Multiple mechanisms for adsorbate-induced resistivity: oxygen and formate on Cu(100)

Simultaneous measurements of changes in the DC resistivity and broadband infrared reflectance induced by oxygen and formate adsorption on epitaxial Cu(100) thin films demonstrate that the mechanism of the resistance change is chemically specific. For oxygen, a linear relationship between the resistivity and reflectance changes confirms that conduction electron scattering is dominant, as previously deduced from infrared measurements on single crystals. On identically prepared Cu films, adsorbed formate induces a comparable resistivity change, but no detectable reflectance change. This difference is inconsistent with the scattering mechanism, for which the ratio of the two effects should depend only on the substrate and not on the adsorbate. The resistivity change induced by the formate may arise from a reduction of the conduction electron density. (C) 1997 Elsevier Science B.V.