A surface stress induced (1×1) → (5×1) reconstruction of an Ir(1OO) surface

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In the present study we have applied the phonon dispersion method to investigate the dynamics of the (1×1) → (5×1) reconstruction of an Ir(1OO) surface. The Ir(1OO) surface has been chosen here mainly because stable and atomicany clean surfaces of both uncreconstructed Ir(100)-(1×1) and reconstructed Ir(100)-(5×1) could be routinely obtained by controlling experimental conditions. The dispersion of surface phonons has been measured along both the \\ ̄ gG X̄ [011] and \\ ̄ gG M̄ [001] directions. Our results indicate that along both directions the frequency of the Rayleigh phonon near the zone boundary is significantly higher on the unreconstructed (1×1) surface. In addition, lattice dynamical calculations in a second nearest neighbour force constant model have also been performed for the unreconstructed Ir(100)-(1×1) surface. The comparison of theory with experimental results reveals that the unreconstructed surface possesses a substantial amount of tensile surface stress. The results presented here allow us to conclude that the surface stress is the major driving force for the surface reconstruction of Ir(100)-(1×1) to Ir(100)-(5×1).