Electronic Transport Properties of Strained Graphene Nanostructures.

Gradinar, Diana Alexandra (2013) Electronic Transport Properties of Strained Graphene Nanostructures. PhD thesis, Lancaster University.

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Abstract

In this thesis we theoretically investigate the influence of mechanical deformations on the electronic transport properties of graphene structures, such as nanoribbons, bilayer graphene, and graphene on hexagonal boron nitrite substrates. We find that homogeneous mechanical deformations can induce the formation of zero-conductance plateaus and conductance resonances in nanoribbons, and outline their robustness in the presence of 'double atom' edge disorders. Furthermore we emphasize that even small percentages of 'single atom' edge defects are strong enough to determine the smearing or even suppression of the observed resonant structure. For the case of inhomogeneous deformations we find that the inhomogeneity developed near the contacts aids the resonant transmission of charge carriers through a mode mixing mechanism or via the sublattice-polarized n = 0 pseudo-magnetic Landau level. We also show that in homogeneously strained bilayer graphene the linear response conductance of an n-p-n junction has a non-monotonic dependence on doping and temperature, which varies in size and form as a function of the crys-tallographic orientation of the principal strain axis. We find that uniaxial strain changes the chirality of the electronic plane-wave states in the vicinity of the Lifshitz transition in the low-energy electron spectrum of this crystal, which results in the observed non-monotonicity of the linear response conductance. Finally, we show that mechanical deformations alter the beating of the lattice mismatch in graphene and hexagonal boron nitride heterostructures, which leads to the formation of strained moire superlattices. We observe that in some cases this determines the opening of minigaps in the second generation mini Dirac cones and finalize our study by identifying an extreme parametric regime where the moire patterns become quasi-1D and the dispersion acquires additional Dirac cones.