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Tip enhanced Raman Spectroscopy on 1,4-Benzenedimethanethiol: a spectroscopic study of conformational changes

Tip enhanced Raman Spectroscopy on 1,4-Benzenedimethanethiol: a spectroscopic study of conformational changes.

Details

1,4-Benzenedimethanethiol (BDMT) is well known to adsorb dissociatively to form Self Assembled Monolayers (SAM) once deposited on crystalline metallic surfaces such as gold or silver. Depending on the substrate different assembly geometries and physical properties can arise, due to the different conformation of the adsorbates. While on Ag surfaces the loss of both thiol protons orientates the molecular plane parallel to the surface and a consequent eventless desorption, on gold the loss of a single thiol proton orientates the molecular plane perpendicular to the surface, eventually leading to a more thermally stable SAM surface up to 423K, when the conformation changes to layered form before desorption. The two conformations are characterized by the absence (Ag) or presence of distinctive S-H Raman peaks and shifts in the CH, CH2 ones, due to the different chemical and conformational states. For this reason BDMT SAM is an ideal model study to perform tip induced conformational changes by mean of TERS-AFM ​setup, where a Force Spectroscopy and Raman spectroscopy can be performed in real time at nanoscale by inducing conformational changes below an AFM tip in contact with the sample, giving the possibility to study morphology related physical changes and the eventual contribution of confinement at the surface.​