Metal oxide coatings can improve the electrochemical stability of cathodes and hence, their cycle-life in rechargeable batteries. However, such coatings often impose an additional electrical and ionic transport resistance to cathode surfaces leading to poor charge-discharge capacity at high C-rates. Here, a mixed oxide (Al2O3)1-x(Ga2O3)x alloy coating, prepared via atomic layer deposition (ALD), on Li[Ni0.5Mn0.3Co0.2]O2 (NMC) cathodes is developed that has increased electron conductivity and demonstrated an improved rate performance in comparison to uncoated NMC. A "co-pulsing" ALD technique was used which allows intimate and controlled ternary mixing of deposited film to obtain nanometer-thick mixed oxide coatings. Co-pulsing allows for independent control over film composition and thickness in contrast to separate sequential pulsing of the metal sources. (Al2O3)1-x(Ga2O3)x alloy coatings were demonstrated to improve the cycle life of the battery. Cycle tests show that increasing Al-content in alloy coatings increases capacity retention; whereas a mixture of compositions near (Al2O3)0.5(Ga2O3)0.5 was found to produce the optimal rate performance.

TiO2-coated Co/C catalysts prepared by atomic layer deposition (ALD) were used to study the effect of TiO2 overcoating on a Co/C catalyst for electrochemical water oxidation. The Co/C catalyst with a thin-layer overcoating of TiO2 (ALD­(TiO2)-Co/C) demonstrated 2.5 times higher turnover frequency (TOF) than the Co/C catalyst for the reaction. The TOF of the ALD­(TiO2)-Co/C catalyst increased when the ALD­(TiO2) coating cycle number was increased from 5 to 60. In addition, the stability of the 60 cycle ALD­(TiO2)-Co/C catalyst was enhanced compared to the Co/C catalyst. This work shows how the ALD synthesis technique can be used to improve the catalytic activity and stability of nonprecious-metal-based catalysts like Co/C for electrochemical water oxidation.

Integration of emerging complex-oxide compounds into sophisticated nanoscale single-crystal geometries faces significant challenges arising from the kinetics of vapor-phase thin-film epitaxial growth. A comparison of the crystallization of the model perovskite SrTiO (STO) on (001) STO and oxidized (001) Si substrates indicates that there is a viable alternative route that can yield three-dimensional epitaxial synthesis, an approach in which STO is crystallized from an amorphous thin film by postdeposition annealing. The crystallization of amorphous STO on single-crystal (001) STO substrates occurs via solid-phase epitaxy (SPE), without nucleation and with a temperature-dependent amorphous/crystalline interface velocity. In comparison, the crystallization of STO on SiO/(001) Si substrates requires nucleation, resulting in a polycrystalline film with crystal sizes on the order of 10 nm. A comparison of the temperature dependence of the nucleation and growth processes for these two substrates indicates that it will be possible to create crystalline STO materials using low-temperature crystallization from a crystalline seed, even in the presence of interfaces with other materials. These processes provide a potential route for the formation of single crystals with intricate three-dimensional nanoscale geometries.

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The growth and properties of alloys in the alternative quaternary alloy system GaAs1−y−zPyBiz were explored. This materials system allows simultaneous and independent tuning of lattice constant and band gap energy, Eg, over a wide range for potential near- and mid-infrared optoelectronic applications by adjusting y and z in GaAs1−y−zPyBiz. Highly tensile-strained, pseudomorphic films of GaAs1−yPy with a lattice mismatch strain of ∼1.2% served as the host for the subsequent addition of Bi. Lattice-matched alloy materials to GaAs were generated by holding y ∼ 3.3z in GaAs1−y−zPyBiz. Epitaxial films with both high Bi content, z ∼ 0.0854, and a smooth morphology were realized with measured band gap energies as low as 1.11–1.01 eV, lattice-matched to GaAs substrates. Density functional theory calculations are used to provide a predictive model for the band gap of GaAs1−y−zPyBiz lattice-matched to GaAs.

We report the use of two Raman signatures, the Bi-induced longitudinal-optical-plasmon-coupled (LOPC) mode and the GaAs Fröhlich scattering intensity, present in nominally undoped (100) GaAs1−yBiy to predict the 300K photoluminescence intensity and Bi composition (y) in GaAs1−yBiy. The LOPC mode is used to calculate the hole concentration in GaAs1−yBiy epitaxial layers. A linear relationship between hole concentration and photoluminescence intensity is found for a range of samples grown at various temperatures and growth rates. In addition, the composition (y) of Bi in GaAs1−yBiy is also found to be linearly related to the GaAs Fröhlich scattering intensity.

W(CO) 6 and H 2 O 2 were used in an atomic layer deposition (ALD)-like process to grow thin WO x films onto TiO 2 powders in a fluidized bed reactor. Carbonyl precursors are not widely used in this application, so that deviations from an ideal ALD process, previously not examined with W(CO) 6 , were identified. The resulting WO x films were a result of both ALD-like and chemical vapor deposition-based growth modes. A chemical reaction mechanism incorporating a combination of these two growth modes was inferred. As the move to expand the range of ALD precursors meets with the desire to scale up these processes, the simultaneous appearance of both these growth modes is likely to become more and more common, and so understanding the interaction of these two types of surface reactions is key to progress in the field. The films were observed to inhibit the anatase-to-rutile phase transformation in the TiO 2 powders upon high temperature annealing, while crystallization of the amorphous WO 3 was also not observed. Changes in the local bonding within the WO 3 were observed and associated with changes in the structural nature of the film and its interface to the substrate.