Microtools for scaling nanomountains.

The scanning tunneling microscope (STM) has become an essential tool for imaging surface features down to the scale of individual atoms. Typically the size of a fingernail, this instrument has tiny motors to skim a needle's tip back and forth across a surface a few hundred times per second. But such scanning rates are too low for using the apparatus to act as a rapidly responding microsensor, to shove atoms and molecules around efficiently to create patterns for microscopic circuits, or to store massive amounts of data. Reaching a higher scanning rate requires miniaturizing the device further.

Now, after 9 years of effort, researchers have succeeded in fabricating the world's smallest STM by means of the same kind of technology used to manufacture computer chips. "Because it's all done in silicon, everything is integrated," says Noel C. MacDonald of Cornell University. "We now know how to make suspended silicon structures. We know how to make them move in three dimensions. And we can do it on a scale on the order of micrometers."

Occupying a volume only slightly larger than a cubic millimeter, this microelectromechanical STM is driven by "finger" motors, each one only 200 micrometers wide. It can scan as quickly as a million times a second. Though still a long way from commercial use, this tiny device represents a significant step toward the ultimate goal of creating large arrays of these instruments on a single chip.

Scratching the surface

In the early days of audio recording, capturing a voice required running a vibrating stylus across the wax surface of a spinning cylinder or disk to create a serrated spiral groove. Replicated in vinyl or some other material, the same groove would cause a needle to vibrate, recreating the original sound.

H. John Mamin and his coworkers at the IBM Almaden Research Center in San Jose, Calif., are pursuing a similar strategy for storing vast amounts of data. Known as thermomechanical recording, this scheme involves focusing brief laser pulses on the tip of a microscopic needle pressed against a spinning disk's surface. The pulses instantly heat the needle, allowing it to sink into the briefly softened plastic to create a chain of tiny, shallow pits.

To make this technique competitive with current data storage methods, the researchers must increase the rate at which a needle can "write" its digital message, going from 100 kilohertz to the megahertz range. Achieving such an improvement requires making the needle and its supporting cantilever as light as possible.