Novel Christmas branched like NiO/NiWO${}_4$/WO${}_3$ (p-p-n) nanowire heterostructures for chemical sensing

Establishing a platform comprising different nanostructured oxides is an emerging idea to develop highly sensitive and selective sensing devices. Herein, novel 3D-heterostructures (p-p-n) consisting of 1D nanowires of NiO and WO${}_3$ along with their intermediate reactive product, i.e., NiWO${}_4$ seed, are produced by a two-steps vapor phase growth method. In-depth morphological and structural investigations describing the growth mechanism of these heterostructures are presented. Finally, the p–p–n heterostructures are integrated into conductometric sensing devices and their performances are investigated toward different gases. It is observed that by modulating the charge-carrier transport with temperature, the heterostructure sensors exhibit selective behavior toward different gas analytes. Indeed, at 300 °C, the heterostructure sensors show relatively selective behavior toward NO${}_2$, while at 400 °C, high selectivity toward VOCs is observed. The improvement in sensing performances is mainly based on charge carrier transport through the two interfaces (one at WO${}_3$/NiWO${}_4$ (n-p) and the other at NiWO${}_4$/NiO (p-p)) and the modulation of charge carriers in the electron depletion layer of WO${}_3$ and hole accumulation layer of NiO and NiWO${}_4$. The remarkable performance of these complex heterostructures with low ppb-level detection limits makes them excellent candidates for chemical/ gas sensing applications in e-noses. (© 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH)