Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 The Effect of the Quantum Point Contacts and Impurities on an Electron in the 2D Electron Gas Engin Cicek 1 , Mustafa Ulas 2 and Afif Siddiki 3,4 1 Department of Physics, Trakya University, 22030 Edirne, Turkey 2 Kirklareli University, Physics Department, Faculty of Arts and Science, Kavakli-Kirklareli, Turkey 3 Istanbul University, Faculty of Sciences, Physics Department, Vezneciler-Istanbul, 34134, Turkey 4 Harvard University, Physics Department, Cambridge, 02138 MA, USA Abstract— In this work, we investigate the geometrical effects of the single and double quantum point contacts (QPCs) and impurity effects on a two dimensional electron gas (2DEG) in the AlGaAs/GaAs heterostructure. For a realistic calculation we take into account the crystal growth parameters and the sample geometries. Next, we solve the three dimensional Poisson equation using the numerical techniques. We show that the QPC’s shape and impurity properties strongly changes the distribution of the two dimensional electron gas (2DEG) and the subband energies of the electron which is the located in the 2DEG. In the last decade, low-dimensional heterostructure systems such as thin films (2D), wires (1D) and quantum dots (0D) [1-3] have received a great deal of attention because of their interesting physical properties [4] and their technological applications in electronic and optical devices. Fabrication techniques affect the electronic properties of the sample so that for a realistic calculations the real sample properties are taking into account [5]. Here we define a square unit cell, with a surface pattern (1.5x1.5 m 2 ) where we process three different techniques (gate, etch and trench gate defined) at the each edge of the sample in the same direction with 0.5 m. For gate defined samples we applied -1.8 V to the gates on the surface, whereas for etch defined samples we etched 62.8 nm from the surface and for trench gate samples we etch the samples 31.4 nm and place gates on this plane with a -1.8 V bias. QPCs are located on the surface with a -1.8 V. The two unlike QPC geometries (X 2 -X 8 ) are used with three different distances of the QPC’s tips. A single impurity is set in the heterostructure at various positions and distances from the 2DEG. To obtain the electron and potential profiles we solved the electrostatics of the system in three dimensions with using a code developed on a fourth order grid, which was successfully applied in previous studies [6,7]. For a realistic calculation we take into account the crystal growth parameters, gate patterns, surface images, densities, QPC and impurity properties explicitly. Our results can enlighten the experimental structures. In our work, 2DEG is located 314 nm below the surface and we dope the heterostructures with two donor layers. The upper donor layer is 40 nm below the surface and its density is 1.7x10 16 m -2 , whereas the other donor layer is located 165 nm below the surface with a fixed doping surface density of 2.5x10 15 m -2 . These donor layers are distributed homogeneously. We compare the electron density distributions and potential profiles where we create the 2DEG with different techniques (etching, gate and trench gated defined structures), QPC shapes and impurity positions. As a result, the edge properties of the 2DEG is strongly affected by the shape of the QPC, impurity position and the which process procedure is used. We can solve the 3D Poisson equation iteratively and take into account these properties and wafer properties of the sample. So that we obtain deep insight of the realistic samples. a) b) Figure: The electron densities of the samples with two different shape of the QPCs ((a)X 8 shape (b)X 2 shape) for the trench gated structures with a same QPC distances (100nm). It is clear from the graphs the X 8 shape QPC is deplete the electrons more efficiently. *Corresponding author: engin_cicek79@hotmail.com [1] H. Akiyama, T. Someya, and H. Sakaki, Phys. Rev. B 53, R10520 (1996). [2] H. Akiyama, T. Someya, and H. Sakaki, Phys. Rev. B 53, R4229 (1996). [3]M. Ulas, E. Cicek and S.S. Dalgic, phys. stat. sol. (b) 241, 2968 (2004) [4] U. Woggon (Ed.), Optical Properties of Semiconductor Quantum Dots (Springer, Heidelberg, 1997). [5] S. Arslan, E. Cicek, D. Eksi, S. Aktas, A. Weichselbaum, and A. Siddiki, Phys. Rev. B 78, 125423(2008). [6] A. Weichselbaum and S. E. Ulloa, Phys. Rev E 68, 056707 (2003). [7] A. Weichselbaum and S. E. Ulloa, Phys. Rev B 74, 085318 (2006). 6th Nanoscience and Nanotechnology Conference, zmir, 2010 242
Poster Session, Tuesday, June 15 Theme A1 - B702 UV-Irradiated Synthesis of Silver Nanoparticles in Gallic Acid Solution Emrah Bulut 1 * and Mahmut Ozacar 1 Department of Chemistry, Art and S cience Faculty, Sakarya University, Sakarya 54187, Turkiye 1 - Abstract-A rapid and facile aqueous-phase UV irradiated method was applied to synthesize silver nanoparticles. Released electrons, (e aq ) which formed by irradiation of gallic acid, were used as a reducer to form metallic silver nanoparticles from Ag + cations. In recent years, the use of noble metal nanoparticles in various fields of research has increased dramatically. This is due to not only the bulk properties of noble metals, such as chemical stability, electrical conductivity and high catalytic activity but also the unique optical, electrical, catalytic properties that are a consequence of nanometer dimensions [1-3]. Also the antibacterial activity of silver ions and their biological impact have been demonstrated by many workers [4]. Silver nanoparticles are especially important and thus many methods are used for their synthesis i.e. chemical, electrochemical and sonoelectrochemical reactions [5-8]. In this work, a rapid and facile aqueous-phase method was applied to synthesize silver nanoparticles. Gallic acid was used as both reducing and stabilizing agent. Mixture of gallic acid and silver nitrate solutions was irradiated by UV lamb to form silver nanoparticles. In this photochemical reduction, hydrated electrons or free organic radicals formed by irradiation of UV light reduce the metal ions to metals. It is strongly anticipated that these radicals can reduce metal ions to metals. HO HO HO Figure 2. Molecular structure of gallic acid COOH Characterizations of the resulting nanoparticles were performed by X-Ray Diffraction (XRD), Scanning Electron Micrographs (SEM) and Electron Diffraction Spectrometry (EDS). Role of the experimental conditions on the particle size are presented and discussed. The sizes of silver nanoparticles were found to be in the range of 50-150 nm using SEM. Also the crystallography of the particles is face centered cubic structure which was investigated by XRD patterns. Figure 3. XRD and EDS Patterns of the silver nanoparticles *Coresponding author: 1Tebulut@sakarya.edu.tr Figure 1. SEM image of the silver nanoparticles Gallic acid was used as a stabilizer as well as a reducing agent like other polyphenols as mentioned at previous work [9], with involving –OH groups and keeps the prepared particles stable because of its molecular structure. Also UV induced gallic acids have a strong reactive activity with some active species such as hydroxyl radicals (·OH) and can released the e - aq with the irradiation of a UV light which is a potential reducing agent for some metal cations. However it stabilizes the newly born Ag 0 clusters and can influence the growth of the nucleation and hence particle size and shape. No other reducing agents were used during silver nanoparticles synthesis. Effects of reactant concentrations on the fabrication of nanoparticles were investigated. [1] P. Magudapathy, P. Gangopadhyay, B.K. Panigrahi, K.G.M. Nair, S. Dhara, Physica B 299, 142 (2001). [2] A. Vaskelis, A. Jagminiene, L. Tamasauskaite–Tamasiunaite, R. Juskenas, Electrochimica Acta 50, 4586 (2005). [3] J. Xu, X. Han, H. Liu, Y. Hu, Colloids and Surfaces A: Physicochem. Eng. Aspects 273 179 (2006). [4] F. Mafune, J. Kohno, Y. Takeda, T. Kondow, H. Sawabe, J. Phys. Chem. B 104, 9111 (2000). [5] Y. Socol, O. Abramson, A. Gedanken, Y. Meshorer, L. Berenstein, A. Zaban, Langmuir 18, 4736 (2002). [6] J. Zhu, X. Liao, H.Y. Chen, Mater. Res. Bull. 36, 1687 (2001). [7] C.R.K. Rao, D.C. Trivedi, Mater. Chem. and Phy. 99, 354 (2006). [8] E. Verne, S. Di Nunzio, M. Bosetti, P. Appendino, B. C. Vitale, G. Maina, M. Cannas, Biomaterials 26, 5111 (2005). [9] E. Bulut, M. Özacar, Ind. Eng. Chem. Res. 48, 5686 (2009). 6th Nanoscience and Nanotechnology Conference, zmir, 2010 243
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