'Doping' Helps Control Size Changes in Nanoscale Materials

FAYETTEVILLE, Ark. – Researchers want to build nanoscale materials because they promise to be five to 10 times stronger than conventional materials, which could lead to longer-lasting computers and other electronic devices. But these materials lose their attractive properties at high temperatures. When it comes to making nanoscale materials retain their size and shape at high temperatures, a little "doping" appears to be in order, according to University of Arkansas scientists.

Panneer Selvam, professor of civil engineering, graduate students Paul Millett and Shubhra Bansal and Ashok Saxena, dean of the College of Engineering reported their findings at the Arkansas Academy of Sciences meeting. The paper won first prize at the meeting for a poster presentation and has been submitted to the Journal of the Arkansas Academy of Science.

When building material atom by atom, temperature increases change the size, shape and properties of the material—an undesirable result for a stable component in a device. Millett, Selvam, Bansal and Saxena created a computer model using copper atoms, a material often used to create connections between devices. The researchers introduced an antimony atom to see how it would affect the properties of the material.

The introduction of a different type of atom, called "doping," prevents the material from changing shape and size and helps it retain its properties. Unlike an alloy, where researchers might use mixtures of different metal atoms to create more desirable properties, a "dopant" atom remains separate from the other atoms in the metal, migrating to its surfaces or edges.

In the simulation, the antimony atom moved through the material to settle at the grain boundary, the place where one layer of copper atoms ends and another layer begins. Having an atom of a different size from the main material changes the distance between the atoms, which appears to allow the material to retain its shape and size when the temperature changes. The researchers ran the simulation with one antimony atom and 1,800 copper atoms, then ran it again with one antimony atom and 10,000 copper atoms.

"We can design new materials using processes like these," Selvam said. "This study tells manufacturers that they can make these particular types of materials."