Novel metal organic chemical vapor deposition routes to solid state ionic compounds

Four new chemical vapor deposition routes to thin film solid state ionic compounds have been discovered. Tetraallyl tungsten and tris (methylvinylketone) tungsten, two novel organometallic precursors were used to deposit tungsten oxide films. These films showed unique properties including lower density (ca. 4.3 g/cm3), fast coloration times (<1s at 1.0 V vs Ag/AgCl) and low coloration efficiency (25 cm2/C). These electrochemical properties are believed to be related to the low density as determined by Rutherford Backscattering Spectrometry (RBS). As-deposited films contained between 7 and 25 at.% carbon, and contained a mixture of the monoclinic and triclinic phases as determined by powder X-ray diffraction measurements. Two new lithium precursors were developed for synthesis of ion conducting and secondary cathode material thin films. Lithium triethyl carboxide was used to deposit lithium cobalt oxide thin films in conjunction with tris (tetramethylheptanedionato) cobalt. To our knowledge, this is the first example of a practical lithium precursor which has sufficient volatility (100 mT at 130°C) and is not air sensitive. X-ray diffraction data of these films indicate the presence of a lithium cobalt oxide system, although the phase composition needs further characterization. Thermogravimetric analysis of the lithium precursor indicates a gradual vapor pressure curve and thus the potential to fine tune vapor transport rates according to the desired properties of the films. Lithium hexamethyldisilazide was used to deposit ion conducting lithium silicate films. The precursor was found to decompose upon transport under hot wall conditions, and an optimization of delivery of silicon and lithium remains under investigation. In an oxygen environment, Li/Si ratios were typically 0.1 in the films, compared to a value of 0.5 in the precursor. A precursor decomposition mechanism was inferred from mass spectral data and decomposition product analysis, which indicated the tendency for cleavage of the Si-N bond and formation of polydimethyl siloxane species. Ionic conductivities of 5*10--8S/cm were achieved. Further work is required to optimize delivery of this precursor, including changing reactor geometry and energetics.