کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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5426072 | 1395874 | 2007 | 11 صفحه PDF | دانلود رایگان |
The co-adsorption of CO and O on the unreconstructed (1Â ÃÂ 1) phase of Ir{1Â 0Â 0} was examined by low energy electron diffraction (LEED) and temperature programmed desorption (TPD). When CO is adsorbed at 188Â K onto the Ir{1Â 0Â 0} surface precovered with 0.5Â ML O, a mixed c(4Â ÃÂ 2)-(2OÂ +Â CO) overlayer is formed. All CO is oxidised upon heating and desorbs as CO2 in three distinct stages at 230Â K, 330Â K and 430Â K in a 2:1:2 ratio. The excess oxygen left on the surface after all CO has reacted forms an overlayer with a LEED pattern with p(2Â ÃÂ 10) periodicity. This overlayer consists of stripes with a local p(2Â ÃÂ 1)-O arrangement of oxygen atoms separated by stripes of uncovered Ir. When CO is adsorbed at 300Â K onto the surface precovered with 0.5Â ML O an apparent (2Â ÃÂ 2) LEED pattern is observed. LEED IV analysis reveals that this pattern is a superposition of diffraction patterns from islands of c(2Â ÃÂ 2)-CO and p(2 Â ÃÂ 1)-O structures on the surface. Heating this co-adsorbed overlayer leads to the desorption of CO2 in two stages at 330Â K and 430Â K; the excess CO (0.1Â ML) desorbs at 590Â K.LEED IV structural analysis of the mixed c(4Â ÃÂ 2) O and CO overlayer shows that both the CO molecules and the O atoms occupy bridge sites. The O atoms show significant lateral displacements of 0.14Â Ã away from the CO molecules; the C-O bond is slightly expanded with respect to the gas phase (1.19Â Ã ); the modifications of the Ir substrate with respect to the bulk-terminated surface are very small.
Journal: Surface Science - Volume 601, Issue 5, 1 March 2007, Pages 1285-1295