Chemical vapor deposition (CVD) of films and coatings involves the chemical reaction of gases on or near a substrate surface. This deposition method can produce coatings with tightly controlled dimensions and novel structures. Furthermore, the non-line-of-sight-deposition capability of CVD facilitates the coating of complex-shaped mechanical components. Atomic layer deposition (ALD) is also a chemical gas phase thin film deposition technique, but unlike CVD, it utilizes ''self-limiting'' surface adsorption reactions (chemisorption) to control the thickness of deposited films. This article provides an overview of CVD and ALD, discusses some of their fundamental and practical aspects, and examines their advantages and limitations versus other vapor processing techniques such as physical vapor deposition in regard to coatings for mechanical applications. Finally, site-specific cross-sectional transmission electron microscopy inside the wear track of an ALD ZnO/ZrO 2 8 bilayers nanolaminate coating determined the mechanisms that control the friction and wear.

Zinc oxide (ZnO) thin films were synthesized by pulsed laser deposition (PLD) and atomic layer deposition (ALD) at 100 8C on glass, and their structural, electrical, and optical properties were compared before and after 300 8C post-deposition annealing in argon, vacuum, and air. The room temperature photoluminescence (PL) of the ALD films grown at 100 8C was characterized by a broad, defect emission band peaking at 605 nm, which decreased in intensity after annealing. In contrast, the PL of the PLD films was dominated by 385 nm emission, and luminescence at 425 nm was also observed. The PL intensity of these films increased after annealing. The data suggest that overall electrical and photoluminescent characteristics of the ALD films are determined by the relative zinc interstitial and oxygen vacancy concentrations which vary with annealing treatment. The electro-optical properties of the PLD films are determined by Zn interstitials. The potential impact of the observed absorption and emission bands on optoelectronic applications is discussed.

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