US, WASHINGTON (ORDO NEWS) — Scientists have created an engine consisting of only 16 atoms. A record small “toy” will allow you to study mysterious phenomena on the border of the classical and quantum world.
The achievement is described in a scientific article published in the journal PNAS.
Less than ever before
A device consisting of 16 atoms does the same thing as any self-respecting engine. It brings its moving part (rotor) into an ordered movement due to the flow of energy from the external environment.
The most approximate idea of the new engine can be obtained by twisting around its axis a pencil lying on the surface of the table. At the same time, the end of the pencil will describe the circle, like a clock hand or a spoke of a wheel. The pencil plays the role of the rotor, and the table – the stator, that is, the fixed part of the engine.
In the new device, the rotor (“pencil”) is a four-atom molecule of acetylene (C 2 H 2 ). It has an oblong shape and looks somewhat like a dumbbell. A stator (“table”) is a substrate of six palladium atoms and six gallium atoms (PdGa). The acetylene molecule literally lies on it and rotates around its axis.
True, unlike a pencil on a table, an acetylene molecule on a palladium-gallium substrate cannot rotate at an arbitrary angle. There are only six different positions that it can take in its rotation. In addition, she also “crawls” on the substrate, as shown in the video below.
By the way, this whole amazing design has a size of less than one nanometer.
“This brings us closer to the ultimate size of molecular motors,” says co-author of the article, Oliver Grning from the Swiss Federal Laboratories for Materials and Technology.
Almost real engine
The new nanomotor is quite difficult to spin with your fingers, but it is still able to draw energy from two sources.
Firstly, it is the thermal energy of the medium in which the molecule is located. For example, at room temperature, the rotor rotates at a speed of several million revolutions per second.
Secondly, this is the energy of an electric field. With the help of high-precision equipment, you can adjust the magnitude of the field so jewelryly that you can turn the rotor literally a fraction of a turn.
Note that when the rotor does not receive too much energy, it almost always (99% of the time) rotates in one direction.
The reason for this is the special form of the stator. It is selected so that it is energetically beneficial for the acetylene molecule to turn in a certain direction, and not in the opposite. This can be compared to a ratchet mechanism that allows the wheel to rotate in only one direction.
According to Groening, this stability sharply distinguishes the new device from other molecular engines . It brings it closer to macroscopic systems, such as, for example, a car engine. The latter, after all, also ensures the rotation of the wheels in a strictly specified direction, and not anywhere.
A similar engine could be part of a nanorobot doing useful work . In addition, such devices can be models of natural molecular engines, such as myosin proteins , which play an important role in muscle function.
However, when the engine receives too much energy (for example, at room temperature), the ratchet resistance is easily overcome, and the rotor rotates in random directions. So in practice, such machines could only work in very exotic conditions, unattainable outside the walls of the laboratory.
On the border of worlds
However, there is another area where such nanomachines would be useful. This study of the physical laws on the border between the classical and the quantum world ( Vesti.Ru talked in detail about this exciting area of research).
16 atoms is already too small to consider an object undeniably classical, but it’s still a bit too much for it to be absolutely quantum. And on this poorly investigated border between the worlds, the authors have already discovered an unexpected effect.
From the point of view of classical physics, there is a minimal portion of energy that must be communicated to the rotor in order for it to turn. In the case of this engine, this means that at a temperature below -256 degrees Celsius and an electric field voltage of less than 30 millivolts, the acetylene molecule will not rotate in any direction.
On the other hand, the laws of quantum physics provide for the so-called tunnel effect . It should lead to the fact that the rotor sometimes still rotates. At the same time, paradoxically, no energy will be spent on this. Therefore, the energy “ratchet”, forcing the molecule to rotate in only one direction, will not work. The rotation caused by the tunneling effect occurs in one direction or another. Each time, the direction is “chosen” randomly, and on average, none prevails over the other.
What scientists have discovered does not fit into either model. On the one hand, they recorded the rotation of the rotor at energies below the “classical limit”. On the other hand, the molecule almost always turned in the same direction.
It seems that with this rotation, the energy ratchet continued to work. This means that the rotor was wasting energy on its rotation, although this contradicts the classical theory of the tunneling effect.
Now, researchers have to figure out why the rotor of their engine behaves in such a strange way – both non-classical and non-quantum. Perhaps this will be the first step towards a deeper understanding of the laws governing matter.
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