亚埃尺度界面原子结构与电子结构研究

项目名称： 亚埃尺度界面原子结构与电子结构研究

项目编号： No.50801040

项目类型： 青年科学基金项目

立项/批准年度： 2009

项目学科： 无线电电子学、电信技术

项目作者： 于荣

作者单位： 清华大学

项目金额： 23万元

中文摘要： 界面（包括固-气界面，即表面）现象广泛存在于块体、薄膜与纳米材料中。相对于晶体内部，界面的原子配位环境由于点阵失配或晶体取向的不同而发生显著的改变，并诱导化学成分偏析，界面原子重构，以及电子状态的变化。材料中的界面不仅呈现出丰富多彩的物理现象，也显著地影响材料的生长与制备过程，以及材料整体的力学与物理性能。本项目在成功建立像差校正电镜平台的基础上，结合先进电子显微学与第一原理计算，对在亚埃尺度定量研究材料中的界面现象做了有意的探索。实现了对氧化物表面弛豫结构在亚埃尺度的直接测量，并达到了皮米量级的测量精度，拓展了电镜表面结构分析的应用范围。揭示了基于离子的电子极化率的极性表面补偿机制。通过对金属间化合物反相畴界面的分析，提出了调控合金催化剂表面结构的"有序畴工程"方法，解出了多层洋葱结构的合金纳米颗粒，为人们调控催化剂表面结构提供了新的思路。通过不全位错及堆垛层错的分析，表明在复杂金属间化合物中，次近邻原子面也对位错滑移有很强的约束，能够显著改变位错的滑移方式。以通讯作者在材料与物理顶级期刊Phys. Rev. Lett.发表论文三篇。

中文关键词： 高分辨电子显微学;表面与界面;原子结构;电子结构;计算

英文摘要： Interface (including surface) phenomena are popular in bulk materials, thin films, and nanomaterials. Due to lattice mismatch or misorientation, the atomic coordination at interfaces are quite different from inner crystal, leading to chemical segregation, atomic reconstruction, and electronic state changes at interfaces. The abundent interfacial phenomena play an important role in controlling the growth process and the overall physical properties of materials. In the current project, based on the platform of spherical aberration corrected transmission electron microscope, the interfacial phenomena in metallic materials, transition metal oxides, and nanomaterials have been investigated at the sub-Angstrom scale. We showed that the surface structure of Co3O4, a typical complex oxide, can be directly imaged and quantitatively analyzed at the sub-angstrom scale. The atomic positions of both light oxygen and heavier cobalt within the surface layers have been measured to an accuracy of several picometers. The surface electronic structure analysis suggests a polarity compensation model based on the electronic polarizability of surface ions. Ordered domains were utilized to construct new nanostructures, i.e., multishell intermetallic onions, which are formed by symmetrical configuration of ordered domains. Through density-functional theory calculations, we have shown that the energy penalties for introducing anti-phase boundaries into the nanoparticles are small in some alloy systems compared to typical surface energies, making it feasible to prepare intermetallic onions by tuning surface energies. The unique surface atomic arrangements would provide opportunities for developing novel materials like efficient catalysts. By combining density-functional theory calculations and aberration-corrected transmission electron microscopy, dislocations in Laves phase was shown to slip in an undulating path. During the slip, the dislocation cores jump up and down between a weakly bound plane and an adjacent strongly bound plane for gliding and atomic shuffling, respectively. This is different from the conventional slip process in simple metals, which is continuous within a single plane, as described in the paradigm of the generalized stacking fault energy. A referee wrote about our work, "I think this paper will have a significant impact on the deformation physics community, spanning everyone from metallurgists, to ceramists and earth scientists."

英文关键词： high-resolution electron microscopy; surfaces and interfaces; atomic structure; electronic structure; calculations