Model shows how copper ‘islands’ become squashed under graphene ‘blanket’

In a collaboration between the US Department of Energy's Ames Laboratory and Northeastern University, scientists have developed a model for predicting the shape of metal nanocrystals, or ‘islands’, sandwiched between or below two-dimensional (2D) materials such as graphene. This advance, reported in a paper in Nanoscale, moves 2D quantum materials a step closer to applications in electronics.

Ames Laboratory scientists are experts in 2D materials, and recently discovered a first-of-its-kind copper and graphite combination, produced by depositing copper on ion-bombarded graphite at high temperatures and in an ultra-high vacuum environment. This produced a distribution of copper islands, embedded under an ultra-thin ‘blanket’ consisting of a few layers of graphene.

"Because these metal islands can potentially serve as electrical contacts or heat sinks in electronic applications, their shape and how they reach that shape are important pieces of information in controlling the design and synthesis of these materials," said Pat Thiel, an Ames Laboratory scientist and professor of chemistry and materials science and engineering at Iowa State University.

Ames Laboratory scientists used scanning tunneling microscopy to painstakingly measure the shapes of more than 100 nanometer-scale copper islands. This provided the experimental basis for a theoretical model developed jointly by researchers at Northeastern University's Department of Mechanical and Industrial Engineering and Ames Laboratory. This model served to explain the data extremely well; the one exception, concerning copper islands less than 10nm tall, will be the basis for further research.

"We love to see our physics applied, and this was a beautiful way to apply it," said Scott Julien, a PhD candidate at Northeastern University. "We were able to model the elastic response of the graphene as it drapes over the copper islands, and use it to predict the shapes of the islands."

The work showed that the top layer of graphene resists the upward pressure exerted by the growing metal island. In effect, the graphene layer squeezes downward and flattens the copper islands. Accounting for these effects, as well as other key energetics, leads to the unanticipated prediction of a universal, or size-independent, shape of the islands, at least for sufficiently large islands of a given metal.

"This principle should work with other metals and other layered materials as well," said Ann Lii-Rosales, a research assistant at Ames Laboratory. "Experimentally we want to see if we can use the same recipe to synthesize metals under other types of layered materials with predictable results."

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