Polymerization and decomposition ofC60on Pt(111) surfaces

The interaction of ${\mathrm{C}}_{60}$ with Pt(111) was investigated at submonolayer, monolayer, and multilayer coverages by Auger electron spectroscopy, x-ray photoelectron spectroscopy (XPS), UV photoelectron spectroscopy (UPS), high-resolution electron-energy-loss spectroscopy (HREELS), and low-energy electron diffraction studies. The Pt(111) surface strongly affects the thermal decomposition of ${\mathrm{C}}_{60}.$ At submonolayer coverages, ${\mathrm{C}}_{60}$ is polymerized on Pt(111) at $T>~300\mathrm{K}$ as was evident from UPS spectra that show a 0.4--0.5 eV shift towards ${E}_{F}$ for the VB features, in comparison to that of multilayer ${\mathrm{C}}_{60}$ films on Pt(111). The polymerization was most clearly evident in HREELS for ${\mathrm{C}}_{60}$ films on Pt(111) annealed to 700 K in the presence of O adatoms or Sn, as seen by the rise in intensity of the ${A}_{g}(2)$ derived mode at 1460 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. As a result, annealing multilayer ${\mathrm{C}}_{60}$ films on Pt(111) to $T>~600\mathrm{K}$ leads to a ${\mathrm{C}}_{60}$ adlayer that is quite different from 1 ML ${\mathrm{C}}_{60}/\mathrm{P}\mathrm{t}(111).$ On annealing ${\mathrm{C}}_{60}$ films on Pt(111) to 900 K, graphite domains appear on the surface and complete fragmentation occurs at 1050 K. HREELS, XPS, and UPS results comparing the ${\mathrm{C}}_{60}$ monolayer to the multilayer were used to study charge-transfer interactions between ${\mathrm{C}}_{60}$ and Pt(111). For 1 ML ${\mathrm{C}}_{60}/\mathrm{P}\mathrm{t}(111)$ at 300 K, UPS spectra show that the ${\mathrm{C}}_{60}$ valence-band features are shifted by about 0.4--0.5 eV towards ${E}_{F},$ while XPS studies show that the $\mathrm{C}(1s)$ core level is shifted by 0.4 eV to a lower binding energy and HREELS studies show that the ${T}_{1u}(1)$ mode is shifted down by 20 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in comparison to multilayer coverages of ${\mathrm{C}}_{60}$ on Pt(111). Based on these shifts it was concluded that charge transfer of two electrons occurs from Pt(111) to monolayer ${\mathrm{C}}_{60}$ upon chemisorption. These charge-transfer interactions contribute to strong binding of the ${\mathrm{C}}_{60}$ monolayer and a low mobility for ${\mathrm{C}}_{60}$ molecules on the Pt(111) surface, which results in the growth of a disordered ${\mathrm{C}}_{60}$ film on Pt(111) at room temperature. Increased mobility of ${\mathrm{C}}_{60}$-derived species on the surface at 900 K results in the growth of an ordered film with a hexagonal structure.