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

了解外延晶体生长的基本机制是非常有意义的，这既是因为生长动力学是了解原子尺度过程的窗口，也是因为人们希望控制和利用生长行为来创造新的纳米材料。这一个人研究人员奖支持一个项目，该项目旨在研究外延生长的新机制，其中生长表面结合的空位和堆积缺陷影响表面形态。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，只对表面敏感，因此忽略了被结合的缺陷的作用，这些缺陷随后被埋在表面之下。该项目利用先进光子源发出的明亮X射线束同时对表面和次表面进行X射线散射的敏感性。我们的目的是了解缺陷合并的机制，以及这些缺陷如何与不断演变的表面形态相关。由于空位和层错开始在表面局部结合，这类系统符合理论描述，因此，这些实验研究为探索更复杂的缺陷系统提供了必要的智力基础。与理论和实验小组的合作将有助于实现一个单一的技术或研究小组无法实现的全面理解。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和教育的一体化。他们的教育经历通过合作研究和直接接触最先进的X射线源得到显著增强，合作研究加强了沟通技能。随着新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运动和排列的基础科学对于理解材料是如何生长的变得至关重要。尽管最近在理解决定原子在表面上聚集的一些机制方面取得了重大进展，但缺陷(即没有占据预期位置的原子)的作用被忽视了。由于缺陷最初可能被合并在表面，然后隐藏在表面之下，因此只对表面敏感的传统实验工具无法看到缺陷。这项个人研究人员奖支持的研究将利用先进光子源的一束X射线，当原子沉积到表面上时，先进光子源是美国最亮的X射线源，以询问表面和亚表面结构。该项目的目标是了解缺陷合并的机制，以及缺陷合并如何与表面上不断演变的原子尺度特征相关。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。该项目将培养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，并有助于学生沟通技能的发展。他们在高级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.