On the growth of polycrystalline diamond on transition metals by microwave-plasma-assisted chemical vapour deposition

The role of transition-metal substrates on the deposition of polycrystalline diamond was investigated using a microwave-plasma-assisted chemical vapour deposition process. Diamond deposition was carried out on the transition elements of the first series (3d block) and on the elements belonging to groups VB and VIB. It was found that the chemical nature of the transition metals plays an important role in the formation of diamond. Similarity in morphological features was observed on the diamond films grown on the substrates belonging to the same group. Micro-Raman (mu-Raman) spectroscopy indicated that diamond films on substrates belonging to groups VB and VIE have lower internal stresses than those deposited on group VIII. An attempt was made to relate the trends observed from the mu-Raman spectroscopy to the chemical properties of the transition elements. The mechanism of diamond growth seem to vary across the period. Elements belonging to the first half of the transition series, namely Ti, V, Nb, Ta, Mo and W, form stable carbides. These elements appear to form diamond by a gas-solid-phase reaction, while transition metals, such as Ni and Co appear to nucleate diamond by precipitation from the molten liquid. It may be noted that Ni and Co do not form stable carbides. This tendency appears to be related to the 3d shell structure of these elements. A mechanism based on the electronic structure of the substrate atoms, particularly on their 3d shell structure, is proposed to account for the above behaviour.