Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 Mechanical Properties in Multiwalled Carbon nanotubes/ PAM composites 1 * 1 , Önder Pekcan 2 1 Department of Physics, , 34469, Turkey 2 0, Turkey Abstract- The mechanical properties of multiwall carbon nanotubes (MWNTs)/polyacrylamide (PAM) composites were studied as a function of nanotube content. Multiwalled carbon nanotube (MWNT) composites with polyacrylamide (PAM) were prepared via free radical crosslinking copolymerisation with different amounts of MWNTs varying in the range between 0.1 and 50 wt%. The PAM-MWNT composite gels were characterized by tensile testing machine. A small content of doped nanotubes dramatically changed Young modulus and toughness, respectively. Carbon nanotubes (CNTs) have been one of the hottest research topics since the discovery [1] because of their special properties and wide potential applications [2]. The mechanical properties of hydrogels with nano materials are best understood using the theories of rubber elasticity and viscoelasticity. To derive relationships between the network characteristics and the mechanical stress- strain behavior, classical and statistical thermodynamics have been used to develop an equation of state for rubber elasticity. It is known the entropic model. From classical thermodynamics, the equation of state for rubber elasticity may be expressed as [3] f U f T L T, V T L, V (1) where f is the refractive force of the elastomer in response to a tensile force, U is the internal energy, L is the length, V is the volume, and T is the temperature. For ideal rubber elastic behavior, the first term in equation 1 is zero. The refractive force and entropy are related through the following Maxwell equation S f L T, V T L, V (2) Stress- strain analysis of the energetic and entropic contributions to the refractive force (Equation 1) indicates that entropy accounts for more than 90% of the stress. After some statistical analysis, shear modulus can be defined by G (3) where , the force per unit area and is the extension ratio. While the thermodynamic and statistical thermodynamic approaches describe observed rubber-elastic behavior at low extensions quite well, the equation is invalid higher elongations [3] Composite gels were prepared via free radical crosslinking copolymerization with different amounts of MWNTs varying in the range between 0.1 and 50 wt%. Compression module of PAM- MWNTs composite gels at 25°C was determined by means of a Hounsfield H5K-S model tensile testing machine. Any loss of water and changing in temperature during the measurements was not observed because of the compression period being less than 1 min. Figure 1(a) and (b) show that young modulus and toughness depend on the content of MWNTs in PAM, respectively. Young modulus increases progressively until 3 wt. % MWNT with increasing nanotube content. At contents above Young modulus(MPa) Toughness(kPa) 0,12 0,10 0,08 0,06 0,04 0,02 2 1 0 0,0 10,0 20,0 30,0 40,0 50,0 60,0 0,0 10,0 20,0 30,0 40,0 50,0 60,0 %MWNT (a) 1.trial 2.trial (b) 1.trial 2.trial Figure 1. (a) Young modulus and (b) Toughness dependence on the MWNTs content in composite gels. 3wt. %MWNTs, the young modulus is decreased marginally with increasing MWNTs content in Figure 1(a). On the other hand, at lower content(3 wt.%), the toughness decreases from the neat composite of 1.3kPa, only exceeding it when the MWNT content is above 20 wt. % (Figure 1(b)), and then increases further as the MWNTs content is raised[4]. This work explores the mechanical properties of PAM- MWNTs composite gels characterized by tensile testing machine. Our results show that a decrease in length brings about an increase in entropy because of changes in the end to end distances of the network chains of PAM-MWNTs composite gels, thermodynamically. Thus, the entropic model for composite elasticity is a reasonable approximation. We thank Argun Talat measure ments. *Corresponding author: evingur@itu.edu.tr Gökçeören for tensile test [1] S. Lijima, Nature 354, 56, (1991). [2] P. J. F. Harris, Int. Mat.Rev. 49, 31, (2004). [3] K. S. Anseth, C. N. Bowman, L. B. Peppas, Biomaterials 17, 1647, (1996). [4] R. Andrews, D. Jacques, D. Qian, T. Rantell, Acc. Chem. Res.35, 1008, (2002). 6th Nanoscience and Nanotechnology Conference, zmir, 2010 383
Poster Session, Tuesday, June 15 Theme A1 - B702 Preparat ion and characterization of CdSe, ZnSe, CuSe, thin films depos ited by t he successive ionic layer adsorption and reaction (SILAR) method B. Gü zeld ir 1 *, A. A 1 and M. S 1 1 Department of Physics, Faculty of Sciences, University of Atatürk, 25240 Erzurum, Turkey Abstract-In this study, the CdSe, ZnSe,CuSe thin films have been directly formed on n- type Si by means of Succesive Ionic Layer Adsorption and Reaction (SILAR) method at room temperature. The films characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The SEM and XRD studies showed that films are covered well with glass and n-type Si substrates and exhibit polycrystalline characterization. The EDAX spectra showed that the expected elements exist in the thin films.Some of the thin film with equal distribution of grains, mostly falling in nanometer regime, was clearly seen. According to the optical characterization, in the future, it can be used solar-cell studies, rectifying contacts, integrated circuits, the other electronic devices and so on. Thin films can be deposited with different methods onto semiconductor substrates. The one of these method is succesive ionic layer adsorption and reaction (SILAR) method. Relatively simple, quick, economical and suitable for large area deposition of any configuration, the SILAR method was reported in mid-1980s [1]. It does not require sophisticated instruments, the substrate need not be conductive and have a high melting point [2]. It applies the same soft growth conditions as cehmical bath deposition (CBD). The difference between CBD and SILAR is that in SILAR the growth is performed layer by layer by dipping the substrate sequentially into stable percursor solutions and rinsing in between the unadsorbed ions from the surface [3]. Single SILAR deposition cycle involves the immersion of the substrate alternately in cationic and anionic precursor solutions and rinsing between every two consecutive immersions with deionized water to avoid homogeneous precipitation in the solution, so that only the tightly adsorbed layer stays on the substrate. The adsorption is a surface phenomenon occurring due to attractive force between ions and surface of substrate. This attractive force is of Van der Waals type that basically orig inates due to the residual or unbalanced force present in the substrate. Thus, ad-atoms can be holding on the surface of the substrate by that residual force [4, 5]. In this study, the SILAR method was used to deposition of CdSe, ZnSe, CuSe thin films on n- type Si. These films were investigated by XRD, SEM and EDAX measurement techniques. One SILAR cycle contained four steps: (i) the substrate was immersed into first reaction containing the aqueous cotion precusor, (ii) rinsed with water, (iii) immersed into the anion solution, and (iv) rinsed with water. Repeated these cycles, a solid solution CdSe, ZnSe, CuSe thin films with desired thickness and composition were grown. The X-ray diffraction patterns are analysed to obtain the structual information of thin film. The spectrophotometer is used to carry out the optical absorption and transmission studies of the film in the wavelength range. It was seen fro m the XRD patterns that the CdSe, ZnSe, CuSe films were polycrystalline with orientation along diffrent planes and phases. The thin film on Si substrate shows improvement in crystallinty. Such increase in crystallinty for Si substrate is attributed to the single crystalline nature of Si substrate. Scanning electron microscopy is well- known the surface studying morphology of metals in thin film form. It was observed that the as-deposited CdSe, ZnSe, CuSe thin films were well coverages without cracks or pinholes to the substrates. One of the important applications of the SEM is the analiztaion of the elemental composition of a material. This microanalization mode of SEM replied upon the monitoring X-rays emitted by surface of the sample under electron irradiation. These X-rays are collected and analyzed to give information on the elemental compounds present in the sample. This technique is called as EDAX and can be used to detect elements of the periodic table with an atomic number greater than eleven. The EDAX spectras show that the expected elements detected in the thin films. The elemental analysis was carried out only for Cd, Zn, Cu, Se and the average atomic percentages were found. Also, small percentage of the other elements were present in the thin films. It is thought that these elements may probably result from Si used as substrate. In summary, the SILAR method was used to deposit CdSe, ZnSe, CuSe thin films on Si subsrate. Structural properties of these thin film were investigated by XRD, SEM and EDAX methods. The films were found to have polycrystalline, homogeneous and covered the substrates well. The quantitative analysis of the films were carried out by using EDAX technique and it was determined that expected elements were present in the thin films. .Some of the thin film with equal distribution of grains, mostly falling in nanometer regime, was clearly seen We would also like to acknowledge under Grant No. TBAG-108T500. *Corresponding author: 1Tbguzeldir84@gmail.com [1] M. Ristov, G. J. Saindinovski, I. Grazdanov, Thin Solid Films 123 63. (1985) [2] Y. F. Nicolau, Appl. Surf. Sci., 22 1061. (1985) [3] J. Puiso, S. Tamulevicius, G. Laukaitis, S. Linross, M. Leskela, V. Snitka, Thin Solid Films, 403 457. (2002) [4] R. S. Patil, C. D. Lokhande, R. S. Mane, H. M. Pathan, Oh-Shim Joo, Sung-Hwan Han, M aterials Science and Eng. B, 129 227 (2006) [5] Biswajit Ghosh, Madhumita Das, Pushan Banerjee and Subrata Das, Semiconductor Science And Techonolgy, 23 1250123 (2008) 6th Nanoscience and Nanotechnology Conference, zmir, 2010 384
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