Thin sol-gel hafnia films have been synthesised from HfCl4, the synthesis has revealed to be a simple route to fabrication of hafnia films with high transparency in the UV-visible range. The films have been fired at different temperatures in air up to 1000°C and have been characterized by X-ray diffraction and Fourier transform infrared spectroscopy. Infrared absorption spectra of hafnia films have allowed to follow the formation of monoclinic crystalline phases together with XRD. Formation of monoclinic hafnia crystallites has been observed upon calcination at temperatures higher than 600°C, as shown by infrared spectroscopy and XRD.
The optical transmission and the refractive index as a function of the temperature of firing have been characterized by UV-Visible spectroscopy and spectroscopic ellipsometry. The hafnia films, after firing at 600°C, had a refractive index of 1.92 with a thickness of around 70 nm.