STRUCTURAL AND PHOTOELECTROCHEMICAL PROPERTIES OF PLASMA DEPOSITED TITANIUM DIOXIDE.

摘要

A glow discharge was used to enhance the reaction rate between titanium tetrachloride and oxygen to deposit thin films of titanium dioxide. Structural, optical, electronic, and photoelectrochemical properties of the films were examined as functions of deposition parameters: temperature (ambient to 700 degrees C), substrate material (Si, sapphire, glass, quartz, NaCl, and Ti), and radio frequency power (5 to 200 watts).; Film structure was studied with x-ray diffraction, SEM, and TEM. Films deposited onto glass substrates were amorphous for temperatures less than 300 degrees C, anatase at 300 and 400 degrees C, a mixture of anatase and rutile at 500 degrees C, and only rutile at 600 degrees C and above. Films deposited on the other substrates showed similar behavior, but the temperatures differed for each substrate. The largest crystallites were obtained using low rf powers (5 to 10 watts) and sapphire substrates.; ESCA and AES showed chlorine present in films deposited at 200 degrees C and below. Chlorine was undetectable in films deposited at or above 400 degrees C. The presence of chlorine in the films affected the electronic properties by acting as an electron acceptor. Dielectric constants for the films ranged from 25 to 166.; Plasma deposited titanium dioxide photoanodes were fabricated with quantum efficiencies of 60 to 80% for the photoelectrolysis of water. Deposited anodes had higher quantum efficiencies than thermally grown anodes prepared in this study. The high long - wavelength photoresponse for the deposited films resulted from their large, well - oriented grain structure. Chlorine exposure of the deposited films during the deposition may have contributed to the superior short - wavelength photoresponse. This is supported by the observed increase in short wavelength photoresponse for the thermally grown photoanodes after being annealed in a chlorine - helium mixture.