Merck

Plasmonic tunnel junctions for single-molecule redox chemistry.

Nature communications (2017-10-24)
Bart de Nijs, Felix Benz, Steven J Barrow, Daniel O Sigle, Rohit Chikkaraddy, Aniello Palma, Cloudy Carnegie, Marlous Kamp, Ravishankar Sundararaman, Prineha Narang, Oren A Scherman, Jeremy J Baumberg
ABSTRACT

Nanoparticles attached just above a flat metallic surface can trap optical fields in the nanoscale gap. This enables local spectroscopy of a few molecules within each coupled plasmonic hotspot, with near thousand-fold enhancement of the incident fields. As a result of non-radiative relaxation pathways, the plasmons in such sub-nanometre cavities generate hot charge carriers, which can catalyse chemical reactions or induce redox processes in molecules located within the plasmonic hotspots. Here, surface-enhanced Raman spectroscopy allows us to track these hot-electron-induced chemical reduction processes in a series of different aromatic molecules. We demonstrate that by increasing the tunnelling barrier height and the dephasing strength, a transition from coherent to hopping electron transport occurs, enabling observation of redox processes in real time at the single-molecule level.

MATERIALS
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Product Description

Sigma-Aldrich
MPP+ iodide, ≥98% (HPLC), powder