World's smallest car is a billionth the size of yours

Posted by Emma Woollacott

Dutch researchers say they've created the world's smallest electric vehicle - consisting of just a single molecule.

Empa researchers say their car travels on four electrically-driven wheels in an almost straight line over a copper surface. They've synthesised a molecule from four rotating motor units - wheels to you and me - which can travel straight ahead in a controlled manner.

"To do this, our car needs neither rails nor petrol; it runs on electricity. It must be the smallest electric car in the world – and it even comes with four-wheel drive," says Empa researcher Karl-Heinz Ernst.

The nano-car has no reverse gear, unfortunately, and needs to be refuelled with electricity after every half revolution of the wheels; this is done via the tip of a scanning tunnelling microscope (STM). In the longer term, the teasm hopes to refuel the device using UV lasers.

Applying a voltage of at least 500 mV causes electrons to 'tunnel' through the molecule, triggering reversible structural changes in each of the four motor units.

This starts with what's called a cis-trans isomerisation taking place at a double bond - a kind of rearrangement – in an extremely unfavourable position in spatial terms, in which large side groups fight for space.

As a result, the two side groups tilt to get past each other and end up back in their energetically more favourable original position, thus completing a half turn of the wheels. If all four wheels turn at the same time, the car travels forwards. After ten STM stimulations, the molecule had moved six nanometres forwards, in a more or less straight line.

"The deviations from the predicted trajectory result from the fact that it is not at all a trivial matter to stimulate all four motor units at the same time," says Ernst.

Well, at least it should be easy to find a parking space.