First-Principles Particle-Swarm Structure Calculations on Metal Substrate Modulated Monolayer to Bilayer Borophene Crystalline Structures toward Nanoelectronics

The possible structures of borophene have attracted great research interests during the past years due to the multicenter bonding characteristics derived from the electron deficiency of elemental boron. Particularly, the diverse structural architectures of borophene obtained in the experiment reveal the substrate-modulation characteristic, yet not fully explored. Herein, the global structures of borophene interfacially confined on Al(111), Ag(111), and Au(111) substrates are identified through the structure-search method based on particle swarm optimization and first-principles calculations. It unveils first the evolvement from monolayer to bilayer or cluster borophene with elevated boron density. Two energetically preferential bilayer structures, i.e., δ3β12 and BL-α5, are confirmed on Al and Ag, and a peculiar cluster layer, IH-BS, is observed on Au, originated from the differences in electronegativities (Au > B > Ag > Al). Notably, both the BL-α5 and IH-BS are semiconducting with band gaps of 1.141 and 1.136 eV, and δ3β12 is metallic. This work demonstrates the substrate-modulated borophene structures with potential applications in nanoelectronics.