An international team is working towards a way to make high-quality crystalline monoisotopic hexagonal boron nitride (hBN) at atmospheric pressure. Their research could open up new ways to make devices based on the carbon allotrope graphene function even more effectively by making the known process of sandwiching a carbon monolayer between two protective layers of hBN work better. It could also open up new research into phenomena that were hinted at such as exotic effects like magic-angle superconductivity.
The hBN crystals used in most experiments have been grown by a team in Japan using a complex high-temperature and high-pressure process. Taniguchi and Watanabe provide their materials to the scientific community at no charge. "They provide hundreds of labs around the world with ultra-pure hBN at no charge. Without their contribution, a lot of what we are doing today would not be possible," says Christoph Stampfer of RWTH Aachen University, Germany, who is part of the team working on the new approach.
The rather successful and useful Japanese does have limitations in that the hBN that can be grown in this way forms crystals limited to about 100 micrometers. A scalable method is now needed if hBN is to become an industrially tenable material. A team led by James Edgar of Kansas State University in the USA has developed the process with which the collaborators have worked.
"I was very excited when Edgar proposed that we test the quality of his hBN", says Stampfer. "His growth method could be suitable for large-scale production". The new method is far indeed much simpler and less costly than previously used methods. "The hBN crystals we received were the largest I have ever seen, and they were all based either on isotopically pure boron-10 or boron-11" adds Jens Sonntag of Aachen. The team used confocal Raman spectroscopy to test the quality of the crystals. hBN graphene sandwiches were then shown to have equivalent performance to those made with the Japanese hBN.
"This is a clear indication of the extremely high quality of these hBN crystals," explains Stampfer. "This is great news for the whole graphene community, because it shows that it is, in principle, possible to produce high quality hBN on a large scale, bringing us one step closer to real applications based on high-performance graphene electronics and optoelectronics. Furthermore, the possibility of controlling the isotopic concentration of the crystals opens the door to experiments that were not possible before."
hBN could be an essential material for the integration of graphene devices into current technology. A scalable synthetic route to the material paves the way. [Sonntag, J., et al., 2D Mater. 2020, DOI: 10.1088/2053-1583/ab89e5]