Electrochemical tip-enhanced Raman spectroscopy imaging with 8 nm lateral resolution

Abstract

Herein, we report tip-enhanced Raman spectroscopy (TERS) hyperspectral imaging under electrochemical control of a non-Raman-resonant molecular compound. A new setup combining a Scanning Tunneling Microscope (STM) and an optical coupling with high signal excitation and collection efficiency enables fast chemical imaging of an opaque functionalized electrode surface upon polarization. Variations in the TERS signal intensity up to 1.8 were observed across the surface, and correlated with topographic heterogeneities. These fluctuations, attributed to enhancement of the local electromagnetic field below the TERS tip, were used to estimate the lateral resolution of the produced hyperspectral image, which was found greater than 8 nm. This work represents an important step towards the use of electrochemical TERS imaging as a unique tool to unravel electrochemical processes at the nanoscale. Keywords: Tip enhanced Raman spectroscopy, Scanning Tunneling Microscopy, Nanospectroscopy, Electrochemistry, Plasmonics