Growth mechanisms of ceria- and zirconia-based epitaxial thin films and hetero-structures grown by pulsed laser deposition

Thin films and epitaxial hetero-structures of doped and undoped CeO2, and 8 mol% Y2O3 stabilized ZrO2 (YSZ), were fabricated by pulsed laser deposition on different single crystal substrates. Reflection high energy electron diffraction was used to monitor in situ the growth mechanism of the films. Two distinct growth mechanisms were identified along the (001) growth direction for the Ce- and Zr-based materials, respectively. While the doped or undoped ceria films showed a 3-dimensional growth mechanism typically characterized by a pronounced surface roughness, YSZ films showed an almost ideal layer-by-layer 2-dimensional growth. Moreover, when the two materials were stacked together in epitaxial hetero-structures, the two different growth mechanisms were preserved. As a result, a 2-dimensional reconstruction of the ceria-based layers determined by the YSZ film growing above was observed. The experimental results are explained in terms of the thermodynamic stability of the low-index surfaces of the two materials using computational analysis performed by density functional theory.