Surface-phonon dispersion investigation of the (1×1)→(5×1) reconstruction of the Ir(100) surface

High-resolution electron-energy-loss spectroscopy has been used to investigate the dispersion of surface phonons on the unreconstructed (1×{}1) and the reconstructed (5×{}1) Ir(100) surface. A significant difference in the dispersion properties of the (1×{}1) and (5×{}1) surfaces is found for both the [011] and the [001] direction. Lattice-dynamical calculations in a second-nearest-neighbor force-constant model fit the experimental results on the (1×{}1) surface if a large amount of surface stress is invoked. Our results suggest that the surface stress is the driving force for the surface reconstruction of Ir(100)-(1×{}1){→}Ir(100)-(5×{}1).