Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 50: Particles and Clusters II

O 50.1: Vortrag

Donnerstag, 29. März 2007, 11:15–11:30, H38

In-plane optical anisotropy of metal clusters studied by reflectance-difference spectroscopy — •José Manuel Flores-Camacho, Li Dong Sun, Nadia Saucedo-Zeni, Günther Weidlinger, Michael Hohage, and Peter Zeppenfeld — Institut für Experimentalphysik, Johannes Kepler Universität Linz, A-4040, Linz, Austria

Reflectance-difference spectra of Ag clusters supported on an insulating, uniaxial substrate for Ag coverages in the 0.1−4.0 nm nominal thickness range are presented. The observed in-plane optical anisotropy is explained in terms of the splitting of the degeneracy of in-plane polarizations due to the presence of the non-equivalent dipole images in the substrate in quasi-electrostatic approximation. Geometrical sources of anisotropy might be excluded in a first approach since scanning electron and atomic force microscopy images reveal randomly arranged oblate spheroidal particles with in-plane rotational symmetry.

Although the presence of at least one source of in-plane anisotropy is necessary, be it cluster or substrate related, we show that reflectance-difference spectroscopy (RDS/RAS) is very sensitive to a number of particle-plasmon resonance related phenomena such as the cluster geometry, the randomness of the system, shape/size distributions, higher-than-dipole interactions between particles, percolation threshold, and the presence of a dielectric shell. From this we propose RDS/RAS as a reliable tool for the monitoring of cluster growth.