Small angle x-ray and neutron scattering studies of plasma-deposited amorphous silicon-hydrogen films

Small-angle scattering measurements using both neutrons and X-rays have been made on a series of plasma-deposited a-Si : H films. One class of sample exhibits strong anisotropic scattering indicating rod-like microstructure normal to the film surface with a dominant rod diameter of ~ 60 Å. Other samples show isotropic scattering with a similar dimension or no scattering at all within the resolution of the experiment.     

金属表面镀高分子膜对真空击穿阈值的影响

探索提高金属表面真空击穿阈值的方法,对脉冲功率技术的发展和应用具有重要意义。在金属表面电子发射理论分析的基础上,采用有限元法计算阴极杆表面电场随二极管电压的变化规律,设计了实验系统,并开展了实验研究。实验对比了在脉宽约30 ns、阴极杆与阳极筒间隙12 mm时,钛合金TC4阴极杆在不同种类高分子膜（膜厚30～60 μm）下真空击穿阈值的变化情况。在表面粗糙度R_z（轮廓最大高度）为0.8 μm的TC4阴极杆表面分别镀环氧树脂膜和丙烯酸膜,实验结果表明,镀丙烯酸膜阴极杆的击穿阈值约505 kV/cm,相对于不镀膜阴极杆,击穿场强提高了约20.6%;在表面粗糙度R_z为0.2 μm的TC4阴极杆表面分别镀聚酰亚胺膜和聚醚醚酮膜,实验结果表明,镀聚酰亚胺膜阴极杆的击穿阈值为584 kV/cm,相对于不镀膜阴极杆,击穿场强提高了约28.1%。因此,在金属表面镀丙烯酸膜、聚酰亚胺膜可以有效提高金属表面的真空击穿阈值。     

Visualization of quench-rewetting phenomena of liquid-film falling during dryout and rewetting on fuel rods in high temperature and pressure BWR operating conditions

Abstract  

Thermal and hydraulic phenomena of the dryout and rewetting on a fuel rod were discussed, based on the transient process observed visually with the surface-temperature variations measured during the transition from dryout to rewetting with a high-speed CCD video movie under BWR-rated high pressure and temperature conditions of 7 MPa and ~559 K (~286°C) in a thermal-hydraulics experimental loop. Liquid film was observed falling under CCFL from the downstream spacer placed in upper side on the electrically heated rod after the dryout. The heater rod surface could be cooled with the liquid film falling in the early stage of the rewetting and then the surface temperatures recovered from unusually elevated levels with quench-rewetting.     

Investigation of the beam propagation in a pumped laser rod

A method investigating the beam propagation in a pumped laser rod is proposed. In this method, the pumped laser rod in a resonator is evenly divided into N segments along the laser rod axis, and each segment is considered as a small thermal lens with thermal focus length of f. Accordingly, the beam radius distributions in the laser rod for the symmetric and asymmetric resonators are thus calculated, respectively. The beam radius distribution in the whole resonator is also calculated. Moreover, the calculated beam distribution in the whole resonator and in the rod is also described in detail.     

Critical temperature changes in many-layer films between plates

Two distinct mechanisms produce two separate terms in the change of the critical temperature T_c in an n-layer (n ↗ 1) film. The interface interaction induces a change ΔT_c, ΔT_c/T_c ⩽ O(2/n). The finite thickness of a film gives another term in the change of T_c, which has the exponent 1/ν≈1.56. Comparison with experiments is made and further experiments are discussed.     

Solution to the problem of Nicolai

We consider the problem of Nicolai on dynamic stability of an elastic cantilever rod loaded by an axial compressive force P and a twisting tangential torque L in continuous formulation. The problem is to find the stability region for non-equal principal moments of inertia of the rod in the space of three parameters: P, L and the parameter α for the ratio of principal moments of inertia. New governing equations and boundary conditions, which form the basis for analytical and numerical studies, are derived. An important detail of this formulation is that the pre-twisting of the rod due to the torque L is taken into account. The singular point on the stability boundary at the critical Euler force P_E is recognized and investigated in detail. For an elliptic cross-section of a uniform rod the stability region is found numerically with the use of the Galerkin method and the exact numerical approach. The obtained numerical results are compared with the analytical formulas of the asymptotic analysis.     

On the influence of free-carrier scattering mechanisms on semiconductor thin-film plasma spectra

IR plasma reflectivity spectra of semiconductor epitaxial layers on transparent substrates have been calculated by using a modified Drude dielectric function including a frequency-dependent relaxation rate of the form γ(ω) = γ₀+bω². Due to multiple reflections within the semiconductor film, weak structures in the bulk reflectivity spectra are enlarged in the film spectra. The sensitivity of the film reflectivity to variations of the relaxation rate is much larger than the bulk reflectivity for frequencies above the plasma edge and consequently this type of measurement is a very promising method for obtaining information about the scattering mechanisms of free carriers.     

The characteristic investigation of spray coated W incorporated in oxide thin films

W incorporated tin oxide (TO) thin films were grown via spray pyrolysis with various tungsten contents. The films were observed to be polycrystalline tetragonal crystal nature with (301) and (211) preferential planes. From EDX analysis, it was seen the tungsten concentrations in the TO films were slightly higher than ones in the starting solutions. Polyhedron-like and small rod like grains were observed in the SEM images. 3 at % W doped tin oxide film has minimum sheet resistance (44.67 Ohm) and resistivity (3.685 × 10^?3 Ohm cm) values and maximum figure of merit (75.74 × 10^?5 Ohm^?1) value. The optical band gap (E_g) of pure film raised from 3.84 to 3.91 eV with 3 at % W contribution level.     

TiO<Subscript>2</Subscript> Nanorod Arrays Sensitized with CdS Quantum Dots for Solar Cell Applications: Effects of Rod Geometry on Photoelectrochemical Performance

CdS quantum dot (QD) sensitized TiO₂ nanorod array (NRA) film electrodes with different rod geometries were fabricated via a solvothermal route followed by a sequentialchemical bath deposition (S-CBD) process. By controlling the solution growth conditions, the rod geometries, especially the tip structures, of the TiO₂ NRAs were tuned. The results indicated that the vertically aligned hierarchical NRAs possessed conically shaped tip geometry, which was favorable for film electrodes due to the reduced reflectance, enhanced light harvesting, fast charge-carrier separation and transfer, suppression of carrier recombination, sufficient electrolyte penetration and subsequent efficient QD assembly. CdS QD sensitized TiO₂ NRA film electrodes with tapered tips exhibited an enhanced photoelectrochemical (PEC) performance, a photocurrent intensity of 5.13 mA/cm² at a potential of 0 V vs. saturated calomel electrode, an open-circuit potential of −0.68 V vs. saturated calomel electrode and an incident photon to current conversion efficiency (IPCE) of 22% in the visible-light region from 400 to 500 nm. The effects of rod geometry on the optical absorption, reflectance, hydrophilic properties and PEC performance of bare TiO₂ and CdS QD sensitized TiO₂ NRA film electrodes were investigated. The mechanism of charge-carrier generation and transfer in these CdS QD sensitized solar cells based on vertically aligned TiO₂ nanorods is discussed.     

Ferroelectric films of deuterated glycine phosphite: Structure and dielectric properties

Polycrystalline textured films of deuterated glycine phosphite consisting of single-crystal blocks with lateral dimensions ～(50–100) μm and a thickness d ～ (1–5) μm have been grown by evaporation on NdGaO₃(100) and α-Al₂O₃ substrates with preliminarily deposited interdigitated electrodes, as well as on Al substrates. The c* (Z) crystallographic axis in the blocks is normal to the film plane, and the a (X) axis and the polar axis b (Y) are oriented in the film plane. The temperature dependences of the capacitance of the structures measured with the interdigitated electrode system reveal a strong dielectric anomaly at the film transition to the ferroelectric state. The phase transition temperature T _c depends on the degree of deuteration D of the glycine phosphite. The maximum value T _c = 275 K obtained in the structures studied corresponds to a degree of deuteration of the glycine phosphite D ～ 50%. The frequency behavior of the dielectric hysteresis loops in glycine phosphite films differs radically from that of the previously studied films of deuterated betaine phosphite, which evidences that polarization switching in these structures proceeds by different mechanisms. It has been that application of a dc bias to the electrodes changes the shape of the dielectric hysteresis loops and shifts them along the electric field axis. The shift of the loops depends on the sign, magnitude, and time of application of the bias. Possible mechanisms underlying the induced unipolarity are discussed.     

基于自由曲面透镜的三基色LED照明系统研究

基于三基色发光二极管(light emitting diode，LED)与方棒的投影照明系统具有色域宽、体积小的优点，但三基色LED和方棒配合使用时，存在投影亮度不高的问题。首先基于光学扩展量匹配原则选择了LED光源，然后设计了一组自由曲面的准直透镜和收集透镜。仿真结果表明:准直透镜出射光线集中在±7.5°内，方棒出射端±30°内的能量利用率为51.7%。实际加工并测试了设计的自由曲面准直透镜和收集透镜。测试结果表明:采用本文设计的没有镀减反增透膜的透镜组，投影机出射亮度比原使用镀了增透减反膜的透镜的系统高1.6%。预计设计的透镜镀减反增透膜后投影机出射亮度有望提升9.8%。     

Explanation for TEM00 operation of heavily doped YAlO3:Er3+

Although pump energy is mainly absorbed at the border of a heavily doped YAlO₃:Er³⁺ rod, fundamental mode laser operation is achieved. The absorption of pumplight in the laser rod, energy transfer mechanisms and the population of the laser levels are discussed. A possible explanation of the inversion maximum in the center of the rod is given.     

Specific features of current flow mechanisms in the semiconductor structure of a photoelectric converter with an <Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript>–<Emphasis Type="Italic">p</Emphasis>-junction and an antireflective porous silicon film

The temperature dependence of forward and reverse branches of the current–voltage characteristic of the semiconductor structure of a photoelectric converter with an n ⁺–p-junction based on single-crystal silicon and an antireflective porous silicon film on the front surface has been studied. The presence of several current flow mechanisms has been revealed. It has been demonstrated that traps that emerge in the process of the formation of the porous silicon film have a considerable effect on the current flow processes in the semiconductor structure under consideration.     

Dose quality determined using ESR imaging

The differences in SO⁻₃ radical distribution produced in gadolinium (Gd)-doped glaserite (K₃Na(SO₄)₂) rod after irradiation with β-, γ-, or X-rays was investigated by an electron spin resonance (ESR) imaging method. In β- or X-irradiated samples, the SO⁻₃ radical distribution showed a steep gradient in the rod. In γ-irradiated samples, the distribution showed only a slight gradient in the rod. From these results, ESR imaging can not only detect the radiation direction and the absorbed dose, but can also be expected to distinguish the dose quality.     

Room temperature magnetic properties of ZnO nanostructured films

The ZnO nanorod array films have been epitaxially deposited on indium tin oxide (ITO) glass along 〈0001〉 direction. It is found that the film is grown in a two-step process including nanoparticle film nucleation and oriented rod growth. The as-prepared ZnO film shows a dominant diamagnetic signal and a weak ferromagnetic signal at room temperature. The room temperature ferromagnetism deteriorated by annealing in air or N₂. The photoluminescent spectra revealed that the intensity of ZnO defect band decreases after annealing. Thus, the decreased ferromagnetism is likely to have resulted from the decrease of oxygen vacancies and defects in the as-prepared film. Moreover, ZnO deposited at various times showed that defects located at or near the interface between the substrate and the film play a major role in ferromagnetism. It suggests that ferromagnetism can be tuned by changing the defects in ZnO.     

Surface chemistry and growth mechanisms studies of homo epitaxial (1 0 0) GaAs by laser molecular beam epitaxy

In this paper, GaAs thin film has been deposited on thermally desorbed (1 0 0) GaAs substrate using laser molecular beam epitaxy. Scanning electron microscopy, in situ reflection high energy electron diffraction and in situ X-ray photoelectron spectroscopy are applied for evaluation of the surface morphology and chemistry during growth process. The results show that a high density of pits is formed on the surface of GaAs substrate after thermal treatment and the epitaxial thin film heals itself by a step flow growth, resulting in a smoother surface morphology. Moreover, it is found that the incorporation of As species into GaAs epilayer is more efficient in laser molecular beam epitaxy than conventional molecular beam epitaxy. We suggest the growth process is impacted by surface chemistry and morphology of GaAs substrate after thermal treatment and the growth mechanisms are discussed in details.     

Longitudinal vibrations in circular rods: A systematic approach

A systematic method is developed for expressing the frequency squared ω² and the corresponding displacement fields of harmonic waves in a long thin rod as an even power series in qa, where q is the wavenumber along the rod and a is a representative transverse dimension. For longitudinal waves in a circular rod, the evaluation is reduced to algebraic recursion, giving coefficients analytically in terms of Poisson's ratio v, to many orders. The second nontrivial coefficient, corresponding to Rayleigh–Love theory in the present longitudinal case and Timoshenko theory in the flexural case, is thus put on a firm footing without reliance on ad hoc physical assumptions. The results are compared to available exact predictions, and shown to be accurate for moderate values of qa (5% accuracy for qa≤1.5) with just two terms. Improvements based on the Rayleigh quotient guarantee positivity and the correct asymptotic power, and the variational principle further ensures that the accuracy improves monotonically with the order of approximation. With these features, accurate results are obtained for larger qa (5% accuracy for qa≤3), so that results are valid for rods that are by no means thin. Application of these methods to the flexural case has been presented separately.     

Morphology and photoluminescence properties of zinc oxide films grown by pulsed laser deposition

Zinc oxide films with different morphologies have been grown by pulsed laser deposition, varying substrate temperature and oxygen pressure. At low oxygen pressure and low substrate temperature continuous films with different roughness have been obtained, while at high substrate temperature a film with sparse hexagonal pyramids has been observed. Increasing the oxygen pressure the film became rougher and at 100 Pa a rod-array has been deposited. The columns of this rod-array grew along the wurtzite c-axis perpendicularly to the substrate surface as proved by X-ray diffraction measurements. Near to the sample borders the columns were slightly tilted towards the center of the sample. The possible growth mechanisms giving rise to the different morphologies have been discussed. Low-temperature photoluminescence measurements allowed to get information about the film quality, showing the variations of the excitonic peak and two defect bands (green and violet-blue) with the different deposition parameters.     

Magneto-optical and optical properties of polycrystalline Со–Р films with nanometer thickness

Features of the optical and magneto-optical properties of polycrystalline Со–Р films with nanometer thickness are established experimentally. It is found that the spectra of optical parameters n and k and magnetic circular dichroism depend largely on film thickness, suggesting that magneto-optical activity is governed by different mechanisms in thin films and bulk materials.     

Electrical-resistivity noise in Ni76Mn24 amorphous film

Magnetoresistance measurements were carried out on amorphous Ni₇₆Mn₂₄ film in the temperature range 1.5–250 K up to magnetic fields of 120 kG, A giant resistivity noise has been observed even in higher magnetic fields, especially at about T = 70 K. Some possible mechanisms are discussed to account for the observed resistivity fluctuations.