Ordering and stabilization of C₆₀ films on the (√3 × √3)R30° Sn/Pt(111) surface alloy

The deposition and growth of C₆₀ on the (√3 × √3)R30° Sn/Pt(111) surface alloy is compared with that on the Pt(111) surface at submonolayer, monolayer and multilayer coverages. We find that alloying Pt(111) with Sn arrests the charge transfer from Pt to adsorbed C₆₀, as seen from the absence of a shift in the T_1u(1) vibrational levels of C₆₀ probed by high resolution electron energy loss spectroscopy (HREELS). From low energy electron diffraction (LEED) observations it is determined that whereas ordering and graphitization of C₆₀ on Pt(111) take place at 900 K, graphitization of C₆₀ is inhibited by Sn alloyed into Pt(111). The rotated hexagonal LEED pattern of the ordered C₆₀ monolayer is stabilized by the presence of Sn on Pt(111) until 1100 K, which is close to the fragmentation temperature of solid C₆₀. Upon heating C₆₀ films on the (√3 × √3)R30° Sn/Pt(111) surface alloy, Sn is dealloyed at about 500 K, and this dealloyed Sn reacts with C₆₀ at 450-700 K, possibly resulting in polymerization. Auger electron spectroscopy annealing studies and the rise in intensity of the unpolarized Raman-active A_g(2) mode at 1467 cm^-1 support this conclusion. High temperature fragmentation of C₆₀ in the presence of Sn leads to HREELS peaks at 250 and 740 cm^-1, prior to the formation of graphite.