Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 MD Simulations of the Tensile Strength of (20,0) Single Walled Carbon Nanotubes Gülay Dereli, * Necati Vardar and Department of Physics, Yildiz Technical University, 34210, Turkey Abstract— We have performed a computer experiment to examine the stability of (20,0) Single Walled Carbon Nanotubes (SWCNTs) with the application of uniaxial strain. A (20,0) single-walled carbon nanotube consisting of 400 atoms with 20 layers is simulated under tensile loading using our developed O(N) parallel tight-binding molecular-dynamics algorithms. It is observed that the simulated carbon nanotube is able to carry the strain up to 118 % of the relaxed tube length in elongation. In this study, the elastic limit, Poisson ratio, Young’s modulus and tensile strength of (20,0) SWCNTs are calculated. There has been increasing attention given to Single-Walled Carbon Nanotubes (SWCNTs) since they are the most durable material against stretching and heating. SWCNTs properties are mostly determined by the chirality of the tubes. Depending on their chirality, carbon nanotubes could be metal or semiconductor. Durability of the nanotubes are examined in terms of the uniaxial compressive or tensile deformations. Single Walled Carbon Nanotubes are specified by chiral vector Ch ( n, m) .The Zigzag SWCNTs that are represented as (n,0) are metallic, if n is a multiple of 3 and all other are semiconducting in unstrained condition. In this study, we have performed a computer experiment to examine structural stability and mechanical properties of (20,0) SWCNT under tensile loading. Deformations due to uniaxial strain are studied using a parallel, Order (N) tightbinding molecular dynamics (O(N) TBMD) simulation code. Parallel O(N) (TBMD) simulation code is designed by G.Dereli et al.[1-3] and applied successfully to SWCNTs simulations[4-7]. A semiconducting (20,0) SWCNT consisting of 400 atoms with 20 layers is simulated. Periodic boundary condition is applied along the tube axis. Velocity Verlet algorithms along with the canonical ensemble molecular dynamics (NVT) is used. In our simulation procedure (20,0) SWCNT is simulated at a specified temperature for a 3000 MD steps of run with a time step of 1 fs. This eliminates the possibility of the system to be trapped in a metastable state. We wait for the total energy per atom to reach the equilibrium state. Next, uniaxial strain is applied to the SWCNT. We further simulate the deformed tube structure under uniaxial strain for another 2000 MD steps. In our study, while the nanotube is axially elongated or contracted, reduction or enlargement of the radial dimension is observed. Strain is obtained from ( LL0)/ L0 where L 0 and L are the tube lengths before and after the strain, respectively. We applied the elongation and calculated the average total energy per atom. Following this procedure, we examined the structural stability, total energy per atom, stress-strain curves, elastic limit, Young’s modulus, tensile strength, and Poisson ratio of (20,0) SWCNT. Deformations affect the physical properties of SWCNTs. We calculated the total energy of (20,0) SWCNTs as -8.29582 eV at zero strain. Figure 1, shows the total energy per atom of (20,0) SWCNT as a function of simulation time. On application of uniaxial strain, the total energy values have changed. Figure 2, gives the total energy values for various strain values. Our studies show that (20,0) SWCNT is stable until 18% uniaxial strain value. Figure 3 indicates that the tube can not sustain its structural stability at 23% strain. Beyond these strain values, bond breakings between the carbon atoms are observed and the tube is no longer stable. Stability of (20,0) SWCNT is compared with the same number of atom but smaller diameter SWCNTs during the study. E (eV/atom) -8,27 -8,28 -8,29 -8,30 -8,31 -8,32 -8,33 -8,34 0 500 1000 1500 2000 2500 3000 MD Step Figure 1: Total energy of (20,0) SWCNT as a function of simulation time E (eV/atom) -6,8 -7,2 -7,6 -8,0 0 1 2 3 4 5 6 7 8 9 12 15 18 21 23 (20,0) -8,4 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 MD Step Figure 2: The effect of strain on the total energies of (20,0) SWCNTs as a function of simulation time. Figure 3: Simulation picture of (20,0) SWCNT under % 23 uniaxial strain 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 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] G. Dereli and B. Süngü, Phys. Rev. B 75, 184104 (2007). [5] G. Dereli, B. Süngü and C. Özdogan, Nanotechnology 18, 24570 (2007). 20 , 075707 ( 2009) 171 (2010). (20,0) 6th Nanoscience and Nanotechnology Conference, zmir, 2010 397
Poster Session, Tuesday, June 15 Theme A1 - B702 Electrochemical Deposition of Lead on Conducting 4-Nitrothiophenol Covered Gold Surfaces Adem Kara, Züleyha Kuda, Ali Yeilda and Duygu Ekinci * Department of Chemistry, Faculty of Science, Atatürk University, 25240 Erzurum, Turkey Abstract— In this study, the electrochemical deposition of lead on Au surfaces covered by self-assembled monolayers of electroactive 4-nitrothiophenol (4-NTP) was investigated by using cyclic voltammetry and chronoamperometry. The resulting structures were characterized by X-ray photoelectron spectroscopy (XPS) and the surface properties of the films were studied using scanning tunneling microscopy (STM). In recent years, self-assembled monolayers (SAMs) of organosulfur compounds such as thiols and disulfides on metal surfaces have proven to be a popular method for the fabrication of well ordered and defined interfaces [1]. Among SAMs, the organized monolayers of aromatic thiols are of great interest due to their high electrical conductivities and strong - stacking interactions, although most of the studies addressed the assembly process of alkanethiols [2,3]. The surface properties of thiol monolayers for various purposes can be easily tailored by changing the chemical nature of the terminal groups attached to the other end of aromatic rings [4]. In this sense, the modification of the metal surface with molecules containing redox active groups has provided an elegant way for the construction of molecular electronic devices. In the fabrication of molecular electronics consisting of metal substrate/organic thin film/metal top contact sandwich structure, the formation of metal on top of the SAM can be achieved by three different methods: i- the deposition of the metal onto functionalized thiol SAMs from the vapor phase [5], ii- electroless metal deposition from solution [6], and iii- electrochemical deposition [7]. Compared to vacuum deposition, electrochemical deposition commonly offers since the amount of the deposit and the kinetics of the deposition process can be controlled [8]. In this study, the electrochemical deposition of lead on Au surfaces covered by self-assembled monolayers of 4- nitrothiophenol (4-NTP) was investigated. 4-NTP has a thiol group that covalently binds to gold surface and a reactive nitro group that undergoes electrochemical reduction. NO 2 S Au PbClO 4 /HClO 4 e - S Au Pb NHOH Previous studies have shown that the terminal –NO 2 group of the 4-NTP SAM can be irreversibly reduced to an electrochemically active terminal group (-NHOH) which exhibits a reversible redox behavior with –NO (Figure 1A) [9]. If such a reduction process of 4-NTP SAM is performed in aqueous solution containing Pb 2+ ions, we believe that the electrocrystallization of metals on the modified Au electrode can be achieved, and it can be used as an effective pathway for the creation of multilayer structures. Figures 1B and 1C show the cyclic voltammograms for the deposition of Pb at bare Au and 4-NTP modified Au electrodes. 600 50 µA 400 200 0 Potential/mV -200 (A) (B) (C) -400 Figure 1. Cyclic voltammograms for (A) 4-NTP modified Au electrode in 0.1 M HClO 4 solution, (B) bare Au electrode in 1 mM PbClO 4+0.1 M HClO 4 solution and (C) 4-NTP modified Au electrode in 1 mM PbClO 4+0.1 M HClO 4 solution. The resulting metallic lead layers on modified Au surfaces were also characterized by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). *Corresponding author dekin@atauni.edu.tr [1] R. G. Nuzzo, D. L. Allara, J. Am. Chem. Soc. 105, 4481 (1983). [2] R. F. Dou, X. Ma, L. Xi, H. L. Yip, K. Y. Wong, W. M. Lau, J. Jia, Q. Xue, W. Yang, H. Ma, A. K. Jen Langmuir, 22, 3049 (2006). [3] Y. Kazzi, H. Awada, M. David, M. Nardin, Surf. and Interface Analys. 39, 691 (2007). [4] C. D. Bain, E. B. Troughton, Y. T. Tao, J. Evall, G. M. Whitesides, R. G. Nuzzo, J. Am. Chem. Soc. 111, 321 (1989). [5] M. J. Tarlov, Langmuir 8, 80 (1992). [6] W. J. Dressick, C. S. Dulcey, J. H. Gregor, G.S. Calabrese, J. M. Calvert, J. Electrochem. Soc. 141, 210 (1994). [7] J. A. M. Sondag-Huethorst, L. G. Fokkink, Langmuir 11, 4823 (1995). [8] H. Hagenstrm, M. J. Esplandi, D. M. Kolb Langmuir, 17, 839 (2001). [9] J. U. Nielsen, M. J. Esplandi, D. M. Kolb Langmuir, 17, 3454 (2001). 6th Nanoscience and Nanotechnology Conference, zmir, 2010 398
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