Amir Farajian (Committee Chair), Sharmila Mukhopadhyay (Committee Member), Raghavan Srinivasan (Committee Member), Daniel Young (Committee Member)
Master of Science in Engineering (MSEgr)
Graphene nanoribbons are among the recently discovered carbon nanostructures, with unique characteristics for novel applications. One of the most important features of graphene nanoribbons, from both basic science and application points of view, is their electrical conductivity. In this research, we study the electrical conductance of single and double layer nanoribbons of specified widths and edge geometries. The calculations are carried out using ab initio quantum mechanical simulations for obtaining the optimized atomic configurations of the nanoribbons and their electronic structures. These results are then used to calculate the conductance characteristics via Green's function approach to the Landauer's formalism. We calculate the density of states and the zero-bias quantum conductance of single- and bi-layer systems, and investigate the modulation effects in bilayer conduction.
Our calculations show that for single-layer graphene nanoribbon with a width of 10 , the one with armchair edge is semiconducting with a band gap of 0.22 eV whereas the one with zigzag edge is metallic. These are in excellent agreement with other works. For bilayer nanoribbons with armchair edge, two different stacking configurations (AA and AB) are considered. The AB-stacked one is semiconducting with a band gap of 0.02 eV whereas the AA-stacked one is metallic. Bilayer zigzag nanoribbons with AA stacking are found to be metallic. Our results show, in agreement with previous studies, that the band gap of a single-layer armchair graphene nanoribbon is reduced when another layer is stacked on top of it. The conductance characteristics of bilayer armchair and zigzag nanoribbons are shown to be different from those obtained by superimposing single-layer characteristics. In particular, the conductance characteristics strongly depend on stacking order (AA or AB). These interesting modulation effects are shown to arise from inter-layer interactions between electronic states. We discuss possible applications of these results in characterization of and device design based on graphene nanoribbons.
Department or Program
Department of Mechanical and Materials Engineering
Year Degree Awarded
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