Nanoscale roughness on metal surfaces can increase tip-enhanced Raman scattering by an order of magnitude

We studied the influence of nanosteps on signal intensity in gap-mode tip-enhanced Raman spectroscopy (TERS). A benzenethiol monolayer adsorbed on an Au substrate was investigated. The correlation between the TERS signal and the local topography on the substrate shows that a 2 nm high sharp step on the Au surface can significantly increase the enhancement. Furthermore, theoretical models were built, and the numerical simulation results were consistent with our experimental results. The findings provide evidence that nanoscale roughness can play a crucial role in the “hot sites ” corresponding to single-molecule surface-enhanced Raman spectroscopy (SERS). Recently, single-molecule gap-mode tip-enhanced Raman spectroscopy (TERS) has been demonstrated by several groups independently.1-3 This provides an unprecedented opportunity for molecular identification and analysis with nanoscale spatial resolution in many areas such as catalysis, bioscience, nanomaterials, etc.4-6 TERS employs a sharp metal tip to create a “hot site”: to excite the localized surface plasmons (LSPs) and consequently enhance the electromag-netic field and Raman signals in the vicinity of the ti