Scanning tunneling microscopy studies of methoxy and formate on Cu(110) surfaces resulting from reactions with methyl formate, methanol, and formic acid

We have used scanning tunneling microscopy (STM) to examine Cu(110)-(2 x 1)O surfaces that have been exposed to methyl formate. Previous work has shown that when Cu(110) surfaces are exposed to methyl formate (CH3OCHO), this results in the presence of adsorbed methoxy (CH3O) and formate (HCOO). Using images of methoxy and formate structures on Cu(110) surfaces arising from reactions involving methanol (CH3OH) and formic acid (HCOOH) as guidelines, we have interpreted our images of Cu(110) surfaces after exposure to methyl formate. Our studies show that the reaction of methyl formate with both the clean and the completely oxygen terminated (2 x 1) surface is negligible. When (2 x 1)O islands are present on the surface, following exposure to methyl formate, we have observed a reduction of the lengths of the (2 x 1)O rows suggesting that reactions occur at the ends of the (2 x 1)O rows. We also have observed the appearance of (5 x 2) islands which we attribute to a structure containing equal numbers of methoxy and formate molecules. At room temperature, these structures disappear from the surface with time, owing to the decomposition of methoxy. Subsequent oxygen exposures trap the remaining formate molecules into structures which can be imaged by STM. We have also obtained insight into the formate-induced restructuring of step edges and reasons as to why the (2 x 1)O row ends are active sites during chemical reactions. (C) 1999 Elsevier Science B.V. All rights reserved.