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transcript
CHAPTER 4
Experimental Results of Aluminium Oxide
(Al2O3) Thin Films
145
Chapter: IV
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Experimental Results of Experimental Results of Experimental Results of Experimental Results of Aluminium Oxide Aluminium Oxide Aluminium Oxide Aluminium Oxide ((((AlAlAlAl2222OOOO3333) ) ) ) Thin FThin FThin FThin Filmsilmsilmsilms
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4.1 Introduction:
In this chapter the results have been given on the observations based on the
experimental studies on aluminum oxide thin films. The details of thin film
deposition have been given in chapter 2. Vacuum evaporated aluminium thin films
were oxidized by using hot water oxidation method. The Al2O3 thin films were
characterized for their crystal structure, surface morphology, optical and
mechanical properties. The surface roughness was measured by using AFM.
Optical signal loss was studied by prism coupling method for optical waveguide
application. Similar to MgO thin film vapor chopping technique was used during
deposition of Al2O3 thin films also. The ambient air exposure effects on the thin
films properties have also been undertaken.
4.2 Crystal structure using X-ray diffraction (XRD):
X-ray diffraction patterns of vapor chopped and nonchopped Al2O3 thin
films are shown in Fig. 4.1. From fig. 4.1 it is seen that, the vapor chopped and
nonchopped thin films have different crystal structure. In the case of vapor
chopped Al2O3 thin films (220), (620) and (422) cubic phases was also observed.
The strong α-Al2O3 phase and (116) rhombohedral phase were observed. On the
other hand (220) cubic and (211) rhombohedral phases were observed in
nonchopped Al2O3 thin films. (620), (422) and α-Al2O3 phases were not present in
nonchopped Al2O3 thin films.
146
NC
0
10
20
30
40
50
60
30 40 50 60 70 80 90 100
2θ (degrees)In
ten
sity
(a
.u.)
(22
0)
(22
1)
VC
0
10
20
30
40
50
60
30 40 50 60 70 80 90 100
2θ (degrees)
Inte
nsi
ty (
a.u
.)
(22
0)
(62
0)
α (42
2)
α
Figure 4.1: XRD patterns of vapor chopped and nonchopped Al2O3 thin films of
300 nm thickness.
The thickness variation effect is plotted in figure 4.2. For lower thicknesses
i. e 200 and 100 nm XRD patterns were blueprints of the 300 nm thickness
deposited vapor chopped and nonchopped Al2O3 thin films. A small intensity
variation was observed, as thickness increases intensity of XRD peak increases.
The intensity increment is an indication of thin film’s crystallinity improvement.
Figure 4.2 XRD patterns for vapor chopped and nonchopped Al2O3 thin films for
different thicknesses.
30 40 50 60 70 80 90 100
Vapor Chopped Al2O
3 thin films
(422)
αααα αααα
(620)
(220)
A- 300 nm
B- 200 nm
C- 100 nm
C
B
A
Inte
nsi
ty (
a.u
.)
2θθθθ (degrees)
30 40 50 60 70 80 90 100
Nonchopped Al2O
3 thin films
(211)
(220)
C
B
A
A- 300 nm
B- 200 nm
C- 100 nm
Inte
nsi
ty (
a.u
.)
2θθθθ (degrees)
147
Aluminium metal peak was observed, indicating the complete oxidation of
aluminium metal films.
4.3 Surface morphology by scanning electron microscope (SEM):
The surface morphology of vapor chopped and nonchopped aluminium
oxide thin films were studied by using scanning electron micrographs. Fig. 4.3
shows the surface morphology of VC and NC Al2O3 thin films.
Figure 4.3 SEM images of vapour chopped and nonchopped Al2O3 thin films of
300 nm.
From figure it is seen that, nonchopped Al2O3 thin films shows fibril
surface morphology whereas vapor chopped Al2O3 thin film gives smooth, dense
continuous thin film surface morphology.
4.4 Atomic Force Microscopy (AFM):
The surface roughness gives additional information about surface
morphology of thin films. Fig. 4.4 shows 2-dimensional and 3-dimensional atomic
force micrographs for vapor chopped and nonchopped aluminium oxide thin films.
From the fig. 4.4 it was observed that, the surface roughness of vapor
chopped thin film was lesser than the nonchopped Al2O3 thin film. The granular
structured grains were observed in vapor chopped as well as nonchopped Al2O3
thin films. The grain size of nonchopped thin film was higher than the vapor
NC VC
148
chopped Al2O3 thin films. Vapor chopped thin film was found to be denser than
the nonchopped Al2O3 thin film. Thickness variation effect on surface roughness
in Al2O3 thin films was not so prominent.
Figure 4.4: 2-dimensional and 3-dimensional atomic force micrographs for vapor
chopped and nonchopped aluminium oxide thin films for 300 nm.
The variation in surface roughness of thin film plays an important role in
optical coatings. It enhances the optical absorbance and affects the optical
properties of thin films
NC VC
NC VC
149
Transmittance
0
10
20
30
40
50
60
70
80
90
100
200 300 400 500 600 700 800
λ (nm)
T%
NC VC
4.5 Optical properties:
Aluminium oxide has enormous potential to be of use in optoelectronics
and microelectronics devices. Al2O3 thin film combines many properties such as
high dielectric constant, high thermal conductivity, wear resistance and protective
coating, mechanical strength, chemical inertness, good adhesion to glass substrate
and transparency over wide wavelength range [1-5]. The refractive index (1.76) of
these films is in the range suitable for optical waveguide purpose [4, 5].
As already mentioned in chapter I, the properties of deposited Al2O3 thin
films depend on the deposition process and optimized parameters. To use the
optical coating thin films in optoelectronic device formation having minimum
optical signal transmission loss due to scattering of light, the reduction in defects
and voids formation and improved surface morphology are the basic requirement.
4.5.1 Optical transmittance:
The optical transmission properties of vapor chopped and nonchopped
Al2O3 thin films showed in figure 4.5
Figure 4.5 Optical transmittance of vapor chopped and nonchopped Al2O3 thin
films thickness 300nm.
150
Scatter diagram
0
20
40
60
80
100
200 300 400 500 600 700 800
λ (nm)
T%
S1 S2 S3 S4 S5
VC
Scattre diagram
0
20
40
60
80
100
200 300 400 500 600 700 800
λ (nm)
T%
S1 S2 S3 S4 S5
NC
In fig. 4.5 it has been clearly seen that, the transmittance go on increasing
with wavelength. It was also found that, the vapor chopped thin films showed
higher transmittance than the nonchopped Al2O3 films. Vapor chopped thin films
showed transmittance in 80-90% range whereas it was in between 55-60% for the
nonchopped thin films
The given transmittance graph (fig. 4.5) is an average transmittance values
of 4-5 samples of vapor chopped and nonchopped Al2O3 thin films. The actual
values of all the 5 samples of 300 nm thickness are plotted in figure 4.6. It is seen
that sample to sample variations are more in the NC films than in the VC films.
Figure 4.6 Scatter diagram for vapor chopped and nonchopped Al2O3 thin films for
300 nm.
The thickness variation effect on Al2O3 thin films are plotted in Fig. 4.7. It
shows the optical transmittances spectra for vapor chopped Al2O3 thin films of
100, 200 and 300 nm thin film thickness. It is clear that, as thickness of thin film
increases, optical transmittance goes on decreasing whereas it increases with
respect to wavelength for all thicknesses.
151
VC
0
10
20
30
40
50
60
70
80
90
100
200 300 400 500 600 700 800
λ (nm)
T %
100 nm 200 nm 300 nm
NC
0
10
20
30
40
50
60
70
80
90
100
200 300 400 500 600 700 800
λ (nm)
T %
100 nm 200 nm 300 nm
Figure 4.7 Optical transmittance spectra for vapor chopped Al2O3 thin films for
different thicknesses.
Figure 4.8 Optical transmittance spectra for nonchopped Al2O3 thin films for
different thicknesses.
Fig. 4.8 shows the optical transmission spectra for nonchopped Al2O3 thin
films for 100, 200 and 300 nm thickness. The optical transmittance spectra have
152
Absorbance
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
200 300 400 500 600 700 800
λ (nm)
Ab
sorb
an
ce (α
t)
NC 100 NC 200 NC 300
VC 100 VC 200 VC 300
same behaviour as vapor chopped thin films. In nonchopped thin films also optical
transmittances varies with thickness variation and was in between 55-85 %.
4.5.2 Optical band gap:
Figure 4.9 shows the absorbance of vapor chopped and nonchopped Al2O3
thin films for different thicknesses. It was observed that, absorbance increases
with increase in thickness of the thin film. Increase in absorbance with decrease in
transmittance is co-related with each other with respect to thickness variation.
Vapor chopped thin films showed the lower absorbance than nonchopped thin
films.
Figure 4.9: Optical absorbance of vapor chopped and nonchopped Al2O3 thin films
for different thicknesses.
Fig. 4.10 a, b and c shows the thickness variation effect in optical band gap
for 100, 200, and 300 nm. Vapor chopped and nonchopped Al2O3 thin films
showed same band gap patterns with different values. The absorption parameter
(αthυ)2 shows the absorption edge moves to shorter wavelength region.
153
NC
0
1
2
3
4
5
1.5 2.5 3.5 4.5 5.5 6.5hυ (eV)
(αthυ
) 2
VC
0
0.1
0.2
0.3
0.4
0.5
0.6
1.5 2.5 3.5 4.5 5.5 6.5
hυ (eV)
(αthυ
) 2
NC
0
0.2
0.4
0.6
0.8
1
1.5 2.5 3.5 4.5 5.5 6.5
hυ (eV)
(αthυ
) 2
VC
0
0.04
0.08
0.12
0.16
1.5 2.5 3.5 4.5 5.5 6.5
hυ (eV)
(αthυ
) 2
Figure 4.10 a) (αthυ)2 against hυ for vapor chopped and nonchopped Al2O3 thin
films for 100 nm thin film thickness
Figure 4.10 b) (αthυ)2 against hυ for vapor chopped and nonchopped Al2O3 thin
films for 200 nm thin film thickness.
The optical band gap values are given in table 4.1 It shows that, optical
band gap increases with increase in thin film thickness as well as due to chopping.
This optical band gap for vapor chopped Al2O3 thin films was in between 4.7-5.8
eV whereas it was in 4.5-5.6 eV range for nonchopped films. There was small
variation in band gap due to vapor chopping whereas thickness effect was found to
be more prominent.
154
NC
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
1.5 2.5 3.5 4.5 5.5 6.5
hυ (eV)
(αthυ
) 2
VC
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
1.5 2.5 3.5 4.5 5.5 6.5
hυ (eV)
(αthυ
) 2
Figure 4.10 c) (αthυ)2 against hυ for vapor chopped and nonchopped Al2O3 thin
films for 300 nm thin film thickness
Table 4.1: Optical Band gap values of vapor chopped and nonchopped Al2O3 thin
films
Number of worker has been reported the optical band gap of aluminum
oxide [8-11]. Obtained band gaps in our case are lesser than the band gap of bulk
aluminium oxide 9.5 eV [12] and are in the reported range.
4.5.3 Refractive index:
The refractive index values of vapor chopped and nonchopped Al2O3 thin
films have been given in table 4.2.Table shows that, the refractive index of vapor
chopped thin films were lower than the nonchopped Al2O3 thin films for 100, 200
and 300 nm thicknesses. It was also observed that, refractive index increases with
increase in thickness of thin film for vapor chopped as well as nonchopped Al2O3
Thin film thickness
(nm)
Band gap (eV)
Nonchopped Vapor chopped
100 4.5 4.7
200 5.0 5.3
300 5.6 5.8
155
thin films. The refractive index for vapor chopped thin films was in the range
1.59-1.66 whereas it was 1.63-1.69 for nonchopped thin films. As per the
references, these values are in acceptable range [4, 14-18].
Table 4.2: Refractive index of vapor chopped and nonchopped Al2O3 thin films for
different thicknesses
4.6 Optical waveguiding properties:
The optical transmission loss was measured by prism coupling method
[19]. Here the deposited Al2O3 thin films act as a optical planar waveguide. The
difference between input optical signal and output signal intensity gives the clear
idea about the optical transmission loss. The columnar grain growth and defects i.
e. voids and cracks obtained in thin film during manufacturing process, scatters the
optical signal which results in transmission loss. The optical transmission loss was
measured in 4-5 samples for to check the results reproducibility.
The optical transmission loss study of Al2O3 thin film waveguide showed
that, optical transmission loss of vapor chopped thin film (3.73 dB/cm) was less
than the nonchopped Al2O3 (6.01 dB/cm) thin film waveguide. These optical
transmission loss values of both VC and NC thin films were lesser than those
reported (10 dB/cm) by Kersten et al. [5]. The effect of thickness variation i. e.
100, 200 and 300 nm is negligible. It differs by ~0.5-0.8 db/cm. so it can be
neglected.
Thin film Thickness
(nm)
Refractive Index
NC VC
100 1.63 1.59
200 1.66 1.62
300 1.69 1.66
156
Scatter diagram
100
150
200
250
300
350
400
50 100 150 200 250 300 350
Thin film thickness (nm)
Ad
hes
ion
(×
103
N/m
2)
NC-1 NC-2 NC-3 NC-4 NC-5
VC-1 VC-2 VC-3 VC-4 VC-5
4.7 Mechanical properties:
4.7.1 Adhesion:
Adhesion of vapor chopped and nonchopped Al2O3 thin films were also
studied. For each case the adhesion of Al2O3 thin films were plotted by measuring
4-5 samples each. The scatter diagram is plotted in fig. 4.11. It can be observed
that, adhesion increases with increase in thickness of thin film as well as due to
vapor chopping.
Figure 4.11: Scatter diagram of adhesion of vapor chopped and nonchopped Al2O3
thin films for different thicknesses.
The adhesion values for different thin film thickness (100, 200 and 300 nm)
have been given in table. 4.3. The table shows that vapor chopped thin films have
higher adhesion than the nonchopped thin films. The average values are given
here.
157
Scatter diagram
0
10
20
30
40
50
60
70
80
90
50 100 150 200 250 300 350
Thickness of thin film (nm)
Intr
insi
c st
ress
(×
10
7 N
/m2)
NC-1 NC-2 NC-3 NC-4 NC-5
VC-1 VC-2 VC-3 VC-4 VC-5
Table 4.3: Adhesion of vapor chopped and nonchopped Al2O3 thin films for
different thicknesses
4.7.2 Intrinsic stress:
The intrinsic stress of vapour chopped and nonchopped Al2O3 thin films
were also studied. The effect of thin film thickness has been given. The fig. 4.12
gives the intrinsic stress of vapor chopped and nonchopped Al2O3 thin films for
different thicknesses.
Figure 4.12: Intrinsic stress of vapor chopped and nonchopped Al2O3 thin films
for different thicknesses.
Thin film Thickness
(nm)
Adhesion (× 103 N/m
2)
NC VC
100 158 ± 7 227 ± 8
200 205 ± 3 270 ± 8
300 286 ± 8 355 ± 3
158
Similar to MgO thin film, the stress of Al2O3 thin films were also studied.
The calculated thermal stress for aluminum oxide thin film was very small, it was
(-1.004 x 107 N/m
2).The negative sign indicates the type of the stress. It was
comprehensive stress. The obtained intrinsic stress values are average values for
100nm, 200nm and 300nm thicknesses have been given in table 4.4. It was
observed that, intrinsic stress decreases with increase in thin film thickness
whereas vapor chopped Al2O3 thin films showed lesser intrinsic stress than
nonchopped thin films.
Table 4.4: Intrinsic stress of vapor chopped and nonchopped Al2O3 thin films for
different thicknesses.
4.8 Ambient air exposure effect:
When the prepared thin film is exposed to ambient air, the properties of
thin film changes with respect to exposure duration. We have already has seen in
the case of magnesium oxide thin films in chapter III. The effect of air exposure
on Al2O3 thin film was also studied. For this measurement, the films were kept in
a dust free container at room temperature and measurements were taken before
and after exposure period. The variation in measurement gives the exposure effect.
The affinity of deposited thin film to adsorb and /or absorb the moisture as well as
other gases is mainly affecting the changes in thin film properties. Aluminium
oxide is an environmentally stable oxide. It shows very small variation in the
optical and mechanical properties.
Thin film thickness
(nm)
Intrinsic stress (× 107 N/m
2)
VC NC
100 58 ± 9 72 ± 4
200 36 ±3 64 ± 6
300 31 ± 8 41 ± 2
159
4.8.1 Crystal structure:
Crystal structure of vapor chopped and nonchopped fresh and air exposed
Al2O3 thin films were studied. Figure 4.13 showed that, the effect of 30 days air
exposure was almost negligible. Thin film was highly stable. There were no
changes in respective phases.
Figure 4.13: Fresh and 30 days air exposed vapor chopped and nonchopped Al2O3
thin films.
4.8.2 Optical Properties:
4.8.2.1 Optical transmittance:
The effect of ambient air exposure on optical transmittance properties of
vapor chopped and nonchopped aluminium oxide thin films of 100 nm for
different durations showed in fig. 4.15 The ambient air exposure for different
duration 1 day, 10, 20 and 30 days were measured. The drastic effect of short term
air exposure was observed on 100 nm as compared to the other 200 and 300 nm
thin film thicknesses. The changes are more in the 300-400 nm wavelength range
as compared to other wavelengths. Due to vapor chopping these changes became
negligible even in the 300-400 nm range. The exposure effect on optical
transmittance was very small so for further thicknesses exposure effect was
studied only after 30 days.
30 40 50 60 70 80 90 100
VC
B
A
(422)
αααα
αααα
(620)
(220)
A- Fresh film
B- Air exposed film
Inte
nsi
ty (
a.u
.)
2θθθθ (degrees)
30 40 50 60 70 80 90 100
A
B
(211)
(220) NC
A- Fresh film
B- Air exposed film
Inte
nsi
ty (
a.u
.)
2θθθθ (degrees)
160
100 nm
20
30
40
50
60
70
80
90
100
300 400 500 600 700 800
λ (nm)
T%
fresh film
1 day
10 days
20 days
30 days
VC
100 nm
20
30
40
50
60
70
80
90
100
300 400 500 600 700 800
λ (nm)
T%
fresh film
1 days
10 days
20 days
30 day
NC
Transmittance of fresh and air exposed Al2O3 thin films
20
30
40
50
60
70
80
90
100
300 400 500 600 700 800
λ (nm)
T %
F 100 nm F 200 nm F 300 nm
A 100 nm A 200 nm A 300 nm
NC
Figure 4.15 Air exposure effect on optical transmittance of vapor chopped and
nonchopped Al2O3 thin films for 100 nm for different durations.
Figure 4.16 Optical transmittance of nonchopped fresh and air exposed Al2O3 thin
films for Air exposure effect study.
The optical transmittance was reduced due to air exposure. This is might be
the adsorption of moisture over the surface of VC and NC Al2O3 thin films. The
figure 4.16 showed very less air exposure effect on optical transmittance of fresh
161
Transmittance of fresh and air exposed Al2O3 thin films
20
30
40
50
60
70
80
90
100
300 400 500 600 700 800
λ (nm)
T %
F 100 nm F 200 nm F 300 nm
A 100 nm A 200 nm A 300 nm
VC
and exposed nonchopped Al2O3 thin films for different thicknesses i. e. 100, 200,
300nm. The thickness variation effect also observed. Higher thicknesses were
getting affected very less as compared to smaller thickness
Fig. 4.17 showed the air exposure effect on vapour chopped Al2O3 thin
films for different durations. It was observed that, air exposure effect on vapor
chopped thin films was comparatively lower than the nonchopped Al2O3 thin
films. There was almost no change due to air exposure on the vapor chopped thin
films. The thickness wise variation are also shown in fig. 4.17
Figure 4.17 Optical transmittance of vapor chopped fresh (F) and air exposed (F)
Al2O3 thin films for Air exposure effect study.
4.8.2.2 Optical band gap:
The effect of air exposure on optical band gap was studied for 30 days. The
optical band gap of fresh and 30 days air exposed vapor chopped and nonchopped
Al2O3 thin films for different thicknesses has been given in fig. The Al2O3 thin
films of thickness 100 nm showed large changes in band gap as compared to the
200 and 300nm thicknesses films.
162
300 nm
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
3.5 4 4.5 5 5.5 6 6.5
hυ (eV)
(αthυ)
2
A- NC A- VC
F- NC F- VC
100 nm
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
2.5 3 3.5 4 4.5 5 5.5 6 6.5
hυ (eV)
(αthυ)
2
A- NC A- VC
F- NC F- VC
200 nm
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
2.5 3 3.5 4 4.5 5 5.5 6 6.5
hυ (eV)
(αthυ
) 2
F-NC F VC
A-NC A-VC
Figure 4.18 Optical band gap of vapor chopped and nonchopped fresh (F) and 30
days air exposed (A) Al2O3 thin films for different thicknesses.
163
Table 4.5: Optical band gap of vapor chopped and nonchopped Al2O3 thin films
for different thicknesses
The obtained values for optical band gap of vapor chopped and nonchopped
thin films have been given in table 4.5. The vapor chopped thin films have higher
band gap than the nonchopped Al2O3 thin films. Both vapor chopped and
nonchopped Al2O3 thin films showed negligible variation in optical band gap due
to air exposure. The Al2O3 thin films remains electrically stable after 30 days and
very small change might be occur after 2 or 3 months in it. The vapor chopped
thin films gives higher stability than the nonchopped thin films. The air exposure
effect with respect to thickness variation on optical band gap was not prominent.
4.8.2.3 Refractive index:
The effect of air exposure on refractive index of vapor chopped and
nonchopped Al2O3 thin film was also studied. Table 4.6 shows the refractive index
for the films of various thicknesses viz. 30 days air exposed effect on VC and NC
Al2O3 thin films. The refractive index of fresh thin films has been given in
previous table 4.6. It was observed that, the variation in refractive index due to air
exposure effect was comparatively higher in Al2O3 thin films of 100nm thickness.
The exposure effect goes on decreasing with increase in thickness of thin film.
The vapor chopped thin films showed lesser air exposure effect than the
nonchopped thin films. Compared to MgO thin films the exposure changes in
Al2O3 thin films are smaller.
Thin film thickness
(nm)
Band gap (eV) after air exposure
Nonchopped Vapor chopped
100 4.2 4.6
200 4.8 5.3
300 5.4 5.7
164
Table 4.6: Refractive index of vapor chopped and nonchopped Al2O3 thin films air
exposed for 30 days.
4.8.3 Optical transmission loss:
The air exposure effect on optical transmission loss of vapor chopped and
nonchopped Al2O3 thin film has shown that, there is very small change in
transmission loss. Optical transmission loss increases due to air exposure. The
fresh nonchopped Al2O3 thin films showed 6.01 dB/cm transmission loss; it
became 8.47 dB/cm whereas vapor chopped thin films vary form 3.73 to 4.86
dB/cm. Again, vapor chopped thin films showed lower loss than the nonchopped
thin films. The obtained transmission loss values were lesser than the reported loss
i. e. 10 dB/cm [5].The variation in surface roughness affects on the optical
transmission loss.
4.8.4 Adhesion:
The air exposure effect study on adhesion of vapor chopped and
nonchopped Al2O3 thin film has been shown that, there is very small change in
adhesion due to air exposure. Adhesion of Al2O3 thin film decreased due to air
exposure. The adhesion after 30 days air exposed Al2O3 thin films showed in
figure 4.19.
There was very small change in adhesion was observed in short term
exposure duration. It was unreadable so direct 30 days exposure effect has been
given. It was also very small almost negligible
Thin film Thickness
(nm)
Refractive Index
NC VC
100 1.651 1.608
200 1.668 1.652
300 1.693 1.678
165
Adhision
0
100
200
300
400
100 200 300
Thin film Thickness (nm)
Ad
hesi
on
(×
10
3 N
/m2)
NC F NC A
VC F VC A
Figure 4.19 Adhesion of Fresh (F) and air exposed (A) vapor chopped and
nonchopped Al2O3 thin films for 30 days.
4.8.5 Intrinsic stress:
The air exposure effect on intrinsic stress of vapor chopped and
nonchopped Al2O3 thin film has shown that, there is very small change in stress
due to air exposure. Intrinsic stress almost remains same after 30 day air exposure,
there was neither increment nor decrement was observed in Al2O3 thin films. The
stress of thin films has been decreased with respect to thickness of thin film
observed in fresh as well as air exposed thin films. Figure 4.20 showed the
intrinsic stress variation with thickness variation after thin film air exposed for 30
days.
166
Intrinsic stress
0
20
40
60
80
100 200 300
Thin film thickness (nm)
Intr
insi
c s
tress
(×
10
7 N
/m2)
VC NC
Figure 4.20: Intrinsic stress of vapor chopped and nonchopped Al2O3 thin film
exposed for 30 days for different thicknesses
4.9 SUMMARY OF SOME IMPORTANT RESULTS:
The summary of some important results observed from the investigation
carried out are as follows:
1. In the case of vapor chopped Al2O3 thin films (220), (620) and (422) cubic
phases was also observed. The strong α-Al2O3 phase and (116)
rhombohedral phase were observed. On the other hand (220) cubic and
(211) rhombohedral phases were observed in nonchopped Al2O3 thin films.
2. Nonchopped Al2O3 thin films showed fibril structure surface morphology
whereas vapor chopped films showed smoothed surface morphology.
3. Surface roughness of vapor chopped thin films was found to be lesser than
the nonchopped Al2O3 thin films.
167
4. Optical transmittance increases due to vapor chopping and decreases due to
thickness.
5. Optical absorption decreases due to vapor chopping as well as decrease in
thin film thickness.
6. Vapor chopped thin films showed comparatively higher band gap than
nonchopped thin films.
7. Refractive index of Al2O3 thin films was found to increase with thin film
thickness.
8. Vapor chopped thin films showed lower refractive index and lower
transmission loss than nonchopped thin films.
9. Adhesion of Al2O3 thin film increases with increase in thin film thickness.
10. Vapor chopped thin films showed higher adhesion than nonchopped Al2O3
thin films.
11. Vapor chopped Al2O3 thin films showed lesser intrinsic stress than
nonchopped thin films.
12. Al2O3 thin films properties remains stable after 30 days.
168
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