Nanostructuring Germanium Nanowires by In Situ TEM Ion Irradiation

Once nanomaterials have been synthesized, inducing further structural modifications is challenging. However, being able to do so in a controlled manner is crucial. In this context, germanium nanowires are irradiated in situ within a transmission electron microscope (TEM) by a 300 keV xenon ion beam at temperatures ranging from room temperature (RT) to 500 °C. The ion irradiation is performed in situ and the evolution of nanowires during irradiation is monitored. At 300 °C and below, where the temperature is low enough to allow amorphization, the ion beam causes the formation of nanostructures within the nanowires. Formation of nanopores and swelling of nanowires is observed for a very low fluence of 2.2 × 10¹⁴ and up to 4.2 × 10¹⁵ ions cm⁻². At higher fluences, the thickness of the nanowires decreases, the nanowires lose their wire-like cylindrical shape and the nanostructuring caused by the ion beam becomes more complex. The nanostructures are observed to be stable upon crystallization when the nanowires are annealed at 530 °C. Furthermore, in situ imaging allows the growth of nanopores during irradiation to be followed at RT and at 300 °C providing valuable insights into the mechanism responsible for the nanostructuring.     

一款小角X射线散射原位测量专用简易样品加热装置

原位加热实验是同步辐射小角X射线散射领域的新热点。本文针对同步辐射小角X射线散射中需要加热并原位实时检测的实验而设计的一款样品简易原位加热专用装置,该装置主要由温控器、样品池、固定架组成,它具有结构简单、操作容易的特点。本文介绍该装置的基本结构、特点并采用该装置进行原位加热干燥褐煤实验,通过分析实验结果验证装置的可行性。     

Goniometry for Interface Studies in Transmission Electron Microscopy

A method using a double-tilt goniometer stage for determining the orientation of crystalline specimens in transmission electron microscopy (TEM) is described. The procedure involves visual identification of two zone axes, and using the corresponding goniometer settings to plot these poles stereographically. Crystal orientations and misorientations can be established rapidly, and the method is intended for use as a practical complement to more precise but time-consuming techniques. The commutative operation of double-tilt stages and their goniometric capability are also discussed. Using Rodrigues-Frank space, it is shown that the set of attainable operations for such stages is represented by points on an hyperboloidal surface.     

Real-Time Reconstruction of Arbitrary Slices for Quantitative and In Situ 3D Characterization of Nanoparticles

A detailed 3D investigation of nanoparticles at a local scale is of great importance to connect their structure and composition to their properties. Electron tomography has therefore become an important tool for the 3D characterization of nanomaterials. 3D investigations typically comprise multiple steps, including acquisition, reconstruction, and analysis/quantification. Usually, the latter two steps are performed offline, at a dedicated workstation. This sequential workflow prevents on-the-fly control of experimental parameters to improve the quality of the 3D reconstruction, to select a relevant nanoparticle for further characterization, or to steer an in situ tomography experiment. Here, an efficient approach to overcome these limitations is presented, based on the real-time reconstruction of arbitrary 2D reconstructed slices through a 3D object. Implementation of this method may lead to generalized implementation of electron tomography for routine nanoparticle characterization in 3D.     

原位动态电子显微学研究进展

随着电镜内原位技术的不断成熟和发展,透射电子显微镜不再仅仅是材料结构表征的工具,还是实现高精度纳米加工、性能测试等的重要手段。这不但丰富了纳米尺度下开展实验研究的方法,也拓宽了透射电子显微镜的应用范围,为纳米科学与技术的迅速发展提供了新的契机。本文侧重作者所在研究小组的研究工作,以"将纳米实验室建在透射电子显微镜里"的构想为主线,从材料的原位生长、结构加工、性能表征和器件构建等四个方面综述了近年来基于透射电子显微镜的代表性原位实验研究进展。     

In Situ Studies on Reaction Mechanisms in Atomic Layer Deposition

During the past decade, atomic layer deposition (ALD) has become an important thin-film deposition method in microelectronics industry, and it has also gained a lot of interest in many other areas, such as nanotechnology. The success of ALD is built on proper surface reactions. In this paper, in situ reaction mechanism studies on ALD processes are reviewed with the aim of building a general understanding on similarities and differences exhibited by various processes and process groups. Also, levels of understanding reaction mechanisms in ALD are discussed. The main methods used to study ALD chemistry in situ under typical process conditions are quadrupole mass spectrometry (QMS), quartz crystal microbalance (QCM), and infrared (IR) spectrometry. These are presented in detail in the review. Various other optical methods, ellipsometry in particular, have been used to study ALD processes too, but they provide little information about the reaction mechanisms. Competent in situ investigations solve the ALD reaction mechanism as balanced equations for the ALD half-reactions. The majority of ALD processes are exploiting ligand exchange reactions, where the ligands of the metal precursor are eliminated by bonding to the Lewis acids of the nonmetal precursors, most commonly hydrogen. These volatile byproducts are usually released during both precursor pulses, and determining their relative amounts is the important task in reaction mechanism studies of such processes. These processes are mechanistically fairly well understood, though some of these also display side-reactions to the ligand exchange reactions. There are also whole groups of processes that are using chemistry almost entirely different from the ligand exchange reactions. The most important such processes involve combustion chemistry, with oxygen, oxygen plasma, or ozone as a precursor or co-reactant. The mechanisms of these processes are complicated and less understood compared with the mechanisms of the ligand exchange reaction processes.     

非水纳米分散系的冷冻蚀刻电镜原位观测

研究了冷冻蚀刻电镜技术原位观测合成的纳米分散系的制样步骤、制样方法 ,并利用冷冻蚀刻电镜技术原位观测了四种纳米分散系中分散相的粒度、粒度分布和聚集状态 .研究结果表明 :蚀刻时间对电镜照片图像质量有较大影响 ,蚀刻时间应根据分散系中分散相含量、粒度大小来选 ;冷冻蚀刻电镜用于原位观测非水纳米分散系 ,具有准确、直观、清晰、立体的特点 ,并且可同时采集多种信息 .     

Study of Morphology and Mechanical Properties of In Situ PP/PS Alloy

The in situ polypropylene (PP)/polystyrene (PS) alloy was prepared in the presence of dicumyl peroxide (DCP). Purified styrene (St) and pre‐polymerized styrene (PSt), forming a dispersed PS phase in the PP matrix would react with PP matrix to form PP‐g‐PS graft co‐polymers acting as a compatibilizer in these alloys, leading to the formation of in situ PP/PS alloys with in situ compatibilizer during reactive blending in a mixer. The morphology development of the alloy was examined by scanning electron microscopy (SEM) and was described using the characteristic length L and the average characteristic length L_m. The shape of the dispersed PS phase was regular and the distribution of PS particles was uniform. Tensile properties of the alloy were improved with mixing time and fluctuated in a certain composition range.     

Observation of Undamped 3D Brownian Motion of Nanoparticles Using Liquid-Cell Scanning Transmission Electron Microscopy

In theory, liquid-cell (scanning) transmission electron microscopy (LC(S)TEM) is the ideal method to measure 3D diffusion of nanoparticles (NPs) on a single particle level, beyond the capabilities of optical methods. However, particle diffusion experiments have been especially hard to explain in LC(S)TEM as the observed motion thus far has been slower than theoretical predictions by 3–8 orders of magnitude due to electron beam effects. Here, direct experimental evidence of undamped diffusion for two systems is shown; charge-neutral 77 nm gold nanoparticles in glycerol and negatively charged 350 nm titania particles in glycerol carbonate. The high viscosities of the used media and a low electron dose rate allow observation of Brownian motion that is not significantly altered by the electron beam. The resulting diffusion coefficient agrees excellently with a theoretical value assuming free diffusion. It is confirmed that the particles are also moving in the direction parallel to the electron beam by simulating STEM images using Monte Carlo simulations. Simulations and experiments show blurring of the particles when these move out of focus. These results make clear that direct observation of 3D diffusion of NPs is possible, which is of critical importance for the study of interparticle interactions or in situ colloidal self-assembly using LC(S)TEM.     

云纹干涉法在线复制变形光栅技术研究

介绍了一种云纹干涉法现场转移高密度光栅的新工艺，将现场转移光栅与实验室测量有机结合起来，同时得到物体变形的面内U、V位移场。从理论上分析讨论该方法的可行性及误差。通过实验验证该方法与传统云纹干涉法具有相同的灵敏度和量程，使云纹干涉法应用范围更加广泛。     

稀氢氟酸中硅表面氢终端的原位拉曼光谱研究

本文用共焦显微拉曼系统原位观察了Ｓｉ（１００）表面氢终端原子在稀氢氟酸中的变化过程。研究表明：在硅片浸入氢氟酸溶液的初期,表面主要被硅和三个氢原子的结合体（Ｓｉ Ｈ３）以及硅和两个氢原子的结合体（Ｓｉ Ｈ２）所覆盖。随着腐蚀过程的延长,Ｓｉ Ｈ３越来越少,Ｓｉ Ｈ２的信号不断增强,并且,硅和单个氢原子的结合体（Ｓｉ Ｈ）的信号也开始出现。最终,硅表面主要被Ｓｉ Ｈ２所覆盖,有少量Ｓｉ Ｈ３和Ｓｉ Ｈ键。本文还表明,拉曼光谱用来原位观察半导体材料表面终端原子键在溶液中的变化是很有用的工具     

Preparation and Properties of Polystyrene/Bacterial Cellulose Nanocomposites by In Situ Polymerization

Polystyrene/bacterial cellulose (PS/BC) nanocomposites were prepared via in situ polymerization. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), themogravimetry (TG), and mechanical testing were employed to characterize the PS/BC nanocomposites. The polystyrene filled in the network of the BC and a lamellar structure was formed. The FTIR results show that no chemical reaction between PS and BC occurred during the polymerization. These composites showed good mechanical properties.     

离子液体热分解机理的原位变温多核核磁共振研究

利用原位变温核磁共振氢谱（¹H NMR）、核磁共振氟谱（¹⁹F NMR）和核磁共振磷谱（³¹P NMR）等NMR技术研究特定温度下离子液体的热分解机理．在温度低至80℃时,1-丁基-3-甲基咪唑阳离子（C₄mim⁺）和六氟磷酸根阴离子（PF₅-）组成的离子液体[C₄mim][PF₅]呈现1个缓慢但明显的分解过程．无水[C₄mim][PF₅]在温度高于80℃时开始分解,生成少量的五氟化磷（PF₅）和氟化氢（HF）,氟化氢中的氢原子来自于1-丁基-3-甲基咪唑环2位上的氢原子．在丢掉这个氢原子后,阳离子成环形成一个卡宾,并与PF₅形成卡宾/PF₅复合物．定量NMR分析显示在分解反应达到平衡状态时,自由态PF₅和卡宾/PF₅复合物的比例为7∶3．     

光纤热极化过程的实时测试研究

通过热极化可以使中心对称的熔石英光纤中产生二阶非线性效应和线性电光效应。为了解各热极化过程参量对热极化产生的线性电光效应的影响,利用全保偏光纤马赫一曾德尔干涉仪构造了一套光纤热极化的实时线性电光效应测试系统,并利用其进行了光纤热极化全过程的监控测试。在线测试了热极化过程的一些参量,例如极化电压、极化时间、以及极化温度等对热极化光纤中产生的线性电光效应的影响。实时测试研究表明,在光纤中施加尽可能高的极化电场将可能在光纤中产生较高的线性电光效应。对侧边抛磨光纤结构的热极化器件,考虑到器件的抗强电场击穿能力,可选用3．o～4．0kV左右的极化直流电压。当施加3．0kV左右的极化电压时,热极化优化时间约为16min,最佳热极化加热温度约为190℃。     

An In Situ Testing Method for Analyzing the Changes of Active Groups in Coal Oxidation at Low Temperatures

This study details an in situ Fourier transform infrared spectroscopy analytical system that was employed to follow chemical variations in the functional groups on coal surface during the oxidation process at low temperatures. In the reported in situ Fourier transform infrared spectroscopy system, a special chamber was used to contain the coal powders, and a gas inlet tube and a programmable heater were used to simulate different reaction atmospheres and temperatures. The comparisons between in situ and ex situ Fourier transform infrared spectroscopy spectra indicate that the in situ Fourier transform infrared spectroscopy data offer a more accurate reflection of changes in the functional groups. The real-time changes of aliphatic hydrocarbon groups and oxygen-containing groups in a lignite coal sample were analyzed from 30°C to 220°C using in situ Fourier transform infrared spectroscopy. The experimental results indicate that the chemical variations in the functional groups are affected by their relative chemical activities. The results show that the presence of aliphatic groups on the coal surface varies with temperature. Over the range of 30–70°C the presence of these groups decreases, but then their abundance increases over the range of 70–180°C and finally decreases again when the temperature is increased to between 180°C and 220°C. With respect to oxygen-containing functional groups, three various trends were observed as the test temperature was varied. Our conclusion was that these variations are a function of the reaction activities of the various oxygen-containing functional groups.     

Determination of Silver by Chemical Vapor Generation with In Situ Trapping Flame Atomic Absorption Spectrometry

ABSTRACT

The hyphenation of chemical vapor generation with an integrated atom trap system for flame atomic absorption spectrometry (CVG-IAT-FAAS) was evaluated for determination of silver in real samples (coal fly ash, sediment, and nickel alloy). The volatile species of silver were formed by reaction with sodium tetrahydroborate(III) in the presence of nitric acid. A new CVG-IAT-FAAS design (versus a water-cooled single silica tube, double-slotted quartz tube) significantly improved the sensitivity and detection limits compared with conventional flame atomic absorption spectrometry (FAAS) for determination of silver. The concentration limit of detection was 0.7 ng mL^?1 for Ag. The overall efficiency of the vapor generation process was estimated to be ca. 12%. For a 2 min in situ preconcentration time, sensitivity was enhanced 143-fold for Ag using the vapor generation atom trapping technique, compared to conventional FAAS. Sensitivity can be further improved by increasing the collection time. The precision of measurement at 10 ng mL^?1 of Ag was 10% RSD. The accuracy of this method was validated by analyses of NRC GBW 07302 (Stream Sediment), BCS CRM No. 346 (Nickel Alloy), NIST SRM 2710 (Montana Soil), NRCC LUTS-1 (Lobster Hepatopancreas), and NIST SRM 1643e (Trace Element in Water) certified reference materials. The measured Ag contents in these five reference materials were in satisfactory agreement with the certified values (spanning the range of 0.066–35 µg g^?1).