Process May Speed Computers : Technology: UCSD scientist develops new way to store images on silicon, which could be used to create a system dramatically faster than most home computers.

Demonstrating a new way to store data that might one day lead to faster computers, a UC San Diego scientist has etched tiny luminescent images on thin silicon wafers, according to today’s journal Science.

Michael Sailor, an assistant professor of chemistry, used electrical current, chemicals and light to etch images of George Washington on a silicon wafer--a process similar to photography, To show it wasn’t a fluke, Sailor also etched a ladybug-sized image of Elvis Presley on the porous silicon.

Which Elvis?

“We chose the young one,” said Sailor, referring to the post office’s recent dilemma of whether to use a youthful or more seasoned image of the rock star on a new postage stamp.

Although silicon has long been the linchpin of the computer industry, until recently researchers have believed it was limited in what it could contribute to the next generation of computers that will rely on light for transmission and storage of data. Today, most home computers, for instance, use computer chips that transmit information through copper or gold wires--a process far slower than the speed of light, or the speed that experts say will one day become commonplace for electronic devices.

“The results of our studies demonstrate several ways of storing images in silicon, all of which might be applicable to optical and holographic display,” Sailor said.

The new technique may have several uses. For instance, it might allow archivists to preserve colorful pictures without the use of pigments. Since color film fades over time, researchers have long looked for better ways to store these images. Sailor’s collections of Washington and Elvis are still too grainy for practical use, but he believes this hurdle can be overcome.

“The state-of-the-art resolution now available with optical disks is about a factor of 100 times smaller than we can now obtain with silicon; that’s the part that still keeps this in the research area,” he said. “But we still have a couple of tricks that we believe will help resolve this problem.”

The technique could also be used to accelerate the speed of computers, Sailor said. “If you wanted the computer to talk to the world using a light beam instead of a wire, you could attach a fiber-optical cable to a silicon chip that had a spot of porous silicon.”

The end result, he said, would be a system dramatically faster than most home computers.

Research using porous silicon, however, is still so cutting-edge that no one yet knows whether it will prove to be practical.

“It’s kind of a nice demonstration of the utility of porous silicon, but it’s a long way from practical application,” said Bruce Parkinson, professor of chemistry at Colorado State University. “They may perfect this, and it may never compete because of some other technology that’s been developed.”

In his research, Sailor projected the reduced black-and-white images of Washington and Elvis onto a 1-centimeter-square wafer of silicon while it was being immersed in an acidic solution that was receiving a small current of electricity. The combination of electricity and chemicals ate into the silicon, re-creating the images on the wafer after 30 minutes.

The resulting images appear almost three-dimensional, like holograms, and are luminescent or have “false colors.” True colors are created by pigments or dyes, and false colors result from the interference of light with itself--or the same phenomenon that happens when you see a rainbow of colors in oil on the pavement, Sailor said.

Silicon, like oil, doesn’t have color, Sailor said. “You are seeing colors, but there’s no pigment.”

Research conducted two years ago by British and French scientists revealed that silicon could be made to emit an intense orange-red light through a chemical etching process. In this process, the chemicals make the silicon porous and spongy by carving it into a collection of thin pillars. Sailor and others have latched onto this work, hoping to better understand the qualities of porous silicon.

Today, scientists are trying to figure out what causes porous silicon to emit light; there are several theories.

Some believe it may be a result of what happens when silicon is made so small that it no longer has an infinite number of atoms. Others say the atomic, or crystal, structure has been altered as the chemicals etch into the silicon. Still others say the silicon reacts and endures a change in its chemical composition and is transformed into another substance, called siloxene.

“Right now, I’ve got the all-of-the-above approach--it could be a combo platter of three,” Sailor said. “I want to understand the reason porous silicon gives off light.”