The focus of this thesis is on using mechanical strain to tailor the electronic properties
of graphene. The first half covers the electro-mechanical coupling for graphene
in different configurations, namely a hexagonal Y-junction, various shaped bubbles on
different substrates, and with kirigami cuts. For all of these cases, a novel combination
of tight-binding electronic structure calculations and molecular dynamics is utilized
to demonstrate how mechanical loading and deformation impacts the resulting electronic
structure and transport. For the Y-junction, a quasi-uniform pseudo magnetic
field induced by strain restricts transport to Landau-level and edge-state-assisted resonant tunneling. For the bubbles, the shape and the nature of the substrate emerge
as decisive factors determining the effectiveness of the nanoscale pseudo magnetic
field tailoring in graphene. Finally, for the kirigami, it is shown that the yield and
fracture strains of graphene, a well-known brittle material, can be enhanced by a factor
of more than three using the kirigami structure, while also leading to significant
enhancements in the localized pseudo magnetic fields.
The second part of the thesis focuses on dissipation mechanisms in graphene
nanomechanical resonators. Thermalization in nonlinear systems is a central concept
in statistical mechanics and has been extensively studied theoretically since the seminal
work of Fermi, Pasta, and Ulam (FPU). Using molecular dynamics and continuum
modeling of a ring-down setup, it is shown that thermalization due to nonlinear mode
coupling intrinsically limits the quality factor of nanomechanical graphene drums and
turns them into potential test beds for FPU physics. The relationship between thermalization rate, radius, temperature and prestrain is explored and investigated.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/16093 |
| Date | 08 April 2016 |
| Creators | Qi, Zenan |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution-NonCommercial-ShareAlike 4.0 International, http://creativecommons.org/licenses/by-nc-sa/4.0 |
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