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Articles you may be interested inThe thermally-induced reaction of thin Ni films with Si: Effect of the substrate orientation

A seeding and multistep deposition process has been developed to nucleate and grow diamond films directly on Ni substrates in a hot filament chemical vapor deposition system. High quality diamond films have been deposited without graphite codeposition on both (100) oriented single-crystal Ni and polycrystalline Ni substrates. Both (100) and (111) oriented diamond nuclei have been observed depending upon the underlying substrate orientations. Molten metallic phases were found surrounding the diamond nuclei, and it is speculated that a liquid layer composed of nickel, carbon, and hydrogen also formed on the diamond surface during the growth. The oriented diamond is believed to have been achieved by the reorientation of seeded diamond particles into alignment with the Ni substrate due to interaction between the diamond and Ni lattices.The heteroepitaxial growth of single-crystal diamond thin films on non-diamond substrates by chemical vapor deposition (CVD) has long been sought due to its enormous potential impact on the microelectronics industry. Promising candidate substrate materials include cBN, /3-SiC, BeO, Ni, Cu, Si, and a few refractory metals such as Ta, W, and Mo. However, apart from reports of heteroepitaxial growth of diamond films on cBN and /3-SiC substrates, 1 " 3 most experiments have yielded randomly oriented, three-dimensional diamond nuclei. The extremely high surface energy of diamond (in the range of 5.3-9.2 J/m 2 for the principal low index planes 4 ) and the existence of interfacial misfit and strain energies between diamond films and non-diamond substrates 5 are believed to be the primary obstacles in forming oriented two-dimensional diamond nuclei.Nickel is one of the few materials that has a close lattice-parameter match with diamond {a = 3.52 A for Ni and a = 3.56 A for diamond). However, its high solubility for carbon and its strong catalytic effect on hydrocarbon decomposition and subsequent graphite formation at low pressures have prevented CVD diamond nucleation on the Ni surface without the deposition of an intermediate graphitic layer. 6 ' 7 The graphitic interlayer generally forms immediately when Ni substrates are placed in a methane-hydrogen CVD environment. This has excluded the possible development of an orientational relationship between the diamond film and the Ni substrate, even though diamond might eventually nucleate and grow on the graphitic interlayer.On the other hand, it has been known for decades that Ni is an effective solvent-catalyst metal for diamond crystallization under high pressure and high temperature (HPHT) conditions. 8 " 10 Although a detailed mechanism of the solvent-catalytic effect has not been completely developed, it is believed that its strong reactivity with carbon actually becomes a virtue in the catalytic HPHT diamond growth process. Thus, it is certainly interesting to consider if this same characteristic can be made useful in the low pressure CVD process. Indeed, Badzian and Badzian 11 have recently performed a study of diamond deposition on thin...

The various crystallographic forms of boron nitride (BN) are of great technological interest because of their demonstrated tribological, high-temperature, thermally conducting, electrically insulating, and wide-bandgap semiconductor properties. Unfortunately, the synthesis of crystalline BN films is still in the early stages of development. Furthermore, although polycrystalline BN films have been prepared by a variety of physical and chemical vapor deposition techniques, the capability does not currently exist for depositing large area single-crystal or oriented films of BN. Such single-crystal films are required for many applications of interest, especially in electronics. The present paper reports on a new approach to the oriented growth of boron nitride using a novel molten layer epitaxy technique. Well-oriented hexagonal boron nitride (h-BN) crystals were obtained with highly faceted crystal shapes. The h-BN was formed via precipitation from a molten, hydrogen-saturated Ni surface layer. Solid cubic BN was utilized as the source material and was dissolved into the substrate surface during a brief high-temperature anneal. It was found that surface melting occurred during this process and the B diffused into the Ni substrate, whereas the N was expelled into the growth chamber. Oriented BN was then precipitated as the surface layer was allowed to resolidify.

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