New XPS Instrument at UC San Diego Gives Researchers a Closer Look at Material Surfaces

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There’s a new machine in town, and it’s in high demand by researchers at University of California San Diego labs and in local industry.

Housed in the university’s Qualcomm Institute (QI) Nano3 shared research facility, the instrument — an X-ray photoelectron spectroscopy (XPS) machine — is helping researchers advance projects ranging from battery research to the development of surface coatings and medical devices.

Flying Electrons

Fabian Martinez Pallares, a 2024 materials science and engineering Ph.D. alumnus from UC San Diego’s Jacobs School of Engineering, arrived at Nano3 last November, shortly after the PHI Genesis XPS system, to serve as the lead specialist responsible for XPS operation and training.

“The XPS system lets us analyze the chemical composition and bonding states of the top few nanometers of a material surface,” he said. “This gives Nano3 users a way to understand not only what elements are present, but also how they are chemically bonded.”

The machine works by firing X-rays at a material’s surface, knocking loose electrons in a process called the photoelectric effect. As those electrons fly free, a detector measures their energy with extreme precision. Because every element holds onto its electrons with a unique, telltale strength, the resulting energy pattern reveals the surface’s composition.

Funding for the new machine was provided by the UC San Diego chancellor, executive vice chancellor, dean of engineering and dean of physical sciences.

That investment fills a regional gap: “Outside of our machine, the next closest XPS that is available is at UC Irvine,” Pallares said.

Booked a Week in Advance

Even though it’s a relatively new acquisition, the machine already has more than 60 users — 25 UC San Diego research labs and 10 industrial partners, including researchers from General Atomics, Illumina, and Biolinq. It’s now booked a week in advance.

One frequent user is David Fenning, who is the Francine Berman Endowed Chair in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at UC San Diego. Fenning’s group is using the tool in its research on semiconductor interface chemistry, tracking how materials hold up under the real-world heat and electrical stress they’ll face in devices like solar cells and LEDs. Fenning calls the XPS machine “a comprehensive surface analysis system,” which, combined with its scanning Auger electron spectroscopy, “allows outstanding determination of chemical state.”

Pallares said many researchers also have found the machine valuable for checking their assumptions and making important corrections.

“Sometimes when researchers perform the XPS analysis, they realize something went wrong in their process,” he said. “For example, XPS can reveal residual surface impurities — which can be bad news for device performance — despite cleaning processes meant to remove those impurities. If researchers know that, for example, sulfur or fluorine is present in their material, they can address the problem. They can extend the time of washing or come up with a different process.”

At Home in Nano3

When the XPS machine first arrived on campus, there was general agreement it should be housed in QI’s Nano3 facility.

“Nano3 is the largest shared use facility in the STEM field outside of health sciences,” said Yu-Hwa Lo, director of Nano3 and professor in the Department of Electrical and Computer Engineering. “Being an interdisciplinary hub, we have experienced technical staff and established operational infrastructure to ensure that this advanced equipment is effectively maintained, broadly accessible and highly impactful.”

As a whole, Nano3 has about 800 users, serving 128 research groups on campus, 75 companies, and 12 research institutions from across the country.

Pallares said he’s glad to support researchers using the XPS machine in Nano3 — from keeping the instrument running to helping users obtain accurate data, process their results and understand what they are seeing. He encourages anyone interested to reach out for orientation and training. He can be reached at fmm003@ucsd.edu.

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