Interaction of oxygen with Pt(210): formation of new oxygen states at higher exposures

The interaction of oxygen with Pt(210) was investigated by means of thermal desorption spectroscopy (TDS) and work function Delta Phi measurements. Two TD states reflecting chemisorbed O atoms appear after moderate O-2, exposures at 413 K. Higher oxygen exposures (3 x 10(1) and 3 x 10(6) L) produce two additional TD states on the low-temperature tail of the TD peaks of chemisorbed O; these additional states cannot be saturated, their filling is thermally activated. Absolute coverages and sticking coefficients (s(0)= 0.4) are evaluated from the TD spectra. The low-exposure oxygen states cause an increase in work function of Pt(210), whereas high-exposure states cause a decrease of the work function. The nature of the oxygen states is discussed and the existence of the high-exposure states is tentatively attributed to subsurface oxygen. (C) 2000 Elsevier Science B.V. All rights reserved.