Experimental analysis of the stability of electrostatic bits for assisted nano-assembly

Scanning probe microscopy(SPM)-based nanolithography with injected charges into layered electrets, such as silicon dioxide (SiO₂) and silicon nitride, is a promising tool with far-reaching applications, such as controlled nano-assembly of macro-molecules and data storage. Despite its potential, some practical limitations exist. This paper describes an experimental investigation of the process of charging and charge dissipation in SiO₂ using an AFM probe tip and surface potential (Kelvin probe) microscopy. The stability of charge bits on hexamethyl disilazane(HMDS)-treated SiO₂ under low dielectric constant liquids, fluorocarbon, and benzene has been demonstrated. Results from a numerical simulation of a theoretical charging model, in which the charge traps are assumed to be localized on the silicon/SiO₂ interface, are also presented. The charge transport mechanism considered is modified Fowler–Nordheim tunneling.     

界面极化注极聚丙烯薄膜驻极体的电荷存储特性研究

本文报道一种基于双层介质界面极化机理的新型驻极体注极技术: 借助辅助层对PP薄膜进行注极. 采用表面电位测试方法考察了注极温度、注极电压对所获PP薄膜驻极体电荷存储性能的影响, 并利用热刺激放电技术研究了其高温电荷存储性能, 同时测试了PP薄膜驻极体在X和Y方向的静电场分布. 结果表明: 界面极化注极是一种比电晕注极更为优异的驻极体形成方法. 在一定温度下, 驻极体表面电位随注极电压的增加而增加, 而且两者呈线性关系, 这一结果与注极过程的电荷积聚方程的分析完全一致. 注极温度的影响研究表明, 在保持注极电压不变(注极电压范围为0.5–3.0 kV)的情况下, 温度低于75 ℃时, 温度的变化对于注极效果的影响不明显; 当注极温度大于75 ℃ 时, PP薄膜驻极体的表面电位随注极温度的增加而增加. 表面电位随时间的变化研究表明, PP薄膜驻极体具有良好的电荷存储稳定性. 对其表面电位分布的测试表明, 界面极化注极所形成的PP薄膜驻极体呈现均匀的静电场分布.     

恒流电晕充电对聚四氟乙烯多孔薄膜驻极体驻极态的影响

利用常温下恒流和恒压电晕充电、充电后的等温表面电位衰减、热刺激放电和扫描电镜等实 验手段研究了恒流和恒压电晕充电技术对聚四氟乙烯多孔薄膜驻极体驻极态的影响.与恒压电晕充电相比较，恒流电晕充电时由于流过薄膜的电流恒定，增加了注入电荷在多孔结构厚度方向界面处的俘获概率，使沉积电荷密度上升，改善了驻极体的储电能力.然而，这些位于不同层深多孔界面处的俘获电荷在这类功能膜储存或使用过程中，经外激发从脱阱位置 以跳动（hopping）模式输运至背电极的路径相对缩短将导致脱阱电荷衰减较快. 关键词： 恒流电晕充电 聚四氟乙烯多孔膜 驻极体 电荷稳定性     

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.     

Analysis on surface charging of insulator prior to flashover in vacuum

Prior to the flashover across an insulator in vacuum, the insulator surface is usually charged. It is of great importance to investigate the charging phenomena for better understanding the flashover characteristics. It is considered that there are two kinds of mechanisms closely related to the surface charging of insulator i.e., the secondary electron emission occurred over an insulator, and while employing a perfect electrode contact ahead of electron emission into vacuum, the charge injection and accumulation occurred inside the surface layer of an insulator. Based on the rigorous analysis of the kinetic processes of both primary and secondary electrons, the related surface charges were theoretically deduced. Involving the detrapping of charges trapped and the recombination of charges injected, the charging process due to charge injection and accumulation was analyzed. Some formulas were given to express the density of surface charges.     

Contact charging between surfaces of identical insulating materials in asymmetric geometries

The charging that occurs when a pair of insulating surfaces of identical chemical composition are rubbed (i.e. triboelectric charging) remains poorly understood. It is believed that asymmetry in contact plays an important role in this charging. To study this phenomenon, we have developed an experimental methodology that asymmetrically rubs two surfaces by contacting a rotating cylinder with a stationary cylinder – the rubbing is asymmetric in that the contacting area is much greater on the rotating cylinder than on the stationary cylinder. We find that the charge transfer occurs with a spatial distribution of charge, in terms of magnitude and polarity, on the contacted area. The direction of the average charge transfer is material dependent: for Teflon–Teflon contact, the surface with the larger contacting area charges positively, but for Nylon–Nylon contact the surface with the larger contacting area charges negatively. This difference is interpreted as being due to a negatively-charged species transferred in the case of Teflon (electrons or negative ions), but a positively-charged species transferred in the case of Nylon (positive ions).     

Corona charging of granular layers of insulating particles at the surface of a grounded electrode

The aim of the present paper is to introduce a simple experimental technique for estimating the corona charging conditions of insulating granules that form a layer at the surface of the grounded electrode of roll-type electrostatic separators. The basic idea consists in measuring the potential at any point on the surface of this layer by means of an electrostatic probe. The capacity of the probe–layer system being constant, the measured potential is proportional to the charge. The results clearly show that the charges imparted to the particles in the corona discharge depend on their positions at the surface of the electrode and on the inter-electrode spacing. This observation could be of use, for instance, to particle charging simulations performed as a preliminary step of any feasibility study of new electrostatic separation applications.     

Improvement of the Si-SiO2 interface stress resistance of thin gate oxides after channel ion implantation

The effect of phosphorus and boron ion implantation into silicon dioxide films is examined with regard to the resistance of the Si-SiO₂ interface under high field constant current stress conditions. Phosphorus and boron ions of various doses and energies have been implanted through a 35 nm thick oxide. The interface stress resistance is found to decrease with increasing ion dose and increase with implant energy. However, at high energies, the stress resistance of the boron implanted samples is significantly less than the phosphorus equivalents due to the creation of a second interface trap level. Post-implant annealing increases the interface stress resistance but the best performance is observed for the case of sacrificial oxidation.     

等离子体表面梯度硅沉积对环氧树脂电气性能的影响

环氧树脂作为常见的绝缘材料,在高压直流电场作用下易在其表面积累电荷,发生电场畸变,导致材料绝缘性能下降,影响电力系统运行可靠性。为改善气固界面的电荷特性和绝缘性能,在大气压等离子体射流技术的基础上,对环氧树脂表面进行等离子体梯度硅沉积处理。对改性前后环氧树脂表面理化特性、表面电导率、表面电荷消散和沿面耐压特性进行了多参数测量。实验结果表明,梯度改性对材料表面的物理形貌和化学组分均有明显影响,不同区域的电导率实现了梯度分布,加快了表面电荷消散速度,表面陷阱能级变浅;梯度改性后的样品沿面闪络电压提升幅度可达30.16%。通过等离子体表面梯度硅沉积处理能够改善环氧树脂表面电气性能,在高压直流设备的绝缘设计方面具有广阔的应用前景。     

Small-amplitude nonlinear dust acoustic wave a magnetized dustyplasma with charge fluctuation

Some properties of nonlinear dust acoustic waves in magnetized dusty plasma with variable charges by reductive perturbation technique have been studied. The effect of adiabatic dust charge variations under the assumption that the ratio of dust charging time to the dust hydrodynamical time is very small, and the nonadiabatic dust charges variations under the assumption that the same ratio is small but finite, are also incorporated. It is seen that the magnetic field and the dust charge variations significantly modify the wave amplitude. It is also seen that in case of adiabatic charge variations, the Korteweg-de Vries (KdV) equation governs the nonlinear dust acoustic wave, whereas in case of nonadiabatic dust charge variations, the wave is governed by the KdV Burger equation. Nonadiabaticity generated anomalous dissipative effect causes generation of the dust acoustic shock wave. Numerical integration of KdV Burger equation shows that the dust acoustic wave admits oscillatory (dispersion dominant) or monotone (dissipation dominant) shock solutions depending on the magnitude of the coefficient of the Burger term     

Electrically tunable resistance of a metal

Electric field-induced tuning of material properties is usually restricted to nonmetals such as semiconductors and piezoelectric ceramics. We show that variations of the electrical resistance of a metal (Pt) in the range of several percent can be reversibly induced at low charging voltages making use of a nanocrystallite-electrolyte composite. The charge-induced resistance variation is analyzed taking into account the modification of the charge carrier density and scattering rate by surface charging. The contribution arising from the charge-induced variation of the lattice constant is found to be small.     

宏观电偶极子对聚丙烯铁电驻极体膜电荷储存及其动态特性的影响

利用栅控恒压电晕充电组合反极性电晕补偿充电法，研究了孔洞(单元电畴)内分布的空间电荷型宏观电偶极子的形成，及其增长对聚丙烯孔洞膜电极化期间的电流特性及电导率的影响. 借助等温表面电位衰减测量、开路和短路热刺激放电电流谱分析等，讨论了宏观电偶极子及其密度变化时的聚丙烯孔洞驻极体膜电荷储存稳定性及电荷动态特性. 实验结果说明：由电极化形成的宏观电偶极子的自身电场提高了聚丙烯孔洞驻极体膜的电导率，从而降低了驻极体膜电荷储存的稳定性. 对呈现弱极化强度的孔洞驻极体膜，以孔洞为畴结构基本单元内的宏观电偶极子，其两性空间电荷的大部分仅仅分别沉积在透镜状孔洞上下两壁的两端. 外激发脱阱电荷从脱阱位置的输运路径，主要是绕孔洞两边沿介质层迁移；而极化强度较高的样品，其两性电荷则分别分布在上下两壁的宽广区域内，脱阱电荷的大部分在驻极体电场驱动下从脱阱位置通过孔洞层间的介质层迁移并衰减.     

介质层充电对光栅光调制器驱动的影响

利用高斯定理分析了二氧化硅层中存在电荷时,光栅光调制器中的空间电场分布,得到了光栅光调制器在介质层存贮电荷影响下的静电力公式. 分析了调制器中二氧化硅介质的充电和放电机理,得到了光栅的位移随介质充放电的变化关系. 通过分析指出当驱动电压的周期和介质的充放电时间常数相近的时候,介质层中存贮的电荷会使得可动光栅被下拉后发生缓慢的回跳. 电压被撤消后,光栅会受到存贮电荷所产生电场的作用而被下拉. 当驱动电压的周期远小于介质的充放电时间常数的时候,随着存贮电荷的增加,光栅在有外加电场时被下拉的距离和外加电场为零时被下拉的距离逐渐相等,光调制器输出光的光强变化逐渐减弱,当存贮电荷产生的电场为外加电场的一半时,器件完全失效. 通过实验对理论分析的结果进行了验证,实验结果和理论分析一致. 文章最后提出了一种消除介质层所存贮的电荷的方法,通过实验证明了这种方法的可行性. 关键词： 微机电系统 光栅光调制器 介质层充电     

Attenuation of the Electric Potential and Field in Disordered Systems

We study the electric potential and field produced by disordered distributions of charge to see why clumps of charge do not produce large potentials or fields. The question is answered by evaluating the probability distribution of the electric potential and field in a totally disordered system that is overall electroneutral. An infinite system of point charges is called totally disordered if the locations of the points and the values of the charges are random. It is called electroneutral if the mean charge is zero. In one dimension, we show that the electric field is always small, of the order of the field of a single charge, and the spatial variations in potential are what can be produced by a single charge. In two and three dimensions, the electric field in similarly disordered electroneutral systems is usually small, with small variations. Interestingly, in two and three dimensional systems, the electric potential is usually very large, even though the electric field is not: large amounts of energy are needed to put together a typical disordered configuration of charges in two and three dimensions, but not in one dimension. If the system is locally electroneutral—as well as globally electroneutral—the potential is usually small in all dimensions. The properties considered here arise from the superposition of electric fields of quasi-static distributions of charge, as in non-metallic solids or ionic solutions. These properties are found in distributions of charge far from equilibrium.     

Effect of the size of macroparticles on their electrostatic interaction in a plasma

The electrostatic interaction of two spherical macroparticles in a plasma has been considered. Primary attention has been focused on investigating the electrostatic interaction at short distances where polarization effects of the surface charge of finite-size macroparticles begin to play a dominant role. The first part of this study is devoted to the interaction of a point charge with a charged conducting sphere in an equilibrium plasma. It has been shown that the presence of a plasma in the system leads to a decrease in the potential barrier when two like-charged macroparticles approach each other and that this decrease proves to be the most significant in the case where the macroparticle radius is comparable to the Debye screening length. The second part of this study is concerned with the interaction of two conducting spheres in the bispherical system of the coordinates under the assumption that the charges of the conducting spheres are constant and under the assumption that the surface potentials of the spheres are constant. The latter case is closer to the physics of electrostatic interaction of two macroparticles in a plasma medium where the electrostatic potential of their surface is determined by the floating potential of the plasma. It has been demonstrated that the interaction potentials in these two cases are substantially different from each other and that, at constant macroparticle charges, the energy of the electrostatic field is an interaction potential, but, in the case of macroparticles with constant surface potentials, which are independent of the interparticle distance, the energy of the electrostatic field is not an interaction potential. In the latter case, account must be taken of the work done by external sources on the macroparticle potentials to maintain them constant. The form of the interaction potential has been established in this case from the analysis of the interaction force in terms of the Maxwell tension tensor. In the third part of this study, the interaction of two macroparticles has been considered in the spherical system of coordinates and analytical expressions for the interaction potentials have been derived for both the case of constant macroparticle charges and the case of constant surface potentials of the macroparticles.     

First-principles calculation of contact electrification and validation by experiment

Contact electrification is one of the most well-known phenomena in physics and examples arise in almost every industry. However, a scientific basis for contact charging remains unknown. Here, we present a theoretical study of contact electrification, supported by experiments, to calculate for the first time charge transfer between material surfaces from first principles physics. Electronic structure calculations and experiments are performed on single-crystal alumina (sapphire) and silicon oxide (quartz) surfaces, which have well-ordered structures that enable rigorous modeling. Both experiments and calculations show that sapphire charges positively and quartz charges negatively. The calculations cannot determine the magnitude of charge densities remaining on separated surfaces from first principles, as these are non-equilibrium effects, but our analysis is consistent with experimentally obtained charge densities of 10 μC/m². These results indicate the possibility of quantitatively predicting and explaining contact electrification from only the molecular structure of material surfaces.     

孔洞聚丙烯驻极体膜中空间电荷与孔洞击穿电荷的俘获特性

对孔洞聚丙烯(PP)驻极体膜系统的研究结果表明：孔洞PP膜中空间电荷的俘获特性随注入的空间电荷量或试样表面电位而变化,注入的电荷量较少时空间电荷主要被俘获在表面深陷阱和近表面次深陷阱中,较多的注入电荷量时空间电荷在进一步填充表层(表面和近表面)陷阱的同时,还将填充体内浅陷阱;这三类陷阱中心所对应的电荷脱阱温度分别约为160℃,138℃和92℃.而孔洞击穿电荷不仅被俘获在与试样表层空间电荷陷阱相似的孔洞表层陷阱中,还有相当的量穿过孔洞表层进入体内、成为浅阱俘获孔洞击穿电荷. 关键词： 孔洞聚丙烯膜 空间电荷 孔洞击穿电荷 俘获特性     

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.     

Characteristics of Au/n-Si surface barrier nuclear radiation detectors with a nanometer native oxide layer

The effect of a surface charge on the characteristics of silicon surface barrier detectors with a nanometer oxide layer is studied. Interaction between the surface charge and a metal or a semiconductor at an oxide layer thickness of less than 1 or more than 2 nm, respectively, is taken into account. The application of silicon detectors with an oxide layer having a thickness of more than 2 nm in detecting nuclear resonance reactions is considered.     

Effect of ground electrode on charge injection and surface potential of corona charged polyethylene film

The surface potential decay measurement is a simple and low cost tool to assess electrical properties of insulation materials; therefore, understanding the physical mechanisms of the surface potential decay becomes necessary. With our recent space charge measurement results on corona charged samples, bipolar charge injection on corona charged samples had been observed. Based on this new fact, it is anticipated that the ground electrode should have significant effect during corona charging and subsequently decay processes. In the paper, low density polyethylene (LDPE) film with gold ground electrode was compared with LDPE film with aluminium ground to study effect of ground electrode on charge injection and surface potential decay processes. Charging current during the corona charging, surface potential decay and space charge dynamics after corona charging in the samples with either gold coated or aluminium ground electrode were measured. Differences have been observed for gold ground electrode when compared with aluminium ground electrode. Higher work function of gold electrode is responsible for the observed differences. A preliminary simulation has also attempted to show that the bipolar injection may take place in corona charged LDPE films.