基于平均二次电子发射系数的航天器表面起电特征分析

为了进一步贴近航天器表面起电环境以得到更加可信的分析结果,针对航天器在恶劣充电环境下的表面起电问题,考虑空间等离子体双麦克斯韦分布情况,建立了基于平均二次电子发射系数的航天器表面起电阈值方程,可在入射电子能量连续分布情况下定量分析航天器表面起电特征,其中双麦分布可更好地描述磁层亚爆期间的恶劣充电环境。经过理论分析,归纳出双麦分布下的两种典型等离子体状态。通过仿真计算,得到了在两种典型等离子体状态下航天器表面电位随等离子体浓度和温度变化的特征。结果表明:电子温度越高,表面负带电电位越高,充电越严重,与此同时,双麦分布下等离子体两种电子组分的浓度比值对带电结果有重要影响。     

Study of temperature effects on the conduction and trapping of charges in the alkali-silicate glass under electron beam irradiation

A scanning electron microscope (SEM) is employed to investigate the temperature effect on the charging behaviour of alkali-silicate glasses under electron beam irradiation using electrostatic influence method (EIM). A modified special arrangement adapted to the SEM allows to study charging mechanisms and charge transport characteristics of these glasses using the simultaneous measurement of displacement and leakage currents. The trapping process during continuous electron irradiation can be directly determined by the EIM. The experimental results reveal that the charging ability of glasses decreases with increasing temperature. The variation of charge process has been confirmed by measuring the surface potential in response to the sample temperature. In this report, we introduce also the secondary electron emission (SEE) yield. It was found the strong dependence of the SEE yield on the temperature variation. The higher is the temperature and the lower is the SEE yield. The trapping ability is analyzed taking into account the regulation mechanisms involved under electron irradiation.     

月表尘埃颗粒带电的机理及应用研究

研究月尘颗粒在电子束环境下以及紫外源辐照下的带电机理,利用数值方法模拟月尘颗粒在不同背景环境下的充电过程,以探索月表尘埃颗粒的带电机理,进而便于地面月尘环境模拟装置选择合适的月尘带电方式进行空间模拟实验.给出了尘埃在电子束环境下的充电方程,并将紫外辐射带电与具体应用相结合.通过模拟结果可知,在电子束环境下,月尘表面的电荷数随粒径尺寸增大,随电子枪辐照束斑半径减少,随电子枪流强的增加而增多;在紫外源的辐照下,月尘表面电荷数随颗粒尺寸的增大以及紫外线辐照度的增加而增多.由月尘颗粒受太阳紫外辐照带电的数值模拟结果可知,月尘需要在太阳长时间的辐照下才可以带上可观的电荷数,地面模拟该过程需增加辐照源来加速实验.通过模拟结果的分析比较并结合"空间环境模拟装置"中对月尘舱的设计要求,最终优选紫外源辐照带电方式作为月尘颗粒的带电方案.     

About the charging effect in X-ray photoelectron spectrometry

Investigations of X-ray photoelectron spectra from electrically nonconductive samples need corrections for the charging effect. This effect is qualitatively well established in the literature but has not been analyzed systematically up to now. Three main contributions determine the resulting mean charging potential at the sample surface: electron emission from the sample, electrons impinging on the sample from the X-ray tube window, and finally electron conduction in the sample surface.     

Effect of the incident electron fluence on the electron emission yield of polycrystalline Al2O3

The electron emission yield due to electron impact on polycrystalline Al₂O₃ is measured with a technique based on the use of a Kelvin probe (KP method) and a pulsed electron beam. The KP method allows the clear discrimination between the external effects of charging and internal ones. The effect of the incident electron fluence on the yield in the region where the yield is higher than one is investigated. An overall drop of the electron emission yield with increasing the electron fluence is observed. This result is clearly associated to the internal effects of positive charging. Indeed, the recombination of the generated secondary electrons with the accumulated holes beneath the irradiated surface leads to the decrease of their mean free path and to the decay of the secondary electron emission yield.     

Computer simulation of charging the silicon dioxide surface and subsurface layers by electron bombardment

A physical model and program of calculating the parameters of charging dielectrics by electron bombardment is described. A method of computer simulation is used to investigate the main processes of charging the subsurface silicon dioxide layers. Dependences of the current density, volume charge density, and electric field strength on the material layer depth are calculated for variable electron beam parameters, irradiation time, and grid potential near the sample surface.     

Backscattered electron imaging for reduced charging of moisturized corn starch granules: implications for versatile imagery of hygroscopic powder specimens

Charging artifacts and surface features of corn starch granules were investigated by scanning electron microscopy. Three types of industrial waxy corn starch granules with different levels of moisture content (0, 10.3, and 24.2%) were prepared and subjected to both secondary electron imaging and backscattered electron imaging. There were no significant charging artifacts in secondary electron images at 3 or 5 kV. However, imaging at higher magnifications and accelerating voltages much lower than 3 kV ranging from 0.1 to 1 kV did not show well-resolved structures. At higher accelerating voltages than 5 kV, charging was manifested as excessive brightness at specific areas and alteration of bright and dark lines in the direction of the raster pattern in secondary electron images of all the types of specimens tested. As the accelerating voltage increased up to 30 kV in secondary electron images, the charging also increased. Meanwhile, no charging was detected in all the backscattered electron images taken at different accelerating voltages. As the accelerating voltage increased in backscattered electron images, the resolution increased with less depth of focus. Consistent results were found in all the types of corn starch granules assayed in this study. These results suggest that a simple and rapid morphological analysis of moisturized starches can be performed by backscattered electron imaging without considerable heat drying of starches. Concomitantly, it allows for imposing a higher accelerating voltage to ensure better image resolution, facilitating morphological characterization of diverse starch granules as they are in native states.     

双麦克斯韦分布尘埃等离子体中尘埃粒子的充电研究

根据充电方程和电荷守恒条件,导出了双麦克斯韦分布的弱电离尘埃等离子体充电频率(电荷弛豫速率),给出了充电电流的计算公式. 对结果分析表明,定向运动速度大小对充电电流和充电频率有一定的影响,充电频率随着定向速度增加而减小,当定向速度远远小于电子的热速度时,充电频率与文献给出的表达式一致. 关键词： 尘埃等离子体 双麦克斯韦分布 充电频率     

Frequency-dependent C(V) spectroscopy of the hole system in InAs quantum dots

The hole system in InAs quantum dots was investigated by frequency-dependent capacitance–voltage spectroscopy. Up to eight distinct charging peaks could be observed and the energy difference between the individual peaks could be estimated. All charging peaks decrease with increasing measurement frequency; however, the lower the energy of the hole level the stronger the decrease. A comparison with the results of the electron system in similar quantum dots yields that for all hole levels the effective mass in the barrier is much larger than in the electron system.     

Analysis of microscopic parameters of surface charging in polymer caused by defocused electron beam irradiation

The relationship between microscopic parameters and polymer charging caused by defocused electron beam irradiation is investigated using a dynamic scattering-transport model. The dynamic charging process of an irradiated polymer using a defocused 30 keV electron beam is conducted. In this study, the space charge distribution with a 30 keV non-penetrating e-beam is negative and supported by some existing experimental data. The internal potential is negative, but relatively high near the surface, and it decreases to a maximum negative value at z = 6 μm and finally tend to 0 at the bottom of film. The leakage current and the surface potential behave similarly, and the secondary electron and leakage currents follow the charging equilibrium condition. The surface potential decreases with increasing beam current density, trap concentration, capture cross section, film thickness and electron–hole recombination rate, but with decreasing electron mobility and electron energy. The total charge density increases with increasing beam current density, trap concentration, capture cross section, film thickness and electron–hole recombination rate, but with decreasing electron mobility and electron energy. This study shows a comprehensive analysis of microscopic factors of surface charging characteristics in an electron-based surface microscopy and analysis.     

Quantum energy and charging energy in point contact MOSFETs acting as single electron transistors

The charging energy and quantum energy in silicon single electron transistors have been investigated. The devices were fabricated in the form of point contact MOSFETs, some of which show the Coulomb blockade oscillations at room temperature. The charging energy and quantum energy were derived by fitting the simulation results to the experimental data. It was clearly found that the quantum energy became comparable with the charging energy when the dot size is smaller than 10–20 nm and the charging energy is more than 20 meV. These results indicate that the quantum effects should be taken into account even in silicon devices when silicon single electron transistors or MOSFETs smaller than about 20 nm are designed.     

Physical and mathematical modeling of the electron-beam-induced charging of ferroelectrics during the process of domain-structure switching

The results of modeling the dynamic charging processes that arise when ferroelectrics are under the action of an electron beam in a scanning electron microscope are presented. Implementation of the model is based on simultaneous solution of the continuity equation and Poisson equation with allowance for the radiation-stimulated intrinsic conductivity of the irradiated sample and with an initial charge distribution determined using the Monte Carlo method. The multidimensional boundary evolutionary problem is solved using grid methods. The model permits one to study the dynamics of the process of the electron-beam-induced charging of ferroelectrics. Estimates for the values of fields generated by charges accumulated during the irradiation process are presented for a set of modeling parameters corresponding to physical data obtained in experimental observations of the polarization switch for a ferroelectric lithium niobate crystal.     

Methodological aspects of the electron-beam investigation of dielectric target charging

The basic characteristics of dielectric target charging with (2–30)-keV electron beams were investigated using the example of a typical insulator, Al₂O₃. A new hypothetical scenario of dielectric charging, based on the reduction of secondary-electron current due to the formation of polarized excitons in the positive layer of a charged target, is proposed on the basis of modeling calculations and the experimental data.     

Internal charging: a preliminary environmental specification forsatellites

Internal charging has been indicated as the cause of many satellite anomalies. In some cases, it has been argued that internal charging has caused satellite system failures. It may be possible to predict the occurrence of an internal charging threat in the future but that does not remove the necessity to know what the environmental threat may be. The existence, for many years now, of energetic electron and internal charging measurements in the inner magnetosphere provides the ability to identify the threat levels and generate internal charging specifications. The specifications must embody the worst-case environments that can be expected from magnetic storms and extreme solar/interplanetary conditions. Internal-charging environment specifications are needed by satellite manufacturers for setting design requirements for their systems. The specifications are also required for defining the worst-case energetic electron flux levels and total fluence levels from events. These are used for electron beam testing to verify that critical systems are immune to internal charging, for performing tests on subsystems, and for use in anomaly investigation programs. Data from the GOES, LANL, and CRRES satellites were used to develop preliminary internal-charging environment specifications for some commonly used orbits such as geosynchronous and Molniya or high earth orbits (HEO), and they are discussed. A specification is also given for a highly elliptical equatorial orbit that is used for lunar-transfer orbital maneuvers. The preliminary environments were used to estimate the shielding required to reduce worst-case electron fluxes to safe levels for these orbits     

Transport properties of surface acoustic wave based single electron transport device in the presence of an impurity potential

We report the transport properties of a surface acoustic wave based single electron transport device, which contains an unintentional quantum dot induced by background impurity potential fluctuations. It is found that the presence of the impurity potential can cause a deviation of the acoustoelectric current from its quantized value. Through the charging effect of the quantum dot induced by the impurity, we get an approximate relationship between the applied gate voltage and its corresponding electrostatic potential barrier height, together with the Coulomb charging energy needed to add a second electron into the dynamic quantum dot. Moreover, the amplitude of the surface acoustic wave is also estimated within a simple model.     

Model study of electron beam charge compensation for positive secondary ion mass spectrometry using a positive primary ion beam

A new modeling approach has been developed to assist in the SIMS analysis of insulating samples. This approach provides information on the charging phenomena occurring when electron and positive primary ion beams impact a low conductivity material held at a high positive potential. The concept of effective leakage resistance aids in the understanding of the dynamic electrical properties of an insulating sample under dynamic analysis conditions. Modeling of steady state electron beam charge compensation involves investigation of electron injection and charge drift. Using a Monte Carlo program to simulate electron injection and dc conduction calculations to predict charge drift, detailed information regarding charging phenomena can be determined.     

The analysis of the charge on a cylindrical dielectric particle in unipolar corona field

In this study, a nonlinear integro-differential equation is derived to express the charging kinetics of stationary and rotational cylindrical dielectric particle in unipolar corona field. An algorithm is developed to solve the derived equation numerically by using Euler method. The variation of charge on the dielectric cylindrical particle is presented and evaluated by considering the variable parameters of the particle, medium and field. Assessments of the numerical results demonstrate that the limit charge value on stationary cylindrical dielectric particle during the charging process in unipolar corona field is less in comparison with the rotational cylindrical particle in identical conditions. Also this is an important factor for electron–ion technology in the aspect of charging kinetic problems.     

Electron emission and charging of natural diamond under irradiation with medium-energy electrons

The processes of charging of a natural diamond crystal irradiated by an electron beam with primary electron energies in the range 1–30 keV have been experimentally investigated. The charging kinetics has been studied as a function of the irradiation dose and the electron-emission properties of the crystal. The following fundamental characteristics have been determined: the second crossover equilibrium energy of the beam electrons and the values of high-voltage surface potentials and accumulated charges.     

Some aspects of the polymers' electrostatic charging effects

The electrical charging of polymers is widely known and applied in many technical processes. However, the molecular and electronic reasons for this phenomenon are not fully understood. We will show that the electrical charging of polymers can be fundamentally described by their electron pair acceptor and donator properties. But polymer charging cannot only discuss on an electronic or molecular level, because during the contact of two polymer particles an enormous number of molecules of similar chemical structure coming into contact and super-molecular effects cause a charge formation. Special AFM techniques showed that oppositely charged domains can be stable side by side. Furthermore, it will be shown that the external conditions, especially the water content of the polymer and the surrounding atmosphere, have an important influence on the charge stability.     

非聚焦电子束照射SiO2薄膜带电效应

采用考虑电子散射、俘获、输运和自洽场的三维数值模型, 模拟了低能非聚焦电子束照射接地SiO₂薄膜的带电效应. 结果表明, 由于电子的迁移和扩散, 电子会渡越散射区域产生负空间电荷分布. 空间电荷呈现在散射区域内为正, 区域外为负的交替分布特性. 对于薄膜负带电, 电子会输运至导电衬底形成泄漏电流, 其暂态过程随泄漏电流的增加趋于平衡. 而正带电暂态过程随返回二次电子的增多而趋于平衡. 在平衡态时, 负带电表面电位随薄膜厚度、陷阱密度的增大而降低, 随电子迁移率、薄膜介电常数的增大而升高;而正带电表面电位受它们影响较小.