Enhanced Photoresponse in WSe2/MoS2 Heterobilayers Optoelectronic Device via Programmable Local Nanostrain Engineering

The application potential of strain engineering in two-dimensional materials (2DMs) 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, inspired by skin edema induced by mosquito bites, a heated atomic force microscopy nanotip-based thermomechanical nanoindentation method 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 adjusted by tuning the parameters of nanoindentation, resulting in a spatially modulated average strain of up to 2.5% on the ring-shaped expansion structure. The local bandgap of the WSe2/MoS2 heterobilayer is spatially regulated through three distinct regions. In particular, the ring-shaped expansion structure exhibits the widest range of bandgap modulation, with 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 tool for enhancing the photoresponse performance of optoelectronic devices based on 2DMs.