Tip-enhanced Raman spectroscopy (TERS) combines the ability of scanning probe microscopy (SPM) to resolve atomic-scale surface features with the single-molecule chemical sensitivity of surface-enhanced Raman spectroscopy (SERS). Here, we report additional insights into the nature of the conformational dynamics of a free-base porphyrin at room temperature adsorbed on a metal surface. We have interrogated the conformational switch between two metastable surface-mediated isomers of meso-tetrakis(3,5-ditertiarybutylphenyl)-porphyrin (H2TBPP) on a Cu(111) surface. At room temperature, the barrier between the porphyrin ring buckled up/down conformations of the H2TBPP-Cu(111) system is easily overcome, and a 2.6 Å lateral resolution by simultaneous TERS and STM analysis is achieved under ultrahigh vacuum (UHV) conditions. This work demonstrates the first UHV-TERS on Cu(111) and shows TERS can unambiguously distinguish the conformational differences between neighboring molecules with Ångstrom-scale spatial resolution, thereby establishing it as a leading method for the study of metal-adsorbate interactions.
Bibliographical noteFunding Information:
Xing C., D.V.C., L.J., and R.P.V.D. acknowledge support from the National Science Foundation Center for Chemical Innovation dedicated to Chemistry at the Space-Time Limit (CaSTL) Grant CHE-1414466. N.C., E.A.P., N.J., T.S., M.C.H., and R.P.V.D. acknowledge support from the Department of Energy Office of Basic Energy Sciences (SISGR Grant DE-FG02-09ER16109) and the National Science Foundation Materials Research Science and Engineering Center (NSF DMR-1121262). G.G., Xu C., and R.P.V.D acknowledge support from the Air Force Office of Scientific Research MURI (FA9550-14-1-0003)
© 2016 American Chemical Society.
- Ultrahigh vacuum
- conformational isomers
- nanoscale chemical imaging
- single molecule spectroscopy
- tip-enhanced Raman spectroscopy