Atomistic insights into the anisotropic mechanical properties and role of ripples on the thermal expansion of h-BCN monolayers

Monolayer boron-carbon-nitrogen (h-BCN) has been studied in comparison with graphene and hexagonal boron nitride (h-BN) using classical molecular dynamics (MD) simulations with an aim to better understand the structural and thermal behaviors and the anisotropic mechanical properties. The structural features of the simulated sample were analyzed using the pair-correlation function and a full width at half maximum (FWHM). As a hetero-structure of h-BN and graphene, the C-C bond in the h-BCN is responsible for an improved FWHM compared to graphene. Consistent with graphene and h-BN, the in-plane lattice parameter of h-BCN shows thermal contraction over a wide range of temperatures and exhibits a system size dependence. The observed thermal contraction is explained by the presence of out-of-plane bending modes excited at finite temperatures. A tensile test has been performed as a suitable means of measuring the mechanical properties of the h-BCN sheet for zigzag and armchair orientations and found that it is mechanically anisotropic and stable under various strain directions and temperatures. The fracture strength of h-BCN is affected by loading direction and temperature. We found that the Young's modulus of h-BCN is smaller than that of graphene but is higher than that of an h-BN monolayer, suggesting that h-BCN has high mechanical stiffness. Our modeling-based findings provide a guide for future experiments concerning the physical properties of this advanced composite material.