Amir Farajian (Advisor), Khalid Lafdi (Committee Member), Sharmila Mukhopadhyay (Committee Member), Ajit Roy (Committee Member), H. Daniel Young (Committee Member)
Doctor of Philosophy (PhD)
Novel silicene-based nanomaterials are designed and characterized by first principle computer simulations to assess the effects of adsorptions and defects on stability, electronic, and thermal properties. To explore quantum thermal transport in nanostructures a general purpose code based on Green's function formalism is developed.
Specifically, we explore the energetics, temperature dependent dynamics, phonon frequencies, and electronic structure associated with lithium chemisorption on silicene. Our results predict the stability of completely lithiated silicene sheets (silicel) in which lithium atoms adsorb on the atom-down sites on both sides of the silicene sheet. Upon complete lithiation, the band structure of silicene is transformed from a zero-gap semiconductor to a 0.368 eV bandgap semiconductor. This new, uniquely stable, two-atom-thick, semiconductor material could be of interest for nanoscale electronic devices.
We further explore the electronic tunability of silicene through molecular adsorption of CO, CO2, O2, N2, and H2O on nanoribbons for potential gas sensor applications. We find that quantum conduction is detectibly modified by weak chemisorption of a single CO molecule on a pristine silicene nanoribbon. Moderate binding energies provide an optimal mix of high detectability and recoverability. With Ag contacts attached to a ~ 1 nm silicene nanoribbon, the interface states mask the conductance modulations caused by CO adsorption, emphasizing length effects for sensor applications. The effects of atmospheric gases: nitrogen, oxygen, carbon dioxide, and water, as well as CO adsorption density and edge-dangling bond defects, on sensor functionality are also investigated. Our results reveal pristine silicene nanoribbons as a promising new sensing material with single molecule resolution.
Next, the thermal conductance of silicene nanoribbons with and without defects is explored by Non-Equilibrium Green's function method as implemented in our ThermTran program that was developed as part of this Ph.D. research. We reveal that the thermal transmission and conductance of pristine silicene ribbons is systematically reduced upon the introduction of hydrogen and silicon vacancy defects. This suggests that defect engineering and/or doping may provide a viable method for tuning the thermal transport of narrow silicene nanoribbons. Our generalized ThermTran program for calculating thermal transport across pristine, defected, contacted, or interfaced, junctions is demonstrated.
Department or Program
Ph.D. in Engineering
Year Degree Awarded
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