The gas-sensing properties and mechanism and the role of the shell thickness of structurally well-defined SnO 2 /NiO heterostructures are studied. One-dimensional (1D) SnO 2 /NiO core− shell nanowires (CSNWs) were produced by a two-step process; singlecrystalline SnO 2 -core nanowires (NWs) were synthesized by vapor− liquid−solid (VLS) deposition and then decorated with a polycrystalline NiO-shell layer by atomic layer deposition (ALD). The thickness of the NiO-shell layer was precisely controlled between 2 and 8.2 nm. The electrical conductance of the sensors was decreased many orders of magnitude with the NiO coating, suggesting that the conductivity of the sensors is dominated by Schottky barrier junctions across the n(core)− p(shell) interfaces. The gas-sensing response of pristine SnO 2 NWs and SnO 2 /NiO CSNWs sensors with various thicknesses of the NiO-shell layers was investigated toward hydrogen at various temperatures. The response of the SnO 2 /NiO-X (X is the number of ALD cycles) CSNWs significantly depends on the thickness of the NiO-shell layer. The SnO 2 /NiO-100 sensor showed the best performance (NiO-shell thickness ca. 4.1 nm), where the radial modulation of the space-charge region is maximized. The sensing response of the SnO 2 /NiO-100 sensor was 114 for 500 ppm of hydrogen at 500 °C, which was about four times higher than the response of pristine SnO 2 NWs. The sensing mechanism is mainly based on the formation of a p−n junction at the p-NiO-shell and the n-SnO 2 -core interface and the modulation of the hole-accumulation region in the NiO-shell layer. The remarkable performance of the SnO 2 /NiO CSNWs sensors toward hydrogen is attributed to the high surface to volume ratio of the 1D SnO 2 core-NWs, the conformal NiO shell layer, and the optimized shell layer thickness radially modulating the space-charge regions.

Hierarchical core-shell (C-S) heterostructures composed of a NiO shell deposited onto stacked-cup carbon nanotubes (SCCNTs) are synthesized by atomic layer deposition (ALD). A film of NiO particles (0.80-21.8 nm in thickness) is uniformly deposited onto the inner and outer walls of the SCCNTs. The electrical resistance of the samples is found to increase of many orders of magnitude with the increasing of the NiO thickness. The response of NiO-SCCNT sensors toward low concentrations of acetone and ethanol at 200 °C is studied. The sensing mechanism is based on the modulation of the hole-accumulation region in the NiO shell layer upon chemisorption of the reducing gas molecules. The electrical conduction mechanism is further studied by the incorporation of an Al 2 O 3 dielectric layer at NiO and SCCNT interfaces. The investigations on NiO-Al 2 O 3 -SCCNT, Al 2 O 3 -SCCNT, and NiO-SCCNT coaxial heterostructures reveal that the sensing mechanism is strictly related to the NiO shell layer. The remarkable performance of the NiO-SCCNT sensors toward acetone and ethanol benefits from the conformal coating by ALD, large surface area of the SCCNTs, and the optimized p-NiO shell layer thickness followed by the radial modulation of the space-charge region.

Ni-based compounds have been widely used for catalytic water splitting in alkaline media. NiO-based nanostructures supported on carbon nanotubes (CNTs) were synthesized by atomic layer deposition (ALD) using NiCp2 and O3 as precursors. NiO-coated CNTs display enhanced catalytic activity for the oxygen evolution reaction. The recorded overpotential of 315 mV at the current density of 10 mA cm–2 in Ar-saturated 1 M KOH is lower than any reported values so far for NiO-based catalysts. Moreover, the overpotential is constant for 12 h electrolysis at current density of 10 mA cm–2, highlighting the stability of our materials. The Tafel slopes of 50 mV dec–1 are also lower than other Ni-based nanostructures previously reported. The study of CVs in the redox region in Fe­(III)-free and Fe­(III)-saturated 1 M KOH solutions proves that the high catalytic activity is intrinsic of the NiO/carbon composite and is not influenced by iron precipitation. The enhanced catalytic activities could be attributed to the conformal and well-distributed NiO layer by ALD and the large surface area and good conductivity of the CNTs network.

Nanocomposites made of stacked‐cup carbon nanotubes coated with NiO (NiO/SCCNTs) via atomic layer deposition (ALD) were synthesized in order to obtain a material exhibiting enhanced and optimized electrochemical performance towards detections of glucose. The structure and morphology were characterized by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). NiO deposited as nanocrystalline particles in the cubic modification, were well dispersed and directly anchored on SCCNTs forming a smooth particulate thin film, which becomes more dense with the increase of the number of ALD cycles. The NiO/SCCNTs samples with various thicknesses of the NiO coating (0.8 nm, 1.7 nm, 4.0 nm, 6.5 nm, 14.0 nm and 21.8 nm) were applied for enzyme‐free glucose sensing. Their electrochemical performance strongly depends on the thickness of the deposited NiO thin film. The best performing glucose sensors respond over a wide concentration range from 2 μM to 2.2 mM (R2=0.9979) with remarkably enhanced sensitivity (1252.3 μA cm−2 mM−1), with a limit of detection (LOD) of 0.10 μM (S/N=3) and with a fast response time (lower than 2 s). The significant performance improvement can be attributed to the conformal NiO coating, high surface to volume ratio and to the optimized thickness of the NiO thin film. The advantage of our sensors is also associated with the conductive supporting material (SCCNTs), simplicity of fabrication, high sensitivity, selectivity, stability and reproducibility for the rapid quantification of glucose.

A novel self-terminating chemical approach for the deposition of WS 2 by atomic layer deposition based on chemisorption of bis(t-butylimino)bis-(dimethylamino)tungsten(VI) followed by sulfurization by H 2 S is reported. A broad spectrum of reaction parameters including temperatures of the reaction chamber and the precursor and durations of every atomic layer deposition (ALD) step are investigated and optimized to reach a high growth per cycle of 1.7 Å and a high quality of the deposited thin films. The self-terminating behavior of this reaction is determined by the variation of the dose of the precursors. Surface-and bulk-sensitive techniques prove that highly pure and well-defined WS 2 layers can be synthesized by ALD. Imaging methods show that WS 2 grows as platelets with a thickness of 6−10 nm and diameter of 30 nm, which do not vary dramatically with the number of ALD cycles. A low deposition temperature process followed by a postannealing under H 2 S is also investigated to produce a conformal WS 2 film. Finally, a reaction mechanism could be proposed by studying the chemisorption of bis(t-butylimino)bis(dimethylamino)tungsten(VI) onto silica and the thermal and chemical reactivities of chemisorbed species by small-molecule analyses.