EFFECTS OF HEAT-TREATMENT ON OXIDATIVE GAS-ADSORPTION FOR LEAD NAPHTHALOCYANINE THIN-FILMS

Thin films of Pb-naphthalocyanine (330 nm thick) prepared by vacuum su blimation were heat-treated at 250 degrees C in air atmosphere for var ious periods. As estimated from the conductance versus temperature cor relations, the adsorption of NO2 and O-2 on the films at room temperat ure, which was only slight after the heat-treatment for 30 min, increa sed very remarkably with prolonging heat-treatment time up to 10 h. Th e 10 h treated him was found to exhibit completely reversible changes in conductance upon exposure to 5 ppm NO2 in N-2 at 210 degrees C. Vis ible light absorption spectra indicated a change from a largely amorph ous state of the as-deposited film to a largely crystalline state of t he film treated for 2 h. X-Ray diffraction analysis showed that the as -deposited film consisted of N-oriented particles, while the proportio n of P-oriented particles increased with prolonging treatment time up to 10 h. The enhancement of gas adsorption was thus attributed to the reconstruction of films during the heat treatment. It appears that a r econstruction-assisted increase in porosity not only facilitates gas d iffusion inside the film, but also increases the number of Pb-naphthal ocyanine molecules accessible NO2 or O-2. (C) 1997 Elsevier Science S. A.