DFT Calculations and Reaxff Development for MD Simulations of H-BN Growth on Nickel Surfaces

DFT CALCULATIONS AND REAXFF DEVELOPMENT FOR MD SIMULATIONS OF H-BN GROWTH ON NICKEL SURFACES

Song Liu, Bin Liu, Adri, van Duin, and James H. Edgar

Department of Chemical Engineering, Kansas State University, Manhattan, Kansas 66506

Hexagonal boron nitride (h-BN), also known as the white graphene, is a layered, 2D material structurally analogous to the carbon-based graphene. Due to its unique structural, electronic, and optical properties, high quality h-BN single crystals have many potential applications, e.g., as ultraviolet light emitters for water purification, or as the neutron detector for sensing fissile materials. Therefore, a detailed mechanistic understanding of h-BN crystal growth is critical to improve the synthesis techniques to produce high quality crystals.

In this work, density functional theory (DFT) and reactive molecular dynamics (MD) simulations – using the ReaxFF force field – were employed to understand the mechanism of h-BN growth on nickel substrates. The energetics and kinetics of diffusion and B-N bond formation on flat and stepped Ni(111) and Ni(211) surfaces were calculated by DFT. Then a ReaxFF force field potential describing the B-Ni and N-Ni interactions was developed from the DFT calculations. These predict that the atomic (B, N) species and B_xN_y subunits bind much stronger at low-coordinated step-edge sites on the Ni(211) surface than the terrace Ni(111) surface, thus, suggesting that the h-BN growth primarily starts from such sites. The pathways for nucleation and growth were investigated. On the step edge sites, growth of h-BN structures with zig-zag edges are more energetically stable. On the flat terrace sites, the calculated energetics suggests that the h-BN structures start with linear BN configurations, followed by branching and formations of 5- and 6-membered rings.

In order to validate the developed ReaxFF force field and confirm the growth pathways, NVT-MD simulations were designed and performed starting from elemental B and N species in the temperature range 1100-1500 K. The elemental B and N species are deposited to a Ni substrate stepwise. The formation of a continuous h-BN network occurs at 1500 K, and is consistent with the paths predicted by DFT calculations. Further mechanistic insights derived from the MD simulations will be presented and discussed in this work as well.