Mechanisms of adsorbate-induced surface resistivity––experimental and theoretical developments

Recent experimental and theoretical developments in explaining adsorbate effects on electronic conduction in metals are critically reviewed. These effects are of more than academic interest, with applications in nanotechnology, chemical sensing, and tribology. The prevailing model treats the metal as a free-electron gas and the adsorbates as independent point scatterers. This model, first developed by Fuchs and Sondheimer and elaborated in recent years by Persson and Volokitin, makes specific quantitative predictions regarding the optical effects of surface resistivity. Some have been accurately verified, including the spectral shape and temperature dependence of the adsorbate-induced reflectance change, and anti-absorption resonances associated with dipole-forbidden vibrations. The model also predicts, however, that the ratio of the adsorbate-induced reflectance and resistivity changes should depend only on the properties of the metal, and not on those of the adsorbate, and this prediction is strongly violated in several recent experiments. Possible explanations of the discrepancy are discussed.