Twisted Helical shaped Graphene Nano-Ribbons: Role of Symmetries and Passivation

TL;DR

This study explores how twisting and passivation affect the structural, mechanical, and electronic properties of graphene nanoribbons, revealing significant effects on their conformations, elasticity, and electronic transitions, including metal-semimetal changes.

Contribution

It provides new insights into the role of passivation and twisting in shaping the properties of graphene nanoribbons, especially regarding electronic band gap modulation and conformational transformations.

Findings

Passivation significantly influences mechanical and electrical properties.

Twisted AGNRs exhibit high elasticity or plasticity depending on passivation.

Torsional strain induces metal-to-semimetal transitions and band gap changes.

Abstract

The Hydrogen and Fluorine planar armchairs graphene nanoribbons (H and F AGNRs), subjected to twist deformation within fixed periodic boundary conditions, eventually morph to a helical conformations are investigated at few tractable points. Unlike structural properties, no effect of symmetries on mechanical properties is observed, though passivation does have a significant effect on mechanical as well as on electrical properties. Hookes law for severely twisted AGNRs indicates the high elasticity of H-AGNRs whereas the F-AGNRs shows plasticity after threshold torsional strain. Torsional stress($E_{\theta}$) is approximated from the variation in total energy(${\Delta}E$) with square of torsional strain(${\theta}^4 {\Sigma}^4$). Further, the effect of passivation on the electronic properties of helical conformations with different torsional strain is decisive in metal-to-semimetal and semimetal-to-metal transition. The band gap response of narrow GNRs N=6, 7 and 8, within a fixed cell under sever twisting arranged itself in two group as (i) monotonously increasing for q=0,2 and (ii) decreasing for q=1, here q=mod(N,3) in effective strain space (${\theta}^2 {\Sigma}^2$). This trend has also been observed for Fluorine passivated AGNRs, though band gap of N=7 F-AGNRs drops from 0.95eV to 0.05eV at extreme torsional strain forming Dirac cone at K allows dissipation less transport for longer wavelength electrons.