Microstructural characterization of diamond films deposited on c-BN crystals

摘要

The morphology and structure of diamond films, deposited on cubic boron nitride (c-BN) crystals by microwave-plasma-enhanced chemical vapor deposition, is studied by high-resolution scanning electron microscopy and micro-Raman spectroscopy. The c-BN crystals, with sizes of 200 to 350 μm and grown by a high-temperature/high-pressure technique, were embedded in a copper holder, and used as substrates in deposition runs of 15 mm to 5 h. The nucleation centers for diamond appear as well-shaped cuboctahedral crystallites, having diameters of approximately 100 nm. With increasing deposition time the diamond crystallites grew larger, forming islands on the c-BN faces. In some cases, epitaxial growth was observed on the (111) c-BN faces where coalesced particles gave rise to very smooth regions. A number of diamond crystals with peculiar shapes are observed, such as a pseudo five-fold symmetry due to multiple twinning. Moreover, both randomly distributed carbon tubes, about 100 nm in diameter and 1 μm in length, and spherically shaped features are observed in samples prepared under the typical conditions of diamond deposition, this effect being ascribed to the influence of plasma-sputtered copper contamination. Quite unusual diamond crystals with a deep, pyramidal-shaped hole in the middle grew on the copper substrate between the c-BN crystals.