Nonequilibrium Pattern Formation In Erosion Processes

barabasiion -beam溅射是一种通过高能粒子的冲击从固体表面去除材料的方法，是一种广泛应用的薄膜加工技术。由于它与许多实验技术、测量工具、清洁和图案化方法的相关性，离子轰击侵蚀表面的形态特征最近得到了很多研究。另一方面，离子束溅射作为纳米级表面图像化的潜在候选物正引起越来越多的兴趣。已知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。但最近，随着正常溅射可以产生规则的纳米级岛屿或量子点的证明，对这项技术的兴趣激增。所观察到的高密度岛，其大小可以随离子能量的变化而调整，显示出高度的空间有序性，并形成规则的六边形晶格。这些结果标志着一种新颖而强大的表面图案技术的出现，该技术具有许多理想的特征，包括材料独立性，可调节的特征尺寸，以及适合廉价的大规模制造。为了将这些进步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，这项资助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相结合的工具来模拟离子轰击过程中的形态演变。由于Bradley和Harper计算出的波纹波长与实验结果一致，因此人们普遍认为，连续介质理论为解决离子溅射中的表面形貌提供了一个令人惊讶的有用工具。PI表明，非线性现象在决定表面形态的长期特征方面起着至关重要的作用，能够解释波纹稳定和量子点的形成。这些工具将被扩展以获得与实验更好的一致性，旨在重现不仅大尺度特征，而且岛屿形状和空间秩序。同时，离散微观模型将被开发来理解各种微观过程（表面扩散、原子分离、再附着等）对表面形貌的影响。同时使用连续体和微观方法有望在揭示图案形成和粗化的一般特征方面发挥关键作用。这些工具将用于研究几个直接引起实验和技术兴趣的问题。首先，初步的理论工作表明，溅射量子点的尺寸色散及其对腐蚀时间的依赖性取决于腐蚀时间，并且存在色散最小的最佳时间。将研究色散对侵蚀参数（如离子能量、离子级联参数和温度）的时间依赖性，旨在确定岛屿形成的最佳条件。其次，最近的实验表明，如果旋转表面，就会出现规则的岛屿。将研究样品旋转对粒径分散有利的条件。第三，溅射成品率是各种表面表征方法的关键指标，它受表面形貌的影响很大。将开发方法来预测形态和产率之间的动态耦合。本研究有望对连续介质理论、建模结果和实验进行全面比较，为离子溅射发展成为成熟的图像化技术提供重要的理论指导。离子束溅射，即通过高能粒子的冲击从固体表面去除材料，是一种广泛应用的薄膜加工技术。由于它与许多实验技术、测量工具、清洁和图案化方法的相关性，离子轰击侵蚀表面的形态特征最近得到了很多研究。另一方面，离子束溅射作为纳米级表面图像化的潜在候选物正引起越来越多的兴趣。已知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。但最近，随着正常溅射可以产生规则的纳米级岛屿或量子点的证明，对这项技术的兴趣激增。所观察到的高密度岛，其大小可以随离子能量的变化而调整，显示出高度的空间有序性，并形成规则的六边形晶格。这些结果标志着一种新颖而强大的表面图案技术的出现，该技术具有许多理想的特征，包括材料独立性，可调节的特征尺寸，以及适合廉价的大规模制造。为了将这些进步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，这项资助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. ***