1. Characterization of flower-like ZnO nanostructure thin film produced by chemical bath deposition method 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 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 3.23x10 13 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. Conclusion 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 E g 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]. Introduction 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. Experimental details 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:H 2 O (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(NO 3 ) 2.6H 2 O 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 95 o C. Heating rate was about 7 o C/min. Substrate was taken out from the bath after 5 minute. In this way, ZnO/p-Si structure was obtained. 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. Referances [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). Fig.1a.Fig.1b. * This study was supported by Mustafa Kemal University Scientific Research Project Comission. Project No: 1004 Y 0102 Fig.2a.Fig.2b. 8 th Nanoscience and Nanotechnology Congress - NANOTRVIII