Size- and Composition-Dependent Electronic and Vibrational Properties of Bimetallic Nanoclusters

技术概要：该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。金属纳米团簇表现出有趣的电子和原子振动现象，这些现象与相应的整体性质显著偏离。本研究的目标是将联合收割机结合最近开发的基于胶束的纳米团簇合成方法与先进的纳米级物理分析的电子和振动性质。将合成自组装的尺寸和形状选择性的57 FePt，57 FePd，57 FeCu和57 FeAu纳米团簇。实验工具，包括X射线光电子能谱，扫描隧道和透射电子显微镜，57 Fe穆斯堡尔谱和57 Fe核共振非弹性X射线散射的协同组合将被用来找到纳米结构形态和电子结构及其大小和成分依赖的振动特性之间的相关性。此外，还将通过国际合作（加拿大），通过分子动力学模拟对支持的团簇的振动动力学进行建模。这项工作的智力价值是基于对以下方面的现有理解的改进：（i）孤立的纳米团簇中纳米合金的形成、结构和热稳定性，（ii）它们的固有电子和振动性质，（iii）这些特性如何由于团簇尺寸效应、团簇-载体相互作用、团簇表面上配体的存在以及纳米合金的组成而改变，以及（iv）声子诱导的结构相变（在铁磁块体因瓦合金中已知）是否持续并且可以在纳米团簇中调谐。由于电子和声子态密度是理解和预测重要材料特性的关键因素，因此该项目将推进电子器件中的电导率和热导率，热容，振动熵，电子-声子耦合和1/f噪声的基本物理现象的现有知识。此外，声子辅助的表面化学反应是否可以在理解金属纳米团簇的催化性能中发挥重要作用，将获得洞察力。非技术性总结：金属纳米团簇表现出有趣的电子和原子振动现象，这些现象与相应的整体性质显著偏离。金属纳米团簇用于光学（纳米光子学），磁性（记录介质），医学（靶向药物输送）和化学（催化材料）。许多问题仍然存在于它们的电子和振动性质的详细性质上，需要更彻底的物理理解来推进这些材料的科学和技术。该项目将提高目前的知识的形成，结构和热稳定性的纳米团簇中的Ni-Al合金，以及参数，可用于调整其固有的物理特性，如团簇的大小，支持和组成。将获得对重要材料特性（包括导电性和导热性）的更深入了解。研究生和本科生将接受培训，并有机会进行最先进的研究，不仅在中央佛罗里达大学，而且在国家和国际用户设施，包括高级光子源（芝加哥）和Spring 8（日本）。K-12学生与本科生合作将负责样品制备。网站名称？为什么？为什么？s科学？将在中小学生中开展科学教育活动。为了鼓励少数民族（西班牙裔）家长接触科学，该网站将提供英文和西班牙文版本。

TECHNICAL SUMMARY:This Award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Metal nanoclusters exhibit intriguing electronic and atomic vibrational phenomena that deviate dramatically from the corresponding bulk properties. The goal of this study is to combine recently developed micelle-based nanocluster synthesis methods with advanced nanoscale physical analysis of both electronic and vibrational properties. Self-assembled size- and shape-selected bimetallic nanoclusters [57FePt, 57FePd, 57FeCu and 57FeAu] will be synthesized. A synergetic combination of experimental tools including X-ray photoelectron spectroscopy, scanning tunneling and transmission electron microscopy, 57Fe Mössbauer spectroscopy, and 57Fe nuclear resonant inelastic X-ray scattering will be used to find correlations between the nanostructure morphology and electronic structure and its size- and composition-dependent vibrational properties. In addition, modeling of the vibrational dynamics of supported clusters will be conducted by molecular dynamics simulations through an international collaboration (Canada). The intellectual merit of this work is based on the improvement of the current understanding on: (i) the formation, the structural and thermal stability of bimetallic alloys in isolated nanoclusters, (ii) their intrinsic electronic and vibrational properties, (iii) how these characteristics change due to cluster size-effects, cluster-support interactions, the presence of ligands on the cluster surface, and the composition of the nanoalloys, and (iv) whether phonon-induced structural phase transitions (known in ferromagnetic bulk Invar alloys) persist and can be tuned in nanoclusters. Since the electron and phonon density of states are key elements in understanding and predicting important materials properties, this project will advance the present knowledge of basic physical phenomena underlying electrical and thermal conductivity, heat capacity, vibrational entropy, electron-phonon coupling, and 1/f noise in electronic devices. In addition, insight will be obtained on whether phonon-assisted surface chemical reactions could play an important role in the comprehension of the catalytic properties of metal nanoclusters. NON-TECHNICAL SUMMARY:Metal nanoclusters exhibit intriguing electronic and atomic vibrational phenomena that deviate dramatically from the corresponding bulk properties. Metal nanoclusters are used in optics (nanophotonics), magnetism (recording media), medicine (targeted drug delivery), and in chemistry (catalytic materials). Many questions remain on the detailed nature of their electronic and vibrational properties, and a more thorough physical understanding is needed to advance the science and technology of these materials. This project will improve the present knowledge on the formation, the structural and thermal stability of bimetallic alloys in nanoclusters, and the parameters that can be used to tune their intrinsic physical properties such as cluster size, support and composition. A deeper insight into important material properties including electrical and thermal conductivity will be obtained. Graduate and undergraduate students will be trained and given the opportunity to conduct state-of-the-art research, not just at the University of Central Florida, but also at national and international user facilities, including the Advanced Photon Source (Chicago) and Spring8 (Japan). K-12 students teamed up with undergraduates will be in charge of the sample preparation. A website entitled ?Why?s of Science? will be setup to disseminate science-related educational activities among primary and middle school students. In order to stimulate the access of minority (Hispanic) parents to science, the website will be available in English and Spanish.