Thin film fabrication of nano-porous 12CaO·7Al 2O 3 crystal and its conversion into transparent conductive films by light illumination

Abstract

Thin film fabrication of crystalline 12CaO·7Al 2O 3 (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 Al 2O 3, Y-stabilized ZrO 2, 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.