Topologically Protected Conduction State at Carbon Foam Surfaces: AnAb initioStudy

Abstract

We report results of ab initio electronic structure and quantum conductance calculations indicating the emergence of conduction at the surface of semiconducting carbon foams. Occurrence of new conduction states is intimately linked to the topology of the surface and not limited to foams of elemental carbon. Our interpretation based on rehybridization theory indicates that conduction in the foam derives from first-and second-neighbor interactions between p orbitals lying in the surface plane, which are related to p ⊥ orbitals of graphene. The topologically protected conducting state occurs on bare and hydrogen-terminated foam surfaces and is thus unrelated to dangling bonds. Our results for carbon foam indicate that the conductance behavior may be further significantly modified by surface patterning. [5,6,8]. Electronic properties of foams [1,[5][6][7] have received much less attention than their structural stability in spite of the obvious possibility to fine-tune the fundamental band gap value in-between zero in sp 2 −bonded graphene and 5.5 eV in sp 3 −bonded diamond by modifying the foam morphology.Here we report results of ab initio electronic structure and quantum conductance calculations indicating the emergence of conduction at the surface of semiconducting carbon foams. Occurrence of new conduction states in these systems is intimately linked to the topology of the surface and not limited to foams of elemental carbon. Our interpretation based on rehybridization theory indicates that conduction in the foam derives from first-and second-neighbor interactions between p orbitals lying in the surface plane, which are related to p ⊥ orbitals of graphene. The topologically protected conducting state occurs on bare and hydrogen-terminated foam surfaces and is thus unrelated to dangling bonds. Our results for carbon foam indicate that the conductance behavior may be further significantly modified by surface patterning.The bulk carbon foam, depicted in Fig. 1(a), is a cellular structure resembling vaguely a fused triangular array of (6,0) zigzag nanotubes. In contrast to a nanotube array, the walls of the foam cells consist of 60% sp 2 bonded atoms shared by two neighboring cells and 40% sp 3 bonded atoms shared by three adjacent cells. Density-functional based tight-binding (DFTB) results indicate that the bulk structure is a semiconductor [6] with a band gap of 2.55 eV.Cleavage normal to the long cell axis may generate two

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