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Proceedings Paper

Angstrom-scale plasmonic hot-spots: a spectroscopic existential proof and unusual photo-chemical activities (Conference Presentation)
Author(s): Zee Hwan Kim
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Paper Abstract

The existence of sub-nm plasmonic hot-spots and its relevance in spectroscopy, microscopy, and photo-chemical applications remain elusive despite a few recent theoretical and experimental evidence. I will present new spectroscopic evidence that angstrom-sized hot-spots do exist on the surfaces of plasmon-excited nanostructures, and that these hot-spots enhance metal - molecule charge-transfer rates. Surface-enhanced Raman scattering (SERS) spectra of 4, 4’-biphenyl dithiols placed in metallic junctions reveal simultaneously blinking Stokes and anti-Stokes spectra, some of which exhibit only one prominent vibrational peak. The activated vibrational modes are found to vary widely between junction-sites. Such site-specific, single-peak spectra could be successfully modeled using single-molecule SERS induced by a hot-spot with a diameter no larger than 3.5 Å, located at specific molecular sites. The model, which assumes the stochastic creation of hot-spots on locally flat metallic surfaces, consistently reproduces the intensity distributions and occurrence statistics of the blinking SERS peaks. We also observe time-resolved Stokes and anti-Stokes SERS spectra of nitrobenzenethiols placed at plasmonic junctions strongly suggesting that such atomic-scale hotspots accelerate the hot-electron transfer between the metallic surface and the molecules, and thus promotes photo-reduction processes on metallic surfaces. This unusual photo-chemical activity of the hot-spots may provide new insight into “chemical” enhancement mechanism in SERS.

Paper Details

Date Published: 17 September 2018
Proc. SPIE 10726, Nanoimaging and Nanospectroscopy VI, 107260G (17 September 2018); doi: 10.1117/12.2323226
Show Author Affiliations
Zee Hwan Kim, Seoul National Univ. (Korea, Republic of)

Published in SPIE Proceedings Vol. 10726:
Nanoimaging and Nanospectroscopy VI
Prabhat Verma; Alexander Egner, Editor(s)

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