A way to reach a rectification ratio thought a theoretical impossibility has been demonstrated by an international research team from the University of Central Florida (UCF), the University of Limerick and the National University of Singapore. This discovery could enable the practical use of molecular diodes.
"It surpassed that limit imposed by theory. You now have a molecular diode that responds comparably to silicon-based diodes," said UCF Professor Enrique del Barco. "It moves something that was only science into a commercial possibility."
Scientists have long been trying to duplicate the capabilities of silicon-based circuitry – including diodes – at the molecular level as that would allow the miniaturisation of computers and other electronics. According to the researchers, molecular diodes would also be cheaper and easier to fabricate than standard diodes.
Diodes are characterised by their rectification ratio, which is the rate between current for positive and negative electrical bias. The rectification ratios of commercial silicon-based diodes have rectification ratios between 105 and 108.
The higher the rectification rate, the more precise the control of current. A fundamental theoretical limitation of a single molecule however has limited molecular diodes to rectification ratios no higher than 103 – far from the commercial values of silicon-based diodes.
To solve this issue, the researchers formed macroscale tunnel junctions based on a single layer of molecular diodes.
The number of molecules conducting current in the junctions changes with the bias polarity, thus multiplying the intrinsic rectification ratio of an individual molecule by three orders of magnitude.
According to the researchers, this method overcame the 103 limitation, resulting in a record-high rectification ratio of 6.3 x 105.