Silver on Pt(100): Alloying vs. surface reconstruction - Two competing mechanisms to reduce surface stress

Phase-coexistence of a Ag/Pt surface-alloy and a pure Pt-hex reconstructed phase has been observed for sub-0.3ML Ag coverage on a Pt(100) surface by scanning tunneling microscopy and temperature-programmed desorption of Ag. We argue that, despite a stronger homoatom interaction, mixing at the surface is observed because the intrinsic tensile stress of the Pt(100) surface facilitates the incorporation of the slightly larger Ag atoms into the surface layer in order to minimize strain energy of the surface. Thus, surface-alloying presents an alternative to surface reconstruction as a means of strain minimization. Therefore, a competition between surface reconstruction and alloying to reduce the stress at the surface exists and, consequently, a two-phase coexistence of an alloy-phase and a pure Pt hex-reconstructed phase are observed.