Principles for Formation of Transversely Modulated Heterophase Nanostructures

本项目将开发一类具有可控横向调制异相纳米结构（TMNS）的新型材料。该研究将整合理论、建模、实验表征和设计具有可控规模和形态的TMNS。本研究的基本思想是利用组成相在晶体衬底上的外延自组装来设计TMNS。这种自组装纳米结构的形成需要在每个相和衬底之间建立外延关系。这些外延关系导致组成相的自组织和具有相干或半相干界面的三维异质外延纳米结构的形成。通过选择不同的衬底或衬底取向以及改变纳米结构层的厚度，可以在一定规模上控制自组装纳米结构的形态，这是其他技术难以实现的。由于组分相的纳米尺度，位错介导的机制被抑制，导致显著的弹性应变。因此，控制这种应力成为操纵薄膜性能的新机制，类似于半导体异质结构。本研究的目标是开发实验验证的理论原理和计算工具，以设计具有外延控制的调制纳米结构的材料。将展示控制形貌、尺度和应力状态的能力。基板上的自组装调制结构可以通过以下两种方式形成：(a)固固相变（多晶、马氏体或共晶），或(b)非晶或液相的共晶结晶。由于这项研究的结果，将开发出新的设计原则，用于在纳米尺度上定制界面的由受控异相纳米结构组成的薄膜材料，以及实现TMNS所需的相关处理、表征和建模技术。纳米结构材料对于广泛的结构和功能应用非常重要，例如传感器、执行器、磁记录介质、耐磨涂层、耐高温或耐腐蚀结构材料和热电器件。这项研究将为设计具有受控异相纳米结构的材料提供一个全新的原理，这将导致材料更强，更好的传感，更耐用，以及其他不可能的新材料，如多层复合结构，其性能可以通过纳米结构的自组装来主动调整。这项研究的广泛影响包括理论和实验相结合的研究和教育方法，确保广泛获得所需的知识，以提高未来工程师和研究人员使用溅射技术，纳米压痕和计算材料科学的兴趣和技能。

TECHNICAL SUMMARYIn this research project, a new class of materials with controlled transversely modulated heterophase nanostructures (TMNS) will be developed. The research will integrate theory, modeling, experimental characterization, and design of TMNS with controlled scale and morphology. The basic idea of this research effort is to design TMNS by exploiting epitaxial self-assembling of constituent phases on a crystalline substrate. Formation of such self-assembled nanostructures requires establishing epitaxial relations between each phase and the substrate. These epitaxial relations lead to self-organization of constituent phases and formation of 3D heteroepitaxial nanostructures with coherent or semi-coherent interfaces. By selecting different substrates or substrate orientations and changing the thickness of the nanostructured layer, it is possible to control morphology of the self-assembled nanostructures on a scale that is difficult to obtain with other techniques. Because of the nanoscale of the component phases, dislocation-mediated mechanisms are suppressed resulting in significant elastic strain. Therefore, controlling this stress becomes a new mechanism for manipulating film properties, similar to semiconductor heterostructures. The goal of this research is to develop experimentally verified theoretical principles and computational tools to design materials with modulated nanostructures using epitaxial control. The ability to control morphology, scale, and stress state will be demonstrated. Self-assembled modulated structures on substrates will be formed as a result of either: (a) solid-solid phase transformation (polymorphic, martensitic, or eutectoid), or (b) eutectic crystallization from an amorphous or liquid phase. As a consequence of this research, new principles of design will be developed for thin film materials consisting of controlled heterophase nanostructures for tailoring of interfaces at the nanoscale, as well as the associated processing, characterization, and modeling techniques necessary to realize TMNS.NON-TECHNICAL SUMMARYNanostructured materials are important for a wide spectrum of structural and functional applications, such as sensors, actuators, magnetic recording media, wear resistant coatings, high temperature or corrosion resistant structural materials, and thermoelectric devices. This research will provide an entirely new principle for designing materials with controlled heterophase nanostructures that will lead to materials that are stronger, better at sensing, and more durable, as well as new materials that would not otherwise be possible such as multilayered composite structures whose properties can be actively tuned through self-assembly of the nanostructures. Broader impacts of this research include a coupled theoretical and experimental approach to research and education that ensures broad access to the knowledge needed to enhance the interest and skills of future engineers and researchers using sputtering techniques, nanoindentation, and computational materials science.