fabrication of transparent conducting oxide nanomaterial at low temperature and study of its...

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International Journal of Nanotechnology and Application (IJNA) ISSN(P): 2277-4777; ISSN(E): 2278-9391 Vol. 4, Issue 6, Dec 2014, 1-6 © TJPRC Pvt. Ltd.

FABRICATION OF TRANSPARENT CONDUCTING OXIDE NANOMAT ERIAL AT LOW

TEMPERATURE AND STUDY OF ITS PROPERTIES

SREEDHAR D1, SRINIVASULU REDDY K 2, VINOD REDDY Y 3 & VASUDEVA RAO V 4 1,2,3Department of Mechanical Engineering, Sreenidhi Institute of Science and Technology, Ghatkesar,

Hyderabad, Telangana, India 4Department of Mechanical and Industrial Engineering, Science Campus, Florida, South Africa

ABSTRACT

In the past years zero-dimensional and one-dimensional nanostructures of binary semiconducting oxides, such as

ZnO, TiO2, GaO, Cd2O3, SiO2 and SnO2, have attracted immense interest but for better development new materials like

ternary oxide semiconductors such as cadmium stannate (Cd2SnO4), galium doped ZnO (GZO), aluminium doped ZnO

(AZO) and zinc tin oxide (ZTO). This paper focuses on synthesis and properties studies of ternary semiconducting oxide,

Zinc-Tin-Oxide (ZnSnO3) which was synthesized with molar ratio of 1:1. Zinc tin oxide (ZTO) nanomaterial has been

successfully synthesised using Solvo-Thermal method in which zinc and tin powders were separately mixed with ethanol

solution under slow stirring. In this process a mild base, Na2CO3 is used as a mineralizer and ethanol as a solvent at

temperature about 100°C. These ZTO nanomaterials are further characterized to study the properties such as morphology

and particle size by using SEM, crystal structure by using XRD, energy band gap by using UV-visible spectroscopy,

elemental analysis and chemical composition by using EDS, and also the weight loss percentage at different temperature

ranges by using TGA. These studies are useful to know the electronic and thermal properties of the material with respect to

the 1:1 composition ratio at 100°C. Due to the nanoscale dimensions these ZTO nanomaterials can be used in developing

solar cells because of its less cost, less weight and other applications.

KEYWORDS: Zinc Tin Oxide (ZTO), SEM, XRD, EDS, UV-visible Spectroscopy and TGA

INTRODUCTION

From the past few years there is much development in nanotechnology for the designing of semiconductors so as

to match the properties of new emerging materials. In the past years zero-dimensional and one-dimensional nanostructures

of binary semiconducting oxides, such as ZnO, TiO2, GaO, Cd2O3, SiO2 and SnO2, have attracted immense interest but

for better development new materials like ternary oxide semiconductors such as cadmium stannate (Cd2SnO4), galium

doped ZnO (GZO), aluminium doped ZnO (AZO) and zinc tin oxide (ZTO)[1-6] are being prepared now a days. So among

all the above ternary semiconducting oxides ZTO, an inexpensive non-toxic material, has high electrical conductivity [2],

electron mobility [3] and attractive optical [4-5] photoluminescence properties [6], thermal properties and other attravtive

properties [7-8]. These properties has attracted in synthesizing and characterizing the ZTO nanomaterials. There are many

different synthesis techniques to synthesize ZTO such as physical vapor deposition (PVD), chemical vapor deposition

(CVD), flame-pyrolysis, laser-ablation, arc discharge, sol-gel method, hydrothermal method and solvo-thermal method. So

in order to reduce the impurities and crystal defects and to improve uniformity, ZTO nanomaterials were prepared by

chemical synthesis method.

2 Sreedhar D, Srinivasulu Reddy K, Vinod Reddy Y & Vasudeva Rao V

Impact Factor (JCC): 1.8003 Index Copernicus Value (ICV): 3.0

This chemical method can have good control over the composition ratio also. In this method preparation of ZTO

was performed with zinc and tin powders as sources by using mild base Na2CO3, as a mineralizer and aqueous ethanol as

a solvent at temperature above 100°C for 12hours. The particle properties such as size and morphology can be changed by

using this method by adjusting of parameters such as molar ratio [2, 3], reaction temperature [6], concentration and

reaction time.

MATERIAL FABRICATION PROCESS

In this synthesis method zinc and tin powders were used as sources of starting materials. In this experimental

process ZnSO4.7H2O and SnCl4.5H2O were dissolved in aqueous ethanol solution separately. Then, the prepared

SnCl4.5H2O solution was slowly added into of ZnSO4.7H2O solution under slow stirring. A molar ratio of Zn:Sn was

maintained as 1:1 throughout this work [2]. Thereafter, sodium carbonate solution was added drop wise into the reaction

mixture under vigorous stirring; Na2CO3 was used as a mineralizer because of its low basicity. With this mixture small

amount of CTAB dissolved in deionised water was slowly added under mild stirring to form the transparent white colored

solution. Thereafter, this solution mixture was transferred into a teflon–lined stainless steel autoclave and subjected to

solvo-thermal conditions in the temperature range of 100°C. After the reaction, autoclave was cooled into room

temperature. Then, the formed products were centrifuged in order to obtain the ZTO nanomaterials. These materials were

washed successively with deionized water and absolute ethanol in order to remove the by-products. Finally, the products

were dried at 80ºC in the oven for 12h. Then after the dried material is taken out and is made into fine powder by using

mortar and pestle. Then the fine powder is taken in to sample holders and is sent for the further characterization. These

ZTO nanomaterials were characterized by using SEM, EDS, XRD, TGA and UV-visible spectroscopy.

Sn(OH)62− + 2Zn(OH)4

2− → ZnSnO3 + ZnO + 4H2O + 6OH−

EXPERIMENTAL RESULTS

To analyze the effects of molar ratio on the formation and morphology of ZnSnO3, solvo-thermal reactions were

carried out around 100°C with Zn:Sn ratio of 1:1.

The morphology and particle size of the prepared ZTO nanomaterials were analyzed with scanning electron

microscope (SEM) [2]. Figure 1 shows the SEM image of ZTO nanomaterials prepared around 100°C. The least size of the

ZnSnO3 nanomaterials synthesized at 100 ºC was found to be 84.7 nm. This observation clearly indicates that the formation

of ZTO nanostructure was effective.

Figure 1: SEM Images of the ZTO Nanomaterials Prepared at 100°C

Fabrication of Transparent Conducting Oxide Nanomaterial at Low Temperature and Study of its Properties 3


The crystal structure of the ZTO nanomaterials prepared at different temperature was characterized using X-Ray

diffraction (XRD). Figure 2 shows the XRD pattern of the ZTO nanomaterials prepared at 100°C. Due to the low reaction

temperature, there is the presence of ZnO along with ZnSnO3 nanomaterials. The particle diameter size of around 70 nm

has been observed by using Debye Scherrer formula (D= K λ/ β cos θ). From the data file 11-0274 of JCPDS, many

diffracted peaks are observed to be of perovskite face-centered zinc tin oxide material [10].

Figure 2 - XRD of ZnSnO3 prepared at 100ºC

Elemental analysis or chemical composition of the ZTO nanomaterials prepared at 100ºC was analyzed using

energy dispersive X-ray spectroscopy in scanning electron microscopy unit. As shown in Figure 3, it is found that the

peaks of Sn, Zn and oxygen are also observed. These data clearly confirm that the ZTO nanomaterials consist of Sn, Zn

and oxygen without any chemical contamination. Table 1 shows the chemical compositions of the ZTO nanomaterials

determined by the energy dispersive spectroscopy analysis (EDS). From this table it is clear that the chemical composition

of the ZTO nanomaterials is well within the expected ratio.

Figure 3: EDS Spectra of the ZTO Nanomaterials

Table 1: Chemical Composition of the ZTO Nanomaterial

Element Wt. % O-K 20.87 Zn-K 28.94 Sn-L 29.78

UV-visible spectroscopy [7] is related to the absorption spectroscopy of the materials in the ultraviolet-visible

spectral region. The optical bandgap of a semiconducting nanomaterial could be obtained from the absorption band edge in

the UV-vis spectrum. The absorbance measurements were carried out over the range of 190 - 800 nm. Figure 4a shows the



UV-visible absorption spectrum of the ZTO nanomaterials prepared at 100ºC. Figure 4b shows the (αhυ)2 v/s hυ graph of

ZTO nanoparticles. The dashed line is the indication of extrapolation. Therefore the band gap value observed is 4.3eV

which is high due to the reaction temperature is at 100 ºC. Better results can be observed at high reaction temperatures

[10].

Figure 4: (a) UV-Visible Spectra and (b) (αhυ)2 v/s hυ of ZnSnO3 Prepared at 100ºC

TGA is a technique used for the measuring of changes in mass as function of temperature. TGA results of the ZTO

nanomaterials prepared at 100°C with molar ratios of 1:1 as shown in the figure 5. From these TGA analyses it is clearly

observed that the weight loss of the material is zero in room temperature (0 to 36°C) and is less at the temperature range of

589°C to 860°C.

Figure 5: TGA of ZnSnO3 Prepared at 100ºC

Table 2: Weight Loss of the ZTO Nanomaterial by TGA

Temp Range °C Wt. loss % 0-36 0

36-250 8.04 250-589 10.04 589-860 3.62 860-1200 6.56

CONCLUSIONS

These results suggest that the solvo-thermal method using Na2CO3 as a mineralizer and aqueous ethanol as a

Fabrication of Transparent Conducting Oxide Nanomaterial at Low Temperature and Study of its Properties 5


solvent would be an efficient method to prepare the ZTO nanomaterials with high band gap. These materials can be

potentially used in the various fields. From the SEM, EDS, XRD, TGA and UV-visible spectroscopy results it can be seen

that the zn:sn composition ratio of 1:1 has better characteristics. The EDS studies revealed that the ZTO nanomaterials

consist of Sn, Zn and oxygen without any other chemical contamination. TGA results shows that the weight loss is zero

under room temperature and is less around 589 to 860°C XRD results suggest that the particle diameter size of ZTO

nanoparticles is approximately around 70 nm. From UV-visible spectroscopy results it is proved that the bandgap of

synthesized ZTO nanomaterial is good when compared with other oxides. So by increasing the temperature and duration

time, the results may be vary and can obtain better results than the above result. Due to the nanoscale dimensions these

ZTO nanomaterials can be used in developing solar cells because of its less cost, less weight and other applications. ZTO is

a very important material in advanced technologies, such as photoelectron chemical cells, gas sensor [9], synergistic flame

retardants, photocatalytic materials and zinc-tin-oxide thin-film transistors [8]. In recent years, ZTO nanomaterials have

been prepared by high temperature, thermal evaporation, sol–gel method, etc. but compared with the recent years;

solvo-thermal method has got more interest because of its stability, simplicity, cost-efficiency, etc.

ACKNOWLEDGEMENTS

The authors would like to thank the management of Sreenidhi Institute of Science and Technology, Hyderabad for

the support and encouragement given for this research work. The authors would like to thank Sri. K.T. Mahhe (Secretary),

Dr. P. Narasimha Reddy (Director) and Dr. T. Ch. Siva Reddy (Head of Mechanical Engineering) of Sreenidhi Institute of

Science & Technology for their support and encouragement

Nomenclature

h = Planks constant.

υ = Frequency

α = Absorption coefficient.

D = Particle diameter size.

K = Shape factor = 0.9.

λ = X-Ray wavelength = 0.1541 nm.

β = Full width at half max (Intensity).

θ = Bragg or diffraction angle.

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