Gas Sensing of NiO‐SCCNT Core–Shell Heterostructures: Optimization by Radial Modulation of the Hole‐Accumulation Layer

Abstract

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.

MoS2 Van der Waals p–n Junctions Enabling Highly Selective Room‐Temperature NO2 Sensor

“…Traditional gas sensors based on metal oxide semiconductors (MOS) [ 10–12 ] suffer greatly from the poor selectivity and the high working temperature, generally in the range of 200–400 °C, which can lead to high power consumption and reduce the sensor lifetime and durability. [ 13 ] Although some MOS sensors have demonstrated sensing properties at RT, [ 14–16 ] the low sensitivity, sluggish response‐recovery speed, and incomplete recovery remain challenging tasks to be overcome.…”

Morphology-controlled MoS2 by low-temperature atomic layer deposition

“…Atomic layer deposition (ALD), due to its high conformality, shows great potential in the precise control of the thicknesses and morphologies of the deposited layers, especially for the preparation of complex nanostructures. 1,[18][19][20][21][22][23] Based on these peculiarities, several TMD nanomaterials with varying morphologies and complex nanostructures have been synthesized by ALD by modifying various deposition parameters and/or by using different substrates and templates. [24][25][26] For example, Mattinen et al deposited a ∼3 nm thick SnS 2 film on 3D nanoscale trench substrates with a depth of 90 and a width of 30 nm.…”

Impact of Different Intermediate Layers on the Morphology and Crystallinity of TiO2 Grown on Carbon Nanotubes by Atomic Layer Deposition

“…In contrast to TiO 2 ‐100/CNTs which shows clear reflections attributed to the anatase phase, the TiO 2 films deposited on Al 2 O 3 and ZnO intermediate layers are amorphous. In addition, any reflection corresponding to the Al 2 O 3 and ZnO phases cannot be observed, which may be attributed to the intrinsic amorphous characteristic of Al 2 O 3 film deposited by ALD [ 22 ] and the low mass loading of the ZnO thin layer after 20 ALD cycles.…”