http://www.sciencemag.org/cgi/content/full/290/5496/1524a
Atom-Scale Research Gets Real
Robert F. Service
Nanotechnology has spawned useful new materials and impressive
technical feats. But the field's most grandiose dreams, and
nightmares, remain the stuff of fiction
In September, speaking to an audience of prominent researchers and
government leaders at a meeting on the future impacts of
nanotechnology, Michael Crow crossed a familiar line. "How many of you
have read The Diamond Age?" the science policy expert and vice provost
of Columbia University in New York City asked his listeners. The book,
by science-fiction novelist Neal Stephenson, depicts a near-future
world in which advances in nanotechnology make it possible to build
essentially anything from scratch, atom by atom, leaving society to
sift through the cultural ramifications of limitless choices. In
response to Crow's question, a few hands fluttered in the air and
quickly dropped. These people, after all, were nanotechnology's
practitioners--not wide-eyed dreamers.
Crow wasn't promoting the book as a prophecy. He mentioned it, he
says, to encourage researchers to think about their unique position at
the dawn of a field that most in the room agreed will be a force in
the coming century. But clearly his question touched a nerve. Since
its inception, nanotechnology has been dominated by fiction, both
unabashed hype and better grounded hope. Science-fiction writers have
dreamt up lush scenarios of life with nanosized robots that do
everything from building gleaming cities to reaming out clogged
coronary arteries. Meanwhile, some researchers have been hard at work
drawing impressive but equally fictional blueprints for arrays of tiny
gears and pistons that could form the foundation of nanomachines--if
anyone ever figures out how to assemble the thousands of atoms needed
to build them.
This year, dystopian fiction came on the scene, as nanotech prophets
of doom made bold new pronouncements of nanotechnology's potential to
destroy humanity and called for either an end to research in the area
or new guidelines to ensure that researchers don't accidentally wipe
out life on the planet (see sidebar, p. 1526). "Nanotechnology seems
to have this wonderful property of having the most extravagant
favorable and unfavorable predictions," says Edward Tenner, a
historian of science at Princeton University in New Jersey.
In response, many researchers at the cutting edge of dealing with
matter on the near-atomic scale have become aggressively matter-
of-fact, squirming at the suggestion of cornucopian nanofactories or
even humbler mass-produced nanodevices. The nearby hurdles, they say,
are challenge enough. "Nanotechnology is a vision, a hope to
manufacture on the length scale of a few atoms," says Don Eigler of
IBM's Almaden Research Center in the hills above San Jose,
California. For now, he says, "nanotechnology doesn't exist."
Yet even the most hard-headed nanoscientists must admit that their
minute world, by whatever name, is on the move. Advances in
manipulating nanosized materials have already led to improvements in
computer data storage, solar cells, and rechargeable
batteries. Computer disk drives alone--which rely on controlling the
thickness of various layers of material on the nanometer
scale--account for a multibillion-dollar market. The field's promise
has prompted the creation of about a dozen nanotech research centers
in U.S. universities alone. The European Community runs several
programs in nanotechnology, including the Nano Network, which contains
18 member research centers working in nanomaterials synthesis. Japan,
Singapore, China, Australia, Canada, Germany, the United Kingdom, and
Russia all support nanotechnology efforts.
And there is more to come. Last month Congress approved the bulk of
the Clinton Administration's request for money to launch a new
National Nanotechnology Initiative. Next year the initiative will
spend some $423 million on nanoscience, with more sure to follow. In
Japan, nanotechnology funding is slated to jump 41% next year to $396
million. Several European countries are ramping up efforts as well.
Some U.S. experts hope that the surge in funding will carry over to
bolster American research in the physical sciences as a whole. Whereas
Congress is 3 years into a 5-year effort to double biomedical research
funding at the National Institutes of Health, "support for physical
sciences and engineering has been stagnant," says Tom Kalil, a White
House specialist on the economics of technology. "We see
[nanotechnology] as a way [of] increasing support for physical
sciences and engineering."
Richard Smalley, a Nobel Prize-winning chemist, thinks the emerging
field may even reverse the long slide in the number of new students
choosing careers in science, just as the space race inspired an
earlier generation. "It was Sputnik that got me into science," Smalley
says. "Of all the impacts of [nanotechnology's rise], the most
important impact--and one that I dearly hope will happen--will to be
to get more American girls and boys interested in science."
All of this activity is leading to some rather grandiose
pronouncements. "This is an area that can have a huge potential payoff
that can be as significant as the development of electricity or the
transistor," says Kalil. And at a 1998 congressional hearing, Neal
Lane, the president's adviser for science and technology and former
National Science Foundation (NSF) director, stated, "If I were asked
for an area of science and engineering that will most likely produce
the breakthroughs of tomorrow, I would point to nanoscale science and
engineering."
But however promising nanotech's future may be, transforming it from
the world of fiction to reality will mean overcoming some daunting
obstacles. Beyond manipulating atoms, nanoscientists must perfect ways
to mass-produce nanosized objects and integrate them with the larger,
human-scale systems around them. And they must do it while working in
an interdisciplinary field that requires new levels of cooperation
among different specialties, raising familiar challenges of herding
academic cats and coaxing them to march in lockstep.
A new hammer
Of course, nanotechnology--in the guise of nanoscale materials--has
already been around for a long time. For the last 100 years, tire
companies have reinforced the rubber in car tires by adding nanosized
carbon particles, called carbon black. And living organisms from
bacteria to beetles rely on nanosized protein-based machines that do
everything from whipping flagella to flexing muscles.
Today, the term "nanotechnology" refers most broadly to the use of
materials with nanoscale dimensions, a size range from 1 to 100
billionths of a meter, or nanometers. Because this range includes
everything from collections of a few atoms to those protein-based
motors, researchers in chemistry, physics, materials science, and
molecular biology all lay stake to some territory in the field. That
tends to make nanotechnology a scientific Rorschach blot: What it
includes depends on whom you ask.
"Nanotechnology is a wonderful umbrella term that takes into account
many things that we were doing before some very helpful tools came
along," says William Tolles, a nanotechnology consultant for the U.S.
Department of Defense. "To a 5-year-old with a hammer, the world looks
like a nail," adds Lester Lave, an economist at Carnegie Mellon
University in Pittsburgh, who studies the development of technology.
"Nanotechnology is a hammer, and nanotechnologists are looking around
to see what they can hit with it."
The development of that hammer was launched by a breakthrough in
manipulating atoms back in the early 1980s. In 1982, physicists
Heinrich Rohrer and Gerd Binnig of IBM's Zurich Research Laboratory in
Switzerland created a new type of microscope, called a scanning
tunneling microscope (STM), that is capable of imaging individual
atoms. By tracking the changes in a tiny electrical current from an
ultrasharp tip to atoms on a surface, Binnig and Rohrer's STM enabled
researchers, essentially, to feel their way along a surface at the
atomic level and create a computerized image of it atom by atom.
Other imaging tools followed close behind. In 1985, Binnig teamed up
with Calvin Quate, an electrical engineer at Stanford University in
Palo Alto, California, to make an atomic force microscope, which
enabled them to image surfaces that do not conduct electricity. And
since then, versions of these microscopes have been developed to
pinpoint atoms' magnetic and chemical signatures.
It wasn't long before researchers used their new tools to jump from
imaging atoms to manipulating them. In 1990, Eigler and Erhard
Schweizer, also of IBM's Almaden Research Center, used an STM to spell
out "IBM" with 35 xenon atoms atop a nickel surface. It was the first
time scientists had built something by manipulating individual
atoms. Since then, Eigler and colleagues have gone on to build a
series of atomic-scale corrals that reveal the wavelike nature of
atoms and their electrons for all to see. "Seeing the electrons in
their quantum state seems to have had a larger psychological effect
than the bare bones of the research itself," Eigler says.
Part of that psychological effect lay in convincing researchers that
they could build structures an atom at a time. It's an idea that
continues to spread. Last year, Wilson Ho, a chemist and physicist at
the University of California, Irvine, showed that he could use an STM
to help forge chemical bonds between iron atoms and carbon monoxide
molecules. Other researchers have used similar techniques to alter the
chemistry of silicon atoms on a surface, transforming them into a key
component of a transistor.
Early advances have gone beyond manipulating atoms. Groundbreaking
work in materials synthesis has given researchers the ability to
control the size and shape of a wide variety of materials at the
nanoscale. Along the way, researchers discovered that in many cases
the large surface-to-volume ratio of nanoscale materials gives them
unique characteristics not shared by their bulk-sized
cousins. Nanosized crystallites made from semiconductors such as
cadmium selenide, for example, fluoresce in different colors of light
as they change sizes. That's already made them a hot property for use
as fluorescent "dyes" in biology experiments, and several companies
are now racing to commercialize the technology.
The large surface area of nanoparticles also makes them ideal
catalysts, whose surface atoms orchestrate chemical reactions. Whereas
bulk gold, for example, is unreactive at room temperature, 3- to
5-nanometer gold particles can promote a number of common reactions
and have already been developed commercially by a Japanese company as
bathroom "odor eaters."
Enhanced properties on the nanoscale continue to be discovered. A
number of companies are experimenting with spiking common plastics
with nanosized particles in order to bolster properties such as
strength and impact resistance. Nanosized probes are being developed
to detect biological weapons such as anthrax. And carbon
nanotubes--tiny, straw-shaped molecules a mere nanometer or so
across--have been shown to conduct either like metals or
semiconductors depending on their precise geometry, and they have
already been incorporated into a range of electrical components such
as transistors and diodes.
Reality gap
For most nanobased applications, the key to progress is
straightforward: Find ways to make very fine particles or layers of
material of a precise size, which, when incorporated directly into a
final plastic or solar cell, all share the same electronic, optical,
and mechanical properties. These simple products are already finding
their way into the marketplace, and their relative ease of production
might always ensure them the biggest share of the business.
Most of the buzz about nanotechnology, however, involves more
sophisticated applications of nanomaterials, such as electronic
devices and tiny chemical sensors. The holdup, so far, is that in most
cases there's no obvious way to transform single demonstration devices
into a working technology. "Nanotechnology is an area that is
profoundly reductionist," says Harvard University chemist George
Whitesides. "We can pick matter apart at its basic level of the atom
and reassemble it." But researchers, he warns, mustn't take that
ability too seriously. "We want to be sure we don't fall completely
over that cliff."
Whitesides's point is that although it is possible to manipulate
individual atoms, it's much harder to do it on a grand scale. In 1998,
for example, researchers led by Cees Dekker at the Delft University of
Technology in the Netherlands reported making the first transistor
using a carbon nanotube as a key component of the device. Work since
has shown that the electronic performance of such transistors can
approach or even surpass that of conventional silicon
transistors. "But there is a problem here," says Tom Theis, who heads
physical sciences research at IBM's Thomas J. Watson Research
Laboratory in Yorktown Heights, New York. When it comes to making
computer chips containing millions of such devices, "it's completely
unmanufacturable."
The problem of manufacturability remains nanotechnology's Achilles'
heel, particularly for the much-hyped possibility of creating
nanosized machines. "The technology is still almost wholly on the
drawing board," John Seely Brown writes in a research paper submitted
to the September NSF meeting. Brown, who heads the famed Xerox Palo
Alto Research Center in California, points out that two of the main
proponents of nanomachines, Ralph Merkle and K. Eric Drexler, built
powerful nano-CAD tools and then ran simulations of the resulting
designs. "The simulations showed definitively that nano devices are
theoretically feasible," Brown writes. "But theoretically feasible and
practically feasible are two different things. And as yet, no-one has
laid out in any detail a route from lab-based simulation or the
extremely elementary nanodevices that have been chemically constructed
to practical development."
But others argue that visionary research serves a purpose, too. Even
if nanogears and pistons cannot be built yet, says Deepak Srivastava,
who heads the computer nanotechnology design group at NASA's Ames
Research Center in Moffett Field, California, the computer designs
still help focus experimentalists on what's worth looking for: "If the
ideas are based on real physics and chemistry, one has to know the
real possibilities."
And of course, experimental science is constantly expanding the scope
of what is feasible. Whitesides and Stephen Chou of Princeton
University have recently pioneered a new rubber stamping method for
patterning surfaces with features as small as 10 nanometers. That is
well below the current size limit of about 200 nanometers faced by
photolithography, the primary patterning tool used by the computer
chip industry. Still, the stamping technique has its own drawbacks: It
has trouble patterning multiple materials in three dimensions, as is
needed for making computer chips, and ensuring proper alignment of all
the various layers of material.
Another patterning alternative making headway is a burgeoning subfield
of chemistry known as self-assembly, in which researchers design
materials to assemble themselves into desired finished structures. For
example, last year IBM researchers led by chemist Christopher Murray
came up with a way to make metallic particles as small as 3 nanometers
and then assemble them into a three-dimensional array. Such
structures could lead to material for future computer disks in which
each nanoparticle stores a bit of data. Still, for now such successes
tend to be the exception rather than the rule.
Future nanoapplications face other grand challenges as well. Even if
particular nanocomponents can be mass-produced, researchers will still
need to figure out how to position them on surfaces or other
structures so they can be used as components in electronic devices,
sensors, and the like. For tiny electronic components, researchers
will then face the major stumbling block of wiring them up to the
macro world.
They will also confront the more mundane challenge of connecting with
one another. By all accounts, nanotechnology will require an
extraordinary range of expertise. Researchers have long embraced the
concept of interdisciplinary research. And organizations such as the
NSF make it a point to finance interdisciplinary centers. Still,
academia remains largely hidebound in disciplines, making it difficult
to pursue research that falls between traditional fields. "There still
exist many elements in the culture of our research universities that
discourage multidisciplinary research," says James Merz, the vice
president for graduate studies and research at the University of Notre
Dame in Indiana.
Among the chief culprits Merz points to are the administrative
autonomy given to separate departments and the fact that faculty
members must obtain tenure from specific departments. Furthermore,
Theis points out, essentially no curricula have been developed to
train future researchers in the field, let alone degree programs to
turn out new nanotech Ph.D.s. Although those impediments aren't
necessarily fatal, they can easily hamper the field's development,
Merz says.
Beset by such challenges, nanoreality is bound to fall short of
nanohype. The danger is that disenchantment with the gap could dampen
financial support for the field, says Mihail Roco of NSF, who heads
the U.S. National Nanotechnology Initiative. That's a scenario well
known to researchers in high-temperature superconductivity, an
enterprise that has struggled to live up to the fanfare that greeted
it in the mid-1980s. Still, unlike superconductivity--a narrow field
whose impact is limited to a comparatively small sphere of
applications--nanotechnology is likely to benefit from its breadth,
says Srivastava. "Since the net is much wider," he says, "the chance
is bigger that you will catch some fish."
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