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Sample records for conduction band electron

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

    Shchemelinin, S.; Breskin, A.

    2017-03-01

    Bare reverse biased silicon photodiodes were exposed to 3 eV 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.

  3. Electron mean free path and conduction-band density-of-states in solid methane as determined from low-energy electron transmission experiments

    NASA Astrophysics Data System (ADS)

    Jay-Gerin, J.-P.; Plenkiewicz, B.; Plenkiewicz, P.; Perluzzo, G.; Sanche, L.

    1985-09-01

    Recently, Plenkiewicz et al. developed a theoretical model for analyzing the current I t transmitted by a thin dielectric film as a function of incident electron energy E. The purpose of this paper is to apply this model to the analysis of recent I t( E) results for solid methane. The analysis permits the determination of both the electron mean free path as a function of energy and the electronic conduction-band density-of-states in the quasi-elastic scattering region. The differences between our results and Kunz's solid methane band structure calculations are also discussed.

  4. Time-Resolved IR-Absorption Spectroscopy of Hot-Electron Dynamics in Satellite and Upper Conduction Bands in GaP

    NASA Technical Reports Server (NTRS)

    Cavicchia, M. A.; Alfano, R. R.

    1995-01-01

    The relaxation dynamics of hot electrons in the X6 and X7 satellite and upper conduction bands in GaP was directly measured by femtosecond UV-pump-IR-probe absorption spectroscopy. From a fit to the induced IR-absorption spectra the dominant scattering mechanism giving rise to the absorption at early delay times was determined to be intervalley scattering of electrons out of the X7 upper conduction-band valley. For long delay times the dominant scattering mechanism is electron-hole scattering. Electron transport dynamics of the upper conduction band of GaP has been time resolved.

  5. Electron scattering in the Δ{sub 1} model of the conduction band of germanium single crystals

    SciTech Connect

    Luniov, S. V. Burban, O. V.; Nazarchuk, P. F.

    2015-05-15

    Electron scattering in the possible Δ{sub 1} models of the conduction band in germanium crystals formed by hydrostatic or uniaxial pressure is investigated. On the basis of the theory of anisotropic scattering, the temperature dependences of the anisotropy parameter of the relaxation times and electron mobility for these models under conditions of scattering at impurity ions, as well as at acoustic and intervalley phonons are obtained. Analysis of the temperature dependences indicates that, in the temperature range of 77–300 K, intervalley scattering becomes substantial. Only for the Δ{sub 1} model formed by uniaxial pressure along the crystallographic direction [100], the electron scattering at intervalley phonons, which correspond to the g transitions, is minor with respect to scattering at acoustic phonons (the intravalley scattering) and impurity ions.

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

    NASA Astrophysics Data System (ADS)

    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.

  7. Effect of isopropyl alcohol on the surface localization and recombination of conduction-band electrons in Degussa P25 TiO sub 2. A pulse-radiolysis time-resolved microwave conductivity study. [Accelerated electrons

    SciTech Connect

    Warman, J.M.; Hass, M.P. de ); Pichat, P. ); Serpone, N. Concordia Univ., Montreal, Quebec )

    1991-10-31

    Conduction-band electrons, formed by pulse radiolysis of Degussa P25 TiO{sub 2} particles, have been monitored by time-resolved microwave conductivity and found to undergo equilibrium localization and eventual recombination at the particle surface. In the presence of isopropyl alcohol recombination is retarded due to surface hole scavenging. The particle bulk can then be pumped with mobile electrons, which survive for seconds.

  8. Electronic structure of the conduction band upon the formation of ultrathin fullerene films on the germanium oxide surface

    NASA Astrophysics Data System (ADS)

    Komolov, A. S.; Lazneva, E. F.; Gerasimova, N. B.; Panina, Yu. A.; Baramygin, A. V.; Zashikhin, G. D.

    2016-06-01

    The results of the investigation of the electronic structure of the conduction band in the energy range 5-25 eV above the Fermi level E F and the interfacial potential barrier upon deposition of aziridinylphenylpyrrolofullerene (APP-C60) and fullerene (C60) films on the surface of the real germanium oxide ((GeO2)Ge) have been presented. The content of the oxide on the (GeO2)Ge surface has been determined using X-ray photoelectron spectroscopy. The electronic properties have been measured using the very low energy electron diffraction (VLEED) technique in the total current spectroscopy (TCS) mode. The regularities of the change in the fine structure of total current spectra (FSTCS) with an increase in the thickness of the APP-C60 and C60 coatings to 7 nm have been investigated. A comparison of the structures of the FSTCS maxima for the C60 and APP-C60 films has made it possible to reveal the energy range (6-10 eV above the Fermi level E F) in which the energy states are determined by both the π* and σ* states and the FSTCS spectra have different structures of the maxima for the APP-C60 and unsubstituted C60 films. The formation of the interfacial potential barrier upon deposition of APP-C60 and C60 on the (GeO2)Ge surface is accompanied by an increase in the work function of the surface E vac- E F by the value of 0.2-0.3 eV, which corresponds to the transfer of the electron density from the substrate to the organic films under investigation. The largest changes occur with an increase in the coating thickness to 3 nm, and with further deposition of APP-C60 and C60, the work function of the surface changes only slightly.

  9. Dual Character of the Electronic Structure of YBa2Cu4O8: The Conduction Bands of CuO2 Planes and CuO Chains

    NASA Astrophysics Data System (ADS)

    Kondo, T.; Khasanov, R.; Karpinski, J.; Kazakov, S. M.; Zhigadlo, N. D.; Ohta, T.; Fretwell, H. M.; Palczewski, A. D.; Koll, J. D.; Mesot, J.; Rotenberg, E.; Keller, H.; Kaminski, A.

    2007-04-01

    We use microprobe angle-resolved photoemission spectroscopy (μARPES) to separately investigate the electronic properties of CuO2 planes and CuO chains in the high temperature superconductor, YBa2Cu4O8. For the CuO2 planes, a two-dimensional (2D) electronic structure is observed and, in contrast to Bi2Sr2CaCu2O8+δ, the bilayer splitting is almost isotropic and 50% larger, which strongly suggests that bilayer splitting has no direct effect on the superconducting properties. In addition, the scattering rate for the bonding band is about 1.5 times stronger than the antibonding band and is independent of momentum. For the CuO chains, the electronic structure is quasi-one-dimensional and consists of a conduction and insulating band. Finally, we find that the conduction electrons are well confined within the planes and chains with a nontrivial hybridization.

  10. Gd3+ spin-lattice relaxation via multi-band conduction electrons in Y(1-x)Gd(x)In3: an electron spin resonance study.

    PubMed

    Cabrera-Baez, M; Iwamoto, W; Magnavita, E T; Osorio-Guillén, J M; Ribeiro, R A; Avila, M A; Rettori, C

    2014-04-30

    Interest in the electronic structure of the intermetallic compound YIn3 has been renewed with the recent discovery of superconductivity at T ∼ 1 K, which may be filamentary in nature. In this work we perform electron spin resonance (ESR) experiments on Gd(3+) doped YIn3 (Y1-xGdxIn3; 0.001 ⪅ x ⩽̸ 0.08), showing that the spin-lattice relaxation of the Gd(3+) ions, due to the exchange interaction between the Gd(3+) localized magnetic moment and the conduction electrons (ce), is processed via the presence of s-, p- and d-type ce at the YIn3 Fermi level. These findings are revealed by the Gd(3+) concentration dependence of the Korringa-like relaxation rate d(ΔH)/dT and g-shift (Δg = g - 1.993), that display bottleneck relaxation behavior for the s-electrons and unbottleneck behavior for the p- and d-electrons. The Korringa-like relaxation rates vary from 22(2) Oe/K for x ⪅ 0.001 to 8(2) Oe/K for x = 0.08 and the g-shift values change, respectively, from a positive Δg = +0.047(10) to a negative Δg = -0.008(4). Analysis in terms of a three-band ce model allows the extraction of the corresponding exchange interaction parameters Jfs, Jfp and Jfd.

  11. Dual character of the electronic structure in YBa2Cu4O8: conduction bands of CuO2 planes and CuO chains

    NASA Astrophysics Data System (ADS)

    Kaminski, A.; Kondo, T.; Khasanov, R.; Karpinski, J.; Kazakov, S. M.; Zhigadlo, N. D.; Ohta, T.; Fretwell, H. M.; Palczewski, A. D.; Koll, J. D.; Mesot, J.; Rotenberg, E.; Keller, H.

    2007-03-01

    We use microprobe Angle-Resolved Photoemission Spectroscopy (μARPES) to separately investigate the electronic properties of CuO2 planes and CuO chains in the high temperature superconductor, YBa2Cu4O8. In the CuO2 planes, a two dimensional (2D) electronic structure with nearly momentum independent bilayer splitting is observed. The splitting energy is 150 meV at (π,0), almost 50% larger than in Bi2Sr2CaCu2O8+δ and the electron scattering at the Fermi level in the bonding band is about 1.5 times stronger than in the antibonding band. The CuO chains have a quasi one dimensional (1D) electronic structure. We observe two 1D bands separated by ˜ 550meV: a conducting band and an insulating band with an energy gap of ˜240meV. We find that the conduction electrons are well confined within the planes and chains with a non-trivial hybridization.

  12. Processable Electronically Conducting Polymers

    DTIC Science & Technology

    1991-01-01

    is also evident in the electronic spectra of the polymer as the (CH)x formed in this manner has a band gap (absorption onset) at -1.9 eV (650 nm) and...an absorption maximum at 2.8 eV (440 nm) (compared to a band gap of 1.4 eV (885 nm) for Shirakawa (CH)x). As is the case with Durham (CH)x, orientation...annulated ring system locks the polymer into a stable conformation, and thus the optical band gaps of the mono- and disubstituted species are at

  13. Conduction-band edge dependence of carbon-coated hematite stimulated extracellular electron transfer of Shewanella oneidensis in bioelectrochemical systems.

    PubMed

    Zhou, Shungui; Tang, Jiahuan; Yuan, Yong

    2015-04-01

    Bacteria-based bioelectrochemical systems (BESs) are promising technologies used for alternative energy generation, wastewater treatment, and environmental monitoring. However, their practical application is limited by the bioelectrode performance, mainly resulting from low extracellular electron transfer (EET) efficiency. In this study, a carbon-coated hematite (C/Hematite) electrode was successfully obtained by a green and solvent-free route, that is, heat treatment in an oxygen-rich environment using solid ferrocene as the precursor. The as-prepared C/Hematite electrode was evaluated as a high-performance electrode material in a Shewanella oneidensis-inoculated BES. The maximum biocurrent density of the Shewanella-attached C/Hematite electrode reached 0.22 ± 0.01 mA cm(-2), which is nearly 6-times higher than that of a bare carbon cloth (CC) electrode (0.036 ± 0.005 mA cm(-2)). Electrochemical measurements revealed that the enhanced conductivity and better energy matching between the outer membrane c-type cytochromes of S. oneidensis and the electrode contributed to the improved EET efficiency. The results of this study demonstrated that the semiconductive properties of iron oxides play important roles for the involved bacterial extracellular respiration activities.

  14. Electronic structure of the conduction band of the interface region of ultrathin films of substituted perylenedicarboximides and the germanium oxide surface

    NASA Astrophysics Data System (ADS)

    Komolov, A. S.; Lazneva, E. F.; Gerasimova, N. B.; Panina, Yu. A.; Baramygin, A. V.; Pshenichnyuk, S. A.

    2016-09-01

    The results of the investigation of the electronic structure of the conduction band and the interfacial potential barrier during the formation of interfaces of dioctyl-substituted perylenedicarboximide (PTCDI-C8) and diphenyl-substituted perylenedicarboximide (PTCDI-Ph) ultrathin films with the oxidized germanium surface have been presented. The experimental results have been obtained using the very low energy electron diffraction (VLEED) technique in the total current spectroscopy (TCS) mode at energies in the range from 5 to 20 eV above the Fermi level E F. The positions of the maxima of the fine structure of total current spectra (FSTCS) of the PTCDI-C8 and PTCDI-Ph films differ significantly in the energy range from 9 to 20 eV above the Fermi level E F, which can be associated with the difference between the substituents of the chosen molecules, dioctyl- and diphenyl-, respectively. At the same time, the positions of the lowenergy maxima in the FSTCS spectra at an energy 6-7 eV above the Fermi level E F for the PTCDI-C8 and PTCDI-Ph films almost coincide with each other. It has been suggested that these maxima are attributed to the electronic states of the perylene core of the molecules under investigation. The process of the formation of interfacial potential barriers of the PTCDI-C8 and PTCDI-Ph films with the oxidized germanium surface has been analyzed. It has been found that the work functions of the surface, E vac- E F, differ little from 4.6 ± 0.1 eV over the entire range of organic coating thicknesses from 0 to 6 nm.

  15. Conduction-band electronic states of YbInCu{sub 4} studied by photoemission and soft x-ray absorption spectroscopies

    SciTech Connect

    Utsumi, Yuki; Kurihara, Hidenao; Maso, Hiroyuki; Tobimatsu, Komei; Sato, Hitoshi; Shimada, Kenya; Namatame, Hirofumi; Hiraoka, Koichi; Kojima, Kenichi; Ohkochi, Takuo; Fujimori, Shin-ichi; Takeda, Yukiharu; Saitoh, Yuji; Mimura, Kojiro; Ueda, Shigenori; Yamashita, Yoshiyuki; Yoshikawa, Hideki; Kobayashi, Keisuke; Oguchi, Tamio; Taniguchi, Masaki

    2011-09-15

    We have studied conduction-band (CB) electronic states of a typical valence-transition compound YbInCu{sub 4} by means of temperature-dependent hard x-ray photoemission spectroscopy (HX-PES) of the Cu 2p{sub 3/2} and In 3d{sub 5/2} core states taken at h{nu}=5.95 keV, soft x-ray absorption spectroscopy (XAS) of the Cu 2p{sub 3/2} core absorption region around h{nu}{approx}935 eV, and soft x-ray photoemission spectroscopy (SX-PES) of the valence band at the Cu 2p{sub 3/2} absorption edge of h{nu}=933.0 eV. With decreasing temperature below the valence transition at T{sub V}=42 K, we have found that (1) the Cu 2p{sub 3/2} and In 3d{sub 5/2} peaks in the HX-PES spectra exhibit the energy shift toward the lower binding-energy side by {approx}40 and {approx}30 meV, respectively, (2) an energy position of the Cu 2p{sub 3/2} main absorption peak in the XAS spectrum is shifted toward higher photon-energy side by {approx}100 meV, with an appearance of a shoulder structure below the Cu 2p{sub 3/2} main absorption peak, and (3) an intensity of the Cu L{sub 3}VV Auger spectrum is abruptly enhanced. These experimental results suggest that the Fermi level of the CB-derived density of states is shifted toward the lower binding-energy side. We have described the valence transition in YbInCu{sub 4} in terms of the charge transfer from the CB to Yb 4f states.

  16. Conduction band valley splitting in Si

    NASA Astrophysics Data System (ADS)

    Klimeck, Gerhard; Boykin, T. B.; Eriksson, M.; Friesen, M.; Coppersmith, S. N.; von Allmen, P.; Oyafuso, F.; Lee, S.

    2004-03-01

    A theory based on localized-orbital approaches is developed to describe the valley splitting observed in silicon nano-structures. The theory is appropriate in the limit of low electron density and relevant for proposed quantum computing architectures. The valley splitting is computed for realistic devices using the quantitative nanoelectronic modeling tool NEMO using the empirical tight binding model sp^3d^5s. The tight binding parameters have been fitted to bulk bandstructure behavior of Si using a genetic algorithm. A 1-D quantum well simulation in NEMO shows the basic features of conduction band valley splitting as a coherent, confinement-induced phenomenon. No additional intervalley scattering parameters are needed. The splitting is in general nonzero even in the absence of electric field. The splitting oscillates as a function of N, the number of layers in the quantum well, with a period that is determined by the location of the valley minimum in the Brillouin zone. The envelope of the splitting decays as N^3. The qualitative physics remain the same irrespective of the details of the quantum well boundaries or the details of the strain treatment in the quantum well.

  17. Carrier-Density Dependence of the Exchange Coupling Between Magnetic Ions and Conduction Band Electrons in Heavily n-TYPE Zn(1-x)MnxSe and Optically Pumped Cd(1-x)MnxTe

    NASA Astrophysics Data System (ADS)

    Lentze, M.; Grabs, P.; Geurts, J.; Rönnburg, K.; Mohler, E.; Roskos, H.

    We report on the analysis of the influence of carrier concentration on the exchange coupling between conduction band electrons and Mn d-electrons in diluted magnetic semiconductors. For this analysis we employed (i) electronic spin-flip Raman spectroscopy on heavily n-doped (Zn,Mn)Se, (ii) time-resolved Faraday rotation on optically pumped (Cd,Mn)Te. With increasing carrier density, a reduction of the exchange energy N0α up to 30 % is observed. It is explained by a weakening of the ferromagnetic character of the coupling of conducton-band electrons to the Mn d-electrons by an admixture of an antiferromagnetic (p-d) coupling contribution to the ferromagnetic (s-d) one for q ≠ 0.

  18. Ballistic-electron-emission spectroscopy of Al{sub x}Ga{sub 1{minus}x}As/GaAs heterostructures: Conduction-band offsets, transport mechanisms, and band-structure effects

    SciTech Connect

    OShea, J.J.; Brazel, E.G.; Rubin, M.E.; Bhargava, S.; Chin, M.A.; Narayanamurti, V.

    1997-07-01

    We report an extensive investigation of semiconductor band-structure effects in single-barrier Al{sub x}Ga{sub 1{minus}x}As/GaAs heterostructures using ballistic-electron-emission spectroscopy (BEES). The transport mechanisms in these single-barrier structures were studied systematically as a function of temperature and Al composition over the full compositional range (0{le}x{le}1). The initial ({Gamma}) BEES thresholds for Al{sub x}Ga{sub 1{minus}x}As single barriers with 0{le}x{le}0.42 were extracted using a model which includes the complete transmission probability of the metal-semiconductor interface and the semiconductor heterostructure. Band offsets measured by BEES are in good agreement with previous measurements by other techniques which demonstrates the accuracy of this technique. BEES measurements at 77 K give the same band-offset values as at room temperature. When a reverse bias is applied to the heterostructures, the BEES thresholds shift to lower voltages in good agreement with the expected bias-induced band-bending. In the indirect band-gap regime ({ital x}{gt}0.45), spectra show a weak ballistic-electron-emission microscopy current contribution due to intervalley scattering through Al{sub x}Ga{sub 1{minus}x}As {ital X} valley states. Low-temperature spectra show a marked reduction in this intervalley current component, indicating that intervalley phonon scattering at the GaAs/Al{sub x}Ga{sub 1{minus}x}As interface produces a significant fraction of this{ital X} valley current. A comparison of the BEES thresholds with the expected composition dependence of the Al{sub x}Ga{sub 1{minus}x}As {Gamma}, {ital L}, and {ital X} points yields good agreement over the entire composition range. {copyright} {ital 1997} {ital The American Physical Society}

  19. The sensitivity of the electron transport within bulk zinc-blende gallium nitride to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient associated with the lowest energy conduction band valley

    NASA Astrophysics Data System (ADS)

    Siddiqua, Poppy; O'Leary, Stephen K.

    2016-09-01

    Within the framework of a semi-classical three-valley Monte Carlo simulation approach, we analyze the steady-state and transient electron transport that occurs within bulk zinc-blende gallium nitride. In particular, we examine how the steady-state and transient electron transport that occurs within this material changes in response to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient associated with the lowest energy conduction band valley. These results are then contrasted with those corresponding to a number of other compound semiconductors of interest.

  20. Electronically Conductive Composite Polymer Membranes.

    DTIC Science & Technology

    1985-09-20

    coats the individual fibers which make up the webs. Clearly, at this loading level ( 10 w/w S Nafion in the Gr), only a small fraction of the...NOO014-82K-0612 Task No. NR 627-838 cc TECHNICAL REPORT NO. 10 Mn Electronically Conductive Composite Polymer Membranes I- I by 0 Reginald M. Penner... 10 of Document Control Data - DO Form 1473. Copies of form available from cognizant contract administrator 85 IV, 03 O88 UNCLASSI FIED SECURITY

  1. Anisotropic electronic conduction in stacked two-dimensional titanium carbide

    PubMed Central

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-01-01

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I−V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane. PMID:26548439

  2. Anisotropic electronic conduction in stacked two-dimensional titanium carbide

    NASA Astrophysics Data System (ADS)

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-11-01

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I-V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane.

  3. Anisotropic electronic conduction in stacked two-dimensional titanium carbide.

    PubMed

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-11-09

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I-V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane.

  4. Elucidation of band structure of charge storage in conducting polymers using a redox reaction.

    PubMed

    Contractor, Asfiya Q; Juvekar, Vinay A

    2014-07-01

    A novel technique to investigate charge storage characteristics of intrinsically conducting polymer films has been developed. A redox reaction is conducted on a polymer film on a rotating disk electrode under potentiostatic condition so that the rate of charging of the film equals the rate of removal of the charge by the reaction. The voltammogram obtained from the experiment on polyaniline film using Fe(2+)/Fe(3+) in HCl as the redox system shows five distinct linear segments (bands) with discontinuity in the slope at specific transition potentials. These bands are the same as those indicated by electron spin resonance (ESR)/Raman spectroscopy with comparable transition potentials. From the dependence of the slopes of the bands on concentration of ferrous and ferric ions, it was possible to estimate the energies of the charge carriers in different bands. The film behaves as a redox capacitor and does not offer resistance to charge transfer and electronic conduction.

  5. F-electron systems: Pushing band theory

    SciTech Connect

    Koelling, D.D.

    1990-08-01

    The f-electron orbitals have always been the incomplete atomic shell acting as a local moment weakly interacting with the remaining electronic structure'' in the minds of most people. So examining them using a band theory where one views them as itinerant once was -- and to some extent even today still is -- considered with some skepticism. Nonetheless, a very significant community has successfully utilized band theory as a probe of the electronic structure of the appropriate actinides and rare earths. Those people actually using the approach would be the first to declare that it is not the whole solution. Instead, one is pushing and even exceeding its limits of applicability. However, the appropriate procedure is to push the model consistently to its limits, patch where possible, and then look to see where discrepancies remain. I propose to offer a selected review of past developments (emphasizing the career to date of A. J. Freeman in this area), offer a list of interesting puzzles for the future, and then make some guesses as to the techniques one might want to use. 27 refs.

  6. Electronic band structure of defect chalcopyrites

    NASA Astrophysics Data System (ADS)

    Jiang, Xiaoshu; Lambrecht, Walter R. L.

    2001-03-01

    The defect chalcopyrites of chemical composition II-III-VI4 in which II, III and VI mean group-II elements such as Cd or Hg, group-III elements such as Al and Ga and group-VI elements such as S, Se, Te, form an interesting family of semiconductor compounds with potential nonlinear optical applications. They can be thought of as derived from the regular I-III-VI2 chalcopyrites by doubling the formula unit and replacing the group I element, for example, Ag by the group-II element and a vacancy in an ordered manner. The chalcopyrites themselves are derived from II-VI compounds by replacing the group-II by a group I and a group-III element. In this contribution we present electronic band structure calculations of some of these compounds, calculated using the linear muffin-tin orbital method combined with the local density functional approximation. We discuss the relation of the band structures of the corresponding zincblende, chalcopyrite and defect chalcopyrite compounds. In particular, the role of the group I or group II d-band energy will be shown to be important. The trends with chemical substutions and the effects of structural distortions c/a and internal parameters accompanying the chemical distortion will be discussed.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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. Spin susceptibility of Anderson impurities in arbitrary conduction bands

    NASA Astrophysics Data System (ADS)

    Fang, Tie-Feng; Tong, Ning-Hua; Cao, Zhan; Sun, Qing-Feng; Luo, Hong-Gang

    2015-10-01

    Spin susceptibility of Anderson impurities is a key quantity in understanding the physics of Kondo screening. Traditional numerical renormalization group (NRG) calculation of the impurity contribution χimp to susceptibility, defined originally by Wilson in a flat wide band, has been generalized before to structured conduction bands. The results brought about non-Fermi-liquid and diamagnetic Kondo behaviors in χimp, even when the bands are not gapped at the Fermi energy. Here, we use the full density-matrix (FDM) NRG to present high-quality data for the local susceptibility χloc and to compare them with χimp obtained by the traditional NRG. Our results indicate that those exotic behaviors observed in χimp are unphysical. Instead, the low-energy excitations of the impurity in arbitrary bands only without gap at the Fermi energy are still a Fermi liquid and paramagnetic. We also demonstrate that unlike the traditional NRG yielding χloc less accurate than χimp, the FDM method allows a high-precision dynamical calculation of χloc at much reduced computational cost, with an accuracy at least one order higher than χimp. Moreover, artifacts in the FDM algorithm to χimp and origins of the spurious non-Fermi-liquid and diamagnetic features are clarified. Our work provides an efficient high-precision algorithm to calculate the spin susceptibility of impurity for arbitrary structured bands, while negating the applicability of Wilson's definition to such cases.

  10. The Electronic Thermal Conductivity of Graphene.

    PubMed

    Kim, Tae Yun; Park, Cheol-Hwan; Marzari, Nicola

    2016-04-13

    Graphene, as a semimetal with the largest known thermal conductivity, is an ideal system to study the interplay between electronic and lattice contributions to thermal transport. While the total electrical and thermal conductivity have been extensively investigated, a detailed first-principles study of its electronic thermal conductivity is still missing. Here, we first characterize the electron-phonon intrinsic contribution to the electronic thermal resistivity of graphene as a function of doping using electronic and phonon dispersions and electron-phonon couplings calculated from first-principles at the level of density-functional theory and many-body perturbation theory (GW). Then, we include extrinsic electron-impurity scattering using low-temperature experimental estimates. Under these conditions, we find that the in-plane electronic thermal conductivity κe of doped graphene is ∼300 W/mK at room temperature, independently of doping. This result is much larger than expected and comparable to the total thermal conductivity of typical metals, contributing ∼10% to the total thermal conductivity of bulk graphene. Notably, in samples whose physical or domain sizes are of the order of few micrometers or smaller, the relative contribution coming from the electronic thermal conductivity is more important than in the bulk limit, because lattice thermal conductivity is much more sensitive to sample or grain size at these scales. Last, when electron-impurity scattering effects are included we find that the electronic thermal conductivity is reduced by 30 to 70%. We also find that the Wiedemann-Franz law is broadly satisfied at low and high temperatures but with the largest deviations of 20-50% around room temperature.

  11. Electronic materials with a wide band gap: recent developments

    PubMed Central

    Klimm, Detlef

    2014-01-01

    The development of semiconductor electronics is reviewed briefly, beginning with the development of germanium devices (band gap E g = 0.66 eV) after World War II. A tendency towards alternative materials with wider band gaps quickly became apparent, starting with silicon (E g = 1.12 eV). This improved the signal-to-noise ratio for classical electronic applications. Both semiconductors have a tetrahedral coordination, and by isoelectronic alternative replacement of Ge or Si with carbon or various anions and cations, other semiconductors with wider E g were obtained. These are transparent to visible light and belong to the group of wide band gap semiconductors. Nowadays, some nitrides, especially GaN and AlN, are the most important materials for optical emission in the ultraviolet and blue regions. Oxide crystals, such as ZnO and β-Ga2O3, offer similarly good electronic properties but still suffer from significant difficulties in obtaining stable and technologically adequate p-type conductivity. PMID:25295170

  12. Conducting polymers in electronic chemical sensors.

    PubMed

    Janata, Jiri; Josowicz, Mira

    2003-01-01

    Conducting organic polymers have found two main kinds of application in electronics so far: as materials for construction of various devices and as selective layers in chemical sensors. In either case, interaction with ambient gases is critical. It may compromise the performance of a device based on conducting polymers, whereas it is beneficial in a sensor. Conductivity has been the primary property of interest. Work function--related to conductivity, but in principle a different property--has received only scant attention. Our aim here is to discuss the usability of conducting polymers in both types of electronic applications in light of these two parameters.

  13. Optical conductivity of ABA stacked graphene trilayer: mid-IR resonance due to band nesting

    NASA Astrophysics Data System (ADS)

    Rashidian, Zeinab; Bludov, Yuliy V.; Ribeiro, Ricardo M.; Peres, N. M. R.; Vasilevskiy, Mikhail I.

    2014-10-01

    The band structure and the optical conductivity of an ABA (Bernal-type) stacked graphene trilayer are calculated. It is shown that, under appropriate doping, a strong resonant peak develops in the optical conductivity, located at the frequency corresponding to approximately 1.4 times the interlayer hopping energy and caused by the ‘nesting’ of two nearly parabolic bands in the electronic spectrum. The intensity of this resonant absorption can be controlled by adjusting the gate voltage. The effect is robust with respect to increasing temperature.

  14. Electronically conducting polymers with silver grains

    NASA Technical Reports Server (NTRS)

    Murphy, Oliver J. (Inventor); Hitchens, G. Duncan (Inventor); Hodko, Dolibor (Inventor)

    1999-01-01

    The present invention provides electronically conducting polymer films formed from photosensitive formulations of pyrrole and an electron acceptor that have been selectively exposed to UV light, laser light, or electron beams. The formulations may include photoinitiators, flexibilizers, solvents and the like. These solutions can be used in applications including printed circuit boards and through-hole plating and enable direct metallization processes on non-conducting substrates. After forming the conductive polymer patterns, a printed wiring board can be formed by sensitizing the polymer with palladium and electrolytically depositing copper.

  15. Production of photocurrent due to intermediate-to-conduction-band transitions: a demonstration of a key operating principle of the intermediate-band solar cell.

    PubMed

    Martí, A; Antolín, E; Stanley, C R; Farmer, C D; López, N; Díaz, P; Cánovas, E; Linares, P G; Luque, A

    2006-12-15

    We present intermediate-band solar cells manufactured using quantum dot technology that show for the first time the production of photocurrent when two sub-band-gap energy photons are absorbed simultaneously. One photon produces an optical transition from the intermediate-band to the conduction band while the second pumps an electron from the valence band to the intermediate-band. The detection of this two-photon absorption process is essential to verify the principles of operation of the intermediate-band solar cell. The phenomenon is the cornerstone physical principle that ultimately allows the production of photocurrent in a solar cell by below band gap photon absorption, without degradation of its output voltage.

  16. Inter-Valence-Subband/Conduction-Band-Transport IR Detectors

    NASA Technical Reports Server (NTRS)

    Ting, David; Gunapala, Sarath; Bandara, Sumith

    2004-01-01

    Infrared (IR) detectors characterized by a combination of (1) high-quantum-efficiency photoexcitation of inter-valence-subband transitions of charge carriers and (2) high-mobility conduction- band transport of the thus-excited charge carriers have been proposed in an effort to develop focal-plane arrays of such devices for infrared imaging. Like many prior quantum-well infrared photodetectors (QWIPs), the proposed devices would be made from semiconductor heterostructures. In order to obtain the combination of characteristics mentioned above, the proposed devices would be designed and fabricated in novel InAs/GaSb superlattice configurations that would exploit a phenomenon known in the semiconductor art as type-II broken-gap band offset.

  17. Intervalley separation in the conduction band of InGaAs measured by terahertz excitation spectroscopy

    SciTech Connect

    Molis, G.; Krotkus, A.; Vaicaitis, V.

    2009-03-02

    Spectral dependencies of terahertz radiation from the femtosecond laser-illuminated surfaces of Ga{sub x}In{sub 1-x}As (x=1, 0.8, and 0.47) have been investigated experimentally at high optical fluencies and laser wavelengths ranging from 600 to 800 nm. The terahertz pulse amplitude increased with the increasing laser photon energy due to larger excess energies of photoexcited electrons and more efficient spatial separation of electrons and holes at the illuminated surface. This increase was stopped with the onset of electron transitions to subsidiary conduction band valleys. Analysis of these experiments was used for evaluating the energy positions of the X and L conduction band valleys in Ga{sub x}In{sub 1-x}As alloys as a function of their composition.

  18. Effects of electron-impurity scattering on density of states in silicene: Impurity bands and band-gap narrowing

    NASA Astrophysics Data System (ADS)

    Liu, S. Y.; Zeng, Y. C.; Lei, X. L.

    2016-12-01

    Considering the interband correlation, we present a generalized multiple-scattering approach of Green's function to investigate the effects of electron-impurity scattering on the density of states in silicene at zero temperature. The reduction of energy gaps in the case of relatively high chemical potential and the transformation of split-off impurity bands into band tails for low chemical potential are found. The dependency of optical conductivity on the impurity concentration is also discussed for frequency within the terahertz regime.

  19. Probing the Spin-Polarized Electronic Band Structure in Monolayer Transition Metal Dichalcogenides by Optical Spectroscopy.

    PubMed

    Wang, Zefang; Zhao, Liang; Mak, Kin Fai; Shan, Jie

    2017-02-08

    We study the electronic band structure in the K/K' valleys of the Brillouin zone of monolayer WSe2 and MoSe2 by optical reflection and photoluminescence spectroscopy on dual-gated field-effect devices. Our experiment reveals the distinct spin polarization in the conduction bands of these compounds by a systematic study of the doping dependence of the A and B excitonic resonances. Electrons in the highest-energy valence band and the lowest-energy conduction band have antiparallel spins in monolayer WSe2 and parallel spins in monolayer MoSe2. The spin splitting is determined to be hundreds of meV for the valence bands and tens of meV for the conduction bands, which are in good agreement with first-principles calculations. These values also suggest that both n- and p-type WSe2 and MoSe2 can be relevant for spin- and valley-based applications.

  20. Probing the Spin-Polarized Electronic Band Structure in Monolayer Transition Metal Dichalcogenides by Optical Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Zefang; Zhao, Liang; Mak, Kin Fai; Shan, Jie

    2017-02-01

    We study the electronic band structure in the K/K' valleys of the Brillouin zone of monolayer WSe2 and MoSe2 by optical reflection and photoluminescence spectroscopy on dual-gated field-effect devices. Our experiment reveals the distinct spin polarization in the conduction bands of these compounds by a systematic study of the doping dependence of the A and B excitonic resonances. Electrons in the highest-energy valence band and the lowest-energy conduction band have antiparallel spins in monolayer WSe2, and parallel spins in monolayer MoSe2. The spin splitting is determined to be hundreds of meV for the valence bands and tens of meV for the conduction bands, which are in good agreement with first principles calculations. These values also suggest that both n- and p-type WSe2 and MoSe2 can be relevant for spin- and valley-based applications

  1. Tuning the electronic band gap of graphene by oxidation

    SciTech Connect

    Dabhi, Shweta D.; Jha, Prafulla K.

    2015-06-24

    Using plane wave pseudo potential density functional theory, we studied the electronic properties of graphene with different C:O ratio. In this work, we discussed the changes that occur in electronic band structure of graphene functionalized with different amount of epoxy group. Electronic band gap depends on C:O ratio in graphene oxide containing epoxy group. The present work will have its implication for making devices with tunable electronic properties by oxidizing graphene.

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

    NASA Astrophysics Data System (ADS)

    Dong, Juan; Shi, Jiangjian; Li, Dongmei; Luo, Yanhong; Meng, Qingbo

    2015-08-01

    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 (ΔEC) 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 ΔEC of about 0.1 eV is obtained. The photovoltage of the cell is thus significantly increased due to the relatively low charge recombination.

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

    NASA Technical Reports Server (NTRS)

    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.

  4. The determination of the conduction mechanism and optical band gap of fluorescein sodium salt

    NASA Astrophysics Data System (ADS)

    Yakuphanoglu, Fahrettin; Sekerci, Memet; Evin, Ertan

    2006-06-01

    The electrical conductivity and optical properties of fluorescein sodium salt in the temperature range of 295-370 K have been investigated. Various conduction models described in the literature were used to elucidate the charge transport mechanism of the compound. It is found that the charge transfer mechanism of the compound is understood in terms of grain boundary scattering. It can be evaluated that the obtained electronic parameters such as mobility, conductivity at room temperature, activation energy and optical band gap suggest that the compound is an organic semiconductor.

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

    PubMed

    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

    2016-07-21

    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 leads to the identification of valence and conduction band spectral features, and allows a precise determination of the position of the band edges, ionization energy and electron affinity of the materials. The comparison reveals an unusually low DOS at the valence band maximum (VBM) of these compounds, which confirms and generalizes previous predictions of strong band dispersion and low DOS at the MAPbI3 VBM. This low DOS calls for special attention when using electron spectroscopy to determine the frontier electronic states of lead halide perovskites.

  6. Convergence of electronic bands for high performance bulk thermoelectrics.

    PubMed

    Pei, Yanzhong; Shi, Xiaoya; LaLonde, Aaron; Wang, Heng; Chen, Lidong; Snyder, G Jeffrey

    2011-05-05

    Thermoelectric generators, which directly convert heat into electricity, have long been relegated to use in space-based or other niche applications, but are now being actively considered for a variety of practical waste heat recovery systems-such as the conversion of car exhaust heat into electricity. Although these devices can be very reliable and compact, the thermoelectric materials themselves are relatively inefficient: to facilitate widespread application, it will be desirable to identify or develop materials that have an intensive thermoelectric materials figure of merit, zT, above 1.5 (ref. 1). Many different concepts have been used in the search for new materials with high thermoelectric efficiency, such as the use of nanostructuring to reduce phonon thermal conductivity, which has led to the investigation of a variety of complex material systems. In this vein, it is well known that a high valley degeneracy (typically ≤6 for known thermoelectrics) in the electronic bands is conducive to high zT, and this in turn has stimulated attempts to engineer such degeneracy by adopting low-dimensional nanostructures. Here we demonstrate that it is possible to direct the convergence of many valleys in a bulk material by tuning the doping and composition. By this route, we achieve a convergence of at least 12 valleys in doped PbTe(1-x)Se(x) alloys, leading to an extraordinary zT value of 1.8 at about 850 kelvin. Band engineering to converge the valence (or conduction) bands to achieve high valley degeneracy should be a general strategy in the search for and improvement of bulk thermoelectric materials, because it simultaneously leads to a high Seebeck coefficient and high electrical conductivity.

  7. Engineering the Electronic Band Structure for Multiband Solar Cells

    SciTech Connect

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

    2010-07-12

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

  8. Engineering the electronic band structure for multiband solar cells.

    PubMed

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

    2011-01-14

    Using the unique features of the electronic band structure of GaN(x)As(1-x) alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the band anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.

  9. Topological Insulators: Electronic Band Structure and Spectroscopy

    NASA Astrophysics Data System (ADS)

    Palaz, S.; Koc, H.; Mamedov, A. M.; Ozbay, E.

    2017-02-01

    In this study, we present the results of our ab initio calculation of the elastic constants, density of states, charge density, and Born effective charge tensors for ferroelectric (rhombohedral) and paraelectric phases (cubic) of the narrow band ferroelectrics (GeTe, SnTe) pseudopotentials. The related quantities such as bulk modulus and shear modulus using obtained elastic constants have also been estimated in the present work. The total and partial densities of states corresponding to the band structure of Sn(Ge)Te(S,Se) were calculated. We also calculated the Born effective charge tensor of an atom (for instance, Ge, Sn, Te, etc.), which is defined as the induced polarization of the solid along the main direction by a unit displacement in the perpendicular direction of the sublattice of an atom at the vanishing electric field.

  10. Electrical conduction and band offsets in Si/HfxTi1-xO2/metal structures

    NASA Astrophysics Data System (ADS)

    Afanas'ev, V. V.; Stesmans, A.; Chen, F.; Li, M.; Campbell, S. A.

    2004-06-01

    The electron energy band alignment in the Si/HfxTi1-xO2/metal (Au,Al) structures is determined as a function of oxide composition using internal photoemission of electrons and photoconductivity measurements. For x⩽0.5 the electron excitations with thresholds corresponding to the band-gap width of amorphous TiO2 (4.4 eV) and HfO2 (5.6 and 5.9 eV) are observed at the same time, suggesting formation of TiO2- and HfO2-like subnetworks. With respect to the Fermi level of Au the conduction band of TiO2 appears to be 1.4 eV below the conduction band of HfO2 which indicates that the valence bands of the two oxides are nearly aligned. This significant downshift of the conduction band due to Ti incorporation leads to low barriers for electrons at the interfaces of HfxTi1-xO2 with Si and Al (˜1 eV or less) strongly impairing insulating properties of the oxide. Crystallization of TiO2 upon high-temperature annealing further enhances leakage currents because of a significantly lower band-gap width of crystallized TiO2 (3.1-3.4 eV).

  11. Electronic band structure of surface-doped black phosphorus

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  12. Electronic energy band structure of the double perovskite Ba2MnWO6.

    PubMed

    Fujioka, Yukari; Frantti, Johannes; Nieminen, Risto M

    2008-06-05

    The electronic and magnetic structures of the double perovskite oxide Ba 2MnWO6 (BMW) were determined by employing the density functional theory within the generalized gradient approximation (GGA) + U approach. BMW is considered a prototype double perovskite due to its high degree of B-site ordering and is a good case study for making a comparison between computations and experiments. By adjusting the U-parameter, the electronic energy band structure and magnetic properties, which were consistent with the experimental results, were obtained. These computations revealed that the valence bands are mainly formed from Mn 3d and O 2p states, while the conduction bands are derived from W 5d and O 2p states. The localized bands composed from Mn 3d states are located in the bandgap. The results imply that the formation of polarons in the conduction band initiate the resonance Raman modes observed as a series of equidistant peaks.

  13. Intervalley energy of GaN conduction band measured by femtosecond pump-probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Marcinkevičius, Saulius; Uždavinys, Tomas K.; Foronda, Humberto M.; Cohen, Daniel A.; Weisbuch, Claude; Speck, James S.

    2016-12-01

    Time-resolved transmission and reflection measurements were performed for bulk GaN at room temperature to evaluate the energy of the first conduction band satellite valley. The measurements showed clear threshold-like spectra for transmission decay and reflection rise times. The thresholds were associated with the onset of the intervalley electron scattering. Transmission measurements with pump and probe pulses in the near infrared produced an intervalley energy of 0.97 ±0.02 eV. Ultraviolet pump and infrared probe reflection provided a similar value. Comparison of the threshold energies obtained in these experiments allowed estimating the hole effective mass in the upper valence band to be 1.4 m0 . Modeling of the reflection transients with rate equations has allowed estimating electron-LO (longitudinal optical) phonon scattering rates and the satellite valley effective mass.

  14. Banded Electron Structure Formation in the Inner Magnetosphere

    NASA Technical Reports Server (NTRS)

    Liemohn, M. W.; Khazanov, G. V.

    1997-01-01

    Banded electron structures in energy-time spectrograms have been observed in the inner magnetosphere concurrent with a sudden relaxation of geomagnetic activity. In this study, the formation of these banded structures is considered with a global, bounce-averaged model of electron transport, and it is concluded that this structure is a natural occurrence when plasma sheet electrons are captured on closed drift paths near the Earth. These bands do not appear unless there is capture of plasma sheet electrons; convection along open drift paths making open pass around the Earth do not have time to develop this feature. The separation of high-energy bands from the injection population due to the preferential advection of the gradient-curvature drift creates spikes in the energy distribution, which overlap to form a series of bands in the energy spectrograms. The lowest band is the bulk of the injected population in the sub-key energy range. Using the Kp history for an observed banded structure event, a cloud of plasma sheet electrons is captured and the development of their distribution function is examined and discussed.

  15. Electronic thermal conductivity of suspended graphene

    SciTech Connect

    Begum, K. Rizwana Sankeshwar, N. S.

    2014-04-24

    Electronic thermal conductivity, κ{sub e}, of suspended graphene is studied for 20KElectrons are assumed to be scattered by impurities, surface roughness, vacancies, inelastic optical phonons and in-plane and flexural acoustic phonons. Numerical calculations of κ{sub e}, as a function of temperature, are presented. At lower temperatures, κ{sub e}, is found to be determined mainly by vacancy (T<50K) and impurity (T<150K) scatterings. Flexural phonons influence κ{sub e} for T > 100K, becoming dominant for T > 250K. Good agreement with recent experimental data is obtained.

  16. Gigahertz-band electronically scanned antennas

    NASA Astrophysics Data System (ADS)

    Bei, Nikolai A.

    2000-12-01

    Foundation and principles of radio lenses construction of centimeter and millimeter wave ranges with controlled refracting index, combining the quality of phased array antennas with optical devices are stated. Possibilities of the electronically scanning with wide-angle sector and high gain are maintained. Construction principles of scanning antennas with controlled lenses, combining the quality of phased array antennas with optical devices, are stated. Possibilities of electronically scanning with broad angle sector and high gain are maintained. Some examples of construction of antennas millimeter range of waves are listed here.

  17. Multiple Converged Conduction Bands in K2Bi8Se13: A Promising Thermoelectric Material with Extremely Low Thermal Conductivity.

    PubMed

    Pei, Yanling; Chang, Cheng; Wang, Zhe; Yin, Meijie; Wu, Minghui; Tan, Gangjian; Wu, Haijun; Chen, Yuexing; Zheng, Lei; Gong, Shengkai; Zhu, Tiejun; Zhao, Xinbing; Huang, Li; He, Jiaqing; Kanatzidis, Mercouri G; Zhao, Li-Dong

    2016-12-21

    We report that K2Bi8Se13 exhibits multiple conduction bands that lie close in energy and can be activated through doping, leading to a highly enhanced Seebeck coefficient and a high power factor with elevated temperature. Meanwhile, the large unit cell, complex low symmetry crystal structure, and nondirectional bonding lead to the very low lattice thermal conductivity of K2Bi8Se13, ranging between 0.42 and 0.20 W m(-1) K(-1) in the temperature interval 300-873 K. Experimentally, we further support the low thermal conductivity of K2Bi8Se13 using phonon velocity measurements; the results show a low average phonon velocity (1605 ms(-1)), small Young's modulus (37.1 GPa), large Grüneisen parameter (1.71), and low Debye temperature (154 K). A detailed investigation of the microstructure and defects was carried out using electron diffraction and transmission microscopy which reveal the presence of a K2.5Bi8.5Se14 minor phase intergrown along the side of the K2Bi8Se13 phase. The combination of enhanced power factor and low thermal conductivity results in a high ZT value of ∼1.3 at 873 K in electron doped K2Bi8Se13 material.

  18. Determination of the first satellite valley energy in the conduction band of wurtzite GaN by near-band-gap photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Piccardo, Marco; Martinelli, Lucio; Iveland, Justin; Young, Nathan; DenBaars, Steven P.; Nakamura, Shuji; Speck, James S.; Weisbuch, Claude; Peretti, Jacques

    2014-06-01

    The position of the first satellite valley in wurtzite GaN is directly determined by near-band-gap photoemission spectroscopy of p-doped GaN activated to negative electron affinity. The photoemission spectra exhibit two structures, with fixed energy position, which originate from electrons accumulated in the conduction band valleys of the bulk material. We assigned the two observed features respectively to Γ and L valleys and obtain an intervalley energy separation of 0.90±0.08 eV, well below the theoretical values of the lowest subsidiary valley energy provided by ab initio calculations.

  19. Shape of impurity electronic absorption bands in nematic liquid crystal

    SciTech Connect

    Aver`yanov, E.M.

    1994-11-01

    The impurity-matrix anisotropic static intermolecular interactions, orientation-statistical properties, and electronic structure of uniaxial impurity molecules are shown to have a significant influence on spectral moments of the electronic absorption bands of impurities in the nematic liquid crystal. 14 refs., 3 figs.

  20. Model development for MODIS thermal band electronic cross-talk

    NASA Astrophysics Data System (ADS)

    Chang, Tiejun; Wu, Aisheng; Geng, Xu; Li, Yonghong; Brinkmann, Jake; Keller, Graziela; Xiong, Xiaoxiong (Jack)

    2016-10-01

    MODerate-resolution Imaging Spectroradiometer (MODIS) has 36 bands. Among them, 16 thermal emissive bands covering a wavelength range from 3.8 to 14.4 μm. After 16 years on-orbit operation, the electronic crosstalk of a few Terra MODIS thermal emissive bands develop substantial issues which cause biases in the EV brightness temperature measurements and surface feature contamination. The crosstalk effects on band 27 with center wavelength at 6.7 μm and band 29 at 8.5 μm increased significantly in recent years, affecting downstream products such as water vapor and cloud mask. The crosstalk issue can be observed from nearly monthly scheduled lunar measurements, from which the crosstalk coefficients can be derived. Most of MODIS thermal bands are saturated at moon surface temperatures and the development of an alternative approach is very helpful for verification. In this work, a physical model was developed to assess the crosstalk impact on calibration as well as in Earth view brightness temperature retrieval. This model was applied to Terra MODIS band 29 empirically for correction of Earth brightness temperature measurements. In the model development, the detector nonlinear response is considered. The impacts of the electronic crosstalk are assessed in two steps. The first step consists of determining the impact on calibration using the on-board blackbody (BB). Due to the detector nonlinear response and large background signal, both linear and nonlinear coefficients are affected by the crosstalk from sending bands. The crosstalk impact on calibration coefficients was calculated. The second step is to calculate the effects on the Earth view brightness temperature retrieval. The effects include those from affected calibration coefficients and the contamination of Earth view measurements. This model links the measurement bias with crosstalk coefficients, detector nonlinearity, and the ratio of Earth measurements between the sending and receiving bands. The correction

  1. Effects of Conductor Expressivity on Secondary School Band Members' Performance and Attitudes toward Conducting

    ERIC Educational Resources Information Center

    Silvey, Brian A.; Koerner, Bryan D.

    2016-01-01

    We investigated the effects of expressive and unexpressive conducting on secondary school band members' and experts' audio evaluations of band performance expressivity. A conductor, who demonstrated either expressive or unexpressive conducting techniques, led both an eighth-grade and a high school band in four separate "run-throughs" of…

  2. Terra MODIS Band 27 Electronic Crosstalk Effect and Its Removal

    NASA Technical Reports Server (NTRS)

    Sun, Junqiang; Xiong, Xiaoxiong; Madhavan, Sriharsha; Wenny, Brian

    2012-01-01

    The MODerate-resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the NASA Earth Observing System (EOS). The first MODIS instrument was launched in December, 1999 on-board the Terra spacecraft. MODIS has 36 bands, covering a wavelength range from 0.4 micron to 14.4 micron. MODIS band 27 (6.72 micron) is a water vapor band, which is designed to be insensitive to Earth surface features. In recent Earth View (EV) images of Terra band 27, surface feature contamination is clearly seen and striping has become very pronounced. In this paper, it is shown that band 27 is impacted by electronic crosstalk from bands 28-30. An algorithm using a linear approximation is developed to correct the crosstalk effect. The crosstalk coefficients are derived from Terra MODIS lunar observations. They show that the crosstalk is strongly detector dependent and the crosstalk pattern has changed dramatically since launch. The crosstalk contributions are positive to the instrument response of band 27 early in the mission but became negative and much larger in magnitude at later stages of the mission for most detectors of the band. The algorithm is applied to both Black Body (BB) calibration and MODIS L1B products. With the crosstalk effect removed, the calibration coefficients of Terra MODIS band 27 derived from the BB show that the detector differences become smaller. With the algorithm applied to MODIS L1B products, the Earth surface features are significantly removed and the striping is substantially reduced in the images of the band. The approach developed in this report for removal of the electronic crosstalk effect can be applied to other MODIS bands if similar crosstalk behaviors occur.

  3. High Thermal Conductivity Graphite Electronic Components

    NASA Astrophysics Data System (ADS)

    Peck, S. O.; Young, G. L.; Mellberg, W. J.; Wellman, A. F.; Cooney, J. E.

    1996-08-01

    This project will apply high thermal conductivity graphite to three major spacecraft electronic components: (1) the thermal plane of a printed wiring board, (2) the subassembly or tray that holds the board, and (3) the equipment panel that the tray mounts on. The complete heat transfer path from chip level heat source to radiative rejection on the exterior surface of the equipment panel will therefore be addressed. Thermal and structural requirements representative of current spacecraft will drive an optimized solution strategy. The project will be completed by fabricating the three prototypical test articles and measuring their performance in a representative space environment.

  4. Electronic Band Structure and Sub-band-gap Absorption of Nitrogen Hyperdoped Silicon.

    PubMed

    Zhu, Zhen; Shao, Hezhu; Dong, Xiao; Li, Ning; Ning, Bo-Yuan; Ning, Xi-Jing; Zhao, Li; Zhuang, Jun

    2015-05-27

    We investigated the atomic geometry, electronic band structure, and optical absorption of nitrogen hyperdoped silicon based on first-principles calculations. The results show that all the paired nitrogen defects we studied do not introduce intermediate band, while most of single nitrogen defects can introduce intermediate band in the gap. Considering the stability of the single defects and the rapid resolidification following the laser melting process in our sample preparation method, we conclude that the substitutional nitrogen defect, whose fraction was tiny and could be neglected before, should have considerable fraction in the hyperdoped silicon and results in the visible sub-band-gap absorption as observed in the experiment. Furthermore, our calculations show that the substitutional nitrogen defect has good stability, which could be one of the reasons why the sub-band-gap absorptance remains almost unchanged after annealing.

  5. Conduction Band Offset and Polarization Effects in InAs Nanowire Polytype Junctions.

    PubMed

    Chen, I-Ju; Lehmann, Sebastian; Nilsson, Malin; Kivisaari, Pyry; Linke, Heiner; Dick, Kimberly A; Thelander, Claes

    2017-02-08

    Although zinc-blende (ZB) and wurtzite (WZ) structures differ only in the atomic stacking sequence, mixing of crystal phases can strongly affect the electronic properties, a problem particularly common to bottom up-grown nanostructures. A lack of understanding of the nature of electronic transport at crystal phase junctions thus severely limits our ability to develop functional nanowire devices. In this work we investigated electron transport in InAs nanowires with designed mixing of crystal structures, ZB/WZ/ZB, by temperature-dependent electrical measurements. The WZ inclusion gives rise to an energy barrier in the conduction band. Interpreting the experimental result in terms of thermionic emission and using a drift-diffusion model, we extracted values for the WZ/ZB band offset, 135 ± 10 meV, and interface sheet polarization charge density on the order of 10(-3) C/m(2). The extracted polarization charge density is 1-2 orders of magnitude smaller than previous experimental results, but in good agreement with first principle calculation of spontaneous polarization in WZ InAs. When the WZ length is reduced below 20 nm, an effective barrier lowering is observed, indicating the increasing importance of tunneling transport. Finally, we found that band-bending at ZB/WZ junctions can lead to bound electron states within an enclosed WZ segment of sufficient length, evidenced by our observation of Coulomb blockade at low temperature. These findings provide critical input for modeling and designing the electronic properties of novel functional devices, such as nanowire transistors, where crystal polytypes are commonly found.

  6. Electronic valence bands in decagonal Al-Ni-Co

    NASA Astrophysics Data System (ADS)

    Theis, W.; Rotenberg, Eli; Franke, K. J.; Gille, P.; Horn, K.

    2003-09-01

    Valence-band photoemission from the s-p region of the tenfold and the two inequivalent twofold surfaces of quasicrystalline decagonal Al71.8Ni14.8Co13.4 reveals strongly dispersing bands. These exhibit a free-electron-like dispersion along quasiperiodic and periodic directions of the decagonal quasicrystal. The experimental photoemission maps are reproduced in detail by a model in which parabolic bands emanate from a set of reciprocal lattice vectors. A parity rule for the principal zone centers is observed.

  7. Effects of Conducting Plane on Band and Choral Musicians' Perceptions of Conductor and Ensemble Expressivity

    ERIC Educational Resources Information Center

    Silvey, Brian A.; Fisher, Ryan A.

    2015-01-01

    The purpose of this study was to examine whether one aspect of conducting technique, the conducting plane, would affect band and/or choral musicians' perceptions of conductor and ensemble expressivity. A band and a choral conductor were each videotaped conducting 1-min excerpts from Morten Lauridsen's "O Magnum Mysterium" while using a…

  8. Spin-resolved conductance of Dirac electrons through multibarrier arrays

    NASA Astrophysics Data System (ADS)

    Dahal, Dipendra; Gumbs, Godfrey; Iurov, Andrii

    We use a transfer matrix method to calculate the transmission coefficient of Dirac electrons through an arbitrary number of square potential barrier in gapped monolayer graphene(MLG) and bilayer graphene (BLG). The widths of barriers may not be chosen equal. The shift in the angle of incidence and the width of the barrier required for resonance are investigated numerically for both MLG and BLG. We compare the effects due to energy gap on these two transmission coefficient for each of these two structures (MLG and BLG). We present our results as functions of barrier width, height as well as incoming electron energy as well as band gap and examine the conditions for which perfect reflection or transmission occurs. Our transmission data are further used to calculate conductivity.

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

    SciTech Connect

    Dong, Juan; Shi, Jiangjian; Li, Dongmei; Luo, Yanhong; Meng, Qingbo

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

    SciTech Connect

    Keleş, Ümit; Çakan, Aslı; Bulutay, Ceyhun

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  12. XANES: observation of quantum confinement in the conduction band of colloidal PbS quantum dots

    NASA Astrophysics Data System (ADS)

    Demchenko, I. N.; Chernyshova, M.; He, X.; Minikayev, R.; Syryanyy, Y.; Derkachova, A.; Derkachov, G.; Stolte, W. C.; Piskorska-Hommel, E.; Reszka, A.; Liang, H.

    2013-04-01

    The presented investigations aimed at development of inexpensive method for synthesized materials suitable for utilization of solar energy. This important issue was addressed by focusing, mainly, on electronic local structure studies with supporting x-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis of colloidal galena nano-particles (NPs) and quantum dots (QDs) synthesized using wet chemistry under microwave irradiation. Performed x-ray absorption near edge structure (XANES) analysis revealed an evidence of quantum confinement for the sample with QDs, where the bottom of the conduction band was shifted to higher energy. The QDs were found to be passivated with oxides at the surface. Existence of sulfate/sulfite and thiosulfate species in pure PbS and QDs, respectively, was identified.

  13. Engineering flat electronic bands in quasiperiodic and fractal loop geometries

    NASA Astrophysics Data System (ADS)

    Nandy, Atanu; Chakrabarti, Arunava

    2015-11-01

    Exact construction of one electron eigenstates with flat, non-dispersive bands, and localized over clusters of various sizes is reported for a class of quasi-one-dimensional looped networks. Quasiperiodic Fibonacci and Berker fractal geometries are embedded in the arms of the loop threaded by a uniform magnetic flux. We work out an analytical scheme to unravel the localized single particle states pinned at various atomic sites or over clusters of them. The magnetic field is varied to control, in a subtle way, the extent of localization and the location of the flat band states in energy space. In addition to this we show that an appropriate tuning of the field can lead to a re-entrant behavior of the effective mass of the electron in a band, with a periodic flip in its sign.

  14. Formation of a protected sub-band for conduction in quantum point contacts under extreme biasing.

    PubMed

    Lee, J; Han, J E; Xiao, S; Song, J; Reno, J L; Bird, J P

    2014-02-01

    Managing energy dissipation is critical to the scaling of current microelectronics and to the development of novel devices that use quantum coherence to achieve enhanced functionality. To this end, strategies are needed to tailor the electron-phonon interaction, which is the dominant mechanism for cooling non-equilibrium ('hot') carriers. In experiments aimed at controlling the quantum state, this interaction causes decoherence that fundamentally disrupts device operation. Here, we show a contrasting behaviour, in which strong electron-phonon scattering can instead be used to generate a robust mode for electrical conduction in GaAs quantum point contacts, driven into extreme non-equilibrium by nanosecond voltage pulses. When the amplitude of these pulses is much larger than all other relevant energy scales, strong electron-phonon scattering induces an attraction between electrons in the quantum-point-contact channel, which leads to the spontaneous formation of a narrow current filament and to a renormalization of the electronic states responsible for transport. The lowest of these states coalesce to form a sub-band separated from all others by an energy gap larger than the source voltage. Evidence for this renormalization is provided by a suppression of heating-related signatures in the transient conductance, which becomes pinned near 2e(2)/h (e, electron charge; h, Planck constant) for a broad range of source and gate voltages. This collective non-equilibrium mode is observed over a wide range of temperature (4.2-300 K) and may provide an effective means to manage electron-phonon scattering in nanoscale devices.

  15. Conductance statistics for the power-law banded random matrix model

    SciTech Connect

    Martinez-Mendoza, A. J.; Mendez-Bermudez, J. A.; Varga, Imre

    2010-12-21

    We study numerically the conductance statistics of the one-dimensional (1D) Anderson model with random long-range hoppings described by the Power-law Banded Random Matrix (PBRM) model. Within a scattering approach to electronic transport, we consider two scattering setups in absence and presence of direct processes: 2M single-mode leads attached to one side and to opposite sides of 1D circular samples. For both setups we show that (i) the probability distribution of the logarithm of the conductance T behaves as w(lnT){proportional_to}T{sup M2/2}, for T<<, for both the critical and the non-critical samples; and (ii) at criticality there is a smooth crossover from localized-like to delocalized-like behavior in the transport properties of the PBRM model by decreasing the fractality of its eigenstates.

  16. Correlation effects and electronic properties of Cr-substituted SZn with an intermediate band.

    PubMed

    Tablero, C

    2005-09-15

    A study using first principles of the electronic properties of S32Zn31Cr, a material derived from the SZn host semiconductor where a Cr atom has been substituted for each of the 32 Zn atoms, is presented. This material has an intermediate band sandwiched between the valence and conduction bands of the host semiconductor, which in a formal band-theoretic picture is metallic because the Fermi energy is located within the impurity band. The potential technological application of these materials is that when they are used to absorb photons in solar cells, the efficiency increases significantly with respect to the host semiconductor. An analysis of the gaps, bandwidths, density of states, total and orbital charges, and electronic density is carried out. The main effects of the local-density approximation with a Hubbard term corrections are an increase in the bandwidth, a modification of the relative composition of the five d and p transition-metal orbitals, and a splitting of the intermediate band. The results demonstrate that the main contribution to the intermediate band is the Cr atom. For values of U greater than 6 eV, where U is the empirical Hubbard term U parameter, this band is unfolded, thus creating two bands, a full one below the Fermi energy and an empty one above it, i.e., a metal-insulator transition.

  17. Electron scattering off the ground-state band and the. gamma. band in sup 150 Nd

    SciTech Connect

    Sandor, R.K.J.; Blok, H.P.; Garg, U.; Girod, M.; Harakeh, M.N.; de Jager, C.W.; de Vries, H. Service de Physique et Techniques Nucleaires, Commissariat a l'Energie Atomique, Bruyeres-le-Chatel, Boite Postale 12, F-91680 Bruyeres-le-Chatel, France Nationaal Instituut voor Kernfysica en Hoge-Energiefysica, sectie K , P.O. Box 4395, 1009AJ Amsterdam, The Netherlands Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556)

    1991-05-01

    Inelastic electron scattering to levels of the ground-state band and the {gamma} band in {sup 150}Nd was studied in a momentum transfer range of 0.5 to 2.8 fm{sup {minus}1}. The extracted transition charge densities were compared to microscopic Hartree-Fock-Boguliubov calculations. The overall agreement between the data and the calculations is good, indicating that the dynamic properties of the rotational collective degrees of freedom in statically deformed nuclei can be well described in this microscopic model.

  18. Electronic transitions in GdN band structure

    SciTech Connect

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

    2014-05-28

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

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

    SciTech Connect

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

    2013-11-04

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

  20. Electron-beam irradiation induced conductivity in ZnS nanowires as revealed by in situ transmission electron microscope

    NASA Astrophysics Data System (ADS)

    Liu, Baodan; Bando, Yoshio; Wang, Mingsheng; Zhi, Chunyi; Fang, Xiaosheng; Tang, Chengchun; Mitome, Masanori; Golberg, Dmitri

    2009-08-01

    Electron transport variations in individual ZnS nanowires synthesized through a chemical vapor deposition process were in situ studied in transmission electron microscope under convergent electron-beam irradiation (EBI). It was found that the transport can dramatically be enhanced using proper irradiation conditions. The conductivity mechanism was revealed based on a detailed study of microstructure and composition evolutions under irradiation. EBI-induced Zn-rich domains' appearance and related O doping were mainly responsible for the conductivity improvements. First-principles theoretical calculations additionally indicated that the generation of midbands within a ZnS band gap might also contribute to the improved conductivity.

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

    PubMed Central

    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 leads to the identification of valence and conduction band spectral features, and allows a precise determination of the position of the band edges, ionization energy and electron affinity of the materials. The comparison reveals an unusually low DOS at the valence band maximum (VBM) of these compounds, which confirms and generalizes previous predictions of strong band dispersion and low DOS at the MAPbI3 VBM. This low DOS calls for special attention when using electron spectroscopy to determine the frontier electronic states of lead halide perovskites. PMID:27364125

  2. Conduction band population in graphene in ultrashort strong laser field: Case of massive Dirac particles

    NASA Astrophysics Data System (ADS)

    Ahmadi, Z.; Goudarzi, H.; Jafari, A.

    2016-05-01

    The Dirac-like quasiparticles in honeycomb graphene lattice are taken to possess a non-zero effective mass. The charge carriers involve to interact with a femtosecond strong laser pulse. Due to the scattering time of electrons in graphene (τ ≈10-100 fs), the one femtosecond optical pulse is used to establish the coherence effect and, consequently, it can be realized to use the time-dependent Schrödinger equation for electron coupled with strong electromagnetic field. Generalized wave vector of relativistic electrons interacting with electric field of laser pulse causes to obtain a time-dependent electric dipole matrix element. Using the coupled differential equations of a two-state system of graphene, the density of probability of population transition between valence (VB) and conduction bands (CB) of gapped graphene is calculated. In particular, the effect of bandgap energy on dipole matrix elements at the Dirac points and resulting CB population (CBP) is investigated. The irreversible electron dynamics is achieved when the optical pulse end. Increasing the energy gap of graphene results in decreasing the maximum CBP.

  3. Discrete Electronic Bands in Semiconductors and Insulators: Potential High-Light-Yield Scintillators

    DOE PAGES

    Shi, Hongliang; Du, Mao-Hua

    2015-05-12

    Bulk semiconductors and insulators typically have continuous valence and conduction bands. In this paper, we show that valence and conduction bands of a multinary semiconductor or insulator can be split to narrow discrete bands separated by large energy gaps. This unique electronic structure is demonstrated by first-principles calculations in several quaternary elpasolite compounds, i.e., Cs2NaInBr6, Cs2NaBiCl6, and Tl2NaBiCl6. The narrow discrete band structure in these quaternary elpasolites is due to the large electronegativity difference among cations and the large nearest-neighbor distances in cation sublattices. We further use Cs2NaInBr6 as an example to show that the narrow bands can stabilize self-trappedmore » and dopant-bound excitons (in which both the electron and the hole are strongly localized in static positions on adjacent sites) and promote strong exciton emission at room temperature. The discrete band structure should further suppress thermalization of hot carriers and may lead to enhanced impact ionization, which is usually considered inefficient in bulk semiconductors and insulators. Finally, these characteristics can enable efficient room-temperature light emission in low-gap scintillators and may overcome the light-yield bottleneck in current scintillator research.« less

  4. Discrete Electronic Bands in Semiconductors and Insulators: Potential High-Light-Yield Scintillators

    SciTech Connect

    Shi, Hongliang; Du, Mao-Hua

    2015-05-12

    Bulk semiconductors and insulators typically have continuous valence and conduction bands. In this paper, we show that valence and conduction bands of a multinary semiconductor or insulator can be split to narrow discrete bands separated by large energy gaps. This unique electronic structure is demonstrated by first-principles calculations in several quaternary elpasolite compounds, i.e., Cs2NaInBr6, Cs2NaBiCl6, and Tl2NaBiCl6. The narrow discrete band structure in these quaternary elpasolites is due to the large electronegativity difference among cations and the large nearest-neighbor distances in cation sublattices. We further use Cs2NaInBr6 as an example to show that the narrow bands can stabilize self-trapped and dopant-bound excitons (in which both the electron and the hole are strongly localized in static positions on adjacent sites) and promote strong exciton emission at room temperature. The discrete band structure should further suppress thermalization of hot carriers and may lead to enhanced impact ionization, which is usually considered inefficient in bulk semiconductors and insulators. Finally, these characteristics can enable efficient room-temperature light emission in low-gap scintillators and may overcome the light-yield bottleneck in current scintillator research.

  5. Electron and hole photoemission detection for band offset determination of tunnel field-effect transistor heterojunctions

    SciTech Connect

    Li, Wei; Zhang, Qin; Kirillov, Oleg A.; Levin, Igor; Richter, Curt A.; Gundlach, David J.; Nguyen, N. V. E-mail: liangxl@pku.edu.cn; Bijesh, R.; Datta, S.; Liang, Yiran; Peng, Lian-Mao; Liang, Xuelei E-mail: liangxl@pku.edu.cn

    2014-11-24

    We report experimental methods to ascertain a complete energy band alignment of a broken-gap tunnel field-effect transistor based on an InAs/GaSb hetero-junction. By using graphene as an optically transparent electrode, both the electron and hole barrier heights at the InAs/GaSb interface can be quantified. For a Al{sub 2}O{sub 3}/InAs/GaSb layer structure, the barrier height from the top of the InAs and GaSb valence bands to the bottom of the Al{sub 2}O{sub 3} conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of the Al{sub 2}O{sub 3} valence band to the bottom of the InAs and GaSb conduction bands. Subsequently, the offset parameter at the broken gap InAs/GaSb interface is extracted and thus can be used to facilitate the development of predicted models of electron quantum tunneling efficiency and transistor performance.

  6. Ab initio electronic structure and optical conductivity of bismuth tellurohalides

    NASA Astrophysics Data System (ADS)

    Schwalbe, Sebastian; Wirnata, René; Starke, Ronald; Schober, Giulio A. H.; Kortus, Jens

    2016-11-01

    We investigate the electronic structure, dielectric, and optical properties of bismuth tellurohalides BiTe X (X =I , Cl, Br) by means of all-electron density functional theory. In particular, we present the ab initio conductivities and dielectric tensors calculated over a wide frequency range, and compare our results with the recent measurements by Akrap et al. [Phys. Rev. B 90, 035201 (2014), 10.1103/PhysRevB.90.035201], Makhnev et al. [Opt. Spectrosc. 117, 764 (2014), 10.1134/S0030400X14110125], and Rusinov et al. [JETP Lett. 101, 507 (2015), 10.1134/S0021364015080147]. We show how the low-frequency branch of the optical conductivity can be used to identify characteristic intra- and interband transitions between the Rashba spin-split bands in all three bismuth tellurohalides. We further calculate the refractive indices and dielectric constants, which in turn are systematically compared to previous predictions and measurements. We expect that our quantitative analysis will contribute to the general assessment of bulk Rashba materials for their potential use in spintronics devices.

  7. Concerning the Optical Absorption Band of the Hydrated Electron,

    DTIC Science & Technology

    methylene blue ) showed marked nonlinear absorption due to saturation of optical transitions, no such change was observed for hydrated electrons even though the light intensity was varied by > 10 to the 7th power up to 200 photons per hydrated electron per sq cm. Consequently the photoexcited state lifetime is estimated to be than 6 x 10 to the -12th power sec. This finding is discussed briefly in terms of three possible origins for the absorption band, namely that involving excitation to a bound excited state, as a photoionization efficiency profile or as a distribution

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

    SciTech Connect

    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.

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

    SciTech Connect

    Yastrubchak, O.; Gluba, L.; Żuk, J.; Sadowski, J.; Krzyżanowska, H.; Domagala, J. Z.; Andrearczyk, T.; Wosinski, T.

    2013-08-07

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

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

    NASA Astrophysics Data System (ADS)

    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.

  11. Beyond the effective mass approximation: A predictive theory of the nonlinear optical response of conduction electrons

    NASA Astrophysics Data System (ADS)

    Yu, Shukai; Heffernan, Kate H.; Talbayev, Diyar

    2017-03-01

    We present an experimental and computational study of the nonlinear optical response of conduction electrons to intense terahertz (THz) electric field. Our observations (saturable absorption and an amplitude-dependent group refractive index) can be understood on the qualitative level as the breakdown of the effective mass approximation. However, a predictive theoretical description of the nonlinear THz propagation has been missing. We propose a model based on the semiclassical electron dynamics, a realistic band structure, and the free electron Drude parameters to accurately calculate the experimental observables in InSb. Our results open a path to modeling of the conduction-electron optical nonlinearity that governs the THz propagation in semiconductors.

  12. Development of an L-Band RF Electron Gun for SASE in the Infrared Region

    NASA Astrophysics Data System (ADS)

    Kashiwagi, Shigeru; Kato, Ryukou; Isoyama, Goro; Hayano, Hitoshi; Urakawa, Junji

    2010-02-01

    We conduct research on Self-Amplified Spontaneous Emission (SASE) in the infrared region using the 40 MeV, 1.3 GHz L-band linac of Osaka University. The linac equipped with a thermionic electron gun can accelerate a high-intensity single-bunch beam though its normalized emittance is high. In order to advance the research on SASE, we have begun development of an RF gun for the L-band linac in collaboration with KEK. We will report conceptual design of the RF gun and present the status of development of another RF gun for STF at KEK.

  13. Electronic Tongue Containing Redox and Conductivity Sensors

    NASA Technical Reports Server (NTRS)

    Buehler, Martin

    2007-01-01

    The Electronic Tongue (E-tongue 2) is an assembly of sensors for measuring concentrations of metal ions and possibly other contaminants in water. Potential uses for electronic tongues include monitoring the chemical quality of water in a variety of natural, industrial, and laboratory settings, and detecting micro-organisms indirectly by measuring microbially influenced corrosion. The device includes a heater, a temperature sensor, an oxidation/reduction (redox) sensor pair, an electrical sensor, an array of eight galvanic cells, and eight ion-specific electrodes.

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

    NASA Astrophysics Data System (ADS)

    Kishi, Ayaka; Oda, Masato; Shinozuka, Yuzo

    2016-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

  16. Charge transport in gapless electron-hole systems with arbitrary band dispersion

    NASA Astrophysics Data System (ADS)

    Das Sarma, S.; Hwang, E. H.

    2015-05-01

    Using the semiclassical Boltzmann transport theory, we analytically consider dc charge transport in gapless electron-hole (both chiral and nonchiral) systems in the presence of resistive scattering due to static disorder arising from random quenched impurities in the background. We obtain the dependence of the Boltzmann conductivity on carrier density and temperature for arbitrary band dispersion in arbitrary dimensionality assuming long-range (˜1 /r ) Coulomb disorder and zero-range white-noise disorder [˜δ (r ) ]. We establish that the temperature and the density dependence of the Boltzmann conductivity manifests scaling behaviors determining, respectively, the intrinsic semimetallic or the extrinsic metallic property of the gapless system. Our results apply equally well to both chiral and nonchiral gapless systems, and provide a qualitative understanding of the dependence of the Boltzmann conductivity on the band dispersion in arbitrary dimensionality.

  17. Quantum Ising model coupled with conducting electrons

    NASA Astrophysics Data System (ADS)

    Yamashita, Yasufumi; Yonemitsu, Kenji

    2005-01-01

    The effect of photo-doping on the quantum paraelectric SrTiO3 is studied by using the one-dimensional quantum Ising model, where the Ising spin describes the effective lattice polarization of an optical phonon. Two types of electron-phonon couplings are introduced through the modulation of transfer integral via lattice deformations. After the exact diagonalization and the perturbation studies, we find that photo-induced low-density carriers can drastically alter quantum fluctuations when the system locates near the quantum critical point between the quantum para- and ferro-electric phases.

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

    SciTech Connect

    Shi, Zhong; Jiang, Hang-Yu; Zhou, Shi-Ming; Hou, Yan-Liang; Ye, Quan-Lin; Su Si, Ming

    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.

  19. Bacteriorhodopsin as an electronic conduction medium for biomolecular electronics.

    PubMed

    Jin, Yongdong; Honig, Tal; Ron, Izhar; Friedman, Noga; Sheves, Mordechai; Cahen, David

    2008-11-01

    Interfacing functional proteins with solid supports for device applications is a promising route to possible applications in bio-electronics, -sensors, and -optics. Various possible applications of bacteriorhodopsin (bR) have been explored and reviewed since the discovery of bR. This tutorial review discusses bR as a medium for biomolecular optoelectronics, emphasizing ways in which it can be interfaced, especially as a thin film, solid-state current-carrying electronic element.

  20. Origins of electronic band gap reduction in Cr/N codoped TiO2.

    PubMed

    Parks Cheney, C; Vilmercati, P; Martin, E W; Chiodi, M; Gavioli, L; Regmi, M; Eres, G; Callcott, T A; Weitering, H H; Mannella, N

    2014-01-24

    Recent studies indicated that noncompensated cation-anion codoping of wide-band-gap oxide semiconductors such as anatase TiO2 significantly reduces the optical band gap and thus strongly enhances the absorption of visible light [W. Zhu et al., Phys. Rev. Lett. 103, 226401 (2009)]. We used soft x-ray spectroscopy to fully determine the location and nature of the impurity levels responsible for the extraordinarily large (∼1 eV) band gap reduction of noncompensated codoped rutile TiO2. It is shown that Cr/N codoping strongly enhances the substitutional N content, compared to single element doping. The band gap reduction is due to the formation of Cr 3d3 levels in the lower half of the gap while the conduction band minimum is comprised of localized Cr 3d and delocalized N 2p states. Band gap reduction and carrier delocalization are critical elements for efficient light-to-current conversion in oxide semiconductors. These findings thus raise the prospect of using codoped oxide semiconductors with specifically engineered electronic properties in a variety of photovoltaic and photocatalytic applications.

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

    SciTech Connect

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

    2009-07-15

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

  2. Affordable, Lightweight, Highly Conductive Polymer Composite Electronic Packaging Structures

    DTIC Science & Technology

    1996-06-01

    matrix composite materials and how various material designs can be utilized in various structural/thermal configurations to produce electronic housings and...conductive polymer composite electronic packaging (i.e., electronic housings and heat sinks). The research will center on predominately polymer

  3. Thermal conduction by electrons in hot dense plasmas

    SciTech Connect

    Khalfaoui, A.H.; Bennaceur, D.

    1997-03-01

    Based on a quantum collective approach, electron conduction opacity is analyzed, taking into account several nonideality effects such as electron-electron (e-e) collisions in addition to electron-ion collisions, dynamic shielding, electron partial degeneracy, and ion coupling. The collision process is based on electron wave functions interacting with the continuum oscillations (plasma waves). The e-e collisions, the main nonideal effect, contribute to the thermal conductivity calculation in the intermediate coupling regime. Hence, the extensively used Lorentz gas approximation cannot be justified for plasma of astrophysical interest. The present results are compared to existing theories of electron conduction in stellar matter. {copyright} {ital 1997} {ital The American Astronomical Society}

  4. Global Kinetic Modeling of Banded Electron Structures in the Plasmasphere

    NASA Technical Reports Server (NTRS)

    Liemohn, M. W.; Khazanov, G. V.

    1997-01-01

    Significant fluxes of 10 eV to 30 keV electrons have been detected in the plasmasphere, appearing as banded structures in energy with broad spatial extents and slowly evolving over several days. It is thought that these populations are decaying plasma sheet electrons injected into the corotating region of near-Earth space. This capture can occur when the convective electric field drops rapidly and the Alfven boundary suddenly outward, trapping the inner edge of the plasma sheet along closed drift paths. Our bounce-averaged kinetic model of superthermal electron transport is able to simulate this capture and the subsequent drift, diffusion, and decay of the plasma cloud. Results of this simulation will be shown and discussed, from the initial injection during the elevated convection to the final loss of the particles. It is thought that not only Coulomb collisions but also wave-particle interactions play a significant role in altering the plasma cloud. Quasilinear diffusion is currently being incorporated into the model and the importance of this mechanism will be examined. Also, the high anisotropy of the trapped population could be unstable and generate plasma waves. These and other processes will be investigated to determine the final fate of the cloud and to quantify where, how, and when the energy of the plasma cloud is deposited. Comparisons with CRRES observations of these events are shown to verify the model and explain the data.

  5. Theory of Auger-electron and appearance-potential spectroscopy for interacting valence-band electrons

    NASA Astrophysics Data System (ADS)

    Nolting, W.; Geipel, G.; Ertl, K.

    1991-12-01

    A theory of Auger-electron spectroscopy (AES) and appearance-potential spectroscopy (APS) is presented for interacting electrons in a nondegenerate energy band, described within the framework of the Hubbard model. Both types of spectroscopy are based on the same two-particle spectral density. A diagrammatic vertex-correction method (Matsubara formalism) is used to express this function in terms of the one-particle spectral density. The latter is approximately determined for arbitrary temperature T, arbitrary coupling strength U/W (U, the intra-atomic Coulomb matrix element; W, the width of the ``free'' Bloch band), and arbitrary band occupations n (0<=n<=2 average number of band electrons per site) by a self-consistent moment method. In weakly coupled systems the electron correlations give rise to certain deformations of the quasiparticle density of states (QDOS) in relation to the Bloch density of states (BDOS), where, however, spontaneous magnetic order is excluded, irrespective of the band filling n. The AE (AP) spectra consist of only one structure a few eV wide (``bandlike'') which is strongly n dependent, but only slightly T dependent, being rather well approximated by a simple self-convolution of the occupied (unoccupied) QDOS. For strongly correlated electrons the Bloch band splits into two quasiparticle subbands. This leads for n<1 to one line in the AE spectrum and three lines in the AP spectrum, and vice versa for n>1. For sufficiently strong correlations U/W additional satellites appear that refer to situations where the two excited quasiparticles (quasiholes) propagate as tightly bound pairs through the lattice without being scattered by other charge carriers. As soon as the satellite splits off from the bandlike part of the spectrum, it takes almost the full spectral weight, conveying the impression of an ``atomiclike'' AE (AP) line shape. The satellite has almost exactly the structure of the free BDOS. If the particle density n as well as the hole

  6. Quantal Heating of Conducting Electrons with Discrete Spectrum

    SciTech Connect

    Vitkalov, S. A.; Bykov, A. A.

    2011-12-23

    Usually heating of conducting electrons by dc electric field results in an increase of electron temperature. In this paper we show that the dc heating of 2D electrons, placed in quantized magnetic fields, results in a peculiar electron distribution, which has the same broadening or an effective 'temperature' as the unbiased electron system. The quantal heating, however, violates strongly the Ohm's Law. In the conducting system with discrete electron spectrum the quantal heating results in spectacular decrease of electron resistance and transition of the electrons into a state with zero differential resistance (ZDR). Finally the heating leads to apparent dc driven metal-insulator transition, which correlates with the transition into the ZDR state. The correlation is very unexpected and is not understood.

  7. Sensory properties of oxide films with high concentrations of conduction electrons

    NASA Astrophysics Data System (ADS)

    Kozhushner, M. A.; Bodneva, V. L.; Belysheva, T. V.; Gerasimov, G. N.; Gromov, V. F.; Ikim, M. I.; Paltiel, Y.; Spiridonova, E. Yu.; Trakhtenberg, L. I.

    2017-03-01

    The dependence of a sensor's response to hydrogen on the temperature and hydrogen pressure in an indium oxide nanostructured film is measured. A theory of sensor's response to reducing gases in nanostructured semiconducting oxides with high concentrations of electrons in the conduction band is developed (using the example of In2O3). It is shown that the capture of conduction electrons by adsorbed oxygen redistributes the electrons in nanoparticles and reduces the surface electron density and the conductivity of a system; the conductivity is proportional to the electron density in nanoparticle contacts, i.e., to the surface electron density. It is found that atomic oxygen ions react with reducing gases (H2, CO) during adsorption of the latter: electrons are released and enter the volumes of nanoparticles; the conductivity of the system grows, creating the sensory effect. Using a model developed earlier to describe the distribution of conduction electrons in a semiconductor nanoparticle, a kinetic scheme corresponding to the above scenario is built and corresponding equations are solved. As a result, a theoretical dependence of a sensor's sensitivity to temperature is found that describes the experimental data well.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  10. Organic photovoltaic cell incorporating electron conducting exciton blocking layers

    SciTech Connect

    Forrest, Stephen R.; Lassiter, Brian E.

    2014-08-26

    The present disclosure relates to photosensitive optoelectronic devices including a compound blocking layer located between an acceptor material and a cathode, the compound blocking layer including: at least one electron conducting material, and at least one wide-gap electron conducting exciton blocking layer. For example, 3,4,9,10 perylenetetracarboxylic bisbenzimidazole (PTCBI) and 1,4,5,8-napthalene-tetracarboxylic-dianhydride (NTCDA) function as electron conducting and exciton blocking layers when interposed between the acceptor layer and cathode. Both materials serve as efficient electron conductors, leading to a fill factor as high as 0.70. By using an NTCDA/PTCBI compound blocking layer structure increased power conversion efficiency is achieved, compared to an analogous device using a conventional blocking layers shown to conduct electrons via damage-induced midgap states.

  11. Toxicity of metal oxide nanoparticles in Escherichia coli correlates with conduction band and hydration energies.

    PubMed

    Kaweeteerawat, Chitrada; Ivask, Angela; Liu, Rong; Zhang, Haiyuan; Chang, Chong Hyun; Low-Kam, Cecile; Fischer, Heidi; Ji, Zhaoxia; Pokhrel, Suman; Cohen, Yoram; Telesca, Donatello; Zink, Jeffrey; Mädler, Lutz; Holden, Patricia A; Nel, Andre; Godwin, Hilary

    2015-01-20

    Metal oxide nanoparticles (MOx NPs) are used for a host of applications, such as electronics, cosmetics, construction, and medicine, and as a result, the safety of these materials to humans and the environment is of considerable interest. A prior study of 24 MOx NPs in mammalian cells revealed that some of these materials show hazard potential. Here, we report the growth inhibitory effects of the same series of MOx NPs in the bacterium Escherichia coli and show that toxicity trends observed in E. coli parallel those seen previously in mammalian cells. Of the 24 materials studied, only ZnO, CuO, CoO, Mn2O3, Co3O4, Ni2O3, and Cr2O3 were found to exert significant growth inhibitory effects; these effects were found to relate to membrane damage and oxidative stress responses in minimal trophic media. A correlation of the toxicological data with physicochemical parameters of MOx NPs revealed that the probability of a MOx NP being toxic increases as the hydration enthalpy becomes less negative and as the conduction band energy approaches those of biological molecules. These observations are consistent with prior results observed in mammalian cells, revealing that mechanisms of toxicity of MOx NPs are consistent across two very different taxa. These results suggest that studying nanotoxicity in E. coli may help to predict toxicity patterns in higher organisms.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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 straightforwardly adapted to waveguide geometries others than the periodically-loaded waveguide considered here since DBE is a general property that can be realized in a variety of structures.

  15. Post-precipitation bias in band-tailed pigeon surveys conducted at mineral sites

    USGS Publications Warehouse

    Overton, C.T.; Schmitz, R.A.; Casazza, M.L.

    2005-01-01

    Many animal surveys to estimate populations or index trends include protocol prohibiting counts during rain but fail to address effects of rainfall preceding the count. Prior research on Pacific Coast band-tailed pigeons (Patagioenas fasciata monilis) documented declines in use of mineral sites during rainfall. We hypothesized that prior precipitation was associated with a short-term increase in use of mineral sites following rain. We conducted weekly counts of band-tailed pigeons at 19 Pacific Northwest mineral sites in 2001 and 20 sites in 2002. Results from regression analysis indicated higher counts ???2 days after rain (11.31??5.00% [x????SE]) compared to ???3 days. Individual index counts conducted ???2 days after rain were biased high, resulting in reduced ability to accurately estimate population trends. Models of band-tailed pigeon visitation rates throughout the summer showed increased mineral-site counts during both June and August migration periods, relative to the July breeding period. Our research supported previous studies recommending that mineral-site counts used to index the band-tailed pigeon population be conducted during July. We further recommend conducting counts >3 days after rain to avoid weather-related bias in index estimation. The design of other population sampling strategies that rely on annual counts should consider the influence of aberrant weather not only coincident with but also preceding surveys if weather patterns are thought to influence behavior or detection probability of target species.

  16. Method of forming electronically conducting polymers on conducting and nonconducting substrates

    NASA Technical Reports Server (NTRS)

    Murphy, Oliver J. (Inventor); Hitchens, G. Duncan (Inventor); Hodko, Dalibor (Inventor); Clarke, Eric T. (Inventor); Miller, David L. (Inventor); Parker, Donald L. (Inventor)

    2001-01-01

    The present invention provides electronically conducting polymer films formed from photosensitive formulations of pyrrole and an electron acceptor that have been selectively exposed to UV light, laser light, or electron beams. The formulations may include photoinitiators, flexibilizers, solvents and the like. These solutions can be used in applications including printed circuit boards and through-hole plating and enable direct metallization processes on non-conducting substrates. After forming the conductive polymer patterns, a printed wiring board can be formed by sensitizing the polymer with palladium and electrolytically depositing copper.

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

    SciTech Connect

    Jones, E.D.; Reno, J.L.; Kotera, Nobuo; Wang, Y.

    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.

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

    DTIC Science & Technology

    2016-01-26

    AFRL-RV-PS- AFRL-RV-PS- TR-2016-0003 TR-2016-0003 EXPERIMENTAL STUDY OF ELECTRONIC QUANTUM INTERFERENCE, PHOTONIC CRYSTAL CAVITY, PHOTONIC BAND...2014 – 11 Jan 2016 4. TITLE AND SUBTITLE Experimental Study of Electronic Quantum Interference, Photonic Crystal Cavity, Photonic Band Edge Effects...tailoring of dispersion and the photonic band gap. The band gap frequency can be matched to tailor the emission from active medium such as quantum

  19. Conduction and Charge Storage in Electron Irradiated Spacecraft Insulators

    DTIC Science & Technology

    1981-07-01

    RADC-TR-8 I1- 98 Final Technical Report July 1981 ’ CONDUCTION AND CHARGE STORAGE SIN ELECTRON IRRADIATED SPACECRAFT INSULATORS IRT Corporation J...some of the parameters which control th’- deposition and transport of keV electrons in representative spacecraft insulators found on the surface of...of the charge deposition centroid, dark, radiation, delayed and surface conductivities. These parameters were then used in a phenomenological

  20. Conduction electron spin resonance in Mg 1 - x Al x B2

    NASA Astrophysics Data System (ADS)

    Likodimos, V.; Koutandos, S.; Pissas, M.; Papavassiliou, G.; Prassides, K.

    2003-01-01

    Conduction electron spin resonance is employed to study the interplay of the electronic and structural properties in the normal state of Mg 1 - x Al x B2 alloys as a function of Al-doping for 0 <= x <= 1. The x-dependence of the spin susceptibility reveals considerable reduction of the total density of states N(EF) with increasing Al concentration, complying with theoretical predictions for a predominant filling effect of the hole σ bands by electron doping. The CESR linewidth exhibits significant broadening, especially prominent in the high-Al-content region, indicative of the presence of enhanced structural disorder, consistent with the presence of compositional fluctuations.

  1. New four-band electrode fabrication to measure in situ electrical property of conducting polymers.

    PubMed

    Xue, Wenbin; Jiang, Xiaoqing; Harima, Yutaka

    2009-03-15

    A simple and renewable four-band platinum electrode for in situ conductivity measurement of polymers is described. A model is developed to evaluate contact resistance between the electrode and polyaniline film and calibrate the film resistances obtained by two-probe and four-probe methods. The conductivity of the film is calculated from the calibrated resistance. By comparing the effects of band thickness, gap width, and film thickness, it is found that the ratio K of the middle gap width to the thickness of the internal two platinum bands is the most important parameter to characterize one four-band electrode. An ideal four-band electrode should have large K and wide middle gap as possible so long as the film can uniformly cover the electrode. Under this case, the influence of contact resistance on the four-probe measurement of film resistance is negligible. It is shown that contact resistance depends on the oxidation state of the film. It rises nonlinearly with increasing film resistance.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    Rangel-Kuoppa, Victor-Tapio

    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.

  4. Electronic crosstalk in Terra MODIS thermal emissive bands

    NASA Astrophysics Data System (ADS)

    Sun, Junqiang; Madhavan, Sriharsha; Xiong, Xiaoxiong; Wang, Menghua

    2015-09-01

    The MODerate-resolution Imaging Spectroradiometer (MODIS) is a legacy Earth remote sensing instrument in the National Aeronautics and Space Administration (NASA) Earth Observing System (EOS). The first MODIS instrument was launched in December 1999 on board the Terra spacecraft. MODIS has 36 bands, among which bands 20-25 and bands 27-36 are thermal emissive bands covering a wavelength range from 3.7μm to 14.2μm. It has been found that there are severe contaminations in Terra bands 27-30 (6.7 μm - 9.73 μm) due to crosstalk of signals among themselves. The crosstalk effect induces strong striping artifacts in the Earth View (EV) images and causes large long-term drifts in the EV brightness temperature (BT) in these bands. An algorithm using a linear approximation derived from on-orbit lunar observations has been developed to correct the crosstalk effect for them. It was demonstrated that the crosstalk correction can substantially reduce the striping noise in the EV images and significantly remove the long-term drifts in the EV BT in the Long Wave InfraRed (LWIR) water vapor channels (bands 27-28). In this paper, the crosstalk correction algorithm previously developed is applied to correct the crosstalk effect in the remaining LWIR bands 29 and 30. The crosstalk correction successfully reduces the striping artifact in the EV images and removes long-term drifts in the EV BT in bands 29-30 as was done similarly for bands 27-28. The crosstalk correction algorithm can thus substantially improve both the image quality and the radiometric accuracy of the Level 1B (L1B) products of the LWIR PV bands, bands 27-30. From this study it is also understood that other Terra MODIS thermal emissive bands are contaminated by the crosstalk effect and that the algorithm can be applied to these bands for crosstalk correction.

  5. Electronic Power Conditioner for Ku-band Travelling Wave Tube

    NASA Astrophysics Data System (ADS)

    Kowstubha, Palle; Krishnaveni, K.; Ramesh Reddy, K.

    2016-07-01

    A highly sophisticated regulated power supply is known as electronic power conditioner (EPC) is required to energise travelling wave tubes (TWTs), which are used as RF signal amplifiers in satellite payloads. The assembly consisting of TWT and EPC together is known as travelling wave tube amplifier (TWTA). EPC is used to provide isolated and conditioned voltage rails with tight regulation to various electrodes of TWT and makes its RF performance independent of solar bus variations which are caused due to varying conditions of eclipse and sunlit. The payload mass and their power consumption is mainly due to the existence of TWTAs that represent about 35 % of total mass and about 70-90 % (based on the type of satellite application) of overall dc power consumption. This situation ensures a continuous improvement in the design of TWTAs and their associated EPCs to realize more efficient and light products. Critical technologies involved in EPCs are design and configuration, closed loop regulation, component and material selection, energy limiting of high voltage (HV) outputs and potting of HV card etc. This work addresses some of these critical technologies evolved in realizing and testing the state of art of EPC and it focuses on the design of HV supply with a HV and high power capability, up to 6 kV and 170 WRF, respectively required for a space TWTA. Finally, an experimental prototype of EPC with a dc power of 320 W provides different voltages required by Ku-band TWT in open loop configuration.

  6. Anomalously low electronic thermal conductivity in metallic vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Lee, Sangwook; Hippalgaonkar, Kedar; Yang, Fan; Hong, Jiawang; Ko, Changhyun; Suh, Joonki; Liu, Kai; Wang, Kevin; Urban, Jeffrey J.; Zhang, Xiang; Dames, Chris; Hartnoll, Sean A.; Delaire, Olivier; Wu, Junqiao

    2017-01-01

    In electrically conductive solids, the Wiedemann-Franz law requires the electronic contribution to thermal conductivity to be proportional to electrical conductivity. Violations of the Wiedemann-Franz law are typically an indication of unconventional quasiparticle dynamics, such as inelastic scattering, or hydrodynamic collective motion of charge carriers, typically pronounced only at cryogenic temperatures. We report an order-of-magnitude breakdown of the Wiedemann-Franz law at high temperatures ranging from 240 to 340 kelvin in metallic vanadium dioxide in the vicinity of its metal-insulator transition. Different from previously established mechanisms, the unusually low electronic thermal conductivity is a signature of the absence of quasiparticles in a strongly correlated electron fluid where heat and charge diffuse independently.

  7. Pure-oxygen radiative shocks with electron thermal conduction

    NASA Technical Reports Server (NTRS)

    Borkowski, Kazimierz J.; Shull, J. Michael

    1990-01-01

    Steady state radiative shock models in gas composed entirely of oxygen are calculated with the purpose of explaining observations of fast-moving knots in Cas A and other oxygen-rich SNRs. Models with electron thermal conduction differ significantly from models in which conduction is neglected. Conduction reduces postshock electron temperatures by a factor of 7-10 and flattens temperature gradients. The O III ion, whose forbidden emission usually dominates the observed spectra, is present over a wide range of shock velocities, from 100 to 170 km/s. The electron temperature in the O III forbidden line formation region is 30,000 K, in agreement with the 20,000 K derived from observations. All models with conduction have extensive warm (T above 4000 K) photoionization zones, which provides better agreement with observed optical O I line strengths.

  8. Anomalously low electronic thermal conductivity in metallic vanadium dioxide.

    PubMed

    Lee, Sangwook; Hippalgaonkar, Kedar; Yang, Fan; Hong, Jiawang; Ko, Changhyun; Suh, Joonki; Liu, Kai; Wang, Kevin; Urban, Jeffrey J; Zhang, Xiang; Dames, Chris; Hartnoll, Sean A; Delaire, Olivier; Wu, Junqiao

    2017-01-27

    In electrically conductive solids, the Wiedemann-Franz law requires the electronic contribution to thermal conductivity to be proportional to electrical conductivity. Violations of the Wiedemann-Franz law are typically an indication of unconventional quasiparticle dynamics, such as inelastic scattering, or hydrodynamic collective motion of charge carriers, typically pronounced only at cryogenic temperatures. We report an order-of-magnitude breakdown of the Wiedemann-Franz law at high temperatures ranging from 240 to 340 kelvin in metallic vanadium dioxide in the vicinity of its metal-insulator transition. Different from previously established mechanisms, the unusually low electronic thermal conductivity is a signature of the absence of quasiparticles in a strongly correlated electron fluid where heat and charge diffuse independently.

  9. Indirect Band Gap Emission by Hot Electron Injection in Metal/MoS2 and Metal/WSe2 Heterojunctions

    NASA Astrophysics Data System (ADS)

    Li, Zhen; Ezhilarasu, Goutham; Chatzakis, Ioannis; Dhall, Rohan; Chen, Chun-Chung; Cronin, Stephen

    Transition metal dichalcogenides (TMDCs), such as MoS2 and WSe2, are free of dangling bonds, therefore make more `ideal' Schottky junctions than bulk semiconductors, which produce recombination centers at the interface with metals, inhibiting charge transfer. Here, we observe a more than 10X enhancement in the indirect band gap PL of TMDCs deposited on various metals, while the direct band gap emission remains unchanged. We believe the main mechanism of light emission arises from photoexcited hot electrons in the metal that are injected into the conduction band of MoS2 and WSe2, and subsequently recombine radiatively with minority holes. Since the conduction band at the K-point is 0.5eV higher than at the Σ-point, a lower Schottky barrier of the Σ-point band makes electron injection more favorable. Also, the Σ band consists of the sulfur pz orbital, which overlaps more significantly with the electron wavefunctions in the metal. This enhancement only occurs for thick flakes, and is absent in monolayer and few-layer flakes. Here, the flake thickness must exceed the depletion width of the Schottky junction, in order for efficient radiative recombination to occur in the TMDC. The intensity of this indirect peak decreases at low temperatures. Reference: DOI: 10.1021/acs.nanolett.5b00885

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

    SciTech Connect

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

    2009-08-03

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

  11. Probing the band structure and local electronic properties of low-dimensional semiconductor structures

    NASA Astrophysics Data System (ADS)

    Walrath, Jenna Cherie

    Low-dimensional semiconductor structures are important for a wide variety of applications, and recent advances in nanoscale fabrication are paving the way for increasingly precise nano-engineering of a wide range of materials. It is therefore essential that the physics of materials at the nanoscale are thoroughly understood to unleash the full potential of nanotechnology, requiring the development of increasingly sophisticated instrumentation and modeling. Of particular interest is the relationship between the local density of states (LDOS) of low-dimensional structures and the band structure and local electronic properties. This dissertation presents the investigation of the band structure, LDOS, and local electronic properties of nanostructures ranging from zero-dimensional (0D) quantum dots (QDs) to two-dimensional (2D) thin films, synthesizing computational and experimental approaches including Poisson-Schrodinger band structure calculations, scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and scanning thermoelectric microscopy (SThEM). A method is presented for quantifying the local Seebeck coefficient (S) with SThEM, using a quasi-3D conversion matrix approach to directly convert temperature gradient-induced voltages S. For a GaAs p-n junction, the resulting S-profile is consistent with that computed using the free carrier concentration profile. This combined computational-experimental approach is expected to enable nanoscale measurements of S across a wide variety of heterostructure interfaces. The local carrier concentration, n, is profiled across epitaxial InAs/GaAs QDs, where SThEM is used to profile the temperature gradient-induced voltage, which is converted to a profile of the local S and finally to an n profile. The S profile is converted to a conduction band-edge profile and compared with Poisson-Schrodinger band-edge simulations. The combined computational-experimental approach suggests a reduced n in the QD center in

  12. Longitudinal and transverse vibration control of electronic conductance of a ladder-like graphene nanoribbon

    NASA Astrophysics Data System (ADS)

    Esmaili, Esmat; Mardaani, Mohammad; Rabani, Hassan

    2016-09-01

    The coherent electronic transport in a lengthy narrow nanoribbon, which the atoms of a part of it vibrate in some special modes, is modeled analytically within the tight-binding and harmonic approximations. For the small vibrations, the longitudinal and transverse modes are discussed separately. Two in-plane and one out-of-plane vibrating modes are assumed for the vibratory part which is considered as the center wire. The modes which cause the phononic excitations leading to electron-phonon (e-ph) interaction, are chosen in order to present exact analytic formulation. Moreover, we suppose that the bonds in the benzene rings in the center wire are the same or not the same as the rings in the other parts. We found that in-plane atomic vibrations have greater influence on the conductance with respect to the out-of-plane one. Since two conductance channels contribute in the transport, in the overlapping region of their energy bands, the conductance is affected more by the e-ph interaction. Furthermore, the increase electron scattering originating from decrease of electron group velocity, destroys the conductance at the edges of the system energy band.

  13. Terra MODIS band 27 electronic crosstalk: cause, impact, and mitigation

    NASA Astrophysics Data System (ADS)

    Sun, J.; Madhavan, S.; Wenny, B. N.; Xiong, X.

    2011-11-01

    MODIS-Terra is one of the key sensors in the suite of remote sensing instruments in the Earth Observing System (EOS). MODIS on the Terra platform was launched into orbit in December of 1999 and has successfully completed eleven plus years of operation. MODIS has 36 spectral channels with wavelengths varying from 0.4 μm to 14.4 μm. The native spatial resolutions for the reflective channels are 2 bands at 0.25 km, 5 bands at 0.5 km and 29 bands at 1km. However, the MODIS L1B product allows the high spatial resolution bands to be aggregated into 1km resolution. All the thermal channels in MODIS (i.e. 3.75μm - 14.24μm) have a native spatial resolution of 1 km. Over the eleven plus years of mission lifetime, the sensor degradation has been carefully monitored using various On-Board Calibrators (OBC). In particular, the thermal channels are monitored using the on-board Black-Body (BB) which is traceable to NIST standards. MODIS also has a unique feature for calibration reference in terms of lunar irradiance. The lunar observations are scheduled for MODIS periodically (at least 9 observations in a calendar year). Based on the lunar observations, it was found that there was a possible signal leak for band 27 from its neighboring bands located on the Long-Wave Infrared (LWIR) focal plane. Further investigations revealed a possible leak from bands 28, 29 and 30. The magnitude of the leak was trended and correction coefficients were derived. In this paper, we demonstrate the across-band signal leak in MODIS band 27, its potential impact on the retrieved Brightness temperature (B.T.). Also, the paper explores a correction methodology to relieve the artifacts due to the across-band signal leak. Finally, the improvement in the band 27 image quality is quantified.

  14. Estimation of π and σ band contributions in the normal state electrical conductivity of (Bi, Pb)-2223 added MgB2 superconductors

    NASA Astrophysics Data System (ADS)

    Tripathi, D.; Dey, T. K.

    2015-06-01

    Temperature dependence of the normal state electrical resistivity of polycrystalline MgB2 added with 0, 0.5, 1, 3 and 5 wt. % of (Bi, Pb)-2223 (Bi1.8Pb0.26Sr2Ca2Cu3O10+x) superconducting powder have been investigated in the light of two band approach based on π and σ bands of MgB2 superconductor. The scattering rates (γσ, γπ) and residual resistivity (ρ0σ,ρ0π) of each band are estimated for the investigated samples. Our observation for pure MgB2 shows much higher scattering rate in π bands, as compared to σ bands and hence indicates 'dirty' nature of the samples. However, the addition of 2223 in MgB2 is found to enhance the scattering rate in both bands, but the enhancement is more pronounced in π bands as compared to σ bands. Contribution of each individual band towards the total electrical conductivity of 2223 added MgB2 pellets are separated. Our analysis confirms that σ band contribution shows a small increase with 2223 addition and reaches nearly 89% for 5 wt. % 2223 added MgB2 polycrystalline pellets. The electron-phonon coupling constant (λ) of pure and 2223 added MgB2 pellets calculated using Mc-Millan expression is found to be nearly invariant with 2223 addition.

  15. Electron conductivity in warm and hot dense matter

    NASA Astrophysics Data System (ADS)

    Starrett, Charles; Charest, Marc; Feinblum, David; Burrill, Daniel

    2015-11-01

    The electronic conductivity of warm and hot dense matter is investigated by combining the Ziman-Evans approach with the recently developed pseudo-atom molecular dynamics (PAMD) method. PAMD gives an accurate description of the electronic and ionic structure of the plasma. The Ziman-Evans approach to conductivity, which takes the electronic and ionic structures as inputs, has been widely used but with numerous different assumptions on these inputs. Here we present a systematic study of these assumptions by comparing results to gold-standard QMD results that are thought to be accurate but are very expensive to produce. The study reveals that some assumptions yield very inaccurate results and should not be used, while others give consistently reasonable results. Finally, we show that the Thomas-Fermi version of PAMD can also be used to give accurate conductivities very rapidly, taking a few minutes per point on a single processor.

  16. Quasi-ballistic Electronic Thermal Conduction in Metal Inverse Opals.

    PubMed

    Barako, Michael T; Sood, Aditya; Zhang, Chi; Wang, Junjie; Kodama, Takashi; Asheghi, Mehdi; Zheng, Xiaolin; Braun, Paul V; Goodson, Kenneth E

    2016-04-13

    Porous metals are used in interfacial transport applications that leverage the combination of electrical and/or thermal conductivity and the large available surface area. As nanomaterials push toward smaller pore sizes to increase the total surface area and reduce diffusion length scales, electron conduction within the metal scaffold becomes suppressed due to increased surface scattering. Here we observe the transition from diffusive to quasi-ballistic thermal conduction using metal inverse opals (IOs), which are metal films that contain a periodic arrangement of interconnected spherical pores. As the material dimensions are reduced from ∼230 nm to ∼23 nm, the thermal conductivity of copper IOs is reduced by more than 57% due to the increase in surface scattering. In contrast, nickel IOs exhibit diffusive-like conduction and have a constant thermal conductivity over this size regime. The quasi-ballistic nature of electron transport at these length scales is modeled considering the inverse opal geometry, surface scattering, and grain boundaries. Understanding the characteristics of electron conduction at the nanoscale is essential to minimizing the total resistance of porous metals for interfacial transport applications, such as the total electrical resistance of battery electrodes and the total thermal resistance of microscale heat exchangers.

  17. Calculation of 2D electronic band structure using matrix mechanics

    NASA Astrophysics Data System (ADS)

    Pavelich, R. L.; Marsiglio, F.

    2016-12-01

    We extend previous work, applying elementary matrix mechanics to one-dimensional periodic arrays (to generate energy bands), to two-dimensional arrays. We generate band structures for the square-lattice "2D Kronig-Penney model" (square wells), the "muffin-tin" potential (circular wells), and Gaussian wells. We then apply the method to periodic arrays of more than one atomic site in a unit cell, specifically to the case of materials with hexagonal lattices like graphene. These straightforward extensions of undergraduate-level calculations allow students to readily determine band structures of current research interest.

  18. Vertical photoionization of liquid-to-supercritical ammonia: thermal effects on the valence-to-conduction band gap.

    PubMed

    Urbanek, Janus; Vöhringer, Peter

    2013-07-25

    We recently reported first femtosecond pump–probe experiments on the geminate recombination dynamics of solvated electrons in fluid ammonia (Urbanek et al., J. Phys. Chem. B 2012, 116, 2223–2233). The electrons were generated through a vertical two-photon ionization at a total energy of 9.3 eV. Here, we present a full Monte Carlo analysis of the time-resolved data to determine the solvated electron’s thermalization distance from the ionization hole, NH(3)(+). The simulations are compared with the experiment over wide thermodynamic conditions to obtain insight into the dependence of the vertical ionization mechanism on the electronic properties of the solvent network. The simulations reveal that the average thermalization distance, , decreases strongly with both increasing temperature, T, and decreasing density, ρ, from 3.2 nm in the cryogenic fluid down to roughly 0.5 nm in the dilute supercritical phase with almost gas-like densities. We combine our results with the current understanding of the T,ρ-dependence of the electronic structure of the liquid phase and discuss in detail the role of thermally induced energy level shifts for the valence-to-conduction band gap. The observed changes of the thermalization distance can be well attributed to a gradual decrease of the excess energy initially imparted on the ejected electron as gas-like conditions are progressively approached.

  19. Electronic properties of Janus silicene: new direct band gap semiconductors

    NASA Astrophysics Data System (ADS)

    Sun, Minglei; Ren, Qingqiang; Wang, Sake; Yu, Jin; Tang, Wencheng

    2016-11-01

    Using first-principles calculations, we propose a new class of materials, Janus silicene, which is silicene asymmetrically functionalized with hydrogen and halogen atoms. Formation energies and phonon dispersion indicated that all the Janus silicene systems exhibit good kinetic stability. As compared to silicane, all Janus silicene systems are direct band gap semiconductors. The band gap of Janus silicene can take any value between 1.91 and 2.66 eV by carefully tuning the chemical composition of the adatoms. In addition, biaxial elastic strain can further reduce the band gap to 1.11 eV (under a biaxial tensile strain up to 10%). According to moderate direct band gap, these materials demonstrate potential applications in optoelectronics, exhibiting a very wide spectral range, and they are expected to be highly stable under ambient conditions.

  20. Molecular and electronic structure of the peptide subunit of Geobacter sulfurreducens conductive pili from first principles.

    PubMed

    Feliciano, Gustavo T; da Silva, Antonio J R; Reguera, Gemma; Artacho, Emilio

    2012-08-02

    The respiration of metal oxides by the bacterium Geobacter sulfurreducens requires the assembly of a small peptide (the GS pilin) into conductive filaments termed pili. We gained insights into the contribution of the GS pilin to the pilus conductivity by developing a homology model and performing molecular dynamics simulations of the pilin peptide in vacuo and in solution. The results were consistent with a predominantly helical peptide containing the conserved α-helix region required for pilin assembly but carrying a short carboxy-terminal random-coiled segment rather than the large globular head of other bacterial pilins. The electronic structure of the pilin was also explored from first principles and revealed a biphasic charge distribution along the pilin and a low electronic HOMO-LUMO gap, even in a wet environment. The low electronic band gap was the result of strong electrostatic fields generated by the alignment of the peptide bond dipoles in the pilin's α-helix and by charges from ions in solution and amino acids in the protein. The electronic structure also revealed some level of orbital delocalization in regions of the pilin containing aromatic amino acids and in spatial regions of high resonance where the HOMO and LUMO states are, which could provide an optimal environment for the hopping of electrons under thermal fluctuations. Hence, the structural and electronic features of the pilin revealed in these studies support the notion of a pilin peptide environment optimized for electron conduction.

  1. Electronically conductive ceramics for high temperature oxidizing environments

    DOEpatents

    Kucera, G.H.; Smith, J.L.; Sim, J.W.

    1983-11-10

    This invention pertains to a high temperature, ceramic composition having electronic conductivity as measured by resistivity below about 500 ohm-cm, chemical stability particularly with respect to cathode conditions in a molten carbonate fuel cell, and composed of an alkali metal, transition metal oxide containing a dopant metal in the crystalline structure to replace a portion of the alkali metal or transition metal.

  2. Electronically conductive ceramics for high temperature oxidizing environments

    DOEpatents

    Kucera, Gene H.; Smith, James L.; Sim, James W.

    1986-01-01

    A high temperature, ceramic composition having electronic conductivity as measured by resistivity below about 500 ohm-cm, chemical stability particularly with respect to cathode conditions in a molten carbonate fuel cell, and composed of an alkali metal, transition metal oxide containing a dopant metal in the crystalline structure to replace a portion of the alkali metal or transition metal.

  3. Inventory Control. Easily Made Electronic Device for Conductivity Experiments.

    ERIC Educational Resources Information Center

    Gadek, Frank J.

    1987-01-01

    Describes how to construct an electronic device to be used in conductivity experiments using a 35 millimeter film canister, nine volt battery replacement snaps, a 200-300 ohm resistor, and a light-emitting diode. Provides a diagram and photographs of the device. (TW)

  4. Higher-than-ballistic conduction of viscous electron flows.

    PubMed

    Guo, Haoyu; Ilseven, Ekin; Falkovich, Gregory; Levitov, Leonid S

    2017-03-21

    Strongly interacting electrons can move in a neatly coordinated way, reminiscent of the movement of viscous fluids. Here, we show that in viscous flows, interactions facilitate transport, allowing conductance to exceed the fundamental Landauer's ballistic limit [Formula: see text] The effect is particularly striking for the flow through a viscous point contact, a constriction exhibiting the quantum mechanical ballistic transport at [Formula: see text] but governed by electron hydrodynamics at elevated temperatures. We develop a theory of the ballistic-to-viscous crossover using an approach based on quasi-hydrodynamic variables. Conductance is found to obey an additive relation [Formula: see text], where the viscous contribution [Formula: see text] dominates over [Formula: see text] in the hydrodynamic limit. The superballistic, low-dissipation transport is a generic feature of viscous electronics.

  5. Two-temperature radiative shocks with electron thermal conduction

    NASA Technical Reports Server (NTRS)

    Borkowski, Kazimierz J.; Shull, J. Michael; Mckee, Christopher F.

    1989-01-01

    The influence of electron thermal conduction on radiative shock structure is studied for both one- and two-temperature plasmas. The dimensionless ratio of the conductive length to the cooling length determines whether or not conduction is important, and shock jump conditions with conduction are established for a collisionless shock front. Approximate solutions are obtained, with the assumptions that the ionization state of the gas is constant and the cooling rate is a function of temperature alone. In the absence of magnetic fields, these solutions indicate that conduction noticeably influences normal-abundance interstellar shocks with velocities 50-100 km/s and dramatically affects metal-dominated shocks over a wide range of shock velocities.

  6. Ultrafast conductivity in a low-band-gap polyphenylene and fullerene blend studied by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Němec, Hynek; Nienhuys, Han-Kwang; Perzon, Erik; Zhang, Fengling; Inganäs, Olle; Kužel, Petr; Sundström, Villy

    2009-06-01

    Time-resolved terahertz spectroscopy and Monte Carlo simulations of charge-carrier motion are used to investigate photoinduced transient conductivity in a blend of a low-band-gap polyphenylene copolymer and fullerene derivative. The optical excitation pulse generates free holes delocalized on polymer chains. We show that these holes exhibit a very high initial mobility as their initial excess energy facilitates their transport over defects (potential barriers) on polymer chains. The conductivity then drops down rapidly within 1 ps, and we demonstrate that this decrease occurs essentially by two mechanisms. First, the carriers loose their excess energy and they thus become progressively localized between the on-chain potential barriers—this results in a mobility decay with a rate of (180fs)-1 . Second, carriers are trapped at defects (potential wells) with a capture rate of (860fs)-1 . At longer time scales, populations of mobile and trapped holes reach a quasiequilibrium state and further conductivity decrease becomes very slow.

  7. Electronic band gap reduction and intense luminescence in Co and Mn ion-implanted SiO{sub 2}

    SciTech Connect

    Green, R. J. St Onge, D. J.; Moewes, A.; Zatsepin, D. A.; Kurmaev, E. Z.; Gavrilov, N. V.; Zatsepin, A. F.

    2014-03-14

    Cobalt and manganese ions are implanted into SiO{sub 2} over a wide range of concentrations. For low concentrations, the Co atoms occupy interstitial locations, coordinated with oxygen, while metallic Co clusters form at higher implantation concentrations. For all concentrations studied here, Mn ions remain in interstitial locations and do not cluster. Using resonant x-ray emission spectroscopy and Anderson impurity model calculations, we determine the strength of the covalent interaction between the interstitial ions and the SiO{sub 2} valence band, finding it comparable to Mn and Co monoxides. Further, we find an increasing reduction in the SiO{sub 2} electronic band gap for increasing implantation concentration, due primarily to the introduction of Mn- and Co-derived conduction band states. We also observe a strong increase in a band of x-ray stimulated luminescence at 2.75 eV after implantation, attributed to oxygen deficient centers formed during implantation.

  8. Indium oxide—a transparent, wide-band gap semiconductor for (opto)electronic applications

    NASA Astrophysics Data System (ADS)

    Bierwagen, Oliver

    2015-02-01

    The present review takes a semiconductor physics perspective to summarize the state-of-the art of In2O3 in relation to applications. After discussing conventional and novel applications, the crystal structure, synthesis of single-crystalline material, band-structure and optical transparency are briefly introduced before focussing on the charge carrier transport properties. The issues of unintentional n-type conductivity and its likely causes, the surface electron accumulation, and the lack of p-type conductivity will be presented. Intentional doping will be demonstrated to control the electron concentration and resistivity over a wide range, but is also subject to compensation. The control of the surface accumulation in relation to Schottky and ohmic contacts will be demonstrated. In the context of scattering mechanisms, the electron mobility and its limits will be discussed. Finally, the Seebeck coefficient and its significance will be shown, and ferromagnetic doping of In2O3 will be critically discussed. With this overview most if not all ingredients for the use of In2O3 as semiconductor material in novel or improved conventional devices will be given.

  9. Molecular Dynamics Simulations of Shocks Including Electronic Heat Conduction and Electron-Phonon Coupling

    NASA Astrophysics Data System (ADS)

    Ivanov, Dmitriy S.; Zhigilei, Leonid V.; Bringa, Eduardo M.; De Koning, Maurice; Remington, Bruce A.; Caturla, Maria Jose; Pollaine, Stephen M.

    2004-07-01

    Shocks are often simulated using the classical molecular dynamics (MD) method in which the electrons are not included explicitly and the interatomic interaction is described by an effective potential. As a result, the fast electronic heat conduction in metals and the coupling between the lattice vibrations and the electronic degrees of freedom can not be represented. Under conditions of steep temperature gradients that can form near the shock front, however, the electronic heat conduction can play an important part in redistribution of the thermal energy in the shocked target. We present the first atomistic simulation of a shock propagation including the electronic heat conduction and electron-phonon coupling. The computational model is based on the two-temperature model (TTM) that describes the time evolution of the lattice and electron temperatures by two coupled non-linear differential equations. In the combined TTM-MD method, MD substitutes the TTM equation for the lattice temperature. Simulations are performed with both MD and TTM-MD models for an EAM Al target shocked at 300 kbar. The target includes a tilt grain boundary, which provides a region where shock heating is more pronounced and, therefore, the effect of the electronic heat conduction is expected to be more important. We find that the differences between the predictions of the MD and TTM-MD simulations are significantly smaller as compared to the hydrodynamics calculations performed at similar conditions with and without electronic heat conduction.

  10. Micro-metric electronic patterning of a topological band structure using a photon beam

    PubMed Central

    Frantzeskakis, E.; De Jong, N.; Zwartsenberg, B.; Huang, Y. K.; Bay, T. V.; Pronk, P.; Van Heumen, E.; Wu, D.; Pan, Y.; Radovic, M.; Plumb, N. C.; Xu, N.; Shi, M.; De Visser, A.; Golden, M. S.

    2015-01-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi2−xSbxTe3−ySey with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi2−xSbxTe3−ySey crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by ‘writing’ micron-sized letters in the Dirac point energy of the system. PMID:26543011

  11. Electronic band structure effects in the stopping of protons in copper [Electronic band structure non-linear effects in the stopping of protons in copper

    DOE PAGES

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

    2016-10-05

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

  12. Electronic band structure effects in the stopping of protons in copper [Electronic band structure non-linear effects in the stopping of protons in copper

    SciTech Connect

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

    2016-10-05

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

  13. Electronic conduction in a model three-terminal molecular transistor.

    PubMed

    He, Haiying; Pandey, Ravindra; Karna, Shashi P

    2008-12-17

    The electronic conduction of a novel, three-terminal molecular architecture, analogous to a heterojunction bipolar transistor, is studied. In this architecture, two diode arms consisting of donor-acceptor molecular wires fuse through a ring, while a gate modulating wire is a pi-conjugated wire. The calculated results show the enhancement or depletion mode of a transistor on applying a gate field along the positive or negative direction. A small gate field is required to switch on the current in the proposed architecture. The changes in the electronic conduction can be attributed to the intrinsic dipolar molecular architecture in terms of the evolution of molecular wavefunctions, specifically the one associated with the terphenyl group of the modulating wire in the presence of the gate field.

  14. Mixed ionic and electronic conducting ceramic membranes for hydrocarbon processing

    DOEpatents

    Van Calcar, Pamela; Mackay, Richard; Sammells, Anthony F.

    2002-01-01

    The invention relates to mixed phase materials for the preparation of catalytic membranes which exhibit ionic and electronic conduction and which exhibit improved mechanical strength compared to single phase ionic and electronic conducting materials. The mixed phase materials are useful for forming gas impermeable membranes either as dense ceramic membranes or as dense thin films coated onto porous substrates. The membranes and materials of this invention are useful in catalytic membrane reactors in a variety of applications including synthesis gas production. One or more crystalline second phases are present in the mixed phase material at a level sufficient to enhance the mechanical strength of the mixture to provide membranes for practical application in CMRs.

  15. Rearrangement of 1D Conducting Nanomaterials towards Highly Electrically Conducting Nanocomposite Fibres for Electronic Textiles

    NASA Astrophysics Data System (ADS)

    Han, Joong Tark; Choi, Sua; Jang, Jeong In; Seol, Seung Kwon; Woo, Jong Seok; Jeong, Hee Jin; Jeong, Seung Yol; Baeg, Kang-Jun; Lee, Geon-Woong

    2015-03-01

    Nanocarbon-based conducting fibres have been produced using solution- or dry-spinning techniques. Highly conductive polymer-composite fibres containing large amounts of conducting nanomaterials have not been produced without dispersants, however, because of the severe aggregation of conducting materials in high-concentration colloidal solutions. Here we show that highly conductive (electrical conductivity ~1.5 × 105 S m-1) polymer-composite fibres containing carbon nanotubes and silver nanowires can be fabricated via a conventional solution-spinning process without any other treatment. Spinning dopes were fabricated by a simple mixing of a polyvinyl alcohol solution in dimethylsulfoxide with a paste of long multi-walled carbon nanotubes dispersed in organic solvents, assisted by quadruple hydrogen-bonding networks and an aqueous silver nanowire dispersion. The high electrical conductivity of the fibre was achieved by rearrangement of silver nanowires towards the fibre skin during coagulation because of the selective favourable interaction between the silver nanowires and coagulation solvents. The prepared conducting fibres provide applications in electronic textiles such as a textile interconnector of light emitting diodes, flexible textile heaters, and touch gloves for capacitive touch sensors.

  16. Rearrangement of 1D conducting nanomaterials towards highly electrically conducting nanocomposite fibres for electronic textiles.

    PubMed

    Han, Joong Tark; Choi, Sua; Jang, Jeong In; Seol, Seung Kwon; Woo, Jong Seok; Jeong, Hee Jin; Jeong, Seung Yol; Baeg, Kang-Jun; Lee, Geon-Woong

    2015-03-20

    Nanocarbon-based conducting fibres have been produced using solution- or dry-spinning techniques. Highly conductive polymer-composite fibres containing large amounts of conducting nanomaterials have not been produced without dispersants, however, because of the severe aggregation of conducting materials in high-concentration colloidal solutions. Here we show that highly conductive (electrical conductivity ~1.5 × 10(5) S m(-1)) polymer-composite fibres containing carbon nanotubes and silver nanowires can be fabricated via a conventional solution-spinning process without any other treatment. Spinning dopes were fabricated by a simple mixing of a polyvinyl alcohol solution in dimethylsulfoxide with a paste of long multi-walled carbon nanotubes dispersed in organic solvents, assisted by quadruple hydrogen-bonding networks and an aqueous silver nanowire dispersion. The high electrical conductivity of the fibre was achieved by rearrangement of silver nanowires towards the fibre skin during coagulation because of the selective favourable interaction between the silver nanowires and coagulation solvents. The prepared conducting fibres provide applications in electronic textiles such as a textile interconnector of light emitting diodes, flexible textile heaters, and touch gloves for capacitive touch sensors.

  17. Rearrangement of 1D Conducting Nanomaterials towards Highly Electrically Conducting Nanocomposite Fibres for Electronic Textiles

    PubMed Central

    Han, Joong Tark; Choi, Sua; Jang, Jeong In; Seol, Seung Kwon; Woo, Jong Seok; Jeong, Hee Jin; Jeong, Seung Yol; Baeg, Kang-Jun; Lee, Geon-Woong

    2015-01-01

    Nanocarbon-based conducting fibres have been produced using solution- or dry-spinning techniques. Highly conductive polymer-composite fibres containing large amounts of conducting nanomaterials have not been produced without dispersants, however, because of the severe aggregation of conducting materials in high-concentration colloidal solutions. Here we show that highly conductive (electrical conductivity ~1.5 × 105 S m−1) polymer-composite fibres containing carbon nanotubes and silver nanowires can be fabricated via a conventional solution-spinning process without any other treatment. Spinning dopes were fabricated by a simple mixing of a polyvinyl alcohol solution in dimethylsulfoxide with a paste of long multi-walled carbon nanotubes dispersed in organic solvents, assisted by quadruple hydrogen-bonding networks and an aqueous silver nanowire dispersion. The high electrical conductivity of the fibre was achieved by rearrangement of silver nanowires towards the fibre skin during coagulation because of the selective favourable interaction between the silver nanowires and coagulation solvents. The prepared conducting fibres provide applications in electronic textiles such as a textile interconnector of light emitting diodes, flexible textile heaters, and touch gloves for capacitive touch sensors. PMID:25792333

  18. Conducting Electronic Polymers by Non-Redox Processes

    DTIC Science & Technology

    1987-12-31

    polyacrylic acid , polyvinylsulfonic acid , polystyrene sulfonic acid . Our electron microscopy study indicated that polyaniline morphology is strongly... Polyaniline derivatized with very stable and nonvolatile acids still seems to yield the most thermally stable conductive polyaniline . A paper concerning...be the optimum acid precursor, the use of a photosynthesized acid to derivatize polyaniline emeraldine free-base films may prove to be an easy method

  19. Electronic thermal conductivity in a superconducting vortex state

    NASA Astrophysics Data System (ADS)

    Adachi, H.; Miranovic, P.; Ichioka, M.; Machida, K.

    2007-10-01

    The longitudinal component of the electronic thermal conductivity κxx in a superconducting vortex state is calculated as a function of magnetic field B. Calculations are performed by taking account of the spatial dependence of normal Green's function g, which was neglected in the previous studies using the Brandt-Pesch-Tewordt method. We discuss the possibility of using κxx(B) as a probe of the pair potential symmetry.

  20. New secondary batteries utilizing electronically conductive polymer cathodes

    NASA Technical Reports Server (NTRS)

    Martin, Charles R.; White, Ralph E.

    1987-01-01

    The objectives are to optimize the transport rates in electronically conductive polypyrrole films by controlling the morphology of the film and to assess the utility of these films as cathodes in a lithium/polypyrrole secondary battery. During this research period, a better understanding was gained of the fundamental electrochemical switching processes within the polypyrrole film. Three publications were submitted based on the work completed.

  1. High frequency conductivity of hot electrons in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Amekpewu, M.; Mensah, S. Y.; Musah, R.; Mensah, N. G.; Abukari, S. S.; Dompreh, K. A.

    2016-05-01

    High frequency conductivity of hot electrons in undoped single walled achiral Carbon Nanotubes (CNTs) under the influence of ac-dc driven fields was considered. We investigated semi-classically Boltzmann's transport equation with and without the presence of the hot electrons' source by deriving the current densities in CNTs. Plots of the normalized current density versus frequency of ac-field revealed an increase in both the minimum and maximum peaks of normalized current density at lower frequencies as a result of a strong injection of hot electrons. The applied ac-field plays a twofold role of suppressing the space-charge instability in CNTs and simultaneously pumping an energy for lower frequency generation and amplification of THz radiations. These have enormous promising applications in very different areas of science and technology.

  2. Electron Exchange and Conduction in Nontronite from First-Principles

    SciTech Connect

    Alexandrov, Vitali Y.; Neumann, Anke; Scherer, Michelle; Rosso, Kevin M.

    2013-01-11

    Fe-bearing clay minerals serve as an important source and sink for electrons in redox reactions in various subsurface geochemical environments, and electron transfer (ET) properties of the Fe2+/Fe3+ redox couple play a decisive role in a variety of physicochemical processes involving clays. Here, we apply first-principles calculations using both periodic GGA+U planewave and Hartree-Fock molecular-cluster frameworks in conjuction with small polaron hopping approach and Marcus electron transfer theory to examine electron exchange mobilities in an Fe-rich smectite, taking nontronite as a case study. GGA+U calculations of the activation barrier for small-polaron migration provide rates of electron hopping that agree very well with values deduced from variable temperature Mössbauer data (M. V. Schaefer, et. al., Environ. Sci. Technol. 45, 540, (2011)), indicating a surprisingly fast electron mobility at room temperature. Based on molecular cluster calculations, we show that the state with tetrahedral Fe2+ ion in the nontronite lattice is about 0.9 eV higher than the one with octahedral Fe2+. Also, evaluation of the ET rates for the Fe2+/Fe3+ electron hopping in tetrahedral (TS) and octahedral sheets (OS), as well as across the sheets (TS–OS) shows that the dominant contribution to the bulk electronic conductivity should come from the ET within the OS. Deprotonation of structural OH groups mediating ET between the Fe ions in the OS is found to decrease the internal reorganization energy and to increase the magnitude of the electronic coupling matrix element, whereas protonation (to OH2 groups) has the opposite effect. Overall, our calculations suggest that the major factors affecting ET rates are the nature and structure of the nearest-neighbor local environment and the degree of covalency of the bonds between Fe and ligands mediating electron hops. The generally higher reorganization energy and weaker electronic coupling found in Fe-bearing clay minerals leads to

  3. Hydrogen production by tuning the photonic band gap with the electronic band gap of TiO₂.

    PubMed

    Waterhouse, G I N; Wahab, A K; Al-Oufi, M; Jovic, V; Anjum, D H; Sun-Waterhouse, D; Llorca, J; Idriss, H

    2013-10-10

    Tuning the photonic band gap (PBG) to the electronic band gap (EBG) of Au/TiO2 catalysts resulted in considerable enhancement of the photocatalytic water splitting to hydrogen under direct sunlight. Au/TiO2 (PBG-357 nm) photocatalyst exhibited superior photocatalytic performance under both UV and sunlight compared to the Au/TiO2 (PBG-585 nm) photocatalyst and both are higher than Au/TiO2 without the 3 dimensionally ordered macro-porous structure materials. The very high photocatalytic activity is attributed to suppression of a fraction of electron-hole recombination route due to the co-incidence of the PBG with the EBG of TiO2 These materials that maintain their activity with very small amount of sacrificial agents (down to 0.5 vol.% of ethanol) are poised to find direct applications because of their high activity, low cost of the process, simplicity and stability.

  4. Band offsets of n-type electron-selective contacts on cuprous oxide (Cu2O) for photovoltaics

    NASA Astrophysics Data System (ADS)

    Brandt, Riley E.; Young, Matthew; Park, Helen Hejin; Dameron, Arrelaine; Chua, Danny; Lee, Yun Seog; Teeter, Glenn; Gordon, Roy G.; Buonassisi, Tonio

    2014-12-01

    The development of cuprous oxide (Cu2O) photovoltaics (PVs) is limited by low device open-circuit voltages. A strong contributing factor to this underperformance is the conduction-band offset between Cu2O and its n-type heterojunction partner or electron-selective contact. In the present work, a broad range of possible n-type materials is surveyed, including ZnO, ZnS, Zn(O,S), (Mg,Zn)O, TiO2, CdS, and Ga2O3. Band offsets are determined through X-ray photoelectron spectroscopy and optical bandgap measurements. A majority of these materials is identified as having a negative conduction-band offset with respect to Cu2O; the detrimental impact of this on open-circuit voltage (VOC) is evaluated through 1-D device simulation. These results suggest that doping density of the n-type material is important as well, and that a poorly optimized heterojunction can easily mask changes in bulk minority carrier lifetime. Promising heterojunction candidates identified here include Zn(O,S) with [S]/[Zn] ratios >70%, and Ga2O3, which both demonstrate slightly positive conduction-band offsets and high VOC potential. This experimental protocol and modeling may be generalized to evaluate the efficiency potential of candidate heterojunction partners for other PV absorbers, and the materials identified herein may be promising for other absorbers with low electron affinities.

  5. Formation of electron strings in narrow band polar semiconductors

    PubMed

    Kusmartsev

    2000-01-17

    We show that linear electron strings may arise in polar semiconductors. A single string consists of M spinless fermions trapped by an extended polarization well of a cigar shape. Inside the string the particles are free although they interact with each other via Coulomb forces. The strings arise as a result of an electronic phase separation associated with an instability of small adiabatic polarons. We have found the length of the string which depends on dielectric constants of semiconductors. The appearance of these electron strings may have an impact on the effect of stripe formation observed in a variety of high- T(c) experiments.

  6. Electronic structure of cerium hydrides: Augmented-plane-wave linear-combination-of-atomic-orbitals energy bands

    NASA Astrophysics Data System (ADS)

    Fujimori, A.; Minami, F.; Tsuda, N.

    1980-10-01

    Electronic energy bands have been calculated for CeH2 and CeH3 using the augmented-plane-wave method and have been fitted by the linear-combination-of-atomic-orbitals interpolation scheme. The partial densities of states and the numbers of electrons on atomic orbitals indicate that hydrogen in CeH2 is almost anionlike. When going from CeH2 to CeH3, shallow bonding levels are found to form between the third hydrogen state and conduction electrons of CeH2, other features of CeH2 being little affected by it. Thus the rare-earth dihydrides are regarded as ionic compounds similar to the saline-element dihydrides except for the presence of d-like conduction electrons.

  7. Conformational statistics of molecules with inner rotation and shapes of their electronic absorption bands

    SciTech Connect

    Aver`yanov, E.M.

    1994-10-01

    The effect of conformational statistics of molecules with inner rotation of {pi}-conjugated fragments on the position, intensity, and electronic absorption band shapes is studied in isotropic molecular media. It is shown that the conformational disorder of molecules with one inner rotation degree of freedom exerts an appreciable effect on the shift, inhomogeneous broadening, and asymmetry of the electronic absorption bands. An interpretation of the available experimental data is give. 19 refs., 1 fig.

  8. The effect of driven electron-phonon coupling on the electronic conductance of a polar nanowire

    SciTech Connect

    Mardaani, Mohammad Rabani, Hassan; Esmaili, Esmat; Shariati, Ashrafalsadat

    2015-08-07

    A semi-classical model is proposed to explore the effect of electron-phonon coupling on the coherent electronic transport of a polar chain which is confined between two rigid leads in the presence of an external electric field. To this end, we construct the model by means of Green's function technique within the nearest neighbor tight-binding and harmonic approximations. For a time-periodic electric field, the atomic displacements from the equilibrium positions are obtained precisely. The result is then used to compute the electronic transport properties of the chain within the Peierls-type model. The numerical results indicate that the conductance of the system shows interesting behavior in some special frequencies. For each special frequency, there is an electronic quasi-state in which the scattering of electrons by vibrating atoms reaches maximum. The system electronic conductance decreases dramatically at the strong electron-phonon couplings and low electron energies. In the presence of damping forces, the electron-phonon interaction has a less significant effect on the conductance.

  9. Strain Dependent Electronic Structure and Band Offset Tuning at Heterointerfaces of ASnO3 (A=Ca, Sr, and Ba) and SrTiO3

    PubMed Central

    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

  10. Strain Dependent Electronic Structure and Band Offset Tuning at Heterointerfaces of ASnO3 (A=Ca, Sr, and Ba) and SrTiO3

    NASA Astrophysics Data System (ADS)

    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

    2017-02-01

    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.

  11. Electronic conductivity studies on oxyhalide glasses containing TMO

    NASA Astrophysics Data System (ADS)

    Vijayatha, D.; Viswanatha, R.; Sujatha, B.; Narayana Reddy, C.

    2016-05-01

    Microwave-assisted synthesis is cleaner, more economical and much faster than conventional methods. The development of new routes for the synthesis of solid materials is an integral part of material science and technology. The electronic conductivity studies on xPbCl2 - 60 PbO - (40-x) V2O5 (1 ≥ x ≤ 10) glass system has been carried out over a wide range of composition and temperature (300 K to 423 K). X-ray diffraction study confirms the amorphous nature of the samples. The Scanning electron microscopic studies reveal the formation of cluster like morphology in PbCl2 containing glasses. The d.c conductivity exhibits Arrhenius behaviour and increases with V2O5 concentration. Analysis of the results is interpreted in view Austin-Mott's small polaron model of electron transport. Activation energies calculated using regression analysis exhibit composition dependent trend and the variation is explained in view of the structure of lead-vanadate glass.

  12. Mixed oxygen ion/electron-conducting ceramics for oxygen separation

    SciTech Connect

    Stevenson, J.W.; Armstrong, T.R.; Armstrong, B.L.

    1996-08-01

    Mixed oxygen ion and electron-conducting ceramics are unique materials that can passively separate high purity oxygen from air. Oxygen ions move through a fully dense ceramic in response to an oxygen concentration gradient, charge-compensated by an electron flux in the opposite direction. Compositions in the system La{sub 1{minus}x}M{sub x}Co{sub 1{minus}y{minus}z}Fe{sub y}N{sub z}O{sub 3{minus}{delta}}, perovskites where M=Sr, Ca, and Ba, and N=Mn, Ni, Cu, Ti, and Al, have been prepared and their electrical, oxygen permeation, oxygen vacancy equilibria, and catalytic properties evaluated. Tubular forms, disks, and asymmetric membrane structures, a thin dense layer on a porous support of the same composition, have been fabricated for testing purposes. In an oxygen partial gradient, the passive oxygen flux through fully dense structures was highly dependent on composition. An increase in oxygen permeation with increased temperature is attributed to both enhanced oxygen vacancy mobility and higher vacancy populations. Highly acceptor-doped compositions resulted in oxygen ion mobilities more than an order of magnitude higher than yttria-stabilized zirconia. The mixed conducting ceramics have been utilized in a membrane reactor configuration to upgrade methane to ethane and ethylene. Conditions were established to balance selectivity and throughput in a catalytic membrane reactor constructed from mixed conducting ceramics.

  13. Waveguide Characterization of S-Band Microwave Mantle Cloaks for Dielectric and Conducting Objects

    PubMed Central

    Vitiello, Antonino; Moccia, Massimo; Papari, Gian Paolo; D’Alterio, Giuliana; Vitiello, Roberto; Galdi, Vincenzo; Andreone, Antonello

    2016-01-01

    We present the experimental characterization of mantle cloaks designed so as to minimize the electromagnetic scattering of moderately-sized dielectric and conducting cylinders at S-band microwave frequencies. Our experimental setup is based on a parallel-plate waveguide system, which emulates a two-dimensional plane-wave scattering scenario, and allows the collection of near-field maps as well as more quantitative assessments in terms of global scattering observables (e.g., total scattering width). Our results, in fairly good agreement with full-wave numerical simulations, provide a further illustration of the mantle- cloak mechanism, including its frequency-sensitivity, and confirm its effectiveness both in restoring the near-field impinging wavefront around the scatterer, and in significantly reducing the overall scattering. PMID:26803985

  14. Development of 256 x 256 Element Impurity Band Conduction Infrared Detector Arrays for Astronomy

    NASA Technical Reports Server (NTRS)

    Domingo, George

    1997-01-01

    This report describes the work performed on a one and a half year advance technology program to develop Impurity Band Conduction (IBC) detectors with very low dark current, high quantum efficiency, and with good repeatable processes. The program fabricated several epitaxial growths of Si:As detecting layers from 15 to 35 microns thick and analyzed the performance versus the thickness and the Arsenic concentration of these epitaxial layers. Some of the epitaxial runs did not yield because of excessive residual impurities. The thicker epitaxial layers and the ones with higher Arsenic concentration resulted in good detectors with low dark currents and good quantum efficiency. The program hybridized six detector die from the best detector wafers to a low noise, 256 x 256 readout array and delivered the hybrids to NASA Ames for a more detailed study of the performance of the detectors.

  15. Experimental Observation of Quantum Confinement in the Conduction Band of CdSe Quantum Dots

    SciTech Connect

    Lee, J I; Meulenberg, R W; Hanif, K M; Mattoussi, H; Klepeis, J E; Terminello, L J; van Buuren, T

    2006-12-15

    Recent theoretical descriptions as to the magnitude of effect that quantum confinement has on he conduction band (CB) of CdSe quantum dots (QD) have been conflicting. In this manuscript, we experimentally identify quantum confinement effects in the CB of CdSe QDs for the first time. Using X-ray absorption spectroscopy, we have unambiguously witnessed the CB minimum shift to higher energy with decreasing particle size and have been able to compare these results to recent theories. Our experiments have been able to identify which theories correctly describe the CB states in CdSe QDs. In particular, our experiments suggest that multiple theories describe the shifts in the CB of CdSe QDs and are not mutually exclusive.

  16. Waveguide Characterization of S-Band Microwave Mantle Cloaks for Dielectric and Conducting Objects.

    PubMed

    Vitiello, Antonino; Moccia, Massimo; Papari, Gian Paolo; D'Alterio, Giuliana; Vitiello, Roberto; Galdi, Vincenzo; Andreone, Antonello

    2016-01-25

    We present the experimental characterization of mantle cloaks designed so as to minimize the electromagnetic scattering of moderately-sized dielectric and conducting cylinders at S-band microwave frequencies. Our experimental setup is based on a parallel-plate waveguide system, which emulates a two-dimensional plane-wave scattering scenario, and allows the collection of near-field maps as well as more quantitative assessments in terms of global scattering observables (e.g., total scattering width). Our results, in fairly good agreement with full-wave numerical simulations, provide a further illustration of the mantle- cloak mechanism, including its frequency-sensitivity, and confirm its effectiveness both in restoring the near-field impinging wavefront around the scatterer, and in significantly reducing the overall scattering.

  17. New secondary batteries utilizing electronically conductive polymer cathodes

    NASA Technical Reports Server (NTRS)

    Martin, Charles R.; White, Ralph E.

    1989-01-01

    The objectives of this project are to optimize the transport rates in electronically conductive polypyrrole films by controlling the morphology of the film and to assess the utility of these films as cathodes in a lithium/polypyrrole secondary battery. During this research period, progress has been made in improving the charge transport rate of the supermolecular-engineered polypyrrole electrode by eliminating the polypyrrole baselayer that hampered earlier work. Also, the fibril density of the polypyrrole electrode was increased, providing more electroactive sites per unit area.

  18. New secondary batteries utilizing electronically conductive polymer cathodes

    NASA Technical Reports Server (NTRS)

    Martin, Charles R.; White, Ralph E.

    1989-01-01

    The objectives of this project are to characterize the transport properties in electronically conductive polymers and to assess the utility of these films as cathodes in lithium/polymer secondary batteries. During this research period, progress has been made in a literature survey of the historical background, methods of preparation, the physical and chemical properties, and potential technological applications of polythiophene. Progress has also been made in the characterization of polypyrrole flat films and fibrillar films. Cyclic voltammetry and potential step chronocoulometry were used to gain information on peak currents and potentials switching reaction rates, charge capacity, and charge retention. Battery charge/discharge studies were also performed.

  19. Theory of electron conductance across a DNA basepair

    NASA Astrophysics Data System (ADS)

    Lee, Myeong; Sankey, Otto

    2008-03-01

    In recent years, research on electron tunneling through DNA basepairs has become more important due to its potential application in DNA sequencing technology. The goal is to recognize and identify a specific DNA base by measuring the hydrogen bond mediated tunneling current across a DNA basepair junction. In this talk, we discuss the results of density functional theory on the intrinsic conduction through DNA basepairs (Watson-Crick basepairs, Wobble basepairs, etc), and in particular the role of the hydrogen bond on the tunneling current.

  20. Electronic conduction in La-based perovskite-type oxides

    PubMed Central

    Ohbayashi, Kazushige; Koumoto, Kunihito

    2015-01-01

    A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo0.5Ni0.5O3±δ was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo0.5Ni0.5O3±δ exhibits a high conductivity of 1.9 × 103 S cm−1 at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 1022 cm−3 and a small effective mass m∗ of 0.10 me. Notably, LaCo0.5Ni0.5O3±δ exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo0.5Ni0.5O3±δ is the most suitable for the fabrication of oxide electrodes and wiring, though La1−xSrxCoO3±δ and La1−xSrxMnO3±δ also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 103 S cm−1 for La0.5Sr0.5CoO3±δ and 1.5 × 103 S cm−1 for La0.6Sr0.4MnO3±δ because oxygen release occurs in La1−xSrxCoO3±δ as elevating temperature and the electrical conductivity of La0.6Sr0.4MnO3±δ slightly decreases at temperatures above 400 K. PMID:27877778

  1. Vibrational renormalisation of the electronic band gap in hexagonal and cubic ice

    NASA Astrophysics Data System (ADS)

    Engel, Edgar A.; Monserrat, Bartomeu; Needs, Richard J.

    2015-12-01

    Electron-phonon coupling in hexagonal and cubic water ice is studied using first-principles quantum mechanical methods. We consider 29 distinct hexagonal and cubic ice proton-orderings with up to 192 molecules in the simulation cell to account for proton-disorder. We find quantum zero-point vibrational corrections to the minimum electronic band gaps ranging from -1.5 to -1.7 eV, which leads to improved agreement between calculated and experimental band gaps. Anharmonic nuclear vibrations play a negligible role in determining the gaps. Deuterated ice has a smaller band-gap correction at zero-temperature of -1.2 to -1.4 eV. Vibrations reduce the differences between the electronic band gaps of different proton-orderings from around 0.17 eV to less than 0.05 eV, so that the electronic band gaps of hexagonal and cubic ice are almost independent of the proton-ordering when quantum nuclear vibrations are taken into account. The comparatively small reduction in the band gap over the temperature range 0 - 240 K of around 0.1 eV does not depend on the proton ordering, or whether the ice is protiated or deuterated, or hexagonal, or cubic. We explain this in terms of the atomistic origin of the strong electron-phonon coupling in ice.

  2. Electronic band structures of graphene nanoribbons with self-passivating edge reconstructions

    NASA Astrophysics Data System (ADS)

    Nguyen, L. Tung; Pham, C. Huy; Nguyen, V. Lien

    2011-07-01

    Using the nearest-neighbor tight-binding approach we study the electronic band structures of graphene nanoribbons with self-passivating edge reconstructions. For zigzag ribbons the edge reconstruction moves both the Fermi energy and the flat band down by several hundred meV, and the flat band is always found to be below the Fermi energy. The states featured by the flat band are shown to be mainly localized at the atoms belonging to several lattice lines closest to the edges. For armchair ribbons the edge reconstruction strongly modifies the band structure in the region close to the Fermi energy, leading to the appearance of a band gap even for ribbons which were predicted to be metallic in the model of standard armchair edges. The gap widths are, however, strongly different in magnitude and behave in different ways regarding the ribbon width.

  3. Theory of thermal conductivity in the disordered electron liquid

    NASA Astrophysics Data System (ADS)

    Schwiete, G.; Finkel'stein, A. M.

    2016-03-01

    We study thermal conductivity in the disordered two-dimensional electron liquid in the presence of long-range Coulomb interactions. We describe a microscopic analysis of the problem using the partition function defined on the Keldysh contour as a starting point. We extend the renormalization group (RG) analysis developed for thermal transport in the disordered Fermi liquid and include scattering processes induced by the long-range Coulomb interaction in the sub-temperature energy range. For the thermal conductivity, unlike for the electrical conductivity, these scattering processes yield a logarithmic correction that may compete with the RG corrections. The interest in this correction arises from the fact that it violates the Wiedemann-Franz law. We checked that the sub-temperature correction to the thermal conductivity is not modified either by the inclusion of Fermi liquid interaction amplitudes or as a result of the RG flow. We therefore expect that the answer obtained for this correction is final. We use the theory to describe thermal transport on the metallic side of the metal-insulator transition in Si MOSFETs.

  4. k - dependent Jeff=1/2 band splitting and the electron-hole asymmetry in SrIrO3

    NASA Astrophysics Data System (ADS)

    Singh, Vijeta; Pulikkotil, J. J.

    2017-02-01

    The Ir ion in Srn+1 IrnO 3 n + 1 series of compounds is octahedrally coordinated. However, unlike Sr2IrO4 (n=1) and Sr3Ir2O7 (n=2) which are insulating due to spin-orbit induced Jeff splitting of the t2g bands, SrIrO3 (n= ∞) is conducting. To explore whether such a splitting is relevant in SrIrO3, and if so to what extent, we investigate the electronic structure of orthorhombic SrIrO3 using density functional theory. Calculations reveal that the crystal field split Ir t2 g bands in SrIrO3 are indeed split into Jeff=3/2 and and Jeff=1/2 states. However, the splitting is found to be strongly k - dependent with its magnitude determined by the Ir - O orbital hybridization. Besides, we find that the spin-orbit induced pseudo-gap, into which the Fermi energy is positioned, is composed of both light electron-like and heavy hole-like bands. These features in the band structure of SrIrO3 suggest that variations in the carrier concentration control the electronic transport properties in SrIrO3, which is consistent with the experiments.

  5. Electronic band structure of TiN/MgO nanostructures

    NASA Astrophysics Data System (ADS)

    Kobayashi, Kazuaki; Takaki, Hirokazu; Shimono, Masato; Kobayashi, Nobuhiko; Hirose, Kenji

    2017-04-01

    Various nanostructured TiN(001)/MgO(001) superlattices based on a repeated slab model with a vacuum region have been investigated by the total energy pseudopotential method. They are rectangular and rectangular parallelepiped TiN(001) dot structures on MgO(001)-2×2 and 3×3 substrates. A rectangular TiN(001) structure on a MgO(001)-2×1 substrate has also been calculated. Their detailed electronic and internal lattice properties were investigated systematically. The internal atomic coordinates in a unit cell were fully relaxed. The rectangular TiN(001) structure on the MgO(001)-2×1 superlattice, which is not a dot owing to its periodicity, corresponds to metallicity. The electronic states of relaxed rectangular TiN(001) dot/MgO(001)-2×2 and MgO(001)-3×3 superlattices are semiconducting. All relaxed rectangular parallelepiped TiN(001) dot/MgO(001)-2×2 and MgO(001)-3×3 superlattices correspond to metallicity. The electronic properties depend on the shape of the TiN dot and the size of the MgO substrate.

  6. Molecular Electronic Angular Motion Transducer Broad Band Self-Noise

    PubMed Central

    Zaitsev, Dmitry; Agafonov, Vadim; Egorov, Egor; Antonov, Alexander; Shabalina, Anna

    2015-01-01

    Modern molecular electronic transfer (MET) angular motion sensors combine high technical characteristics with low cost. Self-noise is one of the key characteristics which determine applications for MET sensors. However, until the present there has not been a model describing the sensor noise in the complete operating frequency range. The present work reports the results of an experimental study of the self-noise level of such sensors in the frequency range of 0.01–200 Hz. Based on the experimental data, a theoretical model is developed. According to the model, self-noise is conditioned by thermal hydrodynamic fluctuations of the operating fluid flow in the frequency range of 0.01–2 Hz. At the frequency range of 2–100 Hz, the noise power spectral density has a specific inversely proportional dependence of the power spectral density on the frequency that could be attributed to convective processes. In the high frequency range of 100–200 Hz, the noise is conditioned by the voltage noise of the electronics module input stage operational amplifiers and is heavily reliant to the sensor electrical impedance. The presented results allow a deeper understanding of the molecular electronic sensor noise nature to suggest the ways to reduce it. PMID:26610502

  7. Nanoscale mapping of optical band gaps using monochromated electron energy loss spectroscopy.

    PubMed

    Zhan, W; Granerød, C S; Venkatachalapathy, V; Johansen, K M H; Jensen, I J T; Kuznetsov, A Yu; Prytz, Ø

    2017-03-10

    Using monochromated electron energy loss spectroscopy in a probe-corrected scanning transmission electron microscope we demonstrate band gap mapping in ZnO/ZnCdO thin films with a spatial resolution below 10 nm and spectral precision of 20 meV.

  8. Shape of impurity electronic absorption bands in a nematic liquid crystal

    SciTech Connect

    Aver`yanov, E.M.

    1995-02-01

    It is shown that the anisotropic intermolecular impurity-matrix interactions, statistical orientation properties, and the electronic structure of the uniaxial impurity molecules considerably affect the spectral moments of the impurity electronic adsorption bands in a nematic liquid crystal. 15 refs., 3 figs.

  9. Nanoscale mapping of optical band gaps using monochromated electron energy loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhan, W.; Granerød, C. S.; Venkatachalapathy, V.; Johansen, K. M. H.; Jensen, I. J. T.; Kuznetsov, A. Yu; Prytz, Ø.

    2017-03-01

    Using monochromated electron energy loss spectroscopy in a probe-corrected scanning transmission electron microscope we demonstrate band gap mapping in ZnO/ZnCdO thin films with a spatial resolution below 10 nm and spectral precision of 20 meV.

  10. Electronic structure and conductivity of ferroelectric hexaferrite: Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Knížek, K.; Novák, P.; Küpferling, M.

    2006-04-01

    Ba0.5Sr1.5Zn2Fe12O22 is a promising multiferroic compound in which the electric polarization is intimately connected to the magnetic state. In principle, ferroelectrity might exist above the room temperature, but the electrical conductivity that increases with increasing temperature limits it to temperatures below ≈130K . We present results of an ab initio electronic structure calculation of the (BaSr)Zn2Fe12O22 system. To improve the description of strongly correlated 3d electrons of iron, the GGA+U method is used. The results show that the electrical conductivity strongly depends on relative fractions of iron and zinc in the tetrahedral sublattice that belongs to the spinel block of the hexaferrite structure. If this sublattice is fully occupied by zinc, the system is an insulator with a gap of ≈1.5eV . If it is occupied equally by Fe and Zn the gap decreases by a factor of 2, and the system is metallic when this sublattice is filled by iron only.

  11. Electronic and ionic conductivities in superionic Li4C60

    NASA Astrophysics Data System (ADS)

    Quintavalle, D.; Márkus, B. G.; Jánossy, A.; Simon, F.; Klupp, G.; Győri, M. A.; Kamarás, K.; Magnani, G.; Pontiroli, D.; Riccò, M.

    2016-05-01

    The 10 GHz microwave conductivity, σ (T ) and high field, 222 GHz electron spin resonance (HF-ESR) of Li4C60 fulleride is measured in a wide temperature range. We suggest that the majority of ESR active sites and at least some of the charge carriers for σ (T ) are electrons bound to a small concentration of surplus or vacancy ions in the polymer phase. Both σ (T ) and the ESR line shape depend on ionic motion. A change of the activation energy of σ (T ) at 125 K coincides with the onset of the ionic DC conductivity. The ESR line shape is determined mainly by Li ionic motion within octahedral voids below 150 K. At higher temperatures, fluctuations due to ionic diffusion change the environment of defects from axial to effectively isotropic on the ESR time scale. σ (T ) data up to 700 K through the depolymerization transition confirm that the monomeric phase of Li4C60 is a metal.

  12. Extreme ultraviolet narrow band emission from electron cyclotron resonance plasmas.

    PubMed

    Zhao, H Y; Zhao, H W; Sun, L T; Zhang, X Z; Wang, H; Ma, B H; Li, X X; Zhu, Y H; Sheng, L S; Zhang, G B; Tian, Y C

    2008-02-01

    Extreme ultraviolet lithography (EUVL) is considered as the most promising solution at and below dynamic random access memory 32 nm half pitch among the next generation lithography, and EUV light sources with high output power and sufficient lifetime are crucial for the realization of EUVL. However, there is no EUV light source completely meeting the requirements for the commercial application in lithography yet. Therefore, ECR plasma is proposed as a novel concept EUV light source. In order to investigate the feasibility of ECR plasma as a EUV light source, the narrow band EUV power around 13.5 nm emitted by two highly charged ECR ion sources -- LECR2M and SECRAL -- was measured with a calibrated EUV power measurement tool. Since the emission lines around 13.5 nm can be attributed to the 4d-5p transitions of Xe XI or the 4d-4f unresolved transition array of Sn VIII-XIII, xenon plasma was investigated. The dependence of the EUV throughput and the corresponding conversion efficiency on the parameters of the ion source, such as the rf power and the magnetic confinement configurations, were preliminarily studied.

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

    NASA Astrophysics Data System (ADS)

    Narimani, M.; Nourbakhsh, Z.

    2016-05-01

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

  14. The effect of contact barriers on space-charge-limited current injection in impurity-band-conduction photodetectors

    NASA Astrophysics Data System (ADS)

    Martin, B. G.

    1994-05-01

    A theoretical investigation was made on the effect of contact barriers on space-charge-limited (SCL) current injection in impurity-band-conduction (IBC) photodetectors. Parmenter and Ruppel [J. Appl. Phys. 30, 1548 (1959)] considered the effect of contact barriers on SCL current injection in insulators. They solved the steady-state, one-dimensional transport equations, obtaining the solution in terms of integrals, which they evaluated for certain limiting cases. We have modified their approach by using the current injection ratios at the contacts as boundary conditions. This is a very general formulation that can be used for any type of contact barrier. We then applied this technique to model contact barriers in IBC devices. The fact that the IBC hopping mobility is several orders of magnitude smaller than the electron mobility enables us to evaluate the integrals and obtain a closed form solution to the transport equations. Calculated results include current versus voltage behavior, electrostatic potential and electric field versus position for a given bias. It is concluded that the injected electron current is dominant for the store-mode applied bias.

  15. Band structure and Fermi surface of electron-doped C60 monolayers.

    PubMed

    Yang, W L; Brouet, V; Zhou, X J; Choi, Hyoung J; Louie, Steven G; Cohen, Marvin L; Kellar, S A; Bogdanov, P V; Lanzara, A; Goldoni, A; Parmigiani, F; Hussain, Z; Shen, Z-X

    2003-04-11

    C60 fullerides are challenging systems because both the electron-phonon and electron-electron interactions are large on the energy scale of the expected narrow band width. We report angle-resolved photoemission data on the band dispersion for an alkali-doped C60 monolayer and a detailed comparison with theory. Compared to the maximum bare theoretical band width of 170 meV, the observed 100-meV dispersion is within the range of renormalization by electron-phonon coupling. This dispersion is only a fraction of the integrated peak width, revealing the importance of many-body effects. Additionally, measurements on the Fermi surface indicate the robustness of the Luttinger theorem even for materials with strong interactions.

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

    NASA Astrophysics Data System (ADS)

    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

  17. Band gaps, ionization potentials, and electron affinities of periodic electron systems via the adiabatic-connection fluctuation-dissipation theorem

    NASA Astrophysics Data System (ADS)

    Trushin, Egor; Betzinger, Markus; Blügel, Stefan; Görling, Andreas

    2016-08-01

    An approach to calculate fundamental band gaps, ionization energies, and electron affinities of periodic electron systems is explored. Starting from total energies obtained with the help of the adiabatic-connection fluctuation-dissipation (ACFD) theorem, these physical observables are calculated according to their basic definition by differences of the total energies of the N -, (N -1 ) -, and (N +1 ) -electron system. The response functions entering the ACFD theorem are approximated here by the direct random phase approximation (dRPA). For a set of prototypical semiconductors and insulators it is shown that even with this quite drastic approximation the resulting band gaps are very close to experiment and of a similar quality to those from the computationally more involved G W approximation. By going beyond the dRPA in the future the accuracy of the calculated band gaps may be significantly improved further.

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

    NASA Astrophysics Data System (ADS)

    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.

  19. Interaction of Cr(3+) with valence and conduction bands in the long persistent phosphor ZnGa2O4:Cr(3+), studied by ENDOR spectroscopy.

    PubMed

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

    2016-09-28

    Cr(3+)-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 (71/69)Ga and (53)Cr nuclei was performed in ZnGa2O4:Cr(3+) to get information on the interaction of Cr(3+) with valence and conduction bands. The positive electron spin density at Ga nuclei revealed a dominant interaction of the (4)A2 ground state of Cr(3+) with the valence band, and a weaker interaction with the conduction band. The latter may occur only in the excited (2)E and (4)T2 states of Cr(3+). It is proposed that when these two interactions are present, pairs of electrons and holes can be generated from excited Cr(3+) in distorted sites undergoing local electric field produced by neighboring defects with opposite charges.

  20. Ag-graphene hybrid conductive ink for writing electronics

    NASA Astrophysics Data System (ADS)

    Xu, L. Y.; Yang, G. Y.; Jing, H. Y.; Wei, J.; Han, Y. D.

    2014-02-01

    With the aim of preparing a method for the writing of electronics on paper by the use of common commercial rollerball pens loaded with conductive ink, hybrid conductive ink composed of Ag nanoparticles (15 wt%) and graphene-Ag composite nanosheets (0.15 wt%) formed by depositing Ag nanoparticles (˜10 nm) onto graphene sheets was prepared for the first time. Owing to the electrical pathway effect of graphene and the decreased contact resistance of graphene junctions by depositing Ag nanoparticles (NPs) onto graphene sheets, the concentration of Ag NPs was significantly reduced while maintaining high conductivity at a curing temperature of 100 ° C. A typical resistivity value measured was 1.9 × 10-7 Ω m, which is 12 times the value for bulk silver. Even over thousands of bending cycles or rolling, the resistance values of writing tracks only increase slightly. The stability and flexibility of the writing circuits are good, demonstrating the promising future of this hybrid ink and direct writing method.

  1. Mixed-valence effects and metamagnetism in a two-band model of correlated electrons

    NASA Astrophysics Data System (ADS)

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

    1986-03-01

    We discuss both continuous and discontinuous transitions form para- to ferromagnetism within a model of electrons in double degenerate and hybridized band. We transform out rigorously the hybridization and obtain a two-band model with the component bands of substantially different width. This band structure is approximated by a band and a level placed in the center of the band. The model is solved both with and without applied magnetic field, within the Hartree-Fock approximation for the intraband and the interband interactions, and treating the Coulomb interactions on the level exactly. The self-consistent solutions for the magnetic moment and the band filling are given allowing for a redistribution of particles between the band and the level. A number of ferromagnetic and mixed-valent-type of configurations is possible, leading to a possibility of appearance of ferromagnetism in a discontinuous way and without the Stoner condition being fulfilled at the transition. Such transition cannot be described within the standard Ginzburg-Landau theory obtained from the Stoner-Wohlfarth model for a single band. The obtained result are used to give a qualitative explanation of the main results observed for the systems Co(S 1 - xSe x) 2 and CoTi 1 - xAl x.

  2. Electronic structure and optical properties of noncentrosymmetric LiGaSe2: Experimental measurements and DFT band structure calculations

    NASA Astrophysics Data System (ADS)

    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.

  3. Topological Metal of NaBi with Ultralow Lattice Thermal Conductivity and Electron-phonon Superconductivity

    PubMed Central

    Li, Ronghan; Cheng, Xiyue; Xie, Qing; Sun, Yan; Li, Dianzhong; Li, Yiyi; Chen, Xing-Qiu

    2015-01-01

    By means of first-principles and ab initio tight-binding calculations, we found that the compound of NaBi is a three-dimensional non-trivial topological metal. Its topological feature can be confirmed by the presence of band inversion, the derived effective Z2 invariant and the non-trivial surface states with the presence of Dirac cones. Interestingly, our calculations further demonstrated that NaBi exhibits the uniquely combined properties between the electron-phonon coupling superconductivity in nice agreement with recent experimental measurements and the obviously anisotropic but extremely low thermal conductivity. The spin-orbit coupling effects greatly affect those properties. NaBi may provide a rich platform to study the relationship among metal, topology, superconductivity and thermal conductivity. PMID:25676863

  4. Universal frequency-dependent conduction of electron glasses

    NASA Astrophysics Data System (ADS)

    Amir, Ariel

    2014-03-01

    Characterizing the frequency-dependent response of amorphous systems and glasses can provide important insights into their physics. Here, we study the response of an electronic glass, where Coulomb interactions are important and have previously been shown to significantly modify the conductance and lead to memory effects and aging. We propose a model which allows us to take the interactions into account in a self-consistent way, and explore the transport properties at all frequencies. Within the model, the response maps exactly to a (linear) network of resistors, self-capacitances and mutual capacitances. The response of this equivalent electric circuit is found numerically, and is shown to obey the universal scaling which is experimentally observed for a large class of amorphous solids.

  5. Observation of interface band structure by ballistic-electron-emission microscopy

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Kaiser, W. J.

    1988-01-01

    The paper reports an advanced ballistic electron spectroscopy technique that was used to directly measure semiconductor band structure properties at a subsurface interface. Two interface systems having contrasting band structures were investigated by this method: Au-Si and Au-GaAs. It is concluded that the proposed method, based on scanning tunneling microscopy, enables the spatially resolved carrier-transport spectroscopy of interfaces.

  6. Hydrogen production by Tuning the Photonic Band Gap with the Electronic Band Gap of TiO2

    PubMed Central

    Waterhouse, G. I. N.; Wahab, A. K.; Al-Oufi, M.; Jovic, V.; Anjum, D. H.; Sun-Waterhouse, D.; Llorca, J.; Idriss, H.

    2013-01-01

    Tuning the photonic band gap (PBG) to the electronic band gap (EBG) of Au/TiO2 catalysts resulted in considerable enhancement of the photocatalytic water splitting to hydrogen under direct sunlight. Au/TiO2 (PBG-357 nm) photocatalyst exhibited superior photocatalytic performance under both UV and sunlight compared to the Au/TiO2 (PBG-585 nm) photocatalyst and both are higher than Au/TiO2 without the 3 dimensionally ordered macro-porous structure materials. The very high photocatalytic activity is attributed to suppression of a fraction of electron-hole recombination route due to the co-incidence of the PBG with the EBG of TiO2 These materials that maintain their activity with very small amount of sacrificial agents (down to 0.5 vol.% of ethanol) are poised to find direct applications because of their high activity, low cost of the process, simplicity and stability. PMID:24108361

  7. Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy

    PubMed Central

    Jobst, Johannes; van der Torren, Alexander J. H.; Krasovskii, Eugene E.; Balgley, Jesse; Dean, Cory R.; Tromp, Rudolf M.; van der Molen, Sense Jan

    2016-01-01

    High electron mobility is one of graphene's key properties, exploited for applications and fundamental research alike. Highest mobility values are found in heterostructures of graphene and hexagonal boron nitride, which consequently are widely used. However, surprisingly little is known about the interaction between the electronic states of these layered systems. Rather pragmatically, it is assumed that these do not couple significantly. Here we study the unoccupied band structure of graphite, boron nitride and their heterostructures using angle-resolved reflected-electron spectroscopy. We demonstrate that graphene and boron nitride bands do not interact over a wide energy range, despite their very similar dispersions. The method we use can be generally applied to study interactions in van der Waals systems, that is, artificial stacks of layered materials. With this we can quantitatively understand the ‘chemistry of layers' by which novel materials are created via electronic coupling between the layers they are composed of. PMID:27897180

  8. Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy

    NASA Astrophysics Data System (ADS)

    Jobst, Johannes; van der Torren, Alexander J. H.; Krasovskii, Eugene E.; Balgley, Jesse; Dean, Cory R.; Tromp, Rudolf M.; van der Molen, Sense Jan

    2016-11-01

    High electron mobility is one of graphene's key properties, exploited for applications and fundamental research alike. Highest mobility values are found in heterostructures of graphene and hexagonal boron nitride, which consequently are widely used. However, surprisingly little is known about the interaction between the electronic states of these layered systems. Rather pragmatically, it is assumed that these do not couple significantly. Here we study the unoccupied band structure of graphite, boron nitride and their heterostructures using angle-resolved reflected-electron spectroscopy. We demonstrate that graphene and boron nitride bands do not interact over a wide energy range, despite their very similar dispersions. The method we use can be generally applied to study interactions in van der Waals systems, that is, artificial stacks of layered materials. With this we can quantitatively understand the `chemistry of layers' by which novel materials are created via electronic coupling between the layers they are composed of.

  9. Spatially resolved band alignments at Au-hexadecanethiol monolayer-GaAs(001) interfaces by ballistic electron emission microscopy

    SciTech Connect

    Junay, A.; Guézo, S. Turban, P.; Delhaye, G.; Lépine, B.; Tricot, S.; Ababou-Girard, S.; Solal, F.

    2015-08-28

    We study structural and electronic inhomogeneities in Metal—Organic Molecular monoLayer (OML)—semiconductor interfaces at the sub-nanometer scale by means of in situ Ballistic Electron Emission Microscopy (BEEM). BEEM imaging of Au/1-hexadecanethiols/GaAs(001) heterostructures reveals the evolution of pinholes density as a function of the thickness of the metallic top-contact. Using BEEM in spectroscopic mode in non-short-circuited areas, local electronic fingerprints (barrier height values and corresponding spectral weights) reveal a low-energy tunneling regime through the insulating organic monolayer. At higher energies, BEEM evidences new conduction channels, associated with hot-electron injection in the empty molecular orbitals of the OML. Corresponding band diagrams at buried interfaces can be thus locally described. The energy position of GaAs conduction band minimum in the heterostructure is observed to evolve as a function of the thickness of the deposited metal, and coherently with size-dependent electrostatic effects under the molecular patches. Such BEEM analysis provides a quantitative diagnosis on metallic top-contact formation on organic molecular monolayer and appears as a relevant characterization for its optimization.

  10. Electron beam fracturing of ZnO nanostructures and modification in optical band gap

    NASA Astrophysics Data System (ADS)

    Siraj, K.; Kanwal, M.; Saleem, S.; Pedarnig, J. D.; Rafique, M. S.; Naseem, S.

    2016-12-01

    In our previous work Siraj et al (J Alloys Comp 563:280, 2013), the electron beam irradiation at high energies (6-15 MeV) at constant dose of 30 Gy produced Zinc oxide elongated nanostructures and modified the optical band gap energies accordingly. In present work, those nanostructures are fractured to smaller sizes by increasing the electron doses to 100 and 200 Gy. The very high temperature gradient induced stresses are responsible for further fracturing of ZnO nanostructures. The optical properties such as refractive index, extinction coefficient and optical band gap energy have also modified when higher cumulative electron doses are used. The optical band gap energies are found to decrease by increasing electron doses at all used electron energies, which is attributed to the production of different defects like vacancies, unpaired bonds, nanovoids, nanocavities, nanocracks and high strains. The electron beam irradiation of ZnO thin films at used parameters (doses and energies) is found to be plausible technique to produce nanostructures of different sizes and accordingly modify the optical band gap energies. The results can be beneficial for optical and optoelectronic industries.

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

    NASA Astrophysics Data System (ADS)

    Chegel, Raad

    2016-06-01

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

  12. Band like Electronic Structures in Square Hollow Quantum Dots by 3D-MHFKS Calculation

    NASA Astrophysics Data System (ADS)

    Takizawa, Tokihiro; Okada, Hoshihito; Matsuse, Takehiro

    To find novel aspects of the electronic structures in quantum dots (QD) from a view point of spatial broken symmetry, 3-dimensional-mesh Hartree-Fock-Kohn-Sham (3D-MHFKS) calculations1 are applied to the interacting electron system of electron number N in a symmetry broken hollow QD. For the case of a square hollow quantum dot confined in square hard wall (HW) potential (SSHQD), the magnetic (B) field dependence of the obtained single particle energy levels and chemical potentials in B-N diagram are shown to have a band like electronic structures over the wide B-field range up to 20T. To clarify the origin of the band like electronic structures in SSHQD, 3D-MHFKS calculations are also applied for the mixed symmetry QD's with a circular hollow in square HW potential (SCHQD) and with a square hollow in circular HW potential (CSHQD).

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

    PubMed

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

    2016-06-08

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  15. Spectrophotometric method for optical band gap and electronic transitions determination of semiconductor materials

    NASA Astrophysics Data System (ADS)

    Sangiorgi, Nicola; Aversa, Lucrezia; Tatti, Roberta; Verucchi, Roberto; Sanson, Alessandra

    2017-02-01

    The optical band gap energy and the electronic processes involved are important parameters of a semiconductor material and it is therefore important to determine their correct values. Among the possible methods, the spectrophotometric is one of the most common. Several methods can be applied to determine the optical band gap energy and still now a defined consensus on the most suitable one has not been established. A highly diffused and accurate optical method is based on Tauc relationship, however to apply this equation is necessary to know the nature of the electronic transitions involved commonly related to the coefficient n. For this purpose, a spectrophotometric technique was used and we developed a graphical method for electronic transitions and band gap energy determination for samples in powder form. In particular, the n coefficient of Tauc equation was determined thorough mathematical elaboration of experimental results on TiO2 (anatase), ZnO, and SnO2. The results were used to calculate the band gap energy values and then compared with the information obtained by Ultraviolet Photoelectron Spectroscopy (UPS). This approach provides a quick and accurate method for band gap determination through n coefficient calculation. Moreover, this simple but reliable method can be used to evaluate the nature of electronic transition that occurs in a semiconductor material in powder form.

  16. Band offsets of n-type electron-selective contacts on cuprous oxide (Cu{sub 2}O) for photovoltaics

    SciTech Connect

    Brandt, Riley E. E-mail: buonassisi@mit.edu; Lee, Yun Seog; Buonassisi, Tonio E-mail: buonassisi@mit.edu; Young, Matthew; Dameron, Arrelaine; Teeter, Glenn; Park, Helen Hejin; Chua, Danny; Gordon, Roy G.

    2014-12-29

    The development of cuprous oxide (Cu{sub 2}O) photovoltaics (PVs) is limited by low device open-circuit voltages. A strong contributing factor to this underperformance is the conduction-band offset between Cu{sub 2}O and its n-type heterojunction partner or electron-selective contact. In the present work, a broad range of possible n-type materials is surveyed, including ZnO, ZnS, Zn(O,S), (Mg,Zn)O, TiO{sub 2}, CdS, and Ga{sub 2}O{sub 3}. Band offsets are determined through X-ray photoelectron spectroscopy and optical bandgap measurements. A majority of these materials is identified as having a negative conduction-band offset with respect to Cu{sub 2}O; the detrimental impact of this on open-circuit voltage (V{sub OC}) is evaluated through 1-D device simulation. These results suggest that doping density of the n-type material is important as well, and that a poorly optimized heterojunction can easily mask changes in bulk minority carrier lifetime. Promising heterojunction candidates identified here include Zn(O,S) with [S]/[Zn] ratios >70%, and Ga{sub 2}O{sub 3}, which both demonstrate slightly positive conduction-band offsets and high V{sub OC} potential. This experimental protocol and modeling may be generalized to evaluate the efficiency potential of candidate heterojunction partners for other PV absorbers, and the materials identified herein may be promising for other absorbers with low electron affinities.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  18. Dispersion of electronic bands in intermetallic compound LiBe and related properties

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.

    2015-10-01

    Based on the all-electron full-potential linearized augmented plane wave within density functional theory calculations dispersion of the electronic band structure, total and the angular momentum resolved projected density of states, the shape of Fermi surface, the electronic charge density distribution and the optical response of the intermetallic LiBe compound are performed. Seeking the influence of the different exchange correlations on the ground state properties of the intermetallic LiBe, calculations are performed within four types of exchange correlations, namely the local density approximation, general gradient approximation, Engel-Vosko generalized gradient approximation and the modified Becke-Johnson potential. It has been found that replacing the exchange correlations exhibit insignificant influence on the bands dispersion, density of states and hence the optical properties. The obtained results suggest that there exists a strong hybridization between the states resulting in covalent bonds. The Fermi surface is formed by two bands and the center of the Fermi surface is formed by holes. The electronic charge density distribution confirms that the charge is attracted toward Be atoms and the calculated bond lengths are in good accordance with the available experimental data. To get deep insight into the electronic structure, the optical properties are investigated and analyzed in accordance with the calculated band structure and the density of states.

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

    NASA Astrophysics Data System (ADS)

    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.

  20. Vanishing Electronic Energy Loss of Very Slow Light Ions in Insulators with Large Band Gaps

    SciTech Connect

    Markin, S. N.; Primetzhofer, D.; Bauer, P.

    2009-09-11

    Electronic energy loss of light ions in nanometer films of materials with large band gaps has been studied for very low velocities. For LiF, a threshold velocity is observed at 0.1 a.u. (250 eV/u), below which the ions move without transferring energy to the electronic system. For KCl, a lower (extrapolated) threshold velocity is found, identical for H and He ions. For SiO{sub 2}, no clear velocity threshold is observed for He particles. For protons and deuterons, electronic stopping is found to perfectly fulfill velocity scaling, as expected for binary ion-electron interaction.

  1. Valence electronic structure of semiconductor quantum dot and wide band gap oxide interfaces by ultraviolet photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Timp, Brooke Andrea

    Energy level alignment is an important factor in efficient charge transfer at an interface between two semiconductors. This topic is explored in model systems that are relevant to quantum dot-sensitized solar cells, inorganic semiconductor nanoparticles adsorbed on single crystal wide band gap oxide substrates, using ultraviolet photoelectron spectroscopy. Cadmium selenide quantum dots are assembled on a ZnO (10 1¯ 0) surface using 3-mercaptopropionic acid linkers. The valence band maximum of the CdSe quantum dots is found to be located at 1.1 +/- 0.1 eV above the valence band maximum of ZnO, nearly independent of the size of the quantum dots (2.1-4.2 nm). This finding suggests that, upon adsorption, there is strong electronic interaction between CdSe quantum dots and the ZnO surface. As a result, varying the quantum dot size mainly tunes the alignment of the conduction band minimum of CdSe with respect to that of the ZnO surface. Sub-monolayer films of PbSe quantum dots are prepared on single crystal substrates, ZnO (10 1 0 ) and TiO2 (110), and exposed to ligand solutions, either hydrazine or 1,2-ethanedithiol (EDT) in acetonitrile. Interfacial energy alignment is measured as a function of quantum dot size, substrate and ligand treatment. The affect of the ligand treatments on the energy alignment is substrate-dependent. The valence band maximum of the dots is size-independent on ZnO due to strong electronic interactions with the substrate; in particular, EDT-treated films show significant enhancement of quantum dot valence band intensity due to electronic coupling with the ZnO surface. In contrast, the quantum dot valence band maximum is size-dependent and shows a smaller shift between ligand treatments for films on TiO2, suggesting weaker quantum dot-substrate interactions. In most cases the measured alignment predicts that electron injection from a photoexcited PbSe quantum dot to either ZnO or TiO2 will necessitate the involvement of higher-lying levels

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

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

    PubMed Central

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

    2017-01-01

    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. PMID:28272444

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

    NASA Astrophysics Data System (ADS)

    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.

  5. A free-electron model for the Dirac bands in graphene

    NASA Astrophysics Data System (ADS)

    Kissinger, G. S.; Satpathy, S.

    2016-11-01

    We present a new method for describing the electronic structure of graphene, by treating the honeycomb lattice as an arrangement of crisscrossing one-dimensional quantum wires. The electrons travel as free particles along the wires and interfere at the three-way junctions formed by the carbon atoms. The approach produces the linearly dispersive Dirac band structure as well as the chiral pseudo-spin-wave functions. When vacancies are incorporated, the model reproduces the well known zero mode states.

  6. Substitutional Electron and Hole Doping of WSe2 : Synthesis, Electrical Characterization, and Observation of Band-to-Band Tunneling

    NASA Astrophysics Data System (ADS)

    Mukherjee, R.; Chuang, H. J.; Koehler, M. R.; Combs, N.; Patchen, A.; Zhou, Z. X.; Mandrus, D.

    2017-03-01

    Transition-metal dichalcogenides (TMDs) such as MoS2 , MoSe2 , and WSe2 have emerged as promising two-dimensional semiconductors. Many anticipated applications of these materials require both p -type and n -type TMDs with long-term doping stability. Here, we report on the synthesis of substitutionally doped WSe2 crystals using Nb and Re as p - and n -type dopants, respectively. Hall coefficient and gate-dependent transport measurements reveal drastically different doping properties between nominally 0.5% Nb- and 0.5% Re-doped WSe2 . While 0.5% Nb-doped WSe2 (WSe2∶Nb ) is degenerately hole doped with a nearly temperature-independent carrier density of approximately 1019 cm-3 , electrons in 0.5% Re-doped WSe2 (WSe2 ∶Re ) are largely trapped in localized states below the mobility edge and exhibit thermally activated behavior. Charge transport in both WSe2∶Nb and WSe2 ∶Re is found to be limited by Coulomb scattering from ionized impurities. Furthermore, we fabricate vertical van der Waals-junction diodes consisting of multilayers of WSe2∶Nb and WSe2 ∶Re . Finally, we demonstrate reverse rectifying behavior as a direct proof of band-to-band tunneling in our WSe2∶Nb /WSe2∶Re diodes.

  7. Conductivity Modifications of Graphene by Electron Donative Organic Molecules

    NASA Astrophysics Data System (ADS)

    Masujima, Hiroaki; Mori, Takehiko; Hayamizu, Yuhei

    2017-03-01

    Graphene has been studied for the application of transparent electrodes in flexible electrical devices with semiconductor organics. Control of the charge carrier density in graphene is crucial to reduce the contact resistance between graphene and the active layer of organic semiconductor. Chemical doping of graphene is an approach to change the carrier density, where the adsorbed organic molecules donate or accept electrons form graphene. While various acceptor organic molecules have been demonstrated so far, investigation about donor molecules is still poor. In this work, we have investigated doping effect in graphene field-effect transistors functionalized by organic donor molecules such as dibenzotetrathiafulvalene (DBTTF), hexamethyltetrathiafulvalene (HMTTF), 1,5-diaminonaphthalene (DAN), and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD). Based on conductivity measurements of graphene transistors, the former three molecules do not have any significant effect to graphene transistors. However, TMPD shows effective n-type doping. The doping effect has a correlation with the level of highest occupied molecular orbital (HOMO) of each molecule, where TMPD has the highest HOMO level.

  8. Electronic band structure trends of perovskite halides: Beyond Pb and Sn to Ge and Si

    NASA Astrophysics Data System (ADS)

    Huang, Ling-yi; Lambrecht, Walter R. L.

    2016-05-01

    The trends in electronic band structure are studied in the cubic A B X3 halide perovskites for A =Cs ; B =Pb , Sn, Ge, Si; and X =I , Br, Cl. The gaps are found to decrease from Pb to Sn and from Ge to Si, but increase from Sn to Ge. The trend is explained in terms of the atom s levels of the group-IV element and the atomic sizes which changes the amount of hybridization with X -p and hence the valence bandwidth. Along the same series spin-orbit coupling also decreases and this tends to increase the gap because of the smaller splitting of the conduction band minimum. Both effects compensate each other to a certain degree. The trend with halogens is to reduce the gap from Cl to I, i.e., with decreasing electronegativity. The role of the tolerance factor in avoiding octahedron rotations and octahedron edge sharing is discussed. The Ge containing compounds have tolerance factor t >1 and hence do not show the series of octahedral rotation distortions and the existence of edge-sharing octahedral phases known for Pb and Sn-based compounds, but rather a rhombohedral distortion. CsGeI3 is found to have a suitable gap for photovoltaics both in its cubic (high-temperature) and rhombohedral (low-temperature) phases. The structural stability of the materials in the different phases is also discussed. We find the rhombohedral phase to have lower total energy and slightly larger gaps but to present a less significant distortion of the band structure than the edge-sharing octahedral phases, such as the yellow phase in CsSnI3. The corresponding silicon based compounds have not yet been synthesized and therefore our estimates are less certain but indicate a small gap for cubic CsSiI3 and CsSiBr3 of about 0.2 ±0.2 eV and 0.8 ±0.6 eV for CsSiCl3. The intrinsic stability of the Si compounds is discussed.

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

    SciTech Connect

    Yamaguchi, Hisato; Ogawa, Shuichi; Watanabe, Daiki; Hozumi, Hideaki; Gao, Yongqian; Eda, Goki; Mattevi, Cecilia; Fujita, Takeshi; Yoshigoe, Akitaka; Ishizuka, Shinji; Adamska, Lyudmyla; Yamada, Takatoshi; Dattelbaum, Andrew M.; Gupta, Gautam; Doorn, Stephen K.; Velizhanin, Kirill A.; Teraoka, Yuden; Chen, Mingwei; Htoon, Han; Chhowalla, Manish; Mohite, Aditya D.; Takakuwa, Yuji

    2016-09-01

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

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

    DOE PAGES

    Yamaguchi, Hisato; Ogawa, Shuichi; Watanabe, Daiki; ...

    2016-09-01

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

  11. Electron concentrations calculated from the lower hybrid resonance noise band observed by Ogo 3.

    NASA Technical Reports Server (NTRS)

    Burtis, W. J.

    1973-01-01

    A noise band at the lower hybrid resonance (LHR) is often detected by the VLF and ELF receivers on Ogo 3, using the electric antenna. In some cases the noise band is at the geometric mean gyrofrequency as measured by the Goddard Space Flight Center (GSFC) magnetometer, and local LHR in a dense H(+) plasma is indicated; in such cases, electron concentration can be calculated, if it is assumed that heavy ions are negligible. Observations at midlatitudes and altitudes of a few earth radii show local concentrations as low as 1.4 electrons/cu cm. In one case the concentrations obtained from the LHR noise band agree with those measured simultaneously by the GSFC ion mass spectrometer within a factor of 2. In another case the concentration is observed to fall by a factor of 2 in 150 km and then to decrease roughly as R to the minus fourth power, in agreement with whistler measurements outside the plasmapause.

  12. Minority-spin band parameters in a NiMnSb thin film determined by spectral conductivity

    SciTech Connect

    Grigorescu, C.E.A.; Trodahl, H.J.; Strickland, N.M.; Bittar, A.; Manea, S.A.; Giapintzakis, J.; Monnereau, O.; Notonier, R.; Kennedy, V.J.

    2004-12-01

    NiMnSb is expected to be a ferromagnetic half metal, an expectation that is based in part on band structure calculations. Here we report optical conductivity studies of the band structure for a film prepared by pulsed laser deposition onto a Si substrate held at a relatively low temperature as is required for some device applications--films which are susceptible to site disorder associated with the vacant site in this half-Heusler compound. We demonstrate that the direct interband transitions are essentially unshifted in comparison with bulk material, though they are somewhat broadened. Below the direct-transition absorption edge we report the presence of indirect spin-reversing transitions between the Fermi energy (E{sub f}) and the extrema of the minority-spin valence and conduction bands, providing a measure of the band edge energies. Both of these edges appear closer to E{sub f} than is seen in well-ordered bulk NiMnSb, with the conduction-band minimum showing weight at only 200 cm{sup -1} above E{sub f}, close enough to have substantial occupation at ambient temperature.

  13. Tuning the electronic band-gap of fluorinated 3C-silicon carbide nanowires

    NASA Astrophysics Data System (ADS)

    Miranda Durán, Álvaro; Trejo Baños, Alejandro; Pérez, Luis Antonio; Cruz Irisson, Miguel

    The possibility of control and modulation of the electronic properties of silicon carbide nanowires (SiCNWs) by varying the wire diameter is well known. SiCNWs are particularly interesting and technologically important, due to its electrical and mechanical properties, allowing the development of materials with specific electronic features for the design of stable and robust electronic devices. Tuning the band gap by chemical surface passivation constitutes a way for the modification of the electronic band gap of these nanowires. We present, the structural and electronic properties of fluorinated SiCNWs, grown along the [111] crystallographic direction, which are investigated by first principles. We consider nanowires with six diameters, varying from 0.35 nm to 2.13 nm, and eight random covering schemes including fully hydrogen- and fluorine terminated ones. Gibbs free energy of formation and electronic properties were calculated for the different surface functionalization schemes and diameters considered. The results indicate that the stability and band gap of SiCNWs can be tuned by surface passivation with fluorine atoms This work was supported by CONACYT infrastructure project 252749 and UNAM-DGAPA-PAPIIT IN106714. A.M. would like to thank for financial support from CONACyT-Retención. Computing resources from proyect SC15-1-IR-27 of DGTIC-UNAM are acknowledged.

  14. Thermodynamic consequence of the new attribution of bands in the electronic absorption spectrum of electron donor-iodine-solvent systems

    NASA Astrophysics Data System (ADS)

    Abramov, Sergey P.

    1999-06-01

    The subject review pays attention to the peculiarities in behaviour of bands in the electronic absorption spectra of electron donor-iodine-solvent systems, the appearance of which is associated with the intermolecular interaction of molecular iodine with electron donor organic molecules. The new concept of the bands’ attribution to the isomeric equilibrium molecular charge-transfer complexes (CTCs) of CTC-I and CTC-II types is considered. The features of possible phase transitions in the solid state are discussed on the basis of the thermodynamic properties and electronic structures of the CTC-I and CTC-II in electron donor-iodine-solvent systems. The stabilisation of the CTC-II structure with the temperature lowering coincided in many cases with the electrons’ localisation in the solid state structures having charge-transfer bonds.

  15. Time-resolved observation of band-gap shrinking and electron-lattice thermalization within X-ray excited gallium arsenide.

    PubMed

    Ziaja, Beata; Medvedev, Nikita; Tkachenko, Victor; Maltezopoulos, Theophilos; Wurth, Wilfried

    2015-12-11

    Femtosecond X-ray irradiation of solids excites energetic photoelectrons that thermalize on a timescale of a few hundred femtoseconds. The thermalized electrons exchange energy with the lattice and heat it up. Experiments with X-ray free-electron lasers have unveiled so far the details of the electronic thermalization. In this work we show that the data on transient optical reflectivity measured in GaAs irradiated with femtosecond X-ray pulses can be used to follow electron-lattice relaxation up to a few tens of picoseconds. With a dedicated theoretical framework, we explain the so far unexplained reflectivity overshooting as a result of band-gap shrinking. We also obtain predictions for a timescale of electron-lattice thermalization, initiated by conduction band electrons in the temperature regime of a few eVs. The conduction and valence band carriers were then strongly non-isothermal. The presented scheme is of general applicability and can stimulate further studies of relaxation within X-ray excited narrow band-gap semiconductors.

  16. Formation of Hubbard-like bands as a fingerprint of strong electron-electron interactions in FeSe

    NASA Astrophysics Data System (ADS)

    Watson, Matthew D.; Backes, Steffen; Haghighirad, Amir A.; Hoesch, Moritz; Kim, Timur K.; Coldea, Amalia I.; Valentí, Roser

    2017-02-01

    We use angle-resolved photoemission spectroscopy (ARPES) to explore the electronic structure of single crystals of FeSe over a wide range of binding energies and study the effects of strong electron-electron correlations. We provide evidence for the existence of "Hubbard-like bands" at high binding energies consisting of incoherent many-body excitations originating from Fe 3 d states in addition to the renormalized quasiparticle bands near the Fermi level. Many high-energy features of the observed ARPES data can be accounted for when incorporating the effects of strong local Coulomb interactions in calculations of the spectral function via dynamical mean-field theory, including the formation of a Hubbard-like band. This shows that over the energy scale of several eV, local correlations arising from the on-site Coulomb repulsion and Hund's coupling are essential for a proper understanding of the electronic structure of FeSe and other related iron-based superconductors.

  17. Effects of extrinsic and intrinsic perturbations on the electronic structure of graphene: Retaining an effective primitive cell band structure by band unfolding

    NASA Astrophysics Data System (ADS)

    Medeiros, Paulo V. C.; Stafström, Sven; Björk, Jonas

    2014-01-01

    We use a band unfolding technique to recover an effective primitive cell picture of the band structure of graphene under the influence of different types of perturbations. This involves intrinsic perturbations, such as structural defects, and external ones, comprising nitrogen substitutions and the inclusion of graphene in adsorbed systems. In such cases, the band unfolding provides a reliable and efficient tool for quantitatively analyzing the effect of doping and defects on the electronic structure of graphene. We envision that this approach will become a standard method in the computational analysis of graphene's electronic structure in related systems.

  18. Observations of Multi-band Structures in Double Star TC-1 PEACE Electron and HIA Ion Data

    NASA Astrophysics Data System (ADS)

    Mohan Narasimhan, K.; Fazakerley, A. N.; Grimald, S.; Dandouras, I. S.; Mihaljcic, B.; Kistler, L. M.; Owen, C. J.

    2015-12-01

    Several authors have reported inner magnetosphere observations of proton distributions confined to narrow energy bands in the range 1 - 25 keV (Smith and Hoffman (1974), etc). These structures have been described as "nose structures", with reference to their appearance in energy-time spectrograms and are also known as "bands" if they occur for extended periods of time. Multi-nose structures have been observed if 2 or more noses appear at the same time (Vallat et al., 2007). Gaps between "noses" (or "bands") have been explained in terms of the competing corotation, convection and magnetic gradient drifts. Charge exchange losses in slow drift paths for steady state scenarios and the role of substorm injections have also been considered (Li et al., 2000; Ebihara et al., 2004). We analyse observations of electron and ion multi-band structures frequently seen in Double-Star TC1 PEACE and HIA data. We present results from statistical surveys conducted using data from the duration of the mission. Furthermore, using a combination of both statistics and simulations, we test previous theories as to possible formation mechanisms and explore other possible explanations.

  19. Effect of boron localized states on the conduction band transport in B{sub x}Ga{sub 1−x}P

    SciTech Connect

    Petznick, S.; Ostheim, L. Klar, P. J.; Liebich, S.; Volz, K.; Stolz, W.

    2014-12-01

    We study the magnetotransport properties of an n-type (B,Ga)P:Te alloy and an n-type GaP:Te reference under hydrostatic pressure up to 17 kilobars in the temperature range from 1.5 to 300 K. The free carrier concentration and the mobility of the reference sample are almost independent of the applied hydrostatic pressure at room temperature. In contrast, the free carrier concentration as well as the mobility in the B{sub 0.012}Ga{sub 0.988}P:Te alloy increase by about 30% over the accessible pressure range. The observations are explained by assuming that a boron-related density of localized states exists in the vicinity of the conduction band edge of the alloy. These boron states act as electron traps as well as efficient scatter centers. Applying hydrostatic pressure shifts the energetic positions of conduction band edge at the X-point (where the electron transport takes place) and of the boron states apart reducing the impact of boron on the electronic transport properties of the alloy.

  20. Electronic band structure of zinc blende CdSe and rock salt PbSe semiconductors with silicene-type honeycomb geometry

    NASA Astrophysics Data System (ADS)

    Delerue, Christophe; Vanmaekelbergh, D.

    2015-09-01

    We report on the electronic band structure of 2D CdSe and PbSe semiconductors that have a silicene-type honeycomb geometry. Atomistic tight-binding calculations are performed on several model systems that bear a strong resemblance to the silicene-type honeycomb structures that were recently obtained by nanocrystal self-assembly. The calculated band structures are compared both to those of 2D quantum wells and graphene-type honeycomb structures. It is found that in silicene type CdSe honeycomb structures, the lowest electron conduction bands (derived from S-type nanocrystal wave functions) form a Dirac-type dispersion, very similar as in graphene. The P-type bands are usually more complex. However, when the hybridization between S- and P-type bands increases, a second Dirac cone and a genuine non-trivial flat band is observed, similar as in the case of graphene-type honeycomb structures of CdSe. There is a strong non-trivial gap between the first and second valence band, hosting the quantum spin Hall effect. Silicene-type PbSe structures show Dirac features in their bands, which however can be clouded due to the multi-valley character of PbSe.

  1. Band-gap measurements of direct and indirect semiconductors using monochromated electrons

    SciTech Connect

    Gu Lin; Srot, Vesna; Sigle, Wilfried; Koch, Christoph; Aken, Peter van; Ruehle, Manfred; Scholz, Ferdinand; Thapa, Sarad B.; Kirchner, Christoph; Jetter, Michael

    2007-05-15

    With the development of monochromators for transmission electron microscopes, valence electron-energy-loss spectroscopy (VEELS) has become a powerful technique to study the band structure of materials with high spatial resolution. However, artifacts such as Cerenkov radiation pose a limit for interpretation of the low-loss spectra. In order to reveal the exact band-gap onset using the VEELS method, semiconductors with direct and indirect band-gap transitions have to be treated differently. For direct semiconductors, spectra acquired at thin regions can efficiently minimize the Cerenkov effects. Examples of hexagonal GaN (h-GaN) spectra acquired at different thickness showed that a correct band-gap onset value can be obtained for sample thicknesses up to 0.5 t/{lambda}. In addition, {omega}-q maps acquired at different specimen thicknesses confirm the thickness dependency of Cerenkov losses. For indirect semiconductors, the correct band-gap onset can be obtained in the dark-field mode when the required momentum transfer for indirect transition is satisfied. Dark-field VEEL spectroscopy using a star-shaped entrance aperture provides a way of removing Cerenkov effects in diffraction mode. Examples of Si spectra acquired by displacing the objective aperture revealed the exact indirect transition gap E{sub g} of 1.1 eV.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  3. Understanding the electronic band structure of Pt-alloys for surface reactivity

    NASA Astrophysics Data System (ADS)

    Jung, Jongkeun; Kim, Beomyoung; Hong, Ji Sook; Jin, Tae Won; Shim, Ji Hoon; Nemsak, Slavomir; Denlinger, Jonathan D.; Masashi, Arita; Kenya, Shimada; Kim, Changyoung; Mun, Bongjin Simon

    In polymer exchange membrane fuel cell (PEMFC), the oxygen reduction reaction (ORR) at cathode side has been continuously investigated due to its critical importance in performance of fuel cell. So far, even with best industrial catalyst made with Pt, the performance of ORR is too far below from the commercial purpose. In 2007, Stamenkovic et al. showed that Pt alloys with 3- dtransition metal exhibited significantly improved ORR performance and pointed out the altered electronic structure of surface as the major contributing factor for enhanced ORR. Since 1990, with the advance of DFT calculation, the trend of surface chemical reactivity is explained with the analysis of d-band structures, known as d-band model. While d-band provides valid insight on surface chemical reactivity based on the valence band DOS, the relation between surface work function and DOS has not been well understood. The element-specific local electronic band structure of Pt alloys are identified by ARPES measurement, and the correlation between surface work function and local charge density is investigated.

  4. Long-term drift induced by the electronic crosstalk in Terra MODIS Band 29

    NASA Astrophysics Data System (ADS)

    Sun, Junqiang; Madhavan, Sriharsha; Xiong, Xiaoxiong; Wang, Menghua

    2015-10-01

    Terra MODerate Resolution Imaging Spectroradiometer (MODIS) is one of the key sensors in the NASA's Earth Observing System, which has successfully completed 15 years of on-orbit operation. Terra MODIS continues to collect valuable information of the Earth's energy radiation from visible to thermal infrared wavelengths. The instrument has been well characterized over its lifetime using onboard calibrators whose calibration references are traceable to the National Institute of Standards and Technology standards. In this paper, we focus on the electronic crosstalk effect of Terra MODIS band 29, a thermal emissive band (TEB) whose center wavelength is 8.55 µm. Previous works have established the mechanism to describe the effect of the electronic crosstalk in the TEB channels of Terra MODIS. This work utilizes the established methodology to apply to band 29. The electronic crosstalk is identified and characterized using the regularly scheduled lunar observations. The moon being a near-pulse-like source allowed easy detection of extraneous signals around the actual Moon surface. First, the crosstalk-transmitting bands are identified along with their amplitudes. The crosstalk effect then is characterized using a moving average mechanism that allows a high fidelity of the magnitude to be corrected. The lunar-based analysis unambiguously shows that the crosstalk contamination is becoming more severe in recent years and should be corrected in order to maintain calibration quality for the affected spectral bands. Finally, two radiometrically well-characterized sites, Pacific Ocean and Libya 1 desert, are used to assess the impact of crosstalk effect. It is shown that the crosstalk contamination induces a long-term upward drift of 1.5 K in band 29 brightness temperature of MODIS Collection 6 L1B, which could significantly impact the science products. The crosstalk effect also induces strong detector-to-detector differences, which result in severe stripping in the Earth view

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

    SciTech Connect

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

    2016-05-09

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

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

    DOE PAGES

    Wang, Zhenbin; Chu, Iek -Heng; Zhou, Fei; ...

    2016-05-09

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

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

    SciTech Connect

    Peterman, D.J.

    1980-01-01

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

  8. Effect of electron-phonon interaction range for a half-filled band in one dimension.

    PubMed

    Hohenadler, Martin; Assaad, Fakher F; Fehske, Holger

    2012-09-14

    We demonstrate that fermion-boson models with nonlocal interactions can be simulated at finite band filling with the continuous-time quantum Monte Carlo method. We apply this method to explore the influence of the electron-phonon interaction range for a half-filled band in one dimension, covering the full range from the Holstein to the Fröhlich regime. The phase diagram contains metallic, Peierls, and phase-separated regions. Nonlocal interactions suppress the Peierls instability, and thereby lead to almost degenerate power-law exponents for charge and pairing correlations.

  9. Phase analysis on dual-phase steel using band slope of electron backscatter diffraction pattern.

    PubMed

    Kang, Jun-Yun; Park, Seong-Jun; Moon, Man-Been

    2013-08-01

    A quantitative and automated phase analysis of dual-phase (DP) steel using electron backscatter diffraction (EBSD) was attempted. A ferrite-martensite DP microstructure was produced by intercritical annealing and quenching. An EBSD map of the microstructure was obtained and post-processed for phase discrimination. Band slope (BS), which was a measure of pattern quality, exhibited much stronger phase contrast than another conventional one, band contrast. Owing to high sensitivity to lattice defect and little orientation dependence, BS provided handiness in finding a threshold for phase discrimination. Its grain average gave a superior result on the discrimination and volume fraction measurement of the constituent phases in the DP steel.

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

    SciTech Connect

    Lambrecht, W.R.L.; Rashkeev, S.N.; Segall, B.

    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.

  11. Ab initio electronic band structure study of III-VI layered semiconductors

    NASA Astrophysics Data System (ADS)

    Olguín, Daniel; Rubio-Ponce, Alberto; Cantarero, Andrés

    2013-08-01

    We present a total energy study of the electronic properties of the rhombohedral γ-InSe, hexagonal ɛ-GaSe, and monoclinic GaTe layered compounds. The calculations have been done using the full potential linear augmented plane wave method, including spin-orbit interaction. The calculated valence bands of the three compounds compare well with angle resolved photoemission measurements and a discussion of the small discrepancies found has been given. The present calculations are also compared with recent and previous band structure calculations available in the literature for the three compounds. Finally, in order to improve the calculated band gap value we have used the recently proposed modified Becke-Johnson correction for the exchange-correlation potential.

  12. Novel Iron-based ternary amorphous oxide semiconductor with very high transparency, electronic conductivity, and mobility

    PubMed Central

    Malasi, A.; Taz, H.; Farah, A.; Patel, M.; Lawrie, B.; Pooser, R.; Baddorf, A.; Duscher, G.; Kalyanaraman, R.

    2015-01-01

    Here we report that ternary metal oxides of type (Me)2O3 with the primary metal (Me) constituent being Fe (66 atomic (at.) %) along with the two Lanthanide elements Tb (10 at.%) and Dy (24 at.%) can show excellent semiconducting transport properties. Thin films prepared by pulsed laser deposition at room temperature followed by ambient oxidation showed very high electronic conductivity (>5 × 104 S/m) and Hall mobility (>30 cm2/V-s). These films had an amorphous microstructure which was stable to at least 500 °C and large optical transparency with a direct band gap of 2.85 ± 0.14 eV. This material shows emergent semiconducting behavior with significantly higher conductivity and mobility than the constituent insulating oxides. Since these results demonstrate a new way to modify the behaviors of transition metal oxides made from unfilled d- and/or f-subshells, a new class of functional transparent conducting oxide materials could be envisioned. PMID:26670421

  13. Novel Iron-based ternary amorphous oxide semiconductor with very high transparency, electronic conductivity, and mobility

    SciTech Connect

    Malasi, A.; Taz, H.; Farah, A.; Patel, M.; Lawrie, Benjamin; Pooser, R.; Baddorf, A.; Duscher, G.; Kalyanaraman, R.

    2015-12-16

    We report that ternary metal oxides of type (Me)2O3 with the primary metal (Me) constituent being Fe (66 atomic (at.) %) along with the two Lanthanide elements Tb (10 at.%) and Dy (24 at.%) can show excellent semiconducting transport properties. Thin films prepared by pulsed laser deposition at room temperature followed by ambient oxidation showed very high electronic conductivity (>5 × 104 S/m) and Hall mobility (>30 cm2/V-s). These films had an amorphous microstructure which was stable to at least 500 °C and large optical transparency with a direct band gap of 2.85 ± 0.14 eV. This material shows emergent semiconducting behavior with significantly higher conductivity and mobility than the constituent insulating oxides. In conclusion, since these results demonstrate a new way to modify the behaviors of transition metal oxides made from unfilled d- and/or f-subshells, a new class of functional transparent conducting oxide materials could be envisioned.

  14. Novel Iron-based ternary amorphous oxide semiconductor with very high transparency, electronic conductivity, and mobility

    DOE PAGES

    Malasi, A.; Taz, H.; Farah, A.; ...

    2015-12-16

    We report that ternary metal oxides of type (Me)2O3 with the primary metal (Me) constituent being Fe (66 atomic (at.) %) along with the two Lanthanide elements Tb (10 at.%) and Dy (24 at.%) can show excellent semiconducting transport properties. Thin films prepared by pulsed laser deposition at room temperature followed by ambient oxidation showed very high electronic conductivity (>5 × 104 S/m) and Hall mobility (>30 cm2/V-s). These films had an amorphous microstructure which was stable to at least 500 °C and large optical transparency with a direct band gap of 2.85 ± 0.14 eV. This material shows emergentmore » semiconducting behavior with significantly higher conductivity and mobility than the constituent insulating oxides. In conclusion, since these results demonstrate a new way to modify the behaviors of transition metal oxides made from unfilled d- and/or f-subshells, a new class of functional transparent conducting oxide materials could be envisioned.« less

  15. Thermal conductivity and electron-phonon relaxation in a metal heated by a subpicosecond laser pulse

    NASA Astrophysics Data System (ADS)

    Petrov, Yu. V.; Anisimov, S. I.

    2006-06-01

    This paper discusses the initial stages of the interaction of subpicosecond laser pulses with metallic targets: the absorption of light, energy transport by electronic thermal conductivity, and electron-phonon relaxation. It is shown that, with moderate surface energy density, hydrodynamic motion begins after the electronic and lattice temperatures equalize. A connection is established between the energy exchange rate between the electrons and the lattice and the electronic thermal conductivity (an analog of the Wiedemann-Franz law).

  16. Bounce resonance scattering of radiation belt electrons by H+ band EMIC waves

    NASA Astrophysics Data System (ADS)

    Cao, Xing; Ni, Binbin; Summers, Danny; Bortnik, Jacob; Tao, Xin; Shprits, Yuri Y.; Lou, Yuequn; Gu, Xudong; Fu, Song; Shi, Run; Xiang, Zheng; Wang, Qi

    2017-02-01

    We perform a detailed analysis of bounce-resonant pitch angle scattering of radiation belt electrons due to electromagnetic ion cyclotron (EMIC) waves. It is found that EMIC waves can resonate with near-equatorially mirroring electrons over a wide range of L shells and energies. H+ band EMIC waves efficiently scatter radiation belt electrons of energy >100 keV from near 90° pitch angles to lower pitch angles where the cyclotron resonance mechanism can take over to further diffuse electrons into the loss cone. Bounce-resonant electron pitch angle scattering rates show a strong dependence on L shell, wave normal angle distribution, and wave spectral properties. We find distinct quantitative differences between EMIC wave-induced bounce-resonant and cyclotron-resonant diffusion coefficients. Cyclotron-resonant electron scattering by EMIC waves has been well studied and found to be a potentially crucial electron scattering mechanism. The new investigation here demonstrates that bounce-resonant electron scattering may also be very important. We conclude that bounce resonance scattering by EMIC waves should be incorporated into future modeling efforts of radiation belt electron dynamics.

  17. Band gap widening at random CIGS grain boundary detected by valence electron energy loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Keller, Debora; Buecheler, Stephan; Reinhard, Patrick; Pianezzi, Fabian; Bissig, Benjamin; Carron, Romain; Hage, Fredrik; Ramasse, Quentin; Erni, Rolf; Tiwari, Ayodhya N.

    2016-10-01

    Cu(In,Ga) Se2 (CIGS) thin film solar cells have demonstrated very high efficiencies, but still the role of nanoscale inhomogeneities in CIGS and their impact on the solar cell performance are not yet clearly understood. Due to the polycrystalline structure of CIGS, grain boundaries are very common structural defects that are also accompanied by compositional variations. In this work, we apply valence electron energy loss spectroscopy in scanning transmission electron microscopy to study the local band gap energy at a grain boundary in the CIGS absorber layer. Based on this example, we demonstrate the capabilities of a 2nd generation monochromator that provides a very high energy resolution and allows for directly relating the chemical composition and the band gap energy across the grain boundary. A band gap widening of about 20 meV is observed at the grain boundary. Furthermore, the compositional analysis by core-loss EELS reveals an enrichment of In together with a Cu, Ga and Se depletion at the same area. The experimentally obtained results can therefore be well explained by the presence of a valence band barrier at the grain boundary.

  18. Size effect on the electronic and optical band gap of CdSe QD

    SciTech Connect

    Sisodia, Namita

    2014-04-24

    Present paper deals with a critical and comprehensive analysis of the dependence of photo emission (PE) electronic band gap and optical absorption (OA) excitonic band gap on the size of CdSe QD, via connecting it with excitonic absorbance wavelength. Excitonic absorbance wavelength is determined through an empirical fit of established experimental evidences. Effective excitonic charge and Bohr radius is determined as a function of size. Increase in size of the CdSe QD results in greater Bohr radius and smaller effective excitonic charge. Excitonic binding energy as a degree of size of QD is also calculated which further relates with the difference in PE electronic and OA optical band gaps. It is also shown that with increase in size of CdSe QD, the excitonic binding energy decreases which consequently increases differences in two band gaps. Our results are very well comparable with the established results. Explanation for the origin of the unusual optical properties of CdSe QD has been also discussed.

  19. Universality of the Hall Conductivity in Interacting Electron Systems

    NASA Astrophysics Data System (ADS)

    Giuliani, Alessandro; Mastropietro, Vieri; Porta, Marcello

    2017-02-01

    We prove the quantization of the Hall conductivity for general weakly interacting gapped fermionic systems on two-dimensional periodic lattices. The proof is based on fermionic cluster expansion techniques combined with lattice Ward identities, and on a reconstruction theorem that allows us to compute the Kubo conductivity as the analytic continuation of its imaginary time counterpart.

  20. Impact of the Electronic Band Structure in High-Harmonic Generation Spectra of Solids.

    PubMed

    Tancogne-Dejean, Nicolas; Mücke, Oliver D; Kärtner, Franz X; Rubio, Angel

    2017-02-24

    An accurate analytic model describing the microscopic mechanism of high-harmonic generation (HHG) in solids is derived. Extensive first-principles simulations within a time-dependent density-functional framework corroborate the conclusions of the model. Our results reveal that (i) the emitted HHG spectra are highly anisotropic and laser-polarization dependent even for cubic crystals; (ii) the harmonic emission is enhanced by the inhomogeneity of the electron-nuclei potential; the yield is increased for heavier atoms; and (iii) the cutoff photon energy is driver-wavelength independent. Moreover, we show that it is possible to predict the laser polarization for optimal HHG in bulk crystals solely from the knowledge of their electronic band structure. Our results pave the way to better control and optimize HHG in solids by engineering their band structure.

  1. Impact of the Electronic Band Structure in High-Harmonic Generation Spectra of Solids

    NASA Astrophysics Data System (ADS)

    Tancogne-Dejean, Nicolas; Mücke, Oliver D.; Kärtner, Franz X.; Rubio, Angel

    2017-02-01

    An accurate analytic model describing the microscopic mechanism of high-harmonic generation (HHG) in solids is derived. Extensive first-principles simulations within a time-dependent density-functional framework corroborate the conclusions of the model. Our results reveal that (i) the emitted HHG spectra are highly anisotropic and laser-polarization dependent even for cubic crystals; (ii) the harmonic emission is enhanced by the inhomogeneity of the electron-nuclei potential; the yield is increased for heavier atoms; and (iii) the cutoff photon energy is driver-wavelength independent. Moreover, we show that it is possible to predict the laser polarization for optimal HHG in bulk crystals solely from the knowledge of their electronic band structure. Our results pave the way to better control and optimize HHG in solids by engineering their band structure.

  2. Electronic band structure and Fermi surface of ferromagnetic Tb: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Döbrich, K. M.; Bihlmayer, G.; Starke, K.; Prieto, J. E.; Rossnagel, K.; Koh, H.; Rotenberg, E.; Blügel, S.; Kaindl, G.

    2007-07-01

    We have investigated the bulk valence-band structure of Tb metal in the ferromagnetic phase by angle-resolved photoelectron spectroscopy and full-potential-linearized-augmented-plane-wave calculations. The experiments were performed at undulator beamline 7.0.1 of the Advanced Light Source using a three-axis rotatable low-temperature goniometer and a display-type photoelectron spectrometer that give access to a large region of momentum space. The results of our calculations, which make use of recent progress in the theoretical description of the magnetic properties of 4f metals, are in remarkably good agreement with experiment. This can be best seen from a comparison of the electronic structure in high-symmetry directions, at critical points, on Fermi contours, and at band crossings with the Fermi level. To our knowledge, the present work represents the most detailed combined experimental and theoretical study of the electronic structure of a magnetic lanthanide metal to date.

  3. Electronic conduction in polymers, carbon nanotubes and graphene.

    PubMed

    Kaiser, Alan B; Skákalová, Viera

    2011-07-01

    In the years since the discovery of organic polymers that exhibited electrical conductivities comparable to some metals, other novel carbon-based conductors have been developed, including carbon nanotubes and graphene (monolayers of carbon atoms). In this critical review, we discuss the common features and the differences in the conduction mechanisms observed in these carbon-based materials, which range from near ballistic and conventional metallic conduction to fluctuation-assisted tunnelling, variable-range hopping and more exotic mechanisms. For each category of material, we discuss the dependence of conduction on the morphology of the sample. The presence of heterogeneous disorder is often particularly important in determining the overall behaviour, and can lead to surprisingly similar conduction behaviour in polymers, carbon nanotube networks and chemically-derived graphene (122 references).

  4. Unraveling the origins of conduction band valley degeneracies in Mg2Si(1-x)Sn(x) thermoelectrics.

    PubMed

    Kim, Chang-Eun; Soon, Aloysius; Stampfl, Catherine

    2016-01-14

    To better understand the thermoelectric efficiency of the Mg-based thermoelectrics, using hybrid density-functional theory, we study the microscopic origins of valley degeneracies in the conduction band of the solid solution Mg2Si(1-x)Sn(x) and its constituent components--namely, Mg2Si and Mg2Sn. In the solid solution of Mg2Si(1-x)Sn(x), the sublattices are expected to undergo either tensile or compressive strain in the light of Vegard's law. Interestingly, we find both tensile strain of Mg2Si and compressive strain of Mg2Sn enhance the conduction band valley degeneracy. We suggest that the optimal sublattice strain as one of the origins of the enhanced Seebeck coefficient in the Mg2Si(1-x)Sn(x) system. In order to visualize the enhanced band valley degeneracy at elevated temperatures, the ground state eigenvalues and weights are projected by convolution functions that account for high temperature effects. Our results provide theoretical evidences for the role of sublattice strain in the band valley degeneracy observed in Mg2Si(1-x)Sn(x).

  5. Room-Temperature Electron Spin Relaxation of Triarylmethyl Radicals at X- and Q-bands

    PubMed Central

    Krumkacheva, Olesya A.; Strizhakov, Rodion K.; Rogozhnikova, Olga Yu.; Troitskaya, Tatiana I.

    2016-01-01

    Triarylmethyl radicals (trityls, TAMs) represent a relatively new class of spin labels. The long relaxation of trityls at room temperature in liquid solutions makes them a promising alternative for traditional nitroxides. In this work we have synthesized a series of TAMs including perdeuterated Finland trityl (D36 form) , mono-, di-, and tri-ester derivatives of Finland-D36 trityl, deuterated form of OX63, dodeca-n-butyl homologue of Finland trityl, and triamide derivatives of Finland trityl with primary and secondary amines attached. We have studied room-temperature relaxation properties of these TAMs in liquids using pulsed Electron Paramagnetic Resonance (EPR) at two microwave frequency bands. We have found the clear dependence of phase memory time (Tm~T2) on magnetic field: room-temperature Tm values are ~1.5-2.5 times smaller at Q-band (34 GHz, 1.2 T) compared to X-band (9 GHz, 0.3 T). This trend is ascribed to the contribution from g-anisotropy that is negligible at lower magnetic fields but comes into play at Q-band. In agreement with this, while T1~Tm at X-band, we observe T1>Tm at Q-band due to increased contributions from incomplete motional averaging of g-anisotropy. In addition, the viscosity dependence shows that (1/Tm-1/T1) is proportional to the tumbling correlation time of trityls. Based on the analysis of previous data and results of the present work, we conclude that in general situation where spin label is at least partly mobile, X-band is most suitable for application of trityls for room-temperature pulsed EPR distance measurements. PMID:26001103

  6. Theoretical Modeling of Low Energy Electronic Absorption Bands in Reduced Cobaloximes

    PubMed Central

    Bhattacharjee, Anirban; Chavarot-Kerlidou, Murielle; Dempsey, Jillian L.; Gray, Harry B.; Fujita, Etsuko; Muckerman, James T.; Fontecave, Marc; Artero, Vincent; Arantes, Guilherme M.; Field, Martin J.

    2015-01-01

    The reduced Co(I) states of cobaloximes are powerful nucleophiles that play an important role in the hydrogen-evolving catalytic activity of these species. In this work we have analyzed the low energy electronic absorption bands of two cobaloxime systems experimentally and using a variety of density functional theory and molecular orbital ab initio quantum chemical approaches. Overall we find a reasonable qualitative understanding of the electronic excitation spectra of these compounds but show that obtaining quantitative results remains a challenging task. PMID:25113847

  7. Theoretical modeling of low-energy electronic absorption bands in reduced cobaloximes.

    PubMed

    Bhattacharjee, Anirban; Chavarot-Kerlidou, Murielle; Dempsey, Jillian L; Gray, Harry B; Fujita, Etsuko; Muckerman, James T; Fontecave, Marc; Artero, Vincent; Arantes, Guilherme M; Field, Martin J

    2014-10-06

    The reduced Co(I) states of cobaloximes are powerful nucleophiles that play an important role in the hydrogen-evolving catalytic activity of these species. In this work we analyze the low-energy electronic absorption bands of two cobaloxime systems experimentally and use a variety of density functional theory and molecular orbital ab initio quantum chemical approaches. Overall we find a reasonable qualitative understanding of the electronic excitation spectra of these compounds but show that obtaining quantitative results remains a challenging task.

  8. Theoretical modeling of low-energy electronic absorption bands in reduced cobaloximes

    SciTech Connect

    Bhattacharjee, Anirban; Chavarot-Kerlidou, Murielle; Dempsey, Jillian L.; Gray, Harry B.; Fujita, Etsuko; Muckerman, James T.; Fontecave, Marc; Artero, Vincent; Arantes, Guilherme M.; Field, Martin J.

    2014-08-11

    Here, we report that the reduced Co(I) states of cobaloximes are powerful nucleophiles that play an important role in the hydrogen-evolving catalytic activity of these species. In this work we have analyzed the low energy electronic absorption bands of two cobaloxime systems experimentally and using a variety of density functional theory and molecular orbital ab initio quantum chemical approaches. Overall we find a reasonable qualitative understanding of the electronic excitation spectra of these compounds but show that obtaining quantitative results remains a challenging task.

  9. Theoretical modeling of low-energy electronic absorption bands in reduced cobaloximes

    DOE PAGES

    Bhattacharjee, Anirban; Chavarot-Kerlidou, Murielle; Dempsey, Jillian L.; ...

    2014-08-11

    Here, we report that the reduced Co(I) states of cobaloximes are powerful nucleophiles that play an important role in the hydrogen-evolving catalytic activity of these species. In this work we have analyzed the low energy electronic absorption bands of two cobaloxime systems experimentally and using a variety of density functional theory and molecular orbital ab initio quantum chemical approaches. Overall we find a reasonable qualitative understanding of the electronic excitation spectra of these compounds but show that obtaining quantitative results remains a challenging task.

  10. Conduction band topology and optical properties of monoclinic ZrO_2

    NASA Astrophysics Data System (ADS)

    Freeman, A. J.; Medvedeva, J. E.; Geller, C. B.

    2004-03-01

    Zirconia is an attractive base material for a wide variety of optical applications, on account of its high refractive index, large band gap and low optical loss. We report highly precise density functional theory calculations on pure, monoclinic zirconia employing the self-consistent screened exchange local-density approximation(R. Asahi, W. Mannstadt, A. J. Freeman, Phys. Rev. B) 59, 7486 (1999) (sX-LDA) with the full-potential linearized augmented plane wave (FLAPW) method(E. Wimmer, H. Krakauer, M. Weinert, A.J. Freeman, Phys. Rev. B) 24, 864 (1981). The sX-LDA substantially reduces the overbinding error in the LDA resulting in a more accurate description of the band gap and excited states in semiconductors(C.B. Geller er al), Appl. Phys. Lett. 79, 368 (2001) and insulators (this work). The predicted sX-LDA indirect band gap of monoclinic ZrO2 is 5.7 eV, in agreement with experiment. The effects of carrier concentration on the effective masses and optical properties of zirconia are discussed.

  11. The optical band gap and surface free energy of polyethylene modified by electron beam irradiations

    NASA Astrophysics Data System (ADS)

    Abdul-Kader, A. M.

    2013-04-01

    In this study, investigations have been carried out on electron beam irradiated ultra high molecular weight polyethylene (UHMWPE). Polyethylene samples were irradiated with 1.5 MeV electron beam at doses ranging from 50 to 500 kGy. Modifications in optical properties and photoluminescence behavior of the polymer were evaluated by UV-vis and photoluminescence techniques. Changes of surface layer composition of UHMWPE produced by electron irradiations were studied by Rutherford back scattering spectrometry (RBS). The change in wettability and surface free energy induced by irradiations was also investigated. The optical absorption studies reveal that both optical band gap and Urbach's energy decreases with increasing electron dose. A correlation between energy gap and the number of carbon atoms in clusters is discussed. Photoluminescence spectra were reveal remarkable decrease in the integrated luminescence intensity with increasing irradiation dose. Contact angle measurements showed that wettability and surface free energy increases with increasing the irradiation dose.

  12. A broad-band VLF-burst associated with ring-current electrons. [geomagnetic storms

    NASA Technical Reports Server (NTRS)

    Maeda, K.

    1982-01-01

    Frequency band broadening takes place just outside of the nighttime plasmasphere, where the density of cold plasma is known to be very low during the later phase of a geomagnetic storm. Instead of the gradual broadening of several hours duration, a burst type broadening of VLF emission lasting less than ten minutes was observed by Explorer 45 in a similar location. The magnetic field component of this emission is very weak and the frequency spreads below the local half electron cyclotron frequency. Corresponding enhancement of the anisotropic ring current electrons is also very sudden and limited below the order of 10 keV without significant velocity dispersion, in contrast to the gradual broadening events. The cause of this type of emission band spreading can be attributed to the generation of the quasielectrostatic whistler mode emission of short wavelength by hot bimaxwellian electrons surging into the domain of relatively low density magnetized cold plasma. The lack of energy dispersion in the enhanced electrons indicates that the inner edge of the plasma sheet, the source of these hot electrons, is not far from the location of this event.

  13. Surface-plasmon enhanced photodetection at communication band based on hot electrons

    SciTech Connect

    Wu, Kai; Zhan, Yaohui E-mail: xfli@suda.edu.cn; Wu, Shaolong; Deng, Jiajia; Li, Xiaofeng E-mail: xfli@suda.edu.cn

    2015-08-14

    Surface plasmons can squeeze light into a deep-subwavelength space and generate abundant hot electrons in the nearby metallic regions, enabling a new paradigm of photoconversion by the way of hot electron collection. Unlike the visible spectral range concerned in previous literatures, we focus on the communication band and design the infrared hot-electron photodetectors with plasmonic metal-insulator-metal configuration by using full-wave finite-element method. Titanium dioxide-silver Schottky interface is employed to boost the low-energy infrared photodetection. The photodetection sensitivity is strongly improved by enhancing the plasmonic excitation from a rationally engineered metallic grating, which enables a strong unidirectional photocurrent. With a five-step electrical simulation, the optimized device exhibits an unbiased responsivity of ∼0.1 mA/W and an ultra-narrow response band (FWHM = 4.66 meV), which promises to be a candidate as the compact photodetector operating in communication band.

  14. The change in dielectric constant, AC conductivity and optical band gaps of polymer electrolyte film: Gamma irradiation

    SciTech Connect

    Raghu, S. Subramanya, K. Sharanappa, C. Mini, V. Archana, K. Sanjeev, Ganesh Devendrappa, H.

    2014-04-24

    The effects of gamma (γ) irradiation on dielectric and optical properties of polymer electrolyte film were investigated. The dielectric constant and ac conductivity increases with γ dose. Also optical band gap decreased from 4.23 to 3.78ev after irradiation. A large dependence of the polymer properties on the irradiation dose was noticed. This suggests that there is a possibility of improving polymer electrolyte properties on gamma irradiation.

  15. Correlation between morphology, electron band structure, and resistivity of Pb atomic chains on the Si(5 5 3)-Au surface.

    PubMed

    Jałochowski, M; Kwapiński, T; Łukasik, P; Nita, P; Kopciuszyński, M

    2016-07-20

    Structural and electron transport properties of multiple Pb atomic chains fabricated on the Si(5 5 3)-Au surface are investigated using scanning tunneling spectroscopy, reflection high electron energy diffraction, angular resolved photoemission electron spectroscopy and in situ electrical resistance. The study shows that Pb atomic chains growth modulates the electron band structure of pristine Si(5 5 3)-Au surface and hence changes its sheet resistivity. Strong correlation between chains morphology, electron band structure and electron transport properties is found. To explain experimental findings a theoretical tight-binding model of multiple atomic chains interacting on effective substrate is proposed.

  16. Micro-metric electronic patterning of a topological band structure using a photon beam

    NASA Astrophysics Data System (ADS)

    Golden, Mark; Frantzeskakis, Emmanouil; de Jong, Nick; Huang, Yingkai; Wu, Dong; Pan, Yu; de Visser, Anne; van Heumen, Erik; van Bay, Tran; Zwartsenberg, Berend; Pronk, Pieter; Varier Ramankutty, Shyama; Tytarenko, Alona; Xu, Nan; Plumb, Nick; Shi, Ming; Radovic, Milan; Varkhalov, Andrei

    2015-03-01

    The only states crossing EF in ideal, 3D TIs are topological surface states. Single crystals of Bi2Se3andBi2Te3 are too defective to exhibit bulk-insulating behaviour, and ARPES shows topologically trivial 2DEGs at EF in the surface region due to downward band bending. Ternary & quaternary alloys of Bi /Te /Se /Sb hold promise for obtaining bulk-insulating crystals. Here we report ARPES data from quaternary, bulk-insulating, Bi-based TIs. Shortly after cleavage in UHV, downward band bending pulls the bulk conduction band below EF, once again frustrating the ``topological only'' ambition for the Fermi surface. However, there is light at the end of the tunnel: we show that a super-band-gap photon beam generates a surface photovoltage sufficient to flatten the bands, thereby recovering the ideal, ``topological only'' situation. In our bulk-insulating quaternary TIs, this effect is local in nature, and permits the writing of arbitrary, micron-sized patterns in the topological energy landscape at the surface. Support from FOM, NWO and the EU is gratefully acknowledged.

  17. Centimeter-long electron transport in marine sediments via conductive minerals.

    PubMed

    Malvankar, Nikhil S; King, Gary M; Lovley, Derek R

    2015-02-01

    Centimeter-long electron conduction through marine sediments, in which electrons derived from sulfide in anoxic sediments are transported to oxygen in surficial sediments, may have an important influence on sediment geochemistry. Filamentous bacteria have been proposed to mediate the electron transport, but the filament conductivity could not be verified and other mechanisms are possible. Surprisingly, previous investigations have never actually measured the sediment conductivity or its basic physical properties. Here we report direct measurements that demonstrate centimeter-long electron flow through marine sediments, with conductivities sufficient to account for previously estimated electron fluxes. Conductivity was lost for oxidized sediments, which contrasts with the previously described increase in the conductivity of microbial biofilms upon oxidation. Adding pyrite to the sediments significantly enhanced the conductivity. These results suggest that the role of conductive minerals, which are more commonly found in sediments than centimeter-long microbial filaments, need to be considered when modeling marine sediment biogeochemistry.

  18. Banded Structures in Electron Pitch Angle Diffusion Coefficients from Resonant Wave Particle Interactions

    NASA Technical Reports Server (NTRS)

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

    2016-01-01

    Electron pitch angle (D (alpha)) and momentum (D(pp)) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L = 4.6 and 6.8 for electron energies 10 keV. Landau (n = 0) resonance and cyclotron harmonic resonances n = +/-1, +/-2,...+/-5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (alpha) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusion coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n = +1 and n = +2. A major contribution to momentum diffusion coefficients appears from n = +2. However, the banded structures in D alpha and Dpp coefficients appear only in the profile of diffusion coefficients for n = +2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The Dpp diffusion coefficient for ECH waves is one to two orders smaller than D alpha coefficients. For chorus waves, Dpp coefficients are about an order of magnitude smaller than D alpha coefficients for the case n does not = 0. In case of Landau resonance, the values of Dpp coefficient are generally larger than the values of D alpha coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89 deg and harmonic resonances n = +1, +2, and +3, whereas for whistler mode waves, the frequencies have been calculated for angle

  19. Electronic structure and conductivity of nanocomposite metal (Au,Ag,Cu,Mo)-containing amorphous carbon films

    SciTech Connect

    Endrino, Jose L.; Horwat, David; Gago, Raul; Andersson, Joakim; Liu, Y.S.; Guo, Jinghua; Anders, Andre

    2008-05-14

    In this work, we study the influence of the incorporation of different metals (Me = Au, Ag, Cu, Mo) on the electronic structure of amorphous carbon (a-C:Me) films. The films were produced at room temperature using a novel pulsed dual-cathode arc deposition technique. Compositional analysis was performed with secondary neutral mass spectroscopy whereas X-ray diffraction was used to identify the formation of metal nanoclusters in the carbon matrix. The metal content incorporated in the nanocomposite films induces a drastic increase in the conductivity, in parallel with a decrease in the band gap corrected from Urbach energy. The electronic structure as a function of the Me content has been monitored by x-ray absorption near edge structure (XANES) at the C K-edge. XANES showed that the C host matrix has a dominant graphitic character and that it is not affected significantly by the incorporation of metal impurities, except for the case of Mo, where the modifications in the lineshape spectra indicated the formation of a carbide phase. Subtle modifications of the spectral lineshape are discussed in terms of nanocomposite formation.

  20. Formation of high conductive nano-crystalline silicon embedded in amorphous silicon-carbide films with large optical band gap

    NASA Astrophysics Data System (ADS)

    Ji, Yang; Shan, Dan; Qian, Mingqing; Xu, Jun; Li, Wei; Chen, Kunji

    2016-10-01

    High conductive phosphorus-doped nano-crystalline Si embedded in Silicon-Carbide (SiC) host matrix (nc-Si:SiC) films were obtained by thermally annealing doped amorphous Si-rich SiC materials. It was found that the room conductivity is increased significantly accompanying with the increase of doping concentrations as well as the enhanced crystallizations. The conductivity can be as high as 630 S/cm for samples with the optical band gap around 2.7 eV, while the carrier mobility is about 17.9 cm2/ V.s. Temperature-dependent conductivity and mobility measurements were performed which suggested that the carrier transport process is strongly affected by both the grain boundaries and the doping concentrations.

  1. Probing radiation damage by alternated current conductivity as a method to characterize electron hopping conduction in DNA molecules

    SciTech Connect

    Gomes, Paulo J.; Coelho, Margarida; Antonio Ribeiro, Paulo; Raposo, Maria; Dionisio, Madalena

    2012-09-17

    Analysis of AC electrical conductivity of deoxyribonucleic acid (DNA) thin films, irradiated with ultraviolet (UV) light, revealed that electrical conduction arises from DNA chain electron hopping between base-pairs and phosphate groups. The hopping distance calculated from correlated barrier hopping model equals the distance between DNA base-pairs, which is consistent with the loss of conductivity with irradiation time arising from a decrease in phosphates groups. In the high frequency regime, at a given frequency, real part of conductivity strongly depends on irradiation time particularly for low dose levels suggesting the use of DNA based films for UV radiation sensors.

  2. Promising electron mobility and high thermal conductivity in Sc2CT2 (T = F, OH) MXenes

    NASA Astrophysics Data System (ADS)

    Zha, Xian-Hu; Zhou, Jie; Zhou, Yuhong; Huang, Qing; He, Jian; Francisco, Joseph S.; Luo, Kan; Du, Shiyu

    2016-03-01

    is determined to be 173 W m-1 K-1 (107 W m-1 K-1). Based on their excellent electron mobilities and high thermal conductivities, both of the Sc2CT2 (T = F, OH) MXenes could be promising candidate materials for the next generation of electronic devices. Electronic supplementary information (ESI) available: Linear fitting functions of the CBM of Sc2CT2 (T = F, OH) under uniaxial strain; the electronic energy bands based on primitive cells; the details of estimating carrier effective mass and the robustness of our predicted electron mobilities. See DOI: 10.1039/c5nr08639f

  3. Electronically conductive polymer binder for lithium-ion battery electrode

    DOEpatents

    Liu, Gao; Xun, Shidi; Battaglia, Vincent S; Zheng, Honghe

    2014-10-07

    A family of carboxylic acid group containing fluorene/fluorenon copolymers is disclosed as binders of silicon particles in the fabrication of negative electrodes for use with lithium ion batteries. These binders enable the use of silicon as an electrode material as they significantly improve the cycle-ability of silicon by preventing electrode degradation over time. In particular, these polymers, which become conductive on first charge, bind to the silicon particles of the electrode, are flexible so as to better accommodate the expansion and contraction of the electrode during charge/discharge, and being conductive promote the flow battery current.

  4. Broad-band conductivity and dielectric spectroscopy of composites of multiwalled carbon nanotubes and poly(ethylene terephthalate) around their low percolation threshold.

    PubMed

    Nuzhnyy, D; Savinov, M; Bovtun, V; Kempa, M; Petzelt, J; Mayoral, B; McNally, T

    2013-02-08

    Composites of multiwalled carbon nanotubes with poly(ethylene terephthalate) (PET-MWCNT) with up to 3 vol% MWCNTs were prepared and characterized by broad-band AC conductivity and dielectric spectroscopy up to the infrared range using several techniques. A very low electrical percolation threshold of 0.07 vol% MWCNTs was revealed from the low-frequency conductivity plateau as well as from DC conductivity, whose values show the same critical power dependence on MWCNT concentration with the exponent t = 4.3. Above the plateau, the AC conductivity increases with frequency up to the THz range, where it becomes overlapped with the absorption of vibrational modes. The temperature dependence down to ~5 K has shown semiconductor behaviour with a concentration-independent but weakly temperature-dependent small activation energy of ~3 meV. The behaviour is compatible with the previously suggested fluctuation-induced tunnelling conductivity model through a thin (~1 nm) polymer contact layer among the adjacent MWCNTs within percolated clusters. At higher frequencies, deviations from the simple universal conductivity behaviour are observed, indicating some distribution of energy barriers for an electron hopping mechanism.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  6. Optical and electronic properties of delafossite CuBO{sub 2}p-type transparent conducting oxide

    SciTech Connect

    Ruttanapun, Chesta E-mail: krchesta@kmitl.ac.th

    2013-09-21

    CuBO{sub 2} delafossite was prepared by solid state reaction and calcined/sintered at 1005 °C. The optical properties of this p-type transparent conducting oxide were investigated. Its crystal structure, morphology, composition, oxygen decomposition, and optical and electronic properties were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, thermal gravimetric analysis (TGA), ultraviolet-visible-near-infrared (UV-VIS-NIR) and fluorescence spectroscopies, Seebeck coefficient, and electrical conductivity measurements. CuBO{sub 2} delafossite possesses a hexagonal space group R3{sup ¯}m. TGA indicated a weight loss of 10%, which was attributed to excess oxygen. The positive Seebeck coefficient confirmed p-type behavior. Emission at 355 nm indicated a direct band type transition, and the UV-VIS-NIR spectrum indicated an optical direct gap of 3.6 eV. Activation energies for carrier production and electrical conduction were 0.147 and 0.58 eV, respectively, indicating the thermal activation of carriers. CuBO{sub 2} delafossite is a p-type transparent conducting oxide with a wide band gap and may have potential in industrial p-type electrodes.

  7. Electronic and Magnetic Properties of Mn_xGa_1-xAs: Role of Mn= Defect Bands

    NASA Astrophysics Data System (ADS)

    Zhao, Yu-Jun; Geng, W. T.; Freeman, A. J.

    2001-03-01

    A detailed description of the electronic structure is crucial for underst anding Mn_xGa_1-xAs, a potential semiconductor spin-device materia l. In this work, a wide range of Mn concentration for Mn_xGa_1-xAs (x=3D3.125%, 6.25%, 12.5%, 25.0%, 50.0%) is studied by first-princip les full-potential linearized augmented plane wave (FLAPW)(Wimme r, Krakauer, Weinert, and Freeman, PRB 24), 864 (1981). calculation s with GGA. At all concentrations studied, the ferromagnetic (FM) state i s lower in energy than the paramagnetic (PM) and antiferromagnetic (AFM) states, confirming that Mn atoms stay magnetic with well localized magnet ic moments of 4.00 μ_B. The calculated band structure shows that Mn d oping also forms defect bands, and makes (Ga,Mn)As p-type conducting by p roviding holes. Furthermore, an s-d population inversion is found in the Mn electronic configuration, which results from the strong Mn p-d mixing. The induced As moments are substantial (about -0.15μB per Mn atom, and almost independent of x) -- in accord with a recent observed negati ve As magnetic circular dichroism (MCD) signal.(B. Beschoten, et al), Phys. Rev. Lett. 83, 3073 (1999).

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

    NASA Astrophysics Data System (ADS)

    Puls, Conor

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

  9. Electronic and thermoelectric properties of van der Waals materials with ring-shaped valence bands

    NASA Astrophysics Data System (ADS)

    Wickramaratne, Darshana; Zahid, Ferdows; Lake, Roger K.

    2015-08-01

    The valence band of a variety of few-layer, two-dimensional materials consist of a ring of states in the Brillouin zone. The energy-momentum relation has the form of a "Mexican hat" or a Rashba dispersion. The two-dimensional density of states is singular at or near the band edge, and the band-edge density of modes turns on nearly abruptly as a step function. The large band-edge density of modes enhances the Seebeck coefficient, the power factor, and the thermoelectric figure of merit ZT. Electronic and thermoelectric properties are determined from ab initio calculations for few-layer III-VI materials GaS, GaSe, InS, InSe, for Bi2Se3, for monolayer Bi, and for bilayer graphene as a function of vertical field. The effect of interlayer coupling on these properties in few-layer III-VI materials and Bi2Se3 is described. Analytical models provide insight into the layer dependent trends that are relatively consistent for all of these few-layer materials. Vertically biased bilayer graphene could serve as an experimental test-bed for measuring these effects.

  10. Electronic and thermoelectric properties of van der Waals materials with ring-shaped valence bands

    SciTech Connect

    Wickramaratne, Darshana E-mail: rlake@ece.ucr.edu; Lake, Roger K. E-mail: rlake@ece.ucr.edu; Zahid, Ferdows

    2015-08-21

    The valence band of a variety of few-layer, two-dimensional materials consist of a ring of states in the Brillouin zone. The energy-momentum relation has the form of a “Mexican hat” or a Rashba dispersion. The two-dimensional density of states is singular at or near the band edge, and the band-edge density of modes turns on nearly abruptly as a step function. The large band-edge density of modes enhances the Seebeck coefficient, the power factor, and the thermoelectric figure of merit ZT. Electronic and thermoelectric properties are determined from ab initio calculations for few-layer III–VI materials GaS, GaSe, InS, InSe, for Bi{sub 2}Se{sub 3}, for monolayer Bi, and for bilayer graphene as a function of vertical field. The effect of interlayer coupling on these properties in few-layer III–VI materials and Bi{sub 2}Se{sub 3} is described. Analytical models provide insight into the layer dependent trends that are relatively consistent for all of these few-layer materials. Vertically biased bilayer graphene could serve as an experimental test-bed for measuring these effects.

  11. Near band-gap electronics properties and luminescence mechanisms of boron nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Museur, L.; Kanaev, A.

    2015-08-01

    The deep ultraviolet luminescence (hν ≥ 5 eV) of multiwall boron nitride nanotubes (BNNTs) is studied with time- and energy-resolved photoluminescence spectroscopy. Two luminescence bands are observed at 5.35 and 5.54 eV. Both emissions undergo a large blue shift of several tens of meV with a linear slope Δ E l u m / Δ E e x c < 1 as the excitation energy Eexc increases. When E e x c ≥ 5.8 eV, the spectral band positions become fixed, which marks the transition between the excitation of donor-acceptor pairs and creation of free charge carriers. We assign the 5.35 eV band to quasi donor-acceptor pair transitions and the band at 5.54 eV to free-bound transitions. Boron and nitrogen atoms distributed along characteristic defect lines in BNNTs should be involved in the luminescence process. The presented results permit a revision of previous assignments of electronic transitions in BNNTs.

  12. Electronically conductive polymer binder for lithium-ion battery electrode

    DOEpatents

    Liu, Gao; Battaglia, Vincent S.; Park, Sang -Jae

    2015-10-06

    A family of carboxylic acid groups containing fluorene/fluorenon copolymers is disclosed as binders of silicon particles in the fabrication of negative electrodes for use with lithium ion batteries. Triethyleneoxide side chains provide improved adhesion to materials such as, graphite, silicon, silicon alloy, tin, tin alloy. These binders enable the use of silicon as an electrode material as they significantly improve the cycle-ability of silicon by preventing electrode degradation over time. In particular, these polymers, which become conductive on first charge, bind to the silicon particles of the electrode, are flexible so as to better accommodate the expansion and contraction of the electrode during charge/discharge, and being conductive promote the flow battery current.

  13. Electronically conductive polymer binder for lithium-ion battery electrode

    DOEpatents

    Liu, Gao; Xun, Shidi; Battaglia, Vincent S.; Zheng, Honghe; Wu, Mingyan

    2015-07-07

    A family of carboxylic acid groups containing fluorene/fluorenon copolymers is disclosed as binders of silicon particles in the fabrication of negative electrodes for use with lithium ion batteries. Triethyleneoxide side chains provide improved adhesion to materials such as, graphite, silicon, silicon alloy, tin, tin alloy. These binders enable the use of silicon as an electrode material as they significantly improve the cycle-ability of silicon by preventing electrode degradation over time. In particular, these polymers, which become conductive on first charge, bind to the silicon particles of the electrode, are flexible so as to better accommodate the expansion and contraction of the electrode during charge/discharge, and being conductive promote the flow battery current.

  14. Conducting Electronic Polymers by Non-Redox Processes

    DTIC Science & Technology

    1988-09-30

    optimized. Use of a weaker oxidant may enable the synth,;sis of more linear and conductive polyaniline emeraldine acid salts. Genies and co-workers found...undergo polymerization to polyaniline at low potentials. Only a small amount of p-dianiline in an acidic aniline solution is needed to allow polyaniline ... polyaniline product shows little evidence of crosslinking. A CV of this polyaniline product taken in an acid solution with no aniline or p-dianiline present

  15. Conducting Electronic Polymers by Non-Redox Processes

    DTIC Science & Technology

    1988-12-31

    systematic detailed observation of competing crystalline phases in a doped polymer. The multiple structures of the erneraldine form of polyaniline , together...states and other properties has been determined. Class I of the emeraldine form of polyaniline consists of materials prepared in the conducting, doped ...tosylic acid doped polyaniline ad polyethyleneoxide. We found that a 50:50 blend of tosylic acid doped polyaniline:PEO could form a homogeneous film

  16. Mechanism of Li+/electron conductivity in rutile and anatase TiO2 nanoparticles

    SciTech Connect

    Sushko, Maria L.; Rosso, Kevin M.; Liu, Jun

    2010-11-08

    Concurrent Li-ion and electron conductivity in rutile and anatase TiO2 nanoparticles was studied using multiscale simulations. We show that charge transport in titania nanoparticles is determined by the competition of charge redistribution towards the particle boundaries and constant Li+ and electron fluxes. In nanoparticles smaller than the Debye length the constant flux prevails and the conductivity has a dual ionic and electronic character, while for larger nanoparticles conductivity becomes predominately ionic. Simulations revealed that the temperature dependence of Li-ion conductivity in anatase is very weak, while in rutile the conductivity decreases with temperature in small nanoparticles and increases in large nanoparticles.

  17. Vibrational structure of defect luminescence bands in GaN from electronic structure calculations

    NASA Astrophysics Data System (ADS)

    Alkauskas, Audrius; van de Walle, Chris G.

    2012-02-01

    Optical methods are among the most powerful to characterize defects in materials. The study of optical signatures based on state-of-the-art electronic structure methods is therefore very important. In this work we investigate the vibrational structure of luminescence bands pertaining to deep defect levels in GaN. Since luminescence lineshapes depend sensitively on defect geometries and vibrational frequencies, these should be described accurately. The latter is achieved through the use of hybrid density functionals. Both quasi-localized and bulk phonons are included in our description. In the case of transitions accompanied by very large lattice relaxations, anharmonic effects become sizeable, and these are also accounted for. For the defects studied a very good agreement with available experimental data is achieved. For instance, in the case of wide luminescence bands the resulting line widths are within 0.05 eV of the experimental values. This work was supported by the Swiss NSF and by NSF.

  18. High-throughput combinatorial database of electronic band structures for inorganic scintillator materials.

    PubMed

    Setyawan, Wahyu; Gaume, Romain M; Lam, Stephanie; Feigelson, Robert S; Curtarolo, Stefano

    2011-07-11

    For the purpose of creating a database of electronic structures of all the known inorganic compounds, we have developed a computational framework based on high-throughput ab initio calculations (AFLOW) and an online repository (www.aflowlib.org). In this article, we report the first step of this task: the calculation of band structures for 7439 compounds intended for the research of scintillator materials for γ-ray radiation detection. Data-mining is performed to select the candidates from 193,456 compounds compiled in the Inorganic Crystal Structure Database. Light yield and scintillation nonproportionality are predicted based on semiempirical band gaps and effective masses. We present a list of materials, potentially bright and proportional, and focus on those exhibiting small effective masses and effective mass ratios.

  19. Unified band-theoretic description of structural, electronic, and magnetic properties of vanadium dioxide phases

    NASA Astrophysics Data System (ADS)

    Xu, Sheng; Shen, Xiao; Hallman, Kent A.; Haglund, Richard F.; Pantelides, Sokrates T.

    2017-03-01

    The debate about whether the insulating phases of vanadium dioxide (V O2 ) can be described by band theory or whether it requires a theory of strong electron correlations remains unresolved even after decades of research. Energy-band calculations using hybrid exchange functionals or including self-energy corrections account for the insulating or metallic nature of different phases but have not yet successfully accounted for the observed magnetic orderings. Strongly correlated theories have had limited quantitative success. Here we report that by using hard pseudopotentials and an optimized hybrid exchange functional, the energy gaps and magnetic orderings of both monoclinic V O2 phases and the metallic nature of the high-temperature rutile phase are consistent with available experimental data, obviating an explicit role for strong correlations. We also identify a potential candidate for the newly found metallic monoclinic phase.

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

    SciTech Connect

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

    2014-08-18

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

  1. Isolated energy level in the band gap of Yb2Si2O7 identified by electron energy-loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Ogawa, Takafumi; Kobayashi, Shunsuke; Wada, Masashi; Fisher, Craig A. J.; Kuwabara, Akihide; Kato, Takeharu; Yoshiya, Masato; Kitaoka, Satoshi; Moriwake, Hiroki

    2016-05-01

    We report the detection of an isolated energy level in the band gap of crystalline Yb2Si2O7 in the low-energy-loss region of its electron energy-loss (EEL) spectrum, obtained using a monochromated scanning transmission electron microscope. The experimental results are corroborated by first-principles calculations of the theoretical EEL spectrum. The calculations reveal that unoccupied Yb 4 f orbitals constitute an isolated energy level about 1 eV below the conduction band minimum (CBM), resulting in a terrace about 1 eV wide at the band edge of the EEL spectrum. In the case of Yb2O3 , no band edge terrace is present because the unoccupied f level lies just below the CBM. We also examined optical absorption properties of Yb2Si2O7 using UV-vis diffuse reflectance spectroscopy, which shows that the isolated energy level could not be detected in the band edge of the obtained absorbance spectrum. These findings demonstrate the utility of low-loss EEL spectroscopy with high energy resolution for probing semilocalized electronic features.

  2. Conductivity and optical band gaps of polyethylene oxide doped with Li{sub 2}SO{sub 4} salt

    SciTech Connect

    Chapi, Sharanappa Raghu, S. Subramanya, K. Archana, K. Mini, V. Devendrappa, H.

    2014-04-24

    The conductivity and optical properties of Li{sub 2}SO{sub 4} doped polyethylene oxide (PEO) films were studied. The polymer electrolyte films are prepared using solution casting technique. The material phase change was confirmed by X-ray diffraction (XRD) technique. Optical absorption study was conducted using UV- Vis. Spectroscopy in the wavelength range 190–1100nm on pure and doped PEO films. The direct and indirect optical band gaps were found decreased from 5.81–4.51eV and 4.84–3.43eV respectively with increasing the Li{sub 2}SO{sub 4}. The conductivity found to increases with increasing the dopant concentration due to strong hopping mechanism at room temperature.

  3. Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra

    SciTech Connect

    Vos, M.; Marmitt, G. G.; Finkelstein, Y.; Moreh, R.

    2015-09-14

    Reflection electron energy loss spectra from some insulating materials (CaCO{sub 3}, Li{sub 2}CO{sub 3}, and SiO{sub 2}) taken at relatively high incoming electron energies (5–40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO{sub 2}, good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E − E{sub gap}){sup 1.5}. For CaCO{sub 3}, the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li{sub 2}CO{sub 3} (7.5 eV) is the first experimental estimate.

  4. Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra

    NASA Astrophysics Data System (ADS)

    Vos, M.; Marmitt, G. G.; Finkelstein, Y.; Moreh, R.

    2015-09-01

    Reflection electron energy loss spectra from some insulating materials (CaCO3, Li2CO3, and SiO2) taken at relatively high incoming electron energies (5-40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO2, good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E - Egap)1.5. For CaCO3, the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li2CO3 (7.5 eV) is the first experimental estimate.

  5. Two-temperature models of old supernova remnants with ion and electron thermal conduction

    NASA Technical Reports Server (NTRS)

    Cui, Wei; Cox, Donald P.

    1992-01-01

    To investigate the potential effects thermal conduction may have on the evolution of old supernova remnants, we present the results of 1D (spherically symmetric) numerical simulations of a remnant in a homogeneous interstellar medium for four different cases: (1) without thermal conduction; (2) with both electron and ion thermal conduction assuming equal temperatures; (3) with electron thermal conduction only, following electron and ion temperatures separately; and (4) with both electron and ion thermal conduction following separate temperatures. We followed the entire evolution until the completion of the remnant bubble collapse. Our most significant result is that in remnant evolution studies concerned principally with either the shell or bubble evolution at late times, reasonable results are obtained with single-temperature models. When the electron and ion temperatures are followed separately, however, ion thermal conduction cannot safely be ignored.

  6. Implementation of electronic crosstalk correction for terra MODIS PV LWIR bands

    NASA Astrophysics Data System (ADS)

    Geng, Xu; Madhavan, Sriharsha; Chen, Na; Xiong, Xiaoxiong

    2015-09-01

    The MODerate-resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the fleet of NASA's Earth Observing Systems (EOS) in space. Terra MODIS has completed 15 years of operation far exceeding its design lifetime of 6 years. The MODIS Level 1B (L1B) processing is the first in the process chain for deriving various higher level science products. These products are used mainly in understanding the geophysical changes occurring in the Earth's land, ocean, and atmosphere. The L1B code is designed to carefully calibrate the responses of all the detectors of the 36 spectral bands of MODIS and provide accurate L1B radiances (also reflectances in the case of Reflective Solar Bands). To fulfill this purpose, Look Up Tables (LUTs), that contain calibration coefficients derived from both on-board calibrators and Earth-view characterized responses, are used in the L1B processing. In this paper, we present the implementation mechanism of the electronic crosstalk correction in the Photo Voltaic (PV) Long Wave InfraRed (LWIR) bands (Bands 27-30). The crosstalk correction involves two vital components. First, a crosstalk correction modular is implemented in the L1B code to correct the on-board Blackbody and Earth-View (EV) digital number (dn) responses using a linear correction model. Second, the correction coefficients, derived from the EV observations, are supplied in the form of LUTs. Further, the LUTs contain time stamps reflecting to the change in the coefficients assessed using the Noise Equivalent difference Temperature (NEdT) trending. With the algorithms applied in the MODIS L1B processing it is demonstrated that these corrections indeed restore the radiometric balance for each of the affected bands and substantially reduce the striping noise in the processed images.

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

    SciTech Connect

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

    2013-10-15

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

  8. Ethical considerations in the conduct of electronic surveillance research.

    PubMed

    Bharucha, Ashok J; London, Alex John; Barnard, David; Wactlar, Howard; Dew, Mary Amanda; Reynolds, Charles F

    2006-01-01

    The extant clinical literature indicates profound problems in the assessment, monitoring, and documentation of care in long-term care facilities. The lack of adequate resources to accommodate higher staff-to-resident ratios adds additional urgency to the goal of identifying more cost-effective mechanisms to provide care oversight. The ever expanding array of electronic monitoring technologies in the clinical research arena demands a conceptual and pragmatic framework for the resolution of ethical tensions inherent in the use of such innovative tools. CareMedia is a project that explores the utility of video, audio and sensor technologies as a continuous real-time assessment and outcomes measurement tool. In this paper, the authors describe the seminal ethical challenges encountered during the implementation phase of this project, namely privacy and confidentiality protection, and the strategies employed to resolve the ethical tensions by applying principles of the interest theory of rights.

  9. Soft capacitor fibers using conductive polymers for electronic textiles

    NASA Astrophysics Data System (ADS)

    Gu, Jian Feng; Gorgutsa, Stephan; Skorobogatiy, Maksim

    2010-11-01

    A novel, highly flexible, conductive polymer-based fiber with high electric capacitance is reported. In its cross section the fiber features a periodic sequence of hundreds of conductive and isolating plastic layers positioned around metallic electrodes. The fiber is fabricated using the fiber drawing method, where a multi-material macroscopic preform is drawn into a sub-millimeter capacitor fiber in a single fabrication step. Several kilometers of fibers can be obtained from a single preform with fiber diameters ranging between 500 and 1000 µm. A typical measured capacitance of our fibers is 60-100 nF m-1 and it is independent of the fiber diameter. Analysis of the fiber frequency response shows that in its simplest interrogation mode the capacitor fiber has a transverse resistance of 5 kΩ m L-1, which is inversely proportional to the fiber length L and is independent of the fiber diameter. Softness of the fiber materials, the absence of liquid electrolyte in the fiber structure, ease of scalability to large production volumes and high capacitance of our fibers make them interesting for various smart textile applications ranging from distributed sensing to energy storage.

  10. Large electronic sputtering yield of nanodimensional Au thin films: Dominant role of thermal conductivity and electron phonon coupling factor

    NASA Astrophysics Data System (ADS)

    Singh, Udai B.; Pannu, Compesh; Agarwal, Dinesh C.; Ojha, Sunil; Khan, Saif A.; Ghosh, Santanu; Avasthi, Devesh K.

    2017-03-01

    Detailed experiments and theoretical calculations on electronic sputtering of Au thin films (5-200 nm) on a quartz substrate are performed, revealing unusually large electronic sputtering, dependent on the thickness of the films. The dependence of electronic thermal conductivity (κe), electron-phonon coupling factor (g), and lattice thermal conductivity (κa) on the effective electron mean free path is taken into account in the thermal spike calculation for nanodimensional systems to elucidate the combined effect of the thickness and grain size on the electronic sputtering yield. The thermal spike simulation with refined parameters for nanodimensional systems gives a better explanation of the electronic sputtering process with a very good correlation between the experimental and theoretical yields than that of the thermal spike model with bulk parameters.

  11. Local Bonding Analysis of the Valence and Conduction Band Features of TiO2

    DTIC Science & Technology

    2007-01-01

    nanocrystalline samples tenuous at best. Hence, the phase of the unannealed TiO2 films cannot conclusively be identified as either anatase or rutile...reveals the local physical origin of the electronic structure in nanocrystalline films . TiO2 has further been chosen as a natural starting point to...thickness ratio is 2:1 for TiO2 . This assump- tion has been verified by XPS studies of the substrate Si 2p core-level spectra with film thickness. The

  12. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Suppression of Anti-resonant Effect in Presence of Band Overlap

    NASA Astrophysics Data System (ADS)

    Xiong, Gang

    2010-07-01

    By exact resolution of coupled ideal chains connecting an extra side site, we show that the so-called "anti-resonant effect" is suppressed when the electron energy is inside the overlap region of extended bands of the ideal tight-binding chains. When the electronic energy is outside the band overlap region, the existence of "anti-resonant effect" is tuned by details of local connectivity around the extra side site and can be suppressed by introduction of magnetic flux.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  14. Microwave band on-chip coil technique for single electron spin resonance in a quantum dot

    NASA Astrophysics Data System (ADS)

    Obata, Toshiaki; Pioro-Ladrière, Michel; Kubo, Toshihiro; Yoshida, Katsuharu; Tokura, Yasuhiro; Tarucha, Seigo

    2007-10-01

    Microwave band on-chip microcoils are developed for the application to single electron spin resonance measurement with a single quantum dot. Basic properties such as characteristic impedance and electromagnetic field distribution are examined for various coil designs by means of experiment and simulation. The combined setup operates relevantly in the experiment at dilution temperature. The frequency responses of the return loss and Coulomb blockade current are examined. Capacitive coupling between a coil and a quantum dot causes photon assisted tunneling, whose signal can greatly overlap the electron spin resonance signal. To suppress the photon assisted tunneling effect, a technique for compensating for the microwave electric field is developed. Good performance of this technique is confirmed from measurement of Coulomb blockade oscillations.

  15. A research of W-band folded waveguide traveling wave tube with elliptical sheet electron beam

    SciTech Connect

    Guo Guo; Wei Yanyu; Yue Lingna; Gong Yubin; Zhao Guoqing; Huang Minzhi; Tang Tao; Wang Wenxiang

    2012-09-15

    Folded waveguide (FWG) traveling wave tube (TWT), which shows advantages in high power capacity, moderate bandwidth, and low-cost fabrication, has become the focus of vacuum electronics recently. Sheet electron beam devices are better suited for producing radiation sources with large power in millimeter wave spectrum due to their characteristics of relatively low space charge fields and large transport current. A FWG TWT with elliptical sheet beam working in W-band is presented in this paper, with the analysis of its dispersion characteristics, coupling impedance, transmission properties, and interaction characteristics. A comparison is also made with the traditional FWG TWT. Simulation results lead to the conclusion that the FWG TWT with elliptical sheet beam investigated in this paper can make full use of relatively large electric fields and thus generate large output power with the same electric current density.

  16. Electron correlations and the minority-spin band gap in half-metallic Heusler alloys.

    PubMed

    Chioncel, L; Arrigoni, E; Katsnelson, M I; Lichtenstein, A I

    2006-04-07

    Electron-electron correlations affect the band gap of half-metallic ferromagnets by introducing nonquasiparticle states just above the Fermi level. In contrast with the spin-orbit coupling, a large asymmetric nonquasiparticle spectral weight is present in the minority-spin channel, leading to a peculiar finite-temperature spin depolarization effects. Using recently developed first-principle dynamical mean-field theory, we investigate these effects for the half-metallic ferrimagnetic Heusler compound FeMnSb. We discuss depolarization effects in terms of strength of local Coulomb interaction U and temperature in FeMnSb. We propose Ni(1-x)Fe(x)MnSb alloys as a perspective materials to be used in spin-valve structures and for experimental search of nonquasiparticle states in half-metallic materials.

  17. Electronic band-gap modified passive silicon optical modulator at telecommunications wavelengths

    PubMed Central

    Zhang, Rui; Yu, Haohai; Zhang, Huaijin; Liu, Xiangdong; Lu, Qingming; Wang, Jiyang

    2015-01-01

    The silicon optical modulator is considered to be the workhorse of a revolution in communications. In recent years, the capabilities of externally driven active silicon optical modulators have dramatically improved. Self-driven passive modulators, especially passive silicon modulators, possess advantages in compactness, integration, low-cost, etc. Constrained by a large indirect band-gap and sensitivity-related loss, the passive silicon optical modulator is scarce and has been not advancing, especially at telecommunications wavelengths. Here, a passive silicon optical modulator is fabricated by introducing an impurity band in the electronic band-gap, and its nonlinear optics and applications in the telecommunications-wavelength lasers are investigated. The saturable absorption properties at the wavelength of 1.55 μm was measured and indicates that the sample is quite sensitive to light intensity and has negligible absorption loss. With a passive silicon modulator, pulsed lasers were constructed at wavelengths at 1.34 and 1.42 μm. It is concluded that the sensitive self-driven passive silicon optical modulator is a viable candidate for photonics applications out to 2.5 μm. PMID:26563679

  18. Energy band alignment and electronic states of amorphous carbon surfaces in vacuo and in aqueous environment

    SciTech Connect

    Caro, Miguel A.; Määttä, Jukka; Lopez-Acevedo, Olga; Laurila, Tomi

    2015-01-21

    In this paper, we obtain the energy band positions of amorphous carbon (a–C) surfaces in vacuum and in aqueous environment. The calculations are performed using a combination of (i) classical molecular dynamics (MD), (ii) Kohn-Sham density functional theory with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional, and (iii) the screened-exchange hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE). PBE allows an accurate generation of a-C and the evaluation of the local electrostatic potential in the a-C/water system, HSE yields an improved description of energetic positions which is critical in this case, and classical MD enables a computationally affordable description of water. Our explicit calculation shows that, both in vacuo and in aqueous environment, the a-C electronic states available in the region comprised between the H{sub 2}/H{sub 2}O and O{sub 2}/H{sub 2}O levels of water correspond to both occupied and unoccupied states within the a-C pseudogap region. These are localized states associated to sp{sup 2} sites in a-C. The band realignment induces a shift of approximately 300 meV of the a-C energy band positions with respect to the redox levels of water.

  19. Electronic band-gap modified passive silicon optical modulator at telecommunications wavelengths.

    PubMed

    Zhang, Rui; Yu, Haohai; Zhang, Huaijin; Liu, Xiangdong; Lu, Qingming; Wang, Jiyang

    2015-11-13

    The silicon optical modulator is considered to be the workhorse of a revolution in communications. In recent years, the capabilities of externally driven active silicon optical modulators have dramatically improved. Self-driven passive modulators, especially passive silicon modulators, possess advantages in compactness, integration, low-cost, etc. Constrained by a large indirect band-gap and sensitivity-related loss, the passive silicon optical modulator is scarce and has been not advancing, especially at telecommunications wavelengths. Here, a passive silicon optical modulator is fabricated by introducing an impurity band in the electronic band-gap, and its nonlinear optics and applications in the telecommunications-wavelength lasers are investigated. The saturable absorption properties at the wavelength of 1.55 μm was measured and indicates that the sample is quite sensitive to light intensity and has negligible absorption loss. With a passive silicon modulator, pulsed lasers were constructed at wavelengths at 1.34 and 1.42 μm. It is concluded that the sensitive self-driven passive silicon optical modulator is a viable candidate for photonics applications out to 2.5 μm.

  20. All-electron GW quasiparticle band structures of group 14 nitride compounds

    NASA Astrophysics Data System (ADS)

    Chu, Iek-Heng; Kozhevnikov, Anton; Schulthess, Thomas C.; Cheng, Hai-Ping

    2014-07-01

    We have investigated the group 14 nitrides (M3N4) in the spinel phase (γ-M3N4 with M = C, Si, Ge, and Sn) and β phase (β-M3N4 with M = Si, Ge, and Sn) using density functional theory with the local density approximation and the GW approximation. The Kohn-Sham energies of these systems have been first calculated within the framework of full-potential linearized augmented plane waves (LAPW) and then corrected using single-shot G0W0 calculations, which we have implemented in the modified version of the Elk full-potential LAPW code. Direct band gaps at the Γ point have been found for spinel-type nitrides γ-M3N4 with M = Si, Ge, and Sn. The corresponding GW-corrected band gaps agree with experiment. We have also found that the GW calculations with and without the plasmon-pole approximation give very similar results, even when the system contains semi-core d electrons. These spinel-type nitrides are novel materials for potential optoelectronic applications because of their direct and tunable band gaps.

  1. All-electron GW quasiparticle band structures of group 14 nitride compounds

    SciTech Connect

    Chu, Iek-Heng; Cheng, Hai-Ping; Kozhevnikov, Anton; Schulthess, Thomas C.

    2014-07-28

    We have investigated the group 14 nitrides (M{sub 3}N{sub 4}) in the spinel phase (γ-M{sub 3}N{sub 4} with M = C, Si, Ge, and Sn) and β phase (β-M{sub 3}N{sub 4} with M = Si, Ge, and Sn) using density functional theory with the local density approximation and the GW approximation. The Kohn-Sham energies of these systems have been first calculated within the framework of full-potential linearized augmented plane waves (LAPW) and then corrected using single-shot G{sub 0}W{sub 0} calculations, which we have implemented in the modified version of the Elk full-potential LAPW code. Direct band gaps at the Γ point have been found for spinel-type nitrides γ-M{sub 3}N{sub 4} with M = Si, Ge, and Sn. The corresponding GW-corrected band gaps agree with experiment. We have also found that the GW calculations with and without the plasmon-pole approximation give very similar results, even when the system contains semi-core d electrons. These spinel-type nitrides are novel materials for potential optoelectronic applications because of their direct and tunable band gaps.

  2. Effect of intercalated lithium on the electronic band structure of indium selenide

    NASA Astrophysics Data System (ADS)

    1990-08-01

    The purpose of the project on Superionics supported by DARPA Contract No. N00014-88-K-0392 is to develop a physical understanding of the elements of a solid state battery consisting of a lithium anode, a lithium-doped borate glass separator and a lithium-intercalated InSe cathode. In this report a theoretical analysis based on a tight-binding model is presented for the electronic structure of both pure and lithium-intercalated InSe. An understanding of the electronic structure is necessary for an understanding of the electrical conductivity due to both electronic motion and lithium-ion motion. The conductivity is an important parameter for the performance of the solid state battery.

  3. Physical properties and electronic band structure of noncentrosymmetric Th7Co3 superconductor.

    PubMed

    Sahakyan, M; Tran, V H

    2016-05-25

    The physical properties of the noncentrosymmetric superconductor Th7Co3 have been investigated by means of ac-magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance and Hall effect measurements. From these data it is established that Th7Co3 is a dirty type-II superconductor with [Formula: see text] K, [Formula: see text] and moderate electron-phonon coupling [Formula: see text]. Some evidences for anisotropic superconducting gap are found, including e.g. reduced specific heat jump ([Formula: see text]) at T c, diminished superconducting energy gap ([Formula: see text]) as compared to the BCS values, power law field dependence of the Sommerfeld coefficient at 0.4 K ([Formula: see text]), and a concave curvature of the [Formula: see text] line. The magnitudes of the thermodynamic critical field and the energy gap are consistent with mean-squared anisotropy parameter [Formula: see text]. The electronic specific heat in the superconducting state is reasonably fitted to an oblate spheroidal gap model. Calculations of scalar relativistic and fully relativistic electronic band structures reveal considerable differences in the degenerate structure, resulting from asymmetric spin-orbit coupling (ASOC). A large splitting energy of spin-up spin-down bands at the Fermi level E F, [Formula: see text] meV is observed and a sizeable ratio [Formula: see text] could classify the studied compound into the class of noncentrosymmetric superconductors with strong ASOC. The noncentrosymmetry of the crystal structure and the atomic relativistic effects are both responsible for an importance of ASOC in Th7Co3. The calculated results for the density of states show a Van Hove singularity just below E F and dominant role of the 6d electrons of Th to the superconductivity.

  4. The Green's function density functional tight-binding (gDFTB) method for molecular electronic conduction.

    PubMed

    Reimers, Jeffrey R; Solomon, Gemma C; Gagliardi, Alessio; Bilić, Ante; Hush, Noel S; Frauenheim, Thomas; Di Carlo, Aldo; Pecchia, Alessandro

    2007-07-05

    A review is presented of the nonequilibrium Green's function (NEGF) method "gDFTB" for evaluating elastic and inelastic conduction through single molecules employing the density functional tight-binding (DFTB) electronic structure method. This focuses on the possible advantages that DFTB implementations of NEGF have over conventional methods based on density functional theory, including not only the ability to treat large irregular metal-molecule junctions with high nonequilibrium thermal distributions but perhaps also the ability to treat dispersive forces, bond breakage, and open-shell systems and to avoid large band lineup errors. New results are presented indicating that DFTB provides a useful depiction of simple gold-thiol interactions. Symmetry is implemented in DFTB, and the advantages it brings in terms of large savings of computational resources with significant increase in numerical stability are described. The power of DFTB is then harnessed to allow the use of gDFTB as a real-time tool to discover the nature of the forces that control inelastic charge transport through molecules and the role of molecular symmetry in determining both elastic and inelastic transport. Future directions for the development of the method are discussed.

  5. Electrochemically oxidized electronic and ionic conducting nanostructured block copolymers for lithium battery electrodes.

    PubMed

    Patel, Shrayesh N; Javier, Anna E; Balsara, Nitash P

    2013-07-23

    Block copolymers that can simultaneously conduct electronic and ionic charges on the nanometer length scale can serve as innovative conductive binder material for solid-state battery electrodes. The purpose of this work is to study the electronic charge transport of poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT-PEO) copolymers electrochemically oxidized with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt in the context of a lithium battery charge/discharge cycle. We use a solid-state three-terminal electrochemical cell that enables simultaneous conductivity measurements and control over electrochemical doping of P3HT. At low oxidation levels (ratio of moles of electrons removed to moles of 3-hexylthiophene moieties in the electrode), the electronic conductivity (σe,ox) increases from 10(-7) S/cm to 10(-4) S/cm. At high oxidation levels, σe,ox approaches 10(-2) S/cm. When P3HT-PEO is used as a conductive binder in a positive electrode with LiFePO4 active material, P3HT is electrochemically active within the voltage window of a charge/discharge cycle. The electronic conductivity of the P3HT-PEO binder is in the 10(-4) to 10(-2) S/cm range over most of the potential window of the charge/discharge cycle. This allows for efficient electronic conduction, and observed charge/discharge capacities approach the theoretical limit of LiFePO4. However, at the end of the discharge cycle, the electronic conductivity decreases sharply to 10(-7) S/cm, which means the "conductive" binder is now electronically insulating. The ability of our conductive binder to switch between electronically conducting and insulating states in the positive electrode provides an unprecedented route for automatic overdischarge protection in rechargeable batteries.

  6. Electronic structures, elastic properties, and minimum thermal conductivities of cermet M{sub 3}AlN

    SciTech Connect

    Wang, Jin; Chen, ZhiQian; Li, ChunMei; Li, Feng; Nie, ChaoYin

    2014-08-15

    The electronic structures and elastic anisotropies of cubic Ti{sub 3}AlN, Zr{sub 3}AlN, and Hf{sub 3}AlN are investigated by pseudopotential plane-wave method based on density functional theory. At the Fermi level, the electronic structures of these compounds are successive with no energy gap between conduct and valence bands, and exhibit metallicity in ground states. In valence band of each partial density of states, the different orbital electrons indicate interaction of corresponding atoms. In addition, the anisotropy of Hf{sub 3}AlN is found to be significantly different from that of Ti{sub 3}AlN and Zr{sub 3}AlN, which involve the differences in the bonding strength. It is notable that Hf{sub 3}AlN is a desired thermal barrier material with the lowest thermal conductivity at high temperature among the three compounds. - Graphical abstract: 1.Young's moduli of anti-perovskite Ti{sub 3}AlN, Zr{sub 3}AlN, and Hf{sub 3}AlN in full space. 2.Electron density differences on crystal planes (1 0 0), (2 0 0), and (1 1 0) of anti-perovskite Zr{sub 3}AlN. - Highlights: • We calculated three anti-perovskite cermets with first-principles theory. • We illustrated 3D Young modulus and found the anomalous anisotropy. • We explained the anomaly and calculated the minimum thermal conductivities.

  7. Band-structure-based collisional model for electronic excitations in ion-surface collisions

    SciTech Connect

    Faraggi, M.N.; Gravielle, M.S.; Alducin, M.; Silkin, V.M.; Juaristi, J.I.

    2005-07-15

    Energy loss per unit path in grazing collisions with metal surfaces is studied by using the collisional and dielectric formalisms. Within both theories we make use of the band-structure-based (BSB) model to represent the surface interaction. The BSB approach is based on a model potential and provides a precise description of the one-electron states and the surface-induced potential. The method is applied to evaluate the energy lost by 100 keV protons impinging on aluminum surfaces at glancing angles. We found that when the realistic BSB description of the surface is used, the energy loss obtained from the collisional formalism agrees with the dielectric one, which includes not only binary but also plasmon excitations. The distance-dependent stopping power derived from the BSB model is in good agreement with available experimental data. We have also investigated the influence of the surface band structure in collisions with the Al(100) surface. Surface-state contributions to the energy loss and electron emission probability are analyzed.

  8. The electronic and transport properties of monolayer transition metal dichalcogenides: a complex band structure analysis

    NASA Astrophysics Data System (ADS)

    Szczesniak, Dominik

    Recently, monolayer transition metal dichalcogenides have attracted much attention due to their potential use in both nano- and opto-electronics. In such applications, the electronic and transport properties of group-VIB transition metal dichalcogenides (MX2 , where M=Mo, W; X=S, Se, Te) are particularly important. Herein, new insight into these properties is presented by studying the complex band structures (CBS's) of MX2 monolayers while accounting for spin-orbit coupling effects. By using the symmetry-based tight-binding model a nonlinear generalized eigenvalue problem for CBS's is obtained. An efficient method for solving such class of problems is presented and gives a complete set of physically relevant solutions. Next, these solutions are characterized and classified into propagating and evanescent states, where the latter states present not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gaps, which describe the tunneling currents in the MX2 materials. The importance of CBS's and tunneling currents is demonstrated by the analysis of the quantum transport across MX2 monolayers within phase field matching theory. Present work has been prepared within the Qatar Energy and Environment Research Institute (QEERI) grand challenge ATHLOC project (Project No. QEERI- GC-3008).

  9. A stretchable and screen-printable conductive ink for stretchable electronics

    NASA Astrophysics Data System (ADS)

    Mohammed, Anwar; Pecht, Michael

    2016-10-01

    Stretchable electronics can offer an added degree of design freedom and generate products with unprecedented capabilities. Stretchable conductive ink serving as interconnect, is a key enabler for stretchable electronics. This paper focuses on the development of a stretchable and screen printable conductive ink which could be stretched more than 500 cycles at 20% strain while maintaining electrical and mechanical integrity. The screen printable and stretchable conductive ink developed in this paper marks an important milestone for this nascent technology.

  10. Electronic and thermoelectric properties of Mexican hat bands in van-der-Waals materials

    NASA Astrophysics Data System (ADS)

    Wickramaratne, Darshana; Zahid, Ferdows; Lake, Roger

    2015-03-01

    Mexican hat dispersions are relatively common in few-layer two-dimensional materials. In one to four monolayers of the group-III chalcogenides (GaS, GaSe, InS, InSe) and Bi2Se3 the valence band undergoes a band inversion from a parabolic to an inverted Mexican hat dispersion as the film thickness is reduced from bulk to a single monolayer. The band inversion is robust against changes in stacking order, omission or inclusion of spin-orbit coupling and the choice of functional. The Mexican hat dispersion results in a 1/√{ E} singularity in the two-dimensional density of states and a step-function turn on in the density of modes. The largest radius of the ring of states occurs for a single monolayer of each material. The dispersion with the largest radius coincides with the maximum power factor and ZT for a material at room temperature. Ab-initio electronic structure calculations are used with a Landauer approach to calculate the thermoelectric transport coefficients. Analytical models of the Mexican hat and the parabolic dispersions are used for comparison and analysis. Vertically biased bilayer graphene could serve as an experimental test-bed for measuring this effect since the radius of the Mexican hat band edge increases linearly with vertical electric field. Support by the NSF and SRC-NRI Project 2204.001 (NSF-ECCS-1124733), FAME, one of six centers of STARnet, a SRC program sponsored by MARCO and DARPA and the use of XSEDE NSF Grant # OCI-1053575.

  11. Low-dimensional transport and large thermoelectric power factors in bulk semiconductors by band engineering of highly directional electronic states.

    PubMed

    Bilc, Daniel I; Hautier, Geoffroy; Waroquiers, David; Rignanese, Gian-Marco; Ghosez, Philippe

    2015-04-03

    Thermoelectrics are promising for addressing energy issues but their exploitation is still hampered by low efficiencies. So far, much improvement has been achieved by reducing the thermal conductivity but less by maximizing the power factor. The latter imposes apparently conflicting requirements on the band structure: a narrow energy distribution and a low effective mass. Quantum confinement in nanostructures and the introduction of resonant states were suggested as possible solutions to this paradox, but with limited success. Here, we propose an original approach to fulfill both requirements in bulk semiconductors. It exploits the highly directional character of some orbitals to engineer the band structure and produce a type of low-dimensional transport similar to that targeted in nanostructures, while retaining isotropic properties. Using first-principle calculations, the theoretical concept is demonstrated in Fe2YZ Heusler compounds, yielding power factors 4 to 5 times larger than in classical thermoelectrics at room temperature. Our findings are totally generic and rationalize the search of alternative compounds with similar behavior. Beyond thermoelectricity, these might be relevant also in the context of electronic, superconducting, or photovoltaic applications.

  12. Hybridization of electronic band structure and enhancement of thermoelectric properties of ZnSb thin film by In doping

    NASA Astrophysics Data System (ADS)

    Zheng, Zhuang-hao; Fan, Ping; Luo, Jing-ting; Liang, Guang-xing

    2017-04-01

    Here we report the In doped ZnSb thermoelectric thin films which were deposited by direct current magnetron co-sputtering with prefabricate layer doping method. The X-ray diffraction result indicates that the peaks of the In doped ZnSb thin films are related to ZnSb phase and are slightly shifted to smaller angle. The calculations of In occupy one of the Sb or Zn location in normal site were performed based on the first-principles and it has lower total energy when the In substitutes the Zn. The thermo-electrical testing experimental results indicate that the Seebeck coefficient increases greatly after In doped due to increase of the total density of states and the complicate of the electronic band structure. The Fermi surface moves to the valence band after In doped that will reduce the electrical conductivity and it corresponds to the testing result. It can be observed that the power factor of the In doped ZnSb is approach two times than that of the thin film without doping.

  13. Electronic structure and band gaps in cationic heterocyclic oligomers. Multidimensional analysis of the interplay of heteroatoms, substituents, molecular length, and charge on redox and transparency characteristics.

    PubMed

    Hutchison, Geoffrey R; Ratner, Mark A; Marks, Tobin J

    2005-03-03

    Oxidative doping of extended pi-conjugated polymers and oligomers produces dramatic changes in optical and electrical properties, arising from polaron and soliton-derived midgap states. Despite the great importance of such changes for materials properties, far less is known about the cationic polaron states than about the neutral, semiconducting or insulating, undoped materials. The systematic, multifactor computational analysis of oligoheterocycles such as oligothiophenes, oligofurans, and oligopyrroles presented here affords qualitative and quantitative understanding of the interplay among skeletal substitution pattern, electronic structure, and the effective band gap reduction on p-doping. A simple linear relation is derived for predicting p-doped oligomer and polymer effective band gaps based on those of the neutral oligomers; this relationship confirms the effectiveness of a "fixed band" approximation and explains the counterintuitive increase of the effective band gap on p-doping of many small band gap oligomers. The present analysis also suggests new candidates for transparent conductive polymers and predicts limiting behavior of ionization potential, electron affinity, and other properties for various polyheterocyclic systems. The results yield insight into materials constraints in electrochromic polymers as well as on p- and n-type conductors and semiconductors.

  14. Transition-metal-substituted indium thiospinels as novel intermediate-band materials: prediction and understanding of their electronic properties.

    PubMed

    Palacios, P; Aguilera, I; Sánchez, K; Conesa, J C; Wahnón, P

    2008-07-25

    Results of density-functional calculations for indium thiospinel semiconductors substituted at octahedral sites with isolated transition metals (M=Ti,V) show an isolated partially filled narrow band containing three t2g-type states per M atom inside the usual semiconductor band gap. Thanks to this electronic structure feature, these materials will allow the absorption of photons with energy below the band gap, in addition to the normal light absorption of a semiconductor. To our knowledge, we demonstrate for the first time the formation of an isolated intermediate electronic band structure through M substitution at octahedral sites in a semiconductor, leading to an enhancement of the absorption coefficient in both infrared and visible ranges of the solar spectrum. This electronic structure feature could be applied for developing a new third-generation photovoltaic cell.

  15. Localized conductive patterning via focused electron beam reduction of graphene oxide

    SciTech Connect

    Kim, Songkil; Henry, Mathias; Kulkarni, Dhaval D.; Zackowski, Paul; Jang, Seung Soon; Tsukruk, Vladimir V.; Fedorov, Andrei G.

    2015-03-30

    We report on a method for “direct-write” conductive patterning via reduction of graphene oxide (GO) sheets using focused electron beam induced deposition (FEBID) of carbon. FEBID treatment of the intrinsically dielectric graphene oxide between two metal terminals opens up the conduction channel, thus enabling a unique capability for nanoscale conductive domain patterning in GO. An increase in FEBID electron dose results in a significant increase of the domain electrical conductivity with improving linearity of drain-source current vs. voltage dependence, indicative of a change of graphene oxide electronic properties from insulating to semiconducting. Density functional theory calculations suggest a possible mechanism underlying this experimentally observed phenomenon, as localized reduction of graphene oxide layers via interactions with highly reactive intermediates of electron-beam-assisted dissociation of surface-adsorbed hydrocarbon molecules. These findings establish an unusual route for using FEBID as nanoscale lithography and patterning technique for engineering carbon-based nanomaterials and devices with locally tailored electronic properties.

  16. Electronically conducting metal oxide nanoparticles and films for optical sensing applications

    SciTech Connect

    Ohodnicki, Jr., Paul R.; Wang, Congjun; Andio, Mark A

    2014-09-16

    The disclosure relates to a method of detecting a change in a chemical composition by contacting a conducting oxide material with a monitored stream, illuminating the conducting oxide material with incident light, collecting exiting light, monitoring an optical signal based on a comparison of the incident light and the exiting light, and detecting a shift in the optical signal. The conducting metal oxide has a carrier concentration of at least 10.sup.17/cm.sup.3, a bandgap of at least 2 eV, and an electronic conductivity of at least 10.sup.-1 S/cm, where parameters are specified at the gas stream temperature. The optical response of the conducting oxide materials is proposed to result from the high carrier concentration and electronic conductivity of the conducting metal oxide, and the resulting impact of changing gas atmospheres on that relatively high carrier concentration and electronic conductivity. These changes in effective carrier densities and electronic conductivity of conducting metal oxide films and nanoparticles are postulated to be responsible for the change in measured optical absorption associated with free carriers. Exemplary conducting metal oxides include but are not limited to Al-doped ZnO, Sn-doped In.sub.2O.sub.3, Nb-doped TiO.sub.2, and F-doped SnO.sub.2.

  17. Phase-operation for conduction electron by atomic-scale scattering via single point-defect

    SciTech Connect

    Nagaoka, Katsumi Yaginuma, Shin; Nakayama, Tomonobu

    2014-03-17

    In order to propose a phase-operation technique for conduction electrons in solid, we have investigated, using scanning tunneling microscopy, an atomic-scale electron-scattering phenomenon on a 2D subband state formed in Si. Particularly, we have noticed a single surface point-defect around which a standing-wave pattern created, and a dispersion of scattering phase-shifts by the defect-potential against electron-energy has been measured. The behavior is well-explained with appropriate scattering parameters: the potential height and radius. This result experimentally proves that the atomic-scale potential scattering via the point defect enables phase-operation for conduction electrons.

  18. Nanoscale probing of electronic band gap and topography of VO2 thin film surfaces by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Yin, W.; Wolf, S.; Ko, C.; Ramanathan, S.; Reinke, P.

    2011-01-01

    The metal-insulator transition (MIT) in vanadium dioxide in the vicinity of room temperature makes it one of the most interesting materials for novel switching device applications. It is therefore essential to have a fundamental understanding of the VO2 surface when it is incorporated into multilayer structures or nanodevices. This study focuses on the surface modification of VO2 in response to the thermal treatment during phase transition. Vacuum annealing at temperatures in the vicinity of the MIT triggers a partial reduction in the surface, and thus initiates a chemical phase transition. Scanning tunneling microscopy and spectroscopy are used to investigate the electronic properties and surface structure of the VO2 thin film on (0001) sapphire substrates. Band gap maps with a high spatial resolution and single point spectroscopy I-V curves are measured as the sample is cycled through the MIT, and thus provide a direct observation of the surface phase transition at the nanoscale. The VO2 surface exhibits a homogeneous insulating behavior with a typical band gap of ˜0.5 eV at room temperature, and the surface becomes more metallic and spatially inhomogeneous in conductivity during MIT, and wide range of surface oxides can be identified. The surface still remains partially metallic after cooling down from a long period anneal, and such irreversible surface electrical change is attributed to the loss of oxygen. The location of metallic islands after thermal cycling is strongly coupled to the topography of the film, and relaxation processes and continued modification of the spatial distribution of the metallic regions are recognized on a longer timescale. The impact of film morphology, strain, surface chemistry, and structural phase transition on the electronic characteristics of VO2 surfaces are discussed.

  19. VLF-emissions from ring current electrons. An interpretation of the band of missing emissions

    NASA Technical Reports Server (NTRS)

    Maeda, K.; Smith, P. H.; Anderson, R. R.

    1976-01-01

    VLF-emissions associated with the enhancement of ring current electrons during magnetic storms and substorms which were detected by the equatorially orbiting S-A satellite (Explorer 45) are described. The emissions observed near the geomagnetic equator consist of essentially two frequency regimes, i.e., one above the electron gyrofrequency, f sub H at the equator and the other below f sub H. This is indicated as a part of the wide-band data obtained during the main phase of the December 17, 1971 magnetic storm. The upper figure is the ac-magnetic field data measured by the search-coil magnetometer with the upper cutoff of 3kHz and the lower figure is the ac-electric field data obtained by the electric field sensor with the upper cutoff of 10kHz. These figures show the time sequence of the observed emissions along the inbound orbit (No. 101) of the satellite as f sub H changes approximately from 3 kHz at 20 UT to 6 kHz at 21 UT. The emissions above f sub H are electrostatic mode, which peak near the frequencies of (n + 1/2) f sub H where n is positive integer, and sometimes emissions up to n = 10 are observed. The emissions below f sub H are whistler mode, which have a conspicuous gap along exactly half electron gyrofrequency, f sub H/2.

  20. 8-band and 14-band kp modeling of electronic band structure and material gain in Ga(In)AsBi quantum wells grown on GaAs and InP substrates

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    The electronic band structure and material gain have been calculated for GaAsBi/GaAs quantum wells (QWs) with various bismuth concentrations (Bi ≤ 15%) within the 8-band and 14-band kp models. The 14-band kp model was obtained by extending the standard 8-band kp Hamiltonian by the valence band anticrossing (VBAC) Hamiltonian, which is widely used to describe Bi-related changes in the electronic band structure of dilute bismides. It has been shown that in the range of low carrier concentrations n < 5 × 1018 cm-3, material gain spectra calculated within 8- and 14-band kp Hamiltonians are similar. It means that the 8-band kp model can be used to calculate material gain in dilute bismides QWs. Therefore, it can be applied to analyze QWs containing new dilute bismides for which the VBAC parameters are unknown. Thus, the energy gap and electron effective mass for Bi-containing materials are used instead of VBAC parameters. The electronic band structure and material gain have been calculated for 8 nm wide GaInAsBi QWs on GaAs and InP substrates with various compositions. In these QWs, Bi concentration was varied from 0% to 5% and indium concentration was tuned in order to keep the same compressive strain (ɛ = 2%) in QW region. For GaInAsBi/GaAs QW with 5% Bi, gain peak was determined to be at about 1.5 μm. It means that it can be possible to achieve emission at telecommunication windows (i.e., 1.3 μm and 1.55 μm) for GaAs-based lasers containing GaInAsBi/GaAs QWs. For GaInAsBi/Ga0.47In0.53As/InP QWs with 5% Bi, gain peak is predicted to be at about 4.0 μm, i.e., at the wavelengths that are not available in current InP-based lasers.

  1. 8-band and 14-band kp modeling of electronic band structure and material gain in Ga(In)AsBi quantum wells grown on GaAs and InP substrates

    SciTech Connect

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

    2015-08-07

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

  2. Characterization of traps at nitrided SiO2/SiC interfaces near the conduction band edge by using Hall effect measurements

    NASA Astrophysics Data System (ADS)

    Hatakeyama, Tetsuo; Kiuchi, Yuji; Sometani, Mitsuru; Harada, Shinsuke; Okamoto, Dai; Yano, Hiroshi; Yonezawa, Yoshiyuki; Okumura, Hajime

    2017-04-01

    The effects of nitridation on the density of traps at SiO2/SiC interfaces near the conduction band edge were qualitatively examined using a simple, newly developed characterization method that utilizes Hall effect measurements and split capacitance–voltage measurements. The results showed a significant reduction in the density of interface traps near the conduction band edge as a result of nitridation, but the interface traps were not completely eliminated by nitridation.

  3. Characterization of borate glasses by W-band pulse electron-nuclear double resonance spectroscopy

    SciTech Connect

    Kordas, George; Goldfarb, Daniella

    2008-10-21

    (100-x) mol % B{sub 2}O{sub 3} x mol %Me{sub 2}O (Me=Li,Na,K) glasses, exposed to {gamma}-{sup 60}Co irradiation to produce paramagnetic states, were characterized by W-band (95 GHz) pulse electron-nuclear double resonance (ENDOR) spectroscopy in order to characterize local structures occurring in the range of compositions between x=16 and x=25 at which the 'boron oxide' anomaly occurs. The high resolution of nuclear frequencies allowed resolving the {sup 7}Li and {sup 11}B ENDOR lines. In the samples with x=16 and x=20 glasses, {sup 11}B hyperfine couplings of 16, 24, and 36 MHz were observed and attributed to the tetraborate, triborate, and boron oxygen hole center (BOHC) structures, respectively. The x=25 samples showed hyperfine couplings of 15 MHz for the tetraborate and 36 MHz for BOHC. Density functional theory (DFT) calculations predicted for these structures negative hyperfine couplings, which were confirmed by W-band ENDOR. This suggests that a spin polarization mechanism accounts for the negative hyperfine structure splitting.

  4. Correlating structure and electronic band-edge properties in organolead halide perovskites nanoparticles.

    PubMed

    Zhu, Qiushi; Zheng, Kaibo; Abdellah, Mohamed; Generalov, Alexander; Haase, Dörthe; Carlson, Stefan; Niu, Yuran; Heimdal, Jimmy; Engdahl, Anders; Messing, Maria E; Pullerits, Tonu; Canton, Sophie E

    2016-06-01

    After having emerged as primary contenders in the race for highly efficient optoelectronics materials, organolead halide perovskites (OHLP) are now being investigated in the nanoscale regime as promising building blocks with unique properties. For example, unlike their bulk counterpart, quantum dots of OHLP are brightly luminescent, owing to large exciton binding energies that cannot be rationalized solely on the basis of quantum confinement. Here, we establish the direct correlation between the structure and the electronic band-edge properties of CH3NH3PbBr3 nanoparticles. Complementary structural and spectroscopic measurements probing long-range and local order reveal that lattice strain influences the nature of the valence band and modifies the subtle stereochemical activity of the Pb(2+) lone-pair. More generally, this work demonstrates that the stereochemical activity of the lone-pair at the metal site is a specific physicochemical parameter coupled to composition, size and strain, which can be employed to engineer novel functionalities in OHLP nanomaterials.

  5. Microstructure, optical property, and electronic band structure of cuprous oxide thin films

    SciTech Connect

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

    2011-11-15

    Cuprous oxide (Cu{sub 2}O) thin films were grown via radio frequency sputtering deposition at various temperatures. The dielectric functions and luminescence properties of the Cu{sub 2}O thin films were measured using spectroscopic ellipsometry and photoluminescence, respectively. High-energy peaks were observed in the photoluminescence spectra. Several critical points (CPs) were found using second derivative spectra of the dielectric functions and the standard critical point model. The electronic band structure and the dielectric functions were calculated using density functional theory, and the CP energies were estimated to compare with the experimental data. We identified the high-energy photoluminescence peaks to quasi-direct transitions which arose from the granular structures of the Cu{sub 2}O thin films.

  6. Conditions for Aeronomic Applicability of the Classical Electron Heat Conduction Formula

    NASA Technical Reports Server (NTRS)

    Cole, K. D.; Hoegy, W. R.

    1998-01-01

    Conditions for the applicability of the classical formula for heat conduction in the electrons in ionized gas are investigated. In a fully ionised gas ( V(sub en) much greater than V(sub ei)), when the mean free path for electron-electron (or electron-ion) collisions is much larger than the characteristic thermal scale length of the observed system, the conditions for applicability break down. In the case of the Venus ionosphere this breakdown is indicated for a large fraction of the electron temperature data from altitudes greater than 180 km, for electron densities less than 10(exp 4)/cc cm. In a partially ionised gas such that V(sub en) much greater than V(sub ei) there is breakdown of the formula not only when the mean free path of electrons greatly exceeds the thermal scale length, but also when the gradient of neutral particle density exceeds the electron thermal gradient. It is shown that electron heat conduction may be neglected in estimating the temperature of joule heated electrons by observed strong 100 Hz electric fields when the conduction flux is limited by the saturation flux. The results of this paper support our earlier aeronomical arguments against the hypothesis of planetary scale whistlers for the 100 Hz electric field signal. In turn this means that data from the 100 Hz signal may not be used to support the case for lightning on Venus.

  7. Physical properties and electronic band structure of noncentrosymmetric Th7Co3 superconductor

    NASA Astrophysics Data System (ADS)

    Sahakyan, M.; Tran, V. H.

    2016-05-01

    The physical properties of the noncentrosymmetric superconductor Th7Co3 have been investigated by means of ac-magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance and Hall effect measurements. From these data it is established that Th7Co3 is a dirty type-II superconductor with {{T}\\text{c}}=1.8+/- 0.02 K, Hc2\\text{orb}<{{H}c2}(0)˜ 10~\\text{kOe}c2p and moderate electron-phonon coupling {λ\\text{el-\\text{ph}}}=0.56 . Some evidences for anisotropic superconducting gap are found, including e.g. reduced specific heat jump (Δ {{C}p}/γ {{T}\\text{c}}=1.01 ) at T c, diminished superconducting energy gap ({{Δ }0}/{{k}\\text{B}}{{T}\\text{c}}=2.17 ) as compared to the BCS values, power law field dependence of the Sommerfeld coefficient at 0.4 K ({{C}p}/T\\propto {{H}0.6} ), and a concave curvature of the {{H}c2}≤ft({{T}\\text{c}}\\right) line. The magnitudes of the thermodynamic critical field and the energy gap are consistent with mean-squared anisotropy parameter < {{a}2}> ˜ 0.23 . The electronic specific heat in the superconducting state is reasonably fitted to an oblate spheroidal gap model. Calculations of scalar relativistic and fully relativistic electronic band structures reveal considerable differences in the degenerate structure, resulting from asymmetric spin-orbit coupling (ASOC). A large splitting energy of spin-up spin-down bands at the Fermi level E F, Δ {{E}\\text{ASOC}}˜ 100 meV is observed and a sizeable ratio Δ {{E}\\text{ASOC}}/{{k}\\text{B}}{{T}\\text{c}}˜ 640 could classify the studied compound into the class of noncentrosymmetric superconductors with strong ASOC. The noncentrosymmetry of the crystal structure and the atomic relativistic effects are both responsible for an importance of ASOC in Th7Co3. The calculated results for the density of states show a Van Hove singularity just below E F and dominant role of the 6d electrons of Th to the superconductivity.

  8. Thermal Conductivity in Nanoporous Gold Films during Electron-Phonon Nonequilibrium

    DOE PAGES

    Hopkins, Patrick E.; Norris, Pamela M.; Phinney, Leslie M.; ...

    2008-01-01

    The reduction of nanodevices has given recent attention to nanoporous materials due to their structure and geometry. However, the thermophysical properties of these materials are relatively unknown. In this article, an expression for thermal conductivity of nanoporous structures is derived based on the assumption that the finite size of the ligaments leads to electron-ligament wall scattering. This expression is then used to analyze the thermal conductivity of nanoporous structures in the event of electron-phonon nonequilibrium.

  9. Electron-spectroscopy and -diffraction study of the conductivity of CVD diamond ( 0 0 1 )2×1 surface

    NASA Astrophysics Data System (ADS)

    Kono, S.; Takano, T.; Shimomura, M.; Goto, T.; Sato, K.; Abukawa, T.; Tachiki, M.; Kawarada, H.

    2003-04-01

    A chemical vapor deposition as-grown diamond (0 0 1) single-domain 2 × 1 surface was studied by electron-spectroscopy and electron-diffraction in ultrahigh vacuum (UHV). In order to change the surface conductivity (SC) of the diamond in UHV, three annealing stages were used; without annealing, annealing at 300 °C and annealing at 550 °C. From low energy electron diffraction and X-ray photoelectron spectroscopic (XPS) studies, an existence of SC was suggested for the first two stages of annealing and an absence of SC was suggested for the last stage of annealing. Changes in C KVV Auger electron spectroscopic spectra, C KVV Auger electron diffraction (AED) patterns and C 1s XPS peak positions were noticed between the annealing stages at 300 and 550 °C. These changes are interpreted as such that the state of hydrogen involvement in a subsurface of diamond (0 0 1)2 × 1 changes as SC changes. In particular, the presence of local disorder in diamond configuration in SC subsurface is pointed out from C KVV AED. From C 1s XPS peak shifts, a lower bound for the Fermi-level for SC layers from the valence band top is presented to be ˜0.5 eV.

  10. Effect of electron temperature anisotropy on near-wall conductivity in Hall thrusters

    SciTech Connect

    Zhang, Fengkui E-mail: yudaren@hit.edu.cn; Kong, Lingyi; Zhang, Xueyi; Li, Wei; Yu, Daren E-mail: yudaren@hit.edu.cn

    2014-06-15

    The electron velocity distribution in Hall thrusters is anisotropic, which not only makes the sheath oscillate in time, but also causes the sheath to oscillate in space under the condition of low electron temperatures. The spatial oscillation sheath has a significant effect on near-wall transport current. In this Letter, the method of particle-in-cell (2D + 3 V) was adopted to simulate the effect of anisotropic electron temperatures on near-wall conductivity in a Hall thruster. Results show that the electron-wall collision frequency is within the same order in magnitude for both anisotropic and isotropic electron temperatures. The near-wall transport current produced by collisions between the electrons and the walls is much smaller than experimental measurements. However, under the condition of anisotropic electron temperatures, the non-collision transport current produced by slow electrons which reflected by the spatial oscillation sheath is much larger and closes to measurements.

  11. Features of the band structure and conduction mechanisms of n-HfNiSn semiconductor heavily Lu-doped

    SciTech Connect

    Romaka, V. A.; Rogl, P.; Romaka, V. V.; Kaczorowski, D.; Stadnyk, Yu. V.; Korzh, R. O.; Krayovskyy, V. Ya.; Kovbasyuk, T. M.

    2015-03-15

    The crystal and electronic structures, energy, kinetic, and magnetic characteristics of n-HfNiSn semiconductor heavily doped with a Lu acceptor impurity in the ranges T = 80–400 K and N{sub A}{sup Lu} ≈ 1.9 × 10{sup 20}−1.9 × 10{sup 21} cm{sup −3} (x = 0.01–0.10) at H ≤ 10 kG is studied. The nature of the structural-defect generation mechanism leading to changes in the band gap and the degree of semiconductor compensation is determined. Its essence is the simultaneous reduction and elimination of donor-type structural defects due to the displacement of ∼1% of Ni atoms from the Hf (4a) site, the generation of acceptor-type structural defects by substituting Ni atoms with Lu atoms at the 4c site, and the generation of donor-type defects such as vacancies at the Sn (4b) site. The results of calculations of the electronic structure of Hf{sub 1−x}Lu{sub x}NiSn are in agreement with experimental data. The results are discussed within the model of a heavily doped and compensated Shklovskii-Efros semiconductor.

  12. Features of the band structure and conduction mechanisms in the n-HfNiSn semiconductor heavily doped with Ru

    SciTech Connect

    Romaka, V. A.; Rogl, P.; Romaka, V. V.; Stadnyk, Yu. V.; Korzh, R. O.; Krayovskyy, V. Ya.; Horyn, A. M.

    2014-12-15

    The crystal and electronic structure and energy and kinetic properties of the n-HfNiSn semiconductor heavily doped with a Ru acceptor impurity are investigated in the temperature and Ru concentration ranges T = 80–400 K and N{sub A}{sup Ru} ≈ 9.5 × 10{sup 19}−5.7 × 10{sup 20} cm{sup −3} (x = 0–0.03), respectively. The mechanism of structural-defect generation is established, which changes the band gap and degree of compensation of the semiconductor and consists in the simultaneous concentration reduction and elimination of donor structural defects by means of the displacement of ∼1% of Ni atoms from the Hf (4a) positions, the generation of acceptor structural defects upon the substitution of Ru atoms for Ni atoms in the 4c positions, and the generation of donor defects in the form of vacancies in the Sn (4b) positions. The calculated electronic structure of HfNi{sub 1−x}Ru{sub x}Sn is consistent with the experiment. The results obtained are discussed within the Shklovsky-Efros model for a heavily doped and compensated semiconductor.

  13. Effect of Dipolar Orientational Polarization on Electronic Conductivity in Ferroelectric Polymer Electrets

    NASA Astrophysics Data System (ADS)

    Yang, Lianyun; Zhu, Lei

    2014-03-01

    The leakage current, ion migration, and dipolar orientational polarization are major losses in ferroelectric polymers. The loss from the leakage current originates from electronic conduction and its behavior could be significantly affected by the internal electric field, which is induced by the dipolar orientational polarization. In this work, the leakage current in the corona charged PVDF electrets is studied under different external electric fields. Under low applied electric field, when no or very few dipoles could flip, the conductivity from the leakage direct current increases upon increasing the electric field. Under higher electric field, the aligned dipole-induced internal field would prevent the electrons from going through so that the conductivity decreases. After all the dipoles are aligned with the external electric field, the conductivity can increase again. This study will help us better understand the interplay between electronic conduction and dipolar orientation in ferroelectric materials.

  14. Optical and electronic properties of conductive ternary nitrides with rare- or alkaline-earth elements

    NASA Astrophysics Data System (ADS)

    Kassavetis, S.; Hodroj, A.; Metaxa, C.; Logothetidis, S.; Pierson, J. F.; Patsalas, P.

    2016-12-01

    Conductive nitrides, such as TiN, are key engineering materials for electronics, photonics, and plasmonics; one of the essential issues for such applications is the ability of tuning the conduction electron density, the resistivity, and the electron scattering. While enhancing the conduction electron density and blueshifting the intraband absorption towards the UV were easily achieved previously, reducing the conduction electron density and redshifting the intraband absorption into the infrared are still an open issue. The latter is achieved in this work by alloying TiN by rare earth (RE = Sc, Y, La) or alkaline earth (AE = Mg, Ca) atoms in Ti substitutional positions. The produced TixRE1-xN and TixAE1-xN thin film samples were grown by a hybrid arc evaporation/sputtering process, and most of them are stable in the B1 cubic structure. Their optical properties were studied in an extensive spectral range by spectroscopic ellipsometry. The ellipsometric spectra were analyzed and quantified by the Drude-Lorentz model, which provided the conduction electron density, the electron mean free path, and the resistivity. The observed interband transitions are firmly assigned, and the optical and electrical properties of TixRE1-xN and TixAE1-xN are quantitatively correlated with their composition and crystal structure.

  15. 12 CFR 7.5008 - Location of a national bank conducting electronic activities.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 12 Banks and Banking 1 2010-01-01 2010-01-01 false Location of a national bank conducting electronic activities. 7.5008 Section 7.5008 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE... because the bank's products or services are accessed through electronic means by customers located in...

  16. Size effects in the conduction electron spin resonance of anthracite and higher anthraxolite.

    PubMed

    Tadyszak, Krzysztof; Strzelczyk, Roman; Coy, Emerson; Maćkowiak, Mariusz; Augustyniak-Jabłokow, Maria A

    2016-03-01

    Electron paramagnetic resonance spectroscopy of conduction electrons, i.e. Conduction Electron Spin Resonance (CESR), is a powerful tool for studies of carbon samples. Conductive samples cause additional effects in CESR spectra that influence the shape and intensity of the signals. In cases where conduction electrons play a dominant role, whilst the influence of localized paramagnetic centres is small or negligible, the effects because of the spins on conduction electrons will dominate the spectra. It has been shown that for some ratios of the bulk sample sizes (d) to the skin depth (δ), which depend on the electrical conductivity, additional size effects become visible in the line asymmetry parameter A/|B|, which is the ratio of the maximum to the absolute, minimum value of the resonance signal. To study these effects the electrical direct current-conductivity and CESR measurements are carried out for two amorphous bulk coal samples of anthracite and a higher anthraxolite. The observed effects are described and discussed in terms of the Dyson theory. Copyright © 2015 John Wiley & Sons, Ltd.

  17. 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

    NASA Astrophysics Data System (ADS)

    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.

  18. Electronic Band Structures of the Highly Desirable III-V Semiconductors: TB-mBJ DFT Studies

    NASA Astrophysics Data System (ADS)

    Rehman, Gul; Shafiq, M.; Saifullah; Ahmad, Rashid; Jalali-Asadabadi, S.; Maqbool, M.; Khan, Imad; Rahnamaye-Aliabad, H.; Ahmad, Iftikhar

    2016-07-01

    The correct band gaps of semiconductors are highly desirable for their effective use in optoelectronic and other photonic devices. However, the experimental and theoretical results of the exact band gaps are quite challenging and sometimes tricky. In this article, we explore the electronic band structures of the highly desirable optical materials, III-V semiconductors. The main reason of the ineffectiveness of the theoretical band gaps of these compounds is their mixed bonding character, where large proportions of electrons reside outside atomic spheres in the intestinal regions, which are challenging for proper theoretical treatment. In this article, the band gaps of the compounds are revisited and successfully reproduced by properly treating the density of electrons using the recently developed non-regular Tran and Blaha's modified Becke-Johnson (nTB-mBJ) approach. This study additionally suggests that this theoretical scheme could also be useful for the band gap engineering of the III-V semiconductors. Furthermore, the optical properties of these compounds are also calculated and compared with the experimental results.

  19. Generic suppression of conductance quantization of interacting electrons in graphene nanoribbons in a perpendicular magnetic field

    NASA Astrophysics Data System (ADS)

    Shylau, A. A.; Zozoulenko, I. V.; Xu, H.; Heinzel, T.

    2010-09-01

    The effects of electron interaction on the magnetoconductance of graphene nanoribbons (GNRs) are studied within the Hartree approximation. We find that a perpendicular magnetic field leads to a suppression instead of an expected improvement of the quantization. This suppression is traced back to interaction-induced modifications of the band structure leading to the formation of compressible strips in the middle of GNRs. It is also shown that the hard-wall confinement combined with electron interaction generates overlaps between forward and backward propagating states, which may significantly enhance backscattering in realistic GNRs. The relation to available experiments is discussed.

  20. Experimental and theoretical investigations of the electronic band structure of metal-organic frameworks of HKUST-1 type

    SciTech Connect

    Gu, Zhi-Gang; Heinke, Lars Wöll, Christof; Neumann, Tobias; Wenzel, Wolfgang; Li, Qiang; Fink, Karin; Gordan, Ovidiu D.; Zahn, Dietrich R. T.

    2015-11-02

    The electronic properties of metal-organic frameworks (MOFs) are increasingly attracting the attention due to potential applications in sensor techniques and (micro-) electronic engineering, for instance, as low-k-dielectric in semiconductor technology. Here, the band gap and the band structure of MOFs of type HKUST-1 are studied in detail by means of spectroscopic ellipsometry applied to thin surface-mounted MOF films and by means of quantum chemical calculations. The analysis of the density of states, the band structure, and the excitation spectrum reveal the importance of the empty Cu-3d orbitals for the electronic properties of HKUST-1. This study shows that, in contrast to common belief, even in the case of this fairly “simple” MOF, the excitation spectra cannot be explained by a superposition of “intra-unit” excitations within the individual building blocks. Instead, “inter-unit” excitations also have to be considered.

  1. Electronic band structure of LaO1-xFxBiS2: A recently invented family of superconductors

    NASA Astrophysics Data System (ADS)

    Kumar, Jagdish; Ahluwalia, P. K.; Awana, V. P. S.

    2013-02-01

    In this paper we present electronic band structure calculations of newly discovered BiS2 layer based LaO0.5F0.5BiS2 superconductor using density functional theory. The force minimization results of atomic positions are in agreement with experiments. From band structure analysis the parent compound LaOBiS2 is found to be an insulator for relaxed atomic positions whereas it exhibits metallic state for experimental coordinates. The substitution of F at O site is found to affect the electronic structure in non-rigid band scenario. The doped compound is found to be metallic having electrons as dominant charge carriers. The major contribution to states at Fermi level in LaFBiS2 comes from Bi-p and La-d orbitals.

  2. Electronic Bands of ScC in the Region 620 - 720 NM

    NASA Astrophysics Data System (ADS)

    Chen, Chiao-Wei; Merer, Anthony; Hsu, Yen-Chu

    2016-06-01

    ScC molecules have been observed by laser-induced fluorescence, following the reaction of laser-ablated scandium metal with acetylene under supersonic jet-cooled conditions. Rotational analyses have been carried out for about 40 bands of Sc{}12C and Sc{}13C in the region 14000 - 16000 cm-1. Two lower states are found, with Ω = 3/2 and 5/2, indicating that the ground state is ^4Π_i or ^2Δ. As yet we cannot distinguish between these alternatives, but note that the ground state of the isoelectronic YC molecule is ^4Π_i. The ground state bond length in ScC is 1.95{}_5 Å, and the vibrational frequency is 712 cm-1. At least eight electronic transitions occur in the region studied, the majority obeying the selection rule ΔΩ = +1. Rotational perturbations are widespread, consistent with a high density of excited electronic states. B. Simard, P.A. Hackett and W.J. Balfour, Chem. Phys. Lett., 230, 103 (1994).

  3. Longitudinal spin relaxation of donor-bound electrons in direct band-gap semiconductors

    NASA Astrophysics Data System (ADS)

    Linpeng, Xiayu; Karin, Todd; Durnev, M. V.; Barbour, Russell; Glazov, M. M.; Sherman, E. Ya.; Watkins, S. P.; Seto, Satoru; Fu, Kai-Mei C.

    2016-09-01

    We measure the donor-bound electron longitudinal spin-relaxation time (T1) as a function of magnetic field (B ) in three high-purity direct band-gap semiconductors: GaAs, InP, and CdTe, observing a maximum T1 of 1.4, 0.4, and 1.2 ms, respectively. In GaAs and InP at low magnetic field, up to ˜2 T, the spin-relaxation mechanism is strongly density and temperature dependent and is attributed to the random precession of the electron spin in hyperfine fields caused by the lattice nuclear spins. In all three semiconductors at high magnetic field, we observe a power-law dependence T1∝B-ν with 3 ≲ν ≲4 . Our theory predicts that the direct spin-phonon interaction is important in all three materials in this regime in contrast to quantum dot structures. In addition, the "admixture" mechanism caused by Dresselhaus spin-orbit coupling combined with single-phonon processes has a comparable contribution in GaAs. We find excellent agreement between high-field theory and experiment for GaAs and CdTe with no free parameters, however a significant discrepancy exists for InP.

  4. The electronic band structures of gadolinium chalcogenides: a first-principles prediction for neutron detecting.

    PubMed

    Li, Kexue; Liu, Lei; Yu, Peter Y; Chen, Xiaobo; Shen, D Z

    2016-05-11

    By converting the energy of nuclear radiation to excited electrons and holes, semiconductor detectors have provided a highly efficient way for detecting them, such as photons or charged particles. However, for detecting the radiated neutrons, those conventional semiconductors hardly behave well, as few of them possess enough capability for capturing these neutral particles. While the element Gd has the highest nuclear cross section, here for searching proper neutron-detecting semiconductors, we investigate theoretically the Gd chalcogenides whose electronic band structures have never been characterized clearly. Among them, we identify that γ-phase Gd2Se3 should be the best candidate for neutron detecting since it possesses not only the right bandgap of 1.76 eV for devices working under room temperature but also the desired indirect gap nature for charge carriers surviving longer. We propose further that semiconductor neutron detectors with single-neutron sensitivity can be realized with such a Gd-chalcogenide on the condition that their crystals can be grown with good quality.

  5. Thermal flux limited electron Kapitza conductance in copper-niobium multilayers

    SciTech Connect

    Cheaito, Ramez; Hattar, Khalid Mikhiel; Gaskins, John T.; Yadav, Ajay K.; Duda, John C.; Beechem, III, Thomas Edwin; Ihlefeld, Jon; Piekos, Edward S.; Baldwin, Jon K.; Misra, Amit; Hopkins, Patrick E.

    2015-03-05

    The interplay between the contributions of electron thermal flux and interface scattering to the Kapitza conductance across metal-metal interfaces through measurements of thermal conductivity of copper-niobium multilayers was studied. Thermal conductivities of copper-niobium multilayer films of period thicknesses ranging from 5.4 to 96.2 nm and sample thicknesses ranging from 962 to 2677 nm are measured by time-domain thermoreflectance over a range of temperatures from 78 to 500 K. The Kapitza conductances between the Cu and Nb interfaces in multilayer films are determined from the thermal conductivities using a series resistor model and are in good agreement with the electron diffuse mismatch model. The results for the thermal boundary conductance between Cu and Nb are compared to literature values for the thermal boundary conductance across Al-Cu and Pd-Ir interfaces, and demonstrate that the interface conductance in metallic systems is dictated by the temperature derivative of the electron energy flux in the metallic layers, rather than electron mean free path or scattering processes at the interface.

  6. Thermal flux limited electron Kapitza conductance in copper-niobium multilayers

    DOE PAGES

    Cheaito, Ramez; Hattar, Khalid Mikhiel; Gaskins, John T.; ...

    2015-03-05

    The interplay between the contributions of electron thermal flux and interface scattering to the Kapitza conductance across metal-metal interfaces through measurements of thermal conductivity of copper-niobium multilayers was studied. Thermal conductivities of copper-niobium multilayer films of period thicknesses ranging from 5.4 to 96.2 nm and sample thicknesses ranging from 962 to 2677 nm are measured by time-domain thermoreflectance over a range of temperatures from 78 to 500 K. The Kapitza conductances between the Cu and Nb interfaces in multilayer films are determined from the thermal conductivities using a series resistor model and are in good agreement with the electron diffusemore » mismatch model. The results for the thermal boundary conductance between Cu and Nb are compared to literature values for the thermal boundary conductance across Al-Cu and Pd-Ir interfaces, and demonstrate that the interface conductance in metallic systems is dictated by the temperature derivative of the electron energy flux in the metallic layers, rather than electron mean free path or scattering processes at the interface.« less

  7. Thermal flux limited electron Kapitza conductance in copper-niobium multilayers

    SciTech Connect

    Cheaito, Ramez; Gaskins, John T.; Duda, John C.; Hopkins, Patrick E.; Hattar, Khalid; Beechem, Thomas E.; Ihlefeld, Jon F.; Piekos, Edward S.; Yadav, Ajay K.; Baldwin, Jon K.; Misra, Amit

    2015-03-02

    We study the interplay between the contributions of electron thermal flux and interface scattering to the Kapitza conductance across metal-metal interfaces through measurements of thermal conductivity of copper-niobium multilayers. Thermal conductivities of copper-niobium multilayer films of period thicknesses ranging from 5.4 to 96.2 nm and sample thicknesses ranging from 962 to 2677 nm are measured by time-domain thermoreflectance over a range of temperatures from 78 to 500 K. The Kapitza conductances between the Cu and Nb interfaces in multilayer films are determined from the thermal conductivities using a series resistor model and are in good agreement with the electron diffuse mismatch model. Our results for the thermal boundary conductance between Cu and Nb are compared to literature values for the thermal boundary conductance across Al-Cu and Pd-Ir interfaces, and demonstrate that the interface conductance in metallic systems is dictated by the temperature derivative of the electron energy flux in the metallic layers, rather than electron mean free path or scattering processes at the interface.

  8. Electron and Ion Conductivity Calculations using the Model of Lee and More

    SciTech Connect

    Hayes, John C.

    2016-09-30

    The following notes describe the ARES implementation of the inverse of the electron conduction coefficient, using the model of Lee and More, Physics of Fluids 27, page 1273, 1984. An addendum describing the modifications for analogous ion conduction coeffiecient appears at the bottom.

  9. Band Degeneracy, Low Thermal Conductivity, and High Thermoelectric Figure of Merit in SnTe-CaTe Alloys

    NASA Astrophysics Data System (ADS)

    Al Rahal Al Orabi, R.; Mecholsky, N.; Hwang, J. P.; Kim, W.; Rhyee, J. S.; Wee, D.; Fornari, M.

    Pure lead-free SnTe has limited thermoelectric potentials because of the low Seebeck coeffcients and the relatively large thermal conductivity. In this study, we provide experimental evidence and theoretical understanding that alloying SnTe with Ca greatly improves the transport properties leading to ZT of 1.35 at 873 K, the highest ZT value so far reported for singly doped SnTe materials. The introduction of Ca (0-9%) in SnTe induces multiple effects: (1) Ca replaces Sn and reduces the hole concentration due to Sn vacancies, (2) the energy gap increases limiting the bipolar transport, (3) several bands with larger effective masses become active in transport, and (4) the lattice thermal conductivity is reduced of about 70% due to the contribution of concomitant scattering terms associated with the alloy disorder and the presence of nanoscale precipitates. An effciency of 10% (for ΔT = 400 K) was predicted for high temperature thermoelectric power generation using SnTe-based n- and p-type materials.

  10. Combined scattering loss of radiation belt relativistic electrons by simultaneous three-band EMIC waves: A case study

    NASA Astrophysics Data System (ADS)

    He, Fengming; Cao, Xing; Ni, Binbin; Xiang, Zheng; Zhou, Chen; Gu, Xudong; Zhao, Zhengyu; Shi, Run; Wang, Qi

    2016-05-01

    Multiband electromagnetic ion cyclotron (EMIC) waves can drive efficient scattering loss of radiation belt relativistic electrons. However, it is statistically uncommon to capture the three bands of EMIC waves concurrently. Utilizing data from the Electric and Magnetic Field Instrument Suite and Integrated Science magnetometer onboard Van Allen Probe A, we report the simultaneous presence of three (H+, He+, and O+) emission bands in an EMIC wave event, which provides an opportunity to look into the combined scattering effect of all EMIC emissions and the relative roles of each band in diffusing radiation belt relativistic electrons under realistic circumstances. Our quantitative results, obtained by quasi-linear diffusion rate computations and 1-D pure pitch angle diffusion simulations, demonstrate that the combined resonant scattering by the simultaneous three-band EMIC waves is overall dominated by He+ band wave diffusion, mainly due to its dominance over the wave power (the mean wave amplitudes are approximately 0.4 nT, 1.6 nT, and 0.15 nT for H+, He+, and O+ bands, respectively). Near the loss cone, while 2-3 MeV electrons undergo pitch angle scattering at a rate of the order of 10-6-10-5 s-1, 5-10 MeV electrons can be diffused more efficiently at a rate of the order of 10-3-10-2 s-1, which approaches the strong diffusion level and results in a moderately or heavily filled loss cone for the atmospheric loss. The corresponding electron loss timescales (i.e., lifetimes) vary from several days at the energies of ~2 MeV to less than 1 h at ~10 MeV. This case study indicates the leading contribution of He+ band waves to radiation belt relativistic electron losses during the coexistence of three EMIC wave bands and suggests that the roles of different EMIC wave bands in the relativistic electron dynamics should be carefully incorporated in future modeling efforts.

  11. Band offsets and electronic structures of interface between In{sub 0.5}Ga{sub 0.5}As and InP

    SciTech Connect

    Cai, Genwang; Wang, Changhong; Wang, Weichao; Liang, Erjun

    2016-02-07

    III–V semiconductor interfacing with high-κ gate oxide is crucial for the high mobility metal-oxide-semiconductor field transistor device. With density functional theory calculations, we explored the band offsets and electronic structures of the In{sub 0.5}Ga{sub 0.5}As/InP interfaces with various interfacial bondings. Among six different bonding interfaces, we found that P-In(Ga) bonding interface showed the highest stability. Local density of states calculations was adopted to calculate the band offsets. Except for the metallic interface, we noticed that neither valence band offset nor conduction band offset depended on the interfacial bondings. For the most stable P-In(Ga) interface, we did not observe any gap states. Furthermore, we explored the P-In(Ga) interfaces with interfacial P-As exchange defects, which slightly modified the interface stability and the band offsets but did not produce any gap states. These findings provide solid evidence that InP could serve as a promising interfacial passivation layer between III–V material and high-κ oxide in the application of high mobility devices.

  12. Band anticrossing in dilute nitrides

    SciTech Connect

    Shan, W.; Yu, K.M.; Walukiewicz, W.; Wu, J.; Ager III, J.W.; Haller, E.E.

    2003-12-23

    Alloying III-V compounds with small amounts of nitrogen leads to dramatic reduction of the fundamental band-gap energy in the resulting dilute nitride alloys. The effect originates from an anti-crossing interaction between the extended conduction-band states and localized N states. The interaction splits the conduction band into two nonparabolic subbands. The downward shift of the lower conduction subband edge is responsible for the N-induced reduction of the fundamental band-gap energy. The changes in the conduction band structure result in significant increase in electron effective mass and decrease in the electron mobility, and lead to a large enhance of the maximum doping level in GaInNAs doped with group VI donors. In addition, a striking asymmetry in the electrical activation of group IV and group VI donors can be attributed to mutual passivation process through formation of the nearest neighbor group-IV donor nitrogen pairs.

  13. Extracting the effective mass of electrons in transparent conductive oxide thin films using Seebeck coefficient

    SciTech Connect

    Wang, Yaqin; Zhu, Junhao; Tang, Wu

    2014-05-26

    A method is proposed that combines Seebeck coefficient and carrier concentration to determine the electron effective mass of transparent conductive oxide (TCO) thin films. Experiments were conducted to test the validity of this approach on the transparent conductive Ga-doped ZnO thin films deposited by magnetron sputtering. An evident agreement of the calculated electron effective mass of the films is observed between the proposed approach and the previous studies. Besides, the optical carrier concentration and mobility derived from the calculated electron effective mass and spectroscopic ellipsometry using a complex dielectric function are consistent with those from direct Hall-effect measurement. The agreements suggest that Seebeck coefficient can serve as an alternative tool for extracting the effective mass of electrons in TCO films.

  14. Resonant enhancement in nanostructured thermoelectric performance via electronic thermal conductivity engineering

    NASA Astrophysics Data System (ADS)

    Patil, Urvesh; Muralidharan, Bhaskaran

    2017-01-01

    The use of an asymmetric broadening in the transport distribution, a characteristic of resonant structures, is proposed as a route to engineer a decrease in electronic thermal conductivity thereby enhancing the electronic figure of merit in nanostructured thermoelectrics. Using toy models, we first demonstrate that a decrease in thermal conductivity resulting from such an asymmetric broadening may indeed lead to an electronic figure of merit well in excess of 1000 in an idealized situation and in excess of 10 in a realistic situation. We then substantiate with realistic resonant structures designed using graphene nano-ribbons by employing a tight binding framework with edge correction that match density functional theory calculations under the local density approximation. The calculated figure of merit exceeding 10 in such realistic structures further reinforces the concept and sets a promising direction to use nano-ribbon structures to engineer a favorable decrease in the electronic thermal conductivity.

  15. Intraband optical conductivity sigma/omega,T/ of Cu, Ag, and Au - Contribution from electron-electron scattering

    NASA Technical Reports Server (NTRS)

    Parkins, G. R.; Lawrence, W. E.; Christy, R. W.

    1981-01-01

    The frequency and temperature dependence of the intraband optical conductivity of the noble metals Cu, Ag and Au is measured and contributions of electron-electron scattering are assessed. Optical measurements were performed at temperatures of 77, 295 and 425 K to obtain values of the Drude electron scattering rate with a linear dependence on temperature which may be attributed to electron-phonon scattering, and a quadratic dependence on photon energy, which is suggestive of electron-electron scattering but is a factor of two to three times greater than would be expected. Comparison of the optical data with dc electrical and thermal resistivity data which also show behavior attributed to electron-electron scattering reveals discrepancies of up to an order of magnitude. Other possible mechanisms for the frequency dependence, including absorptance, electron-surface plasmon interactions, a two-carrier model, and a structure dependence are considered, and it is concluded that the frequency dependence in the Drude scattering rates of the noble metals is not yet quantitatively understood

  16. Valence and conduction band offsets at low-k a-SiO{sub x}C{sub y}:H/a-SiC{sub x}N{sub y}:H interfaces

    SciTech Connect

    King, Sean W. Brockman, Justin; French, Marc; Jaehnig, Milt; Kuhn, Markus; French, Benjamin

    2014-09-21

    In order to understand the fundamental electrical leakage and reliability failure mechanisms in nano-electronic low-k dielectric/metal interconnect structures, we have utilized x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy to determine the valence and conduction band offsets present at interfaces between non-porous and porous low-k a-SiO{sub x}C{sub y}:H interlayer dielectrics and a-SiC{sub x}N{sub y}:H metal capping layers. The valence band offset for such interfaces was determined to be 2.7±0.2 eV and weakly dependent on the a-SiOC:H porosity. The corresponding conduction band offset was determined to be 2.1±0.2 eV. The large band offsets indicate that intra metal layer leakage is likely dominated by defects and trap states in the a-SiOC:H and a-SiCN:H dielectrics.

  17. Directly patternable, highly conducting polymers for broad applications in organic electronics.

    PubMed

    Yoo, Joung Eun; Lee, Kwang Seok; Garcia, Andres; Tarver, Jacob; Gomez, Enrique D; Baldwin, Kimberly; Sun, Yangming; Meng, Hong; Nguyen, Thuc-Quyen; Loo, Yueh-Lin

    2010-03-30

    Postdeposition solvent annealing of water-dispersible conducting polymers induces dramatic structural rearrangement and improves electrical conductivities by more than two orders of magnitude. We attain electrical conductivities in excess of 50 S/cm when polyaniline films are exposed to dichloroacetic acid. Subjecting commercially available poly(ethylene dioxythiophene) to the same treatment yields a conductivity as high as 250 S/cm. This process has enabled the wide incorporation of conducting polymers in organic electronics; conducting polymers that are not typically processable can now be deposited from solution and their conductivities subsequently enhanced to practical levels via a simple and straightforward solvent annealing process. The treated conducting polymers are thus promising alternatives for metals as source and drain electrodes in organic thin-film transistors as well as for transparent metal oxide conductors as anodes in organic solar cells and light-emitting diodes.

  18. Conductivity of solvated electrons in hexane investigated with terahertz time-domain spectroscopy.

    PubMed

    Knoesel, Ernst; Bonn, Mischa; Shan, Jie; Wang, Feng; Heinz, Tony F

    2004-07-01

    We present investigations of the transient photoconductivity and recombination dynamics of quasifree electrons in liquid n-hexane and cyclohexane performed using terahertz time-domain spectroscopy (THz-TDS). Quasifree electrons are generated by two-photon photoionization of the liquid using a femtosecond ultraviolet pulse, and the resulting changes in the complex conductivity are probed by a THz electromagnetic pulse at a variable delay. The detection of time-domain wave forms of the THz electric field permits the direct determination of both the real and the imaginary part of the conductivity of the electrons over a wide frequency range. The change in conductivity can be described by the Drude model, thus yielding the quasifree electron density and scattering time. The electron density is found to decay on a time scale of a few hundred picoseconds, which becomes shorter with increasing excitation density. The dynamics can be described by a model that assumes nongeminate recombination between electrons and positive ions. In addition, a strong dependence of the quasifree electron density on temperature is observed, in agreement with a two-state model in which the electron may exist in either a quasifree or a bound state.

  19. Influence of dye content on the conduction band edge of titania in the steam-treated dye-dispersing titania electrodes.

    PubMed

    Setiawan, Rudi Agus; Nishikiori, Hiromasa; Tanaka, Nobuaki; Fujii, Tsuneo

    2014-01-01

    The titania and dye-dispersing titania electrodes were prepared by a nitric acid-catalyzed sol-gel process. The dye-dispersing titania contains the dye molecules dispersed on the surface of the individual nanosized titania particles. The photo-cyclic voltammetry (Photo-CV) and photoelectric measurements of the dye-dispersing titania electrodes were conducted to clarify the factors changing the conduction band edge of the titania and the open-circuit voltage (Voc ) of the electrodes. The remaining nitrate ions caused a negative shift of conduction band edge of the titania of the dye-dispersing titania. The conduction band edge of the titania was shifted in a negative direction in the electrode containing a greater amount of the dye. These results are due to the adsorption of nitrate ions and the dye-titania complex formation on the titania particle surface. The effect of the dye-titania complex formation on the shift in the titania conduction band edge was greater than that of the adsorption of nitrate ions due to strong interaction between the dye and titania through the carboxylate and quinone-like groups of the dye. The shift in the titania conduction band edge corresponded to the change in the Voc value.

  20. Band offsets and trap-related electron transitions at interfaces of (100)InAs with atomic-layer deposited Al2O3

    NASA Astrophysics Data System (ADS)

    Chou, H.-Y.; O'Connor, E.; O'Mahony, A.; Povey, I. M.; Hurley, P. K.; Dong, Lin; Ye, P. D.; Afanas'ev, V. V.; Houssa, M.; Stesmans, A.

    2016-12-01

    Spectral analysis of optically excited currents in single-crystal (100)InAs/amorphous (a-)Al2O3/metal structures allows one to separate contributions stemming from the internal photoemission (IPE) of electrons into alumina and from the trapping-related displacement currents. IPE spectra suggest that the out-diffusion of In and, possibly, its incorporation in a-Al2O3 lead to the development of ≈0.4 eV wide conduction band (CB) tail states. The top of the InAs valence band is found at 3.45 ± 0.10 eV below the alumina CB bottom, i.e., at the same energy as at the GaAs/a-Al2O3 interface. This corresponds to the CB and the valence band offsets at the InAs/a-Al2O3 interface of 3.1 ± 0.1 eV and 2.5 ± 0.1 eV, respectively. However, atomic-layer deposition of alumina on InAs results in additional low-energy electron transitions with spectral thresholds in the range of 2.0-2.2 eV, which is close to the bandgap of AlAs. The latter suggests the interaction of As with Al, leading to an interlayer containing Al-As bonds providing a lower barrier for electron injection.

  1. Simultaneous conduction of electronic charge and lithium ions in block copolymers.

    PubMed

    Patel, Shrayesh N; Javier, Anna E; Stone, Greg M; Mullin, Scott A; Balsara, Nitash P

    2012-02-28

    The main objective of this work is to study charge transport in mixtures of poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT-PEO) block copolymers and lithium bis(trifluoromethanesulfonyl) imide salt (LiTFSI). The P3HT-rich microphase conducts electronic charge, while the PEO-rich microphase conducts ionic charge. The nearly symmetric P3HT-PEO copolymer used in this study self-assembles into a lamellar phase. In contrast, the morphologies of asymmetric copolymers with P3HT as the major component are dominated by nanofibrils. A combination of ac and dc impedance measurements was used to determine the electronic and ionic conductivities of our samples. The ionic conductivities of P3HT-PEO/LiTFSI mixtures are lower than those of mixtures of PEO homopolymer and LiTFSI, in agreement with published data obtained from other block copolymer/salt mixtures. In contrast, the electronic conductivities of the asymmetric P3HT-PEO copolymers are significantly higher than those of the P3HT homopolymer. This is unexpected because of the presence of the nonelectronically conducting PEO microphase. This implies that the intrinsic electronic conductivity of the P3HT microphase in P3HT-PEO copolymers is significantly higher than that of P3HT homopolymers.

  2. The role of band alignment in p-type conductivity of Na-doped ZnMgO: Polar versus non-polar

    SciTech Connect

    Zhang, H. H.; Pan, X. H. E-mail: yezz@zju.edu.cn; Li, Y.; Ye, Z. Z. E-mail: yezz@zju.edu.cn; Lu, B.; Chen, W.; Huang, J. Y.; Ding, P.; Chen, S. S.; He, H. P.; Lu, J. G.; Chen, L. X.; Ye, C. L.

    2014-03-17

    We investigate the electrical properties of polar and non-polar ZnMgO:Na films that have been fabricated on c-plane and r-plane sapphire substrates using intervened ZnO layers (10–30 nm thick) by pulsed laser deposition. Hall-effect measurements indicate that the a-plane ZnMgO:Na film exhibits p-type conductivity with a carrier concentration of about 3.5 × 10{sup 16} cm{sup −3}, while the polar film shows a compensatory conductivity. Meanwhile, the dependence of the band alignment on the orientation of the ZnMgO/ZnO heterojunctions has been investigated using photoelectron spectroscopy. The heterojunctions form in the type-I straddling alignment with valence band offsets of 0.07 (0.02) eV for the (non-)polar heterojunction. The difference in valence band offsets is primarily attributed to the spontaneous polarization effect. We propose that the smaller valence band offsets and larger conduction band offsets would reduce the Na{sub Zn} acceptor level and enhance the relative intrinsic donor levels. Such effects consequently lead to p-type conductivity in non-polar ZnMgO:Na films. The band alignment of non-polar ZnMgO/ZnO can be used to facilitate p-type doping with a shallower acceptor state in the ZnO-like alloy.

  3. Electronic conduction properties of indium tin oxide: single-particle and many-body transport.

    PubMed

    Lin, Juhn-Jong; Li, Zhi-Qing

    2014-08-27

    Indium tin oxide (Sn-doped In2O3-δ or ITO) is a very interesting and technologically important transparent conducting oxide. This class of material has been extensively investigated for decades, with research efforts mostly focusing on the application aspects. The fundamental issues of the electronic conduction properties of ITO from room temperature down to liquid-helium temperatures have rarely been addressed thus far. Studies of the electrical-transport properties over a wide range of temperature are essential to unravelling the underlying electronic dynamics and microscopic electronic parameters. In this topical review, we show that one can learn rich physics in ITO material, including the semi-classical Boltzmann transport, the quantum-interference electron transport, as well as the many-body Coulomb electron-electron interaction effects in the presence of disorder and inhomogeneity (granularity). To fully reveal the numerous avenues and unique opportunities that the ITO material has provided for fundamental condensed matter physics research, we demonstrate a variety of charge transport properties in different forms of ITO structures, including homogeneous polycrystalline thin and thick films, homogeneous single-crystalline nanowires and inhomogeneous ultrathin films. In this manner, we not only address new physics phenomena that can arise in ITO but also illustrate the versatility of the stable ITO material forms for potential technological applications. We emphasize that, microscopically, the novel and rich electronic conduction properties of ITO originate from the inherited robust free-electron-like energy bandstructure and low-carrier concentration (as compared with that in typical metals) characteristics of this class of material. Furthermore, a low carrier concentration leads to slow electron-phonon relaxation, which in turn causes the experimentally observed (i) a small residual resistance ratio, (ii) a linear electron diffusion thermoelectric power in

  4. Carbon doped PDMS: conductance stability over time and implications for additive manufacturing of stretchable electronics

    NASA Astrophysics Data System (ADS)

    Tavakoli, Mahmoud; Rocha, Rui; Osorio, Luis; Almeida, Miguel; de Almeida, Anibal; Ramachandran, Vivek; Tabatabai, Arya; Lu, Tong; Majidi, Carmel

    2017-03-01

    Carbon doped PDMS (cPDMS), has been used as a conductive polymer for stretchable electronics. Compared to liquid metals, cPDMS is low cost and is easier to process or to print with an additive manufacturing process. However, changes on the conductance of the carbon based conductive PDMS (cPDMS) were observed over time, in particular after integration of cPDMS and the insulating polymer. In this article we investigate the process parameters that lead to improved stability over conductance of the cPDMS over time. Slight modifications to the fabrication process parameters were conducted and changes on the conductance of the samples for each method were monitored. Results suggested that change of the conductance happens mostly after integration of a pre-polymer over a cured cPDMS, and not after integration of the cPDMS over a cured insulating polymer. We show that such changes can be eliminated by adjusting the integration priority between the conductive and insulating polymers, by selecting the right curing temperature, changing the concentration of the carbon particles and the thickness of the conductive traces, and when possible by changing the insulating polymer material. In this way, we obtained important conclusions regarding the effect of these parameters on the change of the conductance over time, that should be considered for additive manufacturing of soft electronics. Also, we show that these changes can be possibly due to the diffusion from PDMS into cPDMS.

  5. Effects of interface oxygen vacancies on electronic bands of FeSe /SrTiO3(001 )

    NASA Astrophysics Data System (ADS)

    Chen, M. X.; Ge, Zhuozhi; Li, Y. Y.; Agterberg, D. F.; Li, L.; Weinert, M.

    2016-12-01

    Modifications of the electronic bands of thin FeSe films due to oxygen vacancies in the supporting SrTiO3(001) substrate—and the interplay with spin-orbit coupling, magnetism, and epitaxy—are investigated by first-principles supercell calculations. Unfolded (k -projected) bands show that the oxygen vacancies both provide electron doping to the interface FeSe layer and also have notable effects on the details of the bands around the Fermi level, including renormalizing the width of the Fe -3 d band near the Fermi level by a factor of about 0.6 and causing a splitting of ˜40 meV at the M point for the checkerboard antiferromagnetic configuration. For an FeSe bilayer, the modifications to the bands are mainly limited to the interface FeSe layer. While spin-orbit-coupling induced band splittings of ˜30 meV at M for the ideal FeSe /SrTiO3 (001) interfaces are comparable to the splitting due to oxygen vacancies, the effects are not simply additive. Calculations and comparison to our scanning tunneling microscopy images of MBE-grown FeSe films on SrTiO3(001) suggest that a common defect may be Se bound to an oxygen vacancy at the interface.

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

    SciTech Connect

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

    2010-08-15

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

  7. Dynamical and anharmonic effects on the electron-phonon coupling and the zero-point renormalization of the band structure

    NASA Astrophysics Data System (ADS)

    Antonius, Gabriel; Poncé, Samuel; Lantagne-Hurtubise, Étienne; Auclair, Gabriel; Côté, Michel; Gonze, Xavier

    2015-03-01

    The electron-phonon coupling in solids renormalizes the band structure, reducing the band gap by several tenths of an eV in light-atoms semiconductors. Using the Allen-Heine-Cardona theory (AHC), we compute the zero-point renormalization (ZPR) as well as the quasiparticle lifetimes of the full band structure in diamond, BN, LiF and MgO. We show how dynamical effects can be included in the AHC theory, and still allow for the use of a Sternheimer equation to avoid the summation over unoccupied bands. The convergence properties of the electron-phonon coupling self-energy with respect to the Brillouin zone sampling prove to be strongly affected by dynamical effects. We complement our study with a frozen-phonon approach, which reproduces the static AHC theory, but also allows to probe the phonon wavefunctions at finite displacements and include anharmonic effects in the self-energy. We show that these high-order components tend to reduce the strongest electron-phonon coupling elements, which affects significantly the band gap ZPR.

  8. PIC Simulations of the Effect of Velocity Space Instabilities on Electron Viscosity and Thermal Conduction

    NASA Astrophysics Data System (ADS)

    Riquelme, Mario A.; Quataert, Eliot; Verscharen, Daniel

    2016-06-01

    In low-collisionality plasmas, velocity-space instabilities are a key mechanism providing an effective collisionality for the plasma. We use particle-in-cell (PIC) simulations to study the interplay between electron- and ion-scale velocity-space instabilities and their effect on electron pressure anisotropy, viscous heating, and thermal conduction. The adiabatic invariance of the magnetic moment in low-collisionality plasmas leads to pressure anisotropy, {{Δ }}{p}j\\equiv {p}\\perp ,j-{p}\\parallel ,j\\gt 0, if the magnetic field {\\boldsymbol{B}} is amplified ({p}\\perp ,j and {p}\\parallel ,j denote the pressure of species j (electron, ion) perpendicular and parallel to {\\boldsymbol{B}}). If the resulting anisotropy is large enough, it can in turn trigger small-scale plasma instabilities. Our PIC simulations explore the nonlinear regime of the mirror, IC, and electron whistler instabilities, through continuous amplification of the magnetic field | {\\boldsymbol{B}}| by an imposed shear in the plasma. In the regime 1≲ {β }j≲ 20 ({β }j\\equiv 8π {p}j/| {\\boldsymbol{B}}{| }2), the saturated electron pressure anisotropy, {{Δ }}{p}{{e}}/{p}\\parallel ,{{e}}, is determined mainly by the (electron-lengthscale) whistler marginal stability condition, with a modest factor of ˜1.5-2 decrease due to the trapping of electrons into ion-lengthscale mirrors. We explicitly calculate the mean free path of the electrons and ions along the mean magnetic field and provide a simple physical prescription for the mean free path and thermal conductivity in low-collisionality β j ≳ 1 plasmas. Our results imply that velocity-space instabilities likely decrease the thermal conductivity of plasma in the outer parts of massive, hot, galaxy clusters. We also discuss the implications of our results for electron heating and thermal conduction in low-collisionality accretion flows onto black holes, including Sgr A* in the Galactic Center.

  9. Electrical conductivity channels in the atmosphere produced by relativistic-electron microbursts from the magnetosphere

    NASA Astrophysics Data System (ADS)

    Borovsky, Joseph E.

    2017-03-01

    The properties of a cylindrical-shaped magnetic-field-aligned channel of electrical conductivity produced by the precipitation of relativistic-electrons into the atmosphere during a spatially localized magnetospheric microburst are estimated. The conducting channel connects the middle atmosphere ( 50 km) to the ionosphere. A channel diameter of 8 km with an electric conductivity of 1.2×10-9 Ω-1m-1 near the bottom and 1.8×10-7 Ω-1m-1 higher up is found. In the fair-weather electric field, the higher-conductivity portions of the channel can carry substantial electrical currents.

  10. Extreme sensitivity of the electric-field-induced band gap to the electronic topological transition in sliding bilayer graphene

    NASA Astrophysics Data System (ADS)

    Lee, Kyu Won; Lee, Cheol Eui

    2015-12-01

    We have investigated the effect of electronic topological transition on the electric field-induced band gap in sliding bilayer graphene by using the density functional theory calculations. The electric field-induced band gap was found to be extremely sensitive to the electronic topological transition. At the electronic topological transition induced by layer sliding, four Dirac cones in the Bernal-stacked bilayer graphene reduces to two Dirac cones with equal or unequal Dirac energies depending on the sliding direction. While the critical electric field required for the band gap opening increases with increasing lateral shift for the two Dirac cones with unequal Dirac energies, the critical field is essentially zero with or without a lateral shift for the two Dirac cones with equal Dirac energies. The critical field is determined by the Dirac energy difference and the electronic screening effect. The electronic screening effect was also found to be enhanced with increasing lateral shift, apparently indicating that the massless helical and massive chiral fermions are responsible for the perfect and imperfect electronic screening, respectively.

  11. Photoconductivities from band states and a dissipative electron dynamics: Si(111) without and with adsorbed Ag clusters

    SciTech Connect

    Vazhappilly, Tijo; Hembree, Robert H.; Micha, David A.

    2016-01-14

    A new general computational procedure is presented to obtain photoconductivities starting from atomic structures, combining ab initio electronic energy band states with populations from density matrix theory, and implemented for a specific set of materials based on Si crystalline slabs and their nanostructured surfaces without and with adsorbed Ag clusters. The procedure accounts for charge mobility in semiconductors in photoexcited states, and specifically electron and hole photomobilities at Si(111) surfaces with and without adsorbed Ag clusters using ab initio energy bands and orbitals generated from a generalized gradient functional, however with excited energy levels modified to provide correct bandgaps. Photoexcited state populations for each band and carrier type were generated using steady state solution of a reduced density matrix which includes dissipative medium effects. The present calculations provide photoexcited electronic populations and photoinduced mobilities resulting from applied electric fields and obtained from the change of driven electron energies with their electronic momentum. Extensive results for Si slabs with 8 layers, without and with adsorbed Ag clusters, show that the metal adsorbates lead to substantial increases in the photomobility and photoconductivity of electrons and holes.

  12. Temperature-independent hole mobility of a smectic liquid-crystalline semiconductor based on band-like conduction.

    PubMed

    Funahashi, Masahiro; Ishii, Tomohiko; Sonoda, Akinari

    2013-08-26

    A liquid-crystalline (LC) phenylterthiophene derivative, which exhibited an ordered smectic phase at room temperature, was purified by vacuum sublimation under a flow of nitrogen. During the sublimation process, thin plates with sizes of 1 mm grew on the surface of the vacuum tube. The crystals exhibited the same X-ray diffraction patterns as the ordered smectic phase of the LC state that was formed through a conventional recrystallization process by using organic solvents. Because of the removal of chemical impurities, the hole mobility in the ordered smectic phase of the vacuum-grown thin plates increased to 1.2×10(-1) cm(2) V(-1) s(-1) at room temperature, whereas that of the LC precipitates was 7×10(-2) cm(2) V(-1) s(-1). The hole mobility in the ordered smectic phase of the vacuum-sublimated sample was temperature-independent between 400 and 220 K. The electric-field dependence of the hole mobility was also very small within this temperature range. The temperature dependence of hole mobility was well-described by the Hoesterey-Letson model. The hole-transport characteristics indicate that band-like conduction affected by the localized states, rather than a charge-carrier-hopping mechanism, is a valid mechanism for hole transport in an ordered smectic phase.

  13. Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn)As epitaxial layers

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    The effect of outdiffusion of Mn interstitials from (Ga,Mn)As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn)As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn)As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn)As, in agreement with the Zener model for ferromagnetic semiconductors.

  14. AlN/GaN high electron mobility transistors on sapphire substrates for Ka band applications

    NASA Astrophysics Data System (ADS)

    Xubo, Song; Yuanjie, Lü; Guodong, Gu; Yuangang, Wang; Xin, Tan; Xingye, Zhou; Shaobo, Dun; Peng, Xu; Jiayun, Yin; Bihua, Wei; Zhihong, Feng; Shujun, Cai

    2016-04-01

    We report the DC and RF characteristics of AlN/GaN high electron mobility transistors (HEMTs) with the gate length of 100 nm on sapphire substrates. The device exhibits a maximum drain current density of 1.29 A/mm and a peak transconductance of 440 mS/mm. A current gain cutoff frequency and a maximum oscillation frequency of 119 GHz and 155 GHz have been obtained, respectively. Furthermore, the large signal load pull characteristics of the AlN/GaN HEMTs were measured at 29 GHz. An output power density of 429 mW/mm has been demonstrated at a drain bias of 10 V. To the authors' best knowledge, this is the earliest demonstration of power density at the Ka band for AlN/GaN HEMTs in the domestic, and also a high frequency of load-pull measurements for AlN/GaN HEMTs. Project supported by the National Natural Science Foundation of China (No. 61306113).

  15. VIIRS day-night band (DNB) electronic hysteresis: characterization and correction

    NASA Astrophysics Data System (ADS)

    Mills, Stephen

    2016-09-01

    The VIIRS Day-Night Band (DNB) offers measurements over a dynamic range from full daylight to the dimmest nighttime. This makes radiometric calibration difficult because effects that are otherwise negligible become significant for the DNB. One of these effects is electronic hysteresis and this paper evaluates this effect and its impact on calibration. It also considers possible correction algorithms. The cause of this hysteresis is uncertain, but since the DNB uses a charge-coupled device (CCD) detector array, it is likely the result of residual charge or charge depletion. The effects of hysteresis are evident in DNB imagery. Steaks are visible in the cross-track direction around very bright objects such as gas flares. Dark streaks are also visible after lightning flashes. Each VIIRS scan is a sequence of 4 sectors: space view (SV); Earth-view (EV); blackbody (BB) view; and solar diffuser (SD) view. There are differences among these sectors in offset that can only be explained as being the result of hysteresis from one sector to the next. The most dramatic hysteresis effect is when the sun illuminates the SD and hysteresis is then observed in the SV and EV. Previously this was hypothesized to be due to stray light leaking from the SD chamber, but more careful evaluation shows that this can only be the result of hysteresis. There is a stray light correction algorithm that treats this as stray light, but there are problems with this that could be remedied by instead using the characterization presented here.

  16. ADVANCED X-BAND TEST ACCELERATOR FOR HIGH BRIGHTNESS ELECTRON AND GAMMA RAY BEAMS

    SciTech Connect

    Marsh, R A; Anderson, S G; Barty, C P; Chu, T S; Ebbers, C A; Gibson, D J; Hartemann, F V; Adolphsen, C; Jongewaard, E N; Raubenheimer, T; Tantawi, S G; Vlieks, A E; Wang, J W

    2010-05-12

    In support of Compton scattering gamma-ray source efforts at LLNL, a multi-bunch test stand is being developed to investigate accelerator optimization for future upgrades. This test stand will enable work to explore the science and technology paths required to boost the current 10 Hz monoenergetic gamma-ray (MEGa-Ray) technology to an effective repetition rate exceeding 1 kHz, potentially increasing the average gamma-ray brightness by two orders of magnitude. Multiple bunches must be of exceedingly high quality to produce narrow-bandwidth gamma-rays. Modeling efforts will be presented, along with plans for a multi-bunch test stand at LLNL. The test stand will consist of a 5.5 cell X-band rf photoinjector, single accelerator section, and beam diagnostics. The photoinjector will be a high gradient standing wave structure, featuring a dual feed racetrack coupler. The accelerator will increase the electron energy so that the emittance can be measured using quadrupole scanning techniques. Multi-bunch diagnostics will be developed so that the beam quality can be measured and compared with theory. Design will be presented with modeling simulations, and layout plans.

  17. Advanced X-Band Test Accelerator for High Brightness Electron and Gamma Ray Beams

    SciTech Connect

    Marsh, Roark; Anderson, Scott; Barty, Christopher; Chu, Tak Sum; Ebbers, Chris; Gibson, David; Hartemann, Fred; Adolphsen, Chris; Jongewaard, Erik; Raubenheimer, Tor; Tantawi, Sami; Vlieks, Arnold; Wang, Juwen; /SLAC

    2012-07-03

    In support of Compton scattering gamma-ray source efforts at LLNL, a multi-bunch test stand is being developed to investigate accelerator optimization for future upgrades. This test stand will enable work to explore the science and technology paths required to boost the current 10 Hz monoenergetic gamma-ray (MEGa-Ray) technology to an effective repetition rate exceeding 1 kHz, potentially increasing the average gamma-ray brightness by two orders of magnitude. Multiple bunches must be of exceedingly high quality to produce narrow-bandwidth gamma-rays. Modeling efforts will be presented, along with plans for a multi-bunch test stand at LLNL. The test stand will consist of a 5.5 cell X-band rf photoinjector, single accelerator section, and beam diagnostics. The photoinjector will be a high gradient standing wave structure, featuring a dual feed racetrack coupler. The accelerator will increase the electron energy so that the emittance can be measured using quadrupole scanning techniques. Multi-bunch diagnostics will be developed so that the beam quality can be measured and compared with theory. Design will be presented with modeling simulations, and layout plans.

  18. Rheology of conductive ink flow for printed electronics on a microfluidic chip

    NASA Astrophysics Data System (ADS)

    Jang, Young-Sik; Song, Simon

    2012-07-01

    Printed electronics have recently attracted extensive attention due to their superior productivity to conventional semiconductor fabrication methods. To develop printing devices optimized for printed electronics, numerical studies on ink flows are often necessary, and, therefore, it is critical to provide accurate ink properties for reliable numerical results. However, it is difficult to find such data in literature since inks for printed electronics contains conductive metallic nanoparticles and they are not only non-Newtonian but expensive. Thus, we propose utilizing a microfluidic chip to investigate rheological properties of conductive inks. By using micro particle image velocimeter along with an immersion oil technique, we examine the flow characteristics of two commercial conductive inks containing Ag nanoparticles on microfluidic chips. We found that the ink flows show a stronger shear-thinning behavior as the Ag content increases. Finally, suitable rheological models applicable to numerical simulations for those inks are suggested after comparing the experimental data to frequently used rheological models.

  19. Demonstration of asymmetric electron conduction in pseudosymmetrical photosynthetic reaction centre proteins in an electrical circuit.

    PubMed

    Kamran, Muhammad; Friebe, Vincent M; Delgado, Juan D; Aartsma, Thijs J; Frese, Raoul N; Jones, Michael R

    2015-03-09

    Photosynthetic reaction centres show promise for biomolecular electronics as nanoscale solar-powered batteries and molecular diodes that are amenable to atomic-level re-engineering. In this work the mechanism of electron conduction across the highly tractable Rhodobacter sphaeroides reaction centre is characterized by conductive atomic force microscopy. We find, using engineered proteins of known structure, that only one of the two cofactor wires connecting the positive and negative termini of this reaction centre is capable of conducting unidirectional current under a suitably oriented bias, irrespective of the magnitude of the bias or the applied force at the tunnelling junction. This behaviour, strong functional asymmetry in a largely symmetrical protein-cofactor matrix, recapitulates the strong functional asymmetry characteristic of natural photochemical charge separation, but it is surprising given that the stimulus for electron flow is simply an externally applied bias. Reasons for the electrical resistance displayed by the so-called B-wire of cofactors are explored.

  20. Band gap and defect states of MgO thin films investigated using reflection electron energy loss spectroscopy

    SciTech Connect

    Heo, Sung; Cho, Eunseog; Lee, Hyung-Ik; Park, Gyeong Su; Kang, Hee Jae; Nagatomi, T.; Choi, Pyungho; Choi, Byoung-Deog

    2015-07-15

    The band gap and defect states of MgO thin films were investigated by using reflection electron energy loss spectroscopy (REELS) and high-energy resolution REELS (HR-REELS). HR-REELS with a primary electron energy of 0.3 keV revealed that the surface F center (FS) energy was located at approximately 4.2 eV above the valence band maximum (VBM) and the surface band gap width (E{sub g}{sup S}) was approximately 6.3 eV. The bulk F center (F{sub B}) energy was located approximately 4.9 eV above the VBM and the bulk band gap width was about 7.8 eV, when measured by REELS with 3 keV primary electrons. From a first-principles calculation, we confirmed that the 4.2 eV and 4.9 eV peaks were F{sub S} and F{sub B}, induced by oxygen vacancies. We also experimentally demonstrated that the HR-REELS peak height increases with increasing number of oxygen vacancies. Finally, we calculated the secondary electron emission yields (γ) for various noble gases. He and Ne were not influenced by the defect states owing to their higher ionization energies, but Ar, Kr, and Xe exhibited a stronger dependence on the defect states owing to their small ionization energies.

  1. A Case Study Exploring the Use of GarageBand[TM] and an Electronic Bulletin Board in Preservice Music Education

    ERIC Educational Resources Information Center

    Vratulis, Vetta; Morton, Charlene

    2011-01-01

    This qualitative research study is an exploration of the merit and shortcomings of using a combination of the music software GarageBand[TM] and an electronic bulletin board to facilitate musical and peer learning in a 3-month elementary music methods curriculum and instruction course. A pedagogical objective of this assignment was to increase the…

  2. Electron thermalization and attachment in pulse-irradiated oxygen studied by time-resolved microwave conductivity

    NASA Astrophysics Data System (ADS)

    Warman, John M.; Cooper, Ronald

    The microwave conductivity of oxygen gas following nanosecond pulsed irradiation has been studied for pressures from 5 to 50 torr. The conductivity is found to decrease by a factor of approx. 20 in the early stages ( tN < 2 x 10 11 s cm -3) following the pulse. This is attributed to a decrease in the electron collision frequency as the initial excess energy of the electrons becomes degraded. A further decrease found at longer times is due to the three-body attachment of electrons to O 2 with a rate constant of 2.4 x 10 -30 cm 6s -1. Above a pressure of approx. 30 torr significant attachment begins to occur while electrons are still superthermal. The time at which the microwave signal is within 10% of the value corresponding to thermal energies is given by τ thP ≈ 15 μs.torr.

  3. Self-assembly of an electronically conductive network through microporous scaffolds.

    PubMed

    Sebastian, H Bri; Bryant, Steven L

    2017-06-15

    Electron transfer spanning significant distances through a microporous structure was established via the self-assembly of an electronically conductive iridium oxide nanowire matrix enveloping the pore walls. Microporous formations were simulated using two scaffold materials of varying physical and chemical properties; paraffin wax beads, and agar gel. Following infiltration into the micropores, iridium nanoparticles self-assembled at the pore wall/ethanol interface. Subsequently, cyclic voltammetry was employed to electrochemically crosslink the metal, erecting an interconnected, and electronically conductive metal oxide nanowire matrix. Electrochemical and spectral characterization techniques confirmed the formation of oxide nanowire matrices encompassing lengths of at least 1.6mm, 400× distances previously achieved using iridium nanoparticles. Nanowire matrices were engaged as biofuel cell anodes, where electrons were donated to the nanowires by a glucose oxidizing enzyme.

  4. Electronically conductive perovskite-based oxide nanoparticles and films for optical sensing applications

    DOEpatents

    Ohodnicki, Jr., Paul R; Schultz, Andrew M

    2015-04-28

    The disclosure relates to a method of detecting a change in a chemical composition by contacting a electronically conducting perovskite-based metal oxide material with a monitored stream, illuminating the electronically conducting perovskite-based metal oxide with incident light, collecting exiting light, monitoring an optical signal based on a comparison of the incident light and the exiting light, and detecting a shift in the optical signal. The electronically conducting perovskite-based metal oxide has a perovskite-based crystal structure and an electronic conductivity of at least 10.sup.-1 S/cm, where parameters are specified at the gas stream temperature. The electronically conducting perovskite-based metal oxide has an empirical formula A.sub.xB.sub.yO.sub.3-.delta., where A is at least a first element at the A-site, B is at least a second element at the B-site, and where 0.8electronically conducting perovskite-based oxides include but are not limited to La.sub.1-xSr.sub.xCoO.sub.3, La.sub.1-xSr.sub.xMnO.sub.3, LaCrO.sub.3, LaNiO.sub.3, La.sub.1-xSr.sub.xMn.sub.1-yCr.sub.yO.sub.3, SrFeO.sub.3, SrVO.sub.3, La-doped SrTiO.sub.3, Nb-doped SrTiO.sub.3, and SrTiO.sub.3-.delta..

  5. Intrinsic evolutions of optical functions, band gap, and higher-energy electronic transitions in VO2 film near the metal-insulator transition region

    NASA Astrophysics Data System (ADS)

    Li, W. W.; Yu, Q.; Liang, J. R.; Jiang, K.; Hu, Z. G.; Liu, J.; Chen, H. D.; Chu, J. H.

    2011-12-01

    Transmittance spectra of (011) vanadium dioxide (VO2) film have been studied in the temperature range of 45-80 °C. Owing to increasing carrier concentration, the near-infrared extinction coefficient and optical conductivity around metal-insulator transition (MIT) rapidly increase with the temperature. Moreover, three electronic transitions can be uniquely assigned and show the hysteresis behavior near the MIT region. It was found that the optical band gap decreases from 0.457 to 0.042 eV before the MIT, then reduces to zero for the metal state. This confirms the fact that the a1g and egπ bands are moved close and finally overlap with the temperature.

  6. Simultaneous electronic and ionic conduction in a block copolymer: application in lithium battery electrodes.

    PubMed

    Javier, Anna E; Patel, Shrayesh N; Hallinan, Daniel T; Srinivasan, Venkat; Balsara, Nitash P

    2011-10-10

    Charging ahead: separate values for the simultaneous electronic and ionic conductivity of a conjugated polymer containing poly(3-hexylthiophene) and poly(ethylene oxide) (P3HT-PEO) were determined by using ac impedance and dc techniques. P3HT-PEO was used as binder, and transporter of electronic charge and Li(+) ions in a LiFePO(4) cathode, which was incorporated into solid-state lithium batteries.

  7. Three dimensional magnetism and coupling to conduction electrons in PdCrO2

    SciTech Connect

    Ong, Khuong P; Singh, David J

    2012-01-01

    We report density functional calculations addressing the electronic structure and magnetic properties of delafossite PdCrO{sub 2}. We find substantial magnetic interactions in the c-axis direction as well as beyond first nearest neighbors in-plane, so that PdCrO{sub 2} is a three-dimensional (3D) frustrated antiferromagnet. We also find substantial coupling between the Cr moments and the Pd derived conduction electrons.

  8. Band- and momentum-dependent electron dynamics in superconducting Ba(Fe1-xCox)2As2 as seen via electronic Raman scattering

    SciTech Connect

    Muschler, B.

    2010-02-24

    We present details of carrier properties in high quality Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} single crystals obtained from electronic Raman scattering. The experiments indicate a strong band and momentum anisotropy of the electron dynamics above and below the superconducting transition highlighting the importance of complex band-dependent interactions. The presence of low energy spectral weight deep in the superconducting state suggests a gap with accidental nodes which may be lifted by doping and/or impurity scattering. When combined with other measurements, our observation of band and momentum dependent carrier dynamics indicate that the iron arsenides may have several competing superconducting ground states.

  9. Hydrogen production by high-temperature water splitting using electron-conducting membranes

    DOEpatents

    Lee, Tae H.; Wang, Shuangyan; Dorris, Stephen E.; Balachandran, Uthamalingam

    2004-04-27

    A device and method for separating water into hydrogen and oxygen is disclosed. A first substantially gas impervious solid electron-conducting membrane for selectively passing hydrogen is provided and spaced from a second substantially gas impervious solid electron-conducting membrane for selectively passing oxygen. When steam is passed between the two membranes at disassociation temperatures the hydrogen from the disassociation of steam selectively and continuously passes through the first membrane and oxygen selectively and continuously passes through the second membrane, thereby continuously driving the disassociation of steam producing hydrogen and oxygen.

  10. A PIC Simulation Study of Electron Viscosity and Thermal Conduction in Collisionless Plasmas

    NASA Astrophysics Data System (ADS)

    Riquelme, Mario; Quataert, Eliot; Verscharen, Daniel

    2016-10-01

    We use particle-in-cell (PIC) simulations to study the interplay between electron- and ion-scale velocity-space instabilities and their effect on electron pressure anisotropy, viscous heating, and thermal conduction. The adiabatic invariance of the magnetic moment in low-collisionality plasmas gives rise to pressure anisotropy, with p⊥ , j -p∥ , j > 0 (< 0) if the magnetic field magnitude | B-> | grows (decreases), where p⊥ , j and p∥ , j denote the pressure of species j [electron or ion] perpendicular and parallel to B-> . If the resulting anisotropy is large enough, it can trigger small-scale plasma instabilities. By imposing a shear in the plasma we either amplify or decrease the magnetic field | B-> | . When | B-> | is amplified, we explored the nonlinear regime of the mirror, ion-cyclotron, and electron whistler instabilities. When | B-> | is decreased, we studied the nonlinear regime of the ion- and electron-firehose instabilities. We discuss the implications of our results for electron heating and thermal conduction in low-collisionality accretion flows onto black holes, like Sgr A*. We also discuss the possible implications for the thermal conductivity of plasma in the outer parts of massive, hot, galaxy clusters.

  11. Conductivity, electric field and electron drift velocity within the equatorial electrojet

    NASA Astrophysics Data System (ADS)

    Rastogi, R. G.; Chandra, H.

    2006-08-01

    Rocket-borne in-situ measurements of electron density and current density made from Thumba, India, on four occasions between 1966 and 1973 and on one flight from Peru in 1965 are studied along with the corresponding ground magnetometer data. The Cowling conductivity is computed using the yearly mean magnetic field values of 1965 and the atmospheric density values from the MSIS 1986 model. The rocket-borne measurements from Thumba cover different geophysical conditions of strong, moderate and partial counter-electrojet events. The vertical profiles of the measured current density and electron density are presented along with the computed Cowling conductivity, electron drift velocity and electric field. The peak current density occurred at 106-107 km over Thumba and at 109 km over Peru compared to 104 km over Brazil. Cowling conductivity peaks occurred at 102 km over Huancayo and 101 km over Thumba, while electron drift velocity and electric field peaks occurred at approximately 105-107 km over Thumba, 108 and 110 km over Huancayo and 104 km over Brazil, respectively. While the electron density near the level of peak current density shows some variability, electron drift velocity and electric field show large variability. We conclude that the local electric field plays an important role in the spatial and temporal variability of the strength of the electrojet.

  12. Printable elastic conductors with a high conductivity for electronic textile applications

    PubMed Central

    Matsuhisa, Naoji; Kaltenbrunner, Martin; Yokota, Tomoyuki; Jinno, Hiroaki; Kuribara, Kazunori; Sekitani, Tsuyoshi; Someya, Takao

    2015-01-01

    The development of advanced flexible large-area electronics such as flexible displays and sensors will thrive on engineered functional ink formulations for printed electronics where the spontaneous arrangement of molecules aids the printing processes. Here we report a printable elastic conductor with a high initial conductivity of 738 S cm−1 and a record high conductivity of 182 S cm−1 when stretched to 215% strain. The elastic conductor ink is comprised of Ag flakes, a fluorine rubber and a fluorine surfactant. The fluorine surfactant constitutes a key component which directs the formation of surface-localized conductive networks in the printed elastic conductor, leading to a high conductivity and stretchability. We demonstrate the feasibility of our inks by fabricating a stretchable organic transistor active matrix on a rubbery stretchability-gradient substrate with unimpaired functionality when stretched to 110%, and a wearable electromyogram sensor printed onto a textile garment. PMID:26109453

  13. Analysis of the electronic crosstalk effect in Terra MODIS long-wave infrared photovoltaic bands using lunar images

    NASA Astrophysics Data System (ADS)

    Wilson, Truman; Wu, Aisheng; Geng, Xu; Wang, Zhipeng; Xiong, Xiaoxiong

    2016-10-01

    The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the key sensors among the suite of remote sensing instruments on board the Earth Observing System Terra and Aqua spacecrafts. For each MODIS spectral band, the sensor degradation has been measured using a set of on-board calibrators. MODIS also uses lunar observations from nearly monthly spacecraft maneuvers, which bring the Moon into view through the space- view port, helping to characterize the scan mirror degradation at a different angles of incidence. Throughout the Terra mission, contamination of the long-wave infrared photovoltaic band (LWIR PV, bands 27-30) signals has been observed in the form of electronic crosstalk, where signal from each of the detectors among the LWIR PV bands can leak to the other detectors, producing a false signal contribution. This contamination has had a noticeable effect on the MODIS science products since 2010 for band 27, and since 2012 for bands 28 and 29. Images of the Moon have been used effectively for determining the contaminating bands, and have also been used to derive correction coefficients for the crosstalk contamination. In this paper, we introduce an updated technique for characterizing the crosstalk contamination among the LWIR PV bands using data from lunar calibration events. This approach takes into account both the "in-band" and "out-of-band" contribution to the signal contamination for each detector in bands 27-30, which is not considered in previous works. The crosstalk coefficients can be derived for each lunar calibration event, providing the time dependence of the crosstalk contamination. Application of these coefficients to Earth-view image data results in a significant reduction in image contamination and a correction of the scene radiance for bands 27-30. Also, this correction shows a significant improvement to certain threshold tests in the MODIS Level-2 Cloud Mask. In this paper, we will detail the methodology used to identify and

  14. Soft conductive elastomer materials for stretchable electronics and voltage controlled artificial muscles.

    PubMed

    Stoyanov, Hristiyan; Kollosche, Matthias; Risse, Sebastian; Waché, Rémi; Kofod, Guggi

    2013-01-25

    Block copolymer elastomer conductors (BEC) are mixtures of block copolymers grafted with conducting polymers, which are found to support very large strains, while retaining a high level of conductivity. These novel materials may find use in stretchable electronics. The use of BEC is demonstrated in a capacitive strain sensor and in an artificial muscle of the dielectric elastomer actuator type, supporting more than 100% actuation strain and capacity strain sensitivity up to 300%.

  15. Extreme Band Engineering of III-Nitride Nanowire Heterostructures for Electronic and Photonic Application

    NASA Astrophysics Data System (ADS)

    Sarwar, ATM Golam

    Bottom-up nanowires are attractive for realizing semiconductor devices with extreme heterostructures because strain relaxation through the nanowire sidewalls allows the combination of highly lattice mismatched materials without creating dislocations. The resulting nanowires are used to fabricate light-emitting diodes (LEDs), lasers, solar cells, and sensors. The aim of this work is to investigate extreme heterostructures, which are impossible or very hard to realize in conventional planar films, exploiting the strain accommodation property of nanowires and engineer their band structure for novel electronic and photonic applications. To this end, in this thesis, III-Nitride semiconductor nanowires are investigated. In the first part of this work, a complete growth phase diagram of InN nanowires on silicon using plasma assisted molecular beam epitaxy is developed, and structural and optical characteristics are mapped as a function of growth parameters. Next, a novel up-side down pendeoepitaxial growth of InN forming mushroom-like microstructures is demonstrated and detail structural and optical characterizations are performed. Based on this, a method to grow strain-free large area single crystalline InN or thin film is proposed and the growth of InN on patterned GaN is investigated. The optimized growth conditions developed for InN are further used to grow InGaN nanowires graded over the whole composition range. Numerical energy band simulation is performed to better understand the effect of polarization charge on photo-carrier transport in these extremely graded nanowires. A novel photodetector device with negative differential photocurrent is demonstrated using the graded InGaN nanowires. In the second part of this thesis, polarization-induced nanowire light emitting diodes (PINLEDs) are investigated. The electrical and optical properties of the nanowire heterostructure are engineered and optimized for ultraviolet and deep ultraviolet applications. The electrical

  16. Single electron bipolar conductance switch driven by the molecular Aharonov-Bohm effect.

    PubMed

    Lee, Joonhee; Tallarida, Nicholas; Rios, Laura; Perdue, Shawn M; Apkarian, Vartkess Ara

    2014-06-24

    We demonstrate a conductance switch controlled by the spin-vibronic density of an odd electron on a single molecule. The junction current is modulated by the spin-flip bistability of the electron. Functional images are provided as wiring diagrams for control of the switch's frequency, amplitude, polarity, and duty-cycle. The principle of operation relies on the quantum mechanical phase associated with the adiabatic circulation of a spin-aligned electron around a conical intersection. The functional images quantify the governing vibronic Hamiltonian.

  17. Measurement of characteristics of an infrared free-electron laser with the L-band at Osaka University

    SciTech Connect

    Okuda, S.; Ishida, S.; Honda, Y.

    1995-12-31

    Free-electron laser (FEL) experiments have been conducted with the 38-MeV L-band electron linac at the Institute of Scientific and Industrial Research, Osaka University. It is a 1.3 GHz RF linac with a thermoionic gun, and equipped with two 12th and one 6th sub-harmonic prebunchers for producing the high-intensity single-bunch beam with a charge up to 67 nC/bunch. For oscillation experiments of FEL, the gun is replaced with that with a smaller cathode area in order to reduce the emittance of the beam. The normalized emittance has been measured to be 200 {pi} mm-mrad. The linac is operated in the long-pulse mode and one of the 12th sub-harmonic bunchers and the 6th sub-harmonic buncher are operated, so that the time duration of the macropulse is 4 {mu}s and the spacing between micropulses is 9.2 ns. The length of the micropulse is 30-40 ps and the charge in each micropulse is 2 nC. The electron beam from the linac is transported to a wiggler which has the period length of 6 cm and the number of periods of 32. The first half of the macropulse is lost in the transport line because the energy of electrons in that part gradually changes and there is a momentum slit in the transport line. An optical resonator is 5.53 m long and the round-trip time of light in it is 37 ns, which is precisely four times as long as the spacing of micropulses. Since the time duration of the macropulse passing through the wiggler is 1.8 {mu}s, the number of amplifications of light in the cavity is 49. The first lasing was achieved in 1994 at wavelengths between 32 and 40 {mu}m and preliminary results were reported at the l6th FEL Conference last year. The laser light was detected with a Ge:Be detector which has the time resolution of 3 {mu}s. Since the time duration of the macropulse of the laser fight is estimated to be less than 2 {mu}s, we could measure only the total energy in a macropulse of the output light.

  18. A promising approach to conductive patterns with high efficiency for flexible electronics

    NASA Astrophysics Data System (ADS)

    Tai, Yan-Long; Yang, Zhen-Guo; Li, Zhi-Dong

    2011-06-01

    A promising approach for conductive patterns with high efficiency for flexible electronics was developed by direct-writing, silver(I) solution (silver nitrate, acetate silver, etc.) with no solid particles as a conductive ink, conductive pen as a writing implement, and polyimide (PI) film as a substrate. The physical properties of the conductive ink were investigated by a dynamic contact angle system, ubbelohde viscometer and surface tension instrument. Conductive properties of silver ink film were investigated by 4-point probe, scanning electron microscope (SEM) and surface profilometer. It is demonstrated how the design of solvent composition in conductive ink affects surface morphology, and conductivity of silver ink films. It can be obtained that conductive patterns drawn on PI substrate not only have good mechanical/electrical fatigue properties, but also have low resistivity. Especially, when the sintering condition is 200 °C for 60 min, the resistivity can be down to 6.6 μΩ cm, 4.25 times the silver bulk resistivity.

  19. Intrinsically Stretchable and Conductive Textile by a Scalable Process for Elastic Wearable Electronics.

    PubMed

    Wang, Chunya; Zhang, Mingchao; Xia, Kailun; Gong, Xueqin; Wang, Huimin; Yin, Zhe; Guan, Baolu; Zhang, Yingying

    2017-04-06

    The prosperous development of stretchable electronics poses a great demand on stretchable conductive materials that could maintain their electrical conductivity under tensile strain. Previously reported strategies to obtain stretchable conductors usually involve complex structure-fabricating processes or utilization of high-cost nanomaterials. It remains a great challenge to produce stretchable and conductive materials via a scalable and cost-effective process. Herein, a large-scalable pyrolysis strategy is developed for the fabrication of intrinsically stretchable and conductive textile in utilizing low-cost and mass-produced weft-knitted textiles as raw materials. Due to the intrinsic stretchability of the weft-knitted structure and the excellent mechanical and electrical properties of the as-obtained carbonized fibers, the obtained flexible and durable textile could sustain tensile strains up to 125% while keeping a stable electrical conductivity (as shown by a Modal-based textile), thus ensuring its applications in elastic electronics. For demonstration purposes, stretchable supercapacitors and wearable thermal-therapy devices that showed stable performance with the loading of tensile strains have been fabricated. Considering the simplicity and large scalability of the process, the low-cost and mass production of the raw materials, and the superior performances of the as-obtained elastic and conductive textile, this strategy would contribute to the development and industrial production of wearable electronics.

  20. Theoretical study of electronic absorption spectroscopy of propadienylidene molecule vis-â-vis the observed diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Reddy, Samala Nagaprasad; Mahapatra, S.

    2012-07-01

    Observation of broad and diffuse interstellar bands (DIBs) at 4881 Å and 5440 Å assigned to the optical absorption spectrum of Y-shaped propadienylidene (H2Cdbnd Cdbnd C:) molecule is theoretically examined in this paper. This molecule apparently absorbs in the same wavelength region as the observed DIBs and was suggested to be a potential carrier of these DIBs. This assignment mostly relied on the experimental data from radioastronomy and laboratory measurements. Motivated by these available experimental data we attempt here a theoretical study and investigate the detailed electronic structure and nuclear dynamics underlying the electronic absorption bands of propadienylidene molecule. Our results show that this molecule indeed absorbs in the wavelength region of the recorded DIBs. Strong nonadiabatic coupling between its energetically low-lying electronic states plays major role, initiates ultrafast internal conversion and contributes to the spectral broadening. Theoretical findings are finally compared with the available experimental and theoretical data and discussed in connection with the recorded DIBs.

  1. Kinetics of band bending and electron affinity at GaAs(001) surface with nonequilibrium cesium overlayers

    SciTech Connect

    Zhuravlev, A. G.; Savchenko, M. L.; Paulish, A. G.; Alperovich, V. L.; Scheibler, H. E.; Jaroshevich, A. S.

    2013-12-04

    The dosage dependences of surface band bending and effective electron affinity under cesium deposition on the Ga-rich GaAs(001) surface, along with the relaxation of these electronic properties after switching off the Cs source are experimentally studied by means of modified photoreflectance spectroscopy and photoemission quantum yield spectroscopy. At small Cs coverages, below half of a monolayer, additional features in the dosage dependence and subsequent downward relaxation of the photoemission current are determined by the variations of band bending. At coverages above half of a monolayer the upward relaxation of the photocurrent is caused supposedly by the decrease of the electron affinity due to restructuring in the nonequilibrium cesium overlayer.

  2. Tunable Mixed Ionic/Electronic Conductivity and Permittivity of Graphene Oxide Paper for Electrochemical Energy Conversion.

    PubMed

    Bayer, Thomas; Bishop, Sean R; Perry, Nicola H; Sasaki, Kazunari; Lyth, Stephen M

    2016-05-11

    Graphene oxide (GO) is a two-dimensional graphitic carbon material functionalized with oxygen-containing surface functional groups. The material is of interest in energy conversion, sensing, chemical processing, gas barrier, and electronics applications. Multilayer GO paper has recently been applied as a new proton conducting membrane in low temperature fuel cells. However, a detailed understanding of the electrical/dielectric properties, including separation of the ionic vs electronic contributions under relevant operating conditions, has so far been lacking. Here, the electrical conductivity and dielectric permittivity of GO paper are investigated in situ from 30 to 120 °C, and from 0 to 100% relative humidity (RH) using impedance spectroscopy. These are related to the water content, measured by thermogravimetric analysis. With the aid of electron blocking measurements, GO is demonstrated to be a mixed electronic-protonic conductor, and the ion transference number is derived for the first time. For RH > 40%, conductivity is dominated by proton transport (with a maximum of 0.5 mS/cm at 90 °C and 100% RH). For RH < 40%, electronic conductivity dominates (with a maximum of 7.4 mS/cm at ∼80 °C and 0% RH). The relative permittivity of GO paper increases with decreasing humidity, from ∼10 at 100% RH to several 1000 at 10% RH. These results underline the potential of GO for application not only as a proton conducting electrolyte but also as a mixed conducting electrode material under appropriate conditions. Such materials are highly applicable in electrochemical energy conversion and storage devices such as fuel cells and electrolyzers.

  3. Strain-induced electronic band convergence: effect on the Seebeck coefficient of Mg2Si for thermoelectric applications.

    PubMed

    Balout, H; Boulet, P; Record, M-C

    2017-04-01

    The present theoretical study, performed using density-functional theory and Boltzmann transport theory formalisms, shows that under 2.246 % isotropic tensile strain, the two energy-lowest conduction bands of Mg2Si overlap. The two, threefold-degenerated orbitals become a unique, sixfold-degenerated orbital. It is demonstrated that such degeneracy implies an increase of the Seebeck coefficient, of the electrical conductivity, of the power factor, and in fine of the figure of merit.

  4. Superconductivity in an electron band just above the Fermi level: possible route to BCS-BEC superconductivity.

    PubMed

    Okazaki, K; Ito, Y; Ota, Y; Kotani, Y; Shimojima, T; Kiss, T; Watanabe, S; Chen, C-T; Niitaka, S; Hanaguri, T; Takagi, H; Chainani, A; Shin, S

    2014-02-28

    Conventional superconductivity follows Bardeen-Cooper-Schrieffer(BCS) theory of electrons-pairing in momentum-space, while superfluidity is the Bose-Einstein condensation(BEC) of atoms paired in real-space. These properties of solid metals and ultra-cold gases, respectively, are connected by the BCS-BEC crossover. Here we investigate the band dispersions in FeTe(0.6)Se(0.4)(Tc = 14.5 K ~ 1.2 meV) in an accessible range below and above the Fermi level(EF) using ultra-high resolution laser angle-resolved photoemission spectroscopy. We uncover an electron band lying just 0.7 meV (~8 K) above EF at the Γ-point, which shows a sharp superconducting coherence peak with gap formation below Tc. The estimated superconducting gap Δ and Fermi energy [Symbol: see text]F indicate composite superconductivity in an iron-based superconductor, consisting of strong-coupling BEC in the electron band and weak-coupling BCS-like superconductivity in the hole band. The study identifies the possible route to BCS-BEC superconductivity.

  5. In situ transmission electron microscopy analysis of conductive filament during solid electrolyte resistance switching

    SciTech Connect

    Fujii, Takashi; Arita, Masashi; Takahashi, Yasuo; Fujiwara, Ichiro

    2011-05-23

    An in situ transmission electron microscopy (TEM) analysis of a solid electrolyte, Cu-GeS, during resistance switching is reported. Real-time observations of the filament formation and disappearance process were performed in the TEM instrument and the conductive-filament-formation model was confirmed experimentally. Narrow conductive filaments were formed corresponding to resistance switching from high- to low-resistance states. When the resistance changed to high-resistance state, the filament disappeared. It was also confirmed by use of selected area diffractometry and energy-dispersive x-ray spectroscopy that the conductive filament was made of nanocrystals composed mainly of Cu.

  6. Electronic promotion effect of double proton transfer on conduction of DNA through improvement of transverse electronic communication of base pairs

    NASA Astrophysics Data System (ADS)

    Liu, Haiying; Li, Genqin; Zhang, Laibin; Li, Jilai; Wang, Meishan; Bu, Yuxiang

    2011-10-01

    The effect of double proton transfer (DPT) on charge migration of DNA was investigated by the nonequilibrium Green's function method combined with density functional theory. The results revealed that DPT not only lowers ionization potentials, but also improves the delocalization of the localized π-orbitals at each base moiety through adjusting energy levels and spatial distributions of their molecular orbitals. Furthermore, DPT leads to both the strengthening of the second-order interactions of the Watson-Crick H-bond zones, and the promotion of the charge transfer transitions between two pairing bases in the UV absorption spectra. Electronic transport calculations indicated that DPT can improve the charge migration along the DNA duplex for specific sequences through enhancing transverse base-to-base electronic communication. This work will provide a new insight into the understanding of DNA charge conduction which can be electronically promoted or regulated by DPT.

  7. Direct Electron Transfer of Enzymes in a Biologically Assembled Conductive Nanomesh Enzyme Platform.

    PubMed

    Lee, Seung-Woo; Lee, Ki-Young; Song, Yong-Won; Choi, Won Kook; Chang, Joonyeon; Yi, Hyunjung

    2016-02-24

    Nondestructive assembly of a nanostructured enzyme platform is developed in combination of the specific biomolecular attraction and electrostatic coupling for highly efficient direct electron transfer (DET) of enzymes with unprecedented applicability and versatility. The biologically assembled conductive nanomesh enzyme platform enables DET-based flexible integrated biosensors and DET of eight different enzyme with various catalytic activities.

  8. Clarification of the measurement of surface spin relaxation via conduction electron spin resonance

    NASA Astrophysics Data System (ADS)

    Eigler, D. M.; Schultz, S.

    1982-12-01

    We clarify the parameterization of the probability of transverse conduction electron spin relaxation. ɛ, at the surface of a metal. Using Walker's boundary condition on the transverse spin magnetization, we have calculated the ɛ and thickness dependence of the spin resonance linewidth. The results are discussed in simple physical terms. The recent work of Allam and Vigouroux is shown to contain errors.

  9. Structural control of mixed ionic and electronic transport in conducting polymers

    SciTech Connect

    Rivnay, Jonathan; Inal, Sahika; Collins, Brian A.; Sessolo, Michele; Stavrinidou, Eleni; Strakosas, Xenofon; Tassone, Christopher; Delongchamp, Dean M.; Malliaras, George G.

    2016-04-19

    Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate), PEDOT:PSS, has been utilized for over two decades as a stable, solution-processable hole conductor. While its hole transport properties have been the subject of intense investigation, recent work has turned to PEDOT:PSS as a mixed ionic/electronic conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in PEDOT:PSS films. We quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical mixed conductor devices. As a result, these findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on mixed conduction.

  10. Structural control of mixed ionic and electronic transport in conducting polymers

    NASA Astrophysics Data System (ADS)

    Rivnay, Jonathan; Inal, Sahika; Collins, Brian A.; Sessolo, Michele; Stavrinidou, Eleni; Strakosas, Xenofon; Tassone, Christopher; Delongchamp, Dean M.; Malliaras, George G.

    2016-04-01

    Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate), PEDOT:PSS, has been utilized for over two decades as a stable, solution-processable hole conductor. While its hole transport properties have been the subject of intense investigation, recent work has turned to PEDOT:PSS as a mixed ionic/electronic conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in PEDOT:PSS films. We quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical mixed conductor devices. These findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on mixed conduction.

  11. Structural control of mixed ionic and electronic transport in conducting polymers

    PubMed Central

    Rivnay, Jonathan; Inal, Sahika; Collins, Brian A.; Sessolo, Michele; Stavrinidou, Eleni; Strakosas, Xenofon; Tassone, Christopher; Delongchamp, Dean M.; Malliaras, George G.

    2016-01-01

    Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate), PEDOT:PSS, has been utilized for over two decades as a stable, solution-processable hole conductor. While its hole transport properties have been the subject of intense investigation, recent work has turned to PEDOT:PSS as a mixed ionic/electronic conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in PEDOT:PSS films. We quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical mixed conductor devices. These findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on mixed conduction. PMID:27090156

  12. Structural control of mixed ionic and electronic transport in conducting polymers

    DOE PAGES

    Rivnay, Jonathan; Inal, Sahika; Collins, Brian A.; ...

    2016-04-19

    Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate), PEDOT:PSS, has been utilized for over two decades as a stable, solution-processable hole conductor. While its hole transport properties have been the subject of intense investigation, recent work has turned to PEDOT:PSS as a mixed ionic/electronic conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in PEDOT:PSS films. Wemore » quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical mixed conductor devices. As a result, these findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on mixed conduction.« less

  13. Discharge parameters and dominant electron conductivity mechanism in a low-pressure planar magnetron discharge

    SciTech Connect

    Baranov, O.; Romanov, M.; Ostrikov, Kostya

    2009-06-15

    Parameters of a discharge sustained in a planar magnetron configuration with crossed electric and magnetic fields are studied experimentally and numerically. By comparing the data obtained in the experiment with the results of calculations made using the proposed theoretical model, conclusion was made about the leading role of the turbulence-driven Bohm electron conductivity in the low-pressure operation mode (up to 1 Pa) of the discharge in crossed electric and magnetic fields. A strong dependence of the width of the cathode sputter trench, associated with the ionization region of the magnetron discharge, on the discharge parameters was observed in the experiments. The experimental data were used as input parameters in the discharge model that describes the motion of secondary electrons across the magnetic field in the ionization region and takes into account the classical, near-wall, and Bohm mechanisms of electron conductivity.

  14. Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

    SciTech Connect

    Wang, R.; Williams, C. C.

    2015-09-15

    Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

  15. Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces.

    PubMed

    Wang, R; Williams, C C

    2015-09-01

    Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

  16. Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

    NASA Astrophysics Data System (ADS)

    Wang, R.; Williams, C. C.

    2015-09-01

    Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

  17. Effect of Precipitating Electrons on Ring Current Energy Content, Ionospheric Conductance, and Thermospheric Properties

    NASA Astrophysics Data System (ADS)

    Chen, M.; Lemon, C. L.; Walterscheid, R. L.; Yoo, B.; Hecht, J. H.; Shprits, Y.; Orlova, K.; Schulz, M.; Evans, J. S.

    2014-12-01

    We investigate how scattering of electrons by waves in the plasma sheet and plasmasphere affects precipitating energy flux distributions during magnetic storms, how the precipitating electrons modify the ionospheric Hall and Pederson conductivity and electric potential, how these processes feedback on magnetospheric particle transport and redistribute the ring current, and how the ionization and energy deposition of precipitating electrons affects thermospheric winds and temperature. Our main approach is to couple simulation models: (1) the magnetically and electrically self-consistent Rice Convection Model - Equilibrium (RCM-E) of the inner magnetosphere, (2) the B3c transport model for electron-proton-hydrogen atom aurora in the ionosphere, and (3) the Thermosphere-Ionsphere-Electrodynamics General Circulation Model (TIEGCM) of the ionosphere and thermosphere. Realistic descriptions of electron pitch-angle diffusion by whistler chorus in the plasma sheet/magnetotail and hiss in the plasmasphere are included in the RCM-E. We use parameterized rates of electron pitch-angle scattering with whistler chorus of Orlova and Shprits [JGR, 2014] that depend on equatorial radial distance, magnetic activity (Kp), and magnetic local time. To study how the precipitating electron energy flux distributions affect ionospheric conductivity and ionospheric electric potential patterns, we have performed a one-way coupling of the RCM-E and ionospheric B3c model. The simulated precipitating electron flux distributions are used to specify the energy flux and particle heating due to precipitating auroral electrons for TIEGCM simulations of the neutral atmosphere. We simulate a storm event and compare simulated quantities with in situ observations.

  18. Evidence of Eu{sup 2+} 4f electrons in the valence band spectra of EuTiO{sub 3} and EuZrO{sub 3}

    SciTech Connect

    Kolodiazhnyi, T.; Valant, M.; Williams, J. R.; Bugnet, M.; Botton, G. A.; Ohashi, N.; Sakka, Y.

    2012-10-15

    We report on optical band gap and valence electronic structure of two Eu{sup 2+}-based perovskites, EuTiO{sub 3} and EuZrO{sub 3} as revealed by diffuse optical scattering, electron energy loss spectroscopy, and valence-band x-ray photoelectron spectroscopy. The data show good agreement with the first-principles studies in which the top of the valence band structure is formed by the narrow Eu 4f{sup 7} electron band. The O 2p band shows the features similar to those of the Ba(Sr)TiO{sub 3} perovskites except that it is shifted to higher binding energies. Appearance of the Eu{sup 2+} 4f{sup 7} band is a reason for narrowing of the optical band gap in the title compounds as compared to their Sr-based analogues.

  19. Evidence of Eu2+ 4f electrons in the valence band spectra of EuTiO3 and EuZrO3

    NASA Astrophysics Data System (ADS)

    Kolodiazhnyi, T.; Valant, M.; Williams, J. R.; Bugnet, M.; Botton, G. A.; Ohashi, N.; Sakka, Y.

    2012-10-01

    We report on optical band gap and valence electronic structure of two Eu2+-based perovskites, EuTiO3 and EuZrO3 as revealed by diffuse optical scattering, electron energy loss spectroscopy, and valence-band x-ray photoelectron spectroscopy. The data show good agreement with the first-principles studies in which the top of the valence band structure is formed by the narrow Eu 4f7 electron band. The O 2p band shows the features similar to those of the Ba(Sr)TiO3 perovskites except that it is shifted to higher binding energies. Appearance of the Eu2+ 4f7 band is a reason for narrowing of the optical band gap in the title compounds as compared to their Sr-based analogues.

  20. Applications of high thermal conductivity composites to electronics and spacecraft thermal design

    NASA Technical Reports Server (NTRS)

    Sharp, G. Richard; Loftin, Timothy A.

    1990-01-01

    Recently, high thermal conductivity continuous graphite fiber reinforced metal matrix composites (MMC's) have become available that can save much weight over present methods of heat conduction. These materials have two or three times higher thermal conductivity in the fiber direction than the pure metals when compared on a thermal conductivity to weight basis. Use of these materials for heat conduction purposes can result in weight savings of from 50 to 70 percent over structural aluminum. Another significant advantage is that these materials can be used without the plumbing and testing complexities that accompany the use of liquid heat pipes. A spinoff of this research was the development of other MMC's as electronic device heat sinks. These use particulates rather than fibers and are formulated to match the coefficient of thermal expansion of electronic substrates in order to alleviate thermally induced stresses. The development of both types of these materials as viable weight saving substitutes for traditional methods of thermal control for electronics packaging and also for spacecraft thermal control applications are the subject of this report.

  1. Development and application of diagnostic instrumentation for measurement of electron density and conductivity

    SciTech Connect

    Bauman, L.E.

    1990-05-01

    The purpose of this contract was to assemble and demonstrate in the laboratory a Faraday rotation system for measurement of electron density and conductivity, with the intent to produce a system suitable for diagnostic support of the development of pulsed, space-based magnetohydrodynamic (MHD) power systems. Two system configurations were tested: (1) a rotating polarizer and (2) a beam splitting polarizer. Due to the short path length plasma produced in the laboratory flame, the long wavelength 496 {mu}m methyl fluoride laser line was used and only the more sensitive rotating polarizer configuration was used for the demonstration experiments. Electron number densities from 2 {times} 10{sup 19} to 9 {times} 10{sup 19} were measured with good agreement to statistical equilibrium (Saha) calculations using emission absorption-measured flame temperatures and neutral seed atom number seed atom nuclear densities. The electron collision frequencies were measured by transmission measurements. Combining these two measurements gave measured electron conductivities of between 4 and 12 mohs/m. These results compared reasonably well with those found with an electron collision frequency model combined with chemical equilibrium calculations and the emission absorption measurements. Ellipticity measurements of electron collision frequency were not possible due to the short path length of the laboratory plasma. 46 refs., 25 figs., 9 tabs.

  2. Defect characterization of electronic conducting pseudo-perovskite systems. Final report

    SciTech Connect

    Anderson, H.U.; Nasrallah, M.; Sparlin, D.M.; Parris, P.E.

    1994-12-31

    The goal of the program has been to study the interrelationships between electrical conductivity, oxidation-reduction kinetics, defect structure, and composition of n- and p-type binary and ternary transition metal oxides. The stimulus for making these studies was the observation that both conducting n and p type oxides displayed a dependence on oxygen activity that was not predicted by the defect chemistry of their majority defects. The project has focused primarily on the understanding of electronic and ionic conduction in the REBO{sub 3} oxides, where RE is a rare earth ion and B is a transition metal ion. This is being done by studying the interrelationships between the electronic and ionic conductivity, the electronic structure of the B site transition metal ion, and the acceptor concentration. The dependence of these characteristics on the oxygen activity, the temperature, and the defect chemistry of the oxide system is being determined. Theoretical mechanisms and models are being developed from the body of experimental results to provide a predictive tool. The effect of dopants and impurities, processing, electrical and thermal stability as a function of oxygen activity and temperature and their relationship to defect chemistry of the perovskite type oxides have been studied extensively by this research team. As a result of the difference in mobility between electronic and ionic defects, the electrical conductivity changes as the concentration of electronic defects changes. Thus, electrodes or resistors consisting of such oxides are susceptible to instabilities in resistance as they are cycled into temperature regimes where thermodynamic equilibrium may be attained. Many of the new energy conversion systems which use such oxides are encountering difficulties as a result of this instability in resistivity.

  3. Electron conductivity in GeTe and GeSe upon ion implantation of Bi

    SciTech Connect

    Fedorenko, Ya. G.

    2015-12-15

    This paper presents results on ion implantation of bismuth in GeTe and GeSe films. The conductivity and the thermopower of amorphous chalcogenide films are investigated. Electron conductivity in the films is attained at the Bi implantation doses higher than (1.5–2) × 10{sup 16} cm{sup −2}. In conjunction with the structural modification in the films as revealed Raman spectroscopy, the results suggest the structural re-arrangement of the amorphous network occurs via weakening the bonds of a lower energy. The onset of electron conductivity is hindered by a stronger bond in an alloy. In GeTe, this is the Ge-Ge bond.

  4. Thermal Moore's law and near-field thermal conductance in carbon-based electronics

    NASA Astrophysics Data System (ADS)

    Rotkin, Slava V.

    2009-08-01

    The novel thermal conductance mechanism, theoretically predicted and experimentally measured in nanotube field-effect transistors (FET), is discussed with respect to the power dissipation problem of modern carbon-based electronics. Such an effect is due to the near-field coupling of the charge carriers in the transistor channel with the local electric field of the surface electromagnetic modes. The coupling leads to a quantum electrodynamic (QED) energy exchange between the hot electrons in FET channel and the optical polar phonon bath being in thermal equilibrium with the substrate. For an example of a NT on silica, this QED coupling mechanism is shown to exceed significantly the interface Kapitza conductance, that is, the classical phonon heat transport. The QED thermal conductance is proposed to play dominant role in the energy dissipation in nanoelectronics with a hetero-interface between the device channel and the polar substrate.

  5. Conducting polymers as electron glasses: surface charge domains and slow relaxation

    PubMed Central

    Ortuño, Miguel; Escasain, Elisa; Lopez-Elvira, Elena; Somoza, Andres M.; Colchero, Jaime; Palacios-Lidon, Elisa

    2016-01-01

    The surface potential of conducting polymers has been studied with scanning Kelvin probe microscopy. The results show that this technique can become an excellent tool to really ‘see’ interesting surface charge interaction effects at the nanoscale. The electron glass model, which assumes that charges are localized by the disorder and that interactions between them are relevant, is employed to understand the complex behavior of conducting polymers. At equilibrium, we find surface potential domains with a typical lateral size of 50 nm, basically uncorrelated with the topography and strongly fluctuating in time. These fluctuations are about three times larger than thermal energy. The charge dynamics is characterized by an exponentially broad time distribution. When the conducting polymers are excited with light the surface potential relaxes logarithmically with time, as usually observed in electron glasses. In addition, the relaxation for different illumination times can be scaled within the full aging model. PMID:26911652

  6. Thermal conductivity of graphene with defects induced by electron beam irradiation

    NASA Astrophysics Data System (ADS)

    Malekpour, Hoda; Ramnani, Pankaj; Srinivasan, Srilok; Balasubramanian, Ganesh; Nika, Denis L.; Mulchandani, Ashok; Lake, Roger K.; Balandin, Alexander A.

    2016-07-01

    We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is analyzed using the Boltzmann transport equation and molecular dynamics simulations. The results are important for understanding phonon - point defect scattering in two-dimensional systems and for practical applications of graphene in thermal management.We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is

  7. Temperature behavior of the conduction electrons in the nitrogen-doped 3C SiC monocrystals as studied by electron spin resonance

    NASA Astrophysics Data System (ADS)

    Savchenko, D.; Kalabukhova, E.; Prokhorov, A.; Lančok, J.; Shanina, B.

    2017-01-01

    The temperature behavior of the electron spin resonance (ESR) spectra of nitrogen donors in n-type bulk 3C SiC monocrystals with (ND - NA) ≈ 1017 cm-3 was studied at T = 10-50 K. The triplet lines due to the hyperfine (hf) interaction with 14N nuclei (I = 1, 99.6%) along with a single line with similar isotropic g values of 2.0050(3) were observed in the ESR spectrum of n-type 3C SiC monocrystals in the temperature interval from 10 to 35 K. The observed reduction of the hf splitting for the nitrogen donor residing cubic position (Nk) in the temperature interval from 15 to 35 K was attributed to the motion narrowing effect of the hf splitting. With further increase of the temperature up to 35 K, only one single line with a Lorentzian lineshape was observed in the ESR spectrum of n-type 3C SiC, which was previously assigned in the literature to the unknown deeper donor center. Based on the temperature behavior of the ESR linewidth, integral intensity, and g-value, we have attributed this signal to the conduction electrons (CEs). The temperature dependence of the CE ESR linewidth was described by an exponential law (Orbach process) with the value of the activation energy ΔE ≈ 40 meV close to the energy separation between 1 s(E) excited energy level and conduction band for nitrogen donors. The nitrogen donor pairs were found in the ESR spectrum of n-type 3C SiC. The electrical characteristics of 3C SiC sample were studied by using the contact-free microwave conductivity. The energy ionization of nitrogen donor Ei = 51.4 meV was obtained from the fitting of the experimental data with the theory.

  8. The C2H, C2, and CN electronic absorption bands in the carbon star HD 19557

    NASA Technical Reports Server (NTRS)

    Goebel, J. H.; Bregman, J. D.; Cooper, D. M.; Goorvitch, D.; Langhoff, S. R.; Witteborn, F. C.

    1983-01-01

    Infrared spectrophotometry of the R-type carbon star HD 19557 is presented. Two unusual spectroscopic features are seen: a 3.1 micron band is lacking and a 2.8 micron band is present. Identifications are proposed for three previously unreported stellar absorption bands with electronic sequences of C2, CN, and C2H. The latter is proposed to be responsible for the 2.8 micron feature. The atmospheric structure of the star is studied with synthetic spectra, and an effective temperature between 2600 K and 3000 K is suggested. No SiC emission is seen at 11.3 microns, indicating that grain formation is not a viable process around the star. The lack of dust in R stars may suggest a salient difference between R and N types.

  9. Systematic study of electronic structure and band alignment of monolayer transition metal dichalcogenides in Van der Waals heterostructures

    NASA Astrophysics Data System (ADS)

    Zhang, Chenxi; Gong, Cheng; Nie, Yifan; Min, Kyung-Ah; Liang, Chaoping; Oh, Young Jun; Zhang, Hengji; Wang, Weihua; Hong, Suklyun; Colombo, Luigi; Wallace, Robert M.; Cho, Kyeongjae

    2017-03-01

    Two-dimensional transition metal dichalcogenides (TMDs) are promising low-dimensional materials which can produce diverse electronic properties and band alignment in van der Waals heterostructures. Systematic density functional theory (DFT) calculations are performed for 24 different TMD monolayers and their bilayer heterostacks. DFT calculations show that monolayer TMDs can behave as semiconducting, metallic or semimetallic depending on their structures; we also calculated the band alignment of the TMDs to predict their alignment in van der Waals heterostacks. We have applied the charge equilibration model (CEM) to obtain a quantitative formula predicting the highest occupied state of any type of bilayer TMD heterostacks (552 pairs for 24 TMDs). The CEM predicted values agree quite well with the selected DFT simulation results. The quantitative prediction of the band alignment in the TMD heterostructures can provide an insightful guidance to the development of TMD-based devices.

  10. Design of Q-band FMCW reflectometry for electron density profile measurement on the Joint TEXT tokamak

    NASA Astrophysics Data System (ADS)

    Linghan, Wan; Zhoujun, Yang; Ruobing, Zhou; Xiaoming, Pan; Chi, Zhang; Xianli, Xie; Bowen, Ruan

    2017-02-01

    The Q-band (33-50 GHz) fast sweep frequency modulated continuous wave (FMCW) reflectometry has been recently developed for electron density profile measurement on the Joint TEXT tokamak. It operates in ordinary mode (O-mode) with a 20 μs sweeping period, covering the density range from 1 × 1019 m-3 to 3 × 1019 m-3. On the bench test, a Yttrium Iron Garnet (YIG) filter is used for the dynamic calibration of the voltage controlled oscillator (VCO) to obtain a linear frequency sweep. Besides, the use of a power combiner helps to improve the side-band suppression level of the single side-band modulator (SSBM). The reconstructed density profiles are presented, which demonstrate the capability of the reflectometry.

  11. A conducting polymer with enhanced electronic stability applied in cardiac models

    PubMed Central

    Mawad, Damia; Mansfield, Catherine; Lauto, Antonio; Perbellini, Filippo; Nelson, Geoffrey W.; Tonkin, Joanne; Bello, Sean O.; Carrad, Damon J.; Micolich, Adam P.; Mahat, Mohd M.; Furman, Jennifer; Payne, David; Lyon, Alexander R.; Gooding, J. Justin; Harding, Sian E.; Terracciano, Cesare M.; Stevens, Molly M.

    2016-01-01

    Electrically active constructs can have a beneficial effect on electroresponsive tissues, such as the brain, heart, and nervous system. Conducting polymers (CPs) are being considered as components of these constructs because of their intrinsic electroactive and flexible nature. However, their clinical application has been largely hampered by their short operational time due to a decrease in their electronic properties. We show that, by immobilizing the dopant in the conductive scaffold, we can prevent its electric deterioration. We grew polyaniline (PANI) doped with phytic acid on the surface of a chitosan film. The strong chelation between phytic acid and chitosan led to a conductive patch with retained electroactivity, low surface resistivity (35.85 ± 9.40 kilohms per square), and oxidized form after 2 weeks of incubation in physiological medium. Ex vivo experiments revealed that the conductive nature of the patch has an immediate effect on the electrophysiology of the heart. Preliminary in vivo experiments showed that the conductive patch does not induce proarrhythmogenic activities in the heart. Our findings set the foundation for the design of electronically stable CP-based scaffolds. This provides a robust conductive system that could be used at the interface with electroresponsive tissue to better understand the interaction and effect of these materials on the electrophysiology of these tissues. PMID:28138526

  12. Parasitic Currents Caused by Different Ionic and Electronic Conductivities in Fuel Cell Anodes.

    PubMed

    Schalenbach, Maximilian; Zillgitt, Marcel; Maier, Wiebke; Stolten, Detlef

    2015-07-29

    The electrodes in fuel cells simultaneously realize electric and ionic conductivity. In the case of acidic polymer electrolytes, the electrodes are typically made of composites of carbon-supported catalyst and Nafion polymer electrolyte binder. In this study, the interaction of the proton conduction, the electron conduction, and the electrochemical hydrogen conversion in such composite electrode materials was examined. Exposed to a hydrogen atmosphere, these composites displayed up to 10-fold smaller resistivities for the proton conduction than that of Nafion membranes. This effect was ascribed to the simultaneously occurring electrochemical hydrogen oxidation and evolution inside the composite samples, which are driven by different proton and electron resistivities. The parasitic electrochemical currents resulting were postulated to occur in the anode of fuel cells with polymer, solid oxide, or liquid alkaline electrolytes, when the ohmic drop of the ion conduction in the anode is higher with the anodic kinetic overvoltage (as illustrated in the graphical abstract). In this case, the parasitic electrochemical currents increase the anodic kinetic overpotential and the ohmic drop in the anode. Thinner fuel cell anodes with smaller ohmic drops for the ion conduction may reduce the parasitic electrochemical currents.

  13. Electrical conductance of DNA molecules with varied density of itinerant pi electrons.

    PubMed

    Gao, Xu-Tuan; Fu, Xue; Mei, Liang-Mo; Xie, Shi-Jie

    2006-06-21

    The electrical transport of DNA is closely related to the density of itinerant pi electrons because of the strong electron-lattice interaction. The resistivities of two typical DNA molecules [poly(dG)-poly(dC) and lambda-DNA] with varied densities of itinerant pi electrons are calculated. It is found that the dependence of the resistivity on the density of itinerant pi electrons is symmetrical about the half-filling state of itinerant pi electrons in poly(dG)-poly(dC). At the half-filling state, the Peierls phase transition takes place and poly(dG)-poly(dC) has a large resistivity. When the density of itinerant pi electrons departs far from the half-filling state, the resistivity of poly(dG)-poly(dC) becomes small. For lambda-DNA, there is no Peierls phase transition due to the aperiodicity of its base pair arrangement. The resistivity of poly(dG)-poly(dC) decreases with increasing length of the molecular chain, but the resistivity of lambda-DNA increases with increasing length. The conducting mechanisms for poly(dG)-poly(dC) and a few lambda-DNA molecules with varied densities of itinerant pi electrons are analyzed.

  14. Role of acoustic phonons in frequency dependent electronic thermal conductivity of graphene

    NASA Astrophysics Data System (ADS)

    Bhalla, Pankaj

    2017-03-01

    We study the effect of the electron-phonon interaction on the finite frequency dependent electronic thermal conductivity of two dimensional graphene. We calculate it for various acoustic phonons present in graphene and characterized by different dispersion relations using the memory function approach. It is found that the electronic thermal conductivity κe (T) in the zero frequency limit follows different power law for the longitudinal/transverse and the flexural acoustic phonons. For the longitudinal/transverse phonons, κe (T) ∼T-1 at the low temperature and saturates at the high temperature. These signatures qualitatively agree with the results calculated by solving the Boltzmann equation analytically and numerically. Similarly, for the flexural phonons, we find that κe (T) shows T 1 / 2 law at the low temperature and then saturates at the high temperature. In the finite frequency regime, we observe that the real part of the electronic thermal conductivity, Re [κe (ω , T) ] follows ω-2 behavior at the low frequency and becomes frequency independent at the high frequency.

  15. Impact of Lone-Pair Electrons on Thermal Conductivity in CuSbS2 Compound

    NASA Astrophysics Data System (ADS)

    Du, Baoli; Zhang, Ruizhi; Chen, Kan; Reece, Michael; Material research institute Team

    Compounds with intrinsically low lattice thermal conductivity are of practical importance for thermoelectric energy conversion. Recent studies suggest that s2 lone pair orbital electrons are a key contributing factor to the anomalously low lattice thermal conductivity of chalcogenide compounds that contain a nominally trivalent group VA element. CuSbS2 has an orthorhombic structure with space group Pnma. The pyramidal SbS5 units are separated by CuS4 tetrahedron so that the base of the square pyramidal units are aligned to face one another, thus directing the Sb lone pair electron density into the void separating the SbS5 units. Different from tetrahedrite, all the Cu atoms are bonded in the CuS4 tetrahedron. So, it has a perfect structure to study the influence of electron lone pair on thermal conductivity without the impact from trigonal coordinated Cu. In this work, the trivalent transition metal atom Fe and IIIA atom Ga without lone-pair electrons were chosen to substitute Sb in CuSbS2. The changes in the bonding environment by foreign atoms and their influences on the thermal properties have been studied and correlated. Marie Curie International Incoming Fellowship of the European Community Human Potential Program under Contract No. PIIF-GA-2013-622847.

  16. Determination of conduction band offsets in type-II In0.27Ga0.73Sb/InxAl1-xAsySb1-y heterostructures grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Glaser, E. R.; Magno, R.; Shanabrook, B. V.; Tischler, J. G.

    2006-12-01

    Low-temperature photoluminescence (PL) has been performed on a set of specially designed In0.27Ga0.73Sb/InxAl1-xAsySb1-y multiple quantum well (MQW) heterostructures grown by molecular beam epitaxy in order to provide a measure of the conduction band offsets in this material system. These alloys are of interest for the development of high-speed heterojunction bipolar transistors (HBTs) that show promise for operation at lower power dissipation than in GaAs - and InP -based HBTs. Excitation power studies revealed evidence for strong electron-hole recombination at 0.56eV within the InGaSb layers of the type-I MQW structure with (x=0.52,y=0.25) , while several weaker indirect transitions involving electrons in the InxAl1-xAsySb1-y and holes in the InGaSb layers were observed between 0.38 and 0.53eV from the nominally type-II MQW samples with (x,y)=(0.67,0.39) and (0.69,0.41). Neglecting small corrections (˜15meV) due to the electron and hole confinement energies, we estimate conduction band offsets of ˜120-150meV in these type-II structures. The general trends of the PL features as a function of excitation power have been reproduced from modeling of the quantum well electron and hole subband energies, including effects due to band bending at the heterointerfaces.

  17. Power factor improvement and thermal conductivity reduction---By band engineering and modulation-doping in nanocomposites

    NASA Astrophysics Data System (ADS)

    Yu, Bo

    Thermoelectrics, as one promising approach for solid-state energy conversion between heat and electricity, is becoming increasingly important within the last a couple of decades as the availability and negative environmental impact of fossil fuels draw increasing attention. Therefore, various thermoelectric materials in a wide working temperature range from room temperature to 1000 °C for power generation or below zero for cooling applications have been intensively studied. In general, the efficiency of thermoelectric devices relies on the dimensionless figure-of-merit (ZT) of the material, defined as ZT=(S2sigma)T/kappa, where S is the Seebeck coefficient, sigma the electrical conductivity, kappa the thermal conductivity (sum of the electronic part, the lattice part, and the bipolar contribution at high temperature region), and T the absolute temperature during operation. Techniques to measure those individual parameters will be discussed in the 2nd chapter while the 1 st chapter mainly covers the fundamental theory of thermoelectrics. Recently, the idea of using various nanostructured materials to further improve the ZT of conventional thermoelectric materials has led to a renewed interest. Among these types of nanostructured materials, nanocomposites which mainly denote for the nano-grained bulk materials or materials with nano-sized inclusions are the major focus of our study. For nanocomposites, the enhancement in ZT mainly comes from the low lattice thermal conductivity due to the suppressed phonon transport by those interfaces or structure features in the nanometer scale without deteriorating the electron transport. In the last few years, we have successfully demonstrated in several materials systems (Bismuth Telluride, Skutterudites, Silicon Germanium) that ball milling followed by hot pressing is an effective way for preparing large quantities of those nanocomposite thermoelectric materials with high ZT values in the bulk form. Therefore, in the 3rd part

  18. Correlative infrared-electron nanoscopy reveals the local structure-conductivity relationship in zinc oxide nanowires

    NASA Astrophysics Data System (ADS)

    Stiegler, J. M.; Tena-Zaera, R.; Idigoras, O.; Chuvilin, A.; Hillenbrand, R.

    2012-10-01

    High-resolution characterization methods play a key role in the development, analysis and optimization of nanoscale materials and devices. Because of the various material properties, only a combination of different characterization techniques provides a comprehensive understanding of complex functional materials. Here we introduce correlative infrared-electron nanoscopy, a novel method yielding transmission electron microscope and infrared near-field images of one and the same nanostructure. While transmission electron microscopy provides structural information up to the atomic level, infrared near-field imaging yields nanoscale maps of chemical composition and conductivity. We demonstrate the method's potential by studying the relation between conductivity and crystal structure in ZnO nanowire cross-sections. The combination of infrared conductivity maps and the local crystal structure reveals a radial free-carrier gradient, which inversely correlates to the density of extended crystalline defects. Our method opens new avenues for studying the local interplay between structure, conductivity and chemical composition in widely different material systems.

  19. Effect of spin-orbit interaction on the electronic structure of indium-antimonide d bands

    SciTech Connect

    Sobolev, V. V. Perevoshchikov, D. A.

    2015-05-15

    The bands and densities of states of d bands in indium antimonide (InSb) are determined taking into account and disregarding the spin-orbit interaction. It is established that taking into account the effect of spin-orbit interaction results also in a substantial change in the dispersion of the obtained bands instead of only in the doublet splitting of the band of core d levels at ∼(0.79–0.86) eV. It is established that it is indium 4d states with e{sub g} and t{sub 2g} symmetry that give the main contribution to the density of states. The calculations are carried out by the LAPW method with the exchange-correlation potential in the generalized gradient approximation (LAPW + GGA)

  20. Further improvements in program to calculate electronic properties of narrow band gap materials

    NASA Technical Reports Server (NTRS)

    Patterson, James D.

    1991-01-01

    Research into the properties of narrow band gap materials during the period 15 Jun. to 15 Dec. 1991 is discussed. Abstracts and bibliographies from papers presented during this period are reported. Graphs are provided.

  1. Thermal Conductivity Measurement of an Electron-Beam Physical-Vapor-Deposition Coating.

    PubMed

    Slifka, A J; Filla, B J

    2003-01-01

    An industrial ceramic thermal-barrier coating designated PWA 266, processed by electron-beam physical-vapor deposition, was measured using a steady-state thermal conductivity technique. The thermal conductivity of the mass fraction 7 % yttria-stabilized zirconia coating was measured from 100 °C to 900 °C. Measurements on three thicknesses of coatings, 170 μm, 350 μm, and 510 μm resulted in thermal conductivity in the range from 1.5 W/(m·K) to 1.7 W/(m·K) with a combined relative standard uncertainty of 20 %. The thermal conductivity is not significantly dependent on temperature.

  2. Thin film electronic devices with conductive and transparent gas and moisture permeation barriers

    DOEpatents

    Simpson, Lin Jay

    2015-07-28

    Thin film electronic devices (or stacks integrated with a substrate) that include a permeation barrier formed of a thin layer of metal that provides a light transmitting and electrically conductive layer, wherein the electrical conductive layer is formed on a surface of the substrate or device layer such as a transparent conducting material layer with pin holes or defects caused by manufacturing and the thin layer of metal is deposited on the conductive layer and formed from a self-healing metal that forms self-terminating oxides. A permeation plug or block is formed in or adjacent to the thin film of metal at or proximate to the pin holes to block further permeation of contaminants through the pin holes.

  3. The dependence of the electronic conductivity of carbon molecular sieve electrodes on their charging states.

    PubMed

    Pollak, Elad; Genish, Isaschar; Salitra, Gregory; Soffer, Abraham; Klein, Lior; Aurbach, Doron

    2006-04-13

    The dependence of the electronic conductivity of activated carbon electrodes on their potential in electrolyte solutions was examined. Kapton polymer films underwent carbonization (1000 degrees C), followed by a mild oxidation process (CO(2) at 900 degrees C) for various periods of time, to obtain carbons of different pore structures. A specially designed cell was assembled in order to measure the conductivity of carbon electrodes at different potentials in solutions. When the carbon electrodes possessed molecular sieving properties, a remarkable dependence of their conductivity on their charging state was observed. Aqueous electrolyte solutions containing ions of different sizes were used in order to demonstrate this phenomenon. As the average pore size of the activated carbons was larger, their molecular sieving ability was lower, and the dependence of their conductivity on their charging state regained its classical form. This behavior is discussed herein.

  4. Effects of Structural Deformation and Tube Chirality on Electronic Conductance of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Svizhenko, Alexei; Maiti, Amitesh; Anantram, M. P.; Biegel, Bryan A. (Technical Monitor)

    2002-01-01

    A combination of large scale classical force-field (UFF), density functional theory (DFT), and tight-binding Green's function transport calculations is used to study the electronic properties of carbon nanotubes under the twist, bending, and atomic force microscope (AFM)-tip deformation. We found that in agreement with experiment a significant change in electronic conductance can be induced by AFM-tip deformation of metallic zigzag tubes and by twist deformation of armchair tubes. The effect is explained in terms of bandstructure change under deformation.

  5. Absolute negative conductivity and spontaneous current generation in semiconductor superlattices with hot electrons

    PubMed

    Cannon; Kusmartsev; Alekseev; Campbell

    2000-08-07

    We study transport through a semiconductor superlattice with an electric field parallel to and a magnetic field perpendicular to the growth axis. Using a semiclassical balance equation model with elastic and inelastic scattering, we find that (1) the current-voltage characteristic becomes multistable in a large magnetic field and (2) "hot" electrons display novel features in their current-voltage characteristics, including absolute negative conductivity and a spontaneous dc current at zero bias. We discuss experimental situations providing hot electrons to observe these effects.

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

    PubMed

    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.

  7. Operation of an ungated diamond field-emission array cathode in a L-band radiofrequency electron source

    SciTech Connect

    Piot, P.; Brau, C. A.; Gabella, W. E.; Ivanov, B.; Mendenhall, M. H.; Choi, B. K.; Blomberg, B.; Mihalcea, D.; Panuganti, H.; Jarvis, J.; Prieto, P.; Reid, J.

    2014-06-30

    We report on the operation of a field-emitter-array cathode in a conventional L-band radio-frequency electron source. The cathode consisted of an array of ∼10{sup 6} diamond tips on pyramids. Maximum current on the order of 15 mA was reached and the cathode did not show appreciable signs of fatigue after weeks of operation. The measured Fowler-Nordheim characteristics, transverse beam density, and current stability are discussed.

  8. Electrical conductivity of a silicone network upon electron irradiation: influence of formulation

    NASA Astrophysics Data System (ADS)

    Roggero, A.; Dantras, E.; Paulmier, T.; Tonon, C.; Lewandowski, S.; Dagras, S.; Payan, D.

    2016-12-01

    In this study, the electrical conductivity of a silicone elastomer filled with inorganic fillers was investigated upon electron irradiation. Neat samples consisting of the isolated polysiloxane matrix (with no fillers) were studied in parallel to identify the filler contribution to this evolution. It was shown that exposure to 400 keV electron doses induced a decrease in electrical conductivity for both the filled and neat materials. This decrease was much more pronounced with the filled samples than with the neat ones. Moreover, the activation energy of electrical conductivity (Arrhenius behaviour) doubled in the filled case, while it varied only weakly for the neat case. In light of these results, structure-property relationships were proposed on the basis of the radiation-induced crosslink processes to which this material is subject. In the framework of electronic percolation theory, it is suggested that the radiation-induced formation of SiO3 crosslinks in the polysiloxane network and SiO4 crosslinks at filler-matrix interfaces affects the percolation path of the material, which can be simply modelled by a network of resistors in series. On one hand, their densification increases the overall resistance of the percolation path, which results in the observed decrease of effective electrical conductivity. On the other hand, the steep increase in activation energy in the filled material attributes to the SiO4 crosslinks becoming the most restrictive barrier along the percolation path. In spite of the misleading likeness of electrical conductivities in the pristine state, this study presented evidence that silicone formulation can affect the evolution of electrical properties in radiative environments. To illustrate this conclusion, the use of this material in space applications, especially when directly exposed to the radiative space environment, was discussed. The decrease in electrical conductivity was associated with a progressively increasing risk for the

  9. Thermally conductive, dielectric PCM-boron nitride nanosheet composites for efficient electronic system thermal management.

    PubMed

    Yang, Zhi; Zhou, Lihui; Luo, Wei; Wan, Jiayu; Dai, Jiaqi; Han, Xiaogang; Fu, Kun; Henderson, Doug; Yang, Bao; Hu, Liangbing

    2016-11-24

    Phase change materials (PCMs) possessing ideal properties, such as superior mass specific heat of fusion, low cost, light weight, excellent thermal stability as well as isothermal phase change behavior, have drawn considerable attention for thermal management systems. Currently, the low thermal conductivity of PCMs (usually less than 1 W mK(-1)) greatly limits their heat dissipation performance in thermal management applications. Hexagonal boron nitride (h-BN) is a two-dimensional material known for its excellent thermally conductive and electrically insulating properties, which make it a promising candidate to be used in electronic systems for thermal management. In this work, a composite, consisting of h-BN nanosheets (BNNSs) and commercialized paraffin wax was developed, which inherits high thermally conductive and electrically insulating properties from BNNSs and substantial heat of fusion from paraffin wax. With the help of BNNSs, the thermal conductivity of wax-BNNS composites reaches 3.47 W mK(-1), which exhibits a 12-time enhancement compared to that of pristine wax (0.29 W mK(-1)). Moreover, an 11.3-13.3 MV m(-1) breakdown voltage of wax-BNNS composites was achieved, which shows further improved electrical insulating properties. Simultaneously enhanced thermally conductive and electrically insulating properties of wax-BNNS composites demonstrate their promising application for thermal management in electronic systems.

  10. Method of forming a dense, high temperature electronically conductive composite layer on a porous ceramic substrate

    DOEpatents

    Isenberg, Arnold O.

    1992-01-01

    An electrochemical device, containing a solid oxide electrolyte material and an electrically conductive composite layer, has the composite layer attached by: (A) applying a layer of LaCrO.sub.3, YCrO.sub.3 or LaMnO.sub.3 particles (32), on a portion of a porous ceramic substrate (30), (B) heating to sinter bond the particles to the substrate, (C) depositing a dense filler structure (34) between the doped particles (32), (D) shaving off the top of the particles, and (E) applying an electronically conductive layer over the particles (32) as a contact.

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

    PubMed

    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.

  12. Low-charge, hard x-ray free electron laser driven with an X-band injector and accelerator

    NASA Astrophysics Data System (ADS)

    Sun, Yipeng; Adolphsen, Chris; Limborg-Deprey, Cecile; Raubenheimer, Tor; Wu, Juhao

    2012-03-01

    After the successful operation of the Free Electron Laser in Hamburg (FLASH) and the Linac Coherent Light Source (LCLS), soft and hard x-ray free electron lasers (FELs) are being built, designed, or proposed at many accelerator laboratories. Acceleration employing lower frequency rf cavities, ranging from L-band to C-band, is usually adopted in these designs. In the first stage bunch compression, higher-frequency harmonic rf system is employed to linearize the beam’s longitudinal phase space, which is nonlinearly chirped during the lower frequency rf acceleration process. In this paper, a hard x-ray FEL design using an all X-band accelerator at 11.424 GHz (from photocathode rf gun to linac end) is presented, without the assistance of any harmonic rf linearization. It achieves LCLS-like performance at low charge using X-band linac drivers, which is more versatile, efficient, and compact than ones using S-band or C-band rf technology. It employs initially 42 microns long (rms), low-charge (10 pC) electron bunches from an X-band photoinjector. An overall bunch compression ratio of roughly 100 times is proposed in a two stage bunch compressor system. The start-to-end macroparticle 3D simulation employing several computer codes is presented in this paper, where space charge, wakefields, and incoherent and coherent synchrotron radiation effects are included. Employing an undulator with a short period of 1.5 cm, a Genesis FEL simulation shows successful lasing at a wavelength of 0.15 nm with a pulse length of 2 fs and a power saturation length as short as 20 meters, which is equivalent to LCLS low-charge mode. Its overall length of both accelerators and undulators is 180 meters (much shorter than the effective LCLS overall length of 1230 meters, including an accelerator length of 1100 meters and an undulator length of 130 meters), which makes it possible to be built in places where only limited space is available.

  13. Quantum transport through disordered 1D wires: Conductance via localized and delocalized electrons

    SciTech Connect

    Gopar, Víctor A.

    2014-01-14

    Coherent electronic transport through disordered systems, like quantum wires, is a topic of fundamental and practical interest. In particular, the exponential localization of electron wave functions-Anderson localization-due to the presence of disorder has been widely studied. In fact, Anderson localization, is not an phenomenon exclusive to electrons but it has been observed in microwave and acoustic experiments, photonic materials, cold atoms, etc. Nowadays, many properties of electronic transport of quantum wires have been successfully described within a scaling approach to Anderson localization. On the other hand, anomalous localization or delocalization is, in relation to the Anderson problem, a less studied phenomenon. Although one can find signatures of anomalous localization in very different systems in nature. In the problem of electronic transport, a source of delocalization may come from symmetries present in the system and particular disorder configurations, like the so-called Lévy-type disorder. We have developed a theoretical model to describe the statistical properties of transport when electron wave functions are delocalized. In particular, we show that only two physical parameters determine the complete conductance distribution.

  14. Gallium ion implantation greatly reduces thermal conductivity and enhances electronic one of ZnO nanowires

    SciTech Connect

    Xia, Minggang; Cheng, Zhaofang; Han, Jinyun; Zhang, Shengli; Zheng, Minrui; Sow, Chorng-Haur; Thong, John T. L.; Li, Baowen

    2014-05-15

    The electrical and thermal conductivities are measured for individual zinc oxide (ZnO) nanowires with and without gallium ion (Ga{sup +}) implantation at room temperature. Our results show that Ga{sup +} implantation enhances electrical conductivity by one order of magnitude from 1.01 × 10{sup 3} Ω{sup −1}m{sup −1} to 1.46 × 10{sup 4} Ω{sup −1}m{sup −1} and reduces its thermal conductivity by one order of magnitude from 12.7 Wm{sup −1}K{sup −1} to 1.22 Wm{sup −1}K{sup −1} for ZnO nanowires of 100 nm in diameter. The measured thermal conductivities are in good agreement with those in theoretical simulation. The increase of electrical conductivity origins in electron donor doping by Ga{sup +} implantation and the decrease of thermal conductivity is due to the longitudinal and transverse acoustic phonons scattering by Ga{sup +} point scattering. For pristine ZnO nanowires, the thermal conductivity decreases only two times when its diameter reduces from 100 nm to 46 nm. Therefore, Ga{sup +}-implantation may be a more effective method than diameter reduction in improving thermoelectric performance.

  15. Conductance of a single electron transistor with a retarded dielectric layer in the gate capacitor

    NASA Astrophysics Data System (ADS)

    Udalov, O. G.; Chtchelkatchev, N. M.; Fedorov, S. A.; Beloborodov, I. S.

    2015-11-01

    We study the conductance of a single electron transistor (SET) with a ferroelectric (or dielectric) layer placed in the gate capacitor. We assume that the ferroelectric (FE) has a retarded response with arbitrary relaxation time. We show that in the case of "fast" but still retarded response of the FE (dielectric) layer an additional contribution to the Coulomb blockade effect appears leading to the suppression of the SET conductance. We take into account fluctuations of the FE (dielectric) polarization using Monte Carlo simulations. For "fast" FE, these fluctuations partially suppress the additional Coulomb blockade effect. Using Monte Carlo simulations, we study the transition from "fast" to "slow" FE. For high temperatures, the peak value of the SET conductance is almost independent of the FE relaxation time. For temperatures close to the FE Curie temperature, the conductance peak value nonmonotonically depends on the FE relaxation time. A maximum appears when the FE relaxation time is of the order of the SET discharging time. Below the Curie point the conductance peak value decreases with increasing the FE relaxation time. The conductance shows the hysteresis behavior for any FE relaxation time at temperatures below the FE transition point. We show that conductance hysteresis is robust against FE internal fluctuations.

  16. The origin of electronic band structure anomaly in topological crystalline insulator group-IV tellurides

    NASA Astrophysics Data System (ADS)

    Ye, Zhen-Yu; Deng, Hui-Xiong; Wu, Hui-Zhen; Li, Shu-Shen; Wei, Su-Huai; Luo, Jun-Wei

    2015-11-01

    Group-IV tellurides have exhibited exotic band structures. Specifically, despite the fact that Sn sits between Ge and Pb in the same column of the periodic table, cubic SnTe is a topological crystalline insulator with band inversion, but both isovalent GeTe and PbTe are trivial semiconductors with normal band order. By performing first-principles band structure calculations, we unravel the origin of this abnormal behaviour by using symmetry analysis and the atomic orbital energy levels and atomic sizes of these elements. In group-IV tellurides, the s lone pair band of the group-IV element is allowed by symmetry to couple with the anion valence p band at the L-point, and such s-p coupling leads to the occurrence of bandgap at the L-point. We find that such s-p coupling is so strong in SnTe that it inverts the band order near the bandgap; however, it is not strong enough in both GeTe and PbTe, so they remain normal semiconductors. The reason for this is the incomplete screening of the core of the relatively tight-binding Ge 4s orbital by its 3d orbitals and the large atomic size and strong relativistic effect in Pb, respectively. Interestingly, we also find that the rhombohedral distortion removes the inversion symmetry and the reduced s-p coupling transforms the α-SnTe back to a normal semiconductor. Our study demonstrates that, in addition to spin-orbital coupling, strain and interface dipole fields, inter-orbital coupling is another effective way to engineer the topological insulators.

  17. Hydrogen production by high temperature water splitting using electron conducting membranes

    DOEpatents

    Balachandran, Uthamalingam; Wang, Shuangyan; Dorris, Stephen E.; Lee, Tae H.

    2006-08-08

    A device and method for separating water into hydrogen and oxygen is disclosed. A first substantially gas impervious solid electron-conducting membrane for selectively passing protons or hydrogen is provided and spaced from a second substantially gas impervious solid electron-conducting membrane for selectively passing oxygen. When steam is passed between the two membranes at dissociation temperatures the hydrogen from the dissociation of steam selectively and continuously passes through the first membrane and oxygen selectively and continuously passes through the second membrane, thereby continuously driving the dissociation of steam producing hydrogen and oxygen. The oxygen is thereafter reacted with methane to produce syngas which optimally may be reacted in a water gas shift reaction to produce CO2 and H2.

  18. Electron-phonon scattering and in-plane electric conductivity in twisted bilayer graphene

    NASA Astrophysics Data System (ADS)

    Ray, N.; Fleischmann, M.; Weckbecker, D.; Sharma, S.; Pankratov, O.; Shallcross, S.

    2016-12-01

    We have surveyed the in-plane transport properties of the graphene twist bilayer using (i) a low-energy effective Hamiltonian for the underlying electronic structure, (ii) an isotropic elastic phonon model, and (iii) the linear Boltzmann equation for elastic electron-phonon scattering. We find that transport in the twist bilayer is profoundly sensitive to the rotation angle of the constituent layers. Similar to the electronic structure of the twist bilayer, the transport is qualitatively different in three distinct angle regimes. At large angles (θ >≈10∘ ) and at temperatures below an interlayer Bloch-Grüneisen temperature of ≈10 K, the conductivity is independent of the twist angle, i.e., the layers are fully decoupled. Above this temperature the layers, even though decoupled in the ground state, are recoupled by electron-phonon scattering and the transport is different both from single-layer graphene as well as the Bernal bilayer. In the small-angle regime θ <≈2∘ , the conductivity drops by two orders of magnitude and develops a rich energy dependence, reflecting the complexity of the underlying topological changes (Lifshitz transitions) of the Fermi surface. At intermediate angles, the conductivity decreases continuously as the twist angle is reduced, while the energy dependence of the conductivity presents two sharp transitions, that occur at specific angle-dependent energies, and that may be related to (i) the well-studied van Hove singularity of the twist bilayer and (ii) a Lifshitz transition that occurs when trigonally placed electron pockets decorate the strongly warped Dirac cone. Interestingly, we find that, while the electron-phonon scattering is dominated by layer symmetric flexural phonons in the small-angle limit, at large angles, in contrast, it is the layer antisymmetric flexural mode that is most important. We examine the role of a layer perpendicular electric field finding that it affects the conductivity strongly at low temperatures

  19. The effects of N-doping and oxygen vacancy on the electronic structure and conductivity of PbTiO3

    NASA Astrophysics Data System (ADS)

    Peijiang, Niu; Jinliang, Yan; Delan, Meng

    2015-04-01

    By using spin-polarized density functional theory calculations, the electron density differences, band structures and density of states of p-type N-doped PbTiO3 have been studied. In addition, the oxygen vacancy in N-doped PbTiO3 is also discussed. After the nitrogen dopant is introduced into the crystal, the N-doped PbTiO3 system is spin-polarized, the spin-down valance bands move to a high energy level and the Fermi energy level moves to the top of the valance bands, finally the band gap is narrowed. In this process, the N-doped PbTiO3 shows typical p-type semiconductor characteristics. When an oxygen vacancy and N impurity coexist in PbTiO3, there is no spin-polarized phenomenon. The conduction bands move downward and the acceptors are found to be fully compensated. The calculation results are mostly consistent with the experimental data. Project supported by the National Natural Science Foundation of China (No. 10974077) and the Innovation Project of Shandong Graduate Education, China (No. SDYY13093).

  20. Electronic structure of NaxCu1-xIn5S8 compounds: X-ray photoemission spectroscopy study and band structure calculations

    NASA Astrophysics Data System (ADS)

    Guillot-Deudon, Catherine; Harel, Sylvie; Mokrani, Arezki; Lafond, Alain; Barreau, Nicolas; Fernandez, Vincent; Kessler, John

    2008-12-01

    The aim of the present work is to complete a preliminary study concerning the electronic band structure investigations of NaxCu1-xIn5S8 compounds with 0≤x≤1 , which are expected to be formed at the Cu(In,Ga)Se2/In2S3 interface. The band structure calculations demonstrate that for the compounds containing both Na and Cu, as the Cu content increases the band gap tends to decrease, and x-ray photoemission spectroscopy measurements show that this variation is mainly due to valence-band-maximum shift along the solid solution. The band gap strongly depends on the nature of the monovalent cation, and the band structure calculations demonstrate that the d electrons of copper are responsible for the shift of the valence band. In addition, it is worth noting that the Cu-containing compounds have indirect gaps.

  1. Defect Physics, Delithiation Mechanism, and Electronic and Ionic Conduction in Layered Lithium Manganese Oxide Cathode Materials

    NASA Astrophysics Data System (ADS)

    Hoang, Khang

    2015-02-01

    Layered Li Mn O2 and Li2Mn O3 are of great interest for lithium-ion battery cathodes because of their high theoretical capacities. The practical application of these materials is, however, limited due to poor electrochemical performance. We herein report a comprehensive first-principles study of defect physics in Li Mn O2 and Li2Mn O3 using hybrid density-functional calculations. We find that manganese antisites have low formation energies in Li Mn O2 and may act as nucleation sites for the formation of impurity phases. The antisites can also occur with high concentrations in Li2Mn O3 ; however, unlike in Li Mn O2 , they can be eliminated by tuning the experimental conditions during preparation. Other intrinsic point defects may also occur and have an impact on the materials' properties and functioning. An analysis of the formation of lithium vacancies indicates that lithium extraction from Li Mn O2 is associated with oxidation at the manganese site, resulting in the formation of manganese small hole polarons; whereas in Li2Mn O3 the intrinsic delithiation mechanism involves oxidation at the oxygen site, leading to the formation of bound oxygen hole polarons ηO+ . The layered oxides are found to have no or negligible bandlike carriers, and they cannot be doped n or p type. The electronic conduction proceeds through hopping of hole and/or electron polarons; the ionic conduction occurs through lithium monovacancy and/or divacancy migration mechanisms. Since ηO+ is not stable in the absence of negatively charged lithium vacancies in bulk Li2Mn O3 , the electronic conduction near the start of delithiation is likely to be poor. We suggest that the electronic conduction associated with ηO+ and, hence, the electrochemical performance of Li2Mn O3 can be improved through nanostructuring and/or ion substitution.

  2. An innovative electronically-conducting matrix of the cathode for sodium sulfur battery

    NASA Astrophysics Data System (ADS)

    Kim, Seong In; Park, Won Il; Jung, Keeyoung; Kim, Chang-Sam

    2016-07-01

    An innovative electronically-conducting cathode matrix, that makes sodium sulfur (NaS) battery excellent in discharge-charge performance, is prepared by surface modification of a carbon felt with inorganic nanoparticles. A carbon felt is dipped into an inorganic-organic hybrid sol, dried, and heat-treated at 600 °C for 2 h in a flowing argon. Coated surface of the felt has been examined by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) and scanning transmission electron microscopy (STEM). The cell prepared with the coated carbon felt shows 92% of charge acceptance and 99.9% of coulombic efficiency at 100 mA cm-2 of current density.

  3. Inhibition of electron thermal conduction by electromagnetic instabilities. [in stellar coronas

    NASA Technical Reports Server (NTRS)

    Levinson, Amir; Eichler, David

    1992-01-01

    Heat flux inhibition by electromagnetic instabilities in a hot magnetized plasma is investigated. Low-frequency electromagnetic waves become unstable due to anisotropy of the electron distribution function. The chaotic magnetic field thus generated scatters the electrons with a specific effective mean free path. Saturation of the instability due to wave-wave interaction, nonlinear scattering, wave propagation, and collisional damping is considered. The effective mean free path is found self-consistently, using a simple model to estimate saturation level and scattering, and is shown to decrease with the temperature gradient length. The results, limited to the assumptions of the model, are applied to astrophysical systems. For some interstellar clouds the instability is found to be important. Collisional damping stabilizes the plasma, and the heat conduction can be dominated by superthermal electrons.

  4. Conduction electrons in acceptor-doped GaAs/GaAlAs heterostructures: a review

    NASA Astrophysics Data System (ADS)

    Zawadzki, Wlodek; Raymond, Andre; Kubisa, Maciej

    2016-05-01

    We review magneto-optical and magneto-transport effects in GaAs/GaAlAs heterostructures doped in GaAlAs barriers with donors, providing two-dimensional (2D) electron gas (2DEG) in GaAs quantum wells (QWS), and additionally doped with smaller amounts of acceptors (mostly Be atoms) in the vicinity of 2DEG. One may also deal with residual acceptors (mostly C atoms). The behavior of such systems in the presence of a magnetic field differs appreciably from those doped in the vicinity of 2DEG with donors. Three subjects related to the acceptor-doped heterostructures are considered. First is the problem of bound states of conduction electrons confined to the vicinity of negatively charged acceptors by the joint effect of a QW and an external magnetic field parallel to the growth direction. A variational theory of such states is presented, demonstrating that an electron turning around a repulsive center has discrete energies above the corresponding Landau levels. Experimental evidence for the discrete electron energies comes from the work on interband photo-magneto-luminescence, intraband cyclotron resonance and quantum magneto-transport (the Quantum Hall and Shubnikov-de Haas effects). An electron rain-down effect at weak electric fields and a boil-off effect at strong electric fields are introduced. It is demonstrated, both theoretically and experimentally, that a negatively charged acceptor can localize more than one electron. The second subject describes experiment and theory of asymmetric quantized Hall and Shubnikov-de Haas plateaus in acceptor-doped GaAs/GaAlAs heterostructures. It is shown that the main features of the plateau asymmetry can be attributed to asymmetric density of Landau states in the presence of acceptors. However, at high magnetic fields, the rain-down effect is also at work. The third subject deals with the so-called disorder modes (DMs) in the cyclotron resonance of conduction electrons. The DMs originate from random distributions of negatively

  5. Roles of the band filling and the d orbitals hybridization on the conduction and magnetism of some Sr-based double perovskites: An LSDA+ U study

    NASA Astrophysics Data System (ADS)

    Yousif, Salah Eldin Ashamallah; Yassin, O. A.

    2011-05-01

    We have systematically investigated the electronic structure and magnetic properties of the double perovskite oxides Sr 2CrZrO 6, Sr 2MnNbO 6, Sr 2FeMoO 6 and Sr 2NiRuO 6 in terms of band filling of different t 2g and e g orbitals. Calculations of density of the states (DOS) were performed within the frame of the local spin density approximation and Hubbard potential (LSDA+ U) employed in the Linear Muffin Tin Orbitals with Atomic Sphere Approximation (LMTO-ASA) method. The DOS of Sr 2FeMoO 6 was obtained and found to agree very well with published reports. Half-metallic character through the spin-down channel and the ferrimagnetic ordering was observed with notable hybridization among the 3d, p and 4d orbitals within Fermi level. A difference between the theoretically expected values and the calculated ones for the magnetic moment (Δ m) of the 3d orbitals is determined and had been found to increase on going from Sr 2CrZrO 6 to Sr 2NiRuO 6. This increment in Δ m indicates increment in the hybridization strength, which leads to long range ordering in Sr 2FeMoO 6 and Sr 2NiRuO 6 compounds. In comparison with reported experiments, the frustrated magnetism and weak ferrimagnetism states are the most possible ones in Sr 2CrZrO 6 in Sr 2MnNbO 6, respectively. The half-metallic character was also seen in Sr 2MnNbO 6 and Sr 2CrZrO 6 compounds while Sr 2NiRuO 6 shows normal metallic conduction and ferromagnetism in accordance with the superexchange interaction e g2-o-e g0 of Goodenough-Kanamori-Anderson (GKA).

  6. Importance of the tuning of band position in optimizing the electronic coupling and photocatalytic activity of nanocomposite

    SciTech Connect

    Jin, Xiaoyan; Mok, Eun Kyung; Baek, Ji-Won; Park, Sang-Hyun; Hwang, Seong-Ju

    2015-10-15

    The electronic coupling and photocatalytic activity of Ag{sub 2}CO{sub 3}–TiO{sub 2} nanocomposite can be optimized by the fine-tuning of the band position of titanium oxide with nitrogen doping. The increase of the valence band energy of TiO{sub 2} by N-doping leads not only to the enhanced absorption of visible light but also to the promoted hole transfer from Ag{sub 2}CO{sub 3} to TiO{sub 2}, resulting in the efficient spatial separation of photogenerated electrons and holes. While the undoped Ag{sub 2}CO{sub 3}–TiO{sub 2} nanocomposite shows an inferior photocatalytic activity to the pure Ag{sub 2}CO{sub 3}, the photocatalyst performance of N-doped nanocomposite is better than those of Ag{sub 2}CO{sub 3} and undoped Ag{sub 2}CO{sub 3}–TiO{sub 2} nanocomposite. This observation underscores a significant enhancement of the photocatalytic activity of nanocomposite upon N-doping, a result of enhanced electronic coupling between the hybridized species. The present results clearly demonstrate the importance of the fine-tuning of band position in optimizing the photocatalytic activity of hybrid-type photocatalysts. - Highlights: • The band position of Ag{sub 2}CO{sub 3}–TiO{sub 2} can be effectively tailored by nitrogen doping. • The N-doping leads to the improvement of charge separation. • The N-doped Ag{sub 2}CO{sub 3}–TiO{sub 2} shows high photocatalytic activity.

  7. Band calculation of lonsdaleite Ge

    NASA Astrophysics Data System (ADS)

    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.

  8. Kinetic Modeling of Electron Conduction-Driven Microinstabilities and Their Relevance for AGN Feedback

    NASA Astrophysics Data System (ADS)

    Roberg-Clark, Gareth; Swisdak, M.; Reynolds, Christopher S.; Drake, James

    2016-04-01

    Since the Intracluster Medium (ICM) is a weakly collisional plasma, the standard Spitzer conduction rate (which relies on collisionality) does not necessarily describe the transport of heat in clusters. In addition, many plasma microinstabilities become unstable at high beta since the magnetic field is easily pliable in the presence of induced pressure anisotropies. These properties imply that the true rate of conduction in an ICM-like plasma could be highly dependent on small-scale effects. We perform 2D kinetic Particle-In-Cell simulations and derive an analytic theory of a conduction-driven electron microinstability present in high-beta collisionless plasmas. We find that scattering by electromagnetic waves significantly reduces the conductive heat flux of electrons in our model. Our results have implications for 1) cool-core clusters in which AGN feedback may play a crucial role in maintaing overall thermodynamic stability, 2) heat flux suppression and scattering by other microinstabilities and 3) basic plasma physics questions that up until this point have not been explored fully.

  9. A mixed ionic and electronic conducting dual-phase membrane with high oxygen permeability.

    PubMed

    Fang, Wei; Liang, Fangyi; Cao, Zhengwen; Steinbach, Frank; Feldhoff, Armin

    2015-04-13

    To combine good chemical stability and high oxygen permeability, a mixed ionic-electronic conducting (MIEC) 75 wt% Ce(0.85)Gd(0.1)Cu(0.05)O(2-δ)-25 wt% La(0.6)Ca(0.4)FeO(3-δ)(CGCO-LCF) dual-phase membrane based on a MIEC-MIEC composite has been developed. Copper doping into Ce(0.9)Gd(0.1)O(2-δ) (CGO) oxide enhances both ionic and electronic conductivity, which then leads to a change from ionic conduction to mixed conduction at elevated temperatures. For the first time we demonstrate that an intergranular film with 2-10 nm thickness containing Ce, Ca, Gd, La, and Fe has been formed between the CGCO grains in the CGCO-LCF one-pot dual-phase membrane. A high oxygen permeation flux of 0.70 mL min(-1) cm(-2) is obtained by the CGCO-LCF one-pot dual-phase membrane with 0.5 mm thickness at 950 °C using pure CO2 as the sweep gas, and the membrane shows excellent stability in the presence of CO2 even at lower temperatures (800 °C) during long-term operation.

  10. Cu Doping in Ligand Free CdS Nanocrystals: Conductivity and Electronic Structure Study.

    PubMed

    Grandhi, G Krishnamurthy; Swathi, K; Narayan, K S; Viswanatha, Ranjani

    2014-07-03

    Ligand-free Cu-doped CdS nanocrystals (NCs) have been synthesized to elucidate their surface electronic structure. The Cu-doped ligand-free NCs unlike their undoped counterparts are shown to be luminescent. We used this Cu-related emission as a probe to study the nature of the surface trap states that results in negligible luminescence in the undoped NCs. The concentration of the sulfide ligands is shown to play a crucial role in the surface passivation of the NCs. Electrical conductivity of these NCs was also studied, and they were shown to exhibit significant conductivity of ∼10(-4) S cm(-1). Further we have shown that the electrical conductivity is closely correlated to the surface charge and hence the trap states of the individual NCs have far-reaching consequences in the device optimization.

  11. Control of Electronic Conduction at an Oxide Heterointerface using Surface Polar Adsorbates

    SciTech Connect

    Bell, Christopher

    2011-08-19

    We study the effect of the surface adsorption of a variety of common laboratory solvents on the conductivity at the interface between LaAlO{sub 3} and SrTiO{sub 3}. This interface possesses a range of intriguing physics, notably a proposed connection between the surface state of the LaAlO{sub 3} and the conductivity buried in the SrTiO{sub 3}. We show that the application of chemicals such as acetone, ethanol, and water can induce a large change (factor of three) in the conductivity. This phenomenon is observed only for polar solvents. These data provide experimental evidence for a general polarization-facilitated electronic transfer mechanism.

  12. Molecular design of electron transport with orbital rule: toward conductance-decay free molecular junctions.

    PubMed

    Tada, Tomofumi; Yoshizawa, Kazunari

    2015-12-28

    In this study, we report our viewpoint of single molecular conductance in terms of frontier orbitals. The orbital rule derived from orbital phase and amplitude is a powerful guideline for the qualitative understanding of molecular conductance in both theoretical and experimental studies. The essence of the orbital rule is the phase-related quantum interference, and on the basis of this rule a constructive or destructive pathway for electron transport is easily predicted. We have worked on the construction of the orbital rule for more than ten years and recently found from its application that π-stacked molecular junctions fabricated experimentally are in line with the concept for conductance-decay free junctions. We explain the orbital rule using benzene molecular junctions with the para-, meta- and ortho-connections and discuss linear π-conjugated chains and π-stacked molecular junctions with respect to their small decay factors in this manuscript.

  13. Electron and hole doping in the relativistic Mott insulator Sr2IrO4 : A first-principles study using band unfolding technique

    NASA Astrophysics Data System (ADS)

    Liu, Peitao; Reticcioli, Michele; Kim, Bongjae; Continenza, Alessandra; Kresse, Georg; Sarma, D. D.; Chen, Xing-Qiu; Franchini, Cesare

    2016-11-01

    We study the effects of dilute La and Rh substitutional doping on the electronic structure of the relativistic Mott insulator Sr2IrO4 using fully relativistic and magnetically noncollinear density functional theory with the inclusion of an on-site Hubbard U . To model doping effects, we have adopted the supercell approach, that allows for a realistic treatment of structural relaxations and electronic effects beyond a purely rigid band approach. By means of the band unfolding technique we have computed the spectral function and constructed the effective band structure and Fermi surface (FS) in the primitive cell, which are readily comparable with available experimental data. Our calculations clearly indicate that La and Rh doping can be interpreted as effective electron and (fractional) hole doping, respectively. We found that both electron and hole doping induce an insulating-to-metal transition (IMT) but with different characteristics. In Sr2 -xLaxIrO4 the IMT is accompanied by a moderate renormalization of the electronic correlation substantiated by a reduction of the effective on-site Coulomb repulsion U -J from 1.6 eV (x =0 ) to 1.4 eV (metallic regime of x =12.5 % ). The progressive closing of the relativistic Mott gap leads to the emergence of connected elliptical electron pockets at (π /2 ,π /2 ) and less intense features at X on the Fermi surface. The average ordered magnetic moment is slightly reduced upon doping, but the canted antiferromagnetic state is perturbed on the Ir-O planes located near the La atoms. The substitution of Ir with the nominally isovalent Rh is accompanied by a substantial hole transfer from the Rh site to the nearest-neighbor Ir sites. This shifts down the chemical potential, creates almost circular disconnected hole pockets in the FS, and establishes the emergence of a two-dimensional metallic state formed by conducting Rh planes intercalated by insulating Ir planes. Finally, our data indicate that hole doping causes a flipping

  14. Molecular and Electronic Structure of Cyclic Trinuclear Gold(I) Carbeniate Complexes: Insights for Structure/Luminescence/Conductivity Relationships

    SciTech Connect

    McDougaldJr, Roy N; Chilukuri, Bhaskar; Jia, Huiping; Perez, Michael R; Rabaa, Hassan; Wang, Xiaoping; Nesterov, Vladimir; Cundari, Thomas R.; Gnade, Bruce E; Omary, Mohammad A

    2014-01-01

    An experimental and computational study of correlations between solid-state structure and optical/electronic properties of cyclotrimeric gold(I) carbeniates, [Au-3(RN=COR')(3)] (R, R' = H, Me, Bu-n, or (c)Pe), is reported. Synthesis and structural and photophysical characterization of novel complexes [Au-3(MeN=(COBu)-Bu-n)(3)], [Au-3((BuN)-Bu-n=COMe)(3)], [Au-3((BuN)-Bu-n=(COBu)-Bu-n)(3)], and [Au-3((c)PeN=COMe)(3)] are presented. Changes in R and R' lead to distinctive variations in solid-state stacking, luminescence spectra, and conductive properties. Solid-state emission and excitation spectra for each complex display a remarkable dependence on the solid-state packing of the cyclotrimers. The electronic structure of [Au-3(RN=COR')(3)] was investigated via molecular and solid-state simulations. Calculations on [Au-3(HN=COH)(3)] models indicate that the infinitely extended chain of eclipsed structures with equidistant Au-Au intertrimer aurophilic bonding can have lower band gaps, smaller Stokes shifts, and reduced reorganization energies (lambda). The action of one cyclotrimer as a molecular nanowire is demonstrated via fabrication of an organic field effect transistor and shown to produce a p-type field effect. Hole transport for the same cyclotrimer-doped within a poly(9-vinylcarbazole) host-produced a colossal increase in current density from similar to 1 to similar to 1000 mA/cm(2). Computations and experiments thus delineate the complex relationships between solid-state morphologies, electronic structures, and optoelectronic properties of gold(I) carbeniates.

  15. The electrically conductive pili of Geobacter species are a recently evolved feature for extracellular electron transfer

    PubMed Central

    Dang, Yan; Walker, David J. F.; Lovley, Derek R.

    2016-01-01

    The electrically conductive pili (e-pili) of Geobactersulfurreducens have environmental and practical significance because they can facilitate electron transfer to insoluble Fe(III) oxides; to other microbial species; and through electrically conductive biofilms. E-pili conductivity has been attributed to the truncated PilA monomer, which permits tight packing of aromatic amino acids to form a conductive path along the length of e-pili. In order to better understand the evolution and distribution of e-pili in the microbial world, type IVa PilA proteins from various Gram-negative and Gram-positive bacteria were examined with a particular emphasis on Fe(III)-respiring bacteria. E-pilin genes are primarily restricted to a tight phylogenetic group in the order Desulfuromonadales. The downstream gene in all but one of the Desulfuromonadales that possess an e-pilin gene is a gene previously annotated as ‘pilA–C’ that has characteristics suggesting that it may encode an outer-membrane protein. Other genes associated with pilin function are clustered with e-pilin and ‘pilA–C’ genes in the Desulfuromonadales. In contrast, in the few bacteria outside the Desulfuromonadales that contain e-pilin genes, the other genes required for pilin function may have been acquired through horizontal gene transfer. Of the 95 known Fe(III)-reducing micro-organisms for which genomes are available, 80 % lack e-pilin genes, suggesting that e-pili are just one of several mechanisms involved in extracellular electron transport. These studies provide insight into where and when e-pili are likely to contribute to extracellular electron transport processes that are biogeochemically important and involved in bioenergy conversions. PMID:28348867

  16. Model GW determination of band gaps and electronic properties of strained layer InAsSb/InAs superlattices

    NASA Astrophysics Data System (ADS)

    Mannstadt, W.; Asahi, R.; Freeman, A. J.; Picozzi, S.; Continenza, A.

    1998-03-01

    A strong interest is still devoted to the InAs_1-xSb_x/InAs(111) system due to the opportunity to tune the band gap as a function of the growth conditions. Lattice mismatch, strain, alloy composition and layers thickness determine the electronic and transport properies of these systems. We investigated this system using our full-potential linearized augmented plane wave (FLAPW) method for thin films (Wimmer,Krakauer,Weinert and A.J.Freeman, Phys.Rev.B24, 864 (1981)) and bulk solids, to study overlayers, sandwiches and superlattices. Our method includes atomic force and total energy determinations of the equilibrium structures, as well as the model GW approximation(F.Gygi and A.Baldereschi, Phys.Rev.Lett. 62, 2160 (1989)) to obtain accurate band gaps. This allows us to investigate the influence of strain, structural relaxation and alloying on the electronic structure and the band gap. Results for bulk InAs, InSb and InAs_1-xSb_x, at different x compositions and for ordered superlattices will be presented.

  17. 2D Tl-Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure.

    PubMed

    Gruznev, D V; Bondarenko, L V; Tupchaya, A Y; Eremeev, S V; Mihalyuk, A N; Chou, J P; Wei, C M; Zotov, A V; Saranin, A A

    2017-01-25

    Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl-Pb compounds on Ge(1 1 1), [Formula: see text]-(Tl, Pb) and [Formula: see text]-(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound is almost identical to the alike (Tl, Pb)/Si(1 1 1)[Formula: see text] system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound contains six Tl atoms and seven Pb atoms per [Formula: see text] unit cell (i.e.  ∼0.67 ML Tl and  ∼0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] and (Tl, Pb)/Ge(1 1 1)[Formula: see text] compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1)[Formula: see text], these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

  18. 2D Tl-Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure

    NASA Astrophysics Data System (ADS)

    Gruznev, D. V.; Bondarenko, L. V.; Tupchaya, A. Y.; Eremeev, S. V.; Mihalyuk, A. N.; Chou, J. P.; Wei, C. M.; Zotov, A. V.; Saranin, A. A.

    2017-01-01

    Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl-Pb compounds on Ge(1 1 1), \\sqrt{3}× \\sqrt{3} -(Tl, Pb) and 3× 3 -(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1)\\sqrt{3}× \\sqrt{3} compound is almost identical to the alike (Tl, Pb)/Si(1 1 1)\\sqrt{3}× \\sqrt{3} system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1)3× 3 compound contains six Tl atoms and seven Pb atoms per 3× 3 unit cell (i.e.  ˜0.67 ML Tl and  ˜0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1)\\sqrt{3}× \\sqrt{3} and (Tl, Pb)/Ge(1 1 1)3× 3 compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1)\\sqrt{3}× \\sqrt{3} , these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

  19. Electron transport and Goos-Hänchen shift in graphene with electric and magnetic barriers: optical analogy and band structure

    NASA Astrophysics Data System (ADS)

    Sharma, Manish; Ghosh, Sankalpa

    2011-02-01

    Transport of massless Dirac fermions in graphene monolayers is analysed in the presence of a combination of singular magnetic barriers and applied electrostatic potential. Extending a recently proposed (Ghosh and Sharma 2009 J. Phys.: Condens. Matter 21 292204) analogy between the transmission of light through a medium with modulated refractive index and electron transmission in graphene through singular magnetic barriers to the present case, we find the addition of a scalar potential profoundly changes the transmission. We calculate the quantum version of the Goos-Hänchen shift that the electron wave suffers upon being totally reflected by such barriers. The combined electric and magnetic barriers substantially modify the band structure near the Dirac point. This affects transport near the Dirac point significantly and has important consequences for graphene-based electronics.

  20. Electronic band structure for occupied and unoccupied states of the natural topological superlattice phase Sb2Te

    NASA Astrophysics Data System (ADS)

    Khalil, L.; Papalazarou, E.; Caputo, M.; Nilforoushan, N.; Perfetti, L.; Taleb-Ibrahimi, A.; Kandyba, V.; Barinov, A.; Gibson, Q. D.; Cava, R. J.; Marsi, M.

    2017-02-01

    We present an experimental study describing the effects of surface termination on the electronic structure of the natural topological superlattice phase Sb2Te . Using scanning angle-resolved photoemission microscopy, we consistently find various nonequivalent regions on the same surface after cleaving various Sb2Te single crystals. We were able to identify three distinct terminations characterized by different Sb/Te surface stoichiometric ratios and with clear differences in their band structure. For the dominating Te-rich termination, we also provide a direct observation of the excited electronic states and of their relaxation dynamics by means of time-resolved angle-resolved photoemission spectroscopy. Our results clearly indicate that the surface electronic structure is strongly affected by the bulk properties of the superlattice.