Coherent x-ray surface scattering applied to Pt (001)*

Scattering using highly coherent light provides information about the very small scale, but over a very large area suitable for an ensemble measurement. We have used coherent x-ray diffraction to study the surfaces Pt (001) single crystal surfaces at high temperature in vacuum and compare them with earlier measurements of Au (001) in similar conditions. Both metals possess a temperature dependent quasi-hexagonal surface reconstruction. The speckled scattering patterns can be quantitatively compared against each other to determine how quickly configuration is changing, even when the macroscopically the system appears in equilibrium. We have been able to obtain measurements of the dynamic temperature dependent surface processes for these two different systems. For Pt (001) we have also directly observed step-flow motion of the terraces, obtaining step-edge velocity as a function of temperature. Our results point to two very different mechanisms at work in lifting the surface reconstruction at high temperature in vacuum.