Hydrogen in polycrystalline diamond: An infrared analysis

Abstract Hydrogen in polycrystalline diamond (PCD) films has been analysed by infrared spectroscopy. A series of differently prepared PCD films exhibiting considerable differences in the shape of the C-H stretch absorption band has been studied. The spectra are consistently explained by a superposition of lines from sp3 hybridized CH3, CH2 and CH groups. The corresponding vibrational frequencies coincide with those of amorphous hydrogenated carbon (a-C:H). Contributions of sp2 hybridized CHn groups are found to be less than 10%. In addition to the known a-C:H lines a diamond specific C-H vibration at 2822 cm-1 has been observed for the first time in PCD. It is shown that hydrogen is incorporated in noncrystalline and defective regions of the PCD film, i.e. at grain boundaries and dislocations. For decreasing grain size (increasing defect content) the hydrogen concentration increases. In many samples the sp3 hybridized CH2 group is dominant (up to 69%). Within a series, where the hydrocarbon concentration in the feed gas was varied, samples with high abundances of sp3CH3 (49%) and sp3CH (28%) have been prepared.