Elastic properties of hydrogenated graphene

TL;DR

This study uses first principles calculations to analyze the structural, phonon, and elastic properties of three hydrogenated graphene conformers, revealing unique elastic behaviors including auxeticity and hyperelasticity.

Contribution

It provides the first comprehensive computational analysis of the elastic properties of all three hydrogenated graphene conformers, including their stability and nonlinear elastic responses.

Findings

Boat-graphane exhibits a small negative Poisson ratio (auxetic behavior).

Chair-graphane shows direction-dependent hyperelastic softening and hardening.

All conformers respond with less lateral contraction than pristine graphene.

Abstract

There exist three conformers of hydrogenated graphene, referred to as chair-, boat-, or washboard-graphane. These systems have a perfect two-dimensional periodicity mapped onto the graphene scaffold, but they are characterized by a $sp^3$ orbital hybridization, have different crystal symmetry, and otherwise behave upon loading. By first principles calculations we determine their structural and phonon properties, as well as we establish their relative stability. Through continuum elasticity we define a simulation protocol addressed to measure by a computer experiment their linear and nonlinear elastic moduli and we actually compute them by first principles. We argue that all graphane conformers respond to any arbitrarily-oriented extention with a much smaller lateral contraction than the one calculated for graphene. Furthermore, we provide evidence that boat-graphane has a small and negative Poisson ratio along the armchair and zigzag principal directions of the carbon honeycomb lattice (axially auxetic elastic behavior). Moreover, we show that chair-graphane admits both softening and hardening hyperelasticity, depending on the direction of applied load.