A bottom-up approach from medium-sized bilayer boron nanoclusters to bilayer borophene nanomaterials.

Inspired by the experimentally observed bilayer B and theoretically predicted bilayer B-B and based on extensive density functional theory calculations, we report herein a series of novel medium-sized bilayer boron nanoclusters B (I), B (II), B (III), B (IV), B (V), B (VI), B (VII), and B (VIII) which are the most stable isomers of the systems reported to date effectively stabilized by optimum numbers of interlayer B-B σ bonds between the inward-buckled atoms on top and bottom layers. Detailed bonding analyses indicate that these bilayer species follow the universal bonding pattern of σ + π double delocalization, rendering three-dimensional aromaticity in the systems. More interestingly, the AA-stacked bilayer structural motif in B (VII) with a B bilayer hexagonal prism at the center can be extended to form bilayer B (IX), B (X), B (XI), B (XII), and B (XIII) which contain one or multiple conjoined B bilayer hexagonal prisms sharing interwoven zig-zag boron triple chains between them. Such bilayer species or their close-lying AB isomers can be viewed as embryos of the newly reported most stable freestanding BL-α bilayer borophenes and quasi-freestanding bilayer borophenes on Ag(111) which are composed of interwoven zig-zag boron triple chains shared by conjoined BL B hexagonal prisms, presenting a bottom-up approach from medium-sized bilayer boron nanoclusters to two-dimensional bilayer borophene nanomaterials.