| Description |
The main objective of this dissertation is to contribute to the understanding of nanomechanics in bilayer Si/Ge thin films and graphene. A set of multiscale modeling and simulations, using finite element analysis (FEA), material point method (MPM) and molecular dynamics (MD) method, have been performed to investigate structural, mechanical and growth properties of several different classes of low-dimensional nanostructures. By using FEA, we find that epitaxially grown Ge quantum dots on both sides of a Si nanoribbon adopt an anticorrelated configuration, in agreement with experiment. In addition, the Ge dots, acting as nanostressors, create a periodic strain field in the Si nanoribbon, which leads to the formation of a new class of single-element strain superlattice as predicted by first-principles electronic structure calculations performed by my collaborators. Also using FEA, we have investigated the morphological instability of strained thin film grown on curved substrates, revealing the physical origin of an antiphase morphology. Another accomplishment presented in this dissertation is the understanding of experimentally observed wiggling phenomenon in SiGe nanoribbons released on an SOI substrate. We build a continuum mechanics model to describe the buckling of the strained SiGe nanoribbon and its interaction with the substrate. Our theoretical model provides new insights to understanding the existing experimental results as well as useful guidance for future experiments, with broad implications in the fabrication of stretchable electronics by strain induced self-assembly. We also utilized solid mechanics analyses and MD simulations to study the maximum asymmetry in strain induced mechanical instability in graphene, a two-dimensional (2D) crystal with the thinnest possible thickness of only one atomic layer. The continuum mechanics theory shows perfect agreement with the atomistic MD simulation, even down to the scale of a few nanometers. |
