Surface study of iridium buffer layers during the diamond bias enhanced nucleation in a HFCVD reactor

摘要

The BEN nucleation of diamond on iridium substrates has been studied in a hot filament reactor. Without a prior BEN stage, no diamond nucleation could be detected. Nucleation is promoted only if a BEN step is applied before the CVD growth with nucleation densities up to 5 10~9 cm~(-2). The present study focuses on the early stages of BEN to better understand its specific role. In this way, samples have been in situ characterized using electron spectroscopies (XPS, Alas, ELS) and further investigated by HR-SEM, AFM, Nano-Auger and Raman spectroscopy. A very different behaviour in the interface formation has been observed, as compared to silicon. First, a substrate roughening takes place during the cleaning step. Second, the formation of a graphite layer was systematically observed, with or without the BEN stage, in the early stages of CVD synthesis. Its crystallinity has been studied from the Raman experiments. The study of the XPS Ir 4f peaks supports a weak chemical bonding between graphite and iridium. Finally, after the BEN stage, spatially resolved Nano-Auger and Raman measurements revealed the presence of diamond nanocrystals.