Borophenes are two-dimensional allotropes of boron (example pictured). Such sheet-like materials, like graphene, for example, can have useful electronic and mechanical properties. However, synthesizing high-quality borophene samples with large single-crystalline areas is challenging. Physical vapor deposition (PVD) approaches using elemental boron, for example, make it difficult to control the growth of the boron sheets and avoid defects. Chemical vapor deposition (CVD) using precursor compounds can offer more control. However, the use of CVD for the synthesis of high-quality crystalline borophenes has been hampered by the lack of a suitable boron precursor.
Marc G. Cuxart, Willi Auwärter, Technical University of Munich, Garching, Germany, Hermann Sachdev, Universität der Bundeswehr München, Neubiberg, Germany, and colleagues have found that diborane can be used as a precursor for the preparation of high-quality atomically thin borophene layers via CVD. The team used this to develop a straightforward and versatile CVD approach to grow borophenes and borophene heterostructures. They obtained diborane from commercial borazine via a freeze-thaw process with a liquid-nitrogen cold trap and dosed it onto a preheated substrate under ultrahigh vacuum (UHV) conditions.
Using this approach, borophenes were grown on Ir(111) and Cu(111) single-crystal substrates. The team also used it for the combined growth of borophene and single-layer hexagonal boron nitride (hBN). For this, they selectively dosed either diborane or borazine onto the substrate by activating or deactivating the cold trap. They found that borophene can be protected from oxidation by a hBN overlayer. The developed method could allow studies of the properties of borophenes and provide opportunities for their application.
- Borophenes made easy,
Marc G. Cuxart, Knud Seufert, Valeria Chesnyak, Wajahat A. Waqas, Anton Robert, Marie-Laure Bocquet, Georg S. Duesberg, Hermann Sachdev, Willi Auwärter,
Sci. Adv. 2021.