Tip-enhanced Raman spectroscopy reveals rich nanoscale adsorption chemistry of 2-mercaptopyridine on Ag

Adsorption of 2-mercatopyridine (2MPy) on Ag surfaces was studied by tip-enhanced Raman spectroscopy (TERS), which allows the measurement of Raman spectra with nanometer scale spatial resolution on flat surfaces that themselves do not show any surface-enhancement Raman scattering (SERS) activity. We found that the adsorption behavior of 2MPy was affected by the parameters of the preparation for the adsorbate layers, i.e., Solution concentration, solution volume, and the exposure time. Besides that, variation of the TERS spectra at randomly chosen sample positions was observed. Only some of the bands appearing in SERS experiments showed up in each TERS measurement. We propose that this is caused by different local adsorption behavior of 2MPy on the Ag surfaces. This observation perfectly demonstrates the advantage of TERS over SERS, i.e., TERS call give localized chemical information on the nanometer scale, whereas SERS can only afford average spectra with micrometer scale resolution. Finally, TERS mapping with a spatial resolution of 24 nm was demonstrated.