The Cr-Cu-Al-Fe-O high-entropy oxide films were synthesized on Si (100) substrate by electron beam evaporating a four-layer metal film and consequent annealing of the film in air. X-ray diffraction, scanning electron microscope, energy-dispersive spectroscopy, transmission electron microscope, and nano-indentation methods were used to characterize the films. The as-deposited film was composed of FCC and BCC phases and had a dense surface. After annealing at 800 and 1000 degrees C in air, oxidative diffusion took place among the Cr-Cu-Al-Fe metal multilayer. The inter-diffusion and oxidation behaviors resulted in the formation of a three-layer composite film: spinel layer, copper-doped SiOx layer, and Co oxide layer. The unreacted Cu grains were also found. At 1000 degrees C, the hardness and elastic modulus of the composite film increased to 9.5 and 147.63 GPa, respectively.
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