钙钛矿氧化物薄膜和异质结的外延生长与物性研究

用激光分子束外延，原子尺度控制的外延生长出多种钙钛矿氧化物薄膜和异质结．原子力显微镜和高分辨透射电镜测量结果表明，薄膜与异质结的表面和界面均达到原子尺度的光滑．制备出在可见光波段透过率大于85％的导电氧化物薄膜；物性研究结果表明，随着含氧量的不同，BaTiO3薄膜具有绝缘体、半导体和导体的不同特性。BaTiO3／SrTiO3超晶格的光学非线性效应比BaTiO3体材增大23倍．首次在La0．9Sr0．1MnO3／SrNb0．01Ti0.99O3(LSMO／SNTO)异质结上，观测到全氧化物p-n结电流和电压的磁调制与正磁电阻效应。在255K条件下，当外加磁场分别为5和1000Oe时，LSMO／SNTO p-n结的磁电阻变化率R／RO达到：46．7％和83．4％；在外加磁场为3T时，在100K条件下，在LSMO／SNTO多层p-n异质结上观测515％的正磁电阻变化率。     

Anisotropy of the upper critical field in c-axis oriented MgB2 thin films

C-axis oriented MgB_2 thin films were synthesized on single-crystal MgO (111) substrates using a chemical vapour deposition technique. The as-formed films revealed a sharp superconducting transition temperature of 38K with the transition width 0.2K. The temperature dependence of the upper critical magnetic field H_{c2}(T) in the films was determined via resistivity for magnetic field H parallel and perpendicular to the c axis of the films. Using the Werthamer－Helfand－Hohenberg formula, we obtained the anisotropy ratio of the upper critical field γ=1.2.     

BaTiO3铁电薄膜的原子层水平外延生长

利用激光分子束外延镀膜设备,实现了原子层水平BaTiO₃(BTO)薄膜的外延生长.高能电子衍射(RHEED)、X射线衍射(XRD)、扫描电子显微镜和透射电子显微镜(TEM)等研究结果表明,薄膜的结构为c-取向单相BTO铁电薄膜,表面非常平整。在此基础上制备了铁电/超导多层异质结构.研究了BTO薄膜的铁电性质。结果表明用激光分子束外延方法有利于改进BTO薄膜的质量,提高薄膜器件的性能。     

化学气相沉积制备MgB2超导薄膜

本文报道了利用化学气相沉积技术制备MgB2超导薄膜.首先在MgO(111)基片上化学气相沉积一层B膜,然后在Mg蒸气环境下对B膜进行后退火处理.退火后得到的MgB2薄膜在MgO(111)基片上呈随即取向生长,Mg、B原子比接近于1∶2.4;薄膜表面光滑致密,晶粒粒度约为0.5μm.电阻测量和直流磁测量表明薄膜超导转变温度为38K,转变宽度仅为0.1K.毕恩公式计算结果显示MgB2薄膜的临界电流密度在0T、10K时高达2×107A/cm2.     

脉冲激光淀积庞磁阻L_(1-x)Sn_xMnO_3薄膜的光电子能谱

１９９３年发现，钙钛矿结构稀土过渡金属的氧化物的磁电阻可达１０’一１０’％称之为庞磁电阻（Ｃｏｌｏｓｓａｌｍａｇｎｅｔｒｅｓｉｓｔａｎｃｅ）．这类氧化物材料，特别是它们的薄膜，在制备高密度磁数据存储器件和磁传感器等方面有十分重要的应用价值，因而受到人们的高度重视．这里，我们仍用脉冲激光淀积技术在ＬａＡＩＯ。卜０）衬底上外延生长了Ｌａｏ。ＳｎｏｌＭｎＯ。薄膜．薄膜的晶体结构由Ｘ射线８／２９扫描确定．我们着重用角分辨Ｘ射线光电子能谱（ＸＰＳ）研究了Ｌ。．ｓｓｎｏｌＭｎＯ。薄膜的表面电子态和最顶层表面…     

Field-Effect Transistor Based on Si with LaAlO3-δ as the Source and Drain

N-type LaAlO3-δ thin films are epitaxially grown on p-type Si substrates. An enhancement mode field-effect transistor is constructed with oxygen deficient LaAlO3-δ as the source and drain, p-type Si as the semiconducting channel, and SiO2 as the gate insulator, respectively. The typical current-voltage behavior with field-effect transistor characteristic is observed. The ON/OFF ratio reaches 14 at a gate voltage of 10 V, the field-effect mobility is lOcm2/V.s at a gate voltage of 2 V, and the transconductance is 5 × 10-6 A/V at a drain-source voltage of 0.8 V at room temperature. The present field-effect transistor device demonstrates the possibility of realizing the integration of multifunctional perovskite oxides and the conventional Si semiconductor.     

Thermal Hysteresis in La2/3 Ca1/3 MnO3 Films Grown on Tilted SrTiO3 Substrates and Influence of External Magnetic Field

Thermal hysteresis in the resistivity of La2/3 Cu1/3MnO3 thin films grown on tilted SrTiO3 substrates is simulated by using the random network model on the basis of mixed-phase percolation between metallic and insulating domains, The metallic-insulating transition temperatures during the warming process are lower than those during the cooling process due to the difference in fraction of metallic domains between warming and cooling process. With an external magnetic field, the metallic-insulating transition temperatures shift to a higher value and the resistivities are reduced. The excellent agreement between the simulation and the experimental data further verifies that phase separation plays a crucial role in the transport process of La2/3Ca1/3MnO3 thin films.