Scanning transmission electron microscopy: A review of high angle annular dark field and annular bright field imaging and applications in lithium-ion batteries

Scanning transmission electron microscopy（STEM） has been shown as powerful tools for material characterization,especially after the appearance of aberration-corrector which greatly enhances the resolution of STEM. High angle annular dark field（HAADF） and annular bright field（ABF） imaging of the aberration-corrected STEM are widely used due to their high-resolution capabilities and easily interpretable image contrasts. However, HAADF mode of the STEM is still limited in detecting light elements due to the weak electron-scattering power. ABF mode of the STEM could detect light and heavy elements simultaneously, providing unprecedented opportunities for probing unknown structures of materials. Atomiclevel structure investigation of materials has been achieved by means of these imaging modes, which is invaluable in many fields for either improving properties of materials or developing new materials. This paper aims to provide a introduction of HAADF and ABF imaging techniques and reviews their applications in characterization of cathode materials, study of electrochemical reaction mechanisms, and exploring the effective design of lithium-ion batteries（LIBs）. The future prospects of the STEM are also discussed.

Enhanced photon emission by field emission resonances and local surface plasmon in tunneling junction

We investigated the photon emission spectra on Ag(111)surface excited by tunneling electrons using a low temperature scanning tunneling microscope in ultrahigh vacuum.Characteristic plasmon modes were illustrated as a function of the bias voltage.The one electron excitation process was revealed by the linear relationship between the luminescence intensity and the tunneling current.Luminescence enhancement is observed in the tunneling regime for the relatively high bias voltages,as well as at the field emission resonance with bias voltage increased up to 9 V.Presence of a silver(Ag)nanoparticle in the tunneling junction results in an abnormally strong photon emission at the high field emission resonances,which is explained by the further enhancement due to coupling between the localized surface plasmon and the vacuum.The results are of potential value for applications where ultimate enhancement of photon emission is desired.

Couple analyzing the acoustic emission characters from hard composite rock fracture

Rock mass is fractured media. Its fracture is a nonlinear process. Theaccumulation of acoustic emission (AF) is closely related to the degree of damage. The dynamicsproblem is simply described based on the non-equilibrium statistical theory of crack evolvement,trying to use the hybrid analysis of the statistical theory and scan electron microscopy (SEM), thecharacters of AE signals from rock damage in a mined-out area is synthetically analyzed andevaluated. These provide an evidence to reverse deduce and accurately infer the position of rockfracture for dynamical hazard control.

Metallic phases of Dong Ujimqin mesosiderite:A field emission scanning electron microscope study

The microstructure of Fe-Ni metallic phases in Dong Ujimqin mesosiderite was studied using the field emission SEM. Taenite is characterized by a zoned structure, consisting of outer clear taenite and inner cloudy zone (CZ). CZ has a typical 'island-honeycomb' microstructure. The average size of the island phase is about 358 nm, suggesting a cooling rate of～0.5℃/Ma at low temperature (【400℃). The Ni concentration profiles across kamacite and zoned taenite were also measured by electron probe microscope analysis (EPMA). Formation of the Fe-Ni metallic phases, microstructure in Dong Ujimqin mesosiderite was discussed based on the new low-temperature Fe-Ni phase diagram.

羟基磷灰石／多孔钛复合植入体-骨界面FE-SEM分析

羟基磷灰石，多孔钛复合植入体．骨界面上骨组织的早期生长状况对该时期它们的界面结合强度有较大影响．羟基磷灰石／多孔钛复合植入体被植入新西兰大白兔股骨窠申，经1，3和5周生长后，进行推出试验，并采用FE-SEM和EDS对试验后样品的断裂面形貌和表面成分进行了研究。结果显示，剪切强度随着植入时间的增加较快递增．同时随着时间的增加，植入体．骨的断裂界面上，组织形态发生了较大的变化，表现为组织变得致密以及厚度增加，并逐渐钙化，形成骨组织。

INFLUENCE OF MAGNETIC FIELD ON ACCURACY OF ECM BY CHANGING THE CONDUCTIVITY OF ANODE FILM

The change of conductivity, thickness and scanning electron microscopy （SEM） appearance of the anode film of CrWMn in 10% NaNO3 at different anode potential either with or without the magnetic field applied are investigated by testing film resistance, galvanostatic transient and using SEM to design magnetic circuit in magnetic assisted electrochemical machining （MAECM）. The experiments show that the anode film has semi-conducting property. Compared with the situation without magnetic field applied, the resistance of the film formed at 1 .SV （anode potential） increased and decreased at 4.0V while B=0.4T and the magnetic north pole points toward anode. The SEM photo demonstrates that the magnetic field will densify the film in the passivation area and quicken dissolution of the anode metal in over-passivation area. Based on the influence of magnetic field on electrochemical machining（ECM） due to the changes of the anode film conductivity behavior, the magnetic north pole should be designed to point towards the workpiece surface that has been machined. Process experiments agree with the results of test analysis.

银耳多糖对麦醇溶蛋白纳米体系的影响及复合物的特性研究

该研究是以提高麦醇溶蛋白(gliadin,Gli)纳米颗粒(gliadin nanoparticles,GNPs)稳定性为目标,利用银耳多糖(Tremella fuciformis polysaccharides,TFPs)的乳化性能,探究TFPs添加量对GNPs稳定性的影响。采用反溶剂法制备银耳多糖和麦醇溶蛋白复合载体颗粒(gliadin-Tremella fuciformis polysaccharides composite nanoparticles,G/T NPs),并利用纳米粒度仪、傅里叶变换红外光谱仪、热场发射扫描电镜对G/T NPs的粒径和电位、相互作用、微观结构进行分析。结果表明,TFPs和Gli之间通过静电作用力和氢键作用力相结合,形成GNPs在内、TFPs外层附着的复合颗粒;TFPs的添加能够有效提高GNPs体系的稳定性,减少颗粒之间的聚集,制得的G/T_(4∶1)NPs的平均粒径、多分散指数(polydispersion index,PDI)、ζ-电位分别为(198.5±2.6)nm、0.269±0.005、(36.7±0.6)mV,且具有pH响应性。该研究为后续构建疏水营养成分的包埋和运载体系奠定了基础。

基于孢粉学及花瓣微观形态学的玫瑰花品种的鉴定

目的对6种玫瑰花花粉粒、花瓣进行显微特征观察,以期为玫瑰花显微鉴定与品种划分提供参考。方法通过使用光学显微镜及扫描电子显微镜对6种玫瑰花的花粉粒和花瓣形貌进行观察,并对花粉粒的9个孢粉学特征指标进行量化分析。结果6种玫瑰花的花粉粒类型均为等级单粒的N_(3)P_(4)C_(5)型,均具沿极轴方向向两极延伸的条状纹饰。其孢粉学数据结果显示:内孔宽度(We)变异系数过大,不能作为鉴别依据;其它指标包括极轴长(P)、赤道轴长(E)、P/E值、外孔长度(Le)、花粉壁沿极轴长度(Exp)、花粉壁沿赤道轴长度(Exe)、花粉壁沿极轴相对厚度(Exe/P)以及花粉壁沿赤道轴相对厚度(Exe/E)差异明显,可综合应用对6种玫瑰花进行品种鉴定。6种玫瑰花花瓣近轴面乳突结构及远轴面条纹形成的盘状结构差异较大,可作为6个品种的鉴别依据。结论从微观角度对6种玫瑰花花瓣微形貌、花粉粒特征及孢粉学研究,为不同品种玫瑰花的鉴别提供了参考依据。

场发射扫描电镜的科学管理与规范操作

扫描电镜具有分辨率高、信号稳定、操作简便等优点,可观察试样的微观形貌,在材料测试中起着重要的作用。扫描电镜主要由真空系统、电子光学系统、显示系统以及附属设备等组成。随着科技的不断发展,扫描电镜变得越来越普及,多数操作人员缺乏系统性的培训,操作水平参差不齐,对设备维护方面不够了解。以FEI Nova NanoSEM 450型场发射扫描电镜为例,介绍了该设备的一系列科学管理与规范操作方法,以期为相关操作人员提供参考。

扫描电镜中透射-反射式STEM明场成像装置的研制及应用

本文研制了一套透射-反射式扫描透射(STEM)明场成像装置,该装置使用背散射电子探头接收经过铂片反射的透射电子信号,可安装在FEI Quanta FEG系列扫描电镜中实现STEM明场成像。分别以埃洛石、Au@ZIF-8纳米颗粒和喷金乳胶标样验证自制STEM明场成像装置的实用性。结果表明:埃洛石STEM明场像的衬度与透射电镜中STEM明场像一致,管腔和管壁具有明显的衬度差异,可以清晰辨识管腔结构;在Au@ZIF-8纳米颗粒的STEM明场像中,Au颗粒衬度较暗,ZIF-8衬度较亮,通过两者之间的衬度差异可以观察到核壳结构;喷金乳胶标样上纳米金颗粒之间可识别的最小距离为2.03 nm,进一步验证了自制STEM明场成像装置具有较高的分辨率。

基于流场仿真的某型涡轮叶片的表面微结构分析

利用流场仿真和扫描电子显微镜观测的方法,对某型涡轮叶片工作前后的表面微形貌进行了分析,研究了高温高压环境对叶片表面形貌变化的影响。首先为了提高计算效率,根据叶片形式,建立了涡轮叶片流场的周期性对称CFD模型,并利用有限体积法对流场的温度和压力进行计算分析;然后利用扫描电镜对工作叶片的表面形貌进行观测,分析叶片表面微缺陷形式;最后根据仿真与试验观测结果,分析了叶片缺陷产生的原因和影响叶片表面微结构变化的因素。结果表明:叶片前缘温度达到最高的860K,在几何结构和波系的共同作用下,叶片前后缘、叶尖、叶根附近流场流动特性复杂,流道内温度和压力分布不均匀;叶片后缘根部出现长约180μm的穿晶/沿晶混合模式的微裂纹,后缘叶尖处有长约30μm的夹杂物裂纹出现,这是叶片热应力、叶片表面金相转变、氧化、氢脆等共同作用的结果;应根据涡轮泵的实际任务情况对涡轮泵地面热试车程序进行合理的安排,尤其在关机阶段要考虑是否对涡轮叶片的冷却采取大气环境隔离措施。研究可为液体火箭发动机涡轮叶片寿命评估提供参考。

17份闽北茶树种质资源花粉形态扫描电镜观察

【目的】明确闽北茶树种质资源花粉形态特征,并探索其亲缘关系。【方法】利用冷场发射扫描电镜观测福建武夷山、建瓯、建阳等闽北茶区17份茶树种质的花粉形态,采用ImageJ 1.48V对花粉的赤道面观、极面观和萌发沟等相关性状特征进行测量,并利用SPSS软件对花粉相关特征指标进行主成分分析和聚类分析。【结果】17份闽北茶树种质资源的花粉属N3P4C5类型,其花粉大小为1 014.01~2 222.26μm^(2),属于中等花粉;花粉的赤道面观分为扁球形、长球形、卵圆形和超长球形,花粉萌发沟长度为12.68~35.49μm,花粉表皮纹饰外壁纹饰均呈现疣状,具有不同程度穿孔。根据花粉萌发沟长、萌发沟长/极轴长、极面观、赤道面观、外壁纹饰5个指标进行系统聚类分析,17份闽北茶树种质资源可分为两类。【结论】根据聚类分析结果和数量性状数据,花粉萌发沟长、萌发沟长/极轴长、极面观、赤道面观、外壁纹饰等性状特征可以为闽北茶树种质资源的亲缘关系以及分类提供理论依据。

Effect of corrosion behavior of cast and extruded ZK60 magnesium alloys processed via friction extrusion

The increasing demand for high-strength,corrosion-resistant magnesium alloys in transportation has led to the development of new processing techniques.In this work,cast and extruded ZK60 magnesium alloys were processed using the innovative solid-phase process,Friction Extrusion(FE).The microstructure was analyzed using Scanning Electron Microscopy(SEM),and Energy Dispersive Spectroscopy(EDS),showing a marked reduction in grain size,uniform solute distribution(Zn and Zr),and second phases after FE processing.Moreover,optical micrographs and Electron Backscatter Diffraction(EBSD)were employed to further evaluate the alloy microstructure.The corro-sion resistance and electrochemical behavior were analyzed using potentiodynamic polarization,Scanning Electrochemical Cell Impedance Microscopy(SECCIM),and atomic emission spectroelectrochemistry analysis(AESEC).Time evolution surface imaging and post-corrosion microstructures were also analyzed to support the understanding of underlying corrosion mechanisms.Corrosion initiation and propagation in FE-processed samples followed grain boundary patterns,differing from cast and extruded ZK60 behaviors.Electrochemical measurements and in-situ time-dependent optical imaging demonstrated that FE processing enhanced corrosion potential,reduced corrosion current,and increased cathodic activity.Additionally,FE processing reduced the disparity in pitting potential between cast and extruded samples,resulting in intermediate pitting potentials.Higher Mg and lower Zn dissolution was observed in the lower anodic currents for FE-processed samples.During aggravated anodic current cycles,Mg dissolution equalized,but the Zn/Mg dissolution ratio increased for FE-processed extruded samples,suggesting less cathodic activation and better resistance to further pitting.

Acoustical properties of a 3D printed honeycomb structure filled with nanofillers:Experimental analysis and optimization for emerging applications

The novelty of this research lies in the successful fabrication of a 3D-printed honeycomb structure filled with nanofillers for acoustic properties,utilizing an impedance tube setup in accordance with ASTM standard E 1050-12.The Creality Ender-3,a 3D printer,was used for printing the honeycomb structures,and polylactic acid(PLA)material was employed for their construction.The organic,inorganic,and polymeric compounds within the composites were identified using fourier transformation infrared(FTIR)spectroscopy.The structure and homogeneity of the samples were examined using a field emission scanning electron microscope(FESEM).To determine the sound absorption coefficient of the 3D printed honeycomb structure,numerous samples were systematically developed using central composite design(CCD)and analysed using response surface methodology(RSM).The RSM mathematical model was established to predict the optimum values of each factor and noise reduction coefficient(NRC).The optimum values for an NRC of 0.377 were found to be 1.116 wt% carbon black,1.025 wt% aluminium powder,and 3.151 mm distance between parallel edges.Overall,the results demonstrate that a 3Dprinted honeycomb structure filled with nanofillers is an excellent material that can be utilized in various fields,including defence and aviation,where lightweight and acoustic properties are of great importance.

A novel approach to improve the field emission characteristics of printed CNT films

A novel post-treatment method, including hard hairbrush and electrical treatment, is performed intentionally to improve the field emission capability and stability of screen-printed carbon nanotubes （CNTs）. Compared with untreated films, the field emission properties of the treated ones are greatly enhanced. Scanning electron microscopy （SEM） and Raman spectrum studies reveal that field emission properties are enhanced by two factors. Firstly, the improved field emission properties of CNT films can be attributed to the more active CNT surface by removing the organic material cover on the CNTs. Secondly, the gener- ation of a high density of structural defects and the lower resistance contact to the topside CNT emitters after treatment are all helpful to improving the field emission properties of the treated CNTs.

不同溅射镀膜制样方式在LiFePO_(4)材料形貌观察中的应用

采用冷场发射扫描电镜对比了三种不同溅射镀膜制样方式对LiFePO_(4)材料进行微观形貌观察及粒径分析的效果。结果表明,采用溅射镀膜黄金、溅射镀膜铂金、不溅射镀膜三种方式制备的样品,通过扫描电子显微镜均能对材料粒径分布进行有效分析。其中观察溅射镀膜铂金和不溅射镀膜的样品,能够清晰的观察LiFePO_(4)材料的微观形貌,采用不溅射镀膜的制样方式能有效地降低人员及耗材的成本;而观察溅射镀膜黄金的样品,由于黄金颗粒较大,很大程度上掩蔽了LiFePO_(4)表面的微观细节特征,从而观察到的微观形貌失真。结果表明:对于LiFePO_(4)正极材料采用冷场扫描电镜观察时,以不溅射镀膜制样方式观察,能够清晰地观察材料表面的微观细节特征,同时有效降低人员设备成本,提高材料形貌观察及粒径分析的效率。

一种表征可吸收胶原蛋白材料孔结构的方法研究

目的研究一种表征可吸收胶原蛋白材料微观形貌的方法,并分析其孔隙率和孔径。方法利用场发射扫描电子显微镜(Scanning Electron Microscope,SEM),在不同的加速电压下对未喷金样品和喷金样品进行拍摄,使用Image J软件对所得的SEM图像的孔隙率和孔径进行分析,并对结果的有效性进行验证。结果样品未喷金时使用低倍加速电压可获得清晰的SEM图像;样品喷金后其耐受电压能力明显提高,即使在较高的加速电压下依然能获得清晰的SEM图像。使用Image J软件可对拍摄的SEM图像的孔径和孔隙率进行分析,其中,平均孔隙率为50.9%,平均孔径为11.9μm;孔隙率离散系数为8.6%,孔径离散系数6.7%。结论场发射SEM结合Image J软件是一种表征可吸收胶原蛋白材料孔结构的有效方法,可解决相关标准中方法缺失的问题。

HITACHI SU5000热场发射扫描电镜的使用及参数选择

以HITACHI SU5000热场发射扫描电镜为例,以金银核壳纳米棒、ZIF-8、碳酸钙纳米微球和聚苯乙烯微球为研究对象,探讨不同参数对扫描电镜图像质量的影响。结果显示,对于导电性良好的样品,选择较高加速电压搭配适宜束流强度,可得到高分辨率的样品形貌。对于半导体样品,选择合适的电压,根据放大倍数来调整束流强度。对于不导电样品,电压和束流过低,聚焦困难;适当提高加速电压,增加电子束的穿透深度,可显著减少荷电现象,图像质量得到改善。

关于质子交换膜燃料电池膜的扫描电子显微镜图像的荷电现象研究

利用蔡司GeminiSEM500场发射扫描电子显微镜观察不导电的质子交换膜燃料电池基底膜在喷镀处理前后,使用不同的二次电子探测器观察图像的荷电情况。结果显示:inlens模式下,即使对隔膜做了喷镀处理,荷电现象依然很明显;而使用SE2模式拍摄的图片,即使是未做喷镀处理,图像的荷电现象明显减少。分析不同的加速电压下,不同的镜筒拍摄模式拍摄的图片的荷电情况,结果显示:随着加速电压增大,图片的荷电效应越大;降低加速电压,可以明显减轻图像的荷电现象,在合适的电压下,对于导电性较差的隔膜样品,使用SE2模式拍摄下,即使不做喷镀处理也可以有效消除图像的荷电现象。

Electrophoretic Deposition of Oxide Nanoparticles for Electron Emission Enhancement

Four oxide nanoparticles,such as yttrium oxide,lanthanum oxide,cerium oxide and zirconium oxide were coated on rhenium filaments by an electrophoretic deposition method.The oxide coatings were examined by scanning electron microscopy,and electron emission characteristics of the oxide-coated rhenium were studied to find alternative oxide materials for replacing the hazardous thorium oxide.Among four oxides tested in this work,yttrium oxide and lanthanum oxide coated rhenium showed enhanced electron emission compared with an uncoated rhenium.However,lanthanum oxide coating evaporated too quickly in a vacuum chamber,and hence yttrium oxide was found to be the only alternative material for use in a routine mass spectrometry.An optimum coating thickness of the yttrium oxide and lanthanum oxide was around 20 μm.