正带电绝缘膜发射的二次电子的轨迹与返回特性

绝缘膜正带电现象在集成电路芯片低能电子束检测方面具有可以利用的前景。采用简化的表面电位分布模型，通过数值方法计算了二次电子从正带电绝缘膜表面发射后的运动轨迹，分析了初始条件和电位分布形态对轨迹特性的影响。在轨迹计算和考虑二次电子发射概率分布的基础上得到了二次电子受局部电场作用而返回表面时的最大初始动能、分布规律，提出了通过简单的一维势垒模型来确定二次电子返回率的方法，为分析电子束照射绝缘膜时正带电效应所产生的二次电子信号衬度现象奠定了基础。     

空间材料二次电子发射过程的理论研究

航天器充放电效应故障大多都会引起卫星灾难性事故,对航天器在轨安全运行产生较大的影响。空间材料的二次电子发射系数是决定卫星表面带电速率和充电平衡电位水平的重要材料特征参数,对于卫星表面带电的预测及卫星带电设计选材具有重要的意义。基于蒙特卡洛方法,从理论上分析了材料二次电子的产生、转移及逃逸过程,获得了材料二次电子发射系数的计算方法。实验结果表明该方法能较好地拟合材料二次电子发射系数随入射电子能量的变化趋势,为航天器充放电效应数值模拟和防护设计提供数据支持。     

航天器表面材料二次电子发射特性研究

航天器在轨表面入射离子、电子产生的二次发射电子流随二次电子发射系数的变化而变化,通过建模仿真对二次电子发射系数对充电电流、充电电位的影响进行验证。通过对航天器用表面材料ITO(Indium tin oxide,氧化铟锡)膜二次发射电子系数测试,测试结果与标准参数基本一致;测试结果表明,二次电子发射系数与材料厚度相关,且随着材料厚度的增加二次电子发射系数减小,因此可以通过改变航天器表面材料厚度的方式影响表面材料的二次电子发射系数,从而控制航天器表面材料的带电状态。     

介质材料带电对二次电子发射影响的研究

航天器充放电效应故障大多都会引起卫星灾难性事故,对航天器在轨安全运行产生较大的影响。二次电子发射系数是决定卫星表面带电速率和充电平衡电位水平的重要材料特征参数。研究介质材料表面带电对二次电子发射影响的理论模型,分析表面正电位激发和负电位阻挡效应,并给出计算结果,为航天器充放电效应数值模拟和防护设计提供数据支持。     

二次电子发射测试设备

材料的二次电子发射现象是1899年科学家坎贝尔发现的,至今已有80多年的历史了。二次发射现象在工业生产和科学研究上有重要的应用,在许多电子器件和仪器中都利用了这一现象,如在电子倍增器,磁控管,和存贮管中,以及在扫描电镜,电子束焊机中。但是,如果对二次发射现象处理不当,就会引起表面带电,甚至造成电击穿。如在高压电真空器件中的击穿、卫星表面的带电击穿等,造成严重的后果。因此,几十年来对二次电子发射的研     

SMILE卫星表面电位特性分析

SMILE卫星在轨科学探测为大倾角椭圆轨道,在轨将遭遇多种等离子体环境,卫星表面带电状态将影响卫星在轨安全性和科学探测任务。在有限元建模的基础上,利用SPIS(Spacecraft Plasma Interaction System)软件仿真和评估了SMILE卫星在轨表面带电特性。仿真结果显示,卫星在不同环境下的表面充电电位存在差异,但不会影响科学载荷的数据获取。通过分析各种等离子体环境下充电电流,发现二次电子发射电流和光照区光电流对卫星表面充电起主导作用。卫星表面ITO膜阻值对卫星电位产生影响。     

抑制二次电子发射方法的研究

电介质和金属表面被激发出来的二次电子(Secondary electron emission,SEE)可以显著地改变该表面附近的电势分布和通量.在一些情况下,如电子束焊机、扫描电子显微镜、透射式电子显微镜、电子衍射仪、俄歇电子能谱仪、电子倍增管等应用中,二次电子的次级倍增效应得到很好的应用.然而在另一些情况下,例如射频放大器、粒子加速器和霍尔推进器、电子真空管、空间宇宙飞行器表面等应用中,二次电子会对仪器产生不利的影响.因此,抑制二次电子发射及研究减少二次电子产额(Secondary electron yield,SEY)是非常有意义的.现有的抑制二次电子发射的研究方法有外加偏置场法和表面处理法,其中通过外加电场或磁场来抑制二次电子的激发会对入射束流、束斑产生不利影响,因此表面处理法更具优势.表面处理法主要分为三类:表面陷阱构造(矩形以及三角形的凹槽、微孔结构、纤维结构、泡沫结构等)、表面镀膜(石墨烯膜、TiN膜等)、表面束流处理(激光刻蚀、磁控溅射法).这些抑制二次电子激发的方法主要为了达到两个目的,一是减少物体表面的真二次电子的发射,二是捕获发射的二次电子,使之不能逃逸.本文总结了一些抑制二次电子激发的方法,比较不同方法或不同影响因素对二次电子的影响.     

高效消除色差的扫描电子显微镜——Magellan

扫描电子显微镜是1965年发明的先进的显微结构研究工具,主要是利用二次电子信号成像来观察样品的表面形态,即用极狭窄的电子束去扫描样黼,通过电子束与样品的相互作用产生各种效应,其中主要是样品的二次电子发射。二次电子能够产生样品表面放大的形貌像,这个像是在样品被扫描时按时序建立起来的,即使用逐点成像的方法获得放大像。     

磁敏弹性体微结构扫描电镜表征原理剖析及前处理方法优化

对试样液氮脆断后进行扫描电镜观察是研究材料微观结构的常用方法,但应用于磁性羟基铁粉填充的磁敏弹性体试样时,却很难获得理想效果。通过对橡胶高分子结晶现象和低温脆断理论的分析,揭示脆断截面无法形成裸露的羟基铁粉链的机理;提出机械切割和抛光相结合的截面处理方法,得到的样品截面可满足扫描电镜对磁敏弹性体表面微结构的表征要求。通过对扫描电镜工作原理和成像理论的分析,阐述磁性材料产生的杂散磁场与扫描电镜磁透镜的磁场、入射电子束、收集器电压产生的耦合作用。这种耦合作用使在样品表面按一定时间和空间顺序做光栅式逐点扫描的入射电子束发生畸变,改变磁敏弹性体发射的二次电子的运行轨迹,使二次电子收集器收集效果变弱,降低图像质量。根据绝缘电阻测试得到不同体积分数羟基铁粉的磁敏弹性体的电导率,确定金属离子真空溅射和粘贴导电胶的试样处理方法。提出磁敏弹性体样品的退磁方案,并得到理想的微观形貌图像。     

空间材料二次电子发射特性测试

空间材料的二次电子发射系数是表征航天器表面充电状态的重要参数 ,对于卫星表面带电的预测及卫星防带电设计选材具有重要的作用。为了测量空间材料二次电子发射特性 ,研制了专门的测试装置。介绍了该实验装置的主要结构、性能及技术指标等 ,通过应用计算机数据采集系统 ,并研制专门的数据处理软件 ,提高了装置的自动测量能力。实验说明 ,该装置用于空间材料的二次电子发射特性测试中测量方便、准确     

Directly created electrostatic micro-domains on hydroxyapatite: probing with a Kelvin Force probe and a protein

Micro-domains of modified surface potential (SP) were created on hydroxyapatite films by direct patterning by mid-energy focused electron beam, typically available as a microprobe of Scanning Electron Microscopes. The SP distribution of these patterns has been studied on sub-micrometer scale by the Kelvin Probe Force Microscopy method as well as lysozyme adsorption. Since the lysozyme is positively charged at physiological pH, it allows us to track positively and negatively charged areas of the SP patterns. Distribution of the adsorbed proteins over the domains was in good agreement with the observed SP patterns.     

Initial adhesion and surface growth of Pseudomonas aeruginosa on negatively and positively charged poly(methacrylates)

The infection risk of biomaterial implants is determined by an interplay of bacterial adhesion and surface growth of the adhering organisms. In this study, we compared initial adhesion and surface growth of Pseudomonas aeruginosa AK1 (zeta potential –7 mV) on negatively charged (PMMA/MAA, zeta potential –18 mV) and positively charged (PMMA/TMAEMA-Cl, zeta-potential +12 mV) methacrylate copolymers in situ in a parallel plate flow chamber. Initial adhesion was measured using phosphate-buffered saline and subsequent surface growth of the adhering bacteria using nutrient broth as growth medium. Initial adhesion was twice as fast on the positively charged methacrylate than on the negatively charged copolymer. Surface growth, however, was absent on the positively charged copolymer, while on the negatively charged methacrylate the number of bacteria increased exponentially during surface growth with a generation time of 32 min. From the results of this study it can be concluded that positively charged biomaterial surfaces might show reduced risks of biomaterials-centred infections, despite being more adhesive.     

Effects of secondary electron emission from a floating surface on the plasma sheath

The paper describes the region between a Maxwellian plasma source and a floating surface by a 1D-3 V fully kinetic, electrostatic particle simulation. The electric field is self-consistently computed from the Poisson equation. The secondary electron emission is modelled by considering an expression for the secondary emission coefficient dependent on the primary electron energy and surface materials and a realistic secondary electron distribution function is introduced at the collector surface. The model is able to simulate the space-charge-limited conditions as well as the positively charged wall cases.     

Preparation of tin oxide gels with versatile pore structures

Hydrous tin oxide gels were subjected to consecutive solvent-evaporation (SE) and CO₂ supercritical (CS) drying steps, followed by re-hydration at low (30%) humidity, and the effects on pore structure of the SE drying duration and particle surface potential of the gel were investigated. The difference in surface potential has been found to impose significant variations in initial pore size distribution, while the SE drying step tends to narrow such differences and simultaneously reduce the mean pore size. It is demonstrated that varieties of pore structures have thus been obtained by simply varying these two parameters.     

FFEA电场及电子轨迹模拟讨论

采用有限差分法 ,对有聚焦极的垂直双门结构的场发射阵列进行了轴对称三维模拟计算 ,得到发射微尖附近的电位和电子轨迹分布图。分别讨论了聚焦极电位、聚焦极孔径以及栅极电位对发射电子束的影响。聚焦极电位相对栅极越负 ,聚焦作用越强。减小聚焦极孔径对大发散角的电子有影响 ,但对聚焦作用的影响不如改变电位明显。栅极电位基本上不影响电子的轨迹 ,仅改变了发射电子的多少。以上结论与实验基本一致     

纳米氧化镁表面修饰制备荷正电微孔陶瓷膜及其性能研究

以硅藻土陶瓷膜为基膜,氯化镁和尿素为原料合成含镁先驱体溶胶,通过浸渍-热分解法对硅藻土基膜进行表面改性制得纳米MgO/SiO_2荷正电微孔陶瓷膜,并对其组成结构及水中四环素去除性能进行研究。结果表明,荷正电的纳米MgO涂层呈现立方型晶粒,并均匀地附着在基膜表面,因此使得荷正电微孔陶瓷膜具有较高的电性能,并且在较宽的pH值范围内带正电,其等电点为10.8。最后对水中四环素的去除性能进行研究,结果表明荷正电微孔陶瓷膜对水中四环素具有很好的去除效果,在室温、常压条件下,其对四环素的COD去除率高达98.8%,色度去除率为99.7%。     

The role of surface charge on the uptake and biocompatibility of hydroxyapatite nanoparticles with osteoblast cells

The objective of this study is to evaluate the effect of hydroxyapatite (HAP) nanoparticles with different surface charges on the cellular uptake behavior and in vitro cell viability and proliferation of MC3T3-E1 cell lines (osteoblast). The nanoparticles' surface charge was varied by surface modification with two carboxylic acids: 12-aminododecanoic acid (positive) and dodecanedioic acid (negative). The untreated HAP nanoparticles and dodecanoic acid modified HAP nanoparticles (neutral) were used as the control. X-ray diffraction (XRD) revealed that surface modifications by the three carboxylic acids did not change the crystal structure of HAP nanoparticles; Fourier transform infrared spectroscopy (FT-IR) confirmed the adsorption and binding of the carboxylic acids on the HAP nanoparticles' surfaces; and zeta potential measurement confirmed that the chemicals successfully modified the surface charge of HAP nanoparticles in water based solution. Transmission electron microscopy (TEM) images showed that positively charged, negatively charged and untreated HAP nanoparticles, with similar size and shape, all penetrated into the cells and cells had more uptake of HAP nanoparticles with positive charge compared to those with negative charge, which might be attributed to the attractive or repulsive interaction between the negatively charged cell membrane and positively/negatively charged HAP nanoparticles. The neutral HAP nanoparticles could not penetrate the cell membrane due to their larger size. MTT assay and LDH assay results indicated that as compared with the polystyrene control, greater cell viability and cell proliferation were measured on MC3T3-E1 cells treated with the three kinds of HAP nanoparticles (neutral, positive, and untreated), among which positively charged HAP nanoparticles showed the strongest improvement for cell viability and cell proliferation. In summary, the surface charge of HAP nanoparticles can be modified to influence the cellular uptake of HAP nanoparticles and the different uptake also influences the behavior of cells. These in vitro results may also provide useful information for investigations of HAP nanoparticle applications in gene delivery and intracellular drug delivery.     

The shock wave structure in a dense electronegative gas containing conductive particles

The structure of a flat shock wave in an electronegative gas containing a rarified suspension of small metallic particles (macroparticles) is considered. When heated due to thermal electron emission, the particles are ionized in the shock compression that occurs in the carrying gas. The emitted electrons adhere to the electronegative neutral molecules, which gives rise to the formation of a multicomponent gas mixture composed of ions, electrons, neutrals, and positively charged macroparticles. The profiles of the corresponding variables are calculated within the Navier-Stokes approximation. The reaction of sticking is analyzed with the use of chemical kinetics equations. The calculations were performed for the case of air, which assumed by binary mixture of molecules O₂ and N₂. The initial temperature and the Mach number of the oncoming flow are T = 500 K and M = 3.     

Development and surface characterization of positively charged filters

Filter media, which have been surface charge modified by modifiers with positive functional groups, are termed positively charged filters. The main aim of the present work was to manufacture positively charged filters for capturing negatively charged particles, mainly bacteria and virus from water. Filters were manufactured with varying ratios of base materials, processing conditions and charge modifiers. Experimental parameters were varied in order to attain filters with a high zeta potential to increase the filtration efficiency. A positive zeta potential of 42.56 mV has been attained with a charge modifier percentage of 100%, a stirring time of 30 minu., vacuum pressure of 15 cm Hg. Statistical analysis was performed to find the most significant parameter for positive charge modification.     

Development of docetaxel nanocapsules for improving in vitro cytotoxicity and cellular uptake in MCF-7 cells

The aim of this study was to fabricate docetaxel loaded nanocapsules (DTX-NCs) with a high payload using Layer-by-Layer (LbL) technique by successive coating with alternate layers of oppositely charged polyelectrolytes. Developed nanocapsules (NCs) were characterized in terms of morphology, particle size distribution, zeta potential (ζ-potential), entrapment efficiency and in vitro release. The morphological characteristics of the NCs were assessed using transmission electron microscopy (TEM) that revealed coating of polyelectrolytes around the surface of particles. The developed NCs successfully attained a submicron particle size while the ζ-potential of optimized NCs alternated between (+) 34.64?±?1.5 mV to (?) 33.25?±?2.1 mV with each coating step. The non-hemolytic potential of the NCs indicated the suitability of the developed formulation for intravenous administration. A comparative study indicated that the cytotoxicity of positively charged NCs (F4) was significant higher (p?in vitro on MCF-7 cells. Furthermore, cell uptake studies evidenced a higher uptake of positive NCs (≥1.2 fold) in comparison to negative NCs. In conclusion, formulated NCs are an ideal vehicle for passive targeting of drugs to tumor cells that may result in improved efficacy and reduced toxicity of encapsulated drug moiety.