Adsorbate-induced reconstruction and overlayer structures of sulfur on Ir(110): An STM study

Abstract

The adsorption of sulfur on the Ir(110) surface was investigated by scanning tunnel microscopy, low energy electron diffraction (LEED), and Auger electron spectroscopy. Upon annealing to 700--1000 K, sulfur induces a missing-row reconstruction of the substrate at minimum coverages of 0.15\ifmmode\pm\else\textpm\fi{}0.05 ML (Monolayer). At 0.5 ML sulfur coverage a $p(2\ifmmode\times\else\texttimes\fi{}2)\ensuremath{-}2S$ structure with $p2\mathrm{mg}$ symmetry is observed, which is compatible with an earlier LEED analysis of that structure. At higher coverages up to saturation, a $c(2\ifmmode\times\else\texttimes\fi{}4)\ensuremath{-}6\mathrm{S}$ structure develops for which a structural model is proposed. At saturation coverage, the LEED pattern exhibits additional streaks at $\frac{1}{4}$ positions in the $[1\ifmmode\bar\else\textasciimacron\fi{}10]$ azimuth. The streaks are due to sulfur dimers in a second adsorbate layer, which can be desorbed by annealing at 1100 K. Surprisingly, the atoms in the dimers seem to be located in on-top positions over sulfur atoms of the first layer, leading to long-range order in the $[1\ifmmode\bar\else\textasciimacron\fi{}10]$ direction only.