Distinguishlbility of oxygen desorption from the surface region with mobility dominant effects in nanocrystalline ceria films

We present an investigation of oxygen ( ¹⁸O) uptake measurements in 1 μm thick nanocrystalline ceria films grown on single crystal Al ₂O ₃(0001) by nuclear reaction analysis (NRA). Oxygen uptake measurements were carried out in the temperature range of 200-600°C at a background ¹⁸O pressure of 4.0 × 10 ^-6 Torr. Average grain size in the as-grown films, synthesized by sol-gel process was ∼3 nm confirmed by high-resolution transmission electron microscopy and x-ray diffraction measurements. From the diffusion depth profiles, changes in intensity and slopes in surface and interface regions indicate complex oxygen mobility effects. Oxygen desorption is clearly distinguishable in the film surface region as a result of shift in the oxygen concentration maxima. It is argued that high defect density in nanocrystalline ceria which is associated with nanograin surface combined with intermediate temperature reducing environment triggers multiple processes such as molecular and ionic diffusion, adsorption, desorption, and isotope exchange interactions. The promising nature of NRA is realized as an effective tool to acquire the depth-dependent information from complex reactions existing in nanocrystalline environment.