par Visart de Bocarmé, Thierry ;Chau, Thoi-Dai ;Kruse, Norbert
Référence European Conference on Surface Science (ECOSS) (23: 2005-09-04->09: Berlin, Allemagne)
Publication Non publié, 2005-09-05
Communication à un colloque
Résumé : The dynamic interaction of pure gold crystals (“tips”) with H2O/CO gas mixtures was studied by means of video-Field Ion Microscopy (FIM). While imaging with nano-scale resolution selected areas of the equivalent of ~100 atomic Au sites were analysed for their chemical composition using short field pulses and injecting respective ions into a time-of-flight mass spectrometer (Pulsed Field Desorption Mass Spectrometry, PFDMS). At room temperature the exposure of a clean Au sample to water gas at 10-4 Pa, in the presence of an electric field of ~10V/nm, led to water adsorption and formation of bright patterns visible by FIM. Additional exposure to CO gas at 5*10-3 Pa led to the removal of the water layer. This was associated with the occurrence of wave fronts which ignited simultaneously in several regions of the Au surface with no preference for a certain crystallographic surface plane being visible. After nucleation ring-like patterns were formed which extended in a nearly concentric manner until the complete removal of the water layer from the tip sample. The build-up of the water surface layer and its titration by carbon monoxide were followed by PFDMS while imaging. The phenomena were completely reversible. Our results suggest that gold crystals in the absence of oxidic supports may be active in the water-gas shift reaction at temperatures as low as 300K.