New Twist on Epitaxial Growth Opens New Possibilities for Two-Dimensional Materials

Some people believe that developing new manufacturing techniques for nanoscale devices, like new types of epitaxy in which crystals are grown on a substrate, may in fact be more critical to producing the next generations of chips than just creating new materials.

Along these lines, researchers at Oak Ridge National Laboratory (ORNL) and the University of Tennessee (UT) have developed a new technique for creating a two-dimensional hybrid material of graphene and boron nitride that has a seamless boundary.

“People call graphene a wonder material that could revolutionize the landscape of nanotechnology and electronics,” ORNL’s An-Ping Li said in a press release. “Indeed, graphene has a lot of potential, but it has limits. To make use of graphene in applications or devices, we need to integrate graphene with other materials.”

Last year, researchers at Rice University developed a process to combine graphene and boron nitride that used lithography techniques to weave the two 2-D materials together. This latest ORNL/UT work, which was published in the journal Science (“Heteroepitaxial Growth of Two-Dimensional Hexagonal Boron Nitride Templated by Graphene Edges”), is based on epitaxy, but with a bit of twist to make the two materials grow together.

The first twist is that the epitaxial growth is oriented horizontally rather than vertically. The graphene is grown on a copper substrate. The edges of the graphene are then etched away and the boron nitride is added through chemical vapor deposition. In this way, the boron nitride does not take on the crystalline structure of the copper substrate but that of the graphene.

“The graphene piece acted as a seed for the epitaxial growth in two-dimensional space, so that the crystallography of the boron nitride is solely determined by the graphene,” UT’s Gong Gu said in the release.

Perhaps even more important than joining the two materials together was that the boundaries between the two materials were atomically precise. It is this atomic precision of the one-dimensional interface between these two materials that could prove the key to seeing the production of practical devices.

In a reference to Nobel laureate Herbert Kroemer’s famous phrase “the interface is the device,” ORNL’s Li said, ““If we want to harness graphene in an application, we have to make use of the interface properties. By creating this clean, coherent, 1-D interface, our technique provides us with the opportunity to fabricate graphene-based devices for real applications.”

While this work could yield applications for devices built around 2-D materials, its effect on current research may have the most immediate impact.

“There is a vast body of theoretical literature predicting wonderful physical properties of this peculiar boundary, in absence of any experimental validation so far,” said Li, who leads an ORNL effort to study atomic-level structure-transport relationships using the lab’s unique four-probe scanning tunneling microscopy facility. “Now we have a platform to explore these properties.”

Image: ORNL

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