A Study on Functional Multi-Layered Ceramic Films and their Electronic States

Application of various fabrication techniques of thin films to several ceramic materials clarified the characteristics and the disadvantages of each technique ; ion plating, sputtering, plasma spraying, spray pyrolysis, slurry coating, slip casting, chemical vapor deposition, and sol-gel process. Lamination of the ceramic materials revealed several problems on fabrication of multi-layered ceramic thin films. The physical properties of the films obtained by these techniques were significantly different : density, porosity, and surface roughness ; deposition rate ; formed crystalline phases and homogeneity of the components. These properties were controlled by selecting an appropriate fabrication technique. It should be particularly noted that thin films with considerably higher quality than those from variousdry processes were successfully fabricated by the wet processes such as slurry coating and slip casting when the size and shape of the material particles, the concentrations and the additives of the wet mixtures, and the sintering procedures were properly chosen. Moreover, completely dense thin films of stabilized zirconia were prepared at the substantially lower sintering temperature of 1000ﾟC by spray pyrolysis using the solutions of the corresponding metal acetylacetonates as the starting materials. Oxide thin films of 1-2 mu m thickness were fabricated by the ion plating technique and shown to be highly resistant against oxidation or 0 reduction and were not affected even at the temperatures higher than 1000ﾟC. It was revealed that the high temperature treatments during the fabrication of the films or application to the high temperature technologies strongly require that the reactivity between the layered ceramics should be negligible, as well as the thermal expansion coefficient and the thermal shrinkage coefficient of the layers should be similar. Transparent SiC thin films with high electrical resistivity were prepared by the sputtering technique. The optical band gap of the films was varied by controlling the partial pressure of CH_4 in the gas phase during the sputtering. Silica thin films with highly dispersed cobalt porphine obtained by the sol-gel process exhibited the changes in their absorption spectrum specific to nitrogen monoxide. A highly sensitive fiber-type sensor for NO was fabricated by coating the film on the cross section of an optical fiber. Highly porous membranes of BA-AI mixed oxides with micropores of 10-20 nm were prepared from the corresponding metal alkoxides, and found to have large permeation coefficient of hydrogen. It was revealed that the permeation of hydrogen was accelerated by dispersing platinum metals into the membranes.