Main > ELECTRONICS. > Molecular Electronics > Gold NanoParticles/DiThiol/2 Au El > Org.: USA. A. (Research) > Report Abstract

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Begin by forming a monolayer of OCTANETHIOL molecules on a GOLD surface, which serves as one electrode. Using a solvent technique, they then remove some of these molecules, replacing them with 1,8-OCTANEDITHIOL
molecules, which are capable of chemically bonding to gold at both ends. By exposing the monolayer to a suspension of gold NANOparticles that are less than 2 nm in diam., the researchers tether nanoparticles to the free ends of the octanedithiol molecules scattered throughout the monolayer. A gold-coated conducting tip of a atomic force microscope is then used to locate & contact individual nanoparticles bonded to the octanedithiol “wires”, thus forming a electrical circuit. The octanethiol molecules, which are bound only to the bottom electrode, serve as molecular insulators, insulating the dithiol wires from one another.
The researchers made current-voltage measurements on > than 4,000 nano
particles, producing only 5 distinct families of curves. These curves corres
pond to integer multiples of a fundamental curve, which they believe repre
sents conduction through a single dithiol molecule attached to both Au contacts. The other curves correspond to conduction through 2 or several dithiol molecules bridging the 2 contacts.
Based on measurements on > than 1,000 single molecules, the researchers peg the resistance of a octanedithiol molecule at about 900 megaohms. When they tried to measure the resistance of octanethiol monolayers (in which chemical bonding to both ends of the molecules is not possible) they obtained resistance values that were > 4 orders of magnitude higher. These measurements also were less reproducible & had a different voltage dependence, they note, “demonstrating that the measurement of intrinsic molecular properties requires chemically bonded contacts”.



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