Electronic structure studies of the C 60 film condensed on 2H-MoS 2 (0001) surface

Abstract

The electronic structure and vibrational spectrum of the C60 film condensed on a 2H-MoS2(0001) surface have been investigated by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), Auger electron spectroscopy (AES) and infrared high-resolution electron-energy-loss spectroscopy (HREELS). AES analysis showed that at low energy side of the main transition, C60 contains a total of three peaks just like that of graphite. However, the energy position of the KLL main Auger transition of C60 looks like that of diamond, indicating that the hybridization of the carbon atoms in C60 is not strictly in sp2 - bonded state but that the curvature of the molecular surface introduces some sp2pz-bonded character into the molecular orbitals. XPS showed that the C 1s binding energy in C60 was 285.0 eV, and its main line was very symmetric and offered no indication of more than a single carbon species. In UPS measurement the valence band spectrum of C60 within 10 eV below the Fermi level (EF) shows a very distinct five-band structure that characterizes the electronic structure of the C60 molecule. HREEL results showed that the spectrum obtained from the C60 film has very rich vibrational structure. At least, four distinct main loss peaks can be identified below 200 meV. The most intense loss was recorded at 66 meV, and relatively less intense losses were recorded at 95, 164 and 197 meV at a primary energy of electron beam EP = 2.0 eV. The other energy-loss peaks at 46, 136, 157 and 186 meV in HREEL spectrum are rather weak. These results have been compared to infrared spectrum data of the crystalline solid C60 taken from recent literatures.