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 polycrystallin e diamond was investigated using a microwave-plasma-assisted chemical vapou r deposition process. Diamond deposition was carried out on the transition elements of the first series (3d block) and on the elements belonging to gr oups VB and VIB. It was found that the chemical nature of the transition me tals plays an important role in the formation of diamond. Similarity in mor phological features was observed on the diamond films grown on the substrat es belonging to the same group. Micro-Raman (mu-Raman) spectroscopy indicat ed that diamond films on substrates belonging to groups VB and VIE have low er internal stresses than those deposited on group VIII. An attempt was mad e to relate the trends observed from the mu-Raman spectroscopy to the chemi cal 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. T hese elements appear to form diamond by a gas-solid-phase reaction, while t ransition metals, such as Ni and Co appear to nucleate diamond by precipita tion from the molten liquid. It may be noted that Ni and Co do not form sta ble carbides. This tendency appears to be related to the 3d shell structure of these elements. A mechanism based on the electronic structure of the su bstrate atoms, particularly on their 3d shell structure, is proposed to acc ount for the above behaviour.