Dirac point resonances due to atoms and molecules adsorbed on graphene and transport gaps and conductance quantization in graphene nanoribbons with covalently bonded adsorbates

摘要

We present a tight binding theory of the Dirac point resonances due toadsorbed atoms and molecules on an infinite 2D graphene sheet based on thestandard tight binding model of the graphene p-band electronic structure andthe extended Huckel model of the adsorbate and nearby graphene carbon atoms.The relaxed atomic geometries of the adsorbates and graphene are calculatedusing density functional theory. Our model includes the effects of the localrehybridization of the graphene from the sp^2 to sp^3 electronic structure thatoccurs when adsorbed atoms or molecules bond covalently to the graphene. Unlikein previous tight-binding models of Dirac point resonances, adsorbed specieswith multiple extended molecular orbitals and bonding to more than one graphenecarbon atom are treated. More accurate and more general analytic expressionsfor the Green's function matrix elements that enter the T-matrix theory ofDirac point resonances than have been available previously are obtained. Westudy H, F, OH and O adsorbates on graphene and for each we find a strongscattering resonance (two resonances for O) near the Dirac point of graphene,by far the strongest and closest to the Dirac point being the resonance for H.We extract a minimal set of tight binding parameters that can be used to modelresonant electron scattering and electron transport in graphene and graphenenanostructures with adsorbed H, F, OH and O accurately and efficiently. We alsocompare our results for the properties of Dirac point resonances due toadsorbates on graphene with those obtained by others using density functionaltheory-based electronic structure calculations, and discuss their relativemerits. We then present calculations of electronic quantum transport ingraphene nanoribbons with these adsorbed species...