Paired composite fermion phase of quantum Hall bilayers at nu=1/2+1/2

We provide numerical evidence for composite fermion pairing in quantum Hall bilayer systems at filling nu=1/2+1/2 for intermediate spacing between the layers. We identify the phase as p_(x)+ip_(y) pairing, and construct high accuracy trial wave functions to describe the ground state on the sphere. For large distances between the layers, and for finite systems, a competing "Hund's rule" state, or composite fermion liquid, prevails for certain system sizes.     

VO$lt;sub$gt;2$lt;/sub$gt;/AZO复合薄膜的制备及其光电特性研究

采用直流磁控溅射和后退火氧化的方法在掺铝氧化锌(AZO)导电玻璃上制备了二氧化钒(VO₂)薄膜,研究了不同的退火温度、退火时间对VO₂/AZO复合薄膜制备的影响,并对复合薄膜的结构、组分、光电特性进行了测试与分析. 结果表明,导电玻璃上的AZO没有改变VO₂的取向生长,但明显改变了VO₂薄膜的表面形貌特征. 与用相同工艺和条件在普通玻璃基底上制备的VO₂薄膜相比,VO₂/AZO复合薄膜的相变温度降低约25 ℃,热滞回线宽度收窄至6 ℃,相变前后可见光透过率均在50%以上,1500 nm处红外透过率约为55%和21%,电阻率变化达3 个数量级. 该复合薄膜表面平滑致密,制备工艺简单,性能稳定,可应用于新型光电器件. 关键词： 2')" href="#">VO₂ AZO 热致相变 光电特性     

Study of 1-3 PZT fibre/epoxy composite force sensor

Lead zirconate titanate (PZT) fibres were prepared by a powder-based extrusion method. Pre-sintered PZT powder mixed with poly(acrylic acid) was spun in a spinnerette to produce fibres. The fibre of ∼400 μm diameter was used to fabricate 1-3 PZT fibre/epoxy composite discs with different volume fractions (ϕ) of PZT. Since the ceramic fibres are rather brittle, their elastic properties cannot be measured directly. In order to determine the properties of the ceramic fibres, effective properties of the fibres/epoxy 1-3 composite were measured. By using a modified series and parallel model, the properties of 1-3 composites can be calculated. Then, the elastic coefficient s_33,fibre^E, relative permittivity ε_33,fibre^T and piezoelectric strain coefficient d_33,fibre of the ceramic fibre could be found. Ring-shaped PZT fibre/epoxy materials composites with different ϕ were fabricated to be used as the sensing material in force sensor applications. The ring-shape composite with ϕ=0.5 was installed into a housing and the sensor was calibrated by different methods and its sensitivity was found to be 144 pC/N within the frequency range of 0.5–6.4 kHz which is much higher than that of a quartz force sensor with a similar structure. PACS 07.07.Df; 72.80.Tm; 77.84.Dy     

Thermal quantum correlations of a spin-1/2 Ising-Heisenberg diamond chain with Dzyaloshinskii-Moriya interaction

We investigate the properties of thermal quantum correlations in an infinite spin-1/2 Ising-Heisenberg diamond chain with Dzyaloshinskii-Moriya(DM) interaction. The thermal quantum discord(TQD) and the thermal entanglement(TE)are discussed as two kinds of important methods to measure the quantum correlation, respectively. It is found that DM interaction plays an important role in the thermal quantum correlations of the system. It can enhance the thermal quantum correlations by increasing DM interaction. Furthermore, the thermal quantum correlations can be promoted by tuning the external magnetic field and the Heisenberg coupling parameter in the antiferromagnetic system. It is shown that the behaviors of TQD differ from those of TE. TQD is more robust against decoherence than TE. For the measurement of TQD, the "regrowth" phenomenon occurs in the ferromagnetic system. We also find that the anisotropy favors the thermal quantum correlations of the system with weak DM interaction.     

ZnSe/SiO2复合薄膜光学常数与荧光光谱的研究

采用溶胶-凝胶工艺与原位生长技术，制备了ZnSe/SiO₂复合薄膜.X射线衍射分 析表明薄膜中ZnSe晶体呈立方闪锌矿结构.X射线荧光分析结果显示薄膜中Zn与Se摩尔比为1 ∶1.01—1∶1.19.利用场发射扫描电子显微镜观察了复合薄膜的表面形貌，结果表明复合薄 膜表面既存在尺寸约为400nm的ZnSe晶粒，也存在尺寸小于100nm的ZnSe晶粒.利用椭偏仪测 量了薄膜椭偏角Ψ，Δ与波长λ的关系，采用Maxwell-Garnett有效介质理论对薄膜的光学 常数、厚度、气孔率、ZnS 关键词： 2复合薄膜')" href="#">ZnSe/SiO₂复合薄膜 光学性质 椭偏光度法 荧光光谱     

NMR determination of 2D electron spin polarization at nu = 1/2

Using a "standard" NMR spin-echo technique we determined the spin polarization P of two-dimensional electrons, confined to GaAs quantum wells, from the hyperfine shift of Ga nuclei located in the wells. Concentrating on the temperature ( 0.05 less, similarT less, similar10 K) and magnetic field ( 7 less, similarB less, similar17 T) dependencies of P at Landau level filling factor nu = 1/2, we find that the results are described well by a simple model of noninteracting composite fermions, although some inconsistencies remain when the two-dimensional electron system is tilted in the magnetic field.     

Enhanced electrochemical performance of sulfur/polyacrylonitrile composite by carbon coating for lithium/sulfur batteries

A carbon-coated sulfur/polyacrylonitrile (C@S/PAN) core-shell structured composite is successfully prepared via a novel solution processing method. The sulfur/polyacrylonitrile (S/PAN) core particle has a diameter of ~ 100 nm, whereas the carbon shell is about 2 nm thick. The as-prepared C@S/PAN composite shows outstanding electrochemical performance in lithium/sulfur (Li/S) batteries delivering a high initial discharge capacity of 1416 mAh g^?1. Furthermore, it exhibits ~ 89% retention of the initial reversible capacity over 200 cycles at a constant current rate of 0.1 C. The improved performance contributed by the unique composition and the core-shell structure, wherein carbon matrix can also withstand the volume change of sulfur during the process of charging and discharging as well as provide channels for electron transport. In addition, polyacrylonitrile (PAN) matrix suppresses the shuttle effect by the covalent bonding between sulfur (S) and carbon (C) in the PAN matrix.

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Graphical abstract Cycling performance of the S/PAN and C@S/PAN electrodes and TEM image of the C@S/PAN composite.

     

ZnO/SiO2 复合薄膜的光学性能

采用溶胶-凝胶法在玻璃衬底上制备ZnO/SiO₂复合薄膜,分别用XRD、TEM、SEM对样品的结构和形貌进行表征,并研究了不同ZnO含量对复合薄膜透过率及荧光特性的影响。结果表明,样品经500 ℃退火处理生成了SiO₂和ZnO,其晶粒尺寸为18.7 nm,薄膜具有双层结构。复合薄膜的透过率随着其中ZnO含量的增加而降低,禁带宽度减小,光学吸收边红移。样品在355 nm波长激发下产生了384 nm的紫外发射峰和440 nm的蓝光发射带,并随ZnO含量的增加而增强,它们分别来自ZnO的电子-空穴复合发光和缺陷发光,及ZnO/SiO₂复合薄膜双层结构的缺陷发光。     

Self-diffusion in core-shell composite 12CO2/13CO2 nanoparticles

A new technique for the generation of multilayered molecular nanoparticles is presented. Core-shell composite nanoparticles of CO(2) with varied composition have been investigated by Fourier-transform infrared spectroscopy over 600 s at 78 K. The isotopically different zones of the particles turned out to have completely different spectra in the nu(3) region: a tub structure (mantle) and a head-and-shoulders structure (core). From the aggregation behavior of both components the particle formation time was found to be 0.1 s. Low-temperature self-diffusion of airborne molecular nanoparticles has been monitored for the first time. The self-diffusion coefficient for (12)CO(2)/(13)CO2 nanocomposites at 78 K was determined from the time evolution of the nu(1) + nu(3) combination band to about 7 x 10(-20) m(2)/s. The work represents a major advance toward nanoengineering of molecular nanoparticles at low temperatures.     

Hg~+离子5d~(10)6s ~2S_(1/2)→5d~96s~2 ~2D_(5/2)钟跃迁同位素位移和超精细结构的理论研究

本文首先在Dirac-Hartree-Fock近似下理论评估了Hg~+离子5d~(10)6s ~2S_(1/2)→5d~96s~2 ~2D_(5/2)钟跃迁的质量位移(mass shift, MS)和场位移(field shift, FS)在其同位素位移(isotope shift, IS)中的相对贡献,发现MS远小于FS而可以被忽略.在此基础上,通过系统地考虑该原子体系中主要的电子关联效应,计算了这条钟跃迁FS的精确值以及涉及到的上下两个能级的超精细结构常数,并得到了几种稳定汞同位素离子该跃迁的IS和超精细结构分裂.其中,计算的~(199)Hg~+和~(198)Hg~+离子之间的钟跃迁频率偏移与已有实验测量值相比误差为2%左右.最终,本文给出了汞离子7种常见同位素该谱线的绝对频率值,为实验上的谱线测量提供了有效的理论依据.     

Electrospun nanofibers of NiO/SiO2 composite

Composite nanofibers with a weight ratio of 30%NiO-70%SiO₂ and diameters ranging from 80 to 100 nm were successfully prepared by electrospinning a precursor mixture of polyvinyl alcohol (PVA)/silica/nickel acetate followed by calcination treatment of the electrospun polymer/inorganic composite fibers. The resulting NiO/SiO₂ composite nanofibers were characterized by TG-DTA, FT-IR spectroscopy, X-ray diffraction and scanning electron microscopy . The results revealed that the crystalline phase of NiO nanoparticles were formed at a temperature higher than 600 °C. The SEM results show that the morphology of the fibers is affected greatly by the calcination temperature.     

复合Ag/SiO_2正弦光栅基底SERS特性分析

当前微流控表面增强拉曼散射(SERS)检测领域常用的贵金属纳米颗粒溶胶单位体积内热点区域数量有限且热点区域范围较小,而贵金属纳米三维阵列结构加工时间长,成本高昂并存在"记忆效应"。本文提出了集成到微流道的复合Ag/SiO_2正弦光栅SERS基底结构,可以利用激光干涉光刻技术进行制备,无需预制掩膜版,可实现大面积、低成本SERS基底简易快速制备。利用严格耦合波分析方法(RCWA)建立了复合正弦光栅表面电场增强数学评估模型,推导了表面等离子体共振(SPP)耦合吸收率数学模型,分析了入射光、复合正弦光栅结构与外界环境介电常数的优化匹配关系,得到了入射光785 nm条件下的最佳复合正弦光栅结构。通过制备加工并实验验证了复合正弦光栅的SERS性能,SERS增强因子(EF)能够达到10~4。     

Preparation and properties of electroless Ni-P-SiO2 composite coatings

Dispersible SiO₂ nanoparticles were co-deposited with electroless Ni-P coating onto AISI-1045 steel substrates in the absence of any surfactants in plating bath. The resulting Ni-P/nano-SiO₂ composite coatings were heat-treated for 1 h at 200 °C, 400 °C, and 600 °C, respectively. The hardness and wear resistance of the heat-treated composite coatings were measured. Moreover, the structural changes of the composite coatings before and after heat treatment were investigated by means of X-ray diffraction (XRD), while their elemental composition and morphology were analyzed using an energy dispersive spectrometer (EDS) and a scanning electron microscope (SEM). Results show that co-deposited SiO₂ particles contributed to increase the hardness and wear resistance of electroless Ni-P coating, and the composite coating heat-treated at about 400 °C had the maximum hardness and wear resistance.     

Bipartite composite fermion States

We study a class of ansatz wave functions in which composite fermions form two correlated "partitions." These "bipartite" composite fermion states are demonstrated to be very accurate for electrons in a strong magnetic field interacting via a short-range 3-body interaction potential over a broad range of filling factors. Furthermore, this approach gives accurate approximations for the exact Coulomb ground state at 2+3/5 and 2+4/7 and is thus a promising candidate for the observed fractional quantum Hall states at the hole conjugate fractions at 2+2/5 and 2+3/7.     

Electrodeposited nickel-cobalt composite coating containing MoS2

Ni-Co/MoS₂ composite coatings were prepared by electrodeposition in a Ni-Co plating bath containing nano-sized MoS₂ particles to be co-deposited. The polarization behavior of the composite plating bath was examined on a PAR-273A potentiostat/galvanostat device. The friction and wear behaviors of the Ni-Co/MoS₂ composite coatings were evaluated with UMT-2MT test rig in a ball-on-disk contact mode. The morphologies of the original and worn surfaces of the composite coatings were observed on scanning electron microscope (SEM). It was found that the introduction of MoS₂ nano-particulates in the electrolyte caused the shift towards larger negatives of the reduction potential of the Ni-Co alloy coating, and the co-deposited MoS₂ showed no significant effect on the electrodeposition process of the Ni-Co alloy coating. However, the co-deposited MoS₂ led to changes in the surface morphology and structure of the composite coating as well. Namely, the peak width of the Ni-Co solid solution for the composite coating is broader as compared to that of the Ni-Co alloy coating. The co-deposited MoS₂ particulates were uniformly distributed in the Ni-Co matrix and contributed to increase tribological properties of the Ni-Co alloy coating.     

NiFeCoP/BeCu复合结构丝的巨磁阻抗效应和磁化频率特性

用化学镀的方法制备了NiFeCoP/CuBe复合结构丝，研究了其巨磁阻抗特性.结果表明复合结构丝在较低频率的驱动电流下就有明显的磁阻抗效应，当驱动电流频率在20kHz时的磁阻抗效应为40％，最大磁阻抗效应出现的频率在180kHz，为97％.利用复数磁导率和等效电路探讨了该复合丝铁磁层磁化过程的频率特性，复合结构丝的特征弛豫频率在1MHz左右.外加直流磁场抑制畴壁移动，在等效电路中与抵消部分并联电路相关. 关键词： 巨磁阻抗效应 磁导率 弛豫频率 等效电路     

Synthesis of PAN/SnCl2 composite as Li-ion battery anode material

A novel process was proposed to synthesize the pyrolytic polyacrylonitrile (PAN)/SnCl₂ composite anode material for Li-ion batteries. The preparation started with the dissolution of PAN and SnCl₂ in dimethylformamide (DMF), followed by drying of the solution and pyrolysis of the dried mixture of PAN and SnCl₂ at 300 °C, leading to homogenous dispersal of SnCl₂ in pyrolytic PAN, which becomes conducting polymer matrix. The composite presented stable cycling capacity of about 490 mAh/g. It is demonstrated that SnCl₂, which has been considered to be an inactive electrode material, can become active by the proposed composite technique. This paves the promising way to prepare electrode materials for Li-ion batteries.     

Observation of negative refraction in the graphene/ferrite composite

An observation of negative refraction in the naturally obtained composition of graphene and barium ferrite is reported. The capacitance and inductance measurements revealed the electric and magnetic resonances accompanied with the negative values of permittivity and permeability in the overlapped frequency range. According to the “left‐handed” media approach such a material is characterized by negative refraction. The derived values of the real part of refractive index are negative at the frequencies above 500 MHz.

     

Studies of the electrochemical properties and thermal stability of LiNi1/3Co1/3Mn1/3O2/LiFePO4 composite cathodes for lithium ion batteries

A series of LiNi_1/3Co_1/3Mn_1/3O₂/LiFePO₄ composite cathodes with the LiFePO₄ mass content ranging from 10 to 30 wt% were prepared by ball milling in order to combine the merits of layered LiNi_1/3Co_1/3Mn_1/3O₂ and olivine LiFePO₄. The structure and morphology of the samples were characterized by X-ray diffraction and scanning electron microscope. The composite cathodes exhibited improved electrochemical performance compared with pristine LiNi_1/3Co_1/3Mn_1/3O₂. Among all the composite cathodes, the one with 20 wt% of LiFePO₄ showed the best electrochemical performance in terms of discharge capacity, cycle stability, and rate capability. Electrochemical impedance spectroscopy showed that mixing of LiFePO₄ in LiNi_1/3Co_1/3Mn_1/3O₂ decreased the internal resistance of the electrode, retarded the formation of SEI film, and facilitated the charge transfer reaction. Differential scanning calorimetry showed that the composite cathode had better thermal stability than pristine LiNi_1/3Co_1/3Mn_1/3O₂.