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Cool molecule beats size barrier

BARC scientists Aswal (left) and Koiry

The bane of silicon-based transistors has been their diminishing size. Below a certain size, they encounter the problem of power dissipation.

Researchers have designed an organic molecule that could come to the rescue of silicon-based transistors1. This organic molecule latches on to a silicon surface showing unique electrical properties that will help in crafting molecular memory devices.

Porphyrin molecule and its derivatives have been found to be good candidates for charge storage devices. To tap this potential, the researchers have designed an organic molecule 5-(4 undecenyloxyphenyl)-10,15,20-triphenylporphyrin (TPP-C11). It is a purple colour solid. On charging it with negative potential, the organic molecules were driven on to the silicon surface.

The organic molecule-Si hybrid is formed in two steps. Firstly, negative potential creates active Si atoms releasing hydrogen free radicals. Secondly, Si atoms react with the organic molecule to form a silicon-carbon bond. The electrochemical deposition of the organic molecules on Si surface is better than self-assembly process. The potential of 0.3 Volt not only drives the molecules on Si surface but also removes any oxide layer, resulting in a clean molecule-Si interface.

"The biggest advantage is the size of the molecule, which is less than 1.5 nm," says lead researcher Dinesh Kumar Aswal from the Technical Physics and Prototype Engineering Division of Bhabha Atomic Research Centre, Mumbai. The researchers say that since the typical size of the molecules is well below 1.5 nm, they will help in overcoming the scaling down limit of silicon transistors.



  1. Koiry, S. P. et al. Electrical bistability in electrografted 5-(4 undecenyloxyphenyl)-10,15,20-triphenylporphyrin monolayer on Si. Chem. Phys. Lett. 453, 68-72 (2008)

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