Al、Co和Mn掺杂对LiNiO2结构的影响

本文采用XRD和EXAFS研究Al、Co和Mn原子掺杂对LiNiO₂材料结构的影响。XRD结果表明掺杂材料具有与LiNiO₂相同的晶体结构，都属于R3m点群，但是晶胞略微缩小，LiNiO₂的层状结构得到改善,阳离子有序度增强。从EXAFS数据拟合结果可以看出，引入掺杂原子Al、Co和Mn减弱了Jahn-Teller畸变，使得NiO₆八面对称性提高。掺杂Al和Co使得第一壳层Ni-O配位键长减小，掺杂Mn原子影响不明显。Al、Co和Mn掺杂使第二壳层Ni-Ni配位键长减小，Co和Mn掺杂使得第二壳层局域有序度提高，而Al的引入使得第二壳层局域有序度降低。     

基于Si3N4/SiNx/Si3N4三明治结构的偏振无关1×2多模干涉型解复用器的设计

提出一种基于Si3N4/SiNx/Si3N4三明治结构多模干涉波导的偏振无关1×2解复用器,用于分离1310和1550 nm两个波长.通过合理选择三明治结构中间层SiNx的折射率,可以调节同一波长两个正交偏振态的拍长相等,实现偏振无关;根据多模干涉原理,通过合理选择多模干涉波导的长度与宽度,可以使两个波长的输出像点分别成正像和反像,实现解复用功能.运用三维有限时域差分法进行建模仿真,对结构参数进行优化,并对器件关键结构参数的制作容差进行了分析.结果表明:该器件多模干涉波导的尺寸为4.6μm×227.7μm,插入损耗低至0.18dB,输出波导间的串扰低至–25.7dB, 3dB带宽可达60 nm.另外,本文提出的器件采用Si3N4/SiO2平台,可有效减小波导尺寸,提高集成度,不仅实现了偏振无关,而且结构紧凑、损耗低,在未来的集成光路中具有潜在的应用价值.     

基于多精度代理模型的高效异型气膜孔设计优化和实验验证

为了提升燃气轮机热端部件表面的气膜冷却效果,本文发展了一套基于多精度代理模型的高效气膜孔优化方法,通过对气膜孔孔型进行优化得到最优的气膜冷却效率。与传统的代理模型优化方法相比,本文构建的多精度代理模型优化方法能有效结合实验数据与高精度数值计算,在保证准确度的同时使优化效率提升64.5%。本文针对业界广泛使用的一种气膜孔进行优化设计,选取后倾角、侧扩角和孔长径比作为三个设计变量,采用遗传算法和序列二次规划混合方法进行优化。并采用3D打印和PSP测量技术对优化孔型进行验证,发现和初始孔型相比优化孔型的面平均气膜冷却效率提升39%。本文的工作证明了多精度代理模型在气膜冷却优化方面的有效性。     

X射线衍射增强成像中的信息分离和信息处理

人们已经利用X射线的高穿透性,发展了较为成熟的X射线成像理论和技术. X射线成像已经广泛应用于众多领域.传统X射线成像受生物样品中组织间吸收系数差别较小和散射噪声较大两个因素的限制,不易利用这种方法获得生物组织的信息. 衍射增强成像方法不但能将有害的散射噪声滤除,而且能利用样品的折射信息, 是一种具有发展潜力的新成像方法. 本文利用衍射增强成像, 通过在摇摆曲线不同部位成像, 然后对信息处理, 得到了清晰的吸收像、消光(小角散射滤除)像、小角散射(角)宽度像和折射像,最后通过一定的算法将各种成分的像合成, 形成细节部位清晰的合成伪彩色像.     

Enhanced resistance switching stability of transparent ITO/TiO2/ITO sandwiches

We report that fully transparent resistive random access memory(TRRAM) devices based on ITO/TiO2/ITO sandwich structure,which are prepared by the method of RF magnetron sputtering,exhibit excellent switching stability.In the visible region(400-800 nm in wavelength) the TRRAM device has a transmittance of more than 80%.The fabricated TRRAM device shows a bipolar resistance switching behaviour at low voltage,while the retention test and rewrite cycles of more than 300,000 indicate the enhancement of switching capability.The mechanism of resistance switching is further explained by the forming and rupture processes of the filament in the TiO 2 layer with the help of more oxygen vacancies which are provided by the transparent ITO electrodes.     

Physical properties of FePt nanocomposite doped with Ag atoms:First-principles study

L10FePt nanocomposite with high magnetocrystalline anisotropy energy has been extensively investigated in the fields of ultra-high density magnetic recording media. However, the order–disorder transition temperature of the nanocomposite is higher than 600℃, which is a disadvantage for the use of the material due to the sustained growth of FePt grain under the temperature. To address the problem, addition of Ag atoms has been proposed, but the magnetic properties of the doped system are still unclear so far. Here in this paper, we use first-principles method to study the lattice parameters,formation energy, electronic structure, atomic magnetic moment and order–disorder transition temperature of L10FePt with Ag atom doping. The results show that the formation energy of a Ag atom substituting for a Pt site is 1.309 eV, which is lower than that of substituting for an Fe site 1.346 eV. The formation energy of substituting for the two nearest Pt sites is2.560 eV lower than that of substituting for the further sites 2.621 eV, which indicates that Ag dopants tend to segregate L10FePt. The special quasirandom structures(SQSs) for the pure FePt and the FePt doped with two Ag atoms at the stable Pt sites show that the order–disorder transition temperatures are 1377℃ and 600℃, respectively, suggesting that the transition temperature can be reduced with Ag atom, and therefore the FePt grain growth is suppressed. The saturation magnetizations of the pure FePt and the two Ag atoms doped FePt are 1083 emu/cc and 1062 emu/cc, respectively,indicating that the magnetic property of the doped system is almost unchanged.     

短链烷基对多取代烷基苯磺酸盐界面性质的影响

利用悬挂滴方法研究了2,5-二乙基-4-壬基苯磺酸钠(292)、2,5-二丙基-4-壬基苯磺酸钠(393)和2,5-二丁基-4-壬基苯磺酸钠(494)在空气-水表面和正癸烷-水界面的扩张流变性质,考察了时间、界面压、工作频率及体相浓度对扩张弹性和粘性的影响。研究发现,在低表面活性剂浓度条件下,表面吸附膜类似弹性膜,其强度由膜内分子的相互作用决定;高浓度下体相与表面间的扩散交换过程控制表面膜的性质。油分子的插入导致界面吸附分子之间相互作用的削弱,扩散交换过程主导界面膜性质;但随着短链烷基长度增加,油分子的影响变小。表面膜的强度在吸附达到平衡前已经决定,而界面膜在吸附饱和后仍然随界面分子重排而变化。     

High-Tc ferromagnetism in a Co-doped ZnO system dominated by the formation of a zinc-blende type Co-rich ZnCoO phase

The modulation of the distribution of magnetic ions embedded in the host is crucial for the functionality of dilute magnetic semiconductors. Through an element-specific structural characterization, we observe the formation and enhancement of an unrevealed Co-doped ZnO phase and consequently magnetic properties from paramagnetism to ferromagnetism are controlled by surface-modification.     

XAFS研究不同pH下土壤对Pb的吸附

利用X射线吸收精细结构光谱(XAFS)研究了不同初始pH条件下土壤吸附Pb(Ⅱ)的微观结构及吸附机理。表明土壤对Pb(Ⅱ)的吸附以形成Pb4(OH)44+的内圈吸附作用为主,其次为外圈吸附。同时,在吸附Pb(Ⅱ)过程中,Pb(Ⅱ)通过置换作用取代土壤中碳酸钙Ca(Ⅱ)的位置,形成含Pb碳酸钙(PbCaCO3)沉淀。土壤对Pb的吸附随初始pH(6.0~8.5)的增大,第一配位层(Pb—O)半径减小(0.172 7~0.166 6nm),内圈吸附比重加大,表明土壤对Pb(Ⅱ)的吸附机制受初始pH的影响。     

缺陷分布对Ag-SiO2薄膜电阻翻转效应的影响

通过改变制备条件,研究了Ag-SiO₂薄膜中的缺陷对电阻翻转效应的影响.对比不同的热处理实验条件, 发现在120 ℃退火的样品经forming过程后具有稳定的电阻转变特性;另一方面, 在Ar/O₂混合气氛下生长的SiO₂具有比在纯Ar下生长的样品更加稳定、重复的电阻转变特性. 通过实验分析,表明热处理、电场作用和样品制备气氛可以改变、调节样品中的缺陷分布 (Ag填隙原子和氧空位缺陷),从而导致Ag-SiO₂中基于缺陷的导电通道结构的形成和湮灭, 提出了提高电阻翻转稳定性的必要条件.