An attempt to prepare carbon nitride by thermal plasma chemical vapor deposition from graphite and nitrogen
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An attempt to prepare carbon nitride by thermal plasma chemical vapor deposition from graphite and nitrogen S. Matsumoto, K. K. Chattopadhyay,a) M. Mieno, and T. Andob) National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba-city 305, Japan (Received 24 June 1996; accepted 26 April 1997)
RF induction thermal plasma was applied to the chemical vapor deposition of carbon nitride from graphite powders and Ar–N2 gas at about 1 atm. Low-density and fragile amorphous powder-like bulk deposits whose color is light yellow were obtained. Elementary analysis by a combustion method and x-ray photoelectron spectroscopy showed that the NyC ratio is higher than that of stoichiometric C3 N4 . Also, a large amount of hydrogen and oxygen are included, which seems to be due to the absorption of moisture and oxygen after exposure to air. Infrared absorption spectra suggest the presence of sp CN and sp 2 CN bonds, and nitrogen-containing polycondensed ring structures. Thermogravimetric analysis with mass spectroscopy shows that the deposits decompose almost completely at 800 ±C, suggesting that the polycondensed rings are not large and not well cross-linked.
I. INTRODUCTION
In recent years, there has been much interest in the synthesis of a hypothetical new compound b –C3 N4 , which has the same structure as b –Si3 N4 and is expected to be as hard as diamond.1 Many attempts have been made to synthesize this material both by physical vapor deposition (PVD) and by chemical vapor deposition (CVD) methods. The former includes methods such as reactive sputtering in a nitrogen atmosphere,2–4 electron beam evaporation of carbon with N1 ion bombardment,5 laser ablation of graphite with simultaneous N beam bombardment of a substrate,6 and dual ion beam deposition.7 The latter includes methods such as plasma excitation of a gas mixture of hydrocarbon and nitrogen.8 However, in most cases, the resulting materials are amorphous, and the nitrogen content is far below that of stoichiometric C3 N4 . Thus, the stability of the crystalline C3 N4 phase as well as its synthesis remain an open question. There have been several reports which claim the synthesis of crystalline C3 N4 .6,9–19 Most of them employed only electron diffraction to identify the crystal structure. However, the existence of a new phase cannot be established by the results of electron diffraction only. In these reported data of electron diffraction, wide disparities in d-values and intensities are seen. For example, in the reports by Niu et al.6 and by Yu et al.,9 the disagreement of the d-values between the theoretical and observed values is large, and their diffraction data seem a)
Present address: Department of Physics, Jadavpur University, Jadavpur, Calcutta 700-032, India. b) Also with Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST). 180
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J. Mater. Res., Vol. 13, No. 1, Jan 1998
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