AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuA

Paper SS2-TuA1
Ultra-Fast Dynamics Measurements of One- and Two-Dimensional Surface State Electrons on Stepped Cu(775)

Tuesday, October 3, 2000, 2:00 pm, Room 209

Session: Stimulated Processes and Excitations
Presenter: D. Mocuta, Columbia University
Authors: X.J. Shen, Columbia University
H. Kwak, Columbia University
D. Mocuta, Columbia University
S. Smadici, Columbia University
R.M. Osgood, Jr., Columbia University
Correspondent: Click to Email
Dynamical questions regarding surface state electrons on metallic surfaces can best be answered in the time domain using ultra-fast nonlinear probes. Of particular interest is the effect of controlled nano-size features on the femtosecond scale dynamics of surface states. In this connection, we have employed the momentum- and time-resolved two photon photoemission technique to study the dispersion and lifetimes of these states on a prototypical nano-structured surface, stepped Cu(775). Here we report on a newly observed one-dimensional surface state (0.27 eV below Fermi level) and an image-like unoccupied state on stepped Cu(775). Both states are dispersive along the step direction but are localized in the direction perpendicular to the steps. The origin of the states is attributed to the step-edge potential confinement and to an Anderson localization mechanism. The lifetime of n=1 electrons on the regular step array of Cu(775) has been measured as a function of their translational momentum, k@sub //@. At the terrace normal, this lifetime is equal to that for flat Cu(111), i.e., t = 16±2 fs. The lifetime decreases symmetrically with k@sub //@ about k@sub //@ = 0 for electrons moving parallel to the step orientation. This is in good agreement with a theoretical calculation of k@sub //@ dependent n=1 lifetime done on Cu(111) by Echenique, et al.@footnote 1@ In contrast, the lifetime is asymmetric in k@sub //@ for the direction perpendicular to the step edges. The asymmetric behavior is attributed to direction-dependent coupling between image and bulk states, leading to a decrease in lifetime of the electrons climbing the steps and an increase for descending electrons. The overlap between the unoccupied localized state and the n=1 image state at k@sub //@ = 0.2 Å@sup -1@ results in an increase in the measured lifetime at this value of the momentum. @FootnoteText@ @footnote 1@J. Osma, I. Sarria, E. V. Chulkov, J. M. Pitarke, and P. M. Echenique, Phys. Rev. B59, 10591 (1999).