Aluminum nitride buffer layer for diamond film growth
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Aluminum nitride buffer layer for diamond film growth V. P. Godbolea) and J. Narayan Department of Materials Science & Engineering, North Carolina State University, Raleigh, North Carolina 27695-7916 (Received 30 August 1995; accepted 8 February 1996)
The role of aluminum nitride (AlN) as a buffer layer on the nucleation and growth of diamond on silicon and steel substrates during hot filament chemical vapor deposition (HF-CVD) has been investigated systematically. The scanning Auger electron microscopy (AES) is employed to study chemistry and content of carbon on the surface and in subsurface regions of AlN as a function of HF-CVD parameters. It is found that AlN offers an excellent diffusion barrier for carbon over a wide range of temperature and hydrocarbon content of CVD gas environment, with simultaneous inhibition of graphitization. It also facilitates nucleation of diamond phase. The surface reactions between AlN and carbon are discussed in terms of hydrogen-assisted phase transformations. We have developed a two-step procedure to obtain a continuous diamond film on steel substrates. The characteristic features of AlN have been exploited to obtain adherent and graphite-free diamond deposits on various types of steels, including low carbon steel, tool steel, high speed steel, and bearing steel.
I. INTRODUCTION
Understanding of nucleation and growth of diamond phase during chemical vapor deposition is the key to deposit diamond films on nondiamond substrates.1–4 The nucleation of diamond phase is critically influenced by CVD deposition parameters as well as substrate variables, including the chemical nature of the substrate. In this regard, the deposition of diamond on iron and its alloys (especially on different types of steels) is found to be particularly cumbersome.3,5–7 The diamond films on these substrates usually have interposing graphitic layers which weaken adhesion and undermine the usefulness of superhard diamond castings. Various studies have shown that transition metals with partially filled 3D shell such as Co, Fe, and Ni promote graphitization during hot filament chemical vapor deposition (HF-CVD) of diamond by stabilizing sp 2 bonding.7–9 It was shown recently7,8 that, by alloying these transition metals with elements such as aluminum (or sodium) which can donate electrons to fill 3D shells and further participate in stabilizing sp 3 bonding, it is possible to grow diamond films without graphitic interlayers. Another approach to solve the problem of graphitization during diamond deposition on iron alloys and steels is to deposit an interposing layer or buffer layer10 on which diamond films can be grown. In this context, the buffer layer is required to have characteristic properties which include: (i) low diffusivity of carbon so as to achieve sufficient surface carbon concentration for onset a)
On leave from Department of Physics, University of Poona, Pune 411 030, India.
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http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 7, Jul 19
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