X-ray photoelectron diffraction study of the initial stages of CVD diamond heteroepitaxy on Ir(001)/SrTiO₃

Bias-treatment (BT) plays an important role in the heteroepitaxial growth of CVD diamond. In this study, an Ir(001)/SrTiO₃ substrate was examined with X-ray photoelectron diffraction (XPD), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), scanning electron microscopy (SEM), and atomic force microscopy (AFM) after a BT process. XPD shows unambiguously that most carbon atoms following the BT process reside in an ordered form. In fact, the XPD patterns are very similar to those from a homoepitaxial CVD diamond (001) surface except for a somewhat smaller degree of angular intensity variation. XPD patterns of Ir 4d core levels from the BT substrate also showed that the short-range order of the Ir(001) crystal was preserved. However, LEED showed no diffraction spots, implying the absence of long-range order at a LEED coherence length greater than the typical one of ∼10 nm. These results prove that the 7-8 nm crystallites seen by SEM and AFM are indeed diamond (001) crystallites. The smaller degree of intensity variation in XPD patterns and the XPS intensity ratio of C 1s/Ir 4d indicates that the diamond crystallites have a height of ∼11 monolayers and are embedded in a disordered carbon matrix about 6 monolayers thick.