Substrate-mediated Borophane Polymorphs through Hydrogenation of Two-dimensional Boron Sheets

TL;DR

This study uses first-principles calculations to identify optimal hydrogen adsorption configurations on various borophene polymorphs and substrates, revealing mechanisms to stabilize 2D boron structures through hydrogenation.

Contribution

It provides detailed insights into hydrogenation sites and mechanisms for different borophene polymorphs and substrates, advancing stabilization strategies for 2D boron materials.

Findings

Optimal hydrogen adsorption sites depend on borophene type and substrate.

Hydrogenation configurations are significantly influenced by metal substrates.

Hydrogenation can stabilize borophene polymorphs by engineering adsorption sites.

Abstract

Two-dimensional boron monolayer (borophene) stands out from the two-dimensional atomic layered materials due to its structural flexibility, tunable electronic and mechanical properties from a large number of allotropic materials. The stability of pristine borophene polymorphs could possibly be improved via hydrogenation with atomic hydrogen (referred to as borophane). However, the precise adsorption structures and the underlying mechanism are still elusive. Employing first-principles calculations, we demonstrate the optimal configurations of freestanding borophanes and the ones grown on metallic substrates. For freestanding {\beta}12 and {\chi}3 borophenes, the energetically favored hydrogen adsorption sites are on the top of the boron atoms with CN=4 (CN: coordination number), while the best absorption sites for {\alpha}' borophene are on the top of the boron atoms with CN=6. With various metal substrates, the hydrogenation configurations of borophene are modulated significantly, attributed to the chemical hybridization strength between B pz and H s orbitals. These findings provide a deep insight into the hydrogenating borophenes and facilitate the stabilization of two-dimensional boron polymorphs by engineering hydrogen adsorption sites and concentrations.