Preparation And Physical Properties Research Of Embedded Oxides

In this thesis, silicon (Si) and zinc oxide (ZnO) nanocrystales embedded in SiO2 matrix thin films were prepared, whose structure and physical properties were analyzed. Furthermore, in order to investigate the effect of imbedded frame on the structure and physical performance, the high temperature superconductor of Bi2Sr2CaCu2Oδ(Bi-2212)with laminated structure was adopted. The crystal powder of (Bi1-xLax)2Sr2CaCu2Oδand (Bi1.7La0.3)2Sr2Ca(Cu1-xMnx)2Oδwere prepared, which are formed by doping La and Mn into different lattice point, and whose structure and physical properties were studied. The details are as followed:1. Si nanocrystales embedded in SiO2 matrix thin films were grown by plasma enhanced chemical vapor deposition (PECVD) at different ratios of the gas flow rate ratio of SiH4 and CO2 mixture (GFRRSC). The films were characterized with Raman spectroscopy, infrared absorption spectroscopy, transmitted spectra and photoluminescence spectroscopy (PL) at room temperature and at low temperatures ranging from 80K to 300K. The results show that due to the quantum confinement effect, with the GFRRSC decrease, averaged Si nano-grain size becomes little, which result in broadening of the optical energy gap. Meanwhile, several PL peaks are present between 1.4 eV-2.4 eV. At 80K, the PL at about 1.7 eV accompanied with phonons is observed, which results from the transition involving Si-0 phonons at Si-SiO2 interface. The stoichiometric SiO2 thin film is prepared in this experiment, which is also a preliminary work for preparing ZnO nanocrystales embedded in SiO2 matrix thin films.2. ZnO nanocrystales embedded in SiO2 matrix thin films were firstly fabricated on Si (100) substrates by PECVD at a low temperature. The as-deposited samples were annealed at a temperature of 500,600,700,800,900℃for one hour, respectively. The structure properties were investigated by X-ray diffraction (XRD), atomic force microscope (AFM) and Raman spectra. The results show ZnO nanocrystals are diffused in SiO2 matrix and with annealing temperature increasing, the grain boundary of ZnO nanocrystals is pinned by SiO2 matrix, which resulting in the little growth and improving the quality of crystallization. The effects of annealing temperature on optical properties of thin films were investigated by photoluminescence (PL) spectra. The results indicate that the annealing process can promote the optical properties, and the optimized annealing temperature is 800℃, at which the uniform film with high ultra violet (UV) PL efficiency can be gotten. Furthermore, it can be concluded that the peaks position of wide emission bands between UV region and visible region maybe originate from the tightly binding center related to the interface state of SiO2 and ZnO crystals.3. Sol-gel method was adopted to prepare the (Bi1-xLax)2Sr2CaCu2Oδ(x=0,0.1,0.2,0.3, 0.4) crystal powder with different nitrates as precursor. Structural characteristic was measured by XRD and Transmission Electron Microscopy (TEM). The temperature dependence of resistance R (T) was measured by the standard four-probe technique, and the magnetization M (T) is recorded using a Quantum Design MPMS superconducting quantum interference device (SQUID) magnetometer. The results show that with increasing of La content, the crystal lattice parameter of c is constant, and a, b become large, and the modulation period along b axis becomes short. Meanwhile, the appearance of diamagnetism state and antiferromagnetic state being coexisted and competed is investigated in details.4. Sol-gel method was adopted to prepare (Bi1.7La0.3)2Sr2Ca(Cu1-xMnx)20s crystal powder with different nitrates as precursor. Structural characteristic was investigated by XRD and TEM. The results show that with the increasing of Mn doping content, the crystal lattice constant a b, c all decrease gradually and the modulation period has changed; meanwhile, the new phases are present, whose intensity gradually enhance. The inner vibration modes change with the increasing of Mn doping content, which is suggested by the Raman and IR spectra analysis. The results of M-T curve analysis show that magnetic properties of the samples are greatly affected by the new generated phase and structure change.