Visualization of atomic scale reaction dynamics of supported nanocatalysts during oxidation and ammonia synthesis using in-situ environmental(scanning) transmission electron microscopy

Reaction dynamics in gases at operating temperatures at the atomic level are the basis of heterogeneous gas-solid catalyst reactions and are crucial to the catalyst function.Supported noble metal nanocatalysts such as platinum are of interest in fuel cells and as diesel oxidation catalysts for pollution control,and practical ruthenium nanocatalysts are explored for ammonia synthesis.Graphite and graphitic carbons are of interest as supports for the nanocatalysts.Despite considerable literature on the catalytic processes on graphite and graphitic supports,reaction dynamics of the nanocatalysts on the supports in different reactive gas environments and operating temperatures at the single atom level are not well understood.Here we present real time in-situ observations and analyses of reaction dynamics of Pt in oxidation,and practical Ru nanocatalysts in ammonia synthesis,on graphite and related supports under controlled reaction environments using a novel in-situ environmental(scanning) transmission electron microscope with single atom resolution.By recording snapshots of the reaction dynamics,the behaviour of the catalysts is imaged.The images reveal single metal atoms,clusters of a few atoms on the graphitic supports and the support function.These all play key roles in the mobility,sintering and growth of the catalysts.The experimental findings provide new structural insights into atomic scale reaction dynamics,morphology and stability of the nanocatalysts.

A Pioneering Approach to the Synthesis of Silver Nanoparticles

Our research introduces a groundbreaking chemical reduction method for synthesizing silver nanoparticles, marking a significant advancement in the field. The nanoparticles were meticulously characterized using various techniques, including optical analysis, structural analysis, transmission electron microscopy (TEM), and field-emission scanning electron microscope (FESEM). This thorough process instills confidence in the accuracy of our findings. The results unveiled that the silver nanoparticles had a diameter of less than 20 nm, a finding of great importance. The absorption spectrum decreased in the peak wavelength range (405 - 394 mm) with increasing concentrations of Ag nanoparticles in the range (1 - 5%). The XRD results indicated a cubic crystal structure for silver nanoparticles with the lattice constant (a = 4.0855 Å), and Miller indices were (111), (002), (002), and (113). The simulation on the XRD pattern showed a face center cubic phase with space group Fm-3m, providing valuable insights into the structure of the nanoparticles.

Electronic structure and spatial inhomogeneity of iron-based superconductor FeS

Iron-based superconductor family FeX(X=S,Se,Te)has been one of the research foci in physics and material science due to their record-breaking superconducting temperature(FeSe film)and rich physical phenomena.Recently,FeS,the least studied Fe X compound(due to the difficulty in synthesizing high quality macroscopic crystals)attracted much attention because of its puzzling superconducting pairing symmetry.In this work,combining scanning tunneling microscopy and angle resolved photoemission spectroscopy(ARPES)with sub-micron spatial resolution,we investigate the intrinsic electronic structures of superconducting FeS from individual single crystalline domains.Unlike FeTe or FeSe,FeS remains identical tetragonal structure from room temperature down to 5 K,and the band structures observed can be well reproduced by our ab-initio calculations.Remarkably,mixed with the 1×1 tetragonal metallic phase,we also observe the coexistence of √5×√5 reconstructed insulating phase in the crystal,which not only helps explain the unusual properties of FeS,but also demonstrates the importance of using spatially resolved experimental tools in the study of this compound.

氧化铝表面Ti修饰对负载金属Mo分散性能的影响

分别用扫描透射-高角环形暗场像(HAADF-STEM)和高分辨电子显微技术(HREM)表征了氧化态和硫化态Mo/Al_2O_3,Mo/6%TiO_2-Al_2O_3,Mo/12%TiO_2-Al_2O_3催化剂中MoO_3颗粒尺寸和MoS_2片晶的层数与长度,发现氧化态催化剂中MoO_3颗粒的平均尺寸从Ti修饰前的0.7nm增加到修饰后的1.0nm;硫化态催化剂中MoS_2片晶的平均层数从1.1增加到1.2,平均长度从3.0nm增加到3.2nm。并从金属-载体相互作用理论解释了其形成机理。基于以上结果,根据MoO_3颗粒和MoS_2片晶中钼原子数变化,研究了催化剂硫化过程中金属晶粒的生长演变过程。

以炭黑为原料温和条件下液相生长碳(质)微带

以炭黑为原料,在温和条件下的无水乙醇相中,培养出从根本上不同于炭黑粒子聚集体结构的微米尺寸的带状结构碳(质)新型材料。采用扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、电子衍射对新材料结构进行了表征。研究结果表明:在温和条件下的有机溶剂中以炭黑为原料制备出形态与结构完全不同于炭黑的带状晶体结构新型碳(质)材料,统计结果显示碳(质)微带的厚度约为1～5μm,宽度约为5～30μm,长度可达数毫米。

纳米粉体高分辨成像的荷电效应与应对策略

为应对纳米粉体在扫描电镜成像中出现的荷电效应,分析荷电效应的形成机理;推导样品与入射电子束响应之间的关系式,揭示样品表面累积的有效电荷密度与电流、每帧扫描时间、放大倍率和电子总产额的关系;在荷电场达到近似于稳态后,建立表面累积电势与束流、放大倍数、电阻率以及电子总产额的关系表达式;分析缓解或消除荷电效应的各种措施的利弊,揭示当代场发射扫描电镜的低电压和高分辨的成像能力,探索场发射扫描电镜的较佳成像策略。结果表明:根据关系表达式可以指导电镜参数设置或者探测器的选择,以克服荷电现象;对纳米粉体表面镀导电膜虽然可以消除荷电效应,但会影响观察纳米粉体的真实形貌;现代场发射扫描电镜能够实现低电压、高分辨成像,可以克服镀膜对粉体形貌造成的影响。

核壳型SAPO-34/AlPO-18分子筛的制备及生长机理

采用水热法制备了核壳型SAPO-34/AlPO-18分子筛,并运用X射线衍射、扫描电镜和超高分辨场发射扫描电镜等方法对样品进行了表征.结果表明,通过改变实验条件可有效调控壳层AlPO-18纳米晶在SAPO-34晶体表面的生长,从而得到具有不同生长区域、生长取向及紧密度的核壳型SAPO-34/AlPO-18分子筛.超高分辨场发射扫描电镜结果发现,核相SAPO-34晶体的外表面结构与壳层AlPO-18纳米晶的生长性质紧密相关,从而推测出核相晶体外表面微细结构诱导壳层分子筛生长的晶化机理.

探针电流对场发射扫描电镜图像的影响

通过对电镜工作原理的研究,分析了不同探针电流对电镜图像分辨率、景深、荷电现象的影响因素,总结了选择最佳探针电流的原则。探针电流升高,束斑直径变大,信噪比变好,但图像分辨率下降,景深减小,荷电现象增强;探针电流降低,束斑直径减小,分辨率增高,景深增加,有利于减弱荷电现象,但是探针电流过小,噪声增大,聚焦困难,图像分辨率反而下降。实验表明,结合样品的特征,灵活地选择探针电流能显著地提高电镜图像质量。

超声显微检测技术在电子封装中的应用与发展

超声显微检测技术应用于电子封装领域始于20世纪80年代,如今已是检测电子封装可靠性和完整性的重要手段,被广泛应用到了电子封装的缺陷检测和精密测量等方面。针对电子封装的超声显微检测存在回波重叠、信噪比低等问题,近年来,发展了许多时频分析方法,用于获得优于常规方法的纵向分辨率,即实现超分辨率。该文首先介绍了超声显微检测的发展历史,对其检测原理和分辨率理论进行了简述;其次,综述了超声显微检测技术在电子封装中的主要应用与发展现状;然后,对超声显微检测的超分辨率成像方法进行了综述,分别介绍了基于小波分析的反卷积、连续小波变换和稀疏表示在实现超分辨率时的原理及适用场景;最后,探讨归纳了电子封装超声显微检测的主要研究方向及难点。

One-pot synthesis and optical properties of In- and Sn-doped ZnO nanoparticles

Colloidal indium-doped zinc oxide (IZO) and tin-doped zinc oxide (ZTO) nanoparticles were successfully prepared in organic solution, with metal acetylacetonate as the precursor and oleylamine as the solvent. The crystal and optical properties were characterized by X-ray diffraction, UV−visible spectrophotometry, and fluorescence spectroscopy, respectively; the surface and structure morphologies were observed by scanning electron microscopy and transmission electron microscopy. The XRD patterns of the IZO and ZTO nanoparticles all exhibited similar diffraction peaks consistent with the standard XRD pattern of ZnO, although the diffraction peaks of the IZO and ZTO nanoparticles were slightly shifted with increasing dopant concentration. With increasing dopant concentration, the fluorescent emission peaks of the IZO nanoparticles exhibited an obvious red shift because of the difference in atomic radii of indium and zinc, whereas those of the ZTO nanoparticles exhibited almost no shift because of the similarity in atomic radii of tin and zinc. Furthermore, the sizes of the IZO and ZTO nanoparticles distributed in the ranges 20–40 and 20–25 nm, respectively, which is attributed to the difference in ionic radii of indium and tin. © 2017, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.

Highly efficient and stable electrooxidation of methanol and ethanol on 3D Pt catalyst by thermal decomposition of In2O3 nanoshells

In this paper In2O3nanoshells have been synthesized via a facile hydrothermal approach. The nanoshells can be completely cracked into pony-size nanocubes by annealing, which are then used as a support of Pt catalyst for methanol and ethanol electrocatalytic oxidation. The prepared In2O3and supported Pt catalysts (Pt/In2O3) were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), field effect scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS) were carried out, indicating the excellent catalytic performance for alcohol electrooxidation can be achieved on Pt/In2O3nanocatalysts due to the multiple active sites, high conductivity and a mass of microchannels and micropores for reactant diffusions arising from 3D frame structures compared with that on the Pt/C catalysts. © 2016 Science Press

The Preparation of Nano Silver by Chemical Reduction Method

A silver nanostructures prepared by using chemical reduction method. The silver nanoparticles were prepared with diameters of about (20 nm). Numerous techniques had been used to study the optical, structural like the UV-Vis absorption spectrometer, Ttransmission Electron Microscopy (TEM), Field-Emission Scanning Electron microscope (FESEM), and X-ray diffraction (XRD). The practical results exhibited the absorption spectrum of the prepared nanoparticles at (357 nm), it was found that there is a relationship between the positions of the optical absorption peak and the size of the silver nanoparticles. The analysis of TEM results showed the presence of nanoparticles in the range (20 nm). The analyzing of XRD results explained the crystal structure for silver nanoparticles. It is found a cubic unit cell have a lattice constants (a = 4.0855 Å), with the Miller indices were (111), (002), (002), and (113).

卤制温度对酱卤藏羊肉品质的影响

为研究卤制温度对酱卤藏羊肉品质的影响,本试验分析了卤制中心温度为30、40、50、60、70、80、90、99℃时对藏羊后腿肉的蒸煮损失、剪切力、蛋白溶解度的影响,并采用SDS-PAGE电泳和扫描与透射电镜研究了对藏羊肉肌原纤维蛋白组分及微观结构的变化。结果表明:随着卤制中心温度的升高,蒸煮损失率由中心温度为30℃时的15.82%逐渐增大到99℃时的41.15%;剪切力随着卤制中心温度的升高而逐渐增大,到70℃时达到最大值,但熟化温度达到80℃后剪切力变小,随后又逐渐增大;蛋白溶解度随着中心温度的升高而呈逐渐降低的趋势。SDS-PAGE和透射与扫描电镜结果表明,随着卤制中心温度的升高,肌原纤维蛋白发生了蛋白降解与交联,肌原纤维束间的空隙逐渐缩小,变得更加密集、紧凑,且肌纤维直径和肌节长度逐渐缩小。因此,卤制中心温度为70℃时是酱卤藏羊肉品质形成的关键温度点。

Sb_2Se_3纳米线的水热合成和表征

分别以SbCl3和不同的硒源(SeO2、Se粉)为原料,采用水合肼(N2H4·H2O)为还原剂,用水热法在150℃下反应24h后合成Sb2Se3纳米粉末。通过X射线粉末衍射(XRD)、透射电镜(TEM)、场发射电子扫描电镜(FESEM)以及高分辨透射电镜等分析方法对产物的物相成分和形貌等进行表征。结果表明,产物的结构为正交晶系的Sb2Se3纳米晶体,其微观形貌为一维纳米线结构。采用不同硒源合成产物的微观形貌基本相似,其中以SeO2作为硒源水热合成的Sb2Se3纳米线比以Se粉作为硒源合成的纳米线要更加窄而薄,而且纳米线尺寸比较均匀一致。纳米线晶体沿[001]方向生长,这与Sb2Se3独特的晶体结构有着密切的联系。

机械热压充填技术三维充填效果体外实验研究

目的通过机械热压充填技术与连续波热牙胶充填技术、冷牙胶侧方加压充填技术的对比,评估机械热压充填技术的三维充填效果。方法收集2014年6月中山大学光华口腔医学院·附属口腔医院颌面外科门诊拔除的新鲜离体前牙60颗进行根管预备后随机分为3组。分别采用机械热压充填技术(A组,20颗)、连续波热牙胶充填技术(B组,20颗)和冷牙胶侧方加压充填技术(C组,20颗)进行根管充填后使用高分辨率的显微CT(microCT)进行扫描。扫描后的离体牙分别自距根尖孔3、6、9mm处切片后进行扫描电镜观察。使用Image J图像处理软件计算空隙区域百分比后采用SPSS统计软件对测量数据进行分析。结果显微CT与扫描电镜的观察结果均显示A组与B组间空隙区域百分比差异无统计学意义(P>0.05)。A、B两组的空隙区域百分比明显低于C组,差异有统计学意义(P<0.05)。结论机械热压充填技术和连续波热牙胶充填技术的三维充填效果优于冷牙胶侧方加压充填技术,而前两种充填技术的三维充填效果无明显差别。

FePO4-coated Li[Li0.2Ni0.13Co0.13Mn0.54]O2 with improved cycling performance as cathode material for Li-ion batteries

Li[Li0.2Ni0.13Coo.13Mn0.54]O2 cathode materials were synthesized by carbonate-based co-precipitation method, and then, its surface was coated by thin layers of FePO4. The prepared samples were characterized by X-ray diffraction （XRD）, field emission scanning electron micro- scope （FESEM）, energy-dispersive spectroscopy （EDS）, and transmission electron microscopy （TEM）. The XRD and TEM results suggest that both the pristine and the coated materials have a hexagonal layered structure, and the FePO4 coating layer does not make any major change in the crystal structure. The FePO4-coated sample exhibits both improved initial discharge capacity and columbic efficiency compared to the pristine one. More significantly, the FePO4 coating layer has a much positive influence on the cycling perfor- mance. The FePO4-coated sample exhibits capacity reten- tion of 82 % after 100 cycles at 0.5℃ between 2.0 and 4.8 V, while only 28 % for the pristine one at the same charge-discharge condition. The electrochemical impe- dance spectroscopy （EIS） results indicate that this improved cycling performance could be ascribed to the presence of FePO4 on the surface of Li[Li0.2Ni0.13Co0.13Mno.54102 par- ticle, which helps to protect the cathode from chemical attacks by HF and thus suppresses the large increase in charge transfer resistance.

Fabrication of single-crystalline ZnSe multipod-based structures

ZnSe multipod-based structures,including tetrapod-like microrods,long microwires,and short nanorods,are selectively prepared by atmospheric pressure thermal evaporation of ZnSe nanoparticles without using any catalyst.The morphologies could be well controlled by simply adjusting the deposition position.The phase structures,morphologies,and optical properties of the products are investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(TEM),and photoluminescence(PL) spectroscopy.A vapor-liquid mechanism is proposed for the formation of ZnSe multipod-based structures.The presented route is expected to be applied to the synthesis of other Ⅱ-Ⅵ groups or other group's semiconductor materials with controllable morphologies.

Assessment of wear micromechanisms on a laser textured cemented carbide tool during abrasive-like machining by FIB/FESEM

The combined use of focused ion beam(FIB)milling and field-emission scanning electron microscopy inspection(FESEM)is a unique and successful approach for assessment of near-surface phenomena at specific and selected locations.In this study,a FIB/FESEM dual-beam platform was implemented to docment and analyze the wear micromechanisms on a laser-surface textured(LST)hardmetal(HM)tool.In particular,changes in surface and microstructural integrity of the laser-sculptured pyramids(effective cutting microfeatures)were characterized after testing the LST-HM tool against a steel workpiece in a workbench designed to simulate an external honing process.It was demonstrated that:(1)laser-surface texturing does not degrade the intrinsic surface integrity and tool effectiveness of HM pyramids;and(2)there exists a correlation between the wear and loading of shaped pyramids at the local level.Hence,the enhanced performance of the laser-textured tool should consider the pyramid geometry aspects rather than the microstructure assemblage of the HM grade used,at least for attempted abrasive applications.