Material Synthesis And Microstructure Formation On Target Induced By Laser Irradiation

With the development of science and economy, many fields need high-performance materials. Novel materials and functional microstructures are required to be developed and utilized. Thus, the discovery of materials and microstructures prepared methods become quite important. Thermal and mechanical effects can be produced in the irradiated bulk or on the irradiated surface by the interaction of lasser with condensed matter. Therefore, pulsed laser ablation can be used for material modification, synthesis of materials and novel microstructure formation. In a word, the studies on the interaction of laser with condensed matter, is very significant in the aspects of developing laser application, fundamental research and new material preparation methods. Pulsed laser ablation (PLA) generally is used to deposit films and micromachining. It is different that this work presented that material could be synthesized on surface of solid targets and novel microstructure could be formed induced by laser irradiation. In the thesis, the subjects investigated are material synthesis and microstructure formation induced by laser ablation. The detailed research contents of this thesis conclude synthesis of materials, microstructure formation, the effect of laser intensity, and theoretical research.Long-pulse microsecond laser and ultrashort-pulse femtosecond laser were used to irradiate 2Al₂O₃+Tb4O7 targets respectively, and the effect of different pulse durations on material synthesis was studied. The results demonstrate that TbAlO₃ was synthesized by microsecond laser irradiation. Tb4+ ion was changed to Tb3+ ion. The materials on target surface were still raw materials after femtosecond laser irradiation. It is analysed that thermal effects play an important role in synthesis of TbAlO₃. During femtosecond laser irradiation, thermal effects can be neglected and the materials can not reach stable phase under recoil pressure condition induced by laser. In addition, EuFeO3 was synthesized by non-focused nanosecond laser irradiation and the effect of irradiated time on syntesis was studied. The research results show that the material synthesis was almost finished with irradiated time 60 s. The above results demonstrate that it is feasible to synthesize materials on target surface directly.Nanosecond laser was used to irradiate the 4CeO2+Tb4O7 target positioned in deionized water and the effect of pulsed laser intensity on the synthesis of rare earth oxide on target was investigated. Measurement results show that CeTbO3+δwith fluorite structure was synthesized on the target surface. The yield of the prepared products depends mainly on the laser intensity. In the present experimental conditions, the increase of the laser intensity contributed to the increase of CeTbO3+δyield. When the laser intensity increases to 1.8×1012 W/cm2, the curve of the ratio content of CeTbO3+δdrives to easement. It can be deduced that there is an optimum laser parameter to obtain maximum yield of the syntietic prduct.Femtosecond laser pulses were used to irradiate target of 4CeO2+Tb4O7 under ambient conditions. Material synthesis and microstructure formation on the target surface were studied. Measurement results demonstrated that solid solution CeTbO3+δwith cubic fluorite structure has been synthesized and distributed on the surface homogeneously. A layer of nanofoamy structure with clusters size 10 nm and droplets with size 20-300 nm was deposited on the irradiated target surface. The formation mechanism has been discussed. Nanofoam materials have large specific surface area and unpaired electrons, and these properties can enhance the ability of surface absorption.Carbon and silicon nanofoams were prepared by nanosecond laser irradiation, and the conditions for nanofoam formation and mechanism have been studied. The effect of the laser intensity on the microstructure formation was also studied. It is analysed that the different microstructures is attributed to the variation of ionization, plasma and clusters induced by laser irradiation. The experimental research results also demonstrate the laser intensity should above a threshold to prepare the nanofoamy structure. The irradiated graphite targets show dark black color. The carbon nanofoam is amorphous carbon and can increase the optical absorption coefficient. Therefor it can be used for extinction devices. We analyse that at proper laser and ambient conditions materials with nanofoamy structure can be obtained easy. The universality of the nanofoam materials induced by laser irradiation was studied.Through the study on the interaction of laser with solid target, material synthesis by pulsed laser irradiation on target surface was realized. The effects of laser parameters on materials synthesis, microstructures formation and physical mechanism have been studied. The study on materials synthesis and microstructres formation induced by laser irradiation is very important for both fundamental research and application.