LOW-TEMPERATURE ADSORPTION-DESORPTION PHENOMENA OF WEAKLY-BOUND OXYGEN STATE ON THIN IRON, PALLADIUM AND TITANIUM FILMS

The measurements of surface potential (SP) have been carried out to di stinguish between elementary steps of surface processes accompanying t he formation of weakly bound oxygen state on thin Fe, Pd and Ti films at 78 K. This state appears under the oxygen pressure higher than 10(- 2) Pa, following the strong chemisorption of oxygen adatoms. Both adso rption and desorption phenomena have been carried out under isothermal conditions. It has been found that weakly bound (activation energy of desorption < 18 kJ/mol), positively polarized oxygen admolecules (del ta(+)), are present on Fe, Pd and Ti surfaces at 78 K, being located o n the top of strongly chemisorbed oxygen adatoms. The electrical natur e of O-2 ordering in the weakly bound oxygen layer has also been consi dered. (C) 1997 Elsevier Science Ltd.