Formation of Cs–H surface compounds

The role of the Ru surface in the formation of Cs–H compounds has been investigated by using thermal desorption spectroscopy (TDS), ultraviolet photoelectron spectroscopy, UPS(21.2 eV) and metastable de-excitation spectroscopy (MDS). Cs atoms pre-adsorbed on Ru(0 0 0 1) surface considerably reduce the effective sticking probability for dissociative adsorption of hydrogen but a saturated Cs adlayer does not stop the hydrogen accommodation. Within the initial hydrogenation stage the system exhibits metallic properties. It represents H−α anions and Cs+ν ions coexisting without creating lateral strong ionic bonds. TDS and MDS indicate that the coadsorbed species exhibit a metal–insulator transition only for a hydrogen exposure in the range of 480–1200 L. The insulating phase is marked out by an additional H−β ionic hydrogen species which is responsible for the entire depletion of the Cs 6s state. A weak H2 desorption peak at 1090 K reveals the formation and decomposition of Cs hydrides at surface defects.