Stabilizing honeycomb borophene by metal decoration: a computational study

Two dimensional monolayer materials have been proved to possess immense potential for applications in electronic and spintronic devices. Of these, boron monolayers exhibit a rich polymorphism of structures, of which the hexagonal structure, identical to graphene, is a possibility. However, honeycomb borophene (hc-B) by itself in its free-standing form is unstable, due to the in-plane sigma bands and the out-of-plane pi bands being partially occupied. Adsorption of light metals on the monolayer can alter the electronic structure of hc-B, due to charge transfer. This is computationally modeled using Density Functional Theory (DFT) for investigating energetics, geometry and electronic structure. In the case of beryllium decorated hc-B, it is found that the bonding sigma and pi bands are pushed below the Fermi level, due to charge transfer, thus stabilizing hc-B. Analysis of the density of states, band structure and charge transfer shows that the stability is greatest when hc-B is made iso-electronic with graphene. Phonon dispersion of the beryllium decorated structure further establishes the relative stability with respect to free-standing hc-B. Studies varying the coverage of beryllium atoms on hc-B show that the electronic structure and therefore the stability of hc-B are coverage dependent.