Invited Paper SS2-MoA1
Action Spectroscopy of Single Adsorbate Motions

Monday, October 15, 2007, 2:00 pm, Room 611

I will discuss an idea of action spectroscopy for a single molecule motion induced by vibrational excitation with a scanning tunneling microscope (STM).¹ A simple formula describing the energy transfer from the vibrational mode excited by tunneling electrons to a reaction coordinate mode through anharmonic coupling to overcome the activation barrier^2,3 is combined with the inelastic tunneling current calculated using the non-equilibrium Keldysh Green's function method. This enables the reaction rate to be calculated as a function of the bias voltage, and is applied to CO hopping on Pd (110)² and CCH rotation on Cu(001).⁴ I propose that the second-derivative of the reaction rate with respect to the bias voltage gives the density of states of the vibrational mode excited by tunneling electrons,⁴ which can not be directly observed with inelastic tunneling spectroscopy because of the negative contribution of the elastic current to the total current, and when a molecule motion is induced by the vibrational excitation.

¹H. Ueba, B.N.J. Persson, Phys. Rev. B 75, 041403(R) (2007).
²T. Komeda et al., Science 255, 2055 (2002).
³B.N.J. Persson, H. Ueba, Surf. Sci. 502/503, 18 (2002).
⁴L.J. Lauhon, W. Ho, Surf. Sci. 451, 219 (2000).