Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The influence of assisting low energy (~150 eV) ion bombardment during the deposition of evaporated C60 on the composition and bonding structure is investigated. Thin films were grown on Si (100) substrates by evaporation of C60 with assisting low-energy (~150 eV) N or Ar ion bombardment at different ion to molecule arrival ratios Iion/Imolecule (4-10) and substrate temperatures (RT-300°C). The film composition and areal density was analysed using elastic recoil detection analysis, while the obtained chemical bond structure was analysed by Raman spectroscopy. Spectroscopic ellipsometry was used to determine the film thickness. Raman spectra of the films grown without ion assistance show similar features as the Raman spectrum of initial C60 powder. The additional N or Ar assistance results in a decomposition of the C60 molecules independent of the ion type and Iion/Imolecule, resulting in a bonding structure similar to that observed in a-C or a-CNx. The N and Ar atomic ratios in the films (16-27 at. % for N and 2-4 at.% for Ar) are proportional to Iion/Imolecule and no saturation limit was reached under the present working conditions. The amount of deposited material decreases with increasing Iion/Imolecule for a given substrate temperature for both type of ions. Besides, it is observed that ion bombardment results in a densification of the films compared to the films obtained without ion assistance. The results are discussed on the basis of ion induced displacements of C atoms in the fullerene molecules resulting in a decomposition of the initial fullerene structure.