Morphology of Ultra-Thin Metal Films Using Infrared Reflection Adsorption Spectroscopy

Abstract

ABSTRACTThe adsorption of carbon monoxide on ultra-thin films of Cu, Ni and Co on Rh(100) and Mo(110) substrates has been studied using infrared reflection absorption spectroscopy (IRAS). The CO vibrational frequency on Cu/Rh(100) and Cu/Mo(110) at low Cu coverage (∼0.1 ML) shows a blue-shift relative to its gas phase stretching frequency (2143 cm−1). This blue-shift is explained as arising from CO adsorbed on well-dispersed Cu adatoms which are either slightly positively charged due to charge transfer from Cu to the substrate or self-polarized because of a strong Cu-substrate interaction. It is further shown that three-dimensional Cu clusters, well-ordered pseudomorphic two dimensional Cu islands and single Cu atoms are distinctively characterized by the CO IR peaks at 2074 cm−1, 2095 cm−1, and 2162 cm−1, respectively. In addition, it is found that IR spectra of CO adsorbed on Ni/Mo(110) show a remarkable sensitivity to surface structural phase transitions at the Ni-Mo interface.