Laser crystallization of amorphous TiO2 on polymer

The deposition of crystalline TiO2 on polymers can boost its use in a large plethora of applications. In this work, we deposited, through the low-temperature atomic layer deposition (LT-ALD) technique, a thin layer of amorphous TiO2 on polymethyl-methacrylate (PMMA), and afterwards, we induced a phase transition from amorphous to crystalline anatase by pulsed UV-laser irradiation. A pulsed UV laser with a low penetration length was used to avoid the heating and damaging of the polymeric substrate. The diffusion of the heat and the temperature behaviour were simulated and discussed. We studied experimentally the effect of the laser fluence and pulse number on the amorphous-crystal transition. We observed the presence of two thresholds for the formation of the crystalline phase: on the fluence and the number of laser shots. Moreover, widening of pre-existing cracks is observed, as soon as fluence and the number of pulses increase. To improve further the quality of the deposited layer, we introduced a ZnO interlayer between TiO2 and the PMMA substrate. The effect of this interlayer was also discussed. Lastly, wettability, as a measure of the overall quality of the layer, was measured and interpreted by using the Cassie model.