HgBCO和PrBCO的正常态的1/f噪声研究

在１００ ～３００Ｋ温度范围内测量了Ｈｇ１２１２ 相块材和薄膜样品的正常态的１／ｆ 噪声,结果显示高质量薄膜的噪声水平为１０４ 量级,已和ＹＢＣＯ 外延膜及单晶相近．还测量了ＰｒＢａ２Ｃｕ３Ｏ７ － δ（ＰｒＢＣＯ） 微桥样品１／ｆ 噪声的尺寸依赖性,发现在ａｂ 面上,存在着与涨落相关的特征尺度,约为１０２μｍ 的量级．样品宽度降到该尺寸以下时,噪声水平急剧下降．在两个体系中,实验结果均和ＤｕｔｔａＨｏｒｎ 热激活模型进行了比较．     

Difference of Oxide Hetero-structure Junctions with Semiconductor Electronic Devices

Charge carrier injection is performed in Pr0.7Ca0.3MnO3 （PCMO） hetero-structure junctions, exhibiting the stability without electric fields and dramatic changes in both resistance and interface barriers, which are entirely different from behaviour of semiconductor devices. The disappearance and reversion of interface barriers suggest that the adjustable resistance switching of such hetero-strueture oxide devices should associate with motion of charge carriers across interfaces. The results suggest that injected carriers should be still staying in devices and result in changes of properties, which lead to a carrier self-trapping and releasing picture in a strongly correlated electronic framework. Observations in PCMO and oxygen deficient CeO2-δ devices show that oxides as functional materials could be used in mieroeleetronics with some novel properties, in which the interface is very important.     

Relationship of Polaron Exchange with Ferromagnetic and Insulator--Metal Transitions in Doped Manganites

We report the experiment results and data analyses based on a polaron exchange model for La0.7Ca0.3MnO3 and Pr0.7（Sr1-xCax）0.3MnO3 epitaxial thin films. In the polaron exchange model with an energy balance condition, critical temperature of Tc for stable ferromagnetic （FM） ordering should depend on △E as kBTc = E0 exp（-△E/kBTc）, where A E denotes the potential barrier for the exchange polarons to overcome. Using the small polaron hopping model, the resistivity peak temperature Tp is a function of the hopping energy Ehop. The dependence of Tp on Ehop is similar to the dependence of Tc on AE, which reveals that the polaron exchange relates to FM and insulator-metal transitions. The result indicates that the polaron exchange model is a simple way for describing the FM ordering, and is very helpful for understanding of complex doped manganites.     

Fantastic Behaviour of High-TC Superconductor Junctions: Tunable Superconductivity

Carrier injection performed in oxygen-deficient YBa2 Cu307_~ （YBCO） hetero-structure junctions exhibits tunable resistance that is entirely different from the behaviour of semiconductor devices. Tunable superconductivity in YBCO junctions, increasing over 20 K in transition temperature, has achieved by using electric processes. To our knowledge, this is the first observation that intrinsic property of high Tc superconductors＇ superconductivity can be adjusted as tunable functional parameters of devices. The fantastic phenomenon caused by carrier injection is discussed based on a proposed charge carrier seff-trapping model and BCS theorv.     

Ag／YBa_2Cu_3O（7－x）、Al／YB_2Cu_3O（7－x）界面特性

利用电学测量方法结合二次离子质谱（ＳＩＭＳ）技术对金属Ａｇ和Ａｌ与ＹＢａ２Ｃｕ３Ｏ（７－ｘ）（ＹＢＣＯ）超导薄膜接触界面电学性质和互扩散特征进行了测试分析．分析结果显示由于Ａｇ和Ａｌ具有不同的化学性质，二者与ＹＢＣＯ界面的互扩散特性有明显不同．这些不同影响到接触界面的电学性质和接触窗口下ＹＢＣＯ的超导性能．在Ａｇ／ＹＢＣＯ样品中，在高于３５０℃以上的温度下氧气氛中退火将引起Ａｇ和Ｏ的界面互扩散，但对ＹＢＣＯ体内Ｏ的分布及ＹＢＣＯ的超导性能影响不大，且有利于在界面形成好的电学接触；在Ａｌ／ＹＢＣＯ样品中，在高于３５０℃以上的温度下氧气氛中退火后，界面则主要发生Ｏ向Ａｌ膜体内的扩散，并在Ａｌ和ＹＢＣＯ界面生成一不导电的氧化层，这些将影响到ＹＢＣＯ体内Ｏ的分布和接触窗口下的ＹＢＣＯ的超导性能．在合适的退火条件（约５００℃氧气氛中）下退火，Ａｇ与ＹＢＣＯ将形成小的接触电阻，利用剥离工艺制备的样品，其界面接触电阻率ρ（ρｃ＝Ｒ×Ａ）高于是１０（－６）Ωｃｍ２．     

高温超导／铁磁多层膜样品制备与输运性质的初步研究

本介绍我们对高温超导／铁磁多层膜样品的初步研究结果。利用准分子脉冲激光淀积方法制备了由高温超导ＹＢａ２Ｃｕ３Ｏ７薄膜与铁磁巨磁电阻材料Ｐｒ．７Ｓｒ．３ＭｎＯ３薄膜组成的三夹层型和台阶边缘结型多层膜样品。对ＹＢａ２Ｃｕ３Ｏ７／Ｐｒ．７Ｓｒ．３ＭｎＯ３多层膜样品输运性质测量表明样品中存在超导转变及铁磁相变。对两种多层膜样品的电阻随温度变化测量曲线进行了讨论。     

正常态金属与氧化物高温超导薄膜界面扩散特性分析

利用二次离子质谱(SIMS)技术,分析了Ag和A1与YBa_2Cu_3O_(7-x)(YBCO)超导薄膜接触界面互扩散.结果显示,它们有不同的互扩散特征.利用SIMS的分析结果,可以很好地理解经高温热处理后,Ag/YBCO和A1/YBCO样品具有不同界面电学性质的原因. 关键词：     

超薄超导YBa2Cu3O7薄膜的外延生长和电阻温度关系

利用紫外脉冲激光源淀积生长氧化物薄膜的技术，我们在ＳｉＴｉＯ３衬底上成功地外延生长了超薄超导ＹＢａ０．２Ｃｕ３Ｏ７薄膜样品．样品ＹＢａ０．２Ｃｕ３Ｏ７层厚度分别为２．４ｎｍ至１０．８ｎｍ（二至九个原胞）．四端引线电阻法测量了样品的电阻温度关系和超导转变．超导零电阻温度分别为１６Ｋ至８１Ｋ．超薄超导薄膜样品显示当ＹＢａ０．２Ｃｕ３Ｏ７层厚度达到和超过四个原胞层厚（９．６ｎｍ）时，厚度变化对样品超导零电阻转变的影响并不十分明显．实验观察到ＹＢａ０．２Ｃｕ３Ｏ７层厚度对样品超导零电阻温度和超导起始转变影响不同．这说明样品中的缺陷对样品性能有着不容忽视的影响．超薄ＹＢａ０．２Ｃｕ３Ｏ７超导薄膜样品的成功制备为进一步的研究提供了有利条件．     

钙钛矿结构氧化物薄膜 的外延生长

在成功地外延生长超导、铁电、铁磁等多种性质的钙钛矿结构氧化物薄膜的基础上,讨论影响氧化物薄膜 外延生长的一些因素.考虑到相形成和薄膜长征动力学,在利用脉冲激光淀积法外延生长氧化物薄膜中衬底温度是十分重要的工艺参数.衬底温度对成相和生长薄膜的取向都有影响.考虑到薄膜是首先在衬底表面成核、成相并生长.因此衬底材料晶格的影响是不容忽视的.观察到衬底材料对薄膜外延生长温度的影响.在适当的工艺条件下,利用低温三步法工艺制备得到有很强织构的外延薄膜.这突出表明界面层的相互作用对钙钛矿结构薄膜的取向有着相当大的影响. 关键词：     

n型掺杂半导体In/Nb-SrTiO3金属异质结变温J～V特性的研究

利用Nb替代Ti的导电Nb-SrTiO3(Nb-STO)衬底我们制备得到了Nb-STO/金属异质结并测量了异质结的J～V曲线.氧化物半导体Nb-STO/金属异质结的J～V曲线显示出与由Schottky势垒模型描述的理想半导体/金属二极管有很多不同.利用对数据拟合的结果,我们讨论了与理想半导体模型的差别.在Nb-STO作为新的氧化物半导体材料被引入器件时,偏离理想的半导体模型应该是正常的.