Mysterious charge transport in self-assembled monolayer transistors...( An international team of researchers...)

An international team of researchers from the Netherlands, Russia and Austria discovered that monolayer coverage and channel length set the mobility in self-assembled monolayer field-effect transistors (SAMFETs). This opens the door to extremely sensitive chemical sensors that can be produced in a cost-effective way. The research was done at Philips Research Eindhoven and Eindhoven University of Technology. The findings were published as an Advanced Online Publication in Nature Nanotechnology.

SAMFETs

The SAMFET is a recent example of the development of 'plastic micro-electronics'- i.e. electronics based on organic materials. Last year, Philips Research managed to build such a transistor by immersing a silicon substrate into solution containing liquid crystalline molecules that self-assemble onto this substrate, resulting in a semi-conductive layer of just a single molecule thick. The monolayer of the SAMFET consists of molecules that are standing upright. Conduction takes place by charges jumping from one molecule to the other.

However, in previous attempts to make a SAMFET, it was observed that as the length of the SAMFET increased, its level of conductivity counterintuitively decreased exponentially. In a joint project Philips Research, the Eindhoven University of Technology (TU/e), the University of Groningen, the Holst Centre, the Enikolopov Institute for Synthetical Polymer Materials in Moscow and the Technical University in Graz, Austria discovered that this decrease is determined by the monolayer coverage, which could be explained with a widely applicable two-dimensional percolation model.

The ultimate chemical sensor

One could compare this to crossing a river by jumping from rock to rock. The closer the rocks are to each other, the quicker one can jump or even walk to the other river bank. So if the monolayer displays more voids, the conductivity decreases dramatically. Up till now, this beh
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