Preparation Of KTN Thin Films And Mechanism Research Of PLD

KTa1-xNbxO3(KTN) thin film is a kind of ferroelectric materials which can be applied widely in the future. It has many good properties, such as photoelectricity, pyroelectricity, nonlinear optical and dielectric characteristics. However, the preparation of KTN thin film is still in experimental stage, many applications of KTN are still not discoveried presently. Many experimental difficulties have not been overcome, such as a high substrate temperature resulting in serious interface interaction, the volatilization of K leading to porous films and compositional deviations from stoichiometric values, and low deposition velocity leading to a long deposition time. Therefore, in order to overcome above difficulties and prepare high-quality KTN thin films, it is very significant to optimize technics parameters and find out an appropriate preparation method. Pulsed laser deposition method is a new thin-film preparation technology with many advantages, and it has been developing very quickly. Combined PLD technology with other technics, high-quality KTN thin films are prepared. In addition, based on accumulated experimental experiences, our researches emphasis is laid on theoretical mechanism on PLD technology. In particular, the relationship of thin films properties and laser parameters, ablation rules and expansion laws of plasma are discussed in detail. It must be noted that, every stages of PLD processes are considered as a uniform whole, namely, results of the ablation stage are utilized as the boundary conditions of expansion stages, and plasma evolvement laws are used to investigate the deposition process of thin films. In fact, a physical dynamic frame of PLD is established in our work.In our experiments, KTN super-tiny powder and high-quality ceramics are prepared by Sol-Gel method and atmosphere sintered respectively, then large-size, even-thickness, high-orientation and transparent KTN thin films are firstly prepared on Si(100) substrate by PLD, and a set of optimized parameters is also obtained. Because of utilizing Sol-Gel method, the proportion of Ta and Nb is uniform in molecular size, which enhances the uniformity of KTN thin films. Moreover, the atmosphere sintering technics helps to eliminate porosity in films, so the compact films are obtained.In the mechanism aspects, based on our experiments and consulting other experiments and local theoretical works of other researchers, physical phenomena in every stage are completely studied in detail, such as twin dynamic interfaces in a bulk target, ejections and expansions of plasma, deposition of thin films. Firstly, the dynamic equation describing plasma density distribution is proposed, an anisotropic plasma density distribution can be obtained from this equation. Then, evolvement laws of plasma in both isothermal stage and adiabatic expansion stage are discussed. The simulation results demonstrate that laser parameters will affect films properties determinately. a). With the increasing of pulsed laser influence, the thickness of KTN film becomes more and more non-uniform, namely, lower laser influence is helpful for improving the thin film uniformity, while excessively low laser influence will decrease deposition velocity. b).For higher laser influence, the proportion of K, Ta and Nb is closer to that of the target. On the contrary, lower laser influence will result in poor-keeping compositions. c). No matter what the laser wavelength is, the thickness distribution of thin film is non-uniform, and a long laser wavelength is harmful for enhancing the uniformity of thin films. It is can be seen that, the results of our dynamic model can offer direct theoretical instructions for optimizing PLD technics parameters.Above conclusions can offer direct theoretical guidance to optimizing technics parameters of PLD technology.About ablation process in PLD technology, unlimited-planar laser-driven ablation model is not be adopted, while laser ablation model for targets with a limited-thickness is proposed, and appropriated boundary conditions an...