Fabrication and Characterization of Nanopatterned Epitaxial Graphene Films for Carbon Based Electronics

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Song, Zhimin
de Heer, Walter A.
Meindl, James D.
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In this thesis, we show that planar graphene ribbons have properties similar to those of nanotubes. Both exhibit semiconducting or metallic properties depending on crystal orientation. The band gap varies approximately as the inverse of the ribbon width. Both can be doped and gated. Due to these similarities, the patterned graphene also has nanotube like transport properties, which include coherent transport, ballistic transport, and high current capabilities. In essential contrast to nanotubes, graphene ribbons can be rationally patterned using standard electron beam lithography methods; functional graphene devices could be fabricated eliminating the need for metal interconnects on the wafer. This would remove many obstacles faced by carbon nanotubes, while retaining the benefits of high carrier mobility and quasi-1D transport. We have produced ultrathin epitaxial graphite films on single-crystal silicon carbide by vacuum graphitization, which show remarkable 2D electron gas (2DEG) behavior. The most highly ordered samples exhibit Shubnikov-de Haas oscillations that correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. The transport properties, which are closely related to those of carbon nanotubes, are dominated by the single epitaxial graphene layer at the silicon carbide interface and reveal the Dirac nature of the charge carriers. Patterned structures show quantum confinement of electrons and phase coherence lengths beyond 1 micrometer at 4 kelvin, with mobilities exceeding 2.5 square meters per volt-second. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nanopatterned epitaxial graphene (NPEG) with the potential for large-scale integration. The research created a foundation for graphene science and technology and established a path toward graphene-based nanoelectronics.
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