Thomas Brugger

Graphene on Ru(0001): A 25 x 25 Supercell

The structure of a single layer of graphene on Ru(0001) has be en studied using surface x-ray diffraction. A surprising superstructure has been determined, whereby 2 5×25 graphene unit cells lie on 23 ×23 unit cells of Ru. Each supercell contains 2 × crystallographically inequivalent subcells caused by co rrugation. Strong intensity oscillations in the superstructure rods d emonstrate that the Ru substrate is also significantly corrugated down to several monolayers, and that the bonding between graphene and Ru is strong and cannot be caused by van der Waals bonds. Charge transfer from the Ru s ubstrate to the graphene expands and weakens the C–C bonds, which helps accommodate the in-plane tensile stress. The elucidation of this superstructure provides important information in the pote ntial application of graphene as a template for nanocluster arrays.

Comparison of electronic structure and template function of single-layer graphene and a hexagonal boron nitride nanomesh on Ru(0001)

Thomas Brugger, Sebastian Günther, Bin Wang, Hugo Dil, 4 Marie-Laure Bocquet, 2 Jürg Osterwalder, Joost Wintterlin, and Thomas Greber ∗ Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland Department Chemie, Ludwig-Maximilian Universität, Butenandtstrasse 5-13, D-81377 München, Germany Université de Lyon, Laboratoire de Chimie, École Normale Supérieure de Lyon, CNRS, France Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen, Switzerland (Dated: July 29, 2008)

Graphene on Ru(0001): a corrugated and chiral structure

We present a structural analysis of the graphene/Ru(0001) system obtained by surface x-ray diffraction. The data were fitted using Fourier-series-expanded displacement fields from an ideal bulk structure plus the application of symmetry constraints. The shape of the observed superstructure rods proves a reconstruction of the substrate, induced by strong bonding of graphene to ruthenium. Both the graphene layer and the underlying substrate are corrugated, with peak-to-peak heights of (0.82±0.15) A and (0.19±0.02) A for graphene and the topmost Ru-atomic layer, respectively. The Ru corrugation decays slowly over several monolayers into the bulk. The system also exhibits chirality, whereby in-plane rotations of up to 2.0° in those regions of the superstructure where the graphene is weakly bound are driven by elastic energy minimization.

Nanotexture Switching of Single-Layer Hexagonal Boron Nitride on Rhodium by Intercalation of Hydrogen Atoms†

The interaction of atomic hydrogen with a single layer of hexagonal boron nitride on rhodium leads to a removal of the h-BN surface corrugation. The process is reversible as the hydrogen may be expelled by annealing to about 500 K whereupon the texture on the nanometer scale is restored. This effect is traced back to hydrogen intercalation. It is expected to have implications for applications, like the storage of hydrogen, the peeling of sp2-hybridized layers from solid substrates or the control of the wetting angle, to name a few.Playing nano-tectonics: The interaction of atomic hydrogen with a single layer of hexagonal boron nitride on rhodium leads to the removal of the h-BN surface corrugation (see picture; blue region: corrugated, orange region: flat). This change of surface texture arises from the intercalation of hydrogen atoms between the h-BN skin and the metal, and can be restored by annealing to about 600 K to expel the hydrogen atoms.

Nano-ice on Boron Nitride Nanomesh: Accessing Proton Disorder

Using variable temperature scanning tunneling microscopy and dI/dz barrier height spectroscopy, the structure of water on h-BN/Rh(111) nanomesh has been investigated. Below its desorption temperature, two distinct phases of water self-assemble within the 3.2 nm unit cell of the nanomesh. In the 2 nm holes, an ordered phase of nano-ice crystals with about 40 molecules is found. The ice crystals arrange in a bilayer honeycomb lattice, where the hydrogen atoms of the lower layer point to the substrate. The phase on the 1 nm wires, is a low density gas phase, which is characterized by contrast modulations and streaky noise in the STM images. Tunneling barrier measurements infer the proton positions in the nano-ice clusters. August 6, 2009 †Physik-Institut, Universität Zürich ‡Physikalisch-Chemisches Institut, Universität Zürich 1 ar X iv :0 90 8. 08 75 v1 [ co nd -m at .m tr lsc i] 6 A ug 2 00 9 Haifeng Ma et al. Boron Nitride Nanomesh: A template . . .

Chiral distortion of confined ice oligomers (N = 5,6).

Ice nuclei have been studied on the hexagonal boron nitride nanomesh (h-BN/Rh(111)), a template with 2 nm wide molecule traps. Scanning tunneling microscopy shows confined clusters, where oligomers with three protrusions are particularly abundant. Together with local barrier height dI/dz maps, it is found that the dipoles of the water molecules arrange in a homodrome, which is consistent with density functional theory calculations. Hydrogen bonds toward the substrate identify h-BN/Rh(111) to be hydrophilic. The substrate distorts the hexamers (n = 6) and possibly pentamers (n = 5), where the experimentally observed footprints of the three protrusions appear more chiral than expected.