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Simultaneous electronic and optical studies of single molecules

Through the last decade much work has gone into measuring the electronic properties of individual small molecules, with the eventual goal of using such structures for electronics and sensing applications. One major challenge is that the molecules are typically 1-2 nm across, 50000x narrower than a human hair, and no good imaging techniques exist to "see" the molecules in actual devices. Conduction in single-molecule devices is through a quantum process called "tunneling". Tunneling depends very strongly on distance, so that current in a single device flows through a volume so small that only one or two molecules can influence the conduction.
Over the same time period, people have learned that metal nanostructures can act like antennas for light. This allows light to be concentrated far more than is possible with conventional lenses. One result is that Raman spectroscopy, a chemical sensing technique used to identify molecules by their "fingerprint" of characteristic vibrations, can detect individual molecules on such optical antennas.
Natelson's group, collaborating with the Rice Laboratory for Nanophotonics, has made a major advance, performing simultaneous electronic and Raman measurements on the same individual molecule. The electrodes used to push current through the molecule also act as an optical antenna. The experiments show that conduction (sensitive to only one or two molecules) and Raman spectra track each other as a function of time. The vibrational fingerprint confirms that conduction takes place through the molecule of interest and that these mass-producable electrode structures give single-molecule optical sensitivity. This paves the way for a wealth of physics and physical chemistry experiments, as well as ultrasensitive chemical sensing technologies.
D. R. Ward, N. J. Halas, J. W. Ciszek, J. M. Tour, Y. Wu, P. Nordlander, and D. Natelson Simultaneous measurements of electronic conduction and Raman response in molecular junctions. Nano Letters, in press (Reprint)

Press Release
(Rice News & Media Relations press release Rice scientists make breakthrough in single-molecule sensing)


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