Nazrul Rosli, Ahmad; Fatimah Wahab, Izzati; Zabidi, Noriza Ahmad; Abu Kassim, Hasan
2015-06-01
Sodium intercalation in graphite (GIC-Na) was investigated by the first principle calculation. The structure of GIC-Na was calculated using density functional theory (DFT) with the aid of CASTEP module of Material Studio. The exchange correlation functional has been treat by local density approximation (LDA) and generalized gradient approximation (GGA). It was shown that, unlike potassium GIC and lithium GIC, the band gap of GIC-Na was not induced and has same value of band gap with bulk graphite.
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.
Valence and conduction band edges charge densities in ZnS compound with zinc-blende structure
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Bechiri, A; Benmakhlouf, F; Bacha, S; Allouache, H; Bouarissa, N, E-mail: bechiri@yahoo.fr
2010-11-15
The electronic valence and conduction charge densities at the {gamma}-dot and X k-points are calculated as a function of position in the unit cell for ZnS in the zinc-blende structure using wave functions derived from empirical pseudopotential band-structure calculations. Detailed plots of the charge density along the [111] direction and in the (110) plane are presented and discussed for the total valence bands and the first and second conduction ones.
Valence and conduction band edges charge densities in ZnS compound with zinc-blende structure
Bechiri, A.; Benmakhlouf, F.; Bacha, S.; Allouache, H.; Bouarissa, N.
2010-11-01
The electronic valence and conduction charge densities at the dot gamma and X k-points are calculated as a function of position in the unit cell for ZnS in the zinc-blende structure using wave functions derived from empirical pseudopotential band-structure calculations. Detailed plots of the charge density along the [111] direction and in the (110) plane are presented and discussed for the total valence bands and the first and second conduction ones.
International Nuclear Information System (INIS)
After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k · p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states (DOS) effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal—oxide semiconductor field effect transistor (MOSFET). It also a provides valuable reference for biaxial tensile strained silicon MOSFET design. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
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
Minaev, Boris; Wang, Yan-Hua; Wang, Chuan-Kui; Luo, Yi; Ågren, Hans
2006-10-01
Harmonic vibrational frequencies and vibronic intensities in the first S 0?S 1 ( ??) absorption band of free-base porphin (H 2 P) are investigated by hybrid density functional theory (DFT) with the standard B3LYP functional. The S 0-S 1 transition probability is calculated using time-dependent DFT with account of Franck-Condon (FC) and Herzberg-Teller (HT) contributions to the electric-dipole transition moments including displacements along all 108 vibrational modes. Two weak wide bands observed in the gas phase absorption spectra of the H 2 P molecule at 626 and 576 nm are interpreted as the 0-0 band of the X 1 A g?1B 3u transition and the 0-1 band with largest contributions from the ?10(a)=1610 cm -1 and ?19(b)=1600 cm -1 modes, respectively, in agreement with previous tentative assignments. Both bands are induced by the HT mechanism, while the FC contributions are negligible. A number of fine structure bands, including combination of two vibrational quanta, are obtained and compared with available spectra from supersonic jet and Shpolskij matrices. Both absorption and fluorescence spectra are interpreted on ground of the linear coupling model and a good fulfillment of the mirror-symmetry rule.
Ma, Haixia; Xiao, Heming; Song, Jirong; Ju, Xuehai; Zhu, Wei; Yu, Kaibei
2008-02-01
4-Amino-1,2,4-triazol-5-one (ATO) was synthesized and single crystals suitable for X-ray measurement were obtained by recrystallization from distilled water at room temperature. The H-bond connections make the molecules of ATO form three-dimensional structure from the structure solution. A density-functional theory method with 6-311++G?? was applied to study the H-bond interactions in the gaseous dimers of ATO. Twelve stable dimers were identified. The corrected binding energy of the most stable dimer (VIII) is predicted to be -53.11 kJ mol -1. The analysis of electron densities at critical bonds also indicates that dimer VIII has the strongest hydrogen bond among all the dimers. At 298.15 K the changes of Gibbs free energies (? G) for the dimerization are -2.87 and -9.67 kJ mol -1 for dimers VI and VIII, respectively. These two dimers can be spontaneously produced from the isolated monomer at room temperature. The bulk state of ATO was also studied using density-functional theory within the generalized gradient approximation. The unit cell parameters compare well with experimental data. An analysis of the electronic structure reveals that ATO is probably an insulator since it has a large band gap of 4.66 eV. The electron density in the N-NH 2 bond is less than those of other bonds, indicating that it is the weakest bond.
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.
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.
Kosobutsky, A. V.; Basalaev, Yu. M.
2014-12-01
Using first-principles theoretical techniques within density functional theory and many-body perturbation theory we investigated the structural and electronic properties of two LiInSe2 crystal modifications, orthorhombic (?-NaFeO2-type) and tetragonal (CuFeS2-type), focusing on the interband transitions and band gaps. It is found that the Tran-Blaha (TB09) functional predicts LiInSe2 to be a direct-gap semiconductor with a significantly larger band gap as compared with that from common local-density and gradient-corrected functionals. The most accurate values of the fundamental energy gaps are calculated within quasiparticle GW approximation and found to be 2.95 eV for the orthorhombic phase and 2.85 eV for the tetragonal one, with equal pressure coefficients of 63 meV/GPa. Our theoretical results eliminate the uncertainty in the band gap of LiInSe2. Moreover, the data obtained define the upper limit of the band gap of solid solutions (Cu,Li)InSe2 and (Ag,Li)InSe2, which can be of interest for applications in optoelectronics.
International Nuclear Information System (INIS)
Full text: The light alkaline-earths form an interesting series of metal oxides from a chemical and structural perspective. Calcium and magnesium oxides are often considered 'ideal' ionic solids and occur naturally in cubic rocksalt structures, whilst beryllium oxide displays some properties typical of covalent solids and occurs in the hexagonal wurtzite structure. A number of theoretical investigations of the electronic structure of these oxides have been reported in the literature (see, for example, Kotani and Akai), and compared with available optical and photoemission measurements. However, these techniques do not reveal the complete band structure and cannot always be compared directly with the calculations. A thorough test of various theoretical models requires measurement of the full band-dispersions of these oxides. Towards this end, some progress has been made by Tjeng et al. using angle-resolved photoemission on MgO, but to our knowledge, similar experiments have not been performed for the other alkaline-earth oxides. We report direct measurements of the full band dispersions of BeO, MgO and CaO using electron momentum spectroscopy and compare our results with LCAO calculations using CRYSTAL98 software. Such comparisons can be used to critically assess the quantitative accuracy of various approximations used in current density functional theories
Band offsets of semiconductor heterostructures: a hybrid density functional study
Wadehra, Amita; Nicklas, Jeremy W.; Wilkins, John W.
2010-01-01
We demonstrate the accuracy of the hybrid functional HSE06 for computing band offsets of semiconductor alloy heterostructures. The highlight of this study is the computation of conduction band offsets with a reliability that has eluded standard density functional theory. A high-quality special quasirandom structure models an infinite random pseudobinary alloy for constructing heterostructures along the (001) growth direction. Our excellent results for a variety of heterostru...
International Nuclear Information System (INIS)
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 CDW instabilities, 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 the band 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-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 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
Optimization of Photonic Band Structures
Richter, Markus
2010-01-01
In this work we study mathematical optimization problems that arise in the design of photonic crystals, whose band structures should exhibit specific properties. To this end we develop a mathematical model for time-harmonic wave propagation in three-dimensional, periodic media. We investigate the dependency of band structures on the medium structure and develop two types of optimization algorithms. The performance of these algorithms is demonstrated through several of numerical experiments.
Band structure from random interactions
Bijker, R
2000-01-01
The anharmonic vibrator and rotor regions in nuclei are investigated in the framework of the interacting boson model using an ensemble of random one- and two-body interactions. We find a predominance of L(P)=0(+) ground states, as well as strong evidence for the occurrence of both vibrational and rotational band structures. This remarkable result suggests that such band structures represent a far more general (robust) property of the collective model space than is generally thought.
Electronic band structure of beryllium oxide
Sashin, V A; Kheifets, A S; Ford, M J
2003-01-01
The energy-momentum resolved valence band structure of beryllium oxide has been measured by electron momentum spectroscopy (EMS). Band dispersions, bandwidths and intervalence bandgap, electron momentum density (EMD) and density of occupied states have been extracted from the EMS data. The experimental results are compared with band structure calculations performed within the full potential linear muffin-tin orbital approximation. Our experimental bandwidths of 2.1 +- 0.2 and 4.8 +- 0.3 eV for the oxygen s and p bands, respectively, are in accord with theoretical predictions, as is the s-band EMD after background subtraction. Contrary to the calculations, however, the measured p-band EMD shows large intensity at the GAMMA point. The measured full valence bandwidth of 19.4 +- 0.3 eV is at least 1.4 eV larger than the theory. The experiment also finds a significantly higher value for the p-to-s-band EMD ratio in a broad momentum range compared to the theory.
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.
International Nuclear Information System (INIS)
The self-consistent relativistic linearized-augmented-plane-wave method is applied to local-density calculation of electronic structure of TmS. It is found that thulium monosulphide is a compound with a trivalent state of thulium. The influence of spin-orbital interaction is shown for different symmetry states of electrons. Calculated densities of states are used for the estimation of the electron-phonon coupling constant. And in conclusion it is shown that TmS is a high temperature Kondo-like system. (author)
Pressure effects on the band structure of gadolinium
International Nuclear Information System (INIS)
APW calculations of the band structure of gadolinium were made to investigate the effects of decrease in lattice parameters coupled with an increase in c/a ratio. It is found that compared with normal pressure results, decreasing the lattice constants lowers the bottom of the band, and increasing c/a modifies the detailed band structure, particularly near GAMMA. Changes in the density of states were computed and it is found that the Fermi energy is now much closer to the levels near K. It is estimated that the density of states at the Fermi energy, and magnetic properties depending on it, are reduced by 15 percent from normal. (auth)
Photonic band gap structure simulator
Chen, Chiping; Shapiro, Michael A.; Smirnova, Evgenya I.; Temkin, Richard J.; Sirigiri, Jagadishwar R.
2006-10-03
A system and method for designing photonic band gap structures. The system and method provide a user with the capability to produce a model of a two-dimensional array of conductors corresponding to a unit cell. The model involves a linear equation. Boundary conditions representative of conditions at the boundary of the unit cell are applied to a solution of the Helmholtz equation defined for the unit cell. The linear equation can be approximated by a Hermitian matrix. An eigenvalue of the Helmholtz equation is calculated. One computation approach involves calculating finite differences. The model can include a symmetry element, such as a center of inversion, a rotation axis, and a mirror plane. A graphical user interface is provided for the user's convenience. A display is provided to display to a user the calculated eigenvalue, corresponding to a photonic energy level in the Brilloin zone of the unit cell.
Slater transition-state band-structure calculations
International Nuclear Information System (INIS)
Slater's transition-state method enables one to calculate excitation energies by means of an artificial state that is halfway between the ground state of an atom or molecule and an excited state. This idea has been adapted to insulators and semiconductors with a band-structure model where a localized hole is created in one cell by removing charge from the top of the valence band and putting it in a delocalized state at the bottom of the conduction band. Significant improvements in calculated band gaps are obtained in most cases over conventional local-density calculations. (c) 2000 The American Physical Society
Electronic band structure of CdF2
International Nuclear Information System (INIS)
Energy distribution curves (EDC) of electrons photoemitted (h?1 = 21.22 eV and h?2 = 40.8 eV) from the valence band (F-2p) and the Cd 4d band of a CdF2 crystal are measured and the valence and conduction band structures are calculated using the local empirical pseudopotential method (EPM). Comparison of the measured and calculated data show that the three main maxima measured in the valence band correspond well to the maxima in X5, L3, and X5 obtained in the calculated histogram of the valence band density of states. The influence of the final-state structure on the position of peaks in the valence band is not observed on EDCs obtained for both, h?1 and h?2 photoemission exciting energies. For Cd 4d band the wide splitting of 1.46 eV is obtained only for h?1 = 21.22 eV while it is not obtained on EDC for h?2 = 40.8 eV. This Cd 4d band splitting may be caused by the influence of the final density-of-states maximum obtained in conduction band in X1-point. The results obtained are compared with reflectivity data available in the literature. (author)
International Nuclear Information System (INIS)
Excited states of 123I were populated via the 116Cd(14N, ?3n) reaction at 65 MeV. The resultant ?-rays were detected using standard ?-ray spectroscopic techniques with the NORDBALL detector array. Two previously known positive-parity ?I = 2 sequences have been extended up to 31/2+ and 41/2+. In addition, a number of ?I = 1 transitions linking the two ?I = 2 sequences have been observed. It is suggested that both ?I = 2 sequences are based on a common configuration. This ?I = 1 band is proposed to be built predominantly on the g7/2[404]7/2+ oblate configuration, based on the energy-level spectra, B(M1)/B(E2) ratios and the theoretical predictions from the particle-rotor model. The previously identified ?I = 1 rotational band built on the prolate g9/2[404]9/2+ orbital has also been extended to higher spins. Another previously identified but weakly populated ?I = 1 band is confirmed and is proposed to be built on the d5/2[413]5/2+ configuration with the ground state of 123I as the bandhead
Schmidt, Vitalij; Rösner, Harald; Peterlechner, Martin; Wilde, Gerhard; Voyles, Paul M.
2015-07-01
Quantitative density measurements from electron scattering show that shear bands in deformed Al88Y7Fe5 metallic glass exhibit alternating high and low density regions, ranging from -9 % to +6 % relative to the undeformed matrix. Small deflections of the shear band from the main propagation direction coincide with switches in density from higher to lower than the matrix and vice versa, indicating that faster and slower motion (stick slip) occurs during the propagation. Nanobeam diffraction analyses provide clear evidence that the density changes are accompanied by structural changes, suggesting that shear alters the packing of tightly bound short- or medium-range atomic clusters. This bears a striking resemblance to the packing behavior in granular shear bands formed upon deformation of granular media.
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.)
International Nuclear Information System (INIS)
High spin states in 85Sr were populated using the reaction 76Ge(13C, 4n) at a beam energy of 52 MeV. Gamma-gamma coincidence measurements along with investigation of directional correlation ratios were utilized to establish the extended level scheme upto I? = (35/2-). One of the positive parity states observed at 3383.3 keV ((I? = 19/2(+)) may be considered as a magnetic rotational (?I = 1) band, the negative parity states built on 3028.0 level show an irregular behaviour and does not exhibit magnetic rotation.
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
2015-01-01
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. PMID:26289434
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
2015-01-01
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. PMID:26289434
Band-Structure of Thallium by the LMTO Method
DEFF Research Database (Denmark)
Holtham, P. M.; Jan, J. P.
1977-01-01
The relativistic band structure of thallium has been calculated using the linear muffin-tin orbital (LMTO) method. The positions and extents of the bands were found to follow the Wigner-Seitz rule approximately, and the origin of the dispersion of the bands was established from the canonical s and p bands for the HCP structure. Energy bands have been evaluated both with and without spin-orbit coupling which is particularly large in thallium. Energy bands close to the Fermi level were found to be mainly 6p like in character. The 6s states lay below the 6p bands and were separated from them by an energy gap. The 6d and 7s bands were found to be far above the Fermi level and the 5d states were found to be far below it. Fermi surface properties and the electronic specific heat are computed and compared with experiment. The joint density of states has also been computed and is in reasonable agreement with experimental optical properties.
Band Structure of Solid Light Quantum Simulators
Quach, James; Su, Chun-Hsu; Greentree, Andrew D; Hollenberg, Lloyd C L
2009-01-01
The conjunction of atom-cavity physics and photonic structures ("solid light" systems) offers new opportunities in terms of more device functionality and the probing of designed emulators of condensed matter systems. By analogy to the one-electron approximation of solid state physics, we discuss the one-polariton approximation to study a solid light system. Using this approximation we apply Bloch states to the Jaynes-Cummings-Hubbard model of optical cavities to analytically determine the energy band structure. We demonstrate how the band structure can inform the phases of the system. We further apply this approach to systems with detuning impurities to show the solid light analogy of the semiconductor.
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...
Band Structure Based Analysis of Certain Photonic Crystal Structures
Wolff, Christian
2011-01-01
Photonic crystals are periodic dielectric structures that may exhibit a complete photonic band gap. First, I discuss geometric properties of the band structure such as band edges. In a second part, I present work on photonic Wannier functions and their use for solving the wave equation. The third part is devoted to applications of the presented methods: A polarization resolved transmission experiment of opel films and an analogy experiment for spontaneous emission inside a photonic crystal.
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)
Band alignment of semiconductors from density-functional theory and many-body perturbation theory
Hinuma, Yoyo; Grüneis, Andreas; Kresse, Georg; Oba, Fumiyasu
2014-10-01
The band lineup, or alignment, of semiconductors is investigated via first-principles calculations based on density functional theory (DFT) and many-body perturbation theory (MBPT). Twenty-one semiconductors including C, Si, and Ge in the diamond structure, BN, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe in the zinc-blende structure, and GaN and ZnO in the wurtzite structure are considered in view of their fundamental and technological importance. Band alignments are determined using the valence and conduction band offsets from heterointerface calculations, the ionization potential (IP) and electron affinity (EA) from surface calculations, and the valence band maximum and conduction band minimum relative to the branch point energy, or charge neutrality level, from bulk calculations. The performance of various approximations to DFT and MBPT, namely the Perdew-Burke-Ernzerhof (PBE) semilocal functional, the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, and the GW approximation with and without vertex corrections in the screened Coulomb interaction, is assessed using the GW?1 approximation as a reference, where first-order vertex corrections are included in the self-energy. The experimental IPs, EAs, and band offsets are well reproduced by GW?1 for most of the semiconductor surfaces and heterointerfaces considered in this study. The PBE and HSE functionals show sizable errors in the IPs and EAs, in particular for group II-VI semiconductors with wide band gaps, but are much better in the prediction of relative band positions or band offsets due to error cancellation. The performance of the GW approximation is almost on par with GW?1 as far as relative band positions are concerned. The band alignments based on average interfacial band offsets for all pairs of 17 semiconductors and branch point energies agree with explicitly calculated interfacial band offsets with small mean absolute errors of both ˜0.1eV, indicating a good overall transitivity of the band offsets. The alignment based on IPs from selected nonpolar surfaces performs comparably well in the prediction of band offsets at most of the considered interfaces. The maximum errors are, however, as large as 0.3, 0.4, and 0.7 eV for the alignments based on the average band offsets, branch point energies, and IPs, respectively. This margin of error should be taken into account when performing materials screening using these alignments.
Fano resonances and band structure of two dimensional photonic structures
Markos, Peter
2015-01-01
We show that the frequency spectrum of two dimensional photonic crystals is strongly influenced by Fano resonances which can be excited already in the linear array of dielectric cylinders. To support this claim, we calculate the transmission of electromagnetic wave through linear array of dielectric cylinders and show that frequencies of observed Fano resonances coincides with position of narrow frequency bands found in the spectra of corresponding two-dimensional photonic crystals. Split of frequency band or overlap of two bands, observed in the band structure of photonic structures are also associated with Fano resonances.
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.
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.
Rotational band structure in 128Ce
International Nuclear Information System (INIS)
The high spin structure of the nucleus 128Ce has been investigated via the 94Mo (37Cl, p2n) reaction at 158 MeV. New bands have been found. Alignments of h11/2 protons and h11/2 neutrons have been observed. (orig.)
International Nuclear Information System (INIS)
In this paper, we use a tight binding Hamiltonian with spin orbit coupling to study the real and complex band structures of relaxed and strained GaAs. A simple d orbital on-site energy shift coupled with appropriate scaling of the off-diagonal terms is found to correctly reproduce the band-edge shifts with strain. Four different ?100? strain combinations, namely, uniaxial compressive, uniaxial tensile, biaxial compressive, and biaxial tensile strain are studied, revealing rich valence band structure and strong relative orientation dependent tunneling. It is found that complex bands are unable to provide unambiguous tunneling paths away from the Brillouin zone center. Tunneling current density distribution over the Brillouin zone is computed using non-equilibrium Green's function approach elucidating a physical picture of band to band tunneling
Energy Technology Data Exchange (ETDEWEB)
Majumdar, Kausik, E-mail: kausik.majumdar@sematech.org [SEMATECH, 257 Fuller Road, STE 2200, Albany, New York 12203 (United States)
2014-05-07
In this paper, we use a tight binding Hamiltonian with spin orbit coupling to study the real and complex band structures of relaxed and strained GaAs. A simple d orbital on-site energy shift coupled with appropriate scaling of the off-diagonal terms is found to correctly reproduce the band-edge shifts with strain. Four different ?100? strain combinations, namely, uniaxial compressive, uniaxial tensile, biaxial compressive, and biaxial tensile strain are studied, revealing rich valence band structure and strong relative orientation dependent tunneling. It is found that complex bands are unable to provide unambiguous tunneling paths away from the Brillouin zone center. Tunneling current density distribution over the Brillouin zone is computed using non-equilibrium Green's function approach elucidating a physical picture of band to band tunneling.
Majumdar, Kausik
2014-05-01
In this paper, we use a tight binding Hamiltonian with spin orbit coupling to study the real and complex band structures of relaxed and strained GaAs. A simple d orbital on-site energy shift coupled with appropriate scaling of the off-diagonal terms is found to correctly reproduce the band-edge shifts with strain. Four different ?100? strain combinations, namely, uniaxial compressive, uniaxial tensile, biaxial compressive, and biaxial tensile strain are studied, revealing rich valence band structure and strong relative orientation dependent tunneling. It is found that complex bands are unable to provide unambiguous tunneling paths away from the Brillouin zone center. Tunneling current density distribution over the Brillouin zone is computed using non-equilibrium Green's function approach elucidating a physical picture of band to band tunneling.
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.
Band-structure parameters by genetic algorithm
International Nuclear Information System (INIS)
A genetic algorithm has been used to solve a complex multidimensional parameter-fitting problem. We will focus on the parameters of an empirical tight-binding Hamiltonian. The method is used to approximate the electronic energy band structure if energy values are known for a few wave vectors of high symmetry. Compared to the usual manual procedure this method is more accurate and automatic. This approach, based on the extended Hueckel theory (EHT), has provided a list of EHT parameters for IV-IV and III-V semiconductors with zinc-blende structure and helped us to find a symmetry in the EHT. copyright 1996 The American Physical Society
Relationship between band populations and band structure in the three-band Hubbard model
International Nuclear Information System (INIS)
We study the two-dimensional three-band Hubbard model by means of a four-pole approximation within the Composite Operator Method framework. The model has been solved by considering as basic composite field a four-component spinor field, which includes the p field, the two Hubbard operators for the d field, and a composite operator describing the p field dressed by the spin excitations of the d field. This solution correctly reproduces many results of numerical simulations. In this manuscript, we investigate the relationship between p-and d- populations and the band structure of the model, by varying the on-site potential, the charge-transfer gap, the doping and the hopping integral between the p orbitals.
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
Measures of residue density in protein structures
Baud, Franck; Karlin, Samuel
1999-01-01
A hierarchy of residue density assessments and packing properties in protein structures are contrasted, including a regular density, a variety of charge densities, a hydrophobic density, a polar density, and an aromatic density. These densities are investigated by alternative distance measures and also at the interface of multiunit structures. Amino acids are divided into nine structural categories according to three secondary structure states and three solvent accessibility levels. To take a...
Microscopic study of the 168Er multiphonon band structure
Gupta, J. B.; Hamilton, J. H.; Ramayya, A. V.
2001-04-01
The dynamic deformation theory with the pairing plus quadrupole interaction is applied to study the multiphonon band structure in 168Er. Three K?=0+, two K?=2+, and K?=4+ bands have been analyzed. The lower four bands are also analyzed in the interacting boson model. The nature of the K?=02 and 03 and K?=4+ bands is discussed.
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...
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
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.
Multiple band structure in 74 Kr
International Nuclear Information System (INIS)
In order to obtain a consistent picture for the structure of the of A ? 70 mass region dominated by shape coexistence phenomena we determine the relevant degrees of freedom dynamically by the effective many body Hamiltonian using the complex version of the EXCITED VAMPIR approach. General symmetry projected Hartree-Fock-Bogolyubov quasi-particle determinants are used as trial configurations and the underlying mean fields as well as the configuration mixing are determined by chains of variational calculations with symmetry projection before variation. We used essentially complex HFB transformation imposing time-reversal and axial symmetry on the quasi particle transformation and include neutron-proton as well as parity mixing in the mean field. In this way we account for time-odd unnatural parity correlation as well as T = 0 and T = 1 neutron-proton pairing in the mean fields. We investigated the lowest even spin positive parity states up to spin 20+ in 74 Kr. For all investigated states from spin 0+ to 10+ the main projected determinant for the yrast solution is prolate deformed and for the first excited state is oblate deformed in the intrinsic system. For higher spins the oblate minimum is going higher in energy. The presence of many prolate minima close in energy with the first one is revealed by the structure of the wave functions and the strong mixing of states found for the intermediate spins result in a very complicate decay pattern. The predicted multiple band structure was confirmed by recent experimental data
Band structure and transport studies on InP nanotube - A first-principles investigation
Chandiramouli, R.
2015-07-01
The band structure and electronic transport property of InP nanotube molecular device are studied using density functional theory with GGA/PBE exchange correlation functional. The substitution of nitrogen in InP nanotube slightly widens the band gap. The substitution of nitrogen and aluminium in InP nanostructure modifies the density of states across InP nanotube. The electron density is found to be more on phosphorus sites than indium sites. The substitution of aluminium increases the electron density, whereas nitrogen substitution decreases the electron density across phosphorus site. The transmission spectrum provides the insight to transmission along InP nanotube molecular device. The transmission pathways get modified with the substitution impurity along InP nanotube molecular device. The results of the present work will give information on tuning the band structure and transport properties of InP nanotube molecular device.
Flux density monitoring of radio stars observable by HIPPARCOS at S-band and X-band
Estalella, R.; Paredes, J. M.; Rius, A.
1983-08-01
Single-dish simultaneous S-band (13 cm) and X-band (3.6 cm) flux density measuremets of radio stars are reported. The aim of the observational program is to monitor the variability and flux density of radio stars with an optical counterpart observable by the future astrometric satellite Hipparcos. From a list of 69 selected radio stars for astrometric purposes, 49 of them have been observed during 1982 with the 64 m antenna of the Madrid DSCC. The number of radio stars that have been detected is 15.
Band edge singularities and density of states in YTaO4 and YNbO4
International Nuclear Information System (INIS)
We study the structural and electronic properties of YTaO4 and YNbO4 by means of accurate first-principle total energy calculations. The calculations are based on density functional theory (DFT). The total energy, electronic band structure, and density of states are calculated via the full potential linear-augmented plane wave approach, as implemented in the WIEN2K code, within the framework of DFT. The results show that the valence bands of tantalate and niobate systems are from O 2p states. Conduction bands are divided into two parts. The lower conduction band is mainly composed of Ta 5d or Nb 4d states and the upper conduction bands involve contribution mainly from Y 4d states of YTaO4 or YNbO4. The efficient band gaps in yttrium tantalate and niobate are determined about 4.8 and 4.1 eV, respectively. The agreement between the calculations and the experimental data is excellent. The efficient band gap and a simple model illustrating excitation and emission process in considered host lattices are discussed. (authors)
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.
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...
Elucidating the stop bands of structurally colored systems through recursion
Amir, Ariel
2012-01-01
Interference phenomena are the source of some of the spectacular colors of animals and plants in nature. In some of these systems, the physical structure consists of an ordered array of layers with alternating high and low refractive indices. This periodicity leads to an optical band structure that is analogous to the electronic band structure encountered in semiconductor physics; namely, specific bands of wavelengths (the stop bands) are perfectly reflected. Here, we present a minimal model for optical band structure in a periodic multilayer and solve it using recursion relations. We present experimental data for various beetles, whose optical structure resembles the proposed model. The stop bands emerge in the limit of an infinite number of layers by finding the fixed point of the recursive relations. In order for these to converge, an infinitesimal amount of absorption needs to be present, reminiscent of the regularization procedures commonly used in physics calculations. Thus, using only the phenomenon of...
Graphene Nanoribbon Conductance Model in Parabolic Band Structure
Directory of Open Access Journals (Sweden)
Mohammad Taghi Ahmadi
2010-01-01
Full Text Available Many experimental measurements have been done on GNR conductance. In this paper, analytical model of GNR conductance is presented. Moreover, comparison with published data which illustrates good agreement between them is studied. Conductance of GNR as a one-dimensional device channel with parabolic band structures near the charge neutrality point is improved. Based on quantum confinement effect, the conductance of GNR in parabolic part of the band structure, also the temperature-dependent conductance which displays minimum conductance near the charge neutrality point are calculated. Graphene nanoribbon (GNR with parabolic band structure near the minimum band energy terminates Fermi-Dirac integral base method on band structure study. While band structure is parabola, semiconducting GNRs conductance is a function of Fermi-Dirac integral which is based on Maxwell approximation in nondegenerate limit especially for a long channel.
Band Structure of Periodically Surface-Scattered Water Waves
Chou, Tom
1997-01-01
Bloch wavefunctions are used to derive dispersion relations for water wave propagation in the presence of an infinite array of periodically arranged surface scatterers. For one dimensional periodicity (stripes), band gaps for wavevectors in the direction of periodicity are found corresponding to multiple Bragg scattering. The dependence of these band gaps as a function of scatterer density, strength, and water depth is analyzed. We find in contrast to band gap behavior in el...
Quasiparticle band structures and thermoelectric transport properties of p-type SnSe
Shi, Guangsha; Kioupakis, Emmanouil
2014-01-01
We used density functional and many-body perturbation theory to calculate the quasiparticle band structures 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 calcul...
APW Band Structure of Cubic BaPb1-xBixO3
Takegahara, Katsuhiko; Kasuya, Tadao
1987-04-01
The self-consistent APW band calculations for the materials of the ideal perovskite structure, BaPbO3 and BaBiO3, and the NaCl type super-cell structure BaPb0.5Bi0.5O3 have been done using the local density approximation. In both BaPbO3 and BaBiO3, the bonding-antibonding splitting of the (Pb, Bi) 6s and O 2p states makes a pair of wide bands of about 15 eV width. At the center of these s-p bands, there are non-bonding O 2p bands with about 4 eV width. The character of these bands is substantially different from the previously reported results of LAPW method. In BaPb0.5Bi0.5O3, due to the potential difference between Pb and Bi sites, each bonding and antibonding s-p band splits into two subbands but the split antibonding bands overlap each other slightly. This result refuses the possibility of the gap formation in the Bi-rich alloys due to the charge density wave because the ordered BaPb0.5Bi0.5O3 offers the upper limit of the charge density in the present system. Then the origin of the insulator property is considered on the standpoint of the spin density wave formation on Bi sites.
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.
Planar electromagnetic band-gap structure based on graphene
Dong, Yanfei; Liu, Peiguo; Yin, Wen-Yan; Li, Gaosheng; Yi, Bo
2015-06-01
Electromagnetic band-gap structure with slow-wave effect is instrumental in effectively controlling electromagnetic wave propagation. In this paper, we theoretically analyze equivalent circuit model of electromagnetic band-gap structure based on graphene and evaluate its potential applications. Graphene electromagnetic band-gap based on parallel planar waveguide is investigated, which display good characteristics in dynamically adjusting the electromagnetic wave propagation in terahertz range. The same characteristics are retrieved in a spiral shape electromagnetic band-gap based on coplanar waveguide due to tunable conductivity of graphene. Various potential terahertz planar devices are expected to derive from the prototype structures.
Engineering the Electronic Band Structure for Multiband Solar Cells
Energy Technology Data Exchange (ETDEWEB)
Lopez, N.; Reichertz, L.A.; Yu, K.M.; Campman, K.; Walukiewicz, W.
2010-07-12
Using the unique features of the electronic band structure of GaNxAs1-x alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the Band Anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.
Tuning the electronic band structure of PCBM by electron irradiation
Yoo Seung; Kum Jong; Cho Sung
2011-01-01
Abstract Tuning the electronic band structures such as band-edge position and bandgap of organic semiconductors is crucial to maximize the performance of organic photovoltaic devices. We present a simple yet effective electron irradiation approach to tune the band structure of [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM) that is the most widely used organic acceptor material. We have found that the lowest unoccupied molecular orbital (LUMO) level of PCBM up-shifts toward the vacuum ener...
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
International Nuclear Information System (INIS)
Density changes between sheared zones and their surrounding amorphous matrix as a result of plastic deformation in a cold-rolled metallic glass (melt-spun Al88Y7Fe5) were determined using high-angle annular dark-field (HAADF) detector intensities supplemented by electron-energy loss spectroscopy (EELS), energy-dispersive X-ray (EDX) and nano-beam diffraction analyses. Sheared zones or shear bands were observed as regions of bright or dark contrast arising from a higher or lower density relative to the matrix. Moreover, abrupt contrast changes from bright to dark and vice versa were found within individual shear bands. We associate the decrease in density mainly with an enhanced free volume in the shear bands and the increase in density with concomitant changes of the mass. This interpretation is further supported by changes in the zero loss and Plasmon signal originating from such sites. The limits of this new approach are discussed. - Highlights: • We describe a novel approach for measuring densities in shear bands of metallic glasses. • The linear relation of the dark-field intensity I/I0 and the mass thickness ?t was used. • Individual shear bands showed abrupt contrast changes from bright to dark and vice versa. • Density changes ranging from about ?10% to +6% were found for such shear bands. • Mixtures of amorphous/medium range ordered domains were found within the shear bands
Energy Technology Data Exchange (ETDEWEB)
Rösner, Harald, E-mail: rosner@uni-muenster.de [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Peterlechner, Martin [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Kübel, Christian [Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology (INT), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen (Germany); Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen (Germany); Schmidt, Vitalij [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Wilde, Gerhard [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444 (China)
2014-07-01
Density changes between sheared zones and their surrounding amorphous matrix as a result of plastic deformation in a cold-rolled metallic glass (melt-spun Al{sub 88}Y{sub 7}Fe{sub 5}) were determined using high-angle annular dark-field (HAADF) detector intensities supplemented by electron-energy loss spectroscopy (EELS), energy-dispersive X-ray (EDX) and nano-beam diffraction analyses. Sheared zones or shear bands were observed as regions of bright or dark contrast arising from a higher or lower density relative to the matrix. Moreover, abrupt contrast changes from bright to dark and vice versa were found within individual shear bands. We associate the decrease in density mainly with an enhanced free volume in the shear bands and the increase in density with concomitant changes of the mass. This interpretation is further supported by changes in the zero loss and Plasmon signal originating from such sites. The limits of this new approach are discussed. - Highlights: • We describe a novel approach for measuring densities in shear bands of metallic glasses. • The linear relation of the dark-field intensity I/I{sub 0} and the mass thickness ?t was used. • Individual shear bands showed abrupt contrast changes from bright to dark and vice versa. • Density changes ranging from about ?10% to +6% were found for such shear bands. • Mixtures of amorphous/medium range ordered domains were found within the shear bands.
Structural and electronic properties of poly(vinyl alcohol) using density functional theory
Dabhi, Shweta; Jha, Prafulla K.
2014-04-01
The first principles calculations have been carried out to investigate the structural, electronic band structure density of states along with the projected density of states for poly(vinyl alcohol). Our structural calculation suggests that the poly(vinyl alcohol) exhibits monoclinic structure. The calculated structural lattice parameters are in excellent agreement with available experimental values. The band structure calculations reveal that the direct and indirect band gaps are 5.55 eV and 5.363 eV respectively in accordance with experimental values.
Structural and electronic properties of poly(vinyl alcohol) using density functional theory
Energy Technology Data Exchange (ETDEWEB)
Dabhi, Shweta, E-mail: shwetadabhi1190@gmail.com; Jha, Prafulla K., E-mail: shwetadabhi1190@gmail.com [Department of Physics, Maharaja Krishnakumasinhji Bhavnagar University, Bhavnagar-364001 (India)
2014-04-24
The first principles calculations have been carried out to investigate the structural, electronic band structure density of states along with the projected density of states for poly(vinyl alcohol). Our structural calculation suggests that the poly(vinyl alcohol) exhibits monoclinic structure. The calculated structural lattice parameters are in excellent agreement with available experimental values. The band structure calculations reveal that the direct and indirect band gaps are 5.55 eV and 5.363 eV respectively in accordance with experimental values.
Structural and electronic properties of poly(vinyl alcohol) using density functional theory
International Nuclear Information System (INIS)
The first principles calculations have been carried out to investigate the structural, electronic band structure density of states along with the projected density of states for poly(vinyl alcohol). Our structural calculation suggests that the poly(vinyl alcohol) exhibits monoclinic structure. The calculated structural lattice parameters are in excellent agreement with available experimental values. The band structure calculations reveal that the direct and indirect band gaps are 5.55 eV and 5.363 eV respectively in accordance with experimental values
Modification of Casimir Forces Due to Band Gaps in Periodic Structures
Villarreal, C.; Esquivel-Sirvent, R.; Cocoletzi, G. H.
The Casimir force between inhomogeneous slabs that exhibit a band-like structure is calculated. The slabs are made of basic unit cells each made of two layers of different materials. As the number of unit cells increases the Casimir force between the slabs changes, since the reflectivity develops a band-like structure characterized by frequency regions of high reflectivity. This is also evident in the difference of the local density of states between free and boundary distorted vacuum, that becomes maximum at frequencies corresponding to the band gaps. The calculations are restricted to vacuum modes with wave vectors perpendicular to the slabs.
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...
Band structure and optical properties of diglycine nitrate crystal
Energy Technology Data Exchange (ETDEWEB)
Andriyevsky, Bohdan [Faculty of Electronics and Informatics, Technical University of Koszalin, 2 Sniadeckich Str., 75-453 Koszalin (Poland)]. E-mail: bandri@tu.koszalin.pl; Ciepluch-Trojanek, Wioleta [Faculty of Electronics and Informatics, Technical University of Koszalin, 2 Sniadeckich Str., 75-453 Koszalin (Poland); Romanyuk, Mykola [Ivan Franko National University of L' viv, 8 Kyrylo and Mefodii Str., 79005 L' viv (Ukraine); Patryn, Aleksy [Faculty of Electronics and Informatics, Technical University of Koszalin, 2 Sniadeckich Str., 75-453 Koszalin (Poland); Jaskolski, Marcin [Faculty of Electronics and Informatics, Technical University of Koszalin, 2 Sniadeckich Str., 75-453 Koszalin (Poland)
2005-07-15
Experimental and theoretical investigations of the electron energy characteristics and optical spectra for diglycine nitrate crystal (DGN) (NH{sub 2}CH{sub 2}COOH){sub 2}.HNO{sub 3}, in the paraelectric phase (T=295K) are presented. Spectral dispersion of light reflection R(E) have been measured in the range of 3-22eV and the optical functions n(E) and k(E) have been calculated using Kramers-Kronig relations. First principal calculations of the electron energy characteristic and optical spectra of DGN crystal have been performed in the frame of density functional theory using CASTEP code (CAmbridge Serial Total Energy Package). Optical transitions forming the low-energy edge of fundamental absorption are associated with the nitrate groups NO{sub 3}. Peculiarities of the band structure and DOS projected onto glycine and NO{sub 3} groups confirm the molecular character of DGN crystal.
EFFECT OF MAGNETIC DISORDER ON THE SPECTRAL DENSITY OF THE d BAND IN FERROMAGNETIC METALS
Kanamori, J.; S. Imada
1988-01-01
It is shown that previous calculations of the spectral density of an extra hole or electron in Fe and Ni can be parametrized with a simple CPA in terms of an exchange splitting parameter and level position in the band both measured in the unit of an effective band width even in the presence of the short range order.
Electronic band structure of lithium, sodium and potassium fluorides
International Nuclear Information System (INIS)
A mixed tight-binding, pseudopotential method is proposed to calculate the energy band structure of large-gap crystals and is tested here on LiF, NaF and KF. Three-centre terms are included in the determination of the valence bands by the tight-binding method and for the conduction bands we use a pseudopotential model proposed by Bassani and Giuliano, modified for the positive ions. By taking into account the polarization corrections, transitions calculated from the energy band structures are compared with experimental data and the agreement is generally good
Band structure of some very neutron deficient cesium isotopes
International Nuclear Information System (INIS)
Experimental data show that the very neutron-deficient A ? 120, Z = 55 cesium isotopes are well deformed and display a wealth of interesting collective structures. Smith have performed high spin spectroscopy using the Gammasphere array and extended the previously observed negative parity band of 117Cs upto high spin. Liden et al have extended the h11/2 negative parity band of 119Cs upto spin I? = 35/2- . Besides this some positive parity bands are also observed in 117,119Cs nuclei. In order to investigate band structure of these very neutron deficient Cs nuclei, Projected Shell Model (PSM) has been employed
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)
The band energy structure of RbKSO4 crystals
Directory of Open Access Journals (Sweden)
O.V.Bovgyra
2007-01-01
Full Text Available The energy band structure of mechanically free and compressed RbKSO4 single crystals is investigated. It is established that the top of the valence band is located at the D point of the Brillouin zone [k = (0.5, 0.5, 0], the bottom of the conduction band lies at the ? point, and the minimum direct band gap Eg is equal to 5.80 eV. The bottom of the conduction band is predominantly formed by the K s, Li p, Rb s, and Rb p states hybridized with the S p and O p antibonding states. The pressure coefficients of the energy position of the valence and conduction band states and the band gap Eg are determined.
Salehi, H.
2011-01-01
The electronic structure, energy band structure, total density of states (DOS) and electronic density of perovskite SrTiO_{3} in the cubic phase are calculated by the using full potential-linearized augmented plane wave (FP-LAPW) method in the framework density functional theory (DFT) with the generalized gradient approximation (GGA) by WIEN2k package. The calculated band structure shows a direct band gap of 2.5 eV at the ? point in the Brillouin zone.The total DOS is comp...
Electronic Band Structure and Sub-band-gap Absorption of Nitrogen Hyperdoped Silicon.
Zhu, Zhen; Shao, Hezhu; Dong, Xiao; Li, Ning; Ning, Bo-Yuan; Ning, Xi-Jing; Zhao, Li; Zhuang, Jun
2015-01-01
We investigated the atomic geometry, electronic band structure, and optical absorption of nitrogen hyperdoped silicon based on first-principles calculations. The results show that all the paired nitrogen defects we studied do not introduce intermediate band, while most of single nitrogen defects can introduce intermediate band in the gap. Considering the stability of the single defects and the rapid resolidification following the laser melting process in our sample preparation method, we conclude that the substitutional nitrogen defect, whose fraction was tiny and could be neglected before, should have considerable fraction in the hyperdoped silicon and results in the visible sub-band-gap absorption as observed in the experiment. Furthermore, our calculations show that the substitutional nitrogen defect has good stability, which could be one of the reasons why the sub-band-gap absorptance remains almost unchanged after annealing. PMID:26012369
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
Electronic structure of heavy fermions: narrow temperature-independent bands
International Nuclear Information System (INIS)
The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from ARPES data reported here for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable. (orig.)
Quasiparticle band structure of rocksalt-CdO determined using maximally localized Wannier functions
International Nuclear Information System (INIS)
CdO in the rocksalt structure is an indirect band gap semiconductor. Thus, in order to determine its band gap one needs to calculate the complete band structure. However, in practice, the exact evaluation of the quasiparticle band structure for the large number of k-points which constitute the different symmetry lines in the Brillouin zone can be an extremely demanding task compared to the standard density functional theory (DFT) calculation. In this paper we report the full quasiparticle band structure of CdO using a plane-wave pseudopotential approach. In order to reduce the computational effort and time, we make use of maximally localized Wannier functions (MLWFs). The MLWFs offer a highly accurate method for interpolation of the DFT or GW band structure from a coarse k-point mesh in the irreducible Brillouin zone, resulting in a much reduced computational effort. The present paper discusses the technical details of the scheme along with the results obtained for the quasiparticle band gap and the electron effective mass.
Fine structure of granular banding in two-phase rimming flow
Thomas, P. J.; Riddell, G. D.; Kooner, S.; King, G. P.
2001-09-01
Solid-liquid two-phase flow inside a partially filled horizontally rotating cylinder is investigated. We document the observation of a new, secondary banding pattern developing in the flow when the solid phase comes out of suspension to accumulate as regularly spaced, circumferential bands on the inner cylinder wall. This secondary pattern, the fine structure, is superposed on the primary pattern which we previously described [O. A. M. Boote and P. J. Thomas, Phys. Fluids 11, 2020 (1999)]. The fine structure is characterized by each of the primary bands adopting a compound structure consisting of three individual, narrower secondary bands. New results on the influence of the physical properties of the solid phase on transitions between characteristic flow states are briefly discussed. It is reported that state-transition boundaries in the phase plane and the wavelength of the primary instability are insensitive to particle size and shape while there exist influences due to the particle density.
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 nearly degenerate dipole bands in 108Ag
Sethi, J.; Palit, R.; Saha, S.; Trivedi, T.; Bhat, G. H.; Sheikh, J. A.; Datta, P.; Carroll, J. J.; Chattopadhyay, S.; Donthi, R.; Garg, U.; Jadhav, S.; Jain, H. C.; Karamian, S.; Kumar, S.; Litz, M. S.; Mehta, D.; Naidu, B. S.; Naik, Z.; Sihotra, S.; Walker, P. M.
2013-08-01
The high spin negative parity states of 108Ag have been investigated with the 11B + 100Mo 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 108Ag 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.
Mass production report of C-band accelerating structures
International Nuclear Information System (INIS)
An X-ray free electron laser (XFEL) is under construction in RIKEN/SPring-8. This facilities is planned to realize the X-ray laser in the spring of 2011. Mitsubishi Heavy Industries (MHI) began mass production of S-Band and C-band accelerating structures and SLED and waveguides from February 2007 for RIKEN X-FEL Project, and completed all components in March 2010. It reports on these mass production results and measurements results of accelerating structures. (author)
Density structures inside the plasmasphere: Cluster observations
Directory of Open Access Journals (Sweden)
F. Darrouzet
2004-07-01
Full Text Available 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 11 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.
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.
Banded Electron Structure Formation in the Inner Magnetosphere
Liemohn, M. W.; Khazanov, G. V.
1997-01-01
Banded electron structures in energy-time spectrograms have been observed in the inner magnetosphere concurrent with a sudden relaxation of geomagnetic activity. In this study, the formation of these banded structures is considered with a global, bounce-averaged model of electron transport, and it is concluded that this structure is a natural occurrence when plasma sheet electrons are captured on closed drift paths near the Earth. These bands do not appear unless there is capture of plasma sheet electrons; convection along open drift paths making open pass around the Earth do not have time to develop this feature. The separation of high-energy bands from the injection population due to the preferential advection of the gradient-curvature drift creates spikes in the energy distribution, which overlap to form a series of bands in the energy spectrograms. The lowest band is the bulk of the injected population in the sub-key energy range. Using the Kp history for an observed banded structure event, a cloud of plasma sheet electrons is captured and the development of their distribution function is examined and discussed.
Electrical properties and band structures of Pb1-x Snx Te alloys
International Nuclear Information System (INIS)
Both p type alloys Pb0.72Sn0.28Te and Pb0.53Sn0.47Te have been studied in the present work. The main obtained results are the following: the materials have a two-valence band structure, the first band following non-parabolic Cohen's dispersion law; at low temperatures, carriers are scattered by ionized impurities; the Coulomb potentials being screened almost completely, impurities act like neutral centers. At room temperature, scattering by acoustic modes can explain lattice mobility behavior; reversing of the thermo-power, for samples with carrier densities of about 1020 cm-3, is possibly due to inter-band scattering between both valence bands; a very simple picture of the band parameters variations as a function of alloy fraction is suggested. (author)
Development of the W-band density profile and fluctuation reflectometer on EAST
Energy Technology Data Exchange (ETDEWEB)
Wang, Y.M.; Gao, X., E-mail: xgao@ipp.ac.cn; Ling, B.L.; Zhang, S.B.; Zhang, T.; Han, X.; Liu, S.C.; Liu, Z.X.; Liu, Y.; Ti, A.
2013-11-15
Highlights: • A X-mode W-band reflectometer is designed and installed on Experimental Advanced Superconducting Tokamak (EAST) for the first time. • Both density profile and fluctuations can be measured by the newly developed reflectometer. • The core density profile has been measured in high magnetic field condition together with V-band reflectometer. • Sawtooth precursor has been measured by fluctuation reflectometer in the low magnetic field condition. -- Abstract: A X-mode polarized W-band reflectometer for plasma density profile and fluctuation measurement is designed and installed on EAST. In measuring the density profile, a voltage controlled oscillator (VCO) is used as the source, allowing a high temporal resolution measurement. The density profile in a plasma with high magnetic field (3.0 T) has been measured by combination of V- and W-band reflectometers. For fluctuation measurements, a frequency synthesizer is used instead of the VCO as a microwave source. The core density fluctuations during sawtooth activity are measured and analyzed.
Photonic band gap of superconductor-medium structure: Two-dimensional triangular lattice
Energy Technology Data Exchange (ETDEWEB)
Liu, Wan-guo; Pan, Feng-ming, E-mail: fmpan@nuaa.edu.cn; Cai, Li-wei
2014-05-15
Highlights: • Plane wave expansion is generalized to superconductor-medium periodic structure. • A wider band gap appears than that in conventional photonic crystals. • Part of original energy levels are rearranged upon consideration of the superconductivity. • Band gap width decreases monotonically with penetration length, but not with the filling factor. • Band gaps can be partially shut down or opened by adjusting filling factor. - Abstract: Based on London theory a general form of wave equation is formulated for both dielectric medium and superconductor. Using the wave equation and applying plane wave expansion, we have numerically calculated the band structures and density of states of a photonic crystal, whose intersection is constructed by a two-dimensional triangular lattice of superconductor padding in dielectric medium. Results indicate a wider band gap in the superconductor-medium photonic crystal than that in conventional photonic crystals. And part of original energy levels are found to be rearranged upon consideration of the superconductivity. The dependence of band gap on penetration length and filling factor is also discussed. Band gap width decreases monotonically with the penetration length, but not with the filling factor. Band gaps can be partially shut down or opened by adjusting filling factor.
(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.
Physics in Superconductors with a Spin Density Wave: Quasiclassical Description of a two-band Model
Moor, Andreas; Volkov, Anatoly; Efetov, Konstantin
2014-03-01
Using a simple model of a two-band superconductor with a spin density wave we investigate the physics in the coexistence regime of the two order parameters, i.e., the spin density wave (SDW) and the superconductivity (SC). We use the quasiclassical Green's functions approach. Our findings concern, i.a., the Knight shift, the proximity and the Josephson effects, and the time and spatial dependence of the magnetic order parameter near the quantum critical point. In particular we find a solution of the stationary equation which describes a domain wall in the magnetic structure. In the center of the domain wall we find a local enhancement of SC. Investigating the stability of a uniform commensurate SDW we obtain the values of the doping parameter at which the first order transition into the state with m = 0 takes place or to the state with an inhomogeneous SDW occurs. We appreciate the financial support from the DFG by the Project EF 11/8-1.
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.
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.
Even- and odd-parity band structures in 125Xe
International Nuclear Information System (INIS)
The level structure of 125Xe has been studied with the (3He,3n?) reaction on an enriched 125Te target using in-beam ?-ray spectroscopic methods. In addition to the negative-parity level structure, an extensive previously unknown positive-parity band structure based on different low-j states was observed. The odd-parity hsub(11/2) level system is well reproduced with the triaxial rotor model. However, the positive-parity band structure is qualitatively interpreted with a particle-plus-vibrating-core model. The observed gsub(7/2) band head at 295.9 keV is an isomeric state with a half-life of 140 +- 30 ns. (author)
Quasi-? and semi-decoupled band structures in 188Pt
International Nuclear Information System (INIS)
A unique and complex transitional region of nuclei, represented by Pt isotopes around N=110, exists between well deformed W and Os nuclei and the spherical Pb nuclei with Z=82. The experimental data on the excited states of 188Pt are rather sparse. In addition, the quasi-? band and the K? = 5-band in this nucleus lack proper description. A detailed analysis and interpretation on these two structures are presented here in this paper
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)
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.
Calculation of electronic structure and density of state for BaTiO3
Salehi, H.; Hosseini, S.M.; N. Shahtahmasebi
2002-01-01
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 wi...
Peculiarities of band structure in bivalent rare earth monosulfides
International Nuclear Information System (INIS)
Total and local partial densities of states in rare-earth (SmS, EuS, YbS) monosulfides were calculated by the Green function method. Calculational results are compared with the x-ray and x-ray electron spectroscopy data. It is established that in YbS and EuS in comparison with SmS a band of metal f-states moves away from the conductivity band bottom thus increasing the energy-gap width. It is concluded with provision for value of charge transfer between sulfur and REE atoms that chemical bond in REE monosulfides is not purely ionic
Wakefield Band Partitioning In Linac Structures
Jones, R. M.; Dolgashev, V.; Bane, K. L. F.; Lin, E.
2002-01-01
In the NLC project multiple bunches of electrons and positrons will be accelerated initially to a centre of mass of 500 GeV and later to 1 TeV or more. In the process of accelerating 192 bunches within a pulse train, wakefields are excited which kick the trailing bunches off axis and can cause luminosity dilution and BBU (Beam Break Up). Several structures to damp the wakefield have been designed and tested at SLAC and KEK and these have been found to successfully damp the w...
Accurate screened exchange band structures for transition metal monoxides MnO, FeO, CoO and NiO
Gillen, Roland; Robertson, John
2012-01-01
We report calculations of the band structures and density of states of the four transition metal monoxides MnO, FeO, CoO and NiO using the hybrid density functional sX-LDA. Late transition metal oxides are prototypical examples of strongly correlated materials, which pose challenges for electronic structure methods. We compare our results with available experimental data and show that our calculations yield accurate predictions for the fundamental band gaps and valence bands...
Calculation of RIXS spectra of cuprates using band structure parameters
Shi, Yifei; Klich, Israel; Benjamin, David; Demler, Eugene
2015-03-01
We explore the quasi particle theory to study the Resonant Inelastic X-ray Scattering(RIXS) by using the band structure parameters. We use both the determinant method(D. Benjamin, I. Klich and E. Demler, Phys. Rev. Lett. 112, 247002(2014)) and the expansion in the core-hole potential. The methods are applied to the (CaxLa1?x)(Ba1 . 75 - xLa0 . 25 + x)Cu3Oy, (x= 0 . 1 and 0 . 4). We find that by using the band structure alone we can obtain quantitative agreement with the experimental data, especially for the position of the peak.
Simulation of the Band Structure of Graphene and Carbon Nanotube
International Nuclear Information System (INIS)
Simulation technique has been performed to simulate the band structure of both graphene and carbon nanotube. Accordingly, the dispersion relations for graphene and carbon nanotube are deduced analytically, using the tight binding model and LCAO scheme. The results from the simulation of the dispersion relation of both graphene and carbon nanotube were found to be consistent with those in the literature which indicates the correctness of the process of simulation technique. The present research is very important for tailoring graphene and carbon nanotube with specific band structure, in order to satisfy the required electronic properties of them.
An algebraic approach to scattering and band structure problems
International Nuclear Information System (INIS)
It is shown that both bound and scattering states of a class of potentials are related to the unitary representations of certain groups. For such systems the scattering matrix can be calculated in a completely algebraic way through the use of the Euclidean group to describe asymptotic behaviour. The band structures associated with a family of periodic potentials can also be obtained from the group theory. These results suggest that an algebraic approach to scattering and band structure problems similar to that applied to bound states is possible
Self-consistent Green's function method for dilute nitride conduction band structure.
Seifikar, Masoud; O'Reilly, Eoin P; Fahy, Stephen
2014-09-10
We present a self-consistent Green's function (SCGF) approach for the Anderson many-impurity model to calculate the band dispersion and density of states near the conduction band edge in GaN(x)As(1-x) dilute nitride alloys. Two different models of the N states have been studied to investigate the band structure of these materials: (1) the two-band model, which assumes all N states have the same energy, EN; (2) a model which includes a full distribution of N states obtained by allowing for direct interaction between N sites. The density of states, projected onto extended and localised states, calculated by the SCGF two-band model, are in excellent agreement with those previously obtained in supercell calculations and reveal a gap in the density of states just above E(N), in contrast with the results of previous non-self-consistent Green's function calculations. However, including the full distribution of N states in a SCGF calculation removes this gap, in agreement with experiment. PMID:25132558
Self-consistent Green's function method for dilute nitride conduction band structure
International Nuclear Information System (INIS)
We present a self-consistent Green's function (SCGF) approach for the Anderson many-impurity model to calculate the band dispersion and density of states near the conduction band edge in GaNxAs1?x dilute nitride alloys. Two different models of the N states have been studied to investigate the band structure of these materials: (1) the two-band model, which assumes all N states have the same energy, EN; (2) a model which includes a full distribution of N states obtained by allowing for direct interaction between N sites. The density of states, projected onto extended and localised states, calculated by the SCGF two-band model, are in excellent agreement with those previously obtained in supercell calculations and reveal a gap in the density of states just above EN, in contrast with the results of previous non-self-consistent Green's function calculations. However, including the full distribution of N states in a SCGF calculation removes this gap, in agreement with experiment. (paper)
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)
Crystal structure, electronic properties and optical band gap of KLa(1?x)Eux(PO3)4
International Nuclear Information System (INIS)
Graphical abstract: Projection along the a axis (a), electronic structure (b) and the Eu3+ concentration effect on the band gap (c) of KLa(1?x)Eux(PO3)4. - Highlights: • Single crystal and Eu3+ doped powders of KLa(PO3)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(1?x)Eux(PO3)4 have been investigated. The KLa(PO3) belongs to P21 space group characterized by three-dimensional framework built of (PO3)n chains. The energy-band structure, density of states, chemical bonds, and the band gap energy of KLa(PO3)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(1?x)Eux(PO3)4 showed that the substitution between Eu3+ and La3+ influenced the distribution of the electronic structure and therefore determined the band gap energy
The electronic band structure of CoS{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Wu Ning [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0111 (United States); Losovyj, Ya B [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0111 (United States); Wisbey, David [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0111 (United States); Belashchenko, K [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0111 (United States); Manno, M [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455 (United States); Wang, L [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455 (United States); Leighton, C [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455 (United States); Dowben, P A [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0111 (United States)
2007-04-16
Angle-resolved and energy-dependent photoemission was used to study the band structure of paramagnetic CoS{sub 2} from high-quality single-crystal samples. A strongly dispersing hybridized Co-S band is identified along the {gamma}-X line. Fermi level crossings are also analysed along this line, and the results are interpreted using band structure calculations. The Fermi level crossings are very sensitive to the separation in the S-S dimer, and it is suggested that the half-metallic gap in CoS{sub 2} may be controlled by the bonding-antibonding splitting in this dimer, rather than by exchange splitting on the Co atoms.
Phonon Band Structure and Thermal Transport Correlation in a Layered Diatomic Crystal
McGaughey, A J H; Landry, E S; Kaviany, M; Hulbert, G M
2006-01-01
To elucidate the relationship between a crystal's structure, its thermal conductivity, and its phonon dispersion characteristics, an analysis is conducted on layered diatomic Lennard-Jones crystals with various mass ratios. Lattice dynamics theory and molecular dynamics simulations are used to predict the phonon dispersion curves and the thermal conductivity. The layered structure generates directionally dependent thermal conductivities lower than those predicted by density trends alone. The dispersion characteristics are quantified using a set of novel band diagram metrics, which are used to assess the contributions of acoustic phonons and optical phonons to the thermal conductivity. The thermal conductivity increases as the extent of the acoustic modes increases, and decreases as the extent of the stop bands increases. The sensitivity of the thermal conductivity to the band diagram metrics is highest at low temperatures, where there is less anharmonic scattering, indicating that dispersion plays a more prom...
Photonic Band Gap structures: A new approach to accelerator cavities
Energy Technology Data Exchange (ETDEWEB)
Kroll, N. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics]|[Stanford Linear Accelerator Center, Menlo Park, CA (United States); Smith, D.R.; Schultz, S. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics
1992-12-31
We introduce a new accelerator cavity design based on Photonic Band Gap (PGB) structures. The PGB cavity consists of a two-dimensional periodic array of high dielectric, low loss cylinders with a single removal defect, bounded on top and bottom by conducting sheets. We present the results of both numerical simulations and experimental measurements on the PGB cavity.
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.
Gutermuth, R A; 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 gas expulsion and dynamical expansion have occured. We estimate stellar volume densities from nearest neighbor distances, and discuss the impact of these densities on the evolution of circumstellar disks and protostellar envelopes in these regions.
Band structures and alignment properties in 74Se
Döring, J.; Johns, G. D.; Riley, M. A.; Tabor, S. L.; Sun, Y.; Sheikh, J. A.
1998-06-01
High-spin states in the even-even nucleus 74Se were investigated via the 65Cu(12C, p2n)74Se reaction at a beam energy of 50 MeV. On the basis of coincidence data three of the known bands were extended to higher spins and two new bands were found. Experimental crossing frequencies were deduced for various band structures and compared with cranked-shell-model results. Previous assignments of g9/2 quasiproton and g9/2 quasineutron alignments along the yrast line were confirmed when a near-prolate shape is assumed. Hartree-Fock-Bogoliubov calculations predict a deformed shape for excited states in 74Se which shows, however, a considerable softness in triaxiality. For the first time in the mass 70 region, band structures and quasiparticle alignments in 74Se were also investigated using the projected shell model. The calculations support the previous conclusions for the positive-parity states and predict that the lowest negative-parity bands are signature partners based on g9/2 quasiproton excitations, with a g9/2 quasineutron crossing at higher frequencies leading to a four-quasiparticle configuration at high spins.
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
Extended Hückel theory for band structure, chemistry, and transport. I. Carbon nanotubes
Kienle, D.; Cerda, J. I.; Ghosh, A. W.
2006-08-01
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, 043715 (2006), following paper]. We find that when it comes to quantum transport through interesting, complex heterostructures including gas molecules adsorbed on nanotubes, the Hückel band structure offers a fair and practical compromise between orthogonal tight-binding theories with limited transferability between environments under large distortion and density functional theories that are computationally quite expensive for the same purpose.
Density Functional Theory of Structural and Electronic Properties of III-N Semiconductors
International Nuclear Information System (INIS)
In this wok, we present the density functional theory (DFT) calculations of cubic III-N based semiconductors by using the full potential linear augmented plane-wave method plus local orbitals as implemented in the WIEN2k code. Our aim is to predict the pressure effect on structural and electronic properties of III-N binaries and ternaries. Results are given for structural properties (e.g., lattice constant, elastic constants, bulk modulus, and its pressure derivative) and electronic properties (e.g., band structure, density of states, band gaps and band widths) of GaAs, GaN, AlN, and InN binaries and GaAsN ternaries. The proposed model uses GGA exchange-correlation potential to determine band gaps of semiconductors at ?, L and X high symmetry points of Brillouin zone. The results are found in good agreement with available experimental data for structural and electronic properties of these semiconductors.
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.
Extensive ?-ray spectroscopy of band structures in 3062Zn32
Gellanki, J.; Rudolph, D.; Ragnarsson, I.; Andersson, L.-L.; Andreoiu, C.; Carpenter, M. P.; Ekman, J.; Fahlander, C.; Johansson, E. K.; Kardan, A.; Reviol, W.; Sarantites, D. G.; Seweryniak, D.; Svensson, C. E.; Waddington, J. C.
2012-09-01
An experimental study of the 62Zn nucleus has been performed by combining the data sets from four fusion-evaporation reaction experiments. Apart from the previously published data, the present results include ten new rotational band structures and two more superdeformed bands. The Gammasphere Ge-detector array in conjunction with the 4? charged-particle detector array Microball allowed for the detection of ? rays in coincidence with evaporated light particles. The deduced level scheme includes some 260 excited states, which are connected with more than 450 ?-ray transitions. Spins and parities of the excited states have been determined via directional correlations of ? rays emitted from oriented states. The experimental characteristics of the rotational bands are analyzed and compared with results from cranked Nilsson-Strutinsky calculations. The present analysis, combined with available experimental results in the A˜60 mass region, can be used to improve the current set of Nilsson parameters in the N=3 and N=4 oscillator shells.
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.
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...
Local density of optical states in the band gap of a finite photonic crysta
Yeganegi, Elahe; Mosk, Allard P; Vos, Willem L
2014-01-01
We study the local density of states (LDOS) in a finite photonic crystal, in particular in the frequency range of the band gap. We propose a new point of view on the band gap, which we consider to be the result of vacuum fluctuations in free space that tunnel in the forbidden range in the crystal. As a result, we arrive at a model for the LDOS that is in two major items modified compared to the well-known expression for infinite crystals. Firstly, we modify the Dirac delta functions to become Lorentzians with a width set by the crystal size. Secondly, building on characterization of the fields versus frequency and position we calculated the fields in the band gap. We start from the fields at the band edges, interpolated in space and position, and incorporating the exponential damping in the band gap. We compare our proposed model to exact calculations in one dimension using the transfer matrix method and find very good agreement. Notably, we find that in finite crystals, the LDOS depends on frequency, on posi...
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)
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.
Development of X-band accelerating structures for high gradients
International Nuclear Information System (INIS)
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. (authors)
The quiet Sun's magnetic flux estimated from CaIIH bright inter-granular G-band structures
Bovelet, Burkart; Wiehr, Eberhard
2012-01-01
We determine the number density and area contribution of small-scale inter-granular calcium-II bright G-band structures in images of the quiet Sun as tracers of kilo-Gauss magnetic flux-concentrations. In a 149" x 117" G-band image of the disk center at the activity minimum, 7593 small inter-granular structures ['IGS']were segmented with the `multiple-level tracking' pattern recognition algorithm ['MLT_4']. The scatter-plot of the continuum versus the G-band brightness sho...
Spectral Density Functionals for Electronic Structure Calculations
Savrasov, S Y
2001-01-01
We introduce a functional of the local spectral electron density which can be used to to compute the total energy and the local spectral function of strongly-correlated materials. We illustrate the applicability of the method by using as an example the long-standing problem of the electronic structure of metallic plutonium.
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...
Electronic structure of BaCu$_2$As$_2$ and SrCu$_2$As$_2$: sp-band metals
Singh, D.J.
2009-01-01
The electronic structures of ThCr$_2$Si$_2$ structure BaCu$_2$As$_2$ and SrCu$_2$As$_2$ are investigated using density functional calculations. The Cu $d$ orbitals are located at 3 eV and higher binding energy, and are therefore chemically inert with little contribution near the Fermi energy. These materials are moderate density of states, sp-band metals with large Fermi surfaces and low anisotropy.
International Nuclear Information System (INIS)
The crystal structure of four bialkali alanates has been calculated by accurate density functional band structure calculations: K2LiAlH6, K2NaAlH6, KNa2AlH6, and LiNa2AlH6. The latter hydride has been synthesized previously, but its crystal structure has not been reported before. The former three have previously been shown to be stable. They are all quite similar to the calculated Na3AlH6 and K3AlH6 structures, which are also presented. The unit cell size and the tilting angle of the AlH6 octahedra are the largest differences between the structures. Total and local densities of states are presented as well as a Hirshfeld charge analysis for all the stable compounds
Band structure of absorptive two-dimensional photonic crystals
van der Lem, Han; Tip, Adriaan; Moroz, Alexander
2003-06-01
The band structure for an absorptive two-dimensional photonic crystal made from cylinders consisting of a Drude material is calculated. Absorption causes the spectrum to become complex and form islands in the negative complex half-plane. The boundaries of these islands are not always formed by the eigenvalues calculated for Bloch vectors on the characteristic path, and we find a hole in the spectrum. For realistic parameter values, the real part of the spectrum is hardly influenced by absorption, typically less than 0.25%. The employed method uses a Korringa-Kohn-Rostoker procedure together with analytical continuation. This results in an efficient approach that allows these band-structure calculations to be done on a Pentium III personal computer.
Structure of superdeformed bands in the A ? 150 mass region
International Nuclear Information System (INIS)
The structure of superdeformed rotational bands recently discovered around 152Dy is discussed within the deformed shell model based on an average Woods-Saxon potential with a monopole pairing force. A comparison with available experimental data is provided and detailed predictions for yet unobserved cases are given. Pronounced variations in the observed rotational pattern are attributed to the angular momentum alignment of the high-N intruder (quasi)particles. (orig.)
Probing the band-structures and carrier dynamics of single GaAsSb nanowire heterostructures
Wang, Yuda; Badada, Bekele; Jackson, Howard; Smith, Leigh; Yuan, Xiaoming; Caroff, Philippe; Fu, Lan; Tan, Hoe; Jagadish, Chennupati
2015-03-01
We present the band structure and carrier relaxation of MOVCD grown single GaAs1-xSbx using photocurrent (PC) spectroscopy and transient Rayleigh Scattering (TRS) spectroscopy techniques. The PC spectroscopy was performed on nanowire devices fabricated using e-beam lithography and deposition of Ti/Au as contacts. The devices show nearly Ohmic behavior and are photosensitive. PC spectra shows an onset of absorption at room temperature in agreement with reported values of bulk GaAs0.6Sb0.4. We also used low temperature (10K) transient Rayleigh scattering (TRS) spectroscopy to measure the band structure as well as carrier relaxation dynamics of individual GaAsSb (x=30% and 40%) nanowires with and without InP passivation layers. The band gaps extracted from the TRS experiments are consistent with both photoluminescence (PL) measurements and theoretical predictions. The InP passivated GaAsSb shows smaller Eg due to the tensile strain from InP on GaAsSb as well as longer lifetimes due to the surface passivation. The carrier density and temperature are extracted by a phenomenological fitting model based on band to band transition theory. We acknowledge the NSF through DMR-1105362, 1105121 and ECCS-1100489, and the Australian Research Council.
Ab initio calculations of band structure and thermophysical properties for SnS2 and SnSe2
He, Xiancong; Shen, Honglie
2012-04-01
The electronic band structure and elastic constants of SnS2 and SnSe2 have been calculated by using density-functional theory (DFT). The calculated band structures show that SnS2 and SnSe2 are both indirect band gap semiconductors. The upper valence bands originate mainly from Sp and Snd electrons, while the lowest conduction bands are mainly from (S, Se) p and Sns states. The calculated elastic constants indicate that the bonding strength along the [100] and [010] direction is stronger than that along the [001] direction and the shear elastic properties of the (010) plane are anisotropic for SnS2 and SnSe2. Both compounds exhibit brittle behavior due to their low B/G ratio. Relationships among volumes, the heat capacity, thermal expansion coefficients, entropy, vibrational energy, internal energy, Gibbs energy and temperature at various pressures are also calculated by using the Debye mode in this work.
Band structure, optical properties and infrared spectrum of glycine sodium nitrate crystal
Hernández-Paredes, J.; Glossman-Mitnik, D.; Esparza-Ponce, H. E.; Alvarez-Ramos, M. E.; Duarte-Moller, A.
2008-03-01
Glycine-sodium nitrate, GSN, crystals were grown from a stoichiometric solution by slow cooling technique and were characterized by optical absorption and FTIR spectroscopy. The data collected by FTIR were compared with the vibrational spectrum theoretically obtained by using DMol code in the local density approximation LDA. Moreover, the crystal band structure, the density of states, and the optical absorption data were calculated by using the CASTEP code within the framework of LDA and the generalized gradient approximation GGA. The calculations are in good agreement with the structure and properties of GSN; e.g., the optical transparency in visible region, the low density, the insulate character, and the bipolar form of glycine molecule.
Band structure of semimagnetic Hg1-yMnyTe quantum wells
Novik, E G; Jungwirth, T; Latussek, V; Becker, C R; Landwehr, G; Buhmann, H; Molenkamp, L W
2004-01-01
The band structure of semimagnetic Hg_1-yMn_yTe/Hg_1-xCd_xTe type-III quantum wells has been calculated using eight-band kp model in an envelope function approach. Details of the band structure calculations are given for the Mn free case (y=0). A mean field approach is used to take the influence of the sp-d exchange interaction on the band structure of QW's with low Mn concentrations into account. The calculated Landau level fan diagram and the density of states of a Hg_0.98Mn_0.02Te/Hg_0.3Cd_0.7Te QW are in good agreement with recent experimental transport observations. The model can be used to interpret the mutual influence of the two-dimensional confinement and the sp-d exchange interaction on the transport properties of Hg_1-yMn_yTe/Hg_1-xCd_xTe QW's.
Nuclear energy density optimization: Shell structure
Kortelainen, M.; McDonnell, J.; Nazarewicz, W.; Olsen, E.; Reinhard, P.-G.; Sarich, J.; Schunck, N.; Wild, S. M.; Davesne, D.; Erler, J.; Pastore, A.
2014-05-01
Background: Nuclear density functional theory is the only microscopical theory that can be applied throughout the entire nuclear landscape. Its key ingredient is the energy density functional. Purpose: In this work, we propose a new parametrization unedf2 of the Skyrme energy density functional. Methods: The functional optimization is carried out using the pounders optimization algorithm within the framework of the Skyrme Hartree-Fock-Bogoliubov theory. Compared to the previous parametrization unedf1, restrictions on the tensor term of the energy density have been lifted, yielding a very general form of the energy density functional up to second order in derivatives of the one-body density matrix. In order to impose constraints on all the parameters of the functional, selected data on single-particle splittings in spherical doubly-magic nuclei have been included into the experimental dataset. Results: The agreement with both bulk and spectroscopic nuclear properties achieved by the resulting unedf2 parametrization is comparable with unedf1. While there is a small improvement on single-particle spectra and binding energies of closed shell nuclei, the reproduction of fission barriers and fission isomer excitation energies has degraded. As compared to previous unedf parametrizations, the parameter confidence interval for unedf2 is narrower. In particular, our results overlap well with those obtained in previous systematic studies of the spin-orbit and tensor terms. Conclusions: unedf2 can be viewed as an all-around Skyrme EDF that performs reasonably well for both global nuclear properties and shell structure. However, after adding new data aiming to better constrain the nuclear functional, its quality has improved only marginally. These results suggest that the standard Skyrme energy density has reached its limits, and significant changes to the form of the functional are needed.
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.
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.
Dual-band metamaterial with a windmill-like structure
Xiong, Han; Hong, Jing-Song; Jin, Da-Lin
2013-01-01
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.
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)
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)
Courrol, L. C.; Monteiro, A. M.; Silva, F. R. O.; Gomes, L.; Vieira, N. D., Jr.; Gidlund, M. A.; Figueiredo Neto, A. M.
2007-05-01
We report here the observation of the enhancement of Europium-tetracycline complex emission in Low Density Lipoprotein (LDL) solutions. Europium emission band of tetracycline solution containing Europium (III) chloride hexahydrate was tested to obtain effective enhancement in the presence of native LDL and oxidized LDL. Europium emission lifetime in the presence of lipoproteins was measured, resulting in a simple method to measure the lipoproteins quantity in an aqueous solution at physiological pH. This method shows that the complex can be used as a sensor to determine the different states of native and oxidized LDL in biological fluids.
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.
Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Shkumat, P. N.; Myronchuk, G. L.; Khvyshchun, M.; Fedorchuk, A. O.; Parasyuk, O. V.; Khyzhun, O. Y.
2015-04-01
High-quality single crystal of cesium mercury tetraiodide, Cs2HgI4, has been synthesized by the vertical Bridgman-Stockbarger method and its crystal structure has been refined. In addition, electronic structure and optical properties of Cs2HgI4 have been studied. For the crystal under study, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that the Cs2HgI4 single crystal surface is very sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface alters the elemental stoichiometry of the Cs2HgI4 surface. To elucidate peculiarities of the energy distribution of the electronic states within the valence-band and conduction-band regions of the Cs2HgI4 compound, we have performed first-principles band-structure calculations based on density functional theory (DFT) as incorporated in the WIEN2k package. Total and partial densities of states for Cs2HgI4 have been calculated. The DFT calculations reveal that the I p states make the major contributions in the upper portion of the valence band, while the Hg d, Cs p and I s states are the dominant contributors in its lower portion. Temperature dependence of the light absorption coefficient and specific electrical conductivity has been explored for Cs2HgI4 in the temperature range of 77-300 K. Main optical characteristics of the Cs2HgI4 compound have been elucidated by the first-principles calculations.
Effects of strain on the band structure of group-III nitrides
Yan, Qimin; Rinke, Patrick; Janotti, Anderson; Scheffler, Matthias; Van de Walle, Chris G.
2014-09-01
We present a systematic study of strain effects on the electronic band structure of the group-III-nitrides (AlN, GaN and InN) in the wurtzite phase. The calculations are based on density functional theory with band-gap-corrected approaches including the Heyd-Scuseria-Ernzerhof hybrid functional (HSE) and quasiparticle G0W0 methods. We study strain effects under realistic strain conditions, hydrostatic pressure, and biaxial stress. The strain-induced modification of the band structures is found to be nonlinear; transition energies and crystal-field splittings show a strong nonlinear behavior under biaxial stress. For the linear regime around the experimental lattice parameters, we present a complete set of deformation potentials (acz, act, D1, D2, D3, D4, D5, D6) that allows us to predict the band positions of group-III nitrides and their alloys (InGaN and AlGaN) under realistic strain conditions. The benchmarking G0W0 results for GaN agree well with the HSE data and indicate that HSE provides an appropriate description for the band structures of nitrides. We present a systematic study of strain effects on the electronic band structure of the group-III nitrides (AlN, GaN, and InN). We quantify the nonlinearity of strain effects by introducing a set of bowing parameters. We apply the calculated deformation potentials to the prediction of strain effects on transition energies and valence-band structures of InGaN alloys and quantum wells (QWs) grown on GaN, in various orientations (including c-plane, m-plane, and semipolar). The calculated band gap bowing parameters, including the strain effect for c-plane InGaN, agree well with the results obtained by hybrid functional alloy calculations. For semipolar InGaN QWs grown in (202¯1), (303¯1), and (303¯1¯) orientations, our calculated deformation potentials have provided results for polarization ratios in good agreement with the experimental observations, providing further confidence in the accuracy of our values.
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
Lamé polynomials, hyperelliptic reductions and Lamé band structure.
Maier, Robert S
2008-03-28
The band structure of the Lamé equation, viewed as a one-dimensional Schrödinger equation with a periodic potential, is studied. At integer values of the degree parameter l, the dispersion relation is reduced to the l=1 dispersion relation, and a previously published l=2 dispersion relation is shown to be partly incorrect. The Hermite-Krichever Ansatz, which expresses Lamé equation solutions in terms of l=1 solutions, is the chief tool. It is based on a projection from a genus-l hyperelliptic curve, which parametrizes solutions, to an elliptic curve. A general formula for this covering is derived, and is used to reduce certain hyperelliptic integrals to elliptic ones. Degeneracies between band edges, which can occur if the Lamé equation parameters take complex values, are investigated. If the Lamé equation is viewed as a differential equation on an elliptic curve, a formula is conjectured for the number of points in elliptic moduli space (elliptic curve parameter space) at which degeneracies occur. Tables of spectral polynomials and Lamé polynomials, i.e. band-edge solutions, are given. A table in the earlier literature is corrected. PMID:17588866
Microscopic study of band structure of some actinide nuclei
International Nuclear Information System (INIS)
Recently, in beam measurements for the actinide region have been performed for gamma ray spectroscopy of even-even and odd mass nuclei. They reveal that these nuclei are well deformed at low spins near the ground state and exhibit very similar collective behavior with regular rotational level sequence. Some non-yrast and isomeric states have been observed in actinide nuclei. The yielded data contain useful information on excited levels and configurations of multi-quasiparticle states and they test strictly current nuclear models. Zhu et al have studied the high spin states in some odd U and Pu nuclei. They have interpreted the experimental data in the framework of cranked shell model and observed that there is striking difference in behavior between the A = 238, 240 even Pu isotopes and other actinide nuclei that require further theoretical investigation. In order to investigate the band structure of some even-even and odd actinide nuclei, the Projected Shell Model (PSM) approach has been employed. In the present piece of work we have obtained the yrast bands, band diagrams and electromagnetic quantities of some even-even and odd mass uranium (U) and protactinium (Pu) nuclei
Anomalous Quasiparticle Lifetime in Graphite Band Structure Effects
Spataru, C D; Rubio, A; Benedict, L X; Echenique, P M; Louie, S G; Spataru, Catalin D.; Cazalilla, Miguel A.; Rubio, Angel; Benedict, Lorin X.; Echenique, Pedro M.; Louie, Steven G.
2001-01-01
We report ab initio calculation of quasiparticle lifetimes in graphite, as determined from the imaginary part of the self-energy operator within the GW aproximation. The inverse lifetime in the energy range from 0.5 to 3.5 eV above the Fermi level presents significant deviations from the quadratic behavior naively expected from Fermi liquid theory. The deviations are explained in terms of the unique features of the band structure of this material. We also discuss the experimental results from different groups and make some predictions for future experiments.
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)
Extended Hückel theory for band structure, chemistry, and transport. II. Silicon
Kienle, D.; Bevan, K. H.; Liang, G.-C.; Siddiqui, L.; Cerda, J. I.; Ghosh, A. W.
2006-08-01
In this second paper, we develop transferable semiempirical extended Hückel theoretical (EHT) parameters for the electronic structure of another technologically important material, namely, silicon. The EHT parameters are optimized to experimental target values of the band dispersion of bulk silicon. We quantitatively benchmark our parameters to bulk electronic properties such as band edge energies and locations, effective masses, and spin-orbit coupling parameters, competitive with a nearest-neighbor sp3d5s* orthogonal tight-binding model for silicon of T. Boykin et al. [Phys. Rev. B 69, 115201 (2004)] that has been widely used to model silicon-based devices (see, e.g., A. Rahman et al. [Jpn. J. Appl. Phys. Part I 44, 2187 (2005)] and J. Wang et al. [Appl. Phys. Lett. 86, 093113 (2005)]). The transferability of the parameters is checked for multiple physical and chemical configurations, specifically, two different reconstructed surfaces, Si(100)-(2×1) and Si(111)-(2×1). The robustness of the parameters to different environments is demonstrated by comparing the surface band structures with density functional theory GW calculations and photoemission/inverse photoemission experiments. We further apply the approach to calculate the one-dimensional band dispersion of an unrelaxed rectangular silicon nanowire and explore the chemistry of surface passivation by hydrogen. Our EHT parameters thus provide a quantitative model of bulk silicon and silicon-based interfaces such as contacts and reconstructed surfaces, which are essential ingredients towards a quantitative quantum transport simulation through silicon-based heterostructures.
Directory of Open Access Journals (Sweden)
H. Salehi
2011-09-01
Full Text Available The electronic structure, energy band structure, total density of states (DOS and electronic density of perovskite SrTiO_{3} in the cubic phase are calculated by the using full potential-linearized augmented plane wave (FP-LAPW method in the framework density functional theory (DFT with the generalized gradient approximation (GGA by WIEN2k package. The calculated band structure shows a direct band gap of 2.5 eV at the ? point in the Brillouin zone.The total DOS is compared with experimental x-ray photoemission spectra. From the DOS analysis, as well as charge-density studies, I have conclude that the bonding between Sr and TiO_{2} is mainly ionic and that the TiO_{2} entities bond covalently.The calculated band structure and density of state of SrTiO_{3} are in good agreement with theoretical and experimental results.
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.
High-Pressure and Electronic Band Structure Studies on MoBC
Falconi, R.; de la Mora, P.; Morales, F.; Escamilla, R.; Camacho, C. O.; Acosta, M.; Escudero, R.
2015-05-01
In this work, high-pressure electrical resistivity measurements and electronic structure analysis on the intermetallic MoBC system are presented. Electrical resistivity measurements up to about 5 GPa using a diamond anvil cell on MoBC revealed that decreases in a non-monotonic way. Using Linearized Augmented Plane Wave method based on Density Functional Theory, we investigate the changes in the electronic structure of this compound as a function of pressure. The states at the Fermi level mainly come from the d orbitals of molybdenum atoms. As the pressure increases, the band width is enhanced and the total density of states at the Fermi level decreases. The Fermi surface for this compound possesses a two-dimensional character which prevails under an applied pressure of about 10 GPa. The results are compared with the chemical pressure effects on induced by the gradual and non-simultaneous elimination of B and C in the compound.
Band-structure calculations of specular reflection in spin valves
International Nuclear Information System (INIS)
Band structure calculations are carried out on three types of spin-valve structures: (1) simple spin valves, (2) dual spin valves, and (3) spin valves with a synthetic antiferromagnet. The effect of specular reflection is studied by comparing the transport properties of spin valves with resistive metallic and insulating layers at the outer boundaries. In the spin valve with a synthetic antiferromagnet, an insulating layer needs to be inserted inside the reference layer to achieve similar enhancement to the giant magnetoresistance as the other two types of spin valves with insulating outer boundaries. Results are analyzed in terms of s - d scattering in the different spin channels with different boundary conditions. [copyright] 2001 American Institute of Physics
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 ...
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.
Relativistic Band Structure and Fermi Surface of PdTe2 by the LMTO Method
DEFF Research Database (Denmark)
Jan, J. P.; Skriver, Hans Lomholt
1977-01-01
The energy bands of the trigonal layer compound PdTe2 have been calculated, using the relativistic linear muffin-tin orbitals method. The bandstructure is separated into three distinct regions with low-lying Te 5s bands, conduction bands formed by Pd 4d and Te 5p states, and high-lying bands formed by Pd 5p, Te 6s and Te 5d states. Density of states and joint density of states have been calculated from the bands determined over the appropriate irreducible zone. The Fermi surface consists of two closed sheets in band 11 and band 13, and sheets in band 12 connected to one another by tubes. The results allow an explanation of most of the de Haas-van Alphen frequencies observed previously.
Touching points in the energy band structure of bilayer graphene superlattices
International Nuclear Information System (INIS)
The energy band structure of the bilayer graphene superlattices with zero-averaged periodic ?-function potentials are studied within the four-band continuum model. Using the transfer matrix method, the study is mainly focused on examining the touching points between adjacent minibands. For the zero-energy touching points the dispersion relation derived shows a Dirac-like double-cone shape with the group velocity which is periodic in the potential strength P with the period of ? and becomes anisotropic at relatively large P. From the finite-energy touching points we have identified those located at zero wave-number. It was shown that for these finite-energy touching points the dispersion is direction-dependent in the sense that it is linear or parabolic in the direction parallel or perpendicular to the superlattice direction, respectively. We have also calculated the density of states and the conductivity which demonstrates a manifestation of the touching points examined. (paper)
Band structure and optical functions of K2ZnCl4 crystals in ferroelectric phase
International Nuclear Information System (INIS)
Band electronic structure (BS), density of states (DOS), and optical functions of K2ZnCl4 crystal for the orthorhombic space group of symmetry Pna21 corresponding to the ferroelectric phase (12 formula units in the crystallographic unit cell) have been calculated for the first time using the density functional theory based code VASP (Vienna Ab-initio Simulation Program). The valence-to-conduction band gap Eg of the crystal is found to be direct in the ?-point of Brillouin zone. The effective masses m* have been calculated for the top valence and bottom conduction bands for different points and directions of Brillouin zone of the crystal and the results obtained have been analyzed. Peculiarities of the photon energy dependences n(E) and k(E) of refractive (n) and absorption (k) indices obtained in the range 0-28 eV have been identified on the basis of BS and DOS of the crystal. Calculated optical functions agree satisfactorily with the experimental data n(E) in the range of crystal's transparency, E < 5 eV.
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.
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.
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...
Semiconductor Nanocrystals: Structure, Properties, and Band Gap Engineering
SMITH, ANDREW M.; NIE, SHUMING
2010-01-01
Semiconductor nanocrystals are tiny light-emitting particles on the nanometer scale. Researchers have studied these particles intensely and have developed them for broad applications in solar energy conversion, optoelectronic devices, molecular and cellular imaging, and ultrasensitive detection. A major feature of semiconductor nanocrystals is the quantum confinement effect, which leads to spatial enclosure of the electronic charge carriers within the nanocrystal. Because of this effect, researchers can use the size and shape of these “artificial atoms” to widely and precisely tune the energy of discrete electronic energy states and optical transitions. As a result, researchers can tune the light emission from these particles throughout the ultraviolet, visible, near-infrared, and mid-infrared spectral ranges. These particles also span the transition between small molecules and bulk crystals, instilling novel optical properties such as carrier multiplication, single-particle blinking, and spectral diffusion. In addition, semiconductor nanocrystals provide a versatile building block for developing complex nanostructures such as superlattices and multimodal agents for molecular imaging and targeted therapy. In this Account, we discuss recent advances in the understanding of the atomic structure and optical properties of semiconductor nanocrystals. We also discuss new strategies for band gap and electronic wave function engineering to control the location of charge carriers. New methodologies such as alloying, doping, strain-tuning, and band-edge warping will likely play key roles in the further development of these particles for optoelectronic and biomedical applications. PMID:19827808
Band structure of ABC-trilayer graphene superlattice
Uddin, Salah; Chan, K. S.
2014-11-01
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.
Self-consistent band structure of the rutile dioxides NbO2, RuO2, and IrO2
Xu, J. H.; Jarlborg, T.; Freeman, A. J.
1989-10-01
The electronic structures of the rutile dioxides NbO2, RuO2, and IrO2 have been determined from self-consistent semirelativistic linear muffin-tin-orbital band calculations. The basis set is completed with s and p functions from ``empty spheres'' inserted in the open parts of the structure. The band results are analyzed in terms of Fermi-surface features, band positions, x-ray photoemission spectra, and joint density-of-state functions. Comparisons with available experimental data are, in general, favorable. In particular, the effects from self-consistency are pointed out by comparison with earlier non-self-consistent band results.
Experimental determination of the band structure of photonic crystals of colloidal silica spheres
International Nuclear Information System (INIS)
A photonic band structure of colloidal crystals of silica spheres is analytically determined by a band model with three fitting parameters: the sphere size, the effective refractive index, and the band-gap. Optical properties of the crystals annealed at various temperatures were characterized by a procedure similar to X-ray diffraction technique, and the width of photonic band-gap measured from the transmission spectra experimentally servers as an additional check on the validation of the model. The photonic band structures defined by the band-gap, the refractive index, and the Brillouin zone are obviously superior to the use of the Bragg's expression involving simple zone folding.
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.
Band-structure analysis from photoreflectance spectroscopy in (Ga,Mn)As
International Nuclear Information System (INIS)
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
Spectral Density Functionals for Electronic Structure Calculations
Savrasov, S Y
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 basis--set dependent. However, it produces the exact total energy and local excitational spectrum provided that the exact functional is extremized. The self--energy of the theory appears as an auxiliary mass operator similar to the introduction of the ground--state Kohn--Sham potential in density functional theory. It is automatically short--ranged in the same region of Hilbert space which defines the local Green function. We exploit this property to find good approximations to the functional. For example, if electronic self--energy is kn...
Quasi Normal Modes description of transmission properties for Photonic Band Gap structures
Settimi, A; Hoenders, B J
2008-01-01
In this paper, we use the 'Quasi Normal Modes' (QNM) approach for discussing the transmission properties of double-side opened optical cavities: in particular, this approach is specified for one dimensional (1D) 'Photonic Band Gap' (PBG) structures. Moreover, we conjecture that the density of the modes (DOM) is a dynamical variable which has the flexibility of varying with respect to the boundary conditions as well as the initial conditions; in fact, the e.m. field generated by two monochromatic counter-propagating pump waves leads to interference effects inside a quarter-wave (QW) symmetric 1D-PBG structure. Finally, here, for the first time, a large number of theoretical assumptions on QNM metrics for an open cavity, never discussed in literature, are proved, and a simple and direct method to calculate the QNM norm for a 1D-PBG structure is reported.
The effects of band structure on recombination processes in narrow gap materials and laser diodes
International Nuclear Information System (INIS)
The work described in this thesis investigates the effects of band structure modifications, brought about by Landau confinement, hydrostatic pressure and uniaxial stress, on recombination processes in narrow-gap materials and laser diodes. The effects of Landau confinement on the characteristics of InSb-based emission devices operating at a wavelength of ?5?m at 77K were studied. The change in performance due to the magnetic field applied along both the cavity and the growth direction and thereby simulating quasi-quantum wire and quasi-quantum dot structures clearly demonstrated the benefits, such as reduced threshold and temperature sensitivity, gained by the reduced dimensionality. On the other hand, suppression of LO-phonon emission due to the discrete nature of the density of states was observed, for the first time, in an interband laser device. Interband recombination dynamics were studied in In1-xGaxSb and PbSe over a range of excited carrier densities and temperatures down to 30K. Detailed analysis of the results found that the Auger-1 mechanism is reduced in In1-xGaxSb as a function of Ga-fraction due to the increased bandgap energy, in good agreement with theoretical predictions. In PbSe, the Auger-1 rate was observed to dominate at low excited carrier concentrations in spite of near-mirror bands, and was found to be approximately constant between 300K and 70K and was seen to be quenched in the low temperature regime. Stimulated emission was seen to be the most efficient recombination mechanism at high excited carrier densities at low temperatures. The Auger coefficient in PbSe was found to be one to two orders of magnitude lower than for materials with a Kane band structure (Hg1-xCdxTe) with comparable bandgap. An experimental technique was developed which enables measurements at high hydrostatic pressures and high magnetic fields at low temperatures. Hydrostatic pressures were applied to a 1.5?m laser diode at different temperatures revealing the effects of pressure on the band structure and hence the laser characteristics. A visible laser diode was measured under the simultaneous application of hydrostatic pressure and uniaxial stress. The change in performance was satisfactorily explained in terms of leakage of carriers into the X-minimum in the cladding region, the process that has been suspected of being one of the major loss mechanisms in visible laser diodes. (author)
Inverse band structure method via genetic algorithm for nanostructures
Kim, Kwiseon; Jones, Wesley B.; Zunger, Alex
2004-03-01
With the increased efficiency and accuracy of electronic structure methods, the inverse problem of material design has been tackled in e.g. Refs [1,2]. The inverse problems are solved by optimization, repeatedly applying the forward solving method while scanning the configuration space. We have implemented the inverse method for semiconductor alloys (iaga) by optimization using a genetic algorithm and PGAPack [3]. The forward solver employed is the parallel folded spectrum electronic structure method (PESCAN) with LDA-based empirical pseudopotentials, which has been run on up to million atom supercells. Hierarchical parallelism is adopted for using the parallel forward solver and the parallel genetic algorithm. Examples of inverse band structure results on AlGaAs alloys and superlattices will be presented. The approach is adaptable to a wide range of applications when combined with the efficient forward solvers. [1] A. Franceschetti and A. Zunger, Nature 402, 60 (1999). [2] G. H. Johannesson, et al., Phys. Rev. Lett. 88, 255506 (2002). [3] D. Levine, PGAPack: Parallel Genetic Algorithm Library (1998), T. Cwik and G. Klimeck, Proc. of 1st NASA/DoD Workshop on Evolvable Hardware, IEEE (1999).
Optical conductivity and x-ray absorption and emission study of the band structure of MnN films
Granville, S.; Ruck, B. J.; Budde, F.; Koo, A.; Downes, J. E.; Trodahl, H. J.; Bittar, A.; Strickland, N.; Williams, G. V.; Lambrecht, W. R.; Learmonth, Timothy; Smith, Kevin E.; Kennedy, V. J.; Markwitz, A.; Schmitt, Thorsten
2005-11-01
The band structure of MnN films prepared by ion assisted deposition has been investigated by optical conductivity and x-ray absorption and emission spectroscopies. X-ray diffraction and extended x-ray absorption fine structure show the films to be nanocrystalline but phase pure and exhibiting the known antiferromagnetic distorted rocksalt phase. X-ray emission spectroscopy of the N K -edge and x-ray absorption near edge spectroscopy of both the N K - and Mn L -edges are used to probe the occupied and empty densities of states, which compare well with the N (2p) and Mn (3d) partial densities of states calculated using the linearized muffin-tin orbital band structure method. A similar comparison is made between the measured optical conductivity and the calculated contribution from interband transitions. It is possible to associate the main features in the measured spectrum with corresponding ones in the calculated optical function. The major differences between calculated and measured spectra can be understood on the basis of a limited electron mean-free-path in these nanocrystalline films, which broadens the features in the joint density of states and relaxes the momentum conservation requirement. The calculated optical functions are analyzed in detail in terms of their dominant band-to-band contributions and in addition the polarization dependence is predicted. Temperature dependent conductivity measurements are also reported and show a clear metallic behavior and a weak Kondo-like low temperature anomaly.
Photonic band structure of two-dimensional metal/dielectric photonic crystals
Zong, Yi-Xin; Xia, Jian-Bai
2015-09-01
An improved plane wave expansion method for the numerical calculation of photonic bands of metal/dielectric photonic crystal (PC) are presented. This method is applied to two-dimensional PCs with frequency-dependent dielectric constants. We obtained the photonic band structure of three kinds of structures: sawtooth, cylinder and hole PCs. The results show that the lowest band-1 is relatively flat, and does not approach zero. Also, there is no complete band-gap that extends throughout the first Brillouin zone for these three structures. However, there are partial band-gaps in different directions in the first Brillouin zone. For the complementary cylinder and hole PCs, their photonic bands are similar except for the lowest three bands; the hole PC’s lowest frequency of band-1 is larger than that of cylinder PC for the configuration R/d??=??0.2.
Perruchas, Sandrine; Boubekeur, Kamal; Canadell, Enric; Misaki, Yohji; Auban-Senzier, Pascale; Pasquier, Claude; Batail, Patrick
2008-03-19
A series of 2D metals, beta-(BDT-TTP)6[Re6Se6Cl8] x (CHCl2-CHCl2)2, 2; beta-(ST-TTP)6[Re6S6Cl8] x (CH2Cl-CHCl2)2, 3; beta-(BDT-TTP)7[Re6S6Cl8]0.5[Re6S7Cl7]0.5 x (CH2Cl2), 4; beta-(BDT-TTP)7[Re6Se6Cl8]0.5[Re6S7Cl7]0.5 x (CH2Cl2), 5; beta-(BDT-TTP)8[Re6S7Cl7] x (CH2Cl2)4, 6 (BDT-TTP and ST-TTP are 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene and 2-(1,3-diselenol-2-ylidene)-5(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, respectively) is reported to have one single beta-slab layered topology despite successive increases of the cluster anion negative charge. The charge density within the templating composite inorganic-neutral molecule slab is shown to remain above a threshold of ca. one negative charge per square nanometer, that is, for cluster anions with two negative charges and higher. Conversely, discrete stacks are shown to be stabilized instead in the semiconducting salts (BDT-TTP)2[Re6S5Cl9], 1 where the cluster anion bears one negative charge only. The electronic structure of salts 2-6 is shown to be very stable and kept almost intact across the series. The templating strategy is shown to fulfill its anticipated potential for deliberate installment of incommensurate band fillings in molecular metals. The deliberate admixture of the 6:1 and 8:1 structures yields novel phases with a 7:1 stoichiometry with the anticipated crystal and electronic structures. The action at the organic-inorganic interface triggered by changing the anion charge yet keeping its shape and volume identical, which ultimately governs the shape of the unit cell, is of paramount importance in defining the Fermi surface of these metallic salts. The present BDT-TTP salts thus provide a series of materials with strongly related but subtly different Fermi surfaces worthy of many physical studies. Shubnikov-de Haas measurements are expected to be particularly interesting since they are especially sensitive to the details of the Fermi surface. PMID:18293968
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...
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.
International Nuclear Information System (INIS)
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
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.
International Nuclear Information System (INIS)
In this research, we used photoluminescence (PL) and photoluminescence excitation (PLE) to visualize the electronic band structure in porous silicon (PS). From the combined results of the PLE measurements at various PL emission energies and the PL measurements under excitation at various PLE absorption energies, we infer that three different electronic band structures, originating from different luminescent origins, give rise to the PL spectrum. Through either thermal activation or diffusive transfer, excited carriers are moved to each of the electronic band structures.
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.
Comparison between ab initio energy band structures of various chlorinated polyethylene derivatives
Assad Abdel-Raouf, Mohamed
1989-09-01
The band structures of various chlorinated polyethylene derivatives are calculated using an ab initio self-consisten field (SCF) linear combination of atomic orbitals (LCAO) technique. The results illustrate that the conduction band is shifted steadily towards lower energies as the number of chlorine atoms in the unit cell increases, and the gap between valence and conduction bands is decreased monotonically. The possibility of n-doping is explored. The comparison between the band structures of the chlorinated polymers and that of polytrifluorochloroethylene shows that the latter possesses a lower-lying conduction band and is, therefore, more adequate for doping.
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.
Wavefunction Properties and Electronic Band Structures of High-Mobility Semiconductor Nanosheet MoS2
Baik, Seung Su; Lee, Hee Sung; Im, Seongil; Choi, Hyoung Joon; Ccsaemp Team; Edl Team
2014-03-01
Molybdenum disulfide (MoS2) nanosheet is regarded as one of the most promising alternatives to the current semiconductors due to its significant band-gap and electron-mobility enhancement upon exfoliating. To elucidate such thickness-dependent properties, we have studied the electronic band structures of bulk and monolayer MoS2 by using the first-principles density-functional method as implemented in the SIESTA code. Based on the wavefunction analyses at the conduction band minimum (CBM) points, we have investigated possible origins of mobility difference between bulk and monolayer MoS2. We provide formation energies of substitutional impurities at the Mo and S sites, and discuss feasible electron sources which may induce a significant difference in the carrier lifetime. This work was supported by NRF of Korea (Grant Nos. 2009-0079462 and 2011-0018306), Nano-Material Technology Development Program (2012M3a7B4034985), and KISTI supercomputing center (Project No. KSC-2013-C3-008). Center for Computational Studies of Advanced Electronic Material Properties.
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
Novel semiconductor solar cell structures: The quantum dot intermediate band solar cell
Energy Technology Data Exchange (ETDEWEB)
Marti, A. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain)]. E-mail: amarti@etsit.upm.es; Lopez, N. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain); Antolin, E. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain); Canovas, E. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain); Stanley, C. [Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Farmer, C. [Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Cuadra, L. [Departamento de Teoria de la Senal y Comunicaciones- Escuela Politecnica Superior, Universidad de Alcala, Ctra. Madrid-Barcelona, km. 33600, 28805-Alcala de Henares (Madrid) (Spain); Luque, A. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain)
2006-07-26
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.
Nuclear energy density optimization: Shell structure
Kortelainen, M; Nazarewicz, W; Olsen, E; Reinhard, P -G; Sarich, J; Schunck, N; Wild, S M; Davesne, D; Erler, J; Pastore, A
2013-01-01
Nuclear density functional theory is the only microscopical theory that can be applied throughout the entire nuclear landscape. Its key ingredient is the energy density functional. In this work, we propose a new parameterization UNEDF2 of the local Skyrme energy density functional. The functional optimization is carried out using the POUNDerS optimization algorithm within the framework of the Skyrme Hartree-Fock-Bogoliubov theory. Compared to the previous parameterization UNEDF1, restrictions on the tensor term of the energy density have been lifted, yielding the most general form of the Skyrme energy density functional up to second order in derivatives of the one-body local density. In order to impose constraints on all the parameters of the functional, selected data on single-particle splittings in spherical doubly-magic nuclei have been included into the experimental dataset. The agreement with both bulk and spectroscopic nuclear properties achieved by the resulting UNEDF2 parameterization is comparable wi...
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.
Fingerprint-Based Structure Retrieval Using Electron Density
Yin, Shuangye; Dokholyan, Nikolay V
2011-01-01
We present a computational approach that can quickly search a large protein structural database to identify structures that fit a given electron density, such as determined by cryo-electron microscopy. We use geometric invariants (fingerprints) constructed using 3D Zernike moments to describe the electron density, and reduce the problem of fitting of the structure to the electron density to simple fingerprint comparison. Using this approach, we are able to screen the entire Protein Data Bank ...
Determination of energy-band dispersion curves in strained-layer structures
International Nuclear Information System (INIS)
Simultaneous measurement of both the conduction- and valence-band dispersion curves in single strained-layer structures is presented. These measurements rely on the application of recent observations regarding breaking of the usual selection rules for interband magnetoluminescence transitions in modulation-doped structures. Low-temperature magneto-luminescence data for three representative InGaAs/GaAs n-type single-strained quantum well structures are presented. For energies approaching 50 meV above the band gap, we find that the conduction band is parabolic with an effective mass of 0.071m0. Over the same energy range, the valence bands are highly nonparabolic
New linear accelerator (Linac) design based on C-band accelerating structures for SXFEL facility
International Nuclear Information System (INIS)
A C-band accelerator structure is one promising technique for a compact XFEL facility. It is also attractive in beam dynamics in maintaining a high quality electron beam, which is an important factor in the performance of a free electron laser. In this paper, a comparison between traditional S-band and C-band accelerating structures is made based on the linac configuration of a Shanghai Soft X-ray Free Electron Laser (SXFEL) facility. Throughout the comprehensive simulation, we conclude that the C-band structure is much more competitive. (authors)
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...
Electronic Structure and Valence Band Spectra of $Bi_{4}Ti_{3}O_{12}$
Postnikov, A V; Mersch, F; Neumann, M; Kurmaev, E Z; Cherkashenko, V M; Nemnonov, S N; Galakhov, V R; Bartkowski, St.
1995-01-01
The x-ray photoelectron valence band spectrum and x-ray emission valence-band spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented (analyzed in the common energy scale) and interpreted on the basis of a band-structure calculation for an idealized I4/mmm structure of this material.
Electronic Structure and Valence Band Spectra of Bi4Ti3O12
Postnikov, A. V.; Bartkowski, St.; Mersch, F.; Neumann, M.; Kurmaev, E. Z.; Cherkashenko, V. M.; Nemnonov, S. N.; Galakhov, V. R.
1995-01-01
The x-ray photoelectron valence band spectrum and x-ray emission valence-band spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented (analyzed in the common energy scale) and interpreted on the basis of a band-structure calculation for an idealized I4/mmm structure of this material.
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.
Electron structure and valence band structure of beryllium orthosilicate and lanthanum beryllate
International Nuclear Information System (INIS)
An analysis of the electron structure and energy spectrum of Be2SiO4- and Be2La2O5 valence zone on the basis of original and known experimental data, using semiempirical methods, is performed. Results on simulation of Be2SiO3- and Be2La2O5 electron structure are generalized. Peculiarities of molecular orbitals single-electron scheme formation are revealed. The sequence of formation and structure of Be2SiO4- and Be2La2O5 valence bands has been established
International Nuclear Information System (INIS)
The Density-Functional method, with Linear Combination of Atomic Orbitals, has been applied to eight crystals; the lattice equilibrium parameters, and the lattice formation energies have been calculated at the Hartree-Fock level (HF), at the hybrid Hartree-Fock Density-Functional level (DFT/HF), and at the Kohn-Sham Density-Functional level (DFT). The band structures and the electronic charge distributions calculated at the DFT and HF levels are compared
Polfus, Jonathan M; Bjørheim, Tor S; Norby, Truls; Haugsrud, Reidar
2012-09-01
The nitrogen related defect chemistry and electronic structure of wide band gap oxides are investigated by density functional theory defect calculations of N(O)(q), NH(O)(×), and (NH2)(O)(·) as well as V(O)(··) and OH(O)(·) in MgO, CaO, SrO, Al(2)O(3), In(2)O(3), Sc(2)O(3), Y(2)O(3), La(2)O(3), TiO(2), SnO(2), ZrO(2), BaZrO(3), and SrZrO(3). The N(O)(q) acceptor level is found to be deep and the binding energy of NH(O)(×) with respect to N(O)' and (OH(O)(·) is found to be significantly negative, i.e. binding, in all of the investigated oxides. The defect structure of the oxides was found to be remarkably similar under reducing and nitriding conditions (1 bar N(2), 1 bar H(2) and 1 × 10(-7) bar H(2)O): NH(O)(×) predominates at low temperatures and [N(O)'] = 2[V(O)(··) predominates at higher temperatures (>900 K for most of the oxides). Furthermore, we evaluate how the defect structure is affected by non-equilibrium conditions such as doping and quenching. In terms of electronic structure, N(O)' is found to introduce isolated N-2p states within the band gap, while the N-2p states of NH(O)(×) are shifted towards, or overlap with the VBM. Finally, we assess the effect of nitrogen incorporation on the proton conducting properties of oxides and comment on their corrosion resistance in nitriding atmospheres in light of the calculated defect structures. PMID:22828729
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.
The Density Functional Theory Study of Structural and Electronical Properties of ZnO Clusters
Directory of Open Access Journals (Sweden)
O.V. Bovgyra
2013-03-01
Full Text Available Density functional theory studies of structural and electronic properties of small clusters were performed. For each cluster an optimization of structure and the basic properties of the band structure were conducted. It was determined that with increasing (n energetically more efficient in the small clusters is stabilization from the ring to fulleren-like structures containing tetragonal and hexagonal faces and all atoms have coordination number equal three. Among the clusters (ZnO12 with doped atoms most stable are clusters where Zn was replaced by Mn, Cu and Co atoms. Band gap in the electronic spectrum of doped clusters decreases due to p-d hybridization orbitals of the impurity atom with the orbitals of the oxygen atom.
Effect of acicular ferrite on banded structures in low-carbon microalloyed steel
Shi, Lei; Yan, Ze-sheng; Liu, Yong-chang; Yang, Xu; Zhang, Cheng; Li, Hui-jun
2014-12-01
The effect of acicular ferrite (AF) on banded structures in low-carbon microalloyed steel with Mn segregation during both isothermal transformation and continuous cooling processes was studied by dilatometry and microscopic observation. With respect to the isothermal transformation process, the specimen isothermed at 550°C consisted of AF in Mn-poor bands and martensite in Mn-rich bands, whereas the specimen isothermed at 450°C exhibited two different morphologies of AF that appeared as bands. At a continuous cooling rate in the range of 4 to 50°C/s, a mixture of AF and martensite formed in both segregated bands, and the volume fraction of martensite in Mn-rich bands was always higher than that in Mn-poor bands. An increased cooling rate resulted in a decrease in the difference of martensite volume fraction between Mn-rich and Mn-poor bands and thereby leaded to less distinct microstructural banding. The results show that Mn segregation and cooling rate strongly affect the formation of AF-containing banded structures. The formation mechanism of microstructural banding was also discussed.
Wang, Jianwei; Zhang, Yong; Wang, Lin-Wang
2015-07-01
We propose a systematic approach that can empirically correct three major errors typically found in a density functional theory (DFT) calculation within the local density approximation (LDA) simultaneously for a set of common cation binary semiconductors, such as III-V compounds, (Ga or In)X with X =N ,P ,As ,Sb , and II-VI compounds, (Zn or Cd)X , with X =O ,S ,Se ,Te . By correcting (1) the binary band gaps at high-symmetry points ? , L , X , (2) the separation of p -and d -orbital-derived valence bands, and (3) conduction band effective masses to experimental values and doing so simultaneously for common cation binaries, the resulting DFT-LDA-based quasi-first-principles method can be used to predict the electronic structure of complex materials involving multiple binaries with comparable accuracy but much less computational cost than a GW level theory. This approach provides an efficient way to evaluate the electronic structures and other material properties of complex systems, much needed for material discovery and design.
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.)
International Nuclear Information System (INIS)
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.
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.
Energy Technology Data Exchange (ETDEWEB)
Kolezynski, A., E-mail: andrzej.kolezynski@agh.edu.p [AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Al. Mickiewicza 30, 30-059 Krakow (Poland)
2010-09-01
Results of theoretical studies of electronic structure (full potential linearized augmented plane Wave method within DFT formalism as implemented in Wien2k package), electron density topology and bonding (Bader's quantum theory of atoms in molecules topological analysis of total electron density obtained from FP-LAPW calculations) in anhydrous cadmium and silver oxalates are presented. Detailed analysis of calculated band structures, densities of states (total and projected ones) and bond critical points shows that despite the differences of crystal structure both these compounds reveal important similarities and suggests that one can expect that they should exhibit very similar properties and behavior during e.g. thermal decomposition process (which is in agreement with experiments).
The electronic band structure of GaBiAs/GaAs layers: Influence of strain and band anti-crossing
Batool, Z.; Hild, K.; Hosea, T. J. C.; Lu, X.; Tiedje, T.; Sweeney, S. J.
2012-06-01
The GaBixAs1-x bismide III-V semiconductor system remains a relatively underexplored alloy particularly with regards to its detailed electronic band structure. Of particular importance to understanding the physics of this system is how the bandgap energy Eg and spin-orbit splitting energy ?o vary relative to one another as a function of Bi content, since in this alloy it becomes possible for ?o to exceed Eg for higher Bi fractions, which occurrence would have important implications for minimising non-radiative Auger recombination losses in such structures. However, this situation had not so far been realised in this system. Here, we study a set of epitaxial layers of GaBixAs1-x (2.3% ? x ? 10.4%), of thickness 30-40 nm, grown compressively strained onto GaAs (100) substrates. Using room temperature photomodulated reflectance, we observe a reduction in Eg, together with an increase in ?o, with increasing Bi content. In these strained samples, it is found that the transition energy between the conduction and heavy-hole valence band edges is equal with that between the heavy-hole and spin-orbit split-off valence band edges at ˜9.0 ± 0.2% Bi. Furthermore, we observe that the strained valence band heavy-hole/light-hole splitting increases with Bi fraction at a rate of ˜15 (±1) meV/Bi%, from which we are able to deduce the shear deformation potential. By application of an iterative strain theory, we decouple the strain effects from our experimental measurements and deduce Eg and ?o of free standing GaBiAs; we find that ?o indeed does come into resonance with Eg at ˜10.5 ± 0.2% Bi. We also conclude that the conduction/valence band alignment of dilute-Bi GaBiAs on GaAs is most likely to be type-I.
Nuclear Parton Densities and Structure Functions
Tehrani, S. Atashbar; Khorramian, Ali N.; Mirjalili, A.
2004-01-01
We calculate nuclear parton distribution functions (PDFs), using the constituent quark model. We find the bounded valon distributions in a nuclear to be related to free valon distributions in a nucleon. By using improved bounded valon distributions for a nuclear with atomic number $A$ and the partonic structure functions inside the valon, we can calculate the nuclear structure function in $x$ space. The results for nuclear structure-function ratio $F_2^A/F_2^D$ at some value...
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
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.
The crystal and electronic band structure of the diamond-like semiconductor Ag{sub 2}ZnSiS{sub 4}
Energy Technology Data Exchange (ETDEWEB)
Brunetta, Carl D.; Karuppannan, Balamurugan; Rosmus, Kimberly A. [Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282 (United States); Aitken, Jennifer A., E-mail: aitkenj@duq.edu [Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282 (United States)
2012-03-05
Highlights: Black-Right-Pointing-Pointer The structure of Ag{sub 2}ZnSiS{sub 4} is solved and refined in the space group Pn using single crystal X-ray diffraction. Black-Right-Pointing-Pointer Electronic band structure calculations show that Ag{sub 2}ZnSiS{sub 4} is a direct band gap semiconductor with a calculated band gap of 1.88 eV. Black-Right-Pointing-Pointer The optical band gap of Ag{sub 2}ZnSiS{sub 4} was experimentally determined as 3.28 eV. - Abstract: Single crystals of the new diamond-like semiconductor Ag{sub 2}ZnSiS{sub 4} have been synthesized using high-temperature, solid state synthesis at 800 Degree-Sign C. The compound crystallizes in the monoclinic, noncentrosymmetric space group Pn with a = 6.4052(1) Angstrom-Sign , b = 6.5484(1) Angstrom-Sign , c = 7.9340(1) Angstrom-Sign , {beta} = 90.455(1) Degree-Sign and R1 (for all data) = 2.42%. The electronic band structure and density of states were calculated using density functional theory (DFT) and the full potential linearized augmented plane wave (LAPW) method within the Wien2k program suite. The calculated band structure suggests that Ag{sub 2}ZnSiS{sub 4} is a direct band gap semiconductor with a calculated band gap of 1.88 eV at the {Gamma}-point. The calculated density of states of Ag{sub 2}ZnSiS{sub 4} is compared with that of AgGaS{sub 2}. The band gap of Ag{sub 2}ZnSiS{sub 4} was also determined experimentally as 3.28 eV via optical diffuse reflectance spectroscopy.
Electronic transitions in GdN band structure
Energy Technology Data Exchange (ETDEWEB)
Vidyasagar, R., E-mail: drsagar@sapphire.kobe-u.ac.jp; Kita, T. [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan); Sakurai, T. [Centre for Support to Research and Education Activities, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan); Ohta, H. [Molecular Photoscience Research Center and Graduate School of Science, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan)
2014-05-28
Using the near-infrared (NIR) absorbance spectroscopy, electronic transitions and spin polarization of the GdN epitaxial film have been investigated; and the GdN epitaxial film was grown by a reactive rf sputtering technique. The GdN film exhibited three broad bands in the NIR frequency regimes; and those bands are attributable primarily to the minority and majority spin transitions at the X-point and an indirect transition along the ?-X symmetric direction of GdN Brillouin zone. We experimentally observe a pronounced red-shift of the indirect band gap when cooling down below the Curie temperature which is ascribed to the orbital-dependent coulomb interactions of Gd-5dxy electrons, which tend to push-up the N-2p bands. On the other hand, we have evaluated the spin polarization of 0.17 (±0.005), which indicates that the GdN epitaxial film has almost 100% spin-polarized carriers. Furthermore, the experimental result of GdN electronic transitions are consistent with the previous reports and are thus well-reproduced. The Arrott plots evidenced that the Curie temperature of GdN film is 36?K and the large spin moment is explained by the nitrogen vacancies and the intra-atomic exchange interaction.
Novel band structures in silicene on monolayer zinc sulfide substrate
Li, Sheng-shi; Zhang, Chang-wen; Yan, Shi-shen; Hu, Shu-jun; Ji, Wei-xiao; Wang, Pei-ji; Li, Ping
2014-10-01
Opening a sizable band gap in the zero-gap silicene without lowering the carrier mobility is a key issue for its application in nanoelectronics. Based on ?rst-principles calculations, we find that the interaction energies are in the range of -0.09?0.3?eV?per Si atom, indicating a weak interaction between silicene and ZnS monolayer and the ABZn stacking is the most stable pattern. The band gap of silicene can be effectively tuned ranging from 0.025 to 1.05?eV in silicene and ZnS heterobilayer (Si/ZnS HBL). An unexpected indirect-direct band gap crossover is also observed in HBLs, dependent on the stacking pattern, interlayer spacing and external strain effects on silicene. Interestingly, the characteristics of Dirac cone with a nearly linear band dispersion relation of silicene can be preserved in the ABS pattern which is a metastable state, accompanied by a small electron effective mass and thus the carrier mobility is expected not to degrade much. These provide a possible way to design effective FETs out of silicene on a ZnS monolayer.
Pardo, V.; Smith, J.C.; Pickett, W. E.
2012-01-01
It was reported earlier [Phys. Rev. Lett. 106, 056401 (2011)] that the skutterudite structure compound CoSb$_3$ displays a unique band structure with a topological transition versus a symmetry-preserving sublattice (Sb) displacement very near the structural ground state. The transition is through a massless Dirac-Weyl semimetal, point Fermi surface phase which is unique in that (1) it appears in a three dimensional crystal, (2) the band critical point occurs at $k$=0, and (3...
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
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
Nuclear Parton Densities and Structure Functions
Tehrani, S. Atashbar; Khorramian, Ali N.; Mirjalili, A.
We calculate nuclear parton distribution functions (PDFs), using the constituent quark model. We find the bounded valon distributions in a nuclear to be related to free valon distributions in a nucleon. By using improved bounded valon distributions for a nuclear with atomic number A and the partonic structure functions inside the valon, we can calculate the nuclear structure function in x space. The results for nuclear structure-function ratio F2A/F_2^D at some values of A, are in good agreement with the experimental data.
Nuclear Parton Densities and Structure Functions
Tehrani, S A; Mirjalili, A; Khorramian, Ali N.
2004-01-01
We calculate nuclear parton distribution functions (PDFs), using the constituent quark model. We find the bounded valon distributions in a nuclear to be related to free valon distributions in a nucleon. By using improved bounded valon distributions for a nuclear with atomic number $A$ and the partonic structure functions inside the valon, we can calculate the nuclear structure function in $x$ space. The results for nuclear structure-function ratio $F_2^A/F_2^D$ at some values of $A$ are in good agreement with the experimental data.
International Nuclear Information System (INIS)
By virtue of the efficiency of the Dirichlet-to-Neumann map method, we have calculated, for H-polarization (TE mode), the band structure of 2D photonic crystals with a square lattice composed of metallic rods embedded in an air background. The rod in the unit cell is chosen to be circular in shape. Here, from a practical point of view, in order to obtain maximum band gaps, we have studied the band structure as a function of the size of the rods. We have also studied the flat bands appearing in the band structures and have shown that for frequencies around the surface plasmon frequency, the modes are highly localized at the interface between the metallic rods and the air background.
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.
Enhanced conduction band density of states in intermetallic EuTSi3 (T = Rh, Ir).
Maurya, Arvind; Bonville, P; Thamizhavel, A; Dhar, S K
2015-09-16
We report on the physical properties of single crystalline EuRhSi3 and polycrystalline EuIrSi3, inferred from magnetization, electrical transport, heat capacity and (151)Eu 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 (151)Eu 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 ([Formula: see text]20-25 K) inferred from both resistivity and specific heat data, for the spin-disorder resistivity in EuIrSi3 ([Formula: see text]240 [Formula: see text] 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. PMID:26289169
Singh, Gurpreet; Dogra, Sukh Dev; Kaur, Sarvpreet; Tripathi, S K; Prakash, Satya; Rai, Bimal; Saini, G S S
2015-10-01
The vibrational properties of glutathione have been investigated by infrared absorption and Raman spectroscopic techniques, and density functional theory calculations at the B3LYP/6-31+G(d,p) level. Assignments of all the experimentally observed vibrational bands have been done with the help of simulated vibrational spectra and potential energy distribution calculations of glutathione water cluster, which includes the effect of hydrogen bonding. Optimized molecular parameters of energy minimized structure have been compared with the available experimental values. Calculated molecular parameters of glutathione-water cluster match well with the experimental values. Some of the calculated molecular parameters and vibrational frequencies of vapor phase glutathione-water cluster suggest participation of some atoms of glutathione in hydrogen bonding. Experimentally observed UV-Visible absorption spectrum of glutathione has also been reported. Observed band at 203nm has been assigned to electronic transitions calculated with time dependent density functional theory. PMID:25978018
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.)
Stability and band gaps of InGaP, BGaP, and BInGaP alloys: Density-functional supercell calculations
Energy Technology Data Exchange (ETDEWEB)
Jenichen, Arndt [Leibniz-Institute for Surface Modification, Permoserstrasse 15, 04303 Leipzig (Germany); Engler, Cornelia [Wilhelm-Ostwald-Institute of Physical and Theoretical Chemistry, University Leipzig, Linnestrasse 2, 04103 Leipzig (Germany)
2010-01-15
Energies and band gaps of (InGa)P, (BGa)P and (BInGa)P alloys, including the antisite boron substitutions, are calculated using supercells and the density-functional method. The influence of the substituent concentration and arrangement on the stability and band gaps is investigated and compared with experimental findings. Linearly corrected band-gap widths reproduce well experimental and GW data. The most stable structures of the ternary alloys are 200/211 arrangements of the substituents. The T-x phase diagram for (InGa)P provides no miscibility gap for usual growth temperatures. However, for (BGa)P alloys a large miscibility gap is obtained between about 2% and 99% boron, what confirms experimental results. In quaternary (BInGa)P, boron and indium atoms prefer the (220) but also the (110) position to each other. A 2:1 ratio is preferred for the indium to the boron content. Supercell with the most probable B{sub 1}In{sub n}Ga{sub 31-n}P{sub 32} structure (n = 2). (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Karlický, František; Zbo?il, Radek; Otyepka, Michal
2012-07-01
Density functional theory calculations of the electronic structure of graphane and stoichiometrically halogenated graphene derivatives (fluorographene and other analogous graphene halides) show: (i) localized orbital basis sets can be successfully and effectively used for such two-dimensional materials; (ii) several functionals predict that the band gap of graphane is greater than that of fluorographene, whereas HSE06 gives the opposite trend; (iii) HSE06 functional predicts quite good values of band gaps with respect to benchmark theoretical and experimental data; (iv) the zero band gap of graphene is opened by hydrogenation and halogenation and strongly depends on the chemical composition of mixed graphene halides; (v) the stability of graphene halides decreases sharply with increasing size of the halogen atom - fluorographene is stable, whereas graphene iodide spontaneously decomposes. In terms of band gap and stability, the C2FBr and C2HBr derivatives seem to be promising materials, e.g., for (opto)electronics applications, because their band gaps are similar to those of conventional semiconductors, and they are expected to be stable under ambient conditions. The results indicate that other fluorinated compounds (CaHbFc and CaFbYc, Y = Cl, Br, I) are stable insulators.
Banded structure and its distribution in friction stir processing of 316L austenitic stainless steel
International Nuclear Information System (INIS)
Highlights: ? Friction stir processing (FSP) as a repair method. ? Sigma phase formed in the FSP zone. ? Low heat input contributes to restrain sigma phase precipitation. - Abstract: Banded structures, which vary with welding parameters, were observed in friction stir processing of 316L austenite stainless steel. Sigma phase precipitation was detected in banded structures by transmission electron microscopy. The amount of banded structure had direct ratio relations with heat input. The higher the heat input, the larger the area of banded structures. This is attributable to slower cooling rate at high heat input, which results in longer exposure to the temperature range for precipitation. The formation of sigma phase produced Cr depletion, which resulted in largely degraded corrosion resistance. The present study suggests that low heat input (i.e. low rotation speeds, low working loads and high welding speed) contributes to restrain sigma phase precipitation.
Detailed structure of the outer disk around HD 169142 with polarized light in H-band
Momose, Munetake; Morita, Ayaka; 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
2015-08-01
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 le r le 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 ? = 7 mm. This can be regarded as another sign of a protoplanet in the TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution, an irregular temperature distribution, or with a combination of both. The depletion factor of surface density in the inner power-law region (r law region. Possible origins for these asymmetries include corrugation of the scattering surface in the outer region, and a shadowing effect by a puffed-up structure in the inner power-law region.
Quadrant-type X-band single-cell structure for high gradient tests
International Nuclear Information System (INIS)
We are building a new high-gradient X-band (11.424 GHz) testbench, called “Shield-B,” for basic studies to establish a acceleration technology with 100MV/m or higher, where various single-cell structures are to be tested. We focus on quadrant-type structures, on which no surface currents associated with magnetic fields flow across cell-to-cell junctions unlike disk-type structures. In this study, we propose a quadrant-type X-band single-cell structure with a heavy damped structure by waveguides, overcoming its issues. (author)
The impurity optical absorption and structure of conduction band in 6H-SiC
International Nuclear Information System (INIS)
The investigation of absorption spectra in n-type nitrogen doped 6H-SiC crystals from the near infrared up to fundamental band region at polarization of electric field (E) of the light wave relatively the optical axis (C) for E parallel to C and E perpendicular to C has been carried out. It is for the first time that at E parallel to C a slight absorption band with maximum at 2.85 eV has been investigated. All absorption bands observed were caused by photoionization of donors (nitrogen) with electron transition in to above-lying minima of the conduction band situated at different critical points of the Brillouin zone. The analysis of data obtained and experimental data available on the photoionization of nitrogen, alongside with theoretical data on the structure of the conduction band make it possible to propose the structure and symmetry of additional extrema in Brillouin zone for 6H-SiC
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.
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.
Band structure and UV optical spectra of TGS crystals in the range of 4-10eV
Energy Technology Data Exchange (ETDEWEB)
Andriyevsky, B. [Department of Electronics and Computer Sciences, Koszalin University of Technology, 2 Sniadeckich Street, PL-75-453 Koszalin, West Pomeranian (Poland)]. E-mail: bandri@tu.koszalin.pl; Esser, N. [ISAS-Institute for Analytical Sciences Department Berlin, Albert-Einstein-Street 9, D-12489 Berlin (Germany); Patryn, A. [Department of Electronics and Computer Sciences, Koszalin University of Technology, 2 Sniadeckich Street, PL-75-453 Koszalin, West Pomeranian (Poland); Cobet, C. [ISAS-Institute for Analytical Sciences Department Berlin, Albert-Einstein-Street 9, D-12489 Berlin (Germany); Ciepluch-Trojanek, W. [Department of Electronics and Computer Sciences, Koszalin University of Technology, 2 Sniadeckich Street, PL-75-453 Koszalin, West Pomeranian (Poland); Romanyuk, M. [Ivan Franko National University of L' viv, Kyrylo-and-Mefodii Street 8, UA-79005 L' viv (Ukraine)
2006-03-15
Theoretical and experimental studies of the band energy structure and optical spectra for triglycine sulphate crystal (TGS) (NH{sub 2}CH{sub 2}COOH){sub 3}.H{sub 2}SO{sub 4}, in the ferroelectric phase have been performed for the first time. First principal DFT calculations of the band structure, density of states and dielectric functions spectra {epsilon}'(E) and {epsilon}{sup '}'(E) of TGS crystal have been done using the computer package Cambridge Serial Total Energy Package (CASTEP) code. Experimental spectral dispersions of the complex reflection ratio {rho}(E) have been measured using the synchrotron radiation at BESSY synchrotron source in the spectral range of 4-10eV and the pseudo-dielectric functions <{epsilon}>=<{epsilon}{sup '}>+i<{epsilon}{sup '}'> were evaluated. Experimental data and theoretically calculated dielectric functions have demonstrated a good agreement. The band energy dispersion of valence and conducting bands have been analyzed and were used to identify the dielectric functions peculiarities.
Energetic band structure of Zn3P2 crystals
International Nuclear Information System (INIS)
Optical functions n, k, ?1, ?2 and d2?2/dE2 have been determined from experimental reflection spectra in the region of 1-10 eV. The revealed electronic transitions are localized in the Brillouin zone. The magnitude of valence band splitting caused by the spin-orbital interaction ?SO is lower than the splitting caused by the crystal field ?CR in the center of Brillouin zone and L and X points. The switching effects are investigated in Zn3P2 crystals. The characteristics of experimental samples with electric switching, adjustable resistors, and time relays based on Zn3P2 are presented.
Structure of Dipole Bands in 112In: Through Lifetime Measurement
International Nuclear Information System (INIS)
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.
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.
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.
Ultrasonic velocity for estimating density of structural ceramics
Klima, S. J.; Watson, G. K.; Herbell, T. P.; Moore, T. J.
1981-01-01
The feasibility of using ultrasonic velocity as a measure of bulk density of sintered alpha silicon carbide was investigated. The material studied was either in the as-sintered condition or hot isostatically pressed in the temperature range from 1850 to 2050 C. Densities varied from approximately 2.8 to 3.2 g cu cm. Results show that the bulk, nominal density of structural grade silicon carbide articles can be estimated from ultrasonic velocity measurements to within 1 percent using 20 MHz longitudinal waves and a commercially available ultrasonic time intervalometer. The ultrasonic velocity measurement technique shows promise for screening out material with unacceptably low density levels.
International Nuclear Information System (INIS)
Band 3 is the major anion transport polypeptide of erythrocytes. It appears to be the binding site of several glycolytic enzymes. Structurally, band 3 is the major protein spanning the erythrocyte membrane and connects the plasma membrane to band 2.1, which binds to the cytoskeleton. In the present study, the authors report an alteration of band 3 molecule that is associated with the following changes: erythrocyte shape change from discoid to thorny cells (acanthocytes), restriction of rotational diffusion of band 3 in the membrane, increase in anion transport, and decrease in the number of high-affinity ankyrin-binding sites. Changes in erythrocyte IgG binding, glyceraldehyde-3-phosphate dehydrogenase, fluorescence polarization (indicative of membrane fluidity), and other membrane proteins as determined by polyacrylamide gel electrophoresis were not detected. Cells containing the altered band 3 polypeptide were obtained from individuals with abnormal erythrocyte morphology. Two-dimensional peptide maps revealed differences in the M/sub r/ 17,000 anion transport segment of band 3 consistent with additions of tyrosines or tyrosine-containing peptides. The data suggest that (i) this alteration of band 3 does not result in accelerated aging as does cleavage and (ii) structural changes in the anion transport region result in alterations in anion transport
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...
Photonic band structure of ZnO photonic crystal slab laser
Yamilov, A; Cao, H
2005-01-01
We recently reported on the first realization of ultraviolet photonic crystal laser based on zinc oxide [Appl. Phys. Lett. {\\bf 85}, 3657 (2004)]. Here we present the details of structural design and its optimization. We develop a computational super-cell technique, that allows a straightforward calculation of the photonic band structure of ZnO photonic crystal slab on sapphire substrate. We find that despite of small index contrast between the substrate and the photonic layer, the low order eigenmodes have predominantly transverse-electric (TE) or transverse-magnetic (TM) polarization. Because emission from ZnO thin film shows strong TE preference, we are able to limit our consideration to TE bands, spectrum of which can possess a complete photonic band gap with an appropriate choice of structure parameters. We demonstrate that the geometry of the system may be optimized so that a sizable band gap is achieved.
Energy Technology Data Exchange (ETDEWEB)
Moustafa, Mohamed, E-mail: moustafa@physik.hu-berlin.de [Institut für Physik, Humboldt Universität zu Berlin, Newtonstr. 15, D-12489 Berlin (Germany); Faculty of Engineering, Pharos University in Alexandria, Canal El Mahmoudia Str., Alexandria (Egypt); Ghafari, Aliakbar; Paulheim, Alexander; Janowitz, Christoph; Manzke, Recardo [Institut für Physik, Humboldt Universität zu Berlin, Newtonstr. 15, D-12489 Berlin (Germany)
2013-08-15
Highlights: ? We performed high resolution ARPES on 1T–ZrS{sub x}Se{sub 2?x}. ? A characteristic splitting of the chalcogen p-derived VB along high symmetry directions was observed. ? The splitting size at the A point of the BZ is found to increase from 0.06 to 0.31 eV from ZrS{sub 2} towards ZrSe{sub 2}. ? Electronic structure calculations based on the DFT were performed using the model of TB–MBJ. ? The calculations show that the splitting is due to SO coupling of the valence bands. -- Abstract: Angle-resolved photoelectron spectroscopy using synchrotron radiation has been performed on 1T–ZrS{sub x}Se{sub 2?x}, where x varies from 0 to 2, in order to study the influence of the spin-orbit interaction in the valence bands. The crystals were grown by chemical vapour transport technique using Iodine as transport agent. A characteristic splitting of the chalcogen p-derived valence bands along high symmetry directions has been observed experimentally. The size of the splitting increases with the increase of the atomic number of the chalcogenide, e.g. at the A point of the Brillouin zone from 0.06 eV to 0.31 eV with an almost linear dependence with x, as progressing from ZrS{sub 2} towards ZrSe{sub 2}, respectively. Electronic structure calculations based on the density functional theory have been performed using the model of Tran–Blaha [1] and the modified version of the exchange potential proposed by Becke and Johnson [2] (TB–MBJ) both with and without spin-orbit (SO) coupling. The calculations show that the splitting is mainly due to spin-orbit coupling and the degeneracy of the valance bands is lifted.
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...
Predicting band structure of 3D mechanical metamaterials with complex geometry via XFEM
Zhao, Jifeng; Li, Ying; Liu, Wing Kam
2015-04-01
Band structure characterizes the most important property of mechanical metamaterials. However, predicting the band structure of 3D metamaterials with complex microstructures through direct numerical simulation (DNS) is computationally inefficient due to the complexity of meshing. To overcome this issue, an extended finite element method (XFEM)-based method is developed to predict 3D metamaterial band structures. Since the microstructure and material interface are implicitly resolved by the level-set function embedded in the XFEM formulation, a non-conforming (such as uniform) mesh is used in the proposed method to avoid the difficulties in meshing complex geometries. The accuracy and mesh convergence of the proposed method have been validated and verified by studying the band structure of a spherical particle embedded in a cube and comparing the results with DNS. The band structures of 3D metamaterials with different microstructures have been studied using the proposed method with the same finite element mesh, indicating the flexibility of this method. This XFEM-based method opens new opportunities in design and optimization of mechanical metamaterials with target functions, e.g. location and width of the band gap, by eliminating the iterative procedure of re-building and re-meshing microstructures that is required by classical DNS type of methods.
Electronic band structures and x-ray photoelectron spectra of ZrC, HfC, and TaC
International Nuclear Information System (INIS)
The band structures and densities of states (DOSs) of ZrC, HfC, and TaC were calculated by the augmented-plane-wave method, and the x-ray photoelectron spectra of valence bands of these compounds were observed. The theoretical energy distribution curves (EDCs) were in good agreement with the experimental EDCs. These band structures resemble each other and also those of TiC obtained by our previous work. This fact suggests that the rigid-band model is applicable to the transition-metal carbides with the rock-salt structure. Their DOSs are divided into three parts. Peak I derived from the C 2s state is isolated from the higher valence-band peak II arising from the C 2p and the valence electrons of the metal atom. Peak III derived from the d and s states of the metal atom is separated by the Fermi level from peak II. The Fermi level lies at the minimum point of the DOS for the group IV carbides, but for TaC it lies at a relatively large DOS point. The DOS at the Fermi level of ZrC, HfC, and TaC are 0.18, 0.16, and 0.65 electrons/(eV primitive cell), respectively. The characteristic mutual differences among these compounds are a stronger localization of d electrons in ZrC and HfC compared with TiC and an enhancement of the photoelectron spectrum intensity of TaC around the Fermi level
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.
Band structure in neutron-deficient 103Cd
International Nuclear Information System (INIS)
A considerable amount of experimental works has been recently done on the light Cadmium isotopes. The main purpose of these studies was to search for Coriolis decoupling mechanism in a transitional region. Negative and positive parity bands occuring in 105Cd, 107Cd, 109Cd, 111Cd have been correctly reproduced within the rotor-plus-particle model using self-consistent prolate core single-particle states. The aim of the present work is using HI reactions, to search for the high spin states in 103Cd where only two low-lying levels are known so far, from on-line radioactivity studies, and to check whether this theoretical description remains still satisfactory
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...
Andriyevsky, B. V.; Romanyuk, N. A.; Romanyuk, N. N.; Myshchyshyn, O. Ya.; Jaskólski, M.; Stadnyk, V. I.
2012-10-01
The genetic origin of a ferroelectric crystal of guanidinium aluminum sulfate hexahydrate has been established and the spectral dependences of the electron density of states, the electron energy, and the optical functions ?1( ??) and ?2( ??) for this crystal have been calculated in terms of the density functional theory. It has been found that there is a weak dependence of the energy of electrons in the upper valence bands on the wave vector. The calculated values of the band gap ( E g ˜ 5.44 eV) and refractive indices are in agreement with the experimental results. It has been shown that there is a strong anisotropy of the spectral band ?2( ??) in the region of 6 eV, which is predominantly formed by the p states of carbon (˜60%) and nitrogen (˜40%) atoms of the C(NH2)3 group.
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 tunable dual-narrowband band-pass filter using plasma quantum well structure
Dai, Yi; Liu, Shao-Bin; Wang, Shen-Yun; Kong, Xiang-Kun; Chen, Chen
2014-06-01
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.
Reducing support loss in micromechanical ring resonators using phononic band-gap structures
International Nuclear Information System (INIS)
In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.
Pardo, V.; Smith, J. C.; Pickett, W. E.
2012-06-01
It was reported earlier [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.106.056401 106, 056401 (2011)] that the skutterudite structure compound CoSb3 displays a unique band structure with a topological transition versus a symmetry-preserving sublattice (Sb) displacement very near the structural ground state. The transition is through a massless Dirac-Weyl semimetal, point Fermi surface phase which is unique in that (1) it appears in a three-dimensional crystal, (2) the band critical point occurs at k=0, and (3) linear bands are degenerate with conventional (massive) bands at the critical point (before inclusion of spin-orbit coupling). Further interest arises because the critical point separates a conventional (trivial) phase from a topological phase. In the native cubic structure this is a zero-gap topological semimetal; we show how spin-orbit coupling and uniaxial strain converts the system to a topological insulator (TI). We also analyze the origin of the linear band in this class of materials, which is the characteristic that makes them potentially useful in thermoelectric applications or possibly as transparent conductors. We characterize the formal charge as Co+ d8, consistent with the gap, with its 3¯ site symmetry, and with its lack of moment. The Sb states are characterized as px (separately, py) ?-bonded Sb4 ring states occupied and the corresponding antibonding states empty. The remaining (locally) pz orbitals form molecular orbitals with definite parity centered on the empty 2a site in the skutterudite structure. Eight such orbitals must be occupied; the one giving the linear band is an odd orbital singlet A2u at the zone center. We observe that the provocative linearity of the band within the gap is a consequence of the aforementioned near-degeneracy, which is also responsible for the small band gap.
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.
Band structure and optical functions of K{sub 2}ZnCl{sub 4} crystals in ferroelectric phase
Energy Technology Data Exchange (ETDEWEB)
Andriyevsky, B., E-mail: bohdan.andriyevskyy@tu.koszalin.pl [Faculty of Electronics and Computer Sciences, Koszalin University of Technology, 2 Sniadeckich Str., PL-75-453, Koszalin (Poland); Stadnyk, V. [Ivan Franko National University of Lviv, 8 Kyrylo-and-Mefodii Str., UA-79005 Lviv (Ukraine); Kohut, Z. [Lviv Polytechnic National University, 12 St. Bandera Str., UA-79013 Lviv (Ukraine); Romanyuk, M. [The Ivan Franko National University of Lviv, 8 Kyrylo-and-Mefodii Str., UA-79005 Lviv (Ukraine); Jaskolski, M. [Faculty of Electronics and Computer Sciences, Koszalin University of Technology, 2 Sniadeckich Str., PL-75-453, Koszalin (Poland)
2010-11-01
Band electronic structure (BS), density of states (DOS), and optical functions of K{sub 2}ZnCl{sub 4} crystal for the orthorhombic space group of symmetry Pna2{sub 1} corresponding to the ferroelectric phase (12 formula units in the crystallographic unit cell) have been calculated for the first time using the density functional theory based code VASP (Vienna Ab-initio Simulation Program). The valence-to-conduction band gap E{sub g} of the crystal is found to be direct in the {Gamma}-point of Brillouin zone. The effective masses m* have been calculated for the top valence and bottom conduction bands for different points and directions of Brillouin zone of the crystal and the results obtained have been analyzed. Peculiarities of the photon energy dependences n(E) and k(E) of refractive (n) and absorption (k) indices obtained in the range 0-28 eV have been identified on the basis of BS and DOS of the crystal. Calculated optical functions agree satisfactorily with the experimental data n(E) in the range of crystal's transparency, E < 5 eV.
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)
DAMPING OF ELECTRON DENSITY STRUCTURES AND IMPLICATIONS FOR INTERSTELLAR SCINTILLATION
International Nuclear Information System (INIS)
The forms of electron density structures in kinetic Alfven wave (KAW) turbulence are studied in connection with scintillation. The focus is on small scales L ? 108-1010 cm where the KAW regime is active in the interstellar medium, principally within turbulent H II regions. Scales at 10 times the ion gyroradius and smaller are inferred to dominate scintillation in the theory of Boldyrev et al. From numerical solutions of a decaying KAW turbulence model, structure morphology reveals two types of localized structures, filaments and sheets, and shows that they arise in different regimes of resistive and diffusive damping. Minimal resistive damping yields localized current filaments that form out of Gaussian-distributed initial conditions. When resistive damping is large relative to diffusive damping, sheet-like structures form. In the filamentary regime, each filament is associated with a non-localized magnetic and density structure, circularly symmetric in cross section. Density and magnetic fields have Gaussian statistics (as inferred from Gaussian-valued kurtosis) while density gradients are strongly non-Gaussian, more so than current. This enhancement of non-Gaussian statistics in a derivative field is expected since gradient operations enhance small-scale fluctuations. The enhancement of density gradient kurtosis over current kurtosis is not obvious, yet it suggests that modest density fluctuations may yield large scintillation events during pield large scintillation events during pulsar signal propagation. In the sheet regime the same statistical observations hold, despite the absence of localized filamentary structures. Probability density functions are constructed from statistical ensembles in both regimes, showing clear formation of long, highly non-Gaussian tails.
Damping of Electron Density Structures and Implications for Interstellar Scintillation
Smith, K. W.; Terry, P. W.
2011-04-01
The forms of electron density structures in kinetic Alfvén wave (KAW) turbulence are studied in connection with scintillation. The focus is on small scales L ~ 108-1010 cm where the KAW regime is active in the interstellar medium, principally within turbulent H II regions. Scales at 10 times the ion gyroradius and smaller are inferred to dominate scintillation in the theory of Boldyrev et al. From numerical solutions of a decaying KAW turbulence model, structure morphology reveals two types of localized structures, filaments and sheets, and shows that they arise in different regimes of resistive and diffusive damping. Minimal resistive damping yields localized current filaments that form out of Gaussian-distributed initial conditions. When resistive damping is large relative to diffusive damping, sheet-like structures form. In the filamentary regime, each filament is associated with a non-localized magnetic and density structure, circularly symmetric in cross section. Density and magnetic fields have Gaussian statistics (as inferred from Gaussian-valued kurtosis) while density gradients are strongly non-Gaussian, more so than current. This enhancement of non-Gaussian statistics in a derivative field is expected since gradient operations enhance small-scale fluctuations. The enhancement of density gradient kurtosis over current kurtosis is not obvious, yet it suggests that modest density fluctuations may yield large scintillation events during pulsar signal propagation. In the sheet regime the same statistical observations hold, despite the absence of localized filamentary structures. Probability density functions are constructed from statistical ensembles in both regimes, showing clear formation of long, highly non-Gaussian tails.
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
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.
Band structure engineering of anatase TiO{sub 2} by metal-assisted P-O coupling
Energy Technology Data Exchange (ETDEWEB)
Wang, Jiajun; Meng, Qiangqiang [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Huang, Jing [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); School of Materials and Chemical Engineering, Anhui Jianzhu University, Hefei, Anhui 230601 (China); Li, Qunxiang, E-mail: liqun@ustc.edu.cn; Yang, Jinlong [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)
2014-05-07
In this work, we demonstrate that the metal-assisted P-O coupling is an effective approach to improve the photoelectrochemical properties of TiO{sub 2}. The (Sc + P) and (In + P) codoping effects on electronic structures and photocatalytic activities of anatase TiO{sub 2} are examined by performing hybrid density functional theory calculations. It is found that the coupling of P dopant with the second-nearest neighboring O atom assisted by acceptor metals (Sc/In) leads to the fully occupied and delocalized intermediate bands within the band gap of anatase TiO{sub 2}, which is driven by the P-O antibonding states (?*). This metal-assisted P-O coupling can prevent the recombination of photogenerated electron-hole pairs and effectively reduce the band gap of TiO{sub 2}. Moreover, the band edge alignments in (Sc + P) and (In + P) codoped anatase TiO{sub 2} are desirable for water-splitting. The calculated optical absorption curves indicate that (Sc + P) and (In + P) codoping in anatase TiO{sub 2} can also effectively enhance the visible light absorption.
Liu, Hao; Xu, Ziqiang
2013-01-01
A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR WiMAX) and the wireless local area network (WLAN) at 3.5?GHz and 5.5?GHz, respectively. PMID:24170984
Effect of nitrogen on the electronic band structure of group III-N-V alloys
International Nuclear Information System (INIS)
We have studied optical transitions at the ? and L points of the Brillouin zone of GaNxAs1-x and AlyGa1-yNxAs1-x alloys using photomodulation spectroscopy. For GaNxAs1-x with N contents between 0% and 2%, the N-induced shift of the conduction-band L minima is found to be only a fraction of the conduction-band edge shift at the ? point. The measurements of AlyGa1-yNxAs1-x further show that there is no correlation between the location of the X conduction-band minima and the observed E+ and E- transitions. The results demonstrate that the N-induced interactions between extended ?, L, and X conduction-band states do not play a significant role in modification of the conduction-band structure of III-N-V alloys. The N-induced change of the conduction-band structure is predominantly influenced by the anticrossing interaction between the extended states of the ? conduction band and the localized states of nitrogen. (c) 2000 The American Physical Society
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
Gutermuth, R. A.; S. T. Megeath; 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...
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.
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...
Analysis of photonic band-gap (PBG) structures using the FDTD method
DEFF Research Database (Denmark)
Tong, M.S.; Cheng, M.
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 technique to perform such numerical studies. The proposed PBG filter structures may be applied in microwave and communication systems.
Band structure and transmission of 3D chiral sonic crystals
Pico, Ruben; Romero-Garcia, Vicent; Sanchez-Morcillo, Victor; Cebrecos, Alejandro; Garcia-Raffi, Lluis Miquel
2012-01-01
We study the properties of a novel type of sonic crystal formed by a periodic array of scatterers with spiral form. Such structures, previously introduced in photonics, present interesting properties related to the symmetry breaking induced by the chirality of its elements. It consists in a 3D periodic structure based on a local geometry that breaks the mirror symmetry with respect to its centre. The unit cell is composed by three elbow elements connecting all the dimensions in a loop: x-y, y...
Pham, C. Huy; Nguyen, T. Thuong; Nguyen, V. Lien
2014-01-01
Energy band structure of the bilayer graphene superlattices with $\\delta$-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 Dirac point of pristine bilayer graphene are exactly analyzed. Magnetic potential is shown also to generate finite-energy Dirac points at the edges of Brillouin zone the positions of which and the related ...
Berne, A.D.; G. Delrieu; 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...
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.
Damping of Electron Density Structures and Implications for Interstellar Scintillation
Smith, Kurt W
2011-01-01
The forms of electron density structures in kinetic Alfven wave turbulence are studied in connection with scintillation. The focus is on small scales $L \\sim 10^8-10^{10}$ cm where the Kinetic Alfv\\'en wave (KAW) regime is active in the interstellar medium. MHD turbulence converts to a KAW cascade, starting at 10 times the ion gyroradius and continuing to smaller scales. These scales are inferred to dominate scintillation in the theory of Boldyrev et al. From numerical solutions of a decaying kinetic Alfv\\'en wave turbulence model, structure morphology reveals two types of localized structures, filaments and sheets, and shows that they arise in different regimes of resistive and diffusive damping. Minimal resistive damping yields localized current filaments that form out of Gaussian-distributed initial conditions. When resistive damping is large relative to diffusive damping, sheet-like structures form. In the filamentary regime, each filament is associated with a non-localized magnetic and density structure,...
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.
International Nuclear Information System (INIS)
Diamond-like Cu-based multinary semiconductors are a rich family of materials that hold promise in a wide range of applications. Unfortunately, accurate theoretical understanding of the electronic properties of these materials is hindered by the involvement of Cu d electrons. Density functional theory (DFT) based calculations using the local density approximation or generalized gradient approximation often give qualitative wrong electronic properties of these materials, especially for narrow-gap systems. The modified Becke-Johnson (mBJ) method has been shown to be a promising alternative to more elaborate theory such as the GW approximation for fast materials screening and predictions. However, straightforward applications of the mBJ method to these materials still encounter significant difficulties because of the insufficient treatment of the localized d electrons. We show that combining the promise of mBJ potential and the spirit of the well-established DFT + U method leads to a much improved description of the electronic structures, including the most challenging narrow-gap systems. A survey of the band gaps of about 20 Cu-based semiconductors calculated using the mBJ + U method shows that the results agree with reliable values to within ±0.2 eV
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...
Band structures in neutron-rich odd mass dysprosium nuclei
International Nuclear Information System (INIS)
The structure of a nucleus is a fingerprint of how neutrons and protons interact in this many particle system to form a bound nucleus. Measuring nuclear properties is of great importance to understand the interactions which bind the protons and neutrons together in an isotope. These basic properties allow us to derive directly or indirectly information on the nuclear structure, as well as, on the strong nuclear force. Comparison of experimental properties of very exotic nuclei to calculations performed with different nuclear models allow testing the predictive power of these models when going to the extremes, or give a hint on how to further improve the nuclear models and their parameters. Neutron-rich nuclei are of particular current interest since they are predicted to reveal new aspects of nuclear structure associated with an excess of neutrons. Hence in the present work, the study of some odd mass Dysprosium isotopes with mass number varying from A = 159 to A = 165 have been undertaken using a framework of calculations known as Projected Shell Model (PSM)
A New Diagnostic of the Radial Density Structure of Be Disks
Draper, Zachary H; Bjorkman, Karen S; Haubois, Xavier; Carciofi, Alex C; Bjorkman, Jon E; Meade, Marilyn R; Okazaki, Atsuo
2011-01-01
We analyze the intrinsic polarization of two classical Be stars in the process of losing their circumstellar disks via a Be to normal B star transition originally reported by Wisniewski et al. During each of five polarimetric outbursts which interrupt these disk-loss events, we find that the ratio of the polarization across the Balmer jump (BJ+/BJ-) versus the V-band polarization traces a distinct loop structure as a function of time. Since the polarization change across the Balmer jump is a tracer of the innermost disk density whereas the V-band polarization is a tracer of the total scattering mass of the disk, we suggest such correlated loop structures in Balmer jump-V band polarization diagrams (BJV diagrams) provide a unique diagnostic of the radial distribution of mass within Be disks. We use the 3-D Monte Carlo radiation transfer code HDUST to reproduce the observed clockwise loops simply by turning "on/off" the mass decretion from the disk. We speculate that counter-clockwise loop structures we observe...
Broad-band flux density variations of the extragalactic radio source 1611+343
Cotton, W. D.; Spangler, S. R.
1979-01-01
A flux density outburst at low radio frequencies (less than about 1 GHz) has been observed in the extragalactic radio source 1611+343 (= DA 406). Observations in the period from June 1976 to September 1978 were made with several telescopes covering the frequency range from 0.325 to 15.5 GHz. The outburst appears to have been simultaneous at all observed frequencies and had a steep spectrum above 0.400 GHz. Some physical implications of these observations are discussed.
Density dependence of the conduction-band energy V0 of excess electrons in fluid xenon
International Nuclear Information System (INIS)
The ground-state energy V0 (relative to vacuum) of quasifree excess electrons in fluid xenon is calculated as a function of fluid density n. The calculations are performed within the framework of the Wigner-Seitz mean-field approximation for nonpolar fluids, using an accurate atomic pseudopotential to model the excess electron-xenon interaction. The calculated values of V0(n) are compared to experimental data and with other theoretical results. copyright 1996 The American Physical Society
Waveform inversion schemes for 3D density structure
Blom, N.; Fichtner, A.
2014-12-01
We develop waveform inversion schemes for density, based on numerical wave propagation, adjoint techniques and various non-seismological constraints to enhance resolution. Density variations drive convection in the Earth and serve as a discriminator between thermal and compositional heterogeneities. However, classical seismological observables and gravity provide only weak constraints, with strong trade-offs. To put additional constraints on density structure, we develop waveform inversion schemes that exploit the seismic waveform itself for the benefit of improved density resolution. Our inversion scheme is intended to incorporate any information that can help to constrain 3D density structure. This includes non-seismological information, such as gravity and the geoid, the mass and moment of inertia of the Earth, and mineral physical constraints on maximum density heterogeneities (assuming reasonable variations in temperature and composition). In a series of initial synthetic experiments, we aim to construct efficient optimisation schemes that allow us to assimilate all the available types of information. For this, we use 2D numerical wave propagation combined with adjoint techniques for the computation of sensitivity kernels. With these kernels, we drive gradient-based optimisation schemes that incorporate our non-seismological constraints. Specifically, we assess the usefulness of an inversion strategy where additional information is used as hard constraints, as opposed to the optimisation of a single objective functional that incorporates all the information. Hard constraints may consist of the Earth's mass or moment of inertia, and are applied by solving a separate optimisation problem to project the initial (unconstrained) solution onto an allowed range. These synthetic experiments will allow us to assess to what extent velocity and density structure need to be coupled in order to obtain useful and meaningful results to a density inversion.
Infrared absorption, multiphonon processes and time reversal effect on Si and Ge band structure
Energy Technology Data Exchange (ETDEWEB)
Kunert, H.W. [Department of Physics, University of Pretoria, 0002 (South Africa); Machatine, A.G.J. [Department of Physics, University of Pretoria, 0002 (South Africa)], E-mail: augusto.machatine@up.ac.za; Malherbe, J.B. [Department of Physics, University of Pretoria, 0002 (South Africa); Barnas, J. [Department of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznan (Poland); Hoffmann, A.; Wagner, M.R. [Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergerstr. 36, 10 623 Berlin (Germany)
2008-11-03
We have examined the effect of Time Reversal Symmetry (TRS) on vibrational modes and on the electronic band structure of Si and Ge. Most of the primary non-interacting modes are not affected by TRS. Only phonons originating from high symmetry lines S and A of the Brillouin Zone (BZ) indicate extra degeneracy. Selection rules for some two and three phonons originating from high symmetry lines are determined. The states of electrons and holes described by electronic band structure due to spin-inclusion are assigned by spinor representations of the double space group. Inclusion of the TRS into the band structure results in extra degeneracy of electrons and holes, and therefore optical selection rules suppose to be modified.
Infrared absorption, multiphonon processes and time reversal effect on Si and Ge band structure
International Nuclear Information System (INIS)
We have examined the effect of Time Reversal Symmetry (TRS) on vibrational modes and on the electronic band structure of Si and Ge. Most of the primary non-interacting modes are not affected by TRS. Only phonons originating from high symmetry lines S and A of the Brillouin Zone (BZ) indicate extra degeneracy. Selection rules for some two and three phonons originating from high symmetry lines are determined. The states of electrons and holes described by electronic band structure due to spin-inclusion are assigned by spinor representations of the double space group. Inclusion of the TRS into the band structure results in extra degeneracy of electrons and holes, and therefore optical selection rules suppose to be modified
Cui, Ning; Liang, Renrong; Wang, Jing; Xu, Jun
2012-06-01
Choosing novel materials and structures is important for enhancing the on-state current in tunnel field-effect transistors (TFETs). In this paper, we reveal that the on-state performance of TFETs is mainly determined by the energy band profile of the channel. According to this interpretation, we present a new concept of energy band profile modulation (BPM) achieved with gate structure engineering. It is believed that this approach can be used to suppress the ambipolar effect. Based on this method, a Si TFET device with a symmetrical tri-material-gate (TMG) structure is proposed. Two-dimensional numerical simulations demonstrated that the special band profile in this device can boost on-state performance, and it also suppresses the off-state current induced by the ambipolar effect. These unique advantages are maintained over a wide range of gate lengths and supply voltages. The BPM concept can serve as a guideline for improving the performance of nanoscale TFET devices.
Transition rate for impact ionization in the approximation of a parabolic band structure
International Nuclear Information System (INIS)
Recently, Alig, Bloom, and Struck have reported a simple model of ionization scattering in semiconductors and insulators. Their model is based upon the random-k approximation to the transition rate for impact ionization, and upon a generic band structure with only two free parameters to describe all materials. The present paper describes the first step in an attempt to understand in detail why such a simple model works so well. The random-k approximation to the transition rate for impact ionization is tested on a highly symmetric band-structure model for which most of the dimensions of the twelve-dimensional transition-rate integral can be treated analytically. The difference near threshold between the random-k approximation and the rigorous result can be much larger than indicated by Kane's Monte Carlo integration for the silicon band structure, but this difference seems to be unimportant in practical problems where impact ionization competes with phonon emission
Direct probing of band-structure Berry phase in diluted magnetic semiconductors
Granada, M.; Lucot, D.; Giraud, R.; LemaÃ®tre, A.; Ulysse, C.; Waintal, X.; Faini, G.
2015-06-01
We report on experimental evidence of the Berry phase accumulated by the charge-carrier wave function in single-domain nanowires made from a (Ga, Mn)(As, P) diluted ferromagnetic semiconductor layer. Its signature on the mesoscopic transport measurements is revealed as unusual patterns in the magnetoconductance that are clearly distinguished from the universal conductance fluctuations. We show that these patterns appear in a magnetic field region where the magnetization rotates coherently and are related to a change in the band-structure Berry phase as the magnetization direction changes. They should thus be considered a band-structure Berry phase fingerprint of the effective magnetic monopoles in the momentum space. We argue that this is an efficient method to vary the band structure in a controlled way and to probe it directly. Hence, (Ga, Mn)As appears to be a very interesting test bench for new concepts based on this geometrical phase.
Nashed, Ramy; Hassan, Walid M I; Ismail, Yehea; Allam, Nageh K
2013-02-01
The band structure and bandgap of Ta(2)O(5) are extremely controversial issues. Herein, the use of a hybrid functional reduces the error in bandgap estimation from 95% to 5% resulting in a bandgap of 3.7 eV. This is expected to help controlling the electronic and structural properties of the material. PMID:23243661
Processing Studies of X-Band Accelerator Structures at the NLCTA
C. Adolphsen; Baumgartner, W.; Jobe, K.; Pimpec, F. Le; Loewen, R.; McCormick, D.; Ross, M.; SMITH, T; Wang, J. W; Higo, T.
2001-01-01
RF processing studies of 1.8-m X-band (11.4 GHz) traveling wave structures at the Next Linear Collider Test Accelerator (NLCTA) have revealed breakdown-related damage at gradients lower than expected from earlier tests with standing wave and shorter, lower group velocity traveling wave structures. To understand this difference, a series of structures with different group velocities and lengths are being processed. In parallel, efforts are being made to improve processing pro...
Dynamics versus structure: breaking the density degeneracy in star formation
Parker, Richard J.
2014-12-01
The initial density of individual star-forming regions (and by extension the birth environment of planetary systems) is difficult to constrain due to the `density degeneracy problem': an initially dense region expands faster than a more quiescent region due to two-body relaxation and so two regions with the same observed present-day density may have had very different initial densities. We constrain the initial densities of seven nearby star-forming regions by folding in information on their spatial structure from the {Q}-parameter and comparing the structure and present-day density to the results of N-body simulations. This in turn places strong constraints on the possible effects of dynamical interactions and radiation fields from massive stars on multiple systems and protoplanetary discs. We apply our method to constrain the initial binary population in each of these seven regions and show that the populations in only three - the Orion Nebula Cluster, ? Oph, and Corona Australis - are consistent with having evolved from the Kroupa universal initial period distribution and a binary fraction of unity.
Dynamics versus structure: breaking the density degeneracy in star formation
Parker, Richard J
2014-01-01
The initial density of individual star-forming regions (and by extension the birth environment of planetary systems) is difficult to constrain due to the "density degeneracy problem": an initially dense region expands faster than a more quiescent region due to two-body relaxation and so two regions with the same observed present-day density may have had very different initial densities. We constrain the initial densities of seven nearby star-forming regions by folding in information on their spatial structure from the $\\mathcal{Q}$-parameter and comparing the structure and present-day density to the results of $N$-body simulations. This in turn places strong constraints on the possible effects of dynamical interactions and radiation fields from massive stars on multiple systems and protoplanetary discs. We apply our method to constrain the initial binary population in each of these seven regions and show that the populations in only three - the Orion Nebula Cluster, $\\rho$ Oph and Corona Australis - are consi...
Full waveform inversion schemes for 3D density structure
Blom, Nienke; Fichtner, Andreas
2014-05-01
We develop full waveform inversion schemes for density, based on numerical wave propagation, adjoint techniques and various non-seismological constraints to enhance resolution. Density variations drive convection in the Earth and serve as a discriminator between thermal and compositional heterogeneities. However, classical seismological observables and gravity provide only weak constraints, with strong trade-offs. To put additional constraints on density structure, we develop full waveform inversion schemes that exploit the complete seismic waveform for the benefit of improved density resolution. Our inversion scheme is intended to incorporate any information that can help to constrain 3D density structure. This includes non-seismological information, such as gravity and mineral physical constraints on maximum density heterogeneities (assuming reasonable variations in temperature and composition). As a trial case, we compare the results of current tomographic models to such constraints. In a series of initial synthetic inversion experiments, we aim to construct efficient optimisation schemes that allow us to assimilate all the available types of information. For this, we use 2D numerical wave propagation combined with adjoint techniques for the computation of sensitivity kernels. With these kernels, we drive gradient-based optimisation schemes that incorporate our non-seismological constraints. Specifically, we assess the usefulness of two different inversion strategies: (i) optimising a single augmented objective functional that incorporates all the constraints we have, and (ii) using an objective functional based on the seismological data only, and using the additional information as hard constraints to project the solution onto an allowed range.
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.
International Nuclear Information System (INIS)
The electronic structure and optical properties of Ag3PO4 were studied by hybrid density functional theory. The results indicated that the band gap is 2.43 eV, which agrees well with the experimental value of 2.45 eV. The conduction bands of Ag3PO4 are mainly attributable to Ag 5s and 5p states, while the valence bands are dominated by O 2p and Ag 4d states. The highest valence band edge potential was 2.67 V (vs. normal hydrogen electrode), which has enough driving force for photocatalytic water oxidation and pollutants degradation. The optical absorption spectrum showed that Ag3PO4 is a visible light response photocatalyst.
3D Global Coronal Density and Magnetic Field Structures during Solar Minimum and Maximum.
Kramar, Maxim; Airapetian, Vladimir
2015-08-01
Knowledge of the coronal electron density and magnetic field is a crucial ingredient in understanding the nature of solar coronal phenomena at all scales. We employ STEREO/COR1 data obtained during minimum and maximum of solar activity (Carrington rotations, CR, 2066 and 2131) to retrieve and analyze the three-dimensional (3D) coronal electron density in the range of heights from 1.5 to 4 Rsun using the tomography method and qualitatively deduce structures of the coronal magnetic field. The 3D electron density analysis is complemented by the 3D STEREO/EUVI emissivity in 195 A band obtained by tomography for the same CR periods. A global 3D thermodynamic MHD model of the solar corona was used to relate the reconstructed 3D density and emissivity to open/closed magnetic field structures. We show that the locations of density maximum can serve as an indicator of current sheet position, while the locations of the maximum of the density gradient can be a reliable indicator of closed-open magnetic field boundaries. We find that the magnetic field configuration during CR 2066 has a tendency to become radially open at heliocentric distances greater than 2.5 Rsun. We also find that the potential field model with a fixed source surface (PFSS) is not consistent with the positions of the boundaries between the regions with open and closed magnetic field structures. This indicates that the assumption of the potential nature of the coronal global magnetic field is not satisfied even during the deep solar minimum. Results of our 3D density reconstruction will help to constrain solar coronal field models and test the accuracy of the magnetic field approximations for coronal modeling.
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
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
Direct Measurement of the Band Structure of a Buried Two-Dimensional Electron Gas
DEFF Research Database (Denmark)
Miwa, Jill; Hofmann, Philip
2013-01-01
We directly measure the band structure of a buried two dimensional electron gas (2DEG) using angle resolved photoemission spectroscopy. The buried 2DEG forms 2 nm beneath the surface of p-type silicon, because of a dense delta-type layer of phosphorus n-type dopants which have been placed there. The position of the phosphorous layer is beyond the probing depth of the photoemission experiment but the observation of the 2DEG is nevertheless possible at certain photon energies where emission from the states is resonantly enhanced. This permits direct access to the band structure of the 2DEG and its temperature dependence.
Band structure engineering of CdSe nanosheet by strain: A first-principles study
Chen, Na; Yu, Guolong; Gu, Xiao; Chen, Li; Xie, Yiqun; Liu, Feng; Wang, Feifei; Ye, Xiang; Shi, Wangzhou
2014-03-01
We report a first principles study on the electronic structure of CdSe nanosheet under strain. Our results suggest that the band structure of CdSe nanosheet experiences a transition from being semiconducting to metallic with increased symmetrical strain. Such transition is not found under asymmetrical (along zigzag or armchair direction) strain. Moreover, the band gap of CdSe nanosheet responds differently among symmetrical, zigzag and armchair strain. A detailed discussion on the strain dependence effect is also presented via the electron localization function, the charge transfer between Cd and Se atoms, and the evolution of energy states at ? and K point.
Band Structure of Carbon Nanotubes in a Perpendicular Electric Field 2.0
Ravaioli, Umberto
The NanoEd Resource Portal, a â??dynamic repository for information dissemination, research and collaborations among the community of nanoscale science and engineering education (NSEE) learners, teachers and researchers,â? provides this interactive simulator. Contributed by Professor Umberto Ravaioli from the University of Illinois at Urbana-Champaign, this simulator performs "band structure calculations for zigzag and armchair type carbon nanotubes (CNT)." This band structure calculator could prove useful for both students and instructors in the field, and could prove valuable in the classroom as well.
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.
Chen, Gang; Gao, Shang-Peng
2012-10-01
The structures of the heptazine-based graphitic C3N4 and the S-doped graphitic C3N4 are investigated by using the density functional theory with a semi-empirical dispersion correction for the weak long-range interaction between layers. The corrugated structure is found to be energetically favorable for both the pure and the S-doped graphitic C3N4. The S doptant is prone to substitute the N atom bonded with only two nearest C atoms. The band structure calculation reveals that this kind of S doping causes a favorable red shift of the light absorption threshold and can improve the electroconductibility and the photocatalytic activity of the graphitic C3N4.
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 Sm2NiMnO6 compound: DFT calculation
International Nuclear Information System (INIS)
The band structure, density of states, electronic charge density, Fermi surface and optical properties of Sm2NiMnO6 compound have been investigated with the support of density functional theory (DFT). The atomic positions of Sm2NiMnO6 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 (EF). The calculated density of states at the EF 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 K2 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
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 and optical properties of sinusoidal superlattices: ZnSe1-xTex
International Nuclear Information System (INIS)
This paper examines the band structure and optical selection rules in superlattices with a sinusoidal potential profile. The analysis is motivated by the recent successful fabrication of high quality ZnSe1-xTex superlattices in which the composition x varies sinusoidally along the growth direction. Although the band alignment in the ZnSe1-xTex sinusoidal superlattices is staggered (type II), they exhibit unexpectedly strong photoluminescence, thus suggesting interesting optical behavior. The band structure of such sinusoidal superlattices is formulated in terms of the nearly-free-electron (NFE) approximation, in which the superlattice potential is treated as a perturbation. The resulting band structure is unique, characterized by a single minigap separating two wide, free-electron-like subbands for both electrons and holes. Interband selection rules are derived for optical transitions involving conduction and valence-band states at the superlattice Brillouin-zone center, and at the zone edge. A number of transitions are predicted due to wave-function mixing of different subband states. It should be noted that the zone-center and zone-edge transitions are especially easy to distinguish in these superlattices because of the large width of the respective subbands. The results of the NFE approximation are shown to hold surprisingly well over a wide range of parameters, particularly when the period of the superlattice is short. (c) 2000 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.
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.
Band structure effects in nitrogen K-edge resonant inelastic X ray scattering from GaN
Strocov, V N; Rubensson, J E; Blaha, P; Paskova, T; Nilsson, P O
2004-01-01
Systematic experimental data on resonant inelastic X-ray scattering (RIXS) in GaN near the N K-edge are presented for the first time. Excitation energy dependence of the spectral structures manifests the band structure effects originating from momentum selectivity of the RIXS process. This finding allows obtaining k-resolved band structure information for GaN crystals and nanostructures.
Photoelectron spectroscopic study of band alignment of polymer/ZnO photovoltaic device structure
International Nuclear Information System (INIS)
Using x-ray photoelectron spectroscopy, we investigated the band alignment of a Ag/poly(3-hexylthiophene-2,5-diyl) (P3HT)/ZnO photovoltaic structure. At the P3HT/ZnO interface, a band bending of P3HT and a short surface depletion layer of ZnO were observed. The offset between the highest occupied molecular orbital of P3HT and the conduction band minimum of ZnO at the interface contributed to the open circuit voltage (Voc) was estimated to be approximately 1.5 ± 0.1 eV, which was bigger than that of the electrically measured effective Voc of P3HT/ZnO photovoltaic devices, meaning that the P3HT/ZnO photovoltaic structure has the potential to provide improved photovoltaic properties.
Reconstruction of band structure induced by electronic nematicity in an FeSe superconductor.
Nakayama, K; Miyata, Y; Phan, G N; Sato, T; Tanabe, Y; Urata, T; Tanigaki, K; Takahashi, T
2014-12-01
We have performed high-resolution angle-resolved photoemission spectroscopy on an FeSe superconductor (T_{c}?8??K), which exhibits a tetragonal-to-orthorhombic structural transition at T_{s}?90??K. At low temperature, we found splitting of the energy bands as large as 50 meV at the M point in the Brillouin zone, likely caused by the formation of electronically driven nematic states. This band splitting persists up to T?110??K, slightly above T_{s}, suggesting that the structural transition is triggered by the electronic nematicity. We have also revealed that at low temperature the band splitting gives rise to a van Hove singularity within 5 meV of the Fermi energy. The present result strongly suggests that this unusual electronic state is responsible for the unconventional superconductivity in FeSe. PMID:25526150
Directory of Open Access Journals (Sweden)
P. Kovacs
2010-04-01
Full Text Available The paper is focused on the automated design and optimization of electromagnetic band gap structures suppressing the propagation of surface waves. For the optimization, we use different global evolutionary algorithms like the genetic algorithm with the single-point crossover (GAs and the multi-point (GAm one, the differential evolution (DE and particle swarm optimization (PSO. The algorithms are mutually compared in terms of convergence velocity and accuracy. The developed technique is universal (applicable for any unit cell geometry. The method is based on the dispersion diagram calculation in CST Microwave Studio (CST MWS and optimization in Matlab. A design example of a mushroom structure with simultaneous electromagnetic band gap properties (EBG and the artificial magnetic conductor ones (AMC in the required frequency band is presented.
Structural band-gap tuning in g-C3N4
Zuluaga, Sebastian; Liu, Li-Hong; Shafiq, Natis; Rupich, Sara M.; Veyan, Jean-François; Chabal, Yves J.; Thonhauser, Timo
g-C$_3$N$_4$ is a promising material for hydrogen production from water via photo-catalysis, if we can tune its band gap to desirable levels. Using a combined experimental and ab initio approach, we uncover an almost perfectly linear relationship between the band gap and structural aspects of g-C$_3$N$_4$, which we show to originate in a changing overlap of wave functions associated with the lattice constants. This changing overlap, in turn, causes the unoccupied $p_z$ states to experience a significantly larger energy shift than any other occupied state ($s$, $p_x$, or $p_y$), resulting in this peculiar relationship. Our results explain and demonstrate the possibility to tune the band gap by structural means, and thus the frequency at which g-C$_3$N$_4$ absorbs light.
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)
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
Electronic structure of ZrS{sub x}Se{sub 2-x} by density functional theory
Energy Technology Data Exchange (ETDEWEB)
Ghafari, Ailakbar; Moustafa, Mohamed; Janowitz, Christoph; Dwelk, Helmut; Manzke, Recardo [Institut fuer Physik, Humboldt-Universitaet zu Berlin, Newtonstr. 15, D-12489 Berlin (Germany); Bouchani, Arash [Physics Department, Islamic Azad University, Kermanshah Branch (Iran, Islamic Republic of)
2011-07-01
The electronic properties of the ZrS{sub x}Se{sub 2-x} (x varies between zero and two) semiconductors have been calculated by density functional theory (using the Wien2K code) employing the full potential Hamiltonian within the Generalized Gradient Approximation (GGA) method. The results obtained for the end members of the series, i.e. ZrS{sub 2} and ZrSe{sub 2} reveal that the valence band maximum and conduction band minimum are located at {gamma} and between {gamma} and K respectively which is in agreement with our photoemission experimental data. Trends in the electronic structure for the whole substitution series are discussed.
Atomic structures of 13-atom clusters by density functional theory
Chen, Hsin-Yi; Wei, Ching-Ming
2007-03-01
The 13-atom cluster structures of the alkaline metals, alkaline earth metals, boron group, 3d, 4d, and 5d transition metals in the periodic table, and Pb are investigated by density functional theory with three kinds of exchange correlation approximation: i) LDA (Local Density Approximation), ii) GGA (Generalized Gradient Approximation) [1], and iii) PBE (Perdew-Burke-Ernzerhof) [2]. The results mainly focus on five 3-D structures: icosahedral, cuboctahedral, hexagonal-closed packed, body-center cubic, decahedral, and the other two layer structures: buckled biplanar (bbp) and garrison-cap biplanar (gbp) structures. Limited by accuracy of exchange correlation approximation, two interesting results are found. The ground states of Ca13, Sr13, Ba13, Sc13, Y13, La13, Ti13, Zr13, and Hf13 are icosahedral structures. The clusters of Ir13, Pt13, Cu13, Ag13, and Au13 are more favorable for layer structures (i.e. bbp and gbp) than the other five 3-D structures. [1] J. P. Perdew et al., Phys. Rev. B 46, 6671 (1992). [2] J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996).
Maximum likelihood density modification by pattern recognition of structural motifs
Energy Technology Data Exchange (ETDEWEB)
Terwilliger, Thomas C.
2004-04-13
An electron density for a crystallographic structure having protein regions and solvent regions is improved by maximizing the log likelihood of a set of structures factors {F.sub.h } using a local log-likelihood function: (x)+p(.rho.(x).vertline.SOLV)p.sub.SOLV (x)+p(.rho.(x).vertline.H)p.sub.H (x)], where p.sub.PROT (x) is the probability that x is in the protein region, p(.rho.(x).vertline.PROT) is the conditional probability for .rho.(x) given that x is in the protein region, and p.sub.SOLV (x) and p(.rho.(x).vertline.SOLV) are the corresponding quantities for the solvent region, p.sub.H (x) refers to the probability that there is a structural motif at a known location, with a known orientation, in the vicinity of the point x; and p(.rho.(x).vertline.H) is the probability distribution for electron density at this point given that the structural motif actually is present. One appropriate structural motif is a helical structure within the crystallographic structure.
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 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.
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.
Multiple-Scale Pattern Recognition Applied to Faint Intergranular G-band Structures
Bovelet, B.; Wiehr, E.
2007-07-01
Small-scale solar magnetic flux concentrations are studied in two-dimensional G-band images at very high spatial resolution and compared with Ca ii H enhancements. Among 970 small-sized G-band intergranular structures (IgS), 45% are co-spatial with isolated locations of Ca ii H excess and thus considered as magnetic (MIgS); they may be even twice as frequent as the known G-band bright points. The IgS are recognized in the G-band image by a new algorithm operating in four steps: (1) A set of equidistant detection levels yields a pattern of primary “cells”; (2) for each cell, the intrinsic intensity profile is normalized to its brightest pixel; (3) the cell sizes are shrunk by a unitary single-intensity clip; (4) features in contact at an appropriate reference level are merged by removal of the respective common dividing lines. Optionally, adjoining structures may be excluded from this merging process ( e.g., chains of segmented IgS), referring to the parameterized number and intensity of those pixels where enveloping feature contours overlap. From the thus recognized IgS pattern, MIgS are then selected by their local Ca ii H contrast and their mean G-band-to-continuum brightness ratio.
Xu, Ziqiang
2013-01-01
A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.1–10.6?GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX) and the wireless local area network (WLAN) at 3.5?GHz and 5.5?GHz, respectively. PMID:24170984
Observation of dark-current signals from the S-band structures of the SLAC linac
International Nuclear Information System (INIS)
It is well known that the electro-magnetic fields in high-gradient RF structures can cause electron emission from the metallic structure walls. If the emitted electrons are captured and accelerated by the accelerating fields so-called dark-current is induced. Dark-currents have been measured and studied for various RF-structures. In this paper the authors present measurements of RF induced signals for the SLC S-band structures. For nominal gradients of 17 MV/m it is shown that the dark-current can be strong enough to significantly reduce the signal-to-noise ratio of the SLC beam wire scanners. They also show results from RF measurements in the dipole band. The measurements are compared to more direct observations of dark-current and it is tried to connect the results to possible effects on the accelerated particle beam
Ferromagnetism and the electronic band structure in (Ga,Mn)(Bi,As) epitaxial layers
International Nuclear Information System (INIS)
Impact of Bi incorporation into (Ga,Mn)As layers on their electronic- and band-structures as well as their magnetic and structural properties has been studied. Homogenous (Ga,Mn)(Bi,As) layers of high structural perfection have been grown by the low-temperature molecular-beam epitaxy technique. Post-growth annealing treatment of the layers results in an improvement of their structural and magnetic properties and an increase in the hole concentration in the layers. The modulation photoreflectance spectroscopy results are consistent with the valence-band model of hole-mediated ferromagnetism in the layers. This material combines the properties of (Ga,Mn)As and Ga(Bi,As) ternary compounds and offers the possibility of tuning its electrical and magnetic properties by controlling the alloy composition.
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.
Dyadic Green's function study of band structures of dispersive photonic crystals
International Nuclear Information System (INIS)
We present here in terms of a dyadic Green's function (DGF) a general description of optical phenomena in photonic crystal (PC) structures, described particularly by frequency-dependent components, assuming that PC structures are decomposed into their relatively simple constituent parts via conductivity tensors. We demonstrate this approach by explicitly calculating the DGFs for electromagnetic waves propagating in the one- and two-dimensional dispersive PCs consisting of a periodic array of identical metallic quantum wells and a periodic square array of identical metallic quantum wires, each embedded in a three-dimensional dispersive medium. By means of the explicit analytic dispersion relations, which result from the frequency poles of the corresponding DGFs, we also calculate the band structures of these dispersive PCs by simple numerical means. Our analysis shows that the band structures calculated from our DGF approach conform well with those calculated from the traditional computational methods.
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.
International Nuclear Information System (INIS)
Ab initio band structure calculations of the orthorhombic Hg3TeCl4 crystals of the symmetry D2h15 were performed and the topology of its valence band was analyzed in the framework of the elementary energy bands concepts. The effective masses of charge carriers were estimated. It was demonstrated that the anisotropy of the effective mass tensor components does not coincide with the mechanical one of the Hg3TeCl4 crystal. A possible reason of this fact was proposed.
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.
Acceleration results from a four-cell, S-band PWT linac structure
International Nuclear Information System (INIS)
We have designed and built a 21 cm long, four-cell S- band Plane Wave Transformer (PWT) linac structure. We have injected an unbunched, 40 keV, 2 ?s, electron beam from a thermionic gun, and have observed, using an energy spectrometer, acceleration up to 3.5 MeV. We discuss these results and our ongoing efforts to develop this structure to serve as an injector to the Compact Ultrafast TErahertz Free Electron Laser (CUTE-FEL). (author)
An efficient approach to the local optimization of finite electromagnetic band-gap structures
DUQUE, David; LANCELLOTTI, Vito; HON, Bastiaan Pieter DE; TIJHUIS, Antonius
2014-01-01
We propose a methodology based on linear embedding via Green's operators (LEGO) and the eigencurrent expansion method (EEM) to efficiently deal with and locally optimize 2-D electrically large electromagnetic band-gap (EBG) structures. In LEGO terminology, the composite EBG structure is broken up (diakopted) into constitutive elements called ``bricks'' that we characterize through scattering operators by invoking Love's equivalence principle, while, at the same ti...
Crystalline and electronic structures of lithium silicates: A density functional theory study
International Nuclear Information System (INIS)
Highlights: ? We calculate crystalline and electronical structures of two lithium silicates, Li2SiO3 and Li4SiO4. ? We examine changes in the binding energy, band gap, electronic density mapping of two lithium silicates. ? The Si 3s and 3p orbital will hybridize strongly in Li2SiO3, but not in Li4SiO4. ? For the first time calculated the mechanical properties of these two lithium silicates. - Abstract: Lithium silicates, such as Li2SiO3 and Li4SiO4, are considered as favorable candidates for the tritium breeding materials of a deuterium–tritium type nuclear fusion reactor. Their bulk structural and electronic properties are investigated using pseudopotential plane wave (PPW) method within density functional theory (DFT). The optimized crystal structure parameters are well consistent with the experimental results. The results indicate that Li2SiO3 and Li4SiO4 are insulators with band gaps of about 5.36 and 5.53 eV, respectively. The valence electrons density of state reveal the covalency properties mainly resulting from the overlapping of O 2p and Si 3p orbital electrons in both lithium silicates. The nonbridging O (NBO) atoms and bridging O (BO) atoms of Li2SiO3 exhibit significantly different electron distributions. The Si 3s and 3p hybridization is observed in Lp hybridization is observed in Li2SiO3, but not in Li4SiO4. The mechanical elastic constants reflected Li4SiO4 might be unstable in some degrees.
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
Investigation of band structure of 103,105Rh using microscopic computational technique
Kumar, Amit; Singh, Suram; Bharti, Arun
2015-08-01
The high-spin structure in 61Cu nucleus is studied in terms of effective two body interaction. In order to take into account the deformed BCS basis, the basis states are expanded in terms of the core eigenfunctions. Yrast band with some other bands havew been obtained and back-bending in moment of inertia has also been calculated and compared with the available experimental data for 61Cu nucleus. On comparing the available experimental as well as other theoretical data, it is found that the treatment with PSM provides a satisfactory explanation of the available data.
Fine Structure Analysis of 4702 oA Band of the Molecule
SURESHKUMAR, Mundan B.; SRIKANT, Sharma R.
1998-01-01
The emission spectrum of the cobalt monochloride molecule has been excited in a high frequency discharge tube source and the (0,0) band of H-system at 4702 \\AA was photo-graphed at an inverse dispersion of 0.973 \\AA/mm in the 5th order of a two meter plane grating spectrograph (Carl-Zeiss). The fine structure analysis of the band has been carried out and the molecular constants are reported for the first time. Rotational isotopic shift due to 37Cl support the analysis. The electronic transiti...
Spatial structures of QCD pair condensates at various densities
Villegas, Kristian Hauser
2015-06-01
The spatial structures of the chiral symmetry breaking(? SB )-quark-antiquark (q q ¯) pair and two-color superconducting(2SC)-quark-quark (q q ) , antiquark-antiquark (q ¯q ¯) , and hole-hole (h h ) pairs are investigated. At low density, it is found that the q q ¯ pair is well localized with average bond length of the order 1 fm . It is then suggested that the pions, which are excitations arising from flavor-space phase fluctuations, exhibit the spatial structure of the underlying q q ¯ -paired ground state. At intermediate density where the quarks form a 2SC state, it is found that the q q and h h pairs are extended and oscillating in real space while the q ¯q ¯ pair remains well localized.
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.
International Nuclear Information System (INIS)
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. (authors)
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.
Band structures of two dimensional solid/air hierarchical phononic crystals
Energy Technology Data Exchange (ETDEWEB)
Xu, Y.L.; Tian, X.G. [State Key Laboratory for Mechanical Structure Strength and Vibration, Xi' an Jiaotong University, Xi' an 710049 (China); Chen, C.Q., E-mail: chencq@tsinghua.edu.cn [Department of Engineering Mechanics, AML and CNMM, Tsinghua University, Beijing 100084 (China)
2012-06-15
The hierarchical phononic crystals to be considered show a two-order 'hierarchical' feature, which consists of square array arranged macroscopic periodic unit cells with each unit cell itself including four sub-units. Propagation of acoustic wave in such two dimensional solid/air phononic crystals is investigated by the finite element method (FEM) with the Bloch theory. Their band structure, wave filtering property, and the physical mechanism responsible for the broadened band gap are explored. The corresponding ordinary phononic crystal without hierarchical feature is used for comparison. Obtained results show that the solid/air hierarchical phononic crystals possess tunable outstanding band gap features, which are favorable for applications such as sound insulation and vibration attenuation.
Compact ultra-wideband antenna with band-notched based on defected ground structure
Directory of Open Access Journals (Sweden)
Reza Karimian
2014-01-01
Full Text Available A simple and very compact planar monopole ultra-wideband antenna with a 3.5 GHz band rejection is proposed in this Letter. The compact antenna is etched on an FR4 substrate with the size of 14 × 16 × 1 mm^3, consists of a tree-shaped radiation patch with modified ground structure. To reject certain frequency band, a pair of parallel strip patch, acting as a parasitic element is used. Prototype of the proposed antenna was constructed and measured. The measured impedance bandwidth of the realised antenna with optimal parameters is from 2.6 to 12 GHz (128% for voltage standing wave ratio <2 with an unwanted band notched from 3.3 to 4 GHz. Moreover, the antenna has good omnidirectional radiation patterns in the H-plane.
International Nuclear Information System (INIS)
Evidence is now quite strong that the elementary hybridization model is the correct way to understand the lattice-coherent Fermi liquid regime at very low temperatures. Many-body theory leads to significant renormalizations of the input parameters, and many of the band-theoretic channels for hybridization are suppressed by the combined effects of Hund's-rule coupling, crystal-field splitting, and the f-f Coulomb repulsion U. Some exploratory calculations based on this picture are described, and some inferences are drawn about the band structures of several heavy-fermion materials. These inferences can and should be tested by suitably modified band-theoretic calculations. We find evidence for a significant Baber-scattering contribution in the very-low-temperature resistivity. A new mechanism is proposed for crossover from the coherent Fermi-liquid regime to the incoherent dense-Kondo regime. 28 refs
High power test of L-band accelerator structure of superKEKB injector linac
International Nuclear Information System (INIS)
Although the actual installation of L-band (1298MHz) accelerator units is suspended from Day One of the superKEKB operation, limited numbers of R and D programs are ongoing for the future use. An L-band 40MW klystron was produced in FY2010 and its performance (30MW output) was confirmed in its high power test done. A travelling wave accelerator structure was produced in FY2010 and was long waiting for the test. The waveguide components were prepared and the 'L-band accelerator test unit' was built by putting all these devices together and is now set in the sector no.1 region of KEKB injector linac. Two weeks pilot run of the unit was done just before the linac summer shutdown. (author)
Band structures of Si/InGaP heterojunctions by using surface-activated bonding
International Nuclear Information System (INIS)
The band structure of p-Si/n-InGaP heterojunctions fabricated by using surface-activated bonding (SAB) was investigated by measuring their current-voltage (I-V) and capacitance-voltage (C-V) characteristics. The I-V characteristics of p-Si/n-InGaP junctions showed rectifying properties similarly to p-Si/n-GaAs junctions. The conduction band discontinuity of the p-Si/n-InGaP junctions was determined to be 0.41 eV from C-V measurements, which indicated that the Si/InGaP junctions revealed the type-I band line-up in contrast to the Si/GaAs junctions. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Band structure, phase transitions, and semiconductor analogs in one-dimensional solid light systems
International Nuclear Information System (INIS)
The conjunction of atom-cavity physics and photonic structures ('solid light' systems) offers new opportunities in terms of more device functionality and the probing of designed emulators of condensed-matter systems. By analogy to the canonical one-electron approximation of solid-state physics, we propose a one-polariton approximation to study these systems. Using this approximation, we apply Bloch states to the uniformly tuned Jaynes-Cummings-Hubbard model to analytically determine the energy-band structure. By analyzing the response of the band structure to local atom-cavity control, we explore its application as a quantum simulator and show phase-transition features absent in mean-field theory. Using this approach for solid light systems, we extend the analysis to include detuning impurities to show the solid light analogy of the semiconductor. This investigation also shows features with no semiconductor analog.
Band structure, phase transitions, and semiconductor analogs in one-dimensional solid light systems
Quach, James; Makin, Melissa I.; Su, Chun-Hsu; Greentree, Andrew D.; Hollenberg, Lloyd C. L.
2009-12-01
The conjunction of atom-cavity physics and photonic structures (“solid light” systems) offers new opportunities in terms of more device functionality and the probing of designed emulators of condensed-matter systems. By analogy to the canonical one-electron approximation of solid-state physics, we propose a one-polariton approximation to study these systems. Using this approximation, we apply Bloch states to the uniformly tuned Jaynes-Cummings-Hubbard model to analytically determine the energy-band structure. By analyzing the response of the band structure to local atom-cavity control, we explore its application as a quantum simulator and show phase-transition features absent in mean-field theory. Using this approach for solid light systems, we extend the analysis to include detuning impurities to show the solid light analogy of the semiconductor. This investigation also shows features with no semiconductor analog.
Calculating the Energy Band Structure Using Sampling and Greens Function Techniques
Khoshnegar, Milad; Arjmandi, Nima; Khorasani, Sina
2012-01-01
In this paper, a new method based on Greens function theory and Fourier transform analysis has been proposed for calculating band structure with high accuracy and low processing time. This method utilizes sampling of potential energy in some points of crystals unit cell with Dirac delta functions, then through lattice Fourier transform gives us a simple and applicable formula for most of nanostructures. Sampling of potential in a crystal lattice of any kind contains accurate approximation of actual potential energy of atoms in the crystal. The step forward regarding the method concentrated on two novel ideas, Firstly, the potential was sampled and approximated by delta functions spread over the unit cell. Secondly, the principal equation of lattice is translated into reciprocal lattice and resulted in a huge reduction of calculations. By this method, it is possible to extract the band structure of any one, two or three dimensional crystalline structure.
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...
Robust topology optimization of three-dimensional photonic-crystal band-gap structures
Men, Han; Freund, Robert M; Peraire, Jaime; Johnson, Steven G
2014-01-01
We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniq...
Rinke, P; Neugebauer, J; Freysoldt, C; Scheffler, M; Rinke, Patrick; Qteish, Abdallah; Neugebauer, Joerg; Freysoldt, Christoph; Scheffler, Matthias
2005-01-01
We report quasiparticle-energy calculations of the electronic bandstructure as measured by valence-band photoemission for selected II-VI compounds and group-III-nitrides. By applying GW as perturbation to the ground state of the fictitious, non-interacting Kohn-Sham electrons of density-functional theory (DFT) we systematically study the electronic structure of zinc-blende GaN, ZnO, ZnS and CdS. Special emphasis is put on analysing the role played by the cation semicore d-electrons that are explicitly included as valence electrons in our pseudopotential approach. Unlike in the majority of previous GW studies, which are almost exlusively based on ground state calculations in the local-density approximation (LDA), we combine GW with exact-exchange DFT calculations in the optimised-effective potential approach (OEPx). This is a much more elaborate and computationally expensive approach. However, we show that applying the OEPx approach leads to an improved description of the d-electron hybridisation compared to t...
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.
International Nuclear Information System (INIS)
The structural, electronic and optical properties of beryllium chalcogenides BeS, BeSe and BeTe using the full-potential linear augmented plane wave (FP-LAPW) method are investigated. The exchange-correlation energy within the local density approximation (LDA) and the generalized gradient approximation (GGA) are described. The Engel-Vosko (EVGGA) formalism is applied for electronic and optical properties. The structural parameters of our model and the transition pressure from zinc-blende (B3) to the NiAs (B8) phase are confirmed. It is found that these compounds have indirect band gaps except for BeTe in NiAs (B8) phase. The results of reflectivity, refractive index and optical dielectric functions of Be compounds are investigated. An agreement is found between our results and those of other theoretical calculations and the experimental data.
Electronic band structure of GaAs/Al{sub x}Ga{sub 1-x}As superlattice in an intense laser field
Energy Technology Data Exchange (ETDEWEB)
Sakiroglu, S., E-mail: serpil.sakiroglu@deu.edu.tr [Physics Department, Faculty of Science, Dokuz Eyluel University, 35160 Izmir (Turkey); Yesilgul, U.; Ungan, F. [Physics Department, Faculty of Science, Cumhuriyet University, 58140 Sivas (Turkey); Duque, C.A. [Instituto de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia); Kasapoglu, E.; Sari, H. [Physics Department, Faculty of Science, Cumhuriyet University, 58140 Sivas (Turkey); Sokmen, I. [Physics Department, Faculty of Science, Dokuz Eyluel University, 35160 Izmir (Turkey)
2012-06-15
We perform theoretical calculations for the band structure of semiconductor superlattice under intense high-frequency laser field. In the frame of the non-perturbative approach, the laser effects are included via laser-dressed potential. Results reveal that an intense laser field creates an additional geometric confinement on the electronic states. Numerical results show that when tuning the strength of the laser field significant changes come in the electronic energy levels and density of states. - Graphical abstract: We have theoretically investigated the influence of an intense, high-frequency, non-resonant laser field on the electronic band structure of GaAs/Al{sub x}Ga{sub 1-x}As semiconductor superlattice. By tuning the strength of the laser field significant changes come in the electronic energy levels and density of states. Highlights: Black-Right-Pointing-Pointer Band structure of GaAs/Al{sub x}Ga{sub 1-x}As superlattice under an ILF is investigated. Black-Right-Pointing-Pointer Dramatic variation of the confinement potential in the well/barrier region is predicted. Black-Right-Pointing-Pointer ILF creates an additional geometric confinement on the electronic states. Black-Right-Pointing-Pointer Significant changes come in the electronic energy levels and density of states.
Band Structure and Fermi-Surface Properties of Ordered beta-Brass
DEFF Research Database (Denmark)
Skriver, Hans Lomholt; Christensen, N. E.
1973-01-01
The band structure of ordered ?-brass (??-CuZn) has been calculated throughout the Brillouin zone by the augmented-plane-wave method. The present band model differs from previous calculations with respect to the position and width of the Cu 3d band. The derived dielectric function ?2(?) and the photoemission spectra agree well with experiments. We find that the main absorption edge as observed in the ?2 trace has contributions from conduction-band transitions as well as transitions from the Cu d states. The comparison to photoemission results indicates that the calculated Cu d bands are too narrow, but that their position relative to the Fermi level is correct. The derived Fermi-surface model allows a detailed interpretation of the de Hass-van Alphen (dHvA) data. The present model has no open orbit along for B?? ?110?. This agrees with dHvA as well as magnetoresistance measurements. Four new extremal cross sections have been found and related to previously unexplained dHvA frequencies. In general, the Fermi-surface dimensions agree extremely well with dHvA measurements, and the ratios between the experimental and the calculated cyclotron masses vary between 1.18 and 1.43.
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...
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.
Design of C-band 50 MW klystron with traveling wave output structure
International Nuclear Information System (INIS)
This paper presents the simulation study of a C-band 50 MW klystron with disc-loaded waveguide traveling wave output structure. The electron gun with a perveance of 1.53 ?P is designed. The gun has a voltage gradient lower than 22.1 kV/mm and a cathode load current lower than 6.3 A/cm2. The beam focusing system is a space-charge balanced flow type with solenoid magnet structure and the focusing beam trajectories have a good laminar condition. A single gap cavity is adopted instead of the traveling wave output structure in the initial beam-wave interaction simulation to decide the parameters of the cavities except the output structure. A C-band disc-loaded waveguide output structure working at ?/2 mode is designed and the dispersion and interaction impedance of the structure are determined by the CST code. The beam-wave interaction system with disc-loaded waveguide output structure is simulated by a three-dimensional PIC code. More than 50 MW output power is obtained. The efficiency is more than 45% and the saturate gain is more than 50 dB. The voltage gradient of the disc-loaded waveguide output structure is 30 percent less than that of the single gap cavity and there is an increase of 4% in efficiency above that of the single gap cavity. (authors)
Influence of nitrogen substitution on the electronic band structure of poly(peri-naphthalene)
Energy Technology Data Exchange (ETDEWEB)
Viruela, P.M. [Dept. Quimica Fisica, Univ. Valencia, 46100 Burjassot (Valencia) (Spain); Viruela, R. [Dept. Quimica Fisica, Univ. Valencia, 46100 Burjassot (Valencia) (Spain); Orti, E. [Dept. Quimica Fisica, Univ. Valencia, 46100 Burjassot (Valencia) (Spain)
1995-03-01
The electronic valence band structure of PPDAN, a chemical modification of poly(peri-naphthalene) where the central two carbon atoms of each naphthalene unit cell are substituted by nitrogen atoms, is theoretically investigated using the nonempirical VEH method. VEH calculations predict that PPDAN is a semiconductor with a small bandgap of 0.64eV when a planar D{sub 2h} structure is assumed for the unit cell. The bandgap increases to 1.3-1.6eV when the more stable C{sub 2v} and C{sub 2h} structures are used. (orig.)
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.
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.
Miss Witcher
2011-10-06
What is Density? Density is the amount of "stuff" in a given "space". In science terms that means the amount of "mass" per unit "volume". Using units that means the amount of "grams" per "centimeters cubed". Check out the following links and learn about density through song! Density Beatles Style Density Chipmunk Style Density Rap Enjoy! ...
Low-lying positive-parity band structure in 150Nd
International Nuclear Information System (INIS)
The stable N = 90 isotones 150Nd, 152Sm, and 154Gd lie in a region of rapid shape change and can be expected for displaying complex collective structure. Although the level structure of 152Sm and 154Gd were studied quite extensively in the recent past, the knowledge of the low-lying level structure of 150Nd is found to be surprisingly poor. The results from our previous investigations for the negative-parity states in 150Nd are suggestive of the enhanced B(E1) strengths (of ms order) for the transitions decaying from the K? = 01- to the K? = 01+ band. Also, a complex coupling between the members of the K? = 21- and the K? = 21+ bands was observed. The present report highlights the new results related to the positive-parity band structure of 150Nd, obtained from a series of ?-ray spectroscopic experiments involving measurements of excitation functions, angular distributions, and ?-? coincidences using the (n,n? ?) reaction
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.
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.
Gladysiewicz, M.; Kudrawiec, R.; Wartak, M. S.
2015-08-01
The electronic band structure and material gain have been calculated for GaAsBi/GaAs quantum wells (QWs) with various bismuth concentrations (Bi ? 15%) within the 8-band and 14-band kp models. The 14-band kp model was obtained by extending the standard 8-band kp Hamiltonian by the valence band anticrossing (VBAC) Hamiltonian, which is widely used to describe Bi-related changes in the electronic band structure of dilute bismides. It has been shown that in the range of low carrier concentrations n QW region. For GaInAsBi/GaAs QW with 5% Bi, gain peak was determined to be at about 1.5 ?m. It means that it can be possible to achieve emission at telecommunication windows (i.e., 1.3 ?m and 1.55 ?m) for GaAs-based lasers containing GaInAsBi/GaAs QWs. For GaInAsBi/Ga0.47In0.53As/InP QWs with 5% Bi, gain peak is predicted to be at about 4.0 ?m, i.e., at the wavelengths that are not available in current InP-based lasers.
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
Phonon Band Structure and Thermal Transport Correlation in a Layered Diatomic Crystal
McGaughey, A. J. H.; Hussein, M. I.; Landry, E. S.; Kaviany, M.; Hulbert, G. M.
2006-01-01
To elucidate the relationship between a crystal's structure, its thermal conductivity, and its phonon dispersion characteristics, an analysis is conducted on layered diatomic Lennard-Jones crystals with various mass ratios. Lattice dynamics theory and molecular dynamics simulations are used to predict the phonon dispersion curves and the thermal conductivity. The layered structure generates directionally dependent thermal conductivities lower than those predicted by density ...
Scientific Electronic Library Online (English)
P. Cabral do, Couto; R. C., Guedes; B. J. Costa, Cabral.
2004-03-01
Full Text Available Electronic properties of liquid water were investigated by sequential Monte Carlo/Quantum mechanics calculations. The density of states (DOS) and HOMO-LUMO gap (E G) of liquid water have been determined by Hartree-Fock and Density Functional Theory (DFT) calculations. The quantum mechanical calculat [...] ions were carried out over uncorrelated supermolecular structures generated by the Monte Carlo simulations. The DFT calculations were performed with a modified B3LYP exchange-correlation functional proposed by Abu-Awwad and Politzer which was parametrized to reproduce valence orbital energies in agreement with experimental ionization potentials of the water molecule. We have analyzed the dependence of the DOS and HOMO-LUMO gap on the number of water molecules and on surface effects. Our prediction for E G is 6:5 ± 0:5 eV in good agreement with a recent experimental prediction of 6.9 eV.
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.
Energy landscape and band-structure tuning in realistic MoS2/MoSe2 heterostructures
Constantinescu, Gabriel C.; Hine, Nicholas D. M.
2015-05-01
While monolayer forms of two-dimensional materials are well characterized both experimentally and theoretically, properties of bilayer heterostructures are not nearly so well known. We employ high-accuracy linear-scaling density functional theory calculations utilizing nonlocal van der Waals functionals to explore the possible constructions of the MoS2/MoSe2 interface. Utilizing large supercells, we vary rotation, translation, and separation of the layers without introducing unrealistic strain. The energy landscape shows very low variations under rotation, with no strongly preferred alignments. By unfolding the spectral function into the primitive cells, we show that the monolayers are more independent than in homo-bilayers and that the electronic band structure of each layer is tunable through rotation, thus influencing hole effective masses.
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)
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.
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.)
Control of Spin Wave Band Structure and Propagation in Two-Dimensional Magnonic Crystals
Sietsema, Glade; Flatté, Michael E.
2015-03-01
We have studied the properties of spin waves in two-dimensional magnonic crystals consisting of a magnetic material arranged in a lattice of cylinders and embedded in a second magnetic material. Dispersion curves, linewidths, and spin wave propagation patterns were obtained from the Landau-Lifshitz-Gilbert equation using the plane wave expansion method. We have examined how these results are affected by various parameters including the shape of the cylinders, the lattice structure, the material properties, and the spin-orbit interaction. Adjusting these values can open or close band gaps and drastically shift the frequency range of the band structure. The spin wave propagation patterns were found to exhibit high directionality dependent on the excitation frequency and can also be modified with the aforementioned parameters. This work was supported in part by DARPA/MESO and by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.
Linear Low Density Polyethylene (LLDPE) as Flexible Substrate for Wrist and Arm Antennas in C-Band
Gogoi, Pragyan Jyoti; Bhattacharyya, Satyajib; Bhattacharyya, Nidhi S.
2015-04-01
This paper focuses on the development and study of linear low density polyethylene as a flexible substrate for conformal antennas for body-worn applications. Thermal stability, tensile strength and elongation at break of the substrate were studied. The permittivity of the substrate was 2.2 and tan ? was found to be 0.0003 at 6 GHz. Since the antenna is being developed for wrist and arm wearing in C-band, the performance of the antenna, such as the S 11 parameter and radiation pattern, were studied with different bending axes and with bending curvature approximating that of the arm and wrist. The performance of a 6 GHz rectangular patch antenna with bending was found to be consistent with the flat profile antenna at the same frequency. A maximum shift in the resonant frequency of ˜20 MHz was observed. The -10 dB bandwidth and directivity of the antenna did not change much with bending. The maximum bending radius in the present study is 10 mm, and S 11 was found to be -17.53 dB at 5.94 GHz and -14.02 dB at 6.06 GHz for a bending axis parallel to the radiating and non-radiating edge, respectively.
Kral, Zdenek
2009-01-01
The characterization of photonic band gap materials (Photonic Crystals) is a fundamental issue in the development of the technologies for their fabrication and future application. This Doctoral Thesis has dealt with the development of optical characterization methods and their implementation to planar photonic structures. According to the objectives established in the present work we have obtained several results that are concluded in the following paragraphs:? We have developed an exp...
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.
Electronic structure of tungsten-doped vanadium dioxide: from band to Mott insulator
Booth, Jamie M.; Drumm, Daniel W.; Casey, Phil S.; Smith, Jackson S.; Russo, Salvy P.
2015-01-01
A common method of adjusting the metal-insulator transition temperature of M1 vanadium dioxide is via disruption of the Peierls pairing by doping, or inputting stress or strain. However, since adding even small amounts of dopants will change the band structure, it is unclear how doped vanadium dioxide retains the insulating character observed in experiments. While strong correlations may be responsible for maintaining a gap, theoretical evidence for this has been very diffic...
Anisotropic exchange interaction of localized conduction-band electrons in semiconductor structures
Kavokin, K. V.
2000-01-01
The spin-orbit interaction in semiconductors is shown to result in an anisotropic contribution into the exchange Hamiltonian of a pair of localized conduction-band electrons. The anisotropic exchange interaction exists in semiconductor structures which are not symmetric with respect to spatial inversion, for instance in bulk zinc-blend semiconductors. The interaction has both symmetric and antisymmetric parts with respect to permutation of spin components. The antisymmetric ...
MATLAB DESIGN & ANALYSIS OF 1D PHOTONIC BAND STRUCTURES USING TRANSFER MATRIX METHOD
S. SARAVANAN, R. S. DUBEY, S. KALAINATHAN
2013-01-01
Presently, the propagation of electromagnetic waves in photonic crystals has become the subject of extensive research due to its remarkable properties. Photonic crystal is an artificial dielectric structure in which the nature of the photons is the same as that of electrons in a semiconductor crystals and it has inspired a lot of fundamental research on light–matter interaction. The tailoring of photonic band gap with designing parameters is a key for the designing of advanced photonic device...
Crystal structure and band gap determination of HfO2 thin films :
Cheynet, M. C.; S. Pokrant; Tichelaar, F.D.; Rouvière, J.L.
2007-01-01
Valence electron energy loss spectroscopy (VEELS) and high resolution transmission electron microscopy (HRTEM) are performed on three different HfO2 thin films grown on Si (001) by chemical vapor deposition (CVD) or atomic layer deposition (ALD). For each sample the band gap (Eg) is determined by low-loss EELS analysis. The Eg values are then correlated with the crystal structure and the chemical properties of the films obtained by HRTEM images and VEELS line scans, respectively. They are dis...
Bound states and band structure-A unified treatment through the quantum Hamilton-Jacobi approach
International Nuclear Information System (INIS)
We analyze the Scarf potential, which exhibits both discrete energy bound states and energy bands, through the quantum Hamilton-Jacobi approach. The singularity structure and the boundary conditions in the above approach, naturally isolate the bound and periodic states, once the problem is mapped to the zero energy sector of another quasi-exactly solvable quantum problem. The energy eigenvalues are obtained without having to solve for the corresponding eigenfunctions explicitly. We also demonstrate how to find the eigenfunctions through this method
Band structure engineering in (Bi1-xSbx)2Te3 ternary topological insulators
Zhang, Jinsong; Chang, Cui-Zu; Zhang, Zuocheng; Wen, Jing; FENG, XIAO; LI, KANG; Liu, Minhao; HE, KE; Wang, Lili; CHEN, XI; Xue, Qi-kun; Ma, Xucun; Wang, Yayu
2011-01-01
Three-dimensional (3D) topological insulators (TI) are novel quantum materials with insulating bulk and topologically protected metallic surfaces with Dirac-like band structure. The spin-helical Dirac surface states are expected to host exotic topological quantum effects and find applications in spintronics and quantum computation. The experimental realization of these ideas requires fabrication of versatile devices based on bulk-insulating TIs with tunable surface states. T...
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
Robust topology optimization of three-dimensional photonic-crystal band-gap structures
Men, Han; Lee, Karen Y. K.; Freund, Robert M.; Peraire, Jaime; Johnson, Steven G.
2014-01-01
We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nea...
Gutermuth, Robert A.; Megeath, S. Thomas; Pipher, Judith L.; Williams, Jonathan P.; Allen, Lori E.; Myers, Philip C.; Raines, S. Nicholas
2005-10-01
We present an analysis of stellar distributions for the young stellar clusters GGD 12-15, IRAS 20050+2720, and NGC 7129, which range in far-IR luminosity from 227 to 5.68×103 Lsolar and are all still associated with their natal molecular clouds. The data used for this analysis include near-IR data obtained with FLAMINGOS on the MMT and newly obtained wide-field 850 ?m emission maps from SCUBA on the JCMT. Cluster size and azimuthal asymmetry are measured via azimuthal and radial averaging methods, respectively. To quantify the deviation of the distribution of stars from circular symmetry, we define an azimuthal asymmetry parameter, and we investigate the statistical properties of this parameter through Monte Carlo simulations. The distribution of young stars is compared to the morphology of the molecular gas using stellar surface density maps and the 850 ?m maps. We find that two of the clusters are not azimuthally symmetric and show a high degree of structure. The GGD 12-15 cluster is elongated and is aligned with newly detected filamentary structure at 850 ?m. IRAS 20050+2720 is composed of a chain of three subclusters, in agreement with Chen and coworkers, although our results show that two of the subclusters appear to overlap. Significant 850 ?m emission is detected toward two of the subclusters but is not detected toward the central subcluster, suggesting that the dense gas may already be cleared there. In contrast to these two highly embedded subclusters, we find an anticorrelation of the stars and dust in NGC 7129, indicating that much of the parental gas and dust has been dispersed. The NGC 7129 cluster exhibits a higher degree of azimuthal symmetry, a lower stellar surface density, and a larger size than the other two clusters, suggesting that the cluster may be dynamically expanding following the recent dispersal of natal molecular gas. These analyses are further evidence that embedded, forming clusters are often not spherically symmetric structures but can be elongated and clumpy and that these morphologies may reflect the initial structure of the dense molecular gas. Furthermore, this work suggests that gas expulsion by stellar feedback results in significant dynamical evolution within the first 3 Myr of cluster evolution. We estimate peak stellar volume densities and discuss the impact of these densities on the evolution of circumstellar disks and protostellar envelopes.
International Nuclear Information System (INIS)
Calculations relative to the band-gap energy shift and carrier spatial density in cadmium oxide are performed in terms of the oxygen partial pressure and substrate temperature relative to the deposition process in the crystal growth of the above material, starting from the consideration of the Fermi energy of an exciton gas. In particular, the band-gap shift experienced by cadmium oxide in terms of the corresponding partial pressure of oxygen is considered as well as the electron spatial density as a function of the pressure in question. Influence of temperature is discussed by estimating the average rate of variation of the band-gap shift versus temperature. In addition, the sensitivity of the above-mentioned shift to temperature is studied by means of a suitable parameter
Energy Technology Data Exchange (ETDEWEB)
Grado-Caffaro, M.A. [SAPIENZA (Scientific Consultants), C/Julio Palacios 11, 9-B, 28029 Madrid (Spain)], E-mail: management@sapienzastudies.com; Grado-Caffaro, M. [SAPIENZA (Scientific Consultants), C/Julio Palacios 11, 9-B, 28029 Madrid (Spain)
2008-06-30
Calculations relative to the band-gap energy shift and carrier spatial density in cadmium oxide are performed in terms of the oxygen partial pressure and substrate temperature relative to the deposition process in the crystal growth of the above material, starting from the consideration of the Fermi energy of an exciton gas. In particular, the band-gap shift experienced by cadmium oxide in terms of the corresponding partial pressure of oxygen is considered as well as the electron spatial density as a function of the pressure in question. Influence of temperature is discussed by estimating the average rate of variation of the band-gap shift versus temperature. In addition, the sensitivity of the above-mentioned shift to temperature is studied by means of a suitable parameter.
International Nuclear Information System (INIS)
High-pressure 155Gd Moessbauer measurements on Gd metal, GdCo5, GdRu2Si2, and Gd2Co17N3 were performed at 4.2 K. The maximum pressures reached were about 18 GPa. The resulting volume reductions of 20 30% were determined using high-pressure x-ray diffraction. The pressure dependence of the electric-field gradients and hyperfine fields obtained for the first three systems was compared with predictions from first-principles band-structure calculations. Significant changes of the hyperfine parameters are observed, especially for elemental Gd metal. With increasing pressure, an increase of the electron density at the Gd nuclei is found in all compounds. The values of the hyperfine field initially increase with pressure. For Gd metal the induced structural phase transitions result in large changes in the electric-field gradient at the nucleus (Vzz). The intermetallic compounds show no structural phase transitions and relatively small changes in Vzz. The combination of experiment and calculations indicates that the transition-metal magnetic moments decrease at high pressure. Although for zero pressure predictions of the electric-field gradient and the hyperfine fields, based on the calculations, are quite accurate, the calculated pressure dependence of the hyperfine parameters for Gd, GdCo5, and GdRu2Si2 does not in all cases lead to a satisfactory agreement with experiment. The application of pressures therefore may give additional stimulus for the improvement of the theoretical description of band structures and hyperfine parameters. copyright 1997 The American Physical Society
Directory of Open Access Journals (Sweden)
Ning Cui
2012-06-01
Full Text Available Choosing novel materials and structures is important for enhancing the on-state current in tunnel field-effect transistors (TFETs. In this paper, we reveal that the on-state performance of TFETs is mainly determined by the energy band profile of the channel. According to this interpretation, we present a new concept of energy band profile modulation (BPM achieved with gate structure engineering. It is believed that this approach can be used to suppress the ambipolar effect. Based on this method, a Si TFET device with a symmetrical tri-material-gate (TMG structure is proposed. Two-dimensional numerical simulations demonstrated that the special band profile in this device can boost on-state performance, and it also suppresses the off-state current induced by the ambipolar effect. These unique advantages are maintained over a wide range of gate lengths and supply voltages. The BPM concept can serve as a guideline for improving the performance of nanoscale TFET devices.
Srivastava, Ankit
2013-01-01
In this paper we present a Graphical Processing Unit accelerated mixed variational formulation for fast phononic band-structure calculation of arbitrarily complex unit cells and report speed gains of a hundred fold over unoptimized serial cpu computations. To the author's knowledge this is the first application of gpu computing to a non-FE/FDTD bandstructure algorithm. The formulation is presented in a form which is applicable to 1-, 2-, and 3-D cases. However, in this paper we concentrate on optimizing the formulation within the paradigm of gpu computing, presenting results for 2-D unit cells. We describe the application of the formulation with a long term view towards highly efficient and massively distributed band-structure algorithms suitable for tackling optimization and inverse problems. We report that the accurate band-structure evaluation over the boundary of the Irreducible Brillouin Zone (IBZ) for the first 18 phononic branches of a complex 2-D unit cell (with 1132 different phases) can be achieved ...
Crystal structure and band gap determination of HfO2 thin films
Cheynet, Marie C.; Pokrant, Simone; Tichelaar, Frans D.; Rouvière, Jean-Luc
2007-03-01
Valence electron energy loss spectroscopy (VEELS) and high resolution transmission electron microscopy (HRTEM) are performed on three different HfO2 thin films grown on Si (001) by chemical vapor deposition (CVD) or atomic layer deposition (ALD). For each sample the band gap (Eg) is determined by low-loss EELS analysis. The Eg values are then correlated with the crystal structure and the chemical properties of the films obtained by HRTEM images and VEELS line scans, respectively. They are discussed in comparison to both experimental and theoretical results published in literature. The HfO2 ALD film capped with poly-Si exhibits the largest band gap (Eg=5.9±0.5eV ), as a consequence of its nanocrystallized orthorhombic structure. The large grains with a monoclinic structure formed in the HfO2 ALD film capped with Ge and the carbon contamination induced by the precursors in the HfO2 CVD film capped with Al2O3 are identified to be the main features responsible for lower band gap values (Eg=5.25±0.5 and 4.3±0.5eV respectively).
International Nuclear Information System (INIS)
Highlights: ? The band structure of anatase containing oxygen vacancy or doped with bismuth or carbon have been calculated. ? The absorption spectra and energy formation of the Bi-defect also have been evaluated. ? The conclusion is that in anatase the Bi atoms cannot replace Ti atoms. ? So the visible part of the experimental absorption spectra has no relation to the Bi-bands in anatase. ? And this is probably associated with carbon impurities or with the accompanying Bi-containing phases. - Abstract: The electronic band structure, frequency-dependent dielectric function and absorption spectra of the anatase containing oxygen vacancy or doped with bismuth or carbon have been calculated with the aid of the pseudopotential plane-wave method. Basing on the calculated data, the available experimental data on the visible light absorption are discussed. The main conclusion is that the Bi3+ ions cannot replace the Ti4+ ions in the structure of anatase. The conclusion is confirmed by the calculations of the energy of the defect formation. The visible light absorption can be explained by the presence of the carbon impurities or additional phases, probably Bi2O3 or Bi4Ti3O12.
Robust topology optimization of three-dimensional photonic-crystal band-gap structures
Men, H.; Lee, K. Y. K.; Freund, R. M.; Peraire, J.; Johnson, S. G.
2014-09-01
We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniques such as a simple approach to impose symmetry constraints. We also demonstrate a technique for \\emph{robust} topology optimization, in which some uncertainty is included in each voxel and we optimize the worst-case gap, and we show that the resulting band gaps have increased robustness to systematic fabrication errors.
Fulvio, D.; Sivaraman, B.; Baratta, G. A.; Palumbo, M. E.; Mason, N. J.
2009-06-01
We present novel measurements of the refractive index, density and integrated band strengths of mid-infrared features of solid N2O at 16 K and of NO2 and N2O4 in two frozen NO2:N2O4 mixtures deposited at 16 and 60 K. The refractive index and density measurements were performed also for frozen O2 deposited at 16 K. In this case, the integrated band strength values could not be determined since O2 is a homonuclear molecule and therefore its fundamental mode is not infrared active. The solid samples were analysed by infrared spectroscopy in the 8000.800 cm -1 range. The sample thickness was measured by the interference curve obtained using a He-Ne laser operating at 543 nm. The refractive index at this laser wavelength was obtained, by numerical methods, from the measured amplitude of the interference curve. The density values were obtained using the Lorentz-Lorenz relation. Integrated band strength values were then obtained by a linear fit of the integrated band intensities plotted versus column density values. The astrophysical relevance of these novel measurements is briefly discussed.
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
A High-Power Test of An X-Band Molybdenum Iris Structure
International Nuclear Information System (INIS)
In order to achieve accelerating gradients above 150 MV/m, alternative materials to copper are being investigated by the CLIC study. The potential of refractory metals has already been demonstrated in tests in which a tungsten-iris and a molybdenum-iris structure reached 150 and 193 MV/m respectively (30 GHz and a pulse length of 15 ns). In order to extend the investigation to the pulse lengths required for a linear collider, a molybdenum-iris structure scaled to X-band was tested at the Next Linear Collider Test Accelerator (NLCTA). The structure conditioned to only 65 MV/m (100 ns pulse length) in the available testing time and much more slowly than is typical of a copper structure. However the structure showed no sign of saturation and a microscopic inspection of the rf surfaces corroborated that the structure was still at an early stage of conditioning. The X-band and 30 GHz results are compared and what has been learned about material quality, surface preparation and conditioning strategy is discussed
High Gradient Test of a Clamped, Molybdenum Iris, X-Band Accelerator Structure at NLCTA
International Nuclear Information System (INIS)
Inspired by the very high gradients (150-195 MV/m) achieved at CERN in 30 GHz accelerator structures made with tungsten and molybdenum irises and operated with short (16 ns) rf pulses [1], an X-band (11.4 GHz) version of this structure design was built at CERN and tested at SLAC. The goals of this experiment were to provide frequency scaling data on high gradient phenomena at similar pulse lengths, and to measure the structure performance at the longer pulse lengths available at SLAC (the CLIC test facility, CTF II, could provide only 16 ns pulses for high power operation and 32 ns pulses for medium power operation). Earlier high gradient tests of 21 GHz to 39 GHz standing-wave, single cells, indicated no significant frequency dependence of the maximum obtainable surface field [2]. The X-band scaling test would check if this was true for travelling-wave, multi-cell structures as well. For the experiment, the CLIC group at CERN built a 30 cell accelerating structure that consisted of copper cells and molybdenum irises that were clamped together. The structure was mounted in a vacuum tank and installed in the Next Linear Collider Test Accelerator (NLCTA) beam line at SLAC where it was operated at high power for more than 700 hours
DEFF Research Database (Denmark)
Hedegaard, Ellen M. J.; Johnsen, Simon
2014-01-01
Exploiting the material gradients inherent to crystal growth techniques, boron doped Ge1xSix (x = 0 to similar to 0.25) samples graded in both band gap and carrier concentration have been prepared by the Czochralski method. Along the length of the Ge1xSix samples x changes continuously, giving rise to changes in the band gap from 0.87 to 0.65 eV. Similarly, gradients in the boron content results in continuous carrier density changes along the sample. This results in samples graded in several material parameters relevant to thermoelectric performance. The present study thereby demonstrates a one-step method for preparing thermoelectrics graded in both carrier concentration and band gap. By careful matching of dopant and material system, it is demonstrated how the gradient in dopant and band gap can work in synergy and mutually enhance the thermoelectric performance over the individual contributions.
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.
Fabrication of the CERN/PSI/ST X-Band accelerating structures
Dehler, Micha; Gudkov, Dmitry; Lebet, Serge; Riddone, Germana; Shi, Jiaru; Citterio, Alessandro; Zennaro, Riccardo; D'Auria, Gerardo; Serpico, Claudio
2011-01-01
In a collaboration between CERN, PSI and Sincrotrone Trieste (ST), a multi- purpose X-band accelerating structure has been designed and fabricated, used for high gradients tests in the CLIC structure testing program and in the FEL projects of PSI and ST. The structure has 72 cells with a phase advance of 5 pi/6 and includes upstream and down-stream wakefield monitors to measure the beam alignment. The SLAC mode launcher design is used to feed it with RF power. Following the CERN fabrication procedures for high-gradient structure, diffusion bonding and brazing in hydrogen atmosphere is used to assemble the cells. After tuning, a vacuum bakeout is required before the feedthroughs for the wake field monitors are welded in as a last step. We describe the experiences gained in finishing the first two structures out of a series of four and present the results from the RF tuning and low level RF tests.
Anisotropic mass density by radially periodic fluid structures.
Torrent, Daniel; Sánchez-Dehesa, José
2010-10-22
This Letter reports physical realization of acoustic metamaterials with anisotropic mass density. These metamaterials consist of a superlattice of two fluidlike components radially periodic. Several structures are spectroscopically characterized at large wavelengths (homogenization limit) by studying the acoustic resonances existing in the circular cavity where they are embedded. This characterization method allows us to extract the diagonal components of the sound speed tensor. Analytical expressions describing the anisotropic behavior as a function of the corrugation parameter are also developed and their predictions are in agreement with measurements. PMID:21231048
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.
Bright, A. M.; Shipton, Z. K.
2003-04-01
Deformation band faults in porous sandstone typically have a "core" of intense deformation associated with the localisation of strain onto discrete slip surfaces. In outcrop, the core is recognisable by its glassy appearance and its increased resistance to erosion with respect to the host rock. Samples of fault core have been collected from the San Rafael Swell, Utah, USA (Navajo Sandstone) and the Cheshire Basin, England (Sherwood Sandstone). Outcrop mapping in both localities reveals that the fault core thickness varies from sandstone (17-22%) and individual deformation bands (7-8%). However, microstructural observations suggest that fluids have moved through these structures during deformation. Cement phases are preferentially located along deformation band boundaries. Clay rims, which are common in the host rock, are absent in the fault core. Additionally preliminary fluid inclusion data show elevated temperatures in healed fault core microfractures. It is essential to characterise the architecture, composition and porosity/permeability of fault core to accurately predict fluid flow parallel and perpendicular to deformation band fault zones.
International Nuclear Information System (INIS)
Doping Calcium in Lanthanum site of LaCrO3 compound increasing the density of states in valance band and decreasing the band gap width because of increases of S electrons in valance band and variety of interaction energies from Cr+3-Cr+4 couple in valance band. We have used Wien2k software for evaluating this mechanisms. Using of 0.25 percent of dopant and a kind of the space group of cell, let us to use one cell in calculations. We have used GGA approximation in this calculations.
Extended Hückel theory for carbon nanotubes: band structure and transport properties.
Zienert, Andreas; Schuster, Jörg; Gessner, Thomas
2013-05-01
Extended Hückel theory (EHT) is a well established method for the description of the electronic structure of molecules and solids. In this article, we present a set of extended Hückel parameters for carbon nanotubes (CNTs), obtained by fitting the ab initio band structure of the (6,0) CNT. The new parameters are highly transferable to different types of CNTs. To demonstrate the versatility of the approach, we perform self-consistent EHT-based electron transport calculations for finite length CNTs with metal electrodes. PMID:23534403
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
Structure design for a 500 GeV S-band linear collider
International Nuclear Information System (INIS)
Constant gradient structures with an accelerating gradient of 20 MeV per meter are commonly used with S-band frequency. The well known features of these travelling wave tubes provide a dedicated design for their use in the next generation linear collider. Some of the required design parameters for this tubes are presented within the whole concept of this collider with an active length of about 30 km. The choice of these parameters is explained and calculations concerning the structure are presented
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.
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 ...
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...
An investigation of the structure of the F-band and envelope in LiF
International Nuclear Information System (INIS)
A detailed study has been made of the growth of the F-centre envelope during proton irradiation of lithium fluoride. Data were taken using a unique in-situ measurement apparatus installed on the ion accelerator at Sussex University. This has revealed the F centre to be an envelope containing a complicated amalgam of defects which are sensitive to the presence of impurities in the crystal. Pure LiF and doped LiF(Mg:Ti) have been used. In nominally pure LiF bands have been seen at ?228-234, 241-245, 260 and 267 nm. In doped samples absorption peaks are seen at <225, 228-234, 241-245, 254, 260, 273 and 267 nm. The 273 nm band is seen only in the highly doped (Mg) samples. The envelope itself peaks at ?254-259 nm. The exact position of the envelope peak is variable with dose, and is thought due to absorption by at least three centres. The richness of the defect variety of this envelope has not previously been appreciated, to the authors knowledge. It has been observed in this ion irradiated material because ion beams produce a high defect density in a very thin layer (microns) of crystal. Colouration effects can therefore be studied to unusually high optical densities. (orig.)
Electronic band structure of CaUO4 from first principles
International Nuclear Information System (INIS)
Band theoretical results are presented on calcium uranate, CaUO4, based on computations within the density functional theory. From pseudo-potential calculations the equation of state is obtained with equilibrium lattice properties in agreement with experiment. For isotropic volume change the bulk modulus amounts to 180 GPa but a much higher value is found for anisotropic compression along the hexagonal c-axis. This is assigned to the short U-O distances in linear uranyl polycation. Scalar relativistic all-electron calculations point to a semiconductor with ?3eV band gap. From density of states, chemical bonding and electron localization function ELF, oxygen is found to behave both as ionic and covalent in the coordination sphere of uranium. The results provide an illustration of the peculiar role of uranyl cation UO22+ according to its chemical environment. - Energy versus volume variation for isotropic and anisotropic compressions within CaUO4. Fit results with Birch EOS are given in inserts.
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.
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
Franklin, S.; Balasubramanian, T.; Nehru, K.; Kim, Youngmee
2009-06-01
The crystal structure of the title rac-propranolol salt, CHNO2+·NO3-, consists of two protonated propranolol residues and nitrate anions. Three virtually flat fragments, characteristics of most of the ?-adrenolytics with oxy-methylene bridge are present in both the cations (A and B). The plane of the propranolol chain is twisted with respect to the plane of the aromatic ring in both the cations. Present study investigates the conformation and hydrogen bonding interactions, which play an important role in biological functions. A gauche conformation is observed for the oxo-methylene bridge of cation A, while a trans conformation prevails in cation B. These conformations are found in majority of ?-blockers. Presence of twenty intermolecular hydrogen bonds mediating through the anions stabilizes the crystal packing. Vibration analysis and earlier theoretical predictions complement the structure analysed. From the UV-Vis spectral analysis for the crystal, the optical band gap is found to be Eg = 5.12 eV, where as the chloride salt has Eg = 3.81 eV. The increase in the band gap may be attributed by the increase in the number of intermolecular hydrogen bonds. Good optical transmittance in the entire visible region and the direct band gap property suggest that it is a suitable candidate for optical applications in UV region.
Fock, J.-H.; Lau, H.-J.; Koch, E. E.
1984-01-01
Photoelectron energy distribution curves from solid CO 2 have been determined for excitation energies from hv = 14 up to 40 eV using synchrotron radiation. A 1:1 correspondence to the gas-phase photoelectron spectrum is observed for the occupied molecular orbitals. The vertical binding energies EBv ( EVAC = 0) and widths (fwhm) of the valence bands of solid CO 2 are determined to be 13.0 and 0.95 eV (1? g); 16.7 and 1.1 eV (1? u); 17.6 and 0.85 eV (3? u) and 18.8 and 0.8 eV (4? g) for the individual bands respectively. The partial photoemission cross sections differ importantly from those of the gas phase in exhibiting pronounced maxima at 5.2 eV (1? g), 4.4-5.3 eV (1? u + 3? u) and 4.2 eV (4? g) above the vacuum level, which is attributed to effects of high density of final (conduction-band) states. Further weaker maxima are observed at higher photon energies. Contrary to the case for the gas phase, the resonances are unperturbed in the solid by degenerate autoionizing molecular Rydberg states. The molecular origin of the resonances in the continuum is discussed and related to X-ray absorption spectra, electron-scattering data and to theoretical cross-section calculations. It is shown that the same set of resonances is observed in the different experiments. The resonances occur however at different energies due to different Coulomb interactions. The photoemission results presented provide also a key to the hitherto unexplained optical spectrum of solid CO 2 in the VUV range, making possible an assignment of the structures observed to Frenkel-type excitons ( hv ? 15 eV) and interband transitions ( hv ? 15 eV).
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.
Band structures and intruder $\\pi$$i_{13/2}$ state in $^{197}$Tl
Pai, H; Bhattacharya, S; Bhattacharya, C; Bhattacharyya, S; Bhattacharjee, T; Chanda, S; Rajbanshi, S; Goswami, A; Gohil, M R; Kundu, S; Ghosh, T K; Banerjee, K; Rana, T K; Pandey, R; Prajapati, G K; Banerjee, S R; Mukhopadhyay, S; Pandit, D; Pal, S; Meena, J K; Mukhopadhyay, P; Chawdhury, A
2013-01-01
The excited states in the odd-A $^{197}$Tl nucleus have been studied by populating them using the $^{197}$Au($\\alpha$, 4n)$^{197}$Tl reactions at the beam energy of 48 MeV. $\\gamma-\\gamma$ coincidence data have been taken using a combination of clover, LEPS and single crystal HPGe detectors. A new band structure has been identified and the intruder $\\pi i_{13/2}$ state could be established for the first time. Precise spin and parity assignment of the excited states have been done through polarization and DCO measurements. Possible configurations of the observed bands have been discussed. The total Routhian surface calculations have been performed to study the shape of $^{197}$Tl for different configurations.
The effect of spin-orbit coupling in band structure of few-layer graphene
Energy Technology Data Exchange (ETDEWEB)
Sahdan, Muhammad Fauzi, E-mail: sahdan89@yahoo.co.id; Darma, Yudi, E-mail: sahdan89@yahoo.co.id [Department of Physics, Institut Teknologi Bandung, Jalan Ganesa 10, Bandung 40132 (Indonesia)
2014-03-24
Topological insulators are electronic materials that have a bulk band gap like an ordinary insulator but have protected conducting states on their edge or surface. This can be happened due to spin-orbit coupling and time-reversal symmetry. Moreover, the edge current flows through their edge or surface depends on its spin orientation and also it is robust against non-magnetic impurities. Therefore, 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 few-layer graphene by using this model with analytical approach. The results of our calculations show that the gap opening occurs at K and K’ point, not only in single layer, but also in bilayer and trilayer graphene.
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
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.
Cohesive band structure of carbon nanotubes for applications in quantum transport.
Arora, Vijay K; Bhattacharyya, Arkaprava
2013-11-21
An integrated cohesive band structure of carbon nanotubes (CNTs) applicable to all chirality directions (n, m), starting from the Dirac cone of a graphene nanolayer in k-space, is demarcated, in direct contrast to dissimilar chiral and achiral versions in the published literature. The electron wave state of a CNT is quantized into one-dimensional (1-D) nanostructure with a wrapping mode, satisfying the boundary conditions from one Dirac K-point to an equivalent neighboring one with an identical phase and returning to the same K point. The repetitive rotation for an identical configuration with added band index (n-m)mod3, yields one metallic (M) with zero bandgap corresponding to (n-m)mod3 = 0, semiconducting state SC1 with (n-m)mod3 = 1 and SC2 with (n-m)mod3 = 2. The band gap and effective mass of SC2 state are twice as large as those of SC1 state. A broad-spectrum expression signifying the linear dependence of the effective mass on the bandgap is obtained. Both the Fermi energy and the intrinsic velocity limiting the current to the saturation level is calculated as a function of the carrier concentration. Limitations of the parabolic approximation are pointed out. Several new features of the band structure are acquired in a seamlessly unified mode for all CNTs, making it suitable for all-encompassing applications. Applications of the theory to high-field transport are advocated with an example of a metallic CNT, in agreement with experimental observations. The mechanism behind the breakdown of the linear current-voltage relation of Ohm's law and the associated surge in resistance are explained on the basis of the nonequilibrium Arora's distribution function (NEADF). These results are important for the performance evaluation and characterization of a variety of applications on CNT in modern nanoscale circuits and devices. PMID:24061093
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.
Atomic-scale structure and band-gap bowing in Cu(In,Ga)Se2
Schnohr, C. S.; Kämmer, H.; Stephan, C.; Schorr, S.; Steinbach, T.; Rensberg, J.
2012-06-01
Mixed systems such as the Cu(In,Ga)Se2 chalcopyrite semiconductor consist of different local atomic arrangements, that is, of different combinations of first-nearest-neighbor cations surrounding the Se anions. The anion position of Cu-III-VI2 compounds is predicted to strongly influence the material band gap. We therefore used extended x-ray absorption fine structure spectroscopy to study the atomic-scale structure of Cu(In,Ga)Se2 as a function of composition. Based on these results, the anion position was modeled for all first-nearest-neighbor configurations using a valence force-field approach. We show that the atomic-scale structure strongly depends on the kind of first-nearest-neighbor atoms. Structural relaxation of the anion occurs with respect to both (i) Cu and group III atoms and (ii) In and Ga atoms. In both cases, the average anion displacement exhibits a nonlinear behavior with changing composition and thus results in two separate but significant contributions to the band gap bowing observed in Cu(In,Ga)Se2.
An Optimized, Grid Independent, Narrow Band Data Structure for High Resolution Level Sets
DEFF Research Database (Denmark)
Nielsen, Michael Bang; Museth, Ken
2004-01-01
Level sets have recently proven successful in many areas of computer graphics including water simulations and geometric modeling. However, current implementations of these level set methods are limited by factors such as computational efficiency, storage requirements and the restriction to a domain enforced by the convex boundaries of an underlying cartesian computational grid. Here we present a novel very memory efficient narrow band data structure, dubbed the Sparse Grid, that enables the representation of grid independent high resolution level sets. The key features our new data structure are: Both memory usage and computational efficiency scales linearly with the size of the interface The values in the narrow band can be compressed using quantization without compromising visual quality The level set propagation is independent of the boundaries of an underlying grid. Unlike previous method that use fixed computational grids with convex boundaries our Sparse Grid can expand and/or contract dynamically inany direction with non-convex boundaries. Our data structure generalizes to any number of dimensions. Our flexible data structure can transparently be integrated with the existing finite difference schemes typically used to numerically solve the level set equation on fixed uniform grids.
Dual-band bandpass filter based on compound metallic grating waveguide structure
Hu, Rui; Liang, Yuzhang; Qian, Siyu; Peng, Wei
2015-02-01
In this paper, we proposed a novel dual-band bandpass filter based on subwavelength compound metallic grating deposited on the waveguide structure by using the finite-difference time domain (FDTD) method. The compound metallic grating is constructed by carving a groove on the top surface of every metal strip. The designed structure generates two remarkable transmission peaks with a dip in-between at normal incidence. Two transmission peaks with narrow bandwidth and high transmission depth is attributed to the existence of grooves in the designed structure. We research the implied physical mechanism of two resonance peaks and one dip by investigating the effect of different structure parameters on transmission spectrum and the electromagnetic field distributions at the location of resonance. It is found that the two resonance peaks are determined by different hybrid modes of F-P like resonance, waveguide resonance mode and SPP mode. Besides, angularly resolved spectra are presented to further reveal physical mechanism of two resonance peaks. This work can be used to develop a dual-band bandpass filter in the telecom wavelength range.
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 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
Shorikov, A O; Anisimov, V I; Sigrist, M
2006-07-01
The phenomenological theory of complex interplay of superconductivity and magnetism in Ho(1-x)Dy(x)Ni(2)B(2)C by Doh et al (1999 Phys. Rev. Lett. 83 5350) is based on the multi-band picture with at least one band which is strongly dominated by Ni 3d-electron orbitals. These orbitals are insensitive to the antiferromagnetic order of the (Ho, Dy) 4f-electrons, found in these alloys. In the present study we show by detailed analysis of the band structure that indeed such a band can be identified. This provides a microscopic justification of the basic idea underlying the phenomenological discussion. PMID:21690812
Purser, Gordon H.
2001-07-01
How to draw the most appropriate Lewis structure for molecules and ions in which nonmetal atoms beyond the second period are bonded to a terminal oxygen atom has been the subject of considerable debate. Recently there has been a shift toward satisfying the octet rule even if formal charges remain on the structure. In this work, the internuclear electron densities of a series of X-O bonds (where X = P, S, or Cl) have been calculated using quantum mechanics and compared to Lewis structures for which the formal charges have been minimized. A direct relationship was found between the internuclear electron density and the bond order predicted from Lewis structures in which formal charges are minimized. This relationship suggests that obeying the octet rule at the expense of having formal charges does not yield the most appropriate Lewis structure. Instructors are urged to teach students to minimize formal charges where possible.
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
International Nuclear Information System (INIS)
Fine structure (FS) of the secondary electron emission spectrum (SEMS) os iridium perpendicular to (111) surface and of the total current spectrum (TCS) of Ir polycrystal was interpreted theoretically. The calculations took account of the energy dependence of the energy band level expansion, the electron-electron and the electron-plasmon contributions into distribution function of nonequilibrium electrons current isotopic component from the electrons scattered within the surface. SEMS and TCS FS was shown to result mainly from the electron structure of the terminal state. The elaborated technique enabled to separate the volume effect in SEMS and TCS from the surface ones. Dependence of SEMS and TCS FS on the geometrical structure and the degree of crystal ordering was proved. In that case, moderation of FS intensity served as a measure of defectiveness within a specimen near-the-surface range
Structural evaluation of Marman V-band coupling and flange with conoseal gasket
Oates, J. H.
1972-01-01
Results are described of a development test program directed at evaluating the structural capabilities of the Marman V-band coupling and flange with conoseal gasket. The intended end use was for the 75K NERVA flight engine propellant lines. Of major importance in the structural evaluation was the ability to predict stresses throughout the assembly for a variety of loading conditions. Computer finite element analysis was used to predict these stresses but, for the subject configuration, large uncertainties were introduced in modeling the complex geometry and boundary conditions. The purpose of the structural tests was to obtain actual stresses and deflections for correlation with, and updating of the finite element model. Results of the incomplete test program are inconclusive with respect to determining suitability for use on the NERVA engine.
Low-power test and tuning of L-band positron capture accelerating structure
International Nuclear Information System (INIS)
An L-band positron capture accelerating structure was designed and fabricated for the Super-KEKB injector linac, and has been confirmed to be successfully tuned by low-power tests. At first, test cells were fabricated based on the design results reported in the last year's conference, and detailed cell dimensions for production version were determined by evaluating the test cells' performances. Next, the production-version cells were machined and confirmed for their resonant frequencies and/or coupling factors to be within predefined tolerances before brazing. After completing the assembly of the accelerating structure by brazing, the resonant frequency of each cell was adjusted to the designed value by dimple tuning, and the coupling factor was confirmed to meet the specified tolerance by Kyhl method. Finally, radiofrequency performances of the whole accelerating structure were measured, in order to confirm the required characteristics. (author)
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.
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.
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.
Osterloh, Frank E
2014-10-01
The Shockley-Queisser analysis provides a theoretical limit for the maximum energy conversion efficiency of single junction photovoltaic cells. But besides the semiconductor bandgap no other semiconductor properties are considered in the analysis. Here, we show that the maximum conversion efficiency is limited further by the excited state entropy of the semiconductors. The entropy loss can be estimated with the modified Sackur-Tetrode equation as a function of the curvature of the bands, the degeneracy of states near the band edges, the illumination intensity, the temperature, and the band gap. The application of the second law of thermodynamics to semiconductors provides a simple explanation for the observed high performance of group IV, III-V, and II-VI materials with strong covalent bonding and for the lower efficiency of transition metal oxides containing weakly interacting metal d orbitals. The model also predicts efficient energy conversion with quantum confined and molecular structures in the presence of a light harvesting mechanism. PMID:26278444
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.
The band structure of two-magnon excitations for a finite 2D lattice
International Nuclear Information System (INIS)
The energy bound structure and the distribution of the states over the first Brillouin zone of two-magnon excitations for finite spin systems has been investigated. It was shown that the energy spectrum of the eigenstates could be arranged into rarefied bands determined by the symmetry types of the spin configurations. It was demonstrated that the elaborated classification of eigenstates is equivalent to splitting of the first Brillouin zone into sub-zones depending on the parity of vector k, exactly in the same way as was obtained within a continuum model approach
Calculation of the band structure of 2d conducting polymers using the network model
International Nuclear Information System (INIS)
the network model has been used to calculate the band structure the gap energy and Fermi level of conducting polymers in two dimensions. For this purpose, a geometrical classification of possible polymer chains configurations in two dimensions has been introduced leading to a classification of the unit cells based on the number of bonds in them. The model has been applied to graphite in 2D, represented by a three bonds unit cell, and, as a new case, the anti-parallel Polyacetylene chains (PA) in two dimensions, represented by a unit cell with four bons. The results are in good agreement with the first principles calculations. (author)
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
Chen, A.-Li; Tong-Li, Liang; Wang, Yue-Sheng
2015-06-01
Combined with the supercell method, band structures of the anti-plane and in-plane modes of two-dimensional (2D) eight-fold solid–solid quasi-periodic phononic crystals (QPNCs) are calculated by using the finite element method. The influences of the supercell on the band structure and the wave localization phenomenon are discussed based on the modal distributions. The reason for the appearance of unphysical bands is analyzed. The influence of the incidence angle on the transmission spectrum is also discussed. Project supported by the National Natural Science Foundation of China (Grant Nos. 11272043 and 10902012) and the Project-sponsored by SRF for ROCS, SEM.
Low-lying levels and high-spin band structures in sup 1 sup 0 sup 2 Rh
Gizon, J; Timar, J; Cata-Danil, G; Nyakó, B M; Zolnai, L; Boston, A J; Joss, D T; Paul, E S; Semple, A T; O'Brien, N J; Parry, C M; Bucurescu, D; Brant, S; Paar, V
1999-01-01
Levels in sup 1 sup 0 sup 2 Rh have been populated in the reaction sup 7 sup 0 Zn+ sup 3 sup 6 S at 130 MeV. The level structure of sup 1 sup 0 sup 2 Rh has been investigated using the EUROGAM II array. Low-lying states and four high-spin bands have been identified. The configurations of low-lying levels and two-quasiparticle bands are interpreted in the frame of the interacting boson-fermion-fermion model. The four observed band structures are also compared with cranked shell model calculations using a modified oscillator potential.
Imai, Koji; Matsuhara, Hideo; Wada, Takehiko; Oyabu, Shinki; Takagi, Toshinobu; Fujishiro, Naofumi; Hanami, Hitoshi
2008-01-01
We present the number counts of Ks-band selected high redshift galaxy populations such as extremely red objects (EROs), B, z & K -band selected galaxies (BzKs) and distant red galaxies (DRGs) in the AKARI NEP field. The final catalogue contains 308 EROs (Ks19.5 population is dominated by the sub-millijansky submillimetre population. We also predict a turnover in in dusty ERO counts around 19
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)
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.
Fratricide-preventing friend identification tag based on photonic band structure coding
Eliyahu, Danny; Sadovnik, Lev S.; Manasson, Vladimir A.
2000-07-01
A new friend foe identification tag based on photonic band structure (PBS) is presented. The tag utilizes frequency-coded radar signal return. Targets that include the passive tag responds selectively to slightly different frequencies generated by interrogating MMW radar. It is possible to use in- and out-of-band gap frequencies or defect modes of the PBS in order to obtain frequency dependent radar waves reflections. This tag can be made in the form of patch attachable such as plate or corner reflectors, to be worn by an individual marine, or to be integrated into the platform camouflage. Ultimately, it can be incorporated as smart skin or a ground or airborne vehicle. The proposed tag takes full advantage of existing sensors for interrogation (minimal chances required), it is lightweight and small in dimensions, it operates in degraded environments, it has no impact on platform vulnerability, it has low susceptibility to spoofing and mimicking (code of the day) and it has low susceptibility to active jamming. We demonstrated the operation of the tag using multi-layer dielectric (Duroid) having periodic structure of metal on top of each of the layers (metal strips in this case). The experimental results are consistent with numerical simulation. The device can be combined with temporal coding to increase target detection and identification resolution.
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.
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.
Numerical demonstration of compound structure broad pass-band optical metamaterial filter
Zhong, M.; Ye, Y. H.
2015-05-01
We have presented a systematic numerical study about a compound structure to obtain a broad pass-band optical metamaterial filter at terahertz frequency. The designed structure consists of periodic composite metallic arrays and dielectric layer. In order to increase the pass-bandwidth of such metamaterial filter, the sidewall length of square hole is increased. The availability of bandwidth enhancement is verified by our simulation in this paper, which is performed through full-wave method by using the commercial software Ansoft HFSS 13.0. Based on analysis of this rich optical response, we found that the effective impedance matched to free space leads to the pass-bandwidth increased. We hope these results are useful to modulate the electromagnetic wave in optoelectronics, such as sensor and spectroscopy in the future.
A combined representation method for use in band structure calculations. 1: Method
Friedli, C.; Ashcroft, N. W.
1975-01-01
A representation was described whose basis levels combine the important physical aspects of a finite set of plane waves with those of a set of Bloch tight-binding levels. The chosen combination has a particularly simple dependence on the wave vector within the Brillouin Zone, and its use in reducing the standard one-electron band structure problem to the usual secular equation has the advantage that the lattice sums involved in the calculation of the matrix elements are actually independent of the wave vector. For systems with complicated crystal structures, for which the Korringa-Kohn-Rostoker (KKR), Augmented-Plane Wave (APW) and Orthogonalized-Plane Wave (OPW) methods are difficult to apply, the present method leads to results with satisfactory accuracy and convergence.
International Nuclear Information System (INIS)
The first part of the review presents basic facts about computational methods, especially about linearized methods of muffin-tin orbitals (LMTO), augmented plane waves (LAPW), and augmented spherical waves (ASW) for a number of energy characteristics of interatomic coupling. The energy band structure and the energetics of the chemical bonding in stoichiometric binary refractory compounds such as monoxides, monocarbides, and mononitrides of transition metals and in dicarbides of yttrium, strontium, and barium are discussed including a study of the equations of state and internal pressures. The electronic structure, properties, and chemical bonding of ternary refractory compounds (Ti and Nb nitrocarbides, Sc oxicarbides) and of vacancy-containing phases of non-stoichiometric refractory compounds are calculated and discussed. The results demonstrate that the studies are fairly fruitful. 83 refs
Salzmann, Christoph G; Loerting, Thomas; Klotz, Stefan; Mirwald, Peter W; Hallbrucker, Andreas; Mayer, Erwin
2006-01-21
We report in situ density values of amorphous ice obtained between 0.3 and 1.9 GPa and 144 to 183 K. Starting from high-density amorphous ice made by pressure-amorphizing hexagonal ice at 77 K, samples were heated at a constant pressure until crystallization to high-pressure ices occurred. Densities of amorphous ice were calculated from those of high-pressure ice mixtures and the volume change on crystallization. In the density versus pressure plot a pronounced change of slope occurs at approximately 0.8 GPa, with a slope of 0.21 g cm(-3) GPa(-1) below 0.8 GPa and a slope of 0.10 g cm(-3) GPa(-1) above 0.8 GPa. Both X-ray diffractograms and Raman spectra of recovered samples show that major structural changes occur up to approximately 0.8 GPa, developing towards those of very high-density amorphous ice reported by (T. Loerting, C. Salzmann, I. Kohl, E. Mayer and A. Hallbrucker, Phys. Chem. Chem. Phys., 2001, 3, 5355) and that further increase of pressure has only a minor effect. In addition, the effect of annealing temperature (T(A)) at a given pressure on the structural changes was studied by Raman spectra of recovered samples in the coupled O-H and decoupled O-D stretching band region: at 0.5 GPa structural changes are observed between approximately 100-116 K, at 1.17 GPa between approximately 121-130 K. Further increase of T(A) or of annealing time has no effect, thus indicating that the samples are fully relaxed. We conclude that mainly irreversible structural changes between 0.3 to approximately 0.8 GPa lead to the pronounced increase in density, whereas above approximately 0.8 GPa the density increase is dominated to a large extent by reversible elastic compression. These results seem consistent with simulation studies by (R. Martonàk, D. Donadio and M. Parrinello, J. Chem. Phys., 2005, 122, 134501) where substantial reconstruction of the topology of the hydrogen bonded network and changes in the ring statistics from e.g. mainly six-membered to mainly nine-membered rings were observed on pressure increase up to 0.9 GPa and further pressure increase had little effect. PMID:16482282
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.
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
Growth and properties of AIIIBV QD structures for intermediate band solar cells
Vysko?il, J.; Gladkov, P.; Pet?í?ek, O.; Hospodková, A.; Pangrác, J.
2015-03-01
Intermediate band solar cells theoretically offer a promising way to significantly increase cell efficiency compared to a single-junction solar cell. We focused on the preparation of antimony containing materials as a covering of QD layers. In this article we discuss how the concentration gradient of GaAsSb strain reducing layers can influence the resulting optical properties of the solar cell structures. The main principle of the structure is that the absorption of light is achieved at QD excited states with a better overlap of electron and hole wave functions. With fast relaxation of carriers to the ground state, the electrons and holes are quickly spatially separated. Two different composition gradients of GaAsSb SRL were used for the solar cell structure. One or five quantum dot stacks were compared. The maximal PC increased approximately 17 times with increasing number of QD layers from 1 to 5. The highest PC was achieved for sample I5A with increasing concentration of Sb in the SRL, especially in the QD absorption region. The possible explanation is a better carrier separation in this type of structure suppressing the radiative recombination rate in QDs. These results suggest a high application potential of this structure for photovoltaics.
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...
Simulation of optical breast density measurements using structured light illumination
Kwong, Jessica; Nouizi, Farouk; Li, Yifan; Chen, Jeon-Hor; Su, Min-Ying; Gulsen, Gultekin
2014-02-01
Breast density is a risk factor for breast cancer and we propose using diffuse optical tomography with structured light illuminations (SLI) to quantify the percentage of the fibroglandular (dense) tissue within the breast. Segmentations of dense tissue from breast MRI cases were used to create a geometric model of the breast. COMSOL-generated Finite Element Method (FEM) meshes were used for simulating photon migration through the breast tissue and reconstructing the absorption maps. In these preliminary simulations, the absorption coefficients of the non-dense and dense tissue were assigned using literature values based on their concentrations of water, lipid, oxy- and deoxyhemoglobin as they are the main chromophores, or absorbers of light, within the breast. Synthetic SLI measurements were obtained using a FEMbased forward solver. During the simulation, 12 distinct patterns consisting of vertical stripes, horizontal stripes, and checkerboard patterns were used for illumination and detection. Using these simulated measurements, FEM-based inverse solvers were used to reconstruct the 3D absorption maps. In this study, the methods are applied to reconstruct the absorption maps for multiple wavelengths (780nm, 830nm, 900nm, 1000nm) using one case as an example. We are currently continuing these simulations with additional cases and reconstructing 3D concentration maps of the chromophores within the dense and non-dense breast tissue.
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...
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
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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
Modelling the metal–semiconductor band structure in implanted ohmic contacts to GaN and SiC
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Here we present a method to model the metal–semiconductor (M–S) band structure to an implanted ohmic contact to a wide band gap semiconductor (WBG) such as GaN and SiC. The performance and understanding of the M–S contact to a WBG semiconductor is of great importance as it influences the overall performance of a semiconductor device. In this work we explore in a numerical fashion the ohmic contact properties to a WBG semiconductor taking into account the partial ionization of impurities and analysing its dependence on the temperature, the barrier height, the impurity level band energy and carrier concentration. The effect of the M–S Schottky barrier lowering and the Schottky barrier inhomogeneities are discussed. The model is applied to a fabricated ohmic contact to GaN where the M–S band structure can be completely determined. (paper)
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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
Energy Technology Data Exchange (ETDEWEB)
Zaytsev, Kirill I., E-mail: kirzay@gmail.com; Katyba, Gleb M.; Yakovlev, Egor V.; Yurchenko, Stanislav O., E-mail: st.yurchenko@mail.ru [Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow 105005 (Russian Federation); Gorelik, Vladimir S. [P. N. Lebedev Physics Institute of the Russian Academy of Sciences, Leninskiy Prospekt 53, Moscow 119991 (Russian Federation)
2014-06-07
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.
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.
Structure of the Lithosphere in Central Europe: Integrated Density Modelling
Bielik, M.; Grin?, M.; Zeyen, H. J.; Plašienka, D.; Pasteka, R.; Kraj?ák, M.; Bošanský, M.; Mikuška, J.
2014-12-01
Firstly, we present new results related to the lithospheric structure and tectonics of the Central Europe and the Western Carpathians. For geophysical study of the lithosphere in Central Europe we calculated four original 2D lithosphere-scales transects crossing this area from the West European Platform in the North to the Aegean Sea in the South and from the Adriatic Sea in the West to the East European Platform in the East. Modelling is based on the joint interpretation of gravity, geoid, topography and surface heat flow data with temperature-dependent density. Wherever possible, crustal structure is constrained by seismic data. The thickness of the lithosphere decreases from the older and colder platforms to the younger and hotter Pannonian Basin with a maximum thickness under the Eastern and Southern Carpathians. The thickness of the Carpathian arc lithosphere varies between 150 km in the North (the Western Carpathians) and about 300 km in the Vrancea zone (the Eastern and Southern Carpathian junction). In the Platform areas it is between 120 and 150 km and in the Pannonian Basin it is about 70 km. The models show that the Moesian Platform is overthrust from the North by the Southern Carpathians and from the South by the Balkanides and characterized by bending of this platform. In all transects, the thickest crust is found underneath the Carpathian Mountains or, as in the case of the Vrancea area, under their immediate foreland. The thickest crust outside the orogens is modelled for the Moesian Platform with Moho depths of up to 45 km. The thinnest crust is located under the Pannonian Basin with about 26-27 km. Secondly, our presentation deals with construction of the stripped gravity map in the Turiec Basin, which represents typical intramontane Neogene depression of the Western Carpathians. Based on this new and original gravity map corrected by regional gravity effect we were able to interpret the geological structure and tectonics of this sedimentary basin. This work was supported by the Slovak Grant Agency VEGA (grants No. 1/0095/12, 2/0067/12) and Slovak Research and Development Agency (grants No. APVV-0827-12, APVV-0194-10).
Krivosheeva, A V; Shaposhnikov, V L; Krivosheev, A E; Borisenko, V E
2002-01-01
The effect of isotopic and unaxial deformation of the crystal lattice on the electronic band structure of indirect band gap semiconductors Mg sub 2 Si and Mg sub 2 Ge has been simulated by means of the linear augmented plane wave method. The reduction of the lattice constant down to 95 % results in a linear increase of the direct transition in magnesium silicide by 48%. The stresses arising under unaxial deformation shift the bands as well as result in splitting of degenerated states. The dependence of the interband transitions on the lattice deformation is nonlinear in this case
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The model of a hopping electron on a two-dimensional lattice placed in a quantised magnetic field is considered. The symmetry of the system is described by the magnetic translation group. Its maximal abelian subgroup defines magnetic Brillouin zone while irreducible representations determine an energy band structure. It turns out, due to an equivalence relation between irreducible representations, that for the characterization of the energy band it is sufficient to use only some quasimomenta from magnetic Brillouin zone. These quasimomenta constitute the magnetic band Brillouin zone.
Band edge electronic structure of transition metal/rare earth oxide dielectrics
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Lucovsky, Gerald [Department of Physics, North Carolina State University, Raleigh, NC 27695-8202 (United States)]. E-mail: gerry_lucovsky@ncsu.edu
2006-10-31
This article addresses band edge electronic structure of transition metal/rare earth (TM/RE) non-crystalline and nano-crystalline elemental and complex oxide high-k dielectrics for advanced semiconductor devices. Experimental approaches include X-ray absorption spectroscopy (XAS) from TM, RE and oxygen core states, photoconductivity (PC), and visible/vacuum ultra-violet (UV) spectroscopic ellipsometry (SE) combined with ab initio theory is applied to small clusters. These measurements are complemented by Fourier transform infra-red absorption (FTIR), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). Two issues are highlighted: Jahn-Teller term splittings that remove d-state degeneracies of states at the bottom of the conduction band, and chemical phase separation and crystallinity in Zr and Hf silicates and ternary (Zr(Hf)O{sub 2}) {sub x}(Si{sub 3}N{sub 4}) {sub y}(SiO{sub 2}){sub 1-x-y} alloys. Engineering solutions for optimization of both classes of high-k dielectric films, including limits imposed on the continued and ultimate scaling of the equivalent oxide thickness (EOT) are addressed.
SMALL-SCALE STRUCTURE OF THE INTERSTELLAR MEDIUM TOWARD ? Oph STARS: DIFFUSE BAND OBSERVATIONS
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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.
Examining Periodic Solar Wind Density Structures Observed in the SECCHI Heliospheric Imagers
Viall, Nicholeen M; Vourlidas, Angelos; Howard, Russell; 10.1007/s11207-010-9633-1
2010-01-01
We present an analysis of small-scale, periodic, solar-wind density enhancements (length-scales as small as \\approx 1000 Mm) observed in images from the Heliospheric Imager (HI) aboard STEREO A. We discuss their possible relationship to periodic fluctuations of the proton density that have been identified at 1 AU using in-situ plasma measurements. Specifically, Viall, Kepko, and Spence (2008) examined 11 years of in-situ solar-wind density measurements at 1 AU and demonstrated that not only turbulent structures, but also non-turbulent periodic density structures exist in the solar wind with scale sizes of hundreds to one thousand Mm. In a subsequent paper, Viall, Spence, and Kasper (2009) analyzed the {\\alpha} to proton solar-wind abundance ratio measured during one such event of periodic density structures, demonstrating that the plasma behavior was highly suggestive that either temporally or spatially varying coronal source plasma created those density structures. Large periodic density structures observed ...
Gutierrez-Arenas, R. A.; MENDOZA, D
2011-01-01
In this paper we describe an application of the finite difference method to obtain the transverse magnetic photonic band gap diagram of a photonic crystal. The strategy of this method is to formulate the Maxwell equations in finite differences in order to write a computational code. We present experiments that confirm the validity of the calculations of the photonic band diagram as well as the refraction indix of such structure. All calculations were made for two dimensional...
Density and molecular column density structure of three molecular cloud cores
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Multi-transition studies using CS, C34S, and H2CO are presented for the dense cores in the molecular clouds M17, S140, and NGC 2024. The typical peak density derived for these cores is -106 cm-3, much larger than the average density in molecular clouds, but the gas density is not strongly correlated with the line intensities within the core itself. A man of line intensity appears to be a map of molecular column density whereas the gas density is evident in the ratios of intensities of different lines. Although the data do not have the spatial resolution to directly see clumps in the core, statistical equilibrium modeling of the data does provides evidence for an inhomogeneous distribution of the dense gas within the telescope beam. Many aspects of the data can best be explained by a model in which the gas with density >105 cm-3 is distributed in numerous small (34S, and H2CO are in reasonable agreement and presents guidelines for future use of these molecules as density probes
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In this paper the effect of pressure on the structural and electronic properties of cubic-LaAlO3 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.
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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.
A genetic algorithm based inverse band structure method for semiconductor alloys
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We present an efficient and accurate method for searching for atomic configurations with target band structure properties. Our approach to this inverse problem is to search the atomic configuration space by repeatedly applying a forward solver, guiding the search toward the optimal configuration using a genetic algorithm. For the forward solver, we relax the atomic positions, then solve the Schroedinger equation using a fast empirical pseudopotential method. We employ a hierarchical parallelism for the combined forward solver and genetic algorithm. This enables the optimization process to run on many more processors than would otherwise be possible. We have optimized AlGaAs alloys for maximum bandgap and minimum bandgap for several given compositions and discuss the results. This approach can be generalized to a wide range of applications in material design
A genetic algorithm based inverse band structure method for semiconductor alloys
Kim, Kwiseon; Graf, Peter A.; Jones, Wesley B.
2005-09-01
We present an efficient and accurate method for searching for atomic configurations with target band structure properties. Our approach to this inverse problem is to search the atomic configuration space by repeatedly applying a forward solver, guiding the search toward the optimal configuration using a genetic algorithm. For the forward solver, we relax the atomic positions, then solve the Schrödinger equation using a fast empirical pseudopotential method. We employ a hierarchical parallelism for the combined forward solver and genetic algorithm. This enables the optimization process to run on many more processors than would otherwise be possible. We have optimized AlGaAs alloys for maximum bandgap and minimum bandgap for several given compositions and discuss the results. This approach can be generalized to a wide range of applications in material design.
Phase transition and band-structure tuning in InN through uniaxial and biaxial strains
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The phase transitions and band structure of InN under uniaxial and biaxial strains are systematically investigated using first-principles calculations. The main findings are summarized as follows: (I) although graphite-like phases are observed for both types of strain, the phase transitions are drastically different: second order for uniaxial strain and first order for biaxial strain. Furthermore, the second-order transition is driven by elastic and dynamical instabilities, whereas the first-order transition is driven only by elastic instability. (II) The wurtzite bandgap is always direct and that of the graphite-like phase is always indirect. Furthermore, the wurtzite bandgap is drastically enhanced by compressive uniaxial strain but reduced by tensile uniaxial strain. However, both biaxial strains greatly reduce the bandgap and eventually the semi-metallic phases are achieved. (paper)
The effect of spin-orbit coupling in band structure and edge states of bilayer graphene
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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