Insights into the electronic and atomic structures of cerium oxide-based ultrathin films and nanostructures using high-brilliance light sources

High-brilliance light sources, such as synchrotrons and free-electron lasers, allow researchers to probe the structural, electronic, anddynamic properties of functional materials at an unprecedented level of detail. Techniques like X-ray photoelectron spectroscopyand X-ray absorption spectroscopy, can reveal atomic-scale information about material behavior under different conditions. Thisthorough understanding can be leveraged to optimize materials for various applications, including energy storage, catalysis, andelectronics. This review focuses on cerium oxide, an important material for catalytic and energy applications, examining the appli-cation of high-brilliance light sources on model systems such as supported thin films and epitaxial nanostructures. We reviewselected studies exploiting the high energy resolution and sensitivity of synchrotron radiation-based X-ray photoelectron spectros-copy and X-ray absorption spectroscopy to explain the factors influencing the material's reducibility, with particular focus ondimensionality effects and on metal-oxide interaction, and the interaction with molecules. The potential of studies conducted underambient pressure conditions is highlighted, and, finally, the perspectives offered by the ultrahigh brilliance and ultrashort free-elec-tron laser pulses for dynamic studies of the processes that take place upon photoexcitation are discussed.