TCE Interaction on Ptx Clusters

Before and after cluster deposition TPD spectra of TCE were recorded and are depicted in Fig. 4.23. Two sets of spectra are shown, covering two temperature ranges from 100-180K and 100-600K (note different scales for temperature and ion current). This step wise approach ensures, that possible contaminants deposited along with the clusters during the synthesis process, get desorbed in the first TPD run. The amount of deposited clusters was kept constant at 0.03 e/nm Ptx, leading to an increase in Pt amount with cluster size. 

Despite the failure of the activation of TCE on clusters observed in TPD, EES experiments of deposited selected clusters of similar sizes were performed. The exclusion of additional molecules and the chemisorption behavior for selected clusters, reduces the origin of possible shifts in peak energy positions in EE spectra to the effect of physisorption induced relaxation shifts. Thus, it allows for uncomplicated comparison of the differences in physisorption on the surfaces and supported clusters (if omitting compensating effects of potential energy and electron relaxation, as discussed in Sect. 2.2.4). 

The MIES and UPS data set for different cluster sizes, after dosage of 0.1 tce/sa and subsequent heating to 180K is presented in Fig.4.24. For the EES, the number of deposited clusters was chosen in such way, that the total amount of platinum is constant and consequently possible cluster induced effects are normalized to the Pt on the surface. 

Further, for two sizes a double amount of clusters has been deposited (two top spectra). Due to the insulating nature of MgO (thus not having density at the Ep in contrast to metals) referencing of the spectra could not be done by individually measuring the WE and adding it to the BE scale. To account for slight different films for each measurements, the WE literature value of 3.5eV [54] for MgO was added as a fixed value for all surfaces consequently also no WE evaluation is presented in 

For UPS with its lower surface sensitivity, the spectra are dominated by the features of the underlying support material (see Appendix Sect. A. 1.6) as submonolayer amounts of TCE are dosed. Spectral features of the clusters, e.g. electron density at Ep, or even the characteristic Pt 5d band double peak structure are not visible (in agreement with results in Sect.4.2). 

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