New Mechanisms in Epitaxial Crystal Growth: The Role of Incorporated Defects Revealed By In-Situ X-ray Scattering

理解外延晶体生长的基本机制是非常有趣的，因为生长动力学是原子尺度过程的窗口，并且因为希望控制和利用生长行为以创建新的纳米级材料。 这个个人研究者奖支持一个项目，以调查外延生长的新机制，其中空位和堆垛层错，在增长的表面纳入影响表面形态。 传统的实验表面工具，如扫描探针技术（STM，AFM）或电子和原子散射，是敏感的表面，因此，忽略了合并的缺陷，随后埋在表面下的作用。 该项目利用先进光子源发出的明亮X射线束，同时对X射线散射的表面和次表面灵敏度进行研究。 我们的目标是要了解的缺陷纳入机制，以及这些缺陷是如何与不断变化的表面形态。 由于空位和堆垛层错开始他们的公司在当地的表面，这样的系统是服从理论描述，因此，这些实验研究提供了一个必不可少的知识基础，探索更复杂的缺陷系统。 与理论和实验小组的合作将有助于实现一个全面的理解，否则无法通过单一的技术或研究小组实现。 该项目涉及研究生、博士后研究人员以及本科生，从而通过培训和指导实现研究与教育的融合。 通过合作研究，他们的教育经验得到了显著的提升，这增强了沟通能力，并通过直接体验最先进的X射线源得到了显著的提升。随着新的设备技术朝着显著更小的长度尺度发展，探索原子如何在表面上移动和排列的基础科学需求对于理解材料如何生长变得至关重要。 虽然最近在理解一些决定表面上原子组装的机制方面取得了重大进展，但缺陷（即未占据预期位置的原子）的作用一直被忽视。 由于缺陷最初可以在表面处结合，然后被埋在其下方，因此仅对表面敏感的常规实验工具无法看到缺陷。 这个个人研究者奖支持的研究将利用先进光子源的X射线束，这是美国最亮的X射线源，当原子沉积在表面上时，询问表面和次表面结构。 该项目的目的是了解缺陷的机制，以及缺陷的合并是如何与表面上不断变化的原子尺度特征相关的。 预计这些实验研究将对生长机制产生重要的新见解，从而为理解材料如何在表面生长提供一个全面的框架。 该项目将培训和指导研究生和博士后研究人员以及本科生。 与其他研究小组的广泛合作将加强本项目的目标，以及帮助学生的沟通技巧的发展。 他们在先进光子源的研究活动将增强他们的教育经验，而这些学生将成为未来科学家的国家资源的一部分，他们可以利用这些新的最先进的设施。

Understanding the fundamental mechanisms of epitaxial crystal growth is of great interest, both because the growth kinetics is a window to atomic-scale processes and because of the desire to control and exploit growth behavior in order to create novel nanoscale materials. This individual investigator award supports a project to investigate new mechanisms of epitaxial growth where vacancies and stacking faults that are incorporated at the growing surface influence the surface morphology. Conventional experimental surface tools, such as scanning-probe techniques (STM, AFM) or electron and atom scattering, are sensitive only to the surface and, therefore, have overlooked the role of incorporated defects, which are subsequently buried below the surface. This project exploits the simultaneous surface and subsurface sensitivity of x-ray scattering using bright x-ray beams from the Advanced Photon Source. The objective is to understand the mechanisms of defect incorporation and how these defects are related to the evolving surface morphology. Because vacancies and stacking faults begin their incorporation locally at the surface, such systems are amenable to theoretical description and, thus, these experimental studies provide an essential intellectual foundation to explore more complex defect systems. Collaborations with theoretical and experimental groups will help achieve a comprehensive understanding that could not otherwise be achieved by a single technique or research group. The project involves graduate students, postdoctoral researchers as well as undergraduates, thereby leading to the integration of research and education though training and mentoring. Their educational experience is significantly enhanced through collaborative research, which strengthens communication skills, and by direct experience with a state-of-the-art x-ray source.With new device technologies moving towards significantly smaller length-scales, the need for fundamental science to explore how atoms move and arrange themselves on surfaces is becoming imperative for understanding how materials grow. Although there has been significant recent progress towards understanding some of the mechanisms that dictate atomic assemblies on surfaces, the role of defects (meaning atoms that do not occupy expected positions) has been overlooked. Because defects can be initially incorporated at the surface and then become buried below it, conventional experimental tools which are sensitive only to the surface cannot see the defects. This individual investigator award supports research that will utilize a beam of x-rays from the Advanced Photon Source, which is the brightest source of x-rays in the United States, to interrogate both the surface and the subsurface structure as atoms are deposited onto a surface. The objective of the project is to understand the mechanism by which defects are incorporated and how the defect incorporation is related to the evolving atomic-scale features on the surface. It is expected that these experimental studies will yield essential new insight to growth mechanisms and, thus, provide a comprehensive framework for understanding how materials grow at surfaces. The project will train and mentor graduate students and postdoctoral researchers as well as undergraduate students. Extensive collaborative work with other research groups will both strengthen the objectives of this project as well as help the development of the students' communication skills. Their research activities at the Advanced Photon Source will enhance their educational experience while these students will become part of a national resource of future scientists who can utilize these new state-of-the-art facilities.