The discovery of ultrananocrystalline (UNCD) films, the third member of the remarkable triad of nanostrucxtured carbons which includes fullerenes and nanotubes had its conceptual foundation in 1991 when a radically different plasma chemistry based on carbon dimer, C2, as the growth and nucleation species was proposed.

The dramatic effect on film electrical conductivity of adding nitrogen to the methane/argon synthesis gas has been studied in detail based on observations begun in 1997. The creation of a useful, ambient temperature, highly conducting n-type UNCD is a breakthrough in diamond science. A high temperature all-diamond pn junction heterostructure diode has shown excellent rectification properties.

To obtain a better understanding of the relationship between the plasma chemistry and film properties, a detailed study of CN/C2 ratios as a function of nitrogen content in the synthesis gas has been undertaken by my collaborator, Dr. Paola Bruno using emission spectroscopic techniques. This work will be discussed in the light of tight binding density functional calculations showing that the reaction of CN with the diamond surface provides a plausible mechanism for the incorporation of nitrogen into UNCD films. *This work was supported by the U.S. Department of Energy, BES-Materials Sciences under Contract W-31-100-ENG-38.

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