ANN ARBOR---University of Michigan engineers have built a device that, for the first time, allows them to watch how ultra-thin layers of "sputter deposited" atoms form on surfaces during growth of coatings.
John Bilello and Steven Yalisove, researchers in the Department of Materials Science and Engineering, built the instrument to help them observe the process of sputtering---a method of "spray painting" films of atoms onto another surface. Sputtering is a common way of coating materials to make them stronger and more impervious to corrosion, friction, wear and temperature. While the technique is used in applications ranging from microelectronics to protecting jet engine turbine blades from high temperature erosion, it was never before possible to monitor the process as it happened.
In 1995, Bilello and Yalisove were the first researchers to use sputtering to make "pin-stripe" coatings, patterns of alternating thick and thin nanolayers that dramatically improved material strength and toughness. These so-called multiscalar microstructures are now receiving increasing attention. But the process demands precision, which is hard to achieve, and, at least in the past, impossible to verify until after the layering is complete.
Their latest advance, however, which bounces non-interactive high intensity X-rays off the atoms being deposited, now allows them to see sputtering deposition---how the layers of atoms arrange themselves on a surface---in real time. "Nobody has ever been able to measure the characteristics of the film while it's going on---until now," said Prof. Bilello.
Observing the process of deposition, they said, could enable scientists to make changes during sputtering to maximize all the functional properties of a material they are coating, including stress and strain. Bilello and Yalisove designed their device for their work in "sputter plasmas"---bombarding argon ions into solid materials targets to vaporize them---a method they liken to "atomic sand blasting."
This process creates a high energy plasma which coats other metals, ceramics and polymers. Eventually, said Prof. Yalisove, the in-situ X-ray characterization technique will be widely available. "As X-ray sources get smaller, and advanced detectors improve in efficiency, we think everyone will need systems similar to our design to help improve manufacturing throughput and quality control," he said.
Funding for the research came from the U.S. Army Research Office and the Defense Advanced Research Projects Agency.