Dynamics of the reconstruction process Ir(100) 1×1→1×5

Abstract

The structure transition Ir(100) 1\ifmmode\times\else\texttimes\fi{}1\ensuremath{\rightarrow}1\ifmmode\times\else\texttimes\fi{}5 is observed by means of low-energy electron diffraction. After the preparation of the metastable and bulklike 1\ifmmode\times\else\texttimes\fi{}1 surface structure the transition is started by thermal activation at T>800 K. Diffraction spot profiles as well as integrated intensities are measured as a function of time for different constant temperatures. It is shown that streaks appear between integral-order spots from which superstructure spots develop. Both spot widths and intensities change rapidly in the beginning of the transition but subsequently vary very slowly without approaching their equilibrium value. A real-space model is proposed according to which linear atomic rows of the first layer are shifted from their initial quadratic hollow positions into hexagonal-close-packed arrangement. The activation energy of the transition is determined from the intensity increase to be W=0.88\ifmmode\pm\else\textpm\fi{}0.03 eV.