SYNTHESIS OF COBALT OXIDE AND TIN OXIDE FILMS BY THE SOL GEL PROCESS:SURFACE AND OPTICAL PROPERTIES

摘要

Thin films of cobalt oxide and tin oxide were prepared by the dipping sol-gel method upon glass, SS and nickeled SS substrates. The aim is to build selective photothermal coatings for medium temperature applications by superimposing tin oxide films upon those of cobalt oxide. Spectral reflectance measurements in both the UV-Vis and the infrared ranges were used to characterize the relevant properties (absorptance and emittance). Also, atomic force microscopy and XPS measurements were made on the films. The XPS data tell us that several phases of cobalt oxide coexist (Co_3O_4, Co_2O_3) in the films under the preparation conditions used. Besides, large amounts of carbon were detected in several configurations: both as graphite particles and carbon bonded to metallic and oxygen atoms. Regarding the tin oxide films, both SnO and SnO_2 phases were detected besides carbon particles as in cobalt oxide. AFM studies made on samples upon glass substrates lead us to conclude that the dipping method yields surface morphologies with relatively low roughness, i.e., smooth film surfaces. By observing several tandem structures, it was found that placing a tin oxide coating upon a cobalt oxide film slightly improves the whole coating selectivity, but adding besides a nickel coating on the SS substrate, improves even more such selectivity value.