Damien Thompson of the University of Limerick, Ireland, worked with Christian Nijhuis of the National University of Singapore and Professor Enrique del Barco of the University of Central Florida have manipulated electrostatic forces to boost the rectification ratio of diodes built with individual molecules.
Researchers have long been trying to duplicate the capabilities of silicon-based diodes at the molecular level for ever smaller systems. While the rectification ratio of the current for positive and negative electrical bias in commercial silicon diodes is between 105 and 108, the theoretical limit for the rectification ratio in a single molecule is just 103.
Reporting in Nature Nanotechnology, the team has exceed that ratio by 100x at the molecular level with a macroscale tunnel junction based on a single layer of molecular diodes. The number of molecules conducting current in those junctions changes with the bias polarity, multiplying the intrinsic rectification ratio of an individual molecule and providing a rectification ratio of 6.3 x 105.
“It surpassed that limit imposed by theory. Definitively, you now have a molecular diode that responds comparably to silicon-based diodes,” said del Barco, who interpreted the data and performed the theoretical modeling that explained how it works. “It moves something that was only science into a commercial possibility.”
This isn’t likely to replace silicon diodes, say the researchers, but could eventually bring about the use of molecular diodes for other applications. The molecular diodes can also be produced in a chemistry lab, would be cheaper and easier to fabricate than standard diodes.
Back in April, researchers at the University of Barcelona used an organic molecule sandwiched between two nano-electrodes to create a 1 nm diode with a rectification ratio of 4000. “In order to go to the next level of miniaturization, we have to use individual molecules as the active components of the circuits,” said Ismael Díez Pérez, who is leading the project. “This approach favours the assembly of thousands of billions of diodes on a silicon chip,” he said.
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