Hannover 2003 – scientific programme

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Q: Quantenoptik

Q 49: Poster: Photonik

Q 49.8: Poster

Thursday, March 27, 2003, 16:30–18:30, Lichthof

2D alumina-based photonic crystals — •Yun Luo, Jinsub Choi, Reinald Hillebrand, Ralf B. Wehrspohn, and Ulrich Gösele — Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle

Deep 2D-photonic crystals made of porous alumina with different r/a were fabricated by imprint lithography and electrochemical etching. The fabricated porous alumina photonic crystals have an interpore distance of 500 nm and an initial pore diameter of 180 nm. Optical reflectivity measurements show a stopgap in Γ-M direction around 1 µm. The pore diameter can be subsequently increased to about 400 nm by isotropic chemical etching. This allows to experimentally determine the gap map. However, fitting the experimental data with a single refractive index yields suprisingly poor agreement. By analyzing with TEM the microstructure of porous alumina, it turned out that the material consists of two different layers. Fitting the optical data with a two layer model, we found that the inner layer, consisting of a high purity alumina, has a refractive index of 1.6-1.7 and the outer layer, which incorporates anions (PO₄²⁻), has a non-uniform refractive index. From the optical data we deduce that the anions incorporated in the outer oxide are concentrated in a region which is 50 nm away from the electrolyte/outer oxide interface. This is in very good agreement with porous alumina models suggested in literature. We will discuss the optical and physical properties of the the inner and the outer layer of porous alumina and compare the bandgaps observed by FT-IR with band structure and reflectivity calculations done by transfer matrix and Sakoda plane wave expansion.