Chemistry Reference
In-Depth Information
Powered electrode
Grounded electrode
Ar
+
Ar
+
1050 Vpp
1050 Vpp
875 Vpp
875 Vpp
700 Vpp
700 Vpp
525 Vpp
525 Vpp
1×10
6
5.0×10
5
350 Vpp
350 Vpp
5×10
5
2.5×10
5
Peak-to-peak voltage
× 5
×1
0
175 Vpp
175 Vpp
0
0
0
5 0 5 0 5 0
0
100
200 300 400
Ion energy in eV
500
600
(a)
(b)
Ion energy in eV
FIGURE 3.30
Ion energy distribution function (Ar
+
) at the RF electrode (a) and grounded
electrode (b). 13.56 MHz-discharge in argon at 5 Pa, parameter: peak-to-peak voltage. (From
Zeuner, M. et al.,
J. Appl. Phys
., 81, 2985, 1997.)
distribution the saddle-shaped structures overlap from ions directly from bulk plasma
and ions from charge transfer collisions.
At the grounded electrode the single peak at the high energy end is seen, only,
Figure 3.30b.
With increasing pressure the elastic collisions will have more influence. This
is connected with increasing ion intensity at the low energy part and disappearing
(multiple) peak structure.
3.7 NONTHERMAL PLASMAS OF ELECTRIC GAS DISCHARGES
3.7.1 I
NTRODUCTION AND
O
VERVIEW
Nonthermal plasmas are usually generated by electric gas discharges due to the
heating of electrons in the electric field and the ionization of the neutral gas atoms
or molecules by electron impact ionization. In this section the heating of electrons in
the electric field is discussed in connection with the dissipation and confinement of
energy. Thereby the evolution and re-distribution of the electron energy distribution
function (EEDF) plays a significant role in electrical gas discharges. It depends on
elementary plasma processes with characteristic time constants, for
•
Production and recombination of charged species
•
Dissociation of molecules and chemical reactions
•
Excitation and de-excitation of neutral and charged atoms/molecules
