Time-Resolved STM Investigations

The occurrence of both reaction pathways has been demonstrated in recent time-resolved STM investigations (Kim and Wintterlin, 2004), which also showed that the reaction takes place at random positions, because the O and CO diffusion barriers are comparable to the activation energy for the CO + O reaction. The most recent theoretical calculations support these findings fully they even suggest that the dominating reaction is between the adsorbed CO and O (Reuter et al., 2004). 

To elucidate the mechanism of metal UPD, a number of studies on Cu and Ag UPD have been performed over the years comprising phenomenological, CV-based studies and microscopic investigations with STM both ex situ and in situ [38,39, 42, 43, 202, 204, 210-214]. While some features, such as the formation of UPD islands, were commonly reported for various systems (different thiols and metals, that is, Ag and Cu) differing interpretations were given with respect to the details such as formation, extension or height, possibly due to the sometimes difficult interpretation of data that, furthermore, can vary with the details of the system and the experimental conditions applied. Some of the issues could be resolved in a recent study on high-quality aromatic SAMs where the UPD process could be extremely slowed down to allow time-resolved in-situ studies [43]. 

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