Thermal dissociation of chemisorbed oxygen molecules on Ag(110): an investigation by scanning tunnelling microscopy

The thermal dissociation of oxygen molecules on Ag(110) was studied by means of scanning tunnelling microscopy. At temperatures around 170 K a fraction of the molecules dissociate to form pairs of O atoms on the unreconstructed surface. The atoms lie in the trenches between the close-packed Ag rows; the intrapair distance is two lattice constants. The O atoms are very reactive with CO at temperatures as low as 70 K. The preferential orientation of the pairs in the [001] direction contrasts with the finding in a previous study (Hahn J R, Lee H J and Ho W 2000 Phys. Rev. Lett. Vol. 85 1914) that electron-induced dissociation exclusively leads to [110]-oriented pairs. The trajectories of thermal and electron-induced dissociations must therefore be different. In the temperature range of the dissociation, several additional oxygen features occur on the surface. These include unreacted O2 molecules, the first nuclei of the added-row reconstruction, and two unidentified O-induced structures. (author)