Elastic Properties of BCN Alloys, Graphene, and h‑BN Monolayers Containing Point Defects

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• Point defects significantly influence the mechanical properties of two-dimensional (2D) materials, often detrimentally affecting strength, stiffness, and elasticity.
• Existing literature presents conflicting reports on the precise role of defects, highlighting an incomplete understanding at the atomic level.

Purpose of the Study:

• To systematically assess the impact of substitutional impurities and vacancies on the mechanical properties of hexagonal boron nitride (h-BN) and graphene monolayers.
• To investigate the mechanical behavior of two-dimensional BCN alloys, representing high concentrations of substitutional impurities in h-BN and graphene.

Main Methods:

• Utilized first-principles calculations to perform a comprehensive computational study.
• Analyzed the effects of varying concentrations of carbon (C) atoms as impurities and vacancies in h-BN and graphene.
• Examined local defect-mediated strain fields to explain observed mechanical property changes.

Main Results:

• In general, point defects decrease the Young's modulus (stiffness) of 2D materials.
• h-BN stiffness decreases rapidly with increasing C concentration in nitrogen (N) positions, with a smaller drop for C in boron (B) positions.
• Specific defect configurations in 2D BCN alloys yield Young's modulus values between those of pristine graphene and h-BN, indicating tunable properties.

Conclusions:

• The mechanical properties of 2D materials, including graphene and h-BN, are significantly affected by point defects and vacancies.
• The observed mechanical weakening in graphene and h-BN due to defects is consistent with most experimental findings.
• Predictions suggest that preferential substitution of B and N atoms with C in 2D BCN alloys can be used to engineer mechanical properties.