UV Raman Studies of Microcrystalline Diamond

ABSTRACTMicrocrystalline diamond films have been prepared in a 13.56 MHz low pressure inductively coupled plasma, in which the pressure of CH4/H2and CH4/CO/H2 plasmas was varied from 45 to 50 mTorr. The bonded structures of the obtained deposits were studied by Raman spectroscopy with 514, 325, and 244 nm excitation wavelength. 514 nm excited Raman spectra exhibit two peaks at ∼1355 cm−1 and ∼1580 cm−1 corresponding to sp2 bonding without CO additive (CH4/H2, plasma). New peaks at ∼1150 cm−1 assigned to sp3-bonded carbon network and at ∼1480 cm−1 appear with CO additive (CH4/CO/H2, plasma). 325 nm excited Raman spectra show a shoulder at ∼1150 cm−1, a clear 1332 cm−1 diamond peak, and the peak at ∼1580 cm−1 is remarkably enhanced. In 244 nm excited Raman scattering, the 1332 cm−1 diamond peak is only enhanced whereas the peak at ∼1580 cm−1 is correspondingly diminished. These features of the Raman spectra imply that the vibrational modes of sp2 sites are resonantly enhanced with 514 nm excitation because the 514 nm (2.4 eV) corresponds to the π-π* transition in sp2-bonded carbon, while the 325 nm (3.8 eV) and 244 nm (5.1 eV) excitations are possibly sufficient to excite the σ state of both sp2- and sp3-bonded carbon