Microstructure-Induced Anisotropic Optical Properties of YF₃ Columnar Thin Films Prepared by Glancing Angle...

Yttrium fluoride (YF₃) columnar thin films (CTFs) were fabricated by electron beam evaporation with the glancing angle deposition method. The microstructures and optical properties of YF₃ CTFs were studied systematically. The YF₃ films grown at different deposition angles are all amorphous. As the deposition angle increases, the columns in YF₃ CTFs become increasingly separated and inclined, and the volume fraction of YF₃ decreases, resulting in lower refractive indices. This phenomenon is attributed to the self-shadowing effect and limited adatom diffusion. The YF₃ CTFs are optically biaxial anisotropic with the long axis (c-axis) parallel to the columns, the short axis (b-axis) perpendicular to the columns, and the other axis (a-axis) parallel to the film interface. The principal refractive index along the b-axis for the 82°-deposited sample is approximately 1.233 at 550 nm. For the 78°-deposited sample, the differences of principal refractive indices between the c-axis and the b-axis and between the a-axis and the b-axis reach the maximum 0.056 and 0.029, respectively. The differences of principal refractive indices were affected by both the deposition angle and the volume fraction of YF₃.