Hamburg 2001 – scientific programme

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O: Oberflächenphysik

O 25: Postersitzung (Grenzfl
äche fest-flüssig, Methodisches, Nanostrukturen, Organische Dünnschichten, Rastersondentechniken, reine Oberfl
ächen, Teilchen und Cluster, Zeitaufgelöste Spektroskopie, Sonstiges)

O 25.75: Poster

Wednesday, March 28, 2001, 15:00–18:00, Foyer zu B

Ultrafast electron dynamics of image potential states on Ni and Co surfaces — •J. Sievers, H. S. Rhie, S. Link, H. A. Dürr, and W. Eberhardt — Forschungszentrum Jülich GmbH, IFF, D-52425 Jülich

Image potential state (IPS) lifetimes and binding energies are well understood on noble metal surfaces. On transition metal surfaces the situation is more complex due to the influence of d-bands. We have investigated the femtosecond electron dynamics of IPSs on Ni and Co surfaces using time-resolved two-photon photoemission (TR2PPE). Using this technique lifetimes of normally unoccupied electronic states can be measured with an accuracy of a fraction of the laser pulse duration. On Ni(111) the first IPS shows an unusually short lifetime, which can be increased by a factor of two after saturation exposure to hydrogen. Surface states are expected to serve as efficient decay channels in the relaxation of IPS. Therefore the increased lifetime could be attributed to the quenching of surface states since it is well known that hydrogen affects the surface electronic structure on Ni(111). For the Ni(100) surface the n=1 state exhibits a longer lifetime following the trend observed on the surfaces of Cu and Ag. We compare these results with thin Ni and Co films grown on Cu(100).