Humidity Sensing Properties of Coexfoliated Heterogeneous WS2/WSe2 Nanohybrids

To-dimensional-layered Van der Waals nanostructures and their hybrids have been in focus since the discovery of graphene. Transition metal dichalcogenides are an important segment of materials of this class which is analogous to graphene and can be exfoliated to mono and few layers form. Excellent interlayer coupling among these nanomaterials may result in fascinating synergistic properties. In this work, a simple liquid-phase coexfoliation technique was utilized to exfoliate WS
₂
and WSe
₂
simultaneously by an optimized mixed solvent strategy. The assynthesized nanohybrids were characterized by using different material characterization techniques. The coexfoliated nanomaterial has shown excellent humidity sensing properties including high reproducibility, stability, and low hysteresis. The response from our humidity sensor varies between 15.4 (at 40% RH) to 57 times (at 80% RH), compared to the reference value of the air (at ~25% RH). The response and recovery times were observed to be 40 and 65 s, respectively, for 60% RH. The performance of coexfoliated sensing layer was compared with individual WS
₂
, and WSe
₂
nanosheets and nanocomposite prepared by exfoliation separately. Better performance of sensors utilizing coexfoliated nanosheets has been attributed to synergistic interfacial effects and high proton conductivity. A mechanism based on heterogeneous WS
₂
/WSe
₂
nanohybrids has been proposed where the interfaces help in creating favorable sites for water adsorption and desorption apart from the sulfur vacancies in the individual WS
₂
or WSe
₂
. This has been attributed to modulation of surface barrier potential through interfacial electron transfer. We believe such sensing mechanism can help in the development of a new generation highly sensitive humidity sensor.