Dresden 2006 – wissenschaftliches Programm

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DS: Dünne Schichten

DS 24: Poster presentation

DS 24.16: Poster

Dienstag, 28. März 2006, 15:00–17:30, P2

Mechanisms of electron emission from silver cluster films under femtosecond laser excitation — •A. Gloskovskii, D.A. Valdaitsev, S.A. Nepijko, and G. Schönhense — Institut für Physik, Johannes Gutenberg - Universität, 55099 Mainz

The electron yield from metal cluster films upon fs-laser irradiation is several orders of magnitude larger than for bulk metal. Depending on various parameters, electrons can be emitted due to different processes. Multiphoton photoemission (nPPE) is basically rather well understood. For the case of metal clusters nPPE can be governed by the strong enhancement of the optical near field caused by plasmon excitation. In this contribution we focus on the alternative emission processes, i.e. thermionic emission, thermally assisted nPPE and optical field emission. In order to understand the differences between the competing channels it is necessary to consider the details in the thermalization of the initially excited electron system. Further, a quantum-statistical model gives a quantitative estimation of the different regimes of emission mechanisms.

A FOCUS PEEM with retarding field imaging energy filter was used in combination with a Spectra Physics laser [MaiTai tunable between 750 and 850 nm ("red", 100 fs) and frequency doubled ("blue", 200 fs)]. UHV-deposited Ag/Si cluster films of various mass thicknesses have been investigated using "blue" and "red" excitation. The Fermi level onset is sharp (less than 150 meV wide) in the "blue" photoelectron spectra, while it is smeared out under "red" laser excitation. A contribution of thermally assisted 2PPE and optical field emission was found in addition to pure 3PPE under "red" laser excitation.