Oxygen coadsorption and reaction with potassium on MgO thin films grown onRu(001)

The adsorption of potassium on MgO thin films supported on Ru(001) has been studied using TDS and XPS. The interaction of K atoms with defect sites in MgO films at low K coverages is evidenced by K desorption at a constant te mperature of 335 K and a K 2p(3/2) binding energy (BE) of 293.5 eV within t heta(K)less than or equal to 1 ML. Upon oxygen adsorption on K submonolayer -covered MgO, a molecular oxygen species desorbing at 390 K is characterize d with an O 1s BE of 533.7 eV, demonstrated further in isotope exchange exp eriments. This molecular oxygen species gradually diminishes with increasin g theta(K). The formation of K2O at theta(K)greater than or equal to 1 ML i s demonstrated by the O 1s peak at 528.0 eV, together with its thermal deso rption at 600 K. A strongly bonded K=O complex evidenced by coincident K an d O-2 desorption at 800-1000 K exists at all theta(K)s studied. (C) 1998 El sevier Science B.V. All rights reserved.