Journal of Physical Science and Application 6 (1) (2016) 71-75
doi: 10.17265/2159-5348/2016.01.020
Synthesis and Characterization of ZnO Nanostructure by Chemical Spray Pyrolysis Method
Nadir F. Habubi1, Noor A. Nema2, and Abdulazeez O. Mousa2
1. Department of Physics, Faculty of Education, University of Al-Mustansiriyah, Baghdad, Iraq
2. Department of Physics, College of Science, University of Babylon, Babylon, Iraq
Abstract: Zinc Oxide (ZnO) nanostructure were synthesized by precipitating Zinc Chloride and analyzed structurally and optically. Samples were prepared at different thickness (62, 66, 74, 86, 92, and 110 nm), and substrate temperature kept at 400 °C in all cas. Compresd Nitrogen was ud as a carrier gas. The samples of the ZnO films were characterized by X-ray diffraction (XRD), and atomic force microscopy (AFM). The XRD results indicated that the synthesized ZnO thin films have a pure wurtzite (hexagonal pha) structure. It can be en that the highest texture coefficient was in (002) plan for nanostructure films. AFM measurement showed the grain size ranging from 62-86 nm. The optical band gap energy (E g) of ZnO nanostructure have two values for the same sample and the
E g decrea with increasing thickness utilizing the optical data using UV-Vis spectrophotometer.
Keywords: ZnO, spray pyrolysis, optical band gap, nanostructure.
1. Introduction
记忆单词
The wide variety of electronic and chemical properties of metal oxides make them exciting materials for basic rearch and for technological applications alike. Oxides span a wide range of electrical properties from wide band-gap insulators to metallicand superconducting [1, 2]. Zinc oxide (ZnO), a wide band gap (3.4 eV) II-VI compound miconductor, has a stable wurtzite (hexagonal pha) structure with lattice spacing a = b = 0.325 nm and c = 0.521 nm [3, 4]. ZnO is one of transparent conducting oxides (TCO) materials who thin films attract much interest becau of typical properties such as high chemical and mechanical stability in hydrogen plasma, high optical transparency in the visible and near-infrared region. Due to the properties ZnO is a promising material for electronic or optoelectronic applications [5, 6]. In this study, ZnO nanostructure were prepared by chemical spray pyrolysis technique. The spray pyrolysis is an attractive method to obtain
Corresponding author:Nadir F. Habubi, Ph.D, Professor, rearch fields: thin films, solar cells, detect
ors. E-mail: *********************.thin films, since it has been proved to be a simple and inexpensive method and it is particularly uful for large area of nanotechnology applications [7, 8]. The main advantages of spray pyrolysis over other similar techniques are no requirement of vacuum, substrates with complex geometries can be coated, uniform and high quality coatings and template-free method to prepare ZnO nanostructures [9, 10].
Here, we report the direct growth of zinc oxide on glass substrates by a chemical spray pyrolysis method. We have also studied the structural, morphological, and same optical properties of the thin films with the aim of understanding physical properties of the obtained ZnO nanostructure.
2. Experimental
The ZnO thin films were deposited on glass substrates by spray pyrolysis technique. The spray solution was prepared from zinc acetate dehydrate (Zn(CH3COO)22H2O) with purity of 99.5% was purchad from Aldrich Chemical Company and distilled water. A few drops of glacial acetic acid were then added to stabilize the solution. Automated spray
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Synthesis and Characterization of ZnO Nanostructure by Chemical Spray Pyrolysis Method
72 pyrolysis equipment is ud for the synthesis of thin film in this work. Nitrogen was ud as a carrier gas and to atomize the spray under constant pressure (4 bar). Glass slides cut in 2.5×2.5 cm pieces are ud as a substrate on which films are grown. The glass slides are cleaned using ethanol, and distilled water. Then the glass slides were ultrasonically cleaned. The substrate temp
erature was maintained to be 400 °C during spraying time with ±10 °C. The ZnO thin films were deposited at different number of sprays (5, 10, 15, 20, 25, and 30). After deposition, film crystal structure was investigated by X-ray diffraction (XRD-6000, Shimadzu X-ray diffractometer ) using CuKα X -ray source. AFM was ud to characterize the surface morphology of the film. The optical properties of the ZnO thin films were characterized by UV–VIS spectrophotometer at room temperature. The thickness of thin films was measured using (LIMF-10 optical thin film measurement).
3. Result and Discussion 3.1 Structural Properties
XRD patterns of the grown ZnO samples are shown in Fig. 1(a-f ) at different number of sprays 5, 10, 15, 20, 25, and 30 respectively. Three prominent diffraction peaks viz. 100, 002, and 101 for the wurtzite structured ZnO pha has been obrved.
The prence of prominent diffraction peaks reveals the polycrystalline nature of the films. Therefore, it can be concluded that all the films deposited in the experimental conditions show strong c-axis 002
orientation growth. In the sample (a ) deposited at 5 sprays interval, becau the low thickness leads
to a very thin film, 002 and 101 diffraction peak was detected. The average crystallite size (G S ) of the films were determined by the Debye-Scherrer formula “1” [11-13] (the peak widths of the strong diffraction planes have been taken from calculation using the equation following equation and their values were listed in Table 1).
GGSS = (0.94 λλ)/(ββββββββββ) (1)
Where (β) is the full width at half maximum of characteristic spectrum in units of radians. The lattice constants (a ) and (c ) of the wurtzite structure can be
a different number of spray (a) 5 spray, (b) 10 spray, (c) 15 spray, (d) 20 spray, (e) 25 spray, and (f) 30 spray .
Table 1 Summary of x-raycharacterization of ZnO thin film. All Rights Rerved.
Synthesis and Characterization of ZnO Nanostructure by Chemical Spray Pyrolysis Method 73
α = 2/√3 δ002(2)
c=2d(002) (3) The strain value (η) and the dislocation density (δ) can be evaluated by using the following relations [13, 16].
η=(β cosθ)/4 (4)
小学一年级数学下册δ=1/(Gs^2) (5) The calculated average crystallite sizes, lattice constants (a) and (c) for the ZnO thin films deposited at different number of sprays are shown in Table 1. Table 1 shows the strain and dislocation density of the ZnO thin film samples (a-f), the strain of the thin film varies from (16.758 to 9.218)×10-4 (lin-2.m-4 ), and the dislocation density of the same thin film samples (a-f) varies from (21.427 to 6.483)×10-14 (lin m-2). The results revealed that the strain and dislocation density decrea with the increasing of the average grain size [17].
For the (002) plane, the calculatedvalues of (a) and (c) lie between a = (2.979 and 3.007) Å and c = (5.160 and 5.208(Å)) (JCPDS data card no. 36–1451). In other words, the film thickness have been measured and shown also in Table 1. Very thin films (below 110 nm) were obtained. The thickness of
films increas with the increa of deposition number of sprays shown in Fig. 2. The smallest grains were found for the (a) (62 nm) and largest for the (f) (approximately 86 nm) film samples shown in Fig. 3.
However, XRD gives the crystallite size as the X-rays determine the crystal structure by determining the clo pack planes and distance between two atoms. The results revealed that the grain size increas with the increasing of thickness. Fig. 4 shows the three-dimensional (3D) surface morphology of the ZnO thin films sample (a-f). The calculated values of surface roughness and the grain sizes from AFM are summarized in Table 1. It has been obrved that a minimum surface roughness has been found for the (b) sample while the (f) sample has the maximum value. 3.2 Optical Properties
The optical characteristic of the samples is investigated from the transmission measurements in the range of 340-700 nm. Fig. 5 shows the transmission in UV-visible spectra region for ZnO thin films at different number of sprays. The films fabricated at 5 sprays have a higher transmission, andtho prepared at
all samples.
samples.
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Synthesis and Characterization of ZnO Nanostructure by Chemical Spray Pyrolysis Method 74
Fig. 4 AFM images of ZnO thin films at different number of spray (a) 5 spray, (b) 10 spray, (c) 15 spray, (d) 20 spray,
sprayed at different number of sprays. It can be obrved that in general, the decrea in number of sprays (the decrea in thickness) improved the transmission [18].
Absorption coefficient α (cm-1) associated with the strong absorption region of the sample was calculated from absorbance (A) and the sample thickness (t) was ud “6” [19].
αα=3.3026AA tt (6) The variation of the absorption coefficient (α (cm-1)) with the photon energy hνν(eV) is related by ud “7”
[20].
ααℎνν=CC(ℎνν−EE gg)12�(7) where C is a constant, assuming the absorption coefficient αcorresponding to the direct band gap energy of the wurtzite structure for ZnO films, in the fundamental absorption region, better linearity was obrved from the (ααℎνν)2 versus ℎννplot Fig. 6, which was ud to determine the band gap energy E g [21]. We note from Fig. 6, two values of the same sample, e.g., sample a have 3.5 and 3.38 (eV), while it is slightly higher than that 3.37 eV previously reported by Chen et al. [22]. Band gap energy increas with decreasing grain size due to quantum size effects.
4. Conclusion
Zinc oxide films have been successfully prepared on glass substrate using the spray pyrolysis technique. The ZnO thin films with hexagonal structure have been synthesized at different number of sprays have nanocrystalline structure. From the XRD measurements, the average crystallite size in the range of 20.55-45.15 nm, and the highest texture coefficient was in (002) plan prepared in this study. The results revealed that the strain and dislocation density are decreasing with the increasing of the average grain size. AFM studies confirmed the uniformity and well grown crystalline morphology of the ZnO films. The grain size of the thin films, calculated from AFM in the range of 62-86 nm. Also, the UV-VIS studies optical studies
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Synthesis and Characterization of ZnO Nanostructure by Chemical Spray Pyrolysis Method 75
showed that their optical band gap energy range 3.29-3.5(eV) for all samples. The higher value of energy gap is for the lower thickness, it’s due to smaller grain size. All the films were transparent in UV-VIS spectra region; with an average optical transmittance of 70%.
Acknowledgement
Authors acknowledge that part of the work reported here, was carried out at University of Babylon, Department of Physics, College of Science, and national center for construction, which is supporting this work.
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