Coherent x-ray scattering experiments of Pt(001) surface dynamics near a roughening transition

We present the results of a series of coherent x-ray scattering temperature-dependent experiments from Pt(001) in high vacuum. The resulting speckled diffraction patterns are analyzed with x-ray photon correlation spectroscopy. We find that the hexagonally reconstructed Pt(001) surface exhibits orientational dynamics below 1640 K and a critical behavior as $T$ increases to ${T}_{\mathrm{R}}$ $=$ 1834 K, near the roughening transition, as proposed by Abernathy et al. [Phys. Rev. Lett. 69, 941 (1992)]. The inverse autocorrelation time constant ${\ensuremath{\tau}}^{\ensuremath{-}1}$ of the surface diverges as $T$ approaches ${T}_{\mathrm{R}}$. The average integrated intensity remains constant below ${T}_{\mathrm{R}}$ but drops suddenly over a narrow temperature range, indicating abrupt lifting of the hexagonal reconstruction with the roughening transition. This behavior is compared to that of Au(001), for which ${\ensuremath{\tau}}^{\ensuremath{-}1}$ approaches a finite value as the reconstruction lifts gradually over a wide temperature range.