Thermoelectrics is the field of study that deals with situations in which a temperature difference creates an electric potential, or vice versa, an electric potential creates a temperature difference. One example of this is the Peltier effect, which is a temperature difference that appears when a voltage is applied between two electrodes connected to a semiconductor material. The Peltier effect allows the electrical control of cooling and heating.
Researchers from University of Groningen and the University of Manchester have now, for the first time, directly detected the Peltier effect in graphene that is either one or two atoms thick. They unambiguously showed that the effect can be switched from heating to cooling by tuning the type and density of the charge carriers inside the material. Their work was published last week in Nature Communications.
They used graphene because of its two-dimensional nature: graphene is a sheet of carbon atoms that is typically only one atom thick. It is therefore the best candidate to demonstrate a fully tuneable Peltier effect. Electrical contacts to graphene allowed to electrically control the cooling and heating via the Peltier effect. To detect this cooling and heating, the researchers constructed sensitive nanoscale thermometers that directly measured the temperature of electrons in graphene. This practical approach is the first of its kind for any two-dimensional material, and its sensitivity is a thousand times better than that of its predecessors, down to 0.1 milliKelvin.
Thermoelectrics can play a role in heat managing and in generating electrical energy from wasted heat. The emerging family of atomically thin materials, like graphene, offers exciting opportunities because it’s relatively easy to tune their thermoelectric properties. Therefore, the scientific interest on the interaction between charge and heat in two-dimensional materials opens the path to both novel fundamental studies, and can help realize more sustainable electronics.