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Titanium dioxide (TiO2), tin dioxide (SnO2), and heterostructured TiO2/SnO2 nanotube (NT) arrays have been fabricated by template-assisted atomic-layer deposition (ALD) for use as anodes in a lithium-ion battery (LIB). TiO2 NT arrays with 8 nm thick walls showed higher capacity (≈250 mA h g−1 after the 50th cycle at a rate of C/10) than the typical theoretical capacity of bulk TiO2 and a radically improved capacity retention property upon cycling. SnO2 NT arrays with different wall thicknesses (8, 10, 13, and 20 nm) were also fabricated and their electrochemical performances were measured. All of the SnO2 NT arrays showed substantially higher initial irreversible capacity and higher reversible capacity than those of bulk TiO2. Thinner walls of the SnO2 NTs result in better capacity retention. Heterotubular structures of TiO2 (5 nm)/SnO2 (10 nm)/TiO2 (5 nm) were successfully fabricated, and displayed a sufficiently high capacity (≈300 mA h g−1 after 50 cycles) with exceptionally improved cycling performance up to the 50th cycle. [ABSTRACT FROM AUTHOR]

Bothenhancing the excitons’ lifetime and ingeniously controllingthe spatial charge transfer are the key to the realization of efficientlyphotocatalytic and artificially photosynthetic devices. Nanostructuredmetal/metal-oxide interfaces often exhibit improved energy conversionefficiency. Understanding the surface potential changes of nano-objectsunder light illumination is crucial in photoelectrochemical cells.Under ultraviolet (UV) illumination, here, we directly observed thecharge separation phenomena at the Au-nanoparticle/TiO2-nanotube interfaces by using Kelvin probe force microscopy. Thesurface potential maps of TiO2nanotubes with and withoutAu nanoparticles were compared on the effect of different substrates.We observed that in a steady state, approximately 0.3 electron perAu particle of about 4 nm in diameter is effectively charged and consequentlyscreens the surface potential of the underlying TiO2nanotubes.Our observations should help design improved photoelectrochemicaldevices for energy conversion applications. [ABSTRACT FROM AUTHOR]

Nanotubes of TiO2 (anatase) and their ordered arrays are emerging, promising candidates as efficient host materials in many applications such as photovoltaic cells, batteries, sensors and catalysts/catalytic supports, but the interplay between these structures and their transport properties has been reported only rarely. Monodisperse, stoichiometric TiO2 nanotubes with smooth morphology and controlled wall thickness were fabricated by template-directed low-temperature atomic layer deposition (ALD), followed by annealing at elevated temperatures. We present a study on the wall thickness-dependent crystallization behaviors due to physical and/or self-confinement, as well as on the corresponding electrical properties. Over certain wall thicknesses, unexpectedly, our TiO2 nanotubes were found to be a new type of mesoporous wide gap semiconductor in which they possess similar porosity, but in terms of conductivity differ from previously known mesoporous photoanodes (i.e., anodized surfaces of Ti films and sintered films consisting of TiO2 nanoparticles). These results were ascribed to the large, elongated anatase domains (by a factor of up to 15–40 wall thicknesses) that developed via boosted crystal growth on porous alumina templates (physical confinement) as well as to the highly curved tubular shape (self-confinement). Indeed, nanotube arrays with walls thicker than 10 nm exhibited an enhancement in conductivity, by more than three orders of magnitude, compared to sintered, mesoporous TiO2 (anatase) particles, approaching the bulk value. The nearly single-crystalline TiO2 nanotubes presented here should allow for a good model system to study TiO2-based surface chemistry and have potential for many applications in photovoltaic and/or catalytic systems. [ABSTRACT FROM AUTHOR]

We report, for the first time, a novel procedure for fabricating multiwall anatase TiO2nanotubes by utilizing templated atomic layer deposition synthesis in conjunction with alternating TiO2/Al2O3nanolaminate structures. [ABSTRACT FROM AUTHOR]

We report on the interplay between nanostructuring and defect activation in dense polycrystalline Bi2Te3 thin films in terms of the thermopower engineering. The Bi2Te3 thin films were prepared at relatively low temperatures (100–160 °C) by atomic layer deposition and their grains showed different sizes in the range of 50–200 nm according to the deposition temperatures. We monitored the conductivity, Seebeck coefficient, and power factor of all samples from the temperature of 50–400 K. By increasing the growth temperature, remarkably, we observed the gradual defect activation from the nominal p-type to n-type in our binary end compound, Bi2Te3 without any alloying. The present results give us an insight on the optimization of thermoelectric materials not only by nanostructuring (i.e., phonon engineering) but also by controlled defect activation (i.e., electron engineering). [ABSTRACT FROM AUTHOR]

Cadmium sulfide (CdS) is a semiconducting absorber for photoelectrochemical (PEC) hydrogen production with suitable electronic band structures. However, it suffers from severe photocorrosion and rapid charge recombination during the desired PEC reactions. Herein, we describe the identification of the optimal junction thickness of CdS/MoS 2 core/sheath heterojunction nanostructures by employing atomic layer deposition (ALD) techniques. ALD-grown MoS 2 sheath layers with different thicknesses were realized on single-crystalline CdS nanorod (NR) arrays on transparent conducting oxide substrates. We further monitored the resulting solar H 2 evolution performance with our heterojunction photoanodes. The results showed that the junction thickness of MoS 2 plays a key role in the reduction of photocorrosion and the enhanced photocurrent density by optimizing the charge separation. A better saturation photocurrent (∼46%) was obtained with the 7 nm-thick MoS 2 @CdS NRs than that with the bare CdS NRs. Moreover, the external quantum efficiency was increased twofold over that of the pristine CdS NRs. The ALD-grown MoS 2 @CdS heterojunction structures provides an efficient and versatile platform for hydrogen production when combining ALD-grown MoS 2 with ideal semiconducting absorbers.

We describe the direct preparation of crystalline Ni 3 S 2 thin films via atomic layer deposition (ALD) techniques at temperatures as low as 250 °C without postthermal treatments. A new ALD chemistry is proposed using bis(1-dimethylamino-2-methyl-2-butoxy) nickel(II) [Ni(dmamb) 2 ] and H 2 S as precursors. Homogeneous and conformal depositions of Ni 3 S 2 films were achieved on 4 in. wafers (both metal and oxide substrates, including Au and SiO 2 ). The resulting crystalline Ni 3 S 2 layers exhibited highly efficient and stable performance as electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline solutions, with a low overpotential of 300 mV and a high turnover frequency for HER and an overpotential of 400 mV for OER (at a current density of 10 mA/cm 2 ). Using our Ni 3 S 2 films as both the cathode and the anode, two-electrode full-cell electrolyzers were constructed, which showed stable operation for 100 h at a current density of 10 mA/cm 2 . The proposed ALD electrocatalysts on planar surfaces exhibited the best performance among Ni 3 S 2 materials for overall water splitting recorded to date.