3D-TOFSIMS characterization of black spots in polymer light emitting diodes

The occurrence and formation of black spots areas in PolyLED devices has been studied by time-of-flight SIMS (TOFSIMS). The composition, shape and position of the black spots is visualised by three-dimensional (3D)-TOFSIMS depth-profiling. It has been established that the formation of non-emissive spots is due to the growth of aluminium oxide clusters at the AlBa/polymer interface. Electron injection in the black spots is lost by the resulting local increase of the resistivity of the cathode.     

High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayers

High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayer (ML) up to 600 °C have been studied and reported in this paper. Ti/Ni multilayer samples having constant layer thicknesses of 50 Å each are deposited on float glass and Si(1 1 1) substrates using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions at room temperatures. The micro-structural parameters and their evolution with temperature for as-deposited as well as annealed multilayer samples up to 600 °C in a step of 100 °C for 1 h are determined by using X-ray diffraction (XRD) and grazing incidence X-ray reflectivity techniques. The X-ray diffraction pattern recorded at 300 °C annealed multilayer sample shows interesting structural transformation (from crystalline to amorphous) because of the solid-state reaction (SSR) and subsequent re-crystallization at higher temperatures of annealing, particularly at ≥400 °C due to the formation of TiNi₃ and Ti₂Ni alloy phases. Sample quality and surface morphology are examined by using atomic force microscopy (AFM) technique for both as-deposited as well as annealed multilayer samples. In addition to this, a temperature dependent dc resistivity measurement is also used to study the structural transformation and subsequent alloy phase formation due to annealing treatment. The corresponding magnetization behavior of multilayer samples after each stage of annealing has been investigated by using Magneto-Optical Kerr Effect (MOKE) technique and results are interpreted in terms of observed micro-structural changes.     

On the correlation between order parameter, superconducting volume fraction and critical current density in R: 123 superconductors

Resistivity and low field ac susceptibility measurements are made on R: 123 superconducting samples with different rare earth elements R. The order parameter dimensionality OPD is deduced from resistivity versus temperature plot using the Aslamazov and Larkin expression, while the analysis of the temperature dependence of ac susceptibility is done employing Beans’ critical state model and with the help of the Ravi expression. With increasing R, the critical temperatures T_c are nearly kept constant (∼90 K), while the crossover temperatures T_o are shifted to lower values. Moreover, the superconducting order parameter OPD is shifted toward 2D behavior. On the other hand, the values of superconducting volume fraction f_g decrease with increasing ac field amplitude H_m for all samples and it is higher in Er: 123 sample than in Nd: 123 sample. Although the values of critical current density J_c at the peak temperature T_m are nearly unchanged with increasing R, the values of J_c(T), at T<T_m and T>T_m, are found to be dependent on the chosen R. The correlation between the above calculated parameters against R is also mentioned.     

Investigations on Chemical Vapour Transport of Intermetallic Phases in the System Co/Fe/Si

The ternary phases existing on the quasi binary section CoSi/FeSi and CoSi₂/β‐FeSi₂ have been investigated by solid state reactions and chemical transport. The solid solution serie Co_xFe_1‐xSi can be described as a regular solution. The transport behaviour calculated is in good agreement with the experiments. The phases have been characterized by X‐ray powder diffraction, EDX and ICP‐OES. The temperature dependence of the resistivity has been measured from 20 K up to room temperature on single crystals.     

YIHn: A New Family of Metal‐rich Hydride Halides

The graphite‐like yttrium hydride halides, YIH_n (0.8 ? n ? 1.0), have been prepared in quantitative yields by heating either YI₃, YH₂ (1:2) or stoichiometric YI₃, YH₂, Y mixtures in sealed Ta ampoules at 900°C. A lower limit of the homogeneity range, n ≈ 2/3, has been determined from dehydrogenation experiments. All YIH_n phases adopt the ZrBr‐type heavy‐atom structure. The hydrogen variation is accompanied by a change in the c lattice constant from 31.162(3) to 31.033(1) Å for n = 0.61(3) to 1.02(3). The YIH_n phases reversibly react with hydrogen at 400‐600°C to form the light green transparent compound YIH₂. However, increasing the reaction temperature above 700°C causes decomposition to an unidentified phase being in equilibrium with YH₂ and YI₃. The arrangement of the heavy atoms in YIH₂ (P m1; a = 3.8579(3) Å, c = 10.997(1) Å) corresponds to a four‐layer I‐Y‐Y‐I slab with the stacking sequence (AbaB) as was found by x‐ray powder diffraction data refinement with the Rietveld method. A miscibility gap exists between YIH and YIH₂. Samples YIH_n (n ? 1.0) show metallic conductivity at room temperature, which changes into semiconducting behavior with decreasing temperature as n approaches its lower value ≈ 2/3.     

μs级负充电时不同体积分数去离子水与乙二醇混合液电性能的实验研究

 以去离子水与乙二醇的混合液（体积分数分别为36.5%,48.7%,59.0%及71.2%，以下简称混合液）作为同轴传输线的绝缘介质，进行了μs级高电压负充电条件下的正电极击穿实验，研究了混合液的击穿电压、击穿时间、相对介电常数及电阻率与体积分数的关系。实验结果表明：在充电电压为20kV时，71.2%的混合液比36.5%的混合液的平均击穿电压提高25.1%，平均击穿时间延长10.49%，而相对介电常数减小868%。同时，随着充电时间的缩短，混合液的击穿电压提高。     

One-step measurements of powder resistivity as a function of relative humidity and its effect on charging

A new one-step technique to measure the effect of ambient humidity on powder resistivity has been previously presented. In this article, we provide more experimental data obtained with five different powders. One-step measurements and traditional multi-step measurements were performed. Also, additional measurements were performed using standard resistivity cell. Results were compared and it could be concluded that the new technique provided meaningful results although significant hysteresis was observed during humidification and drying cycles. Finally, charging of the powder was also measured and it was noticed that it decreases with decreasing resistivity and increasing humidity.     

Kondo合金低温电阻率的自洽计算

从Slave-boson平均场理论出发,对Yoshimori-Kasai模型进行修正,应用相干势近似(CPA)方法计算了Kondo合金低温电阻率。结果表明,当合金中磁性原子浓度大于某个值时,重费米子系统明显地表现出相干性。给出了低温下电阻率的表达式。     

Unusual resistivity broadening in the mixed state of NdBa2Cu3O7−δ crystals grown by a crystal-pulling technique

In order to clarify the origin of a strong peak effect in the magnetization curve of NdBa₂Cu₃O_7−δ crystals, we investigated the superconductivity transition behavior of the in-plane resistivity in static magnetic fields up to 8 T. Comparing the results for the samples exhibiting and not exhibiting the peak effect, we found that the former (peak effect sample) shows lower resistivity above the vortex melting temperature. This implies that the pinning force is effective in the vortex liquid state. We also found that the normal state resistivity behaviors of some samples were unusual, indicating inhomogeneous current flow. These results suggest an existence of sheet-like pinning centers perpendicular to the conduction planes.     

Power spectrum of density fluctuations in a finite reactive-diffusive system: resistance fluctuation spectroscopy

The measurement in thermal equilibrium of the vacancy contribution to the residual resistivity of metals has posed certain difficulties. The recent experiment of Celasco and co-workers represents a new, powerful approach to this problem, via the measurement of the power spectrum of the voltage noise generated by resistivity fluctuations. The latter originate in vacancy number fluctuations. We develop a theory for the power spectrum, incorporating three basic features. Vacancies can be annihilated in the material and they diffuse. Grain boundaries act as sources and sinks for vacancies. Both annihilation (a form of reaction) and diffusion are noisy processes. We therefore set up and solve a reactive-diffusive stochastic equation for the instantaneous density, with appropriatefinite boundary conditions. Assuming for simplicity that the grains are spherical, the power spectrum is evaluated exactly, in closed form. A detailed comparison with experiment is made. The physical origins of different time scales in the problem and the consequent frequency regimes in the power spectrum are analysed. Recognising the very general applicability of our theory, we also mention possible applications to other problems.