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Electron Transport Through Monolayers Made from Isomeric MoleculesIRG 3: J. Liang, Q.Sun, A. Selloni, and G. Scoles Lower right: Schematic of a monolayer containing regions of two thiol isomers: ethylphenyl, EtPh (middle) and phenethyl, PhEt (outer). By positioning the conducting AFM tip over one region or another, the relative conductivity of the two molecules can be measured as a function of voltage. Upper left: 3D height map of a different nanografted specimen, where the two molecules are of different length so that the grafted patch can be seen in both height and current images. Understanding how electrons tunnel through molecular monolayers is an essential basis for “molecular electronics” and for understanding electrical contact through “dirty” metals.
While neither quantitative predictions nor measurements of molecular conductivity have been available, PCCM researchers have recently made breakthroughs on both fronts. Differential measurements of conductivity between monolayers of two isomers– molecules of identical length and chemical composition, but a different sequence of the atoms—were made by using atomic force microscopy (AFM) to fabricate a nanosized patch of one isomer in a monolayer of the other. Both regions were then scanned with a conductive tip AFM to measure their current vs. voltage curves. The measured 30% difference in conductivity between the two is in excellent agreement with predictions made using density functional theory.
Reference: J. Liang, Q. Sun, A. Selloni, and G. Scoles, “Side-by-Side Characterization of Electron Tunneling through Monolayers of Isomeric Molecules: a Combined Experimental and Theoretical Study,” J. Phys. Chem. B (Letter), 110, 24797 (2006).
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