The behavior of oxygen on the basal plane of ruthenium has been studied at temperatures above 300 K using uptake measurements, thermal desorption spectroscopy (TDS) and Auger electron spectroscopy (AES). A temperature-independent initial sticking coefficient of 0.8 ± 0.1 is calculated from uptake measurements made at 320 K and 900 K, while AES data at 320 K gives a value of 0.62 ± 0.05. At 320 K the sticking coefficient declines with exposure more rapidly than at 900 K. Moreover, at 320 K the total oxygen uptake at saturation is less than at 900 K. TDS measurements after saturation exposure show a single high temperature O2 desorption peak (≈ 1350 K) which is larger when the exposure temperature is 900 K than when it is 320 K. In either case, the amount of O2 desorbed is significantly less than the amount adsorbed. A consideration of processes, other than O2 desorption, which can reduce the surface oxygen concentration indicates that penetration into the first few layers beneath the surface makes the most significant contribution. Incorporation of oxygen into the subsurface region, upon heating a surface saturated at 320 K, occurs with a measurable rate at temperatures as low as 400 K. The distribution of oxygen in the first few atomic layers beneath the surface depends strongly on the thermal history of the sample. A model which is qualitatively consistent with the data involves the rapid removal of a large amount of the surface oxygen by incorporation mainly into the first subsurface layer followed by much slower uptake into the deeper layers.
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