Two-Dimensional Van der Waals Epitaxy Kinetics in a Three-Dimensional Perovskite Halide

摘要

The exploration of emerging materials physics and prospective applications oftwo-dimensional materials greatly relies on the growth control of theirthickness, phases, morphologies and film-substrate interactions. Thoughsubstantial progresses have been made for the development of two-dimensionalfilms from conventional layered bulky materials, particular challenges remainon obtaining ultrathin, single crystalline, dislocation-free films fromintrinsically non-Van der Waals-type three-dimensional materials. In thisreport, with the successful demonstration of single crystalline ultrathin largescale perovskite halide material, we reveal and identify the favorable role ofweak Van der Waals film-substrate interaction on the nucleation and growth ofthe two-dimensional morphology out of non-layered materials compared toconventional epitaxy. We also show how the bonding nature of thethree-dimensional material itself affects the kinetic energy landscape ofultrathin films growth. By studying the formation of fractal perovskitesassisted with Monte Carlo simulations, we demonstrate that the competitionbetween the Van der Waals diffusion and surface free energy of the perovskiteleads to film thickening, suggesting extra strategies such as surfacepassivation may be needed for the growth of monolayer and a few layers films.