Ultrananocrystalline Diamond Films from Fullerene Precursors

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Abstract

Fullerenes are unique sources of carbon vapor. The molecule C 60 has an equivalent carbon vapor pressure near to 1 Torr at the very modest temperature of 600 °C. Fragmentation produces primarily carbon dimer C 2 , resulting in highly supersaturated carbon vapor, which condenses, surprisingly, to form ultrananocrystalline diamond films. This new form of diamond (3–5 nm crystallite size) is phase-pure as established by a variety of techniques. Theoretical calculations provide insight into the mechanisms underlying the insertion of C 2 into the (110) and (100) faces of the diamond lattice and show that the carbons are largely π-bonded across two-atom-wide grain boundaries. The electrical conductivity can be controlled by nitrogen additions over many orders of magnitude and results in n-type doping. Tribological, electronic, and MEMS applications of these unusual materials are discussed.