DOI: 10.1002/adma.200501973 Direct Laser Writing of Three-Dimensional Photonic Crystals with a Complete Photonic Bandgap in Chalcogenide Glasses** By Sean Wong, Markus Deubel, Fabian Pérez-Willard, Sajeev John, Geoffrey A. Ozin,* Martin Wegener, and Georg von Freymann* The concept of three-dimensional (3D) photonic crystals (PCs) and photonic bandgap materials [1,2] was introduced nearly twenty years ago. However, the fabrication of high- quality 3D structures for the optical regime still remains a challenge. Three techniques have been discussed: i) direct semiconductor fabrication by using a layer-by-layer (LbL) method, combining high-precision alignment and wafer-fusion techniques; [3–6] ii) templating by means of self-assembly of low-refractive-index colloidal microspheres; [7,8] and iii) holo- graphic laser lithography [9,10] and direct laser writing (DLW) [11,12] to fabricate large-area, defect-free polymer tem- plates. The latter two approaches require subsequent inver- sion [13–15] or double inversion [16,17] steps with high-refractive- index materials. Here we present a novel approach, namely DLW in all-inorganic, high-refractive-index chalcogenide glasses. This approach combines the flexibility of DLW with the benefits of a direct fabrication method, hence eliminating the need for subsequent inversion. The fabrication of wood- pile structures [18] with a complete gap of 3.5 % takes less than two hours. There are two stringent requirements for materials to be suitable for the fabrication of 3D PCs with an omni-direc- tional photonic bandgap (PBG): i) the material has to be transparent over the wavelength region in which the PC is operated, and ii) the index of refraction should allow for an index contrast of at least 1.9 in the final structure to open the PBG. [18] Unfortunately, most of the materials that fulfill requirement (i) do not comply with requirement (ii). This is especially awkward as most of the materials suitable for fabri- cation by using lithographic techniques like holographic laser lithography [9,10] and direct laser writing [11,12] belong to this group (i.e., all-organic photoresists). Prominent materials such as silicon or gallium arsenide, which fulfill both requirements, are however not suitable for 3D lithographic techniques. Therefore, these materials are usually incorporated by means of chemical vapor deposition (CVD) techniques into suitable templates, which are then removed at a later stage. [14,17] Direct fabrication of 3D PCs in high-index materials seems prefer- able, but requires fabrication in a LbL assembly. [19] Each layer has to be fabricated with a whole set of lithography and etch- ing steps. [3–6] Furthermore, ultra-precise alignment and wafer fusion for each additional layer is required at the cost of fabri- cation speed. Therefore, a technique combining both direct fabrication into a high-index material with the high flexibility, speed, and accuracy of direct laser writing is highly desirable. Here, we present for the first time direct laser written 3D PCs with a PBG made from As 2 S 3 chalcogenide glasses. These materials are amorphous semiconductors with high transpar- ency throughout the near-infrared and infrared spectral region. The index of refraction lies between 2.45 and 2.53, [20] sufficient to open a PBG. In As 2 S 3 the position of the absorp- tion edge is found at 530 nm leaving a broad part of the visi- ble spectrum accessible. Chalcogenide glasses are known for their photoinduced metastabilities, [21] which have led to their widespread use in optical storage media like compact disk ROMs (CDRs) and digital versatile disks (DVDs). [21] Chalco- genide glasses not only change their optical properties under photoexposure, but also their chemical properties. This allows for selective chemical etching, making them suitable candi- dates for lithographic techniques. Therefore, chalcogenide glasses have already been used for the fabrication of 3D PCs, but previous work has been limited to opal infiltration [22–24] or LbL techniques, [5,6] where two- or three-beam holographic COMMUNICATIONS Adv. Mater. 2006, 18, 265–269 © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 265 – [*] Prof. G. A. Ozin, Dr. G. von Freymann, S. Wong Materials Chemistry Research Group, Department of Chemistry University of Toronto 80 St. George Street, Toronto, ON M5S 3H6 (Canada) E-mail: gozin@chem.utoronto.ca Dr. G. von Freymann,S. Wong, M. Deubel, Prof. M. Wegener Institut für Nanotechnologie Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft D-76021 Karlsruhe (Germany) E-mail: freymann@int.fzk.de Dr. G. von Freymann,S. Wong, M. Deubel, Prof. M. Wegener Institut für Angewandte Physik, Universität Karlsruhe (TH) D-76128 Karlsruhe (Germany) Dr. G. von Freymann,S. Wong, M. Deubel, Dr. F. Pérez-Willard, Prof. M. Wegener DFG-Center for Functional Nanostructures (CFN) Universität Karlsruhe (TH) D-76128 Karlsruhe (Germany) Prof. S. John, Dr. G. von Freymann Department of Physics, University of Toronto 60. St. George Street, Toronto, ON M5S 1A7 (Canada) [**] GAO and SJ are Government of Canada Research Chairs. We are grateful to the Natural Sciences and Engineering Research Council of Canada (NSERC) for financial support of this work. We acknowl- edge the support by the Center for Functional Nanostructures (CFN) of the Deutsche Forschungsgemeinschaft (DFG) within project A.1.4. The research of G.v.F. is further supported by DFG- projects FR 1671/2-1 and FR 1671/4-3 (Emmy-Noether program) and that of M.W. by We 1497/9–1.