Grain rotation and growth in binary hexagonal two-dimensional materials

Generally polycrystalline structures are formed during large-scale fabrication of 2D materials, with individual crystalline domains separated by grain boundaries. During growth, these grain boundaries move and evolve as neighboring grains interact. We study this dynamic process via Phase Field Crystal (PFC) modeling for 2D hexagonal materials. By tracking the motion of circular grains misoriented with respect to the surrounding crystalline matrix, we analyze the angle dependence of grain boundary dynamics and their implications for grain growth. In particular, due to the continuity of lattice planes across the boundary the grain is expected to rotate towards a larger misorientation angle, as governed by the Cahn-Taylor mechanism for the coupled normal-tangential motion of the boundary. For binary 2D materials like hBN our PFC study indicates a dynamic property beyond this geometrically-controlled effect, particularly for grain misorientations close to 30 degree which show abnormally fast rotation and strong normal-tangential coupling. This behavior can be associated with the change of angle dependence of grain boundary energy in binary materials with lattice inversion symmetry breaking.