By combining ion beam experiments and atomistic simulations we study the production of defects in graphene on Ir(111) under grazing incidence of low energy Xe ions. We demonstrate that the ions are channeled in between graphene and the substrate, giving rise to chains of vacancy clusters with their edges bending down toward the substrate. These clusters self-organize to a graphene nanomesh via thermally activated diffusion as their formation energy varies within the graphene moiré supercell.

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...

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We study the structure and stability of the first water layer on Pt(111) by variable-temperature scanning tunneling microscopy. We find that a high Pt step edge density considerably increases the long-range order of the equilibrium √37 × √37R25.3°- and √39 × √39R16.1°-superstructures, presumably due to the capability of step edges to trap residual adsorbates from the surface. Passivating the step edges with CO or preparing a flat metal surface leads to the formation of disordered structures, which still show the same structural elements as the ordered ones. Coadsorption of Xe and CO proves that the water layer covers the metal surface completely. Moreover, we determine the two-dimensional crystal structure of Xe on top of the chemisorbed water layer which exhibits an Xe-Xe distance close to the one in bulk Xe and a rotation angle of 90° between the close-packed directions of Xe and the close-packed directions of the underlying water layer. CO is shown to replace H(2)O on the Pt(111) surface as has been deduced previously. In addition, we demonstrate that tunneling of electrons into the antibonding state or from the bonding state of H(2)O leads to dissociation of the molecules and a corresponding reordering of the adlayer into a √3 × √3R30°-structure. Finally, a so far not understood restructuring of the adlayer by an increased tunneling current has been observed.

Scanning tunneling microscopy (STM) and thermal desorption spectroscopy (TDS) show that deposition of water molecules onto epitaxial graphene on Ir(111) leads to the formation of an extended and well ordered array of amorphous water clusters. We trace the evolution of this cluster phase as dependent on water exposure and deposition temperature. The formation of separated clusters is due to binding energy differences within the moiré superstructure.