Crystal Growth at the Nanoscale: New Phenomena Revealed by In situ X-ray Scattering

非技术摘要随着新的设备技术朝着明显更小的长度尺度发展，需要基础科学来探索原子如何在表面上移动和排列，这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。此外，非常小的晶体(纳米晶体)会受到以前晶体生长理论中没有考虑到的新力(量子机械力)的影响。这项个人研究人员奖将利用先进光子源的一束X射线，这是美国最亮的X射线源，当原子沉积到表面上时，探测表面和亚表面结构。预计这些实验研究将导致对生长机制的基本新见解，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。先进光子源的研究活动将增强他们的教育经验，同时它们将成为未来科学家的国家资源的一部分，这些科学家可以利用这些新的最先进的设施。技术摘要该项目的主要目的是研究新的原子尺度的机制，这些机制强烈地影响纳米晶体和外延薄膜的生长和演化。特别强调了难以捉摸的地下现象，这些现象是通过原位X射线散射独特地解决的。实验将在简单的“模型”系统上进行，这些系统将导致清晰的解释和基本概念的建立。原位X射线散射的地下敏感性使我们能够对其他表面敏感技术未能解决的问题有新的见解和解决方案。在原子尺度上，我们将了解缺陷是如何被结合到薄膜中的，一旦被结合，这些缺陷是如何影响随后的生长的，以及缺陷是如何与不断演变的表面形态相关的。新的结果将为研究更复杂的系统提供基础和“垫脚石”。这些研究还将揭示界面如何影响外延纳米晶体的生长，以及小晶体尺寸如何表现在其生长动力学中。探索和揭示量子尺寸效应纳米晶体的新生长动力学有望为理解这些系统提供一个新的概念框架。该项目将利用国际和平研究所在先进光子源(APS)开发的原位表面散射设施，其中X射线源的高亮度和仪器设计提供了使这些研究成为可能的新能力。由于该项目涉及有助于理解如何操纵纳米材料的基本问题，这些研究将广泛影响具有重要社会效益的新兴技术，如计算机、通信和医疗技术。教育和研究广泛地融入到该项目中，因为它涉及研究生、博士后和本科生。APS最先进的基础设施为学生和博士后提供了极好的培训机会。

Non-Technical AbstractWith 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. In addition, very small crystals (nanocrystals) are subject to new forces (quantum-mechanical forces) that have not been previously considered in theories of crystal growth. This individual investigator award 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 probe, both, the surface and the subsurface structure as atoms are deposited onto a surface. It is expected that these experimental studies will lead to 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. The research activities at the Advanced Photon Source will enhance their educational experience while they will become part of a national resource of future scientists who can utilize these new state-of-the-art facilities.Technical AbstractThe main thrust of the project investigates new atomic-scale mechanisms that strongly affect the growth and evolution of nanocrystals and epitaxial films. Particular emphasis is given to elusive subsurface phenomena, which are uniquely addressed by in situ x-ray scattering. Experiments will be performed on simple "model" systems that lead to clear interpretations and the establishment of fundamental concepts. The subsurface sensitivity of in situ x-ray scattering enables new insight and solutions to problems that have eluded other surface sensitive techniques. It will be learned, at the atomic-scale, how defects become incorporated into a film, how these affect the subsequent growth once incorporated, and how defects relate to the evolving surface morphology. The new results will provide the foundation and a "stepping stone" for investigating more complex systems. These studies will also reveal how interfaces influence the growth of epitaxial nanocrystals and how the small crystal size is manifested in its growth kinetics. Exploring and exposing the novel growth kinetics of quantum size effect nanocrystals is expected to lead to a new conceptual framework for understanding these systems. The project will utilize the in situ surface scattering facility developed by the PI at the Advanced Photon Source (APS), where the high brightness of the x-ray source and the instrument design provide new capabilities that enable these studies. Because the project addresses fundamental issues that help understand how to manipulate nanomaterials, these studies will broadly impact emerging technologies that have important societal benefits such as computer, communication and medical technologies. Education and research are extensively integrated into the project, as it involves graduate students, postdocs and undergraduates. State-of-the-art infrastructure at the APS offers excellent training opportunities for students and postdocs.