Chemistry Reference
In-Depth Information
As an example the radiative recombination is considered:
dn
e
dt
=−
k
(
2
)
rec
−→
A
+
k
(
2
)
rec
n
e
e
+
A
+
h
ν
·
for
n
e
=
n
A
+
. (3.193)
k
(
2
)
=
1
m
3
s
−
1
.
n
e
(
t
)
=
(3.194)
k
(
2
)
rec
·
t
+
1
/
n
e
(
0
)
4.
Third-orderchemicalreaction:
Product formation depends on three reactant
concentrations.
C
k
(
3
)
A
+
B
+
ABC
−→
AB
+
C.
(3.195)
k
(
3
)
=
dn
AB
dt
=
k
(
3
)
ABC
m
6
s
−
1
.
·
n
A
·
n
B
·
n
C
(3.196)
3.6 BOUNDARY PLASMA-SURFACE, PLASMA SHEATHS
The contact of the plasma with condensed matter, such as gas discharge electrodes,
surrounding solid walls or liquids, immersed probes for the plasma diagnostics or
materials in the plasma surface processing, is one of the most important phenomena
in the plasma physics and chemistry. The transition zone between the plasma and
phase boundary of condensed matter represents a general and complex problem.
In more general sense, the plasma surface interaction describes all phenomena
which are connected with the interaction of charged and neutral plasma particles as
well as photons with solid or liquid phase boundaries, their physical and chemical
processes in the interface of the condensed matter, as well as their influence back to
the plasma properties due to surface recombination of charged and neutral plasma
particles, secondary particles emission, erosion of surface material, and formation
of new compounds by means of heterogeneous chemical reactions. Therefore, the
plasma surface interaction includes collective and synergistic processes involving
charged particles, fast neutrals and meta-stable excited particles, energetic photons,
and chemical reactive atoms and molecules. The particle flux to the surface and the
plasma radiation may initiate manifold elementary processes in the phase bound-
ary due to exchange of charge, energy, momentum, and mass. In dependence on
the surface material at the phase boundary as well as their physical and chemical
modification during interaction with the plasma it is observed a characteristic pene-
tration depth of each kind of plasma particles. The complex surface processes may
include secondary electron or negative ion emission, charge carrier recombination,
(adsorbate) sputtering of surface material, chemical modification of a thin surface
layer, desorption of chemical reaction products (cleaning, plasma etching) or thin
film formation, see Figure 3.26. In molecular plasmas the chemical surface function-
alization, the plasma etching, and thin film deposition take place simultaneously. The
surface processes can be controlled by the plasma parameters and the kinetic energy
of impinging positive ions (reactive ion etching, chemical sputtering, ion-assisted
thin film deposition) as well as the surface temperature.
From the plasma physics point of view the transport of charged particles to
or from the surface is in the focus of interest. This transport is controlled by the
