Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 Electronic Structure of Single Wall Carbon Nanot ubes With Vacancy Defect Gülay Dereli 1 *, 1 , Necati Vardar 1 1 Department of Physics, Yildiz Technical University, 34210, Turkey Abstract-Electronic structure of (12,0) and (14,0) single wall carbon nanotubes (SWCNT) with vacancy defect are studied using Order (N) Tight Binding Molecular Dynamics simulation method (O(N) TBMD) [1-3]. We have obtained the total energy per atom and Fermi energy levels of (12,0) and (14,0) SWCNTs with vacancy defect. The effect of vacancy defects on the electronic band gap is investigated in real space. Change of the electronic band gap values are discussed. An important property of carbon nanotubes is that SWCNT can be either metallic or semiconducting depending on the geometrical structure. Geometrical structure of SWCNT is given by the chiral vector ( ). The armchair SWCNTs ( ) are metallic, and the zigzag SWCNTS ( ) are only metallic when n is a mu ltiple of 3. SWCNTs may have various kinds of defects such as vacancy, either during their growth or when they are part of an electronic circuit. Defects may influence the physical properties of SWCNTs. Theoretical calculations have shown that vacancy defects in SWCNTs can substantially modify their electronic properties [4-12]. In this study, energetic and electronic structures of (12,0) and (14,0) SWCNTs with multi-vacancy defects are studied using order (N) tight binding molecular dynamic (O(N) TBMD) simulation code designed by Dereli et al [1-3] and applied to nanotube simulations successfully [13-16]. We simulated (12,0) metallic and (14,0) semiconducting SWCNTs with multi vacancy defect . We calculated the total energy per atom and the Fermi energy levels during the simulation . (a) eDOS 1,0 nvac=0 (12,0) 0,8 0,6 0,4 0,2 0,0 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 1,0 0,8 0,6 0,4 0,2 0,0 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 1,0 0,8 0,6 0,4 0,2 nvac=0+1 nvac=0+2 0,0 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 Energy (eV) DOS 1,0 0,8 0,6 0,4 0,2 0,0 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 1,0 0,8 0,6 0,4 0,2 0,0 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 1,0 0,8 0,6 0,4 0,2 nvac=0 (14,0) nvac=1 nvac=4 0,0 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 Energy (eV) Figure 2. Electronic density of states of (12,0) and (14,0) SWCNTs with vacancies. Our studies have shown that the vacancy defects can effectively change the energetics and hence the electronic structure of SWCNTs. The research reported here is supported through the Yildiz Technical University Research Fund Project No: 24-01-01-04. The simulations are performed at the Carbon Nanotubes Simulation Laboratory at the Department of Physics, Yildiz Technical University, Istanbul, Turkey. *Corresponding author: gdereli@yildiz.edu.tr (b) Figure 1. a) (12,0) b) (14,0) SWCNTs with vacancy defect We showed that the total energy values increase with the number of vacancies and the Fermi energy levels decrease. The effects of multi vacancy defects on the electronic band gap are given in figure2. Band gap is obtained in real space through the behavior of electronic density of states (eDOS) near the Fermi level . The band gap of (12,0) SWCNT increases from 0.01 eV (perfect CNT) to 0.07eV for one vacancy and 0.13 eV for two vacancies. For (14,0) SWCNT, band gap rapidly decreases from 0.55eV to 0.09 eV for one vacancy and semiconductor-metal transition occurs. 148, 188 (2002). [2] G. Dereli and C. Özdogan, Phys. Rev. B 67, 035416 (2003). [3] G. Dereli and C. Özdogan, Phys. Rev. B 67, 035415 (2003). [4] L. Chico, L. X. Benedict, S. G. Louie, and M. L. Cohen, Phys. Rev. B 54, 2600 (1996) [5] A. J. Lu and B. C. Pan, Phys. Rev. Lett. 92,10,105504 (2004). [6] L-G Tien, C-H,T F-Y Li, and M-H Lee, Phys. Rev. B 72, 245417 (2005). [7] W. Orellana , P. Fuentealba, Surface Science 600, 4305–4309 (2006). [8] Seun g-Hoon Jhi, Carbon 45, 2031–2036 (2007). [9] Susumu Okada, Chemical Physics Letters 447, 263–267 (2007) . [10] H. Ishii, N. Kobayashi, K. Hirose, Surface Science 601, 5266– 5269 (2007). [11] A. R. Rocha, J. E. Padilha, A. Fazzio, and A. J. R. da Silva, Phys. Rev. B 77, 153406 (2008). [12] S. Berber and A. Oshiyama, Phys. Rev. B 77, 165405 (2008). [13] G. Dereli and B. Süngü, Phys. Rev. B 75, 184104 (2007). [14] G. Dereli, B. Süngü and C. Özdogan, Nanotechnology 18, 24570 (2007). [15 201T , 075707 ( 2009) [16 181023 , 171 (2010). 6th Nanoscience and Nanotechnology Conference, zmir, 2010 401
Poster Session, Tuesday, June 15 Theme A1 - B702 The Effect of Annealing Temperature on the Microstructure of TiO 2 Thin Films Deniz Gu ltekin 1 *, Mehmet Oguz Guler 1 , Ozgur Cevher 1 and Hatem Akbulut 1 1 Department of Metallurgical & Materials Engineering, Sakarya University,Sakarya 54187, Turkey Abstract-Titanium dioxide (TiO 2 ) thin films have been prepared on soda lime glass substrates by the sol-gel process. The preparation of covering solution is investigated with the method of orthogonal experimental design, and the heat treatment temperature and time, which influenced on the films properties are discussed. And the TiO 2 thin films had been studied by the means of fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and four probe electrical resistivity tests. Titanium oxide (TiO2) is one of the most extensively studied transition metal oxide. TiO 2 films have excellent photocatalytic properties as well as the high transparency, excellent mechanical and chemical durability of in the visible and near-infrared region of the spectrum [1]. These TiO 2 films carried out for the different applications as in opto-electronic devices, sensors, dye-sensitized photo-voltaic cells, electro chromic displays, planner wave guides, photo-catalysts, etc [2, 3]. The preparation of TiO 2 thin films has received great attention during the past several decades because of its remarkable optical, photo-catalytical and electronic properties [4]. An important aspect in the preparation of TiO 2 photocatalysts for environmental applications is the development of nanostructured TiO 2 powders with a number of favorable properties such as small particle size, high surface area, controlled porosity, and tailor-designed pore size distribution. In particular, a number of recent literatures have focused on the preparation of mesoporous TiO 2 materials with high surface area and tailored framework structure using surfactant template. Owing to their high surface-to-volume ratio and offering more easily accessible surface active sites, a further enhancement in the catalytic activity and process efficiency is expected [5]. TiO 2 films can be synthesized by various thin film deposition techniques, such as thermal evaporation, chemical vapor deposition (CVD), metal organic chemical vapor deposition pulsed laser deposition and sol–gel process [4]. In this study, nanostructured mesoporous TiO2 coatings were prepared by the sol–gel route using Titanium tetrachloride as a precursor. Titanium tetrachloride was first dissolved in a solution composed of ethanol and de-ionized water (volume ratio is 1:1). Then TiCl 4 was added to the solution with the dispersant of polyethylene glycol and stirred for 20 min at 80 °C. After 48 h of aging in the air, de-ionized water and ethanol was applied to remove chloride ions. The gel was dried in an oven at 60 °C for 4 h to remove moisture. We have demonstrated the fabrication and characterization of nanostructured mesoporous TiO2 coatings by the sol–gel dip-coating technique onto soda-lime glass. The preparation method is based on a sol-gel technique using Titanium tetrachloride as precursors. The effects of sol-gel parameters and annealing temparatures on the film properties were investigated. The prepared TiO 2 thin films were characterized using Transmission Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) and Four Probe Electrical Resistivity. We have mainly focused on the effect of annealing temperature on the physical properties of TiO2 films. Postannealing treatment is necessary to convert the deposited amorphous film into titanium oxide (TiO 2 ) crystalline (anatase) phase [4]. In order to investigate the effect of the annealing temperature on the properties of TiO 2 coating, the dried gel was sintered for d ifferent temperatures in a furnace. These films have been characterized using transmission electron microscopy (SEM), X-ray diffraction (XRD), fourier transmission (FTIR) and four probe electrical resistivity. *Corresponding author: dkurt@sakarya.edu.tr [1] M. Sasani Ghamsari, A.R. Bahramian, Materials Letters 62 (2008) 361–364 [2] M. Flischer, H. Meixner, Sens. Actuators B 4 (1991) 437. [3] Y.Q. Li, S.Y. Fu, G. Yang, M. Lee, J. Non-Cryst. Solids 352 (2006) 3339. [4] S. K. Sharma, M. Vishwas, K. N. Raoa, S. Mohana, D. S. Reddyb, K.V.A. Gowda, Journal of Alloys and Compounds 471 (2009) 244–247. [5] J. Zhu, J. Yang , Z. Bian, J. Ren, Y. Liu , Y. Cao, H. Li, H. He, K. Fan, Applied Catalysis B: Environmental 76 (2007) 82–91. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 402
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