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 °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 °C), whereas on either (0001) or (11̄02) 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.
Proton exchanged samples of LiNbO, have been profiled by micro-Raman spectroscopy, secondary ion mass spectroscopy, Rutherford backscattering channeling, and by x-ray diffraction (XRD). Following proton exchange (PE) there are two different phases in addition to pure LiNbO, detected by XRD. After successive annealing steps the outermost phase disappears and an interfacial region forms progressively between PE and LiNbO,. Specific vibrational bands are correlated to electro-optic and nonlinear optical properties of the system, and the recovery of these properties upon amrealing is correlated to chemical bonding changes.
The processes of formation and crystallization of thin films of SrTiO3 prepared by the method of metallo-organic decomposition have been studied with particular emphasis on the relationship between the thermal decomposition of the metallo-organic precursors and the eventual epitaxial alignment of the crystallized films. The films are deposited by spin coating onto single-crystalline silicon and SrTiO3 substrates, pyrolyzed on a hot plate at temperatures ranging from 200 to 450 °C, and subsequently heat treated in a quartz tube furnace at temperatures ranging from 300 to 1200 °C. Heat treatment at temperatures up to 450–500 °C results in the evaporation of solvents and other organic addenda, thermal decomposition of the metallo-organic (primarily metal-carboxylates) precursors, and formation of a carbonate species. This carbonate appears to be an intermediate phase in the reaction of SrCO3 and TiO2 to form SrTiO3. Relevant to this work is the fact that the carbonate species exhibits diffraction lines, indicating the formation of grains that can serve as seeds for the nucleation and growth of randomly oriented SrTiO3 crystallites, thereby leading to a polycrystalline film. Deposition on silicon substrates indeed results in the formation of polycrystalline SrTiO3. However, when the precursor solution is deposited on single-crystalline SrTiO3 substrates, the crystallization process involves a competition between two mechanisms: the random nucleation and growth of crystallites just described, and layer-by-layer solid phase epitaxy. Epitaxial alignment on SrTiO3 substrates can be achieved when the samples are heat treated at temperatures of 1100–1200 °C or at temperatures as low as 600–650 °C when the substrate is heated to about 1100 °C before spin coating.
Thin films of TiO2 were grown on SrTiO3 and Al2O3 using Ti(OC3H7)4 in the absence of any external oxygen source such as H2O or O2. On SrTiO3 (001), epitaxial anatase (001) formed even at temperatures (800 °C) above the anatase to rutile phase transition temperature. In situ reflection high energy electron diffraction (RHEED) was used to monitor structural evolution during growth, and the films were further characterized by Auger electron spectroscopy (AES), transmission electron microscopy (TEM), and x-ray diffraction. Reaction kinetics were monitored using mass spectrometry, and these results, combined with temperature-programmed reaction spectroscopy, gave some insight into the deposition process.
We report the results of Tm3+ doped Ba–Y–Yb–F thin film planar waveguides in glassy form, which produced red, green, blue, and ultraviolet upconverted luminescence when pumped by infrared radiation at λ=960 nm. The films of nominal composition BaYYbF8 doped with 1% Tm have been deposited with both thermal and e-beam evaporation techniques on substrates of fused silica, Si, and GaAs. Planar waveguiding was demonstrated for the films deposited on fused silica. Optimal deposition conditions with respect to the ability of the films to produce upconverted luminescence and low propagation loss are discussed.
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