Abstract
Room-temperature adsorption of oxygen on potassium- and cesium-precovered Cu(110) surfaces was studied by scanning tunneling microscopy. Depending on the alkali-metal precoverage, two different scenarios exist for the structural evolution of the surfaces. For alkali-metal coverages ${\mathrm{\ensuremath{\theta}}}_{\mathrm{alk}}$\ensuremath{\le}0.13 ML [${\mathrm{\ensuremath{\theta}}}_{\mathrm{alk}}$=0.13 corresponds to the (1\ifmmode\times\else\texttimes\fi{}3) missing-row reconstructed Cu(110) surface], oxygen adsorption leads first to a transient contraction of the missing rows into islands of a (1\ifmmode\times\else\texttimes\fi{}2) structure. After longer exposures it causes the local removal of the alkali-metal-induced reconstruction, and the (2\ifmmode\times\else\texttimes\fi{}1) Cu-O ``added-row'' structure with ${\mathrm{\ensuremath{\theta}}}_{\mathrm{O}}$=0.5 is formed. In this structure the alkali-metal atoms are incorporated in the Cu-O chains. For higher alkali-metal precoverages, in the range of the (1\ifmmode\times\else\texttimes\fi{}2) reconstruction (${\mathrm{\ensuremath{\theta}}}_{\mathrm{alk}}$\ensuremath{\approxeq}0.2), more than one-half a monolayer of oxygen can be incorporated into the (1\ifmmode\times\else\texttimes\fi{}2) phase with only a minor structural effect before, at higher oxygen coverages, complex oxygen--alkali-metal--Cu structures with oxygen coverages well above 0.5 ML are formed. The saturation oxygen coverage is drastically enhanced beyond ${\mathrm{\ensuremath{\theta}}}_{\mathrm{O}}$=0.5, the quasisaturation value of the clean surface. Based on mass-transport arguments the substrate is reconstructed for all ratios of oxygen and alkali metal investigated here. Hence, adsorbate-substrate interactions are essential for these structures; they are not dominated by interactions between alkali metals and oxygen, i.e., by adsorbate-adsorbate interactions.
Published Version
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