Abstract

In this work, we report the influences of annealing temperature on the structural, morphological and optical properties of ThO2 thin films. The ThO2 films were deposited on fused quartz and silicon (100) substrates by photochemical metal organic deposition (PMOD) using the hinokitiolate thorium (IV) complex as the precursor. The as-deposited film, as well as the films annealed at temperatures in the range of 300 °C to 1100 °C for two hours were studied. X-ray photoelectron spectroscopy confirmed the deposition of ThO2 films. X-ray diffraction (XRD), atomic force microscopy (AFM), UV-VIS transmittance spectroscopy and spectroscopic ellipsometry were used to study the physical properties of the films. XRD patterns showed the polycrystalline nature and the cubic structure of the films after annealing above 300 °C, as well as the increase in crystallite size with annealing temperature. Annealing at 950 °C promotes the formation of huttonite (β-ThSiO4) in the ThO2 layer. AFM studies revealed an increase in surface roughness with annealing temperature. The transmittance of annealed films deposited on fused quartz is over 80% in the visible range, without an appreciable effect of annealing temperature on the band gap. Annealing at 750 °C produces a film with a low surface roughness and a refractive index of 1.9, indicative of a good density ThO2 with potential use as a reflective mirror in the EUV range.