title: High-quality photonic crystals with a nearly complete band gap obtained by direct inversion of woodpile templates with titanium dioxide.
abstract: Photonic crystal materials are based on a periodic modulation of the dielectric constant on length scales comparable to the wavelength of light. These materials can exhibit photonic band gaps; frequency regions for which the propagation of electromagnetic radiation is forbidden due to the depletion of the density of states. In order to exhibit a full band gap, 3D PCs must present a threshold refractive index contrast that depends on the crystal structure. In the case of the so-called woodpile photonic crystals this threshold is comparably low, approximately 1.9 for the direct structure. Therefore direct or inverted woodpiles made of high refractive index materials like silicon, germanium or titanium dioxide are sought after. Here we show that, by combining multiphoton lithography and atomic layer deposition, we can achieve a direct inversion of polymer templates into TiO2 based photonic crystals. The obtained structures show remarkable optical properties in the near-infrared region with almost perfect specular reflectance, a transmission dip close to the detection limit and a Bragg length comparable to the lattice constant.
authors.affiliation: Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700, Fribourg, Switzerland.|Laboratoire des Multimatériaux et Interfaces - UMR 5615 CNRS / UCBL, Université Claude Bernard Lyon 1, 22 avenue Gaston Berger, 69622 Villeurbanne Cedex, France.|Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700, Fribourg, Switzerland.
authors.forename: Catherine
authors.initials: C
authors.lastname: Marichy
authors.affiliation: Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700, Fribourg, Switzerland.|Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700, Fribourg, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Muller
authors.affiliation: Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700, Fribourg, Switzerland.|Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700, Fribourg, Switzerland.
authors.forename: Luis S
authors.initials: LS
authors.lastname: Froufe-Pérez
authors.affiliation: Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700, Fribourg, Switzerland.|Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700, Fribourg, Switzerland.
authors.forename: Frank
authors.initials: F
authors.lastname: Scheffold