Transmittance of TiO2 Nanoparticle-based Films Deposited by CO2 Laser Heating

Abstract

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.

CO2 laser additive manufacturing of multi-layer heterogeneous transparent films using TiO2 and SiO2 nanoparticles

“…13(b), XRD patterns of QS/TiO2/TiO2/TiO2 film shows several crystallin peaks corresponding to the crystalline planes of (101), ( 112), ( 200), ( 105), (211), and (213) localized at 2𝜃 = 25°, 37°, 48°, 53°, 55°, and 62°, respectively. These peaks are correlated to the anatase crystalline phase of TiO2 with a space group 𝐼4 1 /𝑎𝑚𝑑 (JCPDS78-2486) 8,10,22 . The heterogeneous QS/TiO2/SiO2/TiO2 and QS/SiO2/TiO2/SiO2 films show a few anatase peaks with low intensities, this is caused by the presence of TiO2 with SiO2 layer (Fig.…”

“…Laser sintering of different NPs requires a proper choice of laser processing parameters aiming to trigger efficient sintering, preventing cracking of the sintered films, and damaging the substrates. The temperature required to evaporate EG and subsequently sinter nanoparticles is estimated to be the temperatures at the laser-material interaction zone on the surface of the sample 10 . A heat conduction model was previously developed to predict the temperature as a function of the selected laser processing parameters 11,22 .…”

“…Thermal treatment between 600°𝐶 and 700°𝐶 allows anatase TiO2 to transform to rutile which is thermally more stable at higher temperature (above 700°𝐶) 7,8 . Bougdid et al 10,11 used XRD analysis to show that an amorphous TiO2 film can be transformed to a crystalline anatase phase at a temperature around 325°𝐶 − 400°𝐶. Y. Jiang et al 12 reported that when SiO2 film is annealed at 500℃, the refraction index reaches its minimum, which results from the improvement in the degree of crystallization; therefore, the SiO2 NPs are probably sintered and densified.…”

“…Y. Jiang et al 12 reported that when SiO2 film is annealed at 500℃, the refraction index reaches its minimum, which results from the improvement in the degree of crystallization; therefore, the SiO2 NPs are probably sintered and densified. The optical and microstructural properties of the sintered SiO2 thin films can be improved by an adapted annealing procedure, as investigated in [10][11][12] . The transformation of TiO2 and SiO2 phases depends on the growth process of NPs in the multilayer films, and this transformation depends on the size and concentration of NPs in the initial nanosuspension and the particle packing density 13 .…”