Sb/Si(111) adsorption: hidden phase transitions behind Langmuir-like isotherms.
The experimental study of the thermodynamic and kinetic properties of the Sb/Si(111) interface reveals a surprising behavior: a 2D phase condensates when the Sb coverage increases, indicating strong attractive Sb-Sb interactions, whereas the isotherms present a quasi-Langmuir shape, suggesting that these interactions should be negligible. Ab initio calculations raise this contradiction: while the adsorption site evolves from ternary towards the on-top position with increasing coverage, the character of the Sb-Sb effective interactions changes from repulsive towards attractive, resulting in an almost constant average adsorption energy. A simple (Langmuir) thermodynamic behavior can then be the consequence of a surface phase transition.
Guesmi
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CRMCN-CNRS, associated to Aix-Marseille Universities (Université de la Mediterranée, Université Paul Cézanne), Campus de Luminy, Case 913, 13288 Marseille Cedex 9, France.
Lapena
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Ranguis
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Müller
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Tréglia
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