Composite Co3O4/TiO2 nanotube arrays (NTs) were fabricated via atomic layer deposition (ALD) of Co3O4 thin film onto well-aligned anodized TiO2 NTs. The microscopic morphology, composition, and interfacial plane of the composite structure were characterized by scanning electron microscopy, energy dispersion mapping, X-ray photoelectron spectra, and high-resolution transmission electron microscopy. It was shown that the ultrathin Co3O4 film uniformly coat onto the inner wall of the high aspect ratio (>100:1) TiO2 NTs with film thickness precisely controlled by the number of ALD deposition cycles. The composite structure with ∼4 nm Co3O4 coating revealed optimal photoelectrochemical (PEC) performance in the visible-light range (λ > 420 nm). The photocurrent density reaches as high as 90.4 μA/cm(2), which is ∼14 times that of the pristine TiO2 NTs and 3 times that of the impregnation method. The enhanced PEC performance could be attributed to the finely controlled Co3O4 coating layer that enhances the visible-light absorption, maintains large specific surface area to the electrolyte interface, and facilitates the charge transfer.

SiC fiber-reinforced metal matrix composite is an interesting material for aerospace industry because of its excellent properties. However, these properties are greatly influenced by fiber microstructure and thermal residual stresses introduced by the preparation of the composites. Due to complicated preparation technology, microstructure and thermal stress along SiC fiber radius varies, which makes characterization difficult. Raman spectroscopy is a non-destructive technique which provides information, at micrometer scale, on the phase composition and the crystalline state (structure and texture) of materials. Line scanning was used to assess microstructure along SiC fiber radius embedded in Ti64. The SiC coating is subdivided into three concentric parts across the fiber diameter, according to the differences in intensity and width of SiC transverse optical phonon (TO) band. Part 2 is considered to be a buffer zone connecting Part 1 and Part 3 with different deposition conditions, respectively. Amorphous Si is detected throughout fiber radius, while crystalline Si is only detected in the outer part. Thermal residual stress along fiber radius in the composite was calculated by using SiC TO band shifts with a bare fiber as reference. A cylindrical model was also used to compare with the stress data obtained from Raman shift.

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Ultrathin cobalt oxide (CoO x ) films (<10 nm) have been prepared on both planar and three dimensional substrates by atomic layer deposition (ALD) using Co(Cp) 2 and O 3 as precursors. The optimal temperature window was 150~250 °C with a saturated growth rate of ~0.37 Å/cycle. While the main composition of the thicker film consists of Co 3 O 4 as verified by Raman spectrum, the initial few layers grown by ALD show a mixture of Co 3 O 4 and CoO as revealed by X-ray photoelectron spectrum (XPS). The surface morphology of the film is greatly influenced by the deposition temperature as atomic force microscopy (AFM) and high-resolution transmission electron microscope (HR-TEM) characterization show the formation of crystalline islands and uneven coating on porous structure at high temperatures, while smooth and uniform coating can be obtained at lower temperatures. The role of nucleation sites and crystallization speed on film morphology is discussed. Furthermore, we show that tuning of deposition temperatures could lead to improved catalytic activities as demonstrated in the CO oxidation light off test.Many methods have been developed for thin film fabrication, including spray pyrolysis, chemical vapor deposition (CVD), physical vapor deposition (PVD), pulse laser deposition (PLD), and atomic layer deposition (ALD) 14-20 . Among these methods, ALD attracts great interest due to its self-limiting nature and exceptional coating conformality on three dimensional structures. While ALD generally exhibit a linear growth in the steady state, its growth behavior during the initial nucleation period could deviate considerably from the ideal layer-by-layer growth model, due to the complexity of nucleation and crystallinity of the deposited film 21-24 . While ALD growth of Co 3 O 4 film on silicon-based substrates has been reported 18, 25, 26 , the ultrathin film characteristics during the initial growth stage has rarely reported in previous studies. Since the difference in the ultrathin film's thickness, composition, or morphology could lead to considerable changes in system properties 27, 28 , it is thus of essential importance to understand the growth behavior of ALD grown cobalt oxide at the initial growth stage for the further optimization of CoO x ultrathin films.We report here a comprehensive study on the growth behavior of CoO x ultrathin films (<10 nm) by ALD using Co(Cp) 2 and O 3 as precursors focusing on their composition and surface morphology. The coating conformality of CoO x was evaluated on both planar and three dimensional substrates. At low deposition temperature of 150 °C, films are uniform and smooth, while island and uneven films are obtained after raising deposition temperature to 250 °C. The ultrathin film's composition is a mixture of CoO and Co 3 O 4 , which is different from its steady state counterpart in the bulk film. The obtained films show good CO oxidation catalytic (284.6 eV) peak position. Surface morphology of freshly prepared samples was measured by a tapping mode atomic force microscopy (AF...