Tuning the van der Waals Interaction of Graphene with Molecules via Doping

Abstract

We use scanning tunneling microscopy to visualize and thermal desorption spectroscopy to quantitatively measure that the binding of naphthalene molecules to graphene (Gr), a case of pure van der Waals (vdW) interaction, strengthens with n-and weakens with p-doping of Gr. Density functional theory calculations that include the vdW interaction in a seamless, ab initio way accurately reproduce the observed trend in binding energies. Based on a model calculation, we propose that the vdW interaction is modified by changing the spatial extent of Gr's π orbitals via doping.One of the key properties of graphene (Gr) is the wide-range tunability of its Fermi level and corresponding charge carrier concentration, either by a gate electrode [1], substitutional doping [2], adsorption [3, 4], or charge transfer from a supporting material or intercalation layer [5][6][7][8]. The tunability of the Fermi level through the otherwise rigid band structure results from the material being atomically thin and having a negligible density of states near the Dirac point.In recent years, interest has arisen in using this tunability to control adsorption: For the case of ionic adsorbates, Brar et al. [9] demonstrated a dependence of the ionization state of a Co adatom on the Gr Fermi level position, and Schumacher et al.[10] found a doping-dependent binding energy E b of ionic adsorbates to Gr, with a shift in E b on the order of the shift in the Fermi level induced by doping. For the case of radicals and based on ab initio calculations, Wehling et al.[11] predict dopingdependent adsorbate phase transitions for hydrogenated as well as fluorinated Gr, while Huang et al. [12] find a stronger binding of isolated H radicals for larger magnitudes of doping.For the case of van der Waals (vdW) interaction, the effect of the Gr doping level on the binding energy of adsorbates has not yet been explored. This is surprising, given that the adsorption of simple hydrocarbons to graphite or Gr has been used as a model system to study vdW interactions [13][14][15][16]. Here, we investigate this case with the help of epitaxial Gr on Ir(111), which can be doped from the backside by intercalation of highly electropositive (e. g. Cs, Eu) or -negative (e.g. O) elements into its interface with the substrate, while Gr's other side remains available for the adsorption experiment itself. This strategy not only enables us to achieve large Fermi level shifts on the order of ±1 eV, but also to visualize doping-induced binding energy differences by making using of intercalation patterns [10]. Naphthalene is chosen as a test molecule, since its binding to Gr is a pure vdW case studied previously, both experimentally [14] and theoretically [13]. Our experiments are complemented by density functional theory (DFT) calculations that include the vdW interaction in a seamless, ab initio way (for a recent review, see Ref.[17]).For this paradigmatic case we find in excellent agreement of experiment and theory an increase of the vdW binding energy when changing from p-to n-d...

Hybrid image potential states in molecular overlayers on graphene

“…• , i.e., naphthalene tends to be parallel to graphene at low coverage, which is consistent with the assumption adopted in the previous calculations with large unit cells [33,39]. On the other hand, the dispersion force between the molecules works attractively for the (2 √…”

Self-consistent van der Waals density functional study of benzene adsorption on Si(100)

“…However vdW-DF2 also tends to overestimate separations, since the F x of the Perdew-Wang exchange with refit parameters (PW86R) 56 adopted in vdW-DF2 steeply rises except for sufficiently small s. The overestimation has been avoided in the revised vdW-DF2 (rev-vdW-DF2), 47 where the PW86R exchange is replace by the Becke exchange (B86b) 58 with revised parameters (B86R). Recently, rev-vdW-DF2 has been successfully applied to various adsorption systems [60][61][62][63][64] as well as rare gas and small molecules. 65 In the present paper, we use vdW-DF1, vdW-DF2, opt-vdW-DFs (optPBEvdW, 42 optB88-vdW 42 and optB86b-vdW 43 ) and rev-vdW-DF2 to discuss how the difference among the vdW-DFs influences the relative stability of the adsorption structures of benzene on Si(100).…”

Intercalation of O2 and N2 in the Graphene/Ni Interfaces of Different Morphologies

“…The same is true if N 1s spectra are considered -the binding energy of this line is 405.1 ± 0.1 eV and 405.3 ± 0.1 eV for gr/Ir(111) and gr/Ni(111), respectively, that is characterised for N 2 molecules [51]. (The slight difference in the binding energy for the N 1s line can be assigned to the different interaction strength at the respective gr-metal interface that can change the graphene-adsorbate interaction [52].) Moreover, this N 1s line disappear after gas is fully pumped from the UHV chamber, again supporting our conclusion on the absence of the nitrogen intercalation in the studied gr-metal interfaces.…”