Modeling Intrinsic Wrinkles in Graphene and Their Effects on the Mechanical Properties
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https://doi.org/10.1007/s11837-020-04371-6 Ó 2020 The Minerals, Metals & Materials Society
NANOMECHANICS OF LOW-DIMENSIONAL MATERIALS
Modeling Intrinsic Wrinkles in Graphene and Their Effects on the Mechanical Properties WENQING ZHU,1 YING LIU,1,2 and XIAODING WEI
1,2,3
1.—State Key Laboratory for Turbulence and Complex System, Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing 100871, China. 2.—Beijing Innovation Center for Engineering Science and Advanced Technology, Peking University, Beijing 100871, China. 3.—e-mail: [email protected]
Intrinsic wrinkles (stably existing with or without external stresses applied) with a height ranging from several to tens of nanometers are commonly observed in graphene synthesized on non-ideally flat substrates using chemical vapor deposition techniques. However, such stable intrinsic wrinkles have not been successfully implemented in atomistic modeling, especially in terms of the wrinkle height, defective features, and their effects on the mechanical properties of the material. Here, we propose a ‘‘crack-and-patch’’ modeling approach to resemble the wrinkle formation procedure during the graphene growth on a non-ideal substrate. Wrinkles obtained through this method are stable and have features that agree with the experimental observations. Finally, we carry out the mechanical tests on the wrinkled graphene to examine their mechanical properties, such as effective elastic modulus and strength. The results suggest that wrinkles play a critical role in the mechanical degradation of graphene, because of the complex stress concentration near the ends of the wrinkle.
INTRODUCTION Graphene monolayers have been found to be the strongest materials with Young’s modulus around 1 TPa and strength of 130 GPa.1 Chemical vapor deposition (CVD) has been employed as an effective way to produce large-scale graphene films on substrates including Cu or SiC.2–4 However, the CVD grown graphene often has various types of defects, such as grain boundaries,5 vacancy defects, 6 ripples or wrinkles,7 which could degrade the mechanical properties of the material. The degradation mechanisms associated with grain boundaries and vacancies (or voids) have been well studied both theoretically and numerically.8,9 Besides, intrinsic wrinkles have also been found in CVD graphene, particularly the samples grown on substrates that are not atomically flat.3,10,11 These intrinsic wrinkles, in contrast to the ripples/wrinkles that form due to the nonlinear elastic response of graphene subjected to external loadings (for example, uniaxial stretch or in-plane shear), 12–15 are mechanically (Received June 13, 2020; accepted August 28, 2020)
stable and hardly can be flattened. Experimental evidence has shown that graphene films with these intrinsic wrinkles exhibit notably degraded mechanical properties such as lower stiffness and strength compared with the defect-free samples.16,17 So far, ripples or wrinkles in atomistic models are mainly obtained by applying mecha
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