▎ 摘　　要

We report numeric and analytic calculations of the electrostatic properties for armchair carbon nanotube-graphene junctions. Using a semi-empirical method we first demonstrate that the equilibrium distance between a carbon nanotube and a graphene sheet varies with respect to the diameter of the carbon nanotube. We find significantly reduced values compared to AB-stacked graphene sheets in graphite, while even smaller value is found for a fullerene C-60 implying a dimensionality dependence of the equilibrium distance between graphene and the other sp(2) carbon allotropes. Then, we use conformal mapping and a charge-dipole model to study the charge distribution of the carbon nanotube-graphene junctions in various configurations. We observe that the charges are accumulated/depleted at and near the vicinity of the junctions and that capped carbon nanotubes induce a significantly smaller charge concentration at their ends than the open-end nanotubes. We demonstrate that the carbon nanotube influence on the graphene sheet is limited to only few atomic rows. Such an influence strongly depends on the distance between carbon nanotube and the graphene sheet and scales with the carbon nanotube radius, while the potential difference does not modify the length over which the charge concentration is disturbed by the presence of the tube. By studying the potential landscape of carbon nanotube-graphene junctions, our work could be used as a starting point to model the charge carrier injection in these unconventional systems.