Principles for Formation of Transversely Modulated Heterophase Nanostructures

技术总结在这项研究项目中，将开发一种新型的具有可控横向调制异相纳米结构(TMNS)的材料。这项研究将结合理论、建模、实验表征和设计具有可控规模和形态的TMN。这项研究的基本思想是通过在晶体衬底上利用组成相的外延自组装来设计TMN。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。这些外延关系导致了组成相的自组织和具有相干或半共格界面的3D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并改变纳米结构层的厚度，可以在用其他技术难以获得的规模上控制自组装纳米结构的形态。由于组元相的纳米尺度，位错机制被抑制，导致显著的弹性应变。因此，控制这种应力成为控制薄膜性质的一种新机制，类似于半导体异质结。这项研究的目标是开发经过实验验证的理论原理和计算工具，以利用外延控制来设计具有调制纳米结构的材料。将演示控制形态、比例和应力状态的能力。在衬底上形成自组装调制结构的原因是：(A)固-固相变(多晶型、马氏体型或共析型)，或(B)非晶态或液态的共晶结晶。作为这项研究的结果，将为薄膜材料开发新的设计原则，包括用于在纳米尺度上裁剪界面的受控异相纳米结构，以及实现TMNS所需的相关加工、表征和建模技术。非技术总结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、致动器、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可控异相纳米结构的材料提供一种全新的原理，这些材料将导致更强、更好的传感和更持久的材料，以及原本不可能实现的新材料，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。这项研究的更广泛影响包括理论和实验相结合的研究和教育方法，确保广泛获得必要的知识，以提高使用溅射技术、纳米压痕和计算材料科学的未来工程师和研究人员的兴趣和技能。

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.