Grad stories: Changyeon Yoo

Susan Caraher

Document Type

Article

Publication Date

12-4-2013

Abstract

Grad stories: Changyeon Yoo

UND graduate student Changyeon Yoo shares his background and experience.

What is your hometown?

I'm from JinJu City in South Korea. It's a small city about the same size as Grand Forks. I lived there until I went to university for my undergraduate degree. I did my bachelor's degree in Physics at Seoul National University ? Seoul is a city of about 10 million, so it was quite a change. I like Grand Forks because it is a similar kind of place to where I'm from ? a small town environment ? I'm close to everything.

When did you realize you wanted to pursue Physics as a career?

During high school I took some physics courses and thought I might be good at it, so I chose it for my bachelor's. I really liked it and wanted to get better and build my career; so, I came to the US and did my Masters' degree at the University of Massachusetts-Lowell.

At that time my main field was doing experiments with Femtosecond Lasers. Others in my group were mainly dealing with interactions in silicone but I was mostly interested in glass materials and polymer materials. Once I finished that degree I was looking for a university for my doctoral degree and I learned that Dr. (Kanishka) Marasinghe at UND was working on atomic structure of novel rare earth phosphate glasses using X-ray, which I thought was related to my masters. So I applied with the hope of joining that research group and was accepted.

Can you talk about your summer research experience? You attended a rather prestigious program for graduate students.

Yes, it was NXS 2013 (15th National School on Neutron and X-Ray Scattering). The first week was at the Argonne National Laboratory near Chicago, and the second week was at Oak Ridge National Laboratory in Tennessee.

At the time I was submitting my application I didn't realize it was that good, because others from our group had been there before. But when I went there, it was a really, really great experience. Everything was provided and there was a tight schedule from 8.30 to 6PM each day for the two weeks. The mornings were lectures and in the afternoons we'd work on small experiments related to the morning lectures.

There were only 60 students representing 47 US states ? all graduate students from Physics, Chemistry and Engineering department. I didn't realize it at the time, but I think it is really difficult to get accepted so I feel we were all so lucky to be there.

The Argonne National Laboratory does mostly X-ray related experiments and we talked with researchers and professors there, learned about the equipment and conducted three different experiments. The Oak Ridge National Laboratory does research using neutrons and we did four different experiments. We got to choose three main experiments we want and usually we got to do two of them and five chosen from the school due to scheduling issues. Before I went, I didn't have much knowledge of or background related with neutrons, but I learned that X-ray is good for some experiments, neutrons are better for others, and by comparing the two, we get a much better picture.

It was such a privilege to be able to go to these labs. The researchers gave their time to us and allowed us to take over their laboratories for a week while helping us with lectures and experiments. I feel so lucky.

What was it that you learned at the NXS 2013 School that you brought back to UND and applied to your own research?

My main research is EXAFS (Extended X-Ray Absorption Fine Structure) technique. Our group did a couple of experiments at Argonne for X-Ray diffraction and X-Ray absorption, but we only had a week to conduct and we do most of our analysis at UND afterward. I would love to have had more time to get a deeper knowledge on that subject. There is so much to learn, and it's not possible to get all of that from the books or the lectures. Seeing and doing the experiments related to it helps to understand the knowledge. There are several techniques that are not learned from books or lectures. I am still going through all the lecture notes, videos and files. So, I am still learning! I hope to go back to the Oak Ridge National Laboratory and take some of the new knowledge with me to do some new experiments.

Can you describe your research?

It's related to x-ray absorption. We are trying to find the complex atomic structure of zirconium-doped silicate glass-ceramics. In this glass, the main component is zirconium since zirconium distribution within the glass plays a major role in determining the properties of the glass ceramics. This is a very expensive glass ceramics that is used in high-precision opto-electronic devices, next-generation of mega telescopes, and instrumentation for satellites and spacecraft. It doesn't expand much, because the temperature doesn't effect the glass so it is very good for mirrors designed to work in space telescopes to name only one of the uses. We're interested in finding the main role of the zirconium in the glass ceramics. You could add a different amount of zirconium and then examine to understand the different roles in designing glass for different purposes.

Samples were prepared by Dr. (Richard) Brow's group at the Missouri University of Science and Technology and sent here so we could do the X-ray absorption studies. This technique (EXAFS) sends X-ray with certain energy to interact with the zirconium atoms. After the absorption, the left over energy will be turned into an electron wave outward from the zirconium. Then atoms surrounding the zirconium will reflect it back to the source, the zirconium, in a pattern. By analyzing that pattern we can determine the interference and measure the amount of oxygen atoms, or silicones etc are around the zirconium. From that we can learn what will affect the glass in different ways. We could try to find which temperature or environment is good for certain purposes.

Other research we are interested in is the Rare Earth doped Phosphate Glasses which Dr. Marasinghe and some of the other graduate students have done a lot of experiments. We're also using the EXAFS technique for certain rare earth materials ? the main interest here is to find whether certain environments have very high efficiency lasing properties.

Where would you like to be in 5 years?

I would like to teach. I like working in the lab, but I also enjoy interacting with students. My plan after getting my Ph.D. will be to work as a researcher or a postdoc for a couple of years and then after that, become a professor. Currently, I'm teaching Physics labs for undergraduates which I really like. It's a really good experience and I get joy from helping students understand the application side and the theoretical side of Physics.

What advice would you give to a student considering a graduate degree in Physics?

It's a broad subject so you have many paths. If you are interested more in the application and experiments, you can go down the path related to the chemistry or engineering side, or you could go more into the theory or explanation of the phenomena related to the mathematics and computer programming.

Our department's main focus in the experimental side is general areas of condensed matter Physics and Astrophysics so if you are interested in space, dark energy, galaxy clusters and Supernovae Explosions there's also that path.

Also we have very good faculty members (professors). All very kind, friendly, and listen to what you want to do and they will advise, guide and provide if you need help. So, if you are interested in fields mentioned I strongly recommend our department.

Susan Caraher The School of Graduate Studies

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