MULTIPLE MECHANISMS FOR ADSORBATE-INDUCED RESISTIVITY - OXYGEN AND FORMATE ON CU(100)

Simultaneous measurements of changes in the DC resistivity and broadba nd infrared reflectance induced by oxygen and formate adsorption on ep itaxial Cu(100) thin films demonstrate that the mechanism of the resis tance change is chemically specific. For oxygen, a linear relationship between the resistivity and reflectance changes confirms that conduct ion electron scattering is dominant, as previously deduced from infrar ed measurements on single crystals. On identically prepared Cu films, adsorbed formate induces a comparable resistivity change, but no detec table reflectance change. This difference is inconsistent with the sca ttering mechanism, for which the ratio of the two effects should depen d only on the substrate and not on the adsorbate. The resistivity chan ge induced by the formate may arise from a reduction of the conduction electron density. (C) 1997 Elsevier Science B.V.