This is the report of a DOE-sponsored workshop organized to discuss the status of our understanding of charge-transfer processes on the nanoscale and to identify research and other needs for progress in nanoscience and nanotechnology. The current status of basic electron-transfer research, both theoretical and experimental, is addressed, with emphasis on the distance-dependent measurements, and we have attempted to integrate terminology and notation of solution electron-transfer kinetics with that of conductance analysis. The interface between molecules or nanoparticles and bulk metals is examined, and new research tools that advance description and understanding of the interface are presented. The present state-of-the-art in molecular electronics efforts is summarized along with future research needs. Finally, novel strategies that exploit nanoscale architectures are presented for enhancing the efficiences of energy conversion based on photochemistry, catalysis, and electrocatalysis principles.

We have measured conductance of single-walled semiconducting carbon nanotubes in field-effect transistor (FET) geometry and investigated the device response to alcoholic vapors. We observe significant changes in FET drain current when the device is exposed to various kinds of alcoholic vapors. These responses are reversible and reproducible over many cycles of vapor exposure. Our experiments demonstrate that carbon nanotube FETs are sensitive to a wide range of alcoholic vapors.

This work details a method to make efficacious field-effect transistors from monolayers of polycyclic aromatic hydrocarbons that are able to sense and respond to their chemical environment. The molecules used in this study are functionalized so that they assemble laterally into columns and attach themselves to the silicon oxide surface of a silicon wafer. To measure the electrical properties of these monolayers, we use ultrasmall point contacts that are separated by only a few nanometers as the source and drain electrodes. These contacts are formed through an oxidative cutting of an individual metallic single-walled carbon nanotube that is held between macroscopic metal leads. The molecules assemble in the gap and form transistors with large current modulation and high gate efficiency. Because these devices are formed from an individual stack of molecules, their electrical properties change significantly when exposed to electron-deficient molecules such as tetracyanoquinodimethane (TCNQ), forming the basis for new types of environmental and molecular sensors.chemistry ͉ electronic materials ͉ nanoscience ͉ self-assembly T his work details a method to make chemoresponsive transistors by making devices out of a monolayer of polycyclic aromatic hydrocarbons that are chemically attached to surfaces. The devices are formed through a self-assembly process of organic semiconductors on the oxide surface of a silicon wafer (Fig. 1A) (1, 2). Previous studies on organic field-effect transistors (OFETs) (3, 4) have shown that the path for electrical current is through at most the first few layers of molecules at the oxide interface (5-7). In general, when the semiconducting layers of typical OFETs are scaled down to a monolayer, their properties become poor, presumably due to discontinuities or defects in the films (8-11). The strategy used here circumvents this problem by a chemical functionalization of the molecular semiconductors ( Fig. 1B) so that they both assemble laterally and chemically attach themselves to the substrate (Fig. 1C). The important result is that when ultrasmall point contacts separated by molecular length-scales are used as the source and drain (S͞D) electrodes, transistors can be made that have high gate efficiency and large ON͞OFF ratios from only a monolayer of molecules. The electrical properties of these monolayers are responsive to electron acceptors such as tetracyanoquinodimethane (TCNQ). Results and DiscussionDevice Fabrication. We first describe the devices used to measure the properties of the monolayers and then the structural and electrical characterization of these monolayers. Fig. 2 shows a schematic and micrograph of the devices used. Au (50 nm) on Cr (5 nm) pads, which are separated by 20 m, form the contact to an individual single-walled carbon nanotube (SWNT). The nanotubes were grown by a chemical vapor deposition (CVD) process described elsewhere (12, 13). The nanotube is then oxidatively cut by using an ultrafine lithographic process that produces a very small gap between the nan...

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