Surface resistivity and vibrational damping in adsorbed layers

Abstract

I derive a simple relation between the change in dc resistivity Δρ of a thin metallic film due to adsorption of molecules on the film surface and the electron-hole pair damping (lifetime τ) of the frustrated translations of the adsorbates. From the measured Δρ for several different adsorbate systems, I deduce the corresponding τ, which ranges from ∼${10}^{\mathrm{-}12}$ s for chemisorption systems to ∼${10}^{\mathrm{-}9}$ s for physisorption systems. Theories for the damping of parallel frustrated translations are developed for three limiting cases of the adsorbate-substrate bond; namely, for covalent, ionic, and van der Waals bonds. I study the change in the broadband infrared (ir) light reflectivity caused by the adsorption of molecules on a semi-infinite metal and I discuss the recent ir study by Hirschmugl et al. for the CO-Cu(100) system. Finally, the observation by ir-spectroscopy by Chabal et al. of dipole-forbidden frustrated translations and rotations for H and CO chemisorbed on metals is discussed and the contribution from the excitation of the parallel frustrated translations to the surface resistivity is calculated.