The placement of a single atomic plane of graphene on the surface of a copper film can significantly increase the film’s thermal conductivity, making the hybrid material ideal for more demanding thermal management applications, according to new research from scientists at the University of Manchester, UK and the University of California-Riverside, U.S.
The phenomenon was discovered while studying how the thermal properties of copper films change as graphene synthesized by chemical vapour deposition (CVD) is placed on top of the films. The team attributes the results to changes in the copper’s morphology rather than from the graphene acting as an additional heat-conducting channel. Their research is published in the journal Nano Letters.
“The fact that we observed a substantial increase in the thermal conductivity of the graphene-copper heterofilms took us by surprise at first,” Alexander Balandin of the University of California-Riverside, who led the project along with Konstantin Novoselov of the University of Manchester. “But, after carefully examining the grain sizes in copper before and after graphene had been deposited, we then realized that the act of coating graphene (via CVD) at high temperatures in the copper actually causes the grains in the copper films to grow.”
This increase in grain size is larger than in reference copper films that were simply heated to the same temperatures as those employed in the CVD process, he explained. The larger copper grain size, coupled with the graphene coating, results in higher thermal conductivity.
The researchers say they have only examined thick copper foils thus far, but plan to examine how heat conduction properties change in nanometer-thick copper films coated with graphene. Balandin believes examining these thinner copper films would provide a better understanding of how the phenomenon would work in the context of “real” graphene-copper hybrid interconnects.
“On the theoretical side, we have already developed a relatively simple model to explain how thermal conductivity scales with copper grain size and now plan to put forward a more accurate theory to predict the effect in downscaled copper-graphene hybrids,” he said.
