| It has been observed that three-dimensional Ge nanocrystals (huts and domes) grown on nanoscale ultrathin silicon-on-insulator substrate (SOI) can induce significant bending of the silicon template layer that is localized in the nanometer scale, a behavior that is distinctively different from that observed when these nanocrystals are grown on bulk Si substrate, i.e., overall inducing extended bending of the substrate. I performed atomistic simulations and continuum mechanics calculations to confirm such a localized bending of the Si template layer and to show that its magnitude approaches the maximum value for a freestanding membrane.; Experiments also showed a counterintuitive bending of a nanoscale thin Si substrate induced by a coherently strained Ge islands, grown on SOI. Larger dome islands, representing a thicker film, induce much less bending of the substrate than smaller hut islands, representing a thinner film, in direct contrast to their behavior on thick Si. I have verified theoretically and computationally this counterintuitive bending of ultrathin substrates induced by coherently strained thin films. The complicated bending behavior can be understood by considering evolution of strain sharing between the film and substrate.; I also performed two-dimensional linear elastic finite element analysis to investigate mechanical stability of ultrathin Ge/Si film grown on or bonded to SiO2, using imperfect interface elements between Si and SiO2 to model Si/SiO2 interfacial slippage. It demonstrates that the overall composite film is stable when only the tangential slippage is allowed, however it becomes unstable when normal slippage is allowed: the coherently strained Ge island induces a large local bending of Si layer, and separates the Si layer from the underlying SiO2 forming a void at the Si/SiO2 interface.; Finally, I demonstrate that the generic design principles of a promising novel nanofabrication technology based on nanomechanical architecture of strained bi-layer thin films. It shows an unparalleled level of versatility in making a variety of nanostructures, such as nanotubes, nanorings, nanodrills, and nanocoils, using combinations of different materials with an unprecedented level of control. |
