Regensburg 2004 – scientific programme

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O: Oberflächenphysik

O 45: Zeitaufgelöste Spektroskopie II

O 45.6: Talk

Friday, March 12, 2004, 12:30–12:45, H39

Electron relaxation dynamics in Ag nanoparticles on Graphite — •C. Kennerknecht, M. Merschdorf, and W. Pfeiffer — Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

The properties of supported nanoparticles differ substantially from homogeneous films or bulk material. This makes them interesting for applications, like for example in catalysis [1] or for single electron tunneling devices [2]. We show that 2-photon-photoemission spectroscopy can be used as local time-resolved probe for both relaxation dynamics in the nanoparticles as well as local transient potential shifts that are directly related to the charge transfer between particle and substrat.

Resonant multiphoton photoemission spectra map the transient electron energy distribution in the nanoparticles and reveal the internal thermalization and cooling of the electron gas. A phenomenological model based on the Boltzmann equations that includes the charge transfer between substrate and nanoparticle is used to simulate the transient electron energy distribution. Optimization of the model parameters shows that the injection of excited electrons into the nanoparticle accounts for almost half of the total deposited energy in the nanoparticle strongly influencing the transient electron distribution in the nanoparticles. In agreement with results from tunneling spectroscopy [2] our measurements reveal a rather weak electronic coupling between nanoparticle and substrate.

[1] M. Valden, et al., Science 281, 1647 (1998)

[2] T. Ohgi, et al., Appl. Phys. Lett. 79, 2453 (2001)