Hybrid image potential states in molecular overlayers on graphene

Abstract

The structural and electronic properties of naphthalene adsorbed on graphene are studied from first principles using the van der Waals density functional method. It is shown that naphthalene molecules are stabilized by forming a superstructure with the periodicity of (2 √ 3 × 2 √ 3) and a tilted molecular adsorption geometry on graphene, in good agreement with the scanning tunneling microscopy (STM) experiments on highly oriented pyrolytic graphite. Our results predict that image potential states (IPSs) are induced by intermolecular interaction on the naphthalene overlayer, hybridizing with the IPSs derived from graphene. The resultant hybrid IPSs are characterized by anisotropic effective mass reflecting the molecular structure of naphthalene. By means of STM simulations, we reveal that one of the hybrid IPSs manifests itself as an oval protrusion distinguishable from naphthalene molecular orbitals, which identifies the origin of an experimental STM image previously attributed to the lowest unoccupied molecular orbital of naphthalene.

Screening in Graphene: Response to External Static Electric Field and an Image-Potential Problem

“…Moreover, the information on the image-plane position can be useful for the construction of effective potentials in the systems with more complex geometries like fullerens and nanotubes, where the nearly-free states and the super-atomic orbitals, a subject of intense ongoing research, are inherently linked to IPSs in a flat graphene layer [60][61][62][63][64][65][66][67]. We believe that such a study as ours will not only be restricted to the carbon atoms case, since image-potential states can be realized in many other quasi-2D systems of current interest, like phosphorene, silicene and germanene [68], borophene [69], MXenes [70][71][72], and molecular overlayers on graphene [73].…”

Photoelectron Angular Distribution Induced by Weak Intermolecular Interaction in Highly Ordered Aromatic Molecules

“…Because the HOMO-1 of HBC is distributed over the outer benzene rings in the molecule as shown in Figure d, the HOMO-1 of the HBC molecule can effectively interact with the HOMO-1 of the nearest-neighbor molecules, resulting in the less anisotropy in both E – k ∥ and I – k ∥ relations. Furthermore, the recent theoretical calculations predicted the presence of the lateral π-band dispersion in free-standing monolayers of pentacene and naphthalene with a few tenth meV, which can be enhanced by the hybridization with the substrate band. , …”

“…Furthermore, the recent theoretical calculations predicted the presence of the lateral πband dispersion in free-standing monolayers of pentacene and naphthalene with a few tenth meV, which can be enhanced by the hybridization with the substrate band. 24,42 The other possible origin of the lateral π-band dispersion is the intermolecular interaction with a jellium, based on the homogeneous electron gas model and akin to the substratemediated interaction, under the assumption that the PAH molecules and the surface symmetry of Au(111) are nearly isotropic. In this scenario, the symmetry of the molecular superstructure only exists.…”

Symmetry of Electron Bands in Graphene: (Nearly) Free Electron Versus Tight‐Binding

“…[ 32 ] These bands have long expansion into the vacuum, and are strongly influenced by the image‐potential tail [ 33 ] with even and odd mirror symmetry in the graphene plane. Moreover, they can be easily influenced by applied electric field, [ 34,35 ] adsorbate deposition, [ 36–38 ] or transformed upon variation of the graphene sheet shape. [ 39 ] Notice that the first two unoccupied states are important for, e.g., the description of interlayer states, reactivity, intercalation, [ 40,41 ] and tunneling into graphene, where the inelastic phonon scattering plays a dominant role.…”