Thin film fabrication of nano-porous 12CaO·7Al2O3 crystal and its conversion into transparent conductive films by light illumination |
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Authors: | Yoshitake Toda Masashi MiyakawaKatsuro Hayashi Toshio Kamiya Masahiro HiranoHideo Hosono |
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Affiliation: | a Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan b Hosono Transparent Electro-Active Materials Project, Exploratory Research for Advanced Technology, Japan Science and Technology, KSP C-1232, 3-2-1 Sakato, Takatsu-ku, Kawasaki 213-0012, Japan |
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Abstract: | Thin film fabrication of crystalline 12CaO·7Al2O3 (C12A7) with zeolitic structure was examined, and their electrical and optical properties were measured. Polycrystalline thin films were prepared by post-annealing of amorphous films in oxygen atmosphere at temperatures above 800 °C. Choice of substrates was crucial for obtaining single-phase thin films. Although various oxide substrates (single crystals of Al2O3, Y-stabilized ZrO2, MgO and silica glass) were examined, single-phase films were obtained only for MgO substrates and the other substrates reacted with the CaO component in the films during post-annealing. The optical band gap of C12A7 was evaluated to be 5.9 eV. Hydride ions were incorporated into the film by a thermal treatment in a hydrogen atmosphere at 1200 °C. The resulting transparent thin films were converted into transparent persistent electronic conductors exhibiting an electrical conductivity 6.2×10−1 S cm−1 at 300 K by ultraviolet light illumination. This is the first example of transparent conductive thin film in which conductive areas can be patterned directly by light. |
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Keywords: | Calcium aluminate Transparent conductive oxide Light-induced conductor conversion |
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