Researchers integrate diamond/boron nitride crystalline layers for use in high-power devices (Nanowerk News) Materials researchers at North Carolina State University have developed a new technique to deposit diamond on the surface of cubic boron nitride (c-BN), integrating the two materials into a single crystalline structure ("Direct Conversion of h-BN into c-BN and Formation of Epitaxial c-BN/Diamond Heterostructures").

This could be used to create high-power devices, such as the solid state transformers needed to create the next generation smart power grid, says Jay Narayan, the John C. Fan Distinguished Chair Professor of Materials Science and Engineering at NC State and lead author of a paper describing the research.

It could also be used to create cutting tools, high-speed machining and deep sea drilling equipment, Narayan says. Diamond is hard, but it tends to oxidize, transforming into graphite  which is softer. A coating of c-BN would prevent oxidation. Diamond also interacts with iron, making it difficult to use with steel tools. Again, c-BN would address the problem.

C-BN is a form of boron nitride that has a cubic crystalline structure. It has similar properties to diamond, but holds several advantages: c-BN has a higher bandgap, which is attractive for use in high-power devices; c-BN can be doped to give it positively- and negatively-charged layers, which means it could be used to make transistors; and it forms a stable oxide layer on its surface when exposed to oxygen, making it stable at high temperatures. Earlier this year, Narayan unveiled a faster, less expensive technique for creating c-BN.

To create the epitaxial, or single crystal, diamond/c-BN structures, the researchers begin by creating a substrate of c-BN. This is done using the new technique Narayan published earlier this year. They then use a process called pulse-laser deposition  which is done at 500 degrees Celsius and an optimized atmospheric pressure  to deposit diamond on the surface of the c-BN. The pulse-laser technique allows them to control the thickness of the diamond layer.

This is all done in a single chamber, making the process more energy- and time-efficient, Narayan says. You use only solid state carbon and BN, and its more environmentally benign than conventional techniques.

The researchers were also able to deposit diamond on the c-BN using the conventional chemical vapor deposition technique, which utilizes methane gas, hydrogen gas and a tungsten filament at 900 °C.

The chemical vapor deposition approach works, but our pulsed laser deposition approach works much better, doesnt involve toxic gases, and can be done at much lower temperatures, Narayan says.