The Effect of the Pre-Strain Process on the Strain Engineering of Two-Dimensional Materials and Their Van Der Waals Heterostructures

Two-dimensional (2D) materials and their van der Waals stacked heterostructures (vdWH) are becoming the rising and glowing candidates in the emerging flexible nanoelectronics and optoelectronic industry. Strain engineering proves to be an efficient way to modulate the band structure of 2D materials and their vdWH, which will broaden understanding and practical applications of the material. Therefore, how to apply desired strain to 2D materials and their vdWH is of great importance to get the intrinsic understanding of 2D materials and their vdWH with strain modulation. Here, systematic and comparative studies of strain engineering on monolayer WSe and graphene/WSe heterostructure are studied by photoluminescence (PL) measurements under uniaxial tensile strain. It is found that contacts between graphene and WSe interface are improved, and the residual strain is relieved through the pre-strain process, which thus results in the comparable shift rate of the neutral exciton (A) and trion (A) of monolayer WSe and graphene/WSe heterostructure under the subsequent strain release process. Furthermore, the PL quenching occurred when the strain is restored to the original position also indicates the pre-strain process to 2D materials, and their vdWH is important and necessary for improving the interface contacts and reducing the residual strain. Thus, the intrinsic response of the 2D material and their vdWH under strain can be obtained after the pre-strain treatment. These findings provide a quick, fast and efficient way to apply desired strain and also have important significance in guiding the use of 2D materials and their vdWH in the field of flexible and wearable devices.