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April 15th, 2010

Superior heat transfer ability of graphene-on-substrate demonstrated

Published on April 15th, 2010 | By: pwray@ceramics.org
A) Previous thermal conductivity measurements were performed on suspended graphene. (B) Seol et al. instead studied graphene supported on a substrate. The graphene layer does not conform to the nanoscale roughness of the substrate; rather, it makes contact on the summits of the rough surface, interacting with the substrate through van der Waals forces (red springs).  Credit: E. E. Zumalt/Univ. of Texas at Austin

A) Previous thermal conductivity measurements were performed on suspended graphene. (B) Researchers have now studied graphene supported on a SiO2 substrate. The graphene layer makes contact on the summits of the rough surface, interacting with the substrate through van der Waals forces. Credit: E. E. Zumalt/Univ. of Texas at Austin

Those engineering electronic devices always have had to factor in the use of special materials that can conduct heat away from crucial components. Bulk copper’s thermal conductivity is pretty good at around 400 watts per meter per kelvin, but this ability decreases as the copper approaches film-size dimensions.

Diamond has long been known to have excellent thermal conductivity properties, so carbon forms are a logical area to focus on in the search for better materials. Indeed, researchers had shown in 2008 that a suspended monolayer of graphene and carbon nanotubes have thermal conductivity of 5000 W m-1 K-1 at room temperature.

Now an international team of researchers from the University of Texas at Austin, Boston University, Christopher Newport University and Commissariat à l’Énergie Atomique have taken the next logical step and tested a graphene monolayer on an SiO2 substrate (via mechanical exfoliation). As the graphic above indicates, the graphene doesn’t completely adhere to the substrate, but sits on its high points.

The team found that the graphene–SiO2 combination delivered very good thermal conductivity, around 600 W m–1 K–1 . As Ravi Prasher notes in a commentary about this work,  this is “an order of magnitude lower than that of suspended graphene. However, this is still higher than the thermal conductivities of bulk or thin-film copper.”

According to David Broido, a Boston College professor of physics, the decrease is the result of graphene’s interaction with the substrate. The combination interferes with the vibrational waves of graphene atoms as they bump against the adjacent substrate.

This suggests a promising route for creating a new generation of devices that will consume less energy, be cooler and more reliable, and operate faster than the current generation of silicon and copper devices.

 


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