Preparation and NO2 gas properties of layer-by-layer alternate films of copper phthalocyanine derivatives

Copper phthalocyanine (CuPc) alternate layer-by-layer (LbL) films were fabricated and the electrical properties due to NO₂ gas adsorption were investigated. Water-soluble CuPc, 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 fabrication of the alternate LbL films. UV-visible absorption and ellipsometry measurements were carried out and successive depositions of the CuPc alternate LbL films were confirmed. The average thicknesses of the AB and CuPcTs monolayers were estimated to be about 0.7 and 0.4 nm, respectively. The fundamental electrical properties were investigated 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 investigated. The response to NO₂ gas was also measured and the large increase of conduction currents due to NO₂ gas adsorption was observed. The magnitude of the conduction current after 30 min exposure to 100 ppm NO₂ gas was 10³-10⁴ times larger than that in N₂ gas. Fast response was observed for the thin LbL films.