CO2 Laser Additive Manufacturing of Multi-Layer Heterogeneous Transparent Films Using TiO2 and SiO2 Nanoparticles

CO2 laser additive manufacturing of multi-layer heterogeneous transparent films using anatase- TiO2 and SiO2 nanoparticles (NPs) is reported. The preparation of these films was carried out in two steps; corresponding to (i) evaporation of liquid, and (ii) sintering NPs to form transparent thin films on the quartz substrate (QS). Seven multi-layer films; i.e., QS/SiO2/SiO2/SiO2, QS/TiO2/SiO2/SiO2, QS/SiO2/TiO2/SiO2, QS/SiO2/SiO2/TiO2, QS/TiO2/SiO2/TiO2, QS/TiO2/TiO2/SiO2, QS/TiO2/TiO2/TiO2, were prepared for this study. A heat transfer theoretical model was developed to select the proper laser processing parameters for sintering TiO2 and SiO2 NPs, and preventing the phase transformation of these NPs. Based on the anti-reflection coating (ARC) model, a 55 nm thickness of each layer; i.e., TiO2 and SiO2, was chosen to minimize the reflectance, and enhance the transmittance of the transparent films. The microstructural properties were determined using scanning electron microscopy (SEM) and x-ray dispersive spectroscopy (XRD). UV/Vis/NIR spectrophotometry measurements show that the sintered films are highly transparent, with an average transmittance above 85% in some wavelength ranges. UV/Vis spectrophotometry was carried out to measure the reflectance. The thickness of the coatings was measured with an optical profilometer. The effects of the sequence of the TiO2 and SiO2 layer deposition on the optical properties of films of the same thickness (similar to 155 nm) were investigated. The porosity, transmittance, and reflectance data were utilized to determine the optical constants, refraction index (n(c)), and absorption index (k(c)) of the TiO2/SiO2 coatings.