Atomic layer deposition fuels future solutions to nation's energy challenge
Posted on Monday, July 23, 2007 @ 22:33:21 UTC by vlad
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 The three images illustrate how a combination of anodized aluminum
oxide (AAO) and atomic layer deposition (ALD) provides precisely
controlled, ultra-uniform porous support for new and well-defined
catalysts. Credit: ANL
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.
Source: Argonne National Laboratory
Via: http://www.physorg.com/news104420365.html
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