Machines and electronic devices often generate waste heat that is difficult
to utilize. If electricity could be generated from this waste heat, it would
offer a means for a clean and sustainable power production: Such a
technology would be ideally suited for low-power electronics applications
such as wearables or low-cost Internet-of-Things devices. This includes, for
example, wearable (medical) devices and sensors, with a wide range of
applications in the healthcare and sports industry, in smart buildings and
mobility applications.
Thermoelectric generators, machines that generate electricity by exploiting
temperature differences, already exist but their conversion efficiency is
generally low and only little electricity is produced. Generating more
electricity would require materials that simultaneously have high electrical
conductivity and low thermal conductivity. These two requirements, however,
are often mutually exclusive.
Quantum dots as a solution
In the last few years, several research groups the world over have shown
that thermoelectric conversion can be greatly enhanced by exploiting quantum
effects. For example, by using quantum dots that act as highly selective
energy filters, drastic increases in conversion efficiency have been
reported, some even approaching some of the limits set by the laws of
thermodynamics. The problem: The quantum machines, also called quantum heat
engines, have to be cooled down to temperatures a few degrees above absolute
zero—so something like this is hardly useful in everyday life.
Researchers at Empa might be able to overcome this problem and create a
quantum heat engine that operates at room temperature. Mickael L. Perrin, a
researcher in Empa's Transport at Nanoscale lab led by Michel Calame, came
up with the idea of using graphene nanoribbons—which are an Empa specialty.
The very first graphene nanoribbons were synthesized by another research
group at Empa: Roman Fasel and his colleagues at Empa's Nanotech@Surfaces
lab. For several years now, the Empa researchers have worked on different
approaches to create electronic devices from such nanoribbons.
Operation at room temperature using graphene nanoribbons
Mickael L. Perrin was able to make graphene nanoribbons behave as quantum
dots before, with some of them stable up to a temperature of -123 degrees
Celsius, i.e. at much higher temperatures than the quantum dots used before
for thermoelectric conversion. Now the goal is to integrate such graphene
nanoribbons into a quantum heat engine and make it work at room temperature.
As the nanoribbons are only a few nanometers in size, making contact to them
will require the development of special fabrication techniques, which will
be implemented at the Binnig and Rohrer Nanotechnology Center in the IBM
Research Center in Rüschlikon. Moreover, custom-designed measurement systems
will be needed to characterize the energy conversion efficiency.
If all goes as planned, Perrin may create a tiny heat engine on a chip in
the coming years. Not only could it generate electricity from waste heat,
but conversely, by reversing the operation principle, it would be suited for
efficient cooling.
With his two successful research grants, Mickael L. Perrin will start his
assistant professorship at ETH Zurich, in the Department of Information
Technology and Electrical Engineering, in the next few months. Over the next
years, he will continue his research at Empa, where state-of-the-art
equipment is available for the thermoelectric characterization of quantum
heat engines.
Hopefully only a temporary solution
The funding for Perrin's project comes from the SNSF and the State
Secretariat for Education, Research and Innovation (SERI). Due to the failed
framework agreement between Switzerland and the EU, Switzerland is excluded
from the current European research program, Horizon Europe. To step in, ERC
Starting grants are funded directly by SERI this year. This is the only way
to keep highly talented young researchers in Switzerland. In order to
receive the allocated funding directly from the EU, Mickael L. Perrin and
the other 27 grantees from Switzerland would have to move to a foreign
university that is part of the European Research Area.
Reference:
Maria El Abbassi et al, Controlled Quantum Dot Formation in Atomically
Engineered Graphene Nanoribbon Field-Effect Transistors, ACS Nano (2020).
DOI: 10.1021/acsnano.0c00604
Tags:
Physics