Hydrogenating borophene
The two-dimensional material borophene, which is formed on silver surfaces, has a diverse polymorphism and is predicted to have unusual materials and electronic properties. However, it is highly unstable outside of ultrahigh vacuum conditions and oxidizes readily, which hampers exploration of its properties. Li et al. hydrogenated these materials with atomic hydrogen and showed that borophane has a lower local work function. This material is stable for days in air, and borophene can be recovered simply by thermally driving off the hydrogen.
Science, this issue p. 1143
Abstract
Synthetic two-dimensional polymorphs of boron, or borophene, have attracted attention because of their anisotropic metallicity, correlated-electron phenomena, and diverse superlattice structures. Although borophene heterostructures have been realized, ordered chemical modification of borophene has not yet been reported. Here, we synthesize “borophane” polymorphs by hydrogenating borophene with atomic hydrogen in ultrahigh vacuum. Through atomic-scale imaging, spectroscopy, and first-principles calculations, the most prevalent borophane polymorph is shown to possess a combination of two-center–two-electron boron-hydrogen and three-center–two-electron boron-hydrogen-boron bonds. Borophane polymorphs are metallic with modified local work functions and can be reversibly returned to pristine borophene through thermal desorption of hydrogen. Hydrogenation also provides chemical passivation because borophane reduces oxidation rates by more than two orders of magnitude after ambient exposure.