Effect of oxygen flow ratio on the wetting behavior, microstructure and mechanical properties of CeO_2−x coatings prepared by magnetron sputtering

In this study, cerium oxide (CeO_2−x) coatings were prepared by magnetron sputtering in a gas mixture of Ar and O₂. The effect of oxygen flow ratio (f_O2) on the surface morphology, wetting behavior, chemical composition, microstructure and mechanical properties of CeO_2−x coating were systematically investigated. The results showed that all CeO_2−x coatings exhibited smooth surfaces and similar wetting behaviors with a hydrophobic feature. The water contact angle stabilized around 100°. Surface chemistry varied with different oxygen flow ratios and the presence of excess surface lattice oxygen led to a slight decrease in hydrophobicity. X-ray diffraction (XRD) analyses showed that the coating grown in pure Ar exhibited weak crystalline peaks. While after the incorporation of oxygen, CeO_2−x coatings crystallized in a cubic CeO₂ phase with preferred (111) orientation, and the peak intensity gradually decreased with increasing f_O2. TEM study revealed the face-centered cubic (fcc) crystalline feature of deposited coatings and obtained Fast Fourier Transformation (FFT) pattern confirmed the disordered crystalline structure among the coating deposited at 56% f_O2. The hardness and elastic modulus of the coating could achieve ~ 18.1 GPa and ~ 190.2 GPa when deposited at 7% f_O2, then decreased slightly with further increasing f_O2.