AVS 46th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoA

Paper SS2-MoA10
Atomic Scale Chemistry: Desorption of Ammonia from Cu(111) Induced by Tunneling Electrons

Monday, October 25, 1999, 5:00 pm, Room 607

Session: Reactions on Metals
Presenter: L. Bartels, Columbia University
Authors: L. Bartels, Columbia University
M. Wolf, Fritz-Haber-Insitut der Max-Planck-Gesellschaft, Germany
T. Klamroth, Freie Universität Berlin, Germany
P. Saalfrank, University College London, United Kingdom
A. Kühnle, Freie Universität Berlin, Germany
G. Meyer, Freie Universität Berlin, Germany
K.-H. Rieder, Freie Universität Berlin, Germany
Correspondent: Click to Email
Excitation experiments on individual ammonia molecules on Cu(111) were performed with a low-temperature scanning tunneling microscope (STM) at 15 K. It could be shown that multiple electronic excitation of ammonia molecules can lead to an excitation of their substrate bond sufficient to caues desorption of the molecules from the substrate. This frequently results in their transfer to the STM tip apex. Tunneling spectra acquired with bare metal tips at the adsorption site of ammonia are compared with spectra acquired with ammonia decorated tip apices. The dependence of the desorption yield on the tunneling current at different biases shows a change of the order of the desorption process which nicely correlates with the number of incomming electron energies necessary to make up the binding energy. Excitation with either polarity, i. e. electron and hole attachment, can cause desorption. The change of the net desorption yield at different biases can be related to the standard model of the tunnel junction. Hartree Fock calculations allow to deduce from spectroscopic data that the ammonia modified Cu 4s state near the Fermi edge is responsible for the desorption process.