Towards Coveted Borophene on Insulators, Enabled by Step-Edge Epitax

Borophene, the two-dimensional (2D) monolayer of boron, has drawn tremendous attention due to its unique polymorphism and intriguing properties. The state-of-art syntheses employ the metal substrates that provide strong binding to boron atoms, stabilizing 2D borophene phases. However, the very same strong adhesion [1] that enables monolayer and recently even bilayer [1] growth, prevents subsequent exfoliation and hinders obtaining, characterization or use of free-standing layers. On the other hand, more inert weakly-binding substrates that would ease up exfoliation, do not provide sufficient areal attraction to enable 2D growth. Following our recent work on the lateral, edge-to-step 2D epitaxy [2] we investigate the possibility of borophene growth stabilization through dimensionality reduction on the nucleation stage. Using ab initio calculations of the epitaxial borophene growth on the h-BN surface we propose a novel growth methodology near naturally present 1D-defects. We demonstrate an order of magnitude reduction in the nucleation barrier due to covalent bonding to the exposed substrate while maintaining minimal areal adhesion [3]. This approach not only exemplifies the importance of the lateral epitaxy mechanism in the growth of 2D materials but also provides a practical approach to the synthesis of novel nanomaterials.<br/>[1] Liu, X.; Wang, L.; Yakobson, B. I.; Hersam, M. C. Nano Lett. 2021, 21, 1174;<br/>[2] Bets, K. V.; Gupta, N.; Yakobson, B. I. How the Complementarity at Vicinal Steps Enables Growth of 2D Monocrystals. Nano Lett. 2019, 19, 2027.<br/>[3] Q. Ruan, L. Wang, K.V. Bets, B.I. Yakobson, Step-Edge Epitaxy for Borophene Growth on Insulators, ACS Nano, accepred (2021).