Twisted helical armchair graphene nanoribbons: mechanical and electronic properties

The Hydrogen and Fluorine planar armchairs graphene nanoribbons (H & F AGNRs), subjected to twist deformation within fixed periodic boundary conditions. H-AGNRs is highly elastic in nature, though passivation with Fluorine does induce the plasticity when twisted beyond threshold torsional strain. This plasticity attributes to the wider bond length distribution suggests distortion of benzo-rings. The bandgap response to the effective strain of narrow GNRs $$\varvec{N}=6, 7$$ , and 8 get arranged as (i) monotonously increasing for $$\varvec{q}=0,2$$ and (ii) decreasing for $$\varvec{q}=1$$ ; here, $$\varvec{q}=mod\left( \varvec{N},3 \right) $$ in effective strain space $${{({\varvec{\theta }} }}^{\varvec{2}}\varvec{\varSigma }^{\varvec{2}}\varvec{)}$$ . The effective strain space is found to be more appropriate for gauging the response of torsional strain. This trend has also been observed for Fluorine passivated AGNRs; however, because of higher sensitive response to torsional strain, the bandgap of $$\varvec{N}=$$ 7 F-AGNRs drops from $$\varvec{E}_{\varvec{g}}\simeq 0.95\hbox {eV}$$ to $$ \varvec{E}_{\varvec{g}}\simeq 0.05\hbox {eV}$$ at extreme torsional strain forming Dirac cone at $$\pm \varvec{K}$$ allows dissipationless transport to charge carriers of high kinetic energy at low bias.