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Survey of WO3 thin film structure built on ito/glass substrates by the Raman and xrd spectroscopies Le Van Ngoc1,*, Tran Cao Vinh1, Le Quang Toai1, Nguyen Duc Thinh1 Huynh Thanh Dat2, T

Survey of WO3 thin film structure built on ito/glass substrates

by the Raman and xrd spectroscopies

Le Van Ngoc1,*, Tran Cao Vinh1, Le Quang Toai1, Nguyen Duc Thinh1

Huynh Thanh Dat2, Tran Tuan1, Duong Ai Phuong1

1

University of Science, Vietnam National University - Ho Chi Minh city, 227 Nguyen Van Cu, Vietnam

2

Vietnam National University - Ho Chi Minh city, Linh Trung, Thu Duc, Vietnam

Received 17 January 2009; received in revised form 12 March 2009

Abstract Tungsten oxide film was deposited on ITO-coated glass by using RF magnetron

sputtering method from WO3 ceramic target Thin film preparation – process took place in Ar + O2

plasma The dependence of tungsten oxide film structure on experiment conditions was investigated by X-ray diffraction (XRD) Raman spectroscopy In this paper, we considered that the thickness of ITO layers about 150nm to 350nm clearly effects on the Raman and XRD spectrograms of WO3 films

Keywords: WO3 structure, WO3 /ITO/glass, Raman spectroscopy

1 Introduction

electrochromism and gaseous sensitization are based on the reversible diffusion of particles along the

great advantage

preparation methods have respective advantages in film quality and application

measured approximately 150, 200, 250, 300, 350 nm, respectively From XRD spectrograms, we

*

Corresponding author Tel.: 0908283530

considered that the thickness of ITO coaters clearly effect on WO3 crystalline structure In order to understand what occurred inside and whether nano particle phases exist, we used their Raman

samples with ITO layer about 300nm thickness and more, in Raman spectrum there is an odd peak at

assumption The origin of this peak will be focused on in this paper

2 Experimental

Oxygen and argon gases with high purity (99.999%) were used in deposition processes Our sputtering

were deposited on glass substrates by DC magnetron sputtering with their thickness about 150, 200,

sputtering The power is 100 W and the deposition time is about 30 minutes

nm) In order to analyze broad peaks, included many basic vibration modes of Raman spectrum, we used Origin 7.5 program with Gaussian function This information gives us exact evaluation of the existence of different phases in our films

3 Results and discussion

3.1 The effect of the thickness of ITO layer on XRD spectrum

of 2θ diffraction angle due to the existence of three highest peaks Figure 1 shows XRD pattern of

(001) and (200) (international JCPDC database, JCPDC 5 - 363)

2 0 3 0 4 0 5 0 0

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

3 0 0 0

( 0 0 1 )

( 0 2 0 )

( 2 0 0 )

2 T h e t a ( d e g )

W O 3 p o w d e r s a m p l e

( 4 0 0 )

2 th e ta (d e g )

Fig 1 XRD spectrum of m-WO3 powder

Fig 2 XRD spectra of WO3 films on layers ITO with different thicknesses

Figure 2 is XRD spectra of films on layers ITO with different thicknesses However their peaks distribute in such a small range of the angle 2θ, that we couldn’t confirm whether our films have a

0,3877nm) because the values aren’t clearly distinctive

Analyzing figure 2, we recognized that ITO layer with thickness about 150 nm, XRD shows a sharp peak (200), accompanied by a weaker one (001) Between these peaks was a even weaker peak (020), like a shoulder of (200) font With an increase in the thickness from 150 nm to 350 nm, XRD spectra expose a gradual decrease of the magnitude of peak (200) and a raise of peak (001) Moreover, peak (020) is shown obviously in the case of 250 nm When the ITO layer have a thickness about 300

distance of tetragonal structure (t-WO3) Therefore, we assumed that the crystalline structure of this

preferentially grow along direction (001), (200), however, both of these two possible growth directions lead us to the conclusion that vacant tunnels grew perpendicular to film surface And with

than these ones of powder sample This result shows that the lattice plane distance increases due to a

stress is given by equation:

(2 )

4 tan

f

σ

∆

=

coefficient ∆(2θ) will get a minus value if the total film stress is compressed stress [23] Thus due to

Scherrer equation and all of them valued in 30 nm to 35 nm

3.2 Micro – Raman Studies

thicknesses, we investigated their Raman spectra to find out more helpful information We divided ITO layers into two groups, basing on their thicknesses: 150 – 250 nm group and 300 – 350 nm group

3.2.1 Raman spectrum of WO 3 thin films on ITO layers with thickness, altering from 150 to 250nm

pattern quite greater than this one of powder sample Raman spectra of all three samples show sharp

assumed that the surface and volume rate is negligible

films because the parameters of orthorhombic and monoclinic primary cells are nearly the same

3.2.2 Raman spectrum of WO 3 thin films on ITO layers with thickness, altering from 300 to 350nm

2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 0

5 0 0 0

1 0 0 0 0

1 5 0 0 0

2 0 0 0 0

2 5 0 0 0

3 0 0 0 0

1 2 7 7 7 1

2 6 5 6

3 2 0 1 1 4

7 0 3 7 7 1

7 9 9 4 2 9

R a m a n s h i f t ( c m - 1

)

W O3/ I T O 1 5 0 n m

2 0 3 0 4 0 5 0 0

2 0 0 0

4 0 0 0

6 0 0 0

8 0 0 0

2 T h e t a ( d e g )

W O3/ I T O 1 5 0 n m ( 2 0 0 )

( 0 0 1 )

2 0 3 0 4 0 5 0 0

2 0 0

4 0 0

6 0 0

8 0 0

1 0 0 0

1 2 0 0

1 4 0 0

1 6 0 0

1 8 0 0

2 0 0 0

( 0 2 0 )

( 0 0 1 )

( 2 0 0 )

W O3/ I T O 2 5 0 n m

2 T h e t a ( d e g )

2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0

1 0 0 0

2 0 0 0

3 0 0 0

4 0 0 0

5 0 0 0

6 0 0 0

1 3 0 8 5 7

2 6 9 7 1 4

3 2 3 2

7 0 9 9 4 3

8 0 3 5 4 3

R a m a n s h i f t ( c m - 1

)

W O3/ I T O 2 5 0 n m

2 0 3 0 4 0 5 0 0

1 0 0 0

2 0 0 0

3 0 0 0

4 0 0 0

5 0 0 0

6 0 0 0

7 0 0 0

W O3/ I T O 2 0 0 n m

( 0 0 1 ) ( 2 0 0 )

2 T h e ta ( d e g )

2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 0

5 0 0 0

1 0 0 0 0

1 5 0 0 0

2 0 0 0 0

1 3 0 8 5 7

2 6 8 6 8 6

3 2 3 2

7 0 7 8 8 6

8 0 2 5 1 4

R a m a n s h i f t ( c m - 1 )

W O3/ I T O 2 0 0 n m

2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0

2 0 0 0

4 0 0 0

6 0 0 0

8 0 0 0

1 0 0 0 0

1 2 0 0 0

1 4 0 0 0

1 6 0 0 0

1 2 7 3 2 3

1 7 8 9 3 3

2 6 2 9 2 5

3 2 4 6 5 5

7 0 9 2

8 0 2 3

R a m a n s h i f t ( c m - 1

)

W O3 p o w d e r s a m p l e

Fig 3 XRD patterns and Raman spectrum

of WO3 thin films on ITO layers with

different thichnesses a) 150nm ITO; b) 200nm ITO;

c) 250nm ITO; d) WO3 powder

d)

a)

b)

c)

Comparing between XRD spectra of WO3 films and WO3 powder, we can not deduce any difference

10000

12000

14000

16000

18000

20000

22000

24000

253.257

688.343 799.429

Raman shift ( cm -1

)

W O3/ ITO 350nm

0 500 1000 1500 2000 2500 3000

3500

W O3(001)

2 Theta (deg)

W O3/ ITO 350nm

0 200 400 600 800

1000

(001)

3 / ITO 300nm

2 Theta (deg)

0

10000

20000

30000

40000

50000

130.857

267.657

701.714 802.514

Raman shift ( cm -1

)

W O3/ ITO 300nm

2000

4000

6000

8000

10000

12000

14000

16000

127.323

178.933

262.925

324.655

709.2 802.3

Raman shift ( cm -1 )

patterns of WO3 on ITO layers with different thicknesses a) 300nm ITO; b) 350nm ITO;

c) WO3 powder

a)

b)

c)

Nevertheless, like Raman spectra of WO3/ITO 150 nm, WO3/ITO – 200 nm and WO3/ITO – 250

process It means that the ratio of surface to volume is negligible And some calculations, basing on

annealing process and the breakage of the double bonds W = O also result in the limit of the shift to

In order to understand more about the mentioned peak, we used program Origin 7.5 to analyze the

However, from the experiments of E.Cazzanelli [26], the phase transition from orthorhombic

Fig 5 Raman spectra of WO3 thin film/ITO 300nm/glass substrate

0

644.66cm-1

W O 3/ ITO 300nm

Ram an shift (cm-1 )

Fitting R es ults

WO3 and o-WO3 Therefore, we believed that a pair of peaks at 803 cm-1; 708 cm-1 correspond to

larger than in the later phase

particles are well crystallized For a Raman spectrum of that film, peaks, characterizing crystalline

4 Conclusion

(001) gradually

Fig 6 Raman spectra of WO3 thin film/ITO 350nm/glass substrate

WO3/ ITO 350nm

Raman shift (cm-1 )

Fitting Results

In our experiments, films have many different crystalline structures with m-WO3 and o-WO3

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