Polymerization and decomposition of C-60 on Pt(111) surfaces

The interaction of C-60 With Pt(111) was investigated at submonolayer, mono layer, and multilayer coverages by Auger electron spectroscopy, x-ray photo electron spectroscopy (XPS), UV photoelectron spectroscopy (UPS), high-reso lution electron-energy-loss spectroscopy (HREELS), and low-energy electron diffraction studies. The Pt(lll) surface strongly affects the thermal decom position 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 s how a 0.4-0.5 eV shift towards E-F for the VB features, in comparison to th at 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 prese nce of O adatoms or Sn, as seen by the rise in intensity of the A(g)(2) der ived 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 i s 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 fragmentati on occurs at 1050 K. HREELS, XPS, and UPS results comparing the C-60 monola yer to the multilayer were used to study charge-transfer interactions betwe en 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 shif ted down by 20 cm(-1) in comparison to multilayer coverages of C-60 on Pt(1 11). Based on these shifts it was concluded that charge transfer of two ele ctrons occurs from Pt(111) to monolayer C-60 upon chemisorption. These char ge-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 result s in the growth of a disordered C-60 film on Pt(111) at room temperature. I ncreased mobility of C-60-derived species on the surface at 900 K results i n the growth of an ordered film with a hexagonal structure. [S0163-1829(99) 05503-4].