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DS: Fachverband Dünne Schichten

DS 9: Metal Layers

DS 9.4: Vortrag

Dienstag, 24. März 2009, 10:15–10:30, GER 37

Dielectric properties of ultra-thin metal films around the percolation threshold — •Martin Hövel, Martin Alws, Bruno Gompf, and Martin Dressel — 1.Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany

The dielectric properties of percolating metal films around the insulator-to-metal (IMT) transition are not well understood [1]. By combining Fouriertransform infrared spectroscopy (FITR), spectroscopic ellipsometry, and dc-conductivity measurements on ultra-thin Au films on Si/SiO₂ the effective dielectric properties around the IMT can be described Kramers-Kronig consistent over a very brought frequency range from 500 to 27 000 cm⁻¹. Above a critical thickness d_c, the so called percolation threshold, the films show for low frequencies a typical metallic-like behavior which can be fitted by a simple Drude-Model [2]. Below d_c the frequency behavior is dominated by a "Maxwell-Garnett resonance" which shifts to lower frequencies with increasing film thickness and dies out well above the IMT. A dielectric anomaly with a maximum of є₁ at d_c is observed and can be described by the interplay of this resonance and the onset of the Drude-component. Additionally the temperature dependence of the films were studied. Here also a transition from an activated to a metallic like behavior at d_c was found.

[1] B. Gompf, J. Beister, T. Brandt, J. Pflaum, M. Dressel, Optics Letters 32, 1578 (2007)

[2] T. Brand, M. Hövel, B. Gompf, M. Dressel, Phys. Rev. B 78, 205409, (2008)