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

Paper SS2-TuA6
Femtosecond Measurements of Surface-State-Electron Dynamics on Nanostructured Ni Surfaces

Tuesday, October 3, 2000, 3:40 pm, Room 209

Session: Stimulated Processes and Excitations
Presenter: S. Smadici, Columbia University
Authors: S. Smadici, Columbia University
X.J. Shen, Columbia University
D. Mocuta, Columbia University
R.M. Osgood, Jr., Columbia University
Correspondent: Click to Email
Ultra-fast nonlinear optical probes have recently been shown to enable time-resolved measurements of electron dynamics on metal surfaces. While most measurements have been on flat surfaces, we have recently begun an investigation of the ultra-fast dynamics for electrons confined in surface metallic nano-structures. Here we will describe our femtosecond, momentum- and time-resolved two-photon photoemission measurements of electron lifetimes and dispersion curves on systems with controlled nano-size features obtained by Ag deposition on stepped Ni(977) and Ni(111). Ag deposition reduces the Ni work function and permits the observation of surface and image states at the accessible pulse energies. We will present measurements of the dispersion for the occupied surface state and the unoccupied n=1 image state located ~3Å above the metal surface. We report on band-folding of the Ag induced surface state on Ni(977), with a controllable bandwidth, caused by the periodic step potential. As the Ag coverage is increased the width of the allowed band increases as predicted by a Krönig-Penney model which is appropriate to the periodic potential on this Ag-decorated surface. The n=1 state lifetime measurements on the Ag/Ni(977) system showed a downward trend with increasing parallel momentum. This result is similar to that observed by us on Cu surfaces@footnote 1@ and is consistent with theoretical results indicating the increased importance of elastic and inelastic scattering at higher k@sub //@. The n=0 surface state lifetime showed an unexpected similar behavior when moving away from the terrace normal direction with a variation of ~10 fs over a change of k@sub //@ of 0.2Å@super-1@. This result is explained in terms of a resonant excitation of the n=2 image state, with the detector sampling a mixture of two different photoemission channels. @FootnoteText@ @footnote 1@.X. J. Shen, H. Kwak, A. M. Radojevic, S. Smadici, D. Mocuta, and R.M. Osgood, Jr., submitted to Phys. Rev. Lett.