Simon Berner

Surface Trapping of Atoms and Molecules with Dipole Rings

The trapping of single molecules on surfaces without the formation of strong covalent bonds is a prerequisite for molecular recognition and the exploitation of molecular function. On nanopatterned surfaces, molecules may be selectively trapped and addressed. In a boron nitride nanomesh formed on Rh(111), the pattern consisted of holes 2 nanometers in diameter on a hexagonal superlattice, separated by about 3 nanometers. The trapping was further investigated with density functional theory and the photoemission of adsorbed xenon, where the holes were identified as regions of low work function. The analysis showed that the trapping potential was localized at the rims of the holes.

Supramolecular Assemblies Formed on an Epitaxial Graphene Superstructure

The seminal work of Novoselov et al. has stimulated great interest in the controllable growth of epitaxial graphene monolayers. While initial research was focussed on the use of SiC wafers, the promise of transition metals as substrates has also been demonstrated and both approaches are scalable to large-area production. 12] The growth of graphene on transition metals such as Ru, Rh and Ir leads to a moir!-like superstructure, 10,12,13] similar to that observed for BN monolayers. Here we show that such a superstructure can be used to control the organization of extended supramolecular nanostructures. The formation of two-dimensional supramolecular arrays has received increasing attention over recent years primarily due to potential applications in nanostructure fabrication as well as fundamental interest in self-assembly processes. Such studies can be highly dependent on the nature of the substrate used, and the interplay between surface and adsorbed supramolecular structure is a topic of significant conjecture. Until now metallic surfaces or highly oriented pyrolytic graphite (HOPG) have typically been the surfaces of choice for such studies. Our results demonstrate that graphene is compatible with, and can strongly influence molecular selfassembly. We have studied the adsorption of perylene tetracarboxylic diimide (PTCDI) and related derivatives on a graphene monolayer grown on a Rh(111) heteroepitaxial thin film (Figure 1). In particular, we show that a near-commensur-

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.

Molecular Assembly and Self‐Assemblya: Molecular Nanoscience for Future Technologies

Abstract: In this review the emerging science of single molecules is discussed in the perspective of nanoscale molecular functions and devices. New methods for the controlled assembly of well‐defined molecular nanostructures are presented: self assembly and single molecular positioning. The observation and selective modification of conformation, electronics, and molecular mechanics of individual molecules and molecular assemblies by scanning probes is demonstrated. To complement this scientific review, some of the possible consequences and visions for future developments are discussed, as far as they derive from the presented systems. The prospects of nanoscale science to stimulate technological evolution are exemplified.

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 . . .

Tunable self-assembly of one-dimensional nanostructures with orthogonal directions

High-temperature exposure of a Mo(110) surface to borazine (HBNH)3leads to the formation of two distinctly different self-assembling nanostructures. Depending on the substrate temperature during preparation, either well-aligned, ultra-thin boron nanowires or a single-layer stripe structure of hexagonal boron nitride forms. Both structures show one-dimensional (1D) characteristics, but in directions perpendicular to each other. It is also possible to grow the two phases in coexistence. The relative weights are controlled by the sample temperature during preparation.

Molecular Assembly and Self-Assembly: Molecular Nanoscience for Future Technologies

In this review the emerging science of single molecules is discussed from the perspective of nanoscale molecular functions and devices. New methods for the controlled assembly of well-defined molecular nanostructures are presented: self assembly and single molecular positioning. The observation and selective modification of conformation, electronics, and molecular mechanics of individual molecules and molecular assemblies by scanning probes are demonstrated. To complement this scientific review, some of the possible consequences and visions for future developments are discussed, as far as they derive from the presented systems. Here, the prospects of nanoscale science to stimulate technological evolution are exemplified.

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.

Characterization of molecular overlayers on metal surface in dynamic equilibrium by scanning tunneling microscope

The overlayer structure of [tetra-(3,5-di-tertiary-butylphenyl)porphyrinato] copper (Cu-TBPP) molecules on Ag (001) and chloro(subphthalocyaninato)boron (III) (SubPc) molecules on Ag (111) were analyzed by a UHV scanning tunneling microscope. In the case of approximately 20% coverage, both molecules showed high mobility on the substrates, which caused them to form an overlayer island on terraces. Cu-TBPP molecules formed an oblique lattice on the Ag (001) surface and SubPc molecules formed a hexagonal lattice on Ag (111). From a high-resolution STM image of the overlayer, characteristic protrusion corresponding to the molecular shapes, such as four-lobes of Cu-TBPP and three-lobes of SubPc, were clearly identified.

Controlled underdoping of cuprates using ultraviolet radiation

A method for a controlled change of the doping level of high-temperature superconductors with ultraviolet radiation is presented. With photoemission it is shown that the exposure of Bi2Sr2CaCu2O8+δ samples to the light of a He gas-discharge lamp causes oxygen desorption. From measurements of the Fermi surface, it is found that the oxygen desorption causes a decrease of the doping level of the superconductors. From the desorption cross sections that strongly depend on the photon energy, two different oxygen desorption channels are inferred. This procedure for decreasing the doping level has the advantage that the crystallinity of the sample is not altered and that the doping level can be simultaneously measured by photoelectron spectroscopy.