Preparation and antireflective properties of N-doped Y2O3/AlN composite films on single crystal diamond

N-doped Y2O3/AlN composite films were deposited on single-crystal diamond substrates using radio frequency magnetron sputtering under varying nitrogen flow rates. The effects of the nitrogen content on the microstructure, bonding strength, and infrared transmittance of the films were systematically investigated using a scanning electron microscope, an atomic force microscope, an x-ray diffractometer, an x-ray photoelectron spectrometer, a scratch tester, a UV-vis spectrophotometer, and a Fourier transform infrared spectrometer. The results indicate that varying nitrogen flow rates in N-Y2O3/AlN composite films result in different levels of transmittance enhancement on single-crystal diamond in the 8–10 μm infrared range. With increasing nitrogen flow rate, the cross-sectional morphology of the Y2O3 film changes from dense to porous, accompanied by a gradual grain refinement. The composite film exhibits optimal adhesion strength at a nitrogen flow rate of 8 SCCM and achieves a transmittance of 80.8% in the 8–10 μm infrared range, corresponding to an 11% improvement over bare diamond. This enhancement improves the performance of diamond infrared windows in practical applications.