Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 Influence of Spin Speed on the Structural and Morpholog ical Properties of Sol Gel Derived Nanocrystalline Structure ZnO Films Seval Aksoy 1 *, Yasemin Caglar 1 , Saliha Ilican 1 , Mujdat Caglar 1 1 Department of Physics, Anadolu University, Eskisehir 26470, Turkey Abstract-The nanocrystalline structure ZnO films were deposited onto p-Si substrates by the sol gel method using spin coating technique. The effect of spin speed on the structural and morphological properties of the ZnO films was investigated. X-ray diffraction showed that the films were polycrystalline and had a wurtzite structure. The crystallites are preferentially oriented with (0 0 2) planes parallel to the substrate surface. The nanostructured zinc oxide (ZnO) exhibits a variety of properties such as: semiconducting (II–VI), photoconducting, piezoelectricity, acousto-optical, transparency in the visibleinfrared region, and opto-electrical properties. So, nanostructure ZnO has been studying by many research groups [1-6]. In this study, Zinc acetate dihydrate (ZnAc), 2- methoxyethanol and monoethanolamine (MEA) were used as a starting material, solvent and stabilizer, respectively. The mo lar ratios of ZnAc to MEA were maintained at 1:1. The sol was stirred at 60 o C 2 h to yield a clear and homogeneous solution. The spin speed was maintained at 1000 (S1), 3000 (S3), 4000 (S4), 5000 (S5) rpm for 30 s. After each coating, the coated film was dried at 300°C for 10 min. The coating– drying cycles were repeated ten times. The films were finally annealed at 500 °C for 1 h. The crystalline structure of the films was investigated by the X-ray diffraction (XRD) method with a diffracto meter using CuK radiation (=1.5406Å). The deposited films at high spin speed were uniform, smooth and have a good adherence to the substrates. Figure 1 shows XRD pattern of the nanostructure ZnO films. It is observed that the film deposited at 4000rpm (S4 film) has the best crystalline structure. Texture coefficient (TC), crystalline size and lattice constants of the films were also calculated. Surface morphology of the S4 film has been investigated by field emission scanning electron microscopy (FESEM). Figure 1 shows FESEM image of the nanocrystalline structure ZnO films. It was observed that the surface morphology of the S4 film is almost uniform nanoparticle size distribution. The film exhibits a nanostructure and the spherical crystalline part icle size is approximately 50 nm. Figure 2. FESEM image of the S4 film. This work was supported by Anadolu University Commission of Scientific Research Projects under Grant No: 061039 and 081029. *Corresponding author: 2Tsevala@anadolu.edu.tr Figure 1. XRD patterns of the nanocrystalline structure ZnO films ( :p-Si substrate). [1] http://www.semiconductorslab.com [2] http://www.webjam.com/dfxue [3] http://www.nanoscience.gatech.edu/zlwang/index.htm [4] http://www.science24.com/paper/3870 [5]Wang ZG, Wang MQ, Lin ZH, Xue YH, Huang G, Yao X, 2009. Growth and interconversion of ZnO nanostructure films on different substrates, Appl Surf Sci, 255:4705-4710. [6]Takai O., Futsuhara M., Shimizu G., Lungu C.P., Nozue J., 1998. Nanostructure of ZnO thin films prepared by reactive rf magnetron Sputtering, Thin Solid Films, 318:117–119. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 405
Poster Session, Tuesday, June 15 Theme A1 - B702 The Effect of Annealing Temperature on the Formation of ZnO Thin Films Deniz Gu ltekin 1 *, Mehmet Oguz Guler 1 , Ozgur Cevher 1 , Fatih Kuzak 1 , Hatem Akbulut 1 1 Department of Metallurgical & Materials Engineering, Sakarya University,Sakarya 54187, Turkey Abstract-Thin films of ZnO grown by sol-gel dip coating method onto soda lime glass substrates under different annealing temperatures using zinc acetate precursors. The physical and chemical properties of the deposited thin films were investigated via SEM, XRD, FTIR and 4-probe electrical resistivity techniques. ZnO is one of the compounds studied actively in various fields due to its significant physical and chemical properties. For example, ZnO has much attention as a host material for transparent conducting films because impurity- doped ZnO films show high transparency above 90% in the visible region and low electrical resistivity around 5 x 10 -4 -3]. In a chemical field ZnO is well known as a photocatalyst with high chemical activity. Under irradiation of photons having higher energy than the optical band gap of ZnO, oxidation reactions are promoted on the ZnO surface. There are many techniques to prepare ZnO thin films, including sputtering [4], molecular beam epitaxy [5], chemical vapor deposition [6], spray pyrolysis [7] and sol-gel technique [8], etc. Compared with the others, sol-gel technique is simple, less expensive and has an advantage of large area deposition and the facility of the doping. Owing to the requirement of the commercial process, the sol-gel technique is selected to prepare high-quality ZnO thin films. It is known that the properties of ZnO thin films prepared by sol-gel technique are affected by the precursor materials and the postanneal technique. Especially, the post-anneal technique is a very important factor for the preparation of ZnO thin films. In this work, dried gel films deposited by sol-gel technique were respectively annealed under nitrogen atmosphere and at different temperatures (300 ZnO thin films were deposited by sol-gel technique. Zinc acetate [Zn(CH 3 CO 2 ) 2·2H 2 O] and pure ethyl alcohol were used as the precursor material and the solvent, respectively. Diluted lactic acid solution (molar ratio CH 3 CH(OH)COOH: H 2 O = 1:2) was used as the solvent and stabilizer, which controlled the pH value of the solution to avoid turbidity and precipitate [9]. Zinc acetate was dissolved in pure ethyl alcohol by the molar ratio of 1:85. After stirring the solution with reflu x at 40 °C for 2 h, the lactic acid solution was slowly added drop wise into the dissolved zinc acetate solution to yield a clear and homogeneous solution. Subsequently, the solution was placed in an oven at 65°C for 2 h and used as the coating solution after being cooled to room temperature. Two days after the solution was prepared, the coating was made to increase the viscosity of the solution. To understand the change of the organic composition, the [1] M. Ohyama, H. Kozuka, T. Yoko, S. Sakka, J. Ceram. Soc. Jpn. 104 (1996) 296. [2] D. Bao, H. Gu, A. Kuang, Thin Solid Films 312 (1998) 37. [3] Z.K. Tang, G.K.L. Wong, P. Yu, M. Kawasaki, A. Ohtomo, H. Koinuma, Y. Segawa, Appl. Phys. Lett. 72 (1998) 3270. [4] T. Minami, H. Nanto, S. Takata, J. Appl. Phys. Lett. 14 (1982) 958. [5] K. Emilar, R. Schieck, S. Fiechter, Appl. Surf. Sci. 70 (1993) 707. [6] F.S. Mahmood, R.D. Gould, M.H. Salih, Thin Solid Films 270 (1995) 376. [7] M. Futsuhara, Y. Ishida, R. Baba, A. Fujishima, J. Oil Colour Chem. Assoc. 75 (1992) 236. films annealed under different conditions were analyzed by Fourier t ransform infrared spectra. The crystallinity of the ZnO thin films was identified with a DMax/2200 X-ray diffraction instrument (XRD, Cu K The Sherrer equation and the Bragg law were used to calculate the grain size and the lattice constants, respectively. The surface topography was observed by scanning electron microscopy (SEM). All the above measurements were completed at room temperature. *Corresponding author: dkurt@sakarya.edu.tr 6th Nanoscience and Nanotechnology Conference, zmir, 2010 406
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