Enhancement of diamond nucleation on alumina substrates by the activated species transport method

Abstract

Diamond deposition was carried out by microwave plasma assisted CVD. Al 2O 3 ceramics and sapphire were used as substrates, without surface pre-treatment such as surface scratching. Enhancement of diamond nucleation was investigated using the activated species transport (AST) method which supplies activated diamond species to the substrate in a plasma flame. The AST method was carried out by surrounding the substrate with diamond powder and depositing diamond under conventional growth conditions. A scanning electron microscope was used to investigate the dependence of the diamond nucleation density on the grain size of diamond powder packed around the substrate and on process parameters such as the substrate temperature and methane concentration. Diamond films were characterized by X-ray diffraction and Raman spectroscopy. The results showed that the diamond nucleation density was increased remarkably by the AST method. We also found that the nucleation density was independent of the grain size of diamond powder, and was affected specifically by the substrate temperature. It can be presumed that the diamond powder packed around the substrate was activated in the plasma flame; activated vapor species of diamond were created and transported to nucleate on the substrate surface.