title: Activated vibrational modes and Fermi resonance in tip-enhanced Raman spectroscopy.
abstract: Using p-aminothiophenol (PATP) molecules on a gold substrate and high-vacuum tip-enhanced Raman spectroscopy (HV-TERS), we show that the vibrational spectra of these molecules are distinctly different from those in typical surface-enhanced Raman spectroscopy. Detailed first-principles calculations help to assign the Raman peaks in the TERS measurements as Raman-active and IR-active vibrational modes of dimercaptoazobenzene (DMAB), providing strong spectroscopic evidence for the dimerization of PATP molecules to DMAB under the TERS setup. The activation of the IR-active modes is due to enhanced electromagnetic field gradient effects within the gap region of the highly asymmetric tip-surface geometry. Fermi resonances are also observed in HV-TERS. These findings help to broaden the versatility of TERS as a promising technique for ultrasensitive molecular spectroscopy.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603-146, Beijing 100190, People's Republic of China.
authors.forename: Mengtao
authors.initials: M
authors.lastname: Sun
authors.forename: Yurui
authors.initials: Y
authors.lastname: Fang
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Zhang
authors.forename: Hongxing
authors.initials: H
authors.lastname: Xu
mesh_terms: D018625:Microscopy, Atomic Force / Q000379:methods*; D010636:Phenols / Q000737:chemistry*; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D014732:Vibration
chemical_list: D010636:Phenols; D013438:Sulfhydryl Compounds; C042983:thiophenol