Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 Shape and Size Controlled Synthesis of Zinc Oxide Powder by Solvothermal Method A. Gürkan YILMAZOĞLU, M. Ozan ÖZER, Ender SUVACI Department of Materials Science and Engineering, Anadolu University, 26480 Eskisehir, Turkey Abstract— In this study, effects of synthesis parameters on nucleation and growth of ZnO particles and subsequently on particles’ shape and size during solvothermal process have been investigated. Various particle shape and size were obtained by using different solvent compositions with various alcohol to water ratios. The powder, synthesized in 100% alcohol, has a hexagonal plate-like morphology and particle size ranging from 10 to 15μm. These particles are organometalic complexes of zinc and calcination of them results in zinc oxide structures. Zinc oxide is a material with great potential for a variety of applications, such as optical waveguides, surface acoustic wave devices, varistors, transparent conductive oxides, chemical and gas sensors, and UV-light emitters.[1,2] Its wide bandgap (~3.37 eV at room temperature[1]) makes ZnO a promising material for photonic applications in the UV or blue spectral range. In addition, ZnO doped with transition metals shows great promise for spintronic applications.[3] ZnO exhibits sensitivity to various gas species, namely ethanol (C2H5OH), acetylene (C2H2), and carbon monoxide (CO), which makes it suitable for sensing applications. Moreover, its piezoelectric property (originating from its noncentrosymmetric structure) makes it suitable for electromechanical sensor or actuator applications. In addition, ZnO is biocompatible which makes it suitable for biomedical applications. Furthermore, ZnO is a chemically stable and environmentally friendly material. Consequently, there is considerable interest in studying ZnO in the different size and shape for different application areas. In this study, effect of alcohol to water ratio on size and shape of ZnO powder was investigated during solvothermal synthesis. Various particle shape and size were obtained by using different solvent compositions with various alcohol to water ratios. The powder, synthesized in 100% alcohol, has a hexagonal plate-like morphology and particle size ranging from 10 to 15μm. These particles are organometalic complexes of zinc and calcination of them results in zinc oxide structures. On the other hand, when the amount of water in solvent concentration increases, the powder shapes becomes a square plate and further addition of water results in rod shapes zinc oxide particles with were grown in direction. In experimental studies, as zinc source and pH regulator zincnitratehexahidrate (Zn(NO)3.6H 2 O, Merck), and hexametilentetramine (HMT, C 6 H 12 N 4 , Merck) and alcohol water system to prepare the starting solution for synthesis. Seven different alcohol/water ratio solutions were studied in this study. In 100% alcohol system, organo-zinc complex hexagonal platelets formed. In 90% alcohol 10% water and 80% alcohol 20%water solutions were developed organo-zinc square-like plates. At 60% alcohol 40% water ratio solution system, water start to be dominated in system, and the powders were formed rod-like shape and ZnO formation. After this point decreasing the alcohol/water ration the powders shape were rod-like structure with increasing aspect ratio. c a Figure: (a) In 100% alcohol solution synthesis were developed hexagonal platelet particles. (b) Square plates synthesized in 80% alcohol 20% water solution. (c) 40% alcohol 60% water solution, particles formed like rod grown direction. (d) In 100% water solution rod ZnO were synthesized. [1] U. Özgür, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Doğan, V. Avrutin, S.-J. Cho, H. MorkoA, J. Appl. Phys. 2005, 98, 041301. [2] R. Triboulet, J. Perriere, Prog. Cryst. Growth Charact. Mater. 2003, 47, 65. [3] R. Janisch, P. Gopal, N. A. Spaldin, J. Phys. Condens. Matter 2005, 17, R657. b d 6th Nanoscience and Nanotechnology Conference, zmir, 2010 304
Poster Session, Tuesday, June 15 Theme A1 - B702 Synthesis of SnO 2 Nanoparticles via Sol-Gel Method Hilal Kose 1 *, Emrah Bulut 1 1 1 Department of Chemistry, Arts and Sciences Faculty, Sakarya University, 54187, Sakarya, Turkey Abstract- SnO 2 nanop articles fabricated at different pH values by sol-gel method. Sols were prepared from aqueous solution of tin(II) chloride at room temperature. SEM and XRD analysis were performed to characterize nanoparticles. The results indicate the nanocrystalline nature of the SnO 2 particles. Tin oxide (SnO2), cassiterite structure, is a typical wide band gap n-type semiconductor (3.8 eV) [1] and, one of the most widely used semiconductor oxides due to its chemical and mechanical stabilit ies. The electrical and chemical properties of SnO 2 have been extensively studied because of its application as transparent electrodes for solar cells, liquid crystal displays; antistatic coatings and gas sensors; anodes for lithium ion batteries, transistors, catalyst supports; nano and ultra filtration membranes and anticorrosion coatings [2]. Recently tin oxide-based materials have received considerable attention as promising anode materials for Liion batteries due to their high capacity [3]. SnO 2 nanoparticles can be obtained by different techniques. Among the processing techniques, sol-gel offers advantages such as low cost, low temperatures processing and also precise control of stoichiometry [4]. In this work, sol-gel method was applied to synthesize SnO 2 nanoparticles at different pH values. The SnO 2 precursor solution was prepared from tin chloride by dissolving SnCl 2·2H 2 O in 50 ml of deionized water. The solution was in the form of turbid nature during the first period of the dissolving and then the color was returned to a transparent nature when acetic acid was added. The addition of acetic acid was also aimed to prevent rapid hydrolysis for obtaining nucleation of nano sized species in the solution. After stirring a few hours, the solution pH was adjusted to 7, 8, 9, and 10 by using ammonia solution (%25). Then the solution stirred for 24 h. The resultant sols washed and centrifuged 5 times with deionized water. Finally, sols dried at 150 o C for 2 hours and precalcination was performed at 300 o C. Subsequently, the calcination temperature was increased to 400 o C and the sols were calcinated for two hours at treatment. of spherical nanoparticles in diameter under 100 nm were obtained. Figure 2. XRD diffraction of SnO 2 nanop articles. Figure 2 shows the XRD patterns of the powders obtained at the peak positions in each sample agree well with the reflections of SnO 2 (cassiterite). The XRD diffraction peaks are evidenced that a crystalline type of SnO 2 was obtained. As can be seen from the Figure 2, the width of the reflections is considerably broadened, because of nanocrystalline do main size. In summary, SnO 2 nanoparticles were obtained from solgel method. Strong acidic conditions enhanced the hydrogen bonding among the protonated nanocrystallites, leading to a high degree of agglomeration, while in higher pH value solutions; the coordinated water molecules should suppress the agglomeration among the freshly formed nanocrystallites [2]. Because of this reason, synthesis of SnO 2 nanoparticles was performed at higher pH values such as 7, 8, 9 and 10. The size o f nanocrystallines decreased with reducing pH value to 7. The broad XRD peaks and SEM image indicate the nanocrystalline nature of the SnO2 particles. The small grain size obtained in the present work is believed proper optimization of the precursor colloidal solution used and process parameters such as low heat treatment temperature. *Corresponding author: 0Thkose@sakarya.edu.tr Figure 1. SEM image of SnO 2 nanop articles prepared by sol-gel technique at pH 7. Scanning electron microscopy (SEM) analysis was used to investigate the morphology of the as-synthesized SnO2 samples. As shown in Figure 1, SnO 2 nanoparticles consist [1] J. Rockenberger, U. Felde, M. Tischer, L. Troger, M. Haase, H. Weller, 2000. Near edge X-ray absorption fine structure measurements (XANES) and extended x-ray absorption fine structure measurements (EXAFS) of the valence state and coordination of antimony in doped nanocrystalline SnO 2 , J. Chem. Phys. 112: 4296. [2] Zhang, J., Gao, L., 2004. Synthesis and characterization of nanocrystalline tin oxide by sol–gel method, Journal of Solid State Chemistry, 177: 1425-1430. [3] Ning, Y., Jianhua, W., Yuzhong, G., Xiaolong, Z., 2008. SnO 2 Nanofibers Prepared by Sol-Gel Template Method, Rar e Metal Materials and Engineering, 37: 4. [4] Hamd, W., Wu, Y-C., Boulle, A., Thune, E., Guinebretière, R., 2009. Microstructural study of SnO 2 thin layers deposited on sapphire by sol–gel dip-coating, Thin Solid Films, 518: 1–5. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 305
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