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High-energy shock plasma deposition techniques are used to produce carbon-nitride films containing both crystalline and amorphous components. The structures are examined by high-resolution transmission electron microscopy, parallel-electron-energy loss spectroscopy, and electron diffraction. The crystalline phase appears to be face-centered cubic with a unit cell parameter approx. a = 0.63 nm, and it may be stabilized by calcium and oxygen at about 1-2 at. % levels. 85 at. % of the carbon atoms appear to have trigonal bonding for the crystalline phase, the remaining 15 at. % having tetrahedral bonding. The amorphous carbon-nitride film component varies from essentially nanocrystalline graphite, containing virtually no nitrogen, to amorphous carbon-nitride containing up to 10 at. % N, where the fraction of sp3 bonds ranges up to approx. 85 at. %. There is PEELS evidence that the nitrogen atoms have sp2 trigonal bonds in both the amorphous and crystalline phases.

I. INTRODUCTION 1

Liu and Cohen predicted that a compound having stoichiometry C3N4 could possess hardness rivalling that of diamond. Attempts to synthesize C 3 N 4 have used techniques such as ion implantation,2 rf sputtering of carbon targets in a nitrogen atmosphere,3 plasma deposition of various hyrocarbons,4 nitrogen ion implantation with simultaneous carbon vapor deposition,5 dc magnetron sputtering of a graphite target in a nitrogen ambient,6 shock wave compression of carbon nitride precursors,7 plasma-enhanced chemical vapor deposition,8 ion-assisted dynamic mixing,9 and laser ablation of a carbon target in a stream of atomic nitrogen.10 Mostly, the experimental results indicated formation of amorphous carbon films containing various amounts of nitrogen. Higher nitrogen levels reportedly improve the wear resistance, hardness, and other tribophysical properties. However Niu et al.w claimed they obtained microcrystalline /3-C 3 N 4 , the hexagonal phase predicted by Liu and Cohen.1 This phase was identified by comparing the electron diffraction powder patterns with the Bragg angles predicted, assuming the structure predicted for C3N4 by Liu and Cohen.1 They claimed the overall nitrogen content of these specimens was greater than 40 at. %. Matsumoto et al.n claimed they made crystallites of /3-C 3 N 4 by reacting N atoms and a carbon rod anode in an argon/nitrogen plasma arc at atmospheric pressure. They found six x-ray diffraction peaks identified as /3-C 3 N 4 ; we note that the majority of the deposit was again amorphous carbon, presumably containing nitrogen. No quantitative analysis was presented for either the amorphous or the crystalline forms. J. Mater. Res., Vol. 10, No. 9, Sep 1995 http://journals.cambridge.org

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Gurarie et al.n reported the production of C-N films on silicon substrates, using a high-energy shock plasma deposition chamber. They concluded that carbon nitride films containing up to 25 at. % nitrogen had been obtained. Optical and SEM examinations showed two distinct types of carbon nitride deposits; Typ