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
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
"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
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.
Communications, Office of the VP for Research, UGA
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