Mechanical and optical characteristics of Al-doped C60 filMS

Al-doped C-60 films are grown on GaAs and quartz glass substrates by solid source molecular beam epitaxy. Mechanical and optical properties of the films are investigated by Vickers hardness test, absorption and reflectance spectra, and photoluminescence measurements. Vickers hardness of 250 HV is confirmed for the Al-doped C-60 films with the molecular ratio of At to C-60 of 30, and the Al-doped C-60 films are found to be undissolved in organic solvents. The absorption spectra of pure C-60 films show some peaks caused by the electron transition among the C-60 molecular orbitals. These absorption peaks become less pronounced in Al-doped C-60 films, probably due to Al incorporation in C-60 matrix. In addition, new photoluminescence peaks appear around 1.75, 1.85 and 1.95 eV. The energy of 1.95 eV coincides well with the energy difference between HOMO and LUMO states. These results suggest that the parity forbidden transition is relieved by the molecular distortion due to the Al-C-60 bonding. (c) 2005 Elsevier B.V. All rights reserved.