脉冲激光沉积法制备CMR薄膜及其特性研究

【作者】 高国棉；

【导师】 陈长乐；

【作者基本信息】 西北工业大学 ， 光学工程， 2005， 硕士

【摘要】 本文首先详细分析了在脉冲激光沉积(PLD)过程中激光对靶的烧蚀特性,同时考虑了激光光束的Gauss分布,靶的有限尺寸以及相变、对流和辐射造成的热损耗,采用有限差分法对激光烧蚀靶过程的温度场进行了数值模拟。选用La2/3Sr1/3MnO3靶材,计算得到了表面及内部的温度分布,同时得到了沉积大面积均匀薄膜所需要的激光能量密度应该为2-5 J/cm2,这一结论为PLD技术制备高质量的氧化物薄膜提供了理论依据。用固相反应法和PLD技术成功制备了钙钛矿锰氧化物(包括空穴掺杂型的La1/3(Ca2/3Sr1/3) 2/3MnO3(LCSMO)、电子掺杂型的La0. 9Zr0. 1MnO3) 的块状晶体和薄膜。XID测试表明两种方法制备的样品均为畸变的钙钛矿正交结构。LCSMO薄膜的电阻-温度变化曲线表明该样品具有负磁阻效应,且在液氮温度以上呈现类半导体特性。推测该样品的金属-绝缘体转变温度TP可能在77K以下。La0. 9Zr0. 1MnO3块材存在磁电阻效应,TP点在118K左右。在磁场为0. 7T时的磁电阻值(MR)约为47. 5%,显示了低场磁电阻效应。更多还原

【Abstract】 A three-dimensional numerical model for laser-ablated target using the finite differential technique is given during the process of laser -deposited films in this paper. The model takes into account the finite dimensions of the target; the laser beam is treated as Gauss distribution, and the surface heat losses due to convection and radiation. According to the model a three-dimensional temperature distribution on the surface and inside the target can be obtained. The thickness of ablation and parameter of laser is forecasted. Using the numerical model performs the temperature field of pulse laser ablation and the range of power density of laser is 2 ⁵ J/cm2 on La₂/3Sr₁/3MnO₃ target. The numerical simulation results are considered to be consistent with practical cases.Perovskite crystal and epitaxial growth of thin film of La₁/3（Ca₂/3Sr₁/3） ₂/3MnO₃ was prepared on LaAlO3 （012） single crystal substrate by pulsed laser deposition. The structural and morphology of the film were studied by X-ray diffractometry, infrared transmission and atomic force microscopy. The results show that the film is of preferential orientation. A transport property of thin film was determined using a four-probe method, and the temperature dependence of resistance shows semiconducting behavior, and no metal-semiconductor transition temperature Tp of the films in the temperature range of 77K-400 K. Electron-doped manganese oxide target La₀.9Zr₀.1iMnO₃ has been fabricated. The experimental results shows a metal-insulator transition temperature Tp of 118K and a magnetoresistance radio of-47.5% at 0.7T.更多还原