Transcript 23. Ulusal Kimya Kongresi - Mustafa Kemal University

Characterization of flower-like ZnO nanostructure
thin film produced by chemical bath deposition method
Samed ÇETİNKAYA, Süleyman KAHRAMAN, H.Mustafa ÇAKMAK and H.Ali ÇETİNKARA
Department of Physics, Mustafa Kemal University, Hatay 31034, Turkey
8th Nanoscience and Nanotechnology Congress - NANOTRVIII
Abstract
In this study, flower-like ZnO nanostructure thin film were successfully grown on p-silicon substrate via chemical bath deposition (CBD) method. The grown ZnO was characterized in terms
of X-Ray diffraction (XRD), scanning electron microscopy (SEM) and Ultraviolet Visible (UV-Vis) spectrometry. From the SEM images it was seen that the film consisted of flower-like structures. This
growing behavior was attributed to the limited number of nuclei. All of the observed XRD diffraction peaks were well indexed to hexagonal phase crystalline ZnO. In the XRD patterns, a small shift to
lower 2θ values was observed which might have resulted from impurities, lattice defects or vacancies. The average grain size, microstrain and dislocation density values of the ZnO were calculated
as 25 nm, 1.55x10-3 and 3.23x1013 cm-2, respectively. Through the absorption spectra, Eg value was found as ~3.17 eV. The red shift was attributed to non-stochiometry that Zn+2 ions substitute
oxygen vacancies.
Introduction
Experimental details
ZnO is a useful, economical and environmental material because of its
typical properties such as wide direct band gap (~3.3eV), large exciton
binding energy (60meV), transparency in the visible range, non-toxicity,
abundancy in nature, etc.[1]. As a II-IV binary semiconductor, ZnO
nanostructures have attracted considerable attention because of their good
optical, electrical and easily tunable morphological properties and their
potential applications in solar cells, solar energy-hydrogen conversion
devices, photoelectrochemical (PEC) hydrogen generation applications and
sensors [2]. Up to now, to obtain ZnO interfacial layers several methods have
been used such as sol-gel [3], thermal evaporation [4], successive ionic layer
adsorption-reaction (SILAR) [5]. Among the others, chemical bath deposition
method (CBD) a wet chemical method is a promising technique because it is
simple, environmental friendly, low temperature and cost effective method.
The sample was prepared by using mirror cleaned and polished p-type
Si wafer with (100) orientation. The wafer was chemically cleaned using the
RCA (Radio Corporation of America) cleaning procedures. The native oxide on
the front surface of the substrate was removed in HF:H2O (1:10) solution and
finally the wafer was rinsed in de-ionized water for 30 s before forming ZnO
layer on the p-type Si substrate. 0.1M Zn(NO3)2.6H2O was dissolved in 100 ml
distilled water and the pH value of the zinc nitrate solution was adjusted to
~10 by adding aqueous ammonia. The solution was stirred for 20 minute.
Then, the previously cleaned substrate was immersed and the solution was
heated up to 95oC. Heating rate was about 7oC/min. Substrate was taken out
from the bath after 5 minute. In this way, ZnO/p-Si structure was obtained.
Fig.1a.
Fig.1b.
Fig.2a.
Fig.2b.
Results and discussion
Morphological, structural and optical properties of the film were investigated by using Scanning Electron Microscopy (SEM), X-Ray Diffractometer (XRD)
and Ultraviolet Visible (UV-Vis.) spectrometry. Fig.1(a) shows the SEM images taken at different magnifications of ZnO film. As seen from the Fig. 1(a) flower-like
ZnO nanostructures were grown on p-Si substrate. Each flower-like structure consists of approximately seven rod/rice-like structures.
As shown in Fig.2(a), XRD patterns Crystal structure of the ZnO film was examined by X-ray diffractometer. XRD pattern of the film grown on the Si
substrate. From the Fig.2(a), it can be seen that all diffraction peaks were present and they were well indexed to hexagonal phase crystalline ZnO and the data
were in accordance with the JCPDS 36-1451 card [6]. And also the average grain size, microstrain and dislocation density values of the ZnO were calculated as 25
nm, 1.55x10-3 and 3.23x1013 cm-2, respectively.
As shown in Fig.2(b), Optical absorption spectra in the UV-Vis spectral range (200-110 nm) of the ZnO interfacial layer was determined using a UV-visible
spectrophotometer (Hitachi U-1900). The analysis of the dependence of absorption coefficient on photon energy in the high absorption regions is performed to
obtain the detailed information about the energy band gaps of the structures. The Eg value was found as ~3.17 eV. Typical band gap value of ZnO is ~3.30 eV [7].
The smaller band gap value (red shift) may be caused by non-stochiometry that Zn+2 ions substitute oxygen vacancies.
Conclusion
Referances
In summary, The ZnO thin film was successfully obtained on p-Si
substrate via CBD method. The morphological and structural properties
of the ZnO nanostructure thin film were investigated by SEM, XRD and
UV-Vis spectrometry methods. As can be seen from the SEM images,
flower-like ZnO were grown on p-Si substrate It is revealed from the
XRD patterns of the film reflection peaks of hexagonal structure. The Eg
value was found as ~3.17 eV. From result of the UV-Vis. that the smaller
band gap value of ZnO (red shift) may be caused by non-stochiometry
that Zn+2 ions substitute oxygen vacancies. According to theoretical and
practical results, ZnO exhibits direct inter band transitions [8].
[1] Yan Y, Zhou L, Zou J, Zang Y 2009 Appl. Phys. A: Mater. Sci&Processing 94, 559.
[2] Ergin B, Ketenci E, Atay F 2009 Int. J. of Hydrogen Energy 34 5249-5254.
[3] Yakuphanoğlu F, Farooq W A 2011 Mater. Sci. Sem. Processing 14 207-211.
[4] Badran R I, Umar A, Al-Heniti S, Al-Hajry A, Al-Harbi T 2010 J. of Alloys and Comp.
508 375-379.
[5] Yıldırım M A , Güzeldir B, Ateş A, Sağlam M 2011 Microelect. Eng. 88 3075-3079.
[6] Powder diffraction file 36-1451 for hexagonal Zinc Oxide 1997 JCPDS International Center for Diffraction Data.
[7] Çakmak HM, Kahraman S, Bayansal F, Çetinkaya S 2012 Phil. Mag. Lett.
(doi/abs/10.1080/09500839.2012.661887).
* This study was supported by Mustafa Kemal University Scientific Research Project Comission.
Project No: 1004 Y 0102