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High Resolution He-Scattering Studies of Physisorbed Films
Abstract In bulk matter, the local icosahedral clustering of twelve atoms around a central particle is significantly denser than in the corresponding hcp or fcc clusters /1/. However, icosahedra cannot be stacked to fill completely the 3D space; i.e. no solids with long range order can be formed with icosahedral units. Thus, three dimensional crystals with perfect long range order do not reach the maximum attainable short range density. These competing trends lead to a variety of interesting phenomena; like the fascinating matter of quasicrystals /2/. In two dimensions, the densest possible local arrangement around a central particle is the hexagon. Obviously, hexagons can form a close packed 2D-solid with long range order. Thus, in contrast to the 3D case, in two dimensions the requirements for maximum long range order and maximum short range density are identical. At first glance, this coincidence seems to reduce the “physical interest” in two dimensional systems substantially. However, it turned out that enhanced fluctuation effects due to the reduced dimensionality lead to novel and quite subtle phenomena in these systems. In addition, fascinating aspects arise from the fact that (in experiment) 2D-solids need to be supported by a substrate; in model 2D-systems, the 2D-layer is physisorbed on a single crystal surface. The physisorbed atoms form a modulated structure on the lattice of the substrate surface. The modulation arises from the competing interactions which favor different periodicities; the nearest-neighbor distance preferred by the lateral adatom interaction differs in general from the lattice periodicity which the substrate potential tries to impose. Such modulated systems display a great richness of phases and of phase transitions when the conditions of coverage and/or temperature are varied, and thus have attracted much theoretical /3/ and experimental /4/ interest.
High Resolution He-Scattering Studies of Physisorbed Films
Abstract In bulk matter, the local icosahedral clustering of twelve atoms around a central particle is significantly denser than in the corresponding hcp or fcc clusters /1/. However, icosahedra cannot be stacked to fill completely the 3D space; i.e. no solids with long range order can be formed with icosahedral units. Thus, three dimensional crystals with perfect long range order do not reach the maximum attainable short range density. These competing trends lead to a variety of interesting phenomena; like the fascinating matter of quasicrystals /2/. In two dimensions, the densest possible local arrangement around a central particle is the hexagon. Obviously, hexagons can form a close packed 2D-solid with long range order. Thus, in contrast to the 3D case, in two dimensions the requirements for maximum long range order and maximum short range density are identical. At first glance, this coincidence seems to reduce the “physical interest” in two dimensional systems substantially. However, it turned out that enhanced fluctuation effects due to the reduced dimensionality lead to novel and quite subtle phenomena in these systems. In addition, fascinating aspects arise from the fact that (in experiment) 2D-solids need to be supported by a substrate; in model 2D-systems, the 2D-layer is physisorbed on a single crystal surface. The physisorbed atoms form a modulated structure on the lattice of the substrate surface. The modulation arises from the competing interactions which favor different periodicities; the nearest-neighbor distance preferred by the lateral adatom interaction differs in general from the lattice periodicity which the substrate potential tries to impose. Such modulated systems display a great richness of phases and of phase transitions when the conditions of coverage and/or temperature are varied, and thus have attracted much theoretical /3/ and experimental /4/ interest.
High Resolution He-Scattering Studies of Physisorbed Films
Kern, K. (author) / David, R. (author) / Zeppenfeld, P. (author) / Comsa, G. (author)
1988-01-01
7 pages
Article/Chapter (Book)
Electronic Resource
English
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