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

References:

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