Regulation of sulfur vacancies in vertical nanolamellar MoS2 for ultrathin flexible piezoresistive strain sensors

Abstract

• The vertical MoS 2 nanosheets prepared by magnetron sputtering displayed a piezoresistive effect, which has not been reported previously. • Contact and separation of channels between the vertical MoS 2 nanosheets under strain, leading to excellent piezoresistive properties. • Sulfur vacancies enhance electron transport of in-plane MoS 2 nanosheets. • The flexible sensors were excellent in human motion and bionic flight monitoring. Magnetron-sputtered MoS 2 has applications in piezoresistive functional materials research owing to its unique nanostructure. However, the controlled incorporation of sulfur vacancies and realization of enhanced piezoresistive performance remain significant challenges. In this work, the direct growth of large-area MoS 2 films with tunable sulfur vacancy concentrations was successfully achieved via magnetron sputtering at various temperatures. Microstructural analysis revealed that the application of strain altered the number of conductive channels between the vertical MoS 2 nanosheets, changing the measured resistance and leading to excellent piezoresistive properties. More importantly, the unsaturated electrons due to the sulfur vacancies increased the in-plane carrier concentration of the MoS 2 nanosheets. A deposition temperature of 50°C afforded the highest concentrations of sulfur vacancies and carriers. These MoS 2 films possessed a carrier concentration of 6.58 × 10 17 cm −3 , which was 40.9% higher than that obtained at 150°C, and displayed superior piezoresistive performance. The films exhibited high gauge factors of 2.66 and 23.22 under tensile and compressive strain of ≤0.29%, respectively. These values were 118% and 323% higher, respectively, than those obtained for films deposited at 150°C. This work provides an effective route for modulating and mass producing MoS 2 -based piezoresistive electronic devices.