Structure And Properties Study On Laser Crystallization Of Amorphous TiO₂ Thin Film

Nano-TiO₂ film, as a kind of function thin film, has not only excellent intensity, rigidity, abradability, erosion resistance and compactability, but also photochemical catalysis, photodegradation, disinfection, sterilization and self cleaning. Nowadays,nona-TiO2 applied in many arreas ,such as in purifying the air, liquiding waste processing, self-cleaning glass, light-catalysed sterilization etc.Laser crystallization, a new process using laser as heat source, is widely applied for fabricating nanocrystal thin films on the surface of materials.In this paper, the 3-D heat transference finite element models of the heat source and sample in laser crystallization are built up and optimized using MSC.Marc. With the models, we compute the temperature field of laser crystallization for amorphous TiO₂ thin films under different laser conditions. And then, the mid-frequency unbalance dual-targets magnetron sputtering system is used to prepare the amorphous titanium oxide thin film for research object, when the phase transition from amorphous to nanocrystalline phase is performed by laser crystallization with high power flow CO₂ laser. Comparing simulation results with experimental results, we analyse systemically the influence of the laser processing parameter on the form and the grain of crystals, and study the process of the formation of the crystal and evolvement mechanism in the process.We sum up rules from the simulation results as follows: the temperature on the surface of material has a linear relationship with laser power, the scanning speed and facular radius.The temperature on the surface of samples is increasing with the increment of power, the decrease of scanning speed and the reduction of facular radius.Laser heat source forms drip on heat area, and we obtain the corresponding distribution of temperature field.With laser crystallization of single track scanning, the laser crystallized TiO₂ thin film mainly consists of anatase and rutile phases with diameter of nanometer. The results indicate that when the other parameters keep invariablenes, the anatase ,as debasing the scanningspeed, turns to the mixed crystal of anatase and rutile, meanwhile, the content of rutile and the average grain size of film increase.At the meantime, the hardness and Young's modulusof the film basal system goes up and are higher than the ones of original amorphous one. According to the modulus curve, we can conjecture qualitatively that nano-TiO₂ thin film is good in compatibility of deformation and interface bond strength. The friction coefficient ,the breadth of abrasion mark debase, the friction factor and the width of grinding crack of crystal films are lower than those of original ones. When the defocusing amount is altered only,there is similar condition as debasing the scanningspeed.And when the laser power increases merely, there is also similar condition as debasing the scanning speed.Nano-TiO₂ thin film crystallized by laser crystallization of multiple tracks has good uniformity, and the hardness, Young's modulus, and wearing resistance of thin film are all higher than the original amorphous film.In all, the simulation results are in good agreement with the experimental measurements. The critical temperature of Laser crystallization for amorphous TiO₂ thin film is about 600℃.