Synthesis of Borophan Polymorphs by Borophene Hydrogenation


Borophene hydrogenation

Borophene, a two-dimensional material, which forms on silvery surfaces, has a diverse polymorphism and is expected to have unusual materials and electronic properties. However, it is very unstable outside of ultra-high vacuum conditions and oxidizes easily, making it difficult to explore its properties. Li et al. He hydrogenated these materials with atomic hydrogen and showed that borophan has a lower local work function. This material is stable for days in air and borophene can be recovered simply by thermally expelling the hydrogen.

Sciences, this number p. 1143

Summary

Two-dimensional synthetic polymorphs of boron, or borophene, have attracted attention due to their anisotropic metallicity, electron correlated phenomena, and various superlattice structures. Although borophene heterostructures have been made, the ordered chemical modification of borophene has not yet been reported. Here, we synthesize “borophan” polymorphs by hydrogenating borophene with atomic hydrogen in ultra-high 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 boron-hydrogen-boron bonds. electrons. Borophan polymorphs are metallic with modified local working functions and can be reversibly returned to pristine borophene by thermal desorption of hydrogen. Hydrogenation also provides chemical passivation because borophan reduces oxidation rates by more than two orders of magnitude after environmental exposure.

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