Prediction of two stable freestanding β12 borophanes: Structure, electronic properties, and superconductivity

Borophene has several configurations and shows many unique properties, such as the Dirac point, the negative Poisson's ratio, inherent metallicity, but it is oxidized easily. Recently, ordered chemical modulation of ${\ensuremath{\beta}}_{12}$ borophene grown on the Ag(111) substrate by hydrogenation was experimentally reported, and three configurations of ${\ensuremath{\beta}}_{12}$ borophane were proposed by scanning tunneling microscopy and spectroscopy [Science 371, 1143 (2021)]. In this paper, using first-principles calculations, we study seven configurations of hydrogen atoms adsorbed on freestanding ${\ensuremath{\beta}}_{12}$ borophene not only including the three adsorption structures in above literature, but also other four possible configurations with one or two hydrogen atoms adsorbed on it per unit cell. Among the seven configurations, we predict two stable ${\ensuremath{\beta}}_{12}$ borophanes. They possess the dynamic stability and different anisotropic metallicity from pristine ${\ensuremath{\beta}}_{12}$ borophene and show superconductivity. Based on the Eliashberg equation, the calculated electron-phonon coupling strength are about 0.82 and 0.52, and their superconducting transition temperature ${T}_{\mathrm{c}}$ are 20.51 and 5.90 K, respectively. Thus, these borophanes provide new platforms for two-dimensional superconductivity and antioxidation of borophene.