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

技术摘要：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，这些现象与相应的体性质有很大的不同。本研究的目的是将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电子和振动特性物理分析相结合。将合成自组装尺寸和形状可选择的双金属纳米团簇[57FePt， 57FePd， 57FeCu和57FeAu]。将使用x射线光电子能谱、扫描隧道和透射电子显微镜、57Fe Mössbauer能谱和57Fe核共振非弹性x射线散射等实验工具的协同组合来发现纳米结构形态和电子结构与其尺寸和成分相关的振动特性之间的相关性。此外，支持簇的振动动力学建模将通过国际合作（加拿大）通过分子动力学模拟进行。这项工作的智力价值是基于目前对以下方面认识的改进：(i)在孤立的纳米团簇中双金属合金的形成、结构和热稳定性，（ii）它们的固有电子和振动特性，（iii）这些特性如何因团簇尺寸效应、团簇支持相互作用、团簇表面配体的存在以及纳米合金的组成而变化，以及（iv）声子诱导的结构相变（已知在铁磁块状Invar合金中）是否持续存在并可以在纳米团簇中进行调整。由于状态的电子和声子密度是理解和预测重要材料性质的关键因素，该项目将推进目前对电子设备中电导率和导热性、热容、振动熵、电子-声子耦合和1/f噪声的基本物理现象的了解。此外，还将深入了解声子辅助表面化学反应是否在理解金属纳米团簇的催化性能方面发挥重要作用。非技术概要：金属纳米团簇表现出有趣的电子和原子振动现象，这些现象与相应的体性质有很大的不同。金属纳米团簇用于光学（纳米光子学）、磁学（记录介质）、医学（靶向药物传递）和化学（催化材料）。它们的电子和振动特性的详细性质仍然存在许多问题，需要更彻底的物理理解来推进这些材料的科学和技术。该项目将改进目前对纳米团簇中双金属合金的形成、结构和热稳定性的了解，以及可用于调整其固有物理性质（如团簇大小、支撑和组成）的参数。更深入地了解重要的材料特性，包括电导率和导热性。研究生和本科生将接受培训，并有机会进行最先进的研究，不仅在中佛罗里达大学，而且在国家和国际用户设施，包括先进光子源（芝加哥）和Spring8（日本）。K-12年级的学生将与本科生合作，负责样品的制备。一个名为？为什么?科学？将在中小学生中开展科学教育活动。为了鼓励少数族裔（西班牙裔）父母接触科学，该网站将提供英语和西班牙语版本。

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.