Structure and Properties of a-C:N Films Prepared by Pulsed Excimer Laser Deposition
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STRUCTURE AND PROPERTIES OF a-C:N FILMS PREPARED BY PULSED EXCIMER LASER DEPOSITION Fulin Xiong and R. P. H. Chang Northwestern University, Department of Materials Science and Engineering, and Materials Research Center, Evanston, IL C. W. White Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN
ABSTRACT We present results on the synthesis of a-C:N films deposited by pulsed excimer laser ablation of graphite in a nitrogen gas ambient. Analysis with RBS and forward recoil spectrometry show that the films are hydrogen-free and nitrogen can be incorporated upto 40% by varying the nitrogen gas pressure. Electron microscopy has identified these films to be amorphous. Raman spectroscopy, infrared spectroscopy, and electron energy loss spectroscopy have revealed carbon-nitrogen bonding structures. Compared to a-diamond films prepared by the same technique, the C:N films still possess the properties of high mechanical hardness, chemically inertness and good wear resistance, but incorporation of nitrogen into the films generally degrades their diamondlike properties. The results suggest that nitrogen doping effect is resulted in the films under the present process, instead of carbon-nitrogen compound formation.
INTRODUCTION In 1989, Liu and Cohen' theoretically predicted that there might exist a covalently bound solid material of carbon nitride, whose crystalline form might possess a lower compressibility with the hardness comparable to or greater than that of diamond. This2 material would have a structure similar to ,l-Si3N4 with sp3 hybridized at carbon and sp hybridized at nitrogen. Since then, there is a growing interest in synthesizing this material. A variety of deposition techniques have been employed in the laboratories, .7 3 . pyrolysis5' 6 and shock wave compression such as CVD 2, PVD,3' 4 high temperature with generally inconsistent results are Amorphous C:N films are normally obtained. The the prediction or diversified in the film properties. We present here results of a study on the synthesis of a-C:N films prepared by pulsed excimer laser ablation of graphite in a nitrogen gas ambient. The present study was motivated from a nonequilibrium process generated by pulsed UV excimer ablation, which has been utilized for deposition of many kinds of films. A variety of analytical techniques have been used to characterize the structure and properties of films. We compare the results with those of amorphous diamond films prepared by a similar method in vacuum. EXPERIMENTAL The experiments are carried out in a stainless steel high vacuum chamber with a turbo-molecular pump. The setup of the pulsed excimer laser ablation system for thin
Mat. Res. Soc. Symp. Proc. Vol. 285. ©1993 Materials Research Society
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film deposition has been described elsewhere.8 The typical experimental condition used in this study is given in Table 1. During deposition the chamber is back filled with nitrogen gas with pressure in the range of 20 to 100 mTorr. using a mechanical pump and a throttle valve, the flow rate can b
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