Photonic crystals in biology

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P Poster Session, Tuesday, June 15 Theme A1 - B702 Screening of Antioxidant Activity and Phenolic Content of Selected Food Items Cited in the Holly Quran 1 1 1 USafaa Y. QustiUP P*, Ahmed N. Abo-khatwaP Pand Mona A. Bin LahwaP 1 PDepartment of Biochemistry- King Abdulaziz University- Jeddah, SA. Abstract-Antioxidants are vital substances, which possess the ability to protect the body from damages caused by free radical-induced oxidative stress. A variety of free radical scavenging antioxidants is found in a number of dietary sources. The main objective of this study was to assess the antioxidant activity of a number of fruits, vegetables and grains. Therefore, (16) edible plant materials cited in the Holly Quran were selected to determine their antioxidant properties. The antioxidant capacity of these extracts were investigated based on their ability to scavenge (DPPH) stable free radical. Phenolic content of the extracts was determined using Folin-Ciocalteau reagent. Results of the antioxidant capacity were classified in three categories; (1) Fruits possessing extremely high free radical scavenging activity or antioxidant activity (ICR50R
Poster Session, Tuesday, June 15 Theme A1 - B702 Preparation and Characterization of Nanostructured ZnS Thin Films Grown on Glass and Monocrystalline Si Substrates R. Sahraei 1* , G. Nabiyouni 2 and A. Daneshfar 1 1 Department of Chemistry, University of Ilam, Ilam P.O. Box: 65315-516, Iran 2 Department of Physics, University of Arak, Arak, Iran Abstract— Nanocrystalline zinc sulfide thin films were prepared by a new chemical bath deposition technique onto glass and silicon (111) substrates. Deposition takes place at a temperature of 70 ºC and a pH of 6.0, from an aqueous solution containing zinc acetate, thioacetamide, and ethylenediamine. Microstructure analysis using atomic force microscopy shows that the films deposited on glass substrates contain 28-30 nm clusters, whereas much larger clusters (around 80-120 nm) comprise the films deposited on silicon (111) substrate. X-ray diffraction analysis indicates that both the ZnS films deposited on glass and Si substrates have cubic zincblende structure. Direct band gap energy for these samples was measured to be in the range of 3.97- 4.00 eV. Recently, the II-VI compounds semiconductor thin films have received an intensive attention due to their application in thin film solar cells [1]. Among these metal chalcogenides, ZnS is an important semiconductor material because of its broad direct band gap energy (~3.6 eV) at room temperature [2]. Various techniques have been employed to fabricate ZnS thin films, such as, electrodeposition, pulsed-laser deposition, chemical vapor deposition (CVD), and chemical bath deposition (CBD) [3, 4]. In this work, we report deposition of nanocrystalline zinc sulfide thin films on the glass and mono-crystalline Si substrates using a weak acidic bath in which ethylenediamine acts as a complexing agent and thioacetamide acts as a source of sulfide ions. Atomic force microscopy (AFM), X-ray diffraction (XRD), and UV-Vis spectrophotometery are used to investigate the surface morphology, structural, and optical properties of the nanostructured ZnS thin films. We show how the morphology and surface roughness of the ZnS thin films depend on the substrate type. Figure 1. AFM images (two- dimensional (2D)) of CBD ZnS thin films on (a) Si and glass substrate (b). X-ray diffraction patterns of the ZnS film grown on glass and monocrystalline Si substrate show three distinguished peaks at the angles of 28.6º, 47.7º and 56.5º reveal a cubic lattice structure and can be assigned to the (111), (220), and (311) plans, respectively. Broadening of diffraction peaks in the XRD pattern of the ZnS film is attributed to the nanometer-sized crystallites. The calculated average size of nanocrystallites, using Scherrer equation is found to be about 4.5 and 8 nm for the ZnS films deposited on glass and single crystal Si substrates, respectively. The average transmittance of ZnS films is calculated to be 84%, 78%, 74% and 71%, respectively, in the visible wavelength region. As it is clear from spectra the films have a steep optical absorption feature, indicating good homogeneity in the shape and size of the nanocrystallites and low defect density near the band edge [5]. The band gap energy (E g ) was determined to be in the range of 3.97-4.00 eV for the ZnS films with deposition times varying from 4 to 16 hours. These values are rather larger than the literature value for the bulk ZnS (~ 3.6 eV). The result could be attributed to the quantum size effects as expected from the nanocrystalline nature of the ZnS thin films [6, 7]. Figure 1 (a) and (b) illustrates two-dimensional AFM images of the ZnS thin films deposited on monocrystalline Si and commercial glass slide substrates, respectively. The thin film deposited on Si substrate is made of aggregates (clusters) with a square-like surface morphology, whereas much finer aggregates with an isosceles triangular surface morphology comprise the film deposited on glass substrate. As can be seen, the films deposited on the glass substrate contain smaller clusters (average grain size of around 28-30 nm in diameter) and have more surface aggregates than those deposited on Si substrate (average grain size of around 80-120 nm in diameter). In summary, we have successfully deposited the nanocrystalline ZnS thin films onto glass and monocrystalline Si substrates, from a chemical bath at temperature of 70 °C, and using ethylenediamin as a complexing agent. The XRD measurements indicate that the structure of the ZnS thin films is cubic. In our experiment, based on the optical transmission measurements, the band gap energies are calculated to be between 3.97-4.00 eV for the ZnS films with different thicknesses. Morphology and optical properties of the ZnS films were characterized using AFM and UV-Visible spectroscopy. *Corresponding author: reza_sahrai@yahoo.com [1] M. Bär, A. Ennaoui, J. Klaer, R. Sáez-Araoz, T. Kropp, L. Weinhardt, C. Heske, H.-W. Schock, Ch.-H. Fischer, M.C. Lux-Steiner, Chem. Phys. Lett. 433, 71 (2006). [2] J. Mu, Y. Zhang, Appl. Surf. Sci. 252, 7826 (2006). [3] R.S. Mane, and C.D. Lokhande, Mater. Chem. Phys. 65, 1 (2000). [4] A. Goudarzi, G. Motedayen Aval, S. S. Park, . Choi, R. Sahraei, M.Habib Ullah, A. Avane, and C. S. Ha, Chemistry of Materials 21, 2375 (2009). [5] C. Hubert, N. Naghavi, B. Canava, A. Etcheberry, and D. Lincot, Thin Solid Films 515, 6032 (2007). [6] R. Sahraei, G. Motedayen Aval, A. Baghizadeh, M. Lamehi-Rachti, A. Goudarzi, M. H. Majles Ara, Materials Letters 62, 4345 (2008). [7] K. Yamaguchi, T. Yoshida, D. Lincot, H. Minoura, J. Phys. Chem. B 107, 387 (2003). 6th Nanoscience and Nanotechnology Conference, zmir, 2010 352
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