Plasmonic tunnel junctions for single-molecule redox chemistry

• Published in: Nature communications Vol. 8; no. 1; pp. 994 - 8
• Main Authors: de Nijs, Bart, Benz, Felix, Barrow, Steven J., Sigle, Daniel O., Chikkaraddy, Rohit, Palma, Aniello, Carnegie, Cloudy, Kamp, Marlous, Sundararaman, Ravishankar, Narang, Prineha, Scherman, Oren A., Baumberg, Jeremy J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 20-10-2017; Nature Publishing Group; Nature Portfolio
• Subjects: 639/638/440/947; 639/925/357/341; 639/925/927/1021; 639/925/927/356; Aquatic plants; Cavities; Chemical reactions; Chemical reduction; Current carriers; Electron transport; Electrons; Holes; Humanities and Social Sciences; multidisciplinary; Nanoparticles; Plasmons; Raman spectroscopy; Science; Science (multidisciplinary); Spectroscopy; Tunnel junctions
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-017-00819-7

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.
Plasmons in sub-nm cavities can enable chemical processes within plasmonic hotspots. Here the authors use surface-enhanced Raman spectroscopy to track hot-electron-induced chemical reduction processes in aromatic molecules, thus enabling observation of redox processes at the single-molecule level.