SGER: Structural Evolution at Micro and Nano Scales

先进的技术需要不断减小长度尺度的实体结构。在制造和使用这些结构的过程中，扩散过程会重新安置物质，并且结构会随着时间的推移而改变结构。进化的结构可以自组装成特定的模式，使微纳米制造的新技术成为可能。另一方面，结构的演变可能导致裂纹和空洞的形核和增长，对小特征尺寸的器件造成严重的机械可靠性问题。从根本上说，材料和结构在微观和纳米尺度上的行为不同于它们在宏观和原子尺度上的对应物，并且不太熟悉的物理起源的力量起作用。在微纳米尺度上研究演化结构是一个具有重大科学意义和技术重要性的新领域，固体力学研究人员可以为此做出重大贡献。本研究的长期目标是：(1)建立微纳米尺度结构演化的建模与模拟研究项目；(2)整合研究和教育，促进力学、材料和纳米科学与技术领域的跨学科教育。在SGER项目的范围内，将通过建模和模拟来研究量子点在图案化和应变工程基板上的引导自组装。将与实验研究者建立合作关系，以促进未来的互动。晶格错配异质外延在Stranski-Krastanov （SK）生长过程中自发形成三维相干岛已成为合成自组装量子点的一种有吸引力的技术。然而，岛大小的不均匀性和成核位置的随机性对自组装量子点的器件应用造成了很大的限制。本研究将通过动态建模和仿真，对应变场和表面结构对量子点形成的作用有一个基本的认识，这将为通过引导自组装对量子点合成的系统控制提供基础，从而为实际器件应用提供足够的尺寸均匀性和空间秩序。变分方法将作为建模和仿真的统一框架而发展。该方法通过将质量重定位作为一个独立的运动学变量，以及变形，扩展了连续介质力学中已建立的方法。模型和模拟的结果将指导未来的实验研究。更广泛的影响所提出的研究结果将导致制造微纳米级结构的新思路，用于广泛的应用，包括纳米电子学，光子学和生物医学设备。将培训一名研究生。部分研究成果将被纳入一门新的研究生课程——薄膜力学，该课程将于2004年秋季首次在德克萨斯大学奥斯汀分校开设。其他更广泛的影响包括为本科生提供研究经验（REU）和向公众传播研究成果

Project SummaryIntellectual MeritsAdvanced technologies demand solid structures of decreasing length scales. During fabrication and use of these structures, diffusive processes relocate matter, and the structures change configuration over time. Evolving structures may self-assemble into certain patterns, enabling new techniques for micro and nano fabrication. On the other hand, structural evolution may result in nucleation and growth of cracks and cavities, causing serious mechanical reliability problems for devices with small feature sizes. Fundamentally, the behavior of materials and structures at micro and nano scales differ from their counterparts at both macro and atomistic scales, and forces of less familiar physical origins play roles. The study of evolving structures at micro and nano scales is a new field of great scientific interest and technological importance, to which solid mechanics researchers can make substantial contributions. The long-term objectives of the proposed research are: (1) to develop a research program focusing on modeling and simulation of structural evolution at micro and nano scales; and (2) to integrate research and education to foster interdisciplinary education in the areas of mechanics, materials, and nanoscale science and technology. Within the scope of this SGER project, guided self-assembly of quantum dots on patterned and strain-engineered substrates will be investigated via modeling and simulations. Collaborations with experimental investigators will be established to facilitate future interactions.The spontaneous formation of three-dimensional coherent islands during the Stranski-Krastanov (SK) growth of lattice-mismatched heteroepitaxy has emerged as an attractive technique for the synthesis of self-assembled quantum dots. However, the considerable nonuniformity in the island sizes and the randomness of the nucleation sites have posed significant limitations for device applications of self-assembled quantum dots. The proposed research will develop a fundamental understanding of the role of strain field and surface structures on the formation of quantum dots through dynamic modeling and simulations, which will provide the basis for developing systematic control of quantum dots synthesis via guided self-assembly to achieve sufficient size uniformity and spatial order for practical device applications. A variational approach will be developed as a unifying framework for modeling and simulation. The approach extends the established approach in continuum mechanics by including mass relocation as an independent kinematic variable, in addition to deformation. The results from modeling and simulations will guide experimental investigations in future studies.Broader ImpactsThe results of the proposed research will lead to new ideas for fabricating micro- and nanoscale structures for a wide range of applications including nanoelectronics, photonics, and biomedical devices. One graduate student will be trained. Part of the research results will be incorporated into a new graduate course on Thin Film Mechanics, which will be offered by the PI in Fall 2004 for the first time at the University of Texas-Austin. Other broader impacts include research experience for undergraduates (REU) and dissemination of research results to general public