Growth of Stoichiometric bn Films by Pulsed Laser Evaporation
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GROWTH OF STOICHIOMETRIC BN FILMS BY PULSED LASER EVAPORATION P. T. Murray*, M. S. Donley**, and N. T. McDevitt** * Research Institute, University of Dayton, Dayton, OH 45469 ** AFWAL/MLBM, Materials Laboratory, Wright-Patterson AFB, OH 45433-6533 ABSTRACT The feasibility of growing stoichiometric thin films of BN by pulsed laser evaporation has been investigated. Films grown under high vacuum conditions were N-deficient. This result is consistent with thermodynamic calculations, which indicate that B metal formation, with concomitant N2 desorption, is energetically favored over BN formation. Stoichiometric films were grown in NH3 with substrate temperatures of 400, 500, and 1000 0 C. Analysis of films grown under these conditions by grazing incidence x-ray diffraction indicates the films to be highly oriented, hexagonal BN. INTRODUCTION There is a need for solid lubricant films with superior thermal stability and with tribological properties which are not degraded by air exposure. BN is one such candidate material. Thin films of BN have been grown by a variety of techniques, the most common of which entail reacting NH and B2H at high substrate temperatures [1,2]. Murarka and coworkers [3] found that a substrate temperature of 800 0 C was required to grow stoichiometric BN films; at lower temperatures, the films were N-deficient. Adams and coworkers [4]investigated the properties of films grown between 250 and 600°C. Their results indicated that the films thus grown had a composition of B2 NHx. Yamaguchi and Minakata [5]used a two furnace technique and found-the films grown above 5000C to be stoichiometric.
Despite these advances, there is still a need for improved deposition processes, particularly those which which allow growth of stoichiometric BN at even lower substrate temperatures. The purpose of the work presented here was to determine the feasi-
bility of growing stoichiometric BN films by pulsed laser evaporation (PLE). Among the advantages of PLE are the potential for congruent evaporation, the capability of growing high purity films, and the relative ease with which even refractory materials, such as BN, can be evaporated. An additional advantage, which is particularly pertinent to deposition of BN for high precision tribology applications, is the fact that PLE has the potential of allowing film growth at lower substrate temperatures than conventional processing techniques. EXPERIMENTAL
The apparatus used for film deposition and subsequent surface analysis has been described in detail previously [6]. The system consists of a deposition chamber which is directly connected to a Perkin-Elmer (PHI) Model 550 XPS/AES surface analysis system. A specimen introduction port and transfer arm allow film growth in the deposition chamber and subsequent This work was sponsored by the Materials Laboratory, Air Force Wright Aeronautical Laboratories, Aeronautical Systems Division (AFSC), United States Air Force, Wright-Patterson Air Force Base, OH 45433-6533. Mat. Res. Soc. Symp. Proc. Vol. 128. t 1989 Materials Rese
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