synthesis of nanostructure tio2 thin films using...

Abstract—The purpose of this article was to survey the

microstructure and various properties (optical – electrical –

mechanical) of (TiO2) thin coating on glass-substrate by pulsed-magnetron-sputtering (PMS) method. The coatings were deposited by sputtering pure Ti target at a mixture of 90%Ar and 10% O2 under a constant total working gas pressure of 5x10-3 mbar. The plasma (applied power) with (120 kHz) frequency was varied from 100 W to 225 W for operation time of 25 min. The structural and various properties (optical-electrical-mechanical) of (TiO2) thin coating with the various (applied powers) have been investigated. XRD spectra show the genesis of (TiO/TiO2) rutile-phase, as outcome of plasma

oxygen. The bandgap of the TiO2 increased up to 4.02 eV as the (applied power) increases up to 200 W. The gained data show an increase of TiO2 transmittance and a decrease of its reflectance as (applied power) increases.

Keywords— Titanium dioxide, Transparency, Different (applied

power), DC (PMS)

I. INTRODUCTION

TiO2 films are important as optical films owing to their

high refractive index, high bandgap and transparency on top of wide spectral range, adjustable electrical conductivity and

ecological non-toxicity [1, 2]. TiO2 has four known structures

under ambient conditions: rutile, anatase, brookite and

srilankite, the rutile-structure is the most stable phase [3]. In

literature, variety ways were used to gain TiO2 films. One of

them, the physical vapor depositions (PVD) such as cathodic

arc deposition, arc ion plating, and magnetron sputtering, etc.

[4-6].

Moreover, (PMS) is largely engaged for industrial

application due to numerous advantages like low target

poisoning; which preventing arcing, high fineness film with high deposition and adhesion well to substrate [7, 8]. Little

work by elsewhere [9, 10] reported that the (applied power)

has a major factor to control the optical performance of

Transparent conducting oxide (TCO) coating.

Fayez Mahmoud El-Hossary: is with the Physics Department, Faculty of

Science, Sohag University, Sohag, Egypt.

Ahmed Mohamed Abd El-Rahman: is with the Physics Department,

Faculty of Science, Sohag University, Sohag, Egypt.

Moataz Bellah Hassan Ata: Mechanical Engineering Department, Faculty

of Industrial Education, Sohag University, Sohag, Egypt,

E-mail: [email protected]

Amr Ali Mohamed: Mechanical Engineering Department, Faculty of

Industrial Education, Sohag University, Sohag, Egypt.

In this investigation, further studies on the

effectiveness (applied power) on performance of TiO2

coating on glass substrates elaborated by (PMS). The

samples were investigated using X-ray diffraction (XRD),

UV–visible-IR spectrophotometer, digital low resistance

ohmmeter (DLRO), surface profile and microhardness

tester.

II. EXPERIMENTAL

2.1. Deposition Conditions

We use (PMS) system shown in Fig.1, for the TiO2

film preparation. The glass substrates with a dimension of

10×20×1mm were ultrasonically cleaned in methanol,

and then mounted on a 50 mm diameter sample holder,

which is centered in the front of three guns in the

deposition chamber. A high purity (99.99%) target with

50mm in diameter was used.

Fig. 1 Schematic diagram of the (PMS)

The target and the specimen holder distance were

located at 60mm. After inserting the substrates into the

PMS chamber, the system was evacuated by two stages;

rotary and turbo-pumps from atmospheric pressure to a

base pressure of approximately 5x10-6mbar. Pure argon

plasma sputtering at 200 W at 120 kHz was applied on

the Ti target for 3min to eliminate the oxide layer effect,

sputter the localized states of the grown oxides and to eliminate the sharp surface defects that accountable for

sparking effects. After that, the TiO2 deposition was

carried out in a mixture of 90%Ar and 10% O2 under a

constant total working gas pressure of 5x10-3 mbar. The

(applied power) was varied to 6 levels among 100 W to

225 W. A chrome-alumel thermo-couple was placed close

F. M. El-Hossary, A. M. Abd El-Rahman, Moataz H. Ata and Amr A. Mohamed

Synthesis of Nanostructure TiO2 Films Using Different

Applied Powers of Pulsed Magnetron Sputtering

Int'l Journal of Advances in Mechanical & Automobile Engg. (IJAMAE) Vol. 4, Issue 1(2017) ISSN 2349-1485 EISSN 2349-1493

https://doi.org/10.15242/IJAMAE.IAE0317203 61

to the blank surface sample to measure the sample

temperature during the PMS process. The measured sample

temperature was about 37 ± 3˚C. After the deposition process

was completed, the chamber is permitted to cool down before

venting to atmospheric pressure.

2.2. Characterization And Testing

Crystal structure of the coated substrates was analyzed by

XRD using (Philips-PW1710 diffractometer) with Cu Kα

radiation of λ = 1.541838 Å. The scans were gained with a

0.02° step size in a range from 20° to 100°. For investigating

the anti/reflective film properties, a UV-Vis-IR

spectrophotometer with the wavelength range from 200 to 2500 nm has been used. The measure of films was recorded at

a normal incidence by a blank reference substrate. From the

transmittance spectra T (λ), one can use Swanepoel method to

calculate the (optical constants / absorption coefficient /

optical bandgap) of the TiO2 films. Moreover, the film

thickness was recorded from the T (λ) [11] and cross-checked

by (Talysurf 50) surface roughness measurement. The

electrical resistance of the coated TiO2 has been investigated

using digital low resistance ohmmeter (DLRO).

Microhardness was measured by a LeitzDurimet

microhardness tester equipped with static load of 5gmf. The coefficient of friction (COF) was performed at a mean sliding

speed of 10 mm/s and load of 1N. A 3mm tungsten carbide

(WC) ball was used as counterpart material without

lubrication at ambient-temperature in air atmosphere with

humidity of 35% - 40%.

III. RESULTS AND DISCUSSION

3.1. XRD Analysis

The X-ray diffraction patterns of titanium dioxide/oxide

films were fabricated at different (applied power) are

presented in Fig.2. The rutile (TiO2) is the main phase shown

in the figure for all values of(applied power). The figure

shows also that the orientation of rutile (TiO2) with planes

(311) and (410). The intensity of TiO2 (311) phase

continuously raises with a rise of the (applied power) up to

(200W) and then it decreases again at 225W. The non-

stoichiometric oxide TiO (220) and (131) phase can also be

seen in the spectra with relatively weak intensities for all

values of (applied power). The crystallite sizes have been evaluated by Debye

Scherrer equation [12].

(1)

Where: D is the size of crystallite in nm, k=0.90 is a

dimensionless shape factor, is the wavelength of the incident radiation in nm, θ (rad) is the reflection Bragg angle

and FWHM is the full width at half maxima.

Fig. 2 XRD of TiO2 thin film samples at different

(applied power)

The crystallite size of the TiO2 coated at different

(applied power) is presented in Fig.3. One can observe

from the figure that, the crystallite size increases from

nearly 13.5nm for the film deposited at100 W to

approximately 25nm for the film deposited at 225 W. The

increase of crystallite size with increasing the (applied

power) is owing to the expansion of crystallinity by the

coalescence of small crystallites [13].

Fig. 3 Crystallite size of the TiO2 thin film at different

(applied power)

3.2. Film Thickness And Rate Deposition

The TiO2 films thickness is determined as an average

of five values taken along the step between the film

surface and the substrate surface. The rate deposition is

developed using the formula of t/s, where (t) is the

average thickness of the coated layer in nm, and (s) is the total deposition time in sec.



Fig. 4 Film thickness and deposition rate of TiO2 coatings at

different (applied power)

The variance in the film thickness and the rate deposition at

different (applied power) is exhibited in Fig. 4, it is noticed

that the thickness and the rate deposition increase

continuously with increasing the (applied power). K. Kusaka

et al. [14] reported that as the (applied power) increases, the

quantity of energetic atoms ejected from the target increase,

which in turn increases the film thickness and rate deposition.

Fig. 5 Ra of the TiO2 coatings at different (applied power)

3.3. Mechanical Performance

3.3.1. Roughness

The parameter (Ra) is obtained from the mean height of

peaks and valleys of the surface. Figure.5 illustrates the

relation between Ra of TiO2 coatings at different (applied

power). This figure reveals that the surface roughness

gradually raised with the rising of (applied power). The rising

in the roughness of film surfaces probably due to ion

bombardment, during the plasma processing, and crystallite

size rising [15].It is remarkable to find that Ra does not change significantly as a result of this range of the (applied

power).

3.3.2. Microhardness

Figure.6 shows the film microhardness at different (applied

power). One can notice that, the microhardness increases up

to232 HV as the (applied power) ncreases up to 225W.

The increase in microhardness is owing to the increase of

TiO2 intensity rutile-phase where the rutile-structure is

more densely packed (4.25 g/cm3), than the anatase

structure (3.899 g/cm3) [16]. For this reason the rutile-

structure is more compact, harder and higher wear performance than anatase structure [17].

Fig. 6 Microhardness values of the TiO2 coatings at


3.3.3. Friction Coefficient

Figure.7 shows the (COF) of films at different (applied

power). From this figure, the (COF) increases from nearly

0.51 at (applied power) 100 W to nearly 0.55 as the

(applied power) increases to 225W. The rising in the

(COF) may be refer to enlarge of the crystallite size films.

As the (applied power) increases, the intensity of the TiO2 phase increases as in Fig.2 in which more

energy absorb and the crystallite size/grain increases too

[18]. In addition, Oxidation process leads to increase in

the (COF).

3.4. Optical Properties

3.4.1. Transmittance

The transmission spectra of (TiO2) films fabricated

under varying (applied power) are shown in Fig.8. One

can see that, for all films a sharp increase in the

transmission spectra for the wavelength above 400nm

which is corresponding to the TiO2 characteristic band

edge energy. Consequently, a good transmission of light

in the visible-region of 400-800 nm occurs. The visible-

region oscillations owing to optical interference at the

area inbetween film and substrate. However, a sharp

dropping in transmission in the UV region due to strong

absorption by the TiO2 film [19].



Fig. 7 The (COF) of TiO2 thin film samples at different (applied

power)

Fig. 8 Transmittance plot of the TiO2 coatings at different (applied power)

The visible-region oscillations provide the message that TiO2 film deposited by magnetron sputtering were very

uniform, flat, excellent surface quality and homogeneous

[10].The TiO2 film deposited at (applied power) 200 W has

the highest transmittance value (99.5%) at 550 nm, which the

human eyes are very sensitive to the light-wave. The sample

was deposited at 225 W showed lower transparency than at

200 W, it may be owing to the presence of more amounts of

defects and other contaminations at the surface of the films,

which results more scattering [20]. From Fig.3 and Fig.5, the

large crystallite size at 225 W makes the film surface rough

enough to enhance the scattering light and in turn decreases the transmittance [10].

3.4.2. Bandgap Energy

The energy bandgap was estimated using the Tauc relation

[11]

(2)

The equation gives dependence of the absorption

coefficient (α) upon the photon energy (hv) for near edge

optical absorption in semiconductors. In this equation k is

constant and m=1/2 for TiO2direct bandgap transition

[11]. The bandgap of TiO2 film can specified using the

plots of (αhv)1/2

versus energy (eV) that are explained in Fig. 9 by fitting a straight tangent line to the curves and

determine the intercept to the energy axis Eg. The resulted

values of the Eg of the TiO2 films at different (applied

power) are shown in Fig.10. It can be noticed that the

Eg values of the TiO2thin films are higher than to that

published elsewhere (3.2eV) [15, 21]. One can also

observe that, the Eg values significantly increase to the

maximum value of 4.02eV as the (applied power)

increases to 200W. This increase of the Eg, may be owing

to the high dislocation at the grain boundaries of the TiO2

film, which affects the barrier height in which the charge

accumulate [22].After that, the Eg decrease to 3.97 eV as the (applied power) increases to 225 W. It may be

explained in terms of the existence of more amounts of

defects [20].

Fig. 9 The Plot of (αhυ)1/2 Vs hυ for indirect bandgap

calculation of the TiO2 coatings at different (applied power)

Fig. 10 The energy bandgap values of the TiO2 coatings at different (applied power)



3.4.3. Refractive Index And Extinction Coefficient

The effect of (applied power) on the refractive index at

different wavelengths of the films is plotted in Fig.11. From

Fig. 4, it can be observed that the thickness of the deposited

TiO2thin film increases as the sputtering power increases.

This is obviously due to the increase in sputtering rate due to

the enhancement of the energy of bombarding ions. As a

consequence, the refractive index of the films at various

wavelengths also varies in accordance with the principles of

thin film interference. It is clear that the refractive index

decreasing with increasing the (applied power), as a result of

increasing the thin film thickness [10].

Fig. 11 Dependence of refractive index on wavelength of the TiO2

coatings at different (applied power)

As shown in Fig.12, the extinction coefficient (k) of the

TiO2thin film decreases rapidly towards zero with increasing

the wavelength. L. Skowronski et al. [23] reported that the

extinction coefficient of the TiO2 thin film in the visible-light

region is very low.

Fig. 12 Dependence of extinction coefficient on wavelength of the

TiO2 coatings at different (applied power)

3.5. Electrical Properties

Figure.13 shows the variation of the electrical

resistivity (ρ) of (TiO2) films at different (applied power).

The results indicate that the resistivity of the samples

decreases with increasing the (applied power) and

reached its minimum value of 3.7×10-4Ω.cm for the

sample was deposited at 225W. This trend is attributed to

the increasing in the regular sites of the Ti atoms in the

films network. Since TiO2 is a n-type semiconductor, the

concentration of Ti4+ in TiO2 film forms a donor level

between the bandgap of TiO2 which results in the

reduction of recombination of (photo-generated electrons) and holes [24]. Consequently, Ti4+ ions have more

concentration in films obtained with high (applied power)

regarding the O2- ions, which results increase in the free

electron concentration refers to the low film’s resistivity

[24].On the other hand, the increase in the conductivity is

ascribed to the increase in the crystallite size as the

(applied power) increases, which leads to a decrease in

grain boundaries [21].

Fig. 13 The resistivity values of the TiO2 coatings at


In addition, the higher the crystal orientation the lower

will be resistivity. This is due to the reduction in the

scattering of the carriers at the grain boundaries and

hence resistivity [13].It is interesting to note that the good conductivity of TiO2 films is very compatible with the

conductivity requirements of TCO for application as ARC

in solar cells [25].

IV. CONCLUSION

1- Nanostructure of TiO2 thin films has been obtained

by pulsed magnetron sputtering technique at

different (applied power). 2- Structural composition, mechanical, optical,

electrical properties of the TiO2 coatings is widely

varied with changing the (applied power).

3- (Applied power) at 200W produces the highest

value of transmittance with high energy bandgap

and roughness; but lower reflection, refractive

index, and electrical resistivity.



REFERENCES

[1] G. Valverde Aguilar, J. García Macedo, V. Rentería Tapia, M. Aguilar

Franco, Photoconductivity studies of gold nanoparticles supported on

amorphous and crystalline TiO2 matrix prepared by sol-gel method,

DOI (2013).

[2] Y. Liu, Y. Lin, Y. Wei, C. Liu, Conductor formation through phase

transformation in Ti-oxide thin films, Journal of electronic materials, 41

(2012) 166-171.

[3] J. Haines, J. Leger, X-ray diffraction study of TiO2 up to 49 GPa,

Physica B: Condensed Matter, 192 (1993) 233-237.

[4] J.-i. Nomoto, T. Miyata, T. Minami, Optical and electrical properties of

transparent conducting B-doped ZnO thin films prepared by various

deposition methodsa), Journal of Vacuum Science & Technology A, 29

(2011) 041504.

[5] Q.-B. Ma, Z.-Z. Ye, H.-P. He, S.-H. Hu, J.-R. Wang, L.-P. Zhu, Y.-Z.

Zhang, B.-H. Zhao, Structural, electrical, and optical properties of

transparent conductive ZnO: Ga films prepared by DC reactive

magnetron sputtering, Journal of Crystal Growth, 304 (2007) 64-68.

[6] M. Chen, Z. Pei, X. Wang, C. Sun, L. Wen, Structural, electrical, and

optical properties of transparent conductive oxide ZnO: Al films

prepared by dc magnetron reactive sputtering, Journal of Vacuum

Science & Technology A, 19 (2001) 963-970.

[7] T. Miyagi, M. Kamei, T. Ogawa, T. Mitsuhashi, A. Yamazaki, T. Sato,

Pulse mode effects on crystallization temperature of titanium dioxide

films in pulse magnetron sputtering, Thin Solid Films, 442 (2003) 32-

35.

[8] J. O'brien, P. Kelly, Characterisation studies of the pulsed dual cathode

magnetron sputtering process for oxide films, Surface and Coatings

Technology, 142 (2001) 621-627.

[9] V.V. Kumar, M. Deepak, T. Manju, Influence of sputtering power on

the optical properties of ITO thin films, LIGHT AND ITS

INTERACTIONS WITH MATTER, AIP Publishing, 2014, pp. 22-27.

[10]H.-C. Pan, M.-H. Shiao, C.-Y. Su, C.-N. Hsiao, Influence of sputtering

parameter on the optical and electrical properties of zinc-doped indium

oxide thin films, Journal of Vacuum Science & Technology A, 23

(2005) 1187-1191.

[11]N.A. Bakr, A. Funde, V. Waman, M. Kamble, R. Hawaldar, D.

Amalnerkar, S. Gosavi, S. Jadkar, Determination of the optical

parameters of a-Si: H thin films deposited by hot wire–chemical vapour

deposition technique using transmission spectrum only, Pramana, 76

(2011) 519-531.

[12]S. Mändl, B. Rauschenbach, Anisotropic strain in nitrided austenitic

stainless steel, Journal of Applied Physics, 88 (2000) 3323-3329.

[13]B.R. Kumar, T. Rao, Microstructural, electrical and optical properties of

DC reactive magnetron sputtered zinc aluminum oxide thin films for

optoelectronic devices, Journal of Optoelectronics and Biomedical

Materials Vol, 4 (2012) 35-42.

[14]K. Kusaka, D. Taniguchi, T. Hanabusa, K. Tominaga, Effect of input

power on crystal orientation and residual stress in AlN film deposited

by dc sputtering, Vacuum, 59 (2000) 806-813.

[15]N. Mathews, E.R. Morales, M. Cortés-Jacome, J.T. Antonio, TiO2 thin

films–Influence of annealing temperature on structural, optical and

photocatalytic properties, Solar Energy, 83 (2009) 1499-1508.

[16]F.M. El-Hossary, N.Z. Negm, A.M.A. El-Rahman, M. Raaif, A.A.A.

Elmula, Properties of Titanium Oxynitride Prepared by RF Plasma,

Advances in Chemical Engineering and Science, 5 (2014) 1.

[17]J. Abboud, Effect of processing parameters on titanium nitrided surface

layers produced by laser gas nitriding, Surface and Coatings

Technology, 214 (2013) 19-29.

[18]R. Ahmad, N. Ali, I. Khan, S. Saleem, U. Ikhlaq, N. Khan, Effect of

Power and Nitrogen Content on the Deposition of CrN Films by Using

Pulsed DC Magnetron Sputtering Plasma, Plasma Science and

Technology, 15 (2013) 666.

[19]W. Du, Y. Ye, H. Li, F. Zhao, L. Ji, W. Quan, J. Chen, H. Zhou, Low

temperature preparation of transparent, antireflective TiO2 films

deposited at different O2/Ar ratios by microwave electron cyclotron

resonance magnetron sputtering, Vacuum, 86 (2012) 1387-1392.

[20]M. Rezazadeh Sefideh, Z. Sadeghian, A. Nemati, S.P. Mohammadi, M.

Mozafari, Effects of Processing conditions on the physicochemical

characteristics of titanium dioxide ultrathin films deposited by DC

magnetron sputtering, Ceramics International 34 (2015) 123-167.

[21]F. Hanini, A. Bouabellou, Y. Bouachiba, F. Kermiche, A.

Taabouche, M. Hemissi, D. Lakhdari, Structural, optical and

electrical properties of TiO2 thin films synthesized by sol-gel

technique, IOSR Journal of Engineering, 3 (2013) 21-28.

[22]K. Usha, B. Mondal, D. Sengupta, P. Das, K. Mukherjee, P.

Kumbhakar, Development of multilayered nanocrystalline TiO2

thin films for photovoltaic application, Optical Materials, 36

(2014) 1070-1075.

[23]L. Skowronski, K. Zdunek, K. Nowakowska-Langier, R. Chodun,

M. Trzcinski, M. Kobierski, M. Kustra, A. Wachowiak, W.

Wachowiak, T. Hiller, Characterization of microstructural,

mechanical and optical properties of TiO2 layers deposited by

GIMS and PMS methods, Surface and Coatings Technology, 282

(2015) 16-23.

[24]X. Zhao, Q. Zhao, J. Yu, B. Liu, Development of multifunctional

photoactive self-cleaning glasses, Journal of Non-Crystalline

Solids, 354 (2008) 1424-1430.

[25]D. Hocine, M. Pasquinelli, L. Escoubas, P. Torchio, A. Moreau,

M. Belkaid, Structural and optical study of titanium dioxide thin

films elaborated by APCVD for application in silicon solar cells,

Renewable Energy and Power Quality Journal, DOI (2010).

Moataz Bellah Hassan Ata (Moataz H.

Ata)

Corresponding author, Assistant Professor of

Production Engineering, Mechanical

Engineering Department, Faculty of Industrial

Education, Sohag University, Sohag, Egypt.

General Specialization: Mechanical

Engineering (Design and Production).

Specific Specialization: (Material Science).

Interest

1. Powder metallurgy processing.

2. Functional Graded Materials (FGMs).

3. Smart Materials, Shape Memory Alloys (SMAs).

4. Wood Plastic Composites.

5. Thin Films Coating.



synthesis of nanostructure tio2 thin films using...

Documents