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Sample records for crystal band structure

  1. Band structure characteristics of T-square fractal phononic crystals

    Institute of Scientific and Technical Information of China (English)

    Liu Xiao-Jian; Fan You-Hua

    2013-01-01

    The T-square fractal two-dimensional phononic crystal model is presented in this article.A comprehensive study is performed for the Bragg scattering and locally resonant fractal phononic crystal.We find that the band structures of the fractal and non-fractal phononic crystals at the same filling ratio are quite different through using the finite element method.The fractal design has an important impact on the band structures of the two-dimensional phononic crystals.

  2. Band structures in Sierpinski triangle fractal porous phononic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Kai; Liu, Ying, E-mail: yliu5@bjtu.edu.cn; Liang, Tianshu

    2016-10-01

    In this paper, the band structures in Sierpinski triangle fractal porous phononic crystals (FPPCs) are studied with the aim to clarify the effect of fractal hierarchy on the band structures. Firstly, one kind of FPPCs based on Sierpinski triangle routine is proposed. Then the influence of the porosity on the elastic wave dispersion in Sierpinski triangle FPPCs is investigated. The sensitivity of the band structures to the fractal hierarchy is discussed in detail. The results show that the increase of the hierarchy increases the sensitivity of ABG (Absolute band gap) central frequency to the porosity. But further increase of the fractal hierarchy weakens this sensitivity. On the same hierarchy, wider ABGs could be opened in Sierpinski equilateral triangle FPPC; whilst, a lower ABG could be opened at lower porosity in Sierpinski right-angled isosceles FPPCs. These results will provide a meaningful guidance in tuning band structures in porous phononic crystals by fractal design.

  3. Band structures in the nematic elastomers phononic crystals

    Science.gov (United States)

    Yang, Shuai; Liu, Ying; Liang, Tianshu

    2017-02-01

    As one kind of new intelligent materials, nematic elastomers (NEs) represent an exciting physical system that combines the local orientational symmetry breaking and the entropic rubber elasticity, producing a number of unique physical phenomena. In this paper, the potential application of NEs in the band tuning is explored. The band structures in two kinds of NE phononic crystals (PCs) are investigated. Through changing NE intrinsic parameters, the influence of the porosity, director rotation and relaxation on the band structures in NE PCs are analyzed. This work is a meaningful try for application of NEs in acoustic field and proposes a new intelligent strategy in band turning.

  4. Band structures and localization properties of aperiodic layered phononic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Yan Zhizhong, E-mail: zzyan@bit.edu.cn [Department of Applied Mathematics, Beijing Institute of Technology, Beijing 100081 (China); Zhang Chuanzeng [Department of Civil Engineering, University of Siegen, D-57078 Siegen (Germany)

    2012-03-15

    The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

  5. Band structures and localization properties of aperiodic layered phononic crystals

    Science.gov (United States)

    Yan, Zhi-Zhong; Zhang, Chuanzeng

    2012-03-01

    The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

  6. Photonic crystal digital alloys and their band structure properties.

    Science.gov (United States)

    Lee, Jeongkug; Kim, Dong-Uk; Jeon, Heonsu

    2011-09-26

    We investigated semi-disordered photonic crystals (PCs), digital alloys, and made thorough comparisons with their counterparts, random alloys. A set of diamond lattice PC digital alloys operating in a microwave regime were prepared by alternately stacking two kinds of sub-PC systems composed of alumina and silica spheres of the same size. Measured transmission spectra as well as calculated band structures revealed that when the digital alloy period is short, band-gaps of the digital alloys are practically the same as those of the random alloys. This study indicates that the concept of digital alloys holds for photons in PCs as well.

  7. Band structure of absorptive two-dimensional photonic crystals

    Science.gov (United States)

    van der Lem, Han; Tip, Adriaan; Moroz, Alexander

    2003-06-01

    The band structure for an absorptive two-dimensional photonic crystal made from cylinders consisting of a Drude material is calculated. Absorption causes the spectrum to become complex and form islands in the negative complex half-plane. The boundaries of these islands are not always formed by the eigenvalues calculated for Bloch vectors on the characteristic path, and we find a hole in the spectrum. For realistic parameter values, the real part of the spectrum is hardly influenced by absorption, typically less than 0.25%. The employed method uses a Korringa-Kohn-Rostoker procedure together with analytical continuation. This results in an efficient approach that allows these band-structure calculations to be done on a Pentium III personal computer.

  8. Obtaining the band structure of a complicated photonic crystal by linear operations

    Institute of Scientific and Technical Information of China (English)

    吴良; 叶卓; 何赛灵

    2003-01-01

    Absolute band gaps can be created by lifting the degeneracy in the bands of a photonic crystal.To calculate the band structure of a complicated photonic crystal generated by e.g.symmetry breaking,general forms of all possible linear operations are presented in terms of matrices and a procedure to combine these operations is given.Other forms of linear operations(such as the addition,subtraction,and translation transforms) are also presented to obtain an explicit expression for the Fourier coefficient of the dielectric function in the plane-wave expansion method.With the present method,band structures for various complicated photonic crystals(related through these linear operations) can be obtained easily and quickly.As a numerical example,a large absolute band gap for a complicated photonic crystal structure of GaAs is found in the high region of normalized frequency.

  9. Magnon band structure and magnon density in one-dimensional magnonic crystals

    Science.gov (United States)

    Qiu, Rong-ke; Huang, Te; Zhang, Zhi-dong

    2014-11-01

    By using Callen's Green's function method and the Tyablikov and Anderson-Callen decoupling approximations, we systematically study the magnon band structure and magnon density perpendicular to the superlattice plane of one-dimensional magnonic crystals, with a superlattice consisting of two magnetic layers with ferromagnetic (FM) or antiferromagnetic (AFM) interlayer exchange coupling. The effects of temperature, interlayer coupling, anisotropy and external magnetic field on the magnon-energy band and magnon density in the Kx-direction are investigated in three situations: a) the magnon band of magnetic superlattices with FM interlayer coupling, b) separate and c) overlapping magnon bands of magnetic superlattices with AFM interlayer coupling. In the present work, a quantum approach is developed to study the magnon band structure and magnon density of magnonic crystals and the results are beneficial for the design of magnonic-crystal waveguides or gigahertz-range spin-wave filters.

  10. TUNABLE Band Structures of 2d Multi-Atom Archimedean-Like Phononic Crystals

    Science.gov (United States)

    Xu, Y. L.; Chen, C. Q.; Tian, X. G.

    2012-06-01

    Two dimensional multi-atom Archimedean-like phononic crystals (MAPCs) can be obtained by adding "atoms" at suitable positions in primitive cells of traditional simple lattices. Band structures of solid-solid and solid-air MAPCs are computed by the finite element method in conjunction with the Bloch theory. For the solid-solid system, our results show that the MAPCs can be suitably designed to split and shift band gaps of the corresponding traditional simple phononic crystal (i.e., with only one scatterer inside a primitive cell). For the solid-air system, the MAPCs have more and wider band gaps than the corresponding traditional simple phononic crystal. Numerical calculations for both solid-solid and solid-air MAPCs show that the band gap of traditional simple phononic crystal can be tuned by appropriately adding "atoms" into its primitive cell.

  11. Study of periodic band gap structure of the magnetized plasma photonic crystals

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hai-feng; MA Li; LIU Shao-bin

    2009-01-01

    The characteristics of the periodic band gaps of the one dimension magnetized plasma photonic crystals are studied with the piecewise linear current density recursive convolution (PLCDRC) finite-differential time-domain (FDTD) method. In fre-quency-domain, the transmission coefficients of electromagnetic Gaussian pulses are computed, and the effects of the periodic structure constant, plasma layer thickness and parameters of plasma on the properties of periodic band gaps of magnetized photonic crystals are analyzed. The results show that the periodic band gaps depend strongly on the plasma parameters.

  12. High-Pressure Crystal Structure, Lattice Vibrations, and Band Structure of BiSbO4.

    Science.gov (United States)

    Errandonea, Daniel; Muñoz, Alfonso; Rodríguez-Hernández, Placida; Gomis, Oscar; Achary, S Nagabhusan; Popescu, Catalin; Patwe, Sadeque J; Tyagi, Avesh K

    2016-05-16

    The high-pressure crystal structure, lattice-vibrations, and electronic band structure of BiSbO4 were studied by ab initio simulations. We also performed Raman spectroscopy, infrared spectroscopy, and diffuse-reflectance measurements, as well as synchrotron powder X-ray diffraction. High-pressure X-ray diffraction measurements show that the crystal structure of BiSbO4 remains stable up to at least 70 GPa, unlike other known MTO4-type ternary oxides. These experiments also give information on the pressure dependence of the unit-cell parameters. Calculations properly describe the crystal structure of BiSbO4 and the changes induced by pressure on it. They also predict a possible high-pressure phase. A room-temperature pressure-volume equation of state is determined, and the effect of pressure on the coordination polyhedron of Bi and Sb is discussed. Raman- and infrared-active phonons were measured and calculated. In particular, calculations provide assignments for all the vibrational modes as well as their pressure dependence. In addition, the band structure and electronic density of states under pressure were also calculated. The calculations combined with the optical measurements allow us to conclude that BiSbO4 is an indirect-gap semiconductor, with an electronic band gap of 2.9(1) eV. Finally, the isothermal compressibility tensor for BiSbO4 is given at 1.8 GPa. The experimental (theoretical) data revealed that the direction of maximum compressibility is in the (0 1 0) plane at ∼33° (38°) to the c-axis and 47° (42°) to the a-axis. The reliability of the reported results is supported by the consistency between experiments and calculations.

  13. Magnon band structure and magnon density in one-dimensional magnonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Qiu, Rong-ke, E-mail: rkqiu@163.com [Shenyang University of Technology, Shenyang 110870 (China); Huang, Te [Shenyang University of Technology, Shenyang 110870 (China); Zhang, Zhi-dong [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)

    2014-11-15

    By using Callen's Green's function method and the Tyablikov and Anderson–Callen decoupling approximations, we systematically study the magnon band structure and magnon density perpendicular to the superlattice plane of one-dimensional magnonic crystals, with a superlattice consisting of two magnetic layers with ferromagnetic (FM) or antiferromagnetic (AFM) interlayer exchange coupling. The effects of temperature, interlayer coupling, anisotropy and external magnetic field on the magnon-energy band and magnon density in the K{sub x}-direction are investigated in three situations: a) the magnon band of magnetic superlattices with FM interlayer coupling, b) separate and c) overlapping magnon bands of magnetic superlattices with AFM interlayer coupling. In the present work, a quantum approach is developed to study the magnon band structure and magnon density of magnonic crystals and the results are beneficial for the design of magnonic-crystal waveguides or gigahertz-range spin-wave filters. - Highlights: • A quantum approach has been developed to study the magnon band of magnonic crystals. • The separate and overlapping magnon bands of magnetic superlattices are investigated. • The results are beneficial for the design of gigahertz-range spin-wave filters.

  14. Photonic Band Gaps in Two-Dimensional Crystals with Fractal Structure

    Institute of Scientific and Technical Information of China (English)

    刘征; 徐建军; 林志方

    2003-01-01

    We simulate the changes of the photonic band structure of the crystal in two dimensions with a quasi-fractal structure when it is fined to a fractal. The result shows that when the dielectric distribution is fined, the photonic band structure will be compressed on the whole and the ground photonic band gap (PBG) closed while the next PBGs shrunk, in conjunction with their position declining in the frequency spectrum. Furthermore, the PBGs in the high zone are much more sensitive than those in low zones.

  15. Photonic band structure of ZnO photonic crystal slab laser

    CERN Document Server

    Yamilov, A; Cao, H

    2005-01-01

    We recently reported on the first realization of ultraviolet photonic crystal laser based on zinc oxide [Appl. Phys. Lett. {\\bf 85}, 3657 (2004)]. Here we present the details of structural design and its optimization. We develop a computational super-cell technique, that allows a straightforward calculation of the photonic band structure of ZnO photonic crystal slab on sapphire substrate. We find that despite of small index contrast between the substrate and the photonic layer, the low order eigenmodes have predominantly transverse-electric (TE) or transverse-magnetic (TM) polarization. Because emission from ZnO thin film shows strong TE preference, we are able to limit our consideration to TE bands, spectrum of which can possess a complete photonic band gap with an appropriate choice of structure parameters. We demonstrate that the geometry of the system may be optimized so that a sizable band gap is achieved.

  16. Photonic Band Gap Structures with Periodically Arranged Atoms in a Two-Dimensional Photonic Crystal

    Institute of Scientific and Technical Information of China (English)

    LI Zhi-Yu; CHEN Fang; ZHOU Jian-Ying

    2005-01-01

    @@ Linear transmission, reflection and absorption spectra for a new two-dimensional photonic crystal with periodically arranged resonant atoms are examined. Numerical results show that a twin-gap structure with forbidden bands displaced from a non-doped bandgap structure can be produced as a result of atomic polarization. The absorption spectrum is also significantly altered compared to the single atom entity.

  17. Study on temperature property of band structures in onedimensional photonic crystals

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Using transfer matrix method, the optical transmission properties in one-dimensional (1-D) photonic crystal is analyzed.When the temperature varies, not only the refractive index of the optical medium is changed because of the thermo-optical effect, but also the thickness of the optical medium is changed due to the thermal-expansion effect. Thus, the structure of 1/4 wave-plate stack in original photonic crystal is destroyed and the band structure varies. In this work, the effects of the temperature variation on the first and second band gap in a 1-D photonic crystal are analyzed in detail. It is found that the changes of the starting wavelength, the cut-off wavelength and the forbidden band width depend linearly on the temperature.

  18. Study on electro-optic properties of two-dimensional PLZT photonic crystal band structure

    Institute of Scientific and Technical Information of China (English)

    TONG Kai; WU Xiao-gang; WANG Mei-ting

    2011-01-01

    The band characteristics of two-dimensional (2D) lead lanthanum zirconate titanate (PLZT) photonic cystals are analyzed by finite element method. The electro-optic effect of PLZT can cause the refractive index change when it is imposed by the applied electric field, and the band structure of 2D photonic crystals based on PLZT varies accordingly. The effect of the applied electric field on the structural characteristics of the first and second band gaps in 2D PLZT photonic crystals is analyzed in detail. And the results show that for each band gap, the variations of start wavelength, cut-off wavelength and bandwidth are proportional to quadratic of the electric field.

  19. Growth, Band Structure and Optical Properties of LiSrBO3 Crystal

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The bulk crystal of LiSrBO3(8.39 g) with a size of 21mm × 20mm × 15mm was grown by high temperature solution growth method. The relationship between growth habit and crystal structure was discussed. The transmission spectrum shows an UV absorption edge at about 300 nm. The melting temperature of this crystal was determined to be 942 ℃ by DTA-TG measurement. The band structure of the LiSrBO3 crystal was studied by means of the first principle method. An indirect band gap was found to be about 4.0 eV, and a low dielectric constant was estimated to be about 1.9 in terms of theoretical results.

  20. Band structure and Bloch states in birefringent 1D magnetophotonic crystals: An analytical approach

    CERN Document Server

    Lévy, M; Levy, Miguel; Jalali, Amir A

    2007-01-01

    An analytical formulation for the band structure and Bloch modes in elliptically birefringent magnetophotonic crystals is presented. The model incorporates both the effects of gyrotropy and linear birefringence generally present in magneto-optic thin film devices. Full analytical expressions are obtained for the dispersion relation and Bloch modes in a layered stack photonic crystal and their properties are analyzed. It is shown that other models recently discussed in the literature are contained as special limiting cases of the formulation presented herein.

  1. Detailed study of the TE band structure of two dimensional metallic photonic crystals with square symmetry

    Energy Technology Data Exchange (ETDEWEB)

    Sedghi, Aliasghar [Islamic Azad University, Shabestar (Iran, Islamic Republic of); Valiaghaie, Soma [Islamic Azad University, Sanandaj (Iran, Islamic Republic of); Soufiani, Ahad Rounaghi [Islamic Azad University, Sufian (Iran, Islamic Republic of)

    2014-10-15

    By virtue of the efficiency of the Dirichlet-to-Neumann map method, we have calculated, for H-polarization (TE mode), the band structure of 2D photonic crystals with a square lattice composed of metallic rods embedded in an air background. The rod in the unit cell is chosen to be circular in shape. Here, from a practical point of view, in order to obtain maximum band gaps, we have studied the band structure as a function of the size of the rods. We have also studied the flat bands appearing in the band structures and have shown that for frequencies around the surface plasmon frequency, the modes are highly localized at the interface between the metallic rods and the air background.

  2. Detailed Study of the TE band structure of two dimensional metallic photonic crystals with square symmetry

    Science.gov (United States)

    Sedghi, Aliasghar; Valiaghaie, Soma; Soufiani, Ahad Rounaghi

    2014-10-01

    By virtue of the efficiency of the Dirichlet-to-Neumann map method, we have calculated, for H-polarization (TE mode), the band structure of 2D photonic crystals with a square lattice composed of metallic rods embedded in an air background. The rod in the unit cell is chosen to be circular in shape. Here, from a practical point of view, in order to obtain maximum band gaps, we have studied the band structure as a function of the size of the rods. We have also studied the flat bands appearing in the band structures and have shown that for frequencies around the surface plasmon frequency, the modes are highly localized at the interface between the metallic rods and the air background.

  3. Band structure and optical properties of LiKB4O7 single crystal

    NARCIS (Netherlands)

    Smok, P; Seinert, H; Kityk, [No Value; Berdowski, J

    2003-01-01

    The band structure (BS), electronic charge density distribution and linear optical properties of the LiKB4O7 (LKB4) single crystal are calculated using a self-consistent norm-conserving pseudo-potential method within the framework of the local density approximation theory. Dispersion of the imaginar

  4. Band structure and optical properties of LiKB4O7 single crystal

    NARCIS (Netherlands)

    Smok, P; Seinert, H; Kityk, [No Value; Berdowski, J

    2003-01-01

    The band structure (BS), electronic charge density distribution and linear optical properties of the LiKB4O7 (LKB4) single crystal are calculated using a self-consistent norm-conserving pseudo-potential method within the framework of the local density approximation theory. Dispersion of the imaginar

  5. Band structures in two-dimensional phononic crystals with periodic Jerusalem cross slot

    Science.gov (United States)

    Li, Yinggang; Chen, Tianning; Wang, Xiaopeng; Yu, Kunpeng; Song, Ruifang

    2015-01-01

    In this paper, a novel two-dimensional phononic crystal composed of periodic Jerusalem cross slot in air matrix with a square lattice is presented. The dispersion relations and the transmission coefficient spectra are calculated by using the finite element method based on the Bloch theorem. The formation mechanisms of the band gaps are analyzed based on the acoustic mode analysis. Numerical results show that the proposed phononic crystal structure can yield large band gaps in the low-frequency range. The formation mechanism of opening the acoustic band gaps is mainly attributed to the resonance modes of the cavities inside the Jerusalem cross slot structure. Furthermore, the effects of the geometrical parameters on the band gaps are further explored numerically. Results show that the band gaps can be modulated in an extremely large frequency range by the geometry parameters such as the slot length and width. These properties of acoustic waves in the proposed phononic crystals can potentially be applied to optimize band gaps and generate low-frequency filters and waveguides.

  6. Photonic band structures of two-dimensional photonic crystals with deformed lattices

    Institute of Scientific and Technical Information of China (English)

    Cai Xiang-Hua; Zheng Wan-Hua; Ma Xiao-Tao; Ren Gang; Xia Jian-Bai

    2005-01-01

    Using the plane-wave expansion method, we have calculated and analysed the changes of photonic band structures arising from two kinds of deformed lattices, including the stretching and shrinking of lattices. The square lattice with square air holes and the triangular lattice with circular air holes are both studied. Calculated results show that the change of lattice size in some special ranges can enlarge the band gap, which depends strongly on the filling factor of air holes in photonic crystals; and besides, the asymmetric band edges will appear with the broken symmetry of lattices.

  7. Band structure of one-dimensional plasma photonic crystals using the Fresnel coefficients method

    Science.gov (United States)

    Jafari, A.; Rahmat, A.

    2016-11-01

    The current study has examined the band structures of two types of photonic crystals (PCs). The first is a one-dimensional metamaterial photonic crystal (1DMMPC) composed of double-layered units for which both layers of each unit are dielectric. The second type is a very similar one-dimensional plasma photonic crystal (1DPPC) also composed of double-layered units in which the first layer is a dielectric material but the second is a plasma layer. This study compares the band structures of the 1DMMPC with specific optical characteristics of the 1DPPC using the Fresnel coefficients method and also compares the results of this method with the results of the transfer matrix method. It is concluded that the dependency of the electric permittivity of the plasma layer on the incident field frequency causes differences in the band structures in 1DMMPC and 1DPPC for both TE and TM polarizations and their gaps reside in different frequencies. The band structures of the 1DMMPC and 1DPPC are confirmed by the results of the transfer matrix method.

  8. Crystal structure and band gap of AlGaAsN

    Science.gov (United States)

    Munich, D. P.; Pierret, R. F.

    1987-09-01

    Quantum dielectric theory is applied to the quaternary alloy Al xGa 1- xAs 1- yN y to predict its electronic properties as a function of Al and N mole fractions. Results are presented for the expected crystal structure, minimum electron energy band gap, and direction in k-space of the band gap minimum for all x and y values. The results suggest that, for a proper choice of x and y, Al xGa 1- xAs 1- yN y could exhibit certain advantages over Al xGa 1- xAs when utilized in field-effect transistor structures.

  9. Robust topology optimization of three-dimensional photonic-crystal band-gap structures

    CERN Document Server

    Men, Han; Freund, Robert M; Peraire, Jaime; Johnson, Steven G

    2014-01-01

    We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniq...

  10. Band structures tunability of bulk 2D phononic crystals made of magneto-elastic materials

    Directory of Open Access Journals (Sweden)

    J. O. Vasseur

    2011-12-01

    Full Text Available The feasibility of contactless tunability of the band structure of two-dimensional phononic crystals is demonstrated by employing magnetostrictive materials and applying an external magnetic field. The influence of the amplitude and of the orientation with respect to the inclusion axis of the applied magnetic field are studied in details. Applications to tunable selective frequency filters with switching functionnality and to reconfigurable wave-guides and demultiplexing devices are then discussed.

  11. Band gap structures in two-dimensional super porous phononic crystals.

    Science.gov (United States)

    Liu, Ying; Sun, Xiu-zhan; Chen, Shao-ting

    2013-02-01

    As one kind of new linear cellular alloys (LCAs), Kagome honeycombs, which are constituted by triangular and hexagonal cells, attract great attention due to the excellent performance compared to the ordinary ones. Instead of mechanical investigation, the in-plane elastic wave dispersion in Kagome structures are analyzed in this paper aiming to the multi-functional application of the materials. Firstly, the band structures in the common two-dimensional (2D) porous phononic structures (triangular or hexagonal honeycombs) are discussed. Then, based on these results, the wave dispersion in Kagome honeycombs is given. Through the component cell porosity controlling, the effects of component cells on the whole responses of the structures are investigated. The intrinsic relation between the component cell porosity and the critical porosity of Kagome honeycombs is established. These results will provide an important guidance in the band structure design of super porous phononic crystals.

  12. Crystal structure, conformation, vibration and optical band gap analysis of bis[ rac-propranolol nitrate

    Science.gov (United States)

    Franklin, S.; Balasubramanian, T.; Nehru, K.; Kim, Youngmee

    2009-06-01

    The crystal structure of the title rac-propranolol salt, CHNO2+·NO3-, consists of two protonated propranolol residues and nitrate anions. Three virtually flat fragments, characteristics of most of the β-adrenolytics with oxy-methylene bridge are present in both the cations (A and B). The plane of the propranolol chain is twisted with respect to the plane of the aromatic ring in both the cations. Present study investigates the conformation and hydrogen bonding interactions, which play an important role in biological functions. A gauche conformation is observed for the oxo-methylene bridge of cation A, while a trans conformation prevails in cation B. These conformations are found in majority of β-blockers. Presence of twenty intermolecular hydrogen bonds mediating through the anions stabilizes the crystal packing. Vibration analysis and earlier theoretical predictions complement the structure analysed. From the UV-Vis spectral analysis for the crystal, the optical band gap is found to be Eg = 5.12 eV, where as the chloride salt has Eg = 3.81 eV. The increase in the band gap may be attributed by the increase in the number of intermolecular hydrogen bonds. Good optical transmittance in the entire visible region and the direct band gap property suggest that it is a suitable candidate for optical applications in UV region.

  13. Band Structure of Photonic Crystals Fabricated by Two-Photon Polymerization

    Directory of Open Access Journals (Sweden)

    Mikhail V. Rybin

    2015-01-01

    Full Text Available We study theoretically the band-gap structures of several types of three-dimensional photonic crystals with the fcc lattice symmetry: synthetic opals, inverted yablonovite and woodpile. The samples of inverted yablonovite, inverted yablonovite with a glassy superstructure and woodpile are fabricated by two-photon polymerization through a direct laser writing technique, which allows the creation of complex three-dimensional photonic crystals with a resolution better than 100 nm. A material is polymerized along the trace of a moving laser focus, thus enabling the fabrication of any desirable three-dimensional structure by direct “recording” into the volume of a photosensitive material. The correspondence of the structures of the fabricated samples to the expected fcc lattices is confirmed by scanning electron microscopy. We discuss theoretically how the complete photonic band-gap is modified by structural and dielectric parameters. We demonstrate that the photonic properties of opal and yablonovite are opposite: the complete photonic band gap appears in the inverted opal, and direct yablonovite is absent in direct opal and inverted yablonovite.

  14. Calculation and analysis of complex band structure in dispersive and dissipative two-dimensional photonic crystals

    CERN Document Server

    Brûlé, Yoann; Gralak, Boris

    2015-01-01

    Numerical calculation of modes in dispersive and absorptive systems is performed using the finite element method. The dispersion is tackled in the frame of an extension of Maxwell's equations where auxiliary fields are added to the electromagnetic field. This method is applied to multi-domain cavities and photonic crystals including Drude and Drude-Lorentz metals. Numerical results are compared to analytical solutions for simple cavities and to previous results of the literature for photonic crystals, showing excellent agreement. The advantages of the developed method lie on the versatility of the finite element method regarding geometries, and in sparing the use of tedious complex poles research algorithm. Hence the complex spectrum of resonances of non-hermitian operators and dissipative systems, like two-dimensional photonic crystal made of absorbing Drude metal, can be investigated in detail. The method is used to reveal unexpected features of their complex band structures.

  15. Robust topology optimization of three-dimensional photonic-crystal band-gap structures.

    Science.gov (United States)

    Men, H; Lee, K Y K; Freund, R M; Peraire, J; Johnson, S G

    2014-09-22

    We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniques such as a simple approach to impose symmetry constraints. We also demonstrate a technique for robust topology optimization, in which some uncertainty is included in each voxel and we optimize the worst-case gap, and we show that the resulting band gaps have increased robustness to systematic fabrication errors.

  16. Peculiarities of the band structure of multi-component photonic crystals with different dimensions.

    Science.gov (United States)

    Samusev, A K; Samusev, K B; Rybin, M V; Limonov, M F

    2010-03-24

    In this work we offer a simple analytical method which allows us to determine and study the effects of the selective switching of photonic stop-bands in multi-component photonic crystals (Mc-PhCs) of any dimensionality. The calculations for Mc-PhCs with low dielectric contrast have been performed in the framework of the model based on the scattering form factor analysis. It has been shown that the effects of selective switching of photonic stop-bands predicted theoretically and found experimentally before in three-dimensional (3D) Mc-PhC have a general character and may be observed also in one-dimensional (1D) and two-dimensional (2D) Mc-PhCs. It is found that 1D, 2D and 3D Mc-PhCs demonstrate unexpectedly similar quasi-periodic behaviour of photonic stop-bands as a function of the reciprocal lattice vector. A proper choice of the structural and dielectric parameters can create a resonance photonic stop-band determining the Bragg wavelengths, to which a photonic crystal can never be transparent.

  17. Peculiarities of the band structure of multi-component photonic crystals with different dimensions

    Energy Technology Data Exchange (ETDEWEB)

    Samusev, A K; Samusev, K B; Rybin, M V; Limonov, M F, E-mail: m.rybin@mail.ioffe.r [Ioffe Physical-Technical Institute of the Russian Academy of Sciences, St Petersburg 194021 (Russian Federation)

    2010-03-24

    In this work we offer a simple analytical method which allows us to determine and study the effects of the selective switching of photonic stop-bands in multi-component photonic crystals (Mc-PhCs) of any dimensionality. The calculations for Mc-PhCs with low dielectric contrast have been performed in the framework of the model based on the scattering form factor analysis. It has been shown that the effects of selective switching of photonic stop-bands predicted theoretically and found experimentally before in three-dimensional (3D) Mc-PhC have a general character and may be observed also in one-dimensional (1D) and two-dimensional (2D) Mc-PhCs. It is found that 1D, 2D and 3D Mc-PhCs demonstrate unexpectedly similar quasi-periodic behaviour of photonic stop-bands as a function of the reciprocal lattice vector. A proper choice of the structural and dielectric parameters can create a resonance photonic stop-band determining the Bragg wavelengths, to which a photonic crystal can never be transparent.

  18. Exceptional contours and band structure design in parity-time symmetric photonic crystals

    CERN Document Server

    Cerjan, Alexander; Fan, Shanhui

    2016-01-01

    We investigate the properties of multidimensional parity-time symmetric periodic systems whose non-Hermitian periodicity is an integer multiple of the underlying Hermitian system's periodicity. This creates a natural set of degeneracies which can undergo thresholdless $\\mathcal{PT}$ transitions. We derive a $\\mathbf{k} \\cdot \\mathbf{p}$ perturbation theory suited to the continuous eigenvalues of such systems in terms of the modes of the underlying Hermitian system. In photonic crystals, such thresholdless $\\mathcal{PT}$ transitions are shown to yield significant control over the band structure of the system, and can result in all-angle supercollimation, a $\\mathcal{PT}$-superprism effect, and unidirectional behavior.

  19. Exceptional Contours and Band Structure Design in Parity-Time Symmetric Photonic Crystals.

    Science.gov (United States)

    Cerjan, Alexander; Raman, Aaswath; Fan, Shanhui

    2016-05-20

    We investigate the properties of two-dimensional parity-time symmetric periodic systems whose non-Hermitian periodicity is an integer multiple of the underlying Hermitian system's periodicity. This creates a natural set of degeneracies that can undergo thresholdless PT transitions. We derive a k·p perturbation theory suited to the continuous eigenvalues of such systems in terms of the modes of the underlying Hermitian system. In photonic crystals, such thresholdless PT transitions are shown to yield significant control over the band structure of the system, and can result in all-angle supercollimation, a PT-superprism effect, and unidirectional behavior.

  20. Spectral element method for band-structure calculations of 3D phononic crystals

    Science.gov (United States)

    Shi, Linlin; Liu, Na; Zhou, Jianyang; Zhou, Yuanguo; Wang, Jiamin; Huo Liu, Qing

    2016-11-01

    The spectral element method (SEM) is a special kind of high-order finite element method (FEM) which combines the flexibility of a finite element method with the accuracy of a spectral method. In contrast to the traditional FEM, the SEM exhibits advantages in the high-order accuracy as the error decreases exponentially with the increase of interpolation degree by employing the Gauss-Lobatto-Legendre (GLL) polynomials as basis functions. In this study, the spectral element method is developed for the first time for the determination of band structures of 3D isotropic/anisotropic phononic crystals (PCs). Based on the Bloch theorem, we present a novel, intuitive discretization formulation for Navier equation in the SEM scheme for periodic media. By virtue of using the orthogonal Legendre polynomials, the generalized eigenvalue problem is converted to a regular one in our SEM implementation to improve the efficiency. Besides, according to the specific geometry structure, 8-node and 27-node hexahedral elements as well as an analytic mesh have been used to accurately capture curved PC models in our SEM scheme. To verify its accuracy and efficiency, this study analyses the phononic-crystal plates with square and triangular lattice arrangements, and the 3D cubic phononic crystals consisting of simple cubic (SC), bulk central cubic (BCC) and faced central cubic (FCC) lattices with isotropic or anisotropic scatters. All the numerical results considered demonstrate that SEM is superior to the conventional FEM and can be an efficient alternative method for accurate determination of band structures of 3D phononic crystals.

  1. Investigation of the Band Structure of Graphene-Based Plasmonic Photonic Crystals

    Directory of Open Access Journals (Sweden)

    Pingping Qiu

    2016-09-01

    Full Text Available In this paper, one-dimensional (1D and two-dimensional (2D graphene-based plasmonic photonic crystals (PhCs are proposed. The band structures and density of states (DOS have been numerically investigated. Photonic band gaps (PBGs are found in both 1D and 2D PhCs. Meanwhile, graphene-based plasmonic PhC nanocavity with resonant frequency around 175 THz, is realized by introducing point defect, where the chemical potential is from 0.085 to 0.25 eV, in a 2D PhC. Also, the bending wvaguide and the beam splitter are realized by introducing the line defect into the 2D PhC.

  2. Investigation of the Band Structure of Graphene-Based Plasmonic Photonic Crystals

    Science.gov (United States)

    Qiu, Pingping; Qiu, Weibin; Lin, Zhili; Chen, Houbo; Tang, Yixin; Wang, Jia-Xian; Kan, Qiang; Pan, Jiao-Qing

    2016-01-01

    In this paper, one-dimensional (1D) and two-dimensional (2D) graphene-based plasmonic photonic crystals (PhCs) are proposed. The band structures and density of states (DOS) have been numerically investigated. Photonic band gaps (PBGs) are found in both 1D and 2D PhCs. Meanwhile, graphene-based plasmonic PhC nanocavity with resonant frequency around 175 THz, is realized by introducing point defect, where the chemical potential is from 0.085 to 0.25 eV, in a 2D PhC. Also, the bending wvaguide and the beam splitter are realized by introducing the line defect into the 2D PhC.

  3. Crystal structure re-investigation in wide band gap CIGSe compounds

    Energy Technology Data Exchange (ETDEWEB)

    Souilah, M. [Institut des Materiaux Jean Rouxel, Universite de Nantes, CNRS, 2 rue de la Houssiniere, BP 32229, 44322 Nantes Cedex 03 (France)], E-mail: marc.souilah@cnrs-imn.fr; Rocquefelte, X.; Lafond, A.; Guillot-Deudon, C. [Institut des Materiaux Jean Rouxel, Universite de Nantes, CNRS, 2 rue de la Houssiniere, BP 32229, 44322 Nantes Cedex 03 (France); Morniroli, J.-P. [Laboratoire de Metallurgie Physique et Genie des Materiaux, UMR CNRS 8517, USTL and ENSCL, Bat C6, Cite Scientifique, 59655 Villeneuve d' Ascq Cedex (France); Kessler, J. [Institut des Materiaux Jean Rouxel, Universite de Nantes, CNRS, 2 rue de la Houssiniere, BP 32229, 44322 Nantes Cedex 03 (France)

    2009-02-02

    There is agreement in the literature that Cu(In{sub 1} {sub -} {sub x}Ga{sub x})Se{sub 2} (CIGSe) absorber used in solar cells has an optimum composition (x {approx} 0.3) corresponding to a band gap (1.1-1.2 eV) far below the theoretical value giving the maximum (1.4-1.5 eV). This paper presents a re-investigation of the crystal structure of bulk CIGSe compounds for both stoichiometric and Cu-poor compositions. Regardless of the gallium content, all the stoichiometric compounds are found to adopt the well-known chalcopyrite structure (space group I-42d) while a modification of the structure is evidenced for the high Ga-content Cu-poor compounds. The X-ray diffraction analyses demonstrate that the crystal structure of Cu{sub 0.743}In{sub 0.543} Ga{sub 0.543}Se{sub 2} is derived from that of the stannite structure (space-group I-42m). Ab-initio calculations show a strong dependence of the electronic structure near the Fermi level with the copper content. Such modifications are expected to significantly change the optical properties of Cu-poor CIGSe materials.

  4. QUANTUM-MECHANICAL MODELING OF SPATIAL AND BAND STRUCTURE OF Y3AL5O12 SCINTILLATION CRYSTAL

    Directory of Open Access Journals (Sweden)

    I. I. Vrubel

    2016-05-01

    Full Text Available Spatial and electronic structures of a unit cell of yttrium-aluminum garnet have been studied. Quantum-mechanical model have been presented. Semi-empirical methods PM6 and PM7 have been used for geometry optimization of the crystal unit cell. Band structure has been calculated within density functional theory with the use of PBE exchange-correlation functional. Histograms of metal-oxygen distances for equilibrium geometry have been constructed. Comparison of the used methods has been carried out and recommendation about their applicability for such problems was given. The single-particle wave functions and energies have been calculated. The bandgap was estimated. The band structure was plotted. It was shown that the method gives reliable results for spatial and band structure of Y3Al5O12 scintillation crystal. The results of this work can be used for improvement of characteristics of garnet scintillation crystals.

  5. Birefringence and band structure of CdP{sub 2} crystals

    Energy Technology Data Exchange (ETDEWEB)

    Beril, S.I.; Stamov, I.G. [Tiraspol State Corporative University, Yablocikin Street 5, 2069 Tiraspol, Republic of Moldova (Moldova, Republic of); Syrbu, N.N., E-mail: sirbunn@yahoo.com [Technical University of Moldova, 168 Stefan cel Mare Avenue, 2004 Chisinau, Republic of Moldova (Moldova, Republic of); Zalamai, V.V. [Institute of Applied Physics, Academy of Sciences of Moldova, 5 Academy Street, 2028 Chisinau, Republic of Moldova (Moldova, Republic of)

    2013-08-01

    The spatial dispersion in CdP{sub 2} crystals was investigated. The dispersion is positive (n{sup k||c}>n{sup k||y}) at λ>λ{sub 0} and negative (n{sup k||c}crystals are isotropic for wavelength λ{sub o}=896 nm. Indirect transitions in excitonic region E{sub gx} are nonpolarized due to one pair of bands. Minimal direct energy intervals correspond to transitions Γ{sub 1}→Γ{sub 1} for E{sup ||}c and Γ{sub 2}→Γ{sub 1} for E⊥c. The temperature coefficient of energy gap sifting in the case of temperature changing between 2 and 4.2 K equals to 10.6 meV/K and 3.2 mev/K for Γ{sub 1}→Γ{sub 1} and Γ{sub 2}→Γ{sub 1} band gap correspondingly. Reflectivity spectra were measured for energy interval 1.5–10 eV and optical functions (n, k, ε{sub 1}, ε{sub 2,}d{sup 2}ε{sub 1}/dE{sup 2} and d{sup 2}ε{sub 2}/dE{sup 2}) were calculated by using Kramers–Kronig analyses. All features were interpreted as optical transitions on the basis of both theoretical calculations of band structure.

  6. High-power narrow-vertical-divergence photonic band crystal laser diodes with optimized epitaxial structure

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Lei; Qu, Hongwei; Liu, Yun; Zhang, Yejin; Zheng, Wanhua, E-mail: whzheng@red.semi.ac.cn [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, CAS, Beijing 100083 (China); Laboratory of Solid State Optoelectronics Information Technology, Institute of Semiconductors, CAS, Beijing 100083 (China); Wang, Yufei; Qi, Aiyi [Laboratory of Solid State Optoelectronics Information Technology, Institute of Semiconductors, CAS, Beijing 100083 (China)

    2014-12-08

    900 nm longitudinal photonic band crystal (PBC) laser diodes with optimized epitaxial structure are fabricated. With a same calculated fundamental-mode divergence, stronger mode discrimination is achieved by a quasi-periodic index modulation in the PBC waveguide than a periodic one. Experiments show that the introduction of over 5.5 μm-thick PBC waveguide contributes to only 10% increment of the internal loss for the laser diodes. For broad area PBC lasers, output powers of 5.75 W under continuous wave test and over 10 W under quasi-continuous wave test are reported. The vertical divergence angles are 10.5° at full width at half maximum and 21.3° with 95% power content, in conformity with the simulated angles. Such device shows a prospect for high-power narrow-vertical-divergence laser emission from single diode laser and laser bar.

  7. Finite Element Method for Analysis of Band Structures of 2D Phononic Crystals with Archimedean-like tilings

    Science.gov (United States)

    Li, Jianbao; Wang, Yue-Sheng; Zhang, Chuanzeng

    2010-05-01

    In this paper, a finite element method based on the ABAQUS code and user subroutine is presented to evaluate the propagation of acoustic waves in the two-dimensional phononic crystals with Archimedean-like tilings. Two systems composed of cylinder scatters embedded in a host in Ladybug and Bathroom lattices are considered. Complete and accurate band structures and transmission spectra are obtained to identify the band gaps and eigenmodes. We found that Archimedean-like structures can have some advantages over the traditional square lattice regarding the completeness of the gap and its position and width. Also, due to the same square primitive unit cell and the first Brillouin zone, the two square-like lattices have similar acoustic response in lower bands. The results indicate that the finite element method is precise for the band structure computation of the complex phononic crystals with Archimedean tilings.

  8. A Pseudospectral Time-Domain Algorithm for Calculating the Band Structure of a Two-Dimensional Photonic Crystal

    Institute of Scientific and Technical Information of China (English)

    何江平; 沈林放; 张全; 何赛灵

    2002-01-01

    A pseudospectral time-domain (PSTD) method is developed for calculating the band structure of a two-dimensional photonic crystal. Maxwell's equations are rewritten in terms of period fields by using the Bloch theorem. Instead of spatial finite differences, the fast Fourier transform is used to calculate the spatial derivatives. To reach a similar accuracy, fewer sample points are required in the present PSTD method as compared to the conventional finite-difference time-domain methods. Our numerical simulation shows that the present PSTD method is an efficient and accurate method for calculating the band structure of a photonic crystal.

  9. New bismuth borophosphate Bi{sub 4}BPO{sub 10}: Synthesis, crystal structure, optical and band structure analysis

    Energy Technology Data Exchange (ETDEWEB)

    Babitsky, Nicolay A.; Leshok, Darya Y.; Mikhaleva, Natalia S. [Siberian Federal University, 79 Svobodny Av, Krasnoyarsk, 660041 (Russian Federation); Kuzubov, Aleksandr A., E-mail: alexkuzubov@gmail.com [Siberian Federal University, 79 Svobodny Av, Krasnoyarsk, 660041 (Russian Federation); Institute of Physics SB RAS, Krasnoyarsk 660036 (Russian Federation); Zhereb, Vladimir P. [Siberian Federal University, 79 Svobodny Av, Krasnoyarsk, 660041 (Russian Federation); Kirik, Sergei D., E-mail: kiriksd@yandex.ru [Siberian Federal University, 79 Svobodny Av, Krasnoyarsk, 660041 (Russian Federation)

    2015-08-01

    New bismuth borophosphate Bi{sub 4}BPO{sub 10} was obtained by spontaneous crystallization from the melt of correspondent composition at 804 °C. Crystal structure with orthorhombic lattice parameters: a = 22.5731(3) Å, b = 14.0523(2) Å, c = 5.5149(1) Å, V = 1749.34(4), Z = 8, SG Pcab was determined by X-ray powder diffraction technique. The [Bi{sub 2}O{sub 2}]{sup 2+} -layers, which are typical for bismuth oxide compounds, transform into cationic endless strips of 4 bismuth atoms width directed along the c-axis in Bi{sub 4}BPO{sub 10}. The strips combining stacks are separated by flat triangle [BO{sub 3}]{sup 3−} -anions within stacks. Neighboring stacks are separated by tetrahedral [PO{sub 4}]{sup 3−}-anions and shifted relatively to each other. Bismuth atoms are placed in 5–7 vertex oxygen irregular polyhedra. Bi{sub 4}BPO{sub 10} is stable up to 812 °C, then melts according to the peritectic law. The absorption spectrum in the range 350–700 nm was obtained and the width of the forbidden band was estimated as 3.46 eV. The band electronic structure of Bi{sub 4}BPO{sub 10} was modeled using DFT approach. The calculated band gap (3.56 eV) is in good agreement with the experimentally obtained data. - Graphical abstract: Display Omitted - Highlights: • New bismuth borophosphate with composition Bi{sub 4}BPO{sub 10} was synthesized. • The crystal structure was determined by X-ray powder diffraction technique. • Bismuth-oxygen part [Bi{sub 4}O{sub 3}]{sup 6+} forms endless strips of 4 bismuth atoms width. • Electronic structure was modeled by DFT method. • The calculated band gap (3.56 eV) is very close to the experimental one (3.46 eV)

  10. Study of electronic structures and absorption bands of BaMgF4 crystal with F colour centre

    Institute of Scientific and Technical Information of China (English)

    Kang Ling-Ling; Liu Ting-Yu; Zhang Qi-Ren; Xu Ling-Zhi; Zhang Fei-Wu

    2011-01-01

    The electronic structures of BaMgF4 crystals containing an F colour centre are studied within the framework of the fully relativistic self-consistent Direc-Slate-theory, using a numerically discrete variational (DV-Xα)method. It is concluded from the calculated results that the energy levels of the F colour centre are located in the forbidden band.The optical transition energy from the ground state to the excited state for the F colour centre is about 5.12 eV, which corresponds to the 242-nm absorption band. These calculated results can explain the origin of the absorption bands.

  11. Photonic crystal alloys: a new twist in controlling photonic band structure properties.

    Science.gov (United States)

    Kim, Hee Jin; Kim, Dong-Uk; Roh, Young-Geun; Yu, Jaejun; Jeon, Heonsu; Park, Q-Han

    2008-04-28

    We identified new photonic structures and phenomenon that are analogous to alloy crystals and the associated electronic bandgap engineering. From a set of diamond-lattice microwave photonic crystals of randomly mixed silica and alumina spheres but with a well defined mixing composition, we observed that both bandedges of the L-point bandgap monotonically shifted with very little bowing as the composition was varied. The observed results were in excellent agreement with the virtual crystal approximation theory originally developed for electronic properties of alloy crystals. This result signifies the similarity and correspondence between photonics and electronics.

  12. Acoustic band pinning in the phononic crystal plates of anti-symmetric structure

    Institute of Scientific and Technical Information of China (English)

    Cai Chen; Zhu Xue-Feng; Chen Qian; Yuan Ying; Liang Bin; Cheng Jian-Chun

    2011-01-01

    Acoustic bands are studied numerically for a Lamb wave propagating in an anti-symmetric structure of a onedimensional periodic plate by using the method of supercell plane-wave expansion.The results show that all the bands are pinned in pairs at the Brillouin zone boundary as long as the anti-symmetry remains and acoustic band gaps (ABGs) only appear between certain bands.In order to reveal the relationship between the band pinning and the anti-symmetry,the method of eigenmode analysis is introduced to calculate the displacement fields of different plate structures.Further,the method of harmony response analysis is employed to calculate the reference spectra to verify the accuracy of numerical calculations of acoustic band map,and both the locations and widths of ABGs in the acoustic band map are in good agreement with those of the reference spectra.The investigations show that the pinning effect is very sensitive to the anti-symmetry of periodic plates,and by introducing different types of breakages,more ABGs or narrow pass bands will appear,which is meaningful in band gap engineering.

  13. Low-frequency and tuning characteristic of band gap in a symmetrical double-sided locally resonant phononic crystal plate with slit structure

    Science.gov (United States)

    Wang, X. P.; Jiang, P.; Song, A. L.

    2016-09-01

    In this paper, the low-frequency and tuning characteristic of band gap in a two-dimensional phononic crystal structure, consisting of a square array of aluminum cylindrical stubs deposited on both sides of a thin rubber plate with slit structure, are investigated. Using the finite element method, the dispersion relationships and power transmission spectra of this structure are calculated. In contrast to a typical phononic crystal without slit structure, the proposed slit structure shows band gaps at lower frequencies. The vibration modes of the band gap edges are analyzed to clarify the mechanism of the lowest band gaps. Additionally, the influence of the slit parameters and stub parameters on the band gaps in slit structure are investigated. The geometrical parameters of the slits and stubs were found to influence the band gaps; this is critical to understand for practical applications. These results will help in fabricating phononic crystal structures whose band frequency can be modulated at lower frequencies.

  14. single crystal growth, x-ray structure analysis, optical band gap ...

    African Journals Online (AJOL)

    2015-09-01

    Sep 1, 2015 ... absorption spectra illustrate the change in opticalband gap from 3.01eVto ... Keywords: Single crystal growth; structure analysis; optical Eg; Raman spectra; strain tensor ... Journal of Fundamental and Applied Sciences.

  15. A short remark on the band structure of free-edge platonic crystals

    Science.gov (United States)

    Smith, Michael J. A.; Meylan, Michael H.; McPhedran, Ross C.; Poulton, Chris G.

    2014-10-01

    A corrected version of the multipole solution for a thin plate perforated in a doubly periodic fashion is presented. It is assumed that free-edge boundary conditions are imposed at the edge of each cylindrical inclusion. The solution procedure given here exploits a well-known property of Bessel functions to obtain the solution directly, in contrast to the existing incorrect derivation. A series of band diagrams and an updated table of values are given for the resulting system (correcting known publications on the topic), which shows a spectral band at low frequency for the free-edge problem. This is in contrast to clamped-edge boundary conditions for the same biharmonic plate problem, which features a low-frequency band gap. The numerical solution procedure outlined here is also simplified relative to earlier publications, and exploits the spectral properties of complex-valued matrices to determine the band structure of the structured plate.

  16. Band structure of collective modes and effective properties of binary magnonic crystals

    Science.gov (United States)

    Zivieri, R.; Malagò, P.; Giovannini, L.

    2014-11-01

    In this paper a theoretical study of the band structure of collective modes of binary ferromagnetic systems formed by a submicrometric periodic array of cylindrical cobalt nanodots partially or completely embedded into a permalloy ferromagnetic film is performed. The binary ferromagnetic systems studied are two-dimensional periodic, but they can be regarded as three-dimensional, since the magnetization is non uniform also along the z direction due to the contrast between the saturation magnetizations of the two ferromagnetic materials along the thickness. The dynamical matrix method, a finite-difference micromagnetic approach, formulated for studying the dynamics in one-component periodic ferromagnetic systems is generalized to ferromagnetic systems composed by F ferromagnetic materials. It is then applied to investigate the spin dynamics in four periodic binary ferromagnetic systems differing each other for the volume of cobalt dots and for the relative position of cobalt dots within the primitive cell. The dispersion curves of the most representative frequency modes are calculated for each system for an in-plane applied magnetic field perpendicular to the Bloch wave vector. The dependence of the dispersion curves on the cobalt quantity and position is discussed in terms of distribution of effective "surface magnetic charges" at the interface between the two ferromagnetic materials. The metamaterial properties in the propagative regime are also studied (1) by introducing an effective magnetization and effective "surface magnetic charges" (2) by describing the metamaterial wave dispersion of the most representative mode in each system within an effective medium approximation and in the dipole-exchange regime. It is also shown that the interchange between cobalt and permalloy does not necessarily lead to an interchange of the corresponding mode dispersion. Analogously to the case of electromagnetic waves in two-dimensional photonic crystals, the degree of

  17. Band structure of fcc-C60 solid state crystal study

    Directory of Open Access Journals (Sweden)

    S Javanbakht

    2009-09-01

    Full Text Available We studied the architecture of the C60 cluster to drive its atomic positions which can be seen at room temperature. We then used the obtained carbon positions as a basis set for the fcc structure to construct the fcc-C60 compound. Self consistent calculations were performed based on the density functional theory (DFT utilizing the accurate WIEN2K code to solve the single-particle Kohen-Sham equation within the augmented plane waves plus local orbital (APW+lo method. The cohesive energy has been found to be 1.537 eV for the fcc-C60 . The calculated small cohesive energy that results from the weak Van der Waals-London interactions among a C60 cluster with its nearest neighbors is in good agreement with experiment. The electron densities of states (DOSs were calculated for a C60 macromolecule as well as the fcc-C60 compound and the results were compared with each other. The band gap from DOS calculations has been found to be 0.7 eV. Band structures were also calculated within the generalized gradient approximation (GGA. The band structure calculation results in 1.04 eV for the direct band gap. Two kinds of σ and π bonds were determined in the band structure. Our results are in good agreement with experiment and pseudopotential calculations.

  18. Analysis of band structure, transmission properties, and dispersion behavior of THz wave in one-dimensional parabolic plasma photonic crystal

    Energy Technology Data Exchange (ETDEWEB)

    Askari, Nasim; Eslami, Esmaeil, E-mail: eeslami@iust.ac.ir [Department of Physics, Iran University of Science & Technology, Narmak, Tehran 16846-13114 (Iran, Islamic Republic of); Mirzaie, Reza [Department of Physics, Shahid Beheshti University, G. C., Evin, Tehran 1983969411 (Iran, Islamic Republic of)

    2015-11-15

    The photonic band gap of obliquely incident terahertz electromagnetic waves in a one-dimensional plasma photonic crystal is studied. The periodic structure consists of lossless dielectric and inhomogeneous plasma with a parabolic density profile. The dispersion relation and the THz wave transmittance are analyzed based on the electromagnetic equations and transfer matrix method. The dependence of effective plasma frequency and photonic band gap characteristics on dielectric and plasma thickness, plasma density, and incident angle are discussed in detail. A theoretical calculation for effective plasma frequency is presented and compared with numerical results. Results of these two methods are in good agreement.

  19. Crystal Structure and Band Gap Engineering in Polyoxometalate-Based Inorganic-Organic Hybrids.

    Science.gov (United States)

    Roy, Soumyabrata; Sarkar, Sumanta; Pan, Jaysree; Waghmare, Umesh V; Dhanya, R; Narayana, Chandrabhas; Peter, Sebastian C

    2016-04-04

    We have demonstrated engineering of the electronic band gap of the hybrid materials based on POMs (polyoxometalates), by controlling its structural complexity through variation in the conditions of synthesis. The pH- and temperature-dependent studies give a clear insight into how these experimental factors affect the overall hybrid structure and its properties. Our structural manipulations have been successful in effectively tuning the optical band gap and electronic band structure of this kind of hybrids, which can find many applications in the field of photovoltaic and semiconducting devices. We have also addressed a common crystallographic disorder observed in Keggin-ion (one type of heteropolyoxometalate [POMs])-based hybrid materials. Through a combination of crystallographic, spectroscopic, and theoretical analysis of four new POM-based hybrids synthesized with tactically varied reaction conditions, we trace the origin and nature of the disorder associated with it and the subtle local structural coordination involved in its core picture. While the crystallography yields a centrosymmetric structure with planar coordination of Si, our analysis with XPS, IR, and Raman spectroscopy reveals a tetrahedral coordination with broken inversion symmetry, corroborated by first-principles calculations.

  20. Band structure, density of states, and crystal chemistry of ZrGa{sub 2} and ZrGa{sub 3} single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Reshak, A.H., E-mail: maalidph@yahoo.co.uk [Institute of Complex systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic); School of Material Engineering, Malaysia University of Perlis, P.O Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis (Malaysia); Lakshminarayana, G., E-mail: glnphysics@rediffmail.com [Materials Science and Technology Division (MST-7), Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Ebothe, J. [Laboratoire de Recherche en Nanosciences, E.A. 4682, Université de Reims, 21, rue Clément Ader, 51685 Reims cedex 02 (France); Fedorchuk, A.O. [Lviv National University of Veterinary Medicine and Biotechnologies, Department of Inorganic and Organic Chemistry, Lviv (Ukraine); Fedyna, M.F. [National University of Forestry and Wood Technology of Ukraine Chuprynky Str., 103, 79057 Lviv (Ukraine); Kamarudin, H. [School of Material Engineering, Malaysia University of Perlis, P.O Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis (Malaysia); Mandracci, P. [Politecnico di Torino, Department of Applied Science and Technology, corso Duca degli Abruzzi 24, 10129, Torino (Italy); Auluck, S. [Council of Scientific and Industrial Research - National Physical Laboratory Dr. K.S. Krishnan Marg, New Delhi 110012 (India)

    2013-04-15

    Highlights: ► ZrGa{sub 2} and ZrGa{sub 3} crystals structure was analyzed. ► FP-LAPW method was used to solve the Kohn Sham DFT equations within the framework of the WIEN2K code. ► Electronic band structures are reported. ► The studied crystals exhibit potential optoelectronic applications. -- Abstract: Using FP-LAPW Method we have performed calculations of the band structure of the ZrGa{sub 2} and ZrGa{sub 3} crystals. The all-electron full potential linearized augmented plane wave method was used to solve the Kohn Sham DFT equations. We have explored different approximations using three kinds of exchange-correlation potentials on the electronic structure and we concluded that there is insignificant influence on the band structure and the density of states. It is clear that there exists a difference in the band dispersion with one move from ZrGa{sub 2} to ZrGa{sub 3} that is attributed to the fact that ZrGa{sub 2} has four formula per unit cell (Z = 4) while ZrGa{sub 3} has two formula per unit cell (Z = 2). Despite some similarity in the crystallochemistry of ZrGa{sub 2} to ZrGa{sub 3} some differences are observed in the band structure dispersion. There is a strong hybridization between the states. The interaction of charges between Zr and Ga atoms is due to the strong hybridization, and the covalent bond arises due to the degree of hybridization. Hence, there is a strong covalent bonding between these atoms. We have obtained a space electron charge density distribution in the average unit cell by calculations of the electron charge density distribution. The space electronic charge density contour distribution is illustrated in (1 0 0) and (1 1 0) planes.

  1. Experimental valence-band study of Ti(NiCu) alloys with different compositions and crystal structures

    Science.gov (United States)

    Senkovskiy, B. V.; Usachev, D. Yu.; Fedorov, A. V.; Shelyakov, A. V.; Adamchuk, V. K.

    2012-08-01

    The density of valence-band electronic states of Ti(NiCu) alloys with different crystal structures and elemental compositions has been studied by X-ray photoelectron spectroscopy. It has been established that the change in the crystal state initiated by a martensitic transformation or a transition from the amorphous state to the crystal state does not affect the valence-band electronic state density distribution of the Ti50Ni50 and Ti50Ni25Cu25 alloys. It has been shown that a change in the elemental composition leads to a noticeable redistribution of the electronic density in alloys of the Ti50Ni50 - x Cu x system ( x = 0, 10, 15, 25, 30, 38, 50 at. %). As the copper concentration in the Ti(NiCu) alloys increases, the contribution of the Ni d states in the vicinity of the Fermi level decreases, with the d band of nickel shifting toward higher binding energies, and that of copper, toward lower binding energies.

  2. Diamond Opal-Replica Photonic Crystals and Graphitic Metallic Photonic Band Gap Structures: Fabrication and Properties

    Science.gov (United States)

    Zakhidov, A. A.; Baughman, R. H.; Iqbal, Z.; Khayrullin, I. I.; Ralchenko, V. G.

    1998-03-01

    We demonstrate a new method for the formation of photonic bandgap crystals that operate at optical wavelengths. This method involves the templating of a self-assempled SiO2 lattice with diamond, graphite, or amorphous forms of carbon, followed by the removal of the original SiO2 lattice matrix by chemical means. Such carbon opal replicas are the "air type" of photonic crystal (where air replaces silica spheres) that are most favourable for photonic bandgap formation. Surprisingly, the structure of the original opal lattice having a typical cubic lattice dimension of 250 nm) is reliably replicated down to the nanometer scale using either a diamond, graphite, or amorphous carbon templated material. The optical properties of these photonic bandgap crystals are reported and compared with both theory and experimental results on other types of opal-derived lattices that we have investigated. The graphitic reverse opal is the first example of a network type metallic photonic crystal for the optical domain, for which a large photonic bandgap have been predicted.

  3. Impurity effects on the band structure of one-dimensional photonic crystals: Experiment and theory

    CERN Document Server

    Luna-Acosta, G A; Kuhl, U; Stoeckmann, H -J

    2007-01-01

    We study the effects of single impurities on the transmission in microwave realizations of the photonic Kronig-Penney model, consisting of arrays of Teflon pieces alternating with air spacings in a microwave guide. As only the first propagating mode is considered, the system is essentially one dimensional obeying the Helmholtz equation. We derive analytical closed form expressions from which the band structure, frequency of defect modes, and band profiles can be determined. These agree very well with experimental data for all types of single defects considered (e. g. interstitial, substitutional) and shows that our experimental set-up serves to explore some of the phenomena occurring in more sophisticated experiments. Conversely, based on the understanding provided by our formulas, information about the unknown impurity can be determined by simply observing certain features in the experimental data for the transmission. Further, our results are directly applicable to the closely related quantum 1D Kronig-Penn...

  4. Impurity effects on the band structure of one-dimensional photonic crystals: experiment and theory

    Energy Technology Data Exchange (ETDEWEB)

    Luna-Acosta, G A [Instituto de Fisica, BUAP Apartado Postal J-48, 72570 Puebla (Mexico); Schanze, H; Kuhl, U; Stoeckmann, H-J [Fachbereich Physik der Philipps-Universitaet Marburg, Renthof 5, D-35032 (Germany)], E-mail: gluna@sirio.ifuap.buap.mx

    2008-04-15

    We study the effects of single impurities on the transmission in microwave realizations of the photonic Kronig-Penney model, consisting of arrays of Teflon pieces alternating with air spacings in a microwave guide. As only the first propagating mode is considered, the system is essentially one-dimensional (1D) obeying the Helmholtz equation. We derive analytical closed form expressions from which the band structure, frequency of defect modes and band profiles can be determined. These agree very well with experimental data for all types of single defects considered (e.g. interstitial and substitutional) and show that our experimental set-up serves to explore some of the phenomena occurring in more sophisticated experiments. Conversely, based on the understanding provided by our formulae, information about the unknown impurity can be determined by simply observing certain features in the experimental data for the transmission. Further, our results are directly applicable to the closely related quantum 1D Kronig-Penney model.

  5. Improvement of band selectivity of electromagnetic crystals

    Directory of Open Access Journals (Sweden)

    Nazarko A. I.

    2009-11-01

    Full Text Available The estimation of crystal-like structures band selectivity is considered. Methods of increasing of electromagnetic crystal’s selectivity are proposed. The experimental and theoretical characteristics illustrating possibility of substantial improvement of spectral properties of such structures are presented.

  6. Investigation of the effect of noncircular scatterers on the band structure of anisotropic photonic crystal slabs.

    Science.gov (United States)

    Fathollahi Khalkhali, T; Rezaei, B; Soltani Vala, A; Kalafi, M

    2013-06-01

    Using the supercell approach based on the plane wave expansion method, we analyze the photonic bandgap (PBG) of square and triangular photonic crystal slabs composed of air holes in an anisotropic tellurium background with SiO(2) as cladding material. Two shapes (square and hexagonal) are considered for air holes. We discuss the maximization of the full PBG width as a function of noncircular air hole parameters, their orientation, and also slab thickness. The numerical results show that both structures represent a full PBG with noticeable width, which can be helpful for designing optical devices.

  7. Synthesis,Crystal and Band Structures,and Optical Properties of Mercury Pnictide Halide Hg19As10Br18

    Institute of Scientific and Technical Information of China (English)

    ZOU Jian-Ping; ZHANG Long-Zhu; ZENG Gui-Sheng; LUO Xu-Biao; PENG Qiang

    2011-01-01

    A mercury pnictide halide semiconductor Hg19As10Br18(1) has been prepared by the solid-state reaction and structurally characterized by single-crystal X-ray diffraction analysis.Compound 1 crystallizes in triclinic,space group P with a = 11.262(4),b = 11.352(4),c = 12.309(5) ,α = 105.724(2),β = 105.788(4),γ = 109.0780(10)° and V = 1314.3(8) 3.The structure of 1 is composed of parallel perovskite-like layers bridged by the linearly coordinated Br atoms to form a three-dimensional framework.The optical properties were investigated in terms of the diffuse reflectance spectrum.The electronic band structure along with density of states(DOS) calculated by DFT method indicates that compound 1 is a semiconductor with an indirect band gap,and that the optical absorption is mainly originated from the charge transitions from Br-4p and As-4p to the Hg-6s states.

  8. Band structure of magneto-metallo-dielectric photonic crystals with hybrid one- and two-dimensional periodicity

    Energy Technology Data Exchange (ETDEWEB)

    Reyes-Ayona, E. [Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, Apartado Postal J-48, Puebla 72570 (Mexico); Instituto Nacional de Astrofisica Optica y Electronica, Apartado Postal 51, Puebla 72000 (Mexico); Halevi, P. [Instituto Nacional de Astrofisica Optica y Electronica, Apartado Postal 51, Puebla 72000 (Mexico)

    2012-06-15

    We calculate the band structure of a magneto-metallo-dielectric photonic crystal (PC) with hybrid one- and two-dimensional periodicity. Namely, the permittivity (permeability) is periodic in a plane (single direction). The metallic and magnetic properties are described, respectively, by means of the Drude model and a specific permeability model for Barium-M ferrite. Because of the dispersion of both the permeability and the permittivity, we obtain a non-standard eigenvalue problem which is possible to solve by means of a linearization technique. We found that the first band of this PC is very sensitive to the filling fraction of the magnetic component: by changing this fraction from 0.20 to 0.16 the slope - and effective index of refraction - changes from positive to negative. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. Excitonic spectra and band structure of CdGa{sub 2}Se{sub 4} birefractive crystals

    Energy Technology Data Exchange (ETDEWEB)

    Syrbu, N.N., E-mail: sirbunn@yahoo.com [Technical University of Moldova, 168 Stefan cel Mare Avenue, 2004 Chisinau, Republic of Moldova (Moldova, Republic of); Stamov, I.G. [T.G. Shevchenko State University of Pridnestrovie, 25 Oktyabrya Street 107, 3300 Tiraspol, Republic of Moldova (Moldova, Republic of); Parvan, V.I. [Technical University of Moldova, 168 Stefan cel Mare Avenue, 2004 Chisinau, Republic of Moldova (Moldova, Republic of); Zalamai, V.V. [Institute of Applied Physics, Academy of Sciences of Moldova, 5 Academy Street, 2028 Chisinau, Republic of Moldova (Moldova, Republic of); Tiginyanu, I.M. [Institute of Electronic Engineering and Nanotechnologies, Academy of Sciences of Moldova, 3/3 Academy Street, 2028 Chisinau, Republic of Moldova (Moldova, Republic of)

    2013-11-15

    We report on the intersection of spectral dependences of refractive indices n{sub o} and n{sub e} at the wavelengths 546 nm (λ{sub 0}) and 450 nm (λ{sub 01}) in CdGa{sub 2}Se{sub 4} single crystals. The value of difference Δn=n{sub e}−n{sub o} is equal to zero at the wavelengths involved. When placed between two crossed polarizers, the crystals of CdGa{sub 2}Se{sub 4} exhibit a transmission band at the wavelength of λ{sub 0}=546 nm (300 K). The ground and excited states of three excitonic series (A, B and C) were found out at 13 K in CdGa{sub 2}Se{sub 4} crystals, and other parameters of excitons and bands were determined. In the Γ point of Brillouin zone the effective mass of electrons m{sub c} is equal to 0.14m{sub 0}, and the effective masses of holes m{sub v2} and m{sub v3} are equal to 0.76m{sub 0} and 0.94m{sub 0}, respectively. The hole mass m{sub v1} depends upon the direction of wave vector k: at polarization E∥c, k∥a the mass m{sub v1}=1.15m{sub 0}, and at polarization E∥c, k∥b m{sub v1}=0.84m{sub 0}. The values of valence bands splitting in the center of Brillouin zone by the crystal field (Δ{sub cf}=49 meV) and spin–orbital interaction (Δ{sub so}=351 meV) were determined. The optical functions n, k, ε{sub 1} and ε{sub 2} in polarizations E⊥c and E∥c for the energy diapason from 3 to 6 eV were calculated from the reflectivity spectra by Kramers–Kronig analysis. The evidenced features are discussed on the basis of recent theoretical calculations of the band structure of CdGa{sub 2}Se{sub 4} crystals.

  10. Tailoring the spin waves band structure of 1D magnonic crystals consisting of L-shaped iron/permalloy nanowires

    Science.gov (United States)

    Gubbiotti, G.; Silvani, R.; Tacchi, S.; Madami, M.; Carlotti, G.; Yang, Z.; Adeyeye, A. O.; Kostylev, M.

    2017-03-01

    We have investigated both experimentally and numerically the magnonic band structure of arrays of closely spaced Fe/permalloy nanowires (NWs) with an L-shape cross-section using the Brillouin light scattering technique and GPU-based micromagnetic simulations. NWs consist of a 340 nm wide and 10 nm thick permalloy layer covered by a 170 nm wide Fe overlayer. The thickness of the latter was varied in the range from 0 to 10 nm in order to analyze its influence on the magnonic band structure. We found that both the frequency and the spatial profile of the most intense and dispersive mode, can be efficiently tuned by the presence of the thin Fe NW overlayer. In particular, by increasing the Fe thickness, one observes a substantial frequency increase, while the spatial profile of the mode narrows and moves to the permalloy NW portion not covered by Fe. In addition, the presence of the Fe overlayer causes a significant increase of the number of detected modes and a change of their intensity in the Brillouin spectra as a function of the Bloch wave number. These results show that it is possible to engineer the band structure of magnonic crystals consisting of bi-layered, L-shaped, NWs by a careful control of the overlayer thickness.

  11. Synthesis and Crystal and Band Structures of YbCu_6In_6 with 3D Framework

    Institute of Scientific and Technical Information of China (English)

    LEI Xiao-Wu; YUE Cheng-Yang

    2012-01-01

    A new intermetallic compound,YbCu6In6,has been synthesized by solid-state reaction of the corresponding pure elements in a welded tantalum tube at high temperature.Its crystal structure was established by single-crystal X-ray diffraction.YbCu6In6 crystallizes in tetragonal space group I4/mmm with a = 9.2283(5),c = 5.4015(4),V = 460.00(5) 3,Z = 2,Mr = 1243.20,Dc = 8.976 g/cm3,μ = 38.243 mm-1,F(000) = 1076,and the final R = 0.0258 and wR = 0.0602 for 173 observed reflections with I 〉 2σ(I).The structure of YbCu6In6 belongs to the ThMn12 type.It is isostructural with RECu6In6(RE = Y,Ce,Pr,Nd,Gd,Tb,Dy),containing one-dimensional(1D) [Cu10In6] cluster chain along the c axis,which is interconnected via sharing the Cu(1) atoms to form a three-dimensional(3D) [Cu6In6] framework with Yb atoms encapsulated in the 1D tunnels along the c axis.Band structure calculations based on Density Functional Theory(DFT) method indicate that YbCu6In6 is metallic.

  12. Band structure of semiconductors

    CERN Document Server

    Tsidilkovski, I M

    2013-01-01

    Band Structure of Semiconductors provides a review of the theoretical and experimental methods of investigating band structure and an analysis of the results of the developments in this field. The book presents the problems, methods, and applications in the study of band structure. Topics on the computational methods of band structure; band structures of important semiconducting materials; behavior of an electron in a perturbed periodic field; effective masses and g-factors for the most commonly encountered band structures; and the treatment of cyclotron resonance, Shubnikov-de Haas oscillatio

  13. Crystal structure and band gap determination of HfO2 thin films

    NARCIS (Netherlands)

    Cheynet, M.C.; Pokrant, S.; Tichelaar, F.D.; Rouvière, J.L.

    2007-01-01

    Valence electron energy loss spectroscopy (VEELS) and high resolution transmission electron microscopy (HRTEM) are performed on three different HfO2 thin films grown on Si (001) by chemical vapor deposition (CVD) or atomic layer deposition (ALD). For each sample the band gap (Eg) is determined by

  14. Excitonic spectra and energy band structure of ZnAl2Se4 crystals

    Science.gov (United States)

    Syrbu, N. N.; Zalamai, V. V.; Tiron, A. V.; Tiginyanu, I. M.

    2015-11-01

    Absorption, reflection and wavelength modulated reflection spectra were investigated in ZnAl2Se4 crystals. The energy positions of ground and excited states for three excitonic series (A, B and C) were determined. The main parameters of excitons and more precise values of energy intervals V1(Γ7)-C1(Γ6), V2(Γ6)-C1(Γ6), and V3(Γ7)-C1(Γ6) were estimated. Values of splitting due to crystal field and spin-orbital interaction were calculated. Effective masses of electrons (mC1∗) and holes (mV1∗, mV2∗, mV3∗) were estimated. Reflection spectra contours in excitonic region were calculated using dispersion equations. Optical functions for E > Eg from measured reflection spectra were assigned on the base of Kramers-Kronig relations.

  15. MORPHOLOGY EVOLUTION IN PTFE AS A FUNCTION OF MELT TIME AND TEMPERATURE Ⅰ. HIGH MOLECULAR WEIGHT SINGLE- AND MULTI-MOLECULE FOLDED CHAIN SINGLE CRYSTALS AND BAND STRUCTURES

    Institute of Scientific and Technical Information of China (English)

    J.Yang; K.L.Petersen; R.A.Williams; P.H.Geil; T.C.Long; P.Xu

    2005-01-01

    The effect of sintering dispersed dispersion and nano-emulsion particles of high molecular weight polytetrafluoroethylene (PTFE) on a substrate as a function of "melt" time and temperature is described. Folded chain single crystals parallel to the substrate and as ribbons on-edge (with double striations), as well as bands, are produced for longer sintering times; particle merger and diffusion of individual molecules, crystallizing as folded chain, single (or few) molecule,single crystals when "trapped" on the substrate by cooling occur for shorter sintering times. It is suggested the observed structures develop with sintering time, in a mesomorphic melt. The structure of the nascent particles is also discussed.

  16. Omnidirectional photonic band gap enlarged by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Haifeng [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Nanjing Artillery Academy, Nanjing 211132 (China); Liu Shaobin [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); State Key Laboratory of Millimeter Waves of Southeast University, Nanjing Jiangsu 210096 (China); Kong Xiangkun; Bian Borui; Dai Yi [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)

    2012-11-15

    In this paper, an omnidirectional photonic band gap realized by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure, which is composed of homogeneous unmagnetized plasma and two kinds of isotropic dielectric, is theoretically studied by the transfer matrix method. It has been shown that such an omnidirectional photonic band gap originates from Bragg gap in contrast to zero-n gap or single negative (negative permittivity or negative permeability) gap, and it is insensitive to the incidence angle and the polarization of electromagnetic wave. From the numerical results, the frequency range and central frequency of omnidirectional photonic band gap can be tuned by the thickness and density of the plasma but cease to change with increasing Fibonacci order. The bandwidth of omnidirectional photonic band gap can be notably enlarged. Moreover, the plasma collision frequency has no effect on the bandwidth of omnidirectional photonic band gap. It is shown that such new structure Fibonacci quasiperiodic one-dimensional ternary plasma photonic crystals have a superior feature in the enhancement of frequency range of omnidirectional photonic band gap compared with the conventional ternary and conventional Fibonacci quasiperiodic ternary plasma photonic crystals.

  17. Tunability of band structures in a two-dimensional magnetostrictive phononic crystal plate with stress and magnetic loadings

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Shunzu; Shi, Yang [Key Laboratory of Mechanics on Disaster and Environment in Western China attached to the Ministry of Education of China, Lanzhou University, Lanzhou, Gansu 730000 (China); Department of Mechanics and Engineering Sciences, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China); Gao, Yuanwen, E-mail: ywgao@lzu.edu.cn [Key Laboratory of Mechanics on Disaster and Environment in Western China attached to the Ministry of Education of China, Lanzhou University, Lanzhou, Gansu 730000 (China); Department of Mechanics and Engineering Sciences, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China)

    2017-03-26

    Considering the magneto-mechanical coupling of magnetostrictive material, the tunability of in-plane wave propagation in two-dimensional Terfenol-D/epoxy phononic crystal (PC) plate is investigated theoretically by the plane wave expansion method. Two Schemes, i.e. magnetic field is rotated in x–y plane and x–z plane, are studied, respectively. The effects of amplitude and direction of magnetic field, pre-stress and geometric parameters are discussed. For Scheme-I, band gap reaches the maximum at an optimal angle 45° of magnetic field. However, the optimal angle is 0° for Scheme-II, because band gap decreases monotonically until disappears with the increasing angle. For both cases, higher-order band gaps generate and become stronger as magnetic field amplitude increases, while increasing compressive pre-stress has the opposite effect. Meanwhile, filling fraction plays a key role in controlling band gaps. These results provide possibility for intelligent regulation and optimal design of PC plates. - Highlights: • The in-plane wave propagation in phononic crystal thin plate is tuned theoretically. • Magnetostrictive material is introduced in the study. • The effects of magnetic field and pre-stress are considered. • The variations of band gaps with external stimuli are discussed.

  18. Theoretical analysis of the crystal structure, band-gap energy, polarization, and piezoelectric properties of ZnO-BeO solid solutions

    Science.gov (United States)

    Dong, L.; Alpay, S. P.

    2011-07-01

    The electrical properties, the spontaneous polarization, and the piezoelectric response of ZnO can be tailored by alloying ZnO with BeO for applications such as electrodes in flat panel displays and solar cells, blue and ultraviolet (UV) light emitting devices, and highly sensitive UV detectors. We present here the results of a study that employs density-functional theory to analyze the crystal structure, the band structure, spontaneous polarization, and piezoelectric properties of Zn1-xBexO solid solutions. Our findings indicate that Zn1-xBexO alloys may have a different crystal structure than the end components ZnO and BeO that crystallize in the prototypical wurtzite structure (P63mc). It is shown that orthorhombic lattices with Pmn21, Pna21, or P21 structures may have lower formation energies than the wurtzite lattice at a given Be composition. The band-gap energies of Zn1-xBexO in the wurtzite and the orthorhombic structures are nearly identical and the bowing of the band-gap energy increases with increasing Be concentration. The spontaneous polarization of Zn1-xBexO in the orthorhombic lattice is markedly larger compared to the wurtzite structure while the piezoelectric polarization in the wurtzite and orthorhombic structures varies linearly with the Be concentration.

  19. Effects of Side-Chain and Electron Exchange Correlation on the Band Structure of Perylene Diimide Liquid Crystals: A Density Functional Study

    Energy Technology Data Exchange (ETDEWEB)

    Arantes, J. T.; Lima, M. P.; Fazzio, A.; Xiang, H.; Wei, S. H.; Dalpian, G. M.

    2009-04-01

    The structural and electronic properties of perylene diimide liquid crystal PPEEB are studied using ab initio methods based on the density functional theory (DFT). Using available experimental crystallographic data as a guide, we propose a detailed structural model for the packing of solid PPEEB. We find that due to the localized nature of the band edge wave function, theoretical approaches beyond the standard method, such as hybrid functional (PBE0), are required to correctly characterize the band structure of this material. Moreover, unlike previous assumptions, we observe the formation of hydrogen bonds between the side chains of different molecules, which leads to a dispersion of the energy levels. This result indicates that the side chains of the molecular crystal not only are responsible for its structural conformation but also can be used for tuning the electronic and optical properties of these materials.

  20. 不同背景介质下金属Cu光子晶体带隙%The band structures of metallic photonic crystals filled with different mediums

    Institute of Scientific and Technical Information of China (English)

    杨波; 梁静秋; 梁中翥; 王维彪

    2012-01-01

    提出了一种利用全反射抑制二维光子晶体表面电磁波泄漏的方法,并计算了不同背景介质下的二维金属Cu光子晶体的带隙结构,得到了带隙结构与填充率间的关系曲线.计算方法采用时域有限差分,金属型光子晶体由Cu柱构成.分别计算了以空气为背景介质和以PMMA为背景介质的正方晶格金属型光子晶体的带隙结构.研究结果表明:以PMMA为背景介质的正方晶格金属型光子晶体与以空气为背景介质相比,第一带隙更窄,第二带隙中心频率更低,且在填充率大于0.70时将会出现第三带隙.这对进一步扩展这种光子晶体的应用具有良好的参考意义.%A method is proposed to inhibit the leakage of electromagnetic waves on the surface of 2D photonic crystals u-sing total internal reflection. The band structures of 2D metallic photonic crystals with different background mediums are analyzed. The band structures as a function of the filling factor are obtained via FDTD method. The metallic photonic crystals are composed of Cu columns. Two kinds of background media, air and PMMA, were selected in this study. The band structures of these two 2D square-lattice metallic photonic crystals were analyzed separately. The results indicate that the metallic photonic crystals filled with PMMA have a narrower first band gap and a lower second band gap than the metallic photonic crystals filled with air. A third band gap appears in the metallic photonic crystals with PMMA as the background medium when the filling factor reaches 0.70. This work provides a good reference for the application of photonic crystals.

  1. Photonic band gap of 2D complex lattice photonic crystal

    Institute of Scientific and Technical Information of China (English)

    GUAN Chun-ying; YUAN Li-bo

    2009-01-01

    It is of great significance to present a photonic crystal lattice structure with a wide photonic bandgap. A two-dimension complex lattice photonic crystal is proposed. The photonic crystal is composed of complex lattices with triangular structure, and each single cell is surrounded by six scatterers in an hexagon. The photonic band gaps are calculated based on the plane wave expansion (PWE) method. The results indicate that the photonic crystal has tunable large TM polarization band gap, and a gap-midgap ratio of up to 45.6%.

  2. Band gaps in bubble phononic crystals

    Directory of Open Access Journals (Sweden)

    V. Leroy

    2016-12-01

    Full Text Available We investigate the interaction between Bragg and hybridization effects on the band gap properties of bubble phononic crystals. These latter consist of air cavities periodically arranged in an elastomer matrix and are fabricated using soft-lithography techniques. Their transmission properties are affected by Bragg effects due to the periodicity of the structure as well as hybridization between the propagating mode of the embedding medium and bubble resonance. The hybridization gap survives disorder while the Bragg gap requires a periodic distribution of bubbles. The distance between two bubble layers can be tuned to make the two gaps overlap or to create a transmission peak in the hybridization gap.

  3. Band structure of a 2D photonic crystal based on ferrofluids of Co(1-x)Znx Fe2O4 nanoparticles under perpendicular applied magnetic field

    Science.gov (United States)

    Lopez, Javier; Gonzalez, Luz Esther; Quinonez, Mario; Porras, Nelson; Zambrano, Gustavo; Gomez, Maria Elena

    2014-03-01

    Using a ferrfluid of cobalt-zinc ferrite nanoparticles Co(1 - x)ZnxFe2O4 coated with oleic acid and suspended in ethanol, we have fabricated a 2D photonic crystal (PC) by the application of an external magnetic field perpendicular to the plane of the ferrofluid. The 2D PC is made by rods of nanoparticles organized in a hexagonal structure. By means of the plane-wave expansion method, we study its photonic band structure (PBS) which depends on the effective permittivity and on the area ratio of the liquid phase. Additionaly, taking into account the Maxwell-Garnett theory we calculated the effective permittivity of the rods. We have found that the effective refractive index of the ferrofluid increases with its magnetization. Using these results we calculate the band structure of the photonic crystal at different applied magnetic fields, finding that the increase of the applied magnetic field shifts the band structure to lower frequencies with the appearance of more band gaps. Departamento de Física, Universidad del Valle, A.A. 25360, Cali, Colombia

  4. Contrasting 1D tunnel-structured and 2D layered polymorphs of V2O5: relating crystal structure and bonding to band gaps and electronic structure.

    Science.gov (United States)

    Tolhurst, Thomas M; Leedahl, Brett; Andrews, Justin L; Marley, Peter M; Banerjee, Sarbajit; Moewes, Alexander

    2016-06-21

    New V2O5 polymorphs have risen to prominence as a result of their open framework structures, cation intercalation properties, tunable electronic structures, and wide range of applications. The application of these materials and the design of new, useful polymorphs requires understanding their defining structure-property relationships. We present a characterization of the band gap and electronic structure of nanowires of the novel ζ-phase and the orthorhombic α-phase of V2O5 using X-ray spectroscopy and density functional theory calculations. The band gap is found to decrease from 1.90 ± 0.20 eV in the α-phase to 1.50 ± 0.20 eV in the ζ-phase, accompanied by the loss of the α-phase's characteristic split-off dxy band in the ζ-phase. States of dxy origin continue to dominate the conduction band edge in the new polymorph but the inequivalence of the vanadium atoms and the increased local symmetry of [VO6] octahedra results in these states overlapping with the rest of the V 3d conduction band. ζ-V2O5 exhibits anisotropic conductivity along the b direction, defining a 1D tunnel, in contrast to α-V2O5 where the anisotropic conductivity is along the ab layers. We explain the structural origins of the differences in electronic properties that exist between the α- and ζ-phase.

  5. Photonic Crystal Laser Accelerator Structures

    Energy Technology Data Exchange (ETDEWEB)

    Cowan, Benjamin M

    2003-05-21

    Photonic crystals have great potential for use as laser-driven accelerator structures. A photonic crystal is a dielectric structure arranged in a periodic geometry. Like a crystalline solid with its electronic band structure, the modes of a photonic crystal lie in a set of allowed photonic bands. Similarly, it is possible for a photonic crystal to exhibit one or more photonic band gaps, with frequencies in the gap unable to propagate in the crystal. Thus photonic crystals can confine an optical mode in an all-dielectric structure, eliminating the need for metals and their characteristic losses at optical frequencies. We discuss several geometries of photonic crystal accelerator structures. Photonic crystal fibers (PCFs) are optical fibers which can confine a speed-of-light optical mode in vacuum. Planar structures, both two- and three-dimensional, can also confine such a mode, and have the additional advantage that they can be manufactured using common microfabrication techniques such as those used for integrated circuits. This allows for a variety of possible materials, so that dielectrics with desirable optical and radiation-hardness properties can be chosen. We discuss examples of simulated photonic crystal structures to demonstrate the scaling laws and trade-offs involved, and touch on potential fabrication processes.

  6. One-Dimensional Anisotropic Band Gap Structure

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The band gap structure of one-dimensional anisotropic photonic crystal has been studied by means of the transfer matrix formalism. From the analytic expressions and numeric calculations we see some general characteristics of the band gap structure of anisotropic photonic crystals, each band separates into two branches and the two branches react to polarization sensitively. In the practical case of oblique incidence, gaps move towards high frequency when the angle of incidence increases. Under some special conditions, the two branches become degenerate again.

  7. Preparation, crystal structures, experimental and theoretical electronic band structures of cobalt tellurides in the composition range CoTe{sub 1.3}-CoTe{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Muhler, M. [Institut fuer Technische Chemie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Bensch, W.; Schur, M. [Institut fuer Anorganische Chemie, Christian-Albrechts-Universitaet Kiel, Olshausenstrasse 40, D-24098 Kiel (Germany)

    1998-04-06

    Cobalt tellurides in the composition range CoTe{sub 1.3}-CoTe{sub 2} crystallize in a CdI{sub 2}-type structure with short intra- and interslab Te-Te contacts indicating a polymeric network with multiple Te-Te bonds explaining the very low c/a values of 1.38 to 1.41 of the hexagonal cells. Single-crystal x-ray investigations performed on CoTe{sub 2} confirm the marcasite-type structure in the centrosymmetric space group Pnnm. Experimental valence band spectra (UPS) confirm that the Co tellurides in the composition range CoTe{sub x} (1.3 < x < 2) are metals. The emission at the Fermi level E{sub F} decreases with the Te content and is due to Co 3d and Te 5p states. This assignment is supported by the results of the calculated density of states curve (DOS) which demonstrates that Te p states contribute about 50% in the CdI{sub 2}-type and about 35% in the marcasite-type structure. The Te d states contribute about 15% to the total Te contributions. This behaviour cannot be understood on the basis of a simple tight-binding description, ignoring d-valence states of Te. Core level spectra (XPS) suggest that all CoTe{sub x} samples are best described as intermetallic compounds. Small chemical shifts between the different samples are mainly due to the different Madelung contributions rather than to changes of the electron density located on the Co atoms. An oxidation number for Te <-1 in all CoTe{sub x} samples is deduced, in good agreement with the value of about -1.3 for the Te in CoTe{sub 2} that would be deduced from the relation between the Te-Te distances versus oxidation states of the anion in (Te{sub 2}){sup -11}, Te{sup -11}. The three-dimensional character of the Co tellurides deduced from the crystal structure is further confirmed by the calculated energy dispersion E(k). (author)

  8. MORPHOLOGY EVOLUTION IN PTFE AS A FUNCTION OF MELT TIME AND TEMPERATURE Ⅱ. LOW MOLECULAR WEIGHT FOLDED CHAIN SINGLE CRYSTALS AND BAND STRUCTURES

    Institute of Scientific and Technical Information of China (English)

    J. Yang; P.H. Geil; T. C. Long; P. Xu

    2005-01-01

    The effect of sintering dispersed and bulk, low molecular weight (Mn = 50,000 Da), nano-emulsion polytetrafluoroethylene (PTFE) particles near their melting point is described. With the nascent particles consisting of ca.75 nm diameter, hexagonal, single crystals, sintering at, e.g., 350℃, results, initially, in merger of neighboring particles,followed by individual molecular motion on the substrate and the formation of folded chain, lamellar single crystals and spherulites, and on-edge ribbons. It is suggested these structures develop, with time, in the mesomorphic "melt". Sintering of the bulk resin yields extended chain, band structures, as well as folded chain lamellae; end-surface to end-surface merger,possibly by end-to-end polymerization, occurs with increasing time.

  9. Absolute band gaps in two-dimensional graphite photonic crystal

    Institute of Scientific and Technical Information of China (English)

    Gaoxin Qiu(仇高新); Fanglei Lin(林芳蕾); Hua Wang(王华); Yongping Li(李永平)

    2003-01-01

    The off-plane propagation of electromagnetic (EM) waves in a two-dimensional (2D) graphite photoniccrystal structure was studied using transfer matrix method. Transmission spectra calculations indicatethat such a 2D structure has a common band gap from 0.202 to 0.2035 c/a for both H and E polarizationsand for all off-plane angles form 0° up to 90°. The presence of such an absolute band gap implies that 2Dgraphite photonic crystal, which is much easier and more feasible to fabricate, can exhibit some propertiesof a three-dimensional (3D) photonic crystal.

  10. Theoretical and Experimental Study of the Crystal Structures, Lattice Vibrations, and Band Structures of Monazite-Type PbCrO4, PbSeO4, SrCrO4, and SrSeO4.

    Science.gov (United States)

    Errandonea, Daniel; Muñoz, Alfonso; Rodríguez-Hernández, Placida; Proctor, John E; Sapiña, Fernando; Bettinelli, Marco

    2015-08-03

    The crystal structures, lattice vibrations, and electronic band structures of PbCrO4, PbSeO4, SrCrO4, and SrSeO4 were studied by ab initio calculations, Raman spectroscopy, X-ray diffraction, and optical-absorption measurements. Calculations properly describe the crystal structures of the four compounds, which are isomorphic to the monazite structure and were confirmed by X-ray diffraction. Information is also obtained on the Raman- and IR-active phonons, with all of the vibrational modes assigned. In addition, the band structures and electronic densities of states of the four compounds were determined. All are indirect-gap semiconductors. In particular, chromates are found to have band gaps smaller than 2.5 eV and selenates higher than 4.3 eV. In the chromates (selenates), the upper part of the valence band is dominated by O 2p states and the lower part of the conduction band is composed primarily of electronic states associated with the Cr 3d and O 2p (Se 4s and O 2p) states. Calculations also show that the band gap of PbCrO4 (PbSeO4) is smaller than the band gap of SrCrO4 (SrSeO4). This phenomenon is caused by Pb states, which, to some extent, also contribute to the top of the valence band and the bottom of the conduction band. The agreement between experiments and calculations is quite good; however, the band gaps are underestimated by calculations, with the exception of the bang gap of SrCrO4, for which theory and calculations agree. Calculations also provide predictions of the bulk modulus of the studied compounds.

  11. Band structure calculation of SH waves in nanoscale multilayered piezoelectric phononic crystals using radial basis function method with consideration of nonlocal interface effects.

    Science.gov (United States)

    Yan, Zhizhong; Wei, Chunqiu; Zhang, Chuanzeng

    2017-01-01

    In this paper, the radial basis function (RBF) collocation method based on the nonlocal Eringen piezoelectricity theory is developed to compute the band structures of nanoscale multilayered piezoelectric phononic crystals taking account of nonlocal interface effects. Detailed calculations are performed for anti-plane transverse waves propagating obliquely or vertically in the system. The correctness of the present method is verified by comparing the numerical results with those obtained by applying the transfer matrix method in the case of nonlocal perfect interfaces. The effects of nonlocal interface imperfections are considered by comparing with the nonlocal perfect interfaces. In addition, the influences of the piezoelectric constant, the nanoscale size, the impedance ratio and the incidence angle on the cut-off frequency and band structures are investigated and discussed in detail. Numerical results show that the nonlocal interface discontinuity has more obvious effect on the low-frequency band structures at the microscopic scale than at the macroscopic scale. Furthermore, at the macroscopic scale, the nonlocal interface imperfection has an obvious effect on the high frequency waves, but the effect on the low frequency waves is not obvious, and the nonlocal interface imperfection has no effect on the cut-off frequency at the microscopic scale. Copyright © 2016 Elsevier B.V. All rights reserved.

  12. Using coupling slabs to tailor surface-acoustic-wave band structures in phononic crystals consisting of pillars attached to elastic substrates

    Science.gov (United States)

    Zhang, Heng; Yu, SiYuan; Liu, FuKang; Wang, Zhen; Lu, MingHui; Hu, XiaoBo; Chen, YanFeng; Xu, XianGang

    2017-04-01

    The propagation of surface acoustic waves (SAWs) in two-dimensional phononic crystals (PnCs) with and without coupling-enhancement slabs was theoretically investigated using a three-dimensional finite element method. Different piezoelectric substrates, for example, lithium niobate (LiNbO3), gallium nitride (GaN), and aluminium nitride (AlN), were taken into account. Compared to the PnCs without coupling-enhancement slabs, the coupling between each pillar and its nearest neighbor was largely enhanced in the presence of slabs. The bandwidth of the first directional band gap increased markedly compared with its initial value for the PnCs without a slab (within square symmetry). In addition, with increasing thicknesses of the slabs bonded between neighboring pillars, the first directional band-gap and second directional band gap of the PnCs tend to merge. Therefore, the structure with coupling-enhancement slabs can be used as an excellent electrical band elimination filter for most electro-SAW devices, offering a new strategy to realize chip-scale applications in electroacoustic signal processing, optoacoustic modulation, and even SAW microfluidic devices.

  13. Using coupling slabs to tailor surface-acoustic-wave band structures in phononic crystals consisting of pillars attached to elastic substrates

    Science.gov (United States)

    Zhang, Heng; Yu, SiYuan; Liu, FuKang; Wang, Zhen; Lu, MingHui; Hu, XiaoBo; Chen, YanFeng; Xu, XianGang

    2017-04-01

    The propagation of surface acoustic waves (SAWs) in two-dimensional phononic crystals (PnCs) with and without coupling-enhancement slabs was theoretically investigated using a three-dimensional finite element method. Different piezoelectric substrates, for example, lithium niobate (LiNbO3), gallium nitride (GaN), and aluminium nitride (AlN), were taken into account. Compared to the PnCs without coupling-enhancement slabs, the coupling between each pillar and its nearest neighbor was largely enhanced in the presence of slabs. The bandwidth of the first directional band gap increased markedly compared with its initial value for the PnCs without a slab (within square symmetry). In addition, with increasing thicknesses of the slabs bonded between neighboring pillars, the first directional band-gap and second directional band gap of the PnCs tend to merge. Therefore, the structure with coupling-enhancement slabs can be used as an excellent electrical band elimination filter for most electro-SAW devices, offering a new strategy to realize chip-scale applications in electroacoustic signal processing, optoacoustic modulation, and even SAW microfluidic devices.

  14. Analyzing the photonic band gaps in two-dimensional plasma photonic crystals with fractal Sierpinski gasket structure based on the Monte Carlo method

    Directory of Open Access Journals (Sweden)

    Hai-Feng Zhang

    2016-08-01

    Full Text Available In this paper, the properties of photonic band gaps (PBGs in two types of two-dimensional plasma-dielectric photonic crystals (2D PPCs under a transverse-magnetic (TM wave are theoretically investigated by a modified plane wave expansion (PWE method where Monte Carlo method is introduced. The proposed PWE method can be used to calculate the band structures of 2D PPCs which possess arbitrary-shaped filler and any lattice. The efficiency and convergence of the present method are discussed by a numerical example. The configuration of 2D PPCs is the square lattices with fractal Sierpinski gasket structure whose constituents are homogeneous and isotropic. The type-1 PPCs is filled with the dielectric cylinders in the plasma background, while its complementary structure is called type-2 PPCs, in which plasma cylinders behave as the fillers in the dielectric background. The calculated results reveal that the enough accuracy and good convergence can be obtained, if the number of random sampling points of Monte Carlo method is large enough. The band structures of two types of PPCs with different fractal orders of Sierpinski gasket structure also are theoretically computed for a comparison. It is demonstrate that the PBGs in higher frequency region are more easily produced in the type-1 PPCs rather than in the type-2 PPCs. Sierpinski gasket structure introduced in the 2D PPCs leads to a larger cutoff frequency, enhances and induces more PBGs in high frequency region. The effects of configurational parameters of two types of PPCs on the PBGs are also investigated in detail. The results show that the PBGs of the PPCs can be easily manipulated by tuning those parameters. The present type-1 PPCs are more suitable to design the tunable compacted devices.

  15. Analyzing the photonic band gaps in two-dimensional plasma photonic crystals with fractal Sierpinski gasket structure based on the Monte Carlo method

    Science.gov (United States)

    Zhang, Hai-Feng; Liu, Shao-Bin

    2016-08-01

    In this paper, the properties of photonic band gaps (PBGs) in two types of two-dimensional plasma-dielectric photonic crystals (2D PPCs) under a transverse-magnetic (TM) wave are theoretically investigated by a modified plane wave expansion (PWE) method where Monte Carlo method is introduced. The proposed PWE method can be used to calculate the band structures of 2D PPCs which possess arbitrary-shaped filler and any lattice. The efficiency and convergence of the present method are discussed by a numerical example. The configuration of 2D PPCs is the square lattices with fractal Sierpinski gasket structure whose constituents are homogeneous and isotropic. The type-1 PPCs is filled with the dielectric cylinders in the plasma background, while its complementary structure is called type-2 PPCs, in which plasma cylinders behave as the fillers in the dielectric background. The calculated results reveal that the enough accuracy and good convergence can be obtained, if the number of random sampling points of Monte Carlo method is large enough. The band structures of two types of PPCs with different fractal orders of Sierpinski gasket structure also are theoretically computed for a comparison. It is demonstrate that the PBGs in higher frequency region are more easily produced in the type-1 PPCs rather than in the type-2 PPCs. Sierpinski gasket structure introduced in the 2D PPCs leads to a larger cutoff frequency, enhances and induces more PBGs in high frequency region. The effects of configurational parameters of two types of PPCs on the PBGs are also investigated in detail. The results show that the PBGs of the PPCs can be easily manipulated by tuning those parameters. The present type-1 PPCs are more suitable to design the tunable compacted devices.

  16. Crystal structure and band structure calculations of Pb1/3TaS2 and Sn1/3NbS2

    NARCIS (Netherlands)

    Fang, C.M; Wiegers, G.A; Meetsma, A.; de Groot, R.A.; Haas, C

    The crystal structures of Pb1/3TaS2 and Sn1/3NbS2 were determined using single-crystal X-ray diffraction. The space group is P6(3)22 and the unit cell dimensions are: a = 5.759(1), c = 14.813(1)Angstrom and a = 5.778(1), c = 14.394(1)Angstrom, for the Pb and Sn compounds, respectively. The

  17. Crystal structure and prediction.

    Science.gov (United States)

    Thakur, Tejender S; Dubey, Ritesh; Desiraju, Gautam R

    2015-04-01

    The notion of structure is central to the subject of chemistry. This review traces the development of the idea of crystal structure since the time when a crystal structure could be determined from a three-dimensional diffraction pattern and assesses the feasibility of computationally predicting an unknown crystal structure of a given molecule. Crystal structure prediction is of considerable fundamental and applied importance, and its successful execution is by no means a solved problem. The ease of crystal structure determination today has resulted in the availability of large numbers of crystal structures of higher-energy polymorphs and pseudopolymorphs. These structural libraries lead to the concept of a crystal structure landscape. A crystal structure of a compound may accordingly be taken as a data point in such a landscape.

  18. A study of photoemission using CW and pulsed UV light sources to probe surface slip band structure evolution of single crystal aluminium

    Science.gov (United States)

    Cai, Mingdong; Langford, Stephen; Dickinson, J. Thomas

    2008-03-01

    We report measurements of photoelectron emission from high-purity single crystal aluminum during uniaxial tensile deformation. A 248 nm pulsed excimer laser was used as a light source and the generated photoemission data was compared with that using a filtered mercury lamp. Time-of-flight curves of photoelectrons generated by pulsed excimer laser irradiation were observed showing a two peaked structure. These two peaks correspond to photoelectrons of two energy levels. It was also found that real time total photoelectron charge increases linearly with strain; and the increment is heterogeneous. Photoemission using low-energy photons is sensitive to changes in surface morphology accompanying deformation, including slip line and band formation. The discontinuity in photoelectron intensity and the heterogeneous surface slip band structure prove the production of fresh surface area is not continuous, which is predicted by a recent dislocation dynamics theory based on percolation process. Except for differences in instrumentation and data analysis, the photoemission data from a filtered mercury lamp and from the excimer laser are comparable. Current studies extend the application of the excimer laser into surface dynamics analysis.

  19. Bi-directional evolutionary optimization for photonic band gap structures

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Fei [Centre for Innovative Structures and Materials, School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476, Melbourne, VIC 3001 (Australia); School of Civil Engineering, Central South University, Changsha 410075 (China); Huang, Xiaodong, E-mail: huang.xiaodong@rmit.edu.au [Centre for Innovative Structures and Materials, School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476, Melbourne, VIC 3001 (Australia); Key Laboratory of Advanced Technology for Vehicle Body Design & Manufacture, Hunan University, Changsha, 410082 (China); Jia, Baohua [Centre for Micro-Photonics, Faculty of Engineering & Industrial Science, Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122 (Australia)

    2015-12-01

    Toward an efficient and easy-implement optimization for photonic band gap structures, this paper extends the bi-directional evolutionary structural optimization (BESO) method for maximizing photonic band gaps. Photonic crystals are assumed to be periodically composed of two dielectric materials with the different permittivity. Based on the finite element analysis and sensitivity analysis, BESO starts from a simple initial design without any band gap and gradually re-distributes dielectric materials within the unit cell so that the resulting photonic crystal possesses a maximum band gap between two specified adjacent bands. Numerical examples demonstrated the proposed optimization algorithm can successfully obtain the band gaps from the first to the tenth band for both transverse magnetic and electric polarizations. Some optimized photonic crystals exhibit novel patterns markedly different from traditional designs of photonic crystals.

  20. Soft phononic crystals with deformation-independent band gaps

    Science.gov (United States)

    2017-01-01

    Soft phononic crystals have the advantages over their stiff counterparts of being flexible and reconfigurable. Normally, the band gaps of soft phononic crystals will be modified after deformation due to both geometric and constitutive nonlinearity. Indeed these are important properties that can be exploited to tune the dynamic properties of the material. However, in some instances, it may be that one wishes to deform the medium while retaining the band gap structure. A special class of soft phononic crystals is described here with band gaps that are independent or almost-independent of the imposed mechanical deformation, which enables the design of phononic crystals with robust performance. This remarkable behaviour originates from transformation elasticity theory, which leaves the wave equation and the eigenfrequencies invariant after deformation. The necessary condition to achieve such a property is that the Lagrangian elasticity tensor of the hyperelastic material should be constant, i.e. independent of deformation. It is demonstrated that incompressible neo-Hookean materials exhibit such a unique property. Semilinear materials also possess this property under special loading conditions. Phononic crystals composed of these two materials are studied theoretically and the predictions of invariance, or the manner in which the response deviates from invariance, are confirmed via numerical simulation. PMID:28484331

  1. Microstrip microwave band gap structures

    Indian Academy of Sciences (India)

    V Subramanian

    2008-04-01

    Microwave band gap structures exhibit certain stop band characteristics based on the periodicity, impedance contrast and effective refractive index contrast. These structures though formed in one-, two- and three-dimensional periodicity, are huge in size. In this paper, microstrip-based microwave band gap structures are formed by removing the substrate material in a periodic manner. This paper also demonstrates that these structures can serve as a non-destructive characterization tool for materials, a duplexor and frequency selective coupler. The paper presents both experimental results and theoretical simulation based on a commercially available finite element methodology for comparison.

  2. Crystal symmetry and pressure effects on the valence band structure of γ -InSe and ɛ -GaSe: Transport measurements and electronic structure calculations

    Science.gov (United States)

    Errandonea, D.; Segura, A.; Manjón, F. J.; Chevy, A.; Machado, E.; Tobias, G.; Ordejón, P.; Canadell, E.

    2005-03-01

    This paper reports on Hall effect and resistivity measurements under high pressure up to 3-4 GPa in p -type γ -indium selenide (InSe) (doped with As, Cd, or Zn) and ɛ -gallium selenide (GaSe) (doped with N or Sn). The pressure behavior of the hole concentration and mobility exhibits dramatic differences between the two layered compounds. While the hole concentration and mobility increase moderately and monotonously in ɛ -GaSe, a large increase of the hole concentration near 0.8 GPa and a large continuous increase of the hole mobility, which doubled its ambient pressure value by 3.2 GPa, is observed in γ -InSe. Electronic structure calculations show that the different pressure behavior of hole transport parameters can be accounted for by the evolution of the valence-band maximum in each material under compression. While the shape of the valence band maximum is virtually pressure-insensitive in ɛ -GaSe, it changes dramatically in γ -InSe, with the emergence of a ring-shaped subsidiary maximum that becomes the absolute valence-band maximum as pressure increases. These differences are shown to be a consequence of the presence or absence of a symmetry element (mirror plane perpendicular to the anisotropy axis) in the point group of each polytype ( D3h for the ɛ -polytype and C3v for the γ -polytype), resulting in different selection rules that affect the k⃗•p⃗ interaction between valence bands.

  3. Band gap tunability of magneto-elastic phononic crystal

    Science.gov (United States)

    Bou Matar, O.; Robillard, J. F.; Vasseur, J. O.; Hladky-Hennion, A.-C.; Deymier, P. A.; Pernod, P.; Preobrazhensky, V.

    2012-03-01

    The possibility of control and tuning of the band structures of phononic crystals offered by the introduction of an active magnetoelastic material and the application of an external magnetic field is studied. Two means to obtain large elastic properties variations in magnetoelastic material are considered: Giant magnetostriction and spin reorientation transition effects. A plane wave expansion method is used to calculate the band structures. The magnetoelastic coupling is taken into account through the consideration of an equivalent piezomagnetic material model with elastic, piezomagnetic, and magnetic permeability tensors varying as a function of the amplitude and orientation of the applied magnetic field. Results of contactless tunability of the absolute bandgap are presented for a two-dimensional phononic crystal constituted of Terfenol-D square rod embedded in an epoxy matrix.

  4. Evanescent waves and deaf bands in sonic crystals

    Directory of Open Access Journals (Sweden)

    V. Romero-García

    2011-12-01

    Full Text Available The properties of sonic crystals (SC are theoretically investigated in this work by solving the inverse problem k(ω using the extended plane wave expansion (EPWE. The solution of the resulting eigenvalue problem gives the complex band structure which takes into account both the propagating and the evanescent modes. In this work we show the complete mathematical formulation of the EPWE for SC and the supercell approximation for its use in both a complete SC and a SC with defects. As an example we show a novel interpretation of the deaf bands in a complete SC in good agreement with multiple scattering simulations.

  5. Evanescent waves and deaf bands in sonic crystals

    Science.gov (United States)

    Romero-García, V.; Garcia-Raffi, L. M.; Sánchez-Pérez, J. V.

    2011-12-01

    The properties of sonic crystals (SC) are theoretically investigated in this work by solving the inverse problem k(ω) using the extended plane wave expansion (EPWE). The solution of the resulting eigenvalue problem gives the complex band structure which takes into account both the propagating and the evanescent modes. In this work we show the complete mathematical formulation of the EPWE for SC and the supercell approximation for its use in both a complete SC and a SC with defects. As an example we show a novel interpretation of the deaf bands in a complete SC in good agreement with multiple scattering simulations.

  6. Topological Design of Cellular Phononic Band Gap Crystals

    Directory of Open Access Journals (Sweden)

    Yang Fan Li

    2016-03-01

    Full Text Available This paper systematically investigated the topological design of cellular phononic crystals with a maximized gap size between two adjacent bands. Considering that the obtained structures may sustain a certain amount of static loadings, it is desirable to ensure the optimized designs to have a relatively high stiffness. To tackle this issue, we conducted a multiple objective optimization to maximize band gap size and bulk or shear modulus simultaneously with a prescribed volume fraction of solid material so that the resulting structures can be lightweight, as well. In particular, we first conducted the finite element analysis of the phononic band gap crystals and then adapted a very efficient optimization procedure to resolve this problem based on bi-directional evolutionary structure optimization (BESO algorithm in conjunction with the homogenization method. A number of optimization results for maximizing band gaps with bulk and shear modulus constraints are presented for out-of-plane and in-plane modes. Numerical results showed that the optimized structures are similar to those obtained for composite case, except that additional slim connections are added in the cellular case to support the propagation of shear wave modes and meanwhile to satisfy the prescribed bulk or shear modulus constraints.

  7. Band transport model for discotic liquid crystals

    Science.gov (United States)

    Lever, L. J.; Kelsall, R. W.; Bushby, R. J.

    2005-07-01

    A theoretical model is presented for charge transport in discotic liquid crystals in which a charge is delocalized over more than one lattice site. As such, charge transport is via a banded conduction process in a narrow bandwidth system and takes place over coherent lengths of a few molecules. The coherent lengths are disrupted by the geometrical disorder of the system and are treated as being terminated by quantum tunnel barriers. The transmission probabilities at these barriers have been calculated as a function of the charge carrier energy. Phononic interactions are also considered and the charge carrier scattering rates are calculated for intermolecular and intramolecular vibrations. The results of the calculations have been used to develop a Monte Carlo simulation of the charge transport model. Simulated data are presented and used to discuss the nature of the tunnel barriers required to reproduce experimental data. We find that the model successfully reproduces experimental time of flight data including temperature dependence.

  8. Complete photonic band gaps and tunable self-collimation in the two-dimensional plasma photonic crystals with a new structure

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Hai-Feng, E-mail: hanlor@163.com [Key Laboratory of Radar Imaging and Microwave Photonics (Nanjing University of Aeronautics and Astronautics), Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Nanjing Artillery Academy, Nanjing 211132 (China); Ding, Guo-Wen; Li, Hai-Ming; Liu, Shao-Bin [Key Laboratory of Radar Imaging and Microwave Photonics (Nanjing University of Aeronautics and Astronautics), Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)

    2015-02-15

    In this paper, the properties of complete photonic band gaps (CPBGs) and tunable self-collimation in two-dimensional plasma photonic crystals (2D PPCs) with a new structure in square lattices, whose dielectric fillers (GaAs) are inserted into homogeneous and nomagnetized plasma background are theoretically investigated by a modified plane wave expansion (PWE) method with a novel technique. The novel PWE method can be utilized to compute the dispersion curves of 2D PPCs with arbitrary-shaped cross section in any lattices. As a comparison, CPBGs of PPCs for four different configurations are numerically calculated. The computed results show that the proposed design has the advantages of achieving the larger CPBGs compared to the other three configurations. The influences of geometric parameters of filled unit cell and plasma frequency on the properties of CPBGs are studied in detail. The calculated results demonstrate that CPBGs of the proposed 2D PPCs can be easily engineered by changing those parameters, and the larger CPBGs also can be obtained by optimization. The self-collimation in such 2D PPCs also is discussed in theory under TM wave. The theoretical simulations reveal that the self-collimation phenomena can be found in the TM bands, and both the frequency range of self-collimation and the equifrequency surface contours can be tuned by the parameters as mentioned above. It means that the frequency range and direction of electromagnetic wave can be manipulated by designing, as it propagates in the proposed PPCs without diffraction. Those results can hold promise for designing the tunable applications based on the proposed PPCs.

  9. Tunable Photonic Band Gaps In Photonic Crystal Fibers Filled With a Cholesteric Liquid Crystal

    Institute of Scientific and Technical Information of China (English)

    Thomas; Tanggaard; Larsen; David; Sparre; Hermann; Anders; Bjarklev

    2003-01-01

    A photonic crystal fiber has been filled with a cholesteric liquid crystal. A temperature sensitive photonic band gap effect was observed, which was especially pronounced around the liquid crystal phase transition temperature.

  10. Physical properties and band structure of crystals (3HgTe1–x(Al2Te3x, doped with manganese

    Directory of Open Access Journals (Sweden)

    Maryanchuk P. D.

    2014-06-01

    Full Text Available This paper presents the results of the analysis of magnetic, optical, kinetic properties and band parameters of (3HgTe1–x(Al2Te3x crystals doped by manganese. The behavior of the magnetic susceptibility of the (3HgTe1–x(Al2Te3x: crystals can be explained by the presence of Mn—Тe—Mn—Тe clusters or, more precisely, by their transition from a magnetically ordered to a paramagnetic state at Curie temperature Tc. The temperature dependences of electrical conductivity are typical for semiconductor materials. This is due to the increase in carrier concentration with the increase of temperature. The temperature dependence of the Hall coefficient indicates that electrons and holes participate in the transport phenomena in the studied samples (the conductivity is mixed. In (3HgTe1–x(Al2Te3x: crystals, the electron mobility decreases with increasing temperature, indicating the predominance of the scattering of the charge carriers on thermal vibrations of the crystal lattice. Thermoelectric power for the samples under investigation possesses negative values and increases in absolute value with the rise of temperature. The optical band gap of the samples was defined from the optical studies. We have measured current-voltage characteristics of n-TiO2/(3HgTe1–x(Al2Te3x: and n-TiN/(3HgTe1–x(Al2Te3x: heterojunctions at room temperature. The band gap, the matrix element of the interband interaction and the electron effective mass at the bottom of the conduction band were determined from the concentration dependence of the electrons effective mass at the Fermi level.

  11. Crystal thickness and sphere dispersion dependence of the photonic band gap of silica colloidal crystals

    Institute of Scientific and Technical Information of China (English)

    Yongjun He(何拥军); Zhongchao Wei(韦中超); Yongchun Zhong(钟永春); Jianwei Diao(刁建伟); Hezhou Wang(汪河洲)

    2004-01-01

    Experimental results demonstrate that the band gap of colloidal suspension crystal changes with both the thickness of crystal and the dispersity of micro-spheres.As the thickness decreases,a red shift of band gap is observed,and there is a maximum of red shift.The values of the maximum red shifts are dependent on the standard deviations of micro-spheres.The experimental results are consistent with theoretical calculation.As the colloidal suspension crystal is assembled from micro-spheres with a standard deviation of 8.4% in a thick cell,an incident angles independent broadband is observed,which is explained as an amorphous structure.Two amorphous models are discussed.

  12. Experimental Characterization of Photonic Band Crystals for Tera Hertz Devices

    Science.gov (United States)

    2004-01-01

    SUBTITLE 5. FUNDING NUMBERS Experimental Characterization of Photonic Band Crystals for Tera F49620-01-1-0484 Hertz Devices 6. AUTHOR(S) Dennis W...01-1-0484 REPORT TITLE: Experimental Characterization of Photonic Band Crystals for Tera Hertz Devices SUBMITTED FOR PUBLICATION TO (applicable only

  13. Evidence for a modified-stannite crystal structure in wide band gap Cu-poor CuIn1-xGaxSe2: Impact on the optical properties

    Science.gov (United States)

    Souilah, M.; Lafond, A.; Barreau, N.; Guillot-Deudon, C.; Kessler, J.

    2008-06-01

    The crystal structure of high Ga-content CuIn1-xGaxSe2 (CIGSe) compounds has been further investigated with the help of single crystal x-ray diffraction technique. It is known that CIGSe compounds adopt the chalcopyrite crystal structure. In the case of Cu-poor, Ga-rich CIGSe, the present study shows that an alternative structure should be considered. This structure is derived from that of stannite in which there is a Ga /In segregation on two different atomic planes. The diffuse reflectance measurements of the Cu-poor compound reveal a slightly different band gap and a smoother transition compared with those of the stoichiometric compound.

  14. Method of construction of composite one-dimensional photonic crystal with extended photonic band gaps.

    Science.gov (United States)

    Tolmachev, V; Perova, T; Moore, R

    2005-10-17

    A method of photonic band gap extension using mixing of periodic structures with two or more consecutively placed photonic crystals with different lattice constants is proposed. For the design of the structures with maximal photonic band gap extension the gap map imposition method is utilised. Optimal structures have been established and the gap map of photonic band gaps has been calculated at normal incidence of light for both small and large optical contrast and at oblique incidence of light for small optical contrast.

  15. Solvent micro-evaporation and concentration gradient synergistically induced crystallization of poly(L-lactide) and ring banded supra-structures with radial periodic variation of thickness

    DEFF Research Database (Denmark)

    Huang, Shaoyong; Li, Hongfei; Wen, Huiying

    2014-01-01

    The crystalline morphology and structure of poly(L-lactide) (PLLA) in a PLLA film-chloroform system were investigated by means of wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM) and atomic force microscopy (AFM). Birefringent and nonbirefringent ring banded supra-structure...

  16. Detailed study of flat bands appearing in metallic photonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Vala, Ali Soltani [Department of Solid State Physics, Faculty of Physics, University of Tabriz, PO Box 51665-163, Tabriz (Iran, Islamic Republic of); Research Institute for Applied Physics and Astronomy, University of Tabriz, PO Box 51665-163, Tabriz (Iran, Islamic Republic of); Sedghi, Aliasghar; Hosseini, Naser [Department of Solid State Physics, Faculty of Physics, University of Tabriz, PO Box 51665-163, Tabriz (Iran, Islamic Republic of); Kalafi, Manouchehr [Department of Solid State Physics, Faculty of Physics, University of Tabriz, PO Box 51665-163, Tabriz (Iran, Islamic Republic of); Research Institute for Applied Physics and Astronomy, University of Tabriz, PO Box 51665-163, Tabriz (Iran, Islamic Republic of); Excellence Centre for Photonics, University of Tabriz, PO Box 51665-163, Tabriz (Iran, Islamic Republic of)

    2011-09-15

    It has been difficult to compute the band structures of metallic photonic crystals for H-polarization. The existence of surface plasmon modes is the major reason for difficulty due to the localized nature of these modes. In this study, by virtue of the efficiency of the newly developed Dirichlet-to-Neumann map method, we are able to investigate the details of the flat bands in a two dimensional square lattice with metallic cylinders. We have obtained fine band structure for H polarization around the flat band region which has not been reported to the best of our knowledge. Our numerical results show that for the frequency around the surface plasmon, the modes are highly localized at the interface of the cylindrical metallic rods and air background and also by approaching the modes to the surface plasmon frequency the localization length decreases and the number of field's nodes increases considerably. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Effect of Ar+ ion post-irradiation on crystal structure, magnetic behavior and optical band gap of Co-implanted ZnO wafers

    Science.gov (United States)

    Xu, N. N.; Li, G. P.; Lin, Q. L.; Liu, H.; Bao, L. M.

    2016-12-01

    Single crystals wurtzite ZnO with (001) orientation were implanted with Co+ ions at room temperature (RT). To tune their magnetic behavior as well as the band gap of the implanted wafers, Ar+ ion post-irradiation (PI) was performed using the calculated energy and ion dose. The formed Co clusters present in the high dose Co-implanted ZnO wafer were observed to be absent after the PI, which is quite different from the low dose doped one. It is found that all the implanted samples showed a giant magnetic moment and a narrowing optical band gap, and that the post-irradiated ones exhibited an even further redshifted absorption edge and ferromagnetic behavior but with saturation magnetization (MS) drastically decreased.

  18. Observation of band gaps in the gigahertz range and deaf bands in a hypersonic aluminum nitride phononic crystal slab

    Science.gov (United States)

    Gorisse, M.; Benchabane, S.; Teissier, G.; Billard, C.; Reinhardt, A.; Laude, V.; Defaÿ, E.; Aïd, M.

    2011-06-01

    We report on the observation of elastic waves propagating in a two-dimensional phononic crystal composed of air holes drilled in an aluminum nitride membrane. The theoretical band structure indicates the existence of an acoustic band gap centered around 800 MHz with a relative bandwidth of 6.5% that is confirmed by gigahertz optical images of the surface displacement. Further electrical measurements and computation of the transmission reveal a much wider attenuation band that is explained by the deaf character of certain bands resulting from the orthogonality of their polarization with that of the source.

  19. Modeling of Photonic Band Gap Crystals and Applications

    Energy Technology Data Exchange (ETDEWEB)

    El-Kady, Ihab Fathy [Iowa State Univ., Ames, IA (United States)

    2002-01-01

    In this work, the authors have undertaken a theoretical approach to the complex problem of modeling the flow of electromagnetic waves in photonic crystals. The focus is to address the feasibility of using the exciting phenomena of photonic gaps (PBG) in actual applications. The authors start by providing analytical derivations of the computational electromagnetic methods used in their work. They also present a detailed explanation of the physics underlying each approach, as well as a comparative study of the strengths and weaknesses of each method. The Plane Wave expansion, Transfer Matrix, and Finite Difference time Domain Methods are addressed. They also introduce a new theoretical approach, the Modal Expansion Method. They then shift the attention to actual applications. They begin with a discussion of 2D photonic crystal wave guides. The structure addressed consists of a 2D hexagonal structure of air cylinders in a layered dielectric background. Comparison with the performance of a conventional guide is made, as well as suggestions for enhancing it. The studies provide an upper theoretical limit on the performance of such guides, as they assumed no crystal imperfections and non-absorbing media. Next, they study 3D metallic PBG materials at near infrared and optical wavelengths. The main objective is to study the importance of absorption in the metal and the suitability of observing photonic band gaps in such structures. They study simple cubic structures where the metallic scatters are either cubes or interconnected metallic rods. Several metals are studied (aluminum, gold, copper, and silver). The effect of topology is addressed and isolated metallic cubes are found to be less lossy than the connected rod structures. The results reveal that the best performance is obtained by choosing metals with a large negative real part of the dielectric function, together with a relatively small imaginary part. Finally, they point out a new direction in photonic crystal

  20. Localization and characterization of the metallic band gaps in a ternary metallo-dielectric photonic crystal

    Science.gov (United States)

    Alejo-Molina, Adalberto; Romero-Antequera, David L.; Sánchez-Mondragón, José J.

    2014-02-01

    In this work, we demonstrate the existence of structural metallic band gaps in a ternary material, dielectric-dielectric-metal, and we show analytical equations for their computation. We show the existence of metallic band gaps not only in the lowest band but also for high frequencies. These gaps are structural ones but different and additional to the dielectric ones in the dielectric photonic crystal substrate. Therefore, as the desire properties of both, the dielectric and metallic photonic crystals, are present the applications for this particular structure are straightforward.

  1. Crystal Structures of Furazanes

    OpenAIRE

    Klapötke, Thomas; Schmid, Philipp; Stierstorfer, Jörg

    2015-01-01

    Several nitrogen-rich salts of 3-nitramino-4-nitrofurazane and dinitraminoazoxyfurazane were synthesized and characterized by various spectroscopic methods. The crystal structures were determined by low temperature single crystal X-ray diffraction. Moreover the sensitivities toward thermal and mechanical stimuli were determined by differential thermal analysis (DTA) and BAM (Bundesanstalt für Materialforschung und -prüfung) methods. The standard enthalpies of formation were calculated for all...

  2. Some New Band Characteristics in One-Dimensional Plasma Dielectric Photonic Crystals%Some New Band Characteristics in One-Dimensional Plasma Dielectric Photonic Crystals

    Institute of Scientific and Technical Information of China (English)

    Laxmi SHIVESHWARI

    2011-01-01

    Propagation of electromagnetic waves in one-dimensional plasma dielectric photonic crystals, the superlattice structure consisting of alternating plasma and dielectric materials, is studied theoretically for oblique incidence by using the transfer matrix method. Our results show that complete photonic band gaps for all polarizations can be obtained in one-dimensional plasma dielectric photonic crystals. These structures can exhibit a new type of band or gap, for the incidence other than the normal one, near frequencies where the electric permittivity of the plasma layer changes sign. This new band or gap arises, from the dispersive properties of the plasma layer, only for transverse magnetic polarized waves, and its width increases with the increase in incident angle. This differential behavior under polarization can be utilized in the design of an efficient polarization splitter. The existence of both photonic gaps and resonance transmission bands is demonstrated for experimentally realizable structures such as double electromagnetic barriers.

  3. Maximizing the Optical Band Gap in 2D Photonic Crystals

    DEFF Research Database (Denmark)

    Hougaard, Kristian G.; Sigmund, Ole

    Topology optimization is used to find the 2D photonic crystal designs with the largest relative photonic band gaps. Starting points for the topology optimization are found with an exhaustive binary search on a low resolution grid.......Topology optimization is used to find the 2D photonic crystal designs with the largest relative photonic band gaps. Starting points for the topology optimization are found with an exhaustive binary search on a low resolution grid....

  4. Localized crystallization in shear bands of a metallic glass

    Science.gov (United States)

    Yan, Zhijie; Song, Kaikai; Hu, Yong; Dai, Fuping; Chu, Zhibing; Eckert, Jürgen

    2016-01-01

    Stress-induced viscous flow is the characteristic of atomic movements during plastic deformation of metallic glasses in the absence of substantial temperature increase, which suggests that stress state plays an important role in mechanically induced crystallization in a metallic glass. However, it is poorly understood. Here, we report on the stress-induced localized crystallization in individual shear bands of Zr60Al15Ni25 metallic glass subjected to cold rolling. We find that crystallization in individual shear bands preferentially occurs in the regions neighboring the amorphous matrix, where the materials are subjected to compressive stresses demonstrated by our finite element simulations. Our results provide direct evidence that the mechanically induced crystallization kinetics is closely related with the stress state. The crystallization kinetics under compressive and tensile stresses are interpreted within the frameworks of potential energy landscape and classical nucleation theory, which reduces the role of stress state in mechanically induced crystallization in a metallic glass.

  5. Monolithic phononic crystals with a surface acoustic band gap from surface phonon-polariton coupling.

    Science.gov (United States)

    Yudistira, D; Boes, A; Djafari-Rouhani, B; Pennec, Y; Yeo, L Y; Mitchell, A; Friend, J R

    2014-11-21

    We theoretically and experimentally demonstrate the existence of complete surface acoustic wave band gaps in surface phonon-polariton phononic crystals, in a completely monolithic structure formed from a two-dimensional honeycomb array of hexagonal shape domain-inverted inclusions in single crystal piezoelectric Z-cut lithium niobate. The band gaps appear at a frequency of about twice the Bragg band gap at the center of the Brillouin zone, formed through phonon-polariton coupling. The structure is mechanically, electromagnetically, and topographically homogeneous, without any physical alteration of the surface, offering an ideal platform for many acoustic wave applications for photonics, phononics, and microfluidics.

  6. Crystal Structures of Furazanes

    Directory of Open Access Journals (Sweden)

    Thomas M. Klapötke

    2015-09-01

    Full Text Available Several nitrogen-rich salts of 3-nitramino-4-nitrofurazane and dinitraminoazoxyfurazane were synthesized and characterized by various spectroscopic methods. The crystal structures were determined by low temperature single crystal X-ray diffraction. Moreover the sensitivities toward thermal and mechanical stimuli were determined by differential thermal analysis (DTA and BAM (Bundesanstalt für Materialforschung und -prüfung methods. The standard enthalpies of formation were calculated for all compounds at the CBS-4M level of theory, and the energetic performance was predicted with the EXPLO5 V6.02 computer code.

  7. Acoustic band gaps of the woodpile sonic crystal with the simple cubic lattice

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Liang-Yu; Chen, Lien-Wen, E-mail: chenlw@mail.ncku.edu.t [Department of Mechanical Engineering, National Cheng Kung University, Tainan 70101, Taiwan (China)

    2011-02-02

    This study theoretically and experimentally investigates the acoustic band gap of a three-dimensional woodpile sonic crystal. Such crystals are built by blocks or rods that are orthogonally stacked together. The adjacent layers are perpendicular to each other. The woodpile structure is embedded in air background. Their band structures and transmission spectra are calculated using the finite element method with a periodic boundary condition. The dependence of the band gap on the width of the stacked rods is discussed. The deaf bands in the band structure are observed by comparing with the calculated transmission spectra. The experimental transmission spectra for the {Gamma}-X and {Gamma}-X' directions are also presented. The calculated results are compared with the experimental results.

  8. Optical spectra and band structure of Ag(x)Ga(x)Ge(1-x)Se2 (x = 0.333, 0.250, 0.200, 0.167) single crystals: experiment and theory.

    Science.gov (United States)

    Reshak, A H; Parasyuk, O V; Fedorchuk, A O; Kamarudin, H; Auluck, S; Chyský, J

    2013-12-05

    Theoretical and experimental studies of the Ag(x)Ga(x)Ge(1-x)Se2 (x = 0.333, 0.250, 0.200, 0.167) single crystals are performed. These crystals possess a lot of intrinsic defects which are responsible for their optoelectronic features. The theoretical investigations were performed by means of DFT calculations using different exchange-correlation potentials. The experimental studies were carried out using the modulated VUV ellipsometry for dielectric constants and birefringence studies. The comparison of the structure obtained from X-ray with the theoretically optimized structure is presented. The crucial role of the intrinsic defect states is manifested in the choice of the exchange correlation potential used. The data may be applicable for a large number of the ternary chalcogenides which are sensitive to the presence of the local disordered states near the band edges.

  9. Phonon band structures of the three dimensional latticed pentamode metamaterials

    Directory of Open Access Journals (Sweden)

    Guan Wang

    2017-02-01

    Full Text Available The artificially designed three-dimensional (3D pentamode metamaterials have such an extraordinary characteristic that the solid materials behave like liquids. Meanwhile, the ideal structure of the pentamode metamaterials arranges in the same way as that of the diamond crystals. In the present research, we regard three types of pentamode metamaterials derived from the 3D crystal lattices as research objects. The phonon band structures of the candidate pentamode structures are calculated by using the finite element method (FEM. We illustrate the relation between the ratio of the bulk modulus B and the shear modulus G of different combinations of D and d. Finally, we find out the relationship between the phonon band structure and the structure parameters. It is useful for generating the phonon band structure and controlling elastic wave propagation.

  10. Two-Dimensional Phononic-Photonic Band Gap Optomechanical Crystal Cavity

    Science.gov (United States)

    Safavi-Naeini, Amir H.; Hill, Jeff T.; Meenehan, Seán; Chan, Jasper; Gröblacher, Simon; Painter, Oskar

    2014-04-01

    We present the fabrication and characterization of an artificial crystal structure formed from a thin film of silicon that has a full phononic band gap for microwave X-band phonons and a two-dimensional pseudo-band gap for near-infrared photons. An engineered defect in the crystal structure is used to localize optical and mechanical resonances in the band gap of the planar crystal. Two-tone optical spectroscopy is used to characterize the cavity system, showing a large coupling (g0/2π≈220 kHz) between the fundamental optical cavity resonance at ωo/2π =195 THz and colocalized mechanical resonances at frequency ωm/2π ≈9.3 GHz.

  11. Enhancement of broadband optical absorption in photovoltaic devices by band-edge effect of photonic crystals.

    Science.gov (United States)

    Tanaka, Yoshinori; Kawamoto, Yosuke; Fujita, Masayuki; Noda, Susumu

    2013-08-26

    We numerically investigate broadband optical absorption enhancement in thin, 400-nm thick microcrystalline silicon (µc-Si) photovoltaic devices by photonic crystals (PCs). We realize absorption enhancement by coupling the light from the free space to the large area resonant modes at the photonic band-edge induced by the photonic crystals. We show that multiple photonic band-edge modes can be produced by higher order modes in the vertical direction of the Si photovoltaic layer, which can enhance the absorption on multiple wavelengths. Moreover, we reveal that the photonic superlattice structure can produce more photonic band-edge modes that lead to further optical absorption. The absorption average in wavelengths of 500-1000 nm weighted to the solar spectrum (AM 1.5) increases almost twice: from 33% without photonic crystal to 58% with a 4 × 4 period superlattice photonic crystal; our result outperforms the Lambertian textured structure.

  12. 一维掺杂光子晶体结构参数对带隙结构影响%Effect of Structure Parameter of One Dimensional Doped Photonic Crystal on Photonic Band Gap Structure

    Institute of Scientific and Technical Information of China (English)

    郭立帅

    2012-01-01

    The properties of band - gap of one - dimensional doped photonic crystal are studied by using numerical- ly method based on the transfer matrix method. The result shows that a narrow conduction band appears in the cen- tre of forbidden band in one - dimensional doped photonic crystal. The depth of conduction band appears in the centre of forbidden band has a maximum, which was caused by the number of layers of the second half of impurity where the first one was fixed. It shows that the forbidden band center's conduction band depth was still biggest by means of changing basic level thickness.%基于传输矩阵法,数值研究了掺杂一维光子晶体带隙特征。研究表明:一维掺杂光晶体禁带中心位置出现一个极窄的导带,当杂质前半部分层数给定时,后半部分总存在一个层数,使得禁带中心导带的深度达到最大,在此基础上通过改变基本层厚度发现,禁带中心的导带深度仍然最大,我们可以通过改变基本层厚度厚度,让特定波长的光顺利通过。

  13. Lamb wave band gaps in locally resonant phononic crystal strip waveguides

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Yuanwei, E-mail: yaoyw@scut.edu.cn [Department of Physics, Guangdong University of Technology, Guangzhou 510006 (China); Wu, Fugen [Experiment and Educational Center, Guangdong University of Technology, Guangzhou 510006 (China); Zhang, Xin [Department of Physics, Guangdong University of Technology, Guangzhou 510006 (China); Hou, Zhilin [Department of Physics, South China University of Technology, Guangzhou 510640 (China)

    2012-01-09

    Using finite element method, we have made a theoretically study of the band structure of Lamb wave in a locally resonant phononic crystal strip waveguide with periodic soft rubber attached on the two sides of epoxy main plate. The numerical results show that the Lamb wave band gap based on local resonant mechanism can be opened up in the stub strip waveguides, and the width of the local resonant band gap is narrower than that based on the Bragg scattering mechanism. The results also show that the stub shape and width have influence on the frequency and width of the Lamb wave band gap. -- Highlights: ► The local resonant Lamb wave band gap can be opened up in a stub strip waveguides. ► The width of the local resonant band gap is narrower than that Bragg scattering band gap. ► The shape and width of the stub have strongly influence on the local resonant band gap.

  14. Simultaneous two-dimensional phononic and photonic band gaps in opto-mechanical crystal slabs.

    Science.gov (United States)

    Mohammadi, Saeed; Eftekhar, Ali A; Khelif, Abdelkrim; Adibi, Ali

    2010-04-26

    We demonstrate planar structures that can provide simultaneous two-dimensional phononic and photonic band gaps in opto-mechanical (or phoxonic) crystal slabs. Different phoxonic crystal (PxC) structures, composed of square, hexagonal (honeycomb), or triangular arrays of void cylindrical holes embedded in silicon (Si) slabs with a finite thickness, are investigated. Photonic band gap (PtBG) maps and the complete phononic band gap (PnBG) maps of PxC slabs with different radii of the holes and thicknesses of the slabs are calculated using a three-dimensional plane wave expansion code. Simultaneous phononic and photonic band gaps with band gap to midgap ratios of more than 10% are shown to be readily obtainable with practical geometries in both square and hexagonal lattices, but not for the triangular lattice.

  15. Reflectivity calculated for a 3D silicon photonic band gap crystal with finite support

    CERN Document Server

    Devashish, D; van der Vegt, J J W; Vos, Willem L

    2016-01-01

    We study numerically the reflectivity of three-dimensional (3D) photonic crystals with a complete 3D photonic band gap, with the aim to interpret recent experiments. We employ the finite element method to study crystals with the cubic diamond-like inverse woodpile structure. The high-index backbone has a dielectric function similar to silicon. We study crystals with a range of thicknesses up to ten unit cells ($L \\leq 10 c$). The crystals are surrounded by vacuum, and have a finite support as in experiments. The polarization-resolved reflectivity spectra reveal Fabry-P{\\'e}rot fringes related to standing waves in the finite crystal, as well as broad stop bands with nearly $100~\\%$ reflectivity, even for thin crystals. From the strong reflectivity peaks, it is inferred that the maximum reflectivity observed in experiments is not limited by finite size. The frequency ranges of the stop bands are in excellent agreement with stop gaps in the photonic band structure, that pertain to infinite and perfect crystals. ...

  16. Photonic band gap engineering in 2D photonic crystals

    Indian Academy of Sciences (India)

    Yogita Kalra; R K Sinha

    2006-12-01

    The polarization-dependent photonic band gaps (TM and TE polarizations) in two-dimensional photonic crystals with square lattices composed of air holes in dielectric and vice versa i.e., dielectric rods in air, using the plane-wave expansion method are investigated. We then study, how the photonic band gap size is affected by the changing ellipticity of the constituent air holes/dielectric rods. It is observed that the size of the photonic band gap changes with changing ellipticity of the constituent air holes/dielectric rods. Further, it is reported, how the photonic band gap size is affected by the change in the orientation of the constituent elliptical air holes/dielectric rods in 2D photonic crystals.

  17. Electronic Bands Behaviour at Sinusoidal Potential Presence of Incommensurate Crystals

    OpenAIRE

    Vlokh R.; Vlokh O.; Lukiyanets B.

    2004-01-01

    On the basis of solving the Schrodinger and Mathieu equations, for the case of crystal field perturbed by one-dimensional sinusoidal potential of the modulated phase in uniaxial ferroelectrics, it has been shown that the positions of electronic levels are sensitive to the ratio of periods of the crystal field and the perturbation potential. Considering the energy states as prototypes of bands normalized by perturbation, one can come to the conclusion that the level of the states is the same a...

  18. Crystal structure of gold hydride

    Energy Technology Data Exchange (ETDEWEB)

    Degtyareva, Valentina F., E-mail: degtyar@issp.ac.ru

    2015-10-05

    Highlights: • Volume expansion of metal hydrides is due to the increase in the s-band filling. • AuH structure is similar to that of Hg having one more s electron compared to Au. • Structure stability of both Hg and AuH is governed by the Hume-Rothery rule. - Abstract: A number of transition metal hydrides with close-packed metal sublattices of fcc or hcp structures with hydrogen in octahedral interstitial positions were obtained by the high-pressure-hydrogen technique described by Ponyatovskii et al. (1982). In this paper we consider volume increase of metals by hydrogenation and possible crystal structure of gold hydride in relation with the structure of mercury, the nearest neighbor of Au in the Periodic table. Suggested structure of AuH has a basic tetragonal body-centered cell that is very similar to the mercury structure Hg-t I 2. The reasons of stability for this structure are discussed within the model of Fermi sphere–Brillouin zone interactions.

  19. Generalized thermoelastic wave band gaps in phononic crystals without energy dissipation

    Science.gov (United States)

    Wu, Ying; Yu, Kaiping; Li, Xiao; Zhou, Haotian

    2016-01-01

    We present a theoretical investigation of the thermoelastic wave propagation in the phononic crystals in the context of Green-Nagdhi theory by taking thermoelastic coupling into account. The thermal field is assumed to be steady. Thermoelastic wave band structures of 3D and 2D are derived by using the plane wave expansion method. For the 2D problem, the anti-plane shear mode is not affected by the temperature difference. Thermoelastic wave bands of the in-plane x-y mode are calculated for lead/silicone rubber, aluminium/silicone rubber, and aurum/silicone rubber phononic crystals. The new findings in the numerical results indicate that the thermoelastic wave bands are composed of the pure elastic wave bands and the thermal wave bands, and that the thermal wave bands can serve as the low boundary of the first band gap when the filling ratio is low. In addition, for the lead/silicone rubber phononic crystals the effects of lattice type (square, rectangle, regular triangle, and hexagon) and inclusion shape (circle, oval, and square) on the normalized thermoelastic bandwidth and the upper/lower gap boundaries are analysed and discussed. It is concluded that their effects on the thermoelastic wave band structure are remarkable.

  20. Crystal structure, stability, and optoelectronic properties of the organic-inorganic wide-band-gap perovskite CH3NH3BaI3 : Candidate for transparent conductor applications

    Science.gov (United States)

    Kumar, Akash; Balasubramaniam, K. R.; Kangsabanik, Jiban; Vikram, Alam, Aftab

    2016-11-01

    Structural stability, electronic structure, and optical properties of CH3NH3BaI3 hybrid perovskite are examined from theory as well as experiment. Solution-processed thin films of CH3NH3BaI3 exhibited a high transparency in the wavelength range of 400-825 nm (1.5-3.1 eV for which the photon current density is highest in the solar spectrum) which essentially justifies a high band gap of 4 eV obtained by theoretical estimation. Also, the x-ray diffraction patterns of the thin films match well with the {00 l } peaks of the simulated pattern obtained from the relaxed unit cell of CH3NH3BaI3 , crystallizing in the I 4 /m c m space group, with lattice parameters, a =9.30 Å, c =13.94 Å. Atom projected density of state and band structure calculations reveal the conduction and valence band edges to be comprised primarily of barium d orbitals and iodine p orbitals, respectively. The larger band gap of CH3NH3BaI3 compared to CH3NH3PbI3 can be attributed to the lower electronegativity coupled with the lack of d orbitals in the valence band of Ba2 +. A more detailed analysis reveals the excellent chemical and mechanical stability of CH3NH3BaI3 against humidity, unlike its lead halide counterpart, which degrades under such conditions. We propose La to be a suitable dopant to make this compound a promising candidate for transparent conductor applications, especially for all perovskite solar cells. This claim is supported by our calculated results on charge concentration, effective mass, and vacancy formation energies.

  1. Broadening of effective photonic band gaps in biological chiral structures: From intrinsic narrow band gaps to broad band reflection spectra

    Science.gov (United States)

    Vargas, W. E.; Hernández-Jiménez, M.; Libby, E.; Azofeifa, D. E.; Solis, Á.; Barboza-Aguilar, C.

    2015-09-01

    Under normal illumination with non-polarized light, reflection spectra of the cuticle of golden-like and red Chrysina aurigans scarabs show a structured broad band of left-handed circularly polarized light. The polarization of the reflected light is attributed to a Bouligand-type left-handed chiral structure found through the scarab's cuticle. By considering these twisted structures as one-dimensional photonic crystals, a novel approach is developed from the dispersion relation of circularly polarized electromagnetic waves traveling through chiral media, to show how the broad band characterizing these spectra arises from an intrinsic narrow photonic band gap whose spectral position moves through visible and near-infrared wavelengths.

  2. High-energy band structure of gold

    DEFF Research Database (Denmark)

    Christensen, N. Egede

    1976-01-01

    The band structure of gold for energies far above the Fermi level has been calculated using the relativistic augmented-plane-wave method. The calculated f-band edge (Γ6-) lies 15.6 eV above the Fermi level is agreement with recent photoemission work. The band model is applied to interpret...

  3. Frustrated polymer crystal structures

    Science.gov (United States)

    Lotz, B.; Strasbourg, 67083

    1997-03-01

    Several crystal structures or polymorphs of chiral or achiral polymers and biopolymers with three fold conformation of the helix have been found to conform to a common and -with one exception(Puterman, M. et al, J. Pol. Sci., Pol. Phys. Ed., 15, 805 (1977))- hitherto unsuspected packing scheme. The trigonal unit-cell contains three isochiral helices; the azimuthal setting of one helix differs significantly from that of the other two, leading to a so-called frustrated packing scheme, in which the environment of conformationally identical helices differs. Two variants of the frustrated scheme are analyzed. Similarities with frustrated two dimensional magnetic systems are underlined. Various examples of frustration in polymer crystallography are illustrated via the elucidation or reinterpretation of crystal phases or polymorphs of polyolefins, polyesters, cellulose derivatives and polypeptides. Structural manifestations (including AFM evidence) and morphological consequences of frustration are presented, which help diagnose the existence of this original packing of polymers.(Work done with L. Cartier, D. Dorset, S. Kopp, T. Okihara, M. Schumacher, W. Stocker.)

  4. Band gap of two-dimensional fiber-air photonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Shu, E-mail: yangshu5678@163.com; Li, Masha

    2016-04-15

    A two-dimensional photonic crystal (PC) composed of textile fiber and air is initially discussed in this paper. Textile materials are so called soft materials, which are different from the previous PCs composed of rigid materials. The plain wave expansion method is used to calculate band structure of different PCs by altering component properties or structural parameters. Results show that the dielectric constant of textile fibers, fiber filling ratio and lattice arrangement are effective factors which influence PCs' band gap. Yet lattice constant and fiber diameter make inconspicuous influence on the band gap feature.

  5. Vibronic interaction in crystals with the Jahn-Teller centers in the elementary energy bands concept

    Directory of Open Access Journals (Sweden)

    D.M. Bercha

    2015-09-01

    Full Text Available The order-disorder type phase transition caused by the vibronic interaction (collective Jahn-Teller effect in a monoclinic CuInP2S6 crystal is analyzed. For this purpose, a trigonal protostructure model of CuInP2S6 is created, through a slight change in the crystal lattice parameters of the CuInP2S6 paraelectric phase. In parallel to the group-theoretical analysis, the DFT-based ab initio band structure calculations of the CuInP2S6 protostructure, para-, and ferriphases are performed. Using the elementary energy bands concept, a part of the band structure from the vicinity of the forbidden energy gap, which is created by the d-electron states of copper has been related with a certain Wyckoff position where the Jahn-Teller's centers are localized. A construction procedure of the vibronic potential energy matrix is generalized for the case of crystal using the elementary energy bands concept and the group theoretical method of invariants. The procedure is illustrated by the creation of the adiabatic potentials of the Γ5-Γ5 vibronic coupling for the protostructure and paraphase of the CuInP2S6 crystal. A structure of the obtained adiabatic potentials is analyzed, followed by conclusions on their transformation under a phase transition and the discussion on the possibility for the spontaneous polarization to arise in this crystal.

  6. Frequency bands of negative refraction in finite one-dimensional photonic crystals

    Institute of Scientific and Technical Information of China (English)

    Chen Yuan-Yuan; Huang Zhao-Ming; Shi Jie-Long; Li Chun-Fang; Wang Qi

    2007-01-01

    We have discussed theoretically the negative refraction in finite one-dimensional (1D) photonic crystals (PCs)composed of alternative layers with high index contrast. The frequency bands of negative refraction are obtained with the help of the photonic band structure, the group velocity and the power transmittance, which are all obtained in analytical expression. There shows negative transverse position shift at the endface when negative refraction occurs,which is analysed in detail.

  7. Fluid Sensor Based on Transmission Dip Caused by Mini Stop-Band in Photonic Crystal Slab

    Institute of Scientific and Technical Information of China (English)

    CAO Lei; HUANG Yi-Dong; MAO Xiao-Yu; LI Fei; ZHANG Wei; PENG Jiang-De

    2008-01-01

    We propose a fluid sensor based on transmission dip caused by mini stop-band in photonic crystal slabs. Simulation results show that this novel type of sensors has large detective range (more than 1.5) and relative high sensitivity (4.3×10-5 in certain conditions). The central frequency and bandwidth of the mini stop-bands depend on the structure parameters of PC waveguides, which makes it possible to optimize the detective range and detective sensitivity.

  8. Band warping, band non-parabolicity, and Dirac points in electronic and lattice structures

    Science.gov (United States)

    Resca, Lorenzo; Mecholsky, Nicholas A.; Pegg, Ian L.

    2017-10-01

    We illustrate at a fundamental level the physical and mathematical origins of band warping and band non-parabolicity in electronic and vibrational structures. We point out a robust presence of pairs of topologically induced Dirac points in a primitive-rectangular lattice using a p-type tight-binding approximation. We analyze two-dimensional primitive-rectangular and square Bravais lattices with implications that are expected to generalize to more complex structures. Band warping is shown to arise at the onset of a singular transition to a crystal lattice with a larger symmetry group, which allows the possibility of irreducible representations of higher dimensions, hence band degeneracy, at special symmetry points in reciprocal space. Band warping is incompatible with a multi-dimensional Taylor series expansion, whereas band non-parabolicities are associated with multi-dimensional Taylor series expansions to all orders. Still band non-parabolicities may merge into band warping at the onset of a larger symmetry group. Remarkably, while still maintaining a clear connection with that merging, band non-parabolicities may produce pairs of conical intersections at relatively low-symmetry points. Apparently, such conical intersections are robustly maintained by global topology requirements, rather than any local symmetry protection. For two p-type tight-binding bands, we find such pairs of conical intersections drifting along the edges of restricted Brillouin zones of primitive-rectangular Bravais lattices as lattice constants vary relatively to each other, until these conical intersections merge into degenerate warped bands at high-symmetry points at the onset of a square lattice. The conical intersections that we found appear to have similar topological characteristics as Dirac points extensively studied in graphene and other topological insulators, even though our conical intersections have none of the symmetry complexity and protection afforded by the latter more

  9. Inorganic Crystal Structure Database (ICSD)

    Science.gov (United States)

    SRD 84 FIZ/NIST Inorganic Crystal Structure Database (ICSD) (PC database for purchase)   The Inorganic Crystal Structure Database (ICSD) is produced cooperatively by the Fachinformationszentrum Karlsruhe(FIZ) and the National Institute of Standards and Technology (NIST). The ICSD is a comprehensive collection of crystal structure data of inorganic compounds containing more than 140,000 entries and covering the literature from 1915 to the present.

  10. Experimental investigation of hollow-core photonic crystal fibers with five photonic band-gaps

    Institute of Scientific and Technical Information of China (English)

    YUAN Jin-hui; HOU Lan-tian; WEI Dong-bin; WANG Hai-yun; ZHOU Gui-yao

    2008-01-01

    The hollow-core photonic crystal fibers (HC-PCFs) with integrity structure have been fabricated with an improved twice stack-and-draw technique. The transmission spectrum shows that five photonic band-gaps within 450-1100 nm have been obtained.And the green light transmission in the HC-PCFs'has been observed remarkably.

  11. Crystal structure of ruthenocenecarbonitrile

    Directory of Open Access Journals (Sweden)

    Frank Strehler

    2015-04-01

    Full Text Available The molecular structure of ruthenocenecarbonitrile, [Ru(η5-C5H4C[triple-bond]N(η5-C5H5], exhibits point group symmetry m, with the mirror plane bisecting the molecule through the C[triple-bond]N substituent. The RuII atom is slightly shifted from the η5-C5H4 centroid towards the C[triple-bond]N substituent. In the crystal, molecules are arranged in columns parallel to [100]. One-dimensional intermolecular π–π interactions [3.363 (3 Å] between the C[triple-bond]N carbon atom and one carbon of the cyclopentadienyl ring of the overlaying molecule are present.

  12. Crystal structure of propaquizafop

    Directory of Open Access Journals (Sweden)

    Youngeun Jeon

    2014-12-01

    Full Text Available The title compound, C22H22ClN3O5 {systematic name: 2-(propan-2-ylideneaminooxyethyl (R-2-[4-(6-chloroquinoxalin-2-yloxyphenoxy]propionate}, is a herbicide. The asymmetric unit comprises two independent molecules in which the dihedral angles between the phenyl ring and the quinoxaline ring plane are 75.93 (7 and 82.77 (8°. The crystal structure features C—H...O, C—H...N, and C—H...Cl hydrogen bonds, as well as weak π–π interactions [ring-centroid separation = 3.782 (2 and 3.5952 (19 Å], resulting in a three-dimensional architecture.

  13. Absolute band gaps of a two-dimensional triangular-lattice dielectric photonic crystal with different shapes

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Absolute band gaps of a two-dimensional triangular-lattice photonic crystal are calculated with the finite-difference time-domain method in this paper.Through calculating the photonic band structures of the triangular-lattice photonic crystal consisting of Ge rods immersed in air with different shapes,it is found that a large absolute band gap of 0.098 (2c/a) can be obtained for the structures with hollow triangular Ge rods immersed in air,corresponding to 19.8% of the middle frequency.The influence of the different factors on the width of the absolute band gaps is also discussed.

  14. Accurate evaluation of lowest band gaps in ternary locally resonant phononic crystals

    Institute of Scientific and Technical Information of China (English)

    Wang Gang; Shao Li-Hui; Liu Yao-Zong; Wen Ji-Hong

    2006-01-01

    Based on a better understanding of the lattice vibration modes, two simple spring-mass models are constructed in order to evaluate the frequencies on both the lower and upper edges of the lowest locally resonant band gaps of the ternary locally resonant phononic crystals. The parameters of the models are given in a reasonable way based on the physical insight into the band gap mechanism. Both the lumped-mass methods and our models are used in the study of the influences of structural and the material parameters on frequencies on both edges of the lowest gaps in the ternary locally resonant phononic crystals. The analytical evaluations with our models and the theoretical predictions with the lumped-mass method are in good agreement with each other. The newly proposed heuristic models are helpful for a better understanding of the locally resonant band gap mechanism, as well as more accurate evaluation of the band edge frequencies.

  15. Electronic band structures of binary skutterudites

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Banaras [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Aliabad, H.A. Rahnamaye [Department of Physics, Hakim Sabzevari University, Sabzevar (Iran, Islamic Republic of); Saifullah [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Jalali-Asadabadi, S. [Department of Physics, Faculty of Science, University of Isfahan (UI), 81744 Isfahan (Iran, Islamic Republic of); Khan, Imad [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Ahmad, Iftikhar, E-mail: ahma5532@gmail.com [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan)

    2015-10-25

    The electronic properties of complex binary skutterudites, MX{sub 3} (M = Co, Rh, Ir; X = P, As, Sb) are explored, using various density functional theory (DFT) based theoretical approaches including Green's Function (GW) as well as regular and non-regular Tran Blaha modified Becke Jhonson (TB-mBJ) methods. The wide range of calculated bandgap values for each compound of this skutterudites family confirm that they are theoretically as challenging as their experimental studies. The computationally expensive GW method, which is generally assume to be efficient in the reproduction of the experimental bandgaps, is also not very successful in the calculation of bandgaps. In this article, the issue of the theoretical bandgaps of these compounds is resolved by reproducing the accurate experimental bandgaps, using the recently developed non-regular TB-mBJ approach, based on DFT. The effectiveness of this technique is due to the fact that a large volume of the binary skutterudite crystal is empty and hence quite large proportion of electrons lie outside of the atomic spheres, where unlike LDA and GGA which are poor in the treatment of these electrons, this technique properly treats these electrons and hence reproduces the clear electronic picture of these compounds. - Highlights: • Theoretical and experimental electronic band structures of binary skutterudites are reviewed. • The literature reveals that none of the existing theoretical results are consistent with the experiments. • GW, regular and non-regular TB-mBJ methods are used to reproduce the correct results. • The GW and regular TB-mBJ results are better than the available results in literature. • However, non-regular TB-mBJ reproduces the correct experimental band structures.

  16. Fabrication of Ceramic Layer-by-Layer Infrared Wavelength Photonic Band Gap Crystals

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Henry Hao-Chuan [Iowa State Univ., Ames, IA (United States)

    2004-12-19

    Photonic band gap (PBG) crystals, also known as photonic crystals, are periodic dielectric structures which form a photonic band gap that prohibit the propagation of electromagnetic (EM) waves of certain frequencies at any incident angles. Photonic crystals have several potential applications including zero-threshold semiconductor lasers, the inhibition of spontaneous emission, dielectric mirrors, and wavelength filters. If defect states are introduced in the crystals, light can be guided from one location to another or even a sharp bending of light in micron scale can be achieved. This generates the potential for optical waveguide and optical circuits, which will contribute to the improvement in the fiber-optic communications and the development of high-speed computers.

  17. Self-isospectrality, tri-supersymmetry and band structure

    CERN Document Server

    Correa, Francisco; Nieto, Luis-Miguel; Plyushchay, Mikhail S

    2008-01-01

    We reveal an unexpected hidden supersymmetric structure in a self-isospectral system constructed on the base of the periodic finite-gap associated Lame equation. It admits three different choices of the Z_2-grading, under which three basic nontrivial integrals of motion coherently change their fermionic/bosonic nature, and generate a certain nonlinear supersymmetry. These integrals reflect the band structure, its separability, and characteristic properties of the band-edge states of the system, which can be interpreted as an electron in one-dimensional crystal produced by periodic electric and magnetic fields.

  18. Crystal structure of fipronil

    Directory of Open Access Journals (Sweden)

    Hyunjin Park

    2017-10-01

    Full Text Available The title compound, C12H4Cl2F6N4OS {systematic name: 5-amino-1-[2,6-dichloro-4-(trifluoromethylphenyl]-4-[(trifluoromethanesulfinyl]-1H-pyrazole-3-carbonitrile}, is a member of the phenylpyrazole group of acaricides, and one of the phenylpyrazole group of insecticides. The dihedral angle between the planes of the pyrazole and benzene rings is 89.03 (9°. The fluorine atoms of the trifluoromethyl substituent on the benzene ring are disordered over two sets of sites, with occupancy ratios 0.620 (15:0.380 (15. In the crystal, C—N...π interactions [N...ring centroid = 3.607 (4 Å] together with N—H...N and C—H...F hydrogen bonds form a looped chain structure along [10\\overline{1}]. Finally, N—H...O hydrogen bonds and C—Cl...π interactions [Cl...ring centroid = 3.5159 (16 Å] generate a three-dimensional structure. Additionally, there are a short intermolecular F... F contacts present.

  19. Effective band structure of random alloys.

    Science.gov (United States)

    Popescu, Voicu; Zunger, Alex

    2010-06-11

    Random substitutional A(x)B(1-x) alloys lack formal translational symmetry and thus cannot be described by the language of band-structure dispersion E(k(→)). Yet, many alloy experiments are interpreted phenomenologically precisely by constructs derived from wave vector k(→), e.g., effective masses or van Hove singularities. Here we use large supercells with randomly distributed A and B atoms, whereby many different local environments are allowed to coexist, and transform the eigenstates into an effective band structure (EBS) in the primitive cell using a spectral decomposition. The resulting EBS reveals the extent to which band characteristics are preserved or lost at different compositions, band indices, and k(→) points, showing in (In,Ga)N the rapid disintegration of the valence band Bloch character and in Ga(N,P) the appearance of a pinned impurity band.

  20. Spectrophotometer spectral bandwidth calibration with absorption bands crystal standard.

    Science.gov (United States)

    Soares, O D; Costa, J L

    1999-04-01

    A procedure for calibration of a spectral bandwidth standard for high-resolution spectrophotometers is described. Symmetrical absorption bands for a crystal standard are adopted. The method relies on spectral band shape fitting followed by a convolution with the slit function of the spectrophotometer. A reference spectrophotometer is used to calibrate the spectral bandwidth standard. Bandwidth calibration curves for a minimum spectral transmission factor relative to the spectral bandwidth of the reference spectrophotometer are derived for the absorption bands at the wavelength of the band absorption maximum. The family of these calibration curves characterizes the spectral bandwidth standard. We calibrate the spectral bandwidth of a spectrophotometer with respect to the reference spectrophotometer by determining the spectral transmission factor minimum at every calibrated absorption band of the bandwidth standard for the nominal instrument values of the spectral bandwidth. With reference to the standard spectral bandwidth calibration curves, the relation of the spectral bandwidth to the reference spectrophotometer is determined. We determine the discrepancy in the spectrophotometers' spectral bandwidths by averaging the spectral bandwidth discrepancies relative to the standard calibrated values found at the absorption bands considered. A weighted average of the uncertainties is taken.

  1. Prediction of molecular crystal structures

    CERN Document Server

    Beyer, T

    2001-01-01

    The ab initio prediction of molecular crystal structures is a scientific challenge. Reliability of first-principle prediction calculations would show a fundamental understanding of crystallisation. Crystal structure prediction is also of considerable practical importance as different crystalline arrangements of the same molecule in the solid state (polymorphs)are likely to have different physical properties. A method of crystal structure prediction based on lattice energy minimisation has been developed in this work. The choice of the intermolecular potential and of the molecular model is crucial for the results of such studies and both of these criteria have been investigated. An empirical atom-atom repulsion-dispersion potential for carboxylic acids has been derived and applied in a crystal structure prediction study of formic, benzoic and the polymorphic system of tetrolic acid. As many experimental crystal structure determinations at different temperatures are available for the polymorphic system of parac...

  2. THE CRYSTAL STRUCTURE OF DIPHENYLTELLURIUM DIBROMIDE,

    Science.gov (United States)

    TELLURIUM COMPOUNDS, *ORGANOMETALLIC COMPOUNDS, CRYSTAL STRUCTURE , CRYSTAL STRUCTURE , BROMIDES, SYMMETRY(CRYSTALLOGRAPHY), X RAY DIFFRACTION, FOURIER ANALYSIS, LEAST SQUARES METHOD, MOLECULAR STRUCTURE, CHEMICAL BONDS.

  3. REFINEMENT OF THE CRYSTAL STRUCTURE OF GUANIDINIUM ALUMINUM SULFATE HEXAHYDRATE.

    Science.gov (United States)

    FERROELECTRIC CRYSTALS, * CRYSTAL STRUCTURE ), (*GUANIDINES, CRYSTAL STRUCTURE ), (*ALUMINUM COMPOUNDS, CRYSTAL STRUCTURE ), SULFATES, HYDRATES, X RAY DIFFRACTION, CHROMIUM COMPOUNDS, CRYSTAL LATTICES, CHEMICAL BONDS

  4. Demonstration of Crystal Structure.

    Science.gov (United States)

    Neville, Joseph P.

    1985-01-01

    Describes an experiment where equal parts of copper and aluminum are heated then cooled to show extremely large crystals. Suggestions are given for changing the orientation of crystals by varying cooling rates. Students are more receptive to concepts of microstructure after seeing this experiment. (DH)

  5. Crystal structure of oxamyl

    Directory of Open Access Journals (Sweden)

    Eunjin Kwon

    2016-12-01

    Full Text Available The title compound, C7H13N3O3S [systematic name: (Z-methyl 2-dimethylamino-N-(methylcarbamoyloxy-2-oxoethanimidothioate], is an oxime carbamate acaride, insecticide and nematicide. The asymmetric unit comprises two independent molecules, A and B. The dihedral angles between the mean planes [r.m.s. deviations = 0.0017 (A and 0.0016 Å (B] of the acetamide and oxyimino groups are 88.80 (8° for A and 87.05 (8° for B. In the crystal, N/C—H...O hydrogen bonds link adjacent molecules, forming chains along the a axis. The chains are further linked by C—H...O hydrogen bonds, resulting in a three-dimensional network with alternating rows of A and B molecules in the bc plane stacked along the a-axis direction. The structure was refined as an inversion twin with a final BASF parameter of 0.16 (9.

  6. Stable Band-Gaps in Phononic Crystals by Harnessing Hyperelastic Transformation Media

    CERN Document Server

    Liu, Yan; Feng, Xi-Qiao

    2016-01-01

    The band structure in phononic crystals (PCs) is usually affected by the deformations of their soft components. In this work, hyperelastic transformation media is proposed to be integrated in the PCs'design, to achieve stable elastic band-gaps which is independent with finite mechanical deformations. For a one-dimensional (1D) PC, we demonstrate the semi-linear soft component can keep all elastic wave bands unchanged with the external deformation field. While for neo-Hookean soft component, only S-wave bands can be precisely retained. The change of the P-wave bands can be predicted by using a lumped mass method. Numerical simulations are performed to validate our theory predictions and the robustness of the proposed PCs.

  7. Emulation of two-dimensional photonic crystal defect modes in a photonic crystal with a three-dimensional photonic band gap

    Energy Technology Data Exchange (ETDEWEB)

    Povinelli, M. L.; Johnson, Steven G.; Fan, Shanhui; Joannopoulos, J. D.

    2001-08-15

    Using numerical simulations, we demonstrate the construction of two-dimensional- (2D-) like defect modes in a recently proposed 3D photonic crystal structure. These modes, which are confined in all three dimensions by a complete photonic band gap, bear a striking similarity to those in 2D photonic crystals in terms of polarization, field profile, and projected band structures. It is expected that these results will greatly facilitate the observation of widely studied 2D photonic-crystal phenomena in a realistic, 3D physical system.

  8. Crystal and electronic structures and high-pressure behavior of AgSO4, a unique narrow band gap antiferromagnetic semiconductor: LDA(+U) picture.

    Science.gov (United States)

    Derzsi, Mariana; Stasiewicz, Juliusz; Grochala, Wojciech

    2011-09-01

    We demonstrate that DFT calculations performed with the local density approximation (LDA) allow for significantly better reproduction of lattice constants, the unit cell volume and the density of Ag(II)SO(4) than those done with generalized gradient approximation (GGA). The LDA+U scheme, which accounts for electronic correlation effects, enables the accurate prediction of the magnetic superexchange constant of this strongly correlated material and its band gap at the Fermi level. The character of the band gap places the compound on the borderline between a Mott insulator and a charge transfer insulator. The size of the band gap (0.82 eV) indicates that AgSO(4) is a ferrimagnetic semiconductor, and possibly an attractive material for spintronics. A bulk modulus of 27.0 GPa and a compressibility of 0.037 GPa(-1) were determined for AgSO(4) from the third-order Birch-Murnaghan isothermal equation of state up to 20 GPa. Several polymorphic types compete with the ambient pressure P-1 phase as the external pressure is increased. The P-1 phase is predicted to resist pressure-induced metallization up to at least 20 GPa.

  9. Photonic bands and defect modes in metallo-dielectric photonic crystal slabs

    CERN Document Server

    Zanotto, Simone; Sorba, Lucia; Tredicucci, Alessandro

    2016-01-01

    Photonic components based on structured metallic elements show great potential for device applications where field enhancement and confinement of the radiation on a subwavelength scale is required. In this paper we report a detailed study of a prototypical metallo-dielectric photonic structure, where features well known in the world of dielectric photonic crystals, like band gaps and defect modes, are exported to the metallic counterpart, with interesting applications to infrared science and technology, as for instance in quantum well infrared photodetectors, narrow-band spectral filters, and tailorable thermal emitters.

  10. Coupling between Fano and Bragg bands in photonic band structure of two-dimensional metallic photonic structures

    CERN Document Server

    Markos, Peter

    2016-01-01

    Frequency and transmission spectrum of two-dimensional array of metallic rods is investigated numerically. Based on the recent analysis of the band structure of two-dimensional photonic crystal with dielectric rods [P. Marko\\v{s}, Phys. Rev. A 92 043814 (2015)] we identify two types of bands in the frequency spectrum: Bragg (P) bands resulting from a periodicity and Fano (F) bands which arise from Fano resonances associated with each of the cylinders within the periodic structure. It is shown that the existence of Fano band in a certain frequency range is manifested by a Fano resonance in the transmittance. In particular, we re-examine the symmetry properties of the H- polarized band structure in the frequency range where the spectrum consists of the localized modes associated with the single scatterer resonances and we explore process of formation of Fano bands by identifying individual terms in the expansion of the LCAO states. We demonstrate how the interplay between the two scattering mechanisms affects p...

  11. Study on the vibration band gap and vibration attenuation property of phononic crystals

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Phononic crystals (PCs) are functional materials with periodic structures and elas- tic wave (vibration) band gaps, where propagation of vibrations with frequencies within band gaps is forbidden. PCs with finite periods can restrain the propagation of vibrations with frequencies in band gaps and thus has vibration attenuation property. Worldwide, many institutions and researchers are engaged in the re- search of PCs, however, studies on the vibration attenuation property of PCs are still limited. In this paper, we report our study of band gaps and vibration attenua- tion properties of 1) a simplified PC—periodic mass-spring structures, 2) longitu- dinal vibration of one-dimensional (1D-), 2D-, 3D-PCs, and 3) the flexural vibration of 1D- and 2D-PCs. These studies provide a foundation for the applications of PCs in vibration attenuation.

  12. Study on the vibration band gap and vibration attenuation property of phononic crystals

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Phononic crystals (PCs) are functional materials with periodic structures and elastic wave (vibration) band gaps, where propagation of vibrations with frequencies within band gaps is forbidden. PCs with finite periods can restrain the propagation of vibrations with frequencies in band gaps and thus has vibration attenuation property. Worldwide, many institutions and researchers are engaged in the research of PCs, however, studies on the vibration attenuation property of PCs are still limited. In this paper, we report our study of band gaps and vibration attenuation properties of 1) a simplified PC-periodic mass-spring structures, 2) longitudinal vibration of one-dimensional (1D-), 2D-, 3D-PCs, and 3) the flexural vibration of 1D- and 2D-PCs. These studies provide a foundation for the applications of PCs in vibration attenuation.

  13. Millimeter-wave waveguiding using photonic band structures

    Science.gov (United States)

    Eliyahu, Danny; Sadovnik, Lev S.; Manasson, Vladimir A.

    2000-07-01

    Current trends in device miniaturization and integration, especially in the development of microwave monolithic integrated circuits, calls for flexible, arbitrarily shaped and curved interconnects. Standard dielectric waveguides and microstrip lines are subject to prohibitive losses and their functionality is limited because of their unflexible structures. The problem is addressed by confining the wave- guiding path in a substrate with a Photonic Band Gap structure in a manner that will result in the guided mode being localized within the band gap. Two devices implementing Photonic Band Structures for millimeter waves confinement are presented. The first waveguide is a linear defect in triangular lattice created in a silicon slab (TE mode). The structure consists of parallel air holes of circular cross sections. The silicon was laser drilled to create the 2D crystal. The second device consists of alumina rods arranged in a triangular lattice, surrounded by air and sandwiched between two parallel metal plates (TM mode). Electromagnetic wave (W-band) confinement was obtained in both devices for straight and bent waveguides. Three branch waveguides (intersecting line defects) was studied as well. Measurements confirmed the lowloss waveguide confinement property of the utilizing Photonic Band Gap structure. This structure can find applications in power combiner/splitter and other millimeter wave devices.

  14. MgIn2: Synthesis, Crystal and Band Structure%极性金属间化合物MgIn2的合成、晶体结构及能带特征

    Institute of Scientific and Technical Information of China (English)

    雷晓武; 岳呈阳; 张慧苹

    2012-01-01

    A binary intermetallic compound,MgIn2,has been synthesized by solid-state reaction of the corresponding pure elements in a welded tantalum tube at high temperature.The crystal structure of the title compound was established by single-crystal X-ray diffraction.MgIn2 crystallizes in cubic crystal system,space group Fd-3m (No.227) with a=0.956 13(16) nm,V=0.874 1(3) nm3,Z=8,R1=0.035 3,wR2=0.082 8.The structure of MgIn2 belongs to the CaAl2 type.It is also isostructural with BaAls and features a 3D framework based on [In4]tetrahedron interconnected via comer-sharing.The Mg atoms are located in the space of the 3D framework.The MgIn2 is metallic as indicated by the results from the extended Hückel band structure calculations.ICSD:423608.%在惰性气氛氨气保护下,通过高温固相反应合成得到了一个二元极性金属间化合物MgIn2.经X-射线单晶衍射与元素分析等方法确定了其晶体结构.MgIn2属立方体系,空间群为Fd-3m(No.227),晶体学参数a=0.956 13(16) nm,V=0.8741 (3) nm3,Z=8,R1=0.0353,wR=0.0828.MgIn2属于CaAl2结构类型,其结构特征为[In4]四面体通过共用顶点In原子链接而成的三维框架结构,Mg原子填充在三维框架的空隙中.能带结构计算表明MgIn2属于金属性的化合物.

  15. Wavelet-based method for computing elastic band gaps of one-dimensional phononic crystals

    Institute of Scientific and Technical Information of China (English)

    YAN; ZhiZhong; WANG; YueSheng

    2007-01-01

    A wavelet-based method was developed to compute elastic band gaps of one-dimensional phononic crystals. The wave field was expanded in the wavelet basis and an equivalent eigenvalue problem was derived in a matrix form involving the adaptive computation of integrals of the wavelets. The method was then applied to a binary system. For comparison, the elastic band gaps of the same one-di- mensional phononic crystals computed with the wavelet method and the well- known plane wave expansion (PWE) method are both presented in this paper. The numerical results of the two methods are in good agreement while the computation costs of the wavelet method are much lower than that of PWE method. In addition, the adaptability of wavelets makes the method possible for efficient band gap computation of more complex phononic structures.

  16. Complex band structure and superlattice electronic states

    Science.gov (United States)

    Schulman, J. N.; McGill, T. C.

    1981-04-01

    The complex band structures of the bulk materials which constitute the alternating layer (001) semiconductor-semiconductor superlattice are investigated. The complex bands near the center of the Brillouin zone in the [001] direction are studied in detail. The decay lengths of superlattice states whose energies lie in the bulk band gaps of one of the semiconductors are determined from the dispersion curves of these bands for imaginary k-->. This method is applied using a tight-binding band-structure calculation to two superlattices: the AlAs-GaAs superlattice and the CdTe-HgTe superlattice. The decay lengths of AlAs-GaAs superlattice conduction-band minimum states are found to be substantially shorter than those for the CdTe-HgTe superlattice. These differences in the decay of the states in the two superlattices result in differences in the variation of the conduction-band effective masses with the thickness of the AlAs and CdTe layers. The conduction-band effective masses increase more rapidly with AlAs thickness in the AlAs-GaAs superlattice than with CdTe thickness in the CdTe-HgTe superlattice.

  17. Band Structure of 1-D Photonic Crystal for Oblique Incident Electromagnetic Wave Packet%一维光子晶体斜入射波包的带隙结构

    Institute of Scientific and Technical Information of China (English)

    高洁; 房丽敏; 李华刚; 麦志杰

    2012-01-01

    Dispersion relation of 1-D photonic crystal is deduced by the method of transfer matrix, with coordinate transformation of arbitrary Fourier exponent of electromagnetic wave packet which is obliquely incident. By analyzing the dispersion relation, it is easy to find the difference between the first band gap under obliquely incident wave packet and that of plane wave, respectively. Meanwhile, the former gap is located in the latter one, for the former one is narrower than the latter one in width. Characteristic of band gap is obtained under obliquely incident wave packet, by comparing the first band gap structure with that of plane wave considering edge position and width of the gap. The condition of approximately substituting plane wave for wave packet to calculate band gap is analyzed, according to related factors such as different incident angle of central wave vector and angle spectrum of wave packet. The results demonstrate that the first band gap structure is closely related to incident angle of central wave vector and angle spectrum of wave packet. With smaller incident angle, the first band gap structure caused by wave packet would become closer to that of plane wave; and with smaller angle spectrum of wave packet, the width and position of the first band gap is closer to those of plane wave.%对波包的任意傅里叶分量进行坐标变换后,利用转移矩阵法推导出波包斜入射情形下一维光子晶体的色散关系表达式,利用色散关系曲线分析得出波包斜入射的第一带隙结构,与以往平面波的第一带隙结构不同,波包的带隙宽度小于平面波的带隙宽度,并且在位置上前者带隙包含在后者内部.比较了一维光子晶体分别在波包入射与平面波入射情形下带隙位置和宽度,分析了波包中心入射角的变化以及波包的角分布范围的变化对带隙结构的影响,得到了一维光子晶体对波包斜入射的带隙结构的基本特征,确定了计算波包带

  18. Mini-stop bands in single heterojunction photonic crystal waveguides

    KAUST Repository

    Shahid, N.

    2013-01-01

    Spectral characteristics of mini-stop bands (MSB) in line-defect photonic crystal (PhC) waveguides and in heterostructure PhC waveguides having one abrupt interface are investigated. Tunability of the MSB position by air-fill factor heterostructure PhC waveguides is utilized to demonstrate different filter functions, at optical communication wavelengths, ranging from resonance-like to wide band pass filters with high transmission. The narrowest filter realized has a resonance-like transmission peak with a full width at half maximum of 3.4 nm. These devices could be attractive for coarse wavelength selection (pass and drop) and for sensing applications. 2013 Copyright 2013 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License.

  19. Can photonic crystals be homogenized in higher bands?

    CERN Document Server

    Markel, Vadim A

    2015-01-01

    We consider the conditions under which photonic crystals (PCs) can be viewed as electromagnetically homogeneous at frequencies in the higher photonic bands and, in particular, near the higher-order $\\Gamma$-points. We show that the observation that a purely real isofrequency line of the PC is close to a mathematical circle is insufficient for establishing homogenizability. Complex dispersion points must be included into consideration even in the case of strictly non-absorbing materials. By applying a more careful analysis to the dispersion relations and complex isofrequency lines, we have found that two-dimensional PCs with $C_4$ and $C_6$ symmetries are not electromagnetically homogeneous in the higher photonic bands in spite of the fact that, at some particular frequencies, the real isofrequency lines of these PCs can be circular with high precision.

  20. Formation of Bragg Band Gaps in Anisotropic Phononic Crystals Analyzed With the Empty Lattice Model

    Directory of Open Access Journals (Sweden)

    Yan-Feng Wang

    2016-05-01

    Full Text Available Bragg band gaps of phononic crystals generally, but not always, open at Brillouin zone boundaries. The commonly accepted explanation stems from the empty lattice model: assuming a small material contrast between the constituents of the unit cell, avoided crossings in the phononic band structure appear at frequencies and wavenumbers corresponding to band intersections; for scalar waves the lowest intersections coincide with boundaries of the first Brillouin zone. However, if a phononic crystal contains elastically anisotropic materials, its overall symmetry is not dictated solely by the lattice symmetry. We construct an empty lattice model for phononic crystals made of isotropic and anisotropic materials, based on their slowness curves. We find that, in the anisotropic case, avoided crossings generally do not appear at the boundaries of traditionally defined Brillouin zones. Furthermore, the Bragg “planes” which give rise to phononic band gaps, are generally not flat planes but curved surfaces. The same is found to be the case for avoided crossings between shear (transverse and longitudinal bands in the isotropic case.

  1. Optofluidic tuning of photonic crystal band edge lasers

    DEFF Research Database (Denmark)

    Bernal, Felipe; Christiansen, Mads Brøkner; Gersborg-Hansen, Morten;

    2007-01-01

    We demonstrate optofluidic tuning of polymer photonic crystal band edge lasers with an imposed rectangular symmetry. The emission wavelength depends on both lattice constant and cladding refractive index. The emission wavelength is shown to change 1 nm with a cladding refractive index change of 10......−2. The rectangular symmetry modification alters the emission characteristics of the devices and the relative emission intensities along the symmetry axes depend on cladding refractive index, suggesting a sensor concept based on detection of intensity rather than wavelength....

  2. Broadening of Omnidirectional Photonic Band Gap in Graphene Based one Dimensional Photonic Crystals

    Directory of Open Access Journals (Sweden)

    Neetika Arora

    2015-09-01

    Full Text Available A simple design of one dimensional gradual stacked photonic crystal has been proposed. This structure exhibits a periodic array of alternate layers of Graphene and Silica. These are the materials of low and high refractive indices respectively. Here the structure considered has three stacks .Each stack has five alternate layers of Graphene and silica. The transfer matrix method has been used for numerical computation. In this paper, such a structure has wider reflection bands in comparison to a conventional dielectric PC structure and structure with Sio2 and Si layers for a constant gradual constant ϒ at different incident angle.

  3. A Banding Structure in a Ni-Cu-Si Cast Alloy

    Institute of Scientific and Technical Information of China (English)

    Qi ZHENG; Yufeng ZHENG; Hongyu ZHANG; Xiaofeng SUN; Hengrong GUAN; Zhuangqi HU

    2008-01-01

    The solidified microstructure of a Ni-Cu-Si cast alloy has been investigated, and a kind of banding structure was observed. The results showed that, the banding structure was composed of coarser particles which were Ni3Si type of precipitates and similar to the fine particles precipitate uniformly distributed within matrix of Ni solid solution, in both crystal structure and composition. The formation of bandings was resulted from cast thermal stress and dislocation walls. It was found that the cracks propagated along these bandings in tensile test. The banding structure can be depressed by reducing the cast thermal stress, which can improve the Qtensile ductility.

  4. Flat band degeneracy and near-zero refractive index materials in acoustic crystals

    Directory of Open Access Journals (Sweden)

    Shiqiao Wu

    2016-01-01

    Full Text Available A Dirac-like cone is formed by utilizing the flat bands associated with localized modes in an acoustic crystal (AC composed of a square array of core-shell-structure cylinders in a water host. Although the triply-degeneracy seems to arise from two almost-overlapping flat bands touching another curved band, the enlarged view of the band structure around the degenerate point reveals that there are actually two linear bands intersecting each other at the Brillouin zone center, with another flat band passing through the same crossing point. The linearity of dispersion relations is achieved by tuning the geometrical parameters of the cylindrical scatterers. A perturbation method is used to not only accurately predict the linear slopes of the dispersions, but also confirm the linearity of the bands from first principles. An effective medium theory based on coherent potential approximation is developed, and it shows that a slab made of the AC carries a near-zero refractive index around the Dirac-like point. Full-wave simulations are performed to unambiguously demonstrate the wave manipulating properties of the AC structures such as perfect transmission, unidirectional transmission and wave front shaping.

  5. Quasiparticle Band Structure of BaS

    Institute of Scientific and Technical Information of China (English)

    LU Tie-Yu; CHEN De-Yan; HUANG Mei-Chun

    2006-01-01

    @@ We calculate the band structure of BaS using the local density approximation and the GW approximation (GWA),i.e. in combination of the Green function G and the screened Coulomb interaction W. The Ba 4d states are treated as valence states. We find that BaS is a direct band-gap semiconductor. The result shows that the GWA band gap (Eg-Gw = 3.921 eV) agrees excellently with the experimental result (Eg-EXPT = 3.88 eV or 3.9eV).

  6. Prediction of molecular crystal structures

    Energy Technology Data Exchange (ETDEWEB)

    Beyer, Theresa

    2001-07-01

    The ab initio prediction of molecular crystal structures is a scientific challenge. Reliability of first-principle prediction calculations would show a fundamental understanding of crystallisation. Crystal structure prediction is also of considerable practical importance as different crystalline arrangements of the same molecule in the solid state (polymorphs)are likely to have different physical properties. A method of crystal structure prediction based on lattice energy minimisation has been developed in this work. The choice of the intermolecular potential and of the molecular model is crucial for the results of such studies and both of these criteria have been investigated. An empirical atom-atom repulsion-dispersion potential for carboxylic acids has been derived and applied in a crystal structure prediction study of formic, benzoic and the polymorphic system of tetrolic acid. As many experimental crystal structure determinations at different temperatures are available for the polymorphic system of paracetamol (acetaminophen), the influence of the variations of the molecular model on the crystal structure lattice energy minima, has also been studied. The general problem of prediction methods based on the assumption that the experimental thermodynamically stable polymorph corresponds to the global lattice energy minimum, is that more hypothetical low lattice energy structures are found within a few kJ mol{sup -1} of the global minimum than are likely to be experimentally observed polymorphs. This is illustrated by the results for molecule I, 3-oxabicyclo(3.2.0)hepta-1,4-diene, studied for the first international blindtest for small organic crystal structures organised by the Cambridge Crystallographic Data Centre (CCDC) in May 1999. To reduce the number of predicted polymorphs, additional factors to thermodynamic criteria have to be considered. Therefore the elastic constants and vapour growth morphologies have been calculated for the lowest lattice energy

  7. Wide-field-of-view narrow-band spectral filters based on photonic crystal nanocavities.

    Science.gov (United States)

    Nakagawa, Wataru; Sun, Pang-Chen; Chen, Chyong-Hua; Fainman, Yeshaiahu

    2002-02-01

    We describe a novel approach to implementing wide-field-of-view narrow-band spectral filters, using an array of resonant nanocavities consisting of periodic defects in a two-dimensional three-material photonic-crystal nanostructure. We analyze the transmissivity of this type of filter for a range of wavelengths and in-plane incidence angles as a function of the defect's refractive index, the number of layers in the photonic-crystal reflectors, and the period of the defects and find that this structure diminishes the angular sensitivity of the resonance condition relative to that of a standard multilayer filter.

  8. Two-dimensional photonic crystals with large complete photonic band gaps in both TE and TM polarizations.

    Science.gov (United States)

    Wen, Feng; David, Sylvain; Checoury, Xavier; El Kurdi, Moustafa; Boucaud, Philippe

    2008-08-04

    Photonic crystals exhibiting a photonic band gap in both TE and TM polarizations are particularly interesting for a better control of light confinement. The simultaneous achievement of large band gaps in both polarizations requires to reduce the symmetry properties of the photonic crystal lattice. In this letter, we propose two different designs of two-dimensional photonic crystals patterned in high refractive index thin silicon slabs. These slabs are known to limit the opening of photonic band gaps for both polarizations. The proposed designs exhibit large complete photonic band gaps: the first photonic crystal structure is based on the honey-comb lattice with two different hole radii and the second structure is based on a "tri-ellipse" pattern in a triangular lattice. Photonic band gap calculations show that these structures offer large complete photonic band gaps deltaomega/omega larger than 10% between first and second photonic bands. This figure of merit is obtained with single-mode slab waveguides and is not restricted to modes below light cone.

  9. Maximizing band gaps in plate structures

    DEFF Research Database (Denmark)

    Halkjær, Søren; Sigmund, Ole; Jensen, Jakob Søndergaard

    2006-01-01

    Band gaps, i.e., frequency ranges in which waves cannot propagate, can be found in elastic structures for which there is a certain periodic modulation of the material properties or structure. In this paper, we maximize the band gap size for bending waves in a Mindlin plate. We analyze an infinite...... periodic plate using Bloch theory, which conveniently reduces the maximization problem to that of a single base cell. Secondly, we construct a finite periodic plate using a number of the optimized base cells in a postprocessed version. The dynamic properties of the finite plate are investigated...

  10. Crystal structure of cafenstrole

    Directory of Open Access Journals (Sweden)

    Gihaeng Kang

    2015-08-01

    Full Text Available The title compound (systematic name: N,N-diethyl-3-mesitylsulfonyl-1H-1,2,4-triazole-1-carboxamide, C16H22N4O3S, is a triazole herbicide. The dihedral angle between the planes of the triazole and benzene ring planes is 88.14 (10°. In the crystal, C—H...O hydrogen bonds and weak C—H...π interactions link adjacent molecules, forming one-dimensional chains along the a axis.

  11. Crystal structure of pseudoguainolide

    Directory of Open Access Journals (Sweden)

    Noureddine Beghidja

    2015-03-01

    Full Text Available The lactone ring in the title molecule, C15H22O3 (systematic name: 3,4a,8-trimethyldodecahydroazuleno[6,5-b]furan-2,5-dione, assumes an envelope conformation with the methine C atom adjacent to the the methine C atom carrying the methyl substituent being the flap atom. The other five-membered ring adopts a twisted conformation with the twist being about the methine–methylene C—C bond. The seven-membered ring is based on a twisted boat conformation. No specific interactions are noted in the the crystal packing.

  12. Band structure engineering in organic semiconductors

    Science.gov (United States)

    Schwarze, Martin; Tress, Wolfgang; Beyer, Beatrice; Gao, Feng; Scholz, Reinhard; Poelking, Carl; Ortstein, Katrin; Günther, Alrun A.; Kasemann, Daniel; Andrienko, Denis; Leo, Karl

    2016-06-01

    A key breakthrough in modern electronics was the introduction of band structure engineering, the design of almost arbitrary electronic potential structures by alloying different semiconductors to continuously tune the band gap and band-edge energies. Implementation of this approach in organic semiconductors has been hindered by strong localization of the electronic states in these materials. We show that the influence of so far largely ignored long-range Coulomb interactions provides a workaround. Photoelectron spectroscopy confirms that the ionization energies of crystalline organic semiconductors can be continuously tuned over a wide range by blending them with their halogenated derivatives. Correspondingly, the photovoltaic gap and open-circuit voltage of organic solar cells can be continuously tuned by the blending ratio of these donors.

  13. Crystal structure of nuarimol

    Directory of Open Access Journals (Sweden)

    Gihaeng Kang

    2015-08-01

    Full Text Available The title compound [systematic name: (RS-(2-chlorophenyl(4-fluorophenyl(pyrimidin-5-ylmethanol], C17H12ClFN2O, is a pyrimidine fungicide. The asymmetric unit comprises two independent molecules, A and B, in which the dihedral angles between the plane of the pyrimidine ring and those of the chlorophenyl and fluorophenyl rings are 71.10 (6 and 70.04 (5° in molecule A, and 73.24 (5 and 89.30 (5° in molecule B. In the crystal, O—H...N hydrogen bonds link the components into [010] chains of alternating A and B molecules. The chains are cross-linked by C—H...F hydrogen bonds and weak C—H...π and C—Cl...π [Cl...ring centroid = 3.7630 (8 Å] interactions, generating a three-dimensional network.

  14. Band gap characterization and slow light effects in periodic and quasiperiodic one dimensional photonic crystal

    Science.gov (United States)

    Zaghdoudi, J.; Kuszelewicz, R.; Kanzari, M.; Rezig, B.

    2008-04-01

    Slow light offers many opportunities for photonic devices by increasing the effective interaction length of imposed refractive index changes. The slow wave effect in photonic crystals is based on their unique dispersive properties and thus entirely dielectric in nature. In this work we demonstrate an interesting opportunity to decrease drastically the group velocity of light in one-dimensional photonic crystals constructed form materials with large dielectric constant without dispersion). We use numerical analysis to study the photonic properties of periodic (Bragg mirror) and quasiperiodic one dimensional photonic crystals realized to engineer slow light effects. Various geometries of the photonic pattern have been characterized and their photonic band-gap structure analyzed. Indeed, one dimensional quasi periodic photonic multilayer structure based on Fibonacci, Thue-Morse, and Cantor sequences were studied. Quasiperiodic structures have a rich and highly fragmented reflectivity spectrum with many sharp resonant peaks that could be exploited in a microcavity system. A comparison of group velocity through periodic and quasiperiodic photonic crystals was discussed in the context of slow light propagation. The velocity control of pulses in materials is one of the promising applications of photonic crystals. The material systems used for the numerical analysis are TiO II/SiO II and Te/SiO II which have a refractive index contrast of approximately 1.59 and 3.17 respectively. The proposed structures were modelled using the Transfer Matrix Method.

  15. Production of S-band Accelerating Structures

    CERN Document Server

    Piel, C; Vogel, H; Vom Stein, P

    2004-01-01

    ACCEL currently produces accelerating structures for several scientific laboratories. Multi-cell cavities at S-band frequencies are required for the projects CLIC-driver-linac, DLS and ASP pre-injector linac and the MAMI-C microtron. Based on those projects differences and similarities in design, production technologies and requirements will be addressed.

  16. Thermal tuning the reversible optical band gap of self-assembled polystyrene photonic crystals

    Science.gov (United States)

    Vakili Tahami, S. H.; Pourmahdian, S.; Shirkavand Hadavand, B.; Azizi, Z. S.; Tehranchi, M. M.

    2016-11-01

    Nano-sized polymeric colloidal particles could undergo self-organization into three-dimensional structures to produce desired optical properties. In this research, a facile emulsifier-free emulsion polymerization method was employed to synthesize highly mono-disperse sub-micron polystyrene colloids. A high quality photonic crystal (PhC) structure was prepared by colloidal polystyrene. The reversible thermal tuning effect on photonic band gap position as well as the attenuation of the band gap was investigated in detail. The position of PBG can be tuned from 420 nm to 400 nm by varying the temperature of the PhC structure, reversibly. This reversible effect provides a reconfigurable PhC structure which could be used as thermo-responsive shape memory polymers.

  17. Crystal structure refinement with SHELXL.

    Science.gov (United States)

    Sheldrick, George M

    2015-01-01

    The improvements in the crystal structure refinement program SHELXL have been closely coupled with the development and increasing importance of the CIF (Crystallographic Information Framework) format for validating and archiving crystal structures. An important simplification is that now only one file in CIF format (for convenience, referred to simply as `a CIF') containing embedded reflection data and SHELXL instructions is needed for a complete structure archive; the program SHREDCIF can be used to extract the .hkl and .ins files required for further refinement with SHELXL. Recent developments in SHELXL facilitate refinement against neutron diffraction data, the treatment of H atoms, the determination of absolute structure, the input of partial structure factors and the refinement of twinned and disordered structures. SHELXL is available free to academics for the Windows, Linux and Mac OS X operating systems, and is particularly suitable for multiple-core processors.

  18. Crystal structure refinement with SHELXL

    Energy Technology Data Exchange (ETDEWEB)

    Sheldrick, George M., E-mail: gsheldr@shelx.uni-ac.gwdg.de [Department of Structural Chemistry, Georg-August Universität Göttingen, Tammannstraße 4, Göttingen 37077 (Germany)

    2015-01-01

    New features added to the refinement program SHELXL since 2008 are described and explained. The improvements in the crystal structure refinement program SHELXL have been closely coupled with the development and increasing importance of the CIF (Crystallographic Information Framework) format for validating and archiving crystal structures. An important simplification is that now only one file in CIF format (for convenience, referred to simply as ‘a CIF’) containing embedded reflection data and SHELXL instructions is needed for a complete structure archive; the program SHREDCIF can be used to extract the .hkl and .ins files required for further refinement with SHELXL. Recent developments in SHELXL facilitate refinement against neutron diffraction data, the treatment of H atoms, the determination of absolute structure, the input of partial structure factors and the refinement of twinned and disordered structures. SHELXL is available free to academics for the Windows, Linux and Mac OS X operating systems, and is particularly suitable for multiple-core processors.

  19. Band structure engineering in van der Waals heterostructures via dielectric screening: the GΔW method

    DEFF Research Database (Denmark)

    Winther, Kirsten Trøstrup; Thygesen, Kristian Sommer

    2017-01-01

    precise magnitude is non-trivial to predict because of the non-local nature of the screening in quasi-2D crystals. Moreover, the effect is not captured by effective single-particle methods such as density functional theory. Here we present an efficient and general method for calculating the band gap......The idea of combining different two-dimensional (2D) crystals in van der Waals heterostructures (vdWHs) has led to a new paradigm for band structure engineering with atomic precision. Due to the weak interlayer couplings, the band structures of the individual 2D crystals are largely preserved upon...... formation of the heterostructure. However, regardless of the details of the interlayer hybridisation, the size of the 2D crystal band gaps are always reduced due to the enhanced dielectric screening provided by the surrounding layers. The effect can be significant (on the order of electron volts) but its...

  20. Formation mechanism of the low-frequency locally resonant band gap in the two-dimensional ternary phononic crystals

    Institute of Scientific and Technical Information of China (English)

    Wang Gang; Liu Yao-Zong; Wen Ji-Hong; Yu Dian-Long

    2006-01-01

    The low-frequency band gap and the corresponding vibration modes in two-dimensional ternary locally resonant phononic crystals are restudied successfully with the lumped-mass method. Compared with the work of C. Goffaux and J. Sanchez-Dehesa (Phys. Rev. B 67 14 4301(2003)), it is shown that there exists an error of about 50% in their calculated results of the band structure, and one band is missing in their results. Moreover, the in-plane modes shown in their paper are improper, which results in the wrong conclusion on the mechanism of the ternary locally resonant phononic crystals. Based on the lumped-mass method and better description of the vibration modes according to the band gaps, the locally resonant mechanism in forming the subfrequency gaps is thoroughly analysed. The rule used to judge whether a resonant mode in the phononic crystals can result in a corresponding subfrequency gap is also verified in this ternary case.

  1. Crystal structure of pymetrozine

    Directory of Open Access Journals (Sweden)

    Youngeun Jeon

    2015-07-01

    Full Text Available The title compound, C10H11N5O {systematic name: 6-methyl-4-[(E-(pyridin-3-ylmethylideneamino]-4,5-dihydro-1,2,4-triazin-3(2H-one}, C10H11N5O, is used as an antifeedant in pest control. The asymmetric unit comprises two independent molecules, A and B, in which the dihedral angles between the pyridinyl and triazinyl ring planes [r.m.s. deviations = 0.0132 and 0.0255 ] are 11.60 (6 and 18.06 (4°, respectively. In the crystal, N—H...O, N—H...N, C—H...N and C—H...O hydrogen bonds, together with weak π–π interactions [ring-centroid separations = 3.5456 (9 and 3.9142 (9 Å], link the pyridinyl and triazinyl rings of A molecules, generating a three-dimensional network.

  2. Tuning characteristic of band gap and waveguide in a multi-stub locally resonant phononic crystal plate

    Directory of Open Access Journals (Sweden)

    Xiao-Peng Wang

    2015-10-01

    Full Text Available In this paper, the tuning characteristics of band gaps and waveguides in a locally resonant phononic crystal structure, consisting of multiple square stubs deposited on a thin homogeneous plate, are investigated. Using the finite element method and supercell technique, the dispersion relationships and power transmission spectra of those structures are calculated. In contrast to a system of one square stub, systems of multiple square stubs show wide band gaps at lower frequencies and an increased quantity of band gaps at higher frequencies. The vibration modes of the band gap edges are analyzed to clarify the mechanism of the generation of the lowest band gap. Additionally, the influence of the stubs arrangement on the band gaps in multi-stub systems is investigated. The arrangements of the stubs were found to influence the band gaps; this is critical to understand for practical applications. Based on this finding, a novel method to form defect scatterers by changing the arrangement of square stubs in a multi-stub perfect phononic crystal plate was developed. Defect bands can be induced by creating defects inside the original complete band gaps. The frequency can then be tuned by changing the defect scatterers’ stub arrangement. These results will help in fabricating devices such as acoustic filters and waveguides whose band frequency can be modulated.

  3. Quasiparticle band structure of antiferromagnetic Eu Te

    Energy Technology Data Exchange (ETDEWEB)

    Mathi Jaya, S.; Nolting, W. [Humboldt-Universitaet zu Berlin, Institut fuer Physik, Lehrstuhl Festkoerpertheorie, Invalidenstrasse 110, D-10115 Berlin (Germany)

    1997-11-24

    The temperature-dependent electronic quasiparticle spectrum of the antiferromagnetic semiconductor Eu Te is derived by use of a combination of a many-body model procedure with a tight-binding-'linear muffin tin orbital' (TB - LMTO) band structure calculation. The central part is the d-f model for a single band electron ('test electron') being exchange coupled to the anti ferromagnetically ordered localized moments of the Eu ions. The single-electron Bloch energies of the d-f model are taken from a TB-LMTO calculation for paramagnetic Eu Te. The d-f model is evaluated by a recently proposed moment conserving Green function technique to get the temperature-dependent sublattice-quasiparticle band structure (S-QBS) and sublattice-quasiparticle density of states (S-QDOS) of the unoccupied 5 d-6 s energy bands. Unconventional correlation effects and the appearance of characteristic quasiparticles ('magnetic polarons') are worked out in detail. The temperature dependence of the S-QDOS and S-QBS is mainly provoked by the spectral weights of the energy dispersions. Minority- and majority-spin spectra coincide for all temperatures but with different densities of states. Upon cooling from T{sub N} to T = 0 K the lower conduction band edge exhibits a small blue shift of -0.025 eV in accordance with the experiment. Quasiparticle damping manifesting itself in a temperature-dependent broadening of the spectral density peaks arises from spin exchange processes between (5 d-6 s) conduction band electrons and localized 4 f moments. (author)

  4. Midfrequency band dynamics of large space structures

    Science.gov (United States)

    Coppolino, Robert N.; Adams, Douglas S.; Levine, Marie B.

    2004-09-01

    High and low intensity dynamic environments experienced by a spacecraft during launch and on-orbit operations, respectively, induce structural loads and motions, which are difficult to reliably predict. Structural dynamics in low- and mid-frequency bands are sensitive to component interface uncertainty and non-linearity as evidenced in laboratory testing and flight operations. Analytical tools for prediction of linear system response are not necessarily adequate for reliable prediction of mid-frequency band dynamics and analysis of measured laboratory and flight data. A new MATLAB toolbox, designed to address the key challenges of mid-frequency band dynamics, is introduced in this paper. Finite-element models of major subassemblies are defined following rational frequency-wavelength guidelines. For computational efficiency, these subassemblies are described as linear, component mode models. The complete structural system model is composed of component mode subassemblies and linear or non-linear joint descriptions. Computation and display of structural dynamic responses are accomplished employing well-established, stable numerical methods, modern signal processing procedures and descriptive graphical tools. Parametric sensitivity and Monte-Carlo based system identification tools are used to reconcile models with experimental data and investigate the effects of uncertainties. Models and dynamic responses are exported for employment in applications, such as detailed structural integrity and mechanical-optical-control performance analyses.

  5. Efficient propagation of TM polarized light in photonic crystal components exhibiting band gaps for TE polarized light

    DEFF Research Database (Denmark)

    Borel, Peter Ingo; Frandsen, Lars Hagedorn; Thorhauge, Morten;

    2003-01-01

    We have investigated the properties of TM polarized light in planar photonic crystal waveguide structures, which exhibit photonic band gaps for TE polarized light. Straight and bent photonic crystal waveguides and couplers have been fabricated in silicon-on-insulator material and modelled using a 3...... in a simple photonic crystal coupler with a size of ~ 20 m × 20 m. These promising features may open for the realization of ultra-compact photonic crystal components, which are easily integrated in optical communication networks....

  6. Anisotropic lattice expansion of three-dimensional colloidal crystals and its impact on hypersonic phonon band gaps.

    Science.gov (United States)

    Wu, Songtao; Zhu, Gaohua; Zhang, Jin S; Banerjee, Debasish; Bass, Jay D; Ling, Chen; Yano, Kazuhisa

    2014-05-21

    We report anisotropic expansion of self-assembled colloidal polystyrene-poly(dimethylsiloxane) crystals and its impact on the phonon band structure at hypersonic frequencies. The structural expansion was achieved by a multistep infiltration-polymerization process. Such a process expands the interplanar lattice distance 17% after 8 cycles whereas the in-plane distance remains unaffected. The variation of hypersonic phonon band structure induced by the anisotropic lattice expansion was recorded by Brillouin measurements. In the sample before expansion, a phononic band gap between 3.7 and 4.4 GHz is observed; after 17% structural expansion, the gap is shifted to a lower frequency between 3.5 and 4.0 GHz. This study offers a facile approach to control the macroscopic structure of colloidal crystals with great potential in designing tunable phononic devices.

  7. Photonic band gap of one-dimensional periodic structure containing dispersive left-handed metamaterials

    Institute of Scientific and Technical Information of China (English)

    Zhanshan Wang; Tian Sang; Fengli Wang; Yonggang Wu; Lingyan Chen

    2008-01-01

    Band structures of one-dimensional(1D)photonic crystals(PCs)containing dispersive left-handed metamaterials are studied theoretically.The results show that the structure possesses a type of photonic band gap originating from total internal reflection(TIR).In contrast to photonic band gaps corresponding to zero average refractive index and zero phase.the TIR gap exhibits sharp angular effect and has no polarization effect.It should also be noted that band structures of transverse electric(TE) and transverse magnetic(TM) mode waves are exactly the same in the PCs we studied.

  8. Direct band gap silicon crystals predicted by an inverse design method

    Science.gov (United States)

    Oh, Young Jun; Lee, In-Ho; Lee, Jooyoung; Kim, Sunghyun; Chang, Kee Joo

    2015-03-01

    Cubic diamond silicon has an indirect band gap and does not absorb or emit light as efficiently as other semiconductors with direct band gaps. Thus, searching for Si crystals with direct band gaps around 1.3 eV is important to realize efficient thin-film solar cells. In this work, we report various crystalline silicon allotropes with direct and quasi-direct band gaps, which are predicted by the inverse design method which combines a conformation space annealing algorithm for global optimization and first-principles density functional calculations. The predicted allotropes exhibit energies less than 0.3 eV per atom and good lattice matches, compared with the diamond structure. The structural stability is examined by performing finite-temperature ab initio molecular dynamics simulations and calculating the phonon spectra. The absorption spectra are obtained by solving the Bethe-Salpeter equation together with the quasiparticle G0W0 approximation. For several allotropes with the band gaps around 1 eV, photovoltaic efficiencies are comparable to those of best-known photovoltaic absorbers such as CuInSe2. This work is supported by the National Research Foundation of Korea (2005-0093845 and 2008-0061987), Samsung Science and Technology Foundation (SSTF-BA1401-08), KIAS Center for Advanced Computation, and KISTI (KSC-2013-C2-040).

  9. Complex banded structures in directional solidification processes.

    Science.gov (United States)

    Korzhenevskii, A L; Rozas, R E; Horbach, J

    2016-01-27

    A combination of theory and numerical simulation is used to investigate impurity superstructures that form in rapid directional solidification (RDS) processes in the presence of a temperature gradient and a pulling velocity with an oscillatory component. Based on a capillary wave model, we show that the RDS processes are associated with a rich morphology of banded structures, including frequency locking and the transition to chaos.

  10. Banded electron structures in the plasmasphere

    Energy Technology Data Exchange (ETDEWEB)

    Burke, W.J.; Rubin, A.G.; Hardy, D.A.; Holeman, E.G.

    1995-05-01

    The low-energy plasma analyzer on CRRES has detected significant fluxes of 10-eV to 30-keV electrons trapped on plasmaspheric field lines. On energy versus time spectrograms these electrons appear as banded structures that can span the 2 < L < 6 range of magnetic shells. The authors present an example of banded electron structures, encountered in the nightside plasmasphere during the magnetically quiet January 30, 1991. Empirical analysis suggests that two clouds of low energy electrons were injected from the plasma sheet to L < 4 on January 26 and 27 while the convective electric field was elevated. The energies of electrons in the first cloud were greater than those in the second. DMSP F8 measurements show that after the second injection, the polar cap potential rapidly decreased from >50 to <20 kY. Subsequent encounters with the lower energy cloud on alternating CRRES orbits over the next 2 days showed a progressive, earthward movement of the electrons, inner boundary. Whistler and electron cyclotron harmonic emissions accompanied the most intense manifestations of cloud electrons. The simplest explanation of these measurements is that after initial injection, the AIfven boundary moved Outward, leaving the cloud electrons on closed drift paths. Subsequent fluctuations of the convective electric field penetrated the plasmasphere, transporting cloud elements inward. The magnetic shell distribution of electron temperatures in one of the banded structures suggests that radiative energy losses may be comparable in magnitude to gains due to adiabatic compression.

  11. Photonic Band Modulation in a Two-Dimensional Photonic Crystal with a ne-Dimensional Periodic Dielectric Background

    Institute of Scientific and Technical Information of China (English)

    ZHU Wen-Xing; ZHANG Yan; SHI Jun-Jie

    2008-01-01

    A two-dimensional photonic crystal with a one-dimensional periodic dielectric background is proposed. The photonic band modulation effects due to the periodic background are investigated based on the plane wave expansion method. We find that periodic modulation of the dielectric background greatly alters photonic band structures, especially for the E-polarization modes. The number, width and position of the photonic band gaps (PBGs) sensitively depend on the structure parameters (the layer thicknesses and dielectric constants) of the one-dimensional periodic background.

  12. Spectroscopy of photonic band gaps in mesoporous one-dimensional photonic crystals based on aluminum oxide

    Science.gov (United States)

    Gorelik, V. S.; Voinov, Yu. P.; Shchavlev, V. V.; Bi, Dongxue; Shang, Guo Liang; Fei, Guang Tao

    2016-12-01

    Mesoporous one-dimensional photonic crystals based on aluminum oxide have been synthesized by electrochemical etching method. Reflection spectra of the obtained mesoporous samples in a wide spectral range that covers several band gaps are presented. Microscopic parameters of photonic crystals are calculated and corresponding reflection spectra for the first six band gaps are presented.

  13. Diamond-Structured Photonic Crystals with Graded Air Spheres Radii

    Directory of Open Access Journals (Sweden)

    Dichen Li

    2012-05-01

    Full Text Available A diamond-structured photonic crystal (PC with graded air spheres radii was fabricated successfully by stereolithography (SL and gel-casting process. The graded radii in photonic crystal were formed by uniting different radii in photonic crystals with a uniform radius together along the Г‑Х direction. The stop band was observed between 26.1 GHz and 34.3 GHz by reflection and transmission measurements in the direction. The result agreed well with the simulation attained by the Finite Integration Technique (FIT. The stop band width was 8.2 GHz and the resulting gap/midgap ratio was 27.2%, which became respectively 141.4% and 161.9% of the perfect PC. The results indicate that the stop band width of the diamond-structured PC can be expanded by graded air spheres radii along the Г‑Х direction, which is beneficial to develop a multi bandpass filter.

  14. Structures and growth mechanisms of poly-(3-hydroxybutyrate) (PHB) crystallized from solution and thin melt film

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The spherulitic structures and morphologies of poly-(3-hydroxybutyrate) (PHB) crystallized from a so- lution and a thin melt film were investigated in this study. The formation mechanisms of banded spherulites under different crystallization conditions are proposed. It was found that the formation of banded spherulites was caused by the rhythmic crystal growth of the spherulites and lamellar twisting growth for the polymer crystallization from a thin melt film and a solution, respectively.

  15. Probe spectrum of a four-level atom in a double-band photonic crystal

    Institute of Scientific and Technical Information of China (English)

    Wen Qing-Bo; Wang Jian; Zhang Han-Zhuang

    2004-01-01

    In this paper, the probe absorption spectrum of an atom in a double-band photonic crystal have been studied. In the modes, we assume that one of the two atomic transitions in a A-type atomic system is interacting with free vacuum modes, and another transition is interacting with free vacuum modes, isotropic photonic band gap (PBG) modes and anisotropic PBG modes, separately. The effects of the fine structure of the atomic lower levels on the probe absorption spectrum are investigated in detail in the three cases. The most interesting thing is that the two (four) transparencies at one (two) probe absorption peak(s), caused by the fine structure of the lower levels of an atom, are predicted in the case of isotropic PBG modes.

  16. Spontaneous emission spectrum of a four-level atom in a double-band photonic crystal

    Institute of Scientific and Technical Information of China (English)

    Wang Jian; Yang Dong; Zhang Han-Zhang

    2005-01-01

    The spontaneous emission spectrum from a four-level atom in a double-band photonic crystal has been investigated.We use the model which assumes three atomic transitions. One of the transitions interacts with the free vacuum modes,and the other two transitions couple to the modes of the isotropic photonic band gap (PBG), the anisotropic PBG and another free vacuum. The effects of the fine structure of the lower levels on the spontaneous emission spectrum of an atom are investigated in detail in the three cases. New features of four (two) transparencies with two (one) spontaneous emission peaks, resulting from the fine structure of the lower levels of an atom, are predicted in the case of isotropic PBG modes.

  17. The band-gap enhanced photovoltaic structure

    Science.gov (United States)

    Tessler, Nir

    2016-05-01

    We critically examine the recently suggested structure that was postulated to potentially add 50% to the photo-conversion efficiency of organic solar cells. We find that the structure could be realized using stepwise increase in the gap as long as the steps are not above 0.1 eV. We also show that the charge extraction is not compromised due to an interplay between the contact's space charge and the energy level modification, which result in a flat energy band at the extracting contact.

  18. Differences of Band Gap Characteristics of Square and Triangular Lattice Photonic Crystals in Terahertz Range

    Institute of Scientific and Technical Information of China (English)

    Jie Zha; Zhi-Yong Zhong; Huai-Wu Zhang; Qi-Ye Wen; Yuan-Xun Li

    2009-01-01

    Band gap characteristics of the photonic crystals in terahertz range with square lattice and triangular lattice of GaAs cylinders are comparatively studied by means of plane wave method (PWM). The influence of the radius on the band gap width is analyzed and the critical values where the band gap appears are put forward. The results show that themaximum band gap width of photonic crystal with triangular lattice of GaAs cylinders is much wider than that of photonic crystal with square lattice. The research provides a theoretic basis for the development of terahertz (THz) devices.

  19. Structural colours through photonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    McPhedran, R.C.; Nicorovici, N.A.; McKenzie, D.R.; Rouse, G.W.; Botten, L.C.; Welch, V.; Parker, A.R.; Wohlgennant, M.; Vardeny, V

    2003-10-01

    We discuss two examples of living creatures using photonic crystals to achieve iridescent colouration. The first is the sea mouse (Aphroditidae, Polychaeta), which has a hexagonal close packed structure of holes in its spines and lower-body felt, while the second is the jelly fish Bolinopsis infundibulum, which has an oblique array of high index inclusions in its antennae. We show by measurements and optical calculations that both creatures can achieve strong colours despite having access only to weak refractive index contrast.

  20. Paired modes of heterostructure cavities in photonic crystal waveguides with split band edges

    DEFF Research Database (Denmark)

    Mahmoodian, Sahand; Sukhorukov, Andrey A.; Ha, Sangwoo

    2010-01-01

    We investigate the modes of double heterostructure cavities where the underlying photonic crystal waveguide has been dispersion engineered to have two band-edges inside the Brillouin zone. By deriving and using a perturbative method, we show that these structures possess two modes. For unapodized...... cavities, the relative detuning of the two modes can be controlled by changing the cavity length, and for particular lengths, a resonant-like effect makes the modes degenerate. For apodized cavities no such resonances exist and the modes are always non-degenerate....

  1. Analysis of two-dimensional photonic band gap structure with a rhombus lattice

    Institute of Scientific and Technical Information of China (English)

    Limei Qi; Ziqiang Yang; Xi Gao; Zheng Liang

    2008-01-01

    @@ The relative band gap for a rhombus lattice photonic crystal is studied by plane wave expansion method and high frequency structure simulator (HFSS) simulation. General wave vectors in the first Briliouin zone are derived. The relative band gap as a function of air-filling factor and background material is investigated, respectively, and the nature of photonic band gap for different lattice angles is analyzed by the distribution of electric energy. These results would provide theoretical instruction for designing optical integrated devices using photonic crystal with a rhombus lattice.

  2. THE CRYSTAL STRUCTURE OF ANTIMONY (III) SULFOBROMIDE, SBSBR,

    Science.gov (United States)

    ANTIMONY COMPOUNDS, *SULFUR COMPOUNDS, CRYSTAL STRUCTURE , CRYSTAL STRUCTURE , BROMIDES, SYMMETRY(CRYSTALLOGRAPHY), FOURIER ANALYSIS, MOLECULAR STRUCTURE, CRYSTAL LATTICES, CHEMICAL BONDS, X RAY DIFFRACTION.

  3. Photonic bands, gap maps, and intrinsic losses in three-component 2D photonic crystal slabs

    Institute of Scientific and Technical Information of China (English)

    Hongjun Shen; Huiping Tian; Yuefeng Ji

    2009-01-01

    We obtain the photonic bands and intrinsic losses for the triangular lattice three-component two-dimensional (2D) photonic crystal (PhC) slabs by expanding the electromagnetic field on the basis of waveguide modes of an effective homogeneous waveguide. The introduction of the third component into the 2D PhC slabs influences the photonic band structure and the intrinsic losses of the system. We ex-amine the dependences of the band gap width and gap edge position on the interlayer dielectric constant and interlayer thickness. It is found that the gap edges shift to lower frequencies and the intrinsic losses of each band decrease with the increasing interlayer thickness or dielectric constant. During the design of the real PhC system, the effect of unintentional native oxide surface layer on the optical properties of 2D PhC slabs has to be taken into consideration. At the same time, intentional oxidization of macroporous PhC structure can be utilized to optimize the design.

  4. Self-consistent photonic band structure of dielectric superlattices containing nonlinear optical materials.

    Science.gov (United States)

    Lousse, V; Vigneron, J P

    2001-02-01

    The theory of photonic crystals is extended to include the optical Kerr effect taking place in weak third-order, nonlinear materials present in the unit cell. The influence on the dispersion relations of the illumination caused by a single Bloch mode transiting through the crystal structure is examined. Special attention is given to the modification of the photonic gap width and position. Assuming an instantaneous change of refractive index with illumination, the nonlinear band structure problem is solved as a sequence of ordinary, linear band structure calculations, carried out in a plane-wave field representation.

  5. Theoretical optimization of complete forbidden bands in woodpile-type photonic crystals

    Institute of Scientific and Technical Information of China (English)

    ZHAN Yi; ZHENG Yi; LI Xiu-Xia

    2008-01-01

    Based on the plane-wave method, the optical properties of complete forbidden bands of woodpile structure photonic crystal with an entire lattice rotation of 45°in the x-y plane were theoretically studied in terms ofheight-to-pitch ratios, filling factors, and rotation angles. The calculated results show that the gap to mid-gap ratio changes slightly with a filling fraction ranging from 0.25 to 0.30. The optimum height-to-pitch ratio is about 1.3. The gap to mid-gap ratio reaches more than 0.18 when the rotation angle increases from 40°to 50°and the maximum gap to mid-gap ratio of 0.2 remains unchanged for the rotation angle from 42°to 48°with a constant height-to-pitch ratio of 1.3. The gap to mid-gap ratio reaches the maximum value of 0.2 when the height-to-pitch ratio is 1.3. This woodpile-type photonic crystal can provide large band gaps within a wider parameter range, which makes it convenient to manufacture three-dimensional photonic crystals in the laboratory.

  6. Modulation of the Band Gaps of Phononic Crystals with Thermal Effects

    Science.gov (United States)

    Aly, Arafa H.; Mehaney, Ahmed

    2015-11-01

    Band gaps of elastic waves, both in-plane and shear waves, propagating through one-dimensional perfect/defect phononic crystals (PnCs) that involve thermal effects are studied in this paper. Based on the transfer matrix method and Bloch theory, the expressions of the reflection coefficients and dispersion relation are presented. Elastic waves localization is obtained by immersing a defect layer through a perfect structure. Compared with the periodic structure, we observed that defected PnCs introduced localized modes or peaks within the phononic band gaps. Hence, Numerical simulations are performed to investigate the influences of the defect layer thickness and type on the number and intensity of the localized modes. Moreover, we have observed that temperature changes have prominent effects on the localized modes and band gaps width, especially at plane wave propagation. Such effects could change thermal properties of the PnCs structure such as thermal conductivity and could control the thermal emission contributed by phonons in many engineering structures.

  7. Band Gap Computation of Two Dimensional Photonic Crystal for High Index Contrast Grating Application

    Directory of Open Access Journals (Sweden)

    Gagandeep Kaur

    2014-05-01

    Full Text Available Two Dimensional Photonic Crystal (PHc is convenient type of PHc, It refers to the fact that the dielectric is periodic in Two directions. The study of photonic structure by a simulation method is extremely momentous. At optical frequencies the optical density contained by two dimensional PHc changes periodically. They have the property to strong effect the propagation of light waves at these optical frequencies. A typical linearization method which solves the common nonlinear Eigen values difficulties has been used to achieve structures of the photonic band. There are two method plane wave expansion method (PWE and Finite Difference Time Domain method (FDTD. These Methods are most widely used for band gap calculation of PHc’s. FDTD Method has more smoothness and directness and can be explored effortlessly for simulation of the field circulation inside the photonic structure than PWE method so we have used FDTD Method for Two dimensional PHc’s calculation. In simulation of Two Dimensional band structures, silicon material has 0.543nm lattice constant and 1.46refractive index.

  8. Crystal orientation dependent optical transmittance and band gap of Na{sub 0.5}Bi{sub 0.5}TiO{sub 3}–BaTiO{sub 3} single crystals

    Energy Technology Data Exchange (ETDEWEB)

    He, Chongjun, E-mail: hechongjun@nuaa.edu.cn [College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 (China); Deng, Chenguang; Wang, Jiming; Gu, Xiaorong; Wu, Tong [College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 (China); Zhu, Kongjun [State Key Laboratory of Mechanics and Control of Mechanical Structures, College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Liu, Youwen, E-mail: ywliu@nuaa.edu.cn [College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 (China); Key Laboratory of Radar Imaging and Microwave Photonics, Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)

    2016-02-15

    Optical transmittance spectra of lead-free ferroelectric (1−x)Na{sub 0.5}Bi{sub 0.5}TiO{sub 3}–xBaTiO{sub 3} (NBT–xBT) single crystals poled along different directions have been studied comprehensively. After poled along [001] direction, the transmittance of tetragonal NBT–8%BT crystal is about 70%, which is much higher than that of NBT–2%BT crystal with rhombohedral structure and NBT–5%BT crystal with morphotropic phase boundary (MPB) composition. However, after poled [111] direction, the transmittance of tetragonal NBT–8%BT crystal is the smallest among them. These properties are manifest in view of the crystal structure. Both direct and indirect optical energy band gaps, as well phonon energies were obtained from absorption coefficient spectra by Tauc equations. The band gaps of [001]-poled NBT–xBT crystals increase with BT content, yet the [111]-poled crystals have opposite trends.

  9. Tuning of band gaps for a two-dimensional piezoelectric phononic crystal with a rectangular lattice

    Institute of Scientific and Technical Information of China (English)

    Yize Wang; Fengming Li; Yuesheng Wang; Kikuo Kishimoto; Wenhu Huang

    2009-01-01

    In this paper, the elastic wave propagation in a two-dimensional piezoelectric phononic crystal is studied by considering the mechanic-electric coupling. The gener-alized eigenvalue equation is obtained by the relation of the mechanic and electric fields as well as the Bloch-Floquet the-orem. The band structures of both the in-plane and anti-plane modes are calculated for a rectangular lattice by the plane-wave expansion method. The effects of the lattice constant ratio and the piezoelectricity with different filling fractions are analyzed. The results show that the largest gap width is not always obtained for a square lattice. In some situations, a rectangular lattice may generate larger gaps. The band gap characteristics are influenced obviously by the piezoelectric-ity with the larger lattice constant ratios and the filling frac-tions.

  10. Transparent wide band gap crystals follow indirect allowed transition and bipolaron hopping mechanism

    Directory of Open Access Journals (Sweden)

    Feroz A. Mir

    2014-01-01

    Full Text Available Recently, we carried out structural, optical and dielectric studies on micro-crystals of Oxypeucedanin (C16H14O5, isolated from the roots of plant Prangos pabularia (Mir et al. (2014 [3,4]. The obtained trend in frequency exponent (s with frequency (ω indicates that the universal dynamic response is followed by this compound. From optical absorption spectroscopy, the optical band gap (Eg was estimated around 3.76 eV and system is showing indirect allowed transition. Using Eg in certain relation of s, a close value of s (as much close obtained by fitting ac conductivity was obtained. This method was further used for other similar systems and again same trend was obtained. So a general conclusion was made that the high transmitting wide band insulators or semiconductors may follow bipolaron hopping transport mechanism.

  11. Band Gap Optimization of Two-Dimensional Photonic Crystals Using Semidefinite Programming and Subspace Methods

    CERN Document Server

    Men, Han; Freund, Robert M; Parrilo, Pablo A; Peraire, Jaume

    2009-01-01

    In this paper, we consider the optimal design of photonic crystal band structures for two-dimensional square lattices. The mathematical formulation of the band gap optimization problem leads to an infinite-dimensional Hermitian eigenvalue optimization problem parametrized by the dielectric material and the wave vector. To make the problem tractable, the original eigenvalue problem is discretized using the finite element method into a series of finite-dimensional eigenvalue problems for multiple values of the wave vector parameter. The resulting optimization problem is large-scale and non-convex, with low regularity and non-differentiable objective. By restricting to appropriate eigenspaces, we reduce the large-scale non-convex optimization problem via reparametrization to a sequence of small-scale convex semidefinite programs (SDPs) for which modern SDP solvers can be efficiently applied. Numerical results are presented for both transverse magnetic (TM) and transverse electric (TE) polarizations at several fr...

  12. A Study of Properties of the Photonic Band Gap of Unmagnetized Plasma Photonic Crystal

    Institute of Scientific and Technical Information of China (English)

    LIU Song; ZHONG Shuangying; LIU Sanqiu

    2009-01-01

    In this study,the propagation of electromagnetic waves in one-dimensional plasma photonic crystals(PPCs),namely,superlattice structures consisting alternately of a homogeneous unmagnetized plasma and dielectric material,is simulated numerically using the finite-difference time-domain(FDTD) algorithm.A perfectly matched layer (PML) absorbing technique is used in this simulation.The reflection and transmission coefficients of electromagnetic(EM)waves through PPCs are calculated.The characteristics of the photonic band gap(PBG)are discussed in terms of plasma density,dielectric constant ratios,number of periods,and introduced layer defect.These may provide some useful information for designing plasma photonic crystal devices.

  13. B3LYP, BLYP and PBE DFT band structures of the nucleotide base stacks

    Science.gov (United States)

    Szekeres, Zs; Bogár, F.; Ladik, J.

    DFT crystal orbital (band structure) calculations have been performed for the nucleotide base stacks of cytosine, thymine, adenine, and guanine arranged in DNA B geometry. The band structures obtained with PBE, BLYP, and B3LYP functionals are presented and compared to other related experimental and theoretical results. The influence of the quality of the basis set on the fundamental gap values was also investigated using Clementi's double ζ, 6-31G and 6-31G* basis sets.

  14. Pattern information extraction from crystal structures

    OpenAIRE

    Okuyan, Erhan

    2005-01-01

    Cataloged from PDF version of article. Determining crystal structure parameters of a material is a quite important issue in crystallography. Knowing the crystal structure parameters helps to understand physical behavior of material. For complex structures, particularly for materials which also contain local symmetry as well as global symmetry, obtaining crystal parameters can be quite hard. This work provides a tool that will extract crystal parameters such as primitive vect...

  15. A phenomenological model of electronic band structure in ferroelectric Pb(In{sub 1/2}Nb{sub 1/2})O{sub 3}-Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-PbTiO{sub 3} single crystals around the morphotropic phase boundary determined by temperature-dependent transmittance spectra

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, J.J.; Li, W.W. [Key Laboratory of Polar Materials and Devices, Ministry of Education, Department of Electronic Engineering, East China Normal University, Shanghai 200241 (China); Xu, G.S. [R and D Center of Synthetic Crystals, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201800 (China); Jiang, K. [Key Laboratory of Polar Materials and Devices, Ministry of Education, Department of Electronic Engineering, East China Normal University, Shanghai 200241 (China); Hu, Z.G., E-mail: zghu@ee.ecnu.edu.cn [Key Laboratory of Polar Materials and Devices, Ministry of Education, Department of Electronic Engineering, East China Normal University, Shanghai 200241 (China); Chu, J.H. [Key Laboratory of Polar Materials and Devices, Ministry of Education, Department of Electronic Engineering, East China Normal University, Shanghai 200241 (China)

    2011-10-15

    The optical properties of ferroelectric Pb(In{sub 1/2}Nb{sub 1/2})O{sub 3}-Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-PbTiO{sub 3} (PIN-PMN-PT) single crystals around the morphotropic phase boundary (MPB) have been investigated using ultraviolet-infrared transmittance spectra in the temperature range of 8-300 K. Based on the temperature-dependent spectral measurement of the band gap, we propose a phenomenological model of band structure vs. temperature to explain both the negative and positive band narrowing coefficient dE{sub gd}/dT in ferroelectric PIN-PMN-PT crystals around the MPB where multiple phases coexist. The peculiar positive coefficient only exists in the fragile multiphase region of the MPB, while the negative coefficient, caused by thermal expansion of the lattice and renormalization of the band structure by electron-phonon interaction, exists in the rhombohedral or tetragonal single-phase region as well as in the stationary multiphase region of the MPB. The origin of the positive coefficient is a long-range increasing fraction of coexistence from the monoclinic phase with small band gap to rhombohedral phase with large band gap at elevated temperature. In agreement with optical transmittance results of PMN-PT/PIN-PMN-PT, the model predicts that these unusual positive band narrowing coefficients may exist for all ferroelectrics around the MPB where the coexistence of phases lacks thermodynamic stability.

  16. Resonant behavior and selective switching of stop bands in three-dimensional photonic crystals with inhomogeneous components.

    Science.gov (United States)

    Baryshev, A V; Khanikaev, A B; Inoue, M; Lim, P B; Sel'kin, A V; Yushin, G; Limonov, M F

    2007-08-10

    We demonstrate that, in contrast with the well-studied photonic crystals consisting of two homogeneous components, photonic crystals comprised of inhomogeneous or multiple (three or more) components may bring new opportunities to photonics due to the discovered quasiperiodic resonant behavior of their (hkl) stop bands as a function of the reciprocal lattice vector. A resonant stop band cannot be switched off for any permittivity of structural components. Tuning the permittivity or structural parameters allows the selective on-off switching of nonresonant (hkl) stop bands. This independent manipulation of light at different Bragg wavelengths provides a new degree of freedom to design selective optical switches and waveguides. Transmission experiments performed on synthetic opals confirmed the theoretical predictions.

  17. Hybrid density functional theory band structure engineering in hematite.

    Science.gov (United States)

    Pozun, Zachary D; Henkelman, Graeme

    2011-06-14

    We present a hybrid density functional theory (DFT) study of doping effects in α-Fe(2)O(3), hematite. Standard DFT underestimates the band gap by roughly 75% and incorrectly identifies hematite as a Mott-Hubbard insulator. Hybrid DFT accurately predicts the proper structural, magnetic, and electronic properties of hematite and, unlike the DFT+U method, does not contain d-electron specific empirical parameters. We find that using a screened functional that smoothly transitions from 12% exact exchange at short ranges to standard DFT at long range accurately reproduces the experimental band gap and other material properties. We then show that the antiferromagnetic symmetry in the pure α-Fe(2)O(3) crystal is broken by all dopants and that the ligand field theory correctly predicts local magnetic moments on the dopants. We characterize the resulting band gaps for hematite doped by transition metals and the p-block post-transition metals. The specific case of Pd doping is investigated in order to correlate calculated doping energies and optical properties with experimentally observed photocatalytic behavior.

  18. Berry phase and band structure analysis of the Weyl semimetal NbP

    Science.gov (United States)

    Sergelius, Philip; Gooth, Johannes; Bäßler, Svenja; Zierold, Robert; Wiegand, Christoph; Niemann, Anna; Reith, Heiko; Shekhar, Chandra; Felser, Claudia; Yan, Binghai; Nielsch, Kornelius

    2016-01-01

    Weyl semimetals are often considered the 3D-analogon of graphene or topological insulators. The evaluation of quantum oscillations in these systems remains challenging because there are often multiple conduction bands. We observe de Haas-van Alphen oscillations with several frequencies in a single crystal of the Weyl semimetal niobium phosphide. For each fundamental crystal axis, we can fit the raw data to a superposition of sinusoidal functions, which enables us to calculate the characteristic parameters of all individual bulk conduction bands using Fourier transform with an analysis of the temperature and magnetic field-dependent oscillation amplitude decay. Our experimental results indicate that the band structure consists of Dirac bands with low cyclotron mass, a non-trivial Berry phase and parabolic bands with a higher effective mass and trivial Berry phase. PMID:27667203

  19. Band structure of superdeformed bands in odd-A Hg nuclei

    Institute of Scientific and Technical Information of China (English)

    陈星渠; 邢正

    1997-01-01

    Through particle-rotor model, band structure of superdeformed bands in odd-A Hg nuclei is analysed. An overall and excellent agreement between the calculated and observed kinematic and dynamic moments of inertia is obtained. The electromagnetic transition properties of SD bands can be used to identify the configuration with certainty.

  20. Design of a three-dimensional photonic band gap cavity in a diamondlike inverse woodpile photonic crystal

    Science.gov (United States)

    Woldering, Léon A.; Mosk, Allard P.; Vos, Willem L.

    2014-09-01

    We theoretically investigate the design of cavities in a three-dimensional (3D) inverse woodpile photonic crystal. This class of cubic diamondlike crystals has a very broad photonic band gap and consists of two perpendicular arrays of pores with a rectangular structure. The point defect that acts as a cavity is centered on the intersection of two intersecting perpendicular pores with a radius that differs from the ones in the bulk of the crystal. We have performed supercell band structure calculations with up to 5×5×5 unit cells. We find that up to five isolated and dispersionless bands appear within the 3D photonic band gap. For each isolated band, the electric-field energy is localized in a volume centered on the point defect, hence the point defect acts as a 3D photonic band gap cavity. The mode volume of the cavities resonances is as small as 0.8 λ3 (resonance wavelength cubed), indicating a strong confinement of the light. By varying the radius of the defect pores we found that only donorlike resonances appear for smaller defect radius, whereas no acceptorlike resonances appear for greater defect radius. From a 3D plot of the distribution of the electric-field energy density we conclude that peaks of energy are found in sharp edges situated at the point defect, similar to how electrons collect at such features. This is different from what is observed for cavities in noninverted woodpile structures. Since inverse woodpile crystals can be fabricated from silicon by CMOS-compatible means, we project that single cavities and even cavity arrays can be realized, for wavelength ranges compatible with telecommunication windows in the near infrared.

  1. Fabrication of holographic 3-D polymeric photonic crystals in near-Infrared band and study of Its optical property

    Institute of Scientific and Technical Information of China (English)

    ZHANG Sa-sa; WANG Qing-pu; ZHANG Xing-yu; CHEN Jia-qi; WANG Li

    2008-01-01

    A three-sidewalls-prism holographic method has been provided for the fabrication of 3-D fcc-type polymeric photonic crystal using negative photoresist.Special fabrication treatment has been introduced to ensure the stability of the fabricated nanostructures.The scanning electronic microscopy (SEM) and the diffraction results testified the good dependability of the fabricared structures.The simulation of the partial band structure is in good agreement with the transmission and reflection spectra obtained by Fouricr transform infrared spectroscopy.

  2. Temperature Dependence of the Energy-Band Structure for the Holstein Molecular-Crystal Model%Holstein分子晶体模型能带结构的温度依赖性

    Institute of Scientific and Technical Information of China (English)

    李德俊; 彭金璋; 米贤武; 唐翌

    2008-01-01

    We study the influences of the temperature on the energy-band structure for the Holstein molecular-crystalmodel. We show that the energy-band width and the energy-gap width of a solid are relevant to both the interaction be-tween an electron and thermal phonons and to thermal expansion. For a one-dimensional Li atom lattice chain, under thechosen parameters, the width of the 1s and 2s energy bands narrows as the temperature increases and the energy-gap widthbetween the two bands widens. These results agree qualitatively with those observed experimentally. Studying temperaturedependence of the energy-band structure is of great importance for understanding optical and transporting characteristicsof a solid.%研究了温度对Holstein分子晶体模型能带结构的影响,结果表明固体的能带宽度和禁带宽度都与电子和热声子相互作用以及热膨胀密切相关.对一维Li原子品格链,在所选定的参数下,1s和2s的能带宽度随着温度的增加而变窄,两带之间的禁带宽度变宽,这些结果与实验结果在定性上是一致的.显然,研究能带结构的温度依赖性对于理解固体的光学和输运性质都是十分重要的.

  3. The band gap variation of a two dimensional binary locally resonant structure in thermal environment

    Science.gov (United States)

    Li, Zhen; Wang, Xian; Li, Yue-ming

    2017-01-01

    In this study, the numerical investigation of thermal effect on band gap dynamical characteristic for a two-dimensional binary structure composed of aluminum plate periodically filled with nitrile rubber cylinder is presented. Initially, the band gap of the binary structure variation trend with increasing temperature is studied by taking the softening effect of thermal stress into account. A breakthrough is made which found the band gap being narrower and shifting to lower frequency in thermal environment. The complete band gap which in higher frequency is more sensitive to temperature that it disappears with temperature increasing. Then some new transformed models are created by changing the height of nitrile rubber cylinder from 1mm to 7mm. Simulations show that transformed model can produce a wider band gap (either flexure or complete band gap). A proper forbidden gap of elastic wave can be utilized in thermal environment although both flexure and complete band gaps become narrower with temperature. Besides that, there is a zero-frequency flat band appearing in the first flexure band, and it becomes broader with temperature increasing. The band gap width decreases trend in thermal environment, as well as the wider band gap induced by the transformed model with higher nitrile rubber cylinder is useful for the design and application of phononic crystal structures in thermal environment.

  4. The band gap variation of a two dimensional binary locally resonant structure in thermal environment

    Directory of Open Access Journals (Sweden)

    Zhen Li

    2017-01-01

    Full Text Available In this study, the numerical investigation of thermal effect on band gap dynamical characteristic for a two-dimensional binary structure composed of aluminum plate periodically filled with nitrile rubber cylinder is presented. Initially, the band gap of the binary structure variation trend with increasing temperature is studied by taking the softening effect of thermal stress into account. A breakthrough is made which found the band gap being narrower and shifting to lower frequency in thermal environment. The complete band gap which in higher frequency is more sensitive to temperature that it disappears with temperature increasing. Then some new transformed models are created by changing the height of nitrile rubber cylinder from 1mm to 7mm. Simulations show that transformed model can produce a wider band gap (either flexure or complete band gap. A proper forbidden gap of elastic wave can be utilized in thermal environment although both flexure and complete band gaps become narrower with temperature. Besides that, there is a zero-frequency flat band appearing in the first flexure band, and it becomes broader with temperature increasing. The band gap width decreases trend in thermal environment, as well as the wider band gap induced by the transformed model with higher nitrile rubber cylinder is useful for the design and application of phononic crystal structures in thermal environment.

  5. Photonic Band Structures of BCC Crystals Containing Dispersive Material%由色散材料构成的体心立方晶体的光子能带计算

    Institute of Scientific and Technical Information of China (English)

    李江蛟

    2004-01-01

    计算了小球排列构成的体心立方结构的光子带隙性质,小球的介电函数可以是极化激元型或等离子型.虽然在通常的介电材料体心立方结构中并不容易形成光子带隙,但在我们考虑的这两类情况中均发现绝对带隙.本文中讨论的光子能带结构是由非常有效的矢量波多重散射方法计算,该方法可以精确地处理介电函数在界面附近的突变.%The photonic band gap properties of an array of spheres arranged in the body-center-cubic (BCC) structure have been calculated. The spheres are made up of dielectric material that has dielectric properties describable by the polariton and plasmon-type dispersion relationship. We find that absolute photonic gaps can be obtained in both cases although the BCC structure is known to be unfavorable for the formation of photonic band gaps. The photonic band structures are calculated by an efficient vector-wave multiple scattering method which can deal accurately with the sharp changes of dielectric functions near the interface.

  6. A Theoretical Structure of High School Concert Band Performance

    Science.gov (United States)

    Bergee, Martin J.

    2015-01-01

    This study used exploratory (EFA) and confirmatory factor analysis (CFA) to verify a theoretical structure for high school concert band performance and to test that structure for viability, generality, and invariance. A total of 101 university students enrolled in two different bands rated two high school band performances (a "first"…

  7. Modified low temperature Czochralski growth of xylenol orange doped benzopheone single crystal for fabricating dual band patch antenna

    Science.gov (United States)

    Yadav, Harsh; Sinha, Nidhi; Kumar, Binay

    2016-09-01

    Organic non-linear optical pure and xylenol orange (XO) doped benzophenone (BP) single crystals have been grown by a modified Czochralski technique. A low cost CZ system was designed and fabricated that is suitable for the growth of single crystals of low melting point organic materials. Structural analysis was performed by powder and single crystal XRD. LC-HRMS spectra reveal that the dye molecules are present in the doped crystal. The linear optical characterization was carried out by UV-vis spectroscopy. In the case of the XO doped BP crystal, two absorption peaks were found at 504 nm and 620 nm. The enhancement of photoluminescence intensity of blue emission was observed in the dye doped crystal. Dielectric studies reveal that the XO doped BP has shown improved a dielectric constant with low dielectric loss. A dual band compact circular patch antenna was simulated and fabricated using the XO doped crystal. Resonant frequencies of the dual bands at 4.80 GHz and 9.22 GHz were achieved by introducing a defect ground state in the circular patch antenna. The piezoelectric coefficient (d33) value was increased from 1 to 4 pC/N by XO dye doping, which opens up the possibilities of simultaneous transducer applications.

  8. Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface

    Directory of Open Access Journals (Sweden)

    Vasily F. Shabanov

    2013-08-01

    Full Text Available Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface.

  9. Crystal growth and characterization of the narrow-band-gap semiconductors OsPn₂ (Pn = P, As, Sb).

    Science.gov (United States)

    Bugaris, Daniel E; Malliakas, Christos D; Shoemaker, Daniel P; Do, Dat T; Chung, Duck Young; Mahanti, Subhendra D; Kanatzidis, Mercouri G

    2014-09-15

    Using metal fluxes, crystals of the binary osmium dipnictides OsPn2 (Pn = P, As, Sb) have been grown for the first time. Single-crystal X-ray diffraction confirms that these compounds crystallize in the marcasite structure type with orthorhombic space group Pnnm. The structure is a three-dimensional framework of corner- and edge-sharing OsPn6 octahedra, as well as [Pn2(4-)] anions. Raman spectroscopy shows the presence of P-P single bonds, consistent with the presence of [Pn2(-4)] anions and formally Os(4+) cations. Optical-band-gap and high-temperature electrical resistivity measurements indicate that these materials are narrow-band-gap semiconductors. The experimentally determined Seebeck coefficients reveal that nominally undoped OsP2 and OsSb2 are n-type semiconductors, whereas OsAs2 is p-type. Electronic band structure using density functional theory calculations shows that these compounds are indirect narrow-band-gap semiconductors. The bonding p orbitals associated with the Pn2 dimer are below the Fermi energy, and the corresponding antibonding states are above, consistent with a Pn-Pn single bond. Thermopower calculations using Boltzmann transport theory and constant relaxation time approximation show that these materials are potentially good thermoelectrics, in agreement with experiment.

  10. Crystal structure of fiber structured pentacene thin films

    OpenAIRE

    2007-01-01

    This PhD thesis presents a technique based on the grazing incidence crystal truncation rod (GI-CTR) X-ray diffraction method used to solve the crystal structure of substrate induced fiber structured organic thin films. The crystal structures of pentacene thin films grown on technologically relevant gate dielectric substrates are reported. It is widely recognized, that the intrinsic charge transport properties in organic thin film transistors (OTFTs) depend strongly on the crystal structur...

  11. Crystal growth and structural analysis of zirconium sulphoselenide single crystals

    Indian Academy of Sciences (India)

    K R Patel; R D Vaidya; M S Dave; S G Patel

    2008-08-01

    A series of zirconium sulphoselenide (ZrSSe3–, where = 0, 0.5, 1, 1.5, 2, 2.5, 3) single crystals have been grown by chemical vapour transport technique using iodine as a transporting agent. The optimum condition for the growth of these crystals is given. The stoichiometry of the grown crystals were confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and the structural characterization was accomplished by X-ray diffraction (XRD) studies. The crystals are found to possess monoclinic structure. The lattice parameters, volume, particle size and X-ray density have been carried out for these crystals. The effect of sulphur proportion on the lattice parameter, unit cell volume and X-ray density in the series of ZrSSe3– single crystals have been studied and found to decrease in all these parameters with rise in sulphur proportion. The grown crystals were examined under optical zoom microscope for their surface topography study. Hall effect measurements were carried out on grown crystals at room temperature. The negative value of Hall coefficient implies that these crystals are -type in nature. The conductivity is found to decrease with increase of sulphur content in the ZrSSe3– series. The electrical resistivity parallel to c-axis as well as perpendicular to -axis have been carried out in the temperature range 303–423 K. The results obtained are discussed in detail.

  12. Influence of microgravity on protein crystal structures

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Structural determination and comparison of microgravity and ground grown protein crystals have been carried out in order to investigate the effect of microgravity on the structure of protein crystals. Following the structural studies on the hen egg-white lysozyme cystals grown in space and on the ground, the same kind of comparative studies was performed with acidic phospholipase A2 crystals grown in different gravities. Based on the results obtained so far, a conclusion could be made that microgravity might not be strong enough to change the conformation of polypeptide chain of proteins, but it may improve the bound waters' structure, and this might be an important factor for microgravity to improve the protein crystal quality. In addition, the difference in the improvement between the two kinds of protein crystals may imply that the degree of improvement of a protein crystal in microgravity may be related to the solvent content in the protein crystal.

  13. Ultra-wide acoustic band gaps in pillar-based phononic crystal strips

    Energy Technology Data Exchange (ETDEWEB)

    Coffy, Etienne, E-mail: etienne.coffy@femto-st.fr; Lavergne, Thomas; Addouche, Mahmoud; Euphrasie, Sébastien; Vairac, Pascal; Khelif, Abdelkrim [FEMTO-ST Institute, Université de Franche-Comté, UBFC, CNRS, ENSMM, UTBM, 15B Av. des Montboucons, F-25030 Besançon (France)

    2015-12-07

    An original approach for designing a one dimensional phononic crystal strip with an ultra-wide band gap is presented. The strip consists of periodic pillars erected on a tailored beam, enabling the generation of a band gap that is due to both Bragg scattering and local resonances. The optimized combination of both effects results in the lowering and the widening of the main band gap, ultimately leading to a gap-to-midgap ratio of 138%. The design method used to improve the band gap width is based on the flattening of phononic bands and relies on the study of the modal energy distribution within the unit cell. The computed transmission through a finite number of periods corroborates the dispersion diagram. The strong attenuation, in excess of 150 dB for only five periods, highlights the interest of such ultra-wide band gap phononic crystal strips.

  14. Research on the elastic wave band gaps of curved beam of phononic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Shaogang, Liu; Shidan, Li; Haisheng, Shu, E-mail: shuhaisheng@hrbeu.edu.cn; Weiyuan, Wang; Dongyan, Shi; Liqiang, Dong; Hang, Lin; Wei, Liu

    2015-01-15

    Based on wave equations of Timoshenko curved beam, the theoretical derivation and numerical calculation of the behavior of in-plane and out-of-plane wave propagating in curved beam of phononic crystals (CBPC) are carried out using transfer matrix method combined with the Bloch theorem. Finite CBPC is also simulated by FEM method. It is shown that both in-plane and out-of-plane elastic waves band gaps exist in CBPC. Compared with equivalent straight beam of phononic crystals (SBPC), CBPC has some unique characteristics, such as the first complete in-plane band gap, special in-plane coupling band gap, and out-of-plane coupling band gap. In those band gaps, CBPC has a better property of vibration reduction than the equivalent SBPC in some ways. Furthermore, effects of curvature of CBPC on the in-plane and out-of-plane band gaps are discussed.

  15. Silica photonic crystals with quasi-full band gap in the visible region prepared in ethanol

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hui; WANG Xidong; ZHAO Xiaofeng; LI Wenchao; TANG Qing

    2003-01-01

    Monodisperse silica spheres of 252 nm with a standard deviation of 5.7% are prepared by Stber method. By comparison of both of media, ethanol instead of water is used to assemble opal, and the artificial opal has been prepared by the sedimentation in ethanol of silica spheres. The structure of the opal prepared has been examined and discussed. The results show that the artificial opal has a structure similar to the face-centered cubic (fcc) type packed system with silica spheres. Transmission measurements of the artificial opal have been conducted, which shows that the artificial opal is quasi-full band gap silica photonic crystals in the visible region.

  16. Tunable flat band slow light in reconfigurable photonic crystal waveguides based on magnetic fluids

    DEFF Research Database (Denmark)

    Pu, Shengli; Wang, Haotian; Wang, Ning;

    2013-01-01

    A kind of two-dimensional photonic crystal line-defect waveguide with 45 -rotated square lattice is proposed to present slow light phenomena. Infiltrating the photonic crystal waveguide with appropriate magnetic fluids can generate very wide flat bands of guided modes, which give rise...

  17. All-optical octave-broad ultrafast switching of Si woodpile photonic band gap crystals

    NARCIS (Netherlands)

    Euser, T.G.; Molenaar, Adriaan J.; Fleming, J.G.; Gralak, Boris; Polman, Albert; Vos, Willem L.

    2008-01-01

    We present ultrafast all-optical switching measurements of Si woodpile photonic band gap crystals. The crystals are spatially homogeneously excited and probed by measuring reflectivity over an octave in frequency (including the telecommunication range) as a function of time. After 300 fs, the

  18. Transmission measurement of the photonic band gap of GaN photonic crystal slabs

    NARCIS (Netherlands)

    Caro, J.; Roeling, E.M.; Rong, B.; Nguyen, H.M.; Van der Drift, E.W.J.M.; Rogge, S.; Karouta, F.; Van der Heijden, R.W.; Salemink, H.W.M.

    2008-01-01

    A high-contrast-ratio (30 dB) photonic band gap in the near-infrared transmission of hole-type GaN two-dimensional photonic crystals (PhCs) is reported. These crystals are deeply etched in a 650 nm thick GaN layer grown on sapphire. A comparison of the measured spectrum with finite difference time d

  19. Tuning the band gap in hybrid tin iodide perovskite semiconductors using structural templating.

    Science.gov (United States)

    Knutson, Jeremy L; Martin, James D; Mitzi, David B

    2005-06-27

    Structural distortions within the extensive family of organic/inorganic hybrid tin iodide perovskite semiconductors are correlated with their experimental exciton energies and calculated band gaps. The extent of the in- and out-of-plane angular distortion of the SnI4(2-) perovskite sheets is largely determined by the relative charge density and steric requirements of the organic cations. Variation of the in-plane Sn-I-Sn bond angle was demonstrated to have the greatest impact on the tuning of the band gap, and the equatorial Sn-I bond distances have a significant secondary influence. Extended Hückel tight-binding band calculations are employed to decipher the crystal orbital origins of the structural effects that fine-tune the band structure. The calculations suggest that it may be possible to tune the band gap by as much as 1 eV using the templating influence of the organic cation.

  20. Photonic crystals, light manipulation, and imaging in complex nematic structures

    Science.gov (United States)

    Ravnik, Miha; Å timulak, Mitja; Mur, Urban; Čančula, Miha; Čopar, Simon; Žumer, Slobodan

    2016-03-01

    Three selected approaches for manipulation of light by complex nematic colloidal and non-colloidal structures are presented using different own custom developed theoretical and modelling approaches. Photonic crystals bands of distorted cholesteric liquid crystal helix and of nematic colloidal opals are presented, also revealing distinct photonic modes and density of states. Light propagation along half-integer nematic disclinations is shown with changes in the light polarization of various winding numbers. As third, simulated light transmission polarization micrographs of nematic torons are shown, offering a new insight into the complex structure characterization. Finally, this work is a contribution towards using complex soft matter in optics and photonics for advanced light manipulation.

  1. Design of a 3D photonic band gap cavity in a diamond-like inverse woodpile photonic crystal

    CERN Document Server

    Woldering, Léon A; Vos, Willem L

    2014-01-01

    We theoretically investigate the design of cavities in a three-dimensional (3D) inverse woodpile photonic crystal. This class of cubic diamond-like crystals has a very broad photonic band gap and consists of two perpendicular arrays of pores with a rectangular structure. The point defect that acts as a cavity is centred on the intersection of two intersecting perpendicular pores with a radius that differs from the ones in the bulk of the crystal. We have performed supercell bandstructure calculations with up to $5 \\times 5 \\times 5$ unit cells. We find that up to five isolated and dispersionless bands appear within the 3D photonic band gap. For each isolated band, the electric-field energy is localized in a volume centred on the point defect, hence the point defect acts as a 3D photonic band gap cavity. The mode volume of the cavities resonances is as small as 0.8 $\\lambda^{3}$ (resonance wavelength cubed), indicating a strong confinement of the light. By varying the radius of the defect pores we found that o...

  2. A novel eigenvalue metho d for calculating the band structure of lossy and disp ersive photonic crystals%有耗色散光子晶体带隙结构的本征值分析新方法

    Institute of Scientific and Technical Information of China (English)

    王辉; 沙威; 黄志祥; 吴先良; 沈晶

    2014-01-01

    A novel eigenvalue method is proposed to calculate the band structure of lossy and dispersive photonic crystal (PC). Using an idea from quantum transport problem, a standard linear eigenvalue equation rather than a nonlinear eigenvalue equation is obtained by a rigorous and artful transformation. And the physical parameters of lossy and dispersive PC are obtained by solving the linear eigenvalue equation using finite-difference frequency-domain (FDFD) method. Compared with other methods, the proposed method has great features, such as clear concept, simple calculation, less computing time and storage. A dielectric PC is simulated by the proposed method, and the results accord well with those from the traditional FDFD method, which verifies the validity of the proposed method. Moreover, the dispersion relation of the lossy and dispersive PC is calculated by the proposed method, and the surface plasmon frequency is obtained. Furthermore, the influence of loss on the dispersion relation and eigenmode field distribution is studied. The results provide some theoretical guidance for studying the lossy and dispersive PC.%为计算有耗色散光子晶体的带隙结构,提出了新的本征值分析方法。该方法借助于量子输运问题中的思想,在本征值方程的推导过程中进行了巧妙的变换,将复杂的非线性本征值问题转化为线性本征值问题;并利用频域有限差分(FDFD)方法直接求解线性本征值方程,最终得到有耗色散光子晶体结构的相关物理参数。与其他方法相比,该方法的最大特点为概念清晰、计算简便,最终节省了计算时间及所需内存量。利用该方法,对介质光子晶体结构进行模拟,结果与传统FDFD方法符合较好,从而验证了方法的有效性。此外,利用所提方法计算了有耗色散光子晶体结构的色散曲线,得到了表面等离子波激发的区域,进一步讨论了损耗对其色散曲线及本征模场

  3. Predicting crystal structures of organic compounds.

    Science.gov (United States)

    Price, Sarah L

    2014-04-07

    Currently, organic crystal structure prediction (CSP) methods are based on searching for the most thermodynamically stable crystal structure, making various approximations in evaluating the crystal energy. The most stable (global minimum) structure provides a prediction of an experimental crystal structure. However, depending on the specific molecule, there may be other structures which are very close in energy. In this case, the other structures on the crystal energy landscape may be polymorphs, components of static or dynamic disorder in observed structures, or there may be no route to nucleating and growing these structures. A major reason for performing CSP studies is as a complement to solid form screening to see which alternative packings to the known polymorphs are thermodynamically feasible.

  4. Band Gap and Waveguide States in Two-Dimensional Disorder Phononic Crystals

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-Chun; LIU Zheng-You; LIANG Hong-Yu; XIAO Qing-Wu

    2006-01-01

    @@ The influences of the configurational disorders on phononic band gaps and on waveguide modes are investigated for the two-dimensional phononic crystals consisting of water cylinders periodically arrayed in mercury. Two types of conflgurational disorders, relevant to the cylinder position and cylinder size respectively, are taken into account. It is found that the phononic band gap and the guide band are sensitive to the disorders, and generally become narrower with the increasing disorders. It is also found that the waveguide side walls without disorder can significantly prevent the guide modes in the waveguide from influence by the disorders in the crystals to a large amount.

  5. Enhanced third-harmonic generation in photonic crystals at band-gap pumping

    Science.gov (United States)

    Yurchenko, Stanislav O.; Zaytsev, Kirill I.; Gorbunov, Evgeny A.; Yakovlev, Egor V.; Zotov, Arsen K.; Masalov, Vladimir M.; Emelchenko, Gennadi A.; Gorelik, Vladimir S.

    2017-02-01

    More than one order enhancement of third-harmonic generation is observed experimentally at band-gap pumping of globular photonic crystals. Due to a lateral modulation of the dielectric permittivity in two- and three-dimensional photonic crystals, sharp peaks of light intensity (light localization) arise in the media at the band-gap pumping. The light localization enhances significantly the nonlinear light conversion, in particular, third-harmonic generation, in the near-surface volume of photonic crystal. The observed way to enhance the nonlinear conversion can be useful for creation of novel compact elements of nonlinear and laser optics.

  6. Signature of a three-dimensional photonic band gap observed on silicon inverse woodpile photonic crystals

    CERN Document Server

    Huisman, Simon R; Woldering, Léon A; Leistikow, Merel D; Mosk, Allard P; Vos, Willem L

    2010-01-01

    We have studied the reflectivity of CMOS-compatible three-dimensional silicon inverse woodpile photonic crystals at near-infrared frequencies. Polarization-resolved reflectivity spectra were obtained from two orthogonal crystal surfaces corresponding to 1.88 pi sr solid angle. The spectra reveal broad peaks with high reflectivity up to 67 % that are independent of the spatial position on the crystals. The spectrally overlapping reflectivity peaks for all directions and polarizations form the signature of a broad photonic band gap with a relative bandwidth up to 16 %. This signature is supported with stopgaps in plane wave bandstructure calculations and with the frequency region of the expected band gap.

  7. Determination of Conduction and Valence Band Electronic Structure of LaTiOx Ny Thin Film.

    Science.gov (United States)

    Pichler, Markus; Szlachetko, Jakub; Castelli, Ivano E; Marzari, Nicola; Döbeli, Max; Wokaun, Alexander; Pergolesi, Daniele; Lippert, Thomas

    2017-05-09

    The nitrogen substitution into the oxygen sites of several oxide materials leads to a reduction of the band gap to the visible-light energy range, which makes these oxynitride semiconductors potential photocatalysts for efficient solar water splitting. Oxynitrides typically show a different crystal structure compared to the pristine oxide material. As the band gap is correlated to both the chemical composition and the crystal structure, it is not trivial to distinguish which modifications of the electronic structure induced by the nitrogen substitution are related to compositional and/or structural effects. Here, X-ray emission and absorption spectroscopy are used to investigate the electronic structures of orthorhombic perovskite LaTiOx Ny thin films in comparison with films of the pristine oxide LaTiOx with similar orthorhombic structure and cationic oxidation state. Experiment and theory show the expected upward shift in energy of the valence band maximum that reduces the band gap as a consequence of the nitrogen incorporation. This study also shows that the conduction band minimum, typically considered almost unaffected by nitrogen substitution, undergoes a significant downward shift in energy. For a rational design of oxynitride photocatalysts, the observed changes of both the unoccupied and occupied electronic states have to be taken into account to justify the total band-gap narrowing induced by the nitrogen incorporation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Band gap and transmission properties of one dimensional photonic crystals with NIM-PIM alternant structure%一维正负折射率光子晶体结构禁带及传播特性

    Institute of Scientific and Technical Information of China (English)

    刘名扬; 贺珍妮; 张向东

    2013-01-01

    Transfer matrix method is used to analyze the transmission spectra of one dimensional photon-ic crystals with negative refractive index material and positive refractive index material alternant struc-ture .The bang gaps and dispersive relation of one dimensional photonic crystal are analyzed .The gener-al Bragg gaps and the resonant gap of low frequency exist in the photonic crystal .We also research local-ization of electromagnetic waves in one-dimension random system containing the left-handed material .%采用传递矩阵的方法研究了由正折射率材料和负折射率材料交替排列组成的一维光子晶体结构的透射谱,并对其能带结构和色散关系进行分析,这种正负折射率光子晶体不仅存在一般的布拉格禁带,还存在低频共振禁带。本文也对含左手材料的一维无序结构的局域化进行了分析研究。

  9. Photonic Band Structure of Dispersive Metamaterials Formulated as a Hermitian Eigenvalue Problem

    KAUST Repository

    Raman, Aaswath

    2010-02-26

    We formulate the photonic band structure calculation of any lossless dispersive photonic crystal and optical metamaterial as a Hermitian eigenvalue problem. We further show that the eigenmodes of such lossless systems provide an orthonormal basis, which can be used to rigorously describe the behavior of lossy dispersive systems in general. © 2010 The American Physical Society.

  10. Band-Structure of Thallium by the LMTO Method

    DEFF Research Database (Denmark)

    Holtham, P. M.; Jan, J. P.; Skriver, Hans Lomholt

    1977-01-01

    The relativistic band structure of thallium has been calculated using the linear muffin-tin orbital (LMTO) method. The positions and extents of the bands were found to follow the Wigner-Seitz rule approximately, and the origin of the dispersion of the bands was established from the canonical s...

  11. Band structure engineering in van der Waals heterostructures via dielectric screening: the GΔW method

    Science.gov (United States)

    Winther, Kirsten T.; Thygesen, Kristian S.

    2017-06-01

    The idea of combining different two-dimensional (2D) crystals in van der Waals heterostructures (vdWHs) has led to a new paradigm for band structure engineering with atomic precision. Due to the weak interlayer couplings, the band structures of the individual 2D crystals are largely preserved upon formation of the heterostructure. However, regardless of the details of the interlayer hybridisation, the size of the 2D crystal band gaps are always reduced due to the enhanced dielectric screening provided by the surrounding layers. The effect can be significant (on the order of electron volts) but its precise magnitude is non-trivial to predict because of the non-local nature of the screening in quasi-2D crystals. Moreover, the effect is not captured by effective single-particle methods such as density functional theory. Here we present an efficient and general method for calculating the band gap renormalization of a 2D material embedded in an arbitrary vdWH. The method evaluates the change in the GW self-energy of the 2D material from the change in the screened Coulomb interaction. The latter is obtained using the quantum-electrostatic heterostructure (QEH) model. We benchmark the GΔW method against full first-principles GW calculations and use it to unravel the importance of screening-induced band structure renormalisation in various vdWHs. A main result is the observation that the size of the band gap reduction of a given 2D material when inserted into a heterostructure scales inversely with the polarisability of the 2D material. Our work demonstrates that dielectric engineering via van der Waals heterostructuring represents a promising strategy for tailoring the band structure of 2D materials.

  12. First-principle study of energy band structure of armchair graphene nanoribbons

    Science.gov (United States)

    Ma, Fei; Guo, Zhankui; Xu, Kewei; Chu, Paul K.

    2012-07-01

    First-principle calculation is carried out to study the energy band structure of armchair graphene nanoribbons (AGNRs). Hydrogen passivation is found to be crucial to convert the indirect band gaps into direct ones as a result of enhanced interactions between electrons and nuclei at the edge boundaries, as evidenced from the shortened bond length as well as the increased differential charge density. Ribbon width usually leads to the oscillatory variation of band gaps due to quantum confinement no matter hydrogen passivated or not. Mechanical strain may change the crystal symmetry, reduce the overlapping integral of C-C atoms, and hence modify the band gap further, which depends on the specific ribbon width sensitively. In practical applications, those effects will be hybridized to determine the energy band structure and subsequently the electronic properties of graphene. The results can provide insights into the design of carbon-based devices.

  13. Acoustic band gaps due to diffraction modes in two-dimensional phononic crystals

    Science.gov (United States)

    Kang, Hwi Suk; Lee, Kang Il; Yoon, Suk Wang

    2017-06-01

    In this study, we experimentally and theoretically investigated acoustic band gap control with diffraction modes in two-dimensional (2D) phononic crystals (PCs) consisting of periodic arrays of stainless steel (SS) rods immersed in water. We could classify the acoustic band gaps into two types with diffraction modes in the reflection region, and control the center frequencies of the band gaps by varying the vertical lattice constants. Pressure transmission coefficients and acoustic pressure fields were calculated using the finite element method (FEM), to classify and control the acoustic band gaps. As the vertical lattice constants were varied, the center frequencies of the band gaps, where only normal reflection occurred, were almost constant while those of the band gaps, where additional reflected waves with different propagation directions occurred, decreased with increasing the vertical lattice constants. This work can be used to manipulate acoustic band gap adding, splitting, and shifting.

  14. Graphene Nanoribbon Conductance Model in Parabolic Band Structure

    Directory of Open Access Journals (Sweden)

    Mohammad Taghi Ahmadi

    2010-01-01

    Full Text Available Many experimental measurements have been done on GNR conductance. In this paper, analytical model of GNR conductance is presented. Moreover, comparison with published data which illustrates good agreement between them is studied. Conductance of GNR as a one-dimensional device channel with parabolic band structures near the charge neutrality point is improved. Based on quantum confinement effect, the conductance of GNR in parabolic part of the band structure, also the temperature-dependent conductance which displays minimum conductance near the charge neutrality point are calculated. Graphene nanoribbon (GNR with parabolic band structure near the minimum band energy terminates Fermi-Dirac integral base method on band structure study. While band structure is parabola, semiconducting GNRs conductance is a function of Fermi-Dirac integral which is based on Maxwell approximation in nondegenerate limit especially for a long channel.

  15. Elucidating the stop bands of structurally colored systems through recursion

    CERN Document Server

    Amir, Ariel

    2012-01-01

    Interference phenomena are the source of some of the spectacular colors of animals and plants in nature. In some of these systems, the physical structure consists of an ordered array of layers with alternating high and low refractive indices. This periodicity leads to an optical band structure that is analogous to the electronic band structure encountered in semiconductor physics; namely, specific bands of wavelengths (the stop bands) are perfectly reflected. Here, we present a minimal model for optical band structure in a periodic multilayer and solve it using recursion relations. We present experimental data for various beetles, whose optical structure resembles the proposed model. The stop bands emerge in the limit of an infinite number of layers by finding the fixed point of the recursive relations. In order for these to converge, an infinitesimal amount of absorption needs to be present, reminiscent of the regularization procedures commonly used in physics calculations. Thus, using only the phenomenon of...

  16. Chaos and band structure in a three-dimensional optical lattice.

    Science.gov (United States)

    Boretz, Yingyue; Reichl, L E

    2015-04-01

    Classical chaos is known to affect wave propagation because it signifies the presence of broken symmetries. The effect of chaos has been observed experimentally for matter waves, electromagnetic waves, and acoustic waves. When these three types of waves propagate through a spatially periodic medium, the allowed propagation energies form bands. For energies in the band gaps, no wave propagation is possible. We show that optical lattices provide a well-defined system that allows a study of the effect of chaos on band structure. We have determined the band structure of a body-centered-cubic optical lattice for all theoretically possible couplings, and we find that the band structure for those lattices realizable in the laboratory differs significantly from that expected for the bands in an "empty" body-centered-cubic crystal. However, as coupling is increased, the lattice becomes increasingly chaotic and it becomes possible to produce band structure that has behavior qualitatively similar to the "empty" body-centered-cubic band structure, although with fewer degeneracies.

  17. Crystal structure analysis of intermetallic compounds

    Science.gov (United States)

    Conner, R. A., Jr.; Downey, J. W.; Dwight, A. E.

    1968-01-01

    Study concerns crystal structures and lattice parameters for a number of new intermetallic compounds. Crystal structure data have been collected on equiatomic compounds, formed between an element of the Sc, Ti, V, or Cr group and an element of the Co or Ni group. The data, obtained by conventional methods, are presented in an easily usable tabular form.

  18. Enlargement of Photonic Band Gaps and Physical Picture of Photonic Band Structures

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yan; SHI Jun-Jie

    2006-01-01

    @@ Light propagation in a one-dimensional photonic crystal (PC), consisting of alternative slabs with refractive indices (layer thicknesses) n1 (a) and n2 (b), is investigated. An important optimal parameter matching condition,n1a ≈ n2b, is obtained for the largest photonic band gap (PBG). Moreover, we find that the exact analytical solutions for the electric/magnetic field eigenmodes at the band edges are standing waves with odd or even symmetry about the centre of each layer. The electric/magnetic field eigenfunctions at the top and bottom of the nth band have n and n - 1 nodes in one period of PC, respectively. The PBG arises from the symmetric differences of the field eigenfunctions at the band edges.

  19. Effect of shape of scatterers and plasma frequency on the complete photonic band gap properties of two-dimensional dielectric-plasma photonic crystals

    Science.gov (United States)

    Fathollahi Khalkhali, T.; Bananej, A.

    2016-12-01

    In this study, we analyze complete photonic band gap properties of two-dimensional dielectric-plasma photonic crystals with triangular and square lattices, composed of plasma rods with different geometrical shapes in the anisotropic tellurium background. Using the finite-difference time-domain method we discuss the maximization of the complete photonic band gap width as a function of plasma frequency and plasma rods parameters with different shapes and orientations. The numerical results demonstrate that our proposed structures represent significantly wide complete photonic band gaps in comparison to previously studied dielectric-plasma photonic crystals.

  20. THE CRYSTAL STRUCTURE OF ALPHA-DIMETHYLTELLURIUM DICHLORIDE,

    Science.gov (United States)

    TELLURIUM COMPOUNDS, *ORGANOMETALLIC COMPOUNDS, CRYSTAL STRUCTURE , CRYSTAL STRUCTURE , CHLORIDES, SYMMETRY(CRYSTALLOGRAPHY), MOLECULAR STRUCTURE, CHEMICAL BONDS, X RAY DIFFRACTION, ANISOTROPY, FOURIER ANALYSIS.

  1. Crystal Structure of Isoquinoline Derivatives

    Institute of Scientific and Technical Information of China (English)

    LUO Mei; ZHANG Jia-Hai; ZHOU Shi-Ming; SUN Jie; YIN Hao; HU Ke-Liang

    2011-01-01

    The chiral compound 5H-imidazol[2,3-b]isoquinoline-l-ethanol-5-one-1,2, 3, 10b-tetrahydro- β(S)-phenyl-3(S)-phenyl was synthesized from the direct condensation of 2- cyanophenyacetonitrile with optically active (S)-(+)-2-phenylglycinol in chlorobenzene under dry, anaerobic conditions. ZnCl2 was used as a Lewis acid catalyst in this reaction, and the structure of this compound was determined by X-ray diffraction, NMR, MS and IR. Crystal data of the title compound: C25H22N2O2, Mr = 382.45, P 21 21 21, a = 5.341(5), b = 16.735(5), c = 22.129(5) A, γ = 90°, V = 1978(2)A^3, Z = 4, Dc = 1.284 g/cm^3, the final R = 0.0321 for 2269 observed reflections with I 〉 2 σ(I) and Rw = 0.0771 for all data.

  2. Crystal structure of 2-pentyloxybenzamide

    Directory of Open Access Journals (Sweden)

    Bernhard Bugenhagen

    2014-10-01

    Full Text Available In the title molecule, C12H17NO2, the amide NH2 group is oriented toward the pentyloxy substituent and an intramolecular N—H...O hydrogen bond is formed with the pentyloxy O atom. The benzene ring forms dihedral angles of 2.93 (2 and 5.60 (2° with the amide group and the pentyloxy group mean planes, respectively. In the crystal, molecules are linked by pairs of N—H...O hydrogen bonds, forming inversion dimers with their molecular planes parallel, but at an offset of 0.45 (1 Å to each other. These dimers are ordered into two types of symmetry-related columns extended along the a axis, with the mean plane of one set of dimers in a column approximately parallel to (121 and the other in a column approximately parallel to (1-21. The two planes form a dihedral angle of 85.31 (2°, and are linked via C—H...O hydrogen bonds and C—H...π interactions, forming a three-dimensional framework structure.

  3. Method of fabricating patterned crystal structures

    KAUST Repository

    Yu, Liyang

    2016-12-15

    A method of manufacturing a patterned crystal structure for includes depositing an amorphous material. The amorphous material is modified such that a first portion of the amorphous thin-film layer has a first height/volume and a second portion of the amorphous thin-film layer has a second height/volume greater than the first portion. The amorphous material is annealed to induce crystallization, wherein crystallization is induced in the second portion first due to the greater height/volume of the second portion relative to the first portion to form patterned crystal structures.

  4. Experimental Studies of Band-Structure Properties in Bloch Transistors

    Science.gov (United States)

    Flees, Daniel J.

    1998-03-01

    One of the most striking features in small SIS tunnel junctions is the energy-band structure produced by Josephson coupling and charging effects. These energy bands are analogous to Bloch bands in crystalline solids. The superconducting single-electron (Bloch) transistor is the simplest system in which the energy bands can be readily studied. It consists of a superconducting island coupled to a source and drain through two small tunnel junctions. The elastic tunneling of Cooper-Pairs onto the island mixes the discrete charge states of the island. The shapes of the resulting energy bands can be modified by changing the electrostatic energies of these charge states with a voltage applied to a capacitively coupled gate. The maximum zero-voltage current (supercurrent) of each band depends upon the shape of the band and so the gate modulates the supercurrent. Each band has a different characteristic supercurrent modulation, with excited bands generally having lower currents. Thus! we can use the reduction in super current associated with a transition to an excited band to begin probing aip.org/journal_cgi/ getabs?KEY=PRLTAO&cvips=PRLTAO000078000025004817000001&gifs=No>band- structure properties such as the band-gap.(Daniel J. Flees, Siyuan Han, and J.E. Lukens, Phys. Rev. Lett. 78), 4817 (1997).

  5. Manipulating full photonic band gaps in two dimensional birefringent photonic crystals.

    Science.gov (United States)

    Proietti Zaccaria, Remo; Verma, Prabhat; Kawaguchi, Satoshi; Shoji, Satoru; Kawata, Satoshi

    2008-09-15

    The probability to realize a full photonic band gap in two-dimensional birefringent photonic crystals can be readily manipulated by introducing symmetry reduction or air holes in the crystal elements. The results lie in either creation of new band gaps or enlargement of existing band gaps. In particular, a combination of the two processes produces an effect much stronger than a simple summation of their individual contributions. Materials with both relatively low refractive index (rutile) and high refractive index (tellurium) were considered. The combined effect of introduction of symmetry reduction and air holes resulted in a maximum enlargement of the band gaps by 8.4% and 20.2%, respectively, for the two materials.

  6. Three new chalcohalides, Ba{sub 4}Ge{sub 2}PbS{sub 8}Br{sub 2}, Ba{sub 4}Ge{sub 2}PbSe{sub 8}Br{sub 2} and Ba{sub 4}Ge{sub 2}SnS{sub 8}Br{sub 2}: Syntheses, crystal structures, band gaps, and electronic structures

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Zuohong; Feng, Kai; Tu, Heng; Kang, Lei [Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); University of the Chinese Academy of Sciences, Beijing 100049 (China); Lin, Zheshuai [Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Yao, Jiyong, E-mail: jyao@mail.ipc.ac.cn [Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Wu, Yicheng [Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)

    2014-10-25

    Highlights: • Three new chalcohalides: Ba{sub 4}Ge{sub 2}PbS{sub 8}Br{sub 2}, Ba{sub 4}Ge{sub 2}PbSe{sub 8}Br{sub 2} and Ba{sub 4}Ge{sub 2}SnS{sub 8}Br{sub 2} have been synthesized. • The MQ{sub 5}Br octahedra and GeQ{sub 4} tetrahedra form a three-dimensional framework with Ba{sup 2+} in the channels. • Band Gaps and electronic structures of the three compounds were studied. - Abstract: Single crystals of three new chalcohalides: Ba{sub 4}Ge{sub 2}PbS{sub 8}Br{sub 2}, Ba{sub 4}Ge{sub 2}PbSe{sub 8}Br{sub 2} and Ba{sub 4}Ge{sub 2}SnS{sub 8}Br{sub 2} have been synthesized for the first time. These isostructural compounds crystallize in the orthorhombic space group Pnma. In the structure, the tetra-valent Ge atom is tetrahedrally coordinated with four Q (Q = S, Se) atoms, while the bi-valent M atom (M = Pb, Sn) is coordinated with an obviously distorted octahedron of five Q (Q = S, Se) atoms and one Br atom, showing the stereochemical activity of the ns{sup 2} lone pair electron. The MQ{sub 5}Br (M = Sn, Pb; Q = S, Se) distorted octahedra and the GeQ{sub 4} (Q = S, Se) tetrahedra are connected to each other to form a three-dimensional framework with channels occupied by Ba{sup 2+} cations. Based on UV–vis–NIR spectroscopy measurements and the electronic structure calculations, Ba{sub 4}Ge{sub 2}PbS{sub 8}Br{sub 2}, Ba{sub 4}Ge{sub 2}PbSe{sub 8}Br{sub 2} and Ba{sub 4}Ge{sub 2}SnS{sub 8}Br{sub 2} have indirect band gaps of 2.054, 1.952, and 2.066 eV respectively, which are mainly determined by the orbitals from the Ge, M and Q atoms (M = Pb, Sn; Q = S, Se)

  7. Reducing support loss in micromechanical ring resonators using phononic band-gap structures

    Energy Technology Data Exchange (ETDEWEB)

    Hsu, Feng-Chia; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin [Industrial Technology Research Institute-South, Tainan 709, Taiwan (China); Hsu, Jin-Chen, E-mail: fengchiahsu@itri.org.t, E-mail: hsujc@yuntech.edu.t [Department of Mechanical Engineering, National Yunlin University of Science and Technology, Douliou, Yunlin 64002, Taiwan (China)

    2011-09-21

    In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.

  8. Reducing support loss in micromechanical ring resonators using phononic band-gap structures

    Science.gov (United States)

    Hsu, Feng-Chia; Hsu, Jin-Chen; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin

    2011-09-01

    In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.

  9. The complex band structure for armchair graphene nanoribbons

    Institute of Scientific and Technical Information of China (English)

    Zhang Liu-Jun; Xia Tong-Sheng

    2010-01-01

    Using a tight binding transfer matrix method, we calculate the complex band structure of armchair graphene nanoribbons. The real part of the complex band structure calculated by the transfer matrix method fits well with the bulk band structure calculated by a Hermitian matrix. The complex band structure gives extra information on carrier's decay behaviour. The imaginary loop connects the conduction and valence band, and can profoundly affect the characteristics of nanoscale electronic device made with graphene nanoribbons. In this work, the complex band structure calculation includes not only the first nearest neighbour interaction, but also the effects of edge bond relaxation and the third nearest neighbour interaction. The band gap is classified into three classes. Due to the edge bond relaxation and the third nearest neighbour interaction term, it opens a band gap for N= 3M-1. The band gap is almost unchanged for N = 3M + 1, but decreased for N = 3M. The maximum imaginary wave vector length provides additional information about the electrical characteristics of graphene nmaoribbons, and is also classified into three classes.

  10. Photonic band gaps in quasiperiodic photonic crystals with negative refractive index

    Science.gov (United States)

    Vasconcelos, M. S.; Mauriz, P. W.; de Medeiros, F. F.; Albuquerque, E. L.

    2007-10-01

    We investigate the photonic band gaps in quasiperiodic photonic crystals made up of both positive (SiO2) and negative refractive index materials using a theoretical model based on a transfer matrix treatment. The quasiperiodic structures are characterized by the nature of their Fourier spectrum, which can be dense pure point (Fibonacci sequences) or singular continuous (Thue-Morse and double-period sequences). These substitutional sequences are described in terms of a series of generations that obey peculiar recursion relations. We discussed the photonic band gap spectra for both the ideal cases, where the negative refractive index material can be approximated as a constant in the frequency range considered, as well as the more realistic case, taking into account the frequency-dependent electric permittivity γ and magnetic permeability μ . We also present a quantitative analysis of the results, pointing out the distribution of the allowed photonic bandwidths for high generations, which gives a good insight about their localization and power laws.

  11. Experimental investigation of photonic band gap in one-dimensional photonic crystals with metamaterials

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Yihang, E-mail: eon.chen@yahoo.com.cn [Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon, Hong Kong (China); Laboratory of Quantum Information Technology, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou (China); Wang, Xinggang [Laboratory of Quantum Information Technology, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou (China); Yong, Zehui; Zhang, Yunjuan [Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon, Hong Kong (China); Chen, Zefeng [Laboratory of Quantum Information Technology, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou (China); He, Lianxing; Lee, P.F.; Chan, Helen L.W.; Leung, Chi Wah [Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon, Hong Kong (China); Wang, Yu, E-mail: apywang@inet.polyu.edu.hk [Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon, Hong Kong (China)

    2012-03-19

    Composite right/left-handed transmission lines with lumped element series capacitors and shunt inductors are used to experimentally realize the one-dimensional photonic crystals composed of single-negative metamaterials. The simulated and experimental results show that a special photonic band gap corresponding to zero-effective-phase (zero-φ{sub eff}) may appear in the microwave regime. In contrast to the Bragg gap, by changing the length ratio of the two component materials, the width and depth of the zero-φ{sub eff} gap can be conveniently adjusted while keeping the center frequency constant. Furthermore, the zero-φ{sub eff} gap vanishes when both the phase-matching and impedance-matching conditions are satisfied simultaneously. These transmission line structures provide a good way for realizing microwave devices based on the zero-φ{sub eff} gap. -- Highlights: ► 1D photonic crystals with metamaterials were investigated experimentally. ► Both Bragg gap and zero-φ{sub eff} gap were observed in the microwave regime. ► The width and depth of the zero-φ{sub eff} gap were experimentally adjusted. ► Zero-φ{sub eff} gap was observed to be close when two match conditions were satisfied.

  12. Photonic Crystal Structures with Tunable Structure Color as Colorimetric Sensors

    Directory of Open Access Journals (Sweden)

    Ke-Qin Zhang

    2013-03-01

    Full Text Available Colorimetric sensing, which transduces environmental changes into visible color changes, provides a simple yet powerful detection mechanism that is well-suited to the development of low-cost and low-power sensors. A new approach in colorimetric sensing exploits the structural color of photonic crystals (PCs to create environmentally-influenced color-changeable materials. PCs are composed of periodic dielectrics or metallo-dielectric nanostructures that affect the propagation of electromagnetic waves (EM by defining the allowed and forbidden photonic bands. Simultaneously, an amazing variety of naturally occurring biological systems exhibit iridescent color due to the presence of PC structures throughout multi-dimensional space. In particular, some kinds of the structural colors in living organisms can be reversibly changed in reaction to external stimuli. Based on the lessons learned from natural photonic structures, some specific examples of PCs-based colorimetric sensors are presented in detail to demonstrate their unprecedented potential in practical applications, such as the detections of temperature, pH, ionic species, solvents, vapor, humidity, pressure and biomolecules. The combination of the nanofabrication technique, useful design methodologies inspired by biological systems and colorimetric sensing will lead to substantial developments in low-cost, miniaturized and widely deployable optical sensors.

  13. High-quality photonic crystals with a nearly complete band gap obtained by direct inversion of woodpile templates with titanium dioxide

    CERN Document Server

    Marichy, Catherine; Froufe-Pérez, Luis S; Scheffold, Frank

    2015-01-01

    Photonic crystal materials are based on a periodic modulation of the dielectric constant on length scales comparable to the wavelength of light. These materials can exhibit photonic band gaps; frequency regions for which the propagation of electromagnetic radiation is forbidden due to the depletion of the density of states. In order to exhibit a full band gap, 3D PCs must present a threshold refractive index contrast that depends on the crystal structure. In the case of the so-called woodpile photonic crystals this threshold is comparably low, approximately 1.9 for the direct structure. Therefore direct or inverted woodpiles made of high refractive index materials like silicon, germanium or titanium dioxide are sought after. Here we show that, by combining multiphoton lithography and atomic layer deposition, we can achieve a direct inversion of polymer templates into TiO$_{2}$ based photonic crystals. The obtained structures show remarkable optical properties in the near-infrared region with almost perfect sp...

  14. Photonic crystal type structure in bivalve ligament of Pinctada maxima

    Institute of Scientific and Technical Information of China (English)

    ZHANG GangSheng

    2007-01-01

    The dry ligament of Pinctada maxima normally appears black; however, it can exhibit striking blue structural colors after being wetted by water. The field-mission SEM investigation shows that the ligament is made of lamellae, which, about 35 μm thick, are made of proteins and aragonite fibers of about 78 nm in diameter. In each single lamella, the fibers are highly aligned characterized by a 2D photonic crystal type structure. According to measured reflective spectra and theoretical simulations, the dry and wet ligaments possess photonic stop band at ultraviolet and blue wavelengths, respectively, which are responsible for structural colorations of ligament.

  15. Atomic structure of amorphous shear bands in boron carbide.

    Science.gov (United States)

    Reddy, K Madhav; Liu, P; Hirata, A; Fujita, T; Chen, M W

    2013-01-01

    Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses.

  16. Elastic wave band gaps tuned by configuring radii of rods in two-dimensional phononic crystals with a hybrid square-like lattice

    Science.gov (United States)

    Liu, Rongqiang; Zhao, Haojiang; Zhang, Yingying; Guo, Honghwei; Deng, Zongquan

    2015-12-01

    The plane wave expansion (PWE) method is used to calculate the band gaps of two-dimensional (2D) phononic crystals (PCs) with a hybrid square-like (HSL) lattice. Band structures of both XY-mode and Z-mode are calculated. Numerical results show that the band gaps between any two bands could be maximized by altering the radius ratio of the inclusions at different positions. By comparing with square lattice and bathroom lattice, the HSL lattice is more efficient in creating larger gaps.

  17. Modelling and design of complete photonic band gaps in two-dimensional photonic crystals

    Indian Academy of Sciences (India)

    Yogita Kalra; R K Sinha

    2008-01-01

    In this paper, we investigate the existence and variation of complete photonic band gap size with the introduction of asymmetry in the constituent dielectric rods with honeycomb lattices in two-dimensional photonic crystals (PhC) using the plane-wave expansion (PWE) method. Two examples, one consisting of elliptical rods and the other comprising of rectangular rods in honeycomb lattices are considered with a view to estimate the design parameters for maximizing the complete photonic band gap. Further, it has been shown that complete photonic band gap size changes with the variation in the orientation angle of the constituent dielectric rods.

  18. Mini-stop bands in single-defect photonic crystal waveguides

    CERN Document Server

    Agio, M; Agio, Mario; Soukoulis, Costas M.

    2001-01-01

    We numerically study single-defect photonic crystal waveguides obtained from a triangular lattice of air holes in a dielectric background. It is found that, for medium-high air filling ratios, the transmission has very small values in narrow frequency regions lying inside the photonic band gap - the so-called mini-stop bands. Two types of mini-stop bands are shown to exist; one of which is due to the multimode nature of the waveguide. Their dependence on the length of the waveguide and on the air filling ratio is presented.

  19. Band structure approach to the resonant x-ray scattering

    OpenAIRE

    Elfimov, I. S.; Skorikov, N. A.; Anisimov, V. I.; Sawatzky, G.A.

    2001-01-01

    We study the resonance behaviour of the forbidden 600 and 222 x-ray Bragg peaks in Ge using LDA band structure methods. These Bragg peaks remain forbidden in the resonant dipole scattering approximation even taking into account the non local nature of the band states. However they become allowed at resonance if the eigenstates of the unoccupied conduction band involve a hybridization of p like and d like atomic states. We show that the energy dependence of the resonant behaviour, including th...

  20. Structural engineering of three-dimensional phononic crystals

    Science.gov (United States)

    Delpero, Tommaso; Schoenwald, Stefan; Zemp, Armin; Bergamini, Andrea

    2016-02-01

    Artificially-structured materials are attracting the research interest of a growing community of scientists for the possibility to develop novel materials with advantageous properties that arise from the ability to tailor the propagation of elastic waves, and thus energy, through them. In this work, we propose a three-dimensional phononic crystal whose unit cell has been engineered to obtain a strong wave-attenuation band in the middle of the acoustic frequency range. The combination of its acoustic properties with the dimensions of the unit cell and its static mechanical properties makes it an interesting material for possibly several applications in civil and mechanical engineering, for instance as the core of an acoustically insulating sandwich panel. A sample of this crystal has been manufactured and experimentally tested with respect to its acoustic transmissibility. The performance of the phononic crystal core is remarkable both in terms of amplitude reduction in the transmissibility and width of the attenuation band. A parametric study has been finally conducted on selected geometrical parameters of the unit cell and on their effect on the macroscopic properties of the crystal. This work represents an application-oriented example of how the macroscopic properties of an artificially-structured material can be designed, according to specific needs, by a conventional engineering of its unit cell.

  1. synthesis, characterization and crystal structure of a ...

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    Crystal and molecular structure of the complex ... Coordination chemistry of molybdenum(VI) has attracted considerable attention due to its biochemical significance [1-3] as well as for the efficient catalytic properties in several organic.

  2. Electronic Band Structure and Sub-band-gap Absorption of Nitrogen Hyperdoped Silicon.

    Science.gov (United States)

    Zhu, Zhen; Shao, Hezhu; Dong, Xiao; Li, Ning; Ning, Bo-Yuan; Ning, Xi-Jing; Zhao, Li; Zhuang, Jun

    2015-05-27

    We investigated the atomic geometry, electronic band structure, and optical absorption of nitrogen hyperdoped silicon based on first-principles calculations. The results show that all the paired nitrogen defects we studied do not introduce intermediate band, while most of single nitrogen defects can introduce intermediate band in the gap. Considering the stability of the single defects and the rapid resolidification following the laser melting process in our sample preparation method, we conclude that the substitutional nitrogen defect, whose fraction was tiny and could be neglected before, should have considerable fraction in the hyperdoped silicon and results in the visible sub-band-gap absorption as observed in the experiment. Furthermore, our calculations show that the substitutional nitrogen defect has good stability, which could be one of the reasons why the sub-band-gap absorptance remains almost unchanged after annealing.

  3. Full-band error control and crack-free surface fabrication techniques for ultra-precision fly cutting of large-aperture KDP crystals

    Science.gov (United States)

    Zhang, F. H.; Wang, S. F.; An, C. H.; Wang, J.; Xu, Q.

    2017-06-01

    Large-aperture potassium dihydrogen phosphate (KDP) crystals are widely used in the laser path of inertial confinement fusion (ICF) systems. The most common method of manufacturing half-meter KDP crystals is ultra-precision fly cutting. When processing KDP crystals by ultra-precision fly cutting, the dynamic characteristics of the fly cutting machine and fluctuations in the fly cutting environment are translated into surface errors at different spatial frequency bands. These machining errors should be suppressed effectively to guarantee that KDP crystals meet the full-band machining accuracy specified in the evaluation index. In this study, the anisotropic machinability of KDP crystals and the causes of typical surface errors in ultra-precision fly cutting of the material are investigated. The structures of the fly cutting machine and existing processing parameters are optimized to improve the machined surface quality. The findings are theoretically and practically important in the development of high-energy laser systems in China.

  4. Pattern information extraction from crystal structures

    Science.gov (United States)

    Okuyan, Erhan; Güdükbay, Uğur; Gülseren, Oğuz

    2007-04-01

    Determining the crystal structure parameters of a material is an important issue in crystallography and material science. Knowing the crystal structure parameters helps in understanding the physical behavior of material. It can be difficult to obtain crystal parameters for complex structures, particularly those materials that show local symmetry as well as global symmetry. This work provides a tool that extracts crystal parameters such as primitive vectors, basis vectors and space groups from the atomic coordinates of crystal structures. A visualization tool for examining crystals is also provided. Accordingly, this work could help crystallographers, chemists and material scientists to analyze crystal structures efficiently. Program summaryTitle of program: BilKristal Catalogue identifier: ADYU_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADYU_v1_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: None Programming language used: C, C++, Microsoft .NET Framework 1.1 and OpenGL Libraries Computer: Personal Computers with Windows operating system Operating system: Windows XP Professional RAM: 20-60 MB No. of lines in distributed program, including test data, etc.:899 779 No. of bytes in distributed program, including test date, etc.:9 271 521 Distribution format:tar.gz External routines/libraries: Microsoft .NET Framework 1.1. For visualization tool, graphics card driver should also support OpenGL Nature of problem: Determining crystal structure parameters of a material is a quite important issue in crystallography. Knowing the crystal structure parameters helps to understand physical behavior of material. For complex structures, particularly, for materials which also contain local symmetry as well as global symmetry, obtaining crystal parameters can be quite hard. Solution method: The tool extracts crystal parameters such as primitive vectors, basis vectors and identify the space group from

  5. The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

    Energy Technology Data Exchange (ETDEWEB)

    Sutherland, Kevin Jerome [Iowa State Univ., Ames, IA (United States)

    2001-01-01

    Photonic band gap (PBG) crystals are periodic dielectric structures that manipulate electromagnetic radiation in a manner similar to semiconductor devices manipulating electrons. Whereas a semiconductor material exhibits an electronic band gap in which electrons cannot exist, similarly, a photonic crystal containing a photonic band gap does not allow the propagation of specific frequencies of electromagnetic radiation. This phenomenon results from the destructive Bragg diffraction interference that a wave propagating at a specific frequency will experience because of the periodic change in dielectric permitivity. This gives rise to a variety of optical applications for improving the efficiency and effectiveness of opto-electronic devices. These applications are reviewed later. Several methods are currently used to fabricate photonic crystals, which are also discussed in detail. This research involves a layer-by-layer micro-transfer molding ({mu}TM) and stacking method to create three-dimensional FCC structures of epoxy or titania. The structures, once reduced significantly in size can be infiltrated with an organic gain media and stacked on a semiconductor to improve the efficiency of an electronically pumped light-emitting diode. Photonic band gap structures have been proven to effectively create a band gap for certain frequencies of electro-magnetic radiation in the microwave and near-infrared ranges. The objective of this research project was originally two-fold: to fabricate a three dimensional (3-D) structure of a size scaled to prohibit electromagnetic propagation within the visible wavelength range, and then to characterize that structure using laser dye emission spectra. As a master mold has not yet been developed for the micro transfer molding technique in the visible range, the research was limited to scaling down the length scale as much as possible with the current available technology and characterizing these structures with other methods.

  6. Photonic-crystal fibre: Mapping the structure

    DEFF Research Database (Denmark)

    Markos, Christos

    2015-01-01

    The demonstration of real-time and non-destructive Doppler-assisted tomography of the internal structure of photonic-crystal fibres could aid the fabrication of high-quality fibres with enhanced performance.......The demonstration of real-time and non-destructive Doppler-assisted tomography of the internal structure of photonic-crystal fibres could aid the fabrication of high-quality fibres with enhanced performance....

  7. Beam Steering at Higher Photonic Bands and Design of a Directional Cloak Formed by Photonic Crystals

    Directory of Open Access Journals (Sweden)

    Venkatachalam Subramanian

    2013-02-01

    Full Text Available Beam steering due to anomalous dispersion at higher photonic bands in dielectric photonic crystal is reported in this work. Based on this concept, directional cloak is designed that conceals a larger dimensional scattering object against the normal incident, linearly polarizedelectromagnetic waves.

  8. Electronic structure of heavy fermions: narrow temperature-independent bands

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; Joyce, J.J.; Andrews, A.B.; Thompson, J.D.; Smith, J.L. [Los Alamos National Lab., NM (United States); Moshopoulou, E.; Fisk, Z. [NHMFL, Florida State Univ., Tallahassee, FL (United States); Menovsky, A.A. [Amsterdam Univ. (Netherlands). Natuurkundig Lab.; Canfield, P.C.; Olson, C.G. [Iowa State Univ., Ames, IA (United States). Ames Lab.

    1997-02-01

    The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from ARPES data reported here for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable. (orig.).

  9. The electronic structure of heavy fermions: Narrow temperature independent bands

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; Joyce, J.J.; Smith, J.L.; Andrews, A.B. [and others

    1996-08-01

    The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from photoemission for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable.

  10. Crystal structure of meteoritic schreibersites: determination of absolute structure

    Science.gov (United States)

    Skála, Roman; Císařová, Ivana

    Minerals of the schreibersite nickelphosphide series (Fe,Ni)3P crystallize in the non-centrosymmetric space group Ibar 4. As a consequence, they can possess two different spatial arrangements of the constituting atoms within the unit cell, related by the inversion symmetry operation. Here, we present the crystal structure refinements from single crystal X-ray diffraction data for schreibersite grains from iron meteorites Acuña, Carlton, Hex River Mts. (three different crystals), Odessa (two different crystals), Sikhote Alin, and Toluca aiming for the determination of the absolute structure of the examined crystals. The crystals studied cover the composition range from 58 mol% to 80 mol% Fe3P end-member. Unit-cell parameter a and volume of the unit cell V, as well as certain topological structural parameters tightly correlate with Fe3P content. Unit-cell parameter c, on the other hand, does not show such strong correlation. Eight of the nine crystal structure refinements allowed unambiguous absolute structure assignment. The single crystal extracted from Toluca is, however, of poor quality and consequently the structure refinement did not provide as good results as the rest of the materials. Also, this crystal has only weak inversion distinguishing power to provide unequivocal absolute structure determination. Six of the eight unambiguous absolute structure determinations indicated inverted atomic arrangement compared to that reported in earlier structure refinements (here called standard). Only two grains, one taken from Odessa iron and the other from the Hex River Mts. meteorite, reveal the dominance of standard crystal structure setting.

  11. Photonic-Crystal Band-pass Resonant Filters Design Using the Two-dimensional FDTD Method

    Directory of Open Access Journals (Sweden)

    Hadjira Badaoui

    2011-05-01

    Full Text Available Recently, band-pass photonic crystal filters have attracted great attention due to their important applications in the fields of optical interconnection network and ultrahigh speed information processing. In this paper we propose the design of a new type of photonic crystal band-pass resonant filters realized in one-missing-row waveguide by decreasing proper defects along the waveguide with broadband acceptable bandwidth. Two types of photonic crystal band-pass filters are utilized and optimized using the Two-dimensional finite-difference time-domain (FDTD technique. The first one is based on the Fabry-Perot cavities and in the second one a cavity is introduced in the middle by omitting two neighboring air holes in waveguide. Numerical results show that a band [1.47 and#956;m-1.57 and#956;m] around 1.55um is transmitted with a maximum transmission of about 68% and as a result wide band-pass filters are designed.

  12. The direct-to-indirect band gap crossover in two-dimensional van der Waals Indium Selenide crystals

    Science.gov (United States)

    Mudd, G. W.; Molas, M. R.; Chen, X.; Zólyomi, V.; Nogajewski, K.; Kudrynskyi, Z. R.; Kovalyuk, Z. D.; Yusa, G.; Makarovsky, O.; Eaves, L.; Potemski, M.; Fal’Ko, V. I.; Patanè, A.

    2016-12-01

    The electronic band structure of van der Waals (vdW) layered crystals has properties that depend on the composition, thickness and stacking of the component layers. Here we use density functional theory and high field magneto-optics to investigate the metal chalcogenide InSe, a recent addition to the family of vdW layered crystals, which transforms from a direct to an indirect band gap semiconductor as the number of layers is reduced. We investigate this direct-to-indirect bandgap crossover, demonstrate a highly tuneable optical response from the near infrared to the visible spectrum with decreasing layer thickness down to 2 layers, and report quantum dot-like optical emissions distributed over a wide range of energy. Our analysis also indicates that electron and exciton effective masses are weakly dependent on the layer thickness and are significantly smaller than in other vdW crystals. These properties are unprecedented within the large family of vdW crystals and demonstrate the potential of InSe for electronic and photonic technologies.

  13. Effective permittivity and permeability of one-dimensional dielectric photonic crystal within a band gap

    Institute of Scientific and Technical Information of China (English)

    Guo Ji-Yong; Chen Hong; Li Hong-Qiang; Zhang Ye-Wen

    2008-01-01

    We take a finite dielectric photonic crystal as a homogeneous slab and have extracted the effective parameters. Our systematic study shows that the effective permittivity or permeability of dielectric photonic crystal is negative within a band gap region. This means that the band gap might act as ε-negative materials (ENMs) with ε0, or μ-negative materials (MNMs) with ε>0 and μ<0. Moreover the effective parameters sensitively rely on size, surface termination, symmetry, etc. The effective parameters can be used to design full transmission tunnelling modes and amplify evanescent wave. Several cases are studied and the results show that dielectric photonic band gap can indeed mimic a single negative material (ENM or MNM) under some restrictions.

  14. High-Q band edge mode of plasmonic crystals studied by cathodoluminescence

    Science.gov (United States)

    Honda, Masahiro; Yamamoto, Naoki

    2014-02-01

    We have investigated the quality factor (Q-factor) of the band edge modes in the plasmonic crystal by a cathodoluminescence technique. We have found that the Q-factor at the Γ point depends on the terrace width (D)/period (P) ratio of the plasmonic crystal. The finite-difference time-domain methods predict that the band edge mode at D/P = 3/4 has a high-Q-factor (Q ˜ 250 by Palik's permittivity data and Q ˜ 530 by Johnson and Christy's data). The beam-scan spectral images allowed us to visualize the standing surface plasmon polariton waves at the band edge energies, and a high-Q-factor of ˜200 was observed at D/P ˜ 3/4.

  15. High-Q band edge mode of plasmonic crystals studied by cathodoluminescence

    Energy Technology Data Exchange (ETDEWEB)

    Honda, Masahiro; Yamamoto, Naoki, E-mail: nyamamot@phys.titech.ac.jp [Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551 (Japan)

    2014-02-24

    We have investigated the quality factor (Q-factor) of the band edge modes in the plasmonic crystal by a cathodoluminescence technique. We have found that the Q-factor at the Γ point depends on the terrace width (D)/period (P) ratio of the plasmonic crystal. The finite-difference time-domain methods predict that the band edge mode at D/P = 3/4 has a high-Q-factor (Q ∼ 250 by Palik's permittivity data and Q ∼ 530 by Johnson and Christy's data). The beam-scan spectral images allowed us to visualize the standing surface plasmon polariton waves at the band edge energies, and a high-Q-factor of ∼200 was observed at D/P ∼ 3/4.

  16. Structure of nearly degenerate dipole bands in {sup 108}Ag

    Energy Technology Data Exchange (ETDEWEB)

    Sethi, J. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Palit, R., E-mail: palit@tifr.res.in [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Saha, S.; Trivedi, T. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Bhat, G.H.; Sheikh, J.A. [Department of Physics, University of Kashmir, Srinagar 190 006 (India); Datta, P. [Ananda Mohan College, Kolkata 700009 (India); Carroll, J.J. [US Army Research Laboratory, Adelphi, MD 20783 (United States); Chattopadhyay, S. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Donthi, R. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Garg, U. [University of Notre Dame, Notre Dame, IN 46556 (United States); Jadhav, S.; Jain, H.C. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Karamian, S. [Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Kumar, S. [University of Delhi, Delhi 110007 (India); Litz, M.S. [US Army Research Laboratory, Adelphi, MD 20783 (United States); Mehta, D. [Panjab University, Chandigarh 160014 (India); Naidu, B.S. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Naik, Z. [Sambalpur University, Sambalpur 143005 (India); Sihotra, S. [Panjab University, Chandigarh 160014 (India); and others

    2013-08-09

    The high spin negative parity states of {sup 108}Ag have been investigated with the {sup 11}B + {sup 100}Mo reaction at 39 MeV beam energy using the INGA facility at TIFR, Mumbai. From the γ–γ coincidence analysis, an excited negative parity band has been established and found to be nearly degenerate with the ground state band. The spin and parity of the levels are assigned using angular correlation and polarization measurements. This pair of degenerate bands in {sup 108}Ag is studied using the recently developed microscopic triaxial projected shell model approach. The observed energy levels and the ratio of the electromagnetic transition probabilities of these bands in this isotope are well reproduced by the present model. Further, it is shown that the partner band has a different quasiparticle structure as compared to the yrast band.

  17. Unfolding the band structure of non-crystalline photonic band gap materials.

    Science.gov (United States)

    Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining

    2015-08-20

    Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain.

  18. Structures of cyano-biphenyl liquid crystals

    Science.gov (United States)

    Chu, Yuan-Chao; Tsang, Tung; Rahimzadeh, E.; Yin, L.

    1989-01-01

    The structures of p-alkyl- p'-cyano- bicyclohexanes, C(n)H(2n+1) (C6H10)(C6H10) CN (n-CCH), and p-alkyl- p'-cyano- biphenyls, C(n)H(2n+1) (C6H4)(C6H4) CN (n-CBP), were studied. It is convenient to use an x ray image intensification device to search for symmetric x ray diffraction patterns. Despite the similarities in molecular structures of these compounds, very different crystal structures were found. For the smectic phase of 2CCH, the structure is close to rhombohedral with threefold symmetry. In contrast, the structure is close to hexagonal close-packed with two molecules per unit cell for 4CCH. Since intermolecular forces may be quite weak for these liquid crystals systems, it appears that crystal structures change considerably when the alkyl chain length is slightly altered. Different structures were also found in the crystalline phase of n-CBP for n = 6 to 9. For n = 7 to 9, the structures are close to monclinic. The structures are reminiscent of the smectic-A liquid crystal structures with the linear molecules slightly tilted away from the c-axis. In contrast, the structure is quite different for n = 6 with the molecules nearly perpendicular to the c-axis.

  19. Electronic structure of NiO: Correlation and band effects

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Z. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA)); List, R.S. (Los Alamos National Laboratory, Los Alamos, New Mexico (USA)); Dessau, D.S.; Wells, B.O. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA)); Jepsen, O. (Max-Planck-Institute for Solid State Research, D-7000 Stuttgart 80 (Federal Republic of Germany)); Arko, A.J.; Barttlet, R. (Los Alamos National Laboratory, Los Alamos, New Mexico (USA)); Shih, C.K. (Department of Physics, University of Texas, Austin, Texas (USA)); Parmigiani, F. (IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California (USA)); Huang, J.C.; Lindberg, P.A.P. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA))

    1991-08-15

    We have performed angle-resolved-photoemission experiments and local-density-functional (LDA) band calculations on NiO to study correlation and band effects of this conceptually important compound. Our experimental result suggests a dual nature of the electronic structure of NiO. On the one hand, the LDA band calculation has some relevance to the electronic structure of NiO, and the inclusion of the antiferromagnetic order is essential. For the lower O 2{ital p} bands, the LDA calculation agrees almost perfectly with experimental energy positions and dispersion relations. On the other hand, discrepancies between the experiment and the LDA calculation do exist, especially for the Ni 3{ital d} bands and the O 2{ital p} bands that are heavily mixed with the Ni 3{ital d} bands. It appears that the main discrepancies between the experimental results and the LDA calculation are concentrated in the regions of the insulating gap and the valence-band satellite. In addition to these results, we also report the interesting angle and photon-energy dependence of the satellite emission. The above results show that the angle-resolved-photoemission studies can provide much additional information about the electronic structure of correlated materials like NiO.

  20. Band Structure in Yang-Mills Theories

    CERN Document Server

    Bachas, Constantin

    2016-01-01

    We show how Yang-Mills theory on $S^3\\times R$ can exhibit a spectrum with continuous bands if coupled either to a topological 3-form gauge field, or to a dynamical axion with heavy Peccei-Quinn scale. The basic mechanism consists in associating winding histories to a bosonic zero mode whose role is to convert a circle in configuration space into a helix. The zero mode is, respectively, the holonomy of the 3-form field or the axion momentum. In these models different theta sectors coexist but are not mixed by local operators. Our analysis sheds light on, and extends Seiberg's proposal for modifying the topological sums in quantum field theories. It refutes a recent claim that $B+L$ violation at LHC is unsuppressed.

  1. Pressure effects on crystal and electronic structure of bismuth tellurohalides

    Science.gov (United States)

    Rusinov, I. P.; Menshchikova, T. V.; Sklyadneva, I. Yu; Heid, R.; Bohnen, K.-P.; Chulkov, E. V.

    2016-11-01

    We study the possibility of pressure-induced transitions from a normal semiconductor to a topological insulator (TI) in bismuth tellurohalides using density functional theory and tight-binding method. In BiTeI this transition is realized through the formation of an intermediate phase, a Weyl semimetal, that leads to modification of surface state dispersions. In the topologically trivial phase, the surface states exhibit a Bychkov-Rashba type dispersion. The Weyl semimetal phase exists in a narrow pressure interval of 0.2 GPa. After the Weyl semimetal-TI transition occurs, the surface electronic structure is characterized by gapless states with linear dispersion. The peculiarities of the surface states modification under pressure depend on the band-bending effect. We have also calculated the frequencies of Raman active modes for BiTeI in the proposed high-pressure crystal phases in order to compare them with available experimental data. Unlike BiTeI, in BiTeBr and BiTeCl the topological phase transition does not occur. In BiTeBr, the crystal structure changes with pressure but the phase remains a trivial one. However, the transition appears to be possible if the low-pressure crystal structure is retained. In BiTeCl under pressure, the topological phase does not appear up to 18 GPa due to a relatively large band gap width in this compound.

  2. Unfolding the band structure of GaAsBi

    Science.gov (United States)

    Maspero, R.; Sweeney, S. J.; Florescu, Marian

    2017-02-01

    Typical supercell approaches used to investigate the electronic properties of GaAs(1-x)Bi(x) produce highly accurate, but folded, band structures. Using a highly optimized algorithm, we unfold the band structure to an approximate E≤ft(\\mathbf{k}\\right) relation associated with an effective Brillouin zone. The dispersion relations we generate correlate strongly with experimental results, confirming that a regime of band gap energy greater than the spin-orbit-splitting energy is reached at around 10% bismuth fraction. We also demonstrate the effectiveness of the unfolding algorithm throughout the Brillouin zone (BZ), which is key to enabling transition rate calculations, such as Auger recombination rates. Finally, we show the effect of disorder on the effective masses and identify approximate values for the effective mass of the conduction band and valence bands for bismuth concentrations from 0-12%.

  3. Nucleation and structural growth of cluster crystals

    CERN Document Server

    Leitold, Christian

    2016-01-01

    We study the nucleation of crystalline cluster phases in the generalized exponential model with exponent n=4. Due to the finite value of this pair potential for zero separation, at high densities the system forms cluster crystals with multiply occupied lattice sites. Here, we investigate the microscopic mechanisms that lead to the formation of cluster crystals from a supercooled liquid in the low-temperature region of the phase diagram. Using molecular dynamics and umbrella sampling, we calculate the free energy as a function of the size of the largest crystalline nucleus in the system, and compare our results with predictions from classical nucleation theory. Employing bond-order parameters based on a Voronoi tessellation to distinguish different crystal structures, we analyze the average composition of crystalline nuclei. We find that even for conditions where a multiply-occupied fcc crystal is the thermodynamically stable phase, the nucleation into bcc cluster crystals is strongly preferred. Furthermore, w...

  4. Crystal structure from one-electron theory

    DEFF Research Database (Denmark)

    Skriver, H. L.

    1985-01-01

    The authors have studied the crystal structure of all the 3d, 4d, and 5d transition metals at zero pressure and temperature by means of the linear muffin-tin orbital method and Andersen's force theorem. They find that, although the structural energy differences seem to be overestimated by the the......The authors have studied the crystal structure of all the 3d, 4d, and 5d transition metals at zero pressure and temperature by means of the linear muffin-tin orbital method and Andersen's force theorem. They find that, although the structural energy differences seem to be overestimated...... by the theory, the predicted crystal structures are in accord with experiment in all cases except 79Au. In addition, they have investigated the effect of pressure upon the alkali metals (3Li, 11Na, 37Rb, 55Cs) and selected lanthanide metals (57La, 58Ce, 71Lu) and actinide metals (90Th, 91Pa). In these cases...

  5. Theoretical investigation of band-gap and mode characteristics of anti-resonance guiding photonic crystal fibres

    Institute of Scientific and Technical Information of China (English)

    Yuan Jin-Hui; Sang Xin-Zhu; Yu Chong-Xiu; Xin Xiang-Jun; Zhang Jin-Long; Zhou Gui-Yao; Li Shu-Guang; Hou Lan-Tian

    2011-01-01

    With the full-vector plane-wave method (FVPWM) and the full-vector beam propagation method (FVBPM), the dependences of the band-gap and mode characteristics on material index and cladding structure parameter in anti-resonance guiding photonic crystal fibres (ARGPCFs) are sufficiently analysed. An ARGPCF operating in the near-infrared wavelength is shown. The influences of the high index cylinders, glass interstitial apexes and silica structure on the characteristics of band-gaps and modes are deeply investigated. The equivalent planar waveguide theory is used for analysing such an ARGPCF filled by the isotropic materials, and the resonance and the anti-resonance characteristics can be well predicted.

  6. Band Gap Properties of Magnetoelectroelastic Grid Structures with Initial Stress

    Institute of Scientific and Technical Information of China (English)

    WANG Yi-Ze; LI Feng-Ming

    2012-01-01

    The propagation of elastic waves in magnetoelectroelastic grid structures is studied.Band gap properties are presented and the effects of the magnetoelectroelastic coupling and initial stress are considered. Numerical calculations are performed using the plane-wave expansion method.The results show that the band gap width can be tuned by the initial stress.It is hoped that our results will be helpful for designing acoustic filters with magnetoelectroelastic materials and grid structures.

  7. Impact of the Electronic Band Structure in High-Harmonic Generation Spectra of Solids

    Science.gov (United States)

    Tancogne-Dejean, Nicolas; Mücke, Oliver D.; Kärtner, Franz X.; Rubio, Angel

    2017-02-01

    An accurate analytic model describing the microscopic mechanism of high-harmonic generation (HHG) in solids is derived. Extensive first-principles simulations within a time-dependent density-functional framework corroborate the conclusions of the model. Our results reveal that (i) the emitted HHG spectra are highly anisotropic and laser-polarization dependent even for cubic crystals; (ii) the harmonic emission is enhanced by the inhomogeneity of the electron-nuclei potential; the yield is increased for heavier atoms; and (iii) the cutoff photon energy is driver-wavelength independent. Moreover, we show that it is possible to predict the laser polarization for optimal HHG in bulk crystals solely from the knowledge of their electronic band structure. Our results pave the way to better control and optimize HHG in solids by engineering their band structure.

  8. Impact of the electronic band structure in high-harmonic generation spectra of solids

    CERN Document Server

    Tancogne-Dejean, Nicolas; Kärtner, Franz X; Rubio, Angel

    2016-01-01

    An accurate analytic model describing high-harmonic generation (HHG) in solids is derived. Extensive first-principles simulations within a time-dependent density-functional framework corroborate the conclusions of the model. Our results reveal that: (i) the emitted HHG spectra are highly anisotropic and laser-polarization dependent even for cubic crystals, (ii) the harmonic emission is enhanced by the inhomogeneity of the electron-nuclei potential, the yield is increased for heavier atoms, and (iii) the cutoff photon energy is driver-wavelength independent. Moreover, we show that it is possible to predict the laser polarization for optimal HHG in bulk crystals solely from the knowledge of their electronic band structure. Our results pave the way to better control and optimize HHG in solids by engineering their band structure.

  9. Optimum design of band-gap beam structures

    DEFF Research Database (Denmark)

    Olhoff, Niels; Niu, Bin; Cheng, Gengdong

    2012-01-01

    -sectional area. To study the band-gap for travelling waves, a repeated inner segment of the optimized beams is analyzed using Floquet theory and the waveguide finite element (WFE) method. Finally, the frequency response is computed for the optimized beams when these are subjected to an external time......The design of band-gap structures receives increasing attention for many applications in mitigation of undesirable vibration and noise emission levels. A band-gap structure usually consists of a periodic distribution of elastic materials or segments, where the propagation of waves is impeded...

  10. Design of radial phononic crystal using annular soft material with low-frequency resonant elastic structures

    Science.gov (United States)

    Gao, Nansha; Wu, Jiu Hui; Yu, Lie; Xin, Hang

    2016-10-01

    Using FEM, we theoretically study the vibration properties of radial phononic crystal (RPC) with annular soft material. The band structures, transmission spectra, and displacement fields of eigenmode are given to estimate the starting and cut-off frequency of band gaps. Numerical calculation results show that RPC with annular soft material can yield low-frequency band gaps below 350 Hz. Annular soft material decreases equivalent stiffness of the whole structure effectively, and makes corresponding band gaps move to the lower frequency range. Physical mechanism behind band gaps is the coupling effect between long or traveling wave in plate matrix and the vibrations of corrugations. By changing geometrical dimensions of plate thickness e, the length of silicone rubber h2, and the corrugation width b, we can control the location and width of the first band gap. These research conclusions of RPC structure with annular soft material can potentially be applied to optimize band gaps, generate filters, and design acoustic devices.

  11. Flexural vibration band gaps in thin plates with two-dimensional binary locally resonant structures

    Institute of Scientific and Technical Information of China (English)

    Yu Dian-Long; Wang Gang; Liu Yao-Zong; Wen Ji-Hong; Qiu Jing

    2006-01-01

    The complete flexural vibration band gaps are studied in the thin plates with two-dimensional binary locally resonant structures, i.e. the composite plate consisting of soft rubber cylindrical inclusions periodically placed in a host material. Numerical simulations show that the low-frequency gaps of flexural wave exist in the thin plates. The width of the first gap decreases monotonically as the matrix density increases. The frequency response of the finite periodic thin plates is simulated by the finite element method, which provides attenuations of over 20dB in the frequency range of the band gaps. The findings will be significant in the application of phononic crystals.

  12. Fabrication of 3-D Photonic Band Gap Crystals Via Colloidal Self-Assembly

    Science.gov (United States)

    Subramaniam, Girija; Blank, Shannon

    2005-01-01

    The behavior of photons in a Photonic Crystals, PCs, is like that of electrons in a semiconductor in that, it prohibits light propagation over a band of frequencies, called Photonic Band Gap, PBG. Photons cannot exist in these band gaps like the forbidden bands of electrons. Thus, PCs lend themselves as potential candidates for devices based on the gap phenomenon. The popular research on PCs stem from their ability to confine light with minimal losses. Large scale 3-D PCs with a PBG in the visible or near infra red region will make optical transistors and sharp bent optical fibers. Efforts are directed to use PCs for information processing and it is not long before we can have optical integrated circuits in the place of electronic ones.

  13. Nonequilibrium band structure of nano-devices

    Science.gov (United States)

    Hackenbuchner, S.; Sabathil, M.; Majewski, J. A.; Zandler, G.; Vogl, P.; Beham, E.; Zrenner, A.; Lugli, P.

    2002-03-01

    A method is developed for calculating, in a consistent manner, the realistic electronic structure of three-dimensional (3-D) heterostructure quantum devices under bias and its current density close to equilibrium. The nonequilibrium electronic structure is characterized by local Fermi levels that are calculated self-consistently. We have applied this scheme to predict asymmetric Stark shifts and tunneling of confined electrons and holes in single-dot GaAs/InGaAs photodiodes.

  14. Automated effective band structures for defective and mismatched supercells

    Science.gov (United States)

    Brommer, Peter; Quigley, David

    2014-12-01

    In plane-wave density functional theory codes, defects and incommensurate structures are usually represented in supercells. However, interpretation of E versus k band structures is most effective within the primitive cell, where comparison to ideal structures and spectroscopy experiments are most natural. Popescu and Zunger recently described a method to derive effective band structures (EBS) from supercell calculations in the context of random alloys. In this paper, we present bs_sc2pc, an implementation of this method in the CASTEP code, which generates an EBS using the structural data of the supercell and the underlying primitive cell with symmetry considerations handled automatically. We demonstrate the functionality of our implementation in three test cases illustrating the efficacy of this scheme for capturing the effect of vacancies, substitutions and lattice mismatch on effective primitive cell band structures.

  15. Electronic structure of the valence band of II--VI wide band gap semiconductor interfaces

    OpenAIRE

    1996-01-01

    In this work we present the electronic band structure for (001)--CdTe interfaces with some other II--VI zinc blende semiconductors. We assume ideal interfaces. We use tight binding Hamiltonians with an orthogonal basis ($s p^3 s^*$). We make use of the well--known Surface Green's Function Matching method to calculate the interface band structure. In our calculation the dominion of the interface is constituted by four atomic layers. We consider here anion--anion interfaces only. We have includ...

  16. Structure of crystals of hard colloidal spheres

    Energy Technology Data Exchange (ETDEWEB)

    Pusey, P.N.; van Megen, W.; Bartlett, P.; Ackerson, B.J.; Rarity, J.G.; Underwood, S.M. (Royal Signals and Radar Establishment, Malvern, WR14 3PS, United Kingsom (GB) Department of Applied Physics, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia School of Chemistry, Bristol University, Bristol, BS8 1TS, United Kingdom Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078)

    1989-12-18

    We report light-scattering measurements of powder diffraction patterns of crystals of essentially hard colloidal spheres. These are consistent with structures formed by stacking close-packed planes of particles in a sequence of permitted lateral positions, {ital A},{ital B},{ital C}, which shows a high degree of randomness. Crystals grown slowly, while still containing many stacking faults, show a tendency towards face-centered-cubic packing: possible explanations for this observation are discussed.

  17. Band-structure engineering in conjugated 2D polymers.

    Science.gov (United States)

    Gutzler, Rico

    2016-10-26

    Conjugated polymers find widespread application in (opto)electronic devices, sensing, and as catalysts. Their common one-dimensional structure can be extended into the second dimension to create conjugated planar sheets of covalently linked molecules. Extending π-conjugation into the second dimension unlocks a new class of semiconductive polymers which as a consequence of their unique electronic properties can find usability in numerous applications. In this article the theoretical band structures of a set of conjugated 2D polymers are compared and information on the important characteristics band gap and valence/conduction band dispersion is extracted. The great variance in these characteristics within the investigated set suggests 2D polymers as exciting materials in which band-structure engineering can be used to tailor sheet-like organic materials with desired electronic properties.

  18. Crystal Structure of Macrocalyxin J

    Institute of Scientific and Technical Information of China (English)

    HE Shan; WU Bin; SHI Hao; SUN Cui-Rong

    2007-01-01

    The title compound, (1α,6β, 1 1β, 14α)-1,7:6,20-diepoxy-6,1 1-dihydroxy- 6,7-secoent- kaur-1 6-ene-7,15-dione-14-acetate (macrocalyxin J), is a diterpenoid which was isolated from the leaves of Rabdosia macrocalyx and characterized by single-crystal X-ray diffraction. It crystallizes in orthorhombic, spac e group P212121 with a = 9.3608(8), b = 14.9787(12), c = 15.5750(13)(A), Z = 4, V = 2183.8(3) (A)3, C22H30O9, Mr = 438.46, Dc = 1.334 g/m3, μ(MoKα) = 0.103 mm-1,F(000) = 936, the final R = 0.0532 and wR = 0.1262 for 2252 observed reflections (I > 2σ(I)). In the molecule, three six-membered rings adopt chair, boat and slightly distorted boat conformations,respectively, while both five-membered rings have approximate envelope conformations.

  19. Properties of the Band Gaps in 1D Ternary Lossy Photonic Crystal Containing Double-Negative Materials

    Directory of Open Access Journals (Sweden)

    Alireza Aghajamali

    2014-01-01

    Full Text Available Theoretically, the characteristics matrix method is employed to investigate and compare the properties of the band gaps of the one-dimensional ternary and binary lossy photonic crystals which are composed of double-negative and double-positive materials. This study shows that by varying the angle of incidence, the band gaps for TM and TE waves behave differently in both ternary and binary lossy structures. The results demonstrate that, by increasing the angle of incidence for the TE wave, the width and the depth of zero-n¯, zero-μ, and Bragg gap increase in both ternary and binary structures. On the other hand, the enhancement of the angle of incidence for the TM wave contributes to reduction of the width and the depth of the zero-n¯ and Bragg gaps, and they finally disappear for incidence angles greater than 50° and 60° for the binary structure and 40° and 45° for the ternary structures, respectively. In addition, the details of the edges of the band gaps variations as a function of incidence angle for both structures are studied.

  20. Complete Band-Gap in Two-Dimensional Quasiperiod Photonic Crystals with Hollow Cylinders

    Institute of Scientific and Technical Information of China (English)

    FENG Zhi-Fang; FENG Shuai; REN Kun; LI Zhi-Yuan; CHENG Bing-Ying; ZHANG Dao-Zhong

    2005-01-01

    @@ The transmission properties of quasiperiodic photonic crystals (QPCs) based on the random square-triangle tilingsystem are investigated by the multiple scattering method. The hollow cylinders are introduced in our calculation. It is found that QPCs with hollow cylinders also possess a complete band gap common to s- and p-polarized waves when the inner radius of hollow cylinders is larger than a certain value. The QPCs possessing the complete band gap can be applied to the fields of light emitting, wave-guides, optical filters, high-Q resonators and antennas.

  1. Single-Crystal Semiconductors with Narrow Band Gaps for Solar Water Splitting.

    Science.gov (United States)

    Wang, Tuo; Gong, Jinlong

    2015-09-07

    Solar water splitting provides a clean and renewable approach to produce hydrogen energy. In recent years, single-crystal semiconductors such as Si and InP with narrow band gaps have demonstrated excellent performance to drive the half reactions of water splitting through visible light due to their suitable band gaps and low bulk recombination. This Minireview describes recent research advances that successfully overcome the primary obstacles in using these semiconductors as photoelectrodes, including photocorrosion, sluggish reaction kinetics, low photovoltage, and unfavorable planar substrate surface. Surface modification strategies, such as surface protection, cocatalyst loading, surface energetics tuning, and surface texturization are highlighted as the solutions.

  2. Experimental Study of Electronic Quantum Interference, Photonic Crystal Cavity, Photonic Band Edge Effects for Optical Amplification

    Science.gov (United States)

    2016-01-26

    performed. 2.0 INTRODUCTION Three dimensional (3D) photonic crystals and their optical properties have attracted a lot of attention in the past decade... physical phenomena. The band gap frequency of this system can be varied to tailor to the electronic transition levels of a gain medium such as InAs...quantum dot or an InGaAs quantum well. The band gap can be varied in addition to include either one or two electronic levels of a multi-level system

  3. Crystal structure of levomepromazine maleate

    Directory of Open Access Journals (Sweden)

    Gyula Tamás Gál

    2016-05-01

    Full Text Available The asymmetric unit of the title salt, C19H25N2OS+·C4H3O4− [systematic name: (S-3-(2-methoxyphenothiazin-10-yl-N,N,2-trimethylpropanaminium hydrogen maleate], comprises two (S-levomepromazine cations and two hydrogen maleate anions. The conformations of the two cations are similar. The major difference relates to the orientation of the methoxy substituent at the phenothiazine ring system. The crystal components form a three-dimensional supramolecular network via N—H...O, C—H...O and C—H...π interactions. A comparison of the conformations of the levomepromazine cations with those of the neutral molecule and similar protonated molecules reveals significant conformational flexibility of the phenothiazine ring system and the substituent at the phenothiazine N atom.

  4. Crystal structure of 3-(hydroxymethylchromone

    Directory of Open Access Journals (Sweden)

    Yoshinobu Ishikawa

    2015-07-01

    Full Text Available In the title compound, C10H8O3 (systematic name 3-hydroxymethyl-4H-chromen-4-one, the fused-ring system is slightly puckered [dihedral angle between the rings = 3.84 (11°]. The hydroxy O atom deviates from the heterocyclic ring by 1.422 (1 Å. In the crystal, inversion dimers linked by pairs of O—H...O hydrogen bonds generate R22(12 loops. The dimers are linked by aromatic π–π stacking [shortest centroid–centroid distance = 3.580 (3 Å], and C—H...O hydrogen bonds, generating a three-dimensional network.

  5. Crystal structure of 9-methacryloylanthracene

    Directory of Open Access Journals (Sweden)

    Aditya Agrahari

    2015-04-01

    Full Text Available In the title compound, C18H14O, with systematic name 1-(anthracen-9-yl-2-methylprop-2-en-1-one, the ketonic C atom lies 0.2030 (16 Å out of the anthryl-ring-system plane. The dihedral angle between the planes of the anthryl and methacryloyl moieties is 88.30 (3° and the stereochemistry about the Csp2—Csp2 bond in the side chain is transoid. In the crystal, the end rings of the anthryl units in adjacent molecules associate in parallel–planar orientations [shortest centroid–centroid distance = 3.6320 (7 Å]. A weak hydrogen bond is observed between an aromatic H atom and the O atom of a molecule displaced by translation in the a-axis direction, forming sheets of parallel-planar anthryl groups packing in this direction.

  6. Asymmetric Band Diagrams in Photonic Crystals with a Spontaneous Nonreciprocal Response

    CERN Document Server

    Prudêncio, Filipa R; Paiva, Carlos R

    2015-01-01

    We study the propagation of electromagnetic waves in layered photonic crystals formed by materials with a spontaneous nonreciprocal response, such as Tellegen (axion) media or topological insulators. Surprisingly, it is proven that stratified Tellegen photonic crystals that break simultaneously the space inversion and time reversal symmetries have always symmetric dispersion diagrams. Interestingly, we show that by combining chiral and nonreciprocal materials the photonic band diagrams can exhibit a spectral asymmetry such that . Furthermore, it is demonstrated that in some conditions two juxtaposed Tellegen medium layers have an electromagnetic response analogous to that of a biased ferrite slab.

  7. A note on temperature-dependent band narrowing in oligo-acene crystals

    Energy Technology Data Exchange (ETDEWEB)

    Hannewald, K; Stojanovic, V M; Bobbert, P A [Group Polymer Physics, Eindhoven Polymer Laboratories, Technische Universiteit Eindhoven, PO Box 513, 5600 MB Eindhoven (Netherlands)

    2004-03-31

    We present a theoretical description of polaron band narrowing in oligo-acene crystals due to electron-lattice interaction. The analysis is based on a model which takes both local and nonlocal contributions to the electron-phonon coupling into account. Different approximation schemes are discussed and compared. The theory is supplemented by quantitative ab initio calculations of the temperature dependence of polaron bandwidths in oligo-acene crystals which show the important role of in-plane nonlocal electron-phonon coupling.

  8. A note on temperature-dependent band narrowing in oligo-acene crystals

    Science.gov (United States)

    Hannewald, K.; Stojanovic, V. M.; Bobbert, P. A.

    2004-03-01

    We present a theoretical description of polaron band narrowing in oligo-acene crystals due to electron-lattice interaction. The analysis is based on a model which takes both local and nonlocal contributions to the electron-phonon coupling into account. Different approximation schemes are discussed and compared. The theory is supplemented by quantitative ab initio calculations of the temperature dependence of polaron bandwidths in oligo-acene crystals which show the important role of in-plane nonlocal electron-phonon coupling.

  9. Zero- n bar band gap in two-dimensional metamaterial photonic crystals

    Science.gov (United States)

    Mejía-Salazar, J. R.; Porras-Montenegro, N.

    2015-04-01

    We have theoretically studied metamaterial photonic crystals (PCs) composed by air and double negative (DNG) material. Numerical data were obtained by means of the finite difference time-domain (FDTD) method, with results indicating the possibility for the existence of the zero- n bar non-Bragg gap in two-dimensional metamaterial PCs, which has been previously observed only in one-dimensional photonic superlattices. Validity of the present FDTD algorithm for the study of one-dimensional metamaterial PCs is shown by comparing with results for the transmittance spectra obtained by means of the well known transfer matrix method (TMM). In the case of two-dimensional metamaterial PCs, we have calculated the photonic band structure (PBS) in the limiting case of a one-dimensional photonic superlattice and for a nearly one-dimensional PC, showing a very similar dispersion relation. Finally, we show that due to the strong electromagnetic field localization on the constitutive rods, the zero- n bar non-Bragg gap may only exist in two-dimensional systems under strict geometrical conditions.

  10. The crystal structure and crystal chemistry of fernandinite and corvusite

    Science.gov (United States)

    Evans, H.T.; Post, J.E.; Ross, D.R.; Nelen, J.A.

    1994-01-01

    Using type material of fernandinite from Minasragra, Peru, and corvusite from the Jack Claim, La Sal Mountains, Utah, the properties and crystal chemistry of these minerals have been determined by Rietveld analysis of the powder X-ray-diffraction patterns. The crystal structure of both species is isotypic with the V2O5 -type layer first found for ??-Ag0.68V2O5; it consists of chains of VO6 octahedra linked by opposite corners (parallel to b) condensed by edge-sharing to form the layer. The vanadium has average valence 4.8, and the resulting layer-charge is balanced by varying amounts of Ca, Na, and K in the interlayer region accompanied by labile water. This study has confirmed the validity of fernandinite as a unique mineral species. It is closely related to corvusite, from which it is distinguished on the basis of the dominant interlayer cation: Ca for fernandinite, Na for curvusite. -Authors

  11. Optimum design of band-gap beam structures

    DEFF Research Database (Denmark)

    Olhoff, Niels; Niu, Bin; Cheng, Gengdong

    2012-01-01

    -sectional area. To study the band-gap for travelling waves, a repeated inner segment of the optimized beams is analyzed using Floquet theory and the waveguide finite element (WFE) method. Finally, the frequency response is computed for the optimized beams when these are subjected to an external time......The design of band-gap structures receives increasing attention for many applications in mitigation of undesirable vibration and noise emission levels. A band-gap structure usually consists of a periodic distribution of elastic materials or segments, where the propagation of waves is impeded...... or significantly suppressed for a range of external excitation frequencies. Maximization of the band-gap is therefore an obvious objective for optimum design. This problem is sometimes formulated by optimizing a parameterized design model which assumes multiple periodicity in the design. However, it is shown...

  12. Band Structure in the Doubly Magic Nucleus 56Ni

    Institute of Scientific and Technical Information of China (English)

    DONG Bao-Guo; GUO Hong-Chao

    2004-01-01

    @@ Band structures near yrast lines of the Z = N doubly magic nucleus 56Ni are investigated with the configurationdependent cranked Nilsson-Strutinsky approach. The observed deformed bands are confirmed as highly deformed and their properties are explained theoretically. The calculated transition quadrupole moments Qt, ~ 1.7 eb at low spin as well as the kinematic and dynamic moments of inertia J1) and J(2) for configurations of interest are found to be generally in good agreement with the observed results. Two terminating states at 20+ and 29- for the two observed bands and other terminations in 56Ni are also predicted. It is found that the configuration-dependent cranked Nilsson-Strutinsky approach is better in the description of nuclear properties and band structures at high spin than other models.

  13. Lessons from crystal structures of kainate receptors

    DEFF Research Database (Denmark)

    Møllerud, Stine; Frydenvang, Karla Andrea; Pickering, Darryl S

    2017-01-01

    structure and how they bind agonists, antagonists and ions. The first structure of the ligand-binding domain of the GluK1 subunit was reported in 2005, seven years after publication of the crystal structure of a soluble construct of the ligand-binding domain of the AMPA-type subunit GluA2. Today, a full......-length structure has been determined of GluK2 by cryo electron microscopy to 7.6 Å resolution as well as 84 high-resolution crystal structures of N-terminal domains and ligand-binding domains, including agonist and antagonist bound structures, modulatory ions and mutations. However, there are still many unanswered...

  14. Banded crystallization of tricosane in the presence of kinetic inhibitors during directional solidification

    Science.gov (United States)

    Hutter, Jeffrey L.; Hudson, Stephen; Smith, Christopher; Tetervak, Alexander; Zhang, Jizhong

    2004-12-01

    Driven by the need to prevent crystallization of normal alkanes from diesel fuels in cold climates, the petroleum industry has developed additives to slow the growth of these crystals and alter their morphology. While the utility of such additives has been proven at the operational level, few studies have directly monitored their effect at microscopic scales. Here, we present a study of such additives in model n-alkane systems. We find a dramatic effect on the growth morphology: rather than the usual plate-like growth exhibited by pure wax, we see highly branched microcrystalline meshes. Under certain conditions, these meshes form well-defined bands with spacings larger than 200 μm. We suggest that successive bands form by nucleation via a metastable phase ahead of the inhibited growth front.

  15. All-optical ultrafast switching of Si woodpile photonic band gap crystals

    CERN Document Server

    Euser, T G; Fleming, J G; Gralak, B; Polman, Albert; Vos, W L; Euser, Tijmen G.; Molenaar, Adriaan J.; Gralak, Boris; Polman, Albert; Vos, Willem L.

    2006-01-01

    We present ultrafast all-optical switching measurements of Si woodpile photonic band gap crystals at telecom frequencies. The crystals are homogeneously excited by a two-photon process. We probe the switching by measuring reflectivity over broad frequency ranges as a function of time. At short delay times, we observe that the photonic gap becomes narrower than in the unswitched case. After 1 ps, the complete gap has shifted to higher frequencies. This intricate behavior is the result of competing refractive index changes due to the electronic Kerr effect and to optically excited free carriers. The frequency shift of the band gap as a function of pump intensity agrees well with Fourier modal method calculations with no freely adjustable parameters.

  16. Band gap control in a line-defect magnonic crystal waveguide

    Energy Technology Data Exchange (ETDEWEB)

    Morozova, M. A., E-mail: mamorozovama@yandex.ru; Grishin, S. V.; Sadovnikov, A. V.; Romanenko, D. V.; Sharaevskii, Yu. P.; Nikitov, S. A. [Laboratory ' Metamaterials,' Saratov State University, Astrakhanskaya 83, Saratov 410012 (Russian Federation)

    2015-12-14

    We report on the experimental observation of the spin wave spectrum control in a line-defect magnonic crystal (MC) waveguide. We demonstrate the possibility to control the forbidden frequency band (band gap) for spin waves tuning the line-defect width. In particular, this frequency may be greater or lower than the one of 1D MC waveguide without line-defect. By means of space-resolved Brillouin light scattering technique, we study the localization of magnetization amplitude in the line-defect area. We show that the length of this localization region depends on the line-defect width. These results agree well with theoretical calculations of spin wave spectrum using the proposed model of two coupled magnonic crystal waveguides. The proposed simple geometry of MC with line-defect can be used as a logic and multiplexing block for application in the novel field of magnonic devices.

  17. Crystal structure of putrescine aspartic acid complex

    OpenAIRE

    Ramaswamy, S.; Murthy, MRN

    1990-01-01

    Polyamines, putrescine, spermidine and spermine are ubiquitous biogenic cations believed to be important for a variety of cellular processes. In order to obtain structural information on the interaction of these amines with other biomolecules, the structure of a complex of putrescine with aspartic acid was determined using single crystal X-ray diffraction methods. The crystals belong monoclinic space group $C_2$ with $a = 21.504 \\AA$, $b = 4.779 \\AA$, $c = 8.350 \\AA$ and $\\beta = {97.63}^{\\ci...

  18. Crystal structure of canagliflozin hemihydrate

    Directory of Open Access Journals (Sweden)

    Kai-Hang Liu

    2016-05-01

    Full Text Available There are two canagliflozin molecules (A and B and one water molecule in the asymmetric unit of the title compound, C24H25FO5S·0.5H2O [systematic name: (2S,3R,4R,5S,6R-2-(3-{[5-(4-fluorophenylthiophen-2-yl]methyl}-4-methylphenyl-6-(hydroxymethyl-3,4,5,6-tetrahydro-2H-pyran-3,4,5-triol hemihydrate]. The dihedral angles between the methylbenzene and thiophene rings are 115.7 (4 and 111.7 (4°, while the dihedral angles between the fluorobenzene and thiophene rings are 24.2 (6 and 20.5 (9° in molecules A and B, respectively. The hydropyran ring exhibits a chair conformation in both canagliflozin molecules. In the crystal, the canagliflozin molecules and lattice water molecules are connected via O—H...O hydrogen bonds into a three-dimensional supramolecular architecture.

  19. Crystal structure of canagliflozin hemihydrate.

    Science.gov (United States)

    Liu, Kai-Hang; Gu, Jian-Ming; Hu, Xiu-Rong; Tang, Gu-Ping

    2016-05-01

    There are two canagliflozin mol-ecules (A and B) and one water mol-ecule in the asymmetric unit of the title compound, C24H25FO5S·0.5H2O [systematic name: (2S,3R,4R,5S,6R)-2-(3-{[5-(4-fluoro-phen-yl)thio-phen-2-yl]meth-yl}-4-methylphen-yl)-6-(hy-droxy-meth-yl)-3,4,5,6-tetra-hydro-2H-pyran-3,4,5-triol hemihydrate]. The dihedral angles between the methyl-benzene and thio-phene rings are 115.7 (4) and 111.7 (4)°, while the dihedral angles between the fluoro-benzene and thio-phene rings are 24.2 (6) and 20.5 (9)° in mol-ecules A and B, respectively. The hydro-pyran ring exhibits a chair conformation in both canagliflozin mol-ecules. In the crystal, the canagliflozin mol-ecules and lattice water mol-ecules are connected via O-H⋯O hydrogen bonds into a three-dimensional supra-molecular architecture.

  20. Crystal Structure of 8-Demethoxyrunanine

    Institute of Scientific and Technical Information of China (English)

    WANG Xiao-Ling

    2008-01-01

    A new hasubanane-type alkaloid, 8-demethoxyrunanine, was isolated from Sino- menium acutum and characterized by melting point, HREIMS, 1H NMR, and X-ray diffraction analysis. X-ray diffraction reveals that the title compound crystallizes in the orthorhombic system, space group P212121 with a = 7.308(1), b = 21.742(5), c = 22.893(4) ?, V = 3637.5(11) ?3, Z = 8, Dx = 1.254 g/cm3, F(000) = 1472, μ(MoKα) = 0.087 mm-1, the final R = 0.0438 and wR = 0.0575 for 4497 independent reflections with Rint = 0.0192 and 2091 observed reflections with I > 2σ(I). Four rings (ring A: one benzene ring, ring B: one hexagon carbon ring in a half-chair conformation, ring C: one hexagon carbon ring with α,β-unsaturated ketone segment (-CR2=CR1-C=O) in a screw-boat conformation, and ring D: one nonplanar tetrahydropyrrole) form a hasubanane-type alkaloid.

  1. Hubbard-U band-structure methods

    DEFF Research Database (Denmark)

    Albers, R.C.; Christensen, Niels Egede; Svane, Axel

    2009-01-01

    The last decade has seen a large increase in the number of electronic-structure calculations that involve adding a Hubbard term to the local-density approximation band-structure Hamiltonian. The Hubbard term is then determined either at the mean-field level or with sophisticated many-body techniq...

  2. Analysis of band gap of non-bravais lattice photonic crystal fiber

    Institute of Scientific and Technical Information of China (English)

    Yichao MA; Heming CHEN

    2009-01-01

    This article designs a novel type ofnon-bravais lattice photonic crystal fiber. To form the nesting complexperiod with positive and negative refractive index materials respectively, a cylinder with the same radius and negative refractive index is introduced into the center of each lattice unit cell in the traditional square lattice air-holes photonic crystal fiber. The photonic band-gap of the photonic crystal fiber is calculated numerically by the plane wave expansion method. The result shows that compared with the traditional square photonic band-gap fiber (PBGF),when R/A is 0.35, the refractive index of the substrate, airhole, and medium-column are 1.30, 1.0, and -1.0,respectively. This new PBGF can transmit signal by the photonic band-gap effect. When the lattice constant Λvaries from 1.5 μm to 3.0 μm, the range of the wavelength ranges from 880 nm to 2300 nm.

  3. Crystal structure determination of Jatrorrhizine chloride

    Institute of Scientific and Technical Information of China (English)

    LEI XianRong; YANG JianHua; LIN Xiang; DAI Qin; CHENG Qiang; GUO LingHong; LI Hui

    2009-01-01

    Optimum resolution data of powder X-ray diffraction (PXRD) for Jatrorrhizine (Jat) were collected by an X' Pert Pro MPD diffractometer with an X'celerator detector under the stepwise scanning condition as 8.255 ms and 0.00836°per step,2θrange of 50°-80° and total scanning period of 8-10 min. Indexing of the crystal system and a search of the space group from the powder X-ray diffraction data were conducted by the computational crystallography method. The pilot crystal models of Jat were globally optimized with Monte Carlo method and then refined with the Rietveld method. In parallel with PXRD test,single crystals of Jat were cultured in an aqueous solution by a slow-decreasing temperature method,then its crystal structure was determined by single crystal X-ray diffraction (SCXRD). Both crystal structures from PXRD and SCXRD are identical. The results show that the crystal structure of Jat belongs to a monoclinic system and the space group P21/c. The parameters of cell dimensions from PXRD are a=7.69(A),b= 12.55(A),c=20.89(A),β=106.53°,Z=4,and V=1933.4(A)3,meanwhile the parameters from SCXRD are a=7.72(A),b=12.61(A),c=20.99(A),β=106.38°,Z=4,and V=1961.3(A)3.

  4. Structural and electronic properties of Diisopropylammonium bromide molecular ferroelectric crystal

    Science.gov (United States)

    Alsaad, A.; Qattan, I. A.; Ahmad, A. A.; Al-Aqtash, N.; Sabirianov, R. F.

    2015-10-01

    We report the results of ab-initio calculations based on Generalized Gradient Approximation (GGA) and hybrid functional (HSE06) of electronic band structure, density of states and partial density of states to get a deep insight into structural and electronic properties of P21 ferroelectric phase of Diisopropylammonium Bromide molecular crystal (DIPAB). We found that the optical band gap of the polar phase of DIPAB is ∼ 5 eV confirming it as a good dielectric. Examination of the density of states and partial density of states reveal that the valence band maximum is mainly composed of bromine 4p orbitals and the conduction band minimum is dominated by carbon 2p, carbon 2s, and nitrogen 2s orbitals. A unique aspect of P21 ferroelectric phase is the permanent dipole within the material. We found that P21 DIPAB has a spontaneous polarization of 22.64 consistent with recent findings which make it good candidate for the creation of ferroelectric tunneling junctions (FTJs) which have the potential to be used as memory devices.

  5. One dimensional coordination polymers: Synthesis, crystal structures and spectroscopic properties

    Science.gov (United States)

    Karaağaç, Dursun; Kürkçüoğlu, Güneş Süheyla; Şenyel, Mustafa; Şahin, Onur

    2016-11-01

    Two new one dimensional (1D) cyanide complexes, namely [M(4-aepy)2(H2O)2][Pt(CN)4], (4-aepy = 4-(2-aminoethyl)pyridine M = Cu(II) (1) or Zn(II) (2)), have been synthesized and characterized by vibrational (FT-IR and Raman) spectroscopy, single crystal X-ray diffraction, thermal and elemental analyses techniques. The crystallographic analyses reveal that 1 and 2 are isomorphous and isostructural, and crystallize in the monoclinic system and C2 space group. The Pt(II) ions are coordinated by four cyanide-carbon atoms in the square-planar geometry and the [Pt(CN)4]2- ions act as a counter ion. The M(II) ions display an N4O2 coordination sphere with a distorted octahedral geometry, the nitrogen donors belonging to four molecules of the organic 4-aepy that act as unidentate ligands and two oxygen atoms from aqua ligands. The crystal structures of 1 and 2 are similar each other and linked via intermolecular hydrogen bonding, Pt⋯π interactions to form 3D supramolecular network. Vibration assignments of all the observed bands are given and the spectral features also supported to the crystal structures of the complexes.

  6. Crystal structure of the eukaryotic ribosome.

    Science.gov (United States)

    Ben-Shem, Adam; Jenner, Lasse; Yusupova, Gulnara; Yusupov, Marat

    2010-11-26

    Crystal structures of prokaryotic ribosomes have described in detail the universally conserved core of the translation mechanism. However, many facets of the translation process in eukaryotes are not shared with prokaryotes. The crystal structure of the yeast 80S ribosome determined at 4.15 angstrom resolution reveals the higher complexity of eukaryotic ribosomes, which are 40% larger than their bacterial counterparts. Our model shows how eukaryote-specific elements considerably expand the network of interactions within the ribosome and provides insights into eukaryote-specific features of protein synthesis. Our crystals capture the ribosome in the ratcheted state, which is essential for translocation of mRNA and transfer RNA (tRNA), and in which the small ribosomal subunit has rotated with respect to the large subunit. We describe the conformational changes in both ribosomal subunits that are involved in ratcheting and their implications in coordination between the two associated subunits and in mRNA and tRNA translocation.

  7. Diffusion of a probe nanoparticle in a quantum crystal with narrow vacancy band

    CERN Document Server

    Levchenko, A A; Trusov, A B

    2003-01-01

    The vacancy-assisted diffusion of a probe nanoparticle with a diameter d sub p of a few nm drifting through a quantum crystal with a narrow vacancy band Q sub v Tmelt is considered qualitatively. Below the melting point Tmelt the temperature dependence of the diffusion coefficient of the nanoprobe, D sub p (T), changes significantly at temperatures near T sub t r (T sub m elt> d sub p , the diffusion coefficient D sub p falls almost near exponentially, proportionally with x sub v , if the cross-section of inelastic vacancion-probe particle scattering is weakly dependent on temperature. We believe that our model could be applied for the description of the diffusion of positive charges in hcp sup 4 He crystals grown at pressures higher than the minimal pressure of helium solidification and the diffusion of negative charges in hcp crystals grown from pure parahydrogen.

  8. Modular crystals as modulated structures

    DEFF Research Database (Denmark)

    Elcoro, L.; Perez-Mato, J.M.; Friese, K.;

    2008-01-01

    The use of the superspace formalism is extended to the description and refinement of the homologous series of modular structures with two symmetry-related modules with different orientations. The lillianite homologous series has been taken as a study case. Starting from a commensurate modulated c...

  9. Shear induced structures in crystallizing cocoa butter

    Science.gov (United States)

    Mazzanti, Gianfranco; Guthrie, Sarah E.; Sirota, Eric B.; Marangoni, Alejandro G.; Idziak, Stefan H. J.

    2004-03-01

    Cocoa butter is the main structural component of chocolate and many cosmetics. It crystallizes in several polymorphs, called phases I to VI. We used Synchrotron X-ray diffraction to study the effect of shear on its crystallization. A previously unreported phase (phase X) was found and a crystallization path through phase IV under shear was observed. Samples were crystallized under shear from the melt in temperature controlled Couette cells, at final crystallization temperatures of 17.5^oC, 20^oC and 22.5^oC in Beamline X10A of NSLS. The formation of phase X was observed at low shear rates (90 s-1) and low crystallization temperature (17.5^oC), but was absent at high shear (720 s-1) and high temperature (20^oC). The d-spacing and melting point suggest that this new phase is a mixture rich on two of the three major components of cocoa butter. We also found that, contrary to previous reports, the transition from phase II to phase V can happen through the intermediate phase IV, at high shear rates and temperature.

  10. Electronic structure and optical properties of noncentrosymmetric LiGaSe2: Experimental measurements and DFT band structure calculations

    Science.gov (United States)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Ananchenko, L. N.; Isaenko, L. I.; Yelisseyev, A. P.; Khyzhun, O. Y.

    2017-04-01

    We report on measurements of X-ray photoelectron (XP) spectra for pristine and Ar+ ion-irradiated surfaces of LiGaSe2 single crystal grown by Bridgman-Stockbarger method. Electronic structure of the LiGaSe2 compound is studied from a theoretical and experimental viewpoint. In particular, total and partial densities of states of LiGaSe2 are investigated by density functional theory (DFT) calculations employing the augmented plane wave + local orbitals (APW + lo) method and they are verified by data of X-ray spectroscopy measurements. The DFT calculations indicate that the main contributors to the valence band of LiGaSe2 are the Se 4p states, which contribute mainly at the top and in the upper portion of the valence band, with also essential contributions of these states in the lower portion of the band. Other substantial contributions to the valence band of LiGaSe2 emerge from the Ga 4s and Ga 4p states contributing mainly at the lower ant upper portions of the valence band, respectively. With respect to the conduction band, the calculations indicate that its bottom is composed mainly from contributions of the unoccupied Ga s and Se p states. The present calculations are confirmed experimentally when comparing the XP valence-band spectrum of the LiGaS2 single crystal on a common energy scale with the X-ray emission bands representing the energy distribution of the Ga 4p and Se 4p states. Measurements of the fundamental absorption edges at room temperature reveal that bandgap value, Eg, of LiGaSe2 is equal to 3.47 eV and the Eg value increases up to 3.66 eV when decreasing temperature to 80 K. The main optical characteristics of the LiGaSe2 compound are clarified by the DFT calculations.

  11. Investigation on the properties of omnidirectional photonic band gaps in two-dimensional plasma photonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Hai-Feng, E-mail: hanlor@163.com [Key Laboratory of Radar Imaging and Microwave Photonics, Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Nanjing Artillery Academy, Nanjing 211132 (China); Liu, Shao-Bin; Li, Bing-Xiang [Key Laboratory of Radar Imaging and Microwave Photonics, Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)

    2016-01-15

    The properties of omnidirectional photonic band gaps (OBGs) in two-dimensional plasma photonic crystals (2D PPCs) are theoretically investigated by the modified plane wave expansion method. In the simulation, we consider the off-plane incident wave vector. The configuration of 2D PPCs is the triangular lattices filled with the nonmagnetized plasma cylinders in the homogeneous and isotropic dielectric background. The calculated results show that the proposed 2D PPCs possess a flatbands region and the OBGs. Compared with the OBGs in the conventional 2D dielectric-air PCs, it can be obtained more easily and enlarged in the 2D PPCs with a similar structure. The effects of configurational parameters of the PPCs on the OBGs also are studied. The simulated results demonstrate that the locations of OBGs can be tuned easily by manipulating those parameters except for changing plasma collision frequency. The achieved OBGs can be enlarged by optimizations. The OBGs of two novel configurations of PPCs with different cross sections are computed for a comparison. Both configurations have the advantages of obtaining the larger OBGs compared with the conventional configuration, since the symmetry of 2D PPCs is broken by different sizes of periodically inserted plasma cylinders or connected by the embedded plasma cylinders with thin veins. The analysis of the results shows that the bandwidths of OBGs can be tuned by changing geometric and physical parameters of such two PPCs structures. The theoretical results may open a new scope for designing the omnidirectional reflectors or mirrors based on the 2D PPCs.

  12. Bulk band structure of Bi2Te3

    DEFF Research Database (Denmark)

    Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco

    2014-01-01

    The bulk band structure of Bi2Te3 has been determined by angle-resolved photoemission spectroscopy and compared to first-principles calculations. We have performed calculations using the local density approximation (LDA) of density functional theory and the one-shot GW approximation within the all......-electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where...... distinct differences between the LDA and GW results are present. Overall a superior agreement with GW is found, highlighting the importance of many-body effects in the band structure of this family of topological insulators....

  13. Complex band structure of topological insulator Bi2Se3

    Science.gov (United States)

    Betancourt, J.; Li, S.; Dang, X.; Burton, J. D.; Tsymbal, E. Y.; Velev, J. P.

    2016-10-01

    Topological insulators are very interesting from a fundamental point of view, and their unique properties may be useful for electronic and spintronic device applications. From the point of view of applications it is important to understand the decay behavior of carriers injected in the band gap of the topological insulator, which is determined by its complex band structure (CBS). Using first-principles calculations, we investigate the dispersion and symmetry of the complex bands of Bi2Se3 family of three-dimensional topological insulators. We compare the CBS of a band insulator and a topological insulator and follow the CBS evolution in both when the spin-orbit interaction is turned on. We find significant differences in the CBS linked to the topological band structure. In particular, our results demonstrate that the evanescent states in Bi2Se3 are non-trivially complex, i.e. contain both the real and imaginary contributions. This explains quantitatively the oscillatory behavior of the band gap obtained from Bi2Se3 (0 0 0 1) slab calculations.

  14. Structure analysis on synthetic emerald crystals

    Science.gov (United States)

    Lee, Pei-Lun; Lee, Jiann-Shing; Huang, Eugene; Liao, Ju-Hsiou

    2013-05-01

    Single crystals of emerald synthesized by means of the flux method were adopted for crystallographic analyses. Emerald crystals with a wide range of Cr3+-doping content up to 3.16 wt% Cr2O3 were examined by X-ray single crystal diffraction refinement method. The crystal structures of the emerald crystals were refined to R 1 (all data) of 0.019-0.024 and w R 2 (all data) of 0.061-0.073. When Cr3+ substitutes for Al3+, the main adjustment takes place in the Al-octahedron and Be-tetrahedron. The effect of substitution of Cr3+ for Al3+ in the beryl structure results in progressively lengthening of the Al-O distance, while the length of the other bonds remains nearly unchanged. The substitution of Cr3+ for Al3+ may have caused the expansion of a axis, while keeping the c axis unchanged in the emerald lattice. As a consequence, the Al-O-Si and Al-O-Be bonding angles are found to decrease, while the angle of Si-O-Be increases as the Al-O distance increases during the Cr replacement.

  15. Novel band structures in germanene on aluminium nitride substrate

    Science.gov (United States)

    Ren, Miaojuan; Li, Mingming

    2017-09-01

    Germanene is difficult to grow epitaxially on conventional semiconductor substrates, and to open a sizable band gap is also a hot topic. Using first-principles calculations, we investigate the structural and electronic properties of germanene/aluminium nitride heterobilayers (Ge/AlN HBLs). The results indicate that the Dirac cone with the nearly linear band dispersion of germanene is almost maintained in the band gap of the substrate. Very low effective masses and high carrier mobilities are achieved, and the band gap of germanene can be effectively tuned from 0.004 to 0.46 eV. These results suggest a possible method to design effective field effect transistors that can operate at room temperature.

  16. Radial wave crystals: radially periodic structures from anisotropic metamaterials for engineering acoustic or electromagnetic waves.

    Science.gov (United States)

    Torrent, Daniel; Sánchez-Dehesa, José

    2009-08-07

    We demonstrate that metamaterials with anisotropic properties can be used to develop a new class of periodic structures that has been named radial wave crystals. They can be sonic or photonic, and wave propagation along the radial directions is obtained through Bloch states like in usual sonic or photonic crystals. The band structure of the proposed structures can be tailored in a large amount to get exciting novel wave phenomena. For example, it is shown that acoustical cavities based on radial sonic crystals can be employed as passive devices for beam forming or dynamically orientated antennas for sound localization.

  17. Troublesome Crystal Structures: Prevention, Detection, and Resolution.

    Science.gov (United States)

    Harlow, Richard L

    1996-01-01

    A large number of incorrect crystal structures is being published today. These structures are proving to be a particular problem to those of us who are interested in comparing structural moieties found in the databases in order to develop structure-property relationships. Problems can reside in the input data, e.g., wrong unit cell or low quality intensity data, or in the structural model, e.g., wrong space group or atom types. Many of the common mistakes are, however, relatively easy to detect and thus should be preventable; at the very least, suspicious structures can be flagged, if not by the authors then by the referees and, ultimately, the crystallographic databases. This article describes some of the more common mistakes and their effects on the resulting structures, lists a series of tests that can be used to detect incorrect structures, and makes a strong plea for the publication of higher quality structures.

  18. Determining crystal structures through crowdsourcing and coursework

    OpenAIRE

    2016-01-01

    We show here that computer game players can build high-quality crystal structures. Introduction of a new feature into the computer game Foldit allows players to build and real-space refine structures into electron density maps. To assess the usefulness of this feature, we held a crystallographic model-building competition between trained crystallographers, undergraduate students, Foldit players and automatic model-building algorithms. After removal of disordered residues, a team of Foldit pla...

  19. Determining crystal structures through crowdsourcing and coursework

    OpenAIRE

    Horowitz, Scott; Koepnick, Brian; Jain, Neha; Pikkanen, Petri; Shehzad, Raafay; Viosca, Randy; James Fraser, Robert; Leduc, Robert; Madala, Roman; Shnider, Scott; de Boisblanc, Sharon; Butkovich, Slava; Bliven, Spencer; Koldewey, Philipp; Hettler, Stephen

    2016-01-01

    We show here that computer game players can build high-quality crystal structures. Introduction of a new feature into the computer game Foldit allows players to build and real-space refine structures into electron density maps. To assess the usefulness of this feature, we held a crystallographic model-building competition between trained crystallographers, undergraduate students, Foldit players and automatic model-building algorithms. After removal of disordered residues, a team of Foldit pla...

  20. Crystal Structure of Human Enterovirus 71

    Energy Technology Data Exchange (ETDEWEB)

    Plevka, Pavel; Perera, Rushika; Cardosa, Jane; Kuhn, Richard J.; Rossmann, Michael G. (Purdue); (Sentinext)

    2013-04-08

    Enterovirus 71 is a picornavirus associated with fatal neurological illness in infants and young children. Here, we report the crystal structure of enterovirus 71 and show that, unlike in other enteroviruses, the 'pocket factor,' a small molecule that stabilizes the virus, is partly exposed on the floor of the 'canyon.' Thus, the structure of antiviral compounds may require a hydrophilic head group designed to interact with residues at the entrance of the pocket.

  1. The photonic band structure of one - dimensional Ai/SrF2 low temperature superconductor- dielectric photonic crystal%一维Al/SrF2低温超导体-电介质光子晶体能带结构

    Institute of Scientific and Technical Information of China (English)

    李建锋; 王建; 周峰; 王成伟

    2011-01-01

    基于二流体电子模型和平面波展开法,计算了一维Al/SrF2超导体-电介质光子晶体的能带结构.结果表明:随着超导层厚度的增加,第一光子带隙中心频率和截止频率均发生蓝移,且第一带隙宽度逐渐增加到一个峰值后又逐渐变窄.更重要的是,在低于临界温度的超低温环境中,温度的微小变化,对该类光子晶体的带隙宽度、中心频率以及截止频率均有明显的调制作用.%The photonic band structure of one - dimensional (1D) Al/SrF2 low temperature superconductor - dielectric photonic crystal (PC) was calculated numerically based on the plane - wave expansion method. The two - fluid model was adopted to describe the dielectric properties of the low temperature superconducting system. The simulation results clearly reveal both photonic band gap and a cutoff frequency can be modulated through the thicknesses of the superconductor layers. It is more interesting that with a small variation of ambient temperature, the photonic band gap and a cutoff frequency can be obviously modulated. This work would be of value in the design of photoelectric device for potential applications in extreme low - temperature environment.

  2. Tunable band structure and effective mass of disordered chalcopyrite

    Science.gov (United States)

    Wang, Ze-Lian; Xie, Wen-Hui; Zhao, Yong-Hong

    2017-02-01

    The band structure and effective mass of disordered chalcopyrite photovoltaic materials Cu1- x Ag x Ga X 2 ( X = S, Se) are investigated by density functional theory. Special quasirandom structures are used to mimic local atomic disorders at Cu/Ag sites. A local density plus correction method is adopted to obtain correct semiconductor band gaps for all compounds. The bandgap anomaly can be seen for both sulfides and selenides, where the gap values of Ag compounds are larger than those of Cu compounds. Band gaps can be modulated from 1.63 to 1.78 eV for Cu1- x Ag x Ga Se 2, and from 2.33 to 2.64 eV for Cu1- x Ag x Ga S 2. The band gap minima and maxima occur at around x = 0:5 and x = 1, respectively, for both sulfides and selenides. In order to show the transport properties of Cu1- x Ag x Ga X 2, the effective mass is shown as a function of disordered Ag concentration. Finally, detailed band structures are shown to clarify the phonon momentum needed by the fundamental indirect-gap transitions. These results should be helpful in designing high-efficiency photovoltaic devices, with both better absorption and high mobility, by Ag-doping in CuGa X 2.

  3. Influence of crystal structure on the optically stimulated luminescence properties of feldspars

    DEFF Research Database (Denmark)

    Poolton, N.R.J.; Bøtter-Jensen, L.; Ypma, P.J.M.

    1994-01-01

    Work is presented showing that the crystal structure of feldspar plays an important role in determining the energy positions at which optically stimulated luminescence transitions can occur, their thermo-optical behavior, the transport properties of charge in the conduction and valence bands, and......, and the time decay characteristics of the luminescence. First-order calculations of these effects are presented, and comparison is made with experimental results.......Work is presented showing that the crystal structure of feldspar plays an important role in determining the energy positions at which optically stimulated luminescence transitions can occur, their thermo-optical behavior, the transport properties of charge in the conduction and valence bands...

  4. Study on Band Structure of YbB6 and Analysis of Its Optical Conductivity Spectrum

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The electronic structure of YbB6 crystal was studied by means of density functional (GGA+U) method.The calculations were performed by FLAPW method.The high accurate band structure was achieved.The correlation between the feature of the band structure and the Yb-B6 bonding in YbB6 was analyzed.On this basis, some optical constants of YbB6 such as reflectivity, dielectric function, optical conductivity, and energy-loss function were calculated.The results are in good agreement with the experiments.The real part of the optical conductivity spectrum and the energy-loss function spectrum were analyzed in detail.The assignments of the spectra were carried out to correlate the spectral peaks with the interband electronic transitions, which justify the reasonable part of previous empirical assignments and renew the missed or incorrect ones.

  5. THE CRYSTAL STRUCTURE OF 2,7-DIACETOXYTRANS-15,16-DIMETHYL-15,16-DIHYDROPYRENE,

    Science.gov (United States)

    AROMATIC COMPOUNDS, CRYSTAL STRUCTURE ), (*POLYCYCLIC COMPOUNDS, CRYSTAL STRUCTURE ), (* CRYSTAL STRUCTURE , POLYCYCLIC COMPOUNDS), ESTERS, MOLECULAR STRUCTURE, CHEMICAL BONDS, X RAY DIFFRACTION, SCINTILLATION COUNTERS, CANADA

  6. Photonic Crystal Laser-Driven Accelerator Structures

    Energy Technology Data Exchange (ETDEWEB)

    Cowan, Benjamin M.

    2007-08-22

    Laser-driven acceleration holds great promise for significantly improving accelerating gradient. However, scaling the conventional process of structure-based acceleration in vacuum down to optical wavelengths requires a substantially different kind of structure. We require an optical waveguide that (1) is constructed out of dielectric materials, (2) has transverse size on the order of a wavelength, and (3) supports a mode with speed-of-light phase velocity in vacuum. Photonic crystals---structures whose electromagnetic properties are spatially periodic---can meet these requirements. We discuss simulated photonic crystal accelerator structures and describe their properties. We begin with a class of two-dimensional structures which serves to illustrate the design considerations and trade-offs involved. We then present a three-dimensional structure, and describe its performance in terms of accelerating gradient and efficiency. We discuss particle beam dynamics in this structure, demonstrating a method for keeping a beam confined to the waveguide. We also discuss material and fabrication considerations. Since accelerating gradient is limited by optical damage to the structure, the damage threshold of the dielectric is a critical parameter. We experimentally measure the damage threshold of silicon for picosecond pulses in the infrared, and determine that our structure is capable of sustaining an accelerating gradient of 300 MV/m at 1550 nm. Finally, we discuss possibilities for manufacturing these structures using common microfabrication techniques.

  7. Optimization of band gaps of 2D photonic crystals by the rapid generic algorithm

    Institute of Scientific and Technical Information of China (English)

    SUN Yun-tao

    2011-01-01

    @@ Based on the rapid genetic algorithm (RGA), the band gap structures of square lattices with square scatters are optimized.In the optimizing process, gene codes are used to express square scatters and the fitting function adopts the relative values of the largest absolute photonic band gaps (PBGs).By changing the value of filling factor, three cell forms with large photonic band gaps are obtained.In addition, the comparison between the rapid genetic algorithm and the general genetic algorithm (GGA) is analyzed.

  8. Simultaneous existence of phononic and photonic band gaps in periodic crystal slabs.

    Science.gov (United States)

    Pennec, Y; Djafari Rouhani, B; El Boudouti, E H; Li, C; El Hassouani, Y; Vasseur, J O; Papanikolaou, N; Benchabane, S; Laude, V; Martinez, A

    2010-06-21

    We discuss the simultaneous existence of phononic and photonic band gaps in a periodic array of holes drilled in a Si membrane. We investigate in detail both the centered square lattice and the boron nitride (BN) lattice with two atoms per unit cell which include the simple square, triangular and honeycomb lattices as particular cases. We show that complete phononic and photonic band gaps can be obtained from the honeycomb lattice as well as BN lattices close to honeycomb. Otherwise, all investigated structures present the possibility of a complete phononic gap together with a photonic band gap of a given symmetry, odd or even, depending on the geometrical parameters.

  9. DFT Study of Effects of Potassium Doping on Band Structure of Crystalline Cuprous Azide

    Institute of Scientific and Technical Information of China (English)

    ZHU,Wei-Hua; ZHANG,Xiao-Wen; WEI,Tao; XIAO,He-Ming

    2008-01-01

    The structure and defect formation energies of the K-doped CuN3 were studied using density functional theory within the generalized gradient approximation. The results show that the K-doping breaks the azide symmetry and causes asymmetric atomic displacement. As the K-doping level increases, the band gap of the doped system gradually increases. The K impurity is easily incorporated into the crystal thermodynamically. The Cu vacancy is easily created thermodynamically and the K impurity can serve as nucleation centers for vacancy clustering. Finally the effects of K-doping concentrations on the sensitivity of CuN3 were understood based on electronic structures.

  10. Band gap formation and control in coupled periodic ferromagnetic structures

    Science.gov (United States)

    Morozova, M. A.; Sharaevskaya, A. Yu.; Sadovnikov, A. V.; Grishin, S. V.; Romanenko, D. V.; Beginin, E. N.; Sharaevskii, Yu. P.; Nikitov, S. A.

    2016-12-01

    We demonstrate theoretically and experimentally the formation of additional bandgaps in the spectrum of spin waves in coupled magnonic crystals. We present the analytical model, which reveals the mechanism of bandgaps formation in coupled structures. In particular, the formation of one, two, or three bandgaps in the region of the first Bragg resonance is demonstrated and control of its characteristics by the variation of the complex coupling coefficient between magnonic crystals is shown. The spatially-resolved Brillouin light scattering spectroscopy and microwave measurements demonstrate the bandgap splitting in the spin-wave spectrum. The main advantage of proposed coupled structure, as compared to the conventional magnonic crystal, is the tunability of multiple bandgaps in the spin-wave spectrum, which enables potential applications in the frequency selective magnonic devices.

  11. Synthesis and Crystal Structure of Dehydroandrographolide Dipolycyclophosphate

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The title compound was synthesized and characterized by IR, NMR, H R S I-M S and MS, and its crystal structure was determined by single-crystal X-ray diffraction. The crystal is of orthorhombic system (C4oH52O11P2, Mr= 770.76), space group P21212, with a = 22.562(5), b =29.224(6), c = 7.1953(14) A, V = 4744.2(16) A3, Z = 4, Dc = 1.079 g/cm3, F(000) = 1640 andμ =0.141 mm-1. The final R = 0.0758 and wR = 0.1778 for 2794 observed reflections with I > 2o(I).Intermolecular hydrogen bonds are found between the O atom of carbonyl group and H atoms of olefinic carbon. The absolute configuration of this molecule was confirmed by comparison with that of the original material.

  12. Crystal structure of N-(4-hydroxybenzylacetone thiosemicarbazone

    Directory of Open Access Journals (Sweden)

    Saray Argibay-Otero

    2017-09-01

    Full Text Available The structure of the title compound, C11H15N3OS, shows the flexibility due to the methylene group at the thioamide N atom in the side chain, resulting in the molecule being non-planar. The dihedral angle between the plane of the benzene ring and that defined by the atoms of the thiosemicarbazide arm is 79.847 (4°. In the crystal, the donor–acceptor hydrogen-bond character of the –OH group dominates the intermolecular associations, acting as a donor in an O—H...S hydrogen bond, as well as being a double acceptor in a centrosymmetric cyclic bridging N—H...O,O′ interaction [graph set R22(4]. The result is a one-dimensional duplex chain structure, extending along [111]. The usual N—H...S hydrogen-bonding association common in thiosemicarbazone crystal structures is not observed.

  13. Crystal structure of low-symmetry rondorfite

    Science.gov (United States)

    Rastsvetaeva, R. K.; Zadov, A. E.; Chukanov, N. V.

    2008-03-01

    The crystal structure of an aluminum-rich variety of the mineral rondorfite with the composition Ca16[Mg2(Si7Al)(O31OH)]Cl4 from the skarns of the Verkhne-Chegemskoe plateau (the Kabardino-Balkarian Republic, the Northern Caucasus Region, Russia) was solved in the triclinic space group with the unit-cell parameters a = 15.100(2) Å, b = 15.110(2) Å, c = 15.092(2) Å, α = 90.06(1)°, β = 90.01(1)°, γ = 89.93(1)°, Z = 4, sp. gr. P1. The structural model consisting of 248 independent atoms was determined by the phase-correction method and refined to R = 3.8% with anisotropic displacement parameters based on all 7156 independent reflections with 7156 F > 3σ( F). The crystal structure is based on pentamers consisting of four Si tetrahedra linked by the central Mg tetrahedron. The structure can formally be refined in the cubic space group ( a = 15.105 Å, sp. gr. Fd overline 3 , seven independent positions) with anisotropic displacement parameters to R = 2.74% based on 579 reflections with F > 3σ( F) without accounting for more than 1000 observed reflections, which are inconsistent with the cubic symmetry of the crystal structure.

  14. Ultrawide low frequency band gap of phononic crystal in nacreous composite material

    Energy Technology Data Exchange (ETDEWEB)

    Yin, J.; Huang, J.; Zhang, S., E-mail: zhangs@dlut.edu.cn; Zhang, H.W.; Chen, B.S.

    2014-06-27

    The band structure of a nacreous composite material is studied by two proposed models, where an ultrawide low frequency band gap is observed. The first model (tension-shear chain model) with two phases including brick and mortar is investigated to describe the wave propagation in the nacreous composite material, and the dispersion relation is calculated by transfer matrix method and Bloch theorem. The results show that the frequency ranges of the pass bands are quite narrow, because a special tension-shear chain motion in the nacreous composite material is formed by some very slow modes. Furthermore, the second model (two-dimensional finite element model) is presented to investigate its band gap by a multi-level substructure scheme. Our findings will be of great value to the design and synthesis of vibration isolation materials in a wide and low frequency range. Finally, the transmission characteristics are calculated to verify the results. - Highlights: • A Brick-and-Mortar structure is used to discuss wave propagation through nacreous materials. • A 1D Bloch wave solution of nacreous materials with a tension-shear chain model is obtained. • The band structure and transmission characteristics of nacreous materials with the FE model are examined. • An ultrawide low frequency band gap is found in nacreous materials with both theory and FE model.

  15. Computer simulation of evolution of persistent slip bands in fatigued copper single crystals

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The four evolution stages of persistent slip bands (PSBs), namely, the veins, pass, embryos and well-developed dislocation structures of PSBs can be obtained using electron channeling contrast (ECC) technique in a scanning electron microscopy (SEM). For the four stages, the typical dislocation structures are simulated and the stress field is calculated by the discrete dislocation static method.

  16. Doping-dependent quasiparticle band structure in cuprate superconductors

    NARCIS (Netherlands)

    Eder, R; Ohta, Y.; Sawatzky, G.A

    1997-01-01

    We present an exact diagonalization study of the single-particle spectral function in the so-called t-t'-t ''-J model in two dimensions. As a key result, we find that hole doping leads to a major reconstruction of the quasiparticle band structure near (pi,0): whereas for the undoped system the quasi

  17. Analysis of photonic band-gap structures in stratified medium

    DEFF Research Database (Denmark)

    Tong, Ming-Sze; Yinchao, Chen; Lu, Yilong;

    2005-01-01

    Purpose - To demonstrate the flexibility and advantages of a non-uniform pseudo-spectral time domain (nu-PSTD) method through studies of the wave propagation characteristics on photonic band-gap (PBG) structures in stratified medium Design/methodology/approach - A nu-PSTD method is proposed...

  18. Design for maximum band-gaps in beam structures

    DEFF Research Database (Denmark)

    Olhoff, Niels; Niu, Bin; Cheng, Gengdong

    2012-01-01

    This paper aims to extend earlier optimum design results for transversely vibrating Bernoulli-Euler beams by determining new optimum band-gap beam structures for (i) different combinations of classical boundary conditions, (ii) much larger values of the orders n and n-1 of adjacent upper and lowe...

  19. Determination of nonlinear absorption and refraction in direct and indirect band gap crystals by Z-scan method.

    Science.gov (United States)

    Gaur, Poonam; Sharma, Dimple; Singh, Nageshwar; Malik, B P; Gaur, Arun

    2012-11-01

    A systematic investigation on nonlinear optical properties such as three photon absorption (3PA) wavelength dependent of Kerr type nonlinear refraction in direct and indirect band gap crystals has been reported in the present work. The Z-scan measurements are recorded for both ZnO and CdI(2) with femtosecond laser pulses while the wavelength dependent of the Kerr nonlinearity are in agreement with a two band model. The wavelength dependence of the 3PA is determined by [(3E(photon)/E(g))-1](5/2)[(3E(photon)/E(g))](-9) in the case of direct band gap crystal and [(3E(photon)±ℏΩ/E(g))-1](5/2)[(3E(photon)±ℏΩ/E(g))](-9) in the case of indirect band gap crystal. In the present investigation the value of 3PA in the case of indirect band gap crystal is lower than the direct band gap crystal which is due to the phonon assisted transition. The materials of large band gap with optical nonlinearity and fast response speed should be dominating factor for further photonic devices such as optical limiters, optical switches and optical modulators. The higher order nonlinear optical effects have also been determined in the present study. Copyright © 2012 Elsevier B.V. All rights reserved.

  20. X-Band Photonic Band-Gap Accelerator Structure Breakdown Experiment

    Energy Technology Data Exchange (ETDEWEB)

    Marsh, Roark A.; /MIT /MIT /NIFS, Gifu /JAERI, Kyoto /LLNL, Livermore; Shapiro, Michael A.; Temkin, Richard J.; /MIT; Dolgashev, Valery A.; Laurent, Lisa L.; Lewandowski, James R.; Yeremian, A.Dian; Tantawi, Sami G.; /SLAC

    2012-06-11

    In order to understand the performance of photonic band-gap (PBG) structures under realistic high gradient, high power, high repetition rate operation, a PBG accelerator structure was designed and tested at X band (11.424 GHz). The structure consisted of a single test cell with matching cells before and after the structure. The design followed principles previously established in testing a series of conventional pillbox structures. The PBG structure was tested at an accelerating gradient of 65 MV/m yielding a breakdown rate of two breakdowns per hour at 60 Hz. An accelerating gradient above 110 MV/m was demonstrated at a higher breakdown rate. Significant pulsed heating occurred on the surface of the inner rods of the PBG structure, with a temperature rise of 85 K estimated when operating in 100 ns pulses at a gradient of 100 MV/m and a surface magnetic field of 890 kA/m. A temperature rise of up to 250 K was estimated for some shots. The iris surfaces, the location of peak electric field, surprisingly had no damage, but the inner rods, the location of the peak magnetic fields and a large temperature rise, had significant damage. Breakdown in accelerator structures is generally understood in terms of electric field effects. These PBG structure results highlight the unexpected role of magnetic fields in breakdown. The hypothesis is presented that the moderate level electric field on the inner rods, about 14 MV/m, is enhanced at small tips and projections caused by pulsed heating, leading to breakdown. Future PBG structures should be built to minimize pulsed surface heating and temperature rise.

  1. Effect of shape of scatterers and plasma frequency on the complete photonic band gap properties of two-dimensional dielectric-plasma photonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Fathollahi Khalkhali, T., E-mail: tfathollahi@aeoi.org.ir; Bananej, A.

    2016-12-16

    In this study, we analyze complete photonic band gap properties of two-dimensional dielectric-plasma photonic crystals with triangular and square lattices, composed of plasma rods with different geometrical shapes in the anisotropic tellurium background. Using the finite-difference time-domain method we discuss the maximization of the complete photonic band gap width as a function of plasma frequency and plasma rods parameters with different shapes and orientations. The numerical results demonstrate that our proposed structures represent significantly wide complete photonic band gaps in comparison to previously studied dielectric-plasma photonic crystals. - Highlights: • In this paper, we have investigated plasma photonic crystals. • Plasma is a kind of dispersive medium with its equivalent refractive index related to the frequency of an incident EM wave. • In this work, our simulations are performed using the Meep implementation of the finite-difference time-domain (FDTD) method. • For this study, the lattice structures investigated are triangular and square. • Extensive calculations reveal that almost all of these structures represent wide complete band gaps.

  2. Structure sensitive properties of KTP-type crystals

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Adding various dopants during the growth of the parent KTiOPO4 (KTP) crystal has given rise to an extensive series of KTP-type crystals. The doped KTP or KTP-type crystals often have very subtle structural variations from pure KTP crystals. As a result of these structural changes the KTP-type crystals often exhibit different physical properties, which may be referred to as structure sensitive properties. It is possible to fine-tune the nonlinear optical properties of KTP crystals through doping. This results in a broad range of applications for KTP-type crystals.

  3. Lessons from crystal structures of kainate receptors

    DEFF Research Database (Denmark)

    Møllerud, Stine; Frydenvang, Karla Andrea; Pickering, Darryl S;

    2017-01-01

    synaptic transmission and modulate network excitability by regulating neurotransmitter release. Dysfunction of kainate receptors has been implicated in several neurological disorders such as epilepsy, schizophrenia and depression. Here we provide a review on the current understanding of kainate receptor...... structure and how they bind agonists, antagonists and ions. The first structure of the ligand-binding domain of the GluK1 subunit was reported in 2005, seven years after publication of the crystal structure of a soluble construct of the ligand-binding domain of the AMPA-type subunit GluA2. Today, a full...

  4. Waveguiding in surface plasmon polariton band gap structures

    DEFF Research Database (Denmark)

    Bozhevolnyi, S.I.; Østergaard, John Erland; Leosson, Kristjan

    2001-01-01

    Using near-held optical microscopy, we investigate propagation and scattering of surface plasmon polaritons (SPP's) excited in the wavelength range of 780-820 nm at nanostructured gold-film surfaces with areas of 200-nm-wide scatterers arranged in a 400-nm-period triangular lattice containing line...... defects. We observe the SPP reflection by such an area and SPP guiding along line defects at 782 nm, as well as significant deterioration of these effects is 815 nm, thereby directly demonstrating the SPP band gap effect and showing first examples of SPP channel waveguides in surface band gap structures....

  5. Superlocalization and Formation of Grain Structure in Ni3ge Single Crystals with Different Orientations of Deformation Axes

    Science.gov (United States)

    Solov'eva, Yu. V.; Lipatnikova, Ya. D.; Starenchenko, S. V.; Solov'ev, A. N.; Starenchenko, V. A.

    2017-09-01

    The paper describes the influence of orientation of Ni3Ge single crystal deformation axes on the high-temperature superlocalization of plastic deformation. Mechanical properties of single crystals with different orientations are studied in this paper as well as the slip traces and the evolution of the dislocation structure. Based on these investigations, the observing conditions are described for the superlocalization bands and the formation of the grain structure in local areas of the original single crystal.

  6. Disorder effects on the band structure of ZnGeN2: Role of exchange defects

    Science.gov (United States)

    Skachkov, Dmitry; Quayle, Paul C.; Kash, Kathleen; Lambrecht, Walter R. L.

    2016-11-01

    The role of exchange defects on the band structure of ZnGeN2 is investigated. Exchange defects are defined through the exchange of cations Zn and Ge starting from the ideal P n a 21 crystal structure, which obeys the local octet rule. Each such exchange creates several nitrogen-centered tetrahedra which violate the local octet rule, although overall charge neutrality is preserved. We study several distributions of exchange defects, some with all antisites making up the exchange defect close to each other and with increasing numbers of exchange defects, and others where the two types of antisites ZnGe and GeZn are kept separated from each other. We also compare the results for these models with a fully random distribution of Zn and Ge on the cation sites. We show that for a single-nearest-neighbor exchange defect, the band gap is narrowed by about 0.5 eV due to two effects: (1) the ZnGe antisites form filled acceptor states just above and merging with the valence-band maximum (VBM) of perfect crystal ZnGeN2 and (2) the GeZn antisites form a resonance in the conduction band which lowers the conduction-band minimum (CBM). When more exchange defects are created, these acceptor states broaden into bands which can lower the gap further. When tetrahedra occur surrounded completely by four Zn atoms, states even deeper in the gap are found localized all near these tetrahedra, forming a separate intermediate band. Finally, for phase-segregated ZnGe and GeZn, the gap is significantly more reduced, but no separate band is found to occur. The ZnGe acceptorlike states now form a percolating defect band which is significantly wider and hence reaches deeper into the gap. In all cases, the wave functions near the top of the new VBM remain, to some extent, localized near the ZnGe sites. For a fully random case, the gap is even more severely reduced by almost 3 eV. The total energy of the system increases with the number of octet-rule-violating tetrahedra and the energy cost per

  7. Band structure and optical properties of amber studied by first principles

    Energy Technology Data Exchange (ETDEWEB)

    Rao, Zhi-Fan, E-mail: raozhifan@163.com [Analysis and Testing Center of Yunnan, Kunming University of Science and Technology, Kunming 650093 (China); Zhou, Rong-Feng [Analysis and Testing Center of Yunnan, Kunming University of Science and Technology, Kunming 650093 (China)

    2013-03-01

    The band structure and density of states of amber is studied by the first principles calculation based on density of functional theory. The complex structure of amber has 214 atoms and the band gap is 5.0 eV. The covalent bond is combined C/O atoms with H atoms. The O 2p orbital is the biggest effect near the Fermi level. The optical properties' results show that the reflectivity is low, and the refractive index is 1.65 in visible light range. The highest absorption coefficient peak is at 172 nm and another higher peak is at 136 nm. These convince that the amber would have a pretty sheen and that amber is a good and suitable crystal for jewelry and ornaments.

  8. Atom–atom interactions around the band edge of a photonic crystal waveguide

    Science.gov (United States)

    Hood, Jonathan D.; Goban, Akihisa; Asenjo-Garcia, Ana; Lu, Mingwu; Yu, Su-Peng; Chang, Darrick E.; Kimble, H. J.

    2016-01-01

    Tailoring the interactions between quantum emitters and single photons constitutes one of the cornerstones of quantum optics. Coupling a quantum emitter to the band edge of a photonic crystal waveguide (PCW) provides a unique platform for tuning these interactions. In particular, the cross-over from propagating fields E(x)∝e±ikxx outside the bandgap to localized fields E(x)∝e−κx|x| within the bandgap should be accompanied by a transition from largely dissipative atom–atom interactions to a regime where dispersive atom–atom interactions are dominant. Here, we experimentally observe this transition by shifting the band edge frequency of the PCW relative to the D1 line of atomic cesium for N¯=3.0±0.5 atoms trapped along the PCW. Our results are the initial demonstration of this paradigm for coherent atom–atom interactions with low dissipation into the guided mode. PMID:27582467

  9. Atom-atom interactions around the band edge of a photonic crystal waveguide.

    Science.gov (United States)

    Hood, Jonathan D; Goban, Akihisa; Asenjo-Garcia, Ana; Lu, Mingwu; Yu, Su-Peng; Chang, Darrick E; Kimble, H J

    2016-09-20

    Tailoring the interactions between quantum emitters and single photons constitutes one of the cornerstones of quantum optics. Coupling a quantum emitter to the band edge of a photonic crystal waveguide (PCW) provides a unique platform for tuning these interactions. In particular, the cross-over from propagating fields [Formula: see text] outside the bandgap to localized fields [Formula: see text] within the bandgap should be accompanied by a transition from largely dissipative atom-atom interactions to a regime where dispersive atom-atom interactions are dominant. Here, we experimentally observe this transition by shifting the band edge frequency of the PCW relative to the [Formula: see text] line of atomic cesium for [Formula: see text] atoms trapped along the PCW. Our results are the initial demonstration of this paradigm for coherent atom-atom interactions with low dissipation into the guided mode.

  10. Crystal structure of tris(hydroxylammonium orthophosphate

    Directory of Open Access Journals (Sweden)

    Malte Leinemann

    2015-11-01

    Full Text Available The crystal structure of the title salt, ([H3NOH]+3·[PO4]3−, consists of discrete hydroxylammonium cations and orthophosphate anions. The atoms of the cation occupy general positions, whereas the anion is located on a threefold rotation axis that runs through the phosphorus atom and one of the phosphate O atoms. In the crystal structure, cations and anions are linked by intermolecular O—H...O and N—H...O hydrogen bonds into a three-dimensional network. Altogether, one very strong O—H...O, two N—H...O hydrogen bonds of medium strength and two weaker bifurcated N—H...O interactions are observed.

  11. Synthesis and Band Gap Control in Three-Dimensional Polystyrene Opal Photonic Crystals

    Institute of Scientific and Technical Information of China (English)

    LIU Ye; ZHENG Zhong-Yu; QIN Fei; ZHOU Fei; ZHOU Chang-Zhu; ZHANG Dao-Zhong; MENG Qing-Bo; LI Zhi-Yuan

    2008-01-01

    High-quality three-dimensional polystyrene opal photonic crystals are fabricated by vertical deposition method.The transmission properties with different incident angles and different composite refractive index contrasts are experimentally and theoretically studied. Good agreement between the experiment and theory is achieved. We find that with the increasing incident angle, the gap position shifts to the short wavelength (blue shift) and the gap becomes shallower; and with the increase of refractive index of the opal void materials and decrease the contrast of refractive index, the gap position shifts to the long wavelength (red shift). At the same time, we observe the swelling effects when the sample is immerged in the solutions with different refractive indices, which make the microsphere diameter in solution become larger than that in air. The understanding of band gap shift behaviour may be helpful in designing optical sensors and tunable photonic crystal ultrafast optical switches.

  12. Electronic band structure effects in monolayer, bilayer, and hybrid graphene structures

    Science.gov (United States)

    Puls, Conor

    Since its discovery in 2005, graphene has been the focus of intense theoretical and experimental study owing to its unique two-dimensional band structure and related electronic properties. In this thesis, we explore the electronic properties of graphene structures from several perspectives including the magnetoelectrical transport properties of monolayer graphene, gap engineering and measurements in bilayer graphene, and anomalous quantum oscillation in the monolayer-bilayer graphene hybrids. We also explored the device implications of our findings, and the application of some experimental techniques developed for the graphene work to the study of a complex oxide, Ca3Ru2O7, exhibiting properties of strongly correlated electrons. Graphene's high mobility and ballistic transport over device length scales, make it suitable for numerous applications. However, two big challenges remain in the way: maintaining high mobility in fabricated devices, and engineering a band gap to make graphene compatible with logical electronics and various optical devices. We address the first challenge by experimentally evaluating mobilities in scalable monolayer graphene-based field effect transistors (FETs) and dielectric-covered Hall bars. We find that the mobility is limited in these devices, and is roughly inversely proportional to doping. By considering interaction of graphene's Dirac fermions with local charged impurities at the interface between graphene and the top-gate dielectric, we find that Coulomb scattering is responsible for degraded mobility. Even in the cleanest devices, a band gap is still desirable for electronic applications of graphene. We address this challenge by probing the band structure of bilayer graphene, in which a field-tunable energy band gap has been theoretically proposed. We use planar tunneling spectroscopy of exfoliated bilayer graphene flakes demonstrate both measurement and control of the energy band gap. We find that both the Fermi level and

  13. QUANTITATIVE ANALYSIS OF BANDED STRUCTURES IN DUAL-PHASE STEELS

    Directory of Open Access Journals (Sweden)

    Benoit Krebs

    2011-05-01

    Full Text Available Dual-Phase (DP steels are composed of martensite islands dispersed in a ductile ferrite matrix, which provides a good balance between strength and ductility. Current processing conditions (continuous casting followed by hot and cold rolling generate 'banded structures' i.e., irregular, parallel and alternating bands of ferrite and martensite, which are detrimental to mechanical properties and especially for in-use properties. We present an original and simple method to quantify the intensity and wavelength of these bands. This method, based on the analysis of covariance function of binary images, is firstly tested on model images. It is compared with ASTM E-1268 standard and appears to be more robust. Then it is applied on real DP steel microstructures and proves to be sufficiently sensitive to discriminate samples resulting from different thermo-mechanical routes.

  14. Tunable band-notched line-defect waveguide in a surface-wave photonic crystal

    CERN Document Server

    Gao, Zhen; Zhang, Youming; Xu, Hongyi; Zhang, Baile

    2016-01-01

    We propose and experimentally demonstrate a tunable band-notched line-defect waveguide in a surface-wave photonic crystal, which consists of a straight line-defect waveguide and side-coupled defect cavities. A tunable narrow stopband can be observed in the broadband transmission spectra. We also demonstrate that both the filtering levels and filtering frequencies of the band-notched line-defect waveguide can be conveniently tuned through changing the total number and the pillar height of the side-coupled defect cavities. The band-notch function is based on the idea that the propagating surface modes with the resonance frequencies of the side-coupled defect cavities will be tightly localized around the defect sites, being filtered from the waveguide output. Transmission spectra measurements and direct near-field profiles imaging are performed at microwave frequencies to verify our idea and design. These results may enable new band-notched devices design and provide routes for the realization of tunable surface...

  15. Liquid-crystal photonic-band-gap materials the tunable electromagnetic vacuum

    CERN Document Server

    Busch, K

    1999-01-01

    We demonstrate that when an optically birefringent nematic liquid crystal is infiltrated into the void regions of an inverse opal, photonic-band-gap (PBG) material, the resulting composite material exhibits a completely tunable PBG. $9 In particular, the three- dimensional PBG can be completely opened or closed by applying an electric field which rotates the axis of the nematic molecules relative to the inverse opal backbone. Tunable light localization effects may $9 be realized by controlling the orientational disorder in the nematic. (28 refs).

  16. Wide tunable shift of the reflection band in dual frequency cholesteric liquid crystals.

    Science.gov (United States)

    Oton, Eva; Netter, Estelle

    2017-06-12

    Technologies featuring external control of reflected and transmitted light are lately being explored for a wide range of optical and photonic applications. Yet, the options for spectral band tuning are scarce, especially if dynamic control of either reflected or transmitted light is required. In this work we demonstrate a tunable device capable of shifting the reflected light spectrum of an impinging light using dual frequency cholesteric liquid crystals. Modulating the frequency of the applied signal, the Bragg reflection can be dynamically shifted over a wide spectral range and also switched off. This feature can be applied to color filters, augmented reality, multi-color lasers or tunable windows.

  17. Self-imaging effect in photonic crystal multimode waveguides exhibiting no band gaps

    Institute of Scientific and Technical Information of China (English)

    Tianbao Yu; Xiaoqing Jiang; Qinghua Liao; Wei Qi; Jianyi Yang; Minghua Wang

    2007-01-01

    The properties of the propagating field in multimode photonic crystal waveguides (PCWs) exhibiting no photonic band gaps (PBGs) are investigated. The transmission spectrum shows that the input field can be guided with high efficiency, and resemble index-guided modes owing to the combination of total internal reflection (TIR) and distributed Bragg reflection (DBR). Self-imaging effect happens and the filling fraction determines the beating lengths. The rows of air holes decide DBR coming from the mirrors on both sides of the guiding region, which governs the transmission spectrum. It provides a new way to realize the components for both polarizations by combining PBG and TIR effects in PCWs.

  18. One-dimensional electromagnetic band gap plasma structure formed by atmospheric pressure plasma inhomogeneities

    Science.gov (United States)

    Babitski, V. S.; Callegari, Th.; Simonchik, L. V.; Sokoloff, J.; Usachonak, M. S.

    2017-08-01

    The ability to use plasma columns of pulse discharges in argon at atmospheric pressure to form a one-dimensional electromagnetic band gap structure (or electromagnetic crystal) in the X-band waveguide is demonstrated. We show that a plasma electromagnetic crystal attenuates a microwave propagation in the stopband more than by 4 orders of magnitude. In order to obtain an effective control of the transmission spectrum comparable with a metallic regular structure, the electron concentration in plasma inhomogeneities should vary within the range from 1014 cm-3 to 1016 cm-3, while gas temperature and mean electron energy must be in the range of 2000 K and 0.5 eV, respectively, to lower electron collision frequency around 1010 s-1. We analyze in detail the time evolution response of the electromagnetic crystal according to the plasma parameters for the duration of the discharge. The interest of using atmospheric pressure discharges is to increase the microwave breakdown threshold in discharge volumes, whereby it becomes possible to perform dynamic control of high power microwaves.

  19. Crystal Structures of New Ammonium 5-Aminotetrazolates

    Directory of Open Access Journals (Sweden)

    Martin Lampl

    2014-11-01

    Full Text Available The crystal structures of three salts of anionic 5-aminotetrazole are described. The tetramethylammonium salt (P forms hydrogen-bonded ribbons of anions which accept weak C–H···N contacts from the cations. The cystamine salt (C2/c shows wave-shaped ribbons of anions linked by hydrogen bonds to screw-shaped dications. The tetramethylguanidine salt (P21/c exhibits layers of anions hydrogen-bonded to the cations.

  20. Crystal Structure of a New Cembranolide Diterpene

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    A new cembranoide deterpene was isolated from the soft coral Sinularia Tenella. The crystal and chemical structure of the title compound were determined by means of spectroscopic methods and X-ray diffraction analysis as (1R* , 4R* , 5S* , 12S* , 12R* )-9-acetoxy-cembr-8E, 15 (17)-dien-16,4-olide. It shows a moderate cytotoxicity against P 388 and L 1210 cell lines.

  1. Crystal structure of an archaeal actin homolog.

    Science.gov (United States)

    Roeben, Annette; Kofler, Christine; Nagy, István; Nickell, Stephan; Hartl, F Ulrich; Bracher, Andreas

    2006-04-21

    Prokaryotic homologs of the eukaryotic structural protein actin, such as MreB and ParM, have been implicated in determination of bacterial cell shape, and in the segregation of genomic and plasmid DNA. In contrast to these bacterial actin homologs, little is known about the archaeal counterparts. As a first step, we expressed a predicted actin homolog of the thermophilic archaeon Thermoplasma acidophilum, Ta0583, and determined its crystal structure at 2.1A resolution. Ta0583 is expressed as a soluble protein in T.acidophilum and is an active ATPase at physiological temperature. In vitro, Ta0583 forms sheets with spacings resembling the crystal lattice, indicating an inherent propensity to form filamentous structures. The fold of Ta0583 contains the core structure of actin and clearly belongs to the actin/Hsp70 superfamily of ATPases. Ta0583 is approximately equidistant from actin and MreB on the structural level, and combines features from both eubacterial actin homologs, MreB and ParM. The structure of Ta0583 co-crystallized with ADP indicates that the nucleotide binds at the interface between the subdomains of Ta0583 in a manner similar to that of actin. However, the conformation of the nucleotide observed in complex with Ta0583 clearly differs from that in complex with actin, but closely resembles the conformation of ParM-bound nucleotide. On the basis of sequence and structural homology, we suggest that Ta0583 derives from a ParM-like actin homolog that was once encoded by a plasmid and was transferred into a common ancestor of Thermoplasma and Ferroplasma. Intriguingly, both genera are characterized by the lack of a cell wall, and therefore Ta0583 could have a function in cellular organization.

  2. Electronic band structure effects in the stopping of protons in copper

    Science.gov (United States)

    Quashie, Edwin E.; Saha, Bidhan C.; Correa, Alfredo A.

    2016-10-01

    We present an ab initio study of the electronic stopping power of protons in copper over a wide range of proton velocities v =0.02 -10 a .u . where we take into account nonlinear effects. Time-dependent density functional theory coupled with molecular dynamics is used to study electronic excitations produced by energetic protons. A plane-wave pseudopotential scheme is employed to solve the time-dependent Kohn-Sham equations for a moving ion in a periodic crystal. The electronic excitations and the band structure determine the stopping power of the material and alter the interatomic forces for both channeling and off-channeling trajectories. Our off-channeling results are in quantitative agreement with experiments, and at low velocity they unveil a crossover region of superlinear velocity dependence (with a power of ˜1.5 ) in the velocity range v =0.07 -0.3 a .u . , which we associate to the copper crystalline electronic band structure. The results are rationalized by simple band models connecting two separate regimes. We find that the limit of electronic stopping v →0 is not as simple as phenomenological models suggest and it is plagued by band-structure effects.

  3. From lattice Hamiltonians to tunable band structures by lithographic design

    Science.gov (United States)

    Tadjine, Athmane; Allan, Guy; Delerue, Christophe

    2016-08-01

    Recently, new materials exhibiting exotic band structures characterized by Dirac cones, nontrivial flat bands, and band crossing points have been proposed on the basis of effective two-dimensional lattice Hamiltonians. Here, we show using atomistic tight-binding calculations that these theoretical predictions could be experimentally realized in the conduction band of superlattices nanolithographed in III-V and II-VI semiconductor ultrathin films. The lithographed patterns consist of periodic lattices of etched cylindrical holes that form potential barriers for the electrons in the quantum well. In the case of honeycomb lattices, the conduction minibands of the resulting artificial graphene host several Dirac cones and nontrivial flat bands. Similar features, but organized in different ways, in energy or in k -space are found in kagome, distorted honeycomb, and Lieb superlattices. Dirac cones extending over tens of meV could be obtained in superlattices with reasonable sizes of the lithographic patterns, for instance in InAs/AlSb heterostructures. Bilayer artificial graphene could be also realized by lithography of a double quantum-well heterostructure. These new materials should be interesting for the experimental exploration of Dirac-based quantum systems, for both fundamental and applied physics.

  4. Crystal Structure Refinement of Synthetic Pure Gyrolite

    Directory of Open Access Journals (Sweden)

    Arūnas Baltušnikas

    2015-03-01

    Full Text Available Pure calcium silicate hydrate – gyrolite was prepared under the saturated steam pressure at 473 K temperature in rotating autoclave. The crystal structure of synthetic gyrolite was investigated by X-ray diffraction and refined using Le Bail, Rietveld and crystal structure modelling methods. Background, peak shape parameters and verification of the space group were performed by the Le Bail full pattern decomposition. Peculiarities of interlayer sheet X of gyrolite unit cell were highlighted by Rietveld refinement. Possible atomic arrangement in interlayer sheet X was solved by global optimization method. Most likelihood crystal structure model of gyrolite was calculated by final Rietveld refinement. It was crystallographically showed, that cell parameters are: a = 0.9713(2 nm, b = 0.9715(2 nm, c = 2.2442(3 nm and alfa = 95.48(2 º, beta = 91.45(2 °, gamma = l20.05(3 °.DOI: http://dx.doi.org/10.5755/j01.ms.21.1.5460

  5. Lessons from crystal structures of kainate receptors.

    Science.gov (United States)

    Møllerud, Stine; Frydenvang, Karla; Pickering, Darryl S; Kastrup, Jette Sandholm

    2017-01-01

    Kainate receptors belong to the family of ionotropic glutamate receptors. These receptors assemble from five subunits (GluK1-5) into tetrameric ion channels. Kainate receptors are located at both pre- and postsynaptic membranes in the central nervous system where they contribute to excitatory synaptic transmission and modulate network excitability by regulating neurotransmitter release. Dysfunction of kainate receptors has been implicated in several neurological disorders such as epilepsy, schizophrenia and depression. Here we provide a review on the current understanding of kainate receptor structure and how they bind agonists, antagonists and ions. The first structure of the ligand-binding domain of the GluK1 subunit was reported in 2005, seven years after publication of the crystal structure of a soluble construct of the ligand-binding domain of the AMPA-type subunit GluA2. Today, a full-length structure has been determined of GluK2 by cryo electron microscopy to 7.6 Å resolution as well as 84 high-resolution crystal structures of N-terminal domains and ligand-binding domains, including agonist and antagonist bound structures, modulatory ions and mutations. However, there are still many unanswered questions and challenges in front of us. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'.

  6. Numerical investigation of the flat band Bloch modes in a 2D photonic crystal with Dirac cones.

    Science.gov (United States)

    Zhang, Peng; Fietz, Chris; Tassin, Philippe; Koschny, Thomas; Soukoulis, Costas M

    2015-04-20

    A numerical method combining complex-k band calculations and absorbing boundary conditions for Bloch waves is presented. We use this method to study photonic crystals with Dirac cones. We demonstrate that the photonic crystal behaves as a zero-index medium when excited at normal incidence, but that the zero-index behavior is lost at oblique incidence due to excitation of modes on the flat band. We also investigate the formation of monomodal and multimodal cavity resonances inside the photonic crystals, and the physical origins of their different line-shape features.

  7. A DIRECT DETERMINATION OF THE CRYSTAL STRUCTURE OF 2,3,4,6-TETRANITROANILINE,

    Science.gov (United States)

    ORGANIC NITROGEN COMPOUNDS, CRYSTAL STRUCTURE ), (* CRYSTAL STRUCTURE , EXPLOSIVES), (*EXPLOSIVES, CRYSTAL STRUCTURE ), AROMATIC COMPOUNDS, AMINES, NITRATES, LEAST SQUARES METHOD, FOURIER ANALYSIS, CHEMICAL BONDS.

  8. Structural noise tolerance of photonic crystal optical properties

    Science.gov (United States)

    Odontsengel, Nyam-Erdene; Cai, DongSheng; Cole, James B.

    2016-12-01

    Using nonstandard (NS) finite difference time domain (FDTD) scheme to perform 2D electromagnetic (EM) simulations, we investigate how the optical properties of 2D photonic crystals (PCs) are affected by various different kinds of structural noises in the PC lattice. While the transmission spectrum is strongly affected by noises, the position and the depth of the band gap in the transmission spectrum are remarkably robust. It is shown that rather coarse numerical grids can be used to evaluate various PC structures in NS-FDTD EM simulations. The combination of noises affects transmission spectrum in the same way as the most influential individual noise. It is shown that reducing the most influential individual noise is a very efficient method to make PC more accurate.

  9. Development of X-band accelerating structures for high gradients

    Institute of Scientific and Technical Information of China (English)

    S. Bini; M. G. Grimaldi; L. Romano; F. Ruffino; R. Parodi; V. Chimenti; A. Marcelli; L. Palumbo; B. Spataro; V. A. Dolgashev; S. Tantawi; A.D. Yeremian; Y. Higashi

    2012-01-01

    Short copper standing wave (SW) structures operating at an X-band frequency have been recently designed and manufactured at the Laboratori Nazionali di Frascati of the Istituto Nazionale di Fisica Nucleare (INFN) using the vacuum brazing technique.High power tests of the structures have been performed at the SLAC National Accelerator Laboratory.In this manuscript we report the results of these tests and the activity in progress to enhance the high gradient performance of the next generation of structures,particularly the technological characterization of high performance coatings obtained via molybdenum sputtering.

  10. Engineering Design of a Multipurpose X-band Accelerating Structure

    CERN Document Server

    Gudkov, Dmitry; Samoshkin, Alexander; Zennaro, Riccardo; Dehler, Micha; Raguin, Jean-Yves

    2010-01-01

    Both FEL projects, SwissFEL and Fermi-Elettra each require an X-band RF accelerating structure for optimal bunch compression at the respective injectors. As the CLIC project is pursuing a program for producing and testing the X-band high-gradient RF structures, a collaboration between PSI, Elettra and CERN has been established to build a multipurpose X-band accelerating structure. This paper focuses on its engineering design, which is based on the disked cells jointed together by diffusion bonding. Vacuum brazing and laser beam welding is used for auxiliary components. The accelerating structure consists of two coupler subassemblies, 73 disks and includes a wakefield monitor and diagnostic waveguides. The engineering study includes the external cooling system, consisting of two parallel cooling circuits and an RF tuning system, which allows phase advance tuning of the cell by deforming the outer wall. The engineering solution for the installation and sealing of the wake field monitor feed-through devices that...

  11. Fourier Analysis and Structure Determination--Part III: X-ray Crystal Structure Analysis.

    Science.gov (United States)

    Chesick, John P.

    1989-01-01

    Discussed is single crystal X-ray crystal structure analysis. A common link between the NMR imaging and the traditional X-ray crystal structure analysis is reported. Claims that comparisons aid in the understanding of both techniques. (MVL)

  12. Band structure, band offsets, substitutional doping, and Schottky barriers of bulk and monolayer InSe

    Science.gov (United States)

    Guo, Yuzheng; Robertson, John

    2017-09-01

    We present a detailed study of the electronic structure of the layered semiconductor InSe. We calculate the band structure of the monolayer and bulk material using density functional theory, hybrid functionals, and G W . The band gap of the monolayer InSe is calculated to be 2.4 eV in screened exchange hybrid functional, close to the experimental photoluminescence gap. The electron affinities and band offsets are calculated for vertical stacked-layer heterostructures, and are found to be suitable for tunnel field effect transistors (TFETs) in combination with WS e2 or similar. The valence-band edge of InSe is calculated to lie 5.2 eV below the vacuum level, similar to that for the closed shell systems HfS e2 or SnS e2 . Hence InSe would be suitable to act as a p -type drain in the TFET. The intrinsic defects are calculated. For Se-rich layers, the Se adatom (interstitial) is found to be the most stable defect, whereas for In-rich layers, the Se vacancy is the most stable for the neutral state. Antisites tend to have energies just above those of vacancies. The Se antisite distorts towards a bond-breaking distortion as in the EL2 center of GaAs. Both substitutional donors and acceptors are calculated to be shallow, and effective dopants. They do not reconstruct to form nondoping configurations as occurs in black phosphorus. Finally, the Schottky barriers of metals on InSe are found to be strongly pinned by metal induced gap states (MIGS) at ˜0.5 eV above the valence-band edge. Any interfacial defects would lead to a stronger pinning at a similar energy. Overall, InSe is an effective semiconductor combining the good features of 2D (lack of dangling bonds, etc.) with the good features of 3D (effective doping), which few others achieve.

  13. Energetic stabilization of the Mizoguchi structure for magnetite by band-structure effects

    Science.gov (United States)

    Mishra, S. K.; Satpathy, S.

    1993-03-01

    We show that the Mizoguchi structure is energetically stabilized over the Verwey structure for magnetite by electron hopping on the B sublattice. We use the one-band Cullen-Callen model Hamiltonian for the electronic band structure taking the nearest-neighbor and the second-neighbor Coulomb interactions, U1 and U2, into account. There is a competition between the Coulomb and the band-structure energies. The Coulomb energy tends to favor the Verwey structure while the band-structure energy tends to favor the Mizoguchi structure. We find that for U1band-structure energy) term dominates making the Mizoguchi structure energetically favorable over the Verwey structure. For a larger value of U1, the band-structure effect alone is insufficient, making it necessary to invoke other mechanisms such as the electron-phonon coupling earlier proposed by other authors, to stabilize the Mizoguchi structure. The energy of a single ``reversed-ring'' excitation in the Mizoguchi structure is calculated to be of the order of a few meV. The small energy is consistent with Cullen's explanation of the absence of cell doubling in the Ca plane as observed in diffraction experiments. The Mizoguchi order is unstable with respect to the formation of reversed-ring excitations if only U1 is present, but is stabilized by a small value of U2.

  14. Ab initio molecular crystal structures, spectra, and phase diagrams.

    Science.gov (United States)

    Hirata, So; Gilliard, Kandis; He, Xiao; Li, Jinjin; Sode, Olaseni

    2014-09-16

    Conspectus Molecular crystals are chemists' solids in the sense that their structures and properties can be understood in terms of those of the constituent molecules merely perturbed by a crystalline environment. They form a large and important class of solids including ices of atmospheric species, drugs, explosives, and even some organic optoelectronic materials and supramolecular assemblies. Recently, surprisingly simple yet extremely efficient, versatile, easily implemented, and systematically accurate electronic structure methods for molecular crystals have been developed. The methods, collectively referred to as the embedded-fragment scheme, divide a crystal into monomers and overlapping dimers and apply modern molecular electronic structure methods and software to these fragments of the crystal that are embedded in a self-consistently determined crystalline electrostatic field. They enable facile applications of accurate but otherwise prohibitively expensive ab initio molecular orbital theories such as Møller-Plesset perturbation and coupled-cluster theories to a broad range of properties of solids such as internal energies, enthalpies, structures, equation of state, phonon dispersion curves and density of states, infrared and Raman spectra (including band intensities and sometimes anharmonic effects), inelastic neutron scattering spectra, heat capacities, Gibbs energies, and phase diagrams, while accounting for many-body electrostatic (namely, induction or polarization) effects as well as two-body exchange and dispersion interactions from first principles. They can fundamentally alter the role of computing in the studies of molecular crystals in the same way ab initio molecular orbital theories have transformed research practices in gas-phase physical chemistry and synthetic chemistry in the last half century. In this Account, after a brief summary of formalisms and algorithms, we discuss applications of these methods performed in our group as compelling

  15. Structure-Band Gap Relationships in Hexagonal Polytypes and Low-Dimensional Structures of Hybrid Tin Iodide Perovskites.

    Science.gov (United States)

    Stoumpos, Constantinos C; Mao, Lingling; Malliakas, Christos D; Kanatzidis, Mercouri G

    2017-01-03

    The present study deals with the structural characterization and classification of the novel compounds 1-8 into perovskite subclasses and proceeds in extracting the structure-band gap relationships between them. The compounds were obtained from the employment of small, 3-5-atom-wide organic ammonium ions seeking to discover new perovskite-like compounds. The compounds reported here adopt unique or rare structure types akin to the prototype structure perovskite. When trimethylammonium (TMA) was employed, we obtained TMASnI3 (1), which is our reference compound for a "perovskitoid" structure of face-sharing octahedra. The compounds EASnI3 (2b), GASnI3 (3a), ACASnI3 (4), and IMSnI3 (5) obtained from the use of ethylammonium (EA), guanidinium (GA), acetamidinium (ACA), and imidazolium (IM) cations, respectively, represent the first entries of the so-called "hexagonal perovskite polytypes" in the hybrid halide perovskite library. The hexagonal perovskites define a new family of hybrid halide perovskites with a crystal structure that emerges from a blend of corner- and face-sharing octahedral connections in various proportions. The small organic cations can also stabilize a second structural type characterized by a crystal lattice with reduced dimensionality. These compounds include the two-dimensional (2D) perovskites GA2SnI4 (3b) and IPA3Sn2I7 (6b) and the one-dimensional (1D) perovskite IPA3SnI5 (6a). The known 2D perovskite BA2MASn2I7 (7) and the related all-inorganic 1D perovskite "RbSnF2I" (8) have also been synthesized. All compounds have been identified as medium-to-wide-band-gap semiconductors in the range of Eg = 1.90-2.40 eV, with the band gap progressively decreasing with increased corner-sharing functionality and increased torsion angle in the octahedral connectivity.

  16. THE CRYSTAL STRUCTURE OF 2-(4’-AMINO-5’AMINO PYRIMIDY) -2-PENTENE-4-ONE.

    Science.gov (United States)

    NITROGEN HETEROCYCLIC COMPOUNDS, CRYSTAL STRUCTURE ), (*AMINES, CRYSTAL STRUCTURE ), (*KETONES, CRYSTAL STRUCTURE ), CRYSTAL LATTICES, FOURIER ANALYSIS, LEAST SQUARES METHOD, MOLECULAR STRUCTURE, PYRIMIDINES, CHEMICAL BONDS

  17. Crystal structure of natural phaeosphaeride A

    Directory of Open Access Journals (Sweden)

    Victoria V. Abzianidze

    2015-08-01

    Full Text Available The asymmetric unit of the title compound, C15H23NO5, contains two independent molecules. Phaeosphaeride A contains two primary sections, an alkyl chain consisting of five C atoms and a cyclic system consisting of fused five- and six-membered rings with attached substituents. In the crystal, the molecules form layered structures. Nearly planar sheets, parallel to the (001 plane, form bilayers of two-dimensional hydrogen-bonded networks with the hydroxy groups located on the interior of the bilayer sheets. The network is constructed primarily of four O—H...O hydrogen bonds, which form a zigzag pattern in the (001 plane. The butyl chains interdigitate with the butyl chains on adjacent sheets. The crystal was twinned by a twofold rotation about the c axis, with refined major–minor occupancy fractions of 0.718 (6:0.282 (6.

  18. Determining crystal structures through crowdsourcing and coursework

    Science.gov (United States)

    Horowitz, Scott; Koepnick, Brian; Martin, Raoul; Tymieniecki, Agnes; Winburn, Amanda A.; Cooper, Seth; Flatten, Jeff; Rogawski, David S.; Koropatkin, Nicole M.; Hailu, Tsinatkeab T.; Jain, Neha; Koldewey, Philipp; Ahlstrom, Logan S.; Chapman, Matthew R.; Sikkema, Andrew P.; Skiba, Meredith A.; Maloney, Finn P.; Beinlich, Felix R. M.; Caglar, Ahmet; Coral, Alan; Jensen, Alice Elizabeth; Lubow, Allen; Boitano, Amanda; Lisle, Amy Elizabeth; Maxwell, Andrew T.; Failer, Barb; Kaszubowski, Bartosz; Hrytsiv, Bohdan; Vincenzo, Brancaccio; de Melo Cruz, Breno Renan; McManus, Brian Joseph; Kestemont, Bruno; Vardeman, Carl; Comisky, Casey; Neilson, Catherine; Landers, Catherine R.; Ince, Christopher; Buske, Daniel Jon; Totonjian, Daniel; Copeland, David Marshall; Murray, David; Jagieła, Dawid; Janz, Dietmar; Wheeler, Douglas C.; Cali, Elie; Croze, Emmanuel; Rezae, Farah; Martin, Floyd Orville; Beecher, Gil; de Jong, Guido Alexander; Ykman, Guy; Feldmann, Harald; Chan, Hugo Paul Perez; Kovanecz, Istvan; Vasilchenko, Ivan; Connellan, James C.; Borman, Jami Lynne; Norrgard, Jane; Kanfer, Jebbie; Canfield, Jeffrey M.; Slone, Jesse David; Oh, Jimmy; Mitchell, Joanne; Bishop, John; Kroeger, John Douglas; Schinkler, Jonas; McLaughlin, Joseph; Brownlee, June M.; Bell, Justin; Fellbaum, Karl Willem; Harper, Kathleen; Abbey, Kirk J.; Isaksson, Lennart E.; Wei, Linda; Cummins, Lisa N.; Miller, Lori Anne; Bain, Lyn; Carpenter, Lynn; Desnouck, Maarten; Sharma, Manasa G.; Belcastro, Marcus; Szew, Martin; Szew, Martin; Britton, Matthew; Gaebel, Matthias; Power, Max; Cassidy, Michael; Pfützenreuter, Michael; Minett, Michele; Wesselingh, Michiel; Yi, Minjune; Cameron, Neil Haydn Tormey; Bolibruch, Nicholas I.; Benevides, Noah; Kathleen Kerr, Norah; Barlow, Nova; Crevits, Nykole Krystyne; Dunn, Paul; Silveira Belo Nascimento Roque, Paulo Sergio; Riber, Peter; Pikkanen, Petri; Shehzad, Raafay; Viosca, Randy; James Fraser, Robert; Leduc, Robert; Madala, Roman; Shnider, Scott; de Boisblanc, Sharon; Butkovich, Slava; Bliven, Spencer; Hettler, Stephen; Telehany, Stephen; Schwegmann, Steven A.; Parkes, Steven; Kleinfelter, Susan C.; Michael Holst, Sven; van der Laan, T. J. A.; Bausewein, Thomas; Simon, Vera; Pulley, Warwick; Hull, William; Kim, Annes Yukyung; Lawton, Alexis; Ruesch, Amanda; Sundar, Anjali; Lawrence, Anna-Lisa; Afrin, Antara; Maheshwer, Bhargavi; Turfe, Bilal; Huebner, Christian; Killeen, Courtney Elizabeth; Antebi-Lerrman, Dalia; Luan, Danny; Wolfe, Derek; Pham, Duc; Michewicz, Elaina; Hull, Elizabeth; Pardington, Emily; Galal, Galal Osama; Sun, Grace; Chen, Grace; Anderson, Halie E.; Chang, Jane; Hewlett, Jeffrey Thomas; Sterbenz, Jennifer; Lim, Jiho; Morof, Joshua; Lee, Junho; Inn, Juyoung Samuel; Hahm, Kaitlin; Roth, Kaitlin; Nair, Karun; Markin, Katherine; Schramm, Katie; Toni Eid, Kevin; Gam, Kristina; Murphy, Lisha; Yuan, Lucy; Kana, Lulia; Daboul, Lynn; Shammas, Mario Karam; Chason, Max; Sinan, Moaz; Andrew Tooley, Nicholas; Korakavi, Nisha; Comer, Patrick; Magur, Pragya; Savliwala, Quresh; Davison, Reid Michael; Sankaran, Roshun Rajiv; Lewe, Sam; Tamkus, Saule; Chen, Shirley; Harvey, Sho; Hwang, Sin Ye; Vatsia, Sohrab; Withrow, Stefan; Luther, Tahra K.; Manett, Taylor; Johnson, Thomas James; Ryan Brash, Timothy; Kuhlman, Wyatt; Park, Yeonjung; Popović, Zoran; Baker, David; Khatib, Firas; Bardwell, James C. A.

    2016-09-01

    We show here that computer game players can build high-quality crystal structures. Introduction of a new feature into the computer game Foldit allows players to build and real-space refine structures into electron density maps. To assess the usefulness of this feature, we held a crystallographic model-building competition between trained crystallographers, undergraduate students, Foldit players and automatic model-building algorithms. After removal of disordered residues, a team of Foldit players achieved the most accurate structure. Analysing the target protein of the competition, YPL067C, uncovered a new family of histidine triad proteins apparently involved in the prevention of amyloid toxicity. From this study, we conclude that crystallographers can utilize crowdsourcing to interpret electron density information and to produce structure solutions of the highest quality.

  19. Synthesis and structural characterization of a single-crystal to single-crystal transformable coordination polymer.

    Science.gov (United States)

    Tian, Yuyang; Allan, Phoebe K; Renouf, Catherine L; He, Xiang; McCormick, Laura J; Morris, Russell E

    2014-01-28

    A single-crystal to single-crystal transformable coordination polymer compound was hydrothermally synthesized. The structural rearrangement is induced by selecting a ligand that contains both strong and weaker coordinating groups. Both hydrated and dehydrated structures were determined by single crystal X-ray analysis.

  20. Parameterization and algebraic structure of 3-band orthogonal wavelet systems

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In this paper, a complete parameterization for the 3-band compact wavelet systems is presented. Using the parametric result, a program of the filterbank design is completed, which can give not only the filterbanks but also the graphs of all possible scaling functions and their corresponding wavelets. Especially some symmetric wavelets with small supports are given. Finally an algebraic structure for this kind of wavelet systems is characterized.

  1. Biaxial crystal α-BaTeMo(2)O(9): theory study of large birefringence and wide-band polarized prisms design.

    Science.gov (United States)

    Gao, Z L; Wu, Q; Liu, X T; Sun, Y X; Tao, X T

    2015-02-23

    α-BaTeMo(2)O(9) is a novel biaxial crystal with wide-band transmittance spectrum. The refractive index dispersion curves and birefringence of the α-BaTeMo(2)O(9) crystal were obtained in spectral range of 0.4~5 μm. The origin of the birefringence for the crystal has been calculated and interpreted on the basis of the crystal structure combined with theoretical studies. The polarized directions and formulations of refractive index of optical waves in biaxial α-BaTeMo(2)O(9) were investigated by solving the refractive index ellipsoid equations. Furthermore, polarized prisms based on the α-BaTeMo(2)O(9) crystal used in spectral ranges of 0.4~2.7 μm and 0.48~4.5 μm were designed and characterized. The extinction ratios of both prisms were determined to be larger than 10000:1, which would satisfy the practical requirements. The impacts on extinction ratio for biaxial and uniaxial crystals were also discussed. To our knowledge, it is the first report about biaxial crystals for the polarized prisms, and the results show that the α-BaTeMo(2)O(9) crystal is a promising material for polarized optical components, especially in the range of 3~5 μm.

  2. Crystal structure of Cryptosporidium parvum pyruvate kinase.

    Directory of Open Access Journals (Sweden)

    William J Cook

    Full Text Available Pyruvate kinase plays a critical role in cellular metabolism of glucose by serving as a major regulator of glycolysis. This tetrameric enzyme is allosterically regulated by different effector molecules, mainly phosphosugars. In response to binding of effector molecules and substrates, significant structural changes have been identified in various pyruvate kinase structures. Pyruvate kinase of Cryptosporidium parvum is exceptional among known enzymes of protozoan origin in that it exhibits no allosteric property in the presence of commonly known effector molecules. The crystal structure of pyruvate kinase from C. parvum has been solved by molecular replacement techniques and refined to 2.5 Å resolution. In the active site a glycerol molecule is located near the γ-phosphate site of ATP, and the protein structure displays a partially closed active site. However, unlike other structures where the active site is closed, the α6' helix in C. parvum pyruvate kinase unwinds and assumes an extended conformation. In the crystal structure a sulfate ion is found at a site that is occupied by a phosphate of the effector molecule in many pyruvate kinase structures. A new feature of the C. parvum pyruvate kinase structure is the presence of a disulfide bond cross-linking the two monomers in the asymmetric unit. The disulfide bond is formed between cysteine residue 26 in the short N-helix of one monomer with cysteine residue 312 in a long helix (residues 303-320 of the second monomer at the interface of these monomers. Both cysteine residues are unique to C. parvum, and the disulfide bond remained intact in a reduced environment. However, the significance of this bond, if any, remains unknown at this time.

  3. Diterbium heptanickel: a crystal structure redetermination

    Directory of Open Access Journals (Sweden)

    Volodymyr Levytskyy

    2014-08-01

    Full Text Available The crystal structure of the title compound, Tb2Ni7, was redetermined from single-crystal X-ray diffraction data. In comparison with previous studies based on powder X-ray diffraction data [Lemaire et al. (1967. C. R. Acad. Sci. Ser. B, 265, 1280–1282; Lemaire & Paccard (1969. Bull. Soc. Fr. Mineral. Cristallogr. 92, 9–16; Buschow & van der Goot (1970. J. Less-Common Met. 22, 419–428], the present redetermination affords refined coordinates and anisotropic displacement parameters for all atoms. A partial occupation for one Tb atom results in the non-stoichiometric composition Tb1.962 (4Ni7. The title compound adopts the Ce2Ni7 structure type and can also be derived from the CaCu5 structure type as an intergrowth structure. The asymmetric unit contains two Tb sites (both site symmetries 3m. and five Ni sites (.m., mm2, 3m., 3m., -3m.. The two different coordination polyhedra of Tb are a Frank–Kasper polyhedron formed by four Tb and 12 Ni atoms and a pseudo Frank–Kasper polyhedron formed by two Tb and 18 Ni atoms. The four different coordination polyhedra of Ni are Frank–Kasper icosahedra formed by five Tb and seven Ni atoms, four Tb and eight Ni atoms, three Tb and nine Ni atoms, and six Tb and six Ni atoms, respectively.

  4. Electromagnetic wave control of ceramic/resin photonic crystals with diamond structure

    Directory of Open Access Journals (Sweden)

    Soshu Kirihara, Mitsuo Takeda, Kazuaki Sakoda and Yoshinari Miyamoto

    2004-01-01

    Full Text Available Millimeter-order photonic crystals with the periodic arrangement of the dielectric constant were fabricated by infiltrating the mixed slurry of ceramics and polyester into the epoxy molds with an inverse form of a diamond structure. The epoxy molds are designed and processed by using a CAD/CAM process of stereolithography. The photonic crystals were prepared to have the diamond structure of the ceramic/polyester composite lattice, which is embedded in the epoxy matrix. The ceramic powders mixed with polyester are TiO2, SrTiO3, and BaTiO3 with high dielectric constant. It is possible to control more freely and widely the dielectric constant of the photonic crystals by this method. These ceramic/resin photonic crystals formed the complete photonic band gaps in the microwave band of 7–11 GHz, which can totally reflect the electromagnetic wave for all crystal directions. Attenuation profiles of the transmission amplitude in the band gaps were controlled with the dielectric constant of the composite lattice. The obtained results fairly agreed with the theoretical simulation of the electromagnetic wave propagation through photonic crystals.

  5. 旋转方形散射体对三角晶格磁振子晶体带结构的优化∗%Spin-wave band gaps created by rotating square ro ds in triangular lattice magnonic crystals

    Institute of Scientific and Technical Information of China (English)

    胡晓颖; 郭晓霞; 胡文弢; 呼和满都拉; 郑晓霞; 荆丽丽

    2015-01-01

    用改进的平面波展开法数值计算了正方形散射体三角排列的二维磁振子晶体当散射体旋转时的带结构。结果显示,同样的填充率下,旋转正方柱散射体可以在新的频率范围内打开更多的带隙,或者使低频带隙加宽。说明旋转散射体可以有效地优化带隙。%Recently, magnonic crystals which are the magnetic counterparts of photonic crystals or phononic crystals are becoming a hot area of research. In this paper, band structure of two-dimensional magnotic crystal composed of square rods triangularly arranged are calculated by using the plane-wave expansion method. Spin-wave band structures of two-dimensional magnonic crystal composed of Fe triangularly arranged Fe in an EuO matrix. The results show that when the filling ratio f =0.4, only two absolute band gaps can be found in the case of θ =0◦. The first gap appears between the first band and the second band, the second gap between the sixth band and the seventh band. However, the number of band gaps can be improved by rotating the square rods through θ =25◦, there are eight absolute band gaps that can be found. The first gap appears between the first band and the second band, the fifth gap between the sixth band and the seventh band. The new band gaps can be found, the second gap appears between the third band and the fourth band, the third gap between the fourth band and the fifth band, the fourth gap between the fifth band and the sixth band, the sixth gap between the seventh band and the eighth band, the seventh gap between the eighth band and the ninth band, the eighth gap between the ninth band and the tenth band. These results show that it is possible to create spin-wave gaps by rotating square rods in a two-dimensional magnotic crystal. The numerical results of the normalized gap width ∆Ω/Ωg of the first gap between the first band and the second band always changes with filling fraction f and rotational angles θ. When f

  6. Design of full-k-space flat bands in photonic crystals beyond the tight-binding picture.

    Science.gov (United States)

    Xu, Changqing; Wang, Gang; Hang, Zhi Hong; Luo, Jie; Chan, C T; Lai, Yun

    2015-12-11

    Based on a band engineering method, we propose a theoretical prescription to create a full-k-space flat band in dielectric photonic crystals covering the whole Brillouin Zone. With wave functions distributed in air instead of in the dielectrics, such a flat band represents a unique mechanism for achieving flat dispersions beyond the tight-binding picture, which can enormously reduce the requirement of permittivity contrast in the system. Finally, we propose and numerically demonstrate a unique application based on the full-k-space coverage of the flat band: ultra-sensitive detection of small scatterers.

  7. The band structure of carbonmonoxide on 2-D Au islands on graphene

    KAUST Repository

    Katsiev, Khabiboulakh

    2014-06-01

    The dispersion of the occupied molecular orbitals of carbon monoxide adsorbed on Au 2D islands, vapor-deposited on graphene/Ru(0 0 0 1), is seen to be wave vector dependent, as revealed by angle-resolved photoemission. The band dispersion is similar to CO monolayers adsorbed on many single crystal metal surfaces. Thus not only are the adsorbed gold islands on graphene flat and crystalline, as evident in the dispersion of the Au d-states, but the CO molecular adlayer is both molecular and ordered as well. The experimental angle-resolved photoemission combined with model calculations of the occupied CO band structure, suggest that, in spite of being a very weakly bound adsorbate, the CO adlayer on Au 2D islands on graphene is strongly hybridized to the Au layer. . © 2014 Elsevier B.V. All rights reserved.

  8. Direct observation of the band structure in bulk hexagonal boron nitride

    Science.gov (United States)

    Henck, Hugo; Pierucci, Debora; Fugallo, Giorgia; Avila, José; Cassabois, Guillaume; Dappe, Yannick J.; Silly, Mathieu G.; Chen, Chaoyu; Gil, Bernard; Gatti, Matteo; Sottile, Francesco; Sirotti, Fausto; Asensio, Maria C.; Ouerghi, Abdelkarim

    2017-02-01

    A promising route towards nanodevice applications relies on the association of graphene and transition metal dichalcogenides with hexagonal boron nitride (h -BN ). Due to its insulating nature, h -BN has emerged as a natural substrate and gate dielectric for graphene-based electronic devices. However, some fundamental properties of bulk h -BN remain obscure. For example, the band structure and the position of the Fermi level have not been experimentally resolved. Here, we report a direct observation of parabolic dispersions of h -BN crystals using high-resolution angle-resolved photoemission spectroscopy (ARPES). We find that h -BN exfoliation on epitaxial graphene enables overcoming the technical difficulties of using ARPES with insulating materials. We show trigonal warping of the intensity maps at constant energy. The valence-band maxima are located around the K points, 2.5 eV below the Fermi level, thus confirming the residual p -type character of typical h -BN .

  9. Simultaneous multi-channel CMW-band and MMW-band UWB monocycle pulse generation using FWM effect in a highly nonlinear photonic crystal fiber.

    Science.gov (United States)

    Zhang, Fangzheng; Wu, Jian; Fu, Songnian; Xu, Kun; Li, Yan; Hong, Xiaobin; Shum, Ping; Lin, Jintong

    2010-07-19

    We propose and experimentally demonstrate a scheme to simultaneously realize multi-channel centimeter wave (CMW) band and millimeter wave (MMW) band ultra-wideband (UWB) monocycle pulse generation using four wave mixing (FWM) effect in a highly nonlinear photonic crystal fiber (HNL-PCF). Two lightwaves carrying polarity-reversed optical Gaussian pulses with appropriate time delay and another lightwave carrying a 20 GHz clock signal are launched into the HNL-PCF together. By filtering out the FWM idlers, two CMW-band UWB monocycle signals and two MMW-band UWB monocycle signals at 20 GHz are obtained simultaneously. Experimental measurements of the generated UWB monocycle pulses at individual wavelength, which comply with the FCC regulations, verify the feasibility and flexibility of proposed scheme for use in practical UWB communication systems.

  10. Crystal structure prediction from first principles: The crystal structures of glycine

    Science.gov (United States)

    Lund, Albert M.; Pagola, Gabriel I.; Orendt, Anita M.; Ferraro, Marta B.; Facelli, Julio C.

    2015-04-01

    Here we present the results of our unbiased searches of glycine polymorphs obtained using the genetic algorithms search implemented in MGAC, modified genetic algorithm for crystals, coupled with the local optimization and energy evaluation provided by Quantum Espresso. We demonstrate that it is possible to predict the crystal structures of a biomedical molecule using solely first principles calculations. We were able to find all the ambient pressure stable glycine polymorphs, which are found in the same energetic ordering as observed experimentally and the agreement between the experimental and predicted structures is of such accuracy that the two are visually almost indistinguishable.

  11. A 1D Optomechanical crystal with a complete phononic band gap

    CERN Document Server

    Gomis-Bresco, J; Oudich, M; El-Jallal, S; Griol, A; Puerto, D; Chavez, E; Pennec, Y; Djafari-Rouhani, B; Alzina, F; Martínez, A; Torres, C M Sotomayor

    2014-01-01

    Recent years have witnessed the boom of cavity optomechanics, which exploits the confinement and coupling of optical waves and mechanical vibrations at the nanoscale. Amongst the different physical implementations,optomechanical (OM) crystals built on semiconductor slabs are particularly interesting since they enable the integration and manipulation of multiple OM elements in a single chip and provide GHz phonons suitable for coherent phonon manipulation. Different demonstrations of coupling of infrared photons and GHz phonons in cavities created by inserting defects on OM crystals have been performed. However, the considered structures do not show a complete phononic bandgap at the frequencies of interest, which in principle should allow longer dephasing time, since acoustic leakage is minimized. In this work we demonstrate the excitation of acoustic modes in a 1D OM crystal properly designed to display a full phononic bandgap for acoustic modes at about 4 GHz. The confined phonons have an OM coupling rangin...

  12. Crystal structure, growth and nonlinear optical studies of isonicotinamide p-nitrophenol: A new organic crystal for optical limiting applications

    Science.gov (United States)

    Vijayalakshmi, A.; Vidyavathy, B.; Vinitha, G.

    2016-08-01

    Isonicotinamide p-nitrophenol (ICPNP), a new organic material, was synthesized using methanol solvent. Single crystals of ICPNP were grown using a slow evaporation solution growth technique. Crystal structure of ICPNP is elucidated by single crystal X-ray diffraction analysis. It belongs to monoclinic crystal system with space group of P21/c. It forms two dimensional networks by O-H…O, N-H…O and C-H…O hydrogen bonds. The molecular structure of ICPNP was further confirmed by Fourier transform infrared (FTIR) spectral analysis. The optical transmittance range and the lower cut-off wavelength (421 nm) with the optical band gap (2.90 eV) of the ICPNP crystal were determined by UV-vis-NIR spectral study. Thermal behavior of ICPNP was studied by thermo gravimetric and differential thermal analyses (TG/DTA). The relative dielectric permittivity was calculated for various temperature ranges. Laser damage threshold of ICPNP crystal was found to be 1.9 GW/cm2 using an Nd:YAG laser. A Z-scan technique was employed to measure the nonlinear absorption coefficient, nonlinear refractive index and nonlinear optical susceptibility. Optical limiting behavior of ICPNP was observed at 35 mW input power.

  13. Tailoring quantum structures for active photonic crystals

    DEFF Research Database (Denmark)

    Kuznetsova, Nadezda

    This work is dedicated to the tailoring of quantum structures, with particular attention to the integration of selective area grown (SAG) active material into photonic crystal (PhC) slabs. The platform based on active PhC is vital to the realization of highly efficient elements with low energy...... consumption for on-chip and chip-to-chip optical communication. In order to develop metal-organic vapor phase epitaxial selective area etching and growth, a mask was fabricated in the HSQ e-beam resist including optimization of exposure and development conditions. By use of CBr4 as an etchant, in situ etching...... area and between the structures oriented along the [0-1-1] and [0-11] directions. Strong wavelength dependence with variations of the mask width of a few μm and opening sizes of hundreds of nanometers was observed. Incorporation of an active medium into PhC structures has showed promising results...

  14. Isolation and Crystal Structure of Horminone

    Institute of Scientific and Technical Information of China (English)

    陈晓; 廖仁安; 翁林红; 谢庆兰; 邓锋杰

    2000-01-01

    The horminone (C20H28O4, Mr= 332.85) was first isolated from the leaves of Rabdosia Serra (Maxim) Hara and its crystal structure was determined by X-ray diffraction method. Horminone is orthorhombic with space group P21P21P21, a=7.7186(7), b=9.5506(9), c=24.227(2) A, V=1785.9(3) A3, Z=4, Dc=1.236g/cm3, λ=0. 71073 A , μ(MoKα)=0. 085mm-1, F(000)=720. The structure was refined to R=0. 0369, wR=0.0978 for 2446 reflections with I>2σ(Ⅰ). X-ray diffraction analysis reveals that there are three six-membered rings in the title molecule. Ring A is in the chair conformation, ring C has the structure of quinone and there are two intermolecular hydrogen bonds between two molecules.

  15. Crystal Structure of Cold Compressed Graphite

    Science.gov (United States)

    Amsler, Maximilian; Flores-Livas, José A.; Lehtovaara, Lauri; Balima, Felix; Ghasemi, S. Alireza; Machon, Denis; Pailhès, Stéphane; Willand, Alexander; Caliste, Damien; Botti, Silvana; San Miguel, Alfonso; Goedecker, Stefan; Marques, Miguel A. L.

    2012-02-01

    Through a systematic structural search we found an allotrope of carbon with Cmmm symmetry which we predict to be more stable than graphite for pressures above 10 GPa. This material, which we refer to as Z-carbon, is formed by pure sp3 bonds and it provides an explanation to several features in experimental x-ray diffraction and Raman spectra of graphite under pressure. The transition from graphite to Z-carbon can occur through simple sliding and buckling of graphene sheets. Our calculations predict that Z-carbon is a transparent wide band-gap semiconductor with a hardness comparable to diamond.

  16. Crystal structure of (ferrocenylmethyldimethylammonium hydrogen oxalate

    Directory of Open Access Journals (Sweden)

    Mamadou Ndiaye

    2015-08-01

    Full Text Available The crystal structure of the title salt, [Fe(C5H5(C8H13N](HC2O4, consists of discrete (ferrocenylmethyldimethylammonium cations and hydrogen oxalate anions. The anions are connected through a strong O—H...O hydrogen bond, forming linear chains running parallel to [100]. The cations are linked to the anions through bifurcated N—H...(O,O′ hydrogen bonds. Weak C—H...π interactions between neighbouring ferrocenyl moieties are also observed.

  17. [Crystal and molecular structure of cytisine salts].

    Science.gov (United States)

    Niedźwiecka, Julia; Przybył, Anna K; Kubicki, Maciej

    2012-01-01

    Cytisine is an alkaloid of plant origin. It is a toxic substance, obtained on an industrial scale from Laburnum anagyroides also known as common laburnum. Today is used in the preparation of anti-smoking products as an agonist of nicotinic receptors nAChR-alpha4beta2. Thanks to crystallographic methods we can examine and describe with high accuracy the actual structure of complex chemical compounds. This work aims to present a series of tests carried out on crystals of cytisine salts, after a prior isolation of cytisine from the seeds of laburnum anagyroides.

  18. Crystal structure of hexaaquadichloridoytterbium(III chloride

    Directory of Open Access Journals (Sweden)

    Kevin M. Knopf

    2015-06-01

    Full Text Available The crystal structure of the title compound, [YbCl2(H2O6]Cl, was determined at 110 K. Samples were obtained from evaporated acetonitrile solutions containing the title compound, which consists of a [YbCl2(H2O6]+ cation and a Cl− anion. The cations in the title compound sit on a twofold axis and form O—H...Cl hydrogen bonds with the nearby Cl− anion. The coordination geometry around the metal centre forms a distorted square antiprism. The ytterbium complex is isotypic with the europium complex [Tambrornino et al. (2014. Acta Cryst. E70, i27].

  19. Crystal Structure of Marburg Virus VP24

    OpenAIRE

    Zhang, Adrianna P. P.; Bornholdt, Zachary A.; Abelson, Dafna M.; Saphire, Erica Ollmann

    2014-01-01

    The VP24 protein plays an essential, albeit poorly understood role in the filovirus life cycle. VP24 is only 30% identical between Marburg virus and the ebolaviruses. Furthermore, VP24 from the ebolaviruses is immunosuppressive, while that of Marburg virus is not. The crystal structure of Marburg virus VP24, presented here, reveals that although the core is similar between the viral genera, Marburg VP24 is distinguished by a projecting β-shelf and an alternate conformation of the N-terminal p...

  20. Crystal structure of Marburg virus VP24.

    Science.gov (United States)

    Zhang, Adrianna P P; Bornholdt, Zachary A; Abelson, Dafna M; Saphire, Erica Ollmann

    2014-05-01

    The VP24 protein plays an essential, albeit poorly understood role in the filovirus life cycle. VP24 is only 30% identical between Marburg virus and the ebolaviruses. Furthermore, VP24 from the ebolaviruses is immunosuppressive, while that of Marburg virus is not. The crystal structure of Marburg virus VP24, presented here, reveals that although the core is similar between the viral genera, Marburg VP24 is distinguished by a projecting β-shelf and an alternate conformation of the N-terminal polypeptide.

  1. Elasticity of some mantle crystal structures. II.

    Science.gov (United States)

    Wang, H.; Simmons, G.

    1973-01-01

    The single-crystal elastic constants are determined as a function of pressure and temperature for rutile structure germanium dioxide (GeO2). The data are qualitatively similar to those of rutile TiO2 measured by Manghnani (1969). The compressibility in the c direction is less than one-half that in the a direction, the pressure derivative of the shear constant is negative, and the pressure derivative of the bulk modulus has a relatively high value of about 6.2. According to an elastic strain energy theory, the negative shear modulus derivative implies that the kinetic barrier to diffusion decreases with increasing pressure.

  2. Crystal structure of a DNA catalyst.

    Science.gov (United States)

    Ponce-Salvatierra, Almudena; Wawrzyniak-Turek, Katarzyna; Steuerwald, Ulrich; Höbartner, Claudia; Pena, Vladimir

    2016-01-14

    Catalysis in biology is restricted to RNA (ribozymes) and protein enzymes, but synthetic biomolecular catalysts can also be made of DNA (deoxyribozymes) or synthetic genetic polymers. In vitro selection from synthetic random DNA libraries identified DNA catalysts for various chemical reactions beyond RNA backbone cleavage. DNA-catalysed reactions include RNA and DNA ligation in various topologies, hydrolytic cleavage and photorepair of DNA, as well as reactions of peptides and small molecules. In spite of comprehensive biochemical studies of DNA catalysts for two decades, fundamental mechanistic understanding of their function is lacking in the absence of three-dimensional models at atomic resolution. Early attempts to solve the crystal structure of an RNA-cleaving deoxyribozyme resulted in a catalytically irrelevant nucleic acid fold. Here we report the crystal structure of the RNA-ligating deoxyribozyme 9DB1 (ref. 14) at 2.8 Å resolution. The structure captures the ligation reaction in the post-catalytic state, revealing a compact folding unit stabilized by numerous tertiary interactions, and an unanticipated organization of the catalytic centre. Structure-guided mutagenesis provided insights into the basis for regioselectivity of the ligation reaction and allowed remarkable manipulation of substrate recognition and reaction rate. Moreover, the structure highlights how the specific properties of deoxyribose are reflected in the backbone conformation of the DNA catalyst, in support of its intricate three-dimensional organization. The structural principles underlying the catalytic ability of DNA elucidate differences and similarities in DNA versus RNA catalysts, which is relevant for comprehending the privileged position of folded RNA in the prebiotic world and in current organisms.

  3. Electronic and crystal structures of thermoelectric CaMgSi intermetallic compound

    Energy Technology Data Exchange (ETDEWEB)

    Miyazaki, Hidetoshi, E-mail: miyazaki@nitech.ac.jp [Department of Frontier Materials, Nagoya Institute of Technology, Nagoya 466-8555 (Japan); Inukai, Manabu [Department of Frontier Materials, Nagoya Institute of Technology, Nagoya 466-8555 (Japan); Soda, Kazuo [Department of Quantum Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464-8603 (Japan); Miyazaki, Nobufumi; Adachi, Nozomu; Todaka, Yoshikazu [Department of Mechanical Engineering, Toyohashi University of Technology, Toyohashi 441-8580 (Japan); Nishino, Yoichi [Department of Frontier Materials, Nagoya Institute of Technology, Nagoya 466-8555 (Japan)

    2016-01-15

    Highlights: • We report the electronic and crystal structures of the TiNiSi-type CaMgSi compound. • CaMgSi has a semiconductor-like electronic structure with a small band gap. • CaMgSi is a Mott-type insulator owing to strongly correlated electrons effect. - Abstract: We investigated the electronic and crystal structures of a new thermoelectric material, CaMgSi compound, by using synchrotron radiation photoemission spectroscopy (SR-PES), synchrotron radiation X-ray powder diffraction (SR-XRD) measurements, and electronic band structure calculation to understand the way leading to improvement in the thermoelectric properties of this material. Electronic band structure calculation of the CaMgSi compound using the crystal structure determined from SR-XRD measurement showed a semi-metallic electronic structure with a pseudo-gap at the Fermi level. In contrast to the predicted semi-metallic electronic structure, the SR-PES results showed a small semiconductor-like gap at the Fermi level. This result revealed that the CaMgSi compound is a Mott-type insulator owing to strongly correlated electrons effect in the Ca 3d and Mg 3p states being well hybridized with those in the Si 3p states. The observed electronic structure of the CaMgSi compound suggests that an optimal carrier doping exists to best control the n- and p-type thermoelectric properties and enhance the power factors.

  4. Band gaps in grid structure with periodic local resonator subsystems

    Science.gov (United States)

    Zhou, Xiaoqin; Wang, Jun; Wang, Rongqi; Lin, Jieqiong

    2017-09-01

    The grid structure is widely used in architectural and mechanical field for its high strength and saving material. This paper will present a study on an acoustic metamaterial beam (AMB) based on the normal square grid structure with local resonators owning both flexible band gaps and high static stiffness, which have high application potential in vibration control. Firstly, the AMB with variable cross-section frame is analytically modeled by the beam-spring-mass model that is provided by using the extended Hamilton’s principle and Bloch’s theorem. The above model is used for computing the dispersion relation of the designed AMB in terms of the design parameters, and the influences of relevant parameters on band gaps are discussed. Then a two-dimensional finite element model of the AMB is built and analyzed in COMSOL Multiphysics, both the dispersion properties of unit cell and the wave attenuation in a finite AMB have fine agreement with the derived model. The effects of design parameters of the two-dimensional model in band gaps are further examined, and the obtained results can well verify the analytical model. Finally, the wave attenuation performances in three-dimensional AMBs with equal and unequal thickness are presented and discussed.

  5. Syntheses and Crystal Structures of Pyrazoline Derivants

    Institute of Scientific and Technical Information of China (English)

    SHI Hai-Bin; JI Shun-Jun; ZHANG Yong

    2005-01-01

    Two pyrazoline derivants 1-(2-benzothiazole)-3-phenyl-5-(3-thiophene)-2- pyrazoline (BPTP) and 1-(2-benzothiazole)-3-(2-thiophene)-5-phenyl-2-pyrazoline (BTPP) have been synthe- sized and their crystal structures were determined by X-ray single-crystal diffraction.Crystal of BPTP belongs to triclinic, space group P with a = 9.4430(11), b = 9.9384(13), c = 9.9394(13) (A), α = 83.107(10), β = 79.947(10), γ = 70.221(7)o, V = 862.42(19) (A)3, Z = 2, Dc = 1.392 g/cm3, μ(MoKα) = 0.316 mm-1, F(000) = 376, λ = 0.71070 (A), (Δρ)max = 0.348, (Δρ)min = -0.481 e/(A)3, the final R = 0.0407 and wR = 0.1055 for 2844 observed reflections with I > 2σ(I).Crystal of BTPP is of monoclinic, space group P21/c with a = 11.6158(17), b = 11.2796(18), c = 13.082(2) (A), α = 90, β = 91.087(4), γ = 90o, V = 1713.7(5) (A)3, Z = 4, Dc = 1.401 g/cm3, μ(MoKα) = 0.318 mm-1, Mr = 361.07, F(000) = 752, λ = 0.71070 (A), (Δρ)max = 0.322, (Δρ)min = -0.330 e/(A)3, the final R = 0.0563 and wR = 0.1058 for 3434 observed reflections with I > 2σ(I).

  6. Electronic Structures of PbMoO4 Crystals with F-Type Colour Centres

    Institute of Scientific and Technical Information of China (English)

    CHEN Jian-Yu; ZHANG Qi-Ren; LIU Ting-Yu; SHAO Ze-Xu; PU Chun-Ying

    2007-01-01

    Electronic structures of PbMo04 crystals containing F-type colour centres with the lattice structure optimized are studied within the framework of the fully relativistic self-consistent Dirac-SIater theory, using a numerically discrete variational (DV-Xα) method. The calculated results show that F and F+ centres have donor energy levels in the forbidden band. The optical transition energies are 2.166eV and 2.197eV, respectively, corresponding to the 580 nm absorption bands in PbMoO4 crystal. The 580 nm absorption band in PbMoO4 is originated from the F-type colour centres.

  7. Optical nonreciprocal transmission in an asymmetric silicon photonic crystal structure

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Zheng; Chen, Juguang; Ji, Mengxi; Huang, Qingzhong; Xia, Jinsong; Wang, Yi, E-mail: yingwu2@126.com, E-mail: ywangwnlo@mail.hust.edu.cn [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Wu, Ying, E-mail: yingwu2@126.com, E-mail: ywangwnlo@mail.hust.edu.cn [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)

    2015-11-30

    An optical nonreciprocal transmission (ONT) is realized by employing the nonlinear effects in a compact asymmetric direct-coupled nanocavity-waveguide silicon photonic crystal structure with a high loaded quality factor (Q{sub L}) of 42 360 and large extinction ratio exceeding 30 dB. Applying a single step lithography and successive etching, the device can realize the ONT in an individual nanocavity, alleviating the requirement to accurately control the resonance of the cavities. A maximum nonreciprocal transmission ratio of 21.1 dB as well as a working bandwidth of 280 pm in the telecommunication band are obtained at a low input power of 76.7 μW. The calculated results by employing a nonlinear coupled-mode model are in good agreement with the experiment.

  8. Crossing points in the electronic band structure of vanadium oxide

    Directory of Open Access Journals (Sweden)

    Keshav N. Shrivastava

    2010-03-01

    Full Text Available The electronic band structures of several models of vanadium oxide are calculated. In the models 1-3, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 4 vanadium atoms. In model 1, a=b=c 2.3574 Å; in model 2, a= 4.7148 Å, b= 2.3574 Å and c= 2.3574 Å; and in model 3, a= 4.7148 Å, b= 2.3574 Å and c= 4.7148 Å. In the models 4-6, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 2 vanadium atoms. In model 4, a=b= 4.551 Å and c= 2.851 Å; in model 5, a=b=c= 3.468 Å; and in model 6, a=b=c= 3.171 Å. We have searched for a crossing point in the band structure of all the models. In model 1 there is a point at which five bands appear to meet but the gap is 7.3 meV. In model 2 there is a crossing point between G and F points and there is a point between F and Q with the gap ≈ 3.6608 meV. In model 3, the gap is very small, ~ 10-5 eV. In model 4, the gap is 5.25 meV. In model 5, the gap between Z and G points is 2.035 meV, and in model 6 the gap at Z point is 4.3175 meV. The crossing point in model 2 looks like one line is bent so that the supersymmetry is broken. When pseudopotentials are replaced by a full band calculation, the crossing point changes into a gap of 2.72 x 10-4 eV.

  9. Banding and electronic structures of metal azides——Sensitivity and conductivity

    Institute of Scientific and Technical Information of China (English)

    肖鹤鸣; 李永富

    1995-01-01

    By using both DV-Xα and EH-CO methods, the calculation studies of the structure-property relationships of a series of metal azides, of their clusters’ electronic structures in ground and excited states, of their systems with cation vacancy and the doped Pb(N3)2, as well as their crystal band structures have been conducted. The results show that the sensitivity of ionic-type metal azides varies with the degree of difficulty of electronic transition of the losing charge on N3. A metal azide with cation vacancies has a greater sensitivity than the perfect one. When doped with monovalent metal ions, lead azide’s sensitivity increased; when with trivalent ones, its sensitivity decreased; when with divalent ones, little of it changed. Compared with heavy metal azides. an alkali metal azide has a larger band gap, a smaller band width and a greater transition energy of frontier electron with a smaller amount of losing charge on N3, and thus has lower sensitivity and conductivity than heavy metal azides.

  10. Tunable Lamb wave band gaps in two-dimensional magnetoelastic phononic crystal slabs by an applied external magnetostatic field.

    Science.gov (United States)

    Zhou, Changjiang; Sai, Yi; Chen, Jiujiu

    2016-09-01

    This paper theoretically investigates the band gaps of Lamb mode waves in two-dimensional magnetoelastic phononic crystal slabs by an applied external magnetostatic field. With the assumption of uniformly oriented magnetization, an equivalent piezomagnetic material model is used. The effects of magnetostatic field on phononic crystals are considered carefully in this model. The numerical results indicate that the width of the first band gap is significantly changed by applying the external magnetic field with different amplitude, and the ratio between the maximum and minimum gap widths reaches 228%. Further calculations demonstrate that the orientation of the magnetic field obviously affects the width and location of the first band gap. The contactless tunability of the proposed phononic crystal slabs shows many potential applications of vibration isolation in engineering. Copyright © 2016 Elsevier B.V. All rights reserved.

  11. Crystal structure of yeast Sco1

    Energy Technology Data Exchange (ETDEWEB)

    Abajian, Carnie; Rosenzweig, Amy C. (NWU)

    2010-03-05

    The Sco family of proteins are involved in the assembly of the dinuclear CuA site in cytochrome c oxidase (COX), the terminal enzyme in aerobic respiration. These proteins, which are found in both eukaryotes and prokaryotes, are characterized by a conserved CXXXC sequence motif that binds copper ions and that has also been proposed to perform a thiol:disulfide oxidoreductase function. The crystal structures of Saccharomyces cerevisiae apo Sco1 (apo-ySco1) and Sco1 in the presence of copper ions (Cu-ySco1) were determined to 1.8- and 2.3-{angstrom} resolutions, respectively. Yeast Sco1 exhibits a thioredoxin-like fold, similar to that observed for human Sco1 and a homolog from Bacillus subtilis. The Cu-ySco1 structure, obtained by soaking apo-ySco1 crystals in copper ions, reveals an unexpected copper-binding site involving Cys181 and Cys216, cysteine residues present in ySco1 but not in other homologs. The conserved CXXXC cysteines, Cys148 and Cys152, can undergo redox chemistry in the crystal. An essential histidine residue, His239, is located on a highly flexible loop, denoted the Sco loop, and can adopt positions proximal to both pairs of cysteines. Interactions between ySco1 and its partner proteins yeast Cox17 and yeast COX2 are likely to occur via complementary electrostatic surfaces. This high-resolution model of a eukaryotic Sco protein provides new insight into Sco copper binding and function.

  12. Expansion of lower-frequency locally resonant band gaps using a double-sided stubbed composite phononic crystals plate with composite stubs

    Energy Technology Data Exchange (ETDEWEB)

    Li, Suobin; Chen, Tianning [School of Mechanical Engineering and State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Wang, Xiaopeng, E-mail: xpwang@mail.xjtu.edu.cn [School of Mechanical Engineering and State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Li, Yinggang [Key Laboratory of High Performance Ship Technology of Ministry of Education, Wuhan University of Technology, Wuhan, 430070 (China); Chen, Weihua [School of Mechanical Engineering and State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China)

    2016-06-03

    We studied the expansion of locally resonant complete band gaps in two-dimensional phononic crystals (PCs) using a double-sided stubbed composite PC plate with composite stubs. Results show that the introduction of the proposed structure gives rise to a significant expansion of the relative bandwidth by a factor of 1.5 and decreases the opening location of the first complete band gap by a factor of 3 compared to the classic double-sided stubbed PC plate with composite stubs. Furthermore, more band gaps appear in the lower-frequency range (0.006). These phenomena can be attributed to the strong coupling between the “analogous rigid mode” of the stub and the anti-symmetric Lamb modes of the plate. The “analogous rigid mode” of the stub is produced by strengthening the localized resonance effect of the composite plates through the double-sided stubs, and is further strengthened through the introduction of composite stubs. The “analogous rigid mode” of the stubs expands the out-of-plane band gap, which overlaps with in-plane band gap in the lower-frequency range. As a result, the complete band gap is expanded and more complete band gaps appear. - Highlights: • Expansion of lower-frequency locally resonant BGs using novel composite phononic crystals plates. • The proposed structure expands the relative bandwidth 1.5 times compared to classic doubled-sided stubbed PC plates. • The opening location of the first complete BG decreases 3 times compared to the classic doubled-sided stubbed PC plates. • The concept “analogous rigid mode” is put forward to explain the expansion of lower-frequency BGs.

  13. Modeling of photonic crystal waveguide structures

    Science.gov (United States)

    Richter, Ivan; Kwiecien, Pavel; Šiňor, Milan; Haiduk, Adam

    2007-05-01

    Photonic crystal (PhC) structures and photonic structures based on them represent nowadays very promising structures of artificial origin. Since they exhibit very specific properties and characteristics that can be very difficult (or even impossible) to realize by other means, they represent a significant part of new artificially made metamaterial classes. For studying and modeling properties of PhC structures, we have applied, implemented and partially improved various complementary techniques: the 2D plane wave expansion (PWE) method, and the 2D finite-difference time-domain (FDTD) method with perfectly matched layers. Also, together with these in-house methods, other tools available in the field have been applied, including, e.g. MIT MPB (PWE), F2P (FDTD) and CAMFR (bidirectional expansion and propagation mode matching method) packages. We have applied these methods to several PhC waveguide structure examples, studying the effects of varying the key parameters and geometry. Such a study is relevant for proper understanding of physical mechanisms and for optimization and fabrication recommendations. Namely, in this contribution, we have concentrated on several examples of PhC waveguide structure simulations, of two types of guides (dielectric-rode type and air-hole type), with several geometries: rectangular lattice with either rectangular or chessboard inclusions. The modeling results are compared and discussed.

  14. Temperature dependent spin structures in Hexaferrite crystal

    Energy Technology Data Exchange (ETDEWEB)

    Chao, Y.C. [Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan (China); Lin, J.G., E-mail: jglin@ntu.edu.tw [Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan (China); Chun, S.H.; Kim, K.H. [Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of)

    2016-01-01

    In this work, the Hexaferrite Ba{sub 0.5}Sr{sub 1.5}Zn{sub 2}Fe{sub 12}O{sub 22} (BSZFO) is studied due to its interesting characteristics of long-wavelength spin structure. Ferromagnetic resonance (FMR) is used to probe the magnetic states of BSZFO single crystal and its temperature dependence behavior is analyzed by decomposing the multiple lines of FMR spectra into various phases. Distinguished phase transition is observed at 110 K for one line, which is assigned to the ferro(ferri)-magnetic transition from non-collinear to collinear spin state. - Highlights: • For the first time Ferromagnetic Resonance is used to probe the local magnetic structure of Ba{sub 0.5}Sr{sub 1.5}Zn{sub 2}Fe{sub 12}O{sub 22.} • The multiphases in the single crystal is identified, which provides important information toward its future application for the magnetoelectric devices.

  15. Syntheses and Crystal Structures of Ferrocenoindenes

    Directory of Open Access Journals (Sweden)

    Gerhard Laus

    2013-02-01

    Full Text Available Ferrocenoindenes display planar chirality and thus represent valuable ligands for asymmetric catalysis. Here, we report on the synthesis of novel 3-(1,1-dibromomethyleneferroceno[1,2-a]indene, (Z-3-(1-bromomethylene-6-iodoferroceno[1,2-a]indene, and benzo[5,6-f]ferroceno[2,3,a]inden-1-one. Any application-oriented design of chiral catalysts requires fundamental knowledge about the ligands involved, not only in terms of atom-connectivity, but also in terms of their three-dimensional structure and steric demand. Therefore, the crystal structures of 2-ferrocenylbenzoic acid, ferroceno[1,2-a]indene, and (Z-3-(1-bromomethylene-6-iodoferroceno[1,2-a]indene have been determined. The bond-lengths that can be retrieved therefrom also allow for an estimation of the reactivity of the aryl-iodo, bromo-methylidene and dibromomethylidene moieties.

  16. Crystal structure of human nicotinamide riboside kinase.

    Science.gov (United States)

    Khan, Javed A; Xiang, Song; Tong, Liang

    2007-08-01

    Nicotinamide riboside kinase (NRK) has an important role in the biosynthesis of NAD(+) as well as the activation of tiazofurin and other NR analogs for anticancer therapy. NRK belongs to the deoxynucleoside kinase and nucleoside monophosphate (NMP) kinase superfamily, although the degree of sequence conservation is very low. We report here the crystal structures of human NRK1 in a binary complex with the reaction product nicotinamide mononucleotide (NMN) at 1.5 A resolution and in a ternary complex with ADP and tiazofurin at 2.7 A resolution. The active site is located in a groove between the central parallel beta sheet core and the LID and NMP-binding domains. The hydroxyl groups on the ribose of NR are recognized by Asp56 and Arg129, and Asp36 is the general base of the enzyme. Mutation of residues in the active site can abolish the catalytic activity of the enzyme, confirming the structural observations.

  17. Crystal Structure of Human Nicotinamide Riboside Kinase

    Energy Technology Data Exchange (ETDEWEB)

    Khan,J.; Xiang, S.; Tong, L.

    2007-01-01

    Nicotinamide riboside kinase (NRK) has an important role in the biosynthesis of NAD{sup +} as well as the activation of tiazofurin and other NR analogs for anticancer therapy. NRK belongs to the deoxynucleoside kinase and nucleoside monophosphate (NMP) kinase superfamily, although the degree of sequence conservation is very low. We report here the crystal structures of human NRK1 in a binary complex with the reaction product nicotinamide mononucleotide (NMN) at 1.5 {angstrom} resolution and in a ternary complex with ADP and tiazofurin at 2.7 {angstrom} resolution. The active site is located in a groove between the central parallel {beta} sheet core and the LID and NMP-binding domains. The hydroxyl groups on the ribose of NR are recognized by Asp56 and Arg129, and Asp36 is the general base of the enzyme. Mutation of residues in the active site can abolish the catalytic activity of the enzyme, confirming the structural observations.

  18. The Crystal Structure of Human Argonaute2

    Energy Technology Data Exchange (ETDEWEB)

    Schirle, Nicole T.; MacRae, Ian J. (Scripps)

    2012-07-18

    Argonaute proteins form the functional core of the RNA-induced silencing complexes that mediate RNA silencing in eukaryotes. The 2.3 angstrom resolution crystal structure of human Argonaute2 (Ago2) reveals a bilobed molecule with a central cleft for binding guide and target RNAs. Nucleotides 2 to 6 of a heterogeneous mixture of guide RNAs are positioned in an A-form conformation for base pairing with target messenger RNAs. Between nucleotides 6 and 7, there is a kink that may function in microRNA target recognition or release of sliced RNA products. Tandem tryptophan-binding pockets in the PIWI domain define a likely interaction surface for recruitment of glycine-tryptophan-182 (GW182) or other tryptophan-rich cofactors. These results will enable structure-based approaches for harnessing the untapped therapeutic potential of RNA silencing in humans.

  19. Acousto-optic modulation of a photonic crystal nanocavity with Lamb waves in microwave K band

    CERN Document Server

    Tadesse, Semere A; Liu, Qiyu; Li, Mo

    2015-01-01

    Integrating nanoscale electromechanical transducers and nanophotonic devices potentially can enable new acousto-optic devices to reach unprecedented high frequencies and modulation efficiency. Here, we demonstrate acousto-optic modulation of a photonic crystal nanocavity using Lamb waves with frequency up to 19 GHz, reaching the microwave K band. The devices are fabricated in suspended aluminum nitride membrane. Excitation of acoustic waves is achieved with interdigital transducers with periods as small as 300 nm. Confining both acoustic wave and optical wave within the thickness of the membrane leads to improved acousto-optic modulation efficiency in the new devices than that obtained in previous surface acoustic wave devices. Our system demonstrates a novel scalable optomechanical platform where strong acousto-optic coupling between cavity-confined photons and high frequency traveling phonons can be explored.

  20. Acousto-optic modulation of a photonic crystal nanocavity with Lamb waves in microwave K band

    Energy Technology Data Exchange (ETDEWEB)

    Tadesse, Semere A. [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States); School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455 (United States); Li, Huan; Liu, Qiyu; Li, Mo, E-mail: moli@umn.edu [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

    2015-11-16

    Integrating nanoscale electromechanical transducers and nanophotonic devices potentially can enable acousto-optic devices to reach unprecedented high frequencies and modulation efficiency. Here, we demonstrate acousto-optic modulation of a photonic crystal nanocavity using Lamb waves with frequency up to 19 GHz, reaching the microwave K band. The devices are fabricated in suspended aluminum nitride membrane. Excitation of acoustic waves is achieved with interdigital transducers with period as small as 300 nm. Confining both acoustic wave and optical wave within the thickness of the membrane leads to improved acousto-optic modulation efficiency in these devices than that obtained in previous surface acoustic wave devices. Our system demonstrates a scalable optomechanical platform where strong acousto-optic coupling between cavity-confined photons and high frequency traveling phonons can be explored.

  1. Optical Properties and Band Gap of Single- and Few-Layer MoTe2 Crystals

    Science.gov (United States)

    Aslan, Ozgur Burak; Ruppert, Claudia; Heinz, Tony

    2015-03-01

    Single- and few-layer crystals of exfoliated MoTe2 have been characterized spectroscopically by photoluminescence, Raman scattering, and optical absorption measurements. We find that MoTe2 in the monolayer limit displays strong photoluminescence. On the basis of complementary optical absorption results, we conclude that monolayer MoTe2 is a direct-gap semiconductor with an optical band gap of 1.10 eV. This new monolayer material extends the spectral range of atomically thin direct-gap materials from the visible to the near-infrared. Supported by the NSF through Grant DMR-1124894 for sample preparation and characterization by the O?ce of Naval Research for analysis. C.R. acknowledges support from the Alexander von Humboldt Foundation.

  2. A broad slow frequencies band and high slowing down factor by using one-dimensional hybrid periodic/Fibonacci photonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Ben Ali, N; Kanzari, M, E-mail: naimgi2@yahoo.fr [Photovoltaic and Semiconductor Materials Laboratory, El-Manar University-ENIT PO Box 37, Le belvedere 1002-Tunis (Tunisia)

    2010-11-15

    By using a theoretical model based on Transfer Matrix Method (TMM) for normal incidence simulator, and for serial (S) polarisation, the slowing of light in one-dimensional (1D) hybrid (Fibonacci{sub 1}/periodic/Fibonacci{sub 2}) photonic crystals is studied at visible frequency band. Effects of the periodicity, the non-periodicity and the number of layers of each photonic structure on the slowing down of light are discussed. The higher slowing down factors was obtained by the hybrid Fibonacci{sub 1}/periodic/Fibonacci{sub 2} structures. This slowing down factors is greater than those corresponding to the periodic, the Fibonacci, the Thue-Morse and the Cantor band-gap structures. In addition this hybrid structure gives the possibility to slowing several frequencies

  3. Average and Local Crystal Structures of (Ga(1-x)Znx)(N(1-x)Ox) Solid Solution Nanoparticles.

    Science.gov (United States)

    Feygenson, Mikhail; Neuefeind, Joerg C; Tyson, Trevor A; Schieber, Natalie; Han, Wei-Qiang

    2015-12-07

    We report a comprehensive study of the crystal structure of (Ga(1-x)Znx)(N(1-x)Ox) solid solution nanoparticles by means of neutron and synchrotron X-ray scattering. In our study, we used four different types of (Ga(1-x)Znx)(N(1-x)Ox) nanoparticles, with diameters of 10-27 nm and x = 0.075-0.51, which show energy band gaps from 2.21 to 2.61 eV. Rietveld analysis of the neutron diffraction data revealed that the average crystal structure is hexagonal wurtzite (space group P63mc) for the larger nanoparticles, while the crystal structure of smaller nanoparticles is disordered hexagonal. Pair-distribution-function analysis found that the intermediate crystal structure retains a "motif" of the average one; however, the local structure is more disordered. The implications of disorder on the reduced energy band gap are discussed.

  4. Wakefield Monitor Experiments with X-Band Accelerating Structures

    CERN Document Server

    Lillestøl, Reidar; Corsini, Roberto; Döbert, Steffen; Farabolini, Wilfrid; Malina, Lukas; Pfingstner, Juergen; Wuensch, Walter

    2015-01-01

    The accelerating structures for CLIC must be aligned with a precision of a few um with respect to the beam trajectory in order to mitigate emittance growth due to transverse wake fields. We report on first results from wake field monitor tests in an X-band structure, with a probe beam at the CLIC Test Facility. The monitors are currently installed in the CLIC Two-Beam Module. In order to fully demonstrate the feasibility of using wakefield monitors for CLIC, the precision of the monitors must be verified using a probe beam while simultaneously filling the structure with high power rf used to drive the accelerating mode. We outline plans to perform such a demonstration in the CLIC Test Facility.

  5. Collective Band Structures in Neutron-Rich 108Mo Nucleus

    Institute of Scientific and Technical Information of China (English)

    DING Huai-Bo; WANG Jian-Guo; XU Qiang; ZHU Sheng-Jiang; J. H. Hamilton; A. V. Ramayya; J. K. Hwang; Y. X. Luo; J. O. Rasmussen; I. Y. Lee; CHE Xing-Lai

    2007-01-01

    High spin states in the neutron-rich 108Mo nucleus are studied by measuring prompt γ-rays following the spontaneous fission of 252Cf with a Gammasphere detector array. The ground-state band is confirmed, and the one-phonon γ-vibrational band is updated with spin up to 12 h. A new collective band with the band head level at 1422.4 keV is suggested as a two-phonon γ-vibrational band. Another new band is proposed as a two-quasi-proton excitation band. Systematic characteristics of the collective bands are discussed.

  6. Structural Transitions in Cholesteric Liquid Crystal Droplets

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Ye; Bukusoglu, Emre; Martinez-Gonzalez, Jose A.; Rahimi, Mohammad; Roberts, Tyler F.; Zhang, Rui; Wang, Xiaoguang; Abbott, Nicholas L.; de Pablo, Juan J.

    2016-07-01

    Confinement of cholesteric liquid crystals (ChLC) into droplets leads to a delicate interplay between elasticity, chirality, and surface energy. In this work, we rely on a combination of theory and experiments to understand the rich morphological behavior that arises from that balance. More specifically, a systematic study of micrometer-sized ChLC droplets is presented as a function of chirality and surface energy (or anchoring). With increasing chirality, a continuous transition is observed from a twisted bipolar structure to a radial spherical structure, all within a narrow range of chirality. During such a transition, a bent structure is predicted by simulations and confirmed by experimental observations. Simulations are also able to capture the dynamics of the quenching process observed in experiments. Consistent with published work, it is found that nanoparticles are attracted to defect regions on the surface of the droplets. For weak anchoring conditions at the nanoparticle surface, ChLC droplets adopt a morphology similar to that of the equilibrium helical phase observed for ChLCs in the bulk. As the anchoring strength increases, a planar bipolar structure arises, followed by a morphological transition to a bent structure. The influence of chirality and surface interactions are discussed in the context of the potential use of ChLC droplets as stimuli-responsive materials for reporting molecular adsorbates.

  7. Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Li, Z.Q.; Henriksen, E.A.; Jiang, Z.; Hao, Zhao; Martin, Michael C.; Kim, P.; Stormer, H.L.; Basov, Dimitri N.

    2008-12-10

    We report on infrared spectroscopy of bilayer graphene integrated in gated structures. We observe a significant asymmetry in the optical conductivity upon electrostatic doping of electrons and holes. We show that this finding arises from a marked asymmetry between the valence and conduction bands, which is mainly due to the inequivalence of the two sublattices within the graphene layer and the next-nearest-neighbor interlayer coupling. From the conductivity data, the energy difference of the two sublattices and the interlayer coupling energy are directly determined.

  8. Electronic band structure of calcium selenide under pressure

    Energy Technology Data Exchange (ETDEWEB)

    Louail, L. [Faculty of Sciences, Department of Physics, University of Setif, Setif (Algeria)], E-mail: llouail@yahoo.fr; Haddadi, K.; Maouche, D.; Ali Sahraoui, F.; Hachemi, A. [Faculty of Sciences, Department of Physics, University of Setif, Setif (Algeria)

    2008-09-01

    Energy band structures under pressure of calcium selenide (CaSe) were calculated using the plane-wave pseudopotential code CASTEP. The results show a progressive transition from a direct to an indirect gap semiconductor at a pressure of about 2 GPa, in the B1 phase. An insulator-conductor change was also observed at 70 GPa, in the B2 phase. Concerning CaSe, these two results could not be evidenced in previous literature. Hence, our work is a first attempt in this direction.

  9. Colloidal Photonic Crystals Containing Silver Nanoparticles with Tunable Structural Colors

    Directory of Open Access Journals (Sweden)

    Chun-Feng Lai

    2016-05-01

    Full Text Available Polystyrene (PS colloidal photonic crystals (CPhCs containing silver nanoparticles (AgNPs present tunable structural colors. PS CPhC color films containing a high concentration of AgNPs were prepared using self-assembly process through gravitational sedimentation method. High-concentration AgNPs were deposited on the bottom of the substrate and acted as black materials to absorb background and scattering light. Brilliant structural colors were enhanced because of the absorption of incoherent scattering light, and color saturation was increased by the distribution AgNPs on the PS CPhC surfaces. The vivid iridescent structural colors of AgNPs/PS hybrid CPhC films were based on Bragg diffraction and backward scattering absorption using AgNPs. The photonic stop band of PS CPhCs and AgNPs/PS hybrid CPhCs were measured by UV–visible reflection spectrometry and calculated based on the Bragg–Snell law. In addition, the tunable structural colors of AgNPs/PS hybrid CPhC films were evaluated using color measurements according to the Commission International d’Eclairage standard colorimetric system. This paper presents a simple and inexpensive method to produce tunable structural colors for numerous applications, such as textile fabrics, bionic colors, catalysis, and paints.

  10. Crystal structure engineering for improved performance of emerging nanoscale devices

    Science.gov (United States)

    Chimalgi, Vinay Uday

    Recent advances in growth techniques and increasing number of experimental studies have made nanostructures grown along different crystallographic directions a reality. These new structures could not only benefit the electronic devices used in mainstream information technology but also show great promise for applications in lasers, solid-state lighting, near-field photolithography, free-space quantum cryptography, consumer displays, quantum computation, as well as diagnostic medicine and imaging. However, only few theoretical investigations have been performed on these structures due to the complex nature of the interplay of atomicity, structural fields, polarization, and quantum size-quantization, all strong function of the crystallographic direction. The objective of this work is mainly four-fold: (1) Integrate a computational framework employing a combination of fully atomistic valence force-field molecular mechanics and 20-band sp3s*d5-SO tight-binding based electronic band­structure models, and numerically investigate the effects of internal fields on the electronic and optical properties of zincblende InAs/GaAs quantum dots grown on (100), (110), and (111) orientated substrates. (2) Augment/extend the open source NEMO 3-D bandstructure simulator by incorporating a recently proposed first principles based model to gauge the importance of nonlinear piezoelectricity on the single-particle electronic states and interband optical transitions in emerging In(Ga)N/GaN disk-in-wire LED structures having c-plane and m-plane wurtzite crystal symmetry. (3) Coupling the NEMO 3-D software toolkit with a commercial TCAD simulator to determine the terminal electrical and optical characteristics of InGaN/GaN disk-in-wire LEDs; and (4) Finding an optimum crystallographic device for InGaN/GaN disk-in-wire LEDs to achieve improved internal quantum efficiency (IQE).

  11. Atom-atom interactions around the band edge of a photonic crystal waveguide

    Science.gov (United States)

    Hood, Jonathan D.; Goban, Akihisa; Asenjo-Garcia, Ana; Lu, Mingwu; Yu, Su-Peng; Chang, Darrick E.; Kimble, H. J.

    2016-09-01

    Tailoring the interactions between quantum emitters and single photons constitutes one of the cornerstones of quantum optics. Coupling a quantum emitter to the band edge of a photonic crystal waveguide (PCW) provides a unique platform for tuning these interactions. In particular, the cross-over from propagating fields E(x)∝e±ikxxE(x)∝e±ikxx outside the bandgap to localized fields E(x)∝e-κx|x|E(x)∝e-κx|x| within the bandgap should be accompanied by a transition from largely dissipative atom-atom interactions to a regime where dispersive atom-atom interactions are dominant. Here, we experimentally observe this transition by shifting the band edge frequency of the PCW relative to the D1D1 line of atomic cesium for N¯=3.0±0.5N¯=3.0±0.5 atoms trapped along the PCW. Our results are the initial demonstration of this paradigm for coherent atom-atom interactions with low dissipation into the guided mode.

  12. Junction-type photonic crystal waveguides for notch- and pass-band filtering

    KAUST Repository

    Shahid, Naeem

    2011-01-01

    Evolution of the mode gap and the associated transmission mini stop-band (MSB) as a function of photonic crystal (PhC) waveguide width is theoretically and experimentally investigated. The change of line-defect width is identified to be the most appropriate way since it offers a wide MSB wavelength tuning range. A high transmission narrow-band filter is experimentally demonstrated in a junction-type waveguide composed of two PhC waveguides with slightly different widths. The full width at half maximum is 5.6 nm; the peak transmission is attenuated by only ∼5 dB and is ∼20 dB above the MSBs. Additionally, temperature tuning of the filter were also performed. The results show red-shift of the transmission peak and the MSB edges with a gradient of dλ/dT = 0.1 nm/°C. It is proposed that the transmission MSBs in such junction-type cascaded PhC waveguides can be used to obtain different types of filters. © 2011 Optical Society of America.

  13. Tunable photonic band-gaps in one-dimensional photonic crystals containing linear graded index material

    Science.gov (United States)

    Singh, Bipin K.; Kumar, Pawan; Pandey, Praveen C.

    2014-12-01

    We have demonstrated control of the photonic band gaps (PBGs) in 1-D photonic crystals using linear graded index material. The analysis of PBG has been done in THz region by considering photonic crystals in the form of ten periods of second, third and fourth generation of the Fibonacci sequence as unit cell. The unit cells are constituted of two kinds of layers; one is taken of linear graded index material and other of normal dielectric material. For this investigation, we used a theoretical model based on transfer matrix method. We have obtained a large number of PBGs and their bandwidths can be tuned by changing the grading profile and thicknesses of linear graded index layers. The number of PBGs increases with increase in the thicknesses of layers and their bandwidths can be controlled by the contrast of initial and final refractive index of the graded layers. In this way, we provide more design freedom for photonic devices such as reflectors, filters, optical sensors, couplers, etc.

  14. Crystal structure of strontium dinickel iron orthophosphate

    Directory of Open Access Journals (Sweden)

    Said Ouaatta

    2015-10-01

    Full Text Available The title compound, SrNi2Fe(PO43, synthesized by solid-state reaction, crystallizes in an ordered variant of the α-CrPO4 structure. In the asymmetric unit, two O atoms are in general positions, whereas all others atoms are in special positions of the space group Imma: the Sr cation and one P atom occupy the Wyckoff position 4e (mm2, Fe is on 4b (2/m, Ni and the other P atom are on 8g (2, one O atom is on 8h (m and the other on 8i (m. The three-dimensional framework of the crystal structure is built up by [PO4] tetrahedra, [FeO6] octahedra and [Ni2O10] dimers of edge-sharing octahedra, linked through common corners or edges. This structure comprises two types of layers stacked alternately along the [100] direction. The first layer is formed by edge-sharing octahedra ([Ni2O10] dimer linked to [PO4] tetrahedra via common edges while the second layer is built up from a strontium row followed by infinite chains of alternating [PO4] tetrahedra and FeO6 octahedra sharing apices. The layers are held together through vertices of [PO4] tetrahedra and [FeO6] octahedra, leading to the appearance of two types of tunnels parallel to the a- and b-axis directions in which the Sr cations are located. Each Sr cation is surrounded by eight O atoms.

  15. Crystal structures of five 6-mercaptopurine derivatives

    Directory of Open Access Journals (Sweden)

    Lígia R. Gomes

    2016-03-01

    Full Text Available The crystal structures of five 6-mercaptopurine derivatives, viz. 2-[(9-acetyl-9H-purin-6-ylsulfanyl]-1-(3-methoxyphenylethan-1-one (1, C16H14N4O3S, 2-[(9-acetyl-9H-purin-6-ylsulfanyl]-1-(4-methoxyphenylethan-1-one (2, C16H14N4O3S, 2-[(9-acetyl-9H-purin-6-ylsulfanyl]-1-(4-chlorophenylethan-1-one (3, C15H11ClN4O2S, 2-[(9-acetyl-9H-purin-6-ylsulfanyl]-1-(4-bromophenylethan-1-one (4, C15H11BrN4O2S, and 1-(3-methoxyphenyl-2-[(9H-purin-6-ylsulfanyl]ethan-1-one (5, C14H12N4O2S. Compounds (2, (3 and (4 are isomorphous and accordingly their molecular and supramolecular structures are similar. An analysis of the dihedral angles between the purine and exocyclic phenyl rings show that the molecules of (1 and (5 are essentially planar but that in the case of the three isomorphous compounds (2, (3 and (4, these rings are twisted by a dihedral angle of approximately 38°. With the exception of (1 all molecules are linked by weak C—H...O hydrogen bonds in their crystals. There is π–π stacking in all compounds. A Cambridge Structural Database search revealed the existence of 11 deposited compounds containing the 1-phenyl-2-sulfanylethanone scaffold; of these, only eight have a cyclic ring as substituent, the majority of these being heterocycles.

  16. Crystal Structures of Respiratory Pathogen Neuraminidases

    Energy Technology Data Exchange (ETDEWEB)

    Hsiao, Y.; Parker, D; Ratner, A; Prince, A; Tong, L

    2009-01-01

    Currently there is pressing need to develop novel therapeutic agents for the treatment of infections by the human respiratory pathogens Pseudomonas aeruginosa and Streptococcus pneumoniae. The neuraminidases of these pathogens are important for host colonization in animal models of infection and are attractive targets for drug discovery. To aid in the development of inhibitors against these neuraminidases, we have determined the crystal structures of the P. aeruginosa enzyme NanPs and S. pneumoniae enzyme NanA at 1.6 and 1.7 {angstrom} resolution, respectively. In situ proteolysis with trypsin was essential for the crystallization of our recombinant NanA. The active site regions of the two enzymes are strikingly different. NanA contains a deep pocket that is similar to that in canonical neuraminidases, while the NanPs active site is much more open. The comparative studies suggest that NanPs may not be a classical neuraminidase, and may have distinct natural substrates and physiological functions. This work represents an important step in the development of drugs to prevent respiratory tract colonization by these two pathogens.

  17. Extraction and Crystal Structure of Karounidiol

    Institute of Scientific and Technical Information of China (English)

    巢志茂; 王诚

    2003-01-01

    The title compound of karounidiol (C30H48O2), a main active triterpene component of snakegourd seed, was isolated from unsaponifiable matter of the seed oil of Trichosanthes kirilowii Maxim., and characterized by X-ray diffraction analysis. It crystallizes in orthorhombic system, space group P212121 with C30H48O2·CH3OH·H2O (C31H54O4), a = 7.515(1), b = 14.407(1), c = 27.799(2) (A。), V = 3009.8(5)(A。)3, Z = 4, Dx = 1.087 g/cm3, Mr = 490.77, F(000) = 1088 and μ = 0.086 mm-1. The final R = 0.0840 and wR = 0.2289 for 2752 observed reflections (|F|2 ≥ 2σ|F|2). The molecular crystal structure of karounidiol shows relative stereochemistry of (3α,13α,14β, 20α)-3,29-dihydroxy-13-methyl-26-norolean-7,9(11)-diene. The molecule is composed of five six- membered rings with ring junctures of A/B trans, C/D trans and D/E cis.

  18. Crystal and molecular structure of aflatrem

    Directory of Open Access Journals (Sweden)

    Bruno N. Lenta

    2015-11-01

    Full Text Available The crystal structure of the title compound, C32H39NO4, confirms the absolute configuration of the seven chiral centres in the molecule. The molecule has a 1,1-dimethylprop-2-enyl substituent on the indole nucleus and this nucleus shares one edge with the five-membered ring which is, in turn, connected to a sequence of three edge-shared fused rings. The skeleton is completed by the 7,7-trimethyl-6,8-dioxabicyclo[3.2.1]oct-3-en-2-one group connected to the terminal cyclohexene ring. The two cyclohexane rings adopt chair and half-chair conformations, while in the dioxabicyclo[3.2.1]oct-3-en-2-one unit, the six-membered ring has a half-chair conformation. The indole system of the molecule exhibits a tilt of 2.02 (1° between its two rings. In the crystal, O—H...O hydrogen bonds connect molecules into chains along [010]. Weak N—H...π interactions connect these chains, forming sheets parallel to (10-1.

  19. The crystal structure Escherichia coli Spy.

    Science.gov (United States)

    Kwon, Eunju; Kim, Dong Young; Gross, Carol A; Gross, John D; Kim, Kyeong Kyu

    2010-11-01

    Escherichia coli spheroplast protein y (EcSpy) is a small periplasmic protein that is homologous with CpxP, an inhibitor of the extracytoplasmic stress response. Stress conditions such as spheroplast formation induce the expression of Spy via the Cpx or the Bae two-component systems in E. coli, though the function of Spy is unknown. Here, we report the crystal structure of EcSpy, which reveals a long kinked hairpin-like structure of four α-helices that form an antiparallel dimer. The dimer contains a curved oval shape with a highly positively charged concave surface that may function as a ligand binding site. Sequence analysis reveals that Spy is highly conserved over the Enterobacteriaceae family. Notably, three conserved regions that contain identical residues and two LTxxQ motifs are placed at the horizontal end of the dimer structure, stabilizing the overall fold. CpxP also contains the conserved sequence motifs and has a predicted secondary structure similar to Spy, suggesting that Spy and CpxP likely share the same fold.

  20. Crystal structure of zirconia by Rietveld refinement

    Institute of Scientific and Technical Information of China (English)

    王大宁; 郭永权; 梁开明; 陶琨

    1999-01-01

    The crystal structures and phase transformation of zirconia ceramics have been investigated by means of X-ray powder diffraction and Rietveld powder diffraction profile fitting technique. A structural transition from monoclinic to tetragonal occurs when Y2O3 and CeO2 are doped into zirconia. The space group of the tetragonal structure is P42/nmc, Z=2. The lattice parameters are α=0.362 6(5) nm, c=0.522 6(3)nm for CeO2 doped zirconia and α=0. 360 2(8)nm, c=0. 517 9(1)nm for Y2O3 doped zirconia, respectively. In each unit cell, there are two kinds of equivalent positions, i. e. 2b and 4d, which are occupied by Zr4+, M(M=Y3+, Ce4+) cations and O2- anions, respectively. The crystallographic correlation among the cubic, tetragonal and monoclinic structures of ZrO2 is discussed.