High-Pressure Pulsed Plasma Synthesis of Carbon-Nitride Thin Films
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V. N. Gurarie, A. V. Orlov, L. A Bursill, Peng JuLin, K. W. Nugent and S. Prawer School of Physics, University of Melbourne, Parkville, VIC, 3052, Australia ABSTRACT
In this study a high N2 pressure has been used to enhance the N incorporation into CN films produced by a shock plasma deposition method. Auger spectroscopy indicates that increasing the nitrogen pressure from 0.1 atm to 10 atm results in an increase of nitrogen incorporation into CN films to a maximum of 43 at.%. Nitrogen distribution varies across the surface of the deposit, showing an increase of nitrogen content with depth in the center of the deposition and a decrease with depth at points away from the center. SEM and optical microscopy indicate that under increased nitrogen pressure the grain structure becomes finer. Raman spectra contain sharp peaks characteristic of a distinct crystalline CN phase. TEM diffraction patterns for the films produced under N2 pressure in the range of 0.05-0.1 atm unambiguously show the presence of micron-sized crystals displaying a cubic symmetry, and not the predicted fP-Si 3 N4 type structure. PEELS data suggest that in the crystalline phase a significant fraction of the nitrogen atoms have sp2 trigonal bonds and there is a significant degree of sp3 character for the carbon atoms. INTRODUCTION
Recent theoretical work has predicted that a new ultra-hard compound should be able to be synthesised with a composition C3N4 and a hardness to rival that of diamond [1]. These predictions sparked considerable interest in attempts to experimentally realise this compound [211]. The majority of the experimental work reports the formation of amorphous nitrogen rich carbon films. The investigations show that an enhanced nitrogen content improves wear resistance, hardness, tribological and other properties of these films. In [10,11] nitrogen rich carbon depositions were reported to contain a crystalline component related to the P-C 3 N4
phase. Recently we reported the production of C-N films containing up to 32% nitrogen using a shockplasma method in a nitrogen ambient [12]. The method employed a capacitive discharge of 4 As duration between carbon electrodes in a nitrogen gas ambient of variable pressure in a range of 10 Torr to 100 Torr. Both nanocrystalline and amorphous morphologies were produced. In the present work a new deposition chamber has been constructed which allows the plasma to be produced in a high pressure N2 ambient (up to 20 atm). The aim of the present experiments is to increase the nitrogen content in the CN plasma and to investigate how this affects the nitrogen incorporation into the CN films, as well as the structure and morphology of the films produced. In the present study we used the Auger spectroscopy, Raman spectroscopy, SEM and optical microscopy to study films deposited in this high nitrogen pressure ambient. We also report TEM diffraction and PEELS data on a crystalline phase containing C and N produced by shock plasma deposition, which, however, has a structure different to that predicted for t
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