Tip-Enhanced and Co-Localized AFM-Raman Spectroscopy to Unveil Localized-Plasmon Promoted Direct-Charge Transfers across Nano-electrochemical Interfaces
Abstract
The proposed acquisition of Raman-AFM Hybrid instrument directly impacts the recently awarded Army Research Office grant to Prof. Sanjeev Mukerjee (PI) at Northeastern University Center for Renewable Energy Technology (NUCRET), entitled ÒHarvesting localized plasmons on noble metal nanostructures for efficient electrochemical and photochemical reactionsÓ (ARO Contract # W911NF1910164, which started on March 2019 with the end date of March 2022). Specifically, Raman-AFM Hybrid would enable fundamental studies of direct charge-transfers and reaction mechanism at a specified nanoscale electrochemical interface. In order to promote Localized Surface Plasmon Resonance (LSPR) on a noble-metal nanostructure with meaningful electrochemical reaction-rate, one must rely on an instantaneous Chemical Interface Damping (CID) mechanism. The CID mechanism promote plasmon excitations from noble metal nanostructure directly into LUMO of an adsorbed (substrate) molecule. This direct-carrier injection or plasmon energy transfer into adsorbate are possible when metal-adsorbate electronic states are strongly coupled. Consequently, an instantaneous transient negative ion (TIN) state of the adsorbate is imminent at the electrochemical interface. In this context, ultrafast pump probe spectroscopy is not adequate to resolve this transient event. In this regard, Plasmon Enhanced Raman Scattering is quite helpful to explicitly probe changes in vibrational levels of adsorbate reactant or intermediate molecules that evolved from CID charge transfers. More importantly, when Raman spectroscopy is coupled with a scanning probe microscopy (SPM), localized vibrational spectrum with spatial resolution beyond optical diffraction limit is possible. The following three primary modes of operation is anticipated with the proposed Raman-AFM Hybrid: (i). Tip-Enhanced Raman Spectroscopy (TERS), (ii). Co-localized Raman-AFM and, (iii). In-situ Electrochemical TERS. The TERS-mode enable unique understanding of interaction between noble-metal nanoparticles and 2D-supports at high spatial resolutions and singlemolecule sensitivity; while co-localized Raman-AFM mode provides simultaneous or sequential surface-maps of chemical and electronic properties of plasmonic nanocomposites: noble-metal nanoparticles decorated on 2D layers. Whereas, implementation of in-situ electrochemical TERS mode leads to precise understanding of LSPR promoted direct-charge transfers (through CID) across a specified nano-interface formed between noble-metal and electrolyte. In addition, Diffuse Reflectance UV-Vis spectrometer that to be acquired will serve as preliminary measurement of plasmonic absorption band in plasmonic nanocomposites that are in solid and powdered form. The proposed Raman-AFM Hybrid along with Diffuse Reflectance UV-Vis Spectrometer brings a synergy with existing multi-pronged spectroscopy facilities including ultra-fast laser spectroscopy, and in-situ electrochemical X-ray absorption spectroscopy (XAS). Moreover, acquisition of this instrument, in combination with the prevailing ex-situ characterization tools at PIÕs lab such as XRD, FTIR, XRD, TEM. SEM/EDX and TGA/DSC along with well-equipped electrochemical tools would greatly contribute to the fundamental and mechanistic understanding of plasmon promoted charge-transfers. When solar light coupled plasmon charge promotion are well-understood and optimized, a new era of electrochemistry is possible - with electrodeless and solvated electrons as a means for driving many game-changing electrochemical technologies that are crucial for development of military systems, in both symmetric and asymmetric warfare. Furthermore, the proposed acquisition would promote both educational training and laboratory investigations throughout its entire lifetime to a wider university community of undergraduates, graduates and post-doctoral research associates from varied backgrounds.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 09, 2020
- Source ID
- W911NF2010145
Entities
People
- Sanjeev Mukerjee
Organizations
- Army Contracting Command
- Northeastern University
- United States Army