Fabricating high refractive index titanium dioxide film using electron beam evaporation for all-dielectric metasurfaces
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Research Letters
Fabricating high refractive index titanium dioxide film using electron beam evaporation for all-dielectric metasurfaces Ning An, Integrated Nanoscience Laboratory, Department of Material Science and Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China; Integrated Nanoscience Laboratory, Department of Electronic and Information Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China Kaiyang Wang, Integrated Nanoscience Laboratory, Department of Electronic and Information Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China Haohan Wei, Integrated Nanoscience Laboratory, Department of Material Science and Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China Qinghai Song, Integrated Nanoscience Laboratory, Department of Electronic and Information Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China Shumin Xiao, Integrated Nanoscience Laboratory, Department of Material Science and Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China Address all correspondence to Qinghai Song and Shumin Xiao at [email protected], [email protected] (Received 17 November 2015; accepted 17 March 2016)
Abstract Transparent high refractive index materials are of the central importance for the development of metasurface in visible range. Titanium dioxide (TiO2) has been considered as a perfect candidate due to its wide band gap and high refractive index. However, till now, it is still quite challenging to fabricate high-quality TiO2 films with high refractive indices and low losses. Here we demonstrate the fabrication of high-quality TiO2 film using an electron-beam evaporation method. We show that the post-annealing conditions play key roles in the microstructure crystallographic and the optical refractive index of the TiO2 films. A predominately oriented TiO2 film has been achieved by annealing at 700 °C in oxygen ambient. The refractive index is as high as 2.4, and the corresponding loss is negligible at 632 nm. Further studies on dielectric antennas show that our TiO2 film can be an ideal platform to fabricate metasurface in visible frequency range. We believe that our research will be important for the advances of all-dielectric metasurfaces.
Introduction Metasurface, a novel type of two-dimensional (2D) metamaterial, has gained increasing attention due to the unique abilities in light manipulation.[1] In contrast to the phase changes via propagations in conventional systems, metasurface can introduce abrupt changes on both phase and amplitudes of waves via arrays of optical resonators.[2] In this sense, the dependence of propagation effects can be simply released and thus a number of novel 2D devices have been proposed and experimentally demonstrated in past few years, e.g. anomalous reflection/ refraction.[3,4] surface-wave coupling,[5] high-resolution optical hologram,[6
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