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Fig. 2.11. The temperature dependences of idling dark voltage (a) and short
-
circuit 
current density (b) for uniform heating of the structure being a KEF
-
20 film on the 
surface of the KDB
-
40 (100) substrate 
300
400
500
600
700
800
-8
-6
-4
-2
0
2
4
6
a)
U, мВ
T,K
300
400
500
600
700
800
-1,4
-1,2
-1,0
-0,8
-0,6
-0,4
-0,2
0,0
б)
I, мкА/см
2
T,K
122 

---

On the basis of the experimental data obtained one can state that the films of 
both 
p
-type and 
n
-type deposited on the substrates with opposite type of 
conductivity have the following characteristic features. 
1. For uniform heating with no temperature gradient on these film structures 
there is idling dark voltage; its value is 
~5-10 
mV for temperature 
~800K. 
2. Effective generation of carriers is observed for T
>500K and when the 
temperature increases up to 9
00K there is dark current; its density is ~1,2
-
2,5
mkA
/
cm
2 
for different samples. 
3. Changes in dark voltage and short
-circuit current with the raise in 
temperature and cooling take place smoothly and along one curve with discrepancy 
of results not higher 
than 5%.
The results obtained experimentally confirm a role of the deep energy levels 
in appearing the thermovoltaic effect, namely its manifestation in structures formed 
under vacuum conditions with exclusion of any sources of deep levels but when 
the concentration of the indicated levels is sufficient for their appearing. 
It should be noted that the high Zeebek coefficient of TEC can be caused not 
only by the high concentration of deep levels but also by the presence of 
microlayers of oxide through which
the charge carriers are tunneled. Therefore, an 
increase in this parameter and in other thermovoltaic parameters of film-based 
TECs can be connected with purposeful creation of specially doped areas in the 
process of film growth and, as shown by this work, the ion
-stimulated methods are 
more suitable for this goal. 
2.6.
 
Ion stimulated electron beam physical vapour deposition
 
Electron beam physical vapour deposition (EB
-
PVD) is an effective process 
for dense coatings, high thermal efficiency, and relatively
high deposition rates. 
Additional benefits can be gained in this process with the simultaneous usage of 
ion-assisted deposition. Ion bombardment of the substrate provides a better control 
of the deposition process and the resulting adhesion of the films, 
their morphology 
and chemical composition. By controlling the current density and energy of ions, 
porous, columnar, textured and epitaxial coatings may be obtained.
From common reasons it can be confirmed that the
increase of the degree of 
ionisation of pa
rticles depositing on the substrate, is possible by magnification of
the electron current of the evaporator (at constant
power) and accelerating potential 
on the substrate. Thus,
the current of generated ions and efficiency of the 
extraction them on the su
bstrate accordingly increases. 
Discussing of other physical factors of this process the following must be 
mentioned:
Atoms re-
evaporation (scattering) process due to the ions bombarding the 
substrate: in the literature it is shown that by 
U
b
= 1 keV the sc
attering coefficient 
is ~
1. In our experiments the degree of ionization is 
~
0.15%. Therefore this 
scattering has not been taken into account because it is only ~10-3 part of the flow. 
The estimation of the electrons effect on the ion current: (
a
) 
In the case of reflected 
electrons from the e-beam evaporator - special construction design of the detector 
123 

---

allows us to separate the ionic and electronic constituents in the field of a parallel-
plate capacitor and they are detected separately at different electrodes. 
(
b
) 
In the 
case of secondary processes including ion-electron emission — the ion detecting 
electrode is constructed from pure Ta. In so doing the assessment of the 
instrumental error by measuring the ion current is not more than 10%.
In many cases accelerated gas ions are used for ion- assisted deposition. 
However,
after neutralizing under the 
surface,
the gas ions can cause 
bubbles,
which can tear and damage the structure of the film. Usage of the accelerated 
‘self’ ions, generated as
a result of ionization of evaporated 
atoms,
overcomes 
this problem. In the 
EB
-
PVD
process,
used in the present 
work,
the ions are 
generated by the collision of 
electrons,
which are present in the field of the 
evaporator,
with the evaporated atoms. 
This ionization
takes place in the area near 
to the surface of evaporated 
material,
because in this area there is a high 
concentration of evaporated atoms and a high current density of electrons. 
There
are three groups of 
electrons,
whose contributions are 
approximately
the same 
order of magnitude in the process of 
ionization:
-
electrons of the e-
gun,
which have energy 10 
keV;
-
back-scattered electrons with energies 100
eV
– 10 
keV;
-
secondary electrons with energies 10 – 100 e
V
. 
A vacuum chamber 
equipped
with a turbomolecular pump and a 
6
kW
electron beam evaporator with a 270
o
beam deflection by a permanent magnet 
and 10 
kV
acceleration voltage were used for the deposition of metal films and 
to measure the density of ionic and electronic current with the ion detector. 
The
substrates used were nickel-based 
alloys,
which are an important structural 
material for turbine 
blades,
tubes and 
pipes,
etc. 
The
thickness of the 
Cr
films 
were from 
6.5
µm up to 9.5 µm. A specially designed ion detector was installed 
in the vacuum chamber in the 
position,
where the substrates are usually 
mounted. 
The
operation of the electrostatic detector is based on the separation 
of positive ions and electrons in the field of a parallel - plate capacitor. 
The
construction of the detector and the measuring tract allows delivery of ions to it 
of a bias potential of up to y1.2 
kV
simultaneously with the application of a 
corresponding potential to the substrate. 
Structural
elements of the detector and 
the potentials on its plates are calculated by assuming that the complete 
collection of all ions and 
electrons,
acting on its input window is realised. 
The
dimensions of the detector 
are:
35
х
3
5х
40 mm
3
,
the area of the input
windows 1cm
2
.