Analysis of magnetization in nanocomposite Nd4.5(Fe,Cr)77B18.5 by electron holography and simulation

Magnetization distribution in nanocomposite Nd4.5(Fe,Cr)77B18.5 was studied by electron holography and computer simulation. In order to understand the detailed magnetization distribution, the magnetic flux distribution was calculated taking into account the magnetic charge or the stray field on the basis of magnetization models consisting of small magnetic dipoles and was compared with that in reconstructed phase images experimentally observed. Through the comparison, the characteristic feature in the distribution of the magnetization distribution in the nanocomposite magnetic materials was clarified, and the distribution was found to well correspond to their magnetic properties. It is pointed out that for understanding magnetization, the interpretation of reconstructed phase images should be done through computer simulation just as the analysis of high-resolution electron microscope images. Eventually, it was demonstrated that electron holography with computer simulation is quite useful to analyze detailed magnetization distribution in nanocrystalline magnetic materials at the nanometer scale.     

Electron holography on remanent magnetization distribution of melt-spun Nd-Fe-B magnets

Microstructures and magnetic domain structures of melt-spun Nd-Fe-B permanent magnets were investigated in detail by analytical electron microscopy and electron holography. While the crystal orientation of matrix Nd2Fe14B grains was analyzed by nanobeam electron diffraction, precipitates of a few tens of nanometers at grain boundaries were identified to be alpha-Fe by energy-dispersive X-ray spectroscopy. The detailed magnetization distribution in Nd2Fe14B grains and at their boundaries was visualized by electron holography. Ex situ experimentation with an electromagnet revealed that the domain walls in the demagnetized state and remanent states were pinned at grain boundaries, and Fe precipitates at the grain boundary were situated at the center of the closure domain.     

Magnetization distribution of magnetic vortex of amorphous FeSiB investigated by electron holography and computer simulation

The three-dimensional spin structure of the magnetic vortex of FeSiB, an amorphous soft magnetic material, was investigated by holography observation and computer simulation. Magnetization distribution in the neighborhood of the vortex center was estimated from the phase distribution obtained by holography observation. To confirm this magnetization distribution, sample-tilting experiments were performed: when the sample was tilted with respect to the electron beam direction, the phase-image center was found to shift along the tilting axis. Finite-element computer simulation was carried out to estimate the amount of shifts of the phase-image center in the sample tilting from the experimental magnetization distributions in the no sample-tilting conditions. We found that the simulated shifts of the phase-image center were in good agreement with those in the sample-tilting experiment, thus confirming the magnetization distribution near the vortex center obtained by holography observation.     

Profile structure of magnetic flux lines in type-II superconductor from a rectangular electron hologram

Profile magnetic configuration of a quantized flux line and flux-line lattice penetrating a type-II superconductor thin foil, niobium, was observed by electron holography and Lorentz microscopy using a 300 kV field-emission electron microscope. Each single flux line was distributed periodically as lattice structure in the mixed state just below its critical temperature of 8.5 K, while at low temperature of 5 K the flux lines were weakly bound as bundles. In order to observe the flux-line distribution over a wide area, discrete Fourier transform reconstruction in the holography was extended for a rectangular area without loss of information and data precision.     

迴旋管永磁聚焦系统设计

迴旋管实现永磁包装,迄今尚未见有文献报道。本文提出采用一种适合于迴旋管工作的双均习区径向磁路系统作为永磁聚焦方案,并利用计算机进行了研究,通过设计计算,选用磁能积(BH(max)为20 MGOe的钐钴磁钢。为了调整磁场,在双均匀区添加了一些小电磁线包,它们改变磁场的范围约为5％。 通过计算表明,建立一个8 mm二次谐波迴旋管所需的65007000Gs强磁场系统,约需钐钴磁钢4050kg。这对于研制 8 mm二次谐波永磁聚焦迴旋管以及近厘米波段迴旋管是很吸引人的。本文最后还对提高磁路效率、扩大均匀区等问题进行了简单的讨论。     

High precision phase-shifting electron holography

Today's information-oriented society requires high density and high quality magnetic recording media. The quantitative observation of fine magnetic structures by electron holography is greatly anticipated in the development of such new recording materials. However, the magnetic fields around particles <50 nm have not been observed, because the fields are too weak to observe in the usual way. Here we present a highly precise phase measurement technique: improved phase-shifting electron holography. Using this method, the electric field around a charged polystyrene latex particle (100 nm in diameter) and the magnetic field around iron particles (30 nm in diameter) are observed precisely. A precision of the reconstructed phase image of 2pi/300 rad is achieved in the image of the latex particle.     

Transmission electron microscopy on thin film of high density magnetic composite prepared by FIB method

A thin specimen of a high density magnetic composite (HDMC), which is a type of powder magnetic cores was prepared for transmission electron microscopy (TEM) using a focused ion beam (FIB) method. A homogeneous thin film containing an insulator boundary between the constituent Fe powders was obtained successfully. Using this thin film, detailed flow of magnetic flux was visualized by electron holography, and the magnetic flux density was estimated to be 1.73 +/- 0.09 T being consistent with that of a bulk HDMC (1.70 T). Moreover, through Lorentz microscopy, the characteristic magnetization process of HDMC was observed by applying the magnetic field up to approximately 8 kA/m.     

In situ observations of domain structures and magnetic flux distributions in Mn-Zn and Ni-Zn ferrites by Lorentz microscopy and electron holography

Domain structures and magnetic flux distributions in Mn-Zn and Ni-Zn ferrites are investigated by in situ observations with Lorentz microscopy and electron holography. In situ Lorentz microscopic observation with the magnetic field applied reveals that the domain walls in Mn-Zn ferrite move easily across the grain boundary. On the other hand, each grain of Ni-Zn ferrite is magnetized by domain wall motion inside the grain. By taking a series of holograms with adjustment of the optical axis and astigmatism while the magnetic field is applied, we succeeded in observing the change in magnetic flux distribution quantitatively. Eventually, it is clarified that magnetization rotation does not take place in the magnetization process of Ni-Zn ferrite. The domain wall widths delta in Mn-Zn and Ni-Zn ferrites are evaluated to be 73 and 58 nm, respectively. Furthermore, through direct observation of the domain structure in Ni-Cu-Zn ferrite with Lorentz microscopy, it is found that the grains with size below 1.5 microm diameter are single domain.     

Theory of helical electron beams in gyrotrons

Helical electron beams (HEB) with disturbed axial symmetry of currents density and HEB with locking electrons in magnetic trap are described. The theory of magnetron injection gun (MIG) in space-charge limited current is developed. Systems on permanent magnets forming HEB are considered.     

Development of a magnetizing stage for in situ observations with electron holography and Lorentz microscopy

A magnetizing stage, by which approximately horizontal magnetic fields can be applied to thin-foiled specimens, has been developed so that magnetization process can be observed in situ with electron holography and Lorentz microscopy. It is possible to apply magnetic field up to 200 Oe without serious image distortion by utilizing the magnetizing stage, beam-deflection-back coils and a magnetically shielded objective lens. The devised system can be used to studies of magnetization processes in many soft magnets.     

Measurement of electric potential distributions around FEG-emitters by electron holography

An evaluation technique for field emission guns (FEG-emitters) was established by using electron holography. For performing electron holography under an applied voltage, a specimen holder with the capabilities of three-directional motion as well as voltage application was developed. An unused Schottky emitter and a used emitter that had failed after operating for about 10,000 h were selected for this study. By visualizing the electric potential distributions around the emitters, it was clarified that a change in the edge shape of the emitter led to the change in the strength of the electric field. The observations revealed that electron holography can be applied to evaluate the performances of the various emitters.     

Optical system for double-biprism electron holography

A novel system of electron interferometry and holography using two electron biprisms has been developed. The first biprism is installed in the image plane of the objective lens and the second one is set behind the first magnifying lens, inside the shadow area of the first biprism. The system can independently control two important parameters for interferograms and holograms, the fringe spacing and interference width. Thus, it gives us more flexibility on performing electron interferometry and holography. The good performance of the system was demonstrated using a 1MV field-emission electron microscope. We introduce a variety of optical set-ups for the system and explain the advantages of each set-up in detail, with experimental results.     

Characterization of DLC films by EELS and electron holography

Thickness measurements of diamond-like carbon (DLC) films by electron energy-loss spectroscopy (EELS) and electron holography are discussed. In order to evaluate the thickness by EELS and electron holography, the mean free path for inelastic scattering and mean inner potential of DLC films were determined precisely, respectively. It is found that both the mean free path for inelastic electron scattering and the mean inner potential are sensitive to the preparation methods, namely the density of DLC films. The present work has demonstrated that thickness measurement by EELS is available to DLC films thicker than 20 nm, while electron holography can be applied to thinner films ( approximately 5 nm). Furthermore, close relations are observed between the density of DLC films and the energy-loss spectra.     

In situ off-axis electron holography of metal-oxide hetero-interfaces in oxygen atmosphere

Off-axis electron holography has been extended to in situ observations in gas atmospheres. The Yttria-stabilized zirconia (YSZ)-Pt hetero-interface was characterized by electron holography at high temperature in a vacuum and in an oxygen atmosphere. Analysis of the phase shift profiles revealed high mobility of anions in the oxide in the vicinity of the interface in the oxygen atmosphere. This would compensate for any increase in the number of oxygen vacancies in YSZ through the metal interface.     

场发射枪透射电镜电子全息静电双棱镜二氧化硅细丝的制作

电子全息静电双棱镜二氧化硅细丝是在透射电子显微镜中进行电子全息实验的关键部件,目前国内尚不能制备.本文采用简单易行的方法,加工制作了镀金石英细丝,直径约1 μm,并粘接在电子全息静电双棱镜的电极上,导电性良好,获得了条纹间距优于0.2 nm的电子全息干涉图.     

一维阵列电子注平面聚焦系统磁场分布特性

针对平面集成行波管对一维阵列电子注聚焦的应用需求,设计了4通道电子注平面磁聚焦系统。将各通道磁场轴向和横向分量沿轴分布特征计算结果与测试结果进行对比,确认了Opera软件计算磁场分布特征的准确性。为与轴对称周期永磁(PPM)聚焦系统电子注通道内磁场分布特性进行对比,建立了轴对称PPM聚焦系统模型,测试结果与计算结果一致性较好。通过平面聚焦系统与轴对称PPM聚焦系统电子注通道内的磁场纵向和横向分布特性对比表明,两种聚焦系统电子注通道内纵向和横向磁场具有相同的分布特征,在离轴相同位置的圆周上横向磁场分量与轴向分量的比值均为B_x/B_z≈0.11,该平面聚焦系统可实现一维阵列圆形电子注的良好聚焦。     

晶界添加MgO对（PrNd）30 Gd3 Al0.8 B1.03 Fe余磁体磁性能影响

为研究晶界添加MgO对磁体（PrNd）30Gd3Al0.8B1.03Fe余磁性能的影响,通过球磨混粉方式将其引入到烧结Nd-Fe-B晶界,利用扫描电镜分析磁体的显微组织.观察发现适量地添加MgO可以优化磁体显微结构,提高剩磁,矫顽力和最大磁能积,在当前实验条件下,加入0.2％的MgO磁体的磁性能最佳.     

Electron holographic mapping of two-dimensional doping areas in cross-sectional device specimens prepared by the lift-out technique based on a focused ion beam

Recently, electron holography has been successfully applied to analyze two-dimensional (2D) dopant distribution in semiconductor devices with high resolution and high sensitivity. The preparation of proper specimens is a fundamental step for the practical application of electron holography in the semiconductor industry. Therefore, it is important to explore a reliable and quick specimen preparation method. In our current work, we have tried to use the lift-out technique based on a focused ion beam, to fabricate cross-sectional CMOS device specimens for electron holographic observation. Using the lift-out technique, specimens with a large area and uniform thickness can be prepared directly from integrated circuit wafers in a very short time. Specimens with a complex and unknown dopant distribution were examined using off-axis electron holography. In the reconstructed phase images, the different 2D doping areas in a CMOS device, such as source, drain, well and substrate, were revealed successfully. The advantages and disadvantages of the technique are discussed.     

Study of structure-property relationship of semiconductor nanomaterials by off-axis electron holography

As the scaling down of semiconductor devices, it would be necessary to discover the structure-property relationship of semiconductor nanomaterials at nanometer scale. In this review, the quantitative characterization technique off-axis electron holography is introduced in details, followed by its applications in various semiconductor nanomaterials including group IV, compound and two-dimensional semiconductor nanostructures in static states as well as under various stimuli. The advantages and disadvantages of off-axis electron holography in material analysis are discussed, the challenges facing in-situ electron holographic study of semiconductor devices at working conditions are presented, and all the possible influencing factors need to be considered to achieve the final goal of fulfilling quantitative characterization of the structure-property relationship of semiconductor devices at their working conditions.     

Visualizing the doping profile of a silicon germanium HBT with polysilicon emitter using electron holography

Modern bipolar transistors use polysilicon emitters and an epitaxial grown silicon germanium (SiGe) base. For device optimization, both the SiGe base and the region of the diffused emitter is of special interest. In this paper, electron holography is applied to visualize and directly measure the two-dimensional distribution of the local potential in a high-performance SiGe heterojunction bipolar transistor. Special emphasis is put on investigating the region of the emitter diffused into the epitaxially grown base layer. In addition, we investigate the self-aligned base-link construction. We compare electron holographic measurements of the whole transistor to secondary ion mass spectrometric (SIMS) data and discuss the results.