A novel method for focus assessment in atomic resolution STEM HAADF experiments

Analysis of the Fourier components of through-focal images in scanning transmission electron microscopy with a high angle annular dark field detector is used to assess illumination defocus values. The method is based on a least squares fitting of the peculiar dependence of Fourier components of the high angle annular dark field image on defocus. The validity of the method has been checked against simulations and experiments obtaining a good level of accuracy on the defocus measurement (δf=2 nm) for simulated specimen thickness up to 40 nm. The difference between simulated and experimental Fourier coefficients for large defoci can be used to estimate the specimen thickness at least up to 30 nm but with decreasing precision for larger thickness.     

Quantitative high-resolution HAADF-STEM analysis of inversion boundaries in Sb(2)O(3)-doped zinc oxide

[Formula: see text] -doped ZnO crystals including inversion boundaries were investigated by high-resolution high-angle annular-dark field (HAADF) scanning transmission electron microscopy (STEM). The images were analysed with the aid of the image simulation based on Bethe method and also the retrieval processing using deconvolution. Utility of these two approaches for the HAADF-STEM analysis is discussed.     

Comparison of intensity distributions in tomograms from BF TEM,ADF STEM,HAADF STEM,and calculated tilt series

The three-dimensional (3D) morphology of a nanometer-sized object can be obtained using electron tomography. Variations in composition or density of the object cause variations in the reconstructed intensity. When imaging homogeneous objects, variations in reconstructed intensity are caused by the imaging technique, imaging conditions, and reconstruction. In this paper, we describe data acquisition, image processing, and 3D reconstruction to obtain and compare tomograms of magnetite crystals from bright field (BF) transmission electron microscopy (TEM), annular dark-field (ADF) scanning transmission electron microscopy (STEM), and high-angle annular dark field (HAADF) STEM tilt series. We use histograms, which plot the number of volume elements (voxels) at a given intensity vs. the intensity, to measure and quantitatively compare intensity distributions among different tomograms. In combination with numerical simulations, we determine the influence of maximum tilt angle, tilt increment, contrast changes with tilt (diffraction contrast), and the signal-to-noise ratio (SNR) as well as the choice of the reconstruction approach (weighted backprojection (WB) and sequential iterative reconstruction technique (SIRT)) on the histogram. We conclude that because ADF and HAADF STEM techniques are less affected by diffraction, and because they have a higher SNR than BF TEM, they are better suited for tomography of nanometer-sized crystals.     

Quantitative characterisation of chemical inhomogeneities in Al-Ag using high-resolution Z-contrast STEM

The incoherent imaging model is applied to interpret high-resolution Z-contrast micrographs. A simple method for a column-by-column resolved characterisation of Ag-rich precipitates in Al-Ag is developed. No information on the detailed imaging process is required. Evaluating the high-angle scattering intensities of Al and Ag by image analysis, the number of Ag atoms contained in individual atomic columns can be determined accurately and moreover, the thickness of the thin foil can be calculated. Multislice simulations confirm the broad validity of the incoherent imaging model for Z-contrast STEM and are used to check the method presented. Finally, the image analysis is applied to experimental Z-contrast images of Guinier-Preston zones in Al-3 at% Ag. The Ag content of the individual atomic columns can be determined with an accuracy better than +/-10%.     

傅里叶变换红外光谱学方法用于气体定量分析

本文将傅里叶变换红外光谱学方法运用到CO和CO2气体的定量分析中，通过红外光谱仪系统测量得到待测气体的红外透过率光谱，采用非线性最小二乘拟合算法基于红外标准数据库HITRAN中的CO和CO2气体光谱数据分别对测量得到的光谱进行拟合，得出待测气体的浓度。对于密闭样品池CO透过率光谱测量分析结果的相对误差小于5％；对于近距离大气开放光路CO2透过率光谱测量分析的相对误差小于1％，实验结果表明基于FTIR方法进行气体浓度信息的定量分析是可行的。     

Quantitative energy dispersive x-ray micro-analysis of thin metal specimens using the STEM

This paper gives an outline of the present state of the quantitative energy dispersive x-ray micro-analysis according to the Cliff-Lorimer method in combination with the STEM. Spectrometer efficiency, line intensity fraction, fluorescence yield, ionization cross section and the critical specimen thickness are discussed in particular detail. The main emphasis in this context is placed on the transferability of data given in the literature to other equipment, and on the accuracy of equations for the calculation of the above mentioned parameters.     

Quantitative analysis of image contrast in phase contrast STEM for low dose imaging

This work quantitatively evaluates the contrast in phase contrast images of thin vermiculite crystals recorded by TEM and aberration-corrected bright-field STEM. Specimen movement induced by electron irradiation remains a major problem limiting the phase contrast in TEM images of radiation-sensitive specimens. While spot scanning improves the contrast, it does not eliminate the problem. One possibility is to utilise aberration-corrected scanning transmission electron microscopy (STEM) with an Ångstrom-sized probe to illuminate the sample, and thus further reduce irradiation-induced specimen movement. Vermiculite is relatively radiation insensitive in TEM to electron fluences below 100,000 e⁻/Ų and this is likely to be similar for STEM although different damage mechanisms could occur. We compare the performance of a TEM with a thermally assisted field emission electron gun (FEG) and charge coupled device (CCD) image capture to the performance of STEMs with spherical aberration correction, cold field emission electron sources and photomultiplier tube image capture at a range of electron fluences and similar illumination areas. We show that the absolute contrast of the phase contrast images obtained by aberration-corrected STEM is better than that obtained by TEM. Although the STEM contrast is higher, the efficiency of collection of electrons in bright field STEM is still much less than that in bright field TEM (where for thin samples virtually all the electrons contribute to the image), and the SNR of equivalent STEM images is three times lower. This is better than expected, probably due to the absence of a frequency dependent modulation transfer function in the STEM detection system. With optimisation of the STEM bright field collection angles, the efficiency may approach that of bright field TEM, and if reductions in beam-induced specimen movement are found, STEM could surpass the overall performance of TEM.     

A direct-integration-based structural reliability analysis method using non-probabilistic convex model

In practical structural reliability analysis, there is not only random uncertainty but also fuzzy uncertainty. Aiming at the fuzzy reliability of structure, a novel fuzzy reliability method is proposed based on direct integration method and ellipsoidal convex model. Firstly, the decomposition of fuzzy mathematics principle is used to convert fuzzy reliability model into non-probabilistic reliability model, in which fuzzy variables are converted into interval variables. The upper and lower bounds of interval variables are determined by the possibility distribution function on the membership value. Secondly, multidimensional ellipsoid convex models are constructed to quantify the uncertainty because of the complexity of non-probabilistic reliability. Finally, sigmoid function with adjustable parameter is introduced to direct integration method for approximating the step function, and then direct integration method is used to solve the fuzzy reliability. Numerical examples are investigated to demonstrate the effectiveness of the present method, which provides a feasible way for the structural fuzzy reliability analysis.     

STEM study of Li4Ti5O12 anode material modified with Ag nanoparticles

Comprehensive scanning transmission electron microscopy (STEM) analysis of Li₄Ti₅O₁₂ (LTO) powder modified by deposited Ag nanoparticles was performed. Nanocomposite powders with Ag content of 1 wt.%, 4 wt.%, 10 wt.% were fabricated in a chemical process from suspensions of Ag and LTO. Apart from the STEM results, the presence of pure silver on the surface of the ceramic powder was confirmed by XRD and XPS analyses. The silver particles deposited on the LTO particles were characterized using the EDS mapping technique. The quantified results of the EDS mapping showed a relatively homogenous distribution of silver nanoparticles on the powder surface for every metal content. The mean diameter of the nanoparticles deposited on the LTO powder was about 4 nm in all cases. An increase in the Ag content during chemical surface modification did not cause changes in the microstructure. Focusing on an analysis of the metallic nanoparticles on the ceramic powder, electron tomography was used as an investigative technique. A very precise analysis of three‐dimensional nanostructures is desirable for a comprehensive analysis of complex materials. The quantified analysis of the Ag nanoparticles visualized using electron tomography confirmed the results of the size measurements taken from the two‐dimensional EDS maps.     

Elastoplastic analysis of two-dimensional problems with hole by boundary element method using complex variables

A direct formulation of the boundary element method using complex variable functions for two-dimensional elastoplastic analysis has been developed. Based on the initial stress approach and complex potential fundamental solutions, the method simplified the computer program and reduced the input data and the order of the equation system greatly; the function of the computer program has been improved and the singular solution behaviour in the yield region near the boundary is eliminated. Two numerical examples have shown that the method can be used in practical applications of elastoplastic analysis in engineering.     

Prediction of fretting wear using boundary element method

The simulation method of the fretting wear prediction using boundary element method is developed. The contact pressure and the contact width which is the first step to predict fretting wear are obtained from contact analysis of a semi-infinite solid based on the use of influence functions and patch solutions. The geometrical updating is based on nodal wear depths computed using Archard’s equation for sliding wear. The prediction of fretting wear for two cases of contact problems is performed; one is two-dimensional cylinder on flat contact which is for the comparison with a previous model by finite element method; the other is three-dimensional spherical contact. It is observed that for two-dimensional cylindrical contact the boundary element method developed in this study reduced the calculation time by 1/48 compared to FE method. We also showed the use of developed simulation technique is efficient to predict the fretting wear for three-dimensional spherical contact.     

Reverse engineering of compound surfaces using boundary detection method

This paper proposes an efficient reverse engineering technique for compound surfaces using a boundary detection method. This approach consists in extracting geometric edge information using a vision system, which can be used in order to drastically reduce geometric errors in the vicinity of compound surface boundaries. Through the image-processing technique and the interpolation process, boundaries are reconstructed by either analytic curves (e. g. circle, ellipse, line) or parametric curves (B-spline curve). In other regions, except boundaries, geometric data are acquired on CMM as points inspected using a touch type probe, and then they are interpolated on several surfaces using a B-spline skinning method. Finally, the boundary edge and the skinned surfaces are combined to reconstruct the final compound surface. Through simulations and experimental works, the effectiveness of the proposed method is confirmed.     

聚合物材料静水分析的边界元混合法

随着对聚合物材料力学特性的数值分析研究的不断深入,已有的分析聚合物材料静水力学特性的两种边界元数值分析方法,即拉普拉斯变换法和直接时间域方法,由于各自的缺点,限制了它们的广泛应用.因此简单介绍了数学家提出的求解雷曼卷积的数值方法,以及笔者提出的一种基于雷曼卷积的新的直接时间域边界元方法;在此基础之上,提出了一种结合了已有的两种边界元方法的优点的混合边界元方法,并应用这种方法求解了一个典型问题,与相应的理论解进行了比较,验证了混合边界元方法的准确性.     

Interpretation of O K-edge EELS in zircon using a structural variation approach

This work describes an approach to interpret the near-edge fine structure of electron energy-loss spectroscopy (EELS) of O K-edge in zircon using a structural variation method. The positions and intensities of several peaks in the O K-edge EELS spectrum are assigned to specific structural parameters. It suggests that the near-edge structures in EELS can be used to measure atomic structure changes.     

与Y2O3共同掺杂下Sb2O5掺杂量对SnO2陶瓷压敏电阻电性能的影响

通过在SnO2陶瓷压敏电阻中共同掺杂Sb2O5和Y2O3(0.05％,物质的量分数),采用扫描电镜和阻抗仪研究了Sb2O5掺杂量(0,0.05％,0.10％,0.15％,物质的量分数)对SnO2压敏电阻微观形貌、电压梯度和晶粒电阻的影响.结果表明:随Sb2O5掺杂量增加,SnO2压敏电阻的晶粒尺寸和界面态密度先增大后减...     

A simple method for the removal of thiols on gold surfaces using an NH4OH-H2O2-H2O solution

The removal behavior of self-assembled monolayers (SAMs) of thiol molecules on a gold substrate by an NH(4)OH-H(2)O(2)-H(2)O solution was studied using attenuated total reflectance infrared spectroscopy (ATR-IR) and atomic force microscopy (AFM). Furthermore, the impact of the concentration of NH(4)OH and H(2)O(2) in the solution and reaction temperature on the SAM removal rate and efficiency was explored. The SAM removal rate and efficiency were significantly influenced by the concentration of NH(4)OH rather than H(2)O(2). The solution containing the 2 : 1 molar ratio of NH(4)OH : H(2)O(2) among three different solutions showed the highest removal rate and efficiency in the removal of 11-mercapto-1-undecanol. The increase in the reaction temperature resulted in the enhancement on the SAM removal rate, but it led to the fast delamination of the gold layer. These results may be useful in the regeneration of sensor surfaces relying on gold/thiol chemistry.     

Extraction and parametrization of grain boundary networks in glacier ice,using a dedicated method of automatic image analysis

Microstructure analysis of polar ice cores is vital to understand the processes controlling the flow of polar ice on the microscale. This paper presents an automatic image processing framework for extraction and parametrization of grain boundary networks from images of the NEEM deep ice core. As cross‐section images are acquired using controlled surface sublimation, grain boundaries and air inclusions appear dark, whereas the inside of grains appears grey. The initial segmentation step of the software is to separate possible boundaries of grains and air inclusions from background. A Machine learning approach is utilized to gain automatic, reliable classification, which is required for processing large data sets along deep ice cores. The second step is to compose the perimeter of section profiles of grains by planar sections of the grain surface between triple points. Ultimately, grain areas, grain boundaries and triple junctions of the later are diversely parametrized. High resolution is achieved, so that small grain sizes and local curvatures of grain boundaries can systematically be investigated.     

基于JC法的新型载车台主梁结构可靠度分析

以结构可靠度理论为基础,运用应力一强度干涉模型,结合旋转式立体车库载车台结构的受力特点,建立该结构关键截面承载能力极限状态方程。利用一次二阶矩法并考虑随机参数服从各种分布时梁的强度可靠性设计,建立载车台主梁的可靠度指标与验算点（JC法）的迭代模型,通过数值分析得出结构的可靠度。所建立的新型载车台主梁结构可靠性模型对于立体车库结构的可靠性设计及提升立体车库开发水平,具有一定的指导意义。     

PVD法纳米三氧化二锑/尼龙6性能的研究

采用普通三氧化二锑和高频等离子体生产的纳米三氧化二锑阻燃尼龙6,并对阻燃尼龙6进行了极限氧指数、UL94L阻燃性、热降解性能、力学性能的检测以及纳米粉体分散性的表征分析。结果表明:当添加量为6%时,纳米三氧化二锑可使材料的极限氧指数达30%,热分解温度提高约20℃;以硅烷偶联剂KH-550改性的纳米Sb2O3替代未改性的纳米Sb2O3后,材料的拉伸强度、弯曲强度较大的提高,缺口冲击强度亦有所改善;由高倍透射电镜照片可见,KH-550改性的纳米三氧化二锑在尼龙6中的弥散度比未改性的高。