UK researchers have made a molecular diode that they say could provide the answer to electronic device miniaturisation. 

Geoff Ashwell's group at Cranfield University created a molecular diode from a bilayer of electron-rich and electron-poor molecules. Diodes allow current to move in one direction around a circuit but not the other, and are a vital component of almost all electrical circuits. Because one half of Ashwell's bilayer is electron-rich and the other is electron-poor, it is much easier to move electrons towards the electron-poor side of the bilayer than it is to force more electrons onto the electron-rich half.

Previous attempts to make molecular diodes have achieved only limited success, said Ashwell. The ratio of the currents in the two directions through the diode, known as the current rectification ratio, has typically been around 30 in previous devices. Ashwell's bilayer has a current rectification ratio of 3000. 

According to Ashwell, the key to the diode's success is an aromatic group linking the two halves of the bilayer. The linking group locks the electron-rich and electron-poor molecules into a configuration where electrons cannot easily move between them. 

Ashwell's goal is to make molecular diodes that can compete with traditional solid-state diodes in the constant push to make circuits smaller. 'There is still a long way to go,' said Ashwell, 'but these self-assembling molecules appear to provide a link to the ultimate challenge of electronic device miniaturisation.' 

Ashwell said the main challenge in molecular electronics is the interface between molecular devices and the macroscopic system they form part of. 'Methods are needed to contact single molecules, which may involve the sculpting of nanometer-scale device structures,' he said.  

Clare Boothby