STMs uncover what happens at surface of copper atoms

17 Jun 2002

When foreign atoms and molecules are adsorbed onto surfaces, do they sit directly on top of the substrate atoms or do they settle into the crevices between them?

The answer may be revealed using scanning tunneling microscopes (STMs). Gerhard Meyer and his colleagues at the Free University in Berlin use STMs to manipulate the native copper atoms on a surface. When the STM tip is moved close to the surface, it can exert a force sufficient to overcome the energy barrier that ordinarily prevents the copper atoms from moving along the surface. By moving this copper atom about in the vicinity of an adsorbed CO molecule, a sort of surveyor's grid can be established which allows the position of the visitor to be located with new accuracy.

With this technique, Meyer was able to infer that the CO molecule lies directly on top of a surface atom, instead of between two neighboring atoms. Furthermore, with this grid in place, the carbon monoxide then became a "marker," providing information on how other species, such as nearby C2H4 molecules and lead atoms, registered with the surface. This technique can potentially be used to study adsorption on other metallic surfaces, even very complex ones which cannot be studied with conventional crystallography methods. The results are detailed in the recent Physical Review of Letters.