WorldWideScience

Sample records for conduction band edge

  1. Conduction band edge effective mass of La-doped BaSnO3

    Science.gov (United States)

    James Allen, S.; Raghavan, Santosh; Schumann, Timo; Law, Ka-Ming; Stemmer, Susanne

    2016-06-01

    BaSnO3 has attracted attention as a promising material for applications requiring wide band gap, high electron mobility semiconductors, and moreover possesses the same perovskite crystal structure as many functional oxides. A key parameter for these applications and for the interpretation of its properties is the conduction band effective mass. We measure the plasma frequency of La-doped BaSnO3 thin films by glancing incidence, parallel-polarized resonant reflectivity. Using the known optical dielectric constant and measured electron density, the resonant frequency determines the band edge electron mass to be 0.19 ± 0.01. The results allow for testing band structure calculations and transport models.

  2. Disorder-free localization around the conduction band edge of crossing and kinked silicon nanowires

    Science.gov (United States)

    Keleş, Ümit; ćakan, Aslı; Bulutay, Ceyhun

    2015-02-01

    We explore ballistic regime quantum transport characteristics of oxide-embedded crossing and kinked silicon nanowires (NWs) within a large-scale empirical pseudopotential electronic structure framework, coupled to the Kubo-Greenwood transport analysis. A real-space wave function study is undertaken and the outcomes are interpreted together with the findings of ballistic transport calculations. This reveals that ballistic transport edge lies tens to hundreds of millielectron volts above the lowest unoccupied molecular orbital, with a substantial number of localized states appearing in between, as well as above the former. We show that these localized states are not due to the oxide interface, but rather core silicon-derived. They manifest the wave nature of electrons brought to foreground by the reflections originating from NW junctions and bends. Hence, we show that the crossings and kinks of even ultraclean Si NWs possess a conduction band tail without a recourse to atomistic disorder.

  3. Disorder-free localization around the conduction band edge of crossing and kinked silicon nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Keleş, Ümit; Çakan, Aslı; Bulutay, Ceyhun, E-mail: bulutay@fen.bilkent.edu.tr [Department of Physics, Bilkent University, Bilkent, Ankara 06800 (Turkey)

    2015-02-14

    We explore ballistic regime quantum transport characteristics of oxide-embedded crossing and kinked silicon nanowires (NWs) within a large-scale empirical pseudopotential electronic structure framework, coupled to the Kubo-Greenwood transport analysis. A real-space wave function study is undertaken and the outcomes are interpreted together with the findings of ballistic transport calculations. This reveals that ballistic transport edge lies tens to hundreds of millielectron volts above the lowest unoccupied molecular orbital, with a substantial number of localized states appearing in between, as well as above the former. We show that these localized states are not due to the oxide interface, but rather core silicon-derived. They manifest the wave nature of electrons brought to foreground by the reflections originating from NW junctions and bends. Hence, we show that the crossings and kinks of even ultraclean Si NWs possess a conduction band tail without a recourse to atomistic disorder.

  4. Edge ferromagnetism from Majorana flat bands: application to split tunneling-conductance peaks in high-Tc cuprate superconductors.

    Science.gov (United States)

    Potter, Andrew C; Lee, Patrick A

    2014-03-21

    In mean-field descriptions of nodal d-wave superconductors, generic edges exhibit dispersionless Majorana fermion bands at zero energy. These states give rise to an extensive ground-state degeneracy, and are protected by time-reversal symmetry. We argue that the infinite density of states of these flat bands make them inherently unstable to interactions, and show that repulsive interactions lead to edge ferromagnetism which splits the flat bands. This edge ferromagnetism offers an explanation for the observation of the splitting of zero-bias peaks in edge tunneling in high-Tc cuprate superconductors. We argue that this mechanism for splitting is more likely than previously proposed scenarios and describe its experimental consequences.

  5. Valence and conduction band edges of selenide and sulfide-based kesterites—a study by x-ray based spectroscopy and ab initio theory

    Science.gov (United States)

    Olar, Tetiana; Manoharan, Archana; Draxl, Claudia; Calvet, Wolfram; Ümsur, Bünyamin; Parvan, Vladimir; Chacko, Binoy; Xie, Haibing; Saucedo, Edgardo; Valle-Rios, Laura Elisa; Neldner, Kai; Schorr, Susan; Lux-Steiner, Martha Ch; Lauermann, Iver

    2017-10-01

    Thin film solar cells based on the kesterite material with the general composition Cu2ZnSn(Se,S)4 can be a substitute for the more common chalcopyrites (Cu(In,Ga)(Se,S)2) with a similar band gap range. When replacing the anion sulfide with selenide, the optical band gap of kesterite changes from 1.5 to 1 eV. Here we report on a study of the valence band maximum and conduction band minimum energies of kesterites with either S or Se as the anion. Knowing these positions is crucial for the design of solar cells in order to match the bands of the absorber material with those of the subsequent functional layers like buffer or window layer. Their relative positions were studied using photoelectron spectroscopy of the valence band edge and x-ray absorption spectroscopy of the cations Cu, Zn, and Sn, respectively. The experimental results are interpreted and confirmed in terms of calculations based on density-functional theory and the GW approach of the many-body theory.

  6. Edge conduction in vacuum glazing

    Energy Technology Data Exchange (ETDEWEB)

    Simko, T.M.; Collins, R.E. [Sydney Univ., NSW (Australia). Dept. of Applied Physics; Beck, F.A.; Arasteh, D. [Lawrence Berkeley Lab., CA (United States)

    1995-03-01

    Vacuum glazing is a form of low-conductance double glazing using in internal vacuum between the two glass sheets to eliminate heat transport by gas conduction and convection. An array of small support pillars separates the sheets; fused solder glass forms the edge seal. Heat transfer through the glazing occurs by radiation across the vacuum gap, conduction through the support pillars, and conduction through the bonded edge seal. Edge conduction is problematic because it affects stresses in the edge region, leading to possible failure of the glazing; in addition, excessive heat transfer because of thermal bridging in the edge region can lower overall window thermal performance and decrease resistance to condensation. Infrared thermography was used to analyze the thermal performance of prototype vacuum glazings, and, for comparison, atmospheric pressure superwindows. Research focused on mitigating the edge effects of vacuum glazings through the use of insulating trim, recessed edges, and framing materials. Experimentally validated finite-element and finite-difference modeling tools were used for thermal analysis of prototype vacuum glazing units and complete windows. Experimental measurements of edge conduction using infrared imaging were found to be in good agreement with finite-element modeling results for a given set of conditions. Finite-element modeling validates an analytic model developed for edge conduction.

  7. Edge conduction in monolayer WTe2

    Science.gov (United States)

    Fei, Zaiyao; Palomaki, Tauno; Wu, Sanfeng; Zhao, Wenjin; Cai, Xinghan; Sun, Bosong; Nguyen, Paul; Finney, Joseph; Xu, Xiaodong; Cobden, David H.

    2017-07-01

    A two-dimensional topological insulator (2DTI) is guaranteed to have a helical one-dimensional edge mode in which spin is locked to momentum, producing the quantum spin Hall effect and prohibiting elastic backscattering at zero magnetic field. No monolayer material has yet been shown to be a 2DTI, but recently the Weyl semimetal WTe2 was predicted to become a 2DTI in monolayer form if a bulk gap opens. Here, we report that, at temperatures below about 100 K, monolayer WTe2 does become insulating in its interior, while the edges still conduct. The edge conduction is strongly suppressed by an in-plane magnetic field and is independent of gate voltage, save for mesoscopic fluctuations that grow on cooling due to a zero-bias anomaly, which reduces the linear-response conductance. Bilayer WTe2 also becomes insulating at low temperatures but does not show edge conduction. Many of these observations are consistent with monolayer WTe2 being a 2DTI. However, the low-temperature edge conductance, for contacts spacings down to 150 nm, never reaches values higher than ~20 μS, about half the predicted value of e2/h, suggesting significant elastic scattering in the edge.

  8. New Kronig-Penney Equation Emphasizing the Band Edge Conditions

    Science.gov (United States)

    Szmulowicz, Frank

    2008-01-01

    The Kronig-Penney problem is a textbook example for discussing band dispersions and band gap formation in periodic layered media. For example, in photonic crystals, the behaviour of bands next to the band edges is important for further discussions of such effects as inhibited light emission, slow light and negative index of refraction. However,…

  9. Strain modulated band gap of edge passivated armchair graphene nanoribbons

    CERN Document Server

    Peng, Xihong

    2011-01-01

    First principles calculations were performed to study strain effects on band gap of armchair graphene nanoribbons (AGNRs)with different edge passivation, including H, O, and OH group. The band gap of the H-passivated AGNRs shows a nearly periodic zigzag variation under strain. For O and OH passivation, the zigzag patterns are significantly shifted by a modified quantum confinement due to the edges. In addition, the band gap of the O-passivated AGNRs experiences a direct-to-indirect transition with sufficient tensile strain (~5%). The indirect gap reduces to zero with further increased strain.

  10. Linear scaling calculation of band edge states and doped semiconductors.

    Science.gov (United States)

    Xiang, H J; Yang, Jinlong; Hou, J G; Zhu, Qingshi

    2007-06-28

    Linear scaling methods provide total energy, but no energy levels and canonical wave functions. From the density matrix computed through the density matrix purification methods, we propose an order-N [O(N)] method for calculating both the energies and wave functions of band edge states, which are important for optical properties and chemical reactions. In addition, we also develop an O(N) algorithm to deal with doped semiconductors based on the O(N) method for band edge states calculation. We illustrate the O(N) behavior of the new method by applying it to boron nitride (BN) nanotubes and BN nanotubes with an adsorbed hydrogen atom. The band gap of various BN nanotubes are investigated systematically and the acceptor levels of BN nanotubes with an isolated adsorbed H atom are computed. Our methods are simple, robust, and especially suited for the application in self-consistent field electronic structure theory.

  11. Theory of Double Ladder Lumped Circuits With Degenerate Band Edge

    CERN Document Server

    Sloan, Jeff; Capolino, Filippo

    2016-01-01

    Conventional periodic LC ladder circuits exhibit a regular band edge between a pass and a stop band. Here for the first time we develop the theory of simple yet unconventional double ladder circuits exhibiting a special degeneracy condition referred to as degenerate band edge (DBE). This special DBE condition is associated with four independent eigenstates of the double ladder that coalesce into a single one when the operative frequency coincides with the DBE one. In particular, we show that double ladder resonators may exhibit giant loaded quality factor near the DBE and stable resonance frequency against load variations. These two properties in the proposed circuit are superior to the analogous properties in single ladder circuits. Our proposed analysis leads to analytic expressions for all circuit quantities thus providing insight into the very complex behavior near points of degeneracy in periodic circuits; and provides a design procedure for the use of such double ladder in practical applications. Intere...

  12. Effect of the edge states on the conductance and thermopower in zigzag phosphorene nanoribbons

    Science.gov (United States)

    Ma, R.; Geng, H.; Deng, W. Y.; Chen, M. N.; Sheng, L.; Xing, D. Y.

    2016-09-01

    We study numerically the effect of the edge states on the conductance and thermopower in zigzag phosphorene nanoribbons (ZPNRs) based on the tight-binding model and the scattering-matrix method. It is interesting to find that the band dispersion, conductance, and thermopower can be modulated by applying a bias voltage and boundary potentials to the two layers of the ZPNRs. Under a certain bias voltage, the twofold-degenerate quasi-flat-edge bands split perfectly. The conductance can be switched off, and the thermopower around zero energy increases. In addition, when only the boundary potential of the top layer or bottom layer is adjusted, only one edge band bends and merges into the bulk band. The first conductance plateau is strongly decreased to e2/h around zero energy. In particular, when the two boundary potentials are adjusted, all the edge bands bend and fully merge into the bulk band, and the bulk energy gap is maximized. More interestingly, a pronounced conductance plateau with G =0 is found around zero energy, which is attributable to the opening of the bulk energy gap between the valence and conduction bands. Meanwhile, the thermopower can be enhanced more than twice compared to that of the perfect ZPNRs. The large magnitude of thermopower is ascribed to the appearance of the bulk energy gap around zero energy. Our results show that the modulated ZPNRs are more reliable in a thermoelectric application.

  13. Wild Band Edges: The Role of Bandgap Grading and Band-Edge Fluctuations in High-Efficiency Chalcogenide Devices: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Repins, Ingrid; Mansfield, Lorelle; Kanevce, Ana; Jensen, Soren A.; Kuciauskas, Darius; Glynn, Stephen; Barnes, Teresa; Metzger, Wyatt; Burst, James; Jiang, Chun-Sheng; Dippo, Patricia; Harvey, Steve; Teeter, Glenn; Perkins, Craig; Egaas, Brian; Zakutayev, Andriy; Alsmeier, J.-H.; Lussky, T.; Korte, L.; Wilks, R. G.; Bar, M.; Yan, Y.; Lany, Stephan; Zawadzki, Pawel; Park, Ji-Sang; Wei, Suhuai

    2016-06-16

    Band-edge effects -- including grading, electrostatic fluctuations, bandgap fluctuations, and band tails -- affect chalcogenide device efficiency. These effects now require more careful consideration as efficiencies increase beyond 20%. Several aspects of the relationships between band-edge phenomena and device performance for NREL absorbers are examined. For Cu(In,Ga)Se2 devices, recent increases in diffusion length imply changes to optimum bandgap profile. The origin, impact, and modification of electrostatic and bandgap fluctuations are also discussed. The application of the same principles to devices based on CdTe, kesterites, and emerging absorbers (Cu2SnS3, CuSbS2), considering differences in materials properties and defect formation energies, is examined.

  14. Wild Band Edges: The Role of Bandgap Grading and Band-Edge Fluctuations in High-Efficiency Chalcogenide Devices

    Energy Technology Data Exchange (ETDEWEB)

    Repins, Ingrid; Mansfield, Lorelle; Kanevce, Ana; Jensen, Soren A.; Kuciauskas, Darius; Glynn, Stephen; Barnes, Teresa; Metzger, Wyatt; Burst, James; Jiang, Chun-Sheng; Dippo, Patricia; Harvey, Steve; Teeter, Glenn; Perkins, Craig; Egaas, Brian; Zakutayev, Andriy; Alsmeier, J.-H.; Lussky, T.; Korte, L.; Wilks, R. G.; Bar, M.; Yan, Y.; Lany, Stephan; Zawadzki, Pawel; Park, Ji-Sang; Wei, Suhuai

    2016-11-21

    Band-edge effects - including grading, electrostatic fluctuations, bandgap fluctuations, and band tails - affect chalcogenide device efficiency. These effects now require more careful consideration as efficiencies increase beyond 20%. Several aspects of the relationships between band-edge phenomena and device performance for NREL absorbers are examined. For Cu(In, Ga)Se2 devices, recent increases in diffusion length imply changes to the optimum bandgap profile. The origin, impact, and modification of electrostatic and bandgap fluctuations are also discussed. The application of the same principles to devices based on CdTe, kesterites, and emerging absorbers (Cu2SnS3, CuSbS2), considering differences in materials properties, is examined.

  15. Characterization of the valence and conduction bands in Si nanocrystals

    Science.gov (United States)

    van Buuren, T.; Terminello, L.; Chase, L.; Callcott, T.; Grush, M.

    1998-03-01

    Silicon nanocrystals with a mean diameter between 1 and 4 nm were produced by thermal evaporation of Si in Ar buffer gas and deposited on a substrate. The size-distribution and diameter of the clusters were characterized by atomic force microscopy. The valence and conduction band edges of the Si nanocrystals were measured in-situ using soft x-ray emission (SXE) and absorption (XAS) spectroscopies. The valence band of the smallest Si nanocrystals is shifted by much as 0.7 eV relative to bulk Si. Significant changes in the shape of the spectra are also observed between the Si nanocrytals and bulk Si. We interpret the shift and changes in the spectra of the valence band as resulting from an altered electronic band structure in the confined Si structures. A smaller but proportional shift of the conduction band to higher energy is also observed in the XAS spectra of the silicon nanostructures. We compare the experimentally measured bandgap to recent electronic structure calculations and find, that the experimentally measured bandgap is smaller than that predicted by theory. Work supported by the U.S. Department of Energy, BES-Materials Sciences, under Contract W-7405-ENG-48.

  16. Optofluidic tuning of photonic crystal band edge lasers

    DEFF Research Database (Denmark)

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

    2007-01-01

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

  17. Degenerate-band-edge engineering inspired by nonlocal transformation optics

    Directory of Open Access Journals (Sweden)

    Moccia Massimo

    2016-01-01

    Full Text Available We address the engineering of degenerate-band-edge effects in nonlocal metamaterials. Our approach, inspired by nonlocal-transformation-optics concepts, is based on the approximation of analytically-derived nonlocal constitutive “blueprints”. We illustrate the synthesis procedure, and present and validate a possible implementation based on multilayered metamaterials featuring anisotropic constituents. We also elucidate the physical mechanisms underlying our approach and proposed configuration, and highlight the substantial differences with respect to other examples available in the topical literature.

  18. Degenerate-band-edge engineering inspired by nonlocal transformation optics

    Directory of Open Access Journals (Sweden)

    Moccia Massimo

    2016-01-01

    Full Text Available We address the engineering of degenerate-band-edge effects in nonlocal metamaterials. Our approach, inspired by nonlocal-transformation-optics concepts, is based on the approximation of analytically-derived nonlocal constitutive “blueprints”. We illustrate the synthesis procedure, and present and validate a possible implementation based on multilayered metamaterials featuring anisotropic constituents. We also elucidate the physical mechanisms underlying our approach and proposed configuration, and highlight the substantial differences with respect to other examples available in the topical literature.

  19. Calculation of band edge levels of strained Si/(111)Si{sup 1-x}Ge{sup x}

    Energy Technology Data Exchange (ETDEWEB)

    Song Jianjun; Zhang Heming; Hu Huiyong; Dai Xianying; Xuan Rongxi, E-mail: wmshhsong@tom.co [Key Laboratory of Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi' an 710071 (China)

    2010-01-15

    Calculations were performed on the band edge levels of (111)-biaxially strained Si on relaxed Si{sup 1-x}Ge{sup x} alloy using the k {center_dot} p perturbation method coupled with deformation potential theory. The results show that the conduction band (CB) edge is characterized by six identical valleys, that the valence band (VB) edge degeneracies are partially lifted, and that both the CB and VB edge levels move up in electron energy as the Ge fraction (x) increases. In addition, the dependence of the indirect bandgap and the VB edge splitting energy on x was obtained. Quantitative data from the results supply valuable references for Si-based strained device design. (semiconductor physics)

  20. Dirac Cones, Topological Edge States, and Nontrivial Flat Bands in Two-Dimensional Semiconductors with a Honeycomb Nanogeometry

    Directory of Open Access Journals (Sweden)

    E. Kalesaki

    2014-01-01

    Full Text Available We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattice and the overall geometry influence the band structure, revealing materials with unusual electronic properties. In rocksalt Pb chalcogenides, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende Cd-chalcogenide semiconductors, the honeycomb nanogeometry leads to rich band structures, including, in the conduction band, Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has S-orbital character and is equivalent to the π-π^{⋆} band of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their P-orbital character. We show that the width of the Dirac bands varies between tens and hundreds of meV. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. Recent advancements in colloidal chemistry indicate that these materials can be synthesized from semiconductor nanocrystals.

  1. Low Starting Electron Beam Current in Degenerate Band Edge Oscillators

    CERN Document Server

    Othman, Mohamed A K; Figotin, Alexander; Capolino, Filippo

    2016-01-01

    We propose a new principle of operation in vacuum electron-beam-based oscillators that leads to a low beam current for starting oscillations. The principle is based on super synchronous operation of an electron beam interacting with four degenerate electromagnetic modes in a slow-wave structure (SWS). The four mode super synchronous regime is associated with a very special degeneracy condition in the dispersion diagram of a cold periodic SWS called degenerate band edge (DBE). This regime features a giant group delay in the finitelength SWS and low starting-oscillation beam current. The starting beam current is at least an order of magnitude smaller compared to a conventional backward wave oscillator (BWO) of the same length. As a representative example we consider a SWS conceived by a periodically-loaded metallic waveguide supporting a DBE, and investigate starting-oscillation conditions using Pierce theory generalized to coupled transmission lines (CTL). The proposed super synchronism regime can be straightf...

  2. Black Phosphorus Transistors with Near Band Edge Contact Schottky Barrier

    Science.gov (United States)

    Ling, Zhi-Peng; Sakar, Soumya; Mathew, Sinu; Zhu, Jun-Tao; Gopinadhan, K.; Venkatesan, T.; Ang, Kah-Wee

    2015-12-01

    Black phosphorus (BP) is a new class of 2D material which holds promise for next generation transistor applications owing to its intrinsically superior carrier mobility properties. Among other issues, achieving good ohmic contacts with low source-drain parasitic resistance in BP field-effect transistors (FET) remains a challenge. For the first time, we report a new contact technology that employs the use of high work function nickel (Ni) and thermal anneal to produce a metal alloy that effectively reduces the contact Schottky barrier height (ΦB) in a BP FET. When annealed at 300 °C, the Ni electrode was found to react with the underlying BP crystal and resulted in the formation of nickel-phosphide (Ni2P) alloy. This serves to de-pin the metal Fermi level close to the valence band edge and realizes a record low hole ΦB of merely ~12 meV. The ΦB at the valence band has also been shown to be thickness-dependent, wherein increasing BP multi-layers results in a smaller ΦB due to bandgap energy shrinkage. The integration of hafnium-dioxide high-k gate dielectric additionally enables a significantly improved subthreshold swing (SS ~ 200 mV/dec), surpassing previously reported BP FETs with conventional SiO2 gate dielectric (SS > 1 V/dec).

  3. Band edge discontinuities and carrier transport in c-Si/porous silicon heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Islam, Md Nazrul [QAED-SRG, Space Applications Centre (ISRO), Ahmedabad - 380015 (India); Ram, Sanjay K [Department of Physics, Indian Institute of Technology, Kanpur - 208016 (India); Kumar, Satyendra [Department of Physics, Indian Institute of Technology, Kanpur - 208016 (India)

    2007-10-07

    We have prepared light emitting nanocrystallline porous silicon (PS) layers by electrochemical anodization of crystalline silicon (c-Si) wafer and characterized the c-Si/PS heterojunctions using temperature dependence of dark current-voltage (I-V) characteristics. The reverse bias I-V characteristics of c-Si/PS heterojunctions are found to behave like the Schottky junctions where carrier transport is mainly governed by the carrier generation-recombination in the depletion region formed on the PS side. Fermi level of c-Si gets pinned to the defect levels at the interface resulting in ln(I) {approx} V{sup 1/2}. The barrier height in the reverse bias condition is shown to be equal to the band offset at the conduction band edges. An energy band diagram for the c-Si/PS heterojunction is proposed.

  4. Theoretical Determination of Band Edge Alignments at the Water-CuInS2(112) Semiconductor Interface.

    Science.gov (United States)

    Senftle, Thomas P; Carter, Emily A

    2017-06-06

    Knowledge of a semiconductor electrode's band edge alignment is essential for optimizing processes that occur at the semiconductor/electrolyte interface. Photocatalytic processes are particularly sensitive to such alignments, as they govern the transfer of photoexcited electrons or holes from the surface to reactants in the electrolyte solution. Reconstructions of a semiconductor surface during operation, as well as its interaction with the electrolyte solution, must be considered when determining band edge alignment. Here, we employ density functional theory + U theory to assess the stability of reconstructed CuInS2 surfaces, a system which has shown promise for the active and selective photoelectrocatalytic reduction of CO2 to CH3OH. Using many-body Green's function theory combined with calculations of surface work functions, we determine band edge positions of explicitly solvated, reconstructed CuInS2 surfaces. We find that there is a linear relationship between band edge position and net surface dipole, with the most stable solvent/surface structures tending to minimize this dipole because of generally weak interactions between the surface and solvating water molecules. We predict a conduction band minimum (CBM) of the solvated, reconstructed CuInS2 surface of -2.44 eV vs vacuum at the zero-dipole intercept of the dipole/CBM trendline, in reasonable agreement with the experimentally reported CBM position at -2.64 eV vs vacuum. This methodology offers a simplified approach for approximating the band edge positions at complex semiconductor/electrolyte interfaces.

  5. Inter-band effects of magnetic field on orbital susceptibility and Hall conductivity - case of bismuth

    Energy Technology Data Exchange (ETDEWEB)

    Fukuyama, H. [Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577 (Japan)

    2006-07-03

    Interband effects of magnetic field on orbital susceptibility and Hall conductivity have been theoretically studied with special reference to single crystal bismuth (Bi), whose energy bands near the band-edges are similar to those of Dirac electrons. It has long been known that orbital susceptibilty in Bi has a maximum when the Fermi energy is located in the band-gap and then the density of states at the Fermi energy is vanishing. This implies that the magnetic field induces persistent current even in the insulating state. On the other hand, weak-field Hall conductivity, which reflects transport current, has turned out to be vanishing if the Fermi energy is in the band-gap. Interesting possibility has been pointed out of the inter-band contributions to the Hall conductivity once the Fermi energy lies slightly in the energy band. (Abstract Copyright [2006], Wiley Periodicals, Inc.)

  6. Graphene Nanoribbon Conductance Model in Parabolic Band Structure

    Directory of Open Access Journals (Sweden)

    Mohammad Taghi Ahmadi

    2010-01-01

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

  7. Conduction Band of the Photographic Compound AgCl

    NARCIS (Netherlands)

    Boer, P.K. de; Groot, R.A. de

    1999-01-01

    Electronic structure calculations on the photographic compound AgCl are reported. It is shown that the conduction band has a large Cl-4s character, contrary to the common picture of the conduction band being derived from Ag-5s states. Possible consequences for the photographic process are discussed.

  8. Conduction Band of the Photographic Compound AgCl

    NARCIS (Netherlands)

    Boer, P.K. de; Groot, R.A. de

    1999-01-01

    Electronic structure calculations on the photographic compound AgCl are reported. It is shown that the conduction band has a large Cl-4s character, contrary to the common picture of the conduction band being derived from Ag-5s states. Possible consequences for the photographic process are discussed.

  9. Topologically trivial and nontrivial edge bands in graphene induced by irradiation

    Science.gov (United States)

    Yang, Mou; Cai, Zhi-Jun; Wang, Rui-Qiang; Bai, Yan-Kui

    2016-08-01

    We proposed a minimal model to describe the Floquet band structure of two-dimensional materials with light-induced resonant inter-band transition. We applied it to graphene to study the band features caused by the light irradiation. Linearly polarized light induces pseudo gaps (gaps are functions of wavevector), and circularly polarized light causes real gaps on the quasi-energy spectrum. If the polarization of light is linear and along the longitudinal direction of zigzag ribbons, flat edge bands appear in the pseudo gaps, and if it is in the lateral direction of armchair ribbons, curved edge bands can be found. For the circularly polarized cases, edge bands arise and intersect in the gaps of both types of ribbons. The edge bands induced by the circularly polarized light are helical and those by linearly polarized light are topologically trivial ones. The Chern number of the Floquet band, which reflects the number of pairs of helical edge bands in graphene ribbons, can be reduced into the winding number at resonance.

  10. Performance changes of a grated waveguide at resonance wavelengths next to its band-edges due to modified edge sections

    NARCIS (Netherlands)

    Alatas, H.; Iskandar, Alexander A.; Hoekstra, Hugo; Tjia, May-On

    2010-01-01

    An efficient numerical scheme developed on the basis of Green’s function method is applied to the investigation of structural effects on the performance of planar grated waveguide at the first resonance wavelengths next to the band-edges. Restricting ourselves to the transverse-electric waves, this

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

    Science.gov (United States)

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

    2014-10-01

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

  12. Conductance matrix of multiterminal semiconductor devices with edge channels

    Energy Technology Data Exchange (ETDEWEB)

    Danilovskii, E. Yu., E-mail: danilovskii@mail.ioffe.ru; Bagraev, N. T. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)

    2014-12-15

    A method for determining the conductance matrix of multiterminal semiconductor structures with edge channels is proposed. The method is based on the solution of a system of linear algebraic equations based on Kirchhoff equations, made up of potential differences U{sub ij} measured at stabilized currents I{sub kl}, where i, j, k, l are terminal numbers. The matrix obtained by solving the system of equations completely describes the structure under study, reflecting its configuration and homogeneity. This method can find wide application when using the known Landauer-Buttiker formalism to analyze carrier transport in the quantum Hall effect and quantum spin Hall effect modes. Within the proposed method, the contribution of the contact area resistances R{sub c} to the formation of conductance matrix elements is taken into account. The possibilities of practical application of the results obtained in developing analog cryptographic devices are considered.

  13. Lasing at the band edges of plasmonic lattices

    CERN Document Server

    Schokker, A Hinke

    2014-01-01

    We report room temperature lasing in two-dimensional diffractive lattices of silver and gold plasmon particle arrays embedded in a dye-doped polymer that acts both as waveguide and gain medium. As compared to conventional dielectric distributed feedback lasers, a central question is how the underlying band structure from which lasing emerges is modified by both the much stronger scattering and the disadvantageous loss of metal. We use spectrally resolved back-focal plane imaging to measure the wavelength- and angle dependence of emission below and above threshold, thereby mapping the band structure. We find that for silver particles, the band structure is strongly modified compared to dielectric reference DFB lasers, since the strong scattering gives large stop gaps. In contrast, gold particles scatter weakly and absorb strongly, so that thresholds are higher, but the band structure is not strongly modified. The experimental findings are supported by finite element and fourier modal method calculations of the...

  14. Conduction bands and invariant energy gaps in alkali bromides

    NARCIS (Netherlands)

    Boer, P.K. de; Groot, R.A. de

    1998-01-01

    Electronic structure calculations of the alkali bromides LiBr, NaBr, KBr, RbBr and CsBr are reported. It is shown that the conduction band has primarily bromine character. The size of the band gaps of bromides and alkali halides in general is reinterpreted.

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

    Science.gov (United States)

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

    2013-08-26

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

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

    Science.gov (United States)

    Honda, Masahiro; Yamamoto, Naoki

    2014-02-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-02-24

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

  18. Boundary conditions at closed edge of bilayer graphene and energy bands of collapsed nanotubes

    Science.gov (United States)

    Nakanishi, Takeshi; Ando, Tsuneya

    2016-10-01

    Band structure is systematically studied in an effective-mass scheme in collapsed armchair and zigzag nanotubes based on the model in which collapsed tubes are regarded as bilayer ribbons with closed edges. Boundary conditions at closed edges, describing the connection of the envelope wave functions between the bottom and top layers, are derived. Among electronic states in bilayers, which change sensitively depending on the relative displacement of two layers, those having wave functions matching well with the obtained boundary conditions, i.e., unaffected by the presence of closed edges, constitute important states near the Fermi level in collapsed nanotubes.

  19. Plasmonic band edge effects on the transmission properties of metal gratings

    Directory of Open Access Journals (Sweden)

    D. de Ceglia

    2011-09-01

    Full Text Available We present a detailed analysis of the optical properties of one-dimensional arrays of slits in metal films. Although enhanced transmission windows are dominated by Fabry-Perot cavity modes localized inside the slits, the periodicity introduces surface modes that can either enhance or inhibit light transmission. We thus illustrate the interaction between cavity modes and surface modes in both finite and infinite arrays of slits. In particular we study a grating that clearly separates surface plasmon effects from Wood-Rayleigh anomalies. The periodicity of the grating induces a strong plasmonic band gap that inhibits coupling to the cavity modes for frequencies near the center of the band gap, thereby reducing the transmission of the grating. Strong field localization at the high energy plasmonic band edge enhances coupling to the cavity modes while field localization at the low energy band edge leads to weak cavity coupling and reduced transmission.

  20. Calibration of the EDGES High-band Receiver to Observe the Global 21 cm Signature from the Epoch of Reionization

    Science.gov (United States)

    Monsalve, Raul A.; Rogers, Alan E. E.; Bowman, Judd D.; Mozdzen, Thomas J.

    2017-01-01

    The EDGES High-Band experiment aims to detect the sky-average brightness temperature of the 21 cm signal from the epoch of reionization in the redshift range 14.8≳ z≳ 6.5. To probe this redshifted signal, EDGES High-Band conducts single-antenna measurements in the frequency range 90–190 MHz from the Murchison Radio-astronomy Observatory in Western Australia. In this paper, we describe the current strategy for calibration of the EDGES High-Band receiver and report calibration results for the instrument used in the 2015–2016 observational campaign. We propagate uncertainties in the receiver calibration measurements to the antenna temperature using a Monte Carlo approach. We define a performance objective of 1 mK residual rms after modeling foreground subtraction from a fiducial temperature spectrum using a five-term polynomial. Most of the calibration uncertainties yield residuals of 1 mK or less at 95 % confidence. However, current uncertainties in the antenna and receiver reflection coefficients can lead to residuals of up to 20 mK even in low-foreground sky regions. These dominant residuals could be reduced by (1) improving the accuracy in reflection measurements, especially their phase, (2) improving the impedance match at the antenna-receiver interface, and (3) decreasing the changes with frequency of the antenna reflection phase.

  1. OPTICAL BAND GAP AND CONDUCTIVITY MEASUREMENTS OF POLYPYRROLE-CHITOSAN COMPOSITE THIN FILMS

    Institute of Scientific and Technical Information of China (English)

    Mahnaz M.Abdi; H.N.M.Ekramul Mahmud; Luqman Chuah Abdullah; Anuar Kassim; Mohamad Zaki Ab.Rahman; Josephine Liew Ying Chyi

    2012-01-01

    Electrical conductivity and optical properties of polypyrrole-chitosan (PPy-CHI) conducting polymer composites have been investigated to determine the optical transition characteristics and energy band gap of composite films.The two electrode method and Ⅰ-Ⅴ characteristic technique were used to measure the conductivity of the PPy-CHI thin films,and the optical band gap was obtained from their ultraviolet absorption edges.Depending upon experimental parameter,the optical band gap (Eg) was found within 1.30-2.32 eV as estimated from optical absorption data.The band gap of the composite films decreased as the CHI content increased.The room temperature electrical conductivity of PPy-CHI thin films was found in the range of 5.84 × 10-7-15.25 × 10-7 S.cm-1 depending on the chitosan content.The thermogravimetry analysis (TGA)showed that the CHI can improve the thermal stability of PPy-CHI composite films.

  2. Ultra-Efficient Thermophotovoltaics Exploiting Spectral Filtering by the Photovoltaic Band-Edge

    CERN Document Server

    Ganapati, Vidya; Yablonovitch, Eli

    2016-01-01

    Thermophotovotaics convert thermal radiation from local heat sources to electricity. A new breakthrough in creating highly efficient thin-film solar cells can potentially enable thermophotovoltaic systems with unprecedented high efficiency. The current 28.8% single-junction solar efficiency record, by Alta Devices, was achieved by recognizing that a good solar cell needs to reflect infrared band-edge radiation at the back surface, to effectively recycle infrared luminescent photons. The effort to reflect band-edge luminescence in solar cells has serendipitously created the technology to reflect all infrared wavelengths, which can revolutionize thermophotovoltaics. We have never before had such high back reflectivity for sub-bandgap radiation, permitting step-function spectral control for the first time. Thus, contemporary efficiency advances in solar photovoltaic cells create the possibility of realizing a $>50\\%$ efficient thermophotovoltaic system.

  3. Experimental verification of directional liquid surface wave emission at band edge frequencies

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhenyu, E-mail: wzyu@zju.edu.cn; Zhang, Pei; Zhang, Yongqiang; Nie, Xiaofei

    2013-12-15

    Directional liquid surface wave emission at band edge frequencies is an interesting physical phenomenon and has already been studied in theoretical research. There has been no experimental validation of it to date, however. This paper has as its subject the experimental investigation of the emission effect when a point source is placed inside a finite square array of rigid cylinders standing vertically in liquid. Both the wave patterns and spatial intensities are obtained by experiment and compared with simulated results calculated by using the finite element method. We can see from this comparison that the two results correspond closely both at lower and upper band edge frequency. Obvious directional wave emission along a desired direction is observed in the source structures, confirming previous theoretical predictions. In the future, this method could serve as a directional liquid wave source in applications used in hydraulic and ocean engineering for the concentration of wave energy.

  4. Tangent Bifurcation of Band Edge Plane Waves, Dynamical Symmetry Breaking and Vibrational Localization

    CERN Document Server

    Flach, S

    1995-01-01

    We study tangent bifurcation of band edge plane waves in nonlinear Hamiltonian lattices. The lattice is translationally invariant. We argue for the breaking of permutational symmetry by the new bifurcated periodic orbits. The case of two coupled oscillators is considered as an example for the perturbation analysis, where the symmetry breaking can be traced using Poincare maps. Next we consider a lattice and derive the dependence of the bifurcation energy on the parameters of the Hamiltonian function in the limit of large system sizes. A necessary condition for the occurence of the bifurcation is the repelling of the band edge plane wave's frequency from the linear spectrum with increasing energy. We conclude that the bifurcated orbits will consequently exponentially localize in the configurational space.

  5. Atom–atom interactions around the band edge of a photonic crystal waveguide

    Science.gov (United States)

    Hood, Jonathan D.; Goban, Akihisa; Asenjo-Garcia, Ana; Lu, Mingwu; Yu, Su-Peng; Chang, Darrick E.; Kimble, H. J.

    2016-01-01

    Tailoring the interactions between quantum emitters and single photons constitutes one of the cornerstones of quantum optics. Coupling a quantum emitter to the band edge of a photonic crystal waveguide (PCW) provides a unique platform for tuning these interactions. In particular, the cross-over from propagating fields E(x)∝e±ikxx outside the bandgap to localized fields E(x)∝e−κx|x| within the bandgap should be accompanied by a transition from largely dissipative atom–atom interactions to a regime where dispersive atom–atom interactions are dominant. Here, we experimentally observe this transition by shifting the band edge frequency of the PCW relative to the D1 line of atomic cesium for N¯=3.0±0.5 atoms trapped along the PCW. Our results are the initial demonstration of this paradigm for coherent atom–atom interactions with low dissipation into the guided mode. PMID:27582467

  6. Atom-atom interactions around the band edge of a photonic crystal waveguide.

    Science.gov (United States)

    Hood, Jonathan D; Goban, Akihisa; Asenjo-Garcia, Ana; Lu, Mingwu; Yu, Su-Peng; Chang, Darrick E; Kimble, H J

    2016-09-20

    Tailoring the interactions between quantum emitters and single photons constitutes one of the cornerstones of quantum optics. Coupling a quantum emitter to the band edge of a photonic crystal waveguide (PCW) provides a unique platform for tuning these interactions. In particular, the cross-over from propagating fields [Formula: see text] outside the bandgap to localized fields [Formula: see text] within the bandgap should be accompanied by a transition from largely dissipative atom-atom interactions to a regime where dispersive atom-atom interactions are dominant. Here, we experimentally observe this transition by shifting the band edge frequency of the PCW relative to the [Formula: see text] line of atomic cesium for [Formula: see text] atoms trapped along the PCW. Our results are the initial demonstration of this paradigm for coherent atom-atom interactions with low dissipation into the guided mode.

  7. Femtosecond dynamics of the nonlinear index near the band edge in AlGaAs waveguides

    Science.gov (United States)

    Anderson, K. K.; LaGasse, M. J.; Wang, C. A.; Fujimoto, J. G.; Haus, H. A.

    1990-05-01

    The transient behavior of the nonresonant nonlinear index is investigated in AlGaAs waveguides with femtosecond time resolution. Both the refractive index and the absorption changes are measured by time division interferometry and pump probe techniques. Different mechanisms which contribute to the nonlinear index are distinguished by examining their dynamics, including the optical Stark effect, resonantly excited carriers, and two-photon absorption processes. The relative contribution from each mechanism is a strong function of wavelength near the band edge.

  8. Edge Majoranas on locally flat surfaces: The cone and the Möbius band

    Science.gov (United States)

    Quelle, A.; Smith, C. Morais; Kvorning, T.; Hansson, T. H.

    2016-09-01

    In this paper, we investigate the edge Majorana modes in the simplest possible p x+i py superconductor defined on surfaces with different geometries, the annulus, the cylinder, the Möbius band, and a cone (by cone we mean a cone with the tip cut away so it is topologically equivalent to the annulus and cylinder), and with different configurations of magnetic fluxes threading holes in these surfaces. In particular, we shall address two questions: Given that, in the absence of any flux, the ground state on the annulus does not support Majorana modes while the one on the cylinder does, how is it possible that the conical geometry can interpolate smoothly between the two? Given that in finite geometries edge Majorana modes have to come in pairs, how can a p x+i py state be defined on a Möbius band, which has only one edge? We show that the key to answering these questions is that the ground state depends on the geometry, even though all the surfaces are locally flat. In the case of the truncated cone, there is a nontrivial holonomy, while the nonorientable Möbius band must necessarily support a domain wall.

  9. Efficient light amplification in low gain materials due to a photonic band edge effect.

    Science.gov (United States)

    Ondič, L; Pelant, I

    2012-03-26

    One of the possibilities of increasing optical gain of a light emitting source is by embedding it into a photonic crystal (PhC). If the properties of the PhC are tuned so that the emission wavelength of the light source with gain falls close to the photonic band edge of the PhC, then due to low group velocity of the light modes near the band edge caused by many multiple reflections of light on the photonic structure, the stimulated emission can be significantly enhanced. Here, we perform simulation of the photonic band edge effect on the light intensity of spectrally broad source interacting with a diamond PhC with low optical gain. We show that even for the case of low gain, up to 10-fold increase of light intensity output can be obtained for the two-dimensional PhC consisting of only 19 periodic layers of infinitely high diamond rods ordered into a square lattice. Moreover, considering the experimentally feasible structure composed of diamond rods of finite height - PhC slab - we show that the gain enhancement, even if reduced compared to the ideal case of infinite rods, still remains relatively high. For this particular structure, we show that up to 3.5-fold enhancement of light intensity can be achieved.

  10. Conductivity measurements in a shear-banding wormlike micellar system.

    Science.gov (United States)

    Photinos, Panos J; López-González, M R; Hoven, Corey V; Callaghan, Paul T

    2010-07-01

    Shear banding in the cetylpyridinium chloride/sodium salicylate micellar system is investigated using electrical conductivity measurements parallel to the velocity and parallel to the vorticity in a cylindrical Couette cell. The measurements show that the conductivity parallel to the velocity (vorticity) increases (decreases) monotonically with applied shear rate. The shear-induced anisotropy is over one order of magnitude lower than the anisotropy of the N(c) nematic phase. The steady-state conductivity measurements indicate that the anisotropy of the shear induced low-viscosity (high shear rate) phase is not significantly larger than the anisotropy of the high viscosity (low shear rate) phase. We estimate that the micelles in the shear induced low viscosity band are relatively short, with a characteristic length to diameter ratio of 5-15. The relaxation behavior following the onset of shear is markedly different above and below the first critical value γ1, in agreement with results obtained by other methods. The transient measurements show that the overall anisotropy of the sample decreases as the steady state is approached, i.e., the micellar length/the degree of order decrease.

  11. Higher order equivalent edge currents for fringe wave radar scattering by perfectly conducting polygonal plates

    DEFF Research Database (Denmark)

    Breinbjerg, Olav

    1992-01-01

    An approach for including higher order edge diffraction in the equivalent edge current (EEC) method is proposed. This approach, which applies to monostatic as well as bistatic radar configurations with perfectly conducting polygonal plates, involves three distinct sets of EECs. All of these sets ...

  12. The influences of thickness of spacing layer and the elastic anisotropy on the strain fields and band edges of InAs/GaAs conical shaped quantum dots

    Institute of Scientific and Technical Information of China (English)

    Liu Yu-Min; Yu Zhong-Yuan; Ren Xiao-Min

    2009-01-01

    Based on the continuum elastic theory, this paper presents a finite element analysis to investigate the influences of elastic anisotropy and thickness of spacing layer on the strain field distribution and band edges (both conduction band and valence band) of the InAs/GaAs conical shaped quantum dots. To illustrate these effects, we give detailed comparisons with the circumstances of isolated and stacking quantum dot for both anisotropic and isotropic elastic characteristics. The results show that, in realistic materials design and theoretical predication performances of the optoelectronie devices, both the elastic anisotropy and thickness of the spacing layer of stacked quantum dot should be taken into consideration.

  13. Beyond single-photon localization at the edge of a Photonic Band Gap

    CERN Document Server

    Nikolopoulos, G M; Nikolopoulos, Georgios M.

    2000-01-01

    We study spontaneous emission in an atomic ladder system, with bothtransitions coupled near-resonantly to the edge of a photonic band gapcontinuum. The problem is solved through a recently developed technique andleads to the formation of a ``two-photon+atom'' bound state with fractionalpopulation trapping in both upper states. In the long-time limit, the atom canbe found excited in a superposition of the upper states and a ``direct''two-photon process coexists with the stepwise one. The sensitivity of theeffect to the particular form of the density of states is also explored.

  14. Giant Enhancement of Second Harmonic Generation at Photonic Band Gap Edges

    Institute of Scientific and Technical Information of China (English)

    MA Dong-Li; REN Ming-Liang; DOU Jun-Hong; LI Zhi-Yuan

    2010-01-01

    @@ Second harmonic generation(SHG)in one-dimensional nonlinear photonic crystals made from periodically alternating ferroelectric and dielectric layers is investigated by means of the transfer matrix method.When tunedat the photonic band gap(PBG)edges,the fundamental wave and second harmonic wave slow down,and the filed enhancement takes place within the nonlinear photonic crystal.The phase mismatching can be compensated for to some extent and the second harmonic process will be enhanced.Numerical results show that the enhancement of SHG in the PBG structure can be up to four orders of magnitude compared with the traditional quasi-phase-matching structure.

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

    DEFF Research Database (Denmark)

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

    2010-01-01

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

  16. Topological edge state with zero Hall conductivity in quasi-one dimensional system

    Directory of Open Access Journals (Sweden)

    Xiao-Shan Ye

    2016-09-01

    Full Text Available We explore the structure of the energy spectra of quasi-one dimensional (Q1D system subjected to spin-density-wave SDW states. The structure of the energy spectra opens energy gaps with Zeeman field. Theses gaps result in plateaus for the Quantum Hall conductivity which is associated with edge states. Different from the SSH Hofstadter model, here we show that there are a doublet of edge states contribution to zero Hall conductivity. These edge states are allowed for magnetic control of spin currents. The topological effects predicted here could be tested directly in organic conductors system.

  17. Topological edge state with zero Hall conductivity in quasi-one dimensional system

    Science.gov (United States)

    Ye, Xiao-Shan

    2016-09-01

    We explore the structure of the energy spectra of quasi-one dimensional (Q1D) system subjected to spin-density-wave SDW states. The structure of the energy spectra opens energy gaps with Zeeman field. Theses gaps result in plateaus for the Quantum Hall conductivity which is associated with edge states. Different from the SSH Hofstadter model, here we show that there are a doublet of edge states contribution to zero Hall conductivity. These edge states are allowed for magnetic control of spin currents. The topological effects predicted here could be tested directly in organic conductors system.

  18. Atom-atom interactions around the band edge of a photonic crystal waveguide

    Science.gov (United States)

    Hood, Jonathan D.; Goban, Akihisa; Asenjo-Garcia, Ana; Lu, Mingwu; Yu, Su-Peng; Chang, Darrick E.; Kimble, H. J.

    2016-09-01

    Tailoring the interactions between quantum emitters and single photons constitutes one of the cornerstones of quantum optics. Coupling a quantum emitter to the band edge of a photonic crystal waveguide (PCW) provides a unique platform for tuning these interactions. In particular, the cross-over from propagating fields E(x)∝e±ikxxE(x)∝e±ikxx outside the bandgap to localized fields E(x)∝e-κx|x|E(x)∝e-κx|x| within the bandgap should be accompanied by a transition from largely dissipative atom-atom interactions to a regime where dispersive atom-atom interactions are dominant. Here, we experimentally observe this transition by shifting the band edge frequency of the PCW relative to the D1D1 line of atomic cesium for N¯=3.0±0.5N¯=3.0±0.5 atoms trapped along the PCW. Our results are the initial demonstration of this paradigm for coherent atom-atom interactions with low dissipation into the guided mode.

  19. The study of below and above band-edge imperfection states in In2S3 solar energy materials

    Science.gov (United States)

    Ho, Ching-Hwa

    2012-08-01

    β-In2S3 is a nontoxic buffer layer material usually used in a thin-film solar cell due to a lot of vacancies and surface states naturally existing in the crystal to assist in photoelectric conversion. Transition metal (TM)-incorporated β-In2S3 has also been proposed to increase conversion efficiency in In2S3 since multi-photons absorption by intermediate band (IB) would happen in the sulfide. In this paper, single crystals of undoped and Nb-doped β-In2S3 have been grown by the chemical vapor transport (CVT) method using ICl3 as a transport agent. Optical properties of the imperfection states of the crystals are probed by thermoreflectance (TR), photoconductivity (PC), photoluminescence (PL), surface photoconductive response (SPR), optical absorption and photo-voltage-current (photo V-I) measurements. The TR and optical-absorption measurements confirmed that the undoped and Nb-doped β-In2S3 are direct semiconductors with energy gap of 1.935 eV for undoped β-In2S3, 1.923 eV for β-In2S3:Nb0.005, and 1.901 eV for β-In2S3:Nb0.01. For undoped β-In2S3, PC and PL measurements are used to characterize defect transitions below band gap. The above band-edge transitions of undoped β-In2S3 have also been evaluated using PL, PC, and SPR measurements. For the evaluation of Nb-doped β-In2S3, an intermediate band with energy of ∼0.4 eV below the conduction band edge has been detected in the TR measurements in both β-In2S3:Nb0.005 and β-In2S3:Nb0.01. The photo V-I measurements also verified that the photoelectric-conversion efficiency would be enhanced in the β-In2S3 with higher niobium content. Based on the experimental analyses, the optical behavior of the defects, surface states, and IB (formed by Nb) in the In2S3 crystals is thus explored.

  20. Fermi level stabilization and band edge energies in Cd{sub x}Zn{sub 1−x}O alloys

    Energy Technology Data Exchange (ETDEWEB)

    Detert, Douglas M.; Tom, Kyle B.; Dubon, Oscar D. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (United States); Battaglia, Corsin; Javey, Ali [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720 (United States); Denlinger, Jonathan D. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Lim, Sunnie H. N. [Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Anders, André [Accelerator and Fusion Research Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Yu, Kin M.; Walukiewicz, Wladek [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2014-06-21

    We have measured the band edge energies of Cd{sub x}Zn{sub 1−x}O thin films as a function of composition by three independent techniques: we determine the Fermi level stabilization energy by pinning the Fermi level with ion irradiation, measure the binding energy of valence band states and core levels by X-ray photoelectron spectroscopy, and probe shifts in the conduction band and valence band density of states using soft X-ray absorption and emission spectroscopy, respectively. The three techniques find consensus in explaining the origin of compositional trends in the optical-bandgap narrowing upon Cd incorporation in wurtzite ZnO and widening upon Zn incorporation in rocksalt CdO. The conduction band minimum is found to be stationary for both wurtzite and rocksalt alloys, and a significant upward rise of the valence band maximum accounts for the majority of these observed bandgap changes. Given these band alignments, alloy disorder scattering is found to play a negligible role in decreasing the electron mobility for all alloys. These band alignment details, combined with the unique optical and electrical properties of the two phase regimes, make CdZnO alloys attractive candidates for photoelectrochemical water splitting applications.

  1. Exponential Tails Near the Band Edges of a One-Dimensional Exciton System

    Science.gov (United States)

    Avgin, I.; Boukahil, A.; Zettili, N.; Huber, D. L.

    2003-03-01

    We report the results of studies of the tails near the band edges of a one-dimensional Frenkel exciton system in the Coherent Potential Approximation (CPA). A Gaussian distribution of the transition frequencies with rms width σ (0.1 <= σ <= 2.0) is used. We found that the tails obey two different exponential power laws depending on the value of σ. In the weak disorder limit 0.1 <= σ <= 0.5, the tails of the density of states and the absorption line shape behave like expk|E|^3/2/σ^2 and in the strong disorder limit 0.5 <= σ <= 2.0 the tails behave like exp|E|^2/2σ^2\\. Our CPA results are in excellent agreement with our simulation data for the density of states over the entire range 0.1 <= σ <= 2.0, and with previous investigations for weak disorder.

  2. Oscillator Based on Lumped Double Ladder Circuit with Band Edge Degeneracy

    CERN Document Server

    Oshmarin, Dmitry; Othman, Mohamed A K; Sloan, Jeff; Radfar, Mohammad; Green, Michael M; Capolino, Filippo

    2016-01-01

    An oscillator design based on a periodic, double ladder resonant circuit is proposed. The circuit exhibits a degenerate band edge (DBE) in the dispersion diagram of its phase-frequency eigenstates, and possesses unique resonance features associated with a high Q-factor resonance, compared to a single ladder or a conventional LC tank circuit. This oscillator is shown to have an oscillation threshold that is half that of a single LC ladder circuit having the same total quality factor, and thus is more robust than an LC oscillator in the presence of losses. It is also shown that the output and amplitude of the double-ladder oscillator is much less sensitive to the output loading compared to single-ladder oscillators. We show the analysis and design of such oscillators that potentially lead to enhancing the efficiency of RF components and sources.

  3. Experimental Demonstration of Degenerate Band Edge in Metallic Periodically-Loaded Circular Waveguide

    CERN Document Server

    Othman, Mohamed A K; Atmatzakis, Georgios; Christodoulou, Christos; Capolino, Filippo

    2016-01-01

    We experimentally demonstrate for the first time the degenerate band edge (DBE) condition, namely the degeneracy of four Bloch modes, in loaded circular metallic waveguides. The four modes forming the DBE represent a degeneracy of fourth order occurring in a periodic structure where four Bloch modes, two propagating and two evanescent, coalesce. It leads to a very flat wavenumber-frequency dispersion relation, and the finite length structure's quality factor scales as $N^5$ where $N$ is the number of unit cells. The proposed waveguide in which DBE is observed here is designed by periodically loading a circular waveguide with misaligned elliptical metallic rings, supported by a low-index dielectric. We validate the existence of the DBE in such structure using measurements and we report good agreement between full-wave simulation and the measured response of the waveguide near the DBE frequency; taking into account metallic losses. We correlate our finding to theoretical and simulation results utilizing various...

  4. Band-edge Bilayer Plasmonic Nanostructure for Surface Enhanced Raman Spectroscopy

    CERN Document Server

    Mousavi, S Hamed Shams; Atabaki, Amir H; Adibi, Ali

    2014-01-01

    Spectroscopic analysis of large biomolecules is critical in a number of applications, including medical diagnostics and label-free biosensing. Recently, it has been shown that Raman spectroscopy of proteins can be used to diagnose some diseases, including a few types of cancer. These experiments have however been performed using traditional Raman spectroscopy and the development of the Surface enhanced Raman spectroscopy (SERS) assays suitable for large biomolecules could lead to a substantial decrease in the amount of specimen necessary for these experiments. We present a new method to achieve high local field enhancement in surface enhanced Raman spectroscopy through the simultaneous adjustment of the lattice plasmons and localized surface plasmon polaritons, in a periodic bilayer nanoantenna array resulting in a high enhancement factor over the sensing area, with relatively high uniformity. The proposed plasmonic nanostructure is comprised of two interacting nanoantenna layers, providing a sharp band-edge ...

  5. Giant Amplification in Degenerate Band Edge Slow-Wave Structures Interacting with an Electron Beam

    CERN Document Server

    Othman, Mohamed A K; Figotin, Alexander; Capolino, Filippo

    2015-01-01

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

  6. Non-Markovian Quantum Fluctuations and Superradiance Near a Photonic Band Edge

    CERN Document Server

    Vats, N; Vats, Nipun; John, Sajeev

    1998-01-01

    We discuss a point model for the collective emission of light from N two-level atoms in a photonic bandgap material, each with an atomic resonant frequency near the edge of the gap. In the limit of a low initial occupation of the excited atomic state, our system is shown to possess novel atomic spectra and population statistics. For a high initial excited state population, mean field theory suggests a fractionalized inversion and a macroscopic polarization for the atoms in the steady state, both of which can be controlled by an external d.c. field. This atomic steady state is accompanied by a non--zero expectation value of the electric field operators for field modes located in the vicinity of the atoms. The nature of homogeneous broadening near the band edge is shown to differ markedly from that in free space due to non-Markovian memory effects in the radiation dynamics. Non-Markovian vacuum fluctuations are shown to yield a partially coherent steady state polarization with a random phase. In contrast with t...

  7. Evaluation of Sentinel-2 Red-Edge Bands for Empirical Estimation of Green LAI and Chlorophyll Content

    Directory of Open Access Journals (Sweden)

    José Moreno

    2011-07-01

    Full Text Available ESA’s upcoming satellite Sentinel-2 will provide Earth images of high spatial, spectral and temporal resolution and aims to ensure continuity for Landsat and SPOT observations. In comparison to the latter sensors, Sentinel-2 incorporates three new spectral bands in the red-edge region, which are centered at 705, 740 and 783 nm. This study addresses the importance of these new bands for the retrieval and monitoring of two important biophysical parameters: green leaf area index (LAI and chlorophyll content (Ch. With data from several ESA field campaigns over agricultural sites (SPARC, AgriSAR, CEFLES2 we have evaluated the efficacy of two empirical methods that specifically make use of the new Sentinel-2 bands. First, it was shown that LAI can be derived from a generic normalized difference index (NDI using hyperspectral data, with 674 nm with 712 nm as best performing bands. These bands are positioned closely to the Sentinel-2 B4 (665 nm and the new red-edge B5 (705 nm band. The method has been applied to simulated Sentinel-2 data. The resulting green LAI map was validated against field data of various crop types, thereby spanning a LAI between 0 and 6, and yielded a RMSE of 0.6. Second, the recently developed “Normalized Area Over reflectance Curve” (NAOC, an index that derives Ch from hyperspectral data, was studied on its compatibility with simulated Sentinel-2 data. This index integrates the reflectance curve between 643 and 795 nm, thereby including the new Sentinel-2 bands in the red-edge region. We found that these new bands significantly improve the accuracy of Ch estimation. Both methods emphasize the importance of red-edge bands for operational estimation of biophysical parameters from Sentinel-2.

  8. Compensation of band-edge positions in titanium-doped Ta3N5 photoanode for enhanced water splitting performance: A first-principles insight

    Science.gov (United States)

    Fan, Guozheng; Wang, Xin; Fu, Hongwei; Feng, Jianyong; Li, Zhaosheng; Zou, Zhigang

    2017-08-01

    Ta3N5 is a promising photoanode for solar water splitting. However, it often suffers from high onset potential for water oxidation, which may be partially ascribed to the oxygen impurities in Ta3N5 . Oxygen impurities, which are always introduced into Ta3N5 during the preparation process, are difficult to remove due to the low formation energy of O-doped Ta3N5 . The valence- and conduction-band-edge positions shift almost in parallel towards more positive potentials with addition of oxygen impurities, which may increase the onset potential for water oxidation. In this study, the hybrid-DFT (density functional theory) calculations of Ti-doped Ta3N5 show that as Ti doping concentration increases, both the valence- and conduction-band-edge positions of Ta3N5 move towards more negative potentials, which is opposite to the role of oxygen impurties. In the case of Ti-O codoped Ta3N5 , Ti doping can compensate the effect of oxygen impurities and may reduce the onset potential for water oxidation. Defect formation energies reveal that Ti-O codoped Ta3N5 is thermodynamically stable. Therefore we propose that by controlling the amount of O and Ti, the band-edge positions can be modified to a proper level so that better photoelectrochemical performances for solar water splitting can be achieved.

  9. Effects of Conducting-Gesture Instruction on Seventh-Grade Band Students' Performance Response to Conducting Emblems.

    Science.gov (United States)

    Cofer, R. Shayne

    1998-01-01

    Investigates effects of short-term conducting gesture instruction on seventh-grade band students' recognition of and performance response to musical conducting gestures. Indicates that short-term conducting-gesture instruction has a positive, statistically significant impact on recognition of and performance response to conducting gestures.…

  10. Measurement of InAsSb bandgap energy and InAs/InAsSb band edge positions using spectroscopic ellipsometry and photoluminescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Webster, P. T.; Riordan, N. A.; Liu, S.; Zhang, Y.-H.; Johnson, S. R., E-mail: shane.johnson@asu.edu [Center for Photonics Innovation and School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Steenbergen, E. H. [U. S. Air Force Research Laboratory, AFRL/RXAN, Wright Patterson, Ohio 45433 (United States); Synowicki, R. A. [J. A. Woollam Co., Inc., 645 M. Street, Suite 102, Lincoln, Nebraska 68508 (United States)

    2015-12-28

    The structural and optical properties of lattice-matched InAs{sub 0.911}Sb{sub 0.089} bulk layers and strain-balanced InAs/InAs{sub 1−x}Sb{sub x} (x ∼ 0.1–0.4) superlattices grown on (100)-oriented GaSb substrates by molecular beam epitaxy are examined using X-ray diffraction, spectroscopic ellipsometry, and temperature dependent photoluminescence spectroscopy. The photoluminescence and ellipsometry measurements determine the ground state bandgap energy and the X-ray diffraction measurements determine the layer thickness and mole fraction of the structures studied. Detailed modeling of the X-ray diffraction data is employed to quantify unintentional incorporation of approximately 1% Sb into the InAs layers of the superlattices. A Kronig-Penney model of the superlattice miniband structure is used to analyze the valence band offset between InAs and InAsSb, and hence the InAsSb band edge positions at each mole fraction. The resulting composition dependence of the bandgap energy and band edge positions of InAsSb are described using the bandgap bowing model; the respective low and room temperature bowing parameters for bulk InAsSb are 938 and 750 meV for the bandgap, 558 and 383 meV for the conduction band, and −380 and −367 meV for the valence band.

  11. Measurement of InAsSb bandgap energy and InAs/InAsSb band edge positions using spectroscopic ellipsometry and photoluminescence spectroscopy

    Science.gov (United States)

    Webster, P. T.; Riordan, N. A.; Liu, S.; Steenbergen, E. H.; Synowicki, R. A.; Zhang, Y.-H.; Johnson, S. R.

    2015-12-01

    The structural and optical properties of lattice-matched InAs0.911Sb0.089 bulk layers and strain-balanced InAs/InAs1-xSbx (x ˜ 0.1-0.4) superlattices grown on (100)-oriented GaSb substrates by molecular beam epitaxy are examined using X-ray diffraction, spectroscopic ellipsometry, and temperature dependent photoluminescence spectroscopy. The photoluminescence and ellipsometry measurements determine the ground state bandgap energy and the X-ray diffraction measurements determine the layer thickness and mole fraction of the structures studied. Detailed modeling of the X-ray diffraction data is employed to quantify unintentional incorporation of approximately 1% Sb into the InAs layers of the superlattices. A Kronig-Penney model of the superlattice miniband structure is used to analyze the valence band offset between InAs and InAsSb, and hence the InAsSb band edge positions at each mole fraction. The resulting composition dependence of the bandgap energy and band edge positions of InAsSb are described using the bandgap bowing model; the respective low and room temperature bowing parameters for bulk InAsSb are 938 and 750 meV for the bandgap, 558 and 383 meV for the conduction band, and -380 and -367 meV for the valence band.

  12. Analysis of Band-Edge Dynamics in ZnO and MgZnO Thin Films

    Science.gov (United States)

    Canul, Amrah

    This work investigates the temperature dependence of electron states at the band-edge in ZnO and Mg0.07Zn0.93O thin films. To investigate the band-edge dynamics, we study in-gap states via temperature dependent absorption spectroscopy in the range 77-500K. The in-gap states at the band-edge were analyzed via the Urbach energy model, where the Urbach Energy is a measure of the extent of states into the bandgap. In parallel, we also analyze the temperature dependent Urbach energy via the Wasim model, which separates the relative contributions of defect states and temperature dependent phonon modes to the in-gap states. It was found that the defect contribution to in-gap states at the band-edge was significantly higher for Mg0.07Zn0.93O than in ZnO. Additionally, the phonon contribution to in-gap states was less in Mg 0.07Zn0.93O than in ZnO. The author gratefully acknowledges the National Science Foundation and the U.S. Department of Energy, Office of Basic Energy Science, Division of Materials Science and Engineering under Grant No. DE-FG02-07ER46386.

  13. Optical excitation processes in the near band-edge region of KAlSi3O8 and NaAlSi3O8 feldspar

    DEFF Research Database (Denmark)

    Poolton, N.R.J.; Mauz, B.; Lang, A.;

    2006-01-01

    A complex variety of excitation and relaxation pathways are available for charge in naturally occurring NaAlSi3O8 and KAlpSi(3)O(8) feldspar crystals, when excited with photons in the trans-band-edge energy range 4-12 eV These can involve a mixture of electronic transitions associated with defect...... states, the conduction and valence bands and their associated band-tails. In order to demonstrate that a relationship exists between these processes, combinations of three spectroscopic techniques are deployed in this work: luminescence excitation/emission mapping, energy-resolved photo...... emission in the materials. Luminescence and phosphorescence excitation spectra provide additional, complementary, information regarding the excited states of the blue-emitting defects, including their transition lifetimes and decay paths. Red emission associated with Fe3+ luminescence is mostly isolated...

  14. Edge isolation of transparent conductive polymer (TCP) thin films on flexible substrates using UV laser ablation.

    Science.gov (United States)

    Hsiao, Wen-Tse; Tseng, Shih-Feng; Huang, Kuo-Cheng; Chiang, Donyau; Chen, Ming-Fei

    2012-06-01

    The purpose of this study was to directly use the writing techniques for the complex electrode edge isolation of transparent conductive polymer (TCP) thin films by a nanosecond pulsed UV laser processing system. The processing parameters including the laser pulse energy, the pulse repetition frequency, and the scan speed of galvanometers were examined to ablate the TCP films deposited on polyethylene terephtalate substrates of 188 microm thick. The thickness of TCP films was approximately 20 nm. The laser pulse repetition frequency and the scan speed of galvanometers were applied to calculate the overlapping rate of laser spots and to discuss the patterning region quality. Surface morphology, edge quality, and width and depth of edge isolated patterning structures after laser ablation process were measured by a three-dimensional confocal laser scanning microscope. In addition, the electrical conductivity of ablated TCP films was measured by a four-point probes instrument. After isolated line patterning was formed, the ablated TCP films with a better edge quality were obtained directly when the overlapping rate of laser spots, the scan speed, and the pulse repetition rate were 83.3%, 200 mm/s, and 40 kHz, respectively. The better surface morphology of electrode pattern structures was also obtained when the scan speed and the pulse repetition rate were 500 mm/s and 40 kHz, respectively.

  15. Multi-ion conduction bands in a simple model of calcium ion channels

    CERN Document Server

    Kaufman, I; Tindjong, R; McClintock, P V E; Eisenberg, R S

    2012-01-01

    We report self-consistent Brownian dynamics simulations of a simple electrostatic model of the selectivity filters (SF) of calcium ion channels. They reveal regular structure in the conductance and selectivity as functions of the fixed negative charge Qf at the SF. This structure comprises distinct regions of high conductance (conduction bands) M0, M1, M2 separated by regions of zero-conductance (stop-bands). Two of these conduction bands, M1 and M2, demonstrate high calcium selectivity and prominent anomalous mole fraction effects and can be identified with the L-type and RyR calcium channels.

  16. The conduction bands of MgO, MgS and HfO2

    NARCIS (Netherlands)

    Boer, P.K. de; Groot, R.A. de

    1998-01-01

    Electronic structure calculations for MgO, MgS and HfO2 are reported. It is shown that the conduction bands of MgO and MgS have predominantly anion character, contrary to the common picture of the conduction band being derived from cation states. In transition metal oxides, unoccupied anion states a

  17. A snapback suppressed reverse-conducting IGBT with built-in diode by utilizing edge termination

    Science.gov (United States)

    Chen, Weizhong; Li, Zehong; liu, Yong; Ren, Min; Zhang, Bo; Li, Zhaoji

    2014-06-01

    A reverse-conducting insulated-gate bipolar transistor (RC-IGBT) with anti-parallel built-in diode in edge termination region is proposed. In the view of the cross section structure of the RC-IGBT, the Field Limiting Ring (FLR) and the equipotential ring act as an anode emitter and the N-Collector acts as the cathode emitter of the diode. In the aspect of layout, the anti-parallel built-in diode is integrated in the termination region which surrounds around the active cell region. Compared with the conventional RC-IGBT which integrates diode in active cell region, the proposed device can eliminate the snapback easily and conduct current uniformly at forward conduction of IGBT mode, which are favorable to the increase of conducting capability and the reliability. In addition, the forward voltage drop can be decreased largely, which is favorable to the decrease of conducting energy loss.

  18. The Band-Edge Behavior of the Density of Surfacic States

    Energy Technology Data Exchange (ETDEWEB)

    Kirsch, Werner [Ruhr Universitaet Bochum, Fakultaet fuer Mathematik and SFB-TR 12 (Germany)], E-mail: werner.kirsch@rub.de; Klopp, Frederic [Universite de Paris-Nord, LAGA, UMR 7539 CNRS, Institut Galilee (France)], E-mail: klopp@math.univ-paris13.fr

    2006-05-15

    This paper is devoted to the asymptotics of the density of surfacic states near the spectral edges for a discrete surfacic Anderson model. Two types of spectral edges have to be considered: fluctuating edges and stable edges. Each type has its own type of asymptotics. In the case of fluctuating edges, one obtains Lifshitz tails the parameters of which are given by the initial operator suitably 'reduced' to the surface. For stable edges, the surface density of states behaves like the surface density of states of a constant (equal to the expectation of the random potential) surface potential. Among the tools used to establish this are the asymptotics of the surface density of states for constant surface potentials.

  19. Direct Observation of Electrostatically Driven Band Gap Renormalization in a Degenerate Perovskite Transparent Conducting Oxide

    Energy Technology Data Exchange (ETDEWEB)

    Lebens-Higgins, Z.; Scanlon, D. O.; Paik, H.; Sallis, S.; Nie, Y.; Uchida, M.; Quackenbush, N. F.; Wahila, M. J.; Sterbinsky, G. E.; Arena, Dario A.; Woicik, J. C.; Schlom, D. G.; Piper, L. F. J.

    2016-01-01

    We have directly measured the band gap renormalization associated with the Moss-Burstein shift in the perovskite transparent conducting oxide (TCO), La-doped BaSnO 3 , using hard x-ray photoelectron spectroscopy. We determine that the band gap renormalization is almost entirely associated with the evolution of the conduction band. Our experimental results are supported by hybrid density functional theory supercell calculations. We determine that unlike conventional TCOs where interactions with the dopant orbitals are important, the band gap renormalization in La - BaSnO 3 is driven purely by electrostatic interactions.

  20. Direct Observation of Electrostatically Driven Band Gap Renormalization in a Degenerate Perovskite Transparent Conducting Oxide.

    Science.gov (United States)

    Lebens-Higgins, Z; Scanlon, D O; Paik, H; Sallis, S; Nie, Y; Uchida, M; Quackenbush, N F; Wahila, M J; Sterbinsky, G E; Arena, Dario A; Woicik, J C; Schlom, D G; Piper, L F J

    2016-01-15

    We have directly measured the band gap renormalization associated with the Moss-Burstein shift in the perovskite transparent conducting oxide (TCO), La-doped BaSnO_{3}, using hard x-ray photoelectron spectroscopy. We determine that the band gap renormalization is almost entirely associated with the evolution of the conduction band. Our experimental results are supported by hybrid density functional theory supercell calculations. We determine that unlike conventional TCOs where interactions with the dopant orbitals are important, the band gap renormalization in La-BaSnO_{3} is driven purely by electrostatic interactions.

  1. Segmentation of prostate from ultrasound images using level sets on active band and intensity variation across edges.

    Science.gov (United States)

    Li, Xu; Li, Chunming; Fedorov, Andriy; Kapur, Tina; Yang, Xiaoping

    2016-06-01

    In this paper, the authors propose a novel efficient method to segment ultrasound images of the prostate with weak boundaries. Segmentation of the prostate from ultrasound images with weak boundaries widely exists in clinical applications. One of the most typical examples is the diagnosis and treatment of prostate cancer. Accurate segmentation of the prostate boundaries from ultrasound images plays an important role in many prostate-related applications such as the accurate placement of the biopsy needles, the assignment of the appropriate therapy in cancer treatment, and the measurement of the prostate volume. Ultrasound images of the prostate are usually corrupted with intensity inhomogeneities, weak boundaries, and unwanted edges, which make the segmentation of the prostate an inherently difficult task. Regarding to these difficulties, the authors introduce an active band term and an edge descriptor term in the modified level set energy functional. The active band term is to deal with intensity inhomogeneities and the edge descriptor term is to capture the weak boundaries or to rule out unwanted boundaries. The level set function of the proposed model is updated in a band region around the zero level set which the authors call it an active band. The active band restricts the authors' method to utilize the local image information in a banded region around the prostate contour. Compared to traditional level set methods, the average intensities inside∖outside the zero level set are only computed in this banded region. Thus, only pixels in the active band have influence on the evolution of the level set. For weak boundaries, they are hard to be distinguished by human eyes, but in local patches in the band region around prostate boundaries, they are easier to be detected. The authors incorporate an edge descriptor to calculate the total intensity variation in a local patch paralleled to the normal direction of the zero level set, which can detect weak boundaries

  2. Revisiting the Valence and Conduction Band Size Dependence of PbS Quantum Dot Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Miller, Elisa M.; Kroupa, Daniel M.; Zhang, Jianbing; Schulz, Philip; Marshall, Ashley R.; Kahn, Antoine; Lany, Stephan; Luther, Joseph M.; Beard, Matthew C.; Perkins, Craig L.; van de Lagemaat, Jao

    2016-03-22

    We use a high signal-to-noise X-ray photoelectron spectrum of bulk PbS, GW calculations, and a model assuming parabolic bands to unravel the various X-ray and ultraviolet photoelectron spectral features of bulk PbS as well as determine how to best analyze the valence band region of PbS quantum dot (QD) films. X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) are commonly used to probe the difference between the Fermi level and valence band maximum (VBM) for crystalline and thin-film semiconductors. However, we find that when the standard XPS/UPS analysis is used for PbS, the results are often unrealistic due to the low density of states at the VBM. Instead, a parabolic band model is used to determine the VBM for the PbS QD films, which is based on the bulk PbS experimental spectrum and bulk GW calculations. Our analysis highlights the breakdown of the Brillioun zone representation of the band diagram for large band gap, highly quantum confined PbS QDs. We have also determined that in 1,2-ethanedithiol-treated PbS QD films the Fermi level position is dependent on the QD size; specifically, the smallest band gap QD films have the Fermi level near the conduction band minimum and the Fermi level moves away from the conduction band for larger band gap PbS QD films. This change in the Fermi level within the QD band gap could be due to changes in the Pb:S ratio. In addition, we use inverse photoelectron spectroscopy to measure the conduction band region, which has similar challenges in the analysis of PbS QD films due to a low density of states near the conduction band minimum.

  3. Regional estimation of savanna grass nitrogen using the red-edge band of the spaceborne RapidEye sensor

    Science.gov (United States)

    Ramoelo, A.; Skidmore, A. K.; Cho, M. A.; Schlerf, M.; Mathieu, R.; Heitkönig, I. M. A.

    2012-10-01

    The regional mapping of grass nutrients is of interest in the sustainable planning and management of livestock and wildlife grazing. The objective of this study was to estimate and map foliar and canopy nitrogen (N) at a regional scale using a recent high resolution spaceborne multispectral sensor (i.e. RapidEye) in the Kruger National Park (KNP) and its surrounding areas, South Africa. The RapidEye sensor contains five spectral bands in the visible-to-near infrared (VNIR), including a red-edge band centered at 710 nm. The importance of the red-edge band for estimating foliar chlorophyll and N concentrations has been demonstrated in many previous studies, mostly using field spectroscopy. The utility of the red-edge band of the RapidEye sensor for estimating grass N was investigated in this study. A two-step approach was adopted involving (i) vegetation indices and (ii) the integration of vegetation indices with environmental or ancillary variables using a stepwise multiple linear regression (SMLR) and a non-linear spatial least squares regression (PLSR). The model involving the simple ratio (SR) index (R805/R710) defined as SR54, altitude and the interaction between SR54 and altitude (SR54 * altitude) yielded the highest accuracy for canopy N estimation, while the non-linear PLSR yielded the highest accuracy for foliar N estimation through the integration of remote sensing (SR54) and environmental variables. The study demonstrated the possibility to map grass nutrients at a regional scale provided there is a spaceborne sensor encompassing the red edge waveband with a high spatial resolution.

  4. (Photoelectrochemical Methods for the Determination of the Band Edge Positions of TiO2-Based Nanomaterials

    Directory of Open Access Journals (Sweden)

    Radim Beranek

    2011-01-01

    Full Text Available TiO2-based nanomaterials play currently a major role in the development of novel photochemical systems and devices. One of the key parameters determining the photoactivity of TiO2-based materials is the position of the band edges. Although its knowledge is an important prerequisite for understanding and optimizing the performance of photochemical systems, it has been often rather neglected in recent research, particularly in the field of heterogeneous photocatalysis. This paper provides a concise account of main methods for the determination of the position of the band edges, particularly those suitable for measurements on nanostructured materials. In the first part, a survey of key photophysical and photochemical concepts necessary for understanding the energetics at the semiconductor/solution interface is provided. This is followed by a detailed discussion of several electrochemical, photoelectrochemical, and spectroelectrochemical methods that can be applied for the determination of band edge positions in compact and nanocrystalline thin films, as well as in nanocrystalline powders.

  5. Potential of the Sentinel-2 Red Edge Spectral Bands for Estimation of Eco-Physiological Plant Parameters

    Science.gov (United States)

    Malenovsky, Zbynek; Homolova, Lucie; Janoutova, Ruzena; Landier, Lucas; Gastellu-Etchegorry, Jean-Philippe; Berthelot, Beatrice; Huck, Alexis

    2016-08-01

    In this study we investigated importance of the space- borne instrument Sentinel-2 red edge spectral bands and reconstructed red edge position (REP) for retrieval of the three eco-physiological plant parameters, leaf and canopy chlorophyll content and leaf area index (LAI), in case of maize agricultural fields and beech and spruce forest stands. Sentinel-2 spectral bands and REP of the investigated vegetation canopies were simulated in the Discrete Anisotropic Radiative Transfer (DART) model. Their potential for estimation of the plant parameters was assessed through training support vector regressions (SVR) and examining their P-vector matrices indicating significance of each input. The trained SVR were then applied on Sentinel-2 simulated images and the acquired estimates were cross-compared with results from high spatial resolution airborne retrievals. Results showed that contribution of REP was significant for canopy chlorophyll content, but less significant for leaf chlorophyll content and insignificant for leaf area index estimations. However, the red edge spectral bands contributed strongly to the retrievals of all parameters, especially canopy and leaf chlorophyll content. Application of SVR on Sentinel-2 simulated images demonstrated, in general, an overestimation of leaf chlorophyll content and an underestimation of LAI when compared to the reciprocal airborne estimates. In the follow-up investigation, we will apply the trained SVR algorithms on real Sentinel-2 multispectral images acquired during vegetation seasons 2015 and 2016.

  6. Temperature-dependent dielectric function of bulk SrTiO3: Urbach tail, band edges, and excitonic effects

    Science.gov (United States)

    Gogoi, Pranjal Kumar; Schmidt, Daniel

    2016-02-01

    We report the temperature-dependent complex dielectric function of pristine bulk SrTiO3 between 4.2 and 300 K within the energy range of 0.6-6.5 eV determined by spectroscopic ellipsometry. Fundamental indirect and direct band-gap energies have been extracted and are discussed with regard to existing state-of-the-art theoretical calculations. Furthermore, the dielectric function around the fundamental direct gap is analyzed by considering excitonic states. The excitonic effects, including the Coulomb enhancement of the continuum, are characterized using an extension of the Elliott's formula considering both the real and imaginary parts of the dielectric function. The Urbach tail below the indirect edge shows an unconventional temperature-dependent behavior correlated to the microstructural changes near the structural phase transition around 105 K from the low-temperature tetragonal phase to the cubic phase. The temperature-dependent characterization reveals that the fundamental indirect edge as well as the Urbach tail are affected conspicuously by the structural phase transition while the fundamental direct edge is not. Moreover, the indirect edge follows Varshni's rule only in the cubic phase and the direct edge exhibits an anomalous linear increase with increasing temperature.

  7. Performance of horn-coupled transition edge sensors for L- and S-band optical detection on the SAFARI instrument

    Science.gov (United States)

    Goldie, D. J.; Glowacka, D. M.; Withington, S.; Chen, Jiajun; Ade, P. A. R.; Morozov, D.; Sudiwala, R.; Trappe, N. A.; Quaranta, O.

    2016-07-01

    We describe the geometry, architecture, dark- and optical performance of ultra-low-noise transition edge sensors as THz detectors for the SAFARI instrument. The TESs are fabricated from superconducting Mo/Au bilayers coupled to impedance-matched superconducting β-phase Ta thin-film absorbers. The detectors have phonon-limited dark noise equivalent powers of order 0.5 - 1.0 aW/ √ Hz and saturation powers of order 20 - 40 fW. The low temperature test configuration incorporating micro-machined backshorts is also described, and construction and typical performance characteristics for the optical load are shown. We report preliminary measurements of the optical performance of these TESs for two SAFARI bands; L-band at 110 - 210 μm and S-band 34 - 60 μm .

  8. Valence and conduction band structure of the quasi-two-dimensional semiconductor Sn S2

    Science.gov (United States)

    Racke, David A.; Neupane, Mahesh R.; Monti, Oliver L. A.

    2016-02-01

    We present the momentum-resolved photoemission spectroscopy of both the valence and the conduction band region in the quasi-two-dimensional van der Waals-layered indirect band gap semiconductor Sn S2 . Using a combination of angle-resolved ultraviolet photoemission and angle-resolved two-photon photoemission (AR-2PPE) spectroscopy, we characterize the band structure of bulk Sn S2 . Comparison with density functional theory calculations shows excellent quantitative agreement in the valence band region and reveals several localized bands that likely originate from defects such as sulfur vacancies. Evidence for a moderate density of defects is also observed by AR-2PPE in the conduction band region, leading to localized bands not present in the computational results. The energetic structure and dispersion of the conduction bands is captured well by the computational treatment, with some quantitative discrepancies remaining. Our results provide a broader understanding of the electronic structure of Sn S2 in particular and van der Waals-layered semiconductors in general.

  9. Results from EDGES High-band. I. Constraints on Phenomenological Models for the Global 21 cm Signal

    Science.gov (United States)

    Monsalve, Raul A.; Rogers, Alan E. E.; Bowman, Judd D.; Mozdzen, Thomas J.

    2017-09-01

    We report constraints on the global 21 cm signal due to neutral hydrogen at redshifts 14.8≥slant z≥slant 6.5. We derive our constraints from low-foreground observations of the average sky brightness spectrum conducted with the EDGES High-band instrument between 2015 September 7 and October 26. Observations were calibrated by accounting for the effects of antenna beam chromaticity, antenna and ground losses, signal reflections, and receiver parameters. We evaluate the consistency between the spectrum and phenomenological models for the global 21 cm signal. For tanh-based representations of the ionization history during the epoch of reionization, we rule out, at ≥slant 2σ significance, models with duration of up to {{Δ }}z=1 at z≈ 8.5 and higher than {{Δ }}z=0.4 across most of the observed redshift range under the usual assumption that the 21 cm spin temperature is much larger than the temperature of the cosmic microwave background during reionization. We also investigate a “cold” intergalactic medium (IGM) scenario that assumes perfect Lyα coupling of the 21 cm spin temperature to the temperature of the IGM, but that the latter is not heated by early stars or stellar remants. Under this assumption, we reject tanh-based reionization models of duration {{Δ }}z≲ 2 over most of the observed redshift range. Finally, we explore and reject a broad range of Gaussian models for the 21 cm absorption feature expected in the First Light era. As an example, we reject 100 mK Gaussians with duration (full width at half maximum) {{Δ }}z≤slant 4 over the range 14.2≥slant z≥slant 6.5 at ≥slant 2σ significance.

  10. Transient mid-IR study of electron dynamics in TiO2 conduction band.

    Science.gov (United States)

    Sá, Jacinto; Friedli, Peter; Geiger, Richard; Lerch, Philippe; Rittmann-Frank, Mercedes H; Milne, Christopher J; Szlachetko, Jakub; Santomauro, Fabio G; van Bokhoven, Jeroen A; Chergui, Majed; Rossi, Michel J; Sigg, Hans

    2013-04-07

    The dynamics of TiO2 conduction band electrons were followed with a novel broadband synchrotron-based transient mid-IR spectroscopy setup. The lifetime of conduction band electrons was found to be dependent on the injection method used. Direct band gap excitation results in a lifetime of 2.5 ns, whereas indirect excitation at 532 nm via Ru-N719 dye followed by injection from the dye into TiO2 results in a lifetime of 5.9 ns.

  11. THE EFFECTS OF EDGE BANDING THICKNESS OF ULUDAG FIR BONDED WITH SOME ADHESIVES ON WITHDRAWAL STRENGTHS OF BEECH DOWEL PINS IN COMPOSITE MATERIALS

    Directory of Open Access Journals (Sweden)

    Şeref Kurt

    2009-11-01

    Full Text Available Composite materials and wooden dowels are being used increasingly in the construction of furniture frames and inner decoration. Yet there is little information available concerning the withdrawal strength of various fasteners, and, in particular, dowels in composite materials edged solid wood edge bandings. The aim of this study was to determine the withdrawal strengths of 6, 8, 10 mm diameter dowels produced from beech with respect to edge of a medium-density fiberboard (MDF or particleboard (PB edged with 5, 10 and 15 mm thickness of solid wood edge banding of uludag fir, bonded with different adhesives. According to TS 4539 standard, the effects of edge banding thickness, dimension of dowels, type of composite materials and type of adhesives used for edge banding on the withdrawal strength were determined. The highest (6.37 N/mm² withdrawal strength was obtained in beech dowels with 8 mm diameter for MDF with 5 mm thickness of solid wood edge banding of uludag fir bonded with D-VTKA adhesive. According to results, if the hole wall and the surface of dowel are smooth then the adhesives give better mechanical adhesion with dowels and composite materials.

  12. Edge States of a Periodic Chain with Four-Band Energy Spectrum

    Science.gov (United States)

    Eliashvili, Merab; Kereselidze, Davit; Tsitsishvili, George; Tsitsishvili, Mikheil

    2017-07-01

    Tight-binding model on a finite chain is studied with four-fold alternated hopping parameters t1,2,3,4. Imposing the open boundary conditions, the corresponding recursion is solved analytically with special attention paid to the occurrence of edge states. Corresponding results are strongly corroborated by numeric calculations. It is shown that in the system there exist four different edge phases if the number of sites is odd, and eight edges phases if the chain comprises even number of sites. Phases are labelled by σ1 ≡ sgn(t1t3 - t2t4), σ2 ≡ sgn(t1t4 - t2t3), and σ3 ≡ sgn(t1t2 - t3t4). It is shown that σ1,2,3 represent gauge invariant topological indices emerging in the corresponding infinite chains.

  13. Cryogenic infrared multilayer filters: the origin of low-temperature shift of the pass-band edge

    Science.gov (United States)

    Belyaeva, Alla I.

    1999-11-01

    The design, manufacture and optimum performance of a cut-on IR for the 8-14 micrometers is discussed. The filter is composed of PbTe/ZnS symmetrical stacks deposited on tow sides of a ZnSe(ZnS) substrate. The refractive index of PbTe was found to 5.6 and that of ZnS 2.15. In order to obtain the required pass/stop band profile the principal filter was composed of ten basic periods. The transparent in the mean IR-range multilayer coatings are stable of thermal cycling from 300 up to 8 K with steady optical characteristics in this temperature range. The average transmittance of filters was 75 percent in the desired spectral regions and was constant in the temperature interval 300-8 K. The effect of cooling on the position of the pass band edge of the interference multilayer thin-film coating is experimentally revealed. A model is suggested which explains the origin of low- temperature shift of the pass-band edge within the scope of variation in the optical thickness of a layer with the high refractive index. The result of the carried out numerical analysis are in well agreement with the experimental data and may be used for cryocorrection of the interference IR multilayer thin-film.

  14. Anomalous length dependence of the conductance of graphene nanoribbons with zigzag edges

    KAUST Repository

    Bilić, Ante

    2013-01-01

    Charge transport through two sets of symmetric graphene nanoribbons with zigzag shaped edges in a two-terminal device has been investigated, using density functional theory combined with the non-equilibrium Green\\'s function method. The conductance has been explored as a function of nanoribbon length, bias voltage, and the strength of terminal coupling. The set of narrower nanoribbons, in the form of thiolated linear acenes, shows an anomalous length dependence of the conductance, which at first exhibits a drop and a minimum, followed by an evident rise. The length trend is shown to arise because of a gradual transformation in the transport mechanism, which changes from being governed by a continuum of out-of-plane π type and in-plane state channels to being fully controlled by a single, increasingly more resonant, occupied π state channel. For the set of nanoribbons with a wider profile, a steady increase is observed across the whole length range, owing to the absence of the former transport mechanism. The predicted trends are confirmed by the inclusion of self-interaction correction in the calculations. For both sets of nanoribbons the replacement of the strongly coupling thiol groups by weakly bonding phenathroline has been found to cause a strong attenuation with the length and a generally low conductance. © 2013 American Institute of Physics.

  15. Tunable Band Gap and Conductivity Type of ZnSe/Si Core-Shell Nanowire Heterostructures

    Directory of Open Access Journals (Sweden)

    Yijie Zeng

    2014-10-01

    Full Text Available The electronic properties of zincblende ZnSe/Si core-shell nanowires (NWs with a diameter of 1.1–2.8 nm are calculated by means of the first principle calculation. Band gaps of both ZnSe-core/Si-shell and Si-core/ZnSe-shell NWs are much smaller than those of pure ZnSe or Si NWs. Band alignment analysis reveals that the small band gaps of ZnSe/Si core-shell NWs are caused by the interface state. Fixing the ZnSe core size and enlarging the Si shell would turn the NWs from intrinsic to p-type, then to metallic. However, Fixing the Si core and enlarging the ZnSe shell would not change the band gap significantly. The partial charge distribution diagram shows that the conduction band maximum (CBM is confined in Si, while the valence band maximum (VBM is mainly distributed around the interface. Our findings also show that the band gap and conductivity type of ZnSe/Si core-shell NWs can be tuned by the concentration and diameter of the core-shell material, respectively.

  16. Tunable Band Gap and Conductivity Type of ZnSe/Si Core-Shell Nanowire Heterostructures.

    Science.gov (United States)

    Zeng, Yijie; Xing, Huaizhong; Fang, Yanbian; Huang, Yan; Lu, Aijiang; Chen, Xiaoshuang

    2014-10-31

    The electronic properties of zincblende ZnSe/Si core-shell nanowires (NWs) with a diameter of 1.1-2.8 nm are calculated by means of the first principle calculation. Band gaps of both ZnSe-core/Si-shell and Si-core/ZnSe-shell NWs are much smaller than those of pure ZnSe or Si NWs. Band alignment analysis reveals that the small band gaps of ZnSe/Si core-shell NWs are caused by the interface state. Fixing the ZnSe core size and enlarging the Si shell would turn the NWs from intrinsic to p-type, then to metallic. However, Fixing the Si core and enlarging the ZnSe shell would not change the band gap significantly. The partial charge distribution diagram shows that the conduction band maximum (CBM) is confined in Si, while the valence band maximum (VBM) is mainly distributed around the interface. Our findings also show that the band gap and conductivity type of ZnSe/Si core-shell NWs can be tuned by the concentration and diameter of the core-shell material, respectively.

  17. Edge effects on band gap energy in bilayer 2H-MoS{sub 2} under uniaxial strain

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Liang; Wang, Jin; Dongare, Avinash M., E-mail: dongare@uconn.edu [Department of Materials Science and Engineering and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269 (United States); Namburu, Raju [Computational and Information Sciences Directorate, U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005 (United States); O' Regan, Terrance P.; Dubey, Madan [Sensors and Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, Maryland 20783 (United States)

    2015-06-28

    The potential of ultrathin MoS{sub 2} nanostructures for applications in electronic and optoelectronic devices requires a fundamental understanding in their electronic structure as a function of strain. Previous experimental and theoretical studies assume that an identical strain and/or stress state is always maintained in the top and bottom layers of a bilayer MoS{sub 2} film. In this study, a bilayer MoS{sub 2} supercell is constructed differently from the prototypical unit cell in order to investigate the layer-dependent electronic band gap energy in a bilayer MoS{sub 2} film under uniaxial mechanical deformations. The supercell contains an MoS{sub 2} bottom layer and a relatively narrower top layer (nanoribbon with free edges) as a simplified model to simulate the as-grown bilayer MoS{sub 2} flakes with free edges observed experimentally. Our results show that the two layers have different band gap energies under a tensile uniaxial strain, although they remain mutually interacting by van der Waals interactions. The deviation in their band gap energies grows from 0 to 0.42 eV as the uniaxial strain increases from 0% to 6% under both uniaxial strain and stress conditions. The deviation, however, disappears if a compressive uniaxial strain is applied. These results demonstrate that tensile uniaxial strains applied to bilayer MoS{sub 2} films can result in distinct band gap energies in the bilayer structures. Such variations need to be accounted for when analyzing strain effects on electronic properties of bilayer or multilayered 2D materials using experimental methods or in continuum models.

  18. Optical nonlinearities in semiconductor-doped glasses near and below the band edge

    Science.gov (United States)

    Bindra, K. S.; Oak, S. M.; Rustagi, K. C.

    1998-03-01

    We present a brief review of our recent experimental results on optical nonlinearities in semiconductor-doped glasses. It is shown that even below the absorption edge the nonlinearities are determined by nonlinear absorption. The optical Kerr effect is found to have a susceptibility which is comparable to that for nonlinear refraction. We also find that in degenerate four-wave mixing the observed intensity dependence can be strongly influenced by nonlinear absorption.

  19. Fabrication of high-quality colloidal photonic crystals with sharp band edges for ultrafast all-optical switching

    Institute of Scientific and Technical Information of China (English)

    Feng Tian-Hua; Dai Qiao-Feng; Wu Li-Jun; Guo Qi; Hu Wei; Lan Sheng

    2008-01-01

    Application of the pressure controlled isothermal heating vertical deposition method to the fabrication of colloidal photonic crystals is systematically investigated in this paper. The fabricated samples are characterized by scanning electron microscope and transmission spectrum. High-quality samples with large transmissions in the pass bands and the sharp band edges are obtained and the optimum growth condition is determined. For the best sample, the transmission in the pass bands approaches 0.9 while that in the band gap reaches 0.1. More importantly, the maximum differential transmission as high as 0.1/nm is achieved. In addition, it is found that the number of stacking layers does not increase linearly with concentration of PS spheres in a solution, and a gradual saturation occurs when the concentration of PS spheres exceeds 1.5 wt.%. The uniformity of the fabricated samples is examined by transmission measurements on areas with different sizes. Finally, the tolerance of the fabricated samples to baking was studied.

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

    Science.gov (United States)

    2016-01-26

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

  1. Band gap and conductivity variations of ZnO thin films by doping with Aluminium

    Science.gov (United States)

    Vattappalam, Sunil C.; Thomas, Deepu; T, Raju Mathew; Augustine, Simon; Mathew, Sunny

    2015-02-01

    Zinc Oxide thin films were prepared by Successive Ionic layer adsorption and reaction technique(SILAR). Aluminium was doped for different doping concentrations from 3 at.% to 12 at.% in steps of 3 at.%. Conductivity of the samples were taken at different temperatures. UV Spectrograph of the samples were taken and the band gap of each sample was found from the data. It was observed that as the doping concentration of Aluminium increases, the band gap of the samples decreases and concequently conductivity of the samples increases.

  2. Band gap and conductivity variations of ZnO nano structured thin films annealed under Vacuum

    Science.gov (United States)

    Vattappalam, Sunil C.; Thomas, Deepu; T, Raju Mathew; Augustine, Simon; Mathew, Sunny

    2015-02-01

    Zinc Oxide thin films were prepared by Successive Ionic layer adsorption and reaction technique(SILAR). The samples were annealed under vacuum and conductivity of the samples were taken at different temperatures. UV Spectrograph of the samples were taken and the band gap of each sample was found from the data. All the results were compared with that of the sample annealed under air. It was observed that the band gap decreases and concequently conductivity of the samples increases when the samples are annealed under vacuum.

  3. Theory of thermal conductivity in a multi-band superconductor : Application to pnictides

    Science.gov (United States)

    Mishra, Vivek; Vorontsov, A. B.; Hirschfeld, P. J.; Vekhter, I.

    2010-03-01

    We calculate low temperature thermal conductivity within a two band model for newly discovered ferro-pnictide superconductors. We consider three different cases, sign changing s-wave state, highly anisotropic s-wave state and a state with order parameter nodes on one band. To include the effect of disorder, we have performed fully self-consistent T-matrix approximation including both intraband and interband impurity scatterings. We also study the behavior of the low temperature thermal conductivity under applied magnetic field using a recently developed variant of the Brandt-Pesch-Tewordt approximation, and compare our results with latest experimental data.

  4. Conduction mechanism in Polyaniline-flyash composite material for shielding against electromagnetic radiation in X-band & Ku band

    Science.gov (United States)

    Singh, Avanish Pratap; Anoop Kumar, S.; Chandra, Amita; Dhawan, S. K.

    2011-06-01

    β-Naphthalene sulphonic acid (β-NSA) doped polyaniline (PANI)-flyash (FA) composites have been prepared by chemical oxidative polymerization route whose conductivity lies in the range 2.37-21.49 S/cm. The temperature dependence of electrical conductivity has also been recorded which shows that composites follow Mott's 3D-VRH model. SEM images demonstrate that β-NSA leads to the formation of the tubular structure with incorporated flyash phase. TGA studies show the improvement in thermal stability of composites with increase in loading level of flyash. Complex parameters i.e. permittivity (ɛ* = ɛ'- iɛ″) and permeability (μ*=μ'- iμ″) of PANI-FA composites have been calculated from experimental scattering parameters (S11 & S21) using theoretical calculations given in Nicholson-Ross and Weir algorithms. The microwave absorption properties of the composites have been studied in X-band (8.2 - 12.4 GHz) & Ku-Band (12.4 - 18 GHz) frequency range. The maximum shielding effectiveness observed was 32dB, which strongly depends on dielectric loss and volume fraction of flyash in PANI matrix.

  5. Conduction mechanism in Polyaniline-flyash composite material for shielding against electromagnetic radiation in X-band & Ku band

    Directory of Open Access Journals (Sweden)

    Avanish Pratap Singh

    2011-06-01

    Full Text Available β–Naphthalene sulphonic acid (β–NSA doped polyaniline (PANI–flyash (FA composites have been prepared by chemical oxidative polymerization route whose conductivity lies in the range 2.37–21.49 S/cm. The temperature dependence of electrical conductivity has also been recorded which shows that composites follow Mott's 3D–VRH model. SEM images demonstrate that β–NSA leads to the formation of the tubular structure with incorporated flyash phase. TGA studies show the improvement in thermal stability of composites with increase in loading level of flyash. Complex parameters i.e. permittivity (ɛ* = ɛ′- iɛ″ and permeability (μ*=μ′- iμ″ of PANI-FA composites have been calculated from experimental scattering parameters (S11 & S21 using theoretical calculations given in Nicholson–Ross and Weir algorithms. The microwave absorption properties of the composites have been studied in X-band (8.2 – 12.4 GHz & Ku–Band (12.4 – 18 GHz frequency range. The maximum shielding effectiveness observed was 32dB, which strongly depends on dielectric loss and volume fraction of flyash in PANI matrix.

  6. Inter-Layer Coupling Induced Valence Band Edge Shift in Mono- to Few-Layer MoS2

    Science.gov (United States)

    Trainer, Daniel J.; Putilov, Aleksei V.; Di Giorgio, Cinzia; Saari, Timo; Wang, Baokai; Wolak, Mattheus; Chandrasena, Ravini U.; Lane, Christopher; Chang, Tay-Rong; Jeng, Horng-Tay; Lin, Hsin; Kronast, Florian; Gray, Alexander X.; Xi, Xiaoxing X.; Nieminen, Jouko; Bansil, Arun; Iavarone, Maria

    2017-01-01

    Recent progress in the synthesis of monolayer MoS2, a two-dimensional direct band-gap semiconductor, is paving new pathways toward atomically thin electronics. Despite the large amount of literature, fundamental gaps remain in understanding electronic properties at the nanoscale. Here, we report a study of highly crystalline islands of MoS2 grown via a refined chemical vapor deposition synthesis technique. Using high resolution scanning tunneling microscopy and spectroscopy (STM/STS), photoemission electron microscopy/spectroscopy (PEEM) and μ-ARPES we investigate the electronic properties of MoS2 as a function of the number of layers at the nanoscale and show in-depth how the band gap is affected by a shift of the valence band edge as a function of the layer number. Green’s function based electronic structure calculations were carried out in order to shed light on the mechanism underlying the observed bandgap reduction with increasing thickness, and the role of the interfacial Sulphur atoms is clarified. Our study, which gives new insight into the variation of electronic properties of MoS2 films with thickness bears directly on junction properties of MoS2, and thus impacts electronics application of MoS2. PMID:28084465

  7. Wavelength-tuned light emission via modifying the band edge symmetry: Doped SnO2 as an example

    KAUST Repository

    Zhou, Hang

    2014-03-27

    We report the observation of ultraviolet photoluminescence and electroluminescence in indium-doped SnO2 thin films with modified "forbidden" bandgap. With increasing indium concentration in SnO 2, dominant visible light emission evolves into the ultraviolet regime in photoluminescence. Hybrid functional first-principles calculations demonstrate that the complex of indium dopant and oxygen vacancy breaks "forbidden" band gap to form allowed transition states. Furthermore, undoped and 10% indium-doped SnO2 layers are synthesized on p-type GaN substrates to obtain SnO2-based heterojunction light-emitting diodes. A dominant visible emission band is observed in the undoped SnO 2-based heterojunction, whereas strong near-ultraviolet emission peak at 398 nm is observed in the indium-doped SnO2-based heterojunction. Our results demonstrate an unprecedented doping-based approach toward tailoring the symmetry of band edge states and recovering ultraviolet light emission in wide-bandgap oxides. © 2014 American Chemical Society.

  8. Kondo effect and impurity band conduction in Co:TiO2 magnetic semiconductor

    NARCIS (Netherlands)

    Ramaneti, R.; Lodder, J.C.; Jansen, R.

    2007-01-01

    The nature of charge carriers and their interaction with local magnetic moments in an oxide magnetic semiconductor is established. For cobalt-doped anatase TiO2 films, we demonstrate conduction in a metallic donor-impurity band. Moreover, we observe a clear signature of the Kondo effect in electrica

  9. Observation of conducting edge states in graphene at zero magnetic field

    Science.gov (United States)

    Allen, Monica; Fulga, Ion; Shtanko, Oles; Watanabi, Kenji; Taniguchi, Takashi; Jarillo-Herrero, Pablo; Akhmerov, Anton; Levitov, Leonid; Yacoby, Amir

    2015-03-01

    The electronic nature of edge states confined to the boundaries of a graphene crystal remains an outstanding question. Proposals range from Anderson localization to chiral zero-energy edge modes, but a full microscopic picture of edge transport remains elusive. We directly image current transmission in real space by coupling superconducting electrodes to a graphene crystal and measuring quantum interference as a function of applied magnetic flux. To obtain a more quantitative picture, we employ Fourier techniques to extract the real space current distribution with nanoscale precision. We observe robust confinement of current to the edges of the crystal approaching the Dirac point and show that relative edge and bulk contributions are tunable via electrostatic gating. A strong candidate consistent with our data is the proposal of chiral edge modes that arise from sublattice symmetry breaking at the edge, sustained in all crystallographic edge orientations except atomically perfect armchair. Our techniques also open the door to fast spatial imaging of current distributions along more complicated networks of domains in larger crystals.

  10. The study of below and above band-edge imperfection states in In{sub 2}S{sub 3} solar energy materials

    Energy Technology Data Exchange (ETDEWEB)

    Ho, Ching-Hwa, E-mail: chho@mail.ntust.edu.tw [Graduate Institute of Engineering, Graduate Institute of Applied Science and Engineering, and Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China)

    2012-08-01

    {beta}-In{sub 2}S{sub 3} is a nontoxic buffer layer material usually used in a thin-film solar cell due to a lot of vacancies and surface states naturally existing in the crystal to assist in photoelectric conversion. Transition metal (TM)-incorporated {beta}-In{sub 2}S{sub 3} has also been proposed to increase conversion efficiency in In{sub 2}S{sub 3} since multi-photons absorption by intermediate band (IB) would happen in the sulfide. In this paper, single crystals of undoped and Nb-doped {beta}-In{sub 2}S{sub 3} have been grown by the chemical vapor transport (CVT) method using ICl{sub 3} as a transport agent. Optical properties of the imperfection states of the crystals are probed by thermoreflectance (TR), photoconductivity (PC), photoluminescence (PL), surface photoconductive response (SPR), optical absorption and photo-voltage-current (photo V-I) measurements. The TR and optical-absorption measurements confirmed that the undoped and Nb-doped {beta}-In{sub 2}S{sub 3} are direct semiconductors with energy gap of 1.935 eV for undoped {beta}-In{sub 2}S{sub 3}, 1.923 eV for {beta}-In{sub 2}S{sub 3}:Nb{sub 0.005}, and 1.901 eV for {beta}-In{sub 2}S{sub 3}:Nb{sub 0.01}. For undoped {beta}-In{sub 2}S{sub 3}, PC and PL measurements are used to characterize defect transitions below band gap. The above band-edge transitions of undoped {beta}-In{sub 2}S{sub 3} have also been evaluated using PL, PC, and SPR measurements. For the evaluation of Nb-doped {beta}-In{sub 2}S{sub 3}, an intermediate band with energy of {approx}0.4 eV below the conduction band edge has been detected in the TR measurements in both {beta}-In{sub 2}S{sub 3}:Nb{sub 0.005} and {beta}-In{sub 2}S{sub 3}:Nb{sub 0.01}. The photo V-I measurements also verified that the photoelectric-conversion efficiency would be enhanced in the {beta}-In{sub 2}S{sub 3} with higher niobium content. Based on the experimental analyses, the optical behavior of the defects, surface states, and IB (formed by Nb) in the In

  11. Alternative structure of TiO2 with higher energy valence band edge

    Science.gov (United States)

    Coh, Sinisa; Yu, Peter Y.; Aoki, Yuta; Saito, Susumu; Louie, Steven G.; Cohen, Marvin L.

    2017-02-01

    We propose an alternative structure of TiO2 anatase that has a higher energy oxygen p -like valence band maximum than pristine TiO2 anatase and thus has a much better alignment with the water splitting levels. This alternative structure is unique when considering a large subspace of possible structural distortions of TiO2 anatase. We propose two routes towards this state and argue that one of them might have been realized in the recently discovered so-called black TiO2.

  12. n-GaAs Band-Edge Repositioning by Modification with Metalloporphyrin/Polysiloxane Matrices

    Directory of Open Access Journals (Sweden)

    Hikmat S. Hilal

    2003-01-01

    system was annealed under nitrogen and used for photoelectrochemical study in water/LiCIO4/Fe(CN63-/Fe(CN64− system. The results indicated a positive shift in the value of the flat-band potential of the semiconductor due to MnP. This was manifested by shifting the values of the dark-current onset potential and the photo-current open-circuit potential towards more positive values. These findings are potentially valuable in future applications of solar energy in hydrogen and oxygen production from water.

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

    Science.gov (United States)

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

    2017-05-09

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

  14. Electrically Conductive Photopatternable Silver Paste for High-Frequency Ring Resonator and Band-Pass Filter

    Science.gov (United States)

    Umarji, Govind; Qureshi, Nilam; Gosavi, Suresh; Mulik, Uttam; Kulkarni, Atul; Kim, Taesung; Amalnerkar, Dinesh

    2017-02-01

    In conventional thick-film technology, there are often problems associated with poor edges, rough surfaces, and reproducibility due to process limitations, especially for high-frequency applications. These difficulties can be circumvented by using thin-film technology, but process cost and complexity remain major concerns. In this context, photopatternable thick-film technology can offer a viable alternative due to its Newtonian rheology, which can facilitate formation of the required sharp edges. We present herein a unique attempt to formulate a photopatternable silver paste with organic (photosensitive polymer) to inorganic (silver and glass) ratio of 30:70, developed in-house by us for fabrication of thick-film-based ring resonator and band-pass filter components. The ring resonator and band-pass component structures were realized by exposing screen-printed film to ultraviolet light at wavelength of 315 nm to 400 nm for 30 s to crosslink the photosensitive polymer. The pattern was subsequently developed using 1% sodium carbonate aqueous solution. For comparison, conventional silver and silver-palladium thick films were produced using in-house formulations. The surface topology and microstructural features were examined by stereomicroscopy and scanning electron microscopy. The smoothness and edge definition of the film were assessed by profilometry. The resistivity of the samples was observed and remained in the range from 3.4 μΩ cm to 3.6 μΩ cm. The electrical properties were compared by measuring the insertion loss characteristics. The results revealed that the ring resonator fabricated using the photopatternable silver paste exhibited better high-frequency properties compared with components based on conventional silver or silver-palladium paste, especially in terms of the resonant frequency of 10.1 GHz (versus 10 GHz designed) with bandwidth of 80 MHz. Additionally, the band-pass filter fabricated using the photopatternable silver paste displayed better

  15. Conduction band offset determination between strained CdSe and ZnSe layers using DLTS

    Science.gov (United States)

    Rangel-Kuoppa, Victor-Tapio

    2013-12-01

    The conduction band offset between strained CdSe layers embedded in unintentionally n-type doped ZnSe is measured and reported. Two samples, consisting of thirty Ultra Thin Quantum Wells (UTQWs) of CdSe embedded in ZnSe, grown by Atomic Layer Epitaxy, are used for this study. The thicknesses of the UTQWs are one and three monolayers (MLs) in each sample, respectively. As expected, the sample with one ML UTQWs does not show any energy level in the UTQWs due to the small thickness of the UTQWs, while the thickness of the sample with 3 ML UTQWs is large enough to form an energy level inside the UTQWs. This energy level appears as a majority trap with an activation energy of 223.58 ± 9.54 meV. This corresponds to UTQWs with barrier heights (the conduction band offset) between 742 meV and 784 meV. These values suggest that the band gap misfit between strained CdSe and ZnSe is around 70.5 to 74 % in the conduction band.

  16. Conduction band offset determination between strained CdSe and ZnSe layers using DLTS

    Energy Technology Data Exchange (ETDEWEB)

    Rangel-Kuoppa, Victor-Tapio [Institute of Semiconductor and Solid State Physics, Johannes Kepler Universität, A-4040 Linz (Austria)

    2013-12-04

    The conduction band offset between strained CdSe layers embedded in unintentionally n-type doped ZnSe is measured and reported. Two samples, consisting of thirty Ultra Thin Quantum Wells (UTQWs) of CdSe embedded in ZnSe, grown by Atomic Layer Epitaxy, are used for this study. The thicknesses of the UTQWs are one and three monolayers (MLs) in each sample, respectively. As expected, the sample with one ML UTQWs does not show any energy level in the UTQWs due to the small thickness of the UTQWs, while the thickness of the sample with 3 ML UTQWs is large enough to form an energy level inside the UTQWs. This energy level appears as a majority trap with an activation energy of 223.58 ± 9.54 meV. This corresponds to UTQWs with barrier heights (the conduction band offset) between 742 meV and 784 meV. These values suggest that the band gap misfit between strained CdSe and ZnSe is around 70.5 to 74 % in the conduction band.

  17. Device Physics Analysis of Parasitic Conduction Band Barrier Formation in SiGe HBTs

    Science.gov (United States)

    Roenker, K. P.; Alterovitz, S. A.

    2000-01-01

    This paper presents a physics-based model describing the current-induced formation of a parasitic barrier in the conduction band at the base collector heterojunction in npn SiGe heterojunction bipolar transistors (HBTs). Due to the valence band discontinuity DELTA E(sub v), hole injection into the collector at the onset of base pushout is impeded, which gives rise to formation of a barrier to electron transport which degrades the device's high frequency performance. In this paper, we present results from an analytical model for the height of the barrier calculated from the device's structure as a function of the collector junction bias and collector current density.

  18. Transparent Conducting Oxides for Photovoltaics: Manipulation of Fermi Level, Work Function and Energy Band Alignment

    Directory of Open Access Journals (Sweden)

    Diana E. Proffit

    2010-11-01

    Full Text Available Doping limits, band gaps, work functions and energy band alignments of undoped and donor-doped transparent conducting oxides Zn0, In2O3, and SnO2 as accessed by X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS are summarized and compared. The presented collection provides an extensive data set of technologically relevant electronic properties of photovoltaic transparent electrode materials and illustrates how these relate to the underlying defect chemistry, the dependence of surface dipoles on crystallographic orientation and/or surface termination, and Fermi level pinning.

  19. Exponential tails near the band edges of a one-dimensional disordered exciton system in the Coherent Potential Approximation

    Science.gov (United States)

    Boukahil, Abdelkrim; Zettili, Nouredine; Huber, David

    2012-02-01

    We report the results of studies of the tails near the band edges of a one-dimensional Frenkel exciton system in the Coherent Potential Approximation (CPA). A Gaussian distribution of the transition frequencies with rms width σ (0.1 <=σ<= 2.0) is used. We found that the tails obey two different exponential power laws depending on the value of σ. In the weak disorder limit 0.1 <=σ< 0.5, the tails of the absorption line shape and the density of states behave like exp(-k|E|^3/2 / 2̂), and in the strong disorder limit,0.5 < σ<= 2.0, the tails behave like exp(-|E|^2 / 2̂). In the weak disorder limit, our CPA results are in excellent agreement with previous investigations.

  20. A short course on topological insulators band structure and edge states in one and two dimensions

    CERN Document Server

    Asbóth, János K; Pályi, András

    2016-01-01

    This course-based primer provides newcomers to the field with a concise introduction to some of the core topics in the emerging field of topological insulators. The aim is to provide a basic understanding of edge states, bulk topological invariants, and of the bulk--boundary correspondence with as simple mathematical tools as possible. The present approach uses noninteracting lattice models of topological insulators, building gradually on these to arrive from the simplest one-dimensional case (the Su-Schrieffer-Heeger model for polyacetylene) to two-dimensional time-reversal invariant topological insulators (the Bernevig-Hughes-Zhang model for HgTe). In each case the discussion of simple toy models is followed by the formulation of the general arguments regarding topological insulators. The only prerequisite for the reader is a working knowledge in quantum mechanics, the relevant solid state physics background is provided as part of this self-contained text, which is complemented by end-of-chapter problems.

  1. Transition from spin accumulation into interface states to spin injection in silicon and germanium conduction bands

    Science.gov (United States)

    Jain, Abhinav; Rojas-Sanchez, Juan-Carlos; Cubukcu, Murat; Peiro, Julian; Le Breton, Jean-Christophe; Vergnaud, Céline; Augendre, Emmanuel; Vila, Laurent; Attané, Jean-Philippe; Gambarelli, Serge; Jaffrès, Henri; George, Jean-Marie; Jamet, Matthieu

    2013-04-01

    Electrical spin injection into semiconductors paves the way for exploring new phenomena in the area of spin physics and new generations of spintronic devices. However the exact role of interface states in the electrical spin injection mechanism from a magnetic tunnel junction into a semiconductor is still under debate. Here we demonstrate a clear transition from spin accumulation into interface states to spin injection in the conduction band of n-Si and n-Ge using a CoFeB/MgO tunnel contact. We observe spin signal amplification at low temperature due to spin accumulation into interface states followed by a clear transition towards spin injection in the conduction band from approximately 150 K up to room temperature. In this regime, the spin signal is reduced down to a value compatible with the standard spin diffusion model. More interestingly, in the case of germanium, we demonstrate a significant modulation of the spin signal by applying a back-gate voltage to the conduction channel. We also observe the inverse spin Hall effect in Ge by spin pumping from the CoFeB electrode. Both observations are consistent with spin accumulation in the Ge conduction band.

  2. Coastline change mapping using a spectral band method and Sobel edge operator

    Science.gov (United States)

    Al-Mansoori, Saeed; Al-Marzouqi, Fatima

    2016-10-01

    Coastline extraction has become an essential activity in wake of the natural disasters taking place in some regions such as tsunami, flooding etc. Salient feature of such catastrophes is lack of reaction time available for combating emergency, thus it is the endeavor of any country to develop constant monitoring mechanism of shorelines. This is a challenging task because of the magnitude of changes taking place to the coastline regularly. Previous research findings highlight a need of formulating automation driven methodology for timely and accurate detection of alterations in the coastline impacting sustainability of mankind operating in the coastal zone. In this study, we propose a new approach for automatic extraction of the coastline using remote sensing data. This approach is composed of three main stages. Firstly, classifying pixels of the image into two categories i.e. land and water body by applying two normalized difference indices i.e. Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI). Then, the process of binary conversion of classified image takes place using a local threshold method. Finally, the coastline is extracted by applying Sobel edge operator with a pair of (3×3) kernels. The approach is tested using 2.5m DubaiSat-1 (DS1) and DubaiSat-2 (DS2) images captured to detect and monitor the changes occurring along Dubai coastal zone within a period of six years from 2009 till 2015. Experimental results prove that the approach is capable of extracting the coastlines from DS1 and DS2 images with moderate human interaction. The results of the study show an increase of 6% in Dubai shoreline resulting on account of numerous man-made infrastructure development projects in tourism and allied sectors.

  3. Visualizing band offsets and edge states in bilayer–monolayer transition metal dichalcogenides lateral heterojunction

    Science.gov (United States)

    Zhang, Chendong; Chen, Yuxuan; Huang, Jing-Kai; Wu, Xianxin; Li, Lain-Jong; Yao, Wang; Tersoff, Jerry; Shih, Chih-Kang

    2016-01-01

    Semiconductor heterostructures are fundamental building blocks for many important device applications. The emergence of two-dimensional semiconductors opens up a new realm for creating heterostructures. As the bandgaps of transition metal dichalcogenides thin films have sensitive layer dependence, it is natural to create lateral heterojunctions (HJs) using the same materials with different thicknesses. Here we show the real space image of electronic structures across the bilayer–monolayer interface in MoSe2 and WSe2, using scanning tunnelling microscopy and spectroscopy. Most bilayer–monolayer HJs are found to have a zig-zag-orientated interface, and the band alignment of such atomically sharp HJs is of type-I with a well-defined interface mode that acts as a narrower-gap quantum wire. The ability to utilize such commonly existing thickness terraces as lateral HJs is a crucial addition to the tool set for device applications based on atomically thin transition metal dichalcogenides, with the advantage of easy and flexible implementation. PMID:26778119

  4. Visualizing band offsets and edge states in bilayer-monolayer transition metal dichalcogenides lateral heterojunction

    Science.gov (United States)

    Zhang, Chendong; Chen, Yuxuan; Huang, Jing-Kai; Wu, Xianxin; Li, Lain-Jong; Yao, Wang; Tersoff, Jerry; Shih, Chih-Kang

    2016-01-01

    Semiconductor heterostructures are fundamental building blocks for many important device applications. The emergence of two-dimensional semiconductors opens up a new realm for creating heterostructures. As the bandgaps of transition metal dichalcogenides thin films have sensitive layer dependence, it is natural to create lateral heterojunctions (HJs) using the same materials with different thicknesses. Here we show the real space image of electronic structures across the bilayer-monolayer interface in MoSe2 and WSe2, using scanning tunnelling microscopy and spectroscopy. Most bilayer-monolayer HJs are found to have a zig-zag-orientated interface, and the band alignment of such atomically sharp HJs is of type-I with a well-defined interface mode that acts as a narrower-gap quantum wire. The ability to utilize such commonly existing thickness terraces as lateral HJs is a crucial addition to the tool set for device applications based on atomically thin transition metal dichalcogenides, with the advantage of easy and flexible implementation.

  5. Visualizing band offsets and edge states in bilayer–monolayer transition metal dichalcogenides lateral heterojunction

    KAUST Repository

    Zhang, Chendong

    2016-01-18

    Semiconductor heterostructures are fundamental building blocks for many important device applications. The emergence of two-dimensional semiconductors opens up a new realm for creating heterostructures. As the bandgaps of transition metal dichalcogenides thin films have sensitive layer dependence, it is natural to create lateral heterojunctions (HJs) using the same materials with different thicknesses. Here we show the real space image of electronic structures across the bilayer–monolayer interface in MoSe2 and WSe2, using scanning tunnelling microscopy and spectroscopy. Most bilayer–monolayer HJs are found to have a zig-zag-orientated interface, and the band alignment of such atomically sharp HJs is of type-I with a well-defined interface mode that acts as a narrower-gap quantum wire. The ability to utilize such commonly existing thickness terraces as lateral HJs is a crucial addition to the tool set for device applications based on atomically thin transition metal dichalcogenides, with the advantage of easy and flexible implementation.

  6. Unusual Changes in Electronic Band-Edge Energies of the Nanostructured Transparent n-Type Semiconductor Zr-Doped Anatase TiO2 (Ti1-xZrxO2; x < 0.3).

    Science.gov (United States)

    Mieritz, Daniel G; Renaud, Adèle; Seo, Dong-Kyun

    2016-07-05

    By the establishment of highly controllable synthetic routes, electronic band-edge energies of the n-type transparent semiconductor Zr-doped anatase TiO2 have been studied holistically for the first time up to 30 atom % Zr, employing powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen gas sorption measurements, UV/vis spectroscopies, and Mott-Schottky measurements. The materials were produced through a sol-gel synthetic procedure that ensures good compositional homogeneity of the materials, while introducing nanoporosity in the structure, by achieving a mild calcination condition. Vegard's law was discovered among the homogeneous samples, and correlations were established between the chemical compositions and optical and electronic properties of the materials. Up to 20% Zr doping, the optical energy gap increases to 3.29 eV (vs 3.19 eV for TiO2), and the absolute conduction band-edge energy increases to -3.90 eV (vs -4.14 eV). The energy changes of the conduction band edge are more drastic than what is expected from the average electronegativities of the compounds, which may be due to the unnatural coordination environment around Zr in the anatase phase.

  7. Study on Band Structure of YbB6 and Analysis of Its Optical Conductivity Spectrum

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The electronic structure of YbB6 crystal was studied by means of density functional (GGA+U) method.The calculations were performed by FLAPW method.The high accurate band structure was achieved.The correlation between the feature of the band structure and the Yb-B6 bonding in YbB6 was analyzed.On this basis, some optical constants of YbB6 such as reflectivity, dielectric function, optical conductivity, and energy-loss function were calculated.The results are in good agreement with the experiments.The real part of the optical conductivity spectrum and the energy-loss function spectrum were analyzed in detail.The assignments of the spectra were carried out to correlate the spectral peaks with the interband electronic transitions, which justify the reasonable part of previous empirical assignments and renew the missed or incorrect ones.

  8. Banding and electronic structures of metal azides——Sensitivity and conductivity

    Institute of Scientific and Technical Information of China (English)

    肖鹤鸣; 李永富

    1995-01-01

    By using both DV-Xα and EH-CO methods, the calculation studies of the structure-property relationships of a series of metal azides, of their clusters’ electronic structures in ground and excited states, of their systems with cation vacancy and the doped Pb(N3)2, as well as their crystal band structures have been conducted. The results show that the sensitivity of ionic-type metal azides varies with the degree of difficulty of electronic transition of the losing charge on N3. A metal azide with cation vacancies has a greater sensitivity than the perfect one. When doped with monovalent metal ions, lead azide’s sensitivity increased; when with trivalent ones, its sensitivity decreased; when with divalent ones, little of it changed. Compared with heavy metal azides. an alkali metal azide has a larger band gap, a smaller band width and a greater transition energy of frontier electron with a smaller amount of losing charge on N3, and thus has lower sensitivity and conductivity than heavy metal azides.

  9. Controlling the conduction band offset for highly efficient ZnO nanorods based perovskite solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Juan; Shi, Jiangjian; Li, Dongmei; Luo, Yanhong; Meng, Qingbo, E-mail: qbmeng@iphy.ac.cn [Key Laboratory for Renewable Energy, Chinese Academy of Sciences, Beijing 100190 (China); Beijing Key Laboratory for New Energy Materials and Devices, Beijing 100190 (China); Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2015-08-17

    The mechanism of charge recombination at the interface of n-type electron transport layer (n-ETL) and perovskite absorber on the carrier properties in the perovskite solar cell is theoretically studied. By solving the one dimensional diffusion equation with different boundary conditions, it reveals that the interface charge recombination in the perovskite solar cell can be suppressed by adjusting the conduction band offset (ΔE{sub C}) at ZnO ETL/perovskite absorber interface, thus leading to improvements in cell performance. Furthermore, Mg doped ZnO nanorods ETL has been designed to control the energy band levels. By optimizing the doping amount of Mg, the conduction band minimum of the Mg doped ZnO ETL has been raised up by 0.29 eV and a positive ΔE{sub C} of about 0.1 eV is obtained. The photovoltage of the cell is thus significantly increased due to the relatively low charge recombination.

  10. Electrons in feldspar II: A consideration of the influence of conduction band-tail states on luminescence processes

    DEFF Research Database (Denmark)

    Poolton, H.R.J.; Ozanyan, K.B.; Wallinga, J.

    2002-01-01

    Most natural feldspars contain many charged impurities, and display a range of bond angles, distributed about the ideal. These effects can lead to complications in the structure of the conduction band, giving rise to a tail of energy states (below the high-mobility conduction band) through which ...

  11. Conduction band energy level control of titanium dioxide: toward an efficient visible-light-sensitive photocatalyst.

    Science.gov (United States)

    Yu, Huogen; Irie, Hiroshi; Hashimoto, Kazuhito

    2010-05-26

    Through the use of a strategy that involves narrowing the TiO(2) band gap by shifting its conduction band positively and utilizing the catalytic activity of photoproduced Cu(I) for oxygen reduction, a novel visible-light-sensitive TiO(2) photocatalyst, Cu(II)-grafted Ti(1-3x)W(x)Ga(2x)O(2), was designed and synthesized. The Cu(II)/Ti(1-3x)W(x)Ga(2x)O(2) photocatalyst produced high activity under visible-light irradiation. In fact, it decomposed 2-propanol to CO(2) via acetone under visible light (>400 nm) with a high quantum efficiency of 13%. The turnover number for this reaction exceeded 22, indicating that it functioned catalytically.

  12. Optical conductivity and resistivity in the two-band Emery model

    Science.gov (United States)

    Minh-Tien, Tran

    1994-01-01

    The temperature- and frequency-dependent conductivity due to the scattering of oxygen holes by antiferromagnetic spin fluctuations of the copper spins in the two-band Emergy model is calculated. Using the dynamic spin susceptibility obtained in the mean-field Schwinger boson approach, the resistivity obeys a near linear temperature dependence at high temperatures, whereas at low temperatures a quadratic behaviour holds. At the same time, the optical conductivity contains the Drude peak around zero frequency, whereas the scattering rate of quasiparticle appears to be proportional to frequency. Our results are essentially in agreement with experiments, at least qualitatively, and support the conclusion that the normal-state basal-plane resistivity and optical conductivity of high- Tc superconductors may be explained by two-dimensional spin-fluctuation scattering in the Fermi-liquid picture.

  13. All-printable band-edge modulated ZnO nanowire photodetectors with ultra-high detectivity.

    Science.gov (United States)

    Liu, Xi; Gu, Leilei; Zhang, Qianpeng; Wu, Jiyuan; Long, Yunze; Fan, Zhiyong

    2014-06-05

    High-performance photodetectors are critical for high-speed optical communication and environmental sensing, and flexible photodetectors can be used for a wide range of portable or wearable applications. Here we demonstrate the all-printable fabrication of polycrystalline nanowire-based high-performance photodetectors on flexible substrates. Systematic investigations have shown their ultra-high photoconductive gain, responsivity and detectivity up to 3.3 × 10(17) Jones. Further analysis shows that their high performance originates from the unique band-edge modulation along the nanowire axial direction, where the existence of Schottky barriers in series leads to highly suppressed dark current of the device and also gives rise to fast photoelectric response to low-intensity optical signal owing to barrier height modulation. The discovered rationale in this work can be utilized as guideline to design high-performance photodetectors with other nanomaterial systems. The developed fabrication scheme opens up possibility for future flexible and high-performance integrated optoelectronic sensor circuitry.

  14. Role of band states and trap states in the electrical properties of organic semiconductors: Hopping versus mobility edge model

    KAUST Repository

    Mehraeen, Shafigh

    2013-05-01

    We compare the merits of a hopping model and a mobility edge model in the description of the effect of charge-carrier concentration on the electrical conductivity, carrier mobility, and Fermi energy of organic semiconductors. We consider the case of a composite electronic density of states (DOS) that consists of a superposition of a Gaussian DOS and an exponential DOS. Using kinetic Monte Carlo simulations, we apply the two models in order to interpret the recent experimental data reported for n-doped C60 films. While both models are capable of reproducing the experimental data very well and yield qualitatively similar characteristic parameters for the density of states, some discrepancies are found at the quantitative level. © 2013 American Physical Society.

  15. Spin-Polarized Electron Emission from Superlattices with Zero Conduction Band Offset

    Energy Technology Data Exchange (ETDEWEB)

    Clendenin, James E

    1998-11-09

    Electron spin polarization as high as 86% has been reproducibly obtained from strained Al{sub x}In{sub y}Ga{sub 1-x-y}As/GaAs superlattice with minimal conduction band offset at the heterointerfaces. The modulation doping of the SL provides high polarization and high quantum yield at the polarization maximum. The position of the maximum can be easily tuned to an excitation wavelength by choice of the SL composition. Further improvement of the emitter parameters can be expected with additional optimization of the SL structure parameters.

  16. Discovery of high-performance low-cost n-type Mg3Sb2-based thermoelectric materials with multi-valley conduction bands

    Science.gov (United States)

    Zhang, Jiawei; Song, Lirong; Pedersen, Steffen Hindborg; Yin, Hao; Hung, Le Thanh; Iversen, Bo Brummerstedt

    2017-01-01

    Widespread application of thermoelectric devices for waste heat recovery requires low-cost high-performance materials. The currently available n-type thermoelectric materials are limited either by their low efficiencies or by being based on expensive, scarce or toxic elements. Here we report a low-cost n-type material, Te-doped Mg3Sb1.5Bi0.5, that exhibits a very high figure of merit zT ranging from 0.56 to 1.65 at 300-725 K. Using combined theoretical prediction and experimental validation, we show that the high thermoelectric performance originates from the significantly enhanced power factor because of the multi-valley band behaviour dominated by a unique near-edge conduction band with a sixfold valley degeneracy. This makes Te-doped Mg3Sb1.5Bi0.5 a promising candidate for the low- and intermediate-temperature thermoelectric applications.

  17. Analyses of Effects of Cutting Parameters on Cutting Edge Temperature Using Inverse Heat Conduction Technique

    Directory of Open Access Journals (Sweden)

    Marcelo Ribeiro dos Santos

    2014-01-01

    Full Text Available During machining energy is transformed into heat due to plastic deformation of the workpiece surface and friction between tool and workpiece. High temperatures are generated in the region of the cutting edge, which have a very important influence on wear rate of the cutting tool and on tool life. This work proposes the estimation of heat flux at the chip-tool interface using inverse techniques. Factors which influence the temperature distribution at the AISI M32C high speed steel tool rake face during machining of a ABNT 12L14 steel workpiece were also investigated. The temperature distribution was predicted using finite volume elements. A transient 3D numerical code using irregular and nonstaggered mesh was developed to solve the nonlinear heat diffusion equation. To validate the software, experimental tests were made. The inverse problem was solved using the function specification method. Heat fluxes at the tool-workpiece interface were estimated using inverse problems techniques and experimental temperatures. Tests were performed to study the effect of cutting parameters on cutting edge temperature. The results were compared with those of the tool-work thermocouple technique and a fair agreement was obtained.

  18. Improved characteristics of near-band-edge and deep-level emissions from ZnO nanorod arrays by atomic-layer-deposited Al2O3 and ZnO shell layers

    Directory of Open Access Journals (Sweden)

    He Jr-Hau

    2011-01-01

    Full Text Available Abstract We report on the characteristics of near-band-edge (NBE emission and deep-level band from ZnO/Al2O3 and ZnO/ZnO core-shell nanorod arrays (NRAs. Vertically aligned ZnO NRAs were synthesized by an aqueous chemical method, and the Al2O3 and ZnO shell layers were prepared by the highly conformal atomic layer deposition technique. Photoluminescence measurements revealed that the deep-level band was suppressed and the NBE emission was significantly enhanced after the deposition of Al2O3 and ZnO shells, which are attributed to the decrease in oxygen interstitials at the surface and the reduction in surface band bending of ZnO core, respectively. The shift of deep-level emissions from the ZnO/ZnO core-shell NRAs was observed for the first time. Owing to the presence of the ZnO shell layer, the yellow band associated with the oxygen interstitials inside the ZnO core would be prevailed over by the green luminescence, which originates from the recombination of the electrons in the conduction band with the holes trapped by the oxygen vacancies in the ZnO shell. PACS 68.65.Ac; 71.35.-y; 78.45.+h; 78.55.-m; 78.55.Et; 78.67.Hc; 81.16.Be; 85.60.Jb.

  19. Determination of band edge energies for transparent nanocrystalline TiO{sub 2}-CdS sandwich electrodes prepared by electrodeposition

    Energy Technology Data Exchange (ETDEWEB)

    Flood, Robert; Enright, Brendan; Allen, Michelle; Barry, Sarah; Dalton, Ann; Doyle, Hugh; Tynan, Deidre; Fitzmaurice, Donald [Department of Chemistry, University College Dublin, Dublin (Ireland)

    1995-11-28

    We describe preparation of transparent nanocrystalline semiconductor sandwich electrodes. Specifically, TiO{sub 2}-CdS and CdS-TiO{sub 2} sandwich electrodes have been prepared by electrodeposition of CdS on TiO{sub 2} and TiO{sub 2} on CdS, respectively. Also described are the application of optoelectrochemical techniques for determination of the energy of the conduction band edge at the semiconductor{sub l}iquid electrolyte solution interface (V{sub cb}). Specifically, V{sub cb} has been determined for each semiconductor in nanocrystalline TiO{sub 2}, CdS, TiO{sub 2}-CdS and CdS-TiO{sub 2} electrodes. For TiO{sub 2} and CdS electrodes, V{sub cb} is -0.37 V (SCE) and -0.7 V, respectively, in aqueous solution at pH 2.0. Under similar conditions V{sub cb} for TiO{sub 2} and CdS is -0.47 V and -0.4 V, respectively, in the corresponding TiO{sub 2}-CdS sandwich electrode. Using the results of these and similar experiments, it has been possible to prepare energy level diagrams for nanocrystalline semiconductor sandwich electrodes. Implications for potential applications of these electrodes, particularly in regenerative photoelectrochemical cells, are considered

  20. Observation of electron excitation into silicon conduction band by slow-ion surface neutralization

    CERN Document Server

    Shchemelinin, S

    2016-01-01

    Bare reverse biased silicon photodiodes were exposed to 3eV He+, Ne+, Ar+, N2+, N+ and H2O+ ions. In all cases an increase of the reverse current through the diode was observed. This effect and its dependence on the ionization energy of the incident ions and on other factors are qualitatively explained in the framework of Auger-type surface neutralization theory. Amplification of the ion-induced charge was observed with an avalanche photodiode under high applied bias. The observed effect can be considered as ion-induced internal potential electron emission into the conduction band of silicon. To the best of our knowledge, no experimental evidence of such effect was previously reported. Possible applications are discussed.

  1. A simple model for conduction band states of nitride-based double heteroestructures

    Energy Technology Data Exchange (ETDEWEB)

    Gaggero-Sager, L M; Mora-Ramos, M E, E-mail: lgaggero@uaem.m [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico)

    2009-05-01

    In this work we propose an analytical expression for the approximate modeling of the potential energy function describing conduction band bending in III-V nitride quantum wells. It is an alternative approach to the self-consistent Poisson-Schoedinger calculation. The model considers the influence of the many electron system and the built-in electric field inside the well. Hartree and exchange contributions are included along the lines of a local-density Thomas-Fermi-based theory. The effects due to the modulated doping in the barriers is also considered. We report the calculation of the energy spectrum as a function of several input parameters: alloy composition in the barriers, barrier doping concentration, and quantum well width. Our results could be of usefulness in the study of optoelectronic properties in this kind of systems.

  2. Bias dependent subband edges and the 0.7 conductance anomaly

    DEFF Research Database (Denmark)

    Kristensen, Anders; Bruus, Henrik

    2002-01-01

    The 0.7 (2e(2)/h) conductance anomaly is studied in strongly confined, etched GaAs/GaAlAs quantum point contacts by measuring the differential conductance G as a function of source-drain bias V-sd and gate-source bias V-gs as well as a function of temperature. In the V-gs - V-sd plane we use...

  3. Band-edge electronic structure of β-In2S3: the role of s or p orbitals of atoms at different lattice positions.

    Science.gov (United States)

    Zhao, Zongyan; Cao, Yuechan; Yi, Juan; He, Xijia; Ma, Chenshuo; Qiu, Jianbei

    2012-04-23

    As a promising solar-energy material, the electronic structure and optical properties of Beta phase indium sulfide (β-In(2)S(3)) are still not thoroughly understood. This paper devotes to solve these issues using density functional theory calculations. β-In(2)S(3) is found to be an indirect band gap semiconductor. The roles of its atoms at different lattice positions are not exactly identical because of the unique crystal structure. Additonally, a significant phenomenon of optical anisotropy was observed near the absorption edge. Owing to the low coordination numbers of the In3 and S2 atoms, the corresponding In3-5s states and S2-3p states are crucial for the composition of the band-edge electronic structure, leading to special optical properties and excellent optoelectronic performances.

  4. Label-free antibody detection using band edge fringes in SOI planar photonic crystal waveguides in the slow-light regime.

    Science.gov (United States)

    García-Rupérez, Jaime; Toccafondo, Veronica; Bañuls, María José; Castelló, Javier García; Griol, Amadeu; Peransi-Llopis, Sergio; Maquieira, Ángel

    2010-11-08

    We report experimental results of label-free anti-bovine serum albumin (anti-BSA) antibody detection using a SOI planar photonic crystal waveguide previously bio-functionalized with complementary BSA antigen probes. Sharp fringes appearing in the slow-light regime near the edge of the guided band are used to perform the sensing. We have modeled the presence of these band edge fringes and demonstrated the possibility of using them for sensing purposes by performing refractive index variations detection, achieving a sensitivity of 174.8 nm/RIU. Then, label-free anti-BSA biosensing experiments have been carried out, estimating a surface mass density detection limit below 2.1 pg/mm2 and a total mass detection limit below 0.2 fg.

  5. Fluctuation conductivity in two-band superconductor SmFeAsO0.8F0.2

    Directory of Open Access Journals (Sweden)

    Askerzade I.N.

    2015-09-01

    Full Text Available In this study we have calculated the fluctuation conductivity near critical temperature of SmFeAsO0.8F0.2 superconductor using two-band Ginzburg-Landau theory. It was illustrated that in the absence of external magnetic field, the two-band model reduced to a single effective band theory with modified temperature dependences. The calculations revealed three-dimensional character of fluctuations of conductivity in the new Fe-based superconductor SmFeAsO0.8F0.2. It has been shown that such a model is in good agreement with experimental data for this compound.

  6. Enhanced p-type conductivity and band gap narrowing in heavily Al doped NiO thin films deposited by RF magnetron sputtering.

    Science.gov (United States)

    Nandy, S; Maiti, U N; Ghosh, C K; Chattopadhyay, K K

    2009-03-18

    Stoichiometric NiO, a Mott-Hubbard insulator at room temperature, shows p-type electrical conduction due to the introduction of Ni(2+) vacancies (V(Ni)('')) and self-doping of Ni(3+) ions in the presence of excess oxygen. The electrical conductivity of this important material is low and not sufficient for active device fabrication. Al doped NiO thin films were synthesized by radio frequency (RF) magnetron sputtering on glass substrates at a substrate temperature of 250 °C in an oxygen + argon atmosphere in order to enhance the p-type electrical conductivity. X-ray diffraction studies confirmed the correct phase formation and also oriented growth of NiO thin films. Al doping was confirmed by x-ray photoelectron spectroscopic studies. The structural, electrical and optical properties of the films were investigated as a function of Al doping (0-4 wt%) in the target. The room temperature electrical conductivity increased from 0.01-0.32 S cm (-1) for 0-4% Al doping. With increasing Al doping, above the Mott critical carrier density, energy band gap shrinkage was observed. This was explained by the shift of the band edges due to the existence of exchange and correlation energies amongst the electron-electron and hole-hole systems and also by the interaction between the impurity quasi-particle system.

  7. COMPARING BROAD-BAND AND RED EDGE-BASED SPECTRAL VEGETATION INDICES TO ESTIMATE NITROGEN CONCENTRATION OF CROPS USING CASI DATA

    Directory of Open Access Journals (Sweden)

    Y. Wang

    2016-06-01

    Full Text Available In recent decades, many spectral vegetation indices (SVIs have been proposed to estimate the leaf nitrogen concentration (LNC of crops. However, most of these indices were based on the field hyperspectral reflectance. To test whether they can be used in aerial remote platform effectively, in this work a comparison of the sensitivity between several broad-band and red edge-based SVIs to LNC is investigated over different crop types. By using data from experimental LNC values over 4 different crop types and image data acquired using the Compact Airborne Spectrographic Imager (CASI sensor, the extensive dataset allowed us to evaluate broad-band and red edge-based SVIs. The result indicated that NDVI performed the best among the selected SVIs while red edge-based SVIs didn’t show the potential for estimating the LNC based on the CASI data due to the spectral resolution. In order to search for the optimal SVIs, the band combination algorithm has been used in this work. The best linear correlation against the experimental LNC dataset was obtained by combining the 626.20nm and 569.00nm wavebands. These wavelengths correspond to the maximal chlorophyll absorption and reflection position region, respectively, and are known to be sensitive to the physiological status of the plant. Then this linear relationship was applied to the CASI image for generating an LNC map, which can guide farmers in the accurate application of their N fertilization strategies.

  8. Comparing Broad-Band and Red Edge-Based Spectral Vegetation Indices to Estimate Nitrogen Concentration of Crops Using Casi Data

    Science.gov (United States)

    Wang, Yanjie; Liao, Qinhong; Yang, Guijun; Feng, Haikuan; Yang, Xiaodong; Yue, Jibo

    2016-06-01

    In recent decades, many spectral vegetation indices (SVIs) have been proposed to estimate the leaf nitrogen concentration (LNC) of crops. However, most of these indices were based on the field hyperspectral reflectance. To test whether they can be used in aerial remote platform effectively, in this work a comparison of the sensitivity between several broad-band and red edge-based SVIs to LNC is investigated over different crop types. By using data from experimental LNC values over 4 different crop types and image data acquired using the Compact Airborne Spectrographic Imager (CASI) sensor, the extensive dataset allowed us to evaluate broad-band and red edge-based SVIs. The result indicated that NDVI performed the best among the selected SVIs while red edge-based SVIs didn't show the potential for estimating the LNC based on the CASI data due to the spectral resolution. In order to search for the optimal SVIs, the band combination algorithm has been used in this work. The best linear correlation against the experimental LNC dataset was obtained by combining the 626.20nm and 569.00nm wavebands. These wavelengths correspond to the maximal chlorophyll absorption and reflection position region, respectively, and are known to be sensitive to the physiological status of the plant. Then this linear relationship was applied to the CASI image for generating an LNC map, which can guide farmers in the accurate application of their N fertilization strategies.

  9. Interfacial band-edge engineered TiO2 protection layer on Cu2O photocathodes for efficient water reduction reaction

    Science.gov (United States)

    Choi, Jaesuk; Song, Jun Tae; Jang, Ho Seong; Choi, Min-Jae; Sim, Dong Min; Yim, Soonmin; Lim, Hunhee; Jung, Yeon Sik; Oh, Jihun

    2017-01-01

    Photoelectrochemical (PEC) water splitting has emerged as a potential pathway to produce sustainable and renewable chemical fuels. Here, we present a highly active Cu2O/TiO2 photocathode for H2 production by enhancing the interfacial band-edge energetics of the TiO2 layer, which is realized by controlling the fixed charge density of the TiO2 protection layer. The band-edge engineered Cu2O/TiO2 (where TiO2 was grown at 80 °C via atomic layer deposition) enhances the photocurrent density up to -2.04 mA/cm2 at 0 V vs. RHE under 1 sun illumination, corresponding to about a 1,200% enhancement compared to the photocurrent density of the photocathode protected with TiO2 grown at 150 °C. Moreover, band-edge engineering of the TiO2 protection layer prevents electron accumulation at the TiO2 layer and enhances both the Faraday efficiency and the stability for hydrogen production during the PEC water reduction reaction. This facile control over the TiO2/electrolyte interface will also provide new insight for designing highly efficient and stable protection layers for various other photoelectrodes such as Si, InP, and GaAs. [Figure not available: see fulltext.

  10. Thermally activated conductance of a silicon inversion layer by electrons excited above the mobility edge

    NARCIS (Netherlands)

    Niederer, H.H.J.M.; Mattey, A.P.M.; Sparnaay, M.J.

    1981-01-01

    The thermally activated conductivity sigma of an n-type inversion layer on a (100) oriented silicon surface and its derivative d sigma /dT were measured in the temperature range 1.4K-4.2K. Above T approximately=2.5K both the temperature dependence of (T/ sigma ) (d sigma /dT) and the relation betwee

  11. Polarization-induced electrical conductivity in ultra-wide band gap AlGaN alloys

    Science.gov (United States)

    Armstrong, Andrew M.; Allerman, Andrew A.

    2016-11-01

    Unintentionally doped (UID) AlGaN epilayers graded over Al compositions of 80%-90% and 80%-100% were grown by metal organic vapor phase epitaxy and were electrically characterized using contactless sheet resistance (Rsh) and capacitance-voltage (C-V) measurements. Strong electrical conductivity in the UID graded AlGaN epilayers resulted from polarization-induced doping and was verified by the low resistivity of 0.04 Ω cm for the AlGaN epilayer graded over 80%-100% Al mole fraction. A free electron concentration (n) of 4.8 × 1017 cm-3 was measured by C-V for Al compositions of 80%-100%. Average electron mobility ( μ ¯ ) was calculated from Rsh and n data for three ranges of Al composition grading, and it was found that UID AlGaN graded from 88%-96% had μ ¯ = 509 cm2/V s. The combination of very large band gap energy, high μ ¯ , and high n for UID graded AlGaN epilayers make them attractive as a building block for high voltage power electronic devices such as Schottky diodes and field effect transistors.

  12. Calculated effect of conduction-band offset on CuInSe{sub 2} solar-cell performance

    Energy Technology Data Exchange (ETDEWEB)

    Liu, X.; Sites, J.R. [Physics Department, Colorado State University, Fort Collins, Colorado 80523 (United States)

    1996-01-01

    The band diagram and resulting current-voltage curves for CuInSe{sub 2} solar cells are calculated as functions of conduction-band offset using ADEPT software with and without an indium-rich intermediate layer. In the absence of the intermediate layer, current-voltage curves for CdS/CuInSe{sub 2} solar cells show only a weak dependence on conduction-band offset over a wide range from approximately {minus}0.5 eV to 0.4 eV at room temperature. An indium rich {ital n}-type intermediate layer with 1.3 eV band gap and thickness smaller than the depletion width can increase the open-circuit voltage as much as 30{percent} at large positive band offsets. The highest efficiency, however, is increased by a more modest 6{percent}. Again the cell parameters are relatively flat, but over a somewhat narrower conduction-band offset range. {copyright} {ital 1996 American Institute of Physics.}

  13. THE BAND STRUCTURE AND WORK FUNCTION OF TRANSPARENT CONDUCTING ALUMINUM AND MANGANESE CO-DOPED ZINC OXIDE FILMS

    Institute of Scientific and Technical Information of China (English)

    H.T. Cao; Z.L. Pei; X.B. Zhang; J. Gong; C. Sun; L.S. Wen

    2005-01-01

    Al and Mn co-doped-ZnO films have been prepared at room temperature by DC reactive magnetron sputtering technique. The optical absorption coefficient, apparent and fundamental band gap, and work function of the films have been investigated using optical spectroscopy, band structure analyses and ultraviolet photoelectron spectroscopy (UPS). ZnO films have direct allowed transition band structure, which has been confirmed by the character of the optical absorption coefficient. The apparent band gap has been found directly proportional to N2/3, showing that the effect of Burstein-Moss shift on the band gap variations dominates over the many-body effect. With only standard cleaning protocols, the work function of ZnO: (Al, Mn) and ZnO: Al films have been measured to be 4.26 and 4.21eV, respectively. The incorporation of Mn element into the matrix of ZnO, as a relatively deep donor, can remove some electrons from the conduction band and deplete the density of occupied states at the Fermi energy, which causes a loss in measured photoemission intensity and an increase in the surface work function. Based on the band gap and work function results, the energy band diagram of the ZnO: (Al, Mn)film near its surface is also given.

  14. Determination of conduction and valence band electronic structure of anatase and rutile TiO2

    Indian Academy of Sciences (India)

    Jakub Szlachetko; Katarzyna Michalow-Mauke; Maarten Nachtegaal; Jacinto Sá

    2014-03-01

    Electronic structures of rutile and anatase polymorph of TiO2 were determined by resonant inelastic X-ray scattering measurements and FEFF9.0 calculations. Difference between crystalline structures led to shifts in the rutile Ti -band to lower energy with respect to anatase, i.e., decrease in band gap. Anatase possesses localized states located in the band gap where electrons can be trapped, which are almost absent in the rutile structure. This could well explain the reported longer lifetimes in anatase. It was revealed that HR-XAS is insufficient to study in-depth unoccupied states of investigated materials because it overlooks the shallow traps.

  15. Gate-last TiN/HfO2 band edge effective work functions using low-temperature anneals and selective cladding to control interface composition

    KAUST Repository

    Hinkle, C. L.

    2012-04-09

    Silicon N-metal-oxide-semiconductor (NMOS) and P-metal-oxide-semiconductor (PMOS) band edge effective work functions and the correspondingly low threshold voltages (Vt) are demonstrated using standard fab materials and processes in a gate-last scheme employing low-temperature anneals and selective cladding layers. Al diffusion from the cladding to the TiN/HfO2interface during forming gas anneal together with low O concentration in the TiN enables low NMOS Vt. The use of non-migrating W cladding along with experimentally detected N-induced dipoles, produced by increased oxygen in the TiN, facilitates low PMOS Vt.

  16. A mourning dove banding project conducted in Adams County, Illinois, in 1963

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This study is a description of a Mourning Dove banding project carried out by personnel of the Gardner Unit of the Mark Twain National Wildlife Refuge. The project...

  17. Near Band Edge Emission by Free Exciton Decay and Intrinsic Ferromagnetic Ordering of Cu-Doped SnO2 Hollow Nanofibers.

    Science.gov (United States)

    Mohanapriya, P; Jaya, N Victor

    2015-03-01

    High quality nanocrystalline pristine and Cu-doped SnO2 hollow nanofibers were successfully prepared through simple and effective electrospinning technique. Nanofibers calcined at 600 °C for 3 h were characterized with different analytical techniques such as X-ray diffraction (XRD), Transmission electron Microscope (TEM) and Vibrating sample magnetometer (VSM). Observed TEM images and XRD patterns were corroborate to the formation of tetragonal crystalline SnO2 hollow nanofibers with rutile phase. Excellent optical behaviour was observed for Cu-doped SnO2. Highly intense near band edge emission at 3.58 eV for Cu-doped SnO2 evidences the free exciton decay process in the hollow nanofibers. For the first time we have reported here the near band edge PL emission in Cu-doped SnO2 tubular hollow nanostructure. This study substantiates that material potential for UV-lasing application. In addition to the above, magnetic measurement ascribes that Cu-doped SnO2 exhibit the intrinsic room temperature ferromagnetism within the low field strength. The occurrence of ferromagnetism in Cu-doped SnO2 is directly related to the p-d ferromagnetic exchange coupling between the local magnetic moment of Cu2+ and the polarized valence electrons of surrounding oxygen. Over all this study provides the primary information about tunable multifunctionality of SnO2 hollow nanostructures by adding the non-magnetic Cu ions.

  18. Dirac Cones, Topological Edge States, and Nontrivial Flat Bands in Two-Dimensional Semiconductors with a Honeycomb Nanogeometry

    NARCIS (Netherlands)

    Kalesaki, E.; Delerue, C.; de Morais Smith, C.; Beugeling, W.; Allan, G.; Vanmaekelbergh, D.A.M.

    2014-01-01

    We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattic

  19. X-ray absorption and reflection as probes of the GaN conduction bands: Theory and experiments

    Energy Technology Data Exchange (ETDEWEB)

    Lambrecht, W.R.L.; Rashkeev, S.N.; Segall, B. [Case Western Reserve Univ., Cleveland, OH (United States)] [and others

    1997-04-01

    X-ray absorption measurements are a well-known probe of the unoccupied states in a material. The same information can be obtained by using glancing angle X-ray reflectivity. In spite of several existing band structure calculations of the group III nitrides and previous optical studies in UV range, a direct probe of their conduction band densities of states is of interest. The authors performed a joint experimental and theoretical investigation using both of these experimental techniques for wurtzite GaN.

  20. Band gap and conductivity evaluation of carbon nanotube with hematite for green ammonia synthesis

    Science.gov (United States)

    Rehman, Zia Ur; Yahya, Noorhana; Shafie, A'fza; Soleimani, Hassan; Alqasim, Bilal Hassan; Irfan, Muhammad; Qureshi, Saima

    2016-11-01

    To understand the change in number of electrons, band gap and total energy in the catalyst simulation was performed using Cambridge Serial Total Energy Package (CASTEP). Two catalyst were taken into consideration namely carbon nanotubes (CNTs) and hematite adjacent with CNTs. The simulation based study of the adsorption of hydrogen and nitrogen with reference to change in number of electron and band-gap of carbon nano tubes and hematite mixed with carbon nanotubes was not reported in literature. For this reason carbon nanotubes band gap for different chirality and number of walls was calculated through simulation. After that simulation for number of electrons, band gap and average total energy of CNTs alone and a mixture hematite with CNTs was performed before and after adsorption of hydrogen and nitrogen. From simulation the number of electrons were found to be doubled for hematite mixed with CNTs and average total energy was also increased as compared to similar parameter for CNTs without hematite. In conclusion the hematite with carbon nanotubes is preferred candidate for ammonia synthesis using magnetic induction method. Ammonia synthesis was done using MIM. Ammonia yield was quantified by Kjaldal method.

  1. Effect of band filling on anomalous Hall conductivity and magneto-crystalline anisotropy in NiFe epitaxial thin films

    Directory of Open Access Journals (Sweden)

    Zhong Shi

    2016-01-01

    Full Text Available The anomalous Hall effect (AHE and magneto-crystalline anisotropy (MCA are investigated in epitaxial NixFe1−x thin films grown on MgO (001 substrates. The scattering independent term b of anomalous Hall conductivity shows obvious correlation with cubic magneto-crystalline anisotropy K1. When nickel content x decreasing, both b and K1 vary continuously from negative to positive, changing sign at about x = 0.85. Ab initio calculations indicate NixFe1−x has more abundant band structures than pure Ni due to the tuning of valence electrons (band fillings, resulting in the increased b and K1. This remarkable correlation between b and K1 can be attributed to the effect of band filling near the Fermi surface.

  2. Effect of band filling on anomalous Hall conductivity and magneto-crystalline anisotropy in NiFe epitaxial thin films

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Zhong; Jiang, Hang-Yu; Zhou, Shi-Ming, E-mail: shiming@tongji.edu.cn [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology & Pohl Institute of Solid State Physics, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Hou, Yan-Liang; Ye, Quan-Lin [Department of Physics, Hangzhou Normal University, Hangzhou 310036 (China); Su Si, Ming [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China)

    2016-01-15

    The anomalous Hall effect (AHE) and magneto-crystalline anisotropy (MCA) are investigated in epitaxial Ni{sub x}Fe{sub 1−x} thin films grown on MgO (001) substrates. The scattering independent term b of anomalous Hall conductivity shows obvious correlation with cubic magneto-crystalline anisotropy K{sub 1}. When nickel content x decreasing, both b and K{sub 1} vary continuously from negative to positive, changing sign at about x = 0.85. Ab initio calculations indicate Ni{sub x}Fe{sub 1−x} has more abundant band structures than pure Ni due to the tuning of valence electrons (band fillings), resulting in the increased b and K{sub 1}. This remarkable correlation between b and K{sub 1} can be attributed to the effect of band filling near the Fermi surface.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yubo; Zhang, Jiawei; Wang, Youwei [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Gao, Weiwei; Abtew, Tesfaye A. [Department of Physics, University at Buffalo, SUNY, Buffalo, New York 14260 (United States); Zhang, Peihong, E-mail: pzhang3@buffalo.edu, E-mail: wqzhang@mail.sic.ac.cn [Department of Physics, University at Buffalo, SUNY, Buffalo, New York 14260 (United States); Beijing Computational Science Research Center, Beijing 100084 (China); Zhang, Wenqing, E-mail: pzhang3@buffalo.edu, E-mail: wqzhang@mail.sic.ac.cn [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); School of Chemistry and Chemical Engineering and Sate Key Laboratory of Coordination Chemistry, Nanjing University, Jiangsu 210093 (China)

    2013-11-14

    Diamond-like Cu-based multinary semiconductors are a rich family of materials that hold promise in a wide range of applications. Unfortunately, accurate theoretical understanding of the electronic properties of these materials is hindered by the involvement of Cu d electrons. Density functional theory (DFT) based calculations using the local density approximation or generalized gradient approximation often give qualitative wrong electronic properties of these materials, especially for narrow-gap systems. The modified Becke-Johnson (mBJ) method has been shown to be a promising alternative to more elaborate theory such as the GW approximation for fast materials screening and predictions. However, straightforward applications of the mBJ method to these materials still encounter significant difficulties because of the insufficient treatment of the localized d electrons. We show that combining the promise of mBJ potential and the spirit of the well-established DFT + U method leads to a much improved description of the electronic structures, including the most challenging narrow-gap systems. A survey of the band gaps of about 20 Cu-based semiconductors calculated using the mBJ + U method shows that the results agree with reliable values to within ±0.2 eV.

  4. Nature of the band gap and origin of the conductivity of PbO2 revealed by theory and experiment.

    Science.gov (United States)

    Scanlon, David O; Kehoe, Aoife B; Watson, Graeme W; Jones, Martin O; David, William I F; Payne, David J; Egdell, Russell G; Edwards, Peter P; Walsh, Aron

    2011-12-09

    Lead dioxide has been used for over a century in the lead-acid battery. Many fundamental questions concerning PbO2 remain unanswered, principally: (i) is the bulk material a metal or a semiconductor, and (ii) what is the source of the high levels of conductivity? We calculate the electronic structure and defect physics of PbO2, using a hybrid density functional, and show that it is an n-type semiconductor with a small indirect band gap of ∼0.2  eV. The origin of electron carriers in the undoped material is found to be oxygen vacancies, which forms a donor state resonant in the conduction band. A dipole-forbidden band gap combined with a large carrier induced Moss-Burstein shift results in a large effective optical band gap. The model is supported by neutron diffraction, which reveals that the oxygen sublattice is only 98.4% occupied, thus confirming oxygen substoichiometry as the electron source.

  5. Valence and Conduction Band Densities of States of Metal Halide Perovskites: A Combined Experimental–Theoretical Study

    OpenAIRE

    Endres, James; Egger, David A.; Kulbak, Michael; Kerner, Ross A.; Zhao, Lianfeng; Silver, Scott H.; Hodes, Gary; Rand, Barry P.; Cahen, David; Kronik, Leeor; Kahn, Antoine

    2016-01-01

    We report valence and conduction band densities of states measured via ultraviolet and inverse photoemission spectroscopies on three metal halide perovskites, specifically methylammonium lead iodide and bromide and cesium lead bromide (MAPbI3, MAPbBr3, CsPbBr3), grown at two different institutions on different substrates. These are compared with theoretical densities of states (DOS) calculated via density functional theory. The qualitative agreement achieved between experiment and theory lead...

  6. Conduction band mass determinations for n-type InGaAs/InAlAs single quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Jones, E.D.; Reno, J.L. [Sandia National Labs., Albuquerque, NM (United States); Kotera, Nobuo [Kyushu Inst. of Tech., Iizuka, Fukuoka (Japan); Wang, Y. [Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab.

    1998-05-01

    The authors report the measurement of the conduction band mass in n-type single 27-ML-wide InGaAs/InAlAs quantum well lattice matched to InP using two methods: (1) Magnetoluminescence spectroscopy and (2) far-infrared cyclotron resonance. The magnetoluminescence method utilizes Landau level transitions between 0 and 14 T at 1.4 K. The far infrared cyclotron resonance measurements were made at 4.2 K and to fields as large up to 18 T. The 2D-carrier density N{sub 2D} = 3 {times} 10{sup 11} cm{sup {minus}2} at low temperatures. The magnetoluminescence technique yielded an effective conduction-band mass of m{sub c} = 0.062m{sub 0} while the far infrared cyclotron resonance measurements gave m{sub c} = 0.056m{sub 0}, where m{sub 0} is the free electron mass. Both measurements show no evidence for any significant conduction-band nonparabolicity.

  7. Effect of particle size on band gap and DC electrical conductivity of TiO2 nanomaterial

    Science.gov (United States)

    Avinash, B. S.; Chaturmukha, V. S.; Jayanna, H. S.; Naveen, C. S.; Rajeeva, M. P.; Harish, B. M.; Suresh, S.; Lamani, Ashok R.

    2016-05-01

    Materials reduced to the Nano scale can exhibit different properties compared to what they exhibit on a micro scale, enabling unique applications. When TiO2 is reduced to Nano scale it shows unique properties, of which the electrical aspect is highly important. This paper presents increase in the energy gap and decrease in conductivity with decrease in particle size of pure Nano TiO2 synthesized by hydrolysis and peptization of titanium isopropoxide. Aqueous solution with various pH and peptizing the resultant suspension will form Nano TiO2 at different particle sizes. As the pH of the solution is made acidic reduction in the particle size is observed. And it is confirmed from XRD using Scherer formula and SEM, as prepared samples are studied for UV absorbance, and DC conductivity from room temperature to 400°C. From the tauc plot it was observed, and calculated the energy band gap increases as the particle size decreases and shown TiO2 is direct band gap. From Arrhenius plot clearly we encountered, decrease in the conductivity for the decrease in particle size due to hopping of charge carriers and it is evident that, we can tailor the band gap by varying particle size.

  8. Conductance of Conjugated Molecular Wires: Length Dependence, Anchoring Groups, and Band Alignment

    DEFF Research Database (Denmark)

    Peng, Guowen; Strange, Mikkel; Thygesen, Kristian Sommer

    2009-01-01

    The conductance of π-conjugated molecular wires bonded to gold electrodes at zero bias is studied using density functional theory combined with nonequilibrium Green’s function method. For all systems considered, we find that the conductance length dependence follows the simple exponential law...

  9. Band-edge optical transitions in a nonpolar-plane GaN substrate: exciton-phonon coupling and temperature effects

    Science.gov (United States)

    Wang, M. Z.; Xu, S. J.

    2016-09-01

    We present a detailed investigation of the band-edge optical transitions involving the interacting exciton-phonon system, especially first-order longitudinal optical (LO) phonon-assisted luminescence of bound and free excitons in m- and c-plane GaN substrates in a low temperature range from 4 K to 40 K. The main luminescence features of all of the three kinds of excitons can be well described by the theoretical models that take exciton-LO-phonon coupling into account. The effective Bohr radii of the excitons play a key role in determining the Huang-Rhys factor characterizing the exciton-LO-phonon coupling strength in GaN. An interesting oscillatory structure is found to appear in the low-temperature luminescence spectra of the nonpolar-plane GaN substrate, which needs to be clarified by further investigations.

  10. Quantum conductance of 4,4-bipyridine molecular junctions: Role of electrode work function and local d band

    DEFF Research Database (Denmark)

    Rauba, J.M.C.; Strange, Mikkel; Thygesen, Kristian Sommer

    2008-01-01

    We present density-functional theory calculations for the geometry and conductance of 4,4-bipyridine (BPD) nanojunctions with Au and Pt electrodes. The fact that transport takes place via bipyridine's lowest unoccupied molecular orbital (LUMO) suggests that the Au-BPD junction should have larger...... conductance than the Pt-BPD junction due to the smaller work function of Au as compared to Pt. On the other hand, coupling to the local d band is stronger in the case of Pt and this broadens the LUMO resonance. We find that these effects largely outbalance each other leading to conductances of 0.01G(0) and 0.......02G(0) for the Au and Pt contacts, respectively (G(0)=2e(2)/h is the conductance quantum). The effect of coupling to the electrodes is investigated by means of the group orbital which makes precise the concept of the local band. The construction allows us to explain and rationalize the first...

  11. Interfacially Al-doped ZnO nanowires: greatly enhanced near band edge emission through suppressed electron-phonon coupling and confined optical field.

    Science.gov (United States)

    Wu, Yiming; Dai, Yanmeng; Jiang, Shenlong; Ma, Chao; Lin, Yue; Du, Dongxue; Wu, Yukun; Ding, Huaiyi; Zhang, Qun; Pan, Nan; Wang, Xiaoping

    2017-04-05

    Aluminium (Al)-doped zinc oxide (ZnO) nanowires (NWs) with a unique core-shell structure and a Δ-doping profile at the interface were successfully grown using a combination of chemical vapor deposition re-growth and few-layer AlxOy atomic layer deposition. Unlike the conventional heavy doping which degrades the near-band-edge (NBE) luminescence and increases the electron-phonon coupling (EPC), it was found that there was an over 20-fold enhanced NBE emission and a notably-weakened EPC in this type of interfacially Al-doped ZnO NWs. Further experiments revealed a greatly suppressed nonradiative decay process and a much enhanced radiative recombination rate. By comparing the finite-difference time-domain simulation with the experimental results from intentionally designed different NWs, this enhanced radiative decay rate was attributed to the Purcell effect induced by the confined and intensified optical field within the interfacial layer. The ability to manipulate the confinement, transport and relaxation dynamics of ZnO excitons can be naturally guaranteed with this unique interfacial Δ-doping strategy, which is certainly desirable for the applications using ZnO-based nano-photonic and nano-optoelectronic devices.

  12. Band edge tailoring of InGaAs/AlAsSb coupled double quantum wells for a monolithically integrated all-optical switch.

    Science.gov (United States)

    Feng, Jijun; Akimoto, Ryoichi; Gozu, Shin-ichiro; Mozume, Teruo; Hasama, Toshifumi; Ishikawa, Hiroshi

    2013-07-01

    We demonstrate a compact all-optical Michelson interferometer (MI) gating switch with monolithic integration of two different bandgap energies. Based on the ion-induced intermixing in InGaAs/AlAsSb coupled double quantum wells, the blueshift of the band edge can be tailored. Through phosphorus ion implantation with a dose of 5 × 10(14) cm(-2) and subsequent annealing at 720 °C for 60 s, an implanted sample can acquire a high transmittance compared with the as-grown one. Meanwhile, the cross-phase modulation (XPM) efficiency of a non-implanted sample undergoing the same annealing process decreases little. An implanted part for signal propagation and a non-implanted section for XPM are thus monolithically integrated for an MI switch by an area-selective manner. Full switching of a π-rad nonlinear phase shift is achieved with pump pulse energy of 5.6 pJ at a 10-GHz repetition rate.

  13. Band Structure and Terahertz Optical Conductivity of Transition Metal Oxides: Theory and Application to CaRuO(3).

    Science.gov (United States)

    Dang, Hung T; Mravlje, Jernej; Georges, Antoine; Millis, Andrew J

    2015-09-04

    Density functional plus dynamical mean field calculations are used to show that in transition metal oxides, rotational and tilting (GdFeO(3)-type) distortions of the ideal cubic perovskite structure produce a multiplicity of low-energy optical transitions which affect the conductivity down to frequencies of the order of 1 or 2 mV (terahertz regime), mimicking non-Fermi-liquid effects even in systems with a strictly Fermi-liquid self-energy. For CaRuO(3), a material whose measured electromagnetic response in the terahertz frequency regime has been interpreted as evidence for non-Fermi-liquid physics, the combination of these band structure effects and a renormalized Fermi-liquid self-energy accounts for the low frequency optical response which had previously been regarded as a signature of exotic physics. Signatures of deviations from Fermi-liquid behavior at higher frequencies (∼100  meV) are discussed.

  14. Red shift of the band-edge photoluminescence emission and effects of annealing and capping agent on structural and optical properties of ZnO nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Verma, D.; Kole, A.K.; Kumbhakar, P., E-mail: pathik.kumbhakar@phy.nitdgp.ac.in

    2015-03-15

    Highlights: • Effect of annealing and capping on structural/optical properties of ZnO nanoparticles. • Red shifting in absorption and photoluminescence emission spectra is observed. • Tensile (compressive) strain is present in capped (uncapped) sample. • Synthesized low-toxic ZnO nanoparticles may find their application in bio-imaging. - Abstract: Use of nontoxic and biodegradable capping agents during the synthesis of nanomaterials has drawn a lot of research attention due to their potential applicability in biophotonic and bio-imaging devices. However, here we have reported the synthesis of an uncapped and biodegradable polyvinyl alcohol (PVA) capped ZnO nanoparticles (NPs), by using a simple chemical precipitation method at room temperature, followed by isochronal annealing of the as-synthesized sample at 200, 400, 500 and 600 °C for 2 h in air. The effects of using PVA and thermal annealing on the structural and optical properties of synthesized ZnO NPs have been reported. From the X-ray diffraction data analyses it has been observed that the use of PVA caused tensile strain in the annealed samples, whereas the samples synthesized without PVA capping showed compressive strain. For an estimation of strain and sizes of the NPs, three different models namely, uniform deformation model (UDM), uniform stress deformation model (USDM) and uniform deformation energy density model (UDEDM) have been used. The photoluminescence (PL) emission characteristics of the samples have been reported and they are found to consist of a strong near band-edge UV emission, which is systematically red shifted due to annealing from 371 to 383 nm for the capped and from 372 to 385 nm for the uncapped samples. Such biodegradable capped nanoparticles having UV PL emission might find potential applications as biophotonic materials.

  15. Note: radio frequency inductance-capacitance band-stop filter circuit to perform contactless conductivity measurements in pulsed magnetic fields.

    Science.gov (United States)

    Altarawneh, M M

    2012-09-01

    We present a new technique to perform radio frequency (rf) contactless conductivity measurements in pulsed magnetic fields to probe different ground states in condensed matter physics. The new method utilizes a simple analog band-stop filter circuit implemented in a radio frequency transmission setup to perform contactless conductivity measurements. The new method is more sensitive than the other methods (e.g., the tunnel diode oscillator and the proximity detector oscillator) due to more sensitive dependence of the circuit resonance frequency on the tank circuit inductance (not the transmission line). More important, the new method is more robust than other methods when used to perform measurements in very high magnetic fields, works for a wide range of temperatures (i.e., 300 K-1.4 K) and is less sensitive to noise and mechanical vibrations during pulse magnet operation. The new technique was successfully applied to measure the Shubnikov-de Haas effect in Bi(2)Se(3) in pulsed magnetic fields of up to 60 T.

  16. Improved performance of dye sensitized solar cells using Cu-doped TiO2 as photoanode materials: Band edge movement study by spectroelectrochemistry

    Science.gov (United States)

    Zhou, Li; Wei, Liguo; Yang, Yulin; Xia, Xue; Wang, Ping; Yu, Jia; Luan, Tianzhu

    2016-08-01

    Cu-doped TiO2 nanoparticles are prepared and used as semiconductor materials of photoanode to improve the performance of dye sensitized solar cells (DSSCs). UV-Vis spectroscopy and variable temperature spectroelectrochemistry study are used to characterize the influence of copper dopant with different concentrations on the band gap energies of TiO2 nanoparticles. The prepared Cu-doped TiO2 semiconductor has avoided the formation of CuO during hydrothermal process and lowered the conduction band position of TiO2, which contribute to increase the short circuit current density of DSSCs. At the optimum Cu concentration of 1.0 at.%, the short circuit current density increased from 12.54 to 14.98 mA cm-2, full sun solar power conversion efficiencies increased from 5.58% up to 6.71% as compared to the blank DSSC. This showed that the presence of copper in DSSCs leads to improvements of up to 20% in the conversion efficiency of DSSCs.

  17. Plasmons on the edge of MoS2 nanostructures

    DEFF Research Database (Denmark)

    Andersen, Kirsten; Jacobsen, Karsten Wedel; Thygesen, Kristian Sommer

    2014-01-01

    Using ab initio calculations we predict the existence of one-dimensional (1D), atomically confined plasmons at the edges of a zigzag MoS2 nanoribbon. The strongest plasmon originates from a metallic edge state localized on the sulfur dimers decorating the Mo edge of the ribbon. A detailed analysis...... of the dielectric function reveals that the observed deviations from the ideal 1D plasmon behavior result from single-particle transitions between the metallic edge state and the valence and conduction bands of the MoS2 sheet. The Mo and S edges of the ribbon are clearly distinguishable in calculated spatially...... resolved electron energy loss spectrum owing to the different plasmonic properties of the two edges. The edge plasmons could potentially be utilized for tuning the photocatalytic activity of MoS2 nanoparticles....

  18. Visible-light-driven Cu(II)-(Sr(1-y)Na(y))(Ti(1-x)Mo(x))O3 photocatalysts based on conduction band control and surface ion modification.

    Science.gov (United States)

    Qiu, Xiaoqing; Miyauchi, Masahiro; Yu, Huogen; Irie, Hiroshi; Hashimoto, Kazuhito

    2010-11-03

    Band-gap narrowing is generally considered to be a primary method in the design of visible-light-active photocatalysts because it can decrease the photo threshold to lower energies. However, controlling the valence band by up-shifting the top of the band or inducing localized levels above the band results in quantum efficiencies under visible light much lower than those under UV irradiation (such as those reported for N-doped TiO(2): Science 2001, 293, 269. J. Phys. Chem. B 2003, 107, 5483). Herein, we report a systematic study on a novel, visible-light-driven photocatalyst based on conduction band control and surface ion modification. Cu(II)-(Sr(1-y)Na(y))(Ti(1-x)Mo(x))O(3) photocatalysts were prepared by a soft chemical method in combination with an impregnation technique. It is found that Mo(6+) as well as Na(+) doping in the SrTiO(3) can lower the bottom of the conduction band and effectively extend the absorption edge to the visible light region. The Cu(II) clusters grafted on the surface act as a co-catalyst to efficiently reduce the oxygen molecules, thus consuming the excited electrons. Consequently, photocatalytic decomposition of gaseous 2-propanol into CO(2) is achieved, that is, CH(3)CHOHCH(3) + (9)/(2)O(2) → 3CO(2) + H(2)O. For Cu(II)-(Sr(1-y)Na(y))(Ti(1-x)Mo(x))O(3) at x = 2.0% under visible light irradiation, the maximum CO(2) generation rate can reach 0.148 μmol/h; the quantum efficiency under visible light is calculated to be 14.5%, while it is 10% under UV light irradiation. Our results suggest that high visible light photocatalytic efficiency can be achieved by combining conduction band control and surface ion modification, which provides a new approach for rational design and development of high-performance photocatalysts.

  19. Ge L{sub 3}-edge x-ray absorption near-edge structure study of structural changes accompanying conductivity drift in the amorphous phase of Ge{sub 2}Sb{sub 2}Te{sub 5}

    Energy Technology Data Exchange (ETDEWEB)

    Mitrofanov, K. V. [Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8562 (Japan); Kolobov, A. V., E-mail: a.kolobov@aist.go.jp; Fons, P. [Nanoelectronics Research Institute and Green Nanoelectronics Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8562, Japan and Synchrotron Radiation Research Institute (JASRI), SPring-8, 1-1-1, Kouto, Sayo, Hyogo 679-5198 (Japan); Wang, X.; Tominaga, J. [Nanoelectronics Research Institute and Green Nanoelectronics Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8562 (Japan); Tamenori, Y.; Uruga, T. [Synchrotron Radiation Research Institute (JASRI), SPring-8, 1-1-1, Kouto, Sayo, Hyogo 679-5198 (Japan); Ciocchini, N.; Ielmini, D. [DEIB - Politecnico di Milano, Piazza L. Da Vinci 32, 20133 Milano (Italy)

    2014-05-07

    A gradual uncontrollable increase in the resistivity of the amorphous phase of phase-change alloys, such as Ge{sub 2}Sb{sub 2}Te{sub 5}, known as drift, is a serious technological issue for application of phase-change memory. While it has been proposed that drift is related to structural relaxation, no direct structural results have been reported so far. Here, we report the results of Ge L{sub 3}-edge x-ray absorption measurements that suggest that the drift in electrical conductivity is associated with the gradual conversion of tetrahedrally coordinated Ge sites into pyramidal sites, while the system still remains in the amorphous phase. Based on electronic configuration arguments, we propose that during this process, which is governed by the existence of lone-pair electrons, the concentration of free carriers in the system decreases resulting in an increase in resistance despite the structural relaxation towards the crystalline phase.

  20. Thermal conductivity of the iron-based superconductor FeSe: Nodeless gap with strong two-band character

    Science.gov (United States)

    Bourgeois-Hope, Patrick; Badoux, Sven; Doiron-Leyraud, Nicolas; Taillefer, Louis; Chi, Shun; Liang, Ruixing; Hardy, Walter; Bonn, Doug

    The thermal conductivity κ of the iron-based superconductor FeSe was measured at temperatures down to 50 mK in magnetic fields up to 17 T. In zero magnetic field, the residual linear term in the T = 0 limit, κ0 / T , is vanishingly small. Application of a magnetic field H causes no increase in κ0 / T initially. Those two facts show that there are no zero-energy quasiparticles that carry heat and therefore no nodes in the superconducting gap of FeSe. The full field dependence of κ0 / T has the classic shape of a two-band superconductor, such as MgB2. It rises initially with a characteristic field H* ~=Hc 2 / 25 , and then more slowly up to Hc 2 = 14 T. We interpret this in terms of a small gap ΔA ~=Δ0 / 5 on some part of the Fermi surface, with a large gap ΔB =Δ0 in the region that controls Hc 2.

  1. Thermal Conductivity of the Iron-Based Superconductor FeSe: Nodeless Gap with a Strong Two-Band Character.

    Science.gov (United States)

    Bourgeois-Hope, P; Chi, S; Bonn, D A; Liang, R; Hardy, W N; Wolf, T; Meingast, C; Doiron-Leyraud, N; Taillefer, Louis

    2016-08-26

    The thermal conductivity κ of the iron-based superconductor FeSe was measured at temperatures down to 75 mK in magnetic fields up to 17 T. In a zero magnetic field, the electronic residual linear term in the T=0  K limit, κ_{0}/T, is vanishingly small. The application of a magnetic field B causes an exponential increase in κ_{0}/T initially. Those two observations show that there are no zero-energy quasiparticles that carry heat and therefore no nodes in the superconducting gap of FeSe. The full field dependence of κ_{0}/T has the classic two-step shape of a two-band superconductor: a first rise at very low field, with a characteristic field B^{⋆}≪B_{c2}, and then a second rise up to the upper critical field B_{c2}. This shows that the superconducting gap is very small (but finite) on one of the pockets in the Fermi surface of FeSe. We estimate that the minimum value of the gap, Δ_{min}, is an order of magnitude smaller than the maximum value, Δ_{max}.

  2. Conduction band offset engineering in wide-bandgap Ag(In,Ga)Se2 solar cells by hybrid buffer layer

    Science.gov (United States)

    Umehara, Takeshi; Zulkifly, Faris Akira Bin Mohd; Nakada, Kazuyoshi; Yamada, Akira

    2017-08-01

    Ag(In,Ga)Se2 (AIGS) is one of the promising candidates for the top cell absorber in the tandem structure. However, the conversion efficiency of AIGS solar cells is still lower than that required for the top cell. In this study, to improve the conversion efficiency of AIGS solar cells, we controlled the conduction band offset (CBO) at the buffer layer/ZnO and buffer layer/AIGS interfaces. The reduction in interface recombination at the CdS buffer layer/AIGS interface was achieved by introducing a ZnS(O,OH) buffer layer instead of a CdS buffer layer, although the fill factor (FF) decreased markedly because the CBO at the ZnS(O,OH)/ZnO interface prevented the electron flow under a forward bias. We found that the introduction of a CdS/ZnS(O,OH) hybrid buffer layer is efficient in controlling the CBO at both the buffer layer/AIGS and buffer layer/ZnO interfaces and improving the solar cell conversion efficiency.

  3. Effect of energy band gap in graphene on negative refraction through the veselago lens and electron conductance

    Science.gov (United States)

    Dahal, Dipendra; Gumbs, Godfrey

    2017-01-01

    A remarkable property of intrinsic graphene is that upon doping, electrons and holes travel through the monolayer thick material with constant velocity which does not depend on energy up to about 0.3 eV (Dirac fermions), as though the electrons and holes are massless particles and antiparticles which move at the Fermi velocity vF. Consequently, there is Klein tunneling at a p-n junction, in which there is no backscattering at normal incidence of massless Dirac fermions. However, this process yielding perfect transmission at normal incidence is expected to be affected when the group velocity of the charge carriers is energy dependent and there is non-zero effective mass for the target particle. We investigate how away from normal incidence the combined effect of incident electron energy ɛ and band gap parameter Δ can determine whether a p-n junction would allow focusing of an electron beam by behaving like a Veselago lens with negative refractive index. We demonstrate that there is a specific region in ɛ - Δ space where the index of refraction is negative, i.e., where monolayer graphene behaves as a metamaterial. Outside this region, the refractive index may be positive or there may be no refraction at all. We compute the ballistic conductance across a p-n junction as a function of Δ and ɛ and compare our results with those for a single electrostatic potential barrier and multiple barriers.

  4. Effect of conduction band nonparabolicity on the optical properties in a single quantum well under hydrostatic pressure and electric field

    Indian Academy of Sciences (India)

    S Panda; B Panda

    2012-05-01

    The effect of conduction band nonparabolicity on the linear and nonlinear optical properties such as absorption coefficients, and changes in the refractive index are calculated in the Al0.3Ga0.7As/GaAs heterostructure-based symmetric rectangular quantum well under applied hydrostatic pressure and electric field. The electron envelope functions and energies are calculated in the effective mass equation including the conduction band nonparabolicity. The linear and nonlinear optical properties have been calculated in the density matrix formalism with two-level approximation. The conduction band nonparabolicity shifts the positions of the optical properties and decreases their strength compared to those without this correction. Both the optical properties are enhanced with the applied hydrostatic pressure. While the absorption coefficients are bleached under the combined effect of high pressure and electric field, the bleaching effect is reduced when nonparabolicity is included.

  5. Optical and fundamental band gaps disparity in transparent conducting oxides: new findings for the [Formula: see text] and [Formula: see text] systems.

    Science.gov (United States)

    Sabino, Fernando P; Nunes Oliveira, Luiz; Wei, Su-Huai; Da Silva, Juarez L F

    2017-03-01

    The optical band gap, extracted from absorption measurements, defines the figure of merit for transparent conducting oxides (TCOs). In many oxides, such as [Formula: see text] or [Formula: see text], inversion symmetry introduces a selection rule that blocks transitions from the valence-band maximum to the conduction-band minimum. This raises the absorption threshold and enlarges the optical gap relative to the fundamental band gap. Here, we present density-functional computations identifying two optical gaps, either of which can be detected, depending on the optical light intensity. Under strong illumination, weak transitions from [Formula: see text]-points near the valence-band maximum contribute significantly to the absorption spectrum and define an optical gap matching the fundamental gap. Low optical intensities by contrast give prominence to the large optical gap determined by the selection rule. While experimental conditions have favored observation of the former optical gap in [Formula: see text], in contrast, absorption measurements in [Formula: see text] have focused on the latter. Our findings explain the disparity between the optical and fundamental gaps in bixbyite [Formula: see text] and predict that, measured under low illumination, the optical gap for rutile [Formula: see text] will increase, from 3.60 eV to 4.34 eV.

  6. Studies Conducted of Sodium Carbonate Contaminant Found on the Wing Leading Edge and the Nose Cap of the Space Shuttle Orbiter

    Science.gov (United States)

    Jacobson, Nathan S.; Palou, Jaime J.

    2003-01-01

    In early 2001, three of the space shuttle orbiters were found to have a sodium carbonate contaminant on the wing leading edge and nose cap. These parts are made of a reinforced carbon/carbon material protected by silicon carbide (SiC) and a glass coating. The glass coating is known as Type A and is primarily sodium silicate with particles of SiC. NASA Glenn Research Center's Environmental Durability Branch was asked to determine the chemistry of this deposit formation and assess any possible detrimental effects. At low temperatures, the reverse reaction is favorable. Previous studies of the corrosion of glass show that carbon dioxide in the presence of water does form sodium carbonate on sodium silicate glass (ref. 1). It is quite likely that a similar scenario exists for the orbiter wing leading edge. All three orbiters that formed sodium carbonate were exposed to rain. This formation of sodium carbonate was duplicated in the laboratory. The Type A glass, which coats the wing leading edge and nose cap, was made in a freestanding form and exposed to water in two separate experiments. In one set of experiments, the coating was placed in a petri dish filled with water. As the water evaporated, sodium carbonate formed. In another case, water was slowly dripped on the coating and sodium carbonate formed. The sodium carbonate was detected by chemical analysis and, in some cases, xray diffraction showed a hydrated sodium carbonate. The next step was to examine possible detrimental effects of this sodium carbonate. There are three likely scenarios for the sodium carbonate deposit: (1) it may be removed with a simple rinse, (2) it may remain and flow back into the Type A glass after heating during reentry, or (3) it may remain and flow onto unprotected SiC and/or other parts after heating during reentry. The effect of case 1 is to remove the Na2O constituent from the Type A glass, thus decreasing its effectiveness as a sealant. Even so, overall, it is probably the best

  7. Studies Conducted of Sodium Carbonate Contaminant Found on the Wing Leading Edge and the Nose Cap of the Space Shuttle Orbiter

    Science.gov (United States)

    Jacobson, Nathan S.; Palou, Jaime J.

    2003-01-01

    In early 2001, three of the space shuttle orbiters were found to have a sodium carbonate contaminant on the wing leading edge and nose cap. These parts are made of a reinforced carbon/carbon material protected by silicon carbide (SiC) and a glass coating. The glass coating is known as Type A and is primarily sodium silicate with particles of SiC. NASA Glenn Research Center's Environmental Durability Branch was asked to determine the chemistry of this deposit formation and assess any possible detrimental effects. At low temperatures, the reverse reaction is favorable. Previous studies of the corrosion of glass show that carbon dioxide in the presence of water does form sodium carbonate on sodium silicate glass (ref. 1). It is quite likely that a similar scenario exists for the orbiter wing leading edge. All three orbiters that formed sodium carbonate were exposed to rain. This formation of sodium carbonate was duplicated in the laboratory. The Type A glass, which coats the wing leading edge and nose cap, was made in a freestanding form and exposed to water in two separate experiments. In one set of experiments, the coating was placed in a petri dish filled with water. As the water evaporated, sodium carbonate formed. In another case, water was slowly dripped on the coating and sodium carbonate formed. The sodium carbonate was detected by chemical analysis and, in some cases, xray diffraction showed a hydrated sodium carbonate. The next step was to examine possible detrimental effects of this sodium carbonate. There are three likely scenarios for the sodium carbonate deposit: (1) it may be removed with a simple rinse, (2) it may remain and flow back into the Type A glass after heating during reentry, or (3) it may remain and flow onto unprotected SiC and/or other parts after heating during reentry. The effect of case 1 is to remove the Na2O constituent from the Type A glass, thus decreasing its effectiveness as a sealant. Even so, overall, it is probably the best

  8. Interaction of Cr3+ with valence and conduction bands in the long persistent phosphor ZnGa2O4:Cr3+, studied by ENDOR spectroscopy

    Science.gov (United States)

    Binet, Laurent; Sharma, Suchinder K.; Gourier, Didier

    2016-09-01

    Cr3+-doped zinc gallate ZnGa2O4 is a red-near infrared (IR) long persistent phosphor that can be excited by orange-red light, in the transparency window of living tissues. With this property, persistent luminescence nanoparticles were recently used for in vivo optical imaging of tumors in mice. In order to understand the origin of the excitability of persistent luminescence by visible light in this material, a Q-band ENDOR investigation of 71/69Ga and 53Cr nuclei was performed in ZnGa2O4:Cr3+ to get information on the interaction of Cr3+ with valence and conduction bands. The positive electron spin density at Ga nuclei revealed a dominant interaction of the 4A2 ground state of Cr3+ with the valence band, and a weaker interaction with the conduction band. The latter may occur only in the excited 2E and 4T2 states of Cr3+. It is proposed that when these two interactions are present, pairs of electrons and holes can be generated from excited Cr3+ in distorted sites undergoing local electric field produced by neighboring defects with opposite charges.

  9. Fowler-Nordheim tunneling and conduction-band discontinuity in GaAs/GaAsAl high electron mobility transistor structures

    Science.gov (United States)

    Smoliner, J.; Christanell, R.; Hauser, M.; Gornik, E.; Weimann, G.

    1987-06-01

    Oscillatory structure is observed in the dI/dV characteristics of conventional GaAs/GaAlAs high electron mobility transistor samples at liquid-helium temperature, which can be explained using a Fowler-Nordheim tunneling theory. The position of the oscillations allows a determination of the conduction-band discontinuity, and the depth of the deep donor levels in the GaAlAs for high aluminum concentrations. The fit of the data gives a value of Delta Ec/Delta Eg = 0.61 + or - 0.04 for aluminum concentration 30, 36, and 40 percent. The deep donor level in the GaAlAs was determined to be 130 meV below the conduction band.

  10. Electron heat conductivity of epitaxial graphene on silicon carbide

    Science.gov (United States)

    Alisultanov, Z. Z.; Meilanov, R. P.

    2016-08-01

    The diagonal component of the electron heat conductivity tensor of epitaxial graphene formed in a semiconductor has been investigated within a simple analytical model. It is shown that the heat conductivity sharply changes at a chemical potential close to the substrate band gap edge. Low-temperature expressions for the heat conductivity are derived.

  11. Graphene edges; localized edge state and electron wave interference

    Directory of Open Access Journals (Sweden)

    Enoki Toshiaki

    2012-03-01

    Full Text Available The electronic structure of massless Dirac fermion in the graphene hexagonal bipartite is seriously modified by the presence of edges depending on the edge chirality. In the zigzag edge, strongly spin polarized nonbonding edge state is created as a consequence of broken symmetry of pseudo-spin. In the scattering at armchair edges, the K-K’ intervalley transition gives rise to electron wave interference. The presence of edge state in zigzag edges is observed in ultra-high vacuum STM/STS observations. The electron wave interference phenomenon in the armchair edge is observed in the Raman G-band and the honeycomb superlattice pattern with its fine structure in STM images.

  12. Annealing induced electrical conduction and band gap variation in thermally reduced graphene oxide films with different sp{sup 2}/sp{sup 3} fraction

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Mukesh [Department of Physics, Indian Institute of Technology Guwahati, Guwahati 781039 (India); Yadav, Asha [Centre for Energy, Indian Institute of Technology Guwahati, Guwahati 781039 (India); Kumar, Shailendra [Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Agarwal, Pratima, E-mail: pratima@iitg.ernet.in [Department of Physics, Indian Institute of Technology Guwahati, Guwahati 781039 (India); Centre for Energy, Indian Institute of Technology Guwahati, Guwahati 781039 (India)

    2015-01-30

    Highlights: • Controllable electrical properties of GO from insulator to semimetal behavior with different reduction temperatures. • High conductivity ∼40 S/cm for GO reduced at 400 °C. • Tunable band gap of GO with different reduction temperatures. • A systematic decrease the fraction of sp{sup 3} as compared to sp{sup 2} with increase in reduction temperature. - Abstract: Temperature dependent electrical conductivity of as prepared and thermally reduced graphene oxide (GO) thin films was measured in the range 300–520 K. As prepared GO films show very low conductivity ∼6.8 × 10{sup −6} S/cm at 300 K, which increases slowly till 370 K. A sharp increase in conductivity is observed in the temperature range 370–440 K, beyond which conductivity is thermally activated with activation energy 0.26 eV. Reduced GO films show an increase in conductivity at 300 K with increase in reduction temperature. GO films reduced at 400 °C exhibit high conductivity ∼40 S/cm at 300 K, with very low activation energy 0.05 eV in the measured temperature range 300–520 K. The increase in conductivity after thermal reduction is due to an increase in the ratio sp{sup 2}/sp{sup 3} bonded carbon atoms. The band gap of as prepared GO is 3.20 eV and it is decreased by approximately 0.4 eV in the case of thermally reduced GO at 400 °C in comparison to as prepared GO.

  13. Design of an L-band normally conducting RF gun cavity for high peak and average RF power

    Science.gov (United States)

    Paramonov, V.; Philipp, S.; Rybakov, I.; Skassyrskaya, A.; Stephan, F.

    2017-05-01

    To provide high quality electron bunches for linear accelerators used in free electron lasers and particle colliders, RF gun cavities operate with extreme electric fields, resulting in a high pulsed RF power. The main L-band superconducting linacs of such facilities also require a long RF pulse length, resulting in a high average dissipated RF power in the gun cavity. The newly developed cavity based on the proven advantages of the existing DESY RF gun cavities, underwent significant changes. The shape of the cells is optimized to reduce the maximal surface electric field and RF loss power. Furthermore, the cavity is equipped with an RF probe to measure the field amplitude and phase. The elaborated cooling circuit design results in a lower temperature rise on the cavity RF surface and permits higher dissipated RF power. The paper presents the main solutions and results of the cavity design.

  14. Analysis of the experimental data for impurity-band conduction in Mn-doped InSb

    Energy Technology Data Exchange (ETDEWEB)

    Kajikawa, Yasutomo [Department of Electric and Control Systems Engineering, Interdisciplinary Faculty of Science and Engineering, Shimane University, Matsue (Japan)

    2017-01-15

    The experimental data of the temperature-dependent Hall-effect measurements on Mn-doped p -type InSb samples, which exhibit the anomalous sign reversal of the Hall coefficient to negative at low temperatures, have been analyzed on the basis of the nearest-neighbor hopping model in an impurity band. It is shown that the anomalous sign reversal of the Hall coefficient to negative can be well explained with assuming the hopping Hall factor in the form of A{sub hop} = (k{sub B}T/J{sub 3}) exp(K{sub NNH}T{sub 3}/T) with the negative sign of J{sub 3}. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Critical increase in Na-doping facilitates acceptor band movements that yields ~180 meV shallow hole conduction in ZnO bulk crystals

    Science.gov (United States)

    Parmar, Narendra S.; Yim, Haena; Choi, Ji-Won

    2017-03-01

    Stable p-type conduction in ZnO has been a long time obstacle in utilizing its full potential such as in opto-electronic devices. We designed a unique experimental set-up in the laboratory for high Na-doping by thermal diffusion in the bulk ZnO single crystals. SIMS measurement shows that Na concentration increases by 3 orders of magnitude, to ~3 × 1020 cm‑3 as doping temperature increases to 1200 °C. Electronic infrared absorption was measured for Na-acceptors. Absorption bands were observed near (0.20–0.24) eV. Absorption bands blue shifted by 0.04 eV when doped at 1200 °C giving rise to shallow acceptor level. NaZn band movements as a function of doping temperature are also seen in Photoluminescence emission (PL), Photoluminescence excitation (PLE) and UV-Vis transmission measurements. Variable temperature Hall measurements show stable p-type conduction with hole binding energy ~0.18 eV in ZnO samples that were Na-doped at 1200 °C.

  16. Linear and nonlinear intra-conduction band optical absorption in (In,Ga)N/GaN spherical QD under hydrostatic pressure

    Science.gov (United States)

    El Ghazi, Haddou; Jorio, Anouar; Zorkani, Izeddine

    2014-11-01

    Linear, third-order nonlinear and total optical absorption coefficients of intra-conduction band 1s-1p transition with hydrogenic shallow-donor impurity in wurtzite (In,Ga)N/GaN spherical quantum dot are reported. Hydrostatic pressure effect is investigated within the framework of single band effective-mass approximation using a combination of Quantum Genetic Algorithm (QGA) and Hartree-Fock-Roothaan (HFR) method. The results show that the pressure has a great influence on optical absorption coefficients of QDs. A blue-shift of the resonant peak is observed while the maximum of the amplitude of optical absorption coefficients decreases under hydrostatic pressure effect. A good agreement is shown compared with results of the finding.

  17. Increased conductivities of Cr doped Al{sub 2−x}Cr{sub x}O{sub 3} powders due to band gap narrowing

    Energy Technology Data Exchange (ETDEWEB)

    Badar, Nurhanna [Centre for Nanomaterials Research, Institute of Science, Level 3 Block C, Universiti Teknologi MARA, Shah Alam, Selangor 40450 (Malaysia); School of Physics and Materials Studies, Faculty of Applied Sciences, Universiti Teknologi MARA, Shah Alam, Selangor 40450 (Malaysia); Kamarulzaman, Norlida, E-mail: norlyk@salam.uitm.edu.my [Centre for Nanomaterials Research, Institute of Science, Level 3 Block C, Universiti Teknologi MARA, Shah Alam, Selangor 40450 (Malaysia); School of Physics and Materials Studies, Faculty of Applied Sciences, Universiti Teknologi MARA, Shah Alam, Selangor 40450 (Malaysia); Rusdi, Roshidah; Abdul Aziz, Nor Diyana [Centre for Nanomaterials Research, Institute of Science, Level 3 Block C, Universiti Teknologi MARA, Shah Alam, Selangor 40450 (Malaysia); School of Physics and Materials Studies, Faculty of Applied Sciences, Universiti Teknologi MARA, Shah Alam, Selangor 40450 (Malaysia); Kun Fun, Hoong [School of Physics, Universiti Sains Malaysia, 11800 Penang (Malaysia); Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, P.O. Box 2457, Riyadh 11451 (Saudi Arabia)

    2014-03-15

    A high Cr content in the synthesized Al{sub 2−x}Cr{sub x}O{sub 3} materials was achieved via a new synthesis route, the self propagating combustion method, for investigation of the effect of Cr substitution on the electrical, optical band gap and structural characteristics of the modified Al{sub 2}O{sub 3} materials. X-ray diffraction (XRD) results showed that all the samples were pure and that Cr was successfully substituted in the crystal lattice. The cell parameters and volume are linearly dependent on the Cr content. AC impedance spectroscopy results show that conductivity of the Cr doped samples increases exponentially with Cr content. This is attributed to band gap narrowing of the Al{sub 2−x}Cr{sub x}O{sub 3} powders as obtained from UV–visible spectrophotometric studies.

  18. Correlation of O (1s) and Fe (2p) near edge x-ray absorption fine structure spectra and electrical conductivity of La1-xSrxFe0.75Ni0.25O3-δ

    Science.gov (United States)

    Erat, Selma; Braun, Artur; Ovalle, Alejandro; Piamonteze, Cinthia; Liu, Zhi; Graule, Thomas; Gauckler, Ludwig J.

    2009-10-01

    A-site substitution of La3+ by Sr2+ in polaron conducting ABO3-type perovskite La1-xSrxFe0.75Ni0.25O3-δ causes oxidation of Fe3+ toward Fe4+ and formation of conducting electron holes, as evidenced by Fe (2p) and O (1s) near edge x-ray absorption fine structure spectra. Hole doping is reflected by linear variation of the prepeak ratio eg(↑)/[t2g(↓)+eg(↓)] of oxygen spectra, along with increased conductivity. The significant increase in conductivity due to NiO doping in La1-xSrxFeO3-δ is caused by increased overlap between Fe (3d) and O (2p) and charge transfer from the O (2p) to the Ni (3d) states, as concluded from near edge x-ray absorption fine structure spectra and ligand field multiplet calculations.

  19. Ultra-broad-band electrical spectroscopy of soils and sediments—a combined permittivity and conductivity model

    Science.gov (United States)

    Loewer, M.; Günther, T.; Igel, J.; Kruschwitz, S.; Martin, T.; Wagner, N.

    2017-09-01

    We combined two completely different methods measuring the frequency-dependent electrical properties of moist porous materials in order to receive an extraordinary large frequency spectrum. In the low-frequency (LF) range, complex electrical resistivity between 1 mHz and 45 kHz was measured for three different soils and sandstone, using the spectral induced polarization (SIP) method with a four electrode cell. In the high-frequency (HF) radio to microwave range, complex dielectric permittivity was measured between 1 MHz and 10 GHz for the same samples using dielectric spectroscopy by means of the coaxial transmission line technique. The combined data sets cover 13 orders of magnitude and were transferred into their equivalent expressions: the complex effective dielectric permittivity and the complex effective electrical conductivity. We applied the Kramers-Kronig relation in order to justify the validity of the data combination. A new phenomenological model that consists of both dielectric permittivity and electrical conductivity terms in a Debye- and Cole-Cole-type manner was fitted to the spectra. The combined permittivity and conductivity model accounts for the most common representations of the physical quantities with respect to the individual measuring method. A maximum number of four relaxation processes was identified in the analysed frequency range. Among these are the free water and different interfacial relaxation processes, the Maxwell-Wagner effect, the counterion relaxation in the electrical double layer and the direct-current electrical conductivity. There is evidence that free water relaxation does not affect the electrical response in the SIP range. Moreover, direct current conductivity contribution (bulk and interface) dominates the losses in the HF range. Interfacial relaxation processes with relaxations in the HF range are broadly distributed down to the LF range. The slowest observed process in the LF range has a minor contribution to the HF

  20. Long-time Luminescence Kinetics of Localized excitons and conduction Band Edges Smearing in ZnSe(1-c)Tec Solid Solutions

    DEFF Research Database (Denmark)

    Klochikhin, O.; Ogloblin, S. G.; Permogorov, S.

    2000-01-01

    It is shown that the integrated luminescence intensity of localized excitons in solid solutions ZnSe(1 - c)Tec has a component slowly decaying with time. After the excitation above the mobility threshold, the long-time intensity decreases exponentially, with a fractional exponent changing from...

  1. Geophysical exploration to estimate the surface conductivity of residual argillaceous bands in the groundwater repositories of coastal sediments of EOLGA, Nigeria

    Science.gov (United States)

    George, N. J.; Atat, J. G.; Umoren, E. B.; Etebong, Isong

    2017-06-01

    Electrical geophysical applications exploit a petrophysical relationship governing the electrical properties of rocks/sediments when field data are coupled with laboratory data. Given the robust analytical techniques of electrical method and the interrelationship with laboratory measurements, it seems natural to classify, and hence simplify, the spatially aggregated conductivity information on the basis of rock/sediment lithology. This provides a unique link between lithological sediment/rock parameters and the physical parameters controlling bulk conductivity. In this work vertical electrical sounding (VES) technique employing Schlumberger configuration integrated with sediment and water analysis have been used to determine the conductivity of argillaceous bands of aquifer sands (fine- coarse sands) in Eastern Obolo Local Government Area (EOLGA). The analysis of the data shows that the aquifer systems composing of fine sands, siltstones and coarse sand have bulk and pore-water resistivities ranging from 40.1-2049.4 Ω m (average = 995.18 Ω m) to 2.7-256.9 Ω m (average = 91.2 Ω m) respectively. These ranges respectively correspond to porosity and formation factor of (19.5-40.6%; average = 29.2%) and (7.1-19.7%; average = 12.95%). Within the limit of experimental errors clearly specified in the work, the intrinsic (clay-free) formation factor (Fi) was estimated to be 16.34 while the intrinsic porosity and the conductivity of the pore-scale clay (σA) were respectively estimated to be 20.4% and 3.2679 mS/m. Accounting for this conductivity magnitude of argillaceous bands from bulk conductivity (σb) of aquifer sands makes the aquifer systems in the area to be consistent with Archie's law that is valid only in clay-free sandy formation. The graphical deductions and contour distribution of parameters realised from data processing could be used to derive input parameters for contaminant migration modelling and to improve the quality of model in the study area.

  2. SYNTHESIS, CHARACTERIZATION, THERMAL ANALYSIS, CONDUCTIVITY AND BAND GAPS OF OLIGO {4-[(2-HYDROXYL-1-NAPHTHYL)METHYLENE]-AMINOBENZOIC ACID}

    Institute of Scientific and Technical Information of China (English)

    Ismet Kaya; Ali Bilici

    2009-01-01

    The oxidative polycondensation reaction conditions of 4-[(2-hydroxyl-l-naphthyl)methylene]aminobenzoic acid (4-HNMABA) with H2O2,air O2 and NaOCl were studied in an aqueous alkaline medium between 40℃ and 90℃.The structure of oligo {4-[(2-hydroxyl-1-naphthyl)methylene]aminobenzoic acid} (O-4-HNMABA) was characterized by using 1H-NMR,13C-NMR,FT-IR,UV-Vis,size exclusion chromatography (SEC) and elemental analysis techniques.At the optimum reaction conditions,the yield of O-4-HNMABA was found to be 70% for H2O2 oxidant,94% for air O2 oxidant and 87% for NaOCl oxidant.According to the SEC analysis,the number-average molecular weight (Mn),weight-average molecular weight (Mw) and polydispersity index (PDI) values of O-4-HNMABA were found to be 850,1350 and 1.59,using H2O2,1800,2200 and 1.22,using air O2 and 2200,3000 and 1.36,using NaOCl,respectively.TGA-DTA analyses showed that O-4-HNMABA was more stable than 4-HNMABA.The highest occupied molecular orbital,the lowest unoccupied molecular orbital and electrochemical energy gaps ( Eg) of 4-HNMABA and O-4-HNMABA were found to be -6.34,-6.56; -2.67,-3.04; 3.67 and 3.52 eV,respectively,by cyclic voltammetry (CV).According to UV-Vis measurements,optical band gaps (E,g) of 4-HNMABA and O-4-HNMABA were found to be 3.12 and 3.03 eV,respectively.

  3. Induced changes in refractive index, optical band gap, and absorption edge of polycarbonate-SiO2 thin films by Vis-IR lasers

    Science.gov (United States)

    Ehsani, Hassan; Akhoondi, Somaieh

    2016-09-01

    In this experimental work, we have studied induced changes in refractive index, extinction coefficient, and optical band-gap of Bisphenol-A-polycarbonate (BPA-PC) coated with a uniform and thin, anti-scratch SiO2 film irradiated by visible to near-infrared lasers at 532 nm (green),650 nm(red), and 980 nm (IR)wavelength lasers with different energy densities. Our lasers sources are indium-gallium-aluminum-phosphide, second harmonic of neodymium-YAG-solid state lasers and gallium-aluminum-arsenide-semiconductor laser. The energy densities of our sources have been changed by changing the spot size of incident laser. samples transmission spectra were monitored by carry500 spectrophotometer and induced changes in optical properties are evaluated by using, extrapolation of the transmission spectrum through Swanepoel method and computer application

  4. TiO 2 Conduction Band Modulation with In 2 O 3 Recombination Barrier Layers in Solid-State Dye-Sensitized Solar Cells

    KAUST Repository

    Brennan, Thomas P.

    2013-11-21

    Atomic layer deposition (ALD) was used to grow subnanometer indium oxide recombination barriers in a solid-state dye-sensitized solar cell (DSSC) based on the spiro-OMeTAD hole-transport material (HTM) and the WN1 donor-π-acceptor organic dye. While optimal device performance was achieved after 3-10 ALD cycles, 15 ALD cycles (∼2 Å of In2O 3) was observed to be optimal for increasing open-circuit voltage (VOC) with an average improvement of over 100 mV, including one device with an extremely high VOC of 1.00 V. An unexpected phenomenon was observed after 15 ALD cycles: the increasing VOC trend reversed, and after 30 ALD cycles VOC dropped by over 100 mV relative to control devices without any In2O3. To explore possible causes of the nonmonotonic behavior resulting from In2O3 barrier layers, we conducted several device measurements, including transient photovoltage experiments and capacitance measurements, as well as density functional theory (DFT) studies. Our results suggest that the VOC gains observed in the first 20 ALD cycles are due to both a surface dipole that pulls up the TiO2 conduction band and recombination suppression. After 30 ALD cycles, however, both effects are reversed: the surface dipole of the In2O3 layer reverses direction, lowering the TiO 2 conduction band, and mid-bandgap states introduced by In 2O3 accelerate recombination, leading to a reduced V OC. © 2013 American Chemical Society.

  5. Geophysical exploration to estimate the surface conductivity of residual argillaceous bands in the groundwater repositories of coastal sediments of EOLGA, Nigeria

    Directory of Open Access Journals (Sweden)

    N.J. George

    2017-06-01

    Full Text Available Electrical geophysical applications exploit a petrophysical relationship governing the electrical properties of rocks/sediments when field data are coupled with laboratory data. Given the robust analytical techniques of electrical method and the interrelationship with laboratory measurements, it seems natural to classify, and hence simplify, the spatially aggregated conductivity information on the basis of rock/sediment lithology. This provides a unique link between lithological sediment/rock parameters and the physical parameters controlling bulk conductivity. In this work vertical electrical sounding (VES technique employing Schlumberger configuration integrated with sediment and water analysis have been used to determine the conductivity of argillaceous bands of aquifer sands (fine- coarse sands in Eastern Obolo Local Government Area (EOLGA. The analysis of the data shows that the aquifer systems composing of fine sands, siltstones and coarse sand have bulk and pore-water resistivities ranging from 40.1–2049.4 Ω m (average = 995.18 Ω m to 2.7–256.9 Ω m (average = 91.2 Ω m respectively. These ranges respectively correspond to porosity and formation factor of (19.5–40.6%; average = 29.2% and (7.1–19.7%; average = 12.95%. Within the limit of experimental errors clearly specified in the work, the intrinsic (clay-free formation factor (Fi was estimated to be 16.34 while the intrinsic porosity and the conductivity of the pore-scale clay (σA were respectively estimated to be 20.4% and 3.2679 mS/m. Accounting for this conductivity magnitude of argillaceous bands from bulk conductivity (σb of aquifer sands makes the aquifer systems in the area to be consistent with Archie’s law that is valid only in clay-free sandy formation. The graphical deductions and contour distribution of parameters realised from data processing could be used to derive input parameters for contaminant migration modelling and to improve the

  6. X-ray absorption near edge spectroscopy at the Mn K-edge in highly homogeneous GaMnN diluted magnetic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Sancho-Juan, O.; Cantarero, A.; Garro, N.; Cros, A. [Materials Science Institute, University of Valencia, PO Box 22085, 46071 Valencia (Spain); Martinez-Criado, G.; Salome, M.; Susini, J. [ESRF, Polygone Scientifique Louis Neel, 6 rue Jules Horowitz, 38000 Grenoble (France); Olguin, D. [Dept. de Fisica, CINVESTAV-IPN, 07300 Mexico D.F. (Mexico); Dhar, S.; Ploog, K. [Paul Drude Institute, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2006-06-15

    We have studied by X-ray absorption spectroscopy the local environment of Mn in highly homogeneous Ga{sub 1-x}Mn{sub x}N (0.06edges. In this report, we focus our attention to the X-ray absorption near edge spectroscopy (XANES) results. The comparison of the XANES spectra corresponding to the Ga and Mn edges indicates that Mn is substitutional to Ga in all samples studied. The XANES spectra measured at the Mn absorption edge shows in the near-edge region a double peak and a shoulder below the absorption edge and the main absorption peak after the edge, separated around 15 eV above the pre-edge structure. We have compared the position of the edge with that of MnO (Mn{sup 2+}) and Mn{sub 2}O{sub 3} (Mn{sup 3+}). All samples studied present the same Mn oxidation state, 2{sup +}. In order to interprete the near-edge structure, we have performed ab initio calculations with a 2 x 2 x 1supercell ({proportional_to}6% Mn) using the full potential linear augmented plane wave method as implemented in the Wien2k code. The calculations show the appearance of Mn anti-bonding t{sub 2g} bands, which are responsible for the pre-edge absorption. The shoulder and main absorption peaks are due to transitions from the valence band 1s-states of Mn to the p-contributions of the conduction bands. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Influence of interface traps inside the conduction band on the capacitance–voltage characteristics of InGaAs metal–oxide–semiconductor capacitors

    Science.gov (United States)

    Taoka, Noriyuki; Yokoyama, Masafumi; Kim, Sang Hyeon; Suzuki, Rena; Iida, Ryo; Takenaka, Mitsuru; Takagi, Shinichi

    2016-11-01

    We investigated the influences of the AC response with interface/bulk-oxide traps near the conduction band (CB) and a low effective density of states (DOS) on the accumulation capacitance C acc of an n-type InGaAs metal–oxide–semiconductor (MOS) capacitor. We found that the capacitance associated with the interface traps inside the CB significantly increases C acc compared to the C acc value constrained by a low DOS. These results indicate that accurate characterization inside the CB and considering the capacitance due to the interface traps inside the CB in the MOS capacitance–voltage curves are indispensable for accurate characterization of InGaAs MOS interface properties.

  8. Local measurement of conduction band offset for ZnCdS/ZnSSe nano-structure by Laplace current DLTS cooperated with AFM technique

    Energy Technology Data Exchange (ETDEWEB)

    Litvinov, Vladimir [P.N. Lebedev Physical Institute RAS, Leninsky pr. 53, 119991 Moscow (Russian Federation); Ryazan State Radioengineering University, Gagarina 59/1, 390005 Ryazan (Russian Federation); Kozlovsky, Vladimir; Sannikov, Denis; Sviridov, Dmitry [P.N. Lebedev Physical Institute RAS, Leninsky pr. 53, 119991 Moscow (Russian Federation); Milovanova, Oksana; Rybin, Nikolay [Ryazan State Radioengineering University, Gagarina 59/1, 390005 Ryazan (Russian Federation)

    2010-06-15

    ZnCdS/ZnSSe SQW structure were investigated by current deep level transient spectroscopy (DLTS) with Laplace transform cooperated with atomic force microscopy (AFM) for the first time. Cathodoluminescence (CL) measurements were carried out also. Basing on Laplace current DLTS with AFM and CL data we estimated the conduction band offset of the ZnCdS/ZnSSe interface in the different regions of the structure. Size of the investigated region was commensurable with the diameter of cantilever tip. We demonstrated that Laplace current DLTS-spectrometer switched in the circuit of an AFM cantilever may be used for an investigation of nanostructures. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Edge phonons in black phosphorus

    Science.gov (United States)

    Ribeiro, H. B.; Villegas, C. E. P.; Bahamon, D. A.; Muraca, D.; Castro Neto, A. H.; de Souza, E. A. T.; Rocha, A. R.; Pimenta, M. A.; de Matos, C. J. S.

    2016-07-01

    Black phosphorus has recently emerged as a new layered crystal that, due to its peculiar and anisotropic crystalline and electronic band structures, may have important applications in electronics, optoelectronics and photonics. Despite the fact that the edges of layered crystals host a range of singular properties whose characterization and exploitation are of utmost importance for device development, the edges of black phosphorus remain poorly characterized. In this work, the atomic structure and behaviour of phonons near different black phosphorus edges are experimentally and theoretically studied using Raman spectroscopy and density functional theory calculations. Polarized Raman results show the appearance of new modes at the edges of the sample, and their spectra depend on the atomic structure of the edges (zigzag or armchair). Theoretical simulations confirm that the new modes are due to edge phonon states that are forbidden in the bulk, and originated from the lattice termination rearrangements.

  10. Edge instabilities of topological superconductors

    Science.gov (United States)

    Hofmann, Johannes S.; Assaad, Fakher F.; Schnyder, Andreas P.

    2016-05-01

    Nodal topological superconductors display zero-energy Majorana flat bands at generic edges. The flatness of these edge bands, which is protected by time-reversal and translation symmetry, gives rise to an extensive ground-state degeneracy. Therefore, even arbitrarily weak interactions lead to an instability of the flat-band edge states towards time-reversal and translation-symmetry-broken phases, which lift the ground-state degeneracy. We examine the instabilities of the flat-band edge states of dx y-wave superconductors by performing a mean-field analysis in the Majorana basis of the edge states. The leading instabilities are Majorana mass terms, which correspond to coherent superpositions of particle-particle and particle-hole channels in the fermionic language. We find that attractive interactions induce three different mass terms. One is a coherent superposition of imaginary s -wave pairing and current order, and another combines a charge-density-wave and finite-momentum singlet pairing. Repulsive interactions, on the other hand, lead to ferromagnetism together with spin-triplet pairing at the edge. Our quantum Monte Carlo simulations confirm these findings and demonstrate that these instabilities occur even in the presence of strong quantum fluctuations. We discuss the implications of our results for experiments on cuprate high-temperature superconductors.

  11. Edge transport in the trivial phase of InAs/GaSb

    Science.gov (United States)

    Nichele, Fabrizio; Suominen, Henri J.; Kjaergaard, Morten; Marcus, Charles M.; Sajadi, Ebrahim; Folk, Joshua A.; Qu, Fanming; Beukman, Arjan J. A.; de Vries, Folkert K.; van Veen, Jasper; Nadj-Perge, Stevan; Kouwenhoven, Leo P.; Nguyen, Binh-Minh; Kiselev, Andrey A.; Yi, Wei; Sokolich, Marko; Manfra, Michael J.; Spanton, Eric M.; Moler, Kathryn A.

    2016-08-01

    We present transport and scanning SQUID measurements on InAs/GaSb double quantum wells, a system predicted to be a two-dimensional topological insulator. Top and back gates allow independent control of density and band offset, allowing tuning from the trivial to the topological regime. In the trivial regime, bulk conductivity is quenched but transport persists along the edges, superficially resembling the predicted helical edge-channels in the topological regime. We characterize edge conduction in the trivial regime in a wide variety of sample geometries and measurement configurations, as a function of temperature, magnetic field, and edge length. Despite similarities to studies claiming measurements of helical edge channels, our characterization points to a non-topological origin for these observations.

  12. Sizable band gap in organometallic topological insulator

    Science.gov (United States)

    Derakhshan, V.; Ketabi, S. A.

    2017-01-01

    Based on first principle calculation when Ceperley-Alder and Perdew-Burke-Ernzerh type exchange-correlation energy functional were adopted to LSDA and GGA calculation, electronic properties of organometallic honeycomb lattice as a two-dimensional topological insulator was calculated. In the presence of spin-orbit interaction bulk band gap of organometallic lattice with heavy metals such as Au, Hg, Pt and Tl atoms were investigated. Our results show that the organometallic topological insulator which is made of Mercury atom shows the wide bulk band gap of about ∼120 meV. Moreover, by fitting the conduction and valence bands to the band-structure which are produced by Density Functional Theory, spin-orbit interaction parameters were extracted. Based on calculated parameters, gapless edge states within bulk insulating gap are indeed found for finite width strip of two-dimensional organometallic topological insulators.

  13. Intensive Plasmonic Flash Light Sintering of Copper Nanoinks Using a Band-Pass Light Filter for Highly Electrically Conductive Electrodes in Printed Electronics.

    Science.gov (United States)

    Hwang, Yeon-Taek; Chung, Wan-Ho; Jang, Yong-Rae; Kim, Hak-Sung

    2016-04-06

    In this work, an intensive plasmonic flash light sintering technique was developed by using a band-pass light filter matching the plasmonic wavelength of the copper nanoparticles. The sintering characteristics, such as resistivity and microstructure, of the copper nanoink films were studied as a function of the range of the wavelength employed in the flash white light sintering. The flash white light irradiation conditions (e.g., wavelength range, irradiation energy, pulse number, on-time, and off-time) were optimized to obtain a high conductivity of the copper nanoink films without causing damage to the polyimide substrate. The wavelength range corresponding to the plasmonic wavelength of the copper nanoparticles could efficiently sinter the copper nanoink and enhance its conductivity. Ultimately, the sintered copper nanoink films under optimal light sintering conditions showed the lowest resistivity (6.97 μΩ·cm), which was only 4.1 times higher than that of bulk copper films (1.68 μΩ·cm).

  14. The complex band structure for armchair graphene nanoribbons

    Institute of Scientific and Technical Information of China (English)

    Zhang Liu-Jun; Xia Tong-Sheng

    2010-01-01

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

  15. Edge Matters

    DEFF Research Database (Denmark)

    Earon, Ofri

    2013-01-01

    the building. The research explores and develops the architectural characteristics of correlations between the resident, the singular unit, the building and the given location at the edge zone. It approaches the edge zone of the urban house as a platform for dynamic interactions between these behaviours....... The following text includes the first draft of the first two chapters: introduction and theory. The chapters are not written completely, and some parts are written only as headlines. These headlines and other comments are marked in red. The text is on working progress and far from being finished...

  16. Living edge

    DEFF Research Database (Denmark)

    Earon, Ofri

    2014-01-01

    of the involved actors at the border. By doing so, the study underlines a forgotten, yet important, role of this edge zone – being a zone of commonality between the house and city, between indoors and outdoors, between the man at home and the man at the street. The city of Copenhagen promotes porous borders...... is a collection of material from the case study of an ongoing PhD study titled: LIVING EDGE - The Architectural and Urban Prospect of Domestic Borders. The paper includes a description of the problem analysis, research question, method, discussion and conclusion....

  17. Estimation of various scattering parameters and 2-DEG mobilities from electron mobility calculations in the three conduction bands , L and X of gallium arsenide

    Indian Academy of Sciences (India)

    Sonal Singhal; A K Saxena; S Dasgupta

    2007-10-01

    The electron drift mobility in conduction band of GaAs has been calculated before, but for the first time, we have made attempts to estimate the electron mobilities in higher energy L and X minima. We have also calculated the value of mobility of two-dimensional electron gas needed to predict hetero-structure device characteristics using GaAs. Best scattering parameters have been derived by close comparison between experimental and theoretical mobilities. Room temperature electron mobilities in , L and X valleys are found to be nearly 9094, 945 and 247 cm2 /V-s respectively. For the above valleys, the electron masses, deformation potentials and polar phonon temperatures have been determined to be (0.067, 0.22, 0.39m 0 ), (8.5, 9.5, 6.5 eV), and (416, 382, 542 K) as best values, respectively. The 2-DEG electron mobility in minimum increases to 1.54 × 106 from 1.59 × 105 cm2 /V-s (for impurity concentration of 1014 cm-3) at 10 K. Similarly, the 2-DEG electron mobility values in L and X minima are estimated to be 2.28 × 105 and 1.44 × 105 cm2 /V-s at 10 K, which are about ∼ 4.5 and ∼ 3.9 times higher than normal value with impurity scattering present.

  18. Studies on charge production from Cs2Te photocathodes in the PITZ L-band normal conducting radio frequency photo injector

    CERN Document Server

    Hernandez-Garcia, C; Asova, G; Bakr, M; Boonpornprasert, P; Good, J; Gross, M; Huck, H; Isaev, I; Kalantaryan, D; Khojoyan, M; Kourkafas, G; Lishilin, O; Malyutin, D; Melkumyan, D; Oppelt, A; Otevrel, M; Pathak, G; Renier, Y; Rublack, T; Stephan, F; Vashchenko, G; Zhao, Q

    2016-01-01

    This paper discusses the behavior of electron bunch charge produced in an L-band normal conducting radio frequency cavity (RF gun) from Cs2Te photocathodes illuminated with ps-long UV laser pulses when the laser transverse distribution consists of a flat-top core with Gaussian-like decaying halo. The produced charge shows a linear dependence at low laser pulse energies as expected in the quantum efficiency limited emission regime, while its dependence on laser pulse energy is observed to be much weaker for higher values, due to space charge limited emission. However, direct plug-in of experimental parameters into the space charge tracking code ASTRA yields lower output charge in the space charge limited regime compared to measured values. The rate of increase of the produced charge at high laser pulse energies close to the space charge limited emission regime seems to be proportional to the amount of halo present in the radial laser profile since the charge from the core has saturated already. By utilizing co...

  19. Determination of mobility edge in presence of metal-to-insulator transition

    Science.gov (United States)

    Tito, M. A.; Pusep, Yu. A.

    2017-04-01

    Determination of mobility edge in presence of metal-to-insulator transition Recombination dynamics of excitons was studied in multiple narrow quantum well GaAs/AlGaAs heterostructures. Disorder generated by interface roughness considerably affects transport of the conduction band electrons and at appropriate quantum well width results in a metal-to insulator transition. Localization of the electrons was found to be responsible for the exciton recombination time measured in the vicinity of the metal-to-insulator transition. Measurement of the exciton recombination time as a function of the energy allowed for determination of the critical energy of the mobility edge attributed to the conduction band electrons. The mobility edge energy obtained in this way demonstrates intersection with the Fermi level energy at the critical disorder corresponding to the metal-to-insulator transition.

  20. Edge Detection,

    Science.gov (United States)

    1985-09-01

    PROJECT. T ASK0 Artificial Inteligence Laboratory AREA It WORK UNIT NUMBERS V 545 Technology Square ( Cambridge, HA 02139 I I* CONTOOL1LIN@4OFFICE NAME...ARD-A1t62 62 EDGE DETECTION(U) NASSACNUSETTS INST OF TECH CAMBRIDGE 1/1 ARTIFICIAL INTELLIGENCE LAB E C HILDRETH SEP 85 AI-M-8 N99SI4-8S-C-6595...used to carry out this analysis. cce~iO a N) ’.~" D LI’BL. P p ------------ Sj. t i MASSACHUSETTS INSTITUTE OF TECHNOLOGY i ARTIFICIAL INTELLIGENCE

  1. First-principle study on the effects of Tl doping on the band gap and the band-edge of optical absorption of InI%Tl掺杂对InI禁带宽度和吸收边带影响的第一性原理研究

    Institute of Scientific and Technical Information of China (English)

    徐朝鹏; 王永贞; 张伟; 王倩; 吴国庆

    2014-01-01

    采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法,建立了未掺杂与不同浓度的Tl 原子取代In原子的In1-xTlxI超胞模型,分别对模型进行了几何优化、能带分布、态密度分布和吸收光谱的计算。结果表明: Tl 掺杂浓度越小, In1-xTlxI形成能越低,晶体结构越稳定; Tl的掺入使得InI体系导带向高能方向移动,而价带顶位置基本没变,导致禁带宽度变宽, InI吸收光谱出现明显蓝移现象。%According to the density functional theory, using first-principles plane-wave ultrasoft pseudopotential method, models for a pure InI and different concentrations of Tl-doped InI are set up, and the geomertry optimizations for the modes are carried out. The total density of states, the band structures and the optical absorption are also calculated. The results show that the smaller the doping concentration of Tl, the smaller the formation energy of InI is, thus the more stable the crystal structure is. The Tl doping causes the bottom of conduction band shift to a higher energy, while the location of the top of valence band has no change. This makes the band gap of InI broadened, and the absorption spectrum obviously blue-shifted.

  2. Stoichiometry gradient, cation interdiffusion, and band alignment between a nanosized TiO2 blocking layer and a transparent conductive oxide in dye-sensitized solar cell front contacts.

    Science.gov (United States)

    Salvinelli, Gabriele; Drera, Giovanni; Baratto, Camilla; Braga, Antonio; Sangaletti, Luigi

    2015-01-14

    An angle-resolved photoemission spectroscopy study allowed us to identify cation interdiffusion and stoichiometry gradients at the interface between a nanosized TiO2 blocking layer and a transparent conductive Cd-Sn oxide substrate. A stoichiometry gradient for the Sn cations is already found in the bare Cd-Sn oxide layer. When TiO2 ultrathin layers are deposited by RF sputtering on the Cd-Sn oxide layer, Ti is found to partially replace Sn, resulting in a Cd-Sn-Ti mixed oxide layer with a thickness ranging from 0.85 to 3.3 nm. The band gap profile across the junction has been reconstructed for three TiO2 layers, resulting in a valence band offset decrease (and a conduction band offset increase) with the blocking layer thickness. The results are related to the cell efficiencies in terms of charge injection and recombination processes.

  3. The effects of polaronic mass and conduction band non-parabolicity on a donor binding energy under the simultaneous effect of pressure and temperature basing on the numerical FEM in a spherical quantum dot

    Science.gov (United States)

    Sali, A.; Kharbach, J.; Rezzouk, A.; Ouazzani Jamil, M.

    2017-04-01

    Basing on the numerical Finite Element Method (FEM), we have investigated the influences of polaronic mass and conduction band non-parabolicity on the binding energy of the ground state of an on-center hydrogenic donor impurity in a spherical GaAs / Ga1 - x AlxAs quantum dot structure. The calculations have been made with a realistic potential barrier height in the framework of the effective mass approximation including the combined effect of hydrostatic pressure and temperature. The donor binding energy is computed as a function of dot size, Al concentration x , hydrostatic pressure and temperature both in the absence and presence of polaronic mass and conduction band non-parabolicity effects. We have taken into account the electronic effective mass, dielectric constant, and conduction band offset between the dot and barriers varying with pressure and temperature. It has been found that the binding energy is strongly affected by the effect of polaronic mass and conduction band non-parabolicity for narrow quantum dot and large Al concentration x. The results show again that the donor binding energy increases linearly with the pressure in direct gap regime and its variation is larger for narrower dots only and drops slightly with the temperature. A good agreement is obtained with the existing literature values.

  4. Enhanced power factor and reduced Lorenz number in the Wiedemann-Franz law due to pudding mold type band structures

    Science.gov (United States)

    Usui, Hidetomo; Kuroki, Kazuhiko

    2017-04-01

    We study the relationship between the shape of the electronic band structure and the thermoelectric properties. In order to study the band shape dependence of the thermoelectric properties generally, we first adopt models with band structures having the dispersion E ( k ) ˜ | k | n with n = 2, 4, and 6. We consider one-, two-, and three-dimensional systems and calculate the thermoelectric properties using the Boltzmann equation approach within the constant quasi-particle lifetime approximation. n = 2 corresponds to the usual parabolic band structure, while the band shape for n = 4 and 6 has a flat portion at the band edge, so that the density of states diverges at the bottom of the band. We call this kind of band structure the "pudding mold type band". n ≥ 4 belong to the pudding mold type band, but since the density of states diverges even for n = 2 in the one dimensional system, this is also categorized as the pudding mold type. Due to the large density of states and the rapid change of the group velocity around the band edge, the spectral conductivity of the pudding mold type band structures becomes larger than that of the usual parabolic band structures. It is found that the pudding mold type band has a coexistence of a large Seebeck coefficient and a large electric conductivity and a small Lorenz number in the Wiedemann-Franz law due to the specific band shape. We also find that the low dimensionality of the band structure can contribute to large electronic conductivity and hence a small Lorenz number. We conclude that the pudding mold type band, especially in low dimensional systems, can enhance not only the power factor but also the dimensionless figure of merit due to stronger reduction of the Lorenz number.

  5. Investigation of band gap narrowing in nitrogen-doped La2Ti2O7 with transient absorption spectroscopy.

    Science.gov (United States)

    Yost, Brandon T; Cushing, Scott K; Meng, Fanke; Bright, Joeseph; Bas, Derek A; Wu, Nianqiang; Bristow, Alan D

    2015-12-14

    Doping a semiconductor can extend the light absorption range, however, it usually introduces mid-gap states, reducing the charge carrier lifetime. This report shows that doping lanthanum dititinate (La2Ti2O7) with nitrogen extends the valence band edge by creating a continuum of dopant states, increasing the light absorption edge from 380 nm to 550 nm without adding mid-gap states. The dopant states are experimentally resolved in the excited state by correlating transient absorption spectroscopy with a supercontinuum probe and DFT prediction. The lack of mid-gap states is further confirmed by measuring the excited state lifetimes, which reveal the shifted band edge only increased carrier thermalization rates to the band edge and not interband charge recombination under both ultraviolet and visible excitation. Terahertz (time-domain) spectroscopy also reveals that the conduction mechanism remains unchanged after doping, suggesting the states are delocalized.

  6. Impedance and a.c. conductivity studies on Ba(Nd0.2Ti0.6Nb0.2)O3 ceramic prepared through conventional and microwave sintering route

    Indian Academy of Sciences (India)

    Syed Mahboob; G Prasad; G S Kumar

    2006-08-01

    Electrical conduction studies on Ba(Nd0.2Ti0.6Nb0.2)O3 ceramic samples prepared through conventional and microwave sintering route are presented in this paper. D.C. and a.c. conductivities of these samples as a function of temperature from 300–900 K have been studied. Two types of conduction processes are evident from the frequency dependant conductivity plots, i.e. low-frequency conduction due to short-range hopping and high-frequency conduction due to the localized relaxation (reorientational) hopping mechanism. Grain and grain boundary contributions to the conductivity in these samples are obtained from impedance/admittance measurements via equivalent circuit modelling.

  7. Advanced hyperspectral imaging system with edge enhancement

    Science.gov (United States)

    Yushkov, K. B.; Molchanov, V. Y.

    2017-03-01

    We developed an acousto-optic hyperspectral imaging system with edge enhancement capability. The system is an add-on to a standard light microscope. Edge enhancement operation mode is aimed for analysis of low-contrast microscopic samples, e.g. unstained cytological smears and histological samples, live cells. Edge-enhancement imaging mode is based on a feature of acousto-optic tunable filters to perform band-pass spatial filtering when unturned from noncritical phase matching geometry is diffraction. Switching between standard hyperspectral imaging and edge-enhancement modes is performed by means of a telecentric amplitude mask.

  8. Flat-Band Potentials of Molecularly Thin Metal Oxide Nanosheets.

    Science.gov (United States)

    Xu, Pengtao; Milstein, Tyler J; Mallouk, Thomas E

    2016-05-11

    Exfoliated nanosheets derived from Dion-Jacobson phase layer perovskites (TBAxH1-xA2B3O10, A = Sr, Ca, B = Nb, Ta) were grown layer-by-layer on fluorine-doped tin oxide and gold electrode surfaces. Electrochemical impedance spectra (EIS) of the five-layer nanosheet films in contact with aqueous electrolyte solutions were analyzed by the Mott-Schottky method to obtain flat-band potentials (VFB) of the oxide semiconductors as a function of pH. Despite capacitive contributions from the electrode-solution interface, reliable values could be obtained from capacitance measurements over a limited potential range near VFB. The measured values of VFB shifted -59 mV/pH over the pH range of 4-8 and were in close agreement with the empirical correlation between conduction band-edge potentials and optical band gaps proposed by Matsumoto ( J. Solid State Chem. 1996, 126 (2), 227-234 ). Density functional theory calculations showed that A-site substitution influenced band energies by modulating the strength of A-O bonding, and that subsitution of Ta for Nb on B-sites resulted in a negative shift of the conduction band-edge potential.

  9. Edge-based correlation image registration for multispectral imaging

    Science.gov (United States)

    Nandy, Prabal [Albuquerque, NM

    2009-11-17

    Registration information for images of a common target obtained from a plurality of different spectral bands can be obtained by combining edge detection and phase correlation. The images are edge-filtered, and pairs of the edge-filtered images are then phase correlated to produce phase correlation images. The registration information can be determined based on these phase correlation images.

  10. Impurity levels, impurity bands, excited impurity bands, and band tails: The electronic density of states in quantum wells and heterostructures

    Science.gov (United States)

    Serre, J.; Ghazali, A.; Gold, A.

    1989-04-01

    We have investigated in quantum wells (QW's) and heterostructures (HS's) the modification of the electronic structure near the band edge, which is induced by selective doping. The density of states has been calculated as a function of the relevant parameters, namely, carrier and impurity concentrations (and depletion concentrations for HS's), QW width, and impurity position. Using a multiple-scattering method which includes a finite-range screened potential and impurity concentration to all orders, we have succeeded in obtaining ground-state and excited-state impurity bands (IB's). We observed these bands merging gradually with the lowest conduction subband as the impurity concentration is increased, leading to the formation of a band tail into the energy gap. Other main results obtained for different values of the parameters are the binding energy for a single impurity, the widths and energy shifts of ground- and excited-state IB's, and the contribution of the electron-impurity interaction to the gap shrinkage in the band-tail regime. Our results are compared with experiments and other theories.

  11. Design of transition edge sensor microcalorimeters for optimal performance

    Energy Technology Data Exchange (ETDEWEB)

    Bandler, S.R. E-mail: sbandler@milkyway.gsfc.nasa.gov; Figueroa-Feliciano, E.; Stahle, C.K.; Boyce, K.; Brekosky, R.; Chervenak, J.; Finkbeiner, F.; Kelley, R.; Lindeman, M.; Porter, F.S.; Saab, T

    2004-03-11

    We have developed a model for transition edge sensors to optimize performance under a variety of different conditions. There are three design trade-offs when engineering a microcalorimeter for a particular application: energy resolution, energy range and maximum count rate. All three are interdependent and are determined by various design parameters such as the detector heat capacity, the sharpness of the transition, and the thermal conductance of the detector to the frame. Our model includes all known sources of intrinsic noise in our calorimeters including the observed broad band excess noise. We will present the results of this model, and its predictions for optimally designed microcalorimeters.

  12. Raman spectroscopy investigations of chemically derived zigzag edge graphene nanoribbons

    Directory of Open Access Journals (Sweden)

    R. Nishinakagawa

    2013-09-01

    Full Text Available We fabricated graphene nanoribbons (GNRs chemically derived from expandable graphite. All GNRs exhibit atomically smooth edges that extended over their entire length. We investigated four of the fabricated GNRs using Raman spectroscopy. Two of the investigated GNRs show Raman spectra with a missing D-band peak, while D-band peaks can be clearly observed for the other two GNRs. The two GNRs which do not show the D-band peak are GNRs with zigzag edges, and the two other GNRs which show clearly the D-band peaks are possibly GNRs with armchair edges.

  13. Banded transformer cores

    Science.gov (United States)

    Mclyman, C. W. T. (Inventor)

    1974-01-01

    A banded transformer core formed by positioning a pair of mated, similar core halves on a supporting pedestal. The core halves are encircled with a strap, selectively applying tension whereby a compressive force is applied to the core edge for reducing the innate air gap. A dc magnetic field is employed in supporting the core halves during initial phases of the banding operation, while an ac magnetic field subsequently is employed for detecting dimension changes occurring in the air gaps as tension is applied to the strap.

  14. First-principles calculation of nitrogen-tungsten codoping effects on the band structure of anatase-titania

    OpenAIRE

    2009-01-01

    The electronic properties and photocatalytic activity of nitrogen (N) and/or tungsten (W)-doped anatase are calculated using density functional theory. For N-doping, isolated N 2p states above the top of the valence band are responsible for experimentally observed redshifts in the optical absorption edge. For W-doping, W 5d states below the conduction band lead to band gap narrowing; the transition energy is reduced by 0.2 eV. Addition of W to the N-doped system yields significant band gap na...

  15. Quantization of edge currents along magnetic barriers and magnetic guides

    CERN Document Server

    Dombrowski, N; Raikov, G D

    2010-01-01

    We investigate the edge conductance of particles submitted to an Iwatsuka magnetic field, playing the role of a purely magnetic barrier. We also consider magnetic guides generated by generalized Iwatsuka potentials. In both cases we prove quantization of the edge conductance. Next, we consider magnetic perturbations of such magnetic barriers or guides, and prove stability of the quantized value of the edge conductance. Further, we establish a sum rule for edge conductances. Regularization within the context of disordered systems is discussed as well.

  16. High-energy band structure of gold

    DEFF Research Database (Denmark)

    Christensen, N. Egede

    1976-01-01

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

  17. The roles of the dielectric constant and the relative level of conduction band of high-k composite with Si in improving the memory performance of charge-trapping memory devices

    Directory of Open Access Journals (Sweden)

    Jianxin Lu

    2014-11-01

    Full Text Available The memory structures Pt/Al2O3/(TiO2x(Al2O31−x/Al2O3/p-Si(nominal composition x = 0.05, 0.50 and 0.70 were fabricated by using rf-magnetron sputtering and atomic layer deposition techniques, in which the dielectric constant and the bottom of the conduction band of the high-k composite (TiO2x(Al2O31−x were adjusted by controlling the partial composition of Al2O3. With the largest dielectric constant and the lowest deviation from the bottom of the conduction band of Si, (TiO20.7(Al2O30.3 memory devices show the largest memory window of 7.54 V, the fast programming/erasing speed and excellent endurance and retention characteristics, which were ascribed to the special structural design, proper combination of dielectric constant and band alignment in the high-k composite (TiO20.7(Al2O30.3.

  18. Quantum conductance of zigzag graphene oxide nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Kan, Zhe; Nelson, Christopher; Khatun, Mahfuza, E-mail: mkhatun@bsu.edu [Department of Physics and Astronomy, Center for Computational Nanoscience, Ball State University, Muncie, Indiana 47306 (United States)

    2014-04-21

    The electronic properties of zigzag graphene oxide nanoribbons (ZGOR) are presented. The results show interesting behaviors which are considerably different from the properties of the perfect graphene nanoribbons (GNRs). The theoretical methods include a Huckel-tight binding approach, a Green's function methodology, and the Landauer formalism. The presence of oxygen on the edge results in band bending, a noticeable change in density of states and thus the conductance. Consequently, the occupation in the valence bands increase for the next neighboring carbon atom in the unit cell. Conductance drops in both the conduction and valence band regions are due to the reduction of allowed k modes resulting from band bending. The asymmetry of the energy band structure of the ZGOR is due to the energy differences of the atoms. The inclusion of a foreign atom's orbital energies changes the dispersion relation of the eigenvalues in energy space. These novel characteristics are important and valuable in the study of quantum transport of GNRs.

  19. Quasiparticle band structure of antiferromagnetic Eu Te

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-11-24

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

  20. Hydrostatic pressure effects on the {gamma}-X conduction band mixing and the binding energy of a donor impurity in GaAs-Ga{sub 1-x}Al{sub x}As quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Duque, C.A. [Instituto de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia); Lopez, S.Y. [Facultad de Educacion, Universidad de Antioquia, AA 1226, Medellin (Colombia); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, C.P. 62210, Cuernavaca (Mexico)

    2007-06-15

    Mixing between {gamma} and X valleys of the conduction band in GaAs-Ga{sub 1-x}Al{sub x}As quantum wells is investigated taken into account the effect of applied hydrostatic pressure. This effect is introduced via the pressure-dependent values of the corresponding energy gaps and the main band parameters. The mixing is considered along the lines of a phenomenological model. Variation of the confined ground state in the well as a function of the pressure is reported. The dependencies of the variationally calculated binding energy of a donor impurity with the hydrostatic pressure and well width are also presented. It is shown that the inclusion of the {gamma}-X mixing explains the non-linear behavior in the photoluminescence peak of confined exciton states that has been observed for pressures above 20 kbar. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. Freeze-Drying Process Development and Scale-Up: Scale-Up of Edge Vial Versus Center Vial Heat Transfer Coefficients, Kv.

    Science.gov (United States)

    Pikal, Michael J; Bogner, Robin; Mudhivarthi, Vamsi; Sharma, Puneet; Sane, Pooja

    2016-11-01

    This report presents calculations of the difference between the vial heat transfer coefficient of the "edge vial" and the "center vial" at all scales. The only scale-up adjustment for center vials is for the contribution of radiation from the shelf upon which the vial sits by replacing the emissivity of the laboratory dryer shelf with the emissivity of the production dryer shelf. With edge vials, scales-up adjustments are more complex. While convection is not important, heat transfer from the wall to the bands (surrounding the vial array) by radiation and directly from the band to the vials by both radiation and conduction is important; this radiation heat transfer depends on the emissivity of the vial and the bands and is nearly independent of the emissivity of the dryer walls. Differences in wall temperatures do impact the edge vial effect and scale-up, and estimates for wall temperatures are needed for both laboratory and manufacturing dryers. Auto-loading systems (no bands) may give different edge vial heat transfer coefficients than when operating with bands. Satisfactory agreement between theoretical predictions and experimental values of the edge vial effect indicate that results calculated from the theory are of useful accuracy. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

  2. Orbital Edge States in a Photonic Honeycomb Lattice

    Science.gov (United States)

    Milićević, M.; Ozawa, T.; Montambaux, G.; Carusotto, I.; Galopin, E.; Lemaître, A.; Le Gratiet, L.; Sagnes, I.; Bloch, J.; Amo, A.

    2017-03-01

    We experimentally reveal the emergence of edge states in a photonic lattice with orbital bands. We use a two-dimensional honeycomb lattice of coupled micropillars whose bulk spectrum shows four gapless bands arising from the coupling of p -like photonic orbitals. We observe zero-energy edge states whose topological origin is similar to that of conventional edge states in graphene. Additionally, we report novel dispersive edge states in zigzag and armchair edges. The observations are reproduced by tight-binding and analytical calculations, which we extend to bearded edges. Our work shows the potentiality of coupled micropillars in elucidating some of the electronic properties of emergent two-dimensional materials with orbital bands.

  3. DOPING AND BOND LENGTH CONTRIBUTIONS TO Mn K-EDGE SHIFT IN La1-xSrxMnO3 AND THEIR CORRELATION WITH ELECTRICAL TRANSPORT BEHAVIOUR.

    Energy Technology Data Exchange (ETDEWEB)

    PANDEY,S.K.; KHALID,S.; BINDU, R.; KUMAR, A.; PIMPALE, A.V.

    2006-12-04

    The experimental Mn K-edge x-ray absorption spectra of La{sub 1-x}Sr{sub x}MnO{sub 3}, x = 0 - 0.7 are compared with the band structure calculations using spin polarized density functional theory. It is explicitly shown that there is a correspondence between the inflection point on the absorption edge and the center of gravity of the unoccupied Mn 4p-band. This correspondence has been used to separate the doping and size contributions to edge shift due to variation in number of electrons in valence band and Mn-O bond lengths, respectively when Sr is doped into LaMnO{sub 3}. Such separation is helpful to find the localization behavior of charge carriers and to understand the observed transport properties and type of charge carrier participating in the conduction process in these compounds.

  4. Edge states in polariton honeycomb lattices

    Science.gov (United States)

    Milićević, M.; Ozawa, T.; Andreakou, P.; Carusotto, I.; Jacqmin, T.; Galopin, E.; Lemaître, A.; Le Gratiet, L.; Sagnes, I.; Bloch, J.; Amo, A.

    2015-09-01

    The experimental study of edge states in atomically thin layered materials remains a challenge due to the difficult control of the geometry of the sample terminations, the stability of dangling bonds, and the need to measure local properties. In the case of graphene, localized edge modes have been predicted in zigzag and bearded edges, characterized by flat dispersions connecting the Dirac points. Polaritons in semiconductor microcavities have recently emerged as an extraordinary photonic platform to emulate 1D and 2D Hamiltonians, allowing the direct visualization of the wavefunctions in both real- and momentum-space as well as of the energy dispersion of eigenstates via photoluminescence experiments. Here we report on the observation of edge states in a honeycomb lattice of coupled micropillars. The lowest two bands of this structure arise from the coupling of the lowest energy modes of the micropillars, and emulate the π and π* bands of graphene. We show the momentum-space dispersion of the edge states associated with the zigzag and bearded edges, holding unidimensional quasi-flat bands. Additionally, we evaluate polarization effects characteristic of polaritons on the properties of these states.

  5. Edge-Corrected Mean-Field Hubbard Model: Principle and Applications in 2D Materials

    Directory of Open Access Journals (Sweden)

    Xi Zhang

    2017-05-01

    Full Text Available This work reviews the current progress of tight-binding methods and the recent edge-modified mean-field Hubbard model. Undercoordinated atoms (atoms not fully coordinated exist at a high rate in nanomaterials with their impact overlooked. A quantum theory was proposed to calculate electronic structure of nanomaterials by incorporating bond order-length-strength (BOLS correlation to mean-field Hubbard model, i.e., BOLS-HM. Consistency between the BOLS-HM calculation and density functional theory (DFT calculation on 2D materials verified that (i bond contractions and potential well depression occur at the edge of graphene, phosphorene, and antimonene nanoribbons; (ii the physical origin of the band gap opening of graphene, phosphorene, and antimonene nanoribbons lays in the enhancement of edge potentials and hopping integrals due to the shorter and stronger bonds between undercoordinated atoms; (iii the band gap of 2D material nanoribbons expand as the width decreases due to the increasing under-coordination effects of edges which modulates the conductive behaviors; and (iv non-bond electrons at the edges and atomic vacancies of 2D material accompanied with the broken bond contribute to the Dirac-Fermi polaron (DFP with a local magnetic moment.

  6. Donor impurity-related optical absorption spectra in GaAs-Ga{sub 1-x}Al{sub x}As quantum wells: hydrostatic pressure and {gamma}-X conduction band mixing effects

    Energy Technology Data Exchange (ETDEWEB)

    Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, C.P. 62209, Cuernavaca, MOR (Mexico); Inst. de Ciencia de Materiales de Madrid, CSIC, Sor Juana Ines de la Cruz 3, 28049 Madrid (Spain); Lopez, S.Y. [Fac. de Educacion, Universidad de Antioquia, AA 1226, Medellin (Colombia); Duque, C.A. [Inst. de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia); Velasco, V.R. [Inst. de Ciencia de Materiales de Madrid, CSIC, Sor Juana Ines de la Cruz 3, 28049 Madrid (Spain)

    2007-07-01

    Using a variational procedure within the effective mass approximation, the mixing between the {gamma} and X conduction band valleys in GaAs-Ga{sub 1-x}Al{sub x}As quantum wells is investigated by taking into account the effect of applied hydrostatic pressure. Some optical properties such as donor and/or acceptor binding energy and impurity-related transition energies are calculated and comparisons with available experimental data are presented. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    Energy Technology Data Exchange (ETDEWEB)

    Sahdan, Muhammad Fauzi, E-mail: sahdan89@yahoo.co.id; Darma, Yudi, E-mail: sahdan89@yahoo.co.id [Department of Physics, Institut Teknologi Bandung, Jalan Ganesa 10, Bandung 40132 (Indonesia)

    2014-03-24

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

  8. Band Structure Analysis of La0.7Sr0.3MnO3 Perovskite Manganite Using a Synchrotron

    Directory of Open Access Journals (Sweden)

    Hong-Sub Lee

    2015-01-01

    Full Text Available Oxide semiconductors and their application in next-generation devices have received a great deal of attention due to their various optical, electric, and magnetic properties. For various applications, an understanding of these properties and their mechanisms is also very important. Various characteristics of these oxides originate from the band structure. In this study, we introduce a band structure analysis technique using a soft X-ray energy source to study a La0.7Sr0.3MnO3 (LSMO oxide semiconductor. The band structure is formed by a valence band, conduction band, band gap, work function, and electron affinity. These can be determined from secondary electron cut-off, valence band spectrum, O 1s core electron, and O K-edge measurements using synchrotron radiation. A detailed analysis of the band structure of the LSMO perovskite manganite oxide semiconductor thin film was established using these techniques.

  9. The edges of graphene.

    Science.gov (United States)

    Zhang, Xiuyun; Xin, John; Ding, Feng

    2013-04-01

    The edge of two dimensional (2D) graphene, as the surface of a three dimensional (3D) crystal, plays a crucial role in the determination of its physical, electronic and chemical properties and thus has been extensively studied recently. In this review, we summarize the recent advances in the study of graphene edges, including edge formation energy, edge reconstruction, method of graphene edge synthesis and the recent progress on metal-passivated graphene edges and the role of edges in graphene CVD growth. We expect this review to provide a guideline for readers to gain a clear picture of graphene edges from several aspects, especially the catalyst-passivated graphene edges and their role in graphene CVD growth.

  10. Structures, energy bands and conductivities of (Me3NEt)[Pd(dmit)2]2 and (NEt4)[Pd(dmit)2]2

    Institute of Scientific and Technical Information of China (English)

    方奇; 张斌; 雷虹; 孙岳明; 刘陟; 麦松威

    2002-01-01

    The electrical conductive molecular crystals (Me3NEt)[Pd(dmit)2]2 and (NEt4)[Pd (dmit)2]2 (dmit = 4,5-dimercapto-1,3-dithiole-2-thione) have been prepared, and their crystal structures and conductivity-temperature curves have been determined. The fact that the conductivity at room temperature of (Me3NEt)[Pd(dmit)2]2 (a = 58 Ω· cm-1) is much higher than that of (NEt4)-[Pd(dmit)2]2(cr= 2.2 Q~1 ?cm’1) has been rationally explained by the results of energy band calculations. (MeNEt3)[Pd(dmit)2]2 belongs to monoclinic system, P21/m space group and (NEt4)[Pd (dmit)2]2 belongs to triclinic system, P1 space group. The structural conducting component of the crystals is the planar coordinative anion [Pd(dmit)2]05- which forms the face-to-face dimmer [Pd(dmit)2]2-. These dimers have been further constructed to be a kind of two-dimensional (2-D)conductive molecular sheet by means of S…S intermolecular interactions. The tiny difference of the above 2-D molecular sheets of the two title crystals has resulted in one

  11. Efficient edge-guided full-waveform inversion by Canny edge detection and bilateral filtering algorithms

    Science.gov (United States)

    Xiang, Shiming; Zhang, Haijiang

    2016-11-01

    It is known full-waveform inversion (FWI) is generally ill-conditioned and various strategies including pre-conditioning and regularizing the inversion system have been proposed to obtain a reliable estimation of the velocity model. Here, we propose a new edge-guided strategy for FWI in frequency domain to efficiently and reliably estimate velocity models with structures of the size similar to the seismic wavelength. The edges of the velocity model at the current iteration are first detected by the Canny edge detection algorithm that is widely used in image processing. Then, the detected edges are used for guiding the calculation of FWI gradient as well as enforcing edge-preserving total variation (TV) regularization for next iteration of FWI. Bilateral filtering is further applied to remove noise but keep edges of the FWI gradient. The proposed edge-guided FWI in the frequency domain with edge-guided TV regularization and bilateral filtering is designed to preserve model edges that are recovered from previous iterations as well as from lower frequency waveforms when FWI is conducted from lower to higher frequencies. The new FWI method is validated using the complex Marmousi model that contains several steeply dipping fault zones and hundreds of horizons. Compared to FWI without edge guidance, our proposed edge-guided FWI recovers velocity model anomalies and edges much better. Unlike previous image-guided FWI or edge-guided TV regularization strategies, our method does not require migrating seismic data, thus is more efficient for real applications.

  12. A simple model for the band structure and D.C. conductivity of an infinite C dbond O···H bond N chain perpendicular to the protein backbone

    Science.gov (United States)

    Bende, Attila; Bogár, Ferenc; Ladik, János

    The1 Hartree-Fock crystal orbital (CO) method in its linear combination of atomic orbitals form was applied to determine the band structure of histone proteins taking 0.041e charge transfer per nucleotide base from the PO4- groups of poly(guanilic acid) to the arginine, and lysine side chains in histones (see text). Assuming that there are infinite COs, perpendicular to the main chain, formed by the amide groups of one segment of the protein chain bound together by H-bonds with the C dbond O groups of another segment of the chain, we have calculated the band structure. From this, we have determined the mobility using the deformation potential approximation. Multiplying this with the mobile electron concentration due to the charge transfer between the PO4- groups of DNA and the positive side chains in histones, we have obtained for the direct current (D.C.) electron conductivity sigmafib = 1.07 × 10-9 Omega-1 cm for a single fiber and after division by the cross-section of 9.10 × 10-16 cm2, sigmaspec = 1.18 × 106 Omega-1 cm-1 for the specific conductivity.

  13. Intrinsic spin Hall conductivity in one-, two-, and three-dimensional trivial and topological systems

    Science.gov (United States)

    Matthes, L.; Küfner, S.; Furthmüller, J.; Bechstedt, F.

    2016-08-01

    Ab initio relativistic band structure calculations are performed for the frequency-dependent spin Hall conductivity of three- (3D), two- (2D) and one-dimensional (1D) materials such as bulk semiconductors, atomically thin crystals, and their nanoribbons. Besides the influence of the dimensionality we also study differences between trivial and topological insulators (TIs). The frequency dependence of the conductivity is governed by the band-structure details, while its static value scales with the spin-orbit interaction in 3D but is quantized in units of e2/h for 2D TIs. 1D topological edge states influence the conductivity mainly for vanishing frequencies.

  14. Band alignment of two-dimensional semiconductors for designing heterostructures with momentum space matching

    Science.gov (United States)

    Özçelik, V. Ongun; Azadani, Javad G.; Yang, Ce; Koester, Steven J.; Low, Tony

    2016-07-01

    We present a comprehensive study of the band alignments of two-dimensional (2D) semiconducting materials and highlight the possibilities of forming momentum-matched type I, II, and III heterostructures, an enticing possibility being atomic heterostructures where the constituent monolayers have band edges at the zone center, i.e., Γ valley. Our study, which includes the group IV and III-V compound monolayer materials, group V elemental monolayer materials, transition-metal dichalcogenides, and transition-metal trichalcogenides, reveals that almost half of these materials have conduction and/or valence band edges residing at the zone center. Using first-principles density functional calculations, we present the type of the heterostructure for 903 different possible combinations of these 2D materials which establishes a periodic table of heterostructures.

  15. Band-to-band tunneling distance analysis in the heterogate electron–hole bilayer tunnel field-effect transistor

    Energy Technology Data Exchange (ETDEWEB)

    Padilla, J. L., E-mail: jose.padilladelatorre@epfl.ch [Nanoelectronic Devices Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015 (Switzerland); Departamento de Electrónica y Tecnología de los Computadores, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain); Palomares, A. [Departamento de Matemática Aplicada, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain); Alper, C.; Ionescu, A. M. [Nanoelectronic Devices Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015 (Switzerland); Gámiz, F. [Departamento de Electrónica y Tecnología de los Computadores, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain)

    2016-01-28

    In this work, we analyze the behavior of the band-to-band tunneling distance between electron and hole subbands resulting from field-induced quantum confinement in the heterogate electron–hole bilayer tunnel field-effect transistor. We show that, analogously to the explicit formula for the tunneling distance that can be easily obtained in the semiclassical framework where the conduction and valence band edges are allowed states, an equivalent analytical expression can be derived in the presence of field-induced quantum confinement for describing the dependence of the tunneling distance on the body thickness and material properties of the channel. This explicit expression accounting for quantum confinement holds valid provided that the potential wells for electrons and holes at the top and bottom of the channel can be approximated by triangular profiles. Analytical predictions are compared to simulation results showing very accurate agreement.

  16. On the origin of inter band gap radiative emission in crystalline silicon

    Directory of Open Access Journals (Sweden)

    I. Burud

    2012-12-01

    Full Text Available Crystal imperfections degrade the quality of multicrystalline silicon wafers by introducing alternative recombination mechanisms. Here we use non-destructive hyperspectral imaging to detect photoluminescence signals from radiatively active recombination processes over the wafer with a highly resolved spectral third dimension. We demonstrate that band-to-band recombination can be visually separated from recombination through traps across the whole surface of a wafer using hyperspectral imaging. Our samples are studied in the near infrared wavelength region, 900-1700 nm, which includes the region of the so called D-band emission lines. These constitute four resolved emission lines found in the photoluminescence spectrum of silicon, commonly related to recombination through shallow inter-band gap energy levels near the conduction- and valence band edges. The shape and structure of these emissions from our measurements suggest that all the D-lines have different origins.

  17. Picosecond thermometer in the amide I band of myoglobin

    DEFF Research Database (Denmark)

    Austin, R.H.; Xie, A.; Meer, L. van der;

    2005-01-01

    The amide I and II bands in myoglobin show a heterogeneous temperature dependence, with bands at 6.17 and 6.43 mu m which are more intense at low temperatures. The amide I band temperature dependence is on the long wavelength edge of the band, while the short wavelength side has almost no tempera...

  18. Stability of edge states and edge magnetism in graphene nanoribbons

    OpenAIRE

    Kunstmann, Jens; Özdoğan, Cem; Quandt, Alexander; Fehske, Holger

    2010-01-01

    We critically discuss the stability of edge states and edge magnetism in zigzag edge graphene nanoribbons (ZGNRs). We point out that magnetic edge states might not exist in real systems, and show that there are at least three very natural mechanisms - edge reconstruction, edge passivation, and edge closure - which dramatically reduce the effect of edge states in ZGNRs or even totally eliminate them. Even if systems with magnetic edge states could be made, the intrinsic magnetism would not be ...

  19. Enhancement Effect of Refractive Index Phase Shift Modulation Near Guided-wave Band Edge of Line-defect Photonic Crystal Waveguides%光子晶体线缺陷波导中的折射率相位移调制增强效应

    Institute of Scientific and Technical Information of China (English)

    陈兵; 唐天同

    2011-01-01

    In the phase shift modulation type optical components constructed by traditional dielectric waveguides with the low refractive index constant based on the total inner reflection mechanism,the length of the modulation region is usually millimeter or centimeter order of magnitude,while their horizontal size is micrometer of order of magnitude,therefore,the most typical characteristics of optical waveguide devices are long and narrow.Reducing the size of optical waveguide devices is a hard problem in the development of highly dense integrated optical circuits.The emergence of photonic crystals provides a new approach to develop highly dense integrated optical circuits.The plane wave expansion method is used to calculate the dispersion curves of the line-defect type photonic crystal waveguides.It is observed that there is a large change of wave prorogation constant near the guided-wave band edge,corresponding to a little change of refractive index of the material.If the work frequency is selected near the guided-wave band edge,the phase shift modulation length is expected to largely reduce.The finite-difference time-domain method is used to demonstrate the results above.Calculated results indicate that there is strong enhancement effect of refractive index phase shift modulation near guided-wave band edge:for the refractive index change of 0.46%,the phase shift modulation length in these waveguides is only 11.7% of that in conventional uniform dielectric material.This enhancement effect is originated from the special flat dispersion properties near the guide-wave band edge,and it is expected to be applied to high dense photonic integrated circuits after further research.%在传统的基于全内反射原理的低折射率比介质波导所构建的相位移调制型光学器件中,调制区域的长度通常在毫米到厘米量级.由于器件横向尺寸保持在微米量级,因此狭长结构成为了传统光波导器件的典型特征,这限制了光学器件集

  20. MERIS and the red-edge position

    NARCIS (Netherlands)

    Clevers, J.G.P.W.; Jong, de S.M.; Epema, G.F.; Meer, van der F.; Bakker, W.H.; Skidmore, A.K.; Addink, E.A.

    2002-01-01

    The Medium Resolution Imaging Spectrometer (MERIS) is a payload component of Envisat-1. MERIS will be operated over land with a standard 15 band setting acquiring images with a 300 m spatial resolution. The red-edge position (REP) is a promising variable for deriving foliar chlorophyll concentration

  1. Interaction effects along the edge of a topological superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Hofmann, Johannes S. [Institut fuer Theoretische Physik und Astrophysik, Wuerzburg (Germany); Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Schnyder, Andreas P. [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Assaad, Fakher [Institut fuer Theoretische Physik und Astrophysik, Wuerzburg (Germany)

    2015-07-01

    Topological nodal superconductors, such as d{sub xy}-wave and nodal non-centrosymmetric superconductors, exhibit protected zero-energy flat-band edge states. These zero-energy edge modes are protected by time-reversal and translation symmetry and their stability is guaranteed by the conservation of a quantized topological invariant. Here, we study the fate of these flat-band edge states in the presence of interactions. We find that Hubbard interactions lead to spontaneous breaking of time-reversal or translation symmetry at the edge of the system. For the d{sub xy}-wave superconductor in the presence of attractive Hubbard interactions we find that the flat-band states become unstable towards the formation of a charge-density wave state or a state with s-wave type pairing correlations. Repulsive Hubbard interactions, on the other hand, induce ferromagnetic order at the edge of the d{sub xy}-wave superconductor.

  2. Orbital edge states in a photonic honeycomb lattice

    CERN Document Server

    Milićević, Marijana; Montambaux, Gilles; Carusotto, Iacopo; Galopin, Elisabeth; Lemaître, Aristide; Gratiet, Luc Le; Sagnes, Isabelle; Bloch, Jacqueline; Amo, Alberto

    2016-01-01

    We experimentally reveal the emergence of edge states in a photonic lattice with orbital bands. We use a two-dimensional honeycomb lattice of coupled micropillars whose bulk spectrum shows four gapless bands arising from the coupling of $p$-like photonic orbitals. We observe zero-energy edge states whose topological origin is similar to that of conventional edge states in graphene. Additionally, we report novel dispersive edge states that emerge not only in zigzag and bearded terminations, but also in armchair edges. The observations are reproduced by tight-binding and analytical calculations. Our work shows the potentiality of coupled micropillars in elucidating some of the electronic properties of emergent 2D materials with orbital bands.

  3. Protected Edge Modes without Symmetry

    Directory of Open Access Journals (Sweden)

    Michael Levin

    2013-05-01

    Full Text Available We discuss the question of when a gapped two-dimensional electron system without any symmetry has a protected gapless edge mode. While it is well known that systems with a nonzero thermal Hall conductance, K_{H}≠0, support such modes, here we show that robust modes can also occur when K_{H}=0—if the system has quasiparticles with fractional statistics. We show that some types of fractional statistics are compatible with a gapped edge, while others are fundamentally incompatible. More generally, we give a criterion for when an electron system with Abelian statistics and K_{H}=0 can support a gapped edge: We show that a gapped edge is possible if and only if there exists a subset of quasiparticle types M such that (1 all the quasiparticles in M have trivial mutual statistics, and (2 every quasiparticle that is not in M has nontrivial mutual statistics with at least one quasiparticle in M. We derive this criterion using three different approaches: a microscopic analysis of the edge, a general argument based on braiding statistics, and finally a conformal field theory approach that uses constraints from modular invariance. We also discuss the analogous result for two-dimensional boson systems.

  4. Power spectrum weighted edge analysis for straight edge detection in images

    Science.gov (United States)

    Karvir, Hrishikesh V.; Skipper, Julie A.

    2007-04-01

    Most man-made objects provide characteristic straight line edges and, therefore, edge extraction is a commonly used target detection tool. However, noisy images often yield broken edges that lead to missed detections, and extraneous edges that may contribute to false target detections. We present a sliding-block approach for target detection using weighted power spectral analysis. In general, straight line edges appearing at a given frequency are represented as a peak in the Fourier domain at a radius corresponding to that frequency, and a direction corresponding to the orientation of the edges in the spatial domain. Knowing the edge width and spacing between the edges, a band-pass filter is designed to extract the Fourier peaks corresponding to the target edges and suppress image noise. These peaks are then detected by amplitude thresholding. The frequency band width and the subsequent spatial filter mask size are variable parameters to facilitate detection of target objects of different sizes under known imaging geometries. Many military objects, such as trucks, tanks and missile launchers, produce definite signatures with parallel lines and the algorithm proves to be ideal for detecting such objects. Moreover, shadow-casting objects generally provide sharp edges and are readily detected. The block operation procedure offers advantages of significant reduction in noise influence, improved edge detection, faster processing speed and versatility to detect diverse objects of different sizes in the image. With Scud missile launcher replicas as target objects, the method has been successfully tested on terrain board test images under different backgrounds, illumination and imaging geometries with cameras of differing spatial resolution and bit-depth.

  5. Integral edge seals for phosphoric acid fuel cells

    Science.gov (United States)

    Granata, Jr., Samuel J. (Inventor); Woodle, Boyd M. (Inventor); Dunyak, Thomas J. (Inventor)

    1992-01-01

    A phosphoric acid fuel cell having integral edge seals formed by an elastomer permeating an outer peripheral band contiguous with the outer peripheral edges of the cathode and anode assemblies and the matrix to form an integral edge seal which is reliable, easy to manufacture and has creep characteristics similar to the anode, cathode and matrix assemblies inboard of the seals to assure good electrical contact throughout the life of the fuel cell.

  6. Edge magnetization in Bernal-stacked trilayer zigzag graphene nanoribbons

    Science.gov (United States)

    Pérez, Juan Antonio Casao

    2016-06-01

    We have used a tight-binding Hamiltonian of an ABA-stacked trilayer zigzag graphene nanoribbon with β-alignment edges to study the edge magnetizations. Our model includes the effect of the intralayer next-nearest-neighbor hopping, the interlayer hopping responsible for the trigonal warping and the interaction between electrons, which is considered by a single band Hubbard model in the mean field approximation. Firstly, in the neutral system we analyzed the two magnetic states in which both edge magnetizations reach their maximum value; the first one is characterized by an intralayer ferromagnetic coupling between the magnetizations at opposite edges, whereas in the second state that coupling is antiferromagnetic. The band structure, the location of the edge-state bands and the local density of states resolved in spin are calculated in order to understand the origins of the edge magnetizations. We have also introduced an electron doping so that the number of electrons in the ribbon unit cell is higher than in neutral case. As a consequence, we have obtained magnetization steps and charge accumulation at the edges of the sample, which are caused by the edge-state flat bands.

  7. Unconventional quantized edge transport in the presence of inter-edge coupling in intercalated graphene

    OpenAIRE

    Li, Yuanchang

    2016-01-01

    It is generally believed that the inter-edge coupling destroys the quantum spin Hall (QSH) effect along with the gap opening at the Dirac points. Using first-principles calculations, we find that the quantized edge transport persists in the presence of inter-edge coupling in Ta intercalated epitaxial graphene on SiC(0001), being a QSH insulator with the non-trivial gap of 81 meV. In this case, the band is characterized by two perfect Dirac cones with different Fermi velocities, yet only one m...

  8. Tunable magnetic states on the zigzag edges of hydrogenated and halogenated group-IV nanoribbons

    Science.gov (United States)

    Wang, Tzu-Cheng; Hsu, Chia-Hsiu; Huang, Zhi-Quan; Chuang, Feng-Chuan; Su, Wan-Sheng; Guo, Guang-Yu

    2016-12-01

    The magnetic and electronic properties of hydrogenated and halogenated group-IV zigzag nanoribbons (ZNRs) are investigated by first-principles density functional calculations. Fascinatingly, we find that all the ZNRs have magnetic edges with a rich variety of electronic and magnetic properties tunable by selecting the parent and passivating elements as well as controlling the magnetization direction and external strain. In particular, the electric property of the edge band structure can be tuned from the conducting to insulating with a band gap up to 0.7 eV. The last controllability would allow us to develop magnetic on-off nano-switches. Furthermore, ZNRs such as SiI, Ge, GeI and SnH, have fully spin-polarized metallic edge states and thus are promising materials for spintronics. The calculated magnetocrystalline anisotropy energy can be as large as ~9 meV/edge-site, being 2×103 time greater than that of bulk Ni and Fe (~5 μeV/atom), and thus has great potential for high density magneto-electric data-storage devices. Finally, the calculated exchange coupling strength and thus magnetic transition temperature increases as the applied strain goes from ‑5% to 5%. Our findings thus show that these ZNRs would have exciting applications in next-generation electronic and spintronic nano-devices.

  9. X-ray absorption near edge structure/electron energy loss near edge structure calculation using the supercell orthogonalized linear combination of atomic orbitals method.

    Science.gov (United States)

    Ching, Wai-Yim; Rulis, Paul

    2009-03-11

    Over the last eight years, a large number of x-ray absorption near edge structure (XANES) and/or electron energy loss near edge structure (ELNES) spectroscopic calculations for complex oxides and nitrides have been performed using the supercell-OLCAO (orthogonalized linear combination of atomic orbitals) method, obtaining results in very good agreement with experiments. The method takes into account the core-hole effect and includes the dipole matrix elements calculated from ab initio wavefunctions. In this paper, we describe the method in considerable detail, emphasizing the special advantages of this method for large complex systems. Selected results are reviewed and several hitherto unpublished results are also presented. These include the Y K edge of Y ions segregated to the core of a Σ31 grain boundary in alumina, O K edges of water molecules, C K edges in different types of single walled carbon nanotubes, and the Co K edge in the cyanocobalamin (vitamin B(12)) molecule. On the basis of these results, it is argued that the interpretation of specific features of the calculated XANES/ELNES edges is not simple for complex material systems because of the delocalized nature of the conduction band states. The long-standing notion of the 'fingerprinting' technique for spectral interpretation of experimental data is not tenable. A better approach is to fully characterize the structure under study, using either crystalline data or accurate ab initio modeling. Comparison between calculated XANES/ELNES spectra and available measurements enables us to ascertain the validity of the modeled structure. For complex crystals or structures, it is necessary to use the weighted sum of the spectra from structurally nonequivalent sites for comparison with the measured data. Future application of the supercell-OLCAO method to complex biomolecular systems is also discussed.

  10. X-ray absorption near edge structure/electron energy loss near edge structure calculation using the supercell orthogonalized linear combination of atomic orbitals method

    Energy Technology Data Exchange (ETDEWEB)

    Ching, W.-Y.; Rulis, Paul [Department of Physics, University of Missouri-Kansas City, Kansas City, MO 64110 (United States)

    2009-03-11

    Over the last eight years, a large number of x-ray absorption near edge structure (XANES) and/or electron energy loss near edge structure (ELNES) spectroscopic calculations for complex oxides and nitrides have been performed using the supercell-OLCAO (orthogonalized linear combination of atomic orbitals) method, obtaining results in very good agreement with experiments. The method takes into account the core-hole effect and includes the dipole matrix elements calculated from ab initio wavefunctions. In this paper, we describe the method in considerable detail, emphasizing the special advantages of this method for large complex systems. Selected results are reviewed and several hitherto unpublished results are also presented. These include the Y K edge of Y ions segregated to the core of a {sigma}31 grain boundary in alumina, O K edges of water molecules, C K edges in different types of single walled carbon nanotubes, and the Co K edge in the cyanocobalamin (vitamin B{sub 12}) molecule. On the basis of these results, it is argued that the interpretation of specific features of the calculated XANES/ELNES edges is not simple for complex material systems because of the delocalized nature of the conduction band states. The long-standing notion of the 'fingerprinting' technique for spectral interpretation of experimental data is not tenable. A better approach is to fully characterize the structure under study, using either crystalline data or accurate ab initio modeling. Comparison between calculated XANES/ELNES spectra and available measurements enables us to ascertain the validity of the modeled structure. For complex crystals or structures, it is necessary to use the weighted sum of the spectra from structurally nonequivalent sites for comparison with the measured data. Future application of the supercell-OLCAO method to complex biomolecular systems is also discussed.

  11. X-ray absorption near edge structure/electron energy loss near edge structure calculation using the supercell orthogonalized linear combination of atomic orbitals method

    Science.gov (United States)

    Ching, Wai-Yim; Rulis, Paul

    2009-03-01

    Over the last eight years, a large number of x-ray absorption near edge structure (XANES) and/or electron energy loss near edge structure (ELNES) spectroscopic calculations for complex oxides and nitrides have been performed using the supercell-OLCAO (orthogonalized linear combination of atomic orbitals) method, obtaining results in very good agreement with experiments. The method takes into account the core-hole effect and includes the dipole matrix elements calculated from ab initio wavefunctions. In this paper, we describe the method in considerable detail, emphasizing the special advantages of this method for large complex systems. Selected results are reviewed and several hitherto unpublished results are also presented. These include the Y K edge of Y ions segregated to the core of a Σ31 grain boundary in alumina, O K edges of water molecules, C K edges in different types of single walled carbon nanotubes, and the Co K edge in the cyanocobalamin (vitamin B12) molecule. On the basis of these results, it is argued that the interpretation of specific features of the calculated XANES/ELNES edges is not simple for complex material systems because of the delocalized nature of the conduction band states. The long-standing notion of the 'fingerprinting' technique for spectral interpretation of experimental data is not tenable. A better approach is to fully characterize the structure under study, using either crystalline data or accurate ab initio modeling. Comparison between calculated XANES/ELNES spectra and available measurements enables us to ascertain the validity of the modeled structure. For complex crystals or structures, it is necessary to use the weighted sum of the spectra from structurally nonequivalent sites for comparison with the measured data. Future application of the supercell-OLCAO method to complex biomolecular systems is also discussed.

  12. Importance of non-parabolic band effects in the thermoelectric properties of semiconductors

    OpenAIRE

    Xin Chen; David Parker; Singh, David J.

    2013-01-01

    We present an analysis of the thermoelectric properties of of $n$-type GeTe and SnTe in relation to the lead chalcogenides PbTe and PbSe. We find that the singly degenerate conduction bands of semiconducting GeTe and SnTe are highly non-ellipsoidal, even very close to the band edges. This leads to isoenergy surfaces with a strongly corrugated shape that is clearly evident at carrier concentrations well below 0.005 $e$ per formula unit (7 - 9 $\\times$ 10$^{19}$cm$^{-3}$ depending on material) ...

  13. Edge physics Simulations

    Institute of Scientific and Technical Information of China (English)

    X.Q. Xu; C.S. Chang

    2007-01-01

    @@ The plasma edge includes the pedestal, scrape-off, and divertor regions. A complete edge physics should deal with the plasma, atomic, and the plasma-wall interaction phenomena. The edge provides the source of plasma through ionization of the incoming neutral particles and source of impurity through the wall sputtering. Edge plasma sets a boundary condition for the core confinement physics. Importance of the edge plasma has been elevated to the top list of the ITER physics research needs due to the necessity of the self-organized plasma pedestal and its destruction by edge localized mode activities. Extrapolation of the present tokamak data base predicts that a sufficient pedestal height is a necessary condition for the success of ITER.

  14. Calculation of band structure in (101)-biaxially strained Si

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The structure model used for calculation was defined according to Vegard’s rule and Hooke’s law. Calculations were performed on the electronic structures of(101)-biaxially strained Si on relaxed Si1-X GeX alloy with Ge fraction ranging from X = 0 to 0.4 in steps of 0.1 by CASTEP approach. It was found that [±100] and [00±1] valleys(-4) splitting from the [0±10] valley(-2) constitute the conduction b0and(CB) edge,that valence band(VB) edge degeneracy is partially lifted and that the electron mass is un-altered under strain while the hole mass decreases in the [100] and [010] directions. In addition,the fitted dependences of CB splitting energy,VB splitting energy and indirect bandgap on X are all linear.

  15. Zigzag graphene nanoribbon edge reconstruction with Stone-Wales defects

    DEFF Research Database (Denmark)

    Rodrigues, J. N. B.; Gonçalves, P. A. D; Rodrigues, N. F. G.;

    2011-01-01

    In this paper, we study zigzag graphene nanoribbons with edges reconstructed with Stone-Wales defects, by means of an empirical (first-neighbor) tight-binding method, with parameters determined by ab initio calculations of very narrow ribbons. We explore the characteristics of the electronic band...... structure with a focus on the nature of edge states. Edge reconstruction allows the appearance of a new type of edge states. They are dispersive, with nonzero amplitudes in both sublattices; furthermore, the amplitudes have two components that decrease with different decay lengths with the distance from...... the edge; at the Dirac points one of these lengths diverges, whereas the other remains finite, of the order of the lattice parameter. We trace this curious effect to the doubling of the unit cell along the edge, brought about by the edge reconstruction. In the presence of a magnetic field, the zero...

  16. Bulk Versus Edge in the Quantum Hall Effect

    OpenAIRE

    Kao, Y. -C.; Lee, D.-H.

    1996-01-01

    The manifestation of the bulk quantum Hall effect on edge is the chiral anomaly. The chiral anomaly {\\it is} the underlying principle of the ``edge approach'' of quantum Hall effect. In that approach, $\\sxy$ should not be taken as the conductance derived from the space-local current-current correlation function of the pure one-dimensional edge problem.

  17. Tasting edge effects

    CERN Document Server

    Bocquet, L

    2006-01-01

    We show that the baking of potato wedges constitutes a crunchy example of edge effects, which are usually demonstrated in electrostatics. A simple model of the diffusive transport of water vapor around the potato wedges shows that the water vapor flux diverges at the sharp edges in analogy with its electrostatic counterpart. This increased evaporation at the edges leads to the crispy taste of these parts of the potatoes.

  18. Tasting edge effects

    Science.gov (United States)

    Bocquet, Lydéric

    2007-02-01

    We show that the baking of potato wedges constitutes a crunchy example of edge effects, which are usually demonstrated in electrostatics. A simple model of the diffusive transport of water vapor around the potato wedges shows that the water vapor flux diverges at the sharp edges in analogy with its electrostatic counterpart. This increased evaporation at the edges leads to the crispy taste of these parts of the potatoes.

  19. Influence of a falling edge on high power microwave pulse combination

    Science.gov (United States)

    Li, Jiawei; Huang, Wenhua; Zhu, Qi; Xiao, Renzhen; Shao, Hao

    2016-07-01

    This paper presents an explanation of the influence of a microwave falling edge on high-power microwave pulse combination. Through particle-in-cell simulations, we discover that the falling edge is the driving factor that limits the output power of the combined pulses. We demonstrate that the space charge field, which accumulates to become comparable to the E-field at the falling edge of the former pulse, will trap the electrons in the gas layer and decrease its energy to attain a high ionization rate. Hence, avalanche discharge, caused by trapped electrons, makes the plasma density to approach the critical density and cuts off the latter microwave pulse. An X-band combination experiment is conducted with different pulse intervals. This experiment confirms that the high density plasma induced by the falling edge can cut off the latter pulse, and that the time required for plasma recombination in the transmission channel is several microseconds. To ensure a high output power for combined pulses, the latter pulse should be moved ahead of the falling edge of the former one, and consequently, a beat wave with high peak power becomes the output by adding two pulses with normal amplitudes.

  20. TiO2 Band Restructuring by B and P Dopants.

    Science.gov (United States)

    Li, Lei; Meng, Fanling; Hu, Xiaoying; Qiao, Liang; Sun, Chang Q; Tian, Hongwei; Zheng, Weitao

    2016-01-01

    An examination of the effect of B- and P-doping and codoping on the electronic structure of anatase TiO2 by performing density functional theory calculations revealed the following: (i) B- or P-doping effects are similar to atomic undercoordination effects on local bond relaxation and core electron entrapment; (ii) the locally entrapped charge adds impurity levels within the band gap that could enhance the utilization of TiO2 to absorb visible light and prolong the carrier lifetime; (iii) the core electron entrapment polarizes nonbonding electrons in the upper edges of the valence and conduction bands, which reduces not only the work function but also the band gap; and (iv) work function reduction enhances the reactivity of the carriers and band gap reduction promotes visible-light absorption. These observations may shed light on effective catalyst design and synthesis.

  1. Valence band structure of strained Si/(111)Si1-xGex

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The strained Si techique has been widely adopted in the high-speed and high-performance devices and circuits. Based on the valence band E-k relations of strained Si/(111)Si1-xGex, the valence band and hole effective mass along the [111] and [-110] directions were obtained in this work. In comparison with the relaxed Si, the valence band edge degeneracy was partially lifted, and the significant change was observed band structures along the [111] and [-110] directions, as well as in its corresponding hole effective masses with the increasing Ge fraction. The results obtained can provide valuable references to the investigation concerning the Si-based strained devices enhancement and the conduction channel design related to stress and orientation.

  2. Edge, cavity and aperture tones at very low Mach numbers

    Science.gov (United States)

    Howe, M. S.

    1997-01-01

    This paper discusses self-sustaining oscillations of high-Reynolds-number shear layers and jets incident on edges and corners at infinitesimal Mach number. These oscillations are frequently sources of narrow-band sound, and are usually attributed to the formation of discrete vortices whose interactions with the edge or corner produce impulsive pressures that lead to the formation of new vorticity and complete a feedback cycle of operation. Linearized analyses of these interactions are presented in which free shear layers are modelled by vortex sheets. Detailed results are given for shear flows over rectangular wall apertures and shallow cavities, and for the classical jet edge interaction. The operating stages of self-sustained oscillations are identified with poles in the upper half of the complex frequency plane of a certain impulse response function. It is argued that the real parts of these poles determine the Strouhal numbers of the operating stages observed experimentally for the real, nonlinear system. The response function coincides with the Rayleigh conductivity of the ‘window’ spanned by the shear flow for wall apertures and jet edge interactions, and to a frequency dependent drag coefficient for shallow wall cavities. When the interaction occurs in the neighbourhood of an acoustic resonator, exemplified by the flue organ pipe, the poles are augmented by a sequence of poles whose real parts are close to the resonance frequencies of the resonator, and the resonator can ‘speak’ at one of these frequencies (by extracting energy from the mean flow) provided the corresponding pole has positive imaginary part.

  3. Strain-activated edge reconstruction of graphene nanoribbons

    KAUST Repository

    Cheng, Yingchun

    2012-02-17

    The edge structure and width of graphene nanoribbons (GNRs) are crucial factors for the electronic properties. A combination of experiment and first-principles calculations allows us to determine the mechanism of the hexagon-hexagon to pentagon-heptagon transformation. GNRs thinner than 2 nm have been fabricated by bombardment of graphene with high-energetic Au clusters. The edges of the GNRs are modified in situ by electron irradiation. Tensile strain along the edge decreases the transformation energy barrier. Antiferromagnetism and a direct band gap are found for a zigzag GNR, while a fully reconstructed GNR shows an indirect band gap. A GNR reconstructed on only one edge exhibits ferromagnetism. We propose that strain is an effective method to tune the edge and, therefore, the electronic structure of thin GNRs for graphene-based electronics.

  4. On Edge Detection,

    Science.gov (United States)

    1984-08-01

    T. 0. "On boundary detection." A. I. Memo 183, MIT, 1980. Hildreth, E. C. "Implementation of a theory of edge detection ." A. /. Memo 579, MIT, 1980...Detection." IEEE Trans. PAMI, 6, 678-680, 1983. Marr, 0. C. and Hildreth, E. C, " Theory of edge detection ." Proc. R. Soc. Lond. B, 207, 187-217, 1980. Marr

  5. Two-dimensionally confined topological edge states in photonic crystals

    Science.gov (United States)

    Barik, Sabyasachi; Miyake, Hirokazu; DeGottardi, Wade; Waks, Edo; Hafezi, Mohammad

    2016-11-01

    We present an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states. The topological properties of the system are controlled by the crystal parameters. An interface between two regions of differing band topologies gives rise to topological edge states confined in a dielectric slab that propagate around sharp corners without backscattering. Three-dimensional finite-difference time-domain calculations show these edges to be confined in the out-of-plane direction by total internal reflection. Such nanoscale photonic crystal architectures could enable strong interactions between photonic edge states and quantum emitters.

  6. Two-Dimensionally Confined Topological Edge States in Photonic Crystals

    CERN Document Server

    Barik, Sabyasachi; DeGottardi, Wade; Waks, Edo; Hafezi, Mohammad

    2016-01-01

    We present an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states. The topological properties of the system are controlled by the crystal parameters. An interface between two regions of differing band topologies gives rise to topological edge states confined in a dielectric slab that propagate around sharp corners without backscattering. Three dimensional finite-difference time-domain calculations show these edges to be confined in the out-of-plane direction by total internal reflection. Such nanoscale photonic crystal architectures could enable strong interactions between photonic edge states and quantum emitters.

  7. Band Together!

    Science.gov (United States)

    Olson, Cathy Applefeld

    2011-01-01

    After nearly a decade as band director at St. James High School in St. James, Missouri, Derek Limback knows that the key to building a successful program is putting the program itself above everything else. Limback strives to augment not only his students' musical prowess, but also their leadership skills. Key to his philosophy is instilling a…

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

    Science.gov (United States)

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

    2013-04-24

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

  9. Optical XAFS of ZnO Nanowires at the Zn K-Edge and Related Phenomena

    Energy Technology Data Exchange (ETDEWEB)

    Heigl, F.; Sun, X.H.J; Lam, S.; Sham, T.K.; Gordon, R.; Brewe, D.; Rosenberg, R.; Shenoy, G.; Yablonskikh, M.; MacNaughton, J.; Moewes, A. (APS); (UWO); (Simon); (Saskatchewan)

    2008-10-06

    We report x-ray excited optical luminescence (XEOL) from one-dimensional nanostructures of ZnO excited with photon energies across the Zn K-edge. The optical luminescence shows an UV and a green emission band characteristic of near band edge and defect emission, respectively. The optical channels were used in turn to monitor the Zn K-edge XAFS to high k values. The densities of states of oxygen character in the valence band were also studied with x-ray emission spectroscopy (XES). The Zn K-edge decay dynamics was examined with time-resolved x-ray excited optical luminescence.

  10. Reflection and transmission of ocean wave spectra by a band of randomly distributed ice floes

    CERN Document Server

    Montiel, Fabien; Bennetts, Luke

    2014-01-01

    A new ocean wave/sea-ice interaction model is proposed that simulates how a directional wave spectrum evolves as it travels through an arbitrary finite array of circular ice floes, where wave/ice dynamics are entirely governed by wave scattering effects. The model is applied to characterise the wave reflection and transmission properties of a strip of ice floes, such as an ice edge band. A method is devised to extract the reflected and transmitted directional wave spectra produced by the array. The method builds upon an integral mapping from polar to Cartesian coordinates of the scattered wave components. Sensitivity tests are conducted for a row of floes randomly perturbed from a regular arrangement. Results for random arrays are generated using ensemble averaging. A realistic ice edge band is then reconstructed from field experiments data. Simulations show a good qualitative agreement with the data in terms of transmitted wave energy and directional spreading. In particular, it is observed that short waves ...

  11. Floquet edge states in germanene nanoribbons

    KAUST Repository

    Tahir, M.

    2016-08-23

    We theoretically demonstrate versatile electronic properties of germanene monolayers under circularly, linearly, and elliptically polarized light. We show for the high frequency regime that the edge states can be controlled by tuning the amplitude of the light and by applying a static electric field. For circularly polarized light the band gap in one valley is reduced and in the other enhanced, enabling single valley edge states. For linearly polarized light spin-split states are found for both valleys, being connected by time reversal symmetry. The effects of elliptically polarized light are similar to those of circularly polarized light. The transport properties of zigzag nanoribbons in the presence of disorder confirm a nontrivial nature of the edge states under circularly and elliptically polarized light.

  12. Edge excitations in fractional Chern insulators

    Science.gov (United States)

    Luo, Wei-Wei; Chen, Wen-Chao; Wang, Yi-Fei; Gong, Chang-De

    2013-10-01

    Recent theoretical papers have demonstrated the realization of fractional quantum anomalous Hall states (also called fractional Chern insulators) in topological flat band lattice models without an external magnetic field. Such newly proposed lattice systems play a vital role in obtaining a large class of fractional topological phases. Here we report the exact numerical studies of edge excitations for such systems in a disk geometry loaded with hard-core bosons, which will serve as a more viable experimental probe for such topologically ordered states. We find convincing numerical evidence of a series of edge excitations characterized by the chiral Luttinger liquid theory for the bosonic fractional Chern insulators in both the honeycomb disk Haldane model and the kagome-lattice disk model. We further verify these current-carrying chiral edge states by inserting a central flux to test their compressibility.

  13. Topological edge modes in multilayer graphene systems

    KAUST Repository

    Ge, Lixin

    2015-08-10

    Plasmons can be supported on graphene sheets as the Dirac electrons oscillate collectively. A tight-binding model for graphene plasmons is a good description as the field confinement in the normal direction is strong. With this model, the topological properties of plasmonic bands in multilayer graphene systems are investigated. The Zak phases of periodic graphene sheet arrays are obtained for different configurations. Analogous to Su-Schrieffer-Heeger (SSH) model in electronic systems, topological edge plasmon modes emerge when two periodic graphene sheet arrays with different Zak phases are connected. Interestingly, the dispersion of these topological edge modes is the same as that in the monolayer graphene and is invariant as the geometric parameters of the structure such as the separation and period change. These plasmonic edge states in multilayer graphene systems can be further tuned by electrical gating or chemical doping. © 2015 Optical Society of America.

  14. Density Functional Theory Calculation of the Band Alignment of (101̅0) In(x)Ga(1-x)N/Water Interfaces.

    Science.gov (United States)

    Meng, Andrew C; Cheng, Jun; Sprik, Michiel

    2016-03-03

    Conduction band edge (CBE) and valence band edge (VBE) positions of InxGa1-xN photoelectrodes were computed using density functional theory methods. The band edges of fully solvated GaN and InN model systems were aligned with respect to the standard hydrogen electrode using a molecular dynamics hydrogen electrode scheme applied earlier to TiO2/water interfaces. Similar to the findings for TiO2, we found that the Purdew-Burke-Ernzerhof (PBE) functional gives a VBE potential which is too negative by 1 V. This cathodic bias is largely corrected by application of the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional containing a fraction of Hartree-Fock exchange. The effect of a change of composition was investigated using simplified model systems consisting of vacuum slabs covered on both sides by one monolayer of H2O. The CBE was found to vary linearly with In content. The VBE, in comparison, is much less sensitive to composition. The data show that the band edges straddle the hydrogen and oxygen evolution potentials for In fractions less than 47%. The band gap was found to exceed 2 eV for an In fraction less than 54%.

  15. Casimir edge effects

    CERN Document Server

    Gies, H; Gies, Holger; Klingmuller, Klaus

    2006-01-01

    We compute Casimir forces in open geometries with edges, involving parallel as well as perpendicular semi-infinite plates. We focus on Casimir configurations which are governed by a unique dimensional scaling law with a universal coefficient. With the aid of worldline numerics, we determine this coefficient for various geometries for the case of scalar-field fluctuations with Dirichlet boundary conditions. Our results facilitate an estimate of the systematic error induced by the edges of finite plates, for instance, in a standard parallel-plate experiment. The Casimir edge effects for this case can be reformulated as an increase of the effective area of the configuration.

  16. Adobe Edge Quickstart Guide

    CERN Document Server

    Labrecque, Joseph

    2012-01-01

    Adobe Edge Quickstart Guide is a practical guide on creating engaging content for the Web with Adobe's newest HTML5 tool. By taking a chapter-by-chapter look at each major aspect of Adobe Edge, the book lets you digest the available features in small, easily understandable chunks, allowing you to start using Adobe Edge for your web design needs immediately. If you are interested in creating engaging motion and interactive compositions using web standards with professional tooling, then this book is for you. Those with a background in Flash Professional wanting to get started quickly with Adobe

  17. Theory of edge radiation

    CERN Document Server

    Geloni, Gianluca; Saldin, Evgeni; Schneidmiller, Evgeni; Yurkov, Mikhail

    2008-01-01

    We formulate a complete theory of Edge Radiation based on a novel method relying on Fourier Optics techniques. Similar types of radiation like Transition Undulator Radiation are addressed in the framework of the same formalism. Special attention is payed in discussing the validity of approximations upon which the theory is built. Our study makes consistent use of both similarity techniques and comparisons with numerical results from simulation. We discuss both near and far zone. Physical understanding of many asymptotes is discussed. Based on the solution of the field equation with a tensor Green's function technique, we also discuss an analytical model to describe the presence of a vacuum chamber. In particular, explicit calculations for a circular vacuum chamber are reported. Finally, we consider the use of Edge Radiation as a tool for electron beam diagnostics. We discuss Coherent Edge Radiation, Extraction of Edge Radiation by a mirror, and other issues becoming important at high electron energy and long ...

  18. Adobe Edge Preview 3

    CERN Document Server

    Grover, Chris

    2011-01-01

    Want to use an Adobe tool to design animated web graphics that work on iPhone and iPad? You've come to the right book. Adobe Edge Preview 3: The Missing Manual shows you how to build HTML5 graphics using simple visual tools. No programming experience? No problem. Adobe Edge writes the underlying code for you. With this eBook, you'll be designing great-looking web elements in no time. Get to know the workspace. Learn how Adobe Edge Preview 3 performs its magic.Create and import graphics. Make drawings with Edge's tools, or use art you designed in other programs.Work with text. Build menus, lab

  19. Band calculation of lonsdaleite Ge

    Science.gov (United States)

    Chen, Pin-Shiang; Fan, Sheng-Ting; Lan, Huang-Siang; Liu, Chee Wee

    2017-01-01

    The band structure of Ge in the lonsdaleite phase is calculated using first principles. Lonsdaleite Ge has a direct band gap at the Γ point. For the conduction band, the Γ valley is anisotropic with the low transverse effective mass on the hexagonal plane and the large longitudinal effective mass along the c axis. For the valence band, both heavy-hole and light-hole effective masses are anisotropic at the Γ point. The in-plane electron effective mass also becomes anisotropic under uniaxial tensile strain. The strain response of the heavy-hole mass is opposite to the light hole.

  20. Nanotube-Terminated Zigzag Edge of Phosphorene formed by Self-Rolling Reconstruction

    CERN Document Server

    Gao, Junfeng; Zhang, Gang; Zhang, Yong-Wei

    2016-01-01

    Edge atomic configuration often plays an important role in dictating the properties of finite-sized two-dimensional (2D) materials. By performing ab initio calculations, we identify a highly stable zigzag edge of phosphorene, which is the most stable one among all the considered edges. Surprisingly, this highly stable edge exhibits a novel nanotube-like structure, which is topologically distinctively different from any previously reported edge reconstruction. We further show that this new edge type can form easily, with an energy barrier of only 0.234 eV. It may be the dominant edge type at room temperature in vacuum condition or even under low hydrogen gas pressure. The calculated band structure reveals that the reconstructed edge possesses a bandgap of 1.23 eV. It is expected that this newly found edge structure may stimulate more studies in uncovering other novel edge types and further exploring their practical applications.

  1. Lasing at the band edges of plasmonic lattices

    NARCIS (Netherlands)

    Schokker, A.H.; Koenderink, A.F.

    2014-01-01

    We report room-temperature lasing in two-dimensional diffractive lattices of silver and gold plasmon particle arrays embedded in a dye-doped polymer that acts both as waveguide and gain medium. As compared to conventional dielectric distributed feedback (DFB) lasers, a central question is how the un

  2. Enhanced conductivity of reduced graphene oxide decorated with aluminium oxide nanoparticles by oxygen annealing.

    Science.gov (United States)

    Liu, Hao; Choy, Kwang-Leong; Roe, Martin

    2013-07-07

    A process involving the filtration of graphene oxide (GO) dispersion through an alumina membrane, followed by oxygen annealing to synthesize alumina nanoparticles exclusively at the edges of holes or vacancies in the reduced graphene oxide (rGO) plane, is used to prepare paper-like composites with a 21% enhanced electrical conductivity. Moreover, the rGO/alumina nanocomposites have a smaller band gap and hydrophilic properties.

  3. Edge waves and resonances in two-dimensional phononic crystal plates

    Science.gov (United States)

    Hsu, Jin-Chen; Hsu, Chih-Hsun

    2015-05-01

    We present a numerical study on phononic band gaps and resonances occurring at the edge of a semi-infinite two-dimensional (2D) phononic crystal plate. The edge supports localized edge waves coupling to evanescent phononic plate modes that decay exponentially into the semi-infinite phononic crystal plate. The band-gap range and the number of edge-wave eigenmodes can be tailored by tuning the distance between the edge and the semi-infinite 2D phononic lattice. As a result, a phononic band gap for simultaneous edge waves and plate waves is created, and phononic cavities beside the edge can be built to support high-frequency edge resonances. We design an L3 edge cavity and analyze its resonance characteristics. Based on the band gap, high quality factor and strong confinement of resonant edge modes are achieved. The results enable enhanced control over acoustic energy flow in phononic crystal plates, which can be used in designing micro and nanoscale resonant devices and coupling of edge resonances to other types of phononic or photonic crystal cavities.

  4. Quantization and topological states in the spin Hall conductivity of low-dimensional systems: An ab initio study

    Science.gov (United States)

    Matthes, L.; Küfner, S.; Furthmüller, J.; Bechstedt, F.

    2016-03-01

    Ab initio relativistic band structure calculations are performed for the frequency-dependent spin Hall conductivity of two-dimensional atomically thin crystals and one-dimensional nanoribbons. We study the influence of topology, quantization, and topological edge states. As model systems fully halogenated germanene, GeI, and its zigzag nanoribbons are investigated. GeI represents a topological insulator (TI). For comparison, also the TI germanene and the trivial insulator hydrogenated germanene are studied. For the TIs we demonstrate the quantization of the static spin Hall conductivity. It is hardly influenced by temperature and Fermi level shift. Its frequency dependence is governed by the band-structure details. Topological edge states influence the conductivity mainly for vanishing frequencies.

  5. The Edge supersonic transport

    Science.gov (United States)

    Agosta, Roxana; Bilbija, Dushan; Deutsch, Marc; Gallant, David; Rose, Don; Shreve, Gene; Smario, David; Suffredini, Brian

    1992-01-01

    As intercontinental business and tourism volumes continue their rapid expansion, the need to reduce travel times becomes increasingly acute. The Edge Supersonic Transport Aircraft is designed to meet this demand by the year 2015. With a maximum range of 5750 nm, a payload of 294 passengers and a cruising speed of M = 2.4, The Edge will cut current international flight durations in half, while maintaining competitive first class, business class, and economy class comfort levels. Moreover, this transport will render a minimal impact upon the environment, and will meet all Federal Aviation Administration Part 36, Stage III noise requirements. The cornerstone of The Edge's superior flight performance is its aerodynamically efficient, dual-configuration design incorporating variable-geometry wingtips. This arrangement combines the benefits of a high aspect ratio wing at takeoff and low cruising speeds with the high performance of an arrow-wing in supersonic cruise. And while the structural weight concerns relating to swinging wingtips are substantial, The Edge looks to ever-advancing material technologies to further increase its viability. Heeding well the lessons of the past, The Edge design holds economic feasibility as its primary focus. Therefore, in addition to its inherently superior aerodynamic performance, The Edge uses a lightweight, largely windowless configuration, relying on a synthetic vision system for outside viewing by both pilot and passengers. Additionally, a fly-by-light flight control system is incorporated to address aircraft supersonic cruise instability. The Edge will be produced at an estimated volume of 400 aircraft and will be offered to airlines in 2015 at $167 million per transport (1992 dollars).

  6. Dynamic conductance in double-bend silicene nanosystem

    Science.gov (United States)

    Sun, Yun-Lei; Zhu, Chun; Chen, Jian; Ye, En-Jia

    2017-09-01

    In this work, dynamic conductance transport properties are theoretically investigated in the zigzag silicene nanosystem with a double-bend structure. We numerically study the dc conductance and ac emittance in the nanosystem based on the tight-binding approach, Green's function method and ac transport theory, by considering the second-nearest-neighbor spin-orbit interaction (SOI) and external electric field. The numerical results suggest that the nanosystem undergoes a quantum phase transition driven by the relatively strong SOI, which results in a large dc conductance and a vanishing ac emittance around the Dirac point despite the interface scattering. The distribution of the local density of states in the real space reveals that the SOI induces the quantum edge state by establishing transport paths at the edge of the nanosystem. Further investigation indicates that the dynamic conductance related to the quantum edge state are topologically protected from the geometrical size change of the nanosystem. Finally, the nanosystem can be tuned to be a trivial band insulator without any dc or ac response by applying external electric field.

  7. Polarization-based perturbations to thermopower and electronic conductivity in highly conductive tungsten bronze structured (Sr,Ba)Nb2O6: Relaxors vs normal ferroelectrics

    Science.gov (United States)

    Bock, Jonathan A.; Trolier-McKinstry, Susan; Mahan, Gerald D.; Randall, Clive A.

    2014-09-01

    Electrical conductivity, thermopower, and lattice strain were investigated in the tetragonal tungsten bronze structured (Srx,Ba1-x)Nb2O6-δ system for 0.7>x>0.4 with large values of δ. These materials show attractive thermoelectric characteristics, especially in single-crystal form. Here, the Sr/Ba ratio was changed in order to vary the material between a normal ferroelectric with long-range polarization to relaxor behavior with short-range order and dynamic polarization. The influence of this on the electrical conduction mechanisms was then investigated. The temperature dependence of both the thermopower and differential activation energy for conduction suggests that the electronic conduction is controlled by an impurity band with a mobility edge separating localized and delocalized states. Conduction is controlled via hopping at low temperatures, and as temperature rises electrons are activated above the mobility edge, resulting in a large increase in electrical conductivity. For relaxor ferroelectric-based compositions, when dynamic short-range order polarization is present in the system, trends in the differential activation energy and thermopower show deviations from this conduction mechanism. The results are consistent with the polarization acting as a source of disorder that affects the location of the mobility edge and, therefore, the activation energy for conduction.

  8. Green's function asymptotics near the internal edges of spectra of periodic elliptic operators. Spectral edge case

    KAUST Repository

    Kuchment, Peter

    2012-06-21

    Precise asymptotics known for the Green\\'s function of the Laplace operator have found their analogs for periodic elliptic operators of the second order at and below the bottom of the spectrum. Due to the band-gap structure of the spectra of such operators, the question arises whether similar results can be obtained near or at the edges of spectral gaps. As the result of this work shows, this is possible at a spectral edge when the dimension d ≥ 3. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Extended Klein edges in graphene.

    Science.gov (United States)

    He, Kuang; Robertson, Alex W; Lee, Sungwoo; Yoon, Euijoon; Lee, Gun-Do; Warner, Jamie H

    2014-12-23

    Graphene has three experimentally confirmed periodic edge terminations, zigzag, reconstructed 5-7, and arm-chair. Theory predicts a fourth periodic edge of graphene called the extended Klein (EK) edge, which consists of a series of single C atoms protruding from a zigzag edge. Here, we confirm the existence of EK edges in both graphene nanoribbons and on the edge of bulk graphene using atomic resolution imaging by aberration-corrected transmission electron microscopy. The formation of the EK edge stems from sputtering and reconstruction of the zigzag edge. Density functional theory reveals minimal energy for EK edge reconstruction and bond distortion both in and out of plane, supporting our TEM observations. The EK edge can now be included as the fourth member of observed periodic edge structures in graphene.

  10. Accurate six-band nearest-neighbor tight-binding model for the π-bands of bulk graphene and graphene nanoribbons

    Science.gov (United States)

    Boykin, Timothy B.; Luisier, Mathieu; Klimeck, Gerhard; Jiang, Xueping; Kharche, Neerav; Zhou, Yu; Nayak, Saroj K.

    2011-05-01

    Accurate modeling of the π-bands of armchair graphene nanoribbons (AGNRs) requires correctly reproducing asymmetries in the bulk graphene bands, as well as providing a realistic model for hydrogen passivation of the edge atoms. The commonly used single-pz orbital approach fails on both these counts. To overcome these failures we introduce a nearest-neighbor, three orbital per atom p/d tight-binding model for graphene. The parameters of the model are fit to first-principles density-functional theory -based calculations as well as to those based on the many-body Green's function and screened-exchange formalism, giving excellent agreement with the ab initio AGNR bands. We employ this model to calculate the current-voltage characteristics of an AGNR MOSFET and the conductance of rough-edge AGNRs, finding significant differences versus the single-pz model. These results show that an accurate band structure model is essential for predicting the performance of graphene-based nanodevices.

  11. A New Edge-directed Subpixel Edge Localization Method

    Institute of Scientific and Technical Information of China (English)

    于新瑞; 徐威; 王石刚; 李倩

    2004-01-01

    Localization of the inspected chip image is one of the key problems with machine vision aided surface mount devices (SMD) and other micro-electronic equipments. This paper presents a new edge-directed subpixel edge localization method. The image is divided into two regions, edge and non-edge, using edge detection to emphasize the edge feature. Since the edges of the chip image are straight, they have straight-line characteristics locally and globally. First,the line segments of the straight edge are located to subpixel precision, according to their local straight properties, in a 3 × 3 neighborhood of the edge region. Second, the subpixel midpoints of the line segments are computed. Finally, the straight edge is fitted using the midpoints and the least square method, according to its global straight property in the entire edge region. In this way, the edge is located to subpixel precision. While fitting the edge, the irregular points are eliminated by the angles of the line segments to improve the precision. We can also distinguish different edges and their intersections using the angles of the line segments and distances between the edge points, then give the vectorial result of the image edge with high precision.

  12. Interrelation of Aromaticity and Conductivity of Graphene Dots/Antidots and Related Nanostructures

    Science.gov (United States)

    2016-01-01

    It is illustrated and computationally verified by ab initio density functional theory and simple but powerful order-of-magnitude arguments, based on deformation energy ΔEdef in relation to the uncertainty principle, that the conductivity and aromaticity of graphene and graphene-based structures, such as graphene dots, antidots, and nanoribbons, are negatively interrelated for π aromatic structures, in agreement with recent experimental data. However, for σ aromaticity, the interrelation could be positive, especially for extended periodic structures. We predict that the conductivity of rectangular graphene dots and antidots, is anisotropic with much larger magnitude along the direction perpendicular to the zigzag edges, compared to the conductivity in direction parallel to them. The same is true for the polarizability and electron mobility. This is directly connected with the much higher aromaticity around the armchair edges compared to the aromaticity near the zigzag edges. Furthermore, contrary to what would be expected on the basis of simple arguments for defect states, we predict that antidot patterning could significantly improve the conductivity (sometimes by 1 order of magnitude) in one or both directions, depending on their number, arrangement, and passivation. For narrow atomically precise armchair nanoribbons (AGNRs) of finite length, both conductivity and energy gaps are dominated by lateral and longitudinal quantum confinement, which decrease with increasing length (for a given width), leading to a peculiar behavior of monotonically increasing “maximum conductivity” as the band gaps monotonically decrease. The electron distribution at the band edges of the AGNRs, in agreement with recent experimental data are well-localized at the zigzag edges. Using the concept of gap-determining LUMO–HOMO frontier states to avoid HOMOs and LUMOs localized at the zigzag edges, we can predict with very high accuracy the recently measured band gaps of AGNRs of

  13. Band spectrum is D-brane

    CERN Document Server

    Hashimoto, Koji

    2015-01-01

    We show that band spectrum of topological insulators can be identified as the shape of D-branes in string theory. The identification is based on a relation between the Berry connection associated with the band structure and the ADHM/Nahm construction of solitons whose geometric realization is available with D-branes. We also show that chiral and helical edge states are identified as D-branes representing a noncommutative monopole.

  14. Theory of edge radiation

    Energy Technology Data Exchange (ETDEWEB)

    Geloni, G.; Kocharyan, V.; Saldin, E.; Schneidmiller, E.; Yurkov, M.

    2008-08-15

    We formulate a complete theory of Edge Radiation based on a novel method relying on Fourier Optics techniques. Similar types of radiation like Transition UndulatorRadiation are addressed in the framework of the same formalism. Special attention is payed in discussing the validity of approximations upon which the theory is built. Our study makes consistent use of both similarity techniques and comparisons with numerical results from simulation. We discuss both near and far zone. Physical understanding of many asymptotes is discussed. Based on the solution of the field equation with a tensor Green's function technique, we also discuss an analytical model to describe the presence of a vacuum chamber. In particular, explicit calculations for a circular vacuum chamber are reported. Finally, we consider the use of Edge Radiation as a tool for electron beam diagnostics. We discuss Coherent Edge Radiation, Extraction of Edge Radiation by a mirror, and other issues becoming important at high electron energy and long radiation wavelength. Based on this work we also study the impact of Edge Radiation on XFEL setups and we discuss recent results. (orig.)

  15. High Speed Edge Detection

    Science.gov (United States)

    Prokop, Norman F (Inventor)

    2016-01-01

    Analog circuits for detecting edges in pixel arrays are disclosed. A comparator may be configured to receive an all pass signal and a low pass signal for a pixel intensity in an array of pixels. A latch may be configured to receive a counter signal and a latching signal from the comparator. The comparator may be configured to send the latching signal to the latch when the all pass signal is below the low pass signal minus an offset. The latch may be configured to hold a last negative edge location when the latching signal is received from the comparator.

  16. Structure-Dependent 4-Tert-Butyl Pyridine-Induced Band Bending at TiO2 Surfaces

    Directory of Open Access Journals (Sweden)

    Mats Göthelid

    2011-01-01

    Full Text Available The role of 4-tert butyl pyridine (4TBP adsorption on TiO2 surface band bending has been studied using photoelectron spectroscopy. Surface oxygen vacancies pin the Fermi level near the conduction band edge on rutile (110. 4TBP preferentially adsorbs in those vacancies and shift the Fermi level to lower binding energy in the band gap. This is done by transferring vacancy excess charge into the empty π∗ orbital in the pyridine ring. The anatase (100 surface contains much less oxygen vacancies although the surface is much rougher than the rutile (110. 4TBP adsorption does not have any significant effect on the surface band bending. Thus the positive role associated with 4TBP addition to solar cell electrolytes is suggested to protection against adsorption of other electrolyte components such as Li and I.

  17. Band structure engineering and vacancy induced metallicity at the GaAs-AlAs interface

    KAUST Repository

    Upadhyay Kahaly, M.

    2011-09-20

    We study the epitaxial GaAs-AlAs interface of wide gap materials by full-potential density functional theory. AlAsthin films on a GaAs substrate and GaAsthin films on an AlAs substrate show different trends for the electronic band gap with increasing film thickness. In both cases, we find an insulating state at the interface and a negligible charge transfer even after relaxation. Differences in the valence and conduction band edges suggest that the energy band discontinuities depend on the growth sequence. Introduction of As vacancies near the interface induces metallicity, which opens great potential for GaAs-AlAs heterostructures in modern electronics.

  18. Thin hard crest on the edge of ceramic acetabular liners accelerates wear in edge loading.

    Science.gov (United States)

    Sanders, Anthony P; Dudhiya, Parth J; Brannon, Rebecca M

    2012-01-01

    Ceramic acetabular liners may exhibit a small, sharp crest-an artifact of discontinuous machining steps--at the junction between the concave spherical surface and the interior edge. On 3 ceramic liners, this crest was found to form a 9° to 11° deviation from tangency. Edge loading wear tests were conducted directly on this crest and on a smoother region of the edge. The crest elicited 2 to 15 times greater volumetric wear on the femoral head. The propensity of the crest to rapidly (machining protocols might be a root cause of stripe wear and squeaking in ceramic acetabular bearings.

  19. Band gap engineering via doping: A predictive approach

    Energy Technology Data Exchange (ETDEWEB)

    Andriotis, Antonis N., E-mail: andriot@iesl.forth.gr [Institute of Electronic Structure and Laser, FORTH, P.O. Box 1527, 71110 Heraklio, Crete (Greece); Menon, Madhu, E-mail: super250@uky.edu [Department of Physics and Astronomy and Center for Computational Sciences, University of Kentucky, Lexington, Kentucky 40506 (United States)

    2015-03-28

    We employ an extension of Harrison's theory at the tight binding level of approximation to develop a predictive approach for band gap engineering involving isovalent doping of wide band gap semiconductors. Our results indicate that reasonably accurate predictions can be achieved at qualitative as well as quantitative levels. The predictive results were checked against ab initio ones obtained at the level of DFT/SGGA + U approximation. The minor disagreements between predicted and ab initio results can be attributed to the electronic processes not incorporated in Harrison's theory. These include processes such as the conduction band anticrossing [Shan et al., Phys. Rev. Lett. 82, 1221 (1999); Walukiewicz et al., Phys. Rev. Lett. 85, 1552 (2000)] and valence band anticrossing [Alberi et al., Phys. Rev. B 77, 073202 (2008); Appl. Phys. Lett. 92, 162105 (2008); Appl. Phys. Lett. 91, 051909 (2007); Phys. Rev. B 75, 045203 (2007)], as well as the multiorbital rehybridization. Another cause of disagreement between the results of our predictive approach and the ab initio ones is shown to be the result of the shift of Fermi energy within the impurity band formed at the edge of the valence band maximum due to rehybridization. The validity of our approach is demonstrated with example applications for the systems GaN{sub 1−x}Sb{sub x}, GaP{sub 1−x}Sb{sub x}, AlSb{sub 1−x}P{sub x}, AlP{sub 1−x}Sb{sub x}, and InP{sub 1−x}Sb{sub x}.

  20. Amniotic constriction bands

    Science.gov (United States)

    ... of function of an arm or a leg. Congenital bands affecting the hand often cause the most problems. Alternative Names Pseudo-ainhum; Streeter dysplasia; Amniotic band sequence; Amniotic constriction bands; Constriction band ...

  1. Quantum electrodynamics near a photonic band-gap

    Science.gov (United States)

    Liu, Yanbing; Houck, Andrew

    Quantum electrodynamics predicts the localization of light around an atom in photonic band-gap (PBG) medium or photonic crystal. Here we report the first experimental realization of the strong coupling between a single artificial atom and an one dimensional PBG medium using superconducting circuits. In the photonic transport measurement, we observe an anomalous Lamb shift and a large band-edge avoided crossing when the artificial atom frequency is tuned across the band-edge. The persistent peak within the band-gap indicates the single photon bound state. Furthermore, we study the resonance fluorescence of this bound state, again demonstrating the breakdown of the Born-Markov approximation near the band-edge. This novel architecture can be directly generalized to study many-body quantum electrodynamics and to construct more complicated spin chain models.

  2. Ultra-low threshold avalanche gain from solar-blind photodetector based on graded-band-gap-cubic-MgZnO.

    Science.gov (United States)

    Xie, Xiuhua; Zhang, Zhenzhong; Li, Binghui; Wang, Shuangpeng; Shen, Dezhen

    2015-12-14

    A larger ratio of conduction-band offset to valence-band offset is the unique character for Mg(x)Zn(1-x)O alloys. For this reason, it is feasible to build a quasi-electric forces, caused by the spatial gradient of the conduction edge, exerting on the electrons. In this paper, a novel graded band gap cubic-MgZnO-based solar-blind photodetector is successfully fabricated from Graded-Band-Gap-Cubic-MgZnO/i-MgO/p-Si heterojunction, via changing stoichiometry spatial gradient. Due to quasi-electric fields in non-uniform MgZnO, the multiple carriers are generated under ultra-low threshold bias voltage. The photodetector showed high performance, namely, high responsivity, quantum efficiency, high sensitivity and selectivity towards the solar-blind spectrum, and fast response times.

  3. Cobalt (II) oxide and nickel (II) oxide alloys as potential intermediate-band semiconductors: A theoretical study

    Energy Technology Data Exchange (ETDEWEB)

    Alidoust, Nima [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544-5263 (United States); Lessio, Martina [Department of Chemistry, Princeton University, Princeton, New Jersey 08544-1009 (United States); Carter, Emily A., E-mail: eac@princeton.edu [Department of Mechanical and Aerospace Engineering, Program in Applied and Computational Mathematics, and Andlinger Center for Energy and the Environment, Princeton University, Princeton, New Jersey 08544-5263 (United States)

    2016-01-14

    Solar cells based on single pn junctions, employing single-gap semiconductors can ideally achieve efficiencies as high as 34%. Developing solar cells based on intermediate-band semiconductors (IBSCs), which can absorb light across multiple band gaps, is a possible way to defy this theoretical limit and achieve efficiencies as high as 60%. Here, we use first principles quantum mechanics methods and introduce CoO and Co{sub 0.25}Ni{sub 0.75}O as possible IBSCs. We show that the conduction band in both of these materials is divided into two distinct bands separated by a band gap. We further show that the lower conduction band (i.e., the intermediate band) is wider in Co{sub 0.25}Ni{sub 0.75}O compared with CoO. This should enhance light absorption from the valence band edge to the intermediate band, making Co{sub 0.25}Ni{sub 0.75}O more appropriate for use as an IBSC. Our findings provide the basis for future attempts to partially populate the intermediate band and to reduce the lower band gap in Co{sub 0.25}Ni{sub 0.75}O in order to enhance the potential of this material for use in IBSC solar cell technologies. Furthermore, with proper identification of heterojunctions and dopants, CoO and Co{sub 0.25}Ni{sub 0.75}O could be used in multi-color light emitting diode and laser technologies.

  4. Multi-band Modelling of Appearance

    DEFF Research Database (Denmark)

    Stegmann, Mikkel Bille; Larsen, Rasmus

    2003-01-01

    Earlier work has demonstrated generative models capable of synthesising near photo-realistic grey-scale images of objects. These models have been augmented with colour information, and recently with edge information. This paper extends the active appearance model framework by modelling...... the appearance of both derived feature bands and an intensity band. As a special case of feature-band augmented appearance modelling we propose a dedicated representation with applications to face segmentation. The representation addresses a major problem within face recognition by lowering the sensitivity...

  5. Multi-band Modelling of Appearance

    DEFF Research Database (Denmark)

    2002-01-01

    Earlier work has demonstrated generative models capable of synthesising near photo-realistic grey-scale images of objects. These models have been augmented with colour information, and recently with edge information. This paper extends the Active Appearance Model framework by modelling...... the appearance of both derived feature bands and an intensity band. As a special case of feature-band augmented appearance modelling we propose a dedicated representation with applications to face segmentation. The representation addresses a major problem within face recognition by lowering the sensitivity...

  6. Superpixel edges for boundary detection

    Energy Technology Data Exchange (ETDEWEB)

    Moya, Mary M.; Koch, Mark W.

    2016-07-12

    Various embodiments presented herein relate to identifying one or more edges in a synthetic aperture radar (SAR) image comprising a plurality of superpixels. Superpixels sharing an edge (or boundary) can be identified and one or more properties of the shared superpixels can be compared to determine whether the superpixels form the same or two different features. Where the superpixels form the same feature the edge is identified as an internal edge. Where the superpixels form two different features, the edge is identified as an external edge. Based upon classification of the superpixels, the external edge can be further determined to form part of a roof, wall, etc. The superpixels can be formed from a speckle-reduced SAR image product formed from a registered stack of SAR images, which is further segmented into a plurality of superpixels. The edge identification process is applied to the SAR image comprising the superpixels and edges.

  7. Edge detection by nonlinear dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Yiu-fai

    1994-07-01

    We demonstrate how the formulation of a nonlinear scale-space filter can be used for edge detection and junction analysis. By casting edge-preserving filtering in terms of maximizing information content subject to an average cost function, the computed cost at each pixel location becomes a local measure of edgeness. This computation depends on a single scale parameter and the given image data. Unlike previous approaches which require careful tuning of the filter kernels for various types of edges, our scheme is general enough to be able to handle different edges, such as lines, step-edges, corners and junctions. Anisotropy in the data is handled automatically by the nonlinear dynamics.

  8. The fundamental absorption edge in MnIn{sub 2}Se{sub 4} layer semi-magnetic semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Rincón, C., E-mail: crincon@ula.ve [Centro de Estudios de Semiconductores, Departamento de Física, Facultad de Ciencias, Universidad de Los Andes, Mérida (Venezuela, Bolivarian Republic of); Torrres, T.E. [Laboratorio de Magnetismo, Departamento de Física, Facultad de Ciencias, Universidad de Los Andes, Mérida (Venezuela, Bolivarian Republic of); Instituto de Nanociencia de Aragón, Laboratorio de Microscopías Avanzadas, Universidad de Zaragoza 50009, Zaragoza (Spain); Departamento de Física de la Materia Condensada, Facultad de Ciencias, Universidad de Zaragoza 50009, Zaragoza, Spain. (Spain); Sagredo, V. [Laboratorio de Magnetismo, Departamento de Física, Facultad de Ciencias, Universidad de Los Andes, Mérida (Venezuela, Bolivarian Republic of); Jiménez-Sandoval, Sergio J.; Mares-Jacinto, E. [CINVESTAV Querétaro, Libramiento Norponiente N° 2000, Frac. Real de Juriquilla, Querétaro, Qro. 76230 (Mexico)

    2015-11-15

    From the study of the optical absorption coefficient and photoluminescence spectra of the layer semi-magnetic semiconductor MnIn{sub 2}Se{sub 4} the nature of its fundamental absorption edge is established. It is found that the lowest-energy-gap of this compound is allowed-indirect between parabolic bands that vary from about 1.55–1.43 eV in the temperature range from 10 K to room temperature. In addition, two allowed direct band-to-band transitions beginning at 1.72 and 1.85 eV at 295 K, and at 1.82 and 1.96 eV at 10 K which are related to optical absorption processes between the uppermost Γ{sub 4}(z) and the middle Γ{sub 5}(x) valence bands and the conduction band respectively, are observed in the high energy range. It is also found that the crystal field splitting parameter (Δ{sub cf}) of MnIn{sub 2}Se{sub 4} is of about 0.15 eV nearly independent of the temperature. At energies around 2.2 eV a photoluminescence band related to internal transitions between d-excited levels of Mn{sup +2} ion to its {sup 6}A{sub 1} ground state is also observed in spectra.

  9. Effect of edge roughness on electronic transport in graphene nanoribbon channel metal-oxide-semiconductor field-effect transistors

    Science.gov (United States)

    Basu, D.; Gilbert, M. J.; Register, L. F.; Banerjee, S. K.; MacDonald, A. H.

    2008-01-01

    Results of quantum mechanical simulations of the influence of edge disorder on transport in graphene nanoribbon metal-oxide-semiconductor field-effect transistors (MOSFETs) are reported. The addition of edge disorder significantly reduces ON-state currents and increases OFF-state currents, and introduces wide variability across devices. These effects decrease as ribbon widths increase and as edges become smoother. However, the band gap decreases with increasing width, thereby increasing the band-to-band tunneling mediated subthreshold leakage current even with perfect nanoribbons. These results suggest that without atomically precise edge control during fabrication, MOSFET performance gains through use of graphene will be difficult to achieve in complementary MOS applications.

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

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yan; SHI Jun-Jie

    2006-01-01

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

  11. Edge turbulence in tokamaks

    Science.gov (United States)

    Nedospasov, A. V.

    1992-12-01

    Edge turbulence is of decisive importance for the distribution of particle and energy fluxes to the walls of tokamaks. Despite the availability of extensive experimental data on the turbulence properties, its nature still remains a subject for discussion. This paper contains a review of the most recent theoretical and experimental studies in the field, including mainly the studies to which Wootton (A.J. Wooton, J. Nucl. Mater. 176 & 177 (1990) 77) referred to most in his review at PSI-9 and those published later. The available theoretical models of edge turbulence with volume dissipation due to collisions fail to fully interpret the entire combination of experimental facts. In the scrape-off layer of a tokamak the dissipation prevails due to the flow of current through potential shifts near the surface of limiters of divertor plates. The different origins of turbulence at the edge and in the core plasma due to such dissipation are discussed in this paper. Recent data on the electron temperature fluctuations enabled one to evaluate the electric probe measurements of turbulent flows of particles and heat critically. The latest data on the suppression of turbulence in the case of L-H transitions are given. In doing so, the possibility of exciting current instabilities in biasing experiments (rather than only to the suppression of existing turbulence) is given some attention. Possible objectives of further studies are also discussed.

  12. Doppler lidar wind measurement with the edge technique

    Science.gov (United States)

    Korb, C. Laurence; Gentry, Bruce M.

    1992-01-01

    The edge technique is a new and powerful method for measuring small frequency shifts. Range resolved lidar measurements of winds can be made with high accuracy and high vertical resolution using the edge technique to measure the Doppler shift of an atmospheric backscattered signal from a pulsed laser. The edge technique can be used at near-infrared or visible wavelengths using well developed solid state lasers and detectors with various edge filters. In the edge technique, the laser frequency is located on the steep slope of the spectral response function of a high resolution optical filter. Due to the steep slope of the edge, very small frequency shifts cause large changes in measured signal. The frequency of the outgoing laser pulse is determined by measuring its location on the edge of the filter. This is accomplished by sending a small portion of the beam to the edge detection setup where the incoming light is split into two channels - an edge filter and an energy monitor channel. The energy monitor signal is used to normalize the edge filter signal for magnitude. The laser return backscattered from the atmosphere is collected by a telescope and directed through the edge detection setup to determine its frequency (location on the edge) in a similar manner for each range element. The Doppler shift, and thus the wind, is determined from a differential measurement of the frequency of the outgoing laser pulse and the frequency of the laser return backscattered from the atmosphere. We have conducted simulations of the performance of an edge lidar system using an injection seeded pulsed Nd:YAG laser at 1.06 microns. The central fringe of a Fabry-Perot etalon is used as a high resolution edge filter to measure the shift of the aerosol return.

  13. The Existence of Topological Edge States in Honeycomb Plasmonic Lattices

    CERN Document Server

    Wang, Li; Xiao, Meng; Han, Dezhuan; Chan, C T; Wen, Weijia

    2016-01-01

    In this paper, we investigate the band properties of 2D honeycomb plasmonic lattices consisting of metallic nanoparticles. By means of the coupled dipole method and quasi-static approximation, we theoretically analyze the band structures stemming from near-field interaction of localized surface plasmon polaritons for both the infinite lattice and ribbons. Naturally, the interaction of point dipoles decouples into independent out-of-plane and in-plane polarizations. For the out-of-plane modes, both the bulk spectrum and the range of the momentum $k_{\\parallel}$ where edge states exist in ribbons are similar to the electronic bands in graphene. Nevertheless, the in-plane polarized modes show significant differences, which do not only possess additional non-flat edge states in ribbons, but also have different distributions of the flat edge states in reciprocal space. For in-plane polarized modes, we derived the bulk-edge correspondence, namely, the relation between the number of flat edge states at a fixed $k_\\p...

  14. Smoothness in Binomial Edge Ideals

    Directory of Open Access Journals (Sweden)

    Hamid Damadi

    2016-06-01

    Full Text Available In this paper we study some geometric properties of the algebraic set associated to the binomial edge ideal of a graph. We study the singularity and smoothness of the algebraic set associated to the binomial edge ideal of a graph. Some of these algebraic sets are irreducible and some of them are reducible. If every irreducible component of the algebraic set is smooth we call the graph an edge smooth graph, otherwise it is called an edge singular graph. We show that complete graphs are edge smooth and introduce two conditions such that the graph G is edge singular if and only if it satisfies these conditions. Then, it is shown that cycles and most of trees are edge singular. In addition, it is proved that complete bipartite graphs are edge smooth.

  15. Polarized micro Raman scattering spectroscopy for curved edges of epitaxial graphene

    Energy Technology Data Exchange (ETDEWEB)

    Islam, Md. Sherajul, E-mail: sheraj-ruet@yahoo.com; Makino, T.; Hashimoto, A. [Graduate School of Electrical and Electronic Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507 (Japan); Bhuiyan, A. G. [Department of Electrical and Electronic Engineering, Khulna University of Engineering and Technology, Khulna 9203 (Bangladesh); Tanaka, S. [Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395 (Japan)

    2014-12-15

    This letter performed polarized microscopic laser Raman scattering spectroscopy on the curved edges of transferred epitaxial graphene on SiO{sub 2}/Si. The intensity ratio between the parallel and perpendicular polarized D band is evolved, providing a spectroscopy-based technique to probe the atomic-scale edge structures in graphene. A detailed analysis procedure for non-ideal disordered curved edges of graphene is developed combining the atomic-scale zigzag and armchair edge structures along with some point defects. These results could provide valuable information of the realistic edges of graphene at the atomic-scale that can strongly influence the performance of graphene-based nanodevices.

  16. Edge effects in composites by moire interferometry

    Science.gov (United States)

    Czarnek, R.; Post, D.; Herakovich, C.

    1983-01-01

    The very high sensitivity of moire interferometry has permitted the present edge effect experiments to be conducted at a low average stress and strain level, assuring linear and elastic behavior in the composite material samples tested. Sensitivity corresponding to 2450 line/mm moire was achieved with a 0.408 micron/fringe. Simultaneous observations of the specimen face and edge displacement fields showed good fringe definition despite the 1-mm thickness of the specimens and the high gradients, and it is noted that the use of a carrier pattern and optical filtering was effective in even these conditions. Edge effects and dramatic displacement gradients were confirmed in angle-ply composite laminates.

  17. Strain Gated Bilayer Molybdenum Disulfide Field Effect Transistor with Edge Contacts.

    Science.gov (United States)

    Chai, Yu; Su, Shanshan; Yan, Dong; Ozkan, Mihrimah; Lake, Roger; Ozkan, Cengiz S

    2017-02-10

    Silicon nitride stress capping layer is an industry proven technique for increasing electron mobility and drive currents in n-channel silicon MOSFETs. Herein, the strain induced by silicon nitride is firstly characterized through the changes in photoluminescence and Raman spectra of a bare bilayer MoS2 (Molybdenum disulfide). To make an analogy of the strain-gated silicon MOSFET, strain is exerted to a bilayer MoS2 field effect transistor (FET) through deposition of a silicon nitride stress liner that warps both the gate and the source-drain area. Helium plasma etched MoS2 layers for edge contacts. Current on/off ratio and other performance metrics are measured and compared as the FETs evolve from back-gated, to top-gated and finally, to strain-gated configurations. While the indirect band gap of bilayer MoS2 at 0% strain is 1.25 eV, the band gap decreases as the tensile strain increases on an average of ~100 meV per 1% tensile strain, and the decrease in band gap is mainly due to lowering the conduction band at K point. Comparing top- and strain-gated structures, we find a 58% increase in electron mobility and 46% increase in on-current magnitude, signalling a benign effect of tensile strain on the carrier transport properties of MoS2.

  18. Six-band nearest-neighbor tight-binding model for the π-bands of bulk graphene and graphene nanoribbons

    Science.gov (United States)

    Boykin, Timothy; Luisier, Mathieu; Klimeck, Gerhard; Jiang, Xueping; Kharche, Neerav; Zhou, Yu; Nayak, Saroj

    2012-02-01

    The commonly used single-pz orbital first nearest-neighbor tight-binding model faces two main problems: (i) it fails to reproduce asymmetries in the bulk graphene bands; (ii) it cannot provide a realistic model for hydrogen passivation of the edge atoms. As a result, some armchair graphene nanoribbons (AGNRs) are incorrectly predicted as metallic. A new nearest-neighbor, three orbital per atom p/d tight-binding model [1] is built to address these issues. The parameters of the model are fit to bandstructures obtained from first-principles density-functional theory and many-body perturbation theory within the GW approximation, giving excellent agreement with the ab initio AGNR bands. This model is employed to calculate the current-voltage characteristics of an AGNR MOSFET and the conductance of rough-edge AGNRs, finding significant differences versus the single-pz model. Taken together these results demonstrate the importance of an accurate and computational efficient band structure model for predicting the performance of graphene-based nanodevices. [1] T. B. Boykin, M. Luisier, G. Klimeck, X. Jiang, N. Kharche, Y. Zhou and S. Nayak, J. Appl. Phys. 109, 104304 (2011)

  19. Conductivity and optical studies of plasticized solid polymer electrolytes doped with carbon nanotube

    Energy Technology Data Exchange (ETDEWEB)

    Ibrahim, Suriani, E-mail: sue_83@um.edu.my [Advanced Materials Research Laboratory, Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ahmad, Roslina; Johan, Mohd Rafie [Advanced Materials Research Laboratory, Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur (Malaysia)

    2012-01-15

    Solid polymer electrolyte films based on Poly(ethylene oxide) (PEO) complexed with lithium hexafluorophosphate (LiPF{sub 6}), ethylene carbonate (EC) and amorphous carbon nanotube ({alpha}CNTs) were prepared by the solution cast technique. The conductivity increases from 10{sup -10} to 10{sup -5} Scm{sup -1} upon the addition of salt. The incorporation of EC and {alpha}CNTs to the salted polymer enhances the conductivity significantly to 10{sup -4} and 10{sup -3} Scm{sup -1}. The complexation of doping materials with polymer were confirmed by X-ray diffraction and infrared studies. Optical properties like direct band gap and indirect band gap were investigated for pure and doped polymer films in the wavelength range 200-400 nm. It was found that the energy gaps and band edge values shifted to lower energies on doping. - Highlights: > Optical band gap values show the decreasing trend with an increasing dopant concentration. > It is also observed that the absorption edge shifted to longer wavelength on doping. > Results of the optical measurements indicate the presence of a well-defined {pi}{yields}{pi}* transition associated with the formation of a conjugated C=O and/or C=O electronic structure.

  20. Micromechanics of shear banding

    Energy Technology Data Exchange (ETDEWEB)

    Gilman, J.J.

    1992-08-01

    Shear-banding is one of many instabilities observed during the plastic flow of solids. It is a consequence of the dislocation mechanism which makes plastic flow fundamentally inhomogeneous, and is exacerbated by local adiabatic heating. Dislocation lines tend to be clustered on sets of neighboring glide planes because they are heterogeneously generated; especially through the Koehler multiple-cross-glide mechanism. Factors that influence their mobilities also play a role. Strain-hardening decreases the mobilities within shear bands thereby tending to spread (delocalize) them. Strain-softening has the inverse effect. This paper reviews the micro-mechanisms of these phenomena. It will be shown that heat production is also a consequence of the heterogeneous nature of the microscopic flow, and that dislocation dipoles play an important role. They are often not directly observable, but their presence may be inferred from changes in thermal conductivity. It is argued that after deformation at low temperatures dipoles are distributed a la Pareto so there are many more small than large ones. Instability at upper yield point, the shapes of shear-band fronts, and mechanism of heat generation are also considered. It is shown that strain-rate acceleration plays a more important role than strain-rate itself in adiabatic instability.

  1. Holographic Multi-Band Superconductor

    CERN Document Server

    Huang, Ching-Yu; Maity, Debaprasad

    2011-01-01

    We propose a gravity dual for the holographic superconductor with multi-band carriers. Moreover, the currents of these carriers are unified under a global non-Abelian symmetry, which is dual to the bulk non-Abelian gauge symmetry. We study the phase diagram of our model, and find it qualitatively agrees with the one for the realistic 2-band superconductor, such as MgB2. We also evaluate the holographic conductivities and find the expected mean-field like behaviors in some cases. However, for a wide range of the parameter space, we also find the non-mean-field like behavior with negative conductivities.

  2. HYBASE : HYperspectral BAnd SElection

    NARCIS (Netherlands)

    Schwering, P.B.W.; Bekman, H.H.P.T.; Seijen, H.H. van

    2009-01-01

    Band selection is essential in the design of multispectral sensor systems. This paper describes the TNO hyperspectral band selection tool HYBASE. It calculates the optimum band positions given the number of bands and the width of the spectral bands. HYBASE is used to assess the minimum number of spe

  3. Electronic structure of Al-doped ZnO transparent conductive thin films studied by x-ray absorption and emission spectroscopies

    Energy Technology Data Exchange (ETDEWEB)

    Huang, W. H.; Sun, S. J.; Chiou, J. W. [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Chou, H. [Department of Physics, National Sun Yat-sen University, Kaohsiung 804, Taiwan (China); Chan, T. S.; Lin, H.-J. [National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China); Kumar, Krishna [Department of Electrical and Computer Engineering, University of Waterloo, Ontario N2L 3G1 (Canada); Guo, J.-H. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2011-11-15

    This study used O K-, Zn L{sub 3}-, Zn K-, and Al K-edges x-ray absorption near-edge structure (XANES) and O K-edge x-ray emission spectroscopy (XES) measurements to investigate the electronic structure of transparent Al-doped ZnO (AZO) thin film conductors. The samples were prepared on glass substrates at a low temperature near 77 K by using a standard RF sputtering method. High-purity Ne (5N) was used as the sputtering gas. The crystallography of AZO thin films gradually transformed from the ZnO wurtize structure to an amorphous structure during sample deposition, which suggests the suitability to grow on flexible substrates, eliminating the severe degradation due to fragmentation by repeated bending. The O K- and Zn L{sub 3}-edges XANES spectra of AZO thin films revealed a decrease in the number of both O 2p and Zn 3d unoccupied states when the pressure of Ne was increased from 5 to 100 mTorr. In contrast, Al K-edges XANES spectra showed that the number of unoccupied states of Al 3p increased in conjunction with the pressure of Ne, indicating an electron transfer from Al to O atoms, and suggesting that Al doping increases the negative effective charge of oxygen ions. XES and XANES spectra of O 2p states at the O K-edge also revealed that Al doping not only raised the conduction-band-minimum, but also increased the valence-band-maximum and the band-gap. The results indicate that the reduction in conductivity of AZO thin films is due to the generation of ionic characters, the increase in band-gap, and the decrease in density of unoccupied states of oxygen.

  4. Strain Dependent Electronic Structure and Band Offset Tuning at Heterointerfaces of ASnO3 (A=Ca, Sr, and Ba) and SrTiO3

    Science.gov (United States)

    Baniecki, John D.; Yamazaki, Takashi; Ricinschi, Dan; Van Overmeere, Quentin; Aso, Hiroyuki; Miyata, Yusuke; Yamada, Hiroaki; Fujimura, Norifumi; Maran, Ronald; Anazawa, Toshihisa; Valanoor, Nagarajan; Imanaka, Yoshihiko

    2017-01-01

    The valence band (VB) electronic structure and VB alignments at heterointerfaces of strained epitaxial stannate ASnO3 (A=Ca, Sr, and Ba) thin films are characterized using in situ X-ray and ultraviolet photoelectron spectroscopies, with band gaps evaluated using spectroscopic ellipsometry. Scanning transmission electron microscopy with geometric phase analysis is used to resolve strain at atomic resolution. The VB electronic structure is strain state dependent in a manner that correlated with a directional change in Sn-O bond lengths with strain. However, VB offsets are found not to vary significantly with strain, which resulted in ascribing most of the difference in band alignment, due to a change in the band gaps with strain, to the conduction band edge. Our results reveal significant strain tuning of conduction band offsets using epitaxial buffer layers, with strain-induced offset differences as large as 0.6 eV possible for SrSnO3. Such large conduction band offset tunability through elastic strain control may provide a pathway to minimize the loss of charge confinement in 2-dimensional electron gases and enhance the performance of photoelectrochemical stannate-based devices. PMID:28195149

  5. Extracting roads and curvilinear bands with weak and broken boundaries

    Science.gov (United States)

    Zhou, Shaoguang; Li, Jinhui

    2008-12-01

    In so far as geometric shape is concerned a curvilinear band is very similar to a road segment. Roads may be regarded as a particular type of curvilinear bands. Many methods have been developed for extracting such targets, some of which are based on edge information. It is very difficult to extract roads and curvilinear bands with no clear and continuous boundaries using existing algorithms. To mitigate this problem a new strategy is presented in this paper. Edge lines are detected by means of an improved Burns' method and Dynamic Programming. Target segments are then formed by matching these edge lines. Connecting the obtained segments produces the final results. Experiments prove the efficiency of the proposed method while being applied to extract complicated roads and curvilinear bands in different kinds of images.

  6. Topological Number of Edge States

    CERN Document Server

    Hashimoto, Koji

    2016-01-01

    We show that the edge states of the four-dimensional class A system can have topological charges, which are characterized by Abelian/non-Abelian monopoles. The edge topological charges are a new feature of relations among theories with different dimensions. From this novel viewpoint, we provide a non-Abelian analogue of the TKNN number as an edge topological charge, which is defined by an SU(2) 't Hooft-Polyakov BPS monopole through an equivalence to Nahm construction. Furthermore, putting a constant magnetic field yields an edge monopole in a non-commutative momentum space, where D-brane methods in string theory facilitate study of edge fermions.

  7. Photonic band gap of a graphene-embedded quarter-wave stack

    CERN Document Server

    Fan, Yuancheng; Li, Hongqiang; Chen, Hong; Soukoulis, Costas M

    2013-01-01

    Here, we present a mechanism for tailoring the photonic band structure of a quarter-wave stack without changing its physical periods by embedding conductive sheets. Graphene is utilized and studied as a realistic, two-dimensional conductive sheet. In a graphene-embedded quarter-wave stack, the synergic actions of Bragg scattering and graphene conductance contributions open photonic gaps at the center of the reduced Brillouin zone, that nonexistent in conventional quarter-wave stacks. Such photonic gaps show giant, loss-independent density of optical states at the fixed lower-gap-edges, of even-multiple characteristic frequency of the quarter-wave stack. The novel conductive sheets induced photonic gaps provide a new platform for the enhancement of light-matter interactions.

  8. Enhanced carrier transport along edges of graphene devices.

    Science.gov (United States)

    Chae, Jungseok; Jung, Suyong; Woo, Sungjong; Baek, Hongwoo; Ha, Jeonghoon; Song, Young Jae; Son, Young-Woo; Zhitenev, Nikolai B; Stroscio, Joseph A; Kuk, Young

    2012-04-11

    The relation between macroscopic charge transport properties and microscopic carrier distribution is one of the central issues in the physics and future applications of graphene devices (GDs). We find strong conductance enhancement at the edges of GDs using scanning gate microscopy. This result is explained by our theoretical model of the opening of an additional conduction channel localized at the edges by depleting accumulated charge by the tip.

  9. Electrochemistry of folded graphene edges.

    Science.gov (United States)

    Ambrosi, Adriano; Bonanni, Alessandra; Pumera, Martin

    2011-05-01

    There is enormous interest in the investigation of electron transfer rates at the edges of graphene due to possible energy storage and sensing applications. While electrochemistry at the edges and the basal plane of graphene has been studied in the past, the new frontier is the electrochemistry of folded graphene edges. Here we describe the electrochemistry of folded graphene edges and compare it to that of open graphene edges. The materials were characterized in detail by high-resolution transmission electron microscopy, Raman spectroscopy, high-resolution X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. We found that the heterogeneous electron transfer rate is significantly lower on folded graphene edges compared to open edge sites for ferro/ferricyanide, and that electrochemical properties of open edges offer lower potential detection of biomarkers than the folded ones. It is apparent, therefore, that for sensing and biosensing applications the folded edges are less active than open edges, which should then be preferred for such applications. As folded edges are the product of thermal treatment of multilayer graphene, such thermal procedures should be avoided when fabricating graphene for electrochemical applications.

  10. EDGE COVERING COLORING AND FRACTIONAL EDGE COVERING COLORING

    Institute of Scientific and Technical Information of China (English)

    MIAOLianying; LIUGuizhen

    2002-01-01

    Let G be a graph with edge set E(G).S E(G)is called an edge cover of G if every vertex of G is an end vertex of some edges in S.The edge covering chromatic number of a graph G,denoted by Xc(G),is the maximum size of a partition of E(G) into edge covers of G.It is known that for any graph G with minimum degree δ,δ-1≤Xc(G)≤δ.The fractional edge covering chromatic number of a graph G,denoted by Xcf(G),is the fractional matiching number of the edge covering hypergraph H of G whose vertices are the edges of G and whose hypereges the edge covers of G.In this paper,we study the relation between Xc(G) and δfor any graph G,and give a new simple proof of the inequalities δ-1≤Xc(G)≤δ by the technique of graph coloring.For any graph G,we give an exact formula o Xcf(G),that is,Xcf(G)=min{δ,λ(G)},where λ(G)=minCS/S/2 and the minimum is taken over all noempty subsets S of V(G) and C[S] is the set of edges that have at least one end in S.δ

  11. EDGE COVERING COLORING AND FRACTIONAL EDGE COVERING COLORING

    Institute of Scientific and Technical Information of China (English)

    MIAO Lianying; LIU Guizhen

    2002-01-01

    Let G be a graph with edge set E(G). S _C E(G) is called an edge cover of G if every vertex of G is an end vertex of some edges in S. The edge covering chromatic number of a graph G, denoted by X'c(G) , is the maximum size of a partition of E(G) into edge covers of G. It is known that for any graph G with minimum degree δ, δ - 1 ≤ X'c(G) ≤ δ.The fractional edge covering chromatic number of a graph G, denoted by X'cf(G), is the fractional matching number of the edge covering hypergraph H of G whose vertices are the edges of G and whose hyperedges the edge covers of G. In this paper, we study the relation between X'c(G) and δ for any graph G, and give a new simple proof of the inequalities δ - 1 ≤ X'c(G) ≤ δ by the technique of graph coloring. For any graph G, we give an exact formula of X'cf(G), that is, X'cf(G)=min{δ,λ(G)}, where λ(G)=min |C[S]|/[|S|/2]and the minimum is taken over all noempty subsets S of V(G) and C[S] is the set of edges that have at least one end in S.

  12. Model-based edge detector for spectral imagery using sparse spatiospectral masks.

    Science.gov (United States)

    Paskaleva, Biliana S; Godoy, Sebastián E; Jang, Woo-Yong; Bender, Steven C; Krishna, Sanjay; Hayat, Majeed M

    2014-05-01

    Two model-based algorithms for edge detection in spectral imagery are developed that specifically target capturing intrinsic features such as isoluminant edges that are characterized by a jump in color but not in intensity. Given prior knowledge of the classes of reflectance or emittance spectra associated with candidate objects in a scene, a small set of spectral-band ratios, which most profoundly identify the edge between each pair of materials, are selected to define a edge signature. The bands that form the edge signature are fed into a spatial mask, producing a sparse joint spatiospectral nonlinear operator. The first algorithm achieves edge detection for every material pair by matching the response of the operator at every pixel with the edge signature for the pair of materials. The second algorithm is a classifier-enhanced extension of the first algorithm that adaptively accentuates distinctive features before applying the spatiospectral operator. Both algorithms are extensively verified using spectral imagery from the airborne hyperspectral imager and from a dots-in-a-well midinfrared imager. In both cases, the multicolor gradient (MCG) and the hyperspectral/spatial detection of edges (HySPADE) edge detectors are used as a benchmark for comparison. The results demonstrate that the proposed algorithms outperform the MCG and HySPADE edge detectors in accuracy, especially when isoluminant edges are present. By requiring only a few bands as input to the spatiospectral operator, the algorithms enable significant levels of data compression in band selection. In the presented examples, the required operations per pixel are reduced by a factor of 71 with respect to those required by the MCG edge detector.

  13. Coupling and manipulation of edge states in multilayer phosphorene nanoribbons

    Science.gov (United States)

    Lv, Z. T.; Gao, J. H.; Zhang, X. D.; Jiang, Z. T.

    2017-10-01

    We investigate the couplings among the edge states of the normal zigzag and skewed armchair multilayer phosphorene nanoribbons, as well as the effect of the electric field on the corresponding energy levels, by using the tight-binding Hamiltonian approach. It is found that there appear different transitions from the coupled to uncoupled edge states in the normal zigzag and skewed armchair nanoribbons with the increasing of the nanoribbon width, which is fundamentally attributed to the edge asymmetry of the multilayer phosphorene nanoribbons. Moreover, the energy bands of the multilayer phosphorene nanoribbons can be effectively adjusted by applying the perpendicular electric field. Therefore, this research should be thought of as a useful reference for determining the width, the edge types, and the layer numbers of the nanoribbons in manipulating the properties of the multilayer phosphorene nanoribbons.

  14. Edge-dependent selection rules in magic triangular graphene flakes

    Science.gov (United States)

    Akola, J.; Heiskanen, H. P.; Manninen, M.

    2008-05-01

    The electronic shell and supershell structure of triangular graphene quantum dots has been studied using density functional and tight-binding methods. The density functional calculations demonstrate that the electronic structure close to the Fermi energy is correctly described with a simple tight-binding model, where only the pz orbitals perpendicular to the graphene layer are included. The results show that (i) both at the bottom and at the top of the pz band, a supershell structure similar to that of free electrons confined in a triangular cavity is seen, (ii) close to the Fermi level, the shell structure is that of free massless particles, (iii) triangles with armchair edges show an additional sequence of levels (“ghost states”) absent for triangles with zigzag edges while the latter exhibit edge states, and (iv) the observed shell structure is rather insensitive to the edge roughness.

  15. On the transparent conducting oxide Al doped ZnO: First Principles and Boltzmann equations study

    Energy Technology Data Exchange (ETDEWEB)

    Slassi, A. [Institute of Nanomaterials and Nanotechnology, MAScIR, Rabat (Morocco); LMPHE (URAC 12), Faculté des Sciences, Université Mohammed V-Agdal, Rabat (Morocco); Naji, S. [LMPHE (URAC 12), Faculté des Sciences, Université Mohammed V-Agdal, Rabat (Morocco); Department of Physics, Faculty of Science, Ibb University, Ibb (Yemen); Benyoussef, A. [Institute of Nanomaterials and Nanotechnology, MAScIR, Rabat (Morocco); LMPHE (URAC 12), Faculté des Sciences, Université Mohammed V-Agdal, Rabat (Morocco); Hamedoun, M., E-mail: hamedoun@hotmail.com [Institute of Nanomaterials and Nanotechnology, MAScIR, Rabat (Morocco); El Kenz, A. [LMPHE (URAC 12), Faculté des Sciences, Université Mohammed V-Agdal, Rabat (Morocco)

    2014-08-25

    Highlights: • The incorporation of Al in ZnO increases the optical band edge absorption. • Incorporated Al creates shallow donor states of Al-3s around Fermi level. • Transmittance decreases in the visible and IR regions, while it increases in the UV region. • Electrical conductivity increases and reaches almost the saturation for high concentration of Al. - Abstract: We report, in this work, a theoretical study on the electronic, optical and electrical properties of pure and Al doped ZnO with different concentrations. In fact, we investigate these properties using both First Principles calculations within TB-mBJ approximation and Boltzmann equations under the constant relaxation time approximation for charge carriers. It is found out that, the calculated lattice parameters and the optical band gap of pure ZnO are close to the experimental values and in a good agreement with the other theoretical studies. It is also observed that, the incorporations of Al in ZnO increase the optical band edge absorption which leads to a blue shift and no deep impurities levels are induced in the band gap as well. More precisely, these incorporations create shallow donor states around Fermi level in the conduction band minimum from mainly Al-3s orbital. Beside this, it is found that, the transmittance is decreased in the visible and IR regions, while it is significantly improved in UV region. Finally, our calculations show that the electrical conductivity is enhanced as a result of Al doping and it reaches almost the saturation for high concentration of Al. These features make Al doped ZnO a transparent conducting electrode for optoelectronic device applications.

  16. Extended photoresponse and multi-band luminescence of ZnO/ZnSe core/shell nanorods.

    Science.gov (United States)

    Yang, Qin; Cai, Hua; Hu, Zhigao; Duan, Zhihua; Yang, Xu; Sun, Jian; Xu, Ning; Wu, Jiada

    2014-01-15

    Aligned ZnO/ZnSe core/shell nanorods (NRs) with type-II energy band alignment were fabricated by pulsed laser deposition of ZnSe on the surfaces of hydrothermally grown ZnO NRs. The obtained ZnO/ZnSe core/shell NRs are composed of wurtzite ZnO cores and zinc blende ZnSe shells. The bare ZnO NRs are capable of emitting strong ultraviolet (UV) near band edge (NBE) emission at 325-nm light excitation, while the ZnSe shells greatly suppress the emission from the ZnO cores. High-temperature processing results in an improvement in the structures of the ZnO cores and the ZnSe shells and significant changes in the optical properties of ZnO/ZnSe core/shell NRs. The fabricated ZnO/ZnSe core/shell NRs show optical properties corresponding to the two excitonic band gaps of wurtzite ZnO and zinc blende ZnSe and the effective band gap between the conduction band minimum of ZnO and the valence band maximum ZnSe. An extended photoresponse much wider than those of the constituting ZnO and ZnSe and a multi-band photoluminescence including the UV NBE emission of ZnO and the blue NBE emission of ZnSe are observed.

  17. Significant reduction in NiO band gap upon formation of Lix Ni1-x O alloys: applications to solar energy conversion.

    Science.gov (United States)

    Alidoust, Nima; Toroker, Maytal Caspary; Keith, John A; Carter, Emily A

    2014-01-01

    Long-term sustainable solar energy conversion relies on identifying economical and versatile semiconductor materials with appropriate band structures for photovoltaic and photocatalytic applications (e.g., band gaps of ∼ 1.5-2.0 eV). Nickel oxide (NiO) is an inexpensive yet highly promising candidate. Its charge-transfer character may lead to longer carrier lifetimes needed for higher efficiencies, and its conduction band edge is suitable for driving hydrogen evolution via water-splitting. However, NiO's large band gap (∼ 4 eV) severely limits its use in practical applications. Our first-principles quantum mechanics calculations show band gaps dramatically decrease to ∼ 2.0 eV when NiO is alloyed with Li2O. We show that Lix Ni1-x O alloys (with x=0.125 and 0.25) are p-type semiconductors, contain states with no impurity levels in the gap and maintain NiO's desirable charge-transfer character. Lastly, we show that the alloys have potential for photoelectrochemical applications, with band edges well-placed for photocatalytic hydrogen production and CO2 reduction, as well as in tandem dye-sensitized solar cells as a photocathode. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Layer dependence of the electronic band alignment of few-layer Mo S2 on Si O2 measured using photoemission electron microscopy

    Science.gov (United States)

    Berg, Morgann; Keyshar, Kunttal; Bilgin, Ismail; Liu, Fangze; Yamaguchi, Hisato; Vajtai, Robert; Chan, Calvin; Gupta, Gautam; Kar, Swastik; Ajayan, Pulickel; Ohta, Taisuke; Mohite, Aditya D.

    2017-06-01

    Tailoring band alignment layer-by-layer using heterojunctions of two-dimensional (2D) semiconductors is an attractive prospect for producing next-generation electronic and optoelectronic devices that are ultrathin, flexible, and efficient. The 2D layers of transition metal dichalcogenides (TMDs) in laboratory devices have already shown favorable characteristics for electronic and optoelectronic applications. Despite these strides, a systematic understanding of how band alignment evolves from monolayer to multilayer structures is still lacking in experimental studies, which hinders development of novel devices based on TMDs. Here, we report on the local band alignment of monolayer, bilayer, and trilayer Mo S2 on a 285-nm-thick Si O2 substrate using an approach to probe the occupied electronic states based on photoemission electron microscopy and deep-ultraviolet light. Local measurements of the vacuum level and the valence band edge at the Brillouin zone center show that the addition of layers to monolayer Mo S2 increases the relative work function and pushes the valence band edge toward the vacuum level. We also deduced n -type doping of few-layer Mo S2 and type-I band alignment across monolayer-to-bilayer and bilayer-to-trilayer lateral junctions. Conducted in isolation from environmental effects owing to the vacuum condition of the measurement and an insulating Si O2 substrate, this study shows a metrology to uncover electronic properties intrinsic to Mo S2 semiconducting layers and emerging 2D crystals alike.

  19. Oxygen- and hydroxyl-edge termination of silicene nanoribbons studied by first-principles calculations

    Science.gov (United States)

    Li, Rui; Liu, Zhong-Li; Gu, Yanhong; Zhang, Weiying; Tan, Yonggang

    2016-05-01

    The geometrical structures and electronic properties of the armchair- and zigzag-edge silicene nanoribbons (SiNRs), terminated with oxygen and hydroxyl (ZSiNR-O, ZSiNR-OH, ASiNR-O, ASiNR-OH), have been investigated by using the first-principles method. It is found that the silicene edges are rippled upon the oxygen termination. On one edge of ZSiNR-O, the neighboring Si-O bonds move concordantly right (left) from the silicene plane, while on one edge of ASiNR-O, the neighboring Si-O bonds respectively move right and left to result in larger rippled amplitudes. Comparably, the influence of OH-termination on the silicene edge is small, inducing smaller rippled edges. The electronic structure calculations show that the px electrons of oxygen on the rippled edges of ZSiNR-O sp3 hybridize with the edge Si atoms, forming one more bands. The band gaps of the ASiNR-O and ASiNR-OH also obey the three-family behavior, due to the quantum confinement and the crucial effect of the edges. For ASiNR-OH, by taking account of the new atom chains formed by the hydrogen bonds of the neighboring OHs, the band gaps follow the same hierarchy of Δ3 p >Δ3 p - 1 >Δ3 p - 2 with those of ASiNR-Os.

  20. Atomic-Monolayer MoS2 Band-to-Band Tunneling Field-Effect Transistor

    KAUST Repository

    Lan, Yann Wen

    2016-09-05

    The experimental observation of band-to-band tunneling in novel tunneling field-effect transistors utilizing a monolayer of MoS2 as the conducting channel is demonstrated. Our results indicate that the strong gate-coupling efficiency enabled by two-dimensional materials, such as monolayer MoS2, results in the direct manifestation of a band-to-band tunneling current and an ambipolar transport.

  1. Large area graphene nanomesh: an artificial platform for edge-electrochemical biosensing at the sub-attomolar level.

    Science.gov (United States)

    Zribi, Bacem; Castro-Arias, Juan-Manuel; Decanini, Dominique; Gogneau, Noëlle; Dragoe, Diana; Cattoni, Andrea; Ouerghi, Abdelkarim; Korri-Youssoufi, Hafsa; Haghiri-Gosnet, Anne-Marie

    2016-08-25

    Recent advances in large area graphene growth have led to tremendous applications in a variety of areas. The graphene nanomesh with its tunable band-gap is of great interest for both fundamental research, to explore the effect of edges on both the 2D electrical conduction and its electrochemical behavior, and applications such as nanoelectronic devices or highly sensitive biosensors. Here, we report on the fabrication of a large surface graphene nanomesh by nanoimprint lithography (NIL) to produce controlled artificial edges. The electrochemical response of this high quality single graphene layer imprinted nanomesh shows an enhancement in capacitance associated with faster electron transfer which can be attributed to the high density of edges. The electrochemical performances of this nanomesh graphene platform have been also studied for label-free DNA detection from Hepatitis C virus as a model. We demonstrate that such a nanomesh platform allows direct detection at the sub-attomolar level with more than 90% of molecules located on the imprinted artificial edges. Such a graphene nanomesh electrode will find useful future applications in the field of biosensing.

  2. Edge remap for solids

    Energy Technology Data Exchange (ETDEWEB)

    Kamm, James R.; Love, Edward; Robinson, Allen C; Young, Joseph G.; Ridzal, Denis

    2013-12-01

    We review the edge element formulation for describing the kinematics of hyperelastic solids. This approach is used to frame the problem of remapping the inverse deformation gradient for Arbitrary Lagrangian-Eulerian (ALE) simulations of solid dynamics. For hyperelastic materials, the stress state is completely determined by the deformation gradient, so remapping this quantity effectively updates the stress state of the material. A method, inspired by the constrained transport remap in electromagnetics, is reviewed, according to which the zero-curl constraint on the inverse deformation gradient is implicitly satisfied. Open issues related to the accuracy of this approach are identified. An optimization-based approach is implemented to enforce positivity of the determinant of the deformation gradient. The efficacy of this approach is illustrated with numerical examples.

  3. Absorption enhancement of a dual-band metamaterial absorber

    Science.gov (United States)

    Zhong, Min; Han, Gui Ming; Liu, Shui Jie; Xu, Bang Li; Wang, Jie; Huang, Hua Qing

    2017-02-01

    In this paper, we propose and fabricate a dual-band metamaterial absorber in 6-24 THz region. Electric field distribution reveal that the first absorption band is obtained from localized surface plasmon (LSP) modes which are excited both on inside and outside edges of each circular-patterned metal-dielectric stack, while the second absorption band is excited by LSP modes on outside edges of each stack. Measured results indicate that the absorption band width can be tuned by increasing the radius of circular-patterned layers or reducing the thickness of dielectric spacing layers. Moreover, the designed dual-band metamaterial absorber is independent on circular-patterned dielectric layer combinations.

  4. Effect of Edge Roughness on Static Characteristics of Graphene Nanoribbon Field Effect Transistor

    Directory of Open Access Journals (Sweden)

    Yaser M. Banadaki

    2016-03-01

    Full Text Available In this paper, we present a physics-based analytical model of GNR FET, which allows for the evaluation of GNR FET performance including the effects of line-edge roughness as its practical specific non-ideality. The line-edge roughness is modeled in edge-enhanced band-to-band-tunneling and localization regimes, and then verified for various roughness amplitudes. Corresponding to these two regimes, the off-current is initially increased, then decreased; while, on the other hand, the on-current is continuously decreased by increasing the roughness amplitude.

  5. Band gap narrowing of TiO2 by compensated codoping for enhanced photocatalytic activity

    Institute of Scientific and Technical Information of China (English)

    Jindou Huang; Shuhao Wen; Jianyong Liu; Guozhong He

    2012-01-01

    In this study,we have performed first-principles screened exchanged hybrid density function theory with the HSE06 function calculations of the C-Mo,C-W,N-Nb and N-Ta codoped anatase TiO2 systems to investigate the effect of codoping on the electronic structure of TiO2.The calculated results demonstrate that (W(s)+C(s)) codoped TiO2 narrows the band gap significantly,and have little influence on the position of conduction band edges,therefore,enhances the efficiency of the photocatalytic hydrogen generation from water and the photodegradation of organic pollutants.Moreover,the proper oxygen pressure and temperature are two key factors during synthesis which should be carefully under control so that the desired (W(s)+C(s)) codoped TiO2 can be obtained.

  6. Importance of non-parabolic band effects in the thermoelectric properties of semiconductors.

    Science.gov (United States)

    Chen, Xin; Parker, David; Singh, David J

    2013-11-07

    We present an analysis of the thermoelectric properties of of n-type GeTe and SnTe in relation to the lead chalcogenides PbTe and PbSe. We find that the singly degenerate conduction bands of semiconducting GeTe and SnTe are highly non-ellipsoidal, even very close to the band edges. This leads to isoenergy surfaces with a strongly corrugated shape that is clearly evident at carrier concentrations well below 0.005 e per formula unit (7-9 × 10(19) cm(-3) depending on material). Analysis within Boltzmann theory suggests that this corrugation may be favorable for the thermoelectric transport. Our calculations also indicate that values of the power factor for these two materials may well exceed those of PbTe and PbSe. As a result these materials may exhibit n-type performance exceeding that of the lead chalcogenides.

  7. Cutting Edge Localisation in an Edge Profile Milling Head

    NARCIS (Netherlands)

    Fernandez Robles, Laura; Azzopardi, George; Alegre, Enrique; Petkov, Nicolai

    2015-01-01

    Wear evaluation of cutting tools is a key issue for prolonging their lifetime and ensuring high quality of products. In this paper, we present a method for the effective localisation of cutting edges of inserts in digital images of an edge profile milling head. We introduce a new image data set of 1

  8. Ultra-low values of the absorption coefficient for band-band transitions in moderately doped Si obtained from luminescence

    Science.gov (United States)

    Daub, E.; Würfel, P.

    1996-11-01

    The absolute value of the absorption coefficient αbb(ℏω) for band-band transitions near the band edge was determined in moderately doped silicon by photoluminescence spectra analysis. The major advantage of this method in determining αbb(ℏω) is the lack of interference with free carrier absorption, in contrast to conventional methods like transmission or photothermal deflection measurements. We deduce values for αbb(ℏω), which are nearly five orders of magnitude smaller than the absorption coefficient αfc(ℏω) for free carrier absorption. With this method it is possible to examine in detail the influence of doping on the absorption coefficient for band-band transitions near the absorption edge. The appearance of band tails and band-gap narrowing are very well reflected. With conventional methods, which can only detect the overall absorption of the incident radiation, the determination of αbb(ℏω) in the vicinity of the band edge is impossible for moderately and heavily doped silicon, because it is completely masked by the free carrier absorption.

  9. Giant edge state splitting at atomically precise graphene zigzag edges.

    Science.gov (United States)

    Wang, Shiyong; Talirz, Leopold; Pignedoli, Carlo A; Feng, Xinliang; Müllen, Klaus; Fasel, Roman; Ruffieux, Pascal

    2016-05-16

    Zigzag edges of graphene nanostructures host localized electronic states that are predicted to be spin-polarized. However, these edge states are highly susceptible to edge roughness and interaction with a supporting substrate, complicating the study of their intrinsic electronic and magnetic structure. Here, we focus on atomically precise graphene nanoribbons whose two short zigzag edges host exactly one localized electron each. Using the tip of a scanning tunnelling microscope, the graphene nanoribbons are transferred from the metallic growth substrate onto insulating islands of NaCl in order to decouple their electronic structure from the metal. The absence of charge transfer and hybridization with the substrate is confirmed by scanning tunnelling spectroscopy, which reveals a pair of occupied/unoccupied edge states. Their large energy splitting of 1.9 eV is in accordance with ab initio many-body perturbation theory calculations and reflects the dominant role of electron-electron interactions in these localized states.

  10. Pre-Forming Effects on AHSS Edge Cracking

    Science.gov (United States)

    Chen, Xiaoming; Chen, Ke; Smith, Lorenzo

    2011-08-01

    Edge cracking in advanced high strength steels (AHSS) is a significant failure mode in many sheet metal stamping processes. Edge pre-forming into a wave (or scallop) shape is a common technique used in conventional steels to gather material in high edge stretch regions in preparation for the subsequent edge stretch process. The pre-forms designed for mild steels do not always apply to AHSS because the properties of AHSS can differ greatly from those of conventional steels. This work has studied the effects of pre-forming on AHSS edge cracking. Experiments have been conducted to stretch pre-formed steel strips to failure. Strain distributions of pre-forms with various levels of stretch have been measured using digital image correlation (DIC) technology. Finite element analyses have been performed and compared with the experimental results. Different failure criteria have also been evaluated for use in this type of application.

  11. Conduct disorder

    Science.gov (United States)

    ... Conduct disorder is often linked to attention-deficit disorder . Conduct disorder also can be an early sign of ... child or teen has a history of conduct disorder behaviors. A physical examination and blood tests can help ...

  12. Redox-dependent spatially resolved electrochemistry at graphene and graphite step edges.

    Science.gov (United States)

    Güell, Aleix G; Cuharuc, Anatolii S; Kim, Yang-Rae; Zhang, Guohui; Tan, Sze-yin; Ebejer, Neil; Unwin, Patrick R

    2015-04-28

    The electrochemical (EC) behavior of mechanically exfoliated graphene and highly oriented pyrolytic graphite (HOPG) is studied at high spatial resolution in aqueous solutions using Ru(NH3)6(3+/2+) as a redox probe whose standard potential sits close to the intrinsic Fermi level of graphene and graphite. When scanning electrochemical cell microscopy (SECCM) data are coupled with that from complementary techniques (AFM, micro-Raman) applied to the same sample area, different time-dependent EC activity between the basal planes and step edges is revealed. In contrast, other redox couples (ferrocene derivatives) whose potential is further removed from the intrinsic Fermi level of graphene and graphite show uniform and high activity (close to diffusion-control). Macroscopic voltammetric measurements in different environments reveal that the time-dependent behavior after HOPG cleavage, peculiar to Ru(NH3)6(3+/2+), is not associated particularly with any surface contaminants but is reasonably attributed to the spontaneous delamination of the HOPG with time to create partially coupled graphene layers, further supported by conductive AFM measurements. This process has a major impact on the density of states of graphene and graphite edges, particularly at the intrinsic Fermi level to which Ru(NH3)6(3+/2+) is most sensitive. Through the use of an improved voltammetric mode of SECCM, we produce movies of potential-resolved and spatially resolved HOPG activity, revealing how enhanced activity at step edges is a subtle effect for Ru(NH3)6(3+/2+). These latter studies allow us to propose a microscopic model to interpret the EC response of graphene (basal plane and edges) and aged HOPG considering the nontrivial electronic band structure.

  13. Widely tunable edge emitters

    Science.gov (United States)

    Sarlet, Gert; Wesstrom, Jan-Olof; Rigole, Pierre-Jean; Broberg, Bjoern

    2001-11-01

    We will present the current state-of-the-art in widely tunable edge emitting lasers for WDM applications. Typical applications for a tunable laser will be discussed, and the different types of tunable lasers available today will be compared with respect to the requirements posed by these applications. We will focus on the DBR-type tunable lasers - DBR, SG-DBR and GCSR - which at present seem to be the only tunable lasers mature enough for real-life applications. Their main advantages are that they are all monolithic, with no moving parts, and can be switched from one frequency to the other very rapidly since the tuning is based on carrier injection and not on thermal or mechanical changes. We will briefly discuss the working principle of each of these devices, and present typical performance characteristics. From a manufacturing point of view, rapid characterization of the lasers is crucial; therefore an overview will be given of different characterization schemes that have recently been proposed. For the end user, reliability is the prime issue. We will show results of degradation studies on these lasers and outline how the control electronics that drive the laser can compensate for any frequency drift. Finally, we will also discuss the impact of the requirement for rapid frequency switching on the design of the control electronics.

  14. Topological fate of edge states of single Bi bilayer on Bi(111)

    Science.gov (United States)

    Yeom, Han Woong; Jin, Kyung-Hwan; Jhi, Seung-Hoon

    2016-02-01

    We address the topological nature of electronic states of step edges of Bi(111) films by first-principles band structure calculations. We confirm that the dispersion of step-edge states reflects the topological nature of underlying films, which become topologically trivial at a thickness larger than eight bilayers. This result clearly conflicts with recent claims that the step-edge state at the surface of a bulk Bi(111) crystal or a sufficiently thick Bi(111) film represents nontrivial edge states of the two-dimensional topological insulator phase expected for a very thin Bi(111) film. The trivial step-edge states have a gigantic spin splitting of one-dimensional Rashba bands and substantial intermixing with electronic states of the bulk, which might be exploited further.

  15. Simultaneous Multi-frequency Topological Edge Modes between One-dimensional Photonic Crystals

    OpenAIRE

    Choi, Ka Hei; Ling, C. W.; Lee, K. F.; Tsang, Y. H.; Fung, Kin Hung

    2016-01-01

    We show theoretically that, in the limit of weak dispersion, one-dimensional (1D) binary centrosymmetric photonic crystals can support topological edge modes in all photonic band gaps. By analyzing their bulk band topology, these "harmonic" topological edge modes can be designed in a way that they exist at all photonic band gaps opened at the center of the Brillouin Zone, or at all gaps opened at the zone boundaries, or both. The results may suggest a new approach to achieve robust multi-freq...

  16. Improved Edge Performance in MRF

    Science.gov (United States)

    Shorey, Aric; Jones, Andrew; Durnas, Paul; Tricard, Marc

    2004-01-01

    The fabrication of large segmented optics requires a polishing process that can correct the figure of a surface to within a short distance from its edges-typically, a few millimeters. The work here is to develop QED's Magnetorheological Finishing (MRF) precision polishing process to minimize residual edge effects.

  17. Topological Invariants of Edge States for Periodic Two-Dimensional Models

    Energy Technology Data Exchange (ETDEWEB)

    Avila, Julio Cesar; Schulz-Baldes, Hermann, E-mail: schuba@mi.uni-erlangen.de; Villegas-Blas, Carlos [Instituto de Matematicas, UNAM (Mexico)

    2013-06-15

    Transfer matrix methods and intersection theory are used to calculate the bands of edge states for a wide class of periodic two-dimensional tight-binding models including a sublattice and spin degree of freedom. This allows to define topological invariants by considering the associated Bott-Maslov indices which can be easily calculated numerically. For time-reversal symmetric systems in the symplectic universality class this leads to a Z{sub 2} -invariant for the edge states. It is shown that the edge state invariants are related to Chern numbers of the bulk systems and also to (spin) edge currents, in the spirit of the theory of topological insulators.

  18. Topological invariants of edge states for periodic two-dimensional models

    CERN Document Server

    Avila, Julio Cesar; Villegas-Blas, Carlos

    2012-01-01

    Transfer matrix methods and intersection theory are used to calculate the bands of edge states for a wide class of periodic two-dimensional tight-binding models including a sublattice and spin degree of freedom. This allows to define topological invariants by considering the associated Bott-Maslov indices which can be easily calculated numerically. For time-reversal symmetric systems in the symplectic universality class this leads to a Z_2-invariant for the edge states. It is shown that the edge state invariants are related to Chern numbers of the bulk systems and also to (spin) edge currents, in the spirit of the theory of topological insulators.

  19. Band structure of semiconductors

    CERN Document Server

    Tsidilkovski, I M

    2013-01-01

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

  20. The Robotic Edge Finishing Laboratory

    Energy Technology Data Exchange (ETDEWEB)

    Loucks, C.S.; Selleck, C.B.

    1990-08-01

    The Robotic Edge Finishing Laboratory at Sandia National Laboratories is developing four areas of technology required for automated deburring, chamfering, and blending of machined edges: (1) the automatic programming of robot trajectories and deburring processes using information derived from a CAD database, (2) the use of machine vision for locating the workpiece coupled with force control to ensure proper tool contact, (3) robotic deburring, blending, and machining of precision chamfered edges, and (4) in-process automated inspection of the formed edge. The Laboratory, its components, integration, and results from edge finishing experiments to date are described here. Also included is a discussion of the issues regarding implementation of the technology in a production environment. 24 refs., 17 figs.

  1. Toward edge minability for role mining in bipartite networks

    Science.gov (United States)

    Dong, Lijun; Wang, Yi; Liu, Ran; Pi, Benjie; Wu, Liuyi

    2016-11-01

    Bipartite network models have been extensively used in information security to automatically generate role-based access control (RBAC) from dataset. This process is called role mining. However, not all the topologies of bipartite networks are suitable for role mining; some edges may even reduce the quality of role mining. This causes unnecessary time consumption as role mining is NP-hard. Therefore, to promote the quality of role mining results, the capability that an edge composes roles with other edges, called the minability of edge, needs to be identified. We tackle the problem from an angle of edge importance in complex networks; that is an edge easily covered by roles is considered to be more important. Based on this idea, the k-shell decomposition of complex networks is extended to reveal the different minability of edges. By this way, a bipartite network can be quickly purified by excluding the low-minability edges from role mining, and thus the quality of role mining can be effectively improved. Extensive experiments via the real-world datasets are conducted to confirm the above claims.

  2. Tunneling into and between helical edge states: Fermionic approach

    Science.gov (United States)

    Aristov, D. N.; Niyazov, R. A.

    2016-07-01

    We study the four-terminal junction of spinless Luttinger liquid wires, which describes either a corner junction of two helical edge states of topological insulators or the tunneling from the spinful wire into the helical edge state. We use the fermionic representation and the scattering state formalism, in order to compute the renormalization group (RG) equations for the linear response conductances. We establish our approach by considering a junction between two possibly nonequivalent helical edge states and find an agreement with the earlier analysis of this situation. Tunneling from the tip of the spinful wire to the edge state is further analyzed which requires some modification of our formalism. In the latter case we demonstrate (i) the existence of both fixed lines and conventional fixed points of RG equations, and (ii) certain proportionality relations holding for conductances during renormalization. The scaling exponents and phase portraits are obtained in all cases.

  3. Corner junction as a probe of helical edge states.

    Science.gov (United States)

    Hou, Chang-Yu; Kim, Eun-Ah; Chamon, Claudio

    2009-02-20

    We propose and analyze interedge tunneling in a quantum spin Hall corner junction as a means to probe the helical nature of the edge states. We show that electron-electron interactions in the one-dimensional helical edge states result in Luttinger parameters for spin and charge that are intertwined, and thus rather different from those for a quantum wire with spin rotation invariance. Consequently, we find that the four-terminal conductance in a corner junction has a distinctive form that could be used as evidence for the helical nature of the edge states.

  4. Theory of Edge Detection

    Science.gov (United States)

    Marr, D.; Hildreth, E.

    1980-02-01

    A theory of edge detection is presented. The analysis proceeds in two parts. (1) Intensity changes, which occur in a natural image over a wide range of scales, are detected separately at different scales. An appropriate filter for this purpose at a given scale is found to be the second derivative of a Gaussian, and it is shown that, provided some simple conditions are satisfied, these primary filters need not be orientation-dependent. Thus, intensity changes at a given scale are best detected by finding the zero values of nabla 2G(x, y)* I(x, y) for image I, where G(x, y) is a two-dimensional Gaussian distribution and nabla 2 is the Laplacian. The intensity changes thus discovered in each of the channels are then represented by oriented primitives called zero-crossing segments, and evidence is given that this representation is complete. (2) Intensity changes in images arise from surface discontinuities or from reflectance or illumination boundaries, and these all have the property that they are spatially localized. Because of this, the zero-crossing segments from the different channels are not independent, and rules are deduced for combining them into a description of the image. This description is called the raw primal sketch. The theory explains several basic psychophysical findings, and the operation of forming oriented zero-crossing segments from the output of centre-surround nabla 2G filters acting on the image forms the basis for a physiological model of simple cells (see Marr & Ullman 1979).

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

    Science.gov (United States)

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

    2016-06-21

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

  6. Reflectivity and dynamical conductivity of n-type HgCr/sub 2/Se/sub 4/

    Energy Technology Data Exchange (ETDEWEB)

    Selmi, A.; Faymonville, R.; Schlegel, H. (Technische Hochschule Aachen (Germany, F.R.). Lehrstuhl fuer Experimentalphysik 1A und 1. Physikalisches Inst.)

    Reflectivity measurements have been done on doped n-type HgCr/sub 2/Se/sub 4/ (napprox.=(10/sup 15//10/sup 19/) cm/sup -3/), at various temperatures ((4/300)K) in the infra-red range (anti ..nu..=(40/5000)cm/sup -1/). The spectra show the structure of a plasma edge and reststrahlbands. Data have been analysed by a Kramers-Kronig procedure. The deduced dynamical conductivity shows an anomaly near the plasma frequency ..omega..sub(p). The transmittivity measurements show a strong temperature dependence of the conduction band.

  7. Effect of zirconium oxide nanofiller and dibutyl phthalate plasticizer on ionic conductivity and optical properties of solid polymer electrolyte.

    Science.gov (United States)

    Yasin, Siti Mariah Mohd; Ibrahim, Suriani; Johan, Mohd Rafie

    2014-01-01

    New solid polymer electrolytes (SPE) based on poly(ethylene oxide) (PEO) doped with lithium trifluoromethanesulfonate (LiCF3SO3), dibutyl phthalate (DBP) plasticizer, and zirconium oxide (ZrO2) nanoparticles were prepared by solution-casting technique. The conductivity was enhanced by addition of dibutyl phthalate (DBP) plasticizer and ZrO2 nanofiller with maximum conductivity (1.38 × 10(-4) Scm(-1)). The absorption edge and band gap values showed decreases upon addition of LiSO3CF3, DBP, and ZrO2 due to the formation of localized states in the SPE and the degree of disorder in the films increased.

  8. Keeping the band together: evidence for false boundary disruptive coloration in a butterfly.

    Science.gov (United States)

    Seymoure, B M; Aiello, A

    2015-09-01

    There is a recent surge of evidence supporting disruptive coloration, in which patterns break up the animal's outline through false edges or boundaries, increasing survival in animals by reducing predator detection and/or preventing recognition. Although research has demonstrated that false edges are successful for reducing predation of prey, research into the role of internal false boundaries (i.e. stripes and bands) in reducing predation remains warranted. Many animals have stripes and bands that may function disruptively. Here, we test the possible disruptive function of wing band patterning in a butterfly, Anartia fatima, using artificial paper and plasticine models in Panama. We manipulated the band so that one model type had the band shifted to the wing margin (nondisruptive treatment) and another model had a discontinuous band located on the wing margin (discontinuous edge treatment). We kept the natural wing pattern to represent the false boundary treatment. Across all treatment groups, we standardized the area of colour and used avian visual models to confirm a match between manipulated and natural wing colours. False boundary models had higher survival than either the discontinuous edge model or the nondisruptive model. There was no survival difference between the discontinuous edge model and the nondisruptive model. Our results demonstrate the importance of wing bands in reducing predation on butterflies and show that markings set in from the wing margin can reduce predation more effectively than marginal bands and discontinuous marginal patterns. This study demonstrates an adaptive benefit of having stripes and bands.

  9. Electronic Structures of Silicene Nanoribbons: Two-Edge-Chemistry Modification and First-Principles Study.

    Science.gov (United States)

    Yao, Yin; Liu, Anping; Bai, Jianhui; Zhang, Xuanmei; Wang, Rui

    2016-12-01

    In this paper, we investigate the structural and electronic properties of zigzag silicene nanoribbons (ZSiNRs) with edge-chemistry modified by H, F, OH, and O, using the ab initio density functional theory method and local spin-density approximation. Three kinds of spin polarized configurations are considered: nonspin polarization (NM), ferromagnetic spin coupling for all electrons (FM), ferromagnetic ordering along each edge, and antiparallel spin orientation between the two edges (AFM). The H, F, and OH groups modified 8-ZSiNRs have the AFM ground state. The directly edge oxidized (O1) ZSiNRs yield the same energy and band structure for NM, FM, and AFM configurations, owning to the same s p (2) hybridization. And replacing the Si atoms on the two edges with O atoms (O2) yields FM ground state. The edge-chemistry-modified ZSiNRs all exhibit metallic band structures. And the modifications introduce special edge state strongly localized at the Si atoms in the edge, except for the O1 form. The modification of the zigzag edges of silicene nanoribbons is a key issue to apply the silicene into the field effect transistors (FETs) and gives more necessity to better understand the experimental findings.

  10. Hydrogen-free graphene edges.

    Science.gov (United States)

    He, Kuang; Lee, Gun-Do; Robertson, Alex W; Yoon, Euijoon; Warner, Jamie H

    2014-01-01

    Graphene edges and their functionalization influence the electronic and magnetic properties of graphene nanoribbons. Theoretical calculations predict saturating graphene edges with hydrogen lower its energy and form a more stable structure. Despite the importance, experimental investigations of whether graphene edges are always hydrogen-terminated are limited. Here we study graphene edges produced by sputtering in vacuum and direct measurements of the C-C bond lengths at the edge show ~86% contraction relative to the bulk. Density functional theory reveals the contraction is attributed to the formation of a triple bond and the absence of hydrogen functionalization. Time-dependent images reveal temporary attachment of a single atom to the arm-chair C-C bond in a triangular configuration, causing expansion of the bond length, which then returns back to the contracted value once the extra atom moves on and the arm-chair edge is returned. Our results provide confirmation that non-functionalized graphene edges can exist in vacuum.

  11. Complex band structure and superlattice electronic states

    Science.gov (United States)

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

    1981-04-01

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

  12. Poole-Frenkel Conduction in Cu/Nano-SnO2/Cu Arrangement

    OpenAIRE

    2011-01-01

    It is well known that metal/Tin-dioxide/metal sandwich structures exhibit a field-assisted lowering of the potential barrier between donor-like center and the conduction band edge, known as the Poole-Frenkel effect. This behavior is indicated by a linear dependence of Iog  on 1 / 2 , where is the current density, and is the applied voltage. In this study, the electrical properties of Cu/nano-SnO2/Cu sandwich structures were investigated through current-voltage measurements at room tem...

  13. Band parameters of phosphorene

    DEFF Research Database (Denmark)

    Lew Yan Voon, L. C.; Wang, J.; Zhang, Y.;

    2015-01-01

    Phosphorene is a two-dimensional nanomaterial with a direct band-gap at the Brillouin zone center. In this paper, we present a recently derived effective-mass theory of the band structure in the presence of strain and electric field, based upon group theory. Band parameters for this theory...

  14. Low Power Band to Band Tunnel Transistors

    Science.gov (United States)

    2010-12-15

    the E-field and tunneling at the source- pocket junction you form a parasitic NPN + transistor and the injection mechanism of carriers into the...hypothesis that the 1000 ° C, 5s anneal split lead to a very wide pocket and the accidental formation of a NPN + transistor , while the 1000 ° C, 1s anneal...Low Power Band to Band Tunnel Transistors Anupama Bowonder Electrical Engineering and Computer Sciences University of California at Berkeley

  15. Band structure engineering in organic semiconductors

    Science.gov (United States)

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

    2016-06-01

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

  16. Theory of vortices in hybridized ballistic/diffusive-band superconductors

    Science.gov (United States)

    Tanaka, K.; Eschrig, M.; Agterberg, D. F.

    2007-06-01

    We study the electronic structure in the vicinity of a vortex in a two-band superconductor in which the quasiparticle motion is ballistic in one band and diffusive in the other. This study is based on a model appropriate for such a case, that we have introduced recently [Tanaka , Phys. Rev. B 73, 220501(R) (2006)]. We argue that in the two-band superconductor MgB2 , such a case is realized. Motivated by the experimental findings on MgB2 , we assume that superconductivity in the diffusive band is “weak,” i.e., mostly induced. We examine intriguing features of the order parameter, the current density, and the vortex core spectrum in the “strong” ballistic band under the influence of hybridization with the “weak” diffusive band. Although the order parameter in the diffusive band is induced, the characteristic length scales in the two bands differ due to Coulomb interactions. The current density in the vortex core is dominated by the contribution from the ballistic band, while outside the core the contribution from the diffusive band can be substantial, or even dominating. The current density in the diffusive band has strong temperature dependence, exhibiting the Kramer-Pesch effect when hybridization is strong. A particularly interesting feature of our model is the possibility of additional bound states near the gap edge in the ballistic band, that are prominent in the vortex center spectra. This contrasts with the single band case, where there is no gap-edge bound state in the vortex center. We find the above-mentioned unique features for parameter values relevant for MgB2 .

  17. Self-consistent treatment of v-groove quantum wire band structure in no parabolic approximation

    Directory of Open Access Journals (Sweden)

    Crnjanski Jasna V.

    2004-01-01

    Full Text Available The self-consistent no parabolic calculation of a V-groove-quantum-wire (VQWR band structure is presented. A comparison with the parabolic flat-band model of VQWR shows that both, the self-consistency and the nonparabolicity shift sub band edges, in some cases even in the opposite directions. These shifts indicate that for an accurate description of inter sub band absorption, both effects have to be taken into the account.

  18. An adaptive noise attenuation method for edge and amplitude preservation

    Institute of Scientific and Technical Information of China (English)

    Cai Han-Peng; He Zhen-Hua; Li Ya-Lin; He Guang-Ming; Zou Wen; Zhang Dong-Jun; Liu Pu

    2014-01-01

    Noise intensity distributed in seismic data varies with different frequencies or frequency bands; thus, noise attenuation on the full-frequency band affects the dynamic properties of the seismic reflection signal and the subsequent seismic data interpretation, reservoir description, hydrocarbon detection, etc. Hence, we propose an adaptive noise attenuation method for edge and amplitude preservation, wherein the wavelet packet transform is used to decompose the full-band seismic signal into multiband data and then process these data using nonlinear anisotropic dip-oriented edge-preservingfi ltering. In the fi ltering, the calculated diffusion tensor from the structure tensor can be exploited to establish the direction of smoothing. In addition, the fault confidence measure and discontinuity operator can be used to preserve the structural and stratigraphic discontinuities and edges, and the decorrelation criteria can be used to establish the number of iterations. These parameters can minimize the intervention and subjectivity of the interpreter, and simplify the application of the proposed method. We applied the proposed method to synthetic and real 3D marine seismic data. We found that the proposed method could be used to attenuate noise in seismic data while preserving the effective discontinuity information and amplitude characteristics in seismic refl ection waves, providing high-quality data for interpretation and analysis such as high-resolution processing, attribute analysis, and inversion.

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

    Science.gov (United States)

    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.

  20. Optical study of the band structure of wurtzite GaP nanowires

    KAUST Repository

    Assali, S.

    2016-07-25

    We investigated the optical properties of wurtzite (WZ) GaP nanowires by performing photoluminescence (PL) and time-resolved PL measurements in the temperature range from 4 K to 300 K, together with atom probe tomography to identify residual impurities in the nanowires. At low temperature, the WZ GaP luminescence shows donor-acceptor pair emission at 2.115 eV and 2.088 eV, and Burstein-Moss band-filling continuum between 2.180 and 2.253 eV, resulting in a direct band gap above 2.170 eV. Sharp exciton α-β-γ lines are observed at 2.140–2.164–2.252 eV, respectively, showing clear differences in lifetime, presence of phonon replicas, and temperature-dependence. The excitonic nature of those peaks is critically discussed, leading to a direct band gap of ∼2.190 eV and to a resonant state associated with the γ-line ∼80 meV above the Γ8C conduction band edge.

  1. Fast tracking using edge histograms

    Science.gov (United States)

    Rokita, Przemyslaw

    1997-04-01

    This paper proposes a new algorithm for tracking objects and objects boundaries. This algorithm was developed and applied in a system used for compositing computer generated images and real world video sequences, but can be applied in general in all tracking systems where accuracy and high processing speed are required. The algorithm is based on analysis of histograms obtained by summing along chosen axles pixels of edge segmented images. Edge segmentation is done by spatial convolution using gradient operator. The advantage of such an approach is that it can be performed in real-time using available on the market hardware convolution filters. After edge extraction and histograms computation, respective positions of maximums in edge intensity histograms, in current and previous frame, are compared and matched. Obtained this way information about displacement of histograms maximums, can be directly converted into information about changes of target boundaries positions along chosen axles.

  2. Abnormal Modulation of Dielectric Band Transmittance of Polystyrene Opal

    Institute of Scientific and Technical Information of China (English)

    HU Xiao-Yong; GONG Qi-Huang; CHENG Bing-Ying; ZHANG Dao-Zhong

    2005-01-01

    @@ The abnormal transmittance in the dielectric band edge of a polystyrene opal is observed and analysed. The transmittance is periodically modulated and the period of modulation varies with the wavelength, which destroys the perfect structure of the photonic band gap. The transmittance modulation originates from the propagation of the low order whispering-gallery mode excited in polystyrene spheres. These results indicate that the whisperinggallery mode has a great influence on practical applications of polystyrene opal.

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

    Science.gov (United States)

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

    2017-10-01

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

  4. Observation of banded spherulites and lamellar structures by atomic force microscopy

    Institute of Scientific and Technical Information of China (English)

    姜勇; 罗艳红; 范泽夫; 王霞瑜; 徐军; 郭宝华; 李林

    2003-01-01

    Lamellar structures of banded spherulites of poly(ε-caprolactone)/poly(vinyl chloride) (PCL/PVC) blends are observed using tapping mode atomic force microscopy (AFM). The surface of the PCL/PVC banded spherulites presents to be concentric periodic ups and downs. The period of the bands corresponds to the extinction rings under the polarized optical microscopy observation. The lamellae with edge-on orientation in the ridges and the flat-on lamellae in the valleys of the banded spherulites are observed clearly. The twisting between the edge-on and flat-on lamellae is also observed.

  5. Significant Reduction in NiO Band Gap Upon Formation of LixNi1-xO alloys: Applications To Solar Energy Conversion

    Energy Technology Data Exchange (ETDEWEB)

    Alidoust, Nima; Toroker, Maytal Caspary; Keith, John A.; Carter, Emily A.

    2013-11-21

    Long-term sustainable solar energy conversion relies on identifying economical and versatile semiconductor materials with appropriate band structures for photovoltaic and photocatalytic applications (e.g., band gaps of ~1.5–2.0 eV). Nickel oxide (NiO) is an inexpensive yet highly promising candidate. Its charge-transfer character may lead to longer carrier lifetimes needed for higher efficiencies, and its conduction band edge is suitable for driving hydrogen evolution via water-splitting. However, NiO’s large band gap (~4 eV) severely limits its use in practical applications. Our first-principles quantum mechanics calculations show band gaps dramatically decrease to ~2.0 eV when NiO is alloyed with Li2O. In this paper, we show that LixNi1-xO alloys (with x=0.125 and 0.25) are p-type semiconductors, contain states with no impurity levels in the gap and maintain NiO’s desirable charge-transfer character. Lastly, we show that the alloys have potential for photoelectrochemical applications, with band edges well-placed for photocatalytic hydrogen production and CO2 reduction, as well as in tandem dye-sensitized solar cells as a photocathode.

  6. Orientation Relationships between Ferrite and Cementite by Edge-to-edge Matching Principle

    Institute of Scientific and Technical Information of China (English)

    Ning Zhong; Xiaodong Wang; Zhenghong Guo; Yonghua Rong

    2011-01-01

    The crystallographic features of pearlite were investigated by experiments and edge-to-edge matching principle. Two new orientation relationships between ferrite and cementite were determinated by selected area electron diffraction and then explained by our modified edge-to-edge matching method. The consistence of the experimental results with theoretical prediction confirms the practicability of the modified edge-to-edge matching model.

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

    Directory of Open Access Journals (Sweden)

    Joung-min Cho

    2013-10-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Joung-min, E-mail: cho.j.ad@m.titech.ac.jp; Akiyama, Yuto; Kakinuma, Tomoyuki [Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Tokyo 152-8552 (Japan); Mori, Takehiko [Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Tokyo 152-8552 (Japan); ACT-C, JST, Honcho, Kawaguchi, Saitama 332-0012 (Japan)

    2013-10-15

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

  9. Slope Edge Deformation and Permafrost Dynamics Along the Arctic Shelf Edge, Beaufort Sea, Canada

    Science.gov (United States)

    Paull, C. K.; Dallimore, S.; Caress, D. W.; Gwiazda, R.; Lundsten, E. M.; Anderson, K.; Riedel, M.; Melling, H.

    2015-12-01

    The shelf of the Canadian Beaufort Sea is underlain by relict offshore permafrost that formed in the long intervals of terrestrial exposure during glacial periods. At the shelf edge the permafrost thins rapidly and also warms. This area has a very distinct morphology that we attribute to both the formation and degradation of ice bearing permafrost. Positive relief features include circular to oval shaped topographic mounds, up to 10 m high and ~50 m in diameter which occur at a density of ~6 per km2. Intermixed are circular topographic depressions up to 20 m deep. This topography was investigated using an autonomous underwater vehicle that provides 1 m horizontal resolution bathymetry and chirp profiles, a remotely operated vehicle to document seafloor textures, and sediment cores to sample pore waters. A consistent down-core freshening at rates of 14 to 96 mM Cl- per meter was found in these pore waters near the shelf edge. Downward extrapolation of these trends indicates water with ≤335 mM Cl- should occur at 2.3 to 22.4 m sub-seafloor depths within this shelf edge deformation band. Pore water with 335 mM Cl- or less freezes at -1.4°C. As bottom water temperatures in this area are persistently (<-1.4°C) cold and ground ice was observed in some core samples, we interpret the volume changes associated with mound formation are in part due to pore water freezing. Thermal models (Taylor et al., 2014) predict brackish water along the shelf edge may be sourced in relict permafrost melting under the adjacent continental shelf. Buoyant brackish water is hypothesized to migrate along the base of the relict permafrost, to emerge at the shelf edge and then refreeze when it encounters the colder seafloor. Expansion generated by the formation of ice-bearing permafrost generates the positive relief mounds and ridges. The associated negative relief features may be related to permafrost dynamics also. Permafrost dynamics may have geohazard implications that are unique to the

  10. Computation of Edge-Edge-Edge Events Based on Conicoid Theory for 3-D Object Recognition

    Institute of Scientific and Technical Information of China (English)

    WU Chenye; MA Huimin

    2009-01-01

    The availability of a good viewpoint space partition is crucial in three dimensional (3-D) object rec-ognition on the approach of aspect graph. There are two important events depicted by the aspect graph ap-proach, edge-edge-edge (EEE) events and edge-vertex (EV) events. This paper presents an algorithm to compute EEE events by characteristic analysis based on conicoid theory, in contrast to current algorithms that focus too much on EV events and often overlook the importance of EEE events. Also, the paper provides a standard flowchart for the viewpoint space partitioning based on aspect graph theory that makes it suitable for perspective models. The partitioning result best demonstrates the algorithm's efficiency with more valu-able viewpoints found with the help of EEE events, which can definitely help to achieve high recognition rate for 3-D object recognition.

  11. Density of states of the one-dimensional electron gas: Impurity levels, impurity bands, and the band tail

    Science.gov (United States)

    Gold, A.; Ghazali, A.

    1994-06-01

    The density of states of cylindrical quantum wires is calculated in the presence of charged impurities located in the center of the wire. A multiple-scattering approach (Klauder's fifth approximation), which represents a self-consistent t-matrix approximation, is used. For small impurity densities and in the weak screening limit the ground-state impurity band and four excited-state impurity bands are obtained within our approach. We find good agreement between the numerically obtained spectral densities with the corresponding analytical spectral densities calculated with the single-impurity wave functions. The merging of impurity bands is studied. For large impurity densities we obtain a band tail. We present an analytical expression for the disorder-induced renormalized band-edge energy in the band-tail regime.

  12. Toward an Impurity Band PV: Dynamics of Carriers Generated via Sub-band gap Photons

    Science.gov (United States)

    Sullivan, Joseph; Simmons, Christie; Akey, Austin; Aziz, Michael; Buonassisi, Tonio

    2013-03-01

    Intermediate band solar cells are a pathway to cells that surpass the Shockley-Queisser limit by enabling the utilization of sub-band gap photons. A proposed method for fabricating an intermediate band material is to use impurities that introduce electronic levels within the band gap. At sufficiently high dopant concentrations, band formation may lead to a suppression of Shockley-Reed-Hall recombination, an idea known as ``lifetime recovery''. We investigate a proposed intermediate band material, silicon hyper-doped with sulfur. This material system exhibits strong sub-band gap optical absorption and metallic conductivity at sufficiently high sulfur concentrations, which makes it a strong candidate for an impurity-band material. We employ low-temperature photoconductivity using sub-band gap light to estimate the trapping rate of electrons in the conduction band. We vary the sulfur concentration near the critical value for the metal-insulator transition to test the idea of ``lifetime recovery'' in the S:Si system.

  13. Cosine edge modes in a periodically driven quantum system

    Science.gov (United States)

    Satija, Indubala I.; Zhao, Erhai

    2016-12-01

    Time-periodic (Floquet) topological phases of matter exhibit bulk-edge relationships that are more complex than static topological insulators and superconductors. Finding the edge modes unique to driven systems usually requires numerics. Here we present a minimal two-band model of Floquet topological insulators and semimetals in two dimensions where all the bulk and edge properties can be obtained analytically. It is based on the extended Harper model of quantum Hall effect at flux one-half. We show that periodical driving gives rise to a series of phases characterized by a pair of integers. The model has a most striking feature: the spectrum of the edge modes is always given by a single cosine function, ω (ky) ∝cosky where ky is the wave number along the edge, as if it is freely dispersing and completely decoupled from the bulk. The cosine mode is robust against the change in driving parameters. It also persists in the semimetallic phases with Dirac points.

  14. Engineering the Near-Edge Electronic Structure of SnSe through Strains

    Science.gov (United States)

    Wu, Yabei; Xia, Weiyi; Gao, Weiwei; Ren, Wei; Zhang, Peihong

    2017-09-01

    The discovery of the unprecedented figure of merit Z T of SnSe has sparked a large number of studies on the fundamental physics of this material and further improvement through guided materials design and optimization. Motivated by its rich chemical-bonding characters, unusual multivalley electronic structure, and the sensitivity of the band-edge states to lattice strains, we carry out accurate quasiparticle calculations for the low-temperature phase SnSe under strains. We illustrate how the band-edge states can be engineered by lattice strains, including the size and the nature of the band gap, the positions of the band extrema in the Brillouin zone, and the control of the number of electron and/or hole valleys. The distinct atomic origin and orientation of the wave functions of the different band-edge states dictates the relative shift in their band energy, enabling active control of the near-edge electronic structure of this material. Our work demonstrates that strain engineering is a promising way to manipulate the low-energy electronic structure of SnSe, which can have profound influences on the optical and transport properties of this material.

  15. Variations in the Sea Ice Edge and the Marginal Ice Zone on Different Spatial Scales as Observed from Different Satellite Sensor

    Science.gov (United States)

    Markus, Thorsten; Henrichs, John

    2006-01-01

    and volume scattering characteristics. The Canadian RADARSAT C-band SAR provides data that cover the Arctic Ocean and the MIZ every 3 days. A change-point detection approach was utilized to obtain an ice edge estimate from the RADARSAT data The Quickscat scatterometer provides ice edge information with a resolution of a few kilometers on a near-daily basis. During portions of March and April of 2003 a series of aircraft flights were conducted over the ice edge in the Bering Sea carrying the Polarimetric Scanning Radiometer (PSR), which provides spectral coverage identical with the AMSR-E instrument at a resolution of 500 meters. In this study we investigated these different data sets and analyzed differences in their definition of the sea ice edge and the marginal ice zone and how these differences as well as their individual limitations affect the monitoring of the ice edge dynamics. We also examined how the nature of the sea ice edge, including its location, compactness and shape, changes over the seasons. Our approach was based on calculation of distances between ice edges derived from the satellite and aircraft data sets listed above as well as spectral coherence methods and shape parameters such as tortuosity, curvature, and fractional dimension.

  16. Electronic structure and optical properties of noncentrosymmetric LiGaSe2: Experimental measurements and DFT band structure calculations

    Science.gov (United States)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Ananchenko, L. N.; Isaenko, L. I.; Yelisseyev, A. P.; Khyzhun, O. Y.

    2017-04-01

    We report on measurements of X-ray photoelectron (XP) spectra for pristine and Ar+ ion-irradiated surfaces of LiGaSe2 single crystal grown by Bridgman-Stockbarger method. Electronic structure of the LiGaSe2 compound is studied from a theoretical and experimental viewpoint. In particular, total and partial densities of states of LiGaSe2 are investigated by density functional theory (DFT) calculations employing the augmented plane wave + local orbitals (APW + lo) method and they are verified by data of X-ray spectroscopy measurements. The DFT calculations indicate that the main contributors to the valence band of LiGaSe2 are the Se 4p states, which contribute mainly at the top and in the upper portion of the valence band, with also essential contributions of these states in the lower portion of the band. Other substantial contributions to the valence band of LiGaSe2 emerge from the Ga 4s and Ga 4p states contributing mainly at the lower ant upper portions of the valence band, respectively. With respect to the conduction band, the calculations indicate that its bottom is composed mainly from contributions of the unoccupied Ga s and Se p states. The present calculations are confirmed experimentally when comparing the XP valence-band spectrum of the LiGaS2 single crystal on a common energy scale with the X-ray emission bands representing the energy distribution of the Ga 4p and Se 4p states. Measurements of the fundamental absorption edges at room temperature reveal that bandgap value, Eg, of LiGaSe2 is equal to 3.47 eV and the Eg value increases up to 3.66 eV when decreasing temperature to 80 K. The main optical characteristics of the LiGaSe2 compound are clarified by the DFT calculations.

  17. Full multiple scattering analysis of XANES at the Cd L3 and O K edges in CdO films combined with a soft-x-ray emission investigation

    Energy Technology Data Exchange (ETDEWEB)

    Demchenko, I. N.; Denlinger, J. D.; Chernyshova, M.; Yu, K. M.; Speaks, D. T.; Olalde-Velasco, P.; Hemmers, O.; Walukiewicz, W.; Derkachova, A.; Lawniczak-Jablonska, K.

    2010-07-05

    X-ray absorption near edge structure (XANES) at the cadmium L3 and oxygen K edges for CdO thin films grown by pulsed laser deposition method, is interpreted within the real-space multiple scattering formalism, FEFF code. The features in the experimental spectra are well reproduced by calculations for a cluster of about six and ten coordination shells around the absorber for L3 edge of Cd and K edge of O, respectively. The calculated projected electronic density of states is found to be in good agreement with unoccupied electronic states in experimental data and allows to conclude that the orbital character of the lowest energy of the conductive band is Cd-5s-O-2p. The charge transfer has been quantified and not purely ionic bonding has been found. Combined XANES and resonant inelastic x-ray scattering measurements allow us to determine the direct and indirect band gap of investigated CdO films to be {approx}2.4-eV and {approx}0.9-eV, respectively.

  18. The Variation of Optical Band Gap for ZnO:In Films Prepared by Sol-Gel Technique

    Directory of Open Access Journals (Sweden)

    Guomei Tang

    2013-01-01

    Full Text Available ZnO:In films with different concentrations (0–5 at.% are successfully synthesized on quartz substrates using sol-gel technique. The structure, morphology, and optical properties of ZnO:In films are investigated by X-ray diffraction, atomic force microscopy, and UV-visible spectrophotometer. It is found that all the films with columnar structural morphology grow along the preferred [001] orientation and the incorporation of indium can improve the crystallinity of ZnO films. The transmittance of the films is about 80% in the visible range. A change of the optical absorption edge from blue shift to red shift is observed for ZnO:In films as the doping concentration increases, which means that the optical band gap first increases and then decreases. The blue shift is due to the Burstein-Moss effect. The sharp jump of the absorption edge from blue-shift to red shift is ascribe to the band gap narrowing caused by the merging of the donor and conduction bands of ZnO:In at high doping concentration.

  19. Robust band gap and half-metallicity in graphene with triangular perforations

    Science.gov (United States)

    Gregersen, Søren Schou; Power, Stephen R.; Jauho, Antti-Pekka

    2016-06-01

    Ideal graphene antidot lattices are predicted to show promising band gap behavior (i.e., EG≃500 meV) under carefully specified conditions. However, for the structures studied so far this behavior is critically dependent on superlattice geometry and is not robust against experimentally realistic disorders. Here we study a rectangular array of triangular antidots with zigzag edge geometries and show that their band gap behavior qualitatively differs from the standard behavior which is exhibited, e.g., by rectangular arrays of armchair-edged triangles. In the spin unpolarized case, zigzag-edged antidots give rise to large band gaps compared to armchair-edged antidots, irrespective of the rules which govern the existence of gaps in armchair-edged antidot lattices. In addition the zigzag-edged antidots appear more robust than armchair-edged antidots in the presence of geometrical disorder. The inclusion of spin polarization within a mean-field Hubbard approach gives rise to a large overall magnetic moment at each antidot due to the sublattice imbalance imposed by the triangular geometry. Half-metallic behavior arises from the formation of spin-split dispersive states near the Fermi energy, reducing the band gaps compared to the unpolarized case. This behavior is also found to be robust in the presence of disorder. Our results highlight the possibilities of using triangular perforations in graphene to open electronic band gaps in systems with experimentally realistic levels of disorder, and furthermore, of exploiting the strong spin dependence of the system for spintronic applications.

  20. On the edge: haptic discrimination of edge sharpness.

    Directory of Open Access Journals (Sweden)

    Andy L Skinner

    Full Text Available The increasing ubiquity of haptic displays (e.g., smart phones and tablets necessitates a better understanding of the perceptual capabilities of the human haptic system. Haptic displays will soon be capable of locally deforming to create simple 3D shapes. This study investigated the sensitivity of our haptic system to a fundamental component of shapes: edges. A novel set of eight high quality shape stimuli with test edges that varied in sharpness were fabricated in a 3D printer. In a two alternative, forced choice task, blindfolded participants were presented with two of these shapes side by side (one the reference, the other selected randomly from the remaining set of seven and after actively exploring the test edge of each shape with the tip of their index finger, reported which shape had the sharper edge. We used a model selection approach to fit optimal psychometric functions to performance data, and from these obtained just noticeable differences and Weber fractions. In Experiment 1, participants performed the task with four different references. With sharpness defined as the angle at which one surface meets the horizontal plane, the four JNDs closely followed Weber's Law, giving a Weber fraction of 0.11. Comparisons to previously reported Weber fractions from other haptic manipulations (e.g. amplitude of vibration suggests we are sufficiently sensitive to changes in edge sharpness for this to be of potential utility in the design of future haptic displays. In Experiment 2, two groups of participants performed the task with a single reference but different exploration strategies; one was limited to a single touch, the other unconstrained and free to explore as they wished. As predicted, the JND in the free exploration condition was lower than that in the single touch condition, indicating exploration strategy affects sensitivity to edge sharpness.

  1. EFFECT OF THE DEFECT STATES DENSITY ON OPTICAL BAND GAP OF CdIn2O4 THIN FILM

    Institute of Scientific and Technical Information of China (English)

    H.S. San; Z.G. Wu; B. Li; B.X. Feng

    2005-01-01

    Transparent conducting oxides CdIn2O4 thin films were prepared by radio-frequency reactive sputtering from a Cd-In alloy target in Ar+O2 atmosphere. By transmission spectrum and Hall measurement for different samples prepared at different substrate temperatures, it could be found that the carrier concentration would increase with the decrease of substrate temperature, but absorption edge showed an abrupt variation from a blue shift to a red shift.Theoretically, the paper formulated the effect of high-density point defects on band structures; it embodied the formation of band tailing, Burstein-Moss shift and band-gap narrowing. The density of holes will influence the magnitude of optical band gap and transmittance of light. Since extrapolation method does not fit degenerate semiconductor materials, a more accurate method of obtaining optical band gap is curve fitting. In addition, ionized impurities scattering is the main damping mechanism of the free electrons in CdIn2O4 films, the density of ionized impurities induced by altering substrate temperature will affect the carriers mobility.

  2. Electrical Conductivity.

    Science.gov (United States)

    Hershey, David R.; Sand, Susan

    1993-01-01

    Explains how electrical conductivity (EC) can be used to measure ion concentration in solutions. Describes instrumentation for the measurement, temperature dependence and EC, and the EC of common substances. (PR)

  3. Ionization equilibrium at the transition from valence-band to acceptor-band migration of holes in boron-doped diamond

    Science.gov (United States)

    Poklonski, N. A.; Vyrko, S. A.; Poklonskaya, O. N.; Kovalev, A. I.; Zabrodskii, A. G.

    2016-06-01

    A quasi-classical model of ionization equilibrium in the p-type diamond between hydrogen-like acceptors (boron atoms which substitute carbon atoms in the crystal lattice) and holes in the valence band (v-band) is proposed. The model is applicable on the insulator side of the insulator-metal concentration phase transition (Mott transition) in p-Dia:B crystals. The densities of the spatial distributions of impurity atoms (acceptors and donors) and of holes in the crystal are considered to be Poissonian, and the fluctuations of their electrostatic potential energy are considered to be Gaussian. The model accounts for the decrease in thermal ionization energy of boron atoms with increasing concentration, as well as for electrostatic fluctuations due to the Coulomb interaction limited to two nearest point charges (impurity ions and holes). The mobility edge of holes in the v-band is assumed to be equal to the sum of the threshold energy for diffusion percolation and the exchange energy of the holes. On the basis of the virial theorem, the temperature Tj is determined, in the vicinity of which the dc band-like conductivity of holes in the v-band is approximately equal to the hopping conductivity of holes via the boron atoms. For compensation ratio (hydrogen-like donor to acceptor concentration ratio) K ≈ 0.15 and temperature Tj, the concentration of "free" holes in the v-band and their jumping (turbulent) drift mobility are calculated. Dependence of the differential energy of thermal ionization of boron atoms (at the temperature 3Tj/2) as a function of their concentration N is calculated. The estimates of the extrapolated into the temperature region close to Tj hopping drift mobility of holes hopping from the boron atoms in the charge states (0) to the boron atoms in the charge states (-1) are given. Calculations based on the model show good agreement with electrical conductivity and Hall effect measurements for p-type diamond with boron atom concentrations in the

  4. Edge Ideals of Weighted Graphs

    CERN Document Server

    Paulsen, Chelsey

    2012-01-01

    We study weighted graphs and their "edge ideals" which are ideals in polynomial rings that are defined in terms of the graphs. We provide combinatorial descriptions of m-irreducible decompositions for the edge ideal of a weighted graph in terms of the combinatorics of "weighted vertex covers". We use these, for instance, to say when these ideals are m-unmixed. We explicitly describe which weighted cycles and trees are unmixed and which ones are Cohen-Macaulay, and we prove that all weighted complete graphs are Cohen-Macaulay.

  5. All-graphene edge contacts

    DEFF Research Database (Denmark)

    Jacobsen, Kåre Wedel; Falkenberg, Jesper Toft; Papior, Nick Rübner;

    2016-01-01

    Using ab-initio methods we investigate the possibility of three-terminalgraphene "T-junction" devices and show that these all-graphene edge contactsare energetically feasible when the 1D interface itself is free from foreignatoms. We examine the energetics of various junction structures...... to be in therange of 1-10 kΩμm which is comparable to the best contact resistance reportedfor edge-contacted graphene-metal contacts. We conclude that conductingall-carbon T-junctions should be feasible....

  6. Stretch Band Exercise Program

    Science.gov (United States)

    Skirka, Nicholas; Hume, Donald

    2007-01-01

    This article discusses how to use stretch bands for improving total body fitness and quality of life. A stretch band exercise program offers a versatile and inexpensive option to motivate participants to exercise. The authors suggest practical exercises that can be used in physical education to improve or maintain muscular strength and endurance,…

  7. ZEBRAFISH CHROMOSOME-BANDING

    NARCIS (Netherlands)

    PIJNACKER, LP; FERWERDA, MA

    1995-01-01

    Banding techniques were carried out on metaphase chromosomes of zebrafish (Danio rerio) embryos. The karyotypes with the longest chromosomes consist of 12 metacentrics, 26 submetacentrics, and 12 subtelocentrics (2n = 50). All centromeres are C-band positive. Eight chromosomes have a pericentric C-b

  8. Progressive Band Selection

    Science.gov (United States)

    Fisher, Kevin; Chang, Chein-I

    2009-01-01

    Progressive band selection (PBS) reduces spectral redundancy without significant loss of information, thereby reducing hyperspectral image data volume and processing time. Used onboard a spacecraft, it can also reduce image downlink time. PBS prioritizes an image's spectral bands according to priority scores that measure their significance to a specific application. Then it uses one of three methods to select an appropriate number of the most useful bands. Key challenges for PBS include selecting an appropriate criterion to generate band priority scores, and determining how many bands should be retained in the reduced image. The image's Virtual Dimensionality (VD), once computed, is a reasonable estimate of the latter. We describe the major design details of PBS and test PBS in a land classification experiment.

  9. Edge detection based on morphological amoebas

    CERN Document Server

    Lee, Won Yeol; Kim, Se Yun; Lim, Jae Young; Lim, Dong Hoon

    2011-01-01

    Detecting the edges of objects within images is critical for quality image processing. We present an edge-detecting technique that uses morphological amoebas that adjust their shape based on variation in image contours. We evaluate the method both quantitatively and qualitatively for edge detection of images, and compare it to classic morphological methods. Our amoeba-based edge-detection system performed better than the classic edge detectors.

  10. Spin-dependent electron scattering at graphene edges on Ni(111).

    Science.gov (United States)

    Garcia-Lekue, A; Balashov, T; Olle, M; Ceballos, G; Arnau, A; Gambardella, P; Sanchez-Portal, D; Mugarza, A

    2014-02-14

    We investigate the scattering of surface electrons by the edges of graphene islands grown on Ni(111). By combining local tunneling spectroscopy and ab initio electronic structure calculations we find that the hybridization between graphene and Ni states results in strongly reflecting graphene edges. Quantum interference patterns formed around the islands reveal a spin-dependent scattering of the Shockley bands of Ni, which we attribute to their distinct coupling to bulk states. Moreover, we find a strong dependence of the scattering amplitude on the atomic structure of the edges, depending on the orbital character and energy of the surface states.

  11. Design of non-polarizing thin film edge filters

    Institute of Scientific and Technical Information of China (English)

    GU Pei-fu; ZHENG Zhen-rong

    2006-01-01

    The separation between s- and p-polarization components invariably affects thin film edge filters used for tilted incidence and is a difficult problem for many applications, especially for optical communication. This paper presents a novel design method to obtain edge filters with non-polarization at incidence angle of 45°. The polarization separation at 50% transmittance for a long-wave-pass filter and a short-wave-pass filter is 0.3 nm and 0.1 nm respectively. The design method is based on a broadband Fabry-Perot thin-film interference filter in which the higher or lower interference band at both sides of the main transmittance peak can be used for initial design of long-wave-pass filter or short-wave-pass filter and then can be refined to reduce the transmittance ripples. The spacer 2H2L2H or 2L2H2L of the filter is usually taken. Moreover, the method for expanding the bandwidth of rejection and transmission is explained. The bandwidth of 200 nm for both rejection region and transmission band is obtained at wavelength 1550 nm. In this way, the long-wave-pass and short-wave-pass edge filters with zero separation between two polarization components can easily be fabricated.

  12. Flat edge modes of graphene and of Z 2 topological insulator

    Directory of Open Access Journals (Sweden)

    Mao Shijun

    2011-01-01

    Full Text Available Abstract A graphene nano-ribbon in the zigzag edge geometry exhibits a specific type of gapless edge modes with a partly flat band dispersion. We argue that the appearance of such edge modes are naturally understood by regarding graphene as the gapless limit of a Z 2 topological insulator. To illustrate this idea, we consider both Kane-Mele (graphene-based and Bernevig-Hughes-Zhang models: the latter is proposed for HgTe/CdTe 2D quantum well. Much focus is on the role of valley degrees of freedom, especially, on how they are projected onto and determine the 1D edge spectrum in different edge geometries.

  13. Quadratic band touching points and flat bands in two-dimensional topological Floquet systems

    Science.gov (United States)

    Du, Liang; Zhou, Xiaoting; Fiete, Gregory A.

    2017-01-01

    In this paper we theoretically study, using Floquet-Bloch theory, the influence of circularly and linearly polarized light on two-dimensional band structures with Dirac and quadratic band touching points, and flat bands, taking the nearest neighbor hopping model on the kagome lattice as an example. We find circularly polarized light can invert the ordering of this three-band model, while leaving the flat band dispersionless. We find a small gap is also opened at the quadratic band touching point by two-photon and higher order processes. By contrast, linearly polarized light splits the quadratic band touching point (into two Dirac points) by an amount that depends only on the amplitude and polarization direction of the light, independent of the frequency, and generally renders dispersion to the flat band. The splitting is perpendicular to the direction of the polarization of the light. We derive an effective low-energy theory that captures these key results. Finally, we compute the frequency dependence of the optical conductivity for this three-band model and analyze the various interband contributions of the Floquet modes. Our results suggest strategies for optically controlling band structure and interaction strength in real systems.

  14. On the Edge of Existence

    DEFF Research Database (Denmark)

    Richter, Line

    2016-01-01

    Based on ethnographic fieldwork among Malian migrants and migration brokers in Mali, Algeria, Morocco, and France, this article investigates life in exile on the edge of Europe. Zooming in on the experiences of interlocutors in Morocco and Algeria, the article will explore the experiential...

  15. Failure During Sheared Edge Stretching

    Science.gov (United States)

    Levy, B. S.; van Tyne, C. J.

    2008-12-01

    Failure during sheared edge stretching of sheet steels is a serious concern, especially in advanced high-strength steel (AHSS) grades. The shearing process produces a shear face and a zone of deformation behind the shear face, which is the shear-affected zone (SAZ). A failure during sheared edge stretching depends on prior deformation in the sheet, the shearing process, and the subsequent strain path in the SAZ during stretching. Data from laboratory hole expansion tests and hole extrusion tests for multiple lots of fourteen grades of steel were analyzed. The forming limit curve (FLC), regression equations, measurement uncertainty calculations, and difference calculations were used in the analyses. From these analyses, an assessment of the primary factors that contribute to the fracture during sheared edge stretching was made. It was found that the forming limit strain with consideration of strain path in the SAZ is a major factor that contributes to the failure of a sheared edge during stretching. Although metallurgical factors are important, they appear to play a somewhat lesser role.

  16. Advanced thermoelectrics governed by a single parabolic band: Mg2Si(0.3)Sn(0.7), a canonical example.

    Science.gov (United States)

    Liu, Wei; Chi, Hang; Sun, Hui; Zhang, Qiang; Yin, Kang; Tang, Xinfeng; Zhang, Qingjie; Uher, Ctirad

    2014-04-21

    The well-known single parabolic band (SPB) model has been useful in providing insights into the understanding of transport properties of numerous thermoelectric materials. However, the conduction and valence bands of real semiconductors are rarely truly parabolic which limits the predictive power of the SPB model. The coincidence of the band edges of two parabolic bands, a situation arising in Mg2Si1-xSnx solid solutions when x∼ 0.7, naturally makes the SPB approximation applicable to evaluate all transport parameters. We demonstrate this in the case of Bi-doped Mg2Si0.3Sn0.7 where the minima of the two conduction bands at the X-point of the Brillouin zone coincide. The combination of a large density-of-states effective mass m* ∼ 2.6 me arising from the enhanced valley degeneracy Nv, high mobility μd due to low deformation potential Ed (8.77-9.43 eV), and ultra-low alloy scattering parameter Ea (0.32-0.39 eV) leads to an outstanding power factor, PFmax∝ (m*)(3/2)μd, of up to 4.7 mW m(-1) K(-2) at around 600 K. The specification and improved understanding of scattering parameters using the SPB model are important and instructive for further optimization of the thermoelectric performance of n-type Mg2Si0.3Sn0.7.

  17. Tunable electronic properties of CdS nanoribbons by edge effects

    Science.gov (United States)

    Ma, Ruican; Zhao, Hui; Wang, Yaping; Ji, Weixiao; Li, Ping

    2017-08-01

    Based on first-principles calculations, the electronic properties of Cadmium Sulfide nanoribbons (CdSNRs) have been studied with both zigzag (Z-CdSNRs) and armchair shaped edges (A-CdSNRs). For Z-CdSNRs, the structures with both edges decorated by H or F atoms show half-metallic or semiconducting properties, respectively. Only S-dominated edge decorated by H/F atoms, Z-CdSNRs show metallic properties. Only Cd-dominated edge is hydrogenated, Z-CdSNRs can be observed from a metallic to half metallic transition. But instead of fluorinated, the structures show the metallic properties. However, either edge or both edges are hydrogenated or fluorinated, A-CdSNRs exhibit semiconducting properties, and their band gap decreases monotonically with increasing ribbons width (n). When a stress is applied on the half-hydrogenated A-CdSNRs, their band gap displays a steady decrease trend. Moreover, A-CdSNRs are more stable than Z-CdSNRs, while the hydrogenated systems are more stable than fluorinated systems. The results show that different structures of CdSNRs decorated with the different edges can play different nature as semiconducting - half-metallic - metallic properties. The research has important theoretical significance for the electronic design and assembly of CdSNRs structures, and provides a new perspective for the potential application of CdSNRs in nanoelectronics.

  18. Floquet topological phase transitions and chiral edge states in a kagome lattice

    Energy Technology Data Exchange (ETDEWEB)

    He, Chaocheng; Zhang, Zhiyong, E-mail: zyzhang@nju.edu.cn

    2014-09-05

    The Floquet topological phases and chiral edge states in a kagome lattice under a circularly-polarized driving field are studied. In the off-resonant case, the system exhibits the similar character as the kagome lattice model with staggered magnetic fluxes, but the total band width is damped in oscillation. In the on-resonant case, the degeneracy splitting at the Γ point does not always result in a gap. The positions of the other two gaps are influenced by the flat band. With the field intensity increased, these two gaps undergo closing-then-reopening processes, accompanied with the changing of the winding numbers. - Highlights: • A kagome lattice under a circularly-polarized driving field is studied. • The band structures and chiral edge states are studied via exact Floquet method. • Various modifications of the Floquet band structure are found. • Floquet topological phase transitions appear in both off- and on-resonant cases.

  19. Parallelization of Edge Detection Algorithm using MPI on Beowulf Cluster

    Science.gov (United States)

    Haron, Nazleeni; Amir, Ruzaini; Aziz, Izzatdin A.; Jung, Low Tan; Shukri, Siti Rohkmah

    In this paper, we present the design of parallel Sobel edge detection algorithm using Foster's methodology. The parallel algorithm is implemented using MPI message passing library and master/slave algorithm. Every processor performs the same sequential algorithm but on different part of the image. Experimental results conducted on Beowulf cluster are presented to demonstrate the performance of the parallel algorithm.

  20. Development of edge effects around experimental ecosystem hotspots is affected by edge density and matrix type

    Science.gov (United States)

    Ecological edge effects are sensitive to landscape context. In particular, edge effects can be altered by matrix type and by the presence of other nearby edges. We experimentally altered patch configurations in an African savanna to determine how edge density and matrix type influence edge effect de...

  1. Contacts and Edge State Equilibration in the Fractional Quantum Hall Effect

    OpenAIRE

    Kane, C. L.; Fisher, Matthew P. A.

    1995-01-01

    We develop a simple kinetic equation description of edge state dynamics in the fractional quantum Hall effect (FQHE), which allows us to examine in detail equilibration processes between multiple edge modes. As in the integer quantum Hall effect (IQHE), inter-mode equilibration is a prerequisite for quantization of the Hall conductance. Two sources for such equilibration are considered: Edge impurity scattering and equilibration by the electrical contacts. Several specific models for electric...

  2. Testing Edge versus Hierarchical C2 Organizations using the ELICIT Platform and Common Identification Picture Tool

    Science.gov (United States)

    2011-06-01

    application designed for conducting human-in-the-loop experiments focused on information and social domain phenomena (Martin and Mc Ever, 2008...environment designed to experiment and research differences between Edge and Hierarchical organizational configurations within the information and social ...indicated in the following tables. Tests of Normality ,132 17 ,200* ,927 17 ,191 ,131 17 ,200* ,919 17 ,141 Grupo Edge SIN Edge CON Rend Statistic df Sig

  3. Local density of optical states of an asymmetric waveguide grating at photonic band gap resonant wavelength

    Science.gov (United States)

    Alatas, Husin; Sumaryada, Tony I.; Ahmad, Faozan

    2015-01-01

    We have investigated the characteristics of local density of optical states (LDOS) at photonic band gap resonant wavelength of an asymmetric waveguide grating based on Green's function formulation. It is found that the LDOS of the considered structure exhibits different characteristics in its localization between the upper and lower resonant wavelengths of the corresponding photonic band gap edges.

  4. Dendrometer bands made easy: using modified cable ties to measure incremental growth of trees

    Science.gov (United States)

    Anemaet, Evelyn R.; Middleton, Beth A.

    2013-01-01

    Dendrometer bands are a useful way to make sequential repeated measurements of tree growth, but traditional dendrometer bands can be expensive, time consuming, and difficult to construct in the field. An alternative to the traditional method of band construction is to adapt commercially available materials. This paper describes how to construct and install dendrometer bands using smooth-edged, stainless steel, cable tie banding and attachable rollerball heads. As a performance comparison, both traditional and cable tie dendrometer bands were installed on baldcypress trees at the National Wetlands Research Center in Lafayette, Louisiana, by both an experienced and a novice worker. Band installation times were recorded, and growth of the trees as estimated by the two band types was measured after approximately one year, demonstrating equivalence of the two methods. This efficient approach to dendrometer band construction can help advance the knowledge of long-term tree growth in ecological studies.

  5. Hypersonic aerospace vehicle leading edge cooling using heat pipe, transpiration and film cooling techniques

    Science.gov (United States)

    Modlin, James Michael

    An investigation was conducted to study the feasibility of cooling hypersonic vehicle leading edge structures exposed to severe aerodynamic surface heat fluxes using a combination of liquid metal heat pipes and surface mass transfer cooling techniques. A generalized, transient, finite difference based hypersonic leading edge cooling model was developed that incorporated these effects and was demonstrated on an assumed aerospace plane-type wing leading edge section and a SCRAMJET engine inlet leading edge section. The hypersonic leading edge cooling model was developed using an existing, experimentally verified heat pipe model. Two applications of the hypersonic leading edge cooling model were examined. An assumed aerospace plane-type wing leading edge section exposed to a severe laminar, hypersonic aerodynamic surface heat flux was studied. A second application of the hypersonic leading edge cooling model was conducted on an assumed one-quarter inch nose diameter SCRAMJET engine inlet leading edge section exposed to both a transient laminar, hypersonic aerodynamic surface heat flux and a type 4 shock interference surface heat flux. The investigation led to the conclusion that cooling leading edge structures exposed to severe hypersonic flight environments using a combination of liquid metal heat pipe, surface transpiration, and film cooling methods appeared feasible.

  6. Iliotibial band friction syndrome.

    Science.gov (United States)

    Lavine, Ronald

    2010-07-20

    Published articles on iliotibial band friction syndrome have been reviewed. These articles cover the epidemiology, etiology, anatomy, pathology, prevention, and treatment of the condition. This article describes (1) the various etiological models that have been proposed to explain iliotibial band friction syndrome; (2) some of the imaging methods, research studies, and clinical experiences that support or call into question these various models; (3) commonly proposed treatment methods for iliotibial band friction syndrome; and (4) the rationale behind these methods and the clinical outcome studies that support their efficacy.

  7. Conduct disorders

    NARCIS (Netherlands)

    Buitelaar, J.K.; Smeets, K.C.; Herpers, P.; Scheepers, F.; Glennon, J.; Rommelse, N.N.J.

    2013-01-01

    Conduct disorder (CD) is a frequently occurring psychiatric disorder characterized by a persistent pattern of aggressive and non-aggressive rule breaking antisocial behaviours that lead to considerable burden for the patients themselves, their family and society. This review paper updates diagnostic

  8. Bonds and bands in semiconductors

    CERN Document Server

    Phillips, Jim

    2009-01-01

    This classic work on the basic chemistry and solid state physics of semiconducting materials is now updated and improved with new chapters on crystalline and amorphous semiconductors. Written by two of the world's pioneering materials scientists in the development of semiconductors, this work offers in a single-volume an authoritative treatment for the learning and understanding of what makes perhaps the world's most important engineered materials actually work. Readers will find: --' The essential principles of chemical bonding, electron energy bands and their relationship to conductive and s

  9. Edge detection based on directional space

    Institute of Scientific and Technical Information of China (English)

    YUAN Wei-qi; LI De-sheng

    2006-01-01

    A new method for edge detection based on directional space is proposed.The principle is that:firstly,the directional differential space is set up in which the ridge edge pixels and valley edge pixels are abstracted with the help of the method of logical judgments along the direction of differential function,forming a directional roof edge map;secondly,step edge pixels are abstracted between the neighboring directional ridge edge and directional valley edge along the direction of differential function;finally,the ridge edge map,valley edge map and step edge map gained along different directions are combined into corresponding ridge edge map,valley edge map and step edge map.This method is different from classical algorithms in which the gray differential values of the mutual vertical direction are combined into one gradient value.The experiment of edge detection is made for the images of nature scenery,human body and accumulative raw material,whose result is compared with the one of classical algorithms and showing the robustness of the proposed method.

  10. Novel Dual-band Slot Antenna Design for Bluetooth and UWB Applications

    Science.gov (United States)

    Huang, Hai-Yan; Shao, Wei; Wang, Bing-Zhong; Ma, Xiao-Liang

    2014-05-01

    A novel technique to introduce an additional low frequency band to compact ultra wideband (UWB) slot antennas is proposed in this paper. To get an additional Bluetooth band, a parasitic strip is mounted on the back side of the slot edge. Because of the interaction of the strip and the slot edge, the Bluetooth band can be obtained while a notch band between the Bluetooth band and UWB band also appears. Two types of feeding, coplanar waveguide and microstrip line, are investigated. The proposed antennas are both fabricated on a low-cost FR4 substrate and have compact size (24 mm × 28 mm × 1 mm). The good agreement between measured and simulated results verifies our design.

  11. Diet after gastric banding

    Science.gov (United States)

    ... helps people who have a gastric band stay satisfied longer. This includes things like salad with grilled ... ADAM Health Solutions. About MedlinePlus Site Map FAQs Customer Support Get email updates Subscribe to RSS Follow ...

  12. HYBASE - HYperspectral BAnd SElection tool

    NARCIS (Netherlands)

    Schwering, P.B.W.; Bekman, H.H.P.T.; Seijen, H.H. van

    2008-01-01

    Band selection is essential in the design of multispectral sensor systems. This paper describes the TNO hyperspectral band selection tool HYBASE. It calculates the optimum band positions given the number of bands and the width of the spectral bands. HYBASE is used to calculate the minimum number of

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

    Science.gov (United States)

    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.

  14. Synergistic effects on band gap-narrowing in titania by codoping from first-principles calculations

    OpenAIRE

    2010-01-01

    The large intrinsic band gap in TiO2 has hindered severely its potential application for visible-light irradiation. In this study, we have used a passivated approach to modify the band edges of anatase-TiO2 by codoping of X (N, C) with transition metals (TM=W, Re, Os) to extend the absorption edge to longer visible-light wavelengths. It was found that all the codoped systems can narrow the band gap significantly; in particular, (N+W)-codoped systems could serve as remarkably better photocatal...

  15. Conduction apraxia.

    Science.gov (United States)

    Ochipa, C; Rothi, L J; Heilman, K M

    1994-01-01

    A left hemisphere damaged patient with ideomotor apraxia is described, whose performance on pantomime to verbal command was superior to pantomime imitation. His reception of these same gestures (gesture naming) was spared. This syndrome has been named conduction apraxia. To account for this selective impaired performance on gesture imitation, a separation of the representations for gesture production and reception is proposed and a non-lexical gesture processing route for gesture imitation is suggested. Images PMID:7931387

  16. Conduction apraxia.

    OpenAIRE

    Ochipa, C; Rothi, L J; Heilman, K M

    1994-01-01

    A left hemisphere damaged patient with ideomotor apraxia is described, whose performance on pantomime to verbal command was superior to pantomime imitation. His reception of these same gestures (gesture naming) was spared. This syndrome has been named conduction apraxia. To account for this selective impaired performance on gesture imitation, a separation of the representations for gesture production and reception is proposed and a non-lexical gesture processing route for gesture imitation is...

  17. Edge reconstructions in fractional quantum Hall systems.

    Science.gov (United States)

    Joglekar, Yogesh; Nguyen, Hoang; Murthy, Ganpathy

    2003-03-01

    Two dimensional electron systems exhibiting fractional quantum Hall effects are characterized by a quantized Hall conductance and a dissipationless bulk. The transport in these systems occurs only at the edges where gapless excitations are possible [1]. We present a microscopic calculation of these egde-states at filling factors ν=1/3 and ν=2/5 using the Hamiltonian theory of the fractional quantum Hall effect [2]. We find that the quantum Hall egde undergoes a reconstruction as the confining potential, produced by the background charge density, softens [3,4]. Our results have implications to the tunneling experiments into the edge of a fractional quantum Hall system [5]. 1: X. G.Wen, Phys. Rev. Lett. 64, 2206 (1990). 2: R. Shankar and G. Murthy, Phys. Rev. Lett. 79, 4437 (1997). 3: C. de C. Chamon and X. G. Wen, Phys. Rev. B 49, 8227 (1994). 4: X. Wan, K. Yang, and E. H. Razayi, Phys. Rev. Lett. 88, 056802 (2002). 5: A.M.Chang et al., Phys. Rev. Lett. 86, 143 (2000).

  18. Edge effects in finite elongated carbon nanotubes

    CERN Document Server

    Hod, O; Scuseria, G E; Hod, Oded; Peralta, Juan E.; Scuseria, Gustavo E.

    2006-01-01

    The importance of finite-size effects for the electronic structure of long zigzag and armchair carbon nanotubes is studied. We analyze the electronic structure of capped (6,6), (8,0), and (9,0) single walled carbon nanotubes as a function of their length up to 60 nm, using a divide and conquer density functional theory approach. For the metallic nanotubes studied, most of the physical features appearing in the density of states of an infinite carbon nanotube are recovered at a length of 40 nm. The (8,0) semi-conducting nanotube studied exhibits pronounced edge effects within the energy gap that scale as the inverse of the length of the nanotube. As a result, the energy gap reduces from the value of ~1 eV calculated for the periodic system to a value of ~0.25 eV calculated for a capped 62 nm long CNT. These edge effects are expected to become negligible only at tube lengths exceeding 6 micrometers. Our results indicate that careful tailoring of the nature of the system and its capping units should be applied w...

  19. Saddle-node dynamics for edge detection

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Y.F. [Lawrence Livermore National Lab., CA (United States). Inst. for Scientific Computing Research

    1994-09-01

    The author demonstrates how the formulation of a nonlinear scale-space filter can be used for edge detection and junction analysis. By casting edge-preserving filtering in terms of maximizing information content subject to an average cost function, the computed cost at each pixel location becomes a local measure of edgeness. This computation depends on a single scale parameter and the given image data. Unlike previous approaches which require careful tuning of the filter kernels for various types of edges, this scheme is general enough to be able to handle different edges, such as lines, step edges, corners and junctions. Anisotropy in the data is handled automatically by the nonlinear dynamics.

  20. Propagating edge states in strained honeycomb lattices

    Science.gov (United States)

    Salerno, Grazia; Ozawa, Tomoki; Price, Hannah M.; Carusotto, Iacopo

    2017-06-01

    We investigate the helically propagating edge states associated with pseudo-Landau levels in strained honeycomb lattices. We exploit chiral symmetry to derive a general criterion for the existence of these propagating edge states in the presence of only nearest-neighbor hoppings and we verify our criterion using numerical simulations of both uniaxially and trigonally strained honeycomb lattices. We show that the propagation of the helical edge state can be controlled by engineering the shape of the edges. Sensitivity to chiral-symmetry-breaking next-nearest-neighbor hoppings is assessed. Our result opens up an avenue toward the precise control of edge modes through manipulation of the edge shape.

  1. Tailoring highly conductive graphene nanoribbons from small polycyclic aromatic hydrocarbons: a computational study

    KAUST Repository

    Bilić, A

    2013-06-14

    Pyrene, the smallest two-dimensional mesh of aromatic rings, with various terminal thiol substitutions, has been considered as a potential molecular interconnect. Charge transport through two terminal devices has been modeled using density functional theory (with and without self interaction correction) and the non-equilibrium Green\\'s function method. A tetra-substituted pyrene, with dual thiol terminal groups at opposite ends, has been identified as an excellent candidate, owing to its high conductance, virtually independent of bias voltage. The two possible extensions of its motif generate two series of graphene nanoribbons, with zigzag and armchair edges and with semimetallic and semiconducting electron band structure, respectively. The effects related to the wire length and the bias voltage on the charge transport have been investigated for both sets. The conductance of the nanoribbons with a zigzag edge does not show either length or voltage dependence, owing to an almost perfect electron transmission with a continuum of conducting channels. In contrast, for the armchair nanoribbons a slow exponential attenuation of the conductance with the length has been found, due to their semiconducting nature. © 2013 IOP Publishing Ltd.

  2. Charge-transport model for conducting polymers

    Science.gov (United States)

    Dongmin Kang, Stephen; Jeffrey Snyder, G.

    2016-11-01

    The growing technological importance of conducting polymers makes the fundamental understanding of their charge transport extremely important for materials and process design. Various hopping and mobility edge transport mechanisms have been proposed, but their experimental verification is limited to poor conductors. Now that advanced organic and polymer semiconductors have shown high conductivity approaching that of metals, the transport mechanism should be discernible by modelling the transport like a semiconductor with a transport edge and a transport parameter s. Here we analyse the electrical conductivity and Seebeck coefficient together and determine that most polymers (except possibly PEDOT:tosylate) have s = 3 and thermally activated conductivity, whereas s = 1 and itinerant conductivity is typically found in crystalline semiconductors and metals. The different transport in polymers may result from the percolation of charge carriers from conducting ordered regions through poorly conducting disordered regions, consistent with what has been expected from structural studies.

  3. Edge imaging in intense beams

    Directory of Open Access Journals (Sweden)

    S. Bernal

    2002-06-01

    Full Text Available The appearance of rings of charge observed near the edge of beams from high-perveance guns is described with a simple ray tracing technique inspired by the particle-core model. We illustrate the technique, which has no analog in light optics, with examples from experiments employing solenoid focusing of an electron beam. The rings of charge result from the combined effects of external focusing and space-charge forces acting on paraxial fringe particles with relatively large initial transverse velocities. The model is independent of the physical mechanisms responsible for the fringe particles. Furthermore, the focal length for edge imaging in a uniform focusing channel is derived using a linearized trajectory equation for the motion of fringe particles. Counterintuitively, the focal length decreases as the beam current increases.

  4. Edge Simulation Laboratory Project Report

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, R. H. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Dorf, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Dorr, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Rognlien, T. D. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2011-02-25

    In 2010 The Edge Simulation Laboratory (ESL) embarked upon the plan laid out in the renewal proposal submitted in December 2009. This proposal called for initially parallel efforts addressing the physics of the closed-flux-surface pedestal region, using existing computational tools (GYRO, BOUT++) and analytic modeling, and physics of the scrape-off layer via development of the new edge gyrokinetic code COGENT. Progress in the former area is described in a series of monthly progress reports prepared by General Atomics; these are attached as a set of appendices (describing work done in the month prior to the indicated date). Progress in the latter area, as well as associated theoretical development, is described.

  5. Edge effect in beam monitors

    CERN Document Server

    Cuperus, J H

    1977-01-01

    Quite often, particle-beam monitors have not the same cross-section as the beam pipe or vacuum chamber in which they are mounted. In that case, the electromagnetic field of the beam is distorted in the vicinity of the edges of the monitor. This field, at the junction of two rectangular beam pipes of different dimensions, is computed for a beam with constant charge along its length. Solutions which are less accurate but easier to apply are obtained with a first order approximation. The results are extended to intensity-modulated beams and circular or elliptical cross-sections. The errors, due to the edge effect, for the electrostatic pickup and the wall-current monitor are computed. The final formulas are simple and easy to apply to practical cases. (6 refs).

  6. Edge Recycling and Heat Fluxes in L- and H-mode NSTX Plasmas

    Energy Technology Data Exchange (ETDEWEB)

    V.A. Soukhanovskii; R. Maingi; R. Raman; H. Kugel; B. LeBlanc; A.L. Roquemore; C.J. Lasnier; the NSTX Research Team

    2003-08-05

    Introduction Edge characterization experiments have been conducted in NSTX to provide an initial survey of the edge particle and heat fluxes and their scaling with input power and electron density. The experiments also provided a database of conditions for the analyses of the NSTX global particle sources, core fueling, and divertor operating regimes.

  7. Modelling Combined Heat Exchange in the Leading Edge of Perspective Aircraft Wing

    Directory of Open Access Journals (Sweden)

    Kandinsky Roman O.

    2015-01-01

    Full Text Available In this paper gas dynamic numerical modelling of leading edge flow is presented and thermal loading parameters are determined. Numerical modelling of combined radiative and conductive heat transfer of the wing edge is carried out, thermal state of structure is given and the results are analyzed.

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

    Institute of Scientific and Technical Information of China (English)

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

    2006-01-01

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

  9. Edge adaptive directional total variation

    Directory of Open Access Journals (Sweden)

    Hua Zhang

    2013-11-01

    Full Text Available The directional total variation (DTV model has been proposed very recently for image denoising. However, the DTV model works well when there is just one dominant direction in the image. In this Letter, the authors propose to make the DTV model adaptive to image edge direction so that the proposed model can handle images with several dominant directions. Experiment and comparison show the effectiveness of the proposed method.

  10. EDGE-ORIENTED HEXAGONAL ELEMENTS

    Institute of Scientific and Technical Information of China (English)

    Chao Yang; Jiachang Sun

    2007-01-01

    In this paper, two new nonconforming hexagonal elements are presented, which are based on the trilinear function space Q(3)1 and are edge-oriented, analogical to the case of the rotated Q1 quadrilateral element. A priori error estimates are given to show that the new elements achieve first-order accuracy in the energy norm and second-order accuracy in the L2 norm. This theoretical result is confirmed by the numerical tests.

  11. Edge effects and delamination failures

    Science.gov (United States)

    Herakovich, C. T.

    1989-01-01

    The fundamental relationship between the morphology of a composite laminate and the resulting free edge effects is explored and related to delamination failures. Cross-ply, angle-ply, and quasi-isotropic laminates are discussed in detail. It is shown that the local mismatch in elastic properties of adjacent layers and the global stacking sequence of a laminate both have a significant influence on the interlaminar stresses and delamination failures.

  12. Nonreference Medical Image Edge Map Measure

    Directory of Open Access Journals (Sweden)

    Karen Panetta

    2014-01-01

    Full Text Available Edge detection is a key step in medical image processing. It is widely used to extract features, perform segmentation, and further assist in diagnosis. A poor quality edge map can result in false alarms and misses in cancer detection algorithms. Therefore, it is necessary to have a reliable edge measure to assist in selecting the optimal edge map. Existing reference based edge measures require a ground truth edge map to evaluate the similarity between the generated edge map and the ground truth. However, the ground truth images are not available for medical images. Therefore, a nonreference edge measure is ideal for medical image processing applications. In this paper, a nonreference reconstruction based edge map evaluation (NREM is proposed. The theoretical basis is that a good edge map keeps the structure and details of the original image thus would yield a good reconstructed image. The NREM is based on comparing the similarity between the reconstructed image with the original image using this concept. The edge measure is used for selecting the optimal edge detection algorithm and optimal parameters for the algorithm. Experimental results show that the quantitative evaluations given by the edge measure have good correlations with human visual analysis.

  13. Leading Edge Device Aerodynamic Optimization

    Directory of Open Access Journals (Sweden)

    Marius Gabriel COJOCARU

    2015-12-01

    Full Text Available Leading edge devices are conventionally used as aerodynamic devices that enhance performances during landing and in some cases during takeoff. The need to increase the efficiency of the aircrafts has brought the idea of maintaining as much as possible a laminar flow over the wings. This is possible only when the leading edge of the wings is free from contamination, therefore using the leading edge devices with the additional role of shielding during takeoff. Such a device based on the Krueger flap design is aerodynamically analyzed and optimized. The optimization comprises three steps: first, the positioning of the flap such that the shielding criterion is kept, second, the analysis of the flap size and third, the optimization of the flap shape. The first step is subject of a gradient based optimization process of the position described by two parameters, the position along the line and the deflection angle. For the third step the Adjoint method is used to gain insight on the shape of the Krueger flap that will extend the most the stall limit. All these steps have been numerically performed using Ansys Fluent and the results are presented for the optimized shape in comparison with the baseline configuration.

  14. Edge-driven microplate kinematics

    Science.gov (United States)

    Schouten, Hans; Klitgord, Kim D.; Gallo, David G.

    1993-01-01

    It is known from plate tectonic reconstructions that oceanic microplates undergo rapid rotation about a vertical axis and that the instantaneous rotation axes describing the microplate's motion relative to the bounding major plates are frequently located close to its margins with those plates, close to the tips of propagating rifts. We propose a class of edge-driven block models to illustrate how slip across the microplate margins, block rotation, and propagation of rifting may be related to the relative motion of the plates on either side. An important feature of these edge-driven models is that the instantaneous rotation axes are always located on the margins between block and two bounding plates. According to those models the pseudofaults or traces of disrupted seafloor resulting from the propagation of rifting between microplate and major plates may be used independently to approximately trace the continuous kinematic evolution of the microplate back in time. Pseudofault geometries and matching rotations of the Easter microplate show that for most of its 5 m.y. history, block rotation could be driven by the drag of the Nazca and Pacific plates on the microplate's edges rather than by a shear flow of mantle underneath.

  15. Conductivity Probe

    Science.gov (United States)

    2008-01-01

    The Thermal and Electrical Conductivity Probe (TECP) for NASA's Phoenix Mars Lander took measurements in Martian soil and in the air. The needles on the end of the instrument were inserted into the Martian soil, allowing TECP to measure the propagation of both thermal and electrical energy. TECP also measured the humidity in the surrounding air. The needles on the probe are 15 millimeters (0.6 inch) long. The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  16. 1eV吸收带边GaInAs/GaNAs超晶格太阳能电池的阱层设计%Well layer design for 1eV absorption band edge of GaInAs/GaNAs super-lattice solar cell

    Institute of Scientific and Technical Information of China (English)

    王海啸; 郑新和; 吴渊渊; 甘兴源; 王乃明; 杨辉

    2013-01-01

    使用In, N分离的GaInAs/GaNAs超晶格作为有源区是实现高质量1eV带隙GaInNAs基太阳能电池的重要方案之一。为在实验上生长出高质量相应吸收带边的超晶格结构,本文采用计算超晶格电子态常用的Kronig-Penney模型比较了不同阱层材料选择下,吸收带边为1 eV的GaInAs/GaNAs超晶格相关参数的对应关系以及超晶格应变状态。结果表明:GaNAs与GaInAs作为超晶格阱层材料在实现1 eV的吸收带边时具有不同的考虑和要求;在固定1 eV的吸收带边时, GaNAs材料作为阱层可获得较好的超晶格应变补偿,将有利于生长高质量且充分吸收的太阳能电池有源区。%The GaInAs/GaNAs super-lattice with a feature of space separation of In and N constituents as an active region, is one of the most important ways to achieve 1 eV GaInNAs-based solar cells. To experimentally realize the high-quality super-lattice structure with the required band-gap, Kronig-Penney model is used to obtain the barrier thickness dependence on the well thickness and its composition. Meanwhile, the strain state of GaInAs/GaNAs SLs with various well choices is also discussed. Results show that when both the GaNAs and GaInAs act as the well layers the super-lattice can achieve 1 eV band-gap, and when the GaN0.04As0.96 is considered to act as the well layer, the entire GaInAs/GaNAs SLs have smaller strain accumulations as compared with the case of Ga0.7In0.3As as the well layer in the super-lattice structure.

  17. Cleaved-edge-overgrowth nanogap electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Luber, Sebastian M; Bichler, Max; Abstreiter, Gerhard; Tornow, Marc, E-mail: m.tornow@tu-bs.de [Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall, 85748 Garching (Germany)

    2011-02-11

    We present a method to fabricate multiple metal nanogap electrodes of tailored width and distance in parallel, on the cleaved plane of a GaAs/AlGaAs heterostructure. The three-dimensional patterned structures are obtained by a combination of molecular-beam-epitaxial regrowth on a crystal facet, using the cleaved-edge-overgrowth (CEO) method, and subsequent wet selective etching and metallization steps. SEM and AFM studies reveal smooth and co-planar electrodes of width and distance of the order of 10 nm. Preliminary electrical characterization indicates electrical gap insulation in the 100 M{Omega} range with k{Omega} lead resistance. We propose our methodology to realize multiple electrode geometries that would allow investigation of the electrical conductivity of complex nanoscale objects such as branched organic molecules.

  18. Two-dimensional Kagome phosphorus and its edge magnetism: a density functional theory study.

    Science.gov (United States)

    Yu, Guodong; Jiang, Liwei; Zheng, Yisong

    2015-07-01

    By means of density functional theory calculations, we predict a new two-dimensional phosphorus allotrope with the Kagome-like lattice(Kagome-P). It is an indirect gap semiconductor with a band gap of 1.64 eV. The gap decreases sensitively with the compressive strain. In particular, shrinking the lattice beyond 13% can drive it into metallic state. In addition, both the AA and AB stacked Kagome-P multi-layer structures exhibit a bandgap much smaller than 1.64 eV. Edges in the Kagome-P monolayer probably suffer from the edge reconstruction. An isolated zigzag edge can induce antiferromagnetic (AF) ordering with a magnetic transition temperature of 23 K. More importantly, when applying a stretching strain beyond 4%, such an edge turns to possess a ferromagnetic ground state. A very narrow zigzag-edged Kagome-P ribbon displays the spin moment distribution similar to the zigzag-edged graphene nanoribbon because of the coupling between the opposites edges. But the inter-edge coupling in the Kagome-P ribbon vanishes more rapidly as the ribbon width increases. These properties make it a promising material in spintronics.

  19. Two-dimensional Kagome phosphorus and its edge magnetism: a density functional theory study

    Science.gov (United States)

    Yu, Guodong; Jiang, Liwei; Zheng, Yisong

    2015-06-01

    By means of density functional theory calculations, we predict a new two-dimensional phosphorus allotrope with the Kagome-like lattice(Kagome-P). It is an indirect gap semiconductor with a band gap of 1.64 eV. The gap decreases sensitively with the compressive strain. In particular, shrinking the lattice beyond 13% can drive it into metallic state. In addition, both the AA and AB stacked Kagome-P multi-layer structures exhibit a bandgap much smaller than 1.64 eV. Edges in the Kagome-P monolayer probably suffer from the edge reconstruction. An isolated zigzag edge can induce antiferromagnetic (AF) ordering with a magnetic transition temperature of 23 K. More importantly, when applying a stretching strain beyond 4%, such an edge turns to possess a ferromagnetic ground state. A very narrow zigzag-edged Kagome-P ribbon displays the spin moment distribution similar to the zigzag-edged graphene nanoribbon because of the coupling between the opposites edges. But the inter-edge coupling in the Kagome-P ribbon vanishes more rapidly as the ribbon width increases. These properties make it a promising material in spintronics.

  20. Chemistry at the Edge of Graphene.

    Science.gov (United States)

    Bellunato, Amedeo; Arjmandi Tash, Hadi; Cesa, Yanina; Schneider, Grégory F

    2016-03-16

    The selective functionalization of graphene edges is driven by the chemical reactivity of its carbon atoms. The chemical reactivity of an edge, as an interruption of the honeycomb lattice of graphene, differs from the relative inertness of the basal plane. In fact, the unsaturation of the pz orbitals and the break of the π conjugation on an edge increase the energy of the electrons at the edge sites, leading to specific chemical reactivity and electronic properties. Given the relevance of the chemistry at the edges in many aspects of graphene, the present Review investigates the processes and mechanisms that drive the chemical functionalization of graphene at the edges. Emphasis is given to the selective chemical functionalization of graphene edges from theoretical and experimental perspectives, with a particular focus on the characterization tools available to investigate the chemistry of graphene at the edge.

  1. Edge effect on weevils and spiders

    Directory of Open Access Journals (Sweden)

    R. Horváth

    2002-05-01

    Full Text Available The edge effect on weevils and spiders was tested along oak forest – meadow transects using sweep-net samples at the Síkfökút Project in Hungary. For spiders the species richness was significantly higher in the forest edge than either in the meadow or the forest interior. For weevils the species richness of the forest edge was higher than that of the meadow, but the difference was not statistically significant whereas the species richness of the forest interior was significantly lower than that of the forest edge and the meadow. The composition of the spider assemblage of the edge was more similar to the forest, while the composition of weevils in the edge was more similar to the meadow. Our results based on two invertebrate groups operating on different trophic levels suggest that there is a significant edge effect for the studied taxa resulting in higher species richness in the edge.

  2. Environmental Dataset Gateway (EDG) Search Widget

    Data.gov (United States)

    U.S. Environmental Protection Agency — Use the Environmental Dataset Gateway (EDG) to find and access EPA's environmental resources. Many options are available for easily reusing EDG content in other...

  3. Environmental Dataset Gateway (EDG) REST Interface

    Data.gov (United States)

    U.S. Environmental Protection Agency — Use the Environmental Dataset Gateway (EDG) to find and access EPA's environmental resources. Many options are available for easily reusing EDG content in other...

  4. Optoelectronic Properties for Armchair-Edge Graphene Nanoribbons

    Institute of Scientific and Technical Information of China (English)

    PENG Xin-Xiang; LIAO Wen-Hu; ZHOU Guang-Hui

    2008-01-01

    We study theoretically the electronic and transport property for an armchair-edge graphene nanoribbon (GNR)with 12 and 11 transversal atomic lines, respectively. The GNR is irradiated under an external longitudinal polarized high-frequency electromagnetic field at tow temperatures. Within the framework of linear response theory in the perturbative regime, we examine the joint density of states and the real conductance of the system, It is demonstrated that, by numerical examples, some new photon-assisted intersubband transitions over a certain range of field frequency exist with different selection rules from those of both zigzag-edge GNR and single-walled carbon nanotube. This opto-electron property dependence of armchair-edge GNR on field frequency may be used to detect the high-frequency electromagnetic irradiation.

  5. Imaging of Coulomb-Driven Quantum Hall Edge States

    KAUST Repository

    Lai, Keji

    2011-10-01

    The edges of a two-dimensional electron gas (2DEG) in the quantum Hall effect (QHE) regime are divided into alternating metallic and insulating strips, with their widths determined by the energy gaps of the QHE states and the electrostatic Coulomb interaction. Local probing of these submicrometer features, however, is challenging due to the buried 2DEG structures. Using a newly developed microwave impedance microscope, we demonstrate the real-space conductivity mapping of the edge and bulk states. The sizes, positions, and field dependence of the edge strips around the sample perimeter agree quantitatively with the self-consistent electrostatic picture. The evolution of microwave images as a function of magnetic fields provides rich microscopic information around the ν=2 QHE state. © 2011 American Physical Society.

  6. Effect of Leading Edge Tubercles on Marine Tidal Turbine Blades

    Science.gov (United States)

    Murray, Mark; Gruber, Timothy; Fredriksson, David

    2010-11-01

    This project investigated the impact that the addition of leading edge protuberances (tubercles) have on the effectiveness of marine tidal turbine blades, especially at lower flow speeds. The addition of leading edge tubercles to lifting foils has been shown, in previous research, to delay the onset of stall without significant hydrodynamic costs. The experimental results obtained utilizing three different blade designs (baseline and two tubercle modified) are compared. All blades were designed in SolidWorks and manufactured utilizing rapid prototype techniques. All tests were conducted in the 120 ft tow tank at the U.S. Naval Academy using a specifically designed experimental apparatus. Results for power coefficients are presented for a range of tip speed ratios. Cut-in velocity is also compared between the blade designs. For all test criteria, the tubercle modified blades significantly outperformed the smooth leading edge baseline design blades.

  7. Investigation of a Wedge Adhesion Test for Edge Seals

    Energy Technology Data Exchange (ETDEWEB)

    Kempe, Michael; Wohlgemuth, John; Miller, David; Postak, Lori; Booth, Dennis; Phillips, Nancy

    2016-09-26

    due to inconsistencies in sample history, sample batch, or small changes in sample preparation/assembly from one month to the next. Because the fracture strength of typical edge seal materials is so low, they cannot be relied upon for mechanical strength. A small stress or strain on the edge seal is capable of promoting delamination or tearing causing the edge seal to fail. Because of this, edge seals are very dependent on the processing and construction parameters in the full size PV module such that any long term evaluation of their durability must be conducted on full size modules to be accurate.

  8. Investigation of a wedge adhesion test for edge seals

    Science.gov (United States)

    Kempe, Michael; Wohlgemuth, John; Miller, David; Postak, Lori; Booth, Dennis; Phillips, Nancy

    2016-09-01

    due to inconsistencies in sample history, sample batch, or small changes in sample preparation/assembly from one month to the next. Because the fracture strength of typical edge seal materials is so low, they cannot be relied upon for mechanical strength. A small stress or strain on the edge seal is capable of promoting delamination or tearing causing the edge seal to fail. Because of this, edge seals are very dependent on the processing and construction parameters in the full size PV module such that any long term evaluation of their durability must be conducted on full size modules to be accurate.

  9. Photonic band gap materials

    Science.gov (United States)

    Cassagne, D.

    Photonic band gap materials Photonic band gap materials are periodic dielectric structures that control the propagation of electromagnetic waves. We describe the plane wave method, which allows to calculate the band structures of photonic crystals. By symmetry analysis and a perturbative approach, we predict the appearance of the low energy photonic band gaps of hexagonal structures. We propose new two-dimensional structures called graphite and boron nitride. Using a transfer matrix method, we calculate the transmission of the graphite structure and we show the crucial role of the coupling with external modes. We study the appearance of allowed modes in the photonic band gap by the introduction of localized defects in the periodicity. Finally, we discuss the properties of opals formed by self-organized silica microspheres, which are very promising for the fabrication of three-dimensional photonic crystals. Les matériaux à bandes interdites photoniques sont des structures diélectriques périodiques qui contrôlent la propagation des ondes électromagnétiques. Nous décrivons la méthode des ondes planes qui permet de calculer les structures de bandes des cristaux photoniques. Par une analyse de la symétrie et une approche perturbative, nous précisons les conditions d'existence des bandes interdites de basse énergie. Nous proposons de nouvelles structures bidimensionnelles appelées graphite et nitrure de bore. Grâce à une méthode de matrices de transfert, nous calculons la transmission de la structure graphite et nous mettons en évidence le rôle fondamental du couplage avec les modes extérieurs. Nous étudions l'apparition de modes permis dans la bande interdite grâce à l'introduction de défauts dans la périodicité. Enfin, nous discutons les propriétés des opales constituées de micro-billes de silice auto-organisées, qui sont très prometteuses pour la fabrication de cristaux photoniques tridimensionnels.

  10. Fundamental edge broadening effects during focused electron beam induced nanosynthesis

    Directory of Open Access Journals (Sweden)

    Roland Schmied

    2015-02-01

    Full Text Available The present study explores lateral broadening effects of 3D structures fabricated through focused electron beam induced deposition using MeCpPt(IVMe3 precursor. In particular, the scaling behavior of proximity effects as a function of the primary electron energy and the deposit height is investigated through experiments and validated through simulations. Correlated Kelvin force microscopy and conductive atomic force microscopy measurements identified conductive and non-conductive proximity regions. It was determined that the highest primary electron energies enable the highest edge sharpness while lower energies contain a complex convolution of broadening effects. Moreover, it is demonstrated that intermediate energies lead to even more complex proximity effects that significantly reduce lateral edge sharpness and thus should be avoided if desiring high lateral resolution.

  11. Conductivity and Dielectric Loss of Tungsten-Bronze-Type BaNd2Ti4O12Microwave Ceramics%乌青铜型BaNd2Ti4O12微波介质陶瓷的电导和介电损耗

    Institute of Scientific and Technical Information of China (English)

    夏海廷; 匡小军; 王春海; 李文先; 荆西平; 赵飞; 岳振星

    2011-01-01

    用固相反应合成了乌青铜型钛酸盐陶瓷BaNd2Ti4O12,并用电化学阻抗和微波介质谐振测试表征了不同热处理和钽掺杂对电导和微波介电损耗的影响.电导率随退火气氛(空气,氧气和氮气)的变化与缺陷反应平衡2Oxo—2V**o+O2↑+2e'和TixTie′←→Ti'Ti随氧分压的变化一致,表明BaNd2Ti4O12具有∏型导电性质.在空气和氧气中退火有利于减少包括Vxo,Ti'Ti和弱束缚电子在内的本征缺陷因而降低电导.而在低氧分压的氮气中进行退火处理,增加了缺陷的浓度,同时提高了电导率.在空气/氧气/氮气中的退火处理对微波介电损耗没有明显的影响,表明本征缺陷对微波介电损耗的影响可以忽略.空气退火处理样品的电导率和微波介电损耗低于空气淬火处理的样品:其中电导的变化与缺陷反应平衡相关,但空气退火降低微波介电损耗可能与退火消除晶格热应力有关.五价钽的掺杂降低了电导但增大了微波介电损耗.本研究表明空气退火处理能有效地改善BaNd2Ti4O12陶瓷的品质因子Q×f,其值提高了约12%.%Tungsten-bronze type titanate BaNd2Ti4O12 ceramics were synthesized by solid state reactions.The conductivity and microwave dielectric loss of the samples that were thermally treated under various conditions and Ta-doped were investigated by electrochemical impedance measurement and microwave dielectric resonator measurement.The variation in conductivity with annealing atmospheres of air,O2,and N2 was consistent with the defect equilibriums 2Oxo←→2V**o +O2↑+2e′ and Ti'Ti+e′←→Ti'Ti suggesting n-type conductance for BaNd2Ti4O12.Thermal treatment in air/O2 was found to favor the elimination of the native defects Vxo,Ti′Ti and weakly bound electrons thus decreasing the conductivity.Thermal treatment in a N2atmosphere,which had a low oxygen partial pressure,increased the defect content and the conductivity.Thermal treatment in air/O2/N2

  12. Band Anticrossing in Dilute Germanium Carbides Using Hybrid Functionals

    CERN Document Server

    Stephenson, Chad A; Qi, Meng; Penninger, Michael; Schneider, William; Wistey, Mark A

    2014-01-01

    Dilute germanium carbides (Ge1-xCx) offer a direct bandgap for compact silicon photonics, but widely varying results have been reported. This work uses ab initio simulations with HSE06 hybrid functionals and spin-orbit coupling to study the band structure behavior in the absence of defects. Contrary to Vegard's law, the conduction band minimum at k=0 is consistently found to decrease with increasing C content, while L and X valleys remain nearly unchanged. A vanishing bandgap was observed for all alloys with x>0.017. Conduction bands deviate from a constant-potential band anticrossing model except near the center of the Brillouin zone.

  13. Evaluation of edge detectors using avarage risk

    OpenAIRE

    Spreeuwers, L.J.; Heijden, van der, RW Rob

    1992-01-01

    A new method for evaluation of edge detectors, based on the average risk of a decision, is discussed. The average risk is a performance measure well-known in Bayesian decision theory. Since edge detection can be regarded as a compound decision making process, the performance of an edge detector is context dependent. Therefore, the application of average risk to edge detection is non-trivial. The paper describes a method to estimate the probabilities on a number of different types of (context ...

  14. Poole-Frenkel Conduction in Cu/Nano-SnO2/Cu Arrangement

    Directory of Open Access Journals (Sweden)

    Hossein Mahmoudi Chenari

    2011-01-01

    Full Text Available It is well known that metal/Tin-dioxide/metal sandwich structures exhibit a field-assisted lowering of the potential barrier between donor-like center and the conduction band edge, known as the Poole-Frenkel effect. This behavior is indicated by a linear dependence of Iog  on 1/2, where is the current density, and is the applied voltage. In this study, the electrical properties of Cu/nano-SnO2/Cu sandwich structures were investigated through current-voltage measurements at room temperature. Also, an attempt to explore the governing current flow mechanism was tried. Our results indicate that noticeable feature appearing clearly in the current-voltage characterization is the Poole-Frenkel and space-charge-limited conduction mechanisms.

  15. Conducted Vasoreactivity

    DEFF Research Database (Denmark)

    Postnov, D. E.; Neganova, A Y; Sosnovtseva, Olga

    2015-01-01

    , the underlying mechanisms are debated. Here, we focus on dynamical aspects of the problem hypothesizing the existence of a bistability-powered mechanism for regenerative pulse transmission along the endothelium. Bistability implies that the cell can have two different stable resting potentials and can switch......Conducted vasodilation is part of the physiological response to increasing metabolic demand of the tissue. Similar responses can be elicited by focal electrical or chemical stimulation. Some evidence suggests an endothelial pathway for nondecremental transmission of hyperpolarizing pulses. However...... a theoretical analysis as well as numerical simulations of both single- and multiunit bistable systems mimicking endothelial cells to investigate the self-consistence and stability of the proposed mechanism. We find that the individual cell may switch readily between two stable potentials. An array of coupled...

  16. An edge detection algorithm for imaging ladar

    Institute of Scientific and Technical Information of China (English)

    Qi Wang(王骐); Ziqin Li(李自勤); Qi Li(李琦); Jianfeng Sun(孙剑峰); Juncheng Fu(傅俊诚)

    2003-01-01

    In this paper, the morphological filter based on parametric edge detection is presented and applied toimaging ladar image with speckle noise. This algorithm and Laplacian of Gaussian (LOG) operator arecompared on edge detection. The experimental results indicate the superior performance of this kind ofthe edge detection.

  17. Understanding and preventing the edge effect.

    Science.gov (United States)

    Cheneau, Edouard; Wolfram, Roswitha; Leborgne, Laurent; Waksman, Ron

    2003-02-01

    Edge stenosis, combining neointimal proliferation and negative remodeling, remains a serious limitation of vascular brachytherapy. This review comprehensively presents terminology, definitions, mechanisms, and treatment strategies to better understand the complexities of edge narrowing. The major contributors to this phenomenon are known; understanding the practical solutions will enable us to further minimize the problem of the edge effect.

  18. A Regularized Solution to Edge Detection.

    Science.gov (United States)

    1985-05-01

    Hildreth, E. C. "Implementation of a theory of edge detection ," AI-TR-579, MIT Al Lab, 1980. Lunscher, W. H. H. "The asymptotic optimal frequency domain...filter for edge detection," IEEE Trans. PAMI, 6, 678-680, 1983. Marr, D. C. and Hildreth, E. C. " Theory of edge detection ," Proc. R. Soc. Lond. B

  19. CFAR Edge Detector for Polarimetric SAR Images

    DEFF Research Database (Denmark)

    Schou, Jesper; Skriver, Henning; Nielsen, Allan Aasbjerg;

    2003-01-01

    Finding the edges between different regions in an image is one of the fundamental steps of image analysis, and several edge detectors suitable for the special statistics of synthetic aperture radar (SAR) intensity images have previously been developed. In this paper, a new edge detector...

  20. Single-edge transport in an InAs/GaSb quantum spin Hall insulator

    Science.gov (United States)

    Couëdo, François; Irie, Hiroshi; Suzuki, Kyoichi; Onomitsu, Koji; Muraki, Koji

    2016-07-01

    We report transport measurements in a single edge channel of an InAs/GaSb quantum spin Hall insulator, where the conduction occurs through only one pair of counterpropagating edge modes. By using a specific sample design involving highly asymmetric current paths, we electrically isolate a single edge channel of the two-dimensional topological insulator from the other edge. This enables us to probe a single edge by multiterminal measurements. Both two-terminal and four-terminal resistances show a nearly quantized plateau around h /e2 for a 4-μ m -long edge, indicating quasiballistic transport. Our approach is advantageous in that it allows us to gain insight into a microscopic region from local measurements.