Antireflection Coatings with Helical SiO2 Films Prepared by Using Glancing Angle Deposition

We present the optical and the structural properties of helical SiO2 films fabricated by using a glancing angle deposition (GLAD) technique. The relationships among the refractive index, the porosity, the glancing angle, and the substrate rotation speeds of the helical SiO2 films deposited by using GLAD are studied. The results show that the refractive index decreases and the porosity increases with increasing of glancing angle. The refractive index also depends on the substrate's rotation speed, and it increases as the substrate rotation speed is increased. The minimum refractive index is found to be 1.32 for the helical SiO2 film deposited at a glancing angle of 85 degrees with a substrate rotation speed of 0.07 rpm. As an application, a single layer-anti reflection (AR) coating is fabricated with a helical SiO2 film based on the deposition conditions in which minimum refractive index was obtained. We found that the average reflectance of the AR coating in the wavelength range of 400 nm to 800 run was 1.24 %. The structural and surface morphology of these samples were also investigated by using a scanning electron microscope.