Thickness-dependent optical properties of yttrium fluoride ultrathin films in the visible band

Yttrium fluoride (YF3) thin films with a thickness range of 10.8−1079.0 nm were prepared by electron beam evaporation. Spectroscopic ellipsometry was used to study the thickness-dependent optical properties of YF3 ultrathin films in the 300−820 nm wavelength range. With increasing thicknesses, the refractive indices of the intrinsic YF3 films increase slightly and approach that of bulk YF3 due to the decrease of void fractions. The effective refractive indices of the YF3 films also increase with increasing thicknesses, due to the surface and interface effects besides the contribution of decrease of void fractions.