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Coupling over large distances up to nine lattice constants of ( n ×1) chain structures, formed by alkali and alkaline earth metals on anisotropic surfaces like Mo(1 1 2), occurs mainly by adsorbate-induced Friedel oscillations of the electron system at the surface. We briefly review evidence for this mechanism. It causes wave-like modulations in the adsorbate-induced lateral relaxations in the systems Li/Mo(1 1 2) and Sr/Mo(1 1 2), found by LEED-IV analysis. Within this coupling mechanism the depinning transitions of the low coverage p(8×1) and p(5×1) chain structures of the Sr/Mo(1 1 2) system can be described semi-quantitatively. The collective nature of coupling is demonstrated by adding small amounts of electronegative impurities (oxygen atoms) at concentrations far below one atom per unit cell. These impurities are able to change periodicities and symmetries as well as stabilities of structures, and partly suppress phase transitions. The complexity of these phenomena goes beyond descriptions by the simple one-dimensional coupling mechanism. |
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