A team of researchers belonging to the Tokyo Institute of Technology, including Akiyoshi Kuzume, Kimihisa Yamamoto, and Tetsuya Kambe has successfully fabricated atomically flat oxidized borophene sheets by employing a simple solution-based method. The research revolved around a novel 2D material named borophene, an analog of graphene but instead of carbon atoms, it contains boron atoms. However, synthesizing borophene has been challenging as it can be done either by the use of a substrate to make borophene more stable or by combining boron with hydroxyl groups (OH-), which could give the researchers the atomically flat structure.
The research started with the synthesis of stacked layers of borophene oxide through a process involving potassium borohydride salt (KBH4). X-ray analysis suggested that the 2D-layered structure of the material, which consisted of layers of boron atoms in a hexagonal 2D structure with oxygen atoms as bridges intercalated with layers of potassium atoms. The team then needed to find a way to extract atomically thin layers of the borophene oxide network, which was achieved by putting the material in dimethylformamide, a commonly used organic solvent. Several types of measurements were tested to verify the structure of the exfoliated sheets, including electron microscopy, atomic force microscopy, and spectroscopy. By employing this method, the team was successful in producing atomically flat oxidized borophene sheets. In the final step, the researchers performed resistivity measurements to inspect the conducting properties of stacked borophene sheets and discovered a fascinating characteristic termed anisotropy, which means that the sheets possess different types of conductivity subject to the direction of the current flow. The material acted like a semiconductor in the inter-plane direction, although it exhibited metal-like properties in the in-plane direction of the boron network.
Discovering simple methods for synthesizing borophene as well as borophene-based compounds is vital for the advancement of research on the material and the expansion of its applications. Dr. Kambe explains that like graphene, borophene is expected to possess unique characteristics, including extraordinary mechanical properties and metallic behavior that could prove to be useful in various fields.