CAREER: A Research and Education Program for Studying Particulate-based Tribosystems in Nanotechnology

围绕纳米技术出现的兴奋很大程度上归因于对表面在地形尺度及以下相对运动行为的阐明。从宏观尺度到纳米尺度理解摩擦表面的摩擦、润滑和磨损的摩擦学研究具有重要的科学和工业意义。此外，当真实载荷下的表面相互摩擦时，在充满流体(即空气或液体)的界面上经常会存在磨屑或外来颗粒。这种被称为颗粒增强混合润滑(PAML)的问题是非常动态的，因此很难预测；然而，当颗粒尺寸为纳米或亚微米时，它对纳米技术的进步具有重要的技术意义。随着计算能力的爆炸性增长，通过模拟在不同长度和时间尺度上演变的动态过程，可以很快用多物理方法完全模拟复杂的基于颗粒的摩擦系统，而不会简化问题的范围，如润滑近似和全局应用的磨损率关系。因此，这项工作建议建立一个研究和教育计划，使用多物理建模方法来研究基于PAML的摩擦系统，包括实验验证、基于研究的教育和外部活动。该研究计划的智力优势是将一个通用的、多物理的数值粒子增强混合润滑模型与一个教育计划结合起来，该教育计划将为学生提供将基本摩擦学概念应用于纳米技术前沿问题的经验。由于现有的PAML三重系统模型通常基于单一甚至双重的数学物理描述，它们无法捕获在几个长度和时间尺度上发生的相关PAML现象。例如，化学机械抛光(CMP)是一种基于PAML的工艺，在旋转晶片上沉积薄膜，当其被压在旋转衬垫上时被抛光；衬垫中充斥着含有纳米颗粒的化学反应浆料。这个复杂的基于PAML的问题是纳米器件制造过程中最关键的步骤之一。与大多数PAML过程一样，预测其行为的尝试一直不够充分，因为它们无法捕捉到发生在几个空间尺度上的所有相关物理现象。因此，该研究为PAML系统提供了一种突破性的建模方法，并将以化学机械抛光作为实验试验台进行验证。拟议的研究方法包括三个相互重叠和相关的阶段：(一)建模，(二)验证实验和定性，以及(三)以研究为基础的教育和推广。在第一阶段，将建立一个多物理粒子增强混合润滑数值模型。在第二阶段，将进行纳米表征和化学机械抛光实验，以验证颗粒增强混合润滑模型。在第三阶段，将开发一个采用PAML建模方法的粒子相关摩擦学仿真工具，以培训学生理解复杂摩擦学系统的建模。拟议工作的更广泛影响是，PAML建模框架将在理解与磨损相关的基于粒子的摩擦学方面取得根本性突破。这将推动一系列技术的进步，例如(I)集成电路(IC)和数据存储纳米技术，(Ii)完全关节置换，(Iii)纳米颗粒/流体润滑，(Iv)煤流能源系统，(V)牙齿摩擦学，以及(Vi)在流体环境中遇到颗粒的其他技术。拟议的研究型教育计划还将通过教授学生使用基础摩擦学模型作为更大、更复杂的多物理摩擦学问题的组成部分，对摩擦学社区产生广泛影响。学生将有机会参加一门强化的摩擦学课程，该课程具有战略性协调的作业，旨在教授(1)基本摩擦学问题解决技能，与(2)教育多物理摩擦学模拟工具有关，其中模型可通过实验室实验进行验证。最后，职业研究成果将作为大学前研讨会的材料，旨在增加寻求科学、技术、工程和数学职业的少数族裔学生的数量。

Much of the excitement surrounding the advent of nanotechnology is due to the elucidation of the behavior of surfaces in relative motion at the topography-scale and below. Understanding the tribology study of friction, lubrication, and wear of the rubbing surfaces from the macro-scale to the nanoscale is of great scientific and industrial relevance. Additionally, when real surfaces under load rub together, wear debris or foreign particles often exist in the fluid (i.e., air or liquid) filled interface. This problem known as "particle-Augmented Mixed Lubrication" (PAML) is very dynamic and hence difficult to predict; yet, it is of great technical importance to the advancement of nanotechnology when the particles are nano-sized or sub-micron. With the explosive growth in computational power, complex particulate-based tribosystems can soon be completely modeled with multi-physics approaches by simulating dynamic processes that evolve over varying length and time scales without simplifying the scope of the problem such as lubrication approximations and globally applied wear rate relations. Consequently, this effort proposes to build a research and education program to study PAML-based tribosystems using a multiphysics modeling approach, with experimental validation, research-based education, and outreach.The intellectual merit of this research program is that a generalized, multi-physics numerical particle augmented mixed lubrication model will be developed in conjunction with a educational program that gives students experience in applying fundamental tribology concepts to a cutting-edge problems in nanotechnology. Because existing models of PAML tribosystems are typically based on single or even dual mathematical physics descriptions, they are unable to capture the relevant PAML phenomena that occur over several length and time scales. For example, chemical mechanical polishing (CMP) is a PAML-based process where a rotating wafer, deposited with thin films, is polished as it is pressed against a rotating pad; the pad is flooded with a chemically reactive slurry with nanoparticles in it. This complex PAML-based problem is one of the most critical steps in the fabrication of nano-enabled devices. As with most PAML processes, attempts to predict its behavior have been inadequate in that they were unable to capture all the relevant physics phenomena occurring over several space scales. Therefore, the proposed research offers a breakthrough modeling approach for PAML systems that will be validated by using chemical mechanical polishing as the experimental test-bed. The proposed research approach consists of three overlapping and related phases: (i) modeling, (ii) validation experiments and characterization, and (iii) research-based education and outreach. In phase I, a numerical multi-physics particle augmented mixed lubrication model will be developed. In phase II, nano-characterization and CMP experiments will be conducted to validate the particle augmented mixed lubrication model. In phase III, a particleassociated tribology simulation tool that employs the PAML modeling approach, will be developed to train students to understand modeling of complex tribological systems.The broader impacts of the proposed work are that the PAML modeling framework will yield fundamental breakthroughs in understanding wear associated particle-based tribology. This will enable advancements in a wide range of technologies such as (i) integrated circuit (IC) and data storage nanotechnology, (ii) total joint replacement, (iii) nanoparticulate/fluid lubrication, (iv) coal flow energy systems, (v) dental tribology, and (vi) other technologies that encounters particles in fluidic environments. The proposed research-based education plan will also broadly impact the tribology community by teaching students to use fundamental tribology models as components to a larger more complex multiphysics tribology problem. Students will have the opportunity to participate in an enhanced tribology course with strategically coordinated assignments designed to teach (1) fundamental tribology problemsolving skills, related to (2) an educational multi-physics tribology simulation tool, where models can be (3) validated by laboratory experiments. Finally, the CAREER research results will be used as materials in pre-college workshops which aim to increase the number of minority students pursuing careers in science, technology, engineering, and mathematics.