Paper SS-TuP19
Tunneling Electron-induced Hopping Motion of CO on Ag (110) Surface

Tuesday, October 29, 2013, 6:00 pm, Room Hall B

Inelastic electron tunneling (IET) process can induce motion and reaction of a single molecule at metal surfaces. CO hopping phenomena on Pd(110) and Cu(110) surfaces have been achieved with tunneling electrons from the tip of a scanning tunneling microscope (STM) [1]. This phenomenon is initiated by the excitation of a high-frequency (HF) vibrational mode (C-O stretching mode, ~240 meV) with inelastic tunneling electrons from the tip of scanning tunneling microscopy. The CO hopping, however, cannot be induced on Cu(110), even though the hopping barrier is lower than that on Pd(110). This result ascribed as anharmonic coupling between low-frequency (LF, ~25 meV) modes and the HF mode combined with electron-hole pair creation. W. Ho et al. reported that CO molecules on Ag(110) surface always move when the tip-substrate bias voltage reached beyond 240 meV [2]. It is really interesting because Cu and Ag are very similar to each other in terms of vibrational mode coupling [3].

In this work, we have measured the hopping probability of CO molecule on Ag(110) surface by injecting tunneling electrons from STM tip as a function of sample bias (Vs) up to 320 meV. The probability shows sudden increases at 80 meV, even though there are no vibrational modes correspond to this energy. As one of possibilities, it is considered that direct excitation of either a frustrated rotation or translation mode causes the CO hopping on the Ag(110) surface. The detail of hopping mechanism at the low bias range will be discussed in the presentation.

References;

[1] T. Komeda, Y. Kim, M. Kawai, B.N.J. Persson, H. Ueba, Science295(2002)2055

[2] H.J. Lee, W. Ho, Science286(1999)1719

[3] N. Lorente, H. Ueba, Eur. Phys. J. D35(2005)341