Modification of Semi-metal Oxide and Metal Oxide Powders by Atomic Layer Deposition of Thin Films

This work describes two methods of modifying, and the subsequent characterizing of, oxide nanopowders. The first method, atomic layer deposition, or ALD, is a series of surface-limited reactions that are repeated to deposit a thin, inorganic film on the surface of the nanopowder. Deposition of a thin film is a useful method to alter the surface properties of a material while retaining its bulk properties. Part of this thesis concerns the understanding of the growth mechanism of thin film titanium nitride (a material known for thermal and chemical stability as well as electronic conductivity) on silica through the ALD process. In situ IR spectroscopy was used to observe the changes that occur to the surface in each ALD half-cycle. Previous research has dealt with titanium nitride growth on planar silica substrates, but this was the first time that such growth was studied on a silica nanopowder. Silica is a commonly-used thin film substrate because it can be easily monitored with infrared (IR) spectroscopy. The surface of another nanopowder, lithium titanate spinel (LTS), was studied to determine its suitability as a substrate for thin film growth. Interest exists in LTS for its use as a lithium-ion battery anode. However, a potential disadvantage of this material is its poor electrical contact with the anodic current collector. Several hundred layers of a titanium nitride thin film were deposited on LTS to determine if this would improve the material’s performance as a lithium-ion battery anode. The material was fabricated into a test cell and evaluated against an unmodified LTS cell for comparison. Another modification technique is to use supercritical carbon dioxide (sc-CO2) to dissolve reactants and deposit them on a surface. This technique can be used at temperatures considerably lower than those for ALD. By first depositing a nonvolatile base dissolved in sc-CO2, organosilanes may be catalytically attached to a substrate otherwise not possible at low temperatures