Adsorption of CO on bimetallic RhN/Ru(0001) layers

The adsorption of CO on bimetallic RhN/Ru(0001) layers with N = 0–5 Rh layers has been investigated using Fourier transform infrared spectroscopy, thermal desorption, and low energy electron diffraction. It is found that the morphology as well as the thickness of these ultra thin Rh films lead to characteristic frequency shifts of the internal CO stretch modes as well as variations of the CO desorption energies. For N ≥ 3 ML differences with respect to CO adsorption on Rh(111) single crystal substrates are only very minor. Our findings confirm similar observations and conclusions associated with CO on bimetallic PtN/Ru(0001) layers. Dependent on the coverage of CO adsorbed on Rh/Ru(0001) monolayer films we identify a series of ordered overlayer structures which have been correlated with characteristic CO vibrational spectra.