T. Heitz et al., Quantitative study of C-H bonding in polymerlike amorphous carbon films using in situ infrared ellipsometry, PHYS REV B, 58(20), 1998, pp. 13957-13973
Polymerlike hydrogenated amorphous carbon (a-C:H) films have been deposited
by plasma CVD at low temperature and low pressure. Vibrational properties
have been investigated by in situ infrared ellipsometry as a function of fi
lm thickness. Hydrogen distribution within die films has been changed by va
rying the ion energy impinging on the film surface. Vibrational properties
of C-H stretching and bending modes have been analyzed as function of self-
bias (V-bias) in terms of frequency, bandwidth, and intensity. Absorption s
trengths are associated with effective charges that have been calculated fo
r the different sp(3) CH, groups. In order to make a comparison with values
of organic chemistry, a general review of infrared spectra including alkan
es, alkenes, and aromatic hydrocarbons is presented. A dipole description t
aking into account the local environment of CH bonds is developed showing t
hat methyl and methylene group effective charges are similar for polymeric
a-C:H and CxHy organic compounds. Line broadening and frequency shift effec
ts are found to depend on the type of CH groups and are explained through a
model including strain and dipole-dipole interactions. The sensitivity of
effective charges to the local environment and the determination of CHn gro
up densities are used to propose a description of the hydrogenated network
structure. [S0163-1829(98)01044-3].