Growth defects in diamond films grown by plasma-assisted chemical vapor deposition (CVD) were studied by high resolution electron microscopy. Several features of the microstructure were resolved and their importance to the growth of the diamond film was evaluated. The observations included various twin boundaries of the type ∑ = 3, as well as ∑ = 9, ∑ = 27, and ∑ = 81, which form by an interaction of lower order twins. These higher order boundaries are loci of intersection points of growing planes on two adjacent twins and can serve as an indicator for the local crystal growth direction. The central nucleation site for the growing planes in many cases can be traced back to a quintuplet twin point. A twin quintuplet has five re-entrant angles and thus serves as a preferred nucleation site for new planes as the crystal grows.
Raman spectra were taken of 48 polycrystalline diamond films grown by hot-filament and microwave-plasma chemical vapor deposition (CVD), and one gem-quality diamond, and characterized by fitting the spectra to a model line shape function. The line shape function contains three components: a narrow symmetric line at -1333 cm"1, the Raman line of diamond; a band centered at -1525 cm"1 ascribed to sp2-bonded carbon; and a broad background due to photoluminescence (PL). Four spectral parameters were observed to change from one specimen to another in an interrelated manner: (1) the linewidth of the diamond Raman line, which varies from -3 to -25 cm"1; (2) the intensity in the tails of the diamond Raman line, several halfwidths away from the peak; (3) the peak intensity ratio of the sp2-bonded carbon band to the diamond Raman line, which varies from -0 to -1; and (4) the intensity ratio of the PL background to the diamond Raman peak, which varies from -0.03 to -9. We suggest that the interrelated changes in the Raman spectra are due to changes in the abundance of 5p2-bonded defect structures within the diamond crystallites. Polynuclear aromatic clusters are a possible model for these defect structures. Differences in film morphology, which were observed by SEM imaging, appear to be correlated with the changes in the Raman spectra. The peak position of the diamond Raman line is shifted to higher wave number in the CVD-grown films than in the gem, by as much as 3 cm"1, but this shift is not correlated with the other changes in the Raman spectra. As a function of deposition conditions, the defect-related features of the Raman spectra generally increase with increasing methane concentration or substrate temperature, and decrease with increasing oxygen concentration. A cyclic dependence of the defect-related features on deposition time is observed for one set of films grown by hot-filament CVD.
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