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Doctor of Philosophy (PhD)
Year Degree Awarded
Month Degree Awarded
Properly controlled applied fields can stabilize planar surface morphology, reduce surface roughness, and drive the formation of intriguing nanoscale morphological features, providing a path toward precise nanopatterning for the development of electronic and photonic materials with optimal functionality.
To study the surface morphological evolution of stressed crystalline solids and thin films, we have established a continuum model accounting for stresses, electric fields, temperature gradients, surface energy, wetting potential, and surface diffusional anisotropy. Based on linear stability analysis and self-consistent dynamical simulations, we found that long-wavelength plane-wave perturbations to a planar surface of a uniaxially stressed solid can trigger a nonlinear tip-splitting instability, while sufficiently strong and well controlled electric fields and thermal gradients can alone or synergistically stabilize the planar surface morphology. We established the electrical stressing as a viable physical approach for the surface roughness reduction in conducting thin films. We found that burying quantum dot (QD) arrays in substrate can be used to engineer the surface initial morphological perturbation of the substrate, leading to the formation of designed quantum dot molecules (QDM). We also found that thermal annealing of epitaxial QDs can induce extra thermal mismatch stress, leading to the further evolution of QDs to nanorings, or multiple concentric nanorings, which will eventually evolve into QDs.
Moreover, we have conducted a systematic analysis of pore-edge interactions in graphene nanoribbons (GNRs) using first-principles density functional theory (DFT) calculations and molecular-statics (MS) and molecular-dynamics (MD) computations based on reliable interatomic potentials. We formulated the strongly attractive interactions for nanopores in the vicinity of GNR edges, which can drive the nanopore to migrate toward and coalesce with the GNR edge. The post-coalescence morphological evolution of an armchair GNR edge leads to the formation of a V-shaped edge pattern consisting of zigzag linear segments (facets). DFT calculations show that the zigzag segments forming at the armchair edges can be used to tune the bandgap of the GNR. The bandgap of the patterned GNRs exhibits a linear dependence on the density of the zigzag edge atoms, which is controlled by the size and concentration of the pores introduced in the defect-engineered GNR.
Du, Lin, "Driven Morphological Evolution of Crystal Surfaces, Epitaxial Thin Films, and Two-Dimensional Materials: Morphological Stability and Pattern Formation" (2018). Doctoral Dissertations. 1162.
Available for download on Friday, February 01, 2019