Jeremiah N. Mpagazehe

Probing the elastic response of microalga Scenedesmus dimorphus in dry and aqueous environments through atomic force microscopy

With the re-emergence of microalgae as a replacement feedstock for petroleum-derived oils, researchers are working to understand its chemical and mechanical behavior. In this work, the mechanical properties of microalgae, Scenedesmus dimorphus, were investigated at the subcellular level to determine the elastic response of cells that were in an aqueous and dried state using nano-scale indentation through atomic force microscopy. The elastic modulus of single-celled S. dimorphus cells increased over tenfold from an aqueous state to a dried state, which allows us to better understand the biophysical response of microalgae to stress.

A three-dimensional transient model to predict interfacial phenomena during chemical mechanical polishing using computational fluid dynamics:

Interfacial phenomena between the wafer and the polishing pad during chemical mechanical polishing are an area of great interest as they affect post-chemical mechanical polishing wafer topographies. Traditionally, the Reynolds equation has been used to predict the fluid pressure between the wafer and the polishing pad. However, with computational fluid dynamics it is possible to predict the fluid pressure and obtain insight into the fluid motion at the leading edge and trailing edge of the wafer. Additionally, computational fluid dynamics allows for the added ability to increase the resolution of the fluid physics to the asperity scale. In this study, a model is developed to predict phenomena related to mixed lubrication chemical mechanical polishing using computational fluid dynamics. Contact mechanics between the wafer and the pad are resolved through a Winkler elastic foundation formulation. The wafer is mounted on a ball joint which allows free rotation to occur. Friction between the wafer and the polishing pad causes the wafer to assume a position which produces a sub-ambient pressure distribution similar to that obtained from experiments. The effects of different table speeds on the interfacial fluid pressure, as predicted by the computational fluid dynamics are presented.

Particle Tribology: Granular, Slurry, and Powder Tribosystems

The purpose of this chapter is to give the reader a basic understanding of particles in sliding contact. First, we will describe granular flows (the flow of inelastic particles that transfer momentum primarily through collisions) from a tribology perspective, including modeling and experiments that have been conducted inside and outside of the tribology community. Second, slurry flow (particles in gas or liquids) tribosystems will be discussed including models and experiments related to the flow of particles in fluids. And finally, we conclude with a section on powder lubrication (soft particles which coalesce under load and coat surface asperities), where thick and thin film powder lubrication is discussed along with select modeling and experimental approaches.

Understanding the Mechanical Properties of Microalgae Using Atomic Force Microscopy

From consumer productions to energy production, algae is used in many industrial processes. Understanding the mechanical behavior of algae is important to optimize these processes. To obtain a better understanding of algae cell response, we mechanically characterized single, dried Scenedesmus dimorphus cells. To accomplish this, we used atomic force microscopy (AFM) to image S. dimorphus cells, which enabled us to map the AFM measurements to a location on the individual cells. We were then able to perform force measurements on the AFM to determine the Young’s modulus of S. dimorphus. These findings enable a more detailed understanding of the mechanical properties of a single S. dimorphus cell, which may be useful in many applications.Copyright

A Fluid-Structure Interaction Modeling Approach of Lubricated Bearing-Type Sliding Contacts

In many tribological applications, such as journal bearings and gears, a fluid film is used to accommodate velocity between moving surfaces. To model the behavior of this film and to predict its ability to carry load, the Reynolds equation is predominantly employed. As computational processing power continues to increase, computational fluid dynamics (CFD) is increasingly being employed to predict the fluid behavior in lubrication environments. Using CFD is advantageous in that it can provide a more general approximation to the Navier-Stokes equations than the Reynolds equation. Moreover, using CFD allows for the simulation of multiphase flows as could occur during bearing contamination and bearing exit conditions. Because the bearing surfaces move relative to each other as they obtain equilibrium with the fluid pressure, there is a need to incorporate the moving boundary into the CFD calculation, which is a non-trivial task. In this work, a fluid-structure interaction (FSI) technique is explored as an approach to model the dynamic coupling between the moving bearing surfaces and the lubricant. The benefits of using an FSI approach are discussed and the results of its implementation in a lubricated sliding contact model are presented.Copyright

A Multi-Physics Computational Framework to Predict Dishing and Erosion in Patterned Wafers

The prediction of dishing and erosion caused by CMP is desired as they adversely affect the electrical properties of interconnects in integrated circuits. For a model to properly capture these phenomena, it must account for the time dependent surface evolution in CMP. This work employs the previously introduced Particle-Augmented Mixed Lubrication (PAML) model to predict dishing and erosion in CMP. By using PAML to model the polishing of a patterned wafer, it is possible to predict the dishing and erosion experienced during CMP.Copyright