Adsorption studies of oxygen and carbon monoxide on a Pt (100) surface

Abstract

The adsorption of oxygen and carbon monoxide on a clean Pt (100) surface was investigated using LEED, Auger electron spectroscopy and flash desorption mass spectroscopy. The clean Pt (100) surface was characterized by a sharp (5 × 1) LEED pattern. During oxygen adsorption no new LEED pattern was found up to the saturation coverage of 0.25 at room temperature as determined by quantitative evaluation of the flash desorption spectra. Three oxygen adsorption states were detected by flash desorption with desorption maxima at 520, 690 and 800°C, which could be attributed to atomically adsorbed oxygen. The populations of the different adsorption states in terms of saturation coverages were 0.18, 0.06 and 0.01, respectively. The initial sticking probability of oxygen on Pt (100) at room temperature was 4 × 10 −4. The sticking probability showed little variation with coverage at the initial stages of the adsorption and decreased exponentially in the coverage range 0.05 < θ < 0.20. An explanation is proposed in terms of the different adsorption states and of an activated adsorption model in the limited coverage range given above. The temperature dependence of the total saturation coverage seems to support the activated adsorption model. The adsorption of carbon monoxide was characterized by a (1 × 1), c (4 × 2) LEED pattern and under special conditions a (2 × 2) pattern. Flash desorption showed three desorption maxima at 180, 280 and 450°C. It has been found, that carbon monoxide from the background gas can have a strong influence on the adsorption of oxygen and the carbon monoxide content of the ambient atmosphere has to be minimized for undisturbed oxygen adsorption studies.