Structure of porous two-dimensional boron crystals

In this work, we foresee the structure of a new class of borophenes with smaller two-dimensional (2D) densities of atoms than those explored so far for 2D boron crystals. Boron atoms in the porous borophenes tend to be five-coordinated in contrast with commonly investigated structures with hexagonal holes for which the number of nearest neighbors of each atom varies from three to six. High metallic character is the usual feature of borophenes, however, we have also identified a semimetallic borophene that turns into a semiconductor upon unit-cell expansion. A 10% increase in lattice constant of this structure gives rise to an energy gap of 0.3 eV. This extends to semiconductor industry the possible application of 2D boron crystals.