ULTRAHIGH-VACUUM METALORGANIC CHEMICAL-VAPOR-DEPOSITION GROWTH AND IN-SITU CHARACTERIZATION OF EPITAXIAL TIO2 FILMS

In a two-chamber ultrahigh vacuum system, epitaxial TiO2 thin films have been deposited by metalorganic chemical vapor deposition on single crystal oxide substrates over a temperature range of 250-800-degrees-C, using titanium (IV) isopropoxide as the precursor. During the initial stage of epitaxial film deposition, the growing surface quickly planarized and the film's orientations was determined by the substrate structure. This substrate influence is manifested in the growth of anatase (the low temperature phase of TiO2) on (001) SrTiO3, at high deposition temperatures (800-degrees-C), whereas on either (0001) or (1102BAR) Al2O3 sapphire, epitaxial rutile (the high temperature phase) is formed. In situ Auger electron spectroscopy analyses, before and after growth, revealed a film composition identical to that of a bulk TiO2 standard. No carbon contamination was detected in films grown throughout the deposition temperature range. The decomposition mechanism of this precursor that leads to the absence of incorporated carbon in the deposited film is discussed. X-ray diffraction confirmed the film crystallinity and the structural orientation between the film and substrate. Cross-section transmission electron microscopy showed an abrupt interface between the film and substrate. High tilt angle scanning electron microscopy revealed that the surface of the films became increasingly smooth with increasing growth temperatures. Conditioning the substrate surface at high temperatures in an O2 environment improved the structural quality and surface smoothness of the subsequently deposited films.