Over the last few years, thermoelectric generators have become the focus of increasing research because of their ability to convert waste heat into electricity. Quantum dots, semiconductor crystals with distinctive conductive properties, can be good candidates for thermoelectric generation, since their discrete resonance levels provide excellent energy filters.
In a recent study, researchers at the University of Cambridge, in collaboration with colleagues in Madrid, Rochester, Duisburg and Sheffield, experimentally demonstrated the potential of a standalone nanoscale energy harvester based on resonant tunneling quantum dots. This harvester is based on previous research conducted by part of their team that proposed a three-pronged energy harvester based on two resonance-tunneled quantum dots with different energy levels.
The energy harvester was implemented at the Cavendish Laboratory in Cambridge by a researcher named Gulzat Jaliel. However, the original theoretical proposal for the device was presented by Andrew Jordan in 201
"As my colleagues Rafa and Marcus' article on Coulomb block points, I began to think of mesoscopic circuits," said Jordan, one of the researchers who developed the theory behind the combine. "During my Saturday in Geneva in 2010-2011, we were thinking and calculating about a chaotic quantum-dot kitchen thermal motor, and I ended up publishing another book with Björn and Rafa."
However, the device previously proposed by Jordan and some of his colleagues predicted low power. In the summer of 2013, therefore, when he returned to Geneva for a brief visit, Jordan began a further study of the relationship between resonance tunnels and thermoelectricity. His intuition was that a device using resonant quantum dots would have more power and high efficiency.
"I remember sitting very well in my hotel room on Saturday in Geneva, playing with the equations and realizing that if we just gave the cavity its own temperature and chemical potential, then everything became very simple and we had a good result. the fact that an electron charge is carried over each energy range that an electron picks up, and the charge and energy balance is simple, "Jordan said." Scaling would also be simple, in principle. I wrote the results with Bjorn and Rafa, and Marcus, of course, and the rest is history. "
The recent study began when Dr. Jaliel began. The head, Professor Charles G. Smith, advised her to try the experimental realization of quantum dot energy as part of her graduate work, and she decided to try it, and her project was inspired by previous research by Dr. Jonathan Prans at the Cavendish lab in which he uses a similar device to demonstrate a refrigerator, emphasizing the double role of such devices.
In their recent experiments, Jaliel and her colleagues essentially built an energy harvester by placing two quantum dots near a central cavity, then controlling the energy levels at each point by applying different voltages to the respective piston gates. and heated the cavity, maintaining alternating currents in the nearby channel.
The combine, developed by Jaliel and her associates, can at least reach Carnot efficiency. In addition, it can be optimized to achieve high power in combination with high efficiency at maximum power.
"When electron energy coincides with the quantum dot energy, they can enter or leave the cavity through the points," Gulsat Jaliel, one of the researchers who conducted the study, told Phys.org. "When electrons enter the hot cavity through a point with a lower energy level and exit through the higher energy level, they must take some energy from the cavity to be able to complete the process and therefore generate less thermal energy from the hot cavity. autonomous. "
This experimental setup allowed researchers to realize the new energy harvester. In actual applications, however, the cavity used in their study can be heated using a variety of other sources, including waste heat from other quantum devices.
Interestingly, the power harvesters presented by Jaliel, Jordan and their colleagues could act as a source of green energy when increased to millions or billions, as the waste energy that it collects would also increase in proportion. An additional advantage of this quantum dot based system is that it can be used to charge other devices in situations where there is a low energy supply, such as satellites in places with high temperature gradients.
"The main purpose of our experiment was to show that the theoretical proposition is feasible and reliable," said Jaliel. "Any further industrial application will also be very interesting to see."
Other teams of researchers have built similar energy harvesters in the past. One example of this is a combine produced by Holger Thierschmann et al., Which is also based on a recent study by Sánchez and Büttiker. Compared to this previously developed combine, the device implemented by Jaliel and her colleagues is easier to control while offering more power and efficiency.
When measurements are taken at an estimated base temperature of 75 mK in He 3 / He 4 refrigerator, in fact this new quantum dot energy combine can generate remarkable heat output of 0, 13 fW for a temperature difference for each point of about 67 mK. In future studies, researchers plan to explore three possible strategies for further improving the combine's performance. First, they would like to redesign the dots to gain better control over tunneling speeds, then scale up the device and improve its operating temperature.
"Better control of the speed of point tunneling should allow the almost perfect Carnot efficiency to be realized," said Jaliel. "Power scaling can be achieved with resonant tunneling quantum wells, as predicted by the theoretical part of another study by Bjorn Sotman, Rafael Sanchez, Andrew H Jordan and Marcus Butticker. I tried to experiment this device experimentally with my doctor. D. study, but unfortunately I run out of time before I finish it. I'd really like to release it again if I have the opportunity. "
Scientists offer quantum wells as powerful, easy-to-produce power harvesters
G. Jaliel et al. Experimental Implementation of a Quantum Point Energy Combine, Physical Review Letters (2019). Doi: 10.1103 / PhysRevLett.123.117701: https://journals.aps.org/prl/abrief/10.1103/PhysRevLett.123.11770
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Rafael Sanchez et al. Optimal energy quantum for current conversion, Physical Review B (2011). DOI: 10.1103 / PhysRevB.83.085428
Holger Thierschmann et al. Three-pointed energy harvester with quantum dots attached, Nature Nanotechnology (2015). Doi: 10.1038 / nnano.2015.176
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