Enhanced Growth of Diamond Grains in Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films by Pulsed Laser Deposition with Boron-Blended Graphite Targets

Abstract

Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon composite films were prepared by pulsed laser deposition with boron-blended graphite targets and the effects of the boron-doping on the growth of UNCD grains were investigated. With an increase in the boron content, the grain size was increased from 5 to 23 nm accompanied by the lattice constant approaching that of bulk diamond. The sp3/(sp3+ sp2) ratio estimated from the X-ray photoemission spectra was enhanced by the boron-doping, which might be predominantly attributable to the enlarged grains. The near-edge X-ray absorption fine-structure spectroscopic measurement revealed that boron atoms are preferentially distributed into grain boundaries. On the basis of the results, the roles of the boron atoms in the enhanced crystalline growth are discussed. We consider that the crystalline growth posterior to the nucleation is facilitated by boron atoms neighboring UNCD grains or by boron-containing energetic species in plasma.