NANO: Taking the Initiative

Date: Sat Nov 25 2000 - 05:52:34 MST

Taking the Initiative

Robert Coontz and Phil Szuromi

It has been almost a decade since Science devoted a special issue to
nanotechnology, and even the title of that issue ("Engineering a Small
World," 29 November 1991) reflected the scarcity of actual working
nanotechnology at the time. Like others, we pointed to Richard
Feynman's 1959 lecture "There's Plenty of Room at the Bottom" to
provide some justification for why nanotechnology would emerge as a
discipline from early efforts in atomic imaging and
nanofabrication. The present special issue can reflect only some of
the current trends in this rapidly expanding area.

In the News section (p. 1524), writer Robert Service surveys
nanotechnology's near-term prospects: the role of funding infusions,
such as the U.S. National Nanotechnology Initiative and its European
and Japanese counterparts, and the real promise of new materials and
devices. He also takes a jaundiced view of some of the prophecies of
boom and doom made by the field's boosters and critics. Meanwhile,
amid the nanohype, researchers are forging ahead on several exciting
fronts. Short profiles of five research groups aim to give some sense
of the range of work now under way throughout the world, without
pretending to be exemplary or comprehensive.

Three Reviews focus mainly on nanomechanics, which builds on (or
perhaps below) the advances that have been witnessed in
microelectromechanical systems (MEMS). Some of the MEMS advances are
stunning enough in themselves. For example, micromirror arrays
developed at Lucent can be tilted to steer light beams from one
channel to another for routing fiber-optic signals. Craighead
(p. 1532) discusses how even smaller nanoelectromechanical systems
(NEMS) will have higher resonant frequencies and lower masses that
will facilitate several new applications. Complex freestanding
structures can now be fabricated and used, for example, to sense
adsorbed mass, or as radiofrequency devices in the 1- to 10-megahertz
range. These structures can be set in motion with applied electrical
fields or with piezoelectric driving of supports. Sacrificial
fabrication can also be used to create channel structures of varying
complexity for fluidic systems and molecular separations.

Although many nanomechanical systems have been fabricated in hard,
inorganic materials, polymeric materials are now being exploited for
micromechanics and nanofabrication. Quake and Scherer (p. 1536) point
out that soft polymeric systems have some natural advantages in
fluidics, in that the pumps and valves used in "labs on chips"
normally need soft seals and seats to work seamlessly. Soft materials
can be molded and assembled in layers to leave complex fluidic
networks or to create diffractive optical elements.

Producing complex movements in devices is still a challenge,
especially for potential applications in biological systems. Jager et
al. (p. 1540) review how conducting polymers could solve some
problems. Bimorph actuators produce movement through the differential
expansion of a layer of one material pressed against a dissimilar
material. In polypyrrole-gold bimorphs, an applied electrical field
creates a volume change in the polymer that produces motion (and can
even peel a newly fabricated device from its supports). These
actuators could find use as cell manipulators or as microrobots, all
within a cellular milieu.

Nanotechnologists are now creating devices the performance of which
will be tested and improved by new experiments and by more accurate
theoretical treatments. Although there is still plenty of "room at the
bottom," researchers have done much more than stake out claim sites:
They are digging in.

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