[Paper Review] Effect of edge structures on elastic modulus and fracture of graphene nanoribbons under uniaxial tension

Qiang Lü, Rui Huang|arXiv (Cornell University)|Jul 19, 2010

Carbon Nanotubes in Composites33 references3 citations

TL;DR

This study uses atomistic simulations to investigate how edge structures—armchair and zigzag—impact the elastic modulus and fracture behavior of graphene nanoribbons under uniaxial tension. It reveals that armchair ribbons exhibit lower fracture strain than zigzag ribbons due to edge-controlled heterogeneous nucleation, while hydrogen passivation significantly affects armchair but not zigzag ribbons, with edge chirality and width strongly influencing initial Young's modulus via strain-dependent edge energy effects.

ABSTRACT

Based on atomistic simulations, the nonlinear elastic properties of monolayer graphene nanoribbons under quasistatic uniaxial tension are predicted, emphasizing the effect of edge structures (armchair and zigzag, without and with hydrogen passivation). The results of atomistic simulations are interpreted within a theoretical framework of thermodynamics, which enables determination of the nonlinear functions for the strain-dependent edge energy and the hydrogen adsorption energy, for both zigzag and armchair edges. Due to the edge effects, the initial Young's modulus of graphene nanoribbons under infinitesimal strain varies with the edge chirality and the ribbon width. Furthermore, it is found that the nominal strain to fracture is considerably lower for armchair graphene nanoribbons than for zigzag ribbons. Two distinct fracture mechanisms are identified, with homogeneous nucleation for zigzag ribbons and edge-controlled heterogeneous nucleation for armchair ribbons. Hydrogen passivation of the edges is found to have negligible effect on the mechanical properties of zigzag graphene nanoribbons, but its effect is more significant for armchair ribbons.

Motivation & Objective

• To understand how edge structures (armchair vs. zigzag) influence the mechanical response of graphene nanoribbons under uniaxial tension.
• To quantify the role of ribbon width and edge chirality on the initial elastic modulus.
• To investigate the effect of hydrogen passivation on mechanical properties and fracture mechanisms.
• To identify and differentiate fracture mechanisms across edge types using thermodynamic and atomistic modeling.
• To derive strain-dependent edge energy and hydrogen adsorption energy functions from simulation data.

Proposed method

• Atomistic molecular dynamics simulations under quasistatic uniaxial tension to model mechanical response of monolayer graphene nanoribbons.
• Systematic variation of ribbon width and edge structure (armchair, zigzag, with/without hydrogen passivation).
• Application of thermodynamic framework to interpret simulation results and extract strain-dependent edge energy and hydrogen adsorption energy functions.
• Analysis of stress-strain curves to determine elastic modulus and fracture strain.
• Identification of fracture nucleation sites and mechanisms through atomic-scale observation of bond breaking.
• Comparison of mechanical behavior between zigzag and armchair ribbons to isolate edge-specific effects.

Experimental results

Research questions

• RQ1 How does edge chirality (armchair vs. zigzag) affect the initial elastic modulus of graphene nanoribbons?
• RQ2 What is the influence of ribbon width on the elastic modulus and fracture strain?
• RQ3 How does hydrogen passivation alter the mechanical properties of graphene nanoribbons with different edge structures?
• RQ4 What are the dominant fracture mechanisms in armchair versus zigzag graphene nanoribbons?
• RQ5 How do strain-dependent edge energy and hydrogen adsorption energy vary with deformation?

Key findings

• The initial Young’s modulus of graphene nanoribbons is strongly dependent on edge chirality and ribbon width, with armchair edges showing lower stiffness at small widths.
• Armchair graphene nanoribbons exhibit significantly lower nominal fracture strain than zigzag ribbons, with fracture strain decreasing as ribbon width decreases.
• Zigzag ribbons fail via homogeneous nucleation of cracks, whereas armchair ribbons fail through edge-controlled heterogeneous nucleation.
• Hydrogen passivation has minimal impact on the mechanical properties of zigzag ribbons but significantly increases the fracture strain and modifies the failure mode in armchair ribbons.
• The study derives strain-dependent functions for edge energy and hydrogen adsorption energy, which vary systematically with edge type and deformation.
• Fracture in armchair ribbons is initiated at edge atoms, indicating a strong edge-site sensitivity, while zigzag ribbons show more uniform stress distribution prior to failure.