Oxidation and Reduction of Polycrystalline Cerium Oxide Thin Films in Hydrogen

This study investigates the oxidation state of ceriathin films'surface and subsurface under 100 mTorr hydrogen using ambient pressureX-ray photoelectron spectroscopy. We examine the influence of theinitial oxidation state and sample temperature (25-450 & DEG;C)on the interaction with hydrogen. Our findings reveal that the oxidationstate during hydrogen interaction involves a complex interplay betweenoxidizing hydride formation, reducing thermal reduction, and reducingformation of hydroxyls followed by water desorption. In all studiedconditions, the subsurface exhibits a higher degree of oxidation comparedto the surface, with a more subtle difference for the reduced sample.The reduced samples are significantly hydroxylated and covered withmolecular water at 25 & DEG;C. We also investigate the impact of watervapor impurities in hydrogen. We find that although 1 x 10(-6) Torr water vapor oxidizes ceria, it is probably notthe primary driver behind the oxidation of reduced ceria in the presenceof hydrogen.

Automated summary

This study uses ambient pressure X-ray photoelectron spectroscopy to investigate the oxidation state of ceria thin film's surface and subsurface under 100 mTorr hydrogen. The influence of initial oxidation state and sample temperature on the interaction with hydrogen is examined. The findings reveal a complex interplay between oxidizing hydride formation, reducing thermal reduction, and reducing formation of hydroxyls followed by water desorption during hydrogen interaction.