Abstract
The effect of intrinsic ripples on the mechanical response of the graphene monolayer is investigated under uniaxial loading using molecular dynamics (MD) simulations with a focus on nonlinear behavior at a small strain. The calculated stress-strain response shows a nonlinear relation through the entire range without constant slopes as a result of the competition between ripple softening and bond stretching hardening. For a small strain, entropic contribution is dominant due to intrinsic ripples, leading to elasticity softening. As the ripples flatten at increasing strain, the energetic term due to C–C bonds stretching competes with the entropic contribution, followed by energetic dominant deformation. Elasticity softening is enhanced at increased temperature as the ripple amplitude increases. The study shows that the intrinsic ripple of graphene affects elasticity. This result suggests that a change of ripple amplitudes due to various environmental conditions such as temperature, and substrate interactions can lead to a change of the mechanical properties of graphene. The understanding of the rippling effect on the mechanical behavior of 2D materials is useful for strain-based ripple manipulation for their engineering applications.
Highlights
Graphene has received considerable interest due to its unique properties, potentially leading to a wide range of applications such as display screens [1, 2], energy storage [3,4,5], solar cells [6,7,8], and field-effect transistors [9,10,11]
This initial nonlinearity is similar to the behavior shown in polycrystalline graphene, implying that the effect of intrinsic ripples exists in the pristine graphene
The intrinsic ripples on a graphene monolayer are clearly diminished as strain increases
Summary
Graphene has received considerable interest due to its unique properties, potentially leading to a wide range of applications such as display screens [1, 2], energy storage [3,4,5], solar cells [6,7,8], and field-effect transistors [9,10,11]. As one of its unique properties, suspended graphene is not perfectly flat but forms spontaneous ripples on the surface [12]. The spontaneous roughening of graphene is intriguing because it is attributed to unexpected physical characteristics such as a negative thermal expansion coefficient [14], increasing bandgap [15], and unusual electronic properties [16]. The mechanical properties of graphene have been widely studied experimentally and theoretically. In terms of experimental studies, Lee et al performed a pioneering mechanical test to measure the Young’s modulus and fracture strength of a monolayer graphene
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