Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 Formation of Thermoelectric Nanos tructures by2T Electroche mical Atom-by-atom Codeposition Ümit Demir 1 * 1 Department of Chemistry, Atatürk University, Erzurum 25240, Turkey Abstract-Nanostructures of Bi 2 Te 3 , Sb 2 Te 3 and PbS were electrodeposited using a novel and p ractical electrochemical method, based on simultaneous underpotential deposition of precursors of target compound from the same solution at a constant potential. These nanostructures are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and reflection absorption-FTIR (RA-FTIR) to determine structure, morphology, composition and optic properties. Synthesis of nanomaterials with controlled size, shape and crystalographic orientation has become an important issue in material science research. Since the properties of semiconductor nanocrystals, which possess many novel properties that differ considerably from those of the bulk [1,2], depend both on dimension and superlattice structure. Therefore, the development of synthetic methods that enable their precise control is expected to have a significant impact on progress. Bi2Te 3 and Sb 2 Te 3 with a narrow band gap and other V-VI group semiconductors are best-known materials for TE applications at room temperature and are widely used for thermoelectric (TE), biomedical and optoelectronic applications as heat pumps, power generations, solid state refrigeration, cooling IC chips, biochips, infrared sensors, optoelectronic sensors, photo detectors, and so on. Recently, we have developed a new electrochemical process, based on co-deposition from the same solution at the upd of the precursors of the target compound, which have been used for the electrochemical deposition of PbS, PbTe, ZnS, and CdS in the single crystal form [3-6]. The appropriate electrodeposition potentials based on the underpotential deposition potentials (upd) of precursors have been determined by the cyclic voltammetric measurements. In the present study, we illustrated the detailed growth process of Bi 2 Te 3 and Sb 2 Te 3 [7] nano films and Bi 2 Te 3 nanorodstructured films on single crystalline Au(111) electrodes by using Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Electron Dispersive Spectroscopy (EDS), and UV-v is- NIR Spectroscopy techniques. We found out that that the growth direction (orientation) and thickness of nanostructured Bi 2 TeR 3 can be readily controlled by pH, composition of the solution, and the time of the electrodeposition. The morphological investigation of Bi2Te 3 nanostructures revealed that the film growth follows 3D and 2D nucleation and growth mechanism in acidic and basic solutions, resulting in nanofilms and nanowires, respectively. XRD results show that single crystalline nanostructures of Bi2Te 3 are highly preferentially orientated along the (015) for nanofilms and (110) for nanowires. The growth of Sb 2 Te 3 nanofilms follows the nucleation and three-dimensional (3D) growth mechanism resulting in high crystalline films of Sb 2 Te 3 (110) in hexagonal structure, which were grown at a kinetically preferred orientation at (110) on Au (111). Highly strong quantum confinement effect, for both Sb 2 Te 3 and Bi 2 Te 3 nanostructures, was observed. Figure 1. Bi 2 Te 3 nanostructures; (a) nanofilm, (b) nanowires Figure 2. Nanostructures of Sb 2 Te 3 (a) and PbS (b) Moreover, we applied a new modified electrochemical method [8] to deposit nanostructure of PbS on a thiol modified Au(111) surfaces. Electrochemical deposition was carried out after the stripping of thiol from the surface at different potential pulses. We showed that the size of the PbS nanostructures could be controlled by the electrochemical deposition time and pulse width. In summary, structural and morphological studies indicate that growth of these nanostructures follows atom by atom growth mechanism resulting in highly crystalline nanostructures grown at a kinetically preferred orientation. Absorption measurements as a function of thicknesses indicated that the band gap of the nanostructures increase as the thickness decreases. This study was supported by Atatürk University [1] E. Ronsencher, A. Fiore, B. Vinter, V. Berger, P.Bois, J. Nagle, Science 271, 168 (1996). [2] S.Yanagida, M.Yooshiya, T.Shiragami, C. Pac, H. Mori, H. Fujita, J. Phys. Chem. 94, 3104 (1990). [3] T. Öznülüer, Ü. Demir, Chem. M ater. 17, 935 (2005). Langmuir 22, 4415 (2006). [5] M. Ü. Demir, J. Phys. Chem. C 111, 2670 (2007). [6] T. Öznülüer, F. Bülbül, Ü. Demir, Thin Solid Films 517, 5419 (2009). J. Electroanal. Chem. 633, 253 (2009). 54, 6554 (2009). 6th Nanoscience and Nanotechnology Conference, zmir, 2010 367
Poster Session, Tuesday, June 15 Theme A1 - B702 Mechanical Transfer of Epitaxially Grown Graphene Layers from SiC to SiO x Mahmut Tosun, Cem Çelebi, Görkem Soyumer, Anıl Günay, Cenk Yanık, İsmet İ. Kaya Faculty of Engineering and Natural Sciences, Sabanci University, İstanbul 34956, Turkey Abstract – We study the epitaxial graphene production process from SiC to understand the effects of the parameters such as pressure and temperature as well as the duration of growth. Furthermore, we investigate the efficiency of transferring the graphene layers from SiC to other substrates by means of mechanical cleavage technique. Graphene, a recently discovered two dimensional material has been taking immense attraction in research since it presents novel physics and offers a new era in high frequency electronic devices [1]. Although graphene can be produced by many different methods, epitaxial growth on SiC seems to be the most promising way of producing graphene for large scale integration [2]. AFM measurements of the graphene films show that they conform to the substrate that they stack. Therefore, in order to have higher mobilities, having a smoother surface is essential [3]. Moreover, the interaction of the graphene layers with the underlying substrate is another key parameter in the quality of the graphene films. Therefore an efficient means of transferring the epitaxially grown graphene on to other substrates could improve garphene device fabrication processes [4]. In this work, we analyzed the yield of graphene production process by epitaxial growth from SiC. Furthermore, we study the efficiency of transferring the produced graphene layers from SiC to SiO x . Epitaxial growth of graphene from SiC is done under high vacuum and high temperatures [5]. Direct current heating is applied to n-type, H 2 etched 4H-SiC samples. Carbon face of the SiC samples is chosen for the epitaxial growth due to having rotational stacking on this particular face which results in producing undoped single layer graphene on the top most layer in multilayer films which ranges from 3 layers to 60 layers [6]. The growth pressure is varied between 10 -5 mbar to 10 -7 mbar, the duration is varied between 10 minutes to 60 minutes and the temperature is varied between 1350C˚ and 1600C˚. Characterization of the graphene on SiC samples is done with Raman spectroscopy, atomic force microscopy (AFM) low energy electron diffraction (LEED) and auger electron spectroscopy (AES). Transfer of the graphene layers from SiC to SiO x is performed both at ambient pressure and under vacuum by mechanical cleavage technique. After the transfer, characterization steps are repeated to check the efficiency of the transfer. This work was supported by TUBITAK under Grant No. TBAG-107T855. [1] Geim, A.K. Graphene Status and Prospects. Science 324, 19 June 2009. [2] Geim, A.K. Novoselov K. S. Rise of Graphene. Nature Materials 6, March 2007. [3] Jernigan, [Glenn. Comparison of Epitaxial Graphene on Si-face and C-face 4H SiC Formed by Ultrahigh Vacuum and RF Furnace Production. Nanoletters 9, May 2009. [4] Caldwell, Joshua. Technique for the Dry Transfer of Epitaxial Graphene onto Arbitrary Substrates. ACSNano 4, 2010. [5]Heer, Walt de. Epitaxial Graphene. Solid State Communication 143, 2007. [6]Hass, J. The growth and morphology of epitaxial multilayer graphene. Journal of Physics: Condensed Matter 20, 2008. b. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 368
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