Comparison of the electronic structure and surface geometry of the metastable Cs+O overlayers on Ru(0001)

The postadsorption of 0.25 monolayer of Cs on oxygen-precovered Ru(0001) surfaces with various coverages ranging from 0.25 to 1 results in the formation of metastable O+Cs overlayers. These systems are characterized by only minor changes of the electronic and structural characteristics of the Cs subsystems, due to the presence of coadsorbed oxygen. This indicates a quite weak interaction between the two subsystems as judged from thermal desorption spectroscopy, metastable deexcitation spectroscopy, low-energy electron diffraction measurements, and density-functional theory calculations. The main reason for the development of such metastable phases is seen in the strong O-Ru bonding which is superior to the Cs-O interaction.