Carbon deposition was also probed directly by C 1s XPS after the 6 TPDs, as summarized in Figs. and. Also shown are the C 1s XP spectra measured for Ptfree alumina and Ge/alumina samples after 6 C2D4 TPD. The signals are weak because the coverage of clusters, responsible for most carbon deposition, was small, as is the C 1s photoemission cross section. Nonetheless, it is clear that the C 1s signal for Pt4/alumina is substantially larger than the signal for the alumina support, and after subtracting the support contribution, the net carbon deposition corresponds to ~8 ± 5 C atoms/cluster. The C/Pt ratio was calculated assuming both C and Pt are in the surface layer, in which case C/Pt = (IC•σPt)/(IPt•σC), where IC and IPt are the integrated intensities for the C 1s and Pt 4d peaks, and σC and σPt are the sublevel photoemission cross sections . The C 1s signal for the Pt4Ge/alumina sample is smaller, and after subtracting the support contribution, the carbon deposition is estimated to be 3 ± 3 C atoms/Pt4Ge cluster. Thus, both the absolute number of deposited C atoms/cluster, and the ~3:1 ratio of C deposition on Pt4 compared to Pt4Ge, are consistent with the values derived from analysis of D2 TPD.