Effective pre-treatments of fullerenes to be sublimated for deposition of amorphous carbon films in electron beam excited plasma

Abstract

A pristine C60 fullerene (99%) and a fullerene mixture composed of C60 (60%), C70 (25%) and higher fullerenes up to C96 (15%) were used as precursors for amorphous carbon deposition in electron beam excited plasma. FT-IR spectroscopy confirmed the presence of CH and OH bonds in both of the fullerene powders. Heat treatment in a high vacuum and UV irradiation in air were introduced as pre-deposition treatments of the fullerenes to eliminate elements other than carbon such as hydrogen. Although the deposited carbon films by sublimation of as purchased fullerene mixture had wrinkled surfaces, it was found that the pre-deposition treatments could prevent forming the wrinkles and improve the average surface roughness up to 5nm. These treatments were also able to increase the hardness of deposited carbon films by sublimation of both fullerenes. The decrease of the number of CH and OH bonds, in particular for C60 fullerene, was observed in FT-IR spectra obtained after the pre-deposition treatments. Raman spectra of the deposited carbon films using as purchased and pre-treated fullerene powders confirmed that all of these carbon films possess amorphous structure. The possible causes for the improvement of the surface roughness and hardness are discussed with a review of production methods of fullerenes.