Electrochemical Tip-Enhanced Raman Spectroscopy for the In Situ Characterization of Functional Materials

Abstract

The understanding of the mechanism of operation and failure of functional (nano)materials and surfaces is a prerequisite to the optimization of their performance and design. This can be address with nanoscale-sensitive techniques which can be implemented, in situ/operando under the operating conditions of such functional material. Tip-Enhanced Raman Spectroscopy (TERS) has already demonstrated its ability to characterize functional materials at the nanoscale, though its operation in liquid conditions and under polarization remains challenging.[1] After the first demonstration of liquid TERS in organic solvent in 2016 in our group [2], we could access electrochemical TERS (EC-TERS) mapping with 8-nm resolution in 2019.[3]Our most recent work focuses on the in situ investigation of the reactivity of electrochemically-active molecular architectures immobilized on electrode surfaces by EC-TERS. To this purpose we have developed a configurations enabling EC-TERS implementation in the Scanning Tunneling Microscopy mode (EC-STM-TERS). In this setup using a home-made bipotentiostat synchronized to the CCD detector, relatively high potential sweep rate[4] and broad potential ranges are accessible, enabling real-time assessments of electrochemical processes without compromising the plasmonic coupling at the tip-sample junction. A complex electrochemical mechanism, involving reaction intermediates and multiple reaction paths, could be resolved on electroactive architectures based on nitrobenzene derivatives. Further EC-TERS investigations on nitrobenzene derivatives assembled as mono- or multilayers on the electrode surface emphasized the influence of the structure of the molecular assemblies on their reactivity.In our latest developments, EC-TERS measurements implemented in the Atomic Force Microscopy mode (EC-AFM-TERS) are also accessible, therefore broadening the range of functional materials which can be studied in situ/operando.[1] T Touzalin, S Joiret, E Maisonhaute, IT Lucas “Capturing electrochemical transformations by tip-enhanced Raman spectroscopy”, Current Opinion in Electrochemistry 6 (2017) 46-52[2] T Touzalin, AL Dauphin, S Joiret, IT Lucas, E Maisonhaute “Tip enhanced Raman spectroscopy imaging of opaque samples in organic liquid”, Physical Chemistry Chemical Physics 18 (2016) 15510-15513[3] T Touzalin, S Joiret, IT Lucas, E Maisonhaute “Electrochemical tip-enhanced Raman spectroscopy imaging with 8 nm lateral resolution”, Electrochemistry Communications 108 (2019) 106557[4] M Mattei, G. Kang, G. Goubert, D.V. Chulhai, G.C. Schatz, L. Jensen and R.P. Van Duyne., “Tip-Enhanced Raman Voltammetry: Coverage Dependence and Quantitative Modeling” Nano Lett.(2017) 17, 590−596 Figure 1