Deposition of epitaxial transition metal carbide films and superlattices by simultaneous direct current metal magnetron
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. Birch, M.P. Johansson, and L. Hultman Linko¨ping University, Department of Physics, Thin Film Physics Division, SE-58183, Linko¨ping, Sweden
U. Jansson Uppsala University, Department of Inorganic Chemistry, The Ångstro¨m Laboratory, P.O. Box 538 SE-75121, Uppsala, Sweden (Received 6 March 2000; accepted 30 October 2000)
Thin epitaxial TiC and VC films and superlattices have been deposited on MgO(001) by simultaneous sputtering of the metals and evaporation of C60. It was found that epitaxial growth conditions for TiC could be maintained down to a temperature of 100 °C, while the epitaxial growth of VC required 200 °C. Epitaxial VC films were completely relaxed at all growth temperatures, while a change from a relaxed to a strained growth behavior was observed for TiC films. The structural quality of the TiC films was better than for the VC films. A general observation was that a plasma-assisted deposition process yields films with a higher quality and allows epitaxial growth at lower temperatures than for a pure coevaporation process.
I. INTRODUCTION
The transition metal carbides have many unique properties such as high hardness, high catalytic activity, and a good electrical conductivity.1 In some applications, there is an interest in using epitaxial films or even layered epitaxial structures (superlattices) of carbides. For example, it is well-known from the literature that superlattices of group 4 and 5 transition metal nitrides, e.g. TiN/ VN or TiN/NbN, show a substantial increase in strength and hardness2– 4 and it is likely that superlattices of transition metal carbides will exhibit similar properties. A survey of the literature shows that it is difficult to deposit epitaxial carbide films by conventional chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques. At low deposition temperature these techniques often result in the growth of fine-grained and/or amorphous films, while large-grained or epitaxial films require much higher deposition temperatures.5–8 For example, it has been demonstrated that epitaxial growth of TiC on SiC by a conventional CVD process requires temperatures above 1200 °C.9 In a series of recent publications, we have demonstrated that coevaporation of C60 and the transition metals Ti, V, and Nb can be used to deposit epitaxial films and superlattices of TiC, VC, and NbC at very low temJ. Mater. Res., Vol. 16, No. 3, Mar 2001
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peratures.10–13 It was found that the metals Ti, V, and Nb were able to decompose the C60 molecule already at 100 °C and form a nanocrystalline carbide film. When the deposition temperature was increased, the film microstructure changed from nanocrystalline to epitaxial in a narrow temperature range. Already at 250 °C it was possible to deposit epitaxial TiC films on MgO(001).11 In contrast, the deposition of epitaxial VC and NbC on MgO(001) required higher temperatures of 400–500 °C. A general trend was also that the best epitaxial films were obtained for TiC followed by VC and fi
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