Correlation between Thermal Expansion and Magnetic Characteristics of Fe-Ni Alloys in Fe_(1-x)Ni_x/Cu Superlattices

Thermal expansion behaviors of FeNi alloys were investigated by means of X-ray diffraction technique within a Fe1 -xNix/Cu superiattice structure. It was found that with a Ni concentration of x = 0.35, FeNi alloy layers showed the well-known Invar behavior, but for alloy layers with either lower or higher Ni concentrations, thermal expansion coefficients were larger. Based on results of magnetic measurements it is concluded that FeNi alloy layers with Ni concentrations lower than the Invar composition are in a superparamagnetic state which leads not only to low spontaneous magnetizations but also to large thermal expansions of the alloy layers.     

Prediction for Pareto distribution based on progressively Type-II censored samples

In this paper, we discuss different predictors of times to failure of units censored in multiple stages in a progressively censored sample from Pareto distribution. The best linear unbiased predictors, maximum likelihood predictors and approximate maximum likelihood predictors are considered. We also present two methods for obtaining prediction intervals for the times to failure of units. A numerical simulation study involving two data sets is presented to illustrate the methods of prediction.     

一种支持用户偏好的RDF模糊查询方法

RDF模糊查询是实现语义Web智能检索的重要组成部分,利用Zadeh的Ⅱ型模糊集合理论、α-截集及语言变量概念,提出了支持用户偏好的RDF模糊查询方法,其扩展了SPARQL语言来实现模糊及偏好表达,构造了有序语言值子域表来实现模糊值到相应子域的映射,以确定隶属度区间。利用去模糊化规则,将扩展的查询转换为标准SPARQL,利用现有的SPARQL查询引擎实现模糊查询操作。为验证提出的方法,开发了fp-SPARQL实验系统。实验结果表明,该方法提高了RDF模糊查询效率,增强了用户对查询结果的满意度。     

长/长波双色二类超晶格红外探测器研究

报道了长/长波双色二类超晶格红外焦平面探测器组件的研制。通过能带结构设计和分子束外延技术,获得了表面质量良好的长/长波双色超晶格外延材料。突破了长波超晶格低暗电流钝化、低损伤干法刻蚀等关键技术,制备出像元中心距30 μm的320×256长/长波双色InAs/GaSb超晶格焦平面探测器芯片。将芯片与双色读出电路互连,采用杜瓦封装,与制冷机耦合形成探测器组件。组件双波段50%后截止波长分别为7.7 μm（波段1）和10.0 μm（波段2）。波段1平均峰值探测率达到8.21×10¹⁰ cmW^-1Hz^1/2,NETD实现28.8 mK;波段2平均峰值探测率达到6.15×10¹⁰ cmW^-1Hz^1/2,NETD为37.8 mK,获得了清晰的成像效果,实现长/长波双色探测。     

InAs/GaSb Ⅱ类超晶格长波红外探测器的表面处理研究

开展了In As/Ga Sb Ⅱ类超晶格长波红外探测器的表面处理研究。通过对不同处理工艺形成台面器件的暗电流分析,发现N₂O等离子处理结合快速热退火(RTA)的优化工艺能够显著改善长波器件电学性能。对于50%截止波长12.3μm的长波器件,在液氮温度,-0.05 V偏置下,表面处理后暗电流密度从5.88×10^-1 A/cm²降低至4.09×10^-2 A/cm²,零偏下表面电阻率从17.7Ωcm提高至284.4Ωcm,有效降低侧壁漏电流。但是该表面处理后的器件在大反偏压下仍有较大的侧壁漏电,这可能是由于高浓度的表面电荷使得大反偏下侧壁存在较高的隧穿电流。通过栅控结构器件的变栅压实验,验证了长波器件存在纯并联电阻及表面隧穿两种主要漏电机制。最后,对表面处理前后的暗电流进行拟合,处理后器件表面电荷浓度为3.72×10¹¹ cm^-2。     

双层亚铁磁体超晶格的能谱

对双层亚铁磁超晶格的能谱进行理论研究.采用海森堡模型，利用线性自旋波近似、傅立叶变换和格林函数技术计算出色散关系和外磁场的临界值Bc.结果表明，系统的各个参数如：自旋量子数、层间交换耦合系数、层内交换耦合系数、各向异性参数、外磁场都对系统的磁性有着重要的影响.研究发现，当两个层的自旋量子数相等时，两个能谱简并，当两个层的自旋量子数不相等时，能谱分裂.一般情况下，两支能谱随着层间交换耦合系数、层内交换耦合系数和各项异性参数的增强而差值加大.外磁场的临界值Bc随各向异性参数D1和D2数值的增加而增强，随自旋量子数的增加而增加.层间交换耦合系数与层内交换耦合系数对外磁场的临界值Bc不产生影响.     

Dependence of elastic strain field on the self-organized ordering of quantum dot superlattices

A systematic investigation of the strain distribution of self-organized, lens-shaped quantum dot in the case of growth di- rection on (001) substrate was presented. The three-dimensional finite element analysis for an array of dots was used for the strain calculation. The dependence of the strain energy density distribution on the thickness of the capping layer was investigated in detail when the elastic characteristics of the matrix material were anisotropic. It is shown that the elastic anisotropic greatly influences the stress, strain, and strain energy density in the quantum dot structures. The anisotropic ratio of the matrix material and the combina- tion with different thicknesses of the capping layer, may lead to different strain energy density minimum locations on the capping layer surface, which can result in various vertical ordering phenomena for the next layer of quantum dots, i.e. partial alignment, ran- dom alignment, and complete alignment.     

MOCVD外延Al_2O_3基AlGaN/GaN超晶格的结构和光学特性

通过X射线衍射分析、透射电镜观察、红外透射光谱分析、紫外-可见吸收光谱分析和光致发光试验,研究了用金属有机物化学汽相沉积(MOCVD)的方法,在带有GaN缓冲层的蓝宝石(Al2O3)衬底上生长的AlGaN/GaN超晶格材料的微观结构、光吸收性质和发光特性。X射线衍射结果表明,GaN基材料均为纤锌矿六方结构,薄膜具有良好的结晶质量,薄膜生长沿c轴择优取向。透射电镜观察表明,超晶格试样的周期结构分布均匀,实际周期为13.3nm,且观察到高密度的位错存在于外延膜中。通过光学试验数据,确定了试样的光学吸收边都是在370nm附近,理论计算显示试样为直接跃迁型半导体,禁带宽度约为3.4eV。试样的折射率随光子能量的增加而增加、随波长的增加而减小,计算表明消光系数的极小值位于370nm处。光致发光测试分析表明,超晶格有很好的发光性能,并发现存在黄带发光。     

In-situ ellipsometric measurements of the MBE growth of CdTe/HgTe and CdTe/ZnTe superlattices

Phase modulated ellipsometric data recorded during molecular beam epitaxial growth of CdTe/HgTe and CdTe/ZnTe superlattices on (100) and (211)B oriented Cd_0.96Zn_0.04Te and GaAs substrates are presented. The measurements provide a continuous monitor of the growth process, thickness, growth rate, compositional data, and evidence of interdiffusion in CdTe/HgTe superlattices at elevated temperatures. The thickness measurements are independent of growth kinetics and surface orientation and agree well with those obtained from x-ray diffraction and reflection high energy electron diffraction. Ellipsometry shows that the incorporation of Hg in CdTe is significantly higher on (100) oriented surfaces than on (211)B oriented surfaces. Fine structure in the data from CdTe/ZnTe superlattices may be associated with a surface reconstruction during deposition of each CdTe layer. The experimental results for CdTe/HgTe superlattices compare well with results of thin film multi-layer calculations. The general applicability of ellipsometry as an in-situ analytical technique for epitaxial growth of a range of semiconductor superlattices is discussed.