Enhanced photoresponse in WSe₂/MoS₂ heterobilayers optoelectronic device via programmable local nanostrain engineering

The application potential of tuning two-dimensional materials (2DMs) characteristics through strain engineering for wearable and flexible devices has been widely recognized. However, the challenges lie in achieving accurate deterministic positioning, spatial modulation, controllable magnitude, and permanent nanostrains. Herein, motivated by the skin swelling caused by mosquito bites, a technique utilizing the heated nanotip in atomic force microscopy for thermomechanical nanoindentation is demonstrated. This method enables precise positioning of localized nanostrain and regulation of bandgap in tungsten diselenide (WSe₂)/molybdenum disulfide (MoS₂) heterobilayer transferred onto a flexible polymethyl methacrylate film. The magnitude of strain in the WSe₂/MoS₂ heterobilayer can be controlled by adjusting the parameters of nanoindentation, leading to a spatially modulated average strain of up to 2.5% on the ring-shaped expansion structure (RES). The local bandgap of the WSe₂/MoS₂ heterobilayer is spatially regulated through three distinct regions. In particular, the RES exhibits the largest extent of bandgap modulation, accompanied by a significant change of ~12 meV. The nanostrain significantly enhances the photoresponse speed of the photodetector device. For instance, under illumination from a 405 nm wavelength-laser, the rise time and fall time are reduced by 75% and 87.52%, respectively, compared to the device without strain. Similarly, under illumination from a 532 nm wavelength-laser, the rise time and fall time are reduced by 66.67% and 80.60%, respectively. These findings demonstrate that the proposed method serves as a versatile way for improving the photoresponse of optoelectronic devices based on 2DMs.