We have characterized the surface of a single-atom alloy consisting of a low coverage of Pd deposited onto a Ag(111) surface. For this purpose, we used reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) of adsorbed CO. At low temperatures, a single C–O stretch band at 2047 cm^–1 and a single CO desorption peak at 272 K were observed, corresponding to CO bound to isolated palladium atoms. At palladium coverages above 0.002 ML, palladium aggregates form, as revealed by a C–O stretch peak at 1950 cm^–1 and a desorption peak at 390 K, corresponding to CO bound at the bridge sites between two palladium atoms. The diffusion of palladium from the surface into the subsurface was monitored from the C–O stretches of CO bonded to palladium and to silver atoms. Through RAIRS and TPD of CO, the ratio of surface to subsurface palladium was determined. The results from TPD experiments following H₂ exposures at low temperature indicate that dissociation of H₂ at the palladium sites does not lead to spillover of atomic hydrogen to silver atoms.

中文翻译：

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吸附CO以表征Pd / Ag（111）单原子合金表面的结构

我们已经表征了一种单原子合金的表面，该合金由沉积在Ag（111）表面上的低Pd覆盖率组成。为此，我们使用了反射吸收红外光谱（RAIRS）和吸附的CO的程序升温脱附（TPD）。在低温下，在2047 cm ^-1处有一个C–O伸缩带，在272 K处有一个CO脱附峰观察到，其对应于结合到分离的钯原子上的CO。在钯覆盖率超过0.002 ML时，形成钯聚集体，如1950 cm ^–1处的C–O拉伸峰所示在390 K处有一个解吸峰，该峰对应于在两个钯原子之间的桥键处结合的CO。钯从表面到亚表面的扩散是通过与钯和银原子结合的CO的C–O延伸来监测的。通过RAIRS和CO的TPD，可以确定表面钯与表面钯的比例。TPD实验在低温下暴露于H _2后的结果表明，在钯位点处H _2的解离不会导致氢原子向银原子的溢出。