Low-temperature crystal growth of aluminium-doped zinc oxide nanoparticles in a melted viscous liquid of alkylammonium nitrates for fabrication of their transparent crystal films

We fabricated conductive Al-doped ZnO (AZO) films on glass substrates via a simple drop-coating process of alcoholic dispersion solutions of AZO nanoparticles less than 10 nm in size, which were prepared by hydrolysis reactions of Zn(NO3)(2)center dot 6H(2)O and Al(NO3)(3)center dot 9H(2)O with an excess amount of isopropylamine. After heating at 150 degrees C to completely remove the alcoholic solvents, a by-product that remained, iso-propylammonium nitrate, was melted and functioned as a low-temperature medium for the AZO nanoparticles. Even in the low-temperature medium at 150 degrees C, the AZO nanoparticles could readily grow up to similar to 100 nm, based on Ostwald ripening as a plausible crystal growth mechanism. The medium was evaporated at 240 degrees C, and a highly transparent AZO film appeared on the glass with a transmittance of similar to 83% in the visible region. The electrical conductivity of the AZO films was improved by sintering at 450 degrees C and post-annealing at 450 degrees C in a stream of a mixed gas of N-2 and H-2. The resistivity of the AZO film reached 4.3 x 10(-2) Omega cm in an Al/Zn molar ratio of 2.0%.