Atomic layer deposition fuels future solutions to nation's
energy challenges
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ARGONNE, Ill. (July 20, 2007) — More efficient and less costly solar cells,
solid-state lighting and industrial catalysts are potential applications of
atomic layer deposition (ALD), a technique that researchers at Argonne National
Laboratory are working to perfect. Other potential applications are improved
superconductors and separation membranes.
ALD is a thin-film growth technique that offers the unique capability to coat
complex, three-dimensional objects with precisely fitted layers. The scientists
expose an object to a sequence of reactive gas pulses to apply a film coating
over the object's surface. The chemical reactions between the gases and the
surface naturally terminate after the completion of a "monolayer" exactly
one molecule thick. ALD can deposit a variety of materials, including oxides,
nitrides, sulfides and metals.
What makes ALD more effective and flexible than traditional methods for producing
thin film coatings, such as evaporation, is its ability to coat every nook
and cranny of a complex object.
Scientists use this procedure to fabricate nanostructured catalytic membranes,
or NCMs. These structures enable catalytic reactions that, for example, convert
inexpensive feedstocks into valuable products and synthesize hydrocarbon fuels.
Argonne has filed for a patent on NCMs.
“We are focusing our attention now on measuring the properties of the catalysts
and synthesizing other catalytically relevant materials inside the NCMs,” said
Jeffrey Elam, a research chemist in Argonne's Energy
Systems Division.
Elam, along with Michael Pellin of Argonne's Materials
Science Division, has
been working with NCMs to carry out chemical reactions to produce materials
that help the nation sustain itself in a more cost-effective and efficient
manner.
One of the Argonne researchers' goals has been to improve the effectiveness
of the catalyst in Fischer-Tropsch synthesis. The Fischer-Tropsch process
takes syngas, a mixture of carbon monoxide and hydrogen, and converts it into
hydrocarbon fuels. Syngas can come from a variety of materials, including natural
gas, coal or biomass.
Elam and Pellin hope that Argonne's NCMs can improve the performance of Fischer-Tropsch
catalysts enough to make the production of clean, sulfur-free fuels economically
viable in the next decade or two.
Recently, Argonne researchers also have begun to apply ALD technology to solid-state
lighting, which uses light-emitting
diodes, or LEDs. Unlike incandescent light
bulbs, LEDs consume little electric power and do not burn out or overheat.
They are illuminated by the movement of electrons in a semiconductor and are
considered the most efficient light source in existence. LEDs can be found
in many electronic devices, from digital displays to traffic lights.
LEDs require a conducting electrode to supply electricity to the semiconducting
material, but this electrode must also be transparent to allow the light to
escape. Traditionally, this transparent conducting electrode is made from indium-tin
oxide (ITO); however, ITO is too expensive for mass production.
To replace ITO, Argonne researchers are exploring chains of metal nanoparticles
aligned in a magnetic field to form an electrically conductive web. ALD coatings
are applied to these networks to form a transparent, conducting electrode to
make cheaper LEDs. This research is funded by the U.S. Department of Energy
to develop advanced solid-state lighting technologies that, compared to conventional
lighting technologies, are much more energy efficient, longer lasting and cost-competitive
by 2025.
In cooperation with Northwestern University, Argonne researchers are also
fabricating highly efficient solar cells for converting sunlight into electricity.
These improved, dye-sensitized solar cells (DSSCs) use ALD technology in a
similar way to NCMs – precisely fitted layers of transparent, conducting oxides
and semiconductors are deposited on the inner surfaces of nanoporous membranes.
The researchers aim to eventually commercialize these novel and efficient
solar cells. Because no pure, costly silicon is involved in the fabrication
process—as it generally is with conventional solar cells—the researchers hope
to produce electricity at a much lower cost.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology.
The nation's first national laboratory, Argonne conducts leading-edge basic
and applied scientific research in virtually every scientific discipline. Argonne
researchers work closely with researchers from hundreds of companies, universities,
and federal, state and municipal agencies to help them solve their specific
problems, advance America 's scientific leadership and prepare the nation for
a better future. With employees from more than 60 nations, Argonne is managed
by UChicago
Argonne, LLC for
the U.S.
Department of Energy's Office
of Science.
For more information, please contact
Jenny deAngelis (630/252-5549 or jdeangelis@anl.gov )
at Argonne.
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