A novel borophene featuring heptagonal holes: a common precursor of borospherenes

We propose a novel stable borophene (referred to as H-borophene) by tiling seven-membered rings side by side, which is a novel construction pattern never reported in boron sheets or other sheets. It is able to serve as the common precursor of borospherenes (e.g., B₃₉^-, B₄₀, B₄₁⁺, and B₄₂²⁺). Interestingly, a Dirac point appeared at about 0.33 eV below the Fermi level. We found that nanotubes formed by rolling up H-borophene had a great advantage over other boron nanotubes in the case of high curvature, which accounted for the reason why heptagons were preferred in borospherenes. Our study not only proposes a common precursor of borospherenes, but also expands the construction patterns of monolayer sheets.