Fabrication And Characterization Of YMnO3 And Related Manganese Oxide Thin Films

The preparation and physical properties of Rare-earth manganese oxides thin film have attracted much attention in recent years since it was found that partial substitution of R by Ca, Sr, or Ba results in structural changes and the occurrence of colossal magnetoresistance near the temperatures of spin ordering of Mn ions, which becomes one of focuses and frontiers in the field of condensed matter physics. Yttrium manganese oxide (YMnO₃) with a hexagonal structure, known as ferroelectromagnets due to coexistence of the ferroelectric and magnetic orderings at low temperatures, arouse people's revival interest because of its unique characteristics on chemical composition, crystal structure and related physical properties. Although it has been extensively studied, some issues involved in the preparation of YMnO₃ thin film with different crystal structure and research on relevant interesting physical properties are still necessary to be investigated. In this dissertation, the preparation, optical and electrical properties of YMnO₃ and relevant doped manganese oxides thin films derived from novel chemical solution method have been investigated. The obtained results are listed as the following:1. Preparation and optical band gap energy of YMnO₃ thin film with hexagonal structure: highly (0001)-oriented thin films of YMnO₃ were grown directly on Si substrates by a novel chemical solution process, in which Y(NO3)3?6H2O and Mn(CH3COO)2?4H2O was used as starting materials , acetic acid and water as solvent ; the optical band gap of hexagonal YMnO₃ thin films deposited on fused quartz were evaluated with a UV/VIS spectrophotometer at room temperature in the wavelength range of 200-1100nm in terms of annealing temperature, it was found that the higher the annealing temperature ,the larger the band gap of the samples derived by the above mentioned method, which exhibits an unusual trend, and that the band gap energy of well-crystallized hexagonal YMnO₃ thin film ,with round grains about 50nm in diameter, was 4.28 eV, which was consistent with that of reported.2. Preparation and optical band gap of YMnO₃ thin films with orthorhombic structure: orthorhombic YMnO₃ thin films, which were usually obtained from hexagonal YMnO₃ thin film through annealing under higher pressure, were successfully fabricated for the first time using a very simple chemical solution route under atmospheric pressure at relatively low annealing temperature. The starting materials are Y2O3 and Mn(CH3COO)2?4H2O, the solvents are acetic acid and water. Single-layer YMnO₃ thin films as thick as 750nm could be obtained via single-stepspin coating, which is generally difficult to be realized. The band gap energy of well-crystallized orthorhombic YMnO₃ thin film with rapid thermal annealing at 800oC was estimated to be about 3.05 eV. 3. Preparation of the doped rare-earth manganese oxides La₀.7Sr₀.3MnO₃, Y₀.7Sr₀.3MnO₃ thin films: Sr-doped mixed-valence manganese oxides La₀.7Sr₀.3MnO₃ and Y₀.7Sr₀.3MnO₃ thin films were successfully prepared by SCD; the resultant La₀.7Sr₀.3MnO₃ thin film upon annealing at 700oC exhibits good electrical conductivity; Y₀.7Sr₀.3MnO₃ thin film as thick as about 250nm upon annealing at 800oC was proved to be conducted, which experimentally clarifies the electrical conductivity of Y₀.7Sr₀.3MnO₃ thin film at room temperature.4. Third-order nonlinear optical property of YMnO₃ thin film with orthorhombic structure: The nonlinear optical property of orthorhombic YMnO₃ thin films was investigated firstly. In this dissertation, nonlinear optical refractive index of orthorhombic YMnO₃ thin films was firstly measured using Z-Scan technique and its value was determined to be about 2.068×10-16(m2/W); In addition, the nonlinear absorption coefficient of orthorhombic YMnO₃ thin film was determined to be 8.16×10-10m/W through theoretical fit based on open-aperture Z-Scan curve. All the results offer experimental data for its potential application of orthorhombic YMnO₃ thin fi...