Baran Eren
Weizmann Institute of Science
“Dual Insights from a Single X-ray Beam: Simultaneously AP-XPS and GIXS Measurements on Nanopattered Ceria in Hydrogen”
Abstract
Ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) is the workhorse for in situ interface science studies, yet it seldom captures the simultaneous structural response that governs function. I will present a single-beam approach that records AP-XPS and grazing-incidence X-ray scattering (GIXS) concurrently from the same illuminated area, eliminating run-to-run variability and enabling direct correlation of chemical state, electron density, and nanoscale morphology under reaction conditions. Applied to model ceria under H2 and H2+CO2, the dual readout resolves three coupled trends: (i) subsurface hydrogen uptake (hydride/oxyhydroxide signatures in Ce 4d and O 1s), (ii) increases in electron density tracked via the ceria–Si relative critical angle of X-ray reflection, and (iii) reaction-induced roughening with essentially unchanged external height. These correlations show how hydrogen incorporation and re-oxidation by CO2 reshape both the surface & near-surface chemistry and the X-ray scattering response, revealing relationships that AP-XPS (or any other spectroscopy) alone can miss. I will outline the analysis workflow clarifying which observables are safely transferable across measurement sets. Practical aspects of sample design, gas handling, and fitting strategy will be summarized. Together these advances aim to generalize this single-probe, dual-insight methodology from ceria to broader families of reducible oxides, making AP-XPS a truly chemical-and-structural in situ & operando tool for materials science. I will close with future prospects for this novel platform. Chiefly among them is using Bragg spots for obtaining an X-ray absorption spectra (XAS) with sub-second time resolution.
Dr. Baran Eren is a Senior Scientist and research group leader in the Department of Chemical and Biological Physics at the Weizmann Institute of Science and a Visiting Scientist in the Department of Physical Chemistry at the Fritz Haber Institute. His research focuses on the atomic, electronic, and chemical structure of solid–gas and solid–liquid interfaces. Dr. Eren earned degrees from Boğaziçi University and ETH Zurich and completed his PhD (summa cum laude) in experimental condensed-matter physics at the University of Basel in 2013. From 2014 to 2017, prior to joining the Weizmann Institute, he was a postdoctoral fellow in the Materials Sciences Division at Lawrence Berkeley National Laboratory. As a group leader at the Weizmann Institute, he established a research program using a broad range of interface-sensitive spectroscopy, microscopy, and scattering techniques. Since January 2025, he has been on sabbatical at the Fritz Haber Institute in Germany. He is an Alexander von Humboldt Fellow for Experienced Researchers and is expanding his work to include liquid–gas interfaces.
Date: 11 February 2026, Wednesday
Time: 15:30
Place: SA-240
All interested are cordially invited.