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

The adsorption of sulfur on the Ir(110) surface was investigated by scannin g tunnel microscopy, low energy electron diffraction (LEED), and Auger elec tron spectroscopy. Upon annealing to 700-1000 K, sulfur induces a missing-r ow reconstruction of the substrate at minimum coverages of 0.15+/-0.05 ML ( Monolayer). At 0.5 ML sulfur coverage a p(2X2)-2S structure with p2mg symme try is observed, which is compatible with an earlier LEED analysis of that structure. At higher coverages up to saturation, a c(2X4)-6S structure deve lops for which a structural model is proposed. At saturation coverage, the LEED pattern exhibits additional Streaks at 1/4 positions in the [(1) over bar 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 ato ms in the dimers seem to be located in on-top positions over sulfur atoms o f the first layer, leading to long-range order in the [(1) over bar 10] dir ection only.