Research On The Preparation And Properties Of A Serial Of Molybdate Thin Films By Electrochemical Method

Electrochemical processing is an important technique for functional thin films fabrication in recent years, and also one of the Soft Solution Processing (SSP) methods. Compare to the conventional processing for functional thin films, electrochemical processing has outstanding advantages in controlling of the deposition reaction and the morphologies of thin films, the deposition speed, the consumption of energy, and the impact to environment and equipments etc. Electrochemical processing is being applied in manufacturing for many thin films 。In this thesis, a serial of molybdate thin films with scheelite structure (including CaMoO₄, BaMoO₄, Sr_1-xCa_xMoO₄, Ba_1-xCa_xMoO₄ and Ba_1-xCa_xMoO₄ etc.) were directly prepared on molybdenum substrates by electrochemical technique. The influences of processing conditions on the qualities of as-grown molybdate films were systematically studied. The preparation of polycrystalline molybdate films by constant current and constant potential method were carried out, the impacts of composition ratio of the starting solutions on the composition ratio, lattice parameters and surface morphology of the as-grown molybdate solid-solution films (such as Sr_1-xCa_xMoO₄, Ba_1-xCa_xMoO₄ and Ba_1-x-yCa_xSr_yMoO₄) were also discussed. The growing characteristics of the as-grown polycrystalline molybdate films also studied. The physical and chemical characteristics (including phase structure, surface morphology, composition and composition ratio) of prepared films were characterized by using XRD, SEM, XPS and AFM, and the room temperature photoluminescence propertiesof as-grown films were investigated too.The main conclusions with outstanding innovative features acquired from the present work are mainly as follows:(1) The impact of processing (such as current density, roughness of surface of substrate, reacting time, solution acidity and reacting temperature) on the qualities of as-grown molybdate films, the optimum processing conditions for polycrystalline molybdate films were found. The results show that the concentration of B6* is decided by the current density and pH value of solutions, and the diffusion speed of ions is relied on the temperature. Those processing conditions affect the growing speed, morphology, density and coherence, and the influences of surface roughness of metal substrate on the growing and qualities of the as-grown films are chiefly embodied in the amount of the defect, the size and uniform of the grain etc. To our knowledge, this work was not reported.(2) The uniform, dense and well-crystallized Bai.xCaxMoO4 and Bai.x.yCaxSryMoO4 polycrystalline solid solution thin films were prepared directly on the molybdenum substrate by constant current and constant potential electrochemical method respectively at room temperature, Sri.xCaxMoO4, Bai.xCaxMoO4 and Bai.x.yCaxSryMoO4 polycrystalline solid solution thin films were prepared directly on the molybdenum substrates by using constant potential electrochemical method, and the as-grown thin films were characterized by using XRD, SEM, XPS and AFM. techniques.(3) The relations between the composition ratio of the solution and the composition ratio of the as-grown thin films were acquired, and the influence of the different composition ratio of the solution on the phase structure and the surface morphology were studied too. The researching results indicate that Ca content in the as-grown solid-solution films is lower than that one in the starting solution; moreover the Ca content in prepared Sri.xCaxMoO4 films appears linearity with that one in solutions, so the composition ratio of the as-grown films can be controlled bymodulating the composition ratio of the starting solutions; and when the Ca content of solid-solution Sri.xCaxMoO4 films increases, the diffraction peak of the same plane would shift to the higher 2 6 position. To our knowledge, this work was also not reported.(4) The growing characteristics of CaMoC>4 and BaMoO4 thin films were investigated, furthermore, the growing characteristics of Sri.xCaxMoO4, Bai.xCaxMoO4 and Bai-x.yCaxSryMoO4polycrystalline thin films with different composition ratio were also studied. The researching results show that CaMoO4 film is prefer to grow vertical direction, whereas BaMoO4 films is prefer to grow in horizontal direction, and the composition ratio of solid-solution films will affect the growing direction of the as-grown films. This work was not reported either.(5) The measurements of photoluminescence spectra of as-grown thin films at room temperature reveal that the photoluminescence emission wavelength and the greatest absorption wavelength of a serial molybdate films are decided by the jump of electron in MOO42" tetragonal group. The composition and component of M2+ (Ca2+, Sr2+, Ba2+) has least effect on the photoluminescence spectra, whereas it will impact on the photoluminescence emission intensity. To our knowledge, this work was not reported too.