Dynamic Atomic-scale Metal Oxidation to Correlate with Multi-scale Simulations

动态原子尺度金属氧化与多尺度模拟相关

• 批准号: 1508417
• 负责人: Wissam Saidi
• 金额: $ 45万
• 依托单位: University of Pittsburgh
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1508417&HistoricalAwards=false
• 关键词: Dynamic; Atomic; scale; Metal; Oxidation

NON-TECHNICAL SUMMARYOne of the most important properties for materials exposed to air or water is their environmental stability. As the dimensions of materials systems approach the nanoscale, it is critical to understand on a fundamental level how they interact with their environment at these length scales. Surprisingly, the initial stages are the least well-understood regime of oxidation. Classic models of oxidation assume uniform film growth. This is because classic oxidation analysis relied mostly on thermogravimetric techniques, which measure the weight change of the material during oxidation, and, hence, do not provide information on the materials' structure. Yet, structural changes are well-known to occur during metal oxidation. The potential impact of the proposed research project is the development of a fundamental understanding of nanoscale oxidation processes. This research team expands the experimental understanding of nanoscale oxidation using in situ and ex situ environmental transmission electron microscope to directly compare with a current theoretical effort on the atomistic simulation of oxidation of copper. The results from the in situ and ex situ experiments accelerates the development of computational tools needed to enhance the emergent field of predictive materials design for a critical reaction, oxidation. Oxidation is of world-wide importance, not only for corrosion but also as a bottom up approach to nano-oxide processing. Furthermore, a critical aspect of this project is the education and training of students and post-doc. The combined partnership between complementary experimental and theoretical tools, especially in situ, enriches the education of all participants involved in this project and the development of future leaders who are better equipped to bring to success the emergent field of predictive science and engineering. Results from this research are also incorporated into graduate courses and high school community outreach projects, such as Pennsylvania Junior Academy of Science workshop that has been held annually in Pittsburgh since 2007.TECHNICAL SUMMARYMuch is known about oxygen interaction with metal surfaces and about the macroscopic growth of thermodynamically stable oxides. At present, however, the nanoscale stages of oxidation - from nucleation of the metal oxide to formation of the thermodynamically stable oxide - represent a scientifically challenging and technologically important terra incognito. As engineered materials approach the nanometer regime, control of their environmental stability at this scale becomes crucial. As environmental stability is an essential property of most engineered materials, many oxidation theories exist to explain its mechanisms. However, most classical oxidation theories assume a uniform growing film, where structural changes are not considered due to the lack of traditional experimental procedure to visualize this non-uniform growth under conditions that allow highly controlled surfaces and impurities. Yet, recent studies by this research team reveal that the Cu oxide islands form during the early stages of Cu oxidation, and thereby challenge the common assumption of a uniform oxide formation. This research team correlates experimental results with theoretical predictions where the impact could be a paradigm shift in the fundamental understanding of oxidation where surfaces and defects control the early stages of oxidation. Specifically, this research team integrates experimental in situ and ex situ transmission electron microscopy and X-ray photoelectron spectroscopy with theoretical simulations in order to gain critical insights into the nucleation behavior, morphological evolution of oxide islands during oxidation and coalescence, and quantitative fundamental physical parameters such as diffusion barriers. Although the focus is on oxygen-metal reactions, the methodologies developed are applicable to any epitaxial system and gas-surface reaction. The understanding obtained from combining the unique experimental results and directly correlated theoretical models leads to smarter design paradigms for nano- and mesoscale materials, devices, and processes that utilize surface gas-metal reaction. This is essential to many technical areas, such as high temperature corrosion, electrochemistry, gate oxides and thin film formation, catalysis used for environmental protection, energy generation and storage, and fuel cell reactions.

非技术总结暴露于空气或水的材料的最重要特性之一是其环境稳定性。 随着材料系统的尺寸接近纳米级，在基本层面上了解它们如何在这些长度尺度上与环境相互作用至关重要。令人惊讶的是，初始阶段是最不容易理解的氧化机制。经典的氧化模型假设膜生长均匀。这是因为传统的氧化分析主要依赖于热重技术，该技术测量氧化过程中材料的重量变化，因此不能提供材料结构的信息。然而，众所周知，在金属氧化过程中会发生结构变化。拟议的研究项目的潜在影响是对纳米氧化过程的基本理解的发展。 该研究小组使用原位和非原位环境透射电子显微镜扩展了对纳米级氧化的实验理解，以直接与目前对铜氧化的原子模拟的理论研究进行比较。原位和非原位实验的结果加速了所需的计算工具的发展，以提高预测材料设计的关键反应，氧化的新兴领域。氧化是世界范围内的重要性，不仅腐蚀，而且作为一个自下而上的方法，纳米氧化物处理。此外，该项目的一个重要方面是学生和博士后的教育和培训。互补的实验和理论工具之间的组合伙伴关系，特别是在现场，丰富了参与该项目的所有参与者的教育和未来领导者的发展，他们更有能力使预测科学和工程的新兴领域取得成功。 这项研究的结果也被纳入研究生课程和高中社区外展项目中，例如自2007年以来每年在匹兹堡举行的宾夕法尼亚州青年科学院研讨会。然而，目前，氧化的纳米级阶段-从金属氧化物的成核到化学稳定的氧化物的形成-代表了科学上具有挑战性和技术上重要的领域。随着工程材料接近纳米范围，在这种规模下控制其环境稳定性变得至关重要。 由于环境稳定性是大多数工程材料的基本属性，因此存在许多氧化理论来解释其机制。然而，大多数经典的氧化理论假设一个均匀的生长膜，其中结构的变化不被认为是由于缺乏传统的实验程序可视化这种非均匀生长的条件下，允许高度控制的表面和杂质。然而，该研究小组最近的研究表明，铜氧化物岛在铜氧化的早期阶段形成，从而挑战了均匀氧化物形成的常见假设。该研究小组将实验结果与理论预测相关联，其影响可能是对氧化的基本理解的范式转变，其中表面和缺陷控制氧化的早期阶段。具体而言，该研究团队将实验原位和非原位透射电子显微镜和X射线光电子能谱与理论模拟相结合，以获得对成核行为，氧化物岛在氧化和聚结过程中的形态演变以及扩散势垒等定量基本物理参数的关键见解。虽然重点是氧-金属反应，开发的方法适用于任何外延系统和气体表面反应。 从结合独特的实验结果和直接相关的理论模型获得的理解导致更聪明的设计范例的纳米和中尺度的材料，设备和工艺，利用表面气体-金属反应。这对于许多技术领域都是必不可少的，例如高温腐蚀、电化学、栅氧化物和薄膜形成、用于环境保护的催化、能量产生和存储以及燃料电池反应。