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

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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.