Mechanical Loss Mechanisms in c-axis Gallium Nitride Nanowires

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

The key goal of the proposed research is to experimentally measure quality (Q)-factors for c-axis oriented Gallium Nitride (GaN) nanowires (NWs) over a large ensemble of NW dimensions, while simultaneously developing novel multiscale, coupled physics computational models to quantify the dominant loss mechanisms. A particular emphasis will be placed on understanding size and surface effects on the relative importance of the individual loss mechanisms across a technologically relevant range of length scales. Experimentally, this will be achieved by providing, for the first time, a comprehensive body of experimental data on mechanical resonance position and resonance linewidth for a large ensemble of c-axis GaN NWs, and over a wide range of NW lengths (1 to 20 microns), diameters (10 to 100 nm), vibrational frequencies (100 kHz to 100 MHz), and temperature (4 K to 400 K). Novel multiscale modeling approaches, including the surface Cauchy-Born model and coupled nanoscale energy and momentum equations that capture, for the first time, surface stress effects on both the thermal and mechanical fields, will be developed to simulate and quantitatively predict Q-factor degradation due to intrinsic surface losses and thermoelastic damping of NWs. If successful, this research will make original contributions in the understanding of how surfaces are implicated in the mechanical losses of GaN NWs. It will additionally elucidate the fundamental mechanisms governing size, and temperature effects on energy dissipation in GaN NWs, while delineating the length scales at which each loss mechanism dominates. This project will further quantify, for the first time, the errors introduced in NW modeling if standard bulk continuum models that neglect surface effects are scaled down to the nanoscale. The project further focuses on the involvement of under-represented minorities in the nanoengineering research and education process. It will leverage the training of future nanoengineers in both nanoscale modeling and experiment by the integration of the proposed research into the curriculum. Results and insights will be broadly distributed through professional and physics educational websites.