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

TL;DR

This paper investigates the growth mechanisms of ultrathin two-dimensional perovskite halide films from three-dimensional materials, highlighting the role of Van der Waals interactions and surface energies in controlling film morphology and thickness.

Contribution

It demonstrates the influence of weak Van der Waals interactions on 2D film nucleation and growth from non-layered 3D perovskites, providing new insights into epitaxy of such materials.

Findings

Weak Van der Waals interactions facilitate 2D growth from 3D perovskites.

Surface free energy influences film thickening and morphology.

Monte Carlo simulations reveal competition between diffusion and surface energy.

Abstract

The exploration of emerging materials physics and prospective applications of two-dimensional materials greatly relies on the growth control of their thickness, phases, morphologies and film-substrate interactions. Though substantial progresses have been made for the development of two-dimensional films from conventional layered bulky materials, particular challenges remain on obtaining ultrathin, single crystalline, dislocation-free films from intrinsically non-Van der Waals-type three-dimensional materials. In this report, with the successful demonstration of single crystalline ultrathin large scale perovskite halide material, we reveal and identify the favorable role of weak Van der Waals film-substrate interaction on the nucleation and growth of the two-dimensional morphology out of non-layered materials compared to conventional epitaxy. We also show how the bonding nature of the three-dimensional material itself affects the kinetic energy landscape of ultrathin films growth. By studying the formation of fractal perovskites assisted with Monte Carlo simulations, we demonstrate that the competition between the Van der Waals diffusion and surface free energy of the perovskite leads to film thickening, suggesting extra strategies such as surface passivation may be needed for the growth of monolayer and a few layers films.