Tiny materials reveal a giant research challenge

Small particles are big research at Argonne and around the world. Nanomaterials are clusters of atoms or molecules that measure a few billionths of a meter across. Materials made from these tiny clusters are different from their bulk-made kin — they may be stronger, tougher and more reactive. They may display new electronic properties, may be more chemically reactive and more resistant to friction and wear.

While much about them remains unclear, potential applications for nanomaterials and their properties are proliferating.

Argonne has been revealing the secrets of nanomaterials for more than a decade and is a major center for this research. Argonne is home to a variety of nanotechnology projects, including new types of computer memory and operations, as well as advances in solar energy conversion and environmental cleanup.

CENTER FOR NANOSCIENCE MATERIALS
As part of the National Nanotechnology Initiative, Argonne is planning a Center for Nanoscale Materials, one of five that the Department of Energy (DOE) plans to build across the country. Funding would be supplied by DOE and the State of Illinois. The center will build on Argonne’s materials science, chemistry, physics, biology, computing and engineering strengths to study the behavior of nanostructures as they are formed or processed.

Argonne’s center will support research and nanofabrication for collaborating researchers from many campuses, including the nearby University of Chicago, Northwestern University, Northern Illinois University, University of Illinois at Urbana-Champaign and high-tech industrial firms.

The center will be adjacent to Argonne’s Advanced Photon Source (APS), the nation’s brightest X-ray source for materials research, which will be used to study materials created at the center.

NANOSCIENCE – AN INTERDISCIPLINARY FIELD
"Chemists work with atoms and molecules, moving from the smallest particles to larger ones, while physical scientists work from larger materials down," says J. Murray Gibson, director of the Materials Science Division. "The two disciplines come together as they approach the nanoscale."

"A great deal of research is needed to pave the way to useful applications," says Marion Thurnauer, director of Argonne’s Chemistry Division. "Chemists, physicists and materials scientists are working to understand the mechanisms underlying their observed properties and to develop practical uses."

CHANGING COMPUTER MEMORY
Argonne materials scientists have created and are studying nanoscale crystals of ferroelectric materials that can be altered by an electrical field and retain the changes until intentionally altered again. Ferroelectrics display a permanent electric dipole similar to ferromagnetics. At the nanoscale, these materials can be coded as binary memory by switching the electric dipole moment with an electric field.

Because the crystals retain the coding, these nanomaterials could finally create permanent, programmable random access memory (RAM) — long a computer industry dream. RAM is the computer memory that does the work when someone enters information or gives a command. It can be written to as well as read but — with existing commercial technology — disappears when the computer is shut off.

RAM made with ferroelectric nanomaterials would not be erased in a power failure. Laptops would no longer need back-up batteries, so they could be made lighter and smaller. There would be a similar impact on cell phones.

The first products of this research can be seen in "smart cards" now used in Brazil, China and Japan. Smart cards, which are the size and shape of credit cards, contain ferroelectric memory that can carry substantial amounts of information. Unlike magnetic strips, these memories do not come in contact with their readers and will not wear out. Smart cards are used for employee identification and as ways to pay for gas and public transportation. They may soon hold individual health records for routine doctor visits and emergencies.

CHARGE SEPARATION CHEMISTRY
Much of Argonne’s nanochemistry focuses on "charge separation," a core phenomenon in many chemical reactions.

Argonne chemists have shown that the natural crystalline structure of titanium oxide (titania) becomes distorted and more reactive in particles less than about 20 nanometers in diameter.

Titania is light sensitive. When attached to an appropriate chemical and exposed to light, it attracts and holds an electron from the attached "donor" compound, creating a corresponding positively charged site on the donor. This charge separation creates, in effect, a molecular-scale battery that can drive a chemical reaction.

The trick is to control the distance and longevity of the separation. For computers and electronic components, charge separation must be reversible so current can flow back and forth. For chemistry, it must be permanent.

One program involving Argonne and industrial researchers is working to attach DNA to titania as a way to make highly miniaturized integrated circuits. After appropriate chemical modification, titania film readily adsorbs copper, silver and gold ions. DNA would be used to order the titania in straight, parallel lines. When such a film is exposed to light, charge-transfer electrons convert the ions to pure metal, depositing it on a substrate as a well-ordered circuit.

For more information please contact Rich Greb