Symmetry-Broken Biphasic WS2 Nanowhiskered Heterostructures Enable Field-Induced NO2 Sensing

Abstract

Van der Waals (vdW) materials have garnered ample interest as next-generation sensors and catalysts, owing to high surface-to-volume ratio, defect tunability, easy modulation of active sites, and convenience in device fabrication. However, one major drawback delimiting surface activity of conventional vdW sensors is weak adsorption of target analyte on basal surface compared to the edge-sites, compromising their general applicability. This work categorically averts above limitations by introducing an inversion symmetry-broken biphasic-(hexagonal-rhombohedral) ultralong WS2 heterostructure which harnesses its noncentrosymmetric features during field-induced room-temperature NO2 sensing. Under a +20 V bias, the heterostructure demonstrates an improvement in sensitivity from 75% → 90% alongside response/recovery of 35/80 s. The band-modified energy channels enable in situ modulation of Limit of Detection down to 1 ppm. Surface-analyte interaction mechanisms were identified by the emergence of a giant 40% degree of circular polarization in hybrid-static p–p surface quasi-states upon light–matter interaction, employing helicity-resolved circularly polarized operando Raman spectroscopy and polarity-resolved Stark-field of tuning rate 1.5 cm–1/(kV/cm). Operando UV–vis spectroscopy alongside theoretical calculations indicates that NO2-mediated hole-injection redefines intrinsic A-B excitonic population via Fermi level pinning (FLP). Field effect-transistor (FET)-based sensors harnessing perturbation-mediated band features have been introduced, holding potential toward transformative sensing devices.