Science.gov

Sample records for negative band structure

  1. 16O + 16O molecular structures of positive- and negative-parity superdeformed bands in 34S

    NASA Astrophysics Data System (ADS)

    Taniguchi, Yasutaka

    2016-05-01

    The structures of excited states in 34S are investigated using the antisymmetrized molecular dynamics and generator coordinate method(GCM). The GCM basis wave functions are calculated via energy variation with a constraint on the quadrupole deformation parameter β. By applying the GCM after parity and angular momentum projections, the coexistence of two positive- and one negative-parity super de formed(SD) bands are predicted, and low-lying states and other deformed bands are obtained. The SD bands have structures of 16O + 16O + two valence neutrons in molecular orbitals around the two 16O cores in a cluster picture. The configurations of the two valence neutrons are δ2 and π2 for the positive-parity SD bands and π1δ1 for the negative parity SD band.

  2. Photonic band structure

    SciTech Connect

    Yablonovitch, E.

    1993-05-01

    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}donor{close_quotes} modes. Conversely, the local removal of dielectric material from the photonic crystal produces {open_quotes}acceptor{close_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.

  3. Band structures in 99Rh

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Singh, V.; Singh, K.; Sihotra, S.; Singh, N.; Goswamy, J.; Malik, S. S.; Ragnarsson, I.; Trivedi, T.; Singh, R. P.; Muralithar, S.; Kumar, R.; Bhowmik, R. K.; Palit, R.; Bharti, A.; Mehta, D.

    2014-10-01

    Excited states in the 99Rh nucleus were populated using the fusion-evaporation reaction 75As(28Si,2p2n) at {{E}_{lab}}=120\\;MeV and the de-excitations were investigated through in-beam γ-ray spectroscopic techniques using the INGA spectrometer consisting of 18 clover detectors. The observed band structures are discussed in the framework of tilted axis cranking shell-model calculations. Level structures at low energies are identified as resulting from the rotational bands based on the \\pi {{p}_{1/2}} and \\pi {{g}_{9/2}} configurations. The \\Delta I = 1 coupled bands are observed at higher excitation energies and have been interpreted as based on the \\pi {{g}_{9/2}}\\otimes \

  4. Band Spectra and Molecular Structure

    NASA Astrophysics Data System (ADS)

    Kronig, R. De L.

    2011-06-01

    Introduction; Part I. The Energy Levels of Diatomic Molecules and their Classification by Means of Quantum Numbers: 1. General foundations; 2. Wave mechanics of diatomic molecules; 3. Electronic levels; 4. Vibrational levels; 5. Rotational levels; 6. Stark and Zeeman effect; 7. Energy levels of polyatomic molecules; Part II. Fine Structure and Wave Mechanical Properties of the Energy Levels of Diatomic Molecules: 8. The perturbation function; 9. Rotational distortion of spin multiplets; 10. Fine structure; 11. Perturbations and predissociation; 12. Even and odd levels; 13. Symmetrical and antisymmetrical levels; Part III. Selection Rules and Intensities in Diatomic Molecules: 14. General foundations; 15. Electronic bands; 16. Vibrational bands; 17. Rotational bands; 18. Band spectra and nuclear structure; 19. Transitions in the Stark and Zeeman effect; Part IV. Macroscopic Properties of Molecular Gases: 20. Scattering; 21. Dispersion; 22. Kerr and Faraday effect; 23. Dielectric constants; 24. Magnetic susceptibilities; 25. Specific heats; Part V. Molecule Formation and Chemical Binding: 26. Heteropolar molecules; 27. Homopolar molecules. Chemical forces between two H-atoms and two He-atoms; 28. The general theory of homopolar compounds; Bibliography; Subject index.

  5. Band structure in 113Sn

    NASA Astrophysics Data System (ADS)

    Banerjee, P.; Ganguly, S.; Pradhan, M. K.; Sharma, H. P.; Muralithar, S.; Singh, R. P.; Bhowmik, R. K.

    2016-07-01

    The structure of collective bands in 113Sn, populated in the reaction 100Mo(19F,p 5 n ) at a beam energy of 105 MeV, has been studied. A new positive-parity sequence of eight states extending up to 7764.9 keV and spin (39 /2+) has been observed. The band is explained as arising from the coupling of the odd valence neutron in the g7 /2 or the d5 /2 orbital to the deformed 2p-2h proton configuration of the neighboring even-A Sn isotope. Lifetimes of six states up to an excitation energy of 9934.9 keV and spin 47 /2-belonging to a Δ I =2 intruder band have been measured for the first time, including an upper limit for the last state, from Doppler-shift-attenuation data. A moderate average quadrupole deformation β2=0.22 ±0.02 is deduced from these results for the five states up to spin 43 /2- . The transition quadrupole moments decrease with increase in rotational frequency, indicating a reduction of collectivity with spin, a feature common for terminating bands. The behavior of the kinematic and dynamic moments of inertia as a function of rotational frequency has been studied and total Routhian surface calculations have been performed in an attempt to obtain an insight into the nature of the states near termination.

  6. Structures with negative index of refraction

    DOEpatents

    Soukoulis, Costas M.; Zhou, Jiangfeng; Koschny, Thomas; Zhang, Lei; Tuttle, Gary

    2011-11-08

    The invention provides simplified negative index materials (NIMs) using wire-pair structures, 4-gap single ring split-ring resonator (SRR), fishnet structures and overleaf capacitor SRR. In the wire-pair arrangement, a pair of short parallel wires and continuous wires are used. In the 4-gap single-ring SRR, the SRRs are centered on the faces of a cubic unit cell combined with a continuous wire type resonator. Combining both elements creates a frequency band where the metamaterial is transparent with simultaneously negative .di-elect cons. and .mu.. In the fishnet structure, a metallic mesh on both sides of the dielectric spacer is used. The overleaf capacitor SRR changes the gap capacities to small plate capacitors by making the sections of the SRR ring overlap at the gaps separated by a thin dielectric film. This technique is applicable to conventional SRR gaps but it best deploys for the 4-gap single-ring structures.

  7. Photonic band gap structure simulator

    DOEpatents

    Chen, Chiping; Shapiro, Michael A.; Smirnova, Evgenya I.; Temkin, Richard J.; Sirigiri, Jagadishwar R.

    2006-10-03

    A system and method for designing photonic band gap structures. The system and method provide a user with the capability to produce a model of a two-dimensional array of conductors corresponding to a unit cell. The model involves a linear equation. Boundary conditions representative of conditions at the boundary of the unit cell are applied to a solution of the Helmholtz equation defined for the unit cell. The linear equation can be approximated by a Hermitian matrix. An eigenvalue of the Helmholtz equation is calculated. One computation approach involves calculating finite differences. The model can include a symmetry element, such as a center of inversion, a rotation axis, and a mirror plane. A graphical user interface is provided for the user's convenience. A display is provided to display to a user the calculated eigenvalue, corresponding to a photonic energy level in the Brilloin zone of the unit cell.

  8. Dynamically variable negative stiffness structures

    PubMed Central

    Churchill, Christopher B.; Shahan, David W.; Smith, Sloan P.; Keefe, Andrew C.; McKnight, Geoffrey P.

    2016-01-01

    Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness–based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators. PMID:26989771

  9. Dynamically variable negative stiffness structures.

    PubMed

    Churchill, Christopher B; Shahan, David W; Smith, Sloan P; Keefe, Andrew C; McKnight, Geoffrey P

    2016-02-01

    Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness-based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators. PMID:26989771

  10. Low-loss negative index metamaterials for X, Ku, and K microwave bands

    NASA Astrophysics Data System (ADS)

    Lee, David A.; Vedral, L. James; Smith, David A.; Musselman, Randall L.; Pinchuk, Anatoliy O.

    2015-04-01

    Low-loss, negative-index of refraction metamaterials were designed and tested for X, Ku, and K microwave frequency bands. An S-shaped, split-ring resonator was used as a unit cell to design homogeneous slabs of negative-index metamaterials. Then, the slabs of metamaterials were cut unto prisms to measure experimentally the negative index of refraction of a plane electromagnetic wave. Theoretical simulations using High-Frequency Structural Simulator, a finite element equation solver, were in good agreement with experimental measurements. The negative index of refraction was retrieved from the angle- and frequency-dependence of the transmitted intensity of the microwave beam through the metamaterial prism and compared well to simulations; in addition, near-field electromagnetic intensity mapping was conducted with an infrared camera, and there was also a good match with the simulations for expected frequency ranges for the negative index of refraction.

  11. Low-loss negative index metamaterials for X, Ku, and K microwave bands

    SciTech Connect

    Lee, David A.; Vedral, L. James; Smith, David A.; Pinchuk, Anatoliy O.; Musselman, Randall L.

    2015-04-15

    Low-loss, negative-index of refraction metamaterials were designed and tested for X, Ku, and K microwave frequency bands. An S-shaped, split-ring resonator was used as a unit cell to design homogeneous slabs of negative-index metamaterials. Then, the slabs of metamaterials were cut unto prisms to measure experimentally the negative index of refraction of a plane electromagnetic wave. Theoretical simulations using High-Frequency Structural Simulator, a finite element equation solver, were in good agreement with experimental measurements. The negative index of refraction was retrieved from the angle- and frequency-dependence of the transmitted intensity of the microwave beam through the metamaterial prism and compared well to simulations; in addition, near-field electromagnetic intensity mapping was conducted with an infrared camera, and there was also a good match with the simulations for expected frequency ranges for the negative index of refraction.

  12. Negative capacitance switching via VO{sub 2} band gap engineering driven by electric field

    SciTech Connect

    He, Xinfeng; Xu, Jing; Xu, Xiaofeng Gu, Congcong; Chen, Fei; Wu, Binhe Wang, Chunrui Xing, Huaizhong; Chen, Xiaoshuang; Chu, Junhao

    2015-03-02

    We report the negative capacitance behavior of an energy band gap modulation quantum well with a sandwich VO{sub 2} layer structure. The phase transition is probed by measuring its capacitance. With the help of theoretical calculations, it shows that the negative capacitance changes of the quantum well device come from VO{sub 2} band gap by continuously tuning the temperature or voltage. Experiments reveal that as the current remains small enough, joule heating can be ignored, and the insulator-metal transition of VO{sub 2} can be induced by the electric field. Our results open up possibilities for functional devices with phase transitions induced by external electric fields other than the heating or electricity-heat transition.

  13. Negative capacitance switching via VO2 band gap engineering driven by electric field

    NASA Astrophysics Data System (ADS)

    He, Xinfeng; Xu, Jing; Xu, Xiaofeng; Gu, Congcong; Chen, Fei; Wu, Binhe; Wang, Chunrui; Xing, Huaizhong; Chen, Xiaoshuang; Chu, Junhao

    2015-03-01

    We report the negative capacitance behavior of an energy band gap modulation quantum well with a sandwich VO2 layer structure. The phase transition is probed by measuring its capacitance. With the help of theoretical calculations, it shows that the negative capacitance changes of the quantum well device come from VO2 band gap by continuously tuning the temperature or voltage. Experiments reveal that as the current remains small enough, joule heating can be ignored, and the insulator-metal transition of VO2 can be induced by the electric field. Our results open up possibilities for functional devices with phase transitions induced by external electric fields other than the heating or electricity-heat transition.

  14. Dual-band metamaterial with a windmill-like structure

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

    A broadband negative refractive index metamaterial based on a windmill-like structure is proposed, and investigated numerically and experimentally at the microwave frequency range. From the numerical and experimental results, effect media parameters are retrieved, which clearly show that two broad frequency bands exist in which the permittivity and permeability are negative. The two negative bands are from 9.1 GHz to 10.5 GHz and from 12.05 GHz to 14.65 GHz respectively, and the negative bandwidth is 4 GHz. Due to the good bandwidth performance, the metallic cell with double negative property obtained in this paper is suitable for use in the design of multiband or broadband microwave devices.

  15. Band structure of core-shell semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Pistol, Mats-Erik; Pryor, Craig

    2009-03-01

    We present band structures of strained core-shell nanowires composed of zincblende III-V (binary) semiconductors. We consider all combinations of AlN, GaN, InN, and all combinations of AlP, GaP, AlAs, GaAs, InP, InAs, AlSb, GaSb, and InSb. We compute the γ- and X-conduction band minima as well as the valence band maximum, all as functions of the core and shell radii. The calculations were performed using continuum elasticity theory for the strain, eight-band strain-dependent k.p theory for the γ-point energies, and single band approximation for the X-point conduction minima. We identify structures with type-I, type-II and type-III band alignment, as well as systems in which one material becomes metallic due to a negative band-gap. We identify structures that may support exciton crystals with and without photoexcitation. We have also computed the effective masses, from which the confinement energy may be estimated. All the results [Pistol and Pryor, Phys. Rev. B 78, 115319] are available in graphical and tabular form at www.semiconductor.physics.uiowa.edu

  16. Multiple band structures of {sup 131}Cs

    SciTech Connect

    Sihotra, S.; Palit, R.; Naik, Z.; Joshi, P. K.; Deo, A. Y.; Jain, H. C.; Singh, K.; Goswamy, J.; Mehta, D.; Singh, N.; Malik, S. S.; Praharaj, C. R.

    2008-09-15

    Excited states in {sup 131}Cs were investigated through in-beam {gamma}-ray spectroscopic techniques following its population in the {sup 124}Sn({sup 11}B, 4n) fusion-evaporation reaction at a beam energy of 46 MeV. The previously known level scheme has been substantially extended up to {approx}9 MeV excitation energy and 49/2({Dirac_h}/2{pi}) spin with the addition of seven new band structures. The present level scheme consisting of 15 bands exhibits a variety of collective features in this nucleus at intermediate spin. The excitation energies of the observed levels in different bands and the corresponding ratios of transition strengths, i.e., B(M1)/B(E2), have been compared with the results of projected deformed Hartree-Fock calculations based on various quasiparticle configurations. A strongly coupled band has been reassigned a high-K three-quasiparticle {pi}h{sub 11/2} x {nu}(h{sub 11/2}d{sub 3/2}) configuration based on the properties of this band and that of its new coupled side band. The configurations of these bands are also discussed in the framework of tilted-axis cranking model calculations and the systematics of the odd-A Cs isotopes. Additional three energetically closely placed coupled bands have been assigned different unpaired three-quasiparticle configurations. {gamma}-vibrational bands coupled to the {pi}h{sub 11/2} and {pi}g{sub 7/2} single-particle configurations have been reported in this nucleus. Observation of new E1 transitions linking the opposite-parity {pi}h{sub 11/2} and {pi}d{sub 5/2} bands provides fingerprints of possible octupole correlations.

  17. Nonreciprocal microwave band-gap structures.

    PubMed

    Belov, P A; Tretyakov, S A; Viitanen, A J

    2002-07-01

    An electrically controlled nonreciprocal electromagnetic band-gap material is proposed and studied. The new material is a periodic three-dimensional regular lattice of small magnetized ferrite spheres. In this paper, we consider plane electromagnetic waves in this medium and design an analytical model for the material parameters. An analytical solution for plane-wave reflection from a planar interface is also presented. In the proposed material, a new electrically controlled stop band appears for one of the two circularly polarized eigenwaves in a frequency band around the ferrimagnetic resonance frequency. This frequency can be well below the usual lattice band gap, which allows the realization of rather compact structures. The main properties of the material are outlined. PMID:12241501

  18. Band structure engineering in organic semiconductors

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  19. Band structure engineering in organic semiconductors.

    PubMed

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

    2016-06-17

    A key breakthrough in modern electronics was the introduction of band structure engineering, the design of almost arbitrary electronic potential structures by alloying different semiconductors to continuously tune the band gap and band-edge energies. Implementation of this approach in organic semiconductors has been hindered by strong localization of the electronic states in these materials. We show that the influence of so far largely ignored long-range Coulomb interactions provides a workaround. Photoelectron spectroscopy confirms that the ionization energies of crystalline organic semiconductors can be continuously tuned over a wide range by blending them with their halogenated derivatives. Correspondingly, the photovoltaic gap and open-circuit voltage of organic solar cells can be continuously tuned by the blending ratio of these donors. PMID:27313043

  20. Complex banded structures in directional solidification processes.

    PubMed

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

    2016-01-27

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

  1. Complex banded structures in directional solidification processes.

    PubMed

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

    2016-01-27

    A combination of theory and numerical simulation is used to investigate impurity superstructures that form in rapid directional solidification (RDS) processes in the presence of a temperature gradient and a pulling velocity with an oscillatory component. Based on a capillary wave model, we show that the RDS processes are associated with a rich morphology of banded structures, including frequency locking and the transition to chaos. PMID:26704726

  2. The band-gap enhanced photovoltaic structure

    NASA Astrophysics Data System (ADS)

    Tessler, Nir

    2016-05-01

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

  3. Quasiparticle band structure of vanadium dioxide.

    PubMed

    Sakuma, R; Miyake, T; Aryasetiawan, F

    2009-02-11

    Vanadium dioxide is insulating below 340 K in experiments, whereas the band structure calculated in the local density approximation (LDA) is gapless. We study the self-energy effects using the ab initio GW method. We found that the self-energy depends strongly on the energy, and proper treatment of the dynamical effect is essential for getting precise quasiparticle energies. Off-diagonal matrix elements in the Kohn-Sham basis are also important for disentangling bands. Inclusion of the two effects opens up a direct gap. Our results also suggest that one-shot GW on top of LDA is not enough, and the impact of self-consistency is significant.

  4. Band structure of doubly-odd nuclei around mass 130

    SciTech Connect

    Higashiyama, Koji; Yoshinaga, Naotaka

    2011-05-06

    Nuclear structure of the doublet bands in the doubly-odd nuclei with mass A{approx}130 is studied in terms of a pair-truncated shell model. The model reproduces quite well the energy levels of the doublet bands and the electromagnetic transitions. The analysis of the electromagnetic transitions reveals new band structure of the doublet bands.

  5. Multi-cavity coupling acoustic metamaterials with low-frequency broad band gaps based on negative mass density

    NASA Astrophysics Data System (ADS)

    Yang, Chuanhui; Wu, Jiu Hui; Cao, Songhua; Jing, Li

    2016-08-01

    This paper studies a novel kind of low-frequency broadband acoustic metamaterials with small size based on the mechanisms of negative mass density and multi-cavity coupling. The structure consists of a closed resonant cavity and an open resonant cavity, which can be equivalent to a homogeneous medium with effective negative mass density in a certain frequency range by using the parameter inversion method. The negative mass density makes the anti-resonance area increased, which results in broadened band gaps greatly. Owing to the multi-cavity coupling mechanism, the local resonances of the lower frequency mainly occur in the closed cavity, while the local resonances of the higher frequency mainly in the open cavity. Upon the interaction between the negative mass density and the multi-cavity coupling, there exists two broad band gaps in the range of 0-1800 Hz, i.e. the first-order band gap from 195 Hz to 660 Hz with the bandwidth of 465 Hz and the second-order band gap from 1157 Hz to 1663 Hz with the bandwidth of 506 Hz. The acoustic metamaterials with small size presented in this paper could provide a new approach to reduce the low-frequency broadband noises.

  6. Optimizing the band gap of effective mass negativity in acoustic metamaterials

    NASA Astrophysics Data System (ADS)

    Tan, K. T.; Huang, H. H.; Sun, C. T.

    2012-12-01

    A dual-resonator microstructure design is proposed for acoustic metamaterials to achieve broadband effective mass negativity. We demonstrate the advantage of acoustic wave attenuation over a wider frequency spectrum as compared to the narrow band gap of a single-resonator design. We explicitly confirm the effect of negative effective mass density by analysis of wave propagation using finite element simulations. Examples of practical application like vibration isolation and blast wave mitigation are presented and discussed.

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

    NASA Astrophysics Data System (ADS)

    Amir, Ariel; Vukusic, Peter

    2013-04-01

    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.

  8. Segmental structure in banded mongoose calls

    PubMed Central

    2012-01-01

    In complex animal vocalizations, such as bird or whale song, a great variety of songs can be produced via rearrangements of a smaller set of 'syllables', known as 'phonological syntax' or 'phonocoding' However, food or alarm calls, which function as referential signals, were previously thought to lack such combinatorial structure. A new study of calls in the banded mongoose Mungos mungo provides the first evidence of phonocoding at the level of single calls. The first portion of the call provides cues to the identity of the caller, and the second part encodes its current activity. This provides the first example known in animals of something akin to the consonants and vowels of human speech. See research article http://www.biomedcentral.com/1741-7007/10/97 PMID:23206277

  9. Segmental structure in banded mongoose calls.

    PubMed

    Fitch, W Tecumseh

    2012-01-01

    In complex animal vocalizations, such as bird or whale song, a great variety of songs can be produced via rearrangements of a smaller set of 'syllables', known as 'phonological syntax' or 'phonocoding' However, food or alarm calls, which function as referential signals, were previously thought to lack such combinatorial structure. A new study of calls in the banded mongoose Mungos mungo provides the first evidence of phonocoding at the level of single calls. The first portion of the call provides cues to the identity of the caller, and the second part encodes its current activity. This provides the first example known in animals of something akin to the consonants and vowels of human speech. PMID:23206277

  10. Sustained gamma-band EEG following negative words in depression and schizophrenia

    PubMed Central

    Siegle, Greg J.; Condray, Ruth; Thase, Michael E.; Keshavan, Matcheri; Steinhauer, Stuart R.

    2013-01-01

    Introduction Sustained and elaborative emotional information processing in depression and decreased affective elaboration in schizophrenia are considered hallmarks of these disorders but have not been directly measured. Gamma-band (35–45 Hz) EEG, has been associated with semantic functions such as feature binding and may index these elaborative processing. This study examined whether there were group differences in baseline and sustained gamma-band EEG following emotional stimuli in healthy adults as well as adults with depression and schizophrenia. Methods 24 never-depressed healthy controls, 14 patients with DSM-IV unipolar major depressive disorder, and 15 patients with DSM-IV schizophrenia completed a lexical emotion identification task during EEG assessment. Gamma band EEG (35–45 Hz) in response to negative words was the primary dependent measure. Results As predicted, depressed individuals displayed sustained and increased gamma-band EEG throughout the task, and particularly in the seconds following negative words. Individuals with schizophrenia displayed decreased gamma-band activity throughout the task. Conclusions These data suggest that gamma-band EEG, measured over several seconds, may serve as a useful index of sustained semantic information processing. Depressed individuals appear to engage in sustained elaboration following emotional stimuli, whereas individuals with schizophrenia are not as prone to this type of elaborative processing. PMID:20005267

  11. 5 CFR 9701.321 - Structure of bands.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 5 Administrative Personnel 3 2012-01-01 2012-01-01 false Structure of bands. 9701.321 Section 9701.321 Administrative Personnel DEPARTMENT OF HOMELAND SECURITY HUMAN RESOURCES MANAGEMENT SYSTEM... Structure of bands. (a) DHS may, after coordination with OPM, establish ranges of basic pay for bands,...

  12. 5 CFR 9701.321 - Structure of bands.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 5 Administrative Personnel 3 2011-01-01 2011-01-01 false Structure of bands. 9701.321 Section 9701.321 Administrative Personnel DEPARTMENT OF HOMELAND SECURITY HUMAN RESOURCES MANAGEMENT SYSTEM... Structure of bands. (a) DHS may, after coordination with OPM, establish ranges of basic pay for bands,...

  13. A Theoretical Structure of High School Concert Band Performance

    ERIC Educational Resources Information Center

    Bergee, Martin J.

    2015-01-01

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

  14. Achieving Higher Energies via Passively Driven X-band Structures

    NASA Astrophysics Data System (ADS)

    Sipahi, Taylan; Sipahi, Nihan; Milton, Stephen; Biedron, Sandra

    2014-03-01

    Due to their higher intrinsic shunt impedance X-band accelerating structures significant gradients with relatively modest input powers, and this can lead to more compact particle accelerators. At the Colorado State University Accelerator Laboratory (CSUAL) we would like to adapt this technology to our 1.3 GHz L-band accelerator system using a passively driven 11.7 GHz traveling wave X-band configuration that capitalizes on the high shunt impedances achievable in X-band accelerating structures in order to increase our overall beam energy in a manner that does not require investment in an expensive, custom, high-power X-band klystron system. Here we provide the design details of the X-band structures that will allow us to achieve our goal of reaching the maximum practical net potential across the X-band accelerating structure while driven solely by the beam from the L-band system.

  15. Birefringence and band structure of CdP2 crystals

    NASA Astrophysics Data System (ADS)

    Beril, S. I.; Stamov, I. G.; Syrbu, N. N.; Zalamai, V. V.

    2013-08-01

    The spatial dispersion in CdP2 crystals was investigated. The dispersion is positive (nk||с>nk||у) at λ>λ0 and negative (nk||сbands. Minimal direct energy intervals correspond to transitions Г1→Г1 for Е||с and Г2→Г1 for Е⊥с. The temperature coefficient of energy gap sifting in the case of temperature changing between 2 and 4.2 K equals to 10.6 meV/K and 3.2 mev/K for Г1→Г1 and Г2→Г1 band gap correspondingly. Reflectivity spectra were measured for energy interval 1.5-10 eV and optical functions (n, k, ε1, ε2,d2ε1/dE2 and d2ε2/dE2) were calculated by using Kramers-Kronig analyses. All features were interpreted as optical transitions on the basis of both theoretical calculations of band structure.

  16. A hybridized basis for simple band structures

    NASA Astrophysics Data System (ADS)

    Spałek, J.; Ray, D. K.; Acquarone, M.

    1985-12-01

    We show that a model Hamiltonian representing a degenerate band composed of d equally hybridized and equivalent narrow subbands can be diagonalized for arbitrary d.A simple transformation removing the hybridization entirely is constructed. It gives both the eigenvalues and the eigen-functions in explicit form. The conditions under which the electron-electron intrasite interactions are invariant under the transformation are discussed..An analogous transformation is constructed also for the band part of the degenerate periodic Anderson model with the component bands mixed to the same extent with the atomic level.

  17. Band Structure Characteristics of Nacreous Composite Materials with Various Defects

    NASA Astrophysics Data System (ADS)

    Yin, J.; Zhang, S.; Zhang, H. W.; Chen, B. S.

    2016-06-01

    Nacreous composite materials have excellent mechanical properties, such as high strength, high toughness, and wide phononic band gap. In order to research band structure characteristics of nacreous composite materials with various defects, supercell models with the Brick-and-Mortar microstructure are considered. An efficient multi-level substructure algorithm is employed to discuss the band structure. Furthermore, two common systems with point and line defects and varied material parameters are discussed. In addition, band structures concerning straight and deflected crack defects are calculated by changing the shear modulus of the mortar. Finally, the sensitivity of band structures to the random material distribution is presented by considering different volume ratios of the brick. The results reveal that the first band gap of a nacreous composite material is insensitive to defects under certain conditions. It will be of great value to the design and synthesis of new nacreous composite materials for better dynamic properties.

  18. Engineering the Electronic Band Structure for Multiband Solar Cells

    SciTech Connect

    Lopez, N.; Reichertz, L.A.; Yu, K.M.; Campman, K.; Walukiewicz, W.

    2010-07-12

    Using the unique features of the electronic band structure of GaNxAs1-x alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the Band Anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.

  19. Planar electromagnetic band-gap structure based on graphene

    NASA Astrophysics Data System (ADS)

    Dong, Yanfei; Liu, Peiguo; Yin, Wen-Yan; Li, Gaosheng; Yi, Bo

    2015-06-01

    Electromagnetic band-gap structure with slow-wave effect is instrumental in effectively controlling electromagnetic wave propagation. In this paper, we theoretically analyze equivalent circuit model of electromagnetic band-gap structure based on graphene and evaluate its potential applications. Graphene electromagnetic band-gap based on parallel planar waveguide is investigated, which display good characteristics in dynamically adjusting the electromagnetic wave propagation in terahertz range. The same characteristics are retrieved in a spiral shape electromagnetic band-gap based on coplanar waveguide due to tunable conductivity of graphene. Various potential terahertz planar devices are expected to derive from the prototype structures.

  20. Band structure controlled by chiral imprinting

    NASA Astrophysics Data System (ADS)

    Castro-Garay, P.; Adrian Reyes, J.; Ramos-Garcia, R.

    2007-09-01

    Using the configuration of an imprinted cholesteric elastomer immersed in a racemic solvent, the authors find the solution of the boundary-value problem for the reflection and transmission of incident optical waves due to the elastomer. They show a significant width reduction of the reflection band for certain values of nematic penetration depth, which depends on the volume fraction of molecules from the solvent, whose handedness is preferably absorbed. The appearance of nested band gaps of both handednesses during the sorting mixed chiral process is also obtained. This suggests the design of chemically controlled optical filters and optically monitored chiral pumps.

  1. Thermoreflectance investigation of Th band structure

    SciTech Connect

    Colavita, E.; Paolucci, G.; Rosei, R.

    1982-06-15

    Thermoreflectance measurements have been carried out on thorium bulk samples at about 140 K in the 0.5--5-eV photon energy range. The data are interpreted within the framework of existing energy-band calculations. Several critical-point transitions and a Fermi-surface transition have been clearly identified and located in the Brillouin zone.

  2. Band structures in Sierpinski triangle fractal porous phononic crystals

    NASA Astrophysics Data System (ADS)

    Wang, Kai; Liu, Ying; Liang, Tianshu

    2016-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  4. Surface band structure of Si(111)2×1

    NASA Astrophysics Data System (ADS)

    Chen, B.; Haneman, D.

    1995-02-01

    The surface band structures of the three-bond scission (TBS) model and the Pandey-chain (PC) model have been computed using an ab initio Hartree-Fock program crystal 92. In the case of the bulk energy bands, the method gives the correct shapes and structure but overestimates the valence-band dispersion by about 50%. For the TBS model, the calculated valence-band dispersion came out about 50% wider than measured experimentally. This would suggest that the model is consistent with optical data. In the case of the PC model, the valence-band dispersion was qualitatively similar to those of previous calculations, but the width discrepancy was large. The method overestimates the surface band gap for both TBS and PC models. The significance is discussed.

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

    PubMed

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

    2013-01-01

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

  6. New Band Structures in Aapprox110 Neutron-Rich Nuclei

    SciTech Connect

    Zhu, S. J.; Wang, J. G.; Ding, H. B.; Gu, L.; Xu, Q.; Yeoh, E. Y.; Xiao, Z. G.; Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Liu, S. H.; Li, K.; Luo, Y. X.; Rasmussen, J. O.; Lee, I. Y.; Qi, B.; Meng, J.

    2010-05-12

    The high spin states of neutron-rich nuclei in Aapprox110 region have been carefully investigated by measuring prompt gamma-gamma-gamma coincident measurements populated in the spontaneous fission of {sup 252}Cf with the Gammasphere detector array. Many new collective bands have been discovered. In this proceeding paper, we introduce some interesting new band structures recently observed by our cooperative groups, that is, the one-phonon- and two-phonon gamma-vibrational bands in odd-A {sup 103}Nb, {sup 105}Mo and {sup 107}Tc, the chiral doublet bands in even-even {sup 106}Mo, {sup 110}Ru and {sup 112}Ru, and the pseudospin partner bands with in {sup 108}Tc. The characteristics of these band structures have been discussed.

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

    NASA Astrophysics Data System (ADS)

    Markoš, P.; Kuzmiak, V.

    2016-09-01

    The frequency and transmission spectrum of a two-dimensional array of metallic rods is investigated numerically. Based on the recent analysis of the band structure of two-dimensional photonic crystals with dielectric rods [Phys. Rev. A 92, 043814 (2015), 10.1103/PhysRevA.92.043814], we identify two types of bands in the frequency spectrum: Bragg (P ) bands resulting from a periodicity and Fano (F ) bands which arise from Fano resonances associated with each of the cylinders within the periodic structure. It is shown that the existence of the Fano band in a certain frequency range is manifested by a Fano resonance in the transmittance. In particular, we reexamine the symmetry properties of the H -polarized band structure in the frequency range where the spectrum consists of the localized modes associated with the single-scatterer resonances and we explore the process of formation of Fano bands by identifying individual terms in the expansion of the linear combination of atomic orbitals states. We demonstrate how the interplay between the two scattering mechanisms affects the properties of the resulting band structure when the radius of cylinders is increased. We show that a different character of both kinds of bands is reflected in the spatial distribution of the magnetic field, which displays patterns corresponding to the corresponding irreducible symmetry representations.

  8. Band Structure Controlled by Chiral Imprinting

    NASA Astrophysics Data System (ADS)

    Reyes Cervantes, Adrian; Castro-Garay, P.; Ramos-Garcia, Ruben

    2008-03-01

    Using the configuration of an imprinted cholesteric elastomer immersed in a racemic solvent, we find the solution of the boundary--value problem for the reflection and transmission of incident optical waves due to the elastomer. We show a significant width reduction of the reflection band for certain values of nematic penetration depth, which depends on the volume fraction of molecules from the solvent, whose handedness is preferably absorbed. The appearance of nested bandgaps of both handednesses during the sorting mixed chiral process is also obtained. This suggests the design of chemically controlled optical filters and optically monitored chiral pumps.

  9. Shell model description of band structure in 48Cr

    SciTech Connect

    Vargas, Carlos E.; Velazquez, Victor M.

    2007-02-12

    The band structure for normal and abnormal parity bands in 48Cr are described using the m-scheme shell model. In addition to full fp-shell, two particles in the 1d3/2 orbital are allowed in order to describe intruder states. The interaction includes fp-, sd- and mixed matrix elements.

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

    SciTech Connect

    Arko, A.J.; Joyce, J.J.; Smith, J.L.; Andrews, A.B.

    1996-08-01

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

  11. Band Structure of SnTe Studied by Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Littlewood, P. B.; Mihaila, B.; Schulze, R. K.; Safarik, D. J.; Gubernatis, J. E.; Bostwick, A.; Rotenberg, E.; Opeil, C. P.; Durakiewicz, T.; Smith, J. L.; Lashley, J. C.

    2010-08-01

    We present an angle-resolved photoemission spectroscopy study of the electronic structure of SnTe and compare the experimental results to ab initio band structure calculations as well as a simplified tight-binding model of the p bands. Our study reveals the conjectured complex Fermi surface structure near the L points showing topological changes in the bands from disconnected pockets, to open tubes, and then to cuboids as the binding energy increases, resolving lingering issues about the electronic structure. The chemical potential at the crystal surface is found to be 0.5 eV below the gap, corresponding to a carrier density of p=1.14×1021cm-3 or 7.2×10-2 holes per unit cell. At a temperature below the cubic-rhombohedral structural transition a small shift in spectral energy of the valance band is found, in agreement with model predictions.

  12. Band structure of SnTe studied by photoemission spectroscopy.

    PubMed

    Littlewood, P B; Mihaila, B; Schulze, R K; Safarik, D J; Gubernatis, J E; Bostwick, A; Rotenberg, E; Opeil, C P; Durakiewicz, T; Smith, J L; Lashley, J C

    2010-08-20

    We present an angle-resolved photoemission spectroscopy study of the electronic structure of SnTe and compare the experimental results to ab initio band structure calculations as well as a simplified tight-binding model of the p bands. Our study reveals the conjectured complex Fermi surface structure near the L points showing topological changes in the bands from disconnected pockets, to open tubes, and then to cuboids as the binding energy increases, resolving lingering issues about the electronic structure. The chemical potential at the crystal surface is found to be 0.5 eV below the gap, corresponding to a carrier density of p=1.14 × 10(21)  cm(-3) or 7.2 × 10(-2) holes per unit cell. At a temperature below the cubic-rhombohedral structural transition a small shift in spectral energy of the valance band is found, in agreement with model predictions. PMID:20868120

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

    PubMed Central

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

    2015-01-01

    Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain. PMID:26289434

  14. Band structure in Yang-Mills theories

    NASA Astrophysics Data System (ADS)

    Bachas, Constantin; Tomaras, Theodore

    2016-05-01

    We show how Yang-Mills theory on S3 × ℝ can exhibit a spectrum with continuous bands if coupled either to a topological 3-form gauge field, or to a dynamical axion with heavy Peccei-Quinn scale. The basic mechanism consists in associating winding histories to a bosonic zero mode whose role is to convert a circle in configuration space into a helix. The zero mode is, respectively, the holonomy of the 3-form field or the axion momentum. In these models different θ sectors coexist and are only mixed by (non-local) volume operators. Our analysis sheds light on, and extends Seiberg's proposal for modifying the topological sums in quantum field theories. It refutes a recent claim that B + L violation at LHC is unsuppressed.

  15. Electronic band structure of surface-doped black phosphorus

    NASA Astrophysics Data System (ADS)

    Kim, Jimin; Ryu, Sae Hee; Sohn, Yeongsup; Kim, Keun Su

    2015-03-01

    There are rapidly growing interests in the study of few-layer black phosphorus owing to its promising device characteristics that may impact our future electronics technology. The low-energy band structure of black phosphorus has been widely predicted to be controllable by external perturbations, such as strain and doping. In this work, we attempt to control the electronic band structure of black phosphorous by in-situ surface deposition of alkali-metal atoms. We found that surface doping induces steep band bending towards the bulk, leading to the emergence of new 2D electronic states that are confined within only few phosphorene layers of black phosphorus. Using angle-resolved photoemission spectroscopy, we directly measured the electronic band structure and its evolution as a function of dopant density. Supported by IBS.

  16. Development of X-Band Dielectric-Loaded Accelerating Structures

    SciTech Connect

    Gold, S. H.; Jing, C.; Kanareykin, A.; Gai, W.; Konecny, R.; Power, J. G.; Kinkead, A. K.

    2010-11-04

    This paper presents a progress report on the development and testing of X-band dielectric-loaded accelerating structures. Recent tests on several quartz DLA structures with different inner diameters are reported. Designs for gap-free DLA structures are presented. Also, planned new experiments are discussed, including higher gradient traveling-wave and standing-wave structures and special grooved structures for multipactor suppression.

  17. Broad self-trapped and slow light bands based on negative refraction and interference of magnetic coupled modes.

    PubMed

    Fang, Yun-Tuan; Ni, Zhi-Yao; Zhu, Na; Zhou, Jun

    2016-01-13

    We propose a new mechanism to achieve light localization and slow light. Through the study on the coupling of two magnetic surface modes, we find a special convex band that takes on a negative refraction effect. The negative refraction results in an energy flow concellation effect from two degenerated modes on the convex band. The energy flow concellation effect leads to forming of the self-trapped and slow light bands. In the self-trapped band light is localized around the source without reflection wall in the waveguide direction, whereas in the slow light band, light becomes the standing-waves and moving standing-waves at the center and the two sides of the waveguide, respectively. PMID:26647772

  18. Broad self-trapped and slow light bands based on negative refraction and interference of magnetic coupled modes.

    PubMed

    Fang, Yun-Tuan; Ni, Zhi-Yao; Zhu, Na; Zhou, Jun

    2016-01-13

    We propose a new mechanism to achieve light localization and slow light. Through the study on the coupling of two magnetic surface modes, we find a special convex band that takes on a negative refraction effect. The negative refraction results in an energy flow concellation effect from two degenerated modes on the convex band. The energy flow concellation effect leads to forming of the self-trapped and slow light bands. In the self-trapped band light is localized around the source without reflection wall in the waveguide direction, whereas in the slow light band, light becomes the standing-waves and moving standing-waves at the center and the two sides of the waveguide, respectively.

  19. Millimeter-wave waveguiding using photonic band structures

    NASA Astrophysics Data System (ADS)

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

    2000-07-01

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

  20. Measuring the band structures of periodic beams using the wave superposition method

    NASA Astrophysics Data System (ADS)

    Junyi, L.; Ruffini, V.; Balint, D.

    2016-11-01

    Phononic crystals and elastic metamaterials are artificially engineered periodic structures that have several interesting properties, such as negative effective stiffness in certain frequency ranges. An interesting property of phononic crystals and elastic metamaterials is the presence of band gaps, which are bands of frequencies where elastic waves cannot propagate. The presence of band gaps gives this class of materials the potential to be used as vibration isolators. In many studies, the band structures were used to evaluate the band gaps. The presence of band gaps in a finite structure is commonly validated by measuring the frequency response as there are no direct methods of measuring the band structures. In this study, an experiment was conducted to determine the band structure of one dimension phononic crystals with two wave modes, such as a bi-material beam, using the frequency response at only 6 points to validate the wave superposition method (WSM) introduced in a previous study. A bi-material beam and an aluminium beam with varying geometry were studied. The experiment was performed by hanging the beams freely, exciting one end of the beams, and measuring the acceleration at consecutive unit cells. The measured transfer function of the beams agrees with the analytical solutions but minor discrepancies. The band structure was then determined using WSM and the band structure of one set of the waves was found to agree well with the analytical solutions. The measurements taken for the other set of waves, which are the evanescent waves in the bi-material beams, were inaccurate and noisy. The transfer functions at additional points of one of the beams were calculated from the measured band structure using WSM. The calculated transfer function agrees with the measured results except at the frequencies where the band structure was inaccurate. Lastly, a study of the potential sources of errors was also conducted using finite element modelling and the errors in

  1. Band structures in light neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Bohlen, H. G.; von Oertzen, W.; Kalpakchieva, R.; Massey, T. N.; Dorsch, T.; Milin, M.; Schulz, C.; Kokalova, T.; Wheldon, C.

    2008-05-01

    The structure of beryllium isotopes in the mass range A = 8-12 has been investigated using the properties of different bands, which are populated in specific reactions. The different structures are formed in transfer reactions with neutron stripping on 9,10Be or proton pick-up on 12,13,14C. The slope in the linear dependence of the excitation energies on J(J+1), where J is the spin, has been deduced for 13 bands and compared for common systematics. From the measured moments-of-inertia the α - α distance has been deduced for molecular structures.

  2. Band structures and band offsets of high K dielectrics on Si

    NASA Astrophysics Data System (ADS)

    Robertson, J.

    2002-05-01

    Various high dielectric constant oxides will be used as insulator in ferroelectric memories, dynamic random access memories, and as the gate dielectric material in future complementary metal oxide semiconductor (CMOS) technology. These oxides which have moderately wide bandgaps provide a good test of our understanding of Schottky barrier heights and band offsets at semiconductor interfaces. Metal induced gap states (MIGS) are found to give a good description of these interfaces. The electronic structure and band offsets of these oxides are calculated. It is found that Ta 2O 5 and SrTiO 3 have small or vanishing conduction band offsets on Si. La 2O 3, Y 2O 3, ZrO 2, HfO 2, Al 2O 3 and silicates like ZrSiO 4 have offsets over 1.4 eV for both electrons and holes, making them better gate dielectrics.

  3. Complex band structure of topological insulator Bi2Se3.

    PubMed

    Betancourt, J; Li, S; Dang, X; Burton, J D; Tsymbal, E Y; Velev, J P

    2016-10-01

    Topological insulators are very interesting from a fundamental point of view, and their unique properties may be useful for electronic and spintronic device applications. From the point of view of applications it is important to understand the decay behavior of carriers injected in the band gap of the topological insulator, which is determined by its complex band structure (CBS). Using first-principles calculations, we investigate the dispersion and symmetry of the complex bands of Bi2Se3 family of three-dimensional topological insulators. We compare the CBS of a band insulator and a topological insulator and follow the CBS evolution in both when the spin-orbit interaction is turned on. We find significant differences in the CBS linked to the topological band structure. In particular, our results demonstrate that the evanescent states in Bi2Se3 are non-trivially complex, i.e. contain both the real and imaginary contributions. This explains quantitatively the oscillatory behavior of the band gap obtained from Bi2Se3 (0 0 0 1) slab calculations. PMID:27485021

  4. Complex band structure of topological insulator Bi2Se3

    NASA Astrophysics Data System (ADS)

    Betancourt, J.; Li, S.; Dang, X.; Burton, J. D.; Tsymbal, E. Y.; Velev, J. P.

    2016-10-01

    Topological insulators are very interesting from a fundamental point of view, and their unique properties may be useful for electronic and spintronic device applications. From the point of view of applications it is important to understand the decay behavior of carriers injected in the band gap of the topological insulator, which is determined by its complex band structure (CBS). Using first-principles calculations, we investigate the dispersion and symmetry of the complex bands of Bi2Se3 family of three-dimensional topological insulators. We compare the CBS of a band insulator and a topological insulator and follow the CBS evolution in both when the spin-orbit interaction is turned on. We find significant differences in the CBS linked to the topological band structure. In particular, our results demonstrate that the evanescent states in Bi2Se3 are non-trivially complex, i.e. contain both the real and imaginary contributions. This explains quantitatively the oscillatory behavior of the band gap obtained from Bi2Se3 (0 0 0 1) slab calculations.

  5. Negative-group-delay and non-foster electromagnetic structures

    NASA Astrophysics Data System (ADS)

    Mirzaei, Hassan

    of the feedline. The active approach employs unilateral reactive non-Foster elements, synthesized by NGD networks, in the feedline. Chapters 7 presents the properties of positive-index/negative-index coupled-line structures, where simplified relations describing these structures in the complex-mode band are derived. Based on these relations, the properties of these structures are discussed. By employing these properties, two applications, namely a NGD structure and a novel traveling-wave resonator, are demonstrated. Although this dissertation focuses on non-Foster and negative-group-delay structures, extra work is described in parts of the thesis to explore relevant structures and to propose novel applications. In this regard, in Chapters 4, before presenting the antenna with an embedded matching network and in a relevant application, a frequency-reconfigurable antenna is presented. Moreover, in Chapters 5, passive approaches for squint-free beamforming in series-fed arrays are explored and implemented. Further, in Chapters 6, the applications of positive-index/negative-index guides in constructing a novel type of resonator with multiple resonant frequencies, in a certain bandwidth, are investigated.

  6. Shell model and band structures in 19O

    NASA Astrophysics Data System (ADS)

    von Oertzen, W.; Milin, M.; Dorsch, T.; Bohlen, H. G.; Krücken, R.; Faestermann, T.; Hertenberger, R.; Kokalova, Tz.; Mahgoub, M.; Wheldon, C.; Wirth, H.-F.

    2010-12-01

    We have studied the reaction ( ^7Li, p) on 13C targets at E lab = 44 MeV, populating states in the oxygen isotope 19O . The experiments were performed at the Tandem Laboratory (Maier-Leibniz Laboratorium) using the high-resolution Q3D magnetic spectrometer. States were populated up to an excitation energy of 21MeV, with an overall energy resolution of 45keV. We discuss shell model states and cluster bands related to the rotational bands in the 18O -isotope, using the weak-coupling approach. Similar to 18O , the broken intrinsic reflection symmetry in these states must give rise to rotational bands as parity doublets, so two K = 3/2 bands (parities, + and - are proposed with large moments of inertia. These are discussed in terms of an underlying cluster structure, ( ^14C ⊗ n ⊗ α) . An extended molecular binding diagram is proposed which includes the 14C -cluster.

  7. Anomalous behavior of group velocity and index of refraction in a defect photonic band gap structure

    NASA Astrophysics Data System (ADS)

    Srivastava, Sanjeev K.; Pandey, G. N.; Ojha, S. P.

    2008-02-01

    In the present paper, we have made an analysis to observe the effect of introduction of defect on dispersion relation, group velocity, and effective group index in a conventional photonic band gap (PBG) structure. The study shows that inside the PBG materials group velocity and effective group index becomes negative in both types (conventional as well as defect PBG structure) of structure at a certain range of frequencies. Also, near the edges of the bands it attains very high values of index of refraction. A defect PBG structure gives a very unique feature that group velocity becomes exactly zero at a particular value of frequency and also becomes several hundred times greater than the velocity of light which is not attainable with the conventional PBG structure. Defect PBG structures with such peculiar characteristics are seen in lasing without inversion, in construction of perfect lens, in trapping of photon and other optical devices.

  8. Excitation of Meinel and the first negative band system at the collision of electrons and protons with the nitrogen molecule

    SciTech Connect

    Gochitashvili, Malkhaz R.; Lomsadze, Ramaz A.; Kezerashvili, Roman Ya.

    2010-08-15

    The absolute cross sections for the e-N{sub 2} and p-N{sub 2} collisions for the first negative B{sup 2{Sigma}}{sub u}{sup +}-X{sup 2{Sigma}}{sub g}{sup +} and Meinel A{sup 2{Pi}}{sub u}-X{sup 2{Sigma}}{sub g}{sup +} bands have been measured in the energy region of 400-1500 eV for electrons and 0.4-10 keV for protons, respectively. Measurements are performed in the visible spectral region of 400-800 nm by an optical spectroscopy method. The ratio of the cross sections of the Meinel band system to the cross section of the first negative band system (0,0) does not depend on the incident electron energy. The populations of vibrational levels corresponding to A{sup 2{Pi}}{sub u} states are consistent with the Franck-Condon principle. The ratios of the cross sections of (4,1) to (3,0) bands and (5,2) to (3,0) bands exhibit slight dependence on the proton energy. A theoretical estimation within the quasimolecular approximation provides a reasonable description of the total cross section for the first negative band.

  9. Tunable all-angle negative refraction and photonic band gaps in two-dimensional plasma photonic crystals with square-like Archimedean lattices

    SciTech Connect

    Zhang, Hai-Feng E-mail: lsb@nuaa.edu.cn; Liu, Shao-Bin E-mail: lsb@nuaa.edu.cn; Jiang, Yu-Chi

    2014-09-15

    In this paper, the tunable all-angle negative refraction and photonic band gaps (PBGs) in two types of two-dimensional (2D) plasma photonic crystals (PPCs) composed of homogeneous plasma and dielectric (GaAs) with square-like Archimedean lattices (ladybug and bathroom lattices) for TM wave are theoretically investigated based on a modified plane wave expansion method. The type-1 structure is dielectric rods immersed in the plasma background, and the complementary structure is named as type-2 PPCs. Theoretical simulations demonstrate that the both types of PPCs with square-like Archimedean lattices have some advantages in obtaining the higher cut-off frequency, the larger PBGs, more number of PBGs, and the relative bandwidths compared to the conventional square lattices as the filling factor or radius of inserted rods is same. The influences of plasma frequency and radius of inserted rod on the properties of PBGs for both types of PPCs also are discussed in detail. The calculated results show that PBGs can be manipulated by the parameters as mentioned above. The possibilities of all-angle negative refraction in such two types of PPCs at low bands also are discussed. Our calculations reveal that the all-angle negative phenomena can be observed in the first two TM bands, and the frequency range of all-angle negative refraction can be tuned by changing plasma frequency. Those properties can be used to design the optical switching and sensor.

  10. Tunable all-angle negative refraction and photonic band gaps in two-dimensional plasma photonic crystals with square-like Archimedean lattices

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Feng; Liu, Shao-Bin; Jiang, Yu-Chi

    2014-09-01

    In this paper, the tunable all-angle negative refraction and photonic band gaps (PBGs) in two types of two-dimensional (2D) plasma photonic crystals (PPCs) composed of homogeneous plasma and dielectric (GaAs) with square-like Archimedean lattices (ladybug and bathroom lattices) for TM wave are theoretically investigated based on a modified plane wave expansion method. The type-1 structure is dielectric rods immersed in the plasma background, and the complementary structure is named as type-2 PPCs. Theoretical simulations demonstrate that the both types of PPCs with square-like Archimedean lattices have some advantages in obtaining the higher cut-off frequency, the larger PBGs, more number of PBGs, and the relative bandwidths compared to the conventional square lattices as the filling factor or radius of inserted rods is same. The influences of plasma frequency and radius of inserted rod on the properties of PBGs for both types of PPCs also are discussed in detail. The calculated results show that PBGs can be manipulated by the parameters as mentioned above. The possibilities of all-angle negative refraction in such two types of PPCs at low bands also are discussed. Our calculations reveal that the all-angle negative phenomena can be observed in the first two TM bands, and the frequency range of all-angle negative refraction can be tuned by changing plasma frequency. Those properties can be used to design the optical switching and sensor.

  11. Negative thermal expansion and broad band photoluminescence in a novel material of ZrScMo2VO12

    NASA Astrophysics Data System (ADS)

    Ge, Xianghong; Mao, Yanchao; Liu, Xiansheng; Cheng, Yongguang; Yuan, Baohe; Chao, Mingju; Liang, Erjun

    2016-04-01

    In this paper, we present a novel material with the formula of ZrScMo2VO12 for the first time. It was demonstrated that this material exhibits not only excellent negative thermal expansion (NTE) property over a wide temperature range (at least from 150 to 823 K), but also very intense photoluminescence covering the entire visible region. Structure analysis shows that ZrScMo2VO12 has an orthorhombic structure with the space group Pbcn (No. 60) at room temperature. A phase transition from monoclinic to orthorhombic structure between 70 and 90 K is also revealed. The intense white light emission is tentatively attributed to the n- and p-type like co-doping effect which creates not only the donor- and acceptor-like states in the band gap, but also donor-acceptor pairs and even bound exciton complexes. The excellent NTE property integrated with the intense white-light emission implies a potential application of this material in light emitting diode and other photoelectric devices.

  12. Negative thermal expansion and broad band photoluminescence in a novel material of ZrScMo2VO12.

    PubMed

    Ge, Xianghong; Mao, Yanchao; Liu, Xiansheng; Cheng, Yongguang; Yuan, Baohe; Chao, Mingju; Liang, Erjun

    2016-01-01

    In this paper, we present a novel material with the formula of ZrScMo2VO12 for the first time. It was demonstrated that this material exhibits not only excellent negative thermal expansion (NTE) property over a wide temperature range (at least from 150 to 823 K), but also very intense photoluminescence covering the entire visible region. Structure analysis shows that ZrScMo2VO12 has an orthorhombic structure with the space group Pbcn (No. 60) at room temperature. A phase transition from monoclinic to orthorhombic structure between 70 and 90 K is also revealed. The intense white light emission is tentatively attributed to the n- and p-type like co-doping effect which creates not only the donor- and acceptor-like states in the band gap, but also donor-acceptor pairs and even bound exciton complexes. The excellent NTE property integrated with the intense white-light emission implies a potential application of this material in light emitting diode and other photoelectric devices. PMID:27098924

  13. Negative thermal expansion and broad band photoluminescence in a novel material of ZrScMo2VO12

    PubMed Central

    Ge, Xianghong; Mao, Yanchao; Liu, Xiansheng; Cheng, Yongguang; Yuan, Baohe; Chao, Mingju; Liang, Erjun

    2016-01-01

    In this paper, we present a novel material with the formula of ZrScMo2VO12 for the first time. It was demonstrated that this material exhibits not only excellent negative thermal expansion (NTE) property over a wide temperature range (at least from 150 to 823 K), but also very intense photoluminescence covering the entire visible region. Structure analysis shows that ZrScMo2VO12 has an orthorhombic structure with the space group Pbcn (No. 60) at room temperature. A phase transition from monoclinic to orthorhombic structure between 70 and 90 K is also revealed. The intense white light emission is tentatively attributed to the n- and p-type like co-doping effect which creates not only the donor- and acceptor-like states in the band gap, but also donor-acceptor pairs and even bound exciton complexes. The excellent NTE property integrated with the intense white-light emission implies a potential application of this material in light emitting diode and other photoelectric devices. PMID:27098924

  14. 5 CFR 9701.321 - Structure of bands.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 5 Administrative Personnel 3 2014-01-01 2014-01-01 false Structure of bands. 9701.321 Section 9701.321 Administrative Personnel DEPARTMENT OF HOMELAND SECURITY HUMAN RESOURCES MANAGEMENT SYSTEM (DEPARTMENT OF HOMELAND SECURITY-OFFICE OF PERSONNEL MANAGEMENT) DEPARTMENT OF HOMELAND SECURITY...

  15. 5 CFR 9701.321 - Structure of bands.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 5 Administrative Personnel 3 2013-01-01 2013-01-01 false Structure of bands. 9701.321 Section 9701.321 Administrative Personnel DEPARTMENT OF HOMELAND SECURITY HUMAN RESOURCES MANAGEMENT SYSTEM (DEPARTMENT OF HOMELAND SECURITY-OFFICE OF PERSONNEL MANAGEMENT) DEPARTMENT OF HOMELAND SECURITY...

  16. Band structure of W and Mo by empirical pseudopotential method

    NASA Technical Reports Server (NTRS)

    Sridhar, C. G.; Whiting, E. E.

    1977-01-01

    The empirical pseudopotential method (EPM) is used to calculate the band structure of tungsten and molybdenum. Agreement between the calculated reflectivity, density of states, density of states at the Fermi surface and location of the Fermi surface from this study and experimental measurements and previous calculations is good. Also the charge distribution shows the proper topological distribution of charge for a bcc crystal.

  17. X-Band Photonic Band-Gap Accelerator Structure Breakdown Experiment

    SciTech Connect

    Marsh, Roark A.; Shapiro, Michael A.; Temkin, Richard J.; Dolgashev, Valery A.; Laurent, Lisa L.; Lewandowski, James R.; Yeremian, A.Dian; Tantawi, Sami G.; /SLAC

    2012-06-11

    In order to understand the performance of photonic band-gap (PBG) structures under realistic high gradient, high power, high repetition rate operation, a PBG accelerator structure was designed and tested at X band (11.424 GHz). The structure consisted of a single test cell with matching cells before and after the structure. The design followed principles previously established in testing a series of conventional pillbox structures. The PBG structure was tested at an accelerating gradient of 65 MV/m yielding a breakdown rate of two breakdowns per hour at 60 Hz. An accelerating gradient above 110 MV/m was demonstrated at a higher breakdown rate. Significant pulsed heating occurred on the surface of the inner rods of the PBG structure, with a temperature rise of 85 K estimated when operating in 100 ns pulses at a gradient of 100 MV/m and a surface magnetic field of 890 kA/m. A temperature rise of up to 250 K was estimated for some shots. The iris surfaces, the location of peak electric field, surprisingly had no damage, but the inner rods, the location of the peak magnetic fields and a large temperature rise, had significant damage. Breakdown in accelerator structures is generally understood in terms of electric field effects. These PBG structure results highlight the unexpected role of magnetic fields in breakdown. The hypothesis is presented that the moderate level electric field on the inner rods, about 14 MV/m, is enhanced at small tips and projections caused by pulsed heating, leading to breakdown. Future PBG structures should be built to minimize pulsed surface heating and temperature rise.

  18. Valence-band ordering and magneto-optic exciton fine structure in ZnO

    NASA Astrophysics Data System (ADS)

    Lambrecht, Walter R.; Rodina, Anna V.; Limpijumnong, Sukit; Segall, B.; Meyer, Bruno K.

    2002-02-01

    Using first-principles linear muffin-tin orbital density functional band structure calculations, the ordering of the states in the wurtzite ZnO valence-band maximum, split by crystal-field and spin-orbit coupling effects, is found to be Γ7(5)>Γ9(5)>Γ7(1), in which the number in parentheses indicates the parent state without spin-orbit coupling. This results from the negative spin-orbit splitting, which in turn is due to the participation of the Zn 3d band. The result is found to be robust even when effects beyond the local density approximation on the Zn 3d band position are included. Using a Kohn-Luttinger model parametrized by our first-principles calculations, it is furthermore shown that the binding energies of the excitons primarily derived from each valence band differ by less than the valence-band splittings even when interband coupling effects are included. The binding energies of n=2 and n=1 excitons, however, are not in a simple 1/4 ratio. Our results are shown to be in good agreement with the recent magneto-optical experimental data by Reynolds et al. [Phys. Rev. B 60, 2340 (1999)], in spite of the fact that on the basis of these data these authors claimed that the valence-band maximum would have Γ9 symmetry. The differences between our and Reynolds' analysis of the data are discussed and arise from the sign of the Landé g factor for holes, which is here found to be negative for the upper Γ7 band.

  19. Inter-band optoelectronic properties in quantum dot structure of low band gap III-V semiconductors

    SciTech Connect

    Dey, Anup; Maiti, Biswajit; Chanda, Debasree

    2014-04-14

    A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k{sup →}) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg{sub 1−x}Cd{sub x}Te, and In{sub 1−x}Ga{sub x}As{sub y}P{sub 1−y} lattice matched to InP, as example of III–V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

  20. From lattice Hamiltonians to tunable band structures by lithographic design

    NASA Astrophysics Data System (ADS)

    Tadjine, Athmane; Allan, Guy; Delerue, Christophe

    2016-08-01

    Recently, new materials exhibiting exotic band structures characterized by Dirac cones, nontrivial flat bands, and band crossing points have been proposed on the basis of effective two-dimensional lattice Hamiltonians. Here, we show using atomistic tight-binding calculations that these theoretical predictions could be experimentally realized in the conduction band of superlattices nanolithographed in III-V and II-VI semiconductor ultrathin films. The lithographed patterns consist of periodic lattices of etched cylindrical holes that form potential barriers for the electrons in the quantum well. In the case of honeycomb lattices, the conduction minibands of the resulting artificial graphene host several Dirac cones and nontrivial flat bands. Similar features, but organized in different ways, in energy or in k -space are found in kagome, distorted honeycomb, and Lieb superlattices. Dirac cones extending over tens of meV could be obtained in superlattices with reasonable sizes of the lithographic patterns, for instance in InAs/AlSb heterostructures. Bilayer artificial graphene could be also realized by lithography of a double quantum-well heterostructure. These new materials should be interesting for the experimental exploration of Dirac-based quantum systems, for both fundamental and applied physics.

  1. Measurement of valence band structure in arbitrary dielectric films

    SciTech Connect

    Uhm, Han S.; Choi, Eun H.

    2012-10-15

    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.

  2. Identical band gaps in structurally re-entrant honeycombs.

    PubMed

    Zhu, Zhu-Wei; Deng, Zi-Chen

    2016-08-01

    Structurally re-entrant honeycomb is a sort of artificial lattice material, characterized by star-like unit cells with re-entrant topology, as well as a high connectivity that the number of folded sheets jointing at each vertex is at least six. In-plane elastic wave propagation in this highly connected honeycomb is investigated through the application of the finite element method in conjunction with the Bloch's theorem. Attention is devoted to exploring the band characteristics of two lattice configurations with different star-like unit cells, defined as structurally square re-entrant honeycomb (SSRH) and structurally hexagonal re-entrant honeycomb (SHRH), respectively. Identical band gaps involving their locations and widths, interestingly, are present in the two considered configurations, attributed to the resonance of the sketch folded sheets, the basic component elements for SSRH and SHRH. In addition, the concept of heuristic models is implemented to elucidate the underlying physics of the identical gaps. The phenomenon of the identical bandgaps is not only beneficial for people to further explore the band characteristics of lattice materials, but also provides the structurally re-entrant honeycombs as potential host structures for the design of lattice-based metamaterials of interest for elastic wave control. PMID:27586722

  3. Ultrafast Band Structure Control of a Two-Dimensional Heterostructure.

    PubMed

    Ulstrup, Søren; Čabo, Antonija Grubišić; Miwa, Jill A; Riley, Jonathon M; Grønborg, Signe S; Johannsen, Jens C; Cacho, Cephise; Alexander, Oliver; Chapman, Richard T; Springate, Emma; Bianchi, Marco; Dendzik, Maciej; Lauritsen, Jeppe V; King, Phil D C; Hofmann, Philip

    2016-06-28

    The electronic structure of two-dimensional (2D) semiconductors can be significantly altered by screening effects, either from free charge carriers in the material or by environmental screening from the surrounding medium. The physical properties of 2D semiconductors placed in a heterostructure with other 2D materials are therefore governed by a complex interplay of both intra- and interlayer interactions. Here, using time- and angle-resolved photoemission, we are able to isolate both the layer-resolved band structure and, more importantly, the transient band structure evolution of a model 2D heterostructure formed of a single layer of MoS2 on graphene. Our results reveal a pronounced renormalization of the quasiparticle gap of the MoS2 layer. Following optical excitation, the band gap is reduced by up to ∼400 meV on femtosecond time scales due to a persistence of strong electronic interactions despite the environmental screening by the n-doped graphene. This points to a large degree of tunability of both the electronic structure and the electron dynamics for 2D semiconductors embedded in a van der Waals-bonded heterostructure. PMID:27267820

  4. Plasmonic band structure controls single-molecule fluorescence.

    PubMed

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

    2013-10-22

    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.

  5. Electronic band structure and photoemission: A review and projection

    SciTech Connect

    Falicov, L.M.

    1987-09-01

    A brief review of electronic-structure calculations in solids, as a means of interpreting photoemission spectra, is presented. The calculations are, in general, of three types: ordinary one-electron-like band structures, which apply to bulk solids and are the basis of all other calculations; surface modified calculations, which take into account, self-consistently if at all possible, the presence of a vacuum-solid interface and of the electronic modifications caused thereby; and many-body calculations, which go beyond average-field approximations and consider dynamic rearrangement effects caused by electron-electron correlations during the photoemission process. 44 refs.

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

    SciTech Connect

    Majumdar, Kausik

    2014-05-07

    In this paper, we use a tight binding Hamiltonian with spin orbit coupling to study the real and complex band structures of relaxed and strained GaAs. A simple d orbital on-site energy shift coupled with appropriate scaling of the off-diagonal terms is found to correctly reproduce the band-edge shifts with strain. Four different 〈100〉 strain combinations, namely, uniaxial compressive, uniaxial tensile, biaxial compressive, and biaxial tensile strain are studied, revealing rich valence band structure and strong relative orientation dependent tunneling. It is found that complex bands are unable to provide unambiguous tunneling paths away from the Brillouin zone center. Tunneling current density distribution over the Brillouin zone is computed using non-equilibrium Green's function approach elucidating a physical picture of band to band tunneling.

  7. Structural changes in positively and negatively supercoiled DNA.

    PubMed

    Brahms, S; Nakasu, S; Kikuchi, A; Brahms, J G

    1989-09-15

    The effect of superhelical constraint on the structure of covalently closed circular DNA (cccDNA; pBR322) with positive and negative writhe (superturn) has been investigated as a function of decreasing and increasing specific linking difference (mean superhelical density sigma). At low and moderate negative superhelical densities sigma, the overall average structure is maintained in an unwound B-form slightly modified. The overwound cccDNAs with positive writhe differ from those with negative writhe by an absence of cruciform structure. At high negative densities of supercoiling different changes involving the reversal of twist handedness are shown to lead to the formation of DNA segments in a conformation identical to the left-handed component of form V DNA.

  8. Collective structures and band termination in {sup 107}Sb

    SciTech Connect

    LaFosse, D. R.; Chiara, C. J.; Fossan, D. B.; Lane, G. J.; Sears, J. M.; Smith, J. F.; Starosta, K.; Boston, A. J.; Paul, E. S.; Semple, A. T.

    2000-07-01

    High-spin states in the near proton-dripline nucleus {sup 107}Sb have been identified, and collectivity in this nucleus has been observed for the first time in the form of two rotational bands. One of the observed rotational structures is a {delta}I=1 band, and is interpreted as based on a {pi}(g{sub 9/2}){sup -1}(multiply-in-circle sign){pi}(g{sub 7/2}d{sub 5/2}){sup 2} proton configuration. A second structure has {delta}I=2 character, and is explained as being based on a {pi}h{sub 11/2}(multiply-in-circle sign)[{pi}(g{sub 9/2}){sup -2}(multiply-in-circle sign){pi}(g{sub 7/2}d{sub 5/2}){sup 2}] proton configuration through comparison with cranked Nilsson-Strutinsky model calculations. The calculations predict that this band terminates at a spin of 79/2 ({Dirac_h}/2{pi}). (c) 2000 The American Physical Society.

  9. Band structure engineering in topological insulator based heterostructures.

    PubMed

    Menshchikova, T V; Otrokov, M M; Tsirkin, S S; Samorokov, D A; Bebneva, V V; Ernst, A; Kuznetsov, V M; Chulkov, E V

    2013-01-01

    The ability to engineer an electronic band structure of topological insulators would allow the production of topological materials with tailor-made properties. Using ab initio calculations, we show a promising way to control the conducting surface state in topological insulator based heterostructures representing an insulator ultrathin films on the topological insulator substrates. Because of a specific relation between work functions and band gaps of the topological insulator substrate and the insulator ultrathin film overlayer, a sizable shift of the Dirac point occurs resulting in a significant increase in the number of the topological surface state charge carriers as compared to that of the substrate itself. Such an effect can also be realized by applying the external electric field that allows a gradual tuning of the topological surface state. A simultaneous use of both approaches makes it possible to obtain a topological insulator based heterostructure with a highly tunable topological surface state.

  10. [The study on energy band structure of silicon nanowires with XPS].

    PubMed

    Fu, Zhong; Fu, Yan; Hu, Hui; Shao, Ming-Wang; Pan, Shi-Yan

    2007-09-01

    Silicon nanowires were obtained via oxide-assisted method, which was operated in a high temperature furnace at 1250 degrees C under 1000 Pa for 5 h using Ar as carrier gas. The silicon nanowires were etched with 5% HF aqueous solution for 5 min, and reacted with 1 X 10(-3) mol X L(-1) AuCL3 solution, and Au-modified silicon nanowires were obtained. The crystal structure of the products was characterized with XRD, and both of the patterns of Si and Au were observed. The morphology checked with SEM and TEM indicated large scale uniform silicon nanowires and Au particles on the surface of silicon nanowires. The average diameter of Au nanoparticls was 8 nm. The energy band structures obtained with XPS showed that gold nanoparticles are in negative charge and exist both at donor and acceptor levels. The Fermi level moved towards the top of valence band due to oxygen.

  11. Negative Stains Containing Trehalose: Application to Tubular and Filamentous Structures

    NASA Astrophysics Data System (ADS)

    Harris, J. Robin; Gerber, Max; Gebauer, Wolfgang; Wernicke, Wolfgang; Markl, Jürgen

    1996-02-01

    Several examples are presented that show the successful application of uranyl acetate and ammonium molybdate negative staining in the presence of trehalose for TEM studies of filamentous and tubular structures. The principal benefit to be gained from the inclusion of trehalose stems from the considerably reduced flattening of the large tubular structures and the greater orientational freedom of single molecules due to an increased depth of the negative stain in the presence of trehalose. Trehalose is likely to provide considerable protection to protein molecules and their assemblies during the drying of negatively stained specimens. Some reduction in the excessive density imparted by uranyl acetate around large assemblies is also achieved. Nevertheless, in the presence of 1% (w/v) trehalose, it is desirable to increase the concentration of negative stain to 5% (w/v) for ammonium molybdate and to 4% for uranyl acetate to produce satisfactory image contrast. In general, the ammonium molybdate-trehalose negative stain is more satisfactory than the uranyl acetate-trehalose combination, because of the greater electron beam sensitivity of the uranyl negative stain. Reassembled taxol-stabilized pig brain microtubules, together with collagen fibrils, sperm tails, helical filaments, and reassociated hemocyanin (KLH2), all from the giant keyhole limpet Megathura crenulata, have been studied by negative staining in the presence of trehalose. In all cases satisfactory TEM imaging conditions were readily obtained on the specimens, as long as regions of excessively deep stain were avoided.

  12. Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy

    SciTech Connect

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

    2008-12-10

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

  13. Structural Evolution of a Warm Frontal Precipitation Band During GCPEx

    NASA Technical Reports Server (NTRS)

    Colle, Brian A.; Naeger, Aaron; Molthan, Andrew; Nesbitt, Stephen

    2015-01-01

    A warm frontal precipitation band developed over a few hours 50-100 km to the north of a surface warm front. The 3-km WRF was able to realistically simulate band development, although the model is somewhat too weak. Band genesis was associated with weak frontogenesis (deformation) in the presence of weak potential and conditional instability feeding into the band region, while it was closer to moist neutral within the band. As the band matured, frontogenesis increased, while the stability gradually increased in the banding region. Cloud top generating cells were prevalent, but not in WRF (too stable). The band decayed as the stability increased upstream and the frontogenesis (deformation) with the warm front weakened. The WRF may have been too weak and short-lived with the band because too stable and forcing too weak (some micro issues as well).

  14. Polar semiconductor heterojunction structure energy band diagram considerations

    NASA Astrophysics Data System (ADS)

    Lin, Shuxun; Wen, Cheng P.; Wang, Maojun; Hao, Yilong

    2016-03-01

    The unique nature of built-in electric field induced positive/negative charge pairs of polar semiconductor heterojunction structure has led to a more realistic device model for hexagonal III-nitride HEMT. In this modeling approach, the distribution of charge carriers is dictated by the electrostatic potential profile instead of Femi statistics. The proposed device model is found suitable to explain peculiar properties of GaN HEMT structures, including: (1) Discrepancy in measured conventional linear transmission line model (LTLM) sheet resistance and contactless sheet resistance of GaN HEMT with thin barrier layer. (2) Below bandgap radiation from forward biased Nickel Schottky barrier diode on GaN HEMT structure. (3) GaN HEMT barrier layer doping has negligible effect on transistor channel sheet charge density.

  15. Comment on 'Nonlinear band structure in Bose-Einstein condensates: Nonlinear Schroedinger equation with a Kronig-Penney potential'

    SciTech Connect

    Danshita, Ippei; Tsuchiya, Shunji

    2007-07-15

    In their recent paper [Phys. Rev. A 71, 033622 (2005)], Seaman et al. studied Bloch states of the condensate wave function in a Kronig-Penney potential and calculated the band structure. They argued that the effective mass is always positive when a swallowtail energy loop is present in the band structure. In this Comment, we reexamine their argument by actually calculating the effective mass. It is found that there exists a region where the effective mass is negative even when a swallowtail is present. Based on this fact, we discuss the interpretation of swallowtails in terms of superfluidity.

  16. Analysis of the electronic structure of crystals through band structure unfolding

    NASA Astrophysics Data System (ADS)

    Gordienko, A. B.; Kosobutsky, A. V.

    2016-03-01

    In this work, we consider an alternative implementation of the band structure unfolding method within the framework of the density functional theory, which combines the advantages of the basis of localized functions and plane waves. This approach has been used to analyze the electronic structure of the ordered CuCl x Br1- x copper halide alloys and F 0 center in MgO that enables us to reveal qualitatively the features remaining hidden when using the standard supercell method, because of the complex band structure of systems with defects.

  17. Band structure and optical properties of diglycine nitrate crystal

    NASA Astrophysics Data System (ADS)

    Andriyevsky, Bohdan; Ciepluch-Trojanek, Wioleta; Romanyuk, Mykola; Patryn, Aleksy; Jaskólski, Marcin

    2005-07-01

    Experimental and theoretical investigations of the electron energy characteristics and optical spectra for diglycine nitrate crystal (DGN), (NH 2CH 2COOH) 2·HNO 3, in the paraelectric phase ( T=295 K) are presented. Spectral dispersion of light reflection R( E) have been measured in the range of 3-22 eV and the optical functions n( E) and k( E) have been calculated using Kramers-Kronig relations. First principal calculations of the electron energy characteristic and optical spectra of DGN crystal have been performed in the frame of density functional theory using CASTEP code (CAmbridge Serial Total Energy Package). Optical transitions forming the low-energy edge of fundamental absorption are associated with the nitrate groups NO 3. Peculiarities of the band structure and DOS projected onto glycine and NO 3 groups confirm the molecular character of DGN crystal.

  18. Exciton band structure of monolayer MoS2

    NASA Astrophysics Data System (ADS)

    Wu, Fengcheng; Qu, Fanyao; MacDonald, Allan

    2015-03-01

    We describe a theory of the momentum-dependent exciton spectrum of monolayer molybdenum disulfide. Low-energy excitons occur both at the Brillouin zone center and at the Brillouin-zone corners. We find that binding energies at the Brillouin-zone center deviate qualitatively from the (n - 1 / 2) - 2 pattern of the two-dimensional hydrogenic model. Moreover, the four 2 p states of A series are lower in energy than the corresponding 2 s states and not degenerate. The two-fold ground-state valley degeneracy is lifted linearly at small momenta by electron-hole exchange processes that establish inter valley coherence. We conclude that atlhough monolayer MoS2 is a direct-gap semiconductor when classified by its quasiparticle band structure it may well be an indirect gap material when classified by its excitation spectra, and speculate on the role of this property in luminescence characteristics.

  19. Finite difference time domain method for calculating the band structure of a 2D photonic crystal and simulating the lensing effect

    NASA Astrophysics Data System (ADS)

    Rafiee Dastjerdi, S.; Ghanaatshoar, M.

    2013-08-01

    A finite difference time domain method based on regular Yee's algorithm in an orthogonal coordinate system is utilized to calculate the band structure of a two-dimensional square-lattice photonic crystal comprising dielectric cylinders in air background and to simulate the image formation of mentioned structure incorporating the perfectly matched layer boundary condition. By analyzing the photonic band diagram of this system, we find that the frequency region of effective negative refraction exists in the second band in near-infrared domain. In this case, electromagnetic wave propagates with a negative phase velocity and the evanescent waves can be supported to perform higher image resolution.

  20. Detection of intrathecal immunoglobulin G synthesis by capillary isoelectric focusing immunoassay in oligoclonal band negative multiple sclerosis.

    PubMed

    Halbgebauer, Steffen; Huss, André; Buttmann, Mathias; Steinacker, Petra; Oeckl, Patrick; Brecht, Isabel; Weishaupt, Andreas; Tumani, Hayrettin; Otto, Markus

    2016-05-01

    Oligoclonal immunoglobulin G bands (OCBs) restricted to the cerebrospinal fluid indicate intrathecal inflammation. Using isoelectric focusing and immunoblotting, they are detected in about 95 % of patients with clinically definite multiple sclerosis (MS). To elucidate whether in the remaining 5 % OCBs are truly absent or alternatively missed due to insufficient sensitivity of the routine measurement, we employed a new, highly sensitive nanoscale method for OCB detection. Capillary isoelectric focusing followed by immunological detection served to analyze OCBs in 33 well-characterized OCB-negative and 10 OCB-positive MS patients as well as in 100 OCB-negative control patients with non-inflammatory neurological diseases and 30 OCB-positive control patients with inflammatory neurological diseases. We detected intrathecal immunoglobulin G production in 10 out of 33 MS patients (30 %), initially diagnosed as being OCB-negative, and in all 10 OCB-positive MS patients, but in only 3 out of 100 non-inflammatory neurological controls (3 %) and in 29 of 30 inflammatory neurological controls (97 %). At least about one-third of MS patients without intrathecal immunoglobulin G synthesis according to standard methods are OCB-positive. Advanced methods for OCB detection may increase the analytical sensitivity for detecting OCB in patients with MS who are OCB-negative according to current routine methods.

  1. Collective Band Structures in the Neutron-Rich 107,109Ru Nuclei

    NASA Astrophysics Data System (ADS)

    Zhu, Sheng-jiang; Gan, Cui-yun; J, Hamilton H.; A, Ramayya V.; B, Babu R. S.; M, Sakhaee; W, Ma C.; Long, Gui-lu; Deng, Jing-kang; Zhu, Ling-yan; Li, Ming; Yang, Li-ming; J, Komicki; J, Cole D.; R, Aryaeinejad; Y, Dardenne K.; M, Drigert W.; J, Rasmussen O.; M, Stoyer A.; S, Chu Y.; K, Gregorich E.; M, Mohar F.; S, Prussin G.; I, Lee Y.; N, Johnson R.; F, McGowan K.

    1998-11-01

    The levels in neutron-rich odd-A 107,109Ru nuclei have been investigated by using γ-γ- and γ-γ-γ-coincidence studies of the prompt γ-rays from the spontaneous fission of 252Cf. The ground state bands and the negative parity bands are identified and expanded in both nuclei. Triaxial rotor plus particle model calculations indicate the ground state bands originate from ν(d5/2 + g7/2) quasiparticle configurations and the negative parity bands are from νh11/2 orbital.

  2. Negative-parity high-spin states and a possible magnetic rotation band in 76 59 135Pr

    NASA Astrophysics Data System (ADS)

    Garg, Ritika; Kumar, S.; Saxena, Mansi; Goyal, Savi; Siwal, Davinder; Kalkal, Sunil; Verma, S.; Singh, R.; Pancholi, S. C.; Palit, R.; Choudhury, Deepika; Ghugre, S. S.; Mukherjee, G.; Kumar, R.; Singh, R. P.; Muralithar, S.; Bhowmik, R. K.; Mandal, S.

    2015-11-01

    Excited states in 135Pr have been investigated using the reaction 123Sb(16O,4 n )135Pr at an incident beam energy of 82 MeV. The partial level scheme has been established for negative-parity states with addition of new γ -ray transitions. The directional correlation and polarization measurements have been performed to assign spin parity for most of the reported γ -ray transitions. At high spin, a negative-parity dipole band (Δ I =1 ) has been reported along with the observation of new crossover E 2 transitions. Tilted Axis Cranking (TAC) calculations have been performed by considering a three-quasiparticle (3qp) configuration π (h11/2) 1⊗ν (h11/2) -2 and a five-quasiparticle (5qp) configuration π (h11/2) 1(g7/2) 2⊗ν (h11/2) -2 for the lower and upper parts of the band, respectively. The observed results are compared with the results of the theoretical (TAC) calculations.

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

    DOEpatents

    Gupta, Sandhya; Tuttle, Gary L.; Sigalas, Mihail; McCalmont, Jonathan S.; Ho, Kai-Ming

    2001-08-14

    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.

  4. Band-structure analysis from photoreflectance spectroscopy in (Ga,Mn)As

    SciTech Connect

    Yastrubchak, Oksana; Gluba, Lukasz; Zuk, Jerzy; Wosinski, Tadeusz; Andrearczyk, Tomasz; Domagala, Jaroslaw Z.; Sadowski, Janusz

    2013-12-04

    Modulation photoreflectance spectroscopy has been applied to study the band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn content. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap-transition energy in the (Ga,Mn)As layers with increasing Mn content are interpreted in terms of a disordered valence band, extended within the band gap, formed, in highly Mn-doped (Ga,Mn)As, as a result of merging the Mn-related impurity band with the host GaAs valence band.

  5. Investigation the effect of lattice angle on the band structure in 3D phononic crystals with rhombohedral(II) lattice

    NASA Astrophysics Data System (ADS)

    Aryadoust, M.; Salehi, H.

    2014-12-01

    In this paper, the propagation of acoustic waves in the phononic crystals (PC) of 3D with rhombohedral(II) lattice is studied theoretically. The PC are constituted of nickel spheres embedded in epoxy. The calculations of the band structure and density of states are performed with the plane wave expansion method in the irreducible part of the Brillouin zone (BZ). In this study, we analyze the dependence of the band structures inside (the complete band gap width) and outside the complete band gap (negative refraction of acoustic wave) on the lattice angle in the irreducible part of the first BZ. Also the effect of lattice angle has been analyzed on the band structure of the () and (122) planes. Then, the equifrequency surface is calculated for the high symmetry point in the [111] and [100] directions. The results show that the maximum width of AEBG (0.022) in the irreducible part of the BZ of RHL2 is formed for (105∘) and no AEBG is found for γ > 150∘. Also, the maximum of the first and second AEBG width are 0.1076 and 0.0523 for γ = 133∘ in the () plane and the maximum of the first and second AEBG width are 0.1446 and 0.0998 for γ = 113∘ in the (122) plane. In addition, we have found that frequencies in which negative refraction occurs is constant for all lattice angles.

  6. Band structure of ABC-trilayer graphene superlattice

    SciTech Connect

    Uddin, Salah Chan, K. S.

    2014-11-28

    We investigate the effect of one-dimensional periodic potentials on the low energy band structure of ABC trilayer graphene first by assuming that all the three layers have the same potential. Extra Dirac points having the same electron hole crossing energy as that of the original Dirac point are generated by superlattice potentials with equal well and barrier widths. When the potential height is increased, the numbers of extra Dirac points are increased. The dispersions around the Dirac points are not isotropic. It is noted that the dispersion along the k{sub y} direction for k{sub x} = 0 oscillates between a non-linear dispersion and a linear dispersion when the potential height is increased. When the well and barrier widths are not identical, the symmetry of the conduction and valence bands is broken. The extra Dirac points are shifted either upward or downward depending on the barrier and well widths from the zero energy, while the position of the central Dirac point oscillates with the superlattice potential height. By considering different potentials for different layers, extra Dirac points are generated not from the original Dirac points but from the valleys formed in the energy spectrum. Two extra Dirac points appear from each pair of touched valleys, so four Dirac points appeared in the spectrum at particular barrier height. By increasing the barrier height of superlattice potential two Dirac points merge into the original Dirac point. This emerging and merging of extra Dirac points is different from the equal potential case.

  7. Photonic bands in two-dimensional microplasma arrays. I. Theoretical derivation of band structures of electromagnetic waves

    SciTech Connect

    Sakai, Osamu; Sakaguchi, Takui; Tachibana, Kunihide

    2007-04-01

    Two theoretical approaches appropriate for two-dimensional plasma photonic crystals reveal dispersions of propagating waves including photonic (electromagnetic) band gaps and multiflatbands. A modified plane-wave expansion method yields dispersions of collisional periodical plasmas, and the complex-value solution of a wave equation by a finite difference method enables us to obtain dispersions with structure effects in an individual microplasma. Periodical plasma arrays form band gaps as well as normal photonic crystals, and multiflatbands are present below the electron plasma frequency in the transverse electric field mode. Electron elastic collisions lower the top frequency of the multiflatbands but have little effect on band gap properties. The spatial gradient of the local dielectric constant resulting from an electron density profile widens the frequency region of the multiflatbands, as demonstrated by the change of surface wave distributions. Propagation properties described in dispersions including band gaps and flatbands agree with experimental observations of microplasma arrays.

  8. Fine structure of the band-edge excitons and trions in CdSe/CdS core/shell nanocrystals

    NASA Astrophysics Data System (ADS)

    Shabaev, A.; Rodina, A. V.; Efros, Al. L.

    2012-11-01

    We present a theoretical description of excitons and positively and negatively charged trions in “giant” CdSe/CdS core-shell nanocrystals (NCs). The developed theory provides the parameters describing the fine structure of excitons in CdSe/CdS core/thick shell NCs as a function of the CdSe/CdS conduction band offset and the CdSe core radius. We have also developed a general theory describing the fine structure of positively charged trions created in semiconductor NCs with a degenerate valence band. The calculations take into account the complex structure of the CdSe valence band and interparticle Coulomb and exchange interaction. Presented in this paper are the CdSe core size and CdSe/CdS conduction band offset dependencies (i) of the positively charged trion fine structure, (ii) of the binding energy of the negatively charged trion, and (iii) of the radiative decay time for excitons and trions. The results of theoretical calculations are in qualitative agreement with available experimental data.

  9. Electronic band structure calculations of bismuth-antimony nanowires

    NASA Astrophysics Data System (ADS)

    Levin, Andrei; Dresselhaus, Mildred

    2012-02-01

    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.

  10. Band structures in transmission coefficients generated by Dirac comb potentials

    NASA Astrophysics Data System (ADS)

    Dharani, M.; Shastry, C. S.

    2016-11-01

    Using the threshold conditions and bound state energies investigated earlier by us as a critical input we systematically study the nature of band formation in the transmission coefficient generated by Dirac comb potentials having equispaced (i) attractive, (ii) repulsive and (iii) alternating attractive and repulsive delta terms having same strength and confined within a fixed range. We find that positions of the peaks of transmission coefficient generated by a combination of one attractive and one repulsive delta terms having same strength and separated by gap a is independent of the potential strength and coincide with the energy eigenvalues of 1D box of range a. We further study analytically and numerically the transmission across Dirac comb potentials containing two or three delta terms and these results are useful in the analysis of the transmission in the general case. In the case of Dirac comb potentials containing Na attractive delta terms we find that the nature of the first band and higher bands of the transmission coefficient are different, and if such a potential generates Nb number of bound states, the first band in the transmission coefficient generated by the potential has NT1 =Na -Nb peaks. In the case of higher bands generated by delta comb potential having N delta terms each band has N - 1 peaks. Further we systematically study the behavior of band gaps and band spread as a function of potential strength and number of terms in the Dirac comb. The results obtained by us provide a relation between bound state spectrum, number of delta terms in the Dirac comb and the band pattern which can be explored for potential applications.

  11. Loss of Linear Band Dispersion and Trigonal Structure in Silicene on Ir(111).

    PubMed

    Wei, Wei; Dai, Ying; Huang, Baibiao; Whangbo, Myung-Hwan; Jacob, Timo

    2015-03-19

    The structure of silicene/Ir(111) was examined on the basis of density functional theory. We have found that Ir(111) preserves the 2D character of silicene but significantly distorts its structure from the trigonal one expected for an isolated silicene. The electronic structure of silicene is strongly hybridized with that of Ir(111) so that silicene on Ir(111) loses its linear band dispersion around the Fermi level, giving rise to a metallic band structure; however, silicene/Ir(111) exhibits a hidden linear-dispersive band, which is related to the linear-dispersive conduction band of an isolated silicene.

  12. Quantum structure of negation and conjunction in human thought.

    PubMed

    Aerts, Diederik; Sozzo, Sandro; Veloz, Tomas

    2015-01-01

    We analyze in this paper the data collected in a set of experiments investigating how people combine natural concepts. We study the mutual influence of conceptual conjunction and negation by measuring the membership weights of a list of exemplars with respect to two concepts, e.g., Fruits and Vegetables, and their conjunction Fruits And Vegetables, but also their conjunction when one or both concepts are negated, namely, Fruits And Not Vegetables, Not Fruits And Vegetables, and Not Fruits And Not Vegetables. Our findings sharpen and advance existing analysis on conceptual combinations, revealing systematic deviations from classical (fuzzy set) logic and probability theory. And, more important, our results give further considerable evidence to the validity of our quantum-theoretic framework for the combination of two concepts. Indeed, the representation of conceptual negation naturally arises from the general assumptions of our two-sector Fock space model, and this representation faithfully agrees with the collected data. In addition, we find a new significant and a priori unexpected deviation from classicality, which can exactly be explained by assuming that human reasoning is the superposition of an "emergent reasoning" and a "logical reasoning," and that these two processes are represented in a Fock space algebraic structure. PMID:26483715

  13. Quantum structure of negation and conjunction in human thought

    PubMed Central

    Aerts, Diederik; Sozzo, Sandro; Veloz, Tomas

    2015-01-01

    We analyze in this paper the data collected in a set of experiments investigating how people combine natural concepts. We study the mutual influence of conceptual conjunction and negation by measuring the membership weights of a list of exemplars with respect to two concepts, e.g., Fruits and Vegetables, and their conjunction Fruits And Vegetables, but also their conjunction when one or both concepts are negated, namely, Fruits And Not Vegetables, Not Fruits And Vegetables, and Not Fruits And Not Vegetables. Our findings sharpen and advance existing analysis on conceptual combinations, revealing systematic deviations from classical (fuzzy set) logic and probability theory. And, more important, our results give further considerable evidence to the validity of our quantum-theoretic framework for the combination of two concepts. Indeed, the representation of conceptual negation naturally arises from the general assumptions of our two-sector Fock space model, and this representation faithfully agrees with the collected data. In addition, we find a new significant and a priori unexpected deviation from classicality, which can exactly be explained by assuming that human reasoning is the superposition of an “emergent reasoning” and a “logical reasoning,” and that these two processes are represented in a Fock space algebraic structure. PMID:26483715

  14. Simultaneous Hosting of Positive and Negative Trions and the Enhanced Direct Band Emission in MoSe2/MoS2 Heterostacked Multilayers.

    PubMed

    Kim, Min Su; Seo, Changwon; Kim, Hyun; Lee, Jubok; Luong, Dinh Hoa; Park, Ji-Hoon; Han, Gang Hee; Kim, Jeongyong

    2016-06-28

    Heterostacking of layered transition-metal dichalcogenide (LTMD) monolayers (1Ls) offers a convenient way of designing two-dimensional exciton systems. Here we demonstrate the simultaneous hosting of positive trions and negative trions in heterobilayers made by vertically stacking 1L MoSe2 and 1L MoS2. The charge transfer occurring between the 1Ls of MoSe2 and MoS2 converted the polarity of trions in 1L MoSe2 from negative to positive, resulting in the presence of positive trions in the 1L MoSe2 and negative trions in the 1L MoS2 of the same heterostacked bilayer. Significantly enhanced MoSe2 photoluminescence (PL) in the heterostacked bilayers compared to the PL of 1L MoSe2 alone suggests that, unlike other previously reported heterostacked bilayers, direct band transition of 1L MoSe2 in heterobilayer was enhanced after the vertical heterostacking. Moreover, by inserting hexagonal BN monolayers between 1L MoSe2 and 1L MoS2, we were able to adjust the charge transfer to maximize the MoSe2 PL of the heteromultilayers and have achieved a 9-fold increase of the PL emission. The enhanced optical properties of our heterostacked LTMDs suggest the exciting possibility of designing LTMD structures that exploit the superior optical properties of 1L LTMDs. PMID:27187667

  15. Electric field effects on resonance structures in negative ion photodetachment

    NASA Astrophysics Data System (ADS)

    Slonim, V. Z.; Greene, C. H.

    1991-12-01

    The photodetachment of negative ions in a static electric field exhibits some new characteristic features and has beer considered in various theortical approaches.1 Most of them, however, neglect the short-range interaction between the escaping electron and the atomic core, and must be modified to describe various resonant effects. Experiments2 have shown very rich resonant structure in a dc-field, which can be attributed to the mixing of different excited states in the negative ion, to competition between elastic and inelastic decay channels, and to tunneling effects induced by the field. It is known that various resonant structures in Photoprocesses can be successfully described within standard multichannel quantum defect theory (MQDT). We present a modified MQDT frame transformation approach to extend the standard method to long-range potentials with nonspherical symmetry. In our treatment both the electron-field and electron-atom interactions are treated nonperturbatively and on an equal footing. The resulting theoretical calculations are compared with experimental data on field-modified H? photodetachment in the vicinity of the n = 2 resonances.

  16. Large band gaps in radial phononic crystal structure with round mass block

    NASA Astrophysics Data System (ADS)

    Gao, Nansha; Wu, Jiu Hui; Jing, Li; Lu, Kuan; Yu, Lie

    2016-06-01

    Using the finite element method, we theoretically study the vibration properties of radial phononic crystal (RPC) structure with round mass block. The band structures, transmission spectra, and displacement fields of eigenmode are given to estimate the starting and cut-off frequency of band gaps. Compared to the contrast structure, numerical calculation results show that RPC structure with round mass block can yield several band gaps below 150 kHz. The physical mechanism of band gaps are attributed to the coupling between the longitudinal vibration in round mass block and vibrations in outer frame or coating layer. By changing geometrical dimensions r of round mass block, we can shift the location and width of band gaps. Significantly, as the increase of geometric parameter ratio a1/a2, band width shifts and the more new band gaps appear; the more bands become flat at this moment because of the stronger multiple vibration coupling effect plays a more prominent role in the opening of band gaps. These vibration properties of RPC structure with round mass block can potentially be applied to optimize band gaps, generate filters, and design acoustic devices.

  17. New linear accelerator (Linac) design based on C-band accelerating structures for SXFEL facility

    NASA Astrophysics Data System (ADS)

    Zhang, Meng; Gu, Qiang

    2011-11-01

    A C-band accelerator structure is one promising technique for a compact XFEL facility. It is also attractive in beam dynamics in maintaining a high quality electron beam, which is an important factor in the performance of a free electron laser. In this paper, a comparison between traditional S-band and C-band accelerating structures is made based on the linac configuration of a Shanghai Soft X-ray Free Electron Laser (SXFEL) facility. Throughout the comprehensive simulation, we conclude that the C-band structure is much more competitive.

  18. Band structures in silicene on monolayer gallium phosphide substrate

    NASA Astrophysics Data System (ADS)

    Ren, Miaojuan; Li, Mingming; Zhang, Changwen; Yuan, Min; Li, Ping; Li, Feng; Ji, Weixiao; Chen, Xinlian

    2016-07-01

    Opening a sizable band gap in the zero-gap silicene is a key issue for its application in nanoelectronics. We design new 2D silicene and GaP heterobilayer (Si/GaP HBL) composed of silicene and monolayer (ML) GaP. Based on first-principles calculations, we find that the interaction energies are in the range of -295.5 to -297.5 meV per unit cell, indicating a weak interaction between silicene and gallium phosphide (GaP) monolayer. The band gap changes ranging from 0.06 to 0.44 eV in hybrid HBLs. An unexpected indirect-direct band gap crossover is also observed in HBLs, dependent on the stacking pattern. These provide a possible way to design effective FETs out of silicene on GaP monolayer.

  19. The Band Structure of Polymers: Its Calculation and Interpretation. Part 3. Interpretation.

    ERIC Educational Resources Information Center

    Duke, B. J.; O'Leary, Brian

    1988-01-01

    In this article, the third part of a series, the results of ab initio polymer calculations presented in part 2 are discussed. The electronic structure of polymers, symmetry properties of band structure, and generalizations are presented. (CW)

  20. Electronic transitions in GdN band structure

    SciTech Connect

    Vidyasagar, R. Kita, T.; Sakurai, T.; Ohta, H.

    2014-05-28

    Using the near-infrared (NIR) absorbance spectroscopy, electronic transitions and spin polarization of the GdN epitaxial film have been investigated; and the GdN epitaxial film was grown by a reactive rf sputtering technique. The GdN film exhibited three broad bands in the NIR frequency regimes; and those bands are attributable primarily to the minority and majority spin transitions at the X-point and an indirect transition along the Γ-X symmetric direction of GdN Brillouin zone. We experimentally observe a pronounced red-shift of the indirect band gap when cooling down below the Curie temperature which is ascribed to the orbital-dependent coulomb interactions of Gd-5dxy electrons, which tend to push-up the N-2p bands. On the other hand, we have evaluated the spin polarization of 0.17 (±0.005), which indicates that the GdN epitaxial film has almost 100% spin-polarized carriers. Furthermore, the experimental result of GdN electronic transitions are consistent with the previous reports and are thus well-reproduced. The Arrott plots evidenced that the Curie temperature of GdN film is 36 K and the large spin moment is explained by the nitrogen vacancies and the intra-atomic exchange interaction.

  1. Novel band structures in silicene on monolayer zinc sulfide substrate.

    PubMed

    Li, Sheng-shi; Zhang, Chang-wen; Yan, Shi-shen; Hu, Shu-jun; Ji, Wei-xiao; Wang, Pei-ji; Li, Ping

    2014-10-01

    Opening a sizable band gap in the zero-gap silicene without lowering the carrier mobility is a key issue for its application in nanoelectronics. Based on first-principles calculations, we find that the interaction energies are in the range of -0.09‒0.3 eV per Si atom, indicating a weak interaction between silicene and ZnS monolayer and the ABZn stacking is the most stable pattern. The band gap of silicene can be effectively tuned ranging from 0.025 to 1.05 eV in silicene and ZnS heterobilayer (Si/ZnS HBL). An unexpected indirect-direct band gap crossover is also observed in HBLs, dependent on the stacking pattern, interlayer spacing and external strain effects on silicene. Interestingly, the characteristics of Dirac cone with a nearly linear band dispersion relation of silicene can be preserved in the ABS pattern which is a metastable state, accompanied by a small electron effective mass and thus the carrier mobility is expected not to degrade much. These provide a possible way to design effective FETs out of silicene on a ZnS monolayer.

  2. Band structure in two-dimensional fiber-air phononic crystals

    NASA Astrophysics Data System (ADS)

    Yang, Shu; Yu, Wei-Dong; Pan, Ning

    2011-02-01

    A two-dimensional phononic crystal (PC) composed of textile fiber and air is initially discussed in this paper, which is different from the previous PCs with rigid inclusions. The plain wave expansion method is used to calculate band structure of different PCs by altering fiber material properties and structure parameters. Numerical results show that the effect of material properties of soft fiber on band structure of phononic crystal can be ignored, while the effect of structural parameters is obvious.

  3. Band structures extending to very high spin in Xe126

    NASA Astrophysics Data System (ADS)

    Rønn Hansen, C.; Sletten, G.; Hagemann, G. B.; Herskind, B.; Jensen, D. R.; Bringel, P.; Engelhardt, C.; Hübel, H.; Neußer-Neffgen, A.; Singh, A. K.; Carpenter, M. P.; Janssens, R. V. F.; Khoo, T. L.; Lauritsen, T.; Bednarczyk, P.; Byrski, T.; Curien, D.; Benzoni, G.; Bracco, A.; Camera, F.; Leoni, S.; Clark, R. M.; Fallon, P.; Korichi, A.; Roccaz, J.; Maj, A.; Wilson, J. N.; Lisle, J. C.; Steinhardt, T.; Thelen, O.; Ødegård, S. W.

    2007-09-01

    High-spin states in Xe126 have been populated in the Se82(Ca48,4n)Xe126 reaction in two experiments, one at the VIVITRON accelerator in Strasbourg using the Euroball detector array, and a subsequent one with ATLAS at Argonne using the Gammasphere Ge-detector array. Levels and assignments made previously for Xe126 up to I=20 have been confirmed and extended. Four regular bands extending to a spin of almost I=60, which are interpreted as two pairs of signature partners with opposite parity, are identified for the first time. The α = 0 partner of each pair is connected to the lower-lying levels, whereas the two α = 1 partners remain floating. A fractional Doppler shift analysis of transitions in the strongest populated (π,α)=(-,0) band provides a value of 5.20.50.4 b for the transition quadrupole moment, which can be related to a minimum in the potential-energy surface calculated by the ULTIMATE CRANKER cranked shell-model code at ɛ≈0.35 and γ≈5°. The four lowest bands calculated for this minimum compare well with the two signature pairs experimentally observed over a wide spin range. A sharp upbend at ℏω~1170 keV is interpreted as a crossing with a band involving the j15/2 neutron orbital, for which pairing correlations are expected to be totally quenched. The four long bands extend to within ˜5 spin units of a crossing with an yrast line defined by calculated hyperdeformed transitions and will serve as important stepping stones into the spin region beyond 60ħ for future experiments.

  4. Usefulness of antibody index assessment in cerebrospinal fluid from patients negative for total-IgG oligoclonal bands

    PubMed Central

    2012-01-01

    Background Testing for cerebrospinal fluid (CSF)-restricted oligoclonal bands (OCB) by isoelectric focusing is used to detect intrathecally produced total IgG. By contrast, antibody indices (AI) are assessed to test for intrathecally produced antigen-specific IgG. A number of previous cases reports have suggested that AI testing might be more sensitive than OCB testing in detecting intrathecal IgG synthesis. Findings Here we report on 21 patients with positive AI for either herpes simplex virus, varicella zoster virus, cytomegalovirus, measles virus, rubella virus, or Borrelia burgdorferi in the absence of total-IgG OCB and, accordingly, in the presence of a normal total-IgG CSF/serum ratio. Conclusion Our findings indicate that AI testing should not generally be omitted in OCB-negative patients and provide a rationale for systematic and prospective studies on the comparative sensitivity and specificity of AI and total-IgG OCB testing in infectious and other diseases of the CNS. PMID:22849518

  5. Structure of human chromosomes studied by atomic force microscopy. Part II. Relationship between structure and cytogenetic bands.

    PubMed

    Tamayo, Javier

    2003-03-01

    In the first part of this work, human chromosomes were characterized by atomic force microscopy (AFM) in air and in aqueous solution. The analysis of the images suggests that the last level of organization consists of a radial arrangement of chromatin loops which are anchored to a fiber which is folded giving a pattern of bands which differs in volume. Here the pattern of bands observed by AFM is compared to the cytogenetic map at the 850-band level. Thus thicker and thinner bands are identified as G and R bands, respectively. Finally a model is proposed which links genome sequence, cytogenetics, and chromosome structure. PMID:12648565

  6. Structure of human chromosomes studied by atomic force microscopy. Part II. Relationship between structure and cytogenetic bands.

    PubMed

    Tamayo, Javier

    2003-03-01

    In the first part of this work, human chromosomes were characterized by atomic force microscopy (AFM) in air and in aqueous solution. The analysis of the images suggests that the last level of organization consists of a radial arrangement of chromatin loops which are anchored to a fiber which is folded giving a pattern of bands which differs in volume. Here the pattern of bands observed by AFM is compared to the cytogenetic map at the 850-band level. Thus thicker and thinner bands are identified as G and R bands, respectively. Finally a model is proposed which links genome sequence, cytogenetics, and chromosome structure.

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

    PubMed

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

    2016-05-16

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

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

    PubMed

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

    2016-05-16

    The high-pressure crystal structure, lattice-vibrations, and electronic band structure of BiSbO4 were studied by ab initio simulations. We also performed Raman spectroscopy, infrared spectroscopy, and diffuse-reflectance measurements, as well as synchrotron powder X-ray diffraction. High-pressure X-ray diffraction measurements show that the crystal structure of BiSbO4 remains stable up to at least 70 GPa, unlike other known MTO4-type ternary oxides. These experiments also give information on the pressure dependence of the unit-cell parameters. Calculations properly describe the crystal structure of BiSbO4 and the changes induced by pressure on it. They also predict a possible high-pressure phase. A room-temperature pressure-volume equation of state is determined, and the effect of pressure on the coordination polyhedron of Bi and Sb is discussed. Raman- and infrared-active phonons were measured and calculated. In particular, calculations provide assignments for all the vibrational modes as well as their pressure dependence. In addition, the band structure and electronic density of states under pressure were also calculated. The calculations combined with the optical measurements allow us to conclude that BiSbO4 is an indirect-gap semiconductor, with an electronic band gap of 2.9(1) eV. Finally, the isothermal compressibility tensor for BiSbO4 is given at 1.8 GPa. The experimental (theoretical) data revealed that the direction of maximum compressibility is in the (0 1 0) plane at ∼33° (38°) to the c-axis and 47° (42°) to the a-axis. The reliability of the reported results is supported by the consistency between experiments and calculations. PMID:27128858

  9. Recent Results from Broad-Band Intensity Mapping Measurements of Cosmic Large Scale Structure

    NASA Astrophysics Data System (ADS)

    Zemcov, Michael B.; CIBER, Herschel-SPIRE

    2016-01-01

    Intensity mapping integrates the total emission in a given spectral band over the universe's history. Tomographic measurements of cosmic structure can be performed using specific line tracers observed in narrow bands, but a wealth of information is also available from broad-band observations performed by instruments capable of capturing high-fidelity, wide-angle images of extragalactic emission. Sensitive to the continuum emission from faint and diffuse sources, these broad-band measurements provide a view on cosmic structure traced by components not readily detected in point source surveys. After accounting for measurement effects and astrophysical foregrounds, the angular power spectra of such data can be compared to predictions from models to yield powerful insights into the history of cosmic structure formation. This talk will highlight some recent measurements of large scale structure performed using broad-band intensity mapping methods that have given new insights on faint, distant, and diffuse components in the extragalactic background light.

  10. Fine structure of the amide i band in acetanilide

    NASA Astrophysics Data System (ADS)

    Careri, G.; Gratton, E.; Shyamsunder, E.

    1988-05-01

    Their absorption spectrum of both single crystals and powdered samples of acetanilide (a model system for proteins) has been studied in the amide i region, where a narrow band has been identified as a highly trapped soliton state. The powder-sample spectra have been decomposed using four Lorentzian bands. A strong temperature dependence has been found for the intensity of two of the subbands, which also show a complementary behavior. Polarization studies performed on thin crystals have shown that the subbands have the same polarization. Low-temperature spectra of partially deuterated samples show the presence of the subbands at the same absorption frequencies found using the fitting procedure in the spectra of nondeuterated samples. The soliton model currently proposed to explain the origin of the anomalous amide i component at 1650 cm-1 still holds, but some modification of the model is required to account for the new features revealed by this study.

  11. Band structure of germanium carbides for direct bandgap silicon photonics

    NASA Astrophysics Data System (ADS)

    Stephenson, C. A.; O'Brien, W. A.; Penninger, M. W.; Schneider, W. F.; Gillett-Kunnath, M.; Zajicek, J.; Yu, K. M.; Kudrawiec, R.; Stillwell, R. A.; Wistey, M. A.

    2016-08-01

    Compact optical interconnects require efficient lasers and modulators compatible with silicon. Ab initio modeling of Ge1-xCx (x = 0.78%) using density functional theory with HSE06 hybrid functionals predicts a splitting of the conduction band at Γ and a strongly direct bandgap, consistent with band anticrossing. Photoreflectance of Ge0.998C0.002 shows a bandgap reduction supporting these results. Growth of Ge0.998C0.002 using tetrakis(germyl)methane as the C source shows no signs of C-C bonds, C clusters, or extended defects, suggesting highly substitutional incorporation of C. Optical gain and modulation are predicted to rival III-V materials due to a larger electron population in the direct valley, reduced intervalley scattering, suppressed Auger recombination, and increased overlap integral for a stronger fundamental optical transition.

  12. Collective band structures in the 99Tc nucleus

    NASA Astrophysics Data System (ADS)

    Li, H. J.; Xiao, Z. G.; Zhu, S. J.; Patial, M.; Qi, C.; Cederwall, B.; Zhang, Z.; Wang, R. S.; Yi, H.; Yan, W. H.; Cheng, W. J.; Huang, Y.; Lyu, L. M.; Zhang, Y.; Wu, X. G.; He, C. Y.; Zheng, Y.; Li, G. S.; Li, C. B.; Li, H. W.; Liu, J. J.; Luo, P. W.; Hu, S. P.; Wang, J. L.; Wu, Y. H.

    2015-05-01

    Excited states in 99Tc with energies up to 6 MeV have been populated using the 96Zr(7Li,4 n )99Tc reaction with a laboratory beam energy of 35 MeV. Coincident γ rays from excited nuclei produced in the reactions were detected using an array of coaxial, planar, and clover-type high-purity germanium detectors. A total of 60 new γ -ray transitions and 21 new levels are identified and placed into a new level scheme. Two collective bands assigned to be built on the π g9 /2 [422 ]5 /2 + and π p1 /2 [301 ]1 /2 - Nilsson configurations have been extended with spins up to 35/2 and 33 /2 ℏ , respectively. Backbending and signature inversion have been observed in the yrast band. The large signature splitting of the positive-parity band in 99Tc may be caused by a triaxial deformation, which agrees well with the electromagnetic properties, theoretical calculations based on total Routhian surface, and triaxial particle-rotor model calculations.

  13. Quasiparticle band structures and optical properties of magnesium fluoride

    NASA Astrophysics Data System (ADS)

    Yi, Zhijun; Jia, Ran

    2012-02-01

    The quasiparticle and optical properties of magnesium fluoride (MgF2) are computed within the GW approximation based on many-body perturbation theory (MBPT). The many-body effects appearing in self-energy and electron-hole interactions have an important influence on the electronic and optical properties. The DFT-LDA calculation shows a 6.78 eV band gap. Two methods are employed to evaluate the self-energy within the GW approximation in the present work. The generalized plasmon pole model (GPP) provides a band gap of 12.17 eV, which agrees well with the experimental value of 12.4 eV (Thomas et al 1973 Phys. Status Solidi b 56 163). Another band gap value of 11.30 eV is obtained by using a full frequency-dependent self-energy, which is also not far from the experimental value and is much better than the result from the LDA calculation. The calculated optical spectrum within DFT is significantly different from the experiment. Although the calculated optical absorption threshold within the GW method is close to the experiment, the overall shape of the spectrum is still similar to the case of DFT. However, the overall shape of the spectrum via the Bethe-Salpeter equation (BSE) method agrees well with the experiment.

  14. Quasiparticle band structures and optical properties of magnesium fluoride.

    PubMed

    Yi, Zhijun; Jia, Ran

    2012-02-29

    The quasiparticle and optical properties of magnesium fluoride (MgF(2)) are computed within the GW approximation based on many-body perturbation theory (MBPT). The many-body effects appearing in self-energy and electron-hole interactions have an important influence on the electronic and optical properties. The DFT-LDA calculation shows a 6.78 eV band gap. Two methods are employed to evaluate the self-energy within the GW approximation in the present work. The generalized plasmon pole model (GPP) provides a band gap of 12.17 eV, which agrees well with the experimental value of 12.4 eV (Thomas et al 1973 Phys. Status Solidi b 56 163). Another band gap value of 11.30 eV is obtained by using a full frequency-dependent self-energy, which is also not far from the experimental value and is much better than the result from the LDA calculation. The calculated optical spectrum within DFT is significantly different from the experiment. Although the calculated optical absorption threshold within the GW method is close to the experiment, the overall shape of the spectrum is still similar to the case of DFT. However, the overall shape of the spectrum via the Bethe-Salpeter equation (BSE) method agrees well with the experiment.

  15. Ultra-broad band and dual-band highly efficient polarization conversion based on the three-layered chiral structure

    NASA Astrophysics Data System (ADS)

    Xu, Kai-kai; Xiao, Zhong-yin; Tang, Jing-yao; Liu, De-jun; Wang, Zi-hua

    2016-07-01

    In the paper, a novel three-layered chiral structure is proposed and investigated, which consists of a split-ring resonator sandwiched between two layers of sub-wavelength gratings. This designed structure can achieve simultaneously asymmetric transmission with an extremely broad bandwidth and high amplitude as well as multi-band 90° polarization rotator with very low dispersion. Numerical simulations adopted two kinds of softwares with different algorithms demonstrate that asymmetric parameter can reach a maximum of 0.99 and over than 0.8 from 4.6 to 16.8 GHz, which exhibit magnitude and bandwidth improvement over previous chiral metamaterials in microwave bands (S, C, X and Ku bands). Specifically, the reason of high amplitude is analyzed in detail based on the Fabry-perot like resonance. Subsequently, the highly efficient polarization conversion with very low dispersion between two orthogonal linearly polarized waves is also analyzed by the optical activity and ellipticity. Finally, the electric fields are also investigated and further demonstrate the correctness of the simulated and calculated results.

  16. Energy band structure tailoring of vertically aligned InAs/GaAsSb quantum dot structure for intermediate-band solar cell application by thermal annealing process.

    PubMed

    Liu, Wei-Sheng; Chu, Ting-Fu; Huang, Tien-Hao

    2014-12-15

    This study presents an band-alignment tailoring of a vertically aligned InAs/GaAs(Sb) quantum dot (QD) structure and the extension of the carrier lifetime therein by rapid thermal annealing (RTA). Arrhenius analysis indicates a larger activation energy and thermal stability that results from the suppression of In-Ga intermixing and preservation of the QD heterostructure in an annealed vertically aligned InAs/GaAsSb QD structure. Power-dependent and time-resolved photoluminescence were utilized to demonstrate the extended carrier lifetime from 4.7 to 9.4 ns and elucidate the mechanisms of the antimony aggregation resulting in a band-alignment tailoring from straddling to staggered gap after the RTA process. The significant extension in the carrier lifetime of the columnar InAs/GaAsSb dot structure make the great potential in improving QD intermediate-band solar cell application.

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

    PubMed

    Appalakondaiah, S; Vaitheeswaran, G; Lebègue, S

    2013-05-14

    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

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

    SciTech Connect

    Sharma, G.; Munjal, N.; Vyas, V.; Kumar, R.; Sharma, B. K.; Joshi, K. B.

    2013-10-15

    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.

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

    NASA Astrophysics Data System (ADS)

    Chen, Hui; Zhang, Weiyi; Wang, Zhenlin

    2004-02-01

    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.

  20. One-dimensional electromagnetic band gap structures formed by discharge plasmas in a waveguide

    SciTech Connect

    Arkhipenko, V. I.; Simonchik, L. V. Usachonak, M. S.; Callegari, Th.; Sokoloff, J.

    2014-09-28

    We demonstrate the ability to develop one-dimensional electromagnetic band gap structure in X-band waveguide solely by using the positive columns of glow discharges in neon at the middle pressure. Plasma inhomogeneities are distributed uniformly along a typical X-band waveguide with cross section of 23×10 mm². It is shown that electron densities larger than 10¹⁴ cm ⁻³ are needed in order to create an effective one-dimensional electromagnetic band gap structure. Some applications for using the one-dimensional electromagnetic band gap structure in waveguide as a control of microwave (broadband filter and device for variation of pulse duration) are demonstrated.

  1. Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS

    SciTech Connect

    Kozyukhin, S.; Golovchak, R.; Kovalskiy, A.; Shpotyuk, O.; Jain, H.

    2011-04-15

    High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As{sub x}Se{sub 100-x}, As{sub x}S{sub 100-x}, Ge{sub x}Se{sub 100-x} and Ge{sub x}S{sub 100-x} chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

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

    PubMed

    Rotaru, Mihai; Sykulski, Jan

    2010-01-01

    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.

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

    PubMed

    Farjam, M

    2014-04-16

    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.

  4. Optically decomposed near-band-edge structure and excitonic transitions in Ga₂S₃.

    PubMed

    Ho, Ching-Hwa; Chen, Hsin-Hung

    2014-08-21

    The band-edge structure and band gap are key parameters for a functional chalcogenide semiconductor to its applications in optoelectronics, nanoelectronics, and photonics devices. Here, we firstly demonstrate the complete study of experimental band-edge structure and excitonic transitions of monoclinic digallium trisulfide (Ga₂S₃) using photoluminescence (PL), thermoreflectance (TR), and optical absorption measurements at low and room temperatures. According to the experimental results of optical measurements, three band-edge transitions of EA = 3.052 eV, EB = 3.240 eV, and EC = 3.328 eV are respectively determined and they are proven to construct the main band-edge structure of Ga₂S₃. Distinctly optical-anisotropic behaviors by orientation- and polarization-dependent TR measurements are, respectively, relevant to distinguish the origins of the EA, EB, and EC transitions. The results indicated that the three band-edge transitions are coming from different origins. Low-temperature PL results show defect emissions, bound-exciton and free-exciton luminescences in the radiation spectra of Ga₂S₃. The below-band-edge transitions are respectively characterized. On the basis of experimental analyses, the optical property of near-band-edge structure and excitonic transitions in the monoclinic Ga₂S₃ crystal is revealed.

  5. Optically decomposed near-band-edge structure and excitonic transitions in Ga2S3

    PubMed Central

    Ho, Ching-Hwa; Chen, Hsin-Hung

    2014-01-01

    The band-edge structure and band gap are key parameters for a functional chalcogenide semiconductor to its applications in optoelectronics, nanoelectronics, and photonics devices. Here, we firstly demonstrate the complete study of experimental band-edge structure and excitonic transitions of monoclinic digallium trisulfide (Ga2S3) using photoluminescence (PL), thermoreflectance (TR), and optical absorption measurements at low and room temperatures. According to the experimental results of optical measurements, three band-edge transitions of EA = 3.052 eV, EB = 3.240 eV, and EC = 3.328 eV are respectively determined and they are proven to construct the main band-edge structure of Ga2S3. Distinctly optical-anisotropic behaviors by orientation- and polarization-dependent TR measurements are, respectively, relevant to distinguish the origins of the EA, EB, and EC transitions. The results indicated that the three band-edge transitions are coming from different origins. Low-temperature PL results show defect emissions, bound-exciton and free-exciton luminescences in the radiation spectra of Ga2S3. The below-band-edge transitions are respectively characterized. On the basis of experimental analyses, the optical property of near-band-edge structure and excitonic transitions in the monoclinic Ga2S3 crystal is revealed. PMID:25142550

  6. Band Structure and Effective Mass in Monolayer MoS2.

    PubMed

    Wu, Ming-Ting; Fan, Jun-Wei; Chen, Kuan-Ting; Chang, Shu-Tong; Lin, Chung-Yi

    2015-11-01

    Monolayer transition-metal dichalcogenide is a very promising two-dimensional material for future transistor technology. Monolayer molybdenum disulfide (MoS2), owing to the unique electronic properties of its atomically thin two-dimensional layered structure, can be made into a high-performance metal-oxide-semiconductor field-effect transistor, or MOSFET. In this work, we focus on band structure and carrier mobility calculations for MoS2. We use the tight-binding method to calculate the band structure, including a consideration of the linear combination of different atomic orbitals, the interaction of neighboring atoms, and spin-orbit coupling for different tight-binding matrices. With information about the band structure, we can obtain the density of states, the effective mass, and other physical quantities. Carrier mobility using the Kubo-Greenwood formula is calculated based on the tight-binding band structure. PMID:26726660

  7. Features of the band structure for semiconducting iron, ruthenium, and osmium monosilicides

    SciTech Connect

    Shaposhnikov, V. L. Migas, D. B.; Borisenko, V. E.; Dorozhkin, N. N.

    2009-02-15

    The pseudopotential method has been used to optimize the crystal lattice and calculate the energy band spectra for iron, ruthenium and, osmium monosilicides. It is found that all these compounds are indirect-gap semiconductors with band gaps of 0.17, 0.22, and 0.50 eV (FeSi, RuSi, and OsSi, respectively). A distinctive feature of their band structure is the 'loop of extrema' both in the valence and conduction bands near the center of the cubic Brillouin zone.

  8. Electronic band structure effects in monolayer, bilayer, and hybrid graphene structures

    NASA Astrophysics Data System (ADS)

    Puls, Conor

    Since its discovery in 2005, graphene has been the focus of intense theoretical and experimental study owing to its unique two-dimensional band structure and related electronic properties. In this thesis, we explore the electronic properties of graphene structures from several perspectives including the magnetoelectrical transport properties of monolayer graphene, gap engineering and measurements in bilayer graphene, and anomalous quantum oscillation in the monolayer-bilayer graphene hybrids. We also explored the device implications of our findings, and the application of some experimental techniques developed for the graphene work to the study of a complex oxide, Ca3Ru2O7, exhibiting properties of strongly correlated electrons. Graphene's high mobility and ballistic transport over device length scales, make it suitable for numerous applications. However, two big challenges remain in the way: maintaining high mobility in fabricated devices, and engineering a band gap to make graphene compatible with logical electronics and various optical devices. We address the first challenge by experimentally evaluating mobilities in scalable monolayer graphene-based field effect transistors (FETs) and dielectric-covered Hall bars. We find that the mobility is limited in these devices, and is roughly inversely proportional to doping. By considering interaction of graphene's Dirac fermions with local charged impurities at the interface between graphene and the top-gate dielectric, we find that Coulomb scattering is responsible for degraded mobility. Even in the cleanest devices, a band gap is still desirable for electronic applications of graphene. We address this challenge by probing the band structure of bilayer graphene, in which a field-tunable energy band gap has been theoretically proposed. We use planar tunneling spectroscopy of exfoliated bilayer graphene flakes demonstrate both measurement and control of the energy band gap. We find that both the Fermi level and

  9. Quantitative study of band structure in BaTiO3 particles with vacant ionic sites

    NASA Astrophysics Data System (ADS)

    Oshime, Norihiro; Kano, Jun; Ikeda, Naoshi; Teranishi, Takashi; Fujii, Tatsuo; Ueda, Takeji; Ohkubo, Tomoko

    2016-10-01

    Levels of the conduction band minimum and the valence band maximum in ion-deficient BaTiO3 particles were investigated with optical band gap and ionization energy measurements. Though it is known that the quantification of the band structure in an insulator is difficult, due to the poor electrical conductivity of BaTiO3, systematic variation in the band energy levels was found that correlated with the introduction of vacancies. Photoelectron yield spectroscopy provided direct observation of the occupancy level of electrons, which is altered by the presence of oxygen and barium vacancies. In addition, the conduction band deviation from the vacuum level was determined by optical reflectance spectroscopy. Our results show that: (1) Introduction of oxygen vacancies forms a donor level below the conduction band. (2) The conduction band is shifted to a lower level by a larger number of oxygen vacancies, while the valence band also shifts to a lower level, due to the reduction in the density of O 2p orbitals. (3) Introduction of barium vacancies widens the band gap. Since barium vacancies can induce a small number of oxygen vacancies with accompanying charge compensation, this behavior suppresses any large formation of donor levels in the gap states, indicating that cation vacancies can control the number of both donor and acceptor levels.

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

    SciTech Connect

    Zhang Haifeng; Liu Shaobin; Kong Xiangkun; Bian Borui; Dai Yi

    2012-11-15

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

  11. Interaction of wide band gap single crystals with 248 nm excimer laser radiation. XII. The emission of negative atomic ions from alkali halides

    SciTech Connect

    Kimura, Kenichi; Langford, S. C.; Dickinson, J. T.

    2007-12-01

    Many wide band gap materials yield charged and neutral emissions when exposed to sub-band-gap laser radiation at power densities below the threshold for optical breakdown and plume formation. In this work, we report the observation of negative alkali ions from several alkali halides under comparable conditions. We observe no evidence for negative halogen ions, in spite of the high electron affinities of the halogens. Significantly, the positive and negative alkali ions show a high degree of spatial and temporal overlap. A detailed study of all the relevant particle emissions from potassium chloride (KCl) suggests that K{sup -} is formed by the sequential attachment of two electrons to K{sup +}.

  12. Experimental determination of excitonic band structures of single-walled carbon nanotubes using circular dichroism spectra

    NASA Astrophysics Data System (ADS)

    Wei, Xiaojun; Tanaka, Takeshi; Yomogida, Yohei; Sato, Naomichi; Saito, Riichiro; Kataura, Hiromichi

    2016-10-01

    Experimental band structure analyses of single-walled carbon nanotubes have not yet been reported, to the best of our knowledge, except for a limited number of reports using scanning tunnelling spectroscopy. Here we demonstrate the experimental determination of the excitonic band structures of single-chirality single-walled carbon nanotubes using their circular dichroism spectra. In this analysis, we use gel column chromatography combining overloading selective adsorption with stepwise elution to separate 12 different single-chirality enantiomers. Our samples show higher circular dichroism intensities than the highest values reported in previous works, indicating their high enantiomeric purity. Excitonic band structure analysis is performed by assigning all observed Eii and Eij optical transitions in the circular dichroism spectra. The results reproduce the asymmetric structures of the valence and conduction bands predicted by density functional theory. Finally, we demonstrate that an extended empirical formula can estimate Eij optical transition energies for any (n,m) species.

  13. Band structure engineering through orbital interaction for enhanced thermoelectric power factor

    SciTech Connect

    Zhu, Hong; Sun, Wenhao; Ceder, Gerbrand; Armiento, Rickard; Lazic, Predrag

    2014-02-24

    Band structure engineering for specific electronic or optical properties is essential for the further development of many important technologies including thermoelectrics, optoelectronics, and microelectronics. In this work, we report orbital interaction as a powerful tool to finetune the band structure and the transport properties of charge carriers in bulk crystalline semiconductors. The proposed mechanism of orbital interaction on band structure is demonstrated for IV-VI thermoelectric semiconductors. For IV-VI materials, we find that the convergence of multiple carrier pockets not only displays a strong correlation with the s-p and spin-orbit coupling but also coincides with the enhancement of power factor. Our results suggest a useful path to engineer the band structure and an enticing solid-solution design principle to enhance thermoelectric performance.

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  15. Fine Structure in the Secondary Electron Emission Peak for Diamond Crystal with (100) Negative Electron Affinity Surface

    NASA Technical Reports Server (NTRS)

    Asnin, V. M.; Krainsky, I. L.

    1998-01-01

    A fine structure was discovered in the low-energy peak of the secondary electron emission spectra of the diamond surface with negative electron affinity. We studied this structure for the (100) surface of the natural type-IIb diamond crystal. We have found that the low-energy peak consists of a total of four maxima. The relative energy positions of three of them could be related to the electron energy minima near the bottom of the conduction band. The fourth peak, having the lowest energy, was attributed to the breakup of the bulk exciton at the surface during the process of secondary electron emission.

  16. Analysis of negative material supported helix slow wave structure for traveling-wave tubes

    NASA Astrophysics Data System (ADS)

    Purushothaman, N.; Srivastava, V.; Ghosh, S. K.

    2013-06-01

    We investigate the effect of negative materials used as support structures for helix travelling wave tubes (TWTs). Analysis is carried out with materials having negative permittivity or negative permeability and compared with the positive dielectric support materials. The work attempts to focus on the dispersion relation and interaction impedance as a measure to check for the feasibility of using negative materials in TWT.

  17. Band structure of hydrogenated silicene on Ag(111): Evidence for half-silicane

    NASA Astrophysics Data System (ADS)

    Wang, W.; Olovsson, W.; Uhrberg, R. I. G.

    2016-02-01

    In the case of graphene, hydrogenation removes the conductivity due to the bands forming the Dirac cone by opening up a band gap. This type of chemical functionalization is of the utmost importance for electronic applications. As predicted by theoretical studies, a similar change in the band structure is expected for silicene, the closest analog to graphene. We here report a study of the atomic and electronic structures of hydrogenated silicene with hydrogen on one side, the so-called half-silicane. The ("2 √{3 }×2 √{3 } ") phase of silicene on Ag(111) was used in this Rapid Communication since it can be formed homogeneously across the entire surface of the Ag substrate. Low-energy electron diffraction and scanning tunneling microscopy data clearly show that hydrogenation changes the structure of silicene on Ag(111) resulting in a (1 × 1) periodicity with respect to the silicene lattice. The hydrogenated silicene also exhibits a quasiregular (2 √{3 }×2 √{3 } )-like arrangement of vacancies. Angle-resolved photoelectron spectroscopy revealed two dispersive bands which can be unambiguously assigned to half-silicane. The common top of these bands is located at ˜0.9 eV below the Fermi level. We find that the experimental bands are closely reproduced by the theoretical band structure of free-standing silicene with H adsorbed on the upper hexagonal sublattice.

  18. Fine structure of the red luminescence band in undoped GaN

    SciTech Connect

    Reshchikov, M. A.; Usikov, A.; Helava, H.; Makarov, Yu.

    2014-01-20

    Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8 eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36 eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of the RL band fine structure indicate that the RL band is caused by transitions from a shallow donor (at low temperature) or from the conduction band (above 50 K) to an unknown deep acceptor having an energy level 1.130 eV above the valence band.

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  20. Energy loss of ions at metal surfaces: Band-structure effects

    SciTech Connect

    Alducin, M.; Silkin, V.M.; Juaristi, J.I.; Chulkov, E.V.

    2003-03-01

    We study band-structure effects on the energy loss of protons scattered off the Cu (111) surface. The distance dependent stopping power for a projectile traveling parallel to the surface is calculated within the linear response theory. The self-consistent electronic response of the system is evaluated within the random-phase approximation. In order to characterize the surface band structure, the electronic single-particle wave functions and energies are obtained by solving the Schroedinger equation with a realistic one-dimensional model potential. This potential reproduces the main features of the Cu (111) surface: the energy band gap for electron motion along the surface normal, as well as the binding energy of the occupied surface state and the first image state. Comparison of our results with those obtained within the jellium model allows us to characterize the band-structure effects in the energy loss of protons interacting with the Cu (111) surface.

  1. Electronic structure of Pt based topological Heusler compounds with C1{sub b} structure and 'zero band gap'

    SciTech Connect

    Ouardi, Siham; Shekhar, Chandra; Fecher, Gerhard H.; Kozina, Xeniya; Stryganyuk, Gregory; Felser, Claudia; Ueda, Shigenori; Kobayashi, Keisuke

    2011-05-23

    Besides of their well-known wide range of properties it was recently shown that many of the heavy Heusler semiconductors with 1:1:1 composition and C1{sub b} structure exhibit a zero band gap behavior and are topological insulators induced by their inverted band structure. In the present study, the electronic structure of the Heusler compounds PtYSb and PtLaBi was investigated by bulk sensitive hard x-ray photoelectron spectroscopy. The measured valence band spectra are clearly resolved and in well agreement to the first-principles calculations of the electronic structure of the compounds. The experimental results give clear evidence for the zero band gap state.

  2. The band structure of birefractive CdGa2S4 crystals

    NASA Astrophysics Data System (ADS)

    Stamov, I. G.; Syrbu, N. N.; Parvan, V. I.; Zalamai, V. V.; Tiginyanu, I. M.

    2013-11-01

    In this paper, we report on the spectral dependence of Δn=no-ne for CdGa2S4 single crystals for shorter and longer wavelengths than the isotropic wavelength λ0=485.7 nm (300 K). It was established that Δn is positive at λ>λ0 and it is negative in the spectral range λ<λ0. The isotropic wavelength λ0 exhibits blue spectral shift with temperature decreasing. The ground and excited states of three excitonic series A, B and C with binding energies of 53 meV, 52 meV and 46 meV, respectively, were found out at 10 K. The effective masses of electrons for k=0 were derived from the calculation of excitonic spectra: mc∥(Е∥с)=0.21m0 and mc⊥(Е⊥с)=0.19m0. The holes masses are equal to 0.59m0 and 0.71m0 for Е∥с and Е⊥с, respectively. The value of valence bands splitting, V1-V2, by crystalline field equals 24 meV, and V2-V3 splitting due to the spin-orbital interaction equals to 130 meV. The optical functions n, k, ε1 and ε2 for Е⊥с and Е∥с polarizations were calculated by means of Kramers-Kronig analyses in the energy interval 3-6 eV. The evidenced features are discussed taking into account the results of new theoretical calculations of CdGa2S4 band structure.

  3. Electron microscopy and x-ray diffraction evidence for two Z-band structural states.

    PubMed

    Perz-Edwards, Robert J; Reedy, Michael K

    2011-08-01

    In vertebrate muscles, Z-bands connect adjacent sarcomeres, incorporate several cell signaling proteins, and may act as strain sensors. Previous electron microscopy (EM) showed Z-bands reversibly switch between a relaxed, "small-square" structure, and an active, "basketweave" structure, but the mechanism of this transition is unknown. Here, we found the ratio of small-square to basketweave in relaxed rabbit psoas muscle varied with temperature, osmotic pressure, or ionic strength, independent of activation. By EM, the A-band and both Z-band lattice spacings varied with temperature and pressure, not ionic strength; however, the basketweave spacing was consistently 10% larger than small-square. We next sought evidence for the two Z-band structures in unfixed muscles using x-ray diffraction, which indicated two Z-reflections whose intensity ratios and spacings correspond closely to the EM measurements for small-square and basketweave if the EM spacings are adjusted for 20% shrinkage due to EM processing. We conclude that the two Z-reflections arise from the small-square and basketweave forms of the Z-band as seen by EM. Regarding the mechanism of transition during activation, the effects of Ca(2+) in the presence of force inhibitors suggested that the interconversion of Z-band forms was correlated with tropomyosin movement on actin. PMID:21806939

  4. Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

    SciTech Connect

    Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan

    2015-01-21

    The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO{sub 2}), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO{sub 2} has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance.

  5. An open-structure sound insulator against low-frequency and wide-band acoustic waves

    NASA Astrophysics Data System (ADS)

    Chen, Zhe; Fan, Li; Zhang, Shu-yi; Zhang, Hui; Li, Xiao-juan; Ding, Jin

    2015-10-01

    To block sound, i.e., the vibration of air, most insulators are based on sealed structures and prevent the flow of the air. In this research, an acoustic metamaterial adopting side structures, loops, and labyrinths, arranged along a main tube, is presented. By combining the accurately designed side structures, an extremely wide forbidden band with a low cut-off frequency of 80 Hz is produced, which demonstrates a powerful low-frequency and wide-band sound insulation ability. Moreover, by virtue of the bypass arrangement, the metamaterial is based on an open structure, and thus air flow is allowed while acoustic waves can be insulated.

  6. The C-Band accelerating structures for SPARC photoinjector energy upgrade

    NASA Astrophysics Data System (ADS)

    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

    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.

  7. Fine-structure enhancement — assessment of a simple method to resolve overlapping bands in spectra

    NASA Astrophysics Data System (ADS)

    Barth, Andreas

    2000-05-01

    A simple mathematical procedure — fine-structure enhancement — has been assessed on its ability to resolve overlapping bands in spectra. Its advantages and limitations have been explored using synthetic and experimental spectra. Fine-structure enhancement involves smoothing the original spectrum, multiplying the smoothed spectrum with a weighting factor and subtracting this spectrum from the original spectrum. As a result, the fine-structure of the original spectrum is enhanced in the processed spectrum and bands that overlap in the original spectrum appear as distinct bands in the processed spectrum. To be resolved by fine-structure enhancement, Lorentzian lines have to be separated by more than their quarter width at half maximum, Gaussian lines by more than their half width at half maximum. A comparison of fine-structure enhancement and Fourier self-deconvolution shows that Fourier self-deconvolution has in theory a higher potential to resolve overlapping bands. However, this depends crucially on the correct choice of the parameters. In practice, when parameters commonly used are chosen for Fourier self-deconvolution, fine-structure enhancement leads to similar results. This is demonstrated at the example of the infrared absorbance spectrum of the protein papain, where the amide I band components could be resolved similarly with both methods. Thus, fine-structure enhancement seems to be a simple alternative to Fourier self-deconvolution that does not require specialised software.

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

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

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

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

    PubMed Central

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

    2016-01-01

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

  10. Promoting Photochemical Water Oxidation with Metallic Band Structures.

    PubMed

    Liu, Hongfei; Moré, René; Grundmann, Henrik; Cui, Chunhua; Erni, Rolf; Patzke, Greta R

    2016-02-10

    The development of economic water oxidation catalysts is a key step toward large-scale water splitting. However, their current exploration remains empirical to a large extent. Elucidating the correlations between electronic properties and catalytic activity is crucial for deriving general and straightforward catalyst design principles. Herein, strongly correlated electronic systems with abundant and easily tunable electronic properties, namely La(1-x)Sr(x)BO3 perovskites and La(2-x)Sr(x)BO4 layered perovskites (B = Fe, Co, Ni, or Mn), were employed as model systems to identify favorable electronic structures for water oxidation. We established a direct correlation between the enhancement of catalytic activity and the insulator to metal transition through tuning the electronic properties of the target perovskite families via the La(3+)/Sr(2+) ratio. Their improved photochemical water oxidation performance was clearly linked to the increasingly metallic character. These electronic structure-activity relations provide a promising guideline for constructing efficient water oxidation catalysts.

  11. Band structure of solids from clusters SCF potentials

    SciTech Connect

    Nour, S.; Chermette, H.

    1995-01-05

    The possibilities and limits of the molecular orbital theory to deal with the problem of determining electronic structure of solids have been explored. A cluster model based on the charge neutrality in the solid has been used in test calculations on some III-V semiconductors and have given quite satisfactory results. Recommendations are given to widen the field of applications of this procedure. 33 refs., 5 figs., 2 tabs.

  12. Band structures of 4f and 5f materials studied by angle-resolved photoelectron spectroscopy.

    PubMed

    Fujimori, Shin-ichi

    2016-04-20

    Recent remarkable progress in angle-resolved photoelectron spectroscopy (ARPES) has enabled the direct observation of the band structures of 4f and 5f materials. In particular, ARPES with various light sources such as lasers (hν ~ 7 eV) or high-energy synchrotron radiations (hν >/~ 400 eV) has shed light on the bulk band structures of strongly correlated materials with energy scales of a few millielectronvolts to several electronvolts. The purpose of this paper is to summarize the behaviors of 4f and 5f band structures of various rare-earth and actinide materials observed by modern ARPES techniques, and understand how they can be described using various theoretical frameworks. For 4f-electron materials, ARPES studies of CeMIn5(M = Rh, Ir, and Co) and YbRh2Si2 with various incident photon energies are summarized. We demonstrate that their 4f electronic structures are essentially described within the framework of the periodic Anderson model, and that the band-structure calculation based on the local density approximation cannot explain their low-energy electronic structures. Meanwhile, electronic structures of 5f materials exhibit wide varieties ranging from itinerant to localized states. For itinerant U5f compounds such as UFeGa5, their electronic structures can be well-described by the band-structure calculation assuming that all U5f electrons are itinerant. In contrast, the band structures of localized U5f compounds such as UPd3 and UO2 are essentially explained by the localized model that treats U5f electrons as localized core states. In regards to heavy fermion U-based compounds such as the hidden-order compound URu2Si2, their electronic structures exhibit complex behaviors. Their overall band structures are generally well-explained by the band-structure calculation, whereas the states in the vicinity of EF show some deviations due to electron correlation effects. Furthermore, the electronic structures of URu2Si2 in the paramagnetic and hidden-order phases are

  13. Band structures of 4f and 5f materials studied by angle-resolved photoelectron spectroscopy.

    PubMed

    Fujimori, Shin-ichi

    2016-04-20

    Recent remarkable progress in angle-resolved photoelectron spectroscopy (ARPES) has enabled the direct observation of the band structures of 4f and 5f materials. In particular, ARPES with various light sources such as lasers (hν ~ 7 eV) or high-energy synchrotron radiations (hν >/~ 400 eV) has shed light on the bulk band structures of strongly correlated materials with energy scales of a few millielectronvolts to several electronvolts. The purpose of this paper is to summarize the behaviors of 4f and 5f band structures of various rare-earth and actinide materials observed by modern ARPES techniques, and understand how they can be described using various theoretical frameworks. For 4f-electron materials, ARPES studies of CeMIn5(M = Rh, Ir, and Co) and YbRh2Si2 with various incident photon energies are summarized. We demonstrate that their 4f electronic structures are essentially described within the framework of the periodic Anderson model, and that the band-structure calculation based on the local density approximation cannot explain their low-energy electronic structures. Meanwhile, electronic structures of 5f materials exhibit wide varieties ranging from itinerant to localized states. For itinerant U5f compounds such as UFeGa5, their electronic structures can be well-described by the band-structure calculation assuming that all U5f electrons are itinerant. In contrast, the band structures of localized U5f compounds such as UPd3 and UO2 are essentially explained by the localized model that treats U5f electrons as localized core states. In regards to heavy fermion U-based compounds such as the hidden-order compound URu2Si2, their electronic structures exhibit complex behaviors. Their overall band structures are generally well-explained by the band-structure calculation, whereas the states in the vicinity of EF show some deviations due to electron correlation effects. Furthermore, the electronic structures of URu2Si2 in the paramagnetic and hidden-order phases are

  14. Band structures of 4f and 5f materials studied by angle-resolved photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Fujimori, Shin-ichi

    2016-04-01

    Recent remarkable progress in angle-resolved photoelectron spectroscopy (ARPES) has enabled the direct observation of the band structures of 4f and 5f materials. In particular, ARPES with various light sources such as lasers (hν ∼ 7~\\text{eV} ) or high-energy synchrotron radiations (hν ≳ 400~\\text{eV} ) has shed light on the bulk band structures of strongly correlated materials with energy scales of a few millielectronvolts to several electronvolts. The purpose of this paper is to summarize the behaviors of 4f and 5f band structures of various rare-earth and actinide materials observed by modern ARPES techniques, and understand how they can be described using various theoretical frameworks. For 4f-electron materials, ARPES studies of \\text{Ce}M\\text{I}{{\\text{n}}5} (M=\\text{Rh} , \\text{Ir} , and \\text{Co} ) and \\text{YbR}{{\\text{h}}2}\\text{S}{{\\text{i}}2} with various incident photon energies are summarized. We demonstrate that their 4f electronic structures are essentially described within the framework of the periodic Anderson model, and that the band-structure calculation based on the local density approximation cannot explain their low-energy electronic structures. Meanwhile, electronic structures of 5f materials exhibit wide varieties ranging from itinerant to localized states. For itinerant \\text{U}~5f compounds such as \\text{UFeG}{{\\text{a}}5} , their electronic structures can be well-described by the band-structure calculation assuming that all \\text{U}~5f electrons are itinerant. In contrast, the band structures of localized \\text{U}~5f compounds such as \\text{UP}{{\\text{d}}3} and \\text{U}{{\\text{O}}2} are essentially explained by the localized model that treats \\text{U}~5f electrons as localized core states. In regards to heavy fermion \\text{U} -based compounds such as the hidden-order compound \\text{UR}{{\\text{u}}2}\\text{S}{{\\text{i}}2} , their electronic structures exhibit complex behaviors. Their overall band structures

  15. Photonic band gap characteristics of one-dimensional graphene-dielectric periodic structures

    NASA Astrophysics Data System (ADS)

    Al-sheqefi, F. U. Y.; Belhadj, W.

    2015-12-01

    In this paper, we study theoretically, the transmission properties of a one-dimensional graphene-dielectric periodic structure by using the transfer matrix method. Within the framework of this method, we confirm earlier finding that a periodic structure composed of a stack of monolayer graphene sheets separated by dielectric slabs, possesses photonic band-gap (PBG) properties and supports a series of bandpass and band-stop regions at low-terahertz frequencies. Our calculations showed that the suggested structure possesses in addition to the structural Bragg gaps, a new type of band gap that exhibits a rather versatile behavior with varying angle of incidence. We find this type of band gap is omnidirectional (omni-gap) for both transverse electric (TE) and transverse magnetic (TM) polarizations. Our results show that 1D graphene-dielectric periodic structures are very good candidates for band gap engineering. Specifically, we demonstrate the existence of a band gap region for both polarizations which survives for incident angles as high as 80°. Moreover, we show how our proposed structure can also function as a highly efficient polarization splitter. It is also found that the band gaps can be tuned by tuning the properties of the graphene via a gate voltage. In order to investigate difference between the omni-gap and Bragg PBG, we plot the electromagnetic field profiles for some critical frequencies. The proposed structure is promising and can work as a gate tunable perfect stop filter which completely blocks both polarizations, and may have many other potential applications.

  16. Electronic structure and band alignment at an epitaxial spinel/perovskite heterojunction.

    PubMed

    Qiao, Liang; Li, Wei; Xiao, Haiyan; Meyer, Harry M; Liang, Xuelei; Nguyen, N V; Weber, William J; Biegalski, Michael D

    2014-08-27

    The electronic properties of solid-solid interfaces play critical roles in a variety of technological applications. Recent advances of film epitaxy and characterization techniques have demonstrated a wealth of exotic phenomena at interfaces of oxide materials, which are critically dependent on the alignment of their energy bands across the interface. Here we report a combined photoemission and electrical investigation of the electronic structures across a prototypical spinel/perovskite heterojunction. Energy-level band alignment at an epitaxial Co3O4/SrTiO3(001) heterointerface indicates a chemically abrupt, type I heterojunction without detectable band bending at both the film and substrate. The unexpected band alignment for this typical p-type semiconductor on SrTiO3 is attributed to its intrinsic d-d interband excitation, which significantly narrows the fundamental band gap between the top of the valence band and the bottom of the conduction band. The formation of the type I heterojunction with a flat-band state results in a simultaneous confinement of both electrons and holes inside the Co3O4 layer, thus rendering the epitaxial Co3O4/SrTiO3(001) heterostructure to be a very promising material for high-efficiency luminescence and optoelectronic device applications.

  17. Triple photonic band-gap structure dynamically induced in the presence of spontaneously generated coherence

    SciTech Connect

    Gao Jinwei; Bao Qianqian; Wan Rengang; Cui Cuili; Wu Jinhui

    2011-05-15

    We study a cold atomic sample coherently driven into the five-level triple-{Lambda} configuration for attaining a dynamically controlled triple photonic band-gap structure. Our numerical calculations show that three photonic band gaps with homogeneous reflectivities up to 92% can be induced on demand around the probe resonance by a standing-wave driving field in the presence of spontaneously generated coherence. All these photonic band gaps are severely malformed with probe reflectivities declining rapidly to very low values when spontaneously generated coherence is gradually weakened. The triple photonic band-gap structure can also be attained in a five-level chain-{Lambda} system of cold atoms in the absence of spontaneously generated coherence, which however requires two additional traveling-wave fields to couple relevant levels.

  18. Quasiparticle band structure of the almost-gapless transition-metal-based Heusler semiconductors

    NASA Astrophysics Data System (ADS)

    Tas, M.; Şaşıoǧlu, E.; Galanakis, I.; Friedrich, C.; Blügel, S.

    2016-05-01

    Transition-metal-based Heusler semiconductors are promising materials for a variety of applications ranging from spintronics to thermoelectricity. Employing the G W approximation within the framework of the FLAPW method, we study the quasiparticle band structure of a number of such compounds being almost gapless semiconductors. We find that in contrast to the s p -electron based semiconductors such as Si and GaAs, in these systems, the many-body corrections have a minimal effect on the electronic band structure and the energy band gap increases by less than 0.2 eV, which makes the starting point density functional theory (DFT) a good approximation for the description of electronic and optical properties of these materials. Furthermore, the band gap can be tuned either by the variation of the lattice parameter or by the substitution of the s p -chemical element.

  19. Deformation analysis of ferrite/pearlite banded structure under uniaxial tension using digital image correlation

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaochuan; Wang, Yong; Yang, Jia; Qiao, Zhixia; Ren, Chunhua; Chen, Cheng

    2016-10-01

    The ferrite/pearlite banded structure causes the anisotropic behavior of steel. In this paper, digital image correlation (DIC) was used to analyze the micro deformation of this microstructure under uniaxial tension. The reliability of DIC for this application was verified by a zero-deformation experiment. The results show that the performance of DIC can satisfy the requirements of the tensile deformation measurement. Then, two uniaxial tensile tests in different directions (longitudinal direction and transverse direction) were carried out and DIC was used to measure the micro deformation of the ferrite/pearlite banded structure. The measured results show that the ferrite bands undergo the main deformation in the transverse tension, which results in the relatively weaker tensile properties in the transverse direction than in the longitudinal direction. This work is useful to guide the modification of the bands morphology and extend the application scope of DIC.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  1. Curvature effects in the band structure of carbon nanotubes including spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Liu, Hong; Heinze, Dirk; Thanh Duc, Huynh; Schumacher, Stefan; Meier, Torsten

    2015-11-01

    The Kane-Mele model was previously used to describe effective spin-orbit couplings (SOCs) in graphene. Here we extend this model and also incorporate curvature effects to analyze the combined influence of SOC and curvature on the band structure of carbon nanotubes (CNTs). The extended model then reproduces the chirality-dependent asymmetric electron-hole splitting for semiconducting CNTs and in the band structure for metallic CNTs shows an opening of the band gap and a change of the Fermi wave vector with spin. For chiral semiconducting CNTs with large chiral angle we show that the spin-splitting configuration of bands near the Fermi energy depends on the value of \\text{mod}(2n+m,3) .

  2. Band structure of silicene in the tight binding approximation

    SciTech Connect

    Gert, A. V. Nestoklon, M. O.; Yassievich, I. N.

    2015-07-15

    The electronic structure of silicene is simulated by the tight binding method with the basis sp{sup 3}d{sup 5}s*. The results are in good agreement with ab initio calculations. The effective Hamiltonian of silicene in the vicinity of the Dirac point is constructed by the method of invariants. Silicon atoms in silicene are located in two parallel planes displaced perpendicularly to each other by Δ{sub z}; the energy spectrum essentially depends on this displacement. Using the tight binding technique, the coefficients of the effective Hamiltonian are determined for various values of Δ{sub z}.

  3. Band structure properties of (BGa)P semiconductors for lattice matched integration on (001) silicon

    SciTech Connect

    Hossain, Nadir; Sweeney, Stephen; Hosea, Jeff; Liebich, Sven; Zimprich, Martin; Volz, Kerstin; Stolz, Wolfgang; Kunert, Bernerdette

    2013-12-04

    We report the band structure properties of (BGa)P layers grown on silicon substrate using metal-organic vapour-phase epitaxy. Using surface photo-voltage spectroscopy we find that both the direct and indirect band gaps of (BGa)P alloys (strained and unstrained) decrease with Boron content. Our experimental results suggest that the band gap of (BGa)P layers up to 6% Boron is large and suitable to be used as cladding and contact layers in GaP-based quantum well heterostructures on silicon substrates.

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

    SciTech Connect

    Shao, Yang; Yao, Kefu; Liu, Xue; Li, Mo

    2013-10-21

    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.

  5. The LDA+U calculation of electronic band structure of GaAs

    NASA Astrophysics Data System (ADS)

    Bahuguna, B. P.; Sharma, R. O.; Saini, L. K.

    2016-05-01

    We present the electronic band structure of bulk gallium arsenide (GaAs) using first principle approach. A series of calculations has been performed by applying norm-conserving pseudopotentials and ultrasoft non-norm-conserving pseudopotentials within the density functional theory. These calculations yield too small band gap as compare to experiment. Thus, we use semiemperical approach called local density approximation plus the multi-orbital mean-field Hubbard model (LDA+U), which is quite effective in order to describe the band gap of GaAs.

  6. Engineering the electronic structure and band gap of boron nitride nanoribbon via external electric field

    NASA Astrophysics Data System (ADS)

    Chegel, Raad

    2016-06-01

    By using the third nearest neighbor modified tight binding (3NN-TB) method, the electronic structure and band gap of BNNRs under transverse electric fields are explored. The band gap of the BNNRs has a decreasing with increasing the intensity of the applied electric field, independent on the ribbon edge types. Furthermore, an analytic model for the dependence of the band gap in armchair and zigzag BNNRs on the electric field is proposed. The reduction of E g is similar for some N a armchair and N z zigzag BNNRs independent of their edges.

  7. Unfolding of collapsed polymers in shear flow: effects of colloid banding structures in confining channels.

    PubMed

    Chen, Hsieh; Alexander-Katz, Alfredo

    2014-03-01

    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.

  8. Predicted band structures of III-V semiconductors in the wurtzite phase

    SciTech Connect

    De, A.; Pryor, Craig E.

    2010-04-15

    While non-nitride III-V semiconductors typically have a zinc-blende structure, they may also form wurtzite crystals under pressure or when grown as nanowhiskers. This makes electronic structure calculation difficult since the band structures of wurtzite III-V semiconductors are poorly characterized. We have calculated the electronic band structure for nine III-V semiconductors in the wurtzite phase using transferable empirical pseudopotentials including spin-orbit coupling. We find that all the materials have direct gaps. Our results differ significantly from earlier ab initio calculations, and where experimental results are available (InP, InAs, and GaAs) our calculated band gaps are in good agreement. We tabulate energies, effective masses, and linear and cubic Dresselhaus zero-field spin-splitting coefficients for the zone-center states. The large zero-field spin-splitting coefficients we find may facilitate the development of spin-based devices.

  9. Observation of Nonlinear Looped Band Structure of Bose-Einstein condensates in an optical lattice

    NASA Astrophysics Data System (ADS)

    Goldschmidt, Elizabeth; Koller, Silvio; Brown, Roger; Wyllie, Robert; Wilson, Ryan; Porto, Trey

    2016-05-01

    We study experimentally the stability of excited, interacting states of bosons in a double-well optical lattice in regimes where the nonlinear interactions are expected to induce ``swallow-tail'' looped band structure. By carefully preparing different initial coherent states and observing their subsequent decay, we observe distinct decay rates, which provide direct evidence for multi-valued band structure. The double well lattice both stabilizes the looped band structure and allows for dynamic preparation of different initial states, including states within the loop structure. We confirm our state preparation procedure with dynamic Gross-Pitaevskii calculations. The excited loop states are found to be more stable than dynamically unstable ground states, but decay faster than expected based on a mean-field stability calculation, indicating the importance of correlations beyond a mean-field description. Now at Georgia Tech Research Institute.

  10. Coexisting Honeycomb and Kagome Characteristics in the Electronic Band Structure of Molecular Graphene.

    PubMed

    Paavilainen, Sami; Ropo, Matti; Nieminen, Jouko; Akola, Jaakko; Räsänen, Esa

    2016-06-01

    We uncover the electronic structure of molecular graphene produced by adsorbed CO molecules on a copper (111) surface by means of first-principles calculations. Our results show that the band structure is fundamentally different from that of conventional graphene, and the unique features of the electronic states arise from coexisting honeycomb and Kagome symmetries. Furthermore, the Dirac cone does not appear at the K-point but at the Γ-point in the reciprocal space and is accompanied by a third, almost flat band. Calculations of the surface structure with Kekulé distortion show a gap opening at the Dirac point in agreement with experiments. Simple tight-binding models are used to support the first-principles results and to explain the physical characteristics behind the electronic band structures.

  11. Polarization-dependent diffraction in all-dielectric, twisted-band structures

    SciTech Connect

    Kardaś, Tomasz M.; Jagodnicka, Anna; Wasylczyk, Piotr

    2015-11-23

    We propose a concept for light polarization management: polarization-dependent diffraction in all-dielectric microstructures. Numerical simulations of light propagation show that with an appropriately configured array of twisted bands, such structures may exhibit zero birefringence and at the same time diffract two circular polarizations with different efficiencies. Non-birefringent structures as thin as 3 μm have a significant difference in diffraction efficiency for left- and right-hand circular polarizations. We identify the structural parameters of such twisted-band matrices for optimum performance as circular polarizers.

  12. Research on the large band gaps in multilayer radial phononic crystal structure

    NASA Astrophysics Data System (ADS)

    Gao, Nansha; Wu, Jiu Hui; Guan, Dong

    2016-04-01

    In this paper, we study the band gaps (BGs) of new proposed radial phononic crystal (RPC) structure composed of multilayer sections. The band structure, transmission spectra and eigenmode displacement fields of the multilayer RPC are calculated by using finite element method (FEM). Due to the vibration coupling effects between thin circular plate and intermediate mass, the RPC structure can exhibit large BGs, which can be effectively shifted by changing the different geometry values. This study shows that multilayer RPC can unfold larger and lower BGs than traditional phononic crystals (PCs) and RPC can be composed of single material.

  13. The electronic structures of vanadate salts: Cation substitution as a tool for band gap manipulation

    NASA Astrophysics Data System (ADS)

    Dolgos, Michelle R.; Paraskos, Alexandra M.; Stoltzfus, Matthew W.; Yarnell, Samantha C.; Woodward, Patrick M.

    2009-07-01

    The electronic structures of six ternary metal oxides containing isolated vanadate ions, Ba 3(VO 4) 2, Pb 3(VO 4) 2, YVO 4, BiVO 4, CeVO 4 and Ag 3VO 4 were studied using diffuse reflectance spectroscopy and electronic structure calculations. While the electronic structure near the Fermi level originates largely from the molecular orbitals of the vanadate ion, both experiment and theory show that the cation can strongly influence these electronic states. The observation that Ba 3(VO 4) 2 and YVO 4 have similar band gaps, both 3.8 eV, shows that cations with a noble gas configuration have little impact on the electronic structure. Band structure calculations support this hypothesis. In Pb 3(VO 4) 2 and BiVO 4 the band gap is reduced by 0.9-1.0 eV through interactions of (a) the filled cation 6 s orbitals with nonbonding O 2 p states at the top of the valence band, and (b) overlap of empty 6 p orbitals with antibonding V 3 d-O 2 p states at the bottom of the conduction band. In Ag 3VO 4 mixing between filled Ag 4 d and O 2 p states destabilizes states at the top of the valence band leading to a large decrease in the band gap ( Eg=2.2 eV). In CeVO 4 excitations from partially filled 4 f orbitals into the conduction band lower the effective band gap to 1.8 eV. In the Ce 1-xBi xVO 4 (0≤ x≤0.5) and Ce 1-xY xVO 4 ( x=0.1, 0.2) solid solutions the band gap narrows slightly when Bi 3+ or Y 3+ are introduced. The nonlinear response of the band gap to changes in composition is a result of the localized nature of the Ce 4 f orbitals.

  14. International X-Band Linear Collider Accelerator Structure R&D

    SciTech Connect

    Wang, J.W.; /SLAC

    2009-03-04

    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.

  15. [Structure of human erythrocyte band 3: two-dimensional crystallographic analysis of the membrane domain].

    PubMed

    Hirai, Teruhisa; Yamaguchi, Tomohiro

    2015-07-01

    Band 3 (also known as anion exchanger 1, AE1) is one of the most abundant membrane proteins in human erythrocytes. Band 3 has 911 amino acids and consists of two structurally and functionally distinct domains. One is a 40-kDa N-terminal cytoplasmic domain and the other is a 55-kDa C-terminal membrane domain. The cytoplasmic domain maintains red cell shape through interactions with cytoskeletal proteins, such as protein 4.1, protein 4.2, ankyrin, and spectrin. On the other hand, the membrane domain mediates electroneutral exchange of anions, such as bicarbonate and chloride across the erythrocyte membrane. We reported the three-dimensional structure of the outward-open membrane domain of band 3, which was cross-linked between K539 and K851 with H2DIDS, at 7.5 Å resolution using cryo-electron crystallography. Although the results showed significantly improved resolution as compared with previous structural analyses, we could not assign all α-helices because of low resolution and uncertainty persists regarding the fold of band 3. However, we recognized that band 3 has internal repeats, because the structure exhibited distinctive anti-parallel V-shaped motifs, which protrude from the membrane bilayer on both sides. One of the helices in the motif is very long and highly tilted with respect to the normal structure of the bilayer.

  16. Collective band structures in the. gamma. -soft nucleus /sup 135/Nd

    SciTech Connect

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

    1987-03-01

    The low-lying band structure of /sup 135/Nd has been extended to higher spins using the /sup 112/Cd(/sup 27/Al,p3n..gamma..)/sup 135/Nd and /sup 116/Sn(/sup 24/Mg,2p3n..gamma..)/sup 135/Nd reactions. Two distinct high-spin structures have been identified. The ..delta..J = 1 band built on the ..nu..h/sub 11/2/(514)(9/2)/sup -/ ground state was observed to have a band crossing at J/sup ..pi../ = (25/2)/sup -/. 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 ..delta..J = 1 band structure with no signature splitting was observed to be built on a J/sup ..pi../ = (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 ..delta..J = 1 band, which is thought to be based on a ..nu..h/sub 11/2/x..pi..h/sub 11/2/x..pi..g/sub 7/2/ three-quasiparticle configuration.

  17. GaN m -plane: Atomic structure, surface bands, and optical response

    NASA Astrophysics Data System (ADS)

    Landmann, M.; Rauls, E.; Schmidt, W. Â. G.; Neumann, M. Â. D.; Speiser, E.; Esser, N.

    2015-01-01

    Density-functional-theory calculations are combined with many-body perturbation theory in order to elucidate the geometry, electronic, and optical properties of the w z -GaN (1 1 ¯00 ) surface, i.e., the so-called m -plane. The optical absorption and reflection anisotropy related to electronic transitions between surface states are identified by comparison with measured data covering transition energies from 2.4 up to 5.4 eV. Our results show a surface relaxation mechanism consistent with the electron counting rule that causes a moderate buckling of the GaN surface dimers and gives rise to two distinct surface states: The doubly occupied N dangling bonds form a surface band that is resonant with the GaN valence-band edge at the center of the Brillouin zone, whereas the empty Ga dangling bonds occur within the GaN band gap closely following the dispersion of the conduction-band edge. These two states contribute strongly to the formation of surface excitons that redshift the optical absorption with respect to the bulk optical response. The surface optical absorption i.e., the excitonic onset below the bulk band gap followed by a broad absorption band at higher energies related to the dispersion of the surface band structure, is calculated in agreement with the experimental data.

  18. Observation of 'Band' Structures in Spacecraft Observations of Inner Magnetosphere Plasma Electrons

    NASA Astrophysics Data System (ADS)

    Mohan Narasimhan, Kirthika; Fazakerley, Andrew; Milhaljcic, Branislav; Grimald, Sandrine; Dandouras, Iannis; Owen, Chris

    2013-04-01

    In previous studies, several authors have reported inner magnetosphere observations of proton distributions confined to narrow energy bands in the range of 1-25 keV. These structures have been known as "nose structures", with reference to their appearance in energy-time spectrograms and are known as "bands" if they are observed for extended periods of time. These proton structures have been studied quite extensively with multiple mechanisms proposed for their formation, not all of which apply for electrons. We examine Double-Star TC1 PEACE electron data recorded in the inner magnetosphere (L<15) near the equatorial plane to see if these features are also observed in the electron energy spectra. These "bands" also appear in electron spectrograms, spanning an energy range of 0.2-30 keV, and are shown to occur predominantly towards the dayside and dusk sectors. We also see multiple bands in some instances. We investigate the properties of these multi-banded structures and carry out a statistical survey analysing them as a function of geomagnetic activity, looking at both the Kp and Auroral Indices, in an attempt to explain their presence.

  19. Electron-Phonon Renormalization of Electronic Band Structures of C Allotropes and BN Polymorphs

    NASA Astrophysics Data System (ADS)

    Tutchton, Roxanne M.; Marchbanks, Christopher; Wu, Zhigang

    The effect of lattice vibration on electronic band structures has been mostly neglected in first-principles calculations because the electron-phonon (e-ph) renormalization of quasi-particle energies is often small (< 100 meV). However, in certain materials, such as diamond, the electron-phonon coupling reduces the band gap by nearly 0.5 eV, which is comparable to the many-body corrections of the electronic band structures calculated using the density functional theory (DFT). In this work, we compared two implementations of the Allen-Heine-Cardona theory in the EPW code and the ABINIT package respectively. Our computations of Si and diamond demonstrate that the ABINIT implementation converges much faster. Using this method, the e-ph renormalizations of electronic structures of three C allotropes (diamond, graphite, graphene) and four BN polymorphs (zincblend, wurtzite, mono-layer, and layered-hexagonal) were calculated. Our results suggest that (1) all of the zero-point renormalizations of band gaps in these materials, except for graphene, are larger than 100 meV, and (2) there are large variations in e-ph renormalization of band gaps due to differences in crystal structure. This work was supported by a U.S. DOE Early Career Award (Grant No. DE-SC0006433). Computations were carried out at the Golden Energy Computing Organization at CSM and the National Energy Research Scientific Computing Center (NERSC).

  20. UWB Band-notched Adjustable Antenna Using Concentric Split-ring Slots Structure

    NASA Astrophysics Data System (ADS)

    Yin, Y.; Hong, J. S.

    2014-09-01

    In this paper, a kind of concentric split-ring slots structure is utilized to design a novel triple-band-notched UWB antenna. Firstly, a concentric split-ring slots structure that has a higher VSWR than that of a single slot at notch frequency is presented. What's more, the structure is very simple and feasible to obtain notched-band at different frequency by adjustment of the length of slot. Secondly, a triple-band-notched antenna, whose notched bands are at 3.52-3.81 GHz for WiMAX and 5.03-5.42 GHz and 5.73-56.17 GHz for WLAN, is designed by using this structure. At last, a compact size of 24 × 30 mm2 of the proposed antenna has been fabricated and measured and it is shown that the proposed antenna has a broadband matched impedance (3.05-14 GHz, VSWR < 2), relatively stable gain and good omnidirectional radiation patterns at low bands.

  1. Ab initio theory for ultrafast magnetization dynamics with a dynamic band structure

    NASA Astrophysics Data System (ADS)

    Mueller, B. Y.; Haag, M.; Fähnle, M.

    2016-09-01

    Laser-induced modifications of magnetic materials on very small spatial dimensions and ultrashort timescales are a promising field for novel storage and spintronic devices. Therefore, the contribution of electron-electron spin-flip scattering to the ultrafast demagnetization of ferromagnets after an ultrashort laser excitation is investigated. In this work, the dynamical change of the band structure resulting from the change of the magnetization in time is taken into account on an ab initio level. We find a large influence of the dynamical band structure on the magnetization dynamics and we illustrate the thermalization and relaxation process after laser irradiation. Treating the dynamical band structure yields a demagnetization comparable to the experimental one.

  2. Valence-band electronic structure evolution of graphene oxide upon thermal annealing for optoelectronics

    DOE PAGES

    Yamaguchi, Hisato; Ogawa, Shuichi; Watanabe, Daiki; Hozumi, Hideaki; Gao, Yongqian; Eda, Goki; Mattevi, Cecilia; Fujita, Takeshi; Yoshigoe, Akitaka; Ishizuka, Shinji; et al

    2016-04-08

    We report valence band electronic structure evolution of graphene oxide (GO) upon its thermal reduction. Degree of oxygen functionalization was controlled by annealing temperatures, and an electronic structure evolution was monitored using real-time ultraviolet photoelectron spectroscopy. We observed a drastic increase in density of states around the Fermi level upon thermal annealing at ~600 °C. The result indicates that while there is an apparent band gap for GO prior to a thermal reduction, the gap closes after an annealing around that temperature. This trend of band gap closure was correlated with electrical, chemical, and structural properties to determine a setmore » of GO material properties that is optimal for optoelectronics. The results revealed that annealing at a temperature of ~500 °C leads to the desired properties, demonstrated by a uniform and an order of magnitude enhanced photocurrent map of an individual GO sheet compared to as-synthesized counterpart.« less

  3. Direct probing of band-structure Berry phase in diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Granada, M.; Lucot, D.; Giraud, R.; Lemaître, A.; Ulysse, C.; Waintal, X.; Faini, G.

    2015-06-01

    We report on experimental evidence of the Berry phase accumulated by the charge-carrier wave function in single-domain nanowires made from a (Ga, Mn)(As, P) diluted ferromagnetic semiconductor layer. Its signature on the mesoscopic transport measurements is revealed as unusual patterns in the magnetoconductance that are clearly distinguished from the universal conductance fluctuations. We show that these patterns appear in a magnetic field region where the magnetization rotates coherently and are related to a change in the band-structure Berry phase as the magnetization direction changes. They should thus be considered a band-structure Berry phase fingerprint of the effective magnetic monopoles in the momentum space. We argue that this is an efficient method to vary the band structure in a controlled way and to probe it directly. Hence, (Ga, Mn)As appears to be a very interesting test bench for new concepts based on this geometrical phase.

  4. Electronic Band Structures and Native Point Defects of Ultrafine ZnO Nanocrystals.

    PubMed

    Zeng, Yu-Jia; Schouteden, Koen; Amini, Mozhgan N; Ruan, Shuang-Chen; Lu, Yang-Fan; Ye, Zhi-Zhen; Partoens, Bart; Lamoen, Dirk; Van Haesendonck, Chris

    2015-05-20

    Ultrafine ZnO nanocrystals with a thickness down to 0.25 nm are grown by a metalorganic chemical vapor deposition method. Electronic band structures and native point defects of ZnO nanocrystals are studied by a combination of scanning tunneling microscopy/spectroscopy and first-principles density functional theory calculations. Below a critical thickness of ∼1 nm ZnO adopts a graphitic-like structure and exhibits a wide band gap similar to its wurtzite counterpart. The hexagonal wurtzite structure, with a well-developed band gap evident from scanning tunneling spectroscopy, is established for a thickness starting from ∼1.4 nm. With further increase of the thickness to 2 nm, VO-VZn defect pairs are easily produced in ZnO nanocrystals due to the self-compensation effect in highly doped semiconductors. PMID:25923131

  5. Electronic band structure and optical properties of the cubic, Sc, Y and La hydride systems

    SciTech Connect

    Peterman, D.J.

    1980-01-01

    Electronic band structure calculations are used to interpret the optical spectra of the cubic Sc, Y and La hydride systems. Self-consistent band calculations of ScH/sub 2/ and YH/sub 2/ were carried out. The respective joint densities of states are computed and compared to the dielectric functions determined from the optical measurements. Additional calculations were performed in which the Fermi level or band gap energies are rigidly shifted by a small energy increment. These calculations are then used to simulate the derivative structure in thermomodulation spectra and relate the origin of experimental interband features to the calculated energy bands. While good systematic agreement is obtained for several spectral features, the origin of low-energy interband transitions in YH/sub 2/ cannot be explained by these calculated bands. A lattice-size-dependent premature occupation of octahedral sites by hydrogen atoms in the fcc metal lattice is suggested to account for this discrepancy. Various non-self-consistent calculations are used to examine the effect of such a premature occupation. Measurements of the optical absorptivity of LaH/sub x/ with 1.6 < x < 2.9 are presented which, as expected, indicate a more premature occupation of the octahedral sites in the larger LaH/sub 2/ lattice. These experimental results also suggest that, in contrast to recent calculations, LaH/sub 3/ is a small-band-gap semiconductor.

  6. Band Structure of Helimagnons in MnSi Resolved by Inelastic Neutron Scattering.

    PubMed

    Kugler, M; Brandl, G; Waizner, J; Janoschek, M; Georgii, R; Bauer, A; Seemann, K; Rosch, A; Pfleiderer, C; Böni, P; Garst, M

    2015-08-28

    A magnetic helix realizes a one-dimensional magnetic crystal with a period given by the pitch length λh. Its spin-wave excitations-the helimagnons-experience Bragg scattering off this periodicity, leading to gaps in the spectrum that inhibit their propagation along the pitch direction. Using high-resolution inelastic neutron scattering, the resulting band structure of helimagnons was resolved by preparing a single crystal of MnSi in a single magnetic-helix domain. At least five helimagnon bands could be identified that cover the crossover from flat bands at low energies with helimagnons basically localized along the pitch direction to dispersing bands at higher energies. In the low-energy limit, we find the helimagnon spectrum to be determined by a universal, parameter-free theory. Taking into account corrections to this low-energy theory, quantitative agreement is obtained in the entire energy range studied with the help of a single fitting parameter.

  7. Band Structures of Periodic Carbon Nanotube Junctions and Their Symmetries Analyzed by the Effective Mass Approximation

    NASA Astrophysics Data System (ADS)

    Tamura, Ryo; Tsukada, Masaru

    1999-03-01

    The band structures of the periodic nanotube junctions are investigated by the effective mass theory and the tight binding model. The periodic junctions are constructed by introducing pairs of a pentagonal defect and a heptagonal defect periodically in the carbon nanotube. We treat the periodic junctions composed by two kinds of metallic nanotubes with almost same radii, the ratio of which is between 0.7 and 1. The discussed energy region is near the undoped Fermi level. The energy bands are expressed with closed analytical forms by the effective mass theory. They are similar to the dispersion relation of Kronig-Penny model and coincide well with the numerical results by the tight binding model. The width of the gap and the band are in inverse proportion to the length of the unit cell. The degeneracy and repulsion between the two bands are determined only from symmetries.

  8. Enlarged band gap and electron switch in graphene-based step-barrier structure

    SciTech Connect

    Lu, Wei-Tao Ye, Cheng-Zhi; Li, Wen

    2013-11-04

    We study the transmission through a step-barrier in gapped graphene and propose a method to enlarge the band gap. The step-barrier structure consists of two or more barriers with different strengths. It is found that the band gap could be effectively enlarged and controlled by adjusting the barrier strengths in the light of the mass term. Klein tunneling at oblique incidence is suppressed due to the asymmetry of step-barrier, contrary to the cases in single-barrier and superlattices. Furthermore, a tunable conductance channel could be opened up in the conductance gap, suggesting an application of the structure as an electron switch.

  9. Crystal structure and band gap of AlGaAsN

    NASA Astrophysics Data System (ADS)

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

    1987-09-01

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

  10. Structural studies and band gap tuning of Cr doped ZnO nanoparticles

    SciTech Connect

    Srinet, Gunjan Kumar, Ravindra Sajal, Vivek

    2014-04-24

    Structural and optical properties of Cr doped ZnO nanoparticles prepared by the thermal decomposition method are presented. X-ray diffraction studies confirmed the substitution of Cr on Zn sites without changing the wurtzite structure of ZnO. Modified form of W-H equations was used to calculate various physical parameters and their variation with Cr doping is discussed. Significant red shift was observed in band gap, i.e., a band gap tuning is achieved by Cr doping which could eventually be useful for optoelectronic applications.

  11. Effective parameters in beam acoustic metamaterials based on energy band structures

    NASA Astrophysics Data System (ADS)

    Jing, Li; Wu, Jiu Hui; Guan, Dong; Hou, Mingming; Kuan, Lu; Shen, Li

    2016-07-01

    We present a method to calculate the effective material parameters of beam acoustic metamaterials. The effective material parameters of a periodic beam are calculated as an example. The dispersion relations and energy band structures of this beam are calculated. Subsequently, the effective material parameters of the beam are investigated by using the energy band structures. Then, the modal analysis and transmission properties of the beams with finite cells are simulated in order to confirm the correctness of effective approximation. The results show that the periodic beam can be equivalent to the homogeneous beam with dynamic effective material parameters in passband.

  12. Dependence of the band structure of C-60 monolayers on molecularorientations and doping observed by angle resolved photoemission

    SciTech Connect

    Brouet, V.; Yang, W.L.; Zhou, X.J.; Hussain, Z.; Shen, Z.X.

    2008-01-17

    We present angle resolved photoemission studies of C60monolayers deposited on Ag surfaces. The electronic structure of thesemonolayers is derived from the partial filling of the narrow, 6-folddegenerated, C60 conduction band. By comparing the band structure in twomonolayers deposited, respectively, on Ag(111) and Ag(100), we show thatthe molecular degree of freedom, in this case the relative orientationsbetween C60 molecules, is essential to describe the band structure. Wefurther show that the evolution of the band as a function of doping doesnot follow a rigid band-filling picture. Phase separation is observedbetween a metallic and an insulating phase, which might be a result ofstrong correlations.

  13. Band structure engineering and thermoelectric properties of charge-compensated filled skutterudites

    SciTech Connect

    Shi, Xiaoya; Yang, Jiong; Wu, Lijun; Salvador, James R.; Zhang, Cheng; Villaire, William L.; Haddad, Daad; Yang, Jihui; Zhu, Yimei; Li, Qiang

    2015-10-12

    Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co4Sb12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing the Yb content, we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively.

  14. Band structure engineering and thermoelectric properties of charge-compensated filled skutterudites

    DOE PAGES

    Shi, Xiaoya; Yang, Jiong; Wu, Lijun; Salvador, James R.; Zhang, Cheng; Villaire, William L.; Haddad, Daad; Yang, Jihui; Zhu, Yimei; Li, Qiang

    2015-10-12

    Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co4Sb12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing the Yb content,more » we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively.« less

  15. The Calculation of the Band Structure in 3D Phononic Crystal with Hexagonal Lattice

    NASA Astrophysics Data System (ADS)

    Aryadoust, Mahrokh; Salehi, H.

    2015-12-01

    In this article, the propagation of acoustic waves in the phononic crystals (PCs) of three dimensions with the hexagonal (HEX) lattice is studied theoretically. The PCs are constituted of nickel (Ni) spheres embedded in epoxy. The calculations of the band structure and the density of states are performed using the plane wave expansion (PWE) method in the irreducible part of the Brillouin zone (BZ). In this study, we analyse the dependence of the band structures inside (the complete band gap width) on c/a and filling fraction in the irreducible part of the first BZ. Also, we have analysed the band structure of the ALHA and MLHKM planes. The results show that the maximum width of absolute elastic band gap (AEBG) (0.045) in the irreducible part of the BZ of HEX lattice is formed for c/a=6 and filling fraction equal to 0.01. In addition, the maximum of the first and second AEBG widths are 0.0884 and 0.0474, respectively, in the MLHKM plane, and the maximum of the first and second AEBG widths are 0.0851 and 0.0431, respectively, in the ALHA plane.

  16. Band Structure Engineering and Thermoelectric Properties of Charge-Compensated Filled Skutterudites

    PubMed Central

    Shi, Xiaoya; Yang, Jiong; Wu, Lijun; Salvador, James R.; Zhang, Cheng; Villaire, William L.; Haddad, Daad; Yang, Jihui; Zhu, Yimei; Li, Qiang

    2015-01-01

    Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co4Sb12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing the Yb content, we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively. PMID:26456013

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

    PubMed

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

    2013-02-01

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

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

    SciTech Connect

    Kevin Jerome Sutherland

    2001-05-01

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

  19. Damping Effect Studies for X-band Normal Conducting High Gradient Standing Wave Structures

    SciTech Connect

    Pei, S.; Li, Z.; Tantawi, S.G.; Dolgashev, V.A.; Wang, J.; /SLAC

    2009-08-03

    The Multi-TeV colliders should have the capability to accelerate low emittance beam with high rf efficiency, X-band normal conducting high gradient accelerating structure is one of the promising candidate. However, the long range transverse wake field which can cause beam emittance dilution is one of the critical issues. We examined effectiveness of dipole mode damping in three kinds of X-band, {pi}-mode standing wave structures at 11.424GHz with no detuning considered. They represent three damping schemes: damping with cylindrical iris slot, damping with choke cavity and damping with waveguide coupler. We try to reduce external Q factor below 20 in the first two dipole bands, which usually have very high (R{sub T}/Q){sub T}. The effect of damping on the acceleration mode is also discussed.

  20. Photoelectron spectroscopic study of band alignment of polymer/ZnO photovoltaic device structure

    SciTech Connect

    Nagata, T.; Chikyow, T.; Oh, S.; Wakayama, Y.; Yamashita, Y.; Yoshikawa, H.; Kobayashi, K.; Ikeno, N.

    2013-01-28

    Using x-ray photoelectron spectroscopy, we investigated the band alignment of a Ag/poly(3-hexylthiophene-2,5-diyl) (P3HT)/ZnO photovoltaic structure. At the P3HT/ZnO interface, a band bending of P3HT and a short surface depletion layer of ZnO were observed. The offset between the highest occupied molecular orbital of P3HT and the conduction band minimum of ZnO at the interface contributed to the open circuit voltage (Voc) was estimated to be approximately 1.5 {+-} 0.1 eV, which was bigger than that of the electrically measured effective Voc of P3HT/ZnO photovoltaic devices, meaning that the P3HT/ZnO photovoltaic structure has the potential to provide improved photovoltaic properties.

  1. Mini-Dirac cones in the band structure of a copper intercalated epitaxial graphene superlattice

    NASA Astrophysics Data System (ADS)

    Forti, S.; Stöhr, A.; Zakharov, A. A.; Coletti, C.; Emtsev, K. V.; Starke, U.

    2016-09-01

    The electronic band structure of an epitaxial graphene superlattice, generated by intercalating a monolayer of Cu atoms, is directly imaged by angle-resolved photoelectron spectroscopy. The 3.2 nm lateral period of the superlattice is induced by a varying registry between the graphene honeycomb and the Cu atoms as imposed by the heteroepitaxial interface Cu/SiC. The carbon atoms experience a lateral potential across the supercell of an estimated value of about 65 meV. The potential leads to strong energy renormalization in the band structure of the graphene layer and the emergence of mini-Dirac cones. The mini-cones’ band velocity is reduced to about half of graphene's Fermi velocity. Notably, the ordering of the interfacial Cu atoms can be reversibly blocked by mild annealing. The superlattice indeed disappears at ∼220 °C.

  2. Interacting quasi-band theory for electronic states in compound semiconductor alloys: Wurtzite structure

    NASA Astrophysics Data System (ADS)

    Kishi, Ayaka; Oda, Masato; Shinozuka, Yuzo

    2016-05-01

    This paper reports on the electronic states of compound semiconductor alloys of wurtzite structure calculated by the recently proposed interacting quasi-band (IQB) theory combined with empirical sp3 tight-binding models. Solving derived quasi-Hamiltonian 24 × 24 matrix that is characterized by the crystal parameters of the constituents facilitates the calculation of the conduction and valence bands of wurtzite alloys for arbitrary concentrations under a unified scheme. The theory is applied to III-V and II-VI wurtzite alloys: cation-substituted Al1- x Ga x N and Ga1- x In x N and anion-substituted CdS1- x Se x and ZnO1- x S x . The obtained results agree well with the experimental data, and are discussed in terms of mutual mixing between the quasi-localized states (QLS) and quasi-average bands (QAB): the latter bands are approximately given by the virtual crystal approximation (VCA). The changes in the valence and conduction bands, and the origin of the band gap bowing are discussed on the basis of mixing character.

  3. Interacting quasi-band theory for electronic states in compound semiconductor alloys: Wurtzite structure

    NASA Astrophysics Data System (ADS)

    Kishi, Ayaka; Oda, Masato; Shinozuka, Yuzo

    2016-05-01

    This paper reports on the electronic states of compound semiconductor alloys of wurtzite structure calculated by the recently proposed interacting quasi-band (IQB) theory combined with empirical sp3 tight-binding models. Solving derived quasi-Hamiltonian 24 × 24 matrix that is characterized by the crystal parameters of the constituents facilitates the calculation of the conduction and valence bands of wurtzite alloys for arbitrary concentrations under a unified scheme. The theory is applied to III–V and II–VI wurtzite alloys: cation-substituted Al1‑ x Ga x N and Ga1‑ x In x N and anion-substituted CdS1‑ x Se x and ZnO1‑ x S x . The obtained results agree well with the experimental data, and are discussed in terms of mutual mixing between the quasi-localized states (QLS) and quasi-average bands (QAB): the latter bands are approximately given by the virtual crystal approximation (VCA). The changes in the valence and conduction bands, and the origin of the band gap bowing are discussed on the basis of mixing character.

  4. Electronic structure descriptor for the discovery of narrow-band red-emitting phosphors

    DOE PAGES

    Wang, Zhenbin; Chu, Iek -Heng; Zhou, Fei; Ong, Shyue Ping

    2016-05-09

    Narrow-band red-emitting phosphors are a critical component of phosphor-converted light-emitting diodes for highly efficient illumination-grade lighting. In this work, we report the discovery of a quantitative descriptor for narrow-band Eu2+-activated emission identified through a comparison of the electronic structures of known narrow-band and broad-band phosphors. We find that a narrow emission bandwidth is characterized by a large splitting of more than 0.1 eV between the two highest Eu2+ 4f7 bands. By incorporating this descriptor in a high-throughput first-principles screening of 2259 nitride compounds, we identify five promising new nitride hosts for Eu2+-activated red-emitting phosphors that are predicted to exhibit goodmore » chemical stability, thermal quenching resistance, and quantum efficiency, as well as narrow-band emission. Lastly, our findings provide important insights into the emission characteristics of rare-earth activators in phosphor hosts and a general strategy to the discovery of phosphors with a desired emission peak and bandwidth.« less

  5. Band structures of 182Os studied by GCM based on 3D-CHFB

    NASA Astrophysics Data System (ADS)

    Horibata, Takatoshi; Oi, Makito; Onishi, Naoki; Ansari, Ahmad

    1999-02-01

    Band structure properties of 182Os are investigated through a particle number and angular momentum constrained generator coordinate (GCM) calculation based on self-consistent threedimensional cranking solutions. From the analysis of the wave function of the lowest GCM solution, we confirm that this nucleus shows a tilted rotational motion in its yrast states, at least with the present set of force parameters of the pairing-plus-quadrupole interaction Hamiltonian. A close examination of the behaviour of the other GCM solutions reveals a sign of a possible occurrence of multi-band crossing in the nucleus. We have also found a new potential curve along the prime meridian on the globe of the J = 18 h̷ sphere. Along this new solution the characters of proton and neutron gap parameters get interchanged. Namely, Δ p almost vanishes while Δ n grows to a finite value close to the one corresponding to the principal axis rotation (PAR). A state in the new solution curve at the PAR point turns out to have almost the same characteristic features of an yrare s-band state which is located just above the g-band in our calculation. This fact suggests a new type of seesaw vibrational mode of the proton and the neutron pairing, occurring through a wobbling motion. This mode is considered to bridge the g-band states and the s-band states in the backbending region.

  6. Automatically inferred Markov network models for classification of chromosomal band pattern structures.

    PubMed

    Granum, E; Thomason, M G

    1990-01-01

    A structural pattern recognition approach to the analysis and classification of metaphase chromosome band patterns is presented. An operational method of representing band pattern profiles as sharp edged idealized profiles is outlined. These profiles are nonlinearly scaled to a few, but fixed number of "density" levels. Previous experience has shown that profiles of six levels are appropriate and that the differences between successive bands in these profiles are suitable for classification. String representations, which focuses on the sequences of transitions between local band pattern levels, are derived from such "difference profiles." A method of syntactic analysis of the band transition sequences by dynamic programming for optimal (maximal probability) string-to-network alignments is described. It develops automatic data-driven inference of band pattern models (Markov networks) per class, and uses these models for classification. The method does not use centromere information, but assumes the p-q-orientation of the band pattern profiles to be known a priori. It is experimentally established that the method can build Markov network models, which, when used for classification, show a recognition rate of about 92% on test data. The experiments used 200 samples (chromosome profiles) for each of the 22 autosome chromosome types and are designed to also investigate various classifier design problems. It is found that the use of a priori knowledge of Denver Group assignment only improved classification by 1 or 2%. A scheme for typewise normalization of the class relationship measures prove useful, partly through improvements on average results and partly through a more evenly distributed error pattern. The choice of reference of the p-q-orientation of the band patterns is found to be unimportant, and results of timing of the execution time of the analysis show that recent and efficient implementations can process one cell in less than 1 min on current standard

  7. Three-Dimensional Structure of Vertebrate Muscle Z-Band: The Small-Square Lattice Z-Band in Rat Cardiac Muscle

    PubMed Central

    Burgoyne, Thomas; Morris, Edward P.; Luther, Pradeep K.

    2015-01-01

    The Z-band in vertebrate striated muscle crosslinks actin filaments of opposite polarity from adjoining sarcomeres and transmits tension along myofibrils during muscular contraction. It is also the location of a number of proteins involved in signalling and myofibrillogenesis; mutations in these proteins lead to myopathies. Understanding the high-resolution structure of the Z-band will help us understand its role in muscle contraction and the role of these proteins in the function of muscle. The appearance of the Z-band in transverse-section electron micrographs typically resembles a small-square lattice or a basketweave appearance. In longitudinal sections, the Z-band width varies more with muscle type than species: slow skeletal and cardiac muscles have wider Z-bands than fast skeletal muscles. As the Z-band is periodic, Fourier methods have previously been used for three-dimensional structural analysis. To cope with variations in the periodic structure of the Z-band, we have used subtomogram averaging of tomograms of rat cardiac muscle in which subtomograms are extracted and compared and similar ones are averaged. We show that the Z-band comprises four to six layers of links, presumably α-actinin, linking antiparallel overlapping ends of the actin filaments from the adjoining sarcomeres. The reconstruction shows that the terminal 5–7 nm of the actin filaments within the Z-band is devoid of any α-actinin links and is likely to be the location of capping protein CapZ. PMID:26362007

  8. Evolution of structural relaxation spectra of glycerol within the gigahertz band

    NASA Astrophysics Data System (ADS)

    Franosch, T.; Göauttze, W.; Mayr, M. R.; Singh, A. P.

    1997-03-01

    The structural relaxation spectra and the crossover from relaxation to oscillation dynamics, as measured by Wuttke et al. [Phys. Rev. Lett. 72, 3052 (1994)] for glycerol within the GHz band by depolarized light scattering, are described by the solutions of a schematic mode coupling theory model. The applicability of scaling laws for the discussion of the model solutions is considered.

  9. k.p Parameters with Accuracy Control from Preexistent First-Principles Band Structure Calculations

    NASA Astrophysics Data System (ADS)

    Sipahi, Guilherme; Bastos, Carlos M. O.; Sabino, Fernando P.; Faria Junior, Paulo E.; de Campos, Tiago; da Silva, Juarez L. F.

    The k.p method is a successful approach to obtain band structure, optical and transport properties of semiconductors. It overtakes the ab initio methods in confined systems due to its low computational cost since it is a continuum method that does not require all the atoms' orbital information. From an effective one-electron Hamiltonian, the k.p matrix representation can be calculated using perturbation theory and the parameters identified by symmetry arguments. The parameters determination, however, needs a complementary approach. In this paper, we developed a general method to extract the k.p parameters from preexistent band structures of bulk materials that is not limited by the crystal symmetry or by the model. To demonstrate our approach, we applied it to zinc blende GaAs band structure calculated by hybrid density functional theory within the Heyd-Scuseria-Ernzerhof functional (DFT-HSE), for the usual 8 ×8 k.p Hamiltonian. Our parameters reproduced the DFT-HSE band structure with great accuracy up to 20% of the first Brillouin zone (FBZ). Furthermore, for fitting regions ranging from 7-20% of FBZ, the parameters lie inside the range of values reported by the most reliable studies in the literature. The authors acknowledge financial support from the Brazilian agencies CNPq (Grant #246549/2012-2) and FAPESP (Grants #2011/19333-4, #2012/05618-0 and #2013/23393-8).

  10. Design of UWB monopole antenna with dual notched bands using one modified electromagnetic-bandgap structure.

    PubMed

    Liu, Hao; Xu, Ziqiang

    2013-01-01

    A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.1-10.6 GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX) and the wireless local area network (WLAN) at 3.5 GHz and 5.5 GHz, respectively. PMID:24170984

  11. Doping and strain dependence of the electronic band structure in Ge and GeSn alloys

    NASA Astrophysics Data System (ADS)

    Xu, Chi; Gallagher, James; Senaratne, Charutha; Brown, Christopher; Fernando, Nalin; Zollner, Stefan; Kouvetakis, John; Menendez, Jose

    2015-03-01

    A systematic study of the effect of dopants and strain on the electronic structure of Ge and GeSn alloys is presented. Samples were grown by UHV-CVD on Ge-buffered Si using Ge3H8 and SnD4 as the sources of Ge and Sn, and B2H6/P(GeH3)3 as dopants. High-energy critical points in the joint-density of electronic states were studied using spectroscopic ellipsometry, which yields detailed information on the strain and doping dependence of the so-called E1, E1 +Δ1 , E0' and E2 transitions. The corresponding dependencies of the lowest direct band gap E0 and the fundamental indirect band gap Eindwere studied via room-T photoluminescence spectroscopy. Of particular interest for this work were the determination of deformation potentials, band gap renormalization effects, Burstein-Moss shifts due to the presence of carriers at band minima, and the dependence of other critical point parameters, such as amplitudes and phase angles, on the doping concentration. The selective blocking of transitions due to high doping makes it possible to investigate the precise k-space location of critical points. These studies are complemented with detailed band-structure calculations within a full-zone k-dot- p approach. Supported by AFOSR under DOD AFOSR FA9550-12-1-0208 and DOD AFOSR FA9550-13-1-0022.

  12. Multiple-Scale Pattern Recognition Applied to Faint Intergranular G-band Structures

    NASA Astrophysics Data System (ADS)

    Bovelet, B.; Wiehr, E.

    2007-07-01

    Small-scale solar magnetic flux concentrations are studied in two-dimensional G-band images at very high spatial resolution and compared with Ca ii H enhancements. Among 970 small-sized G-band intergranular structures (IgS), 45% are co-spatial with isolated locations of Ca ii H excess and thus considered as magnetic (MIgS); they may be even twice as frequent as the known G-band bright points. The IgS are recognized in the G-band image by a new algorithm operating in four steps: (1) A set of equidistant detection levels yields a pattern of primary “cells”; (2) for each cell, the intrinsic intensity profile is normalized to its brightest pixel; (3) the cell sizes are shrunk by a unitary single-intensity clip; (4) features in contact at an appropriate reference level are merged by removal of the respective common dividing lines. Optionally, adjoining structures may be excluded from this merging process ( e.g., chains of segmented IgS), referring to the parameterized number and intensity of those pixels where enveloping feature contours overlap. From the thus recognized IgS pattern, MIgS are then selected by their local Ca ii H contrast and their mean G-band-to-continuum brightness ratio.

  13. Design of UWB monopole antenna with dual notched bands using one modified electromagnetic-bandgap structure.

    PubMed

    Liu, Hao; Xu, Ziqiang

    2013-01-01

    A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.1-10.6 GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX) and the wireless local area network (WLAN) at 3.5 GHz and 5.5 GHz, respectively.

  14. Valley-dependent band structure and valley polarization in periodically modulated graphene

    NASA Astrophysics Data System (ADS)

    Lu, Wei-Tao

    2016-08-01

    The valley-dependent energy band and transport property of graphene under a periodic magnetic-strained field are studied, where the time-reversal symmetry is broken and the valley degeneracy is lifted. The considered superlattice is composed of two different barriers, providing more degrees of freedom for engineering the electronic structure. The electrons near the K and K' valleys are dominated by different effective superlattices. It is found that the energy bands for both valleys are symmetric with respect to ky=-(AM+ξ AS) /4 under the symmetric superlattices. More finite-energy Dirac points, more prominent collimation behavior, and new crossing points are found for K' valley. The degenerate miniband near the K valley splits into two subminibands and produces a new band gap under the asymmetric superlattices. The velocity for the K' valley is greatly renormalized compared with the K valley, and so we can achieve a finite velocity for the K valley while the velocity for the K' valley is zero. Especially, the miniband and band gap could be manipulated independently, leading to an increase of the conductance. The characteristics of the band structure are reflected in the transmission spectra. The Dirac points and the crossing points appear as pronounced peaks in transmission. A remarkable valley polarization is obtained which is robust to the disorder and can be controlled by the strain, the period, and the voltage.

  15. Effects of strain on the band structure of group-III nitrides

    NASA Astrophysics Data System (ADS)

    Yan, Qimin; Rinke, Patrick; Janotti, Anderson; Scheffler, Matthias; Van de Walle, Chris G.

    2014-09-01

    We present a systematic study of strain effects on the electronic band structure of the group-III-nitrides (AlN, GaN and InN) in the wurtzite phase. The calculations are based on density functional theory with band-gap-corrected approaches including the Heyd-Scuseria-Ernzerhof hybrid functional (HSE) and quasiparticle G0W0 methods. We study strain effects under realistic strain conditions, hydrostatic pressure, and biaxial stress. The strain-induced modification of the band structures is found to be nonlinear; transition energies and crystal-field splittings show a strong nonlinear behavior under biaxial stress. For the linear regime around the experimental lattice parameters, we present a complete set of deformation potentials (acz, act, D1, D2, D3, D4, D5, D6) that allows us to predict the band positions of group-III nitrides and their alloys (InGaN and AlGaN) under realistic strain conditions. The benchmarking G0W0 results for GaN agree well with the HSE data and indicate that HSE provides an appropriate description for the band structures of nitrides. We present a systematic study of strain effects on the electronic band structure of the group-III nitrides (AlN, GaN, and InN). We quantify the nonlinearity of strain effects by introducing a set of bowing parameters. We apply the calculated deformation potentials to the prediction of strain effects on transition energies and valence-band structures of InGaN alloys and quantum wells (QWs) grown on GaN, in various orientations (including c-plane, m-plane, and semipolar). The calculated band gap bowing parameters, including the strain effect for c-plane InGaN, agree well with the results obtained by hybrid functional alloy calculations. For semipolar InGaN QWs grown in (202¯1), (303¯1), and (303¯1¯) orientations, our calculated deformation potentials have provided results for polarization ratios in good agreement with the experimental observations, providing further confidence in the accuracy of our values.

  16. Quasiparticle bands and structural phase transition of iron from Gutzwiller density-functional theory

    NASA Astrophysics Data System (ADS)

    Schickling, Tobias; Bünemann, Jörg; Gebhard, Florian; Boeri, Lilia

    2016-05-01

    We use the Gutzwiller density-functional theory to calculate ground-state properties and band structures of iron in its body-centered-cubic (bcc) and hexagonal-close-packed (hcp) phases. For a Hubbard interaction U =9 eV and Hund's-rule coupling J =0.54 eV , we reproduce the lattice parameter, magnetic moment, and bulk modulus of bcc iron. For these parameters, bcc is the ground-state lattice structure at ambient pressure up to a pressure of pc=41 GPa where a transition to the nonmagnetic hcp structure is predicted, in qualitative agreement with experiment (pcexp=10 ,...,15 GPa ) . The calculated band structure for bcc iron is in good agreement with ARPES measurements. The agreement improves when we perturbatively include the spin-orbit coupling.

  17. Nonlinear optical response of semiconductor-nanocrystals-embedded photonic band gap structure

    SciTech Connect

    Liao, Chen; Zhang, Huichao; Tang, Luping; Zhou, Zhiqiang; Lv, Changgui; Cui, Yiping; Zhang, Jiayu

    2014-04-28

    Colloidal CdSe/ZnS core/shell nanocrystals (NCs), which were dispersed in SiO{sub 2} sol, were utilized to fabricate a SiO{sub 2}:NCs/TiO{sub 2} all-dielectric photonic band gap (PBG) structure. The third-order nonlinear refractive index (n{sub 2}) of the PBG structure was nearly triple of that of the SiO{sub 2}:NCs film due to the local field enhancement in the PBG structure. The photoinduced change in refractive index (Δn) could shift the PBG band edge, so the PBG structure would show significant transmission modification, whose transmission change was ∼17 folds of that of the SiO{sub 2}:NCs film. Under excitation of a 30 GW/cm{sup 2} femtosecond laser beam, a transmission decrease of 80% was realized.

  18. Ferromagnetism and the electronic band structure in (Ga,Mn)(Bi,As) epitaxial layers

    NASA Astrophysics Data System (ADS)

    Yastrubchak, O.; Sadowski, J.; Gluba, L.; Domagala, J. Z.; Rawski, M.; Żuk, J.; Kulik, M.; Andrearczyk, T.; Wosinski, T.

    2014-08-01

    Impact of Bi incorporation into (Ga,Mn)As layers on their electronic- and band-structures as well as their magnetic and structural properties has been studied. Homogenous (Ga,Mn)(Bi,As) layers of high structural perfection have been grown by the low-temperature molecular-beam epitaxy technique. Post-growth annealing treatment of the layers results in an improvement of their structural and magnetic properties and an increase in the hole concentration in the layers. The modulation photoreflectance spectroscopy results are consistent with the valence-band model of hole-mediated ferromagnetism in the layers. This material combines the properties of (Ga,Mn)As and Ga(Bi,As) ternary compounds and offers the possibility of tuning its electrical and magnetic properties by controlling the alloy composition.

  19. Ferromagnetism and the electronic band structure in (Ga,Mn)(Bi,As) epitaxial layers

    SciTech Connect

    Yastrubchak, O.; Sadowski, J.; Domagala, J. Z.; Andrearczyk, T.; Wosinski, T.

    2014-08-18

    Impact of Bi incorporation into (Ga,Mn)As layers on their electronic- and band-structures as well as their magnetic and structural properties has been studied. Homogenous (Ga,Mn)(Bi,As) layers of high structural perfection have been grown by the low-temperature molecular-beam epitaxy technique. Post-growth annealing treatment of the layers results in an improvement of their structural and magnetic properties and an increase in the hole concentration in the layers. The modulation photoreflectance spectroscopy results are consistent with the valence-band model of hole-mediated ferromagnetism in the layers. This material combines the properties of (Ga,Mn)As and Ga(Bi,As) ternary compounds and offers the possibility of tuning its electrical and magnetic properties by controlling the alloy composition.

  20. Electromagnetic wave band structure due to surface plasmon resonances in a complex plasma.

    PubMed

    Vladimirov, S V; Ishihara, O

    2016-07-01

    The dielectric properties of complex plasma containing either metal or dielectric spherical inclusions (macroparticles, dust) are investigated. We focus on surface plasmon resonances on the macroparticle surfaces and their effect on electromagnetic wave propagation. It is demonstrated that the presence of surface plasmon oscillations can significantly modify plasma electromagnetic properties by resonances and cutoffs in the effective permittivity. This leads to related branches of electromagnetic waves and to the wave band gaps. The conditions necessary to observe the band-gap structure in laboratory dusty plasma and/or space (cosmic) dusty plasmas are discussed.

  1. Electromagnetic wave band structure due to surface plasmon resonances in a complex plasma.

    PubMed

    Vladimirov, S V; Ishihara, O

    2016-07-01

    The dielectric properties of complex plasma containing either metal or dielectric spherical inclusions (macroparticles, dust) are investigated. We focus on surface plasmon resonances on the macroparticle surfaces and their effect on electromagnetic wave propagation. It is demonstrated that the presence of surface plasmon oscillations can significantly modify plasma electromagnetic properties by resonances and cutoffs in the effective permittivity. This leads to related branches of electromagnetic waves and to the wave band gaps. The conditions necessary to observe the band-gap structure in laboratory dusty plasma and/or space (cosmic) dusty plasmas are discussed. PMID:27575225

  2. Investigation of band structure of {sup 103,105}Rh using microscopic computational technique

    SciTech Connect

    Kumar, Amit; Singh, Suram; Bharti, Arun

    2015-08-28

    The high-spin structure in {sup 61}Cu nucleus is studied in terms of effective two body interaction. In order to take into account the deformed BCS basis, the basis states are expanded in terms of the core eigenfunctions. Yrast band with some other bands havew been obtained and back-bending in moment of inertia has also been calculated and compared with the available experimental data for {sup 61}Cu nucleus. On comparing the available experimental as well as other theoretical data, it is found that the treatment with PSM provides a satisfactory explanation of the available data.

  3. Topological band order, structural, electronic and optical properties of XPdBi (X = Lu, Sc) compounds

    NASA Astrophysics Data System (ADS)

    Narimani, M.; Nourbakhsh, Z.

    2016-05-01

    In this paper, the structural, electronic and optical properties of LuPdBi and ScPdBi compounds are investigated using the density functional theory by WIEN2K package within the generalized gradient approximation, local density approximation, Engel-Vosco generalized gradient approximations and modified Becke-Johnson potential approaches. The topological phases and band orders of these compounds are studied. The effect of pressure on band inversion strength, electron density of states and the linear coefficient of the electronic specific heat of these compounds is investigated. Furthermore, the effect of pressure on real and imaginary parts of dielectric function, absorption and reflectivity coefficients of these compounds is studied.

  4. B4N and Fe3BN nitrides bands structure and theoretical determination of bulk modulus

    NASA Astrophysics Data System (ADS)

    dos Santos, A. V.

    2007-06-01

    With the evolution of material science there was some technological evolution as well as the need of finding new links which could be applied to diverse areas of knowledge. Thus, in this article, we study nitrides bands structures which contain boron, in two different stoichiometries Fe3BN and B4N. The choice of these compounds is meant to plan new links and to understand nitrides fundamental state properties facing these new crystalline structures. In order to resolve the compound band structure we used the method of linear Muffin Tin orbital (LMTO), with atomic sphere approximation (ASA). By using this method we obtained the energy of formation as a function of the lattice parameter as one of the results. We find the equilibrium lattice parameter of 6.9755 a.u., for the Fe3BN nitride, and in B4N, we have 6.8589 a.u. We also discuss in this article the charge transference between sites and the influence of pressure on the compound properties, as well as the Bulk modulus that is 239.82 GPa for Fe3BN and 105.48 GPa for B4N. We show the behaviour of the density of states (DOS) of the new band structure found for the proposed crystalline structure Fe3BN, in which the B atom replace the Fe atom in the corner of the structure γ‧- Fe4N.

  5. Structural characteristic correlated to the electronic band gap in Mo S2

    NASA Astrophysics Data System (ADS)

    Chu, Shengqi; Park, Changyong; Shen, Guoyin

    2016-07-01

    The structural evolution with pressure in bulk Mo S2 has been investigated by high-pressure x-ray diffraction using synchrotron radiation. We found that the out-of-plane S-Mo-S bond angle θ increases and that in in-plane angle ϕ decreases linearly with increasing pressure across the known semiconducting-to-metal phase transition, whereas the Mo-S bond length and the S-Mo-S trilayer thickness display only little change. Extrapolating the experimental result along the in-plane lattice parameter with pressure, both S-Mo-S bond angles trend to those found in monolayer Mo S2 , which manifests as a structural characteristic closely correlating the electronic band gap of Mo S2 to its physical forms and phases, e.g., monolayer as direct band gap semiconductor, multilayer or bulk as indirect band gap semiconductor, and high-pressure (>19 GPa ) bulk form as metal. Combined with the effects of bond strength and van der Waals interlayer interactions, the structural correlations between the characteristic bond angle and electronic band gaps are readily extendible to other transition metal dichalcogenide systems (M X2 , where M =Mo , W and X =S , Se, Te).

  6. Metal-induced gap states in ferroelectric capacitors and its relationship with complex band structures

    NASA Astrophysics Data System (ADS)

    Junquera, Javier; Aguado-Puente, Pablo

    2013-03-01

    At metal-isulator interfaces, the metallic wave functions with an energy eigenvalue within the band gap decay exponentially inside the dielectric (metal-induced gap states, MIGS). These MIGS can be actually regarded as Bloch functions with an associated complex wave vector. Usually only real values of the wave vectors are discussed in text books, since infinite periodicity is assumed and, in that situation, wave functions growing exponentially in any direction would not be physically valid. However, localized wave functions with an exponential decay are indeed perfectly valid solution of the Schrodinger equation in the presence of defects, surfaces or interfaces. For this reason, properties of MIGS have been typically discussed in terms of the complex band structure of bulk materials. The probable dependence on the interface particulars has been rarely taken into account explicitly due to the difficulties to include them into the model or simulations. We aim to characterize from first-principles simulations the MIGS in realistic ferroelectric capacitors and their connection with the complex band structure of the ferroelectric material. We emphasize the influence of the real interface beyond the complex band structure of bulk materials. Financial support provided by MICINN Grant FIS2009-12721-C04-02, and by the European Union Grant No. CP-FP 228989-2 ``OxIDes''. Computer resources provided by the RES.

  7. Electronic band structure effects in the stopping of protons in copper

    NASA Astrophysics Data System (ADS)

    Quashie, Edwin E.; Saha, Bidhan C.; Correa, Alfredo A.

    2016-10-01

    We present an ab initio study of the electronic stopping power of protons in copper over a wide range of proton velocities v =0.02 -10 a .u . where we take into account nonlinear effects. Time-dependent density functional theory coupled with molecular dynamics is used to study electronic excitations produced by energetic protons. A plane-wave pseudopotential scheme is employed to solve the time-dependent Kohn-Sham equations for a moving ion in a periodic crystal. The electronic excitations and the band structure determine the stopping power of the material and alter the interatomic forces for both channeling and off-channeling trajectories. Our off-channeling results are in quantitative agreement with experiments, and at low velocity they unveil a crossover region of superlinear velocity dependence (with a power of ˜1.5 ) in the velocity range v =0.07 -0.3 a .u . , which we associate to the copper crystalline electronic band structure. The results are rationalized by simple band models connecting two separate regimes. We find that the limit of electronic stopping v →0 is not as simple as phenomenological models suggest and it is plagued by band-structure effects.

  8. G0W0 band structure of CdWO4.

    PubMed

    Laasner, Raul

    2014-03-26

    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. PMID:24599225

  9. Exploring the Electronic Band Structure of Organometal Halide Perovskite via Photoluminescence Anisotropy of Individual Nanocrystals.

    PubMed

    Täuber, Daniela; Dobrovolsky, Alexander; Camacho, Rafael; Scheblykin, Ivan G

    2016-08-10

    Understanding electronic processes in organometal halide perovskites, flourishing photovoltaic, and emitting materials requires unraveling the origin of their electronic transitions. Light polarization studies can provide important information regarding transition dipole moment orientations. Investigating individual methylammonium lead triiodide perovskite nanocrystals enabled us to detect the polarization of photoluminescence intensity and photoluminescence excitation, hidden in bulk samples by ensemble averaging. Polarization properties of the crystals were correlated with their photoluminescence spectra and electron microscopy images. We propose that distortion of PbI6 octahedra leads to peculiarities of the electronic band structure close to the band-edge. Namely, the lowest band transition possesses a transition dipole moment along the apical Pb-I-Pb bond resulting in polarized photoluminescence. Excitation of photoluminescence above the bandgap is unpolarized because it involves molecular orbitals delocalized both in the apical and equatorial directions of the perovskite octahedron. Trap-assisted emission at 77 K, rather surprisingly, was polarized similar to the bandgap emission.

  10. Band gap and electronic structure of MgSiN{sub 2}

    SciTech Connect

    Quirk, J. B. Råsander, M.; McGilvery, C. M.; Moram, M. A.; Palgrave, R.

    2014-09-15

    Density functional theory calculations and electron energy loss spectroscopy indicate that the electronic structure of ordered orthorhombic MgSiN{sub 2} is similar to that of wurtzite AlN. A band gap of 5.7 eV was calculated for both MgSiN{sub 2} (indirect) and AlN (direct) using the Heyd-Scuseria-Ernzerhof approximation. Correction with respect to the experimental room-temperature band gap of AlN indicates that the true band gap of MgSiN{sub 2} is 6.2 eV. MgSiN{sub 2} has an additional direct gap of 6.3 eV at the Γ point.

  11. An analysis of five negative sprite-parent discharges and their associated thunderstorm charge structures

    NASA Astrophysics Data System (ADS)

    Boggs, Levi D.; Liu, Ningyu; Splitt, Michael; Lazarus, Steven; Glenn, Chad; Rassoul, Hamid; Cummer, Steven A.

    2016-01-01

    In this study we analyze the discharge morphologies of five confirmed negative sprite-parent discharges and the associated charge structures of the thunderstorms that produced them. The negative sprite-parent lightning took place in two thunderstorms that were associated with a tropical disturbance in east central and south Florida. The first thunderstorm, which moved onshore in east central Florida, produced four of the five negative sprite-parent discharges within a period of 17 min, as it made landfall from the Atlantic Ocean. These negative sprite-parents were composed of bolt-from-the-blue (BFB), hybrid intracloud-negative cloud-to-ground (IC-NCG), and multicell IC-NCGs discharges. The second thunderstorm, which occurred inland over south Florida, produced a negative sprite-parent that was a probable hybrid IC-NCG discharge and two negative gigantic jets (GJs). Weakened upper positive charge with very large midlevel negative charge was inferred for both convective cells that initiated the negative-sprite-parent discharges. Our study suggests tall, intense convective systems with high wind shear at the middle to upper regions of the cloud accompanied by low cloud-to-ground (CG) flash rates promote these charge structures. The excess amount of midlevel negative charge results in these CG discharges transferring much more charge to ground than typical negative CG discharges. We find that BFB discharges prefer an asymmetrical charge structure that brings the negative leader exiting the upper positive charge region closer to the lateral positive screening charge layer. This may be the main factor in determining whether a negative leader exiting the upper positive region of the thundercloud forms a BFB or GJ.

  12. Photonic stop bands in quasi-random nanoporous anodic alumina structures

    NASA Astrophysics Data System (ADS)

    Maksymov, Ivan; Ferré-Borrull, Josep; Pallarès, Josep; Marsal, Lluis F.

    2012-10-01

    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.

  13. Band structure and reflectivity of omnidirectional Si-based mirrors with a Gaussian profile refractive index

    NASA Astrophysics Data System (ADS)

    Arriaga, J.; Saldaña, X. I.

    2006-08-01

    Using the transfer matrix method we calculate the band structure for a one-dimensional photonic crystal consisting of alternating layers of two dielectric materials A and B with refractive indices nA and nB, respectively. The refractive index of layer A is constant and the refractive index for layer B varies according to the envelope of a Gaussian function. We find that under certain circumstances it is possible to obtain a 100% reflectivity for both polarizations (TE and TM) and any value of the incident angle of the electromagnetic waves. The interval of maximum reflectivity coincides with the photonic band gap of the structure. By an adequate selection of the parameters forming the structure, it is possible to tune the interval of frequencies with maximum reflectivity. This could be used in the fabrication of the so-called omnidirectional mirrors.

  14. Band structure and itinerant magnetism in quantum critical NbFe2

    SciTech Connect

    Subedi, A. P.; Singh, David J

    2010-01-01

    We report first-principles calculations of the band structure and magnetic ordering in the C14 Laves phase compound NbFe{sub 2}. The magnetism is itinerant in the sense that the moments are highly dependent on ordering. We find an overestimation of the magnetic tendency within the local spin-density approximation, similar to other metals near magnetic quantum critical points. We also find a competition between different magnetic states due to band-structure effects. These lead to competing magnetic tendencies due to competing interlayer interactions, one favoring a ferrimagnetic solution and the other an antiferromagnetic state. While the structure contains Kagome lattice sheets, which could, in principle, lead to strong magnetic frustration, the calculations do not show dominant nearest-neighbor antiferromagnetic interactions within these sheets. These results are discussed in relation to experimental observations.

  15. Band structure and electron-phonon coupling in H3S : A tight-binding model

    NASA Astrophysics Data System (ADS)

    Ortenzi, L.; Cappelluti, E.; Pietronero, L.

    2016-08-01

    We present a robust tight-binding description, based on the Slater-Koster formalism, of the band structure of H3S in the Im3 ¯m structure, stable in the range of pressure P =180 -220 GPa. We show that the interatomic hopping between the 3 s and 3 p orbitals (and partially between the 3 p orbitals themselves) of sulfur is fundamental to capturing the relevant physics associated with the Van Hove singularities close to the Fermi level. Comparing the model so defined with density functional theory calculations we obtain a very good agreement not only of the overall band structure but also of the low-energy states and the Fermi surface properties. The description in terms of Slater-Koster parameters permits us also to evaluate at a microscopic level a hopping-resolved linear electron-lattice coupling which can be employed for further tight-binding analyses also at a local scale.

  16. Engineered band structure for an enhanced performance on quantum dot-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Jin, Bin Bin; Wang, Ye Feng; Wei, Dong; Cui, Bin; Chen, Yu; Zeng, Jing Hui

    2016-06-01

    A photon-to-current efficiency of 2.93% is received for the Mn-doped CdS (MCdS)-quantum dot sensitized solar cells (QDSSCs) using Mn:ZnO (MZnO) nanowire as photoanode. Hydrothermal synthesized MZnO are spin-coated on fluorine doped tin oxide (FTO) glass with P25 paste to serve as photoanode after calcinations. MCdS was deposited on the MZnO film by the successive ionic layer adsorption and reaction method. The long lived excitation energy state of Mn2+ is located inside the conduction band in the wide bandgap ZnO and under the conduction band of CdS, which increases the energetic overlap of donor and acceptor states, reducing the "loss-in-potential," inhibiting charge recombination, and accelerating electron injection. The engineered band structure is well reflected by the electrochemical band detected using cyclic voltammetry. Cell performances are evidenced by current density-voltage (J-V) traces, diffuse reflectance spectra, transient PL spectroscopy, and incident photon to current conversion efficiency characterizations. Further coating of CdSe on MZnO/MCdS electrode expands the light absorption band of the sensitizer, an efficiency of 4.94% is received for QDSSCs.

  17. Semianalytical formulation on the scattering of proximity equilibration cell closed ring photonic band gap structures

    NASA Astrophysics Data System (ADS)

    Liu, Yunhong; Alexopoulos, Nicolaos G.

    2007-12-01

    A novel semianalytical methodology is used to analyze a periodic array of printed metallic closed ring elements in a multilayered dielectric structure. This approach is unique in that it is the first methodology capable in modeling structures with resonant implants and interelement dimensions well beyond the effective medium theory. In addition, it yields computational efficiency by 2 orders of magnitude over standard computational methods in computing the scattering parameters for proximity equilibration cell (PEC) closed ring multilayered (electromagnetic band gap and photonic band gap (PBG)) structures. Moreover, it provides physical insight in the implementation of metallic implants for practical applications. This methodology satisfies the Kramers-Kronig relations and causality, and therefore it allows for the development of semianalytical expressions for the composite's wave impedance, index of refraction, as well as the permittivity and permeability parameters accounting for full dispersion. For general artificial multilayered structures (PBG metamaterials) with centrosymmetric scattering matrices, the composite may be replaced by an equivalent homogeneous dispersive magneto-dielectric material and may be used for the design of integrated circuits, filters, and antennas using standard methods. Otherwise, use of the scattering matrix approach to obtain the effective parameters is valid only for semi-infinite structures. The upper band edge is determined by the host material uniquely and the bandwidth is determined by the shunt susceptance for different PEC ring inclusions.

  18. Determination of the valence band structure of an alkali phosphorus oxynitride glass: A synchrotron XPS study on LiPON

    NASA Astrophysics Data System (ADS)

    Schwöbel, André; Precht, Ruben; Motzko, Markus; Carrillo Solano, Mercedes A.; Calvet, Wolfram; Hausbrand, René; Jaegermann, Wolfram

    2014-12-01

    Lithium phosphorus oxynitride (LiPON) is a solid state electrolyte commonly used in thin film batteries (TFBs). Advanced TFBs face the issue of detrimental electrode-electrolyte interlayer formation, related to the electronic structure of the interface. In this contribution, we study the valence band structure of LiPON using resonant photoemission and synchrotron photoemission with variable excitation energies. The identification of different valence band features is done according to the known valence band features of meta- and orthophosphates. Additionally we compare our results with partial density of states simulations from literature. We find that the valence band structure is similar to the known metaphosphates with an additional contribution of nitrogen states at the top of the valence band. From the results we conclude that synchrotron X-ray photoemission (XPS) is a useful tool to study the valence band structure of nitridated alkali phosphate glasses.

  19. Factor Structure and Construct Validity of the Scale for the Assessment of Negative Symptoms.

    ERIC Educational Resources Information Center

    Sayers, Steven L.; And Others

    1996-01-01

    Confirmatory factor analysis (CFA) was used to examine the underlying structure of negative symptoms of schizophrenia as measured by the Scale for the Assessment of Negative Symptoms (SANS). CFA results from the assessment of 401 patients were largely supported by CFA results from a second assessment of 345 patients. (SLD)

  20. Banded structures in electron pitch angle diffusion coefficients from resonant wave-particle interactions

    NASA Astrophysics Data System (ADS)

    Tripathi, A. K.; Singhal, R. P.; Khazanov, G. V.; Avanov, L. A.

    2016-04-01

    Electron pitch angle (Dαα) and momentum (Dpp) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L = 4.6 and 6.8 for electron energies ≤10 keV. Landau (n = 0) resonance and cyclotron harmonic resonances n = ±1, ±2, … ±5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (α) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusion coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n = +1 and n = +2. A major contribution to momentum diffusion coefficients appears from n = +2. However, the banded structures in Dαα and Dpp coefficients appear only in the profile of diffusion coefficients for n = +2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The Dpp diffusion coefficient for ECH waves is one to two orders smaller than Dαα coefficients. For chorus waves, Dpp coefficients are about an order of magnitude smaller than Dαα coefficients for the case n ≠ 0. In case of Landau resonance, the values of Dpp coefficient are generally larger than the values of Dαα coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89° and harmonic resonances n = +1, +2, and +3, whereas for whistler mode waves, the frequencies have been calculated for angle 10° and Landau

  1. Complex band structures of transition metal dichalcogenide monolayers with spin-orbit coupling effects.

    PubMed

    Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

    2016-09-01

    Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2, where M  =  Mo, W; X  =  S, Se, Te) while including spin-orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed.

  2. Small-scale-structure of the interstellar medium probed through diffuse band observations.

    PubMed

    Cordiner, Martin A; Fossey, Stephen J; Smith, Arfon M; Sarre, Peter J

    2006-01-01

    The carriers of the diffuse interstellar band spectrum represent an important baryonic component of the interstellar medium (ISM) and it is expected that their identification will contribute significantly to the understanding of the chemistry and physics of interstellar clouds. It is widely held that the carriers are linked to the presence of dust grains on account of the good correlation of their strengths with interstellar reddening, so they offer an important potential route to improving our understanding of the composition and chemistry of grains and grain surfaces. In addition to the challenge of making the spectral assignments, an important current question concerns the spatial distribution and physical state of interstellar material, with recent observational atomic and molecular line absorption studies suggesting that diffuse clouds are more 'clumpy' than previously thought. We describe here high signal-to-noise optical observations made at the Anglo-Australian Telescope using UCLES that were undertaken to investigate the spatial distribution of diffuse band carriers. We describe the first detection of 'small-scale-structure' in the diffuse band carrier distribution in the ISM, and comment on the possibilities that these data hold for contributing to the solution of the diffuse band problem and our understanding of the nature of small-scale-structure in the diffuse ISM.

  3. Strain effect on graphene nanoribbon carrier statistic in the presence of non-parabolic band structure

    NASA Astrophysics Data System (ADS)

    Izuani Che Rosid, N. A.; Ahmadi, M. T.; Ismail, Razali

    2016-09-01

    The effect of tensile uniaxial strain on the non-parabolic electronic band structure of armchair graphene nanoribbon (AGNR) is investigated. In addition, the density of states and the carrier statistic based on the tight-binding Hamiltonian are modeled analytically. It is found that the property of AGNR in the non-parabolic band region is varied by the strain. The tunable energy band gap in AGNR upon strain at the minimum energy is described for each of n-AGNR families in the non-parabolic approximation. The behavior of AGNR in the presence of strain is attributed to the breakable AGNR electronic band structure, which varies the physical properties from its normality. The linear relation between the energy gap and the electrical properties is featured to further explain the characteristic of the deformed AGNR upon strain. Project supported by the Ministry of Higher Education (MOHE), Malaysia under the Fundamental Research Grant Scheme (FRGS) (Grant No.Q.J130000.7823.4F477). We also thank the Research Management Center (RMC) of Universiti Teknologi Malaysia (UTM) for providing an excellent research environment.

  4. Complex band structures of transition metal dichalcogenide monolayers with spin-orbit coupling effects.

    PubMed

    Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

    2016-09-01

    Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2, where M  =  Mo, W; X  =  S, Se, Te) while including spin-orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed. PMID:27367475

  5. Complex band structures of transition metal dichalcogenide monolayers with spin-orbit coupling effects

    NASA Astrophysics Data System (ADS)

    Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

    2016-09-01

    Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2, where M  =  Mo, W; X  =  S, Se, Te) while including spin-orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed.

  6. Complex band structures of transition metal dichalcogenide monolayers with spin–orbit coupling effects

    NASA Astrophysics Data System (ADS)

    Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

    2016-09-01

    Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2, where M  =  Mo, W; X  =  S, Se, Te) while including spin–orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed.

  7. 17. DETAIL, ROOF STRUCTURE (4 x 5 NEGATIVE) U.S. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    17. DETAIL, ROOF STRUCTURE (4 x 5 NEGATIVE) - U.S. General Services Administration, Central Heating Plant, C & D Streets between Twelfth & Thirteenth Streets Southwest, Washington, District of Columbia, DC

  8. 109. Catalog OPark Structure/Construction & Maintenance, 95 Panorama, Negative Number ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    109. Catalog O-Park Structure/Construction & Maintenance, 95 Panorama, Negative Number P 664b ca. 1930s OLD THORNTON GAP ENTRANCE. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  9. Demonstration of molecular beam epitaxy and a semiconducting band structure for I-Mn-V compounds

    SciTech Connect

    Jungwirth, T.; Novak, V.; Cukr, M.; Zemek, J.; Marti, X.; Horodyska, P.; Nemec, P.; Holy, V.; Maca, F.; Shick, A. B.; Masek, J.; Kuzel, P.; Nemec, I.; Gallagher, B. L.; Campion, R. P.; Foxon, C. T.; Wunderlich, J.

    2011-01-15

    Our ab initio theory calculations predict a semiconducting band structure of I-Mn-V compounds. We demonstrate on LiMnAs that high-quality materials with group-I alkali metals in the crystal structure can be grown by molecular beam epitaxy. Optical measurements on the LiMnAs epilayers are consistent with the theoretical electronic structure. Our calculations also reproduce earlier reports of high antiferromagnetic ordering temperature and predict large, spin-orbit-coupling-induced magnetic anisotropy effects. We propose a strategy for employing antiferromagnetic semiconductors in high-temperature semiconductor spintronics.

  10. Experimental studies of W-band accelerator structures at high field

    NASA Astrophysics Data System (ADS)

    Hill, Marc Edward

    2001-06-01

    A high-gradient electron accelerator is desired for high- energy physics research, where frequency scalings of breakdown and trapping of itinerant beamline particles dictates operation of the accelerator at short wavelengths. The first results of design and test of a high-gradient mm-wave linac with an operating frequency at 91.392 GHz (W-band) are presented. A novel approach to particle acceleration is presented employing a planar, dielectric lined waveguide used for particle acceleration. The traveling wave fields in the planar dielectric accelerator (PDA) are analyzed for an idealized structure, along with a circuit equivalent model used for understanding the structure as a microwave circuit. Along with the W-band accelerator structures, other components designed and tested are high power rf windows, high power attenuators, and a high power squeeze-type phase shifter. The design of the accelerator and its components where eased with the aide of numerical simulations using a finite-difference electromagnetic field solver. Manufacturing considerations of the small, delicate mm-wave components and the steps taken to reach a robust fabrication process are detailed. These devices were characterized under low power using a two-port vector network analyzer to verify tune and match, including measurements of the structures' fields using a bead-pull. The measurements are compared with theory throughout. Addition studies of the W-band structures were performed under high power utilizing a 11.424 GHz electron linac as a current source. Test results include W-band power levels of 200 kW, corresponding to fields in the PDA of over 20 MV/m, higher than any collider. Also presented are the first measurements of the quadrapole component of the monopole accelerating field.

  11. Wide-band-gap wrinkled nanoribbon-like structures in a continuous metallic graphene sheet

    NASA Astrophysics Data System (ADS)

    Li, Si-Yu; Zhou, Mei; Qiao, Jia-Bin; Duan, Wenhui; He, Lin

    2016-08-01

    To generate a moderate band gap in a graphene monolayer is a very important but rather difficult task. A rare working solution of this problem is to cut it into one-dimensional (1D) nanometer-wide ribbons. Here we show that, instead of cutting the graphene monolayer, a wide band gap can be created in a unique 1D strained structure, i.e., a wrinkled graphene-nanoribbon-like (GNR-like) structure, of a continuous graphene sheet via strong hybridization between the graphene and the metal substrate. The wrinkled GNR-like structures with widths of only a few nanometers are observed in a continuous graphene sheet grown on a Rh foil by using thermal strain engineering. Spatially resolved scanning tunneling spectroscopy revealed a band-gap opening of a few hundred meV in the GNR-like structure in an otherwise continuous metallic graphene sheet, directly demonstrating the realization of a metallic-semiconducting-metallic junction entirely in a graphene monolayer.

  12. Rotational Structure of the Ir/fir Bands of Small Pahs

    NASA Astrophysics Data System (ADS)

    Pirali, O.; Gruet, S.; Vervloet, M.; Goubet, M.; Huet, T. R.; Georges, R.; Soulard, P.; Asselin, P.

    2013-06-01

    Accurate spectroscopic measurements in the laboratory of PAH molecules are required to better understand their excitation/relaxation processes which could be responsible for the Unidentified Infrared Bands observed in various objects in space. In particular very few is known concerning the rotational structure of the IR/FIR bands of PAHs. We used the high resolution Fourier Transform interferometer of the AILES beamline of synchrotron SOLEIL to record the rotationally resolved spectra of several IR/FIR vibrational modes of naphthalene (C_{10}H_{8}) and its derivatives: quinoline (C_9H_7N), isoquinoline (C_9H_7N), azulene (C_{10}H_{8}), quinoxaline (C_8H_6N_2), quinazoline (C_8H_6N_2). Firstly, the intense band associated with the ν_{46} CH bending out of plane mode of naphthalene recorded under jet conditions (Jet-AILES experiment developed on the AILES beamline by the IPR-LADIR-PhLAM consortium) revealed transitions involving low J and Ka rotational quantum numbers. These new data permitted to accurately fit the ground state rotational constants and to improve the ν_{46} band constants. As a second step, we performed the rotational analysis of the low frequency ν_{47} and ν_{48} bands of naphthalene recorded at room-temperature in the long absorption pathlength cell from ISMO. As a last step, the high resolution spectra of several bands of azulene, quinoline, isoquinoline and quinoxaline were recorded at room temperature and analyzed using the same procedure. All the rotational constants fitted in the present work were compared to the results of anharmonic DFT calculations realized at various levels of accuracy. S. Albert, et al.; Faraday Discussions, 150, 51 (2011)

  13. Structural Coloration of Colloidal Fiber by Photonic Band Gap and Resonant Mie Scattering.

    PubMed

    Yuan, Wei; Zhou, Ning; Shi, Lei; Zhang, Ke-Qin

    2015-07-01

    Because structural color is fadeless and dye-free, structurally colored materials have attracted great attention in a wide variety of research fields. In this work, we report the use of a novel structural coloration strategy applied to the fabrication of colorful colloidal fibers. The nanostructured fibers with tunable structural colors were massively produced by colloidal electrospinning. Experimental results and theoretical modeling reveal that the homogeneous and noniridescent structural colors of the electrospun fibers are caused by two phenomena: reflection due to the band gap of photonic structure and Mie scattering of the colloidal spheres. Our unprecedented findings show promise in paving way for the development of revolutionary dye-free technology for the coloration of various fibers. PMID:26066732

  14. High power experimental studies of hybrid photonic band gap accelerator structures

    NASA Astrophysics Data System (ADS)

    Zhang, JieXi; Munroe, Brian J.; Xu, Haoran; Shapiro, Michael A.; Temkin, Richard J.

    2016-08-01

    This paper reports the first high power tests of hybrid photonic band gap (PBG) accelerator structures. Three hybrid PBG (HPBG) structures were designed, built and tested at 17.14 GHz. Each structure had a triangular lattice array with 60 inner sapphire rods and 24 outer copper rods sandwiched between copper disks. The dielectric PBG band gap map allows the unique feature of overmoded operation in a TM02 mode, with suppression of both lower order modes, such as the TM11 mode, as well as higher order modes. The use of sapphire rods, which have negligible dielectric loss, required inclusion of the dielectric birefringence in the design. The three structures were designed to sequentially reduce the peak surface electric field. Simulations showed relatively high surface fields at the triple point as well as in any gaps between components in the clamped assembly. The third structure used sapphire rods with small pin extensions at each end and obtained the highest gradient of 19 MV /m , corresponding to a surface electric field of 78 MV /m , with a breakdown probability of 5 ×10-1 per pulse per meter for a 100-ns input power pulse. Operation at a gradient above 20 MV /m led to runaway breakdowns with extensive light emission and eventual damage. For all three structures, multipactor light emission was observed at gradients well below the breakdown threshold. This research indicated that multipactor triggered at the triple point limited the operational gradient of the hybrid structure.

  15. Observation of wakefields in a beam-driven photonic band gap accelerating structure.

    SciTech Connect

    Conde, M.; Yusof, Z.; Power, J. G.; Jing, C.; Gao, F.; Antipov, S.; Xu, P.; Zheng, S.; Chen, H.; Tang, C.; Gai, W.; High Energy Physics; Euclid Techlabs LLC; Tsinghua Univ.

    2009-12-01

    Wakefield excitation has been experimentally studied in a three-cell X-band standing wave photonic band gap (PBG) accelerating structure. Major monopole (TM{sub 01}- and TM{sub 02}-like) and dipole (TM{sub 11}- and TM{sub 12}-like) modes were identified and characterized by precisely controlling the position of beam injection. The quality factor Q of the dipole modes was measured to be {approx}10 times smaller than that of the accelerating mode. A charge sweep, up to 80 nC, has been performed, equivalent to {approx} 30 MV/m accelerating field on axis. A variable delay low charge witness bunch following a high charge drive bunch was used to calibrate the gradient in the PBG structure by measuring its maximum energy gain and loss. Experimental results agree well with numerical simulations.

  16. Band structure and optical properties of amber studied by first principles

    NASA Astrophysics Data System (ADS)

    Rao, Zhi-Fan; Zhou, Rong-Feng

    2013-03-01

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

  17. Photonic band structures solved by a plane-wave-based transfer-matrix method.

    PubMed

    Li, Zhi-Yuan; Lin, Lan-Lan

    2003-04-01

    Transfer-matrix methods adopting a plane-wave basis have been routinely used to calculate the scattering of electromagnetic waves by general multilayer gratings and photonic crystal slabs. In this paper we show that this technique, when combined with Bloch's theorem, can be extended to solve the photonic band structure for 2D and 3D photonic crystal structures. Three different eigensolution schemes to solve the traditional band diagrams along high-symmetry lines in the first Brillouin zone of the crystal are discussed. Optimal rules for the Fourier expansion over the dielectric function and electromagnetic fields with discontinuities occurring at the boundary of different material domains have been employed to accelerate the convergence of numerical computation. Application of this method to an important class of 3D layer-by-layer photonic crystals reveals the superior convergency of this different approach over the conventional plane-wave expansion method.

  18. Influence of structural parameters on tunable photonic band gaps modulated by liquid crystals

    NASA Astrophysics Data System (ADS)

    Huang, Aiqin; Zheng, Jihong; Jiang, Yanmeng; Zhou, Zengjun; Tang, Pingyu; Zhuang, Songlin

    2011-10-01

    Tunable photonic crystals (PCs), which are infiltrated with nematic liquid crystals (LCs), tune photonic band gap (PBG) by rotating directors of LCs when applied with the external electrical field. Using the plane wave expansion method, we simulated the PBG structure of two-dimensional tunable PCs with a triangular lattice of circular column, square column and hexagon column, respectively. When PCs are composed of LCs and different substrate materials such as germanium (Ge) and silicon (Si), the influence of structural parameters including column shape and packing ration on PBG is discussed separately. Numerical simulations show that absolute PBG can't be found at any conditions, however large tuning range of polarized wave can be achieved by rotating directors of LCs. The simulation results provide theoretical guidance for the fabrication of field-sensitive polarizer with big tunable band range.

  19. Electronic Properties of ZnO: Band Structure and Directional Compton Profiles

    NASA Astrophysics Data System (ADS)

    Sharma, G.; Mishra, M. C.; Dhaka, M. S.; Kothari, R. K.; Joshi, K. B.; Sharma, B. K.

    2013-12-01

    The electronic band structure and directional Compton profiles (DCPs) of ZnO are studied in this work. Calculations are performed considering a set of three schemes based on density functional theory (DFT), the Hartree-Fock (HF) method, and a hybrid scheme. All band structures predict direct bandgaps. The best agreement with experiment is, however, shown by the hybrid scheme. The three schemes are also applied to compute DCPs along [100], [110], and [001] directions. These are compared with measurements made on single crystals of ZnO employing a 59.54 keV gamma-ray Compton spectrometer. Calculations overestimate the momentum density in the low-momentum region while underestimate the anisotropies. Positions of extremes in anisotropies deduced from calculations are well reproduced by the measured anisotropies in some cases. Within the experimental limits, the DCPs from the HF method are in better agreement with the measurements compared with DFT.

  20. Band structure of topological insulators from noise measurements in tunnel junctions

    NASA Astrophysics Data System (ADS)

    Cascales Sandoval, Juan Pedro; Martinez, Isidoro; Guerrero, Ruben; Chang, Cui-Zu; Katmis, Ferhat; Moodera, Jagadeesh; Aliev, Farkhad

    The unique properties of spin-polarized surface or edge states in topological insulators (TIs) make these quantum coherent systems interesting from the point of view of both fundamental physics and their implementation in low power spintronic devices. Here we present such a study in TIs, through tunnelling and noise spectroscopy utilizing TI/Al2O3/Co tunnel junctions with bottom TI electrodes of either Bi2Te3 or Bi2Se3. We demonstrate that features related to the band structure of the TI materials show up in the tunnelling conductance and even more clearly through low frequency noise measurements. The bias dependence of 1/f noise reveals peaks at specific energies corresponding to band structure features of the TI. TI tunnel junctions could thus simplify the study of the properties of such quantum coherent systems that can further lead to the manipulation of their spin-polarized properties for technological purposes.

  1. Observations of LHR noise with banded structure by the sounding rocket S29 barium-GEOS

    NASA Technical Reports Server (NTRS)

    Koskinen, H. E. J.; Holmgren, G.; Kintner, P. M.

    1983-01-01

    The measurement of electrostatic noise near the lower hybrid frequency made by the sounding rocket S29 barium-GEOS is reported. The noise is related to the spin of the rocket and reaches well below the local lower hybrid resonance frequency. Above the altitude of 300 km the noise shows banded structure roughly organized by the hydrogen cyclotron frequency. Simultaneously with the banded structure a signal near the hydrogen cyclotron frequency is detected. This signal is also spin modulated. The character of the noise strongly suggests that it is locally generated by the rocket payload disturbing the plasma. If this interpretation is correct, plasma wave experiments on other spacecrafts are expected to observe similar phenomena.

  2. Multitude of bands in ^156Dy

    NASA Astrophysics Data System (ADS)

    Riedinger, L. L.; Hartley, D. J.; Curien, D.; Dudek, J.; Gall, B.; Allmond, M.; Beausang, C.; Carpenter, M. P.; Chiara, C. J.; Janssens, R. V. F.; Kondev, F. G.; Lauritsen, T.; McCutchan, E. A.; Stefanescu, I.; Zhu, S.; Garrett, P. E.; Kulp, W. D.; Wood, J. L.; Riley, M. A.; Wang, X. F.; Schunck, N.; Yu, C. H.; Sharpey-Schafer, J.; Majola, S.; Simpson, J.

    2009-10-01

    A Gammasphere measurement was performed on rotational bands in ^156Dy using the ^148Nd(^12C,4n) reaction at 65 MeV with the Atlas accelerator at Argonne. The projectile was chosen to populate many bands at low to medium spins. We have added new transitions and new bands to the family of negative-parity structures in this N = 90 nucleus. The lowest lying bands in this region have generally been associated with octupole vibrational modes, converting to two-quasiparticle bands at moderate frequencies. There are deviations from this picture in ^156Dy, due perhaps to the robustness of the octupole vibration through the first band crossing.

  3. Type IIIb bursts and their fine structure in frequency band 18-30 MHz

    NASA Astrophysics Data System (ADS)

    Melnik, V. N.; Rucker, H. O.; Konovalenko, A. A.; Shevchuk, N. V.; Abranin, E. P.; Dorovskyy, V. V.; Lecacheux, A.

    2010-01-01

    This paper deals with Type IIIb bursts, which were observed in the frequency band from 18 to 30 MHz. These bursts have fine frequency structures contrary to usual Type III bursts. The main properties of Type IIIb bursts such as number of striae in a burst, their frequency drift rates, durations, frequency widths of stria, emission fluxes are presented. It is also shown that parameters of stria bursts depend on the position of active areas on the solar disk.

  4. On the structure of the two-stream instability-complex G-Hamiltonian structure and Krein collisions between positive- and negative-action modes

    NASA Astrophysics Data System (ADS)

    Zhang, Ruili; Qin, Hong; Davidson, Ronald C.; Liu, Jian; Xiao, Jianyuan

    2016-07-01

    The two-stream instability is probably the most important elementary example of collective instabilities in plasma physics and beam-plasma systems. For a warm plasma with two charged particle species, the instability diagram of the two-stream instability based on a 1D warm-fluid model exhibits an interesting band structure that has not been explained. We show that the band structure for this instability is the consequence of the Hamiltonian nature of the warm two-fluid system. Interestingly, the Hamiltonian nature manifests as a complex G-Hamiltonian structure in wave-number space, which directly determines the instability diagram. Specifically, it is shown that the boundaries between the stable and unstable regions are locations for Krein collisions between eigenmodes with different Krein signatures. In terms of physics, this rigorously implies that the system is destabilized when a positive-action mode resonates with a negative-action mode, and that this is the only mechanism by which the system can be destabilized. It is anticipated that this physical mechanism of destabilization is valid for other collective instabilities in conservative systems in plasma physics, accelerator physics, and fluid dynamics systems, which admit infinite-dimensional Hamiltonian structures.

  5. Structural Biomass Estimation from L-band Interferometric SAR and Lidar

    NASA Astrophysics Data System (ADS)

    Treuhaft, R. N.; Chapman, B. D.; Goncalves, F.; Hensley, S.; dos Santos, J. R.; Graca, P. A.; Dutra, L.

    2011-12-01

    After a review of biomass estimation from interferometric SAR (InSAR) at all bands over the last 15 years, and a brief review of lidar biomass estimation, this paper discusses structure and biomass estimation from simultaneously acquired (not repeat-track) InSAR at L-band. We will briefly discuss the history of regression of biomass to InSAR raw observations (coherence and phase) and structural parameters (height, standard deviation, Fourier component). Lidar biomass estimation from functions of the waveform will be discussed. We review our structural and biomass estimation results for C-band InSAR at vertical polarization for 12-14 baselines in La Selva Biological Station, Costa Rica. C-band vertical scales were between 12 and 100 m for structure estimation, but only between 50 and 100 m for biomass estimation, due to phase calibration problems at the shorter vertical wavelengths (larger baselines). Most of the talk will be spent on L-band, simultaneously acquired multibaseline InSAR, also at La Selva, acquired at vertical polarization. Because the vertical interferometric scale is proportional to the radar altitude times the wavelength over the baseline length, the AirSAR aircraft had to be flown very low (1.2 km) to realize vertical scales at L-band of 60 m and higher. Our lidar biomass estimation suggests that vertical scales of 14 m-100 m are optimal for biomass estimation. We will try three different approaches to biomass estimation with the limited high vertical scales we have available: 1) We will regress biomass to Fourier transforms as in the C-band and lidar study, but with 60 m - 100+ m vertical scales we do not expect accuracies to be as high as for the lidar demonstration (58 Mg/ha RMS scatter of estimated about field biomass for biomasses up to 450 Mg/ha), which used Fourier vertical wavelengths of 15 m-20 m. In addition to using Fourier components, 2) we will report the use of the derivative of the InSAR complex coherence with respect to Fourier

  6. Deformation behavior of metallic glasses with shear band like atomic structure: a molecular dynamics study.

    PubMed

    Zhong, C; Zhang, H; Cao, Q P; Wang, X D; Zhang, D X; Ramamurty, U; Jiang, J Z

    2016-01-01

    Molecular dynamics simulations were employed to investigate the plastic deformation within the shear bands in three different metallic glasses (MGs). To mimic shear bands, MG specimens were first deformed until flow localization occurs, and then the volume of the material within the localized regions was extracted and replicated. Homogeneous deformation that is independent of the size of the specimen was observed in specimens with shear band like structure, even at a temperature that is far below the glass transition temperature. Structural relaxation and rapid cooling were employed to examine the effect of free volume content on the deformation behavior. This was followed by detailed atomic structure analyses, employing the concepts of Voronoi polyhedra and "liquid-like" regions that contain high fraction of sub-atomic size open volumes. Results suggest that the total fraction of atoms in liquid-like regions is a key parameter that controls the plastic deformation in MGs. These are discussed in the context of reported experimental results and possible strategies for synthesizing monolithic amorphous materials that can accommodate large tensile plasticity are suggested. PMID:27480496

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

    SciTech Connect

    Dakshinamoorthy, M.; Iyakutti, K.

    1984-12-15

    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).

  8. Deformation behavior of metallic glasses with shear band like atomic structure: a molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Zhong, C.; Zhang, H.; Cao, Q. P.; Wang, X. D.; Zhang, D. X.; Ramamurty, U.; Jiang, J. Z.

    2016-08-01

    Molecular dynamics simulations were employed to investigate the plastic deformation within the shear bands in three different metallic glasses (MGs). To mimic shear bands, MG specimens were first deformed until flow localization occurs, and then the volume of the material within the localized regions was extracted and replicated. Homogeneous deformation that is independent of the size of the specimen was observed in specimens with shear band like structure, even at a temperature that is far below the glass transition temperature. Structural relaxation and rapid cooling were employed to examine the effect of free volume content on the deformation behavior. This was followed by detailed atomic structure analyses, employing the concepts of Voronoi polyhedra and “liquid-like” regions that contain high fraction of sub-atomic size open volumes. Results suggest that the total fraction of atoms in liquid-like regions is a key parameter that controls the plastic deformation in MGs. These are discussed in the context of reported experimental results and possible strategies for synthesizing monolithic amorphous materials that can accommodate large tensile plasticity are suggested.

  9. Resonant inelastic x-ray scattering as a band structure probe of high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Kanasz-Nagy, Marton; Shi, Yifei; Klich, Israel; Demler, Eugene

    I will analyze recent resonant inelastic x-ray scattering (RIXS) experimental data on YBa2Cu3O6 + x [Minola et al., Phys. Rev. Lett. 114, 217003 (2015)] within quasi-particle theory. This measurement has been performed with the incoming photon energy detuned at several values from the resonance maximum, and, surprisingly, the data shows much weaker dependence on detuning than expected from recent measurements on a different cuprate superconductor, Bi2Sr2CuO6 + x [Guarise et al., Nat. Commun. 5, 5760 (2014)]. I will demonstrate, that this discrepancy, originally attributed to collective magnetic excitations, can be understood in terms of the differences between the band structures of these materials. We found good agreement between theory and experiment over a large range of dopings [M. Kanasz-Nagy et al., arXiv:1508.06639]. Moreover, I will demonstrate that the RIXS signal depends sensitively on excitations at energies well above the Fermi surface, that are inaccessible to traditionally used band structure probes, such as angle-resolved photoemission spectroscopy. This makes RIXS a powerful probe of band structure, not suffering from surface preparation problems and small sample sizes, making it potentially applicable to a wide range of materials. The work of M. K.-N. was supported by the Harvard-MIT CUA, NSF Grant No. DMR-1308435, AFOSR Quantum Simulation MURI, the ARO-MURI on Atomtronics, and ARO MURI Quism program.

  10. Efficient evaluation of epitaxial MoS2 on sapphire by direct band structure imaging

    NASA Astrophysics Data System (ADS)

    Kim, Hokwon; Dumcenco, Dumitru; Fregnaux, Mathieu; Benayad, Anass; Kung, Yen-Cheng; Kis, Andras; Renault, Olivier; Lanes Group, Epfl Team; Leti, Cea Team

    The electronic band structure evaluation of two-dimensional metal dichalcogenides is critical as the band structure can be greatly influenced by the film thickness, strain, and substrate. Here, we performed a direct measurement of the band structure of as-grown monolayer MoS2 on single crystalline sapphire by reciprocal-space photoelectron emission microscopy with a conventional laboratory ultra-violet He I light source. Arrays of gold electrodes were deposited onto the sample in order to avoid charging effects due to the insulating substrate. This allowed the high resolution mapping (ΔE = 0.2 eV Δk = 0.05 Å-1) of the valence states in momentum space down to 7 eV below the Fermi level. The high degree of the epitaxial alignment of the single crystalline MoS2 nuclei was verified by the direct momentum space imaging over a large area containing multiple nuclei. The derived values of the hole effective mass were 2.41 +/-0.05 m0 and 0.81 +/-0.05 m0, respectively at Γ and K points, consistent with the theoretical values of the freestanding monolayer MoS2 reported in the literature. HK acknowledges the french CEA Basic Technological Research program (RTB) for funding.

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

    PubMed

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

    2014-09-22

    We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniques such as a simple approach to impose symmetry constraints. We also demonstrate a technique for robust topology optimization, in which some uncertainty is included in each voxel and we optimize the worst-case gap, and we show that the resulting band gaps have increased robustness to systematic fabrication errors. PMID:25321732

  12. Deformation behavior of metallic glasses with shear band like atomic structure: a molecular dynamics study

    PubMed Central

    Zhong, C.; Zhang, H.; Cao, Q. P.; Wang, X. D.; Zhang, D. X.; Ramamurty, U.; Jiang, J. Z.

    2016-01-01

    Molecular dynamics simulations were employed to investigate the plastic deformation within the shear bands in three different metallic glasses (MGs). To mimic shear bands, MG specimens were first deformed until flow localization occurs, and then the volume of the material within the localized regions was extracted and replicated. Homogeneous deformation that is independent of the size of the specimen was observed in specimens with shear band like structure, even at a temperature that is far below the glass transition temperature. Structural relaxation and rapid cooling were employed to examine the effect of free volume content on the deformation behavior. This was followed by detailed atomic structure analyses, employing the concepts of Voronoi polyhedra and “liquid-like” regions that contain high fraction of sub-atomic size open volumes. Results suggest that the total fraction of atoms in liquid-like regions is a key parameter that controls the plastic deformation in MGs. These are discussed in the context of reported experimental results and possible strategies for synthesizing monolithic amorphous materials that can accommodate large tensile plasticity are suggested. PMID:27480496

  13. Deformation behavior of metallic glasses with shear band like atomic structure: a molecular dynamics study.

    PubMed

    Zhong, C; Zhang, H; Cao, Q P; Wang, X D; Zhang, D X; Ramamurty, U; Jiang, J Z

    2016-08-02

    Molecular dynamics simulations were employed to investigate the plastic deformation within the shear bands in three different metallic glasses (MGs). To mimic shear bands, MG specimens were first deformed until flow localization occurs, and then the volume of the material within the localized regions was extracted and replicated. Homogeneous deformation that is independent of the size of the specimen was observed in specimens with shear band like structure, even at a temperature that is far below the glass transition temperature. Structural relaxation and rapid cooling were employed to examine the effect of free volume content on the deformation behavior. This was followed by detailed atomic structure analyses, employing the concepts of Voronoi polyhedra and "liquid-like" regions that contain high fraction of sub-atomic size open volumes. Results suggest that the total fraction of atoms in liquid-like regions is a key parameter that controls the plastic deformation in MGs. These are discussed in the context of reported experimental results and possible strategies for synthesizing monolithic amorphous materials that can accommodate large tensile plasticity are suggested.

  14. Non-negative matrix factorization and term structure of interest rates

    NASA Astrophysics Data System (ADS)

    Takada, Hellinton H.; Stern, Julio M.

    2015-01-01

    Non-Negative Matrix Factorization (NNMF) is a technique for dimensionality reduction with a wide variety of applications from text mining to identification of concentrations in chemistry. NNMF deals with non-negative data and results in non-negative factors and factor loadings. Consequently, it is a natural choice when studying the term structure of interest rates. In this paper, NNMF is applied to obtain factors from the term structure of interest rates and the procedure is compared with other very popular techniques: principal component analysis and Nelson-Siegel model. The NNMF approximation for the term structure of interest rates is better in terms of fitting. From a practitioner point of view, the NNMF factors and factor loadings obtained possess straightforward financial interpretations due to their non-negativeness.

  15. Janus kinases and focal adhesion kinases play in the 4.1 band: a superfamily of band 4.1 domains important for cell structure and signal transduction.

    PubMed Central

    Girault, J. A.; Labesse, G.; Mornon, J. P.; Callebaut, I.

    1998-01-01

    The band 4.1 domain was first identified in the red blood cell protein band 4.1, and subsequently in ezrin, radixin, and moesin (ERM proteins) and other proteins, including tumor suppressor merlin/schwannomin, talin, unconventional myosins VIIa and X, and protein tyrosine phosphatases. Recently, the presence of a structurally related domain has been demonstrated in the N-terminal region of two groups of tyrosine kinases: the focal adhesion kinases (FAK) and the Janus kinases (JAK). Additional proteins containing the 4.1/JEF (JAK, ERM, FAK) domain include plant kinesin-like calmodulin-binding proteins (KCBP) and a number of uncharacterized open reading frames identified by systematic DNA sequencing. Phylogenetic analysis of amino acid sequences suggests that band 4.1/JEF domains can be grouped in several families that have probably diverged early during evolution. Hydrophobic cluster analysis indicates that the band 4.1/JEF domains might consist of a duplicated module of approximately 140 residues and a central hinge region. A conserved property of the domain is its capacity to bind to the membrane-proximal region of the C-terminal cytoplasmic tail of proteins with a single transmembrane segment. Many proteins with band 4.1/JEF domains undergo regulated intra- or intermolecular homotypic interactions. Additional properties common to band 4.1/JEF domains of several proteins are binding of phosphoinositides and regulation by GTPases of the Rho family. Many proteins with band 4. 1/JEF domains are associated with the actin-based cytoskeleton and are enriched at points of contact with other cells or the extracellular matrix, from which they can exert control over cell growth. Thus, proteins with band 4.1/JEF domain are at the crossroads between cytoskeletal organization and signal transduction in multicellular organisms. Their importance is underlined by the variety of diseases that can result from their mutations. Images Fig. 1 Fig. 2 Fig. 4 Fig. 5 PMID:9990861

  16. Measurement of valence band structure in boron-zinc-oxide films by making use of ion beams

    SciTech Connect

    Uhm, Han S.; Kwon, Gi C.; Choi, Eun H.

    2011-12-26

    Measurement of valence band structure in the boron-zinc oxide (BZO) films was developed using the secondary electron emission due to the Auger neutralization of ions. The energy distribution profile of the electrons emitted from boron-zinc-oxide films was measured and rescaled so that Auger self-convolution arose; thus, revealing the detailed structure of the valence band and suggesting 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.

  17. A High-Power Test of An X-Band Molybdenum Iris Structure

    SciTech Connect

    Grudiev, A.

    2005-02-18

    In order to achieve accelerating gradients above 150 MV/m, alternative materials to copper are being investigated by the CLIC study. The potential of refractory metals has already been demonstrated in tests in which a tungsten-iris and a molybdenum-iris structure reached 150 and 193 MV/m respectively (30 GHz and a pulse length of 15 ns). In order to extend the investigation to the pulse lengths required for a linear collider, a molybdenum-iris structure scaled to X-band was tested at the Next Linear Collider Test Accelerator (NLCTA). The structure conditioned to only 65 MV/m (100 ns pulse length) in the available testing time and much more slowly than is typical of a copper structure. However the structure showed no sign of saturation and a microscopic inspection of the rf surfaces corroborated that the structure was still at an early stage of conditioning. The X-band and 30 GHz results are compared and what has been learned about material quality, surface preparation and conditioning strategy is discussed.

  18. Quasiparticle band structures and thermoelectric transport properties of p-type SnSe

    SciTech Connect

    Shi, Guangsha; Kioupakis, Emmanouil

    2015-02-14

    We used density functional and many-body perturbation theory to calculate the quasiparticle band structures and electronic transport parameters of p-type SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The Pnma phase has an indirect band gap of 0.829 eV, while the Cmcm has a direct band gap of 0.464 eV. Both phases exhibit multiple local band extrema within an energy range comparable to the thermal energy of carriers from the global extrema. We calculated the electronic transport coefficients as a function of doping concentration and temperature for single-crystal and polycrystalline materials to understand the previous experimental measurements. The electronic transport coefficients are highly anisotropic and are strongly affected by bipolar transport effects at high temperature. Our results indicate that SnSe exhibits optimal thermoelectric performance at high temperature when doped in the 10{sup 19}–10{sup 20 }cm{sup −3} range.

  19. Band Structure of Helimagnons in MnSi Resolved by Inelastic Neutron Scattering.

    PubMed

    Kugler, M; Brandl, G; Waizner, J; Janoschek, M; Georgii, R; Bauer, A; Seemann, K; Rosch, A; Pfleiderer, C; Böni, P; Garst, M

    2015-08-28

    A magnetic helix realizes a one-dimensional magnetic crystal with a period given by the pitch length λh. Its spin-wave excitations-the helimagnons-experience Bragg scattering off this periodicity, leading to gaps in the spectrum that inhibit their propagation along the pitch direction. Using high-resolution inelastic neutron scattering, the resulting band structure of helimagnons was resolved by preparing a single crystal of MnSi in a single magnetic-helix domain. At least five helimagnon bands could be identified that cover the crossover from flat bands at low energies with helimagnons basically localized along the pitch direction to dispersing bands at higher energies. In the low-energy limit, we find the helimagnon spectrum to be determined by a universal, parameter-free theory. Taking into account corrections to this low-energy theory, quantitative agreement is obtained in the entire energy range studied with the help of a single fitting parameter. PMID:26371678

  20. Observation of Wakefield Suppression in a Photonic-Band-Gap Accelerator Structure

    DOE PAGES

    Simakov, Evgenya I.; Arsenyev, Sergey A.; Buechler, Cynthia E.; Edwards, Randall L.; Romero, William P.; Conde, Manoel; Ha, Gwanghui; Power, John G.; Wisniewski, Eric E.; Jing, Chunguang

    2016-02-10

    We report experimental observation of higher order mode (HOM) wakefield suppression in a room-temperature traveling-wave photonic band gap (PBG) accelerating structure at 11.700 GHz. It has been long recognized that PBG structures have potential for reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in a room-temperature PBG structure was conducted in 2005. Since then, the importance of PBG accelerator research has been recognized by many institutions. However, the full experimental characterization of the wakefield spectrum and demonstration of wakefield suppression when the accelerating structure is excited by an electron beam has not been performed to date. Wemore » conducted an experiment at the Argonne Wakefield Accelerator (AWA) test facility and observed wakefields excited by a single high charge electron bunch when it passes through a PBG accelerator structure. Lastly, excellent HOM suppression properties of the PBG accelerator were demonstrated in the beam test.« less

  1. Band structure calculation of GaSe-based nanostructures using empirical pseudopotential method

    NASA Astrophysics Data System (ADS)

    Osadchy, A. V.; Volotovskiy, S. G.; Obraztsova, E. D.; Savin, V. V.; Golovashkin, D. L.

    2016-08-01

    In this paper we present the results of band structure computer simulation of GaSe- based nanostructures using the empirical pseudopotential method. Calculations were performed using a specially developed software that allows performing simulations using cluster computing. Application of this method significantly reduces the demands on computing resources compared to traditional approaches based on ab-initio techniques and provides receiving the adequate comparable results. The use of cluster computing allows to obtain information for structures that require an explicit account of a significant number of atoms, such as quantum dots and quantum pillars.

  2. Infrared optical properties and band structure of α-Sn/Ge superlattices on Ge substrates

    NASA Astrophysics Data System (ADS)

    Olajos, J.; Vogl, P.; Wegscheider, W.; Abstreiter, G.

    1991-11-01

    Short-period α-Sn/Ge strained-layer superlattices have been prepared on [001] Ge substrates by low-temperature molecular-beam epitaxy. We have achieved almost-defect-free and thermally stable single-crystalline structures. Photocurrent measurements in a series of Sn1Gem (m>10) superlattices reveal a shift of the fundamental energy gap to smaller energies with decreasing Ge layer thickness m, in good agreement with band-structure calculations. A direct fundamental energy gap is predicted for a slightly increased lateral lattice constant in α-Sn/Ge superlattices.

  3. The properties of photoconductivity of the Ila-type diamond related to the band gap structure

    NASA Astrophysics Data System (ADS)

    Altukhov, A. A.; Feshchenko, V. S.; Shepelev, V. A.; Popov, A. V.

    2016-08-01

    We investigate the properties of the photosensitivity spectra of the UV photodetectors based on natural diamond. The effect of the structural defects associated with nitrogen impurities to the photosensitivity is analyzed. We confirm that the polychrome light bias application enhances the photosensitivity of these detectors in the spectral range 240-340 nm due to the quasi-two-photon absorption which originates due to the complicated structure of the band gap impurity states of a natural diamond. The possibility to influence the photosensitivity spectra in the λ<220 nm spectral range of these detectors by the polychrome light bias application is revealed.

  4. Valence-band electronic structure of silicon nitride studied with the use of soft-x-ray emission

    NASA Astrophysics Data System (ADS)

    Carson, R. D.; Schnatterly, S. E.

    1986-02-01

    We have studied the valence-band electronic structure of α-phase, β-phase, and amorphous silicon nitride samples, using Si L-x-ray emission. Our results are compared with a recent band-structure calculation and show that Si 3d states are necessary to properly describe the upper-valence-band and lower-conduction-band density of states. A prominent feature is seen above the valence band which is attributed to conduction-band states that are populated by the incident electron beam. By reducing the energy of the electron beam it is possible to enhance the surface emission relative to bulk emission, and such spectra are also presented and discussed.

  5. Quasi-particle band structure of potassium-doped few-layer black phosphorus with GW approximation

    NASA Astrophysics Data System (ADS)

    Kim, Han-Gyu; Baik, Seung Su; Choi, Hyoung Joon

    We calculate the quasi-particle band structure of pristine and potassium-doped black phosphorus (BP) by using the GW approximation. We obtain band gaps of pristine bulk and few-layer BP and compare them with the result of the density functional calculations and experimental measurements. For potassium-doped cases, we calculate the electronic band structure of potassium-doped few-layer BPs with various doping densities. We obtain the critical doping density for the band-gap closing, and the energy-band dispersions when the band gap is inverted. We discuss Dirac semimetal properties of doped few-layer BPs obtained by the GW approximation. This work was supported by NRF of Korea (Grant No. 2011-0018306) and KISTI supercomputing center (Project No. KSC-2015-C3-039).

  6. The hybridizations of cobalt 3 d bands with the electron band structure of the graphene/cobalt interface on a tungsten substrate

    NASA Astrophysics Data System (ADS)

    Hwang, Jinwoong; Hwang, Choongyu; Chung, Nak-Kwan; N'Diaye, A. D.; Schmid, A. K.; Denlinger, Jonathan

    2016-08-01

    The interface between graphene and a ferromagnetic substrate has attracted recent research interests due to its potential for spintronic applications. We report an angle-resolved photoemission spectroscopy study on the interface between graphene and cobalt epitaxially grown on a tungsten substrate. We find that the electron band structure of the interface exhibits clear discontinuities at the crossing points with cobalt 3 d bands. These observations indicate strong hybridizations between the electronic states in the interface and provide an important clue to understand the intriguing electromagnetic properties of the graphene/ferromagnet interface.

  7. Band structure and spin texture of Bi2Se3 3 d ferromagnetic metal interface

    NASA Astrophysics Data System (ADS)

    Zhang, Jia; Velev, Julian P.; Dang, Xiaoqian; Tsymbal, Evgeny Y.

    2016-07-01

    The spin-helical surface states in a three-dimensional topological insulator (TI), such as Bi2Se3 , are predicted to have superior efficiency in converting charge current into spin polarization. This property is said to be responsible for the giant spin-orbit torques observed in ferromagnetic metal/TI structures. In this work, using first-principles and model tight-binding calculations, we investigate the interface between the topological insulator Bi2Se3 and 3 d -transition ferromagnetic metals Ni and Co. We find that the difference in the work functions of the topological insulator and the ferromagnetic metals shift the topological surface states down about 0.5 eV below the Fermi energy where the hybridization of these surface states with the metal bands destroys their helical spin structure. The band alignment of Bi2Se3 and Ni (Co) places the Fermi energy far in the conduction band of bulk Bi2Se3 , where the spin of the carriers is aligned with the magnetization in the metal. Our results indicate that the topological surface states are unlikely to be responsible for the huge spin-orbit torque effect observed experimentally in these systems.

  8. Crustal Structure Beneath Taiwan Using Frequency-band Inversion of Receiver Function Waveforms

    NASA Astrophysics Data System (ADS)

    Tomfohrde, D. A.; Nowack, R. L.

    Receiver function analysis is used to determine local crustal structure beneath Taiwan. We have performed preliminary data processing and polarization analysis for the selection of stations and events and to increase overall data quality. Receiver function analysis is then applied to data from the Taiwan Seismic Network to obtain radial and transverse receiver functions. Due to the limited azimuthal coverage, only the radial receiver functions are analyzed in terms of horizontally layered crustal structure for each station. In order to improve convergence of the receiver function inversion, frequency-band inversion (FBI) is implemented, in which an iterative inversion procedure with sequentially higher low-pass corner frequencies is used to stabilize the waveform inversion. Frequency-band inversion is applied to receiver functions at six stations of the Taiwan Seismic Network. Initial 20-layer crustal models are inverted for using prior tomographic results for the initial models. The resulting 20-1ayer models are then simplified to 4 to 5 layer models and input into an alternating depth and velocity frequency-band inversion. For the six stations investigated, the resulting simplified models provide an average estimate of 38 km for the Moho thickness surrounding the Central Range of Taiwan. Also, the individual station estimates compare well with the recent tomographic model of and the refraction results of Rau and Wu (1995) and the refraction results of Ma and Song (1997).

  9. Strain-tunable band parameters of ZnO monolayer in graphene-like honeycomb structure

    NASA Astrophysics Data System (ADS)

    Behera, Harihar; Mukhopadhyay, Gautam

    2012-10-01

    We present ab initio calculations which show that the direct-band-gap, effective masses and Fermi velocities of charge carriers in ZnO monolayer (ML-ZnO) in graphene-like honeycomb structure are all tunable by application of in-plane homogeneous biaxial strain. Within our simulated strain limit of ±10%, the band gap remains direct and shows a strong non-linear variation with strain. Moreover, the average Fermi velocity of electrons in unstrained ML-ZnO is of the same order of magnitude as that in graphene. The results promise potential applications of ML-ZnO in mechatronics/straintronics and other nano-devices such as the nano-electromechanical systems (NEMS) and nano-optomechanical systems (NOMS).

  10. Periodic dielectric structure for production of photonic band gap and method for fabricating the same

    DOEpatents

    Ozbay, Ekmel; Tuttle, Gary; Michel, Erick; Ho, Kai-Ming; Biswas, Rana; Chan, Che-Ting; Soukoulis, Costas

    1995-01-01

    A method for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap.

  11. Periodic dielectric structure for production of photonic band gap and method for fabricating the same

    DOEpatents

    Ozbay, E.; Tuttle, G.; Michel, E.; Ho, K.M.; Biswas, R.; Chan, C.T.; Soukoulis, C.

    1995-04-11

    A method is disclosed for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap. 42 figures.

  12. The effect of spin-orbit coupling in band structure of few-layer graphene

    SciTech Connect

    Sahdan, Muhammad Fauzi Darma, Yudi

    2014-03-24

    Topological insulators are electronic materials that have a bulk band gap like an ordinary insulator but have protected conducting states on their edge or surface. This can be happened due to spin-orbit coupling and time-reversal symmetry. Moreover, the edge current flows through their edge or surface depends on its spin orientation and also it is robust against non-magnetic impurities. Therefore, topological insulators are predicted to be useful ranging from spintronics to quantum computation. Graphene was first predicted to be the precursor of topological insulator by Kane-Mele. They developed a Hamiltonian model to describe the gap opening in graphene. In this work, we investigate the band structure of few-layer graphene by using this model with analytical approach. The results of our calculations show that the gap opening occurs at K and K’ point, not only in single layer, but also in bilayer and trilayer graphene.

  13. A novel band-pass filter based on a periodically drilled SIW structure

    NASA Astrophysics Data System (ADS)

    Coves, A.; Torregrosa-Penalva, G.; San-Blas, A. A.; Sánchez-Soriano, M. A.; Martellosio, A.; Bronchalo, E.; Bozzi, M.

    2016-04-01

    The design and fabrication of a band-pass step impedance filter based on high and low dielectric constant sections has been realized on substrate integrated waveguide (SIW) technology. The overall process includes the design of the ideal band-pass prototype filter, where the implementation of the impedance inverters has been carried out by means of waveguide sections of lower permittivity. This can be practically achieved by implementing arrays of air holes along the waveguide. Several SIW structures with and without arrays of air holes have been simulated and fabricated in order to experimentally evaluate their relative permittivity. Additionally, the equivalent filter in SIW technology has been designed and optimized. Finally, a prototype of the designed filter has been fabricated and measured, showing a good agreement between measurements and simulations, which demonstrates the validity of the proposed design approach.

  14. Band gap widening and quantum tunnelling effects of Ag/MgO/p-Si MOS structure

    NASA Astrophysics Data System (ADS)

    Kamarulzaman, Norlida; Badar, Nurhanna; Fadilah Chayed, Nor; Firdaus Kasim, Muhd

    2016-10-01

    MgO films of various thicknesses were fabricated via the pulsed laser deposition method. The MgO thin films obtained have the advantage of high quality mirror finish, good densification and of uniform thickness. The MgO thin films have thicknesses of between 43 to 103 nm. They are polycrystalline in nature with oriented growth mainly in the direction of the [200] and [220] crystal planes. It is observed that the band gap of the thin films increases as the thickness decreases due to quantum effects, however, turn-on voltage has the opposite effect. The decrease of the turn-on as well as the tunnelling voltage of the thinner films, despite their larger band gap, is a direct experimental evidence of quantum tunnelling effects in the thin films. This proves that quantum tunnelling is more prominent in low dimensional structures.

  15. Evolution of band structures in MoS2-based homo- and heterobilayers

    NASA Astrophysics Data System (ADS)

    Zhu, H. L.; Zhou, C. J.; Huang, X. J.; Wang, X. L.; Xu, H. Z.; Lin, Yong; Yang, W. H.; Wu, Y. P.; Lin, W.; Guo, F.

    2016-02-01

    Density functional theory calculations have been performed to elucidate the detailed evolution of band structures in MoS2-based homo- and heterobilayers. By constructing the energy-band alignments we observed that biaxial tensile and compressive strain in the constituent transition-metal dichalcogenide (TMD) monolayer shifts the states at the K C, Q C, and K V points down and up, respectively, while the states at the ΓV point are almost unaltered. In contrast, interlayer coupling tends to modify the states at the ΓV and Q C points by splitting the band-edge states of two strained or unstrained constituent TMD monolayers, while it does not affect the states at the K C and K V points. Considering the combined actions of strain and interlayer coupling, the relevant electronic parameters, especially the detailed evolution processes, of the band structures of the investigated bilayer systems can be clearly described. When further applying the extra biaxial strain to the three bilayer systems, it is found that energy differences ΔE(K C  -  Q C) and ΔE(K V  -  ΓV) decrease linearly as the increasing of the biaxial strain. According to the varying trends of ΔE(K C  -  Q C) and ΔE(K V  -  ΓV), MoS2 bilayer will maintain the indirect-bandgap character under any compressive or tensile strain. Differently, WS2/MoS2 heterobilayer transforms interestingly to the direct-bandgap material under the strain from  -1.6% to  -1.2% with the valence band maximum and conduction band minimum located at the K C and K V point respectively. The direct-to-indirect bandgap transition can be obtained for the WSe2/MoS2 heterobilayer when applying much larger extra tensile or compressive strain. The results offer an effective route to verify and tailor the electronic properties of TMD homo- and heterostructures and can be helpful in evaluating the performance of TMD-based electronic devices.

  16. Giant amplification in degenerate band edge slow-wave structures interacting with an electron beam

    NASA Astrophysics Data System (ADS)

    Othman, Mohamed A. K.; Veysi, Mehdi; Figotin, Alexander; Capolino, Filippo

    2016-03-01

    We propose a new amplification regime based on a synchronous operation of four degenerate electromagnetic (EM) modes in a slow-wave structure and the electron beam, referred to as super synchronization. These four EM modes arise in a Fabry-Pérot cavity when degenerate band edge (DBE) condition is satisfied. The modes interact constructively with the electron beam resulting in superior amplification. In particular, much larger gains are achieved for smaller beam currents compared to conventional structures based on synchronization with only a single EM mode. We demonstrate giant gain scaling with respect to the length of the slow-wave structure compared to conventional Pierce type single mode traveling wave tube amplifiers. We construct a coupled transmission line model for a loaded waveguide slow-wave structure exhibiting a DBE, and investigate the phenomenon of giant gain via super synchronization using the Pierce model generalized to multimode interaction.

  17. Cohesive band structure of carbon nanotubes for applications in quantum transport.

    PubMed

    Arora, Vijay K; Bhattacharyya, Arkaprava

    2013-11-21

    An integrated cohesive band structure of carbon nanotubes (CNTs) applicable to all chirality directions (n, m), starting from the Dirac cone of a graphene nanolayer in k-space, is demarcated, in direct contrast to dissimilar chiral and achiral versions in the published literature. The electron wave state of a CNT is quantized into one-dimensional (1-D) nanostructure with a wrapping mode, satisfying the boundary conditions from one Dirac K-point to an equivalent neighboring one with an identical phase and returning to the same K point. The repetitive rotation for an identical configuration with added band index (n-m)mod3, yields one metallic (M) with zero bandgap corresponding to (n-m)mod3 = 0, semiconducting state SC1 with (n-m)mod3 = 1 and SC2 with (n-m)mod3 = 2. The band gap and effective mass of SC2 state are twice as large as those of SC1 state. A broad-spectrum expression signifying the linear dependence of the effective mass on the bandgap is obtained. Both the Fermi energy and the intrinsic velocity limiting the current to the saturation level is calculated as a function of the carrier concentration. Limitations of the parabolic approximation are pointed out. Several new features of the band structure are acquired in a seamlessly unified mode for all CNTs, making it suitable for all-encompassing applications. Applications of the theory to high-field transport are advocated with an example of a metallic CNT, in agreement with experimental observations. The mechanism behind the breakdown of the linear current-voltage relation of Ohm's law and the associated surge in resistance are explained on the basis of the nonequilibrium Arora's distribution function (NEADF). These results are important for the performance evaluation and characterization of a variety of applications on CNT in modern nanoscale circuits and devices.

  18. Optical Transitions and Electronic Band structure of Cuprous Oxide Thin Films

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

    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^2ɛ/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 γ 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 γ valence band and the M and X conduction bands, respectively. The physical origin of the quasi-direct transitions was attributed to the grain boundaries.

  19. Cohesive band structure of carbon nanotubes for applications in quantum transport

    NASA Astrophysics Data System (ADS)

    Arora, Vijay K.; Bhattacharyya, Arkaprava

    2013-10-01

    An integrated cohesive band structure of carbon nanotubes (CNTs) applicable to all chirality directions (n, m), starting from the Dirac cone of a graphene nanolayer in k-space, is demarcated, in direct contrast to dissimilar chiral and achiral versions in the published literature. The electron wave state of a CNT is quantized into one-dimensional (1-D) nanostructure with a wrapping mode, satisfying the boundary conditions from one Dirac K-point to an equivalent neighboring one with an identical phase and returning to the same K point. The repetitive rotation for an identical configuration with added band index (n - m)mod3, yields one metallic (M) with zero bandgap corresponding to (n - m)mod3 = 0, semiconducting state SC1 with (n - m)mod3 = 1 and SC2 with (n - m)mod3 = 2. The band gap and effective mass of SC2 state are twice as large as those of SC1 state. A broad-spectrum expression signifying the linear dependence of the effective mass on the bandgap is obtained. Both the Fermi energy and the intrinsic velocity limiting the current to the saturation level is calculated as a function of the carrier concentration. Limitations of the parabolic approximation are pointed out. Several new features of the band structure are acquired in a seamlessly unified mode for all CNTs, making it suitable for all-encompassing applications. Applications of the theory to high-field transport are advocated with an example of a metallic CNT, in agreement with experimental observations. The mechanism behind the breakdown of the linear current-voltage relation of Ohm's law and the associated surge in resistance are explained on the basis of the nonequilibrium Arora's distribution function (NEADF). These results are important for the performance evaluation and characterization of a variety of applications on CNT in modern nanoscale circuits and devices.

  20. Comment on ``Photonic bands in two-dimensional microplasma array. I. Theoretical derivation of band structures of electromagnetic waves'' [J. Appl. Phys. 101, 073304 (2007)

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-feng; Liu, Shao-bin; Kong, Xiang-kun; Zhou, Liang; Li, Chun-zao; Bian, Bo-rui

    2011-07-01

    Recently, theoretical derivation of band structures of electromagnetic waves in two-dimensional microplasma array has been induced by Osamu Sakai et al. [J. Appl. Phys. 101, 073304 (2007)] using a modified plane wave expansion (PWE) method and a frequency-dependent finite difference time-domain (FDTD) method. This report reveals band diagrams with the effects of plasma electron collision frequency, especially focuses on the TE wave by nonmagnetized plasma. Although the band diagrams of TE wave and formulas of calculation look correct at first glance, there are some mistakes in the report which are unfortunately ignored by the authors. The correct formulas of the modified PWE method and FDTD method will be proposed.

  1. Experimental high gradient testing of a 17.1 GHz photonic band-gap accelerator structure

    NASA Astrophysics Data System (ADS)

    Munroe, Brian J.; Zhang, JieXi; Xu, Haoran; Shapiro, Michael A.; Temkin, Richard J.

    2016-03-01

    We report the design, fabrication, and high gradient testing of a 17.1 GHz photonic band-gap (PBG) accelerator structure. Photonic band-gap (PBG) structures are promising candidates for electron accelerators capable of high-gradient operation because they have the inherent damping of high order modes required to avoid beam breakup instabilities. The 17.1 GHz PBG structure tested was a single cell structure composed of a triangular array of round copper rods of radius 1.45 mm spaced by 8.05 mm. The test assembly consisted of the test PBG cell located between conventional (pillbox) input and output cells, with input power of up to 4 MW from a klystron supplied via a TM01 mode launcher. Breakdown at high gradient was observed by diagnostics including reflected power, downstream and upstream current monitors and visible light emission. The testing procedure was first benchmarked with a conventional disc-loaded waveguide structure, which reached a gradient of 87 MV /m at a breakdown probability of 1.19 ×10-1 per pulse per meter. The PBG structure was tested with 100 ns pulses at gradient levels of less than 90 MV /m in order to limit the surface temperature rise to 120 K. The PBG structure reached up to 89 MV /m at a breakdown probability of 1.09 ×10-1 per pulse per meter. These test results show that a PBG structure can simultaneously operate at high gradients and low breakdown probability, while also providing wakefield damping.

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

    SciTech Connect

    Luo, J. W.; Franceschetti, A.; Zunger, A.

    2008-01-01

    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 {rho}{sub XX}. Here we introduce a DCM 'figure of merit' R{sub 2}(E) which is proportional to the ratio between the biexciton density of states {rho}{sub XX} and the single-exciton density of states {rho}{sub x}, restricted to single-exciton and biexciton states that are coupled by Coulomb interactions. Using R{sub 2}(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 E{sub 0} (the energy at which R{sub 2}(E) becomes {ge}1) is reduced, suggesting improved DCM. However, whether the normalized E{sub 0}/{var_epsilon}{sub g} increases or decreases as the dot size increases depends on dot material.

  3. 8-band and 14-band kp modeling of electronic band structure and material gain in Ga(In)AsBi quantum wells grown on GaAs and InP substrates

    SciTech Connect

    Gladysiewicz, M.; Wartak, M. S.; Kudrawiec, R.

    2015-08-07

    The electronic band structure and material gain have been calculated for GaAsBi/GaAs quantum wells (QWs) with various bismuth concentrations (Bi ≤ 15%) within the 8-band and 14-band kp models. The 14-band kp model was obtained by extending the standard 8-band kp Hamiltonian by the valence band anticrossing (VBAC) Hamiltonian, which is widely used to describe Bi-related changes in the electronic band structure of dilute bismides. It has been shown that in the range of low carrier concentrations n < 5 × 10{sup 18 }cm{sup −3}, material gain spectra calculated within 8- and 14-band kp Hamiltonians are similar. It means that the 8-band kp model can be used to calculate material gain in dilute bismides QWs. Therefore, it can be applied to analyze QWs containing new dilute bismides for which the VBAC parameters are unknown. Thus, the energy gap and electron effective mass for Bi-containing materials are used instead of VBAC parameters. The electronic band structure and material gain have been calculated for 8 nm wide GaInAsBi QWs on GaAs and InP substrates with various compositions. In these QWs, Bi concentration was varied from 0% to 5% and indium concentration was tuned in order to keep the same compressive strain (ε = 2%) in QW region. For GaInAsBi/GaAs QW with 5% Bi, gain peak was determined to be at about 1.5 μm. It means that it can be possible to achieve emission at telecommunication windows (i.e., 1.3 μm and 1.55 μm) for GaAs-based lasers containing GaInAsBi/GaAs QWs. For GaInAsBi/Ga{sub 0.47}In{sub 0.53}As/InP QWs with 5% Bi, gain peak is predicted to be at about 4.0 μm, i.e., at the wavelengths that are not available in current InP-based lasers.

  4. The Brillouin zones and band gaps of a two-dimensional phononic crystal with parallelogram lattice structure

    NASA Astrophysics Data System (ADS)

    Hu, JiaGuang; Xu, Wen

    2014-06-01

    We present a detailed theoretical study on the acoustic band structure of two-dimensional (2D) phononic crystal. The 2D phononic crystal with parallelogram lattice structure is considered to be formed by rigid solid rods embedded in air. For the circular rods, some of the extrema of the acoustic bands appear in the usual high-symmetry points and, in contrast, we find that some of them are located in other specific lines. For the case of elliptic rods, our results indicate that it is necessary to study the whole first Brillouin zone to obtain rightly the band structure and corresponding band gaps. Furthermore, we evaluate the first and second band gaps using the plane wave expansion method and find that these gaps can be tuned by adjusting the side lengths ratio R, inclined angle θ and filling fraction F of the parallelogram lattice with circular rods. The results show that the largest value of the first band gap appears at θ=90° and F=0.7854. In contrast, the largest value of the second band gap is at θ=60° and F=0.9068. Our results indicate that the improvement of matching degree between scatterers and lattice pattern, rather than the reduction of structural symmetry, is mainly responsible for the enhancement of the band gaps in the 2D phononic crystal.

  5. Resonant tunneling diode based on band gap engineered graphene antidot structures

    NASA Astrophysics Data System (ADS)

    Palla, Penchalaiah; Ethiraj, Anita S.; Raina, J. P.

    2016-04-01

    The present work demonstrates the operation and performance of double barrier Graphene Antidot Resonant Tunnel Diode (DBGA-RTD). Non-Equilibrium Green's Function (NEGF) frame work with tight-binding Hamiltonian and 2-D Poisson equations were solved self-consistently for device study. The interesting feature in this device is that it is an all graphene RTD with band gap engineered graphene antidot tunnel barriers. Another interesting new finding is that it shows negative differential resistance (NDR), which involves the resonant tunneling in the graphene quantum well through both the electron and hole bound states. The Graphene Antidot Lattice (GAL) barriers in this device efficiently improved the Peak to Valley Ratio to approximately 20 even at room temperature. A new fitting model is developed for the number of antidots and their corresponding effective barrier width, which will help in determining effective barrier width of any size of actual antidot geometry.

  6. Finding structures with specific properties in complex configurational spaces using multi-target inverse band structure approach

    NASA Astrophysics Data System (ADS)

    Piquini, Paulo; Zunger, Alex

    2009-03-01

    The conventional strategy to look for materials with desired properties is to use physical intuition to select some candidates among an enormous number of possibilities.Apart the very special cases, the solutions to these search problems are far from obvious. The inverse band structure (IBS) approach, on the other hand, search for the desired electronic structures (instead of atomic configurations) from the beginning. Here we illustrate the power of this inverse approach by applying it to the simultaneous engineering of multi-target problems, which encompass huge configurational spaces: (i) the search of a specific band gap in the quaternary (In,Ga)(As,Sb) semiconductors(a) lattice-matched to InP and, (ii) the stacking sequence of (In,Ga)As/InP superlattices leading to band gaps and strains within the range suitable for thermophotovoltaic applications(b). [3pt] (a) P. Piquini, P.A. Graf, and A. Zunger, Phys. Rev. Lett. 100, 186403 (2008); [0pt] (b) P. Piquini and A. Zunger, Phys. Rev. B 78, 161302 (2008)

  7. High gain low noise L-band preamplifier with cascade double-pass structure

    NASA Astrophysics Data System (ADS)

    Jia, Dongfang; Wang, Yanyong; Bao, Huanmin; Yang, Tianxin; Li, Shichen

    2005-06-01

    An optimized two-stage-cascade double-pass structure L-band preamplifier was proposed and experimentally studied to overcome the shortcomings of low gain coefficient and high noise figure of L-band erbium-doped fiber amplifier (EDFA). The fiber lengthes of 6.5 and 32.5 m, pump powers of 130 and 119 mW for the first and second stages respectively are used in the experiment. When input signal power is -30 dBm, the amplifier can provide gain above 38.84 dB in a wavelength range of 34 nm (1568---1602 nm), gain ripple less than 2.04 dB (40.88---38.84 dB), and noise figures lower than 5.29 dB with the lowest value of 3.95 dB at 1590 nm. Experimental and simulation results show that this low cost and high pump efficiency amplifier is suitable for the application as an L-band preamplifier in the broadband fiber communication system.

  8. 1D-TlInSe2: Band Structure, Dielectric Function and Nanorods

    NASA Astrophysics Data System (ADS)

    Mamedov, Nazim; Wakita, Kazuki; Akita, Seiji; Nakayama, Yoshikazu

    2005-01-01

    Linear combination of atomic orbitals (LCAO) analysis of the electronic band states has been completed for one-dimensional (1D) TlInSe2 having rod-like ground state shape of bulky crystal. The total scenario of the occurrence of the band states from the atomic states has been established. According to this scenario, in dipole approximation the optical transitions at band gap (point T of Brillouin zone) are either entirely forbidden or allowed for T2-T10 transitions in e\\perpc configuration provided that either initial or terminate state has T2 symmetry and both are Se-like. As a whole, the obtained results on the electronic spectrum, including dielectric function, are applicable to all obtained 1D-TlInSe2 nanorods which were as thin as 30--50 nm in cross-section, and apparently preserved tetragonal crystal structure of bulky material. The thermal instabilities developing already in bulky samples of 1D-TlInSe2 are considered to be an ultimate source of the nanoparticles emerging in plenty during nanorods preparation. The nanoplates of a chemically similar but 2D material, TlInS2, are demonstrated for comparison to show the absence of nanoparticles in that case. A possibility of nanoparticle preparation using laser excited coherent phonon trains in the nanorods of 1D-TlInSe2 is figured out.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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 π 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 γ1. 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.

  10. Band structure characterization of WS2 grown by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Tanabe, Iori; Gomez, Michael; Coley, William C.; Le, Duy; Echeverria, Elena M.; Stecklein, Gordon; Kandyba, Viktor; Balijepalli, Santosh K.; Klee, Velveth; Nguyen, Ariana E.; Preciado, Edwin; Lu, I.-Hsi; Bobek, Sarah; Barroso, David; Martinez-Ta, Dominic; Barinov, Alexei; Rahman, Talat S.; Dowben, Peter A.; Crowell, Paul A.; Bartels, Ludwig

    2016-06-01

    Growth by chemical vapor deposition (CVD) leads to multilayer WS2 of very high quality, based on high-resolution angle-resolved photoemission spectroscopy. The experimental valence band electronic structure is considered to be in good agreement with that obtained from density functional theory calculations. We find the spin-orbit splitting at the K ¯ point to be 420 ± 20 meV with a hole effective mass of -0.35 ± 0.02 me for the upper spin-orbit component (the branch closer to the Fermi level) and -0.43 ± 0.07 me for the lower spin-orbit component. As predicted by theory, a thickness-dependent increase of bandwidth is observed at the top of the valence band, in the region of the Brillouin zone center. The top of the valence band of the CVD-prepared films exhibits a substantial binding energy, consistent with n-type behavior, and in agreement with transistor characteristics acquired using devices incorporating the same WS2 material.

  11. Theoretical investigation of the band structure of picene single crystals within the GW approximation

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Susumu; Morikawa, Yoshitada; Schindlmayr, Arno

    2014-01-01

    We investigate the band dispersion and related electronic properties of picene single crystals within the GW approximation for the electronic self-energy. The width of the upper highest occupied molecular orbital (HOMOu) band along the Γ-Y direction, corresponding to the b crystal axis in real space along which the molecules are stacked, is determined to be 0.60 eV and thus 0.11 eV larger than the value obtained from density-functional theory. As in our recent study of rubrene using the same methodology [S. Yanagisawa, Y. Morikawa, and A. Schindlmayr, Phys. Rev. B 88, 115438 (2013)], this increase in the bandwidth is due to the strong variation of the GW self-energy correction across the Brillouin zone, which in turn reflects the increasing hybridization of the HOMOu states of neighboring picene molecules from Γ to Y. In contrast, the width of the lower HOMO (HOMOl) band along Γ-Y remains almost unchanged, consistent with the fact that the HOMOl(Γ) and HOMOl(Y) states exhibit the same degree of hybridization, so that the nodal structure of the wave functions and the matrix elements of the self-energy correction are very similar.

  12. High Stability CFRP Support Structure for Ka Band Multi-Spot Cluster

    NASA Astrophysics Data System (ADS)

    Yarza, A.; Cano, J.; Ozores, E.

    2012-07-01

    In the recent days, Ka band mission are being implemented for telecommunication satellites as emergent technology. EADS CASA Espacio (ASTRIUM) has been doing developments able to face up the demanding requirements associated to this frequency band where aspects such as in orbit stability o manufacturing accuracy are essential. Once it has been demonstrated the capability to offer excellent antenna reflectors with low mass, very low ohmic losses, excellent RF performances and very stable in orbit thermoelastic behaviour, improvements at feeder-chain level have been developed with the aim to cover the global antenna mission with excellent performances. This paper presents the product developed to accommodate a KA band multi-spot cluster to cover a telecommunication mission. It includes a description of the tasks carried out until the current development status, with the definition of the mechanical specification used as applicable and the solutions applied to meet the requirements. A CFRP structure is proposed with the aim to achieve a light mass concept, structurally speaking optimized and capable to assemble multiple feeder chain and make independent the thermomechanical behaviour of each one. Moreover, the design with CFRP leads to very stable thermoelastic behaviour of the assembly and the feeder-chain with the scope to guaranty the stability of the RF-beam for the correct electrical performances. The compatibility between the carbon fibre structure and the Aluminium feeder chain is solved by means of isostatic devices that are capable to absorb the thermal stresses coming from the different thermal expansion coefficients of the materials used. The proposed design is to be confirmed over a Qualification Model, already manufactured, with the scope to be implemented as flight hardware in a commercial spacecraft. The product is to be tested in a full qualification environmental test campaign where the capability to withstand the dynamic loads and the thermal

  13. SILICOMB PEEK Kirigami cellular structures: mechanical response and energy dissipation through zero and negative stiffness

    NASA Astrophysics Data System (ADS)

    Virk, K.; Monti, A.; Trehard, T.; Marsh, M.; Hazra, K.; Boba, K.; Remillat, C. D. L.; Scarpa, F.; Farrow, I. R.

    2013-08-01

    The work describes the manufacturing, testing and parametric analysis of cellular structures exhibiting zero Poisson’s ratio-type behaviour, together with zero and negative stiffness effects. The cellular structures are produced in flat panels and curved configurations, using a combination of rapid prototyping techniques and Kirigami (Origami and cutting) procedures for PEEK (Polyether Ether Ketone) thermoplastic composites. The curved cellular configurations show remarkable large deformation behaviours, with zero and negative stiffness regimes depending also on the strain rate applied. These unusual stiffness characteristics lead to a large increase of energy absorption during cyclic tests.

  14. The band-gap structures and recovery rules of generalized n-component Fibonacci piezoelectric superlattices

    NASA Astrophysics Data System (ADS)

    Liu, Da; Zhang, Weiyi

    2011-04-01

    In this communication, the band-gap structures of n-CF piezoelectric superlattices have been calculated using the transfer-matrix-method, the self-similarity behavior and recovery rule have been systematically analyzed. Consistent with the rigorous mathematical proof by Hu et al. [A. Hu, Z.X. Wen, S.S. Jiang, W.T. Tong, R.W. Peng, D. Feng, Phys. Rev. B 48 (1993) 829], we find that the n-CF sequences with 2≤n≤4 are identified as quasiperiodic. The imaginary wave numbers are characterized by the self-similar spectrum, their major peaks can all be properly indexed. In addition, we find that the n=5 sequence belongs to a critical case which lies at the border between quasiperiodic and non-quasiperiodic structures. The frequency range of the self-similarity pattern approaches zero and a unique indexing of imaginary wave numbers becomes impossible. Our study offers the information on the critical 5-CF superlattice which was not available before. The classification of band-gap structures and the scaling laws around fixed points are also given.

  15. Periodic dielectric structure for production of photonic band gap and devices incorporating the same

    DOEpatents

    Ho, Kai-Ming; Chan, Che-Ting; Soukoulis, Costas

    1994-08-02

    A periodic dielectric structure which is capable of producing a photonic band gap and which is capable of practical construction. The periodic structure is formed of a plurality of layers, each layer being formed of a plurality of rods separated by a given spacing. The material of the rods contrasts with the material between the rods to have a refractive index contrast of at least two. The rods in each layer are arranged with their axes parallel and at a given spacing. Adjacent layers are rotated by 90.degree., such that the axes of the rods in any given layer are perpendicular to the axes in its neighbor. Alternating layers (that is, successive layers of rods having their axes parallel such as the first and third layers) are offset such that the rods of one are about at the midpoint between the rods of the other. A four-layer periocity is thus produced, and successive layers are stacked to form a three-dimensional structure which exhibits a photonic band gap. By virtue of forming the device in layers of elongate members, it is found that the device is susceptible of practical construction.

  16. Effect of species structure and dielectric constant on C-band forest backscatter

    NASA Technical Reports Server (NTRS)

    Lang, R. H.; Landry, R.; Kilic, O.; Chauhan, N.; Khadr, N.; Leckie, D.

    1993-01-01

    A joint experiment between Canadian and USA research teams was conducted early in Oct. 1992 to determine the effect of species structure and dielectric variations on forest backscatter. Two stands, one red pine and one jack pine, in the Petawawa National Forestry Institute (PNFI) were utilized for the experiment. Extensive tree architecture measurements had been taken by the Canada Centre for Remote Sensing (CCRS) several months earlier by employing a Total Station surveying instrument which provides detailed information on branch structure. A second part of the experiment consisted of cutting down several trees and using dielectric probes to measure branch and needle permittivity values at both sites. The dielectric and the tree geometry data were used in the George Washington University (GWU) Vegetation Model to determine the C band backscattering coefficients of the individual stands for VV polarization. The model results show that backscatter at C band comes mainly from the needles and small branches and the upper portion of the trunks acts only as an attenuator. A discussion of variation of backscatter with specie structure and how dielectric variations in needles for both species may affect the total backscatter returns is provided.

  17. Energy-band structure and intrinsic coherent properties in two weakly linked Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Li, Wei-Dong; Zhang, Yunbo; Liang, J.-Q.

    2003-06-01

    The energy-band structure and energy splitting due to quantum tunneling in two weakly linked Bose-Einstein condensates were calculated by using the instanton method. The intrinsic coherent properties of Bose-Josephson junction (BJJ) were investigated in terms of energy splitting. For EC/EJ≪1, the energy splitting is small and the system is globally phase coherent. In the opposite limit, EC/EJ≫1, the energy splitting is large and the system becomes phase dissipated. Our results suggest that one should investigate the coherence phenomena of BJJ in proper condition such as EC/EJ˜1.

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

    PubMed

    Cerjan, Alexander; Raman, Aaswath; Fan, Shanhui

    2016-05-20

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

  19. S- plus C-band erbium-doped fiber amplifier in parallel structure

    NASA Astrophysics Data System (ADS)

    Yeh, Chien-Hung; Lee, Chien-Chung; Chi, Sien

    2004-11-01

    A new S- plus C-band erbium-doped fiber amplifier (EDFA) module with coupled structure over 96 nm gain bandwidth of 1480-1576 nm has been experimentally investigated and demonstrated. For this proposed configuration, 30 and 36.2 dB peak gains are observed at 1506 and 1532 nm, respectively, when the input signal power is -25 dBm. In addition, this proposed amplifier module also can provide a broadband amplified spontaneous emission (ASE) light source from 1480 to 1572 nm.

  20. Electronic band structure imaging of three layer twisted graphene on single crystal Cu(111)

    SciTech Connect

    Marquez Velasco, J.; Kelaidis, N.; Xenogiannopoulou, E.; Tsoutsou, D.; Tsipas, P.; Speliotis, Th.; Pilatos, G.; Likodimos, V.; Falaras, P.; Dimoulas, A.; Raptis, Y. S.

    2013-11-18

    Few layer graphene (FLG) is grown on single crystal Cu(111) by Chemical Vapor Deposition, and the electronic valence band structure is imaged by Angle-Resolved Photo-Emission Spectroscopy. It is found that graphene essentially grows polycrystalline. Three nearly ideal Dirac cones are observed along the Cu Γ{sup ¯}K{sup ¯} direction in k-space, attributed to the presence of ∼4° twisted three layer graphene with negligible interlayer coupling. The number of layers and the stacking order are compatible with Raman data analysis demonstrating the complementarity of the two techniques for a more accurate characterization of FLG.

  1. Complex band structure under plane-wave nonlocal pseudopotential Hamiltonian of metallic wires and electrodes

    SciTech Connect

    Yang, Chao

    2009-07-17

    We present a practical approach to calculate the complex band structure of an electrode for quantum transport calculations. This method is designed for plane wave based Hamiltonian with nonlocal pseudopotentials and the auxiliary periodic boundary condition transport calculation approach. Currently there is no direct method to calculate all the evanescent states for a given energy for systems with nonlocal pseudopotentials. On the other hand, in the auxiliary periodic boundary condition transport calculation, there is no need for all the evanescent states at a given energy. The current method fills this niche. The method has been used to study copper and gold nanowires and bulk electrodes.

  2. First principles electronic band structure and phonon dispersion curves for zinc blend beryllium chalcogenide

    SciTech Connect

    Dabhi, Shweta Mankad, Venu Jha, Prafulla K.

    2014-04-24

    A detailed theoretical study of structural, electronic and Vibrational properties of BeX compound is presented by performing ab-initio calculations based on density-functional theory using the Espresso package. The calculated value of lattice constant and bulk modulus are compared with the available experimental and other theoretical data and agree reasonably well. BeX (X = S,Se,Te) compounds in the ZB phase are indirect wide band gap semiconductors with an ionic contribution. The phonon dispersion curves are represented which shows that these compounds are dynamically stable in ZB phase.

  3. Electronic band structure calculation of GaNAsBi alloys and effective mass study

    NASA Astrophysics Data System (ADS)

    Habchi, M. M.; Ben Nasr, A.; Rebey, A.; El Jani, B.

    2013-11-01

    Electronic band structures of GaNxAs1-x-yBiy dilute nitrides-bismides have been determined theoretically within the framework of the band anticrossing (BAC) model and k ṡ p method. We have developed computer codes based on our extended BAC model, denoted (16 × 16), in which the dimension of the used states basis was equal to 16. We have investigated the band gap and the spin orbit splitting as a function of Bi composition for alloys lattice matched to GaAs. We have found that the substitution of As element by N and Bi impurities leads to a significant reduction of band gap energy by roughly 198 meV/%Bi. Meanwhile, spin orbit splitting increases by 56 meV/%Bi regardless N content. There is an excellent agreement between the model predictions and experiment reported in the literature. In addition, alloys compositions and oscillator strengths of transition energies have been calculated for GaNAsBi alloys which represent active zone of temperature insensitive (1.55 μm and 1.3 μm) wavelength laser diodes intended for optical fiber communications. A crossover at about 0.6 eV has occurred between Eg and Δso of GaN.039As.893Bi.068. When the quaternary is lattice mismatched to GaAs, resonance energy increases with Bi content if N content decreases. On the other hand, effective mass behavior of carriers at Γ point has been discussed with respect to alloy composition, k-directions and lattice mismatch.

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

    SciTech Connect

    Kevin Jerome Sutherland

    2001-06-27

    Over the last ten years, photonic band gap (PBG) theory and technology have become an important area of research because of the numerous possible applications ranging from high-efficiency laser diodes to optical circuitry. This research concentrates on reducing the length scale in the fabrication of layered photonic band gap structures and developing procedures to improve processing consistency. Various procedures and materials have been used in the fabrication of layered PBG structures. This research focused on an economical micro transfer molding approach to create the final PBG structure. A poly dimethylsiloxane (PDMS) rubber mold was created from a silicon substrate. It was filled with epoxy and built layer-by-layer to create a 3-D epoxy structure. This structure was infiltrated with nanoparticle titania or a titania sol-gel, then fired to remove the polymer mold, leaving a monolithic ceramic inverse of the epoxy structure. The final result was a lattice of titania rolds that resembles a face-centered tetragonal structure. The original intent of this research was to miniaturize this process to a bar size small enough to create a photonic band gap for wavelengths of visible electro-magnetic radiation. The factor limiting progress was the absence of a silicon master mold of small enough dimensions. The Iowa State Microelectronics Research Center fabricated samples with periodicities of 2.5 and 1.0 microns with the existing technology, but a sample was needed on the order of 0.3 microns or less. A 0.4 micron sample was received from Sandia National Laboratory, which was made through an electron beam lithography process, but it contained several defects. The results of the work are primarily from the 2.5 and 1.0 micron samples. Most of the work focused on changing processing variables in order to optimize the infiltration procedure for the best results. Several critical parameters were identified, ranging from the ambient conditions to the specifics of the

  5. The role of beryllium in the band structure of MgZnO: Lifting the valence band maximum

    NASA Astrophysics Data System (ADS)

    Chen, S. S.; Pan, X. H.; Chen, W.; Zhang, H. H.; Dai, W.; Ding, P.; Huang, J. Y.; Lu, B.; Ye, Z. Z.

    2014-09-01

    We investigate the effect of Be on the valence band maximum (VBM) of MgZnO by measuring the band offsets of MgxZn1-xO/BexMgyZn1-x-yO heterojunctions using X-ray photoelectron spectroscopy measurements. MgxZn1-xO and BexMgyZn1-x-yO films have been grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The valence band offset ( Δ E V) of Mg0.15Zn0.85O ( E g = 3.62 eV)/Be0.005Mg0.19Zn0.805O ( E g = 3.73 eV) heterojunction is 0.01 eV and Be0.005Mg0.19Zn0.805O has a lower VBM. The increased Mg composition is the main factor for the reduction of VBM. The VBM of MgxZn1-xO is lower by 0.03 eV with the enlargement of E g from 3.62 eV to 3.73 eV by increasing Mg composition. Considering the effect of increased Mg composition, it is concluded that the little amount of Be makes the VBM go up by 0.02 eV when the E g of the alloy is 3.73 eV. The Δ E V of Mg0.11Zn0.89O ( E g = 3.56 eV)/Be0.007Mg0.12Zn0.873O ( E g = 3.56 eV) heterojunction is calculated to be 0.03 eV and Be0.007Mg0.12Zn0.873O has a higher VBM than Mg0.11Zn0.89O, which means that a little amount Be lifts the VBM by 0.03 eV when the E g of the alloy is 3.56 eV. The experimental measurements have offered a strong support for the theoretical research that alloying Be in MgxZn1-xO alloys is hopeful to form a higher VBM and to enhance the p-type dopability of MgZnO.

  6. Advances in X-Band TW Accelerator Structures Operating in the 100 MV/M Regime

    SciTech Connect

    Higo, Toshiyasu; Higashi, Yasuo; Matsumoto, Shuji; Yokoyama, Kazue; Adolphsen, Chris; Dolgashev, Valery; Jensen, Aaron; Laurent, Lisa; Tantawi, Sami; Wang, Faya; Wang, Juwen; Dobert, Steffen; Grudiev, Alexej; Riddone, Germana; Wuensch, Walter; Zennaro, Riccardo; /CERN

    2012-07-05

    A CERN-SLAC-KEK collaboration on high gradient X-band accelerator structure development for CLIC has been ongoing for three years. The major outcome has been the demonstration of stable 100 MV/m gradient operation of a number of CLIC prototype structures. These structures were fabricated using the technology developed from 1994 to 2004 for the GLC/NLC linear collider initiative. One of the goals has been to refine the essential parameters and fabrication procedures needed to realize such a high gradient routinely. Another goal has been to develop structures with stronger dipole mode damping than those for GLC/NLC. The latter requires that the surface temperature rise during the pulse be higher, which may increase the breakdown rate. One structure with heavy damping has been RF processed and another is nearly finished. The breakdown rates of these structures were found to be higher by two orders of magnitude compared to those with equivalent acceleration mode parameters but without the damping features. This paper presents these results together with some of the earlier results from non-damped structures.

  7. Anisotropy of inter-band transitions and band structure of Cs3Zn6B9O21 nonlinear optical crystals

    NASA Astrophysics Data System (ADS)

    Bovgyra, O. V.; Kurlak, V. Y.; Chrunik, M.; Majchrowski, A.; Jaroszewicz, L. R.; Ozga, K.

    2016-06-01

    Polarized optical functions near the fundamental absorption edge of novel Cs3Zn6B9O21 nonlinear optical crystals possessing a wide UV transparency down to 190 nm were investigated. The anisotropy of optical functions is not well studied yet which restrains the further strategy of the formation on its base of solid state compounds with desirable properties. The studies were performed using a band structure calculations as well as the experimental measurements of fundamental polarized UV absorption edge and X-ray photoelectron spectra of the studied crystals. The experimental data were used for evaluation of scissor factors of the band structure. The results of the calculations were compared with the XPS and polarized absorption optical spectra of the investigated crystals. The introduction of the scissor factor was performed in order to obtain a sufficient agreement with experiment. The observed anisotropy of absorption may be explained by the anisotropy of carrier effective masses.

  8. Disgust proneness and obsessive-compulsive symptoms in a clinical sample: structural differentiation from negative affect.

    PubMed

    Olatunji, Bunmi O; Ebesutani, Chad; David, Bieke; Fan, Qianqian; McGrath, Patrick B

    2011-10-01

    Although a growing body of research has revealed robust associations between disgust and obsessive-compulsive disorder (OCD) symptoms, there remains a paucity of research examining the specificity of this association in clinical samples. The present study employed structural equation modeling to differentiate disgust from negative affect in the prediction of OCD symptoms in a clinical sample (n=153). Results indicate that disgust and negative affect latent factors were independently related to OCD symptoms. However, when both variables were simultaneously modeled as predictors, latent disgust remained significantly associated with OCD symptoms, whereas the association between latent negative affect and OCD symptoms became nonsignificant. Multiple statistical tests of mediation converged in support of disgust as a significant intervening variable between negative affect and OCD symptoms. The implications of these findings for further delineating the role of individual differences in disgust proneness in the development of OCD are discussed.

  9. Correlation of Photocatalytic Activity with Band Structure of Low-dimensional Semiconductor Nanostructures

    NASA Astrophysics Data System (ADS)

    Meng, Fanke

    Photocatalytic hydrogen generation by water splitting is a promising technique to produce clean and renewable solar fuel. The development of effective semiconductor photocatalysts to obtain efficient photocatalytic activity is the key objective. However, two critical reasons prevent wide applications of semiconductor photocatalysts: low light usage efficiency and high rates of charge recombination. In this dissertation, several low-dimensional semiconductors were synthesized with hydrothermal, hydrolysis, and chemical impregnation methods. The band structures of the low-dimensional semiconductor materials were engineered to overcome the above mentioned two shortcomings. In addition, the correlation between the photocatalytic activity of the low-dimensional semiconductor materials and their band structures were studied. First, we studied the effect of oxygen vacancies on the photocatalytic activity of one-dimensional anatase TiO2 nanobelts. Given that the oxygen vacancy plays a significant role in band structure and photocatalytic performance of semiconductors, oxygen vacancies were introduced into the anatase TiO2 nanobelts during reduction in H2 at high temperature. The oxygen vacancies of the TiO2 nanobelts boosted visible-light-responsive photocatalytic activity but weakened ultraviolet-light-responsive photocatalytic activity. As oxygen vacancies are commonly introduced by dopants, these results give insight into why doping is not always beneficial to the overall photocatalytic performance despite increases in absorption. Second, we improved the photocatalytic performance of two-dimensional lanthanum titanate (La2Ti2 O7) nanosheets, which are widely studied as an efficient photocatalyst due to the unique layered crystal structure. Nitrogen was doped into the La2Ti2O7 nanosheets and then Pt nanoparticles were loaded onto the La2Ti2O7 nanosheets. Doping nitrogen narrowed the band gap of the La2Ti 2O7 nanosheets by introducing a continuum of states by the valence

  10. Negative thermal expansion in CuCl: An extended x-ray absorption fine structure study

    SciTech Connect

    Vaccari, M.; Grisenti, R.; Fornasini, P.; Rocca, F.; Sanson, A.

    2007-05-01

    Extended x-ray absorption fine structure (EXAFS) has been measured from liquid helium to ambient temperature at the Cu K edge of copper chloride (CuCl) to investigate the local origin of negative thermal expansion. A quantitative analysis of the first coordination shell, performed by the cumulant method, reveals that the nearest-neighbor Cu-Cl interatomic distance undergoes a strong positive expansion, contrasting with the much weaker negative expansion of the crystallographic distance between average atomic positions below 100 K. The anisotropy of relative thermal vibrations, monitored by the ratio {gamma} between perpendicular and parallel mean square relative displacements, is considerably high, while the diffraction thermal factors are isotropic. The relative perpendicular vibrations measured by EXAFS are related to the tension mechanism and to the transverse acoustic modes, which are considered responsible for negative thermal expansion in zinc-blende structures.

  11. Automatic control of negative emotions: evidence that structured practice increases the efficiency of emotion regulation.

    PubMed

    Christou-Champi, Spyros; Farrow, Tom F D; Webb, Thomas L

    2015-01-01

    Emotion regulation (ER) is vital to everyday functioning. However, the effortful nature of many forms of ER may lead to regulation being inefficient and potentially ineffective. The present research examined whether structured practice could increase the efficiency of ER. During three training sessions, comprising a total of 150 training trials, participants were presented with negatively valenced images and asked either to "attend" (control condition) or "reappraise" (ER condition). A further group of participants did not participate in training but only completed follow-up measures. Practice increased the efficiency of ER as indexed by decreased time required to regulate emotions and increased heart rate variability (HRV). Furthermore, participants in the ER condition spontaneously regulated their negative emotions two weeks later and reported being more habitual in their use of ER. These findings indicate that structured practice can facilitate the automatic control of negative emotions and that these effects persist beyond training.

  12. Automatic control of negative emotions: Evidence that structured practice increases the efficiency of emotion regulation

    PubMed Central

    Christou-Champi, Spyros; Farrow, Tom F. D.; Webb, Thomas L.

    2015-01-01

    Emotion regulation (ER) is vital to everyday functioning. However, the effortful nature of many forms of ER may lead to regulation being inefficient and potentially ineffective. The present research examined whether structured practice could increase the efficiency of ER. During three training sessions, comprising a total of 150 training trials, participants were presented with negatively valenced images and asked either to “attend” (control condition) or “reappraise” (ER condition). A further group of participants did not participate in training but only completed follow-up measures. Practice increased the efficiency of ER as indexed by decreased time required to regulate emotions and increased heart rate variability (HRV). Furthermore, participants in the ER condition spontaneously regulated their negative emotions two weeks later and reported being more habitual in their use of ER. These findings indicate that structured practice can facilitate the automatic control of negative emotions and that these effects persist beyond training. PMID:24678930

  13. Formation of ordered cellular structures in suspension via label-free negative magnetophoresis

    PubMed Central

    Krebs, Melissa D.; Erb, Randall M.; Yellen, Benjamin B.; Samanta, Bappaditya; Bajaj, Avinash; Rotello, Vincent M.; Alsberg, Eben

    2009-01-01

    The creation of ordered cellular structures is important for tissue engineering research. Here we present a novel strategy for the assembly of cells into linear arrangements by negative magnetophoresis using inert, cytocompatible magnetic nanoparticles. In this approach, magnetic nanoparticles dictate the cellular assembly without relying on cell binding or uptake. The linear cell structures are stable and can be further cultured without the magnetic field or nanoparticles, making this an attractive tool for tissue engineering. PMID:19326920

  14. Crystal lattice and band structure of the intermediate high-pressure phase of PbSe.

    PubMed

    Streltsov, S V; Manakov, A Yu; Vokhmyanin, A P; Ovsyannikov, S V; Shchennikov, V V

    2009-09-23

    In the present paper the results of fitting synchrotron diffraction data are obtained for the intermediate high-pressure phase (9.5 GPa) of the lead selenide based compound Pb(1-x)Sn(x)Se (x = 0.125)-an optoelectronic as well as a thermoelectric material-for two types of lattice symmetries Pnma (space group #62) and Cmcm (space group #63). Both lattice parameters and positions of atoms for the above mentioned structures have been used in calculations of the electron structure of high-pressure phases. The main difference between the electronic properties for Cmcm and Pnma structures established in electronic structure calculations is that in the first one the PbSe compound was found to be a metal, while in the second a small semiconductor gap (E(G) = 0.12 eV) was obtained. Moreover, the forces in the Cmcm structure are an order of magnitude larger than those calculated for the Pnma lattice. In the optimized, Pnma structure within a generalized gradient approximation (GGA), the band gap increases up to E(G) = 0.27 eV. The result coincides with the data on thermoelectric power and electrical resistance data pointing to a semiconductor gap of ∼0.2 eV at ∼9.5 GPa. Thus, the Pmna type of lattice seems to be a preferable version for the intermediate phase compared with the Cmcm one. PMID:21832372

  15. The Internal Structure of Positive and Negative Affect: A Confirmatory Factor Analysis of the PANAS

    ERIC Educational Resources Information Center

    Tuccitto, Daniel E.; Giacobbi, Peter R., Jr.; Leite, Walter L.

    2010-01-01

    This study tested five confirmatory factor analytic (CFA) models of the Positive Affect Negative Affect Schedule (PANAS) to provide validity evidence based on its internal structure. A sample of 223 club sport athletes indicated their emotions during the past week. Results revealed that an orthogonal two-factor CFA model, specifying error…

  16. 108. Catalog OPark Structure/Construction & Maintenance, 26 Roads, Negative Number ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    108. Catalog O-Park Structure/Construction & Maintenance, 26 Roads, Negative Number P 138b (Photographer and date unknown) PARAPET UNDER CONSTRUCTION AT CRESCENT ROCK OVERLOOK. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  17. Band structure and transmission characteristics of complex phononic crystals by multi-level substructure scheme

    NASA Astrophysics Data System (ADS)

    Yin, J.; Zhang, S.; Zhang, H. W.; Chen, B. S.

    2015-10-01

    A fast scheme based on the multi-level substructure technique is proposed for the band structure and transmission characteristics calculation of phononic crystals uniformly. The main idea is that finite element models of phononic crystals are divided into several domains by a special multi-level decomposition. For the band structure calculation, the upscaling calculation is employed to condense the internal stiffness matrix of the unit cell into the Bloch boundary. Due to the internal stiffness matrix does not change along with reduced wave vectors in an iteration process, the scheme can reduce the computational scale and improve the efficiency greatly, meanwhile it does not introduce approximation into the traditional finite element model. For the transmission characteristics calculation, the unit cell of the phononic crystal is periodic which is taken as a substructure with the same coefficient matrix. Moreover, the downscaling calculation of internal displacements can be selected flexibly. Some closely watched examples of the three-dimensional locally resonant, defect state of Lamb wave and Bragg waveguide are analyzed. Numerical results indicate that the proposed scheme is efficient and accurate, which may widely be applicable and suitable for complex phononic crystal problems, and provides a reliable numerical tool to optimize and design crystal devices.

  18. Correlating structure and electronic band-edge properties in organolead halide perovskites nanoparticles.

    PubMed

    Zhu, Qiushi; Zheng, Kaibo; Abdellah, Mohamed; Generalov, Alexander; Haase, Dörthe; Carlson, Stefan; Niu, Yuran; Heimdal, Jimmy; Engdahl, Anders; Messing, Maria E; Pullerits, Tonu; Canton, Sophie E

    2016-06-01

    After having emerged as primary contenders in the race for highly efficient optoelectronics materials, organolead halide perovskites (OHLP) are now being investigated in the nanoscale regime as promising building blocks with unique properties. For example, unlike their bulk counterpart, quantum dots of OHLP are brightly luminescent, owing to large exciton binding energies that cannot be rationalized solely on the basis of quantum confinement. Here, we establish the direct correlation between the structure and the electronic band-edge properties of CH3NH3PbBr3 nanoparticles. Complementary structural and spectroscopic measurements probing long-range and local order reveal that lattice strain influences the nature of the valence band and modifies the subtle stereochemical activity of the Pb(2+) lone-pair. More generally, this work demonstrates that the stereochemical activity of the lone-pair at the metal site is a specific physicochemical parameter coupled to composition, size and strain, which can be employed to engineer novel functionalities in OHLP nanomaterials. PMID:27189431

  19. Band-structure-based collisional model for electronic excitations in ion-surface collisions

    SciTech Connect

    Faraggi, M.N.; Gravielle, M.S.; Alducin, M.; Silkin, V.M.; Juaristi, J.I.

    2005-07-15

    Energy loss per unit path in grazing collisions with metal surfaces is studied by using the collisional and dielectric formalisms. Within both theories we make use of the band-structure-based (BSB) model to represent the surface interaction. The BSB approach is based on a model potential and provides a precise description of the one-electron states and the surface-induced potential. The method is applied to evaluate the energy lost by 100 keV protons impinging on aluminum surfaces at glancing angles. We found that when the realistic BSB description of the surface is used, the energy loss obtained from the collisional formalism agrees with the dielectric one, which includes not only binary but also plasmon excitations. The distance-dependent stopping power derived from the BSB model is in good agreement with available experimental data. We have also investigated the influence of the surface band structure in collisions with the Al(100) surface. Surface-state contributions to the energy loss and electron emission probability are analyzed.

  20. Band structure of topological insulators from noise measurements in tunnel junctions

    SciTech Connect

    Cascales, Juan Pedro Martínez, Isidoro; Aliev, Farkhad G.; Katmis, Ferhat; Moodera, Jagadeesh S.; Chang, Cui-Zu; Guerrero, Rubén

    2015-12-21

    The unique properties of spin-polarized surface or edge states in topological insulators (TIs) make these quantum coherent systems interesting from the point of view of both fundamental physics and their implementation in low power spintronic devices. Here we present such a study in TIs, through tunneling and noise spectroscopy utilizing TI/Al{sub 2}O{sub 3}/Co tunnel junctions with bottom TI electrodes of either Bi{sub 2}Te{sub 3} or Bi{sub 2}Se{sub 3}. We demonstrate that features related to the band structure of the TI materials show up in the tunneling conductance and even more clearly through low frequency noise measurements. The bias dependence of 1/f noise reveals peaks at specific energies corresponding to band structure features of the TI. TI tunnel junctions could thus simplify the study of the properties of such quantum coherent systems that can further lead to the manipulation of their spin-polarized properties for technological purposes.

  1. First-principles calculation of diamagnetic band structure. II. Spectrum and wave functions

    NASA Astrophysics Data System (ADS)

    Schellnhuber, Hans-Joachim; Obermair, Gustav M.; Rauh, Alexander

    1981-05-01

    The diamagnetic band structure is calculated by means of a variational method. This is done for the simplest nontrivial crystal potential which is characterized by two elementary wave vectors in the plane normal to the magnetic field. The numerical calculations are highly accurate and provide an energy spectrum which is simultaneously correct in the high-field (Landau) case, in the magnetic breakdown area, and in the low-field (Onsager) regime. For comparison we calculate also the spectrum of the effective Peierls-Onsager Hamiltonian (POH) which has been used so far almost exclusively to describe the diamagnetic phenomena in solids. This semiclassical theory turns out to be in serious disagreement with the first-principles spectrum when the effective POH refers to a degenerate Bloch band. We show also that the invariance group of the POH is different from that of the original Hamiltonian. The structure of the wave functions is analyzed in terms of two superposed space periods, one being related to the Larmor radius, the other to the lattice constant.

  2. Quasiparticle band structure of infinite hydrogen fluoride and hydrogen chloride chains

    NASA Astrophysics Data System (ADS)

    Buth, Christian

    2006-10-01

    We study the quasiparticle band structure of isolated, infinite (HF)∞ and (HCl)∞ bent (zigzag) chains and examine the effect of the crystal field on the energy levels of the constituent monomers. The chains are one of the simplest but realistic models of the corresponding three-dimensional crystalline solids. To describe the isolated monomers and the chains, we set out from the Hartree-Fock approximation, harnessing the advanced Green's function methods local molecular orbital algebraic diagrammatic construction (ADC) scheme and local crystal orbital ADC (CO-ADC) in a strict second order approximation, ADC(2,2) and CO-ADC(2,2), respectively, to account for electron correlations. The configuration space of the periodic correlation calculations is found to converge rapidly only requiring nearest-neighbor contributions to be regarded. Although electron correlations cause a pronounced shift of the quasiparticle band structure of the chains with respect to the Hartree-Fock result, the bandwidth essentially remains unaltered in contrast to, e.g., covalently bound compounds.

  3. The role of beryllium in the band structure of MgZnO: Lifting the valence band maximum

    SciTech Connect

    Chen, S. S.; Pan, X. H. E-mail: yezz@zju.edu.cn; Chen, W.; Zhang, H. H.; Dai, W.; Ding, P.; Huang, J. Y.; Lu, B.; Ye, Z. Z. E-mail: yezz@zju.edu.cn

    2014-09-22

    We investigate the effect of Be on the valence band maximum (VBM) of MgZnO by measuring the band offsets of Mg{sub x}Zn{sub 1−x}O/Be{sub x}Mg{sub y}Zn{sub 1−x−y}O heterojunctions using X-ray photoelectron spectroscopy measurements. Mg{sub x}Zn{sub 1−x}O and Be{sub x}Mg{sub y}Zn{sub 1−x−y}O films have been grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The valence band offset (ΔE{sub V}) of Mg{sub 0.15}Zn{sub 0.85}O (E{sub g} = 3.62 eV)/Be{sub 0.005}Mg{sub 0.19}Zn{sub 0.805}O (E{sub g} = 3.73 eV) heterojunction is 0.01 eV and Be{sub 0.005}Mg{sub 0.19}Zn{sub 0.805}O has a lower VBM. The increased Mg composition is the main factor for the reduction of VBM. The VBM of Mg{sub x}Zn{sub 1−x}O is lower by 0.03 eV with the enlargement of E{sub g} from 3.62 eV to 3.73 eV by increasing Mg composition. Considering the effect of increased Mg composition, it is concluded that the little amount of Be makes the VBM go up by 0.02 eV when the E{sub g} of the alloy is 3.73 eV. The ΔE{sub V} of Mg{sub 0.11}Zn{sub 0.89}O (E{sub g} = 3.56 eV)/Be{sub 0.007}Mg{sub 0.12}Zn{sub 0.873}O (E{sub g} = 3.56 eV) heterojunction is calculated to be 0.03 eV and Be{sub 0.007}Mg{sub 0.12}Zn{sub 0.873}O has a higher VBM than Mg{sub 0.11}Zn{sub 0.89}O, which means that a little amount Be lifts the VBM by 0.03 eV when the E{sub g} of the alloy is 3.56 eV. The experimental measurements have offered a strong support for the theoretical research that alloying Be in Mg{sub x}Zn{sub 1−x}O alloys is hopeful to form a higher VBM and to enhance the p-type dopability of MgZnO.

  4. Experimental study of X-band dielectric-loaded accelerating structures

    NASA Astrophysics Data System (ADS)

    Jing, Chunguang

    A joint Argonne National Laboratory (ANL)/Naval Research Laboratory (NRL) program is under way to investigate X-band dielectric-loaded accelerating (DLA) structures, using high-power 11.424GHz radiation from the NRL Magnicon facility. As an advanced accelerator concepts, the dielectric-loaded accelerator offers the potential for a simple, inexpensive alternative to high-gradient RF linear accelerators. In this thesis, a comprehensive account of X-band DLA structure design, including theoretical calculation, numerical simulation, fabrication and testing, is presented in detail. Two types of loading dielectrics, alumina and MgxCa1-xTiO 3 (MCT), are investigated. For alumina (with dielectric constant 9.4), no RF breakdown has been observed up to 5 MW of drive power (equivalent to 8MV/m accelerating gradient) in the high power RF testing at NRL, but multipactor was observed to absorb a large fraction of the incident microwave power. Experimental results on suppression of multipactor using TiN coating on the inner surface of the dielectric are also reported. For MCT (with dielectric constant 20), although we did not observe dielectric breakdown in the structures, breakdown did occur at the ceramic joint, where the electric field is greatly enhanced (estimated to be around 100MV/m) due to the micro-scale vacuum gap. In addition, the MCT structure showed significantly less multipactor for the same level of RF field. The thesis also introduced a new design, a multilayered dielectric-loaded accelerating structure, to improve the performance over the conventional one layer DLA structure. Results of analysis for the case of a four layered DLA structure indicate a large reduction of RF power attenuation and an increase of shunt impedance for the structure. Beyond the main contents, the appendices of the thesis present two individual projects prompted by the experimental study of the dielectric-loaded accelerating structure. Appendix A shows a resonant loop technique that can

  5. Band structure, optical properties and infrared spectrum of glycine sodium nitrate crystal

    NASA Astrophysics Data System (ADS)

    Hernández-Paredes, J.; Glossman-Mitnik, D.; Esparza-Ponce, H. E.; Alvarez-Ramos, M. E.; Duarte-Moller, A.

    2008-03-01

    Glycine-sodium nitrate, GSN, crystals were grown from a stoichiometric solution by slow cooling technique and were characterized by optical absorption and FTIR spectroscopy. The data collected by FTIR were compared with the vibrational spectrum theoretically obtained by using DMol code in the local density approximation LDA. Moreover, the crystal band structure, the density of states, and the optical absorption data were calculated by using the CASTEP code within the framework of LDA and the generalized gradient approximation GGA. The calculations are in good agreement with the structure and properties of GSN; e.g., the optical transparency in visible region, the low density, the insulate character, and the bipolar form of glycine molecule.

  6. A combined representation method for use in band structure calculations. 1: Method

    NASA Technical Reports Server (NTRS)

    Friedli, C.; Ashcroft, N. W.

    1975-01-01

    A representation was described whose basis levels combine the important physical aspects of a finite set of plane waves with those of a set of Bloch tight-binding levels. The chosen combination has a particularly simple dependence on the wave vector within the Brillouin Zone, and its use in reducing the standard one-electron band structure problem to the usual secular equation has the advantage that the lattice sums involved in the calculation of the matrix elements are actually independent of the wave vector. For systems with complicated crystal structures, for which the Korringa-Kohn-Rostoker (KKR), Augmented-Plane Wave (APW) and Orthogonalized-Plane Wave (OPW) methods are difficult to apply, the present method leads to results with satisfactory accuracy and convergence.

  7. Structure of the K{sup {pi}} = 4{sup +} bands in {sup 186,188}Os

    SciTech Connect

    Phillips, A. A.; Garrett, P. E.; Demand, G. A.; Finlay, P.; Green, K. L.; Leach, K. G.; Schumaker, M. A.; Svensson, C. E.; Wong, J.; Bettermann, L.; Braun, N.; Burke, D. G.; Faestermann, T.; Kruecken, R.; Wirth, H.-F.; Hertenberger, R.

    2009-01-28

    The structures of {sub 3}{sup +} states in Os have been debated over several decades. Based on measured B(E2) values they were interpreted in {sup 186-192}Os as K{sup {pi}} = 4{sup +} two-phonon vibrations, whereas inelastic scattering, and (t,{alpha}) work imply a hexadecapole phonon description. To clarify the nature of these K{sup {pi}} = 4{sup +} bands in {sup 186,188}Os, we performed a ({sup 3}He,d) reaction on {sup 185,187}Re targets using 30 MeV {sup 3}He beams and a Q3D spectrograph. Absolute cross sections were obtained for excited states up to 3 MeV at 9 angles from 5 deg. to 50 deg. Results indicate a significant (5/2){sup +}[402]{sub {pi}}+(3/2){sup +}[402]{sub {pi}} component in agreement with quasiparticle phonon model predictions for a single hexadecapole phonon structure.

  8. Detection of beam induced dipole-mode signals in the SLC S-band structures

    SciTech Connect

    Seidel, M.; Adolphsen, C.; Assmann, R.; Whittum, D.H.

    1997-06-01

    Beam emittance dilution caused by wakefield effects is one of the important issues in the SLC linac. The detection of beam induced dipole mode signals in the C-band range could provide a direct measure of the strength of transverse wakefield kicks the beam experiences in the accelerating structures. The authors investigate the applicability of these microwave signals for the beam steering purposes. The RF distribution system in the linac sectors 2, 6 and 29 has been equipped with a simple experimental setup to observe the beam induced dipole mode signals. The paper discusses the setup, the mode-structure of the observed signals as well as experimental results from beam steering scans, obtained during the 95/96 SLC runs.

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  10. Breakdown Characteristics Study on an 18 Cell X-band Structure

    SciTech Connect

    Wang Faya

    2009-01-22

    A CLIC designed 18 cells, low group velocity (2.4% to 1.0% c), X-band (11.4 GHz) accelerator structure (denoted T18) was designed at CERN, its cells were built at KEK, and it was assembled and tested at SLAC. An interesting feature of this structure is that the gradient in the last cell is about 50% higher than that in the first cell. This structure has been RF conditioned at SLAC NLCTA for about 1400 hours where it incurred about 2200 breakdowns. This paper presents the characteristics of these breakdowns, including 1) the breakdown rate dependence on gradient, pulse width and conditioning time, 2) the breakdown distribution along the structure, 3) relation between breakdown and pulsed heating dependence study and 4) electric field decay time for breakdown changing over the whole conditioning time. Overall, this structure performed very well, having a final breakdown rate of less than 1e-6/pulse/m at 106 MV/m with 230 ns pulse width.

  11. Breakdown Characteristics Study on an 18 Cell X-band Structure

    SciTech Connect

    Wang, Faya

    2008-11-12

    A CLIC designed 18 cells, low group velocity (2.4% to 1.0% c), X-band (11.4 GHz) accelerator structure (denoted T18) was designed at CERN, its cells were built at KEK, and it was assembled and tested at SLAC. An interesting feature of this structure is that the gradient in the last cell is about 50% higher than that in the first cell. This structure has been RF conditioned at SLAC NLCTA for about 1400 hours where it incurred about 2200 breakdowns. This paper presents the characteristics of these breakdowns, including (1) the breakdown rate dependence on gradient, pulse width and conditioning time, (2) the breakdown distribution along the structure, (3) relation between breakdown and pulsed heating dependence study and (4) electric field decay time for breakdown changing over the whole conditioning time. Overall, this structure performed very well, having a final breakdown rate of less than 1e-6/pulse/m at 106 MV/m with 230 ns pulse width.

  12. Europium underneath graphene on Ir(111): Intercalation mechanism, magnetism, and band structure

    NASA Astrophysics Data System (ADS)

    Schumacher, Stefan; Huttmann, Felix; Petrović, Marin; Witt, Christian; Förster, Daniel F.; Vo-Van, Chi; Coraux, Johann; Martínez-Galera, Antonio J.; Sessi, Violetta; Vergara, Ignacio; Rückamp, Reinhard; Grüninger, Markus; Schleheck, Nicolas; Meyer zu Heringdorf, Frank; Ohresser, Philippe; Kralj, Marko; Wehling, Tim O.; Michely, Thomas

    2014-12-01

    The intercalation of Eu underneath Gr on Ir(111) is comprehensively investigated by microscopic, magnetic, and spectroscopic measurements, as well as by density functional theory. Depending on the coverage, the intercalated Eu atoms form either a (2 ×2 ) or a (√{3 }×√{3 }) R 30∘ superstructure with respect to Gr. We investigate the mechanisms of Eu penetration through a nominally closed Gr sheet and measure the electronic structures and magnetic properties of the two intercalation systems. Their electronic structures are rather similar. Compared to Gr on Ir(111), the Gr bands in both systems are essentially rigidly shifted to larger binding energies resulting in n doping. The hybridization of the Ir surface state S1 with Gr states is lifted, and the moiré superperiodic potential is strongly reduced. In contrast, the magnetic behavior of the two intercalation systems differs substantially, as found by x-ray magnetic circular dichroism. The (2 ×2 ) Eu structure displays plain paramagnetic behavior, whereas for the (√{3 }×√{3 }) R 30∘ structure the large zero-field susceptibility indicates ferromagnetic coupling, despite the absence of hysteresis at 10 K. For the latter structure, a considerable easy-plane magnetic anisotropy is observed and interpreted as shape anisotropy.

  13. Influence of the sequence on the ab initio band structures of single and double stranded DNA models

    NASA Astrophysics Data System (ADS)

    Bogár, Ferenc; Bende, Attila; Ladik, János

    2014-06-01

    The solid state physical approach is widely used for the characterization of electronic properties of DNA. In the simplest case the helical symmetry is explicitly utilized with a repeat unit containing only a single nucleotide or nucleotide pair. This model provides a band structure that is easily interpretable and reflects the main characteristic features of the single nucleotide or a nucleotide pair chain, respectively. The chemical variability of the different DNA chains is, however, almost completely neglected in this way. In the present work we have investigated the effect of the different sequences on the band structure of periodic DNA models. For this purpose we have applied the Hartree-Fock crystal orbital method for single and double stranded DNA chains with two different subsequent nucleotides in the repeat unit of former and two different nucleotide pairs in the latter case, respectively. These results are compared to simple helical models with uniform sequences. The valence and conduction bands related to the stacked nucleotide bases of single stranded DNA built up only from guanidine as well as of double stranded DNA built up only from guanidine-cytidine pairs showed special properties different from the other cases. Namely, they had higher conduction and lower valence band positions and this way larger band gaps and smaller widths of these bands. With the introduction of non-uniform guanidine containing sequences band structures became more similar to each other and to the band structures of other sequences without guanidine. The maximal bandwidths of the non-uniform sequences are considerably smaller than in the case of uniform sequences implying smaller charge carrier mobilities both in the conduction and valence bands.

  14. Observation of high-spin oblate band structures in {sup 141}Pm

    SciTech Connect

    Gu, L.; Zhu, S. J.; Wang, J. G.; Yeoh, E. Y.; Xiao, Z. G.; Zhang, M.; Liu, Y.; Ding, H. B.; Xu, Q.; Zhang, S. Q.; Meng, J.; Zhu, L. H.; Wu, X. G.; He, C. Y.; Li, G. S.; Wang, L. L.; Zheng, Y.; Zhang, B.

    2011-06-15

    The high-spin states of {sup 141}Pm have been investigated through the reaction {sup 126}Te({sup 19}F,4n) at a beam energy of 90 MeV. A previous level scheme has been updated with spins up to 49/2({h_bar}/2{pi}). Six collective bands at high spins are newly observed. Based on the systematic comparison, one band is proposed as a decoupled band; two bands with strong {Delta}I=1 M1 transitions inside the bands are suggested as the oblate bands with {gamma} {approx}-60 deg.; three other bands with large signature splitting have been proposed with the oblate-triaxial deformation with {gamma}{approx} -90 deg. The triaxial n-particle-n-hole particle rotor model calculations for one of the oblate bands in {sup 141}Pm are in good agreement with the experimental data. The other characteristics for these bands have been discussed.

  15. Physical properties and electronic band structure of noncentrosymmetric Th7Co3 superconductor.

    PubMed

    Sahakyan, M; Tran, V H

    2016-05-25

    The physical properties of the noncentrosymmetric superconductor Th7Co3 have been investigated by means of ac-magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance and Hall effect measurements. From these data it is established that Th7Co3 is a dirty type-II superconductor with [Formula: see text] K, [Formula: see text] and moderate electron-phonon coupling [Formula: see text]. Some evidences for anisotropic superconducting gap are found, including e.g. reduced specific heat jump ([Formula: see text]) at T c, diminished superconducting energy gap ([Formula: see text]) as compared to the BCS values, power law field dependence of the Sommerfeld coefficient at 0.4 K ([Formula: see text]), and a concave curvature of the [Formula: see text] line. The magnitudes of the thermodynamic critical field and the energy gap are consistent with mean-squared anisotropy parameter [Formula: see text]. The electronic specific heat in the superconducting state is reasonably fitted to an oblate spheroidal gap model. Calculations of scalar relativistic and fully relativistic electronic band structures reveal considerable differences in the degenerate structure, resulting from asymmetric spin-orbit coupling (ASOC). A large splitting energy of spin-up spin-down bands at the Fermi level E F, [Formula: see text] meV is observed and a sizeable ratio [Formula: see text] could classify the studied compound into the class of noncentrosymmetric superconductors with strong ASOC. The noncentrosymmetry of the crystal structure and the atomic relativistic effects are both responsible for an importance of ASOC in Th7Co3. The calculated results for the density of states show a Van Hove singularity just below E F and dominant role of the 6d electrons of Th to the superconductivity. PMID:27120582

  16. Physical properties and electronic band structure of noncentrosymmetric Th7Co3 superconductor.

    PubMed

    Sahakyan, M; Tran, V H

    2016-05-25

    The physical properties of the noncentrosymmetric superconductor Th7Co3 have been investigated by means of ac-magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance and Hall effect measurements. From these data it is established that Th7Co3 is a dirty type-II superconductor with [Formula: see text] K, [Formula: see text] and moderate electron-phonon coupling [Formula: see text]. Some evidences for anisotropic superconducting gap are found, including e.g. reduced specific heat jump ([Formula: see text]) at T c, diminished superconducting energy gap ([Formula: see text]) as compared to the BCS values, power law field dependence of the Sommerfeld coefficient at 0.4 K ([Formula: see text]), and a concave curvature of the [Formula: see text] line. The magnitudes of the thermodynamic critical field and the energy gap are consistent with mean-squared anisotropy parameter [Formula: see text]. The electronic specific heat in the superconducting state is reasonably fitted to an oblate spheroidal gap model. Calculations of scalar relativistic and fully relativistic electronic band structures reveal considerable differences in the degenerate structure, resulting from asymmetric spin-orbit coupling (ASOC). A large splitting energy of spin-up spin-down bands at the Fermi level E F, [Formula: see text] meV is observed and a sizeable ratio [Formula: see text] could classify the studied compound into the class of noncentrosymmetric superconductors with strong ASOC. The noncentrosymmetry of the crystal structure and the atomic relativistic effects are both responsible for an importance of ASOC in Th7Co3. The calculated results for the density of states show a Van Hove singularity just below E F and dominant role of the 6d electrons of Th to the superconductivity.

  17. Electronic band structure trends of perovskite halides: Beyond Pb and Sn to Ge and Si

    NASA Astrophysics Data System (ADS)

    Huang, Ling-yi; Lambrecht, Walter R. L.

    2016-05-01

    The trends in electronic band structure are studied in the cubic A B X3 halide perovskites for A =Cs ; B =Pb , Sn, Ge, Si; and X =I , Br, Cl. The gaps are found to decrease from Pb to Sn and from Ge to Si, but increase from Sn to Ge. The trend is explained in terms of the atom s levels of the group-IV element and the atomic sizes which changes the amount of hybridization with X -p and hence the valence bandwidth. Along the same series spin-orbit coupling also decreases and this tends to increase the gap because of the smaller splitting of the conduction band minimum. Both effects compensate each other to a certain degree. The trend with halogens is to reduce the gap from Cl to I, i.e., with decreasing electronegativity. The role of the tolerance factor in avoiding octahedron rotations and octahedron edge sharing is discussed. The Ge containing compounds have tolerance factor t >1 and hence do not show the series of octahedral rotation distortions and the existence of edge-sharing octahedral phases known for Pb and Sn-based compounds, but rather a rhombohedral distortion. CsGeI3 is found to have a suitable gap for photovoltaics both in its cubic (high-temperature) and rhombohedral (low-temperature) phases. The structural stability of the materials in the different phases is also discussed. We find the rhombohedral phase to have lower total energy and slightly larger gaps but to present a less significant distortion of the band structure than the edge-sharing octahedral phases, such as the yellow phase in CsSnI3. The corresponding silicon based compounds have not yet been synthesized and therefore our estimates are less certain but indicate a small gap for cubic CsSiI3 and CsSiBr3 of about 0.2 ±0.2 eV and 0.8 ±0.6 eV for CsSiCl3. The intrinsic stability of the Si compounds is discussed.

  18. Measurements of band gap structure in diamond compressed to 370 GPa

    NASA Astrophysics Data System (ADS)

    Gamboa, Eliseo; Fletcher, Luke; Lee, Hae-Ja; Zastrau, Ulf; Gauthier, Maxence; Gericke, Dirk; Vorberger, Jan; Granados, Eduardo; Heimann, Phillip; Hastings, Jerome; Glenzer, Siegfried

    2015-06-01

    We present the first measurements of the electronic structure of dynamically compressed diamond demonstrating a widening of the band gap to pressures of up to 370 +/- 25 GPa. The 8 keV free electron laser x-ray beam from the Linac Coherently Light Source (LCLS) has been focussed onto a diamond foil compressed by two counter-propagating laser pulses to densities of up to 5.3 g/cm3 and temperatures of up to 3000 +/- 400 K. The x-ray pulse excites a collective interband transition of the valence electrons, leading to a plasmon-like loss. We find good agreement with the observed plasmon shift by including the pressure dependence of the band gap as determined from density functional theory simulations. This work was performed at the Matter at Extreme Conditions (MEC) instrument of LCLS, supported by the DOE Office of Science, Fusion Energy Science under Contract No. SF00515. This work was supported by DOE Office of Science, Fusion Energy Science under F.

  19. Micro-metric electronic patterning of a topological band structure using a photon beam

    PubMed Central

    Frantzeskakis, E.; De Jong, N.; Zwartsenberg, B.; Huang, Y. K.; Bay, T. V.; Pronk, P.; Van Heumen, E.; Wu, D.; Pan, Y.; Radovic, M.; Plumb, N. C.; Xu, N.; Shi, M.; De Visser, A.; Golden, M. S.

    2015-01-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi2−xSbxTe3−ySey with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi2−xSbxTe3−ySey crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by ‘writing’ micron-sized letters in the Dirac point energy of the system. PMID:26543011

  20. Micro-metric electronic patterning of a topological band structure using a photon beam.

    PubMed

    Frantzeskakis, E; De Jong, N; Zwartsenberg, B; Huang, Y K; Bay, T V; Pronk, P; Van Heumen, E; Wu, D; Pan, Y; Radovic, M; Plumb, N C; Xu, N; Shi, M; De Visser, A; Golden, M S

    2015-01-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi(2-x)Sb(x)Te(3-y)Se(y) with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi(2-x)Sb(x)Te(3-y)Se(y) crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by 'writing' micron-sized letters in the Dirac point energy of the system. PMID:26543011

  1. SMALL-SCALE STRUCTURE OF THE INTERSTELLAR MEDIUM TOWARD {rho} Oph STARS: DIFFUSE BAND OBSERVATIONS

    SciTech Connect

    Cordiner, M. A.; Smith, A. M.; Sarre, P. J.; Fossey, S. J.

    2013-02-10

    We present an investigation of small-scale structure in the distribution of large molecules/dust in the interstellar medium through observations of diffuse interstellar bands (DIBs). High signal-to-noise optical spectra were recorded toward the stars {rho} Oph A, B, C, and DE using the University College London Echelle Spectrograph on the Anglo-Australian Telescope. The strengths of some of the DIBs are found to differ by about 5%-9% between the close binary stars {rho} Oph A and B, which are separated by a projected distance on the sky of only c. 344 AU. This is the first star system in which such small-scale DIB strength variations have been reported. The observed variations are attributed to differences between a combination of carrier abundance and the physical conditions present along each sightline. The sightline toward {rho} Oph C contains relatively dense, molecule-rich material and has the strongest {lambda}{lambda}5850 and 4726 DIBs. The gas toward DE is more diffuse and is found to exhibit weak ''C{sub 2}'' (blue) DIBs and strong yellow/red DIBs. The differences in diffuse band strengths between lines of sight are, in some cases, significantly greater in magnitude than the corresponding variations among atomic and diatomic species, indicating that the DIBs can be sensitive tracers of interstellar cloud conditions.

  2. The electronic and transport properties of monolayer transition metal dichalcogenides: a complex band structure analysis

    NASA Astrophysics Data System (ADS)

    Szczesniak, Dominik

    Recently, monolayer transition metal dichalcogenides have attracted much attention due to their potential use in both nano- and opto-electronics. In such applications, the electronic and transport properties of group-VIB transition metal dichalcogenides (MX2 , where M=Mo, W; X=S, Se, Te) are particularly important. Herein, new insight into these properties is presented by studying the complex band structures (CBS's) of MX2 monolayers while accounting for spin-orbit coupling effects. By using the symmetry-based tight-binding model a nonlinear generalized eigenvalue problem for CBS's is obtained. An efficient method for solving such class of problems is presented and gives a complete set of physically relevant solutions. Next, these solutions are characterized and classified into propagating and evanescent states, where the latter states present not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gaps, which describe the tunneling currents in the MX2 materials. The importance of CBS's and tunneling currents is demonstrated by the analysis of the quantum transport across MX2 monolayers within phase field matching theory. Present work has been prepared within the Qatar Energy and Environment Research Institute (QEERI) grand challenge ATHLOC project (Project No. QEERI- GC-3008).

  3. A PPM-focused klystron at X-band with a traveling-wave output structure

    SciTech Connect

    Eppley, K.R.

    1995-07-05

    We have developed algorithms for designing disk-loaded traveling-wave output structures for X-band klystrons to be used in the SLAC NLC. We use either a four- or five-cell structure in a {pi}/2 mode. The disk radii are tapered to produce an approximately constant gradient. The matching calculation is not performed on the tapered structure, but rather on a coupler whose input and output cells are the same as the final cell of the tapered structure, and whose interior cells are the same as the penultimate cell in the tapered structure. 2-D calculations using CONDOR model the waveguide as a radial transmission line of adjustable impedance. 3-D calculations with MAFIA model the actual rectangular waveguide and coupling slot. A good match is obtained by adjusting the impedance of the final cell. In 3-D, this requires varying both the radius of the cell and the width of the aperture. When the output cell with the best match is inserted in the tapered structure, we obtain excellent cold-test agreement between the 2-D and 3-D models. We use hot-test simulations with CONDOR to design a structure with maximum efficiency and minimum surface fields. We have designed circuits at 11.424 Ghz for different perveances. At 440 kV, microperveance 1.2, we calculated 81 MW, 53 percent efficiency, with peak surface field 76 MV/m. A microperveance 0.6 design was done using a PPM stack for focusing. At 470 kV, 193 amps, we calculated 58.7 MW, 64.7 percent efficiency, peak surface field 62.3 MV/m. At 500 kV, 212 amps, we calculated 67.1 MW, 63.3 percent efficiency, peak surface field 66.0 MV/m. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  4. A PPM-focused klystron at X-band with a traveling-wave output structure

    NASA Astrophysics Data System (ADS)

    Eppley, Kenneth R.

    1995-07-01

    We have developed algorithms for designing disk-loaded traveling-wave output structures for X-band klystrons to be used in the SLAC NLC. We use either a four- or five-cell structure in a π/2 mode. The disk radii are tapered to produce an approximately constant gradient. The matching calculation is not performed on the tapered structure, but rather on a coupler whose input and output cells are the same as the final cell of the tapered structure, and whose interior cells are the same as the penultimate cell in the tapered structure. 2-D calculations using CONDOR model the waveguide as a radial transmission line of adjustable impedance. 3-D calculations with MAFIA model the actual rectangular waveguide and coupling slot. A good match is obtained by adjusting the impedance of the final cell. In 3-D, this requires varying both the radius of the cell and the width of the aperture. When the output cell with the best match is inserted in the tapered structure, we obtain excellent cold-test agreement between the 2-D and 3-D models. We use hot-test simulations with CONDOR to design a structure with maximum efficiency and minimum surface fields. We have designed circuits at 11.424 Ghz for different perveances. At 440 kV, microperveance 1.2, we calculated 81 MW, 53 percent efficiency, with peak surface field 76 MV/m. A microperveance 0.6 design was done using a PPM stack for focusing. At 470 kV, 193 amps, we calculated 58.7 MW, 64.7 percent efficiency, peak surface field 62.3 MV/m. At 500 kV, 212 amps, we calculated 67.1 MW, 63.3 percent efficiency, peak surface field 66.0 MV/m.

  5. Preparation of Low Band Gap Fibrillar Structures by Solvent Induced Crystallization

    NASA Astrophysics Data System (ADS)

    Wang, Hsin-Wei; Pentzer, Emily; Emerick, Todd; Russell, Thomas

    2014-03-01

    Solution-induced crystallization of the low band gap polymer poly[ N-9''-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) was shown to give fibril-like structures of 40-60 nm width and ~ 0.5 μm length. These structures, formed by heating and cooling PCDTBT in a marginal solvent, were characterized by AFM, TEM, GI-WAXS, and steady state absorption and emission spectroscopy. The width of the PCDTBT structures suggests that the polymer chains are oriented perpendicular to the fiber axis, while the observed undulated structures, as revealed by AFM, suggest that the nanostructures may be composed of smaller crystalline units, suggesting a crystal face-specific assembly. Surprisingly, no spectroscopic signatures in either absorption or emission were observed upon crystallization of PCDTBT, in sharp contrast to the well-known conjugated polymer poly(3-hexyl thiophene) (P3HT). The solution-based crystallization of PCDTBT offers insight into the self-assembly of conjugated polymers and a better understanding of their role in photovoltaic devices

  6. Band-gap nonlinear optical generation: The structure of internal optical field and the structural light focusing

    SciTech Connect

    Zaytsev, Kirill I. Katyba, Gleb M.; Yakovlev, Egor V.; Yurchenko, Stanislav O.; Gorelik, Vladimir S.

    2014-06-07

    A novel approach for the enhancement of nonlinear optical effects inside globular photonic crystals (PCs) is proposed and systematically studied via numerical simulations. The enhanced optical harmonic generation is associated with two- and three-dimensional PC pumping with the wavelength corresponding to different PC band-gaps. The interactions between light and the PC are numerically simulated using the finite-difference time-domain technique for solving the Maxwell's equations. Both empty and infiltrated two-dimensional PC structures are considered. A significant enhancement of harmonic generation is predicted owing to the highly efficient PC pumping based on the structural light focusing effect inside the PC structure. It is shown that a highly efficient harmonic generation could be attained for both the empty and infiltrated two- and three-dimensional PCs. We are demonstrating the ability for two times enhancement of the parametric decay efficiency, one order enhancement of the second harmonic generation, and two order enhancement of the third harmonic generation in PC structures in comparison to the nonlinear generations in appropriate homogenous media. Obviously, the nonlinear processes should be allowed by the molecular symmetry. The criteria of the nonlinear process efficiency are specified and calculated as a function of pumping wavelength position towards the PC globule diameter. Obtained criterion curves exhibit oscillating characteristics, which indicates that the highly efficient generation corresponds to the various PC band-gap pumping. The highest efficiency of nonlinear conversions could be reached for PC pumping with femtosecond optical pulses; thus, the local peak intensity would be maximized. Possible applications of the observed phenomenon are also discussed.

  7. Rotational band structures in sup 127 Cs: Shape changes induced by h sub 11/2 neutron alignment

    SciTech Connect

    Liang, Y.; Ma, R.; Paul, E.S.; Xu, N.; Fossan, D.B. ); Wyss, R.A. )

    1990-09-01

    Several rotational bands have been populated to high spin in {sup 127}Cs following the {sup 120}Sn({sup 11}B,4{ital n}) reaction. Rotational bands built on low-lying proton {ital g}{sub 7/2}, {ital d}{sub 5/2}, and {ital g}{sub 9/2} (hole) orbitals, and the unique-parity {ital h}{sub 11/2} orbital were observed and identified. For the {pi}{ital g}{sub 9/2} (hole) case, both signatures were seen in a strongly coupled {Delta}{ital I}=1 band, while for the other cases, decoupled {Delta}{ital I}=2 bands were observed with strong in-band quadrupole transitions. Through comparisons with cranked-shell-model calculations, these band structures are understood to be associated with a prolate ({gamma}{approximately}0{degree}) deformed nuclear shape. At frequencies above {h bar}{omega}=0.3 MeV, the rotational alignment of a pair of {ital h}{sub 11/2} neutrons was observed for each of the {ital h}{sub 11/2}, {ital g}{sub 7/2}, and {ital d}{sub 5/2} bands. This neutron alignment is predicted to drive the nuclear core away from a prolate shape towards the collectively rotating oblate ({gamma}={minus}60{degree}) shape. Changes in the measured signature splittings for the bands below and above the alignment are consistent with the shape changes.

  8. Band structure effects on resonant tunneling in III-V quantum wells versus two-dimensional vertical heterostructures

    NASA Astrophysics Data System (ADS)

    Campbell, Philip M.; Tarasov, Alexey; Joiner, Corey A.; Ready, W. Jud; Vogel, Eric M.

    2016-01-01

    Since the invention of the Esaki diode, resonant tunneling devices have been of interest for applications including multi-valued logic and communication systems. These devices are characterized by the presence of negative differential resistance in the current-voltage characteristic, resulting from lateral momentum conservation during the tunneling process. While a large amount of research has focused on III-V material systems, such as the GaAs/AlGaAs system, for resonant tunneling devices, poor device performance and device-to-device variability have limited widespread adoption. Recently, the symmetric field-effect transistor (symFET) was proposed as a resonant tunneling device incorporating symmetric 2-D materials, such as transition metal dichalcogenides (TMDs), separated by an interlayer barrier, such as hexagonal boron-nitride. The achievable peak-to-valley ratio for TMD symFETs has been predicted to be higher than has been observed for III-V resonant tunneling devices. This work examines the effect that band structure differences between III-V devices and TMDs has on device performance. It is shown that tunneling between the quantized subbands in III-V devices increases the valley current and decreases device performance, while the interlayer barrier height has a negligible impact on performance for barrier heights greater than approximately 0.5 eV.

  9. Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn)As epitaxial layers

    SciTech Connect

    Yastrubchak, O. Gluba, L.; Żuk, J.; Wosinski, T. Andrearczyk, T.; Domagala, J. Z.; Sadowski, J.

    2014-01-07

    The effect of outdiffusion of Mn interstitials from (Ga,Mn)As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn)As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn)As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn)As, in agreement with the Zener model for ferromagnetic semiconductors.

  10. Band alignment of ultra-thin hetero-structure ZnO/TiO{sub 2} junction

    SciTech Connect

    Shen, Kai; Wu, Kunjie; Wang, Deliang

    2014-03-01

    Graphical abstract: - Highlights: • Band alignment at the ZnO/TiO{sub 2} hetero-structural interface with different ZnO coating thickness was studied. • The valence band offset was decreased with increased ZnO coating layer thickness. • The interface dipole was responsible for the decreased band offset. - Abstract: The band alignment at the ZnO/TiO{sub 2} hetero-structure interface was measured by high resolution X-ray photoelectron spectroscopy. The valence band offset (E{sub ZnO}−E{sub TiO{sub 2}}){sub Valence} was linearly changed from 0.27 to 0.01 eV at the interface with increased ZnO coating thickness from 0.7 to 7 nm. The interface dipole presented at the ZnO/TiO{sub 2} interface was responsible for the decreased band offset. The band alignment of the ZnO/TiO{sub 2} heterojunction is a type II alignment.

  11. Band structure parameters of Zn 1- xCd xSe investigated by spin-flip Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Wolverson, D.; Karimov, O. Z.; Davies, J. J.; Irvine, S. J. C.; Ahmed, M. U.; Telfer, S. A.; Prior, K. A.; Ogata, K.; Fujita, Sz; Fujita, Sg

    2000-06-01

    Spin-flip Raman scattering spectroscopy has been applied to the study of the wide band-gap semiconductor material Zn 1- xCd xSe in order to determine for the first time the dependence on the composition, x, of the gyromagnetic ratio of electrons in the Γ 6 conduction band. The experimental values for the Zn 1- xCd xSe, Zn 1- xMg xSe and ZnS xSe 1- x alloy systems are discussed in terms of the k·p perturbation theory for the band structure near the direct band gap and it is found that the observed dependence on composition can be reproduced well only when the five-band level of approximation is used together with the addition of a third-order perturbation term. Simple interpolation schemes have been used to estimate the band structures between the binary end-members of each alloy, taking into account the bowing of the fundamental band gap and making reasonable assumptions about the behaviour of the spin-orbit coupling parameter.

  12. Combating multidrug-resistant Gram-negative bacteria with structurally nanoengineered antimicrobial peptide polymers.

    PubMed

    Lam, Shu J; O'Brien-Simpson, Neil M; Pantarat, Namfon; Sulistio, Adrian; Wong, Edgar H H; Chen, Yu-Yen; Lenzo, Jason C; Holden, James A; Blencowe, Anton; Reynolds, Eric C; Qiao, Greg G

    2016-01-01

    With the recent emergence of reports on resistant Gram-negative 'superbugs', infections caused by multidrug-resistant (MDR) Gram-negative bacteria have been named as one of the most urgent global health threats due to the lack of effective and biocompatible drugs. Here, we show that a class of antimicrobial agents, termed 'structurally nanoengineered antimicrobial peptide polymers' (SNAPPs) exhibit sub-μM activity against all Gram-negative bacteria tested, including ESKAPE and colistin-resistant and MDR (CMDR) pathogens, while demonstrating low toxicity. SNAPPs are highly effective in combating CMDR Acinetobacter baumannii infections in vivo, the first example of a synthetic antimicrobial polymer with CMDR Gram-negative pathogen efficacy. Furthermore, we did not observe any resistance acquisition by A. baumannii (including the CMDR strain) to SNAPPs. Comprehensive analyses using a range of microscopy and (bio)assay techniques revealed that the antimicrobial activity of SNAPPs proceeds via a multimodal mechanism of bacterial cell death by outer membrane destabilization, unregulated ion movement across the cytoplasmic membrane and induction of the apoptotic-like death pathway, possibly accounting for why we did not observe resistance to SNAPPs in CMDR bacteria. Overall, SNAPPs show great promise as low-cost and effective antimicrobial agents and may represent a weapon in combating the growing threat of MDR Gram-negative bacteria.

  13. Combating multidrug-resistant Gram-negative bacteria with structurally nanoengineered antimicrobial peptide polymers.

    PubMed

    Lam, Shu J; O'Brien-Simpson, Neil M; Pantarat, Namfon; Sulistio, Adrian; Wong, Edgar H H; Chen, Yu-Yen; Lenzo, Jason C; Holden, James A; Blencowe, Anton; Reynolds, Eric C; Qiao, Greg G

    2016-01-01

    With the recent emergence of reports on resistant Gram-negative 'superbugs', infections caused by multidrug-resistant (MDR) Gram-negative bacteria have been named as one of the most urgent global health threats due to the lack of effective and biocompatible drugs. Here, we show that a class of antimicrobial agents, termed 'structurally nanoengineered antimicrobial peptide polymers' (SNAPPs) exhibit sub-μM activity against all Gram-negative bacteria tested, including ESKAPE and colistin-resistant and MDR (CMDR) pathogens, while demonstrating low toxicity. SNAPPs are highly effective in combating CMDR Acinetobacter baumannii infections in vivo, the first example of a synthetic antimicrobial polymer with CMDR Gram-negative pathogen efficacy. Furthermore, we did not observe any resistance acquisition by A. baumannii (including the CMDR strain) to SNAPPs. Comprehensive analyses using a range of microscopy and (bio)assay techniques revealed that the antimicrobial activity of SNAPPs proceeds via a multimodal mechanism of bacterial cell death by outer membrane destabilization, unregulated ion movement across the cytoplasmic membrane and induction of the apoptotic-like death pathway, possibly accounting for why we did not observe resistance to SNAPPs in CMDR bacteria. Overall, SNAPPs show great promise as low-cost and effective antimicrobial agents and may represent a weapon in combating the growing threat of MDR Gram-negative bacteria. PMID:27617798

  14. Dual-band bandpass terahertz wave filter based on microstrip resonant structure

    NASA Astrophysics Data System (ADS)

    Liu, Yu-hang; Li, Jiu-sheng

    2012-03-01

    The terahertz (THz) band, which refers to the spectral region between 0.1 and 10THz, covers the fingerprints of many chemical and biological materials. Within the past few years, there are increasing demands for experiments in terahertz frequencies, in different areas such as biotechnology, nanotechnology, space science, security, chemical and biological sensing, terahertz wave communications, and medical diagnostics. For potential applications, the functional devices, such as beam polarizers, switchs and filters, are crucial components for a terahertz system. Terahertz wave filter based on two kinds of microstrip resonant structures, has been characterized by terahertz time-domain spectroscopy in the region from 0.1 to 3THz. The experimental results for the frequency dependence of the transmittance of the terahertz wave filter show that the terahertz wave transmittance peak is of 79.5% at 0.5THz and 82.5% at 0.81THz.

  15. Diffuse Interstellar Bands as Probes of Small-Scale Interstellar Structure

    NASA Astrophysics Data System (ADS)

    Smith, K. T.; Cordiner, M. A.; Sarre, P. J.

    2014-02-01

    We present observations which probe the small-scale structure of the interstellar medium using diffuse interstellar bands (DIBs). Towards HD 168075/6 in the Eagle Nebula, significant differences in DIB absorption are found between the two lines of sight, which are separated by 0.25 pc, and λ 5797 exhibits a velocity shift. Similar data are presented for four stars in the μ Sgr system. We also present a search for variations in DIB absorption towards κ Vel, where the atomic lines are known to vary on scales of ~ 10 AU. Observations separated by ~ 9 yr yielded no evidence for changes in DIB absorption strength over this scale, but do reveal an unusual DIB spectrum.

  16. Terahertz dual-band metamaterial absorber based on graphene/MgF(2) multilayer structures.

    PubMed

    Su, Zhaoxian; Yin, Jianbo; Zhao, Xiaopeng

    2015-01-26

    We design an ultra-thin terahertz metamaterial absorber based on graphene/MgF(2) multilayer stacking unit cells arrayed on an Au film plane and theoretically demonstrate a dual-band total absorption effect. Due to strong anisotropic permittivity, the graphene/MgF(2) multilayer unit cells possess a hyperbolic dispersion. The strong electric and magnetic dipole resonances between unit cells make the impedance of the absorber match to that of the free space, which induces two total absorption peaks in terahertz range. These absorption peaks are insensitive to the polarization and nearly omnidirectional for the incident angle. But the absorption intensity and frequency depend on material and geometric parameters of the multilayer structure. The absorbed electromagnetic waves are finally converted into heat and, as a result, the absorber shows a good nanosecond photothermal effect. PMID:25835924

  17. Magnonic band structure investigation of one-dimensional bi-component magnonic crystal waveguides.

    PubMed

    Ma, Fu Sheng; Lim, Hock Siah; Zhang, Vanessa Li; Ng, Ser Choon; Kuok, Meng Hau

    2012-01-01

    The magnonic band structures for exchange spin waves propagating in one-dimensional magnonic crystal waveguides of different material combinations are investigated using micromagnetic simulations. The waveguides are periodic arrays of alternating nanostripes of different ferromagnetic materials. Our results show that the widths and center frequencies of the bandgaps are controllable by the component materials, the stripe widths, and the orientation of the applied magnetic field. One salient feature of the bandgap frequency plot against stripe width is that there are n-1 zero-width gaps for the nth bandgap for both transversely and longitudinally magnetized waveguides. Additionally, the largest bandgap widths are primarily dependent on the exchange constant contrast between the component materials of the nanostructured waveguides. PMID:22943207

  18. The effect of spin-orbit coupling in band structure and edge states of bilayer graphene

    SciTech Connect

    Sahdan, Muhammad Fauzi; Darma, Yudi

    2015-04-16

    Topological insulators are predicted to be useful ranging from spintronics to quantum computation. Graphene was first predicted to be the precursor of topological insulator by Kane-Mele. They developed a Hamiltonian model to describe the gap opening in graphene. In this work, we investigate the band structure of bilayer grapheme and also its edge states by using this model with analytical approach. The results of our calculation show that the gap opening occurs at K and K’ point in bilayer graphene.In addition, a pair of gapless edge modes occurs both in the zigzag and arm-chair configurations are no longer exist. There are gap created at the edge even though thery are very small.

  19. Pressure effect on electronic band structures of NiAs-type chromium chalcogenides

    NASA Astrophysics Data System (ADS)

    Takagaki, M.; Kawakami, T.; Shirai, M.; Motizuki, K.

    1998-01-01

    Pressure influence on the electronic band structure of NiAs-type CrTe is studied for non-magnetic and ferromagnetic states by using a self-consistent LAPW method. The total energy is calculated as a function of the lattice spacing a, keeping the ratio c/a as the observed value. The ferromagnetic state is found to be always stable energetically. For the ferromagnetic state, which is realized below T C = 340 K, the theoretical lattice spacing a is obtained as 4.18 Å, which agrees fairly well with the observed one. The magnetic moment arises from mainly the Cr-site and it is remarkably reduced by the pressure as observed. A small magnetic moment is induced at Te-site in the direction antiparallel to the moment at the Cr-site.

  20. van der Waals binding and band structure effects in graphene overlayers and graphane multilayers

    NASA Astrophysics Data System (ADS)

    Hyldgaard, Per; Rohrer, Jochen

    2011-03-01

    We study graphene formation (by selective Si evaporation) and adhesion on SiC surfaces as well as stacking and binding of graphane multilayers using a number of versions of the van der Waals Density Functional (vdW-DF) method and plane-wave density functional theory calculations. For the graphene/SiC systems and for the graphane multilayers we document that the bonding is entirely dominated by van der Waals (vdW) forces. At the same time we find that dispersive forces acting on the layers produce significant modifications in the graphene and graphane band structure. We interpret the changes and discuss a competition between wave function hybridization and interaction with the charge enhancement (between the layers) that results from density overlap. Supported by Svenska Vetenskapsrådet VR #621-2008-4346.

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

    SciTech Connect

    Liu, Lei; Qu, Hongwei; Liu, Yun; Zhang, Yejin; Zheng, Wanhua; Wang, Yufei; Qi, Aiyi

    2014-12-08

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

  2. Physical properties and band structure of reactive molecular beam epitaxy grown oxygen engineered HfO{sub 2{+-}x}

    SciTech Connect

    Hildebrandt, Erwin; Kurian, Jose; Alff, Lambert

    2012-12-01

    We have conducted a detailed thin film growth structure of oxygen engineered monoclinic HfO{sub 2{+-}x} grown by reactive molecular beam epitaxy. The oxidation conditions induce a switching between (111) and (002) texture of hafnium oxide. The band gap of oxygen deficient hafnia decreases with increasing amount of oxygen vacancies by more than 1 eV. For high oxygen vacancy concentrations, defect bands form inside the band gap that induce optical transitions and p-type conductivity. The resistivity changes by several orders of magnitude as a function of oxidation conditions. Oxygen vacancies do not give rise to ferromagnetic behavior.

  3. Influence of GaAs surface termination on GaSb/GaAs quantum dot structure and band offsets

    SciTech Connect

    Zech, E. S.; Chang, A. S.; Martin, A. J.; Canniff, J. C.; Millunchick, J. M.; Lin, Y. H.; Goldman, R. S.

    2013-08-19

    We have investigated the influence of GaAs surface termination on the nanoscale structure and band offsets of GaSb/GaAs quantum dots (QDs) grown by molecular-beam epitaxy. Transmission electron microscopy reveals both coherent and semi-coherent clusters, as well as misfit dislocations, independent of surface termination. Cross-sectional scanning tunneling microscopy and spectroscopy reveal clustered GaSb QDs with type I band offsets at the GaSb/GaAs interfaces. We discuss the relative influences of strain and QD clustering on the band offsets at GaSb/GaAs interfaces.

  4. Ab initio calculations of quasiparticle band structure in correlated systems: LDA++ approach

    NASA Astrophysics Data System (ADS)

    Lichtenstein, A. I.; Katsnelson, M. I.

    1998-03-01

    We discuss a general approach to a realistic theory of the electronic structure in materials containing correlated d or f electrons. The main feature of this approach is the taking into account of the energy dependence of the electron self-energy with the momentum dependence being neglected (local approximation). It allows us to consider such correlation effects as the non-Fermi-step form of the distribution function, the enhancement of the effective mass including Kondo resonances,'' the appearance of the satellites in the electron spectra, etc. To specify the form of the self-energy, it is useful to distinguish (according to the ratio of the on-site Coulomb energy U to the bandwidth W) three regimes-strong, moderate, and weak correlations. In the case of strong interactions (U/W>1-rare-earth system) the Hubbard-I approach is the most suitable. Starting from an exact atomic Green function with the constrained density matrix nmm' the band-structure problem is formulated as the functional problem on nmm' for f electrons and the standard local-denisty-approximation functional for delocalized electrons. In the case of moderate correlations (U/W~1-metal-insulator regime, Kondo systems) we start from the d=∞ dynamical mean-field iterative perturbation scheme of Kotliar and co-workers and also make use of our multiband atomic Green function for constrained nmm'. Finally for the weak interactions (U/W<1-transition metals) the self-consistent diagrammatic fluctuation-exchange approach of Bickers and Scalapino is generalized to the realistic multiband case. We present two-band, two-dimensional model calculations for all three regimes. A realistic calculation in the Hubbard-I scheme with the exact solution of the on-site multielectron problem for f(d) shells was performed for mixed-valence 4f compound TmSe, and for the classical Mott insulator NiO.

  5. Vibrational dynamics and band structure of methyl-terminated Ge(111).

    PubMed

    Hund, Zachary M; Nihill, Kevin J; Campi, Davide; Wong, Keith T; Lewis, Nathan S; Bernasconi, M; Benedek, G; Sibener, S J

    2015-09-28

    A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD3-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH3-Ge(111) and CH3-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers.

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

    SciTech Connect

    Carlisle, J.A.; Shirley, E.L.; Hudson, E.A.

    1997-04-01

    Soft x-ray fluorescence (SXF) spectroscopy using synchrotron radiation offers several advantages over surface sensitive spectroscopies for probing the electronic structure of complex multi-elemental materials. Due to the long mean free path of photons in solids ({approximately}1000 {angstrom}), SXF is a bulk-sensitive probe. Also, since core levels are involved in absorption and emission, SXF is both element- and angular-momentum-selective. SXF measures the local partial density of states (DOS) projected onto each constituent element of the material. The chief limitation of SXF has been the low fluorescence yield for photon emission, particularly for light elements. However, third generation light sources, such as the Advanced Light Source (ALS), offer the high brightness that makes high-resolution SXF experiments practical. In the following the authors utilize this high brightness to demonstrate the capability of SXF to probe the band structure of a polycrystalline sample. In SXF, a valence emission spectrum results from transitions from valence band states to the core hole produced by the incident photons. In the non-resonant energy regime, the excitation energy is far above the core binding energy, and the absorption and emission events are uncoupled. The fluorescence spectrum resembles emission spectra acquired using energetic electrons, and is insensitive to the incident photon`s energy. In the resonant excitation energy regime, core electrons are excited by photons to unoccupied states just above the Fermi level (EF). The absorption and emission events are coupled, and this coupling manifests itself in several ways, depending in part on the localization of the empty electronic states in the material. Here the authors report spectral measurements from highly oriented pyrolytic graphite.

  7. Vibrational dynamics and band structure of methyl-terminated Ge(111)

    SciTech Connect

    Hund, Zachary M.; Nihill, Kevin J.; Sibener, S. J.; Campi, Davide; Bernasconi, M.; Wong, Keith T.; Lewis, Nathan S.; Benedek, G.

    2015-09-28

    A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD{sub 3}-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH{sub 3}-Ge(111) and CH{sub 3}-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers.

  8. Effect of implementation of a Bragg reflector in the photonic band structure of the Suzuki-phase photonic crystal lattice.

    PubMed

    Martinez, Luis Javier; Alija, Alfonso Rodriguez; Postigo, Pablo Aitor; Galisteo-López, J F; Galli, Matteo; Andreani, Lucio Claudio; Seassal, Christian; Viktorovitch, Pierre

    2008-06-01

    We investigate the change of the photonic band structure of the Suzuki-phase photonic crystal lattice when the horizontal mirror symmetry is broken by an underlying Bragg reflector. The structure consists of an InP photonic crystal slab including four InAsP quantum wells, a SiO(2) bonding layer, and a bottom high index contrast Si/SiO(2) Bragg mirror deposited on a Si wafer. Angle- and polarization-resolved photoluminescence spectroscopy has been used for measuring the photonic band structure and for investigating the coupling to a polarized plane wave in the far field. A drastic change in the k-space photonic dispersion between the structure with and without Bragg reflector is measured. An important enhancement on the photoluminescence emission up to seven times has been obtained for a nearly flat photonic band, which is characteristic of the Suzuki-phase lattice.

  9. Structural Basis for Negative Cooperativity in Growth Factor Binding to an EGF Receptor

    SciTech Connect

    Alvarado, Diego; Klein, Daryl E.; Lemmon, Mark A.

    2010-09-27

    Transmembrane signaling by the epidermal growth factor receptor (EGFR) involves ligand-induced dimerization and allosteric regulation of the intracellular tyrosine kinase domain. Crystallographic studies have shown how ligand binding induces dimerization of the EGFR extracellular region but cannot explain the high-affinity and low-affinity classes of cell-surface EGF-binding sites inferred from curved Scatchard plots. From a series of crystal structures of the Drosophila EGFR extracellular region, we show here how Scatchard plot curvature arises from negatively cooperative ligand binding. The first ligand-binding event induces formation of an asymmetric dimer with only one bound ligand. The unoccupied site in this dimer is structurally restrained, leading to reduced affinity for binding of the second ligand, and thus negative cooperativity. Our results explain the cell-surface binding characteristics of EGF receptors and suggest how individual EGFR ligands might stabilize distinct dimeric species with different signaling properties.

  10. Structure and evolution of the Ivy protein family, unexpected lysozyme inhibitors in Gram-negative bacteria

    PubMed Central

    Abergel, Chantal; Monchois, Vincent; Byrne, Deborah; Chenivesse, Sabine; Lembo, Frédérique; Lazzaroni, Jean-Claude; Claverie, Jean-Michel

    2007-01-01

    Part of an ancestral bactericidal system, vertebrate C-type lysozyme targets the peptidoglycan moiety of bacterial cell walls. We report the crystal structure of a protein inhibitor of C-type lysozyme, the Escherichia coli Ivy protein, alone and in complex with hen egg white lysozyme. Ivy exhibits a novel fold in which a protruding five-residue loop appears essential to its inhibitory effect. This feature guided the identification of Ivy orthologues in other Gram-negative bacteria. The structure of the evolutionary distant Pseudomonas aeruginosa Ivy orthologue was also determined in complex with hen egg white lysozyme, and its antilysozyme activity was confirmed. Ivy expression protects porous cell-wall E. coli mutants from the lytic effect of lysozyme, suggesting that it is a response against the permeabilizing effects of the innate vertebrate immune system. As such, Ivy acts as a virulence factor for a number of Gram-negative bacteria-infecting vertebrates. PMID:17405861

  11. Selective Negative Allosteric Modulation Of Metabotropic Glutamate Receptors – A Structural Perspective of Ligands and Mutants

    PubMed Central

    Harpsøe, Kasper; Isberg, Vignir; Tehan, Benjamin G.; Weiss, Dahlia; Arsova, Angela; Marshall, Fiona H.; Bräuner-Osborne, Hans; Gloriam, David E.

    2015-01-01

    The metabotropic glutamate receptors have a wide range of modulatory functions in the central nervous system. They are among the most highly pursued drug targets, with relevance for several neurological diseases, and a number of allosteric modulators have entered clinical trials. However, so far this has not led to a marketed drug, largely because of the difficulties in achieving subtype-selective compounds with desired properties. Very recently the first crystal structures were published for the transmembrane domain of two metabotropic glutamate receptors in complex with negative allosteric modulators. In this analysis, we make the first comprehensive structural comparison of all metabotropic glutamate receptors, placing selective negative allosteric modulators and critical mutants into the detailed context of the receptor binding sites. A better understanding of how the different mGlu allosteric modulator binding modes relates to selective pharmacological actions will be very valuable for rational design of safer drugs. PMID:26359761

  12. Correlation between morphology, electron band structure, and resistivity of Pb atomic chains on the Si(5 5 3)-Au surface.

    PubMed

    Jałochowski, M; Kwapiński, T; Łukasik, P; Nita, P; Kopciuszyński, M

    2016-07-20

    Structural and electron transport properties of multiple Pb atomic chains fabricated on the Si(5 5 3)-Au surface are investigated using scanning tunneling spectroscopy, reflection high electron energy diffraction, angular resolved photoemission electron spectroscopy and in situ electrical resistance. The study shows that Pb atomic chains growth modulates the electron band structure of pristine Si(5 5 3)-Au surface and hence changes its sheet resistivity. Strong correlation between chains morphology, electron band structure and electron transport properties is found. To explain experimental findings a theoretical tight-binding model of multiple atomic chains interacting on effective substrate is proposed.

  13. Parametric analysis of a cylindrical negative Poisson’s ratio structure

    NASA Astrophysics Data System (ADS)

    Wang, Yuanlong; Wang, Liangmo; Ma, Zheng-dong; Wang, Tao

    2016-03-01

    Much research related to negative Poisson’s ratio (NPR), or auxetic, structures is emerging these days. Several types of 3D NPR structure have been proposed and studied, but almost all of them had cuboid shapes, which were not suitable for certain engineering applications. In this paper, a cylindrical NPR structure was developed and researched. It was expected to be utilized in springs, bumpers, dampers and other similar applications. For the purpose of parametric analysis, a method of parametric modeling of cylindrical NPR structures was developed using MATLAB scripts. The scripts can automatically establish finite element models, invoke ABAQUS, read results etc. Subsequently the influences of structural parameters, including number of cells, number of layers and layer heights, on the uniaxial compression behavior of cylinder NPR structures were researched. This led to the conclusion that the stiffness of the cylindrical NPR structure was enhanced on increasing the number of cells and reducing the effective layer height. Moreover, small numbers of layers resulted in a late transition area of the load-displacement curve from low stiffness to high stiffness. Moreover, the middle contraction regions were more apparent with larger numbers of cells, smaller numbers of layers and smaller effective layer heights. The results indicate that the structural parameters had significant effects on the load-displacement curves and deformed shapes of cylindrical NPR structures. This paper is conducive to the further engineering applications of cylindrical NPR structures.

  14. Parallel variable-band Choleski solvers for computational structural analysis applications on vector multiprocessor supercomputers

    NASA Technical Reports Server (NTRS)

    Poole, E. L.; Overman, A. L.

    1991-01-01

    A Choleski method used to solve linear systems of equations that arise in large scale structural analyses is described. The method uses a novel variable-band storage scheme and is structured to exploit fast local memory caches while minimizing data access delays between main memory and vector registers. Several parallel implementations of this method are described for the CRAY-2 and CRAY Y-MP computers demonstrating the use of microtasking and autotasking directives. A portable parallel language, FORCE, is also used for two different parallel implementations, demonstrating the use of CRAY macrotasking. Results are presented comparing the matrix factorization times for three representative structural analysis problems from runs made in both dedicated and multi-user modes on both the CRAY-2 and CRAY Y-MP computers. CPU and wall clock timings are given for the various parallel methods and are compared to single processor timings of the same algorithm. Computation rates over 1 GIGAFLOP (1 billion floating point operations per second) on a four processor CRAY-2 and over 2 GIGAFLOPS on an eight processor CRAY Y-MP are demonstrated as measured by wall clock time in a dedicated environment. Reduced wall clock times for the parallel methods relative to the single processor implementation of the same Choleski algorithm are also demonstrated for runs made in multi-user mode.

  15. Structure and Evolution of Band-shaped Convective Rainbands in Typhoon Marokot (2009)

    NASA Astrophysics Data System (ADS)

    Zhang, Y.

    2012-12-01

    Typhoon Morakot struck Taiwan on the night of Friday 7 August 2009 as a Category 1 storm (with sustained winds of 80 knots). Although the center made landfall in Hualien county along the central east coast of Taiwan, it was southern Taiwan that received the heaviest rainfall (2878 mm of rain in three days), resulting in the worst flooding over Taiwan in 50 years. This record-breaking rainfall is produced by the continuous impingement of typhoon rainbands with the steep terrain along the southern Central Mountain Range (CMR). In this study, rainband structures of Typhoon Morakot (2009) are analyzed and compared with the observations using outputs from the cloud-resolving WRF model with high spatial resolution (1-km horizontal grid spacing). The characteristics of the unique band-shaped convective rainband in TC Morakot are explained with respect to the following details: (i) horizontal shape, (ii) structure, and (iii) development and evolution process. The kinematic and precipitation structures of convective-scale elements in the Morakot rainbands are analyzed and compared with those of Hurricanes Katrina and Rita (2005).

  16. Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

    NASA Astrophysics Data System (ADS)

    Gao, Weiwei; Gao, Xiang; Abtew, Tesfaye; Sun, Yiyang; Zhang, Shengbai; Zhang, Peihong

    The quasiparticle band gaps of organic-inorganic hybrid perovskites are often determined (and can be controlled) by various factors, complicating predictive materials optimization. Here we report a comprehensive investigation on the band gap formation mechanism in CH3NH3PbI3 by decoupling various contributing factors which ultimately determine their electronic structure and quasiparticle band gap. Four major factors, namely, quasiparticle self-energy, spin-orbit coupling, volume (lattice constant) effects, and structural distortions due to the presence of organic molecules, and their influences on the quasiparticle band structure of organometal hybrid perovskites are illustrated. We find that although methylammonium cations do not contribute directly to the electronic states near band edges, they play an important role in defining the band gap through a lattice distortion mechanism and by controlling the overall lattice constants (thus the chemical bonding of the optically active PbI3-). The spin-orbit coupling effects drastically reduce the electron and hole effective masses in these systems, which is beneficial for high carrier mobilities and small exciton binding energies. This work is supported by the National Natural Science Foundation of China (Grant No. 11328401), NSF (Grant No. DMR-0946404 and DMR-1506669), and the SUNY Networks of Excellence.

  17. Investigation of the vertical structure of clouds over the Western Ghats, India using X-band and Ka-band Doppler radar observations

    NASA Astrophysics Data System (ADS)

    Das, Subrata Kumar

    Investigation of the vertical structure of clouds over the Western Ghats, India using X-band and Ka-band Doppler radar observations Subrata Kumar Das*, S. M. Deshpande, K. Chakravarty and M. C. R. Kalapureddy Indian Institute of Tropical Meteorology, Pune, India ABSTRACT The Western Ghats (WGs) located parallel to the west coast of India receives a huge amount of rainfall during the Indian summer monsoon (ISM) in which topography plays a huge role in it. To understand the dynamics and microphysics of monsoon precipitating clouds over the WGs, a High Altitude Cloud Physics Laboratory (HACPL) has been setup at Mahabaleshwar (17.92 oN, 73.6 oE, ~1.4 km AMSL) in 2012. As part of this laboratory, a mobile X-band (9.5 GHz) and Ka-band (35.29 GHz) dual-polarization Doppler weather radar system is installed at Mandhardev (18.04 oN, 73.87 oE, ~1.3 km AMSL, at 26 km radial distance from the HACPL). The X-band radar shows the dominant cloud movement is from the western side of the WGs to the eastern side, crossing the HACPL and the radar site. The cloud occurrence statistics show a sudden reduction within a distance of ~30 km on the eastern side of WGs indicates the possibility of a rain shadow area. Further, we investigate the vertical structure of cloud over the HACPL, and identified four cloud modes viz., shallow cumulus mode, congestus mode, deep convective mode, and overshooting convection mode. The frequency distribution of cloud-cell base height (CBH) and cloud-cell top height (CTH) shows most of the clouds with base below 2.5 km and tops usually not exceeding 9 km. This indicates the dominance of warm-rain process in the WGs region. The positive relationships between surface rainfall rates and CTH and 0oC isotherm level have observed. Details will be presented in the upcoming symposium.

  18. Impacts of Annealing Conditions on the Flat Band Voltage of Alternate La2O3/Al2O3 Multilayer Stack Structures.

    PubMed

    Feng, Xing-Yao; Liu, Hong-Xia; Wang, Xing; Zhao, Lu; Fei, Chen-Xi; Liu, He-Lei

    2016-12-01

    The mechanism of flat band voltage (VFB) shift for alternate La2O3/Al2O3 multilayer stack structures in different annealing condition is investigated. The samples were prepared for alternate multilayer structures, which were annealed in different conditions. The capacitance-voltage (C-V) measuring results indicate that the VFB of samples shift negatively for thinner bottom Al2O3 layer, increasing annealing temperature or longer annealing duration. Simultaneously, the diffusion of high-k material to interfaces in different multilayer structures and annealing conditions is observed by X-ray photoelectron spectroscopy (XPS). Based on the dipole theory, a correlation between the diffusion effect of La towards bottom Al2O3/Si interface and VFB shift is found. Without changing the dielectric constant k of films, VFB shift can be manipulated by controlling the single-layer cycles and annealing conditions of alternate high-k multilayer stack. PMID:27620192

  19. Impacts of Annealing Conditions on the Flat Band Voltage of Alternate La2O3/Al2O3 Multilayer Stack Structures.

    PubMed

    Feng, Xing-Yao; Liu, Hong-Xia; Wang, Xing; Zhao, Lu; Fei, Chen-Xi; Liu, He-Lei

    2016-12-01

    The mechanism of flat band voltage (VFB) shift for alternate La2O3/Al2O3 multilayer stack structures in different annealing condition is investigated. The samples were prepared for alternate multilayer structures, which were annealed in different conditions. The capacitance-voltage (C-V) measuring results indicate that the VFB of samples shift negatively for thinner bottom Al2O3 layer, increasing annealing temperature or longer annealing duration. Simultaneously, the diffusion of high-k material to interfaces in different multilayer structures and annealing conditions is observed by X-ray photoelectron spectroscopy (XPS). Based on the dipole theory, a correlation between the diffusion effect of La towards bottom Al2O3/Si interface and VFB shift is found. Without changing the dielectric constant k of films, VFB shift can be manipulated by controlling the single-layer cycles and annealing conditions of alternate high-k multilayer stack.

  20. Impacts of Annealing Conditions on the Flat Band Voltage of Alternate La2O3/Al2O3 Multilayer Stack Structures

    NASA Astrophysics Data System (ADS)

    Feng, Xing-Yao; Liu, Hong-Xia; Wang, Xing; Zhao, Lu; Fei, Chen-Xi; Liu, He-Lei

    2016-09-01

    The mechanism of flat band voltage (VFB) shift for alternate La2O3/Al2O3 multilayer stack structures in different annealing condition is investigated. The samples were prepared for alternate multilayer structures, which were annealed in different conditions. The capacitance-voltage (C-V) measuring results indicate that the VFB of samples shift negatively for thinner bottom Al2O3 layer, increasing annealing temperature or longer annealing duration. Simultaneously, the diffusion of high- k material to interfaces in different multilayer structures and annealing conditions is observed by X-ray photoelectron spectroscopy (XPS). Based on the dipole theory, a correlation between the diffusion effect of La towards bottom Al2O3/Si interface and VFB shift is found. Without changing the dielectric constant k of films, VFB shift can be manipulated by controlling the single-layer cycles and annealing conditions of alternate high- k multilayer stack.

  1. X-band dielectric loaded RF driven accelerator structures: Theoretical and experimental investigations

    NASA Astrophysics Data System (ADS)

    Zou, Peng

    An important area of application of high-power radio frequency (RF) and microwave sources is particle acceleration. A major challenge for the current worldwide research and development effort in linear accelerator is the search for a compact and affordable very-high-energy accelerator technology for the next generation supercolliders. It has been recognized for sometime that dielectric loaded accelerator structures are attractive candidates for the next generation very-high-energy linear accelerators, because they possess several distinct advantages over conventional metallic iris- loaded accelerator structures. However, some fundamental issues, such as RF breakdown in the dielectric, Joule heating, and vacuum properties of dielectric materials, are still the subjects of intense investigation, requiring the validation by experiments conducted at high power levels. An X-band traveling-wave accelerator based on dielectric-lined waveguide has been designed and constructed. Numerical calculation, bench measurements, and 3-D electromagnetic field simulation of this dielectric loaded accelerator are presented. One critical technical problem in constructing such dielectric loaded accelerator is efficient coupling of RF power into the dielectric-lined circular waveguide. A coupling scheme has been arrived at by empirical methods. Field distribution in this coupling configuration has been studied by numerical simulation. In the conventional iris-loaded accelerator structures, the peak surface electric field E s is in general found to be at least a factor of 2 higher than the axial acceleration field Ea. Because the peak surface electric field causes electric breakdown of the structure, it represents a direct limitation on the maximum acceleration gradient that can be obtained. A novel hybrid dielectric-iris-loaded periodic accelerator structure is proposed to utilize the advantages of both dielectric-lined waveguides and conventional iris-loaded structures. Numerical

  2. Structural Basis for a Reciprocating Mechanism of Negative Cooperativity in Dimeric Phosphagen Kinase Activity

    SciTech Connect

    Wu, X.; Ye, S; Guo, S; Yan, W; Bartlam, M; Rao, Z

    2010-01-01

    Phosphagen kinase (PK) family members catalyze the reversible phosphoryl transfer between phosphagen and ADP to reserve or release energy in cell energy metabolism. The structures of classic quaternary complexes of dimeric creatine kinase (CK) revealed asymmetric ligand binding states of two protomers, but the significance and mechanism remain unclear. To understand this negative cooperativity further, we determined the first structure of dimeric arginine kinase (dAK), another PK family member, at 1.75 {angstrom}, as well as the structure of its ternary complex with AMPPNP and arginine. Further structural analysis shows that the ligand-free protomer in a ligand-bound dimer opens more widely than the protomers in a ligand-free dimer, which leads to three different states of a dAK protomer. The unexpected allostery of the ligand-free protomer in a ligand-bound dimer should be relayed from the ligand-binding-induced allostery of its adjacent protomer. Mutations that weaken the interprotomer connections dramatically reduced the catalytic activities of dAK, indicating the importance of the allosteric propagation mediated by the homodimer interface. These results suggest a reciprocating mechanism of dimeric PK, which is shared by other ATP related oligomeric enzymes, e.g., ATP synthase. - Wu, X., Ye, S., Guo, S., Yan, W., Bartlam, M., Rao, Z. Structural basis for a reciprocating mechanism of negative cooperativity in dimeric phosphagen kinase activity.

  3. Syntheses, crystal and band structures, and optical properties of a selenidoantimonate and an iron polyselenide

    SciTech Connect

    Liu, Guang-Ning; Zhu, Wen-Juan; Zhang, Ming-Jian; Xu, Bo; Liu, Qi-Sheng; Zhang, Zhen-Wei; Li, Cuncheng

    2014-10-15

    A new selenidoantimonate (CH{sub 3}NH{sub 4})[Mn(phen){sub 2}](SbSe{sub 4})·phen (1, phen=1,10-phenanthroline) and an iron polyselenide [Fe(phen){sub 2}](Se{sub 4}) (2) were obtained under hydro(solvo)thermal conditions. Compound 1 represents the first example of a selenidoantimonate anion as a ligand to a transition-metal π-conjugated ligand complex cation. Compound 2 containing a κ{sup 2}Se{sup 1},Se{sup 4} chelating tetraselenide ligand, represents the only example of a tetraselenide ligand to a Fe complex cation. Compounds 1 and 2 exhibit optical gaps of 1.71 and 1.20 eV, respectively and their thermal stabilities have been investigated by thermogravimetric analyses. The electronic band structure along with the density of states calculated by the DFT method indicate that the optical absorptions mainly originate from the charge transitions from the Se 4p and Mn 3d states to the phen p–π{sup ⁎} orbital for 1 and the Se 4p and Fe 3d states to the phen p–π{sup ⁎} orbital for 2. - Graphical abstract: Two metal–Se complexes, representing the only example of a selenidoantimonate ligand to a TM π-conjugated ligand complex, and a tetraselenide ligand to a Fe complex cation, were synthesized. - Highlights: • The first π-conjugated ligand complex containing selenidoantimonate was isolated. • The first example of a tetraselenide ligand to a Fe complex cation was reported. • We found that phen can adjust the optical band gaps of metal–Se complexes.

  4. Large-area 2D periodic crystalline silicon nanodome arrays on nanoimprinted glass exhibiting photonic band structure effects.

    PubMed

    Becker, C; Lockau, D; Sontheimer, T; Schubert-Bischoff, P; Rudigier-Voigt, E; Bockmeyer, M; Schmidt, F; Rech, B

    2012-04-01

    Two-dimensional silicon nanodome arrays are prepared on large areas up to 50 cm² exhibiting photonic band structure effects in the near-infrared and visible wavelength region by downscaling a recently developed fabrication method based on nanoimprint-patterned glass, high-rate electron-beam evaporation of silicon, self-organized solid phase crystallization and wet-chemical etching. The silicon nanodomes, arranged in square lattice geometry with 300 nm lattice constant, are optically characterized by angular resolved reflection measurements, allowing the partial determination of the photonic band structure. This experimentally determined band structure agrees well with the outcome of three-dimensional optical finite-element simulations. A 16% photonic bandgap is predicted for an optimized geometry of the silicon nanodome arrays. By variation of the duration of the selective etching step, the geometry as well as the optical properties of the periodic silicon nanodome arrays can be controlled systematically.

  5. Physical properties and electronic band structure of noncentrosymmetric Th7Co3 superconductor

    NASA Astrophysics Data System (ADS)

    Sahakyan, M.; Tran, V. H.

    2016-05-01

    The physical properties of the noncentrosymmetric superconductor Th7Co3 have been investigated by means of ac-magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance and Hall effect measurements. From these data it is established that Th7Co3 is a dirty type-II superconductor with {{T}\\text{c}}=1.8+/- 0.02 K, Hc2\\text{orb}<{{H}c2}(0)∼ 10~\\text{kOe}c2p and moderate electron–phonon coupling {λ\\text{el-\\text{ph}}}=0.56 . Some evidences for anisotropic superconducting gap are found, including e.g. reduced specific heat jump (Δ {{C}p}/γ {{T}\\text{c}}=1.01 ) at T c, diminished superconducting energy gap ({{Δ }0}/{{k}\\text{B}}{{T}\\text{c}}=2.17 ) as compared to the BCS values, power law field dependence of the Sommerfeld coefficient at 0.4 K ({{C}p}/T\\propto {{H}0.6} ), and a concave curvature of the {{H}c2}≤ft({{T}\\text{c}}\\right) line. The magnitudes of the thermodynamic critical field and the energy gap are consistent with mean-squared anisotropy parameter < {{a}2}> ∼ 0.23 . The electronic specific heat in the superconducting state is reasonably fitted to an oblate spheroidal gap model. Calculations of scalar relativistic and fully relativistic electronic band structures reveal considerable differences in the degenerate structure, resulting from asymmetric spin–orbit coupling (ASOC). A large splitting energy of spin-up spin-down bands at the Fermi level E F, Δ {{E}\\text{ASOC}}∼ 100 meV is observed and a sizeable ratio Δ {{E}\\text{ASOC}}/{{k}\\text{B}}{{T}\\text{c}}∼ 640 could classify the studied compound into the class of noncentrosymmetric superconductors with strong ASOC. The noncentrosymmetry of the crystal structure and the atomic relativistic effects are both responsible for an importance of ASOC in Th7Co3. The calculated results for the density of states show a Van Hove singularity just below E F and dominant role of the 6d electrons of Th to the superconductivity.

  6. Physical properties and electronic band structure of noncentrosymmetric Th7Co3 superconductor

    NASA Astrophysics Data System (ADS)

    Sahakyan, M.; Tran, V. H.

    2016-05-01

    The physical properties of the noncentrosymmetric superconductor Th7Co3 have been investigated by means of ac-magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance and Hall effect measurements. From these data it is established that Th7Co3 is a dirty type-II superconductor with {{T}\\text{c}}=1.8+/- 0.02 K, Hc2\\text{orb}<{{H}c2}(0)˜ 10~\\text{kOe}c2p and moderate electron-phonon coupling {λ\\text{el-\\text{ph}}}=0.56 . Some evidences for anisotropic superconducting gap are found, including e.g. reduced specific heat jump (Δ {{C}p}/γ {{T}\\text{c}}=1.01 ) at T c, diminished superconducting energy gap ({{Δ }0}/{{k}\\text{B}}{{T}\\text{c}}=2.17 ) as compared to the BCS values, power law field dependence of the Sommerfeld coefficient at 0.4 K ({{C}p}/T\\propto {{H}0.6} ), and a concave curvature of the {{H}c2}≤ft({{T}\\text{c}}\\right) line. The magnitudes of the thermodynamic critical field and the energy gap are consistent with mean-squared anisotropy parameter < {{a}2}> ˜ 0.23 . The electronic specific heat in the superconducting state is reasonably fitted to an oblate spheroidal gap model. Calculations of scalar relativistic and fully relativistic electronic band structures reveal considerable differences in the degenerate structure, resulting from asymmetric spin-orbit coupling (ASOC). A large splitting energy of spin-up spin-down bands at the Fermi level E F, Δ {{E}\\text{ASOC}}˜ 100 meV is observed and a sizeable ratio Δ {{E}\\text{ASOC}}/{{k}\\text{B}}{{T}\\text{c}}˜ 640 could classify the studied compound into the class of noncentrosymmetric superconductors with strong ASOC. The noncentrosymmetry of the crystal structure and the atomic relativistic effects are both responsible for an importance of ASOC in Th7Co3. The calculated results for the density of states show a Van Hove singularity just below E F and dominant role of the 6d electrons of Th to the superconductivity.

  7. Design considerations for negative Poisson ratio structures under large deflection for MEMS applications

    NASA Astrophysics Data System (ADS)

    Levy, O.; Krylov, S.; Goldfarb, I.

    2006-10-01

    Negative Poisson ratio (NPR) materials based on a re-entrant honeycomb structure expand in the direction perpendicular to an externally exerted tension. This feature makes NPR structures attractive for use in microsensors and actuators as versatile motion transformers. When implemented in microdevices, where slender and flexible micromachined elements are widely used, the NPR material can tolerate large deflections. In the present work, motivated by the development of an optical sensor based on a photonic crystal device attached to a NPR based structure, we analyze the behavior of re-entrant honeycomb structures under large deflections. The model of the structure is built using extensible elastica theory for the description of geometrically nonlinear beams with an extensible axis. Results provided by the analytical model are compared with numerical results obtained by the finite element method. It is shown that the Poisson ratio (ν), which is defined entirely by the initial geometry of the structure undergoing small deflections, becomes strain dependent at large deflections. The extensibility of the beam's axis has a strong influence on the ν of the structure at large deflections and leads to the appearance of a minimum on the strain-ν curve. An example of design is demonstrated which yields a desired strain-independent ν of the NPR structure under large deflections.

  8. Detecting forest structure and biomass with C-band multipolarization radar - Physical model and field tests

    NASA Technical Reports Server (NTRS)

    Westman, Walter E.; Paris, Jack F.

    1987-01-01

    The ability of C-band radar (4.75 GHz) to discriminate features of forest structure, including biomass, is tested using a truck-mounted scatterometer for field tests on a 1.5-3.0 m pygmy forest of cypress (Cupressus pygmaea) and pine (Pinus contorta ssp, Bolanderi) near Mendocino, CA. In all, 31 structural variables of the forest are quantified at seven sites. Also measured was the backscatter from a life-sized physical model of the pygmy forest, composed of nine wooden trees with 'leafy branches' of sponge-wrapped dowels. This model enabled independent testing of the effects of stem, branch, and leafy branch biomass, branch angle, and moisture content on radar backscatter. Field results suggested that surface area of leaves played a greater role in leaf scattering properties than leaf biomass per se. Tree leaf area index was strongly correlated with vertically polarized power backscatter (r = 0.94; P less than 0.01). Field results suggested that the scattering role of leaf water is enhanced as leaf surface area per unit leaf mass increases; i.e., as the moist scattering surfaces become more dispersed. Fog condensate caused a measurable rise in forest backscatter, both from surface and internal rises in water content. Tree branch mass per unit area was highly correlated with cross-polarized backscatter in the field (r = 0.93; P less than 0.01), a result also seen in the physical model.

  9. Effect of tree structure on X-band microwave signature of conifers

    NASA Technical Reports Server (NTRS)

    Mougin, Eric; Lopes, Armand; Karam, Mostafa A.; Fung, Adrian K.

    1993-01-01

    Experimental studies are performed on some coniferous trees (Austrian pine, Nordmann spruce, and Norway spruce) to investigate the relation between the tree architecture and radar signal at X-band. For a single tree, the RCS is measured as a function of the scatterer location at 90 deg incidence. It is found that the main scatterers are the leafy branches and the difference between sigma(vv) and sigma(hh) is significant at the upper portion of the tree. At the lower portion of the tree, sigma(vv) and sigma(hh) have almost the same level. For a group of trees the angular trends of sigma(vv) and sigma(hh) are measured. It is found that the levels of sigma(vv) and sigma(hh) are of the same order, but their angular trends vary from one tree species to the other depending on the tree species structure. The interpretation of these experimental results is carried out with the help of a theoretical model which accounts for the structure of the tree. According to this theoretical study, the major scattering trend is due to the leaves, while the perturbation to the angular trend and the level difference between sigma(vv) and sigma(hh) are due to the branch orientation distributions (i.e., the tree architecture).

  10. Synthesis, physical properties and band structure of non-magnetic Y3AlC

    NASA Astrophysics Data System (ADS)

    Ghule, S. S.; Garde, C. S.; Ramakrishnan, S.; Singh, S.; Rajarajan, A. K.; Laad, Meena

    2016-10-01

    Y3AlC has been synthesized by arc melting and subsequent annealing. Rietveld analysis of the powder x-ray diffraction (XRD) data confirms cubic Pm-3m structure. Electrical resistivity (ρ) of Y3AlC exhibits metallic behaviour. No sign of superconductivity is observed down to the lowest measurement temperatures of 4.2 K in ρ, and 2 K in magnetic susceptibility (χ) and specific heat (Cp) measurements. The value of the electronic specific heat coefficient γ is 1.36 mJ/K2 mol from which the density of states (DOS) at the Fermi energy (EF) is obtained as 0.57 states/eV.unit cell. The value of Debye temperature θD is estimated to be 315 K. Electronic band structure calculations of Y3AlC reveal a pseudo-gap in the DOS at EF leading to a small value of 0.5 states/eV unit cell which matches quite well with that obtained from γ. Non-zero value of the DOS indicates metallic behaviour as confirmed by our ρ data. Covalent and ionic bonding seem to co-exist with metallic bonding in Y3AlC as indicated by van Arkel- Ketelaar triangle for Zintl-like systems.

  11. Metal-to-Insulator Transition in Au Chains on Si(111)-5×2-Au by Band Filling: Infrared Plasmonic Signal and Ab Initio Band Structure Calculation.

    PubMed

    Hötzel, Fabian; Seino, Kaori; Chandola, Sandhya; Speiser, Eugen; Esser, Norbert; Bechstedt, Friedhelm; Pucci, Annemarie

    2015-09-17

    The Si(111)-5×2-Au surface is increasingly of interest because it is one of the rare atomic chain systems with quasi-one-dimensional properties. For the deposition of 0.7 monolayers of Au, these chains are metallic. Upon the evaporation of an additional submonolayer amount of gold, the surface becomes insulating but keeps the 5×2 symmetry. This metal-to-insulator transition was in situ monitored based on the infrared plasmonic signal change with coverage. The phase transition is theoretically explained by total-energy and band-structure calculations. Accordingly, it can be understood in terms of the occupation of the originally half-filled one-dimensional band at the Fermi level. By annealing the system, the additional gold is removed from the surface and the plasmonic signal is recovered, which underlines the stability of the metallic structure. So, recent results on the infrared plasmonic signals of the Si(111)-5 × 2-Au surface are supported. The understanding of potential one-dimensional electrical interconnects is improved.

  12. Effects of impurity size and heavy doping on energy-band-structure parameters of various impurity-Si systems

    NASA Astrophysics Data System (ADS)

    Van Cong, H.

    2016-04-01

    The effects of impurity size and heavy doping on energy-band-structure parameters of various donor (or acceptor)-Si systems were investigated. A satisfactory description was obtained for intrinsic properties such as: the effective dielectric constant, effective impurity ionization energy, effective intrinsic band gap, being doping-independent, and critical impurity density, Ncn(cp) GMM, which is derived from our simple generalized Mott model (GMM), as well as for extrinsic properties such as: the Fermi energy, reduced band gap, optical band gap, being doping-dependent, and critical impurity density, Ncn(cp) SSS, which is determined by our complicated spin-susceptibility-singularity (SSS) method. That gives: Ncn(cp) SSS ≡ Ncn(cp) GMM for all the studied donor (or acceptor)-Si systems.

  13. Pronounced negative thermal expansion from a simple structure : Cubic ScF{sub 3}.

    SciTech Connect

    Greve, B. K.; Martin, K. L.; Lee, P. L.; Chupas, P. J.; Chapman, K. W.; Wilkinson, A. P.; X-Ray Science Division; Georgia Inst. of Tech.

    2010-10-19

    Scandium trifluoride maintains a cubic ReO{sub 3} type structure down to at least 10 K, although the pressure at which its cubic to rhombohedral phase transition occurs drops from >0.5 GPa at {approx}300 K to 0.1-0.2 GPa at 50 K. At low temperatures it shows strong negative thermal expansion (NTE) (60-110 K, {alpha}{sub l} {approx} -14 ppm K{sup -1}). On heating, its coefficient of thermal expansion (CTE) smoothly increases, leading to a room temperature CTE that is similar to that of ZrW{sub 2}O{sub 8} and positive thermal expansion above {approx}1100 K. While the cubic ReO{sub 3} structure type is often used as a simple illustration of how negative thermal expansion can arise from the thermally induced rocking of rigid structural units, ScF{sub 3} is the first material with this structure to provide a clear experimental illustration of this mechanism for NTE.

  14. Surface Organelles Assembled by Secretion Systems of Gram-Negative Bacteria: Diversity in Structure and Function

    PubMed Central

    Thanassi, David G.; Bliska, James B.; Christie, Peter J.

    2012-01-01

    Gram-negative bacteria express a wide variety of organelles on their cell surface. These surface structures may be the end products of secretion systems, such as the hair-like fibers assembled by the chaperone/usher and type IV pilus pathways, which generally function in adhesion to surfaces and bacterial-bacterial and bacterial-host interactions. Alternatively, the surface organelles may be integral components of the secretion machinery itself, such as the needle complex and pilus extensions formed by the type III and type IV secretion systems, which function in the delivery of bacterial effectors inside host cells. Bacterial surface structures perform functions critical for pathogenesis and have evolved to withstand forces exerted by the external environment and cope with defenses mounted by the host immune system. Given their essential roles in pathogenesis and exposed nature, bacterial surface structures also make attractive targets for therapeutic intervention. This review will describe the structure and function of surface organelles assembled by four different Gram-negative bacterial secretion systems: the chaperone/usher pathway, the type IV pilus pathway, and the type III and type IV secretion systems. PMID:22545799

  15. Band structure of cavity-type hypersonic phononic crystals fabricated by femtosecond laser-induced two-photon polymerization

    NASA Astrophysics Data System (ADS)

    Rakhymzhanov, A. M.; Gueddida, A.; Alonso-Redondo, E.; Utegulov, Z. N.; Perevoznik, D.; Kurselis, K.; Chichkov, B. N.; El Boudouti, E. H.; Djafari-Rouhani, B.; Fytas, G.

    2016-05-01

    The phononic band diagram of a periodic square structure fabricated by femtosecond laser pulse-induced two photon polymerization is recorded by Brillouin light scattering (BLS) at hypersonic (GHz) frequencies and computed by finite element method. The theoretical calculations along the two main symmetry directions quantitatively capture the band diagrams of the air- and liquid-filled structure and moreover represent the BLS intensities. The theory helps identify the observed modes, reveals the origin of the observed bandgaps at the Brillouin zone boundaries, and unravels direction dependent effective medium behavior.

  16. An Angle Resolved Photoemission Survey of the Band Structure of the Heavy Fermion Superconductor, CeCoIn5

    NASA Astrophysics Data System (ADS)

    Reber, Theodore; Rameau, Jonathon; Hu, Rongwei; Petrovic, Cedomir; Johnson, Peter

    2015-03-01

    With the highest Tc of the non-radioactive heavy fermion materials, CeCoIn5 has been extensively studied by a host of techniques. However direct measurements of the band structure via angle resolved photo-emission spectroscopy has been limited to just a few experiments. We will present our studies of the momentum, temperature, photon energy and polarization dependence of the band structure of CeCoIn5. We will compare our results with theory and other experimental results. Present address: Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University

  17. Structural diversity of the 3-micron absorption band in Enceladus’ plume from Cassini VIMS: Insights into subsurface environmental conditions

    NASA Astrophysics Data System (ADS)

    Dhingra, Deepak; Hedman, Matthew M.; Clark, Roger N.

    2015-11-01

    Water ice particles in Enceladus’ plume display their diagnostic 3-micron absorption band in Cassini VIMS data. These near infrared measurements of the plume also exhibit noticeable variations in the character of this band. Mie theory calculations reveal that the shape and location of the 3-micron band are controlled by a number of environmental and structural parameters. Hence, this band provides important insights into the properties of the water ice grains and about the subsurface environmental conditions under which they formed. For example, the position of the 3-micron absorption band minimum can be used to distinguish between crystalline and amorphous forms of water ice and to constrain the formation temperature of the ice grains. VIMS data indicates that the water ice grains in the plume are dominantly crystalline which could indicate formation temperatures above 113 K [e.g. 1, 2]. However, there are slight (but observable) variations in the band minimum position and band shape that may hint at the possibility of varying abundance of amorphous ice particles within the plume. The modeling results further indicate that there are systematic shifts in band minimum position with temperature for any given form of ice but the crystalline and amorphous forms of water ice are still distinguishable at VIMS spectral resolution. Analysis of the eruptions from individual source fissures (tiger stripes) using selected VIMS observations reveal differences in the 3-micron band shape that may reflect differences in the size distributions of the water ice particles along individual fissures. Mie theory models suggest that big ice particles (>3 micron) may be an important component of the plume.[1] Kouchi, A., T. Yamamoto, T. Kozasa, T. Kuroda, and J. M. Greenberg (1994) A&A, 290, 1009-1018 [2] Mastrapa, R. M. E., W. M. Grundy, and M. S. Gudipati (2013) in M. S. Gudipati and J. Castillo-Rogez (Eds.), The Science of Solar System Ices, pp. 371.

  18. Model calculations of the energy band structures of double stranded DNA in the presence of water and Na + ions

    NASA Astrophysics Data System (ADS)

    Bende, Attila; Bogár, Ferenc; Ladik, János

    2011-02-01

    Using the ab initio Hartree-Fock crystal orbital method in its linear combination of atomic orbitals form we have calculated the band structures of poly( G˜- C˜) and poly( Ö T˜). Here, besides the nucleotide bases, the sugar and phosphate parts of the nucleotide were also taken into account together with their first water shell and Na + ions. We use the notation with a tilde above the abbreviation of a base for the whole nucleotide; for instance poly( G˜) means a guanine base with the deoxyribose and PO 4- groups to which it is bound. The obtained band structures were compared with previous single chain calculations as well as with the earlier poly( G˜- C˜) and poly( Ö T˜) calculation without water but in the presence of counterions. One finds that all the bands of poly( G˜- C˜) and poly( Ö T˜) are shifted considerably upwards as compared to the previous single chain results (poly( G˜), poly( C˜), poly( Ã) and poly( T˜)). This effect is explained by the ˜0.2 e charge transfer from the sugars of both chains to the nucleotide bases. The fundamental gaps between the nucleotide base-type highest filled and lowest unfilled bands are decreased in both cases by 1-3 eV, because the valence bands are purine-type and the conduction bands pyrimidine-type, respectively, while in the case of single homopolynucleotides they belong to the same base. We also pointed out that the LUMO is mainly Na +-like in both investigated cases and several unoccupied bands (belonging to the Na + ions, the phosphate group and the water molecules) can be found between this and the first unoccupied pyrimidine-like empty band.

  19. Application of mid-infrared free-electron laser tuned to amide bands for dissociation of aggregate structure of protein.

    PubMed

    Kawasaki, Takayasu; Yaji, Toyonari; Ohta, Toshiaki; Tsukiyama, Koichi

    2016-01-01

    A mid-infrared free-electron laser (FEL) is a linearly polarized, high-peak powered pulse laser with tunable wavelength within the mid-infrared absorption region. It was recently found that pathogenic amyloid fibrils could be partially dissociated to the monomer form by the irradiation of the FEL targeting the amide I band (C=O stretching vibration), amide II band (N-H bending vibration) and amide III band (C-N stretching vibration). In this study, the irradiation effect of the FEL on keratin aggregate was tested as another model to demonstrate an applicability of the FEL for dissociation of protein aggregates. Synchrotron radiation infrared microscopy analysis showed that the α-helix content in the aggregate structure decreased to almost the same level as that in the monomer state after FEL irradiation tuned to 6.06 µm (amide I band). Both irradiations at 6.51 µm (amide II band) and 8.06 µm (amide III band) also decreased the content of the aggregate but to a lesser extent than for the irradiation at the amide I band. On the contrary, the irradiation tuned to 5.6 µm (non-absorbance region) changed little the secondary structure of the aggregate. Scanning-electron microscopy observation at the submicrometer order showed that the angular solid of the aggregate was converted to non-ordered fragments by the irradiation at each amide band, while the aggregate was hardly deformed by the irradiation at 5.6 µm. These results demonstrate that the amide-specific irradiation by the FEL was effective for dissociation of the protein aggregate to the monomer form. PMID:26698057

  20. Resonant coupling and negative differential resistance in metal/ferrocenyl alkanethiolate/STM structures

    NASA Astrophysics Data System (ADS)

    Wang, Shuchun; Lu, Wenchang; Zhao, Qingzhong; Bernholc, J.

    2006-11-01

    Recent experimental studies demonstrated that self-assembled molecules sandwiched between metallic contacts can perform logic functions based on negative differential resistance (NDR). To understand the mechanism of NDR, the electronic structure and transport properties of one such junction, ferrocenyl alkanethiolate attached to a gold surface and probed with a scanning tunneling microscope tip, are investigated by large scale ab initio calculations. The I-V characteristics show strong NDR features at both positive and negative biases, in good agreement with the experimental data. The voltage-dependent transmission, potential drop profile, and molecular level alignment under bias suggest that the ferrocenyl group acts like a quantum dot and that the NDR features are due to resonant coupling between the highest occupied molecular orbital and the density of states of gold leads. The strength of the individual NDR peaks can be tuned by changing the tunneling distance or using suitable spacer layers.

  1. Electrically tunable negative refraction in core/shell-structured nanorod fluids.

    PubMed

    Su, Zhaoxian; Yin, Jianbo; Guan, Yanqing; Zhao, Xiaopeng

    2014-10-21

    We theoretically investigate optical refraction behavior in a fluid system which contains silica-coated gold nanorods dispersed in silicone oil under an external electric field. Because of the formation of a chain-like or lattice-like structure of dispersed nanorods along the electric field, the fluid shows a hyperbolic equifrequency contour characteristic and, as a result, all-angle broadband optical negative refraction for transverse magnetic wave propagation can be realized. We calculate the effective permittivity tensor of the fluid and verify the analysis using finite element simulations. We also find that the negative refractive index can vary with the electric field strength and external field distribution. Under a non-uniform external field, the gradient refraction behavior can be realized. PMID:25087913

  2. Compared electronic structure of negative ions M p C{/n -}: I. Normal elements in Hückel theory

    NASA Astrophysics Data System (ADS)

    Leleyter, M.

    1989-03-01

    Negative cluster ions M p C{/n -} (M normal element, n<10, p=1-4) produced by various experimental techniques from carbides show in their emission intensities a very strong even-odd effect according to the parity of the carbon atom number n. This is in particular the case when M=N, F, Cl ( p=1), M=H, Al, Si, S ( p=1, 2) or M=B ( p=1-4). The largest intensities of M p C{/n -} ions always take place for even n except in the cases of NC{/n -}, B2C{/n -} and Al2C{/n -}, for which the maxima of emission occur for odd n. This oscillating behaviour corresponds to alternations in the stability of the clusters which are mainly due to the fact that, in Pitzer and Clementi model (linear chains in the sp hybridization within the framework of Hückel theory), the HOMO (highest occupied molecular orbital) of the clusters lies in a double degenerate π level band: a cluster with a complete HOMO is always more stable than a cluster with a nearly empty HOMO. This result involves that the total number of π electrons is the main factor governing the parity of the stability alternations. Accordingly, since the knowledge of the π electron number requires the determination of the σ electron number too, these alternations enable us to infer a very likely electronic structure of the ions.

  3. Variety of Band Structures in Light Sn, In, and Cd Nuclei

    NASA Astrophysics Data System (ADS)

    Wolinska-Cichocka, M.; Kownacki, J.; Ruchowska, E.

    2003-04-01

    Selected experimental results retrieved from 98Mo (16O, xnyp) reaction are discussed and compared with the up-to-day known data. The collective configurations in selected Z=48--50, N=55--66 nuclei are presented in terms of Cranked Shell Model (CSM) and rigid rotor description. The special interest was put on: (1) Systematical behaviour of intruder bands especially for low spin levels, (2) The collective, strongly coupled bands, where the band members are connected by Delta I=1 transitions, (3) Smooth band termination in the A=104--120 mass region.

  4. Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson's Ratio.

    PubMed

    Dai, Zhaohe; Weng, Chuanxin; Liu, Luqi; Hou, Yuan; Zhao, Xuanliang; Kuang, Jun; Shi, Jidong; Wei, Yueguang; Lou, Jun; Zhang, Zhong

    2016-01-01

    In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson's ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on. PMID:27608928

  5. Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson’s Ratio

    PubMed Central

    Dai, Zhaohe; Weng, Chuanxin; Liu, Luqi; Hou, Yuan; Zhao, Xuanliang; Kuang, Jun; Shi, Jidong; Wei, Yueguang; Lou, Jun; Zhang, Zhong

    2016-01-01

    In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson’s ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on. PMID:27608928

  6. Gram-Negative Marine Bacteria: Structural Features of Lipopolysaccharides and Their Relevance for Economically Important Diseases

    PubMed Central

    Anwar, Muhammad Ayaz; Choi, Sangdun

    2014-01-01

    Gram-negative marine bacteria can thrive in harsh oceanic conditions, partly because of the structural diversity of the cell wall and its components, particularly lipopolysaccharide (LPS). LPS is composed of three main parts, an O-antigen, lipid A, and a core region, all of which display immense structural variations among different bacterial species. These components not only provide cell integrity but also elicit an immune response in the host, which ranges from other marine organisms to humans. Toll-like receptor 4 and its homologs are the dedicated receptors that detect LPS and trigger the immune system to respond, often causing a wide variety of inflammatory diseases and even death. This review describes the structural organization of selected LPSes and their association with economically important diseases in marine organisms. In addition, the potential therapeutic use of LPS as an immune adjuvant in different diseases is highlighted. PMID:24796306

  7. Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson's Ratio.

    PubMed

    Dai, Zhaohe; Weng, Chuanxin; Liu, Luqi; Hou, Yuan; Zhao, Xuanliang; Kuang, Jun; Shi, Jidong; Wei, Yueguang; Lou, Jun; Zhang, Zhong

    2016-09-09

    In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson's ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on.

  8. Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson’s Ratio

    NASA Astrophysics Data System (ADS)

    Dai, Zhaohe; Weng, Chuanxin; Liu, Luqi; Hou, Yuan; Zhao, Xuanliang; Kuang, Jun; Shi, Jidong; Wei, Yueguang; Lou, Jun; Zhang, Zhong

    2016-09-01

    In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson’s ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on.

  9. Valence-band electronic structure of iron phthalocyanine: An experimental and theoretical photoelectron spectroscopy study

    NASA Astrophysics Data System (ADS)

    Brena, Barbara; Puglia, Carla; de Simone, Monica; Coreno, Marcello; Tarafder, Kartick; Feyer, Vitaly; Banerjee, Rudra; Göthelid, Emmanuelle; Sanyal, Biplab; Oppeneer, Peter M.; Eriksson, Olle

    2011-02-01

    The electronic structure of iron phthalocyanine (FePc) in the valence region was examined within a joint theoretical-experimental collaboration. Particular emphasis was placed on the determination of the energy position of the Fe 3d levels in proximity of the highest occupied molecular orbital (HOMO). Photoelectron spectroscopy (PES) measurements were performed on FePc in gas phase at several photon energies in the interval between 21 and 150 eV. Significant variations of the relative intensities were observed, indicating a different elemental and atomic orbital composition of the highest lying spectral features. The electronic structure of a single FePc molecule was first computed by quantum chemical calculations by means of density functional theory (DFT). The hybrid Becke 3-parameter, Lee, Yang and Parr (B3LYP) functional and the semilocal 1996 functional of Perdew, Burke and Ernzerhof (PBE) of the generalized gradient approximation (GGA-)type, exchange-correlation functionals were used. The DFT/B3LYP calculations find that the HOMO is a doubly occupied π-type orbital formed by the carbon 2p electrons, and the HOMO-1 is a mixing of carbon 2p and iron 3d electrons. In contrast, the DFT/PBE calculations find an iron 3d contribution in the HOMO. The experimental photoelectron spectra of the valence band taken at different energies were simulated by means of the Gelius model, taking into account the atomic subshell photoionization cross sections. Moreover, calculations of the electronic structure of FePc using the GGA+U method were performed, where the strong correlations of the Fe 3d electronic states were incorporated through the Hubbard model. Through a comparison with our quantum chemical calculations we find that the best agreement with the experimental results is obtained for a Ueff value of 5 eV.

  10. Synthesis, physical properties, and band structure of the layered bismuthide PtBi2

    NASA Astrophysics Data System (ADS)

    Xu, C. Q.; Xing, X. Z.; Xu, Xiaofeng; Li, Bin; Chen, B.; Che, L. Q.; Lu, Xin; Dai, Jianhui; Shi, Z. X.

    2016-10-01

    We report details of single-crystal growth of stoichiometric bismuthide PtBi2 whose structure consists of alternate stacking of a Pt layer and Bi bilayer along the c axis. The compound crystallizes in space group P 3 with a hexagonal unit cell of a =b =6.553 Å,c =6.165 Å . Its T -dependent resistivity is typical of a metal whereas a large anisotropy was observed for the in-plane and interplane electrical transport. The magnetization data show opposite sign for fields parallel and perpendicular to the Pt layers, respectively. The magnetic field response of this material shows clearly two types of charge carriers, consistent with the multiple Fermi surfaces revealed in our band structure calculations. The hydrostatic pressure is shown to suppress the resistivity at high T systematically but has little bearing on its low-T transport. Through calorimetric measurements, the density of states at the Fermi level and the Debye temperature are determined to be 0.94 eV-1 per molecule and 145 K, respectively. In addition, the electronic structures and parity analyses are also presented. We find a minimum value of 0.05 eV gap opening at around 2 eV under the Fermi level by invoking spin-orbit interaction. A slab calculation further indicates a surface Dirac cone appearing in the gap of bulk states. We discuss the possibility of PtBi 2 being a candidate for a bulk topological metal, in analogy to the recently proposed topological superconductor β -PdBi2 .

  11. Non-negative structural sparse representation for high resolution hyperspectral imaging

    NASA Astrophysics Data System (ADS)

    Meng, Guiyu; Li, Guangyu; Dong, Weisheng; Shi, Guangming

    2014-11-01

    High resolution hyperspectral images have important applications in many areas, such as anomaly detection, target recognition and image classification. Due to the limitation of the sensors, it is challenging to obtain high spatial resolution hyperspectral images. Recently, the methods that reconstruct high spatial resolution hyperspectral images from the pair of low resolution hyperspectral images and high resolution RGB image of the same scene have shown promising results. In these methods, sparse non-negative matrix factorization (SNNMF) technique was proposed to exploit the spectral correlations among the RGB and spectral images. However, only the spectral correlations were exploited in these methods, ignoring the abundant spatial structural correlations of the hyperspectral images. In this paper, we propose a novel algorithm combining the structural sparse representation and non-negative matrix factorization technique to exploit the spectral-spatial structure correlations and nonlocal similarity of the hyperspectral images. Compared with SNNMF, our method makes use of both the spectral and spatial redundancies of hyperspectral images, leading to better reconstruction performance. The proposed optimization problem is efficiently solved by using the alternating direction method of multipliers (ADMM) technique. Experiments on a public database show that our approach performs better than other state-of-the-art methods on the visual effect and in the quantitative assessment.

  12. Structural, vibrational, and quasiparticle band structure of 1,1-diamino-2,2-dinitroethelene from ab initio calculations

    SciTech Connect

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

    2014-01-07

    The effects of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme, are found to agree well with experiments. The calculated vibrational frequencies demonstrate the dependence of the intra and inter-molecular interactions on FOX-7 under pressure. In addition, we also found a significant increment in the N–H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen, and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with generalized gradient approximation, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials.

  13. On the influence of tetrahedral covalent-hybridization on electronic band structure of topological insulators from first principles

    SciTech Connect

    Zhang, X. M.; Xu, G. Z.; Liu, E. K.; Wang, W. H. Wu, G. H.; Liu, Z. Y.

    2015-01-28

    Based on first-principles calculations, we investigate the influence of tetrahedral covalent-hybridization between main-group and transition-metal atoms on the topological band structures of binary HgTe and ternary half-Heusler compounds, respectively. Results show that, for the binary HgTe, when its zinc-blend structure is artificially changed to rock-salt one, the tetrahedral covalent-hybridization will be removed and correspondingly the topologically insulating band character lost. While for the ternary half-Heusler system, the strength of covalent-hybridization can be tuned by varying both chemical compositions and atomic arrangements, and the competition between tetrahedral and octahedral covalent-hybridization has been discussed in details. As a result, we found that a proper strength of tetrahedral covalent-hybridization is probably in favor to realizing the topologically insulating state with band inversion occurring at the Γ point of the Brillouin zone.

  14. Experimental and theoretical investigations of the electronic band structure of metal-organic frameworks of HKUST-1 type

    SciTech Connect

    Gu, Zhi-Gang; Heinke, Lars Wöll, Christof; Neumann, Tobias; Wenzel, Wolfgang; Li, Qiang; Fink, Karin; Gordan, Ovidiu D.; Zahn, Dietrich R. T.

    2015-11-02

    The electronic properties of metal-organic frameworks (MOFs) are increasingly attracting the attention due to potential applications in sensor techniques and (micro-) electronic engineering, for instance, as low-k-dielectric in semiconductor technology. Here, the band gap and the band structure of MOFs of type HKUST-1 are studied in detail by means of spectroscopic ellipsometry applied to thin surface-mounted MOF films and by means of quantum chemical calculations. The analysis of the density of states, the band structure, and the excitation spectrum reveal the importance of the empty Cu-3d orbitals for the electronic properties of HKUST-1. This study shows that, in contrast to common belief, even in the case of this fairly “simple” MOF, the excitation spectra cannot be explained by a superposition of “intra-unit” excitations within the individual building blocks. Instead, “inter-unit” excitations also have to be considered.

  15. Brilliant Structurally Colored Films with Invariable Stop-Band and Enhanced Mechanical Robustness Inspired by the Cobbled Road.

    PubMed

    Zhang, Xin; Wang, Fen; Wang, Lei; Lin, Ying; Zhu, Jianfeng

    2016-08-31

    Recently, structural colors have attracted great concentrations because the coloration is free from chemical- or photobleaching. However, the color saturation and mechanical robustness are generally competitive properties in the fabrication of PCs (photonic crystals) films. Besides, the structure of PCs and their derivatives are easy to be invaded by liquids and lead to band gap shifts due to the change of refractive index or periodicity. To solve those problems, we infiltrate polydimethylsiloxane (PDMS) into the intervals between regularly arrayed hollow SiO2 nanospheres, inspired by the cobbled road prepared by embedding stone in the bulk cement matrix. Consequently, the as-prepared PCs films show brilliant colors, invariable stop-bands, and excellent mechanical robustness. Moreover, the water contact angle even reached 166° after a sandpaper abrasion test. The combination of brilliant colors, invariable stop-bands, and excellent robustness is significant for potential application in paint and external decoration of architectures. PMID:27509171

  16. Tuning the band structures of a one-dimensional width-modulated magnonic crystal by a transverse magnetic field

    SciTech Connect

    Di, K.; Lim, H. S. Zhang, V. L.; Ng, S. C.; Kuok, M. H.; Nguyen, H. T.; Cottam, M. G.

    2014-02-07

    Theoretical studies, based on three independent techniques, of the band structure of a one-dimensional width-modulated magnonic crystal under a transverse magnetic field are reported. The band diagram is found to display distinct behaviors when the transverse field is either larger or smaller than a critical value. The widths and center positions of bandgaps exhibit unusual non-monotonic and large field-tunability through tilting the direction of magnetization. Some bandgaps can be dynamically switched on and off by simply tuning the strength of such a static field. Finally, the impact of the lowered symmetry of the magnetic ground state on the spin-wave excitation efficiency of an oscillating magnetic field is discussed. Our finding reveals that the magnetization direction plays an important role in tailoring magnonic band structures and hence in the design of dynamic spin-wave switches.

  17. 3D-structures with arbitrary shapes created in negative resists by grayscale proton beam writing

    NASA Astrophysics Data System (ADS)

    Menzel, F.; Spemann, D.; Koal, T.; Butz, T.

    2011-10-01

    The direct and maskless technique of proton beam writing (PBW) was used for grayscale lithography which allows to create 3D microstructures with arbitrary surface topographies. For this purpose, several micrometer thick layers of the negative resists ma-N and SU-8 were irradiated with 2.25 MeV H+ and 1.125 MeV H2+ in arbitrary shapes using different fluences on different areas with values smaller than the threshold fluence for complete exposure. These irradiations result in multilevel microstructures, whose heights increase with increasing fluence. However, the comparison of the measured structure height with calculated predictions from SRIM simulations disproves the assumption that the structure height is proportional to the linear energy transfer (LET). In fact, the fluence reduction below the threshold for sufficient exposure is responsible for grayscale structuring due to reduced etching of the insufficiently exposed regions. The artifacts obtained with the first grayscale structures created by PBW in ma-N and strongly affecting the structure quality could be reduced by optimizing the scanning procedure, e.g. reducing the pixel distance. Therewith, a micro-Fresnel-lens could be fabricated in ma-N. The first PBW grayscale structures in SU-8 exhibited very strong mechanical instabilities which could be reduced by the use of a post exposure bake step, normally omitted for PBW with SU-8.

  18. Effects of Electrode Layer Band Structure on the Performance of Multilayer Graphene-hBN-Graphene Interlayer Tunnel Field Effect Transistors.

    PubMed

    Kang, Sangwoo; Prasad, Nitin; Movva, Hema C P; Rai, Amritesh; Kim, Kyounghwan; Mou, Xuehao; Taniguchi, Takashi; Watanabe, Kenji; Register, Leonard F; Tutuc, Emanuel; Banerjee, Sanjay K

    2016-08-10

    Interlayer tunnel field-effect transistors based on graphene and hexagonal boron nitride (hBN) have recently attracted much interest for their potential as beyond-CMOS devices. Using a recently developed method for fabricating rotationally aligned two-dimensional heterostructures, we show experimental results for devices with varying thicknesses and stacking order of the graphene electrode layers and also model the current-voltage behavior. We show that an increase in the graphene layer thickness results in narrower resonance. However, due to a simultaneous increase in the number of sub-bands and decrease of sub-band separation with an increase in thickness, the negative differential resistance peaks becomes less prominent and do not appear for certain conditions at room temperature. Also, we show that due to the unique band structure of odd number of layer Bernal-stacked graphene, the number of closely spaced resonance conditions increase, causing interference between neighboring resonance peaks. Although this can be avoided with even number of layer graphene, we find that in this case the bandgap opening present at high biases tend to broaden the resonance peaks. PMID:27416362

  19. Magnetostatic Surface Waves in Ferrite-Nonlinear Nonmagnetic Negative Permittivity Material Structure

    NASA Astrophysics Data System (ADS)

    Ass'ad, A. I.; Ashour, H. S.; Shabat, M. M.

    Magnetostatic surface waves have been investigated in a layered system of a nonlinear nonmagnetic negative permittivity material (NPM) and Ferrite (YIG). We derived the dispersion relation before numerically solving the dispersion relation of the TE nonlinear magnetostatic surface waves (NMSSW) in the proposed structure and the power flow. We found out that the wave effective nonlinear refractive index is much smaller in the forward direction than in the backward direction and consequently, the power flow is lower for the forward direction than the backward direction.

  20. Negative differential gain in quantum dot systems: Interplay of structural properties and many-body effects

    SciTech Connect

    Goldmann, E. Jahnke, F.; Lorke, M.; Frauenheim, T.

    2014-06-16

    The saturation behaviour of optical gain with increasing excitation density is an important factor for laser device performance. For active materials based on self-organized InGaAs/GaAs quantum dots, we study the interplay between structural properties of the quantum dots and many-body effects of excited carriers in the optical properties via a combination of tight-binding and quantum-kinetic calculations. We identify regimes where either phase-space filling or excitation-induced dephasing dominates the saturation behavior of the optical gain. The latter can lead to the emergence of a negative differential material gain.

  1. Microscopic nuclear structure models and methods: chiral symmetry, wobbling motion and γ–bands

    NASA Astrophysics Data System (ADS)

    Sheikh, Javid A.; Bhat, Gowhar H.; Dar, Waheed A.; Jehangir, Sheikh; Ganai, Prince A.

    2016-06-01

    A systematic investigation of the nuclear observables related to the triaxial degree of freedom is presented using the multi-quasiparticle triaxial projected shell model (TPSM) approach. These properties correspond to the observation of γ-bands, chiral doublet bands and the wobbling mode. In the TPSM approach, γ-bands are built on each quasiparticle configuration and it is demonstrated that some observations in high-spin spectroscopy that have remained unresolved for quite some time could be explained by considering γ-bands based on two-quasiparticle configurations. It is shown in some Ce-, Nd- and Ge-isotopes that the two observed aligned or s-bands originate from the same intrinsic configuration with one of them as the γ-band based on a two-quasiparticle configuration. In the present work, we have also performed a detailed study of γ-bands observed up to the highest spin in dysposium, hafnium, mercury and uranium isotopes. Furthermore, several measurements related to chiral symmetry breaking and wobbling motion have been reported recently. These phenomena, which are possible only for triaxial nuclei, have been investigated using the TPSM approach. It is shown that doublet bands observed in lighter odd–odd Cs-isotopes can be considered as candidates for chiral symmetry breaking. Transverse wobbling motion recently observed in 135Pr has also been investigated and it is shown that TPSM approach provides a reasonable description of the measured properties.

  2. Hybrid functional band gap calculation of SnO{sub 6} containing perovskites and their derived structures

    SciTech Connect

    Lee, Hyewon; Cheong, S.W.; Kim, Bog G.

    2015-08-15

    We have studied the properties of SnO{sub 6} octahedra-containing perovskites and their derived structures using ab initio calculations with different density functionals. In order to predict the correct band gap of the materials, we have used B3LYP hybrid density functional, and the results of B3LYP were compared with those obtained using the local density approximation and generalized gradient approximation data. The calculations have been conducted for the orthorhombic ground state of the SnO{sub 6} containing perovskites. We also have expended the hybrid density functional calculation to the ASnO{sub 3}/A'SnO{sub 3} system with different cation orderings. We propose an empirical relationship between the tolerance factor and the band gap of SnO{sub 6} containing oxide materials based on first principles calculation. - Graphical abstract: (a) Structure of ASnO{sub 3} for orthorhombic ground state. The green ball is A (Ba, Sr, Ca) cation and the small (red) ball on edge is oxygen. SnO{sub 6} octahedrons are plotted as polyhedron. (b) Band gap of ASnO{sub 3} as a function of the tolerance factor for different density functionals. The experimental values of the band gap are marked as green pentagons. (c) ASnO{sub 3}/A'SnO{sub 3} superlattices with two types cation arrangement: [001] layered structure and [111] rocksalt structure, respectively. (d) B3LYP hybrid functional band gaps of ASnO{sub 3}, [001] ordered superlattices, and [111] ordered superlattices of ASnO{sub 3}/A'SnO{sub 3} as a function of the effective tolerance factor. Note the empirical linear relationship between the band gap and effective tolerance factor. - Highlights: • We report the hybrid functional band gap calculation of ASnO{sub 3} and ASnO{sub 3}/A'SnO{sub 3}. • The band gap of ASnO{sub 3} using B3LYP functional reproduces the experimental value. • We propose the linear relationship between the tolerance factor and the band gap.

  3. Attenuation structure beneath the volcanic front in northeastern Japan from broad-band seismograms

    NASA Astrophysics Data System (ADS)

    Takanami, Tetsuo; Selwyn Sacks, I.; Hasegawa, Akira

    2000-10-01

    Anelastic structure in the asthenosphere beneath the volcanic front in northeastern Japan arc is estimated by using the spectral amplitude ratio data of P and S waves from about 100 events which occurred in the subducting Pacific slab below Japan. These earthquakes occurred within a 90 km radius centered about the station Sawauchi (SWU), with focal depths ranging from 60 to 200 km. Waveforms were recorded by the Carnegie broad-band three-component seismograph and were corrected for instrument responses, crustal reverberations, corner frequencies, and superimposed noise. Ray paths and travel times of P and S waves are calculated using a three-dimensional velocity model [Zhao, D., Hasegawa, A., Horiuchi, S., 1992. J. Geophys. Res. 97, 19909-19928]. We find a low- Q region ( QS˜70) extending down to 55 km depth from the lower crust beneath the volcanic front. Using Q-temperature laboratory results [Sato, H., Sacks, I.S., Murase, T., Muncill, G., Fukushima, H., 1989. J. Geophys. Res. 94, 10647-10661], this implies a temperature of about 130°C higher than the eastern forearc region and about 30°C higher than the western backarc region, in good agreement with the tomographic results of Zhao et al. [Zhao, D., Hasegawa, A., Horiuchi, S., 1992. J. Geophys. Res. 97, 19909-19928]. This suggests that low velocities in the crust and uppermost mantle beneath SWU may be explained by a subsolidus temperature increase without partial melting.

  4. The electronic band structures of gadolinium chalcogenides: a first-principles prediction for neutron detecting.

    PubMed

    Li, Kexue; Liu, Lei; Yu, Peter Y; Chen, Xiaobo; Shen, D Z

    2016-05-11

    By converting the energy of nuclear radiation to excited electrons and holes, semiconductor detectors have provided a highly efficient way for detecting them, such as photons or charged particles. However, for detecting the radiated neutrons, those conventional semiconductors hardly behave well, as few of them possess enough capability for capturing these neutral particles. While the element Gd has the highest nuclear cross section, here for searching proper neutron-detecting semiconductors, we investigate theoretically the Gd chalcogenides whose electronic band structures have never been characterized clearly. Among them, we identify that γ-phase Gd2Se3 should be the best candidate for neutron detecting since it possesses not only the right bandgap of 1.76 eV for devices working under room temperature but also the desired indirect gap nature for charge carriers surviving longer. We propose further that semiconductor neutron detectors with single-neutron sensitivity can be realized with such a Gd-chalcogenide on the condition that their crystals can be grown with good quality. PMID:27049355

  5. The band structure of VO2 measured by angle-resolved photoemission

    NASA Astrophysics Data System (ADS)

    Moreschini, Luca; Chang, Young Jun; Innocenti, Davide; Walter, Andrew L.; Kim, Young Su; Gaines, Geoffrey; Bostwick, Aaron; Denlinger, Jonathan; Rotenberg, Eli

    2011-03-01

    The origin of the 340K metal-insulator transition (MIT) in VO2 is still under debate. the main reason is that no direct experimental verifications of the electronic structure of VO2 exist up to this point. The quality of the available single crystals is not sufficient for ARPES measurements, so that photoemission is limited to angle-integrated mode. New opportunities are offered by oxide films, on which data of equal or even higher quality have been reported (Saeki et al., PRB 2009). WIth the in situ pulsed-laser-deposition (PLD) system available on beamline 7.0.1 at the Advanced Light Source we have grown VO2(001) films on a TiO2 substrate and measured the Fermi surface of the metallic phase. These results will permit a direct comparison with the existing band calculations and open the way to the study of the MIT as a function, e.g., of film thickness or electron doping with Cr. Work supported by U.S. DOE (DE-AC02-05CH11231 for ALS), the Max Planck Society, and the Swiss National Science Foundation (PBELP2-125484).

  6. Detailed Structure of the Outer Disk Around HD 169142 with Polarized Light in H-band

    NASA Technical Reports Server (NTRS)

    Momose, Munetake; Morita, Ayaka; Fukagawa, Misato; Muto, Takayuki; Takeuchi, Taku; Hashimoto, Jun; Honda, Mitsuhiko; Kudo, Tomoyuki; Okamoto, Yoshiko K.; Kanagawa, Kazuhiro D.; Tanaka, Hidekazu; Grady, Carol A.; Sitko, Michael L.; Akiyama, Eiji; Currie, Thayne; Follette, Katherine B.; Mayama, Satoshi; Kusakabe, Nobuhiko; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph C.; Egner, Sebastian; Feldt, Markus; McElwain, Michael W.

    2015-01-01

    Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0.''2=r=1.''2, or 29=r=174 AU, is successfully detected. The azimuthally-averaged radial profile of the PI shows a double power-law distribution, in which the PIs in r = 29-52 AU and r = 81.2-145 AU respectively show r-3-dependence. These two power-law regions are connected smoothly with a transition zone (TZ), exhibiting an apparent gap in r = 40-70 AU. The PI in the inner power-law region shows a deep minimum whose location seems to coincide with the point source at lambda = 7 mm. This can be regarded as another sign of a protoplanet in TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution or with an irregular temperature distribution or with the combination of both. The depletion factor of surface density in the inner power-law region (r <50 AU) is derived to be =0.16 from a simple model calculation. The obtained PI image also shows small scale asymmetries in the outer power-law region. Possible origins for these asymmetries include corrugation of the scattering surface in the outer region, and shadowing effect by a puffed up structure in the inner power-law region.

  7. The electronic band structures of gadolinium chalcogenides: a first-principles prediction for neutron detecting

    NASA Astrophysics Data System (ADS)

    Li, Kexue; Liu, Lei; Yu, Peter Y.; Chen, Xiaobo; Shen, D. Z.

    2016-05-01

    By converting the energy of nuclear radiation to excited electrons and holes, semiconductor detectors have provided a highly efficient way for detecting them, such as photons or charged particles. However, for detecting the radiated neutrons, those conventional semiconductors hardly behave well, as few of them possess enough capability for capturing these neutral particles. While the element Gd has the highest nuclear cross section, here for searching proper neutron-detecting semiconductors, we investigate theoretically the Gd chalcogenides whose electronic band structures have never been characterized clearly. Among them, we identify that γ-phase Gd2Se3 should be the best candidate for neutron detecting since it possesses not only the right bandgap of 1.76 eV for devices working under room temperature but also the desired indirect gap nature for charge carriers surviving longer. We propose further that semiconductor neutron detectors with single-neutron sensitivity can be realized with such a Gd-chalcogenide on the condition that their crystals can be grown with good quality.

  8. Band structure of 146Ce studied through γ-γ angular correlation measurements

    NASA Astrophysics Data System (ADS)

    Yamada, S.; Taniguchi, A.; Okano, K.; Aoki, K.

    The β-decay of 146La was studied using the on-line isotope separator KUR-ISOL. Gamma-gamma angular correlation measurements were performed with a 4-Ge detectors system. Spin assignments of three levels were made: 3+ for the 1576.5 keV level, 4+ for the 1627.1 keV level and 5+ for the 1810.2 keV level. The mixing ratios (E2/M1) were deduced to be δ183.2= 0.25 +/- 0.08, δ638.9= 0.33 +/- 0.05, δ959.0= 1.19+0.16-0.14, δ1015.9= 5.4+3.1-1.5 and δ1318.1= 6.5+1.7-1.1. These were compared to the calculated values obtained in three cases involving different Majorana force parameter values. The band structure of 146Ce is discussed based on the results of calculation using the IBM-2 theory.

  9. ANOTHER LOOK AT THE EASTERN BANDED STRUCTURE: A STELLAR DEBRIS STREAM AND A POSSIBLE PROGENITOR

    SciTech Connect

    Grillmair, C. J.

    2011-09-01

    Using the Sloan Digital Sky Survey Data Release 7, we re-examine the Eastern Banded Structure (EBS), a stellar debris stream first discovered in Data Release 5 and more recently detected in velocity space by Schlaufman et al. The visible portion of the stream is 18{sup 0} long, lying roughly in the Galactic Anticenter direction and extending from Hydra to Cancer. At an estimated distance of 9.7 kpc, the stream is {approx}170 pc across on the sky. The curvature of the stream implies a fairly eccentric box orbit that passes close to both the Galactic center and to the Sun, making it dynamically distinct from the nearby Monoceros, Anticenter, and GD-1 streams. Within the stream is a relatively strong, 2{sup 0}-wide concentration of stars with a very similar color-magnitude distribution that we designate Hydra I. Given its prominence within the stream and its unusual morphology, we suggest that Hydra I is the last vestige of EBS's progenitor, possibly already unbound or in the final throes of tidal dissolution. Though both Hydra I and the EBS have a relatively high-velocity dispersion, given the comparatively narrow width of the stream and the high frequency of encounters with the bulge and massive constituents of the disk that such an eccentric orbit would entail, we suggest that the progenitor was likely a globular cluster and that both it and the stream have undergone significant heating over time.

  10. Pressure Effect on Electronic Band Structure of NiAs-Type CrTe

    NASA Astrophysics Data System (ADS)

    Takagaki, Masafumi; Kawakami, Takuya; Tanaka, Norikazu; Shirai, Masafumi; Motizuki, Kazuko

    1998-03-01

    Pressure influence on the electronic band structure of NiAs-type CrTe is studied for non-magnetic, ferromagnetic and antiferromagnetic states by using a self-consistent LAPW method. The total energy is calculated as a function of the lattice spacing a, keeping the ratio c/a as the observed value. The ferromagnetic state is stable energetically among three states for a>3.83 A. For a<3.83 A, the energy of antiferromagnetic state becomes lower than that of ferromagnetic state. Therefore pressure-induced ferromagnetic→antiferromagnetic transition is expected at about 20 GP. For the ferromagnetic state, which is realized below T C=340 K, the theoretical lattice spacing a is obtained as 4.180 A, which agrees fairly well with the observed one (a obs=3.981). The magnetic moment arises from mainly Cr-site and it is remarkably reduced by the pressure as observed. A small magnetic moment is induced at Te-site in the direction antiparallel to the moment at Cr-site.

  11. Microwave band gap and cavity mode in spoof-insulator-spoof waveguide with multiscale structured surface

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Xiao, Jun Jun; Han, Dezhuan; Qin, Fei Fei; Zhang, Xiao Ming; Yao, Yong

    2015-05-01

    We propose a multiscale spoof-insulator-spoof (SIS) waveguide by introducing periodic geometry modulation in the wavelength scale to a SIS waveguide made of a perfect electric conductor. The MSIS consists of multiple SIS subcells. The dispersion relationship of the fundamental guided mode of the spoof surface plasmon polaritons (SSPPs) is studied analytically within the small gap approximation. It is shown that the multiscale SIS possesses microwave band gap (MBG) due to the Bragg scattering. The ‘gap maps’ in the design parameter space are provided. We demonstrate that the geometry of the subcells can efficiently adjust the effective refraction index of the elementary SIS and therefore further control the width and the position of the MBG. The results are in good agreement with numerical calculations by the finite element method (FEM). For finite-sized MSIS of given geometry in the millimeter scale, FEM calculations show that the first-order symmetric SSPP mode has zero transmission in the MBG within frequency range from 4.29 to 5.1 GHz. A cavity mode is observed inside the gap at 4.58 GHz, which comes from a designer ‘point defect’ in the multiscale SIS waveguide. Furthermore, ultrathin MSIS waveguides are shown to have both symmetric and antisymmetric modes with their own MBGs, respectively. The deep-subwavelength confinement and the great degree of control of the propagation of SSPPs in such structures promise potential applications in miniaturized microwave device.

  12. Do ecohydrology and community dynamics feed back to banded-ecosystem structure and productivity?

    NASA Astrophysics Data System (ADS)

    Callegaro, Chiara; Ursino, Nadia

    2016-04-01

    Mixed communities including grass, shrubs and trees are often reported to populate self-organized vegetation patterns. Patterns of survey data suggest that species diversity and complementarity strengthen the dynamics of banded environments. Resource scarcity and local facilitation trigger self organization, whereas coexistence of multiple species in vegetated self-organizing patches, implying competition for water and nutrients and favorable reproduction sites, is made possible by differing adaptation strategies. Mixed community spatial self-organization has so far received relatively little attention, compared with local net facilitation of isolated species. We assumed that soil moisture availability is a proxy for the environmental niche of plant species according to Ursino and Callegaro (2016). Our modelling effort was focused on niche differentiation of coexisting species within a tiger bush type ecosystem. By minimal numerical modelling and stability analysis we try to answer a few open scientific questions: Is there an adaptation strategy that increases biodiversity and ecosystem functioning? Does specific adaptation to environmental niches influence the structure of self-organizing vegetation pattern? What specific niche distribution along the environmental gradient gives the highest global productivity?

  13. Theoretical investigation into tunable band gaps of an Euler- Bernoulli beam with 2DOF LR structures

    NASA Astrophysics Data System (ADS)

    Xingqian, Zhao; Changgeng, Shuai; Yan, Gao; Rustighi, Emiliano

    2016-09-01

    This paper is concerned with an intelligent phonotic crystals (IPC) consisting of an Euler-Bernoulli beam attached with 2DOF locally resonant (LR) structures. The novel design of the dielectric electroactive polymer (DEAP) rings acting as the springs of oscillators is presented that could be employed to control the transmission of flexural waves on the beam. Tunable band gaps (BGs) can be realized by changing the stiffness of each oscillator driven by the external electric field, where the DEAPs transform electric energy directly into mechanical work under the applied voltage. Discrete copper (Cu) strips are then attached to the DEAP to allow the deformation of DEAP rings. The transfer matrix (TM) theory is adopted to assist readers to better understand the formation of the BG. Simulation results show that this particular configuration is effective for attenuating the flexural waves at low frequencies below 1000Hz where the tunable BGs may occur. Moreover, it is found that a wider BG can be achieved and shifts towards higher frequencies by increasing the applied voltages.

  14. Ecosystem structure, function, and composition in rangelands are negatively affected by livestock grazing.

    PubMed

    Eldridge, David J; Poore, Alistair G B; Ruiz-Colmenero, Marta; Letnic, Mike; Soliveres, Santiago

    2016-06-01

    Reports of positive or neutral effects of grazing on plant species richness have prompted calls for livestock grazing to be used as a tool for managing land for conservation. Grazing effects, however, are likely to vary among different response variables, types, and intensity of grazing, and across abiotic conditions. We aimed to examine how grazing affects ecosystem structure, function, and composition. We compiled a database of 7615 records reporting an effect of grazing by sheep and cattle on 278 biotic and abiotic response variables for published studies across Australia. Using these data, we derived three ecosystem measures based on structure, function, and composition, which were compared against six contrasts of grazing pressure, ranging from low to heavy, two different herbivores (sheep, cattle), and across three different climatic zones. Grazing reduced structure (by 35%), function (24%), and composition (10%). Structure and function (but not composition) declined more when grazed by sheep and cattle together than sheep alone. Grazing reduced plant biomass (40%), animal richness (15%), and plant and animal abundance, and plant and litter cover (25%), but had no effect on plant richness nor soil function. The negative effects of grazing on plant biomass, plant cover, and soil function were more pronounced in drier environments. Grazing effects on plant and animal richness and composition were constant, or even declined, with increasing aridity. Our study represents a comprehensive continental assessment of the implications of grazing for managing Australian rangelands. Grazing effects were largely negative, even at very low levels of grazing. Overall, our results suggest that livestock grazing in Australia is unlikely to produce positive outcomes for ecosystem structure, function, and composition or even as a blanket conservation tool unless reduction in specific response variables is an explicit management objective.

  15. Ecosystem structure, function, and composition in rangelands are negatively affected by livestock grazing.

    PubMed

    Eldridge, David J; Poore, Alistair G B; Ruiz-Colmenero, Marta; Letnic, Mike; Soliveres, Santiago

    2016-06-01

    Reports of positive or neutral effects of grazing on plant species richness have prompted calls for livestock grazing to be used as a tool for managing land for conservation. Grazing effects, however, are likely to vary among different response variables, types, and intensity of grazing, and across abiotic conditions. We aimed to examine how grazing affects ecosystem structure, function, and composition. We compiled a database of 7615 records reporting an effect of grazing by sheep and cattle on 278 biotic and abiotic response variables for published studies across Australia. Using these data, we derived three ecosystem measures based on structure, function, and composition, which were compared against six contrasts of grazing pressure, ranging from low to heavy, two different herbivores (sheep, cattle), and across three different climatic zones. Grazing reduced structure (by 35%), function (24%), and composition (10%). Structure and function (but not composition) declined more when grazed by sheep and cattle together than sheep alone. Grazing reduced plant biomass (40%), animal richness (15%), and plant and animal abundance, and plant and litter cover (25%), but had no effect on plant richness nor soil function. The negative effects of grazing on plant biomass, plant cover, and soil function were more pronounced in drier environments. Grazing effects on plant and animal richness and composition were constant, or even declined, with increasing aridity. Our study represents a comprehensive continental assessment of the implications of grazing for managing Australian rangelands. Grazing effects were largely negative, even at very low levels of grazing. Overall, our results suggest that livestock grazing in Australia is unlikely to produce positive outcomes for ecosystem structure, function, and composition or even as a blanket conservation tool unless reduction in specific response variables is an explicit management objective. PMID:27509764

  16. Band gap engineering and \\vec{k}\\cdot \\vec{\\pi } electronic structure of lead and tin tellurides

    NASA Astrophysics Data System (ADS)

    Behera, S. S.; Tripathi, G. S.

    2016-06-01

    We study the effect of the variation of energy gap on the k\\cdot π electronic structure of PbTe and SnTe, using a six-level basis at the L point. The basis functions in both the systems have the same transformation properties. However, the basis functions of the band edge states in SnTe are reversed with respect to the same in PbTe. Band dispersions are obtained analytically for a two band model. As the band gap decreases, the bands become linear. Far bands are included in the electronic dispersion, using perturbation theory. Fermi energy and the Density of States at the Fermi energy, { D }({\\varepsilon }F), are calculated for different carrier concentrations and energy gaps through a self-consistent approach. Interesting results are seen when the energy gap is reduced from the respective equilibrium values. For both the systems, the Fermi energy increases as the gap is decreased. The behavior of { D }({\\varepsilon }F) is, however, different. It decreases with the gap. It is also on expected lines. Calculated values of the electronic effective mass, as a function of temperature, energy gap and carrier concentration, are compared with previously published data. As distinguished from a first principles calculation, the work has focused on the carrier dependent electronic parameters for use both by theorists and experimenters as well.

  17. Electronic Band Structures of the Highly Desirable III-V Semiconductors: TB-mBJ DFT Studies

    NASA Astrophysics Data System (ADS)

    Rehman, Gul; Shafiq, M.; Saifullah; Ahmad, Rashid; Jalali-Asadabadi, S.; Maqbool, M.; Khan, Imad; Rahnamaye-Aliabad, H.; Ahmad, Iftikhar

    2016-07-01

    The correct band gaps of semiconductors are highly desirable for their effective use in optoelectronic and other photonic devices. However, the experimental and theoretical results of the exact band gaps are quite challenging and sometimes tricky. In this article, we explore the electronic band structures of the highly desirable optical materials, III-V semiconductors. The main reason of the ineffectiveness of the theoretical band gaps of these compounds is their mixed bonding character, where large proportions of electrons reside outside atomic spheres in the intestinal regions, which are challenging for proper theoretical treatment. In this article, the band gaps of the compounds are revisited and successfully reproduced by properly treating the density of electrons using the recently developed non-regular Tran and Blaha's modified Becke-Johnson (nTB-mBJ) approach. This study additionally suggests that this theoretical scheme could also be useful for the band gap engineering of the III-V semiconductors. Furthermore, the optical properties of these compounds are also calculated and compared with the experimental results.

  18. Phase and frequency structure of superradiance pulses generated by relativistic Ka-band backward-wave oscillator

    NASA Astrophysics Data System (ADS)

    Rostov, V. V.; Romanchenko, I. V.; Elchaninov, A. A.; Sharypov, K. A.; Shunailov, S. A.; Ul'masculov, M. R.; Yalandin, M. I.

    2016-08-01

    Phase and frequency stability of electromagnetic oscillations in sub-gigawatt superradiance (SR) pulses generated by an extensive slow-wave structure of a relativistic Ka-band backward-wave oscillator were experimentally investigated. Data on the frequency tuning and radiation phase stability of SR pulses with a variation of the energy and current of electron beam were obtained.

  19. Design, realization and test of C-band accelerating structures for the SPARC_LAB linac energy upgrade

    NASA Astrophysics Data System (ADS)

    Alesini, D.; Bellaveglia, M.; Biagini, M. E.; Boni, R.; Brönnimann, M.; Cardelli, F.; Chimenti, P.; Clementi, R.; Di Pirro, G.; Di Raddo, R.; Ferrario, M.; Ficcadenti, L.; Gallo, A.; Kalt, R.; Lollo, V.; Palumbo, L.; Piersanti, L.; Schilcher, T.

    2016-11-01

    The energy upgrade of the SPARC_LAB photo-injector at LNF-INFN (Frascati, Italy) has been originally conceived replacing one low gradient (13 MV/m) 3 m long SLAC type S-band traveling wave (TW) section with two 1.4 m long C-band accelerating sections. Due to the higher gradients reached by such structures, a higher energy beam can be obtained within the same accelerator footprint length. The use of C-band structures for electron acceleration has been adopted in a few FEL linacs in the world, among others, the Japanese Free Electron Laser at SPring-8 and the SwissFEL at Paul Scherrer Institute (PSI). The C-band sections are traveling wave, constant impedance structures with symmetric input and output axial couplers. Their design has been optimized for the operation with a SLED RF pulse compressor. In this paper we briefly review their design criteria and we focus on the construction, tuning, low and high-power RF tests. We also illustrate the design and realization of the dedicated low level RF system that has been done in collaboration with PSI in the framework of the EU TIARA project. Preliminary experimental results appear to confirm the operation of such structures with accelerating gradients larger than 35 MV/m.

  20. Valence state, hybridization and electronic band structure in the charge ordered AlV2O4.

    PubMed

    Kalavathi, S; Amirthapandian, S; Chandra, Sharat; Sahu, P Ch; Sahu, H K

    2014-01-01

    The valence state, hybridization and electronic band structure of charge ordered AlV2O4 are investigated by measuring the electron energy loss spectra (EELS) and performing band structure calculations using the WIEN2k code. White line ratio and O K edges of V2O5, VO2, V2O3 and AlV2O4, obtained using electron energy loss spectroscopy, are analysed specifically to probe systematically the VO6 octahedra in all of them. The systematic decrease of the L2 intensity and the O K edge intensity from V(5+) in V2O5 to AlV2O4 indicates a progressive increase in the occupancy of the hybridized states, which is corroborated by the absence of a transition from O 1s to hybridized 2t(2g). Band structure calculations on the parent charge frustrated cubic phase and the charge ordered rhombohedral phase clearly document a band gap in the charge ordered state. From the structural information obtained after convergence and the spectroscopic information from EELS, it appears that partial orbital occupancy may lead to a deviation from an integral valence state on all the vanadium in this exotic charge ordered spinel system.

  1. Observations of Multi-band Structures in Double Star TC-1 PEACE Electron and HIA Ion Data

    NASA Astrophysics Data System (ADS)

    Mohan Narasimhan, K.; Fazakerley, A. N.; Grimald, S.; Dandouras, I. S.; Mihaljcic, B.; Kistler, L. M.; Owen, C. J.

    2015-12-01

    Several authors have reported inner magnetosphere observations of proton distributions confined to narrow energy bands in the range 1 - 25 keV (Smith and Hoffman (1974), etc). These structures have been described as "nose structures", with reference to their appearance in energy-time spectrograms and are also known as "bands" if they occur for extended periods of time. Multi-nose structures have been observed if 2 or more noses appear at the same time (Vallat et al., 2007). Gaps between "noses" (or "bands") have been explained in terms of the competing corotation, convection and magnetic gradient drifts. Charge exchange losses in slow drift paths for steady state scenarios and the role of substorm injections have also been considered (Li et al., 2000; Ebihara et al., 2004). We analyse observations of electron and ion multi-band structures frequently seen in Double-Star TC1 PEACE and HIA data. We present results from statistical surveys conducted using data from the duration of the mission. Furthermore, using a combination of both statistics and simulations, we test previous theories as to possible formation mechanisms and explore other possible explanations.

  2. Kohn-Sham Band Structure Benchmark Including Spin-Orbit Coupling for 2D and 3D Solids

    NASA Astrophysics Data System (ADS)

    Huhn, William; Blum, Volker

    2015-03-01

    Accurate electronic band structures serve as a primary indicator of the suitability of a material for a given application, e.g., as electronic or catalytic materials. Computed band structures, however, are subject to a host of approximations, some of which are more obvious (e.g., the treatment of the exchange-correlation of self-energy) and others less obvious (e.g., the treatment of core, semicore, or valence electrons, handling of relativistic effects, or the accuracy of the underlying basis set used). We here provide a set of accurate Kohn-Sham band structure benchmarks, using the numeric atom-centered all-electron electronic structure code FHI-aims combined with the ``traditional'' PBE functional and the hybrid HSE functional, to calculate core, valence, and low-lying conduction bands of a set of 2D and 3D materials. Benchmarks are provided with and without effects of spin-orbit coupling, using quasi-degenerate perturbation theory to predict spin-orbit splittings. This work is funded by Fritz-Haber-Institut der Max-Planck-Gesellschaft.

  3. Valence state, hybridization and electronic band structure in the charge ordered AlV2O4.

    PubMed

    Kalavathi, S; Amirthapandian, S; Chandra, Sharat; Sahu, P Ch; Sahu, H K

    2014-01-01

    The valence state, hybridization and electronic band structure of charge ordered AlV2O4 are investigated by measuring the electron energy loss spectra (EELS) and performing band structure calculations using the WIEN2k code. White line ratio and O K edges of V2O5, VO2, V2O3 and AlV2O4, obtained using electron energy loss spectroscopy, are analysed specifically to probe systematically the VO6 octahedra in all of them. The systematic decrease of the L2 intensity and the O K edge intensity from V(5+) in V2O5 to AlV2O4 indicates a progressive increase in the occupancy of the hybridized states, which is corroborated by the absence of a transition from O 1s to hybridized 2t(2g). Band structure calculations on the parent charge frustrated cubic phase and the charge ordered rhombohedral phase clearly document a band gap in the charge ordered state. From the structural information obtained after convergence and the spectroscopic information from EELS, it appears that partial orbital occupancy may lead to a deviation from an integral valence state on all the vanadium in this exotic charge ordered spinel system. PMID:24285259

  4. Dynamical and anharmonic effects on the electron-phonon coupling and the zero-point renormalization of the band structure

    NASA Astrophysics Data System (ADS)

    Antonius, Gabriel; Poncé, Samuel; Lantagne-Hurtubise, Étienne; Auclair, Gabriel; Côté, Michel; Gonze, Xavier

    2015-03-01

    The electron-phonon coupling in solids renormalizes the band structure, reducing the band gap by several tenths of an eV in light-atoms semiconductors. Using the Allen-Heine-Cardona theory (AHC), we compute the zero-point renormalization (ZPR) as well as the quasiparticle lifetimes of the full band structure in diamond, BN, LiF and MgO. We show how dynamical effects can be included in the AHC theory, and still allow for the use of a Sternheimer equation to avoid the summation over unoccupied bands. The convergence properties of the electron-phonon coupling self-energy with respect to the Brillouin zone sampling prove to be strongly affected by dynamical effects. We complement our study with a frozen-phonon approach, which reproduces the static AHC theory, but also allows to probe the phonon wavefunctions at finite displacements and include anharmonic effects in the self-energy. We show that these high-order components tend to reduce the strongest electron-phonon coupling elements, which affects significantly the band gap ZPR.

  5. Balancing positive and negative plant interactions: how mosses structure vascular plant communities.

    PubMed

    Gornall, Jemma L; Woodin, Sarah J; Jónsdóttir, Ingibjorg S; van der Wal, René

    2011-07-01

    Our understanding of positive and negative plant interactions is primarily based on vascular plants, as is the prediction that facilitative effects dominate in harsh environments. It remains unclear whether this understanding is also applicable to moss-vascular plant interactions, which are likely to be influential in low-temperature environments with extensive moss ground cover such as boreal forest and arctic tundra. In a field experiment in high-arctic tundra, we investigated positive and negative impacts of the moss layer on vascular plants. Ramets of the shrub Salix polaris, herb Bistorta vivipara, grass Alopecurus borealis and rush Luzula confusa were transplanted into plots manipulated to contain bare soil, shallow moss (3 cm) and deep moss (6 cm) and harvested after three growing seasons. The moss layer had both positive and negative impacts upon vascular plant growth, the relative extent of which varied among vascular plant species. Deep moss cover reduced soil temperature and nitrogen availability, and this was reflected in reduced graminoid productivity. Shrub and herb biomass were greatest in shallow moss, where soil moisture also appeared to be highest. The relative importance of the mechanisms by which moss may influence vascular plants, through effects on soil temperature, moisture and nitrogen availability, was investigated in a phytotron growth experiment. Soil temperature, and not nutrient availability, determined Alopecurus growth, whereas Salix only responded to increased temperature if soil nitrogen was also increased. We propose a conceptual model showing the relative importance of positive and negative influences of the moss mat on vascular plants along a gradient of moss depth and illustrate species-specific outcomes. Our findings suggest that, through their strong influence on the soil environment, mat-forming mosses structure the composition of vascular plant communities. Thus, for plant interaction theory to be widely applicable to

  6. Structure of the dominant negative S17N mutant of Ras

    PubMed Central

    Nassar, Nicolas; Singh, Kavita; Garcia-Diaz, Miguel

    2010-01-01

    The use of the dominant negative mutant of Ras has been crucial in elucidating the cellular signaling of Ras in response to the activation of various membrane-bound receptors. Although several point mutants of Ras exhibit a dominant negative effect, the asparagine to serine mutation at position 17 (S17N) remains the most popular and the most effective at inhibiting the activation of endogenous Ras. It is now widely accepted that the dominant negative effect is due to the ability of the mutant to sequester upstream activators and its inability to activate downstream effectors. Here, we present the crystal structure of RasS17N in the GDP-bound form. In the three molecules that populate the asymmetric unit, the Mg2+ ion that normally coordinates the β-phosphate is absent because of steric hindrance from the Asn17 side chain. Instead, a Ca2+ ion is coordinating the α-phosphate. Also absent from one molecule is electron density for Phe28, a conserved residue that normally stabilizes the nucleotide’s guanine base. Except for Phe28, the nucleotide makes conserved interactions with Ras. Combined, the inability of Phe28 to stabilize the guanine base and the absence of a Mg2+ ion to neutralize the negative charges on the phosphates explain the weaker affinity of GDP for Ras. Our data suggest that the absence of the Mg2+ should also dramatically affect GTP binding to Ras and the proper positioning of Thr35 necessary for the activation of switch 1 and the binding to downstream effectors, a prerequisite for the triggering of signaling pathways. PMID:20131908

  7. Structural and Functional Characterization of the LPS Transporter LptDE from Gram-Negative Pathogens.

    PubMed

    Botos, Istvan; Majdalani, Nadim; Mayclin, Stephen J; McCarthy, Jennifer Gehret; Lundquist, Karl; Wojtowicz, Damian; Barnard, Travis J; Gumbart, James C; Buchanan, Susan K

    2016-06-01

    Incorporation of lipopolysaccharide (LPS) into the outer membrane of Gram-negative bacteria is essential for viability, and is accomplished by a two-protein complex called LptDE. We solved crystal structures of the core LptDE complexes from Yersinia pestis, Klebsiella pneumoniae, Pseudomonas aeruginosa, and a full-length structure of the K. pneumoniae LptDE complex. Our structures adopt the same plug and 26-strand β-barrel architecture found recently for the Shigella flexneri and Salmonella typhimurium LptDE structures, illustrating a conserved fold across the family. A comparison of the only two full-length structures, SfLptDE and our KpLptDE, reveals a 21° rotation of the LptD N-terminal domain that may impart flexibility on the trans-envelope LptCAD scaffold. Utilizing mutagenesis coupled to an in vivo functional assay and molecular dynamics simulations, we demonstrate the critical role of Pro231 and Pro246 in the function of the LptD lateral gate that allows partitioning of LPS into the outer membrane. PMID:27161977

  8. Structural, electronic, mechanical, and transport properties of phosphorene nanoribbons: Negative differential resistance behavior

    NASA Astrophysics Data System (ADS)

    Maity, Ajanta; Singh, Akansha; Sen, Prasenjit; Kibey, Aniruddha; Kshirsagar, Anjali; Kanhere, Dilip G.

    2016-08-01

    Structural, electronic, mechanical, and transport properties of two different types of phosphorene nanoribbons are calculated within the density functional theory and nonequilibrium Green's function formalisms. Armchair nanoribbons turn out to be semiconductors at all widths considered. Zigzag nanoribbons are metallic in their layer-terminated structure, but undergo Peierls-like transition at the edges. Armchair nanoribbons have smaller Young's modulus compared to a monolayer, while zigzag nanoribbons have larger Young's modulus. Edge reconstruction further increases the Young's modulus of zigzag nanoribbons. A two-terminal device made of zigzag nanoribbons show negative differential resistance behavior that is robust with respect to edge reconstruction. We have also calculated the I -V characteristics for two nonzero gate voltages. The results show that the zigzag nanoribbons display strong p -type character.

  9. Top-Down Strategies for the Structural Elucidation of Intact Gram-negative Bacterial Endotoxins

    PubMed Central

    O’Brien, John P.; Needham, Brittany D.; Brown, Dusty B.; Trent, M. Stephen

    2014-01-01

    Re-modelling of lipopolysaccharides, which are the primary constituent of the outer cell membrane of Gram-negative bacteria, modulates pathogenesis and resistance to microbials. Reported herein is the characterization of intact Gram-negative bacterial lipooligosaccharides (LOS) via a new strategy utilizing online liquid chromatography (LC) coupled with ultraviolet photodissociation (UVPD) mass spectrometry. Compared to collision-based MS/MS methods, UVPD and UVPD/HCD promoted a greater array of cleavages within both the glycan and lipid moieties, including C-C, C-N, C-O cleavages in the acyl chains as well as glycosidic and cross-ring cleavages, thus providing the most far-reaching structural characterization of LOS. This LC-MS/MS strategy affords a robust analytical method to structurally characterize complex mixtures of bacterial endotoxins that maintains the integrity of the core oligosaccharide and lipid A domains of LOS, providing direct feedback about the cell envelope architectures and LOS modification strategies involved in resistance host innate immune defense. PMID:25386333

  10. ERP analysis of cognitive sequencing: a left anterior negativity related to structural transformation processing.

    PubMed

    Hoen, M; Dominey, P F

    2000-09-28

    A major objective of cognitive neuroscience is to identify those neurocomputational processes that may be shared by multiple cognitive functions vs those that are highly specific. This problem of identifying general vs specialized functions is of particular interest in the domain of language processing. Within this domain, event related brain potential (ERP) studies have demonstrated a left anterior negativity (LAN) in a range 300-700 ms, associated with syntactic processing, often linked to grammatical function words. These words have little or no semantic content, but rather play a role in encoding syntactic structure required for parsing. In the current study we test the hypothesis that the LAN reflects the operation of a more general sequence processing capability in which special symbols encode structural information that, when combined with past elements in the sequence, allows the prediction of successor elements. We recorded ERPs during a non-linguistic sequencing task that required subjects (n = 10) to process special symbols possessing the functional property defined above. When compared to ERPs in a control condition, function symbol processing elicits a left anterior negative shift between temporal and spatial characteristics quite similar to the LAN described during function word processing in language, supporting our hypothesis. These results are discussed in the context of related studies of syntactic and cognitive sequence processing.

  11. Structural insight into negative DNA supercoiling by DNA gyrase, a bacterial type 2A DNA topoisomerase

    PubMed Central

    Papillon, Julie; Ménétret, Jean-François; Batisse, Claire; Hélye, Reynald; Schultz, Patrick; Potier, Noëlle; Lamour, Valérie

    2013-01-01

    Type 2A DNA topoisomerases (Topo2A) remodel DNA topology during replication, transcription and chromosome segregation. These multisubunit enzymes catalyze the transport of a double-stranded DNA through a transient break formed in another duplex. The bacterial DNA gyrase, a target for broad-spectrum antibiotics, is the sole Topo2A enzyme able to introduce negative supercoils. We reveal here for the first time the architecture of the full-length Thermus thermophilus DNA gyrase alone and in a cleavage complex with a 155 bp DNA duplex in the presence of the antibiotic ciprofloxacin, using cryo-electron microscopy. The structural organization of the subunits of the full-length DNA gyrase points to a central role of the ATPase domain acting like a ‘crossover trap’ that may help to sequester the DNA positive crossover before strand passage. Our structural data unveil how DNA is asymmetrically wrapped around the gyrase-specific C-terminal β-pinwheel domains and guided to introduce negative supercoils through cooperativity between the ATPase and β-pinwheel domains. The overall conformation of the drug-induced DNA binding–cleavage complex also suggests that ciprofloxacin traps a DNA pre-transport conformation. PMID:23804759

  12. Active pneumatic vibration isolation system using negative stiffness structures for a vehicle seat

    NASA Astrophysics Data System (ADS)

    Danh, Le Thanh; Ahn, Kyoung Kwan

    2014-02-01

    In this paper, an active pneumatic vibration isolation system using negative stiffness structures (NSS) for a vehicle seat in low excitation frequencies is proposed, which is named as an active system with NSS. Here, the negative stiffness structures (NSS) are used to minimize the vibratory attraction of a vehicle seat. Owing to the time-varying and nonlinear behavior of the proposed system, it is not easy to build an accurate dynamic for model-based controller design. Thus, an adaptive intelligent backstepping controller (AIBC) is designed to manage the system operation for high-isolation effectiveness. In addition, an auxiliary control effort is also introduced to eliminate the effect of the unpredictable perturbations. Moreover, a radial basis function neural network (RBFNN) model is utilized to estimate the optimal gain of the auxiliary control effort. Final control input and the adaptive law for updating coefficients of the approximate series can be obtained step by step using a suitable Lyapunov function. Afterward, the isolation performance of the proposed system is assessed experimentally. In addition, the effectiveness of the designed controller for the proposed system is also compared with that of the traditional backstepping controller (BC). The experimental results show that the isolation effectiveness of the proposed system is better than that of the active system without NSS. Furthermore, the undesirable chattering phenomenon in control effort is quite reduced by the estimation mechanism. Finally, some concluding remarks are given at the end of the paper.

  13. Band structure engineering of ZnO1-xSex alloys

    NASA Astrophysics Data System (ADS)

    Mayer, Marie A.; Speaks, Derrick T.; Yu, Kin Man; Mao, Samuel S.; Haller, Eugene E.; Walukiewicz, Wladek

    2010-08-01

    ZnO1-xSex films have been prepared through pulsed laser deposition as a step toward stable films with a band gap appropriate for water splitting. The films show a clear red shift in absorption with increasing Se content and a shift in the flat band voltage toward spontaneity. Due to the films' electron affinities, there exists a natural tunnel junction between these n- ZnO1-xSex films when grown on the p-side of a Si diode. The overall performance, emphasized by flat band potential measurements, can be improved by growing films on Si p-n diodes.

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

    SciTech Connect

    Askari, Nasim; Eslami, Esmaeil; Mirzaie, Reza

    2015-11-15

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

  15. Photonic band gap response of structurally modified non-close-packed inverse opals by template directed multilayer atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Graugnard, Elton; Gaillot, Davy P.; King, Jeffrey S.; Summers, Christopher J.

    2006-04-01

    We report the controllable and tunable fabrication of structurally modified non-close-packed inverse shell opals using multi-layer atomic layer deposition and present a model and simulation algorithm to calculate the structural parameters critical to fabrication. This powerful, flexible and unique technique enables opal inversion, structural modification and backfilling and was applied to the fabrication of TiO II non-close-packed inverse opals. Using successive conformal backfilling it was possible to tune the Bragg peak over 600 nm and enhance the Bragg peak width by >50%. Additionally, band structure calculations, using dielectric functions approximating the true network topology, were used to predict the optical properties during the fabrication process. 3D finite-difference-time-domain results predict experimentally achievable structures with a complete band gap as large as 7.2%. Additionally, the refractive index requirement was predicted to decrease from 3.3 in an 86% infiltrated inverse shell opal to 3.0 in an optimized non-close-packed inverse shell opal. It was also shown for these structures that the complete photonic band gap peak can be statically tuned by over 70% by increasing the backfilled thickness.

  16. Filling-Enforced Gaplessness in Band Structures of the 230 Space Groups.

    PubMed

    Watanabe, Haruki; Po, Hoi Chun; Zaletel, Michael P; Vishwanath, Ashvin

    2016-08-26

    Nonsymmorphic symmetries like screws and glides produce electron band touchings, obstructing the formation of a band insulator and leading, instead, to metals or nodal semimetals even when the number of electrons in the unit cell is an even integer. Here, we calculate the electron fillings compatible with being a band insulator for all 230 space groups, for noninteracting electrons with time-reversal symmetry. Our bounds are tight-that is, we can rigorously eliminate band insulators at any forbidden filling and produce explicit models for all allowed fillings-and stronger than those recently established for interacting systems. These results provide simple criteria that should help guide the search for topological semimetals and, also, have implications for both the nature and stability of the resulting nodal Fermi surfaces. PMID:27610868

  17. Subcortical Band Heterotopia (SBH) in Rat Offspring Following Maternal Hypothyroxinemia: Structural and Functional Characteristics

    EPA Science Inventory

    Thyroid hormones (TH) play crucial roles in brain maturation, neuronal migration, and neocortical lamination. Subcortical band heterotopia (SBH) represent a class of neuronal migration errors in humans that are often associated with childhood epilepsy. We have previously reported...

  18. Effect of spin-orbit interaction on the electronic structure of indium-antimonide d bands

    SciTech Connect

    Sobolev, V. V. Perevoshchikov, D. A.

    2015-05-15

    The bands and densities of states of d bands in indium antimonide (InSb) are determined taking into account and disregarding the spin-orbit interaction. It is established that taking into account the effect of spin-orbit interaction results also in a substantial change in the dispersion of the obtained bands instead of only in the doublet splitting of the band of core d levels at ∼(0.79–0.86) eV. It is established that it is indium 4d states with e{sub g} and t{sub 2g} symmetry that give the main contribution to the density of states. The calculations are carried out by the LAPW method with the exchange-correlation potential in the generalized gradient approximation (LAPW + GGA)

  19. Band structure and optical transitions in LaFeO3: theory and experiment.

    PubMed

    Scafetta, Mark D; Cordi, Adam M; Rondinelli, James M; May, Steven J

    2014-12-17

    The optical absorption properties of LaFeO(3) (LFO) have been calculated using density functional theory and experimentally measured from several high quality epitaxial films using variable angle spectroscopic ellipsometry. We have analyzed the calculated absorption spectrum using different Tauc models and find the model based on a direct-forbidden transition gives the best agreement with the ab initio band gap energies and band dispersions. We have applied this model to the experimental data and determine the band gap of epitaxial LFO to be ∼2.34 eV, with a slight dependence on strain state. This approach has also been used to analyze the higher indirect transition at ∼3.4 eV. Temperature dependent ellipsometry measurements further confirm our theoretical analysis of the nature of the transitions. This works helps to provide a general approach for accurate determination of band gaps and transition energies in complex oxide materials. PMID:25406799

  20. Electronic Band Structure, Optical, Thermal and Bonding Properties of XMg2O4(X = Si, Ge) Spinel Compounds

    NASA Astrophysics Data System (ADS)

    Semari, F.; Ouahrani, T.; Khachai, H.; Khenata, R.; Rabah, M.; Bouhemadou, A.; Murtaza, G.; Amin, B.; Rached, D.

    2013-07-01

    Bonding nature as well as structural, optoelectronic and thermal properties of the cubic XMg2O4(X = Si, Ge) spinel compounds have been calculated using a full-potential augmented plane-wave plus local orbitals (FP-APW+lo) method within the density functional theory. The exchange-correlation potential was treated with the PBE-GGA approximation to calculate the total energy. Moreover, the modified Becke-Johnson potential (TB-mBJ) was also applied to improve the electronic band structure calculations. The computed ground-state parameters (a, B, B‧ and u) are in excellent agreements with the available theoretical data. Calculations of the electronic band structure and bonding properties show that these compounds have a direct energy band gap (Γ-Γ) with a dominated ionic character and the TB-mBJ approximation yields larger fundamental band gaps compared to those obtained using the PBE-GGA. Optical properties such as the complex dielectric function ɛ(ω), reflectivity R(ω) and energy loss function L(ω), for incident photon energy up to 40 eV, have been predicted. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the effects of pressure P and temperature T on the thermal expansion coefficient, Debye temperature and heat capacity for the considered compounds are investigated for the first time.