A re-interpretation of the Cu [formula omitted]/Sn surface phase diagram

Abstract

The coverage dependent structural phase transitions of Sn on Cu {1 0 0} have been re-examined by low energy electron diffraction (LEED). Double scattering LEED pattern simulations have been applied both to a range of possible new models and to previously suggested structures with the aim of identifying the most likely surface geometries throughout the sub-monolayer coverage regime. A model consistent with both the Sn surface coverage and the complex split beam LEED pattern observed has been suggested for the low coverage ( θ Sn=0.21 ML) ordered phase based on a p(2×2) structure with “light” antiphase domain walls. We also demonstrate that higher coverage p(2×6) ( θ Sn=0.37 ML) and p(3√2×√2) R45° ( θ Sn=0.50 ML) structures based on c(2×2) local periodicity yield a consistent explanation of the LEED data. While the simulations identify likely structures, the limitations of this approach mitigate against definitive structural assignments. However simulations for models based on c(2×2) structures incorporating defects in the form of periodic density modulations combined with substrate reconstruction lead to an enhanced agreement with observed LEED data compared to overlayer models previously suggested.