Multi-layered material dissipates heat in electronic devices

This is the claim of researchers who have developed a fast and efficient way to make a carbon material that could be used to dissipate heat in electronic devices. The team, from KAUST in Saudi Arabia, claims that the material could have additional uses in applications ranging from gas sensors to solar cells.

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Many electronic devices use graphite films to dissipate heat generated by their electronic components. Although graphite is a naturally occurring form of carbon, heat management of electronics is a demanding application and usually relies on the use of high-quality micrometre-thick manufactured graphite films.

"However, the method used to make these graphite films, using polymer as a source material, is complex and very energy intensive," said Geetanjai Deokar, a postdoc in Pedro Costa's lab, who led the work. The films are made in a multistep process that requires temperatures of up to 3200^oC and which cannot produce films any thinner than a few micrometres.

Deokar, Costa and their colleagues are said to have developed a quick, energy-efficient way to make graphite sheets that are approximately 100nm thick. The team grew nanometre-thick graphite films (NGF) on nickel foils using chemical vapor deposition (CVD) in which the nickel catalytically converts hot methane gas into graphite on its surface. "We achieved NGFs with a CVD growth step of just five minutes at a reaction temperature of 900^oC," Deokar said in a statement.

The NGFs, which could be grown in sheets of up to 55cm², grew on both sides of the foil. According to KAUST, it could be extracted and transferred to other surfaces without the need of a polymer supporting layer, which is a common requirement when handling single-layer graphene films.

Working with Alessandro Genovese, an electron microscopy specialist, the team captured cross-sectional transmission electron microscopy (TEM) images of the NGF on nickel. "Observing the interface of the graphite films to the nickel foil was an unprecedented achievement that will shed additional light on the growth mechanisms of these films," Costa said.

In terms of thickness, NGF sits between commercially available micrometre-thick graphite films and single-layer graphene. "NGFs complement graphene and industrial graphite sheets, adding to the toolbox of layered carbon films," Costa said.

Due to its flexibility, NGF could lend itself to heat management in flexible phones appearing on the market. "NGF integration would be cheaper and more robust than what could be obtained with a graphene film," Costa added.

The team at KAUST said that NGFs could find many applications in addition to heat dissipation. One feature was that some sections of the NGF were just a few carbon sheets thick. "Remarkably, the presence of the few-layer graphene domains resulted in a reasonable degree of visible light transparency of the overall film," Deokar said.

The team proposed that conducting, semi-transparent NGFs could be used as a component of solar cells, or as a sensor material for detecting NO₂ gas. "We plan to integrate NGFs in devices where they would act as a multifunctional active material," Costa said.

The team’s findings are published in Nature Scientific Reports.