The optical properties of alumina films prepared by electron beam evaporation at oblique incidence

• Alumina thin films deposited by EBPVD with the oblique angle deposition (OAD) method.
• The refractive index decreases with the increase of the inclined angle.
• The porosity increases with the increase of the inclined angle.
• The porosity varies with increasing substrate temperature.

The optical properties of alumina thin films deposited by using electron beam evaporation with the oblique angle deposition (OAD) method are reported. The relationships between the refractive index, the porosity, the inclined angles, and substrate temperatures are studied. The results show that the refractive index decreases with the increase of the inclined angle, the porosity increases with the increase of the inclined angle, the porosity decreases with the increase of the substrate temperature when the inclined angle is approximately smaller than 40°, and the porosity increases with the increase of the substrate temperature when the inclined angle is approximately larger than 40°. The morphology is investigated by using scanning electron microscope (SEM). The morphology images illustrate the cause of the porosity varies with the substrate temperature. So the oblique angle deposition method is an effective way to control the microstructure of thin films.