Preparation and Characterization of Needle-like ZnO onTiO2 Nanoparticles by Solution-Immersion Method and RF Magnetron

Sputtering

N.A.M. Asib1 2, a, A. Aadila1 2, b, A.N. Afaah1 2, c, M. Rusop1 3, d, Z. Khusaimi1, e 1NANO-SciTech Centre, Institute of Sciences,

2Faculty of Applied Sciences,

3NANO-ElecTronic Centre, Faculty of Electrical Engineering,

Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia

aamierahasib@yahoo.com, baadilaazizali@gmail.com, cafaahabdullah@yahoo.com, dnanouitm@gmail.com, ezurai142@salam.uitm.edu.my

Keywords: Needle-like ZnO, TiO2 nanoparticles, Solution-immersion method, RF magnetron sputtering

Abstract. Needle-like zinc oxide (ZnO) nanostructures was deposited on titanium dioxide (TiO2)

nanoparticles by solution-immersion method and Radio Frequency (RF) magnetron sputtering with

diffferent RF powers, respectively on a glass substrate to synthesis nanocomposites of ZnO/TiO2.

Field Emission Scanning Electrons Microscope (FESEM) images demonstrate that needle-like ZnO

(112-1110 nm) are deposited on the surface of the TiO2 nanoparticles with the diameter of

approximately 36.3-62.9 nm. At 200 W, more needle-like ZnO with smallest average diameter (112

nm) appeared on the TiO2 nanoparticles, which also has the smallest average size of 36.3 nm. The

compositions of elements in the nanocomposites were showed by Energy Dispersive X-ray

Spectrometry (EDX). All elements of Ti, O, and Zn are observed as major components which

confirm the presence of TiO2 and ZnO in the composite. X-ray Diffraction (XRD) patterns of the

nanocomposites show ZnO formed on TiO2 nanoparticles are hexagonal with a wurtzite structure

and it revealed ZnO/TiO2 thin films were succesfully deposited as nanocomposites of ZnTiO3 at 100

W, Zn2TiO4 at 150 W and Zn2Ti3O8 at 200 W and above.

Introduction

Zinc oxide (ZnO) is an n-type semiconductor with a wide direct band-gap of 3.37 eV at room

temperature. ZnO have become one of the most widely studied metal oxide material due to the

attracting and unique properties of ZnO that able to exhibit high-transparency in the visible region,

near-UV emission, magnetic, high-conductivity [1], also have semiconducting and piezoelectric

dual properties [2]. However, its properties can be adjusted by controlling size and morphology [3].

The wide applications of ZnO can be found in numerous areas such as varistor, gas sensor [4], UV

photodetector material, high-efficient green phosphor, field emission displays and solar cell [3].

ZnO is also a very widely used photocatalyst due to its high activity and low cost [5].

In the last decade, titanium dioxide (TiO2) especially in thin film form have received wide

attention over the years, either as an optical coatings or as a protective layers for very large scale

integrated circuits because of their excellent properties. To demonstrate, TiO2-based nanomaterials

is good for the degradation of environmental contaminants due to high photocatalytic activity, low

cost, non-toxic, and excellent chemical stability [6]. Thus, it is worth mentioning that the

photocatalytic properties of TiO2 can be greatly influenced by modification of its surface and

coupling with other sulfides or oxides. For instance, the photocatalytic properties of TiO2 can be

greatly enhanced by coupling with ZnO [5].

Nowadays, it is reported that a wide variety of techniques such as sol–gel [7], hydrothermal

crystallization [1], pulsed laser deposition (PLD) also sputtering [1, 7] were used for the deposition

of porous TiO2 nanostructures. Here, attempts will be taken to produce nanostructures of TiO2 by

Advanced Materials Research Vol. 832 (2014) pp 596-601Online available since 2013/Nov/21 at www.scientific.net© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.832.596

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using RF magnetron sputtering. Compared to other methods, RF magnetron sputtering is of

particular interest for its simplicity in producing optical coatings that having high density, adhesion,

hardness and good uniformity of thickness over a large area [8]. Sputtering methods also provide

more freedom in selection of the deposition parameters [9].

Besides that, porous ZnO films must be deposited in controlled scale of film surfaces, either

nano or micro-scale structures in order to improve the photocatalytic activity[10]. There are various

techniques used such as pulsed laser deposition [10, 11], physical vapor deposition, molecular beam

epitaxy (MBE) [11], and sol–gel [9, 10]. Comparatively, solution method process are more

attractive due to low cost, the precursors are homogenous, has high-purity with specific surface

area, and allows growth of nanostructures at low temperature [11, 12].

Experimental Procedure

Preparation of TiO2 nanoparticles. TiO2 nanoparticles were deposited on glass substrates by RF

magnetron sputtering using a pure TiO2 solid target. The target to substrate distance was kept fixed

at 22 cm. 50 sccm of argon and 2 sccm of oxygen were used for sputter deposition. Argon was used

as a carrier medium and oxygen as reactive gas. TiO2 nanoparticles were deposited at different RF

powers which vary from 100 W to 300 W with increment rate of 50 W. Meanwhile, the working

pressure was maintained at 5 mTorr. After one hour of deposition, all the samples were annealed at

450 ⁰C for 1 hour, using annealing chamber to crystallize the samples.

Preparation of needle-like ZnO. Solution-immersion method was used to fabricate needle-like

ZnO on TiO2 nanoparticles. TiO2 nanoparticles film was immersed in a centrifuged tube. The

precursor solution is aqueous solution of zinc nitrate hexahydrate (Zn (NO3)2.6H2O) and stabilizer

hexamethylenetetramine, HMTA (C6H12N4) were dissolved in deionized (DI) water. The precursor

solution was stirred thoroughly with a magnetic stirrer for 1 hour at 60 ⁰C and then aged for 24

hours. TiO2 films were placed inside centrifuged tubes and the solution will be poured until the

films were fully immersed. The centrifuged tubes were placed inside water bath at 70-90 °C for 4

hours. As a result, ZnO nanostructures will grow on the TiO2 nanoparticles and becomes ZnO/TiO2

nanocomposites. The sample were dried in oven and subsequently, annealed at 500 ⁰C for 1 hour.

Lastly, the samples were characterized by FESEM, EDX and XRD.

Results and Discussion

FESEM images. Fig. 1 (a) shows FESEM (at 10 000x magnification and 5.0 kV) image of surface

morphology for TiO2 nanoparticles formed at 200 W, on a glass substrate by RF magnetron

sputtering method with the average diameter of 36.3 nm. Later on, needle-like ZnO were fabricated

on the sputtered TiO2 films by solution-immersion method as shown in Fig. 1 (b-f).

It was observed that the surface morphologies and roughness of TiO2 films were different at

various sputtering powers. The highest roughness of TiO2 deposited at power of 300 W, can be

regarded as a factor of higher hydrophilicity [13] and higher energy sputtering [14] as compared to

the smoothest layers deposited at 200 W. Thus, the deposited TiO2 nanostructure is optimized at 200

W as it has the lowest roughness or the smoothest surface [15].

After fabrication of ZnO by solution-immersion process on the TiO2 nanoparticles as shown in

Fig. 1 (b-f), the needle-like ZnO in the range diameter of 112 to 1110 nm grow vertically and

horizontally on the TiO2 nanoparticles. Figure 1 (d) reveals that at 200 W, the needle-like ZnO with

smallest diameter (112 nm) were deposited on the smallest size of TiO2 nanoparticles and it

confirms that the needle-like were deposited with dense arrays and small diameter size. Meanwhile,

the largest diameter of needle-like ZnO with less dense arrays was deposited at 300 W on the

largest size of TiO2 nanoparticles (62.9 nm) as shown in Figure 1 (f). Thus, we can see that more

nanostructures of ZnO appeared in the film sputtered at 200 W compared to other samples. The

denser the film, more surface contact will exist between ZnO structures and the condition will

improve the mobility of electrons in the films and will contribute to better electrical properties [16].

Advanced Materials Research Vol. 832 597

Fig. 1, FESEM images of (a)TiO2 nanoparticles deposited at 200 W, and deposited of needle-like

ZnO on TiO2 nanoparticles sputtered at (b) 100 W, (c)150 W, (d) 200 W, (e) 250 W, and (f) 300 W.

Table 1, The diameter size of TiO2 nanoparticles and needle-like ZnO deposited at various RF

powers.

EDX analysis. Figure 2 (a) and (b) show EDX of the ZnO/TiO2 nanocomposites deposited at 100

W. There are two area were examined on the sample. First was the dark area (spectrum 1) which

represented as TiO2 nanoparticles and second was the bright area (spectrum 2) on top of the dark

area, represented as ZnO nanostructures.

Fig. 2, (a-b) EDX of the ZnO/TiO2 nanocomposites deposited at 100 W.

The EDX for Fig. 2 (a) confirm the elemental composition of Ti and O in the film as detected in

spotted area (spectrum 1). Meanwhile, at another spotted area (spectrum 2) in Fig. 2 (b), Zn and O

were observed as major components which confirmed the growth of ZnO on the TiO2 nanoparticles

for each samples. Other elements such as Si, Na and Ca were also detected in the samples due to the

existence of chemical composition ( SiO2, Na2O and CaO) in the glass substrate. In order to prevent

charging and distortion of the image during the scanning and captured process by FESEM, the

Power [W] Diameter size of TiO2 [nm] Diameter size of ZnO [nm]

100

150

200

250

300

50.2

44.9

36.3

41.6

62.9

400

560

112

880

1110

(a)

(e) (d)

(c) (b)

(f)

(a) (b)

598 Nanoscience, Nanotechnology and Nanoengineering

sample must be electrically connected to the sample holder [17]. Thus, carbon paint was used to

allow a path for the electrons to travel and connect with ground. This caused some low level

impurities to the sample, which have been detected by EDX as element C.

XRD analysis. Fig. 2 (a-e) show the XRD patterns of the samples with different RF powers.The

crystallinity of the film and the corresponding chemical formula for each peaks were determined by

XRD as shown in the figures below.

20 30 40 50 60 70

0

500

1000

1500

2000

2500

3000

3500

4000

(00

2)

(10

1)

Inte

nsi

ty (

counts

)

2 Theta (°)

ZnT

iO3

ZnT

iO3

Zn

TiO

3

(100)

20 30 40 50 60 70

200

400

600

800

1000

1200

1400

1600

(002)

(10

1)

(100

)Z

nT

iO3

ZnT

i O3

Zn

2T

iO4

Zn

2T

iO4

Zn

2T

iO4

Inte

nsi

ty (

counts

)

2 Theta(°)

20 30 40 50 60 70

0

1000

2000

3000

4000

5000

(10

1)

(002

)

(100

)T

iO2

Zn

2T

i 3O

8

Zn

2T

i 3O

8

Zn

2T

i 3O

8

Zn

2T

i 3O8

Zn

2T

i 3O

8

Inte

nsi

ty (

coun

ts)

2Theta (°)

20 30 40 50 60 70

0

500

1000

1500

2000

2500

3000

(10

1)

(002)

(10

0)

TiO

2

Zn

2T

i 3O

8

Zn

2T

i 3O

8

Zn

2T

i 3O

8

Inte

nsi

ty (

counts

)

2Theta(°)

Fig. 3, XRD patterns of ZnO/TiO2 nanocomposites deposited at (a) 100 W, (b) 150 W, (c) 200 W,

(d) 250 W, and (e) 300 W.

The obvious peaks were observed at angles (2θ) of 31.2⁰, 33.9⁰ and 35.7⁰ which correspond to

ZnO phase (100), (002) and (101) crystal planes, according to JCPDS 36-1451. Meanwhile, there

are additional peaks found at 47.1⁰, 56.1⁰ and 62.4⁰. This revealed that the needle-like ZnO formed

on TiO2 nanoparticles are hexagonal with a wurtzite structure as reported by Li Shi Wang et al.[18].

M. H. Habibi et al. reported that the intensities of the (100) peak was higher than the other peaks for

all the films, showing that there is highly oriented ZnTiO3 on the glass substrate [6]. The highest

intensity of (100) peak was observed in sample of 200 W and according to Wuff’s theorem, the

largest phase is suggested to be the phase which has the lowest surface energies [19].

For sample that deposited at 100W, all the observed peaks are corresponding to the peak of

ZnO/TiO2 nanocomposites which reported as ZnTiO3. Meanwhile, at 150 W the hexagonal ZnTiO3

were decomposed into cubic Zn2TiO4.When the RF power was further increased to 250 W, the peak

of TiO2 corresponding to crystal plane of (100) were observed at 250 W and above. The peak of

TiO2 then were decomposed into cubic Zn2Ti3O8

Conclusion

In summary, the needle-like ZnO nanostructures on TiO2 nanoparticles by the solution-

immersion method and RF magnetron sputtering, respectively were successfully prepared on the

glass substrates. The deposition of TiO2 nanoparticles on the substrate was controlled by RF powers

in the range of 100-300 W. The obtained ZnO/TiO2 nanocomposites are characterized by different

techniques: FESEM, EDX and XRD. At 200 W, more needle-like ZnO with smallest average

diameter (112 nm) appeared on the TiO2 nanoparticles, which also has the smallest average size of

36.3 nm . Zn, Ti and O were observed as major components in the thin films. The XRD results

showed the needle-like ZnO formed on TiO2 nanoparticles are hexagonal with a wurtzite structure.

20 30 40 50 60 70

200

400

600

800

1000

1200

1400

1600 (10

0)

(00

2) (1

01

)

Inte

nsi

ty (

counts

)

Zn

2T

i 3O

8

TiO

2

2Theta (°)

(a) (b) (c)

(d) (e)

Advanced Materials Research Vol. 832 599

It was found that ZnO/TiO2 thin films were succesfully deposited as nanocomposites with chemical

formula of ZnTiO3 at 100 W, Zn2TiO4 at 150 W and Zn2Ti3O8 at 200 W and above.

Acknowledgement We would like to express our gratitude to Research Management Institute, Universiti Teknologi

MARA (UiTM), Shah Alam, Selangor, Malaysia for financial support.

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Nanoscience, Nanotechnology and Nanoengineering 10.4028/www.scientific.net/AMR.832 Preparation and Characterization of Needle-Like ZnO on TiO2 Nanoparticles by Solution-Immersion

Method and RF Magnetron Sputtering 10.4028/www.scientific.net/AMR.832.596