Abstract
CVD growth of uniform conformal polycrystalline diamond (PCD) coatings over complex three dimensional structures is very important material processing technique. It has been found that the nucleation and subsequent growth period is very critical for successful development of CVD diamond based technologies. There are many methods of enhancing diamond nucleation on foreign substrates-ultrasonic treatment with diamond seed suspension being the best among them. A combination of ultrasonic seeding (US) technique with prior treatment (PT) of the substrate under CVD diamond growth conditions for brief period of time, has found to be very effective in enhancing the diamond nucleation during CVD growth—together they are known as NNP. But successive usage of the same seeding suspension up to ten cycles deteriorates the seeding efficiency. 6th seeding cycle onwards the silicon substrates are barely get covered by diamond crystallites. Five different diamond micron grits were used for seeding the silicon substrates and it is observed that US with the sub-micron particles (0.25 μm) is very effective in efficient nucleation of PCD on Si substrates. PT of the substrate somewhat negates the effect of successive use of the same seeding slurry but it is best to avoid recycling of the same seeding suspension using micron size diamond grits.
Highlights
Diamond is one of the most astonishing materials on earth
2-2 was seeded with 6 - 12 μm grit size, whereas sample 3-1 was seeded with bigger 10 - 20 μm grits, but it appears that since none of them were pre-treated, they do not have different grain sizes, but their polycrystals are appearing to be comparable in size. 1-3, 2-2 and 3-1 samples were seeded with gradual increase in grit size (Table 1), which are well reflected in the optical micrographs in Figure 2(a)-(d) with apparent successive bigger polycrystalline diamond (PCD) crystal sizes
2) Quality and crystallinity of PCD coatings are satisfactorily high (~94%) with usage of different grit sizes, but usage of the biggest seed particle size considerably degrades the quality (76%) and its crystallinity (FWHM 12.5 cm−1) with introduction of large internal stress (2.44 GPa). 3) Successive reuse of the same diamond suspension (1st, 2nd, 3rd and so on) for seeding silicon substrates, progressively decreases the resulting PCD grain sizes, may be because, successive use of the ultrasonic force disintegrates the large diameter grits into smaller ones
Summary
Diamond is one of the most astonishing materials on earth. in terms of aesthetic significance, which has wondered human beings for ages, and for its technological superiority over others. Angus of Case Western University pioneered the role of atomic hydrogen in facilitating growth of diamond and removing graphite under chemical vapour deposition (CVD) conditions [7] These experiments proceeded very slowly and were looked at like a suspicious process among scientific community [8]. It is until recently that in the year 1982 a Japanese group at NIRIM successfully developed a very innovative process of synthesising metastable diamond by CVD technique [9] [10] This so called metastable CVD growth [11] is a stable growth of diamond phase with capillary rise in pressure up to 4 GPa under CVD conditions [12] [13]. It is essential to further understand the nucleation and growth mechanisms of CVD diamond [16] for advancement of knowledge in this field, which can add to the existing database
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