A "four-wheel drive car" less than one billionth the length of an average SUV has been built and operated by researchers in the Netherlands and Switzerland. The molecular machine is about 1 nm long and uses electrons as fuel as it navigates across a copper surface. The tiny device could find use in nanometre-sized robotics or as tiny transporters that shift molecules around.
Constructed from a single molecule, the nano car sports four-wheel drive, with each "wheel" acting as a separate motor. It is able to travel in an almost straight line, across a copper surface. Instead of carrying its own battery, the car receives electricity from the tip of a scanning tunneling microscope, positioned above it. People who dismiss EVs because of their limited range, however, aren't likely to be impressed - the nano car requires a 500-millivolt charge once every half-revolution of its wheels.
The car doesn't carry its own fuel supply, but it's relatively easy to provide one. Provided that the temperature is kept at is 7K, there's enough energy in the system to provide the vibrational boost. That leaves the matter of the electrons. The authors fed these to the molecule using an scanning tunneling microscope tip. Placing it on a metal surface (in this case, copper) provided the electrons with some place to go afterwards.
Remarkably, it all worked. The authors gave one of the molecules 10 pulses of electrons, and watched it relocate after each one, moving a total of six nanometers by the time the last was delivered. It didn't move in a straight line, however, as it appears that there are some instances where one or more of the wheels doesn't actually turn. That can cause the molecule to move a shorter distance or even veer off to the side.