Scientist Uses Advance Photon Source to Study Nano-Scale Materials

Emerging new technologies utilize advanced materials that are assembled on exceedingly small scales of length. Because of their small size, these nano-scale materials often exhibit unique properties that can potentially be harnessed for applications and new science. In order to do this however, one needs a comprehensive understanding and characterization of their physical behavior on the atomic scale. Professor Paul Miceli is doing just that with the Advanced Photon Source (APS) at Argonne National Laboratory in Argonne, Ill. The APS is the brightest source of x-rays in North America. This machine, which is one kilometer in circumference, allows scientists to collect data with unprecedented detail and in short time frames.

“The Advanced Photon Source’s x-ray beam is a billion times more intense than what I can see in my lab,” says Miceli.

He deposits thin layers, typically one atom thick, onto a surface from a vapor and then studies the structures by scattering the intense x-ray beam. By doing this, Miceli can determine how the atoms rearrange themselves on the surface so he can develop a better understanding of how nano-structures grow. Because of the unprecedented brightness of the x-ray beam, he is able to observe the materials as they grow in real time. In addition to the unique aspect of the x-ray beam, these studies are facilitated by an extensive ultra-high-vacuum growth-and-analysis chamber residing at the APS that was designed and developed by Miceli.

“My findings pertain to basic science about how atoms organize themselves,” says Miceli.

Because the x-ray beam can probe both the surface and the subsurface of the materials, Miceli’s research has made discoveries that could not be achieved by other techniques. For example, his research found that nano-clusters of missing atoms become incorporated into metallic crystals as they grow. This discovery is important because it brings new insight to theories of crystal growth, and it forces scientists to think about how atomic-scale mechanisms might lead to the missing atoms. Such effects, which also have practical implications for technological applications of nano-materials, have not been considered in current theories.

Other studies by Miceli have shown that the growth of some metallic nano-crystals cannot be explained by conventional theories of crystal growth. For example, quantum-mechanical effects on the conduction electrons in very small nano-crystals can change the energy of the crystal, and Miceli showed that the statistical mechanics of coarsening — when large crystals become larger while small crystals get smaller and vanish — does not follow the conventional theories that have worked successfully in materials science over the past 50 years. In fact, he has found that atoms can move over metallic nano-crystalline surfaces thousands of times faster than normal crystals, illustrating the many surprises and challenges that nano-scale materials present to scientists.

Miceli works with four graduate students and one undergraduate student. He also collaborates with Edward Conrad, a professor at the Georgia Institute of Technology, and Chinkyo Kim, a professor from Kyung He University in Seoul, South Korea. Kim is currently visiting MU on a one-year sabbatical with Miceli’s group. The photo shows, from left to right in the back row: Nick Cobblah, Yiyao Chen, Shawn Hayden, Michael Gramlich, Jesse Kremenak. Seated in the front row are Paul Miceli and Chinkyo Kim.

Miceli’s research has been supported by the National Science Foundation (NSF) and the Petroleum Research Fund. His scattering facilities at the APS have received financial support from the NSF, the Department of Energy, and MU, as well as the Georgia Institute of Technology where he has collaborated with Conrad on developing the APS project.

Written by Laura Lindsey
Director of Communications and Marketing
The College of Arts and Science
University of Missouri Columbia

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