Mechano/acousto-electric coupling between ReS₂ and surface acoustic wave

Abstract Two-dimensional (2D) materials are promising candidates for developing next generation electronic/optoelectronic devices with programmable multi functions, due to their widely tunable properties by various physical stimuli. Mechanical strain is one of the most promising means to effectively modulate the physical properties of 2D materials. Nevertheless, few studies reported micro/nano scale controllable strain application platforms, limiting the development of novel mechano-electrical/optoelectrical devices based on 2D materials. This work proposes surface acoustic wave (SAW) device as a controllable strain modulation platform for 2D materials with sub-micro scale resolution. The platform uses the piezoelectric material (LiNbO₃) as the substrate, which is deposited with interdigitated transducers (IDT) to generate SAW on the surface. The propagation of SAW causes surface deformation, which is then transferred to the 2D materials on the substrate. The period of the surface deformation/strain is related with that of SAW, which is determined by the period of IDT with nano meter scale. It is demonstrated that the photo luminescence spectrum of a 2D ReS₂ flake on this platform gradually shifts with the SAW excitation power, which reaches a shift of 3 nm as the SAW excitation power achieves 26 dBm, corresponding to a band gap increase of 5 meV. Meanwhile, the platform is also capable to provide acousto-electric coupling between SAW and 2D materials, which is demonstrated by the shift of the SAW resonant frequency due to the re-distribution of photo-generated carriers in ReS₂ upon light illumination.