Size Determination of Au Aerosol Nanoparticles by Off-Line TEM/STEM Observations

Determination of particle size distributions of Au aerosol nanoparticles has been performed by a TEM/STEM investigation. The particles are generated by an evaporation/condensation method and are size-selected by differential mobility analyzers (DMA) based on their electrical mobility. Off-line TEM measurements resulted in equivalent projected area diameters assuming that the particles are spherical in shape. In this paper critical factors such as magnification calibration, sampling, image analysis, beam exposure and, particle shape are treated. The study shows that the measures of central tendency; mean, median and mode, are equal as expected from a narrow size distribution. Moreover, the correlation between TEM/STEM and DMA are good, in practice 1:1. Also, STEM has the advantage over TEM due to enhanced contrast and is proposed as an alternative route for determination of particle size distributions of nanoparticles with lower contrast.     

Preparation of metallized GaN/sapphire cross sections for TEM analysis using wedge polishing

The tripod polisher has been used successfully in the past, in the preparation of difficult Si-based TEM cross-section specimens. Good TEM specimens, with large electron transparent areas, can be prepared in a relatively short time. In addition, wedge polishing considerably reduces the ion milling time because of the thinness of the final specimen. For metallized GaN on sapphire substrates, there are problems not inherent to Si-based materials: (1) sapphire is a difficult material to thin due to its high hardness and its mechanical instability when thinned below 20 m; (2) delamination of metal layers from the GaN can occur during polishing and/or ion milling; (3) markedly different ion milling rates for the metals and semiconductors. In this paper, wedge polishing has been modified to make it suitable for preparation of metallized GaN/sapphire samples or other metallized semiconductors and ceramics for TEM analysis. Using this method, TEM cross section specimens can be prepared with reasonably large thin areas.     

Numerical simulation aided relative optical density analysis of TEM images for soot morphology determination

The relative optical density (ROD) method provides a means to measure three-dimensional information about soot aggregates from two-dimensional transmission electron microscopy (TEM) micrographs of soot. The method is dependent on accurate calibration of the relationship between the measured soot ROD in TEM images and the actual soot thickness perpendicular to the imaging plane. A novel calibration method based on the comparison between probability distributions of measured soot ROD in TEM images and that of virtual soot thickness of numerically simulated soot is introduced. Soot aggregates of various prescribed fractal structure parameters were numerically generated using a tunable cluster-cluster aggregation model. The probability histograms of the local soot thickness for the simulated soot aggregates and ROD of the TEM images of flame generated soot aggregates were found to be quite similar and were used as a basis to establish a quantitative relationship between ROD and the local soot thickness. The calibration constant obtained from the analysis of the simulated soot was found to be insensitive to the fractal structure parameters over a wide range. The calibrated ROD method is successfully applied to the morphology analysis of soot aggregates generated in an atmospheric laminar co-flow ethylene-air diffusion flame based on thermophoretic sampling (TS) and TEM analysis techniques. With the ROD method, an overlap coefficient is introduced to identify and eliminate non-soot-aggregate structures and the selection of a cut-off overlap coefficient was found to have little influence on the final results over a relatively wide range. ROD is independent of empirical constants and human judgments and has been found to be an accurate and reliable TEM image analysis method for studying the morphology of soot aggregates.     

Substrate preparation techniques for direct investigation by TEM of single wall carbon nanotubes grown by chemical vapor deposition

We have investigated and evaluated different TEM sample preparation techniques for studying carbon single-walled nanotube (C-SWNT) nucleation and growth, issued from CVD processes when the catalyst is supported on a substrate. This kind of study requires means to observe individual and isolated tubes. It implies using synthesis conditions able to produce only a low density of tubes and to thin the substrate to electron transparency, to observe the nanotubes and the catalytic particles from which they have grown in their native state. We have tested two approaches, depending if the substrate is thinned after or before the synthesis. The low tube density requirement led us to exclude all the techniques where the substrate is thinned to electron transparency after the synthesis. We have shown, that, with this last approach, all TEM preparation techniques dramatically suffer from a lack of control of thin areas with respect to the location of the tubes, which is unknown. However we have demonstrated that the suitable approach is to perform synthesis directly on transparent substrates presenting several holes. We have tested the capabilities and the potentialities of these supports for studying the size distribution and composition of the catalytic particles, the nucleation mode, the diameter and helicity of the tubes. These results are very promising and represent an important step for performing specific nanoscale TEM analyses necessary for the study of the growth mechanism of nanotubes on substrates.     

A guide on FIB preparation of samples containing stress corrosion crack tips for TEM and atom-probe analysis

The preparation of samples containing stress corrosion crack tips for 3D atom-probe tomography and transmission electron microscopy is of ultimate importance for understanding the mechanisms controlling crack propagation. In this paper, it will be shown that a focused ion beam machine equipped with an in situ micromanipulator is an ideal tool to systematically prepare such demanding samples. The methodology is described and discussed in detail, and several results are presented to demonstrate the potential of the technique.     

Dry Ashing Preparation of (Quasi)solid Samples for the Determination of Inorganic Elements by Atomic/Mass Spectrometry

Abstract:

This work presents an overview of the development of dry ashing preparation techniques for solid and quasisolid sample analysis by atomic and inorganic mass spectrometry, including flame/graphite furnace atomic absorption spectrometry, chemical vapor generation atomic absorption/fluorescence spectrometry, and inductively coupled plasma–optical emission/mass spectrometry. This article also summarizes all of the dry ashing methods reported in the past 20 years. The dry ashing methods applied to sample preparation are classified as electrothermal ashing, microwave ashing, oxygen combustion, and other special ashing methods including laser, ultraviolet (UV)/ozone, and plasma. Moreover, the development of relevant devices is discussed in context.     

Structural characterization of the sol–gel oxide powders from the ZnO–TiO2–SiO2 system

This work is a study that deals with the synthesis by the sol–gel method and the structural characterization of the oxide powders belonging to the ternary system ZnO–TiO₂–SiO₂ (ZTS). The sol–gel synthesis starts from inorganic precursors, which have been processed under the variation of different technological parameters. We have investigated the dependence of the gelling time on pH and on the temperature of synthesis as well as on water and ammonia amounts. In the case of ZTS samples, the shortest gelling duration appears for low pH values when ZnO content is increased and at small ammonia concentrations when the ZnO content is decreased, respectively. On the contrary, ZTS samples containing high amounts of TiO₂ provide evidence of a short gelling time for high pH and large ammonia amounts. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy provided structural information on these ternary oxide powders. These analyses revealed that relative high amounts of ZnO yields in a change from octahedral [ ZnO₆] units to tetrahedral [ ZnO₄] units in the powder structure. Optical phonons specific for SiO₂ and TiO₂ in both octahedral and tetrahedral groups are shown. High thermal and chemical stability was put in evidence by differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) in the 20–1000 C temperature range.     

A Modified Technique for the Preparation of SO2 from Sulphates and Sulphides for Sulphur Isotope Analyses

Abstract

A modified technique for the conversion of sulphates and sulphides to SO₂ with the mixture of V₂O₅—SiO₂ for sulphur isotopic analyses is described. This technique is more suitable for routine analysis of large number of samples. Modification of the reaction vessel and using manifold inlet system allows to analyse up to 24 samples every day. The modified technique assures the complete yield of SO₂, consistent oxygen isotope composition of the SO₂ gas and reproducibility of δ³⁴S measurements being within 0.10‰. It is observed, however, oxygen in SO₂ produced from sulphides differs in δ¹⁸O with respect to that produced from sulphates.     

Preparation and structure analysis of nano-iron/mesocarbon microbead composites made from a coal tar pitch with addition of ferrocene

Nano-iron/mesocarbon microbead composites have been synthesized from a coal tar pitch by heating at 415 °C with ferrocene under pressure. The resulting composites were characterized using the combined techniques including SEM, TEM, XRD and EDS. The effect of ferrocene addition on the growth and structure of mesocarbon microbeads was discussed. It was found that nano-iron particles were of sizes 10-40 nm and mainly existed in the form Fe-O and Fe_1−xS. The iron particles, which had dispersed homogeneously in pristine and carbonized spheres, accelerated the nucleation and growth of spheres and consequently enhanced the structural ordering of spheres. The addition of ferrocene introduced a tendency to order in the microtexture of spheres.     

Theoretical analysis of a simple yet efficient portable magnetic separator design for separation of magnetic nano/micro-carriers from human blood flow

A technology that could physically remove substances from the blood such as biological, chemical, or radiological toxins could dramatically improve treatment of disease. One method in development proposes to use magnetic-polymer spheres to selectively bind toxins and remove them by magnetic filtration. Although magnetic filtration is a developed technology, the clinical boundary conditions described here require a new filter design. We investigated the removal of toxin-bound magnetic carriers from the blood stream using 2-D FEMLAB simulations. The magnetic separator consisted of a permanent magnet with parallel ferromagnetic prisms on the faces and in contact with a straight tube carrying the magnetic-polymer spheres in suspension. We varied the following parameters: blood flow velocity, the size, and number of ferromagnetic prisms, and the ferromagnetic material in both prisms and magnets. The capture efficiency reached maximum values when the depth of the prisms equaled the diameter of the tubing and the saturation magnetization of the prism material equaled twice that of the magnet. With this design a piece of 2 mm (diameter) tube carrying the fluid resulted in 95% capture of 2.0 μm magnetic-polymer spheres at 10 cm/s flow velocity.     

Magnetic and in vitro heating properties of implants formed in situ from injectable formulations and containing superparamagnetic iron oxide nanoparticles (SPIONs) embedded in silica microparticles for magnetically induced local hyperthermia

The biological and therapeutic responses to hyperthermia, when it is envisaged as an anti-tumor treatment modality, are complex and variable. Heat delivery plays a critical role and is counteracted by more or less efficient body cooling, which is largely mediated by blood flow. In the case of magnetically mediated modality, the delivery of the magnetic particles, most often superparamagnetic iron oxide nanoparticles (SPIONs), is also critically involved. We focus here on the magnetic characterization of two injectable formulations able to gel in situ and entrap silica microparticles embedding SPIONs. These formulations have previously shown suitable syringeability and intratumoral distribution in vivo. The first formulation is based on alginate, and the second on a poly(ethylene-co-vinyl alcohol) (EVAL). Here we investigated the magnetic properties and heating capacities in an alternating magnetic field (141 kHz, 12 mT) for implants with increasing concentrations of magnetic microparticles. We found that the magnetic properties of the magnetic microparticles were preserved using the formulation and in the wet implant at 37 °C, as in vivo. Using two orthogonal methods, a common SLP (20 W g⁻¹) was found after weighting by magnetic microparticle fraction, suggesting that both formulations are able to properly carry the magnetic microparticles in situ while preserving their magnetic properties and heating capacities.     

大气SO2柱总量遥感反演算法比较分析及验证

卫星遥感技术已成为城市污染气体SO₂监测和全球火山活动监测及预警的重要手段. 目前新的PCA (principal component analysis)算法有效减小了反演数据噪声, 并替代之前业务算法BRD (band residual difference)用于边界层SO₂柱总量产品的反演. 然而, 目前对PCA算法反演产品精度的评价和验证研究较少, 缺少与BRD算法产品进行长时间序列的比较以评估算法适用性, 尤其在中国大气污染重点城市区域. 本文利用地基多轴差分吸收光谱仪(MAX-DOAS)观测及多尺度空气质量模式系统(RAMS-CMAQ)大气化学模式模拟等数据, 评估PCA和BRD 反演算法的精度及误差. 另外, 选取洁净海洋地区、中国大气污染重点城市区域和高浓度火山喷发三种情况, 比较分析PCA 与BRD SO₂ 总量的时空格局变化差异及对不同SO₂总量下的适用性, 并对两种算法反演不确定性进行分析讨论. 结果表明, 在中国京津冀、珠江三角洲和长江三角洲区域, PCA SO₂总量反演值低于BRD, BRD反演结果更接近于地基的MAX-DOAS观测值, 冬季BRD和PCA SO₂总量值低于RAMS-CMAQ 模拟结果, 夏季7月和8月BRD SO₂总量值高于RAMS-CMAQ 模拟结果. 在SO₂总量接近于0 值的洁净海洋地区, PCA 算法产品噪声水平低于BRD算法, 但PCA 反演结果整体偏差大于BRD算法. 在高浓度火山喷发情况下, 当SO₂总量大于25 DU时BRD SO₂总量反演值低于PCA, 且随着SO₂ 总量增大, 两种算法反演值差异亦增大. 该研究对于OMI (Ozone Monitering Instrument) SO₂产品的应用具有重要的参考价值, 通过分析不同反演算法的差异及对其不确定性追因, 对于算法改进研究也具有重要的科学意义.