Buckyball microwave plasmas: Fragmentation and diamond-film growth

Abstract

Microwave discharges (2.45 GHz) have been generated in C60-containing Ar. The gas mixtures were produced by flowing Ar over fullerene-containing soot at a variety of temperatures. Optical spectroscopy shows that the spectrum is dominated by the d 3Πg–a 3Πu Swan bands of C2 and particularly the Δv=−2, −1, 0, +1, and +2 sequences. These results give direct evidence that C2 is in fact one of the products of C60 fragmentation brought about, at least in part, by collisionally induced dissociation. C60 has been used as a precursor in a plasma-enhanced chemical vapor deposition experiment to grow diamond-thin films. The films, grown in an Ar/H2 gas mixture (0.14% carbon content, 100 Torr, 20 sccm Ar, 4 sccm H2, 1500 W, 850 °C substrate temperature) were characterized with scanning electron microscopy, x-ray diffraction, and Raman spectroscopy. The growth rate was found to be ∼0.6 μm/h. Assuming a linear dependence on carbon concentration, a growth rate at least six times higher than commonly observed using methane as a precursor would be predicted at a carbon content of 1% based on C60. Energetic and mechanistic arguments are advanced to rationalize this result based on C2 as the growth species.