Preparation And Characterization Studies Of Co-BaTiO₃ Nano-composite Films And C_xH_1-x Films

This thesis consists of two parts: the preparation and characterization studies of Co-BaTiO₃ nano-composite films; and the preparation and characterization studies of C_xH_1-x films.Recently, there has been increasing interest in the nano-composite films with ferroelectric matrix. Although the related studies are few, some interesting phenomena have been discovered in the ferroelectric matrix-nano-metal composite materials. For example, the modulate effects of metal particles absorption spectrum are caused by the superhigh dielectric constant and matrix dielectric constant, and the functions of secondary harmonic of ferroelectric films are enhanced by metal particles. Remarkably, many new physical phenomena and some new style quantum-dot devices may be produced by making use of the mechanism of exciting the ferroelectric-quantum dot by the ferroelectric-quantum dot films through the outfield.In part one, the principle of the pulse laser deposition (PLD) and the preparation methods of BaTiO₃ films are discussed systematically; the structure, growth characteristic and mechanism of BaTiO₃ and BaTiO₃ nano-metal composite films are studied; and the optical properties of BaTiO₃ and BaTiO₃ nano-metal composite films are analyzed in detail. The main contents of this part contain the following aspects: 1. The principle, characteristic and research actuality of pulse laser deposition technique are introduced systematically. Comparing with the other methods, the advantages of the PLD technique are:(1) The films deposited by PLD method has the same components of the target material. This is helpful in preparing multi-component system films.(2) The deposited rate could be controlled, and the atom-layer growth may be reached if the growth rate is as slow as possible.(3) The device preparation is possible because of the short preparation period and high efficiency of the PLD.(4) It can grow in original position, which will provide favorable conditions for multilayer structure including the preparation of the quantum-dot supper-lattice.Therefore, the PLD method is suitable for the preparation of complex oxide nano-metal composite films.2. The theoretical and experimental studies have indicated that: the critical thickness of BaTiO₃ in the nano-composite films deposited on single crystal MgO (100) is greater than or equal to 10nm; the BaTiO₃ base is in tetragonal phase with a≈0.424nm, c≈0.407nm, and the film has single orientation. The average diameter of Co particles embed in the films is 15nm, and these particles are in elemental metal state. HRTEM and XRD analyses show that there are hcp as well as fcc structural phase exist in the Co nano-particles. The reason for this phenomenon may be that there is little discrepancy in the Gibbs free energies for the two phases.The Co: BaTiO₃ nano-composite films deposited on Si substrates show quite different structural characteristics from those of Co: BaTiO₃/MgO (100) nano-composite films. Firstly, when the film thickness is small (≤300nm), BaTiO₃ base is in single c axis orientation. HRTEM, XRD and AFM analyses indicate that the orientation in the flat paralleling to the substrate is disorder, owing to the larger crystal lattice mismatch, although the BaTiO₃ crystal particles are in c axis orientation. Secondly, when the film thickness is augmented to about 100nm, the BaTiO₃ crystal lattices transformed into close-cubic structure with a/c ratio varying in 1.0021～1.0083 due to the stress relaxation, and the crystal orientation is also decreased, with increasing Co particle concentration. In the films of Co: BaTiO₃/Si (100), the diameter of Co particles is in Lorentz distribution, and the average diameter varies in the range of 15-30nm.This study indicates that: Co: BaTiO₃ nano-composite films with single orientation (or preferred orientation) could grow on both MgO (100) single crystal substrate and Si (100) single crystal substrate; Co particles are in elemental metal state and the diameter of the particles could be controlled.3. In this thesis, the optical properties of BaTiO₃ nano-composite films are studied in three aspects:(1) Absorption spectrum and reflecting spectrumThrough the studies of absorption and reflecting spectrum, the optical band gap of BaTiO₃ nano-composite films, Eg, is estimated in the range of 3.5 eV～4.0 eV, the analyzing of the intra-band electron transition of BaTiO₃/MgO (100) nano-composite films is consistent with theoretical prediction, and it is found that in high energy region, there are obvious varieties in the fine structure of conduction band and valence band of both Co: BaTiO₃/MgO(100) and Co: BaTiO₃/Si(100) nano-composite films when the Co particles are embedded fore and after. The positions and topological properties of the critical point of the density of combination state vary apparently with the concentration of Co nano-particle. The effects and varieties of plasmon at Co nano-particle surface are also studied using the reflecting spectrum of Co: BaTiO₃/Si (100), and these works are not reported elsewhere to our knowledge.(2) The details of electron transition between conduction band and valence band have been further studied using the photoluminescence spectrum of Co: BaTiO₃/MgO (100) nano-composite films, and a new photoemission peak appears in the range of 1.9～2.2eV. This phenomenon may be applied in tunable semiconductor laser.(3) The Raman spectrum analyses of BaTiO₃/MgO (100) nano-composite films indicate that the Raman peak would be greatly enhanced at proper concentration and size of Co particles.4. The valence band spectrum of Co: BaTiO₃/Si (100) nano-composite films are amply analyzed using the UPS spectrum. The studies show that the position of the top of valence band changes and the optical band gap diminishes with increasing Co nano-particle concentration. These observations are not given using other spectrum methods. Meanwhile, obvious varieties of the fine structure of valence band have occurred, and new sub-band has appeared (sample Si-7^# and Si-8^#) with increasing Co nano-particle concentration. This is consistent with the conclusion from spectrum analysis.Since the C_xH_1-x coating on the shell surface is typically used in the radiation-induced implosion research of inertial confinement fusion (ICF), the study on C_xH_1-x coating becomes very significant for the implosion kinetics and radiation hydromechanics researches. Therefore, the second part of this thesis describes the mechanism of low-pressure plasma CVD (LPP-CVD) technology, the fabrication, and the deposition mechanism, and studies the properties of C_xH_1-x films.1. The C_xH_1-x films are successfully fabricated by LPP-CVD technology. There are many dangling bonds on the surface of C_xH_1-x films. If these C_xH_1-x films are not properly treated, they would react with oxygen and water in the air and form some oxygenic group when they are exposed to the atmosphere. When they are treated in-situ using H⁺ ions for a period of time, the oxygenic groups in the films are remarkably decreased, and the C_xH_1-x films become very stable in the atmosphere. From the FT-IR and XPS results, it is found that there have not only C-C bonds but also have some C=C bonds in the C_xH_1-x films, and there are the evidence of sp³ hybridization and sp² hybridization.2. The effects of the H₂ flow and the time of H⁺ treatment on the stable time, the density of surface dangling bonds and the electron localization of the C_xH_1-x films are systematically investigated. It is concluded that the considerable time duration of the H⁺ treatment on C_xH_1-x films is an effective way to decrease the density of surface dangling bonds.3. To deposit C_xH_1-x coatings uniformly, a special bounce pan is invented to keep the shell bouncing in the deposition process. This technology could make high quality C_xH_1-x coatings with the thickness uniformity better than 95%, and could make batch production of C_xH_1-x coatings possible.4. The UV-VIS spectrum of C_xH_1-x films indicate that the reflective index of C_xH_1-x films is very sensitive to the structures of the films, and it is very difficult to find the rule of the changes of the refractive index with the changing of the coating parameters since the change range of the fabrication parameters for the C_xH_1-x films by CVD is very small.