Optical, structural, and mechanical properties of gadolinium trifluoride thin films grown on amorphous substrates

Since excimer laser applications extend to deep and vacuum UV wavelengths at 248 nm, 193 nm and 157 nm, renewed research interest has recently arisen on fluoride thin films due to their unrivaled position as wide-bandgap material for the vacuum UV (VUV). Among these materials, only a very limited number can act as the high refractive index component in multiplayer interference stacks. Besides LaF3, gadolinium tri-fluoride is a potential candidate especially for wavelengths at about and below 200nm. We report on the evaluation of the structural properties, the optical properties with emphasis to the DUV - spectral range, and the mechanical properties of GdF3 single layer by means of XRD, GIXR, AFM measurements, spectral photometry and by ex-situ mechanical stress analysis using the laser beam deflection method to measure the substrate deformation. The samples were deposited onto fused silica and silicon substrates by a low-loss evaporation technology in a BAK 640 coating plant applying various deposition conditions.