电子全息的数字重现及其在微电磁场测量中的应用

阐述了用数字方法重现电子全息图及实现噪声消除、位相差放大的基本原理，将它应用到微电磁场测量中，给出了实验结果。

利用数字重现电子全息图观测微电磁场分布

采用数字方法重构电子全息图，分别研究了荷电乳剂小球（０３１μｍ）的微电场分布及强磁材料中磁畴的磁力线分布精细结构．利用噪声消除及位相差放大技术提高了重现分辨率，并获得了一些新结果．

基于导线阵列的微电磁力驱动细胞运动的研究

在硅片上制作多层交叉网格导线。当给导线通上适当电流并控制通电导线的电流方向,在相应的导线交叉网格区域会产生一个微电磁场,对磁场中的微磁粒子产生吸引力。如果把细胞和这些磁粒子结合在一起,就可以利用该微电磁场对细胞进行定位。改变不同导线的通电时序形成运动的微电磁场,进而可以控制微磁粒子的运动,也就控制了细胞的运动。仿真结果证明,采用导线阵列产生的运动微电磁场,可以对细胞进行精确定位和运动控制。

导线阵列驱动微磁粒子运动及发热量仿真

磁粒子根据所包裹的外层物质,可以与细胞产生选择性黏附,该特性可用于细胞分离、分选、药物运输等。基于载流导线阵列对磁性粒子的微电磁力作用,当磁粒子和细胞联结在一起时,便可对细胞进行定位和运动控制。改变不同导线的通电时序,就可以形成运动的微电磁场,从而控制微磁粒子运动,也就控制了细胞的运动。仿真结果证明,采用导线阵列产生的运动微电磁场,可以对细胞进行精确定位和运动控制。同时,也对导线发热量进行了仿真,结果表明,在驱动磁粒子运动时,导线的发热量在允许的范围内。

Microstructures and formation mechanism of headstand pyrocarbon cones developed by electromagnetic-field-assisted CVD

Novel headstand pyrocarbon cones （HPCs） with hollow structure were developed on the surfaces of pyrocarbon layers of the carbon/carbon （C/C） composites at 650-750 °C by the electromagnetic-field-assisted chemical vapor deposition in the absence of catalysts. The fine microstructures of the HPCs were characterized by high-resolution transmission electron microscopy. The results show that the textural features of the HPCs directly transfer from turbostratic structure in roots to a well-ordered high texture in stems. And the degree of high texture ordering decreases gradually from the stem to the tail of the HPCs. The formation mechanism of the HPCs was inferred as the comprehensive effect of polarization induction on electromagnetic fields and particle-filler property under disruptive discharge.

全息术与器件

TB877 2000021096电子全息的数字重现及其在微电磁场测量中的应用=Digital reconstruction of electron hologramsand its applications to measurement of electromagneticmicrofields[刊,中]/肖体乔,张映箕,徐洪杰(中科院上海原子核研究所.上海),陈建文(中科院上海光机所.上海(201800))//电子显微学报.-1999,18(5).-554-561阐述了用数字方法重现电子全息图及实现噪声消除,位相差放大的基本原理。

Ferromagnetism of Mn-doped ZnO nanoparticles prepared by sol-gel process at room temperature

Mn-doped ZnO diluted magnetic semiconductor nanoparticles are prepared by an ultrasonic assisted sol-gel process.Transmission electron microscopy shows pseudo-hexagonal nanoparticles with an average size of about 24 nm.From the analysis of X-ray diffraction,the Mn-doped ZnO nanoparticles are identified to be a wurtzite structure without any impurity phases.The magnetic properties are measured by using superconducting quantum interference device.For the ZnO with 2% Mn doping concentration,a good hysteresis loop indicates fine ferromagnetism with a Curie temperature higher than 350 K.

DC casting of light alloys under magnetic fields

The working principle of LFEC（Low frequency electromagnetic casting） process developed in Northeastern University, China was introduced and the metallurgical results of LFEC were discussed according to the casting practices. The low frequency field around the mold produces Lorenz force, which can be divided into two parts： one is the potential force which will be balanced by a pressure gradient of the liquid and results in the formation of a convex surface meniscus and improves the surface quality; the other is the rotary force which stirs the liquid in the mold to refine the microstructures and homogenize the distribution of alloying elements. LFEC can refine microstructures remarkably, improve surface quality of the ingots, depress macrosegregation and eliminate cracks. Some new technologies, such as horizontal direct chill casting under low-frequency electromagnetic field （HLEC）, DC casting of hollow billets under electromagnetic fields （HBEC）, electromagnetic modifying of hypereutectic A1-Si alloys（EMM）, air film casting under static magnetic field （AFCM）, and multi-ingots casting under low-frequency magnetic field （MLFEC） were developed based on LFEC.

Active Field Canceling System in Next Generation Nano-Fab

ELF （extremely low frequency） magnetic fields from power-line current influence the yield of CMOS foundry. The poor yield happens because of ELF magnetic fields inducing directly the measurement or process equipment for cutting-edge chips below 28 nm process. The equipments of electron microscopes, including SEM （scanning electron microscope）, TEM （transmission electron microscopy）, STEM （scanning transmission electron microscopy） and EBLS （electron beam lithography system） are very susceptible to ELF magnetic fields emanating from various electrical power sources outside of the building and within next generation CMOS foundry recommends a maximum of 0.3 mG. The active canceling method uses active coils with current sensing field via sensor and inducing man-made electromagnetic field to reduce the stray magnetic field. Unfortunately, the conventional system takes more time to products field because of parasitical capacitance and resistance in long coil. The longer canceling coil the system construct, the more time it takes. Besides, canceling system should spend more time on calibrating non-linear current amplifier through software design. This research designs simpler anti-electro-magnetic system instead of typical frame and develops one turn canceling coil structure to reduce delaying time. Several parallel cells generate field up to 23.81 mG controlled by MPU （micro processor unit）. This system decreases the power-line inducing filed below 0.3 mG.

Magnetic and microwave absorption properties of Ni_(1-x)Zn_xFe_2O_4 nanocrystalline synthesized by sol-gel method

Ni1-xZnxFe2O4(0≤x≤1,in steps of 0.1) nanocrystallines were synthesized by sol-gel route.The doping effects of zinc on structural,magnetic and microwave absorption properties were investigated in detail.X-ray diffraction(XRD) results show that all the samples are single-phase spinel structure.The magnetic and microwave absorption properties are strongly dependent on the zinc content,which can be understood in terms of the cations redistribution in spinel tetrahedral and octahedral sites with the increase of zinc content.The magnetic measurement shows the antiferromagnetic nature of the samples for x=0.9 and x=1.0.The saturation magnetization reaches the maximum of 3.35μB/f.u.at x=0.5.The optimal reflection loss(RL) of-29.6 dB is found at 6.5 GHz for an absorber thickness of 5 mm.The RL values exceeding 10 dB are obtained for the absorber in the range of 3.9-8.9 GHz.These Ni1-xZnxFe2O4 nanocrystallines may be attractive candidates for electromagnetic wave absorption materials.

Superposition of Stationary Wave Fields Via Atom Microscopy

We investigate one-dimensional position microscopy of a three-level atom moving through a stationary wave region under the condition of electromagnetically induced transparency.The precise position information of an atom is observed on the resonance absorption and dispersion distribution spectrum of a weak probe field.Single and multiple localization peaks are observed in specific directions of the corresponding wave numbers and phase of the standing wave fields.The strength of space-independent Rabi frequency reduces the position uncertainty in the localized peaks without disturbing the probability of the atom.In a hot atomic medium the localized probability of an atom is reduced which depends upon the temperature of that medium.Our results provide useful applications in the development of laser cooling,atom nanolithography and Bose-Einstein condensation.