Nanotech: Bigger Isn't Better
Wu, Corinna, Science News
Over the years, scientists haven't settled for merely observing worlds existing on grains of sand, they've also created them.
Once, all motors, engines, or pumps were noisy iron masses that could only be moved with great difficulty. Now, some are delicate wisps that can only be seen under an electron microscope. When researchers at AT&T Bell Laboratories carved early microdevices out of silicon in 1987, they moved one step closer to realizing people's dreams of using tiny robots to perform a multitude of tasks.
In fact, "microscopic" no longer accurately describes the objects that scientists are now creating. Only the word "nanoscopic" will do. For example, carbon nanotubes, first created in 1991, have been tapped as potential super-thin wires, miniature test tubes, and tiny sensors. Some scientists hope to construct working machine parts so small they contain only a few thousand atoms.
"We believe that nanotechnology will be revolutionary," says Chris Peterson, executive director of the Foresight Institute in Palo Alto, Calif. "It will affect how we make the physical objects around us, how we cure disease, limit pollution."
So far, scientists have usually taken a top-down approach to nanotechnology. They whittle away a chunk of material, leaving small features on the surface. This technique has worked marvelously well, says Peterson. After all, "the whole computer industry is based on this." The tiny wires and electronic circuits on computer chips are etched into slices of silicon. Miniature motors and engines carved with top-down methods, however, have yet to find practical applications.
To break through to the next level of smallness, a new generation of devices will have to be built from the bottom up.
By using atoms, molecules, or nanometer-size aggregates as building blocks, scientists hope to exercise the ultimate control over the devices they construct. Materials made in this way could possess unusual properties, an approach that has "exciting potential," says Ronald Breslow, past president of the American Chemical Society. New nanocomposites, in which nanometer-size particles of one component are mixed into another material, can be vast improvements over their conventionally made counterparts.
One strategy for bottom-up construction is known as self-assembly, a process by which components come together without human intervention to form an ordered, functioning system. Nature abounds with self-assembled objects. The water molecules in a raindrop automatically aggregate to form a smooth, curved surface. A cell is more complex, but it, too, contains all the information it needs to assemble itself. The key challenge for scientists in coming decades will be to cause self-assembly to take place "rationally and by design," says George M. …