CO2 laser-assisted sintering of TiO2 nanoparticles for transparent films

Abstract

Nanoelectrospray laser deposition (NELD) of nanoparticles (NPs) on various substrates has attracted considerable attention as a fast, cost-effective, and scalable technique for precise control of heating time and zone. In this work, NELD-assisted sintering of titanium dioxide (TiO2) NPs on borosilicate glass and quartz substrates is addressed. A [Formula: see text] CO2 laser was used for patterning and sintering titania nanoparticles in ambient air. The effects of laser dose and deposition process parameters on the morphological, structural, and optical characteristics of the sintered TiO2 patterns were characterized using optical microscopy, scanning electron microscopy, and x-ray diffraction. The results point out that the anatase phase was preserved after laser sintering, without the appearance of any TiO2 rutile traces. We show that the improvement in the morphological properties of TiO2 patterns is due to the laser sintering of a dense layer of ceramic with enhanced interconnectivity and connection between single nanoparticles. A theoretical model was developed to select the temperature required to sinter TiO2 nanoparticles and to correlate it with the laser power and scanning speed to prevent cracking on the substrate and sintered nanoparticles and also to get transparent TiO2 films. An optical transmittance of [Formula: see text] was achieved. The experimental data were in accordance with the theoretical model, predicting the success of the model.

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

“…It is known 18,19 that the laser-assisted densification and sintering of NPs requires a proper choice of laser processing parameters aiming to control the temperature at the laser-material interaction zone and therefore trigger efficient sintering and minimize substrate damage. In our recently published paper 15 , we developed a heat conduction model to select laser processing parameters for sintering TiO2 NPs and controlling phase transformation. We showed that the calculated temperature based on the laser processing parameters depends on the thermophysical properties of TiO2, including thermal conductivity, thermal diffusivity, heat-specific capacity, and the temperature where the deposition is performed.…”

“…Based on our theoretical study in ref. 15 , 2 𝑊 power combined with 2 𝑚𝑚/𝑠 scanning speed was chosen as the threshold laser dose; corresponding to 350 − 400°𝐶 temperature, at which the TiO2 Nps can be properly sintered, as they showed the original yellow color of the anatase phase of TiO2 (see the sintered line in the inset of Fig. 3(b)).…”

“…The lower thermal expansion coefficient of both substrates makes them more resistant to thermal shock during the laser sintering-assisted deposition of TiO2 NPs and, therefore, less prone to cracking due to thermal stress. We previously reported 15 that the laser sintering process depends on different factors, including the laser dose, temperature, and thermophysical properties of TiO2 such as density, thermal diffusivity, and thermal conductivity. These physical properties of TiO2 affect the temperature induced by the laser beam during the laser sintering of NPs.…”

“…J. Toledo et al 14 studied the influence of annealing temperature on the structural property of TiO2, and they reported using XRD analysis that amorphous TiO2 can be transformed to anatase at a temperature around 400°C. Kar et al 15 reported that the TiO2 film was preserved as an anatase polycrystalline phase after sintering at a temperature between 350°C and 400°C. Sta et al 12 investigated that the identified peaks of a TiO2 film sintered at 600°C correspond to the tetragonal anatase phase of TiO2.…”

“…Sta et al 12 investigated that the identified peaks of a TiO2 film sintered at 600°C correspond to the tetragonal anatase phase of TiO2. Compared to the conventional deposition methods using thermal annealing in a furnace, the laser processing of sol-gel TiO2 films is a straightforward tool and introduces several advantages to laser additive manufacturing technology 15,16 . Hartmann et al 17 examined the laser (𝜆 = 193 𝑛𝑚) sintering of anatase TiO2 films (NPs size: 8-10 nm), and they observed that the size of the sintered TiO2 crystallite increased and reached 200 𝑛𝑚.…”