Harigaya, Kikuo; Imamura, Hiroshi
2011-01-01
Bilayer graphene nanoribbon with zigzag edge is investigated with the tight binding model. Two stacking structures, alpha and beta, are considered. The band splitting is seen in the alpha structure, while the splitting in the wave number direction is found in the beta structure. The local density of states in the beta structure tend to avoid sites where interlayer hopping interactions are present. The calculation is extended to the boron-carbon-nitride systems. The qualitati...
Harigaya, Kikuo
2011-01-01
Bilayer graphene nanoribbon with zigzag edge is investigated with the tight binding model. Two stacking structures, alpha and beta, are considered. The band splitting is seen in the alpha structure, while the splitting in the wave number direction is found in the beta structure. The local density of states in the beta structure tend to avoid sites where interlayer hopping interactions are present. The calculation is extended to the boron-carbon-nitride systems. The qualitative properties persist when zigzag edge atoms are replaced with borons and nitrogens.
Band structure, density of states, and crystal chemistry of ZrGa2 and ZrGa3 single crystals
International Nuclear Information System (INIS)
Highlights: ? ZrGa2 and ZrGa3 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 ZrGa2 and ZrGa3 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 ZrGa2 to ZrGa3 that is attributed to the fact that ZrGa2 has four formula per unit cell (Z = 4) while ZrGa3 has two formula per unit cell (Z = 2). Despite some similarity in the crystallochemistry of ZrGa2 to ZrGa3 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
Band structure of semiconductors
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
Hybrid density functional theory study of Cu(In1?xGaxSe2 band structure for solar cell application
Directory of Open Access Journals (Sweden)
Xu-Dong Chen
2014-08-01
Full Text Available Cu(In1?xGaxSe2 (CIGS alloy based thin film photovoltaic solar cells have attracted more and more attention due to its large optical absorption coefficient, long term stability, low cost and high efficiency. However, the previous theoretical investigation of this material with first principle calculation cannot fulfill the requirement of experimental development, especially the accurate description of band structure and density of states. In this work, we use first principle calculation based on hybrid density functional theory to investigate the feature of CIGS, with B3LYP applied in the CuIn1?xGaxSe2 stimulation of the band structure and density of states. We report the simulation of the lattice parameter, band gap and chemical composition. The band gaps of CuGaSe2, CuIn0.25Ga0.75Se2, CuIn0.5Ga0.5Se2, CuIn0.75Ga0.25Se2 and CuInSe2 are obtained as 1.568 eV, 1.445 eV, 1.416 eV, 1.275 eV and 1.205 eV according to our calculation, which agree well with the available experimental values. The band structure of CIGS is also in accordance with the current theory.
Photoemission and Band Structure
International Nuclear Information System (INIS)
Principally through experimental work in the past twenty-five years, it has become apparent that in most solids photoemission is a process in which the photoelectron is excited a significant distance from the surface and the optical excitation process is closely related to the electronic or band structure of the solid. After excitation, the electron must pass through a certain distance of the solid before it can reach the surface and escape into vacuum. Both the excitation and escape processes depend on the electronic or band structure of the solid. By making three types of measurement: (1) the spectral distribution of the quantum yield, (2) the energy distribution of the electrons excited by monochromatic light, and (3) that of the optical constants of the solid, much can often be learned about the band structure of the solid. Conversely, the quantum structure (band structure, phonon spectra, etc. ) determines the manner in which electrons are optically excited in the solid and the probability of their moving to the surface. The probability of escape over the surface is determined by the potential barrier at the surface, (i. e. the work function of a metal or electron affinity of a semiconductor or insulator). In this paper a simple relationship will first be developed between parameters of the electronic structure such as the band structure and the height of the surface potential barrier on the one hand and the photoemission quantities such as the quantum yield and energy distributions on the other hand. This part of the paper will be illustrated by examples from specific solids. The last part of the paper will take the opposite approach. Here we will show how photoemission and optical measurements can be used to determine important apsects of the band structure. Illustrations will be given from semiconductors such as Si, GaAs and CdTe and from metals such as Cu and Ni. (author)
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.
Kim, Y H; Görling, A; Kim, Yong-Hoon; Staedele, Martin; Goerling, Andreas
2002-01-01
We calculate the imaginary part of the frequency-dependent dielectric function of bulk silicon by applying time-dependent density-functional theory based on the exact-exchange (EXX) Kohn-Sham (KS) band structure and the adiabatic local-density approximation (ALDA) kernel. The position of the E2 absorption peak calculated with the EXX band structure at the independent-particle level is in excellent agreement with experiments, which demonstrates the good quality of EXX `KS quasiparticles'. The excitonic E1 peak that is missing at the independent-particle level remains absent if two-particle interaction effects are taken into account within the time-dependent LDA, demonstrating the incapability of the ALDA kernel to describe excitonic effects.
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.
Band structures of defective graphenes
Energy Technology Data Exchange (ETDEWEB)
Hatanaka, Masashi, E-mail: mhatanaka@xug.biglobe.ne.j [Department of Green and Sustainable Chemistry, School of Engineering, Tokyo Denki University, 2-2 Kanda Nishiki-cho, Chiyoda-ku, Tokyo 101-8457 (Japan)
2011-03-15
Band structures of defective graphenes are analyzed by crystal orbital method. In laterally slipped faults, there appear {sigma} bands consisting of weakly interacted dangling bonds. The peculiar {sigma} bands cross with frontier {pi} bands, and the resultant double occupation leads to the disappearance of ferromagnetic interactions. On the other hand, in longitudinally slipped faults, there are no crossings of the {sigma} bands within the frontier levels, and the ferromagnetic interactions result from polycarbene-type spin alignment. - Research Highlights: Band structures in defective graphenes are analyzed. Lateral slipping in graphenes quenches the ferromagnetic interactions. In the lateral slipping modes, {sigma} bands cross with {pi} frontier bands and reduce the magnetism. Longitudinal slipping in graphenes causes carbene-type ferromagnetic interactions.
Energy Technology Data Exchange (ETDEWEB)
Brouet, V.; Yang, W.L.; Zhou, X.J.; Hussain, Z.; Moore, R.G.; He, R.; Lu, D.H.; Shen, Z.X.; Laverock, J.; Dugdale, S.; Ru, N.; Fisher, I.R.
2010-02-15
We present a detailed ARPES investigation of the RTe{sub 3} family, which sets this system as an ideal 'textbook' example for the formation of a nesting driven Charge Density Wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDW instabilities, from the opening of large gaps on the best nested parts of Fermi Surface (FS) (up to 0.4eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k-space. An additional advantage of RTe{sub 3} is that the band structure can be very accurately described by a simple 2D tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure, by comparing our ARPES measurements with Linear Muffin-Tin Orbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and, for the first time, of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k-space, the evolution of the CDW wave vector with R and the shape of the residual metallic pockets. Finally, we give an estimation of the CDW interaction parameters and find that the change in the electronic density of states n(Ef), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.
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.
Energy Technology Data Exchange (ETDEWEB)
Simon, L; Vonau, F; Aubel, D [Laboratoire de Physique et de Spectroscopie Electronique, CNRS-UMR7014, 4, rue des Freres Lumiere, 68093 Mulhouse (France)
2007-09-05
The authors show that an accurate determination of the band structure can be achieved by using Fourier transform scanning tunnelling microscopy (FT-STM) techniques in the case of a semi-metallic ErSi{sub 2} layer grown on a Si(111) substrate. This material provides an ideally confined 2D electron and hole gas that is reflected in a complex standing wave pattern at 77 K. The quasi-particles exist over a wide energy range from -800 to +300 meV without mixing with silicon bulk excitations. The Fourier transform of dI/dV maps have been successfully interpreted using the concept of the joint density of states (JDOS), which will be properly introduced. We present here an intuitive interpretation of the quasiparticle interference process based on a geometric construction which also allows us to clearly demonstrate that hole-hole and hole-electron quantum interferences dominate over electron-electron quantum interference.
Energy Technology Data Exchange (ETDEWEB)
Hussain, Zahid; Brouet, Veronique; Yang, Wanli; Zhou, Xingjiang; Hussain, Zahid; Moore, R.G.; He, R.; Lu, D. H.; Shen, Z.X.; Laverock, J.; Dugdale, S.B.; Ru, N.; Fisher, R.
2008-01-16
We present a detailed angle-resolved photoemission spectroscopy (ARPES) investigation of the RTe3 family, which sets this system as an ideal"textbook" example for the formation of a nesting driven charge density wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDWinstabilities, from the opening of large gaps on the best nested parts of Fermi surface (up to 0.4 eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k space. An additional advantage of RTe3 is that theband structure can be very accurately described by a simple two dimensional tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure by comparing our ARPES measurements with the linear muffin-tinorbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k space, the evolution of the CDW wave vector with R, and the shape of the residual metallic pockets. Finally, we give an estimation of the CDWinteraction parameters and find that the change in the electronic density of states n (EF), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.
DEFF Research Database (Denmark)
Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco; Eustáquio de Carvalho, Vagner; Orlando Ladeira, Luiz; Gomes Teixeira, Nayara; Avellar Soares, Edmar; Friedrich, Christoph; Blügel, Stefan; Hofmann, Philip
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 Bi2T...
Quasirelativistic band structure of bismuth telluride
International Nuclear Information System (INIS)
The band structure of bismuth telluride belonging to the group of the Asub(2)Ssup(5)BsUb(3)-type crystals with the Dsub(3d)sup(5) symmetry is under consideration. The Bi2Te3 band structure was calculated using the Pauli equation pseudopotential method. Calculation results are presented for the Brillouin zone symmetric points. The energy bands are classified according to their symmetry. The evailable basic parameters of the bismuth telluride band structure are compared with the result of other paper. Analysis of the calculated band structure shows that there is some difference of the band behaviour in the direction perpendicular to quintet (GITAL, KA, XU) layers that of bands lying in the quintet plane (other Brillouin zone directions). In the first case the energy band dispersion is well below than that in the second case. This fact conforms with a lower current carrier mobility in the direction perpendicular to the layers, as compared to other crystal directions
Band Structure of SnTe Studied by Photoemission Spectroscopy
Littlewood, P. B.; Mihaila, B.; Schulze, R. K.; Safarik, D. J.; Gubernatis, J. E.; Bostwick, A.; Rotenberg, E.; Opeil, C. P.; Durakiewicz, T.; Smith, J. L.; Lashley, J. C.
2010-08-01
We present an angle-resolved photoemission spectroscopy study of the electronic structure of SnTe and compare the experimental results to ab initio band structure calculations as well as a simplified tight-binding model of the p bands. Our study reveals the conjectured complex Fermi surface structure near the L points showing topological changes in the bands from disconnected pockets, to open tubes, and then to cuboids as the binding energy increases, resolving lingering issues about the electronic structure. The chemical potential at the crystal surface is found to be 0.5 eV below the gap, corresponding to a carrier density of p=1.14×1021cm-3 or 7.2×10-2 holes per unit cell. At a temperature below the cubic-rhombohedral structural transition a small shift in spectral energy of the valance band is found, in agreement with model predictions.
DEFF Research Database (Denmark)
Michiardi, Matteo; Aguilera, Irene
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.
Structure of rotational bands in 253No
International Nuclear Information System (INIS)
In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the 253 No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the 9/2-[734]? ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work. (orig.)
Photonic band structure and omnidirectional band gap in anisotropic superlattice
Energy Technology Data Exchange (ETDEWEB)
Ouchani, N.; Bria, D.; Nougaoui, A. [Laboratoire de Dynamique et d' Optique des Materiaux, Departement de Physique, Faculte des Sciences, Universite Mohamed I, B.P. 524, 60000 Oujda (Morocco); Djafari-Rouhani, B. [Laboratoire de Dynamique et Structure des Materiaux Moleculaires, UMR CNRS 8024, UFR de Physique, Universite de Lille 1, 59655 Villeneuve d' Ascq (France)
2006-06-15
We investigate theoretically the photonic band structure of one-dimensional superlattices (SL) composed of alternating anisotropic layers with their principal axes oriented at arbitrary directions. The dispersion relation of second order is calculated analytically by using the 4 x 4 matrix method which is based on the boundary conditions of the electric and magnetic fields at each interface. It is shown that such structures can exhibit coupled electromagnetic modes between transverse magnetic TM and transverse electric TE modes, and dispersion curves that do not exist in superlattices composed only of isotropic layers. For a given value of the wave vector k {sub ?} (parallel to the layers), the dispersion curves (frequency ?) versus k {sub B} (where k {sub B} is the Bloch wave vector of the periodic system along the axis of the superlattice) are illustrated. Specific applications of these results are given for the case of the biaxial superlattice. We show that with an appropriate choice of the superlattice parameters an absolute (or omnidirectional) band gap for these coupled electromagnetic waves can be obtained. The band gap width depends on the anisotropic parameters of the media forming the SL. (author)
Electronic Structure of Calcium Hexaboride within the Weighted Density Approximation
Wu, Z; Cohen, R E
2004-01-01
We report calculations of the electronic structure of CaB$_6$ using the weighted density approximation (WDA) to density functional theory. We find a semiconducting band structure with a sizable gap, in contrast to local density approximation (LDA) results, but in accord with recent experimental data. In particular, we find an $X$-point band gap of 0.8 eV. The WDA correction of the LDA error in describing the electronic structure of CaB$_6$ is discussed in terms of the orbital character of the bands and the better cancelation of self-interactions within the WDA.
Unfolding the band structure of non-crystalline photonic band gap materials
Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining
2015-08-01
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.
International Nuclear Information System (INIS)
The level structure of 104Ag has been studied through the 103Rh(?,3n?) reaction at E?=40 and 45 MeV. The principal features of the proposed level scheme are in agreement with those obtained earlier through heavy ion reaction. A two-quasiparticle-plus-rotor model calculation has been performed, and the results are compared with experimental data. (orig.)
Tezuka, Masaki; Arita, Ryotaro; Aoki, Hideo
2005-01-01
Density-matrix renormalization group is used to study the pairing when both of electron-electron and electron-phonon interactions are strong in the Holstein-Hubbard model at half-filling in a region intermediate between the adiabatic (Migdal's) and antiadiabatic limits. We have found: (i) the pairing correlation obtained for a one-dimensional system is nearly degenerate with the CDW correlation in a region where the phonon-induced attraction is comparable with the electron-e...
Photonic band structure and omnidirectional band gap in anisotropic superlattice
International Nuclear Information System (INIS)
We investigate theoretically the photonic band structure of one-dimensional superlattice (SL) composed of alternating anisotropic layers with their principal axis oriented at arbitrary directions. The dispersion relation of order two is calculated analytically by using the 4 x 4 matrix method which is based on boundary conditions of the electric and magnetic fields at each interface. It is shown that such structures can exhibit coupled electromagnetic modes between transverse magnetic TM and transverse electric TE modes, and dispersion curves that do not exist in superlattices composed only of isotropic layers. For a given value of the wave vector kparallel (parallel to the layers), the dispersion curves (frequency ?) versus kB (where kB is the Bloch wave vector of the periodic system along the axis of the superlattice) is illustrated. Specific applications of these results are given for the case of biaxial superlattice. With an appropriate choice of the superlattice parameters, we show that it is possible to realise, for these coupled electromagnetic waves, an absolute (or omnidirectional) band gap of width depending on the anisotropic parameters of the media forming the SL. (author)
Band structure of CdTe under high pressure
International Nuclear Information System (INIS)
The band structures and density of states of cadmium telluride (CdTe) under various pressures ranging from normal to 4.5 Mbar are obtained. The electronic band structure at normal pressure of CdTe (ZnS structure) is analyzed and the direct band gap value is found to be 1.654 eV. CdTe becomes metal and superconductor under high pressure but before that it undergoes structural phase transition from ZnS phase to NaCl phase. The equilibrium lattice constant, bulk modulus and the phase transition pressure at which the compounds undergo structural phase transition from ZnS to NaCl are predicted from the total energy calculations. The density of states at the Fermi level (N(EF)) gets enhanced after metallization, which leads to the superconductivity in CdTe. In our calculation, the metallization pressure (PM = 1.935 Mbar) and the corresponding reduced volume ((V/V0)M = 0.458) are estimated. Metallization occurs via direct closing of band gap at ? point. (author)
International Nuclear Information System (INIS)
The band structures of 121,123I nuclei have been studied using a version of the particle-rotor-model in which the experimental excitation energies of the neighbouring (A-1) cores can be fed directly as input parameters. The calculations have been carried out with axially symmetric Nilsson potential with both prolate and oblate deformations. The parameters of the model have been chosen from earlier theoretical work and experimental odd-even mass differences. Only the Coriolis attenuation factor has been treated as adjustable parameter. The theoretical band structures are in very good agreement with the available experimental data. (orig.)
Holz, M; Chen, S H
1979-05-01
We developed a rapid-scanning, light-scattering densitometer by which extensive measurements of band migration speeds and band profiles of chemotactic bands of Escherichia coli in motility buffer both with and without serine have been made. The purpose is to test the applicability of the phenomenological model proposed by Keller and Segel (J. Theor. Biol. 1971. 30:235) and to determine the motility (mu) and chemotactic (delta) coefficients of the bacteria. We extend the previous analytical solution of the simplified Keller-Segel model by taking into account the substrate diffusion which turns out to be significant in the case of oxygen. We demonstrate that unique sets of values of mu and delta can be obtained for various samples at different stages of migration by comparing the numerical solution of the model equation and the experimental data. The rapid-scanning technique also reveals a hitherto unobserved time-dependent fine structure in the bacterial band. We give a qualitative argument to show that the fine structure is an example of the dissipative structure that arises from a nonlinear coupling between the bacterial density and the oxygen concentration gradient. Implications for a further study of the dissipative structure in testing the Keller-Segel model of chemotaxis are briefly discussed. PMID:400469
Production of S-band Accelerating Structures
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.
Band structure analysis in SiGe nanowires
Energy Technology Data Exchange (ETDEWEB)
Amato, Michele [' Centro S3' , CNR-Istituto Nanoscienze, via Campi 213/A, 41100 Modena (Italy); Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy); Palummo, Maurizia [European Theoretical Spectroscopy Facility (ETSF) (Italy); CNR-INFM-SMC, Dipartimento di Fisica, Universita di Roma, ' Tor Vergata' , via della Ricerca Scientifica 1, 00133 Roma (Italy); Ossicini, Stefano, E-mail: stefano.ossicini@unimore.it [' Centro S3' , CNR-Istituto Nanoscienze, via Campi 213/A, 41100 Modena (Italy) and Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy) and European Theoretical Spectroscopy Facility - ETSF (Italy) and Centro Interdipartimentale ' En and Tech' , Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy)
2012-06-05
One of the main challenges for Silicon-Germanium nanowires (SiGe NWs) electronics is the possibility to modulate and engine their electronic properties in an easy way, in order to obtain a material with the desired electronic features. Diameter and composition constitute two crucial ways for the modification of the band gap and of the band structure of SiGe NWs. Within the framework of density functional theory we present results of ab initio calculations regarding the band structure dependence of SiGe NWs on diameter and composition. We point out the main differences with respect to the case of pure Si and Ge wires and we discuss the particular features of SiGe NWs that are useful for future technological applications.
Band structure mapping of bilayer graphene via quasiparticle scattering
Directory of Open Access Journals (Sweden)
Matthew Yankowitz
2014-09-01
Full Text Available A perpendicular electric field breaks the layer symmetry of Bernal-stacked bilayer graphene, resulting in the opening of a band gap and a modification of the effective mass of the charge carriers. Using scanning tunneling microscopy and spectroscopy, we examine standing waves in the local density of states of bilayer graphene formed by scattering from a bilayer/trilayer boundary. The quasiparticle interference properties are controlled by the bilayer graphene band structure, allowing a direct local probe of the evolution of the band structure of bilayer graphene as a function of electric field. We extract the Slonczewski-Weiss-McClure model tight binding parameters as ?0 = 3.1 eV, ?1 = 0.39 eV, and ?4 = 0.22 eV.
X-Band Structure Development at KEK
Higo, Toshiyasu
2015-10-01
X-band accelerator structure development at KEK has been driven targeting the linear colliders in worldwide collaborations. It is based on the technologies developed with high-precision machining, precise assembly and bonding method to preserve the precision. With maximally utilizing the merits of such technologies, the long-range wakefield was suppressed in parallel to realize the high gradient. The latter needs more study and development to actually realize the stable operation at a gradient of 100 MV/m or higher in the view point of the present paper. The worldwide collaboration studies are extensively on-going and the understanding of the vacuum breakdown has been advancing. By describing the development at KEK toward the X-band wakefield suppressed high-gradient accelerator structure, this paper shows how such structures have been evolved and may serve to show a room for the future studies.
One-dimensional electromagnetic band gap structures formed by discharge plasmas in a waveguide
Energy Technology Data Exchange (ETDEWEB)
Arkhipenko, V. I.; Simonchik, L. V., E-mail: l.simonchik@dragon.bas-net.by; Usachonak, M. S. [B.I. Stepanov Institute of Physics of the NAS of Belarus, Ave. Nezavisimostsi 68, 220072 Minsk (Belarus); Callegari, Th.; Sokoloff, J. [Université de Toulouse, UPS, INPT, LAPLACE, Laboratoire Plasma et Conversion d' Energie, 118 route de Narbonne, F-31062 Toulouse cedex 9 (France)
2014-09-28
We demonstrate the ability to develop one-dimensional electromagnetic band gap structure in X-band waveguide solely by using the positive columns of glow discharges in neon at the middle pressure. Plasma inhomogeneities are distributed uniformly along a typical X-band waveguide with cross section of 23×10 mm². It is shown that electron densities larger than 10¹? cm ?³ are needed in order to create an effective one-dimensional electromagnetic band gap structure. Some applications for using the one-dimensional electromagnetic band gap structure in waveguide as a control of microwave (broadband filter and device for variation of pulse duration) are demonstrated.
Photonic-Crystal Waveguides with Disorder: Measurement of a Band-Edge Tail in the Density of States
Huisman, S R; Stobbe, S; Mosk, A P; Herek, J L; Lagendijk, A; Lodahl, P; Vos, W L; Pinkse, P W H
2012-01-01
We measure localized and extended mode profiles at the band edge of slow-light photonic-crystal waveguides using phase-sensitive near-field microscopy. High-resolution band structures are obtained and interpreted, allowing the retrieval of the optical density of states (DOS). This constitutes a first observation of the DOS of a periodic system with weak disorder. The Van Hove singularity in the DOS expected at the band edge of an ideal 1D periodic structure is removed by the disorder. The Anderson-localized states form a "tail" in the density of states, as predicted by Lifshitz for solid-state systems.
Band structure and hole scattering in p-PbTe
International Nuclear Information System (INIS)
Mobility (u), thermoemf (?), and temperature dependences of the Hall constant (R) in p-PbTe were calculated. While calculating considered has been the effect of the free electron mass contribution to the density mass of states at the band bottom and to the effective width of the forbidden band in the framework of the Cane type model, which leads to the absence of a ''mirror property'' of conductivity and valency bands. It is shown that, while taking into account the temperature dependence of the Hall factor, the appearance of maximum on R(T) curves may be explained only with due account of the contribution from interband scattering. Taking account of acoustic and optical mechanisms of scattering, it becomes possible to explain satisfactorily the temperature and concentration dependences of u, the temperature dependences of R and concentration dependences of ? up to concentrations of about 1020 cm-3 at heavy band parameters of msub(h)=1msub(e), ?0.18 eV. Qualitative considerations of the shape of isoenergetic surfaces of a heavy band were undertaken to explain the concentration dependences of b=usub(h)/usub(l) and causes of deviation of experimental and calculated values of ?. It is shown that the above surfaces have a complicated structure, and the heavy band may be substantially nonparabolic
Banded frequency structure from linear mode conversion in inhomogeneous plasmas
International Nuclear Information System (INIS)
Linear mode conversion of unmagnetized Langmuir waves into transverse electromagnetic waves in an inhomogeneous plasma is investigated numerically. It is shown that the presence of a tunneling region and density well near the mode conversion region can significantly influence the mode conversion efficiency. The density cavity acts as a resonator, such that the mode conversion efficiency shifts from zero to a local maximum (up to 100% efficiency) with variation of the cavity width on scales of order the Langmuir wavelength. In this way, Langmuir waves with a smooth (structureless) frequency dependence can be selectively mode converted to produce narrow frequency bands of electromagnetic radiation. Applications are discussed to banded frequency fine structure in electromagnetic emissions at the electron plasma frequency in Earth's foreshock and the solar wind, type III solar radio bursts, and lower ionospheric auroral roar emissions
Band structure and chemical bonding in transition metal carbides and nitrides
International Nuclear Information System (INIS)
The electronic structure and chemical bonding of the nitrides and carbides of Ti, V, Zr, and Nb are studied. The augmented plane wave method is used and results are discussed in terms of energy bands and density of states
Emission bands of phosphorus and calculation of band structure of rare earth phosphides
International Nuclear Information System (INIS)
The method of x-ray emission spectroscopy has been used to investigate the electronic structure of monophosphides of rare-earth metals (REM). The fluorescence K bands of phosphorus have been obtained in LaP, PrP, SmP, GdP, TbP, DyP, HoP, ErP, TmP, YbP, and LuP and also the Lsub(2,3) bands of phosphorus in ErP, TmP, YbP, and LuP. Using the Green function technique involving the muffin-tin potential, the energy spectrum for ErP has been calculated in the single-electron approximation. The hystogram of electronic state distribution N(E) is compared with the experimental K and Lsub(2,3) bands of phosphorus in ErP. The agreement between the main details of N(E) and that of x-ray spectra allows to state that the model used provides a good description of the electron density distribution in crystals of REM monophosphides. In accordance with the character of the N(E) distribution the compounds under study are classified as semimetals or semiconductors with a very narrow forbidden band
Band structure in Platinum nuclei (A ? 182)
International Nuclear Information System (INIS)
In this thesis, the author studies the band structure in Platinum nuclei and has divided his work in 5 parts: in the first, the author makes a general presentation of nucleus physics with a high angular momentum and introduces to the deformed nucleus notion -axial, triaxial or mixing of different deformations. The notion of form co-existence will be used to interpret the experimental results. In the second part, the author describes the detection means which have been used to make measurements. An abstract of theoretical notions, usefull for the understanding of fusion-evaporation reaction is presented. The author explains the details, performances and different modes of using of 'Chateau de cristal' and others used spectrometers. In the third part, the author presents all experimental data. He has effected ? coincidence measurements for Pt, Au and Ir nuclei. In the fourth part, for a classical analysis or an interpretation in the frame of cranking model the author presents theoretical models which are adapted at the study of high spin states and band structures
Photonic band structure of highly deformable, self-assembling systems
Bermel, Peter A.; Warner, Mark
2001-01-01
We calculate the photonic band structure at normal incidence of highly deformable, self-assembling systems - cholesteric elastomers subjected to external stress. Cholesterics display brilliant reflection and lasing owing to gaps in their photonic band structure. The band structure of cholesteric elastomers varies sensitively with strain, showing new gaps opening up and shifting in frequency. A novel prediction of a total band gap is made, and is expected to occur in the vici...
Photonic-Crystal Waveguides with Disorder: Measurement of a Band-Edge Tail in the Density of States
Huisman, S. R.; Ctistis, G.; Stobbe, S.; Mosk, A. P.; Herek, J L; Lagendijk, A.; Lodahl, P.; Vos, W.L.; Pinkse, P.W.H.
2012-01-01
We measure localized and extended mode profiles at the band edge of slow-light photonic-crystal waveguides using phase-sensitive near-field microscopy. High-resolution band structures are obtained and interpreted, allowing the retrieval of the optical density of states (DOS). This constitutes a first observation of the DOS of a periodic system with weak disorder. The Van Hove singularity in the DOS expected at the band edge of an ideal 1D periodic structure is removed by the...
Photoemission and density functional theory study of Ir(111); energy band gap mapping
Pletikosi?, I.; Kralj, M.; Šok?evi?, D.; Brako, R.; Lazi?, P.; Pervan, P.
2010-04-01
We have performed combined angle-resolved photoemission spectroscopy (ARPES) experiments and density functional theory (DFT) calculations of the electronic structure of the Ir(111) surface, with the focus on the existence of energy band gaps. The investigation was motivated by the experimental results suggesting Ir(111) as an ideal support for the growth of weakly bonded graphene. Therefore, our prime interest was electronic structure around the \\bar {\\mathrm {K}} symmetry point. In accordance with DFT calculations, ARPES has shown a wide energy band gap with the shape of a parallelogram centred around the \\bar {\\mathrm {K}} point. Within the gap three surface states were identified; one just below the Fermi level and two spin-orbit split surface states at the bottom of the gap.
Photoemission and density functional theory study of Ir(111); energy band gap mapping
International Nuclear Information System (INIS)
We have performed combined angle-resolved photoemission spectroscopy (ARPES) experiments and density functional theory (DFT) calculations of the electronic structure of the Ir(111) surface, with the focus on the existence of energy band gaps. The investigation was motivated by the experimental results suggesting Ir(111) as an ideal support for the growth of weakly bonded graphene. Therefore, our prime interest was electronic structure around the K-bar symmetry point. In accordance with DFT calculations, ARPES has shown a wide energy band gap with the shape of a parallelogram centred around the K-bar point. Within the gap three surface states were identified; one just below the Fermi level and two spin-orbit split surface states at the bottom of the gap.
Band-gap structures for matter waves
Damon, F.; Condon, G.; Cheiney, P.; Fortun, A.; Georgeot, B.; Billy, J.; Guéry-Odelin, D.
2015-09-01
Spatial gaps correspond to the projection in position space of the gaps of a periodic structure whose envelope varies spatially. They can be easily generated in cold atomic physics using finite-size optical lattice, and provide a new kind of tunnel barrier which can be used as a versatile tool for quantum devices. We present in detail different theoretical methods to quantitatively describe these systems, and show how they can be used in one dimension to realize matter wave Fabry-Perot cavities. We also provide experimental and numerical results that demonstrate the interest of spatial gap structures for phase space engineering. We then generalize the concept of spatial gaps in two dimensions and show that this enables one to design multiply connected cavities which generate a quantum dot structure for atoms or allow one to construct curved wave guides for matter waves. At last, we demonstrate that modulating in time the amplitude of the periodic structure offers a wide variety of possible atom manipulations including the control of the scattering of an incoming wave packet, the loading of cavities delimited by spatial gaps, their coupling by multiphonon processes or the realization of a tunable source of atoms. This large range of possibilities offered by space and time engineering of optical lattices demonstrates the flexibility of such band-gap structures for matter wave control, quantum simulators, and atomtronics.
A Theoretical Structure of High School Concert Band Performance
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"…
Electronic Band Structures of Compounds with Fluorite, Rocksalt, and Zinc-Blende Structures.
Kim, Sehun
A Mixed-Basis Band Structure Interpolation Scheme (MBBSIS) for fcc d-band metals has been extended to handle compounds with the fluorite, rocksalt and zinc-blende structures. The pseudopotential parameters for these compounds have been determined by fitting to first-principles calculation or to an empirical band-structure model using a nonlinear least-squares procedure. Semi-empirical band structures were then obtained by adjusting the parameters to improve the agreement between the calculated bands and data from Angle Resolved Photoelectron Spectroscopy and X-ray Photoelectron Spectroscopy measurements. Approximate valence charge densities were plotted using the eigenfunctions of the interpolation scheme to illustrate bonding effects of the rocksalt compounds TiC, TiN and TiO. The partial densities-of-states (DOS) for the zinc-blende compound CuCl were obtained by projecting the s-, p-, and d-like components out of the mixed basis. The results are compared with experimental DOS obtained from photoemission or x-ray emission data in the literature. An ARPES apparatus equipped with a noble gas discharge lamp and an electrostatic analyzer was used to collect ARPES spectra of PtGa(,2). Since no previous band structure of PtGa(,2) exists, the MBBSIS parameters for AuGa(,2) were adjusted to optimize agreement between the PtGa(,2) XPS spectrum and the calculated MBBSIS DOS. The ARPES data collected for PtGa(,2)(111) was used to check the accuracy of the d-band positions, determined by the above procedure.
DEFF Research Database (Denmark)
Dery, H.; Tromborg, Bjarne; Eisenstein, G.
2003-01-01
We describe carrier-carrier scattering dynamics in an inverted quantum well structure including the nonparabolic nature of the valance band. A solution of the semiconductor Bloch equations yields strong evidence to a large change in the temporal evolution of the carrier distributions compared to the case of parabolic bands. The nonparabolic bands and the consequent change in the density of states reduce considerably the degree of gain saturation while decreasing the time constant governing the r...
Photonic Crystal Narrow Band Filters Using Biperiodic Structures
Djavid, M.; A Ghaffari; Monifi, F.; M. S. Abrishamian
2008-01-01
In this study, we propose a new type of photonic crystal band-pass and band-stop filter based on biperiodic structure. Usually two types of photonic crystal band-pass filters are utilized in optical circuit. In the first one Fabry-Perot cavities are used while in the second one cavity-coupled waveguide are used. We optimize the second structure in this study. Then we show that by little changing in the band-pass structure, a band-stop filter is attained. Using Finite-Difference Time-Domain (F...
Li, Wenqing; Walther, Christian F J; Kuc, Agnieszka; Heine, Thomas
2013-07-01
The performance of a wide variety of commonly used density functionals, as well as two screened hybrid functionals (HSE06 and TB-mBJ), on predicting electronic structures of a large class of en vogue materials, such as metal oxides, chalcogenides, and nitrides, is discussed in terms of band gaps, band structures, and projected electronic densities of states. Contrary to GGA, hybrid functionals and GGA+U, both HSE06 and TB-mBJ are able to predict band gaps with an appreciable accuracy of 25% and thus allow the screening of various classes of transition-metal-based compounds, i.e., mixed or doped materials, at modest computational cost. The calculated electronic structures are largely unaffected by the choice of basis functions and software implementation, however, might be subject to the treatment of the core electrons. PMID:26583978
Band structure of SnTe studied by Photoemission Spectroscopy
Littlewood, P B; Mihaila, B.; Schulze, R. K.; Safarik, D. J.; Gubernatis, J. E.; Bostwick, A; Rotenberg, E.; Opeil, C.P.; Durakiewicz, T.; Smith, J. L.; J. C. Lashley
2010-01-01
We present an angle-resolved photoemission spectroscopy study of the electronic structure of SnTe, and compare the experimental results to ab initio band structure calculations as well as a simplified tight-binding model of the p-bands. Our study reveals the conjectured complex Fermi surface structure near the L-points showing topological changes in the bands from disconnected pockets, to open tubes, and then to cuboids as the binding energy increases, resolving lingering is...
Electronic structure and electron momentum density in TiSi
Energy Technology Data Exchange (ETDEWEB)
Ghaleb, A.M. [Department of Physics, College of Science, University of Kirkuk, Kirkuk (Iraq); Mohammad, F.M. [Department of Physics, College of Science, University of Tikreet, Tikreet (Iraq); Sahariya, Jagrati [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India); Sharma, Mukesh [Physics Division, Forensic Science Laboratory, Jaipur, Rajasthan (India); Ahuja, B.L., E-mail: blahuja@yahoo.com [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India)
2013-03-01
We report the electron momentum density in titanium monosilicide using {sup 241}Am Compton spectrometer. Experimental Compton profile has been compared with the theoretical profiles computed using linear combination of atomic orbitals (LCAO). The energy bands, density of states and Fermi surface structures of TiSi are reported using the LCAO and the full potential linearized augmented plane wave methods. Theoretical anisotropies in directional Compton profiles are interpreted in terms of energy bands. To confirm the conducting behavior, we also report the real space analysis of experimental Compton profile of TiSi.
Relationships between magnetic foot points and G-band bright structures
Ishikawa, R.; Tsuneta, S.; Kitakoshi, Y.; Katsukawa, Y.; Bonet, J. A.; Vargas Domínguez, S.; Rouppe van der Voort, L. H. M.; Sakamoto, Y.; Ebisuzaki, T.
2007-09-01
Aims:Magnetic elements are thought to be described by flux tube models, and are well reproduced by MHD simulations. However, these simulations are only partially constrained by observations. We observationally investigate the relationship between G-band bright points and magnetic structures to clarify conditions, which make magnetic structures bright in G-band. Methods: The G-band filtergrams together with magnetograms and dopplergrams were taken for a plage region covered by abnormal granules as well as ubiquitous G-band bright points, using the Swedish 1-m Solar Telescope (SST) under very good seeing conditions. Results: High magnetic flux density regions are not necessarily associated with G-band bright points. We refer to the observed extended areas with high magnetic flux density as magnetic islands to separate them from magnetic elements. We discover that G-band bright points tend to be located near the boundary of such magnetic islands. The concentration of G-band bright points decreases with inward distance from the boundary of the magnetic islands. Moreover, G-band bright points are preferentially located where magnetic flux density is higher, given the same distance from the boundary. There are some bright points located far inside the magnetic islands. Such bright points have higher minimum magnetic flux density at the larger inward distance from the boundary. Convective velocity is apparently reduced for such high magnetic flux density regions regardless of whether they are populated by G-band bright points or not. The magnetic islands are surrounded by downflows. Conclusions: These results suggest that high magnetic flux density, as well as efficient heat transport from the sides or beneath, are required to make magnetic elements bright in G-band.
Electron density and carriers of the diffuse interstellar bands
Gnacinski, P.; Sikorski, J. K.; Galazutdinov, G. A.
2007-01-01
We have used the ionisation equilibrium equation to derive the electron density in interstellar clouds in the direction to 13 stars. A linear relation was found, that allows the determination of the electron density from the Mg I and Mg II column densities in diffuse clouds. The comparison of normalised equivalent width of 12 DIBs with the electron density shows that the DIBs equivalent width do not change with electron density varying in the range ne=0.01-2.5 cm^-3. There...
Density structures inside the plasmasphere: Cluster observations
DEFF Research Database (Denmark)
Darrouzet, F.; Decreau, P.M.E.; De Keyser, J.; Masson, A.; Gallagher, D.L.; Santolik, O.; Sandel, B.R.; Trotignon, J.G.; Rauch, J.L.; Le Guirriec, E.; Canu, P.; Sedgemore-Schulthess, F.; Andre, M.; Lemaire, J.F.
2004-01-01
The electron density profiles derived from the EFW and WHISPER instruments on board the four Cluster spacecraft reveal density structures inside the plasmasphere and at its outer boundary, the plasmapause. We have conducted a statistical study to characterize these density structures. We focus on the plasmasphere crossing on I I April 2002, during which Cluster observed several density irregularities inside the plasmasphere, as well as a plasmaspheric plume. We derive the density gradient vector...
Photoelectron diffraction and band structure effects in ARXPS from the valence bands of GeS
International Nuclear Information System (INIS)
X-ray photoelectron spectra of the valence band region of GeS are measured in dependence on polar and azimuthal angle. The anisotropy of the valence band structures is due to both, influences of initial state wave function and photoelectron diffraction. By these means in addition to the symmetry character of initial states the atomic nature of different valence band peaks can also be explained. (author)
Photonic band structure of highly deformable, self-assembling systems
Bermel, P A; Bermel, Peter A.; Warner, Mark
2001-01-01
We calculate the photonic band structure at normal incidence of highly deformable, self-assembling systems - cholesteric elastomers subjected to external stress. Cholesterics display brilliant reflection and lasing owing to gaps in their photonic band structure. The band structure of cholesteric elastomers varies sensitively with strain, showing new gaps opening up and shifting in frequency. A novel prediction of a total band gap is made, and is expected to occur in the vicinity of the previously observed de Vries bandgap, which is only for one polarisation.
Optimum design of band-gap beam structures
DEFF Research Database (Denmark)
Olhoff, Niels; Niu, Bin; Cheng, Gengdong
2012-01-01
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 optimizi...
Universality of Mallmann correlations for nuclear band structures
International Nuclear Information System (INIS)
It is shown that the Mallmann's energy ratio correlations, first time proposed 50 years ago for the ground state bands of the even-even nuclei, are universal: all band structures in collective nuclei obey the same systematics. Based on a second order anharmonic vibrator description, parameter-free recurrence relations are proposed for Mallmann-type energy ratios, which can be used to extrapolate band structures to higher spin.
Band Structure and Quantum Confined Stark Effect in InN/GaN superlattices
DEFF Research Database (Denmark)
Gorczyca, I.; Suski, T.
2012-01-01
InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite InN/GaN(0001) superlattices are investigated, and the variation of the band gap with the thicknesses of the well and the barrier is discussed. Superlattices of the form mInN/nGaN with n ? m are simulated using band structure calculations in the Local Density Approximation with a semiempirical correction for the gap error. The calculated band gap shows a strong decrease with the thickness (m) of the InN well. In superlattices containing a single layer of InN (m = 1) the band gap increases weakly with the GaN barrier thickness n, reaching a saturation value around 2 eV. In superlattices with n = m and n > 5 the band gap closes and the systems become “metallic”. These effects are related to the existence of the built-in electric fields that strongly influence valence- and conduction-band profiles and thus determine effective band gap and emission energies of the superlattices. Varying the widths of the quantum wells and barriers one may tune band gaps over a wide spectral range, which provides flexibility in band gap engineering.
Li, Tsung-Lung; Lu, Wen-Cai
2015-10-01
In this work, Koopmans' theorem for Kohn-Sham density functional theory (KS-DFT) is applied to the photoemission spectra (PES) modeling over the entire valence-band. To examine the validity of this application, a PES modeling scheme is developed to facilitate a full valence-band comparison of theoretical PES spectra with experiments. The PES model incorporates the variations of electron ionization cross-sections over atomic orbitals and a linear dispersion of spectral broadening widths. KS-DFT simulations of pristine rubrene (5,6,11,12-tetraphenyltetracene) and potassium-rubrene complex are performed, and the simulation results are used as the input to the PES models. Two conclusions are reached. First, decompositions of the theoretical total spectra show that the dissociated electron of the potassium mainly remains on the backbone and has little effect on the electronic structures of phenyl side groups. This and other electronic-structure results deduced from the spectral decompositions have been qualitatively obtained with the anionic approximation to potassium-rubrene complexes. The qualitative validity of the anionic approximation is thus verified. Second, comparison of the theoretical PES with the experiments shows that the full-scale simulations combined with the PES modeling methods greatly enhance the agreement on spectral shapes over the anionic approximation. This agreement of the theoretical PES spectra with the experiments over the full valence-band can be regarded, to some extent, as a collective validation of the application of Koopmans' theorem for KS-DFT to valence-band PES, at least, for this hydrocarbon and its alkali-adsorbed complex. PMID:25974677
All-Optical Reconstruction of Crystal Band Structure.
Vampa, G; Hammond, T J; Thiré, N; Schmidt, B E; Légaré, F; McDonald, C R; Brabec, T; Klug, D D; Corkum, P B
2015-11-01
The band structure of matter determines its properties. In solids, it is typically mapped with angle-resolved photoemission spectroscopy, in which the momentum and the energy of incoherent electrons are independently measured. Sometimes, however, photoelectrons are difficult or impossible to detect. Here we demonstrate an all-optical technique to reconstruct momentum-dependent band gaps by exploiting the coherent motion of electron-hole pairs driven by intense midinfrared femtosecond laser pulses. Applying the method to experimental data for a semiconductor ZnO crystal, we identify the split-off valence band as making the greatest contribution to tunneling to the conduction band. Our new band structure measurement technique is intrinsically bulk sensitive, does not require a vacuum, and has high temporal resolution, making it suitable to study reactions at ambient conditions, matter under extreme pressures, and ultrafast transient modifications to band structures. PMID:26588381
Prediction of Band Structure of $Bi_2Te_3$-related Binary and Ternary Thermoelectric Materials
Ryu, Byungki; Oh, Min-Wook; Kim, Bong-Seo; Lee, Ji Eun; Joo, Sung-Jae; Min, Bok-Ki; Lee, HeeWoong; Park, Sudong
2015-01-01
Density functional calculations have performed to study the band structures of $Bi_2Te_3$-related binary ($Bi_2Te_3$, $Sb_2Te_3$, $Bi_2Se_3$, and $Sb_2Se_3$) and $Sb$/$Se$ doped ternary compounds [$(Bi_{1-x}Sb_x)_2Te_3$ and $Bi_2(Te_{1-y}Se_y)_3$]. It is found that the band gap can be increased by $Sb$ doping and it is monotonically increased by $Se$ doping. In ternary compounds, the change of the conduction band structure is more significant, as compared to the change of va...
Electronic band structure of pseudodirect chalcopyrite semiconductors. 1
International Nuclear Information System (INIS)
The band structure of the chalcopyrite semiconductor CdSiP2 is calculated using the empirical pseudopotential method applied successfully already in the case of ZnSiP2. The band structure is in good agreement with recent experimental data, especially with the inverse crystal field splitting found by Shileika et al. The influence of the three contributions to the deviation of the chalcopyrite structure from a cubic one (antisymmetric cation potential, tetragonal compression and distortion of the anion sublattice) on the band structure and the optical transition energies is investigated in detail for both ZnSiP2 and CdSiP2. (author)
Band structures and shape coexistence in {sup 187}Pt
Energy Technology Data Exchange (ETDEWEB)
Hojman, D. [Comision Nacional de Energia Atomica, Departamento de Fisica, Buenos Aires (Argentina); CONICET, Buenos Aires (Argentina); Cardona, M.A. [Comision Nacional de Energia Atomica, Departamento de Fisica, Buenos Aires (Argentina); CONICET, Buenos Aires (Argentina); Universidad Nacional de San Martin, Buenos Aires (Argentina); Roussiere, B.; Sauvage, J. [IN2P3/CNRS/Universite Paris-Sud, Institut de Physique Nucleaire, Orsay (France); Riley, M.A.; Tabor, S.L.; Hoffman, C.R.; Aguilar, A.; Cluff, W.T.; Hinners, T.; Lagergren, K.; Lee, S.; Perry, M.; Pipidis, A.; Tripathi, V. [Florida State University, Department of Physics, Tallahassee, Florida (United States)
2012-06-15
High-spin states in {sup 187}Pt have been studied by means of {gamma}-ray spectroscopy techniques. Known bands have been significantly extended and new bands have been found. The band structures are discussed in the framework of the cranking model and negative-parity states are compared with calculations performed with a semi-microscopic axial-rotor plus one-quasiparticle coupling model. Shape coexistence is observed from low excitation energy. (orig.)
Band structures and shape coexistence in 187Pt
International Nuclear Information System (INIS)
High-spin states in 187Pt have been studied by means of ?-ray spectroscopy techniques. Known bands have been significantly extended and new bands have been found. The band structures are discussed in the framework of the cranking model and negative-parity states are compared with calculations performed with a semi-microscopic axial-rotor plus one-quasiparticle coupling model. Shape coexistence is observed from low excitation energy. (orig.)
Band structure approach to the resonant x-ray scattering
Elfimov, I. S; Skorikov, N. A.; V. I. Anisimov; 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 behav...
Design of a Miniaturized Dual Wide Band Frequency Selective Structure
Shwetanki Singh; Partha Pratim Sarkar; Sarkar, D.; Biswas, S
2013-01-01
This paper deals with the frequency selective property of a structure comprising of a two dimensional array of patches. This frequency selective surface (FSS) acts like a dual band reject filter. The proposed design has been investigated theoretically using Ansoft Designer® software in which the reflection and transmission band have been predicted by the method known as Method of Moment which is most complicated but its accuracy is best. Efforts have been given to achieve dual high band rejec...
Lei, X.; Liang, X. X.; Zhao, G. J.; Song, T. L.
2014-03-01
The electronic band structure and phonon dispersion of wurtzite BN are studied by the first principle calculations. The local density approximation (LDA) and the generalized gradient approximation (GGA) exchange-correlation potentials are applied in the calculations and compared. The computational results for the band structure and density of states with indirect band gaps as well as the phonon dispersive curves and density of states are obtained. The corresponding dielectric and thermodynamic properties are discussed. The conclusions are consistent with other theoretical results and experimental data.
Shell model description of band structure in 48Cr
International Nuclear Information System (INIS)
The band structure for normal and abnormal parity bands in 48Cr are described using the m-scheme shell model. In addition to full fp-shell, two particles in the 1d3/2 orbital are allowed in order to describe intruder states. The interaction includes fp-, sd- and mixed matrix elements
Design of a Miniaturized Dual Wide Band Frequency Selective Structure
Directory of Open Access Journals (Sweden)
Shwetanki Singh
2013-01-01
Full Text Available This paper deals with the frequency selective property of a structure comprising of a two dimensional array of patches. This frequency selective surface (FSS acts like a dual band reject filter. The proposed design has been investigated theoretically using Ansoft Designer® software in which the reflection and transmission band have been predicted by the method known as Method of Moment which is most complicated but its accuracy is best. Efforts have been given to achieve dual high band reject filtering with high band ratio (approx 3.18.
Density structures inside the plasmasphere: Cluster observations
DEFF Research Database (Denmark)
Darrouzet, F.; Decreau, P.M.E.
2004-01-01
The electron density profiles derived from the EFW and WHISPER instruments on board the four Cluster spacecraft reveal density structures inside the plasmasphere and at its outer boundary, the plasmapause. We have conducted a statistical study to characterize these density structures. We focus on the plasmasphere crossing on I I April 2002, during which Cluster observed several density irregularities inside the plasmasphere, as well as a plasmaspheric plume. We derive the density gradient vectors from simultaneous density measurements by the four spacecraft. We also determine the normal velocity of the boundaries of the plume and of the irregularities from the time delays between those boundaries in the four individual density profiles, assuming they are planar. These new observations yield novel insights about the occurrence of density irregularities, their geometry and their dynamics. These in-situ measurements are compared with global images of the plasmasphere from the EUV imager on board the IMAGE satellite.
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 ?–? 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.
Coupled Line Band Pass Filter with Defected Ground Structure for Wide Band Application
Abhiruchi Nagpal,; Dr. P.K. Singhal
2014-01-01
In this paper a novel wideband microstrip band pass filter is proposed. The band pass filter is designed with coupling between two L-shaped microstriplines and is terminated with a high impedance line. The three circle shapes are etched out at the ground plane and is called defected ground structure (DGS), which provides better return loss as well as it reduces harmonics. Simulated and measured results both are in true agreement with each other. Results show that the defected m...
Structure of rotational bands in {sup 253}No
Energy Technology Data Exchange (ETDEWEB)
Herzberg, R.D.; Moon, S.; Butler, P.A.; Page, T.; Amzal, N.; Bastin, J.E.; Cocks, J.F.C.; Darby, I.G.; Gray-Jones, C.; Hammond, N.J.; Herzberg, A.; Humphreys, R.D.; Jones, G.D.; Page, R.D.; Page, T.; Pritchard, A. [University of Liverpool, Oliver Lodge Laboratory, Liverpool (United Kingdom); Eeckhaudt, S.; Greenlees, P.T.; Dorvaux, O.; Jones, P.M.; Julin, R.; Juutinen, S.; Kankaanpaeae, H.; Kettunen, H.; Kuusiniemi, P.; LeCoz, Y.; Leino, M.; Leppaenen, A.P.; Muikku, M.; Nieminen, P.; Nyman, M.; Rahkila, P.; Sandzelius, M.; Saren, J.; Scholey, C.; Trzaska, W.H.; Uusitalo, J. [University of Jyvaeskylae, Department of Physics, Jyvaeskylae (Finland); Afanasjev, A.V. [Mississippi State University, Department of Physics and Astronomy, Mississippi, MS (United States); Becker, F.; Houry, M.; Huerstel, A.; Korten, W.; Lucas, R.; Theisen, C. [DAPNIA/SPhN CEA-Saclay, Saclay (France); Bender, M. [Universite Bordeaux and CNRS/IN2P3, Centre d' Etudes Nucleaires de Bordeaux Gradignan, Bordeaux (France); Bruyneel, B.; Reiter, P.; Wiens, A. [Universitaet zu Koeln, Institut fuer Kernphysik, Koeln (Germany); Eskola, K. [University of Helsinki, Department of Physics, Helsinki (Finland); Gerl, J.; Hessberger, F.; Schlegel, C.; Wollersheim, H.J. [GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt (Germany); Grahn, T.; Pakarinen, J. [University of Liverpool, Oliver Lodge Laboratory, Liverpool (United Kingdom); University of Jyvaeskylae, Department of Physics, Jyvaeskylae (Finland); Hauschild, K. [IN2P3-CNRS, CSNSM, Orsay Campus (France); Heenen, P.H. [Universite Libre de Bruxelles, Service de Physique Nucleaire Theorique, Bruxelles (Belgium); Helariutta, K. [University of Jyvaeskylae, Department of Physics, Jyvaeskylae (Finland); University of Helsinki, Department of Physics, Helsinki (Finland); Khoo, T.L.; Lister, C.J. [Argonne National Laboratory, Argonne, IL (United States)
2009-12-15
In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the {sup 253} No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the 9/2{sup -}[734]{sub {nu}} ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work. (orig.)
Band structure calculations for Ba$_{6}$Ge$_{25}$ and Ba$_{4}$Na$_{2}$Ge$_{25}$ clathrates
Zerec, I; Thalmeier, P; Grin, Y; Zerec, Ivica; Yaresko, Alexander; Thalmeier, Peter; Grin, Yuri
2002-01-01
Electronic band structures for Ba$_{6}$Ge$_{25}$ and Ba$_{4}$Na$_{2}$Ge$_{25}$ clathrates are calculated using linear muffin-tin orbital method within the local density approximation. It is found that barium states strongly contribute to the density of states at the Fermi level and thus can influence the transport properties of the compounds. A sharp peak of the density of states is found just at the Fermi level. It is also shown that the shifting of barium atoms toward experimentally deduced split positions in Ba$_{6}$Ge$_{25}$ produces a splitting of this peak which may therefore be interpreted as a band Jahn-Teller effect. If the locking of the barium atoms at the observed structural phase transition is assumed, this reduction of the density of states at the Fermi level can qualitatively account for the experimentally observed decrease of the magnetic susceptibility and electrical resistivity at the phase transition.
Relationships between magnetic foot points and G-band bright structures
Ishikawa, R; Kitakoshi, Y; Katsukawa, Y; Bonet, J A; Domínguez, S Vargas; van der Voort, L H M Rouppe; Sakamoto, Y; Ebisuzaki, T
2008-01-01
Magnetic elements are thought to be described by flux tube models, and are well reproduced by MHD simulations. However, these simulations are only partially constrained by observations. We observationally investigate the relationship between G-band bright points and magnetic structures to clarify conditions, which make magnetic structures bright in G-band. The G-band filtergrams together with magnetograms and dopplergrams were taken for a plage region covered by abnormal granules as well as ubiquitous G-band bright points, using the Swedish 1-m Solar Telescope (SST) under very good seeing conditions. High magnetic flux density regions are not necessarily associated with G-band bright points. We refer to the observed extended areas with high magnetic flux density as magnetic islands to separate them from magnetic elements. We discover that G-band bright points tend to be located near the boundary of such magnetic islands. The concentration of G-band bright points decreases with inward distance from the boundar...
Computing the band structure and energy gap of penta-graphene by using DFT and G0W0 approximations
Einollahzadeh, H.; R S Dariani; Fazeli, S. M.
2015-01-01
In this paper, we consider the optimum coordinate of the penta-graphene. Penta-graphene is a new stable carbon allotrope which is stronger than graphene. Here, we compare the band gap of penta-graphene with various density functional theory (DFT) methods. We plot the band structure of penta-graphene which calculated with the generalized gradient approximation functional, about Fermi energy.
(100) ideal-surface band structure for the series of Cu-based chalcopyrites
Tototzintle-Huitle, H
2005-01-01
We use the Surface Green Function Matching (SGFM) method and a tight-binding hamiltonian to calculate the (100)-surface electronic band structure and local density of states of the series of Cu-based A^{I}B^{III}C2^{VI} chalcopyrites . We find four surface states in the optical gap energy region of s-p character and three surface states in the conduction band region of p-character. We show the trends of different characteristics within the series by means of figures and tables so that the quantitave behavior can be evaluated as well. We did not find Frontier Induced Semi-Infinite states of non-dispersive character in the studied range of energy within the valence band as we found in the case of the (112) surface electronic band structure for CuInSe2.
Hybrid density functional calculations of the band gap of GaxIn1-xN
Wu, Xifan; Walter, Eric J.; Rappe, Andrew M.; Car, Roberto; Selloni, Annabella
2009-09-01
Recent theoretical work has provided evidence that hybrid functionals, which include a fraction of exact (Hartree-Fock) exchange in the density functional theory exchange and correlation terms, significantly improve the description of band gaps of semiconductors compared with local and semilocal approximations. Based on a recently developed order- N method for calculating the exact exchange in extended insulating systems, we have implemented an efficient scheme to determine the hybrid functional band gap. We use this scheme to study the band gap and other electronic properties of the ternary compound In1-xGaxN using a 64-atom supercell model.
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 ? and ? bonds were determined in the band structure. Our results are in good agreement with experiment and pseudopotential calculations.
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.
Multi bunch dynamics in detuned x-band structures
International Nuclear Information System (INIS)
The multi bunch dynamics of a 2 x 250 GeV version of the JLC is studied. The rf-properties of detuned x-band tubes are calculated with the Computer codes URMEL and MAFIA. The dispersion curve found with these codes is compared with an equivalent circuit model. The calculation of the dipole mode loss parameters is investigated in detail. Tracking calculations are used to investigate the misalignment tolerances for detuned x-band structures. Also tilted x-band tubes are considered. (author)
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 lower eigenfrequencies of maximized band-gaps, and (iii) different values of a minimum cross-sectional area constraint. The periodicity of the optimum beams and the attenuation of their band-gaps are also di...
Design for maximum band-gaps in beam structures
DEFF Research Database (Denmark)
Olhoff, Niels; Niu, Bin
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 lower eigenfrequencies of maximized band-gaps, and (iii) different values of a minimum cross-sectional area constraint. The periodicity of the optimum beams and the attenuation of their band-gaps are also discussed.
Chaos and structure of level densities
International Nuclear Information System (INIS)
Two coexisting facets of warm nuclei, quantum chaos and structure of the level density, are considered. A newly developed combinatorial level-density model is presented, and the role of collective enhancements discussed. An example of extreme parity enhancement is shown. (author)
Band structure in the N = 88 nucleus 151Eu
International Nuclear Information System (INIS)
The nucleus 151Eu has been studied following the 152Sm(d,3n?) reaction. A decoupled band based on the 11/2- isomer is strongly populated and spins up to 27/2- are assigned. The positive parity are less strongly populated and the maximum spin observed is 13/2+. The limited number of transitions observed do however, suggest band structure based on the 7/2+ state at 21.5 keV. (Author)
QUANTITATIVE ANALYSIS OF BANDED STRUCTURES IN DUAL-PHASE STEELS
Benoit Krebs; Alain Hazotte; Lionel Germain; Mohamed Gouné
2011-01-01
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 intensit...
Calculation of electronic structure and density of state for BaTiO3
Directory of Open Access Journals (Sweden)
H. Salehi
2002-12-01
Full Text Available The electronic structure, density of state (DOS and electronic density of state inparaelectric cubic crystal Ba TiO3 are studied using full potential-linearized augmented plane wave (FP-LAPW method in the framework of the density functional theory (DFT with the generalized gradient approximation (GGA by the WIEN2K package. The results show a direct band gap of 1.8 eV at the point in the Brillouin zone. The calculated band structure and density of state of BaTiO3 are in good agreement with theoretical and experimental results.
Ahmadpour Monazam, Mohammad Reza; Hingerl, Kurt; Puschnig, Peter
2013-08-01
The quasiparticle band structure and dielectric function for the so-called magic sequence SiGe2Si2Ge2SiGe12 (or ?12) structure [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.108.027401 108, 027401 (2012)] are calculated by many-body perturbation theory (MBPT) within an ab initio framework. On top of density functional calculations within the local density approximation (LDA) leading to a fundamental band gap of 0.23 eV, we have computed the quasiparticle band structure within the G0W0 approach, opening the gap to 0.61 eV. Moreover, we have calculated the optical properties by solving the Bethe-Salpeter equation (BSE) for the electron-hole two-particle correlation function. When comparing the imaginary part of the dielectric function obtained at various levels of approximation-i.e., the independent particle approximation (or random phase approximation) based on (i) the LDA or (ii) GW band structures, and (iii) the BSE including local field effects and electron-hole correlations—we observe that the important first transition is better explained by taking into account excitonic effects. Moreover, the onset transition originating from the direct transition of the magic sequence structure is also investigated.
Self-isospectrality, tri-supersymmetry and band structure
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.
Deformation Bands: Strain Localization Structures in Highly Porous Sandstone
Fossen, H.; Schultz, R. A.; Shipton, Z. K.; Mair, K.
2007-12-01
Deformation bands are the most common strain localization feature found in deformed porous sandstones and sediments, including Quaternary deposits, soft gravity slides and tectonically affected sandstones in hydrocarbon reservoirs and aquifers. They occur as various types of tabular deformation zones where grain reorganization occurs by grain sliding, rotation and/or fracture during overall dilation, shearing, and/or compaction. These structures form in rocks and sediments where porosity exceeds approximately 15 percent, where the pore space allows for a more flexible grain reorganization that that seen in non- and low-porosity rocks. Deformation bands with a significant component of shear are most common and typically accommodate shear offsets of millimeters to centimeters. They can occur as single structures or cluster zones, and are the main deformation element of fault damage zones in porous rocks. Factors such as porosity, mineralogy, grain size and shape, lithification, state of stress and burial depth control the type of deformation band formed. The different types are controlled by deformation mechanisms: cataclasis, rigid grain reorganization (granular flow) and cementation and/or dissolution (wet diffusion). Most bands show a reduction in porosity and permeability, usually between 0 and 3 orders of magnitude. Of the different types, phyllosilicate bands and most notably cataclastic deformation bands show the largest reduction in permeability, and thus have the greatest potential to influence fluid flow. This is particularly so where the bands occur in clusters, and if dissolution accompanies the cataclasis. Disaggregation bands, where non-cataclastic, granular flow is the dominant mechanism, show less influence on fluid flow unless assisted by chemical compaction or cementation.
Novel structural flexibility identification in narrow frequency bands
International Nuclear Information System (INIS)
A ‘Sub-PolyMAX’ method is proposed in this paper not only for estimating modal parameters, but also for identifying structural flexibility by processing the impact test data in narrow frequency bands. The traditional PolyMAX method obtains denominator polynomial coefficients by minimizing the least square (LS) errors of frequency response function (FRF) estimates over the whole frequency range, but FRF peaks in different structural modes may have different levels of magnitude, which leads to the modal parameters identified for the modes with small FRF peaks being inaccurate. In contrast, the proposed Sub-PolyMAX method implements the LS solver in each subspace of the whole frequency range separately; thus the results identified from a narrow frequency band are not affected by FRF data in other frequency bands. In performing structural identification in narrow frequency bands, not in the whole frequency space, the proposed method has the following merits: (1) it produces accurate modal parameters, even for the modes with very small FRF peaks; (2) it significantly reduces computation cost by reducing the number of frequency lines and the model order in each LS implementation; (3) it accurately identifies structural flexibility from impact test data, from which structural deflection under any static load can be predicted. Numerical and laboratory examples are investigated to verify the effectiveness of the proposed method. (paper)
Band structure analysis of the conduction-band mass anisotropy in 6H and 4H SiC
Lambrecht, Walter R. L.; Segall, Benjamin
1995-01-01
The band structures of 6H and 4H SiC calculated by means of the FP-LMTO method are used to determine the effective mass tensors for their conduction-band minima. The results are shown to be consistent with recent optically detected cyclotron resonance measurements and predict an unusual band filling dependence for 6H-SiC.
Dependence of band structures on stacking and field in layered graphene
Aoki, M; Aoki, Masato; Amawashi, Hiroshi
2007-01-01
Novel systems of layered graphene are attracting interest for theories and applications. The stability, band structures of few-layer graphite films, and their dependence on electric field applied along the c-axis are examined within the density functional theory. We predict that those of Bernal type and also rhombohedral type tri- and tetra-layer graphite films exhibit stability. The rhombohedral-type systems including AB-bilayer, show variable band gap induced by perpendicular electric field, whereas the other systems such as the Bernal-type films stay semi-metallic.
Aközbek, N.; Mattiucci, N.; Bloemer, M. J.; Sanghadasa, M.; D'Aguanno, G.
2014-04-01
We report theoretical predictions and experimental results on the formation of pass bands and stop bands of extraordinary acoustic transmission in multilayer structures based on alternating layers of acoustic metamaterial and air. The metamaterial layers can be made of any acoustically hard material perforated with a two-dimensional array of subwavelength apertures. In this way, it is possible to tailor the density and speed of sound of an otherwise acoustically bulk hard material with fixed properties. The sonic band structure allows transmission passband and stop bandgaps that depend on the layer thicknesses and effective properties of the metamaterials. In addition, we show the existence of resonant tunneling due to the formation of an acoustic passband in a spectral region of low transmission for a single layer. This opens the possibility to engineer different types of phononic materials to manipulate and control acoustic waves.
Scientific Electronic Library Online (English)
Nagendra, Kushwaha; Raj, Kumar.
2014-06-01
Full Text Available In this paper, single and dual band EBG structures for wider bandwidth are proposed. In each of the discussed EBGs, a metallic patch of regular geometry is chosen for the unit element. The patch is further modified by cutting slots to get extra inductance and capacitance which results into lower cut [...] -off frequency and larger bandwidth. The proposed EBG structures are compared with the standard mushroom type EBG with respect to surface wave attenuation. The -20 dB cut-off frequencies and bandwidths of the various EBGs are compared. The effect of unit element size, gap between unit elements and via diameter on the transmission response is presented. Among the discussed EBGs, the swastika type structure is compact, single band and has wider bandwidth. The square patch with a single disconnected loop type slot EBG and the Fractal EBG are dual band. While square patch is more compact, the fractal EBG has wider bandwidth. All the EBGs can be useful in the design of antenna and other microwave circuits.
DEFF Research Database (Denmark)
Christensen, N. Egede; Feuerbacher, B.
1974-01-01
The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure is obtained from an ad hoc potential based on a Dirac-Slater atomic calculation for the ground-state configuration and with full Slater exchange in the atomic as well as in the crystal potential. The selection of this best potential is justified by comparing the calculated band structure to Fermi-surface experiments and to optical-reflectance measurements up to 5-eV photon energy. The temperature and strain responses in the band structure are estimated from band calculations with four different lattice constants. The band structure was determined in the entire Brillouin zone and is applied to a calculation of photoemission spectra from W single crystals. The nondirect as well as the direct models for bulk photoemission processes are investigated. The emission from the three low-index surfaces (100), (110), and (111) exhibits strong dependence on direction and acceptance cone. According to the present band model there should essentially be no emission normal to the (110) face for photon energies between 9.4 and 10.6 eV. Experimental observation of emission in this gap, however, implies effects not included in the simple bulk models. In particular, effects arising from surface emission have been considered, i.e., emission of those electrons which are excited in a single-step process from initial states near the surface to final states outside the crystal. The electrons that are emitted from the surface in directions perpendicular to the crystal planes carry information on the one-dimensional surface density of states. The present work includes a crude estimate of this surface density of states, which is derived from the bulk band structure by narrowing the d bands according to an effective number of neighbors per surface atom. Estimates of surface relaxation effects are also included.
Band-gap corrected density functional theory calculations for InAs/GaSb type II superlattices
Wang, Jianwei; Zhang, Yong
2014-12-01
We performed pseudopotential based density functional theory (DFT) calculations for GaSb/InAs type II superlattices (T2SLs), with bandgap errors from the local density approximation mitigated by applying an empirical method to correct the bulk bandgaps. Specifically, this work (1) compared the calculated bandgaps with experimental data and non-self-consistent atomistic methods; (2) calculated the T2SL band structures with varying structural parameters; (3) investigated the interfacial effects associated with the no-common-atom heterostructure; and (4) studied the strain effect due to lattice mismatch between the two components. This work demonstrates the feasibility of applying the DFT method to more exotic heterostructures and defect problems related to this material system.
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.
Electronic band structure and optical properties of the cubic, Sc, Y and La hydride systems
International Nuclear Information System (INIS)
Electronic band structure calculations are used to interpret the optical spectra of the cubic Sc, Y and La hydride systems. Self-consistent band calculations of ScH2 and YH2 were carried out. The respective joint densities of states are computed and compared to the dielectric functions determined from the optical measurements. Additional calculations were performed in which the Fermi level or band gap energies are rigidly shifted by a small energy increment. These calculations are then used to simulate the derivative structure in thermomodulation spectra and relate the origin of experimental interband features to the calculated energy bands. While good systematic agreement is obtained for several spectral features, the origin of low-energy interband transitions in YH2 cannot be explained by these calculated bands. A lattice-size-dependent premature occupation of octahedral sites by hydrogen atoms in the fcc metal lattice is suggested to account for this discrepancy. Various non-self-consistent calculations are used to examine the effect of such a premature occupation. Measurements of the optical absorptivity of LaH/sub x/ with 1.6 2 lattice. These experimental results also suggest that, in contrast to recent calculations, LaH3 is a small-band-gap semiconductor
Band structure and optical properties of amber studied by first principles
International Nuclear Information System (INIS)
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
Inter-band optoelectronic properties in quantum dot structure of low band gap III-V semiconductors
International Nuclear Information System (INIS)
A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k?) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg1?xCdxTe, and In1?xGaxAsyP1?y lattice matched to InP, as example of III–V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors
Waveguiding in surface plasmon polariton band gap structures
DEFF Research Database (Denmark)
Bozhevolnyi, S.I.; Østergaard, John Erland
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.
Electronic band structure of magnetic bilayer graphene superlattices
Energy Technology Data Exchange (ETDEWEB)
Pham, C. Huy; Nguyen, T. Thuong [Theoretical and Computational Physics Department, Institute of Physics, VAST, 10 Dao Tan, Ba Dinh Distr., Hanoi 10000 (Viet Nam); SISSA/International School for Advanced Study, Via Bonomea 265, I-34136 Trieste (Italy); Nguyen, V. Lien, E-mail: nvlien@iop.vast.ac.vn [Theoretical and Computational Physics Department, Institute of Physics, VAST, 10 Dao Tan, Ba Dinh Distr., Hanoi 10000 (Viet Nam); Institute for Bio-Medical Physics, 109A Pasteur, 1st Distr., Hochiminh City (Viet Nam)
2014-09-28
Electronic band structure of the bilayer graphene superlattices with ?-function magnetic barriers and zero average magnetic flux is studied within the four-band continuum model, using the transfer matrix method. The periodic magnetic potential effects on the zero-energy touching point between the lowest conduction and the highest valence minibands of pristine bilayer graphene are exactly analyzed. Magnetic potential is shown also to generate the finite-energy touching points between higher minibands at the edges of Brillouin zone. The positions of these points and the related dispersions are determined in the case of symmetric potentials.
Multi-band and broadband acoustic metamaterial with resonant structures
International Nuclear Information System (INIS)
We design an acoustic metamaterial (AM) with multi-band of negative modulus composed of different sized split hollow spheres (SHSs). From acoustic transmitted experiment, the AM exhibits simultaneously negative modulus at frequencies 914, 1298 and 1514 Hz. Based on the multi-band designed concept, broadband AM is fabricated by arraying gradually sized SHS. The transmission results indicate that this medium can achieve negative modulus at the frequency range from 900 to 1500 Hz. This kind of broadband AM is very convenient to couple with other structures to gain the double-negative AM.
Multi-band and broadband acoustic metamaterial with resonant structures
Energy Technology Data Exchange (ETDEWEB)
Ding Changlin; Zhao Xiaopeng, E-mail: xpzhao@nwpu.edu.cn [Smart Materials Laboratory, Department of Applied Physics, Northwestern Polytechnical University, Xi' an 710129 (China)
2011-06-01
We design an acoustic metamaterial (AM) with multi-band of negative modulus composed of different sized split hollow spheres (SHSs). From acoustic transmitted experiment, the AM exhibits simultaneously negative modulus at frequencies 914, 1298 and 1514 Hz. Based on the multi-band designed concept, broadband AM is fabricated by arraying gradually sized SHS. The transmission results indicate that this medium can achieve negative modulus at the frequency range from 900 to 1500 Hz. This kind of broadband AM is very convenient to couple with other structures to gain the double-negative AM.
Structurally tunable resonant absorption bands in ultrathin broadband plasmonic absorbers.
Butun, Serkan; Aydin, Koray
2014-08-11
Light absorption is a fundamental optical process playing significantly important role in wide variety of applications ranging from photovoltaics to photothermal therapy. Semiconductors have well-defined absorption bands with low-energy edge dictated by the band gap energy, therefore it is rather challenging to tune the absorption bandwidth of semiconductors. However, resonant absorbers based on plasmonic nanostructures and optical metamaterials emerged as alternative light absorbers due to spectrally selective absorption bands resulting from optical resonances. Recently, a broadband plasmonic absorber design was introduced by Aydin et al. with a reasonably high broadband absorption. Based on that design, here, structurally tunable, broadband absorbers with improved performance are demonstrated. This broadband absorber has a total thickness of 190 nm with 80% average measured absorption (90% simulated absorption) over the entire visible spectrum (400 - 700 nm). Moreover, the effect of the metal and the oxide thicknesses on the absorption spectra are investigated and results indicate that the shorter and the longer band-edge of broadband absorption can be structurally tuned with the metal and the oxide thicknesses, as well as with the resonator size. Detailed numerical simulations shed light on the type of optical resonances that contribute to the broadband absorption response and provide a design guideline for realizing plasmonic absorbers with structurally tunable bandwidths. PMID:25321029
Analysis of tunable photonic band structure in an extrinsic plasma photonic crystal
King, Tzu-Chyang; Yang, Chih-Chiang; Hsieh, Pei-Hung; Chang, Tsung-Wen; Wu, Chien-Jang
2015-03-01
In this work, we theoretically investigate the tunable photonic band structure (PBS) for an extrinsic plasma photonic crystal (PPC). The extrinsic PPC is made of a bulk cold plasma layer which is influenced by an externally periodic static magnetic field. The PBS can be tuned by the variation of the magnitude of externally applied magnetic field. In addition, we also show that the PBS can be changed as a function of the electron density as well as the thickness variation.
Extended Hückel theory for band structure, chemistry, and transport. I. Carbon nanotubes
Kienle, D.; Cerdá, J. I.; Ghosh, A.W.
2006-01-01
We describe a semiempirical atomic basis extended Hückel theoretical (EHT) technique that can be used to calculate bulk band structure, surface density of states, electronic transmission, and interfacial chemistry of various materials within the same computational platform. We apply this method to study multiple technologically important systems, starting with carbon nanotubes and their interfaces and silicon-based heterostructures in our follow-up paper [D. Kienle et al., J. Appl. Phys. 100,...
Chaos and structure of level densities
Energy Technology Data Exchange (ETDEWEB)
Moller, Peter [Los Alamos National Laboratory; Aberg, Sven [LUND SWEDEN; Uhrenholt, Henrik [LUND SWEDEN; Ickhikawa, Takatoshi [RIKEN
2008-01-01
The energy region of the first few MeV above the ground state shows interesting features of the nucleus. Beyond an ordered energy region just above the ground-state the dynamics changes, and chaotic features are observed in the neutron resonance region. The statistical properties of energies and wave-functions are common to all chaotic nuclei. However, if instead a global property, like the local level-density function is studied, strong structure effects emerge. In this contribution we discuss these two different facets of warm nuclei. In section 2 the onset of chaos with increasing excitation energy is discussed, with both experimental observations and proposed theoretical mechanisms as starting points. The structure of level densities in the same excitation energy region based on the two different starting points, is treated in section 3, where we give a short presentation of a newly developed combinatorial level-density modell. Some results from the model are presented and discussed. Two coexisting facets of warm nuclei, quantum chaos and structure of the level density, are considered. A newly developed combinatorial level-density model is presented, and the role of collective enhancements discussed. An example of extreme parity enhancement is shown.
RF tests of a band overlap free DAW accelerating structure
International Nuclear Information System (INIS)
This paper deal with the results of measurements on a six cells Disk-and-Washer structure. The RF structure operating at 3600 Mhz is optimized for a BETA = 1 electron beam, trying to avoid the overlap between the band of the accelerating modes and the bands of the dangerous beam deflecting modes. The cavity geometry was not optimized for the maximum shunt impedance, but nevertheless a characteristic shunt impedance Z/Q of 1500 ohm was obtained. Measurements on the six cells prototype section built following this design shown a perfect agreement (in frequency and field distribution) with the computations. The measured characteristic shunt impedance Z/Q of the prototype was 1500 ohm in agreement with the computations. The dangerous dipole modes inducing beam breakup were (as computed) 40 MHz apart from the operating frequency of the structure showing the correctness of the assumptions made
Reduced Bloch mode expansion for periodic media band structure calculations
Hussein, Mahmoud I
2008-01-01
Reduced Bloch mode expansion is presented for fast periodic media band structure calculations. The expansion employs a natural basis composed of a selected reduced set of Bloch eigenfunctions. The reduced basis is selected within the irreducible Brillouin zone at high symmetry points determined by the medium's crystal structure and group theory (and possibly at additional related points). At each of the reciprocal lattice selection points, a number of Bloch eigenfunctions are selected up to the frequency range of interest for the band structure calculations. Since it is common to initially discretize the periodic unit cell and solution field using some choice of basis, reduced Bloch mode expansion is practically a secondary expansion that uses a selected set of Bloch eigenvectors. Such expansion therefore keeps, and builds on, any favorable attributes a primary expansion approach might exhibit. Being in line with the well known concept of modal analysis, the proposed approach maintains accuracy while reducing...
Coupling effect of quantum wells on band structure
Jie, Chen; Weiyou, Zeng
2015-10-01
The coupling effects of quantum wells on band structure are numerically investigated by using the Matlab programming language. In a one dimensional finite quantum well with the potential barrier V0, the calculation is performed by increasing the number of inserted barriers with the same height Vb, and by, respectively, varying the thickness ratio of separated wells to inserted barriers and the height ratio of Vb to V0. Our calculations show that coupling is strongly influenced by the above parameters of the inserted barriers and wells. When these variables change, the width of the energy bands and gaps can be tuned. Our investigation shows that it is possible for quantum wells to achieve the desired width of the bands and gaps.
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.
Optimum design of band-gap beam structures
DEFF Research Database (Denmark)
Olhoff, Niels; Niu, Bin
2012-01-01
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 in the present paper that such an a priori assumption is not necessary since, in general, just the maximization of the gap between two consecutive natural frequencies leads to significant design periodicity. The aim of this paper is to maximize frequency gaps by shape optimization of transversely vibrating Bernoulli–Euler beams subjected to free, standing wave vibration or forced, time-harmonic wave propagation, and to study the associated creation of periodicity of the optimized beam designs. The beams are assumed to have variable cross-sectional area, given total volume and length, and to be made of a single, linearly elastic material without damping. Numerical results are presented for different combinations of classical boundary conditions, prescribed orders of the upper and lower natural frequencies of maximized natural frequency gaps, and a given minimum constraint value for the beam cross-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-harmonic loading with different excitation frequencies, in order to investigate the attenuation levels in prescribed frequency band-gaps. The results demonstrate that there is almost perfect correlation between the band-gap size/location of the emerging band structure and the size/location of the corresponding natural frequency gap in the finite structure.
Development of X-band accelerating structures for high gradients
Bini, S.; Chimenti, V.; Marcelli, A.; Palumbo, L.; Spataro, B.; A. Dolgashev, V.; Tantawi, S.; D. Yeremian, A.; Higashi, Y.; G. Grimaldi, M.; Romano, L.; Ruffino, F.; Parodi, R.
2012-07-01
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.
A NOVEL TRIPLE-BAND ELECTROMAGNETIC BANDGAP (EBG) STRUCTURE
Tran Minh Tuan; Dao Ngoc Chien; Huynh Nguyen Bao Phuong
2013-01-01
A novel triple-band uni-planar electromagnetic bandgap (UC-EBG) structure is proposed in this paper. This EBG structure can be considered as distorted uni-planar compact-EBG (DUC-EBG) which is connected together by the meandered line inductor. Split ring resonators (SRR) are embedded in four pad corners and two L-shaped slots are etched at the central pad. The proposed EBG structure is modelled in three equivalent circuits. By using in-house developed computational code based on the FDTD meth...
Joint density of states of wide-band-gap materials by electron energy loss spectroscopy
International Nuclear Information System (INIS)
Kramers-Kronig analysis for parallel electron energy loss spectroscopy (PEELS) data is developed as a software package. When used with a JEOL 4000EX high-resolution transmission electron microscope (HRTEM) operating at 100 keV this allows us to obtain the dielectric function of relatively wide band gap materials with an energy resolution of approx 1.4 eV. The imaginary part of the dielectric function allows the magnitude of the band gap to be determined as well as the joint-density-of-states function. Routines for obtaining three variations of the joint-density of states function, which may be used to predict the optical and dielectric response for angle-resolved or angle-integration scattering geometries are also described. Applications are presented for diamond, aluminum nitride (AlN), quartz (SiO2) and sapphire (Al2O3). The results are compared with values of the band gap and density of states results for these materials obtained with other techniques. (authors)
Engineering Design of a Multipurpose X-band Accelerating Structure
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...
Investigation of the band structure of Zn{sub x}Mg{sub 1-x}O alloys
Energy Technology Data Exchange (ETDEWEB)
Franz, Christian; Czerner, Michael; Giar, Marcel; Heinemann, Markus; Heiliger, Christian [I. Physikalisches Institut, Justus Liebig University Giessen (Germany)
2011-07-01
We investigate the electronic structure of Zn{sub x}Mg{sub 1-x}O alloys as a function of composition ab initio by means of density functional theory. Thereby, we model the alloys by using the coherent potential approximation (CPA) implemented in a Korringa-Kohn-Rostoker Green's function method. Within the CPA the band structure itself is not well defined but we can analyze the Bloch spectral functions. Out of these spectral functions we extract effective masses, the positions of band edges, and the band gap. All these quantities are discussed with respect to their dependence of composition.
Planar Dielectric Accelerator Structures at W-band
International Nuclear Information System (INIS)
We describe the operating principles, design, fabrication, assembly, and bench-test of a miniature planar dielectric traveling-wave accelerator structure made from dielectric brazed to oxygen-free electronic grade (OFE) copper. This work focuses on alumina ceramic (AL995) and diamond as dielectrics. This two-port device is matched to WR10 at input and output, and designed for charged particle acceleration at 91.392 GHz (W-band)
Tailoring the Phonon Band Structure in Binary Colloidal Mixtures
Fornleitner, J.; Kahl, G; Likos, C. N.
2010-01-01
We analyze the phonon spectra of periodic structures formed by two-dimensional mixtures of dipolar colloidal particles. These mixtures display an enormous variety of complex ordered configurations [J. Fornleitner {\\it et al.}, Soft Matter {\\bf 4}, 480 (2008)], allowing for the systematic investigation of the ensuing phonon spectra and the control of phononic gaps. We show how the shape of the phonon bands and the number and width of the phonon gaps can be controlled by chang...
Cell and band structures in cold rolled polycrystalline copper
DEFF Research Database (Denmark)
Ananthan, V.S.; Leffers, Torben; Hansen, Niels
1991-01-01
The effect of plastic strain on the deformation microstructure has been investigated in polycrystalline copper rolled at room temperature to 5, 10, 20, and 30% reduction in thickness equivalent strain 0.06-0.42). Results from transmission electron microscopy (TEM) observations show that dense dislocation walls (DDWs) and cells develop during the initial stages of cold rolling. Grains having a high density of DDWs are described as high wall density (HWD) structures, and grains having a low densit...
Collective band structures in doubly odd 136La nucleus
International Nuclear Information System (INIS)
Using heavy-ion nuclear reaction and in-beam ?-ray spectroscopy technique, high spin states of 136La have been studied. The nuclear reaction used is 130Te(11B, 5n) with a beam energy 60 MeV. The level scheme with three collective band structures has been updated with spin up to 20 ?. The collective backbending has been observed in ?h11/2 direct x ?h11/2 band. According to the TRS calculations, this backbending is due to the alignment of a pair of h11/2 neutrons. The signature splitting and inversion for the ?h11/2 direct x ?h11/2 band were also discussed. Other two bands based on 12- and 16+ levels were proposed as oblate deformation with ??-60 degree. They most probably originate from four- and six- quasiparticle configurations, that is, ?h11/2 direct x ?g7/2h11/22 and ?g7/2 direct x ?g7/22d5/2h11/22 respectively. (authors)
Band structure mapping of photonic crystal intersubband detectors
Schartner, S.; Golka, S.; Pflügl, C.; Schrenk, W.; Andrews, A. M.; Roch, T.; Strasser, G.
2006-10-01
The authors report on a quantum well infrared detector embedded in a surface-plasmon waveguide and processed into a deeply etched photonic crystal structure. The device was characterized by collecting the polarization dependent response spectra at different angles of incidence. With this method it is possible to map the photonic band structure by directly detecting the modes of the photonic crystal. It therefore represents a new and direct characterization procedure for photonic crystals. The device shows a strong mixing between TE and TM polarized modes, which is caused by the asymmetric vertical waveguide design.
Hybrid density functional calculations of the surface electronic structure of GdN
Marsoner Steinkasserer, Lukas Eugen; Paulus, Beate; Gaston, Nicola
2015-06-01
Rare-earth nitrides are a promising class of materials for application in spintronics, with GdN a particularly well-studied example. Here we perform band-structure calculations employing a hybrid density functional, which enables the band gap to be more accurately predicted through the inclusion of short-range exact exchange. The sensitivity of the band gap to the exchange term is demonstrated. The surface electronic structure is simulated through the use of slab models of the GdN(111) surface, which provide a consistent description of metallic surface states in the majority-spin channel.
Spectral Density Functionals for Electronic Structure Calculations
Savrasov, S.Y.; G. Kotliar
2003-01-01
We introduce a spectral density functional theory which can be used to compute energetics and spectra of real strongly--correlated materials using methods, algorithms and computer programs of the electronic structure theory of solids. The approach considers the total free energy of a system as a functional of a local electronic Green function which is probed in the region of interest. Since we have a variety of notions of locality in our formulation, our method is manifestly...
Energy Technology Data Exchange (ETDEWEB)
Schwöbel, André, E-mail: aschwoebel@surface.tu-darmstadt.de [Technische Universität Darmstadt, Materials Science Department, Surface Science Division, Jovanka-Bontschits-Str. 2, 64287 Darmstadt (Germany); Precht, Ruben; Motzko, Markus; Carrillo Solano, Mercedes A. [Technische Universität Darmstadt, Materials Science Department, Surface Science Division, Jovanka-Bontschits-Str. 2, 64287 Darmstadt (Germany); Calvet, Wolfram [Helmholzzentrum Berlin GmbH, Solar Energy Research, Heterogeneous Materials Systems, Albert Einstein Straße 15, 12489 Berlin (Germany); Hausbrand, René; Jaegermann, Wolfram [Technische Universität Darmstadt, Materials Science Department, Surface Science Division, Jovanka-Bontschits-Str. 2, 64287 Darmstadt (Germany)
2014-12-01
Highlights: • In situ photoemission of LiPON solid Li-ion electrolyte. • We find that the valence band is similar to the known phosphates. • We find evidence for a resonance at the O1s edge shown by a Fano profile. • We find that the top of the valence band is due to N2p states. - Abstract: Lithium phosphorus oxynitride (LiPON) is a solid state electrolyte commonly used in thin film batteries (TFBs). Advanced TFBs face the issue of detrimental electrode–electrolyte interlayer formation, related to the electronic structure of the interface. In this contribution, we study the valence band structure of LiPON using resonant photoemission and synchrotron photoemission with variable excitation energies. The identification of different valence band features is done according to the known valence band features of meta- and orthophosphates. Additionally we compare our results with partial density of states simulations from literature. We find that the valence band structure is similar to the known metaphosphates with an additional contribution of nitrogen states at the top of the valence band. From the results we conclude that synchrotron X-ray photoemission (XPS) is a useful tool to study the valence band structure of nitridated alkali phosphate glasses.
International Nuclear Information System (INIS)
Highlights: • In situ photoemission of LiPON solid Li-ion electrolyte. • We find that the valence band is similar to the known phosphates. • We find evidence for a resonance at the O1s edge shown by a Fano profile. • We find that the top of the valence band is due to N2p states. - Abstract: Lithium phosphorus oxynitride (LiPON) is a solid state electrolyte commonly used in thin film batteries (TFBs). Advanced TFBs face the issue of detrimental electrode–electrolyte interlayer formation, related to the electronic structure of the interface. In this contribution, we study the valence band structure of LiPON using resonant photoemission and synchrotron photoemission with variable excitation energies. The identification of different valence band features is done according to the known valence band features of meta- and orthophosphates. Additionally we compare our results with partial density of states simulations from literature. We find that the valence band structure is similar to the known metaphosphates with an additional contribution of nitrogen states at the top of the valence band. From the results we conclude that synchrotron X-ray photoemission (XPS) is a useful tool to study the valence band structure of nitridated alkali phosphate glasses
Cell and band structures in cold rolled polycrystalline copper
DEFF Research Database (Denmark)
Ananthan, V.S.; Leffers, Torben
1991-01-01
The effect of plastic strain on the deformation microstructure has been investigated in polycrystalline copper rolled at room temperature to 5, 10, 20, and 30% reduction in thickness equivalent strain 0.06-0.42). Results from transmission electron microscopy (TEM) observations show that dense dislocation walls (DDWs) and cells develop during the initial stages of cold rolling. Grains having a high density of DDWs are described as high wall density (HWD) structures, and grains having a low density of DDWs are described as low wall density (LWD) structures. These structures are characterised by cell size, misorientation across the cell walls, and the crystallographic orientation of the grains in which they appear. The DDWs in the HWD structures have special characteristics, extending along several cells and having a misorientation across them greater than that across ordinary cell boundaries at the same strain. The DDWs appear to have a macroscopically determined orientation. Analysis of their crystallographic orientation shows that they are not, as frequently reported in the literature, parallel to {111} planes. It is suggested that the DDWs separate regions of the crystal having different operating slip systems. Two generations of microbands are found to develop with increasing deformation. The first generation microbands are related to a continuous development of the structure according to the principle of grain subdivision, whereas the second generation microbands relate to localised shear on {111}. Finally, the evolution of the deformation microstructure in copper is compared with that observed in other face centred cubic metals, especially aluminium.
Density Structure at the Edge of the Horsehead Nebula
Habart, E.; Abergel, A.; Boulanger, F.; Teyssier, D.; Verstraete, L.
We will present near- and mid-infrared imaging observations of gas and dust emission of the Horsehead nebula emerging from the molecular cloud L1630. The 5-8.5 micron band of the ISOCAM camera has revealed that the edge of the Horsehead nebula, illuminated by an O star (? Ori, ? ˜100), presents a remarkably sharp bright filament (Abergel et al., 2000, 2001). This photo-dissociation region (PDR), seen edge-on, is an ideal target to study the gas density structure and the penetration of UV radiations across typical PDRs. Since much of the energy transfer that takes place between stars and gas occurs in photo-dissociation regions (PDRs), understanding their physical conditions is important in determining their role in regulating the star formation process. Using SOFI (Son of ISAAC) at the NTT, we have obtained an image of the Horsehead nebula in the 1-0 S(1) emission line of H2 at 2.12 microns revealing narrow filaments (width around 1 arcsec) spatially coincident with the aromatic emission. We have used the recent developments of the PDR model of Le Bourlot et al. (1993) to analyse our data. The adujstement of the brightness pr ofiles with the model strongly constrains the geometry and the density structure of individual structures. Moreover, the combination of H2 and ISOCAM data allows independant measurements of the local density, using the ratio IH_2 / IIR which depends very strongly on the local density, but neither on the total column density nor on the geometry.
Crystal structure, electrical properties and electronic band structure of tantalum ditelluride
Vernes, A; Bensch, W; Heid, W; Naether, C
1998-01-01
Motivated by the unexpectedly strong influence of the Te atoms on the structural and bonding properties of the transition metal tellurides, we have performed a detailed study of TaTe sub 2. Experimentally, this comprises a crystal structure determination as well as electrical resistivity measurements. The former analysis leads to an accurate update of the structural data reported in the 1960s, while the latter provides evidence for the mainly electronic character of scattering processes leading to the electrical conductivity. In addition, the electronic properties of TaTe sub 2 have been calculated using the TB-LMTO method. The partial density of states reflects the close connection of the Ta zigzag chains and the Te-Te network. This finding explains the charge transfer in the system in a rather simple way. The orthogonal-orbital character of the bands proved the existence of pi-bonds. The Fermi-surface study supports the interpretation of the experimental resistivity measurements. (author)
Simple metamaterial structure enabling triple-band perfect absorber
Van Dung, Nguyen; Son Tung, Bui; Khuyen, Bui Xuan; Yoo, Young Joon; Kim, Young Ju; Rhee, Joo Yull; Dinh Lam, Vu; Pak Lee, Young
2015-09-01
Two resonators in metamaterial usually correspond only to two absorption peaks. In this report, by breaking the symmetry, we could create multi-fundamental resonances at GHz frequencies in both simulation and experiment. First, a dual-band metamaterial absorber (MA) was achieved for 4.6 and 10.6 GHz. Next, by modifying the relative position of inner square, the triple-band MA was obtained with enhanced absorption properties. In addition, dependence on the polarization of the incident electromagnetic (EM) wave was clarified. The mechanism is elucidated to be an alteration of the coupling strength, which is made by changing the geometrical configuration of the inner square and the outer ring. It is shown that our structural configuration can be applied to the fields where the interaction with a wide range of EM waves exists or is needed.
Dual-band metamaterial with a windmill-like structure
International Nuclear Information System (INIS)
A broadband negative refractive index metamaterial based on a windmill-like structure is proposed, and investigated numerically and experimentally at the microwave frequency range. From the numerical and experimental results, effect media parameters are retrieved, which clearly show that two broad frequency bands exist in which the permittivity and permeability are negative. The two negative bands are from 9.1 GHz to 10.5 GHz and from 12.05 GHz to 14.65 GHz respectively, and the negative bandwidth is 4 GHz. Due to the good bandwidth performance, the metallic cell with double negative property obtained in this paper is suitable for use in the design of multiband or broadband microwave devices. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Indian Academy of Sciences (India)
S Chakraborty; R Ramesh; J M Lough
2000-03-01
Density, 18O and 13C were measured along two tracks, one close to the central growth axis and the other, ?20° off the axis, in a coral (Porites lutea) collected from the Stanley Reef, Central Great Barrier Reef, Australia. The 18O variations in the coral are well correlated with sea surface temperature changes. The common variances between the two tracks were about 60% in the 18O, 13C and the skeletal density variations. Part of the noise (40%) could be due to the difficulty of sampling exactly time contemporaneous parts of each band along the two tracks and part of it could be due to genuine intraband variability. In spite of the intraband variability, the time series obtained from the two tracks are similar, indicating that the dominant causative factor for the isotopic variations is external, i.e., the environmental conditions that prevail during the growth of the coral; density band formation does not appear to be directly controlled by the sea surface temperature.
Kishigi, Keita; Hasegawa, Yasumasa
2000-01-01
We theoretically study how the coexistent state of the charge density wave and the spin density wave in the one-dimensional quarter filled band is enhanced by magnetic fields. We found that when the correlation between electrons is strong the spin density wave state is suppressed under high magnetic fields, whereas the charge density wave state still remains. This will be observed in experiments such as the X-ray measurement.
Shimazaki, Tomomi; Asai, Yoshihiro
2009-04-28
A screened Hartree-Fock (HF) exchange potential with the dielectric constant was previously reported by Shimazaki and Asai [Chem. Phys. Lett. 466, 91 (2008)], in which the inverse of the dielectric constant was used to represent a fraction of the HF exchange term. In that report, the experimentally obtained value for the dielectric constant was employed. Herein, we discuss a self-consistent technique, in which the value of the dielectric constant can be automatically determined. This technique enables the energy band structure to be determined without using the experimental value. The band energy structure of diamond is calculated, a self-consistent procedure is determined to give closer bandgaps compared with the local density approximation and the generalized gradient approximation. PMID:19405611
Air Density Measurements in a Mach 10 Wake Using Iodine Cordes Bands
Balla, Robert J.; Everhart, Joel L.
2012-01-01
An exploratory study designed to examine the viability of making air density measurements in a Mach 10 flow using laser-induced fluorescence of the iodine Cordes bands is presented. Experiments are performed in the NASA Langley Research Center 31 in. Mach 10 air wind tunnel in the hypersonic near wake of a multipurpose crew vehicle model. To introduce iodine into the wake, a 0.5% iodine/nitrogen mixture is seeded using a pressure tap at the rear of the model. Air density was measured at 56 points along a 7 mm line and three stagnation pressures of 6.21, 8.62, and 10.0 MPa (900, 1250, and 1450 psi). Average results over time and space show rho(sub wake)/rho(sub freestream) of 0.145 plus or minus 0.010, independent of freestream air density. Average off-body results over time and space agree to better than 7.5% with computed densities from onbody pressure measurements. Densities measured during a single 60 s run at 10.0 MPa are time-dependent and steadily decrease by 15%. This decrease is attributed to model forebody heating by the flow.
Zerveas, George; Caruso, Enrico; Baccarani, Giorgio; Czornomaz, Lukas; Daix, Nicolas; Esseni, David; Gnani, Elena; Gnudi, Antonio; Grassi, Roberto; Luisier, Mathieu; Markussen, Troels; Osgnach, Patrik; Palestri, Pierpaolo; Schenk, Andreas; Selmi, Luca; Sousa, Marilyne; Stokbro, Kurt; Visciarelli, Michele
2016-01-01
We present and thoroughly compare band-structures computed with density functional theory, tight-binding, k · p and non-parabolic effective mass models. Parameter sets for the non-parabolic ?, the L and X valleys and intervalley bandgaps are extracted for bulk InAs, GaAs and InGaAs. We then consider quantum-wells with thickness ranging from 3 nm to 10 nm and the bandgap dependence on film thickness is compared with experiments for In0.53Ga0.47 As quantum-wells. The impact of the band-structure on the drain current of nanoscale MOSFETs is simulated with ballistic transport models, the results provide a rigorous assessment of III-V semiconductor band structure calculation methods and calibrated band parameters for device simulations.
A NOVEL TRIPLE-BAND ELECTROMAGNETIC BANDGAP (EBG STRUCTURE
Directory of Open Access Journals (Sweden)
Tran Minh Tuan
2013-01-01
Full Text Available A novel triple-band uni-planar electromagnetic bandgap (UC-EBG structure is proposed in this paper. This EBG structure can be considered as distorted uni-planar compact-EBG (DUC-EBG which is connected together by the meandered line inductor. Split ring resonators (SRR are embedded in four pad corners and two L-shaped slots are etched at the central pad. The proposed EBG structure is modelled in three equivalent circuits. By using in-house developed computational code based on the FDTD method, simulated results of dispersion diagrams are presented by complete triple-bandgap. The central frequency of the bandgaps can be reduced to the lower region without increasing the size of the EBG cell. Moreover, an array of 4×5 EBG cells was simulated, fabricated and measured to verify the bandgap characteristic through the transmission coefficient S21. This proposed EBG can be used for multi-band applications, such as dual/triple antennas.
Band structure approach to the resonant x-ray scattering
Elfimov, I S; Anisimov, V I; Sawatzky, G A
2002-01-01
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 the phase of the scattering, is a direct measure of this p-d hybridization.and obtain quantitative agreement with experiment. A simple physical picture involving a product of dipole and quadrupolar transition matrix elements explains this behaviour and shows that it should be generally true for cases where the resonating atom is not at an inversion center. This has strong implications for the description of the resonance behavior of x-ray scattering in materials where the resonant atom is not at an inversion center such as ...
Band structure in the polymer quantization of the harmonic oscillator
International Nuclear Information System (INIS)
We discuss the detailed structure of the spectrum of the Hamiltonian for the polymerized harmonic oscillator and compare it with the spectrum in the standard quantization. As we will see the non-separability of the Hilbert space implies that the point spectrum consists of bands similar to the ones appearing in the treatment of periodic potentials. This feature of the spectrum of the polymeric harmonic oscillator may be relevant for the discussion of the polymer quantization of the scalar field and may have interesting consequences for the statistical mechanics of these models. (paper)
International Nuclear Information System (INIS)
Background and purpose: We previously determined that the density of a rapidly migrating DNA end-binding complex (termed 'band-A') predicts radiosensitivity of human normal and tumor cells. The goal of this study was first to identify the protein components of band-A and to determine if the protein levels of band-A components would correlate with band-A density and radiosensitivity. Patients and methods: DNA end-binding protein complex (DNA-EBC) protein components were identified by adding antibodies specific for a variety of DNA repair-associated proteins to the DNA-EBC reaction and then noting which antibodies super-shifted various DNA-EBC bands. Band-A levels were correlated with SF2 for a panel of primary human fibroblasts heterozygous for sequence-proven mutations in BRCA1 or BRCA2. The nuclear protein levels of band-A components were determined in each BRCA1 heterozygote by western hybridization. Results: DNA-EBC analysis of human nuclear proteins revealed 10 identifiable bands. The density of the most rapidly migrating DNA-EBC band correlated closely with both BRCA-mutation status and radiosensitivity (r2=0.85). This band was absent in cells with homozygous mutations in their ataxia-telangiectasia-mutated protein (ATM) genes. This band was also completely supershifted by the addition of antibodies to ATM, Ku70, DNA ligase III, Rpa32, Rpa14, DNA ligase IV, XRCC4, WRN, BLM, RAD51 and p53. However, the intranuclear concentrations of these proteins did not correlate with either the SF2 or DNA-EBC density. Neither BRCA1 or BRCA2 could be detected in band-A. Conclusions: DNA-EBC analysis of human nuclear extracts resulted in 10 bands, at least six of which contained ATM. The density of one of the DNA-EBCs predicted the radiosensitization caused by BRCA haploinsufficiency, and this band contains Ku70, ATM, DNA ligase III, Rpa32, Rpa14, DNA ligase IV, XRCC4, WRN, BLM, RAD51 and p53 but not BRCA 1 or 2. The density of band-A was independent of the nuclear concentration of any of its known component
International Nuclear Information System (INIS)
We have investigated trap density of states (trap DOS) in n-channel organic field-effect transistors based on N,N?’-bis(cyclohexyl)naphthalene diimide (Cy-NDI) and dimethyldicyanoquinonediimine (DMDCNQI). A new method is proposed to extract trap DOS from the Arrhenius plot of the temperature-dependent transconductance. Double exponential trap DOS are observed, in which Cy-NDI has considerable deep states, by contrast, DMDCNQI has substantial tail states. In addition, numerical simulation of the transistor characteristics has been conducted by assuming an exponential trap distribution and the interface approximation. Temperature dependence of transfer characteristics are well reproduced only using several parameters, and the trap DOS obtained from the simulated characteristics are in good agreement with the assumed trap DOS, indicating that our analysis is self-consistent. Although the experimentally obtained Meyer-Neldel temperature is related to the trap distribution width, the simulation satisfies the Meyer-Neldel rule only very phenomenologically. The simulation also reveals that the subthreshold swing is not always a good indicator of the total trap amount, because it also largely depends on the trap distribution width. Finally, band transport is explored from the simulation having a small number of traps. A crossing point of the transfer curves and negative activation energy above a certain gate voltage are observed in the simulated characteristics, where the critical VG above which band transport is realized is determined by the sum of the trapped and free charge states below the conduction band edge
Mesospheric ozone densities retrieved from OSIRIS observations of the oxygen A-band dayglow
Sheese, Patrick
The Odin satellite was launched into orbit in early 2001 with one of its main objectives being to investigate ozone and ozone-related chemistry in the middle atmosphere. One of Odin's two instruments is the OSIRIS instrument, which scans the Earth's limb, observing Rayleigh-scattered sunlight with high vertical resolution and near-global coverage. An important feature that OSIRIS observes in the mesosphere is the emission of molecular oxygen A-band dayglow, the intensity of which is dependent on local ozone density. A kinetic-photochemical model of the A-band dayglow has been developed in order to forward model the OSIRIS observations. The model takes into account the most current measurements of photochemical reaction coefficients, line strengths, and incident solar flux, and assumes an MSIS background atmosphere. The observations and forward model are used in an iterative optimal estimation technique to solve the inverse problem of retrieving ozone density profiles between altitudes of 70 - 95 km. The results form a climatological database of upper mesospheric ozone, which is compared with near-coincident ozone retrievals from the SABER instrument aboard the TIMED satellite. A detailed error analysis is performed on the retrievals determining the sensitivity of the results to different sources of error, such as instrument noise, errors in the forward model parameters, and errors in the retrieval method itself. The retrievals are also examined to determine vertical, latitudinal, and seasonal variations. Variations are compared to previous and concurrent measurements from a number of other sources.
Effect of band hybridization on the electronic structure of V(100) at interfaces
International Nuclear Information System (INIS)
We have investigated the role of s-p-d hybridization on the interface electronic structure of V(100)-M single interfaces, where M is a nonmagnetic metal having s, sp, or sd electrons near the Fermi level; in the sd case we consider two different configurations with full and partially filled d-bands. We have calculated the interface local density of states, using an empirical tight-binding hamiltonian within the Green-function-matching formalism. We find that if M is a metal not having p or d electrons at the Fermi level, the interface local density of states at the vanadium site retains the features of the surface local density of states. Surface electronic properties of V(100) are expected in the vanadium side for these interfaces. (Author)
International Nuclear Information System (INIS)
We present a divergence-free method to determine the characteristics of band structures and projected band structures of transverse acoustic phonons in Fibonacci superlattices. A set of bandedge equations is formulated to solve the band structures for the phonon instead of using the traditional dispersion relation. Numerical calculations show band structures calculated by the present method for the Fibonacci superlattice without numerical instability, which may occur in traditional methods. Based on the present formalism, the band structure for the acoustic phonons has been characterized by closure points and the projected bandgaps of the forbidden bands. The projected bandgaps are determined by the projected band structure, which is characterized by the cross points of the projected bandedges. We observed that the band structure and projected band structure and their characteristics were quite different for different generation orders and the basic layers for the Fibonacci superlattice. In this study, concise rules to determine these characteristics of the band structure and the projected band structure, including the number and the location of closure points of forbidden bands and those of projected bandgaps, in Fibonacci superlattices with arbitrary generation order and basic layers are proposed.
Electronic band structure of silver-deficient hexagonal AgB$_2$
Shein, I R; Ivanovskii, A L
2004-01-01
Structural, cohesive properties as well as energy band structure of metastable hexagonal AgB$_2$ and silver-deficient borides Ag$_{0.875}$B$_2$ and Ag$_{0.750}$B$_2$ were investigated by means of the projected augmented wave method in the framework of the density functional theory (VASP package). We found that the density of states at the Fermi level for nonstoichiometric diborides is almost constant within a range of vacancy content up to 25%. The formation energy of metal vacancies in silver diboride is the least among all 4d metal diborides, i.e. for AgB$_2$ is possible to expect the wide homogeneity region.
Carricart-Ganivet, J. P.; Vásquez-Bedoya, L. F.; Cabanillas-Terán, N.; Blanchon, P.
2013-09-01
Density banding in skeletons of reef-building corals is a valuable source of proxy environmental data. However, skeletal growth strategy has a significant impact on the apparent timing of density-band formation. Some corals employ a strategy where the tissue occupies previously formed skeleton during as the new band forms, which leads to differences between the actual and apparent band timing. To investigate this effect, we collected cores from female and male colonies of Siderastrea siderea and report tissue thicknesses and density-related growth parameters over a 17-yr interval. Correlating these results with monthly sea surface temperature (SST) shows that maximum skeletal density in the female coincides with low winter SSTs, whereas in the male, it coincides with high summer SSTs. Furthermore, maximum skeletal densities in the female coincide with peak Sr/Ca values, whereas in the male, they coincide with low Sr/Ca values. Both results indicate a 6-month difference in the apparent timing of density-band formation between genders. Examination of skeletal extension rates also show that the male has thicker tissue and extends faster, whereas the female has thinner tissue and a denser skeleton—but both calcify at the same rate. The correlation between extension and calcification, combined with the fact that density banding arises from thickening of the skeleton throughout the depth reached by the tissue layer, implies that S. siderea has the same growth strategy as massive Porites, investing its calcification resources into linear extension. In addition, differences in tissue thicknesses suggest that females offset the greater energy requirements of gamete production by generating less tissue, resulting in differences in the apparent timing of density-band formation. Such gender-related offsets may be common in other corals and require that environmental reconstructions be made from sexed colonies and that, in fossil corals where sex cannot be determined, reconstructions must be duplicated in different colonies.
Band Structure and Transport Properties of $CrO_{2}$
Lewis, S P; Sasaki, T; Lewis, Steven P.; Allen, Phillip B.; Sasaki, Taizo
1996-01-01
Local Spin Density Approximation (LSDA) is used to calculate the energy bands of both the ferromagnetic and paramagnetic phases of metallic CrO_2. The Fermi level lies in a peak in the paramagnetic density of states, and the ferromagnetic phase is more stable. As first predicted by Schwarz, the magnetic moment is 2 \\mu_B per Cr atom, with the Fermi level for minority spins lying in an insulating gap between oxygen p and chromium d states ("half-metallic" behavior.) The A_1g Raman frequency is predicted to be 587 cm^{-1}. Drude plasma frequencies are of order 2eV, as seen experimentally by Chase. The measured resistivity is used to find the electron mean-free path l, which is only a few angstroms at 600K, but nevertheless, resistivity continues to rise as temperature increases. This puts CrO_2 into the category of "bad metals" in common with the high T_c superconductors, the high T metallic phase of VO_2, and the ferromagnet SrRuO_3. In common with both SrRuO_3 and Sr_2RuO_4, the measured specific heat \\gamma ...
International Nuclear Information System (INIS)
A detailed theoretical study of structural, electronic and Vibrational properties of BeX compound is presented by performing ab-initio calculations based on density-functional theory using the Espresso package. The calculated value of lattice constant and bulk modulus are compared with the available experimental and other theoretical data and agree reasonably well. BeX (X = S,Se,Te) compounds in the ZB phase are indirect wide band gap semiconductors with an ionic contribution. The phonon dispersion curves are represented which shows that these compounds are dynamically stable in ZB phase
Energy Technology Data Exchange (ETDEWEB)
Dabhi, Shweta, E-mail: venu.mankad@gmail.com; Mankad, Venu, E-mail: venu.mankad@gmail.com; Jha, Prafulla K., E-mail: venu.mankad@gmail.com [Department of Physics, Maharaja Krishnakumasinhji Bhavnagar University, Bhavnagar-364001 (India)
2014-04-24
A detailed theoretical study of structural, electronic and Vibrational properties of BeX compound is presented by performing ab-initio calculations based on density-functional theory using the Espresso package. The calculated value of lattice constant and bulk modulus are compared with the available experimental and other theoretical data and agree reasonably well. BeX (X = S,Se,Te) compounds in the ZB phase are indirect wide band gap semiconductors with an ionic contribution. The phonon dispersion curves are represented which shows that these compounds are dynamically stable in ZB phase.
Ardisana, R. N.; Miller, C. A.; Sivaguru, M.; Fouke, B. W.
2013-12-01
Corals are a key reservoir of biodiversity in coastal, shallow water tropical marine environments, and density banding in their aragonite skeletons is used as a sensitive record of paleoclimate. Therefore, the cellular response of corals to environmental change and its expression in skeletal structure is of significant importance. Chromatophores, pigment-bearing cells within the ectoderm of hermatypic corals, serve to both enhance the photosynthetic activity of zooxanthellae symbionts, as well as protect the coral animal from harmful UV radiation. Yet connections have not previously been drawn between chromatophore tissue density and the development of skeletal density bands. A histological analysis of the coral Montastrea faveolata has therefore been conducted across a bathymetric gradient of 1-20 m on the southern Caribbean island of Curaçao. A combination of field and laboratory photography, serial block face imaging (SBFI), two-photon laser scanning microscopy (TPLSM), and 3D image analysis has been applied to test whether M. faveolata adapts to increasing water depth and decreasing photosynthetically active radiation by shifting toward a more heterotrophic lifestyle (decreasing zooxanthellae tissue density, increasing mucocyte tissue density, and decreasing chromatophores density). This study is among the first to collect and evaluate histological data in the spatial context of an entire unprocessed coral polyp. TPLSM was used to optically thin section unprocessed tissue biopsies with quantitative image analysis to yield a nanometer-scale three-dimensional map of the quantity and distribution of the symbionts (zooxanthellae) and a host fluorescent pigments (chromatophores), which is thought to have photoprotective properties, within the context of an entire coral polyp. Preliminary results have offered new insight regarding the three-dimensional distribution and abundance of chromatophores and have identified: (1) M. faveolata tissue collected from 8M SWD do not contain the abundant chromatophores present in M. faveolata collected from 20M SWD; and (2) a distinct difference in size and distribution of chromatophores between M. faveolata collected from 8-20M SWD. These results suggest that chromatophore cells may have an important photoenhancing function (reflection of light to help facilitate the collection of usable light that reaches the symbiotic algae for effective photosynthesis) rather than a photoinhibitive function (absorbing or refract light that may be harmful to zooxanthellae) which has been previously hypothesized.
Covariant density functional theory: Reexamining the structure of superheavy nuclei
Agbemava, S. E.; Afanasjev, A. V.; Nakatsukasa, T.; Ring, P.
2015-11-01
A systematic investigation of even-even superheavy elements in the region of proton numbers 100 ?Z ?130 and in the region of neutron numbers from the proton-drip line up to neutron number N =196 is presented. For this study we use the five most up-to-date covariant energy density functionals of different types, with a nonlinear meson coupling, with density-dependent meson couplings, and with density-dependent zero-range interactions. Pairing correlations are treated within relativistic Hartree-Bogoliubov theory based on an effective separable particle-particle interaction of finite range and deformation effects are taken into account. This allows us to assess the spread of theoretical predictions within the present covariant models for the binding energies, deformation parameters, shell structures, and ? -decay half-lives. Contrary to the previous studies in covariant density functional theory, it was found that the impact of N =172 spherical shell gap on the structure of superheavy elements is very limited. Similar to nonrelativistic functionals, some covariant functionals predict the important role played by the spherical N =184 gap. For these functionals (NL3*, DD-ME2, and PC-PK1) there is a band of spherical nuclei along and near the Z =120 and N =184 lines. However, for other functionals (DD-PC1 and DD-ME ? ) oblate shapes dominate at and in the vicinity of these lines. Available experimental data are, in general, described with comparable accuracy and do not make it possible to discriminate between these predictions.
Refractory Coated/Lined Low Density Structures Project
National Aeronautics and Space Administration — The innovation in this proposed effort is the development of refractory coated or lined low density structures. Lightweight structures are desirable for space...
Analysis of photonic band-gap structures in stratified medium
DEFF Research Database (Denmark)
Tong, Ming-Sze; Yinchao, Chen
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 in solving the Maxwell's equations numerically. It expands the temporal derivatives using the finite differences, while it adopts the Fourier transform (FT) properties to expand the spatial derivatives in Maxwell's equations. In addition, the method makes use of the chain-rule property in calculus together with the transformed space technique in order to make the algorithm flexible in terms of non-uniform spatial sampling. Findings - Through the studies of the wave propagation characteristics on PBG structures in stratified medium, it has been found that the proposed method retains excellent accuracy in the occasions where the spatial distributions contain step of up to five times larger than the original size, while simultaneously the flexibility of non-uniform sampling offers further savings on computational storage. Research limitations/implications - Research has been mainly limited to the simple one-dimensional (1D) periodic and defective cases of PBG structures. Nevertheless, the findings reveal strong implications that flexibility of sampling and memory savings can be realized in multi-dimensional structures. Practical implications - The proposed method can be applied to various practical structures in electromagnetic and microwave applications once the Maxwell's equations are appropriately modeled. Originality/value - The method validates its values and properties through extensive studies on regular and defective 1D PBG structures in stratified medium, and it can be further extended to solving more complicated structures. CPY Emerald Group Publishing Limited.
Structural Evolution of a Warm Frontal Precipitation Band During GCPEx
Colle, Brian A.; Naeger, Aaron; Molthan, Andrew; Nesbitt, Stephen
2015-01-01
A warm frontal precipitation band developed over a few hours 50-100 km to the north of a surface warm front. The 3-km WRF was able to realistically simulate band development, although the model is somewhat too weak. Band genesis was associated with weak frontogenesis (deformation) in the presence of weak potential and conditional instability feeding into the band region, while it was closer to moist neutral within the band. As the band matured, frontogenesis increased, while the stability gradually increased in the banding region. Cloud top generating cells were prevalent, but not in WRF (too stable). The band decayed as the stability increased upstream and the frontogenesis (deformation) with the warm front weakened. The WRF may have been too weak and short-lived with the band because too stable and forcing too weak (some micro issues as well).
Quasiparticle band structures and thermoelectric transport properties of p-type SnSe
Shi, Guangsha; Kioupakis, Emmanouil
2015-03-01
We used density functional and many-body perturbation theory to calculate the band structure and electronic transport parameters of p-type SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The Pnma phase has an indirect band gap of 0.829 eV while the Cmcm has a direct band gap of 0.464 eV. Both phases exhibit multiple local band extrema within an energy range comparable to the thermal energy of carriers from the global extrema. We calculated the electronic transport coefficients within the constant relaxation time approximation as a function of doping concentration and temperature for single-crystal and polycrystalline materials to understand experimental measurements. The electronic transport coefficients are highly anisotropic and are strongly affected by bipolar transport effects at low doping and high temperature. Our results indicate that SnSe exhibits optimal thermoelectric performance at high temperature when doped in the 1019-1020 cm-3 range. This work was supported in part by the National Science Foundation (DMR-1254314) and in part by CSTEC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science. Computational resources were provided by the DOE NERSC facility.
Band structure of ABC-trilayer graphene superlattice
International Nuclear Information System (INIS)
We investigate the effect of one-dimensional periodic potentials on the low energy band structure of ABC trilayer graphene first by assuming that all the three layers have the same potential. Extra Dirac points having the same electron hole crossing energy as that of the original Dirac point are generated by superlattice potentials with equal well and barrier widths. When the potential height is increased, the numbers of extra Dirac points are increased. The dispersions around the Dirac points are not isotropic. It is noted that the dispersion along the ky direction for kx?=?0 oscillates between a non-linear dispersion and a linear dispersion when the potential height is increased. When the well and barrier widths are not identical, the symmetry of the conduction and valence bands is broken. The extra Dirac points are shifted either upward or downward depending on the barrier and well widths from the zero energy, while the position of the central Dirac point oscillates with the superlattice potential height. By considering different potentials for different layers, extra Dirac points are generated not from the original Dirac points but from the valleys formed in the energy spectrum. Two extra Dirac points appear from each pair of touched valleys, so four Dirac points appeared in the spectrum at particular barrier height. By increasing the barrier height of superlattice potential two Dirac points merge into the original Dirac point. This emerging and merging of extra Dirac points is different from the equal potential case
X-band coaxial standing-wave linear accelerator structure
International Nuclear Information System (INIS)
A new high efficiency X-Band, standing-wave linear accelerator cavity structure has been developed. It utilizes a shaped coaxial cavity as the coupling cavity between accelerating cavities for ?/2 mode operation, hence the overall diameter is extremely small while maintaining a very high shunt impedance. The coupling cavity and accelerating cavity are easily machined on opposite sides of a single cell, eliminating any subassembly steps. Cavity geometries were developed using the computer codes LACC and LALA. Prototype 1.5 MeV and 4.0 MeV, 20 cm long accelerators are now under development. The accelerators employ a stepped field focusing technique to keep the beam focused at low field levels. The beam dynamics code PARMELA was used to optimize the longitudinal bunching and transverse beam characteristics. The accelerator design parameters, as well as experimental results, are presented
Anomalous decay of an atom in structured band gap reservoirs
Giraldi, Filippo
2010-01-01
We analyze the spontaneous emission of a two-level atom interacting with a special class of structured reservoirs of field modes with band gap edge coinciding with the atomic transition frequency. The exact time evolution of the population of the excited level is evaluated analytically through series of Fox-$H$ functions. Over estimated long time scales, inverse power law relaxations emerge, with powers decreasing continuously to $2$ according to the choice of the special reservoir. No trapping of the population of the excited level emerges. The same results are recovered in presence of $N-1$ atoms, each one in the ground state, described by the Dicke model. The power of the inverse power law decay results to be independent of $N$. A critical number $N_{\\alpha}^{\\left(\\star\\right)}$ is evaluated, such that, for $N \\gg N_{\\alpha}^{\\left(\\star\\right)}$, the inverse power law decay vanishes.
Band-structure analysis from photoreflectance spectroscopy in (Ga,Mn)As
Energy Technology Data Exchange (ETDEWEB)
Yastrubchak, Oksana; Gluba, Lukasz; Zuk, Jerzy [Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin (Poland); Wosinski, Tadeusz; Andrearczyk, Tomasz; Domagala, Jaroslaw Z. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Sadowski, Janusz [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland and MAX-Lab, Lund University, 22100 Lund (Sweden)
2013-12-04
Modulation photoreflectance spectroscopy has been applied to study the band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn content. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap-transition energy in the (Ga,Mn)As layers with increasing Mn content are interpreted in terms of a disordered valence band, extended within the band gap, formed, in highly Mn-doped (Ga,Mn)As, as a result of merging the Mn-related impurity band with the host GaAs valence band.
Medeiros, Paulo V. C.; Stafström, Sven; Björk, Jonas
2014-01-01
We use a band unfolding technique to recover an effective primitive cell picture of the band structure of graphene under the influence of different types of perturbations. This involves intrinsic perturbations, such as structural defects, and external ones, comprising nitrogen substitutions and the inclusion of graphene in adsorbed systems. In such cases, the band unfolding provides a reliable and efficient tool for quantitatively analyzing the effect of doping and defects on the electronic structure of graphene. We envision that this approach will become a standard method in the computational analysis of graphene's electronic structure in related systems.
Ab initio complex band structure of conjugated polymers: Effects of hydrid DFT and GW schemes
Ferretti, Andrea; Martin-Samos, Layla; Bussi, Giovanni; Ruini, Alice; Montanari, Barbara; Harrison, Nicholas M
2012-01-01
The non-resonant tunneling regime for charge transfer across nanojunctions is critically dependent on the so-called \\beta{} parameter, governing the exponential decay of the current as the length of the junction increases. For periodic materials, this parameter can be theoretically evaluated by computing the complex band structure (CBS) -- or evanescent states -- of the material forming the tunneling junction. In this work we present the calculation of the CBS for organic polymers using a variety of computational schemes, including standard local, semilocal, and hybrid-exchange density functionals, and many-body perturbation theory within the GW approximation. We compare the description of localization and \\beta{} parameters among the adopted methods and with experimental data. We show that local and semilocal density functionals systematically underestimate the \\beta{} parameter, while hybrid-exchange schemes partially correct for this discrepancy, resulting in a much better agreement with GW calculations an...
Handbook of the band structure of elemental solids from Z = 1 to Z = 112
Papaconstantopoulos, Dimitris A
2015-01-01
This handbook presents electronic structure data and tabulations of Slater-Koster parameters for the whole periodic table. This second edition presents data sets for all elements up to Z = 112, Copernicium, whereas the first edition contained only 53 elements. In this new edition, results are given for the equation of state of the elements together with the parameters of a Birch fit, so that the reader can regenerate the results and derive additional information, such as Pressure-Volume relations and variation of Bulk Modulus with Pressure. For each element, in addition to the equation of state, the energy bands, densities of states, and a set of tight-binding parameters is provided. For a majority of elements, the tight-binding parameters are presented for both a two- and three-center approximation. For the hcp structure, new three-center tight-binding results are given. Other new material in this edition include: energy bands and densities of states of all rare-earth metals, a discussion of the McMillan-Gas...
Band structures of ZnTe:O alloys with isolated oxygen and with clustered oxygen impurities
Energy Technology Data Exchange (ETDEWEB)
Ling, Chen, E-mail: chen.ling@tema.toyota.com; Zhou, Li Qin; Banerjee, Debasish; Jia, Hongfei
2014-01-25
Highlights: • Band structures of ZnTe:O alloy highly depends on the status of oxygen. • Clustered oxygen lowers the bandgap while isolated oxygen increases the bandgap. • The solar adsorption efficiency of ZnTe:O can be improved by oxygen clustering. -- Abstract: First-principles calculations reveal that band structures of ZnTe:O alloys highly depend on the configuration of oxygen in the alloy. For alloys with isolated oxygen, the calculated band structure shows the formation of intermediate states between valence and conduction band and the shift of conduction band to higher energy level. It expands the gap between valence and conduction band. For alloys with clustered oxygen, the formation of intermediate band is still observed, while the gap between valence and conduction band is decreased. For alloys with oxygen impurities adjacent to Zn vacancy, the band structure only shows the decrease of the gap between valence and conduction band without the formation of any intermediate band. These results suggest the critical role of Zn–O bonding in determining the energy level of the impurity states. On the basis of our results, a possible band engineering approach is suggested in order to improve the performance of ZnTe:O alloy as intermediate band solar adsorbent.
Scientific Electronic Library Online (English)
Federico F., Santiñaque; Máximo E., Drets.
Full Text Available Previous research using microdensitometric scanning and computer graphic image analysis showed that T-banded segments of human metaphase chromosomes usually exhibit an asymmetrical distribution of high density (HD) chromatin between sister chromatids. Here, we employed the same methods to analyze HD [...] chromatin distribution at opposite ends of T-banded human lymphocyte chromosomes. This study revealed that in most chromosomes with an asymmetrical distribution of HD chromatin at both ends, the highest densities of each arm were located in opposite chromatids. The frequency of this configuration was 0.792 per chromosome, indicating that the highest chromatin densities of the terminal segments of T-banded human chromosomes were non-randomly distributed at opposite chromosome arms. The possible relationship of this observation to the mode of replication of the terminal chromosome region is briefly discussed.
Energy Technology Data Exchange (ETDEWEB)
Rougieux, F. E.; Macdonald, D. [Research School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, ACT 0200 (Australia)
2014-03-24
The state of bistable defects in crystalline silicon such as iron-boron pairs or the boron-oxygen defect can be changed at room temperature. In this letter, we experimentally demonstrate that the chemical state of a group of defects can be changed to represent a bit of information. The state can then be read without direct contact via the intensity of the emitted band-band photoluminescence signal of the group of defects, via their impact on the carrier lifetime. The theoretical limit of the information density is then computed. The information density is shown to be low for two-dimensional storage but significant for three-dimensional data storage. Finally, we compute the maximum storage capacity as a function of the lower limit of the photoluminescence detector sensitivity.
Energy Technology Data Exchange (ETDEWEB)
Ushio, Hideki [Tokyo National College of Technology, Hachioji (Japan); Kamimura, Hiroshi [Science Univ. of Tokyo (Japan). Inst. of Physics
1997-12-30
The authors have separated a hole carrier and a localized spin, by treating the exchange interaction between the spins of a carrier hole and a localized spin in a mean field sense. Then they have constructed the effective one-electron-type band structure for the hole carriers in the presence of the antiferromagnetic (AF) ordering of the localized spins. In the case of the undoped La{sub 2}CuO{sub 4} all the energy bands are fully occupied by electrons so that La{sub 2}CuO{sub 4} is an insulator. In this sense the present energy bands which include the many body effect fully is completely different from the ordinary energy band in the local density functional method. The top of the highest valence band is at ({pi}/a, {pi}/a, 0)-point, and the calculated Fermi surface is small as far as the spin correlation length of the AF order is larger than the mean free path. Based on this energy band and Fermi surfaces the authors have calculated various normal state properties and explained their anomalous features, such as the x-dependence of the electronic specific heat, the linear temperature dependence of the resistivity down to {Tc}, the x-dependence of the Hall coefficient with the sign change, the large T dependence of R{sub H}, the incommensurate peak of the neutron scattering and the instability at x = 0.125.
Solar spectral fine structure in 18-23 GHz band
Scientific Electronic Library Online (English)
J. R., Cecatto; K. R., Subramanian; H. S., Sawant.
1999-09-01
Full Text Available On 30th June 1989 high sensitivity-spectral resolution observations of solar radio bursts were carried out in the frequency range of 18 - 23 GHz. The burst observed at 17:46 UT was different from the 60 bursts observed so far in the sense that it exhibited a frequency fine structure superimposed on [...] the ongoing burst in its rising phase, i.e. an additional enhancement of the flux density of the order of 10 SFU, observed only in the 21 and 22 GHz frequency channels, lasting for about 4 s. Interaction of an emerging loop with an adjacent loop accelerated particles in that loop from which the broadband burst was emitted due to the gyrosynchrotron emission. The observed fine structure is interpreted as due to thermal gyro-emission at 6th harmonic of the gyrofrequency originated from a hot kernel with short lifetime located at the top of emerging loop. We derived the hot kernel source parameters, th e temperature as 8 ´10(7) K, the magnetic field as 1250 G and the density as 5 ×10(12) cm-3.
Kuhns, P L; Hoch, M J R; Reyes, A P; Moulton, W G; Wang, L; Leighton, C
2006-04-28
Highly spin polarized (SP) and half-metallic ferromagnetic systems are of considerable current interest and of potential importance for spintronic applications. Recent work has demonstrated that Co1-xFexS2 is a highly polarized ferromagnet (FM) where the spin polarization can be tuned by alloy composition. Using 59Co FM-NMR as a probe, we have measured the low-temperature spin relaxation in this system in magnetic fields from 0 to 1.0 T for 0FM system, permits information to be obtained on the d-band density of states at the Fermi level. The results are compared with independent density of states values inferred from electronic specific heat measurements and band structure calculations. It is shown that FM-NMR can be an important method for investigating highly SP systems. PMID:16712272
Energy Technology Data Exchange (ETDEWEB)
Ferhi, M., E-mail: ferhi.mounir@gmail.com [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National des Recherches en Sciences des Matériaux, Technopole de Borj Cedria, BP 73, 8027 Soliman (Tunisia); Horchani-Naifer, K.; Bouzidi, C. [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National des Recherches en Sciences des Matériaux, Technopole de Borj Cedria, BP 73, 8027 Soliman (Tunisia); Elhouichet, H. [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National des Recherches en Sciences des Matériaux, Technopole de Borj Cedria, BP 73, 8027 Soliman (Tunisia); Département de Physique, Faculté des Sciences de Tunis, Campus ElManar 2092 (Tunisia); Ferid, M. [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National des Recherches en Sciences des Matériaux, Technopole de Borj Cedria, BP 73, 8027 Soliman (Tunisia)
2014-10-01
Graphical abstract: Projection along the a axis (a), electronic structure (b) and the Eu{sup 3+} concentration effect on the band gap (c) of KLa{sub (1?x)}Eu{sub x}(PO{sub 3}){sub 4}. - Highlights: • Single crystal and Eu{sup 3+} doped powders of KLa(PO{sub 3}){sub 4} have been synthesized. • The crystal structure has been resolved. • Electronic properties have been performed by DFT method. • The chemical bonding properties have been discussed. • The experimental and computed optical band gaps have been compared and discussed. - Abstract: Crystal structure, electronic properties and optical band gap energies for KLa{sub (1?x)}Eu{sub x}(PO{sub 3}){sub 4} have been investigated. The KLa(PO{sub 3}) belongs to P2{sub 1} space group characterized by three-dimensional framework built of (PO{sub 3}){sub n} chains. The energy-band structure, density of states, chemical bonds, and the band gap energy of KLa(PO{sub 3}){sub 4} have been investigated by the Density Functional Theory (DFT) method. It has an insulator character with a direct band gap of about 5.11 eV. The experimental band gap energies of KLa{sub (1?x)}Eu{sub x}(PO{sub 3}){sub 4} showed that the substitution between Eu{sup 3+} and La{sup 3+} influenced the distribution of the electronic structure and therefore determined the band gap energy.
High spin structure in a coupled bands model
International Nuclear Information System (INIS)
A coupled bands model proposed earlier is developed. It is a modification of the band crossing models with Coriolis interaction and conserves rotational invariance. It is applied to the phenomenological description of energies and transition rates for crossing rotational bands in even-even nuclei. Information on the strengths of band interactions has been deduced by a fit to experimental energies. The strange clockwise circling dependence of reduced transition probabilities on squared rotational frequencies in the yrast line has been described, and information on interband E2 moment matrix elements has been deduced by a fit to experimental transition rates. (author)
Rietveld analysis and electronic bands structure on Tc superconductors systems
International Nuclear Information System (INIS)
A procedure for simultaneous refinement of structural and micro-structural disorder parameters for polycrystalline YBa2Cu3O7-x system is proposed. It is based on Rietveld method combined with Fourier analysis for broadened peaks Another purpose of this paper consists in electronic structure determination studied by using the self-consistent Tight Binding Linear Muffin-Tin Orbital Atomic Spheres Approximation TB-LMTO-ASA methods. The Rietveld method uses an analytical function that describes the profiles, usually pseudo-Voigt (pV) or Pearson VII (PVII). The parameters of the analytical profiles describe its amplitude, position and peak shape. The full width at half maximum (FWHM) is supposed to vary with the diffraction angle in agreement with the Caglioti, Paoletti and Ricci's relationship. The best structural parameters are determined in the least squares sense by the minimisation a classical residual using the Marquardt method. In this case, the peak profiles were modelled by the pseudo-Voigt function corrected by the instrumental asymmetry. The physical information obtained are: scale factor, lattice parameters, atomic position and displacements, atomic occupation numbers, temperature factor (isotropy or anisotropy), preferred orientation parameter, crystalline size and micro-strain along different crystallographic directions, distributions of crystallite size and micro-strain functions. This procedure was implemented on computer code and it has a friendly graphical interface based on pull down menus technique. From the experimental point of view the X-ray diffraction data were collected using a horizontal powder diffractometer in the Bragg-Brentano (BB) geometry with a Ni filtered CuK?, ? = 1.54178 A, at room temperature using a DRON 2 set-up. The diffraction profiles were measured with a proportional gas detector, a single channel pulse-height discrimination and a standard associated counting circuit. The electronic band calculations are based on the TB-LMTO program version 47 under 2.03 LINUX operating system version. The main steps of our calculations are: the generation of the overlapping potentials from the atomic Hartree potentials and the finding of the MT-radii, the calculation and drawing of the sphere overlaps, the finding of the interstitial spheres, the generation of the structure constants and the performing of self-consistent calculations. The LMTO method can be regarded as an LCAO (linear combination atomic orbitals) formalism in which the muffin-tin potential (MT), rather than the atomic potential, defines the set of basis functions used to construct the trial functions of the variational procedure. (authors)
Directory of Open Access Journals (Sweden)
Arpan Deyasi and Gourab Kumar Ghosh
2012-12-01
Full Text Available Transmission coefficient, eigen states and tunneling current density of a potentially symmetric quantum double barrier structure has been numerically computed using transfer matrix technique for qualitative analysis of resonant tunneling probability when realistic band structure of higher band gap material is taken into account. GaAs/AlxGa1-xAs material composition is taken as an example for calculation, and thickness of the barrier and well regions are varied along with material compositions of AlxGa1-xAs to study the effect on electrical parameters; and also to observe the existence of quasi-bound states. Effective mass mismatch at junctions is considered following envelope function approximation, and conduction band discontinuity is taken into account for computational purpose. Under low biasing condition, negative differential regions (NDR can be obtained which speaks in favor of tunneling current.
Yanagisawa, Susumu; Morikawa, Yoshitada; Schindlmayr, Arno
2014-01-01
We investigate the band dispersion and related electronic properties of picene single crystals within the GW approximation for the electronic self-energy. The width of the upper highest occupied molecular orbital (HOMOu) band along the ?-Y direction, corresponding to the b crystal axis in real space along which the molecules are stacked, is determined to be 0.60 eV and thus 0.11 eV larger than the value obtained from density-functional theory. As in our recent study of rubrene using the same methodology [S. Yanagisawa, Y. Morikawa, and A. Schindlmayr, Phys. Rev. B 88, 115438 (2013)], this increase in the bandwidth is due to the strong variation of the GW self-energy correction across the Brillouin zone, which in turn reflects the increasing hybridization of the HOMOu states of neighboring picene molecules from ? to Y. In contrast, the width of the lower HOMO (HOMOl) band along ?-Y remains almost unchanged, consistent with the fact that the HOMOl(?) and HOMOl(Y) states exhibit the same degree of hybridization, so that the nodal structure of the wave functions and the matrix elements of the self-energy correction are very similar.
Novel semiconductor solar cell structures: The quantum dot intermediate band solar cell
International Nuclear Information System (INIS)
The Quantum Dot Intermediate Band Solar Cell (QD-IBSC) has been proposed for studying experimentally the operating principles of a generic class of photovoltaic devices, the intermediate band solar cells (IBSC). The performance of an IBSC is based on the properties of a semiconductor-like material which is characterised by the existence of an intermediate band (IB) located within what would otherwise be its conventional bandgap. The improvement in efficiency of the cell arises from its potential (i) to absorb below bandgap energy photons and thus produce additional photocurrent, and (ii) to inject this enhanced photocurrent without degrading its output photo-voltage. The implementation of the IBSC using quantum dots (QDs) takes advantage of the discrete nature of the carrier density of states in a 0-dimensional nano-structure, an essential property for realising the IB concept. In the QD-IBSC, the IB arises from the confined electron states in an array of quantum dots. This paper reviews the operation of the first prototype QD-IBSCs and discusses some of the lessons learnt from their characterisation
Systematic design of phononic band-gap materials and structures by topology optimization
DEFF Research Database (Denmark)
Sigmund, Ole; Jensen, Jakob Søndergaard
2003-01-01
Phononic band-gap materials prevent elastic waves in certain frequency ranges from propagating, and they may therefore be used to generate frequency filters, as beam splitters, as sound or vibration protection devices, or as waveguides. In this work we show how topology optimization can be used to design and optimize periodic materials and structures exhibiting phononic band gaps. Firstly, we optimize infinitely periodic band-gap materials by maximizing the relative size of the band gaps. Then, ...
Structure of negative parity yrast bands in odd mass 125-131Ce nuclei
Indian Academy of Sciences (India)
Arun Bharti; Suram Singh; S K Khosa
2010-04-01
The negative parity yrast bands of neutron-deficient 125-131Ce nuclei are studied by using the projected shell model approach. Energy levels, transition energies and $B(M1)/B(E2)$ ratios are calculated and compared with the available experimental data. The calculations reproduce the band-head spins of negative parity yrast bands and indicate the multi-quasiparticle structure for these bands.
Global Kinetic Modeling of Banded Electron Structures in the Plasmasphere
Liemohn, M. W.; Khazanov, G. V.
1997-01-01
Significant fluxes of 10 eV to 30 keV electrons have been detected in the plasmasphere, appearing as banded structures in energy with broad spatial extents and slowly evolving over several days. It is thought that these populations are decaying plasma sheet electrons injected into the corotating region of near-Earth space. This capture can occur when the convective electric field drops rapidly and the Alfven boundary suddenly outward, trapping the inner edge of the plasma sheet along closed drift paths. Our bounce-averaged kinetic model of superthermal electron transport is able to simulate this capture and the subsequent drift, diffusion, and decay of the plasma cloud. Results of this simulation will be shown and discussed, from the initial injection during the elevated convection to the final loss of the particles. It is thought that not only Coulomb collisions but also wave-particle interactions play a significant role in altering the plasma cloud. Quasilinear diffusion is currently being incorporated into the model and the importance of this mechanism will be examined. Also, the high anisotropy of the trapped population could be unstable and generate plasma waves. These and other processes will be investigated to determine the final fate of the cloud and to quantify where, how, and when the energy of the plasma cloud is deposited. Comparisons with CRRES observations of these events are shown to verify the model and explain the data.
Measurements of band gap structure in diamond compressed to 370 GPa
Gamboa, Eliseo; Fletcher, Luke; Lee, Hae-Ja; Zastrau, Ulf; Gauthier, Maxence; Gericke, Dirk; Vorberger, Jan; Granados, Eduardo; Heimann, Phillip; Hastings, Jerome; Glenzer, Siegfried
2015-06-01
We present the first measurements of the electronic structure of dynamically compressed diamond demonstrating a widening of the band gap to pressures of up to 370 +/- 25 GPa. The 8 keV free electron laser x-ray beam from the Linac Coherently Light Source (LCLS) has been focussed onto a diamond foil compressed by two counter-propagating laser pulses to densities of up to 5.3 g/cm3 and temperatures of up to 3000 +/- 400 K. The x-ray pulse excites a collective interband transition of the valence electrons, leading to a plasmon-like loss. We find good agreement with the observed plasmon shift by including the pressure dependence of the band gap as determined from density functional theory simulations. This work was performed at the Matter at Extreme Conditions (MEC) instrument of LCLS, supported by the DOE Office of Science, Fusion Energy Science under Contract No. SF00515. This work was supported by DOE Office of Science, Fusion Energy Science under F.
Band Structure of the Mn5Si3-, Tb5Si3-, and Tb5Ge3-type Compounds
Zabidi, N. A.; Kassim, H. A.; Shrivastava, K. N.
2010-12-01
The results of the band structure studies on Tb5Si3 and Tb5Ge3 as well as Mn5Si3 single crystals are reported. The compounds Tb5Si3 and Tb5Ge3 are metamagnetic because of a strong effect of magnetic field on the magnetization. The spin polarized and nonpolarized calculations give similar results in band structure for all of the compounds. The Fermi energy of Mn5Si3 is higher compared to Tb5Si3 and Tb5Ge3 while binding energy for Mn5Si3 is lower than in the other two compounds. The band gaps found in the Mn5Si3 compound are a bit higher when spin polarization is introduced in the calculation. The densities of states calculations show no electrons in the conduction band. This is the special finding of the present work. The bands Tb5Si3 and Tb5Ge3 but not Mn5Si3 exhibit metamagnetic behavior assigned to valence band electrons.
Refractory Coated/Lined Low Density Structures Project
National Aeronautics and Space Administration — This project addresses the development of refractory coated or lined low density structures applicable for advanced future propulsion system technologies. The...
Band structure and optical properties of highly anisotropic LiBa2[B10O16(OH)3] decaborate crystal
International Nuclear Information System (INIS)
The band structure (BS), charge density distribution and linear-optical properties of the anisotropic crystal LiBa2[B10O16(OH)3] (LBBOH) are calculated using a self-consistent norm-conserving pseudopotential method within the framework of the local-density approximation theory. A high anisotropy of the band energy gap (4.22 eV for the E parallel b, 4.46 eV for the E parallel c) and giant birefringence (up to 0.20) are found. Comparison of the theoretically calculated and the experimentally measured polarised spectra of the imaginary part of the dielectric susceptibility ?2 shows a good agreement. The anisotropy of the charge density distribution, BS dispersion and of the optical spectra originate from anisotropy between the 2pzB-2pzO and 2py,xB-2py,yO bonding orbitals. The observed anisotropy in the LBBOH is principally different from that of ?-BaB2O4 (BBO) single crystals. In the LBBOH single crystals the anisotropy of optical and charge density distribution is caused by different projection of the orbitals originating from particular borate clusters on the particular crystallographic axes, contrary to the BBO, where the anisotropy is caused prevailingly by a different local site symmetry of oxygen within the borate planes. The observed anisotropy is analysed in terms of the band energy dispersion and space charge density distribution
Design and analysis of defected ground structure transformer for dual-band antenna
Directory of Open Access Journals (Sweden)
Wai-Wa Choi
2014-12-01
Full Text Available This study presents a novel dual-band antenna design methodology utilising a dual-frequency impedance transformer with defected ground structure (DGS. The proposed dual-frequency DGS impedance transformer generates a second resonant frequency from a conventional single-band antenna, resulting dual-band operation. Simulation studies illustrate that the adopted design achieves versatile configurations for arbitrary operating frequencies and diverse input impedance ranges in planar antenna structures. To experimentally verify the proposed design methodology, a dual-frequency DGS impedance transformer was implemented for a 2.4 GHz monopole antenna to obtain a 900/2400 MHz dual-band antenna. Measurement shows that the 10 dB return loss bandwidth in 900 MHz band is 34.4 MHz, whereas that in 2400 MHz band is wider than 530 MHz. Typical monopole radiation patterns are observed at both operating bands.
Photonic band structures in one-dimensional photonic crystals containing Dirac materials
Wang, Lin; Wang, Li-Gang
2015-09-01
We have investigated the band structures of one-dimensional photonic crystals (1DPCs) composed of Dirac materials and ordinary dielectric media. It is found that there exist an omnidirectional passing band and a kind of special band, which result from the interaction of the evanescent and propagating waves. Due to the interface effect and strong dispersion, the electromagnetic fields inside the special bands are strongly enhanced. It is also shown that the properties of these bands are invariant upon the lattice constant but sensitive to the resonant conditions.
Labute, Montiago; Henkelman, Graeme; McMahon, Benjamin
2005-03-01
We have calculated the complete minimum-energy reaction path for the hydroxylation of camphor by the P450 enzyme from Pseudomonas putida using the nudged elastic band method of Jonsson and co-workers[1]. Single-point force and energy calculations on pathway images were performed at the hybrid density functional level of theory (B3LYP) with large basis sets for the iron atom (6-311+G) and O2 ligand (6-31+G*) on a 100 atom active site extracted from a recent high-resolution crystal structure[2]. Our model includes the heme group liganded to both Cys357 and dioxygen and we also include Thr251 and Asp252, which have been shown to significantly affect product yield by mutational studies[3]. We find that, upon transfer of the 2nd electron to the active site, the Fe-O2 moiety is unstable and decays to a Fe-OOH- intermediate via a Asp252-H2O proton transfer chain. The barrier for dioxygen cleavage and the identity of the reactive species will be discussed. [1] H. Jonsson, G. Mills, K.W. Jacobsen, in Classical and Quantum Dynamics in Condensed Phase Simulation, World Scientific (1998). [2] I. Schlichting, et al., Science 287, no. 5458, p. 1615-1622 (2000). [3] R. Davydov, et al., J. Am. Chem. Soc., 123: 1403-1415 (2001).
Prabhakar, Sanjay; Melnik, Roderick; Bonilla, Luis L.; Badu, Shyam
2014-11-01
We investigate the in-plane oscillations of relaxed-shape graphene due to externally applied tensile edge stress along both the armchair and zigzag directions. We show that the total elastic energy density is enhanced with temperature for the case of applied tensile edge stress along the zigzag direction. Thermoelectromechanical effects are treated via pseudomorphic vector potentials to analyze the influence of these coupled effects on the band structures of bilayer-graphene quantum dots. We report that the level crossing between the ground and first-excited states in the localized edge states can be achieved with accessible values of temperature. In particular, the level-crossing point extends to higher temperatures with decreasing externally applied tensile edge stress along the armchair direction. This kind of level crossing is absent in the states formed at the center of the graphene sheet due to the presence of threefold symmetry.
Energy Technology Data Exchange (ETDEWEB)
Sun, Shih-Jye [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Lin, Ken-Huang; Li, Jia-Yun [Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Ju, Shin-Pon, E-mail: jushin-pon@mail.nsysu.edu.tw [Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 807, Taiwan (China)
2014-10-07
The simulated annealing basin-hopping method incorporating the penalty function was used to predict the lowest-energy structures for ultrathin tungsten nanowires and nanotubes of different sizes. These predicted structures indicate that tungsten one-dimensional structures at this small scale do not possess B.C.C. configuration as in bulk tungsten material. In order to analyze the relationship between multi-shell geometries and electronic transfer, the electronic and structural properties of tungsten wires and tubes including partial density of state and band structures which were determined and analyzed by quantum chemistry calculations. In addition, in order to understand the application feasibility of these nanowires and tubes on nano-devices such as field emitters or chemical catalysts, the electronic stability of these ultrathin tungsten nanowires was also investigated by density functional theory calculations.
Vibrational dynamics and band structure of methyl-terminated Ge(111)
Hund, Zachary M.; Nihill, Kevin J.; Campi, Davide; Wong, Keith T.; Lewis, Nathan S.; Bernasconi, M.; Benedek, G.; Sibener, S. J.
2015-09-01
A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD3-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH3-Ge(111) and CH3-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers.
Vibrational dynamics and band structure of methyl-terminated Ge(111).
Hund, Zachary M; Nihill, Kevin J; Campi, Davide; Wong, Keith T; Lewis, Nathan S; Bernasconi, M; Benedek, G; Sibener, S J
2015-09-28
A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD3-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH3-Ge(111) and CH3-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers. PMID:26429030
Band structures in 121Xe and 119Xe excited by 12C induced reactions
International Nuclear Information System (INIS)
Band structures in 119,121Xe produced by 110,112Cd (12C,3n) reaction have been investigated using in-beam ? spectroscopic techniques. Details of the structures of the hsub(11/2) and gsub(7/2) bands are presented. A new dsub(3/2) decoupled band has been observed in 121Xe and a possible gsub(9/2) band in 119Xe. These collective features are discussed in the framework of the triaxial-rotor-plus-particle model, and the IFBA model. (orig.)
Estimating tropical forest structure using LIDAR AND X-BAND INSAR
Palace, M. W.; Treuhaft, R. N.; Keller, M. M.; Sullivan, F.; Roberto dos Santos, J.; Goncalves, F. G.; Shimbo, J.; Neumann, M.; Madsen, S. N.; Hensley, S.
2013-12-01
Tropical forests are considered the most structurally complex of all forests and are experiencing rapid change due to anthropogenic and climatic factors. The high carbon stocks and fluxes make understanding tropical forests highly important to both regional and global studies involving ecosystems and climate. Large and remote areas in the tropics are prime targets for the use of remotely sensed data. Radar and lidar have previously been used to estimate forest structure, with an emphasis on biomass. These two remote sensing methods have the potential to yield much more information about forest structure, specifically through the use of X-band radar and waveform lidar data. We examined forest structure using both field-based and remotely sensed data in the Tapajos National Forest, Para, Brazil. We measured multiple structural parameters for about 70 plots in the field within a 25 x 15 km area that have TanDEM-X single-pass horizontally and vertically polarized radar interferometric data. High resolution airborne lidar were collected over a 22 sq km portion of the same area, within which 33 plots were co-located. Preliminary analyses suggest that X-band interferometric coherence decreases by about a factor of 2 (from 0.95 to 0.45) with increasing field-measured vertical extent (average heights of 7-25 m) and biomass (10-430 Mg/ha) for a vertical wavelength of 39 m, further suggesting, as has been observed at C-band, that interferometric synthetic aperture radar (InSAR) is substantially more sensitive to forest structure/biomass than SAR. Unlike InSAR coherence versus biomass, SAR power at X-band versus biomass shows no trend. Moreover, airborne lidar coherence at the same vertical wavenumbers as InSAR is also shown to decrease as a function of biomass, as well. Although the lidar coherence decrease is about 15% more than the InSAR, implying that lidar penetrates more than InSAR, these preliminary results suggest that X-band InSAR may be useful for structure and biomass estimation over large spatial scales not attainable with airborne lidar. In this study, we employed a set of less commonly used lidar metrics that we consider analogous to field-based measurements, such as the number of canopy maxima, measures of canopy vegetation distribution diversity and evenness (entropy), and estimates of gap fraction. We incorporated these metrics, as well as lidar coherence metrics pulled from discrete Fourier transforms of pseudowaveforms, and hypothetical stand characteristics of best-fit synthetic vegetation profiles into multiple regression analysis of forest biometric properties. Among simple and complex measures of forest structure, ranging from tree density, diameter at breast height, and various canopy geometry parameters, we found strong relationships with lidar canopy vegetation profile parameters. We suggest that the sole use of lidar height is limited in understanding biomass in a forest with little variation across the landscape and that there are many parameters that may be gleaned by lidar data that inform on forest biometric properties.
The 22Na band structure: the first Jsup(?)=6+ level
International Nuclear Information System (INIS)
Angular correlation and DSAM (Doppler shift attenuation method) lifetime measurements are reported for the 22Na 3706keV level. This level is shown to be the Jsup(?)=6+ member of the ground state band and decays to the Jsup(?)=4+ and 5+ states through E2 transitions of strengths: 6.9+-0.7 and 12.1+-1.6W.u., respectively. The experimental strengths of transitions between the 22Na ground state band members are reviewed and compared to the predictions of different models
International Nuclear Information System (INIS)
We demonstrated direct band gap (DBG) electroluminescence (EL) at room temperature from n-type bulk germanium (Ge) using a fin type asymmetric lateral metal/Ge/metal structure with TiN/Ge and HfGe/Ge contacts, which was fabricated using a low temperature (<400?°C) process. Small electron and hole barrier heights were obtained for TiN/Ge and HfGe/Ge contacts, respectively. DBG EL spectrum peaked at 1.55??m was clearly observed even at a small current density of 2.2??A/?m. Superlinear increase in EL intensity was also observed with increasing current density, due to superlinear increase in population of elections in direct conduction band. The efficiency of hole injection was also clarified
Electronic band structures of graphene nanoribbons with self-passivating edge reconstructions
International Nuclear Information System (INIS)
Using the nearest-neighbor tight-binding approach we study the electronic band structures of graphene nanoribbons with self-passivating edge reconstructions. For zigzag ribbons the edge reconstruction moves both the Fermi energy and the flat band down by several hundred meV, and the flat band is always found to be below the Fermi energy. The states featured by the flat band are shown to be mainly localized at the atoms belonging to several lattice lines closest to the edges. For armchair ribbons the edge reconstruction strongly modifies the band structure in the region close to the Fermi energy, leading to the appearance of a band gap even for ribbons which were predicted to be metallic in the model of standard armchair edges. The gap widths are, however, strongly different in magnitude and behave in different ways regarding the ribbon width.
Calculation of the band structure of GdCo2, GdRh2 e GdIr2 by the APW method
International Nuclear Information System (INIS)
The band structure of GdCo2, GdRh2, GdIr2 has been calculated by the APW method. A histogram of the density of states is presented for each compound. The bands are transition-metal-like, with s-d hybridization near the Fermi level. The 5d character near the Fermi level increases as one goes from Co to Ir
Koskinen, Pekka; Fampiou, Ioanna; Ramasubramaniam, Ashwin
2014-05-01
Monolayer transition-metal dichalcogenides (TMDCs) display valley-selective circular dichroism due to the presence of time-reversal symmetry and the absence of inversion symmetry, making them promising candidates for valleytronics. In contrast, in bilayer TMDCs both symmetries are present and these desirable valley-selective properties are lost. Here, by using density-functional tight-binding electronic structure simulations and revised periodic boundary conditions, we show that bending of bilayer MoS2 sheets breaks band degeneracies and localizes states on separate layers due to bending-induced strain gradients across the sheets. We propose a strategy for employing bending deformations in bilayer TMDCs as a simple yet effective means of dynamically and reversibly tuning their band gaps while simultaneously tuning valley-selective physics.
Enhanced conduction band density of states in intermetallic EuTSi3 (T = Rh, Ir)
Maurya, Arvind; Bonville, P.; Thamizhavel, A.; Dhar, S. K.
2015-09-01
We report on the physical properties of single crystalline EuRhSi3 and polycrystalline EuIrSi3, inferred from magnetization, electrical transport, heat capacity and 151Eu Mössbauer spectroscopy. These previously known compounds crystallise in the tetragonal BaNiSn3-type structure. The single crystal magnetization in EuRhSi3 has a strongly anisotropic behaviour at 2 K with a spin-flop field of 13 T, and we present a model of these magnetic properties which allows the exchange constants to be determined. In both compounds, specific heat shows the presence of a cascade of two close transitions near 50 K, and the 151Eu Mössbauer spectra demonstrate that the intermediate phase has an incommensurate amplitude modulated structure. We find anomalously large values, with respect to other members of the series, for the RKKY Néel temperature, for the spin-flop field (13 T), for the spin-wave gap (? 20–25 K) inferred from both resistivity and specific heat data, for the spin-disorder resistivity in EuIrSi3 (? 240 ? ? cm) and for the saturated hyperfine field (52 T). The enhanced values of the quantities that depend on the electronic density of states at the Fermi level, imply that the latter must be strongly enhanced in these two materials. EuIrSi3 exhibits a giant magnetoresistance ratio, with values exceeding 600% at 2 K in a field of 14 T.
Mao, Y.; Liang, X. X.; Zhao, G. J.; Song, T. L.
2014-03-01
Lattice parameters and band structure of the ternary mixed crystal AlxGa1-xAs of zinc blende structure are calculated by first-principle calculations within the framework of the density functional theory. The results for the equilibrium lattice parameters and band gaps of AlxGa1-xAs for the Al-composition varying from 0.0 to 1.0 by step of 0.125 are presented and discussed. The results show that the lattice constants vary with the composition almost linearly following the Vegard's law. The electron band gap at Gamma; point exhibits non-linear behavior versus the composition. The Al-3s, 3p states shift to high energy region in the conduction band with increasing the Al concentration. It leads to an increase of the band gap and the blue shift phenomenon.
International Nuclear Information System (INIS)
Lattice parameters and band structure of the ternary mixed crystal AlxGa1-xAs of zinc blende structure are calculated by first-principle calculations within the framework of the density functional theory. The results for the equilibrium lattice parameters and band gaps of AlxGa1-xAs for the Al-composition varying from 0.0 to 1.0 by step of 0.125 are presented and discussed. The results show that the lattice constants vary with the composition almost linearly following the Vegard's law. The electron band gap at Gamma; point exhibits non-linear behavior versus the composition. The Al-3s, 3p states shift to high energy region in the conduction band with increasing the Al concentration. It leads to an increase of the band gap and the blue shift phenomenon
Phononic band gaps and vibrations in one- and two-dimensional mass-spring structures
DEFF Research Database (Denmark)
Jensen, Jakob Søndergaard
2003-01-01
The vibrational response of finite periodic lattice structures subjected to periodic loading is investigated. Special attention is devoted to the response in frequency ranges with gaps in the band structure for the corresponding infinite periodic lattice. The effects of boundaries, viscous damping, and imperfections are studied by analyzing two examples; a 1-D filter and a 2-D wave guide. In 1-D the structural response in the band gap is shown to be insensitive to damping and small imperfections...
The magneto-optical properties of semiconductors and the band structure of gallium nitride
Shields, P A
2001-01-01
the wells, and observing a resonant phenomenon from an undoped GaN/Al sub x Ga sub 1 sub - sub x N single heterojunction. The oscillating peak intensity was understood in terms of the changing screening efficiency of the two-dimensional electron gas. Finally, many-body effects within an electron-hole plasma in ln sub x Al sub y Ga sub 1 sub - sub x sub - sub y As quantum wells have been explored to study the effects of mass renormalisation at carrier densities typically present in laser devices. A peak in the mass renormalisation confirms the importance of excitonic correlations in the excited plasma. This thesis has applied magneto-optical techniques to enable a better understanding of the band structure of gallium nitride, particularly the complex behaviour expected as a result of strong valence band mixing. Effective hole masses are deduced from free excitonic-like transitions observed in magneto-reflectivity, to give a heavy A hole mass of 1.3 m sub o and the first experimental suggestion of a light B ban...
InN/GaN Superlattices: Band Structures and Their Pressure Dependence
DEFF Research Database (Denmark)
Gorczyca, Iza; Suski, Tadek
2013-01-01
Creation of short-period InN/GaN superlattices is one of the possible ways of conducting band gap engineering in the green-blue range of the spectrum. The present paper reports results of photoluminescence experiments, including pressure effects, on a superlattice sample consisting of unit cells with one monolayer of InN and 40 monolayers of GaN. The results are compared with calculations performed for different types of superlattices: InN/GaN, InGaN/GaN, and InN/InGaN/GaN with single monolayers of InN and/or InGaN. The superlattices are simulated by band structure calculations based on the local density approximation (LDA) with a semi-empirical correction for the ‘‘LDA gap error’’. A similarity is observed between the results of calculations for an InGaN/GaN superlattice (with one monolayer of InGaN) and the experimental results. This indicates that the fabricated InN quantum wells may contain some Ga atoms due to interdiffusion
Band structure and optical properties of hexagonal In-rich InxAl1-xN alloys
International Nuclear Information System (INIS)
Full potential linear augmented plane wave calculations have been performed to study the electronic and optical properties of In-rich InxAl1-xN alloys in the hexagonal wurtzite structure. Compositions of x = 0.9375, 0.8125 and 0.6875 are considered which follow from replacing one, three and five In atoms by Al in the 32-atom supercell. The new form of exchange correlation, i.e. Engel-Vosko’s generalized gradient approximation within density functional theory, is employed. The calculations yield the band structure and total density of states as well as the imaginary part ?2(?) of the ordinary and extraordinary dielectric function. The calculated dependence of the bandgap on the composition is in good agreement with recent experimental studies. A reversal of the valence band ordering is found between x = 0.8125 and 0.6875. The absorption features in the high-energy range of ?2(?) are related to critical points of the band structure. The transition energies for these van Hove singularities are determined and their bowing parameters are discussed. (paper)
International Nuclear Information System (INIS)
Photonic band structures are investigated for both diamond and hexagonal diamond crystals composed of dielectric spheres, and absolute photonic band gaps (PBGs) are found in both cases. In agreement with both Karathanos and Moroz's calculations, a large PBG occurs between the eighth and ninth bands in diamond crystal, but a PBG in hexagonal diamond crystal is found to occur between the sixteenth and seventeenth bands because of the doubling of dielectric spheres in the primitive cell. To explore the physical mechanism of how the photonic band gap might be broadened, we have compared the electric field distributions (|E|2) of the 'valence' and 'conduction' band edges. Results show that the field intensity for the 'conduction' band locates in the inner core of the sphere while that of the 'valence' band concentrates in the outer shell. With this motivation, double-layer spheres are designed to enhance the corresponding photonic band gaps; the PBG is increased by 35% for the diamond structure, and 14% for the hexagonal diamond structure
Energy Technology Data Exchange (ETDEWEB)
Appalakondaiah, S.; Vaitheeswaran, G., E-mail: gvaithee@gmail.com [Advanced Centre of Research in High Energy Materials (ACRHEM), University of Hyderabad, Prof. C. R. Rao Road, Gachibowli, Hyderabad 500 046, Andhra Pradesh (India); Lebègue, S. [Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2, UMR CNRS 7036), Institut Jean Barriol, Université de Lorraine, BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-lès-Nancy (France)
2014-01-07
The effects of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme, are found to agree well with experiments. The calculated vibrational frequencies demonstrate the dependence of the intra and inter-molecular interactions on FOX-7 under pressure. In addition, we also found a significant increment in the N–H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen, and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with generalized gradient approximation, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials.
Valor, A; Robledo, L M
2000-01-01
We derive the equations for approximate particle number projection based on mean field wave functions with finite range density dependent forces. As an application ground bands of even-A superdeformed nuclei in the A=150 and A=190 regions are calculated with the Gogny force. We discuss nuclear properties such as quadrupole moments, moments of inertia and quasiparticle spectra, among others, as a function of the angular momentum. We obtain a good overall description.
Hybrid density functional calculations of the band gap of Ga$_x$In$_{1-x}$N
Wu, Xifan; Walter, Eric J.; Rappe, Andrew M.; Car, Roberto; Selloni, Annabella
2009-01-01
Recent theoretical work has provided evidence that hybrid functionals, which include a fraction of exact (Hartree Fock) exchange in the density functional theory (DFT) exchange and correlation terms, significantly improve the description of band gaps of semiconductors compared with local and semilocal approximations. Based on a recently developed order-$N$ method for calculating the exact exchange in extended insulating systems, we have implemented an efficient scheme to det...
Determination of conduction and valence band electronic structure of anatase and rutile TiO2
Indian Academy of Sciences (India)
Jakub Szlachetko; Katarzyna Michalow-Mauke; Maarten Nachtegaal; Jacinto Sá
2014-03-01
Electronic structures of rutile and anatase polymorph of TiO2 were determined by resonant inelastic X-ray scattering measurements and FEFF9.0 calculations. Difference between crystalline structures led to shifts in the rutile Ti -band to lower energy with respect to anatase, i.e., decrease in band gap. Anatase possesses localized states located in the band gap where electrons can be trapped, which are almost absent in the rutile structure. This could well explain the reported longer lifetimes in anatase. It was revealed that HR-XAS is insufficient to study in-depth unoccupied states of investigated materials because it overlooks the shallow traps.
Chen, Shibin; Li, Dichen; Zhi-Hui, Yuan
2013-06-01
A new kind of heterostructures containing 3D diamond and 2D holes structures, and diamond-structure photonic crystals and 2D holes-structure photonic crystals fabricated by stereolithography and gel-casting with alumina were studied at microwave range, respectively. The heterostructures were designed by 2D holes structure embedded in 3D diamond structure, in which the lattice of three kinds of structures was equivalent. It was found that the band gaps of photonic crystal heterostructure were broadened by 124.6% and 150% comparing to that of diamond-structure crystal and 2D aerial holes structure. Experimental results showed the band gap broadened was not connected with a linear superposition of the band gap of 2D and 3D photonic crystals, which was the superposition of partial overlap.
High gradient test of X-band accelerating structure at GLCTA
International Nuclear Information System (INIS)
GLCTA (Global Linear Collider Test Accelerator) is the high power test facility for X-band acceleration. We have installed an X-band 60cm structure in April 2004 and have been processing it for more than 3 months. Now it is under test on long-term operation. We report here the installation process and high power test result to date. (author)
Energy Technology Data Exchange (ETDEWEB)
Khyzhun, O.Y., E-mail: khyzhun@ipms.kiev.ua [Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv 03142 (Ukraine); Bekenev, V.L.; Denysyuk, N.M. [Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv 03142 (Ukraine); Parasyuk, O.V. [Department of Inorganic and Physical Chemistry, Eastern European National University, 13 Voli Avenue, Lutsk 43025 (Ukraine); Fedorchuk, A.O. [Department of Inorganic and Organic Chemistry, Lviv National University of Veterinary Medicine and Biotechnologies, Pekarska St., 50, 79010 Lviv (Ukraine)
2014-01-05
Highlights: • Electronic structure of TlPb{sub 2}Cl{sub 5} is calculated by the FP-LAPW method. • The valence band is dominated by contributions of Cl 3p states. • Contributions of Pb 6p{sup *} states dominate at the bottom of the conduction band. • The FP-LAPW data allow concluding that TlPb{sub 2}Cl{sub 5} is an indirect-gap material. • XPS core-level and valence-band spectra of polycrystalline TlPb{sub 2}Cl{sub 5} are measured. -- Abstract: We report on first-principles calculations of total and partial densities of states of atoms constituting TlPb{sub 2}Cl{sub 5} using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations reveal that the valence band of TlPb{sub 2}Cl{sub 5} is dominated by contributions of the Cl 3p-like states, which contribute mainly at the top of the valence band with also significant contributions throughout the whole valence-band region. In addition, the bottom of the conduction band of TlPb{sub 2}Cl{sub 5} is composed mainly of contributions of the unoccupied Pb 6p-like states. Our FP-LAPW data indicate that the TlPb{sub 2}Cl{sub 5} compound is an indirect-gap material with band gap of 3.42 eV. The X-ray photoelectron core-level and valence-band spectra for pristine and Ar{sup +} ion-irradiated surfaces of a TlPb{sub 2}Cl{sub 5} polycrystalline sample were measured. The measurements reveal high chemical stability and confirm experimentally the low hygroscopicity of TlPb{sub 2}Cl{sub 5} surface.
Band structures in 98Ru and 99Ru
International Nuclear Information System (INIS)
The level schemes of 98sup(,)99Ru were studied with the reactions 8Mo(?,3n?) and 98Mo(?,4n?) at Esub(?) = 35 to 55 MeV, using a large variety of in-beam ?-ray detection techniques and conversion-electron measurements. A search for the 3- state was carried out with the reaction 98Ru(p,p'). The ground-state band of 98Ru was excited up to Jsup(?) = (12)+ and a negative-parity band up to (15)-. New levels in 98Ru were found at Esub(x) = 2285 (Jsup(?) = 4+), 2435 (Jsup(?) = (3-,4+), 2671, 3540, 4224, 4847, 4915 (Jsup(?) = (12)sup()), 4989 (Jsup(?) = (12sup())), 5521 (Jsup(?) = (13)-), 5889, 6591 (Jsup(?) = (15)-), and 7621 keV. New unambiguous spin and parity assignments were made for the levels at Esub(x) = 2014 and 3852 keV, as Jsup(?) = 3+ and 9-, respectivley. New levels in 99Ru were found at Esub(x) = 1976, 2021 (Jsup(?) = (15/2+)), 2393, 2401 (Jsup(?) = (17/2+)), 2875 (? = (+)), 3037, 3201 (Jsup(?) = (23/2)-), 3460 (J = (17/2)), 3484 (Jsup(?) = (21/2+)), 3985, 4224 (Jsup(?) = (27/2-)), and 5359 keV. The 1070 keV, Jsup(?) = 11/2- level in 99Ru has a half-life of 2.8 ns. A strongly excited negative-parity band is built on this level. A positive-parity band based on the ground state was excited up to Jsup(?) = (21/2+). The level schemes are well reproduced by the interacting boson model in the vibrational limit. (orig.)
Band structure in odd-odd 86Nb
International Nuclear Information System (INIS)
Odd-odd 86Nb has been investigated to explore the interaction between single-particle and collective degrees of freedom. High-spin states were populated using the 58Ni(32S,3pn)86Nb reaction at 135 MeV. Cascades of 3 or more ? rays were detected with the early implementation of GAMMA-SPHERE while the evaporated charged particles were observed in the 96-element MICROBALL for channel selection. States have been observed with spins up to 3l? and rotational frequencies over 1.2 MeV/?. New bands appear at about 2.5 MeV and eventually become yrast. The level spacings in the yrast positive parity band show a large signature splitting whose phase reverses at the 10+ state, probably due to competition between quasiparticle alignment and rotation. The B(M1) values in this band also exhibit a large alteration, with strengths varying by an order of magnitude depending on the signatures of the states
Features of the band structure for semiconducting iron, ruthenium, and osmium monosilicides
International Nuclear Information System (INIS)
The pseudopotential method has been used to optimize the crystal lattice and calculate the energy band spectra for iron, ruthenium and, osmium monosilicides. It is found that all these compounds are indirect-gap semiconductors with band gaps of 0.17, 0.22, and 0.50 eV (FeSi, RuSi, and OsSi, respectively). A distinctive feature of their band structure is the 'loop of extrema' both in the valence and conduction bands near the center of the cubic Brillouin zone.
Band structures in odd-even bromine isotopes A=77-81
International Nuclear Information System (INIS)
The collective bands in odd-even bromine isotopes A=77, 79 and 81 are studied within our deformed configuration-mixing shell model based on self-consistently derived single-particle states. The calculated K=3/2- negative-parity ground band and the K=9/2+ positive-parity band agree reasonably well with experiment. An attempt is made to study the structure of the three quasi-particle band of high-spin states built on the J=13/2- level in these nuclei. (orig.)
DEFF Research Database (Denmark)
Domadiya, Parthkumar Gandalal; Manconi, Elisabetta; Vanali, Marcello; Andersen, Lars Vabbersgaard; Ricci, Andrea
2015-01-01
Adding periodicity to structures leads to wavemode interaction, which generates pass- and stop-bands. The frequencies at which stop-bands occur are related to the periodic nature of the structure. Thus structural periodicity can be shaped in order to design vibro-acoustic filters for reducing vibration and noise transmission. The aim of this paper is to investigate, numerically and experimentally, stop-bands in periodic one-dimensional structures. Two methods for pre-dicting stop-bands are descr...
The band structure of BeTe a combined experimental and theoretical study
Nagelstrasser, M; Fischer, F; Litz, T; Waag, A; Fleszar, A; Hanke, W; Steinrück, H P; Landwehr, Gottfried
1998-01-01
Using angle-resolved synchrotron-radiation photoemission spectroscopy we have determined the dispersion of the valence bands of BeTe(100) along $\\Gamma X$, i.e. the [100] direction. The measurements are analyzed with the aid of a first-principles calculation of the BeTe bulk band structure as well as of the photoemission peaks as given by the momentum conserving bulk transitions. Taking the calculated unoccupied bands as final states of the photoemission process, we obtain an excellent agreement between experimental and calculated spectra and a clear interpretation of almost all measured bands. In contrast, the free electron approximation for the final states fails to describe the BeTe bulk band structure along $\\Gamma X$ properly.
Simple inverted band structure model for cadmium arsenide (Cd3As2)
International Nuclear Information System (INIS)
The development of a simple Hamiltonian yielding the inverted band structure of Cd3As2 in the 4 mm (C4v12) low-temperature phase is proposed. The presented theory takes into account the spin orbit interaction and tetragonal distortion of lattice in the low symmetry. The authors obtain k-linear terms in the band structure and therefore a splitting in k-space of spin degenerate energy bands. The reported band model contains only one new crystal field parameter d = cr|Z> in addition to well known Kildal's set. The first evaluation of this shows that (0.028 < d < 0.072) eV using optical absorption edge data. The finite width of the anisotropic heavy and light hole bands is pointed out. (authors)
Energy Technology Data Exchange (ETDEWEB)
Zhou, Xiaoling; Chen, Changqing, E-mail: chencq@tsinghua.edu.cn
2013-12-15
The band structures of two locally resonant phononic crystals (LRPCs) with periodic multilayered cylindrical inclusions embedded in an elastic matrix are investigated by the finite-element method. The inclusions consist of electroactive polymer layer(s). Tunability of the band gaps of the phononic crystals by applying electric field upon the electroactive layer is demonstrated. A simple analytical expression is presented on the relationship between the stop band boundaries and the electric field. Good agreement between the analytical and numerical predictions is obtained. The effects of initial stress on the band structures are explored. It is found that tensile initial stress shifts up the band gaps while compressive initial stress shifts down or even closes them.
International Nuclear Information System (INIS)
The band structures of two locally resonant phononic crystals (LRPCs) with periodic multilayered cylindrical inclusions embedded in an elastic matrix are investigated by the finite-element method. The inclusions consist of electroactive polymer layer(s). Tunability of the band gaps of the phononic crystals by applying electric field upon the electroactive layer is demonstrated. A simple analytical expression is presented on the relationship between the stop band boundaries and the electric field. Good agreement between the analytical and numerical predictions is obtained. The effects of initial stress on the band structures are explored. It is found that tensile initial stress shifts up the band gaps while compressive initial stress shifts down or even closes them
Band structure of Heusler compounds studied by photoemission and tunneling spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Arbelo Jorge, Elena
2011-07-01
Heusler compounds are key materials for spintronic applications. They have attracted a lot of interest due to their half-metallic properties predicted by band structure calculations. The aim of this work is to evaluate experimentally the validity of the predictions of half metallicity by band structure calculations for two specific Heusler compounds, Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa. Two different spectroscopy methods for the analysis of the electronic properties were used: Angular Resolved Ultraviolet Photoemission Spectroscopy (ARUPS) and Tunneling Spectroscopy. Heusler compounds are prepared as thin films by RF-sputtering in an ultra high vacuum system. For the characterization of the samples, bulk and surface crystallographic and magnetic properties of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa are studied. X-ray and electron diffraction reveal a bulk and surface crossover between two different types of sublattice order (from B2 to L2{sub 1}) with increasing annealing temperature. X-ray magnetic circular dichroism results show that the magnetic properties in the surface and bulk are identical, although the magnetic moments obtained are 5 % below from the theoretically predicted. By ARUPS evidence for the validity of the predicted total bulk density of states (DOS) was demonstrated for both Heusler compounds. Additional ARUPS intensity contributions close to the Fermi energy indicates the presence of a specific surface DOS. Moreover, it is demonstrated that the crystallographic order, controlled by annealing, plays an important role on broadening effects of DOS features. Improving order resulted in better defined ARUPS features. Tunneling magnetoresistance measurements of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa based MTJ's result in a Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} spin polarization of 44 %, which is the highest experimentally obtained value for this compound, although it is lower than the 100 % predicted. For Co{sub 2}MnGa no high TMR was achieved. Unpolarized tunneling spectroscopy reveals contribution of interface states close to the Fermi energy. Additionally magnon excitations due to magnetic impurities at the interface are observed. Such contributions can be the reason of a reduced TMR compared to the theoretical predictions. Nevertheless, for energies close to the Fermi energy and for Co{sub 2}MnGa, the validity of the band structure calculations is demonstrated with this technique as well.
Structure of Dipole Bands in 112In: Through Lifetime Measurement
Trivedi, T.; Palit, R.; Sethi, J.; Saha, S.; Kumar, S.; Naik, Z.; Parkar, V. V.; Naidu, B. S.; Deo, A. Y.; Raghav, A.; Joshi, P. K.; Jain, H. C.; Sihotra, S.; Mehta, D.; Jain, A. K.; Choudhury, D.; Negi, D.; Roy, S.; Chattopadhyay, S.; Singh, A. K.; Singh, P.; Biswas, D. C.; Bhowmik, R. K.; Muralithar, S.; Singh, R. P.; Kumar, R.; Rani, K.
2012-09-01
High-spin states of the 112In nucleus have been populated via 100Mo(16O, p3n) reaction at 80 MeV beam energy. Lifetimes of excited states of dipole bands have been measured using Doppler-shift attenuation method. The B(M1) transition rates deduced from the measured lifetimes show a rapid decrease with increasing angular momentum. The decrease in B(M1) values are well accounted by the prediction of tilted axis cranking calculations. These measurements confirm the presence of shears mechanism in this nuclei.
Probing the graphite band structure with resonant soft-x-ray fluorescence
Energy Technology Data Exchange (ETDEWEB)
Carlisle, J.A.; Shirley, E.L.; Hudson, E.A. [Lawrence Berkeley National Lab., CA (United States)] [and others
1997-04-01
Soft x-ray fluorescence (SXF) spectroscopy using synchrotron radiation offers several advantages over surface sensitive spectroscopies for probing the electronic structure of complex multi-elemental materials. Due to the long mean free path of photons in solids ({approximately}1000 {angstrom}), SXF is a bulk-sensitive probe. Also, since core levels are involved in absorption and emission, SXF is both element- and angular-momentum-selective. SXF measures the local partial density of states (DOS) projected onto each constituent element of the material. The chief limitation of SXF has been the low fluorescence yield for photon emission, particularly for light elements. However, third generation light sources, such as the Advanced Light Source (ALS), offer the high brightness that makes high-resolution SXF experiments practical. In the following the authors utilize this high brightness to demonstrate the capability of SXF to probe the band structure of a polycrystalline sample. In SXF, a valence emission spectrum results from transitions from valence band states to the core hole produced by the incident photons. In the non-resonant energy regime, the excitation energy is far above the core binding energy, and the absorption and emission events are uncoupled. The fluorescence spectrum resembles emission spectra acquired using energetic electrons, and is insensitive to the incident photon`s energy. In the resonant excitation energy regime, core electrons are excited by photons to unoccupied states just above the Fermi level (EF). The absorption and emission events are coupled, and this coupling manifests itself in several ways, depending in part on the localization of the empty electronic states in the material. Here the authors report spectral measurements from highly oriented pyrolytic graphite.
Full Band Structure Calculation of Two-photon Indirect Absorption in Bulk Silicon
Cheng, J. L.; Rioux, J.; J. E. Sipe
2010-01-01
Degenerate two-photon indirect absorption in silicon is an important limiting effect on the use of silicon structures for all-optical information processing at telecommunication wavelengths. We perform a full band structure calculation to investigate two-photon indirect absorption in bulk silicon, using a pseudopotential description of the energy bands and an adiabatic bond charge model to describe phonon dispersion and polarization. Our results agree well with some recent e...
R&D; of X-band Accelerating Structure for Compact XFEL at SINAP
Fang, Wencheng; Zhang, Meng; Zhao, Zhentang; Aksoy, Avni; Yava?, Omer; Angal-Kalinin, Deepa; Clarke, James; Bocchetta, Carlo; Wawrzyniak, Adriana; Boland, Mark; D'Auria, Gerardo; Di Mitri, Simone; Serpico, Claudio; Ekelöf, Tord; Ruber, Roger; Ziemann, Volker; Gazis, Evangelos; Grudiev, Alexej; Latina, Andrea; Schulte, Daniel; Stapnes, Steinar; Wuensch, Walter
2014-01-01
One compact hard X-ray FEL facility is being planned at SINAP, and X-band high gradient accelerating structure is the most competetive scheme for this plan. X-band accelerating structure is designed to switch between 60MV/m and 80MV/m, and carries out 6GeV and 8GeV by 130 meters linac respectively. In this paper, brief layout of compact XFEL will be introduced, and in particular the prototype design of dedicated X-band acceleration RF system is also presented.
Realization of Band-Notch UWB Monopole Antenna Using AMC Structure
Directory of Open Access Journals (Sweden)
Pradeep Kumar
2013-06-01
Full Text Available This article presents the design, simulation and testing of an Ultra Wide Band (UWB planar monopole antenna with WLAN band-notch characteristic. The proposed antenna consists, the combination of planar monopole antenna with partial ground and a pair of AMC structures. The AMC structure used for the design is mushroom-like. Design equation of EBG parameters is also proposed for FR4 substrate using transmission line model. Using proposed equations, Mushroom-like EBG structure is integrated along the feed line of a monopole antenna for WLAN (5 GHz – 6 GHz band rejection. TheCurrent distribution and equivalent circuit model of antenna is used to explain band-notch characteristic of EBG resonator. The proposed antenna is fabricated on an FR4 substrate with a thickness of 1.6 mmand ?r = 4.4. The measured VSWR characteristic is less than 2 for complete UWB band except for WLAN band i.e. 5 GHz – 6 GHz. The gain of the proposed structure is around 2 dBi – 6.7 dBi for complete UWBband except for WLAN band where it is reduced to -4 dBi. The measured radiation pattern of proposed antenna is omnidirectional along H plane and bidirectional in E plane. A nearly constant group delaywith variations < 2ns, except for the notched bandwidth makes proposed antenna suitable for UWB application.
On the band structure of YBa2 Cu3 O7
International Nuclear Information System (INIS)
One compares the general features of the band structure of YBa2 Cu3 O7, as obtained from a rough tight analysis, in the two structures which have been proposed so far. The structure most recently put forward seems a priori more favourable to high threedimensional Tc superconductivity in a weak coupling limit
Structural failure of two-density-layer cohesionless biaxial ellipsoids
Hirabayashi, Masatoshi
2014-01-01
This paper quantitatively evaluates structural failure of biaxial cohesionless ellipsoids that have a two-density-layer distribution. The internal density layer is modeled as a sphere, while the external density layer is the rest of the part. The density is supposed to be constant in each layer. The present study derives averaged stresses over the whole volume of these bodies and uses limit analysis to determine their global failure. The upper bound condition of global failure is considered in terms of the size of the internal layer and the aspect ratio of the shape. The result shows that the two-density-layer causes the body to have different strength against structural failure.
Model comparison for the density structure along solar prominence threads
Arregui, I
2015-01-01
Quiescent solar prominence fine structures are typically modelled as density enhancements, called threads, which occupy a fraction of a longer magnetic flux tube. The profile of the mass density along the magnetic field is however unknown and several arbitrary alternatives are employed in prominence wave studies. We present a comparison of theoretical models for the field-aligned density along prominence fine structures. We consider Lorentzian, Gaussian, and parabolic profiles. We compare their theoretical predictions for the period ratio between the fundamental transverse kink mode and the first overtone to obtain estimates for the ratio of densities between the central part of the tube and its foot-points and to assess which one would better explain observed period ratio data. Bayesian parameter inference and model comparison techniques are developed and applied. Parameter inference requires the computation of the posterior distribution for the density gradient parameter conditional on the observable period...
Structural, electronic and phonon properties of MoTa and MoNb: a density functional investigation
Energy Technology Data Exchange (ETDEWEB)
Bayhan, Ue [Mehmet Akif Ersoy Ueniversitesi, Fen-Edebiyat Fakueltesi, Fizik Boeluemue, Burdur (Turkey); Arikan, N [Ahi Evran Ueniversitesi, Egitim Fakueltesi, Ilkgretim Boeluemue, Fen Bilgisi Anabilim Dali, Kirsehir (Turkey); Ugur, S; Ugur, G; Civi, M, E-mail: ubayhan@mehmetakif.edu.t [Gazi Ueniversitesi, Fen-Edebiyat Fakueltesi, Fizik Boeluemue, Teknikokullar, Ankara (Turkey)
2010-07-15
First-principles calculations were performed to investigate the structural, electronic and phonon properties of MoTa and MoNb in the CsCl (B2) phase. The calculated lattice constants, static bulk modulus and first-order pressure derivative of the bulk modulus are in good agreement with available experimental data and previous theoretical predictions. Electronic band structures and partial and total densities of states have been derived for MoTa and MoNb. The band structures show metallic character; the conductivity is mostly governed by Mo-4d and Ta-5d (Nb-4d) states. A linear-response approach to the density functional theory is used to derive phonon dispersion curves and the density of states for MoTa and MoNb. Zone centre optical phonon modes of MoTa and MoNb are found to be at 6.46 and 7.24 THz, respectively.
Structural, electronic and phonon properties of MoTa and MoNb: a density functional investigation
International Nuclear Information System (INIS)
First-principles calculations were performed to investigate the structural, electronic and phonon properties of MoTa and MoNb in the CsCl (B2) phase. The calculated lattice constants, static bulk modulus and first-order pressure derivative of the bulk modulus are in good agreement with available experimental data and previous theoretical predictions. Electronic band structures and partial and total densities of states have been derived for MoTa and MoNb. The band structures show metallic character; the conductivity is mostly governed by Mo-4d and Ta-5d (Nb-4d) states. A linear-response approach to the density functional theory is used to derive phonon dispersion curves and the density of states for MoTa and MoNb. Zone centre optical phonon modes of MoTa and MoNb are found to be at 6.46 and 7.24 THz, respectively.
Energy Technology Data Exchange (ETDEWEB)
Johnson, Benjamin, E-mail: benjamin.johnson@alumni.tu-berlin.de [Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489 Berlin (Germany); Klaer, Jo; Merdes, Saoussen; Gorgoi, Mihaela; Höpfner, Britta; Vollmer, Antje; Lauermann, Iver [Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489 Berlin (Germany)
2013-10-15
Highlights: ? Near Edge X-ray Absorption Fine Structure investigated as tool for probing the conduction band in Cu(In,Ga)S{sub 2}. ? Absorption edge of anion contains most pertinent electronic information. ? Development of Cu(In,Ga){sub 2} band gap with increased Ga content reflected in anion absorption edge positions. ? Correspondence with theory found. -- Abstract: A non-optimized interface band alignment in a heterojunction-based solar cell can have negative effects on the current and voltage characteristics of the resulting device. To evaluate the use of Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS) as a means to measure the conduction band position, Cu(In,Ga)S{sub 2} chalcopyrite thin film surfaces were investigated as these form the absorber layer in solar cells with the structure ZnO/buffer/Cu(In,Ga)S{sub 2}/Mo/glass. The composition dependence of the structure of the conduction bands of CuIn{sub x}Ga{sub 1?x}S{sub 2} has been revealed for x = 0, 0.67 and 1 with both hard and soft NEXAFS and the resulting changes in conduction band offset at the junction with the buffer layer discussed. A comprehensive study of the positions of the absorption edges of all elements was carried out and the development of the conduction band with Ga content was observed, also with respect to calculated densities of states.
Effective three-band structure in Fe-based superconductors
Möckli, David; de Mello, E. V. L.
2014-01-01
We present self-consistent calculations of the multi-gap structure measured in some Fe-based superconductors. These materials are known to have structural disorder in real space and a multi-gap structure due to the $3d$ Fe-orbitals contributing to a complex Fermi surface topology with hole and electron pockets. Different experiments identify three s-wave like superconducting gaps with a single critical temperature ($T_c$). We investigate the temperature dependence of these g...
Tuning of band structures in porous phononic crystals by grading design of cells.
Wang, Kai; Liu, Ying; Yang, Qin-shan
2015-08-01
As the results of the evolution of species, grading structures widely exist in the nature and display distinguish advantages. In this manuscript, grading concept is introduced to redesign the topological structure of pores with the aim to see the effects of grading on the band structure in porous phononic crystals. Circular pores are considered and the crossing grading is made. The wave dispersion in graded structures is investigated comparatively to the normal ones under the same porosity. The band gaps in grading structures are given, as well as the vibration modes of the unit cell corresponding to the absolute band gap (ABG) edges. The results show that the grading structure greatly decreases the critical porosity for the opening of the ABGs. Wider ABGs could be obtained at lower frequencies along with the increase of the porosity. Through controlling the topological parameters of the grading structure, the band structure could be tuned. These results will provide an important guidance in the band tuning in porous phononic crystals by grading design of cells. PMID:25890636
Model comparison for the density structure across solar coronal waveguides
Arregui, I; Ramos, A Asensio
2015-01-01
The spatial variation of physical quantities, such as the mass density, across solar atmospheric waveguides governs the timescales and spatial scales for wave damping and energy dissipation. The direct measurement of the spatial distribution of density, however, is difficult and indirect seismology inversion methods have been suggested as an alternative. We applied Bayesian inference, model comparison, and model-averaging techniques to the inference of the cross-field density structuring in solar magnetic waveguides using information on periods and damping times for resonantly damped magnetohydrodynamic (MHD) transverse kink oscillations. Three commonly employed alternative profiles were used to model the variation of the mass density across the waveguide boundary. Parameter inference enabled us to obtain information on physical quantities such as the Alfv\\'en travel time, the density contrast, and the transverse inhomogeneity length scale. The inference results from alternative density models were compared a...
Fine structure of the red luminescence band in undoped GaN
Energy Technology Data Exchange (ETDEWEB)
Reshchikov, M. A., E-mail: mreshchi@vcu.edu [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284 (United States); Usikov, A. [Nitride Crystals, Inc., 181E Industry Ct., Ste. B, Deer Park, New York 11729 (United States); Saint-Petersburg National Research University of Information Technologies, Mechanics and Optics, 49 Kronverkskiy Ave., 197101 Saint Petersburg (Russian Federation); Helava, H.; Makarov, Yu. [Nitride Crystals, Inc., 181E Industry Ct., Ste. B, Deer Park, New York 11729 (United States)
2014-01-20
Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8?eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36?eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of the RL band fine structure indicate that the RL band is caused by transitions from a shallow donor (at low temperature) or from the conduction band (above 50?K) to an unknown deep acceptor having an energy level 1.130?eV above the valence band.
Chen, Lih-Shan; Weng, Min-Hung; Huang, Tsung-Hui; Chen, Han-Jan; Su, Sheng-Fu; Houng, Mau-Phon
2004-10-01
A tapped-line stepped-impedance resonator band-pass filter was implemented using a low temperature cofired multilayer-ceramic structure. By constructing a multilayer structure, a compact band-pass filter was realized. Moreover, the multilayer structure demonstrated an extra cross-coupling effect that produced extra transmission zeros in the stopband and, hence, realized a highly steep passband skirt. The center frequency of the fabricated band-pass filter was 6.075 GHz and the 3 dB fractional bandwidth was 18%. The measured insertion loss and return loss of the filter were -0.31 dB and -28 dB, respectively. The measured response of the fabricated band-pass filter was in good agreement with simulated results.
Electronic band structure and properties of the solid solution Eu1- x Fe x O
Anoshina, O. V.; Zhukov, V. P.; Borukhovich, A. S.
2015-11-01
The electronic band structure of the solid solution Eu1- x Fe x O ( x = 0.0625, 0.125) involved in the composition of the spintronic composite EuO: Fe has been calculated using the full-potential linearized augmented- plane-wave (FLAPW) method. The calculations have been performed with the correction of the exchange-correlation potential in the framework of the generalized gradient approximation (GGA + U). It has been shown that iron and europium cations have the oxidation state close to 2+. In this case, the iron cations are in the high-spin state with the magnetic moment close to 4 ?B, which explains the significant increase in the Curie temperature of the composite upon doping of EuO with iron. It has been demonstrated that there is a small transfer of the electron density from Eu2+ cations to Fe2+ cations. It has been argued that the main factor providing a high concentration of Eu3+ cations in the composite is, probably, the presence of Eu2O3 nanoclusters in the structure.
Ab initio calculations of quasiparticle band structure in correlated systems LDA++ approach
Lichtenstein, A I
1997-01-01
We discuss a general approach to a realistic theory of the electronic structure in materials containing correlated d- or f- electrons. The main feature of this approach is the taking into account the energy dependence of the electron self-energy with the momentum dependence being neglected (local approximation). In the case of strong interactions (U/W>>1 - rare-earth system) the Hubbard-I approach is the most suitable. Starting from an exact atomic Green function with the constrained density matrix the band structure problem is formulated as the functional problem on Nmm' for f-electrons and the standard LDA-functional for delocalized electrons. In the case of moderate correlations (U/W=1 metal-insulator regime) we start from the dynamical mean field iterative perturbation scheme (IPS) of G. Kotliar et. al. and also make use of our multiband atomic Green function. Finally for the weak interactions (U/W<1 -transition metals) the self-consistent diagrammatic fluctuation- exchange (FLEX)-approach of N. Bicker...
Khadraoui, Z.; Horchani-Naifer, K.; Ferhi, M.; Ferid, M.
2015-09-01
Single crystals of TbPO4 were grown by high temperature solid-state reaction and identified by means of X-ray diffraction, infrared and Raman spectroscopies analysis. The electronic properties of TbPO4 such as the energy band structures, density of states were carried out using density functional theory (DFT). We have employed the LDA+U functional to treat the exchange correlation potential by solving Kohn-Sham equation. The calculated total and partial density of states indicate that the top of valance band is mainly built upon O-2p states and the bottom of the conduction band mostly originates from Tb-5d states. The population analysis indicates that the P-O bond was mainly covalent and Tb-O bond was mainly ionic. The emission spectrum, color coordinates and decay curve were employed to reveal the luminescence properties of TbPO4. Moreover, the optical properties including the dielectric function, absorption spectrum, refractive index, extinction coefficient, reflectivity and energy-loss spectrum are investigated and analyzed. The results are discussed and compared with the available experimental data.
An open-structure sound insulator against low-frequency and wide-band acoustic waves
Chen, Zhe; Fan, Li; Zhang, Shu-yi; Zhang, Hui; Li, Xiao-juan; Ding, Jin
2015-10-01
To block sound, i.e., the vibration of air, most insulators are based on sealed structures and prevent the flow of the air. In this research, an acoustic metamaterial adopting side structures, loops, and labyrinths, arranged along a main tube, is presented. By combining the accurately designed side structures, an extremely wide forbidden band with a low cut-off frequency of 80 Hz is produced, which demonstrates a powerful low-frequency and wide-band sound insulation ability. Moreover, by virtue of the bypass arrangement, the metamaterial is based on an open structure, and thus air flow is allowed while acoustic waves can be insulated.
Plasma density measurements using chirped pulse broad-band Raman amplification
Vieux, G; Farmer, J P; Hur, M S; Issac, R C; Jaraszynski, D A
2013-01-01
Stimulated Raman backscattering is used as a non-destructive method to determine the density of plasma media at localized positions in space and time. By colliding two counter-propagating, ultra-short laser pulses with a spectral bandwidth larger than twice the plasma frequency, amplification occurs at the Stokes wavelengths, which results in regions of gain and loss separated by twice the plasma frequency, from which the plasma density can be deduced. By varying the relative delay between the laser pulses, and therefore the position and timing of the interaction, the spatio-temporal distribution of the plasma density can be mapped out.
Structures électromagnétiques à bandes interdites pour des applications de filtre
Badr El Din El Shaarawy, Heba
2009-01-01
The increasing development of wireless applications turns out to new requirements for transceiver architectures that have to feature excellent microwave performances (linearity, spurious rejection, noise figure and bandwidth) and enhanced integration density that is achieved through the miniaturization of the modules as well as the introduction of multi standard functionalities. All these requirements translate to the need of filter circuits as miniaturized as possible and featuring the highe...
Ion band-state fusion: Reactions, power density, and the quantum reality question
International Nuclear Information System (INIS)
The effects that limit deuterium-deuterium (D-D) fusion in bound systems, as opposed to those limiting D-D fusion in free space, are the result of quantum-mechanical particle-particle wave function correlation, which may inhibit wave function overlap. Whether or not this occurs at room temperature is determined by system energy minimization, not Gamow theory. A counterintuitive example, known from atomic physics, that demonstrates how this alternative criterion may alter the relevant quantum mechanics is illustrated by the helium atom. At room temperature, near-complete overlap of the two helium electrons takes place when energy is minimized, while Gamow theory predicts negligible overlap. On the other hand, energy minimization does not predict that no nucleus-nucleus overlap ever occurs in any normal molecule. In D+ ion band-state matter, D+-D+ overlap occurs if the distributed charge view of quantum reality is correct, in which case D+ band-state matter converts to 4He++ band-state matter, releasing heat throughout a crystal lattice. This occurs in the limit x ? 1 in PdDx (in agreement with experiments), provided adequate crystalline order is present. Further deuterium loading requires that additional injected deuterium occupy ionic band-like states in which only a small fraction of each additional deuterium atom occupies a lattice unit cell. Then, in each nuclear reaction, again to minimize energy of the entire system, the energy is distributed over many lattice sites, inhibiting production of energetic particles. Theory shows that steady-state power is proportional to the loading current. These points are discussed. An expression for P is derived, and possible cold fusion reactions are summarized. 23 refs., 1 fig
International Nuclear Information System (INIS)
The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO2), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO2 has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance
Density structure of the Horsehead nebula photo-dissociation region
Habart, E.; Abergel, A.; Walmsley, C. M.; Teyssier, D.; Pety, J.
2005-07-01
We present high angular resolution images of the H2 1-0 S(1) line emission obtained with the Son of ISAAC (SOFI) at the New Technology Telescope (NTT) of the Horsehead nebula. These observations are analysed in combination with H? line emission, aromatic dust, CO and dust continuum emissions. The Horsehead nebula illuminated by the O9.5V star ? Ori (? ˜ 60) presents a typical photodissociation region (PDR) viewed nearly edge-on and offers an ideal opportunity to study the gas density structure of a PDR. The H2 fluorescent emission observations reveal extremely sharp and bright filaments associated with the illuminated edge of the nebula which spatially coincides with the aromatic dust emission. Analysis of the H2 fluorescent emission, sensitive to both the far-UV radiation field and the gas density, in conjunction with the aromatic dust and H? line emission, brings new constraints on the illumination conditions and the gas density in the outer PDR region. Furthermore, combination of this data with millimeter observations of CO and dust continuum emission allows us to trace the penetration of the far-UV radiation field into the cloud and probe the gas density structure throughout the PDR. From comparison with PDR model calculations, we find that i) the gas density follows a steep gradient at the cloud edge, with a scale length of 0.02 pc (or 10'') and nH˜ 104 and 105 cm-3 in the H2 emitting and inner cold molecular layers respectively; and ii) this density gradient model is essentially a constant pressure model, with P˜ 4 × 106 K cm-3. The constraints derived here on the gas density profile are important for the study of physical and chemical processes in PDRs and provide new insight into the evolution of interstellar clouds. Also, this work shows the strong influence of the density structure on the PDR spatial stratification and illustrates the use of different tracers to determine this density structure.
Band structure and electronic transport properties of the superconductor NbO
International Nuclear Information System (INIS)
Electrical resistivity and Hall coefficients measured on a single crystal of NbO agree well with a conventional interpretation based on local-density approximation band theory and electron-phonon scattering. The superconducting transition temperature Tc=1.5 K is consistent with the measured magnitude of the linear resistivity at room temperature
Band structure features of nonlinear optical yttrium aluminium borate crystal.
Czech Academy of Sciences Publication Activity Database
Reshak, Ali H; Auluck, S.; Majchrowski, A.; Kityk, I. V.
2008-01-01
Ro?. 10, ?. 10 (2008), s. 1445-1448. ISSN 1293-2558 Institutional research plan: CEZ:AV0Z60870520 Keywords : Electronic structure * DFF * FPLAPW * LDA Subject RIV: BO - Biophysics Impact factor: 1.742, year: 2008
Coupling of the electronic band structure with A{sub g} phonon modes in Y123 and Y124 systems
Energy Technology Data Exchange (ETDEWEB)
Khosroabadi, H.; Mossalla, B.; Akhavan, M. [Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365, 9161 Tehran (Iran)
2006-09-15
Ab initio frozen-phonon calculations have been performed for k=0 A{sub g} Raman modes of two superconducting systems Y123 and Y124. We have used the local density approximation pseudopotential method in our calculations by VASP code. Results have been compared with other computational and experimental data for similar systems. Then we present changes of electronic band structure with the change of ionic positions in each A{sub g} mode for both systems. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
A tunable dual-narrowband band-pass filter using plasma quantum well structure
International Nuclear Information System (INIS)
A tunable dual-narrowband pass-band filter is designed. A one-dimensional photonic crystal (1D PC) is comprised of alternate dielectric layer and vacuum layer. Two quantum wells (QWs) as defects can be constructed by sandwiching two plasma slabs symmetrically in the 1D PC, and a dual-narrowband pass-band filter is formed. The conventional finite-difference time-domain (FDTD) method and piecewise linear current density recursive convolution (PLCDRC)—FDTD method are applied to the dielectric and plasma, respectively. The simulation results illustrate that the dual-narrowband frequencies can be tuned by changing the plasma frequency. The pass band interval and the half-power bandwidths (?3-dB band widths) are related to the space interval between two QWs
A Study of Temperature-dependent Properties of N-type delta-doped Si Band-structures in Equilibrium
Ryu, Hoon; Klimeck, Gerhard
2010-01-01
A highly phosphrous delta-doped Si device is modeled with a quantum well with periodic boundary conditions and the semi-empirical spds* tight-binding band model. Its temperature-dependent electronic properties are studied. To account for high doping density with many electrons, a highly parallelized self-consistent Schroedinger-Poisson solver is used with atomistic representations of multiple impurity ions. The band-structure in equilibrium and the corresponding Fermi-level position are computed for a selective set of temperatures. The result at room temperature is compared with previous studies and the temperature-dependent electronic properties are discussed further in detail with the calculated 3-D self-consistent potential profile.
Huang, Huaqing
2015-08-01
We theoretically investigate the effect of extended line defects (ELDs) on thermal transport properties of carbon nanotubes (CNTs) using nonequilibrium Green's function method. Our study shows that the thermal conductance of CNTs with ELDs can be 25% lower than that of pristine CNTs. By extending the application of the recently developed unfolding method for electronic structures to phonon spectra, we find that the unfolded phonon bands of defected CNTs are split with obvious gap opening, leading to lower phonon transmissions. Further phonon local density of states analysis reveals that the change of bonding configuration near the ELD in defected CNTs can tail the degree of phonon localization. Our results indicate that introducing ELDs might be an efficient way to control thermal conduction of CNTs. The extended unfolding method for phonon systems, found to be efficient in this work, is expected to be applicable to other systems with densely folded phonon bands. PMID:26174107
Burgoyne, Thomas; Morris, Edward P; Luther, Pradeep K
2015-11-01
The Z-band in vertebrate striated muscle crosslinks actin filaments of opposite polarity from adjoining sarcomeres and transmits tension along myofibrils during muscular contraction. It is also the location of a number of proteins involved in signalling and myofibrillogenesis; mutations in these proteins lead to myopathies. Understanding the high-resolution structure of the Z-band will help us understand its role in muscle contraction and the role of these proteins in the function of muscle. The appearance of the Z-band in transverse-section electron micrographs typically resembles a small-square lattice or a basketweave appearance. In longitudinal sections, the Z-band width varies more with muscle type than species: slow skeletal and cardiac muscles have wider Z-bands than fast skeletal muscles. As the Z-band is periodic, Fourier methods have previously been used for three-dimensional structural analysis. To cope with variations in the periodic structure of the Z-band, we have used subtomogram averaging of tomograms of rat cardiac muscle in which subtomograms are extracted and compared and similar ones are averaged. We show that the Z-band comprises four to six layers of links, presumably ?-actinin, linking antiparallel overlapping ends of the actin filaments from the adjoining sarcomeres. The reconstruction shows that the terminal 5-7nm of the actin filaments within the Z-band is devoid of any ?-actinin links and is likely to be the location of capping protein CapZ. PMID:26362007
Phonon structure in dispersion curves and density of states of massive Dirac Fermions
Li, Zhou
2013-01-01
Dirac fermions exist in many solid state systems including graphene, silicene and other two dimensional membranes such as are found in group VI dichalcogenides, as well as on the surface of some insulators where such states are protected by topology. Coupling of those fermions to phonons introduces new structures in their dispersion curves and, in the case of massive Dirac fermions, can shift and modify the gap. We show how these changes present in angular-resolved photoemission spectroscopy of the dressed charge carrier dispersion curves and scanning tunneling microscopy measurements of their density of states. In particular we focus on the region around the band gap. In this region the charge carrier spectral density no longer consists of a dominant quasiparticle peak and a smaller incoherent phonon related background. The quasiparticle picture has broken down and this leads to important modification in both dispersion curves and density of states.
On the structure of collective bands in 78Kr
International Nuclear Information System (INIS)
Using 16O, 19F, and 12C induced reactions high spin states in 78Kr were excited. The targets consisted of 65Cu, 69Ni, and 68Zn. On the base of gamma spectroscopic methods as ??-coincidences, angular distributions and excitation functions a level scheme of 78Kr is proposed. Four bands could be identified, which decay mostly by stretched E2-transitions. From recoil distance Doppler shift as well as Doppler shift attenuation measurements lifetimes of about 20 states were measured. The ?-decay of the 103 keV isomeric state and the ground state in 78Rb was observed and the half-lifes determined. Altogether a very good agreement of the level scheme and the E2- and E1-transition strength with predictions of the interacting boson model were found. Using a Monte Carlo code the ?-decay of the continuum of highly excited nuclei is described. Entry states, mean ?-energies, ?-spectra, mean multiplicities, multipolarities, and mean feeding times as well as e.g. their second moments were calculated for the reactions 58Ni(16O,2p)72Se and 68Zn(12C,2n)78Kr. The results are discussed and compared with experimental data. (HSI)
Ma, Jing; Zhou, Jian-Ping; Yang, Jia; Zhao, Hong-Sheng; Chen, Xiao-Ming; Deng, Chao-Yong
2015-06-01
Bi2Te3 is known to be an excellent thermoelectric material as well as a topological insulator. We prepare Bi 2 Te 3 { 0 1 1 ¯ 5 } nanosheets with a hydrothermal method and find that the interplanar spacings have a little difference though they belong to a same family of crystal planes. Then, we investigate the structural and electronic properties of Bi 2 Te 3 { 0 1 1 ¯ 5 } nanoribbons with one to six atomic layers by density-functional theory. The results indicate that the nanoribbons exhibit insulator with a band gap except the three-atomic-layer ribbon, which unexpectedly shows a metallic behavior with a gapless band structure.
DEFF Research Database (Denmark)
Svane, Axel; Christensen, Niels Egede
2010-01-01
The electronic band structures of PbS, PbSe, and PbTe in the rocksalt structure are calculated with the quasiparticle self-consistent GW (QSGW) approach with spin-orbit coupling included. The semiconducting gaps and their deformation potentials as well as the effective masses are obtained. The GW approximation provides a correct description of the electronic structure around the gap, in contrast to the local-density approximation, which leads to inverted gaps in the lead chalcogenides. The QSGW calculations are in good quantitative agreement with experimental values of the gaps and masses. At moderate hole doping a complex filamental Fermi-surface structure develops with ensuing large density of states. The pressure-induced gap closure leads to linear (Dirac-type) band dispersions around the L point.
Curvature effects in the band structure of carbon nanotubes including spin-orbit coupling
Liu, Hong; Heinze, Dirk; Thanh Duc, Huynh; Schumacher, Stefan; Meier, Torsten
2015-11-01
The Kane-Mele model was previously used to describe effective spin-orbit couplings (SOCs) in graphene. Here we extend this model and also incorporate curvature effects to analyze the combined influence of SOC and curvature on the band structure of carbon nanotubes (CNTs). The extended model then reproduces the chirality-dependent asymmetric electron-hole splitting for semiconducting CNTs and in the band structure for metallic CNTs shows an opening of the band gap and a change of the Fermi wave vector with spin. For chiral semiconducting CNTs with large chiral angle we show that the spin-splitting configuration of bands near the Fermi energy depends on the value of \\text{mod}(2n+m,3) .
Model comparison for the density structure along solar prominence threads
Arregui, I.; Soler, R.
2015-06-01
Context. Quiescent solar prominence fine structures are typically modelled as density enhancements, called threads, which occupy a fraction of a longer magnetic flux tube. This is justified from the spatial distribution of the imaged plasma emission or absorption of prominences at small spatial scales. The profile of the mass density along the magnetic field is unknown, however, and several arbitrary alternatives are employed in prominence wave studies. The identification and measurement of period ratios from multiple harmonics in standing transverse thread oscillations offer a remote diagnostics method to probe the density variation of these structures. Aims: We present a comparison of theoretical models for the field-aligned density along prominence fine structures. They aim to imitate density distributions in which the plasma is more or less concentrated around the centre of the magnetic flux tube. We consider Lorentzian, Gaussian, and parabolic profiles. We compare theoretical predictions based on these profiles for the period ratio between the fundamental transverse kink mode and the first overtone to obtain estimates for the density ratios between the central part of the tube and its foot-points and to assess which one would better explain observed period ratio data. Methods: Bayesian parameter inference and model comparison techniques were developed and applied. To infer the parameters, we computed the posterior distribution for the density gradient parameter that depends on the observable period ratio. The model comparison involved computing the marginal likelihood as a function of the period ratio to obtain the plausibility of each density model as a function of the observable. We also computed the Bayes factors to quantify the relative evidence for each model, given a period ratio observation. Results: A Lorentzian density profile, with plasma density concentrated around the centre of the tube, seems to offer the most plausible inversion result. A Gaussian profile would require unrealistically high values of the density gradient parameter, and a parabolic density distribution does not enable us to obtain well-constrained posterior probability distributions. However, our model comparison results indicate that the evidence points to the Gaussian and parabolic profiles for period ratios in between 2 and 3, while the Lorentzian profile is preferred for higher period ratio values. The method we present can be used to obtain information on the plasma structure along threads, provided period ratio measurements become widely available.
International Nuclear Information System (INIS)
The use of localized Gaussian basis functions for large scale first principles density functional calculations with periodic boundary conditions (PBC) in 2 dimensions and 3 dimensions has been made possible by using a dual space approach. This new method is applied to the study of electronic properties of II--VI (II=Zn, Cd, Hg; VI=S, Se, Te, Po) and III--V (III=Al, Ga; V=As, N) semiconductors. Valence band offsets of heterojunctions are calculated including both bulk contributions and interfacial contributions. The results agree very well with available experimental data. The p(2x1) cation terminated surface reconstructions of CdTe and HgTe (100) are calculated using the local density approximation (LDA) with two-dimensional PBC and also using the ab initio Hartree--Fock (HF) method with a finite cluster. The LDA and HF results do not agree very well. copyright 1995 American Vacuum Society
A Ku-band high power density AlGaN/GaN HEMT monolithic power amplifier
Energy Technology Data Exchange (ETDEWEB)
Ge Qin; Chen Xiaojuan; Luo Weijun; Yuan Tingting; Pang Lei; Liu Xinyu, E-mail: lixy@ime.ac.cn [Key Laboratory of Microwave Devices and Integrated Circuit, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China)
2011-08-15
A high power density monolithic power amplifier operated at Ku band is presented utilizing a 0.3 {mu}m AlGaN/GaN HEMT production process on a 2-inch diameter semi-insulating (SI) 4H-SiC substrate by MOCVD. Over the 12-14 GHz frequency range, the single chip amplifier demonstrates a maximum power of 38 dBm (6.3 W), a peak power added efficiency (PAE) of 24.2% and linear gain of 6.4 to 7.5 dB under a 10% duty pulse condition when operated at V{sub ds} = 25 V and V{sub gs} = -4 V. At these power levels, the amplifier exhibits a power density in excess of 5 W/mm.
A Ku-band high power density AlGaN/GaN HEMT monolithic power amplifier
International Nuclear Information System (INIS)
A high power density monolithic power amplifier operated at Ku band is presented utilizing a 0.3 ?m AlGaN/GaN HEMT production process on a 2-inch diameter semi-insulating (SI) 4H-SiC substrate by MOCVD. Over the 12-14 GHz frequency range, the single chip amplifier demonstrates a maximum power of 38 dBm (6.3 W), a peak power added efficiency (PAE) of 24.2% and linear gain of 6.4 to 7.5 dB under a 10% duty pulse condition when operated at Vds = 25 V and Vgs = -4 V. At these power levels, the amplifier exhibits a power density in excess of 5 W/mm.
International Nuclear Information System (INIS)
We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field, leading to nonlinear behavior of the band structure, which also has nonlinear dependence on the temperature. The similar analysis for every arbitrary lattice structure is also possible to be developed by this approach as presented in this work. We also present some examples and discuss the results
Inertial amplification of continuous structures: Large band gaps from small masses
Frandsen, Niels M M; Jensen, Jakob S; Hussein, Mahmoud I
2016-01-01
Wave motion in a continuous elastic rod with a periodically attached inertial-amplification mechanism is investigated. The mechanism has properties similar to an "inerter" typically used in vehicle suspensions, however here it is constructed and utilized in a manner that alters the intrinsic properties of a continuous structure. The elastodynamic band structure of the hybrid rod-mechanism structure yields band gaps that are exceedingly wide and deep when compared to what can be obtained using standard local resonators, while still being low in frequency. With this concept, a large band gap may be realized with as much as twenty times less added mass compared to what is needed in a standard local resonator configuration. The emerging inertially enhanced continuous structure also exhibits unique qualitative features in its dispersion curves. These include the existence of a characteristic double-peak in the attenuation constant profile within gaps and the possibility of coalescence of two neighbouring gaps crea...
Extension of Modularity Density for Overlapping Community Structure
Chen, Mingming; Szymanski, Boleslaw K
2015-01-01
Modularity is widely used to effectively measure the strength of the disjoint community structure found by community detection algorithms. Although several overlapping extensions of modularity were proposed to measure the quality of overlapping community structure, there is lack of systematic comparison of different extensions. To fill this gap, we overview overlapping extensions of modularity to select the best. In addition, we extend the Modularity Density metric to enable its usage for overlapping communities. The experimental results on four real networks using overlapping extensions of modularity, overlapping modularity density, and six other community quality metrics show that the best results are obtained when the product of the belonging coefficients of two nodes is used as the belonging function. Moreover, our experiments indicate that overlapping modularity density is a better measure of the quality of overlapping community structure than other metrics considered.
Electronic structure and optical band gap of CoFe2O4 thin films
Ravindra, A. V.; Padhan, P.; Prellier, W.
2012-01-01
Electronic structure and optical band gap of CoFe2O4 thin films grown on (001) oriented LaAlO3 have been investigated. Surprisingly, these films show additional Raman modes at room temperature as compared to a bulk spinel structure. The splitting of Raman modes is explained by considering the short-range ordering of Co and Fe cations in octahedral site of spinel structure. In addition, an expansion of band-gap is observed with the reduction of film thickness, which is explai...
Polarization-dependent diffraction in all-dielectric, twisted-band structures
Karda?, Tomasz M.; Jagodnicka, Anna; Wasylczyk, Piotr
2015-11-01
We propose a concept for light polarization management: polarization-dependent diffraction in all-dielectric microstructures. Numerical simulations of light propagation show that with an appropriately configured array of twisted bands, such structures may exhibit zero birefringence and at the same time diffract two circular polarizations with different efficiencies. Non-birefringent structures as thin as 3 ?m have a significant difference in diffraction efficiency for left- and right-hand circular polarizations. We identify the structural parameters of such twisted-band matrices for optimum performance as circular polarizers.
Influence of distortion on the electronic band structure of CuInSe2
Tototzintle-Huitle, H; Rodríguez, José Alberto; Baquero, R
2005-01-01
We present a tight-binding calculation of the influence of distorsion on the bulk electronic structure of the chalcopyrite CuInSe2. We calculate the ideal case and then the effect of the inclusion of the distortions. We analyze our results in detail and conclude from a comparison with other work that the distortions must be included in the Hamiltonian to get a proper account of the electronic band structure. We use our new Hamiltonian to study the effect that both the tetragonal and the anionic distortion have on the (112) surface electronic band structure. We find this effect non-negligible.
Band Structure and Quantum Confined Stark Effect in InN/GaN superlattices
DEFF Research Database (Denmark)
Gorczyca, I.; Suski, T.; Christensen, Niels Egede; Svane, Axel
2012-01-01
InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite InN/GaN(0001) superlattices are investigated, and the variation of the band gap with the thicknesses of the well and the barrier is discussed. Superlattices of the form mInN/nGaN with n ? m are simulated usin...
Effect of Symmetry Breaking on Electronic Band Structure: Gap Opening at the High Symmetry Points
Guillaume Vasseur; Yannick Fagot-Revurat; Bertrand Kierren; Muriel Sicot; Daniel Malterre
2013-01-01
Some characteristic features of band structures, like the band degeneracy at high symmetry points or the existence of energy gaps, usually reflect the symmetry of the crystal or, more precisely, the symmetry of the wave vector group at the relevant points of the Brillouin zone. In this paper, we will illustrate this property by considering two-dimensional (2D)-hexagonal lattices characterized by a possible two-fold degenerate band at the K points with a linear dispersion (Dirac points). By co...
Band gap structure modification of amorphous anodic Al oxide film by Ti-alloying
DEFF Research Database (Denmark)
Canulescu, Stela; Rechendorff, K.; Borca, C. N.; Jones, N. C.; Bordo, Kirill; Schou, Jørgen; Nielsen, Lars Pleth; Hoffmann, S. V.; Ambat, Rajan
2014-01-01
The band structure of pure and Ti-alloyed anodic aluminum oxide has been examined as a function of Ti concentration varying from 2 to 20 at.?%. The band gap energy of Ti-alloyed anodic Al oxide decreases with increasing Ti concentration. X-ray absorption spectroscopy reveals that Ti atoms are not located in a TiO2 unit in the oxide layer, but rather in a mixed Ti-Al oxide layer. The optical band gap energy of the anodic oxide layers was determined by vacuum ultraviolet spectroscopy in the energy...
Band structure properties of (BGa)P semiconductors for lattice matched integration on (001) silicon
Energy Technology Data Exchange (ETDEWEB)
Hossain, Nadir; Sweeney, Stephen [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH (United Kingdom); Hosea, Jeff [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH, UK and Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, Johor Bahru 81310 (Malaysia); Liebich, Sven; Zimprich, Martin; Volz, Kerstin; Stolz, Wolfgang [Material Sciences Center and Faculty of Physics, Philipps-University, 35032 Marburg (Germany); Kunert, Bernerdette [NAsP III/V GmbH, Am Knechtacker 19, 35041 Marburg (Germany)
2013-12-04
We report the band structure properties of (BGa)P layers grown on silicon substrate using metal-organic vapour-phase epitaxy. Using surface photo-voltage spectroscopy we find that both the direct and indirect band gaps of (BGa)P alloys (strained and unstrained) decrease with Boron content. Our experimental results suggest that the band gap of (BGa)P layers up to 6% Boron is large and suitable to be used as cladding and contact layers in GaP-based quantum well heterostructures on silicon substrates.
Band structure properties of (BGa)P semiconductors for lattice matched integration on (001) silicon
International Nuclear Information System (INIS)
We report the band structure properties of (BGa)P layers grown on silicon substrate using metal-organic vapour-phase epitaxy. Using surface photo-voltage spectroscopy we find that both the direct and indirect band gaps of (BGa)P alloys (strained and unstrained) decrease with Boron content. Our experimental results suggest that the band gap of (BGa)P layers up to 6% Boron is large and suitable to be used as cladding and contact layers in GaP-based quantum well heterostructures on silicon substrates
The machining of the disks of X band accelerator structure
International Nuclear Information System (INIS)
To achieve the manufacturing of disks of the accelerator structure for the high gradient field, KEK develops to manufacture high precision disks. In manufacturing high precision disks, it is important for us to make sure the process sheet of the disk and report actual evidence. By this study we report how to manufacture the disks and the criteria of disk. (author)
Information on the band structure of ferromagnetic Ni from ?SR-Knight shift measurements
International Nuclear Information System (INIS)
The authors present results on the temperature dependence of the Knight shift of the hyperfine field at a positive muon in ferromagnetic Nickel and show that the results allow a determination of the Stoner gap, that is the gap between the top of the majority d-band and the Fermi energy. The consistency of the analysis supports the SWS-model but the obtained value for the Stoner gap is far below the predictions of most ferromagnetic band structure calculations. (Auth.)
Periodic and Non-Periodic Band Random Matrices: Structure of Eigenstates
Izrailev, Felix; Molinari, Luca; ?yczkowski, Karol
1996-01-01
The structure of eigenstates for the ensembles of standard and periodic Band Random Matrices (BRM) is analysed. The main attention is drawn to the scaling properties of the inverse participation ratio and other measures of localization length. Numerical data are compared with analytical results recently derived for standard BRMs of very large band size. The data for periodic and standard BRM allow us to exhibit the influence of boundary conditions on the properties of eigenstates.
Berne, A.D.; Delrieu, G.; Andrieu, H.
2005-01-01
The present study aims at a preliminary approach of multiradar compositing applied to the estimation of the vertical structure of precipitation¿an important issue for radar rainfall measurement and prediction. During the HYDROMET Integrated Radar Experiment (HIRE¿98), the vertical profile of reflectivity was measured, on the one hand, with an X-band vertically pointing radar system, and, on the other hand, with an X-band RHI scanning protocol radar. The analysis of the raw data highlights the...
Gutermuth, R. A.; Megeath, S. T.; Pipher, J. L.; Williams, J. P.; Allen, L E.; Myers, P.C.; Raines, S. N.
2004-01-01
We present an analysis of K-band stellar distributions for the young stellar clusters GGD 12-15, IRAS 20050+2720, and NGC 7129. We find that the two deeply embedded clusters, GGD 12-15 and IRAS 20050+2720, are not azimuthally symmetric and show a high degree of structure which traces filamentary structure observed in 850 micron emission maps. In contrast, the NGC 7129 cluster is circularly symmetric, less dense, and anti-correlated to 850 micron emission, suggesting recent g...
Superlattice band structure: New and simple energy quantification condition
International Nuclear Information System (INIS)
Assuming an approximated effective mass and using Bastard's boundary conditions, a simple method is used to calculate the subband structure for periodic semiconducting heterostructures. Our method consists to derive and solve the energy quantification condition (EQC), this is a simple real equation, composed of trigonometric and hyperbolic functions, and does not need any programming effort or sophistic machine to solve it. For less than ten wells heterostructures, we have derived and simplified the energy quantification conditions. The subband is build point by point; each point presents an energy level. Our simple energy quantification condition is used to calculate the subband structure of the GaAs/Ga0.5Al0.5As heterostructures, and build its subband point by point for 4 and 20 wells. Our finding shows a good agreement with previously published results
Area Efficient Interpolator Using Half-Band Symmetric Structure
Rajesh Mehra; Shaily Verma
2013-01-01
In this paper a cost effective Interpolator has been designed and simulated. An area efficient method has been presented to implement cost effective interpolator for wireless communication systems. Interpolator is particularly useful for smoothing signals such as sinusoids or baseband I/Q waveforms. For these signals, interpolation filter is used to accurately produce new samples of the waveform without reducing signal quality. In this paper three structures for interpolator has been used nam...
Dong Q.-L.; Yang J; Jiang Z.-T.; Sheng Z.-M.; Zhang J
2013-01-01
The energy band structures of the warm dense plasmas with micro-structures inherited from single-walled carbon nanotubes are studied in detail by using the symmetry-adapted tight-binding model with the electron-ion core Coulomb interactions as the plasma effects. It is found that both the symmetry and the degeneracy of the calculated bands normal for the solid micro-structured targets may be destroyed by the electron-ion core Coulomb interactions. Moreover, the calculated Fermi levels of the ...
Study of the structure of the valence band edge in bismuth-antimony telluride films
International Nuclear Information System (INIS)
The behaviour of kinetic coefficients in Bi2-xSbxTe3 films with high hole concentrations is studied. The temperature dependences of the coefficients of heat conduction, Hall coefficient and thermal e.m.f. of films with different hole concentrations are given. The effect of the heavy hole zone on the transfer phenomenon is studied. The obtained results explicitly reveals the two-band pattern of the Bi2-xSexTe3 valence band. The effective mass of the state density in the second subband is estimated
International Nuclear Information System (INIS)
Density-functional calculations of the electronic structure and atomic positions are reported for Li2WO4. This compound is found to be very different from the tungstate scintillators such as PbWO4 in that both the valence and conduction bands are much less dispersive. This leads to a substantially larger band gap. The difference is understood in terms of the crystal structure, in particular, the longer O-O distances connecting the WO4 tetrahedra
Effect of structured packing density on performance of air dehumidifier
International Nuclear Information System (INIS)
An experimental study has been conducted to investigate the performance of a liquid desiccant air dehumidifier equipped with a structured packing made of wood for three different densities using triethylene glycol (TEG) as the liquid desiccant. The structured packing densities used were 77, 100 and 200 m2/m3. The performance of the dehumidifier was expressed in terms of the moisture removal rate and the dehumidifier effectiveness under different air and desiccant parameters, i.e. the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and inlet TEG concentration. In general, the trend in the dehumidifier performance was similar to that reported by other investigators using random packing. The effect of packing density on moisture removal rate and dehumidifier effectiveness is assessed. The differences in the effectiveness of different packing densities are attributed to the wetting condition. Lower effectiveness of the column is shown with the packing density of 200 m2/m3 compared to the other two packing densities when the air flow rate, inlet concentration and desiccant flow rate are increased. However, higher effectiveness is shown when either the inlet temperature of the air or desiccant is increased
Connecting the density structure of molecular clouds and star formation.
Kainulainen, Jouni
2015-08-01
In the current paradigm of turbulence-regulated interstellar medium (ISM), star formation rates of entire galaxies are intricately linked to the density structure of the individual molecular clouds in the ISM. This density structure is essentially encapsulated in the probability distribution function of volume densities (rho-PDF), which directly affects the star formation rates predicted by analytic models. Contrasting its fundamental role, the rho-PDF function and its evolution have remained virtually unconstrained by observations. I describe in this contribution our recent progress in attaining observational constraints for the rho-PDFs of molecular clouds. Specifically, I review our first systematic determination of the rho-PDFs in Solar neighborhood molecular clouds. I will also present new evidence of the time evolution of the projected rho-PDFs, i.e., column density PDFs. These results together enable us to build the first observationally constrained link between the evolving density structure of molecular clouds and the star formation within. Finally, I discuss our work to expand the analysis into a Galactic context and to observationally connect the physical processes acting at the scale of molecular clouds with star formation at the scale of galaxies.
Pan, Xiaoyang; Yi, Zhiguo
2015-12-16
A facile, one-step hydrothermal method has been developed to fabricate tin oxide-reduced graphene oxide (Sn-RGO) nanocomposites with tunable composition, morphology, and energy band structure by utilizing graphene oxide (GO) as a multifunctional two-dimensional scaffold. By adjusting the GO concentration during synthesis, a variety of tin oxide nanomaterials with diverse composition and morphology are obtained. Simultaneously, the varying of GO concentration can also narrow the bandgap and tune the band edge positions of the Sn-RGO nanocomposites. As a result, the Sn-RGO nanocomposites with controllable composition, morphology, and energy band structure are obtained, which exhibit efficient photoactivities toward methyl orange (MO) degradation under visible-light irradiation. It is expected that our work would point to the new possibility of using GO for directing synthesis of semiconductor nanomaterials with tailored structure and physicochemical properties. PMID:26581093
Photonic band gaps in materials with triply periodic surfaces and related tubular structures
Michielsen, K
2003-01-01
We calculate the photonic band gap of triply periodic bicontinuous cubic structures and of tubular structures constructed from the skeletal graphs of triply periodic minimal surfaces. The effect of the symmetry and topology of the periodic dielectric structures on the existence and the characteristics of the gaps is discussed. We find that the C(I2-Y**) structure with Ia3d symmetry, a symmetry which is often seen in experimentally realized bicontinuous structures, has a photonic band gap with interesting characteristics. For a dielectric contrast of 11.9 the largest gap is approximately 20% for a volume fraction of the high dielectric material of 25%. The midgap frequency is a factor of 1.5 higher than the one for the (tubular) D and G structures.
Medium- and high-spin band structure of the chiral-candidate nucleus 134Pr
International Nuclear Information System (INIS)
Complete text of publication follows. Medium- and high-spin structure of the 134Pr nucleus has been studied using the 116Cd(23Na,5n) reaction in order to search for new rotational bands and obtain a more complete picture of the structure and special features of this nucleus. The level scheme of 134Pr has been extended. Nine new rotational bands have been found, among which one positive parity band might be the chiral-partner candidate of the yrare ?h11/2?h11/2 band, while five of them are the expected two-quasiparticle negative-parity bands. The relative placement of the two previously known isomeric states has been established, and thus the ground state of the nucleus has been unambiguously determined. The tentatively assigned spin and parity values of the previously known states have been unambiguously determined. Experimental Routhians and aligned angular momenta, as well as B(M1)/B(E2) ratios have been derived from the data and compared with predictions of Total Routhian Surface calculations, and results of the geometrical model of Donau and Frauendorf, respectively. On the basis of these comparisons, and on the basis of comparison with neighboring nuclei, tentative configurations have been assigned to the new bands.
Band structures in two-dimensional phononic crystals with periodic Jerusalem cross slot
International Nuclear Information System (INIS)
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
Energy Technology Data Exchange (ETDEWEB)
Reshak, A.H. [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Khan, Wilayat, E-mail: walayat76@gmail.com [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic)
2014-04-01
Highlights: • FP-LAPW technique is used for calculating the electronic structure. • The band structure shows that the calculated compound is semiconductor. • The complex dielectric function has been calculated. • Nonlinear optical properties has also been calculated. • This compound can be used for molecular engineering of the crystals. - Abstract: Self-consistent calculations is performed using the full potential linear augmented plane wave (FP-LAPW) technique based on density functional theory (DFT) to investigate the electronic band structure, density of states, electronic charge density, linear and non-linear optical properties of ?-LiAlTe{sub 2} compound having tetragonal symmetry with space group I4{sup ¯}2d. The electronic structure are calculated using the Ceperley Alder local density approach (CA-LDA), Perdew Burke and Ernzerhof generalize gradient approach (PBE-GGA), Engel–Vosko generalize gradient approach (EVGGA) and modified Becke Johnson approach (mBJ). Band structure calculations of (?-LiAlTe{sub 2}) depict semiconducting nature with direct band gap of 2.35 eV (LDA), 2.48 eV (GGA), 3.05 eV (EVGGA) and 3.13 eV (mBJ), which is comparable to experimental value. The calculated electronic charge density show ionic interaction between Te and Li atoms and polar covalent interaction between Al and Te atoms. Some optical susceptibilities like dielectric constants, refractive index, extension co-efficient, reflectivity and energy loss function have been calculated and analyzed on the basis of electronic structure. The compound ?-LiAlTe{sub 2} provides a considerable negative value of birefringence of ?0.01. Any anisotropy observed in the linear optical properties which are in favor to enhance the nonlinear optical properties. The symbol ?{sub abc}{sup (2)}(?) represents the second order nonlinear optical susceptibilities, possess six non-zero components in this symmetry (tetragonal), called: 1 2 3, 2 1 3, 2 3 1, 1 3 2, 3 1 2 and 3 2 1 components, in which 1 2 3 is the dominant one having value 26.49 pm/V.
International Nuclear Information System (INIS)
Highlights: • FP-LAPW technique is used for calculating the electronic structure. • The band structure shows that the calculated compound is semiconductor. • The complex dielectric function has been calculated. • Nonlinear optical properties has also been calculated. • This compound can be used for molecular engineering of the crystals. - Abstract: Self-consistent calculations is performed using the full potential linear augmented plane wave (FP-LAPW) technique based on density functional theory (DFT) to investigate the electronic band structure, density of states, electronic charge density, linear and non-linear optical properties of ?-LiAlTe2 compound having tetragonal symmetry with space group I4¯2d. The electronic structure are calculated using the Ceperley Alder local density approach (CA-LDA), Perdew Burke and Ernzerhof generalize gradient approach (PBE-GGA), Engel–Vosko generalize gradient approach (EVGGA) and modified Becke Johnson approach (mBJ). Band structure calculations of (?-LiAlTe2) depict semiconducting nature with direct band gap of 2.35 eV (LDA), 2.48 eV (GGA), 3.05 eV (EVGGA) and 3.13 eV (mBJ), which is comparable to experimental value. The calculated electronic charge density show ionic interaction between Te and Li atoms and polar covalent interaction between Al and Te atoms. Some optical susceptibilities like dielectric constants, refractive index, extension co-efficient, reflectivity and energy loss function have been calculated and analyzed on the basis of electronic structure. The compound ?-LiAlTe2 provides a considerable negative value of birefringence of ?0.01. Any anisotropy observed in the linear optical properties which are in favor to enhance the nonlinear optical properties. The symbol ?abc(2)(?) represents the second order nonlinear optical susceptibilities, possess six non-zero components in this symmetry (tetragonal), called: 1 2 3, 2 1 3, 2 3 1, 1 3 2, 3 1 2 and 3 2 1 components, in which 1 2 3 is the dominant one having value 26.49 pm/V
Analysis of photonic band-gap (PBG) structures using the FDTD method
DEFF Research Database (Denmark)
Tong, M.S.; Cheng, M.; Lu, Y.L.; Chen, Y.C.; Krozer, Viktor; Vahldieck, R.
2004-01-01
In this paper, a number of photonic band-gap (PBG) structures, which are formed by periodic circuit elements printed oil transmission-line circuits, are studied by using a well-known numerical method, the finite-difference time-domain (FDTD) method. The results validate the band-stop filter behavior of these structures, and the computed results generally match well with ones published in the literature. It is also found that the FDTD method is a robust, versatile, and powerful numerical techniqu...
High-spin structures in 108Pd: ?-vibrational band and two-quasineutron excitations
International Nuclear Information System (INIS)
The high-spin structures of the 108Pd nucleus have been studied with the 100Mo(11B,p2n?) reaction at 43 MeV incident energy. ?-?-t,?-?-charged-particle coincidences and directional correlation ratios were measured using the SACI-PERERE ? spectrometer formed by four Compton suppressed HPGe detectors and a 4? charged-particle ancillary detector system. Recent results for the ?-vibrational band and the ?h11/2x?(g7/2,d5/2) negative parity structures have been confirmed and complemented. A new band tentatively based on the second lowest (?h11/2) excitation has been observed
Tests of octupole band structures using proton scattering and gamma-ray spectroscopy
International Nuclear Information System (INIS)
In many even-even nuclei, bands of negative parity states have been interpreted as open-quotes octupole bandsclose quotes, which are sequences of vibrational or rotational excitations coupled to a low energy octupole phonon. Careful experimental examination of these structures is of interest because octupole phonons are generally considered to be unstable at high angular momentum. Results from experimental studies of octupole band structures in three nuclei are presented. Two of these nuclei, 144,146Nd, have been studied via inelastic scattering of 35 MeV protons. The third nucleus, 74Se, has been examined using the techniques of high spin gamma-ray spectroscopy
International Nuclear Information System (INIS)
We have studied the electronic structure of C and N co-doped TiO2 using hard x-ray photoelectron spectroscopy and first-principles density functional theory calculations. Our results reveal overlap of the 2p states of O, N, and C in the system which shifts the valence band maximum towards the Fermi level. Combined with optical data we show that co-doping is an effective route for band gap reduction in TiO2. Comparison of the measured valence band with theoretical photoemission density of states reveals the possibility of C on Ti and N on O site
Multi-quasiparticle {gamma}-band structure in neutron-deficient Ce and Nd isotopes
Energy Technology Data Exchange (ETDEWEB)
Sheikh, J.A. [Physics Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831 (United States); Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 (United States); Department of Physics, University of Kashmir, Srinagar, 190 006 (India); Bhat, G.H. [Department of Physics, University of Kashmir, Srinagar, 190 006 (India); Palit, R.; Naik, Z. [Tata Institute of Fundamental Research, Colaba, Mumbai, 400 005 (India); Sun, Y. [Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 (United States); Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)], E-mail: sunyang@sjtu.edu.cn
2009-06-01
The newly developed multi-quasiparticle triaxial projected shell model approach is employed to study the high-spin band structures in neutron-deficient even-even Ce- and Nd-isotopes. It is observed that {gamma}-bands are built on each intrinsic configuration of the triaxial mean-field deformation. Due to the fact that a triaxial configuration is a superposition of several K-states, the projection from these states results in several low-lying bands originating from the same intrinsic configuration. This generalizes the well-known concept of the surface {gamma}-oscillation in deformed nuclei based on the ground-state to {gamma}-bands built on multi-quasiparticle configurations. This new feature provides an alternative explanation on the observation of two I=10 aligning states in {sup 134}Ce and both exhibiting a neutron character.
Multi-Quasiparticle Gamma-Band Structure in Neutron-Deficient Ce and Nd Isotopes
Energy Technology Data Exchange (ETDEWEB)
Sheikh, Javid [ORNL; Bhat, G. H. [University of Kashmir, Srinagar, India; Palit, R. [Tata Institute of Fundamental Research, Mumbai, India; Naik, Z. [Tata Institute of Fundamental Research, Mumbai, India; Sun, Y. [Shanghai Jiao Tong University, Shanghai
2009-01-01
The newly developed multi-quasiparticle triaxial projected shell-model approach is employed to study the high-spin band structures in neutron-deficient even-even Ce and Nd isotopes. It is observed that gamma bands are built on each intrinsic configuration of the triaxial mean-field deformation. Due to the fact that a triaxial configuration is a superposition of several K states, the projection from these states results in several low-lying bands originating from the same intrinsic configuration. This generalizes the well-known concept of the surface gamma oscillation in deformed nuclei based on the ground state to gamma bands built on multi-quasiparticle configurations. This new feature provides an alternative explanation on the observation of two I=10 aligning states in ^{134}Ce and both exhibiting a neutron character.
Band structure engineering and vacancy induced metallicity at the GaAs-AlAs interface
Upadhyay Kahaly, M.
2011-09-20
We study the epitaxial GaAs-AlAs interface of wide gap materials by full-potential density functional theory. AlAsthin films on a GaAs substrate and GaAsthin films on an AlAs substrate show different trends for the electronic band gap with increasing film thickness. In both cases, we find an insulating state at the interface and a negligible charge transfer even after relaxation. Differences in the valence and conduction band edges suggest that the energy band discontinuities depend on the growth sequence. Introduction of As vacancies near the interface induces metallicity, which opens great potential for GaAs-AlAs heterostructures in modern electronics.
Electronic band structure and specific features of Sm{sub 2}NiMnO{sub 6} compound: DFT calculation
Energy Technology Data Exchange (ETDEWEB)
Reshak, A.H. [Institute of complex systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Azam, Sikander, E-mail: sikander.physicst@gmail.com [Institute of complex systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic)
2013-09-15
The band structure, density of states, electronic charge density, Fermi surface and optical properties of Sm{sub 2}NiMnO{sub 6} compound have been investigated with the support of density functional theory (DFT). The atomic positions of Sm{sub 2}NiMnO{sub 6} compound were optimized by minimizing the forces acting on the atoms, using the full potential linear augmented plane wave method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel–Vosko GGA (EVGGA) to treat the exchange correlation potential by solving Kohn–Sham equations. The calculation shows that the compound is metallic with strong hybridization near the Fermi energy level (E{sub F}). The calculated density of states at the E{sub F} is about 21.60, 24.52 and 26.21 states/eV, and the bare linear low-temperature electronic specific heat coefficient (?) is found to be 3.74, 4.25 and 4.54 mJ/mol K{sup 2} for EVGGA, GGA and LDA, respectively. The Fermi surface is composed of two sheets. The bonding features of the compounds are analyzed using the electronic charge density in the (011) crystallographic plane. The dispersion of the optical constants was calculated and discussed. - Highlights: • The compound is metallic with strong hybridization near the Fermi energy. • The density of states at the Fermi energy is calculated. • The bare linear low-temperature electronic specific heat coefficient is obtained. • Fermi surface is composed of two sheets. • The bonding features are analyzed using the electronic charge density.
Band Structure Engineering and Thermoelectric Properties of Charge-Compensated Filled Skutterudites
Shi, Xiaoya; Yang, Jiong; Wu, Lijun; Salvador, James R.; Zhang, Cheng; Villaire, William L.; Haddad, Daad; Yang, Jihui; Zhu, Yimei; Li, Qiang
2015-10-01
Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co4Sb12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing the Yb content, we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively.
Band Structure and Optical Properties of Dilute Ge:C Alloys
Stephenson, Chad; O'Brien, William; Qi, Meng; Penninger, Michael; Schneider, William; Gillett-Kunnath, Miriam; Zajicek, Jaroslav; Wistey, Mark
2015-03-01
The last major missing piece to achieving integrated Si photonics is an efficient light emitter. Dilute Ge:C alloys offer a new route to create efficient lasers directly within conventional CMOS electronics. Although neither Ge nor C emits light, Ge:C is a highly mismatched alloy, similar to GaAsN, in which band anticrossing is expected to create a direct bandgap. We have performed ab initio band structure simulations using hybrid functionals and spin-orbit coupling that show a sharp decrease in bandgap at the direct conduction band valley with C incorporation, turning Ge:C into a direct bandgap semiconductor and even a semi-metal. We report on the optical properties, highlighting the strength of free carrier absorption due to the changes in the band structure. Some of its potential applications include integrated light emitters, modulators, and photodetectors. With the three-band system, Ge:C also has potential for use in upconverting structures. We also report successful incorporation of C in Ge using hybrid gas+solid source molecular beam epitaxy (MBE) using a precursor gas, tetra(germyl)methane (4GeMe), that prevents undesirable C-C bonds and interstitial incorporation.
The Antiferromagnetic Band Structure of La2CuO4 Revisited
Perry, J K; Perry, Jason K.; Tahir-Kheli, Jamil; III, William A. Goddard
2000-01-01
Using the Becke-3-LYP functional, we have performed band structure calculations on the high temperature superconductor parent compound, La2CuO4. For the restricted spin paramagnetic case (rho(alpha) equal to rho(beta)), the B3LYP band structure agrees well with the standard LDA band structure. It has a metallic ground state with a single Cu x2-y2/O p(sigma) band crossing the Fermi level. For the unrestricted spin case (rho(alpha) not equal to rho(beta)), a spin polarized antiferromagnetic state is found with a band gap of 2.0 eV, agreeing well with experiment. This state is 1.0 eV (per formula unit) lower than the calculated paramagnetic state. This large energy difference is particularly startling given that the ferromagnetic state is also calculated to be 0.82 eV lower than the paramagnetic state. The apparent high energy of the spin restricted state is attributed to an overestimate of on-site Coulomb repulsion which is corrected in the unrestricted spin calculations. The stabilization of the total energy w...
Comparing photonic band structure calculation methods for diamond and pyrochlore crystals.
Vermolen, E C M; Thijssen, J H J; Moroz, A; Megens, M; van Blaaderen, A
2009-04-27
The photonic band diagrams of close-packed colloidal diamond and pyrochlore structures, have been studied using Korringa-Kohn-Rostoker (KKR) and plane-wave calculations. In addition, the occurrence of a band gap has been investigated for the binary Laves structures and their constituent large- and small-sphere substructures. It was recently shown that these Laves structures give the possibility to fabricate the diamond and pyrochlore structures by self-organization. The comparison of the two calculation methods opens the possibility to study the validity and the convergence of the results, which have been an issue for diamond-related structures in the past. The KKR calculations systematically give a lower value for the gap width than the plane-wave calculations. This difference can partly be ascribed to a convergence issue in the plane-wave code when a contact point of two spheres coincides with the grid. PMID:19399068
Kinetic-energy density functional: Atoms and shell structure
International Nuclear Information System (INIS)
We present a nonlocal kinetic-energy functional which includes an anisotropic average of the density through a symmetrization procedure. This functional allows a better description of the nonlocal effects of the electron system. The main consequence of the symmetrization is the appearance of a clear shell structure in the atomic density profiles, obtained after the minimization of the total energy. Although previous results with some of the nonlocal kinetic functionals have given incipient structures for heavy atoms, only our functional shows a clear shell structure for most of the atoms. The atomic total energies have a good agreement with the exact calculations. Discussion of the chemical potential and the first ionization potential in atoms is included. The functional is also extended to spin-polarized systems. copyright 1996 The American Physical Society
The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique
Energy Technology Data Exchange (ETDEWEB)
Kevin Jerome Sutherland
2001-05-01
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.
Model Comparison for the Density Structure across Solar Coronal Waveguides
Arregui, I.; Soler, R.; Asensio Ramos, A.
2015-10-01
The spatial variation of physical quantities, such as the mass density, across solar atmospheric waveguides governs the timescales and spatial scales for wave damping and energy dissipation. The direct measurement of the spatial distribution of density, however, is difficult, and indirect seismology inversion methods have been suggested as an alternative. We applied Bayesian inference, model comparison, and model-averaging techniques to the inference of the cross-field density structuring in solar magnetic waveguides using information on periods and damping times for resonantly damped magnetohydrodynamic transverse kink oscillations. Three commonly employed alternative profiles were used to model the variation of the mass density across the waveguide boundary. Parameter inference enabled us to obtain information on physical quantities such as the Alfvén travel time, the density contrast, and the transverse inhomogeneity length scale. The inference results from alternative density models were compared and their differences quantified. Then, the relative plausibility of the considered models was assessed by performing model comparison. Our results indicate that the evidence in favor of any of the three models is minimal, unless the oscillations are strongly damped. In such a circumstance, the application of model-averaging techniques enables the computation of an evidence-weighted inference that takes into account the plausibility of each model in the calculation of a combined inversion for the unknown physical parameters.
Dielectric band structure of crystals: General properties, and calculations for silicon
International Nuclear Information System (INIS)
We shift the dielectric band structure method, orginially proposed by Baldereschi and Tosatti for the description of microscopic electronic screening in crystals. Some general properties are examined first, including the requirements of causality and stability. The specific test case of silicon is then considered. Dielectric bands are calculated, according to several different prescriptions for the construction of the dielectric matrix. It is shown that the results allow a very direct appraisal of the screening properties of the system, as well as of the quality of the dielectric model adopted. The electronic charge displacement induced by ?sub(25') and X3 phonon-like displacements of the atoms is also calculated and compared with the results of existent full self-consistent calculations. Conclusions are drawn on the relative accuracies of the dielectric band structures. (author)
Kozub, V I; Khondaker, S I; Shlimak, I S
1999-01-01
A simple two-band model is suggested explaining recently reported unusual features for hopping magnetoresistance and the metal-insulator transition in 2D structures. The model implies that the conductivity is dominated by the upper Hubbard band (D^- band). Experimental studies of hopping magnetoresistance for Si delta doped GaAs/AlGaAs heterostructure give additional evidences for the model.
Junquera, Javier; Aguado-Puente, Pablo
2013-03-01
At metal-isulator interfaces, the metallic wave functions with an energy eigenvalue within the band gap decay exponentially inside the dielectric (metal-induced gap states, MIGS). These MIGS can be actually regarded as Bloch functions with an associated complex wave vector. Usually only real values of the wave vectors are discussed in text books, since infinite periodicity is assumed and, in that situation, wave functions growing exponentially in any direction would not be physically valid. However, localized wave functions with an exponential decay are indeed perfectly valid solution of the Schrodinger equation in the presence of defects, surfaces or interfaces. For this reason, properties of MIGS have been typically discussed in terms of the complex band structure of bulk materials. The probable dependence on the interface particulars has been rarely taken into account explicitly due to the difficulties to include them into the model or simulations. We aim to characterize from first-principles simulations the MIGS in realistic ferroelectric capacitors and their connection with the complex band structure of the ferroelectric material. We emphasize the influence of the real interface beyond the complex band structure of bulk materials. At metal-isulator interfaces, the metallic wave functions with an energy eigenvalue within the band gap decay exponentially inside the dielectric (metal-induced gap states, MIGS). These MIGS can be actually regarded as Bloch functions with an associated complex wave vector. Usually only real values of the wave vectors are discussed in text books, since infinite periodicity is assumed and, in that situation, wave functions growing exponentially in any direction would not be physically valid. However, localized wave functions with an exponential decay are indeed perfectly valid solution of the Schrodinger equation in the presence of defects, surfaces or interfaces. For this reason, properties of MIGS have been typically discussed in terms of the complex band structure of bulk materials. The probable dependence on the interface particulars has been rarely taken into account explicitly due to the difficulties to include them into the model or simulations. We aim to characterize from first-principles simulations the MIGS in realistic ferroelectric capacitors and their connection with the complex band structure of the ferroelectric material. We emphasize the influence of the real interface beyond the complex band structure of bulk materials. Financial support provided by MICINN Grant FIS2009-12721-C04-02, and by the European Union Grant No. CP-FP 228989-2 ``OxIDes''. Computer resources provided by the RES.
International Nuclear Information System (INIS)
We compare defect energy levels of point defects in ?-quartz using density functionals of different accuracy: a standard generalized-gradient-approximation functional and a hybrid functional. The latter is known to improve the description of band gaps through the incorporation of a fraction of Hartree-Fock exchange. The separations between the defect levels are found to be preserved when going from the standard to the more accurate hybrid functional, indicating that they are already well described with the standard functional. We also find that the defect wave functions obtained with the two functionals are very similar. Consequently, the defect energy levels pertaining to the hybrid functional can be obtained through the perturbational method
A real-space stochastic density matrix approach for density functional electronic structure.
Beck, Thomas L
2015-11-25
The recent development of real-space grid methods has led to more efficient, accurate, and adaptable approaches for large-scale electrostatics and density functional electronic structure modeling. With the incorporation of multiscale techniques, linear-scaling real-space solvers are possible for density functional problems if localized orbitals are used to represent the Kohn-Sham energy functional. These methods still suffer from high computational and storage overheads, however, due to extensive matrix operations related to the underlying wave function grid representation. In this paper, an alternative stochastic method is outlined that aims to solve directly for the one-electron density matrix in real space. In order to illustrate aspects of the method, model calculations are performed for simple one-dimensional problems that display some features of the more general problem, such as spatial nodes in the density matrix. This orbital-free approach may prove helpful considering a future involving increasingly parallel computing architectures. Its primary advantage is the near-locality of the random walks, allowing for simultaneous updates of the density matrix in different regions of space partitioned across the processors. In addition, it allows for testing and enforcement of the particle number and idempotency constraints through stabilization of a Feynman-Kac functional integral as opposed to the extensive matrix operations in traditional approaches. PMID:25969148
Dang, Hung T.; Mravlje, Jernej; Georges, Antoine; Millis, Andrew J.
2015-09-01
Density functional plus dynamical mean field calculations are used to show that in transition metal oxides, rotational and tilting (GdFeO3-type) distortions of the ideal cubic perovskite structure produce a multiplicity of low-energy optical transitions which affect the conductivity down to frequencies of the order of 1 or 2 mV (terahertz regime), mimicking non-Fermi-liquid effects even in systems with a strictly Fermi-liquid self-energy. For CaRuO3, a material whose measured electromagnetic response in the terahertz frequency regime has been interpreted as evidence for non-Fermi-liquid physics, the combination of these band structure effects and a renormalized Fermi-liquid self-energy accounts for the low frequency optical response which had previously been regarded as a signature of exotic physics. Signatures of deviations from Fermi-liquid behavior at higher frequencies (˜100 meV ) are discussed.
Logsdail, Andrew J.; Mora-Fonz, David; Scanlon, David O.; Catlow, C. Richard A.; Sokol, Alexey A.
2015-12-01
We perform a systematic investigation of (100) surfaces for rocksalt-structured group 2 metal oxides, namely MgO, CaO, SrO and BaO, using GGA and Hybrid-DFT exchange-correlation functionals. We examine the structural, energetic and electronic properties of the surfaces, with a specific focus on the surface ionisation potential and band bending; the latter of which we quantify by examining the density of states as a function of depth from the system surface. We report structural and energetic results in-line with previous experimental work when we use the Hybrid-DFT method, and for the electronic structure we find inequivalent band bending for the valence and conduction bands, which results in reduced ionisation potentials and the closure of the band gap at the surface when compared to bulk systems. We also report downward bending of the conduction band for MgO that brings it below the vacuum potential, unlike previous theoretical investigations, and thus indicates an origin of the positive electron affinity found in the experiment.
Band gap structure modification of amorphous anodic Al oxide film by Ti-alloying
DEFF Research Database (Denmark)
Canulescu, Stela; Rechendorff, K.
2014-01-01
The band structure of pure and Ti-alloyed anodic aluminum oxide has been examined as a function of Ti concentration varying from 2 to 20 at.?%. The band gap energy of Ti-alloyed anodic Al oxide decreases with increasing Ti concentration. X-ray absorption spectroscopy reveals that Ti atoms are not located in a TiO2 unit in the oxide layer, but rather in a mixed Ti-Al oxide layer. The optical band gap energy of the anodic oxide layers was determined by vacuum ultraviolet spectroscopy in the energy range from 4.1 to 9.2?eV (300–135?nm). The results indicate that amorphous anodic Al2O3 has a direct band gap of 7.3?eV, which is about ?1.4?eV lower than its crystalline counterpart (single-crystal Al2O3). Upon Ti-alloying, extra bands appear within the band gap of amorphous Al2O3, mainly caused by Ti 3d orbitals localized at the Ti site.
Band gap structure modification of amorphous anodic Al oxide film by Ti-alloying
International Nuclear Information System (INIS)
The band structure of pure and Ti-alloyed anodic aluminum oxide has been examined as a function of Ti concentration varying from 2 to 20 at.?%. The band gap energy of Ti-alloyed anodic Al oxide decreases with increasing Ti concentration. X-ray absorption spectroscopy reveals that Ti atoms are not located in a TiO2 unit in the oxide layer, but rather in a mixed Ti-Al oxide layer. The optical band gap energy of the anodic oxide layers was determined by vacuum ultraviolet spectroscopy in the energy range from 4.1 to 9.2?eV (300–135?nm). The results indicate that amorphous anodic Al2O3 has a direct band gap of 7.3?eV, which is about ?1.4?eV lower than its crystalline counterpart (single-crystal Al2O3). Upon Ti-alloying, extra bands appear within the band gap of amorphous Al2O3, mainly caused by Ti 3d orbitals localized at the Ti site
Band structures of 182Os studied by GCM based on 3D-CHFB
Horibata, Takatoshi; Oi, Makito; Onishi, Naoki; Ansari, Ahmad
1999-02-01
Band structure properties of 182Os are investigated through a particle number and angular momentum constrained generator coordinate (GCM) calculation based on self-consistent threedimensional cranking solutions. From the analysis of the wave function of the lowest GCM solution, we confirm that this nucleus shows a tilted rotational motion in its yrast states, at least with the present set of force parameters of the pairing-plus-quadrupole interaction Hamiltonian. A close examination of the behaviour of the other GCM solutions reveals a sign of a possible occurrence of multi-band crossing in the nucleus. We have also found a new potential curve along the prime meridian on the globe of the J = 18 h? sphere. Along this new solution the characters of proton and neutron gap parameters get interchanged. Namely, ? p almost vanishes while ? n grows to a finite value close to the one corresponding to the principal axis rotation (PAR). A state in the new solution curve at the PAR point turns out to have almost the same characteristic features of an yrare s-band state which is located just above the g-band in our calculation. This fact suggests a new type of seesaw vibrational mode of the proton and the neutron pairing, occurring through a wobbling motion. This mode is considered to bridge the g-band states and the s-band states in the backbending region.
Band structures of 182Os studied by GCM based on 3D-CHFB
International Nuclear Information System (INIS)
Band structure properties of 182Os are investigated through a particle number and angular momentum constrained generator coordinate (GCM) calculation based on self-consistent three-dimensional cranking solutions. From the analysis of the wave function of the lowest GCM solution, we confirm that this nucleus shows a tilted rotational motion in its yrast states, at least with the present set of force parameters of the pairing-plus-quadrupole interaction Hamiltonian. A close examination of the behaviour of the other GCM solutions reveals a sign of a possible occurrence of multi-band crossing in the nucleus. We have also found a new potential curve along the prime meridian on the globe of the J = 18(?/2?) sphere. Along this new solution the characters of proton and neutron gap parameters get interchanged. Namely, ?p almost vanishes while ?n grows to a finite value close to the one corresponding to the principal axis rotation (PAR). A state in the new solution curve at the PAR point turns out to have almost the same characteristic features of an yrast s-band state which is located just above the g-band in our calculation. This fact suggests a new type of seesaw vibrational mode of the proton and the neutron pairing, occurring through a wobbling motion. This mode is considered to bridge the g-band states and the s-band states in the backbending region
Band structure analysis of an analytically solvable Hill equation with continuous potential
Morozov, G. V.; Sprung, D. W. L.
2015-03-01
This paper concerns analytically solvable cases of Hill’s equation containing a continuously differentiable periodic potential. We outline a procedure for constructing the Floquet-Bloch fundamental system, and analyze the band structure of the system. The similarities to, and differences from, the cases of a piecewise constant periodic potential and the Mathieu potential, are illuminated.
Band structure analysis of an analytically solvable Hill equation with continuous potential
International Nuclear Information System (INIS)
This paper concerns analytically solvable cases of Hill’s equation containing a continuously differentiable periodic potential. We outline a procedure for constructing the Floquet–Bloch fundamental system, and analyze the band structure of the system. The similarities to, and differences from, the cases of a piecewise constant periodic potential and the Mathieu potential, are illuminated. (paper)
Fast magnetic response in gigahertz-band for columnar-structured Fe nanoparticle assembly
Energy Technology Data Exchange (ETDEWEB)
Ogawa, T., E-mail: tomoyuki@ecei.tohoku.ac.jp; Tate, R. [Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, 6-6-05 Aza-Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Kura, H. [New Industry Creation Hatchery Center (NICHe), Tohoku University, 6-6-10 Aza-Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Oikawa, T.; Hata, K. [Samsung R and D Institute Japan Co., Ltd., 2-7 Sugasawa-cho, Tsurumi-ku, Yokohama 230-0027 (Japan)
2014-05-07
High density Fe-based ferromagnetic nanoparticle (NP) assembly is expected to have unique magnetic properties, such as superferromagnetism and super-spin-glass, different from magnetically isolated NP systems due to strong dipole interactions among the NPs. A high dipole interaction field, H{sub dip}, of ?3.5 kOe can result in a high effective internal field to the magnetic moment of the NP, expecting for ultra-fast magnetic response, that is, a high magnetic resonance frequency, f{sub r}, of ?10 GHz. However, for a simply molded Fe NP assembly, a low f{sub r} was observed due to inhomogeneous distribution of the internal field, implying the necessity of a unidirectional state of H{sub dip} for higher f{sub r}. In this study, we fabricated a columnar Fe NP assembly for realizing the unidirectional state of H{sub dip} by applying our uniquely developed external field-induced agglomeration method for monodispersed Fe NPs (13 nm in average size) as a function of the field (0–30 kOe) and volume fraction of the Fe NPs (0.5%–51%) in a polymer matrix with dimensions of 4 mm × 4 mm × 0.7 mm{sup t}. A columnar-structured Fe NP assembly was successfully achieved along an in-plane direction (defined as the x-axis) under optimized conditions. From static magnetization curves, induced uniaxial magnetic anisotropy was observed according to the shape of the columnar structure of the Fe NP assembly, where easy and hard axes of magnetization were realized along the parallel (x-axis) and normal directions (in-plane y-axis and z-axis in the thickness direction) to the external field during the process, respectively. Interestingly, this fabricated columnar-structured Fe NP assembly exhibited very high f{sub r} in the range from 3 to 11 GHz judging from the complex susceptibility spectra obtained. The f{sub r} values were well-scaled by a modified Snoek's-limit-law using demagnetization factors quantitatively estimated from the static magnetization curves. Thus, shape-induced anisotropy originating from the unidirectional state of H{sub dip} in the columnar structure of the Fe NP assembly plays an important role for high frequency magnetic response in the GHz-band.
Nonlinear optical response of semiconductor-nanocrystals-embedded photonic band gap structure
Energy Technology Data Exchange (ETDEWEB)
Liao, Chen; Zhang, Huichao; Tang, Luping; Zhou, Zhiqiang; Lv, Changgui; Cui, Yiping; Zhang, Jiayu, E-mail: jyzhang@seu.edu.cn [Advanced Photonic Center, Southeast University, Nanjing 210096 (China)
2014-04-28
Colloidal CdSe/ZnS core/shell nanocrystals (NCs), which were dispersed in SiO{sub 2} sol, were utilized to fabricate a SiO{sub 2}:NCs/TiO{sub 2} all-dielectric photonic band gap (PBG) structure. The third-order nonlinear refractive index (n{sub 2}) of the PBG structure was nearly triple of that of the SiO{sub 2}:NCs film due to the local field enhancement in the PBG structure. The photoinduced change in refractive index (?n) could shift the PBG band edge, so the PBG structure would show significant transmission modification, whose transmission change was ?17 folds of that of the SiO{sub 2}:NCs film. Under excitation of a 30?GW/cm{sup 2} femtosecond laser beam, a transmission decrease of 80% was realized.
Results from the CLIC X-Band Structure Test Program at NLCTA
Energy Technology Data Exchange (ETDEWEB)
Adolphsen, Chris; Bowden, Gordon; Dolgashev, Valery; Laurent, Lisa; Tantawi, Sami; Wang, Faya; Wang, Juwen W.; /SLAC; Doebert, Steffen; Grudiev, Alexej; Riddone, Germana; Wuensch, Walter; Zennaro, Riccardo; /CERN; Higashi, Yasuo; Higo, Toshiyasu; /KEK, Tsukuba
2009-07-06
As part of a SLAC-CERN-KEK collaboration on high gradient X-band structure research, several prototype structures for the CLIC linear collider study have been tested using two of the high power (300 MW) X-band rf stations in the NLCTA facility at SLAC. These structures differ in terms of their fabrication (brazed disks and clamped quadrants), gradient profile (amount by which the gradient increases along the structure, which optimizes efficiency and maximizes sustainable gradient) and HOM damping (use of slots or waveguides to rapidly dissipate dipole mode energy). The CLIC goal in the next few years is to demonstrate the feasibility of a CLIC-ready baseline design and to investigate alternatives that could increase efficiency. This paper summarizes the high gradient test results from NLCTA in support of this effort.
Results from the CLIC X-Band Structure Test Program at NLCTA
International Nuclear Information System (INIS)
As part of a SLAC-CERN-KEK collaboration on high gradient X-band structure research, several prototype structures for the CLIC linear collider study have been tested using two of the high power (300 MW) X-band rf stations in the NLCTA facility at SLAC. These structures differ in terms of their fabrication (brazed disks and clamped quadrants), gradient profile (amount by which the gradient increases along the structure, which optimizes efficiency and maximizes sustainable gradient) and HOM damping (use of slots or waveguides to rapidly dissipate dipole mode energy). The CLIC goal in the next few years is to demonstrate the feasibility of a CLIC-ready baseline design and to investigate alternatives that could increase efficiency. This paper summarizes the high gradient test results from NLCTA in support of this effort.
Surface plasmon polariton band gap structures: implications to integrated plasmonic circuits
DEFF Research Database (Denmark)
Bozhevolnyi, S. I.; Volkov, V. S.
2001-01-01
Conventional photonic band gap (PBG) structures are composed of regions with periodic modulation of refractive index that do not allow the propagation of electromagnetic waves in a certain interval of wavelengths, i.e., that exhibit the PBG effect. The PBG effect is essentially an interference phenomenon related to strong multiple scattering of light in periodic media. The interest to the PBG structures has dramatically risen since the possibility of efficient waveguiding around a sharp corner of a line defect in the PBG structure has been pointed out. Given the perspective of integrating various PBG-based components within a few hundred micrometers, we realized that other two-dimensional waves, e.g., surface plasmon polaritons (SPPs), might be employed for the same purpose. The SPP band gap (SPPBG) has been observed for the textured silver surfaces by performing angular measurements of the surface reflectivity. Here we report the results of our experimental and theoretical investigations of waveguiding in the SPPBG structures.
IPS observations of heliospheric density structures associated with active regions
Hick, P.; Jackson, B. V.; Altrock, R.; Woan, G.; Slater, G.
1996-01-01
Interplanetary scintillation (IPS) measurements of the 'disturbance factor' g, obtained with the Cambridge (UK) array can be used to explore the heliospheric density structure. We have used these data to construct synoptic (Carrington) maps, representing the large-scale enhancements of the g-factor in the inner heliosphere. These maps emphasize the stable corotating, rather than the transient heliospheric density enhancements. We have compared these maps with Carrington maps of Fe XIV observations National Solar Observatory ((NSO), Sacramento Peak) and maps based on Yohkoh Soft X-Ray Telescope (SXT) X-ray observations. Our results indicate that the regions of enhanced g tend to map to active regions rather than the current sheet. The implication is that act ve regions are the dominant source of the small-scale (approximately equal 200 km) density variations present in the quiet solar wind.
Band parameters of phosphorene
Voon, L. C. Lew Yan; Wang, J.; Zhang, Y.; Willatzen, M.
2015-09-01
Phosphorene is a two-dimensional nanomaterial with a direct band-gap at the Brillouin zone center. In this paper, we present a recently derived effective-mass theory of the band structure in the presence of strain and electric field, based upon group theory. Band parameters for this theory are computed using a first-principles theory based upon the generalized-gradient approximation to the density-functional theory. These parameters and Hamiltonian will be useful for modeling physical properties of phosphorene.
Band parameters of phosphorene
DEFF Research Database (Denmark)
Lew Yan Voon, L. C.; Wang, J.
2015-01-01
Phosphorene is a two-dimensional nanomaterial with a direct band-gap at the Brillouin zone center. In this paper, we present a recently derived effective-mass theory of the band structure in the presence of strain and electric field, based upon group theory. Band parameters for this theory are computed using a first-principles theory based upon the generalized-gradient approximation to the density-functional theory. These parameters and Hamiltonian will be useful for modeling physical properties of phosphorene.
Covariant density functional theory: Reexamining the structure of superheavy nuclei
Agbemava, S E; Nakatsukasa, T; Ring, P
2015-01-01
A systematic investigation of even-even superheavy elements in the region of proton numbers $100 \\leq Z \\leq 130$ and in the region of neutron numbers from the proton-drip line up to neutron number $N=196$ is presented. For this study we use five most up-to-date covariant energy density functionals of different types, with a non-linear meson coupling, with density dependent meson couplings, and with density-dependent zero-range interactions. Pairing correlations are treated within relativistic Hartree-Bogoliubov (RHB) theory based on an effective separable particle-particle interaction of finite range and deformation effects are taken into account. This allows us to assess the spread of theoretical predictions within the present covariant models for the binding energies, deformation parameters, shell structures and $\\alpha$-decay half-lives. Contrary to the previous studies in covariant density functional theory, it was found that the impact of $N=172$ spherical shell gap on the structure of superheavy elemen...
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.
International Nuclear Information System (INIS)
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.
Energy Technology Data Exchange (ETDEWEB)
Piquini, P.; Zunger, A.
2008-10-01
Thermophotovoltaic (TPV) devices are intended to absorb photons from hot blackbody radiating objects, often requiring semiconductor absorbers with band gap of {approx_equal} 0.6 eV. The random In{sub x}Ga{sub 1-x}As alloy lattice matched (x{sub In}=0.53) to a (001) InP substrate has a low-temperature band gap of 0.8 eV, about 0.2 eV too high for a TPV absorber. Bringing the band gap down by raising the In concentration induces strain with the substrate, leading to a two-dimensional (2D) {yields} three-dimensional (3D) morphological transition occurring before band gaps suitable for TPV applications are achieved. We use the inverse band structure approach, based on a genetic algorithm and empirical pseudopotential calculations, to search for lattice-matched InAs/GaAs multiple-repeat unit structures with individual layer thicknesses lower than the critical thickness for a 2D {yields} 3D transition. Despite the fact that quantum confinement usually increases band gaps, we find a quantum superlattice structure with the required reduced gap (and a significant optical transition) that matches all target requirements. This is explained by the predominance of (potential-energy) level anticrossing effects over (kinetic) quantum confinement effects.
International Nuclear Information System (INIS)
Thermophotovoltaic (TPV) devices are intended to absorb photons from hot blackbody radiating objects, often requiring semiconductor absorbers with band gap of ? 0.6 eV. The random InxGa1-xAs alloy lattice matched (xIn=0.53) to a (001) InP substrate has a low-temperature band gap of 0.8 eV, about 0.2 eV too high for a TPV absorber. Bringing the band gap down by raising the In concentration induces strain with the substrate, leading to a two-dimensional (2D) ? three-dimensional (3D) morphological transition occurring before band gaps suitable for TPV applications are achieved. We use the inverse band structure approach, based on a genetic algorithm and empirical pseudopotential calculations, to search for lattice-matched InAs/GaAs multiple-repeat unit structures with individual layer thicknesses lower than the critical thickness for a 2D ? 3D transition. Despite the fact that quantum confinement usually increases band gaps, we find a quantum superlattice structure with the required reduced gap (and a significant optical transition) that matches all target requirements. This is explained by the predominance of (potential-energy) level anticrossing effects over (kinetic) quantum confinement effects
Towards Tidal Tomography: Using Earth's Body-Tide Signal to Constrain Deep-Mantle Density Structure
Lau, Harriet; Yang, Hsin-Ying; Davis, James; Mitrovica, Jerry; Tromp, Jeroen; Latychev, Konstantin
2015-04-01
Luni-solar forcings drive long wavelength deformation at timescales ranging from 8 hours to 18.6 years. We propose that globally distributed GPS estimates of this deformation within the semi-diurnal band provide a new and independent constraint on long-wavelength deep mantle structure. A particular target of "tidal tomography" is the buoyancy structure of LLSVPs, which constitute a large volumetric fraction of the mantle. Constraining this structure is the key to understanding the longevity of the LLSVPs, and indeed the evolution of the entire mantle and Earth system. To this end, we begin by reporting on the development of a new normal-mode theory, based on relatively recent advances in free oscillation seismology, which is capable of predicting semi-diurnal body tides on a laterally heterogeneous, rotating and anelastic Earth. We next present the results of a suite of benchmark tests involving comparisons with predictions based on both classical tidal Love number theory for 1-D Earth models and finite-volume simulations that incorporate 3-D elastic and density structure. We find that body tide deformation is most sensitive to long wavelength, deep mantle structure, and, in particularly, to shear wave velocity and density structure. When combined with results from seismological datasets, this sensitivity provides a powerful tool to investigate the buoyancy structure of the LLSVPs. For example, adopting a variety of seismic tomography models a priori, we perform an extensive parameter search to determine misfits between model predictions based on the new theory and GPS-derived estimates of the semi-diurnal body tide displacements. Preliminary results, focusing only on density structure, have indicated that the observations are best fit when the LLSVPs have a bulk density greater than average mantle, in broad agreement with previous inferences based upon seismic normal mode inversions. In follow-up work, we have mapped out trade-offs related to the adopted seismic tomography model, deep mantle buoyancy structure, and topography of both the core-mantle boundary (CMB) and 670 km seismic discontinuity. The goal of this analysis is to address the following question: given all available models of shear-wave velocity structure and topography at internal discontinuities, what are the bounds on the buoyancy structure of the LLSVPs lie that satisfy space-geodetic measurements of body tide deformation -- a dataset currently unexploited in investigations of deep mantle structure.
Band structure investigations of GaN films using modulation spectroscopy
International Nuclear Information System (INIS)
The paper presents investigation results concerning band structure of gallium nitride and position of intrinsic and associate defect levels. Main optical characteristics (transmission, reflection and luminescence) were measured in both ordinary and ?-modulation mode for epitaxy-grown GaN films, allowing to determine valence band splitting caused by spin-orbital interaction (48meV) and crystalline field (10meV). Analysis of photoluminescence spectra made it possible to identify main recombination mechanisms involving donor and acceptor levels formed by intrinsic point defects VN?,V'Ga, and their associates
Surface band structure of arsenic terminated Ge(111) from angle resolved photoemission
International Nuclear Information System (INIS)
The authors carried out experimental and theoretical determinations of the dispersion of the surface state of 1 x 1 Ge(111):As. The arsenic coverage was achieved using an As MBE source and the experimental surface bands were obtained by carrying out and angle-resolved photoemission study. The results indicate that Ge(111):As is an ideal topology surface. The lone pair orbitals on the As atoms form a band of surface states with a dispersion characteristic of dangling bond states on an ideal 1 x 1 surface. The structural simplicity and chemical stability of the surface make it an optimal system to study with a variety of surface sensitive probes
Erasure Codes with a Banded Structure for Hybrid Iterative-ML Decoding
Soro, Alexandre; Lacan, Jerome; Roca, Vincent
2009-01-01
This paper presents new FEC codes for the erasure channel, LDPC-Band, that have been designed so as to optimize a hybrid iterative-Maximum Likelihood (ML) decoding. Indeed, these codes feature simultaneously a sparse parity check matrix, which allows an efficient use of iterative LDPC decoding, and a generator matrix with a band structure, which allows fast ML decoding on the erasure channel. The combination of these two decoding algorithms leads to erasure codes achieving a very good trade-off between complexity and erasure correction capability.
International Nuclear Information System (INIS)
To design half-metallic materials in thin film form for spintronic devices, the electronic structures of full Heusler alloys (Mn2FeSi, Fe2MnSi, Fe2FeSi, Fe2CoSi, and Co2FeSi) with an L21 structure have been investigated using density functional theory calculations with Gaussian-type functions in a periodic boundary condition. Considering the metal composition, layer thickness, and orbital symmetries, a 5-layered Co2FeSi thin film, whose surface consists of a Si layer, was found to have stable half-metallic nature with a band gap of ca. 0.6 eV in the minority spin state. Using the group theory, the difference between electronic structures in bulk and thin film conditions was discussed. - Highlights: ? Electronic band structure calculations of L21 full Heusler alloy thin films. ? Spintronic materials. ? Electronic properties dependency on layer thickness.
Directory of Open Access Journals (Sweden)
Dong Q.-L.
2013-11-01
Full Text Available The energy band structures of the warm dense plasmas with micro-structures inherited from single-walled carbon nanotubes are studied in detail by using the symmetry-adapted tight-binding model with the electron-ion core Coulomb interactions as the plasma effects. It is found that both the symmetry and the degeneracy of the calculated bands normal for the solid micro-structured targets may be destroyed by the electron-ion core Coulomb interactions. Moreover, the calculated Fermi levels of the micro-structured warm dense plasmas are about 1 eV higher than those of the original carbon nanotubes, while the transition energies of the warm dense plasmas are almost always smaller than those for the original carbon nanotubes.
Energy Technology Data Exchange (ETDEWEB)
Anisimov, V.I.; Korotin, M.A.; Afanasyev, I.V. (AN SSSR, Sverdlovsk. Inst. Fiziki Metallov (USSR))
1989-10-15
The failure of the local density approximation (LDA) for the description of the electronic structure narrow-band transition metal oxides is discussed. It has been shown that the self-interaction correction (SIC) method improves the value of the bandgap, but can distort the valence states distribution. We propose the ''prescription'' of the potential construction which corrects only the potentials acting upon the electrons in vacant states and leaves unchanged the potential for occupied states. The use of this correction in the self-consistent LDA electronic structure calculation of NiO not only gave the correct value of the bandgap, {approx equal} 4 eV, but also significantly improved the value of the magnetic moment on nickel. It has been shown that the magnetic moment on nickel exists independently of the magnetic order type, that corroborates the localized nature of magnitude moments in NiO. By contrast with the usual LDA calculations, which lead to the nonmagnetic metallic ground state for La{sub 2}CuO{sub 4}, self-consistent LDA calculations with the corrections suggested by the present authors gave stable antiferromagnetic solutions with a copper magnetic moment value 0.38 mu{sub B} and a semiconductor type of electronic structure with bandgap value of 0.78 eV. (orig.).
International Nuclear Information System (INIS)
Spin wave excitations and the stability of the (0, ?) ordered spin density wave (SDW) state are investigated within the minimal two-band model for iron pnictides including a Hund's coupling term. The SDW state is shown to be stable in two distinct doping regimes-for finite hole doping in the lower SDW band for small second-neighbour hoppings, and for low electron doping in the upper SDW band for comparable first-neighbour and second-neighbour hoppings. In both cases, Hund's coupling strongly stabilizes the SDW state due to the generation of additional ferromagnetic spin couplings involving the inter-orbital part of the particle-hole propagator. The spin wave energies for the two-band model are very similar to the one-band t-t' Hubbard model results obtained earlier, and are in agreement with the findings from inelastic neutron scattering studies of iron pnictides. (fast track communication)
Naddafi, Rahmat; Pettersson, Kurt; Eklöv, Peter
2010-01-01
The zebra mussel (Dreissena polymorpha) provides one example of successful invaders in novel environments. However, little attention has been devoted to exploring the factors regulating zebra mussel density and population size structure at the local scale. We tested effects of physicochemical factors and fish predation on the density of zebra mussels at several sites and between years in a natural lake. Water depth and roach (Rutilus rutilus) density were the most important variables affectin...
Experimental Studies Of W-band Accelerator Structures At High Field
Hill, M E
2001-01-01
A high-gradient electron accelerator is desired for high- energy physics research, where frequency scalings of breakdown and trapping of itinerant beamline particles dictates operation of the accelerator at short wavelengths. The first results of design and test of a high-gradient mm-wave linac with an operating frequency at 91.392 GHz (W-band) are presented. A novel approach to particle acceleration is presented employing a planar, dielectric lined waveguide used for particle acceleration. The traveling wave fields in the planar dielectric accelerator (PDA) are analyzed for an idealized structure, along with a circuit equivalent model used for understanding the structure as a microwave circuit. Along with the W-band accelerator structures, other components designed and tested are high power rf windows, high power attenuators, and a high power squeeze-type phase shifter. The design of the accelerator and its components where eased with the aide of numerical simulations using a finite-difference electromagneti...
Low frequency phononic band structures in two-dimensional arc-shaped phononic crystals
Energy Technology Data Exchange (ETDEWEB)
Xu, Zhenlong, E-mail: zhenlongxu1000@163.com [Faculty of Electro Mechanical Engineering, Guangdong University of Technology, Guangzhou, 510006 (China); Meizhouwan Vocational Technology College, Putian, 351254 (China); Wu, Fugen [Department of Experiment Education, Guangdong University of Technology, Guangzhou, 510006 (China); Guo, Zhongning [Faculty of Electro Mechanical Engineering, Guangdong University of Technology, Guangzhou, 510006 (China)
2012-07-02
The low frequency phononic band structures of two-dimensional arc-shaped phononic crystals (APCs) were studied by the transfer matrix method in cylindrical coordinates. The results showed the first phononic band gaps (PBGs) of APCs from zero Hz with low modes. Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials. These properties can be efficiently used in a structure for low frequencies that are forbidden, or in a device that permits a narrow window of frequencies. -- Highlights: ? We report a new class of quasi-periodic hetero-structures, arc-shaped phononic crystals (APCs). ? The results show the first PBGs start with zero Hz with low modes. ? Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials.
Method of projection operators for photonic band structures with perfectly conducting elements
Suzuki, Toshio; Yu, Paul K. L.
1998-01-01
We introduce the method of projection operators based on plane-wave expansion to compute photonic band structures in periodic media containing perfectly conducting elements. Eigenfunctions of a unit configuration potential generate suitable projection operators in the form of a set of eigenvectors in the Fourier domain. By simply applying a projection operator onto a proper subspace, a quadratic or cubic eigensystem for finitely conducting media can be transformed into an ordinary symmetric eigensystem in the limit of perfect conductors. The procedure is equivalent to finding solutions of wave equations under the condition that the electromagnetic fields are entirely zero inside periodic perfect conductors. The methodology developed here, in fact, can be viewed as a generalization of the conventional metal waveguide or cavity theory. The method is numerically handy, fast, and readily extendible to general metallodielectric photonic crystals. As examples, we present photonic band structures in two-dimensional metal and metallodielectric cylinder structures.
Effect of Symmetry Breaking on Electronic Band Structure: Gap Opening at the High Symmetry Points
Directory of Open Access Journals (Sweden)
Guillaume Vasseur
2013-12-01
Full Text Available Some characteristic features of band structures, like the band degeneracy at high symmetry points or the existence of energy gaps, usually reflect the symmetry of the crystal or, more precisely, the symmetry of the wave vector group at the relevant points of the Brillouin zone. In this paper, we will illustrate this property by considering two-dimensional (2D-hexagonal lattices characterized by a possible two-fold degenerate band at the K points with a linear dispersion (Dirac points. By combining scanning tunneling spectroscopy and angle-resolved photoemission, we study the electronic properties of a similar system: the Ag/Cu(111 interface reconstruction characterized by a hexagonal superlattice, and we show that the gap opening at the K points of the Brillouin zone of the reconstructed cell is due to the symmetry breaking of the wave vector group.
Directory of Open Access Journals (Sweden)
S. H. Zahraei
2014-04-01
Full Text Available In this paper, using plane ware expansion method the polarization-dependent band structures are investigated in two dimensional photonic crystal waveguide with a square lattice composed of GaAs elliptic elements in air background. Then, the changes of the band structure with changing ellipticity of the elliptic elements are discussed. It is observed that by increasing the ellipticity of elements the size of the photonic band gap and the guiding eigen frequency will increase
S. H. Zahraei; Gharaati, A.
2014-01-01
In this paper, using plane ware expansion method the polarization-dependent band structures are investigated in two dimensional photonic crystal waveguide with a square lattice composed of GaAs elliptic elements in air background. Then, the changes of the band structure with changing ellipticity of the elliptic elements are discussed. It is observed that by increasing the ellipticity of elements the size of the photonic band gap and the guiding eigen frequency will increase
On the Tripropellant Rod-shaped Structure ofthe Band Gap of One-dimensional Phononic Crystals
Directory of Open Access Journals (Sweden)
QIU Xue-yun
2013-03-01
Full Text Available In this paper, the lumped mass method is employed to computerize the band gap property and comparison with the one-dimensional and two-component structure is made. It is showed in the research that the one-dimensional and three-component phononic crystal is efficient in broadening the frequency range of band gaps and reducing the start stopping frequency. Before and after inserting NBR into two-component crystal (Aluminum/plastics, guaranteeing lattice constant SymbolaA@ of two models is 0.3 m and free degree is 300. The band 1 gap starting frequency 463.7 Hz and stopping frequency 2 108.1Hz can be reduced by three-component (Aluminum / NBR / plastic material phononic crystal when composition ratio is one. When three-component phononic crystal lattice constant SymbolaA@ increases from 0.03 m to 0.42 m, the band 1 starting frequency reduces from 18 943 Hz to 1 353.1 Hz and stopping frequency reduces from 37 799 Hz to 2 699.9 Hz. When lattice constant is 0.3 m, the length of Aluminum is fixed value 0.15 m, the total length of NBR and plastics is fixed value 0.15 m and increasing NBR length from 0 m to 0.15 m, the band 1 starting frequency reduces from 2 359.8 Hz to 1 664.7 Hz and stopping frequency reduces from 5 888.0 Hz to 4 065.3 Hz. Meanwhile, there is a peak of 3 043.6 Hz in low frequency zone of the variation of the band 1 gaps, and this is of positive significance for broadening the band property of one-dimensional phononic crystal.
All-electron GW quasiparticle band structures of group 14 nitride compounds
International Nuclear Information System (INIS)
We have investigated the group 14 nitrides (M3N4) in the spinel phase (?-M3N4 with M = C, Si, Ge, and Sn) and ? phase (?-M3N4 with M = Si, Ge, and Sn) using density functional theory with the local density approximation and the GW approximation. The Kohn-Sham energies of these systems have been first calculated within the framework of full-potential linearized augmented plane waves (LAPW) and then corrected using single-shot G0W0 calculations, which we have implemented in the modified version of the Elk full-potential LAPW code. Direct band gaps at the ? point have been found for spinel-type nitrides ?-M3N4 with M = Si, Ge, and Sn. The corresponding GW-corrected band gaps agree with experiment. We have also found that the GW calculations with and without the plasmon-pole approximation give very similar results, even when the system contains semi-core d electrons. These spinel-type nitrides are novel materials for potential optoelectronic applications because of their direct and tunable band gaps
Theoretical study of the structural stability for fcc-CHx phases using density functional theory
Directory of Open Access Journals (Sweden)
M Dadsetani
2011-09-01
Full Text Available Recently, a new carbon modification, namly n-diamond, have been reported, whose structure is still a matter of debate. It is important to note that the synthesis of n-diamond was carried out in the presence of hydrogen or methan. In this work we evaluate the structural stability of five fcc-CHx phases by means of first-principle calculation. The total energy is obtained as a function of the isotropic, tetragonal and rhombohedral deformations for the bulk structures. First, we analyze the C2H (cuprite, CH (zincblende, CH (rocksalt and CH2 (fluorite structures.It is found that the four systems show a minimum in the total energy for the isotropic and rhombohedral deformations, but are unstable against tetragonal deformation. In the second part, we explore the structural stability of CH2 in the pyrite structure. We find that CH2 (pyrite with the hydrogen atoms defined by the internal parameter u=0.35 and a lattice parameter of 3.766 Å is elastically stable, providing a possible explanation for the experimental observation of fcc-carbon in materials prepared in the presence of hydrogen or methan. In final, we calculate density of states, band structure and EELS spectrum of CH2 (pyrite and compare them with n-diamond.
Density Functional Study of the structural properties in Tamoxifen
de Coss-Martinez, Romeo; Tapia, Jorge A.; Quijano-Quiñones, Ramiro F.; Canto, Gabriel I.
2013-03-01
Using the density functional theory, we have studied the structural properties of Tamoxifen. The calculations were performed with two methodological approaches, which were implemented in SIESTA and Spartan codes. For SIESTA, we considerate a linear combination of atomic orbitals method, using pseudopotentials and the van der Waals approximation for the exchange-correlation potential. Here we analyzed and compared the atomic structure between our results and other theoretical study. We found differences in the bond lengths between the results, that could be attributed to code approaches in each one. Using the density functional theory, we have studied the structural properties of Tamoxifen. The calculations were performed with two methodological approaches, which were implemented in SIESTA and Spartan codes. For SIESTA, we considerate a linear combination of atomic orbitals method, using pseudopotentials and the van der Waals approximation for the exchange-correlation potential. Here we analyzed and compared the atomic structure between our results and other theoretical study. We found differences in the bond lengths between the results, that could be attributed to code approaches in each one. This work was supported under Grant FOMIX 2011-09 N: 170297 of Ph.D. A. Tapia.
Band structure engineering of monolayer MoS2 on h-BN: first-principles calculations
International Nuclear Information System (INIS)
We have carried out first-principles calculations and theoretical analysis to explore the structural and electronic properties of MoS2/n-h-BN heterostructures consisting of monolayer MoS2 on top of h-BN substrates with one to five layers. We find that the MoS2/n-h-BN heterostructures show indirect bandgap features with both of CBM (in the K point) and VBM (in the ? point) localized on the monolayer MoS2. Difference charge density and surface bands indicate there is no obvious charge exchange in the heterostructure systems. We show that the changes from a direct bandgap in monolayer free-stranding MoS2 to an indirect bandgap in MoS2/n-h-BN heterostructure is induced by the strain. Moreover, we find that the bandgaps of MoS2/n-h-BN heterostructures decrease with increasing number of h-BN layers, which is proposed to result from the different strain distributions in MoS2 due to the varieties of lattice mismatch rates between MoS2 and h-BN layers. Our results suggest that the MoS2/n-h-BN heterostructure could serve as a prototypical example for band structure engineering of 2D crystals with atomic layer precision. (paper)
Cheng-yuan Liu; Tao Jiang; Su, C
2013-01-01
In this study, a novel Ultra-wideband (UWB) bandpass filter with single notched band based Microstrip line and Coplanar Waveguide (CPW) Hybrid Structure is presented which can effectively restrain the electromagnetic interference between systems, to ensure immunity of the system. The proposed filter is based on microstrip-fed CPW resonant structure, among which, two identical structure microstrip feeder and open-ended coplanar waveguide are located in the upper and lower layers of the dielect...
Energy density of self-field-dominated plasma structures
International Nuclear Information System (INIS)
Linear dimensions and internal structure of high-density plasma lumps ejected in any direction 0 degree ? ? ? 90 degree from the pinch region of plasma focus discharges (electrode axis at ? = 0 degree) are recorded via plasma contact prints on CR-39 targets and ion filters. The internal structure is displayed by the nonuniform distribution of D+ etched tracks (ion energy E ? 1.5 MeV) which form the image on the target. The impacting-plasma structure from the low-energy ions (E ? 50 keV) is obtained via oxidation of dangling bonds in the surface layers of monocrystals silicon targets. The scaling of pinch emission parameters with the capacitor bank energy W, is tested on three plasma focus machines (6 kJ ? W ? 30 kJ). The image spatial resolution is ? 10 ?m on the CR-39, and better than 1 ?m on the silicon targets
Two-dimensional microwave band-gap structures of different dielectric materials
Indian Academy of Sciences (India)
E D V Nagesh; G Santosh Babu; V Subramanian; V Sivasubramanian; V R K Murthy
2005-12-01
We report the use of low dielectric constant materials to form two-dimensional microwave band-gap structures for achieving high gap-to-midgap ratio. The variable parameters chosen are the lattice spacing and the geometric structure. The selected geometries are square and triangular and the materials chosen are PTFE ($\\varepsilon = 2.1$), PVC ($\\varepsilon = 2.38$) and glass ($\\varepsilon = 5.5$). Using the plane-wave expansion method, proper lattice spacing is selected for each structure and material. The observed experimental results are analyzed with the help of the theoretical prediction.
Medium- and high-spin band structure of the chiral-candidate nucleus 134Pr
International Nuclear Information System (INIS)
Medium- and high-spin states of 134Pr were populated using the 116Cd(23Na,5n) reaction and studied with the GAMMASPHERE spectrometer. Several new bands have been found in this nucleus, one of them being linked to the previously observed chiral-candidate twin-band structure. The ground state of 134Pr could be determined through establishing a level structure that connects the two previously known long-lived isomeric states. Unambiguous spin-parity assignments for the excited states could be performed based on the known 2- spin-parity of the ground state combined with the present experimental data. Intrinsic single-particle configurations have been assigned to the newly observed bands on the basis of the measured B(M1)/B(E2) ratios, alignments, band-crossing frequencies, bandhead spins, the observed single-particle configurations in the neighboring nuclei, and taking into account the predictions of total Routhian surface and tilted-axis cranking calculations.
DEFF Research Database (Denmark)
Islam, M. Fhokrul; Bohr, Henrik
2008-01-01
Beyond the second row of elements in the Mendeleev periodic table, the consideration of the relativistic effect is important in determining proper configurations of atoms and ions, in many cases. Many important quantities of interest in determining physical and chemical properties of matter, such as the effective charge, root mean square radii, and higher moments of radii used in many calculations, e.g. in the determinations of legend stabilization bond energies depend on whether the treatment is relativistic or not. In general, these quantities for a given l-orbital having two different j-values, e.g. d(3/2) and d(5/2), differ from each other, hence, making it necessary to treat them as separate orbitals. This also necessitates characterizing bands with their j-values in many instants and not l-values, particularly for "d" and f-orbitals. For example, in Au, 5d(3/2) and 5d(5/2) are to be dealt with as two distinct bands. The observed enhancement of laser induced field emission in W, which is not understood in terms of non-relativistic band-structures, can be explained in terms of the expected relativistic band structure. Spin-orbit coupling, which is the manifestation of the relativistic effect, is a prime factor in facilitating intersystem crossing in bio-molecules.
Shinozuka, Yuzo; Oda, Masato
2015-09-01
The interacting quasi-band model proposed for electronic states in simple alloys is extended for compound semiconductor alloys with general lattice structures containing several atoms per unit cell. Using a tight-binding model, a variational electronic wave function for quasi-Bloch states yields a non-Hermitian Hamiltonian matrix characterized by matrix elements of constituent crystals and concentration of constituents. Solving secular equations for each k-state yields the alloy’s energy spectrum for any type of randomness and arbitrary concentration. The theory is used to address III-V (II-VI) alloys with a zincblende lattice with crystal band structures well represented by the sp3s* model. Using the resulting 15 × 15 matrix, the concentration dependence of valence and conduction bands is calculated in a unified scheme for typical alloys: Al1-xGaxAs, GaAs1-xPx, and GaSb1-xPx. Results agree well with experiments and are discussed with respect to the concentration dependence, direct-indirect gap transition, and band-gap-bowing origin.
The structure of an active acoustic metamaterial with tunable effective density
Energy Technology Data Exchange (ETDEWEB)
Baz, A [Mechanical Engineering Department, University of Maryland, College Park, MD (United States)], E-mail: baz@umd.edu
2009-12-15
A new class of one-dimensional active acoustic metamaterials (AAMMs) with programmable effective densities is presented. The proposed AAMM is capable of producing densities that are orders of magnitudes lower or higher than the ambient fluid. Such characteristics are achieved by using an array of fluid cavities separated by piezoelectric diaphragms that are controlled to generate constant densities over wide frequency bands. The piezodiaphragms are augmented with passive electrical components to broaden the operating frequency bandwidth and enable densities higher than the fluid medium to be generated. The use of these components is shown to be essential to maintain the closed-loop compliance of the piezodiaphragm away from the zone of elastic instabilities. The values of the passive components are selected on a rational basis in order to ensure a balance between the frequency bandwidth and control voltage. With this unique structure of the AAMM, physically realizable acoustic cloaks can be implemented and objects treated with these active metamaterials can become acoustically invisible.
The structure of an active acoustic metamaterial with tunable effective density
International Nuclear Information System (INIS)
A new class of one-dimensional active acoustic metamaterials (AAMMs) with programmable effective densities is presented. The proposed AAMM is capable of producing densities that are orders of magnitudes lower or higher than the ambient fluid. Such characteristics are achieved by using an array of fluid cavities separated by piezoelectric diaphragms that are controlled to generate constant densities over wide frequency bands. The piezodiaphragms are augmented with passive electrical components to broaden the operating frequency bandwidth and enable densities higher than the fluid medium to be generated. The use of these components is shown to be essential to maintain the closed-loop compliance of the piezodiaphragm away from the zone of elastic instabilities. The values of the passive components are selected on a rational basis in order to ensure a balance between the frequency bandwidth and control voltage. With this unique structure of the AAMM, physically realizable acoustic cloaks can be implemented and objects treated with these active metamaterials can become acoustically invisible.
Directory of Open Access Journals (Sweden)
Yano Akira
2012-11-01
Full Text Available Abstract Background Plant growth and development depend on the availability of light. Lighting systems therefore play crucial roles in plant studies. Recent advancements of light-emitting diode (LED technologies provide abundant opportunities to study various plant light responses. The LED merits include solidity, longevity, small element volume, radiant flux controllability, and monochromaticity. To apply these merits in plant light response studies, a lighting system must provide precisely controlled light spectra that are useful for inducing various plant responses. Results We have developed a plant lighting system that irradiated a 0.18 m2 area with a highly uniform distribution of photon flux density (PFD. The average photosynthetic PFD (PPFD in the irradiated area was 438 micro-mol m–2 s–1 (coefficient of variation 9.6%, which is appropriate for growing leafy vegetables. The irradiated light includes violet, blue, orange-red, red, and far-red wavelength bands created by LEDs of five types. The PFD and mixing ratio of the five wavelength-band lights are controllable using a computer and drive circuits. The phototropic response of oat coleoptiles was investigated to evaluate plant sensitivity to the light control quality of the lighting system. Oat coleoptiles irradiated for 23 h with a uniformly distributed spectral PFD (SPFD of 1 micro-mol m–2 s–1 nm–1 at every peak wavelength (405, 460, 630, 660, and 735 nm grew almost straight upwards. When they were irradiated with an SPFD gradient of blue light (460 nm peak wavelength, the coleoptiles showed a phototropic curvature in the direction of the greater SPFD of blue light. The greater SPFD gradient induced the greater curvature of coleoptiles. The relation between the phototropic curvature (deg and the blue-light SPFD gradient (micro-mol m–2 s–1 nm–1 m–1 was 2 deg per 1 micro-mol m–2 s–1 nm–1 m–1. Conclusions The plant lighting system, with a computer with a graphical user interface program, can control the PFD and mixing ratios of five wavelength-band lights. A highly uniform PFD distribution was achieved, although an intentionally distorted PFD gradient was also created. Phototropic responses of oat coleoptiles to the blue light gradient demonstrated the merit of fine controllability of this plant lighting system.
Zong, YiXin; Xia, JianBai
2015-07-01
The plane-wave expansion (PWE) method is employed to calculate the photonic band structures of metal/dielectric (M/D) periodic systems. We consider a one-dimensional (1D)M/D superlattice with ametal layer characterized by a frequency-dependent dielectric function. To calculate the photonic band of such a system, we propose a new method and thus avoid solving the nonlinear eigenvalue equations. We obtained the frequency dispersions and the energy distributions of eigen-modes of 1D superlattices. This general method is applicable to calculate the photonic band of a broad class of physical systems, e.g. 2D and 3D M/D photonic crystals. For comparison, we present a simple introduction of the finite-difference (FD) method to calculate the same system, and the agreement turns out to be good. But the FD method cannot be applied to the TM modes of the M/D superlattice.
Energy Technology Data Exchange (ETDEWEB)
Saini, Hardev S.; Singh, Mukhtiyar [Department of Physics, Kurukshetra University, Kurukshetra 136119 (Haryana) (India); Reshak, Ali H. [School of Complex Systems, FFWP - South Bohemia University, 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); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra 136119 (Haryana) (India)
2012-03-25
Highlights: Black-Right-Pointing-Pointer These compounds are characterized as narrow band gap semiconductors with a maximum gap (1.27 eV) for ZnGeAs{sub 2}. Black-Right-Pointing-Pointer A good agreement of band gaps with experiments is obtained within mBJLDA formalism. Black-Right-Pointing-Pointer The band gap decreases with the substitution of either one or both cations in reference compound, ZnGeAs{sub 2}. Black-Right-Pointing-Pointer The ionic/covalent character for A-As/B-As bond has been described on the basis of electro-negativity difference of the atoms. Black-Right-Pointing-Pointer The d-states of transition metal, Zn are localized deeper in valence band (E < 5 eV), showing no effective role to decide the magnitude of semiconducting band gap. - Abstract: The electronic properties of ABAs{sub 2} (A = Zn, Cd; B = Ge, Sn) compounds have been investigated using WIEN2k implementation of full potential linearized augmented plane wave (FPLAPW) method with an aim to study the effect of changing local environment by substituting cation(s) with corresponding next group element in reference compound (ZnGeAs{sub 2}) on these properties. The exchange and correlation (XC) effects are taken into account by an orbital independent modified Becke-Johnson (mBJ) potential as coupled with Local Density Approximation (LDA) for these calculations. We predict a direct band gap in all these compounds and observe that the band gap decreases with the change of either one or both cations. The calculated band gaps are in better agreement with corresponding experimental ones as compared to other calculations. The electronic band structure is analyzed in terms of contributions from various electrons and the covalency of two bonds, Zn-As and Ge-As has been discussed with respect to substitutions.
Zhong, Hong-Xia; Shi, Jun-Jie; Yang, Li
2015-01-01
We report many-body perturbation theory calculations of excited-state properties of distorted 1-T diamond-chain monolayer rhenium disulfide (ReS2) and diselenide (ReSe2). Electronic self-energy substantially enhances their quasiparticle band gaps and, surprisingly, converts monolayer ReSe2 to a direct-gap semiconductor, which was, however, regarded to be an indirect one by density-functional-theory calculations. Their optical absorption spectra are dictated by strongly bound excitons. Unlike hexagonal structures, the lowest-energy bright exciton of distorted 1-T ReS2 exhibits a perfect figure-8 shape polarization dependence but those of ReSe2 only exhibit a partial polarization dependence, which results from two nearly-degenerated bright excitons whose polarization preferences are not aligned. Our first-principles calculations are in agreement with experiments and pave the way for optoelectronic applications.
Band structure and electronic properties of the incommensurate misfit compound (LaS)1.18VS2
International Nuclear Information System (INIS)
The electronic properties of the incommensurate misfit compound (LaS)1.18VS2 are investigated by different methods. Linear muffin-tin orbital atomic-sphere approximation band-structure calculation shows that this material should be a metal with a Fermi level located near a minimum of the density of states. Experimentally, the electrical resistivity is hopping-like while the magnetic susceptibility is metallic-like with a strong enhancement. We suggest that these paradoxical properties can be reconciled by taking into account the effects of incommensurability and electronic correlations. A comparison with commensurate LiVS2 and with Ti or Cr incommensurate misfit derivatives is discussed. (author)
Analysis of the Band-Structure in (Ga, MnAs Epitaxial Layers by Optical Methods
Directory of Open Access Journals (Sweden)
O. Yastrubchak
2012-03-01
Full Text Available The ternary III-V semiconductor (Ga, MnAs has recently drawn a lot of attention as the model diluted ferromagnetic semiconductor, combining semiconducting properties with magnetism. (Ga, MnAs layers are usually gown by the low-temperature molecular-beam epitaxy (LT-MBE technique. Below a magnetic transition temperature, TC, substitutional Mn2+ ions are ferromagnetically ordered owing to interaction with spin-polarized holes. However, the character of electronic states near the Fermi energy and the electronic structure in ferromagnetic (Ga, MnAs are still a matter of controversy. The photoreflectance (PR spectroscopy was applied to study the band-structure evolution in (Ga, MnAs layers with increasing Mn content. We have investigated thick (800-700 nm and 230-300 nm (Ga, MnAs layers with Mn content in the wide range from 0.001 % to 6 % and, as a reference, undoped GaAs layer, grown by LT-MBE on semi-insulating (001 GaAs substrates. Our findings were interpreted in terms of the model, which assumes that the mobile holes residing in the valence band of ferromagnetic (Ga, MnAs and the Fermi level position determined by the concentration of valence-band holes. The ternary III-V semiconductor (Ga, MnAs has recently drawn a lot of attention as the model diluted ferromagnetic semiconductor, combining semiconducting properties with magnetism. (Ga, MnAs layers are usually gown by the low-temperature molecular-beam epitaxy (LT-MBE technique. Below a magnetic transition temperature, TC, substitutional Mn2+ ions are ferromagnetically ordered owing to interaction with spin-polarized holes. However, the character of electronic states near the Fermi energy and the electronic structure in ferromagnetic (Ga, MnAs are still a matter of controversy. The photoreflectance (PR spectroscopy was applied to study the band-structure evolution in (Ga, MnAs layers with increasing Mn content. We have investigated thick (800-700 nm and 230-300 nm (Ga, MnAs layers with Mn content in the wide range from 0.001 % to 6 % and, as a reference, undoped GaAs layer, grown by LT-MBE on semi-insulating (001 GaAs substrates. Our findings were interpreted in terms of the model, which assumes that the mobile holes residing in the valence band of ferromagnetic (Ga, MnAs and the Fermi level position determined by the concentration of valence-band holes. The ternary III-V semiconductor (Ga, MnAs has recently drawn a lot of attention as the model diluted ferromagnetic semiconductor, combining semiconducting properties with magnetism. (Ga, MnAs layers are usually gown by the low-temperature molecular-beam epitaxy (LT-MBE technique. Below a magnetic transition temperature, TC, substitutional Mn2+ ions are ferromagnetically ordered owing to interaction with spin-polarized holes. However, the character of electronic states near the Fermi energy and the electronic structure in ferromagnetic (Ga, MnAs are still a matter of controversy. The photoreflectance (PR spectroscopy was applied to study the band-structure evolution in (Ga, MnAs layers with increasing Mn content. We have investigated thick (800-700 nm and 230-300 nm (Ga, MnAs layers with Mn content in the wide range from 0.001 % to 6 % and, as a reference, undoped GaAs layer, grown by LT-MBE on semi-insulating (001 GaAs substrates. Our findings were interpreted in terms of the model, which assumes that the mobile holes residing in the valence band of ferromagnetic (Ga, MnAs and the Fermi level position determined by the concentration of valence-band holes.
Energy-band structure of NbC studied with angle-resolved photoelectron spectroscopy
International Nuclear Information System (INIS)
The (100) face of NbC/sub 0.83/ has been studied using angle-resolved photoelectron spectroscopy and synchrotron radiation as the excitation source. The experimental results are compared with the theoretical energy-band structure calculated for stoichiometric NbC using the linear augmented-plane-wave method. A good agreement between theory and experiment is found for the main structures in the experimental spectra. The origin of the experimental features that cannot be explained by the calculated energy bands is discussed in terms of surface and vacancy-induced effects. A resonant enhancement of the emission close to the Fermi energy at photon energies above the Nb 4p threshold is presented and discussed
Deformed configurations, band structures and spectroscopic properties of $N = 50$ Ge and Se nuclei
Indian Academy of Sciences (India)
S K Ghorui; C R Praharaj
2014-04-01
The deformed configurations and rotational band structures in $N=50$ Ge and Se nuclei are studied by deformed Hartree–Fock with quadrupole constraint and angular momentum projection. Apart from the `almost’ spherical HF solution, a well-deformed configuration occurs at low excitation. A deformed well-mixed $\\Omega = 1/2^+$ neutron orbit comes down in energy (from the shell above $N = 50$) to break the $N = 50$ spherical shell closure. A = 7? isomer is predicted in 84Se at fairly low excitation energy. At higher excitation energies (8 MeV), a deformed band with = 7/2+–1/2? (based on $h_{11/2}$) neutron 1p–1h excitation, for 82Ge and 84Se, is shown in our calculation. Our study gives insight into possible deformed structures at spherical shell closure.
Optical properties and electronic band structure of Cu2ZnSnSe4kesterite semiconductor
International Nuclear Information System (INIS)
Optical properties of a kesterite-type semiconductor Cu2ZnSnSe4 have been studied by optical absorption, spectroscopic ellipsometry, and thermoreflectance measurements. Optical absorption measurements suggest that Cu2ZnSnSe4 is a direct-gap semiconductor having the band gap of ?1.02 eV at 300 K. The complex dielectric-function spectra, ? (E)=?1(E)+i?2(E), measured by spectroscopic ellipsometry reveal distinct structures at energies of the critical points in the Brillouin zone. Thermoreflectance spectrum facilitates the precision determination of the critical point energy. By performing the band-structure calculation, these critical points are successfully assigned to specific points in the Brillouin zone (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Tight binding electronic band structure calculation of achiral boron nitride single wall nanotubes
International Nuclear Information System (INIS)
In this paper we report the Tight-Binding method, for the electronic structure calculations of achiral single wall Boron Nitride nanotubes. We have used the contribution of ? electron only to define the electronic band structure for the solid. The Zone-folding method is used for the Brillouin Zone definition. Calculation of tight binding model parameters is done by fitting them to available experimental results of two-dimensional hexagonal monolayers of Boron Nitride. It has been found that all the boron nitride nanotubes (both zigzag and armchair) are constant gap semiconductors with a band gap of 5.27eV. All zigzag BNNTs are found to be direct gap semiconductors while all armchair nanotubes are indirect gap semiconductors. (author)
Infrared photoreflectance investigation of resonant levels and band edge structure in InSb.
Chen, Xiren; Jung, Jinwook; Qi, Zhen; Zhu, Liangqing; Park, Sehun; Zhu, Liang; Yoon, Euijoon; Shao, Jun
2015-11-15
Temperature-dependent infrared photoreflectance (PR) is employed on InSb for clarifying resonant levels (RLs) and band edge structure. Abundant PR features are well resolved around the bandgap and are verified to be of electronic inter-level transitions rather than the Franz-Keldysh oscillations. The evolution of the critical energies with temperature reveals the nature of the PR processes, from which one acceptor RL, two donor RLs, and a shallow acceptor level are quantitatively identified, and a detailed band edge structure is derived. The results show that temperature-dependent infrared PR analysis can serve as an efficient vehicle for clarifying both bound and resonant levels in semiconductors. PMID:26565858
High energy density capacitors using nano-structure multilayer technology
Energy Technology Data Exchange (ETDEWEB)
Barbee, T.W. Jr.; Johnson, G.W.; O`Brien, D.W.
1992-08-01
Today, many pulse power and industrial applications are limited by capacitor performance. While incremental improvements are anticipated from existing capacitor technologies, significant advances are needed in energy density to enable these applications for both the military and for American economic competitiveness. We propose a program to research and develop a novel technology for making high voltage, high energy density capacitors. Nano-structure multilayer technologies developed at LLNL may well provide a breakthrough in capacitor performance. Our controlled sputtering techniques are capable of laying down extraordinarily smooth sub-micron layers of dielectric and conductor materials. With this technology, high voltage capacitors with an order of magnitude improvement in energy density may be achievable. Well-understood dielectrics and new materials will be investigated for use with this technology. Capacitors developed by nano-structure multilayer technology are inherently solid state, exhibiting extraordinary mechanical and thermal properties. The conceptual design of a Notepad capacitor is discussed to illustrate capacitor and capacitor bank design and performance with this technology. We propose a two phase R&D program to address DNA`s capacitor needs for electro-thermal propulsion and similar pulse power programs. Phase 1 will prove the concept and further our understanding of dielectric materials and design tradeoffs with multilayers. Nano-structure multilayer capacitors will be developed and characterized. As our materials research and modeling prove successful, technology insertion in our capacitor designs will improve the possibility for dramatic performance improvements. In Phase 2, we will make Notepad capacitors, construct a capacitor bank and demonstrate its performance in a meaningful pulse power application. We will work with industrial partners to design full scale manufacturing and move this technology to industry for volume production.
Kotmool, K.; Bovornratanaraks, T.; Yoodee, K.
2015-10-01
An ab initio study of structural phase transformations and band structure under high pressure was performed on a ternary semiconductor, AgInTe2. Based on DFT within both LDA and GGA exchange-correlation, US-PP, and plane wave basis set, were employed for this work. Transition pressures and calculated parameters with transformation pathway was identified to be; chalcopyrite?cd-B1?cd-Cmcm, were in good agreement with experiments. We also predicted a higher pressure phase based on supercell with size 2×2×2 of B2 structure in which all the configuration of cation structures were accounted to compare and clarify its'cations-disordered state. The predicted structure probably appeared at around 40 GPa from cd-Cmcm to cd-B2. In the case of band structure calculation, NC-PP in which 4p10 electrons of In were not treated, was also employed in chalcopyrite at a pressure range of 0-4 GPa to improve a very narrow band gap of US-PP, and this failure will be discussed. Partial density of state (PDOS), and electronic population analysis were also calculated to finely investigate the electronic transition around the Fermi level. Our calculated results were in good agreement with experiments. The direct energy gap (Eg) was linearly proportional to pressure with increasing rate of 46.4 and 44.6 meV/GPa. In addition, at ambient conditions, Eg was equal to 1.02 eV and 0.95 eV for GGA and LDA, respectively. Band structure from all the calculations have shown a higher second band gap (Eg?) which could occur due to crystal-field splitting.
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.
1987-01-01
The microtubules of mature nucleated erythrocytes are organized into a marginal band that is confined to a single plane at the periphery and that contains essentially the same number of microtubule profiles in each individual cell. Developing erythrocytes can be isolated in homogeneous and synchronously developing populations from chicken embryos. For these reasons, these cells offer a particularly accessible system for study of the pathway leading to a specific microtubule structure in a nor...
Band Structures of $^{182}$ Os Studied by GCM based on 3D-CHFB
Horibata, Takatoshi; Oi, Makito; Onishi, Naoki; Ansari, Ahmad
1998-01-01
Band structure properties of $^{182}$Os are investigated through a particle number and angular momentum constrained generator coordinate(GCM) calculation based on self-consistent three-dimensional cranking solutions. From the analysis of the wave function of the lowest GCM solution, we confirm that this nucleus shows a tilted rotational motion in its yrast states, at least with the present set of force parameters of the pairing-plus-quadrupole interaction Hamiltonian. A clos...
Theoretical analysis of electronic band structure of 2- to 3-nm Si nanocrystals.
Czech Academy of Sciences Publication Activity Database
Hapala, Prokop; K?sová, Kate?ina; Pelant, Ivan; Jelínek, Pavel
2013-01-01
Ro?. 87, ?. 19 (2013), "195420-1"-"195420-13". ISSN 1098-0121 R&D Projects: GA ?R GD202/09/H041; GA ?R(CZ) GBP108/12/G108 Grant ostatní: AV?R(CZ) M100101207 Institutional support: RVO:68378271 Keywords : Si nanoparticles * electronic band structure * nanoparticles * luminescence Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.664, year: 2013
Energy Technology Data Exchange (ETDEWEB)
Khyzhun, O.Y., E-mail: khyzhun@ipms.kiev.ua [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv UA-03142 (Ukraine); Bekenev, V.L. [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv UA-03142 (Ukraine); Atuchin, V.V. [Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Galashov, E.N.; Shlegel, V.N. [Nikolaev Institute of Inorganic Chemistry, SB RAS, Novosibirsk 630090 (Russian Federation)
2013-07-15
Total and partial densities of states of the atoms constituting zinc tungstate, ZnWO{sub 4}, have been calculated using the ab initio full potential linearized augmented plane wave (FP-LAPW) method. The theoretical data reveal that main contributors in the valence band of ZnWO{sub 4} are the Zn 3d-, W 5d- and O 2p-like states: the Zn 3d- and W 5d-like states contribute mainly at the bottom, whilst the O 2p-like states at the top of the valence band, with also significant portions of contributions of the above states throughout the whole valence-band region of the tungstate under study. In addition, data of our band-structure FP-LAPW calculations indicate that the conduction band of ZnWO{sub 4} is dominated by contributions of the W 5d-like states. To verify the theoretical findings, high-quality inclusion-free ZnWO{sub 4} single crystals were specially grown along the [010] direction for the present experimental studies employing the low thermal gradient Czochralski technique. It has been established that, comparison on a common energy scale of the X-ray photoelectron valence-band spectrum and the X-ray emission bands representing the energy distribution of mainly the Zn 3d-, W 5d- and O 2p-like states of ZnWO{sub 4} confirm experimentally the present FP-LAPW theoretical data regarding the occupations of the valence band of zinc tungstate. - Graphical abstract: Display Omitted - Highlights: • Total and partial densities of states of the atoms constituting ZnWO{sub 4} are calculated. • Zn 3d and W 5d states are dominant contributors at the bottom of the valence band. • Contributions of O 2p states dominate at the top of the valence band. • Bottom of the conduction band is dominated by contributions of W 5d* states. • The theoretical results are confirmed experimentally by X-ray spectroscopy data.
A density functional theory investigation of the electronic structure and spin moments of magnetite
Noh, Junghyun
2014-08-01
We present the results of density functional theory (DFT) calculations on magnetite, Fe3O4, which has been recently considered as electrode in the emerging field of organic spintronics. Given the nature of the potential applications, we evaluated the magnetite room-temperature cubic phase in terms of structural, electronic, and magnetic properties. We considered GGA (PBE), GGA + U (PBE + U), and range-separated hybrid (HSE06 and HSE(15%)) functionals. Calculations using HSE06 and HSE(15%) functionals underline the impact that inclusion of exact exchange has on the electronic structure. While the modulation of the band gap with exact exchange has been seen in numerous situations, the dramatic change in the valence band nature and states near the Fermi level has major implications for even a qualitative interpretation of the DFT results. We find that HSE06 leads to highly localized states below the Fermi level while HSE(15%) and PBE + U result in delocalized states around the Fermi level. The significant differences in local magnetic moments and atomic charges indicate that describing room-temperature bulk materials, surfaces and interfaces may require different functionals than their low-temperature counterparts.
Single crystal growth, transport, and electronic band structure of YCoGa{sub 5}
Energy Technology Data Exchange (ETDEWEB)
Zhu, Xiangde, E-mail: xdzhu@hmfl.ac.cn [High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031 (China); Lu, Wenjian, E-mail: wjlu@issp.ac.cn [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Ning, Wei; Qu, Zhe [High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031 (China); Li, Li; Qi, T.F.; Cao, Gang [Department of Physics and Astronomy and Center for Advanced Materials, University of Kentucky, Lexington, KY 40506 (United States); Petrovic, Cedomir [Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973 (United States); Zhang, Yuheng [High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031 (China)
2013-11-25
Highlights: •Single crystals of YCoGa{sub 5} were grown from the Ga self-flux method for the first time. •No superconductivity is observed down to 1.75 K. •The s–d scattering is the major scattering mechanism for resistivity. •We figure out that the physics origin of the similar properties between YCoG{sub 5}, YbCoGa{sub 5} and LuCoGa{sub 5}. -- Abstract: Single crystal of YCoGa{sub 5} has been grown via Ga self-flux. In this paper, we report the single crystal growth, crystallographic parameters, resistivity, heat capacity, and band structure results of YCoGa{sub 5}. YCoGa{sub 5} accommodates the HoCoGa{sub 5} type structure (space group P4/mmm (No. 123), Z = 1, a = 4.2131(6) ?, c = 6.7929(13) ?, which is isostructural to the extensively studied heavy fermion superconductor system CeMIn{sub 5} (M = Co, Rh, Ir) and the unconventional superconductor PuCoGa{sub 5} with T{sub c} = 18.5 K. No superconductivity is observed down to 1.75 K. Band structure calculation results show that its band at the Fermi level is mainly composed of Co-3d and Ga-4p electrons states, which explains its similarity of physical properties to YbCoGa{sub 5} and LuCoGa{sub 5}.
Shape optimization of phononic band gap structures incorporating inertial amplification mechanisms
Yuksel, Osman; Yilmaz, Cetin
2015-10-01
The aim of this study is to obtain a wide and deep phononic gap at low frequencies in a two-dimensional periodic solid structure with embedded inertial amplification mechanisms. Size and shape optimizations are performed on the building block mechanism of the periodic structure to maximize phononic gap (stop band) width and depth. It is shown that shape optimization offers a wider and deeper gap, when both size and shape optimized mechanisms have the same mass and stiffness values. Analysis of the shape optimized mechanism is carried out using two different finite element models, one using beam elements and the other using shell elements. Both models produced similar results for the stop band width and depth. A two-dimensional periodic structure is constructed with the shape optimized building block mechanisms. Moreover, experimental and numerical frequency response results of this periodic structure are obtained. The matching frequency response results indicate that the two-dimensional periodic structure has a wide and deep phononic gap for in-plane excitations. Furthermore, due to proper selection of the out-of-plane thickness of the periodic structure, out-of-plane vibration modes do not occur within the phononic gap.
Weakly nonlinear dispersion and stop-band effects for periodic structures
DEFF Research Database (Denmark)
Sorokin, Vladislav; Thomsen, Jon Juel
Continua and structures composed of periodically repeated elements (cells) are used in many fields of science and technology. Examples of continua are composite materials, consisting of alternating volumes of substances with different properties, mechanical filters and wave guides. Examples of engineering periodic structures include some building frames, bridge trusses, cranes, railway tracks, and compound pipes. Thus dynamic analysis of spatially periodic structures is relevant for many applications, and attracts much attention. An essential feature of periodic structures is the presence of frequency band-gaps, i.e. frequency ranges in which elastic waves cannot propagate. Most existing analytical methods in the field are based on Floquet theory [1]; e.g. this holds for the classical Hill’s method of infinite determinants [1,2], and themethod of space-harmonics [3]. However, application of these methods for studying nonlinear problems isimpossible or cumbersome, since Floquet theory is applicable only for linear systems. Thus the nonlinear effects for periodic structures are not yet fully uncovered, while at the same time applications may demand effects of nonlinearity on structural response to be accounted for.The paper deals with analytically predicting dynamic response for nonlinear elastic structures with a continuous periodic variation in structural properties. Specifically, for a Bernoulli-Euler beam with aspatially continuous modulation of structural properties in the axial direction, not necessarily small, we consider the effects of weak nonlinearity on the dispersion relation and frequency band-gaps. A novel approach, the Method of Varying Amplitudes [4], is employed. This approach is inspired by the method of direct separation of motions [5], and may be considered a natural continuation of the classical methods of harmonic balance [2] and averaging [6]. It implies representing a solution in the form of a harmonic serieswith varying amplitudes, but, in contrast to averaging methods, the amplitudes are not required to varyslowly. The approach is strongly related also to Hill’s method of infinite determinants [1,2], and to the method of space-harmonics [3]. As a result, a shift of band-gaps to a higher frequency range is revealed,while the width of the band-gaps appears relatively insensitive to (weak) nonlinearity. The results are validated by numerical simulation, and explanations of the effects suggested. The work is carried out with financial support from the Danish Council for Independent Research and COFUND: DFF – 1337-00026
Large band gaps in two-dimensional phononic crystals with self-similarity structure
Gao, Nansha; Wu, Jiu Hui; Yu, Lie
2015-11-01
In this paper, we study the band gaps (BGs) of two-dimensional (2D) phononic crystals (PCs) composed of self-similarity shape inclusions embedded in the homogenous matrix. The dispersion relations, transmission spectra, and displacement fields of eigenmodes of the proposed structures are calculated by use of finite element method. Due to the simultaneous mechanisms of the Bragg scattering, the structure can exhibit low-frequency BGs, which can be effectively shifted by changing the geometries and degree of the self-similarity structure. The BGs are significantly dependent upon the geometrical parameters and degree of the self-similarity structure. It is concluded that, the PCs with self-similarity structure, can modulate the location and width of BGs. But it must be pointed out, the shape of self-similarity inclusion exercises a great influence on the BGs. The study in this paper is relevant to the design of tuning BGs and isolators in the low-frequency range.
Density of mixed alkali borate glasses: A structural analysis
International Nuclear Information System (INIS)
Density of mixed alkali borate glasses has been correlated with the glass structure. It is assumed that in such glasses each alkali oxide associates with a proportional quantity of B2O3. The number of BO3 and BO4 units related to each type of alkali oxide depends on the total concentration of alkali oxide. It is concluded that in mixed alkali borate glasses the volumes of structural units related to an alkali ion are the same as in the corresponding binary alkali borate glass. This reveals that each type of alkali oxide forms its own borate matrix and behaves as if not affected with the presence of the other alkali oxide. Similar conclusions are valid for borate glasses with three types of alkali oxide
Density of mixed alkali borate glasses: A structural analysis
Energy Technology Data Exchange (ETDEWEB)
Doweidar, H. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt)]. E-mail: hdoweidar@mans.edu.eg; El-Damrawi, G.M. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt); Moustafa, Y.M. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt); Ramadan, R.M. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt)
2005-05-15
Density of mixed alkali borate glasses has been correlated with the glass structure. It is assumed that in such glasses each alkali oxide associates with a proportional quantity of B{sub 2}O{sub 3}. The number of BO{sub 3} and BO{sub 4} units related to each type of alkali oxide depends on the total concentration of alkali oxide. It is concluded that in mixed alkali borate glasses the volumes of structural units related to an alkali ion are the same as in the corresponding binary alkali borate glass. This reveals that each type of alkali oxide forms its own borate matrix and behaves as if not affected with the presence of the other alkali oxide. Similar conclusions are valid for borate glasses with three types of alkali oxide.
Nonlinear Density Fluctuation Field Theory for Large Scale Structure
Zhang, Yang
2008-01-01
We develop the effective field theory of density fluctuations for a Newtonian self-gravitating N-body system in quasi-equilibrium, apply it to a homogeneous universe with small density fluctuations. Keeping the density fluctuation up to the second order, we obtain the nonlinear field equation of the 2-pt correlation \\xi(r), which contains the 3-pt correlation and formal ultra-violet divergences. By the Groth-Peebles hierarchical ansatz and the mass renormalization, the equation becomes closed with two new terms beyond the Gaussian approximation, and their coefficients are taken as parameters. The analytic solution is obtained in terms of the hypergeometric functions, which is checked numerically. With one single set of fixed two parameters, the correlation $\\xi(r)$ and the corresponding power spectrum P(k) match simultaneously the results from all the major surveys, such as APM, SDSS, 2dfGRS, and REFLEX. The model gives a unifying understanding of several seemingly unrelated features of large scale structure ...
Near Infrared Imaging Survey of Bok Globules: Density Structure
Kandori, R; Tamura, M; Tatematsu, K; Aikawa, Y; Naoi, T; Sugitani, K; Nakaya, H; Nagayama, T; Nagata, T; Kurita, M; Kato, D; Nagashima, C; Sato, S; Kandori, Ryo; Nakajima, Yasushi; Tamura, Motohide; Tatematsu, Ken'ichi; Aikawa, Yuri; Naoi, Takahiro; Sugitani, Koji; Nakaya, Hidehiko; Nagayama, Takahiro; Nagata, Tetsuya; Kurita, Mikio; Kato, Daisuke; Nagashima, Chie; Sato, Shuji
2005-01-01
On the basis of near-infrared imaging observations, we derived visual extinction (Av) distribution toward ten Bok globules through measurements of both the color excess (E_{H-K}) and the stellar density at J, H, and Ks (star count). Radial column density profiles for each globule were analyzed with the Bonnor-Ebert sphere model. Using the data of our ten globules and four globules in the literature, we investigated the stability of globules on the basis of xi_max, which characterizes the Bonnor-Ebert sphere as well as the stability of the equilibrium state against the gravitational collapse. We found that more than half of starless globules are located near the critical state (xi_max = 6.5 +/- 2). Thus, we suggest that a nearly critical Bonnor-Ebert sphere characterizes the typical density structure of starless globules. Remaining starless globules show clearly unstable states (xi_max > 10). Since unstable equilibrium states are not long maintained, we expect that these globules are on the way to gravitationa...
Finding and characterising WHIM structures using the luminosity density method
Nevalainen, J; Tempel, E; Branchini, E; Roncarelli, M; Giocoli, C; Heinamaki, P; Saar, E; Bonamente, M; Einasto, M; Finoguenov, A; Kaastra, J; Lindfors, E; Nurmi, P; Ueda, Y
2014-01-01
We have developed a new method to approach the missing baryons problem. We assume that the missing baryons reside in a form of Warm Hot Intergalactic Medium, i.e. the WHIM. Our method consists of (a) detecting the coherent large scale structure in the spatial distribution of galaxies that traces the Cosmic Web and that in hydrodynamical simulations is associated to the WHIM, (b) map its luminosity into a galaxy luminosity density field, (c) use numerical simulations to relate the luminosity density to the density of the WHIM, (d) apply this relation to real data to trace the WHIM using the observed galaxy luminosities in the Sloan Digital Sky Survey and 2dF redshift surveys. In our application we find evidence for the WHIM along the line of sight to the Sculptor Wall, at redshifts consistent with the recently reported X-ray absorption line detections. Our indirect WHIM detection technique complements the standard method based on the detection of characteristic X-ray absorption lines, showing that the galaxy l...
Density structure of the Horsehead nebula photo-dissociation region
Habart, E; Walmsley, C M; Teyssier, D; Pety, J
2005-01-01
We present high angular resolution images of the H$_2$ 1-0 S(1) line emission obtained with the Son of ISAAC (SOFI) at the New Technology Telescope (NTT) of the Horsehead nebula. These observations are analysed in combination with H$\\alpha$ line emission, aromatic dust, CO and dust continuum emissions. The Horsehead nebula illuminated by the O9.5V star $\\sigma$ Ori ($\\chi \\sim$ 60) presents a typical photodissociation region (PDR) viewed nearly edge-on and offers an ideal opportunity to study the gas density structure of a PDR. The H$_2$ fluorescent emission observations reveal extremely sharp and bright filaments associated with the illuminated edge of the nebula which spatially coincides with the aromatic dust emission. Analysis of the H$_2$ fluorescent emission, sensitive to both the far-UV radiation field and the gas density, in conjunction with the aromatic dust and H$\\alpha$ line emission, brings new constraints on the illumination conditions and the gas density in the outer PDR region. Furthermore, com...
Directory of Open Access Journals (Sweden)
Cheng-yuan Liu
2013-01-01
Full Text Available In this study, a novel Ultra-wideband (UWB bandpass filter with single notched band based Microstrip line and Coplanar Waveguide (CPW Hybrid Structure is presented which can effectively restrain the electromagnetic interference between systems, to ensure immunity of the system. The proposed filter is based on microstrip-fed CPW resonant structure, among which, two identical structure microstrip feeder and open-ended coplanar waveguide are located in the upper and lower layers of the dielectric substrate. The Complementary Split-Ring Resonators is embedded on the lower structure in the middle of a length of approximately 1/2 wavelength CPW which gets the adjustable notch band, thereby gaining the dual band. Experiment results demonstrated that the bandwidth of filter designed is from 3.1 to 10.6 GHz (-3 dB bandwidth, fractional bandwidth of 92% at the central frequency 6.8 GHz and the notch band can be changed optionally from 3.6 to 9 GHz.
Quasiparticle band structure for the Hubbard systems: Application to. alpha. -CeAl sub 2
Energy Technology Data Exchange (ETDEWEB)
Costa-Quintana, J.; Lopez-Aguilar, F. (Departamento de Fisica, Grupo de Electromagnetismo, Universidad Autonoma de Barcelona, Bellaterra, E-08193 Barcelona, Spain (ES)); Balle, S. (Departament de Fisica, Universitat de les Illes Balears, E-07071 Palma de Mallorca, Spain (ES)); Salvador, R. (Control Data Corporation, TALLAHASSEE, FL (USA) Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida 32306-4052 (USA))
1990-04-01
A self-energy formalism for determining the quasiparticle band structure of the Hubbard systems is deduced. The self-energy is obtained from the dynamically screened Coulomb interaction whose bare value is the correlation energy {ital U}. A method for integrating the Schroedingerlike equation with the self-energy operator is given. The method is applied to the cubic Laves phase of {alpha}-CeAl{sub 2} because it is a clear Hubbard system with a very complex electronic structure and, moreover, this system provides us with sufficient experimental data for testing our method.
Quasiparticle band structure for the Hubbard systems: Application to ?-CeAl2
International Nuclear Information System (INIS)
A self-energy formalism for determining the quasiparticle band structure of the Hubbard systems is deduced. The self-energy is obtained from the dynamically screened Coulomb interaction whose bare value is the correlation energy U. A method for integrating the Schroedingerlike equation with the self-energy operator is given. The method is applied to the cubic Laves phase of ?-CeAl2 because it is a clear Hubbard system with a very complex electronic structure and, moreover, this system provides us with sufficient experimental data for testing our method
Photonic amorphous diamond structure with a 3D photonic band gap.
Edagawa, Keiichi; Kanoko, Satoshi; Notomi, Masaya
2008-01-11
We report that a full three-dimensional (3D) photonic band gap (PBG) is formed in a photonic amorphous structure in spite of complete lack of lattice periodicity. It is numerically shown that the structure "photonic amorphous diamond" possesses a sizable 3D PBG (18% of the center frequency for Si-air dielectric contrast) and that it can confine light at a defect as strongly as conventional photonic crystals can. These findings present important new insight into the origin of 3D PBG formation and open new possibilities in developing 3D PBG materials. PMID:18232763
The Subsurface Structure and Density of Cometary Nuclei
Lamy, P. L.; Herique, A.; Toth, I.
2015-05-01
Little is known about the internal structure and density of cometary nuclei. Indirect evidences available so far are not compelling and these questions essentially remain a matter of speculation. It is therefore important to fully exploit the potential sources of information and this is particularly the case of radar observations which have the capability to probe the first few meters of cometary nuclei when they come sufficiently close to Earth. We review the available results and find that proper data are available for eight nuclei yielding their geometric radar albedo and the dielectric permittivity of their subsurface assuming that the scattering of the radar beam is predominantly specular. The range of permittivity is quite broad, extending from 1.7 to 3.1 although a more realistic interval is probably 2 to 3.1 implying pronounced diversity in the subsurface properties of cometary nuclei. A novel interpretation of these results is performed based on the calculation of the dielectric permittivity of various samples of three-phase mixtures of ice, dust and vacuum using two mixing formulas and on the introduction of ternary diagrams where the three axes correspond to the volumetric fraction of the three phases. The derived values of the permittivity supplemented by a general constraint on the dust-to-ice mass ratio define restricted regions in the ternary diagrams broadly imposing that the ice fraction lies in the range 0.1 to 0.2, the dust fraction in the range 0.2 to 0.5, and the porosity in the range 35 % to 75 %. The density of the subsurface of the considered eight nuclei is only constrained to the broad range 500 to 2000 kg m-3 due to the poorly known density of the dust phase. However, the results unambiguously reveal considerable variation among cometary nuclei of the structure and properties of their subsurface layers.
Density driven structural transformations in amorphous semiconductor clathrates
Tulk, C. A.; dos Santos, A. M.; Neuefeind, J. C.; Molaison, J. J.; Sales, B. C.; Honkimäki, V.
2015-01-01
The pressure induced crystalline collapse at 14.7 GPa of the semiconductor clathrate Sr8Ga16Ge30 and its polyamorphic structures are reported up to 35 GPa. In-situ total scattering measurements under pressure allow the direct microscopic inspection of the mechanisms associated with the pressure induced amorphization in these systems, as well as the structure of the recovered phase. It is observed that, between 14.7 and 35 GPa, the second peak in the structure factor function gradually disappears. Analysis of the radial distribution function extracted from those data indicates a systematic lengthening of the nearest-neighbor framework bonds. This feature is associated with gradual cage collapse and breakdown of the tetrahedral structure. This suggests a change in the local bonding in the high density amorphous form, similarly to that observed in other semiconductor clathrates and elemental silicon. Upon recovery from high pressure, the sample remains amorphous and, while there is some indication of the guest-host cage reforming, it does not seem that the tetrahedral coordination is fully reestablished. As such, the compression-decompression process in these systems gives rise to three distinct amorphous forms.
Density driven structural transformations in amorphous semiconductor clathrates
Energy Technology Data Exchange (ETDEWEB)
Tulk, Christopher A [ORNL; dos Santos, Antonio M. [Oak Ridge National Laboratory (ORNL); Neuefeind, Joerg C [ORNL; Molaison, Jamie J [ORNL; Sales, Brian C [ORNL; Honkimaeki, Veijo [ESRF
2015-01-01
The pressure induced crystalline collapse at 14.7 GPa and polyamorphic structures of the semiconductor clathrate Sr8Ga16Ge30 are reported up to 35 GPa. In-situ total scattering measurements under pressure allow the direct microscopic inspection of the mechanisms associated with pressure induced amorphization in these systems, as well as the structure of the recovered phase. It is observed that, between 14.7 and 35 GPa the second peak in the structure factor function gradually disappears. Analysis of the radial distribution function extracted from those data indicate that this feature is associated with gradual cage collapse and breakdown of the tetrahedral structure with the consequent systematic lengthening of the nearest-neighbor framework bonds. This suggests an overall local coordination change to an even higher density amorphous form. Upon recovery from high pressure, the sample remains amorphous, and while there is some indication of the guest-host cage reforming, it doesn't seem that the tetrahedral coordination is recovered. As such, the compresion-decompression process in this systems gives rise to three distict amorphous forms.
Kulathuraan, K; Mohanraj, K; Natarajan, B
2016-01-01
In this work, an attempt has been made to fabricate porous silicon (PS) from p-type crystalline silicon (c-Si) wafers by using the electrochemical etching process at six different current densities (40, 60, 75, 100, 125 and 150mA/cm(2)) with constant time (30min). The influence of varying current density on morphological, structural, optical and electrical properties of PS samples were analyzed by using SEM, AFM, XRD, FT-IR, PL and electrical (I-V) techniques, respectively. Microstructural images clearly showed that the average pore diameter and thickness increase with increase current densities up to 100mA/cm(2) and decrease for 125mA/cm(2). It could be related to breaking of pore walls and exposing to the next layer of c-Si. Further increase the current density about 150mA/cm(2), the average pore diameter increase as in the case of first layer (40-100mA/cm(2)) of c-Si wafer. The result is reflected in PL emission band (at 708nm) and the intensity of the emission band shifted towards red region. The X-ray diffraction pattern confirm the formation of porous silicon as appeared as a broad peak at 2?=69.3° belongs to (400) reflection. The FTIR study supports the X-ray diffraction analysis that shows the vibrational bands of S-H2 and Si-O-Si at 2109cm(-1), 915cm(-1) and 615cm(-1) and 1107cm(-1), respectively. The I-V characteristic of PS exhibited rectifying behavior with different values of ideality factor (?) and barrier height (?b). It is concluded from the experimental results that the formed pores developed up to 100mA/cm(2) in the top layer of c-Si and the formed pores exposed to the next layer of c-Si when increase the high electrochemical etching process (above 100mA/cm(2)). PMID:26186397
Hildebrandt, Erwin; Kurian, Jose; Alff, Lambert
2012-01-01
We have conducted a detailed thin film growth structure of oxygen engineered monoclinic HfO$_{2\\pm x}$ grown by reactive molecular beam epitaxy (MBE). The oxidation conditions induce a switching between ($\\bar{1}11$) and (002) texture of hafnium oxide. The band gap of oxygen deficient hafnia decreases with increasing amount of oxygen vacancies by more than 1 eV. For high oxygen vacancy concentrations, defect bands form inside the band gap that induce optical transitions and ...
Vibrational Features of Water at the Low-Density/High-Density Liquid Structural Transformations
Khusnutdinoff, Ramil M
2011-01-01
A structural transformation in water upon compression was recently observed at the temperature $T=277$~K in the vicinity of the pressure $p \\approx 2\\;000$~Atm [R.M. Khusnutdinoff, A.V. Mokshin, J. Non-Cryst. Solids \\textbf{357}, 1677 (2011)]. It was found that the transformations are related with the principal structural changes within the first two coordination shells as well as the deformation of the hydrogen-bond network. In this work we study in details the influence of these structural transformations on the vibrational molecular dynamics of water by means of molecular dynamics simulations on the basis of the model Amoeba potential ($T=290$~K, $p=1.0 \\div 10\\;000$~Atm). The equation of state and the isothermal compressibility are found for the considered ($p$,$T$)-range. The vibrational density of states extracted for $THz$-frequency range manifests the two distinct modes, where the high-frequency mode is independent on pressure whereas the low-frequency one has the strong, non-monotonic pressure-depend...
International Nuclear Information System (INIS)
The title compound was synthesized by employing high-temperature solution reaction methods at 840 °C. Single-crystal XRD analysis showed that it crystallizes in the orthorhombic noncentrosymmetric space group Fdd2, with unit cell parameters a = 13.326(3) ?, b = 14.072(3) ?, c = 10.238(2) ?, Z = 16, and V = 1919.9(7) ?3. It has two independent and interpenetrating 3D frameworks consisting of [B4O9]6? groups bridged by O atoms, with intersecting channels occupied by Na+ and Li+ cations. The IR spectrum further confirmed the presence of both BO3 and BO4 groups. UV–vis diffuse reflectance spectrum showed a band gap of about 3.88 eV. Solid-state fluorescence spectrum exhibited the maximum emission peak at around 337.8 nm. Furthermore we have performed theoretical calculations by employing the state-of-the-art all-electron full potential linearized augmented plane wave (FP-LAPW) method to solve the Kohn Sham equations. We have optimized the atomic positions taken from our XRD data by minimizing the forces. The optimized atomic positions are used to calculate the electronic band structure, the atomic site-decomposed density of states, electron charge density and the chemical bonding features. The calculated electronic band structure and densities of states suggested that this single crystal possesses a wide energy band gap of about 2.80 eV using the local density approximation, 2.91 eV by generalized gradient approximation, 3.21 eV for the Engel–Vosko generalized gradient approximation and 3.81 eV using modified Becke–Johnson potential (mBJ). This compares well with our experimentally measured energy band gap of 3.88 eV. From our calculated electron charge density distribution, we obtain an image of the electron clouds that surround the molecules in the average unit cell of the crystal. The chemical bonding features were analyzed and the substantial covalent interactions were observed between O and O, B and O, Li and O as well as Na and O atoms. -- Highlights: ? The compound synthesized by employing high-temperature solution reaction method. ? XRD analysis showed that it crystallizes in the noncentrosymmetric group Fdd2. ? The IR spectrum further confirmed the presence of both BO3 and BO4 groups. ? UV–vis diffuse reflectance spectrum showed a band gap of about 3.88 eV ? We have performed theoretical calculations by employing FP-LAPW method.
DEFF Research Database (Denmark)
Domadiya, Parthkumar Gandalal; Manconi, Elisabetta
2015-01-01
Adding periodicity to structures leads to wavemode interaction, which generates pass- and stop-bands. The frequencies at which stop-bands occur are related to the periodic nature of the structure. Thus structural periodicity can be shaped in order to design vibro-acoustic filters for reducing vibration and noise transmission. The aim of this paper is to investigate, numerically and experimentally, stop-bands in periodic one-dimensional structures. Two methods for pre-dicting stop-bands are described: the first method applies to infinite periodic structures using a wave approach; the second method deals with the evaluation of a vibration level difference (VLD) in a finite periodic structure embedded within an infinite one-dimensional waveguide. This VLD is defined to predict the performance in terms of noise and vibration insulation of periodic cells embedded in an otherwise uniform structure. Numerical examples are presented, and results are discussed and validated experimentally. Very good agreement between the numerical and experimental models in terms of stop-bands is shown. In particular, the results show that the stop-bands obtained using a wave approach (applied to a single cell of the structure) predict those obtained from the VLD of the corresponding finite periodic structure.
High power testing of X-band dielectric-loaded accelerating structures
International Nuclear Information System (INIS)
A program is under way at Argonne National Laboratory, in collaboration with the Naval Research Laboratory (NRL), to develop RF-driven dielectric-loaded accelerating (DLA) structures, with the ultimate goal of demonstrating a compact, high-gradient linear accelerator based on this technology. In this paper, we report on the most recent results from a series of high power tests that are under way at NRL's X-band Magnicon facility. The design of the latest DLA structure has been fundamentally changed from the previous generation; it now has a modular construction that separates the RF coupler from the dielectric section. In this paper we present a detailed description of the design of the new structure and of the experimental setup used during the high power tests. In addition, we will report on experimental results of high power tests carried out on an alumina-based (?=9.4) DLA structure
Bonding, structures, and band gap closure of hydrogen at high pressures
Goncharov, Alexander F; Wang, Hui; Yang, Jianjun; Struzhkin, Viktor V; Howie, Ross T; Gregoryanz, Eugene
2012-01-01
We have studied dense hydrogen and deuterium experimentally up to 320 GPa and using ab initio molecular dynamic (MD) simulations up to 370 GPa between 250 and 300 K. Raman and optical absorption spectra show significant anharmonic and quantum effects in mixed atomic and molecular dense phase IV of hydrogen. In agreement with these observations, ab initio MD simulations near 300 K show extremely large atomic motions, which include molecular rotations, hopping and even pair fluctuations suggesting that phase IV may not have a well-defined crystalline structure. The structurally diverse layers (molecular and graphene-like) are strongly coupled thus opening an indirect band gap; moreover, at 300 GPa we find fast synchronized intralayer structural fluctuations. At 370 GPa the mixed structure collapses to form a metallic molecular Cmca-4 phase, which exhibit a new interstitial valence charge bonding scheme.
HOM-Free Linear Accelerating Structure for e+ e- Linear Collider at C-Band
Kubo, K
2003-01-01
HOM-free linear acceleration structure using the choke mode cavity (damped cavity) is now under design for e sup + e sup - linear collider project at C-band frequency (5712 MHz). Since this structure shows powerful damping effect on most of all HOMs, there is no multibunch problem due to long range wakefields. The structure will be equipped with the microwave absorbers in each cells and also the in-line dummy load in the last few cells. The straightness tolerance for 1.8 m long structure is closer than 30 (micro)m for 25% emittance dilution limit, which can be achieved by standard machining and braising techniques. Since it has good vacuum pumping conductance through annular gaps in each cell, instabilities due to the interaction of beam with the residual-gas and ions can be minimized.
Scientific Electronic Library Online (English)
Clas, Persson; Omer, Nur; Magnus, Willander; Erasmo A. de Andrada e, Silva; Antonio Ferreira da, Silva.
2006-06-01
Full Text Available Electronic band-edge structure and optical properties of Si1-xGe x are investigated theoretically emloying a full-potential linearized augmented plane wave (FPLAPW) method. The exchange-correlation potential in the local density approximation (LDA) is corrected by an on-site Coulomb potential (i.e., [...] within the LDA+U SIC approach) acting asymmetrically on the atomic-like orbitals in the muffin-tin spheres. The electronic structure of the Si1-xGe x is calculated self-consistently, assuming a Td symmetrized Hamiltonian and a linear behavior of the valence-band eigenfunctions for Si, SiGe, and Ge with respect to Ge composition x, assuming randomly alloyed crystal structure. i.e., a "virtual-crystal like" approximation (VCA). We show that this approach yields accurate band-gap energies, effective masses, dielectric function, and optical properties of Si1-xGe x. We perform absorption measurements showing the band-gap energy for x
International Nuclear Information System (INIS)
The thermoelectric and thermodynamic properties of polycrystalline InxCo4Sb12 (0.0 ? x ? 0.26) skutterudites were investigated and analysed between 2 and 800 K by means of electrical resistivity, thermopower, thermal conductivity and specific heat measurements. Hall effect, sound velocity and thermal expansion measurements were also made in order to gain insights into the transport and elastic properties of these compounds. The impact of the In filling on the crystal structure as well as the thermal dynamics of the In atoms were tracked down to 4 K using powder neutron diffraction experiments. Analyses of the transport data were compared with the evolution of the electronic band structure with x determined theoretically within the Korringa–Kohn–Rostoker method with the coherent potential approximation. These calculations indicate that In gives rise to a remarkably large p-like density of states located at the conduction band edge. The electrical properties show typical trends of heavily doped semiconductors regardless of the In content. The thermal transport in CoSb3 is strongly influenced by the presence of In in the voids of the crystal structure resulting in a drop in the lattice thermal conductivity values in the whole temperature range. The low value of the Grüneisen parameter suggests that this decrease mainly originates from enhanced mass-fluctuations and point-defect scattering mechanisms. The highest thermoelectric figure of merit ZT ? 1.0 at 750 K was achieved at the maximum In filling fraction, i.e. for x = 0.26. (paper)
Hirokazu Fukidome; Takayuki Ide; Yusuke Kawai; Toshihiro Shinohara; Naoka Nagamura; Koji Horiba; Masato Kotsugi; Takuo Ohkochi; Toyohiko Kinoshita; Hiroshi Kumighashira; Masaharu Oshima; Maki Suemitsu
2014-01-01
Graphene exhibits unusual electronic properties, caused by a linear band structure near the Dirac point. This band structure is determined by the stacking sequence in graphene multilayers. Here we present a novel method of microscopically controlling the band structure. This is achieved by epitaxy of graphene on 3C-SiC(111) and 3C-SiC(100) thin films grown on a 3D microfabricated Si(100) substrate (3D-GOS (graphene on silicon)) by anisotropic etching, which produces Si(111) microfacets as wel...
Bhat, G H; Sun, Y; Palit, R
2015-01-01
Band structures of the neutron-rich Mo- and Ru-isotopes around A $\\sim $ 110 are investigated using the triaxial projected shell model (TPSM) approach employing multi-quasiparticle configuration space. The mass region under investigation depicts a rich variety of band structures with well developed $\\gamma$- and $\\gamma\\gamma$-bands, and quasiparticle excitations based on them. It is demonstrated that TPSM provides a reasonable description of most of the observed properties, in particular, detailed structure variations observed in Mo-isotopes are well reproduced in the present work.
The band structure of carbonmonoxide on 2-D Au islands on graphene
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.
An L-band widely tunable erbium-doped fiber laser with all-fiber structure
International Nuclear Information System (INIS)
We report on a widely tunable L-band erbium-doped fiber ring laser with the exploitation of an all-fiber Lyot fiber. The all-fiber Lyot filter is constructed from a polarizer, a short section of polarization-maintaining fiber and polarization controllers. Theoretical analysis shows that the laser oscillating wavelength can be tuned by changing the polarization rotation angle. By adjusting the polarization controllers, the laser can be tuned continuously over the full L band (1559.84–1603.19 nm) with a tunability of 43 nm, a side-mode suppression ratio over 44 dB, and power uniformity better than 1.2 dB. The simple and efficient tuning mechanism allows the building of inexpensive widely tunable fiber lasers with all-fiber structure. (paper)
International Nuclear Information System (INIS)
A method to retrieve characteristics of ordered particulate structures, such as photonic crystals, is proposed. It is based on the solution of the inverse problem using data on the photonic band gap (PBG). The quasicrystalline approximation (QCA) of the theory of multiple scattering of waves and the transfer matrix method (TMM) are used. Retrieval of the refractive index of particles is demonstrated. Refractive indices of the artificial opal particles are estimated using the published experimental data. - Highlights: • A method to retrieve characteristics of photonic crystals is proposed. • The method is based on the inverse problem solution using the photonic band gap data. • Retrieval of the refractive index of photonic crystal particles is demonstrated. • Retrieval results show inhomogeneous distribution of synthetic opal particle pores
Structural stability of TiO2 at high pressure in density-functional theory based calculations.
Wu, Xiang; Holbig, Eva; Steinle-Neumann, Gerd
2010-07-28
A new study on the pressure-induced phase transitions of TiO(2) has been performed using all-electron density-functional theory based computations with the projector augmented wave and the linearized augmented plane wave methods considering five experimentally observed structures. The static results yield a picture that is consistent with experiments, i.e., phase transitions with pressure are predicted as rutile --> monoclinic baddeleyite (MI) --> orthorhombic I (OI) --> cotunnite (OII) on compression, and OII --> OI --> MI --> columbite (TiO(2)II) on decompression. The elasticities of these five polymorphs are compared. Except for the baddeleyite structure, which is considerably softer than the other polymorphs, all phases show a zero pressure bulk modulus in the range of 200-240 GPa, consistent with compression results and the single crystal elastic constant; on the basis of these results we can say that the cotunnite phase is not a superhard TiO(2) polymorph as has been suggested previously. We further find that the rutile and columbite structures are energetically very similar, with the columbite structure favored slightly. All polymorphs are predicted as insulating with comparable band gaps (?1.7-2.3 eV). Crystal field splitting for the Ti 3d electronic states leads to two distinct conduction bands in rutile and TiO(2)II for energies smaller than 8 eV, while there is a single conduction band for the other high pressure structures. PMID:21399308
Structural stability of TiO2 at high pressure in density-functional theory based calculations
International Nuclear Information System (INIS)
A new study on the pressure-induced phase transitions of TiO2 has been performed using all-electron density-functional theory based computations with the projector augmented wave and the linearized augmented plane wave methods considering five experimentally observed structures. The static results yield a picture that is consistent with experiments, i.e., phase transitions with pressure are predicted as rutile ? monoclinic baddeleyite (MI) ? orthorhombic I (OI) ? cotunnite (OII) on compression, and OII ? OI ? MI ? columbite (TiO2II) on decompression. The elasticities of these five polymorphs are compared. Except for the baddeleyite structure, which is considerably softer than the other polymorphs, all phases show a zero pressure bulk modulus in the range of 200-240 GPa, consistent with compression results and the single crystal elastic constant; on the basis of these results we can say that the cotunnite phase is not a superhard TiO2 polymorph as has been suggested previously. We further find that the rutile and columbite structures are energetically very similar, with the columbite structure favored slightly. All polymorphs are predicted as insulating with comparable band gaps (?1.7-2.3 eV). Crystal field splitting for the Ti 3d electronic states leads to two distinct conduction bands in rutile and TiO2II for energies smaller than 8 eV, while there is a single conduction band for the other high pressure structures.
Structural stability of TiO{sub 2} at high pressure in density-functional theory based calculations
Energy Technology Data Exchange (ETDEWEB)
Wu Xiang; Holbig, Eva; Steinle-Neumann, Gerd, E-mail: xiang.wu@pku.edu.c [Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth D-95440 (Germany)
2010-07-28
A new study on the pressure-induced phase transitions of TiO{sub 2} has been performed using all-electron density-functional theory based computations with the projector augmented wave and the linearized augmented plane wave methods considering five experimentally observed structures. The static results yield a picture that is consistent with experiments, i.e., phase transitions with pressure are predicted as rutile {yields} monoclinic baddeleyite (MI) {yields} orthorhombic I (OI) {yields} cotunnite (OII) on compression, and OII {yields} OI {yields} MI {yields} columbite (TiO{sub 2}II) on decompression. The elasticities of these five polymorphs are compared. Except for the baddeleyite structure, which is considerably softer than the other polymorphs, all phases show a zero pressure bulk modulus in the range of 200-240 GPa, consistent with compression results and the single crystal elastic constant; on the basis of these results we can say that the cotunnite phase is not a superhard TiO{sub 2} polymorph as has been suggested previously. We further find that the rutile and columbite structures are energetically very similar, with the columbite structure favored slightly. All polymorphs are predicted as insulating with comparable band gaps ({approx}1.7-2.3 eV). Crystal field splitting for the Ti 3d electronic states leads to two distinct conduction bands in rutile and TiO{sub 2}II for energies smaller than 8 eV, while there is a single conduction band for the other high pressure structures.
Three-dimensional structure of dilute pyroclastic density currents
Andrews, B. J.
2013-12-01
Unconfined experimental density currents dynamically similar to pyroclastic density currents (PDCs) suggest that cross-stream motions of the currents and air entrainment through currents' lateral margins strongly affects PDC behavior. Experiments are conducted within an air-filled tank 8.5 m long by 6.1 m wide by 2.6 m tall. Currents are generated by feeding heated powders down a chute into the tank at controlled rates to form dilute, particle-laden, turbulent gravity currents that are fed for 30 to 600 seconds. Powders include 5 ?m aluminum oxide, 25 ?m talc, 27 ?m walnut, 76 ?m glass beads and mixtures thereof. Experiments are scaled such that Froude, densimetric and thermal Richardson, particle Stokes and Settling numbers, and thermal to kinetic energy densities are all in agreement with dilute PDCs; experiments have lower Reynolds numbers that natural currents, but the experiments are fully turbulent, thus the large scale structures should be similar. The experiments are illuminated with 3 orthogonal laser sheets (650, 532, and 450 nm wavelengths) and recorded with an array of HD video cameras and a high speed camera (up to 3000 fps); this system provides synchronous observation of a vertical streamwise and cross-stream planes, and a horizontal plane. Ambient temperature currents tend to spread out radially from the source and have long run out distances, whereas warmer currents tend to focus along narrow sectors and have shorter run outs. In addition, when warm currents lift off to form buoyant plumes, lateral spreading ceases. The behavior of short duration currents are dominated by the current head; as eruption duration increases, current transport direction tends to oscillate back and forth (this is particularly true for ambient temperature currents). Turbulent structures in the horizontal plane show air entrainment and advection downstream. Eddies illuminated by the vertical cross-stream laser sheet often show vigorous mixing along the current margins, particularly after the current head has passed. In some currents, the head can persist as a large, vertically oriented vortex long after the bulk of the current has lifted off to form a coignimbrite plume. These unconfined experiments show that three-dimensional structures can affect PDC behavior and suggest that our typical cross-sectional or 'cartoon' understanding of PDCs misses what may be very important parts of PDC dynamics.
Directory of Open Access Journals (Sweden)
Jing Ma
2015-06-01
Full Text Available Bi2Te3 is known to be an excellent thermoelectric material as well as a topological insulator. We prepare Bi 2 Te 3 { 0 1 1 ? 5 } nanosheets with a hydrothermal method and find that the interplanar spacings have a little difference though they belong to a same family of crystal planes. Then, we investigate the structural and electronic properties of Bi 2 Te 3 { 0 1 1 ? 5 } nanoribbons with one to six atomic layers by density-functional theory. The results indicate that the nanoribbons exhibit insulator with a band gap except the three-atomic-layer ribbon, which unexpectedly shows a metallic behavior with a gapless band structure.
Advanced density matrix renormalization group method for nuclear structure calculations
Legeza, Ö; Poves, A; Dukelsky, J
2015-01-01
We present an efficient implementation of the Density Matrix Renormalization Group (DMRG) algorithm that includes an optimal ordering of the proton and neutron orbitals and an efficient expansion of the active space utilizing various concepts of quantum information theory. We first show how this new DMRG methodology could solve a previous $400$ KeV discrepancy in the ground state energy of $^{56}$Ni. We then report the first DMRG results in the $pf+g9/2$ shell model space for the ground $0^+$ and first $2^+$ states of $^{64}$Ge which are benchmarked with reference data obtained from Monte Carlo shell model. The corresponding correlation structure among the proton and neutron orbitals is determined in terms of the two-orbital mutual information. Based on such correlation graphs we propose several further algorithmic improvement possibilities that can be utilized in a new generation of tensor network based algorithms.
Advanced density matrix renormalization group method for nuclear structure calculations
Legeza, Ã.-.; Veis, L.; Poves, A.; Dukelsky, J.
2015-11-01
We present an efficient implementation of the Density Matrix Renormalization Group (DMRG) algorithm that includes an optimal ordering of the proton and neutron orbitals and an efficient expansion of the active space utilizing various concepts of quantum information theory. We first show how this new DMRG methodology could solve a previous 400 keV discrepancy in the ground state energy of 56Ni. We then report the first DMRG results in the p f +g 9 /2 shell model space for the ground 0+ and first 2+ states of 64Ge which are benchmarked with reference data obtained from a Monte Carlo shell model. The corresponding correlation structure among the proton and neutron orbitals is determined in terms of two-orbital mutual information. Based on such correlation graphs we propose several further algorithmic improvement possibilities that can be utilized in a new generation of tensor network based algorithms.
Mayer, Marie Annette
New technologies motivate the development of new semiconducting materials, for which structural, electrical and chemical properties are not well understood. In addition to new materials systems, there are huge opportunities for new applications, especially in solar energy conversion. In this dissertation I explore the role of band structure engineering of semiconducting oxides for solar energy. Due to the abundance and electrochemical stability of oxides, the appropriate modification could make them appealing for applications in both photovoltaics and photoelectrochemical hydrogen production. This dissertation describes the design, synthesis and evaluation of the alloy ZnO1-xSe x for these purposes. I review several methods of band structure engineering including strain, quantum confinement and alloying. A detailed description of the band anticrossing (BAC) model for highly mismatched alloys is provided, including the derivation of the BAC model as well as recent work and potential applications. Thin film ZnOxSe1-x samples are grown by pulsed laser deposition (PLD). I describe in detail the effect of growth conditions (temperature, pressure and laser fluence) on the chemistry, structure and optoelectronic properties of ZnOxSe1-x. The films are grown using different combinations of PLD conditions and characterized with a variety of techniques. Phase pure films with low roughness and high crystallinity were obtained at temperatures below 450¢ªC, pressures less than 10-4 Torr and laser fluences on the order of 1.5 J/cm 2. Electrical conduction was still observed despite heavy concentrations of grain boundaries. The band structure of ZnO1-xSex is then examined in detail. The bulk electron affinity of a ZnO thin film was measured to be 4.5 eV by pinning the Fermi level with native defects. This is explained in the framework of the amphoteric defect model. A shift in the ZnO1-xSe x valence band edge with x is observed using synchrotron x-ray absorption and emission spectroscopy. Measurement of the optical absorption coefficient, ?, shows a significant red shift as well as an increase in the low energy density of states with x. Fitting ? revealed that the initial Se defect level is located 0.9 eV above the valence band edge and the coupling strength of the interaction is 1.2 eV. Optical reflection data are good agreement with the absorption onset at 2 eV. Taking the derivative of this data reveals experimental observation of the matrix-like band at higher energies. ZnO1-xSex is explicitly evaluated for photoelectrochemical applications. An introduction to semiconductor electrochemistry is followed by flat band, photocurrent, and spectrally resolved photocurrent measurements. The flat band measurements are in excellent agreement with the measurements of the ZnO electron affinity using bulk methods, but show that the conduction band edge of ZnO1-xSex is too low for spontaneous water splitting. Measurements of the incident photon to current conversion efficiency (IPCE) indicated that photons with energies greater than 2 eV excite carriers that do conduct and induce chemical reactions. Tandem ZnO1-xSe x/Si devices are made with a natural Ohmic contact between the p-Si and n-ZnO1-xSex. Electrochemical testing proves that the presence of the tandem photovoltaic provides an overpotential of ˜0.5 V to electrons enabling the reduction of H+ in solution. Finally, the carrier scattering and recombination lifetimes in ZnO 1-xSex are considered. Resistivity, Hall effect and Seebeck coefficient measurements are used to probe the scattering lifetime, while the recombination lifetime is investigated using photoluminescence spectroscopy. Electrochemical photocurrent measurements in light and dark are a function of the product of both lifetimes. Results indicate that significant scattering in the lateral direction does not prohibit the photoelectrochemical device from operating, but defects from high fluence growth are extremely detrimental to the recombination lifetime. A textured or otherwise irregular crystal that does not function well
Study on the energy band structure and photoelectrochemical performances of spinel Li4Ti5O12
International Nuclear Information System (INIS)
Highlights: • Spinel Li4Ti5O12 possesses more positive potential of valence band and wider band gap than TiO2. • Spinel Li4Ti5O12 displays typical n-type semiconductor characteristic and excellent UV-excitateded photocatalysis activity. • Our preliminary study will open new perspectives in investigation of other lithium-based compounds for new photocatalysts. - Abstract: Energy band structure, photoelectrochemical performances and photocatalysis activity of spinel Li4Ti5O12 are investigated for the first time in this paper. Li4Ti5O12 possesses more positive valence band potential and wider band gap than TiO2 due to its valence band consisting of Li1s and Ti3d orbitals mixed with O2p. Li4Ti5O12 shows typical photocatalysis material characteristics and excellent photocatlytic activity under UV irradiation
Energy Technology Data Exchange (ETDEWEB)
1991-12-31
This report briefly summaries our research accomplishments made during the period of July 1, 1989 to December 13, 1991. A number of significant progresses were achieved in our studies of several different classes of low-dimensional solid state materials. On the basis of tight-binding band electronic structure calculations, we investigated the electronic properties of various organic conducting salts, cuprate superconductors, and transition-metal oxide and chalcogenide metals to find structure-property correlations governing of the physical properties of these low-dimensional materials. By employing a number of different quality basis sets, we also carried out extensive ab initio SCF-MO/MP2 calculations on model molecular systems to accurately describe the weak intermolecular contact interactions governing the structures of organic donor slats and molecular crystals. Our research efforts led to about 80 publications and two important computer programs.
Energy Technology Data Exchange (ETDEWEB)
1991-01-01
This report briefly summaries our research accomplishments made during the period of July 1, 1989 to December 13, 1991. A number of significant progresses were achieved in our studies of several different classes of low-dimensional solid state materials. On the basis of tight-binding band electronic structure calculations, we investigated the electronic properties of various organic conducting salts, cuprate superconductors, and transition-metal oxide and chalcogenide metals to find structure-property correlations governing of the physical properties of these low-dimensional materials. By employing a number of different quality basis sets, we also carried out extensive ab initio SCF-MO/MP2 calculations on model molecular systems to accurately describe the weak intermolecular contact interactions governing the structures of organic donor slats and molecular crystals. Our research efforts led to about 80 publications and two important computer programs.
Electronic band structure of ZnO-rich highly mismatched ZnO1?xTex alloys
International Nuclear Information System (INIS)
We synthesized ZnO1?xTex alloys with Te composition x?structure while samples with higher Te content are polycrystalline with random grain orientation. Electron microscopy images show a random distribution of Te atoms with no observable clustering. We found that the incorporation of a small concentration of Te (x???0.003) redshifts the ZnO optical absorption edge by more than 1?eV. The minimum band gap obtained in this work is 1.8?eV for x?=?0.23. The optical properties of the alloys are explained by the modification of the valence band of ZnO, due to the anticrossing interactions of the localized Te states with the ZnO valence band extended states. Hence, the observed large band gap reduction is primarily originating from the upward shift of the valence band edge. We show that the optical data can be explained by the band anticrossing model with the localized level of Te located at 0.95?eV above the ZnO valence band and the band anticrossing coupling constant of 1.35?eV. These parameters allow the prediction of the compositional dependence of the band gap as well as the conduction and the valence band offsets in the full composition range of ZnO1?xTex alloys
On the Design of Laser Structured Ka Band Multi-Chip Module
Directory of Open Access Journals (Sweden)
Ghulam Mehdi
2013-09-01
Full Text Available The rapid prototyping of millimeter wave (MMW multi-chip module (MCM on low-cost ceramic-polymer composite substrate using laser ablation process is presented. A Ka band MCM front-end receiver is designed, fabricated and tested. The complete front-end receiver module except the IF and power distribution sections is realized on the single prescribed substrate. The measured receiver gain, noise figure and image rejection is 37 dB, 4.25 dB and 40 dB respectively. However, it deduced from the experimental results of the two front-end modules that the complex permittivity characteristics of the substrate are altered after the laser ablation process. The effective permittivity alteration phenomenon is further validated through the characterization and comparison of various laser ablated and chemically etched Ka band parallel-coupled band-pass filters. A simple and experimentally verified method is worked out to utilize the laser ablation structuring process on the prescribed substrate. It is anticipated that the proposed method can be applied to other laminated substrates as well with the prescribed manufacturing process.
Quasiparticle band structure and optical properties of NH{sub 3}BH{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Bheema Lingam, C. [School of Physics, University of Hyderabad, Hyderabad 500 046 (India); Ramesh Babu, K.; Vaitheeswaran, G. [Advanced Centre of Research in High Energy Materials (ACRHEM), University of Hyderabad, Hyderabad 500 046 (India); Tewari, Surya P. [School of Physics, University of Hyderabad, Hyderabad 500 046 (India); Advanced Centre of Research in High Energy Materials (ACRHEM), University of Hyderabad, Hyderabad 500 046 (India); Lebegue, S. [Laboratoire de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036), Institut Jean Barriol, Nancy Universite BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-les-Nancy (France)
2011-01-15
The quasiparticle band structure of the low temperature orthorhombic phase of NH{sub 3}BH{sub 3} is studied by using the GW approximation. It is found that NH{sub 3}BH{sub 3} is an insulator with a value of the band gap of 5.90 eV with GGA and of 9.60 eV with the GW approximation. Then, the optical properties of NH{sub 3}BH{sub 3} are obtained by the calculation of the dielectric function, corrected by a scissor shift operation corresponding to the GW correction on the band gap. Also, the optical anisotropy in NH{sub 3}BH{sub 3} is analyzed through the refractive index and static dielectric constants along the different crystallographic directions. Finally, it is found that the energy loss function has a prominent peak at 22.26 eV; at these frequencies (above 22.26 eV) NH{sub 3}BH{sub 3} becomes transparent. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique
Energy Technology Data Exchange (ETDEWEB)
Kevin Jerome Sutherland
2001-06-27
Over the last ten years, photonic band gap (PBG) theory and technology have become an important area of research because of the numerous possible applications ranging from high-efficiency laser diodes to optical circuitry. This research concentrates on reducing the length scale in the fabrication of layered photonic band gap structures and developing procedures to improve processing consistency. Various procedures and materials have been used in the fabrication of layered PBG structures. This research focused on an economical micro transfer molding approach to create the final PBG structure. A poly dimethylsiloxane (PDMS) rubber mold was created from a silicon substrate. It was filled with epoxy and built layer-by-layer to create a 3-D epoxy structure. This structure was infiltrated with nanoparticle titania or a titania sol-gel, then fired to remove the polymer mold, leaving a monolithic ceramic inverse of the epoxy structure. The final result was a lattice of titania rolds that resembles a face-centered tetragonal structure. The original intent of this research was to miniaturize this process to a bar size small enough to create a photonic band gap for wavelengths of visible electro-magnetic radiation. The factor limiting progress was the absence of a silicon master mold of small enough dimensions. The Iowa State Microelectronics Research Center fabricated samples with periodicities of 2.5 and 1.0 microns with the existing technology, but a sample was needed on the order of 0.3 microns or less. A 0.4 micron sample was received from Sandia National Laboratory, which was made through an electron beam lithography process, but it contained several defects. The results of the work are primarily from the 2.5 and 1.0 micron samples. Most of the work focused on changing processing variables in order to optimize the infiltration procedure for the best results. Several critical parameters were identified, ranging from the ambient conditions to the specifics of the procedure. It is believed that most critical for fabrication of high quality samples is control of the temperature of the sample during and after infiltration, and the rate and amount of time spent applying epoxy to the PDMS.
Energy band structure of CuInS2 and optical spectra of CuInS2 nanocrystals
Shabaev, A.; Mehl, M. J.; Efros, Al. L.
2015-07-01
Using first principles calculations we describe the energy band structure of bulk CuInS2. The energy band parameters for the multiband effective mass approximation that describes the band edges of this semiconductor are obtained by fitting them to the first principles spectra. Within the multiband effective mass approximation we develop a theoretical description for the structure of band-edge levels and optical properties of the CuInS2 nanocrystals. For the nanocrystals of spherical shape, the optical transitions are weakly allowed between the electron and hole ground states due to the tetragonal symmetry of the crystal lattice, resulting in a large Stokes shift of photoluminescence up to 300 meV in the smallest nanocrystals. This theory of the band-edge optical transitions in CuInS2 NCs can be applied to spherical NCs made of other chalcopyrite compounds.
Angle-resolved photoemission study of USb2: The 5f band structure
Guziewicz, E.; Durakiewicz, T.; Butterfield, M. T.; Olson, C. G.; Joyce, J. J.; Arko, A. J.; Sarrao, J. L.; Moore, D. P.; Morales, L.
2004-01-01
Single crystal antiferromagnetic USb2 was studied at 15 K by angle-resolved photoemission with an overall energy resolution of 24 meV. The measurements unambiguously show the dispersion of extremely narrow bands situated near the Fermi level. The peak at the Fermi level represents the narrowest feature observed in 5f-electron photoemission to date. The natural linewidth of the feature just below the Fermi level is not greater than 10 meV. Normal emission data indicate a three dimensional aspect to the electronic structure of this layered material.
Angle-resolved photoemission study of USb2: the 5f band structure
Guziewicz, E; Butterfield, M T; Olson, C G; Joyce, J J; Arko, A J; Sarrao, J L; Moore, D P; Morales, L
2003-01-01
Single crystal antiferromagnetic USb2 was studied at 15K by angle-resolved photoemission with an overall energy resolution of 24 meV. The measurements unambiguously show the dispersion of extremely narrow bands situated near the Fermi level. The peak at the Fermi level represents the narrowest feature observed in 5f-electron photoemission to date. The natural linewidth of the feature just below the Fermi level is not greater than 10 meV. Normal emission data indicate a three dimensional aspect to the electronic structure of this layered material.
Stojetz, B; Miko, C; Triozon, F; Forró, L; Strunk, C
2006-01-01
Magnetotransport measurements in large diameter multiwall carbon nanotubes (20-40 nm) demonstrate the competition of a magnetic-field dependent bandstructure and Altshuler-Aronov-Spivak oscillations. By means of an efficient capacitive coupling to a backgate electrode, the magnetoconductance oscillations are explored as a function of Fermi level shift. Changing the magnetic field orientation with respect to the tube axis and by ensemble averaging, allows to identify the contributions of different Aharonov-Bohm phases. The results are in qualitative agreement with numerical calculations of the band structure and the conductance.
DEFF Research Database (Denmark)
Ruaro, Andrea; Thaysen, Jesper; Jakobsen, Kaj Bjarne
2014-01-01
This work presents an application of a planar electromagnetic band gap (EBG) structure with a perspective product implementation in the back of the mind. The focus is on the integration of such structure under the constraint of space and system coexistence. It is discovered that it is possible to achieve simultaneously both the enhancement of the antenna radiation efficiency and the shrinking of its dimensions, while making the device more resilient to out-of-band electromagnetic interference (E...
Excitonic spectra and band structure of CdGa2Se4 birefractive crystals
International Nuclear Information System (INIS)
We report on the intersection of spectral dependences of refractive indices no and ne at the wavelengths 546 nm (?0) and 450 nm (?01) in CdGa2Se4 single crystals. The value of difference ?n=ne?no is equal to zero at the wavelengths involved. When placed between two crossed polarizers, the crystals of CdGa2Se4 exhibit a transmission band at the wavelength of ?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 CdGa2Se4 crystals, and other parameters of excitons and bands were determined. In the ? point of Brillouin zone the effective mass of electrons mc is equal to 0.14m0, and the effective masses of holes mv2 and mv3 are equal to 0.76m0 and 0.94m0, respectively. The hole mass mv1 depends upon the direction of wave vector k: at polarization E?c, k?a the mass mv1=1.15m0, and at polarization E?c, k?b mv1=0.84m0. The values of valence bands splitting in the center of Brillouin zone by the crystal field (?cf=49 meV) and spin–orbital interaction (?so=351 meV) were determined. The optical functions n, k, ?1 and ?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 CdGa2Se4 crystals
Role of c-axis pairs in V2O3 from the band-structure point of view
Elfimov, I. S; T. Saha-Dasgupta; Korotin, M.A.
2003-01-01
The common interpretation of the LDA band structure of V$_{2}$O$_{3}$ is that the apparent splitting of the $a_{1g}$ band into a low intensity structure deep below the Fermi energy and a high intensity feature above it, is due to the bonding-antibonding coupling of the vertical V-V pair. Using tight-binding fitting to --as well as first-principles NMTO downfolding of-- the spin-up LDA+U $a_{1g}$ band, we show that there are other hopping integrals which are equally important...
Cho, Sungjin; Kim, Boseung; Min, Dongki; Park, Junhong
2015-10-01
This paper presents a two-dimensional heat-exhaust and sound-proof acoustic meta-structure exhibiting tunable multi-band negative effective mass density. The meta-structure was composed of periodic funnel-shaped units in a square lattice. Each unit cell operates simultaneously as a Helmholtz resonator (HR) and an extended pipe chamber resonator (EPCR), leading to a negative effective mass density creating bandgaps for incident sound energy dissipation without transmission. This structure allowed large heat-flow through the cross-sectional area of the extended pipe since the resonance was generated by acoustic elements without using solid membranes. The pipes were horizontally directed to a flow source to enable small flow resistance for cooling. Measurements of the sound transmission were performed using a two-load, four-microphone method for a unit cell and small reverberation chamber for two-dimensional panel to characterize the acoustic performance. The effective mass density showed significant frequency dependent variation exhibiting negative values at the specific bandgaps, while the effective bulk modulus was not affected by the resonator. Theoretical models incorporating local resonances in the multiple resonator units were proposed to analyze the noise reduction mechanism. The acoustic meta-structure parameters to create broader frequency bandgaps were investigated using the theoretical model. The negative effective mass density was calculated to investigate the creation of the bandgaps. The effects of design parameters such as length, cross-sectional area, and volume of the HR; length and cross-sectional area of the EPCR were analyzed. To maximize the frequency band gap, the suggested acoustic meta-structure panel, small neck length, and cross-sectional area of the HR, large EPCR length was advantageous. The bandgaps became broader when the two resonant frequencies were similar.
Non-empirical energy density functional for the nuclear structure
International Nuclear Information System (INIS)
The energy density functional (EDF) formalism is the tool of choice for large-scale low-energy nuclear structure calculations both for stable experimentally known nuclei whose properties are accurately reproduced and systems that are only theoretically predicted. We highlight in the present dissertation the capability of EDF methods to tackle exotic phenomena appearing at the very limits of stability, that is the formation of nuclear halos. We devise a new quantitative and model-independent method that characterizes the existence and properties of halos in medium- to heavy-mass nuclei, and quantifies the impact of pairing correlations and the choice of the energy functional on the formation of such systems. These results are found to be limited by the predictive power of currently-used EDFs that rely on fitting to known experimental data. In the second part of this dissertation, we initiate the construction of non-empirical EDFs that make use of the new paradigm for vacuum nucleon-nucleon interactions set by so-called low-momentum interactions generated through the application of renormalization group techniques. These soft-core vacuum potentials are used as a step-stone of a long-term strategy which connects modern many-body techniques and EDF methods. We provide guidelines for designing several non-empirical models that include in-medium many-body effects at various levels of approximation, and can be handled in state-of-the art nuclear structure codes. In the present work, the first step is initiated through the adjustment of an operator representation of low-momentum vacuum interactions using a custom-designed parallel evolutionary algorithm. The first results highlight the possibility to grasp most of the relevant physics for low-energy nuclear structure using this numerically convenient Gaussian vertex. (author)
Notaros, Jelena; Popovi?, Miloš A
2015-03-15
We demonstrate a finite-difference approach to complex-wavevector band structure simulation and its use as a tool for the analysis and design of periodic leaky-wave photonic devices. With the (usually real) operating frequency and unit-cell refractive index distribution as inputs, the eigenvalue problem yields the complex-wavevector eigenvalues and Bloch modes of the simulated structure. In a two-dimensional implementation for transverse-electric fields with radiation accounted for by perfectly matched layer boundaries, we validate the method and demonstrate its use in simulating the complex-wavevector band structures and modal properties of a silicon photonic crystal waveguide, an array-antenna-inspired grating coupler with unidirectional radiation, and a recently demonstrated low-loss Bloch-mode-based waveguide crossing array. Additionally, we show the first direct solution of the recently proposed open-system low-loss Bloch modes. We expect this method to be a valuable tool in photonics design, enabling the rigorous analysis and synthesis of advanced periodic and quasi-periodic photonic devices. PMID:25768180
Energy Technology Data Exchange (ETDEWEB)
Liu, Xiaojian; Fan, Youhua, E-mail: yhfan@hit.edu.cn; An, Yumin
2013-11-15
The influences of the T-square fractal holes on the band structures of two-dimensional phononic crystals with periodic distributed void pores are studied. Through using the finite element method, the dispersion relations in the two-dimensional phonoinc crystals with different level fractal holes are illustrated. The absolute bandgap can be easily formed in the phononic crystal with high level fractal holes, but hardly for first level ones. And the frequencies of the band structure are decreased with the increase of the fractal level. By analyzing the vibration modes of the unit cell of the phononic crystal, we find the origin of the lower frequency band is due to the locally resonant mechanism. Moreover, the impacts of the size of the fractal hole on the band structure are studied.
The electronic structure and band gap of LiFePO4 and LiMnPO4
Zhou, F; Maxisch, T; Ceder, G; Morgan, D; Zhou, Fei; Kang, Kisuk; Maxisch, Thomas; Ceder, Gerbrand; Morgan, Dane
2004-01-01
Materials with the olivine LixMPO4 structure form an important new class of materials for rechargeable Li batteries. There is significant interest in their electronic properties because of the importance of electronic conductivity in batteries for high rate applications. The density of states of LixMPO4 (x = 0, 1 and M = Fe, Mn) has been determined with the ab initio GGA+U method, appropriate for these correlated electron systems. Computed results are compared with the optical gap of LiFePO4, as measured using UV-Vis-NIR diffuse reflectance spectroscopy. The results obtained from experiment (3.8-4.0 eV) and GGA+U computations (3.7 eV) are in very good agreement. However, standard GGA, without the same level of treatment of electron correlation, is shown to make large errors in predicting the electronic structure. It is argued that olivines are likely to be polaronic conductors with extrinsically determined carrier levels and that their electronic conductivity is therefore not simply related to the band gap.
Kadas, Krisztina; Kern, Georg; Hafner, Jurgen
1999-01-01
We present ab initio local-density-functional electronic structure calculations for the (111) and (-1-1-1) surfaces of cubic BN. The energetically stable reconstructions, namely the N adatom, N3 triangle models on the (111), the (2x1), boron and nitrogen triangle patterns on the (-1-1-1) surface are investigated. Band structure and properties of the surface states are discussed in detail.
International Nuclear Information System (INIS)
A path-integral calculation of the energy band structure for the sine-Gordon potential with the help of the instanton method is presented. The periodic pseudoparticle configuration obtained recently is seen to be responsible for tunneling at a finite energy which leads to the level splitting of excited states. The lowest band structure due to the tunneling of vacuum instantons is recovered from our result in the low energy limit. The above result is obtained by considering a half period of the classical solution as a kinklike configuration (with nontrivial topological charge). On the other hand if a full period of the solution is treated as a nontopological (bouncelike) pseudoparticle configuration, the imaginary parts of energy eigenvalues can be calculated. We then obtain the Bogomolny-Fateyev relation which is well known in perturbation theory at large order. The agreement of our results with those of WKB calculations also resolves a controversy concerning the method: In fact this method yields the same correct result as the method of complex paths
Effect of point defects on band-gap properties in diamond structure photonic crystals
Dai, Wei; Wang, Hong; Chen, Shibin; Li, Dichen; Zhou, Di
2012-01-01
Three dimensional diamond structure photonic crystals (PCs) with point defects fabricated by rapid prototyping and gel casting with alumina were studied at microwave frequencies. The sphere, ellipsoid, and cylinder point defects were introduced in the PCs first and it was found that the localization of electromagnetic wave is the strongest in ellipsoid point defect photonic crystals. Then, the size change of the ellipsoid point defect was studied to find out the optimal size. When the size of the ellipsoid point defect is close to one unit cell, the Q factor, which represents the localization intensity of the electromagnetic wave, will be the biggest. Based on the optimal size of ellipsoid point defect, more ellipsoid point defects were introduced into one diamond PC structure. Three point defect resonant modes were found in a photonic crystal with three ellipsoid point defects and the distance between each defect was twice of the lattice constant. A guided band was observed in the forbidden band gap in a photonic crystal with five ellipsoid point defects, in which the distance between each defect was of one lattice constant.
Collective band structure of {sup 166,168}Hf in IBM and DPPQ models
Energy Technology Data Exchange (ETDEWEB)
Gupta, J.B. [University of Delhi, Ramjas College, Delhi (India)
2013-10-15
{sup 166,168}Hf are the lightest isotopes of Hf, for which the spectral information for non-yrast levels is now available from recent experiments. The algebraic Interacting Boson Model IBM-1 is employed to reproduce their level structures and to predict the E2 transition probabilities. The pairing plus quadrupole model is used to predict their spectra and E2 transition rates and the static moments in a microscopic approach. The spin assignments I{sup {pi}} of new levels and their K-band structures are studied. The validity of the inclusion of {sup 166,168}Hf as members of a U(12) super group is studied using various empirical observables. The potential energy surfaces for the two isotopes are compared and the filling of the nucleons in Nilsson orbits is analyzed, to yield a consistent comprehensive view of the spectra of the two Z = 72 isotopes. (orig.)
The valence band structure of Ag{sub x}Rh{sub 1–x} alloy nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Yang, Anli [Synchrotron X-ray Station at SPring-8, National Institute for Materials Science (NIMS), 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Sakata, Osami, E-mail: SAKATA.Osami@nims.go.jp [Synchrotron X-ray Station at SPring-8, National Institute for Materials Science (NIMS), 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Synchrotron X-ray Group, Quantum Beam Unit, NIMS, 1-1-1 Kouto, Sayo-cho, Hyogo 679-5148 (Japan); Kusada, Kohei; Kobayashi, Hirokazu [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); Division of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Yayama, Tomoe; Ishimoto, Takayoshi [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); INAMORI Frontier Research Center, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Yoshikawa, Hideki [Surface Chemical Analysis Group, Nano Characterization Unit, NIMS, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Koyama, Michihisa [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7 Goban-cho, Chiyoda-ku, Tokyo 102-0076 (Japan); INAMORI Frontier Research Center, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); International Institute for Carbon-Neutral Energy Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); and others
2014-10-13
The valence band (VB) structures of face-centered-cubic Ag-Rh alloy nanoparticles (NPs), which are known to have excellent hydrogen-storage properties, were investigated using bulk-sensitive hard x-ray photoelectron spectroscopy. The observed VB spectra profiles of the Ag-Rh alloy NPs do not resemble simple linear combinations of the VB spectra of Ag and Rh NPs. The observed VB hybridization was qualitatively reproduced via a first-principles calculation. The electronic structure of the Ag{sub 0.5}Rh{sub 0.5} alloy NPs near the Fermi edge was strikingly similar to that of Pd NPs, whose superior hydrogen-storage properties are well known.
The valence band structure of AgxRh1–x alloy nanoparticles
International Nuclear Information System (INIS)
The valence band (VB) structures of face-centered-cubic Ag-Rh alloy nanoparticles (NPs), which are known to have excellent hydrogen-storage properties, were investigated using bulk-sensitive hard x-ray photoelectron spectroscopy. The observed VB spectra profiles of the Ag-Rh alloy NPs do not resemble simple linear combinations of the VB spectra of Ag and Rh NPs. The observed VB hybridization was qualitatively reproduced via a first-principles calculation. The electronic structure of the Ag0.5Rh0.5 alloy NPs near the Fermi edge was strikingly similar to that of Pd NPs, whose superior hydrogen-storage properties are well known.
Giant Amplification in Degenerate Band Edge Slow-Wave Structures Interacting with an Electron Beam
Othman, Mohamed A K; Figotin, Alexander; Capolino, Filippo
2015-01-01
We advance here a new amplification regime based on synchronous operation of four degenerate electromagnetic (EM) modes and the electron beam referred to as super synchronization. These four EM modes arise in a Fabry-Perot cavity (FPC) when degenerate band edge (DBE) condition is satisfied. The modes interact constructively with the electron beam resulting in superior amplification. In particular, much larger gains are achieved for smaller beam currents compared to conventional structures allowing for synchronization with only a single EM mode. We construct a mutli transmission line (MTL) model for a loaded waveguide slow-wave structure exhibiting a DBE, and investigate the phenomenon of giant gain via super synchronization using generalized Pierce model.
Engineering design and fabrication of tapered damped X-Band accelerating structures
Solodko, A; Gudkov, D; Riddone, G; Grudiev, A; Atieh, S; Taborelli, M
2011-01-01
The accelerating structures (AS) are one of the main components of the Compact LInear Collider (CLIC), under study at CERN. Each accelerating structure contains about 30 copper discs, which form the accelerating cavity. The requirements of different technical systems, such as vacuum and cooling, have to be considered during the engineering design. A fully featured AS is very challenging and requires several technologies. Different damping methods, waveguides, vacuum manifolds, slots and chokes, result in various design configurations. In the CLIC AS each cell is damped by means of four waveguides coupled to the cell. The vacuum manifolds combine a number of functions such as damping, vacuum pumping and cooling. A silicon carbide absorber, fixed inside of each manifold, is required for effective damping of Higher Order Modes (HOMs). This paper describes the engineering design of the X-band AS with damping material, and focuses on few technical solutions.
The energy band structure of A{sub x}Fe{sub 2}Se{sub 2} (A = K, Rb) superconductors
Energy Technology Data Exchange (ETDEWEB)
Zabidi, Noriza A. [Physics Department, Centre for Defence Foundation Studies, Universiti Pertahanan Nasional Malaysia, Kuala Lumpur 59200 (Malaysia); Azhan, Muhd. Z. [Defence Science Department, Faculty of Defence Science and Technology, Universiti Pertahanan Nasional Malaysia, Kuala Lumpur 59200 (Malaysia); Rosli, A. N. [Faculty of Science and Technology, Universiti Sains Islam Malaysia, Nilai 71800, Negeri Sembilan (Malaysia); Shrivastava, Keshav N. [School of Physics, University of Hyderabad, Hyderabad 500046 (India)
2014-03-05
We study the band structure of antiferromagnetic A{sub x}Fe{sub 2}Se{sub 2} (A = K, Rb) superconductors by using first-principles electronic structure calculations which is density functional theory. In the vicinity of iron-vacancy, we identify the valence electrons of A{sub x}Fe{sub 2}Se{sub 2} will be filled up to the Fermi level and no semiconducting gap is observed. Hence, the A{sub x}Fe{sub 2}Se{sub 2} is a metallic instead of semiconducting which leads to superconductivity in the orbital-selective Mott phase. Similarly, there is non-vanishing density of states at the Fermi level.
Low Density Structures in the Local Universe. I. Diffuse Agglomerates of Galaxies
Karachentsev, I D; Melnyk, O V; Elyiv, A A; Makarov, D I
2012-01-01
This paper is the first of a series considering the properties of distribution of nearby galaxies in the low density regions. Among 7596 galaxies with radial velocities V_{LG}15 degr there are 3168 field galaxies (i.e. 42%) that do not belong to pairs, groups or clusters in the Local universe. Applying to this sample the percolation method with a radius of r_0=2.8 Mpc, we found 226 diffuse agglomerates with n>=4 number of members. The structures of eight most populated objects among them (n>=25) are discussed. These non-virialized agglomerates are characterized by a median dispersion of radial velocities of about 170 km/s, the linear size of around 6 Mpc, integral K-band luminosity of 3*10^{11} L_sun, and a formal virial-mass-to-luminosity ratio of about 700 M_sun/L_sun. The mean density contrast for the considered agglomerates is only
Bonding and Band Structure of ZrS2 and ZrSe2
Isomäki, H.; von Boehm, J.
1981-08-01
The charge density transfer, the minimum optical transitions and the valence densities of states (VDOS) calculated within the X? theory with the self-consistent symmetrized orthogonalized plane wave (SCSOPW) method (? = 1, 240 OPW/k) are presented for ZrS2 and ZrSe2. A small chalcogen pz-type charge density transfer together with another one in the gap between the layers in the directions from the chalcogen atoms to the Zr atoms are associated with the interlayer bonding. The minimum optical gaps are found to be from ?2- to L1+ in agreement with Bullett's result. VDOS agree closely with the X-ray photoemission results. The importance of including the three-peaked structure of VDOS in the interpretation of the optical spectra is stressed.
Results from the CLIC X-BAND structure test program at the NLCTA
Adolphsen, Chris; Dolgashev, Valery; Laurent, Lisa; Tantawi, Sami; Wang, Faya; Wang, W Juwen; Doebert, Steffen; Grudiev, Alexej; Riddone, Germana; Wuensh, Walter; Zennaro, Riccardo; Higashi, Yasuo; Higo, Toshiyasu
2010-01-01
As part of a SLAC-CERN-KEK collaboration on high gradient X-band structure research, several prototype structures for the CLIC linear collider study have been tested using two of the high power (300 MW) X-band rf stations in the NLCTA facility at SLAC. These structures differ in terms of their manufacturing (brazed disks and clamped quadrants), gradient profile (amount by which the gradient increases along the structure which optimizes efficiency and maximizes sustainable gradient) and HOM damping (use of slots or waveguides to rapidly dissipate dipole mode energy). The CLIC goal in the next few years is to demonstrate the feasibility of a CLIC-ready baseline design and to investigate alternatives which could bring even higher efficiency. This paper summarizes the high gradient test results from the NLCTA in support of this effort.
Influence of the sequence on the ab initio band structures of single and double stranded DNA models
Bogár, Ferenc; Bende, Attila; Ladik, János
2014-06-01
The solid state physical approach is widely used for the characterization of electronic properties of DNA. In the simplest case the helical symmetry is explicitly utilized with a repeat unit containing only a single nucleotide or nucleotide pair. This model provides a band structure that is easily interpretable and reflects the main characteristic features of the single nucleotide or a nucleotide pair chain, respectively. The chemical variability of the different DNA chains is, however, almost completely neglected in this way. In the present work we have investigated the effect of the different sequences on the band structure of periodic DNA models. For this purpose we have applied the Hartree-Fock crystal orbital method for single and double stranded DNA chains with two different subsequent nucleotides in the repeat unit of former and two different nucleotide pairs in the latter case, respectively. These results are compared to simple helical models with uniform sequences. The valence and conduction bands related to the stacked nucleotide bases of single stranded DNA built up only from guanidine as well as of double stranded DNA built up only from guanidine-cytidine pairs showed special properties different from the other cases. Namely, they had higher conduction and lower valence band positions and this way larger band gaps and smaller widths of these bands. With the introduction of non-uniform guanidine containing sequences band structures became more similar to each other and to the band structures of other sequences without guanidine. The maximal bandwidths of the non-uniform sequences are considerably smaller than in the case of uniform sequences implying smaller charge carrier mobilities both in the conduction and valence bands.
Detailed structure of the outer disk around HD 169142 with polarized light in H-band
Momose, Munetake; Fukagawa, Misato; Muto, Takayuki; Takeuchi, Taku; Hashimoto, Jun; Honda, Mitsuhiko; Kudo, Tomoyuki; Okamoto, Yoshiko K; Kanagawa, Kazuhiro D; Tanaka, Hidekazu; Grady, Carol A; Sitko, Michael L; Akiyama, Eiji; Currie, Thayne; Follette, Katherine B; Mayama, Satoshi; Kusakabe, Nobuhiko; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D; Carson, Joseph C; Egner, Sebastian; Feldt, Markus; Goto, Miwa; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S; Henning, Thomas; Hodapp, Klaus W; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R; Kuzuhara, Masayuki; Kwon, Jungmi; Matsuo, Taro; McElwain, Michael W; Miyama, Shoken; Morino, Jun-Ichi; Moro-Martin, Amaya; Nishimura, Tetsuo; Pyo, Tae-Soo; Serabyn, Eugene; Suenaga, Takuya; Suto, Hiroshi; Suzuki, Ryuji; Takahashi, Yasuhiro H; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L; Watanabe, Makoto; Wisniewski, John; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide
2015-01-01
Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0.2" <= r <= 1.2", or 29 <= r <= 174 AU, is successfully detected. The azimuthally-averaged radial profile of the PI shows a double power-law distribution, in which the PIs in r=29-52 AU and r=81.2-145 AU respectively show r^{-3}-dependence. These two power-law regions are connected smoothly with a transition zone (TZ), exhibiting an apparent gap in r=40-70 AU. The PI in the inner power-law region shows a deep minimum whose location seems to coincide with the point source at \\lambda = 7 mm. This can be regarded as another sign of a protoplanet in TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution or with an irregular temperature distribution or with the combination of both. The depletion factor of surface density in the inner...
International Nuclear Information System (INIS)
A novel approach for the enhancement of nonlinear optical effects inside globular photonic crystals (PCs) is proposed and systematically studied via numerical simulations. The enhanced optical harmonic generation is associated with two- and three-dimensional PC pumping with the wavelength corresponding to different PC band-gaps. The interactions between light and the PC are numerically simulated using the finite-difference time-domain technique for solving the Maxwell's equations. Both empty and infiltrated two-dimensional PC structures are considered. A significant enhancement of harmonic generation is predicted owing to the highly efficient PC pumping based on the structural light focusing effect inside the PC structure. It is shown that a highly efficient harmonic generation could be attained for both the empty and infiltrated two- and three-dimensional PCs. We are demonstrating the ability for two times enhancement of the parametric decay efficiency, one order enhancement of the second harmonic generation, and two order enhancement of the third harmonic generation in PC structures in comparison to the nonlinear generations in appropriate homogenous media. Obviously, the nonlinear processes should be allowed by the molecular symmetry. The criteria of the nonlinear process efficiency are specified and calculated as a function of pumping wavelength position towards the PC globule diameter. Obtained criterion curves exhibit oscillating characteristics, which indicates that the highly efficient generation corresponds to the various PC band-gap pumping. The highest efficiency of nonlinear conversions could be reached for PC pumping with femtosecond optical pulses; thus, the local peak intensity would be maximized. Possible applications of the observed phenomenon are also discussed
Structural and electronic properties of SrAl2O4:Eu2+ from density functional theory calculations
International Nuclear Information System (INIS)
Highlights: •Persistent phosphor SrAl2O4:Eu2+ was synthesized and studied. •Ab initio calculations of its electronic properties were performed. •Lowest position of the Eu 4f states in the band gap was determined. •Position of the Eu 4f states agrees with the charge transfer transition. -- Abstract: A stoichiometric micro-sized powder SrAl2O4:Eu2+ was synthesized by traditional solid state reaction at 1250 °C. Low-temperature spectroscopic measurements revealed two luminescence bands at 450 nm and 512 nm; their origin was discussed. Theoretical calculations of the structural and optical properties of SrAl2O4:Eu2+ in the framework of the density functional theory (DFT) were carried out; the obtained results were compared with the corresponding experimental data. For the first time, the position of the lowest 4f states of Eu in the host’s band gap was calculated for both available Sr positions to be at about 4.5–5 eV above the top of the valence band. Reliability of this result is confirmed by good agreement with the experimental value of the O(2p)–Eu(4f) charge transfer energy, which is equal to about 4.9 eV
Structure and parametrization of stochastic maps of density matrices
International Nuclear Information System (INIS)
The most general evolution of the density matrix of a quantum system with a finite-dimensional state space is by stochastic maps which take a density matrix linearly into the set of density matrices. These dynamical stochastic maps form a linear convex set that may be viewed as supermatrices. The property of Hermiticity of density matrices renders an associated supermatrix Hermitian and hence diagonalizable. The positivity of the density matrix does not make the associated supermatrix positive though. If the map itself is positive, it is called completely positive and it has a simple parametrization. This is extended to all positive (not completely positive) maps. A general dynamical map that does not preserve the norm of the density matrices it acts on can be thought of as the contraction of a norm-preserving map of an extended system. The reconstruction of such extended dynamics is also given
Study on high-precision diffusion bonding for X-band accelerator structure
International Nuclear Information System (INIS)
In order to realize X-band accelerator structures for linear colliders, the fabrication process of a high-precision machining of disks followed by a reliable bonding with least deformation is one of the key issues to realize their tight tolerances. Through studies of various bonding technologies, we reached a copper to copper diffusion bonding technique as a suitable solution based on the present-day technologies. Based on the technique, a few structures, such as M2, with 1.3m in length and 80mm in diameter were fabricated successfully. Then aiming at a longer and thinner structure (1.8m long and 61mm in diameter), a new technique called 'pre-bonding' was invented to make the stacking/bonding technology more reliable. Main features obtained from 'pre-bonding' are a better straightness and a small disk to disk slippage by applying a large axial pressure while heating at much lower temperature than that of annealing for copper material. Key parameters, such as pressure, temperature and period were carefully studied and optimized. Based on the technology, two structures, DDS3 and RDDS1, were successfully fabricated. (author)
High-gradient experiment on X-band disk-loaded structures
International Nuclear Information System (INIS)
The high-gradient performance of two travelling-wave X-band accelerating structures 20 cm long has been studied. One of the structures, KEK, was conditioned up to an average accelerating gradient (Eav) of 68 MV/m in 600 hours, while the other, CERN, reached 85 MV/m in 50 hours. In the latter case the maximum output power was fed from the SLED system and the maximum field inside the structure was 138 MV/m. This maximum level was limited by the available power from the klystron. Operation at the Eav=50 MV/m level was found to be stable for both structures. The associated dark current at this level was less than a few ?A for CERN but 20 to 30 ?A for KEK. Since the two electrical designs are almost the same the difference in dark current must be attributed to the difference in the two fabrication techniques. Modified Fowler-Northeim plots of downstream dark current showed a change of slope, a kink, around 50 to 60 MV/m above which the field enhancement factor was substantially increased. (author)
International Nuclear Information System (INIS)
The optimized-effective-potential (OEP) method and a method developed recently by Krieger, Li, and Iafrate (KLI) are applied to the band-structure calculations of noble-gas and alkali halide solids employing the self-interaction-corrected (SIC) local-spin-density (LSD) approximation for the exchange-correlation energy functional. The resulting band gaps from both calculations are found to be in fair agreement with the experimental values. The discrepancies are typically within a few percent with results that are nearly the same as those of previously published orbital-dependent multipotential SIC calculations, whereas the LSD results underestimate the band gaps by as much as 40%. As in the LSD---and it is believed to be the case even for the exact Kohn-Sham potential---both the OEP and KLI predict valence-band widths which are narrower than those of experiment. In all cases, the KLI method yields essentially the same results as the OEP
Yang, H. Q.; Song, T. L.; Liang, X. X.; Zhao, G. J.
2015-01-01
In this work, the electronic band structure and the effective mass of the ternary alloy GaxIn1-xP are studied by the first principle calculations. The software QUANTUM ESPRESSO and the generalized gradient approximation (GGA) for the exchange correlations have been used in the calculations. We calculate the lattice parameter, band gap and effective mass of the ternary alloy GaxIn1-xP for the Ga composition x varying from 0.0 to 1.0 by the step of 0.125. The effect of the Ga composition on the lattice parameter and the electronic density of states are discussed. The results show that the lattice parameter varies with the composition almost linearly following the Vegard's law. A direct-to-indirect band-gap crossover is found to occur close to x = 0.7. The effective masses are also calculated at ?(000) high symmetry point along the [100] direction. The results show that the band gap and the electron effective mass vary nonlinearly with composition x.
International Nuclear Information System (INIS)
The presence of shear bands in the deformed material before final annealing is very important for Goss and Cube textures formation in silicon steel [S.C. Paolinelli, M.A. Cunha, J. Magn. Magn. Mater. 255 (2003) pp. 379. [1]; J.T. Park, J.A. Szpunar, Acta Mater., 51 (2003) 3037. ]. The increase of the hot-band grain size can increase the number of shear bands, which favor the nucleation of these orientations. In this work, the effect of the hot band grain size variation, promoted by varying the hot rolling finishing temperature, on final structure and magnetic properties was investigated for 3% Si alloy. It was found that the increase of the hot-band grain size increases the occurrence of shear bands and promotes an increase of ? fiber fraction and a reduction of ? fiber fraction, improving the magnetic induction. On the other hand, the final grain size is reduced when the hot-band grain size is larger than 190 ?m, deteriorating the core loss values in spite of the texture benefits. The reduction of final grain size was explained by the increase of the number of nuclei at the beginning of the recrystallization caused by the increase of shear bands in the deformed material
Energy Technology Data Exchange (ETDEWEB)
Paolinelli, Sebastiao da Costa [Research Department Arcelor Mittal Inox Brasil, Praca Primeiro de Maio, 9, Timoteo, MG-35180018 (Brazil)], E-mail: sebastiao.paolinelli@arcelormittal.com.br; Cunha, Marco Antonio da [Research Department Arcelor Mittal Inox Brasil, Praca Primeiro de Maio, 9, Timoteo, MG-35180018 (Brazil); Barros Cota, Andre [Physics Department, Redemat Universidade Federal de Ouro Preto, Campus Universitario, Ouro Preto, MG-3540000 (Brazil)
2008-10-15
The presence of shear bands in the deformed material before final annealing is very important for Goss and Cube textures formation in silicon steel [S.C. Paolinelli, M.A. Cunha, J. Magn. Magn. Mater. 255 (2003) pp. 379. [1]; J.T. Park, J.A. Szpunar, Acta Mater., 51 (2003) 3037. ]. The increase of the hot-band grain size can increase the number of shear bands, which favor the nucleation of these orientations. In this work, the effect of the hot band grain size variation, promoted by varying the hot rolling finishing temperature, on final structure and magnetic properties was investigated for 3% Si alloy. It was found that the increase of the hot-band grain size increases the occurrence of shear bands and promotes an increase of {eta} fiber fraction and a reduction of {gamma} fiber fraction, improving the magnetic induction. On the other hand, the final grain size is reduced when the hot-band grain size is larger than 190 {mu}m, deteriorating the core loss values in spite of the texture benefits. The reduction of final grain size was explained by the increase of the number of nuclei at the beginning of the recrystallization caused by the increase of shear bands in the deformed material.
Energy Technology Data Exchange (ETDEWEB)
Hong, S.Y.
2000-02-01
In search of very small band-gap polymers, the authors have quantum-chemically investigated the electronic structures of various polypentafulvalenes (PFVs) fused with six-membered rings. Geometrical parameters of the polymers were optimized through semiempirical Hartree-Fock band calculations at the Austin Model 1 (AM1) level. Electronic structures of the polymers were obtained through modified extended Hueckel band calculations by adopting AM1-optimized geometries. It is predicted that poly(di-vinylenedioxy-pentafulvalene) and poly(di-vinylenedithia-pentafulvalene) would possess nearly zero band gaps (corresponding to {lambda}{sub max}) despite their large bond-length alternation of {approximately}0.1 A. However, these polymers are expected to be very susceptible to oxidation. Poly(di-butylene-pentafulvalene) and poly(dipyrazinopentafulvalene) are estimated to possess band gaps comparable with that (1.13 eV) of PFV. The calculated band gap of poly(di-ethylenedioxy-pentafulvalene) is 0.77 eV, smaller than that of PFV by 0.36 eV. The authors explained the evolution of band gaps of the polymers through molecular orbital arguments.
International Nuclear Information System (INIS)
The effect of outdiffusion of Mn interstitials from (Ga,Mn)As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn)As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn)As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn)As, in agreement with the Zener model for ferromagnetic semiconductors
Fong, Wen-fai; Margutti, Raffaella; Zauderer, B Ashley
2015-01-01
We present a comprehensive catalog and analysis of broad-band afterglow observations for 103 short-duration gamma-ray bursts (GRBs), comprised of all short GRBs from November 2004 to March 2015 with prompt follow-up observations in the X-ray, optical, near-infrared and/or radio bands. These afterglow observations have uncovered 71 X-ray detections, 30 optical/NIR detections, and 4 radio detections. Employing the standard afterglow synchrotron model, we perform joint probability analyses for a subset of 38 short GRBs with well-sampled light curves to infer the burst isotropic-equivalent energies and circumburst densities. For this subset, we find median isotropic-equivalent gamma-ray and kinetic energies of E_gamma,iso~2x10^51 erg, and E_K,iso~(1-3)x10^51 erg, respectively, depending on the values of the model input parameters. We further find that short GRBs occur in low-density environments, with a median density of n~(3-15)x10^-3 cm^-3, and that ~80-95% of bursts have densities of less than 1 cm^-3. We inve...
Development of x-band thermionic RF electron gun using choke structure
International Nuclear Information System (INIS)
At the University of Tokyo, we are developing a compact Compton scattering X-ray source to apply to the medical application. X-band (11.424 GHz) 3.5-cell thermionic cathode RF electron gun is adopted as an electron beam injector. We chose Nd: YAG laser which can switch a wavelength and energy (532 nm/ 1.4J, 1064 nm/ 2J) as a photon source to collide the electron beam. Now, we are developing a new RF electron gun which contains new two key ideas to achieve more efficient operation. First, choke structure is adopted as an RF interceptor, which allows spring to have only to role as a stabilizer of the cathode rod, therefore stable operation will realize. Second, cylindrical waveguide is adopted as the coupler for feeding RF to the cavity. It also enables the gun to operate with few RF problems. In this presentation, we will report the details of new X-band thermionic cathode RF-gun and experimental results on cavity property measurement. (author)
Band Structures of $^{182}Os$ Studied by GCM based on 3D-CHFB
Horibata, T; Onishi, N; Ansari, A; Horibata, Takatoshi; Oi, Makito; Onishi, Naoki; Ansari, Ahmad
1999-01-01
Band structure properties of $^{182}$Os are investigated through a particle number and angular momentum constrained generator coordinate(GCM) calculation based on self-consistent three-dimensional cranking solutions. From the analysis of the wave function of the lowest GCM solution, we confirm that this nucleus shows a tilted rotational motion in its yrast states, at least with the present set of force parameters of the pairing-plus-quadrupole interaction Hamiltonian. A close examination of behavior of other GCM solutions reveals a sign of a possible occurrence of multi-band crossing in the nucleus. Furthermore, in the course of calculations, we have also found a new potential curve along the prime meridian on the globe of the $J=18\\hbar$ sphere. Along this new solution the characters of proton and neutron gap parameters get interchanged. Namely, $\\Delta_p$ almost vanishes while $\\Delta_n$ grows to a finite value close to the one corresponding to the principal axis rotation(PAR). A state in the new solution c...
SMALL-SCALE STRUCTURE OF THE INTERSTELLAR MEDIUM TOWARD ? Oph STARS: DIFFUSE BAND OBSERVATIONS
International Nuclear Information System (INIS)
We present an investigation of small-scale structure in the distribution of large molecules/dust in the interstellar medium through observations of diffuse interstellar bands (DIBs). High signal-to-noise optical spectra were recorded toward the stars ? Oph A, B, C, and DE using the University College London Echelle Spectrograph on the Anglo-Australian Telescope. The strengths of some of the DIBs are found to differ by about 5%-9% between the close binary stars ? Oph A and B, which are separated by a projected distance on the sky of only c. 344 AU. This is the first star system in which such small-scale DIB strength variations have been reported. The observed variations are attributed to differences between a combination of carrier abundance and the physical conditions present along each sightline. The sightline toward ? Oph C contains relatively dense, molecule-rich material and has the strongest ??5850 and 4726 DIBs. The gas toward DE is more diffuse and is found to exhibit weak ''C2'' (blue) DIBs and strong yellow/red DIBs. The differences in diffuse band strengths between lines of sight are, in some cases, significantly greater in magnitude than the corresponding variations among atomic and diatomic species, indicating that the DIBs can be sensitive tracers of interstellar cloud conditions.
International Nuclear Information System (INIS)
We have conducted a detailed thin film growth structure of oxygen engineered monoclinic HfO2±x grown by reactive molecular beam epitaxy. The oxidation conditions induce a switching between (111) and (002) texture of hafnium oxide. The band gap of oxygen deficient hafnia decreases with increasing amount of oxygen vacancies by more than 1 eV. For high oxygen vacancy concentrations, defect bands form inside the band gap that induce optical transitions and p-type conductivity. The resistivity changes by several orders of magnitude as a function of oxidation conditions. Oxygen vacancies do not give rise to ferromagnetic behavior.
Energy Technology Data Exchange (ETDEWEB)
Hildebrandt, Erwin; Kurian, Jose; Alff, Lambert [Institute of Materials Science, Technische Universitaet Darmstadt, 64287 Darmstadt (Germany)
2012-12-01
We have conducted a detailed thin film growth structure of oxygen engineered monoclinic HfO{sub 2{+-}x} grown by reactive molecular beam epitaxy. The oxidation conditions induce a switching between (111) and (002) texture of hafnium oxide. The band gap of oxygen deficient hafnia decreases with increasing amount of oxygen vacancies by more than 1 eV. For high oxygen vacancy concentrations, defect bands form inside the band gap that induce optical transitions and p-type conductivity. The resistivity changes by several orders of magnitude as a function of oxidation conditions. Oxygen vacancies do not give rise to ferromagnetic behavior.
DENSITY OF VIBRATIONAL STATES OF CHEMICALLY AND STRUCTURALLY DISORDERED POLYACETYLENE
Zannoni, G.; Zerbi, G.
1983-01-01
Normal mode calculations on two possible kinds of chemical disorder in trans-PA are presented. These chemical defects show characteristic localized modes, which seem to find corresponding bands in the vibrational spectra. Comparison with the literature data indicates that the vibrational assignment of trans-PA is still quite uncertain.
Topology of time-reversal invariant energy bands with adiabatic structure
Gat, Omri
2015-01-01
We classify the topology of bands defined by the energy states of quantum systems with scale separation between slow and fast degrees of freedom, invariant under fermionic time reversal. Classical phase space transforms differently from momentum space under time reversal, and as a consequence the topology of adiabatic bands is different from that of Bloch bands. We show that bands defined over a two-dimensional phase space are classified by the Chern number, whose parity must be equal to the parity of the band rank. Even-rank bands are equivalently classified by the Kane-Mele index, an integer equal to one half the Chern number.
Single-Multi-Single Mode Structure Based Band Pass/Stop Fiber Optic Filter With Tunable Bandwidth
Tripathi, Saurabh Mani; Kumar, Arun; Marin, Emmanuel; Meunier, Jean-Pierre
2010-01-01
We present a simple, efficient and easy to fabricate single-multi-single mode (SMS) fiber-based tunable bandwidth optical bandpass/bandstop filter. The device exploits the transmission characteristics of an SMS structure near its critical wavelength. Using both temperature and strain tuning, we show that the device can be switched between band pass to band stop modes and that the filter bandwidth in each mode can be dynamically tuned. We present a theoretical analysis of the observed behavior...
Band structure and Fermi surface of CeB6 studied by angle-resolved photoemission spectroscopy
International Nuclear Information System (INIS)
We report high-resolution angle-resolved photoemission spectroscopy on CeB6 to study the electronic band structure and the Fermi surface. We observed several dispersive bands located at EF-6eV binding energy, which are attributed to the B 2p and Ce 5d states. We found a large ellipsoidal electronlike Fermi surface centered at X points in the cubic Brillouin zone relevant to the quadrupolar ordering in CeB6
International Nuclear Information System (INIS)
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??m-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
Diffuse interstellar bands as probes of small-scale interstellar structure
Smith, Keith T; Sarre, Peter J
2013-01-01
We present observations which probe the small-scale structure of the interstellar medium using diffuse interstellar bands (DIBs). Towards HD 168075/6 in the Eagle Nebula, significant differences in DIB absorption are found between the two lines of sight, which are separated by 0.25 pc, and {\\lambda}5797 exhibits a velocity shift. Similar data are presented for four stars in the {\\mu} Sgr system. We also present a search for variations in DIB absorption towards {\\kappa} Vel, where the atomic lines are known to vary on scales of ~10 AU. Observations separated by ~9 yr yielded no evidence for changes in DIB absorption strength over this scale, but do reveal an unusual DIB spectrum.
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.
A Compact Narrow-Band Bandstop Filter Using Spiral-Shaped Defected Microstrip Structure
Directory of Open Access Journals (Sweden)
J. Wang
2014-04-01
Full Text Available A novel compact narrow-band bandstop filter is implemented by using the proposed spiral-shaped defected microstrip structure (SDMS in this paper. Compared with other DMSs, the presented SDMS exhibits the advantage of compact size and narrow stopband. Meanwhile, an approximate design rule of the SDMS is achieved and the effects of the dimensions on the resonant frequency and 3 dB fractional bandwidth (FBW are analyzed in detail. Both the simulation and measurement results of the fabricated bandstop filter show that it has a 10 dB stopband from 3.4 GHz to 3.6 GHz with more than 45 dB rejection at the center frequency.
The effect of spin-orbit coupling in band structure and edge states of bilayer graphene
Energy Technology Data Exchange (ETDEWEB)
Sahdan, Muhammad Fauzi; Darma, Yudi, E-mail: yudi@fi.itb.ac.id [Department of Physics, InstitutTeknologi Bandung, Jalan Ganesa 10, Bandung 40132 (Indonesia)
2015-04-16
Topological insulators are predicted to be useful ranging from spintronics to quantum computation. Graphene was first predicted to be the precursor of topological insulator by Kane-Mele. They developed a Hamiltonian model to describe the gap opening in graphene. In this work, we investigate the band structure of bilayer grapheme and also its edge states by using this model with analytical approach. The results of our calculation show that the gap opening occurs at K and K’ point in bilayer graphene.In addition, a pair of gapless edge modes occurs both in the zigzag and arm-chair configurations are no longer exist. There are gap created at the edge even though thery are very small.
The effect of spin-orbit coupling in band structure and edge states of bilayer graphene
International Nuclear Information System (INIS)
Topological insulators are predicted to be useful ranging from spintronics to quantum computation. Graphene was first predicted to be the precursor of topological insulator by Kane-Mele. They developed a Hamiltonian model to describe the gap opening in graphene. In this work, we investigate the band structure of bilayer grapheme and also its edge states by using this model with analytical approach. The results of our calculation show that the gap opening occurs at K and K’ point in bilayer graphene.In addition, a pair of gapless edge modes occurs both in the zigzag and arm-chair configurations are no longer exist. There are gap created at the edge even though thery are very small
Degeneracy and Inversion of Band Structure for Wigner Crystals on a Toroidal Helix
Zampetaki, A V; Schmelcher, P
2014-01-01
We explore the formation of Wigner crystals for charged particles on a toroidal helix. Focusing on certain commensurate cases we show that the ground state undergoes a pitchfork bifurcation from the totally symmetric polygonic to a zig-zag-like configuration with increasing radius of the helix. Remarkably, we find that for a specific value of the helix radius, below the bifurcation point, the vibrational frequency spectrum collapses to a single frequency. This allows for an essentially independent small-amplitude motion of the individual particles and consequently localized excitations can propagate in time without significant spreading. Increasing the radius beyond the degeneracy point, the band structure is inverted, with the out-of-phase oscillation mode becoming lower in frequency than the mode corresponding to the center of mass motion.
Mondal, Puja; Ghosh, Sankalpa
2015-12-01
The surface states of the three-dimensional (3D) topological insulators are described by a two-dimensional (2D) massless dirac equation. A gate-voltage-induced one-dimensional potential barrier on such surfaces creates a discrete bound state in the forbidden region outside the dirac cone. Even for a single barrier it is shown that such a bound state can create an electrostatic analogue of Shubnikov de Haas oscillation which can be experimentally observed for relatively smaller size samples. However, when these surface states are exposed to a periodic arrangement of such gate-voltage-induced potential barriers, the band structure of the same was significantly modified. This is expected to significantly alter the properties of the macroscopic system. We also suggest that, within suitable limits, the system may offer ways to control electron spin electrostatically, which may be practically useful.
Energy Technology Data Exchange (ETDEWEB)
Benam, M.R., E-mail: m_benam@pnu.ac.ir [Department of Physics, Payame Noor University, P.O. BOX 19395-3697 (Iran, Islamic Republic of); Abdoshahi, N.; Majidiyan Sarmazdeh, M. [Department of Physics, Payame Noor University, P.O. BOX 19395-3697 (Iran, Islamic Republic of)
2014-08-01
In this paper the effect of pressure on the structural and electronic properties of cubic-LaAlO{sub 3} including the equilibrium lattice constant, bulk modulus, derivative of bulk modulus and band structure have been calculated by density functional theory (DFT) using GGA, LDA, and PBEsol exchange correlation potentials. It is found that the change of the lattice constant with pressure has an exponential behavior: with increasing pressure, the lattice constant decreases first sharply at low pressures, and then more slowly at high pressures. Furthermore, the lattice constant calculated by the PBEsol method and the bulk modulus calculated by LDA and PBEsol methods are closer to the available experimental values than those obtained using other exchange correlation potentials. Regarding the electronic properties, it is shown that an increase in pressure increases the band gap, the change being 0.26 eV at 34.00 GPa. The total density of state (t-DOS) calculations demonstrate that increasing pressure has a significant effect on the core and conduction band, but little effect on the valence band. The band structure calculations indicate that, in this material, the band gap changes from indirect to direct at a pressure of about 25 GPa. Also, increasing pressure produces a clear curvature in the band structure near the bottom of the conduction band, a behavior consistent with the strong pressure dependence of the transport properties.
Tanaka, H.; Mori, S.; Morioka, N.; Suda, J.; Kimoto, T.
2014-12-01
We calculated the phonon-limited hole mobility in rectangular cross-sectional [001], [110], [111], and [112]-oriented germanium nanowires, and the hole transport characteristics were investigated. A tight-binding approximation was used for holes, and phonons were described by a valence force field model. Then, scattering probability of holes by phonons was calculated taking account of hole-phonon interaction atomistically, and the linearized Boltzmann's transport equation was solved to calculate the hole mobility at low longitudinal field. The dependence of the hole mobility on nanowire geometry was analyzed in terms of the valence band structure of germanium nanowires, and it was found that the dependence was qualitatively reproduced by considering an average effective mass and the density of states of holes. The calculation revealed that [110] germanium nanowires with large height along the [001] direction show high hole mobility. Germanium nanowires with this geometry are also expected to exhibit high electron mobility in our previous work, and thus they are promising for complementary metal-oxide-semiconductor (CMOS) applications.
International Nuclear Information System (INIS)
We calculated the phonon-limited hole mobility in rectangular cross-sectional [001], [110], [111], and [112]-oriented germanium nanowires, and the hole transport characteristics were investigated. A tight-binding approximation was used for holes, and phonons were described by a valence force field model. Then, scattering probability of holes by phonons was calculated taking account of hole-phonon interaction atomistically, and the linearized Boltzmann's transport equation was solved to calculate the hole mobility at low longitudinal field. The dependence of the hole mobility on nanowire geometry was analyzed in terms of the valence band structure of germanium nanowires, and it was found that the dependence was qualitatively reproduced by considering an average effective mass and the density of states of holes. The calculation revealed that [110] germanium nanowires with large height along the [001] direction show high hole mobility. Germanium nanowires with this geometry are also expected to exhibit high electron mobility in our previous work, and thus they are promising for complementary metal-oxide-semiconductor (CMOS) applications
Barnett, Alex H
2010-01-01
In this paper, we consider band-structure calculations governed by the Helmholtz or Maxwell equations in piecewise homogeneous periodic materials. Methods based on boundary integral equations are natural in this context, since they discretize the interface alone and can achieve high order accuracy in complicated geometries. In order to handle the quasi-periodic conditions which are imposed on the unit cell, the free-space Green's function is typically replaced by its quasi-periodic cousin. Unfortunately, the quasi-periodic Green's function diverges for families of parameter values that correspond to resonances of the empty unit cell. Here, we bypass this problem by means of a new integral representation that relies on the free-space Green's function alone, adding auxiliary layer potentials on the boundary of the unit cell itself. An important aspect of our method is that by carefully including a few neighboring images, the densities may be kept smooth and convergence rapid. This framework results in an integr...
Kogelschatz, M.; Cunge, G.; Sadeghi, N.
2006-03-01
SiCl{x} radicals, the silicon etching by-products, are playing a major role in silicon gate etching processes because their redeposition on the wafer leads to the formation of a SiOCl{x} passivation layer on the feature sidewalls, which controls the final shape of the etching profile. These radicals are also the precursors to the formation of a similar layer on the reactor walls, leading to process drifts. As a result, the understanding and modelling of these processes rely on the knowledge of their densities in the plasma. Actinometry technique, based on optical emission, is often used to measure relative variations of the density of the above mentioned radicals, even if it is well known that the results obtained with this technique might not always be reliable. To determine the validity domain of actinometry in industrial silicon-etching high density plasmas, we measure the RF source power and pressure dependences of the absolute densities of SiCl{x} (x=0{-}2), SiF and SiBr radicals, deduced from UV broad band absorption spectroscopy. These results are compared to the evolution of the corresponding actinometry signals from these radicals. It is shown that actinometry predicts the global trends of the species density variations when the RF power is changed at constant pressure (that is to say when only the electron density changes) but it completely fails if the gas pressure, hence the electron temperature, changes.
Electronic band structure of platinum low-index surfaces: an ab initio and tight-binding study. II
Scientific Electronic Library Online (English)
H.J., Herrera-Suárez; A, Rubio-Ponce; D, Olguín.
2012-02-01
Full Text Available Presentamos el cálculo de la estructura electrónica de bandas de la superficie ideal del Pt(100) y Pt(110). El cálculo se realizó utilizando la teoría del funcional de la densidad y el método de enlace fuerte. Como resultado de nuestro cálculo presentamos una discusión detallada de los estados reson [...] antes y los estados de superficie. Para la superficie ideal del Pt(100) mostramos que tanto los estados de superficie como los estados resonantes concuerdan aceptablemente con datos experimentales. Para el caso de Pt(110) hallamos que los estados resonantes y de superficie característicos de la dimensionalidad de la superficie, son independientes de la reconstrucción y se reproducen aceptablemente en nuestro cálculo. Al igual que en el trabajo anterior, utilizamos la teoría del funcional de la densidad con el método de ondas planas aumentadas, mientras que los cálculos empíricos se han hecho utilizando el método de enlace fuerte junto con el método de empalme de las funciones de Green. Abstract in english We present the calculated electronic band structure of ideal Pt(100) and Pt(110) surface by using density functional theory and the empirical tight-binding method. A detailed discussion of the surface- and resonance-states is given. It is shown that the calculated surface- and resonance-states of id [...] eal Pt(100) surfaces agree very well with the available experimental data. For Pt(110), some of the surface- and resonance-states are characteristic of the low symmetry of the surface and are identified as being independent of surface reconstruction effects. As in the previous paper, the density functional calculations were performed using the full potential linearized augmented plane wave method, and the empirical calculations were performed using the tight-binding method and Surface Green's Function Matching Method.
International Nuclear Information System (INIS)
The spontaneous emission (SE) of InGaN/GaN quantum well (QW) structure with silver(Ag) coated on the n-GaN layer has been investigated by using six-by-six K-P method taking into account the electron-hole band structures, the photon density of states of surface plasmon polariton (SPP), and the evanescent fields of SPP. The SE into SPP mode can be remarkably enhanced due to the increase of electron-hole pairs near the Ag by modulating the InGaN/GaN QW structure or increasing the carrier injection. However, the ratio between the total SE rates into SPP mode and free space will approach to saturation or slightly decrease for the optimized structures with various distances between Ag film and QW layer at a high injection carrier density. Furthermore, the Ga-face QW structure has a higher SE rate than the N-face QW structure due to the overlap region of electron-hole pairs nearer to the Ag film.
A Spectroscopic Study of Hydra I: The Possible Progenitor of the Eastern Banded Structure
Kimmig, Brian; Hargis, Jonathan R.; Willman, Beth; Caldwell, Nelson; Strader, Jay; Walker, Matthew G.
2015-01-01
We present initial results of an MMT/Hectochelle spectroscopic study of the Hydra I spatial overdensity located along the Eastern Banded Structure (EBS) stellar stream. The extended double-lobed structure and strength of the overdensity suggest that Hydra I may be the stream's progenitor and undergoing active disruption. With its distance of only ~10 kpc, Hydra I presents a unique opportunity to study the disruption of a star cluster or dwarf galaxy. In past work, SDSS/SEGUE velocities revealed Hydra I to be a kinematically cold structure. However, the small number of candidate members and the significant SEGUE velocity uncertainties (~10 - 15 km/s) precludes testing the nature of Hydra I. To better understand its chemo-dynamic properties, we have begun a spectroscopic survey of the Hydra I/EBS region in order to (i) obtain a robust, velocity-based selection of candidate member stars, (ii) use precise velocities to measure the velocity dispersion, (iii) study the spatial distribution of spectroscopic members, and (iv) measure its proper motion. At present, we have surveyed a ~3 deg x ~3 deg region, which encompasses the entire ~4 sq. deg spatial extent of Hydra I. We have obtained a total of 1354 spectra in this region, with RV uncertainties smaller than ~5 km/s at magnitudes brighter than g~21.6. This work presents our confirmation of Hydra I as a cold halo structure, as well as a more detailed analysis of the membership and spatial/velocity structure of Hydra I.
International Nuclear Information System (INIS)
Ultraviolet and X-ray excited photoemission spectra and Cu K?5 X-ray emission spectra are used to measure the valence band density of states in CuGaTe2 and CuInTe2. In both compounds the density of states exhibits five structures which are ascribed to Cu 3d-Te 5p hybridized states, Ga 4s/In 5s-Te 5p bonding states, and Te 5s states. The valence band density of states of all Ga- and In-containing Cu-III-VI2 is calculated in an atomic orbital basis with the noble metal d states explicitly included. The agreement between theory and experiment is good for CuGaTe2 and except the In 5s-VI p bonding states also for the Cu-In-VI2 chalcopyrites. Larger discrepancies between theory and experiment are found for CuGaS2 and CuGaSe2. (author)
New density-independent interactions for nuclear structure calculations
Directory of Open Access Journals (Sweden)
Bennaceur K.
2014-03-01
Full Text Available We present a new two-body finite-range and momentum-dependent but density-independent effective interaction, which can be interpreted as a regularized zerorange force. We show that no three-body or density-dependent terms are needed for a correct description of saturation properties in infinite matter, that is, on the level of lowenergy density functional, the physical three-body effects can be efficiently absorbed in effective two-body terms. The new interaction gives a satisfying equation of state of nuclear matter and opens up extremely interesting perspectives for the mean-field and beyond-mean-field descriptions of atomic nuclei.
International Nuclear Information System (INIS)
We introduce a modified transfer matrix (MTM) method for the calculation of the bending vibration band structure of one-dimensional phononic crystal (PC) Euler beams. A particular combination of hyperbolic functions and triangular functions is introduced to transform the state parameters of the transfer matrix (TM) method into four initial parameters, which have the explicit meanings of the displacement, rotation angle, bending moment and shear force at one beam end. The method is used to calculate the band structures of two PC Euler beams constructed from aluminum-Lucite and 100 kinds of materials. The effectiveness and high efficiency of the MTM method are demonstrated by the results. Several advantages make it a proper choice for the calculation of the bending vibration band structure of PC Euler beams.
International Nuclear Information System (INIS)
Two-dimensional silicon nanodome arrays are prepared on large areas up to 50 cm2 exhibiting photonic band structure effects in the near-infrared and visible wavelength region by downscaling a recently developed fabrication method based on nanoimprint-patterned glass, high-rate electron-beam evaporation of silicon, self-organized solid phase crystallization and wet-chemical etching. The silicon nanodomes, arranged in square lattice geometry with 300 nm lattice constant, are optically characterized by angular resolved reflection measurements, allowing the partial determination of the photonic band structure. This experimentally determined band structure agrees well with the outcome of three-dimensional optical finite-element simulations. A 16% photonic bandgap is predicted for an optimized geometry of the silicon nanodome arrays. By variation of the duration of the selective etching step, the geometry as well as the optical properties of the periodic silicon nanodome arrays can be controlled systematically. (paper)
Chen, Daru; Yang, Tzong-Jer; Wu, Jin-Jei; Shen, Linfang; Liao, Kun-Lin; He, Sailing
2008-10-13
We propose a novel band-rejection fiber filter based on a Bragg fiber of transversal resonant structure, which can also be used as a fiber sensor. Defect layers are introduced in the periodic high/low index structure in the cladding of the Bragg fiber. Coupling between the core mode and the defect mode results in large confinement loss for some resonant wavelengths inside the band gap of the Bragg fiber. A segment of the Bragg fiber of transversal resonant structure can be used as a band-rejection fiber filter, whose characteristics are mainly determined by the defect layer. The loss peak wavelength of the Bragg fiber is dependent on the refractive index and the thickness of the defect layer which indicates its applications of refractive index and strain sensing. PMID:18852756
DEFF Research Database (Denmark)
Hvatov, Alexander; Sorokin, Sergey
2013-01-01
Analysis of wave-guide properties of infinite periodic structures is a well establish research subject. The existence of frequency stop-bands, in which transmission of the vibro-acoustic energy is impossible, suggests that these structures may be used for vibro-isolation. In any technical application, however, only a finite segment of such a structure can be used. This paper is concerned with comparison of the eigenfrequency spectra of finite periodic structures with location of stop-bands for their infinite counterparts. Special attention is paid to eigenfrequencies of a single periodicity cell with various boundary conditions. Two classical models of periodic structures are considered, for which closed form solutions are obtained and analyzed. The regular and irregular eigenfrequencies of periodicity cells and finite periodic structures are identified, and the eigenmodes are compared.
The Structure of the Local Interstellar Medium V: Electron Densities
Redfield, Seth; Falcon, Ross E.
2008-01-01
We present a comprehensive survey of CII* absorption detections toward stars within 100 pc in order to measure the distribution of electron densities present in the local interstellar medium (LISM). Using high spectral resolution observations of nearby stars obtained by GHRS and STIS onboard the Hubble Space Telescope, we identify 13 sight lines with 23 individual CII* absorption components, which provide electron density measurements, the vast majority of which are new. We ...
Energy Technology Data Exchange (ETDEWEB)
Nayebi, Payman [Physics Department, Amirkabir University of Technology, Tehran Polytechnic, 424 Hafez Ave., P.B. 15875-4413, Tehran (Iran, Islamic Republic of); Mirabbaszadeh, Kavoos, E-mail: mirabbas@aut.ac.ir [Physics Department, Amirkabir University of Technology, Tehran Polytechnic, 424 Hafez Ave., P.B. 15875-4413, Tehran (Iran, Islamic Republic of); Shamshirsaz, Mahnaz [New Technologies Research Center, Amirkabir University of Technology, Tehran Polytechnic, 424 Hafez Ave., P.B. 15875-4413, Tehran (Iran, Islamic Republic of)
2013-05-01
In this work, the structural, electronic structure and optical properties of CuXY{sub 2}(X=In, Ga and Y=S, Se) chalcopyrite semiconductors have been computed with density functional theory using numerical atomic orbital pseudopotential method with both local-density and generalized gradient approximations. The geometrical parameters like equilibrium lattice constant and anion displacement are in reasonable agreement with the experimental data and other theoretical results. Also electronic properties like band structures and density of states have been studied. The band structures show that CuXY{sub 2} compounds are semiconductors with a direct band gap and there is hybridization between Cu (d) with S (p) orbital in CuInS{sub 2} and CuGaS{sub 2} and hybridization between Cu (d) with Se (p) orbital in CuInSe{sub 2} and CuGaSe{sub 2}. Furthermore, the optical properties, real part of the dielectric function, refractive index, reflectivity and absorption coefficients are calculated from the imaginary part of the dielectric function, which are compatible with the experimental data and earlier theoretical results.
The Structure of the Local Interstellar Medium V: Electron Densities
Redfield, Seth
2008-01-01
We present a comprehensive survey of CII* absorption detections toward stars within 100 pc in order to measure the distribution of electron densities present in the local interstellar medium (LISM). Using high spectral resolution observations of nearby stars obtained by GHRS and STIS onboard the Hubble Space Telescope, we identify 13 sight lines with 23 individual CII* absorption components, which provide electron density measurements, the vast majority of which are new. We employ several strategies to determine more accurate CII column densities from the saturated CII resonance line, including, constraints of the line width from the optically thin CII* line, constraints from independent temperature measurements of the LISM gas based on line widths of other ions, and third, using measured SII column densities as a proxy for CII column densities. The sample of electron densities appears consistent with a log-normal distribution and an unweighted mean value of n_e(CII_SII) = 0.11^+0.10_-0.05 cm^-3. Seven indivi...