Extreme Mechanics Letters, 60, 101978(2023)

Abstract: 

Strain engineering has been adopted as a convenient way to tune the band structure of two-dimensional (2D) materials. While uniaxial strain can be easily applied, achieving nonvolatile biaxial strain is still challenging, hindering the investigation of biaxial strain engineering. Taking ReS2 as a demo, we showed that bubbles formed simultaneously during mechanical exfoliation can serve as a convenient platform for investigating work function tunability of 2D materials under biaxial strains. Equi-biaxial tensile strain at the bubble vertex, varying with the bubble sizes, was revealed in situ by lateral force microscopy, as can be predicted by an interfacial strong-shear model. It is found that the local work function of ReS2 increases with the biaxial tensile strain, leading to the decrease of detected surface potential by kelvin probe force microscopy (KPFM). First-principles calculations, which show that a biaxial strain of 0.2 % can increase the work function of tri-layer ReS2 by 0.35 %, revealed that the increased work function under biaxial tensile strain stemmed from the strain-tunable band energies. These findings pave a convenient way to investigate the biaxial strain engineering of ReS2 and tune its local working function for potentially constructing electronic devices of high performance, which could be easily extended to other 2D materials.

Link:   https://doi.org/10.1016/j.eml.2023.101978