Polymerization and decomposition of C60 on Pt(111) surfaces

The interaction of 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(lll) surface strongly affects the thermal decomposition of C-60. At submonolayer coverages, C-60 is polymerized on Pt(111) at T greater than or equal to 300 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 C-60 films on Pt(111). The polymerization was most clearly evident in HREELS for 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 cm(-1). As a result, annealing multilayer C-60,, films on Pt(111) to T greater than or equal to 600 K leads to a C-60 adlayer that is quite different from 1 ML C-60/Pt(111). On annealing 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 C-60 monolayer to the multilayer were used to study charge-transfer interactions between C-60 and Pt(111). For 1 ML C-60/Pt(111) at 300 K, UPS spectra show that the C-60 valence-band features are shifted by about 0.4-0.5 eV towards E-F, while XPS studies show that the 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 cm(-1) in comparison to multilayer coverages of C-60 on Pt(111). Based on these shifts it was concluded that charge transfer of two electrons occurs from Pt(111) to monolayer C-60 upon chemisorption. These charge-transfer interactions contribute to strong binding of the C-60 monolayer and a low mobility for C-60 molecules on the Pt(111) surface, which results in the growth of a disordered C-60 film on Pt(111) at room temperature. Increased mobility of C-60-derived species on the surface at 900 K results in the growth of an ordered film with a hexagonal structure. [S0163-1829(99)05503-4].