Nanoscale Dehydrogenation Observed by Tip-Enhanced Raman Spectroscopy

Abstract

This study shows evidence of nanoscale dehydrogenation occurring during tip-enhanced Raman spectroscopy (TERS) measurements. The near-field TERS spectra obtained locally on a self-assembled monolayer of 2,13-bis(aldehyde)-[7]thiaheterohelicene molecules showed vibrational frequencies in good agreement with that predicted by density functional theory calculations, except for the L-mode at ∼2000 cm −1 , which is ascribed to a CC triple bond, implying that the benzene rings had been dehydrogenated during the experiments. Using peak analysis, incorporated with the molecular adsorption orientation deduced from high-resolution STM imaging, we conclude that one side benzene ring protruding upward was dehydrogenated as a result of pyrolysis, with the Ag tip serving as both local heat source and catalyst.

Mechanistic Studies of Plasmon Chemistry on Metal Catalysts

“…However,t od ate the effect of local heating on the chemical reactions has not been completely described. [37] Yu et al used scanning electrochemical microscopy (SECM) to investigate the effects of both the hot carriers and local heating generated by the LSP on photoelectrochemical reactions. [57] Thel ocal heating mechanism was also applied to explain the dehydrogenation from phenyl rings in 2,13-bis(aldehyde)- [7]thiaheterohelicene molecules observed during TERS measurements.…”

“…[57] Thel ocal heating mechanism was also applied to explain the dehydrogenation from phenyl rings in 2,13-bis(aldehyde)- [7]thiaheterohelicene molecules observed during TERS measurements. [37] Yu et al used scanning electrochemical microscopy (SECM) to investigate the effects of both the hot carriers and local heating generated by the LSP on photoelectrochemical reactions. [58] They clarified that photooxidation was enhanced by the hot carriers and the local heating, thereby causing ap otential shift.…”

“…Tipenhanced Raman spectroscopy (TERS) not only provides chemical information of the molecules before and after reactions but the LSP also induces reactions at the nanogap. [35,36,37] Recently,ascanning tunneling microscope combined with optical excitation (photon-STM) was applied to observe plasmon-induced chemical reactions at as ingle-molecule level. [34] Plasmon-induced bond dissociation reactions were also investigated with TERS.…”

“…[34] Plasmon-induced bond dissociation reactions were also investigated with TERS. [35,36,37] Recently,ascanning tunneling microscope combined with optical excitation (photon-STM) was applied to observe plasmon-induced chemical reactions at as ingle-molecule level. [38,39] An ultrahigh vacuum condition and the atomically well-defined surfaces of metal single crystals are necessary to obtain molecular-scale mechanistic insights.T hese allow the electronic structure of the molecules adsorbed on metal surfaces to be investigated with ac ombination of STM experiments and density functional theory (DFT) calculations.T he findings obtained using the STM provide deep insights into the mechanisms of the plasmon-induced chemical reactions at the single-molecule level that cannot be accessed by the conventional macroscopic analysis methods.…”

Mechanistic Studies of Plasmon Chemistry on Metal Catalysts

“…A pioneering study applied time‐resolved TERS to plasmon chemistry to monitor the formation of DMAB from p NTP . Plasmon‐induced bond dissociation reactions were also investigated with TERS …”