Fabrication of cerium oxide films with thickness and hydrophobicity gradients

Abstract

Versatile surfaces with hydrophobicity gradients have attracted intensive attention because of their tunable wettability. Here, cerium oxide films are prepared on tilted substrates by magnetron sputtering, the induced thickness gradient strongly influences the structural, morphological and wetting properties. It is found that the surface hydrophobicity is positively proportional to the root-mean-square (RMS) roughness and thickness variations, larger thickness gradient brings more obvious gradient hydrophobic surfaces. The results show that the RMS roughness gradient increases from 0 nm/cm, 0.08 nm/cm to 0.16 nm/cm and the thickness gradient increases from 0 nm/cm, 12.0 nm/cm to 13.2 nm/cm, with the tilt angle changing from 0°, 30° to 60°, respectively. Correspondingly, the hydrophobicity gradient increases from 0°/cm, 1.6°/cm to 2.7°/cm, respectively. Our study offers practicable method a method for developing hydrophobicity gradient surfaces, which can be used for droplet movement applications.