understand the CE mechanism. Specifically, Professor Cronin's group at USC performs Raman spectroscopy of single molecules on various SERS substrates, which enables a direct comparison with the theoretical calculations preformed at the Jensen's group at PSU. The Raman spectra are collected under various electrochemical conditions in order to explore the role of the molecule-metal energy level alignment and decouple the vibrational-mode-specific chemical enhancement from the uniform chemical enhancement. Professor Jensen's first principles calculations provide a detailed theoretical framework for interpreting chemical enhancement in SERS and GERS spectra to facilitate a better understanding of the chemical enhancement mechanism. Students in both groups experience the interdisciplinary training opportunities. Both groups' are actively engaged in outreach activities to local high school teachers and general public.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
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This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
This project was designed to gain a deeper understanding into the physical mechanisms underlying Surface Enhanced Raman Scattering (SERS) and Graphene Enhanced Raman Scattering (GERS) phenomena. Prior to this study, the quantitative theoretical treatment of the SERS enhancement mechanism has focused largely on classical electrodynamics, with limited insight into the chemical interactions between molecular adsorbates and metallic substrates. In addition to the enhancement provided by classical electromagnetics, there is an additional chemical component that can lead to both an overall uniform enhancement and, on top of that, a vibrational-mode-specific enhancement, which makes SERS and GERS spectra appear quite different from bulk solution Raman spectra.
The experimental portion of this work was carried out at USC and was directly compared with the theoretical calculations preformed at PSU. In addition to static SERS spectra, electrochemical tuning of SERS and GERS surfaces were obtained to vary the molecule-metal energy level alignment and local electric fields experienced by the surface-bound molecules. Prof. Jensen?s first principles calculations have provided a detailed theoretical framework for understanding the SERS and GERS spectra under working electrochemical conditions. In doing so, we were able to close the gap between theory and experiment.
Raman spectroscopy is a powerful tool that gives the precise vibrational energies of molecules, which provide the unique fingerprint for chemical identification. As such, Raman spectroscopy is extremely useful for a vast number of applications. However, the Raman scattering cross-section of most molecules is extremely small, which generally limits its potential uses. SERS can be used to improve the small Raman intensities, thus making Raman spectroscopy related applications more practical. SERS enhancements with single molecule detection sensitivity have been reported, but this magnitude of enhancement cannot be produced reliably. Typically, electromagnetic enhancement factors of 106-108 can be reproducibly achieved. However, there are currently no systematic ways of controlling the chemical enhancement part of SERS, and theory suggests only an approximate picture for why some modes can be enhanced by one to two orders of magnitude and others remain unchanged. The development of robust, reliable SERS substrates exhibiting 1010 enhancement would enable single molecule detection and identification at low laser powers (< 1 mW) with handheld spectrometers that can be used for a wide range of applications in chemical, environmental, and threat detection monitoring.
Last Modified: 12/30/2021
Modified by: Stephen Cronin
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