Nanoscale Dehydrogenation Observed by Tip-Enhanced Raman Spectroscopy

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.