Strain-engineered piezotronic effects in flexible monolayer MoS₂ continuous thin films

The rapid development of flexible devices has progressed their applications in robotics, artificial intelligence, and healthcare. Herein, we used graphene and two-dimensional (2D) transition-metal dichalcogenide (TMD)-based monolayer MoS₂ continuous films fabricated by chemical vapor deposition (CVD) and transferred onto a flexible polyethylene terephthalate (PET) substrate for the fabrication of a flexible device. Owing to the application of strain-engineering concepts, such as compression and stretching, the flexible device can be electromechanically operated by the piezotronic effect based on the coupling and screening phenomena. The flexible device showed significant mechanical strength with a strain-gauge value of 495 at an applied strain of − 0.34 % (i.e., compressive direction), which is ∼8.95 times higher than that of a standard metallic gauge-factor value. Furthermore, the flexible device operated at a cryogenic temperature (210 K) showed a maximum gauge-factor value at a stretching of 0.34 %, which may be due to the reduced screening effect caused by enriching the piezocharges in MoS₂. These findings pave the way for practical applications of the next generation flexible devices in several fields, including biomedical diagnoses, surgical robots, prostheses, and human-machine interfaces.