University of Nebraska-Lincoln College of EngineeringOnline: Spring 2012
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  John Woolam left, Electrical Engineering graduate student Brian Rodenhausen works with Biological Systems Engineering graduate student Tadas Kasputis on biomedical thin films applications using ellipsometry.  

 

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Ellipsometry measures thin films applied as coatings to the surfaces of materials. In electronics these thin coatings control how a material can store data, display images on screens, or determine how well a solar cell converts light into energy. Ellipsometry plays an important role in measuring coatings for these important, everyday applications and more. It’s worth wondering: without ellipsometry, would we enjoy the proliferation of electronic technology we have today? How did ellipsometry become a renowned area of strength at the University of Nebraska? And what are its possibilities for the future?


Past | Present | Future

PAST
Brace photoAs early as 1888, scientists in Europe were studying how light reflects off materials: the way each material has its own light signature, with light reflected from a sample displaying a unique elliptical polarization pattern, each revealing useful properties of the material.

By the 1900s, a young physics professor at the University of Nebraska named DeWitt Bristol Brace—American-born but educated in Germany—was experimenting with this work. He was such a force that Nebraska was building a lab to be named for him, when he died abruptly in 1905 at age 46.

Brace’s students carried on his work—some going on to work with high regard in the U.S. Department of Commerce, for the Bureau of Standards (now known as the National Institute of Standards and Technology, or “NIST”).

Engineering became its own college at Nebraska in 1909, and aspects of physics continue to be prominent in engineering studies—particularly Electrical Engineering; with the 2011 opening of Jorgensen Hall, Physics and “EE” (in Scott Engineering Center) are now neighbors across 16th Street.

In his article “Polarization on the Prairie,” Ron Synowicki, who earned a B.S. in Physics and an M.S. in Electrical Engineering at UNL, wrote that in 1956, EE Professor Nick Bashara founded the Electrical Materials Laboratory in the basement of Ferguson Hall, where he studied the effects of undesired porosity in thin films.

 

“Pores lowered the density of the material,” Synowicki wrote, “which also lowered the dielectric constant of the films, causing semiconductor devices to fail. The lower dielectric constant appeared as a lower refractive index at optical wavelengths. Thus, it was possible to determine the quality of a deposited film by monitoring the refractive index. Correctly determining that index required precise knowledge of the film thickness, however; Bashara recognized that ellipsometry was perfectly suited for simultaneously measuring the refractive index and thickness of thin films. In 1961, work began in the Electrical Materials Laboratory. Bashara's ellipsometers were primarily homebuilt, often by heavily modifying commercial Gaertner and Rudolph ellipsometer systems.”

Bashara photoBashara revived ellipsometry research at Nebraska. Throughout the 1960s and 1970s, Bashara and his students made the University of Nebraska internationally famous for ellipsometry studies. They published 85 papers in major scientific journals and had 15 master’s or doctorate degrees granted from the university by the time Bashara retired in 1980. One graduate student was Rasheed Azzam, who arrived in 1967 and worked with Bashara on generalized ellipsometry and in pursuit of new instrumentation and analysis techniques. Bashara and Azzam also hosted the second and third international conferences on ellipsometry in 1968 and 1975 at UNL. Their collaboration led to the book Ellipsometry and Polarized Light, published in 1977 as the first English language text on this subject. “Researchers still turn to this text today,” Synowicki noted, “as the ‘bible’ of ellipsometry.”

 
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