Chirality and width effects on elastic and fracture properties of nanoribbons with coronene edges

Coronenes are a class of polycyclic aromatic hydrocarbons consisting of fused benzene rings arranged in a specific pattern. The structure of coronenes can vary depending on the number of fused benzene rings, with the most common form being hexabenzocoronene, which consists of six benzene rings fused in a circular arrangement. In 2012, coronene-based nanoribbons (CNRs) were successfully synthesized. Although several properties of CNRs have already been studied, a complete characterization of the mechanical properties of CNRs and the effect of the edges are lacking. This study examines how the width and chirality of CNRs affect their mechanical properties under tensile stress. Nanoribbons of rectangular shape and the same width as the CNRs are also studied for the determination of the edge effects on these properties. CNRs of different widths are analyzed, from which the elastic constants are obtained. Results indicate a transition in the mechanical properties from quasi-1D to 2D systems, with the most significant change observed between the narrowest and second-narrowest CNRs considered here. The peak stress is approximately 40 GPa larger for AC-CNRs than for ZZ-CNRs. The response to strain also differs between CNRs with armchair (AC-CNR) and zigzag (ZZ-CNR) edges due to variations in bonding orientations, with AC-CNRs sustaining larger strains than ZZ-CNRs. Fracture patterns are similar for all widths except for the narrowest nanoribbons. Furthermore, the elastic constants of CNRs exhibit an increase with width, approaching the graphene value of 1 TPa, as expected. However, an interesting trend of the Young's modulus of CNRs with increasing width is observed: the first five AC-CNRs of smallest widths present larger Young's moduli than those of the first five ZZ-CNRs of smallest widths, and invert for the CNRs with larger values of width. This result is then discussed in terms of the differences in the shape of the edges between AC and ZZ CNRs.