Simple surface reactions like the CO-oxidation on single crystal Pt surfaces show a rich variety of pattern formation under specific reaction parameters. To visualize those patterns we have conceived several unique imaging methods starting around 1990. The interaction of a multitude of micrometer scale concentration waves and fronts on the surface complicate our understanding the underlying mechanisms for such patterns. Experiments with modified catalytic activity using stationary, inactive boundaries have therefore been designed to isolate individual features (for example single pulses) and interaction mechanisms in order to study them quantitatively. Since 2001 we have been able to dynamically change the surface catalytic activity in real time and space by focusing an addressable laser beam to differentially heat a Pt(110) single crystal surface. The combination between the fixed microstructures of metals with different catalytic activities and local laser heating of the surface has been recently explored.
Reconstruction on open surfaces of Ir, Pt and Au, i.e. (001) and (110) surfaces of fcc metals, is caused by the relativistic effect through increase of the d-hole density of the valence state. The reconstruction of Pt(001) and Pt(110) surfaces is lifted by adsorption of CO and NO molecules and its lifting is caused by reduction of the d-hole density due to donation of lone-pair electrons of these molecules. Although oscillation in the reaction rate of CO oxidation and fantastic two-dimensional images corresponding to various oscillation patterns on Pt(001) and Pt(110) surfaces were observed by Ertl's group, these phenomena can be explained by the change of the d-hole density enhanced by the relativistic effect. Finally, laser-induced desortion of NO from Pt(111) and Pt(111)-Ge surface alloy is also discussed using the relativistic effect.
Gerhard Ertl received the 2007 Nobel Prize in Chemistry in recognition of his major contributions in the field of surface science. This includes studies of fundamental molecular processes at the gas-solid interface and the methodological foundations for an entire field of research. This paper provides a personal view of his research, including remarkable characteristics, surface elementary steps, from adsorption isotherms to chemical oscillations, visualized surface reactions, and a new approach to surface reactions. It also describes the research environment in Germany.
The electronic structure of nanographene having open edges around its circumference crucially depends on its edge shape. The circumference of an arbitrary shaped nanographene sheet is described in terms of a combination of zigzag and armchair edges. According to theoretical suggestions, nanographene has a nonbonding π-electron state (edge state) localized in zigzag edges. This is reminiscent of the nonbonding π-electron state appearing in non-Kekulé-type aromatic molecules. The localized spins of the edge states can give rises to unconventional magnetism in nanographene, such as carbon-only ferromagnetism, magnetic switching phenomenon, spin glass state, etc. STM/STS investigations of well defined graphene edges which are hydrogen terminated in ultra-high vacuum condition confirm the presence of edge states around zigzag edges, in good agreement with theoretical works. The feature of the edge state depends on the detailed edge shape. The edge state in a short zigzag edge embedded between armchair edges becomes less localized due to the state mixing with the adjacent armchair edges. The electrons in the edge state in a finite-length zigzag edge are subjected to electron confinement effect.
We demonstrated spin injection into a graphene thin film at room temperature. The thickness of the graphene thin film was typically 8−16 nm. In addition to a conventional 2-terminal “local” measurement scheme, a 4-terminal “non-local” measurement was introduced for excluding spurious signals and providing reliable results. In the non-local measurement, an electric current path and a spin current path were completely separated and difference in electrochemical potential of spin current were detected. We detected 200 nV of an output voltage in the non-local measurements, which directly indicated the spin injection and spin current generation in the graphene. This was the first direct demonstration of spin current detection in molecules at room temperature.
Since the experimental discovery of graphene (single layer of graphite) in 2004, the research of single and multi-layer graphene has attracted much attention both theoretically and experimentally. In this article, from the experimental point of view, we describe the simple and special preparation of single and multi-layer graphene devices and report our recent stydy on superconducting proximity effect in multilayer graphene. As the gate voltage is swept, the proximity-induced superconductivity in multilayer graphene shows the bipolar behavior, from the hole supercurrent to the electron supercurrent. The following unusual facts are found: (1) for an arbitrary normal state resistance, the electron critical supercurrent is larger than the hole critical supercurrent, indicating the breakdown of the electron-hole symmetry. (2) The temperature dependence of the critical supercurrent cannot be explained by the standard theory for the superconducting proximity effect.
Theoretical methods to determine the work function of metal surfaces using the density functional theory are reviewed. Evaluation of the Fermi energy relative to the vacuum level is usually done by utilizing rapid convergence of a local scalar potential obtained by subtracting the exchange-correlation potential from the total effective potential. We checked dependence on thickness deff of the vacuum layer, which is 1/deff, both for the Fermi energy and the vacuum level in finite slab models. Agreement between the theory and the experiments is shown for some typical metals.