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Physics student makes quantum dots discovery

Published September 24, 2013

It’s a liquid version of the Hatfields and McCoys.

The relationship between certain polymers and nanocrystal silicon can best be described as unstable. The duo just doesn’t like one another, separating like water and oil when drying.

But NDSU physics and math undergraduate student Austin Usselman has found a way to bring some harmony to the predicament. His research could help make solar cells and other electronic devices more efficient.

And he’s only a junior. 

“I watched a lot of my friends get short-term summer jobs,” said Usselman, who worked under the direction of NDSU physics professor Erik Hobbie. “I got one that basically started my career. I didn’t expect to be as hands on as I have been. I will always be grateful for the opportunity to do this research.”

Usselman, from Hazen, N.D., emailed a handful of professors last year hoping to find any job in a lab to gain experience.

Hobbie invited Usselman to study quantum dots at NDSU’s Research and Technology Park. Quantum dots are nanocrystals discovered by scientists in the 1980s. The subject was new to Usselman, who was interested in astrophysics in high school.

“He is gaining hands-on experience doing research, which is valuable for nurturing any type of problem-solving ability,” Hobbie said. “He will get his name on a publication as an undergraduate, which will make his resume stand out.”

The subject of Usselman’s research happened by accident. Usselman was attempting another project when through microscopic projection he and Hobbie noticed the instability within the polymer and nanocrystal mixture. Silicon nanocrystals are tiny pieces of crystalline silicon that are being studied for use in the production of such things as solar cells, solid-state lighting, and biomedical imaging agents.

A coffee-ring effect occurred as the mixture dried. In addition, the nanocrystals and polymer separated. The coffee-ring effect is a term used to describe when a droplet containing small solids dries, and the solids are then deposited at the edge of the droplet.

Through a lengthy process of trial-and-error, Usselman learned he could eliminate the separation in low molecular weight solutions by applying the mixture to a glass cover slip with a specialized blade. He tried different application speeds before finding the separation could be eliminated by slowly applying the mixture, pausing every 15 micrometers before starting again. 

Hobbie said Usselman’s work could help NDSU researchers put a more homogenous coating of a silicon nanocrystal and polymer mix onto solar cells, creating a more efficient product.

“This will have an impact,” Hobbie said. “Scientifically, it will have an impact and it will have impact in terms of applications.”

The research could also have a positive impact on the efficiency of solid state LEDs and optical sensors.

Usselman’s work on the project isn’t finished. He is now measuring different concentrations of polystyrene and quantum dots in the polymer-nanocrystal mixture by comparing the strength of photoluminescence during separation.

He’s hoping this project can be a springboard to future research success. And it’s sparked an intense interest in quantum dots.

“It’s really comforting to have such nice people around to guide you through the first couple steps of a new experience,” Usselman said. “I believe it has given me the confidence and experience I will need to further succeed in the scientific community, and I am excited to see where I end up and what I end up accomplishing.”

This research is supported by National Science Foundation EPSCoR award EPS-0814442. 


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