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Thermally Induced Structural Evolution of Silicon- and Oxygen-Containing Hydrogenated Amorphous Carbon: A Combined Spectroscopic and Molecular Dynamics Simulation Investigation
journal contribution
posted on 2018-02-12, 00:00 authored by Filippo Mangolini, James Hilbert, J. Brandon McClimon, Jennifer R. Lukes, Robert W. CarpickSilicon-
and oxygen-containing hydrogenated amorphous carbon (a-C:H:Si:O)
coatings are amorphous thin-film materials composed of hydrogenated
amorphous carbon (a-C:H), doped with silicon and oxygen. Compared
to a-C:H, a-C:H:Si:O exhibits much lower susceptibility to oxidative
degradation and higher thermal stability, making a-C:H:Si:O attractive
for many applications. However, the physical mechanisms for this improved
behavior are not understood. Here, the thermally induced structural
evolution of a-C:H:Si:O was investigated in situ by X-ray photoelectron
and absorption spectroscopy, as well as molecular dynamics (MD) simulations.
The spectroscopy results indicate that upon high vacuum annealing,
two thermally activated processes with a Gaussian distribution of
activation energies with mean value E and standard
deviation σ take place in a-C:H:Si:O: (a) ordering and clustering
of sp2 carbon (E ± σ = 0.22
± 0.08 eV) and (b) conversion of sp3- to sp2-bonded carbon (E ± σ = 3.0 ± 1.1
eV). The experimental results are in qualitative agreement with the
outcomes of MD simulations performed using a ReaxFF potential. The
MD simulations also indicate that the higher thermal stability of
a-C:H:Si:O compared to a-C:H (with similar fraction of sp2-bonded carbon and hydrogen content) derives from the significantly
lower fraction of strained carbon–carbon sp3 bonds
in a-C:H:Si:O compared to a-C:H, which are more likely to break at
elevated temperatures.