Enhanced anomalous diffusion of sputtered atoms in nanosized pores

Plasma sputtering deposition of platinum catalysts in porous anodic aluminum oxide (AAO) templates is shown to generate an anomalous superdiffusion concentration profile. The growth of an overlayer between the hexagonal array of pores is shown to enhance the diffusion into the pores, leading to a diffusion coefficient having superlinear time dependence. The Pt clusters in the pores have a mean size of 10 nm and almost concentrate on the inner pore surface, and are present up to a depth of 6 μm.     

二维宽带相位梯度超表面设计及实验验证

针对圆极化波, 通过同极化反射超表面结构单元的空间排布, 设计实现了一种二维非色散高效相位梯度超表面. 同极化反射相位可以通过同极化反射超表面结构单元金属线的面内旋转来自由调控. 实现的相位梯度超表面可对左右旋入射波产生相反的相位梯度. 当线极化波入射到超表面上时, 反射波被分为两束向相反方向传播的圆极化波. 仿真了线极化波垂直入射时的反射功率密度谱, 仿真结果与理论上设计的异常反射方向一致. 制作了厚度为2 mm的超表面样品, 测试了其镜面反射率曲线. 实验结果表明, 线极化波垂直入射时, 超表面在9.5-19.0 GHz的镜面反射率降至-5 dB以下.     

MgO/Pt界面对增强Co/Ni多层膜垂直磁各向异性及热稳定性的研究

采用直流磁控溅射法在玻璃基片上制备了Pt底层和MgO/Pt双底层的Co/Ni多层膜样品, 通过反常霍尔效应研究了不同MgO厚度和退火温度对样品垂直磁各向异性(perpendicular magnetic anisotropy, PMA)的影响. 随着底层中MgO厚度的逐渐增加, 样品的矫顽力也随之增强, 霍尔电阻变化不大; 对样品进行退火处理后发现, 单纯Pt底层的Co/Ni多层膜随着退火温度的升高, 霍尔电阻逐渐降低, 矫顽力则迅速降低, 热稳定性较差; 而当MgO/Pt双底层的样品在200 ℃退火后矫顽力大幅增加, 霍尔电阻略微有所减小, 更高的退火温度使得Co和Ni合金化, 导致多层膜的PMA特征减弱.     

A crystal plasticity finite element model for flow stress anomalies in Ni3Al single crystals

This paper presents a dislocation density-based non-Schmid constitutive model to address the anomalous thermo-mechanical behaviour of the L1₂ intermetallic single-crystal Ni₃Al. Ni₃Al is used as a strengthening precipitate (γ′ phase) in Ni-based superalloys. Addressing such anomalous behaviour by accounting for temperature-dependent flow stress and hardening evolution, as well as orientation-dependent tension–compression asymmetry, is necessary for modelling superalloys across a range of temperatures. While hardening in cube-slip systems results from statistically stored dislocations (SSDs), hardening in octahedral slip systems is due to both SSDs and cross-slip dislocations (CSDs). The constitutive model incorporates hardening evolution due to SSDs and CSDs. Experimental data for Ni₃Al-type single crystals, available in the literature, are used to calibrate material parameters. Subsequently, results of crystal plasticity FEM simulations are compared with experimental data for several orientations under constant strain rate and creep loading conditions for a wide range of temperatures. The model is able to correctly predict the response of L1₂ intermetallic single crystals including features of anomalous flow stress and non-Schmid yield behaviour.     

Pressure tuning of the anomalous Hall effect in the kagome superconductor CsV3Sb5

Controlling the anomalous Hall effect(AHE)inspires potential applications of quantum materials in the next generation of electronics.The recently discovered quasi-2D kagome superconductor CsV₃Sb₅ exhibits large AHE accompanying with the charge-density-wave(CDW)order which provides us an ideal platform to study the interplay among nontrivial band topology,CDW,and unconventional superconductivity.Here,we systematically investigated the pressure effect of the AHE in CsV₃Sb₅.Our high-pressure transport measurements confirm the concurrence of AHE and CDW in the compressed CsV₃Sb₅.Remarkably,distinct from the negative AHE at ambient pressure,a positive anomalous Hall resistivity sets in below 35 K with pressure around 0.75 GPa,which can be attributed to the Fermi surface reconstruction and/or Fermi energy shift in the new CDW phase under pressure.Our work indicates that the anomalous Hall effect in CsV₃Sb₅ is tunable and highly related to the band structure.     

Current carrying states in the disordered quantum anomalous Hall effect

In a quantum Hall effect, flat Landau levels may be broadened by disorder. However, it has been found that in the thermodynamic limit, all extended (or current carrying) states shrink to one single energy value within each Landau level. On the other hand, a quantum anomalous Hall effect consists of dispersive bands with finite widths. We numerically investigate the picture of current carrying states in this case. With size scaling, the spectrum width of these states in each bulk band still shrinks to a single energy value in the thermodynamic limit, in a power law way. The magnitude of the scaling exponent at the intermediate disorder is close to that in the quantum Hall effects. The number of current carrying states obeys similar scaling rules, so that the density of states of current carrying states is finite. Other states in the bulk band are localized and may contribute to the formation of a topological Anderson insulator.     

在冲击载荷作用下弹塑性圆板的反直观动力行为数值分析

对周边简支理想弹塑性圆板受脉冲载荷作用时的动力行为进行了数值计算与分析,揭示了板类结构反直观动力行为的客观存在性．通过分析发现,随着脉冲强度的增加,存在几个窄的载荷区域,板的响应是反直观的,而且在此附近,结构参数、载荷等因素的微小改变将导致响应模式的很大差异,表明反直观行为对这些参数的极其敏感性．进一步计算表明,这一特殊的动力行为主要与板内力间的相互耦合作用密切相关,同时,卸载后的结构反弹到另一侧时发生较大的反向塑性变形,导致能量的进一步耗散,使板呈现反常的动力响应．这一现象是几何与材料两种非线性相互作用的结果。     

Intensity‐Enhanced Apodization Effect on an Axially Illuminated Circular‐Column Particle‐Lens

A particle can function as a refractive lens to focus a plane wave, generating a narrow, high intensive, weak‐diverging beam within a sub‐wavelength volume, known as the ‘photonic nanojet’. It is known that apodization method, in the form of an amplitude pupil‐mask centrally situated on a particle‐lens, can further reduce the waist of a photonic nanojet, however, it usually lowers the intensity at the focus due to blocking the incident light. In this paper, the anomalously intensity‐enhanced apodization effect was discovered for the first time via numerical simulation of focusing of the axially illuminated circular‐column particle‐lenses, and a greater than 100% peak intensity increase was realised for the produced photonic nanojets.     

托卡马克离子温度梯度湍流输运同位素定标修正中杂质的影响

托卡马克实验发现,在不同参数条件下,等离子体能量约束经验定标律会有或大或小的修正.为解释这种修正现象发生的原因,应用回旋动理学方法,对含重(钨)杂质等离子体离子温度梯度(ITG)(包括杂质模)湍流输运的同位素效应进行了数值研究.结果表明钨杂质效应极大地修改了同位素定标律和有效电荷效应.随着杂质离子电荷数Z和电荷集中度f_z的变化,同位素定标律在较大范围内变化. ITG模最大增长率定标大约为M_i~(-0.48→-0.12),杂质模的定标为M_i~(-0.46→-0.3),其中, M_i表示主离子质量数.在ITG模湍流中,有效电荷数越大,关于M_i的拟合指数偏离-0.5越远,表现为同位素质量依赖减弱.在两种模中,杂质电荷集中度越大,同位素质量依赖越弱.研究了杂质效应使定标关系发生偏离的原因,证实杂质种类、杂质电荷数和杂质浓度的不同,是引起同位素质量依赖发生改变的重要原因.结果证实并解释了不同参数条件下托卡马克同位素定标的差异性.研究成果可以为ITER实验安排及杂质相关输运实验中选择装置材料、工作气体和设置其他参数提供理论参考.     

基于啁啾相移光纤光栅的滤波器设计及应用

相移光纤光栅作为透射型带通滤波器件降低了使用成本和插入损耗.在光通信和传感领域有着较高的应用价值.啁啾相移光纤光栅的透射峰波长和数量由相移点的位置和数量来确定,透射峰特性受相移量的影响.采用分段切趾的方法获得满足光通信要求的滤波特性,利用传输矩阵法分析了切趾前后透射峰特性的变化,结果表明:切趾改善了滤波器的幅度和相位响应,依据滤波器的设计要求选取不同的切趾函数以及切趾比例;切趾还大大减弱了透射峰波长和深度对相移量的敏感度,适当切趾后相移量的影响可以忽略.并提出一种应用双通道啁啾相移光纤光栅滤波器产生脉冲毫米波副载波信号的方案.