The diode is a very simple-sounding little electronic device: it allows current to flow easily in one direction, but not the other. But while the quest to miniaturize them to the molecular scale has worked in the past, only now is it a truly practical proposition.
A team from Columbia University has created a new single-molecule diode: a string of atoms that allows electrons to flow along it in one direction but not the other. But what makes this different to those that have gone before it is how well it performs.
In truth, there’s no such thing as a perfect diode. In an ideal world, infinite current could flow along the component in one direction and zero in the other; in reality, the devices can’t carry infinite current and always allow at least a little to pass in the opposite direction, too. How well a diode works is characterized, in part, by the maximum forward current and the ratio of the two. In the past, single-molecule diodes have only carried small currents in one direction, and even then they’ve allowed a current as large as 1/50th of the forward current to flow back through them, too.
The new molecule, however, can carry 0.1 microamps in one direction-a lot to be carried by a single molecule-and allows just 1/250th of that to flow back through. That means the device, which uses a single thiophene-1,1-dioxide molecule surrounded by an ionic liquid, could actually be used in nano-scale electronic systems, unlike its predecessors. Perhaps unsurprisingly, though, the team are already trying to improve upon their new success