物理化学学报 >> 2019, Vol. 35 >> Issue (5): 539-545.doi: 10.3866/PKU.WHXB201806012

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原位透射电子显微镜观察电荷驱动的氧化物纳米颗粒水中自组装

赵喆1,卢岳1,张振华2,隋曼龄1,*()   

  1. 1 北京工业大学，固体微结构与性能研究所，北京 100124
    2 杭州电子科技大学，浙江(杭电)创新材料研究院，杭州 310018
  • 收稿日期:2018-05-09 发布日期:2018-10-19
  • 通讯作者: 隋曼龄 E-mail:mlsui@bjut.edu.cn
  • 基金资助:
    国家重点研发计划(2016YFB0700700);国家自然科学基金(51621003);北京市重点项目(KZ201310005002)

In situ Liquid Environmental TEM Observation of Self-Assembly of Oxide Nanoparticles Driven by Electric Charge

Zhe ZHAO1,Yue LU1,Zhenhua ZHANG2,Manling SUI1,*()   

  1. 1 Beijing University of Technology, Institute of Microstructure and Property of Advanced Materials, Beijing 100124, P. R. China
    2 Hangzhou Dianzi University, Innovative Center for Advanced Materials, Hangzhou 310018, P. R. China
  • Received:2018-05-09 Published:2018-10-19
  • Contact: Manling SUI E-mail:mlsui@bjut.edu.cn
  • Supported by:
    the National Key Research and Development Program of China(2016YFB0700700);the National Natural Science Foundation of China(51621003);the Scientific Research Key Program of Beijing Municipal Commission of Education, China(KZ201310005002)

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摘要：

以四氧化三钴Co3O4纳米棒为研究对象，我们利用液体环境透射电子显微镜，原位观察了四氧化三钴纳米棒在水中的自组装过程。研究发现在电子束辐照的水环境下，四氧化三钴纳米棒的晶面存在互补式自组装现象。随着纳米棒之间的距离越来越近，纳米棒之间的相对运动速率逐渐增加，纳米棒之间的相互作用力逐渐增加。通过进一步分析纳米棒的形貌发现，纳米棒的暴露晶面大多数为{100}、{110}以及{111}晶面，而Co3O4属于极性氧化物，这些晶面往往会带有一定的电荷。在液体环境下，正是由于这些易暴露面都带有不同大小的电荷，在晶面电荷的驱动下，电荷属性相反的四氧化三钴纳米棒会互相吸引，形貌结构上进行互补，实现快速驱动的纳米棒之间自组装。

关键词: 四氧化三钴, 纳米棒, 自组装, 原位, 液体环境透射电镜

Abstract:

The self-assembly of nanoparticles can effectively control morphology and surface exposure during materials processing and has promising potential applications in the synthesis and exploration of different types of materials. As the process often occurs in liquid solvents, it is difficult to observe and study the dynamic process and mechanism of the self-assembly of nanoparticles in situ. With the recent development of environmental transmission electron microscopy (TEM), researchers have been able to observe and study the dynamic processes of various chemical reactions in liquid environments in real time on the nanometer- and atomic scale. In this paper, we used advanced in situ liquid environmental TEM to characterize the self-assembly process of Co3O4 nanorods in water and study the mechanism of self-assembly. A self-assembly phenomenon of the Co3O4 nanorods in water was discovered under the influence of electron beam irradiation that caused a change in the dielectric constant and increased the electrical conductivity in the irradiated water. The movement of the nanorods was initiated and energized in the irradiated water. As the distance between the nanorods decreased, the drift velocity of the nanorods and the interaction force between them increased. By analyzing the nanorods' movement (including the distance and the rotation angle) as a function of time, the variation of the mean square displacement with respect to time was obtained. Based on the Stokes-Einstein equation, the driving force was estimated, and we found that the driving force increases with the decreasing distance and that the maximum value of the driving force is approximately 12 pN. By characterizing the morphology of the Co3O4 nanorods, we found that the exposed crystal facets of the nanorods are mostly in the {100}, {110}, and {111} planes. As Co3O4 is a polar metal oxide, these crystalline planes tend to carry certain electric charge according to the terminative Co or O atoms. In a conductive aqueous environment, it is because of these easily exposable surfaces with different surface charges that the Co3O4 nanorods will attract each other under the driving force of opposite electric charges. Furthermore, self-assembly of nanorods with a complementary morphology can be driven quickly. The polarity of the residual surface charge plays a decisive role in the effective assembly of nanorods. It is already known that surface charge compensation takes place on polar crystal surfaces; however, this work provides a deeper understanding of the incomplete nature of this surface charge compensation. The results presented here may provide important experimental data and theoretical reference for artificially regulating the metal oxide self-assembly process.

Key words: Cobalt oxide, Nanorod, Self-assembling, In situ, Liquid environmental TEM