Oxygen coadsorption and reaction with potassium on MgO thin films grown on Ru(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 temperature of 335 K and a K 2p(3/2) binding energy (BE) of 293.5 eV within theta(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 characterized with an O 1s BE of 533.7 eV, demonstrated further in isotope exchange experiments. This molecular oxygen species gradually diminishes with increasing theta(K). The formation of K2O at theta(K)greater than or equal to 1 ML is demonstrated by the O 1s peak at 528.0 eV, together with its thermal desorption at 600 K. A strongly bonded K=O complex evidenced by coincident K and O-2 desorption at 800-1000 K exists at all theta(K)s studied. (C) 1998 Elsevier Science B.V. All rights reserved.