What are heat enigine

Quantum motor with high efficiency

Gas turbines or diesel generators generate electricity by using heat to drive mechanical rotational movements. A new type of heat engine on the nanoscale, on the other hand, manages without any mechanical components. As the developers report in the journal "Nature Nanotechnology", the tiny machine achieves an efficiency comparable to that of modern gas turbines. Such nanopower plants could only deliver very small amounts of electricity. In principle, however, these should be sufficient for operating sensors.

Together with his colleagues, Heiner Linke from Lund University implemented an unconventional idea developed over 15 years ago: Individual electrons are exchanged between two reservoirs at different temperatures. In conventional heat engines, on the other hand, the heat flow between the reservoirs is used to convert thermal energy into mechanical energy.

Microscope image of the nanopower plant

Linke and his team used two filigree metal wires, each with different temperatures, as a heat reservoir. In between they positioned a tiny structure made of nanowires, a so-called quantum dot. Due to the tiny dimensions, quantum mechanical effects lead to novel physical properties. In this case the nanostructure acts as a filter to only let electrons with a certain energy through.

In the experiments, individual electrons now migrated across the quantum dot from the warmer to the colder electrode - driven by the temperature difference. A tiny current flow at around one volt could be measured. "Our approach shows that heat can be converted directly into electricity with high efficiency and without any intermediate steps," explains Linke. The efficiency of the nanogenerator is around 70 percent of the theoretically possible maximum. Conventional heat engines achieve similar values.

However, the thermoelectric nano power plant is still a basic experiment. The temperature difference between the reservoirs was only about one degree and the absolute temperatures were close to absolute zero. Specific applications are hardly possible when frozen in this way. However, Linke can imagine that this principle can be used to construct maintenance-free nanopower plants that use heated electrons in solar cells or computer processors. For example, sensors or quantum circuits can be operated with the tiny current yield.