title: Conformational Contrast of Surface-Mediated Molecular Switches Yields Ångstrom-Scale Spatial Resolution in Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy.
abstract: 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.
authors: Naihao
authors: N
authors: Chiang
authors: Department of Chemistry, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors: Xing
authors: X
authors: Chen
authors: Guillaume
authors: G
authors: Goubert
authors: Department of Chemistry, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors: Dhabih V
authors: DV
authors: Chulhai
authors: Xu
authors: X
authors: Chen
authors: Eric A
authors: EA
authors: Pozzi
authors: Department of Chemistry, University of Illinois at Chicago , Chicago, Illinois 60607, United States.
authors: Nan
authors: N
authors: Jiang
authors: Mark C
authors: MC
authors: Hersam
authors: Tamar
authors: T
authors: Seideman
authors: Department of Chemistry, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors: Lasse
authors: L
authors: Jensen
authors: Richard P
authors: RP
authors: Van Duyne
keywords: Ultrahigh vacuum; conformational isomers; nanoscale chemical imaging; single molecule spectroscopy; tip-enhanced Raman spectroscopy