Microstructure, hardness and optical properties of Er2O3 films deposited on diamond-coated and Si(100) substrates by radio frequency magnetron sputtering

Abstract Er2O3 anti-reflection films were deposited on the surface of the chemical vapor deposited diamond films and Si(100) substrates by radio frequency magnetron sputtering. The microstructure of the Er2O3 thin films and the interfacial layer were investigated by means of scanning electron microscopy, X-ray diffraction, atomic force microscopy and transmission electron microscopy. The refractive index, hardness and transmittance of the films were measured by ellipsometry, nanoindentation measurements, and Fourier transformed infrared spectroscopy. Results revealed that the bias induces the formation of a monoclinic phase and the nucleation of the Er2O3 thin films is mainly observed along the (222) plane. A high-resolution TEM image revealed a 2.5-nm-thick amorphous layer at the interface between the Si substrate and Er2O3 film. Notably, monoclinic Er2O3 films can considerably improve the transmittance of the diamond film in the long-wavelength infrared range of 8–12 μm via the reduction of the refractive index. However, the introduction of the monoclinic phase led to the decrease of the hardness and elastic modulus of the films; hence, controlling a suitable amount of the monoclinic phase may play an extremely important role in the mechanical and optical properties of the Er2O3 films.