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1

Electron momentum density, band structure, and structural properties of SrS  

Energy Technology Data Exchange (ETDEWEB)

The electron momentum density, the electronic band structure, and the structural properties of SrS are presented in this paper. The isotropic Compton profile, anisotropies in the directional Compton profiles, the electronic band structure and density of states are calculated using the ab initio periodic linear combination of atomic orbitals method with the CRYSTAL06 code. Structural parameters of SrS-lattice constants and bulk moduli in the B1 and B2 phases-are computed together with the transition pressure. The computed parameters are well in agreement with earlier investigations. To compare the calculated isotropic Compton profile, measurement on polycrystalline SrS is performed using 5Ci-{sup 241}Am Compton spectrometer. Additionally, charge transfer is studied by means of the Compton profiles computed from the ionic model. The nature of bonding in the isovalent SrS and SrO compounds is compared on the basis of equal-valenceelectron-density profiles and the bonding in SrS is found to be more covalent than in SrO.

Sharma, G., E-mail: gsphysics@gmail.com [University of Kota, Department of Pure and Applied Physics (India); Munjal, N.; Vyas, V. [Banasthali University, Department of Physics (India); Kumar, R.; Sharma, B. K. [University of Rajasthan, Department of Physics (India); Joshi, K. B. [MLS University, Department of Physics (India)

2013-10-15

2

Electron momentum density, band structure, and structural properties of SrS  

International Nuclear Information System (INIS)

The electron momentum density, the electronic band structure, and the structural properties of SrS are presented in this paper. The isotropic Compton profile, anisotropies in the directional Compton profiles, the electronic band structure and density of states are calculated using the ab initio periodic linear combination of atomic orbitals method with the CRYSTAL06 code. Structural parameters of SrS—lattice constants and bulk moduli in the B1 and B2 phases—are computed together with the transition pressure. The computed parameters are well in agreement with earlier investigations. To compare the calculated isotropic Compton profile, measurement on polycrystalline SrS is performed using 5Ci-241Am Compton spectrometer. Additionally, charge transfer is studied by means of the Compton profiles computed from the ionic model. The nature of bonding in the isovalent SrS and SrO compounds is compared on the basis of equal-valenceelectron-density profiles and the bonding in SrS is found to be more covalent than in SrO

2013-10-01

3

Electronic band structure of Cu2O by spin density functional theory  

International Nuclear Information System (INIS)

The band structure of Cu2O is calculated using density functional theory in the generalized gradient approximation. By taking spin-orbit coupling into account the split between the ?7+ and the ?8+ valence band states is obtained as 128 meV. The highest valence band shows a noticeable nonparabolicity close to the ? point. This is important for the quantitative description of excitons in this material, which is considered to be the best candidate for the confirmation that Bose-Einstein condensation also occurs in excitonic systems.

2009-01-07

4

From Metal Cluster to Metal Nanowire: A Topological Analysis of Electron Density and Band Structure Calculation  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract:We investigate a theoretical model of molecular metalwire constructed from linear polynuclear metal complexes. In particular we study the linear Crn metal complex and Cr molecular metalwire. The electron density distributions of the model nanowire and the linear Crn metal complexes, with n = 3, 5, and 7, are calculated by employing CRYSTAL98 package with topological analysis. The preliminary results indicate that the bonding types between any two neighboring Cr are all the same, namely the polarized open-shell interaction. The pattern of electron density distribution in metal complexes resembles that of the model Cr nanowire as the number of metal ions increases. The conductivity of the model Cr nanowire is also tested by performing the band structure calculation.

Yu Wang

2002-01-01

5

Band structure and optical properties of antimony-sulfobromide: density functional calculation  

Science.gov (United States)

The electronic structure, linear, and non-linear optical properties of ferroelectric-semiconductor SbSBr are investigated in the non-polar (paraelectric) and polar (ferroelectric) phase, using the density functional methods in the generalized gradient approximation. The electronic band structure obtained shows that SbSBr has an indirect forbidden gap of 2.16 and 2.21 eV in the paraelectric and ferroelectric phase, respectively. The linear photon-energy dependent dielectric functions and some optical functions, such as absorption and extinction coefficients, refractive index, energy-loss function, reflectivity, and optical conductivity in both phases and photon-energy dependent second-order susceptibilities in the ferroelectric phase are calculated. Moreover, some important optical parameters, such as the effective number of valence electrons and the effective optical dielectric constant, are calculated in both phases.

Akkus, Harun; Mamedov, Amirullah M.; Kazempour, Ali; Akbarzadeh, Hadi

2008-03-01

6

Electron momentum density and band structure calculations of {alpha}- and {beta}-GeTe  

Energy Technology Data Exchange (ETDEWEB)

We have measured isotropic experimental Compton profile of {alpha}-GeTe by employing high energy (662 keV) {gamma}-radiation from a {sup 137}Cs isotope. To compare our experiment, we have also computed energy bands, density of states, electron momentum densities and Compton profiles of {alpha}- and {beta}-phases of GeTe using the linear combination of atomic orbitals method. The electron momentum density is found to play a major role in understanding the topology of bands in the vicinity of the Fermi level. It is seen that the density functional theory (DFT) with generalised gradient approximation is relatively in better agreement with the experiment than the local density approximation and hybrid Hartree-Fock/DFT. - Highlights: > Compton profile of {alpha}-GeTe using a 20 Ci {sup 137}Cs Compton spectrometer. > Compared experimental Compton data with density functional theory. > Reported energy bands and density of states of {alpha}- and {beta}-GeTe. > EVED profiles analysed to check the covalent character.

Vadkhiya, Laxman [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India); Arora, Gunjan [Department of Physics, Techno India NJR Institute of Technology, Udaipur 313002, Rajasthan (India); Rathor, Ashish [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, 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)

2011-12-15

7

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

2013-04-15

8

Density-functional band-structure calculations for La-, Y-, and Sc-filled CoP3-based skutterudite structures  

International Nuclear Information System (INIS)

The crystal structure, thermodynamic stability, and electronic structure of La-, Y-, and Sc-filled CoP3 are predicted from density-functional band-structure calculations. The size of the cubic voids in the skutterudite structure is changed much less than the difference in size between the different filling atoms, and we expect that the larger rattling amplitude of the smaller Sc and Y atoms may decrease the lattice thermal conductivity of Sc- and Y-filled structures significantly compared to La-filled structures. The solubility of La, Y, and Sc in CoP3 is calculated to be around 5, 3-6 %, and below 1% at 0 K, respectively. Based on similar systems, this is expected to increase considerably if Fe is substituted for Co. Fe substitution is also expected to compensate the increased charge carrier concentration of the filled structures that is seen in the calculated electron density of states. In conclusion, Sc- or Y-filled (FeCo)P3 skutterudite structures are promising materials for thermoelectric applications

2004-11-15

9

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

10

The band structure of WO3 and non-rigid-band behaviour in Na0.67WO3 derived from soft x-ray spectroscopy and density functional theory  

Science.gov (United States)

The electronic structure of single-crystal WO3 and Na0.67WO3 (a sodium-tungsten bronze) has been measured using soft x-ray absorption and resonant soft x-ray emission oxygen K-edge spectroscopies. The spectral features show clear differences in energy and intensity between WO3 and Na0.67WO3. The x-ray emission spectrum of metallic Na0.67WO3 terminates in a distinct Fermi edge. The rigid-band model fails to explain the electronic structure of Na0.67WO3 in terms of a simple addition of electrons to the conduction band of WO3. Instead, Na bonding and Na 3s-O 2p hybridization need to be considered for the sodium-tungsten bronze, along with occupation of the bottom of the conduction band. Furthermore, the anisotropy in the band structure of monoclinic ?-WO3 revealed by the experimental spectra with orbital-resolved geometry is explained via density functional theory calculations. For ?-WO3 itself, good agreement is found between the experimental O K-edge spectra and the theoretical partial density of states of O 2p orbitals. Indirect and direct bandgaps of insulating WO3 are determined from extrapolating separations between spectral leading edges and accounting for the core-hole energy shift in the absorption process. The O 2p non-bonding states show upward band dispersion as a function of incident photon energy for both compounds, which is explained using the calculated band structure and experimental geometry.

Chen, B.; Laverock, J.; Piper, L. F. J.; Preston, A. R. H.; Cho, S. W.; DeMasi, A.; Smith, K. E.; Scanlon, D. O.; Watson, G. W.; Egdell, R. G.; Glans, P.-A.; Guo, J.-H.

2013-04-01

11

Photonic band structure  

International Nuclear Information System (INIS)

We learned how to create 3-dimensionally periodic dielectric structures which are to photon waves, as semiconductor crystals are to electron waves. That is, these photonic crystals have a photonic bandgap, a band of frequencies in which electromagnetic waves are forbidden, irrespective of propagation direction in space. Photonic bandgaps provide for spontaneous emission inhibition and allow for a new class of electromagnetic micro-cavities. If the perfect 3-dimensional periodicity is broken by a local defect, then local electromagnetic modes can occur within the forbidden bandgap. The addition of extra dielectric material locally, inside the photonic crystal, produces open-quotes donorclose quotes modes. Conversely, the local removal of dielectric material from the photonic crystal produces open-quotes acceptorclose quotes modes. Therefore, it will now be possible to make high-Q electromagnetic cavities of volume approx-lt 1 cubic wavelength, for short wavelengths at which metallic cavities are useless. These new dielectric micro-resonators can cover the range all the way from millimeter waves, down to ultraviolet wavelengths

1993-05-01

12

Band structures of defective graphenes  

Energy Technology Data Exchange (ETDEWEB)

Band structures of defective graphenes are analyzed by crystal orbital method. In laterally slipped faults, there appear {sigma} bands consisting of weakly interacted dangling bonds. The peculiar {sigma} bands cross with frontier {pi} bands, and the resultant double occupation leads to the disappearance of ferromagnetic interactions. On the other hand, in longitudinally slipped faults, there are no crossings of the {sigma} bands within the frontier levels, and the ferromagnetic interactions result from polycarbene-type spin alignment. - Research Highlights: Band structures in defective graphenes are analyzed. Lateral slipping in graphenes quenches the ferromagnetic interactions. In the lateral slipping modes, {sigma} bands cross with {pi} frontier bands and reduce the magnetism. Longitudinal slipping in graphenes causes carbene-type ferromagnetic interactions.

Hatanaka, Masashi, E-mail: mhatanaka@xug.biglobe.ne.j [Department of Green and Sustainable Chemistry, School of Engineering, Tokyo Denki University, 2-2 Kanda Nishiki-cho, Chiyoda-ku, Tokyo 101-8457 (Japan)

2011-03-15

13

Excitation spectra and ground-state properties from density functional theory for the inverted band-structure systems ?-HgS, HgSe and HgTe  

International Nuclear Information System (INIS)

We have performed a systematic density-functional study of the mercury chalcogenide compounds ?-HgS, HgSe, and HgTe using an all-electron full-potential linear muffin-tin orbital (FP-LMTO) method. We find that, in the zinc-blende structure, both HgSe and HgTe are semimetals whereas ?-HgS has a small spin-orbit induced band gap. Our calculated relativistic photoemission and inverse photoemission spectra (PES and IPES, respectively) reproduce very well the most recently measured spectra, as do also our theoretical optical spectra. In contrast to the normal situation, we find that the local density approximation (LDA) to the density functional gives calculated equilibrium volumes in much better agreement with experiment than does the generalized gradient corrected functional (GGA). We also address the problem of treating relativistic p electrons with methods based on a scalar-relativistic basis set, and show that the effect is rather small for the present systems. (author)

2002-01-01

14

ARPES study of the evolution of band structure and charge density wave properties in RTe3 ( R=Y , La, Ce, Sm, Gd, Tb, and Dy)  

Energy Technology Data Exchange (ETDEWEB)

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.

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

15

Doping-induced changes in the valence band edge structure of homoepitaxial B-doped diamond films below Mott's critical density  

International Nuclear Information System (INIS)

Heavily boron-doped p-type diamond is a key material for developing diamond-based applications in various fields. We obtain information about changes in the valence band edge of homoepitaxial boron-doped diamond films around and below Mott's critical density for a metal-non-metal transition. For a boron concentration of about 2-3 x 1020 cm-3, where this transition is expected to occur, a metal-like behaviour is observed at room temperature (RT) with the Fermi-level lying 0.1 eV above the valence band edge. For a boron concentration about 4 x 1019 cm-3, which is well below the critical density, the valence band edge is quite different from that of lightly doped samples. It is proposed as an explanation for these experimental differences that the excited-states of acceptors overlap. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

2009-09-01

16

Band Structure and Effective Masses of ZnMgO  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze the influence of the Mg concentration on several important properties of the band structure of ZnMgO alloys in wurtzite structure using ab initio calculations. For this purpose, the band structure for finite concentrations is defined in terms of the Bloch spectral density, which can be calculated within the coherent potential approximation. We investigate the concentration dependence of the band gap and the crystal-field splitting of the valence bands. The effecti...

Franz, Christian; Giar, Marcel; Heinemann, Markus; Czerner, Michael; Heiliger, Christian

2013-01-01

17

Band structures in 129Cs  

International Nuclear Information System (INIS)

The 122Sn(11B,4n) fusion-evaporation reaction at Elab=60 MeV was used to populate excited states in 129Cs, and the deexcitations were investigated using in-beam ?-ray spectroscopic techniques. The level scheme of 129Cs is established up to ?8 MeV excitation energy and 47/2 h spin. The observed band structures are interpreted for their configurations in the framework of cranking model calculations and systematic of the neighboring 55Cs isotopes. A negative-parity ?I=1 coupled band has been assigned the ?h11/2 x ?(h11/2)2 configuration as solution of the tilted-axis cranking, which coexists with the ?h11/2 yrast band resulting from the principal-axis cranking. A new band has been identified as a ?-vibrational band built on the ?h11/2 orbital. A pair of strongly coupled positive-parity bands exhibiting similar features have been assigned different unpaired three-quasiparticle configurations involving the ?h11/2 x ?h11/2 component. The previously identified unfavored signature partners of the ?d5/2 and ?g7/2 bands are reassigned as ? vibrations of the core coupled to the ?g7/2 single-particle configuration, and the favored signature of the ?d5/2 band, respectively.

2009-04-01

18

Susceptibilities for first principles band structures  

Science.gov (United States)

We present a parallel implementation of a new method for calculating the unenhanced susceptibility proposed by us recently. Our implementation uses the first principles LMTO band structure within the tight binding approach as input to calculate the joint density of states. The susceptibility is then obtained by integrating over the product of the joint density of states and a Lindhard function. Our program, which has a simple friendly user interface, runs on the PC with a quadputer board, a Meiko Surface running CSTools powered either by T800 or i860 compute boards and the Intel iPSC/860 hypercube in Daresbury. Our method incorporates the troublesome matrix elements naturally and our results on Pd and Ni show that the decrease in ?( q) as we go away from the Brillouin zone centre is due mainly to the matrix elements rather than to the band energies.

Crockford, D. J.; Yeung, W.

1993-04-01

19

Band structure of FeBO3: Implications for tailoring the band gap of nanoparticles  

Science.gov (United States)

The energy band structure of a transparent, green, room-temperature ferromagnetic FeBO3 has been calculated using density functional theory within the generalized gradient approximation (GGA) and the GGA+U approach. The electronic structure of FeBO3 is predicted to be antiferromagnetic and insulating, both in perfect agreement with available experiments. The predicted band structure, in particular, the shapes of the valence and conduction band edges, provides great insights into tailoring the optical band gap of FeBO3 nanoparticles: for the particle size close to 3 nm, the visible spectral region extends from green up to blue due to quantum confinement.

Shang, Shunli; Wang, Yi; Liu, Zi-Kui; Yang, Chia-En; Yin, Shizhuo

2007-12-01

20

Band Structure of New ReFeAsO Superconductors  

Directory of Open Access Journals (Sweden)

Full Text Available We investigate the band structure of Fe-based superconductors using the first-principle method of density-functional theory. We calculated the band structure and the density of states at the Fermi level for ReFeAsO (Re = Sm, Er superconductors. Our calculations indicate that the maximum critical superconducting transition temperature Tc will be observed for compounds with Sm and Er at 55 and 46 K, respectively.

Hyun-Tak Kim

2013-05-01

 
 
 
 
21

Electron energy loss studies of the valence band density of states of scandium  

International Nuclear Information System (INIS)

Electron energy loss spectroscopy of the scandium (0001) surface has indicated both core level and valence band excitation loss structure. Comparison to theoretically calculated bulk densities of states for scandium shows good agreement with the experimental results. (author)

1981-02-01

22

Quasirelativistic band structure of bismuth telluride  

International Nuclear Information System (INIS)

The band structure of bismuth telluride belonging to the group of the Asub(2)Ssup(5)BsUb(3)-type crystals with the Dsub(3d)sup(5) symmetry is under consideration. The Bi2Te3 band structure was calculated using the Pauli equation pseudopotential method. Calculation results are presented for the Brillouin zone symmetric points. The energy bands are classified according to their symmetry. The evailable basic parameters of the bismuth telluride band structure are compared with the result of other paper. Analysis of the calculated band structure shows that there is some difference of the band behaviour in the direction perpendicular to quintet (GITAL, KA, XU) layers that of bands lying in the quintet plane (other Brillouin zone directions). In the first case the energy band dispersion is well below than that in the second case. This fact conforms with a lower current carrier mobility in the direction perpendicular to the layers, as compared to other crystal directions

1985-09-01

23

Potential barrier and band structure of closed edge graphene  

Science.gov (United States)

The atomic structure, electron distribution, work function, and band structure of closed edge graphene are investigated with density functional theory. Field emission performance of closed edge graphene is compared with that of open edge graphene. We provide a possible explanation for the field emission microscopy image change after high emission current, which appeals to the experimentalists for further investigation.

He, Chunshan; Wang, Weiliang

2013-08-01

24

Pseudopotential band structure of indium nitride  

International Nuclear Information System (INIS)

The band structure, density of states and the imaginary part of the dielectric function have been calculated for indium nitride by a pseudopotential method. Comparison with published reflectance data permits the identification of principal optical transitions at the GAMMA,M,K, and H symmetry points and we have been able to correct previous transition assignments. The calculated long-wavelength refractive index of 2.88 +- 0.5 compares well with experiment. The material has a direct energy gap at the zone center and the spherically symmetric extrema are well described by scalar effective masses of 0.17m0, 0.5m0 (holes), and 0.12m0 (electrons)

1986-01-15

25

Elementary energy bands in band structure calculations of some wide-bandgap crystals  

Energy Technology Data Exchange (ETDEWEB)

Semiconducting Tl{sub 3}AsS{sub 4} crystal was chosen as an example to show that its valence band is composed of the elementary energy bands. Their topology and symmetry obtained in the empty-lattice approximation is confirmed by ab initio band structure calculations. It was shown that these elementary energy bands correspond to the Wyckoff position c in a unit cell. Earlier predictions that the largest electron density distribution is focused in the vicinity of this position, similarly to the case of YAlO{sub 3} and SbSI crystals, is confirmed. A conclusion on the common topology and symmetry of the elementary energy bands in electronic and phonon spectra is presented. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Sznajder, M. [Institute of Physics, University of Rzeszow, Rejtana 16a, 35-310 Rzeszow (Poland); Bercha, D.M. [Institute of Physics, University of Rzeszow, Rejtana 16a, 35-310 Rzeszow (Poland); Institute of Physics and Chemistry of Solid State, Uzhgorod National University, 54 Voloshin Str. 88000 Uzhgorod (Ukraine); Rushchanskii, K.Z. [Institute of Physics and Chemistry of Solid State, Uzhgorod National University, 54 Voloshin Str. 88000 Uzhgorod (Ukraine)

2004-01-01

26

Electronic structure and charge density of zirconium diboride  

Energy Technology Data Exchange (ETDEWEB)

Self-consistent calculations of the electronic band structure of zirconium diboride, ZrB{sub 2}, have been performed. The total and individual band charge densities are analysed in terms of their site (zirconium or boron) symmetry and plotted. The total charge density shows very little charge asymmetry about either site. 6 refs., 6 figs., 37 tabs.

Switendick, A.C.

1990-01-01

27

Modeling charged defects inside density functional theory band gaps  

Science.gov (United States)

Density functional theory (DFT) has emerged as an important tool to probe microscopic behavior in materials. The fundamental band gap defines the energy scale for charge transition energy levels of point defects in ionic and covalent materials. The eigenvalue gap between occupied and unoccupied states in conventional DFT, the Kohn–Sham gap, is often half or less of the experimental band gap, seemingly precluding quantitative studies of charged defects. Applying explicit and rigorous control of charge boundary conditions in supercells, we find that calculations of defect energy levels derived from total energy differences give accurate predictions of charge transition energy levels in Si and GaAs, unhampered by a band gap problem. The GaAs system provides a good theoretical laboratory for investigating band gap effects in defect level calculations: depending on the functional and pseudopotential, the Kohn–Sham gap can be as large as 1.1 eV or as small as 0.1 eV. We find that the effective defect band gap, the computed range in defect levels, is mostly insensitive to the Kohn–Sham gap, demonstrating it is often possible to use conventional DFT for quantitative studies of defect chemistry governing interesting materials behavior in semiconductors and oxides despite a band gap problem.

Schultz, Peter A.; Edwards, Arthur H.

2014-05-01

28

Band structure of superlattice with ?-like potential  

International Nuclear Information System (INIS)

Band structure of superlattice with ?-like potential has been calculated taking into account interaction of carriers of different kinds. Superlattices of semiconductors with degenerated valence band and zero-gap semiconductors have been considered. For the latter semimetal-semiconductor transition has been obtained. (author). 8 refs, 1 fig

1993-01-01

29

Highly deformed band structure in 57Co  

International Nuclear Information System (INIS)

Rotational bands have been found in 57Co using the 28Si(32S,3p) reaction at 130 MeV. The bands, extending the mass 60 region of large deformation down to Z=27, are signature-partner sequences. Their quadrupole moments are similar to those of bands in the neighboring nuclei. The features of the new bands are described by Skyrme Hartree-Fock calculations favoring a configuration assignment with one neutron and one proton excited in the respective 1g9/2 intruder orbital. An attempt to describe the magnetic (M1) properties of the signature-partner structure is also presented

2002-03-01

30

Band structure of boron doped carbon nanotubes  

CERN Document Server

We present {\\it ab initio} and self-consistent tight-binding calculations on the band structure of single wall semiconducting carbon nanotubes with high degrees (up to 25 %) of boron substitution. Besides a lowering of the Fermi energy into the valence band, a regular, periodic distribution of the p-dopants leads to the formation of a dispersive ``acceptor''-like band in the band gap of the undoped tube. This comes from the superposition of acceptor levels at the boron atoms with the delocalized carbon $\\pi$-orbitals. Irregular (random) boron-doping leads to a high concentration of hybrids of acceptor and unoccupied carbon states above the Fermi edge.

Wirtz, L; Wirtz, Ludger; Rubio, Angel

2003-01-01

31

The surface band structure of W(112)  

International Nuclear Information System (INIS)

Both the experimental and theoretical band structure of the W(112) surface are presented, with the theoretical band structure calculated by the film-LAPW (linearized augmented plane waves) method. The results permit one to compare the W(112) and Mo(112) band structures and illuminate the similarities. It is found that for the W(112) surface the main photoemission features combine contributions from both the surface and bulk, as has been previously noted for Mo(112). The main differences between the electronic structures of the furrowed W(112) and Mo(112) surfaces are seen in the width of occupied bands. The differences are attributed to the extent of localization of valence 4d and 5s electrons in Mo and 5d and 6s electrons in W. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2004-03-01

32

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.)

2009-12-01

33

Multiple band structures in 191Hg  

International Nuclear Information System (INIS)

The level structure of the nucleus 191Hg has been considerably extended from previous studies by using the 160Gd(36S, 5n) reaction in conjunction with an array of Compton-suppressed germanium detectors. A series of 13 different level sequences has been established in addition to three superdeformed bands. A majority of the band structures can be understood in cranked shell model calculations assuming on oblate collective nuclear shape. There is some evidence for the onset of triaxiality. Finally, two bands of single-particle character have been found. They are interpreted as being associated with a prolate non-collective shape (?=-120deg). (orig.)

1992-01-01

34

Band Structure Engineering for Electron Tunneling Devices  

Science.gov (United States)

Negative differential resistance devices based on electron tunneling have potential applications in the frequency range above 200 GHz, where conventional field -effect and bipolar transistors have not yet been able to operate. High-speed performance depends primarily on increasing the peak current density and reducing the parasitic resistance. The room temperature peak-to-valley current ratio also must be maximized and the peak voltage should be reduced to reduce the power dissipated in the device. Two-terminal negative differential resistance devices are also stepping stones in the development of three-terminal devices based on coherent electron transport. In the future, these novel devices may offer the prospect of continued downscaling of integrated circuit components to nanometer dimensions, where conventional device concepts apparently fail. We apply standard techniques of molecular beam epitaxy to the growth of novel semiconductor heterostructures for electron tunneling devices. The samples are characterized by current and conductance values, measured as a function of device bias and temperature. The observed electrical characteristics are interpreted in terms of the energy band alignments of the heterojunctions and the energy levels and elastic tunneling current flows predicted by calculations based on a two-band model of the bulk band structures of the constituent materials. Such experiments have yielded nine new results that bear on the development of quantum-effect devices: observation of intervalley coupling at a GaAs/AlAs heterointerface, the crystallographic orientation dependence of the excess valley current in AlAs tunneling barriers, negative differential resistance at room temperature in single tunneling barriers of AlGaSb, the longest coherence distance (24 nm) of any resonant tunneling device (InAs/AlSb) resonant tunneling of holes in GaSb/AlSb quantum wells, interband tunneling in polytype InAs/AlSb/GaSb heterostructures, resonant interband tunneling in this system with low-temperature peak-to-valley current ratios greater than 60:1, substantial negative differential conductance in polytype quantum wells wider than 100 nm, and resonant interband coupling in a single -barrier InAs/GaSb/InAs structure. The achievement of large peak-to-valley ratios in wide InAs quantum wells suggests the possibility of high-speed three-terminal tunneling devices.

Beresford, John Roderic

1990-01-01

35

Unfolding first-principles band structures.  

Science.gov (United States)

A general method is presented to unfold band structures of first-principles supercell calculations with proper spectral weight, allowing easier visualization of the electronic structure and the degree of broken translational symmetry. The resulting unfolded band structures contain additional rich information from the Kohn-Sham orbitals, and absorb the structure factor that makes them ideal for a direct comparison with angle resolved photoemission spectroscopy experiments. With negligible computational expense via the use of Wannier functions, this simple method has great practical value in the studies of a wide range of materials containing impurities, vacancies, lattice distortions, or spontaneous long-range orders. PMID:20867120

Ku, Wei; Berlijn, Tom; Lee, Chi-Cheng

2010-05-28

36

Confidence bands for densities, logarithmic point of view  

CERN Document Server

Let $f$ be a probability density and $C$ be an interval on which $f$ is bounded away from zero. By establishing the limiting distribution of the uniform error of the kernel estimates $f_n$ of $f$, Bickel and Rosenblatt (1973) provide confidence bands $B_n$ for $f$ on $C$ with asymptotic level $1-\\alpha\\in]0,1[$. Each of the confidence intervals whose union gives $B_n$ has an asymptotic level equal to one; pointwise moderate deviations principles allow to prove that all these intervals share the same logarithmic asymptotic level. Now, as soon as both pointwise and uniform moderate deviations principles for $f_n$ exist, they share the same asymptotics. Taking this observation as a starting point, we present a new approach for the construction of confidence bands for $f$, based on the use of moderate deviations principles. The advantages of this approach are the following: (i) it enables to construct confidence bands, which have the same width (or even a smaller width) as the confidence bands provided by Bickel ...

Mokkadem, A; Mokkadem, Abdelkader; Pelletier, Mariane

2006-01-01

37

Band structure anisotropy in semiconductor quantum wells  

Energy Technology Data Exchange (ETDEWEB)

The focus of this research is an investigation of energy band anisotropy in simple quantum well structures. This anisotropy results from the asymmetry of the periodic potential within the crystal lattice. For sufficiently high doping levels, band structure anisotropy is expected to play an important role in the evaluation of the electronic and optical properties of the quantum well structures. The analysis uses a model based on a 6x6 Luttinger-Kohn k.p approach for bulk material valence band structure together with the Envelope Function Approximation. The model is used to analyze Si/SiGe, AlGaAs/GaAs, and GaAs/InGaAs quantum wells for the 001 and the 110 growth directions. The resulting band structures show significant anisotropy for materials grown in both the 110 and 001 directions. In all cases the materials grown in the 110 direction show a more pronounced anisotropy than the materials grown in the 001 directions. For the 001 growth directions, the band structures were effectively isotropic for values of k-parallel less than 0.4 inverse angstrom for Si/SiGe, 0.6 inverse angstrom for GaAs/AlGaAs, and 0.5 inverse angstrom for InGaAs/GaAs.

Novotny, S.J.

1999-03-01

38

Photonic band structure and omnidirectional band gap in anisotropic superlattice  

International Nuclear Information System (INIS)

We investigate theoretically the photonic band structure of one-dimensional superlattice (SL) composed of alternating anisotropic layers with their principal axis oriented at arbitrary directions. The dispersion relation of order two is calculated analytically by using the 4 x 4 matrix method which is based on boundary conditions of the electric and magnetic fields at each interface. It is shown that such structures can exhibit coupled electromagnetic modes between transverse magnetic TM and transverse electric TE modes, and dispersion curves that do not exist in superlattices composed only of isotropic layers. For a given value of the wave vector kparallel (parallel to the layers), the dispersion curves (frequency ?) versus kB (where kB is the Bloch wave vector of the periodic system along the axis of the superlattice) is illustrated. Specific applications of these results are given for the case of biaxial superlattice. With an appropriate choice of the superlattice parameters, we show that it is possible to realise, for these coupled electromagnetic waves, an absolute (or omnidirectional) band gap of width depending on the anisotropic parameters of the media forming the SL. (author)

2004-01-01

39

Measurement of valence band structure in arbitrary dielectric films  

International Nuclear Information System (INIS)

A new way of measuring the band structure of various dielectric materials using the secondary electron emission from Auger neutralization of ions is introduced. The first example of this measurement scheme is the magnesium oxide (MgO) films with respect to the application of the films in the display industries. The density of state in the valence bands of MgO film and MgO film with a functional layer (FL) deposited over a dielectric surface reveals that the density peak of film with a FL is considerably less than that of film, thereby indicating a better performance of MgO film with functional layer in display devices. The second example of the measurement is the boron-zinc oxide (BZO) films with respect to the application of the films to the development of solar cells. The measurement of density of state in BZO film suggests that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film. Secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials.

2012-10-01

40

Orbital Localization, Charge Transfer, and Band Gaps in Semilocal Density-Functional Theory  

Science.gov (United States)

We derive an exchange energy functional of generalized gradient form with a corresponding potential that changes discontinuously at integer particle numbers. The functional is semilocal, yet incorporates key features that are connected to the derivative discontinuity of Kohn-Sham density-functional theory. We validate our construction for several paradigm systems and explain how it addresses central well-known deficiencies of antecedent semilocal methods, i.e., the description of charge transfer, properly localized orbitals, and band gaps. We find, e.g., an improved shell structure for atoms, eigenvalues that more closely correspond to ionization energies, and an improved description of band structure where localized states are lowered in energy.

Armiento, R.; Kümmel, S.

2013-07-01

 
 
 
 
41

Band structure calculations of Cu(In1-xGax)Se2  

International Nuclear Information System (INIS)

First principles density calculations of the band structure, and density of states of the Cu(In1-xGax)Se2 in the chalcopyrite type structure have been carried out using the density functional theory. The relationship between the band gap and chemical composition in the structure is discussed. The effective masses of the electrons and holes in the different composition crystals are reported.

2010-10-25

42

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)

2005-12-05

43

Band structure in 77,79Sr  

International Nuclear Information System (INIS)

We have investigated the structure of the collective bands in 77,79Sr within our deformed configuration mixing (DCM) shell model based on Hartree-Fock states. In our model, the single particle orbits 1p3/2, 0f5/2, 1p1/2 and 0g9/2 are taken as the configuration space with 56Ni as the core. A modified Kuo interaction for this basis space is used in our calculation. The different levels are classified into collective bands on the basis of the B(E2) values among them. The calculated collective bands and the B(E2) values are compared with available experimental data. Our calculation is able to reproduce the identical bands observed in 77Sr, 78Sr and 78Rb. (author)

1997-04-01

44

Maximizing band gaps in plate structures  

DEFF Research Database (Denmark)

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

Halkjær, Søren; Sigmund, Ole

2006-01-01

45

Electronic band structure of helical iodine chains  

Energy Technology Data Exchange (ETDEWEB)

The electronic band structure of helical iodine chains was calculated within the empirical tight binding approach. The screw symmetry of the system was used to reduce the size of the problem to a single atom with four atomic orbitals. The overlap parameters were fitted to reproduce the DFT results for a linear iodine chain. The obtained results for helical chains have shown the energy band splitting due to the overlap between p orbitals introduced by the structure twisting. The splitting magnitude depends on the pitch of the helix. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Rybkovskiy, Dmitry [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov street, 119991 Moscow (Russian Federation); Moscow State Institute of Radio Engineering, Electronics and Automation (Technical University), 78 Vernadskogo Prospect, 119454 Moscow (Russian Federation); Osadchy, Alexander; Obraztsova, Elena [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov street, 119991 Moscow (Russian Federation)

2012-12-15

46

Self-consistent, relativistic, ferromagnetic band structure of gadolinium  

International Nuclear Information System (INIS)

An initial self-consistent calculation of the ground state magnetic band structure of gadolinium is described. A linearized APW method was used which included all single particle relativistic effects except spin-orbit coupling. The spin polarized potential was obtained in the muffin-tin form using the local spin density approximation for exchange and correlation. The most striking and unorthodox aspect of the results is the position of the 4f spin-down ''bands'' which are required to float just on top of the Fermi level in order to obtain convergence. If the 4f states (l = 3 resonance) are removed from the occupied region of the conduction bands the magnetic moment is approximately .75 ?/sub B//atom; however, as the 4f spin-down states are allowed to find their own position they hybridize with the conduction bands at the Fermi level and the moment becomes smaller. Means of improving the calculation are discussed

1977-08-18

47

Density of states of the lowest exciton band and the exciton bandwidth in coronene single crystals  

International Nuclear Information System (INIS)

The thermo-absorption spectra of coronene single crystals were investigated over the temperature range between 193 and 287 K. The density of states and the exciton bandwidth of the lowest exciton band were obtained from the thermo-absorption spectra for the 0-1 absorption band region. The density of states function of the lowest exciton band, we observed in coronene has double peaks, as is expected for the one-dimensional model. The peak-to-peak energy separation gives the exciton a bandwidth of 490 cm-1. The bandwidth obtained (490 cm-1) is larger compared with the magnitude 370 cm-1 reported for coronene at 10 K. This difference can be explained in terms of the structural phase change that occurs at 140-180 K

2005-04-01

48

Density of states of the lowest exciton band and the exciton bandwidth in coronene single crystals  

Energy Technology Data Exchange (ETDEWEB)

The thermo-absorption spectra of coronene single crystals were investigated over the temperature range between 193 and 287 K. The density of states and the exciton bandwidth of the lowest exciton band were obtained from the thermo-absorption spectra for the 0-1 absorption band region. The density of states function of the lowest exciton band, we observed in coronene has double peaks, as is expected for the one-dimensional model. The peak-to-peak energy separation gives the exciton a bandwidth of 490 cm{sup -1}. The bandwidth obtained (490 cm{sup -1}) is larger compared with the magnitude 370 cm{sup -1} reported for coronene at 10 K. This difference can be explained in terms of the structural phase change that occurs at 140-180 K.

Totoki, R. [Department of Physics, Konan University, Okamoto, Kobe 658-8501 (Japan); Aoki-Matsumoto, T. [Department of Physics, Konan University, Okamoto, Kobe 658-8501 (Japan); Mizuno, K. [Department of Physics, Konan University, Okamoto, Kobe 658-8501 (Japan)]. E-mail: mizuno@konan-u.ac.jp

2005-04-15

49

Production of S-band Accelerating Structures  

CERN Document Server

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.

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

2004-01-01

50

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.)

1991-01-01

51

Rotational band structure in sup 128 Ce  

Energy Technology Data Exchange (ETDEWEB)

The high spin structure of the nucleus {sup 128}Ce has been investigated via the {sup 94}Mo ({sup 37}Cl, p2n) reaction at 158 MeV. New bands have been found. Alignments of h{sub 11/2} protons and h{sub 11/2} neutrons have been observed. (orig.).

Cata-Danil, G.; Bucurescu, D. (Grenoble-1 Univ., 38 (France). Inst. des Sciences Nucleaires Institutul de Fizica Atomica, Bucharest (Romania)); Nyako, B.M. (Grenoble-1 Univ., 38 (France). Inst. des Sciences Nucleaires Institute of Nuclear Research, Debrecen (Hungary)); Gizon, J.; Barci, V.; Gizon, A.; Andre, S.; Foin, C.; Genevey, J. (Grenoble-1 Univ., 38 (France). Inst. des Sciences Nucleaires); Curien, D.; Merdinger, J.C. (Strasbourg-1 Univ., 67 (France). Centre de Recherches Nucleaires); Hildingsson, L.; Klamra, W. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden)); Zolnai, L. (Institute of Nuclear Research, Debrecen (Hungary))

1991-06-01

52

Rotational band structure in128Ce  

Science.gov (United States)

The high spin structure of the nucleus128Ce has been investigated via the94Mo (37Cl, p2n) reaction at 158 MeV. New bands have been found. Alignments of h11/2 protons and h11/2 neutrons have been observed.

C?ta-Danil, G.; Nyakó, B. M.; Gizon, J.; Barci, V.; Bucurescu, D.; Curien, D.; Gizon, A.; André, S.; Foin, C.; Genevey, J.; Hildingsson, L.; Klamra, W.; Merdinger, J. Vc.; Zolnai, L.

1991-06-01

53

Band structure analysis in SiGe nanowires  

International Nuclear Information System (INIS)

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.

2012-06-05

54

Band Structure and Electrical Conductivity in Semiconductors  

Science.gov (United States)

In this experiment, we will, 1. understand how conductivity in semiconductors depends on carrier concentration and mobility, and how these depend on temperature, 2. distinguish between intrinsic and extrinsic temperature regimes and identify the applicable temperature range from an examination of measured data, 3. appreciate and utilize the advantages of the four-probe resistance measurement technique, 4. calculate the energy band gap for doped Si and pure Ge, 5. calculate the temperature dependent coefficient of the majority carriers, 6. through experimental realizations, appreciate a physical understanding of the band gap structure of semiconductors.

Khalid, Asma; Anwar, Muhammad S.; Zia, Wasif

2012-07-08

55

Band to band tunneling in III-V semiconductors: Implications of complex band structure, strain, orientation, and off-zone center contribution  

Science.gov (United States)

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

56

FAST TRACK COMMUNICATION: Bychkov Rashba dominated band structure in an In0.75Ga0.25As In0.75Al0.25As device with spin-split carrier densities of <1011 cm-2  

Science.gov (United States)

We demonstrate that a Bychkov-Rashba dominated band structure can be stabilized in a nominally undoped In0.75Ga0.25As-In0.75Al0.25As quantum well. The transport properties of this system have been measured at 1.7 and 4.2 K and the Rashba coefficient ? has been determined in enhancement and depletion modes with an insulated front gate. In enhancement mode, ? is 1 × 10-11 eV m with carrier densities ns between 1.4 and 1.9 × 1011 cm-2. In depletion mode, with ns12. The combination of the two spin-split subbands in ?xx can be separated using a magnetic field modulation technique where analogue d?xx/dB or d2?xx/dB2 signals are measured directly. The In0.75Ga0.25As-In0.75Al0.25As quantum well will have applications both in one-dimensional systems and in gate-induced two-dimensional electron gases where a dominant Bychkov-Rashba spin-splitting is required without the complications of an embedded strained InAs well and without a significant contribution from the interface asymmetry at the In0.75Al0.25As barriers.

Holmes, S. N.; Simmonds, P. J.; Beere, H. E.; Sfigakis, F.; Farrer, I.; Ritchie, D. A.; Pepper, M.

2008-11-01

57

Rotational band structure in 133Pr  

Science.gov (United States)

The level structure of the odd proton nucleus 133Pr has been investigated. Excited states up to spin (45/2) have been observed. The yrast band, built on a decoupled h11/2 proton, shows an up-bend at ??=0.43 MeV when two additional h11/2 protons align. Two positive parity side bands, based on the g7/2(5/2)+[413] proton configuration, are established with opposite signature. Both show a band crossing at ??c=0.27 MeV with a gain in alignment ~=8?, when two h11/2 protons decouple. This low crossing frequency is partly explained by a reduction in the proton pairing gap caused by the g7/2 proton.

Hildingsson, L.; Beausang, C. W.; Fossan, D. B.; Piel, W. F., Jr.

1986-06-01

58

Rotational band structure in /sup 133/Pr  

Energy Technology Data Exchange (ETDEWEB)

The level structure of the odd proton nucleus /sup 133/Pr has been investigated. Excited states up to spin (45/2) have been observed. The yrast band, built on a decoupled h/sub 11/2/ proton, shows an up-bend at h..omega.. = 0.43 MeV when two additional h/sub 11/2/ protons align. Two positive parity side bands, based on the g/sub 7/2/(5/2)/sup +/(413) proton configuration, are established with opposite signature. Both show a band crossing at h..omega../sub c/ = 0.27 MeV with a gain in alignment roughly-equal8h, when two h/sub 11/2/ protons decouple. This low crossing frequency is partly explained by a reduction in the proton pairing gap caused by the g/sub 7/2/ proton.

Hildingsson, L.; Beausang, C.W.; Fossan, D.B.; Piel, W.F. Jr.

1986-06-01

59

Continuity chords of bands and band structure of semiconducting compounds with TlSe-type structure  

International Nuclear Information System (INIS)

All the simple band representations of the space group D/sub 4h//sup 18/ are constructed. Using the concept of band representation and continuity chord, developed by Zak, it is shown that for semiconducting compounds with TlSe-type structure it is possible to extract some useful information about the character of localization of basic functions, belonging to the same band, i.e. in fact about the nature of the chemical bond responsible for the observed band structure. In particular, from the comparison with a calculated band structure of the ternary semiconducting compounds with TlSe-type structure, it is shown that the lower four valence bands correspond to s-states of chalcogen atoms. Two following valence bands correspond to s-states of three-valent cations. Then, a large group of ten valence bands is produced by p/sub z/-states of chalcogen atoms and p/sub x/-, p/sub y/-, p/sub z/-states of three-valent cations. (author)

1985-09-01

60

Bychkov-Rashba dominated band structure in an In0.75Ga0.25As-In0.75Al0.25As device with spin-split carrier densities of 11 cm-2  

International Nuclear Information System (INIS)

We demonstrate that a Bychkov-Rashba dominated band structure can be stabilized in a nominally undoped In0.75Ga0.25As-In0.75Al0.25As quantum well. The transport properties of this system have been measured at 1.7 and 4.2 K and the Rashba coefficient ? has been determined in enhancement and depletion modes with an insulated front gate. In enhancement mode, ? is 1 x 10-11 eV m with carrier densities ns between 1.4 and 1.9 x 1011 cm-2. In depletion mode, with ns11 cm-2, ? was reduced to 0.7 x 10-11 eV m. The wavefunction penetration into the In0.75Al0.25As barriers, i.e. the interface asymmetry, makes no contribution to ? in this system. We minimize the Zeeman energy spin-splitting in this high g-factor system by analysing only the Shubnikov-de Haas structure below 0.5 T, i.e. for Landau level filling factors >12. The combination of the two spin-split subbands in ?xx can be separated using a magnetic field modulation technique where analogue d?xx/dB or d2?xx/dB2 signals are measured directly. The In0.75Ga0.25As-In0.75Al0.25As quantum well will have applications both in one-dimensional systems and in gate-induced two-dimensional electron gases where a dominant Bychkov-Rashba spin-splitting is required without the complications of an embedded strained InAs well and without a significant contribution from the interface asymmetry at the In0.75Al0.25As barriers. (fast track communication)

2008-11-26

 
 
 
 
61

Rotational band structures in sup 154 Gd  

Energy Technology Data Exchange (ETDEWEB)

The N=90 rare earth nucleus {sup 154}Gd has been studied in the spin regime of I{le}26 {Dirac h} by using the reaction {sup 150}Nd({sup 9}Be,5n){sup 154}Gd at 55 MeV. Gamma-gamma coincidence and angular correlation data were obtained using the TESSA2 array. Two positive parity sequences have been extended to 26{sup +} and four negative parity structures have each been observed up to spins of I=22-24 {Dirac h}. The rotational structures observed in {sup 154}Gd are interpreted within the framework of the cranked shell model (CSM) in terms of quasiparticle excitations. The characteristics of the rotational band sequences and the band crossings that occur are compared with those in neighbouring nuclei and to the predictions of this model. (author).

Morrison, J.D.; Cranmer-Gordon, H.W.; Forsyth, P.D.; Howe, D.; Sharpey-Schafer, J.F. (Liverpool Univ. (UK). Oliver Lodge Lab.); Simpson, J. (Daresbury Lab. (UK)); Riley, M.A. (Niels Bohr Inst., Copenhagen (Denmark))

1989-12-01

62

High spin band structure in 200Tl  

International Nuclear Information System (INIS)

The nuclei of mass 200 region with a few particles and holes configuration near the 208Pb doubly magic shell closure has drawn considerable experimental and theoretical attention in the past few decades. In this context, band structure of Thallium isotopes (Z=81) with one proton hole to Z=82 shell closure are interesting to investigate as a function of angular momentum to understand the various angular momentum coupling of the valence particles or holes with the underlying core

2013-12-01

63

Band structure and hole scattering in p-PbTe  

International Nuclear Information System (INIS)

Mobility (u), thermoemf (?), and temperature dependences of the Hall constant (R) in p-PbTe were calculated. While calculating considered has been the effect of the free electron mass contribution to the density mass of states at the band bottom and to the effective width of the forbidden band in the framework of the Cane type model, which leads to the absence of a ''mirror property'' of conductivity and valency bands. It is shown that, while taking into account the temperature dependence of the Hall factor, the appearance of maximum on R(T) curves may be explained only with due account of the contribution from interband scattering. Taking account of acoustic and optical mechanisms of scattering, it becomes possible to explain satisfactorily the temperature and concentration dependences of u, the temperature dependences of R and concentration dependences of ? up to concentrations of about 1020 cm-3 at heavy band parameters of msub(h)=1msub(e), ?0.18 eV. Qualitative considerations of the shape of isoenergetic surfaces of a heavy band were undertaken to explain the concentration dependences of b=usub(h)/usub(l) and causes of deviation of experimental and calculated values of ?. It is shown that the above surfaces have a complicated structure, and the heavy band may be substantially nonparabolic

1979-03-01

64

Band structures of all polycrystalline forms of silicon dioxide  

Science.gov (United States)

The band structures and density of states of all polycrystalline forms of SiO2 with known crystal structures are calculated using a first-principles orthogonalized linear combination of atomic orbitals method. These include 4:2-coordinated polymorphs of ?-quartz, ?-quartz, ?-tridymite, ?-crystobalite, ?-crystobalite, keatite, coesite, and two idealized forms of ?-crystobalites, as well as the 6:3-coordinated stishovite. Linear relations between the band gaps and the average Si-O bond lengths and the minimum Si-O-Si angles are firmly established. The electronic structure of stishovite is found to be very much different from the 4:2-coordinated oxides and shows more covalency in the bonding character.

Li, Y. P.; Ching, W. Y.

1985-02-01

65

Electronic band structure of transparent conductor. Nb-doped anatase TiO2  

International Nuclear Information System (INIS)

We have investigated electronic band structure of a transparent conducting oxide, Nb-doped anatase TiO2 (TNO), by means of first-principles band calculations and photoemission measurements. The band calculations revealed that Nb 4d orbitals are strongly hybridized with Ti 3d ones to form a d-nature condition band, without impurity states in the in-gap region, resulting in high carrier density exceeding 1021 cm-3 and excellent optical transparency in the visible region. Furthermore, we confirmed that the results of valence band and core-level photoemission measurements are consistent with prediction by the present band calculations. (author)

2008-11-01

66

Electronic structure of periodic curved surfaces -- topological band structure  

CERN Document Server

Electronic band structure for electrons bound on periodic minimal surfaces is differential-geometrically formulated and numerically calculated. We focus on minimal surfaces because they are not only mathematically elegant (with the surface characterized completely in terms of "navels") but represent the topology of real systems such as zeolites and negative-curvature fullerene. The band structure turns out to be primarily determined by the topology of the surface, i.e., how the wavefunction interferes on a multiply-connected surface, so that the bands are little affected by the way in which we confine the electrons on the surface (thin-slab limit or zero thickness from the outset). Another curiosity is that different minimal surfaces connected by the Bonnet transformation (such as Schwarz's P- and D-surfaces) possess one-to-one correspondence in their band energies at Brillouin zone boundaries.

Aoki, H; Takeda, D; Morise, H

2001-01-01

67

Band structure and optical properties of opal photonic crystals  

CERN Document Server

A theoretical approach for the interpretation of reflectance spectra of opal photonic crystals with fcc structure and (111) surface orientation is presented. It is based on the calculation of photonic bands and density of states corresponding to a specified angle of incidence in air. The results yield a clear distinction between diffraction in the direction of light propagation by (111) family planes (leading to the formation of a stop band) and diffraction in other directions by higher-order planes (corresponding to the excitation of photonic modes in the crystal). Reflectance measurements on artificial opals made of self-assembled polystyrene spheres are analyzed according to the theoretical scheme and give evidence of diffraction by higher-order crystalline planes in the photonic structure.

Pavarini, E; Soci, C; Galli, M; Marabelli, F; Comoretto, D

2005-01-01

68

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

1977-01-01

69

Multiple band structures in {sup 169}Ta.  

Energy Technology Data Exchange (ETDEWEB)

Rotational structures in the {sup 169}Ta nucleus were studied via the {sup 124}Sn({sup 51}V, 6n) reaction. These data were obtained as a side channel of an experiment focusing on {sup 171}Ta, but the sensitivity provided by the Gammasphere spectrometer proved sufficient for a significant extension of the level scheme of this rare-earth nucleus. Over 170 new transitions and four new band structures were placed in {sup 169}Ta, including the intruder {pi}i{sub 13/2} structure. Linking transitions between all of the sequences were identified, and the relative excitation energies between the different configurations were determined for the first time. The rotational sequences were interpreted within the framework of the cranked shell model.

Hartley, D. J.; Mohr, W. H.; Vanhoy, J. R.; Riley, M. A.; Aguilar, A.; Teal, C.; Janssens, R. V. F.; Carpenter, M. P.; Hecht, A. A.; Lauritsen, T.; Moore, E. F.; Zhu, S.; Kondev, F. G.; Djongolov, M. K.; Danchev, M.; Riedinger, L. L.; Hagemann, G. B.; Sletten, G.; Chowdhury, P.; Tandel, S. K.; Ma, W. C.; Odegard, S. W.; U.S. Naval Academy; Florida State Univ.; Univ. of Tennessee; Niels Bohr Inst.; Univ. of Massachusetts; Mississippi State Univ.; Univ. of Oslo

2006-01-01

70

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

1991-01-01

71

Band-structure parameters by genetic algorithm  

Energy Technology Data Exchange (ETDEWEB)

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 H{umlt u}ckel 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} {ital 1996 The American Physical Society.}

Starrost, F.; Bornholdt, S.; Solterbeck, C.; Schattke, W. [Institut fuer Theoretische Physik, Universitaet Kiel, Leibnizstrasse 15, D-24118 Kiel (Germany)

1996-05-01

72

Band structure in strongly deformed nuclei  

International Nuclear Information System (INIS)

New information about rotational bands of strongly deformed nuclei as obtained through in-beam ?-spectroscopic studies as well as Coulomb excitation experiments shall be discussed. Most of the experimental results shall be interpreted within the cranking model considering the motion of independent particles in a rotating deformed potential. The relevant experimental results concern the second band crossing in yrast bands (backbending), the band crossing in side bands and the low-spin members of the s band. Experimental evidence that the backbending behaviour of the yrast bands in the Os nuclei is caused by the crossing of the g band with an isub(13/2) two-quasi-neutron band shall be provided. Furthermore a study of B(E2) values of transitions within and between rotational bands as obtained in a Coulomb excitation experiment shall be discussed. (orig.)

1980-01-01

73

Band structure in strongly deformed nuclei  

Science.gov (United States)

New information about rotational bands of strongly deformed nuclei as obtained through in-beam ?-spectroscopic studies as well as Coulomb excitation experiments shall be discussed. Most of the experimental results shall be interpreted within the cranking model considering the motion of independent particles in a rotating deformed potential. The relevant experimental results concern the second band crossing in yrast bands (backbending), the band crossing in side bands and the low-spin members of the s band. Experimental evidence that the backbending behaviour of the yrast bands in the Os nuclei is caused by the crossing of the g band with an i{13}/{2} two-quasi-neutron band shall be provided. Furthermore a study of B(E2) values of transitions within and between rotational bands as obtained in a Coulomb excitation experiment shall be discussed.

Lieder, Rainer M.

1980-09-01

74

Photonic Crystal Narrow Band Filters Using Biperiodic Structures  

Directory of Open Access Journals (Sweden)

Full Text Available In this study, we propose a new type of photonic crystal band-pass and band-stop filter based on biperiodic structure. Usually two types of photonic crystal band-pass filters are utilized in optical circuit. In the first one Fabry-Perot cavities are used while in the second one cavity-coupled waveguide are used. We optimize the second structure in this study. Then we show that by little changing in the band-pass structure, a band-stop filter is attained. Using Finite-Difference Time-Domain (FDTD method we achieve output efficiency over 98% for band-pass filter and below 3% for band-stop filter. Also we investigate filter tunability parameters which affecting central frequency of these filters. Further analysis shows that the central frequency of transmission band (stop band can be changed by altering the refractive index of bigger rods in biperiodic structure.

M. Djavid

2008-01-01

75

Elucidating the stop bands of structurally colored systems through recursion  

Science.gov (United States)

Interference is 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: specific bands of wavelengths (the stop bands) are perfectly reflected. Here, we present a minimal model for optical band structure in a periodic multilayer structure and solve it using recursion relations. The stop bands emerge in the limit of an infinite number of layers by finding the fixed point of the recursion. We compare to experimental data for various beetles, whose optical structure resembles the proposed model. Thus, using only the phenomenon of interference and the idea of recursion, we are able to elucidate the concept of band structure in the context of the experimentally observed high reflectance and iridescent appearance of structurally colored beetles.

Amir, Ariel; Vukusic, Peter

2013-04-01

76

Electronic band structure and intermolecular interaction in substituted thiophene polymorphs  

International Nuclear Information System (INIS)

Total energy calculations based on a density-functional tight-binding scheme have been performed on polymorphic modifications of various thiophene crystals. The electronic band structures exhibit a quasi-one-dimensional interaction in the triclinic crystals, while the monoclinic modifications show no dispersion over the whole Brillouin zone. The main interaction mechanism can be described as a d-? wave function overlap between sulfur and carbon. The strong intermolecular interaction may induce an interchain excitation, responsible for the different optical properties of the polymorphs

2001-06-15

77

Etched distributed Bragg reflectors as three-dimensional photonic crystals: photonic bands and density of states.  

Science.gov (United States)

The photonic band dispersion and density of states (DOS) are calculated for the three-dimensional (3D) hexagonal structure corresponding to a distributed Bragg reflector patterned with a 2D triangular lattice of circular holes. Results for the Si/SiO(2) and GaAs/Al(x)Ga(1-x)As systems determine the optimal parameters for which a gap in the 2D plane occurs and overlaps the 1D gap of the multilayer. The DOS is considerably reduced in correspondence with the overlap of 2D and 1D gaps. Also, the local density of states (i.e., the DOS weighted with the squared electric field at a given point) has strong variations depending on the position. Both results imply substantial changes of spontaneous emission rates and patterns for a local emitter embedded in the structure and make this system attractive for the fabrication of a 3D photonic crystal with controlled radiative properties. PMID:12366275

Pavarini, E; Andreani, L C

2002-09-01

78

Etched distributed Bragg reflectors as three-dimensional photonic crystals photonic bands and density of states  

CERN Document Server

The photonic band dispersion and density of states (DOS) are calculated for the three-dimensional (3D) hexagonal structure corresponding to a distributed Bragg reflector patterned with a 2D triangular lattice of circular holes. Results for the Si/SiO$_2$ and GaAs/AlGaAs systems determine the optimal parameters for which a gap in the 2D plane occurs and overlaps the 1D gap of the multilayer. The DOS is considerably reduced in correspondence with the overlap of 2D and 1D gaps. Also, the local density of states (i.e., the DOS weighted with the squared electric field at a given point) has strong variations depending on the position. Both results imply substantial changes of spontaneous emission rates and patterns for a local emitter embedded in the structure and make this system attractive for the fabrication of a 3D photonic crystal with controlled radiative properties.

Pavarini, E

2002-01-01

79

Electron density and carriers of the diffuse interstellar bands  

CERN Document Server

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 interstellar medium. The comparison of normalised equivalent width of 12 DIBs with the electron density shows that the DIBs equivalent width do not change with varying electron density. Therefore the DIBs carriers (1) can be observed only in one ionisation stage, or (2) the DIBs are arising in cloud regions (cores or cloud coronas) for which we can not determine the electron density.

Gnacinski, P; Galazutdinov, G A

2007-01-01

80

Band structures in doubly odd Rh98  

Science.gov (United States)

Excited states in the transitional doubly odd Rh98 nucleus were populated in the As75(Si28,2p3n) fusion-evaporation reaction using the 120-MeV incident Si28 beam. The subsequent de-excitations were investigated through in-beam ?-ray spectroscopic techniques using an early implementation phase of the Indian National Gamma Array (INGA) spectrometer equipped with 18 clover Ge detectors. The level structures in Rh98 have been established up to excitation energy ?10 MeV and angular momentum ˜23?. The previously reported level schemes are considerably modified and extended substantially. Significant expansion of the level scheme at low excitation energies stipulates that the previously reported 842-726-994-980-265 keV ?-transition cascade in Rh98 is not directly based on the ground state (T1/2 = 8.7 min). Tilted-axis cranking (TAC) shell-model calculations have been used to put the present level scheme of Rh98 in perspective. Level structures have been interpreted in terms of the rotational bands based on the ?p1/2??h11/2 [triaxiality parameter (?) = 25?], and ?f5/2??h11/2 proton-neutron configurations having moderate quadrupole deformation (?2 ? 0.13) and the admixtures. Excited band structures are based on the ?p1/2/f5/2??(g9/2)2??h11/2 configuration and the fully stretched [?p1/2??(h11/2)2??d5/2]13- configuration.

Kumar, S.; Sihotra, S.; Singh, K.; Singh, V.; Sandeep, Goswamy, J.; Singh, N.; Mehta, D.; Malik, S. S.; Palit, R.; Kumar, R.; Singh, R. P.; Muralithar, S.; Bhowmik, R. K.

2014-03-01

 
 
 
 
81

Temperature dependence of the electronic band structure of (111) surface Si  

International Nuclear Information System (INIS)

The temperature dependence of the electronic band structure of the (111) surface Si has been investigated.The self-consistent pseudopotential method within bounds of the layered superlattice model was used. The peculiarities of the temperature dependence of direct and indirect band gap and electronic density of states of the (111) surface Si are discussed in details

2011-01-01

82

Carrier-carrier relaxation kinetics in quantum well semiconductor structures with nonparabolic energy bands  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We describe carrier-carrier scattering dynamics in an inverted quantum well structure including the nonparabolic nature of the valance band. A solution of the semiconductor Bloch equations yields strong evidence to a large change in the temporal evolution of the carrier distributions compared to the case of parabolic bands. The nonparabolic bands and the consequent change in the density of states reduce considerably the degree of gain saturation while decreasing the time constant governing th...

Dery, H.; Tromborg, Bjarne; Eisenstein, G.

2006-01-01

83

Band structures of rare earth metals  

International Nuclear Information System (INIS)

Recent magnetic, optical and neutron scattering experiments made possible by the availability of high purity samples are providing increasingly detailed information about the electronic structure of the rare earth metals. The first calculations for the paramagnetics state of these fascinating metals have long served as a valuable heuristic model for understanding many earlier experimental results. It is expected that more accurate calculations for the magnetic ground state will be equally valuable in fostering the traditionally fruitful interaction between theory and experiment. Such calculations present a formidable challenge since they require a relativistic approach to spin polarization and a suitable treatment of the highly localized 4f-shell. The calculations can be guided by comparison with precise experimental results and by self-consistent calculations for non-magnetic metals with similar electronic structures. In this paper we review the present status of band structure calculations for the rare earth metals, and give details of a self-consistent, relativistic, ferromagneitc calculation for gadolinium

1978-09-07

84

XPS band emission and density of states of CoAl  

International Nuclear Information System (INIS)

An investigation of the electronic structure of an ordered equimolar CoAl alloy is discussed on the basis of a recently calculated self-consistent band structure and a measured XPS valence band spectrum. The valence band and core lines of CoAl by XPS are reported for the first time. Experimental and calculated values of the spectra have been compared

1981-11-01

85

Electronic structure and electron momentum density in TiSi  

Energy Technology Data Exchange (ETDEWEB)

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.

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

86

Electronic structure and electron momentum density in TiSi  

International Nuclear Information System (INIS)

We report the electron momentum density in titanium monosilicide using 241Am 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

2013-03-01

87

Creation of partial band gaps in anisotropic photonic-band-gap structures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The photonic-band-gap (PBG) structure composed of an anisotropic-dielectric sphere in uniform dielectric medium is studied by solving Maxwell’s equations using the plane-wave expansion method. In particular, for a uniaxial material with large principal refractive indices and sufficient anisotropy between them, the photonic band structures possess a full band gap in the whole Brillouin zone for a diamond lattice. Furthermore, in the 1/3 partial Brillouin zone where the Bloch wave vector has ...

1998-01-01

88

The band structure of 128Ba  

International Nuclear Information System (INIS)

The nucleus 128Ba has been studied using the 122Sn(12C,6n)-reaction at 106 MeV. The yrast band is observed up to Isup(?) = 20+ with a band crossing at (h/2?)?sub(c) = 0.41 MeV. The data is interpreted within the cranked shell model. (Auth.)

1984-01-01

89

The Band Structure of 128Ba  

Science.gov (United States)

The nucleus 128Ba has been studied using the 122Sn(12C, 6n)-reaction at 106 MeV. The yrast band is observed up to I? = 20+ with a band crossing at hslash?c = 0.41 MeV. The data is interpreted within the cranked shell model.

Hildingsson, L.; Hubert, Ph; Johnson, A.; Klamra, W.; Lindblad, Th

1984-01-01

90

Multiple band structures in 68Ge  

International Nuclear Information System (INIS)

Low- and high-spin states of 68Ge are investigated through in-beam ?-ray spectroscopy via the 58Ni(12C,2p), 63Cu(7Li,2n), and 52Cr(19F,p2n) reactions. A surprising richness of collective bands is observed in 68Ge including three even parity bands built on 8+ levels, the lower two of which are assigned as rotational aligned bands built on both proton and neutron (g/sub 9/2/)2 configurations, and three odd parity bands built on ? and ? configurations that include the g/sub 9/2/ orbit. Details of the multiple bands and other levels observed in 68Ge are presented. Rotation-aligned model calculations and interacting boson model calculations for 68Ge are also described

1981-01-01

91

Band structure derived properties of HfO2 from first principles calculations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electronic band structures and optical properties of cubic, tetragonal, and monoclinic phases of HfO2 are calculated using the first-principles linear augmented plane-wave method, within the density functional theory and generalized gradient approximation, and taking into account full-relativistic contributions. From the band structures, the electron- and hole-effective masses were obtained. Relativistic effects play an important role, which is reflected in the effective...

Garcia, Joelson Cott; Lino, A. T.; Scolfaro, L. M. R.; Leite, J. R.; Freire, V. N.; Farias, G. A.; Silva Jr, E. F. Da

2012-01-01

92

Graphene Nano ribbon Conductance Model in Parabolic Band Structure  

International Nuclear Information System (INIS)

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 nano ribbon (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

2010-01-01

93

Graphene Nanoribbon Conductance Model in Parabolic Band Structure  

Directory of Open Access Journals (Sweden)

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.

Mohammad Taghi Ahmadi

2010-01-01

94

Band gap and effective mass of multilayer BN/graphene/BN: van der Waals density functional approach  

Science.gov (United States)

Using the van der Waals density functional theory method (DFT-D2), we have investigated thickness dependent energy band gaps and effective masses of multilayer BN/graphene/BN structures by changing the stacking order. The band gap is substantially dependent on the stacking order. For instance, the calculated band gap in ABA stacking is about 150 meV, whereas it becomes 31 meV in ABC stacking. No significant thickness dependent band gap is observed in both ABA and ABC stackings although the band gap is gradually increasing with the BN thickness in ABA stacking. In addition, the effective mass is found to be strongly dependent on the stacking order. The effective mass in ABA stacking is much larger than that found in ABC stacking. On the other hand, the effective mass along K-M direction is smaller than that along K-? direction in ABA stacking. However, it is independent on the band direction in ABC stacking. We have found that the inclusion of van der Waals interaction alters thickness dependent band gap and effective mass of BN/graphene/BN multilayer systems compared with those found with standard density functional theory.

Hashmi, Arqum; Hong, Jisang

2014-05-01

95

Photoelectron diffraction and band structure effects in ARXPS from the valence bands of GeS  

International Nuclear Information System (INIS)

X-ray photoelectron spectra of the valence band region of GeS are measured in dependence on polar and azimuthal angle. The anisotropy of the valence band structures is due to both, influences of initial state wave function and photoelectron diffraction. By these means in addition to the symmetry character of initial states the atomic nature of different valence band peaks can also be explained. (author)

1985-11-01

96

Studies on energy band structure of NbC and NbN using DFT  

International Nuclear Information System (INIS)

Energy band structure of NbC and NbN are calculated using generalized gradient approximation (GGA) within density functional theory (DFT) including five high symmetry points W, L, ?, X and K. The lowest band corresponds to 2s band of non metal (C and N) atoms and the next lowest band is formed by 2p nonmetal. The decomposing points of t2g states (?25), eg states (?12) and C and N 2p states (?15) show interesting behavior different from earlier reports. (author)

2010-06-01

97

Band structure of the solid state - interpretation of the nature of the chemical bond in some transition metal compounds in terms of energy band structure calculations  

International Nuclear Information System (INIS)

The nature of chemical binding for some transition metal compounds (ScN, ScO, TiC, TiN, Tio, VC, VN, VO) with NaCl structure is discussed in terms of energy band structure calculations. The discussion is based on the wave functions and energy eigenvalues, as calculated by the 'Quasi self sonsistent APW method' as well as on the energy eigen values and eigen vectors resulting from the Slater-Koster LCAO-Tight binding interpolation scheme. The LCAO-TB l-like partial density of states can be used to analyse the valence bands. This analysis shows, that the deepest valence band has predominantly s-character. The following bands, which can be derived in essence from the atomic 2p states of the of the non metal are characterized not only by the partial p-like density of states but also by a substantial contribution from the d-like partial density of states, which is decreasing going from a particular Carbide to the corresponding Oxide. For the valence bands, which can be associated with the atomic 3d states of the metal, the density of states exhibits besides the partial d-density of states small contributions from the partial p-like density of states. The decomposition of the d-like partial density of states into an esub(g)-like and a tsub(2g)-like contribution is discussed. By analyzing the APW crystal wave functions the partial l-like charges inside each atomic sphere can be obtained. If the APW total charges within the atomic spheres are compared with the charges of a hypothetical crystal, which correspond to a superposition of the charge densities of the neutral atoms, a transfer of electrons from the metal to the non-metal sphere is found for all compounds under investigation. (orig.)

1975-11-01

98

Field modulation in bilayer graphene band structure  

Energy Technology Data Exchange (ETDEWEB)

Using an external electric field, one can modulate the band gap of Bernal stacked bilayer graphene by breaking the A-B-tilde symmetry. We analyze strain effects on the bilayer graphene using the extended Hueckel theory and find that reduced interlayer distance results in higher band gap modulation, as expected. Furthermore, above about 2.5 A interlayer distance, the band gap is direct, follows a convex relation with the electric field and saturates to a value determined by the interlayer distance. However, below about 2.5 A, the band gap is indirect, the trend becomes concave and a threshold electric field is observed, which also depends on the stacking distance. (fast track communication)

Raza, Hassan; Kan, Edwin C [School of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853 (United States)], E-mail: hr89@cornell.edu

2009-03-11

99

Band structure of /sup 128/Ba  

Energy Technology Data Exchange (ETDEWEB)

The nucleus /sup 128/Ba has been studied using the /sup 122/Sn(/sup 12/C,6n)-reaction at 106 MeV. The yrast band is observed up to Isup(..pi..) = 20/sup +/ with a band crossing at (h/2..pi..)..omega..sub(c) = 0.41 MeV. The data is interpreted within the cranked shell model.

Hildingsson, L.; Hubert, Ph.; Johnson, A.; Klamra, W.; Lindblad, Th. (Research Institute of Physics, Stockholm, Sweden)

1984-01-01

100

Rotational band structures in 129La  

International Nuclear Information System (INIS)

High spin states in the odd proton nucleus 129La have been investigated using the techniques of in-beam ?-ray spectroscopy. Nine rotational bands have been observed in 129La, seven for the first time. Various band crossings were observed at rotational frequencies in the range ? ? = 0.28-0.57 MeV. The data are mainly discussed within the framework of the cranked shell model. (author)

1992-01-01

 
 
 
 
101

Collective band structure in "6"6Zn  

International Nuclear Information System (INIS)

The collective nature of states in "6"6Zn has been studied by carrying out a deformed configuration mixing shell model calculation in 1psub(3/2)0fsub(5/2)1psub(1/2)0gsub(9/2) model space. An effective interaction obtained for this space by Kuo has been used. The collective structure for 2 positive-parity bands and 5 negative-parity bands is identified. A qualitative understanding of the backbending at the J = 6"+ state in the yrast positive-parity band is given in terms of the band crossing of the ground-state band and the more deformed excited band arising from 2p2h excitation to the gsub(9/2) orbit. Several high-spin members of the observed bands as well as in-band E2 transition strengths have been predicted. (orig.)

1981-11-30

102

High power density pulsed X-band heterojunction bipolar transistors  

Science.gov (United States)

Abrupt junction Npn AlGaAs/GaAs heterojunction bipolar transistors giving 10 GHz output power density of 6.2 mW/sq microns (18.7 W per mm emitter length) are reported. Pulse length was 300 nS with 33 percent duty cycle. Associated gain and power-added efficiency were 5.0 dB and 46 percent, respectively. Associated peak power was 561 mW. Peak and average powers were measured as a function of pulse length at fixed duty cycle and found to increase sharply from CW values for pulse lengths less than 1000 nS.

Adlerstein, M. G.; Zaitlin, M. P.; Flynn, G.; Hoke, W.; Huang, J.

1991-01-01

103

Conductance and density of states anomalies as resonances of energy bands in disordered coupled chains  

CERN Document Server

We show that off-diagonal nearest neighbor disorder in quasi-one-dimensional single particle tight-binding coupled chains leads to anomalies in the density of states and in the mean conductance, that can be interpreted as due to specific resonances of the band structure of the perfect system underlying the disordered one. We demonstrate that this phenomenology may appear not necessarily at the energy E=0 as reported so far in the literature and we show that also the even-odd chain number effect on the mean conductance is ruled by the same resonances. For different cases we provide a series expansion for the resonant contribution to the mean conductance. These expansions allow to make predictions well verified numerically.

Alloatti, L

2006-01-01

104

Multi-band, highly absorbing, microwave metamaterial structures  

Science.gov (United States)

A further example of multi-band absorption using ultra-thin, polarization-insensitive, wide-angled metamaterial absorbers that operate in multi-frequency bands within the microwave regime is presented in this work. The basic structure geometry is utilised to create multi-band highly absorbing structures by incorporating the scalability property of the metamaterials. Simulation results verify the structure's ability for high absorption. The multi-band absorbers are promising candidates as absorbing elements in scientific and technical applications because of its multi-band absorption, polarization insensitivity, and wide-angle response. Finally, the current distributions for those structures are presented to gain a better insight into the physics behind the multiple absorption mechanism.

Kollatou, T. M.; Dimitriadis, A. I.; Assimonis, S. D.; Kantartzis, N. V.; Antonopoulos, C. S.

2014-05-01

105

Band structure of CdTe-ZnTe superlattice  

International Nuclear Information System (INIS)

We perform an empirical tight-binding band structure calculation for the superlattice CdTe-ZnTe. We examine the effect of strain and valence band offset on it. We find that the 6% lattice mismatch causes strain to play an important role. The trend of the superlattice band gap for all widths considered is to decrease as the valence band offset increases. We have found two interface states not reported before. This is our main result. They lie in energy about 100 meV above the valence band edge. Since this energy is about equal to the difference between our calculated superlattice band gap and the value reported experimentally, we claim that optical absorption is measuring the transitions from these interface states to the conduction band. New more detailed experiments could settle this interesting problem. (author). 8 refs, 2 figs, 2 tabs

1988-01-01

106

The band energy structure of RbKSO4 crystals  

Directory of Open Access Journals (Sweden)

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.

O.V.Bovgyra

2007-01-01

107

Electron Transport and Band Structure in Phosphorus-Doped Polycrystalline Silicon Films  

Energy Technology Data Exchange (ETDEWEB)

We study transport mechanisms, effective mass, and band structure by measuring the resistivity, Hall, and Seebeck and Nernst coefficients in heavily phosphorus-doped polycrystalline silicon films made by thermal crystallization of amorphous silicon. We observe a change in transport mechanism which results in an increase in electron mobility from 10% to 80% of the single-crystal silicon mobility as the carrier concentration increases from 10{sup 19} to 10{sup 20} cm{sup -3}. Our measurements of effective mass at the Fermi level indicate that as the carrier concentration increases, there is a shift from impurity-band transport to conduction-band transport, and that the electron effective mass is lower in the impurity band than in the conduction band of Si. The shift to conduction-band transport improves electron mobility with carrier density by improving intragrain carrier mean free path lengths and relaxation times.

Young, D. L.; Branz, H. M.; Liu, F.; Reedy, R.; To, B.; Wang, Q.

2009-01-01

108

Cluster structure and deformed bands in the 38Ar nucleus  

International Nuclear Information System (INIS)

The structure of the 38Ar nucleus is investigated by the 34S+? orthogonality condition model (OCM). The energy spectra, electromagnetic transitions and ? spectroscopic factors are calculated. The excited states can be grouped into several bands according to the leading configurations of their wave functions, and the structures of the bands are discussed. The first excited K?=0+ band is found to be predominantly 34S+? cluster states. It is also shown that the observed energies and E2 transitions of the band are well reproduced by the model. The existence of a negative-parity doublet band of the band is also predicted. The strength of the ?-cluster states is shown to be spread over several levels due to mixing of shell-model states and various ?-cluster states

2013-06-17

109

Atomic structure of amorphous shear bands in boron carbide  

Science.gov (United States)

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

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

2013-09-01

110

Band structure of metal diboride AlB2 under high pressure  

International Nuclear Information System (INIS)

The band structure, density of states (DOS), electronic charge distribution and superconductivity of Aluminium diboride (AlB2) as a function of pressure are investigated. The normal pressure, band structure, DOS and superconducting transition temperature of AlB2 agree well with the previous calculations. The high pressure band structure exhibits significant deviations from the normal pressure band structure. It is found that, the charge transfer from s state to p and d states will cause superconductivity in AlB2. According to the present calculation, at normal pressure, the superconducting transition of AlB2 occurs at 13.57 K which is comparable with the previous theoretical observation of 9K. On further increase of pressure, Tc increases considerably and its maximum value may exceed 32K (at .683 Mbar). The high pressure Tc values are reported for the first time and this metal diboride (AlB2) is identified as pressure induced superconductors. (author)

2007-12-27

111

Band structures and shape coexistence in {sup 187}Pt  

Energy Technology Data Exchange (ETDEWEB)

High-spin states in {sup 187}Pt have been studied by means of {gamma}-ray spectroscopy techniques. Known bands have been significantly extended and new bands have been found. The band structures are discussed in the framework of the cranking model and negative-parity states are compared with calculations performed with a semi-microscopic axial-rotor plus one-quasiparticle coupling model. Shape coexistence is observed from low excitation energy. (orig.)

Hojman, D. [Comision Nacional de Energia Atomica, Departamento de Fisica, Buenos Aires (Argentina); CONICET, Buenos Aires (Argentina); Cardona, M.A. [Comision Nacional de Energia Atomica, Departamento de Fisica, Buenos Aires (Argentina); CONICET, Buenos Aires (Argentina); Universidad Nacional de San Martin, Buenos Aires (Argentina); Roussiere, B.; Sauvage, J. [IN2P3/CNRS/Universite Paris-Sud, Institut de Physique Nucleaire, Orsay (France); Riley, M.A.; Tabor, S.L.; Hoffman, C.R.; Aguilar, A.; Cluff, W.T.; Hinners, T.; Lagergren, K.; Lee, S.; Perry, M.; Pipidis, A.; Tripathi, V. [Florida State University, Department of Physics, Tallahassee, Florida (United States)

2012-06-15

112

Band structures and shape coexistence in 187Pt  

International Nuclear Information System (INIS)

High-spin states in 187Pt have been studied by means of ?-ray spectroscopy techniques. Known bands have been significantly extended and new bands have been found. The band structures are discussed in the framework of the cranking model and negative-parity states are compared with calculations performed with a semi-microscopic axial-rotor plus one-quasiparticle coupling model. Shape coexistence is observed from low excitation energy. (orig.)

2012-06-01

113

Band structures in {sup 123}I  

Energy Technology Data Exchange (ETDEWEB)

Excited states of {sup 123}I were populated via the {sup 116}Cd({sup 14}N, {alpha}3n) reaction at 65 MeV. The resultant {gamma}-rays were detected using standard {gamma}-ray spectroscopic techniques with the NORDBALL detector array. Two previously known positive-parity {delta}I = 2 sequences have been extended up to 31/2{sup +} and 41/2{sup +}. In addition, a number of {delta}I = 1 transitions linking the two {delta}I = 2 sequences have been observed. It is suggested that both {delta}I = 2 sequences are based on a common configuration. This {delta}I = 1 band is proposed to be built predominantly on the g{sub 7/2}[404]7/2{sup +} 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 {delta}I = 1 rotational band built on the prolate g{sub 9/2}[404]9/2{sup +} orbital has also been extended to higher spins. Another previously identified but weakly populated {delta}I = 1 band is confirmed and is proposed to be built on the d{sub 5/2}[413]5/2{sup +} configuration with the ground state of {sup 123}I as the bandhead.

Wang, S-Y [Department of Physics, Jilin University, Changchun 130021 (China); Komatsubara, T [Institute of Physics and Tandem Accelerator Center, University of Tsukuba, Ibaraki 305 (Japan); Ma, Y-J [Department of Physics, Jilin University, Changchun 130021, People' s Republic of (China); Furuno, K [Institute of Physics and Tandem Accelerator Center, University of Tsukuba, Ibaraki 305 (Japan); Zhang, Y-H [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Liu, Y-Z [Department of Physics, Jilin University, Changchun 130021, People' s Republic of (China); Hayakawa, T [Institute of Physics and Tandem Accelerator Center, University of Tsukuba, Ibaraki 305 (Japan); Mukai, J [Institute of Physics and Tandem Accelerator Center, University of Tsukuba, Ibaraki 305 (Japan); Iwata, Y [Department of Physics, Faculty of Science, Hiroshima University, Hiroshima 724 (Japan); Morikawa, T [Department of Physics, Faculty of Science, Kyushu University, Fukuoka 812 (Japan); Hagemann, G B [Niels Bohr Institute, Tandem Accelerator Laboratory, Risoe DK-4000, Roskilde (Denmark); Sletten, G [Niels Bohr Institute, Tandem Accelerator Laboratory, Risoe DK-4000, Roskilde (Denmark); Nyberg, J [Niels Bohr Institute, Tandem Accelerator Laboratory, Risoe DK-4000, Roskilde (Denmark); Jerrestam, D [Niels Bohr Institute, Tandem Accelerator Laboratory, Risoe DK-4000, Roskilde (Denmark); Jensen, H J [Niels Bohr Institute, Tandem Accelerator Laboratory, Risoe DK-4000, Roskilde (Denmark); Espino, J [Niels Bohr Institute, Tandem Accelerator Laboratory, Risoe DK-4000, Roskilde (Denmark); Gascon, J [Niels Bohr Institute, Tandem Accelerator Laboratory, Risoe DK-4000, Roskilde (Denmark); Gjoerup, N [Niels Bohr Institute, Tandem Accelerator Laboratory, Risoe DK-4000, Roskilde (Denmark); Cederwall, B [Manne Siegbahn Institute of Physics, S-10405 Stockholm (Sweden); Tjoem, P O [Department of Physics, University of Oslo (Norway)

2006-03-01

114

Investigation of the XPS valence band structure from Sn chalcogenides  

International Nuclear Information System (INIS)

XPS valence band spectra reflect the electronic density of states weighted with cross-sections. The spectra will give additional information about the symmetry of the electron wave function, if they are measured in dependence on the electron emission angles. Valence band spectra of SnS, SnSe, SnTe, and SnS_2 are measured partly in dependence on the polar angle THETA. These measurements allow an identification of the symmetry of valence orbitals from intensity variations of the valence band maxima. (author)

1981-12-01

115

Electronic band structure and linear optical properties of paraelectric KIO3  

International Nuclear Information System (INIS)

The electronic energy band structure, partial (PDOS) and total density of states (DOS), and linear optical properties of the paraelectric KIO3 single crystal are calculated using density functional theory (DFT) in its local density approximation (LDA). The calculated band structure for paraelectric KIO3 indicates that the crystal has a direct bandgap. Using LDA and generalized gradient approximation (GGA), structural optimization has been performed. The optical spectra of the paraelectric KIO3 in the photon energy range up to 30 eV are investigated under the scissor approximation. The real and imaginary parts of the frequency-dependent linear dielectric function, as well as related quantities such as energy-loss function, refractive index and effective number of valence electrons, are calculated. The calculated structural optimization and bandgap of the paraelectric KIO3 have been compared with experimental data and have been found to be in good agreement with the experimental results.

2009-03-25

116

Electronic band structure and linear optical properties of paraelectric KIO{sub 3}  

Energy Technology Data Exchange (ETDEWEB)

The electronic energy band structure, partial (PDOS) and total density of states (DOS), and linear optical properties of the paraelectric KIO{sub 3} single crystal are calculated using density functional theory (DFT) in its local density approximation (LDA). The calculated band structure for paraelectric KIO{sub 3} indicates that the crystal has a direct bandgap. Using LDA and generalized gradient approximation (GGA), structural optimization has been performed. The optical spectra of the paraelectric KIO{sub 3} in the photon energy range up to 30 eV are investigated under the scissor approximation. The real and imaginary parts of the frequency-dependent linear dielectric function, as well as related quantities such as energy-loss function, refractive index and effective number of valence electrons, are calculated. The calculated structural optimization and bandgap of the paraelectric KIO{sub 3} have been compared with experimental data and have been found to be in good agreement with the experimental results.

Erdinc, Bahattin; Akkus, Harun [Physics Department, Yuzuncu Yil University, 65080 Van (Turkey)], E-mail: bahattinerdinc@yyu.edu.tr

2009-03-25

117

Development of the W-band density profile and fluctuation reflectometer on EAST  

Energy Technology Data Exchange (ETDEWEB)

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.

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

118

Development of the W-band density profile and fluctuation reflectometer on EAST  

International Nuclear Information System (INIS)

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

2013-11-01

119

Electronic band structure and photoemission spectra of graphene on silicon substrate  

Science.gov (United States)

Synergizing graphene on silicon based nanostructures is pivotal in advancing nano-electronic device technology. A combination of molecular dynamics and density functional theory has been used to predict the electronic energy band structure and photo-emission spectrum for graphene-Si system with silicon as a substrate for graphene. The equilibrium geometry of the system after energy minimization is obtained from molecular dynamics simulations. For the stable geometry obtained, density functional theory calculations are employed to determine the energy band structure and dielectric constant of the system. Further the work function of the system which is a direct consequence of photoemission spectrum is calculated from the energy band structure using random phase approximations.

Javvaji, Brahmanandam; Ravikumar, Abhilash; Shenoy, B. M.; Roy Mahapatra, D.; Rahman, M. R.; Hegde, G. M.

2014-03-01

120

Structure of nearly degenerate dipole bands in 108Ag  

International Nuclear Information System (INIS)

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

2013-08-09

 
 
 
 
121

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-08-09

122

Structure of nearly degenerate dipole bands in 108Ag  

Science.gov (United States)

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.

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

123

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.

2013-01-23

124

Quasiparticle band structure of rocksalt-CdO determined using maximally localized Wannier functions.  

Science.gov (United States)

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. PMID:23235114

Dixit, H; Lamoen, D; Partoens, B

2013-01-23

125

First-Principles Study of the Band Gap Structure of Oxygen-Passivated Silicon Nanonets  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract A net-like nanostructure of silicon named silicon nanonet was designed and oxygen atoms were used to passivate the dangling bonds. First-principles calculation based on density functional theory with the generalized gradient approximation (GGA were carried out to investigate the energy band gap structure of this special structure. The calculation results show that the indirect–direct band gap transition occurs when the nanonets are properly designed. This band gap transition is dominated by the passivation bonds, porosities as well as pore array distributions. It is also proved that Si–O–Si is an effective passivation bond which can change the band gap structure of the nanonets. These results provide another way to achieve a practical silicon-based light source.

Lin Linhan

2009-01-01

126

Structure of rotational bands in {sup 253}No  

Energy Technology Data Exchange (ETDEWEB)

In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the {sup 253} No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the 9/2{sup -}[734]{sub {nu}} ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work. (orig.)

Herzberg, R.D.; Moon, S.; Butler, P.A.; Page, T.; Amzal, N.; Bastin, J.E.; Cocks, J.F.C.; Darby, I.G.; Gray-Jones, C.; Hammond, N.J.; Herzberg, A.; Humphreys, R.D.; Jones, G.D.; Page, R.D.; Page, T.; Pritchard, A. [University of Liverpool, Oliver Lodge Laboratory, Liverpool (United Kingdom); Eeckhaudt, S.; Greenlees, P.T.; Dorvaux, O.; Jones, P.M.; Julin, R.; Juutinen, S.; Kankaanpaeae, H.; Kettunen, H.; Kuusiniemi, P.; LeCoz, Y.; Leino, M.; Leppaenen, A.P.; Muikku, M.; Nieminen, P.; Nyman, M.; Rahkila, P.; Sandzelius, M.; Saren, J.; Scholey, C.; Trzaska, W.H.; Uusitalo, J. [University of Jyvaeskylae, Department of Physics, Jyvaeskylae (Finland); Afanasjev, A.V. [Mississippi State University, Department of Physics and Astronomy, Mississippi, MS (United States); Becker, F.; Houry, M.; Huerstel, A.; Korten, W.; Lucas, R.; Theisen, C. [DAPNIA/SPhN CEA-Saclay, Saclay (France); Bender, M. [Universite Bordeaux and CNRS/IN2P3, Centre d' Etudes Nucleaires de Bordeaux Gradignan, Bordeaux (France); Bruyneel, B.; Reiter, P.; Wiens, A. [Universitaet zu Koeln, Institut fuer Kernphysik, Koeln (Germany); Eskola, K. [University of Helsinki, Department of Physics, Helsinki (Finland); Gerl, J.; Hessberger, F.; Schlegel, C.; Wollersheim, H.J. [GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt (Germany); Grahn, T.; Pakarinen, J. [University of Liverpool, Oliver Lodge Laboratory, Liverpool (United Kingdom); University of Jyvaeskylae, Department of Physics, Jyvaeskylae (Finland); Hauschild, K. [IN2P3-CNRS, CSNSM, Orsay Campus (France); Heenen, P.H. [Universite Libre de Bruxelles, Service de Physique Nucleaire Theorique, Bruxelles (Belgium); Helariutta, K. [University of Jyvaeskylae, Department of Physics, Jyvaeskylae (Finland); University of Helsinki, Department of Physics, Helsinki (Finland); Khoo, T.L.; Lister, C.J. [Argonne National Laboratory, Argonne, IL (United States)

2009-12-15

127

Band structure characteristics of T-square fractal phononic crystals  

International Nuclear Information System (INIS)

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

2013-03-01

128

Correlated band structure of 3d2 vanadates  

International Nuclear Information System (INIS)

We study the correlated band structure and the momentum-resolved spectra for 3d2 vanadates, like La O3 and YVO3, using a combination of a first-principles technique and dynamical mean-field theory with a Monte Carlo impurity solver. The self-energy for the effective 3d bands is calculated using maximum-entropy spectral analysis of the Monte Carlo results and a self-consistent procedure. We use this self-energy to calculate the full momentum-resolved spectrum and the correlated band structure, which we compare to available spectroscopy experimental results. We also discuss the effects of the lattice distortions and chemistry

2008-02-25

129

Locally resonant periodic structures with low-frequency band gaps  

Science.gov (United States)

Presented in this paper are study results of dispersion relationships of periodic structures composited of concrete and rubber, from which the frequency band gap can be found. Two models with fixed or free boundary conditions are proposed to approximate the bound frequencies of the first band gap. Studies are conducted to investigate the low-frequency and directional frequency band gaps for their application to engineering. The study finds that civil engineering structures can be designed to block harmful waves, such as earthquake disturbance.

Cheng, Zhibao; Shi, Zhifei; Mo, Y. L.; Xiang, Hongjun

2013-07-01

130

Active Narrow-Band Vibration Isolation of Large Engineering Structures  

Science.gov (United States)

We present a narrow-band tracking control method using a variant of the Least Mean Squares (LMS) algorithm to isolate slowly changing periodic disturbances from engineering structures. The advantage of the algorithm is that it has a simple architecture and is relatively easy to implement while it can isolate disturbances on the order of 40-50 dB over decades of frequency band. We also present the results of an experiment conducted on a flexible truss structure. The average disturbance rejection achieved is over 40 dB over the frequency band of 5 Hz to 50 Hz.

Rahman, Zahidul; Spanos, John

1994-01-01

131

Density functional theory and electronic structure  

International Nuclear Information System (INIS)

The paper presents an overview of the density functional theory and provides a brief appraisal of the latest developments of the theory. Particular emphasis is placed on the understanding of the electronic structure of materials via the density functional theory. 37 refs, 1 tab

1987-01-01

132

X-band RF structure thermal analysis and tests  

International Nuclear Information System (INIS)

The design of X-band multi-cell RF structures for particle accelerators requires an accurate estimation of the sensitivity to the mechanical deformations induced by the surface power loss on the metallic walls. The prediction of these effects is important for conceiving a tuning strategy that assures the correct structure operation when integrated into the accelerator complex. An experimental technique is proposed for preliminary testing of the mechanical deformations caused by a thermal load that can generate in the RF cavity a temperature gradient profile as close as possible to the real one induced by the electromagnetic power loss. Because we want to find a method that can be easily and cheaply implemented in the laboratory, a thermal radiator with uniform heating power density, placed on the axis of the RF cavity, has been chosen as heating source. A multi-physics finite-element code (ANSYS) has allowed comparing the measured temperature gradients with the computed ones. The good agreement validates the application of the code, which has been extended to the joint solution of the electromagnetic and thermal problem. Thus the sensitivity to deformations can be directly evaluated

2007-07-21

133

Area Efficient Interpolator Using Half-Band Symmetric Structure  

Directory of Open Access Journals (Sweden)

Full Text Available 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 namely Direct Form FIR Polyphase, Nyquist Filter and Half-Band Low pass Filter. The developed interpolator has been compared for performance and implementation cost using Mat Lab. The results show that the performance of all the designs is almost similar, but cost variation is very high. The Half-Band structure shows 52% of reduction in multipliers as compared to Direct Form FIR Polyphase structure. The Half-Band structure is further implemented in Transposed Structure and Symmetric Structure. The Half-Band symmetric structure shows 27% reduction in multipliers as compared to Direct Form FIR Polyphase, Nyquist Filter and Half-Band Low pass Filter structure to provide cost effective solution for wireless applications.

Rajesh Mehra

2013-01-01

134

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)

1972-01-01

135

Photonic band gap of superconductor-medium structure: Two-dimensional triangular lattice  

Science.gov (United States)

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.

Liu, Wan-guo; Pan, Feng-ming; Cai, Li-wei

2014-05-01

136

Band Structure and Optical Properties of Ordered AuCu3  

DEFF Research Database (Denmark)

The optical spectra of ordered AuCu3 have been measured at low temperatures by a direct ellipsometric technique. We find several structural elements above the absorption edge as well as in the infrared. The measured spectra are interpreted in terms of the interband absorption calculated from an ab initio band structure obtained by the relativistic linear muffin-tin orbitals method. The band calculation reveals that ordered AuCu3 has distinct copper and gold d bands positioned in and hybridizing with an s band common to copper and gold. The calculated state density is found to be in good agreement with experiment. The Fermi surface is presented and is found to originate mainly in copper 4s and 4p states.

Skriver, Hans Lomholt; Lengkeek, H. P.

1979-01-01

137

A DFT study on structural, vibrational properties, and quasiparticle band structure of solid nitromethane  

Science.gov (United States)

We report a detailed theoretical study of the structural and vibrational properties of solid nitromethane using first principles density functional calculations. The ground state properties were calculated using a plane wave pseudopotential code with either the local density approximation, the generalized gradient approximation, or with a correction to include van der Waals interactions. Our calculated equilibrium lattice parameters and volume using a dispersion correction are found to be in reasonable agreement with the experimental results. Also, our calculations reproduce the experimental trends in the structural properties at high pressure. We found a discontinuity in the bond length, bond angles, and also a weakening of hydrogen bond strength in the pressure range from 10 to 12 GPa, picturing the structural transition from phase I to phase II. Moreover, we predict the elastic constants of solid nitromethane and find that the corresponding bulk modulus is in good agreement with experiments. The calculated elastic constants show an order of C11> C22 > C33, indicating that the material is more compressible along the c-axis. We also calculated the zone center vibrational frequencies and discuss the internal and external modes of this material under pressure. From this, we found the softening of lattice modes around 8-11 GPa. We have also attempted the quasiparticle band structure of solid nitromethane with the G0W0 approximation and found that nitromethane is an indirect band gap insulator with a value of the band gap of about 7.8 eV with G0W0 approximation. Finally, the optical properties of this material, namely the absorptive and dispersive part of the dielectric function, and the refractive index and absorption spectra are calculated and the contribution of different transition peaks of the absorption spectra are analyzed. The static dielectric constant and refractive indices along the three inequivalent crystallographic directions indicate that this material has a considerable optical anisotropy.

Appalakondaiah, S.; Vaitheeswaran, G.; Lebègue, S.

2013-05-01

138

Measured energy-momentum densities of the valence band of aluminium  

International Nuclear Information System (INIS)

The energy-resolved momentum densities of the valence band of a thin polycrystalline aluminium film have been measured using electron momentum spectroscopy (EMS). The spectrometer used for these measurements has estimated energy and momentum resolutions of 0.9 eV and 0.10 atomic units respectively. The valence band of aluminium was clearly resolved, resembling very closely that of a free-election parabola. The measurement has been compared to linear muffin-tin orbital (LMTO) calculations for spherically averaged crystalline aluminium. Comparison has also been made between the experiment and Monte-Carlo simulations which take into account additional elastic and inelastic scattering events not considered in the LMTO calculations. The final agreement obtained between the measurement and theory for the dispersion and relative intensities of the aluminium valence band is excellent when lifetime broadening of the band is allowed for. 21 refs., 11 figs

1996-01-01

139

Band structure of fcc-C60 solid state crystal study  

Directory of Open Access Journals (Sweden)

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.

S Javanbakht

2009-09-01

140

Structural evolution of the intruder band in 118Sn  

International Nuclear Information System (INIS)

Excited states of the positive-parity intruder band in 118Sn have been studied via the 116Cd(7Li, 1p4n) reaction at 7Li energy of 48 MeV using techniques of in-beam ?-ray spectroscopy. This intruder band has been observed up to 7187 keV with spin (16+). The structural evolution of this intruder band with increasing angular momentum has been discussed in terms of the aligned angular momentum and the ratio of the E-Gamma Over Spin (E-GOS) curve. (authors)

2009-10-01

 
 
 
 
141

Band structures and localization properties of aperiodic layered phononic crystals  

International Nuclear Information System (INIS)

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

2012-03-15

142

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)

1976-01-01

143

Effect of density of state on isotope effect exponent of two-band superconductors  

Energy Technology Data Exchange (ETDEWEB)

The exact formula of T {sub c}'s equation and the isotope effect exponent of two-band s-wave superconductors in weak-coupling limit are derived by considering the influence of two kinds of density of state: constant and van Hove singularity. The paring interaction in each band consisted of two parts: the electron-phonon interaction and non-electron-phonon interaction are included in our model. We find that the interband interaction of electron-phonon show more effect on isotope exponent than the intraband interaction and the isotope effect exponent with constant density of state can fit to experimental data, MgB{sub 2} and high-T {sub c} superconductor, better than van Hove singularity density of state.

Udomsamuthirun, P. [Department of Physics, Faculty of Science, Srinakharinwirot University, Sukumvit 23, Bangkok 10110 (Thailand)]. E-mail: udomsamut55@yahoo.com; Kumvongsa, C. [Department of Basic Science, School of Science, The University of the Thai Chamber of Commerce, Dindaeng, Bangkok 10400 (Thailand); Burakorn, A. [Department of Physics, Faculty of Science, Srinakharinwirot University, Sukumvit 23, Bangkok 10110 (Thailand); Changkanarth, P. [Department of Physics, Faculty of Science, Srinakharinwirot University, Sukumvit 23, Bangkok 10110 (Thailand); Yoksan, S. [Department of Physics, Faculty of Science, Srinakharinwirot University, Sukumvit 23, Bangkok 10110 (Thailand)

2005-09-15

144

Density Banding in Coral Skeletons: A Biotic Response to Sea Surface Temperature?  

Science.gov (United States)

Density bands in the CaCO3 (aragonite) skeleton of scleractinian corals are commonly used as chronometers, where crystalline couplets of high and low density bands represent the span of one year. This provides a sensitive reconstructive tool for paleothermometry, paleoclimatology and paleoecology. However, the detailed mechanisms controlling aragonite nucleation and crystallization events and the rate of skeletal growth remain uncertain. The organic matrix, composed of macromolecules secreted by the calicoblastic ectoderm, is closely associated with skeletal precipitation and is itself incorporated into the skeleton. We postulate that density banding is primarily controlled by changes in the rate of aragonite crystal precipitation mediated by the coral holobiont response to changes in sea surface temperature (SST). To test this hypothesis, data were collected from coral skeleton-tissue biopsies (2.5 cm in diameter) extracted from four species of Montastraea growing on the fringing reef tract of Curacao, Netherlands Antilles (annual mean variation in SST is 29° C in mid-September to 26° C in late February). Samples were collected in the following three contextual modes: 1) at two sites (Water Plant and Playa Kalki) along a lateral 25 km spatial transect; 2) across a vertical bathymetric gradient from 5 to 15 m water depth at each site; and 3) at strategic time periods spanning the 3° C annual variations in SST. Preliminary results indicate that skeletal density banding is also expressed in the organic matrix, permitting biochemical characterization and correlation of the organic matrix banding to the skeletal banding. In addition, both surficial and ectodermal mucins were characterized in terms of total protein content, abundance and location of their anionic, cationic, and neutral macromolecular constituents. Furthermore, the ratio of mucocytes in the oral ectoderm to gastrodermal symbiotic zooxanthellae has permitted estimates of seasonal carbon allocation by the coral holobiont. Our nanometer-scale optical analyses of crystal morphology, arrangement, and densities have revealed consistent changes between high and low skeletal density bands. Mass spectrometry, newly developed immunohistochemical staining, fluorescence and polarized light microscopy are in progress to further quantify and model these observations.

Hill, C. A.; Oehlert, A. M.; Piggot, A. M.; Yau, P. M.; Fouke, B. W.

2008-12-01

145

Collective band structures in the ?-soft nucleus 135Nd  

Science.gov (United States)

The low-lying band structure of 135Nd has been extended to higher spins using the 112Cd(27Al,p3n?)135Nd and 116Sn(24Mg,2p3n?)135Nd reactions. Two distinct high-spin structures have been identified. The ?J=1 band built on the ?h11/2[514](9/2)- ground state was observed to have a band crossing at J?=(25/2)-. This band crossing is associated with a loss of the moderate signature splitting found below the backbend. Cranked-shell model calculations suggest that this structure involves the alignment of a pair of h11/2 protons and that the loss of signature splitting can be attributed to a shape change from a triaxial shape at low spins to a prolate axial shape above the backbend. A second ?J=1 band structure with no signature splitting was observed to be built on a J?=(17/2)(+) state at 1954 keV. Values for the ratios of reduced transition rates B(M1; I -->I-1)/B(E2 I-->I-1) and B(M1; I-->I-1)/B(E2 I-->I-2) have been extracted from transitions in the two bands. Comparisons with theoretical predictions helped in the identification of the structure of the second ?J=1 band, which is thought to be based on a ?h11/2??h11/2??g7/2 three-quasiparticle configuration.

Piel, W. F., Jr.; Beausang, C. W.; Fossan, D. B.; Hildingsson, L.; Paul, E. S.

1987-03-01

146

Collective band structures in the ?-soft nucleus /sup 135/Nd  

International Nuclear Information System (INIS)

The low-lying band structure of /sup 135/Nd has been extended to higher spins using the /sup 112/Cd(/sup 27/Al,p3n?)/sup 135/Nd and /sup 116/Sn(/sup 24/Mg,2p3n?)/sup 135/Nd reactions. Two distinct high-spin structures have been identified. The ?J = 1 band built on the ?h/sub 11/2/[514](9/2)"- ground state was observed to have a band crossing at J/sup ?/ = (25/2)"-. This band crossing is associated with a loss of the moderate signature splitting found below the backbend. Cranked-shell model calculations suggest that this structure involves the alignment of a pair of h/sub 11/2/ protons and that the loss of signature splitting can be attributed to a shape change from a triaxial shape at low spins to a prolate axial shape above the backbend. A second ?J = 1 band structure with no signature splitting was observed to be built on a J/sup ?/ = (17/2)/sup (+)/ state at 1954 keV. Values for the ratios of reduced transition rates B(M1; I ?I-1)/B(E2; I?I-1) and B(M1; I?I-1)/B(E2; I?I-2) have been extracted from transitions in the two bands. Comparisons with theoretical predictions helped in the identification of the structure of the second ?J = 1 band, which is thought to be based on a ?h/sub 11/2/x?h/sub 11/2/x?g/sub 7/2/ three-quasiparticle configuration

1987-01-01

147

Progress on energy band structure studies of wide-band-gap semiconductors in NSRL  

International Nuclear Information System (INIS)

In this paper, authors report the progress on energy band structure studies of wide-band-gap semiconductors in NSRL. The energy band structure of ZnO and its native point defects have been calculated by using FP-LMTO method for the first time. Authors confirmed theoretically that Zn is the main factor to induce the native n-type conductivity in ZnO, which effects on the spectral properties of ZnO are also discussed. The energy band dispersion of both bulk and surface states on wurtzite (GaN(0001) has been studied by using synchrotron radiation angle resolved photo-electron spectroscopy (SRARPES). A theoretical calculation of the atomic and electronic structure of ?-SiC(110) surface is also presented by using FPLAPW method for the first time. The results show that the surface is characterized by a top-layer bond-length-contracting rotation relaxation and the surface relaxation induces the change from metallic to semiconducting characterization

2003-06-01

148

Band gap and structure of single crystal BiI3: Resolving discrepancies in literature  

Science.gov (United States)

Bismuth tri-iodide (BiI3) is an intermediate band gap semiconductor with potential for room temperature gamma-ray detection applications. Remarkably, very different band gap characteristics and values of BiI3 have been reported in literature, which may be attributed to its complicated layered structure with strongly bound BiI6 octahedra held together by weak van der Waals interactions. Here, to resolve this discrepancy, the band gap of BiI3 was characterized through optical and computational methods and differences among previously reported values are discussed. Unpolarized transmittance and reflectance spectra in the visible to near ultraviolet (UV-Vis) range at room temperature yielded an indirect band gap of 1.67 +/- 0.09 eV, while spectroscopic ellipsometry detected a direct band gap at 1.96 +/- 0.05 eV and higher energy critical point features. The discrepancy between the UV-Vis and ellipsometry results originates from the low optical absorption coefficients (? ~ 102 cm-1) of BiI3 that renders reflection-based ellipsometry insensitive to the indirect gap for this material. Further, electronic-structure calculations of the band structure by density functional theory methods are also consistent with the presence of an indirect band gap of 1.55 eV in BiI3. Based on this, an indirect band gap with a value of 1.67 +/- 0.09 eV is considered to best represent the band gap structure and value for single crystal BiI3.

Podraza, Nikolas J.; Qiu, Wei; Hinojosa, Beverly B.; Xu, Haixuan; Motyka, Michael A.; Phillpot, Simon R.; Baciak, James E.; Trolier-McKinstry, Susan; Nino, Juan C.

2013-07-01

149

The Three-Dimensional Structure of the Zodiacal Dust Bands  

Science.gov (United States)

Using observations of the infrared sky brightness by the Cosmic Background Explorer (COBE) 1Diffuse Infrared Background Experiment (DIRBE) and Infrared Astronomical Satellite (IRAS), we have created maps of the surface brightness Fourier-filtered to suppress the smallest (15°). Dust bands associated with the Themis, Koronis, and Eos families are readily evident. A dust band associated with the Maria family is also present. The parallactic distances to the emitting regions of the Koronis, Eos, and Maria dust bands were found to be 1.4 to 2.5 AU. A weak dust band associated with the Eunomia/Io family is evident, together with another weak and previously unattributed dust band, which may split further into two band pairs, potentially associated with the Hygiea or Vesta family. The brightnesses of the blended Themis/Koronis bands and the Eos dust band vary with ecliptic longitude, such that the northern or southern component of the band pair becomes brighter when its tilt brings it into the ecliptic plane. We attribute the brightness variations to the motion of the Earth within the emitting region, and conclude that at least some dust-band particles are on Earth-crossing orbits. For the Themis and Koronis families, the tilt is sufficient that the Earth may pass to the edges of the emitting region, where the density is highest, leading to "glints" two or four times a year. We compared the observed distributions to theoretically motivated, empirical models for the three-dimensional distribution of asteroid family dust. In the torus model, the dust is distributed among the asteroid family members with the same distributions of proper orbital inclination and semimajor axis but a random ascending node. In the migrating model, particles are presumed to be under the influence of Poynting-Robertson drag, so that they are distributed throughout the inner Solar System. The migrating model is better able to match the parallactic variation of dust-band latitude as well as the 12- to 60-?m spectrum of the dust bands. The annual brightness variations can be explained only by the migrating model. Upper limits are placed on the dust density associated with the Nysa and Flora families—both of the large, inner-belt families with wide inclination dispersions. The association of five (and potentially seven) dust bands with the largest asteroid families suggests that dust bands are an integral part of asteroid families. If nonfamily asteroids produce dust at a rate similar to that of the families with the lowest dust density, then they can account for the brightness of the zodiacal light in the ecliptic. The National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) is responsible for the design, development, and operation of the Cosmic Background Explorer (COBE). Scientific guidance is provided by the COBE Science Working Group. GSFC is also responsible for the development of the analysis software and for the production of the mission data sets.

Reach, William T.; Franz, Bryan A.; Weiland, Janet L.

1997-06-01

150

The surface band structure of ?-Ga2O3  

International Nuclear Information System (INIS)

Ga2O3 belongs to the group of transparent conducting oxides (TCOs) with a wide band gap and electrical conductivity. It exhibits the largest band gap with Eg = 4.8 eV and thus a unique transparency from the visible into the UV region. The information on the electronic structure of ?-Ga2O3 is very scarce. This is in part due to the challenging problem of growing high purity single crystals. Transparent semiconducting ?-Ga2O3 single crystals were grown by the Czochralski method from an iridium crucible under a dynamic protective atmosphere to control partial pressures of volatile species of Ga2O3. The investigated samples were characterized by different techniques (LEED, Laue, and STM). The experimental valence band structure of the of ?-Ga2O3 single crystals along ?-Z and A-M symmetry directions of the (100)-surface of Brillouin zone was determined by high-resolution angle-resolved photoelectron spectroscopy (ARPES) utilizing synchrotron radiation. The experimental band structure is compared and discussed with the theoretical calculations. The effect of changing the temperature from 300 K to 20 K on the experimental band structure ?-Ga2O3 was studied.

2011-03-01

151

Band structure of Charge Ordered Doped Antiferromagnets  

CERN Document Server

We study the distribution of electronic spectral weight in a doped antiferromagnet with various types of charge order and compare to angle resolved photoemission experiments on lightly doped La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) and electron doped Nd$_{2-x}$Ce$_x$CuO$_{4\\pm\\delta}$. Calculations on in-phase stripe and bubble phases for the electron doped system are both in good agreement with experiment including in particular the existence of in-gap spectral weight. In addition we find that for in-phase stripes, in contrast to anti-phase stripes, the chemical potential is likely to move with doping. For the hole doped system we find that ``staircase'' stripes which are globally diagonal but locally vertical or horizontal can reproduce the photoemission data whereas pure diagonal stripes cannot. We also calculate the magnetic structure factors of such staircase stripes and find that as the stripe separation is decreased with increased doping these evolve from diagonal to vertical separated by a coexistence region. T...

Granath, M

2004-01-01

152

The structure of shear bands in idealized granular materials  

Energy Technology Data Exchange (ETDEWEB)

The structure of shear bands in granular materials was investigated by numerically simulating an idealized assembly of two-dimensional particles. Flexible stress-controlled boundaries were used instead of periodic boundaries to avoid constraining the motion of particles within the tested specimen. The particle displacement, particle rotations and rotations of the particle neighborhoods (macro-rotation) were examined within the shear band. The shear band width was found to decrease with axial strain from 18 and 15 times the average particle radius. The particle rotations and macro-rotations were concentrated inside the shear bands. The numerical simulations suggest that the particle rotations are induced by macro-rotations, and support the use of the micropolar theory for examining instable phenomena within granular materials. 18 refs., 6 figs.

Bardet, J.P.; Proubet, J. [Univ. of Southern California, Los Angeles, CA (United States)

1992-03-01

153

G0W0 band structure of CdWO4  

Science.gov (United States)

The full quasiparticle band structure of CdWO4 is calculated within the single-shot GW (G0W0) approximation using maximally localized Wannier functions, which allows one to assess the validity of the commonly used scissor operator. Calculations are performed using the Godby–Needs plasmon pole model and the accurate contour deformation technique. It is shown that while the two methods yield identical band gap energies, the low-lying states are given inaccurately by the plasmon pole model. We report a band gap energy of 4.94 eV, including spin–orbit interaction at the DFT–LDA (density functional theory–local density approximation) level. Quasiparticle renormalization in CdWO4 is shown to be correlated with localization distance. Electron and hole effective masses are calculated at the DFT and G0W0 levels.

Laasner, Raul

2014-03-01

154

Band structure of neutron rich Se and Ge isotopes  

Science.gov (United States)

The band structure of the neutron-rich Se and Ge isotopes has been studied in terms of the full-fledged shell model. The monopole and quadrupole pairing plus quadrupole-quadrupole interaction is employed as an effective interaction. The model reproduces well the energy levels of high-spin states as well as the low-lying states. In order to investigate the structure of the high-spin states and low-lying collective states, the energy spectra in the shell model are compared with those in the quantum-number-projected generator coordinate method. It is shown that the triaxial components play essential roles in describing the ? bands.

Yoshinaga, N.; Higashiyama, K.

2013-07-01

155

Theoretical calculation of band structure and superconductivity under pressure  

International Nuclear Information System (INIS)

We present a brief review of a theoretical calculation of band structure and superconducting transition temperature (Tc) in the high pressure phases of 5B group elements such as phosphorus (P), arsenic (As). We also report the calculations done on the transition metal zirconium (Zr) in the high pressure bcc phase and transition metal carbide NbC. The effect of pressure on the band structure is obtained by means of the linear muffin-tin orbital method. The superconducting transition temperature (Tc) is calculated using either McMillan or Allen-Dyne's formula. The calculated values of Tc are compared with the available experimental data. (author). 29 refs., 6 tabs

1993-01-01

156

Band structure model of magnetic coupling in semiconductors  

CERN Multimedia

We present a unified band structure model to explain magnetic ordering in Mn-doped semiconductors. This model is based on the $p$-$d$ and $d$-$d$ level repulsions between the Mn ions and host elements and can successfully explain magnetic ordering observed in all Mn doped II-VI and III-V semiconductors such as CdTe, GaAs, ZnO, and GaN. This model, therefore, provides a simple guideline for future band structure engineering of magnetic semiconductors.

Dalpian, G M; Gong, X G; Silva, A J R; Fazzio, A; Dalpian, Gustavo M.; Wei, Su-Huai; Silva, Ant\\^onio J. R. da

2005-01-01

157

Chaos and structure of level densities  

Energy Technology Data Exchange (ETDEWEB)

The energy region of the first few MeV above the ground state shows interesting features of the nucleus. Beyond an ordered energy region just above the ground-state the dynamics changes, and chaotic features are observed in the neutron resonance region. The statistical properties of energies and wave-functions are common to all chaotic nuclei. However, if instead a global property, like the local level-density function is studied, strong structure effects emerge. In this contribution we discuss these two different facets of warm nuclei. In section 2 the onset of chaos with increasing excitation energy is discussed, with both experimental observations and proposed theoretical mechanisms as starting points. The structure of level densities in the same excitation energy region based on the two different starting points, is treated in section 3, where we give a short presentation of a newly developed combinatorial level-density modell. Some results from the model are presented and discussed. Two coexisting facets of warm nuclei, quantum chaos and structure of the level density, are considered. A newly developed combinatorial level-density model is presented, and the role of collective enhancements discussed. An example of extreme parity enhancement is shown.

Moller, Peter [Los Alamos National Laboratory; Aberg, Sven [LUND SWEDEN; Uhrenholt, Henrik [LUND SWEDEN; Ickhikawa, Takatoshi [RIKEN

2008-01-01

158

Tuning the optical band gap of quantum dot assemblies by varying network density.  

Science.gov (United States)

The effect of bulk network density on the extent of quantum confinement (probed by optical band gap) in CdSe quantum dot gels is evaluated. The CdSe gels were produced from controlled removal of surface thiolate ligands from CdSe quantum dots by adding 3% tetranitromethane. Two main techniques were employed to systematically vary the bulk density. First, different amounts of oxidizing agent were added to change the monolith density of the wet gel, followed by supercritical CO(2) drying to yield CdSe aerogels with different bulk densities. Experimental results suggest that a gradual and almost linear band gap decrease is observed when increasing the bulk density at the aerogel level. The fact that quantum confinement effects are largely preserved in aerogel constructs is consistent with SAXS data revealing the fractal nature of the network. Second, for a constant amount of oxidant, different drying techniques were used to yield CdSe gels with a larger density variation: aerogels (supercritical CO(2) dried), ambigels (hexane dried), and xerogels (acetone dried). A nonlinear trend for band gap decrease was found when comparing CdSe aerogels, ambigels, and xerogels, and the more dense ambi- and xerogels have broader absorption edges, suggestive of resonance transfer effects due to dipole-dipole interactions in non-homogeneous interacting systems. This is attributed to increased aggregation in the denser constructs (supported by TEM and SAXS data). Together, these data suggest that highly porous architectures, such as aerogels, are best suited for maintaining localized quantum confinement effects in 3D connected nanoparticle networks. PMID:19572742

Yu, Hongtao; Liu, Yi; Brock, Stephanie L

2009-07-28

159

Density-functional approach to the absorption bands in a dense, partially ionized plasma  

International Nuclear Information System (INIS)

One of the main problems, which appear in the calculation of photon absorption cross sections in plasmas, is the inclusion of the spectrum due to the bound-bound atomic transitions. In the case of high density plasmas and high-Z atoms the photo-absorption cross-section is often dominated by many lines. For high density plasmas these lines merge into broad bands and one may try to use, from the beginning, a fully statistical approach. In this paper we will use a statistical approach based on the Landau fluctuation theory. The method is connected with the fluctuations around the density-functional (DFT) solution. The final formula for the line 'width' is obtained by averaging the bound-bound cross-section with the fluctuation probability. If the dependence of the oscillator strengths upon the density fluctuation is neglected, the procedure leads to Gaussian line shapes. (author) 1 tab., 7 refs

1991-09-01

160

Correlated band structure of 3d{sup 2} vanadates  

Energy Technology Data Exchange (ETDEWEB)

We study the correlated band structure and the momentum-resolved spectra for 3d{sup 2} vanadates, like La O{sub 3} and YVO{sub 3}, using a combination of a first-principles technique and dynamical mean-field theory with a Monte Carlo impurity solver. The self-energy for the effective 3d bands is calculated using maximum-entropy spectral analysis of the Monte Carlo results and a self-consistent procedure. We use this self-energy to calculate the full momentum-resolved spectrum and the correlated band structure, which we compare to available spectroscopy experimental results. We also discuss the effects of the lattice distortions and chemistry.

Heilmann, David; Pavarini, Eva [Institut fuer Festkoerperforschung, Forschungszentrum Juelich (Germany)

2008-07-01

 
 
 
 
161

Electronic structure of the diamond (111) 1 x 1 surface: Valence-band structure, band bending, and band gap states  

International Nuclear Information System (INIS)

Photoemission, LEED, and AES measurements were made on the mechanically polished (111) surface of a type IIa diamond. No emission from filled states in the fundamental gap was found over the photon energy range 13.3 eV< or =h?< or =200 eV. This result, coupled with the sharp 1 x 1 LEED patterns which were obtained and the relative cleanliness (of elements which can be detected by AES) of the diamond (< or approx. =1 at.% oxygen, <0.5 at.% Si) suggests hydrogen termination of the lattice. Photoelectric yield measurements demonstrate the photoelectric threshold to be at band gap energy radiation. Investigation of the photoemission electron distribution curves (EDC's) shows that, while the electron affinity at the surface is always positive, band bending is sufficient to result in an effective negative electron affinity under certain conditions. A variable surface dipole on the atomic scale, possibly due to the adsorption--desorption of a background gas, is reported. A study of the relative cross section of the upper (p-like) versus the lower (s-like) portion of the diamond valence band indicates comparable cross sections at a photon energy h?=160 eV

1980-01-01

162

Sieve-based confidence intervals and bands for L\\'{e}vy densities  

CERN Multimedia

The estimation of the L\\'{e}vy density, the infinite-dimensional parameter controlling the jump dynamics of a L\\'{e}vy process, is considered here under a discrete-sampling scheme. In this setting, the jumps are latent variables, the statistical properties of which can be assessed when the frequency and time horizon of observations increase to infinity at suitable rates. Nonparametric estimators for the L\\'{e}vy density based on Grenander's method of sieves was proposed in Figueroa-L\\'{o}pez [IMS Lecture Notes 57 (2009) 117--146]. In this paper, central limit theorems for these sieve estimators, both pointwise and uniform on an interval away from the origin, are obtained, leading to pointwise confidence intervals and bands for the L\\'{e}vy density. In the pointwise case, our estimators converge to the L\\'{e}vy density at a rate that is arbitrarily close to the rate of the minimax risk of estimation on smooth L\\'{e}vy densities. In the case of uniform bands and discrete regular sampling, our results are consis...

Figueroa-López, José E

2011-01-01

163

Insights on Coral Adaptation from Polyp and Colony Morphology, Skeletal Density Banding and Carbonate Depositional Facies  

Science.gov (United States)

As one of the core reservoirs of primary production in the world's oceans, tropical coral reefs support a complex ecosystem that directly impacts over ninety percent of marine organisms at some point in their life cycle. Corals themselves are highly complex organisms and exhibit a range of growth forms that range from branching to massive, foliaceous, columnar, encrusting, free living and laminar coralla. Fierce competition over scarce resources available to each individual coral species creates niche specialization. Throughout the Phanerozic geological record, this has driven speciation events and created distinct skeletal growth morphologies that have differential abilities in feeding strategy. In turn, this has presumably led to the development of niche specialization that can be quantitatively measured through hierarchical morphological differences from the micrometer to the meter scale. Porter (1976) observed significant differences in skeletal morphology between Caribbean coral species that reflects an adaptive geometry based on feeding strategy. Within the Montastraea species complex there are four major morphologies; columnar, bouldering, irregular mounding, and skirted. Each morphotype can be found forming high abundance along the bathymetric gradient of coral reefs that grow along the leeward coast of Curacao, Netherlands Antilles. We have undertaken a study to determine the relative relationships amongst coral morphology, skeletal density and feeding strategy by comparing the morphometric measurements of individual polyps as well as the entire colony along spatial and bathymetric gradients. Polyp diameter, mouth size, interpolyp area, and interpolyp distance were measured from high-resolution images taken on a stereoscope, and evaluated with AxioVision image analysis software. These high-resolution optical analyses have also revealed new observations regarding folded tissue structures of the outer margin of polyps in the Montastrea complex. Skeletal densities were measured in vertical cross-sections of each whole corallum using standard X-ray techniques utilizing a calibrated step wedge to portray banding and overall density. The combination of the stereoscope and X-ray analyses across spatial and temporal gradients provide insight into how coral reef carbonate depositional facies are affected by changes in key environmental parameters, such as increased pollution, or changing photosynthetic activity with depth or sea surface temperature fluctuations.

Oehlert, A. M.; Hill, C. A.; Piggot, A. M.; Fouke, B. W.

2008-12-01

164

Band structure analysis of the conduction-band mass anisotropy in 6H and 4H SiC  

CERN Document Server

The band structures of 6H and 4H SiC calculated by means of the FP-LMTO method are used to determine the effective mass tensors for their conduction-band minima. The results are shown to be consistent with recent optically detected cyclotron resonance measurements and predict an unusual band filling dependence for 6H-SiC.

Lambrecht, W R L; Lambrecht, Walter R. L.; Segall, Benjamin

1995-01-01

165

Local density of optical states in the band gap of a finite photonic crysta  

CERN Document Server

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...

Yeganegi, Elahe; Mosk, Allard P; Vos, Willem L

2014-01-01

166

Band structure loops and multistability in cavity-QED  

CERN Document Server

We calculate the band structure of ultracold atoms located inside a laser-driven optical cavity. For parameters where the atom-cavity system exhibits bistability, the atomic band structure develops loop structures akin to the ones predicted for Bose-Einstein condensates in ordinary (non-cavity) optical lattices. However, in our case the nonlinearity derives from the cavity back-action rather than from direct interatomic interactions. We find both bi- and tri-stable regimes associated with the lowest band, and show that the multistability we observe can be analyzed in terms of swallowtail catastrophes. Dynamic and energetic stability of the mean-?eld solutions is also discussed, and we show that the bistable solutions have, as expected, one unstable and two stable branches. The presence of loops in the atomic band structure has important implications for proposals concerning Bloch oscillations of atoms inside optical cavities [Peden et al., Phys. Rev. A 80, 043803 (2009), Prasanna Venkatesh et al., Phys. Rev. ...

Venkatesh, B Prasanna; O'Dell, D H J

2011-01-01

167

Manipulating the extraordinary acoustic transmission through metamaterial-based acoustic band gap structures  

Science.gov (United States)

We report theoretical predictions and experimental results on the formation of pass bands and stop bands of extraordinary acoustic transmission in multilayer structures based on alternating layers of acoustic metamaterial and air. The metamaterial layers can be made of any acoustically hard material perforated with a two-dimensional array of subwavelength apertures. In this way, it is possible to tailor the density and speed of sound of an otherwise acoustically bulk hard material with fixed properties. The sonic band structure allows transmission passband and stop bandgaps that depend on the layer thicknesses and effective properties of the metamaterials. In addition, we show the existence of resonant tunneling due to the formation of an acoustic passband in a spectral region of low transmission for a single layer. This opens the possibility to engineer different types of phononic materials to manipulate and control acoustic waves.

Aközbek, N.; Mattiucci, N.; Bloemer, M. J.; Sanghadasa, M.; D'Aguanno, G.

2014-04-01

168

Surface electron band structure and VLEED reflectivity for Al(111)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The 2D layer Green function scattering method is used to calculate the energy of surface states and resonances at Gamma-bar for Al(111) for both below and above the vacuum level. The surface barrier potential is represented by an empirical form. The above vacuum level surface electron band structure for this surface has not been calculated before and it is important in understanding many surface phenomena. The geometric structure of the Al(111) surface is known from intensit...

Read, M. N.

2008-01-01

169

Volume and surface photoemission from tungsten. I. Calculation of band structure and emission spectra  

DEFF Research Database (Denmark)

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.

1974-01-01

170

Band structure and optical properties of amber studied by first principles  

International Nuclear Information System (INIS)

The band structure and density of states of amber is studied by the first principles calculation based on density of functional theory. The complex structure of amber has 214 atoms and the band gap is 5.0 eV. The covalent bond is combined C/O atoms with H atoms. The O 2p orbital is the biggest effect near the Fermi level. The optical properties' results show that the reflectivity is low, and the refractive index is 1.65 in visible light range. The highest absorption coefficient peak is at 172 nm and another higher peak is at 136 nm. These convince that the amber would have a pretty sheen and that amber is a good and suitable crystal for jewelry and ornaments

2013-03-01

171

Band structure for a bend-core liquid crystal fiber  

Science.gov (United States)

We study the propagation of optical fields in a cylindrical fiber of a banana bend-core liquid crystal formed by uniformly tilted coaxial cylindrical smectic layers, surrounded by vacuum. By solving numerically Maxwell's equations, we find the band structure in both uniaxial and biaxial limits. For the biaxial case, we show that the backward propagation is restricted to certain narrow frequency band gaps, whereas for the forward one the fiber behaves similarly to a standard waveguide. We also find that the fiber modes are elliptically polarized slowly leaky modes whose attenuation coefficients are damped oscillating functions of frequency.

Palomares, Laura O.; Castro-Garay, P.; Reyes, J. Adrian

2009-05-01

172

Structure within redshift-magnitude bands, morphological evolution  

International Nuclear Information System (INIS)

The distribution of redshifts within individual redshift-magnitude bands contains a significant periodic structure ''X-groups'' which cross the bands at a steep angle. Six independent cluster samples indicate that the pattern appears to be fixed in redshift and magnitude. Five compact E-dominated groups of galaxies are superposed and shown to concentrate at the boundaries between X-groups. Morphology is shown to be ordered across X-groups, suggesting evolutionary sequences linking groups. All correlations are demonstrated with several independent data samples

1979-11-01

173

Band structures of rare gas solids within the GW approximation  

CERN Document Server

Band structures for solid rare gases (Ne, Ar) have been calculated using the GW approximation. All electron and pseudopotential ab initio calculations were performed using Gaussian orbital basis sets and the dependence of particle-hole gaps and electron affinities on basis set and treatment of core electrons is investigated. All electron GW calculations have a smaller particle-hole gap than pseudopotential GW calculations by up to 0.2 eV. Quasiparticle electron and hole excitation energies, valence band widths and electron affinities are generally in very good agreement with those derived from optical absorption and photoemission measurements.

Galamic-Mulaomerovic, S

2004-01-01

174

Band structure tunability in MoS2 under interlayer compression: A DFT and GW study  

Science.gov (United States)

The electronic band structures of MoS2 monolayer and 2H1 bulk polytype are studied within density-functional theory (DFT) and many-body perturbation theory (GW approximation). Interlayer van der Waals (vdW) interactions, responsible for bulk binding, are calculated with the postprocessing Wannier functions method. From both fat bands and Wannier functions analysis, it is shown that the transition from a direct band gap in the monolayer to an indirect band gap in bilayer or bulk systems is triggered by medium- to short-range electronic interactions between adjacent layers, which arise at the equilibrium interlayer distance determined by the balance between vdW attraction and exchange repulsion. The semiconductor-to-semimetal (S-SM) transition is found from both theoretical methods: around c=10.7 Å and c=9.9 Å for DFT and GW, respectively. A metallic transition is also observed for the interlayer distance c=9.7 Å. Dirac conelike band structures and linear bands near Fermi level are found for shorter c lattice parameter values. The VdW correction to total energy was used to estimate the pressure at which S-SM transition takes place from a fitting to a model equation of state.

Espejo, C.; Rangel, T.; Romero, A. H.; Gonze, X.; Rignanese, G.-M.

2013-06-01

175

First-Principles Band Calculations on Electronic Structures of Ag-Doped Rutile and Anatase TiO2  

International Nuclear Information System (INIS)

The electronic structures of Ag-doped rutile and anatase TiO2 are studied by first-principles band calculations based on density functional theory with the full-potential linearized-augmented-plane-wave method. New occupied bands are found between the band gaps of both Ag-doped rutile and anatase TiO2. The formation of these new bands can be explained mainly by their orbitals of Ag 4d states mixed with Ti 3d states and are supposed to contribute to their visible light absorption. (condensed matter: electronicstructure, electrical, magnetic, and opticalproperties)

2009-07-01

176

Charge-Density-Wave Phase of 1T-TiSe2: The Influence of Conduction Band Population  

Science.gov (United States)

The charge-density-wave phase of TiSe2 was studied by angle-resolved photoelectron spectroscopy and resistivity measurements investigating the influence of the band gap size and of a varying population of the conduction band. A gradual suppression of the charge-density-wave-induced electronic superstructure is observed for a variation of the band gap in the ternary compounds TiCxSe2-x with C=(S,Te) as well as for an occupation of only the conduction band by H2O adsorption-induced band bending. These observations point to an optimum band gap and support an excitonic driving force for the charge-density wave.

May, Matthias M.; Brabetz, Christine; Janowitz, Christoph; Manzke, Recardo

2011-10-01

177

Effect of metal vacancies on the electronic band structure of hexagonal Nb, Zr and Y diborides  

CERN Multimedia

Energy band structures of metal-deficient hexagonal diborides M$_{0.75}$B$_2$ (M = Nb, Zr and Y) were calculated using the full-potential LMTO method. The metal vacancies change the density of states near the Fermi level and this effect is quite different for III-V group transition metal diborides. Contradictory data on superconductivity in diborides may be supposed to be connected with nonstoichiometry of samples. Vacancy formation energies are estimated and analyzed.

Shein, I R; Medvedeva, N I; Ivanovskii, A L

2002-01-01

178

Structure of the four quasiparticle band in 84Sr  

Science.gov (United States)

The high spin levels in 84Sr have been populated through the 59Co(28Si, 3p) reaction using 98 MeV 28Si beam. A regular band structure was found to develop above the 12+ state with a deformation parameter ?=0.21+/-0.04 and ?=8°+/-6°. The projected Hartree-Fock calculations predict a two proton and two neutron aligned configuration for this band. The predicted quadrupole moment for this configuration is also in good agreement with the experimental values obtained from the lifetime measurements. In addition, a large enhancement in B(M1)/B(E2) transition rates has been observed in the negative parity band above the 11- state.

Chattopadhyay, S.; Jain, H. C.; Jhingan, M. L.; Praharaj, C. R.

1994-07-01

179

Doping dependent quasiparticle band structure in cuprate superconductors  

CERN Multimedia

We present an exact diagonalization study of the single particle spectral function in the so-called t-t'-t''-J model in 2D. As a key result, we find that unlike the `pure' t-J model, hole doping leads to a major reconstruction of the quasiparticle band structure near (pi,0): whereas for the undoped system the quasiparticle states near (pi,0) are deep below the top of the band at (pi/2,pi/2), hole doping shifts these states up to E_F, resulting in extended flat band regions close to E_F and around (pi,0). This strong doping-induced deformation can be directly compared to angle resolved photoemission results on Sr_2 Cu Cl_2 O_2, underdoped Bi2212 and optimally doped Bi2212. We propose the interplay of long range hopping and decreasing spin correlations as the mechanism of this deformation.

Eder, R; Sawatzky, G A

1996-01-01

180

Extensive ?-ray spectroscopy of band structures in 3062Zn32  

Science.gov (United States)

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.

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

 
 
 
 
181

Rotational band structure in "1"3"3Pr  

International Nuclear Information System (INIS)

The level structure of the odd proton nucleus "1"3"3Pr has been investigated. Excited states up to spin (45/2) have been observed. The yrast band, built on a decoupled h/sub 11/2/ proton, shows an up-bend at h? = 0.43 MeV when two additional h/sub 11/2/ protons align. Two positive parity side bands, based on the g/sub 7/2/(5/2)"+[413] proton configuration, are established with opposite signature. Both show a band crossing at h?/sub c/ = 0.27 MeV with a gain in alignment roughly-equal8h, when two h/sub 11/2/ protons decouple. This low crossing frequency is partly explained by a reduction in the proton pairing gap caused by the g/sub 7/2/ proton

1986-01-01

182

Three-dimensional photonic band gaps in woven structures  

Energy Technology Data Exchange (ETDEWEB)

In this paper, we studied the photonic properties of dielectric fibres woven into three-dimensional (3D) structures. Such fibres can be fabricated on the micrometre scale, and hence the gaps are in the far-infrared to the infrared regime. The vector-wave transfer matrix method is applied to evaluate the photonic band structures. We have also employed the constant-frequency dispersion surface scheme to investigate the development of a full band gap. Such a 3D absolute gap is observed in a rectangular lattice, but at a fairly large dielectric constant for the fibres. Ways to improve on this have been suggested. Our study indicates that woven structures are promising materials for realizing the 3D photonic insulator in the infrared regime. (author)

Tsai Yachih; Shung, K.W.K. [Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 30043 (China); Pendry, J.B. [Blackett Laboratory, Imperial College, London SW7 2BZ (United Kingdom)

1998-02-02

183

Three-dimensional photonic band gaps in woven structures  

CERN Document Server

In this paper, we studied the photonic properties of dielectric fibres woven into three-dimensional (3D) structures. Such fibres can be fabricated on the micrometre scale, and hence the gaps are in the far-infrared to the infrared regime. The vector-wave transfer matrix method is applied to evaluate the photonic band structures. We have also employed the constant-frequency dispersion surface scheme to investigate the development of a full band gap. Such a 3D absolute gap is observed in a rectangular lattice, but at a fairly large dielectric constant for the fibres. Ways to improve on this have been suggested. Our study indicates that woven structures are promising materials for realizing the 3D photonic insulator in the infrared regime. (author)

Tsai Ya Chih; Pendry, J B

1998-01-01

184

Nuclear energy density optimization: Shell structure  

Science.gov (United States)

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.

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

185

Optimum design of band-gap beam structures  

DEFF Research Database (Denmark)

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 Bernoulliâ??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.

Olhoff, Niels; Niu, Bin

2012-01-01

186

A NOVEL TRIPLE-BAND ELECTROMAGNETIC BANDGAP (EBG) STRUCTURE  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A novel triple-band uni-planar electromagnetic bandgap (UC-EBG) structure is proposed in this paper. This EBG structure can be considered as distorted uni-planar compact-EBG (DUC-EBG) which is connected together by the meandered line inductor. Split ring resonators (SRR) are embedded in four pad corners and two L-shaped slots are etched at the central pad. The proposed EBG structure is modelled in three equivalent circuits. By using in-house developed computational code based on the FDTD meth...

2013-01-01

187

Rectangular patch antennas over electromagnetic band gap structures  

Science.gov (United States)

In this paper, I propose a new design of a defected structure (DS) for use as an electromagnetic band gap (EBG) configuration to enhance the performance of low profile microstrip antennas. The proposed defected structure embodies a honeycomb lattice of cylindrical air holes. The proposed DS is applied to three different configurations using a dielectric substrate (dielectric constant 6 and thickness 1.5 mm); namely: a dielectric substrate backed by a defected ground plane, a defected dielectric substrate backed by a normal substrate and a defected dielectric substrate backed by a defected ground plane. The simulated values of the transmission coefficient S 21 for the last one show two well-defined stop bands around 8.5 and 9.5 GHz, respectively. The first band has been used to reduce mutual coupling in a microstrip array. On the other hand, the stop band defined around 9.5 GHz has been applied to enhance the characteristics of a rectangular patch antenna and improve the operational 10-dB bandwidth.

Areed, Nihal F. F.

2011-06-01

188

Engineering Design of a Multipurpose X-band Accelerating Structure  

CERN Multimedia

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...

Gudkov, Dmitry; Samoshkin, Alexander; Zennaro, Riccardo; Dehler, Micha; Raguin, Jean-Yves

2010-01-01

189

Partial cross sections and density of states effects in the valence band photoemission from solid nitrogen  

International Nuclear Information System (INIS)

Photoelectron energy distribution curves from solid nitrogen have been measured for excitation energies ranging from threshold (14.2 eV) to 40 eV using Synchrotron Radiation. The partial cross sections for the emission from the 3sigmasub(g), 1?sub(u) and 2sigmasub(u) derived valence bands show pronounced maxima 3.4 eV, 2.9 eV and 3.0 eV above the vacuum level respectively which we interpret as being due to a high density of conduction band final states. These states are closely related to the ?sub(g)* negative-ion shape resonance for molecular nitrogen. (orig.)

1982-01-01

190

Coexistent State of Charge Density Wave and Spin Density Wave in One-Dimensional Quarter Filled Band Systems under Magnetic Fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

Kishigi, Keita; Hasegawa, Yasumasa

2000-01-01

191

Density banding in corals: barcodes of past and current climate change  

Science.gov (United States)

The predicted sea surface temperature (SST) rise over the next decades is likely hazardous to coral health because precipitation of the calcareous skeleton depends primarily on SST. Temperature modulates vertical growth and density of the skeleton with seasonal SST changes resulting in an alternation of high-density and low-density bands (HDB and LDB). Notably, growth rates and the timing of the HDBs and LDBs relative to the seasons differ on a global scale within geographic regions. In this contribution, we use combined information of skeletal density and seasonally resolved oxygen isotope SST estimates from massive Porites from a Late Miocene (9 Ma) reef in the eastern Mediterranean Sea (Crete, Greece) to understand reef vulnerability over short and geological periods of time. Three types of HDB-SST relationships have been found: (1) coincidence of HDB with summer, (2) winter or (3) autumn and spring. The latter doubles HDBs in a year and implies maximum calcification is coupled to the taxon-specific optimum SST during the transitional seasons and reduced at its respective critical winter and summer SSTs. Modeling with a nonlinear temperature-calcification relationship reproduces the climate barcode of density bands. The model should be relevant for other poikilothermic carbonate producers in reefs and platforms and has implications for judging geographic distributions and causes of extinctions of corals, benthic carbonate communities and entire carbonate systems. With regard to the causes underlying expansion and demise of carbonate platforms and reefs in geological history, we expect the model predictions to help for a deeper understanding of biotic responses during hyperthermals or coolings and possibly also for identifying regions in the modern ocean where corals are endangered or taking advantage of global warming.

Brachert, T. C.; Reuter, M.; Krüger, S.; Böcker, A.; Lohmann, H.; Mertz-Kraus, R.; Fassoulas, C.

2013-12-01

192

Plasmonic band structure controls single-molecule fluorescence.  

Science.gov (United States)

Plasmonics and photonic crystals are two complementary approaches to tailor single-emitter fluorescence, using strong local field enhancements near metals on one hand and spatially extended photonic band structure effects on the other hand. Here, we explore the emergence of spontaneous emission control by finite-sized hexagonal arrays of nanoapertures milled in gold film. We demonstrate that already small lattices enable highly directional and enhanced emission from single fluorescent molecules in the central aperture. Even for clusters just four unit cells across, the directionality is set by the plasmonic crystal band structure, as confirmed by full-wave numerical simulations. This realization of plasmonic phase array antennas driven by single quantum emitters opens a flexible toolbox to engineer fluorescence and its detection. PMID:24020654

Langguth, Lutz; Punj, Deep; Wenger, Jérôme; Koenderink, A Femius

2013-10-22

193

Electronic band structure of the superconductor Sr2RuO4  

International Nuclear Information System (INIS)

A local-density electronic-band-structure calculation was performed for a recently discovered non-copper-layered perovskite superconductor, Sr2RuO4. It was found that the electronic structure near the Fermi energy is essentially described by antibonding bands of the Ru d var-epsilon and O p? states. Although two holes in the bands are predominantly situated in a d var-epsilon(xy)-p? state in the ab plane, the hole occupations in the other d var-epsilon-p? states vertical to the plane are not negligibly small, possibly in conjunction with the smallness of tetragonal distortion of the RuO6 octahedron. Associated with the antibonding d var-epsilon-p? bands, the density of states at the Fermi energy is relatively high (4.36 states/eVcell) but not enough to account for the observed specific-heat constant ?exp and temperature-independent magnetic susceptibility ?exp. We found a large Stoner factor, which may explain most of the mass enhancement involved in ?exp. Certain similarities and dissimilarities in the electronic properties to the cuprate superconductors are discussed

1995-01-01

194

Band gap engineering of NaTaO3 using density functional theory: a charge compensated codoping strategy.  

Science.gov (United States)

In this theoretical study, we employ a codoping strategy to reduce the band gap of NaTaO3 aimed at improving the photocatalytic activity under visible light. The systematic study includes the effects of metal (W) and nonmetal (N) codoping on the electronic structure of NaTaO3 in comparison to the effect of individual dopants. The feasibility of the introduction of N into the NaTaO3 crystal structure is found to be enhanced in the presence of W, as indicated by the calculated formation energy. This codoping leads to formation of a charge compensated system, beneficial for the minimization of vacancy related defect formation. The electronic structure calculations have been carried out using a hybrid density functional for an accurate description of the proposed system. The introduction of W in place of Ta leads to the appearance of donor states below the conduction band, while N doping in place of oxygen introduces isolated acceptor states above the valence band. The codoping of N and W also passivates undesirable discrete midgap states. This feature is not observed in the case of (Cr, N) codoped NaTaO3 in spite of its charge compensated nature. We have also studied charge non-compensated codoping using several dopant pairs, including anion-anion and cation-anion pairs. However, this non-compensated codoping introduces localized states in between the valence band and the conduction band, and hence may not be effective in enhancing the photocatalytic properties of NaTaO3. The optical spectrum shows that the absorption curve for the (W, N)-codoped NaTaO3 is extended to the visible region due to narrowing of the band gap to 2.67 eV. Moreover, its activity for the photo decomposition of water to produce both H2 and O2 remains intact. Hence, based on the present investigation we can propose (W, N) codoped NaTaO3 as a promising photocatalyst for visible light driven water splitting. PMID:25007948

Modak, Brindaban; Srinivasu, K; Ghosh, Swapan K

2014-07-23

195

Graphene on Ru(0001): Evidence for two graphene band structures  

Energy Technology Data Exchange (ETDEWEB)

High-resolution photoemission illustrates that the band structure of graphene on Ru(0001) exhibits a well-defined splitting. This splitting is largest with the graphene directly on the Ru(0001) substrate, whereas with a chemisorbed oxygen spacer layer between the graphene and the metal substrate, this splitting is considerably reduced. This splitting is attributed to a combination of chemical interactions between graphene and Ru(0001) and to screening of the former by the latter, not spin-orbit coupling.

Katsiev K.; Vescovo E.; Losovyj, Y.; Zhou, Z.; Liu, L.; Dowben, P.A.; Goodman, D.W.

2012-05-03

196

Novel band structure of odd-A 107Cd  

International Nuclear Information System (INIS)

The odd-A 107Cd nucleus is situated in a transitional region between spherical and deformed nuclei. In the 1970s and 1980s, a number of experiments to study the low spin states of 107Cd were carried out by several authors. The high spin states of 107Cd were studied by Jerrestam et al. in 1992. In the present paper, we discuss the spectroscopic features and lifetimes of the negative parity band structure of 107Cd

2012-12-01

197

Band Structure Analysis of Crystals with Discontinuous Metallic Wires  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The band structure for normal propagation of crystals with finite straight metallic wires is studied for different wire diameters and lengths. The crystal is considered as a set of parallel grids. Dispersion characteristics are obtained by using a transmission line model where the parameters are calculated from the reflection and transmission coefficients of the grids. These coefficients are computed rigourously with a Finite Difference Time Domain (FDTD) code. Simulated and experimental resu...

Boutayeb, Halim; Denidni, Tayeb; Sebak, Abdelrazik; Talbi, Larbi

2005-01-01

198

Air Density Measurements in a Mach 10 Wake Using Iodine Cordes Bands  

Science.gov (United States)

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.

Balla, Robert J.; Everhart, Joel L.

2012-01-01

199

Nonlocal pseudopotentials in complex band-structure and photoemission calculations  

Energy Technology Data Exchange (ETDEWEB)

Based on a recently proposed localization procedure, a nonlocal pseudopotential scheme is derived to calculate potential coefficients V{sub {rvec G}{rvec G}{sup {prime}}}({rvec k}) which can be decomposed into terms, each being quadratic in {rvec k} and multiplied by a function of ({rvec G}{minus}{rvec G}{sup {prime}}), thus making them applicable to some important cases where local potential coefficients are required. Electronic structure calculations for semiconductors are in agreement with well-known semiempirical local pseudopotential band structures, as shown for GaAs. Nevertheless, the potential may significantly deviate from the semiempirical results. In order to test wave functions and transition probabilities, we prove the success of the procedure in a more troublesome case, i.e., applying it to a transition-metal compound as the experimentally well-investigated layered crystal TiSe{sub 2}, which up to now was not treated with a pseudopotential. Photoemission spectra within the one-step model are presented using Pendry`s method of complex band-structure calculation. The latter formalism had to be slightly generalized for the quasilocal properties of the potential. The agreement of the spectra with experimental data shows this method to be a reliable and practical tool to use nonlocal pseudopotentials for conduction-band wave functions of electron spectroscopies. {copyright} {ital 1997} {ital The American Physical Society}

Boedicker, A.; Schattke, W. [Institut fuer Theoretische Physik, Leibnizstrae 15, D-24118 Kiel (Germany)

1997-02-01

200

Nonlocal pseudopotentials in complex band-structure and photoemission calculations  

International Nuclear Information System (INIS)

Based on a recently proposed localization procedure, a nonlocal pseudopotential scheme is derived to calculate potential coefficients Vrvec Grvec G'(rvec k) which can be decomposed into terms, each being quadratic in rvec k and multiplied by a function of (rvec G-rvec G'), thus making them applicable to some important cases where local potential coefficients are required. Electronic structure calculations for semiconductors are in agreement with well-known semiempirical local pseudopotential band structures, as shown for GaAs. Nevertheless, the potential may significantly deviate from the semiempirical results. In order to test wave functions and transition probabilities, we prove the success of the procedure in a more troublesome case, i.e., applying it to a transition-metal compound as the experimentally well-investigated layered crystal TiSe2, which up to now was not treated with a pseudopotential. Photoemission spectra within the one-step model are presented using Pendry's method of complex band-structure calculation. The latter formalism had to be slightly generalized for the quasilocal properties of the potential. The agreement of the spectra with experimental data shows this method to be a reliable and practical tool to use nonlocal pseudopotentials for conduction-band wave functions of electron spectroscopies. copyright 1997 The American Physical Society

1997-02-01

 
 
 
 
201

Band structural properties of MoS2 (molybdenite)  

International Nuclear Information System (INIS)

Semiconductivity and superconductivity in MoS2 (molybdenite) can be understood in terms of the band structure of MoS2. The band structural properties of MoS2 are presented here. The energy dependence of nsub(eff) and epsilon(infinity)sub(eff) is investigated. Using calculated values of nsub(eff) and epsilon(infinity)sub(eff), the Penn gap has been determined. The value thus obtained is shown to be in good agreement with the reflectivity data and also with the value obtained from the band structure. The Ravindra and Srivastava formula has been shown to give values for the isobaric temperature gradient of Esub(G)[(deltaEsub(G)/deltaT)sub(P)], which are in agreement with the experimental data, and the contribution to (deltaEsub(G)/deltaT)sub(P) due to the electron lattice interaction has been evaluated. In addition, the electronic polarizability has been calculated using a modified Lorentz-Lorenz relation. (author)

1980-01-01

202

Electronic band structure, doping, and defects in the semiconducting Half Heusler compound CoTiSb  

Science.gov (United States)

We report transport and electronic band structure measurements on epitaxial films of the Half Heusler compound CoTiSb. CoTiSb belongs to the family of Half Heuslers with 18 valence electrons per formula unit that are predicted to be semiconducting despite being composed of all metallic components. Here the CoTiSb films were grown by molecular beam epitaxy on a lattice matched InAlAs buffer. The films are epitaxial and single crystalline, as measured by reflection high-energy electron diffraction and X-ray diffraction. Scanning tunnelling spectroscopy and temperature-dependent transport measurements reveal that the films are semiconducting, with unintentionally doped carrier concentrations comparable to that of highly doped conventional compound semiconductors. These carrier concentrations can be modulated by doping with Sn. The band structure of the films was measured by angle resolved photoemission spectroscopy at the MAX-Lab Synchrotron facility. The bulk bands are in general agreement with density functional theory calculations, with a valence band maximum at ? and surface states within the bulk band gap. The effects of defects are explored in order to explain the ARPES results.

Kawasaki, Jason; Johansson, Linda; Hjort, Martin; Timm, Rainer; Schultz, Brian; Balasubramanian, Thiagarajan; Mikkelsen, Anders; Palmstrom, Chris

2013-03-01

203

Collinear load study for X-band linear accelerator structure  

International Nuclear Information System (INIS)

The collinear load consists of few disk-loaded cavities coated with high-resistance material on the inside walls. The load terminates the accelerator section and forms a part of actual accelerating structure with collinear to the electron beam. Not only can it dissipate residual RF power of the accelerator section in the form of skin losses, but also the particles are still accelerated in the structure. In this paper, the design and technology of an X-band constant power-loss collinear load are described in detail and some results are presented

2002-08-11

204

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport  

Science.gov (United States)

We have investigated trap density of states (trap DOS) in n-channel organic field-effect transistors based on N,N '-bis(cyclohexyl)naphthalene diimide (Cy-NDI) and dimethyldicyanoquinonediimine (DMDCNQI). A new method is proposed to extract trap DOS from the Arrhenius plot of the temperature-dependent transconductance. Double exponential trap DOS are observed, in which Cy-NDI has considerable deep states, by contrast, DMDCNQI has substantial tail states. In addition, numerical simulation of the transistor characteristics has been conducted by assuming an exponential trap distribution and the interface approximation. Temperature dependence of transfer characteristics are well reproduced only using several parameters, and the trap DOS obtained from the simulated characteristics are in good agreement with the assumed trap DOS, indicating that our analysis is self-consistent. Although the experimentally obtained Meyer-Neldel temperature is related to the trap distribution width, the simulation satisfies the Meyer-Neldel rule only very phenomenologically. The simulation also reveals that the subthreshold swing is not always a good indicator of the total trap amount, because it also largely depends on the trap distribution width. Finally, band transport is explored from the simulation having a small number of traps. A crossing point of the transfer curves and negative activation energy above a certain gate voltage are observed in the simulated characteristics, where the critical VG above which band transport is realized is determined by the sum of the trapped and free charge states below the conduction band edge.

Cho, Joung-min; Akiyama, Yuto; Kakinuma, Tomoyuki; Mori, Takehiko

2013-10-01

205

The crystal and electronic band structure of the diamond-like semiconductor Ag2ZnSiS4  

International Nuclear Information System (INIS)

Highlights: ? The structure of Ag2ZnSiS4 is solved and refined in the space group Pn using single crystal X-ray diffraction. ? Electronic band structure calculations show that Ag2ZnSiS4 is a direct band gap semiconductor with a calculated band gap of 1.88 eV. ? The optical band gap of Ag2ZnSiS4 was experimentally determined as 3.28 eV. - Abstract: Single crystals of the new diamond-like semiconductor Ag2ZnSiS4 have been synthesized using high-temperature, solid state synthesis at 800 °C. The compound crystallizes in the monoclinic, noncentrosymmetric space group Pn with a = 6.4052(1) ?, b = 6.5484(1) ?, c = 7.9340(1) ?, ? = 90.455(1)° 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 Ag2ZnSiS4 is a direct band gap semiconductor with a calculated band gap of 1.88 eV at the ?-point. The calculated density of states of Ag2ZnSiS4 is compared with that of AgGaS2. The band gap of Ag2ZnSiS4 was also determined experimentally as 3.28 eV via optical diffuse reflectance spectroscopy.

2012-03-05

206

Electronic structure of alkane chains. Complete one-dimensional band structures of the valence states  

Science.gov (United States)

Several ultrathin films of oriented alkane chains were studied by ultraviolet photoelectron spectroscopy using UV photons in the energy range of 20-200 eV. From the experimental data the full valence band structure has been determined for self-assembled films of long-chain n-alkanethiols, Langmuir-Blodgett films of Cd-arachidate and thin films of hexatriacontane. Significant deviations from band structures obtained by ab initio calculations of Karpfen are found at the boundary of the one-dimensional Brillouin zone. Furthermore it is demonstrated that a mapping of the one-dimensional band structure can be used for precisely determining tilt angles of alkane chains.

Zubrägel, Ch.; Schneider, F.; Neumann, M.; Hähner, G.; Wöll, Ch.; Grunze, M.

1994-03-01

207

Radiosensitivity is predicted by DNA end-binding complex density, but not by nuclear levels of band components  

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

2004-09-01

208

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)

2013-01-01

209

Dual-band metamaterial with a windmill-like structure  

Science.gov (United States)

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.

Xiong, Han; Hong, Jing-Song; Jin, Da-Lin

2013-01-01

210

Crossing points in the electronic band structure of vanadium oxide  

Directory of Open Access Journals (Sweden)

Full Text Available The electronic band structures of several models of vanadium oxide are calculated. In the models 1-3, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 4 vanadium atoms. In model 1, a=b=c 2.3574 Å; in model 2, a= 4.7148 Å, b= 2.3574 Å and c= 2.3574 Å; and in model 3, a= 4.7148 Å, b= 2.3574 Å and c= 4.7148 Å. In the models 4-6, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 2 vanadium atoms. In model 4, a=b= 4.551 Å and c= 2.851 Å; in model 5, a=b=c= 3.468 Å; and in model 6, a=b=c= 3.171 Å. We have searched for a crossing point in the band structure of all the models. In model 1 there is a point at which five bands appear to meet but the gap is 7.3 meV. In model 2 there is a crossing point between G and F points and there is a point between F and Q with the gap ? 3.6608 meV. In model 3, the gap is very small, ~ 10-5 eV. In model 4, the gap is 5.25 meV. In model 5, the gap between Z and G points is 2.035 meV, and in model 6 the gap at Z point is 4.3175 meV. The crossing point in model 2 looks like one line is bent so that the supersymmetry is broken. When pseudopotentials are replaced by a full band calculation, the crossing point changes into a gap of 2.72 x 10-4 eV.

Keshav N. Shrivastava

2010-03-01

211

The quiet Sun's magnetic flux estimated from CaIIH bright inter-granular G-band structures  

CERN Document Server

We determine the number density and area contribution of small-scale inter-granular Ca II bright G-band structures in images of the quiet Sun as tracers of kilo-Gauss magnetic flux-concentrations. In a 149 arcsec X 117 arcsec G-band image of the disk center at the activity minimum, 7593 small inter-granular structures were segmented with the `multiple-level tracking' pattern recognition algorithm. The scatter-plot of the continuum versus the G-band brightness shows the known magnetic and non-magnetic branches. These branches are largely disentangled by applying an intrinsic Ca II excess criterion. The thus obtained 2995 structures contain 1152 G-band bright points (BP) and 1843 G-band faint points (FP). They show a tendency toward increasing size with decreasing G-band excess, as expected from the `hot wall' picture. Their Ca H and G-band brightness are slightly related, resembling the known relation of Ca II and magnetic field strength. The magnetic flux density of each individual BP and FP is estimated from...

Bovelet, Burkart; 10.1051/0004-6361:200809717

2012-01-01

212

Narrow bands and electronic structure in unconventional high-TC superconductors  

International Nuclear Information System (INIS)

Electronic structure details play a marginal role in the superconductive properties of conventional superconductors. Electronic energies are by far the most important in these materials and the only relevant electronic parameter, with respect to superconductivity, is essentially the density of states N(0). Cooper oxides and fullerene compounds are characterized by narrow band dispersions and by electronic structures of hundreds meV. This feature is reflected in the high sensitivity of these materials to fine tuning of electron quantities, as shown by the phase diagram of these materials. A similar situation is encountered in recently discovered superconducting MgB2, where the Fermi edge lies only ?0.5 eV below the top of the ?-bands. We discuss the relevance of these low electronic energy scales in the context of the theory of nonadiabatic electron-phonon coupling, which is achieved when Fermi energies are of the same order as phonon frequencies

2002-11-01

213

Narrow bands and electronic structure in unconventional high-T{sub C} superconductors  

Energy Technology Data Exchange (ETDEWEB)

Electronic structure details play a marginal role in the superconductive properties of conventional superconductors. Electronic energies are by far the most important in these materials and the only relevant electronic parameter, with respect to superconductivity, is essentially the density of states N(0). Cooper oxides and fullerene compounds are characterized by narrow band dispersions and by electronic structures of hundreds meV. This feature is reflected in the high sensitivity of these materials to fine tuning of electron quantities, as shown by the phase diagram of these materials. A similar situation is encountered in recently discovered superconducting MgB{sub 2}, where the Fermi edge lies only {approx}0.5 eV below the top of the {sigma}-bands. We discuss the relevance of these low electronic energy scales in the context of the theory of nonadiabatic electron-phonon coupling, which is achieved when Fermi energies are of the same order as phonon frequencies.

Cappelluti, E.; Grimaldi, C.; Pietronero, L.; Straessler, S

2002-11-15

214

Ultrafast band-structure variations induced by fast Au ions in BeO  

Energy Technology Data Exchange (ETDEWEB)

Auger-electron spectra associated with Be atoms in the pure metal lattice and in an oxide have been investigated for 1.8 MeV/u {sup 129}Au{sup 41+} ions and 2.7 keV primary electrons. The excitation and local energy transfer by such fast primary particles in solids is dominated by electronic processes. The electron-induced spectrum is compared to calculated band-structure results and it is relatively well understood. For the heavy-ion case, however, we observe a significant variation of the Auger electron spectrum, related to a variation of the electronic band structure. This spectrum points to a formation of a metal-like meta-stable electronic density of states.

Schiwietz, G., E-mail: schiwietz@helmholtz-berlin.d [Helmholtz-Zentrum Berlin f. Materialien und Energie, Institut G-I2, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Czerski, K. [Helmholtz-Zentrum Berlin f. Materialien und Energie, Institut G-I2, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Grande, P.L. [Univ. Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, 91501-970 Porto Alegre, RS (Brazil); Koteski, V. [VINCA Institute, Dept. of Physical Chemistry, POB 522, Belgrade 11001 (Serbia); Staufenbiel, F. [Helmholtz-Zentrum Berlin f. Materialien und Energie, Institut G-I2, Hahn-Meitner-Platz 1, 14109 Berlin (Germany)

2011-05-01

215

A first principle study of band structure of III-nitride compounds  

International Nuclear Information System (INIS)

The band structure of both phases, zinc-blende and wurtzite, of aluminum nitride, indium nitride and gallium nitride has been studied using computational methods. The study has been done using first principle full-potential linearized augmented plane wave (FP-LAPW) method, within the framework of density functional theory (DFT). For the exchange correlation potential, generalized gradient approximation (GGA) and an alternative form of GGA proposed by Engel and Vosko (GGA-EV) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show a significant improvement over other theoretical work and are closer to the experimental data

2005-12-15

216

A first principle study of band structure of III-nitride compounds  

Energy Technology Data Exchange (ETDEWEB)

The band structure of both phases, zinc-blende and wurtzite, of aluminum nitride, indium nitride and gallium nitride has been studied using computational methods. The study has been done using first principle full-potential linearized augmented plane wave (FP-LAPW) method, within the framework of density functional theory (DFT). For the exchange correlation potential, generalized gradient approximation (GGA) and an alternative form of GGA proposed by Engel and Vosko (GGA-EV) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show a significant improvement over other theoretical work and are closer to the experimental data.

Ahmed, Rashid [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)]. E-mail: rasofi@hotmail.com; Akbarzadeh, H. [Department of Physics, Isfahan University of Technology, 841546 Isfahan (Iran, Islamic Republic of); Fazal-e-Aleem [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)

2005-12-15

217

Electron momentum distribution in vanadium: Compton scattering measurements and band-structure calculation  

International Nuclear Information System (INIS)

The [100], [110], and [111] Compton profiles and reciprocal form factors have been derived from Compton scattering measurements made with 60-keV "2"4"1Am ? rays on single-crystal samples of vanadium. The same quantities have also been obtained theoretically on the basis of a self-consistent linear-muffin-tin-orbital band-structure calculation, using the local-density approximation for the exchange-correlation potential. An r-space procedure was adopted to calculate the reciprocal form factor B(r) directly from the wave functions. The experimental and theoretical results are compared with previous 412-keV Compton scattering measurements and other band-structure calculations. All calculations overestimate the Compton profile anisotropies at low momenta

1986-01-15

218

Gender-related differences in the apparent timing of skeletal density bands in the reef-building coral Siderastrea siderea  

Science.gov (United States)

Density banding in skeletons of reef-building corals is a valuable source of proxy environmental data. However, skeletal growth strategy has a significant impact on the apparent timing of density-band formation. Some corals employ a strategy where the tissue occupies previously formed skeleton during as the new band forms, which leads to differences between the actual and apparent band timing. To investigate this effect, we collected cores from female and male colonies of Siderastrea siderea and report tissue thicknesses and density-related growth parameters over a 17-yr interval. Correlating these results with monthly sea surface temperature (SST) shows that maximum skeletal density in the female coincides with low winter SSTs, whereas in the male, it coincides with high summer SSTs. Furthermore, maximum skeletal densities in the female coincide with peak Sr/Ca values, whereas in the male, they coincide with low Sr/Ca values. Both results indicate a 6-month difference in the apparent timing of density-band formation between genders. Examination of skeletal extension rates also show that the male has thicker tissue and extends faster, whereas the female has thinner tissue and a denser skeleton—but both calcify at the same rate. The correlation between extension and calcification, combined with the fact that density banding arises from thickening of the skeleton throughout the depth reached by the tissue layer, implies that S. siderea has the same growth strategy as massive Porites, investing its calcification resources into linear extension. In addition, differences in tissue thicknesses suggest that females offset the greater energy requirements of gamete production by generating less tissue, resulting in differences in the apparent timing of density-band formation. Such gender-related offsets may be common in other corals and require that environmental reconstructions be made from sexed colonies and that, in fossil corals where sex cannot be determined, reconstructions must be duplicated in different colonies.

Carricart-Ganivet, J. P.; Vásquez-Bedoya, L. F.; Cabanillas-Terán, N.; Blanchon, P.

2013-09-01

219

Determination of the Rb atomic number density in dense rubidium vapors by absorption measurements of Rb2 triplet bands  

International Nuclear Information System (INIS)

A simple and accurate way of determining atom number densities in dense rubidium vapors is presented. The method relies on the experimental finding that the reduced absorption coefficients of the Rb triplet satellite bands between 740 nm and 750 nm and the triplet diffuse band between 600 nm and 610 nm are not temperature dependent in the range between 600 K and 800 K. Therefore, the absolute values of the reduced absorption coefficients of these molecular bands can provide accurate information about atomic number density of the vapor. The rubidium absorption spectrum was measured by spatially resolved white-light absorption in overheated rubidium vapor generated in a heat pipe oven. The absolute values for the reduced absorption coefficients of the triplet bands were determined at lower vapor densities, by using an accurate expression for the reduced absorption coefficient in the quasistatic wing of the Rb D1 line, and measured triplet satellite bands to the resonance wing optical depth ratio. These triplet satellite band data were used to calibrate in absolute scale the reduced absorption coefficients of the triplet diffuse band at higher temperatures. The obtained values for the reduced absorption coefficient of these Rb molecular features can be used for accurate determination of rubidium atomic number densities in the range from about 5 x 1016 cm-3 to 1 x 1018 cm-3

2008-02-01

220

Effects of crystalline structural transition on electronic-band structure of chromium-doped indium oxide  

International Nuclear Information System (INIS)

The electronic-band structure parameters of chromium-doped indium oxide films with crystalline structural transition were determined by fitting the dielectric functions of Drude and Adachi's model to near-normal reflectance spectra. The evaluated optical bandgap shows a maximum at an intermediate state and decreases respectively toward highly and less ideally crystallized states. We explain this phenomenon by combining the effect of intrinsic bandgap narrowing with the Burstein–Moss shift, both due to the crystalline structural transition. This work provides important insights into electronic-band structures of less ideally structured materials.

2012-01-01

 
 
 
 
221

Damped structure for JLC X-band linac  

International Nuclear Information System (INIS)

Accelerating structures with damping ports for higher modes have been investigated to apply to the JLC X-band linac. The external Q values were evaluated by Slater's tuning method using the computer code MAFIA. It was found by examining the dependence of the external Q value on the geometry of the iris of the damping ports that the structure with circumferential waveguides 11 mm wide was effective in damping the TM110 mode . The external Q values for some of the other higher modes were evaluated and it was found that TE111 mode is hard to damp in such a structure, though its impedance is expected not to be high. To estimate the degradation of the accelerating mode due to the damping ports, the dependence of the Q value and r/Q value on the geometry of the damping port were calculated. Those were about 16% and 4.2%, respectively. (Author) 7 refs., 7 figs., tab

1992-11-01

222

Influence of indium clustering on the band structure of semiconducting ternary and quaternarynitride alloys  

DEFF Research Database (Denmark)

The electronic band structures of InxGa1-xN, InxAl1-xN, and InxGayAl1-x-yN alloys are calculated by ab initio methods using a supercell geometry, and the effects of varying the composition and atomic arrangements methods using a supercell geometry, and the effects of varying the composition and atomic arrangements are examined. Particular attention is paid to the magnitude of and trends in bowing of the band gaps. Indium composition fluctuation (clustering) is simulated by different distributions of In atoms and it is shown that it strongly influences the band gaps. The gaps are considerably smaller when the In atoms are clustered than when they are uniformly distributed. An explanation of this phenomenon is proposed on the basis of an analysis of the density of states and the bond lengths, performed in detail for ternary alloys. Results for the band gaps of InxGayAl1-x-yN quaternary alloys show a similar trend. It is suggested that the large variation in the band gaps determined on samples grown in differentlaboratories is caused by different degrees of In clustering.

Gorczyca,, I.; Łepkowski, S. P.

2009-01-01

223

Band structure and effective mass of InN under pressure  

International Nuclear Information System (INIS)

Calculations of the electronic band structure and effective mass of InN are performed within the density functional theory by means of the linear muffin-tin-orbital method. The results show a pronounced nonparabolicity of the conduction band. Calculated variations of the highest occupied conduction band energy and electron effective mass with free electron concentration are presented and compared to available experimental data. Pressure effects are studied. Both the fundamental band gap and the electron effective mass increase with hydrostatic pressure, but due to the nonparabolic character of the conduction band of InN the pressure coefficient of the effective mass decreases with electron concentration. Experimental verification of this behavior has been performed on three n-type samples of InN with different electron concentrations. The measurements and calculations agree in the description of the dependence of effective mass and its pressure coefficient on electron concentration. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2008-05-01

224

Lamé polynomials, hyperelliptic reductions and Lamé band structure.  

Science.gov (United States)

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

Maier, Robert S

2008-03-28

225

A NOVEL TRIPLE-BAND ELECTROMAGNETIC BANDGAP (EBG STRUCTURE  

Directory of Open Access Journals (Sweden)

Full Text Available A novel triple-band uni-planar electromagnetic bandgap (UC-EBG structure is proposed in this paper. This EBG structure can be considered as distorted uni-planar compact-EBG (DUC-EBG which is connected together by the meandered line inductor. Split ring resonators (SRR are embedded in four pad corners and two L-shaped slots are etched at the central pad. The proposed EBG structure is modelled in three equivalent circuits. By using in-house developed computational code based on the FDTD method, simulated results of dispersion diagrams are presented by complete triple-bandgap. The central frequency of the bandgaps can be reduced to the lower region without increasing the size of the EBG cell. Moreover, an array of 4×5 EBG cells was simulated, fabricated and measured to verify the bandgap characteristic through the transmission coefficient S21. This proposed EBG can be used for multi-band applications, such as dual/triple antennas.

Tran Minh Tuan

2013-01-01

226

Band structure and superconductivity in Lu at high pressures  

Energy Technology Data Exchange (ETDEWEB)

We report here the effect of pressure on the band structure and the superconducting behavior of the hcp metal lutetium. The present work shows that the average of the square of the phonon frequency is considerably increased under pressure and this effect is taken into account while calculating T/sub c/. The calculated T/sub c/ values are in fairly good agreement with the experimental trends. The question of s..-->..d valence transfer under pressure as well as Heine's fifth-power law are discussed. We also report the variation of other parameters such as the electronic specific heat and conduction bandwidth with pressure.

Asokamani, R.; Rajagopalan, M.; Suvasini, M.B.; Sundararajan, V.

1986-06-01

227

X-BAND TRAVELING WAVE RF DEFLECTOR STRUCTURES  

Energy Technology Data Exchange (ETDEWEB)

Design studies on the X-Band transverse RF deflectors operating at HEM{sub ll} mode have been made for two different applications. One is for beam measurement of time-sliced emittance and slice energy spread for the upgraded LCLS project, its optimization in RF efficiency and system design are carefully considered. Another is to design an ultra-fast RF kicker in order to pick up single bunches from the bunch-train of the B-factory storage ring. The challenges are to obtain very short structure filling time with high RF group velocity and good RF efficiency with reasonable transverse shunt impedance. Its RF system will be discussed.

Wang, J.W.; Tantawi, S.; /SLAC

2008-12-18

228

Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

We report on infrared spectroscopy of bilayer graphene integrated in gated structures. We observe a significant asymmetry in the optical conductivity upon electrostatic doping of electrons and holes. We show that this finding arises from a marked asymmetry between the valence and conduction bands, which is mainly due to the inequivalence of the two sublattices within the graphene layer and the next-nearest-neighbor interlayer coupling. From the conductivity data, the energy difference of the two sublattices and the interlayer coupling energy are directly determined.

Li, Z.Q.; Henriksen, E.A.; Jiang, Z.; Hao, Zhao; Martin, Michael C.; Kim, P.; Stormer, H.L.; Basov, Dimitri N.

2008-12-10

229

Band structure of odd-mass lanthanum nuclei  

Science.gov (United States)

Negative parity energy states in 121-131La have been studied using Projected Shell Model (PSM). Some nuclear structure properties like yrast spectra, back-bending in moment of inertia, reduced transition probabilities and band diagrams have been described. The experimental feature of the co-existence of prolate-oblate shapes in 125-131La isotopes has been satisfactorily explained by PSM results. Comparison of the theoretical data with their experimental counterparts has also been made. From the calculations, it is found that the yrast states arise because of multi-quasiparticle states.

Sharma, Deepti; Verma, Preeti; Singh, Suram; Bharti, Arun; Khosa, S. K.

2014-04-01

230

Band structure and superconductivity in Lu at high pressures  

International Nuclear Information System (INIS)

We report here the effect of pressure on the band structure and the superconducting behavior of the hcp metal lutetium. The present work shows that the average of the square of the phonon frequency is considerably increased under pressure and this effect is taken into account while calculating T/sub c/. The calculated T/sub c/ values are in fairly good agreement with the experimental trends. The question of s?d valence transfer under pressure as well as Heine's fifth-power law are discussed. We also report the variation of other parameters such as the electronic specific heat and conduction bandwidth with pressure

1986-06-01

231

Anomalous quasiparticle lifetime in graphite: Band structure effects  

International Nuclear Information System (INIS)

We report ab initio calculations of quasiparticle lifetimes in graphite, as determined from the imaginary part of the self-energy operator within the GW approximation. 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

2001-05-15

232

Tunneling and the band structure of chaotic systems  

International Nuclear Information System (INIS)

The dispersion laws of chaotic periodic systems are computed using the semiclassical periodic orbit theory to approximate the trace of the powers of the evolution operator. Aside from the usual real trajectories, complex orbits are also included. These turn out to be fundamental for a proper description of the band structure since they incorporate conduction processes through tunneling mechanisms. The results obtained, illustrated with the kicked-Harper model, are in excellent agreement with numerical simulations, even in the extreme quantum regime. (authors). 14 refs., 1 fig

1994-01-01

233

A study of higher-band dipole wakefields in X-band accelerating structures for the G/NLC  

CERN Document Server

The X-band linacs for the GLC/NLC (Global Linear Collider/Next Linear Collider) have evolved from the DDS (Damped Detuned Structure) series [1,2]. The present series of accelerating structures are each 60 cm in length and incorporate both damping and detuning of the dipole modes which comprise the wakefield. In order to adequately damp the wakefield the dipole frequencies of adjacent structures are interleaved. The properties of the first dipole band have been extensively studied. However, limited analysis has been done on the higher order dipole bands. Here, we calculate the contribution of the higher order bands of the interleaved structures to the wakefield using a mode matching computer code [3]. Beam dynamics issues are also studied by tracking the beam through the complete linac using the particle beam tracking code LIAR [4].

Jones, R M

2004-01-01

234

Carrier Multiplication in Semiconductor Nanocrystals: Theoretical Screening of Candidate Materials Based on Band-Structure Effects  

International Nuclear Information System (INIS)

Direct carrier multiplication (DCM) occurs when a highly excited electron-hole pair decays by transferring its excess energy to the electrons rather than to the lattice, possibly exciting additional electron-hole pairs. Atomistic electronic structure calculations have shown that DCM can be induced by electron-hole Coulomb interactions, in an impact-ionization-like process whose rate is proportional to the density of biexciton states ?XX. Here we introduce a DCM 'figure of merit' R2(E) which is proportional to the ratio between the biexciton density of states ?XX and the single-exciton density of states ?x, restricted to single-exciton and biexciton states that are coupled by Coulomb interactions. Using R2(E), we consider GaAs, InAs, InP, GaSb, InSb, CdSe, Ge, Si, and PbSe nanocrystals of different sizes. Although DCM can be affected by both quantum-confinement effects (reflecting the underly electronic structure of the confined dot-interior states) and surface effects, here we are interested to isolate the former. To this end the nanocrystal energy levels are obtained from the corresponding bulk band structure via the truncated crystal approximation. We find that PbSe, Si, GaAs, CdSe, and InP nanocrystals have larger DCM figure of merit than the other nanocrystals. Our calculations suggest that high DCM efficiency requires high degeneracy of the corresponding bulk band-edge states. Interestingly, by considering band structure effects we find that as the dot size increases the DCM critical energy E0 (the energy at which R2(E) becomes (ge)1) is reduced, suggesting improved DCM. However, whether the normalized E0/(varepsilon)g increases or decreases as the dot size increases depends on dot material

2008-01-01

235

Prediction of composition for stable half-Heusler phases from electronic-band-structure analyses  

Energy Technology Data Exchange (ETDEWEB)

This report describes a procedure to predict the frequently occurring non-stoichiometry of the half-Heusler XYZ alloys (viz. deviations from the equiatomic 1:1:1 composition and the usually accompanied narrow homogeneity regions) from ab initio calculated electronic-band-structure characteristics. The essential feature of this approach is to utilize the valence electron content (VEC) and the calculated electronic band structure to expose factors that according to rigid-band considerations should determine the possible deviations from 1:1:1 stoichiometry and direction of the stable solid-solution regions. These means have been used to predict the direction of equilibrium solid-solution regions for a number of ternary phase diagrams that comprise half-Heusler phases and the predictions have been tested with experimental data from literature and presently synthesized and microprobe analysed samples of NiTiSn, PtTiSn, CoTiSb, PtMnSb, NiMnSb, and CoMnSb. The predictions are made based on maximum band filling of bonding states identified through the crystal-orbital-Hamilton population (COHP) analysis and density-of-states (DOS) integration.

Offernes, L. [Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo (Norway)], E-mail: Laila.offernes@kjemi.uio.no; Ravindran, P.; Seim, C.W.; Kjekshus, A. [Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo (Norway)

2008-06-30

236

The indirect to direct band gap transition in multilayered MoS2 as predicted by screened hybrid density functional theory  

Science.gov (United States)

Molybdenite (MoS2) undergoes a transition from an indirect to direct gap semiconductor exhibiting strong photoluminescence when confined in a 2D monolayer. We investigate the effect of interlayer interactions on the band structure and density of states using the screened hybrid functional of Heyd, Scuseria, and Ernzerhof. We show that for the bulk and monolayer systems, our short-range screened hybrid functional produces band gaps in good agreement with experiment. Our functional includes only interlayer interactions of non-van der Waals origin, predicts properties consistent with recent experiments, and provides predictions for few-layered systems.

Ellis, Jason K.; Lucero, Melissa J.; Scuseria, Gustavo E.

2011-12-01

237

Bulk Inversion Asymmetry effects on the band structure of zincblende heterostructures in an 8-band Effective Mass Approximation model  

CERN Document Server

We have developed an 8-band Effective Mass Approximation model that describes the zero field spin splitting in the band structure of zincblende heterostructures due to bulk inversion asymmetry (BIA). We have verified that our finite difference Hamiltonian transforms in almost all situations according to the true $D_{2d}$ or $C_{2v}$ symmetry of [001] heterostructures. This makes it a computationally efficient tool for the accurate description of the band structure of heterostructures for spintronics. We first compute the band structure for an AlSb/GaSb/AlSb quantum well (QW), which presents only BIA, and delineate its effects. We then use our model to find the band structure of an AlSb/InAs/GaSb/AlSb QW and the relative contribution of structural and bulk inversion asymmetry to the spin splitting. We clarify statements about the importance of these contributions and conclude that, even for our small gap QW, BIA needs to be taken into account for the proper description of the band structure.

Cartoixa, X; McGill, T C

2002-01-01

238

Quasiparticle semiconductor band structures including spin-orbit interactions.  

Science.gov (United States)

We present first-principles calculations of the quasiparticle band structure of the group IV materials Si and Ge and the group III-V compound semiconductors AlP, AlAs, AlSb, InP, InAs, InSb, GaP, GaAs and GaSb. Calculations are performed using the plane wave pseudopotential method and the 'one-shot' GW method, i.e. G(0)W(0). Quasiparticle band structures, augmented with the effects of spin-orbit, are obtained via a Wannier interpolation of the obtained quasiparticle energies and calculated spin-orbit matrix. Our calculations explicitly treat the shallow semicore states of In and Ga, which are known to be important in the description of the electronic properties, as valence states in the quasiparticle calculation. Our calculated quasiparticle energies, combining both the ab initio evaluation of the electron self-energy and the vector part of the pseudopotential representing the spin-orbit effects, are in generally very good agreement with experimental values. These calculations illustrate the predictive power of the methodology as applied to group IV and III-V semiconductors. PMID:23396813

Malone, Brad D; Cohen, Marvin L

2013-03-13

239

Electronic Band Structure and Optical Properties of Srn+1TinO3n+1 Ruddlesden-Popper Homologous Series  

Science.gov (United States)

State-of-the-art calculations of electronic band structures, density of states and frequency-dependent optical properties have been reported for Srn+1TinO3n+1 (n=1, 2, 3, ?) compounds. These materials possess indirect wide energy band gaps. The frequency dependent optical properties of n=1,2,3 compounds show considerable anisotropy and positive birefringence. The conduction band minimum is originates from Ti-d states, while the valence band maximum is governed by O-p states. The bandwidth of the Ti-d states is responsible for the decrease in the energy band gap as n changes from 1 to 2, 3, and ?. We have analyzed the degree of hybridization on the basis of the ratio of the orbital overlapping within the muffin tin sphere.

Reshak, Ali Hussain; Auluck, Sushil; Kityk, Ivan

2008-07-01

240

Band Structure and Transport Properties of $CrO_{2}$  

CERN Document Server

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 ...

Lewis, S P; Sasaki, T; Lewis, Steven P.; Allen, Phillip B.; Sasaki, Taizo

1996-01-01

 
 
 
 
241

Valence-band orbital character of CdO: A synchrotron-radiation photoelectron spectroscopy and density functional theory study  

Science.gov (United States)

N-type CdO is a transparent conducting oxide (TCO) which has promise in a number of areas including solar cell applications. In order to realize this potential a detailed knowledge of the electronic structure of the material is essential. In particular, standard density functional theory (DFT) methods struggle to accurately predict fundamental material properties such as the band gap. This is largely due to the underestimation of the Cd 4d binding energy, which results in a strong hybridization with the valence-band (VB) states. In order to test theoretical approaches, comparisons to experiment need to be made. Here, synchrotron-radiation photoelectron spectroscopy (SR-PES) measurements are presented, and comparison with three theoretical approaches are made. In particular the position of the Cd 4d state is measured with hard x-ray PES, and the orbital character of the VB is probed by photon energy dependent measurements. It is found that LDA + U using a theoretical U value of 2.34 eV is very successful in predicting the position of the Cd 4d state. The VB photon energy dependence reveals the O 2p photoionization cross section is underestimated at higher photon energies, and that an orbital contribution from Cd 5p is underestimated by all the DFT approaches.

Mudd, J. J.; Lee, Tien-Lin; Muñoz-Sanjosé, V.; Zúñiga-Pérez, J.; Payne, D. J.; Egdell, R. G.; McConville, C. F.

2014-04-01

242

Photonic band gaps in three-dimensional network structures with short-range order  

International Nuclear Information System (INIS)

We present a systematic study of photonic band gaps (PBGs) in three-dimensional (3D) photonic amorphous structures (PASs) with short-range order. From calculations of the density of optical states (DOS) for PASs with different topologies, we find that tetrahedrally connected dielectric networks produce the largest isotropic PBGs. Local uniformity and tetrahedral order are essential to the formation of PBGs in PASs, in addition to short-range geometric order. This work demonstrates that it is possible to create broad, isotropic PBGs for vector light fields in 3D PASs without long-range order.

2011-12-01

243

DENSITY AND SURFACE STRUCTURE OF ICE ACCRETIONS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The dependence of accreted ice density on growth conditions has been investigated by growing deposits on rotating and fixed cylinders. The local density of the accretions has been measured by X-ray contact micrography on calibrated normal sections. The results show that the local density is higher than that given by Macklin's relationship. The latter may be considered valid only for the mean density of rotating cylinders, which contain lobes and correlated air channels. Lobes are absent in fi...

Prodi, F.; Levi, L.

1987-01-01

244

The electronic structure of NaIrO3, Mott insulator or band insulator?  

Science.gov (United States)

Motivated by the unveiled complexity of nonmagnetic insulating behavior in the pentavalent post-perovskite NaIrO3, we have studied its electronic structure and phase diagram in the plane of Coulomb repulsive interaction and spin-orbit coupling by using the newly developed local density approximation plus Gutzwiller method. Our theoretical study proposes that the metal-insulator transition can be generated by two different physical pictures: renormalized band insulator or Mott insulator regime. For the realistic material parameters in NaIrO3, Coulomb interaction U = 2.0 eV (J = U/4) and spin-orbit coupling strength ? = 0.33 eV, it tends to favor the renormalized band insulator picture as revealed by our study.

Du, Liang; Sheng, Xianlei; Weng, Hongming; Dai, Xi

2013-01-01

245

Band structure, Fermi surface, superconductivity, and resistivity of actinium under high pressure  

Energy Technology Data Exchange (ETDEWEB)

The electronic band structures of fcc actinium (Ac) have been calculated for a wide range of pressures by reducing the unit-cell volume from 1.0V/sub 0/ to 0.5V/sub 0/ with use of the relativistic augmented-plane-wave method. The density of states and Fermi-surface cross sections corresponding to various volumes are obtained. Calculations for the band-structure-related quantities such as electron-phonon mass enhancement factor lambda, superconducting transition temperature T/sub c/, and resistivity rho corresponding to different volumes are performed. It is seen that T/sub c/ increases with pressure, i.e., with decreasing volume. A new empirical relation for the volume dependence of T/sub c/ is proposed and its validity is checked using the T/sub c/ values obtained from the above band-structure results. The resistivity rho first increases with increasing pressure (i.e., with decreasing volume) and then decreases for higher pressures (i.e., for smaller volumes).

Dakshinamoorthy, M.; Iyakutti, K.

1984-12-15

246

Electronic structure of metals of the beginning and the end of the third transition period. 1. Energy-band structure (review)  

International Nuclear Information System (INIS)

The papers connected with the calculation of the energetic band structure of elements of the beginning and the end of the third transition period, such as Lu, Hf, Ir, Pt and Au, are considered. It is noted that the best agreement between theoretical and experimental ata is observed in casds when the crystalline potential is plotted on relativistic wave functions with complete Slater exchange. The application of the relativistic method of attached flat waves to calculate band structure and partial densities of transition metal states is considered. The effect of relativistic effects on the energetic band structure and energy distribution of complete and partical densities of states of the elements of the third transition period is discussed

1981-01-01

247

Analysis of photonic band-gap structures in stratified medium  

DEFF Research Database (Denmark)

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.

Tong, Ming-Sze; Yinchao, Chen

2005-01-01

248

Reading data stored in the state of metastable defects in silicon using band-band photoluminescence: Proof of concept and physical limits to the data storage density  

Science.gov (United States)

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.

Rougieux, F. E.; Macdonald, D.

2014-03-01

249

A Tri-band-notched UWB Antenna with Low Mutual Coupling between the Band-notched Structures  

Directory of Open Access Journals (Sweden)

Full Text Available A compact printed U-shape ultra-wideband (UWB antenna with triple band-notched characteristics is presented. The proposed antenna, with compact size of 24×33 mm2, yields an impedance bandwidth of 2.8-12GHz for VSWR less than 2, except the notched bands. The notched bands are realized by introducing two different types of slots. Two C-shape half-wavelength slots are etched on the radiating patch to obtain two notched bands in 3.3-3.7GHz for WiMAX and 7.25-7.75GHz for downlink of X-band satellite communication systems. In order to minimize the mutual coupling between the band-notched structures, the middle notched band in 5-6GHz for WLAN is achieved by using a U-slot defected ground structure. The parametric study is carried out to understand the mutual coupling. Surface current distributions and equivalent circuit are used to illustrate the notched mechanism. The performance of this antenna both by simulation and by experiment indicates that the proposed antenna is suitable and a good candidate for UWB applications.

C. M. Luo

2013-12-01

250

Band structure of the spectra of Hamiltonians of regular polynucleotide duplexes  

Science.gov (United States)

We calculate the band structure of the spectra of Hamiltonians of regular DNA duplexes and show that in single-stranded periodic polynucleotides whose period is determined by the number m of nucleotides in an elementary cell, the spectrum consists of m nonintersecting energy bands. In DNA duplexes, the number of energy bands is equal to 2m, and the bands can intersect. Discrete energy levels can be present in forbidden bands in the case of (semi)bounded chains or duplexes.

Lakhno, V. D.; Sultanov, V. B.

2013-09-01

251

Tunable band structure effects on ballistic transport in graphene nanoribbons  

International Nuclear Information System (INIS)

Graphene nanoribbons (GNR) in mutually perpendicular electric and magnetic fields are shown to exhibit dramatic changes in their band structure and electron transport properties. A strong electric field across the ribbon induces multiple chiral Dirac points, closing the semiconducting gap in armchair GNRs. A perpendicular magnetic field induces partially formed Landau levels as well as dispersive surface-bound states. Each of the applied fields on its own preserves the even symmetry Ek=E-k of the subband dispersion. When applied together, they reverse the dispersion parity to be odd and gives Ee,k=-Eh,-k and mix the electron and hole subbands within the energy range corresponding to the change in potential across the ribbon. This leads to oscillations of the ballistic conductance within this energy range.

2010-08-30

252

X-band coaxial standing-wave linear accelerator structure  

International Nuclear Information System (INIS)

A new high efficiency X-Band, standing-wave linear accelerator cavity structure has been developed. It utilizes a shaped coaxial cavity as the coupling cavity between accelerating cavities for ?/2 mode operation, hence the overall diameter is extremely small while maintaining a very high shunt impedance. The coupling cavity and accelerating cavity are easily machined on opposite sides of a single cell, eliminating any subassembly steps. Cavity geometries were developed using the computer codes LACC and LALA. Prototype 1.5 MeV and 4.0 MeV, 20 cm long accelerators are now under development. The accelerators employ a stepped field focusing technique to keep the beam focused at low field levels. The beam dynamics code PARMELA was used to optimize the longitudinal bunching and transverse beam characteristics. The accelerator design parameters, as well as experimental results, are presented

1986-09-01

253

Nuclear energy density optimization: Shell structure  

CERN Multimedia

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...

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

254

Photonic band-structure calculations using the boundary element method  

Science.gov (United States)

A boundary element method is developed for calculating the photon modes of periodic structures whose unit cells consist of piecewise homogeneous dielectric materials of arbitrary shapes. Green's function techniques are used to derive integral equations for these structures. These equations involve integrals over the boundaries between the regions, which are discretized and solved numerically. Thus the full set of Maxwell's equations with boundary conditions in d independent variables is changed into an integral equation in d-1 variables. We calculate the mode frequencies and field patterns for wave vectors throughout the Brillouin zone, thus allowing the determination of photonic band gaps. We show that this method generally provides improved calculational efficiency as compared to alternative approaches, and that it is more effective in treating high-frequency modes. Previously we have discussed this approach for electronic states in nanostructuresfootnote P. A. Knipp and T. L. Reinecke, Phys. Rev. B 54, 1880 (1996). and for photonic modes in waveguides. Here we extend this technique for photonic modes in periodic structures. Illustrative examples are given here for several two-dimensional systems.

Knipp, P. A.; Reinecke, T. L.

1997-03-01

255

Study of band structure of neutron-rich Pr isotopes  

Science.gov (United States)

The newly established bands in 151,153Pr are studied by using projected shell model approach. The calculated level scheme is in good agreement with the experimental data and the reflection-symmetric-quasi-particle rotor model. The present calculations predict proton g9/2, K = 9/2 band as the lowest positive parity band in both the nuclei.

Ram, Daya; Krishan, Gopal; Devi, Rani; Khosa, S. K.

2013-04-01

256

The Importance of Static Correlation in the Band Structure of High Temperature Superconductors  

CERN Document Server

Recently we presented a new band structure for La(2-x)Sr(x)CuO(4) and other high temperature superconductors in which a second narrow band was seen to cross the primary band at the Fermi level. The existence of this second Fermi level band is in complete disagreement with the commonly accepted LDA band structure. Yet it provided a crucial piece of physics which led to an explanation for superconductivity and other unusual phenomena in these materials. In this work we present details as to the nature of the failure of conventional methods in deriving the band structure of the cuprates. In particular, we use a number of chemical analogues to describe the problem of static correlation in the band structure calculations and show how this can be corrected with the predictable outcome of a Fermi level band crossing.

Perry, J K

1999-01-01

257

Strain Engineering of the Band Structure and Picosecond Carrier Dynamics of Single Semiconductor Nanowires Probed by Modulated Rayleigh Scattering Microscopy  

Science.gov (United States)

The band structure and carrier dynamics of GaAs, GaAs/GaP and InP semiconductor nanowires is explored using a variety of optical spectroscopy techniques including two newly developed techniques called Photomodulated and Transient Rayleigh scattering spectroscopy. The stress and electronic band structure of as-grown highly strained GaAs/GaP core/shell nanowire is studied via room temperature Raman scattering by phonons and low temperature photoluminescence spectroscopy. Raman measurements reveal the uniaxial nature of the shell-induced stress in the core GaAs nanowire with a significantly different degree of compression in the radial plane and axial direction of the nanowire. The uniaxial stress dramatically modifies the electronic band structure of the nanowire. Raman measurements predict that the shell-induced stress should shift the band gap of GaAs to higher energies by ~260 meV which is experimentally confirmed by low temperature photoluminescence spectroscopy. Furthermore, it is predicted that the uniaxial stress in the nanowire removes the degeneracy of the heavy and light hole valence bands at the zone center by ~100 meV. In order to probe the electronic band structure of single nanowires with high spatial and spectral resolution, the new technique of Photomodulated Rayleigh Scattering spectroscopy (PMRS) is introduced. We show that by photomodulating the dielectric function of the nanowire, the background-free and robust differential Rayleigh spectrum measures the band structure of the nanowire with exceptionally high energy resolution. PMRS measurements are performed on zincblende GaAs and zincblende and wurtzite InP nanowires at both room and low temperature. Furthermore, we show that the diameters of the nanowires can be extracted from the PMRS spectra with an uncertainty of only a few nanometers. By extending the PMRS spectroscopy into time domain, we introduce Transient Rayleigh Scattering spectroscopy (TRS) to study the ultrafast carrier dynamics and cooling within the band structure of single nanowires with picosecond time resolution. Due to many body effects, the Rayleigh cross-section is sensitive to the occupation of the electronic band structure by photo injected carriers which allows one to simultaneously measure the density and temperature of the photo injected electron-hole plasma as a function of time after excitation. The time dependent density and temperature of the plasma provide direct insight into the various mechanisms dominating the dynamics and cooling of carriers within the electronic band structure including ambipolar diffusion, recombination processes and emission of optical and acoustic phonons. Specifically, TRS of a single GaAs/AlGaAs core-shell nanowire is presented which quantifies various fundamental properties of nanowire including carrier mobility, recombination rates and the energy-loss rate of plasma due to optical and acoustic phonon emission. Similar measurements on a single InP nanowire with hexagonal wurtzite symmetry reveals the dynamics associated with various energy bands including the coupling of A, B and C valence bands to the lowest conduction band as well as the theoretically predicted second conduction band. The second conduction band is experimentally measured at 236-240 meV higher than the first conduction band. The second conduction band is theoretically calculated at 238 meV above the first conduction band.

Montazeri, Mohammad

258

Method of manufacturing flexible metallic photonic band gap structures, and structures resulting therefrom  

Energy Technology Data Exchange (ETDEWEB)

A method of manufacturing a flexible metallic photonic band gap structure operable in the infrared region, comprises the steps of spinning on a first layer of dielectric on a GaAs substrate, imidizing this first layer of dielectric, forming a first metal pattern on this first layer of dielectric, spinning on and imidizing a second layer of dielectric, and then removing the GaAs substrate. This method results in a flexible metallic photonic band gap structure operable with various filter characteristics in the infrared region. This method may be used to construct multi-layer flexible metallic photonic band gap structures. Metal grid defects and dielectric separation layer thicknesses are adjusted to control filter parameters.

Gupta, Sandhya (Bloomington, MN); Tuttle, Gary L. (Ames, IA); Sigalas, Mihail (Ames, IA); McCalmont, Jonathan S. (Ames, IA); Ho, Kai-Ming (Ames, IA)

2001-08-14

259

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.

2009-05-04

260

Experimental determination of the band structure of photonic crystals of colloidal silica spheres  

Science.gov (United States)

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.

Liu, K.; Schmedake, T. A.; Tsu, R.

2009-05-01

 
 
 
 
261

Bychkov-Rashba dominated band structure in an In{sub 0.75}Ga{sub 0.25}As-In{sub 0.75}Al{sub 0.25}As device with spin-split carrier densities of <10{sup 11} cm{sup -2}  

Energy Technology Data Exchange (ETDEWEB)

We demonstrate that a Bychkov-Rashba dominated band structure can be stabilized in a nominally undoped In{sub 0.75}Ga{sub 0.25}As-In{sub 0.75}Al{sub 0.25}As quantum well. The transport properties of this system have been measured at 1.7 and 4.2 K and the Rashba coefficient {alpha} has been determined in enhancement and depletion modes with an insulated front gate. In enhancement mode, {alpha} is 1 x 10{sup -11} eV m with carrier densities n{sub s} between 1.4 and 1.9 x 10{sup 11} cm{sup -2}. In depletion mode, with n{sub s}<1.4 x 10{sup 11} cm{sup -2}, {alpha} was reduced to 0.7 x 10{sup -11} eV m. The wavefunction penetration into the In{sub 0.75}Al{sub 0.25}As barriers, i.e. the interface asymmetry, makes no contribution to {alpha} in this system. We minimize the Zeeman energy spin-splitting in this high g-factor system by analysing only the Shubnikov-de Haas structure below 0.5 T, i.e. for Landau level filling factors >12. The combination of the two spin-split subbands in {rho}{sub xx} can be separated using a magnetic field modulation technique where analogue d{rho}{sub xx}/dB or d{sup 2}{rho}{sub xx}/dB{sup 2} signals are measured directly. The In{sub 0.75}Ga{sub 0.25}As-In{sub 0.75}Al{sub 0.25}As quantum well will have applications both in one-dimensional systems and in gate-induced two-dimensional electron gases where a dominant Bychkov-Rashba spin-splitting is required without the complications of an embedded strained InAs well and without a significant contribution from the interface asymmetry at the In{sub 0.75}Al{sub 0.25}As barriers. (fast track communication)

Holmes, S N; Pepper, M [Toshiba Research Europe Limited, Cambridge Research Laboratory, 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ (United Kingdom); Simmonds, P J; Beere, H E; Sfigakis, F; Farrer, I; Ritchie, D A [Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE (United Kingdom)], E-mail: s.holmes@crl.toshiba.co.uk

2008-11-26

262

Quasiparticle band structures of six II-VI compounds: ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe  

International Nuclear Information System (INIS)

Quasiparticle band structures of six II-VI compounds (ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe in the zinc-blende and wurtzite structures) are calculated using the GW approximation. Results for band structures, calculated using the ab initio pseudopotential method within the local-density approximation (LDA), are given along with the energies of the quasiparticle excitations at symmetry points. Comparisons are made with measured values and trends in the GW corrections to the LDA band structures are examined

1994-10-15

263

Band structures of ZnTe:O alloys with isolated oxygen and with clustered oxygen impurities  

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Band structures of ZnTe:O alloy highly depends on the status of oxygen. • Clustered oxygen lowers the bandgap while isolated oxygen increases the bandgap. • The solar adsorption efficiency of ZnTe:O can be improved by oxygen clustering. -- Abstract: First-principles calculations reveal that band structures of ZnTe:O alloys highly depend on the configuration of oxygen in the alloy. For alloys with isolated oxygen, the calculated band structure shows the formation of intermediate states between valence and conduction band and the shift of conduction band to higher energy level. It expands the gap between valence and conduction band. For alloys with clustered oxygen, the formation of intermediate band is still observed, while the gap between valence and conduction band is decreased. For alloys with oxygen impurities adjacent to Zn vacancy, the band structure only shows the decrease of the gap between valence and conduction band without the formation of any intermediate band. These results suggest the critical role of Zn–O bonding in determining the energy level of the impurity states. On the basis of our results, a possible band engineering approach is suggested in order to improve the performance of ZnTe:O alloy as intermediate band solar adsorbent.

Ling, Chen, E-mail: chen.ling@tema.toyota.com; Zhou, Li Qin; Banerjee, Debasish; Jia, Hongfei

2014-01-25

264

Band structures of ZnTe:O alloys with isolated oxygen and with clustered oxygen impurities  

International Nuclear Information System (INIS)

Highlights: • Band structures of ZnTe:O alloy highly depends on the status of oxygen. • Clustered oxygen lowers the bandgap while isolated oxygen increases the bandgap. • The solar adsorption efficiency of ZnTe:O can be improved by oxygen clustering. -- Abstract: First-principles calculations reveal that band structures of ZnTe:O alloys highly depend on the configuration of oxygen in the alloy. For alloys with isolated oxygen, the calculated band structure shows the formation of intermediate states between valence and conduction band and the shift of conduction band to higher energy level. It expands the gap between valence and conduction band. For alloys with clustered oxygen, the formation of intermediate band is still observed, while the gap between valence and conduction band is decreased. For alloys with oxygen impurities adjacent to Zn vacancy, the band structure only shows the decrease of the gap between valence and conduction band without the formation of any intermediate band. These results suggest the critical role of Zn–O bonding in determining the energy level of the impurity states. On the basis of our results, a possible band engineering approach is suggested in order to improve the performance of ZnTe:O alloy as intermediate band solar adsorbent

2014-01-25

265

Electronic density of states and the x-ray photoelectron spectra of the valence band of Cu-Pd alloys  

International Nuclear Information System (INIS)

We present self-consistent-field Korringa-Kohn-Rostoker coherent-potential-approximation calculations of the electronic density of states of random Cu/sub c/Pd/sub 1-c/ alloys. We find strong hybridization of the palladium d bands with the copper d bands over the entire concentration range. We do not obtain a palladium virtual bound state for the copper-rich alloys and therefore contradict the interpretation generally placed on valence-band x-ray photoelectron spectroscopy (XPS) spectra for Cu-Pd. Nevertheless, our first-principles calculations of the XPS spectra are in excellent agreement with recent measurements, and we discuss why this is so. Furthermore, we compare our density of states at the Fermi energy with specific-heat measurements

1986-02-15

266

Band structures in doubly-odd 120I nucleus  

International Nuclear Information System (INIS)

Two new collective bands have been identified in 120I nucleus from the cross-bombardment results of 108Pd(16O,p3n) and 114Cd(11B,5n) reactions. Of these, a strongly coupled band, based on ?g7/2xyh11/2 quasiparticles, exhibits energy staggering in odd even spin states. The other band, based on ?h11/2xyg7/2 configuration, is decoupled in nature and shows a band-crossing at h?=0.39 MeV due to alignment of an h11/2 quasineutron pair. (orig.)

1995-06-01

267

High spin structure in a coupled bands model  

International Nuclear Information System (INIS)

A coupled bands model proposed earlier is developed. It is a modification of the band crossing models with Coriolis interaction and conserves rotational invariance. It is applied to the phenomenological description of energies and transition rates for crossing rotational bands in even-even nuclei. Information on the strengths of band interactions has been deduced by a fit to experimental energies. The strange clockwise circling dependence of reduced transition probabilities on squared rotational frequencies in the yrast line has been described, and information on interband E2 moment matrix elements has been deduced by a fit to experimental transition rates. (author)

1980-01-01

268

On the multi-orbital band structure and itinerant magnetism of iron-based superconductors  

Energy Technology Data Exchange (ETDEWEB)

This paper explains the multi-orbital band structures and itinerant magnetism of the iron-pnictide and chalcogenide superconductors. We first describe the generic band structure of a single, isolated FeAs layer. Use of its Abelian glide-mirror group allows us to reduce the primitive cell to one FeAs unit. For the lines and points of high symmetry in the corresponding large, square Brillouin zone, we specify how the one-electron Hamiltonian factorizes. From density-functional theory, and for the observed structure of LaOFeAs, we generate the set of eight Fe d and As p localized Wannier functions and their tight-binding (TB) Hamiltonian, h (k). For comparison, we generate the set of five Fe d Wannier orbitals. The topology of the bands, i. e. allowed and avoided crossings, specifically the origin of the d{sup 6} pseudogap, is discussed, and the role of the As p orbitals and the elongation of the FeAs{sub 4} tetrahedron emphasized. We then couple the layers, mainly via interlayer hopping between As p{sub z} orbitals, and give the formalism for simple tetragonal and body-centered tetragonal (bct) stackings. This allows us to explain the material-specific 3D band structures, in particular the complicated ones of bct BaFe{sub 2}As{sub 2} and CaFe{sub 2}As{sub 2} whose interlayer hoppings are large. Due to the high symmetry, several level inversions take place as functions of k{sub z} or pressure, and linear band dispersions (Dirac cones) are found at many places. The underlying symmetry elements are, however, easily broken by phonons or impurities, for instance, so that the Dirac points are not protected. Nor are they pinned to the Fermi level because the Fermi surface has several sheets. From the paramagnetic TB Hamiltonian, we form the band structures for spin spirals with wavevector q by coupling h (k) and h (k + q). The band structure for stripe order is studied in detail as a function of the exchange potential, {delta}, or moment, m, using Stoner theory. Gapping of the Fermi surface (FS) for small {delta} requires matching of FS dimensions (nesting) and d-orbital characters. The interplay between pd hybridization and magnetism is discussed using simple 4 x 4 Hamiltonians. The origin of the propeller-shaped Fermi surface is explained in detail. Finally, we express the magnetic energy as the sum over band-structure energies and this enables us to understand to what extent the magnetic energies might be described by a Heisenberg Hamiltonian, and to address the much discussed interplay between the magnetic moment and the elongation of the FeAs{sub 4} tetrahedron. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Andersen, O.K.; Boeri, L. [Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart (Germany)

2011-01-15

269

Optical Transitions and Electronic Band structure of Cuprous Oxide Thin Films  

Science.gov (United States)

Cu2O thin films were grown on Si and SiO2/Si substrates via RF sputtering deposition at various temperatures. The Cu2O thin films had a smooth surface when grown at RT, but developed grain boundaries when grown at 300 ^oC. We observed the high-energy photoluminescence (PL) peaks at 3.18 eV (Ep) and 3.27 eV (Eq). The dielectric functions of the Cu2O thin films were measured using spectroscopic ellipsometry. To estimate the critical point (CP) energies, we applied the standard critical point (SCP) model to the second derivative spectra of the dielectric functions (d^2?/dE^2). We also calculated the electronic band structure of bulk Cu2O by using the screened HSE hybrid density functional. Based on the band structure, the CP was estimated as 2.05 eV (E0A(E0B)), 2.77 eV (E0C(E0D)) at the ? point, 4.17 eV (E1A) and 6.10 eV (E2) at the X point, 4.94 eV (E1B) at the R point. The experimental CP energies are consistent with the HSE results, but are systematically smaller than the calculated values by 0.3-0.8 eV due to large electron-hole interaction in CuO2 that was not included in the simulations. The high-energy peaks in the PL spectra at 3.18 eV (Ep) and 3.27 eV (Eq) were attributed to the quasi-direct transitions between the ? valence band and the M and X conduction bands, respectively. The physical origin of the quasi-direct transitions was attributed to the grain boundaries.

Lee, Hosun; Park, Jun-Woo; Jang, Hyungkeun; Kim, Sung; Choi, Suk-Ho; Kang, Joongoo; Wei, Su-Huai

2012-02-01

270

Lunar banding in the scleractinian coral Montastraea faveolata: Fine-scale structure and influence of temperature  

Science.gov (United States)

Lunar cycles play an important role in controlling biological rhythms in many organisms, including hermatypic corals. Coral spawning is correlated with environmental factors, including surface seawater temperature (SST) and lunar phase. Calcium carbonate skeletons of corals possess minute structures that, when viewed via X-radiography, produce high-density (HD) annual banding patterns. Some corals possess dissepiments that serve as the microstructural base for upward corallite growth. Here we report the results of detailed structural analysis of the skeleton of Montastraea faveolata (Scleractinia) (Ellis and Solander, 1786) and quantify the number of dissepiments that occur between HD bands, including interannual and intercorallite variability. Using a 30 year database, spanning from 1961 to 1991, we confirm earlier speculation by several authors that the frequencies of these microbands within a year is tightly linked to the lunar cycle. We also demonstrate that the frequency distribution of the number of these dissepiments per year is skewed to lower numbers. Extensive statistical analyses of long-term daily SST records (University of Puerto Rico, Mayaguez) revealed that precipitation of dissepiments is suppressed in years of cooler-than-average seawater temperature. We propose that dissepiment deposition is driven primarily by lunar cycle and seawater temperature, particularly at lower temperatures, and banding is generally unaffected by normal or high temperatures. These fine-scale banding patterns are also strongly correlated with the number of lunar months between reproductive spawning events in average or warmer-than-average seawater temperature years. This microbanding may represent another proxy for high-resolution estimates of variance in marine palaeo-temperatures, particularly during cooler SST years.

Winter, Amos; Sammarco, Paul W.

2010-10-01

271

Spin-dependent electronic band structure of Co/Cu(001) with different film thicknesses  

Energy Technology Data Exchange (ETDEWEB)

Spin- and angle-resolved photoemission spectroscopy (SARPES) has been applied to the study of spin-polarized electronic structures of face-centered tetragonal (fct) Co thin films with thicknesses from 2 to 9.5 monolayers (MLs). We have clearly observed two dispersive majority and minority spin band structures originating from the bulk-like bands. These observed band structures show narrower width for thinner film due to an in-plane lattice expansion at the Co-Cu interface.

Miyamoto, K; Iori, K; Sakamoto, K; Kimura, A; Taniguchi, M [Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526 (Japan); Qiao, S; Shimada, K; Namatame, H [Hiroshima Synchrotron Radiation Center, Hiroshima University, 2-313 Kagamiyama, Higashi-Hiroshima 739-0046 (Japan)], E-mail: kmiyamoto@hiroshima-u.ac.jp

2008-06-04

272

Electronic band structure in porous silicon studied by photoluminescence and photoluminescence excitation spectroscopy  

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.

2004-10-01

273

Electronic band structure calculations of bismuth-antimony nanowires  

Science.gov (United States)

Alloys of bismuth and antimony received initial interest due to their unmatched low-temperature thermoelectric performance, and have drawn more recent attention as the first 3D topological insulators. One-dimensional bismuth-antimony (BiSb) nanowires display interesting quantum confinement effects, and are expected to exhibit even better thermoelectric properties than bulk BiSb. Due to the small, anisotropic carrier effective masses, the electronic properties of BiSb nanowires show great sensitivity to nanowire diameter, crystalline orientation, and alloy composition. We develop a theoretical model for calculating the band structure of BiSb nanowires. For a given crystalline orientation, BiSb nanowires can be in the semimetallic, direct semiconducting, or indirect semiconducting phase, depending on nanowire diameter and alloy composition. These ``phase diagrams'' turn out to be remarkably similar among the different orientations, which is surprising in light of the anisotropy of the bulk BiSb Fermi surface. We predict a novel direct semiconducting phase for nanowires with diameter less than ˜15 nm, over a narrow composition range. We also find that, in contrast to the bulk and thin film BiSb cases, a gapless state with Dirac dispersion cannot be realized in BiSb nanowires.

Levin, Andrei; Dresselhaus, Mildred

2012-02-01

274

Level Structures and Double ?-BANDS in 105Mo, 108Mo and 112Ru  

Science.gov (United States)

The level structures of 105,108Mo and 112Ru have been carefully investigated by measuring prompt ? - ? - ? coincident measurements of neutron-rich nuclei populated in the spontaneous fission of 252Cf. In 105Mo five new collective bands are observed. The three bands are proposed as single-neutron excitation bands built on the 3/2+[411], 1/2+[411] and 5/2+[413] Nilsson orbitals, respectively. The other two bands are candidates for one-phonon K = 9/2 and two-phonon K = 13/2 ?-vibrational bands, respectively. This is the first observation of such ?-vibrational collective band structures in odd-A nuclei. In 108Mo and 112Ru, the one-phonon ?-vibrational bands have been extended and two-phonon ?-vibrational bands have been identified for the first time.

Zhu, S. J.; Ding, H. B.; Hamilton, J. H.; Ramayya, A. V.; Che, X. L.; Hwang, J. K.; Luo, Y. X.; Rasmussen, J. O.; Li, K.; Goodin, C.; Liu, S.; Chen, Y. J.; Li, M. L.; Daniel, A. V.; Ter-Akopian, G. M.

2008-08-01

275

Ab initio quasiparticle band structure of ABA and ABC-stacked graphene trilayers  

Science.gov (United States)

We obtain the quasiparticle band structure of ABA and ABC-stacked graphene trilayers through ab initio density-functional theory (DFT) and many-body quasiparticle calculations within the GW approximation. To interpret our results, we fit the DFT and GW ? bands to a low-energy tight-binding model, which is found to reproduce very well the observed features near the K point. The values of the extracted hopping parameters are reported and compared with available theoretical and experimental data. For both stackings, the self-energy corrections lead to a renormalization of the Fermi velocity, an effect also observed in previous calculations on monolayer graphene. They also increase the separation between the higher-energy bands, which is proportional to the nearest-neighbor interlayer hopping parameter ?1. Both features are brought to closer agreement with experiment through the self-energy corrections. Finally, other effects, such as trigonal warping, electron-hole asymmetry, and energy gaps, are discussed in terms of the associated parameters.

Menezes, Marcos G.; Capaz, Rodrigo B.; Louie, Steven G.

2014-01-01

276

Theoretical and experimental study of the unoccupied electronic band structure of Ru(001) by electron reflection  

International Nuclear Information System (INIS)

Very-low-energy electron diffraction (VLEED) is used to study the unoccupied electronic states of Ru(001). Experimental and theoretical data are presented for reflection of electrons with energies of the specular beam between 7 and 32 eV and at different angles of incidence between 3"0 and 28"0 in both the Gamma-barK-bar and Gamma-barM-bar directions. Two sharp reflection minima at kinetic energies of 11.1 and 12.3 eV (relative to the vacuum level) corresponding to a final-state peak in Ru(001) angle-resolved photoemission and secondary-electron emission are observed near normal incidence. Theoretical VLEED intensity and band-structure calculations are carried out to confirm the origin of the experimental spectral features. An energy-dependent optical potential is shown to be sufficient to explain the observed narrow spectral structures. The observed minima can be reproduced excellently with the imaginary part of the optical potential equal to -0.6 eV at 11 eV above the vacuum level. The minimum at 12.3 eV can clearly be correlated with a high density of states in the volume band structure, whereas the other one is assigned to a Shockley-type surface state. The effects of several other parameters on the theoretical spectra are discussed

1986-05-15

277

Collective structures and smooth band termination in 109Sn  

International Nuclear Information System (INIS)

Six rotational bands up to energies Ex = 24.7 MeV and spins J?=(79/2-) have been identified in 109Sn using the GAMMASPHERE ?-detector array. Four of the bands show smoothly decreasing dynamic moments of inertia at rotational frequencies ??>0.6 MeV. The bands arise at medium spins from a coupling of a valence d5/2, g7/2 or h11/2 neutron to the deformed 2p2h proton excitation of the Z=50 core 108Sn. At very high ?? these bands show the typical behaviour of smoothly terminating bands, i.e. a gradual alignment of the angular momenta of the valence particles and holes corresponding to a transition from high collectivity to noncollective states. (orig.)

1996-12-01

278

Effect of Dimension & Material Composition on Transmission Coefficient and Tunneling Current of Double Quantum Barrier Structure with Band Nonparabolicity  

Directory of Open Access Journals (Sweden)

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.

Arpan Deyasi and Gourab Kumar Ghosh

2012-12-01

279

Functional topography of band 3: specific structural alteration linked to functional aberrations in human erythrocytes.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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, we 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 di...

Kay, M. M.; Bosman, G. J.; Lawrence, C.

1988-01-01

280

Collective band structures of neutron-rich 112,114,116Pd nuclei  

International Nuclear Information System (INIS)

The high spin level structures in very neutron-rich nuclei, 112,114,116Pd have been studied by observing the prompt ?-rays from the spontaneous fission of 252Cf. The ground state bands are expanded up to 16+ and the ?-vibrational bands have been identified. New octupole bands possibly based on the proton configurations are also observed in 114,116Pd. The collective band behavior is discussed

1997-06-01

 
 
 
 
281

Electronic structure and band parameters for ZnX (X = O, S, Se, Te)  

CERN Multimedia

First-principles density-functional calculations have been performed for zinc monochalcogenides with zinc-blende- and wurtzite-type structures. It is shown that the local-density approximation underestimates the band gap, misplaces the energy levels of the Zn-3d states, and overestimates the crystal-field splitting energy. Without spinorbit coupling, the order of the states at the top of VB is found to be normal for all the ZnX phases considered. Upon inclusion of the spinorbit coupling in calculations, ZnO in zinc-blende- and wurtzite-type phases become anomalous. It is shown that the Zn-3d electrons are responsible for the anomalous order. The effective masses of electrons and holes have been calculated and found that holes are much anisotropic and heavier than the electrons in agreement with experimental findings. The typical errors in calculated band gaps and related parameters originate from strong Coulomb correlations, which are found to be highly significant in ZnO. The LDA+U approach is found to corre...

Karazhanov, S Z; Grossner, U; Kjekhus, A; Fjellvag, H; Svensson, B G

2006-01-01

282

Density Functional Theory / Nudged Elastic Band Investigation of the Hydroxylation Reaction Mechanism Catalyzed by P450cam  

Science.gov (United States)

We have calculated the complete minimum-energy reaction path for the hydroxylation of camphor by the P450 enzyme from Pseudomonas putida using the nudged elastic band method of Jonsson and co-workers[1]. Single-point force and energy calculations on pathway images were performed at the hybrid density functional level of theory (B3LYP) with large basis sets for the iron atom (6-311+G) and O2 ligand (6-31+G*) on a 100 atom active site extracted from a recent high-resolution crystal structure[2]. Our model includes the heme group liganded to both Cys357 and dioxygen and we also include Thr251 and Asp252, which have been shown to significantly affect product yield by mutational studies[3]. We find that, upon transfer of the 2nd electron to the active site, the Fe-O2 moiety is unstable and decays to a Fe-OOH- intermediate via a Asp252-H2O proton transfer chain. The barrier for dioxygen cleavage and the identity of the reactive species will be discussed. [1] H. Jonsson, G. Mills, K.W. Jacobsen, in Classical and Quantum Dynamics in Condensed Phase Simulation, World Scientific (1998). [2] I. Schlichting, et al., Science 287, no. 5458, p. 1615-1622 (2000). [3] R. Davydov, et al., J. Am. Chem. Soc., 123: 1403-1415 (2001).

Labute, Montiago; Henkelman, Graeme; McMahon, Benjamin

2005-03-01

283

Electronic Structure and Properties of YBa2 Cu3 O(7-delta): A Low Dimensional, Low Density of States Superconductor.  

Science.gov (United States)

The electronic structure of the high T/sub c/ superconductor, YBa2 Cu3 O(7-delta), determined from highly precise all-electron local density calculations yields a relatively simple highly 2D electronic band structure consisting of two 2D Cu sub 2 -O and t...

S. Massidda J. Yu A. J. Freeman D. D. Koelling

1987-01-01

284

Structure of nearly degenerate dipole bands in Ag  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The high spin negative parity states of Ag have been investigated with the B+Mo reaction at 39 MeV beam energy using the INGA facility at TIFR, Mumbai. From the ?-? coincidence analysis, an excited negative parity band has been established and found to be nearly degenerate with the ground state band. The spin and parity of the levels are assigned using angular correlation and polarization measurements. This pair of degenerate bands in Ag is studied using the recently developed microscopic t...

Sethi, J.; Palit, R.; Saha, S.; Trivedi, T.; Donthi, R.; Jadhav, S.; Jain, Hc; Naidu, Bs; Bhat, Gh; Sheikh, Ja; Datta, P.; Carroll, Jj; Litz, Ms; Chattopadhyay, S.; Garg, U.

2013-01-01

285

Band structure and optical properties of highly anisotropic LiBa2[B10O16(OH)3] decaborate crystal  

International Nuclear Information System (INIS)

The band structure (BS), charge density distribution and linear-optical properties of the anisotropic crystal LiBa2[B10O16(OH)3] (LBBOH) are calculated using a self-consistent norm-conserving pseudopotential method within the framework of the local-density approximation theory. A high anisotropy of the band energy gap (4.22 eV for the E parallel b, 4.46 eV for the E parallel c) and giant birefringence (up to 0.20) are found. Comparison of the theoretically calculated and the experimentally measured polarised spectra of the imaginary part of the dielectric susceptibility ?2 shows a good agreement. The anisotropy of the charge density distribution, BS dispersion and of the optical spectra originate from anisotropy between the 2pzB-2pzO and 2py,xB-2py,yO bonding orbitals. The observed anisotropy in the LBBOH is principally different from that of ?-BaB2O4 (BBO) single crystals. In the LBBOH single crystals the anisotropy of optical and charge density distribution is caused by different projection of the orbitals originating from particular borate clusters on the particular crystallographic axes, contrary to the BBO, where the anisotropy is caused prevailingly by a different local site symmetry of oxygen within the borate planes. The observed anisotropy is analysed in terms of the band energy dispersion and space charge density distribution

2003-05-01

286

FAST TRACK COMMUNICATION: Field modulation in bilayer graphene band structure  

Science.gov (United States)

Using an external electric field, one can modulate the band gap of Bernal stacked bilayer graphene by breaking the A-\\tilde {\\mathrm {B}} symmetry. We analyze strain effects on the bilayer graphene using the extended Hückel theory and find that reduced interlayer distance results in higher band gap modulation, as expected. Furthermore, above about 2.5 Å interlayer distance, the band gap is direct, follows a convex relation with the electric field and saturates to a value determined by the interlayer distance. However, below about 2.5 Å, the band gap is indirect, the trend becomes concave and a threshold electric field is observed, which also depends on the stacking distance.

Raza, Hassan; Kan, Edwin C.

2009-03-01

287

Crystal structure, electron density and chemical bonding in inorganic compounds studied by the Electric Field Gradient  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The goal of solid state physics and chemistry is to gain deeper understanding of the basic principles of condensed matter. This ongoing process is achieved by the combination of experimental methods and theoretical models. One theoretical approach are the so-called first-principles calculations, which are based on the concept of density functional theory (DFT). In order to test the reliability of a band structure calculation, its results have to be compared with experiments. Since the electro...

Koch, Katrin

2009-01-01

288

Band structure of sup 7 sup 9 Br  

CERN Document Server

High-spin states of sup 7 sup 9 Br have been studied in the reaction sup 7 sup 6 Ge( sup 7 Li, 4n gamma) at 32 MeV. A gamma-detector array with twelve Compton-suppressed HPGe detectors was used. The positive-parity yrast states, interpreted as a rotationally aligned g sub ( sub 9 sub ( sub 2 sub ) sub ) proton band, and the negative-parity ground state band have been extended to spins of (33(2 sup +)) and (25(2 sup -)), respectively. Lifetime measurements indicate that both bands have a similar quadrupole deformation of beta sub 2 approx 0.2. The positive-parity alpha = -(1(2)) band has been identified. Several new inter-band transitions are observed. A cranked-shell model analysis shows that the nu g sub ( sub 9 sub ( sub 2 sub ) sub ) and pi g sub ( sub 9 sub ( sub 2 sub ) sub ) alignments occur in the positive-parity and the negative-parity bands at rotational frequencies of Planck constant omega approx 0.6 and 0.4 MeV, respectively. The level energies and the electromagnetic properties of the g sub ( sub ...

Ray, I; Bhattacharya, S; Saha-Sarkar, M; Sethi, B; Chatterjee, J M; Chattopadhyay, S; Goswami, A; Muralithar, S; Singh, R P; Bhowmik, R K

1999-01-01

289

Electronic, superconducting, and optical properties of technetium from its augmented-plane-wave band structure  

International Nuclear Information System (INIS)

The detailed energy-band structure of hexagonal-close-packed technetium, corresponding to the atomic configuration 4d55s2 of its seven outermost valence electrons, has been obtained throughout the Brillouin zone using the composite-wave variational version of the augmented-plane-wave (APW) method in conjunction with the X? (? = 0.702 99) exchange approximation for obtaining the potentials. From the band-structure data the electronic density of states (DOS) and the angular-momentum--decomposed DOS were calculated by the accurate Gilat-Raubenheimer method. These quantities were used to calculate the electron-phonon coupling constant and the transition temperature (T/sub c/) using the theories of Gaspari and Gyorffy and of McMillan. Also studied were the Fermi surface and the optical properties of Tc via the imaginary part of the interband dielectric constant for bound electrons, the latter being the first of such a study on Tc to date. The superconducting properties and the Fermi surface which could be compared to experiments show, in general, satisfactory agreement

1983-04-15

290

Fiber Felts as Low Density Structural Materials.  

Science.gov (United States)

Short fiber felts structures can be made which provide improvements in properties over foams. In applications where resistance to compression set or stress relaxation are important, bonded fiber felts excel due to the flexing of individual fibers within t...

J. V. Milewski S. E. Newfield

1981-01-01

291

Density functional study of electronic structure, elastic and optical properties of MNH2 (M=Li, Na, K, Rb).  

Science.gov (United States)

We report a systematic first principles density functional study on the electronic structure, elastic and optical properties of nitrogen based solid hydrogen storage materials LiNH2, NaNH2, KNH2, and RbNH2. The ground state structural properties are calculated by using standard density functional theory, and also dispersion corrected density functional theory. We find that van der Waals interactions are dominant in LiNH2 whereas they are relatively weak in other alkali metal amides. The calculated elastic constants show that all the compounds are mechanically stable and LiNH2 is found to be a stiffer material among the alkali metal amides. The melting temperatures are calculated and follow the order RbNH2 < KNH2 < NaNH2 < LiNH2. The electronic band structure is calculated by using the Tran-Blaha modified Becke-Johnson potential and found that all the compounds are insulators, with a considerable band gap. The [NH2](-) derived states completely dominate in the entire valence band region while the metal atom states occupy the conduction band. The calculated band structure is used to analyze the different interband optical transitions occurring between valence and conduction bands. Our calculations show that these materials have considerable optical anisotropy. PMID:24841335

Babu, K Ramesh; Vaitheeswaran, G

2014-06-11

292

Effect of non-spherical potential on the band structure of metallic dysprosium  

International Nuclear Information System (INIS)

The effect of non-spherical part of the crystal potential on the band structure of dysprosium metal in the warped muffin-tin approximation has been studied using the augmented plane wave method. The band structure is not significantly affected by this factor in the present case. The maximum change in energy eigenvalues is 0.002 Ryd. (author)

1986-10-01

293

Electronic structure of the substitutional vacancy in graphene: density-functional and Green's function studies  

International Nuclear Information System (INIS)

We study the electronic structure of graphene with a single substitutional vacancy using a combination of the density-functional, tight-binding and impurity Green's function approaches. Density-functional studies are performed with the all-electron spin-polarized linear augmented plane wave (LAPW) method. The three sp2? dangling bonds adjacent to the vacancy introduce localized states (V?) in the mid-gap region, which split due to the crystal field and a Jahn–Teller distortion, while the pz? states introduce a sharp resonance state (V?) in the band structure. For a planar structure, symmetry strictly forbids hybridization between the ? and the ? states, so that these bands are clearly identifiable in the calculated band structure. As to the magnetic moment of the vacancy, the Hund's rule coupling aligns the spins of the four localized V?1??, V?2? and V?? electrons, resulting in an S = 1 state, with a magnetic moment of 2?B, which is reduced by about 0.3?B due to the anti-ferromagnetic spin polarization of the ? band itinerant states in the vicinity of the vacancy. This results in the net magnetic moment of 1.7?B. Using the Lippmann–Schwinger equation, we reproduce the well-known ?1/r decay of the localized V? wave function with distance, and in addition, find an interference term coming from the two Dirac points, previously unnoticed in the literature. The long-range nature of the V? wave function is a unique feature of the graphene vacancy and we suggest that this may be one of the reasons for the widely varying relaxed structures and magnetic moments reported from the supercell band calculations in the literature. (paper)

2012-08-01

294

Electronic band structure and Fermi surface of ytterbium under high pressure  

International Nuclear Information System (INIS)

The energy band structure of fcc ytterbium has been calculated by the relativistic augmented plane wave (RAPW) method for a wide range of pressures by reduction of the unit cell volume between 1.0 Vsub(o) to 0.5 Vsub(o) where Vsub(o) is the volume of the unit cell at normal pressure. The metal is observed to undergo a metal ? semiconductor transition for a compression of V/Vsub(o) 0.8. and a semiconductor to metal transition at V/Vsub(o) = 0.6. The possibility of a valence change from 2"+ to 3"+ has been predicted for the volume range V = 0.6 Vsub(o) to 0.5 Vsub(o). The changes in the Fermi surface topology, density of states, and resistivity have been investigated for the first time to provide confirmatory evidence for the above results. (author)

1986-01-01

295

Density-Functional Tight-Binding Simulations of Curvature-Controlled Layer Decoupling and Band-Gap Tuning in Bilayer MoS2  

Science.gov (United States)

Monolayer transition-metal dichalcogenides (TMDCs) display valley-selective circular dichroism due to the presence of time-reversal symmetry and the absence of inversion symmetry, making them promising candidates for valleytronics. In contrast, in bilayer TMDCs both symmetries are present and these desirable valley-selective properties are lost. Here, by using density-functional tight-binding electronic structure simulations and revised periodic boundary conditions, we show that bending of bilayer MoS2 sheets breaks band degeneracies and localizes states on separate layers due to bending-induced strain gradients across the sheets. We propose a strategy for employing bending deformations in bilayer TMDCs as a simple yet effective means of dynamically and reversibly tuning their band gaps while simultaneously tuning valley-selective physics.

Koskinen, Pekka; Fampiou, Ioanna; Ramasubramaniam, Ashwin

2014-05-01

296

Structures of High Density Molecular Fluids  

Energy Technology Data Exchange (ETDEWEB)

The goal of this proposal is to develop an in-situ probe for high density molecular fluids. We will, therefore, use Coherent Anti-Stokes Raman Spectroscopy (CARS) applied to laser heated samples in a diamond-anvil cell (DAC) to investigate molecular fluids at simultaneous conditions of high temperatures (T > 2000K) and high pressures (P > 10 GPa.) Temperatures sufficient to populate vibrational levels above the ground state will allow the vibrational potential to be mapped by CARS. A system capable of heating and probing these samples will be constructed. Furthermore, the techniques that enable a sample to be sufficiently heated and probed while held at static high pressure in a diamond-anvil-cell will be developed. This will be an in-situ investigation of simple molecules under conditions relevant to the study of detonation chemistry and the Jovain planet interiors using state of the art non-linear spectroscopy, diamond-anvil-cells, and laser heating technology.

Baer, B; Cynn, H; Iota, V; Yoo, C-S

2002-02-01

297

Elastic band structures of two-dimensional solid phononic crystal with negative Poisson's ratios  

International Nuclear Information System (INIS)

In this paper, the elastic band structures of two-dimensional solid phononic crystals (PCs) with both negative and positive Poisson's ratios are investigated based on the finite difference domain method. Systems with different combinations of mass density ratio and shear modulus ratio, filling fractions and lattices are considered. The numerical results show that for the PCs with both large mass density ratio and shear modulus ratio, the first bandgap becomes narrower with its upper edge becoming lower as Poisson's ratio of the scatterers decreases from -0.1 to -0.9. Generally, introducing the material with a negative Poisson's ratio for scatterers will make this bandgap lower and narrower. For the PCs with large mass density ratio and small shear modulus ratio, the first bandgap becomes wider with Poisson's ratio of the scatterers decreasing and that of the host increasing. It is easy to obtain a wide low-frequency bandgap by embedding scatterers with a negative Poisson's ratio into the host with a positive Poisson's ratio. The PCs with large filling fractions are more sensitive to the variations of Poisson's ratios. Use of negative Poisson's ratio provides us a way of tuning bandgaps.

2012-11-01

298

Band structure effects for dripped neutrons in neutron star crust  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The outer layers of a neutron star are supposed to be formed of a solid Coulomb lattice of neutron rich nuclei. At densities above neutron drip density (about one thousandth of nuclear saturation density), this lattice is immersed in a neutron fluid. Bragg scattering of those dripped neutrons by the nuclei which has been usually neglected is investigated, within a simple mean field model with Bloch type boundary conditions. The main purpose of this work is to provide some es...

Chamel, Nicolas

2004-01-01

299

Band diagram determination of MOS structures with different gate materials on 3C-SiC substrate  

Science.gov (United States)

MOS capacitors were fabricated on 3C-SiC n-type substrate (001) with a 10-µm N-type epitaxial layer. An SiO2 layer of the thickness tOX ?55 nm was deposited by PECVD. Circular Al, Ni, and Au gate contacts 0.7 mm in diameter were formed by ion beam sputtering and lift-off. Energy band diagrams of the MOS capacitors were determined using the photoelectric, electric, and optical measurement methods. Optical method (ellipsometry) was used to determine the gate and dielectric layer thicknesses and their optical indices: the refraction n and the extinction k coefficients. Electrical method of C = f(VG) characteristic measurements allowed to determine the doping density ND and the flat band voltage VFB in the semiconductor. Most of the parameters which were necessary for the construction of the band diagrams and for determination of the basic physical properties of the structures (e.g. the effective contact potential difference ?MS) were measured by several photoelectric methods and calculated using the measurement data. As a result, complete energy band diagrams have been determined for MOS capacitors with three different gate materials and they are demonstrated for two different gate voltages VG: for the flat-band in the semiconductor (VG = VFB) and for the flat-band in the dielectric (VG = VG0).

Piskorski, K.; Przewlocki, H. M.; Esteve, R.; Bakowski, M.

2011-09-01

300

Intramesoporous Silica Structure Differentiating Protein Loading Density  

Energy Technology Data Exchange (ETDEWEB)

We report that hydrothermal aging temperature had a critical effect on intramesoporous structure of mesoporous silica and thus the intramesoporous structure affected protein loading in the mesoporous silica significantly. For a neutral protein Immunoglobulin G with a Y-like molecular shape, the larger desorption pore size allowed the larger protein loading. For a charged protein glucose oxidase with an elliptical molecular shape, the larger surface area resulted in the larger protein loading. Fluorescence emission spectra from tyrosinyl and tryptophanyl residues of the proteins in mesoporous silicas indicated that the charged protein was electrostatically attached inside the mesopores in a way of monolayer, while the neutral protein IgG could continue to aggregate after the monolayer occupancy.

Wen, Qi; Li, Xiaolin; Chen, Baowei; Yao, Pei; Lei, Chenghong; Liu, Jun

2012-05-15

 
 
 
 
301

Electronic band structure of LaCoO3/Y/Mn compounds  

International Nuclear Information System (INIS)

Spin polarization effects on electronic properties of pure LaCoO3 and doped compounds (La0.5Y0.5CoO3, LaCo0.5Mn0.5O3) in the rhombohedral phase have been studied. We have employed the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA+U) under density functional theory (DFT). The calculated band structures along with total as well as partial densities of states reveal that Y and Mn impurities have a significant effect on the structural and electronic properties of LaCoO3. It is found that Mn alters insulating behavior of this compound to the half metallic for spin up state. Obtained results show that the magnetic moment for the Co-3d state is near 3.12?B in LaCoO3 compound which increases and decreases with addition of Y and Mn dopants respectively.

2013-02-01

302

Electronic band structure of LaCoO{sub 3}/Y/Mn compounds  

Energy Technology Data Exchange (ETDEWEB)

Spin polarization effects on electronic properties of pure LaCoO{sub 3} and doped compounds (La{sub 0.5}Y{sub 0.5}CoO{sub 3}, LaCo{sub 0.5}Mn{sub 0.5}O{sub 3}) in the rhombohedral phase have been studied. We have employed the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA+U) under density functional theory (DFT). The calculated band structures along with total as well as partial densities of states reveal that Y and Mn impurities have a significant effect on the structural and electronic properties of LaCoO{sub 3}. It is found that Mn alters insulating behavior of this compound to the half metallic for spin up state. Obtained results show that the magnetic moment for the Co-3d state is near 3.12{mu}{sub B} in LaCoO{sub 3} compound which increases and decreases with addition of Y and Mn dopants respectively.

Rahnamaye Aliabad, H.A., E-mail: rahnama@sttu.ac.ir [Department of Physics, Hakim Sabzevari University, Sabzevar (Iran, Islamic Republic of); Hesam, V. [Department of Physics, Khayyam Institute of Higher Education, Mashhad (Iran, Islamic Republic of); Ahmad, Iftikhar; Khan, Imad [Department of Physics, University of Malakand, Chakdara (Pakistan)

2013-02-01

303

Band offset determination of the GaAs/GaAsN interface using the density functional theory method  

International Nuclear Information System (INIS)

The GaAs/GaAsN interface band offset is calculated from first principles. The electrostatic potential at the core regions of the atoms is used to estimate the interface potential and align the band structures obtained from respective bulk calculations. First, it is shown that the present method performs well on the well-known conventional/conventional AlAs/GaAs (001) superlattice system. Then the method is applied to a more challenging nonconventional/conventional GaAsN/GaAs (001) system, and consequently type I band lineup and valence-band offset of about 35 meV is obtained for a nitrogen concentration of about 3%, in agreement with the recent experiments. We also investigate the effect of strain on the band lineup. For the GaAsN layer longitudinally strained to the GaAs lattice constant, the type II lineup with a nearly vanishing band offset is found, suggesting that the anisotropic strain along the interface is the principal cause for the often observed type I lineup

2008-08-06

304

Spatial structure of a vortex in low density neutron matter  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study in a fully selfconsistent approach the structure of a vortex in low density superfluid neutron matter. We determine that the matter density profile of a vortex shows a significant depletion in the region of the core, a feature never reported for a vortex state in a Fermi superfluid.

Yu, Yongle; Bulgac, Aurel

2002-01-01

305

Structure of f-bands and valent transitions in rare-earth metals  

International Nuclear Information System (INIS)

On the basis of results of band calculations performed energy-level transitions in rare earth metals (REM) are connected with the 4f band structure and position in energy spectrum. It is shown that energy-level transition in the REM band picture reveals itself as the change of width of the edge hybrid band. The performed analysis of the 4f band structure permits to separate a REM group, in which compounds revealing the valent instability is possible. Those are metals with the Fermi level near the edge hybrid f-d band: Ce, Pr ower edge of 4f subband), Tb, Dy (lower edge of 4f subhand), Sm, Eu (top of 4f subband), Tm, Yb (top of 4f subband)

1985-04-01

306

Cluster structure and deformed bands in the {sup 38}Ar nucleus  

Energy Technology Data Exchange (ETDEWEB)

The structure of the {sup 38}Ar nucleus is investigated by the {sup 34}S+? orthogonality condition model (OCM). The energy spectra, electromagnetic transitions and ? spectroscopic factors are calculated. The excited states can be grouped into several bands according to the leading configurations of their wave functions, and the structures of the bands are discussed. The first excited K{sup ?}=0{sup +} band is found to be predominantly {sup 34}S+? cluster states. It is also shown that the observed energies and E2 transitions of the band are well reproduced by the model. The existence of a negative-parity doublet band of the band is also predicted. The strength of the ?-cluster states is shown to be spread over several levels due to mixing of shell-model states and various ?-cluster states.

Sakuda, T., E-mail: sakuda@cc.miyazaki-u.ac.jp [Department of Physics, University of Miyazaki, Miyazaki 889-2192 (Japan); Ohkubo, S., E-mail: shigeo@cc.u-kochi.ac.jp [Department of Applied Science and Environment, University of Kochi, Kochi 780-8515 (Japan); Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047 (Japan)

2013-06-17

307

InN/GaN Superlattices: Band Structures and Their Pressure Dependence  

DEFF Research Database (Denmark)

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 â??â??LDA gap errorâ??â??. 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

Gorczyca, Iza; Suski, Tadek

2013-01-01

308

The magneto-optical properties of semiconductors and the band structure of gallium nitride  

CERN Document Server

the wells, and observing a resonant phenomenon from an undoped GaN/Al sub x Ga sub 1 sub - sub x N single heterojunction. The oscillating peak intensity was understood in terms of the changing screening efficiency of the two-dimensional electron gas. Finally, many-body effects within an electron-hole plasma in ln sub x Al sub y Ga sub 1 sub - sub x sub - sub y As quantum wells have been explored to study the effects of mass renormalisation at carrier densities typically present in laser devices. A peak in the mass renormalisation confirms the importance of excitonic correlations in the excited plasma. This thesis has applied magneto-optical techniques to enable a better understanding of the band structure of gallium nitride, particularly the complex behaviour expected as a result of strong valence band mixing. Effective hole masses are deduced from free excitonic-like transitions observed in magneto-reflectivity, to give a heavy A hole mass of 1.3 m sub o and the first experimental suggestion of a light B ban...

Shields, P A

2001-01-01

309

Calculation of the band structure of GdCo_2, GdRh_2 e GdIr_2 by the APW method  

International Nuclear Information System (INIS)

The band structure of GdCo_2, GdRh_2, GdIr_2 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

1974-01-01

310

Shaping topological properties of the band structures in a shaken optical lattice  

Digital Repository Infrastructure Vision for European Research (DRIVER)

To realize band structures with non-trivial topological properties in an optical lattice is an exciting topic in current studies on ultra cold atoms. Here we point out that this lofty goal can be achieved by using a simple scheme of shaking an optical lattice, which is directly applicable in current experiments. The photon-assistant band hybridization leads to the production of an effective spin-orbit coupling, in which the band index represents the pseudospin. When this spi...

Zhang, Shao-liang; Zhou, Qi

2014-01-01

311

The crystal and electronic band structure of the diamond-like semiconductor Ag{sub 2}ZnSiS{sub 4}  

Energy Technology Data Exchange (ETDEWEB)

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.

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

312

Stability and band gaps of InGaAs, BGaAs, and BInGaAs alloys: Density-functional supercell calculations  

International Nuclear Information System (INIS)

The influence of arrangement and content of substituents (B, In) in BGaAs, InGaAs, and BInGaAs alloys on the stabilities and band gaps is investigated using density-functional supercell calculations. The stability of ternary alloys decreases from InGaAs over BGaAs to GaAsN. Typical substituent structures show the following stability order: isolated substituents - [110] chains - clusters - twisted [111] chains - (200/211) arrangements (most stable). This is valid for both the In- and B-poor as well as the In- and B-rich alloys. From the fact that grown InGaAs provides a different gap than the most stable arrangement one can conclude that other structures (isolated indium atoms or InmAs clusters) are formed during the growth. Simultaneous substitutions (BInGaAs) of larger (In) and smaller (B) atoms prefer arrangements in larger distances (220) for isovalent boron substitution and in In-B bonds for antisite boron substitution. The high degree boron antisite substitution induces partially occupied acceptor bands which lead to a strong reduction of the band gap in comparison to the isovalent substitution. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2007-06-01

313

Theoretical studies on band structure and optical properties of 3C-SiC by FPLAPW  

International Nuclear Information System (INIS)

The band structure and optical properties of 3C-SiC are studied by using a full potential linearized augmented plane waves (FPLAPW) method. The imaginary and real parts of the dielectric function have been obtained from the band structure calculation. The critical point structure of the dielectric function is analyzed to identify the optical transition. The refractive index, extinction coefficient and reflectivity have been calculated from obtained dielectric function. The calculated results are in agreement with the experiments

2005-06-01

314

Hybrid functional study of band structures of GaAs1-xNx and GaSb1-xNx alloys  

Science.gov (United States)

Band structures of GaAs1-xNx and GaSb1-xNx alloys are studied in the framework of the density functional theory within the hybrid functional scheme (HSE06). We find that the scheme gives a clear improvement over the traditional (semi)local functionals in describing, in a qualitative agreement with experiments, the bowing of electron energy band gap in GaAs1-xNx alloys. In the case of GaSb1-xNx alloys, the hybrid functional used makes the study of band structures possible ab initio without any empirical parameter fitting. We explain the trends in the band gap reductions in the two materials that result mainly from the positions of the nitrogen-induced states with respect to the bottoms of the bulk conduction bands.

Virkkala, Ville; Havu, Ville; Tuomisto, Filip; Puska, Martti J.

2012-02-01

315

Investigation on band structure and electronic transport properties of indium nitride nanoribbon - A first-principles study  

Science.gov (United States)

The band structure and electronic transport property of indium nitride nanoribbon are investigated by employing first-principles calculation using density functional theory. The nanoribbon of pure InN, oxygen, fluorine and gallium substituted InN nanoribbon and defect InN nanoribbon are studied and analyzed. The band structure of pure InN, oxygen, fluorine and gallium substituted InN shows semiconducting nature whereas defect InN nanoribbon shows a metallic nature. The density of states of InN nanoribbon provides insight for the localization of charges in valence and conduction bands. The transport property are studied in terms of transmission spectrum, pure and gallium substituted InN has almost same transmission, in contrast oxygen and fluorine substituted InN shows a different fashion in transmission spectrum. The presence of defect modifies the transmission that depends on the geometry of the structure and position of the defect in the nanostructure. The information provided in the present study will enhance the electronic transport property to tailor new material with improved performance in optoelectronic devices.

Chandiramouli, R.; Sriram, S.

2014-01-01

316

Band Jahn-Teller effect on the density of states of the magnetic high-T{sub c} superconductors: A model study  

Energy Technology Data Exchange (ETDEWEB)

We report here a mean-field study of competing antiferromagnetism, superconductivity and lattice strain phases and their effect on the local density of states of the cuprate system. Our model Hamiltonian incorporating these interactions is reported earlier [G.C. Rout et al., Physica C, 2007]. The analytic expression for superconducting, antiferromagnetism and lattice strain order parameters are calculated and solved self-consistently. The interplay of these order parameters is investigated considering the calculated density of states (DOSs) of the conduction electrons. The DOS displays multiple gap structures with multiple peaks. It is suggested that the tunneling conductance data obtained from the scanning tunneling microscopy (STM) measurements could be interpreted by using the quasi-particle bands calculated from our model Hamiltonian. We have discussed the mechanism to calculate the order parameters from the conductance data.

Pradhan, B. [Department of Physics, Govt. Science College, Malkangiri 764 048 (India); Mohanta, K.L. [Department of Physics, ITER, Siksha ' O' Anusandhan University, Bhubaneswar 751 030 (India); Rout, G.C., E-mail: gcr@iopb.res.in [Condensed Matter Physics Group, Dept. of Applied Physics and Ballistics, F.M. University, Balasore 756 019 (India)

2012-05-15

317

``Shears bands`` in Pb nuclei - a new nuclear structure effect  

Energy Technology Data Exchange (ETDEWEB)

In nuclei in the mass region around A = 190-200 a large number of regular dipole sequences have recently been found. In these bands the gain in angular momentum may not be created by collective rotation as is usual for more deformed nuclei, but stems from aligning the proton and neutron spins in the direction of the total spin axis. Calculations within the framework of the tilted axis cranking model reproduce the available experimental data and support the alignment picture. (orig.).

Korten, W. [Bonn Univ. (Germany). Inst. fuer Strahlen- und Kernphysik; Baldsiefen, G. [Bonn Univ. (Germany). Inst. fuer Strahlen- und Kernphysik; Neffgen, M. [Bonn Univ. (Germany). Inst. fuer Strahlen- und Kernphysik; Huebel, H. [Bonn Univ. (Germany). Inst. fuer Strahlen- und Kernphysik; Chmel, S. [Bonn Univ. (Germany). Inst. fuer Strahlen- und Kernphysik; Pohler, W. [Bonn Univ. (Germany). Inst. fuer Strahlen- und Kernphysik; Severen, U.J. van [Bonn Univ. (Germany). Inst. fuer Strahlen- und Kernphysik; Willsau, P. [Bonn Univ. (Germany). Inst. fuer Strahlen-und Kernphysik; Frauendorf, S. [Forschungzentrum Rossendorf, Dresden (Germany); Meng, J. [Forschungzentrum Rossendorf, Dresden (Germany); Grawe, H. [Hahn-Meitner-Institut fuer Kernforschung Berlin G.m.b.H. (HMI) (Germany); Heese, J. [Hahn-Meitner-Institut fuer Kernforschung Berlin G.m.b.H. (HMI) (Germany); Kluge, H. [Hahn-Meitner-Institut fuer Kernforschung Berlin G.m.b.H. (HMI) (Germany); Maier, K.H. [Hahn-Meitner-Institut fuer Kernforschung Berlin G.m.b.H. (HMI) (Germany); Schubart, R. [Hahn-Meitner-Institut fuer Kernforschung Berlin G.m.b.H. (HMI) (Germany); Spohr, K. [Hahn-Meitner-Institut fuer Kernforschung Berlin G.m.b.H. (HMI) (Germany)

1995-12-31

318

Comparative studies on photonic band structures of diamond and hexagonal diamond using the multiple scattering method  

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

2004-02-18

319

Exciton spectra and energy band structure of CuGaSe{sub 2} single crystals  

Energy Technology Data Exchange (ETDEWEB)

Photoreflectivity, wavelength modulation spectroscopy and photoluminescence measurements of CuGaSe{sub 2} are used to determine the exciton and band parameters as well as the energy band structure of CuGaSe{sub 2} at photon energies higher than the fundamental band gap. The spectral dependences of the real {epsilon}{sub 1} and imaginary {epsilon}{sub 2} components of the complex dielectric function {epsilon}(E) = {epsilon}{sub 1} (E) + i{epsilon}{sub 2}(E) are calculated using the Kramers-Kronig relations. As a result, the energy band structure of CuGaSe{sub 2} at photon energies higher than the fundamental band gap is derived from the analysis of the structures observed both in the {epsilon} ({omega}) and in the wavelength modulated reflectivity spectra.

Levchenko, S; Tezlevan, V E; Arushanov, E [Institute of Applied Physics, Academy of Sciences of Moldova, Chisinau, MD 2028 (Moldova, Republic of); Syrbu, N N [Laboratory of Optoelectronics, Technical University of Moldova, 168, Bul. Stefan cel Mare, Chisinau, MD-2012 (Moldova, Republic of); Merino, J M; Leon, M [Universidad Autonoma de Madrid, Departamento Fisica Aplicada, C-XII, 28049 Madrid (Spain)], E-mail: maximo.leon@uam.es

2008-03-07

320

Compact electromagnetic bandgap structures for notch band in ultra-wideband applications.  

Science.gov (United States)

This paper introduces a novel approach to create notch band filters in the front-end of ultra-wideband (UWB) communication systems based on electromagnetic bandgap (EBG) structures. The concept presented here can be implemented in any structure that has a microstrip in its configuration. The EBG structure is first analyzed using a full wave electromagnetic solver and then optimized to work at WLAN band (5.15-5.825 GHz). Two UWB passband filters are used to demonstrate the applicability and effectiveness of the novel EBG notch band feature. Simulation results are provided for two cases studied. PMID:22163430

Rotaru, Mihai; Sykulski, Jan

2010-01-01

 
 
 
 
321

Visualizing the influence of point defects on the electronic band structure of graphene  

Science.gov (United States)

The supercell approach enables us to treat the electronic structure of defective crystals, but the calculated energy bands are too complicated to understand or compare with angle-resolved photoemission spectra because of inevitable zone folding. We discuss how to visualize supercell band structures more effectively by incorporating unfolded spectral weights and orbital decompositions into them. We then apply these ideas to gain a better understanding of the band structure of graphene containing various types of point defects, including nitrogen impurity, hydrogen adsorbate, vacancy defects and the Stone–Wales defect.

Farjam, M.

2014-04-01

322

Effective properties and band structures of lamellar subwavelength crystals: Plane-wave method revisited  

Science.gov (United States)

The plane-wave method used to compute the band structure of photonic crystals is revisited in light of recent mathematical results about the Fourier factorization of products of discontinuous functions. Highly accurate numerical predictions for the effective index and for the band structure are obtained for two- and three-dimensional dielectric lamellar crystals with high dielectric contrasts. At the same time, we clarify some aspects related to the effective properties of multidimensional crystals by establishing clear links between their band structures and their effective indices.

Lalanne, Philippe

1998-10-01

323

Plasma density measurements using chirped pulse broad-band Raman amplification  

CERN Document Server

Stimulated Raman backscattering is used as a non-destructive method to determine the density of plasma media at localized positions in space and time. By colliding two counter-propagating, ultra-short laser pulses with a spectral bandwidth larger than twice the plasma frequency, amplification occurs at the Stokes wavelengths, which results in regions of gain and loss separated by twice the plasma frequency, from which the plasma density can be deduced. By varying the relative delay between the laser pulses, and therefore the position and timing of the interaction, the spatio-temporal distribution of the plasma density can be mapped out.

Vieux, G; Farmer, J P; Hur, M S; Issac, R C; Jaraszynski, D A

2013-01-01

324

Influence of the surface band structure on electron emission spectra from metal surfaces  

Science.gov (United States)

Electron distributions produced by grazing impact of fast protons on Mg(0001), Cu(111), Ag(111), and Au(111) surfaces are investigated, focusing on the effects of the electronic band structure. The process is described within the band-structure-based approximation, which is a perturbative method that includes an accurate representation of the electron-surface interaction, incorporating information of the electronic band structure of the solid. For all the studied surfaces, the presence of partially occupied surface electronic states produces noticeable structures in double-differential—energy- and angle-resolved—electron emission probabilities from the valence band. For Mg, Cu, and Ag these structures remain visible in electron emission spectra after adding contributions coming from core electrons, which might make possible their experimental detection, but for Au they are hidden by inner-shell emission.

Archubi, C. D.; Faraggi, M. N.; Silkin, V. M.; Gravielle, M. S.

2014-04-01

325

Influence of the surface band structure on electron emission spectra from metal surfaces  

CERN Multimedia

Electron distributions produced by grazing impact of fast protons on Mg(0001), Cu(111), Ag(111) and Au(111) surfaces are investigated, focusing on the effects of the electronic band structure. The process is described within the Band-Structure-Based approximation, which is a perturbative method that includes an accurate representation of the electron-surface interaction, incorporating information of the electronic band structure of the solid. For all the studied surfaces, the presence of partially occupied surface electronic states produces noticeable structures in double differential - energy- and angle- resolved - electron emission probabilities from the valence band. These structures remain visible in electron emission spectra after adding contributions coming from core electrons, which might make it possible their experimental detection.

Archubi, C D; Silkin, V M; Gravielle, M S

2013-01-01

326

Quaternary sulfide Ba6Zn6ZrS14: synthesis, crystal structure, band structure, and multiband physical properties.  

Science.gov (United States)

Ba6Zn6ZrS14 was synthesized by a traditional salt-melt method with KI as flux. The pale yellow crystals of Ba6Zn6ZrS14 crystallize in the tetragonal space group I4/mcm with a=16.3481 (4)?Å and c=9.7221(6)?Å. The structure features unique one-dimensional parallel [Zn6S9](6-) and [ZrS5](6-) straight chains. The D2h-symmetric [Zn6S9](6-) cluster serves as the building block of the [Zn6S9](6-) chains. A powder sample was investigated by X-ray diffraction, optical absorption, and photoluminescence measurements. The compound shows multiple-absorption character with three optical absorption edges around 1.78, 2.50, and 2.65?eV, respectively, which are perfectly consistent with the results of first-principles calculations. Analysis of the density of states further revealed that the three optical absorption bands are attributable to the three S(3p(6))?Zr(4d(0)) transitions due to the splitting of the Zr 4d orbitals in the D4h crystal field. The multiband nature of Ba6Zn6ZrS14 also results in photocatalytic activity under visible-light irradiation and three band-edge emissions. PMID:24700506

Zhang, Xian; He, Jianqiao; Chen, Wei; Zhang, Ketian; Zheng, Chong; Sun, Junliang; Liao, Fuhui; Lin, Jianhua; Huang, Fuqiang

2014-05-12

327

Tunneling density of states of MgB2: Evidence for a dominant ?-band contribution  

International Nuclear Information System (INIS)

Weakly-transmitting junctions usable for tunneling spectroscopy experiments were fabricated from polycrystalline bulk samples of magnesium diboride with a niobium counter-electrode. A strong nonlinear conductance-versus-voltage behavior for voltages above the values corresponding to the energy gaps of the electrodes was interpreted as a fingerprint of the electron-phonon interaction in superconducting MgB2. A partial Eliashberg spectral function ?2(?)F(?) was extracted from the data by the numeric inversion of the standard strong-coupling Eliashberg equations. In a full agreement with recent theoretical simulations for magnesium diboride, we have observed a dominant contribution from the ?-band of this two-band superconductor. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2005-03-01

328

Ion band-state fusion: Reactions, power density, and the quantum reality question  

International Nuclear Information System (INIS)

The effects that limit deuterium-deuterium (D-D) fusion in bound systems, as opposed to those limiting D-D fusion in free space, are the result of quantum-mechanical particle-particle wave function correlation, which may inhibit wave function overlap. Whether or not this occurs at room temperature is determined by system energy minimization, not Gamow theory. A counterintuitive example, known from atomic physics, that demonstrates how this alternative criterion may alter the relevant quantum mechanics is illustrated by the helium atom. At room temperature, near-complete overlap of the two helium electrons takes place when energy is minimized, while Gamow theory predicts negligible overlap. On the other hand, energy minimization does not predict that no nucleus-nucleus overlap ever occurs in any normal molecule. In D"+ ion band-state matter, D"+-D"+ overlap occurs if the distributed charge view of quantum reality is correct, in which case D"+ band-state matter converts to "4He"+"+ band-state matter, releasing heat throughout a crystal lattice. This occurs in the limit x ? 1 in PdD_x (in agreement with experiments), provided adequate crystalline order is present. Further deuterium loading requires that additional injected deuterium occupy ionic band-like states in which only a small fraction of each additional deuterium atom occupies a lattice unit cell. Then, in each nuclear reaction, again to minimize energy of the entire system, the energy is distributed over many lattice sites, inhibiting production of energetic particles. Theory shows that steady-state power is proportional to the loading current. These points are discussed. An expression for P is derived, and possible cold fusion reactions are summarized. 23 refs., 1 fig

1993-12-01

329

First-principles band-structure calculations and X-ray photoelectron spectroscopy studies of the electronic structure of TlPb2Cl5  

International Nuclear Information System (INIS)

Highlights: • Electronic structure of TlPb2Cl5 is calculated by the FP-LAPW method. • The valence band is dominated by contributions of Cl 3p states. • Contributions of Pb 6p* states dominate at the bottom of the conduction band. • The FP-LAPW data allow concluding that TlPb2Cl5 is an indirect-gap material. • XPS core-level and valence-band spectra of polycrystalline TlPb2Cl5 are measured. -- Abstract: We report on first-principles calculations of total and partial densities of states of atoms constituting TlPb2Cl5 using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations reveal that the valence band of TlPb2Cl5 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 TlPb2Cl5 is composed mainly of contributions of the unoccupied Pb 6p-like states. Our FP-LAPW data indicate that the TlPb2Cl5 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+ ion-irradiated surfaces of a TlPb2Cl5 polycrystalline sample were measured. The measurements reveal high chemical stability and confirm experimentally the low hygroscopicity of TlPb2Cl5 surface

2014-01-05

330

First-principles band-structure calculations and X-ray photoelectron spectroscopy studies of the electronic structure of TlPb{sub 2}Cl{sub 5}  

Energy Technology Data Exchange (ETDEWEB)

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.

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

331

Microscopic Study of Band Structures in 98-102Sr and 100-104Zr Isotopes  

International Nuclear Information System (INIS)

The properties of the high spin states of the neutron-rich 98-102Sr and 100-104Zr isotopes have been studied using the projected shell model. In particular, the upbending phenomenon is investigated for these isotopes along the yrast line. The results show that the occurrence of upbending phenomenon is attributed to the band crossing between ground state band and 2-qp neutron band having configuration 2?h11/2[- 3/2, 5/2], K = 1. Furthermore, the neutron two-quasi-particle structure of side bands in 98Sr and 102Zr is discussed in this paper. (nuclear physics)

2011-11-15

332

Bistability and diode action in left-handed band-gap structures  

International Nuclear Information System (INIS)

Full text: Periodic structures made from layers of right-handed and left-handed material exhibit in addition to the conventional Bragg-scattering band-gap a novel band gap around the frequency of vanishing average refractive index. Using the transfer-matrix method and the pseudospectral time-domain method we study the properties of linear and nonlinear defect layers in this novel band gap and compare them with a Bragg gap. The defect modes in these two types of band gaps show differences with respect to sensitivity to defect layer position, bistability, transmission tunability, and diode effects. Copyright (2005) Australian Institute of Physics

2005-02-04

333

Valence Band Density of States of Cu3Si Studied by Soft X-Ray Emission Spectroscopy and a First-Principle Molecular Orbital Calculation  

Science.gov (United States)

A systematic study of the valence band structure of Cu3Si has been performed by soft X-ray emission spectroscopy and a first-principle molecular orbital calculation using the discrete-variational (DV)-X? cluster model. The existence of Cu 4s, 4p states in the valence band and their important contributions to the valence band as that of Cu 3d are indicated together with previously reported ones. The high-binding energy peak in the Si L2,3 emission spectrum is considered to originate mainly from the Si-Si 3s bonding state but also have a certain contribution of Si 3s bonding state with Cu 4s, 4p. On the other hand, the low-binding energy peaks in the Si L2,3 emission band are attributed to both the antibonding states of Si 3s and the bonding states of Si 3d with Cu 4s, 4p and Cu 3d. The bonding states of Si 3s with Cu 4s, 4p and Cu 3d are expected to exist in the lower part of the valence band for ?\\prime-Cu3Si on the basis of the theoretical calculations. As for Si p states, the high-binding energy peak and the low-binding energy peak in the Si K? emission spectrum should be attributed to the Si 3p bonding state and antibonding state with Cu 3d and Cu 4s, 4p, respectively, according to the theoretical calculations. A comparison is made between experimental spectra and theoretical density of states.

An, Zhenlian; Kamezawa, Chihiro; Hirai, Masaaki; Kusaka, Masahiko; Iwami, Motohiro

2002-12-01

334

Yrast band structure of light 170-182Pt isotopes  

International Nuclear Information System (INIS)

The neutron rich Pt isotopes with only 4 proton holes (two proton bosons) have been studied for long. For example, 196Pt is cited as the best example of an O(6) nucleus. Gupta et al., in empirical studies of ground band energies of medium mass shape transitional nuclei, calculated the vibrational content of the low spin I = 2 state in 182-196Pt isotopes and noted a phase transition at N = 110 (A = 188), with lighter isotopes showing significant deformation effects. The deformation for Pt is maximum at N = 104, (A = 182)

2012-12-01

335

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.

2012-09-18

336

Band gaps and structural properties of graphene halides and their derivates: a hybrid functional study with localized orbital basis sets.  

Science.gov (United States)

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 C(2)FBr and C(2)HBr 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 (C(a)H(b)F(c) and C(a)F(b)Y(c), Y = Cl, Br, I) are stable insulators. PMID:22830726

Karlický, František; Zbo?il, Radek; Otyepka, Michal

2012-07-21

337

Band structure of Heusler compounds studied by photoemission and tunneling spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

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.

Arbelo Jorge, Elena

2011-07-01

338

Probing the graphite band structure with resonant soft-x-ray fluorescence  

International Nuclear Information System (INIS)

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 (?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

1997-04-01

339

Probing the graphite band structure with resonant soft-x-ray fluorescence  

Energy Technology Data Exchange (ETDEWEB)

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.

Carlisle, J.A.; Shirley, E.L.; Hudson, E.A. [Lawrence Berkeley National Lab., CA (United States)] [and others

1997-04-01

340

Theoretical Study of Conformations and Electronic Band Structures for Two Benzoxazole Polymers.  

Science.gov (United States)

The extended Huckel method within the tight-bonding approximation was applied to two benzoxazole polymers of a type much studied because of their excellent mechanical properties. Specifically, band structure calculations were carried out in part to identi...

K. Nayak J. E. Mark

1985-01-01

 
 
 
 
341

Banded structure and its distribution in friction stir processing of 316L austenitic stainless steel  

Science.gov (United States)

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.

Chen, Y. C.; Fujii, H.; Tsumura, T.; Kitagawa, Y.; Nakata, K.; Ikeuchi, K.; Matsubayashi, K.; Michishita, Y.; Fujiya, Y.; Katoh, J.

2012-01-01

342

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.

2012-01-01

343

Enhanced fluctuations of the tunneling density of states near bottoms of Landau bands measured by a local spectrometer  

CERN Document Server

We have found that the local density of states fluctuations (LDOSF) in a disordered metal, detected using an impurity in the barrier as a spectrometer, undergo enhanced (with respect to SdH and dHvA effects) oscillations in strong magnetic fields, omega _c\\tau > 1. We attribute this to the dominant role of the states near bottoms of Landau bands which give the major contribution to the LDOSF and are most strongly affected by disorder. We also demonstrate that in intermediate fields the LDOSF increase with B in accordance with the results obtained in the diffusion approximation.

Holder, J P; Fal'ko, V I; Jouault, B; Faini, G; Laruelle, F; Bedel, E; Fal'ko, Vladimir I.

1999-01-01

344

Enhanced fluctuations of the tunneling density of states near the bottom of a landau band measured by a local spectrometer  

Science.gov (United States)

We have found that the local density of state fluctuations (LDOSF) in a disordered metal, detected using an impurity in the barrier as a spectrometer, undergo enhanced (with respect to Shubnikov-de Haas and de Haas-van Alphen effects) oscillations in strong magnetic fields, omega(c)tau>/=1. We attribute this to the dominant role of the states near the bottom of Landau bands which give the major contribution to the LDOSF and are most strongly affected by disorder. We also demonstrate that in intermediate fields the LDOSF increase with field B in accordance with the results obtained in the diffusion approximation. PMID:11017568

Holder; Savchenko; Fal'ko; Jouault; Faini; Laruelle; Bedel

2000-02-14

345

Photonic band-structure and optical S-matrix analyses of the proposed superconducting nanostructures  

CERN Document Server

Special optical structures composed of superconducting nanostructure based on the elemental type-II and layered high-Tc superconductors are proposed. The photonic band structure and the optical S-matrix are calculated for these proposed structures for different geometrical values. Such structures produce terahertz (THz) photonic band gap, which is controlled by the temperature and geometrical parameters. In addition, the proposed structures show controllable optical reflectance and transmittance in the considered terahertz range. The calculations are performed in a special frequency range in which the refractive index of the layered superconductors has negative value according to the previous analyses.

Khakestar, Ali Sobhani; Mehrany, Khashayar; fardmanesh, Mehdi

2011-01-01

346

Simple inverted band structure model for cadmium arsenide (Cd3As2)  

International Nuclear Information System (INIS)

The development of a simple Hamiltonian yielding the inverted band structure of Cd3As2 in the 4 mm (C4v12) low-temperature phase is proposed. The presented theory takes into account the spin orbit interaction and tetragonal distortion of lattice in the low symmetry. The authors obtain k-linear terms in the band structure and therefore a splitting in k-space of spin degenerate energy bands. The reported band model contains only one new crystal field parameter d = cr|Z> in addition to well known Kildal's set. The first evaluation of this shows that (0.028 < d < 0.072) eV using optical absorption edge data. The finite width of the anisotropic heavy and light hole bands is pointed out. (authors)

2003-01-01

347

High-resolution angle-resolved photoemission study of the Ag band structure along ?  

International Nuclear Information System (INIS)

High-resolution angle-resolved photoelectron spectra have been obtained from the (111) face of an Ag crystal for normal electron emission. These spectra made it possible to determine experimentally the valence-band structure of Ag along the high-symmetry line ? with better accuracy than previously [P. S. Wehner et al., Phys. Rev. B 19, 6164 (1979)], and also revealed a second flat band near point GAMMA in the conduction bands 23 eV above the Fermi level. The new binding energies at points GAMMA and L were used along with the data of other workers to construct an experimental band structure of Ag with the mixed-basis interpolation scheme of Smith [Phys. Rev. B 9, 1365 (1974)]. The augmented-plane-wave calculations of Eckhardt, Fritsche, and Noffke [J. Phys. F 14, 97 (1984)] agree very well with the experimentally determined bands

1985-09-15

348

Photoluminescence and the band structure of InAsSb strained-layer superlattices  

International Nuclear Information System (INIS)

Infrared photoluminescence measurements were performed on InAs/sub 0.13/Sb/sub 0.87/ /InSb strained-layer superlattices. In thick layered structures we observed very low energy transitions proving that a type II superlattice occurs in the InAsSb system. Band structures were calculated based on estimates of the band offsets and strain shifts obtained from the photoluminescence data

1988-07-18

349

Electronic structure of graphene on a reconstructed Pt(100) surface: Hydrogen adsorption, doping, and band gaps  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We probe the structure and electronic band structure of graphene grown on a Pt(100) substrate using scanning tunneling microscopy, low energy electron diffraction, and angle-resolved photoemission spectroscopy. It is found that the graphene layer lacks a well-defined azimuthal orientation with respect to the substrate, causing a circular smearing of the p band instead of a well-defined Dirac cone near the Fermi level. The graphene is found to be electron doped placing the Dirac point similar ...

Ulstrup, Soren; Nilsson, Louis; Miwa, Jill A.; Balog, Richard; Bianchi, Marco; Hornekaer, Liv; Hofmann, Philip

2013-01-01

350

Application of Hyperspectral Band Elimiation Technique to PVT Images of Composite Structures  

Directory of Open Access Journals (Sweden)

Full Text Available A new approach to NDT of composite structures using Band Elimination of the analyzed image index by Hyperspectral image analysis approach is presented and discussed. The matrix Band Elimination technique allows the monitoring and analysis of a components structure based on Filtering of bands and correlation between sequentially pulsed thermal images and their indices. The technique produces several matrices resulting from frame deviation and pixel redistribution calculations for intelligent classification and property prediction. The obtained results proved the technique to be capable of identifying damaged components with ability to model various types of damage under different conditions.

Mahmoud Zaki Iskandarani

2012-10-01

351

Dual-Band Terahertz Left-Handed Metamaterial with Fishnet Structure  

International Nuclear Information System (INIS)

We present the design of a dual-band left-handed metamaterial with fishnet structure in the terahertz regime. Its left-handed properties are described by the retrieved effective electromagnetic parameters. We introduce an equivalent circuit which offers a theoretical explanation for the left-handed behavior of the dual-band fishnet metamaterial, and investigate its losses receiving higher figure of merit. The design is beneficial to the development of frequency agile and broadband THz materials and devices. The dual-band fishnet metamaterial can be extended to infrared and optical frequency ranges by regulating the structural parameters. (fundamental areas of phenomenology (including applications))

2011-01-01

352

Low-lying levels and high-spin band structures in 102Rh  

International Nuclear Information System (INIS)

Levels in 102Rh have been populated in the reaction 70Zn+36S at 130 MeV. The level structure of 102Rh 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

1999-10-18

353

Study of the 4f and valence band density of states in rare-earth metals  

International Nuclear Information System (INIS)

The 4f and valence states of all metallic rare earths have been studied using x-ray photoelectron spectroscopy (XPS) for the occupied part and bremsstrahlung isochromat spectroscopy (BIS) for the unoccupied part. It is found that the bandwidth increases from Gd to Lu, and that the valence band spectra are in fair agreement with APW calculations. The intensities of the 4f final-state multiplets are well described in terms of the coefficients of fractional parentage. There is a symmetry between the fsup(n) XPS and fsup(14-n) BIS spectra. The observed energies of the 4f excitations correspond to transitions to completely screened final states. These values enable one to predict the elements which are liable to interconfiguration fluctuation when their 4f levels are shifted to Esub(F) by the chemical environment or by compression. The large Coulomb correlation energies, U which prevent the formation of 4f bands in these elements, are directly obtained from the spectra observed and are found to be in good agreement with recent calculations. The linewidths and singularity indices of the XPS and BIS 4f lines are determined and discussed. (author)

1981-01-01

354

Tuning two-dimensional band structure of Cu(111) surface-state electrons that interplay with artificial supramolecular architectures  

Science.gov (United States)

We report on the modulation of two-dimensional (2D) bands of Cu(111) surface-state electrons by three isostructural supramolecular honeycomb architectures with different periodicity or constituent molecules. Using Fourier-transformed scanning tunneling spectroscopy and model calculations, we resolved the 2D band structures and found that the intrinsic surface-state band is split into discrete bands. The band characteristics including band gap, band bottom, and bandwidth are controlled by the network unit cell size and the nature of the molecule-surface interaction. In particular, Dirac cones emerge where the second and third bands meet at the K points of the Brillouin zone of the supramolecular lattice.

Wang, Shiyong; Wang, Weihua; Tan, Liang Z.; Li, Xing Guang; Shi, Zilang; Kuang, Guowen; Liu, Pei Nian; Louie, Steven G.; Lin, Nian

2013-12-01

355

Retrieval of stratospheric aerosol density profiles from SCIAMACHY limb radiance measurements in the O2 A-band  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper we present an approach to retrieve stratospheric aerosol number densities in the altitude range 10–40 km from SCIAMACHY limb radiance measurements in the spectral range of the O2 A absorption band, near 760 nm. Here, the characteristic light paths differ for the measured light in the O2 A band and in the spectral continuum next to the absorption band. This difference is used to distinguish the effect of stratospheric aerosol scattering and ground reflection on the limb measurement. The capability to disentangle both effects is illustrated for SCIAMACHY limb observations over the Libyan desert, where the measurements are not affected by tropospheric clouds. Comparison of the SCIAMACHY retrieval and the SAGE II aerosol extinction product between 75 degrees Southern and Northern latitude shows the clear need for prior knowledge of the mean size of the stratospheric aerosol for the SCIAMACHY retrieval. We found best agreement between SCIAMACHY and SAGE II aerosol extinction for the period 2003–2005 for a prior choice of the mean aerosol size radius of 0.2 ?m. The overall agreement between both data sets is in the range <50% root mean square difference at 14–30 km with a minimum of 30% at 22 km.

I. Aben

2011-03-01

356

Retrieval of stratospheric aerosol density profiles from SCIAMACHY limb radiance measurements in the O2 A-band  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper we present an approach to retrieve stratospheric aerosol number densities in the altitude range 10–40 km from SCIAMACHY limb radiance measurements in the spectral range of the O2 A absorption band, near 760 nm. Here, the characteristic light paths differ for the measured light in the O2 A-band and in the spectral continuum next to the absorption band. This difference is used to distinguish the effect of stratospheric aerosol scattering and ground reflection on the limb measurement. The capability to disentangle both effects is illustrated for SCIAMACHY limb observations over the Libyan desert, where the measurements are not affected by tropospheric clouds. Comparison of the SCIAMACHY retrieval and the SAGE II aerosol extinction product between 75° southern and northern latitude shows the clear need for prior knowledge of the mean size of the stratospheric aerosol for the SCIAMACHY retrieval. We found best agreement between SCIAMACHY and SAGE II aerosol extinction for the period 2003–2005 for a prior choice of the mean aerosol size radius of 0.2 ?m. The overall agreement between both data sets is in the range <50% root mean square difference at 14–30 km with a minimum of 30% at 22 km.

I. Aben

2011-11-01

357

Control over band structure and tunneling in bilayer graphene induced by velocity engineering.  

Science.gov (United States)

The band structure and transport properties of massive Dirac fermions in bilayer graphene with velocity modulation in space are investigated in the presence of a previously created band gap. It is pointed out that velocity engineering may be considered as a factor to control the band gap of symmetry-broken bilayer graphene. The band gap is direct and independent of velocity value if the velocity modulated in two layers is set up equally. Otherwise, in the case of interlayer asymmetric velocity, not only is the band gap indirect, but also the electron-hole symmetry fails. This band gap is controllable by the ratio of the velocity modulated in the upper layer to the velocity modulated in the lower layer. In more detail, the shift of momentum from the conduction band edge to the valence band edge can be engineered by the gate bias and velocity ratio. A transfer matrix method is also elaborated to calculate the four-band coherent conductance through a velocity barrier possibly subjected to a gate bias. Electronic transport depends on the ratio of velocity modulated inside the barrier to that for surrounding regions. As a result, a quantum version of total internal reflection is observed for thick enough velocity barriers. Moreover, a transport gap originating from the applied gate bias is engineered by modulating the velocities of the carriers in the upper and lower layers. PMID:24275200

Cheraghchi, Hosein; Adinehvand, Fatemeh

2014-01-01

358

Photonic band structure of ZnO photonic crystal slab laser  

CERN Multimedia

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.

Yamilov, A; Cao, H

2005-01-01

359

Spatially resolved methane band photometry of Jupiter. III - Cloud vertical structures for several axisymmetric bands and the Great Red Spot  

International Nuclear Information System (INIS)

The paper presents cloud structure models for Jupiter's Great Red Spot, Equatorial and North Tropical Zones, North and South Temperate Zones, and North and South Polar Regions. The models are based on images of Jupiter in three methane bands and nearby continuum radiative transfer calculations include multiple scattering and absorption from three aerosol layers. The model results include the transition in the upper-cloud altitude to 3 km lower altitude from the tropical zones to temperate zones and polar regions, a N/S asymmetry in cloud thickness in the tropical and temperature zones, and the presence of aerosols up to about 0.3 bar in the Great Red Spot and Equatorial Zone. It is concluded that polarization data are sensitive to aerosols in and above the upper cloud layer but insensitive to deeper cloud structure

1980-01-01

360

Small tin oxide grains: structural and electronic properties evaluated using the density functional theory  

International Nuclear Information System (INIS)

This study is motivated by the complex properties of tin oxides and by the lack of detailed theoretical information on the clustered state of these materials. Therefore small grains of a columnar and a spherical shape with a rutile lattice and a size up to 100 atoms have been considered and their structural and electronic properties evaluated using the density functional theory. The calculations show that the rutile skeleton is retained starting from a size of 20 atoms and the absence of reconstruction is particularly evident in the spherical grains. However, reconstruction also occurs and the physical force behind it is an increase in the coordination among tin-oxygen and oxygen-oxygen atoms. The binding energy has a primary dependence on the grain size, whereas only marginal effects arise from the grain structure. The density of states has bands below and above the Fermi levels which are not observed in the crystalline material and are therefore peculiar to the clustered state

2007-01-17

 
 
 
 
361

Small tin oxide grains: structural and electronic properties evaluated using the density functional theory  

Energy Technology Data Exchange (ETDEWEB)

This study is motivated by the complex properties of tin oxides and by the lack of detailed theoretical information on the clustered state of these materials. Therefore small grains of a columnar and a spherical shape with a rutile lattice and a size up to 100 atoms have been considered and their structural and electronic properties evaluated using the density functional theory. The calculations show that the rutile skeleton is retained starting from a size of 20 atoms and the absence of reconstruction is particularly evident in the spherical grains. However, reconstruction also occurs and the physical force behind it is an increase in the coordination among tin-oxygen and oxygen-oxygen atoms. The binding energy has a primary dependence on the grain size, whereas only marginal effects arise from the grain structure. The density of states has bands below and above the Fermi levels which are not observed in the crystalline material and are therefore peculiar to the clustered state.

Mazzone, A M [CNR-IMM, Sezione di Bologna, Via Gobetti 101, 40129-Bologna (Italy)

2007-01-17

362

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

1976-08-15

363

Raman scattering from layered superconductors: Effects of charge ordering, two-band superconductivity, and structural disorder  

Science.gov (United States)

Subject of this dissertation is the investigation with experimental means of how the Raman response of three structurally similar materials -- MgB2, NbSe2, and CaC6 -- is affected by superconductivity (all three), charge ordering (NbSe2), or crystalline order-to-disorder phase transitions (CaC6). Universal characteristics of spectral renormalization pertaining to the superconducting phase transition are observed in all three compounds. Yet, the crystalline and electronic structures are sufficiently distinct, such that specific for each compound characteristics are imposed on this superconductivity-induced renormalization. Consequently, the method of polarized Raman scattering has been used to establish a variety of physical concepts: (1) Multi-band superconductivity in the layered superconductor MgB2 and its primary mediation by the strongly coupled 640 cm--1 E2g phonon. Additionally, it is shown how a Josephson-like coupling of two SC condensates in the reciprocal space is responsible for an exotic collective mode, the Leggett's resonance. (2) Interplay between the superconducting and the incommensurate charge-density-wave order parameters in NbSe2, which has been found to be consistent with an isotropic multi-band superconductivity scenario. This scenario is proposed in the frame of a picture that involves a combined 'superconductivity plus charge-density-wave' order parameter. (3) The Fano-Breit-Wigner line-shape formalism to account for an anti-resonance interference in the low temperature Raman response from NbSe2, in the polarization geometry corresponding to the non-symmetric E 2g symmetry channel. (4) Validity of the double resonant Raman scattering picture in the presence of disorder in the graphite intercalation compound CaC6. Simultaneously, it is explored how disorder suppresses superconductivity. To that end, the CaC6 superconducting coherence peak, too, is presented. All these phenomena are manifestations of electron-phonon coupling in solids. It is probed by inelastic light scattering under the specific constraints of respective crystalline symmetries. Each case, therefore, remains intriguingly unique. The experiments have been performed in a state of the art optical laboratory with low temperatures and high magnetic fields infrastructure, of which a detailed account is given.

Mialitsin, Aleksej

364

The C-Band accelerating structures for SPARC photoinjector energy upgrade  

Science.gov (United States)

The use of C-Band structures for electron acceleration and production of high quality beams has been proposed and adopted in several linac projects all over the world. The two main projects that adopted such type of structures are the Japanese Free Electron Laser (FEL) project in Spring-8 and the SwissFEL project at Paul Scherrer Institute (PSI). Also the energy upgrade of the SPARC photo-injector at LNF-INFN (Italy) from 150 to more than 240 MeV will be done by replacing a low gradient S-Band accelerating structure with two C-band structures. The structures are Traveling Wave (TW) and Constant Impedance (CI), have symmetric axial input couplers and have been optimized to work with a SLED RF input pulse. The paper presents the design criteria of the structures, the realization procedure and the low and high power RF test results on a prototype. The high power tests have been carried out by the Frascati INFN Laboratories in close collaboration with the Japanese Laboratory KEK. Experimental results confirmed the feasibility of the operation of the prototype at 50 MV/m with about 10-6 breakdowns per pulse per meter. Such high gradients have not been reached before in C-Band systems and demonstrated the possibility to use C-band accelerators, if needed, at such high field level. The results of the internal inspection of the structure after the high power test are also presented.

Alesini, D.; Boni, R.; Di Pirro, G.; Di Raddo, R.; Ferrario, M.; Gallo, A.; Lollo, V.; Marcellini, F.; Palumbo, L.; Spizzo, V.; Mostacci, A.; Campogiani, G.; Persichelli, S.; Enomoto, A.; Higo, T.; Kakihara, K.; Kamitani, T.; Matsumoto, S.; Sugimura, T.; Yokoyama, K.; Verdú-Andrés, S.

2013-05-01

365

Band gap and band parameters of InN and GaN from quasiparticle energy calculations based on exact-exchange density-functional theory  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have studied the electronic structure of InN and GaN employing G0W0 calculations based on exact-exchange density-functional theory. For InN our approach predicts a gap of 0.7 eV. Taking the Burnstein-Moss effect into account, the increase of the apparent quasiparticle gap with increasing electron concentration is in good agreement with the observed blue shift of the experimental optical absorption edge. Moreover, the concentration dependence of the effective mass, which r...

Rinke, Patrick; Qteish, Abdallah; Winkelnkemper, Momme; Bimberg, Dieter; Neugebauer, Joerg; Scheffler, Matthias

2006-01-01

366

Effect of structured packing density on performance of air dehumidifier  

International Nuclear Information System (INIS)

An experimental study has been conducted to investigate the performance of a liquid desiccant air dehumidifier equipped with a structured packing made of wood for three different densities using triethylene glycol (TEG) as the liquid desiccant. The structured packing densities used were 77, 100 and 200 m2/m3. The performance of the dehumidifier was expressed in terms of the moisture removal rate and the dehumidifier effectiveness under different air and desiccant parameters, i.e. the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and inlet TEG concentration. In general, the trend in the dehumidifier performance was similar to that reported by other investigators using random packing. The effect of packing density on moisture removal rate and dehumidifier effectiveness is assessed. The differences in the effectiveness of different packing densities are attributed to the wetting condition. Lower effectiveness of the column is shown with the packing density of 200 m2/m3 compared to the other two packing densities when the air flow rate, inlet concentration and desiccant flow rate are increased. However, higher effectiveness is shown when either the inlet temperature of the air or desiccant is increased

2004-09-01

367

Full waveform inversion schemes for 3D density structure  

Science.gov (United States)

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.

Blom, Nienke; Fichtner, Andreas

2014-05-01

368

Influence of strain on band structure of semiconductor nanostructures  

Directory of Open Access Journals (Sweden)

Full Text Available The influence of the mechanical strain on the electronic structure of the asymmetric (In,GaAs/GaAs quantum well is considered. Both the direct influence of strain on the orbital part of the electronic structure and an indirect influence through the strain dependent Rashba and Dresselhaus Hamiltonians are taken into account. The analyzed quantum well is taken to have a triangular shape, and is oriented along the <110> direction. For this direction, there exists both the intrinsic and strain-induced spin-orbit interaction. For all analyzed types of spin-orbit interaction, subband splittings depend linearly on the in-plane wave vector. On the other hand, the electronic structure for the Rashba type of the strain-induced spin-orbit interaction shows isotropic dependence in the k-space, while the electronic structure due to the Dresselhaus type shows anisotropy. Furthermore, the Rashba strain-induced spin-orbit interaction increases subband splitting, while the effect of the Dresselhaus Hamiltonian on the electronic structure is opposite to the intrinsic spin-orbit interaction for certain polar angles.

Rai?evi? Nevena

2009-01-01

369

Comments on "Band gap and band parameters of InN and GaN from quasiparticle energy calculations based on exact-exchange density-functional theory" [Appl. Phys. Lett. 89, 161919 (2006)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An oversight of some previous density functional calculations of the band gaps of wurtzite and cubic InN and of wurtzite GaN by Rinke et al. [Appl. Phys. Lett. 89,161919, 2006] led to an inaccurate and misleading statement relative to limitations of density functional theory (DFT) for the description of electronic properties of these materials. These comments address this statement. In particular, they show that some local density approximation (LDA) calculations have correc...

Bagayoko, D.; Franklin, L.; Zhao, G. L.

2011-01-01

370

Coupling of the electronic band structure with A{sub g} phonon modes in Y123 and Y124 systems  

Energy Technology Data Exchange (ETDEWEB)

Ab initio frozen-phonon calculations have been performed for k=0 A{sub g} Raman modes of two superconducting systems Y123 and Y124. We have used the local density approximation pseudopotential method in our calculations by VASP code. Results have been compared with other computational and experimental data for similar systems. Then we present changes of electronic band structure with the change of ionic positions in each A{sub g} mode for both systems. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Khosroabadi, H.; Mossalla, B.; Akhavan, M. [Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365, 9161 Tehran (Iran)

2006-09-15

371

Coupling of the electronic band structure with Ag phonon modes in Y123 and Y124 systems  

International Nuclear Information System (INIS)

Ab initio frozen-phonon calculations have been performed for k=0 Ag Raman modes of two superconducting systems Y123 and Y124. We have used the local density approximation pseudopotential method in our calculations by VASP code. Results have been compared with other computational and experimental data for similar systems. Then we present changes of electronic band structure with the change of ionic positions in each Ag mode for both systems. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2006-09-01

372

Band structure and transmission of 3D chiral sonic crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Pico, Ruben; Romero-garcia, Vicent; Sanchez-morcillo, Victor; Cebrecos, Alejandro; Garcia-raffi, Lluis Miquel

2012-01-01

373

Precise fabrication of X-band accelerating structure  

International Nuclear Information System (INIS)

An accelerating structure with a/?=0.16 is being fabricated to study a precise fabrication method. A frequency control of each cell better than 10-4 level is required to realize a detuned structure. The present machining level is nearly 1 MHz/11.4 GHz in relative frequency error, which just satisfies the above requirement. To keep this machining precision, the diffusion bonding technique is found preferable to join the cells. Various diffusion conditions were tried. The frequency change can be less than 1 MHz/11.4 GHz and it can be controlled well better than that. (author)

1993-08-25

374

Ab initio density functional theory investigation of structural and electronic properties of silicon carbide nanotube bundles  

International Nuclear Information System (INIS)

By using ab initio density functional theory the structural and electronic properties of isolated and bundled (8,0) and (6,6) silicon carbide nanotubes (SiCNTs) are investigated. Our results show that for such small diameter nanotubes the inter-tube interaction causes a very small radial deformation, while band splitting and reduction of the semiconducting energy band gap are significant. We compared the equilibrium interaction energy and inter-tube separation distance of (8,0) SiCNT bundle with (10,0) carbon nanotube (CNT) bundle where they have the same radius. We found that there is a larger inter-tube separation and weaker inter-tube interaction in the (8,0) SiCNT bundle with respect to (10,0) CNT bundle, although they have the same radius

2008-10-01

375

Ab initio density functional theory investigation of structural and electronic properties of silicon carbide nanotube bundles  

Energy Technology Data Exchange (ETDEWEB)

By using ab initio density functional theory the structural and electronic properties of isolated and bundled (8,0) and (6,6) silicon carbide nanotubes (SiCNTs) are investigated. Our results show that for such small diameter nanotubes the inter-tube interaction causes a very small radial deformation, while band splitting and reduction of the semiconducting energy band gap are significant. We compared the equilibrium interaction energy and inter-tube separation distance of (8,0) SiCNT bundle with (10,0) carbon nanotube (CNT) bundle where they have the same radius. We found that there is a larger inter-tube separation and weaker inter-tube interaction in the (8,0) SiCNT bundle with respect to (10,0) CNT bundle, although they have the same radius.

Moradian, Rostam [Physics Department, Faculty of Science, Razi University, Kermanshah (Iran, Islamic Republic of); Nano Science and Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of); Department of Nano Science, Computational Physical Science Research Laboratory, Institute for Studies in Theoretical Physics and Mathematics (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of)], E-mail: moradian.rostam@gmail.com; Behzad, Somayeh; Chegel, Raad [Physics Department, Faculty of Science, Razi University, Kermanshah (Iran, Islamic Republic of)

2008-10-01

376

Density of states for high-Tc superconductors in the Kronig-Penney superlattice structure  

Energy Technology Data Exchange (ETDEWEB)

The densities of states (DOSs) at various thickness ratios for superlattices with a periodic superconducting/normal material structure are calculated by using Green functions derived in accordance with the Kronig-Penney model. The DOSs sharply increase near the band edges resulting from Fermi-level nesting. Increasing the thickness of the superconducting layers, the corresponding DOS of the superconducting state will dominate that of the normal state showing the competition of Cooper paired electrons and normal electrons manipulated by the proximity effect. The enhanced DOS near the band edges is crucial for the retention of high critical temperatures for the recently fabricated YBaCuO/Dy(Pr)BaCuO superlattices. (orig.).

Lue Juhtzeng; Liang Yenpang (Dept. of Physics, National Tsing Hua Univ., Hsinchu (Taiwan))

1993-03-29

377

Density of states for high-Tc superconductors in the Kronig-Penney superlattice structure  

International Nuclear Information System (INIS)

The densities of states (DOSs) at various thickness ratios for superlattices with a periodic superconducting/normal material structure are calculated by using Green functions derived in accordance with the Kronig-Penney model. The DOSs sharply increase near the band edges resulting from Fermi-level nesting. Increasing the thickness of the superconducting layers, the corresponding DOS of the superconducting state will dominate that of the normal state showing the competition of Cooper paired electrons and normal electrons manipulated by the proximity effect. The enhanced DOS near the band edges is crucial for the retention of high critical temperatures for the recently fabricated YBaCuO/Dy(Pr)BaCuO superlattices. (orig.)

1993-03-29

378

Electronic structure of two-dimensional hexagonal diselenides: Charge density waves and pseudogap behavior  

International Nuclear Information System (INIS)

We theoretically study the electronic structure (spectral functions and Fermi surfaces) of incommensurate pseudogap and charge density wave (CDW) and commensurate CDW phases of quasi-two-dimensional diselenides 2H-TaSe2 and 2H-NbSe2. The incommensurate pseudogap regime is described within the scenario based on short-range-order CDW fluctuations, considered within the static Gaussian random field model. In contrast, e.g., to high-Tc cuprates, layered dichalcogenides have several different CDW scattering vectors and an electronic spectrum with two bands at the Fermi level. For this, we present a theoretical background for the description of multiple scattering processes within a multiple-band electronic spectrum. Theoretical spectral functions and Fermi surfaces thus obtained are compared with recent ARPES experimental data, demonstrating rather good qualitative agreement.

2012-04-01

379

Shell structure of the 58Ni charge density  

International Nuclear Information System (INIS)

A very-high momentum-transfer (q=780 MeV/c), elastic electron-scattering experiment on 58Ni has been performed using the 600-MeV linac of Saclay. The charge density, extracted from (e,e) and muonic-x-ray data, exhibits considerably less structure than predicted by Hartree-Fock calculations

1975-10-06

380

3D Coronal Density Reconstruction and Retrieving the Magnetic Field Structure during Solar Minimum  

CERN Multimedia

Measurement of the coronal magnetic field is a crucial ingredient in understanding the nature of solar coronal phenomena at all scales. We employed STEREO/COR1 data obtained during a deep minimum of solar activity in February 2008 (Carrington rotation CR 2066) to retrieve and analyze the three-dimensional (3D) coronal electron density in the range of heights from 1.5 to 4 Rsun using a tomography method. With this, we qualitatively deduced structures of the coronal magnetic field. The 3D electron density analysis is complemented by the 3D STEREO/EUVI emissivity in the 195 A band obtained by tomography for the same CR. A global 3D 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 density maximum locations can serve as an indicator of current sheet position, while the locations of the density gradient maximum can be a reliable indicator of coronal hole boundaries. We find that the magnetic field configuration du...

Kramar, M; Miki?, Z; Davila, J

2014-01-01

 
 
 
 
381

Mixed conduction in doped semiconductor structures related to quasi-metallic conduction in the impurity band  

International Nuclear Information System (INIS)

Mixed conduction due to simultaneous contributions from allowed states in the valence band and extended impurity (acceptor) states, which occur in the impurity band at high impurity concentrations because of the Anderson transition, is observed in a series of GaAs/AlGaAs structures. Mixed conduction manifests itself in the existence of a minimum in the temperature dependence of the carrier concentration and a noticeable bend in the temperature dependences of the conductivity. Expressions for the mixed conductivity on which the calculations are based were derived taking into account the spectrum of impurity states in the quantum wells (the upper and lower Hubbard impurity bands), their occupancies, and the sign of charge carriers in the valence and the impurity bands; the important assumption was made that the width of impurity bands is much smaller than the spacing from the valence band. The calculation results agree well with the experiment and were used to determine the binding energies for the upper and lower Hubbard bands, the acceptor concentration, and the degree of compensation. It is shown that formulas commonly used for the calculation of mixed conductivity need significant corrections in the case of narrow impurity bands.

2010-04-01

382

Quasiparticle band structures of ?-HgS, HgSe, and HgTe  

Science.gov (United States)

The electronic structures of mercury chalcogenides in the zinc-blende strucrure have been calculated by the LDA, GW (one-shot, G0W0) and quasi-particle self-consistent GW (QSGW) approximations including spin-orbit coupling (SO). The slight tendency to overestimation of the band gaps by QSGW is avoided by using a hybrid scheme (20% LDA and 80 % QSGW. The results of G0W0 depend strongly starting wave functions and are thus quite different from those from QSGW. Within QSGW HgS is found to be a semiconductor, with a ?6 s-like conduction-band minimum state above the valence-band top ?7 and ?8 (``negative'' SO splitting). HgSe and HgTe have ``negative'' gaps (inverted band structure). In HgTe the ?7 state is below ?6 due to the large Te SO splitting, in contrast HgSe where ?6 is below ?7.

Christensen, Niels E.; Svane, Axel; Cardona, Manuel; Chantis, Athanasios; van Schilfgaarde, Mark; Kotani, Takao

2012-02-01

383

Determination of the band structure of LuNi2B2C  

International Nuclear Information System (INIS)

We present de Haas-van Alphen (dHvA) investigations on the nonmagnetic borocarbide superconductor LuNi2B2C which have been performed by use of the torque method in high magnetic fields up to 32 T and at low temperatures down to 50 mK. The complex band structure is extracted from the quantum oscillations in the normal state. In comparison with full-potential-local-orbital calculations of the band structure we are able to assign the observed dHvA frequencies to the different bands. Temperature dependent dHvA investigations allowed the extraction of the effective band masses for the several Fermi-surface sheets. We observe an enhancement of the effective masses compared to the theoretical calculations which is due to electron-phonon interaction. Finally, we are able to examine the angular dependence of the electron-phonon coupling for the different Fermi-surface sheets. (orig.)

2007-03-26

384

Band structure engineering of anatase TiO2 by metal-assisted P-O coupling  

Science.gov (United States)

In this work, we demonstrate that the metal-assisted P-O coupling is an effective approach to improve the photoelectrochemical properties of TiO2. The (Sc + P) and (In + P) codoping effects on electronic structures and photocatalytic activities of anatase TiO2 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 TiO2, 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 TiO2. Moreover, the band edge alignments in (Sc + P) and (In + P) codoped anatase TiO2 are desirable for water-splitting. The calculated optical absorption curves indicate that (Sc + P) and (In + P) codoping in anatase TiO2 can also effectively enhance the visible light absorption.

Wang, Jiajun; Meng, Qiangqiang; Huang, Jing; Li, Qunxiang; Yang, Jinlong

2014-05-01

385

Band structure engineering of anatase TiO2 by metal-assisted P-O coupling  

International Nuclear Information System (INIS)

In this work, we demonstrate that the metal-assisted P-O coupling is an effective approach to improve the photoelectrochemical properties of TiO2. The (Sc + P) and (In + P) codoping effects on electronic structures and photocatalytic activities of anatase TiO2 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 TiO2, 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 TiO2. Moreover, the band edge alignments in (Sc + P) and (In + P) codoped anatase TiO2 are desirable for water-splitting. The calculated optical absorption curves indicate that (Sc + P) and (In + P) codoping in anatase TiO2 can also effectively enhance the visible light absorption

2014-05-07

386

First-principles studies of quasiparticle band structures of cubic YH3 and LaH3  

International Nuclear Information System (INIS)

Quasiparticle band structures for the cubic trihydrides YH3 and LaH3 have been calculated by evaluating the self-energy in the GW approximation using ab initio pseudopotentials and plane waves. These are the protype metal hydrides that exhibit switchable optical properties. For both materials, the local-density approximation (LDA) yields semimetallic energy bands with a direct overlap of about 1 eV. We find the self-energy correction to the LDA energies opens a gap at Gamma of 0.8-0.9 eV for LaH3 and 0.2-0.3 eV for YH3, where the latter is in sharp contrast to a previous study using linear-muffin-tin orbitals. The quasiparticle band gaps are analyzed as a function of an initial shift in the LDA bands used to evaluate the random-phase approximation screening in constructing the self-energy. We also make a comparison of results obtained by using two different pseudopotentials, each designed to better approximate exchange and correlation between the semicore states and valence states of Y and La

2002-10-10

387

Electronic- and band-structure evolution in low-doped (Ga,Mn)As  

Energy Technology Data Exchange (ETDEWEB)

Modulation photoreflectance spectroscopy and Raman spectroscopy have been applied to study the electronic- and band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn doping in the range of low Mn content, up to 1.2%. 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 with increasing Mn content in very low-doped (Ga,Mn)As layers with n-type conductivity are interpreted as a result of merging the Mn-related impurity band with the host GaAs valence band. On the other hand, an increase in the band-gap-transition energy with increasing Mn content in (Ga,Mn)As layers with higher Mn content and p-type conductivity indicates the Moss-Burstein shift of the absorption edge due to the Fermi level location within the valence band, determined by the free-hole concentration. The experimental results are consistent with the valence-band origin of mobile holes mediating ferromagnetic ordering in the (Ga,Mn)As diluted ferromagnetic semiconductor.

Yastrubchak, O.; Gluba, L.; ?uk, J. [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Sadowski, J. [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland); MAX-Lab, Lund University, 22100 Lund (Sweden); Krzy?anowska, H. [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Department of Physics and Astronomy, Vanderbilt University, 6506 Stevenson Center, Nashville, Tennessee 37325 (United States); Domagala, J. Z.; Andrearczyk, T.; Wosinski, T. [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland)

2013-08-07

388

Two-zone heterogeneous structure within shear bands of a bulk metallic glass  

Energy Technology Data Exchange (ETDEWEB)

Shear bands, the main plastic strain carrier in metallic glasses, are severely deformed regions often considered as disordered and featureless. Here we report the observations of a sandwich-like heterogeneous structure inside shear bands in Pd{sub 40.5}Ni{sub 40.5}P{sub 19} metallic glass sample after plastic deformation by high-resolution transmission electron microscopy. The experimental results suggest a two-step plastic deformation mechanism with corresponding microstructure evolution at atomic scale, which may intimately connected to the stability of the shear band propagation and the overall plastic deformability.

Shao, Yang; Yao, Kefu; Liu, Xue [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Li, Mo [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245 (United States)

2013-10-21

389

Modeling of two-dimensional density structure in eastern Taiwan  

Science.gov (United States)

Taiwan is located on the tectonic boundary between the Eurasian Plate and the Philippine Sea Plate. The northern terminus of the Philippine Mobile Belt is in Taiwan, where accreted parts of the Luzon Arc and Luzon forearc form the Huatung Longitudinal Valley and the eastern Coastal Range of Taiwan, respectively. The Huatung Longitudinal Valley is a complex collection of tectonic plate fragments and volcanic intrusions. Besides, the distribution of the positive gravity anomalies is in the vicinity of Huatung area and there show the maximum value of the Bouguer gravity in this area. In this study, we use the gravity forward and inversion method to investigate two geological profiles in Ruisui and Yuli area of the Huatung Longitudinal Valley. In order to derive the reliable density structure, we examine several geophysical and geological profiles using the Bouguer anomaly value along each profile. In modeling of subsurface density structure, available seismic and well data are used to possibly constrain the geometric and/or densities. The effect of two-dimensional density model is calculated using the Talwani technique. Then, we use tried and error method to modify the model and finally get a reliable density structure that conform with observed gravity data. The Bouguer gravity increases eastward from the Central Mountain Range to eastern Taiwan offshore. The depth of strata and fault location in Ruisui and Yuli area of the Huatung Longitudinal Valley will be obtained by gravity modeling. Moreover, the results shows igneous rock existing beneath the Huatung Longitudinal Valley area and it extends along with the depth to the east. In short, it is the cause of the highest gravity anomalies in Taiwan. If more velocity structure, seismic and drill data constrained, we expect to derive the more detailed subsurface structure and deep strata information in this area using gravity data modeling.

Hsu, Tzu-Yuan; Yen, Horng-Yuan

2014-05-01

390

Quasiparticle self-consistent GW calculations for PbS, PbSe, and PbTe: Band structure and pressure coefficients  

DEFF Research Database (Denmark)

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.

Svane, Axel; Christensen, Niels Egede

2010-01-01

391

Precision photonic band structure calculation of Abrikosov periodic lattice in type-II superconductors  

CERN Document Server

We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field, leading to nonlinear behavior of the band structure, which also has nonlinear dependence on the temperature. The similar analysis for every arbitrary lattice structure is also possible to be developed by this approach as presented in this work. We also present some examples and discuss the results.

Kokabi, Alireza; Khorasani, Sina; Fardmanesh, Mehdi

2011-01-01

392

Precision photonic band structure calculation of Abrikosov periodic lattice in type-II superconductors  

International Nuclear Information System (INIS)

We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field, leading to nonlinear behavior of the band structure, which also has nonlinear dependence on the temperature. The similar analysis for every arbitrary lattice structure is also possible to be developed by this approach as presented in this work. We also present some examples and discuss the results

2007-09-01

393

One step retrieval of formaldehyde vertical column density from OMI UV2 band  

Science.gov (United States)

We explore the possibility of using a one-step fitting approach for the retrieval of formaldehyde vertical column density from space based spectrometers such as the Ozone Monitoring Instrument (OMI). Our traditional two step approach, direct fitting of slant columns followed by air mass factor (AMF) conversion to vertical columns, is unable to account for the AMF wavelength dependence. This dependence is not significant for wavelengths above 330 nm, with changes around 2% to 3% between 330 nm and 360 nm. However below 330 nm the AMFs may vary up to 8% between 320 nm and 330 nm where two of the strongest absorption features for formaldehyde reside. It is therefore important to extend the fitting window below 327.5 (actual lower limit for the OMI operational retrieval). At the same time we are able to calculate averaging kernels directly rather than approximating them by using scattering weights at a given wavelength.

Gonzalez Abad, G.; Chance, K.; Liu, X.

2013-12-01

394

Unfolding of collapsed polymers in shear flow: Effects of colloid banding structures in confining channels  

Science.gov (United States)

Using hydrodynamic simulations, we demonstrate that confined colloidal suspensions can greatly enhance the unfolding of collapsed single polymers in flow. When colloids come in direct contact with the polymers due to the flow, the collapsed chains become flattened or elongated on the surface of the colloids, increasing the probability of forming large chain protrusions that the flow can pull out to unfold the polymers. This phenomenon may be suppressed if the colloid size is commensurate with the confining channels, where the colloids form well-defined banding structures. Here, we analyze the colloid banding structures in detail and their relation to the chain unfolding. We find that for colloid volume fractions up to 30%, the confined colloids form simple cubic (sc), hexagonal (hex), or a mixture of sc + hex structures. By directly changing the heights of the confining channels, we show that the collapsed polymers unfold the most in the mixed sc + hex structures. The diffuse (not well-defined) bands in the mixed sc + hex structures provide the highest collision probability for the colloids and the polymers, thus enhancing unfolding the most. Without colloidal suspensions, we show that the confining channels alone do not have an observable effect on the unfolding of collapsed polymers. The well-defined colloid bands also suppress the unfolding of noncollapsed polymers. In fact, the average size for noncollapsed chains is even smaller in the well-defined bands than in a channel without any colloids. The appearance of well-defined bands in this case also indicates that lift forces experienced by the polymers in confinement are negligible compared to those exerted by the colloidal band structures. Our results may be important for understanding the dynamics of mixed colloid polymer solutions.

Chen, Hsieh; Alexander-Katz, Alfredo

2014-03-01

395

Photonic stop bands in quasi-random nanoporous anodic alumina structures  

CERN Document Server

The existence of photonic stop bands in the self-assembled arrangement of pores in porous anodic alumina structures is investigated by means of rigorous 2D finite- difference time-domain calculations. Self-assembled porous anodic alumina shows a random distribution of domains, each of them with a very definite triangular pattern, constituting a quasi-random structure. The observed stop bands are similar to those of photonic quasicrystals or random structures. As the pores of nanoporous anodic alumina can be infiltrated with noble metals, nonlinear or active media, it makes this material very attractive and cost-effective for applications including inhibition of spontaneous emission, random lasing, LEDs and biosensors.

Maksymov, Ivan; Pallares, Josep; Marsal, Lluis F

2011-01-01

396

Inference of upper-mantle density structure from seismic velocities  

Science.gov (United States)

The inverse problem for the determination of density structure from perturbations in the gravity field is highly nonunique. The combination of gravity data and other observables can, however, be used to make inferences about the Earth's density structure in three dimensions. We use the three-dimensional shear-wave velocity model of Nettles and Dziewonski (2005) to make a forward prediction of the Earth's gravity field using simple assumptions about the relationship between perturbations in shear velocity and density. A scaling factor f=0.25 relating perturbations in shear velocity and density (?/?? = f · ?vS/vS) is determined empirically by comparison of observed variations in shear velocity in oceanic regions with density variations predicted from a simple model of conductive cooling. This value agrees well with f=0.27 based on the laboratory results of Jackson et al. (1992). The observed gravity signal in the oceans is explained well by this simple thermal-scaling approach. Behavior in some continental regions, such as the Basin and Range and the East African rift zone, is found to be similar to that in the oceans: the high topography in these regions appears to be supported by hot, low-density mantle underneath, a result also found by Kaban and Mooney (2001) for the Basin and Range. A velocity-to-density scaling relationship based only on thermal considerations is clearly inadequate in regions of continental craton, where such scaling leads to unrealistically large perturbations in the predicted gravity field. This result suggests that non-thermal effects must counteract the high density that would occur due to thermal effects alone, consistent with the suggestion of Jordan (1975) and other workers that density increases due to cool temperatures in the continental roots must be balanced by density decreases due to compositional variations. Using the compositional derivatives for density and shear velocity with respect to Mg# determined by Lee (2003), and an assumption of neutral buoyancy in the continental roots, yields perturbations in temperature in agreement with those obtained by Artemieva and Mooney (2001) based on heat-flow and heat-production data and perturbations in Mg# that are generally consistent with values observed for cratonic mantle xenoliths.

Nettles, M.; Dziewonski, A. M.

2005-12-01

397

Microscopic Description of Band Structure at Very Extended Shapes in the A ~ 110 Mass Region  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recent experiments have confirmed the existence of rotational bands in the A \\~ 110 mass region with very extended shapes lying between super- and hyper-deformation. Using the projected shell model, we make a first attempt to describe quantitatively such a band structure in 108Cd. Excellent agreement is achieved in the dynamic moment of inertia J(2) calculation. This allows us to suggest the spin values for the energy levels, which are experimentally unknown. It is found tha...

Lee, Ching-tsai; Sun, Yang; Zhang, Jing-ye; Guidry, Mike; Wu, Cheng-li

2001-01-01

398

Band-structure trend in cuprates and correlation with $T_{c max}$  

CERN Document Server

By calculation and analysis of the band structures of 15 superconducting cuprates, we have identified the energy of the so-called axial-orbital as the essential material dependent parameter. It controls the range of the intralayer hopping, the perpendicular hopping, the Cu 4s-character of the conduction-band orbital, and correlates with the observed Tc at optimal doping. We discuss how it may be influenced.

Pavarini, E; Saha-Dasgupta, T; Jepsen, O; Andersen, O K

2001-01-01

399

Extended Hückel theory for band structure, chemistry, and transport. II. Silicon  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

2006-01-01

400

Relativistic Band-Structure Calculations for CeTIn$_5$(T=Ir and Co)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In order to investigate electronic properties of recently discovered heavy fermion superconductors CeTIn$_5$ (T=Ir and Co), we employ the relativistic linear augmented-plane-wave (RLAPW) method to clarify the energy band structures and Fermi surfaces of those materials. The obtained energy bands mainly due to the large hybridization between Ce $4f$ and In 5$p$ states well reproduce the Fermi surfaces consistent with the de Haas-van Alphen experimental results. However, when ...

Maehira, T.; Hotta, T.; Ueda, K.; Hasegawa, A.

2002-01-01

 
 
 
 
401

Information on the band structure of ferromagnetic Ni from ?SR-Knight shift measurements  

International Nuclear Information System (INIS)

The authors present results on the temperature dependence of the Knight shift of the hyperfine field at a positive muon in ferromagnetic Nickel and show that the results allow a determination of the Stoner gap, that is the gap between the top of the majority d-band and the Fermi energy. The consistency of the analysis supports the SWS-model but the obtained value for the Stoner gap is far below the predictions of most ferromagnetic band structure calculations. (Auth.)

1978-09-07

402

Effects of polarization on the band-structure of delafossite transparent conductive oxides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We use hybrid functionals and restricted self-consistent GW, state-of-the-art theoretical approaches for quasiparticle band structures, to study the electronic states of delafossite Cu(Al,In)O$_2$, the first p-type and bipolar transparent conductive oxides. We show that self-consistent GW gives remarkably wider band gaps than all the other approaches used so far. Accounting for polaronic effects in the GW scheme we recover a very nice agreement with experiments. Furthermore,...

Vidal, Julien; Trani, Fabio; Bruneval, Fabien; Marques, Miguel A. L.; Botti, Silvana

2009-01-01

403

Study on band gap structure of Fibonacci quantum superlattices by using the transfer matrix method  

Science.gov (United States)

The scattering properties of particles in a one-dimensional Fibonacci sequence based potential have been analyzed by means of the Transfer Matrix Method. The electronic band gaps are examined comparatively with those obtained using the corresponding periodic potentials. The reflection coefficient shows self-similar properties for the Fibonacci superlattices. Moreover, by using the generalized Bragg's condition, the band gaps positions are derived from the golden mean involved in the design of the superlattice structure.

Ferrando, V.; Castro-Palacio, J. C.; Marí, B.; Monsoriu, J. A.

2014-02-01

404

Effects of the Temporal Fine Structure in Different Frequency Bands on Mandarin Tone Perception  

Science.gov (United States)

This letter evaluates the relative contributions of temporal fine structure cues in various frequency bands to Mandarin tone perception using novel “auditory chimaeras”. Our results confirm the importance of temporal fine structure cues to lexical tone perception and the dominant region of lexical tone perception is found, namely the second to fifth harmonics can contribute no less than the fundamental frequency itself.

Yang, Lin; Zhang, Jianping; Shao, Jian; Yan, Yonghong

405

International X-Band Linear Collider Accelerator Structure R&D  

Energy Technology Data Exchange (ETDEWEB)

For more than fifteen years before the International Technology Recommendation Panel (ITRP) decision in August, 2004, there were intensive R&D activities and broad international collaboration among the groups at SLAC, KEK, FNAL, LLNL and other labs for the room temperature X-Band accelerator structures. The goal was to provide an optimized design of the main linac structure for the NLC (Next Linear Collider) or GLC (Global Linear Collider). There have been two major challenges in developing X-band accelerator structures for the linear colliders. The first is to demonstrate stable, long-term operation at the high gradient (65 MV/m) that is required to optimize the machine cost. The second is to strongly suppress the beam induced long-range wakefields, which is required to achieve high luminosity. More than thirty X-band accelerator structures with various RF parameters, cavity shapes and coupler types have been fabricated and tested since 1989. A summary of the main achievements and experiences are presented in this talk including the structure design, manufacturing techniques, high power performance, and other structure related issues. Also, the new progress in collaborating with the CLIC, high gradient structures and X-Band structure applications for RF deflectors and others are briefly introduced.

Wang, J.W.; /SLAC

2009-03-04

406

Analytical solution for band-gap structures in photonic crystal with sinusoidal period  

International Nuclear Information System (INIS)

In this Letter an approximate analytic method was described. The method was used to analyze the band gaps of holographic photonic crystals, having sinusoidal periodic structure. The results obtained were compared with those obtained from the analysis by plane wave expansion method. It shows that the method suggested is suitable for analyzing the photonic crystals having non-step function periodic structure

2004-01-26

407

Density functional study of electronic structure, elastic and optical properties of MNH2 (M=Li, Na, K, Rb)  

Science.gov (United States)

We report a systematic first principles density functional study on the electronic structure, elastic and optical properties of nitrogen based solid hydrogen storage materials LiNH2, NaNH2, KNH2, and RbNH2. The ground state structural properties are calculated by using standard density functional theory, and also dispersion corrected density functional theory. We find that van der Waals interactions are dominant in LiNH2 whereas they are relatively weak in other alkali metal amides. The calculated elastic constants show that all the compounds are mechanically stable and LiNH2 is found to be a stiffer material among the alkali metal amides. The melting temperatures are calculated and follow the order RbNH2 valence band region while the metal atom states occupy the conduction band. The calculated band structure is used to analyze the different interband optical transitions occurring between valence and conduction bands. Our calculations show that these materials have considerable optical anisotropy.

Babu, K. Ramesh; Vaitheeswaran, G.

2014-06-01

408

Near-edge band structures and band gaps of Cu-based semiconductors predicted by the modified Becke-Johnson potential plus an on-site Coulomb U  

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 propertie