Nervous energy

The emerging technology of plastic electronic circuits has been boosted by the construction of the first molecular diodes.

The diodes, which have high production yields, are just one molecule thick and while similar structures appear in nature they have always been beyond the capabilities of any man-made machine or process — until now.

Scientists hope molecular electronics will enable them to build a working circuit in a single layer of molecules and embed it in a host material. They appear in nature as self-organised structures for conducting an electrical charge, as in mammals' nerve systems and plant photosynthesis.

If artificial processes mimicking nature's designs could be perfected there would be a ready market for the technology, particularly now that plastic products such as flexible and roll-up displays, are being commercialised. An added attraction is that they could be fabricated at low temperatures.

But making them has not been easy. Layers of single molecules are prone to flaws — with gaps forming spontaneously as the material organises itself. Well-defined diodes made through molecular electronics can only be created when the molecules are sandwiched between two metallic electrodes. The trouble is that the flaws lead to short circuits, with the current easily crossing the 1-2nm thick gap that opens up between the electrodes. So scientists at