High entropy alloys (HEAs) are considered as advanced materials with excellent properties, such as superior oxidation and corrosion resistance, high hardness and hydrophobicity and excellent thermal stability. The fabrication of thin films of non-metallic compounds such as oxides and nitrides has demonstrated further improvements in various properties of these high entropy-based materials. In this study, AlCoCrCu0.5FeNi high entropy oxide (HEO) thin films were deposited by radio frequency (RF) reactive magnetron sputtering from a custom-made target using three different oxygen flow fractions (RN) of 12.5, 25 and 50%. The microstructure, composition and physical properties of the HEO films were measured using a wide range of characterization methods. X-ray diffraction (XRD) detected a phase transformation from FCC to spinel structure with an increase in RN from 12.5 to 25%, while a further increase in RN from 25 to 50% retained a weak spinel phase as confirmed by transmission electron microscopy (TEM) analysis. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) measured a decrease in both the average agglomerated grain size from 88 to 30 nm and the surface roughness from 6.81 to 1.16 nm with the increase in oxygen fraction from 12.5 to 50%. The film deposited at the highest RN of 50%, had the highest oxygen concentration of 42.7% as determined by energy dispersive spectroscopy (EDS) and 38.4% as determined by X-ray photoelectron spectroscopy (XPS). XPS measurements also indicated a significant presence of surface protective oxides of Al2O3 and Cr2O3 for all the HEO thin films. The film deposited at RN of 25% achieved the highest hardness of 11 GPa, while the film deposited at RN of 50% displayed the highest water contact angle (WCA) of 111°.
- High entropy oxide (HEO)
- Reactive magnetron sputtering
- Thin films