Measuring Nanoparticles

Some objects are so tiny, even a quarter-million dollar atomic force microscope can’t capture an accurate image. Particles drift from side to side. They expand and contract. Even the microscope can shift ever so slightly.

But when measuring nanoparticles, the smallest discrepancy can mean a big error.

That’s where physics professor Matt Trawick’s lab comes in. This summer, four students worked with Trawick to develop algorithms that can correct for the shifts that occur during imaging.

“Correcting the images is computationally intensive,” Trawick says. “If we weren’t smart about the algorithms we used, it might take eight years for a regular computer to correct a single image. We’re trying to be clever and make it so that you can correct them in just a few seconds.”

It starts with a gold mica layer covered with a substrate. Then a layer of nanoparticles is placed on top, followed by another, and then another. Each layer is imaged and corrected to see how the nanoparticle film assembly changes over time, and how the layers of nanoparticles interact with one another. The data is then given to chemistry professor Mike Leopold, whose students will use the findings for their own research.

“We’re essentially taking what’s already a pretty powerful tool of microscopy and making it even more powerful,” Trawick says. “One of the things that we’re interested in doing is developing algorithms and tools that can be useful not only to us as we study whatever itty-bitty stuff we’re curious about, but also giving these tools to other scientists all over the world so they can use them for studying whatever itty-bitty stuff they’re interested in studying.”

Each of the four students focuses on a particular aspect of image correction. For example, Greg Hamilton, ’17, works to correct for tip sample convolution.

“The idea is that the shape of the tip that we’re using to poke the surface determines what kind of picture we’re going to get back,” he says. “If you imagine basically outlining a quarter with a really fat crayon, the shape you get is going to get really fat. If we know a little bit about what the tip looks like, then we know a little bit about how to correct the image for the shape of the tip.”

Working in Trawick’s lab, which Hamilton is continuing to do this fall, is right in line with his interests. He plans to major in math and physics, with a minor in computer science. “There’s a lot of geometry involved and I’ve dealt with four or five computer languages just with this project,” he says. “Physics-wise, the atomic force microscope has a lot to do with voltages and electrical properties. I knew that I wanted to major or minor in all three of those, but I didn’t expect that this would have an application to all three. It’s been really good for my critical analysis and problem solving.”

Hamilton’s experience is just what Trawick hopes to see from the students working in his research lab.

“At an undergraduate place like UR, the whole reason that we’re here is this split mission of figuring stuff out and teaching students,” he says. “When I have just four students working with me in my laboratory, I can come in and spend all day working with them one-on-one or one-on-two to solve the really difficult problems. I know it’s really good experience for them, and it helps me do my other job, which is figuring out what in the heck is going on with the sciencey stuff.”