Microstructural and optical properties of transparent thick films deposited by using TiO2 nanoparticles and CO2 laser (Invited Paper)

A CO2 laser additive manufacturing technique for depositing transparent thick TiO2 films on quartz substrates is reported. Thick TiO2 films are prepared in three stages, i.e., wet deposition using the spin-coating technique, evaporation of liquid using a lamp, and CO2 laser-assisted sintering of nanoparticles (NPs) to form a transparent film. A heat transfer model is presented for laser processing parameter selection. Different concentrations of anatase TiO2 suspensions are used to control the thickness and adjust the optical properties. SEM revealed that the absorbed CO2 laser energy promotes the formation of necking and coalescence between TiO2 NPs. A transmittance above ~85% can be achieved in some visible and IR ranges. A minimum reflectance can be achieved by controlling the sintering power and TiO2 concentration. The effect of laser power on morphological and optical properties is reported. The effects of TiO2 concentration on the refraction and absorption indices are investigated. Raman analysis is carried out to give a better insight into film microstructures. XRD analysis revealed that the sintered films are preserved as anatase TiO2.