Adsorbate motions induced by vibrational mode coupling |
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Authors: | H Ueba |
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Institution: | Department of Electronics, University of Toyama, Gofuku, Toyama, Japan |
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Abstract: | Adsorbate motions are discussed with a primary attention focused on the coupling between a vibrational mode excited by ultrafast laser heated hot-electrons or by inelastic tunneling electrons with scanning tunneling microscope and the reaction coordinate (RC) mode. Recent experimental results have demonstrated an efficient reaction pathways involving an indirect excitation of a frustrated translational mode, rather than its direct excitation for adsorbate hopping on surfaces. Elementary processes are briefly described for hopping of CO molecules on a laser heated stepped Pt surface, where excitation of the frustrated rotation mode has been found to plays an indispensable. Calculation of the inelastic tunneling current (ITC) for excitation of the C-O stretch mode of a CO molecule is combined with a theory of anharmonic mode coupling to activate the frustrated translation mode above the barrier. The hopping rate as a function of the bias voltage agrees with the experimental result. An unified theory of single-, and two-electron processes for ITC-induced motions induced by an indirect excitation of the RC-mode via mode coupling is also applied to reproduce a crossover from hopping to desorption of a single NH3 molecule on Cu(1 0 0) with an increase in the tunneling current. |
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Keywords: | Adsorbate Ultrafast surface dynamics Femtosecond laser Surface chemical reaction Scanning tunneling microscope Inelastic electron tunneling Vibrational excitation Anharmonic coupling |
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