SnO2 -SiO2 1D Core-Shell Nanowires Heterostructures for Selective Hydrogen Sensing

Abstract

SnO2 is one of the most employed n-type semiconducting metal oxide (SMOX) in chemo-resistive gas-sensing although it presents serious limitations due to a low selectivity. Herein, we introduce one-dimensional (1D) SnO2-SiO2 core-shell nanowires (CSNWs). SnO2 nanowires (NWs) are synthesized by vapor–liquid–solid deposition and the amorphous SiO2-shell layer with varying thicknesses (1.8-10.5 nm) was grown by atomic layer deposition (ALD). SiO2-coated SnO2 CSNWs show lower baseline conductance as compared to the Pristine SnO2 NWs, due to an enhancement of the electron depletion layer. The SnO2-SiO2/N CSNWs (N representing the number of SiO 2 ALD cycles) sensors show a dramatic improvement of the selectivity towards hydrogen. Moreover, the sensing-response markedly depends on the thickness of the SiO2-shell layer and the working temperature. The SnO2-SiO2/60 CSNWs sensor (ca. 4.8 nm SiO2 shell thickness) was the best performing sensor in terms of selectivity and sensitivity exhibiting a response of 160 (ca. 7-folds higher than the pristine SnO2 NWs) towards 500 ppm of hydrogen at 500 °C with a lower detection limit at ppb-level (0.082 ppm). The selectivity and enhanced sensing-response are related to the masking effect of the SiO2 shell and an increased in the width of the electron depletion layer due to the strong electronic coupling between the SnO2 core and SiO2-shell layer, respectively. The remarkable sensing performances of the SnO2-SiO2/N CSNWs can be attributed to the homogeneous and conformal SiO2 shell layer by ALD,<br>electronic coupling between the core and the shell, the optimized shell thickness and high surface area provided by the 1D SnO2 NWs network.<br>

Role of Heterojunctions of Core–Shell Heterostructures in Gas Sensing

“…The isothermal response transients and the response of all the sensors at 200 °C (the optimal working temperature) are shown in Figure c,d. CNT-NiO(200) and CNT-SnO 2 (50) CSHS show typical p- and n-type sensing responses related to their intrinsic cations and anions deficiencies, respectively. ,,,,, The thickness of the NiO shell was fixed to 5.5–6.5 nm (200 ALD cycles) since it has already been optimized in our previous study . Noticeably, at this thickness which is similar to the Debye length, λ D , the whole layer participates in the resistance modulation and the sensing response is maximized .…”

“…Indeed, the sensing responses of heterostructured materials discussed in the literature are very disparate and not always related to the p–n semiconductor heterojunction ,,, but could be limited to the core or the shell material. ,, For example, it was demonstrated that although depositing a second material conformally onto already contacted (core–core junctions) 1D SnO 2 nanowires (SnO 2 -core) or carbon nanotubes (CNTs-core) modifies both the width and the thickness of the depletion region at the interface, the sensing responses were exclusively attributed to the core materials. ,, In that case, the shell-layers modified the surface of the already fabricated devices without dramatically modifying the underlying transduction mechanism. ,,,,, Alternatively, a change in the order of device/geometry and materials fabrication (e.g., by adding shell–shell junctions to the core–shell heterojunction and omitting the direct core–core junction) could result in a response related to (i) the shell layer, (ii) the core axis, or (iii) the p–n interface. ,,, A study on CNT-NiO core–shell heterostructures (CSHS) demonstrated that the response was strongly related to the NiO shell . Indeed, when an insulating alumina buffer layer was introduced between the NiO shell and the CNT-core substrate, the transduction mechanism and the response were not affected, but only the baseline resistance of the device increased.…”

Compositing MXenes with hierarchical ZIF-67/cobalt hydroxideviacontrollablein situetching for a high-performance supercapacitor

“…The hierarchical core–shell/yolk–shell/hollow (CS/YS/Ho) structure has been studied in depth because of the controllable structure and large specific surface area. 14–16 Therefore, they are widely used in sensing, 17 drug delivery, 18 photocatalysis/electrocatalysis, 19,20 and electrochemical energy storage. 21,22 The traditional strategy for the CS/YS/Ho structure is mainly focused on the template method and demands multiple synthesis steps.…”