The Stability of Phases in Thin Multilayered Films

技术概述：结构中具有大表面积体积比的材料可以表现出与其体积形式不同的尺寸相关的物理和化学性质。这些变化可能与晶体学转变到称为伪晶的新相有关。本研究将通过提供使用多层薄膜结构的系统研究来阐明这种相稳定性行为的基础。模型金属体系的长度尺度和组成可以用接近原子的加工精度来控制，这将允许确定晶格错配、层厚度和组成对伪晶相形成和稳定性的影响。这些材料的实时、原位薄膜生长应力将被测量并与界面应力演化相关联。分子动力学（MD）模拟将用于探索沉积过程中伪晶形成的动力学，将实验与建模相结合。这些结果将与生长后相和界面的结构和化学表征有关。该程序将能够描述内在薄膜应力如何驱动跨界面的成分混合，这可以从热力学上促进相变。经典热力学将用于预测和解释相稳定性准则。结果将在预测相图的框架内发展，其中长度尺度是一个状态变量，类似于传统冶金相图中使用的温度和压力，用于确定相变区域。非技术总结：当材料尺寸变得非常小时，材料可以改变其结构中原子的排列方式。这种原子重排通常会导致材料性质的变化，如导电性、光学外观或物理强度。这些原子重排往往是偶然发现的。这项研究旨在开发一个预测图表，让科学家了解原子重排何时发生，作为大小的函数。这些结果将为如何预测和设计不断减小的材料尺寸的原子结构提供地图。通过这笔拨款，美国的技术劳动力将得到增长。这将通过研究生和一名博士后的教育来实现。这些人将通过他们在位于阿拉巴马大学校园内的信息技术材料（MINT）多学科研究中心的互动参与行业。此外，该计划还将通过纳米科学与工程高中研究实习计划吸引阿拉巴马州当地的高中生，该计划在首席研究员？NSF终身成就奖。在此资助期间，材料教育工作将扩大到包括通过在UA校园举办的夏令营对初中和高中教师进行指导。通过直接教育中等教育教师如何在课堂上结合材料实例，材料教育的影响将吸引更广泛、更多样化的学生。

TECHNICAL SUMMARY:Materials in structures with large surface area-to-volume ratios can exhibit size dependent physical and chemical properties that are different than their bulk form. These changes can be related to crystallographic transformations to new phases called pseudomorphs. This research will elucidate the underpinnings of this phase stability behavior by providing a systemic study using multilayered thin film architectures. Model metallic systems whose length scales and compositions can be controlled with near atomic processing precision will allow the influence of lattice misfit, layer thickness, and composition on pseudomorphic phase formation and stability to be determined. Real-time, in situ thin film growth stresses of these materials will be measured and correlated to the interfacial stress evolution. Molecular Dynamics (MD) simulations will be used to explore the kinetics of pseudomorphic formation during deposition, merging experiments with modeling. These results will be related to post-growth structural and chemical characterization of the phases and interfaces. The program will be able to delineate how intrinsic film stress drives compositional intermixing across interfaces which can thermodynamically promote phase transformations. Classical thermodynamics will be used to predict and explain phase stability criteria. The results will be developed within the framework of a predictive phase diagram, where length scale is a state variable similar to temperature and pressure used in traditional metallurgy phase diagrams, in determining phase transition regions. NON-TECHNICAL SUMMARY:When material sizes become very small, a material can alter how it arranges its atoms within its structure. This atomic rearrangement often results in changes in the materials properties such as its electrical conduction, its optical appearance or its physical strength. Too often these atomic rearrangements are serendipitously discovered. This research aims at developing a predictive diagram to let scientists understand when atomic rearrangements occur as a function of size. The results will provide maps on how to predict and engineer atomic structure for ever decreasing material sizes. Through this grant, the technical workforce of the United States will be grown. This will be achieved through the education of graduate and one post-doctoral students. These individuals will engage industry through their interaction in the multi-disciplinary research center, Materials for Information Technology (MINT) situated on the campus of the University of Alabama (UA). In addition, the program will engage local Alabaman high school students through the Nanoscience and Engineering High School Research Internship Program, successfully initiated during the principle investigator?s NSF Career award. Materials education efforts during this grant will be broadened to include instruction to middle and high school teachers through summer camps held on the campus of UA. By directly educating secondary education teachers on how to incorporate materials examples in their classroom, the impact of materials education will engage a broader and more diverse number of students.