Single-molecule vibrational spectroscopy and inelastic-tunneling-electron- induced diffusion of formate adsorbed on Ni(110)

We have investigated the inelastic-tunneling-electron-induced vibrational excitation of single formate (HCOOand DCOO-) molecules adsorbed on Ni(110) using a low-temperature scanning tunneling microscope (STM). Formate molecules adsorbed on the long-bridge site can be moved laterally along [11̄0] by the injection of tunneling electrons from the STM tip. Using an isotope-labeled molecule, the diffusion probability and distance were found to be enhanced significantly when the applied voltage reaches the energies of specific vibrational modes, that is, C-H bending and C-H stretching modes. Inelastic electron tunneling spectroscopy based on STM (STM-IETS) and scanning tunneling spectroscopy was used to identify the vibrational and electronic state of a single formate molecule adsorbed at different sites. The STM-IETS spectrum of formate adsorbed at the short-bridge site exhibited a broad peak at 80 mV and a sharp resonance peak at 360 mV. The former peak is assigned to the electronic states generated by the metal-molecule hybridization; the latter peak is assigned to the C-H stretching mode. The STM-IETS spectrum of formate adsorbed at the long-bridge site showed features similar to those of formate adsorbed at the short-bridge site, but the intensity of the broad peak appearing at near the Fermi level was markedly suppressed, indicating a weak metal-molecule interaction.