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Hydrogen Rules
You would think that an
element as ubiquitous as hydrogen would have been
studied until there was no more to learn. Not so,
say Drs. Chris G. Van de Walle of the Palo Alto
Research Center (PARC) and Jörg Neugebauer of the
Fritz Haber Institute in Berlin in a report published
in the June 5 issue of the journal Nature
(www.nature.com).
Since hydrogen is so plentiful
on Earth (as a component of water, hydrocarbons,
etc.), it can easily be incorporated in materials
– even in ultra-clean laboratory settings. Understanding
the nature and behavior of hydrogen is crucial in
the development of better materials for fuel cells,
biochemical sensors, and semiconductor devices.
In today’s silicon chips hydrogen plays an essential
role because it heals imperfections at the interface
between the silicon and the silicon dioxide in the
transistors.
Using sophisticated computer
models, which reduce the need for expensive testing,
the researchers found that the behavior of hydrogen
varies greatly depending on the material in which
it is incorporated. In some materials, adding hydrogen
increases conductivity while in others
it reduces conductivity. Understanding
why this happens is crucial to predicting how hydrogen
will act in new materials. As described in Nature
, hydrogen’s behavior is governed by a Universal
Alignment rule, which says that a single energy
level describes the electrical behavior of hydrogen
in every material.
Remarkably, the rule applies
not only to solids but also to liquids. Hydrogen
ions play an important role in chemical and biological
reactions, and therefore the new rule will be useful
to scientists in those fields, as well. This new
knowledge will allow scientists to build novel materials
faster and can assist researchers working in such
diverse fields as UV lasers, wireless communication,
and hydrogen-based energy systems.
Chris G. Van de Walle,
a Principal Scientist at the Palo Alto Research
Center (PARC), won the David Adler Award in 2002
from the American Physical Society. He received
his Ph.D. in 1986 from Stanford University. Before
joining PARC in 1991, Dr. Van de Walle was a postdoctoral
scientist at the IBM T. J. Watson Research Center
in Yorktown Heights, New York (1986-1988), a Senior
Member of Research Staff at Philips Laboratories
in Briarcliff Manor, New York (1988-1991), and an
Adjunct Professor of Materials Science at Columbia
University (1991). Dr. Van de Walle develops and
employs first-principles techniques to model the
structure and behavior of materials. He has performed
extensive studies of semiconductor interfaces (including
the development of a widely used model for band
offsets) and of defects and impurities in semiconductors,
with particular emphasis on doping problems. Recently,
he has been focusing his attention on novel materials
for electronics and optoelectronics, and on the
behavior of hydrogen in a wide range of materials.
Dr. Van de Walle has published over 180 research
papers, has nine patents, and has given 68 invited
talks at international conferences. He is a Fellow
of the American Physical Society (APS), a Senior
Member of the IEEE , and the recipient
of a Humboldt Award for Senior US Scientist
. He has chaired three conferences, and will
be Program Chair for the 27 th International Conference
on the Physics of Semiconductors, to be held in
Flagstaff, Arizona, in 2004.
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