Transmission electron microscopy study of the diamond nucleation layer on iridium

The carbon nucleation layer formed during bias enhanced nucleation (BEN) of diamond on iridium has been studied by transmission electron microscopy (TEM) in high resolution (HRTEM) and high angle annular dark field (HAADF) mode. To improve the imaging, a sandwich structure has been formed by depositing an additional 10-nm-thick layer of iridium on top of the nucleation layer before TEM sample preparation. A thin interlayer of about 1 nm was found on flat iridium films and also on iridium samples which had been roughened during BEN. A quantitative evaluation of the HAADF images allowed to determine the mean effective thickness of the carbon layer to 0.75 ± 0.23 nm. In the high resolution images of the BEN treated samples, besides small amorphous regions, the interface is dominated by atomically resolved areas with iridium's lattice constant. The texture of the Ir covering layer indicates that the BEN layer does not form a completely closed film. After 2 min growth 8-nm-high epitaxial diamond crystals at a mean distance of about 25 nm are clearly visible. Amorphous carbon deposited during BEN has apparently been etched completely during this short growth step.