Collaborative Research: Highly Ordered Nanoscale Patterns Produced by Ion Bombardment of Solid Surfaces: Theory and Experiment

合作研究：离子轰击固体表面产生的高度有序的纳米级图案：理论与实验

• 批准号: 2117509
• 负责人: Karl Ludwig
• 金额: $ 31.5万
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-01-01 至 2024-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2117509&HistoricalAwards=false
• 关键词: Collaborative; Research; Highly; Ordered; Nanoscale

When a flat solid surface is bombarded with a broad ion beam, patterns can emerge spontaneously, including surface ripples with a wavelength as short as one ten-thousandth of the width of a human hair. If the patterns formed were not almost always disordered, this fascinating type of self-organization could become a widely employed method of fabricating structures with feature sizes too small to be produced by conventional techniques. A central goal of this collaborative theoretical and experimental research is therefore to develop and refine methods of producing highly ordered surface ripples by ion bombardment. Surfaces patterns of this kind could be used in a variety of applications, including ones in which extreme ultraviolet light must be manipulated or analyzed. This project involves graduate, undergraduate and high school students who are working in a field that bridges basic research and applications. In addition to experiencing, and contributing to, an important topic in current materials research, the students are learning to use a wide range of theoretical, simulation and materials characterization tools that will translate well to future careers in industry or academia. Beyond working with the materials research communities at their home institutions, the project is providing the students with a broader perspective through participation in the exciting, multi-disciplinary environments at national x-ray scattering facilities.This collaboration brings together two principal investigators who have individually made seminal theoretical and experimental contributions to the field of ion beam nanopatterning, producing a team that is uniquely positioned to advance the field. Two key strategies are being employed in working toward the goal of producing surface ripples with an exceptional degree of order. These strategies are also leading to important steps forward in our understanding of the fundamental processes that take place during ion bombardment. The first strategy is to study the onset of pattern formation that occurs as the angle of ion incidence or the sample temperature is varied through a threshold value. Near-threshold behavior is being examined in three different regimes: 1) the higher energy regime in which sputtering is important; 2) the low-energy regime in which sputtering is negligible, a largely unexplored frontier of the field; and 3) the high-temperature regime in which the surface remains crystalline, resulting in better quality material for electronic/photonic applications. The equation of motion becomes simpler near these transitions and can be rigorously derived. In addition, it has a high degree of universality, i.e., it is to a large extent independent of the choice of target material and ion species. Studying near-threshold behavior was the key to making fundamental advances in the theory of phase transitions, and the same is proving to be true for ion-induced pattern formation. Finally, and most importantly, almost perfectly ordered ripple patterns are in certain circumstances predicted to form close to threshold. The second central strategy of the project is to exploit the power of real-time x-ray scattering. The extreme sensitivity of grazing-incidence small-angle x-ray scattering to surface disturbances makes it an ideal method to study the near-threshold behavior of the nanopatterns and to rigorously test the theory. Moreover, the research team is taking advantage of the increasing coherent x-ray flux available at new and upgraded synchrotron sources to develop coherent x-ray scattering as a powerful new approach to investigating surface dynamics at the nanoscale. Coherent scattering gives entirely new insight, going beyond study of the average surface evolution to measure the time-dependent fluctuations of the microstructure around the average kinetics, enabling novel tests of the detailed theoretical predictions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

当平坦的固体表面被宽离子束轰炸时，图案可能会自发出现，包括波长短于人毛宽度的十分之一的表面涟漪。如果形成的模式并不总是总是无序的，那么这种引人入胜的自组织可能会成为一种广泛使用的结构方法，其特征大小太小而无法通过传统技术产生。因此，这项协作理论和实验研究的一个核心目标是开发和完善通过离子轰击产生高度有序的表面波纹的方法。这种表面模式可以用于多种应用中，包括必须操纵或分析极端紫外线的应用。该项目涉及毕业生，本科和高中生，这些学生正在一个桥接基础研究和应用的领域工作。除了经验并为当前材料研究中的一个重要主题做出贡献外，学生还学习使用广泛的理论，模拟和材料表征工具，可以很好地转化为行业或学术界的未来职业。除了与他们的家庭机构的材料研究社区合作外，该项目还通过参与国家X射线散射设施的令人兴奋的多学科环境来为学生提供更广泛的看法。这项合作汇集了两个单独的精神分裂和实验性的主要研究人员，这些研究人员对IION BEAM NANOPERTIEN的领域构成了一小组的实现，这是一个既定的，这是一个实现了一小组的领域，以实现这一目标。正在采用两种关键策略，以旨在以特殊程度的秩序产生表面波纹。这些策略也导致了我们对离子轰炸过程中发生的基本过程的理解前进的重要步骤。第一个策略是研究随着离子发射率或样品温度的角度而发生的模式形成的开始，通过阈值变化。在三种不同的制度中正在研究接近阈值的行为：1）溅射很重要的较高能量制度； 2）溅射可以忽略不计的低能状态，这是该领域的很大程度上未开发的前沿； 3）表面保持晶体的高温状态，从而为电子/光子应用提供了更好的材料。运动方程在这些过渡附近变得更加简单，并且可以严格得出。此外，它具有高度的普遍性，即在很大程度上与目标物质和离子物种的选择无关。研究接近阈值的行为是在相变理论中取得基本进步的关键，事实证明，这一过程对于离子诱导的模式形成也是如此。最后，最重要的是，在某些情况下，几乎完美有序的波纹模式被预测形成接近阈值。该项目的第二个核心策略是利用实时X射线散射的力量。放牧的小角度X射线散射对表面干扰的极端敏感性使其成为研究纳米模式的近阈值行为并严格检验该理论的理想方法。此外，研究团队正在利用新的和升级的同步加速器来源可用的相干X射线通量，以开发连贯的X射线散射，这是一种在纳米级调查表面动力学的有力新方法。一致的散射提供了全新的见解，超越了对平均表面演变的研究，以衡量微观结构围绕平均动力学的时间依赖性波动，从而实现了对详细理论预测的新颖测试。这奖反映了NSF的立法使命，并认为通过基金会的智力综述和广泛的评论，它值得通过评估来进行评估。

项目成果

In situ GISAXS observation of ion-induced nanoscale pattern formation on crystalline Ge(001) in the reverse epitaxy regime

反向外延体系中离子诱导的晶体 Ge(001) 纳米级图案形成的原位 GISAXS 观察

• DOI: 10.1103/physrevb.104.235434
• 发表时间: 2021
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Erb, Denise J.;Myint, Peco;Evans-Lutterodt, Kenneth;Ludwig, Karl;Facsko, Stefan
• 通讯作者: Facsko, Stefan