Electrical properties and gas response in alternate layer-by-layer films of copper phthalocyanine dyes

Alternate layer-by-layer (LbL) films were fabricated using two kinds of copper phthalocyanine (CuPc) dyes and the electrical properties due to NO ₂ gas adsorption were investigated. Water-soluble CuPc dyes, that is, cationic Alcian blue, pyridine variant (AB) and anionic copper phthalocyanine-3,4′,4″,4″′-tetrasulfonic acid, tetrasodium salt (CuPcTs) were used for the alternate LbL films. Successive depositions of the CuPc alternate LbL films were confirmed using UV-visible absorption and ellipsometry measurements. The average thicknesses of the AB and CuPcTs monolayers were estimated to be 0.7 nm and 0.4 nm, respectively. The fundamental electrical properties were examined for the CuPc alternate LbL films with Au gap electrodes and the properties in the direction parallel to the surfaces of the LbL films were measured. The conduction currents were considered to be dominated by hopping conduction. The response to NO₂ gas was also measured and the large increase in conduction currents due to NO ₂ gas adsorption was observed. The magnitude of the conduction current after 30min exposure to 100 ppm NO₂ gas was 10 ⁴-10⁴ times larger than that in N₂ gas.