Coherent X-ray Scattering Experiments of Pt (001) Surface Dynamics near Roughening Transition

We will 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. \textbf{69}, 941 (1992)]. The inverse autocorrelation time constant $\tau ^{-1}$ of the surface diverges as $T$ approaches $T_{R}$. 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 $\tau^{-1}$ approaches a finite value as the reconstruction lifts gradually over a wide temperature range.