The effect of fluence on the hardening of C-60 films irradiated with He and N ions

The hardness (H) and the Young modulus (E) of thin C-60 films deposited on Si substrate and ion irradiated are studied via the nanoindentation techniq ue. C-60 films 170 nm thick were irradiated with 170 keV N and 30 keV He io ns. The hardness and the Young modulus were measured as a function of the f luence phi and of the transferred nuclear (S-n) plus electronic (S-e) energ y density sigma(t) = phi(S-n + S-e). The results show an increase of H from 0.33 GPa for the pristine C-60 film to approximate to 15 GPa after the irr adiations with the highest fluences. Similarly E raises from 23 to 180 GPa after the irradiations. It is observed that the curves of H and E follow th e relation between the number of destroyed C-60 molecules measured via Rama n spectroscopy and the average deposited energy density sigma(t), reaching the highest values when the films are fully amorphized. (C) 1999 Elsevier S cience B.V. All rights reserved.