UBC Theses and Dissertations
Graphenylene nanotubes : structure, electronic properties and potential applications Koch, Andrew Thomas
The electronic properties of a new type of carbon nanotube, based on the graphenylene motif, are investigated using density functional and tight-binding methods. Analogous to conventional graphene-based carbon nanotubes, a two-dimensional graphenylene sheet can be “rolled” into a seamless cylinder in armchair, zigzag, or chiral orientations. The resulting nanotube can be described using the familiar (n,m) nomenclature and possesses four-, six-, and twelve-membered rings. Density functional theory-based geometry relaxations predict that graphenylene nanotubes, like their two-dimensional counterpart, exhibit three distinct bond lengths between carbon atoms, indicating a non-uniform electron distribution. The dodecagonal rings form pores, 3.3 Å in diameter in the two-dimensional case, which become saddle-shaped paraboloids in smaller-diameter graphenylene nanotubes. Electronic structure calculations in density functional theory predict zigzag graphenylene nanotubes to be small-band-gap semiconductors, with a generally decreasing band gap as the diameter increases. Interestingly, the calculations predict metallic characteristics for armchair graphenylene nanotubes with small diameters (< 2 nm), and semiconducting characteristics with a small band gap for armchair graphenylene nanotubes with larger diameters. Similar to conventional carbon nanotubes, graphenylene nanotubes with indices mod(n-m,3)=0 exhibit a band gap approximately equal to that of armchair graphenylene nanotubes with comparable diameters.
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