Theoretical state-of-the art in adsorbate motions and reactions induced by inelastic tunneling current with STM

Current understanding of the physical mechanisms of motion and reaction of single adsorbates induced by inelastic tunneling current with scanning tunneling microscope (STM) is described in relation to various novel experimental results. It is a central issue to elucidate how the energy stored in the specific vibrational mode excited by tunneling electrons activates the configurational change of an adsorbate, in competing with the vibrational relaxation. There are two reaction paths, i.e., direct or indirect excitation of the reaction coordinate (RC) mode to overcome the relevant potential barrier. This includes vibrational ladder climbing in the potential well following a direct excitation of the RC mode, and indirect excitation of the RC mode through its anharmonic coupling to the vibrational mode excited by tunneling electrons. A unified picture is proposed for a qualitative scenario of mode selective control of different motions of single adsorbates by a combination of bias voltage and tunneling current.