Determination of Optical Properties of Thin Films from Ketteler-Helmholtz Dispersion Relations: Application to the Case of Ultraviolet Irradiated Zirconium Oxide

Abstract

A new method based on the Ketteler-Helmholtz dispersion relations is described. This method allows accurately determining the optical properties of thin films from a single transmittance curve. The case of zirconium oxide thin film postdeposition irradiated with ultraviolet light is analysed. The effect of ultraviolet irradiation is compared with low temperature postdeposition heating. It is shown that both processes have a comparable effect on the optical properties of the films. However, as our analysis leads to inferring that ultraviolet irradiation produces smoother film surfaces, the use of ultraviolet irradiation is an interesting alternative to the heating process. Accordingly, the reduction of light scattering from the interface with air provides films of better optical quality, which is especially valuable in case of multilayer systems.

UV-A Treatment of ZrO2 Thin Films Fabricated by Environmental Friendlier Water-Based Solution Processing: Structural and Optical Studies

“…Moreover, the decrease in roughness with UV-A treatment points that UV treatment is capable to reduce the organic residues due to the oxygen radicals [33] and has the potential to substitute thermal annealing process. A similar trend in roughness has been observed in earlier studies [10,34] in ZrO2 films irradiated by UV = 230 nm. The change in roughness can be due to the changes linked with grains' configuration and structure densification that may occur in the due course of processes that take place because of UV-A treatment of the films [35,36].…”

“…The synthesis of ZrO 2 has been carried out with a variety of techniques based on both vacuum and solution processing [3,[10][11][12]. However, the key point is that tailor-made properties of ZrO 2 thin films can be achieved with the right choice of various factors, in both pre-and post-deposition procedures.…”

“…In recent years, a different approach that can decrease the curing temperature of solution-processed oxide films and improve the properties, has been developed and has gained increasing interest because the modern era of technology is heading towards transparent and flexible applications which require low temperature processing. Therefore the paradigm of heat treatment has changed in due course of its development to low temperature annealing [15] and even better the ultraviolet (UV)/photo annealing [10,11,16,17]. Here, the latter approach has emerged as a promising alternative to high temperature treatments because the film surface can be directly processed, without heating, using appropriate energy of light which can enhance the ionic diffusion in the oxide films as well [18].…”

“…The UV spectrum (100−400 nm) is categorized into three groups known as UV-A (320−400 nm), UV-B (290−320 nm), and UV-C (100−290 nm). The mechanism of UV irradiation has been studied for ZrO 2 films using wavelengths of 185 nm and 254 nm [10,19] that fall in the category of UV-C. The wavelengths are comparable to oxygen molecule bond energies and therefore can induce oxygen radicals and ozone [19] which, due to the low activation energy, further give boost to the oxidation rate [11].…”

“…More studies include dielectric and electric properties [11,16,21] of UV treated ZrO 2 films for TFT applications. Desforges et al [10] studied the Ketteler-Helmholtz dispersion relations to determine the optical properties of UV irradiated ZrO 2 thin films from a single transmittance curve and also observed reduction in surface roughness of these films. However, there are quite a few reports which have employed high wavelength side of the UV spectrum to investigate the induced changes.…”