Many scientists believe that graphene - a 2D sheet of carbon just one atom thick - might replace silicon as the electronic material of choice in the future thanks to its unique electronic and mechanical properties. As electronic devices become ever smaller, local heating (which slows devices down) becomes more important, and silicon especially suffers in this respect. Materials with a higher thermal conductivity can spread this waste heat away more efficiently than materials with a lower thermal conductivity.

Clément Faugeras of the Laboratoire National des Champs Magnétiques Intense in Grenoble, France, and colleagues in the UK and Czech Republic, made measurements on a circle-shaped graphene membrane in their experiments. The membrane was placed on a metallic plate, which acts as an ideal heat sink.

The researchers obtained their results by illuminating the sample with laser light and measuring the local temperature under the laser spot.

Raman scattering
When an object is illuminated with a laser beam, part of the incoming energy is reflected by the solid, part is transmitted through it and the rest is absorbed by the material. Faugeras and colleagues were interested in the fraction of energy absorbed because it heats up the material and acts as a local source of heat. Raman scattering signals can correspond to the emission or to the absorption of a phonon (vibration of the crystal lattice), and the ratio of these two signals can be used to determine the total number of phonons, which in turn, gives the lattice temperature.

A commonly used heat equation is then used to calculate the thermal properties of graphene, explains Faugeras.

The researchers derived a thermal conductivity of 630 Wm–1K–1 for graphene. This value is higher than that of copper, which has a thermal conductivity of around 250 Wm–1K–1 and silicon (150 Wm–1K–1).

"This high thermal conductivity, together with graphene's excellent electrical properties means that the material could be promising for carbon-based electronics," Faugeras told nanotechweb.org.

The team is now also looking at using this type of graphene membrane for magneto-optical studies. "High magnetic fields are extremely powerful tools for studying electron-electron and electron-phonon interactions, and we would like to get an insight into these many-body interactions with optical methods," said Faugeras.

The work was reported in ACS Nano.

•  This article was updated on 22 Apr 2010