Stark spectroscopy of a probe lithium beam excited with two dye lasers as a technique to study a high-power ion-beam diode

A non-disturbing measurement of electric field distributions is a subject of special interest in plasma physics and high-voltage devices. In this paper we describe a diagnostic technique for remote sensing of electric fields via injection of a probe beam of lithium atoms and cascade excitation of resonance fluorescence with two broadband dye lasers. The fluorescence spectrum was recorded using a monochromator equipped with an optical multi-channel analyser. The magnitude of the local electric field was retrieved from the Stark-shifted components of the 3d-2p lithium spectral line. The technique was applied to measurements of the electric field in the applied-B-field high-voltage diode of the 1 TW KALIF ion-beam accelerator.     

Differential phase contrast (DPC) mapping electric fields: Optimising experimental conditions

DPC in Scanning Transmission Electron Microscopy (STEM) is a valuable method for mapping the electric fields in semiconductor materials. However, optimising the experimental conditions can be challenging. In this paper, we test and compare critical experimental parameters, including the convergence angle, camera length, acceleration voltage, sample configuration, and orientation using a four-quadrant segmented detector and a Si specimen containing layers of different As concentrations. The DPC measurements show a roughly linear correlation with the estimated electric fields, until the field gets close to the detection limitation, which is ∼0.5 mV/nm with a sample thickness of ∼145 nm. These results can help inform which technique to use for different user cases: When the electric field at a planar junction is above ∼0.5 mV/nm, DPC with a segmented detector is practical for electric field mapping. With a planar junction, the DPC signal-to-noise ratio can be increased by increasing the specimen thickness. However, for semiconductor devices with electric fields smaller than ∼0.5 mV/nm, or for devices containing curved junctions, DPC is unreliable and techniques with higher sensitivity will need to be explored, such as 4D STEM using a pixelated detector.     

场发射俄歇电子能谱显微分析

场发射俄歇电子能谱的显微分析是一项新的分析技术,可对微尺度样品进行点、线、面的元素组分及元素化学态分析。本文简要介绍这项新技术的功能原理和在微电子器件检测等方面的具体应用。     

外加电场制备CdS纳米线阵列、纳米带和纳米管

在外加电场的条件下利用物理热蒸发法成功制备出CdS纳米线阵列、纳米带和纳米管,纳米线阵列沿平行于电场方向生长。借助SEM、EDX和TEM以及XRD,研究了外加电场对CdS纳米线生长的影响。结果表明：外加电场大大促进了CdS纳米线定向排列生长;但是,低温区获得的CdS纳米带和纳米管没有任何方向性。     

Improvements to differential voltage contrast and light and electron scanning beam analysis of solar cells

Differential voltage contrast (DVC) in conjunction with light and electron beam scanning (LEBEAMS) technique were used for measuring the electric potential, field, and charge distribution in solar cells. The DVC is based on enhancement or retardation of secondary electron emission, generated by an electron beam, due to local changes in the potential of a semiconductor device. The information provided by this technique is invaluable to the development of any device. Solar cells have been studied by the DVC technique, both under electrical bias (DVC) and under illumination (DVC in conjunction with LEBEAMS); however, the conditions of the previous did not replicate the normal illumination conditions of a solar cell. The goal of this research was to redesign and expand the previous LEBEAMS experiments to produce accurate profiles of quasi Fermi energies on solar cells.     

Microelectrical characterizations of junctions in solar cell devices by scanning Kelvin probe force microscopy

Scanning Kelvin probe force microscopy was applied to the microelectrical characterizations of junctions in solar cell devices. Surface Fermi-level pinning effects on the surface potential measurement were avoided by applying a bias voltage (V_b) to the device and taking the V_b-induced potential and electric field changes. Two characterizations are presented: the first is a direct measurement of Bi-induced junction shift in GaInNAs(Bi) cells; the second is a junction-uniformity measurement in a-Si:H devices. In the first characterization, using Bi as a surfactant during the molecular beam epitaxy growth of GaInNAs(Bi) makes the epitaxial layer smoother. However, the electrical potential measurement exhibits a clear Bi-induced junction shift to the back side of the absorber layer, which results in significant device degradation. In the second characterization, the potential measurement reveals highly non-uniform electric field distributions across the n–i–p junction of a-Si:H devices; the electric field concentrates much more at both n/i and i/p interfaces than in the middle of the i-layer. This non-uniform electric field is due possibly to high defect concentrations at the interfaces. The potential measurements further showed a significant improvement in the electric field uniformity by depositing buffer layers at the interfaces, and this indeed improved the device performance.     

Ultrastructural modifications of cell membranes induced by "electroporation" on melanoma xenografts

Electroporation (EP) has been widely employed in the past years as a safe and effective technique to drive drugs and DNA plasmids into target cells both for experimental and therapeutic purposes. Despite the large bulk of literature on this topic, often describing successful outcomes, there is a lack of knowledge about the intimate mechanism(s) controlling this phenomenon. In this paper, we describe a number of ultrastructural alterations in the cellular membranes following the exposure of orthotopic melanomas and red blood cells to trains of biphasic pulses. Specifically, melanoma xenografts grown in nude mice were subject to trains of eight biphasic pulses using an electric field of 1250 or 2450 V/cm, excised after 5 min and processed for electron microscopy. The freeze-fracturing analysis of both cell types evidenced defects in the dynamic assembly of lipids and proteins, which generate "areas with rough structure" and intensive clustering of intramembrane proteins. Such modifications could be the hallmarks of lipid and protein alterations, of protein cohesion reduction, and of changes in lipid orientation inside cell membranes, as postulated in several mathematical models applied to electroporation, and warrant further investigations.     

外加电场条件下制备定向排列的硅纳米线

在外加电场的条件下,利用物理热蒸发法制备出定向排列的非晶硅纳米线,借助扫描电镜、X射线能谱分析仪和透射电镜等对硅纳米线进行了研究。结果表明：定向排列的硅纳米线以两种形式存在,一种是分散的平行排列,另一种是象麻花状的定向排列。同时,硅纳米线一般都处在两个结点之间;当电场不稳定时,可得到部分分叉的硅纳米线。     

Neutron scattering studies of BiFeO3 multiferroics: a review for microscopists

Application of the neutron scattering technique in the study of crystal and magnetic properties of multiferroic BiFeO₃ is presented. The crucial role of the neutron scattering technique, complementary to X-ray diffraction method and transmission electron microscopy, is shown. Especially the ultra high-resolution time-of-flight (TOF) neutron diffraction technique used by Sosnowska et al. to detect the magnetic cycloid ordering and its role in studies of physical properties of BiFeO₃ and its alloys are reviewed. The first inelastic neutron scattering patterns of magnetic excitations in BiFeO₃ are also presented. Applications of different microscopy techniques such as transmission electron microscopy (TEM), scanning electron microscopy ( SEM), field emission TEM and SEM (FESEM and FETEM), magnetic force microscope (MFM) and polarization force microscopy (PFM) bring insight on the fundamental problem of ferroelectricity and confirm the potential of BiFeO₃ multiferroic material for nanoscale devices.     

压电材料平面渗透裂纹的机电耦合场

为提高压电传感器和换能器的品质,针对材料缺陷导致的压电元器件失效或不稳定,用复变函数的方法,结合椭圆形夹杂内的电场强度和电位移为常量这一早期研究结果,研究了压电材料平面电渗透裂纹的机电耦合场及其奇异性。解答表明,切向电场强度和法向电位移在裂纹尖端有由机械载荷引起的奇异,而与电载荷无关;应力强度因子与纯弹性材料结果一致。     

In Situ Mechanical and Electrical Characterization of Individual TiO(2) Nanofibers Using a Nanomanipulator System

Young's modulus and electrical resistivity of individual titanium dioxide (TiO₂) nanofibers were characterized using a nanomanipulator system installed in a focused ion beam‐scanning electron microscope (FIB‐SEM) dual‐beam Scanning Electron Microscope system. Young's modulus of individual nanofibers was deduced from the analysis of their in situ resonance behavior in response to an oscillating electric field. The electrical behavior of a single nanofiber was also analyzed by a two‐point method probed by a nanomanipulator. These results will contribute to the design of devices based on single TiO₂ nanofibers, as well as devices based on nanofiber networks. The methods presented here can also be applied to characterize other one‐dimensional nanostructures. SCANNING 34: 341–346, 2012. © 2012 Wiley Periodicals, Inc.     

Investigations on the structure of the extracted ion beam from an electron cyclotron resonance ion source

Using improved beam diagnostic tools, the structure of an ion beam extracted from an electron cyclotron resonance ion source (ECRIS) becomes visible. Especially viewing targets to display the beam profile and pepper pot devices for emittance measurements turned out to be very useful. On the contrary, diagnostic tools integrating over one space coordinate like wire harps for profile measurements or slit-slit devices, respectively slit-grid devices to measure the emittance might be applicable for beam transport investigations in a quadrupole channel, but are not very meaningful for investigations regarding the given ECRIS symmetry. Here we try to reproduce the experimentally found structure on the ion beam by simulation. For the simulation, a certain model has to be used to reproduce the experimental results. The model is also described in this paper.     

Material surfaces for electron-optical equipment

Electron-beam inspection systems for VLSICs and electron-beam pattern generation require exact positioning of the electron beam on the specimen. In this connection the question arises as to what properties the walls and diaphragms in the ambience of the path of the electron beam are required to have with respect to material, surface layers and cleanness in order to exclude their collecting electric charges that will undesirably influence the electron beam. Experimental investigations of this problem by means of electron-shadow projection show that the conductivity of a material should not be the sole criterion for its choice, but that its behavior under exposure to backscattered electrons and secondary electron emission must also be taken into account. Graphite of poor conductivity was found to be particularly favorable. Electroplated surfaces are often less favorable than untreated surfaces. Magnetic materials always exhibit minor defects. For cleaning, a carefully controlled ultrasonic technique using conventional cleaning agents is necessary and sufficient.     

Microwave band on-chip coil technique for single electron spin resonance in a quantum dot

Microwave band on-chip microcoils are developed for the application to single electron spin resonance measurement with a single quantum dot. Basic properties such as characteristic impedance and electromagnetic field distribution are examined for various coil designs by means of experiment and simulation. The combined setup operates relevantly in the experiment at dilution temperature. The frequency responses of the return loss and Coulomb blockade current are examined. Capacitive coupling between a coil and a quantum dot causes photon assisted tunneling, whose signal can greatly overlap the electron spin resonance signal. To suppress the photon assisted tunneling effect, a technique for compensating for the microwave electric field is developed. Good performance of this technique is confirmed from measurement of Coulomb blockade oscillations.     

Scanning electron microscopy observation of the substructural evolution of aluminium alloys during cold rolling and partial annealing

Classical etching techniques for revealing cold deformation and partial recrystallisation in metals have been optimised for optical microscopy, which is limited by its resolution. Detailed studies of the mechanisms involved in recovery and recrystallisation during heat treatment are generally made by transmission electron microscopy. The limitation of this technique, with a few exceptions, is its small field of view and the small fraction of the sample available for inspection. The present article departs from the statement that etching, which is a surface alteration technique, must have effects that are detectable by scanning electron microscope (SEM). It was found that carefully adapted polishing and etching procedures allow for substructural investigations by SEM, resulting in various advantages compared with both optical microscopy and TEM.     

基于磁质谱原理的新型同位素质量分离器的数值研究

基于磁质谱原理设计了新型同位素质量分离器。不同质量的离子在轴对称电场和磁场中聚焦于不同位置并进入各自收集器,从而实现质量分离。由哈密顿原理推导出离子在分离器中运动轨迹的解析方程,结合电子恒温磁流体力学方程构建等离子体束流轨迹的混合数学模型。基于该混合数学模型,应用matlab模拟等离子体束流的聚焦和质量分离。从仿真结果可以看出,当忽略鞘层屏蔽效应时,束流在电场力作用下绕着对称轴做螺旋运动;当考虑鞘层屏蔽效应时,电子在弱磁场中受束缚作用较小,在鞘层中迅速积累,外电场很大程度上被鞘层屏蔽,束流运动半径迅速增加,尚未聚焦就到达外电极。随着轴向磁场的增强,鞘层屏蔽效应减弱。通过选取适当的磁场强度,可使不同质量的离子按荷质比的顺序分离,聚焦点的距离取决于离子质量。本研究对等离子体束流电磁控制进行了探索,该结果可为高纯度物质质量分离器的研制奠定理论基础。     

On the application of quantum transport theory to electron sources

Electron sources (e.g., field emitter arrays, wide band-gap (WBG) semiconductor materials and coatings, carbon nanotubes, etc.) seek to exploit ballistic transport within the vacuum after emission from microfabricated structures. Regardless of kind, all sources strive to minimize the barrier to electron emission by engineering material properties (work function/electron affinity) or physical geometry (field enhancement) of the cathode. The unique capabilities of cold cathodes, such as instant ON/OFF performance, high brightness, high current density, large transconductance to capacitance ratio, cold emission, small size and/or low voltage operation characteristics, commend their use in several advanced devices when physical size, weight, power consumption, beam current, and pulse repletion frequency are important, e.g., RF power amplifier such as traveling wave tubes (TWTs) for radar and communications, electrodynamic tethers for satellite deboost/reboost, and electric propulsion systems such as Hall thrusters for small satellites. The theoretical program described herein is directed towards models to evaluate emission current from electron sources (in particular, emission from WBG and Spindt-type field emitter) in order to assess their utility, capabilities and performance characteristics. Modeling efforts particularly include: band bending, non-linear and resonant (Poole-Frenkel) potentials, the extension of one-dimensional theory to multi-dimensional structures, and emission site statistics due to variations in geometry and the presence of adsorbates. Two particular methodologies, namely, the modified Airy approach and metal-semiconductor statistical hyperbolic/ellipsoidal model, are described in detail in their present stage of development.     

Field emission from diamond particles studied by scanning field emission microscopy

Field emission properties from diamond particles (DPs) are studied. The DPs with thin chemically vapor deposited (CVD) diamond overcoat, dispersed onto metal substrate, essentially exhibit negative electron affinity (NEA). Field emission, approximately 1mA/cm(2) under a macroscopic electric field of 3.5kV/mm are observed. Microscopic electrical properties were studied by scanning tunneling microscopy/spectroscopy. Most parts of the DP surface exhibit narrow gap and p-type characteristics. The localized regions, which have wide gap like bulk diamond properties, are randomly distributed near the top of DP. The field emission current distribution depicted by scanning field emission microscopy (SFEM) show that the electron emission is originating from a localized region on the selected DPs. We found, through SFEM measurement, some favorable field emission spots ("hot spots") where measured emission current is several orders higher than that of the other DPs ("normal spots"). Field emission spectroscopy (FES) results suggest that a poorly conducting layer is present along the electron path from the metal electrode to vacuum.We propose two models for field emission from "hot spots", which involve two main mechanisms. One is electron injection from the metal substrate to the DP, which is attributed to the electric field enhancement at intrinsic non-doped diamond (i-diamond) layer sandwiched between the metal substrate and the surface conductive layer (p-diamond) of the CVD diamond overcoat on the DP. The other is electron emission at the top site of NEA DP through the local i-diamond region or the depletion region of the p-diamond, which is caused by the applied electric field.     

Off-axis and inline electron holography: A quantitative comparison

Capable of quantitatively imaging static magnetic and electric potentials and even strain electron holography is a very versatile and powerful TEM technique. In this paper we compare off-axis electron holography with a recently developed focal series reconstruction algorithm and phase retrieval based on the transport of intensity equation. Based on theoretical considerations and simulations we compare the different techniques with respect to parameters such as the coherence requirements, field of view, resolution, noise properties, and other required experimental conditions.     

Microfabrication and characterization of gated amorphous diamond-based field emission electron sources.

Gated field emission electron sources of amorphous diamond (a-D) coated Si tips and a-D diodes on a rough Si substrate were studied, detailing the deposition and characterization of the thin film, the fabrication processes and the emission behavior of the electron sources. Mechanisms responsible for the emission process of the a-D coated devices are proposed. A comparison of the field emission performance of the two types of devices is presented. In addition, future improvements of the a-D diode on a rough Si cathode are discussed.