[ExI] Smallest nanomotor yet: 16 atoms

[Stuart LaForge]

https://www.advancedsciencenews.com/the-worlds-smallest-motor/

Excerpt:

Not only has a motor been constructed from just 16 atoms, its movement  
has been directly observed by scanning tunneling microscopy (see the  
inset in the video below).

The colorful parts of the video are a computer simulation of the  
motor. In this simulation, the grey spinning unit represents a  
molecule of acetylene, which is made of just two carbon atoms and two  
protons.

The Swiss team who built this motor, placed the acetylene rotor on a  
base (the blue and red atoms), which is a part of a crystal that is  
made from 12 atoms of palladium and gallium.

Once in place, the system was cooled down to 17 degrees above absolute  
zero. At this temperature, an electrical current was applied, which  
gave rise to the controlled spinning motion.


The Engineering

“For a motor to actually do useful work, it is essential that [it]  
allows the rotor to move in only one direction,” says Oliver Gröning,  
the project lead.

Just imagine if a car motor randomly changed the direction of  
crankshaft rotation. A trip to the grocery store would be slightly  
less predictable. This is a problem that has been facing research in  
the field of atomic scale engines for a long time.

In fact, at temperatures higher than 17° above absolute zero, this  
system behaved in the same way, with the acetylene unit spinning  
randomly on the base. At low temperatures however, the energetic  
barrier for rotation in one direction became significantly higher than  
the barrier in the other direction.

“The motor therefore has 99% directional stability, which  
distinguishes it from other similar molecular motors,” says Gröning.

This difference in the energetic favorability of rotation in one  
direction is provided by the base. The palladium gallium crystal  
structure allows movement across the surface in one direction more  
easily than in the other direction.

Energy Harvesting

Harvesting the kinetic energy provided by the pint-sized motor is by  
no means straightforward. The team is currently working on  
understanding the processes involved in this molecular machine, work  
that may one day allow the acetylene rotor to be put to work.
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If cooling the motor down to 17K and applying an electric current  
causes the rotor to spin in one direction, then would using  
low-temperature thermal fluctuations torque the motor and generate an  
electric current like a Brownian ratchet?

Stuart LaForge