Site-Dependent TERS Study of a Porphyrin Molecule on Ag(100) at 7 K
Atif Ghafoor, Ben Yang, Yin-jie Yu, Yu-fan Zhang, Xian-biao Zhang, Gong Chen, Yao Zhang*, Yang Zhang, Zhen-chao Dong*
As an important technique for structural analysis at sub-nanometer scale, tip-enhanced Raman spectroscopy (TERS) offers a fascinating prospect in the field of single-molecule imaging. In this work, we apply the TERS technique at cryogenic temperature (~7 K) to study an isolated free-base porphyrin molecule adsorbed on the Ag(100) surface. By exploiting the atomically confined nanocavity plasmon field underneath the tip apex, we demonstrate distinct local vibrational information for the chemical constituents within a single molecule through site-dependence TERS spectra. Further TERS mapping images can identify different spatial features among different vibrational peaks, enabling to resolve the vibrational modes associated with the single N−H bonds at sub-nanometer scale. This study will provide deep insights into the understanding of molecular adsorption configurations and local vibrational information within a single molecule.
关键词：Tip-enhanced Raman spectroscopy, Spatial mapping, Adsorption configuration, Porphyrin