Surface and Interface Free Energies of Epitaxial Nanocrystals

技术综述：提出研究外延金属纳米晶体的表面和界面能，并将其与原子结构联系起来。二氧化钛上的外延金纳米晶将作为模型系统进行研究。外延提供了界面均匀性，也提供了更好的控制纳米晶体的形状。之所以选择TiO2，是因为其作为催化剂载体的可还原氧化物的功能，以及在文献中对其表面的广泛了解。金纳米晶体将采用PI团队开发的沉积和退火技术合成。利用像差校正扫描透射电子显微镜和透射电子显微镜表征金纳米晶体及其界面的结构。结构数据将用于测量金纳米晶体的表面和界面能作为尺寸的函数。在理论方面，将从第一性原理计算不同外延的界面和三线几何形状、局域电子态密度以及Au在TiO2上的能量。实验与理论的结合有望大大提高对纳米晶体表面和界面的结构和性质关系的理解。非技术概要：材料技术的大部分，化学工业的主要组成部分，以及医学诊断和治疗中令人兴奋的新发展都依赖于支撑金属纳米颗粒的特性。金属纳米颗粒的特殊功能来自于其表面和界面及其载体的协同作用。然而，现代研究在很大程度上避免了负载纳米颗粒的复杂性；纳米粒子对于实验表征来说太小了，而对于严格的理论研究来说又太大了。本项目利用透射电子显微镜像差校正原子分辨率成像技术的最新进展，结合纳米晶体的合成和理论，研究纳米晶体的表面和界面。这项研究将与拓展工作相结合，包括高中访问和本科教育。这个研究项目的结果将被纳入基于网络的教育材料中，用于教授学生原子结构和衍射，基础设施已经到位（见http://emaps.mrl.uiuc.edu/或谷歌网络地图）。这个特别的网站现在被列为学习电子衍射和电子衍射模式索引在标准透射电子显微镜工作场所的最佳网络资源之一。

TECHNICAL SUMMARY: It is proposed to investigate the surface and interfacial energies of epitaxial metal nanocrystals and correlate them with their atomic structure. Epitaxial Au nanocrystals on TiO2 will be used as a model system for study. Epitaxy provides interfacial uniformity and also provides better control of nanocrystalline shapes. TiO2 is selected because of its function as a reducible oxide for catalyst support and the extensive knowledge about its surfaces in the literature. The Au nanocrystals will be synthesized using the deposition and annealing technique developed in the PI's group. Aberration-corrected scanning transmission electron microscopy and transmission electron microscopy will be used to characterize the structure of the Au nanocrystals and their interfaces. The structural data will be used to measure the surface and interfacial energies of the Au nanocrystals as a function of size. On the theoretical front, the interfacial and triple-line geometries, the local electronic density of states, and the energy of Au on TiO2 for different epitaxies will be computed from first-principles. The combination of experiment with theory is expected to lead to significantly improved understanding of the structure and property relationships in nanocrystal surfaces and interfaces.NON-TECHNICAL SUMMARY: Substantial parts of materials technology, major components of chemical industry, and exciting new developments in medical diagnostics and treatments rely on the properties of supported metallic nanoparticles. The unusual functions of metallic nanoparticles come from the synergistic interactions of surfaces and interfaces of nanoparticles and their support. However, modern studies have largely avoided the complexity of supported nanoparticles; nanoparticles are too small for experimental characterization and too big for rigorous theoretical investigations. This project is to study nanocrystal surfaces and interfaces by taking advantage of the recent progress in atomic resolution imaging using aberration-correction in transmission electron microscopy and combining it with nanocrystal synthesis and theory. The research will be integrated with outreach efforts, including high school visits and undergraduate education. Results from this research project will be incorporated in the web-based educational materials for teaching students about atomic structure and diffraction, infrastructure for which is already in place (see http://emaps.mrl.uiuc.edu/ or google webemaps). This particular website is now listed as one of the best web resources for learning electron diffraction and electron diffraction pattern indexing in the standard transmission electron microscopy workplace.