Abstract
Among the most fascinating nanostructure morphologies are spirals, hybrids of somewhat obscure topology and dimensionality with technologically attractive properties. Here, we investigate mechanical and electromechanical properties of graphene spirals upon elongation by using density-functional tight-binding, continuum elasticity theory, and classical force field molecular dynamics. It turns out that electronic properties are governed by interlayer interactions as opposed to strain effects. The structural behavior is governed by van der Waals interaction: in its absence spirals unfold with equidistant layer spacings, ripple formation at spiral perimeter, and steadily increasing axial force; in its presence, on the contrary, spirals unfold via smooth local peeling, complex geometries, and nearly constant axial force. These electromechanical trends ought to provide useful guidelines not only for additional theoretical investigations but also for forthcoming experiments on graphene spirals.
Highlights
Nanostructure morphologies, such as cages, tubes, wires, stacks, and ribbons, are often classified according to their dimensionality and topology.[1]
The structural behavior is governed by van der Waals interaction: in its absence spirals unfold with equidistant layer spacings, ripple formation at spiral perimeter, and steadily increasing axial force; in its presence, on the contrary, spirals unfold via smooth local peeling, complex geometries, and nearly constant axial force
The experimental synthesis of such spirals is experimentally feasible, and the theoretically predicted electronic properties suggest that experimental efforts would be worth their while.[9,10]
Summary
Nanostructure morphologies, such as cages, tubes, wires, stacks, and ribbons, are often classified according to their dimensionality and topology.[1]. Spirals are different from helical molecules, such as foldamers, which have very small diameter with only one or two covalent bonds along the azimuthal direction, and which are a familiar research topic in chemistry.[2] A familiar helical molecule made of carbon is helicene, the smallest graphene spiral.[3] Graphene spirals of larger diameter could be synthesized from monomers of appropriate size,[4,5] but succesful synthesis has so far remained elusive Another approach would be to isolate smaller spirals out of graphite screw dislocations, the largest spiral structures that already exist.[6,7,8] Even though experiments are still lacking, graphene spirals of this intermediate few-nanomater diameter would be the most interesting ones. We begin by investigating electronic properties in constrained geometries with van der Waals interaction omitted and end by investigating the mechanical behavior of finite spirals with van der Waals interaction included
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