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

Abstract

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 ∼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 ∼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 ∼700 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.