Dresden 2003 – wissenschaftliches Programm

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O: Oberflächenphysik

O 17: Zeitaufgelöste Spektroskopie I

O 17.5: Vortrag

Dienstag, 25. März 2003, 12:15–12:30, FOE/ORG

Time-resolved two-photon photoemission from a buried interface — •M. Rohleder, K. Duncker, W. Berthold, J. Güdde, and U. Höfer — Fachbereich Physik, Philipps-Universtät, D-35032 Marburg

Time-resolved two-photon photoemission (2PPE) has been used to study electronic states that are localized at the interface between a Cu(100) crystal and Ar films as thick as 70 monolayers (ML). A first laser pulse excites an electron into the normally unoccupied state. A second laser pulse lifts the electron into the Ar conduction band, from where it can escape into the vacuum without any appreciable loss of energy or momentum. We show that with increasing layer thickness the states evolve from quantum-well-like resonances into well-defined bound states that arise from the screened image-potential of the metal. In comparison to the image-potential states of the clean surface, the interface states are modified by the potential inside the dielectric layers. Screening reduces their binding energies and also results in longer lifetimes, as the wavefunctions are more extended. The Rydberg series does not converge to the vacuum energy but to the Ar conduction band minimum. Numerical simulations based on a one-dimensional atomic potential provide a good quantitative description of the physical properties of these novel states.