Research On Change The Wettability Of Non-metalic Oxide Single Crystals By Laser Irradiation

In this paper, the excimer laser with wavelength of248nm is used to irradiateZrO₂, ZnO and SrTiO₃single crystals. The results show that the water contact angle isincreased from67°to approximately151°for ZrO₂, the water contact angle isincreased from75°to approximately121°for ZnO, and the CA of SrTiO₃is increasedfrom69to approximately131°. Combined with the AFM, XRD, SEM measurements,and Cassie-Baxter model, the mechanisms are analyzed and discussed. The uniquemicro or micro-nano surface structure induced by laser irradiation is the prominentfactor to the great increase of the hydrophobicity. Under the annealing treatments, thelaser irradiated samples carried out both in oxygen and vacuum atmosphere. Thewater contact angle decreases abruptly in oxygen annealing, and annealing does notchange in vacuum. The results indicate that the wettability can be altered by thevariation of chemical composition，whereas it is not very stable. Laser-inducedvariation of surface morphology is permanent for wettability.In addition, the excimer laser with wavelength of248nm and the325nm He：Cdcontinuous laser are used to irradiate ZnO and SrTiO₃single crystals for photoinducedhydrophilicity. The mechanism shows that laser irradiation will generate electron-holepairs, and some of the holes can react with lattice oxygen to form surface oxygenvacancies. Meanwhile, the defective sites are kinetically more favorable for hydroxyladsorption than oxygen adsorption, the surface hydrophilicity is improved. Thehydroxyl groups adsorbed on the defective sites can be replaced gradually by oxygenatoms, when the laser irradiated samples were placed in air. Subsequently, the surfaceevolves back to its original state （before UV irradiation）. Combined with the XPSmeasurements, the alteration of surface chemical composition is the main contributorto the enhancement of hydrophilicity. However, it is not stable.