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http://myweb.rz.uni-augsburg.de/~eckern/WEH-287/ABSTRACTS/ruitenbeek.pdf

Quantum properties of atomic-sized conductors

First-principles band theory, properly augmented by topological considerations, has provided a remarkably successful framework for predicting new classes of topological materials. This Colloquium discusses the underpinnings of the topological band theory and its materials applications.

Colloquium : Topological band theory

Recent advancements in experimental studies of wetting phenomena have helped to bridge the gap between the progress made in theory and simulation over the past decade, and the experimental evidence or verification of the theoretical predictions. These developments include new measurements of the equilibrium thickness of precursor wetting films on solid and liquid substrates and at the liquid/gas interface, experimental studies of critical adsorption, as well as measurements of the dynamics of wetting and spreading and the nucleation of wetting layers in simple and complex systems. There have also been some recent results on dewetting of solid substrates by liquid films.

Wetting: Statics and dynamics

Water adsorption and the wetting of metal surfaces

Water adsorbed in submonolayer coverage on Ag(111) at 70 K forms hydrogen-bonded networks. High resolution images in combination with calculation reveal that single protrusions represent a cyclic water hexamer with the intermolecular bond stretched to the silver lattice constant of 0.29 nm. Scanning tunneling spectroscopy indicates that the bond length within the two-dimensional hydrogen-bonded water layer is shortened. The spectra contain further information about the vibrational modes of water molecules.

Intermolecular bond length of ice on Ag(111).

The spreading of a microscopic nonvolatile liquid drop on a homogeneous solid substrate has been studied by molecular dynamics simulations of Lennard-Jones systems. The substrate is assumed to be continuous without atomic structure and exerting a long-range Lennard-Jones potential on liquid particles in the drop. A molecular precursor film is observed to spread initially with nearly constant speed, crossing over later to diffusive spreading. These results are compared with recent molecular dynamics results of a volatile liquid on a structured substrate.

Molecular dynamics of a microscopic droplet on solid surface.

Water adsorbed on Ag(111) at 70 K forms circular clusters that consist of six molecules. In scanning tunneling microscopy, this cyclic hexamer is imaged as a protrusion for voltages below V(SS)=-93 meV and as a depression for voltages above V(SS). The electronic density of states, however, increases around V(SS). We explain this counterintuitive result with the aid of calculated images by a change from constructive to destructive interference between different tunneling channels due to a field induced reorientation of the molecule under the tunneling tip.

Imaging water on Ag(111): field induced reorientation and contrast inversion.

Scanning tunneling microscopy at low temperature reveals that upon dissociative adsorption of oxygen on Ag(001) “hot” adatoms have separated in a far-ranged transient motion to two different intrapair distances around 2 and 4 nm, corresponding to 7 and 14 surface lattice constants, respectively Manipulation experiments on oxygen atoms displaying different contrasts in the images and model calculations suggest that the transient motion ends up not only in the stable fourfold hollow site but also in two metastable sites

Far-ranged transient motion of “hot” oxygen atoms upon dissociation

Atom resolved scanning tunneling microscopy images are known to depend on the nature of the tip and its interaction with the surface. We present a new method for determining barrier height and tip-surface interactions. For Cu(100) images, two distinct tip types are seen. At larger tunnel currents there is evidence for forces acting between tip and surface. We show that a molecular dynamics simulation of tip and surface is able to quantitatively explain the results, and gives a good estimate of both absolute tip-surface separation and the site dependent forces on individual atoms.

Jouko Nieminen

Papers

Intermolecular bond length of ice on Ag(111).

Molecular dynamics of a microscopic droplet on solid surface.

Imaging water on Ag(111): field induced reorientation and contrast inversion.

Far-ranged transient motion of “hot” oxygen atoms upon dissociation

Quantitative scanning tunneling microscopy at atomic resolution: Influence of forces and tip configuration.