2D layered materials are beginning to confirm their ground-breaking role in many applications, and nanoscale heat flow plays a crucial role in modern electronics and optoelectronic applications.
Scientists from the European Graphene Flagship, led by researchers at the Institute of Photonic Sciences (ICFO), have recently succeeded in observing and following, in real-time, the way in which nanoscale heat flow occurs in the so-called van der Waals stacks, which consist of graphene encapsulated by the dielectric two-dimensional material hexagonal boron nitride (hBN). Graphene can conduct electricity and heat incredibly well, despite being only a single atom thick.
The van der Waals stacks can consist of materials with dramatically different physical properties, while the interfaces between them are ultraclean and atomically sharp.
In the new study, published in Nature Nanotechnology, ICFO researchers, led by ICREA professor at ICFO Frank Koppens, worked in collaboration with researchers from:
- The Netherlands;
- Germany; and
- The UK.
How does the nanoscale heat flow occur?
The researchers have identified a highly surprisingly effect: rather than staying within the graphene sheet, the heat flows to the surrounding hBN sheets. According to the ICFO, this heat transfer process occurs on an ultrafast timescale of picoseconds and is therefore dominant over competing heat transfer processes.
The heat transfer process happens through hot graphene electrons that couple to hyperbolic phonon-polaritons in the hBN sheets. These phonon-polaritons propagate within the hBN as light does in an optical fibre; however, in this case for infrared wavelengths and at the nanometre scale. These hyperbolic modes are very efficient at carrying heat away.
The results of this work will have extensive implications for many applications based on hBN-encapsulated graphene, sometimes referred to as the next generation graphene platform, owing to its electrical properties. It will particularly provide direction to optoelectronic device design, where these heat flow processes can be thoroughly exploited.