Optical properties of nanocrystalline Y2O3 thin films grown on quartz substrates by electron beam deposition

• Nanocrystalline Y2O2 films are prepared on substrates at different temperatures, Ts.
• Films have a low porosity (0.02–0.12) and are transparent for VIS and NIR range.
• Specimens exhibit smooth surface with RMS roughness in the range of 1.7–3.8 nm.
• For 323 K ⩽ Ts ⩽ 673 K values of the refractive index n are between 1.79 and 1.90.
• The changes in n vs. Ts arise from changes in grain sizes (1.6–22 nm) and porosity.

Yttrium oxide thin films of a thickness 221–341 nm were formed onto quartz substrates by reactive physical vapor deposition in an oxygen atmosphere. An electron beam gun was applied as a deposition source. The effect of substrate temperature during film deposition (in the range of 323–673 K) on film structure, surface morphology and optical properties was investigated. The surface morphology studies (with atomic force microscopy and diffuse spectra reflectivity) show that the film surface was relatively smooth with RMS surface roughness in the range of 1.7–3.8 nm. XRD analysis has revealed that all diffraction lines belong to a cubic Y2O3 structure. The films consisted of small nanocrystals. Their average grain size increases from 1.6 nm to 22 nm, with substrate temperature rising from 323 K to 673 K. Optical examinations of transmittance and reflectance were performed in the spectral range of 0.2–2.5 μm. Optical constants and their dispersion curves were determined. Values of the refractive index of the films were in the range of n = 1.79–1.90 (at 0.55 μm) for substrate temperature during film deposition of 323–673 K. The changes in the refractive index upon substrate temperature correspond very well with the increase in the nanocrystals grain diameter and with film porosity.