Nonequilibrium Pattern Formation In Erosion Processes

离子束溅射是通过高能粒子的撞击从固体表面去除材料，是一种广泛使用的薄膜处理技术。 由于其相关的一些实验技术，测量工具，清洗和图案化的方法，表面的形态特征的离子轰击侵蚀已被大量研究的后期。 另一方面，离子束溅射作为纳米级表面图案化的潜在候选者吸引了越来越多的兴趣。 人们已经知道，倾斜离子束的侵蚀会产生规则的自组织波纹，这是量子线的潜在模板。 但是，随着最近证明正常溅射可以导致规则的纳米级岛或量子点，对这种技术的兴趣最近蓬勃发展。 所观察到的高密度岛，其大小可以调整与离子能量，显示高度的空间有序性，并形成一个规则的六方晶格。 这些结果标志着一种新颖而强大的表面图案化技术的出现，该技术具有许多理想的特征，包括材料独立性，可调特征尺寸以及适用于廉价的大规模制造。 为了将这些进展转化为可行的图案化技术，我们需要更好地理解影响表面形态的基本过程。 因此，本基金的研究目标是获得对离子轰击侵蚀表面形态的主要物理因素的一致理解。 该研究将使用数值和分析工具的组合来模拟离子轰击过程中的形态演变。 由于布拉德利和哈珀计算的涟漪波长与实验一致，它被普遍接受，连续理论提供了一个令人惊讶的有用的工具，在解决离子溅射的表面形态。 PI表明，非线性现象在确定表面形态的长期特征方面起着至关重要的作用，能够解释涟漪稳定和量子点形成。 这些工具将得到扩展，以获得更好的协议与实验，旨在再现不仅是大规模的功能，而且岛屿的形状和空间秩序。 同时，将开发离散微观模型，以了解各种微观过程（表面扩散，原子分离，再附着等）对表面形态的影响。 同时使用的连续和微观的方法，预计将发挥至关重要的作用，揭示两个图案的形成和粗糙化的通用功能。 这些工具将被用来调查几个问题的直接实验和技术利益。 首先，初步的理论工作表明，溅射量子点的尺寸分散，以及它的依赖性，取决于腐蚀时间，并存在一个最佳的时间，在该时间分散是最小的。 将研究分散度对侵蚀参数（例如离子能量、离子级联参数和温度）的时间依赖性，旨在确定岛形成的最佳条件。 其次，最近的实验表明，如果表面旋转，就会出现规则的岛屿。 将调查的条件下，从样品旋转的大小分散的好处。 第三，溅射产率，各种表面表征方法的关键量，很大程度上受表面形貌的影响。 将开发方法来预测形态和产率之间的动态耦合。 本研究将对连续介质理论、模拟结果和实验结果进行全面的比较，并为离子溅射成为一种成熟的图案化技术提供重要的理论指导。 离子束溅射是通过高能粒子的撞击从固体表面去除材料，是一种广泛使用的薄膜加工技术。 由于其相关的一些实验技术，测量工具，清洗和图案化的方法，表面的形态特征的离子轰击侵蚀已被大量研究的后期。 另一方面，离子束溅射作为纳米级表面图案化的潜在候选者吸引了越来越多的兴趣。 人们已经知道，倾斜离子束的侵蚀会产生规则的自组织波纹，这是量子线的潜在模板。 但是，随着最近证明正常溅射可以导致规则的纳米级岛或量子点，对这种技术的兴趣最近蓬勃发展。 所观察到的高密度岛，其大小可以调整与离子能量，显示高度的空间有序性，并形成一个规则的六方晶格。 这些结果标志着一种新颖而强大的表面图案化技术的出现，该技术具有许多理想的特征，包括材料独立性，可调特征尺寸以及适用于廉价的大规模制造。 为了将这些进展转化为可行的图案化技术，我们需要更好地理解影响表面形态的基本过程。 因此，本基金的研究目标是获得对离子轰击侵蚀表面形态的主要物理因素的一致理解。 ***

0108494BarabasiIon-beam sputtering, the removal of material from the surface of solids through the impact of energetic particles, is a widely used thin film processing technique. Due to its relevance to a number of experimental techniques, measuring tools, cleaning and patterning methods, the morphological features of surfaces eroded by ion bombardment have been much investigated of late. On the other hand, ion-beam sputtering is attracting increased interest as a potential candidate for nanoscale surface patterning. Erosion with oblique ion beams has been known to create regular self-organization ripples, potential templates for quantum wires. But the interest in this technique has boomed recently following the recent demonstration that normal sputtering can lead to regular nanoscale islands or quantum dots. The observed high density islands, whose size can be tuned with the ion energy, display a high degree of spatial ordering and form a regular hexagonal lattice. These results signal the emergence of a novel and powerful technique for surface patterning with a number of desirable features that include material independence, tunable feature size, as well as suitability for inexpensive mass fabrication. To turn these advances into a viable patterning technology, we need to develop a better understanding of the fundamental processes that affect the surface morphology. Therefore, the research goal of this grant is to obtain a coherent understanding of the primary physical factors contributing to the morphology of surfaces eroded by ion bombardment. The research will use a combination of numerical and analytical tools to model the morphological evolution during ion bombardment. Since Bradley and Harper have calculated the ripple wavelength in agreement with experiments, it is generally accepted that continuum theories offer a surprisingly useful tool in addressing the surface morphology in ion sputtering. The PI has shown that nonlinear phenomena play a crucial role in determining the long-time features of the surface morphology, being able to account for ripple stabilization and quantum dot formation. These tools will be expanded to obtain better agreement with experiments, aiming to reproduce not only the large scale features, but also the island shapes and spatial ordering. In parallel, discrete microscopic models will be developed to understand the effect of various microscopic processes (surface diffusion, atom detachment, reattachment, etc) on the surface morphology. The simultaneous use of the continuum and microscopic approaches is expected to play a crucial role in uncovering the generic features of both pattern formation and roughening. These tools will be used to investigate several problems of immediate experimental and technological interest. First, preliminary theoretical work indicates that the size dispersion, as well as its dependence of the sputtered quantum dots, depends on erosion time, and exists an optimal time at which the dispersion is minimal. This time dependence of the dispersion on the erosion parameters (such as ion energy, ion cascade parameters and temperature) will be investigated, aiming to determine the optimal condition for island formation. Second, recent experiments have demonstrated that regular islands appear if the surface is rotated. Investigations will be made into the conditions under which the size dispersion benefits from sample rotation. Third, the sputtering yield, a key quantity for various surface characterization methods, is greatly affected by the surface morphology. Methods will be developed to predict the dynamic coupling between the morphology and the yield. This research is expected to lead to a comprehensive comparison between the continuum theory, modeling results and experiments, and could offer critical theoretical guidance to turn ion sputtering into a mature patterning technology. %%%Ion-beam sputtering, the removal of material from the surface of solids through the impact of energetic particles, is a widely used thin film processing technique. Due to its relevance to a number of experimental techniques, measuring tools, cleaning and patterning methods, the morphological features of surfaces eroded by ion bombardment have been much investigated of late. On the other hand, ion-beam sputtering is attracting increased interest as a potential candidate for nanoscale surface patterning. Erosion with oblique ion beams has been known to create regular self-organization ripples, potential templates for quantum wires. But the interest in this technique has boomed recently following the recent demonstration that normal sputtering can lead to regular nanoscale islands or quantum dots. The observed high density islands, whose size can be tuned with the ion energy, display a high degree of spatial ordering and form a regular hexagonal lattice. These results signal the emergence of a novel and powerful technique for surface patterning with a number of desirable features that include material independence, tunable feature size, as well as suitability for inexpensive mass fabrication. To turn these advances into a viable patterning technology, we need to develop a better understanding of the fundamental processes that affect the surface morphology. Therefore, the research goal of this grant is to obtain a coherent understanding of the primary physical factors contributing to the morphology of surfaces eroded by ion bombardment. ***