Ternary TiO2/MoS2/ZnO hetero-nanostructure based multifunctional sensing devices

Abstract

Novel sensing applications benefit from multifunctional nanomaterials responsive to various external stimuli such as mechanics, electricity, light, humidity, or pollution. While few such materials occur naturally, the careful design of synergized nanomaterials unifies the cross-coupled properties which are weak or absent in single-phase materials. In this study, 2D MoS₂ integrated with ultrathin dielectric oxide layers forms hetero-nanostructures with significant impacts on carrier transport. The ternary TiO₂/MoS₂/ZnO hetero-nanostructures, along with their individual properties, improve the performance of multifunctional sensing devices. The synthesized hetero-nanostructure exhibits a responsivity of up to 16 mA/W to 700 nm light and responds to 5 ppm ammonia gas at room temperature. These enhancements are attributed to interface charge transfer and photogating effects. The ternary TiO₂/MoS₂/ZnO hetero-nanostructure is compatible with existing semiconductor fabrication technologies, making it feasible to integrate into flexible, lightweight semiconductor devices and circuits. These results may inspire new photodetectors and sensing devices based on two-dimensional (2D) layered materials for IoT applications.

Keywords: Gas sensor; Molybdenum disulfide; Multifunctional sensor; Photodetector; Ternary hetero-nanostructure; Titanium dioxide; Two-dimensional material; Zinc oxide.

Fig. 1

Scanning electron microscope (SEM) images of the sample with a a MoS₂ layer deposited on TiO₂ coated Si substrate, and b a ZnO layer on top of TiO₂/MoS₂ composite. All scale bars 2 μm. c Optical image of the MoS₂ sample

Fig. 2

EDX of a TiO₂/MoS₂, and b TiO₂/MoS₂/ZnO composite

Fig. 3

Raman spectra of a TiO/MoS₂, and b TiO/MoS₂/ZnO

Fig. 4

a Typical I–V characteristics of the prototype. Photocurrents of the prototype to light of different colors of the same intensity with b 2 V bias, and c 0 V bias. The estimated d rise time τ_on, and e recovery time τ_off to red light with 0 V bias at room temperature

Fig. 5

a Response of the prototype following the variation of the distance D between the prototype and the red light source, and b the corresponding photocurrent as a function of red-light illumination density

Fig. 6

Performance of the self-powered prototype to the same intensity of red light illumination with different load resistances: a Time response, b the output photovoltage, and c the output photocurrent

Fig. 7

a The responses of the prototype at room temperature to 10 ppm NO₂ gas, and b the relationship between the response strength and the NO₂ gas concentrations at room temperature and 5 V bias