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Plenarvorträge - DPG-Tagungen

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Oberflächenphysik Mittwoch<br />

and electronic properties are observed. In contrast to silver islands grown<br />

on germanium (001) the orientation of the crystal lattice is not fixed if<br />

cluster melting is neglected. However, some of the clusters show hexagonal<br />

facets at the top. STS is sensitive to occupied and unoccupied states<br />

near the Fermi level and reveals the existence of distinct states in the<br />

tunneling conductivity of the substrate as well as on the clusters. Thus,<br />

the richly structured density of states of the germanium (001) surface<br />

has been discovered and serves as STM/STS condition test.<br />

O 28.69 Mi 16:00 Bereich C<br />

Application of the variable phase theory to the systems with<br />

quasistationary states. — •Oleg Kidun 1 , Jamal Berakdar 1 ,<br />

and Natasha Fominykh 2 — 1 Max-Planck Institut fuer Mikrostrukturphysik,<br />

Halle, Germany — 2 Institute of Physics, St. Petersburg State<br />

University, St. Petersburg, Russia<br />

We develop a method of investigation of the quasistationary (QS)<br />

states of different physical systems based on the variable phase approach<br />

[1-3]. We consider the modification of the physical properties of the QS<br />

states (energy position and resonance width) under the spatial transformation<br />

of the potential field as well as its asymptotical behavior. The<br />

role of the possible nonlocality of the potential in the observability of<br />

the QS states is also estimated. The realization of our approach in the<br />

studies of molecules and nanostructures is discussed.<br />

[1] F. Calogero, Variable Phase Approach in Potential Scattering, AP,<br />

NY (1967)<br />

[2] V. Babikov, Method of the Phase Functions in Quantum Mechanics,<br />

Nauka, Moscow (1969)<br />

[3] O. Kidun, N. Fominykh, J. Berakdar, J. Phys. A 35, 9413 (2001)<br />

O 28.70 Mi 16:00 Bereich C<br />

Electron dynamics of buried interface states in Ar/Cu(100)<br />

probed by time-resolved two-photon photoemission — •M.<br />

Rohleder, W. Berthold, K. Duncker, J. Güdde, and U.<br />

Höfer — Fachbereich Physik und Zentrum für Materialwissenschaften,<br />

Philipps-Universtät, D-35032 Marburg<br />

We demonstrate for the system Ar/Cu(100) how in favourable cases the<br />

dynamics of electronic states located at the interface between a metal and<br />

an insulator can be investigated by means of time-resolved two-photon<br />

photoemission (2PPE). The interface states of Ar/Cu are located above<br />

the vacuum level in the band gaps of both the Cu(100) surface and the<br />

Ar films which were as thick as 70 monolayers (ML). With increasing<br />

layer thickness the states evolve from quantum-well-like resonances into<br />

well-defined bound states which arise from the screened image-potential<br />

of the metal. Electrons excited into these states decay on timescales between<br />

100 fs and 250 fs by electron-hole pair excitation in the metal and<br />

– for thin Ar layers (

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