States Modulation in Graphene Nanoribbons through Metal Contacts

We are reporting the results of density functional calculations of the electronic structure of finite graphene nanoribbons adsorbed on Au, Pd, and Ti electrodes. While the interaction of nanoribbons with the Au contact is more characteristic of a physisorbed state, the adsorption of Pd and Ti involves much stronger state mixing as in chemisorption. Metal-induced gap states, which can potentially short-circuit the device, are clearly revealed for the first time, allowing us to evaluate their penetration length. The evanescence of MIGS is primarily governed by the band gap of the nanoribbon, and we can estimate an acceptable minimal length for an effective transport channel to a few nanometers. Different impacts of the presence of metal-induced gap states on the properties of graphene nanoribbons are discussed in terms of charge transfer and electrostatics.