Vibrational studies of microcrystalline diamond and diamond-like carbon by high resolution electron energy loss spectroscopy

摘要

High resolution electron energy loss spectroscopy (HREELS) has been applied to investigate the vibrational states of microcrystalline diamond and diamond-like carbon (DLC) films prepared in a low pressure inductively coupled plasma. The CO additive to a CH_4/H_2 plasma exhibits different phonon density of states. Without CO additive, the HREELS spectrum shows a faint peak at approx 1500 cm~(-1) due to C=C stretching vibration of sp~2 bonds, indicating that the sample is mainly composed of DLC. On the other hand, the HREELS profiles show a peak at approx 1100 cm~(-1) assigned to C-C stretching vibration of sp~3 sites with CO additive. The intensity of the peak becomes strong and a shoulder centered at approx700 cm~(-1) corresponding to the bending vibration of sp~3 bonded carbons appears with increasing Co additive. It consequently implies that the Co additive brings about the decrease of the fraction of sp~2 bonded carbons in the resultant films, and it is qualitatively in agreement with the previous characterizations by Raman spectroscopy, transmission electron microscopy, and reflection high energy electron diffraction.