Abstract
The development of molecular-based electronic devices is highly dependent on the knowledge of the interaction between molecules and solid surfaces. Naphthalene adsorption on graphene, as a model of interface system, is investigated by using first principles calculations based on the van der Waals density functional method. At low coverage, naphthalene tends to be parallel to the surface, while at higher coverage, i.e. one molecule per (2√3×2√3) R30° unit cell of graphene (as shown in figure), the molecule becomes slightly tilted, in good agreement with experimental results. The tilted configuration resulting from the balance between intermolecular interaction and naphthalene-graphene interaction. We next investigate the unoccupied states of the tilted naphthalene on graphene and focus on the image potential states (IPSs) as observed experimentally on the naphthalene-graphite interface. The lowest graphene IPS (LGIPS) is hybridized with unoccupied states of the naphthalene layer. We find that IPS-like state also exist in naphthalene layer, naphthalene IPSs (NIPSs). This is interesting because IPS usually appears in solid surfaces. The NIPS then hybridize with the LGIPS forming the new IPS states. Unlike the effective mass of LGIPS, which is isotropic, the effective mass of the new IPS is anisotropic. This is essentially due to the geometry of the naphthalene layer with large vacancies.
