MEMS Seminar

"Multi-Scale Simulation of Nanoscale Materials and the Evolving Role of Mechanics", Huck Beng Chew, Assistant Professor, U. of Illinois at Urbana-Champaign, Dept. of Aerospace Engineering
Wednesday, 2 September 2015 - 1:30pm
125 Hudson

The advancement in computational capabilities and increasing accuracy of modeling tools are opening new opportunities to define the role of mechanics in non-traditional, interdisciplinary areas. In this talk, I will highlight two such examples in which multi-scale modeling and simulations have uncovered nanoscale mechanics principles which are guiding the design and development of novel materials with unprecedented properties.

 My first example focuses on the mechanics of deformation in high-capacity lithium ion battery electrodes using silicon-based electrodes, which have order of magnitude higher charge carrying capacity than conventional graphite electrodes. The problem with silicon is that it cracks massively during repeated electrochemical cycles, and eventually delaminates from the current collector. I will discuss our use of multi-scale computational tools, spanning density functional theory, molecular dynamics, and meso-scale finite element simulations, to elucidate the underlying mechanisms of deformation, fracture, and failure of lithiated silicon electrode materials. The uncovered mechanisms have explained a number of intriguing experimental observations, including plasticity of these electrode materials, the cracking patterns in silicon thin film electrodes, and the abrupt capacity fade after a critical number of charge cycles. Understanding these mechanisms and their interrelationship with the atomic structure of the electrode material can provide insights for the design of novel fracture-resistant electrode materials to improve cycle life.

In my second example, I will discuss recent efforts to elucidate the nanomechanics of plasma-graphene interaction and their effects on nanoscale patterning of graphene. Hydrogen-plasma experiments have been shown to narrow graphene only from the edges, or to selectively produce circular or hexagonal holes in the basal plane of graphene, but the underlying plasma-graphene chemistry is unknown. Here, we model the hydrogen-plasma etching of monolayer graphene on SiO2 substrates using scale-bridging molecular dynamics simulations. We uncover distinct etching mechanisms, operative within narrow plasma ion energy windows, which fully explain the differing plasma-graphene reactions observed experimentally. Understanding the complex plasma-graphene chemistry opens up a means for controlled patterning of graphene nanostructures.