Nanodiamond films with dendrite structure formed by needle crystallites

• Structural properties of nanocrystalline diamond films were investigated.
• The nanodiamond films consist of globules having dendrite internal structure.
• Needle-like diamonds of micrometer length are forming the cores of the globules.
• Thermal oxidation allowed selective removal of the smallest diamond fractions.
• The model of the nanodiamond globular structures growth is proposed.

Nanocrystalline diamond coatings, consisting of tightly packed globular structures, were obtained using a direct current plasma assisted chemical vapor deposition method. Composition of the globules from diamond crystallites of different size and from graphitic material was revealed using a combination of thermogravimetry analysis, Raman spectroscopy and scanning electron microscopy. The smallest diamond and graphitic fractions were selectively removed from the nanodiamond films by thermal oxidation in air at a temperature of 620 °C. The rest of the film material consisted of diamond needle-like crystallites, forming the “skeletons” of the globules. Mechanisms including the formation of the dendrite structure of the nanodiamond films with the “skeletons” formed by the needle crystallites are discussed.

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