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.

Ultrastructural Analysis of the Ontogenetic Development of Shoot Induced from Embryonic Axes of Costa Rican Bean Varieties (<i>Phaseolus vulgaris</i>L.) under <i>in Vitro</i>Conditions by Scanning Electronic Microscopy

Common bean (Phaseolus vulgaris L.) is an economic important crop and one of the major grain legumes for human consumption in Latin America, Africa and Asia. A morphological study of shoot induced from embryonic axes development in four Costa Rican bean varieties (Brunca, Huetar, Guaymi and Bribri) cultivated on MS media with or without 5 mg·L–1 de N6-benzylaminopurine (BAP) by scanning electron microscopy (SEM) was developed in the present work. Micrographs showed similarities and differences in the ultrastructure of the apical dome, epidermal surface, stomata and different types of trichomes in the varieties cultivated on organogenesis media. Genotypes with advantageous morphological characteristics for genetic transformation, in particular an exposed apical dome, were identified. This work will contribute to the optimization of the in vitro regeneration of four common bean varieties.

Evolution of pore systems in low-maturity oil shales during thermal upgrading--Quantified by dynamic SEM and machine learning

In-situ upgrading by heating is feasible for low-maturity shale oil,where the pore space dynamically evolves.We characterize this response for a heated substrate concurrently imaged by SEM.We systematically follow the evolution of pore quantity,size(length,width and cross-sectional area),orientation,shape(aspect ratio,roundness and solidity)and their anisotropy—interpreted by machine learning.Results indicate that heating generates new pores in both organic matter and inorganic minerals.However,the newly formed pores are smaller than the original pores and thus reduce average lengths and widths of the bedding-parallel pore system.Conversely,the average pore lengths and widths are increased in the bedding-perpendicular direction.Besides,heating increases the cross-sectional area of pores in low-maturity oil shales,where this growth tendency fluctuates at<300℃ but becomes steady at>300℃.In addition,the orientation and shape of the newly-formed heating-induced pores follow the habit of the original pores and follow the initial probability distributions of pore orientation and shape.Herein,limited anisotropy is detected in pore direction and shape,indicating similar modes of evolution both bedding-parallel and bedding-normal.We propose a straightforward but robust model to describe evolution of pore system in low-maturity oil shales during heating.

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.

Mssbauer and electron microscopy study of martensitic transformations in an Fe-Mn-Mo alloy

The kinetic,morphological,crystallographic,and magnetic characteristics of thermally induced martensites in Fe-13.4wt% Mn-5.2wt%Mo alloy were investigated by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,and M（o｜¨）ssbauer spectroscopy.The experimental results reveal that two types of thermal-induced martensites,e（hcp） andα＇（bcc） martensites,are formed in the as-quenched condition,and these transformations have athermal characters.Mo addition to the Fe-Mn alloy does not change the coexistence ofεandα＇ martensites with the Mn content between 10wt%and 15wt%.Besides,M（o｜¨）ssbauer spectra reveal a paramagnetic character with a singlet for theγ（fcc） austenite andεmartensite phases and a ferromagnetic character with a broad sextet for theα＇ martensite phase. The volume fraction ofα＇ martensite forming in the quenched alloy is much more than that of theεmartensite.

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。

硼砂煅制工艺优化及质量评价

目的 优化硼砂煅制工艺,并对其进行质量评价。方法 以铺设厚度、煅制温度、煅制时间为影响因素,失水率、蓬松度、粉碎率、四硼酸钠含量为评价指标,星点设计-效应面法优化硼砂煅制工艺。采用扫描电镜(SEM)、热重分析(TG)、拉曼光谱、X射线衍射(XRD),比较硼砂煅制前后质量差异。结果 最佳条件为铺设厚度2 cm,煅制温度365℃,煅制时间100 min。煅制后,硼砂微观形态、成分组成、晶型结构发生变化,失去全部结晶水而转变为非晶体状态。结论 该方法稳定可行,可用于工业大批量生产煅硼砂。

水体pH对福寿螺和中国圆田螺存活及器官结构的影响

近年来,福寿螺(Pomacea canaliculata)同本地螺类竞争力的研究主要集中在温度、干旱和饥饿等因素。为探究酸碱胁迫下福寿螺与华南地区常见淡水螺中国圆田螺(Cipangopaludina chinesis)的响应特征,本研究以五种不同的水体pH作为梯度,对福寿螺和中国圆田螺进行处理,以研究其存活情况,并利用扫描电镜观察两种螺类肝脏和头部的表面结构变化。结果显示:两种螺在酸碱胁迫下都会出现一定程度的死亡,福寿螺在水体pH值4.5、6.5、8.5、10.5的存活率均高于中国圆田螺,对酸碱适应范围更广,但pH 2.5处理下中国圆田螺存活率更高。同时,扫描电镜结果显示,酸碱胁迫下两种螺头足部和肝脏存在明显的外表破损,但中国圆田螺肝脏和头足部损伤更为严重。结果表明,福寿螺比本地中国圆田螺具有更强的酸碱耐受性和适应性。

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。

西藏光核桃资源花粉粒的进化研究

分析光核桃花粉粒形态变化特征,揭示其种质资源内部花粉进化规律。对西藏47份光核桃种质资源的花粉粒进行电镜扫描观察结果发现,有10个材料的光核桃花粉粒外壁形态呈椭圆球形,外壁纹饰呈简单的直纹平行型,穿孔较少或没有,这些材料最为原始;有9个材料的花粉粒外部形态特征条纹复杂,纹孔较多且密,与较为原始材料比较属于进化类型;其他材料则介于两类之间。光核桃资源不是都处于原始阶段,其内部发生了进化,不同类型的资源为光核桃新品种选育和研究提供了丰富的材料。

冷冻扫描电镜制样方法及其在含水样品中的应用

常规扫描电镜要求所观察的样品必须干燥、无水,而一些含水样品在干燥过程中会发生结构变化,无法真实反映样品的结构信息。冷冻扫描电镜无需对样品进行干燥处理,可以直接分析含水样品表面、界面和内部结构,是研究高度含水样品的强有力工具。样品的制样方法在冷冻扫描电镜技术中占有重要地位,它直接关系到样品真实形貌特征的反映和对超微结构的正确解读。本文综述了冷冻扫描电镜的制样方法,并阐述冷冻扫描电镜技术在天然气水合物、微生物、乳液、水凝胶、动植物等含水样品中的应用。

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。

基于SEM和MIP试验结构性黏土压缩过程中微观孔隙的变化规律

为探求土体在变形过程中微结构形态的演化规律,对湛江结构性黏土进行室内压缩试验,通过真空冷冻升华干燥法对天然土和压缩后土制样,进行扫描电子显微镜扫描试验和压汞试验,基于灰度计算土的三维孔隙率,分析压缩过程中微观孔隙的变化规律。结果表明,较二值化处理获得的二维孔隙率,三维孔隙率物理意义明确,求取方法简单,有较高准确性。湛江天然黏土孔径为1.0～0.1μm的小孔隙组占优,其孔隙体积占总孔隙体积的73%。压缩过程中,P>k前,各孔径组分变化甚微。P>k后,随压力的增大,小孔隙含量表现为先增加后降低。各孔隙组对外力的敏感度与孔隙体积含量正相关。由于压汞过程存在"瓶颈"效应,其结果可能会夸大小孔隙的分布密度而低估大孔隙的分布密度。结构性黏土压缩过程中微观结构形态的演化可分为结构微调、结构破损、结构固化3个阶段。该研究有助于深入了解土的变形机制,为结构性土的工程设计提供科学的依据。

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。

弱动力扰动作用下岩石微裂隙演化特征及灾害防控

【目的】高应力叠加弱动力扰动是诱发冲击地压的关键因素,但不同扰动幅值、频率、卸载范围下的岩石微裂纹扩展特征和能量耗散规律尚不明确,无法为冲击地压防治提供技术支撑。【方法】基于真三轴卸载动力扰动试验,分析了不同扰动幅值(5、10 MPa)、频率(4、10 Hz)、三向应力卸载(0、12MPa)下深部围岩失稳破坏规律,并结合SEM扫描分析了岩石微裂隙特征。通过锚杆拉拔试验,优化了锚杆肋间距和肋高,提高了其吸能支护作用,提出了“吸能锚杆-低阻抗混凝土注浆-喷浆-挂网”组合支护技术。利用传感器对巷道进行长期监测,得到治理前后压力与振动数据。【结果和结论】研究表明:(1)随着扰动幅值和频率的增加,裂纹增加显著且不规则,岩石断口的方向分形维数降低。当扰动为10MPa、10Hz时,分形维数降至最低值0.62,孔隙方向角80°~120°孔隙定向频率达到最大值的52%,约为原始岩石的1.68倍。说明岩石受扰动后颗粒的应力不均匀,导致应力集中,断裂方向明显。(2)随着扰动幅值和频率的增加,SEM图像的微孔隙面积先快速增加,后缓慢增加且增加趋势越来越小。扰动频率每增加2 Hz,岩石微裂隙面积增加约24.13%。(3)现场测试表明随着锚杆肋间距和肋高增加,拉拔曲线形态由“弹塑性阶段-破坏失效阶段-残余阶段”逐渐过渡为“弹塑性阶段-微量屈服阶段-大量强化阶段-破坏失效阶段-残余阶段”,肋间距48mm、肋高2mm的螺纹钢锚杆吸能效果最好。经现场监测可将巷道压力稳定在36 N左右,峰值加速度控制在8000mm/s^(2)以内。研究揭示了卸载动力扰动作用下围岩破坏及能量释放规律,提出的“吸能锚杆-低阻抗混凝土注浆-喷浆-挂网”支护技术,可为类似深部工程提供理论指导。

块状非晶剪切带和微裂纹形核扩展的SEM原位研究

在扫描电镜(SEM)中对Zr_(57)Cu_(15.4)Ni_(12.6)Al_(10)Nb_5块状非晶单边缺口试样进行了原位拉伸;用原子力显微镜(AFM)研究了剪切带的三维形貌。研究表明,拉伸时缺口前方产生剪切带,它们逐步发展、长大,尽管剪切带由剪应力产生,正应力在其形成和扩展过程中起重要作用。两剪切带相交时会形成割阶,其长度随相交剪切带中应变量升高而增大,当主剪切带中应变集中足够大后,剪切微裂纹沿主剪切带和基体的交界线形核扩展,并沿剪切面向试样内部扩展几十微米;在正应力作用下,该剪切(Ⅱ型)裂纹张开成Ⅰ型,并快速贯穿试样厚度,然后沿横向快速扩展导致断裂。

脱落种植体表面刮治与喷砂处理的扫描电镜(SEM)和X射线能谱仪(EDS)分析

目的观察刮治和喷砂对脱落种植体表面的影响。方法对临床上因种植体周围炎脱落的Bego Semado S系列种植体进行表面刮治和喷砂,扫描电镜(scanning electronic microscopy,SEM)下观察形态,用X射线能谱仪(energy dispersive X-ray spectrometer,EDS)进行表面元素分析。结果 SEM下观察,刮治能够清洁种植体表面,喷砂后能进一步清洁种植体表面。元素分析表明喷砂能够大幅降低脱落种植体表面的C元素含量(P<0.05),提升种植体表面Ti元素的原子百分比(P<0.05)。结论在Bego Semado S系列种植体周围炎的治疗中,进行喷砂处理是必要的。

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。