外场环境下纳米晶表面行为的原位电子显微学研究

发布时间：2018-01-27 06:26

本文关键词： 透射电子显微镜原位透射电镜环境透射电镜表面结构表面动态行为　出处：《浙江大学》2017年博士论文　论文类型：学位论文

【摘要】：研究材料表面原子结构及电子结构对于理解其催化、电学、光学、超导等性能具有极其重要的意义;随尺寸减小,材料表面原子比例大幅增加,表面对其性能具有更加决定性的影响。过去几十年里,以扫描隧道显微镜(STM)为代表的传统表面研究手段在确定微米级晶体的表面原子结构方面取得了巨大成功,但也在研究纳米材料的表面结构、表面应力应变、表面动态行为、表面成分及价态分析等方面遇到了巨大困难。本论文利用浙大电镜中心国际先进的环境透射电子显微镜(ETEM)、球差校正透射电镜、原位样品杆等设备,发展出一套利用原位透射电镜在外场环境中研究纳米材料表面行为的方法。以被最广泛研究的TiO2等体系为突破口,实现了对纳米晶表面原子结构的确定、少数晶面及棱角处的原子结构研究、外场环境原子尺度观察表面动态行为、结构演变及表面催化反应。透射电镜在这些传统表面研究手段难以适用的方面所取得的成功展示了其在表面科学领域中的巨大应用潜力,具体成果如下:(1)通过原位透射电镜,我们首次从侧视视角确定了 TiO2(1×4)-(001)重构表面原子排布,给出了 ADM表面重构模型最直接的实验证据。结束了关于这一重构表面原子结构长达十多年的争议。(2)首次在实验中揭示了 TiO2(102)、(103)、(301)等少数晶面的原子结构及不同晶面之间棱角处原子结构。(3)首次在氧气环境下原子尺度观察了 TiO2(001)表面(1×4)重构的形成过程,并观察到“1×3”、“1×5”、“1×4”等表面结构之间的动态演变;结合理论计算,我们揭示了应力驱动的(1×4)表面重构机理。(4)利用球差校正扫描透射电镜(STEM),我们原子尺度原位研究了锐钛矿TiO2(101)、(100)、(001)、(102)等不同表面的稳定性;发现TiO2不同晶面在高温下能够通过表面重构、结构演变等行为降低体系能量;首次从表面结构的视角阐述了 TiO2的稳定性问题,解释了锐钛矿TiO2纳米晶相变温度高于理论值的原因。(5)以石墨烯包裹的Pt纳米颗粒作为反应平台,首次实现了原子尺度在同一实验中实时对比Pt不同表面的催化活性,证明了 Pt(100)及(110)表面相比Pt(111)表面具有更好的催化石墨烯氧化性能。(6)氧气条件下原位原子尺度观察了 MoO2纳米棒的动态结构演变;揭示了其顶端表面周期性振荡荡分解和侧壁表面的逐层生长现象;结合DFT理论计算发现,电子束辐照引起的顶端晶面氧流失导致了优先生长晶面的改变及形貌的重构。
[Abstract]:It is very important to study the surface atomic structure and electronic structure of materials for understanding their catalytic, electrical, optical and superconducting properties. As the size decreases, the atomic ratio on the surface of the material increases significantly, and the surface has a more decisive effect on its properties. Scanning tunneling microscope (STM) as the representative of the traditional surface research methods in the determination of the surface atomic structure of micron crystals has achieved great success, but also in the study of the surface structure of nanomaterials. Great difficulties have been encountered in the analysis of surface stress and strain, surface dynamic behavior, surface composition and valence state. In this paper, ETEM, an international advanced environmental transmission electron microscope (ETEM), is used in the electron microscope center of Zhejiang University. Spherical aberration correction transmission electron microscope, in situ sample rod and other equipment. A method for studying the surface behavior of nanocrystalline materials using in situ transmission electron microscopy (TEM) was developed. The atomic structure of nanocrystalline surface was determined by using the most widely studied systems such as TiO2 as the breakthrough point. The atomic structure of a few crystal planes and corners is studied, and the surface dynamic behavior is observed at the atomic scale in the external field. The structural evolution and surface catalytic reaction. The success of transmission electron microscopy in the application of these traditional surface research methods shows its great application potential in the field of surface science. The results are as follows: (1) by in situ transmission electron microscopy, we have for the first time determined the surface atomic arrangement of TiO2(1 脳 4 ~ 4 ~ (-0 ~ (001)) from a side-view angle. The most direct experimental evidence of the ADM surface reconstruction model is given. The conclusion of the controversy over the atomic structure of the reconstructed surface for more than a decade is given. ). The atomic structure of a few crystal planes and the atomic structure at the angles between different crystal faces are observed for the first time on the atomic scale of TiO2O001) in oxygen environment. The forming process of reconstruction. The dynamic evolution of surface structures such as "1 脳 3", "1 脳 5" and "1 脳 4" was observed. Combined with theoretical calculations, we reveal the stress-driven surface reconstruction mechanism of 1 脳 4) using spherical aberration corrected scanning transmission electron microscope (STEMM). We have studied in situ the stability of different surfaces such as anatase TiO2O101O101O1001O102at atomic scale. It is found that the energy of TiO2 can be reduced by surface reconstruction and structural evolution at high temperature. The stability of TiO2 is discussed for the first time from the point of view of surface structure. The reason why the phase transition temperature of anatase TiO2 nanocrystalline is higher than the theoretical value is explained. It is the first time that the catalytic activity of Pt on different surfaces can be compared in the same experiment at atomic scale for the first time. It has been proved that the catalytic graphene oxidation performance on the surface of Ptn100) and Pt110) is better than that of PtC111). The dynamic structure evolution of MoO2 nanorods was observed in situ at atomic scale under oxygen condition. The periodic oscillatory oscillation decomposition of the top surface and the growth of the lateral surface layer by layer are revealed. Based on the DFT theory, it is found that oxygen loss in the apical plane induced by electron beam irradiation leads to the change of the preferential growth plane and the reconstruction of the morphology.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.1;TN16

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