Evolution of ordered nanoporous phases during h-BN growth: Controlling the route from gas-phase precursor to 2D material by $\textit{in-situ}$ monitoring

TL;DR

This study uses helium atom scattering to monitor and control the formation of novel nanoporous phases during h-BN growth via CVD, revealing intermediate structures that can be exploited for advanced 2D material engineering.

Contribution

It uncovers and characterizes metastable nanoporous phases during h-BN CVD growth, providing new insights into the synthesis process and potential for material engineering.

Findings

Discovery of a metastable (3×3) structure before h-BN formation

Identification of a (3×4) structure from excess deposition

Linking nanoporous structures to precursor dehydrogenation and polymerisation

Abstract

Large-area single-crystal monolayers of two-dimensional (2D) materials such as graphene and hexagonal boron nitride (h-BN) can be grown by chemical vapour deposition (CVD). However, the high temperatures and fast timescales at which the conversion from a gas-phase precursor to the 2D material appear, make it extremely challenging to simultaneously follow the atomic arrangements. We utilise helium atom scattering to discover and control the growth of novel 2D h-BN nanoporous phases during the CVD process. We find that prior to the formation of h-BN from the gas-phase precursor, a metastable $(3\times3)$ structure is formed, and that excess deposition on the resulting 2D h-BN leads to the emergence of a $(3\times4)$ structure. We illustrate that these nanoporous structures are produced by partial dehydrogenation and polymerisation of the borazine precursor upon adsorption. These steps are largely unexplored during the synthesis of 2D materials and we unveil the rich phases during CVD growth. Our results provide significant foundations for 2D materials engineering in CVD, by adjusting or carefully controlling the growth conditions and thus exploiting these intermediate structures for the synthesis of covalent self-assembled 2D networks.