08 February 2016 Directing energy flow with graphene in Nature Physics

Optical image of a G–BN–G device

The study carried out by MIT, NIMS and ICFO used graphene to control electron energy transport in nano-devices. Directing the energy flow of electrons is at the heart of photovoltaics and photodetection. As electrons in graphene collide vary rapidly, completely new concepts for real-life applications can be explored.

When light hits graphene, the electronic thermal equilibrium is reached in really fast timescales, in the order of femtoseconds. Therefore, detecting and controlling electron thermalization process in graphene and in nanoscale devices in general remains challenging even with the most advanced ultrafast laser techniques.

In a recent study published by Nature Physics, researchers from M.I.T, the National Institute of material Sciences (NIMS) from Japan, and ICFO researchers Mathieu Massicotte and ICREA Prof. at ICFO Frank Koppens, with the use of graphene, have been able to overcome this challenge and control and manipulate and modulate electron energy transport in nanoscale materials.

In their study, the researchers developed in a graphene–boron nitride–graphene (G–BN–G) vdW heterostructure (two-dimensional van der Waals (vdW) materials) through which optically excited carriers are transported from one graphene layer to the other. By applying an interlayer bias voltage and light, researchers saw that they were able to control and direct the pathway of the electrons within the graphene layers. That is they were able to control the interlayer carrier transport to a point where they could determine it to occur faster or slower than the intralayer scattering events, thus effectively tuning the electron thermalization pathways in graphene.

This new study paves the way to new techniques that can use graphene to improve solar cells and energy harvesting devices by enabling them to capture and use more photo-excited electrons.