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Monolayer coverage and channel length set the mobility in self-assembled monolayer field-effect transistors


The mobility of self-assembled monolayer field-effect transistors (SAMFETs) traditionally decreases dramatically with increasing channel length. Recently, however, SAMFETs using liquid-crystalline molecules have been shown to have bulk-like mobilities that are virtually independent of channel length. Here, we reconcile these scaling relations by showing that the mobility in liquid crystalline SAMFETs depends exponentially on the channel length only when the monolayer is incomplete. We explain this dependence both numerically and analytically, and show that charge transport is not affected by carrier injection, grain boundaries or conducting island size. At partial coverage, that is when the monolayer is incomplete, liquid-crystalline SAMFETs thus form a unique model system to study size-dependent conductance originating from charge percolation in two dimensions.

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Figure 1: SAM growth.
Figure 2: SAM microstructure.
Figure 3: Spatially resolved connectivity.
Figure 4: Visualization of the SAM.
Figure 5: Electrical transport versus monolayer coverage.
Figure 6: Scaling of extracted linear and saturated device mobility.


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The authors acknowledge financial support from the Dutch Technology Foundation STW, the EU project ONE-P (no. 212311), the Austrian Nanoinitiative and H. C. Starck GmbH. We thank M. Kaiser for FIB-TEM imaging. We thank the Cornell High Energy Synchrotron Source for provision of synchrotron radiation facilities and D. Smilgies for his assistance in using beamline G2.

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S.M., E.S., P.H., P.B. M.K., R.J. and D.L. conceived and designed the experiments. S.M., E.S., P.H., H.W., A.M., R.R. and M.K. performed the experiments. S.P. synthesized the materials. All authors discussed the results, commented on the manuscript and co-wrote the paper.

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Correspondence to Dago M. de Leeuw.

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Mathijssen, S., Smits, E., van Hal, P. et al. Monolayer coverage and channel length set the mobility in self-assembled monolayer field-effect transistors. Nature Nanotech 4, 674–680 (2009).

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