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Spring 1993

Research Magazine > ARCHIVE > Spring 93 > Article

Ions Unlock Eons of Secrets
by Cara D. Runsick

For eons, lovers have shared their secrets beneath the starry spring skies.

The skies, on the other hand, have hoarded a few of theirs.

Chemist Nigel Adams plans to wrest them away. With a pair of sensitive instruments fashioned in the University of Georgia, Adams may help shake loose the secrets of how stars are born -- and along the way, illuminate the complex chemistry that creates computer chips.

His breakthrough devices, the "selected ion flow tube" and a modified form of the "flowing afterglow," can assess chemical reactions that take place in faraway clouds of dust and gas like the Orion Nebula, a nursery for new stars, or on the minuscule surface of a silicon chip.

The instruments make it possible to measure the rates and products of gaseous chemical reactions more precisely than ever. For this reason, they have been adapted by scientists all over the world to meet a wide variety of research needs.

"The real beauty of the apparatus is its flexibility," Adams said. "We can look at ion reactions involving almost anything you can get into a gas or vapor phase."

That's what led him and others to the computer chip, one of the more practical applications of his new technology.

The types of chemical reactions that take place where new stars are forming are closely related to those that etch the pathways on silicon wafers. The two processes share a common chemical reaction called "recombination" in which ions -- relatively simple charged molecules -- combine with one another or with electrons to form chemicals that carry no electrical charges.

In etching silicon chips for computers, engineers choose the path they want to etch onto the wafer surface and physically protect it, just as you would use masking tape when painting woodwork.

The chips are then bathed in a mixture of ions; the ions damage the silicon surface -- except along the protected paths. An electrical discharge into the ion bath sparks the ionic recombination reaction, which then creates compounds that remove silicon from the damaged areas of the chip.

The protected strips are undamaged, so the silicon-removing compounds leave them intact. These are the tiny raised tracings we see when we look closely at a chip.

Before scientists like Adams began making detailed studies of recombination reactions, silicon etching was perfected by trial and error -- "something of a black art," Adams said.

The knowledge gained from Adams' instruments could make the process more precise, and therefore more efficient and economical. It also can approximate the enigmatic chemical reactions of distant nebulae.

"We know, or we think we know, a lot about the life cycles of stars once they have formed," Adams said, "but we don't know as much about their formation in these dust clouds. The flowing afterglow allows us to study, in the lab, the reactions occurring in these clouds."

The instruments allow researchers to set the reactions in motion in a flowing gas system, much like beach balls being carried along on a stream. But the "beach balls" in this case are ions and electrons that may react with one another if they collide.

Because the ions and electrons literally float from one end of the instrument to the other, researchers can tell how long reactions take by measuring how far the ions travel before the charges are neutralized. To do this, they use a sensitive probe to measure loss of charge as the reactions occur along the length of the stream.

Keeping the reactions moving also means the products are physically separated from the starting gases. "This allows us to characterize the reaction more precisely than would be possible if the reactants were mixed in with the products in a stationary system," Adams said.

The types of chemistry involved in spawning stars and creating computer chips is found in many other places, including parts of the earth's atmosphere -- giving Adams' instruments myriad possible applications.

Research Communications, Office of the VP for Research, UGA
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