Accommodating borophene forms heterostructure with graphene

Nanomaterials could form the basis for many emerging technologies, including extremely tiny, flexible and transparent electronics. But while many nanomaterials exhibit promising electronic properties, scientists and engineers are still working on ways to integrate these materials together to create semiconductors and circuits.

Now, in an important step towards creating intergrated circuits from nanomaterials, engineers at Northwestern University have created heterostructures from the two-dimensional (2D) materials graphene and borophene.

"If you were to crack open an integrated circuit inside a smartphone, you'd see many different materials integrated together," said Mark Hersam, professor of materials science and engineering, who led the research. "However, we've reached the limits of many of those traditional materials. By integrating nanomaterials like borophene and graphene together, we are opening up new possibilities in nanoelectronics." Hersam and applied physics PhD student Xiaolong Liu report this work in a paper in Science Advances.

Any integrated circuit contains many materials that perform different functions, like conducting electricity or keeping components electrically isolated. But while transistors within circuits have become smaller and smaller – thanks to advances in materials and manufacturing – they are close to reaching the limit of how small they can get.

Ultrathin 2D materials like graphene have the potential to bypass that limit, but integrating 2D materials together is difficult. These materials are only one atom thick, so if the two materials' atoms do not line up perfectly the integration is unlikely to be successful. Unfortunately, most 2D materials do not match up at the atomic scale, presenting challenges for 2D integrated circuits.

Borophene, the 2D version of boron that Hersam and co-workers first synthesized in 2015, is polymorphic, meaning it can take on many different structures and adapt itself to its environment. That makes it ideal for combining with other 2D materials, like graphene.

To test whether it was possible to integrate the two materials into a single heterostructure, Hersam's lab grew both graphene and borophene on the same substrate. They grew the graphene first, since it grows at a higher temperature, then deposited boron on the same substrate and let it grow in regions where there was no graphene. This process produced lateral interfaces where, because of borophene's accommodating nature, the two materials stitched together at the atomic scale.

The lab characterized the resulting 2D heterostructure using a scanning tunneling microscope and found that the electronic transition across the interface was exceptionally abrupt – which means it could be ideal for creating tiny electronic devices.

"These results suggest that we can create ultrahigh density devices down the road," Hersam said. Ultimately, he hopes to achieve increasingly complex 2D structures that lead to novel electronic devices and circuits. He and his team are now working on creating additional heterostructures with borophene, combining it with an increasing number of the hundreds of known 2D materials.

"In the last 20 years, new materials have enabled miniaturization and correspondingly improved performance in transistor technology," Hersam said. "Two-dimensional materials have the potential to make the next leap."

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