Diamond nucleation and growth on reactive transition-metal substrates
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Diamond deposition on group VIII transition metals of Cr, Mn, Fe, Co, and Ni has been achieved by a multi-step chemical vapor deposition process consisting of (i) seeding the substrate with diamond powders, (ii) annealing the seeded substrate in hydrogen at high temperatures, and (iii) diamond nucleation and growth. It was found that high quality diamond can be grown on these substrates, and the often accompanied graphite formation, which has been the main obstacle in the deposition of diamond on these metal surfaces, can be largely suppressed by the above step-deposition procedure. This technique was further extended to the processes of depositing diamond on steels and Co-bonded WC materials. I. INTRODUCTION Recent reports on heteroepitaxial nucleation of diamond on nickel substrates by hot filament chemical vapor deposition (CVD) involving substrate seeding and annealing followed by diamond nucleation and growth has important scientific and technological implications. 12 The technique is potentially applicable to a variety of other metallic materials which have similar physical and chemical properties to Ni. These materials include the group VIII transition metals of Mn, Fe, and Co, and together with Ni, they are common alloy elements of many types of steels and other important engineering materials such as cobalt-bonded tungsten carbide (CoWC). They have generally been considered extremely difficult for diamond nucleation due to the formation of graphite. By utilizing the multi-step deposition technique, CVD diamond deposition can be accomplished on these substrates, and thus a number of new applications can be explored. This paper reports experimental results of diamond deposition on these metals using the multistep growth process developed for Ni. The underlying principle for these experiments is that the group VIII transition metals of Cr, Mn, Fe, and Co, similar to Ni, all possess unsaturated of-shell electrons (from 3d5 of both Cr and Mn to 3d& of Ni). Because of the incomplete filling of the J-orbital, these metals have specific chemical interactions with carbon. Except Cr, these metals can dissolve carbon to form solid solutions, but are generally considered weak carbide formers. They catalyze graphite formation at low pressures, address: AT&T Bell Laboratories, 600 Mountain Avenue, Murray Hill, New Jersey 07974. b) Present address: Kobe Steel USA Inc., Electronic Materials Center, Research Triangle Park, North Carolina 27709. c) Present address: Centra Sviluppo Materiali, Via di Castel Romano 100, Roma 00129, Italy.
thus making direct diamond nucleation on these metal substrates difficult under typical CVD conditions.3"7 On the other hand, these metals are well-known solventcatalysts for diamond crystallization under high pressure and high temperature (HPHT) conditions.8-9 Some relevant physical and chemical properties of these metals are shown in Table I. As postulated in the HPHT literature,10 diamond can be successfully crystallized from/on a Ni surface when Ni and C form an intermediate compound/com
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