Simulated mechanical properties of finite-size graphene nanoribbons

Abstract

There are many simulation studies of mechanical properties of graphene nanoribbons (GNR), but there is a lack of agreement regarding elastic and plastic behavior. In this paper we aim to analyze mechanical properties of finite-size GNR, including elastic modulus and fracture, as a function of ribbon size. We present classical molecular dynamics simulations for three different empirical potentials which are often used for graphene simulations: AIREBO, REBO-scr and REAXFF. Ribbons with and without H-passivation at the borders are considered, and the effects of strain rate and different boundaries are also explored. We focus on zig-zag GNR, but also include some armchair GNR examples. Results are strongly dependent on the empirical potential employed. Elastic modulus under uniaxial tension can depend on ribbon size, unlike predictions from continuum-scale models and from some atomistic simulations, and fracture strain and progress vary significantly amongst the simulated potentials. Because of that, we have also carried out quasi-static ab-initio simulations for a selected size, and find that the fracture process is not sudden, instead the wave function changes from Blöch states to a strong interaction between localized waves, which decreases continuously with distance. All potentials show good agreement with DFT in the linear elastic regime, but only the REBO-scr potential shows reasonable agreement with DFT both in the nonlinear elastic and fracture regimes. This would allow more reliable simulations of GNRs and GNR-based nanostructures, to help interpreting experimental results and for future technological applications.

Inducing a topological transition in graphene nanoribbons superlattices by external strain

“…Figure 3 displays the Stress-Strain curves for all four cases. The unmodulated AGNR show the typical behavior seen for GNR [37]: an initial linear elastic region, followed by a nonlinear elastic region, ending in brittle fracture. The elastic module depends on ribbon width [37], but they both fracture near 13.8% strain.…”

“…The unmodulated AGNR show the typical behavior seen for GNR [37]: an initial linear elastic region, followed by a nonlinear elastic region, ending in brittle fracture. The elastic module depends on ribbon width [37], but they both fracture near 13.8% strain. The elastic modulus of both modulated 7-AGNR is similar to the one for the 7-AGNR unmodulated ribbon.…”

“…MD simulations were carried out with the LAMMPS software [47], using the REBOscr potential. [48] It has been shown that this potential gives a reliable description of the strain-stress processes (including bond breaking) in AGNRs and other C-based systems [37,38]. Studied superlattices have finite size and were thermalized at 10 K. We used long periodic superlattices, and homogeneous strain was applied, with a strain rate of 1×10 9 s −1 .…”

Inducing a topological transition in graphene nanoribbon superlattices by external strain

“…3 displays the stress-strain curves for all four cases. The unmodulated AGNR shows the typical behavior seen for GNRs: 49 an initial linear elastic region, followed by a nonlinear elastic region, ending in brittle fracture. The elastic modulus depends on ribbon width, 49 but they both fracture near 13.8% strain.…”

“…The unmodulated AGNR shows the typical behavior seen for GNRs: 49 an initial linear elastic region, followed by a nonlinear elastic region, ending in brittle fracture. The elastic modulus depends on ribbon width, 49 but they both fracture near 13.8% strain. The elastic modulus of both modulated 7-AGNR is similar to the one for the 7-AGNR unmodulated ribbon.…”