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In the sizzling hot area of molecular electronics this year, one key development was the fabrication, by three different groups, of nanoscale wires with segments of varying chemical or dopant composition (C&EN, Feb. 11, page 7). The devices were the first to contain more than one junction within an individual nanowire or nanotube. The work was done by groups led by Charles M. Lieber of Harvard [Nature, 415, 617 (2002)]; Lars Samuelson of Lund University, Sweden [Nano Lett., 2, 87 (2002)]; and Peidong Yang of UC Berkeley [Nano Lett., 2, 83 (2002)]. The patterned self-assembly of integrated semiconductor devices such as LEDs on surfaces was demonstrated by George M. Whitesides and coworkers at Harvard [Science, 296, 323 (2002); C&EN, April 15, page 13]. Patterned solder-coated areas placed on the substrates doubled as self-assembly receptors and as electrical connections. A technique for transforming coated films into polymer-covered liquid-crystal layers could lead to cheaper, thinner, more flexible liquid-crystal displays. It was developed by Dirk J. Broer at Eindhoven University of Technology and Philips Research Laboratories, Eindhoven, the Netherlands, and coworkers [Nature, 417, 55 (2002); C&EN, May 6, page 11]. Phaedon Avouris of IBM and colleagues found that carbon-nanotube-based transistors can outperform silicon transistors--suggesting that it might be feasible to replace silicon with carbon nanotubes in electronic devices when the size of silicon-based circuits can no longer be reduced [Appl. Phys. Lett., 80, 3817 (2002); C&EN, June 3, page 9]. Paul L. McEuen and Daniel C. Ralph of Cornell and coworkers and (independently) a group led by Hongkun Park of Harvard created transistors in which a single molecule of a transition-metal organic complex bridges a nanometer-scale gap between electrodes [Nature, 417, 722 and 725 (2002); C&EN, June 17, page 4]. A team led by Benjamin R. Mattes of Santa Fe Science & Technology showed that dopable polymers can be electrochemically cycled for up to 1 million cycles in ionic liquids without failure--suggesting that ionic liquids could be useful for fabricating and operating polymer electrochemical devices [Science, 297, 983 (2002); C&EN, July 8, page 26]. Groups led by Chang-Beom Eom of the University of Wisconsin, Madison, and Xiaoxing Xi at Pennsylvania State University, independently developed oriented thin films of magnesium diboride that are potentially useful for making superconducting devices [Appl. Phys. Lett., 81, 1851 (2002); Nat. Mater., 1, 35 (2002); C&EN, Sept. 9, page 11]. These would require less cooling than current niobium-based superconductor circuits. Shahed U. M. Khan and coworkers at Duquesne University created a modified form of the water-splitting catalyst titanium dioxide that boosted more than eightfold the efficiency with which the material converts solar energy into hydrogen fuel [Science, 297, 2243 (2002); C&EN, Sept. 30, page 25]. A team led by Yet-Ming Chiang of MIT found that doping lithium iron phosphate with metal ions boosts its electrical conductivity by an astonishing eight orders of magnitude [Nat. Mater., 1, 123 (2002); C&EN, Sept. 30, page 25]. LiFePO4 is a potentially inexpensive electrode material for high-power-density lithium batteries. A simple procedure for converting an insulating calcium-aluminum oxide to a transparent electrical conductor by heating the material and then exposing it to UV light was developed by Hideo Hosono of Tokyo Institute of Technology and coworkers [Nature, 419, 462 (2002); C&EN, Oct. 7, page 9]. Transparent conductors could be useful in optoelectronics. A group led by Carlo D. Montemagno of UCLA devised a switch based on mutant F1-ATP synthase that can turn a biomolecular nanomotor off and on [Nat. Mater., 1, 173 (2002); C&EN, Nov. 11, page 36]. Harry L. Anderson of Oxford University, Franco Cacialli of University College London, and coworkers prepared polyrotaxanes--polymer wires sheathed by cyclo- dextrin rings. They demonstrated that the coated wires act as semiconductors and used them to prepare blue and green LEDs [Nat. Mater., 1, 160 (2002); C&EN, Nov. 18, page 17]. And John T. Fourkas of Boston College and coworkers used multiphoton absorption to encode and read out 3-D data in molecular glasses and highly cross-linked polymers [Nat. Mater., 1, 225 (2002); C&EN, Nov. 25, page 8]. "The materials are inexpensive, easy to process, and can store and read data robustly with an unamplified laser," Fourkas tells C&EN. Another key molecular electronics advance this year, Fourkas notes, was the first demonstration of single-molecule electroluminescence, by Robert M. Dickson and coworkers at the Georgia Institute of Technology [Proc. Natl. Acad. Sci. USA, 99, 10272 (2002)].
LED ARRAY
Whitesides' group demonstrated the self-assembly of LEDs on
surfaces patterned with solder. NANOGAP A
single-molecule transistor based on a divanadium complex (red
= vanadium) was developed by Park and
coworkers. | |||||||||
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Chemical &
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