透射电镜原位研究Ni／C催化剂的表面形态

催化剂在使用过程中,表面形态的变化直接关系到催化剂的使用寿命,因此研究烧结、晶粒长大等问题一直是催化剂表面化学的主要课题。采用透射电镜(TEM)原位加热技术,在加热过程中,直接观察催化剂表面形态的变化,对研究烧结机理,可提供有价值的信息。本文在真空气氛下,采用这一技术,观察了在673～973K范围Ni/C催化剂表面形态的变化,发现在较低温度下(673～773K),烧结过程包含颗粒迁移和原子迁移;在高温(973K)主要发生原子迁移。     

离子注入过程中银纳晶的原位透射电镜研究

离子注入法已被广泛地用来改善玻璃的物理特性,如折射率、光吸收性能等[1]。金属离子注入玻璃后形成纳米晶体,它们的大小和密度在衬底的不同深度分布不同,这些分布对注入条件非常敏感,而且可以通过热处理加以改善。纳米晶体决定吸收带的光学特性,比如光学吸收带随纳米晶体大小的增加而产生红移现象。传统的理论将吸收波峰与纳晶的大小联系起来,通过吸收谱的特征来推断纳晶的大小,但这一理论只能给出一个平均直径。为了获得纳米晶体的大小、形状、密度和注入条件的关系,作者用透射电镜原位观察Ag注入非晶SiO2过程中银纳晶的形成和演化,通过…     

透射电镜原位拉伸研究金属材料形变机制

透射电镜原位拉伸方法是研究材料形变机制的一种直观而有效的手段。将拉伸实验与高分辨透射电镜相结合,通过在原子尺度上直接观察,实时地记录应力应变作用下晶体材料微观结构的演变及位错的产生和运动等,直观地揭示材料在弹性及塑性阶段的形变机理。本文将重点回顾近年来作者用透射电镜原位拉伸方法在研究金属材料形变机制方面的工作进展。主要包括纳米金属材料的晶界发射和吸收不全位错、晶粒旋转长大等变形机制,及金属材料在变形过程中的几种可逆形变机制。     

Si衬底气相生长金刚石薄膜的成核机制

本文根据热力学成核理论，研究了Ｓｉ衬底表面气相生长金刚石薄膜的成核机理，提出了与实验相符的理论分析。     

双金属合金纳米颗粒的原位透射电镜研究

实时监测双金属合金纳米颗粒在合成过程及工作条件下,形貌、组成、结构等的动态演变,有助于理解其合成及催化机理,从而实现高性能双金属合金的合理设计、调控与合成。虽然相较于原位谱学技术,原位透射电镜的能量分辨率和精确度不高,但其可以在热、电等外场作用下实时观测和分析气相或液相环境中样品的微观结构、组成及形貌的动态变化,且空间分辨率可以达到纳米甚至原子量级,是重要的结构分析技术。本文简要归纳原位透射电镜在双金属合金纳米颗粒方面的应用研究,并探讨未来研究的挑战与机遇。     

高分辨率原位环境透射电镜的发展与应用

材料受周围环境的影响而产生的结构或成分变化一直都是材料科学和工业研发领域最关注的方向之一。随着材料研究的纳米化,外场导致的材料在亚纳米或原子尺度上的结构变化越来越成为认知材料宏观和纳米材料特性之根本。在诸如纳米催化剂的催化机制,材料的氧化-还原机制,纳米材料的生长或受力形变,电、磁场对材料纳米尺度结构的影响及微量气体探测等很多研究中有许多问题都需要一种特殊的电子显微镜即高分辨率原位环境电镜来帮助寻求答案。本文简要地回顾了环境透射电镜技术的发展思路,对于现代气体环境透射电镜的主流技术作了初步介绍,特别强调了高分辨率环境电镜的重要性以及在环境电镜中实现高分辨率所需要关注的一些技术环节,并力图通过具体实验实例使读者充分了解高分辨率原位环境电镜在材料科学研究中的重要性。     

钨丝上原位加热生长的WO3-x纳米棒的结构与缺陷研究

WO3-x(x：0～1)是一种优良的光、电、气致色变半导体材料。本研究通过在电化学腐蚀的钨丝针尖上原位加热生长了一系列的样品，发现了一种新奇的WO3-x结构，电子衍射和高分辨研究证明其是一种非常有序的晶体丝织构行为。图1是生长WO3-x纳米棒特征的SEM图像，钨针尖上布满了垂直表面二     

生如夏花(透射电镜中原位生长的Ag晶体)

正作品名称:生如夏花作品简介:透射电镜中原位生长的Ag晶体"生如夏花",出自于印度诗人泰戈尔的诗《飞鸟集》里的"花葬",原句是:Let life be beautiful like summer flowers and death like autumn leaves.使生如夏花之绚烂,死如秋叶之静美。该花的7种颜色示意夏季里的花更加绚丽多彩,如辉煌灿烂的生命。"生如"夏花可反映出电镜实验过程中该"花朵"原位生长的过程。     

纳米复合ZnO粉体烧结过程晶粒生长的分析

根据ZnO晶粒生长动力学方程,确定了晶粒生长的动力学指数和激活能,研究了纳米复合ZnO粉体的烧结过程以及烧结过程中的晶粒生长规律。实验结果表明:由纳米复合ZnO粉体制备的陶瓷,其晶粒生长动力学指数n为3,激活能Q为(185±26)kJ/mol。与微米粉体相比,纳米复合ZnO粉体的晶粒生长动力学指数和激活能都比较小,因此液相烧结的温度低,晶粒生长速度加快。     

In situ HREM observation of nucleation and growth of nanotwins beneath the solid-liquid interface in Si

Nucleation and growth of nanotwins in Si grown from Al-Si liquid have been observed directly using an in situ heating experiment in a high-resolution transmission electron microscope. Nanotwins are nucleated at the triple point between a vacuum and the solid-liquid interface. When two parallel twins, the mirror planes of which are separated slightly, encounter each other, very complicated atomic arrangements are formed. The structure of the perturbed region is discussed tentatively in terms of the high-pressure phases in Si.     

In situ high temperature TEM observation of interaction between multi-walled carbon nanotube and in situ deposited gold nano-particles

Interaction between multi-walled carbon nanotubes (MWNTs) and deposited gold nano-particles has been dynamically observed in a 200 kV transmission electron microscope (TEM) using a specimen heating holder. Gold particles with diameters of several tens of microns were mixed with MWNTs to mount on the heating element of a specimen heating holder. The gold particles were instantaneously heated to 1373 K to deposit gold nano-particles on the MWNTs from a very short distance. The MWNTs were then heated to 1073 K to observe interaction between the deposited gold nano-particles and MWNTs. Some gold nano-particles drilled through the wall of the MWNT and entered the capillary space of the MWNTs. To characterize the mechanism of the transition of the gold nano-particles into the capillary space of the MWNT, high resolution TEM observation of the deformed wall of MWNT was also carried out.     

In situ optical monitoring of the movpe growth of ZnSe on GaAs

In situ optical reflection measurement was employed to study surface processes during the MOVPE growth of ZnSe films under an alternate supply of diethylzinc (DEZn) and dimethylselenide (DMSe) using H₂ and/or N₂ as carrier gases. We have found that the time-dependent reflection signal exhibits a unique saw-toothed pattern during the DEZn supply, which is attributed to the adsorption and structural change of the DEZn. In contrast, the influence of DMSe on the time-dependent signal appears to be rather marginal. A growth mechanism is proposed based on these experimental results, through which the important role of ambient hydrogen is discussed.     

In situ control of gan growth by molecular beam epitaxy

Methods to determine GaN surface temperature, surface composition, and growth rates using in situ desorption mass spectroseopy (DMS) and reflection high energy electron diffraction (RHEED) are demonstrated for molecular beam epitaxial growth of GaN using NH₃. Using these methods, the GaN surface temperature, T_s, and GaN growth rates as a function of T_s, Ga flux, and NH₃ flux were obtained. Surface temperatures were determined from DMS and RHEED measurements of the temperature at which Ga condenses on GaN. NH₃-limited and Ga-limited growth regimes are identified and the transition between these regimes is shown to be abrupt. NH₃-limited samples have a weakly reconstructed (2 × 2) RHEED pattern, while Ga-limited samples reveal a transmission pattern. Atomic force microscopy showed that NH₃-limited samples exhibit atomic steps while Ga-limited samples exhibit faceting.     

透射电子显微镜原位磁场双倾样品杆的研制

本文简述了透射电镜磁场双倾样品杆的设计方案,展示了Philips/FEI透射电镜磁场双倾样品杆的研制成果.利用该样品杆可以产生100 Oe的连续磁场,也可以产生140 Oe以上的瞬间磁场.通过“U”型磁组件和样品杯的巧妙设计,尽可能的减小了电子束在横向磁场中的偏移量.     

UWB TEM HORN ANTENNA FOR THE ASPHALT PAVEMENT INVESTIGATION简

A simple Ultra-WideBand （UWB） exponentially-tapered Transverse ElectroMagnetic （TEM） horn antenna is presented for the asphalt detection based on Ground Penetrating Radar （GPR） In order to reduce the reflections from the antenna aperture, some absorbing material is loaded on the outer surface of the conductor. Comparing with the traditional TEM horn antenna, the proposed antenna has a small size and a large impedance bandwidth. Simulated and measured results show that the proposed TEM horn antenna has a low Voltage Standing Wave Ratio （VSWR） below 2 over the whole band from 0.35 GHz to 12 GHz, good radiation characteristics, and small late-time ringing, which can perfectly meet the requirements of the GPR application.     

马氏体钢亚晶结构的TEM研究

现代马氏体钢Ｇ Ｘ12ＣｒＭｏＶＮｂＮ 10 1 1作为耐热抗形变材料广泛用于发电工业。钢的蠕变强度是和其微结构密切相关的[1] 。本文报道用ＴＥＭ定量研究退火和蠕变过程中马氏体钢亚晶结构变化的实验结果。实验所用材料为铸造马氏体钢Ｇ Ｘ12ＣｒＭｏＶＮｂＮ 10 1 1,其化学成份 (ｗｔ .% ,ｂａｌ .Ｆｅ)为0 13Ｃ、0 2 9Ｓｉ、0 82Ｍｎ、9 5 1Ｃｒ、1 0 2Ｍｏ、0 0 5 9Ｎｂ、0 5 2Ｎｉ、0 19Ｖ、1 0 2Ｗ、0 0 14Ｐ、0 0 4 14Ｎ、0 0 14Ａｌ。材料的初始态由热处理确定 ,其过程为 1343Ｋ 12ｈ ,空冷 + 10 0 3Ｋ 12ｈ ,空冷 + 10 …     

SiC纳米线的孪晶机制的透射电子显微学研究

本文对溶胶-凝胶法制得的SiC微孪晶纳米线进行了微结构与孪晶机制的详细研究,利用会聚束电子衍射(CBED)及其动力学模拟技术间接证明了它是一种关于(111)面的60°旋转孪晶.并在此基础上对SiC微孪晶纳米线的生长机理进行了讨论.