Picocavity Plasmon-Enhanced Vibrational Spectroscopy of Single-Molecule Chemical Processes of 4,4'-Dimercaptoazobenzene
Raman scattering measurement technology based on plasmon enhancement mechanism can improve the Raman scattering cross-sections of molecules by several orders of magnitude.Accordingly,they have a wide range of application prospects for trace substance identification and tracking.Many previous studies have reported identification of single-molecules when the enhancement factor reaches～1010.Measuring physical and chemical behaviors at the single-molecule level is expected to provide richer and more accurate results compared to measuring the statistical behavior of an ensemble of many molecules.This study uses a radially polarized laser to excite a picocavity hotspot in a longitudinally polarized plasmonic antenna.We achieve an accurate observation of the chemical processes of individual molecules using their vibrational spectra.In particular,we observe that 4-nitrobenzenethiol dimerized into 4,4'-dimercaptoazobenzene and that a single-molecule of the latter briefly switched from trans-to cis-conformation;it then desorbs from the gold atom and reverts to trans-conformation.This study preliminarily shows the power of picocavity plasmon-enhanced vibrational spectroscopy in investigating single-molecule chemical kinetics.
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