CHEMICAL & ENGINEERING
NEWBflffllHWWEEK SA WRAY DALTON
MOLECULAR
ELECTRONICS
MOLECULE-BASED CIRCUITRY REVISITED Faked results implausible, but true molecular devices still may be possible
I
N AN EFFORT TO SET T H E
record straight, researchers in the U.S. and the Netherlands have investigated the feasibility of constructing molecular electronics devices that were reported to have been built and tested in a series ofresearch papers later judged to be fraudulent. The new studies conclude that microscopic structures of the type described in the original reports do not function as claimed and cannot function in that way owing to fundamental limitations and other problems. The idea that a single molecule or just a small handful ofmolecules can function as the active element in electronic devices gained support over the past fewyears as researchers in various institutions reported incremental advances in molecule-based circuitry So when Jan Hendrik Schôn and coworkers at Lucent Technologies' Bell Labs reported that they had succeeded in preparing functioning field-effect transistors (FETs) based on self-assembled monolayers (SAMs) of organic molecules, excited researchers in several labs tried to reproduce Schon's results. But none was successful. Then last year, an investigatory committee concluded that Schôn fabricated much of the data presented to support his claims, and he was fired (C&EN, Sept. 30,2002, page 9). As shock waves from the research-fraud announcement reverberated through the molecular electronics community many HTTP://WWW.CEN-ONLINE.ORG
scientists continued to wonder whether it still might be possible to observe the electrical-transport properties reported in the Bell Labs papers using the type of
SAMFETs described in jjj those publications. Now, f groups ofscientists working independently at IBM's T. J. Watson Research Center in Yorktown Heights, N Y , and at Dutch universities report that, based on numerous experiments, their results contradict Schôn's claims. The team in the Netherlands includes Delft University of Technology research associateJeong-O Lee and physics professor Cees Dekker and their coworkers at Delft, Eindhoven University of Technology, and the University of Twente. That group prepared SAMFETs using five phenylenebased ττ-conjugated molecules: 1,4-benzenedithiol, 1,4-phenylenediisocyanide, and 4,4 ' -biphenyldithiol—molecules that were mentioned in the Bell Labs pa pers —and 1,3-benzenedithiol and a related benzonitrile (Nano Lett., published online Jan. 1, http://dx. doi.org/10.1021/nl025882+).
In total, the Dutch group re ports, more than 1,000 devices were fabricated. Yet despite care ful preparation and characteriza tion, most failed owing to shortcircuiting. Of those that worked, only two FEIs made from 1,3-ben zenedithiol exhibited an appre ciable gate effect, a key electrical property But the magnitude ofthe effect was negligible compared with the claims made by Schôn. IBM staff scientists Chérie R. Kagan, Richard Martel, and their coworkers investigated SAMFETs
prepared from biphenyldithiols and related molecules. They conclude that, although the devices described in the Bell Labs papers cannot function as claimed, the chapter on molecular FETs remains open. Based on an analysis of electrostatics and charge tunneling, the group says that by adhering to certain geometrical constraints on the lengths and thicknesses of FET components (for example, a minimum molecular length of 2.5 to 3 nm), it may still be possible to prepare functioning FETs from monolayers of organic molecules (Nano Lett., published online Dec. 19, http:// dx doi.org/10.1021/nl0259075).-
SMALL SCALE Using microscopic electronic devices such as those prepared in the Netherlands (left) and at IBM, researchers measure electrical transport properties of biphenyldithiols and related molecules.
MITCH JAC0BY
C&EN / JANUARY
27, 2003
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