AVS 54th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP6
STM Study of Temperature Effect on Electron Induced Hopping Motion of CO/Cu(110)

Tuesday, October 16, 2007, 6:00 pm, Room 4C

Session: Surface Science Poster Session
Presenter: T. Okada, The University of Tokyo, Japan
Authors: T. Okada, The University of Tokyo, Japan
S. Katano, Tohoku University, Japan
Y. Kim, RIKEN, Japan
M. Kawai, The University of Tokyo, Japan
Correspondent: Click to Email

Scanning tunneling microscope (STM) enabled the observation and manipulation of the single isolated molecule, and we can follow the molecular motion precisely with its high spatial resolution (~ 0.1 nm).1 In this study, we investigated hopping motion of carbon monoxide (CO) on metal surface, which is one of the most simple and fundamental molecular motions at surfaces. Same as thermal diffusion, vibrations of the adsorbates are important because some vibrations couple with surface motions strongly. For example, a study using STM has revealed that internal stretching vibration of CO on Pd(110) (~ 250 meV) plays an important role.2 We can control the energy of innelasticaly tunneled electrons from the tip of STM precisely, and those electrons can excite the vibration of aimed molecule. And recently, time resolved SFG study on Pt(553) has revealed that hindered rotation mode of CO (~ 51 meV) also contributes to hopping motion.3 They performed the experiment at 100 K where hindered translation mode (~ 4 meV) is thermally excited enough. We took notice of this temperature effect. We performed the experiments at 4.8 ~ 45 K using STM (LT-STM, Omicron GmbH) equipped in an ultrahigh-vacuum chamber (< 3×10-9 Pa). The Cu(110) surface was cleaned by cycles of Ar ion sputtering and annealing cycles, and exposed to CO molecules below 50 K. First, by Inelastic Electron Tunneling Spectroscopy (STM-IETS) on CO/Cu(110) obtained at 4.8 K, the vibrational peaks of two surface parallel vibrations (hindered translation and hindered rotation) are clearly observed. Then, I tried Action spectroscopy on single CO molecule at various temperatures. In that spectra, the sudden change of the yields of hopping motion which corresponds to the internal stretching vibration of CO was observed. It means that anharmonic coupling between vibrations enables hopping motion of CO on Cu(110) surface easily. And temperature dependence of the yields of hopping motion does not obey the simple Arrhenius law. In the presentation, I will discuss the coupling between vibrations and molecular motions from these results.

1 B. G. Briner, M. Doering, H.-P. Rust, and A. M. Bradshaw, Science 278, 257 (1997).
2 T. Komeda, Y. Kim, Maki Kawai, B. N.J. Persson, and H. Ueba, Science 295, 2055 (2002).
3 E. H. G. Backus, A. Eichler, A. W. Kleyn, M. Bonn, Science 310, 1790 (2005).