This image shows the novel solution process for the bottom-up synthesis of crystalline-stacked boron atomic layers, and illustrates how conductivity measurements revealed the electronic properties of the layers. Image: Tokyo Tech.
This image shows the novel solution process for the bottom-up synthesis of crystalline-stacked boron atomic layers, and illustrates how conductivity measurements revealed the electronic properties of the layers. Image: Tokyo Tech.

Since its discovery and characterization in 2004, graphene has been the focus of a great deal of research effort across multiple fields. Graphene is a very versatile two-dimensional (2D) carbon material comprising a thin sheet of carbon with a thickness of one atom. It is not only stronger than the strongest steel, but also has a myriad of interesting chemical, electronic and mechanical characteristics that have left scientists wondering if other 2D materials could have similar useful properties.

One novel 2D material that was recently reported is borophene, an analogue of graphene that consists of boron atoms instead of carbon atoms. But as one would expect for 2D sheets of any material, the synthesis of borophene has proved to be challenging. Researchers either need to use a substrate to make borophene more stable or couple boron with hydroxyl groups (OH-), which produces a structure that isn’t atomically flat.

In a recent study conducted at Tokyo Institute of Technology in Japan, a research team that included Tetsuya Kambe, Akiyoshi Kuzume and Kimihisa Yamamoto successfully synthesized atomically flat oxidized borophene sheets through a simple solution-based method. They report this method in a paper in the Journal of the American Chemical Society.

First, they synthesized stacked layers of borophene oxide in a fairly simple process that utilized a potassium borohydride salt (KBH4). An X-ray analysis revealed the 2D-layered structure of this material, in which layers of boron atoms form a hexagonal 2D network with oxygen atoms, as bridges are intercalated with layers containing potassium atoms.

The next step was to find a way to exfoliate atomically thin layers of borophene oxide, which the researchers achieved by immersing the material in dimethylformamide, a commonly used organic solvent. They performed various types of measurements to verify the structure of the exfoliated sheets, including electron microscopy, spectroscopy and atomic force microscopy. These confirmed that the proposed method was effective at producing the desired atomically flat, oxidized borophene sheets.

Finally, the researchers performed resistivity measurements to analyze the conducting properties of stacked borophene sheets and found an interesting characteristic referred to as anisotropy. This means the sheets exhibited different types of conductivity depending on the direction of the current flow. The material behaved like a semiconductor in the inter-plane direction, whereas it exhibited metal-like behavior in the in-plane direction. The researchers also elucidated the mechanisms behind these two types of conducting behaviors.

"It is important to note that our boron sheets can be handled easily at ambient conditions," says Kambe, indicating that this pioneering research could be the basis for finding potential applications for borophene.

Finding facile methods for the synthesis of borophene and borophene-based compounds is crucial to conducting further research on this interesting material and its potential uses. "Like graphene, borophene is expected to have unique properties, including extraordinary mechanical characteristics and metallic behavior that could be exploited in a variety of fields," says Kambe.

This story is adapted from material from the Tokyo Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.