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. A heat transfer theoretical model was developed to select the proper laser processing parameters. 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. The microstructural properties were determined using SEM and XRD analysis. UV/Vis/NIR spectrophotometry measurements show that the sintered films are highly transparent, with an average transmittance above 85% in some wavelength ranges. The effects of the sequence of the TiO2 and SiO2 layer deposition on the optical properties of films were investigated. The porosity, transmittance, and reflectance data were utilized to determine the optical constants, refraction index, and absorption index of the TiO2/SiO2 coatings. Our results provide a comprehensive understanding of the ARC properties of the TiO2/SiO2 coatings.
Nanoelectrospray laser deposition (NELD) of semiconductor and metal nanoparticles is a powerful and potential technology for the on-demand printing of precise and complex functional microarchitectures. In this study, a CO2 laser is used to deposit and sinter titanium dioxide (TiO2) nanoparticles on borosilicate and quartz substrates for transparent film applications. The CO2 laser is chosen for sintering because TiO2 has a lower spectral absorption at 10.6 μm wavelength. Therefore, the 10.6 μm laser can transmit through the deposited TiO2 films, and then, the whole film thickness can be thermally modified by the heating effect of laser. The effects of wet-deposition process parameters and laser processing parameters on the morphological, optical, and structural properties of TiO2 patterns are examined. The TiO2 microstructure and surface morphology were studied by optical and scanning electron microscopy techniques. X-ray diffraction (XRD) was used to investigate the structural characteristics after laser sintering. The optical transmittance of the wet and sintered TiO2 films was characterized by UV/Vis/NIR spectrophotometry. We established that the overall improvement of the morphological and optical properties of the sintered films originates from the enhanced bonding and physical interconnectivity of TiO2 nanoparticles, resulting in the formation of a dense and compact ceramic layer. XRD data points out that the anatase phase of TiO2 is preserved after laser sintering, eliminating the presence of TiO2 rutile traces. An average transmittance above ~90% was achieved in the NIR region.
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