GROSS REARRANGEMENT OF METAL ATOMS DURING SURFACE-REACTIONS

We have used STM to observe changes in surface structure during the re action of formic acid and methanol with oxygen precovered Cu(110). The reactivity pattern of oxygen on Cu(110) is strongly coverage and reac tant dependent. This is partly due to the nature of the p(2 x 1) oxyge n layer itself, which is an added row structure consisting of Cu-O cha ins in the [001] direction. Cu is unstable at the end of these chains and seeks an alternative, stable location during reactions. With metha nol this location is associated with the methoxy layer itself. Formate resulting from formic acid adsorption, however, prefers to bond to th e original surface layer, leaving the Cu atoms to diffuse elsewhere. I f the surface is partially covered by oxygen this 'elsewhere' is the s tep, where Cu builds up between the diminishing O islands creating a s awtooth structure. When the surface is fully covered by the p(2 x 1) l ayer, however, the copper can only diffuse over the (2 x 1) layer itse lf, where it is converted into the higher coverage c(6 x 2) structure by rearrangement and compression of the original p(2 x 1) layer.