Determination of optical and microstructural parameters of ceria films

Light-matter interactions are of tremendous importance in a wide range of fields from solar energy conversion to photonics. Here the optical dispersion behavior of undoped and 20 mol. Sm doped ceria thin films, both dense and porous, were evaluated by UV-Vis optical transmission measurements, with the objective of determining both intrinsic and microstructural properties of the films. Films, ranging from 14 to 2300 nm in thickness, were grown on single crystal YSZ(100) and MgO(100) using pulsed laser deposition (both dense and porous films) and chemical vapor deposition (porous films only). The transmittance spectra were analyzed using an in-house developed methodology combining full spectrum fitting and envelope treatment. The index of refraction of ceria was found to fall between 2.65 at a wavelength of 400 nm and 2.25 at 800 nm, typical of literature values, and was relatively unchanged by doping. Reliable determination of film thickness, porosity, and roughness was possible for films with thickness ranging from 500 to 2500 nm. Physically meaningful microstructural parameters were extracted even for films so thin as to show no interference fringes at all.