透射电镜三维重构确定杂化嵌段共聚物两相空间分布

多金属氧酸盐(POM)簇-聚合物杂化物是一类兼有无机材料催化性能和聚合物可加工性的,具有优异应用前景的杂化材料。POM簇-聚合物杂化物中两相的空间分布对材料的性能有至关重要的影响。但该材料纳米尺度的3D两相空间形貌和结构无法用常规的透射电镜观察和表征。本文利用透射电镜的三维重构技术,选择合适的参数和方法进行二维图像的采集、图像匹配对中及重构,并完成立体模型的构建,从而通过构建的模型对三种杂化共聚物的两相空间分布进行了确认和分析。     

透射电镜三维重构技术在螺旋纳米材料手性判断中的应用

螺旋材料在手性催化、手性拆分以及手性光学材料等领域的潜在应用价值引起了研究者的广泛兴趣,手性的判断在研究应用中也显得尤为重要。单一的透射电镜和扫描电镜的二维图像不能作为准确判定螺旋材料手性的唯一依据。透射电镜三维重构技术可作为一种直观有效的方法确定螺旋材料的手性。本文通过透射电镜的三维重构技术对两种单手螺旋的3-氨基苯酚-甲醛树脂及单手螺旋碳质纳米管样品的手性做出了判断。     

基于小角X射线散射聚烯烃催化剂三维模型重构

以从小角X射线散射(SAXS)方法获得的相关函数和吸附法获得的孔隙率为基本参数,采用截断高斯场法重构出聚烯烃催化剂的三维模型。结果表明,所构建的催化剂三维模型的孔隙率值和相关函数值与催化剂实验值很吻合,重构效果良好。在重构三维模型过程中,采用SAXS方法可直接获取相关函数的三维形式,比从二维图像中提取相关函数后还需要扩展为三维形式的过程更简便。并且SAXS法的表征达到纳米尺度远非一般二维图像的分辨率能达到,而且统计性充分,其相关函数数据更加丰富且可靠。本文建立的催化剂三维模型,可以为获取扩散、渗透、导热等有效热质传输系数,以及更好地预测催化剂的破碎情况建立了基础。     

Keggin结构钼硅酸铵、钨硅酸铵纳米颗粒的室温固相合成、结构及性能研究

采用室温固相法合成了钼硅酸铵、钨硅酸铵两种纳米颗粒 ,用元素分析确定其分子组成 ,它们的结构、性质、颗粒大小、表面形状分别用红外光谱、X -射线粉末衍射、透射电镜和热分析进行了研究 .结果表明 ,两种纳米颗粒的大小分别在 30nm和 4 0nm左右 ,长期放置易发生团聚 ,在水和无水乙醇中呈乳液分布 ,形成纳米颗粒后 ,两种杂多阴离子的热稳定性均明显降低     

电子断层三维重构技术在材料微观结构分析中的应用

电子断层三维重构技术是在透射电镜基础上发展起来的,用以解析材料三维结构的一种技术。本文以美国FEI公司Tecnai G~2 F20透射电镜三维重构系统——Xplore 3D系统为例,探讨了样品制备与取向的选择、样品漂移问题的成因与校正、降低缺失锲存在造成的模型失真及空间分辨率的提高等问题,从以上四个方面详细介绍电子断层三维重构技术的要点及在材料微观结构方面的应用经验。     

三维立体结构微纳电极研究

基于体硅加工工艺和纳米材料技术,研制微电机系统(MEMS)尺度敏感微结构与纳米铂颗粒的复合结构,提高微电极电化学性能,制备具有三维立体微结构的安培型微电极传感器.利用硅的各向异性湿法腐蚀技术在毫米级的工作电极表面实现微米级的锥体形微池阵列,以H2O2为检测对象考察立体电极结构对传感器性能的改进效果,实验证明,立体结构的设计使传感器具有更低的检出限(8 μmol/L)及更高的灵敏度(在 0～200 μmol/L浓度范围内检测灵敏度提高约85%),且具有较好的线性和重复性.利用电化学方法在电极表面沉积铂黑,通过微观形貌分析和电化学特性考察,比较了在平面微电极和立体微电极上修饰纳米材料的效果.立体结构为电沉积铂纳米颗粒提供了更为理想的微环境,改善了纳米材料修饰的效果;立体结构微电极与纳米颗粒的尺寸效应相结合,进一步提高了电极的催化效率和电化学特性.     

有序纳米金颗粒的多层组装

采用LB技术组装了一种三维有序的由十八胺修饰的纳米金颗粒多层结构.这是一种新的组装纳米颗粒三维有序聚集体的方法.为了扩大这种方法的适用范围,在组装过程中,将有机小分子1-苯基-5-巯基四氮唑引进结构,形成了新的纳米金颗粒多层聚集体.这两种多层膜经透射电子显微镜和小角X射线衍射测量证明构成多层膜的单层膜上的纳米金颗粒是有序的,并且颗粒在层与层之间的排列也是有序的.     

室温固相反应合成钼磷酸铵、钨磷酸铵纳米微粒

采用室温固相反应法合成了钼磷酸铵、钨磷酸铵两种多金属氧酸盐纳米微粒，用元素分析确定了其分子组成。它们的结构、性质、颗粒大小、表面形状分别用IR，X-射线粉末衍射、透射电镜和热分析等手段进行了研究。结果表明：两种多金属氧酸盐都为Keggin结构，晶粒分别为34nm和32nm左右，形成纳米微粒后的两种杂多阴离子的热稳定性均明显降低。     

金属介电核壳结构复合材料的制备、性质及应用

金属介电核壳结构复合纳米颗粒因其独特的结构而具有许多奇异的性质,尤其表现在表面等离子体共振特性上。通过改变金属纳米颗粒的大小和核壳的相对尺寸,可实现光学共振在很宽波段内的可调特性。这一特性不仅在光子学,而且在生物光子学、生物医学等领域都有广泛的应用前景。本文介绍了几种金属介电核壳结构纳米颗粒的制备、性质及其应用。     

框架核酸在蛋白精确组装中的应用

除了作为遗传信息的载体,DNA所展现出的特殊的材料性能引起了广泛关注。基于碱基互补配对原则的精确性和可编程性使得核酸纳米结构的构建逐步从一维单链发展到二维平面以及三维立体结构。计算机辅助工具的进步也促进了各种大小和形状的DNA纳米结构的自动化设计,而近年来构建的“框架核酸（Framework Nucleic Acids, FNAs）”为生物大分子纳米尺度上的精确排列提供了新方法,其固有的生物学功能以及可定制的特性使得其在物理,化学和生物等领域具有十分广阔的应用前景。本综述阐述了精确自组装的框架核酸的概念,并概述了框架核酸在蛋白精确组装等领域的最新进展。我们重点论述了框架核酸的优势所带来的对蛋白空间排布及其性能的调控能力,讨论了该领域存在的挑战,并对该领域的发展机遇进行了展望。     

Recent advances in electron tomography: TEM and HAADF-STEM tomography for materials science and semiconductor applications.

Electron tomography is a well-established technique for three-dimensional structure determination of (almost) amorphous specimens in life sciences applications. With the recent advances in nanotechnology and the semiconductor industry, there is also an increasing need for high-resolution three-dimensional (3D) structural information in physical sciences. In this article, we evaluate the capabilities and limitations of transmission electron microscopy (TEM) and high-angle-annular-dark-field scanning transmission electron microscopy (HAADF-STEM) tomography for the 3D structural characterization of partially crystalline to highly crystalline materials. Our analysis of catalysts, a hydrogen storage material, and different semiconductor devices shows that features with a diameter as small as 1-2 nm can be resolved in three dimensions by electron tomography. For partially crystalline materials with small single crystalline domains, bright-field TEM tomography provides reliable 3D structural information. HAADF-STEM tomography is more versatile and can also be used for high-resolution 3D imaging of highly crystalline materials such as semiconductor devices.     

Nano‐Structural Observation of in situ Silica in Natural Rubber Matrix by Three Dimensional Transmission Electron Microscopy

Summary: Three dimensional (3D) nanostructures of particulate silicas in natural rubber (NR) were observed for the first time by use of 3D transmission electron microscopy (3D‐TEM) combined with electron tomography. The method enabled us to visualize and evaluate structural characteristics in 3D space, such as the size and the volume of in situ silica generated in the NR matrix by the sol‐gel reaction of tetraethoxysilane, at nanometer scale resolution.

The reconstructed mass density view of the silica in an in situ silica‐filled natural rubber vulcanizate, as determined by 3D‐TEM.     

Characterization of 3D DNA Assemblies Using Cryogenic Electron Microscopy

DNA nanotechnology utilizes DNA double strands as building units for self-assembly of DNA nanostructures.The specific base-pairing interaction between DNA molecules is the basis of these assemblies.After decades of development,this technology has been able to construct complex and programmable structures.With the increase in delicate nature and complexity of the synthesized nanostructures,a characterization technology that can observe these structures in three dimensions has become necessary,and developing such a technology is considerably challenging.DNA assemblies have been studied using different characterization methods including atomic force microscopy(AFM),scanning electron microscopy(SEM),and transmission electron microscopy(TEM).However,the three-dimensional(3D)DNA assemblies always collapse locally due to the dehydration during the drying process.Cryogenic electron microscopy(cryo-EM)can overcome the challenge by maintaining three-dimensional morphologies of the cryogenic samples and reconstruct the 3D models from cryogenic samples accordingly by collecting thousands of two-dimensional(2D)projection images,which can restore their original morphologies in solution.Here,we have reviewed several typical cases of 3D DNA-assemblies and highlighted the applications of cryo-EM in characterization of these assemblies.By comparing with some other characterization methods,we have shown how cryo-EM promoted the development of structural characterization in the field of DNA nanotechnology.     

Hetero-assembly of gold nanoparticles on a DNA origami template

Hetero-assembling of spherical building blocks with well-defined spatial distribution holds great significance in developing chiral nanostructures. Herein, a strategy for hetero-assembling of gold nanoparticles(Au NPs) was demonstrated using rigid bifacial DNA origami as templates. By tuning the sizes and the fixed location of Au NPs on DNA origami, right-handed and left-handed Au NPs nanostructures were respectively constructed. Gel electrophoresis indicated the formation of the DNA origami-Au NPs complex and transmission electron microscopy(TEM) visually displayed the arrangement of Au NPs in these two chiral structures. The spatial configuration and 3D geometry of Au NPs were further illustrated by the stereographic TEM with tilting angles from ?30° to 30°. This strategy provides a universal approach to construct the asymmetrical 3D geometries, which may have potential applications in biomimicking and nanophotonics.     

Shape-controlled synthesis of 3D and 1D structures of CdS in a binary solution with L-cysteine's assistance

A facile L-cysteine-assisted route was designed for the selectively controlled synthesis of 1D and novel, interesting 3D CdS spherical nanostructures constructed from CdS nanorods (or nanopolypods) in a binary solution. By controlling reaction conditions such as the molar ratio between Cd(OAc)2 and L-cysteine and the volume ratio of the mixed solvents, the synthesis of various 3D architectural structures and 1D wirelike structures in large quantities can be controlled. This is the first reported case of the direct growth of novel 3D self-assemblies of CdS nanorods (or nanopolypods). The morphology, structure, and phase composition of the as-prepared CdS products were examined by using various techniques (X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), high-resolution TEM, and Raman spectroscopy). On the basis of the results from TEM studies and our analysis, we speculate that in the present synthesis the L-cysteine dominates nucleation growth and the ethylenediamine (en)-dominated, oriented-assembly process. Interestingly, the products obtained show a gradient evolution in color from light-yellow to dark-yellow, which implies that their intrinsic optical properties change, possibly due to variations in their special morphologies and structures. This facile solution-phase L-cysteine-assisted method could be extended for the controlled preparation of other metal chalcogenides nanostructures with complex morphologies.     

不同形貌ZnO纳米结构的电子显微分析

控制实验合成条件,利用溶胶-凝胶法和化学溶液生长法制备出不同形貌的ZnO纳米结构。采用X射线衍射仪(XRD)、扫描电子显微镜( SEM) 以及透射电子显微镜(TEM)等多种测试手段对ZnO纳米结构的微观形态及晶相进行了分析。结果表明:3种ZnO纳米结构形貌虽不同,但均具有Z nO六方纤锌矿晶相结构。ZnO纳米棒和花状ZnO纳米结构为单晶,生长方向均沿(0001)方向。ZnO纳米球则为多晶。     

Synthesis of dandelion-like three-dimensional nickel nanostructures via solvothermal route

The objectives of the present research are synthesizing three-dimensional （3D） nickel nanostructures and investigating their magnetic properties. Thus a template-free method was used to prepare 3D dandelion-like nickel nanostructures via reducing of nickel chloride with hydrazine hydrate in ethylene glycol solution at 100 ℃. The resulting Ni nanostructures were characterized by means of powder X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and selected-area electron diffraction （SAED）. And the magnetic properties of the 3D Ni nanostructures were measured as well. Results indicated that solvothermal process could be successfully used to prepare 3D dandelion-like nanostructures of Ni at a relatively mild temperature of 100℃. And the conclusions were made as follows： as-prepared Ni samples had obvious shape anisotropy and were composed of fine nanocrystallites, while they had significantly enhanced ferromagnetic properties than bulk Ni and Ni nanoparticles.     

Three-dimensional pore structure of chromatographic adsorbents from electron tomography

The pore structure of chromatographic adsorbents directly influences macromolecular partitioning and transport in chromatography. Quantitative structural characterization of chromatographic media has generally been performed in terms of the mean pore size or, at best, the pore size distribution (PSD), but more detailed information on, e.g., connectivity has been lacking. We have applied electron tomography, a 3D TEM technique that views a sample from multiple perspectives and allows reconstruction of the volumetric structure, to capture the internal details of microporous chromatographic media with nanometer-scale resolution. Visualization of reconstructions of three adsorbents, Toyopearl SP-650 C, SP-550 C, and CM Sepharose FF, provides thorough and direct information on the geometry and the interconnectivity of the pore network. The structures are qualitatively consistent with in situ AFM images, and quantitative data for the porosities and PSDs from the analysis of tomographic data agree reasonably well with inverse size-exclusion chromatography results. For a more straightforward representation of the networking and size features of the disordered pore space, a 3D thinning algorithm was used to derive pore skeletons and consequently quantitative data on distributions of local path lengths, widths, tortuosities, and connectivities. Such enriched structural information can be instrumental in more discriminate structural evaluation and construction of engineered pore models for the study of solute intraparticle transport.     

Synthesis and growth mechanism of titanate and titania one-dimensional nanostructures self-assembled into hollow micrometer-scale spherical aggregates

Three-dimensional, dendritic micrometer-scale spheres of alkali metal hydrogen titanate 1D nanostructures (i.e., nanowires and nanotubes) have been generated using a modified hydrothermal technique in the presence of hydrogen peroxide and an alkali metal hydroxide solution. Sea-urchin-like assemblies of these 1D nanostructures have been transformed into their hydrogen titanate analogues (lepidocrocite HxTi2-x/4squarex/4O4 (x approximately 0.7, square: vacancy)) by neutralization as well as into their corresponding anatase TiO2 nanostructured counterparts through a moderate high-temperature annealing dehydration process without destroying the 3D hierarchical structural motif. The as-prepared hollow spheres of titanate and titania 1D nanostructures have overall diameters, ranging from 0.8 to 1.2 microm, while the interior of these aggregates are vacuous with a diameter range of 100 to 200 nm. The constituent, component titanate and TiO2 1D nanostructures have a diameter range of 7+/-2 nm and lengths of up to several hundred nanometers. A proposed two-stage growth mechanism of these hollow micrometer-scale spheres was supported by time-dependent scanning electron microscopy, atomic force microscopy, and inductively coupled plasma atomic emission spectrometry data. We have also demonstrated that these assemblies are active photocatalysts for the degradation of synthetic Procion Red dye under UV light illumination.