Site-Selective Deposition of Nanostructured ZnO Thin Films from Solutions Containing Polyvinylpyrrolidone

When soluble zinc salts are hydrolyzed in water, usually elongated micrometer-sized zincite crystals are formed. In this study, polyvinylpyrrolidone (PVP) in a methanolic solution is used as an agent to control the morphology of the deposition product. It prevents crystal growth and yields zinc oxide nanocrystals. Thin films consisting of zinc oxide nanocrystals are formed on self-assembled monolayers (SAMs) of sulfonate-terminated alkylsiloxanes. Patterned films are deposited after local decomposition of the SAM by UV irradiation. The films fabricated from methanolic solutions containing PVP are particularly smooth, uniform and stable. Their thickness is determined by the deposition time and the molar ratio [PVP]:[Zn 2+ ], so that films of arbitrary thickness and nearly constant roughness can be obtained. The crystal grains are oriented preferentially with (001) direction perpendicular to the substrate surface. The films show ultraviolet, orange-red and green-yellow photoluminescence; the latter is quenched by heat treatment. Based on the obtained experimental results, a deposition mechanism is suggested.