导电炭黑微观结构及其应用性能

以乙炔炭黑、副产炭黑和炉法导电炭黑为研究对象,较为系统地分析了与导电炭黑应用性能密切相关的微晶结构、表面性质、颗粒形貌和粒度分布特征,探讨了导电炭黑微观结构对应用性能的影响。研究结果表明,导电炭黑的微观结构决定了其应用性能,而决定应用性能的关键在于其与基体材料的匹配性。副产炭黑在橡胶和塑料中导电性能较好,乙炔炭黑在锂离子电极材料中的导电性能较好。     

用扫描隧道显微镜(STM)观察纳米粉体的形貌

将不导电的纳米粉体压成薄片,在薄片的表面溅射上金膜,再经过适当的处理,将薄片固定在样品台上,这样制得样品可用于纳米粉体形貌,由于用于ＳＴＭ观察的样品必须导电这一限制,使得样品表面溅射的金膜厚度对成像有很大影响,此类工作可安排在学生物理实验的小型科研实验课程中。     

ZnO∶W透明导电薄膜的调制生长与表面氢化处理

采用射频磁控溅射法,在不同溅射功率下沉积ZnO∶W薄膜层55min,然后通入体积分数为5%的氢气,并保持溅射参数不变,表面氢化处理8min,获得了表面具有绒面结构的ZnO∶W透明导电薄膜。对样品的显微形貌、结构和表面绒度等性能进行了测试与分析,结果表明:在200 W的溅射功率条件下,氢化处理8 min获得的ZnO∶W样品表面绒度达到92.82,同时具备优异的导电性能(电阻率均值3.93×10~(-4)Ω·cm)。这种表面绒面结构有望进一步提高ZnO透明导电电极电池的转换效率。     

下电极对ZnO薄膜电阻开关特性的影响

本文采用直流磁控溅射法在三种不同的下电极(BEs)上制备了ZnO薄膜, 获得了W/ZnO/BEs存储器结构. 研究了不同的下电极材料对器件电阻开关特性的影响. 研究结果表明, 以不同下电极所制备的器件都具有单极性电阻开关特性. 在低阻态时, ZnO薄膜的导电机理为欧姆传导, 而高阻态时薄膜的导电机理为空间电荷限制电流. 不同下电极与ZnO薄膜之间的肖特基势垒高度对电阻开关过程中的操作电压有较大的影响, 并基于导电细丝模型对不同下电极上ZnO薄膜的低阻态阻值及reset电流的变化进行了解释. 关键词： ZnO薄膜 电阻开关 下电极     

La0.7Ca0.3 MnO3和CeO2混合块状样品电输运性质及使用分形迭代电阻网络模型的计算模拟

固相反应方法制得的La0.7Ca0.3MnO3(LCMO)粉末与CeO2粉末均匀混合后压块烧结,对其进行了电阻率随温度变化的测量.观察到样品电阻率存在绝缘体-金属转变.研究了烧结工艺、CeO2的混合比例与样品的电阻率、结构和表面形貌的关系.结果表明,制备工艺对材料性能有相当大的影响,其中较低温度的烧结主要影响小晶粒及其晶粒间界,而高温长时间烧结将影响大晶粒的形成.利用三维随机电阻网络(RRN)模型和蒙特卡罗方法对这种混合块状样品的输运性质进行了模拟,模拟中使用了一种新的RRN平均方法.该模型得到的数值模拟结果与实验结果在定性上是一致的.这说明以RRN模型来理解LCMO(x)-CeO2(1-x)复合体系的导电状况是合理的,提出的随机电阻网络平均方法是合适的.     

高气压大电流放电条件下的电极烧蚀

归纳了影响开关电极烧蚀量的因素,包括开关电极材料、放电条件等,分析了开关电极烧蚀特征与烧蚀后表面形貌,总结了开关电极烧蚀的主要机制电极加热和电极材料去除机制。为了延长开关工作寿命,提出了减少开关电极烧蚀的措施,包括选用抗烧蚀性能优异的材料作为开关电极材料、采用合适的开关电极结构和优化的放电条件等。     

照明模式SNOM中样品对近场光场分布的影响

在同时考虑样品的形貌及材料光学参量和入射光偏振模式的情况下,利用基于边界元方法编写的二维矢量电磁场计算程序,对工作在照明模式下的扫描近场光学显微镜（Scanning Near-field Optical Microscope,SNOM）的近场矢量电磁场分布进行了数值计算模拟研究.结果表明,在没有表面形貌特征时,探针的光能量透射率随样品材料的折射率和损耗角的增加而增大,而样品表面光斑尺寸受折射率和损耗角的影响很小；对有形貌特征的探针扫描像研究结果表明,SNOM的分辨率随着样品的折射率和损耗角的增加而提高；对SNOM不同的工作模式的扫描成像信号进行的计算结果表明,恒定间距扫描方式比恒定高度扫描方式对样品表面的细节有较强的分辨能力.     

高定向热解石墨表面局域导电增强现象的扫描探针显微学研究

基于导电型原子力显微镜和扫描隧道显微镜的对比观察,研究高定向热解石墨表面上残留石墨片的导电增强现象.根据样品电阻的测量数据,将这种现象归结为导电针尖与石墨表面的点接触问题,并且发现接触电导和接触点处局域的电子密度成正比,从而确定石墨表面的局域导电增强现象的原因在于残留在石墨表面的石墨片具有较高的电子密度. 关键词： 扫描隧道显微镜 导电原子力显微镜 高定向热解石墨 导电性     

一种用于光谱分析的封闭环形电离针

光谱分析中广泛采用高频引燃低压交流电弧,利用高频引燃回路的高频电流耦合到电弧回路,击穿分析间隙。(1) 这也就是平常所说的高频电花引燃。金属电极在激发过程中,由于空气的氧化作用在电极表面复上一层导电性能极差的氧化膜,致使放电不能正常进行,放电点会游移至侧面。所以有人主张在激发前先将金属棒电极进行预氧化处理,以防止上述现象的出现。(2)光源的稳定性很大程度上决定于引燃的稳定性。为了保证激发平稳极易电离导通,在“电弧”工作状态、“低压火花”工作状态或“高频火花”状态,一般都在分析间隙间加装一只直针形的金属电离针,即电极活化针。在分析间隙之间加装一只引发电离针,系利用了电离针的尖端放电作用,增强局部的电场强度,并改变上下电极间的电场分布,使空气中的离子(宇宙线等引起的)在合成电场作     

Buck变换器内部本质安全性能评价判别式研究

为了建立起Buck变换器内部本质安全性能评价的相关判别式,首先以简单电感电路的电弧放电为研究对象,基于热引燃理论,采用持续发热点热源温度场模型,将初始燃烧容积的温度由最高值下降至气体混合物燃烧温度的时间是否大于化学反应的时间作为判断火花能否成功引燃气体混合物的临界条件,得到了相应的火花放电时间临界值的表达式。然后,基于爆炸性试验数据对采用等效电阻法和放电电流线性模型算得的Buck变换器电感开路电弧放电能量表达式进行了修正,进而建立了Buck变换器内部本质安全性能评价的能量判别式和放电时间判别式。验证结果表明了所求放电时间临界值的合理性和所建立判别式的正确性。     

Optimal design of shock ignition target in order to stop generated hot electrons within the cold fuel

Generation of hot electrons (HEs) within ignitor pulse interaction with pre-compressed fuel is an important challenge in the shock ignition approach. Target optimization in order to prevent the destructive effects of HE is the main goal of the present work. In the first stage, the spectrum of electron energy generated during the interaction of ignitor pulse at different widths with the HiPER pre-compressed target has been estimated by applying particle simulation tool. Then, by changing the thickness of the cold fuel in the range of 185–225 μm, the corresponding areal densities are calculated using 1D hydrodynamic simulations. Finally, in order to assess the energy fusion yield, the iso-gain curves are obtained for different ignitor time windows as well as target thicknesses. Simulation results indicate that by decreasing the baseline, target thickness leads to a 17–70% increase in the fuel areal density. Subsequently, it has been demonstrated that by properly adjusting the parameters of ignitor pulse launch time and its width and employing a target with areal density high enough to stop the HEs, energy gain above 140 can be achieved. Optimal areas for shell thickness and ignitor time window are identified.     

Shock ignition of thermonuclear fuel with high areal density

A novel method by C. Zhou and R. Betti [Bull. Am. Phys. Soc. 50, 140 (2005)] to assemble and ignite thermonuclear fuel is presented. Massive cryogenic shells are first imploded by direct laser light with a low implosion velocity and on a low adiabat leading to fuel assemblies with large areal densities. The assembled fuel is ignited from a central hot spot heated by the collision of a spherically convergent ignitor shock and the return shock. The resulting fuel assembly features a hot-spot pressure greater than the surrounding dense fuel pressure. Such a nonisobaric assembly requires a lower energy threshold for ignition than the conventional isobaric one. The ignitor shock can be launched by a spike in the laser power or by particle beams. The thermonuclear gain can be significantly larger than in conventional isobaric ignition for equal driver energy.     

激光脉冲参数对冲击点火的影响

针对激光脉冲参数对冲击点火的影响进行理论分析和数值模拟.首先从冲击波的产生和碰撞过程出发,理论分析冲击脉冲峰值功率、脉宽和上升沿时间对点火的影响;然后通过数值模拟,以点火时间窗口作为评价标准,验证理论分析结果.研究表明:冲击脉冲峰值功率是点火成败的关键因素之一,脉冲宽度则需达到百皮秒以提供足够的点火能量,上升沿时间在小于600 ps的情况下不会对点火造成明显影响. 关键词： 冲击点火 激光冲击脉冲 点火时间窗口     

Process and performance of hot dip zinc coatings containing ZnO and Ni-P under layers as barrier protection

A new coating system of under layer for hot dip zinc coating was explored as an effective coating for steel especially for application in relatively high aggressive environments. The influence of different barrier layers formed prior to hot dip galvanization was investigated to optimize high performance protective galvanic coatings. The deposition of ZnO and Ni-P inner layers and characteristics of hotdip zinc coatings were explored in this study. The coating morphology was characterized by scanning electron microscope (SEM) analysis. The hot dip zinc coatings containing under layer showed substantial improvement in their properties such as good adhesion, and high hardness. In addition, a decrease in the thickness of the coating layer and an enhancement of the corrosion resistance were found. Open circuit potential (OCP) of different galvanized layers in different corrosive media viz. 5% NaCl and 0.5 M H₂SO₄ solutions at 25 ± 1 °C was measured as a function of time. A nobler OCP was exhibited for samples treated with ZnO and Ni than sample of pure Zn; this indicates a dissolution process followed by passivation due to the surface oxide formation. The high negative OCP can be attributed to the better alloying reaction between Zn and Fe and to the sacrificial nature of the top pure zinc layer.     

Electron-stimulated processes in boron nitride-based ceramics

The low-energy electron radiation resistance of boron nitride-based BN + Si₃N₄ and BN + SiO₂ ceramics proposed as a construction material for ion space engines was studied. It was shown that a reduced silicon phase is formed on the BN + Si₃N₄ ceramics surface in the high-temperature region (～900 K), which results from material thermal destruction. The BN + SiO₂ ceramics exhibits high thermal stability and is not prone to destruction due to electron-stimulated oxygen desorption (the cross section of this process does not exceed 10^?20 cm²). It is preferable to use such ceramics as a construction material. Based on the results obtained, some models were proposed that explain variations in the erosion rate of ceramic units of ion engines under electron and ion irradiation.     

Stress,Roughness and Reflectivity Properties of Sputter-Deposited B_4C Coatings for X-Ray Mirrors

Boron carbide(B_4C) coatings have high reflectivity and are widely used as mirrors for free-electron lasers in the x-ray range. However, B_4C coatings fabricated by direct-current magnetron sputtering show a strong compressive stress of about-3 GPa. By changing the argon gas pressure and nitrogen-argon gas mixing ratio, we are able to reduce the intrinsic stress to less than-1 GPa for a 50-nm-thick B_4C coating. It is found that the stress in a coating deposited at 10 m Torr is-0.69 GPa, the rms roughness of the coating surface is 0.53 nm, and the coating reflectivity is 88%, which is lower than those of coatings produced at lower working pressures. When the working gas contains 8% nitrogen and 92% argon, the B4 C coating shows not only-1.19 GPa stress but also a low rms roughness of 0.16 nm, and the measured reflectivity is 93% at the wavelength of 0.154 nm.     

Effects of Thickness and Temperature on Thermoelectric Properties of Bi_2Te_3-Based Thin Films

Bi_2Te_3 thin films and GeTe/B_2Te_3 superlattices of different thicknesses are prepared on the silicon dioxide substrates by magnetron sputtering technique and thermally annealed at 573 K for 30 min. Thermoelectric(TE)measurements indicate that optimal thickness and thickness ratio improve the TE performance of Bi_2Te_3 thin films and GeTe/B_2Te_3 superlattices, respectively. High TE performances with figure-of-merit(ZT) values as high as 1.32 and 1.56 are achieved at 443 K for 30 nm and 50 nm Bi_2Te_3 thin films, respectively. These ZT values are higher than those of p-type Bi_2Te_3 alloys as reported. Relatively high ZT of the GeTe/B_2Te_3 superlattices at 300-380 K were 0.62-0.76. The achieved high ZT value may be attributed to the unique nano-and microstructures of the films,which increase phonon scattering and reduce thermal conductivity. The results indicate that Bi_2Te_3-based thin films can serve as high-performance materials for applications in TE devices.     

激光聚变冲击波点火的热斑形成机制

通过对冲击波点火内爆过程的数值模拟分析点火热斑压缩及形成机制。分析了传统中心点火的内爆过程,热斑主要经历冲击波压缩和惯性压缩过程,点火主要通过惯性压缩来实现。并仔细分析了冲击波点火的内爆压缩过程,从内爆角度来看冲击波点火并不是压缩和点火分开的两步过程,点火冲击波实际参与压缩过程,点火冲击波对热斑的直接影响很有限,热斑仍然主要通过壳层的惯性压缩实现点火。利用惯性压缩的定标关系及冲击波碰撞对壳层影响规律分析了热斑增压的物理机制,冲击波点火是通过点火冲击波与回冲击波的碰撞来提高壳层的密度,从而实现热斑压力的提升。     

Microstructure and friction and wear behavior of laser boronizing composite coatings on titanium substrate

Three kinds of laser boronizing composite coatings were in situ synthesized on Ti substrate by using powders of B, BN and B₄C as starting materials. Microstructures of the laser boronizing composite coatings were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM); and their worn surface morphologies were also observed by using SEM. Moreover, the friction and wear behavior of the boronizing composite coatings under dry sliding condition were evaluated using a UMT-2MT friction and wear tester. It was found that all the three types of laser boronizing composite coatings had higher microhardness and better wear resistance than pure Ti substrate; and their microstructure and wear resistance varied with varying pre-placed powders of B, BN, and B₄C. Under the same dry sliding test conditions, the wear resistance of the three kinds of laser boronizing composite coatings, i.e., sample 1 prepared from pre-placed B, sample 2 obtained from pre-placed BN, and sample 3 fabricated from pre-placed B₄C, is ranked in an order of sample 1 > sample 2 > sample 3, which, surprisingly, well conforms to their order of hardness and friction coefficients.     

Effect of carbon addition on synthesis of BN nanolayers encapsulating Fe fine particles and BN nanotubes

Boron nitride (BN) nanolayers encapsulating iron (Fe) fine particles and BN nanotubes were synthesized by annealing mixture powders of hematite, boron and carbon (C) at 1473 K for 2 h in a nitrogen atmosphere. The particles exhibited good soft magnetic properties. The thickness of BN nanolayers increased in the range of 10-100 nm with increasing C content in the mixture powders, which results in providing improvement of oxidation resistance of the particles. In the BN layers, no C was detected. BN nanotubes with diameters of ∼100 nm were also synthesized, and they had cup-stacked and bamboo-like structures.