环境扫描电子显微镜中真空系统特点及成像信号分析

环境扫描电子显微镜(ESEM)是针对常规扫描电子显微镜(SEM)在使用过程中暴露出来的一些重大缺陷而设计的.它淘汰了SEM中繁琐、复杂的样品准备工作,扩大了仪器的使用范围,并使图像更清晰.着重介绍了ESEM的工作原理、与此有关的真空系统构成及成像信号分析.     

环境扫描电子显微镜的关键技术

环境扫描电子显微镜在气体压力高达6600Pa，温度高达1500℃，具有任何气体种类的多气环境里，都可提供高分辨率的二次电子成像。如此优良性能的获得，取决于两项新技术：一是将柱形电子导管的真空环境与样品室环境分开；二是使用了一个在样品室非真空环境下仍然能起作用的二次电子探头。这些问题的解决是开发ESEM的关键。     

可分析含水、含油、不导电绝缘样品的环境扫描电子显微镜(ESEM)通过进口验收并开始对外服务

在人类进入廿一世纪的今天 ,人们对常规的扫描电子显微镜 (ＳｃａｎｎｉｎｇＥｌｅｃｔｒｏｎＭｉｃｒｏｓｃｏｐｅＳＥＭ )已不陌生 ,ＳＥＭ已经应用于人类生活的各个方面。然而 ,受仪器原理和结构的限制 ,ＳＥＭ在遇到不导电样品和含水、含油的样品时就显得无能为力了。近十多年发展起来的环境扫描电子显微镜 (ＥｎｖｉｒｏｎｍｅｎｔＳｃａｎｎｉｎｇＥｌｅｃｔｒｏｎＭｉｃｒｏｓｃｏｐｅＥＳＥＭ)由于 (1)采用新的多重压差狭缝使真空度为 1～ 2 6 6 0Ｐａ的样品室与仪器的其它高真空部分隔离 ,从而保证ＥＳＥＭ能对含水、含油样品进行…     

扫描电子显微镜对样品的要求及其制备

<正>作为一种有效分析工具,扫描电子显微镜(SEM)可以对多种类型材料的表面形貌进行观察;若联合多种探测器,还可以实现对材料元素、组分及结晶进行分析。在检定SEM过程中,许多检定员操作系统技术熟练,但往往容易忽略检定前的准备工作。本文着重介绍样品制备方面的要求及其制备方法。     

纳米SiO_2材料的制备及其发光性能研究

采用溶胶-凝胶法制备了纳米SiO2,样品在800℃下煅烧2h。X-射线衍射(XRD)及扫描电子显微镜(SEM)测试结果表明,该材料具有非晶态结构,颗粒尺寸为90~100nm。该样品在紫外灯照射下发出强烈的黄绿色可见光;对样品进行荧光光谱分析表明,该材料可以发射出较强的490nm的蓝绿光和弱的520nm的绿光。     

直线加速器真空故障维修经验总结

医科达医用直线加速器真空系统是加速器重要的组成部分。它包括电子枪、加速管以及靶。它们必须工作在真空度为10-6 Torr(1 Torr=133.329 Pa)以上的高真空环境中。真空的作用是:避免加速管内放电击穿,防止电子枪阴极灯丝氧化,减少电子与残余气体的碰撞损失。真空度越高,剂量率越稳定,电子枪灯丝损耗越小。     

强自旋轨道耦合化合物Sr_2IrO_4的制备与表征

采用传统固相反应法,成功制备了Sr2IrO4化合物,并用X射线衍射(XRD)和扫描电子显微镜(SEM)对所制备的样品进行了表征。通过改变煅烧时间和煅烧温度探索了Sr2IrO4化合物的最优制备工艺。XRD和SEM分析表明,在最优制备工艺下得到具有结晶度高、颗粒形状规则、大小分布均匀的纯相Sr2IrO4样品。     

一种RDX基PBX炸药力学性能和本构关系研究

利用分离式霍普金森压杆(SHPB)对一种RDX基PBX炸药进行了高应变率加载试验,得到了其在不同应变率(300~1 200 s-1)范围内的力学性能,并用扫描电子显微镜(SEM)对回收样品进行了微观分析。结果表明:材料的力学性能和损伤均具有明显的应变率效应。采用含损伤的ZWT非线性黏弹性本构模型,对试验数据进行了拟合,拟合曲线和试验曲线吻合良好。     

激光照射原位生成SiC晶须时粘结剂对晶须的影响

进行了含粘结剂和不含粘结剂的SiC纳米颗粒激光照射原位生成SiC晶须的比对试验,用X射线衍射仪(XRD)和扫描电子显微镜(SEM)分析了晶须的相组成和微观形貌,研究了粘结剂对生成晶须的影响。结果表明,在适当的激光参数下,不含粘结剂和含粘结剂的样品中均有晶须生成,不含粘结剂样品中晶须数量较少,而含粘结剂样品中晶须数量众多,且尺寸、形态各异。SiC纳米颗粒中掺入粘结剂可大幅度提高SiC晶须的生成数量,但并不影响晶须的纯度。     

二次炭化、二次活化对活性炭纤维结构的影响

采用二次炭化、二次活化的方法处理商业粘胶基活性炭纤维,遗过热处理实现对材料的改性.并用等温氮吸脱附测试、X射线衍射(XRD)、扫描电子显微镜(SEM)等分析方法对样品材料进行了测试.实验结果表明制备的材料孔结构扩宽,比表面积增大,吸附性能增强.     

Characterization of Failure Behavior of Brittle Matrix Composites; at Room and Elevated Temperatures

In this study, a systematic tensile testing scheme was carried out on specimens made of unidirectional Nicalon/CAS II ceramic matrix composite with 30% and 40% fiber volume fractions to characterize the tensile failure behavior of brittle matrix composites at room and elevated temperatures. The tests were conducted inside the chamber of a scanning electron microscope (SEM). Utilizing an innovative in-situ tensile testing technique (1), the whole damage history of the specimen under continuous tensile loading was monitored through SEM and hardcopies showing the continuous damage accumulations in the specimens were captured using a video processor through a computer equipped with an Imaging Advanced Frame Grabber (AFG) digital imaging analyzer system. Finally, an analytical model which incorporates the observed damage progression and is based on the microstructure of the composite was developed.     

Characterization load-induced cracks in balsa wood

The nature of load-induced cracks in balsa wood was studied byin situ testing of compact tension specimens within the specimen chamber of a scanning electron microscope. The cracks propagated in a generally straight path parallel to the grain, but they could not be described as parallel-sided cracks as assumed in fracture mechanics modelling. Frequently, wood cells were seen to bridge the crack walls, suggesting that the cracks cannot be considered as traction-free. The propagation of the cracks was associated with splitting within the cell walls, and fracture perpendicular to the cell walls could sometimes be seen.     

Liquid helium cooled sample stage for scanning electron microscope

A cryogenic stage is described for use with a Cambridge S4-10 scanning electron microscope. The stage is operated with liquid helium in direct contact with the back of the sample to be irradiated by the electron beam. This bath cryostat principle will work at temperatures between 1.5 K and 4.2 K with good cooling performance. The installation of the stage within the microscope does not require any modification of the microscope chamber or the detector arrangement. A precision adjustment of the sample perpendicular to the electron beam is achieved by micrometric screws.     

Fatigue crack initiation in AA2024: A coupled micromechanical testing and crystal plasticity study

A new combined experimental and modelling approach has been developed in order to understand the physical mechanisms that lead to crack nucleation in a polycrystalline aluminium alloy AA2024 undergoing cyclic loading. Four‐point bending low‐cycle fatigue tests were performed inside the chamber of a scanning electron microscope on specimens with a through‐thickness central hole, introduced to localize stresses and strains in a small region on the top surface of the sample. Fatigue crack initiation and small crack growth mechanisms were analyzed through high‐resolution scanning electron microscope images, local orientation measurements using electron‐back‐scattered‐diffraction, and local strain measurements using digital image correlation. A crystal plasticity finite element model was developed to simulate the cyclic deformation behaviour of AA2024. Two‐dimensional Voronoi‐based microstructures were generated, and the material parameters for the constitutive equations (including both isotropic and kinematic hardening) were identified using monotonic and fully reversed cyclic tests. A commonly used fatigue crack initiation criterion found in the literature, the maximum accumulated plastic slip, was evaluated in the crystal plasticity finite element model but could not predict the formation of cracks away from the edge of the hole in the deformed specimens. A new criterion combining 2 parameters: The maximum accumulated slip over each individual (critical) slip system and the maximum accumulated slip over all slip systems were formulated to reproduce the experimental locations of crack nucleation in the microstructure.     

Ion bombardment in electron microscopy investigations

Transmission electron microscopy, transmission high energy electron diffraction, reflection high energy electron diffraction and scanning electron microscopy were employed to evaluate the possibilities of ion bombardment used in the preparation of electron microscope specimens. The experimental results show that the uncontrolled use of ion bombardment for thinning of metal foils, cleaning layers or crystal surfaces etc. may often lead to incorrect interpretation of the electron microscopy investigations. In contrast, it is stressed that controlled ion bombardment directly in the column of the electron microscope is a very useful method for the observation and study of some very interesting phenomena which occur to the structure of the specimens during ion bombardment.     

Damaging micromechanisms characterization of a ferritic ductile cast iron

Damaging micromechanisms in a ferritic ductile cast iron were investigated by using a scanning electron microscope with a microtensile holder. Strain rate influence was investigated: tensile tests were performed according to a step by step experimental procedure and specimens surfaces were observed by means of a scanning electron microscope (SEM) during the test (“in situ” tests). Experimental results do not confirm matrix-graphite nodules debonding as the main damaging micromechanisms involved in ferritic ductile irons failure.     

Effects of thermal exposure on cyclic deformation and fracture behavior of Ti600 titanium alloy

Effects of thermal exposure on cyclic deformation and fracture behavior of Ti600 alloy were investigated by laser scanning confocal microscope (LSCM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results demonstrated that both the nonthermal exposure (NTE) specimens and the thermal exposure (TE) specimens showed the cyclic softening, within a total strain amplitude range from ±0.45% to ±1.00%. During thermal exposure, since the harder α₂ (Ti₃Al) phase precipitated in the α_p (primary α) phase, the resistance of crack propagation of α_p phase could be increased by the precipitation of α₂ phase. Therefore, the fracture behavior of TE specimens is different with that of NTE specimens. For the NTE and TE specimens, the crack mainly passes through the α_p phase with “cutting” and “bypass”, respectively.     

Recent advances in electron imaging, image interpretation and applications: environmental scanning electron microscopy

One of the latest developments in electron microscopy is the environmental scanning electron microscope (ESEM), which enables soft, moist and/or electrically insulating materials to be viewed without pre-treatment, unlike conventional scanning electron microscopy, in which specimens must be solid, dry and usually electrically conductive. Such an advance has significant implications for studies of the 'native' surfaces of specimens including rocks and minerals, polymers, biological tissues and cells, food and pharmaceutical products, precious artefacts and forensic material, for example. Previous types of electron microscopes made scientists think carefully about the physics of electron-beam interactions with specimens and, hence, the interpretation of images. We now face additional factors influencing the emission and detection of electron signals, unique to the imaging of specimens in the partial vacuum of an ESEM. Just as importantly, we must consider the thermodynamic and kinetic stability of specimens, as appropriate, and explore the possibilities for new applications, particularly those of a dynamic nature. This paper briefly describes some of the issues involved and reviews the current state of understanding.     

Study of anti-corrosion and anti-wear properties on superhydrophobic aluminium alloy surfaces

To improve the wear and corrosion resistance of aluminium alloys in salt environments, we produced superhydrophobic surfaces via high-speed electrical discharge machining. The specimens were characterised using a scanning electron microscope and a laser scanning confocal microscope and through contact angle (CA) measurement, measurement of electrochemical corrosion at an electrochemical workstation and wear testing. Results showed that the superhydrophobic specimens had a water CA of 151.5°. The corrosion of the as-obtained superhydrophobic specimens was significantly reduced by more than 50%, indicating their excellent anti-corrosion properties. The wear of as-obtained superhydrophobic specimens were reduced by approximately 10–35% in dry conditions and by approximately 45–85% in 3.5% NaCl solution, revealing their excellent anti-wear properties in both dry and salt environments.     

电磁铸造与普通连续铸造2024铝合金的组织性能对比

采用电磁铸造技术和普通连续铸造技术铸造了2024变形铝合金，采用光学显微镜和扫描电镜分析了其显微组织，而且对其进行了固溶处理加人工时效。结果表明电磁铸造锭内部组织细小均匀，有高的硬度和良好的疲劳性能，电磁铸造试样的硬度大约是普通连续铸造铸坯的2倍，疲劳性能是普通连续铸造铸坯的3倍。电磁铸造铸坯还有良好的耐磨性，磨损失重量是普通连续铸造的一半。