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Titanium dioxide atomic layer deposition (ALD) is shown to proceed selectively on oxidized surfaces with minimal deposition on hydrogen-terminated silicon using titanium tetrachloride (TiCl4) and titanium tetra-isopropoxide [Ti(OCH(CH3)2)4, TTIP] precursors. Ex situ x-ray photoelectron spectroscopy shows a more rapid ALD nucleation rate on both Si-OH and Si-H surfaces when water is the oxygen source. Eliminating water delays the oxidation of the hydrogen-terminated silicon, thereby impeding TiO2 film growth. For deposition at 170°C, the authors achieve ~2 nm of TiO2 on SiO2 before substantial growth takes place on Si-H. On both Si-H and Si-OH, the surface reactions proceed during the first few TiCl4/TTIP ALD exposure steps where the resulting products act to impede subsequent growth, especially on Si-H surfaces. Insight from this work helps expand understanding of "inherent" substrate selective ALD, where native differences in substrate surface reaction chemistry are used to promote desired selective-area growth. [ABSTRACT FROM AUTHOR]

Conformal atomic layer deposition (ALD) of Al2O3 and TiO2 thin films on Kevlar®, poly(p-phenylene terephthalamide) (PPTA) fibers at 50 and 100 °C affects the fiber cut resistance. Systematic studies of ALD coatings between 10 to 400 A thick formed at 50 and 100 °C revealed excellent conformality, and trends in cutting performance depended on materials and process details. Å 50 Å/50 Å TiO2/Al2O3 bilayer formed at 50 °C increased cut resistance of PPTA by 30% compared to untreated fiber materials. In situ infrared analysis shows that trimethylaluminum (TMA) Al2O3 precursor reacts sub-surface with PPTA and tends to degraded mechanical performance. The TiCl4 TiO2 precursor reacts to form a barrier that limits TMA/PPTA interactions, allowing a harder Al2O3 layer to form on top of TiO2. The thin ALD coatings do not substantially affect durability, flexibility, or weight of the PPTA, making ALD a potentially viable means to enhance the protective properties of Kevlar and other polymer fiber systems. [ABSTRACT FROM AUTHOR]