Although the question of whether nanorobots can exist remains unresolved, progress nevertheless continues apace on a range of nanoscale techniques and molecular electronic devices.
The first nanoscale light source based on a single carbon nanotube (acting as a field-effect transistor) was demonstrated by Phaedon Avouris, James A. Misewich, Richard Martel, and coworkers at IBM's T. J. Watson Research Center, Yorktown Heights, N.Y. [Science, 300, 783 (2003)]. An IBM group including Avouris, Martel, and Marcus Freitag also generated an electrical current in a single carbon nanotube by shining light on it [Nano Lett., 3, 1067 (2003)]. Both studies have implications for miniature photonic and optoelectronic devices.
A technique for changing nanotube electrical properties was devised by Robert C. Haddon and coworkers at the University of California, Riverside. They showed that functionalizing conductive metallic nanotubes with dichlorocarbene caused the nanotubes to take on semiconducting properties [Science, 301, 1501 (2003)].
Michael S. Strano of the University of Illinois, Urbana-Champaign, James M. Tour and Richard E. Smalley of Rice University, and coworkers found this year that functionalizing nanotubes with diazonium reagents differentiates metallic and semiconducting single-walled carbon nanotubes and makes it possible to separate and manipulate them, based on differences in electronic structure [Science, 301, 1519 (2003)]. And Ming Zheng of DuPont Central Research & Development, Wilmington, Del., and coworkers showed that certain sequences of DNA can wrap helically around single-walled carbon nanotubes and also permit them to be separated, based on optical features [Science, 302, 1545 (2003)].
Victor I. Klimov and coworkers at Los Alamos National Laboratory showed that amplified spontaneous emission--an important step toward tunable IR lasers--can be achieved in the near-IR region using nanocrystals of lead salts [J. Phys. Chem. B, published online Nov. 21, http://dx.doi.org/10.1021/jp0311660].
In a moving development, the first nanometer-sized, electrically driven synthetic motor--a gold rotor and a multiwalled carbon nanotube axis on a silicon chip--was built by Alex Zettl and coworkers at the University of California, Berkeley, and Lawrence Berkeley National Laboratory [Nature, 424, 408 (2003)].
Molecular electronics display-related developments this year included a polymer-based electroluminescent device that can be switched between glowing red or green by reversing the direction of current flow. It was produced by Luisa De Cola at the University of Amsterdam, Klemens Brunner at Philips Research Laboratories, Eindhoven, the Netherlands, and coworkers [Nature, 421, 54 (2003)]. The device could simplify the fabrication and increase the brightness of displays, light sources, and color switches.
A new solution-processing method can be used to pattern red, green, and blue electroluminescent polymers with resolution that exceeds what's required for flat-screen, full-color organic light-emitting diode displays. Formerly, the resolution of wet-chemical patterning processes for electroluminescent polymers wasn't high enough to create such displays. The new method was developed by Klaus Meerholz at the University of Munich (now at the University of Cologne); Heinrich Becker of Covion Organic Semiconductors, Frankfurt; Oskar Nuyken at the Technical University of Munich; and coworkers [Nature, 421, 829 (2003)].
A novel technique for aligning liquid crystals--developed by Roeland J. M. Nolte of the University of Nijmegen, the Netherlands, and coworkers--eliminates the current need for clean-room conditions in liquid-crystal display manufacture [Angew. Chem. Int. Ed., 42, 1812 (2003)].
Chemistry professor James R. Heath of California Institute of Technology and coworkers devised a method for producing ultrahigh-density arrays of aligned nanowires and nanowire circuits [Science, 300, 112 (2003)]. And a TechnionIsrael Institute of Technology team led by Erez Braun and Kinneret Keren created a field-effect transistor by binding a single-wall carbon nanotube to a DNA strand and fabricating gold leads to the nanotube [Science, 302, 1380 (2003)]. Techniques like this "will pave the way for integration of molecular components into useful microelectronics," a researcher commented.
In addition, many research teams are working to develop soft, flexible electronic technologies based on conducting fibers or organic thin-film materials. In one such study, Xiangfeng Duan and coworkers at Nanosys, in Medford, Mass., and Palo Alto, Calif., devised a low-cost, low-temperature process for fabricating high-performance thin-film transistors on flexible substrates [Nature, 425, 274 (2003)]. The technology takes "nanoelectronics in a new direction," Duan tells C&EN, "exploiting nanomaterials not for electronic miniaturization, but for better and cheaper electronics over large areas."
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