Chemistry Reference
In-Depth Information
Energy-deficient
regime
Monomer-deficient
regime
W
/
F
FIGURE 8.48
Deposition rate for constant monomer flow rate in relation to energy density,
presents the energy- and monomer-deficient regimes.
This parameter is a measure of the energy input per particle during the flow through
the active plasma zone in relation to the thermal energy
kT
(see Chapter 4 and
[319,320]).
Yasuda introduced the composite power parameter, which includes additionally
the monomer mass [305]
Cp
10
9
[J/kg] with
W
power input [Watt]
into the active plasma zone, where the polymerization occurs,
F
flow rate [cm
3
(STP)/min],
M
molecular mass of the monomer [g].
For a constant monomer flow rate, increasing power leads to linear increasing
deposition rate. This is the energy-deficient regime. The following saturation of
the deposition rate is caused by limited monomer concentration in this monomer-
deficient regime [321] (see Figure 8.48). Increasing monomer flow rate at constant
power causes a linear increase of the deposition rate up to a maximum value and
beyond this region a decrease is observed due to the reduced residence time of the
monomer particles in the active plasma zone.
The deposition of thin films, but also of powders and oily substances is observed
[322]. Powder formation is supported by low flow rates, long residence times of
the particles in the active plasma, and therefore polymerization reactions in the
volume. Film formation at the substrate is assisted by shorter residence times
of the active species in the plasma. Oil deposition at the substrate occurs for
short residence times and therefore low cross linking [144]. The quality of the
deposited material depends on the plasma parameter, in particular on electron energy
and density.
=
W
/
FM
·
1.34
·
8.2.4.1.2.1 Plasma Polymerization of Hydrocarbons
A broad spectrum of hydrocarbons is investigated in various plasma systems.
The deposition rate depends on the chemical structure; compounds with multiple
bounds and cyclic structures show in general higher deposition rates than saturated
