Optical properties of transparent TiO 2 films by sintering anatase nanoparticles with a CO 2 laser

A novel CO 2 laser additive manufacturing technique is reported in this paper for depositing transparent TiO 2 films on quartz substrates using anatase TiO 2 nanoparticles (NPs). Single- and double-layers of TiO 2 films were prepared in two stages: (i) wet deposition using the spin-coating technique, and (ii) laser-assisted both drying of the wet layer and then sintering of the dried NPs to form a film. A theoretical model is presented to select and optimize the laser processing parameters. Scanning electron microscopy (SEM) revealed that the laser heating induces necking and coalescence of TiO 2 NPs without cracking the sintered films or damaging the quartz substrate. An anti-reflection coating (ARC) model is utilized to select the film material and film thickness, aiming to reduce the reflectance and enhance the transmittance at certain wavelengths. UV/Vis spectrophotometry showed transmittance above ∼90% in the visible (Vis) range. The effect of laser power on the enhancement of transmittance is presented in this paper. Different concentrations of TiO 2 NPs were used to optimize the film thickness. Single layer ( ∼110nm thick) and double layer films of the same total thickness as the single layer were analyzed to infer the effects of interface on the transmittance of TiO 2 films. The transmittance of the single layer is higher, same as that of the double layer. Therefore, the difference in the transmittance of the single- and double-layer may be due to the effect of interface. The optical properties of the anti-reflection TiO 2 coating in the UV–Vis ranges were investigated. X-ray diffraction (XRD) analysis showed that the thickness affects the crystallinity of the sintered TiO 2 films.