Growth and characterization of hydrophobic anti-reflection CaF₂ films

CaF₂ films of thicknesses in the range of 50–200 nm were deposited by thermal evaporation on glass substrates. A series of CaF₂ films were also grown by oblique angle deposition in which the orientation of the substrate with the horizontal direction was varied from 0° to 75°. CaF₂ films are crystalline and show X-ray reflections corresponding to (111), (220), and (311) crystal planes of the cubic phase. The surface morphology of the films was analyzed by atomic force microscopy and it is found that surface roughness increases with an increase in the deposition angle. The water contact angle studies on CaF₂ films show that the wettability properties of the films depend on the film thickness and hydrophobicity enhances with the angled deposition. Optical studies found that CaF₂ films have high transmittance (> 85%) and good anti-reflection properties in the wavelength range of 400–1000 nm. The study shows that the anti-reflection and hydrophobic properties of CaF₂ films can be modified by the oblique angle thermal evaporation.