Exploring the structure and properties of α-sheet based bilayer borophenes.

Recent experimental realizations of bilayer boron materials motivated us to study the structure and properties of α-sheet-based bilayer borophenes with interlayer covalent bonds. As shown here, at least three stacking variations are possible: AA, AB, and [Formula: see text]. The on-top AA-stacking has been obtained experimentally supported on a metallic substrate. The AB-stacking is the most stable among neutral freestanding structures, whereas the AA and [Formula: see text] stacking sequences are very close in energy, both for neutral and negatively charged cases. The studied bilayer borophenes exhibit extraordinarily high electric conductivity with values as high as [Formula: see text] for the experimentally observed AA-stacking. The highly stable AB-stacking bilayer, reported here for the first time, exhibits an anisotropic conductivity with an average value of [Formula: see text]. Contrary to the AA-stacking bilayer that retains the 6-fold fold rotational symmetry of the α-sheet, the AB-stacking structure has 2-fold symmetry, which leads to the anisotropic transport properties.