Investigation of ultrafast electron dynamics of nickel film and micro-nano-structure film

The electron thermalization and relaxation processes in ferromagnetic nickel thin film and micro-nano- structure film have been studied by measuring the transient change after excitation by a femtosecond laser pulse. The measurements indicate that the electron thermalization time is between 18 and 47 fs. This is somewhat faster than the value reported before. And the thermalization time of the micro-nano-structure film is much longer than the nickel film. We deduce that it is caused by the discontinuity of the electron band close to the Fermi level in the micro-nano-structure nickel film.     

A NEW APPROACH TO STRUCTURES OF NICKEL CLUSTERS

A transferable tight-binding potential for nickel was used with molecular-dynamics methods and simulated-annealing techniques to study the structure properties of nickel clusters Ni_n (n≤55), The mean coordination number and structure of some clusters and their relative stability have been obtained.     

Deposition Behavior and Mechanism of Ni Nanoparticles on Surface of SiC Particles in Solution Systems

Ni-deposited SiC particles are prepared successfully by a facile chemical reaction approach. The structure and morphology analyses demonstrate the Ni nanoparticles have been deposited on the surface of SiC particles. The deposition behavior of Ni on the surface of SiC particles is investigated. Pd-Sn catalytic nuclei formed in the pretreatment process promote the redox reaction and lead to the reduction of Ni^2＋ to metal nickel. Moreover, the kinetic mechanism of the reaction process of Ni%2＋ and H2PO^-2 has also been discussed in detail. Kinetic models have been established.     

Porosity Evaluation and the Power Spectral Densities Analyses of Carbon-Nickel Composite Films Annealed at Different Temperatures

The densification and the fractal dimensions of carbon-nickel films annealed at different temperatures 300,500,800,and 1000℃with emphasis on porosity evaluation are investigated.For this purpose,the refractive index of films is determined from transmittance spectra.Three different regimes are identified,T500℃,500℃T800℃and T800℃.The Rutherford backscattering spectra show that with increasing the annealing temperature,the concentration of nickel atoms into films decreases.It is shown that the effect of annealing temperatures for increasing films densification at T500℃and T800℃is greater than the effect of nickel concentrations.It is observed that the effect of decreasing nickel atoms into films at 500℃T800℃strongly causes improving porosity and decreasing densification.The fractal dimensions of carbon-nickel films annealed from 300 to 500℃are increased,while from 500 to 1000℃these characteristics are decreased.It can be seen that at 800℃,Elms have maximum values of porosity and roughness.     

Micropolarizer of Ordered Ni Nanowire Arrays Embedded in Porous Anodic Alumina Membrane

A micropolarizer of nickel nanowire arrays within an anodic alumina membrane(AAM) was fabricated by anodization of pure Al and electrodeposition of Ni,resperctively,X-ray diffraction,scanning electron microscopy and transmission-electron microscopy reveal that the nanowires are polyscrstal and have an average diameter of 70nm.Spectrophotometer measurements show that the nickel nanowire arrays embedded in the AAM can only transmit polarized light vertical to the wires.An extinction ratio of 25 to 30dB and an average insertion loss of 1.07dB in the wavelength range of 1-2.5um were obtained ,respectively.Thus,Ni nanowire/AAM can be used as a wire grid type micropolarizer.     

Structural and Thermodynamic Properties of Liquid Transition Metals with Different Embedded—Atom Method Models

Pair distribution functions and constant-volume heat capacities of liquid copper,silver and nickel have been calculated by molecular dynamics simulations with four different versions of the embedded-atom method (EAM) model,namely,the versions of Johnson,Mei,Cai and Pohlong,The simulated structural properties with the four potential models show reasonable agreement with experiments and have little difference with each other,while the calculated heat capacities with the different EAM versions show remarkable discrepancies.Detailed analyses of the energy of the liquid metallic system show that,to predict successfully the heat capacity,an EAM model should match the state equation first proposed by Rose.     

Preparation and study on performance of submicron nickel powder for multilayer chip positive temperature coefficient resistance

Base metal nickel is often used as the inner electrode in multilayer chip positive temperature coefficient resistance (PTCR).The fine grain of ceramic powders and base metal nickel are necessary.This paper uses reducing hydrazine to gain submicron nickel powder whose diameter was 200-300 nm through adjusting the consumption of nucleating agent PVP properly.The submicron nickel powder could disperse well and was fit for co-fired of multilayer chip PTCR.It analyes the submicron nickel powder through x-ray Diffraction (XRD) and calculates the diameter of nickel by PDF cards.Using XRD analyses it obtains several conclusions:If the molar ratio of hydrazine hydrate and nickel sulfate is kept to be a constant,when enlarging the molar ratio of NaOH/Ni 2+,the diameter of nickel powder would become smaller.When the temperature in the experiment raises to 70-80 C,nickel powder becomes smaller too.And if the molar ratio of NaOH/Ni 2+ is 4,when molar ratio of (C 2 H 5 O) 2 /Ni 2+ increases,the diameter of nickel would reduce.Results from viewing the powders by optical microscope should be the fact that the electrode made by submicron nickel powder has a better formation and compactness.Furthermore,the sheet resistance testing shows that the electrode made by submicron nickel is smaller than that made by micron nickel.     

Studies on the characteristics of Barkhausen emission and evaluation of the critical fields for domain wall notion in nickel

Acoustic Barkhausen Emission(ABE)and ElectromagneticBarkhausen Emission(EBE)have been measured.Explanations of the re-sponse of nickel to an applied magnetic field are considered using energydensity diagrams and critical fields deduced using Kersten's modifiedtheory.These theoretical models are correlated with ABE and EBEmeasurements,providing further confirmation of the origins of ABE beingnon-180°domain wall motion.This paper also shows that the motion ofdomain walls,on increasing the magnetising fields from saturation to satu-ration,follows the sequence of 71°-180°-109°.Values of criticalfields correponding to 71°,180°and 109°wall motions in nickel are de-termined using these techniques.     

Theoretical study of the hyperfine interaction constants,Landé g-factors,and electric quadrupole moments for the low-lying states of the 61Niq+(q=11,12,14,and 15) ions

Highly charged nickel ions have been suggested as candidates for the ultra-precise optical clock, meanwhile the relevant experiment has been carried out. In the framework of the multiconfiguration Dirac–Hartree–Fock(MCDHF)method, we calculated the hyperfine interaction constants, the Landég-factors, and the electric quadrupole moments for the low-lying states in the 61Ni11+,61Ni12+,61Ni14+, and61Ni15+ ions. These states are clock states of the selected clock transitions in highly charged nickel ions(see Fig. 1). Based on discussing the effects of the electron correlations, the Breit interaction, and quantum electrodynamics(QED) effect on these physical quantities, reasonable uncertainties were obtained for our calculated results. In addition, the electric quadrupole frequency shifts and the Zeeman frequency shifts of the clock transitions concerned were analyzed.     

Light—induced nonlinear effects of dispersion relation of ultracold Bose gas

We have investigated the optical properties of Λ-configuration ultracold dense Bose gas interacting with two laser pulses, which usually result in electromagnetically induced transparency. With the nonrelativistic quantum electrodynamics and taking into account the atomic dipole－dipole interaction and local field effect, we have derived the Maxwell－Bloch equations of the system. The dispersion relation of an ultracold Bose gas has been obtained and the light-induced nonlinear effects have been analysed. The light-induced nonlinear effects are different from the effects induced by two-body collision of Bose－Einstein condensation atoms which have a frequency shift of transparent window.     

稠苯芳杂环及其烷基质子化学位移的计算

本文提出了予测稠苯芳杂环及其烷基链上质子化学位移的计算方法。 将稠苯芳杂环化合物用凯库勒式表示,计算式为为需考虑的苯环内的乙烯基效应。σ_mi,ci为各苯环的环流效应。σ_1,Hc为各芳杂环的屏蔽效应,对杂环上质子它就是该单独芳杂环上相应质子的δ值,对苯环上质子要将它分解为各结构因素的效应,即:σ_1,He=(1/2)^d-1δ_x=y(或σ_z)+σ_c-c·σ_m,H. σ_x-y与σ_z为杂原子或其基团的屏蔽效应,σ_c=c为存在于芳杂环中的乙烯基的效应,σ_m,Hc为芳杂环的环流效应,d为对不同质子所考虑的键数。有取代基时需考虑取代基的效应。计算环上烷基质子的公式为:δ=σ_p,CH3+ασ_c,CH3+βσ_t,CH3+σ_l,G σ_l,G为稠苯芳杂环基的某级效应。     

Structural phase transitions at clean and metal-covered Si(111) surfaces investigated by RHEED spot analysis

Structural phase transitions between various kinds of superlattice structures formed on a Si(111) surface have been investigated by spot analysis of reflection high-energy electron diffraction (RHEED). Reversible transitions induced by temperature changes and irreversible ones induced by metal depositions were observed. Detailed discussions on the dynamics of the phase transitions are made by quantitative analyses of integrated spot intensity and profile. For a phase transition of 7′7  1′1 structures on a clean Si(111) surface, a hysteresis with temperature difference of 5°C. between in heating and cooling processes was found in the spot intensity change, indicating a first-order transition. Hysteresis was hardly recognized, on the other hand, for transitions of Au-induced superstructures (5×2-Au or ×-Au)  1×1-Au. The spot profiles were found to be broadened during the transition of Si(111)-×-Au  1×1-Au, which was a signature of a continuous transition, while the profiles remained unchanged during the transitions of the 7×7  1×1 and 5×2-Au  1×1-Au phases. Structural conversions induced by In adsorption on the Si(111) surface kept at constant temperatures were also analyzed. The conversions at room temperature were totally dependent on the initial substrate surface structures; the 7×7 surface did not show any structural conversion with In adsorption, while the ×-In surface successively converted to a 2×2 and a × phase with coverage increase. The structural transitions at elevated temperatures were sensitively dependent on the temperatures. Sequences of transitions among the 7×7, 4×1, ×, 1×, and ×4 were quantitatively revealed as changes in RHEED spot intensity.     

ErP5O14非晶玻璃的红外量子剪裁

研究了Er_1.0P₅O₁₄铒非晶玻璃的红外量子剪裁现象. 从吸收谱和激发光谱的计算比较中肯定了Er_1.0P₅O₁₄非晶 玻璃的1537.0 nm红外荧光为多光子量子剪裁荧光. 从Er_1.0P₅O₁₄非晶玻璃的可见和红外荧光发射光谱中发现激发²H_11/2, ⁴G_11/2和⁴G_9/2能级所导致的⁴I_13/2→⁴I_15/2量子剪裁红外荧光很强;基于自发辐射速率、无辐射弛豫速率和能量传递速率等参数的计算,对其量子剪裁机理进行了分析.发现起源于基态的强下转换能量传递{²H_11/2→⁴I_9/2,⁴I_15/2→⁴I_13/2},{⁴G_11/2→⁴I_13/2, ⁴I_15/2→²H_11/2},{⁴G_9/2→⁴F_7/2,⁴I_15/2→⁴I_13/2}和{⁴G_9/2→⁴I_13/2, ⁴I_15/2→²H_11/2}是导致Er_1.0P₅O₁₄非晶玻璃具有强的三光子和四光子量子剪裁红外荧光的原因.研究结果对改善太阳能电池效率有一定意义.     

1-forms over the moduli space of irreducible connections defined by the spectrum of Dirac operators

Let (P) be the moduli space of irreducible connections of a G-principal bundle P over a closed Riemannian spin manifold M. Let D_A be the Dirac operator of M coupled to a connection A of P and f a smooth function on M. We consider a smooth variation A(u) of A with tangent vector ω and denote T_ω:= (D_A(u)−f) (u=0. The coefficients of the asymptotic expansion of trace (T_ω · e^-t(D_A−f)2) near t=0 define 1-forms a^(k)_f, K=0, 1, 2, … on (P). In this paper we calculate aa⁽⁰⁾_f, a⁽¹⁾_f, a⁽²⁾_f and study some of their properties. For instance using the 1-form a⁽²⁾_f for suitable functions f we obtain a foliation of codimension 5 of the space of G-instantons of S⁴.     

Phase formation and magnetic properties of Nd2Fe14B-type Nd16Co76B8−xCx alloys and their hydrides

An attempt is made to synthesize Nd₂Co₁₄C compound by mechanical alloying Nd₁₆Co₇₆B_8−xC_x (0x8) alloys and subsequent annealing. Phase formation and magnetic properties of Nd₂Fe₁₄B-type Nd₁₆Co₇₆B_8−xC_x alloys and their hydrides are investigated. The Nd₂Co₁₄(B,C) phase with Nd₂Fe₁₄B-type structure is formed for Nd₁₆Co₇₆B_8−xC_x (0x7) alloys, while NdCo₇C_δ phase with TbCu₇-type structure is observed in Nd₁₆Co₇₆C₈ alloy. The lattice parameter c of the Nd₂Co₁₄(B,C) phase decreases with increasing the carbon content. A limit volume of the unit cell to form the Nd₂Fe₁₄B-type structure is estimated to be 0.870 nm³. The spin-reorientation temperature T_SR increases with increasing the carbon content, due to an enhancement of magnetocrystalline anisotropy caused by carbon substitution for boron. After hydrogenation, the lattice expansion is observed for Nd₁₆Co₇₆B_8−xC_x (0x7) alloys. The spin-reorientation temperature of Nd₁₆Co₇₆B_8−xC_xH_y (0x7) is much lower than that of the host alloys. Some structural and magnetic properties of hypothetic Nd₂Co₁₄C and Nd₂Co₁₄CH_y compounds are estimated by extrapolation.