Berlin 2008 – scientific programme

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DS: Fachverband Dünne Schichten

DS 36: Vibrational Spectroscopy of Nanolayers with Optical Probes

DS 36.3: Talk

Friday, February 29, 2008, 11:15–11:30, H 2013

Infrared properties of ultra-thin metal films at and below the percolation threshold — •Bruno Gompf, Martin Alws, Martin Hövel, and Martin Dressel — 1.Physikalisches Institut, Universität Stuttgart

Whereas the optical properties of thicker metal films are well understood, little has been done at and below the percolation threshold especially in the infrared region. We have studied ultra-thin gold films on Si/SiO2 in the thickness range from 1 nm to 10 nm over a very broad frequency range between 500 cm⁻¹ and 40.000 cm⁻¹ with FTIR spectroscopy and spectroscopic ellipsometry. Thicker continuous films show a normal Drude behaviour, i.e. with increasing frequency the reflectivity decreases. Below the percolation threshold an anomaly occurs: in a certain spectral range the reflectivity becomes smaller than that of the bare substrate indicating an antireflection coating of nm thickness for infrared light. This anomaly can in principle be understood by the divergence of the dielectric function at the metal-to-insulator transition.