Preparation of CuO thin films on porous BaTiO₃ by self-assembled multibilayer film formation and application as a CO₂ sensor

Preparation of CuO thin films by decomposition of self-assembled multibilayer films as a molecular template was investigated. Furthermore, the CO₂ sensing property of the resultant CuO thin films on a porous BaTiO₃ was investigated as a capacitive type sensor. Self-assembled bilayer films of a few 1000 layers thickness can be readily obtained by casting an aqueous suspension composed of dimethyldihexadecylammoniun bromide (DC1-16), Cu(CH₃CO₂)₂, hexadecylethylenediamine and poly(vinyl alcohol). Divalent copper ions (Cu²⁺) which are associated with two hexadecylethylenediamine molecules were arranged in the hydrophobic layer of the multibilayer film. Rapid heating to the combustion temperature of DC1-16 was desirable for removing organic molecules in the multibilayer template. Thin films of CuO can be obtained by calcination at temperatures higher than 573 K. The resultant CuO thin films were porous and consisted of fine particles. The capacitance of CuO thin films prepared from self-assembled multibilayer films as a molecular template on the BaTiO₃ porous substrate exhibited a high sensitivity to CO₂, which is twice that of a conventional mixed oxide capacitor of CuO-BaTiO₃. The capacitance of CuO thin films on BaTiO₃ increases with increasing CO₂ concentration in the range from 100 ppm to 50% at 873 K. Consequently, it is concluded that CuO thin films on BaTiO₃ were appropriate capacitive type CO₂ sensors.