Microstructure, hardness, resistivity and thermal stability of sputtered oxide films of AlCoCrCu0.5NiFe high-entropy alloy

The sputtered oxide films of AlCoCrCu0.5NiFe high-entropy alloy were deposited on the silicon wafer using radio frequency sputter system, and subsequently were annealed at 500, 700 or 900 °C. Surprisingly, the sputtered films are of simple structure. With no oxygen addition to the working gas, the AlCoCrCu0.5NiFe high-entropy alloy film is amorphous. When the oxygen content in the working gas is between 10 and 50%, the sputtered oxide films are HCP with lattice constants of a = 0.3583 nm and c = 0.4950 nm. Before annealing, both the resistivity and thickness of the oxide film decrease with increasing oxygen content and the hardness value reaches maximum at 30% O2. No new phases in the oxide films form during annealing, indicating the oxide films are very stable at high temperature. However, the crystal grains tend to grow up and the micro-hole size among grains increases with the annealing temperature. The resistivity of the oxide film steps up with annealing temperature, whereas the hardness value decreases. The oxide-film thickness changes very little during annealing.