After completing his Ph.D. in materials science at Binghamton University, Shawn Sallis joined the ALS as a postdoc. For the last four years he’s worked with Wanli Yang on higher-capacity batteries.
How did you become interested in synchrotron research?
My thesis advisor at Binghamton University had actually been a graduate student and postdoc at Brookhaven National Lab, so I’ve been doing x-ray spectroscopy since my first year of grad school. My advisor and I met when he taught two classes on soft x-ray spectroscopy during an overview course, and I talked to him immediately after that because he talked about the new x-ray free electron lasers, and it seemed really cool. That was my “in” to x-ray spectroscopy.
We started with transparent conducting oxides, which are very interesting, because they’re everywhere. The touchscreen in your phone works because there’s a transparent conducting oxide layer in it. There’s hope to put them in more things, like coupling them with OLEDs to get transparent screens. The electronics that control pixels in most TVs are made with amorphous silicon, which is not transparent, so you lose half the backlight, and your backlight needs to be twice as bright as it otherwise would need to be if the electronics were transparent.
I was also a doctoral fellow in residence at the ALS for two years.
What kind of research do you do now?
I work with Wanli Yang. When I first came, we were just putting together the new iRIXS endstation. We were working on resonant inelastic x-ray scattering as a technique and writing software to control everything, and I’ve been part of developing how the measurements are done from the beginning. RIXS is an x-ray absorption scan, but you’re taking the x-rays that come out, and you’re energy-resolving at the detector, so you have another spectrum at every point of your x-ray absorption spectra.
As you go through the absorption edge, there’s special resonances with the states that change the spectrum that you get out of the emission spectrum. Sometimes, there’s interesting features. Our group has been studying the possibility for reversible oxygen redox in a battery. Oxygen isn’t supposed to participate; you’re not supposed to be able to move electrons on and off the oxygen—at least, not reversibly. We’re seeing a lot of materials where it seems like it is reversible. It’s a way of getting more capacity out of your battery.
What’s coming next in this field?
In the past, the process has been “throw everything in the pot and see what happens.” It works, but it takes a very long time. We’re trying to work toward being able to simulate what the RIXS map should look like. We start with the density functional theory and use that to create the map. Instead of measuring 50 to 100 different materials, you could simulate them and then pick the five or ten best candidates.
The software I developed for the endstation is mostly to improve quality of life. At every energy, you end up with a 2D image, and there’s a whole bunch of processing steps you have to do to each individual image. You have to sum each of those individual images, and that gives you a line, and then, you have to stack the lines together. So, that’s a complicated process that I managed to automate, and now anyone who comes to the beamline to do RIXS can use my procedures.
A lot of what I do is data analysis, and I’ve had a couple of large datasets, which took me accidentally into machine learning. I’m on a joint Molecular Foundry–ALS project to simulate x-ray absorption, and there’s hope to push that into simulating RIXS.
What do you do in your spare time?
I’ve been doing martial arts since I was 16. I was doing one school back in New York, and when I moved here, there was no dojo for that nearby, so I had to switch and start over, but I’ve been doing Japanese karate for more than half my life. The people in the dojo become like a family, so once I joined the dojo, it instantly came with a friend group. I also got lucky, and about half the people I hung out with in Binghamton have actually moved to Fremont to work in tech, so a good portion of my friend group ended up following me to California.