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Sample records for electronic energy band

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Quest for band renormalization and self-energy in correlated f-electron systems

    SciTech Connect

    Durakiewicx, Tomasz

    2009-01-01

    Coexisting energy scales are observed in f-electron materials. Information about some of the low-energy scales is imprinted in the electron self-energy which can be measured by angle-resolved photoemission (ARPES). Such measurements in d-electron materials over the last decade were based on high energy- and momentum-resolution ARPES techniques used to extract the self-energy information from measured spectra. Simultaneously, many-body theoretical approaches have been developed to find a link between self-energy and many-body interactions. Here we show the transcription of such methods from d-electrons to f-electrons by presenting the first example of low energy scales in f-electron material USb{sub 2}, measured with synchrotron-based ARPES. Proposed approach will help in answering the fundamental questions about the complex nature of the heavy fermion state.

  16. 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.

  17. 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.

  18. Transition metal d -band occupancy in skutterudites studied by electron energy-loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Prytz, Ø.; Taftø, J.; Ahn, C. C.; Fultz, B.

    2007-03-01

    The transition-metal 3d occupancy of a series of thermoelectric skutterudites is investigated using electron energy-loss spectroscopy. We find that bonding causes an emptying of the 3d states in the binary skutterudites CoP3 , CoAs3 , CoSb3 , and NiP3 , while compared to the pure Fe the 3d occupancy in LaFe4P12 is significantly increased, consistent with the idea that each interstitial La atom (rattler) donates three electrons to compensate for missing valence electron of Fe as compared to Co. These experimental results are in agreement with previous models suggesting a predominantly covalent bonding between transition metal and pnictogen atoms in skutterudites, and provide evidence of charge transfer from La to the Fe-P complex in LaFe4P12 .

  19. 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.

  20. Design study of an S-band RF cavity of a dual-energy electron LINAC for the CIS

    NASA Astrophysics Data System (ADS)

    Lee, Byeong-No; Park, Hyungdal; Song, Ki-baek; Li, Yonggui; Lee, Byung Cheol; Cha, Sung-su; Lee, Jong-Chul; Shin, Seung-Wook; Chai, Jong-seo

    2014-01-01

    The design of a resonance frequency (RF) cavity for the dual-energy S-band electron linear accelerator (LINAC) has been carried out for the cargo inspection system (CIS). This Standing-wave-type RF cavity is operated at a frequency under the 2856-MHz resonance frequency and generates electron beams of 9 MeV (high mode) and 6 MeV (low mode). The electrons are accelerated from the initial energy of the electron gun to the target energy (9 or 6 MeV) inside the RF cavity by using the RF power transmitted from a 5.5-MW-class klystron. Then, electron beams with a 1-kW average power (both high mode and low mode) bombard an X-ray target a 2-mm spot size. The proposed accelerating gradient was 13 MV/m, and the designed Q value was about 7100. On going research on 15-MeV non-destructive inspections for military or other applications is presented.

  1. 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.

  2. Absolutely continuous energy bands in the electronic spectrum of quasiperiodic ladder networks

    NASA Astrophysics Data System (ADS)

    Pal, Biplab; Chakrabarti, Arunava

    2014-06-01

    The energy spectra of quasi-one-dimensional quasiperiodic ladder networks are analyzed within a tight binding description. In particular, we show that if a selected set of sites in each strand of a ladder is tunnel-coupled to quantum dots attached from a side, absolutely continuous subbands can be generated in the spectrum if one tunes the dot potential and the dot-strand coupling appropriately. Typical cases with two and three strand Fibonacci ladders in the off-diagonal model are discussed in details. We also discuss the possibility of re-entrant insulator-metal transition for a general n-strand ladder network when n becomes large. The observations remain valid even in the case of a disordered ladder network with the same constituents. The results are analytically exact.

  3. Calculation of the Energy-Band Structure of the Kronig-Penney Model Using the Nearly-Free and Tightly-Bound-Electron Approximations

    ERIC Educational Resources Information Center

    Wetsel, Grover C., Jr.

    1978-01-01

    Calculates the energy-band structure of noninteracting electrons in a one-dimensional crystal using exact and approximate methods for a rectangular-well atomic potential. A comparison of the two solutions as a function of potential-well depth and ratio of lattice spacing to well width is presented. (Author/GA)

  4. A shock-tube determination of the CN ground state dissociation energy and electronic transition moments for the CN violet and red band systems

    NASA Technical Reports Server (NTRS)

    Arnold, J. O.; Nicholls, R. W.

    1973-01-01

    The CN ground state dissociation energy and the sum of squares of the electronic transition moments of the CN violet bands have been simultaneously determined from spectral emission measurements behind incident shock waves. The unshocked test gases were composed of various CO2-CO-N2-Ar mixtures, and the temperatures behind the incident shocks ranged from 3500 to 8000 K. The variation of the electronic transition moment with internuclear separation was found to be small for both the CN violet and red band systems.

  5. Reconstructing the energy band electronic structure of pulsed laser deposited CZTS thin films intended for solar cell absorber applications

    NASA Astrophysics Data System (ADS)

    Pandiyan, Rajesh; Oulad Elhmaidi, Zakaria; Sekkat, Zouheir; Abd-lefdil, Mohammed; El Khakani, My Ali

    2017-02-01

    We report here on the use of pulsed KrF-laser deposition (PLD) technique for the growth of high-quality Cu2ZnSnS4 (CZTS) thin films onto Si, and glass substrates without resorting to any post sulfurization process. The PLD-CZTS films were deposited at room temperature (RT) and then subjected to post annealing at different temperatures ranging from 200 to 500 °C in Argon atmosphere. The X-ray diffraction and Raman spectroscopy confirmed that the PLD films crystallize in the characteristic kesterite CZTS structure regardless of their annealing temperature (Ta), but their crystallinity is much improved for Ta ≥ 400 °C. The PLD-CZTS films were found to exhibit a relatively dense morphology with a surface roughness (RMS) that increases with Ta (from ∼14 nm at RT to 70 nm at Ta = 500 °C with a value around 40 nm for Ta = 300-400 °C). The optical bandgap of the PLD-CZTS films, was derived from UV-vis transmission spectra analysis, and found to decrease from 1.73 eV for non-annealed films to ∼1.58 eV for those annealed at Ta = 300 °C. These band gap values are very close to the optimum value needed for an ideal solar cell absorber. In order to achieve a complete reconstruction of the one-dimensional energy band structure of these PLD-CZTS absorbers, we have combined both XPS and UPS spectroscopies to determine their chemical bondings, the position of their valence band maximum (relative to Fermi level), and their work function values. This enabled us to sketch out, as accurately as possible, the band alignment of the heterojunction interface formed between CZTS and both CdS and ZnS buffer layer materials.

  6. Theoretical study on electronic structure of bathocuproine: Renormalization of the band gap in the crystalline state and the large exciton binding energy

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Susumu; Hatada, Shin-No-Suke; Morikawa, Yoshitada

    Bathocuproine (BCP) is a promising organic material of a hole blocking layer in organic light-emitting diodes or an electron buffer layer in organic photovoltaic cells. The nature of the unoccupied electronic states is a key characteristic of the material, which play vital roles in the electron transport. To elucidate the electronic properties of the molecular or crystalline BCP, we use the GW approximation for calculation of the fundamental gap, and the long-range corrected density functional theory for the molecular optical absorption. It is found that the band gap of the BCP single crystal is 4.39 eV, and it is in agreement with the recent low-energy inverse photoemission spectroscopy measurement. The polarization energy is estimated to be larger than 1 eV, demonstrating the large polarization effects induced by the electronic clouds surrounding the injected charge. The theoretical optical absorption energy is 3.68 eV, and the exciton binding energy is estimated to be 0.71 eV, implying the large binding in the eletron-hole pair distributed around the small part of the molecular region. This work was supported by the Grants-in-Aid for Young Scientists (B) (No. 26810009), and for Scientific Research on Innovative Areas ``3D Active-Site Science'' (No. 26105011) from Japan Society for the Promotion of Science.

  7. Probing optical band gaps at the nanoscale in NiFe₂O₄ and CoFe₂O₄ epitaxial films by high resolution electron energy loss spectroscopy

    SciTech Connect

    Dileep, K.; Loukya, B.; Datta, R.; Pachauri, N.; Gupta, A.

    2014-09-14

    Nanoscale optical band gap variations in epitaxial thin films of two different spinel ferrites, i.e., NiFe₂O₄ (NFO) and CoFe₂O₄ (CFO), have been investigated by spatially resolved high resolution electron energy loss spectroscopy. Experimentally, both NFO and CFO show indirect/direct band gaps around 1.52 eV/2.74 and 2.3 eV, and 1.3 eV/2.31 eV, respectively, for the ideal inverse spinel configuration with considerable standard deviation in the band gap values for CFO due to various levels of deviation from the ideal inverse spinel structure. Direct probing of the regions in both the systems with tetrahedral A site cation vacancy, which is distinct from the ideal inverse spinel configuration, shows significantly smaller band gap values. The experimental results are supported by the density functional theory based modified Becke-Johnson exchange correlation potential calculated band gap values for the different cation configurations.

  8. High energy electron irradiation of interstellar carbonaceous dust analogs: Cosmic ray effects on the carriers of the 3.4 µm absorption band.

    PubMed

    Maté, Belén; Molpeceres, Germán; Jiménez-Redondo, Miguel; Tanarro, Isabel; Herrero, Víctor J

    2016-11-01

    The effects of cosmic rays on the carriers of the interstellar 3.4 μm absorption band have been investigated in the laboratory. This band is attributed to stretching vibrations of CH3 and CH2 in carbonaceous dust. It is widely observed in the diffuse interstellar medium (ISM), but disappears in dense clouds. Destruction of CH3 and CH2 by cosmic rays could become relevant in dense clouds, shielded from the external ultraviolet field. For the simulations, samples of hydrogenated amorphous carbon (a-C:H) have been irradiated with 5 keV electrons. The decay of the band intensity vs electron fluence reflects a-C:H dehydrogenation, which is well described by a model assuming that H2 molecules, formed by the recombination of H atoms liberated through CH bond breaking, diffuse out of the sample. The CH bond destruction rates derived from the present experiments are in good accordance with those from previous ion irradiation experiments of HAC. The experimental simplicity of electron bombardment has allowed the use of higher energy doses than in the ion experiments. The effects of cosmic rays on the aliphatic components of cosmic dust are found to be small. The estimated cosmic ray destruction times for the 3.4 μm band carriers lie in the 10(8) yr range and cannot account for the disappearance of this band in dense clouds, which have characteristic lifetimes of 3 × 10(7) yr. The results invite a more detailed investigation of the mechanisms of CH bond formation and breaking in the intermediate region between diffuse and dense clouds.

  9. High energy electron irradiation of interstellar carbonaceous dust analogs: Cosmic ray effects on the carriers of the 3.4 µm absorption band

    PubMed Central

    Maté, Belén; Molpeceres, Germán; Jiménez-Redondo, Miguel; Tanarro, Isabel; Herrero, Víctor J.

    2017-01-01

    The effects of cosmic rays on the carriers of the interstellar 3.4 μm absorption band have been investigated in the laboratory. This band is attributed to stretching vibrations of CH3 and CH2 in carbonaceous dust. It is widely observed in the diffuse interstellar medium (ISM), but disappears in dense clouds. Destruction of CH3 and CH2 by cosmic rays could become relevant in dense clouds, shielded from the external ultraviolet field. For the simulations, samples of hydrogenated amorphous carbon (a-C:H) have been irradiated with 5 keV electrons. The decay of the band intensity vs electron fluence reflects a-C:H dehydrogenation, which is well described by a model assuming that H2 molecules, formed by the recombination of H atoms liberated through CH bond breaking, diffuse out of the sample. The CH bond destruction rates derived from the present experiments are in good accordance with those from previous ion irradiation experiments of HAC. The experimental simplicity of electron bombardment has allowed the use of higher energy doses than in the ion experiments. The effects of cosmic rays on the aliphatic components of cosmic dust are found to be small. The estimated cosmic ray destruction times for the 3.4 μm band carriers lie in the 108 yr range and cannot account for the disappearance of this band in dense clouds, which have characteristic lifetimes of 3 × 107 yr. The results invite a more detailed investigation of the mechanisms of CH bond formation and breaking in the intermediate region between diffuse and dense clouds. PMID:28133388

  10. High-energy Electron Irradiation of Interstellar Carbonaceous Dust Analogs: Cosmic-ray Effects on the Carriers of the 3.4 μm Absorption Band

    NASA Astrophysics Data System (ADS)

    Maté, Belén; Molpeceres, Germán; Jiménez-Redondo, Miguel; Tanarro, Isabel; Herrero, Víctor J.

    2016-11-01

    The effects of cosmic rays on the carriers of the interstellar 3.4 μm absorption band have been investigated in the laboratory. This band is attributed to stretching vibrations of CH3 and CH2 in carbonaceous dust. It is widely observed in the diffuse interstellar medium, but disappears in dense clouds. Destruction of CH3 and CH2 by cosmic rays could become relevant in dense clouds, shielded from the external ultraviolet field. For the simulations, samples of hydrogenated amorphous carbon (a-C:H) have been irradiated with 5 keV electrons. The decay of the band intensity versus electron fluence reflects a-C:H dehydrogenation, which is well described by a model assuming that H2 molecules, formed by the recombination of H atoms liberated through CH bond breaking, diffuse out of the sample. The CH bond destruction rates derived from the present experiments are in good accordance with those from previous ion irradiation experiments of HAC. The experimental simplicity of electron bombardment has allowed the use of higher-energy doses than in the ion experiments. The effects of cosmic rays on the aliphatic components of cosmic dust are found to be small. The estimated cosmic-ray destruction times for the 3.4 μm band carriers lie in the 108 yr range and cannot account for the disappearance of this band in dense clouds, which have characteristic lifetimes of 3 × 107 yr. The results invite a more detailed investigation of the mechanisms of CH bond formation and breaking in the intermediate region between diffuse and dense clouds.

  11. Energy ranges and pitch angles of outer radiation belt electrons depleted by an intense dayside hydrogen band EMIC wave event on February 23, 2014

    NASA Astrophysics Data System (ADS)

    Engebretson, M. J.; Posch, J. L.; Huang, C. L.; Kanekal, S. G.; Fok, M. C. H.; Rodger, C. J.; Smith, C. W.; Spence, H. E.; Baker, D. N.; Kletzing, C.; Wygant, J. R.

    2015-12-01

    Although most studies of the effect of EMIC waves on relativistic electrons have focused on wave events in the afternoon sector in the outer plasmasphere or plume region, strong magnetospheric compressions provide an additional stimulus for EMIC wave generation across a large range of local times and L shells. We present here observations of the effects of an intense, long-duration hydrogen band EMIC wave event on February 23, 2014 that was stimulated by a gradual 4-hour rise and subsequent sharp increases in solar wind pressure. Large-amplitude linearly polarized hydrogen band EMIC waves (up to 25 nT p-p) that included triggered emissions appeared for over 4 hours at both Van Allen Probes while these spacecraft were outside the plasmapause, in a region with densities ~5-20 cm-3, as they passed near apogee from late morning through local noon. Observations of radiation belt electrons by the REPT and MagEIS instruments on these spacecraft showed that these waves caused significant depletions of more field-aligned electrons at ultrarelativistic energies from 5.2 MeV down to ~2 MeV, and some depletions at energies down to below 1 MeV as well.

  12. 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.

  13. 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.

  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. Toward Revealing the Critical Role of Perovskite Coverage in Highly Efficient Electron-Transport Layer-Free Perovskite Solar Cells: An Energy Band and Equivalent Circuit Model Perspective.

    PubMed

    Huang, Like; Xu, Jie; Sun, Xiaoxiang; Du, Yangyang; Cai, Hongkun; Ni, Jian; Li, Juan; Hu, Ziyang; Zhang, Jianjun

    2016-04-20

    Currently, most efficient perovskite solar cells (PVKSCs) with a p-i-n structure require simultaneously electron transport layers (ETLs) and hole transport layers (HTLs) to help collecting photogenerated electrons and holes for obtaining high performance. ETL free planar PVKSC is a relatively new and simple structured solar cell that gets rid of the complex and high temperature required ETL (such as compact and mesoporous TiO2). Here, we demonstrate the critical role of high coverage of perovskite in efficient ETL free PVKSCs from an energy band and equivalent circuit model perspective. From an electrical point of view, we confirmed that the low coverage of perovskite does cause localized short circuit of the device. With coverage optimization, a planar p-i-n(++) device with a power conversion efficiency of over 11% was achieved, implying that the ETL layer may not be necessary for an efficient device as long as the perovskite coverage is approaching 100%.

  16. 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.

  17. 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.

  18. Direct band gap measurement of Cu(In,Ga)(Se,S){sub 2} thin films using high-resolution reflection electron energy loss spectroscopy

    SciTech Connect

    Heo, Sung; Lee, Hyung-Ik; Park, Jong-Bong; Ko, Dong-Su; Chung, JaeGwan; Kim, KiHong; Kim, Seong Heon; Yun, Dong-Jin; Ham, YongNam; Park, Gyeong Su; Song, Taewon; Lee, Dongho Nam, Junggyu; Kang, Hee Jae; Choi, Pyung-Ho; Choi, Byoung-Deog

    2015-06-29

    To investigate the band gap profile of Cu(In{sub 1−x},Ga{sub x})(Se{sub 1−y}S{sub y}){sub 2} of various compositions, we measured the band gap profile directly as a function of in-depth using high-resolution reflection energy loss spectroscopy (HR-REELS), which was compared with the band gap profile calculated based on the auger depth profile. The band gap profile is a double-graded band gap as a function of in-depth. The calculated band gap obtained from the auger depth profile seems to be larger than that by HR-REELS. Calculated band gaps are to measure the average band gap of the spatially different varying compositions with respect to considering its void fraction. But, the results obtained using HR-REELS are to be affected by the low band gap (i.e., out of void) rather than large one (i.e., near void). Our findings suggest an analytical method to directly determine the band gap profile as function of in-depth.

  19. Energy band alignment at the nanoscale

    NASA Astrophysics Data System (ADS)

    Deuermeier, Jonas; Fortunato, Elvira; Martins, Rodrigo; Klein, Andreas

    2017-01-01

    The energy band alignments at interfaces often determine the electrical functionality of a device. Along with the size reduction into the nanoscale, functional coatings become thinner than a nanometer. With the traditional analysis of the energy band alignment by in situ photoelectron spectroscopy, a critical film thickness is needed to determine the valence band offset. By making use of the Auger parameter, it becomes possible to determine the energy band alignment to coatings, which are only a few Ångström thin. This is demonstrated with experimental data of Cu2O on different kinds of substrate materials.

  20. Electroabsorption Spectroscopy Measurements of the Exciton Binding Energy, ElectronHole Reduced Effective Mass, and Band Gap in the Perovskite CHsub3NHsub3PbIsub3

    DTIC Science & Technology

    2016-07-28

    evidence that the primary photoexcitations (as opposed to recombination mechanisms ) can be described in terms of free carrier generation as transitions to a...Electroabsorption Spectroscopy Measurements of the Exciton Binding Energy , Electron−Hole Reduced Effective Mass, and Band Gap in the Perovskite...98195-1700, United States *S Supporting Information ABSTRACT: We use electroabsorption (EA) spectroscopy to measure the exciton binding energy (EB

  1. Mapping the Copper energy band using the quantum well states

    NASA Astrophysics Data System (ADS)

    Wu, J.; Choi, J.; Owens, T.; Qiu, Z. Q.; Rotenberg, E.; Smith, N. V.

    2006-03-01

    Quantum well states (QWS) of copper electrons in Cu/Co/Cu(100) system are investigated using Angle Resolved Photoemission Electron Spectroscopy (ARPES). The samples were grown epitaxially at room temperature and measured in situ at beamlime 7 of the Advanced Light Source (ALS). Photoemission intensity oscillates with both the electron energy and the Cu film thickness. By counting the thickness oscillation periodicity at a given energy, we can determine the out-of-plane electron momentum without the need of the phase value in the phase accumulation model. This allows the experimental determination of the E-k relation (energy band) for the Cu film. We here report the Cu energy band determined in this way at different in-plane momentum. In addition, by fitting the oscillation as a function of the Cu thickness, we also determined the phase value of the quantization condition as a function of the energy and in-plane momentum.

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

    PubMed

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

    2016-07-05

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

  3. 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.

  4. Observation of mini-band formation in the ground and high-energy electronic states of super-lattice solar cells

    NASA Astrophysics Data System (ADS)

    Usuki, Takanori; Matsuochi, Kouki; Nakamura, Tsubasa; Toprasertpong, Kasidit; Fukuyama, Atsuhiko; Sugiyama, Masakazu; Nakano, Yoshiaki; Ikari, Tetsuo

    2016-03-01

    Multiple Quantum wells (MQWs) have been studied as one promising material for high-efficiency nextgeneration solar cells. However, a portion of photo-excited carriers recombine in MQWs, resulting in the degradation of cell performance. Super-lattice (SL) structures, where quantum states in neighboring quantum wells strongly couple with each other, have been proposed for the carrier collection improvement via the tunneling transport through mini-bands. Therefore, it is important to characterize mini-band formation in various types of SL structures. We examined p-i-n GaAs-based solar cells whose i layers contain 20 stacks of InGaAs/GaAsP MQW structures with 2.1-nm GaAsP barriers (thin-barrier cell), with 2.1-nm barriers and 3-nm GaAs interlayers in between GaAsP barriers and InGaAs wells (stepbarrier cell), and with 7.8-nm barriers (thick-barrier cell). We investigated the optical absorption spectra of the SL solar cells using piezoelectric photo-thermal (PPT) spectroscopy. In the thick-barrier cell, one exciton peak was observed near the absorption edge of MQWs. On the other hand, we confirmed a split of the exciton peak for the thin-barrier SL, suggesting the formation of mini-band. Moreover, in the step-barrier cell, the mini-band at the ground state disappears since thick GaAs interlayers isolate each quantum-well ground state and, instead, the mini-band formation of highenergy states could be observed. By estimating from the energy-level calculation, this is attributed to the mini-band formation of light-hole states. This can well explain the improvement of carrier collection efficiency (CCE) of the thinbarrier and the step-barrier cells compared with the thick-barrier cell.

  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. 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.

  7. High energy electron cooling

    SciTech Connect

    Parkhomchuk, V.

    1997-09-01

    High energy electron cooling requires a very cold electron beam. The questions of using electron cooling with and without a magnetic field are presented for discussion at this workshop. The electron cooling method was suggested by G. Budker in the middle sixties. The original idea of the electron cooling was published in 1966. The design activities for the NAP-M project was started in November 1971 and the first run using a proton beam occurred in September 1973. The first experiment with both electron and proton beams was started in May 1974. In this experiment good result was achieved very close to theoretical prediction for a usual two component plasma heat exchange.

  8. 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).

  9. Energy bands and gaps near an impurity

    NASA Astrophysics Data System (ADS)

    Mihóková, E.; Schulman, L. S.

    2016-10-01

    It has been suggested that in the neighborhood of a certain kind of defect in a crystal there is a bend in the electronic band. We confirm that this is indeed possible using the Kronig-Penney model. Our calculations also have implications for photonic crystals.

  10. 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.

  11. The Torsion-Inversion-Bending Energy Levels in the S1( n, π*) Electronic State of Acetaldehyde . A High-Resolution Study of the Bands #7 to #20 in the Jet-Cooled Fluorescence Excitation Spectrum

    NASA Astrophysics Data System (ADS)

    Liu, Haisheng; Lim, Edward C.; Niño, Alfonso; Muñoz-Caro, Camelia; Judge, Richard H.; Moule, David C.

    1998-07-01

    The band assignments and analyses of the jet-cooled high-resolution laser-induced fluorescence excitation spectrum of acetaldehyde that results from theS1(n, π*) electronic state have been extended to +600 cm-1from the 000system origin. The new assignments start at Band #7 and finish at Band #21. Bands #8 and #9, originally assigned to 1420, have now been assigned to 1530. The assignments of the lower energy bands remain unaltered. The origins of the bands that involve the torsional modes ν15(v= 1 to 4) in combination with the wagging mode ν14(v= 1 and 2) and the ν10(v= 1) were determined by analyses with a rigid rotational Hamiltonian. These origins were fitted to a set of levels that were derived from a torsion-wagging-bending Hamiltonian that employed flexible large amplitude coordinates. The resulting potential surface was found to have barriers to torsion and inversion of 712.5 and 638.6 cm-1, respectively, with minima in the potential hypersurface at θ = 59.9° and α = 33.5° for the torsion and wagging coordinates.

  12. Eastern Band of Cherokee Strategic Energy Plan

    SciTech Connect

    Souther Carolina Institute of energy Studies-Robert Leitner

    2009-01-30

    The Eastern Band of Cherokee Indians was awarded a grant under the U.S. Department of Energy Tribal Energy Program (TEP) to develop a Tribal Strategic Energy Plan (SEP). The grant, awarded under the “First Steps” phase of the TEP, supported the development of a SEP that integrates with the Tribe’s plans for economic development, preservation of natural resources and the environment, and perpetuation of Tribal heritage and culture. The Tribe formed an Energy Committee consisting of members from various departments within the Tribal government. This committee, together with its consultant, the South Carolina Institute for Energy Studies, performed the following activities: • Develop the Tribe’s energy goals and objectives • Establish the Tribe’s current energy usage • Identify available renewable energy and energy efficiency options • Assess the available options versus the goals and objectives • Create an action plan for the selected options

  13. Experimental study of energy harvesting in UHF band

    NASA Astrophysics Data System (ADS)

    Bernacki, Ł.; Gozdur, R.; Salamon, N.

    2016-04-01

    A huge progress of down-sizing technology together with trend of decreasing power consumption and, on the other hand, increasing efficiency of electronics give the opportunity to design and to implement the energy harvesters as main power sources. This paper refers to the energy that can be harvested from electromagnetic field in the unlicensed frequency bands. The paper contains description of the most popular techniques and transducers that can be applied in energy harvesting domain. The overview of current research and commercial solutions was performed for bands in ultra-high frequency range, which are unlicensed and where transmission is not limited by administrative arrangements. During the experiments with Powercast’s receiver, the same bands as sources of electromagnetic field were taken into account. This power source is used for conducting radio-communication process and excess energy could be used for powering the extra electronic circuits. The paper presents elaborated prototype of energy harvesting system and the measurements of power harvested in ultra-high frequency range. The evaluation of RF energy harvesters for powering ultra-low power (ULP) electronic devices was performed based on survey and results of the experiments.

  14. 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.

  15. 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.

  16. Ionization By Impact Electrons in Solids: Electron Mean Free Path Fitted Over A Wide Energy Range

    SciTech Connect

    Ziaja, B; London, R A; Hajdu, J

    2005-06-09

    We propose a simple formula for fitting the electron mean free paths in solids both at high and at low electron energies. The free-electron-gas approximation used for predicting electron mean free paths is no longer valid at low energies (E < 50 eV), as the band structure effects become significant at those energies. Therefore we include the results of the band structure calculations in our fit. Finally, we apply the fit to 9 elements and 2 compounds.

  17. 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.

  18. 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

  19. 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

  20. 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.

  1. Ultrafast laser-induced modifications of energy bands of non-metal crystals

    NASA Astrophysics Data System (ADS)

    Gruzdev, Vitaly

    2009-10-01

    Ultrafast laser-induced variations of electron energy bands of transparent solids significantly influence ionization and conduction-band electron absorption driving the initial stage of laser-induced damage (LID). The mechanisms of the variations are attributed to changing electron functions from bonding to anti-bonding configuration via laser-induced ionization; laser-driven electron oscillations in quasi-momentum space; and direct distortion of the inter-atomic potential by electric field of laser radiation. The ionization results in the band-structure modification via accumulation of broken chemical bonds between atoms and provides significant contribution to the overall modification only when enough excited electrons are accumulated in the conduction band. The oscillations are associated with modification of electron energy by pondermotive potential of the oscillations. The direct action of radiation's electric field leads to specific high-frequency Franz-Keldysh effect (FKE) spreading the allowed electron states into the bands of forbidden energy. Those processes determine the effective band gap that is a laser-driven energy gap between the modified electron energy bands. Among those mechanisms, the latter two provide reversible band-structure modification that takes place from the beginning of the ionization and are, therefore, of special interest due to their strong influence on the initial stage of the ionization. The pondermotive potential results either in monotonous increase or oscillatory variations of the effective band gap that has been taken into account in some ionization models. The classical FKE provides decrease of the band gap. We analyzing the competition between those two opposite trends of the effective-band-gap variations and discuss applications of those effects for considerations of the laser-induced damage and its threshold in transparent solids.

  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. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Correlations of Energy Ratios for Collective Nuclear Bands

    NASA Astrophysics Data System (ADS)

    Zamfir, N. V.; Bucurescu, D.; Căta-Danil, G.; Ivaşcu, M.; Mărginean, N.

    2009-01-01

    It is shown that the Mallmann's energy correlations, introduced a long time ago for the ground state bands of the even-even nuclei are, in fact, universal. Various bands in all collective nuclei (even-even, odd-even, and odd-odd) obey the same systematics. This unique, universal behaviour indicates the same spin dependence of the energy of the levels and, consequently, a common structure of all collective bands. Based on the second-order anharmonic vibrator description, parameter-free recurrence relations between energy ratios are deduced. These relations can be used to predict levels of higher spins in various bands.

  15. Correlations of Energy Ratios for Collective Nuclear Bands

    NASA Astrophysics Data System (ADS)

    Zamfir, N. V.; Bucurescu, D.; Căta-Danil, G.; Ivaşcu, M.; Mărginean, N.

    2009-03-01

    It is shown that the Mallmann's energy correlations, introduced a long time ago for the ground state bands of the even-even nuclei are, in fact, universal. Various bands in all collective nuclei (even-even, odd-even, and odd-odd) obey the same systematics. This unique, universal behaviour indicates the same spin dependence of the energy of the levels in all bands in all collective nuclei. Based on a second-order anharmonic vibrator description, parameter-free recurrence relations between energy ratios are deduced. These relations can be used to predict levels of higher spins in various bands.

  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. 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. 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.

  19. Electronic band gaps and exciton binding energies in monolayer M oxW1 -xS2 transition metal dichalcogenide alloys probed by scanning tunneling and optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Rigosi, Albert F.; Hill, Heather M.; Rim, Kwang Taeg; Flynn, George W.; Heinz, Tony F.

    2016-08-01

    Using scanning tunneling spectroscopy (STS) and optical reflectance contrast measurements, we examine band-gap properties of single layers of transition metal dichalcogenide (TMDC) alloys: Mo S2 , M o0.5W0.5S2 , M o0.25W0.75S2 , M o0.1W0.9S2 , and W S2 . The quasiparticle band gap, spin-orbit separation of the excitonic transitions at the K /K' point in the Brillouin zone, and binding energies of the A exciton are extracted from STS and optical data. The exciton binding energies change roughly linearly with tungsten concentration. For our samples on an insulating substrate, we report quasiparticle band gaps from 2.17 ± 0.04 eV (Mo S2) to 2.38 ± 0.06 eV (W S2) , with A exciton binding energies ranging from 310 to 420 meV.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  2. 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.

  3. Nanoscale Studies of Energy Band Gaps and Band Offsets in Compound Semiconductor Heterostructures

    NASA Astrophysics Data System (ADS)

    Chang, Alexander S.

    The identification of the precise band offsets at semiconductor interfaces is crucially important for the successful development of electronic and optoelectronic devices. However, issues at the interfaces, such as strain or defects, needs to be investigated for precise band tuning of semiconductor heterostructures. In this dissertation, the nanometer-scale structural and electronic properties of InGaAs(Sb)N/GaAs interfaces, InGaN/GaN QDs, and GaSb/GaAs QDs are investigated using a combination of XSTM and STS. The influence of Sb incorporation on the InGaAs(Sb)N/GaAs band alignment is investigated. At the InGaAsN/GaAs (InGaAsSbN/GaAs) interfaces, type II (type I) band offsets are observed, due to strain-induced splitting of the valence band and the incorporation of Sb. Band tuning of both conduction and valence band edges with the incorporation of Sb can be used to engineer the band structure with strong confinement of electrons and holes in the InGaAsSbN quantum well layer, which is promising for light emitting applications. The influence of the growth substrate on InGaN/GaN QD formation and properties is examined. The QD density, dimension, and band gaps are compared for different InGaN QDs on free-standing GaN or GaN/AlN/sapphire substrates. We present different sources using nucleation on different substrates, and discuss their influences on the electronic band structure. Our work suggests that a wide variety of InGaN QD dimension, density, and band structure can be achieved by using different starting substrate and number of layers of InGaN QD stacks. Furthermore, the influence of strain and dislocation on the GaSb/GaAs QD band alignment is investigated using both experimental and computational tools. A combination of cross-sectional transmission electron microscopy (XTEM), XSTM, and STS reveals the formation of misfit dislocations and both coherent and semi-coherent clustered QDs, independent of Sb- vs. As-termination of the GaAs surface. Furthermore, finite

  4. 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.

  5. 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.

  6. 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.

  7. Calculation of Energy Diagram of Asymmetric Graded-Band-Gap Semiconductor Superlattices.

    PubMed

    Monastyrskii, Liubomyr S; Sokolovskii, Bogdan S; Alekseichyk, Mariya P

    2017-12-01

    The paper theoretically investigates the peculiarities of energy diagram of asymmetric graded-band-gap superlattices with linear coordinate dependences of band gap and electron affinity. For calculating the energy diagram of asymmetric graded-band-gap superlattices, linearized Poisson's equation has been solved for the two layers forming a period of the superlattice. The obtained coordinate dependences of edges of the conduction and valence bands demonstrate substantial transformation of the shape of the energy diagram at changing the period of the lattice and the ratio of width of the adjacent layers. The most marked changes in the energy diagram take place when the period of lattice is comparable with the Debye screening length. In the case when the lattice period is much smaller that the Debye screening length, the energy diagram has the shape of a sawtooth-like pattern.

  8. 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.

  9. 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).

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. The energy band structure of Si and Ge nanolayers

    NASA Astrophysics Data System (ADS)

    Wu, Xueke; Huang, Weiqi; Huang, Zhongmei; Qin, Chaojie; Tang, Yanlin

    2016-12-01

    First-principles calculation based on density functional theory (DFT) with the generalized gradient approximation (GGA) were carried out to investigate the energy band gap structure of Si and Ge nanofilms. Calculation results show that the band gaps of Si(111) and Ge(110) nanofilms are indirect structures and independent of film thickness, the band gaps of Si(110) and Ge(100) nanofilms could be transfered into the direct structure for nanofilm thickness of less than a certain value, and the band gaps of Si(100) and Ge(111) nanofilms are the direct structures in the present model thickness range (about 7 nm). Moreover, the changes of the band gaps on the Si and Ge nanofilms follow the quantum confinement effects. It will be a good way to obtain direct band gap emission in Si and Ge materials, and to develop Si and Ge laser on Si chip.

  18. Fe-substituted indium thiospinels: New intermediate band semiconductors with better absorption of solar energy

    NASA Astrophysics Data System (ADS)

    Chen, Ping; Chen, Haijie; Qin, Mingsheng; Yang, Chongyin; Zhao, Wei; Liu, Yufeng; Zhang, Wenqing; Huang, Fuqiang

    2013-06-01

    The indium thiospinels In2S3 and MgIn2S4 are promising host for the intermediated band (IB) photovoltaic materials due to their ideal band gap value. Here, the optical properties and electronic structure of Fe-doped In2S3 and MgIn2S4 have been investigated. All the Fe-substituted semiconductors exhibit two additional absorption bands at about 0.7 and 1.25 eV, respectively. The results of first-principles calculations revealed that the Fe substituted at the octahedral In site would introduce a partially filled IB into the band gap. Thanks to the formation of IB, the Fe-substituted semiconductors have the ability to absorb the photons with energies below the band gap. With the wide-spectrum absorption of solar energy, these materials possess potential applications in photovoltaic domain.

  19. 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.

  20. A low energy electron magnetometer

    NASA Technical Reports Server (NTRS)

    Singh, J. J.; Wood, G. M., Jr.; Rayborn, G. H.; White, F. A.

    1979-01-01

    The concept of a highly sensitive magnetometer based on the deflection of low energy electron beams in magnetic fields is analyzed. Because of its extremely low mass and consequently high e/m ratio, a low energy electron is easily deflected in a magnetic field, thus providing a basis for very low field measurement. Calculations for a specific instrument design indicate that a low energy electron magnetometer (LEEM) can measure magnetic fields as low as 1000 nT. The anticipated performance of LEEM is compared with that of the existing high resolution magnetometers in selected applications. The fast response time of LEEM makes it especially attractive as a potential instrument for magnetic signature analysis in large engineering systems.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  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. Characteristic energy range of electron scattering due to plasmaspheric hiss

    NASA Astrophysics Data System (ADS)

    Ma, Q.; Li, W.; Thorne, R. M.; Bortnik, J.; Reeves, G. D.; Kletzing, C. A.; Kurth, W. S.; Hospodarsky, G. B.; Spence, H. E.; Baker, D. N.; Blake, J. B.; Fennell, J. F.; Claudepierre, S. G.; Angelopoulos, V.

    2016-12-01

    We investigate the characteristic energy range of electron flux decay due to the interaction with plasmaspheric hiss in the Earth's inner magnetosphere. The Van Allen Probes have measured the energetic electron flux decay profiles in the Earth's outer radiation belt during a quiet period following the geomagnetic storm that occurred on 7 November 2015. The observed energy of significant electron decay increases with decreasing L shell and is well correlated with the energy band corresponding to the first adiabatic invariant μ = 4-200 MeV/G. The electron diffusion coefficients due to hiss scattering are calculated at L = 2-6, and the modeled energy band of effective pitch angle scattering is also well correlated with the constant μ lines and is consistent with the observed energy range of electron decay. Using the previously developed statistical plasmaspheric hiss model during modestly disturbed periods, we perform a 2-D Fokker-Planck simulation of the electron phase space density evolution at L = 3.5 and demonstrate that plasmaspheric hiss causes the significant decay of 100 keV-1 MeV electrons with the largest decay rate occurring at around 340 keV, forming anisotropic pitch angle distributions at lower energies and more flattened distributions at higher energies. Our study provides reasonable estimates of the electron populations that can be most significantly affected by plasmaspheric hiss and the consequent electron decay profiles.

  7. 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.

  8. Strain-Induced Energy Band Gap Opening in Two-Dimensional Bilayered Silicon Film

    NASA Astrophysics Data System (ADS)

    Ji, Z.; Zhou, R.; Lew Yan Voon, L. C.; Zhuang, Y.

    2016-10-01

    This work presents a theoretical study of the structural and electronic properties of bilayered silicon film (BiSF) under in-plane biaxial strain/stress using density functional theory (DFT). Atomic structures of the two-dimensional (2-D) silicon films are optimized by using both the local-density approximation (LDA) and generalized gradient approximation (GGA). In the absence of strain/stress, five buckled hexagonal honeycomb structures of the BiSF with triangular lattice have been obtained as local energy minima, and their structural stability has been verified. These structures present a Dirac-cone shaped energy band diagram with zero energy band gaps. Applying a tensile biaxial strain leads to a reduction of the buckling height. Atomically flat structures with zero buckling height have been observed when the AA-stacking structures are under a critical biaxial strain. Increase of the strain between 10.7% and 15.4% results in a band-gap opening with a maximum energy band gap opening of ˜0.17 eV, obtained when a 14.3% strain is applied. Energy band diagrams, electron transmission efficiency, and the charge transport property are calculated. Additionally, an asymmetric energetically favorable atomic structure of BiSF shows a non-zero band gap in the absence of strain/stress and a maximum band gap of 0.15 eV as a -1.71% compressive strain is applied. Both tensile and compressive strain/stress can lead to a band gap opening in the asymmetric structure.

  9. Quantitative analysis on electric dipole energy in Rashba band splitting

    PubMed Central

    Hong, Jisook; Rhim, Jun-Won; Kim, Changyoung; Ryong Park, Seung; Hoon Shim, Ji

    2015-01-01

    We report on quantitative comparison between the electric dipole energy and the Rashba band splitting in model systems of Bi and Sb triangular monolayers under a perpendicular electric field. We used both first-principles and tight binding calculations on p-orbitals with spin-orbit coupling. First-principles calculation shows Rashba band splitting in both systems. It also shows asymmetric charge distributions in the Rashba split bands which are induced by the orbital angular momentum. We calculated the electric dipole energies from coupling of the asymmetric charge distribution and external electric field, and compared it to the Rashba splitting. Remarkably, the total split energy is found to come mostly from the difference in the electric dipole energy for both Bi and Sb systems. A perturbative approach for long wave length limit starting from tight binding calculation also supports that the Rashba band splitting originates mostly from the electric dipole energy difference in the strong atomic spin-orbit coupling regime. PMID:26323493

  10. 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.

  11. 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.

  12. 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.

  13. Propagation Energies Inferred from Deformation Bands in Sandstone

    NASA Astrophysics Data System (ADS)

    Schultz, R. A.; Soliva, R.

    2011-12-01

    The J-integral is used to calculate the band propagation energies Jband for pure and shear-enhanced compaction bands from four sandstones from around the world. The value obtained previously for the Valley of Fire (Utah) site assumed compactional offsets only across the bands; shearing offsets along these and shear-enhanced compaction bands (SECBs) from the Buckskin Gulch (Utah) and the recently reported Boncavaï quarry near Mornas (France) are consistent with trigonometrically obtained estimates calculated from band thickness and angle to the maximum compressive principal stress. Compactional offsets were calculated from porosity reductions from host rock to band. Cataclastic deformation bands from the Quartier de l'Etang quarry near Orange (France) were also analyzed for comparison with bands having smaller ratios of shear/compaction. Normal and shear stresses resolved across the bands at the time of their formation were estimated from stratigraphic overburden and friction coefficients for porous sandstones measured in the laboratory. Assuming that the SECBs may be characterized by small-scale yielding, so that Jband is equivalent to the strain energy release rate G, the values of Jband can be compared to the previous values. SECBs having strike-slip offsets from Valley of Fire have Jband = 11.1 kJ/m2, consistent with the previously reported range of GIc = 10-60 kJ/m2 calculated by using the J-integral approach by Rudnicki and Sternlof [2005]. Pure compaction bands (PCBs) from the same site have Jband = 5.5 kJ/m2, implying that less work is required to propagate PCBs than SECBs. The value of Jband for the Buckskin Gulch site, 60.5 kJ/m2, is consistent with the lower range of values for strain energy release rate obtained previously, GIc = 55-120 kJ/m2. Band propagation energy for SECBs from the Boncavaï quarry site, Jband = 16.4 kJ/m2, is comparable to that for similar structures from the Valley of Fire site. Cataclastic deformation bands at the Orange quarry

  14. Low energy electron magnetometer using a monoenergetic electron beam

    NASA Technical Reports Server (NTRS)

    Singh, J. J.; Wood, G. M.; Rayborn, G. H.; White, F. A. (Inventor)

    1983-01-01

    A low energy electron beam magnetometer utilizes near-monoenergetic electrons thereby reducing errors due to electron energy spread and electron nonuniform angular distribution. In a first embodiment, atoms in an atomic beam of an inert gas are excited to a Rydberg state and then electrons of near zero energy are detached from the Rydberg atoms. The near zero energy electrons are then accelerated by an electric field V(acc) to form the electron beam. In a second embodiment, a filament emits electrons into an electrostatic analyzer which selects electrons at a predetermined energy level within a very narrow range. These selected electrons make up the electron beam that is subjected to the magnetic field being measured.

  15. 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.

  16. 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.

  17. 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.

  18. The calculation of band gap energy in zinc oxide films

    NASA Astrophysics Data System (ADS)

    Arif, Ali; Belahssen, Okba; Gareh, Salim; Benramache, Said

    2015-01-01

    We investigated the optical properties of undoped zinc oxide thin films as the n-type semiconductor; the thin films were deposited at different precursor molarities by ultrasonic spray and spray pyrolysis techniques. The thin films were deposited at different substrate temperatures ranging between 200 and 500 °C. In this paper, we present a new approach to control the optical gap energy of ZnO thin films by concentration of the ZnO solution and substrate temperatures from experimental data, which were published in international journals. The model proposed to calculate the band gap energy with the Urbach energy was investigated. The relation between the experimental data and theoretical calculation suggests that the band gap energies are predominantly estimated by the Urbach energies, film transparency, and concentration of the ZnO solution and substrate temperatures. The measurements by these proposal models are in qualitative agreements with the experimental data; the correlation coefficient values were varied in the range 0.96-0.99999, indicating high quality representation of data based on Equation (2), so that the relative errors of all calculation are smaller than 4%. Thus, one can suppose that the undoped ZnO thin films are chemically purer and have many fewer defects and less disorder owing to an almost complete chemical decomposition and contained higher optical band gap energy.

  19. 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.

  20. Energy band gaps in graphene nanoribbons with corners

    NASA Astrophysics Data System (ADS)

    Szczȩśniak, Dominik; Durajski, Artur P.; Khater, Antoine; Ghader, Doried

    2016-05-01

    In the present paper, we study the relation between the band gap size and the corner-corner length in representative chevron-shaped graphene nanoribbons (CGNRs) with 120° and 150° corner edges. The direct physical insight into the electronic properties of CGNRs is provided within the tight-binding model with phenomenological edge parameters, developed against recent first-principle results. We show that the analyzed CGNRs exhibit inverse relation between their band gaps and corner-corner lengths, and that they do not present a metal-insulator transition when the chemical edge modifications are introduced. Our results also suggest that the band gap width for the CGNRs is predominantly governed by the armchair edge effects, and is tunable through edge modifications with foreign atoms dressing.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. Characterization of a 2D soft x-ray tomography camera with discrimination in energy bands

    SciTech Connect

    Romano, A.; Pacella, D.; Gabellieri, L.; Tilia, B.; Piergotti, V.; Mazon, D.; Malard, P.

    2010-10-15

    A gas detector with a 2D pixel readout is proposed for a future soft x-ray (SXR) tomography with discrimination in energy bands separately per pixel. The detector has three gas electron multiplier foils for the electron amplification and it offers the advantage, compared with the single stage, to be less sensitive to neutrons and gammas. The energy resolution and the detection efficiency of the detector have been accurately studied in the laboratory with continuous SXR spectra produced by an electronic tube and line emissions produced by fluorescence (K, Fe, and Mo) in the range of 3-17 keV. The front-end electronics, working in photon counting mode with a selectable threshold for pulse discrimination, is optimized for high rates. The distribution of the pulse amplitude has been indirectly derived by means of scans of the threshold. Scans in detector gain have also been performed to assess the capability of selecting different energy ranges.

  7. Effect of Γ-X band mixing on the donor binding energy in a Quantum Wire

    NASA Astrophysics Data System (ADS)

    Vijaya Shanthi, R.; Jayakumar, K.; Nithiananthi, P.

    2015-02-01

    To invoke the technological applications of heterostructure semiconductors like Quantum Well (QW), Quantum Well Wire (QWW) and Quantum Dot (QD), it is important to understand the property of impurity energy which is responsible for the peculiar electronic & optical behavior of the Low Dimensional Semiconductor Systems (LDSS). Application of hydrostatic pressure P>35kbar drastically alters the band offsets leading to the crossover of Γ band of the well & X band of the barrier resulting in an indirect transition of the carrier and this effect has been studied experimentally and theoretically in a QW structure. In this paper, we have investigated the effect of Γ-X band mixing due to the application of hydrostatic pressure in a GaAs/AlxGa1-xAs QWW system. The results are presented and discussed for various widths of the wire.

  8. 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.

  9. 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.

  10. Including the relativistic kinetic energy in a spline-augmented plane-wave band calculation

    SciTech Connect

    Fehrenbach, G.M.; Schmidt, G.

    1997-03-01

    The first-order relativistic correction to the kinetic energy of an electron, the mass-velocity term, is not bounded from below. It can, therefore, not be used within a variational framework. To overcome this deficiency we developed a method to include the entire relativistic kinetic energy {radical}(p{sup 2}c{sup 2}+m{sub 0}{sup 2}c{sup 4}){minus}m{sub 0}c{sup 2} in a spline-augmented plane-wave band calculation. The first results for silver are quite promising, especially for d and p states: The analysis of the energies of the core states as well as of the valence band structure suggests that the energies of d bands are reproduced within 1 mRy. However, the combination of the relativistic kinetic energy with the Darwin term leads to energies which are too low for s-like valence states by 10 mRy. Therefore, the s and d valence band complex is spread out and the Fermi level is lowered by the same amount as the s states. We expect to overcome these deficiencies in future investigations by using a alternative form of the relativistic potential correction along the lines proposed by Douglas and Kroll. {copyright} {ital 1997} {ital The American Physical Society}

  11. Energy Efficient Electronics Cooling Project

    SciTech Connect

    Steve O'Shaughnessey; Tim Louvar; Mike Trumbower; Jessica Hunnicutt; Neil Myers

    2012-02-17

    Parker Precision Cooling Business Unit was awarded a Department of Energy grant (DE-EE0000412) to support the DOE-ITP goal of reducing industrial energy intensity and GHG emissions. The project proposed by Precision Cooling was to accelerate the development of a cooling technology for high heat generating electronics components. These components are specifically related to power electronics found in power drives focused on the inverter, converter and transformer modules. The proposed cooling system was expected to simultaneously remove heat from all three of the major modules listed above, while remaining dielectric under all operating conditions. Development of the cooling system to meet specific customer's requirements and constraints not only required a robust system design, but also new components to support long system functionality. Components requiring further development and testing during this project included pumps, fluid couplings, cold plates and condensers. All four of these major categories of components are required in every Precision Cooling system. Not only was design a key area of focus, but the process for manufacturing these components had to be determined and proven through the system development.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. Photonic Band Gap resonators for high energy accelerators

    SciTech Connect

    Schultz, S.; Smith, D.R.; Kroll, N. |

    1993-12-31

    We have proposed that a new type of microwave resonator, based on Photonic Band Gap (PBG) structures, may be particularly useful for high energy accelerators. We provide an explanation of the PBG concept and present data which illustrate some of the special properties associated with such structures. Further evaluation of the utility of PBG resonators requires laboratory testing of model structures at cryogenic temperatures, and at high fields. We provide a brief discussion of our test program, which is currently in progress.

  17. 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.

  18. 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.

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

    SciTech Connect

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

    2005-07-15

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

  20. STABILITY IN BCC TRANSITION METALS: MADELUNG AND BAND-ENERGY EFFECTS DUE TO ALLOYING

    SciTech Connect

    Landa, A; Soderlind, P; Ruban, A; Peil, O; Vitos, L

    2009-08-28

    The phase stability of the bcc Group VB (V, Nb, and Ta) transition metals is explored by first-principles electronic-structure calculations. Alloying with a small amount of a neighboring metal can either stabilize or destabilize the bcc phase. This counterintuitive behavior is explained by competing mechanisms that dominate depending on particular dopand. We show that band-structure effects dictate stability when a particular Group VB metal is alloyed with its nearest neighbors within the same d-transition series. In this case, the neighbor with less (to the left) and more (to the right) d electrons, destabilize and stabilize bcc, respectively. When alloying with neighbors of different d-transition series, electrostatic Madelung energy dominates over the band energy and always stabilizes the bcc phase.

  1. Energy Band Gap Study of Semiconducting Single Walled Carbon Nanotube Bundle

    NASA Technical Reports Server (NTRS)

    Elkadi, Asmaa; Decrossas, Emmanuel; El-Ghazaly, Samir

    2013-01-01

    The electronic properties of multiple semiconducting single walled carbon nanotubes (s-SWCNTs) considering various distribution inside a bundle are studied. The model derived from the proposed analytical potential function of the electron density for an individual s-SWCNT is general and can be easily applied to multiple nanotubes. This work demonstrates that regardless the number of carbon nanotubes, the strong coupling occurring between the closest neighbours reduces the energy band gap of the bundle by 10%. As expected, the coupling is strongly dependent on the distance separating the s-SWCNTs. In addition, based on the developed model, it is proposed to enhance this coupling effect by applying an electric field across the bundle to significantly reduce the energy band gap of the bundle by 20%.

  2. Energy Band Gap Study of Semiconducting Single Walled Carbon Nanotube Bundle

    NASA Technical Reports Server (NTRS)

    Elkadi, Asmaa; Decrossas, Emmanuel; El-Ghazaly, Samir

    2013-01-01

    The electronic properties of multiple semiconducting single walled carbon nanotubes (s-SWCNTs) considering various distribution inside a bundle are studied. The model derived from the proposed analytical potential function of electron density for na individual s-SWCNT is general and can be easily applied to multiple nanotubes. This work demonstrates that regardless the number of carbon nanotubes, the strong coupling occurring between the closet neighbors reduces the energy band gap of the bundle by 10%. As expected, the coupling is strongly dependent on the distance separating the s-SWCNTs. In addition, based on the developed model, it is proposed to enhance this coupling effect by applying an electric field across the bundle to significantly reduce the energy band gap of the bundle by 20%.

  3. 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.

  4. The Effect of Carbon Nanotube on Band Gap Energy of TiO2 Nanoparticles

    NASA Astrophysics Data System (ADS)

    Taleshi, F.

    2015-05-01

    A composite of TiO2-carbon nanotubes (CNTs) was synthesized via a sol-gel method. The structure and morphology of the nanocomposite samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The optical properties of the samples were studied using UV-Vis spectroscopy. The results show that CNTs can decrease the value of band gap energy of TiO2 nanoparticles considerably.

  5. Housing Electrons: Relating Quantum Numbers, Energy Levels, and Electron Configurations.

    ERIC Educational Resources Information Center

    Garofalo, Anthony

    1997-01-01

    Presents an activity that combines the concepts of quantum numbers and probability locations, energy levels, and electron configurations in a concrete, hands-on way. Uses model houses constructed out of foam board and colored beads to represent electrons. (JRH)

  6. Mass, energy, and the electron

    SciTech Connect

    Mulligan, Bernard . E-mail: mulligan.3@osu.edu

    2006-08-15

    The two-component solutions of the Dirac equation currently in use are not separately a particle equation or an antiparticle equation. We present a unitary transformation that uncouples the four-component, force-free Dirac equation to yield a two-component spinor equation for the force-free motion of a relativistic particle and a corresponding two-component, time-reversed equation for an antiparticle. The particle-antiparticle nature of the two equations is established by applying to the solutions of these two-component equations criteria analogous to those applied for establishing the four-component particle and antiparticle solutions of the four-component Dirac equation. Wave function solutions of our two-component particle equation describe both a right and a left circularly polarized particle. Interesting characteristics of our solutions include spatial distributions that are confined in extent along directions perpendicular to the motion, without the artifice of wave packets, and an intrinsic chirality (handedness) that replaces the usual definition of chirality for particles without mass. Our solutions demonstrate that both the rest mass and the relativistic increase in mass with velocity of the force-free electron are due to an increase in the rate of Zitterbewegung with velocity. We extend this result to a bound electron, in which case the loss of energy due to binding is shown to decrease the rate of Zitterbewegung.

  7. 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.

  8. Energy-band structure of CdTe and Si: a sp 3(s ∗) 2k.p model

    NASA Astrophysics Data System (ADS)

    Boujdaria, Kais; Zitouni, Omar

    2004-01-01

    The energy bands of the direct-band-gap semiconductor (CdTe) as well as the indirect-band-gap semiconductor (Si), throughout the entire Brillouin zone, have been obtained by diagonalizing a 24×24 k.p Hamiltonian referred to basis states at k=0. We extend the sp 3s ∗ basis functions by the inclusion of sV∗ orbitals. We find that the sp 3'd'(s ∗) 2k.p model is fairly sufficient to describe the electronic structure of these systems over a wide energy range, obviating the use of any d orbitals. Finally, the comparison with available theoretical results shows that the present model reproduces known results for bulk CdTe and Si, that is, their band structure, including s and p valence bands and the lowest two conduction bands.

  9. 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.

  10. 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.

  11. 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

  12. Determination of Energy Band Alignment in Ultrathin Hf-based Oxide/Pt System

    NASA Astrophysics Data System (ADS)

    Ohta, A.; Murakami, H.; Higashi, S.; Miyazaki, S.

    2013-03-01

    Effect of incorporating a third element into HfO2 on the electronic structures has been studied by high resolution x-ray photoelectron spectroscopy (XPS). Hf-IIIa (La, Y, Gd, and Dy) oxide and Hf-Ti oxide films were deposited on a Pt layer by metal organic chemical vapor deposition (MOCVD) and co-sputtering and followed by post-deposition annealing in O2 ambience at 500°C. The energy bandgap (Eg) of these Hf-based oxide films was determined by analyzing the energy loss spectra of O 1s photoelectrons in consideration of the overlap with Hf 4s core-line signals. From analyses of the valence band signals and the cut-off energy for photoelectrons, the valence band offset between the Hf based-oxide, and the Pt electrode and the work function value of the Pt layer were evaluated. By combining the oxide bandgap values, the valence band line-ups, and the Pt work function value, the energy band profile of the Hf-based oxide/Pt has been determined.

  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. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Simulations and measurements in scanning electron microscopes at low electron energy.

    PubMed

    Walker, Christopher G H; Frank, Luděk; Müllerová, Ilona

    2016-11-01

    The advent of new imaging technologies in Scanning Electron Microscopy (SEM) using low energy (0-2 keV) electrons has brought about new ways to study materials at the nanoscale. It also brings new challenges in terms of understanding electron transport at these energies. In addition, reduction in energy has brought new contrast mechanisms producing images that are sometimes difficult to interpret. This is increasing the push for simulation tools, in particular for low impact energies of electrons. The use of Monte Carlo calculations to simulate the transport of electrons in materials has been undertaken by many authors for several decades. However, inaccuracies associated with the Monte Carlo technique start to grow as the energy is reduced. This is not simply associated with inaccuracies in the knowledge of the scattering cross-sections, but is fundamental to the Monte Carlo technique itself. This is because effects due to the wave nature of the electron and the energy band structure of the target above the vacuum energy level become important and these are properties which are difficult to handle using the Monte Carlo method. In this review we briefly describe the new techniques of scanning low energy electron microscopy and then outline the problems and challenges of trying to understand and quantify the signals that are obtained. The effects of charging and spin polarised measurement are also briefly explored. SCANNING 38:802-818, 2016. © 2016 Wiley Periodicals, Inc.

  20. Electron Attachment to Molecules at Low Electron Energies

    NASA Technical Reports Server (NTRS)

    Chutjian, A.; Garscadden, A.; Wadehra, J. M.

    1994-01-01

    One of the most efficient ways of producing negative ions is by the process of dissociative electron attachment to molecules. Here, a diatomic or polyatomic molecule dissociates, by the impact of a low energy electron, into component atoms (or smaller molecular species) while the incident electron attaches itself to one of the dissociating fragments.

  1. Graphene oxide quantum dot-sensitized porous titanium dioxide microsphere: Visible-light-driven photocatalyst based on energy band engineering.

    PubMed

    Zhang, Yu; Qi, Fuyuan; Li, Ying; Zhou, Xin; Sun, Hongfeng; Zhang, Wei; Liu, Daliang; Song, Xi-Ming

    2017-03-11

    We report a novel graphene oxide quantum dot (GOQD)-sensitized porous TiO2 microsphere for efficient photoelectric conversion. Electro-chemical analysis along with the Mott-Schottky equation reveals conductivity type and energy band structure of the two semiconductors. Based on their energy band structures, visible light-induced electrons can transfer from the p-type GOQD to the n-type TiO2. Enhanced photocurrent and photocatalytic activity in visible light further confirm the enhanced separation of electrons and holes in the nanocomposite.

  2. Single track nanodosimetry of low energy electrons

    NASA Astrophysics Data System (ADS)

    Bantsar, A.; Grosswendt, B.; Pszona, S.; Kula, J.

    2009-02-01

    Auger-electron-emitting radionuclides (for instance, 125I) with a predominant energy spectrum below 3 keV are an active area of research towards the clinical application of radiopharmaceuticals. Hence, the necessity for an adequate description of the effects of radiation by low-energy electrons on nanometric biological targets seems to be unquestionable. Experimental nanodosimetry for low-energy electrons has been accomplished with a device named JET COUNTER. The present paper describes, for the first time, nanodosimetric experiments in nanometer-sized cavities of nitrogen using low energy electrons ranging from 100 eV to 2 keV.

  3. Vibrational effects on surface energies and band gaps in hexagonal and cubic ice

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    Surface energies of hexagonal and cubic water ice are calculated using first-principles quantum mechanical methods, including an accurate description of anharmonic nuclear vibrations. We consider two proton-orderings of the hexagonal and cubic ice basal surfaces and three proton-orderings of hexagonal ice prism surfaces, finding that vibrations reduce the surface energies by more than 10%. We compare our vibrational densities of states to recent sum frequency generation absorption measurements and identify surface proton-orderings of experimental ice samples and the origins of characteristic absorption peaks. We also calculate zero point quantum vibrational corrections to the surface electronic band gaps, which range from -1.2 eV for the cubic ice basal surface up to -1.4 eV for the hexagonal ice prism surface. The vibrational corrections to the surface band gaps are up to 12% smaller than for bulk ice.

  4. Dynamical and anharmonic effects on the electron-phonon coupling and the zero-point renormalization of the band structure

    NASA Astrophysics Data System (ADS)

    Antonius, Gabriel; Poncé, Samuel; Lantagne-Hurtubise, Étienne; Auclair, Gabriel; Côté, Michel; Gonze, Xavier

    2015-03-01

    The electron-phonon coupling in solids renormalizes the band structure, reducing the band gap by several tenths of an eV in light-atoms semiconductors. Using the Allen-Heine-Cardona theory (AHC), we compute the zero-point renormalization (ZPR) as well as the quasiparticle lifetimes of the full band structure in diamond, BN, LiF and MgO. We show how dynamical effects can be included in the AHC theory, and still allow for the use of a Sternheimer equation to avoid the summation over unoccupied bands. The convergence properties of the electron-phonon coupling self-energy with respect to the Brillouin zone sampling prove to be strongly affected by dynamical effects. We complement our study with a frozen-phonon approach, which reproduces the static AHC theory, but also allows to probe the phonon wavefunctions at finite displacements and include anharmonic effects in the self-energy. We show that these high-order components tend to reduce the strongest electron-phonon coupling elements, which affects significantly the band gap ZPR.

  5. Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

    NASA Astrophysics Data System (ADS)

    Gao, Weiwei; Gao, Xiang; Abtew, Tesfaye A.; Sun, Yi-Yang; Zhang, Shengbai; Zhang, Peihong

    2016-02-01

    The quasiparticle band gap is one of the most important materials properties for photovoltaic applications. Often the band gap of a photovoltaic material is determined (and can be controlled) by various factors, complicating predictive materials optimization. An in-depth understanding of how these factors affect the size of the gap will provide valuable guidance for new materials discovery. Here we report a comprehensive investigation on the band gap formation mechanism in organic-inorganic hybrid perovskites by decoupling various contributing factors which ultimately determine their electronic structure and quasiparticle band gap. Major factors, namely, quasiparticle self-energy, spin-orbit coupling, and structural distortions due to the presence of organic molecules, and their influences on the quasiparticle band structure of organic-inorganic hybrid perovskites are illustrated. We find that although methylammonium cations do not contribute directly to the electronic states near band edges, they play an important role in defining the band gap by introducing structural distortions and controlling the overall lattice constants. The spin-orbit coupling effects drastically reduce the electron and hole effective masses in these systems, which is beneficial for high carrier mobilities and small exciton binding energies.

  6. 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.

  7. Electron momentum spectroscopy study of amantadine: binding energy spectra and valence orbital electron density distributions

    NASA Astrophysics Data System (ADS)

    Litvinyuk, I. V.; Zheng, Y.; Brion, C. E.

    2000-11-01

    The electron binding energy spectrum and valence orbital electron momentum density distributions of amantadine (1-aminoadamantane), an important anti-viral and anti-Parkinsonian drug, have been measured by electron momentum spectroscopy. Theoretical momentum distributions, calculated at the 6-311++G** and AUG-CC-PVTZ levels within the target Hartree-Fock and also the target Kohn-Sham density functional theory approximations, show good agreement with the experimental results. The results for amantadine are also compared with those for the parent molecule, adamantane, reported earlier (Chem. Phys. 253 (2000) 41). Based on the comparison tentative assignments of the valence region ionization bands of amantadine have been made.

  8. Electronic correlation contributions to structural energies

    NASA Astrophysics Data System (ADS)

    Haydock, Roger

    2015-03-01

    The recursion method is used to calculate electronic excitation spectra including electron-electron interactions within the Hubbard model. The effects of correlation on structural energies are then obtained from these spectra and applied to stacking faults. http://arxiv.org/abs/1405.2288 Supported by the Richmond F. Snyder Fund and Gifts.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Attainment of Electron Beam Suitable for Medium Energy Electron Cooling

    SciTech Connect

    Seletskiy, Sergei M.

    2005-01-01

    Electron cooling of charged particle beams is a well-established technique at electron energies of up to 300 keV. However, up to the present time the advance of electron cooling to the MeV-range energies has remained a purely theoretical possibility. The electron cooling project at Fermilab has recently demonstrated the ¯rst cooling of 8.9 GeV/c antiprotons in the Recycler ring, and therefore, has proved the validity of the idea of relativistic electron cool- ing. The Recycler Electron Cooler (REC) is the key component of the Teva- tron Run II luminosity upgrade project. Its performance depends critically on the quality of electron beam. A stable electron beam of 4.3 MeV car- rying 0.5 A of DC current is required. The beam suitable for the Recycler Electron Cooler must have an angular spread not exceeding 200 ¹rad. The full-scale prototype of the REC was designed, built and tested at Fermilab in the Wideband laboratory to study the feasibility of attaining the high-quality electron beam. In this thesis I describe various aspects of development of the Fermilab electron cooling system, and the techniques used to obtain the electron beam suitable for the cooling process. In particular I emphasize those aspects of the work for which I was principally responsible.

  14. Energy efficiency of electron plasma emitters

    SciTech Connect

    Zalesski, V. G.

    2011-12-15

    Electron emission influence from gas-discharge plasma on plasma emitter energy parameters is considered. It is shown, that electron emission from plasma is accompanied by energy contribution redistribution in the gas-discharge from plasma emitter supplies sources-the gas-discharge power supply and the accelerating voltage power supply. Some modes of electron emission as a result can be realized: 'a probe measurements mode,' 'a transitive mode,' and 'a full switching mode.'.

  15. High Resolution Emission Spectroscopy of the Alpha Pi-1 - Chi Sigma-1(+) Fourth Positive Band System of CO from Electron Impact

    NASA Technical Reports Server (NTRS)

    Beegle, Luther W.; Ajello, Joseph M.; James, Geoffrey K.; Alvarez, Marcos; Dziczek, Dariusz

    2000-01-01

    We report electron-impact induced fluorescence spectra [300 mA full width at half maximum (FWHM)] of CO for 20 and 100 eV impact energies of the spectral region of 1300 to 2050 A and high resolution spectra (FWHM) of the v'=5 to v"=l and the v'=3 to v"=O bands showing that the rotational structure of the band system are modeled accurately. The excitation function of the (0,1) band (1597 A) was measured from electron impact in the energy range from threshold to 750 eV and placed on an absolute scale from modem calibration standards.

  16. 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).

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. Stability in bcc transition metals: Madelung and band-energy effects due to alloying.

    PubMed

    Landa, A; Söderlind, P; Ruban, A V; Peil, O E; Vitos, L

    2009-12-04

    The phase stability of group VB (V, Nb, and Ta) transition metals is explored by first-principles electronic-structure calculations. Alloying with a small amount of a neighboring metal can either stabilize or destabilize the body-centered-cubic phase relative to low-symmetry rhombohedral phases. We show that band-structure effects determine phase stability when a particular group VB metal is alloyed with its nearest neighbors within the same d-transition series. In this case, the neighbor with less (to the left) and more (to the right) d electrons destabilize and stabilize bcc, respectively. When alloying with neighbors of higher d-transition series, electrostatic Madelung energy dominates and stabilizes the body-centered-cubic phase. This surprising prediction invalidates current understanding of simple d-electron bonding that dictates high-symmetry cubic and hexagonal phases.

  2. 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

  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. Alignment of electronic energy levels at electrochemical interfaces.

    PubMed

    Cheng, Jun; Sprik, Michiel

    2012-08-28

    The position of electronic energy levels in a phase depends on the surface potentials at its boundaries. Bringing two phases in contact at an interface will alter the surface potentials shifting the energy levels relative to each other. Calculating such shifts for electrochemical interfaces requires a combination of methods from computational surface science and physical chemistry. The problem is closely related to the computation of potentials of electrochemically inactive electrodes. These so-called ideally polarizable interfaces are impossible to cross for electrons. In this perspective we review two density functional theory based methods that have been developed for this purpose, the workfunction method and the hydrogen insertion method. The key expressions of the two methods are derived from the formal theory of absolute electrode potentials. As an illustration of the workfunction method we review the computation of the potential of zero charge of the Pt(111)-water interface as recently published by a number of groups. The example of the hydrogen insertion method is from our own work on the rutile TiO(2)(110)-water interface at the point of zero proton charge. The calculations are summarized in level diagrams aligning the electronic energy levels of the solid electrode (Fermi level of the metal, valence band maximum and conduction band minimum of the semiconductor) to the band edges of liquid water and the standard potential for the reduction of the hydroxyl radical. All potentials are calculated at the same level of density functional theory using the standard hydrogen electrode as common energy reference. Comparison to experiment identifies the treatment of the valence band of water as a potentially dangerous source of error for application to electrocatalysis and photocatalysis.

  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. Energy level control: toward an efficient hot electron transport.

    PubMed

    Jin, Xiao; Li, Qinghua; Li, Yue; Chen, Zihan; Wei, Tai-Huei; He, Xingdao; Sun, Weifu

    2014-08-07

    Highly efficient hot electron transport represents one of the most important properties required for applications in photovoltaic devices. Whereas the fabrication of efficient hot electron capture and lost-cost devices remains a technological challenge, regulating the energy level of acceptor-donor system through the incorporation of foreign ions using the solution-processed technique is one of the most promising strategies to overcome this obstacle. Here we present a versatile acceptor-donor system by incorporating MoO3:Eu nanophosphors, which reduces both the 'excess' energy offset between the conduction band of acceptor and the lowest unoccupied molecular orbital of donor, and that between the valence band and highest occupied molecular orbital. Strikingly, the hot electron transfer time has been shortened. This work demonstrates that suitable energy level alignment can be tuned to gain the higher hot electron/hole transport efficiency in a simple approach without the need for complicated architectures. This work builds up the foundation of engineering building blocks for third-generation solar cells.

  7. Energy level control: toward an efficient hot electron transport

    PubMed Central

    Jin, Xiao; Li, Qinghua; Li, Yue; Chen, Zihan; Wei, Tai-Huei; He, Xingdao; Sun, Weifu

    2014-01-01

    Highly efficient hot electron transport represents one of the most important properties required for applications in photovoltaic devices. Whereas the fabrication of efficient hot electron capture and lost-cost devices remains a technological challenge, regulating the energy level of acceptor-donor system through the incorporation of foreign ions using the solution-processed technique is one of the most promising strategies to overcome this obstacle. Here we present a versatile acceptor-donor system by incorporating MoO3:Eu nanophosphors, which reduces both the ‘excess' energy offset between the conduction band of acceptor and the lowest unoccupied molecular orbital of donor, and that between the valence band and highest occupied molecular orbital. Strikingly, the hot electron transfer time has been shortened. This work demonstrates that suitable energy level alignment can be tuned to gain the higher hot electron/hole transport efficiency in a simple approach without the need for complicated architectures. This work builds up the foundation of engineering building blocks for third-generation solar cells. PMID:25099864

  8. Hot Electron Energy Relaxation in Quantum Wells

    NASA Astrophysics Data System (ADS)

    Yang, Chia-Hung

    We present experimental results on hot electron relaxation in doped bulk GaAs and quantum wells. Using steady state photoluminescence we measured the electron -LO phonon scattering time for thermalized hot electrons in quantum wells. The results are in good agreement with our theoretical calculation of electron-LO phonon interaction in two dimensional systems. Within random phase approximation, the emitted LO phonons may couple to two dimensional plasmons. Both the screening and phonon reabsorption properties can be drastically changed as a function of electron density, temperature and phonon lifetime. Theoretical energy relaxation rates, including dynamical screening and phonon reabsorption effects, will be presented. For hot electrons with energies well above the LO phonon energy, we developed a two-beam, lock-in technique to measure the energy-resolved cooling rate. In the case of quantum wells, hot electrons relax at a constant rate. For heavily doped bulk GaAs, the relaxation rate is inversely proportional to electron kinetic energy. The new method demonstrates itself as a valuable way to study the fast initial relaxation which would otherwise need femtosecond pulse laser techniques.

  9. Electronic Quasiparticle Renormalization on the Spin Wave Energy Scale

    NASA Astrophysics Data System (ADS)

    Schäfer, J.; Schrupp, D.; Rotenberg, Eli; Rossnagel, K.; Koh, H.; Blaha, P.; Claessen, R.

    2004-03-01

    High-resolution photoemission data of the (110) iron surface reveal the existence of well-defined metallic surface resonances in good correspondence to band calculations. Close to the Fermi level, their dispersion and momentum broadening display anomalies characteristic of quasiparticle renormalization due to coupling to bosonic excitations. Its energy scale exceeds that of phonons by far, and is in striking coincidence with that of the spin wave spectrum in iron. The self-energy behavior thus gives spectroscopic evidence of a quasiparticle mass enhancement due to electron-magnon coupling.

  10. 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.

  11. Hydration Effect on Amide I Infrared Bands in Water: An Interpretation Based on an Interaction Energy Decomposition Scheme.

    PubMed

    Farag, Marwa H; Ruiz-López, Manuel F; Bastida, Adolfo; Monard, Gérald; Ingrosso, Francesca

    2015-07-23

    The sensitivity of some infrared bands to the local environment can be exploited to shed light on the structure and the dynamics of biological systems. In particular, the amide I band, which is specifically related to vibrations within the peptide bonds, can give information on the ternary structure of proteins, and can be used as a probe of energy transfer. In this work, we propose a model to quantitatively interpret the frequency shift on the amide I band of a model peptide induced by the formation of hydrogen bonds in the first solvation shell. This method allows us to analyze to what extent the electrostatic interaction, electronic polarization and charge transfer affect the position of the amide I band. The impact of the anharmoniticy of the pontential energy surface on the hydration induced shift is elucidated as well.

  12. 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.

  13. 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.

  14. Pressure dependence of the band-gap energy in BiTeI

    NASA Astrophysics Data System (ADS)

    Güler-Kılıç, Sümeyra; Kılıç, ćetin

    2016-10-01

    The evolution of the electronic structure of BiTeI, a layered semiconductor with a van der Waals gap, under compression is studied by employing semilocal and dispersion-corrected density-functional calculations. Comparative analysis of the results of these calculations shows that the band-gap energy of BiTeI decreases till it attains a minimum value of zero at a critical pressure, after which it increases again. The critical pressure corresponding to the closure of the band gap is calculated, at which BiTeI becomes a topological insulator. Comparison of the critical pressure to the pressure at which BiTeI undergoes a structural phase transition indicates that the closure of the band gap would not be hindered by a structural transformation. Moreover, the band-gap pressure coefficients of BiTeI are computed, and an expression of the critical pressure is devised in terms of these coefficients. Our findings indicate that the semilocal and dispersion-corrected approaches are in conflict about the compressibility of BiTeI, which result in overestimation and underestimation, respectively. Nevertheless, the effect of pressure on the atomic structure of BiTeI is found to be manifested primarily as the reduction of the width of the van der Waals gap according to both approaches, which also yield consistent predictions concerning the interlayer metallic bonding in BiTeI under compression. It is consequently shown that the calculated band-gap energies follow qualitatively and quantitatively the same trend within the two approximations employed here, and the transition to the zero-gap state occurs at the same critical width of the van der Waals gap.

  15. Diffraction of electrons at intermediate energies

    NASA Astrophysics Data System (ADS)

    Ascolani, H.; Barrachina, R. O.; Guraya, M. M.; Zampieri, G.

    1992-08-01

    We present a theory of the elastic scattering of electrons from crystalline surfaces that contains both low-energy-electron-diffraction (LEED) effects at low energies and x-ray-photoelectron- and Auger-electron-diffraction (XPD/AED) effects at intermediate energies. The theory is based on a cluster-type approach to the scattering problem and includes temperature effects. The transition from one regime to the other may be explained as follows: At low energies all the scattered waves add coherently, and the intensity is dominated by LEED effects. At intermediate energies the thermal vibration of the atoms destroys the long-range coherency responsible for the LEED peaks, but affects little the interference of those waves that share parts of their paths inside the solid. Thus, the interference of these waves comes to dominate the intensity, giving rise to structures similar to those observed in XPD/AED experiments. We perform a calculation of the elastic reflection of electrons from Cu(001) that is in good agreement with the experiment in the range 200-1500 eV. At low energies the intensity is dominated by LEED peaks; at 400 eV LEED peaks and XPD/AED structures coexist; and above this energy the intensity is dominated by the latter. We analyze the contributions to the intensity at intermediate energies of the interferences in the incoming and outgoing parts of the electron path.

  16. Applications in Energy, Optics and Electronics.

    ERIC Educational Resources Information Center

    Rosenberg, Robert; And Others

    1980-01-01

    Discusses the applications of thin films in energy, optics and electronics. The use of thin-film technologies for heat mirrors, anti-reflection coatings, interference filters, solar cells, and metal contacts is included. (HM)

  17. Atomic electron binding energies in fermium

    SciTech Connect

    Das, M.P.

    1981-02-01

    Calculations of the binding energies of electrons in fermium by using a relativistic local-density functional theory are reported. It is found that relaxation effects are nonnegligible for inner core orbitals. Calculated orbital binding energies are compared with those due to nonlocal Dirac-Fock calculations and also with those determined experimentally from conversion electron spectroscopy. Finally the usefulness of the local-density approximation for the study of heavy atomic and condensed systems is discussed.

  18. 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.

  19. Electron energy-distribution functions in gases

    SciTech Connect

    Pitchford, L.C.

    1981-01-01

    Numerical calculation of the electron energy distribution functions in the regime of drift tube experiments is discussed. The discussion is limited to constant applied fields and values of E/N (ratio of electric field strength to neutral density) low enough that electron growth due to ionization can be neglected. (GHT)

  20. Simple Experimental Verification of the Relation between the Band-Gap Energy and the Energy of Photons Emitted by LEDs

    ERIC Educational Resources Information Center

    Precker, Jurgen W.

    2007-01-01

    The wavelength of the light emitted by a light-emitting diode (LED) is intimately related to the band-gap energy of the semiconductor from which the LED is made. We experimentally estimate the band-gap energies of several types of LEDs, and compare them with the energies of the emitted light, which ranges from infrared to white. In spite of…

  1. Band offset formation at semiconductor heterojunctions through density-based minimization of interface energy

    NASA Astrophysics Data System (ADS)

    Tung, Raymond T.; Kronik, Leeor

    2016-08-01

    It is well known that the magnitude of band offset (BO) at any semiconductor heterojunction is directly derivable from the distribution of charge at that interface and that the latter is decided by a minimization of total energy. However, the fact that BO formation is governed by energy minimization has not been explicitly used in theoretical BO models, likely because the equilibrium charge densities at heterojunction interfaces appear difficult to predict, except via explicit calculation. In this paper, electron densities at a large number of (100), (110), and (111) oriented heterojunctions between lattice-matched, isovalent semiconductors with the zinc blende (ZB) structure have been calculated by first-principles methods and analyzed in detail for possible common characteristics among energy-minimized densities. Remarkably, the heterojunction electron density was found to largely depend only on the immediate, local atomic arrangement. In fact, it is so much so that a juxtaposition of local electron-densities generated in oligo-cells (LEGOs) accurately reproduced the charge densities that minimize the energy for the heterojunctions. Furthermore, the charge distribution for each bulk semiconductor was found to display a striking separability of its electrostatic effect into two neutral parts, associated with the cation and the anion, which are approximately transferrable among semiconductors. These discoveries form the basis of a neutral polyhedra theory (NPT) that approximately predicts the equilibrium charge density and BO of relaxed heterojunctions from the energy minimization requirement. Well-known experimentally observed characteristics of heterojunctions, such as the insensitivity of BO to heterojunction orientation and the identity of interface bonds, the transitivity rule, etc., are all in good agreement with the NPT. Therefore, energy minimization, which essentially decides the electronic properties of all other solid and molecular systems, also governs

  2. 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.

  3. Determining Energy Distributions of HF-Accelerated Electrons at HAARP

    DTIC Science & Technology

    2015-11-18

    are presented for selected modification mechanisms (electron heating or electron acceleration energy ), total RF-plasma energy transfer flux, and...suprathermal accelerated electron energy spectra [Gustavsson et al., 2005] using inversion techniques similar to those described by Rees and Luckey [1974...primary excitation mechanisms include electron impact excitation by energetic electrons with kinetic energy exceeding the respective energies of 1.96 and

  4. 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.

  5. 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.

  6. Electronic Devices and Systems. Energy Technology Series.

    ERIC Educational Resources Information Center

    Technical Education Research Centre-Southwest, Waco, TX.

    This course in electronic devices and systems is one of 16 courses in the Energy Technology Series developed for an Energy Conservation-and-Use Technology curriculum. Intended for use in two-year postsecondary technical institutions to prepare technicians for employment, the courses are also useful in industry for updating employees in…

  7. 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

  8. Esaki Diodes in van der Waals Heterojunctions with Broken-Gap Energy Band Alignment.

    PubMed

    Yan, Rusen; Fathipour, Sara; Han, Yimo; Song, Bo; Xiao, Shudong; Li, Mingda; Ma, Nan; Protasenko, Vladimir; Muller, David A; Jena, Debdeep; Xing, Huili Grace

    2015-09-09

    van der Waals (vdW) heterojunctions composed of two-dimensional (2D) layered materials are emerging as a solid-state materials family that exhibits novel physics phenomena that can power a range of electronic and photonic applications. Here, we present the first demonstration of an important building block in vdW solids: room temperature Esaki tunnel diodes. The Esaki diodes were realized in vdW heterostructures made of black phosphorus (BP) and tin diselenide (SnSe2), two layered semiconductors that possess a broken-gap energy band offset. The presence of a thin insulating barrier between BP and SnSe2 enabled the observation of a prominent negative differential resistance (NDR) region in the forward-bias current-voltage characteristics, with a peak to valley ratio of 1.8 at 300 K and 2.8 at 80 K. A weak temperature dependence of the NDR indicates electron tunneling being the dominant transport mechanism, and a theoretical model shows excellent agreement with the experimental results. Furthermore, the broken-gap band alignment is confirmed by the junction photoresponse, and the phosphorus double planes in a single layer of BP are resolved in transmission electron microscopy (TEM) for the first time. Our results represent a significant advance in the fundamental understanding of vdW heterojunctions and broaden the potential applications of 2D layered materials.

  9. 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.

  10. High Energy Electron Detection with ATIC

    NASA Technical Reports Server (NTRS)

    Chang, J.; Schmidt, W. K. H.; Adams, James H., Jr.; Ahn, H.; Ampe, J.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    The ATIC (Advanced Thin Ionization Calorimeter) balloon-borne ionization calorimeter is well suited to record and identify high energy cosmic ray electrons. The instrument was exposed to high-energy beams at CERN H2 bean-dine in September of 1999. We have simulated the performance of the instrument, and compare the simulations with actual high energy electron exposures at the CERN accelerator. Simulations and measurements do not compare exactly, in detail, but overall the simulations have predicted actual measured behavior quite well.

  11. 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.

  12. Theory of directed electronic energy transfer.

    PubMed

    Andrews, David L; Crisp, Richard G

    2006-03-01

    The migration of electronic energy between molecules or chromophores in molecular solids is a well-studied phenomenon. The ability to exert control over the directionality of this transfer, by a variety of methods involving applied electrical or optical fields, holds promise for advances in fields including nanoelectronics and energy harvesting materials. In this paper, we review in detail a number of methods for directing energy transfer, also identifying potential applications.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. Band Gap Engineering in a 2D Material for Solar-to-Chemical Energy Conversion.

    PubMed

    Hu, Jun; Guo, Zhenkun; Mcwilliams, Peter E; Darges, John E; Druffel, Daniel L; Moran, Andrew M; Warren, Scott C

    2016-01-13

    The electronic structure of 2D semiconductors depends on their thickness, providing new opportunities to engineer semiconductors for energy conversion, electronics, and catalysis. Here we show how a 3D semiconductor, black phosphorus, becomes active for solar-to-chemical energy conversion when it is thinned to a 2D material. The increase in its band gap, from 0.3 eV (3D) to 2.1 eV (2D monolayer), is accompanied by a 40-fold enhancement in the formation of chemical products. Despite this enhancement, smaller flakes also have shorter excited state lifetimes. We deduce a mechanism in which recombination occurs at flake edges, while the "van der Waals" surface of black phosphorus bonds to chemical intermediates and facilitates electron transfer. The unique properties of black phosphorus highlight its potential as a customizable material for solar energy conversion and catalysis, while also allowing us to identify design rules for 2D photocatalysts that will enable further improvements in these materials.

  18. Energy selection is not correlated in the Qx and Qy bands of a Mg-porphyrin embedded in a protein.

    PubMed Central

    Suisalu, A; Mauring, K; Kikas, J; Herenyi, L; Fidy, J

    2001-01-01

    The Qx-Qy splitting observed in the fluorescence excitation spectra of Mg-mesoporphyrin-IX substituted horseradish peroxidase (MgMP-HRP) and of its complex with naphthohydroxamic acid (NHA) was studied by spectral hole burning techniques. The width of a hole directly burnt in the Qy band and that of a satellite hole indirectly produced in Qy as a result of hole burning in Qx was compared. We also studied the dependence of the satellite hole in the Qy band on the burning frequency used in the Qx band. Both the directly and indirectly burnt holes were very broad in the (higher energy) Qy band. The width of the satellite hole in the Qy band was equal to the entire width of the inhomogeneously broadened band, independently from the position of hole burning in Qx. This is indicative of a clear lack of correlation between the electronic transition energies of the Qx and Qy bands. A photoproduct was produced by laser irradiation of the MgMP-HRP/NHA complex and was identified as a species with lowered Q-splitting. Conversion of the photoproduct could be achieved by thermal activation measured in temperature-cycling experiments, with a characteristic temperature of 25 K. We attribute the phototransformation to a conformational change of MgMP. PMID:11159420

  19. Mapping of valence energy losses via energy-filtered annular dark-field scanning transmission electron microscopy.

    PubMed

    Gu, Lin; Sigle, Wilfried; Koch, Christoph T; Nelayah, Jaysen; Srot, Vesna; van Aken, Peter A

    2009-08-01

    The advent of electron monochromators has opened new perspectives on electron energy-loss spectroscopy at low energy losses, including phenomena such as surface plasmon resonances or electron transitions from the valence to the conduction band. In this paper, we report first results making use of the combination of an energy filter and a post-filter annular dark-field detector. This instrumental design allows us to obtain energy-filtered (i.e. inelastic) annular dark-field images in scanning transmission electron microscopy of the 2-dimensional semiconductor band-gap distribution of a GaN/Al(45)Ga(55)N structure and of surface plasmon resonances of silver nanoprisms. In comparison to other approaches, the technique is less prone to inelastic delocalization and relativistic artefacts. The mixed contribution of elastic and inelastic contrast is discussed.

  20. 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.

  1. Stability of electron energy in the Fermilab electron cooler

    SciTech Connect

    Shemyakin, A.; Carlson, K.; Prost, L.R.; Saewert, G.; /Fermilab

    2009-02-01

    A powerful electron beam (4.3 MeV, 0.1 A DC) generated by an electrostatic accelerator has been used at Fermilab for three years to cool antiprotons in the Recycler ring. For electron cooling to be effective, the electron energy should not deviate from its optimum value by more than 500V. The main tool for studying the energy stability is the electron beam position in a high-dispersion area. The energy ripple (frequencies above 0.2 Hz) was found to be less than 150 eV rms; the main cause of the ripple is the fluctuations of the chain current. In addition, the energy can drift to up to several keV that is traced to two main sources. One of them is a drift of the charging current, and another is a temperature dependence of generating voltmeter readings. The paper describes the efforts to reach the required level of stability as well as the setup, diagnostics, results of measurements, and operational experience.

  2. 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.

  3. 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.

  4. Image simulation for electron energy loss spectroscopy

    SciTech Connect

    Oxley, Mark P.; Pennycook, Stephen J.

    2007-10-22

    In this paper, aberration correction of the probe forming optics of the scanning transmission electron microscope has allowed the probe-forming aperture to be increased in size, resulting in probes of the order of 1 Å in diameter. The next generation of correctors promise even smaller probes. Improved spectrometer optics also offers the possibility of larger electron energy loss spectrometry detectors. The localization of images based on core-loss electron energy loss spectroscopy is examined as function of both probe-forming aperture and detector size. The effective ionization is nonlocal in nature, and two common local approximations are compared to full nonlocal calculations. Finally, the affect of the channelling of the electron probe within the sample is also discussed.

  5. Image simulation for electron energy loss spectroscopy

    DOE PAGES

    Oxley, Mark P.; Pennycook, Stephen J.

    2007-10-22

    In this paper, aberration correction of the probe forming optics of the scanning transmission electron microscope has allowed the probe-forming aperture to be increased in size, resulting in probes of the order of 1 Å in diameter. The next generation of correctors promise even smaller probes. Improved spectrometer optics also offers the possibility of larger electron energy loss spectrometry detectors. The localization of images based on core-loss electron energy loss spectroscopy is examined as function of both probe-forming aperture and detector size. The effective ionization is nonlocal in nature, and two common local approximations are compared to full nonlocal calculations.more » Finally, the affect of the channelling of the electron probe within the sample is also discussed.« less

  6. 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.

  7. 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

  8. Electronic structure of reconstructed InAs(001) surfaces - identification of bulk and surface bands based on their symmetries

    NASA Astrophysics Data System (ADS)

    Olszowska, Natalia; Kolodziej, Jacek J.

    2016-02-01

    Using angle-resolved photoelectron spectroscopy (ARPES) band structures of indium- and arsenic-terminated InAs(001) surfaces are investigated. These surfaces are highly reconstructed, elementary cells of their lattices contain many atoms in different chemical configurations, and moreover, they are composed of domains having related but different reconstructions. These domain-type surface reconstructions result in the reciprocal spaces containing regions with well-defined k→∥-vector and regions with not-well-defined one. In the ARPES spectra most of the surface related features appear as straight lines in the indeterminate k→∥-vector space. It is shown that, thanks to differences in crystal and surface symmetries, the single photon energy ARPES may be successfully used for classification of surface and bulk bands of electronic states on complex, highly reconstructed surfaces instead of the most often used variable photon energy studies.

  9. Electronic energy loss spectra from mono-layer to few layers of phosphorene

    NASA Astrophysics Data System (ADS)

    Mohan, Brij; Thakur, Rajesh; Ahluwalia, P. K.

    2016-05-01

    Using first principles calculations, electronic and optical properties of few-layers phosphorene has been investigated. Electronic band structure show a moderate band gap of 0.9 eV in monolayer phosphorene which decreases with increasing number of layers. Optical properties of few-layers of phosphorene in infrared and visible region shows tunability with number of layers. Electron energy loss function has been plotted and huge red shift in plasmonic behaviours is found. These tunable electronic and optical properties of few-layers of phosphorene can be useful for the applications of optoelectronic devices.

  10. 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.

  11. On Puthoff's Semiclassical Electron and Vacuum Energy

    NASA Astrophysics Data System (ADS)

    Pereira, N. R.

    2016-12-01

    A possible connection between a point electron and vacuum energy was recently claimed by Puthoff (Int. J. Theor. Phys. 46, 3005 (2007)). He envisions a point electron as an ideally conducting spherical shell with a distributed charge on the surface, in equilibrium with the radiation pressure from electromagnetic vacuum fluctuations on the outside, and claims that his analysis demonstrates the reality of high-energy-density vacuum fluctuation fields. The present paper finds, instead, that the analysis is meaningless without specific knowledge on the cutoff frequency that is a free parameter in the model.

  12. Electron energy loss spectrometry of interstellar diamonds

    NASA Technical Reports Server (NTRS)

    Bernatowicz, Thomas J.; Gibbons, Patrick C.; Lewis, Roy S.

    1990-01-01

    The results are reported of electron energy loss spectra (EELS) measurements on diamond residues from carbonaceous meteorites designed to elucidate the structure and composition of interstellar diamonds. Dynamic effective medium theory is used to model the dielectric properties of the diamonds and in particular to synthesize the observed spectra as mixtures of diamond and various pi-bonded carbons. The results are shown to be quantitatively consistent with the idea that diamonds and their surfaces are the only contributors to the electron energy loss spectra of the diamond residues and that these peculiar spectra are the result of the exceptionally small grain size and large specific surface area of the interstellar diamonds.

  13. Stable topological insulators achieved using high energy electron beams

    PubMed Central

    Zhao, Lukas; Konczykowski, Marcin; Deng, Haiming; Korzhovska, Inna; Begliarbekov, Milan; Chen, Zhiyi; Papalazarou, Evangelos; Marsi, Marino; Perfetti, Luca; Hruban, Andrzej; Wołoś, Agnieszka; Krusin-Elbaum, Lia

    2016-01-01

    Topological insulators are potentially transformative quantum solids with metallic surface states which have Dirac band structure and are immune to disorder. Ubiquitous charged bulk defects, however, pull the Fermi energy into the bulk bands, denying access to surface charge transport. Here we demonstrate that irradiation with swift (∼2.5 MeV energy) electron beams allows to compensate these defects, bring the Fermi level back into the bulk gap and reach the charge neutrality point (CNP). Controlling the beam fluence, we tune bulk conductivity from p- (hole-like) to n-type (electron-like), crossing the Dirac point and back, while preserving the Dirac energy dispersion. The CNP conductance has a two-dimensional character on the order of ten conductance quanta and reveals, both in Bi2Te3 and Bi2Se3, the presence of only two quantum channels corresponding to two topological surfaces. The intrinsic quantum transport of the topological states is accessible disregarding the bulk size. PMID:26961901

  14. 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.

  15. Spectroscopy of the simplest Criegee intermediate CH2OO: simulation of the first bands in its electronic and photoelectron spectra.

    PubMed

    Lee, Edmond P F; Mok, Daniel K W; Shallcross, Dudley E; Percival, Carl J; Osborn, David L; Taatjes, Craig A; Dyke, John M

    2012-09-24

    CH(2)OO, the simplest Criegee intermediate, and ozone are isoelectronic. They both play very important roles in atmospheric chemistry. Whilst extensive experimental studies have been made on ozone, there were no direct gas-phase studies on CH(2)OO until very recently when its photoionization spectrum was recorded and kinetics studies were made of some reactions of CH(2)OO with a number of molecules of atmospheric importance, using photoionization mass spectrometry to monitor CH(2)OO. In order to encourage more direct studies on CH(2)OO and other Criegee intermediates, the electronic and photoelectron spectra of CH(2)OO have been simulated using high level electronic structure calculations and Franck-Condon factor calculations, and the results are presented here. Adiabatic and vertical excitation energies of CH(2)OO were calculated with TDDFT, EOM-CCSD, and CASSCF methods. Also, DFT, QCISD and CASSCF calculations were performed on neutral and low-lying ionic states, with single energy calculations being carried out at higher levels to obtain more reliable ionization energies. The results show that the most intense band in the electronic spectrum of CH(2) OO corresponds to the B(1)A' ← X(1)A' absorption. It is a broad band in the region 250-450 nm showing extensive structure in vibrational modes involving O-O stretching and C-O-O bending. Evidence is presented to show that the electronic absorption spectrum of CH(2)OO has probably been recorded in earlier work, albeit at low resolution. We suggest that CH(2)OO was prepared in this earlier work from the reaction of CH(2)I with O(2) and that the assignment of the observed spectrum solely to CH(2)IOO is incorrect. The low ionization energy region of the photoelectron spectrum of CH(2)OO consists of two overlapping vibrationally structured bands corresponding to one-electron ionizations from the highest two occupied molecular orbitals of the neutral molecule. In each case, the adiabatic component is the most intense

  16. Electrospun Fibers for Energy, Electronic, & Environmental Applications

    NASA Astrophysics Data System (ADS)

    Bedford, Nicholas M.

    applications, fibers consisting of the commonly used organic photovoltaic electron donor/acceptor pair P3HT:PCBM were made by coaxial electrospinning. The inclusion of P3HT:PCBM fibers into an active layer of a organic photovoltaic device led to a ˜ 50% increase in power conversion efficiency over a thin film device of identical chemical composition and thickness. The inclusion of biological photosynthetic moieties into electrically relevant conjugated polymers was also explored for electrical applications. Polymeric fibers consisting largely of PEDOT:PSS were doped with thylakoid vesicles from spinach, and were found to act as photo-detectors. Native PEDOT:PSS does not exhibit such properties. For environmental applications, photocatalytic degradation membranes were also created by electrospinning cellulosic fibers which could be used as platforms to efficiently bind the photocatalyst TiO2. Employing different fiber-titania binding strategies, titania nanoparticles of various sizes and band gap configurations were successfully incorporated into mats of non-woven cellulosic nanofibers. These mats were found to successfully degrade dyes and relevant fresh water toxins such as microcystin-LR.

  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. Applications for Energy Recovering Free Electron Lasers

    SciTech Connect

    George Neil

    2007-08-01

    The availability of high-power, high-brilliance sources of tunable photons from energy-recovered Free Electron Lasers is opening up whole new fields of application of accelerators in industry. This talk will review some of the ideas that are already being put into production, and some of the newer ideas that are still under development.

  20. Electron energy flux in the solar wind.

    NASA Technical Reports Server (NTRS)

    Ogilvie, K. W.; Scudder, J. D.; Sugiura, M.

    1971-01-01

    Description of studies of electrons between 10 eV and 9.9 keV in the solar wind. The transport of energy in the rest frame of the plasma is evaluated and shown to be parallel to the interplanetary magnetic field. The presence of electrons from solar events causes this energy-flux density to exceed the heat flow due to thermal electrons. In one such event, the observations are shown to be consistent with the solar-electron observations made at higher energies. When observations are made at a point connected to the earth's bow shock by an interplanetary-field line, a comparatively large energy flux along the field toward the sun is observed, but the heat flow remains outwardly directed during this time interval. In either situation the heat flow is found to be consistent with measurements made on Vela satellites by a different method. These values, less than .01 ergs/sq cm/sec, are sufficiently low to require modifications to the Spitzer-Harm conductivity formula for use in solar-wind theories.

  1. Emittance and Energy Measurements of Low-Energy Electron Beam Using Optical Transition Radiation Techniques

    NASA Astrophysics Data System (ADS)

    Sakamoto, Fumito; Iijima, Hokuto; Dobashi, Katsuhiro; Imai, Takayuki; Ueda, Toru; Watanabe, Takahiro; Uesaka, Mitsuru

    2005-03-01

    Emittance and energy of an electron beam in the range of 8 to 22 MeV were measured via optical transition radiation (OTR) techniques. The beam divergence effect on observations of the far-field OTR image at low energies was studied by means of numerical analysis. The numerical analysis indicates that if the beam divergence is under 1.5 mrad, a simultaneous single-shot measurement of emittance and energy is possible. The results of the single-shot experiment agree with independent measurements conducted using the quadrupole scan method and an electron spectrometer. The experiments were performed with an S-band linac at the Nuclear Engineering Research Laboratory, The University of Tokyo (UTNL).

  2. 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.

  3. Sub-band gap photo-enhanced secondary electron emission from high-purity single-crystal chemical-vapor-deposited diamond

    NASA Astrophysics Data System (ADS)

    Yater, J. E.; Shaw, J. L.; Pate, B. B.; Feygelson, T. I.

    2016-02-01

    Secondary-electron-emission (SEE) current measured from high-purity, single-crystal (100) chemical-vapor-deposited diamond is found to increase when sub-band gap (3.06 eV) photons are incident on the hydrogenated surface. Although the light does not produce photoemission directly, the SEE current increases by more than a factor of 2 before saturating with increasing laser power. In energy distribution curves (EDCs), the emission peak shows a corresponding increase in intensity with increasing laser power. However, the emission-onset energy in the EDCs remains constant, indicating that the bands are pinned at the surface. On the other hand, changes are observed on the high-energy side of the distribution as the laser power increases, with a well-defined shoulder becoming more pronounced. From an analysis of this feature in the EDCs, it is deduced that upward band bending is present in the near-surface region during the SEE measurements and this band bending suppresses the SEE yield. However, sub-band gap photon illumination reduces the band bending and thereby increases the SEE current. Because the bands are pinned at the surface, we conclude that the changes in the band levels occur below the surface in the electron transport region. Sample heating produces similar effects as observed with sub-band gap photon illumination, namely, an increase in SEE current and a reduction in band bending. However, the upward band bending is not fully removed by either increasing laser power or temperature, and a minimum band bending of ˜0.8 eV is established in both cases. The sub-band gap photo-excitation mechanism is under further investigation, although it appears likely at present that defect or gap states play a role in the photo-enhanced SEE process. In the meantime, the study demonstrates the ability of visible light to modify the electronic properties of diamond and enhance the emission capabilities, which may have potential impact for diamond-based vacuum electron

  4. Sub-band gap photo-enhanced secondary electron emission from high-purity single-crystal chemical-vapor-deposited diamond

    SciTech Connect

    Yater, J. E. Shaw, J. L.; Pate, B. B.; Feygelson, T. I.

    2016-02-07

    Secondary-electron-emission (SEE) current measured from high-purity, single-crystal (100) chemical-vapor-deposited diamond is found to increase when sub-band gap (3.06 eV) photons are incident on the hydrogenated surface. Although the light does not produce photoemission directly, the SEE current increases by more than a factor of 2 before saturating with increasing laser power. In energy distribution curves (EDCs), the emission peak shows a corresponding increase in intensity with increasing laser power. However, the emission-onset energy in the EDCs remains constant, indicating that the bands are pinned at the surface. On the other hand, changes are observed on the high-energy side of the distribution as the laser power increases, with a well-defined shoulder becoming more pronounced. From an analysis of this feature in the EDCs, it is deduced that upward band bending is present in the near-surface region during the SEE measurements and this band bending suppresses the SEE yield. However, sub-band gap photon illumination reduces the band bending and thereby increases the SEE current. Because the bands are pinned at the surface, we conclude that the changes in the band levels occur below the surface in the electron transport region. Sample heating produces similar effects as observed with sub-band gap photon illumination, namely, an increase in SEE current and a reduction in band bending. However, the upward band bending is not fully removed by either increasing laser power or temperature, and a minimum band bending of ∼0.8 eV is established in both cases. The sub-band gap photo-excitation mechanism is under further investigation, although it appears likely at present that defect or gap states play a role in the photo-enhanced SEE process. In the meantime, the study demonstrates the ability of visible light to modify the electronic properties of diamond and enhance the emission capabilities, which may have potential impact for diamond-based vacuum electron

  5. Electronic excitation of molecular hydrogen by low-energy electrons

    NASA Astrophysics Data System (ADS)

    Hargreaves, Leigh

    2016-09-01

    Molecular hydrogen is the most abundant element in the universe, particularly in interstellar plasmas such as atmospheres of gas giant planets and stars. Electron collision data for hydrogen is critical to interpreting the spectroscopy of interstellar objects, as well as being of applied value for modelling technological plasmas. Hydrogen is also fundamentally interesting, as while highly accurate wave functions for this simple molecule are available, providing an accurate, ab initio, treatment the collision dynamics has proven challenging, on account of the need to have a complete description of channel coupling and polarization effects. To date, no single theoretical approach has been able to replicate experimental results across all transitions and incident energies, while the experimental database that is available is far from complete and not all available measurements are in satisfactory agreement. In this talk, we present differential and integral cross section measurements for electronic excitation cross sections for molecular hydrogen by low-energy electron impact. The data were measured at incident energies below 20eV, using a well-tested crossed beam apparatus and employing a moveable gas source approach to ensure that background contributions to the scattering are accurately accounted for. These measurements are compared with new theoretical results employing the convergent close coupling approach.

  6. Edge effects on band gap energy in bilayer 2H-MoS2 under uniaxial strain

    NASA Astrophysics Data System (ADS)

    Dong, Liang; Wang, Jin; Namburu, Raju; O'Regan, Terrance P.; Dubey, Madan; Dongare, Avinash M.

    2015-06-01

    The potential of ultrathin MoS2 nanostructures for applications in electronic and optoelectronic devices requires a fundamental understanding in their electronic structure as a function of strain. Previous experimental and theoretical studies assume that an identical strain and/or stress state is always maintained in the top and bottom layers of a bilayer MoS2 film. In this study, a bilayer MoS2 supercell is constructed differently from the prototypical unit cell in order to investigate the layer-dependent electronic band gap energy in a bilayer MoS2 film under uniaxial mechanical deformations. The supercell contains an MoS2 bottom layer and a relatively narrower top layer (nanoribbon with free edges) as a simplified model to simulate the as-grown bilayer MoS2 flakes with free edges observed experimentally. Our results show that the two layers have different band gap energies under a tensile uniaxial strain, although they remain mutually interacting by van der Waals interactions. The deviation in their band gap energies grows from 0 to 0.42 eV as the uniaxial strain increases from 0% to 6% under both uniaxial strain and stress conditions. The deviation, however, disappears if a compressive uniaxial strain is applied. These results demonstrate that tensile uniaxial strains applied to bilayer MoS2 films can result in distinct band gap energies in the bilayer structures. Such variations need to be accounted for when analyzing strain effects on electronic properties of bilayer or multilayered 2D materials using experimental methods or in continuum models.

  7. Electron impact ionization at relativistic energies

    NASA Astrophysics Data System (ADS)

    Belkacem, Ali; Cole, Kyra; Hertlein, Marcus; Feinberg, Benedict; Schriel, Ralf; Adaniya, Hidehito; Neumann, Nadine

    2004-05-01

    We used an ion time-of-flight set up based on a pulsed high-voltage extraction technique to study the charge state distribution of He, Ne, Ar, Kr and Xe atoms after impact of 0.2 to 1.5 GeV electrons. The relativistic electron beam is produced at the booster beamline at the Advanced Light Source at the Lawrence Berkeley National Laboratory. The yield of ions drops drastically with the charge state number. Our measurements show that the ratio of doubly-charge to singly-charged ions reaches an asymptotic limit of 0.0028 for He already at electron energies below 40 MeV. However we observe a very pronounced energy dependence of the ratio of the doubly-charged to singly-charged ions for the heavier atoms such as Kr and Xe in the 0.2 - 1.5 GeV energy range. This energy dependence takes place way above the energy at which theories based on the equivalent photon method or the born- approximation predict the asymptotic limit to be reached. This may be an indication of new physics coming into play in the photoionization process due to relativistic effects.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. Low Energy Electron Scattering from Fuels

    NASA Astrophysics Data System (ADS)

    Lopes, M. C. A.; Silva, D. G. M.; Bettega, M. H. F.; da Costa, R. F.; Lima, M. A. P.; Khakoo, M. A.; Winstead, C.; McKoy, V.

    2012-11-01

    In order to understand and optimize processes occurring during the ignition of plasma and its consequences in post-discharge for an internal combustion engine, especially considering the spark plug, we have produced in this work some basic information necessary to modeling spark ignition in alcohol- fuelled engines. Total cross sections of electron scattering by methanol and ethanol molecules in the energy range from 60 to 500 eV are reported, using the linear transmission method based on the Beer-Lambert law to first approximation. Aditionally to that, measurements and calculations of differential cross sections for elastic low-energy (rotationally unresolved) electron scattering were also discussed, for impact energies of 1, 2, 5, 10, 15, 20, 30, 50, and 100 eV and for scattering angles of 5°-130°. The measurements were obtained using the relative flow method with an aperture source, and calculations using two different implementations of the Schwinger multichannel method, one that takes all electrons into account and is adapted for parallel computers, and another that uses pseudopotentials and considers only the valence electrons.

  15. 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.

  16. Threshold conditions, energy spectrum and bands generated by locally periodic Dirac comb potentials

    NASA Astrophysics Data System (ADS)

    Dharani, M.; Shastry, C. S.

    2016-01-01

    We derive expressions for polynomials governing the threshold conditions for different types of locally periodic Dirac comb potentials comprising of attractive and combination of attractive and repulsive delta potential terms confined symmetrically inside a one dimensional box of fixed length. The roots of these polynomials specify the conditions on the potential parameters in order to generate threshold energy bound states. The mathematical and numerical methods used by us were first formulated in our earlier works and it is also very briefly summarized in this paper. We report a number of mathematical results pertaining to the threshold conditions and these are useful in controlling the number of negative energy states as desired. We further demonstrate the correlation between the distribution of roots of these polynomials and negative energy eigenvalues. Using these results as basis, we investigate the energy bands in the positive energy spectrum for the above specified Dirac comb potentials and also for the corresponding repulsive case. In the case of attractive Dirac comb the base energy of the each band excluding the first band coincides with specific eigenvalue of the confining box whereas in the repulsive case it coincides with the band top. We deduce systematic correlation between band gaps, band spreads and box eigenvalues and explain the physical reason for the vanishing of band pattern at higher energies. In the case of Dirac comb comprising of orderly arranged attractive and repulsive delta potentials, specific box eigenvalues occur in the middle of each band excluding the first band. From our study we find that by controlling the number and strength parameters of delta terms in the Dirac comb and the size of confining box it is possible to generate desired types of band formations. We believe the results from our systematic analysis are useful and relevant in the study of various one dimensional systems of physical interest in areas like nanoscience.

  17. Low Energy Electron Impact Excitation of Water

    NASA Astrophysics Data System (ADS)

    Ralphs, Kevin; Serna, Gabriela; Hargreaves, Leigh R.; Khakoo, Murtadha A.; Winstead, Carl; McKoy, B. Vincent

    2011-10-01

    We present normalized absolute differential and integral cross-section measurements for the low energy electron impact excitation of the lowest dissociative 3B1, 1B1,3A1 and 1A1 states of H2O. The DCS were taken at incident energies of 9 eV, 10 eV, 12 eV, 15 eV and 20 eV and scattering angles of 15° to 130° and normalized to the elastic electron scattering measurements of. The DCS were obtained after a sophisticated unfolding of the electron energy loss spectrum of water using photoabsorption data in the literature as investigated by Thorn et al.. Our measurements extend those of to near-threshold energies. We find both important agreements and differences between our DCS and those of. Comparison to our theory (multi-channel Schwinger) and that of earlier work will also be presented. Funded by an NSF grant # RUI-PHY 0968874.

  18. 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.

  19. 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.

  20. 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.

  1. Energy Bands and Thermoelectricity of Filled Skutterudite EuRu4As_{12}

    NASA Astrophysics Data System (ADS)

    Shankar, A.; Rai, D. P.; Sandeep; Khenata, R.; Thapa, R. K.; Mandal, P. K.

    2016-11-01

    Density functional theory-based calculations of the elastic and electronic properties with magnetic moments of the filled skutterudite EuRu4As_{12} have been performed in its ferromagnetic ground state. The full-potential linearized augmented plane wave (FP-LAPW) method has been used for the study presented here. The numerical values of the elastic parameters are estimated within the framework of the Voigt-Reuss-Hill approximations. The energy band structure calculation performed near the Fermi energy level shows the metallic nature of the material with a high value of Seebeck coefficient ( S). The presence of an exchange splitting of Eu-4 f states suggests their appreciable contribution toward the magnetic behavior. The analysis of the thermal transport properties confirms the result obtained from the electronic structure calculation with Seebeck coefficient of 118 μ{V/K} and the figure of merit ( ZT) value of 0.51, at room temperature. The estimated values of S and ZT indicate the possibility of the thermoelectric applications of the sample material.

  2. Low Energy Electron Scattering from Fuels

    NASA Astrophysics Data System (ADS)

    Lopes, M. Cristina A.

    2012-06-01

    We report an investigation of processes that occur during the ignition of the plasma and its consequences in post-discharge time for an internal combustion engine, in order to find the appropriate parameters to be used in cars that operate with lean mixtures air-fuel. The relevance of this theme has attracted much attention, and has been one of the subjects of collaboration between experimental and theoretical groups in the USA and Brazil. We have produced some basic information necessary to modeling spark ignition in alcohol- fuelled engines. Total cross sections of electron scattering by methanol and ethanol molecules were obtained, using the linear transmission method based on the Beer-Lambert law to first approximation. Measurements and calculations of differential cross sections for low-energy (rotationally unresolved) electron scattering were also obtained, for scattering angles of 5 --130 . The measurements were taken using the relative flow method with an aperture source, and calculations using two different implementations of the Schwinger multichannel method, one that takes all electrons into account and is adapted for parallel computers, and another that uses pseudopotentials and considers only the valence electrons. Additionally to these, computer simulation studies of electronic discharge in mixtures of ethanol were performed, using a Zero-Dimensional Plasma Kinetic solver. Previous reported models for combustion of ethanol and cross sections data for momentum transfer of electron collisions with ethanol were used. The time evolutions of the main species densities are reported and the ignition time delay discussed.

  3. Multi-band Eilenberger Theory of Superconductivity: Systematic Low-Energy Projection

    NASA Astrophysics Data System (ADS)

    Nagai, Yuki; Nakamura, Hiroki

    2016-07-01

    We propose the general multi-band quasiclassical Eilenberger theory of superconductivity to describe quasiparticle excitations in inhomogeneous systems. With the use of low-energy projection matrix, the M-band quasiclassical Eilenberger equations are systematically obtained from N-band Gor'kov equations. Here M is the internal degrees of freedom in the bands crossing the Fermi energy and N is the degree of freedom in a model. Our framework naturally includes inter-band off-diagonal elements of Green's functions, which have usually been neglected in previous multi-band quasiclassical frameworks. The resultant multi-band Eilenberger and Andreev equations are similar to the single-band ones, except for multi-band effects. The multi-band effects can exhibit the non-locality and the anisotropy in the mapped systems. Our framework can be applied to an arbitrary Hamiltonian (e.g., a tight-binding Hamiltonian derived by the first-principle calculation). As examples, we use our framework in various kinds of systems, such as noncentrosymmetric superconductor CePt3Si, three-orbital model for Sr2RuO4, heavy fermion CeCoIn5/YbCoIn5 superlattice, a topological superconductor with the strong spin-orbit coupling CuxBi2Se3, and a surface system on a topological insulator.

  4. Energy Impacts of Wide Band Gap Semiconductors in U.S. Light-Duty Electric Vehicle Fleet.

    PubMed

    Warren, Joshua A; Riddle, Matthew E; Graziano, Diane J; Das, Sujit; Upadhyayula, Venkata K K; Masanet, Eric; Cresko, Joe

    2015-09-01

    Silicon carbide and gallium nitride, two leading wide band gap semiconductors with significant potential in electric vehicle power electronics, are examined from a life cycle energy perspective and compared with incumbent silicon in U.S. light-duty electric vehicle fleet. Cradle-to-gate, silicon carbide is estimated to require more than twice the energy as silicon. However, the magnitude of vehicle use phase fuel savings potential is comparatively several orders of magnitude higher than the marginal increase in cradle-to-gate energy. Gallium nitride cradle-to-gate energy requirements are estimated to be similar to silicon, with use phase savings potential similar to or exceeding that of silicon carbide. Potential energy reductions in the United States vehicle fleet are examined through several scenarios that consider the market adoption potential of electric vehicles themselves, as well as the market adoption potential of wide band gap semiconductors in electric vehicles. For the 2015-2050 time frame, cumulative energy savings associated with the deployment of wide band gap semiconductors are estimated to range from 2-20 billion GJ depending on market adoption dynamics.

  5. Design, realization and test of C-band accelerating structures for the SPARC_LAB linac energy upgrade

    NASA Astrophysics Data System (ADS)

    Alesini, D.; Bellaveglia, M.; Biagini, M. E.; Boni, R.; Brönnimann, M.; Cardelli, F.; Chimenti, P.; Clementi, R.; Di Pirro, G.; Di Raddo, R.; Ferrario, M.; Ficcadenti, L.; Gallo, A.; Kalt, R.; Lollo, V.; Palumbo, L.; Piersanti, L.; Schilcher, T.

    2016-11-01

    The energy upgrade of the SPARC_LAB photo-injector at LNF-INFN (Frascati, Italy) has been originally conceived replacing one low gradient (13 MV/m) 3 m long SLAC type S-band traveling wave (TW) section with two 1.4 m long C-band accelerating sections. Due to the higher gradients reached by such structures, a higher energy beam can be obtained within the same accelerator footprint length. The use of C-band structures for electron acceleration has been adopted in a few FEL linacs in the world, among others, the Japanese Free Electron Laser at SPring-8 and the SwissFEL at Paul Scherrer Institute (PSI). The C-band sections are traveling wave, constant impedance structures with symmetric input and output axial couplers. Their design has been optimized for the operation with a SLED RF pulse compressor. In this paper we briefly review their design criteria and we focus on the construction, tuning, low and high-power RF tests. We also illustrate the design and realization of the dedicated low level RF system that has been done in collaboration with PSI in the framework of the EU TIARA project. Preliminary experimental results appear to confirm the operation of such structures with accelerating gradients larger than 35 MV/m.

  6. 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.

  7. 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.

  8. Acceleration of polarized electrons UPTO ultrahigh energies

    NASA Astrophysics Data System (ADS)

    Koop, I.; Otboev, A.; Shatunov, P.; Shatunov, Yu.; Mane, S.

    2016-12-01

    A wide world discussion have been opened few years ago about future e + e - collider after the Higgsboson discovery. Besides utterly high luminosity this machine has to operate with polarized beams. We shall overview in this paper problems and practical possibilities to satisfy second requirements of the future collider. The radiative beam polarization at this 100 km machine will be very long procedure. On other side, at the present time there are developed intensive polarized electron sources based on ArGa photo cathodes with polarization about 90 percents. We show, that fast electron synchrotron equipped pair Siberian Snake is able to provide to accelerate polarized electrons up to the top energy of the collider.

  9. 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

  10. Energy Transformation in Molecular Electronic Systems

    SciTech Connect

    Kasha, Michael

    1999-05-17

    This laboratory has developed many new ideas and methods in the electronic spectroscopy of molecules. This report covers the contract period 1993-1995. A number of the projects were completed in 1996, and those papers are included in the report. The DOE contract was terminated at the end of 1995 owing to a reorganizational change eliminating nationally the projects under the Office of Health and Environmental Research, U. S. Department of Energy.

  11. Low-energy electron scattering from cyanamide

    NASA Astrophysics Data System (ADS)

    Wang, Kedong; Guo, Shuangcheng; Meng, Ju; Huang, Xiaotian; Wang, Yongfeng

    2016-09-01

    The low-energy electron collisions with cyanamide molecule are investigated by using the UK molecular R -matrix codes for electron energies ranging from 0.01 eV to 10 eV. Three models including static-exchange, static-exchange plus polarization, and close-coupling (CC) approximations are employed to reveal the dynamic interaction. Elastic (integrated and differential), momentum-transfer, and excitation cross sections from the ground state to the three low-lying electron excited states have been presented. Two shape resonances, two core-excited resonances, and two Feshbach resonances are detected in the CC approximation. The role of active space in the target and scattering problem including the resonances is discussed. The precise resonance parameters are found to be sensitive to the treatment of polarization effects employed. These resonances may be responsible for the fragments observed in a recent experiment of the dissociative electron attachments to cyanamide. Since the cyanamide molecule has a large permanent dipole moment, a Born closure procedure is used to account for the contribution of partial waves higher than l =4 to obtain converged cross sections.

  12. An electron energy-loss study of picene and chrysene based charge transfer salts

    SciTech Connect

    Müller, Eric; Mahns, Benjamin; Büchner, Bernd; Knupfer, Martin

    2015-05-14

    The electronic excitation spectra of charge transfer compounds built from the hydrocarbons picene and chrysene, and the strong electron acceptors F{sub 4}TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) and TCNQ (7,7,8,8-tetracyanoquinodimethan) have been investigated using electron energy-loss spectroscopy. The corresponding charge transfer compounds have been prepared by co-evaporation of the pristine constituents. We demonstrate that all investigated combinations support charge transfer, which results in new electronic excitation features at low energy. This might represent a way to synthesize low band gap organic semiconductors.

  13. 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.

  14. Electron transport and electron energy distributions within the wurtzite and zinc-blende phases of indium nitride: Response to the application of a constant and uniform electric field

    SciTech Connect

    Siddiqua, Poppy; Hadi, Walid A.; Salhotra, Amith K.; O'Leary, Stephen K.; Shur, Michael S.

    2015-03-28

    Within the framework of an ensemble semi-classical three-valley Monte Carlo electron transport simulation approach, we critically contrast the nature of the electron transport that occurs within the wurtzite and zinc-blende phases of indium nitride in response to the application of a constant and uniform electric field. We use the electron energy distribution and its relationship with the electron transport characteristics in order to pursue this analysis. For the case of zinc-blende indium nitride, only a peak corresponding to the electrons within the lowest energy conduction band valley is observed, this peak being seen to broaden and shift to higher energies in response to increases in the applied electric field strength, negligible amounts of upper energy conduction band valley occupancy being observed. In contrast, for the case of wurtzite indium nitride, in addition to the aforementioned lowest energy conduction band valley peak in the electron energy distribution, and its broadening and shifting to higher energies in response to increases in the applied electric field strength, beyond a certain critical electric field strength, 30 kV/cm for the case of this particular material, upper energy conduction band valley occupancy is observed, this occupancy being further enhanced in response to further increases in the applied electric field strength. Reasons for these results are provided. The potential for device consequences is then commented upon.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. Energy band gap and optical transition of metal ion modified double crossover DNA lattices.

    PubMed

    Dugasani, Sreekantha Reddy; Ha, Taewoo; Gnapareddy, Bramaramba; Choi, Kyujin; Lee, Junwye; Kim, Byeonghoon; Kim, Jae Hoon; Park, Sung Ha

    2014-10-22

    We report on the energy band gap and optical transition of a series of divalent metal ion (Cu(2+), Ni(2+), Zn(2+), and Co(2+)) modified DNA (M-DNA) double crossover (DX) lattices fabricated on fused silica by the substrate-assisted growth (SAG) method. We demonstrate how the degree of coverage of the DX lattices is influenced by the DX monomer concentration and also analyze the band gaps of the M-DNA lattices. The energy band gap of the M-DNA, between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), ranges from 4.67 to 4.98 eV as judged by optical transitions. Relative to the band gap of a pristine DNA molecule (4.69 eV), the band gap of the M-DNA lattices increases with metal ion doping up to a critical concentration and then decreases with further doping. Interestingly, except for the case of Ni(2+), the onset of the second absorption band shifts to a lower energy until a critical concentration and then shifts to a higher energy with further increasing the metal ion concentration, which is consistent with the evolution of electrical transport characteristics. Our results show that controllable metal ion doping is an effective method to tune the band gap energy of DNA-based nanostructures.

  20. Energy Dependence and Scaling Property of Localization Length near a Gapped Flat Band

    NASA Astrophysics Data System (ADS)

    Ge, Li; Tureci, Hakan

    Using a tight-binding model for a one-dimensional Lieb lattice, we show that the localization length near a gapped flat band behaves differently from the typical Urbach tail in a band gap: instead of reducing monotonically as the energy E moves away from the flat band energy Ef, the presence of the flat band causes a nonmonotonic energy dependence of the localization length. This energy dependence follows a scaling property when the energy is within the spread (W) of uniformly distributed diagonal disorder, i.e. the localization length is only a function of (E-Ef)/W. Several other lattices are compared to distinguish the effect of the flat band on the localization length, where we eliminate, shift, or duplicate the flat band, without changing the dispersion relations of other bands. Using the top right element of the Green's matrix, we derive an analytical relation between the density of states and the localization length, which shines light on these properties of the latter, including a summation rule for its inverse. This work is partially supported by NSF under Grant No. DMR-1506987.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Band energy control of molybdenum oxide by surface hydration

    SciTech Connect

    Butler, Keith T. Walsh, Aron; Crespo-Otero, Rachel; Buckeridge, John; Scanlon, David O.; Bovill, Edward; Lidzey, David

    2015-12-07

    The application of oxide buffer layers for improved carrier extraction is ubiquitous in organic electronics. However, the performance is highly susceptible to processing conditions. Notably, the interface stability and electronic structure is extremely sensitive to the uptake of ambient water. In this study we use density functional theory calculations to asses the effects of adsorbed water on the electronic structure of MoO{sub x}, in the context of polymer-fullerene solar cells based on PCDTBT. We obtain excellent agreement with experimental values of the ionization potential for pristine MoO{sub 3} (010). We find that IP and EA values can vary by as much as 2.5 eV depending on the oxidation state of the surface and that adsorbed water can either increase or decrease the IP and EA depending on the concentration of surface water.

  7. Band energy control of molybdenum oxide by surface hydration

    NASA Astrophysics Data System (ADS)

    Butler, Keith T.; Crespo-Otero, Rachel; Buckeridge, John; Scanlon, David O.; Bovill, Edward; Lidzey, David; Walsh, Aron

    2015-12-01

    The application of oxide buffer layers for improved carrier extraction is ubiquitous in organic electronics. However, the performance is highly susceptible to processing conditions. Notably, the interface stability and electronic structure is extremely sensitive to the uptake of ambient water. In this study we use density functional theory calculations to asses the effects of adsorbed water on the electronic structure of MoOx, in the context of polymer-fullerene solar cells based on PCDTBT. We obtain excellent agreement with experimental values of the ionization potential for pristine MoO3 (010). We find that IP and EA values can vary by as much as 2.5 eV depending on the oxidation state of the surface and that adsorbed water can either increase or decrease the IP and EA depending on the concentration of surface water.

  8. Spin-dependent energy bands and spin polarization in two-dimensional spin-orbit lateral superlattices.

    PubMed

    Zhang, R L; Qi, D X; Wang, D L; Li, J; Peng, R W; Huang, R S; Wang, Mu

    2013-02-01

    In this work, we theoretically investigate the spin-split energy bands of electrons and spin-polarized transport in two-dimensional (2D) spin-orbit lateral superlattices (SOLSLs), where the square rods with Rashba spin-orbit coupling (SOC) are distributed periodically by applying gate voltages on the semiconductor. Within the Landauer framework of ballistic transport, the energy bands, the electrical conductance, the spin polarization and the spin-dependent electronic charge distributions have been calculated. It is found that the energy minibands are formed and the energy levels are split up by the Rashba SOC. As a result, the spin-polarized conductance is obtained even in the absence of external magnetic fields and magnetic materials. Meanwhile, the spin polarization can approach high values in the SOLSLs by manipulating the strength of SOC. Furthermore, the spin-dependent electronic charge distributions have been obtained, which present a clear picture of spin-polarized conductance. Our investigations have the potential applications in spin-based quantum devices and semiconductor spintronics.

  9. High-resolution electron microscopy and electron energy-loss spectroscopy of giant palladium clusters

    NASA Astrophysics Data System (ADS)

    Oleshko, V.; Volkov, V.; Gijbels, R.; Jacob, W.; Vargaftik, M.; Moiseev, I.; van Tendeloo, G.

    1995-12-01

    Combined structural and chemical characterization of cationic polynuclear palladium coordination compounds Pd561L60(OAc)180, where L=1,10-phenantroline or 2,2'-bipyridine has been carried out by high-resolution electron microscopy (HREM) and analytical electron microscopy methods including electron energy-loss spectroscopy (EELS), zero-loss electron spectroscopic imaging, and energy-dispersive X-ray spectroscopy (EDX). The cell structure of the cluster matter with almost completely uniform metal core size distributions centered around 2.3 ±0.5 nm was observed. Zero-loss energy filtering allowed to improve the image contrast and resolution. HREM images showed that most of the palladium clusters had a cubo-octahedral shape. Some of them had a distorted icosahedron structure exhibiting multiple twinning. The selected-area electron diffraction patterns confirmed the face centered cubic structure with lattice parameter close to that of metallic palladium. The energy-loss spectra of the populations of clusters contained several bands, which could be assigned to the delayed Pd M4, 5-edge at 362 eV, the Pd M3-edge at 533 eV and the Pd M2-edge at 561 eV, the NK-edge at about 400 eV, the O K-edge at 532 eV overlapping with the Pd M3-edge and the carbon C K-edge at 284 eV. Background subtraction was applied to reveal the exact positions and fine structure of low intensity elemental peaks. EELS evaluations have been confirmed by EDX. The recorded series of the Pd M-edges and the N K-edge in the spectra of the giant palladium clusters obviously were related to Pd-Pd- and Pd-ligand bonding.

  10. Effect of Electronic Acceptor Segments on Photophysical Properties of Low-Band-Gap Ambipolar Polymers

    PubMed Central

    Li, Yuanzuo; Cui, Jingang; Zhao, Jianing; Liu, Jinglin; Song, Peng; Ma, Fengcai

    2013-01-01

    Stimulated by a recent experimental report, charge transfer and photophysical properties of donor-acceptor ambipolar polymer were studied with the quantum chemistry calculation and the developed 3D charge difference density method. The effects of electronic acceptor strength on the structure, energy levels, electron density distribution, ionization potentials, and electron affinities were also obtained to estimate the transporting ability of hole and electron. With the developed 3D charge difference density, one visualizes the charge transfer process, distinguishes the role of molecular units, and finds the relationship between the role of DPP and excitation energy for the three polymers during photo-excitation. PMID:23365549

  11. Effect of electronic acceptor segments on photophysical properties of low-band-gap ambipolar polymers.

    PubMed

    Li, Yuanzuo; Cui, Jingang; Zhao, Jianing; Liu, Jinglin; Song, Peng; Ma, Fengcai

    2013-01-01

    Stimulated by a recent experimental report, charge transfer and photophysical properties of donor-acceptor ambipolar polymer were studied with the quantum chemistry calculation and the developed 3D charge difference density method. The effects of electronic acceptor strength on the structure, energy levels, electron density distribution, ionization potentials, and electron affinities were also obtained to estimate the transporting ability of hole and electron. With the developed 3D charge difference density, one visualizes the charge transfer process, distinguishes the role of molecular units, and finds the relationship between the role of DPP and excitation energy for the three polymers during photo-excitation.

  12. 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.

  13. 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.

  14. Electronic energy transfer: Localized operator partitioning of electronic energy in composite quantum systems

    NASA Astrophysics Data System (ADS)

    Khan, Yaser; Brumer, Paul

    2012-11-01

    A Hamiltonian based approach using spatially localized projection operators is introduced to give precise meaning to the chemically intuitive idea of the electronic energy on a quantum subsystem. This definition facilitates the study of electronic energy transfer in arbitrarily coupled quantum systems. In particular, the decomposition scheme can be applied to molecular components that are strongly interacting (with significant orbital overlap) as well as to isolated fragments. The result defines a consistent electronic energy at all internuclear distances, including the case of separated fragments, and reduces to the well-known Förster and Dexter results in their respective limits. Numerical calculations of coherent energy and charge transfer dynamics in simple model systems are presented and the effect of collisionally induced decoherence is examined.

  15. Direct observation of radiation-belt electron acceleration from electron-volt energies to megavolts by nonlinear whistlers.

    PubMed

    Mozer, F S; Agapitov, O; Krasnoselskikh, V; Lejosne, S; Reeves, G D; Roth, I

    2014-07-18

    The mechanisms for accelerating electrons from thermal to relativistic energies in the terrestrial magnetosphere, on the sun, and in many astrophysical environments have never been verified. We present the first direct observation of two processes that, in a chain, cause this acceleration in Earth's outer radiation belt. The two processes are parallel acceleration from electron-volt to kilovolt energies by parallel electric fields in time-domain structures (TDS), after which the parallel electron velocity becomes sufficiently large for Doppler-shifted upper band whistler frequencies to be in resonance with the electron gyration frequency, even though the electron energies are kilovolts and not hundreds of kilovolts. The electrons are then accelerated by the whistler perpendicular electric field to relativistic energies in several resonant interactions. TDS are packets of electric field spikes, each spike having duration of a few hundred microseconds and containing a local parallel electric field. The TDS of interest resulted from nonlinearity of the parallel electric field component in oblique whistlers and consisted of ∼ 0.1 msec pulses superposed on the whistler waveform with each such spike containing a net parallel potential the order of 50 V. Local magnetic field compression from remote activity provided the free energy to drive the two processes. The expected temporal correlations between the compressed magnetic field, the nonlinear whistlers with their parallel electric field spikes, the electron flux and the electron pitch angle distributions were all observed.

  16. Propagation of low energy solar electrons

    NASA Technical Reports Server (NTRS)

    Anderson, K. A.; Mcfadden, J. P.; Lin, R. P.

    1981-01-01

    Two events are reported in which 2-10 keV electrons of solar energy have undergone significant adiabatic mirroring and pitch angle scattering in large scale magnetic structures in the interplanetary medium within a distance of about 0.5 AU from the earth. Electrons of 3 keV, typical of the energies measured, have a speed of about one-tenth of the speed of light, so that their travel time from the sun at 0 deg pitch angle would be about 100 minutes. Their cyclotron radius is about 20 km for a pitch angle of 30 deg, and a field of magnitude of 5 nT, and the cyclotron period is about 7.1 milliseconds. The electrons are scattered by spatial variations in the interplanetary magnetic field. When the spatial variations are convected past a stationary spacecraft by a 500 km/sec solar wind, they are seen as temporal fluctuations at a frequency of about 3 Hz.

  17. Study of Low Energy Electron Inelastic Scattering Mechanisms Using Spin Sensitive Techniques

    NASA Astrophysics Data System (ADS)

    Hsu, Hongbing

    1995-01-01

    Spin sensitive electron spectroscopies were used to study low energy electron inelastic scattering from metal surfaces and thin films. In these experiments, a beam of spin polarized electrons from a GaAs source is directed on the sample surface, and the spin polarization and intensity are measured as a function of energy loss and scattering angle by a Mott electron polarimeter coupled with a concentric hemispherical energy analyzer. Systematic studies of the angular dependence of inelastically scattered electrons were conducted on a Cu(100) surface, and Mo/Cu(100), non-magnetized Fe/Cu(100), and Co/Cu(100) films. The polarization and intensity of scattered electrons were measured as function of energy loss and scattering angle. Further studies were also conducted on Ag(100) surface and amorphous Cu/Ag(100) films. From the experimental results, the angular distributions of dipole and impact scattered electrons can be determined individually and both are found to peak in the specular scattering direction. Preliminary studies were conducted on magnetized Co/Cu(100) films. The spin dependent scattering intensity asymmetry was measured, with a clearly observable peak at energy loss of ~1 eV, which coincides with the band splitting. The polarizations of secondary electrons produced by an unpolarized primary beam were also measured. The polarizations can be related to the band polarization of magnetized cobalt films.

  18. 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.

  19. 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

  20. Electron-electron correlations in square-well quantum dots: direct energy minimization approach.

    PubMed

    Goto, Hidekazu; Hirose, Kikuji

    2011-04-01

    Electron-electron correlations in two-dimensional square-well quantum dots are investigated using the direct energy minimization scheme. Searches for groundstate charges and spin configurations are performed with varying the sizes of dots and the number of electrons. For a two-electron system, a standout difference between the configurations with and without counting correlation energy is demonstrated. The emergence and melting of Wigner-molecule-like structures arising from the interplay between the kinetic energy and Coulombic interaction energy are described. Electron-electron correlation energies and addition energy spectra are calculated, and special electron numbers related to peculiar effects of the square well are extracted.

  1. 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

  2. Comprehensive studies of the electronic structure of pristine and potassium doped chrysene investigated by electron energy-loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Roth, Friedrich; Mahns, Benjamin; Schönfelder, Ronny; Hampel, Silke; Nohr, Markus; Büchner, Bernd; Knupfer, Martin

    2012-09-01

    We have performed electron energy-loss spectroscopy studies in order to investigate the electronic properties of chrysene molecular solids. The valence band electronic excitation spectra and the C 1s core level excitations have been measured for pristine and potassium doped chrysene. The core level studies show a fine structure which signals the presence of four close lying conduction bands close to the Fermi level. Upon potassium doping, these bands are filled with electrons, and we have reached a doping level of about K2.7chrysene. Furthermore, undoped chrysene is characterized by an optical gap of about 3.3 eV and five, relatively weak, excitonic features following the excitation onset. Doping induces major changes in the electronic excitation spectra, with a new, prominent low energy excitation at about 1.3 eV. The results of a Kramers-Kronig analysis indicate that this new feature can be assigned to a charge carrier plasmon in the doped material, and momentum dependent studies reveal a negative plasmon dispersion.

  3. Electronic band structure and optical gain of GaNxBiyAs1-x-y/GaAs pyramidal quantum dots

    NASA Astrophysics Data System (ADS)

    Song, Zhi-Gang; Bose, Sumanta; Fan, Wei-Jun; Li, Shu-Shen

    2016-04-01

    The electronic band structure and optical gain of GaNxBiyAs1-x-y/GaAs pyramidal quantum dots (QDs) are investigated using the 16-band k ṡ p model with constant strain. The optical gain is calculated taking both homogeneous and inhomogeneous broadenings into consideration. The effective band gap falls as we increase the composition of nitrogen (N) and bismuth (Bi) and with an appropriate choice of composition we can tune the emission wavelength to span within 1.3 μm-1.55 μm, for device application in fiber technology. The extent of this red shift is more profound in QDs compared with bulk material due to quantum confinement. Other factors affecting the emission characteristics include virtual crystal, strain profile, band anticrossing (BAC), and valence band anticrossing (VBAC). The strain profile has a profound impact on the electronic structure, specially the valence band of QDs, which can be determined using the composition distribution of wave functions. All these factors eventually affect the optical gain spectrum. With an increase in QD size, we observe a red shift in the emission energy and emergence of secondary peaks owing to transitions or greater energy compared with the fundamental transition.

  4. The nature of the low energy band of the Fenna-Matthews-Olson complex: vibronic signatures.

    PubMed

    Caycedo-Soler, Felipe; Chin, Alex W; Almeida, Javier; Huelga, Susana F; Plenio, Martin B

    2012-04-21

    Based entirely upon actual experimental observations on electron-phonon coupling, we develop a theoretical framework to show that the lowest energy band of the Fenna-Matthews-Olson complex exhibits observable features due to the quantum nature of the vibrational manifolds present in its chromophores. The study of linear spectra provides us with the basis to understand the dynamical features arising from the vibronic structure in nonlinear spectra in a progressive fashion, starting from a microscopic model to finally performing an inhomogeneous average. We show that the discreteness of the vibronic structure can be witnessed by probing the diagonal peaks of the nonlinear spectra by means of a relative phase shift in the waiting time resolved signal. Moreover, we demonstrate that the photon-echo and non-rephasing paths are sensitive to different harmonics in the vibrational manifold when static disorder is taken into account. Supported by analytical and numerical calculations, we show that non-diagonal resonances in the 2D spectra in the waiting time, further capture the discreteness of vibrations through a modulation of the amplitude without any effect in the signal intrinsic frequency. This fact generates a signal that is highly sensitive to correlations in the static disorder of the excitonic energy albeit protected against dephasing due to inhomogeneities of the vibrational ensemble.

  5. 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.

  6. Spins, Parity, Excitation Energies, and Octupole Structure of an Excited Superdeformed Band in {sup 194}Hg and Implications for Identical Bands

    SciTech Connect

    Hackman, G.; Khoo, T.L.; Carpenter, M.P.; Lauritsen, T.; Calderin, I.J.; Janssens, R.V.; Ackermann, D.; Ahmad, I.; Agarwala, S.; Blumenthal, D.J.; Fischer, S.M.; Nisius, D.; Reiter, P.; Young, J.; Amro, H.; Lopez-Martens, A.; Hannachi, F.; Korichi, A.; Amro, H.; Moore, E.F.; Lee, I.Y.; Macchiavelli, A.O.; Do Nakatsukasa, T.

    1997-11-01

    An excited superdeformed band in {sup 194}Hg , observed to decay directly to both normal-deformed and superdeformed yrast states, is proposed to be a K{sup {pi}}=2{sup {minus}} octupole vibrational band, based on its excitation energies, spins, and likely parity. The transition energies are identical to those of the yrast superdeformed band in {sup 192}Hg , but originate from levels with different spins and parities. The evolution of transition energies with spin suggests that cancellations between pairing and particle alignment are partly responsible for the identical transition energies. {copyright} {ital 1997} {ital The American Physical Society}

  7. Oligomeric state of human erythrocyte band 3 measured by fluorescence resonance energy homotransfer.

    PubMed Central

    Blackman, S M; Piston, D W; Beth, A H

    1998-01-01

    The oligomeric state of the erythrocyte anion exchange protein, band 3, has been assayed by resonance energy homotransfer. Homotransfer between oligomeric subunits, labeled with eosin-5-maleimide at Lys430 in the transmembrane domain, has been demonstrated by steady-state and time-resolved fluorescence spectroscopy, and is readily observed by its depolarization of the eosin fluorescence. Polarized fluorescence measurements of HPLC-purified band 3 oligomers indicate that eosin homotransfer increases progressively with increasing species size. This shows that homotransfer also occurs between labeled band 3 dimers as well as within the dimers, making fluorescence anisotropy measurements sensitive to band 3 self-association. Treatment of ghost membranes with either Zn2+ or melittin, agents that cluster band 3, significantly decreases the anisotropy as a result of the increased homotransfer within the band 3 clusters. By comparison with the anisotropy of species of known oligomeric state, the anisotropy of erythrocyte ghost membranes at 37 degrees C is consistent with dimeric and/or tetrameric band 3, and does not require postulation of a fraction of large clusters. Proteolytic removal of the cytoplasmic domain of band 3, which significantly increases the rotational mobility of the transmembrane domain, does not affect its oligomeric state, as reported by eosin homotransfer. These results support a model in which interaction with the membrane skeleton restricts the mobility of band 3 without significantly altering its self-association state. PMID:9675213

  8. 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

  9. Towards a comprehensive electronic database of polycyclic aromatic hydrocarbons and its application in constraining the identities of possible carriers of the diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Tan, Xiaofeng

    2009-01-01

    A theoretical approach is developed to pre-select individual polycyclic aromatic hydrocarbons (PAHs) as possible carriers of the diffuse interstellar bands (DIBs). In this approach, a computer program is used to enumerate all PAH molecules with up to a specific number of fused benzene rings. Fast quantum chemical calculations are then employed to calculate the electronic transition energies, oscillator strengths, and rotational constants of these molecules. An electronic database of all PAHs with up to any specific number of benzene rings can be constructed this way. Comparison of the electronic transition energies, oscillator strengths, and rotational band contours of all PAHs in the database with astronomical spectra allows one to constrain the identities of individual PAHs as possible carriers of some of the intense narrow DIBs. Using the current database containing up to 10 benzene rings we have pre-selected 8 closed-shell PAHs as possible carriers of the famous λ6614 DIB.

  10. Energy Band and Josephson Dynamics of Spin-Orbit Coupled Bose-Einstein Condensates

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Yu, Zi-Fa; Xue, Ju-Kui

    2015-10-01

    We theoretically investigate the energy band structure and Josephson dynamics of a spin-orbit coupled Bose-Einstein condensate in a double-well potential. We study the energy band structure and the corresponding tunneling dynamics of the system by properly adjusting the SO coupling, Raman coupling, Zeeman field and atomic interactions. The coupled effects of SO coupling, Raman coupling, Zeeman field and atomic interactions lead to the appearance of complex energy band structure including the loop structure. Particularly, the emergence of the loop structure in energy band also depends on SO coupling, Raman coupling, Zeeman field and atomic interactions. Correspondingly, the Josephson dynamics of the system are strongly related to the energy band structure. Especially, the emergence of the loop structure results in complex tunneling dynamics, including suppression-revival transitions and self-trapping of atoms transfer between two spin states and two wells. This engineering provides a possible means for studying energy level and corresponding dynamics of two-species SO coupled BECs. Supported by the National Natural Science Foundation of China under Grant Nos. 11274255 and 11305132, by Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant No. 20136203110001, by the Natural Science Foundation of Gansu province under Grant No. 2011GS04358, and by Creation of Science and Technology of Northwest Normal University under Grant Nos. NWNU-KJCXGC-03-48, NWNU-LKQN-12-12

  11. 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.

  12. Low energy electron beam induced vacancy activation in GaN

    SciTech Connect

    Nykaenen, H.; Suihkonen, S.; Sopanen, M.; Kilanski, L.

    2012-03-19

    Experimental evidence on low energy electron beam induced point defect activation in GaN grown by metal-organic vapor phase epitaxy (MOVPE) is presented. The GaN samples are irradiated with a 5-20 keV electron beam of a scanning electron microscope and investigated by photoluminescence and positron annihilation spectroscopy measurements. The degradation of the band-to-band luminescence of the irradiated GaN films is associated with the activation of point defects. The activated defects were identified as in-grown Ga-vacancies. We propose that MOVPE-GaN contains a significant concentration of passive V{sub Ga}-H{sub n} complexes that can be activated by H removal during low energy electron irradiation.

  13. Low energy electron beam induced vacancy activation in GaN

    NASA Astrophysics Data System (ADS)

    Nykänen, H.; Suihkonen, S.; Kilanski, L.; Sopanen, M.; Tuomisto, F.

    2012-03-01

    Experimental evidence on low energy electron beam induced point defect activation in GaN grown by metal-organic vapor phase epitaxy (MOVPE) is presented. The GaN samples are irradiated with a 5-20 keV electron beam of a scanning electron microscope and investigated by photoluminescence and positron annihilation spectroscopy measurements. The degradation of the band-to-band luminescence of the irradiated GaN films is associated with the activation of point defects. The activated defects were identified as in-grown Ga-vacancies. We propose that MOVPE-GaN contains a significant concentration of passive VGa-Hn complexes that can be activated by H removal during low energy electron irradiation.

  14. 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.

  15. Low-energy electron collisions with thiophene.

    PubMed

    da Costa, R F; Varella, M T do N; Lima, M A P; Bettega, M H F

    2013-05-21

    We report on elastic integral, momentum transfer, and differential cross sections for collisions of low-energy electrons with thiophene molecules. The scattering calculations presented here used the Schwinger multichannel method and were carried out in the static-exchange and static-exchange plus polarization approximations for energies ranging from 0.5 eV to 6 eV. We found shape resonances related to the formation of two long-lived π∗ anion states. These resonant structures are centered at the energies of 1.00 eV (2.85 eV) and 2.82 eV (5.00 eV) in the static-exchange plus polarization (static-exchange) approximation and belong to the B1 and A2 symmetries of the C2v point group, respectively. Our results also suggest the existence of a σ∗ shape resonance in the B2 symmetry with a strong d-wave character, located at around 2.78 eV (5.50 eV) as obtained in the static-exchange plus polarization (static-exchange) calculation. It is worth to mention that the results obtained at the static-exchange plus polarization level of approximation for the two π∗ resonances are in good agreement with the electron transmission spectroscopy results of 1.15 eV and 2.63 eV measured by Modelli and Burrow [J. Phys. Chem. A 108, 5721 (2004)]. The existence of the σ∗ shape resonance is in agreement with the observations of Dezarnaud-Dandiney et al. [J. Phys. B 31, L497 (1998)] based on the electron transmission spectra of dimethyl(poly)sulphides. A comparison among the resonances of thiophene with those of pyrrole and furan is also performed and, altogether, the resonance spectra obtained for these molecules point out that electron attachment to π∗ molecular orbitals is a general feature displayed by these five-membered heterocyclic compounds.

  16. Low-energy electron collisions with thiophene

    NASA Astrophysics Data System (ADS)

    da Costa, R. F.; Varella, M. T. do N.; Lima, M. A. P.; Bettega, M. H. F.

    2013-05-01

    We report on elastic integral, momentum transfer, and differential cross sections for collisions of low-energy electrons with thiophene molecules. The scattering calculations presented here used the Schwinger multichannel method and were carried out in the static-exchange and static-exchange plus polarization approximations for energies ranging from 0.5 eV to 6 eV. We found shape resonances related to the formation of two long-lived π* anion states. These resonant structures are centered at the energies of 1.00 eV (2.85 eV) and 2.82 eV (5.00 eV) in the static-exchange plus polarization (static-exchange) approximation and belong to the B1 and A2 symmetries of the C2v point group, respectively. Our results also suggest the existence of a σ* shape resonance in the B2 symmetry with a strong d-wave character, located at around 2.78 eV (5.50 eV) as obtained in the static-exchange plus polarization (static-exchange) calculation. It is worth to mention that the results obtained at the static-exchange plus polarization level of approximation for the two π* resonances are in good agreement with the electron transmission spectroscopy results of 1.15 eV and 2.63 eV measured by Modelli and Burrow [J. Phys. Chem. A 108, 5721 (2004), 10.1021/jp048759a]. The existence of the σ* shape resonance is in agreement with the observations of Dezarnaud-Dandiney et al. [J. Phys. B 31, L497 (1998), 10.1088/0953-4075/31/11/004] based on the electron transmission spectra of dimethyl(poly)sulphides. A comparison among the resonances of thiophene with those of pyrrole and furan is also performed and, altogether, the resonance spectra obtained for these molecules point out that electron attachment to π* molecular orbitals is a general feature displayed by these five-membered heterocyclic compounds.

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

    SciTech Connect

    Detert, Douglas M.; Tom, Kyle B.; Dubon, Oscar D.; Battaglia, Corsin; Javey, Ali; Denlinger, Jonathan D.; Lim, Sunnie H. N.; Anders, André; Yu, Kin M.; Walukiewicz, Wladek

    2014-06-21

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

  18. 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.

  19. 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.

  20. Effects of optical band gap energy, band tail energy and particle shape on photocatalytic activities of different ZnO nanostructures prepared by a hydrothermal method

    NASA Astrophysics Data System (ADS)

    Klubnuan, Sarunya; Suwanboon, Sumetha; Amornpitoksuk, Pongsaton

    2016-03-01

    The dependence of the crystallite size and the band tail energy on the optical properties, particle shape and oxygen vacancy of different ZnO nanostructures to catalyse photocatalytic degradation was investigated. The ZnO nanoplatelets and mesh-like ZnO lamellae were synthesized from the PEO19-b-PPO3 modified zinc acetate dihydrate using aqueous KOH and CO(NH2)2 solutions, respectively via a hydrothermal method. The band tail energy of the ZnO nanostructures had more influence on the band gap energy than the crystallite size. The photocatalytic degradation of methylene blue increased as a function of the irradiation time, the amount of oxygen vacancy and the intensity of the (0 0 0 2) plane. The ZnO nanoplatelets exhibited a better photocatalytic degradation of methylene blue than the mesh-like ZnO lamellae due to the migration of the photoelectrons and holes to the (0 0 0 1) and (0 0 0 -1) planes, respectively under the internal electric field, that resulted in the enhancement of the photocatalytic activities.

  1. Femtosecond spectroscopy of electron-electron and electron-phonon energy relaxation in Ag and Au

    NASA Astrophysics Data System (ADS)

    Groeneveld, Rogier H. M.; Sprik, Rudolf; Lagendijk, Ad

    1995-05-01

    We show experimentally that the electron distribution of a laser-heated metal is a nonthermal distribution on the time scale of the electron-phonon (e-ph) energy relaxation time τE. We measured τE in 45-nm Ag and 30-nm Au thin films as a function of lattice temperature (Ti=10-300 K) and laser-energy density (Ul=0.3-1.3 J cm-3), combining femtosecond optical transient-reflection techniques with the surface-plasmon polariton resonance. The experimental effective e-ph energy relaxation time decreased from 710-530 fs and 830-530 fs for Ag and Au, respectively, when temperature is lowered from 300 to 10 K. At various temperatures we varied Ul between 0.3-1.3 J cm-3 and observed that τE is independent from Ul within the given range. The results were first compared to theoretical predictions of the two-temperature model (TTM). The TTM is the generally accepted model for e-ph energy relaxation and is based on the assumption that electrons and lattice can be described by two different time-dependent temperatures Te and Ti, implying that the two subsystems each have a thermal distribution. The TTM predicts a quasiproportional relation between τE and Ti in the perturbative regime where τE is not affected by Ul. Hence, it is shown that the measured dependencies of τE on lattice temperature and energy density are incompatible with the TTM. It is proven that the TTM assumption of a thermal electron distribution does not hold especially under our experimental conditions of low laser power and lattice temperature. The electron distribution is a nonthermal distribution on the picosecond time scale of e-ph energy relaxation. We developed a new model, the nonthermal electron model (NEM), in which we account for the (finite) electron-electron (e-e) and electron-phonon dynamics simultaneously. It is demonstrated that incomplete electron thermalization yields a slower e-ph energy relaxation in comparison to the thermalized limit. With the NEM we are able to give a consistent

  2. High-Energy Anomaly in the Band Dispersion of the Ruthenate Superconductor

    NASA Astrophysics Data System (ADS)

    Iwasawa, H.; Yoshida, Y.; Hase, I.; Shimada, K.; Namatame, H.; Taniguchi, M.; Aiura, Y.

    2012-08-01

    We reveal a “high-energy anomaly” (HEA) in the band dispersion of the unconventional ruthenate superconductor Sr2RuO4, by means of high-resolution angle-resolved photoemission spectroscopy (ARPES) with tunable energy and polarization of incident photons. This observation provides another class of correlated materials exhibiting this anomaly beyond high-Tc cuprates. We demonstrate that two distinct types of band renormalization associated with and without the HEA occur as a natural consequence of the energetics in the bandwidth and the energy scale of the HEA. Our results are well reproduced by a simple analytical form of the self-energy based on the Fermi-liquid theory, indicating that the HEA exists at a characteristic energy scale of the multielectron excitations. We propose that the HEA universally emerges if the systems have such a characteristic energy scale inside of the bandwidth.

  3. Electronic Spectroscopy of [FePAH](+) Complexes in the Region of the Diffuse Interstellar Bands: Multireference Wave Function Studies on [FeC6H6](+).

    PubMed

    Lanza, Mathieu; Simon, Aude; Ben Amor, Nadia

    2015-06-11

    The low-energy states and electronic spectrum in the near-infrared-visible region of [FeC6H6](+) are studied by theoretical approaches. An exhaustive exploration of the potential energy surface of [FeC6H6](+) is performed using the density functional theory method. The ground state is found to be a (4)A1 state. The structures of the lowest energy states ((4)A2 and (4)A1) are used to perform multireference wave function calculations by means of the multistate complete active space with perturbation at the second order method. Contrary to the density functional theory results ((4)A1 ground state), multireference perturbative calculations show that the (4)A2 state is the ground state. The vertical electronic spectrum is computed and compared with the astronomical diffuse interstellar bands, a set of near-infrared-visible bands detected on the extinction curve in our and other galaxies. Many transitions are found in this domain, corresponding to d → d, d → 4s, or d → π* excitations, but few are allowed and, if they are, their oscillation strengths are small. Even though some band positions could match some of the observed bands, the relative intensities do not fit, making the contribution of the [Fe-C6H6](+) complexes to the diffuse interstellar bands questionable. This work, however, lays the foundation for the studies of polycyclic aromatic hydrocarbons (PAHs) complexed to Fe cations that are more likely to possess d → π* and π → π* transitions in the diffuse interstellar bands domain. PAH ligands indeed possess a larger number of π and π* orbitals, respectively, higher and lower in energy than those of C6H6, which are expected to lead to lower energy d → π* and π → π* transitions in [FePAH](+) than in [FeC6H6](+) complexes.

  4. 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).

  5. Pairing mechanism of heavily electron doped FeSe systems: dynamical tuning of the pairing cutoff energy

    NASA Astrophysics Data System (ADS)

    Bang, Yunkyu

    2016-11-01

    We studied the pairing mechanism of the heavily electron doped FeSe (HEDIS) systems, which commonly have one incipient hole band—a band top below the Fermi level by a finite energy distance ε b —at Γ point and ordinary electron bands at M points in Brillouin zone (BZ). We found that the system allows two degenerate superconducting solutions with the exactly same T c in clean limit: the incipient {s}{he}+/- -gap ({{{Δ }}}h-\

  6. Effect of electron correlations on the Fe3Si and α -FeSi2 band structure and optical properties

    NASA Astrophysics Data System (ADS)

    Sandalov, Igor; Zamkova, Natalia; Zhandun, Vyacheslav; Tarasov, Ivan; Varnakov, Sergey; Yakovlev, Ivan; Solovyov, Leonid; Ovchinnikov, Sergey

    2015-11-01

    We use the Vienna ab initio simulation package (vasp) for evaluation of the quasiparticle spectra and their spectral weights within Hedin's GW approximation (GWA) for Fe3Si and α -FeSi2 within the non-self-consistent one-shot approximation G0W0 and self-consistent scGWA with the vertex corrections in the particle-hole channel, taken in the form of two-point kernel. As input for G0W0 , the band structure and wave functions evaluated within the generalized gradient corrected local-density approximation to density functional theory (GGA) have been used. The spectral weights of quasiparticles in these compounds deviate from unity everywhere and show nonmonotonic behavior in those parts of bands where the delocalized states contribute to their formation. The G0W0 and scGWA spectral weights are the same within 2%-5%. The scGWA shows a general tendency to return G0W0 bands to their GGA positions for the delocalized states, while in the flat bands it flattens even more. Variable angle spectroscopic ellipsometry measurements at T =296 K on grown single-crystalline ˜50 -nm-thick films of Fe3Si on n -Si(111) wafer have been performed in the interval of energies ω ˜(1.3 -5 ) eV. The comparison of G0W0 and scGW theory with experimental real and imaginary parts of permittivity, refractive index, extinction and absorption coefficients, reflectivity, and electron energy loss function shows that both G0W0 and scGW qualitatively describe experiment correctly, the position of the low-energy peaks is described better by the scGW theory, however, its detailed structure is not observed in the experimental curves. We suggest that the angle-resolved photoemission spectroscopy experiments, which can reveal the fine details of the quasiparticle band structure and spectral weights, could help to understand (i) if the scGWA with this type of vertex correction is sufficiently good for description of these iron silicides and, possibly, (ii) why some features of calculated permittivity are

  7. Simulation of energy-dependent electron diffusion processes in the Earth's outer radiation belt

    NASA Astrophysics Data System (ADS)

    Ma, Q.; Li, W.; Thorne, R. M.; Nishimura, Y.; Zhang, X.-J.; Reeves, G. D.; Kletzing, C. A.; Kurth, W. S.; Hospodarsky, G. B.; Henderson, M. G.; Spence, H. E.; Baker, D. N.; Blake, J. B.; Fennell, J. F.; Angelopoulos, V.

    2016-05-01

    The radial and local diffusion processes induced by various plasma waves govern the highly energetic electron dynamics in the Earth's radiation belts, causing distinct characteristics in electron distributions at various energies. In this study, we present our simulation results of the energetic electron evolution during a geomagnetic storm using the University of California, Los Angeles 3-D diffusion code. Following the plasma sheet electron injections, the electrons at different energy bands detected by the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron Proton Telescope (REPT) instruments on board the Van Allen Probes exhibit a rapid enhancement followed by a slow diffusive movement in differential energy fluxes, and the radial extent to which electrons can penetrate into depends on energy with closer penetration toward the Earth at lower energies than higher energies. We incorporate radial diffusion, local acceleration, and loss processes due to whistler mode wave observations to perform a 3-D diffusion simulation. Our simulation results demonstrate that chorus waves cause electron flux increase by more than 1 order of magnitude during the first 18 h, and the subsequent radial extents of the energetic electrons during the storm recovery phase are determined by the coupled radial diffusion and the pitch angle scattering by EMIC waves and plasmaspheric hiss. The radial diffusion caused by ULF waves and local plasma wave scattering are energy dependent, which lead to the observed electron flux variations with energy dependences. This study suggests that plasma wave distributions in the inner magnetosphere are crucial for the energy-dependent intrusions of several hundred keV to several MeV electrons.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Atomic and electronic structures evolution of the narrow band gap semiconductor Ag2Se under high pressure

    NASA Astrophysics Data System (ADS)

    Naumov, P.; Barkalov, O.; Mirhosseini, H.; Felser, C.; Medvedev, S. A.

    2016-09-01

    Non-trivial electronic properties of silver telluride and other chalcogenides, such as the presence of a topological insulator state, electronic topological transitions, metallization, and the possible emergence of superconductivity under pressure have attracted attention in recent years. In this work, we studied the electronic properties of silver selenide (Ag2Se). We performed direct current electrical resistivity measurements, in situ Raman spectroscopy, and synchrotron x-ray diffraction accompanied by ab initio calculations to explore pressure-induced changes to the atomic and electronic structure of Ag2Se. The temperature dependence of the electrical resistivity was measured up to 30 GPa in the 4-300 K temperature interval. Resistivity data showed an unusual increase in the thermal energy gap of phase I, which is a semiconductor under ambient conditions. Recently, a similar effect was reported for the 3D topological insulator Bi2Se3. Raman spectroscopy studies revealed lattice instability in phase I indicated by the softening of observed vibrational modes with pressure. Our hybrid functional band structure calculations predicted that phase I of Ag2Se would be a narrow band gap semiconductor, in accordance with experimental results. At a pressure of ~7.5 GPa, Ag2Se underwent a structural transition to phase II with an orthorhombic Pnma structure. The temperature dependence of the resistivity of Ag2Se phase II demonstrated its metallic character. Ag2Se phase III, which is stable above 16.5 GPa, is also metallic according to the resistivity data. No indication of the superconducting transition is found above 4 K in the studied pressure range.

  13. Strategic Energy Management Plan for the Santa Ynez Band of Chumash Indians

    SciTech Connect

    Davenport, Lars; Smythe, Louisa; Sarquilla, Lindsey; Ferguson, Kelly

    2015-03-27

    This plan outlines the Santa Ynez Band of Chumash Indians’ comprehensive energy management strategy including an assessment of current practices, a commitment to improving energy performance and reducing overall energy use, and recommended actions to achieve these goals. Vision Statement The primary objective of the Strategic Energy Management Plan is to implement energy efficiency, energy security, conservation, education, and renewable energy projects that align with the economic goals and cultural values of the community to improve the health and welfare of the tribe. The intended outcomes of implementing the energy plan include job creation, capacity building, and reduced energy costs for tribal community members, and tribal operations. By encouraging energy independence and local power production the plan will promote self-sufficiency. Mission & Objectives The Strategic Energy Plan will provide information and suggestions to guide tribal decision-making and provide a foundation for effective management of energy resources within the Santa Ynez Band of Chumash Indians (SYBCI) community. The objectives of developing this plan include; Assess current energy demand and costs of all tribal enterprises, offices, and facilities; Provide a baseline assessment of the SYBCI’s energy resources so that future progress can be clearly and consistently measured, and current usage better understood; Project future energy demand; Establish a system for centralized, ongoing tracking and analysis of tribal energy data that is applicable across sectors, facilities, and activities; Develop a unifying vision that is consistent with the tribe’s long-term cultural, social, environmental, and economic goals; Identify and evaluate the potential of opportunities for development of long-term, cost effective energy sources, such as renewable energy, energy efficiency and conservation, and other feasible supply- and demand-side options; and Build the SYBCI’s capacity for

  14. Energy transformation in molecular electronic systems

    SciTech Connect

    Kasha, M.

    1985-07-25

    Our new optical pumping spectroscopy (steady state, and double-laser pulse) allows the production and study of the unstable rare tautomer in its ground and excited states, including picosecond dynamic studies. Molecules under study here included 7-azaindole (model for biological purines), 3-hydroxyflavone (model for plant flavones), lumichrome, and other heterocyclics. New detailed molecular mechanisms for proton transfer are derived, especially with catalytic assisting molecules. A new proton-transfer laser of extraordinary efficiency has become a side dividend, possibly worth of industrial development. The excited and highly reactive singlet molecular oxygen species /sup 1/..delta../sub g/) has proven to be ubiquitous in chemical peroxide systems and in physically excited sensitizer-oxygen systems. Hyperbaric oxygen mechanisms in biology probably involve singlet oxygen. We have undertaken a spectroscopic study of tris - dibenzoylmethane chelates of Al, Gd, Eu, and Yb trivalent ions. These chelates offer a variety of electronic behaviors, from Z-effects on ..pi..-electron spin-orbital coupling (Al, Gd) to Weissman intramolecular energy transfer to 4f mestable levels (Eu, Gd). Elegant new spectroscopic resolution at 77K permits separation of tautomeric, parasitic self-absorption, dissociation, and cage effects to be resolved. 18 refs., 4 figs.

  15. Energy transformation in molecular electronic systems

    NASA Astrophysics Data System (ADS)

    Kasha, M.

    1985-07-01

    Our new optical pumping spectroscopy allows the production and study of the unstable rate tautomer in its ground and excited states, including picosecond dynamic studies. Molecules under study here included 7-azaindole 3-hydroxyflavone, lumichrome, and other heterocyclics. New detailed molecular mechanisms for proton transfer are derived, especially with catalytic assisting molecules. A new proton-transfer laser of extraordinary efficiency has become a side dividend, possibly worthy of industrial development. The excited and highly reactive singlet molecular oxygen species (1) DELTA sub g has proven to be ubiquitous in chemical peroxide systems and in physically excited sensitizer-oxygen systems. Hyperbaric oxygen mechanisms in biology probably involve singlet oxygen. We have undertaken a spectroscopic study of trisdibenzoylmethane chelates of Al, Gd, Eu, and Yb trivalent ions. These chelates offer a variety of electronic behaviors, from Z-effects on (PI)--electron spin-orbital coupling (Al, Gd) to Weissman intramolecular energy transfer to 4f mestable levels (Eu, Gd). Elegant new spectroscopic resolution at 77K permits separation of tautomeric, parasitic self-absorption, dissociation, and cage effects to be resolved.

  16. 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.

  17. 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.

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

    SciTech Connect

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

    2013-10-15

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

  19. Synthesis, characterization and band gap energy of poly(ɛ-caprolactone)/Sr-MSA nano-composite

    NASA Astrophysics Data System (ADS)

    Kannammal, L.; Palanikumar, S.; Meenarathi, B.; Yelilarasi, A.; Anbarasan, R.

    2014-04-01

    A mercaptosuccinic acid (MSA) decorated Sr nano-particle (NP) was prepared and characterized by using various analytical techniques and was used as a chemical initiator for the ring opening polymerization (ROP) of ɛ-caprolactone (CL). The ROP of CL was carried out at various experimental conditions under N2 atmosphere with mild stirring. The initiating efficiency of MSA-decorated Sr NP was tested in terms of Fourier transform infrared-relative intensity, melting temperature (Tm), degradation temperature (Td) and molecular weight (Mw) of poly(ɛ-caprolactone) (PCL), differential scanning calorimetry, UV-visible spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis and gel permeation chromatography analytical techniques. The nuclear magnetic resonance spectrum confirms the chemical structure of PCL. While increasing the [M/I] ratio, the Mw of PCL was linearly increased. The band gap energy of Sr was determined from the UV-visible spectrum. The reflectance study proves the hydrophobic nature of the Sr-hybrid and its nano-composite formation with PCL.

  20. Half-filled energy bands induced negative differential resistance in nitrogen-doped graphene.

    PubMed

    Li, Xiao-Fei; Lian, Ke-Yan; Qiu, Qi; Luo, Yi

    2015-03-07

    Nitrogen-doping brings novel properties and promising applications into graphene, but the underlying mechanism is still in debate. To determine the key factor in motivating the negative differential resistance (NDR) behaviour of nitrogen-doped graphene, the electronic structure and transport properties of an 11-dimer wide nitrogen-doped armchair graphene nanoribbon (N-AGNR) were systematically studied by first principles calculations. Both the effect of interaction between N-dopants and the effect of doping-sublattice on the NDR were examined for the first time. Taking into account the two effects, N-AGNR becomes metallic or semiconducting depending on the doping configuration, and its Fermi level varies in a large range. NDR was firmly verified not to be intrinsic for N-AGNRs. However, it is totally determined by whether nitrogen-doping induces half-filled energy bands (HFEBs) because it is HFEBs that cross the Fermi level and determine the transport properties of N-AGNR under low biases. With the bias increasing, the transmission spectrum near the Fermi level showed a flag shape, and therefore, the corresponding transport channel is totally suppressed at a certain bias, resulting in the NDR behaviour with a configuration-dependent peak-to-valley current ratio (PVCR) up to 10(4). Our findings give new insights into the microscopic mechanism of chemical doping induced NDR behaviour and will be useful in building NDR-based nanodevices in the future.

  1. 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.

  2. Suprathermal Electron Strahl Widths in the Presence of Narrow-band Whistler Waves in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Kajdič, P.; Alexandrova, O.; Maksimovic, M.; Lacombe, C.; Fazakerley, A. N.

    2016-12-01

    We perform the first statistical study of the effects of the interaction of suprathermal electrons with narrow-band whistler mode waves in the solar wind (SW). We show that this interaction does occur and that it is associated with enhanced widths of the so-called strahl component. The latter is directed along the interplanetary magnetic field away from the Sun. We do the study by comparing the strahl pitch angle widths in the SW at 1 AU in the absence of large scale discontinuities and transient structures, such as interplanetary shocks, interplanetary coronal mass ejections, stream interaction regions, etc. during times when the whistler mode waves were present and when they were absent. This is done by using the data from two Cluster instruments: Spatio Temporal Analysis of Field Fluctuations experiment (STAFF) data in the frequency range between ∼0.1 and ∼200 Hz were used for determining the wave properties and Plasma Electron And Current Experiment (PEACE) data sets at 12 central energies between ∼57 eV (equivalent to ∼10 typical electron thermal energies in the SW, E T ) and ∼676 eV (∼113 E T ) for pitch angle measurements. Statistical analysis shows that, during the intervals with the whistler waves, the strahl component on average exhibits pitch angle widths between 2° and 12° larger than during the intervals when these waves are not present. The largest difference is obtained for the electron central energy of ∼344 eV (∼57 E T ).

  3. Coulomb Energy Differences in T = 1 Mirror Rotational Bands in 50Fe and 50Cr

    NASA Astrophysics Data System (ADS)

    Lenzi, S. M.; Mărginean, N.; Napoli, D. R.; Ur, C. A.; Zuker, A. P.; de Angelis, G.; Algora, A.; Axiotis, M.; Bazzacco, D.; Belcari, N.; Bentley, M. A.; Bizzeti, P. G.; Bizzeti-Sona, A.; Brandolini, F.; von Brentano, P.; Bucurescu, D.; Cameron, J. A.; Chandler, C.; de Poli, M.; Dewald, A.; Eberth, H.; Farnea, E.; Gadea, A.; Garces-Narro, J.; Gelletly, W.; Grawe, H.; Isocrate, R.; Joss, D. T.; Kalfas, C. A.; Klug, T.; Lampman, T.; Lunardi, S.; Martínez, T.; Martínez-Pinedo, G.; Menegazzo, R.; Nyberg, J.; Podolyak, Zs.; Poves, A.; Ribas, R. V.; Rossi Alvarez, C.; Rubio, B.; Sánchez-Solano, J.; Spolaore, P.; Steinhardt, T.; Thelen, O.; Tonev, D.; Vitturi, A.; von Oertzen, W.; Weiszflog, M.

    2001-09-01

    Gamma rays from the N = Z-2 nucleus 50Fe have been observed, establishing the rotational ground state band up to the state Jπ = 11+ at 6.994 MeV excitation energy. The experimental Coulomb energy differences, obtained by comparison with the isobaric analog states in its mirror 50Cr, confirm the qualitative interpretation of the backbending patterns in terms of successive alignments of proton and neutron pairs. A quantitative agreement with experiment has been achieved by exact shell model calculations, incorporating the differences in radii along the yrast bands, and properly renormalizing the Coulomb matrix elements in the pf model space.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  5. Triple Hybrid Energy Harvesting Interface Electronics

    NASA Astrophysics Data System (ADS)

    Uluşan, H.; Chamanian, S.; Pathirana, W. M. P. R.; Zorlu, Ö.; Muhtaroğlu, A.; Külah, H.

    2016-11-01

    This study presents a novel triple hybrid system that combines simultaneously generated power from thermoelectric (TE), vibration-based electromagnetic (EM) and piezoelectric (PZT) harvesters for a relatively high power supply capability. In the proposed solution each harvesting source utilizes a distinct power management circuit that generates a DC voltage suitable for combining the three parallel supplies. The circuits are designed and implemented in 180 nm standard CMOS technology, and are terminated with a schottky diode to avoid reverse current flow. The harvested AC signal from the EM harvester is rectified with a self-powered AC-DC doubler, which utilizes active diode structures to minimize the forward- bias voltage drop. The PZT interface electronics utilizes a negative voltage converter as the first stage, followed by synchronous power extraction and DC-to-DC conversion through internal switches, and an external inductor. The ultra-low voltage DC power harvested by the TE generator is stepped up through a charge-pump driven by an LC oscillator with fully- integrated center-tapped differential inductors. Test results indicate that hybrid energy harvesting circuit provides more than 1 V output for load resistances higher than 100 kΩ (10 μW) where the stand-alone harvesting circuits are not able to reach 1 V output. This is the first hybrid harvester circuit that simultaneously extracts energy from three independent sources, and delivers a single DC output.

  6. Free electrons and ionic liquids: study of excited states by means of electron-energy loss spectroscopy and the density functional theory multireference configuration interaction method.

    PubMed

    Regeta, Khrystyna; Bannwarth, Christoph; Grimme, Stefan; Allan, Michael

    2015-06-28

    The technique of low energy (0-30 eV) electron impact spectroscopy, originally developed for gas phase molecules, is applied to room temperature ionic liquids (IL). Electron energy loss (EEL) spectra recorded near threshold, by collecting 0-2 eV electrons, are largely continuous, assigned to excitation of a quasi-continuum of high overtones and combination vibrations of low-frequency modes. EEL spectra recorded by collecting 10 eV electrons show predominantly discrete vibrational and electronic bands. The vibrational energy-loss spectra correspond well to IR spectra except for a broadening (∼0.04 eV) caused by the liquid surroundings, and enhanced overtone activity indicating a contribution from resonant excitation mechanism. The spectra of four representative ILs were recorded in the energy range of electronic excitations and compared to density functional theory multireference configuration interaction (DFT/MRCI) calculations, with good agreement. The spectra up to about 8 eV are dominated by π-π* transitions of the aromatic cations. The lowest bands were identified as triplet states. The spectral region 2-8 eV was empty in the case of a cation without π orbitals. The EEL spectrum of a saturated solution of methylene green in an IL band showed the methylene green EEL band at 2 eV, indicating that ILs may be used as a host to study nonvolatile compounds by this technique in the future.

  7. Reflection Electron Energy Loss Spectroscopy of Iron Monosilicide

    NASA Astrophysics Data System (ADS)

    Parshin, A. S.; Igumenov, A. Yu.; Mikhlin, Yu. L.; Pchelyakov, O. P.; Zhigalov, V. S.

    2017-02-01

    X-ray photoelectron spectra, reflection electron energy loss spectra, and inelastic electron scattering cross section spectra of iron monosilicide FeSi are investigated. It is shown that the spectra of inelastic electron scattering cross section have advantages over the reflection electron energy loss spectra in studying the processes of electron energy losses. An analysis of the fine structure of the inelastic electron scattering cross section spectra allows previously unresolved peaks to be identified and their energy, intensity, and nature to be determined. The difference between energies of fitting loss peaks in the spectra of inelastic electron scattering cross section of FeSi and pure Fe are more substantial than the chemical shifts in X-ray photoelectron spectra, which indicates the possibility of application of the fine structure of the spectra of inelastic electron scattering cross section for elemental analysis.

  8. Effect of Strong Correlations on the High Energy Anomaly in Hole- and Electron-Doped High-Tc Superconductors

    SciTech Connect

    Moritz, B.; Schmitt, F.; Meevasana, W.; Johnston, S.; Motoyama, E.M.; Greven, M.; Lu, D.H.; Kim, C.; Scalettar, R.T.; Shen, Z.-X.; Devereaux, T.P.; /SLAC, SIMES

    2010-02-15

    Recently, angle-resolved photoemission spectroscopy (ARPES) has been used to highlight an anomalously large band renormalization at high binding energies in cuprate superconductors: the high energy 'waterfall' or high energy anomaly (HEA). This paper demonstrates, using a combination of new ARPES measurements and quantum Monte Carlo simulations, that the HEA is not simply the byproduct of matrix element effects, but rather represents a cross-over from a quasi-particle band at low binding energies near the Fermi level to valence bands at higher binding energy, assumed to be of strong oxygen character, in both hole- and electron-doped cuprates. While photoemission matrix elements clearly play a role in changing the aesthetic appearance of the band dispersion, i.e. the 'waterfall'-like behavior, they provide an inadequate description for the physics that underlies the strong band renormalization giving rise to the HEA. Model calculations of the single-band Hubbard Hamiltonian showcase the role played by correlations in the formation of the HEA and uncover significant differences in the HEA energy scale for hole- and electron-doped cuprates. In addition, this approach properly captures the transfer of spectral weight accompanying both hole and electron doping in a correlated material and provides a unifying description of the HEA across both sides of the cuprate phase diagram.

  9. Quasiparticle self-consistent GW study of cuprates: electronic structure, model parameters, and the two-band theory for Tc

    PubMed Central

    Jang, Seung Woo; Kotani, Takao; Kino, Hiori; Kuroki, Kazuhiko; Han, Myung Joon

    2015-01-01

    Despite decades of progress, an understanding of unconventional superconductivity still remains elusive. An important open question is about the material dependence of the superconducting properties. Using the quasiparticle self-consistent GW method, we re-examine the electronic structure of copper oxide high-Tc materials. We show that QSGW captures several important features, distinctive from the conventional LDA results. The energy level splitting between and is significantly enlarged and the van Hove singularity point is lowered. The calculated results compare better than LDA with recent experimental results from resonant inelastic xray scattering and angle resolved photoemission experiments. This agreement with the experiments supports the previously suggested two-band theory for the material dependence of the superconducting transition temperature, Tc. PMID:26206417

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. Wavelet package frequency-band energy ratios of human EEG signals in sleeping

    NASA Astrophysics Data System (ADS)

    Wang, Li; Han, Qingpeng; Wang, Ping; Wen, Bangchun

    2005-12-01

    Human EEG (Electroencephalogram) signals, including 4 rhythms i.e. δ, θ, α, β, are typically nonlinear. They just coincide with different human sleeping states. The wavelet package decomposition and reconstruction techniques are firstly introduced in order to analyze the nonlinear EEG. A 6 level decomposition of EEG was achieved with "db20" as the mother wavelet, and the above 4 rhythms were combined with specialized 8 frequency sub-bands obtained in wavelet package transform. The four frequency band energy ratios, with normalized values, were calculated from the reconstructed signals. These frequency band energy ratios are used as quantify estimation indexes for human sleeping states. The experimental results confirm the proposed method to be effective.

  17. Lateral energy band profile modulation in tunnel field effect transistors based on gate structure engineering

    NASA Astrophysics Data System (ADS)

    Cui, Ning; Liang, Renrong; Wang, Jing; Xu, Jun

    2012-06-01

    Choosing novel materials and structures is important for enhancing the on-state current in tunnel field-effect transistors (TFETs). In this paper, we reveal that the on-state performance of TFETs is mainly determined by the energy band profile of the channel. According to this interpretation, we present a new concept of energy band profile modulation (BPM) achieved with gate structure engineering. It is believed that this approach can be used to suppress the ambipolar effect. Based on this method, a Si TFET device with a symmetrical tri-material-gate (TMG) structure is proposed. Two-dimensional numerical simulations demonstrated that the special band profile in this device can boost on-state performance, and it also suppresses the off-state current induced by the ambipolar effect. These unique advantages are maintained over a wide range of gate lengths and supply voltages. The BPM concept can serve as a guideline for improving the performance of nanoscale TFET devices.

  18. Energy band alignment in chalcogenide thin film solar cells from photoelectron spectroscopy.

    PubMed

    Klein, Andreas

    2015-04-10

    Energy band alignment plays an important role in thin film solar cells. This article presents an overview of the energy band alignment in chalcogenide thin film solar cells with a particular focus on the commercially available material systems CdTe and Cu(In,Ga)Se2. Experimental results from two decades of photoelectron spectroscopy experiments are compared with density functional theory calculations taken from literature. It is found that the experimentally determined energy band alignment is in good agreement with theoretical predictions for many interfaces. These alignments, in particular the theoretically predicted alignments, can therefore be considered as the intrinsic or natural alignments for a given material combination. The good agreement between experiment and theory enables a detailed discussion of the interfacial composition of Cu(In,Ga)Se2/CdS interfaces in terms of the contribution of ordered vacancy compounds to the alignment of the energy bands. It is furthermore shown that the most important interfaces in chalcogenide thin film solar cells, those between Cu(In,Ga)Se2 and CdS and between CdS and CdTe are quite insensitive to the processing of the layers. There are plenty of examples where a significant deviation between experimentally-determined band alignment and theoretical predictions are evident. In such cases a variation of band alignment of sometimes more than 1 eV depending on interface preparation can be obtained. This variation can lead to a significant deterioration of device properties. It is suggested that these modifications are related to the presence of high defect concentrations in the materials forming the contact. The particular defect chemistry of chalcogenide semiconductors, which is related to the ionicity of the chemical bond in these materials and which can be beneficial for material and device properties, can therefore cause significant device limitations, as e.g. in the case of the CuInS2 thin film solar cells or for new

  19. Excitation energies and spins of the yrast superdeformed band in {sup 191}Hg

    SciTech Connect

    Siem, S.; Reiter, P.; Khoo, T.L.; Lauritsen, T.; Carpenter, M.P.; Ahmad, I.; Calderin, I.J.; Duguet, T.; Fischer, S.M.; Gassmann, D.; Hackman, G.; Janssens, R.V.F.; Nisius, D.; Heenen, P.-H.; Amro, H.; Moore, E.F.; Doessing, T.; Garg, U.; Kharraja, B.; Hannachi, F.

    2004-07-01

    The excitation energies and spins of the levels in the yrast superdeformed band of {sup 191}Hg have been determined from two single-step {gamma} transitions and the quasicontinuum spectrum connecting the superdeformed and normal-deformed states. The results are compared with those from theoretical mean-field calculations with different interactions. A discussion of pairing in superdeformed states is also included.

  20. 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.

  1. Photon and electron collimator effects on electron output and abutting segments in energy modulated electron therapy

    SciTech Connect

    Olofsson, Lennart; Karlsson, Magnus G.; Karlsson, Mikael

    2005-10-15

    In energy modulated electron therapy a large fraction of the segments will be arranged as abutting segments where inhomogeneities in segment matching regions must be kept as small as possible. Furthermore, the output variation between different segments should be minimized and must in all cases be well predicted. For electron therapy with add-on collimators, both the electron MLC (eMLC) and the photon MLC (xMLC) contribute to these effects when an xMLC tracking technique is utilized to reduce the x-ray induced leakage. Two add-on electron collimator geometries have been analyzed using Monte Carlo simulations: One isocentric eMLC geometry with an isocentric clearance of 35 cm and air or helium in the treatment head, and one conventional proximity geometry with a clearance of 5 cm and air in the treatment head. The electron fluence output for 22.5 MeV electrons is not significantly affected by the xMLC if the shielding margins are larger than 2-3 cm. For small field sizes and 9.6 MeV electrons, the isocentric design with helium in the treatment head or shielding margins larger than 3 cm is needed to avoid a reduced electron output. Dose inhomogeneity in the matching region of electron segments is, in general, small when collimator positions are adjusted to account for divergence in the field. The effect of xMLC tracking on the electron output can be made negligible while still obtaining a substantially reduced x-ray leakage contribution. Collimator scattering effects do not interfere significantly when abutting beam techniques are properly applied.

  2. Ultra-Short Electron Bunch and X-Ray Temporal Diagnostics with an X-Band Transverse Deflector

    SciTech Connect

    Ding, Y.; Emma, P.; Frisch, J.; Huang, Z.; Loos, H.; Krejcik, P.; Wang, M-H.; Behrens, C.; /DESY

    2011-12-13

    The measurement of ultra-short electron bunches on the femtosecond time scale constitutes a very challenging problem. In X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of sub-ten femtosecond X-ray pulses is possible, and some efforts have been put into both ultra-short electron and X-ray beam diagnostics. Here we propose a single-shot method using a transverse rf deflector (X-band) after the undulator to reconstruct both the electron bunch and X-ray temporal profiles. Simulation studies show that about 1 fs (rms) time resolution may be achievable in the LCLS and is applicable to a wide range of FEL wavelengths and pulse lengths. The jitter, resolution and other related issues will be discussed. The successful operation of the Linac Coherent Light Source (LCLS), with its capability of generating free-electron laser (FEL) X-ray pulses from a few femtoseconds (fs) up to a few hundred fs, opens up vast opportunities for studying atoms and molecules on this unprecedented ultrashort time scale. However, tremendous challenges remain in the measurement and control of these ultrashort pulses with femtosecond precision, for both the electron beam (e-beam) and the X-ray pulses. For ultrashort e-beam bunch length measurements, a standard method has been established at LCLS using an S-band radio-frequency (rf) deflector, which works like a streak camera for electrons and is capable of resolving bunch lengths as short as {approx} 10 fs rms. However, the e-beam with low charges of 20 pC at LCLS, which is expected to be less than 10 fs in duration, is too short to be measured using this transverse deflector. The measurement of the electron bunch length is helpful in estimating the FEL X-ray pulse duration. However, for a realistic beam, such as that with a Gaussian shape or even a spiky profile, the FEL amplification varies along the bunch due to peak current or emittance variation. This will cause differences between the temporal

  3. Interfacial Properties of Monolayer and Bilayer MoS2 Contacts with Metals: Beyond the Energy Band Calculations

    PubMed Central

    Zhong, Hongxia; Quhe, Ruge; Wang, Yangyang; Ni, Zeyuan; Ye, Meng; Song, Zhigang; Pan, Yuanyuan; Yang, Jinbo; Yang, Li; Lei, Ming; Shi, Junjie; Lu, Jing

    2016-01-01

    Although many prototype devices based on two-dimensional (2D) MoS2 have been fabricated and wafer scale growth of 2D MoS2 has been realized, the fundamental nature of 2D MoS2-metal contacts has not been well understood yet. We provide a comprehensive ab initio study of the interfacial properties of a series of monolayer (ML) and bilayer (BL) MoS2-metal contacts (metal = Sc, Ti, Ag, Pt, Ni, and Au). A comparison between the calculated and observed Schottky barrier heights (SBHs) suggests that many-electron effects are strongly suppressed in channel 2D MoS2 due to a charge transfer. The extensively adopted energy band calculation scheme fails to reproduce the observed SBHs in 2D MoS2-Sc interface. By contrast, an ab initio quantum transport device simulation better reproduces the observed SBH in 2D MoS2-Sc interface and highlights the importance of a higher level theoretical approach beyond the energy band calculation in the interface study. BL MoS2-metal contacts generally have a reduced SBH than ML MoS2-metal contacts due to the interlayer coupling and thus have a higher electron injection efficiency. PMID:26928583

  4. Interfacial Properties of Monolayer and Bilayer MoS2 Contacts with Metals: Beyond the Energy Band Calculations.

    PubMed

    Zhong, Hongxia; Quhe, Ruge; Wang, Yangyang; Ni, Zeyuan; Ye, Meng; Song, Zhigang; Pan, Yuanyuan; Yang, Jinbo; Yang, Li; Lei, Ming; Shi, Junjie; Lu, Jing

    2016-03-01

    Although many prototype devices based on two-dimensional (2D) MoS2 have been fabricated and wafer scale growth of 2D MoS2 has been realized, the fundamental nature of 2D MoS2-metal contacts has not been well understood yet. We provide a comprehensive ab initio study of the interfacial properties of a series of monolayer (ML) and bilayer (BL) MoS2-metal contacts (metal = Sc, Ti, Ag, Pt, Ni, and Au). A comparison between the calculated and observed Schottky barrier heights (SBHs) suggests that many-electron effects are strongly suppressed in channel 2D MoS2 due to a charge transfer. The extensively adopted energy band calculation scheme fails to reproduce the observed SBHs in 2D MoS2-Sc interface. By contrast, an ab initio quantum transport device simulation better reproduces the observed SBH in 2D MoS2-Sc interface and highlights the importance of a higher level theoretical approach beyond the energy band calculation in the interface study. BL MoS2-metal contacts generally have a reduced SBH than ML MoS2-metal contacts due to the interlayer coupling and thus have a higher electron injection efficiency.

  5. Electronic band structure and specific features of Sm2NiMnO6 compound: DFT calculation

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Azam, Sikander

    2013-09-01

    The band structure, density of states, electronic charge density, Fermi surface and optical properties of Sm2NiMnO6 compound have been investigated with the support of density functional theory (DFT). The atomic positions of Sm2NiMnO6 compound were optimized by minimizing the forces acting on the atoms, using the full potential linear augmented plane wave method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel-Vosko GGA (EVGGA) to treat the exchange correlation potential by solving Kohn-Sham equations. The calculation shows that the compound is metallic with strong hybridization near the Fermi energy level (EF). The calculated density of states at the EF is about 21.60, 24.52 and 26.21 states/eV, and the bare linear low-temperature electronic specific heat coefficient (γ) is found to be 3.74, 4.25 and 4.54 mJ/mol K2 for EVGGA, GGA and LDA, respectively. The Fermi surface is composed of two sheets. The bonding features of the compounds are analyzed using the electronic charge density in the (011) crystallographic plane. The dispersion of the optical constants was calculated and discussed.

  6. EUV studies of N2 and O2 produced by low energy electron impact

    NASA Technical Reports Server (NTRS)

    Morgan, H. D.; Mentall, J. E.

    1983-01-01

    The emission spectra resulting from electron impact excitation on molecular nitrogen and oxygen in the 500-1200 A spectral region are investigated. Electron energies are from 0 to 300 eV. Numerous bands of N2 are found between 800 and 1000 A. Excitation functions are measured for the NII 916 A, the OI 879 A, and the OII 834 multiplets, and nitrogen band emission. Cross sections were measured at 200 eV for several of the band emissions plus the NI 1135 A, NI 1164 A, NI 1177 A, NII 776 A, NII 1084 A, OI 1152 A, OI 1041 A, OI 999 A, OI 989 A, OI 879 A, OII 834 A, OII 616 A, OII 555 A, OII 539 A, and OII 718 A multiplets.

  7. Atomistic potentials based energy flux integral criterion for dynamic adiabatic shear banding

    NASA Astrophysics Data System (ADS)

    Xu, Yun; Chen, Jun

    2015-02-01

    The energy flux integral criterion based on atomistic potentials within the framework of hyperelasticity-plasticity is proposed for dynamic adiabatic shear banding (ASB). System Helmholtz energy decomposition reveals that the dynamic influence on the integral path dependence is originated from the volumetric strain energy and partial deviatoric strain energy, and the plastic influence only from the rest part of deviatoric strain energy. The concept of critical shear banding energy is suggested for describing the initiation of ASB, which consists of the dynamic recrystallization (DRX) threshold energy and the thermal softening energy. The criterion directly relates energy flux to the basic physical processes that induce shear instability such as dislocation nucleations and multiplications, without introducing ad-hoc parameters in empirical constitutive models. It reduces to the classical path independent J-integral for quasi-static loading and elastic solids. The atomistic-to-continuum multiscale coupling method is used to simulate the initiation of ASB. Atomic configurations indicate that DRX induced microstructural softening may be essential to the dynamic shear localization and hence the initiation of ASB.

  8. Thermal electron energy distribution measurements in the ionosphere.

    NASA Technical Reports Server (NTRS)

    Hays, P. B.; Nagy, A. F.

    1973-01-01

    A recoverable payload instrumented for twilight airglow studies was launched by an Aerobee 150 from the White Sands Test Range on Feb. 8, 1971 at 13.56 UT. The payload included a low energy electron spectrometer (HARP) and a cylindrical Langmuir probe. The HARP electron spectrometer is a new device designed to make high resolution differential electron flux measurements. Measurements of ionospheric electron energy distribution in the range from about 0.2 to 4.0 eV are presented.

  9. Energy Measurements of Trapped Electrons from a Plasma Wakefield Accelerator

    SciTech Connect

    Kirby, Neil; Berry, Melissa; Blumenfeld, Ian; Decker, Franz-Josef; Hogan, Mark J.; Ischebeck, Rasmus; Iverson, Richard; Siemann, Robert H.; Walz, Dieter; Auerbach, David; Clayton, Christopher E.; Huang, Chengkun; Johnson, Devon; Joshi, Chandrashekhar; Lu, Wei; Marsh, Kenneth A.; Mori, Warren B.; Zhou, Miaomiao; Katsouleas, Thomas; Muggli, Patric

    2006-11-27

    Recent electron beam driven plasma wakefield accelerator experiments carried out at SLAC indicate trapping of plasma electrons. More charge came out of than went into the plasma. Most of this extra charge had energies at or below the 10 MeV level. In addition, there were trapped electron streaks that extended from a few GeV to tens of GeV, and there were mono-energetic trapped electron bunches with tens of GeV in energy.

  10. Energy Measurements of Trapped Electrons from a Plasma Wakefield Accelerator

    SciTech Connect

    Kirby, Neal; Auerbach, David; Berry, Melissa; Blumenfeld, Ian; Clayton, Christopher E.; Decer, Franz-Josef; Hogan, Mark J.; Huang, Chengkun; Ischebeck, Rasmus; Iverson, Richard; Johnson, Devon; Joshi, Chadrashekhar; Katsouleas, Thomas; Lu, Wei; Marsh, Kenneth A.; Mori, Warren B.; Muggli, Patric; Oz, Erdem; Siemann, Robert H.; Walz, Dieter; Zhou, Miaomiao; /SLAC /UCLA /Southern California U.

    2007-01-03

    Recent electron beam driven plasma wakefield accelerator experiments carried out at SLAC indicate trapping of plasma electrons. More charge came out of than went into the plasma. Most of this extra charge had energies at or below the 10 MeV level. In addition, there were trapped electron streaks that extended from a few GeV to tens of GeV, and there were mono-energetic trapped electron bunches with tens of GeV in energy.

  11. Energy distribution asymmetry of electron precipitation signatures at Mars

    NASA Astrophysics Data System (ADS)

    Soobiah, Y. I. J.; Barabash, S.; Nilsson, H.; Stenberg, G.; Lundin, R.; Coates, A. J.; Winningham, J. D.; Frahm, R. A.

    2013-02-01

    The different types of asymmetry observed in the energy distributions of electrons and heavy-ions (M/Q=16-44) during signatures of electron precipitation in the Martian ionosphere have been classified. This has been achieved using the space plasma instrumentation of MEX ASPERA-3 from peri-centre altitude to 2200 km. ASPERA-3 ELS observes signatures of electron precipitation on 43.0% of MEX orbits. Unaccelerated electrons in the form of sudden electron flux enhancements are the most common type of electron precipitation signature at Mars and account for ∼70% of the events observed in this study. Electrons that form unaccelerated electron precipitation signatures are either local ionospheric electrons with enhanced density, or electrons transported from another region of ionosphere, solar wind or tail, or a combination of local and transported electrons. The heating of electrons has a strong influence on the shape of most electron energy spectra from accelerated precipitation signatures. On most occasions the general flow of heavy-ions away from Mars is unchanged during the precipitation of electrons, which is thought to be the result of the finite gyroradius effect of the heavy-ions on crustal magnetic field lines. Only ∼17% of events show some form of heavy-ion acceleration that is either concurrent or at the periphery of an electron precipitation signature. The most common combination of electron and heavy-ion energy distributions for signatures of electron precipitation involves electrons that visually have very little asymmetry or are isotropic and heavy-ions that have a upward net flux, and suggest the upward current associated with aurora. Due to a lack of reliable measurements of electrons travelling towards Mars, it is likely we miss further evidence of upward currents. The second most common combination of electron and heavy-ion energy distributions for signatures of electron precipitation, are those distributions of electrons that are asymmetric and

  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. Wide energy electron precipitations and their impact on the middle atmosphere associated with the pulsating aurora

    NASA Astrophysics Data System (ADS)

    Miyoshi, Y.; Oyama, S. I.; Saito, S.; Turunen, E. S.; Kurita, S.; Kero, A.; Verronen, P. T.; Kataoka, R.; Ebihara, Y.; Kletzing, C.; Reeves, G. D.; Santolik, O.; Clilverd, M. A.; Rodger, C. J.; Tsuchiya, F.

    2015-12-01

    The pulsating aurora is caused by intermittent precipitations of tens keV electrons. It is also expected that not only tens keV electrons but also sub-relativistic/relativistic electrons precipitate simultaneously into the polar ionosphere owing to whistler-mode wave-particle interactions. We analyzed a pulsating aurora event in November 2012 using several ground-based observation data from EISCAT radar, riometer, sub-ionospheric radio wave receivers, and the Van Allen Probes satellite. The electron density profile obtained from EISCA Tromsø VHF radar identifies electron density enhancements at >68 km altitudes. The electron energy spectrum derived from the Markov Chain Monte Carlo (MCMC) method indicates the wide energy electron precipitations from 10 - 200 keV, suggesting precipitation of the population from the outer belt. The riometer and network of sub-ionospheric radio wave observations also show energetic electron precipitations coinciding with the electron density enhancements at 68 km altitude. During this period, footprint of the Van Allen Probe-A satellite was very close to Tromsø, and the satellite observed rising tone emissions of the lower-band chorus (LBC) waves near the equatorial plane. Using the satellite-observed LBC and trapped electrons as an initial condition, we conducted a computer simulation of the wave-particle interactions. The simulation showed simultaneous precipitation of electrons at both tens of keV and a few hundred keV. This result is consistent with the energy spectrum estimated with the MCMC method. This result revealed that electrons with a wide energy range from the plasma sheet to the outer belt simultaneously precipitate into the polar ionosphere in association with the pulsating aurora. Using the Sodankylä Ion Chemistry (SIC) model that is a detailed coupled neutral and ion chemistry model of the upper atmosphere, we also discuss the possible impacts on the middle atmosphere due to precipitations of wide energy electrons.

  14. Electron polarimetry at low energies in Hall C at JLab

    NASA Astrophysics Data System (ADS)

    Gaskell, D.

    2013-11-01

    Although the majority of Jefferson Lab experiments require multi-GeV electron beams, there have been a few opportunities to make electron beam polarization measurements at rather low energies. This proceedings will discuss some of the practical difficulties encountered in performing electron polarimetry via Mo/ller scattering at energies on the order of a few hundred MeV. Prospects for Compton polarimetry at very low energies will also be discussed. While Mo/ller scattering is likely the preferred method for electron polarimetry at energies below 500 MeV, there are certain aspects of the polarimeter and experiment design that must be carefully considered.

  15. Electron polarimetry at low energies in Hall C at JLab

    SciTech Connect

    Gaskell, D.

    2013-11-07

    Although the majority of Jefferson Lab experiments require multi-GeV electron beams, there have been a few opportunities to make electron beam polarization measurements at rather low energies. This proceedings will discuss some of the practical difficulties encountered in performing electron polarimetry via Mo/ller scattering at energies on the order of a few hundred MeV. Prospects for Compton polarimetry at very low energies will also be discussed. While Mo/ller scattering is likely the preferred method for electron polarimetry at energies below 500 MeV, there are certain aspects of the polarimeter and experiment design that must be carefully considered.

  16. Band gap energy and optical transitions in polyenes formed by thermal decomposition of polyvinyl alcohol

    NASA Astrophysics Data System (ADS)

    Kulak, A. I.; Bondarava, G. V.; Shchurevich, O. A.

    2013-07-01

    The band gap of the ensemble of oligoene clusters formed by thermocatalytic decomposition of polyvinyl alcohol is parametrized using optical absorption spectra. A band gap energy of E gm =1.53 ± 0.02 eV at the end of an infinite polyene chain is found by extrapolating the energies of π → π* transitions in clusters with a number of double bonds varying from 4 to 12. This value is close to the band gap of trans-polyacetylene and the lower bound for the Tauc energy E gT =1.50 eV, which characterizes the minimum interband transition energy. E gT is essentially independent of the concentration of oligoene clusters, which is determined by the concentration of the AlCl3 thermal decomposition catalyst. The Urbach energy determined from the long wavelength edge of the spectrum falls from 2.21 to 0.66 eV as the AlCl3 concentration is raised from 11.1 to 41.7 mmol per mol of polyvinyl alcohol structural units.

  17. Energy transfer from Rhodamine-B to Oxazine-170 in the presence of photonic stop band

    NASA Astrophysics Data System (ADS)

    Kedia, Sunita; Sinha, Sucharita

    2015-03-01

    Photonic crystals can effectively suppress spontaneous emission of embedded emitter in the direction were photonic stop band overlaps emission band of emitter. This property of PhC has been successfully exploited to enhance energy transfer from a donor Rhodamine-B dye to an acceptor Oxazine-170 dye by inhibiting the fluorescence emission of donor in a controlled manner. Self-assembled PhC were synthesized using RhB dye doped polystyrene microspheres subsequently infiltrated with O-170 dye molecules dissolved in ethanol. An angle dependent enhancement of emission intensity of acceptor via energy transfer in photonic crystal environment was observed. These results were compared with observations made on a dye mixture solution of the same two dyes. Restricted number of available modes in photonic crystal inhibited de-excitation of donor thereby enabling efficient transfer of energy from excited donor to acceptor dye molecules.

  18. Excited-state lifetime of adenine near the first electronic band origin

    NASA Astrophysics Data System (ADS)

    Kang, Hyuk; Chang, Jinyoung; Lee, Sang Hak; Ahn, Tae Kyu; Kim, Nam Joon; Kim, Seong Keun

    2010-10-01

    The excited-state lifetime of supersonically cooled adenine was measured in the gas phase by femtosecond pump-probe transient ionization as a function of excitation energy between 36 100 and 37 500 cm-1. The excited-state lifetime of adenine is ˜2 ps around the 0-0 band of the L1b ππ ∗ state (36 105 cm-1). The lifetime drops to ˜1 ps when adenine is excited to the L1a ππ ∗ state with the pump energy at 36 800 cm-1 and above. The excited-state lifetimes of L1a and L1b ππ∗ states are differentiated in accordance with previous frequency-resolved and computational studies.

  19. Sterilization of foods with low-energy electrons (``soft-electrons'')

    NASA Astrophysics Data System (ADS)

    Hayashi, Toru; Takahashi, Yoko; Todoriki, Setsuko

    1998-06-01

    Electrons with an energy of 300 keV or lower were defined as "Soft-electrons", which showed several advantages over conventional irradiation with gamma-rays or high-energy electrons in decontamination of grains and spices. Energies of electrons necessary to reduce microbial loads to levels lower than 10 CFU/g were 60 keV for brown rice, 75 keV for wheat, 100 keV for white pepper, coriander and basil, 130 keV for buckwheat, 160 keV for rough rice, and 210 keV for black pepper. Electrons with such energies did not significantly influence the quality.

  20. High-gradient C-band linac for a compact x-ray free-electron laser facility

    NASA Astrophysics Data System (ADS)

    Inagaki, T.; Kondo, C.; Maesaka, H.; Ohshima, T.; Otake, Y.; Sakurai, T.; Shirasawa, K.; Shintake, T.

    2014-08-01

    An electron linac using a C-band rf frequency, 5.712 GHz, has enabled us to obtain an acceleration gradient of more than 35 MV/m reliably. A C-band accelerator system has been developed and constructed for the compact x-ray FEL facility, SACLA, in order to fit within the available site length at SPring-8, and to reduce construction costs. An accelerator unit consists of two 1.8 m-long accelerator structures, a cavity-type rf pulse compressor and a 50 MW pulsed klystron. In order to achieve a compact rf source and to obtain extremely stable rf fields in the accelerator structures, an oil-filled, high-voltage pulse modulator combined with an extremely stable, inverter-type, high voltage charger was developed. SACLA uses 64 sets of these accelerator units in order to achieve a final beam energy of 8.5 GeV. After rf conditioning for 1 700 hours, the maximum acceleration gradient achieved was 38 MV/m. The typical trip rate for each accelerator unit at 35 MV/m and 30 pps is about once per day. Dark current from the accelerator structures is less than 5 pC, which causes a negligible effect on the beam monitors. The phase and amplitude stability of the rf fields were measured to be 0.03 degree and 0.01% rms, respectively, which is sufficient for the XFEL operation of SACLA. Since the first beam commissioning in 2011, the C-band accelerator has demonstrated fairly stable performance under continuous operation for 20 000 hours.

  1. Computer Simulation of Reflection High Energy Electron Diffraction and Low Energy Electron Diffraction

    NASA Astrophysics Data System (ADS)

    Flexner, Soren; Davidson, Bruce; Odonnell, James; Eckstein, J. N.

    2000-03-01

    Simulation software for Reflection High Energy Electron Diffraction (RHEED) and Low Energy Electron Diffraction (LEED) imaging has been developed using the C programming language. This software models experimental electron diffraction patterns obtained in-situ during deposition of oxide films by molecular beam epitaxy in our lab. Using the kinematical approximation the software considers the phase contributions from scatterers via a modifiable, finite, two or three-dimensional real lattice to construct the RHEED and LEED images. We have found quantitative agreement in the positions of diffraction maxima, and proceed to use the software to explore the qualitative aspects of La and Mn termination in LaMnO2, surface Jahn-Teller distortion in perovskites, terracing in various materials, and domain formation in a-axis DBCO resulting from in-plane rotation of the c-axis. In addition the software is used to examine proposed surface reconstructions capable of producing, e.g. the elevated half-order streaks seen along the [100] azimuth during growth of LaMnO2.

  2. Electron energy recovery system for negative ion sources

    DOEpatents

    Dagenhart, W.K.; Stirling, W.L.

    1979-10-25

    An electron energy recovery system for negative ion sources is provided. The system, employing crossed electric and magnetic fields, separates the electrons from the ions as they are extracted from the ion source plasma generator and before the ions are accelerated to their full energy. With the electric and magnetic fields oriented 90/sup 0/ to each other, the electrons remain at approximately the electrical potential at which they were generated. The electromagnetic forces cause the ions to be accelerated to the full accelerating supply voltage energy while being deflected through an angle of less than 90/sup 0/. The electrons precess out of the accelerating field region into an electron recovery region where they are collected at a small fraction of the full accelerating supply energy. It is possible, by this method, to collect > 90% of the electrons extracted along with the negative ions from a negative ion source beam at < 4% of full energy.

  3. Electron energy distributions in a metal-polymer-vacuum system

    SciTech Connect

    Yumaguzin, Yu. M.; Kornilov, V. M.; Lachinov, A. N.

    2006-08-15

    The energy distributions of electrons emitted from a metal coated with a polymer (polydiphenylene phthalide) is studied experimentally using field electron spectroscopy. A considerable decrease in the electron work function for the metal-polymer-vacuum system as compared to pure metal is observed. Analysis of the energy distributions of emitted electrons shows that the distribution in the case with the polymer is broader and displaced towards low energies, and its high-energy edge is slightly extended. The effect of emission voltage on the shape of the energy distribution of emitted electrons is studied. A model is proposed to explain the substantial decrease in the effective electron work function in the case when the metal electrode is coated with a polymer film.

  4. Is the electron radiation length constant at high energies?

    PubMed

    Hansen, H D; Uggerhøj, U I; Biino, C; Ballestrero, S; Mangiarotti, A; Sona, P; Ketel, T J; Vilakazi, Z Z

    2003-07-04

    Experimental results for the radiative energy loss of 149, 207, and 287 GeV electrons in a thin Ir target are presented. From the data we conclude that at high energies the radiation length increases in accordance with the Landau-Pomeranchuk-Migdal (LPM) theory and thus electrons become more penetrating the higher the energy. The increase of the radiation length as a result of the LPM effect has a significant impact on the behavior of high-energy electromagnetic showers.

  5. Ultrafast electronic and vibrational dynamics in brominated aluminum corroles: Energy relaxation and triplet formation

    PubMed Central

    Stensitzki, T.; Yang, Y.; Berg, A.; Mahammed, A.; Gross, Z.; Heyne, K.

    2016-01-01

    We combined femtosecond (fs) VIS pump–IR probe spectroscopy with fs VIS pump–supercontinuum probe spectroscopy to characterize the photoreaction of the hexacoordinated Al(tpfc-Br8)(py)2 in a comprehensive way. Upon fs excitation at ∼400 nm in the Soret band, the excitation energy relaxes with a time constant of (250 ± 80) fs to the S2 and S1 electronic excited states. This is evident from the rise time of the stimulated emission signal in the visible spectral range. On the same time scale, narrowing of broad infrared signals in the C=C stretching region around 1500 cm−1 is observed. Energy redistribution processes are visible in the vibrational and electronic dynamics with time constants between ∼2 ps and ∼20 ps. Triplet formation is detected with a time constant of (95 ± 3) ps. This is tracked by the complete loss of stimulated emission. Electronic transition of the emerging triplet absorption band overlaps considerably with the singlet excited state absorption. In contrast, two well separated vibrational marker bands for triplet formation were identified at 1477 cm−1 and at 1508 cm−1. These marker bands allow a precise identification of triplet dynamics in corrole systems. PMID:27226980

  6. 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.

  7. 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.

  8. Fragile surface zero-energy flat bands in three-dimensional chiral superconductors

    NASA Astrophysics Data System (ADS)

    Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi

    2015-12-01

    We study surface zero-energy flat bands in three-dimensional chiral superconductors with pz(px+i py) ν -wave pairing symmetry (ν is a nonzero integer), based on topological arguments and tunneling conductance. It is shown that the surface flat bands are fragile against (i) the surface misorientation and (ii) the surface Rashba spin-orbit interaction. The fragility of (i) is specific to chiral SCs, whereas that of (ii) happens for general odd-parity SCs. We demonstrate that these flat-band instabilities vanish or suppress a zero-bias conductance peak in a normal/insulator/superconductor junction, which behavior is clearly different from high-Tc cuprates and noncentrosymmetric superconductors. By calculating the angle-resolved conductance, we also discuss a topological surface state associated with the coexistence of line and point nodes.

  9. Atomic electron energies including relativistic effects and quantum electrodynamic corrections

    NASA Technical Reports Server (NTRS)

    Aoyagi, M.; Chen, M. H.; Crasemann, B.; Huang, K. N.; Mark, H.

    1977-01-01

    Atomic electron energies have been calculated relativistically. Hartree-Fock-Slater wave functions served as zeroth-order eigenfunctions to compute the expectation of the total Hamiltonian. A first order correction to the local approximation was thus included. Quantum-electrodynamic corrections were made. For all orbitals in all atoms with 2 less than or equal to Z less than or equal to 106, the following quantities are listed: total energies, electron kinetic energies, electron-nucleus potential energies, electron-electron potential energies consisting of electrostatic and Breit interaction (magnetic and retardation) terms, and vacuum polarization energies. These results will serve for detailed comparison of calculations based on other approaches. The magnitude of quantum electrodynamic corrections is exhibited quantitatively for each state.

  10. Energy parameters of precipitating auroral electrons obtained by using photometric observations

    SciTech Connect

    Ono, Takayuki; Morishima, Kei )

    1994-02-15

    The authors present a ground based photometric method for measuring both the average energy and total energy flux for active discrete auroras. They make use of a multichannel photometer, with a narrow field of view. They monitor auroral emissions from atomic states and molecular bands, and by determining intensity ratios, are able to infer information relative to energy parameters of precipitating electrons in discrete arcs. They are able to look along magnetic axes. One observation is that there is a relationship between the energy flux and average energy, which can be considered ohmic in character, consistent with a model that precipitating electrons are accelerated along field lines by potential differences which can exist along these field lines.

  11. 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.

  12. 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.

  13. Oxide/Water Interfaces: How the Surface Chemistry Modifies the Electronic Energy Alignment

    NASA Astrophysics Data System (ADS)

    Sprik, Michiel

    2014-03-01

    The minimum of the d-electron conduction band of an aqueous transition metal oxide electrode is typically no more than a few 100 mV away from the standard hydrogen electrode (SHE). Because of this favourable alignment of the electronic energy levels (near) metallic transition metal oxides with partly filled d bands can be used as electrocatalysts while the compounds with finite electronic gap can be used as photocatalysts. However, because of their ionic character, transition metal-oxide surfaces also show amphiphilic acid-base activity. At low pH the basic sites are protonated and at high pH the acidic sites deprotonated creating an electrical double layer with corresponding surface potential. The alignment of the electronic energy levels, and by implication their redox activity, is therefore pH dependent. In fact, even in absence of protonic surface charge, the coordination with water molecules is already capable of shifting the electronic energy levels of the oxide by 1 eV or more. Computation of the electronic energies in transition metal oxide electrodes requires therefore a detailed modeling of their aqueous surface chemistry. The solvation energy of the proton is the common energy reference for both redox potentials on the SHE scale and acidity constants (pKa). Computation of the H+ solvation energy is therefore a key component in a unified treatment of redox and acid-base chemistry. In this talk we outline the Density Functional Theory based Molecular Dynamics (DFTMD) method we have developed for this purpose. The central tool of our approach is a method for reversible insertion of protons in the aqueous part of the DFTMD model system. As an illustration we discuss the application to the rutile TiO2/water and MnO2/water interface.

  14. Search for two-{gamma} sum-energy peaks in the decay out of superdeformed bands

    SciTech Connect

    Blumenthal, D.; Khoo, T.L.; Lauritsen, T.

    1995-08-01

    The spectrum of {gamma}rays decaying out of the superdeformed (SD) band in {sup 192}Hg has a quasicontinuous distribution. Whereas methods to construct level schemes from discrete lines in coincidence spectra are well established, new techniques must still be developed to extract information from coincidences involving quasicontinuous {gamma}rays. From an experiment using Eurogam, we obtained impressively clean 1- and 2-dimensional {gamma} spectra from pairwise or single gates, respectively, on the transitions of the SD band in {sup 192}Hg. We investigated methods to exploit the 2-dimensional quasicontinuum spectra coincident with the SD band to determine the excitation energy of the SD band above the normal yrast line. No strong peaks were observed in the 2-{gamma} sum spectra; only candidates of peaks at a 2-3 {sigma} level were found. This suggests that 2-{gamma} decay is not the dominant decay branch out of SD bands, consistent with the observed multiplicity of 3.2. We shall next search for peaks in sum-spectra of 3 {gamma}s.

  15. Effects of Side-Chain and Electron Exchange Correlation on the Band Structure of Perylene Diimide Liquid Crystals: A Density Functional Study

    SciTech Connect

    Arantes, J. T.; Lima, M. P.; Fazzio, A.; Xiang, H.; Wei, S. H.; Dalpian, G. M.

    2009-04-01

    The structural and electronic properties of perylene diimide liquid crystal PPEEB are studied using ab initio methods based on the density functional theory (DFT). Using available experimental crystallographic data as a guide, we propose a detailed structural model for the packing of solid PPEEB. We find that due to the localized nature of the band edge wave function, theoretical approaches beyond the standard method, such as hybrid functional (PBE0), are required to correctly characterize the band structure of this material. Moreover, unlike previous assumptions, we observe the formation of hydrogen bonds between the side chains of different molecules, which leads to a dispersion of the energy levels. This result indicates that the side chains of the molecular crystal not only are responsible for its structural conformation but also can be used for tuning the electronic and optical properties of these materials.

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

    PubMed

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

    2012-04-23

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

  17. Temperature dependence of electronic band transition in Mn-doped SnO{sub 2} nanocrystalline films determined by ultraviolet-near-infrared transmittance spectra

    SciTech Connect

    Chen, X.G.; Li, W.W.; Wu, J.D.; Sun, J.; Jiang, K.; Hu, Z.G.; Chu, J.H.

    2012-01-15

    Highlights: Black-Right-Pointing-Pointer The temperature dependence of electronic structures has been investigated by transmittance spectra from 5.3 to 300 K. Black-Right-Pointing-Pointer The optical band gap shows a red shift with increasing Mn composition and decreases with the temperature. Black-Right-Pointing-Pointer The band gap narrowing parameter [E{sub g}(5.3 K)-E{sub g}(300 K)] linearly decreases with the Mn composition. Black-Right-Pointing-Pointer There are two temperature regimes for the Urbach energy. -- Abstract: Mn-doped SnO{sub 2} (SMO) nanocrystalline films with the composition from 2.5 to 12.5% have been prepared on quartz substrates by pulsed laser deposition. The temperature dependence of electronic structures and optical constants in the SMO films have been investigated by transmittance spectra from 5.3 to 300 K. Optical response functions have been extracted by fitting the transmittance spectra in the photon energy range of 0.5-6.5 eV with the Adachi's model. It was found that the absorption edge presents a red-shift trend with increasing Mn composition, and the optical band gap (OBG) is varied between 4.22 and 3.44 eV. Moreover, as the Mn composition increases, the temperature dependence of OBG becomes weaker. The band gap narrowing value [(5.3 K)-(300 K)] has been reduced from 98 to 3 meV and linearly decreases with the Mn composition. The phenomena could be attributed to the transition from low doping level SnO{sub 2} band-like states to Mn-related localized states. Moreover, the Urbach energy shows the degree of the structural disorder, which could be explained by an empirical formulas in different temperature regimes.

  18. Advancing Efficient All-Electron Electronic Structure Methods Based on Numeric Atom-Centered Orbitals for Energy Related Materials

    NASA Astrophysics Data System (ADS)

    Blum, Volker

    This talk describes recent advances of a general, efficient, accurate all-electron electronic theory approach based on numeric atom-centered orbitals; emphasis is placed on developments related to materials for energy conversion and their discovery. For total energies and electron band structures, we show that the overall accuracy is on par with the best benchmark quality codes for materials, but scalable to large system sizes (1,000s of atoms) and amenable to both periodic and non-periodic simulations. A recent localized resolution-of-identity approach for the Coulomb operator enables O (N) hybrid functional based descriptions of the electronic structure of non-periodic and periodic systems, shown for supercell sizes up to 1,000 atoms; the same approach yields accurate results for many-body perturbation theory as well. For molecular systems, we also show how many-body perturbation theory for charged and neutral quasiparticle excitation energies can be efficiently yet accurately applied using basis sets of computationally manageable size. Finally, the talk highlights applications to the electronic structure of hybrid organic-inorganic perovskite materials, as well as to graphene-based substrates for possible future transition metal compound based electrocatalyst materials. All methods described here are part of the FHI-aims code. VB gratefully acknowledges contributions by numerous collaborators at Duke University, Fritz Haber Institute Berlin, TU Munich, USTC Hefei, Aalto University, and many others around the globe.

  19. A compact, versatile low-energy electron beam ion source

    SciTech Connect

    Zschornack, G.; König, J.; Schmidt, M.; Thorn, A.

    2014-02-15

    A new compact Electron Beam Ion Source, the Dresden EBIT-LE, is introduced as an ion source working at low electron beam energies. The EBIT-LE operates at an electron energy ranging from 100 eV to some keV and can easily be modified to an EBIT also working at higher electron beam energies of up to 15 keV. We show that, depending on the electron beam energy, electron beam currents from a few mA in the low-energy regime up to about 40 mA in the high-energy regime are possible. Technical solutions as well as first experimental results of the EBIT-LE are presented. In ion extraction experiments, a stable production of low and intermediate charged ions at electron beam energies below 2 keV is demonstrated. Furthermore, X-ray spectroscopy measurements confirm the possibility of using the machine as a source of X-rays from ions excited at low electron energies.

  20. A compact, versatile low-energy electron beam ion source.

    PubMed

    Zschornack, G; König, J; Schmidt, M; Thorn, A

    2014-02-01

    A new compact Electron Beam Ion Source, the Dresden EBIT-LE, is introduced as an ion source working at low electron beam energies. The EBIT-LE operates at an electron energy ranging from 100 eV to some keV and can easily be modified to an EBIT also working at higher electron beam energies of up to 15 keV. We show that, depending on the electron beam energy, electron beam currents from a few mA in the low-energy regime up to about 40 mA in the high-energy regime are possible. Technical solutions as well as first experimental results of the EBIT-LE are presented. In ion extraction experiments, a stable production of low and intermediate charged ions at electron beam energies below 2 keV is demonstrated. Furthermore, X-ray spectroscopy measurements confirm the possibility of using the machine as a source of X-rays from ions excited at low electron energies.

  1. An extension of the Eisberg-Resnick treatment for electron energies in many-electron atoms

    NASA Astrophysics Data System (ADS)

    Whitaker, M. A. B.; Bennett, I.

    1989-03-01

    Eisberg and Resnick present a simple argument for the energy of an electron in a multielectron atom using the concept of shielding from electrons in inner shells. The results of such a treatment are unfortunately confined so as to be out of range of experimental values. Here, the effect of electrons in outer shells is included, and, in the nonrelativistic region, energies are obtained for electrons in the first and second shells in reasonable agreement with experiment.

  2. Augustine Band of Cahuilla Indians Energy Conservation and Options Analysis - Final Report

    SciTech Connect

    Paul Turner

    2008-07-11

    The Augustine Band of Cahuilla Indians was awarded a grant through the Department of Energy First Steps program in June of 2006. The primary purpose of the grant was to enable the Tribe to develop energy conservation policies and a strategy for alternative energy resource development. All of the work contemplated by the grant agreement has been completed and the Tribe has begun implementing the resource development strategy through the construction of a 1.0 MW grid-connected photovoltaic system designed to offset a portion of the energy demand generated by current and projected land uses on the Tribe’s Reservation. Implementation of proposed energy conservation policies will proceed more deliberately as the Tribe acquires economic development experience sufficient to evaluate more systematically the interrelationships between conservation and its economic development goals.

  3. Spectral shape variation of interstellar electrons at high energies

    NASA Technical Reports Server (NTRS)

    Tan, L. C.

    1985-01-01

    The high energy electron spectrum analysis has shown that the electron intensity inside the H2 cloud region, or in a spiral arm, should be much lower than that outside it and the observed electron energy spectrum should flatten again at about 1 TeV. In the framework of the leady box model the recently established rigidity dependence of the escape pathlength of cosmic rays would predict a high energy electron spectrum which is flatter than the observed one. This divergence is explained by assuming that the leaky box model can only apply to cosmic ray heavy nuclei, and light nuclei and electrons in cosmic rays may have different behaviors in the interstellar propagation. Therefore, the measured data on high energy electrons should be analyzed based on the proposed nonuniform galactic disk (NUGD) mode.

  4. PROGRESS OF HIGH-ENERGY ELECTRON COOLING FOR RHIC.

    SciTech Connect

    FEDOTOV,A.V.

    2007-09-10

    The fundamental questions about QCD which can be directly answered at Relativistic Heavy Ion Collider (RHIC) call for large integrated luminosities. The major goal of RHIC-I1 upgrade is to achieve a 10 fold increase in luminosity of Au ions at the top energy of 100 GeV/nucleon. Such a boost in luminosity for RHIC-II is achievable with implementation of high-energy electron cooling. The design of the higher-energy cooler for RHIC-II recently adopted a non-magnetized approach which requires a low temperature electron beam. Such electron beams will be produced with a superconducting Energy Recovery Linac (ERL). Detailed simulations of the electron cooling process and numerical simulations of the electron beam transport including the cooling section were performed. An intensive R&D of various elements of the design is presently underway. Here, we summarize progress in these electron cooling efforts.

  5. LAT Perspectives in Detection of High Energy Cosmic Ray Electrons

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander; Ormes, J. F.; Funk, Stefan

    2007-01-01

    The GLAST Large Area Telescope (LAT) science objectives and capabilities in the detection of high energy electrons in the energy range from 20 GeV to approx. 1 TeV are presented. LAT simulations are used to establish the event selections. It is found that maintaining the efficiency of electron detection at the level of 30% the residual hadron contamination does not exceed 2-3% of the electron flux. LAT should collect approx. ten million of electrons with the energy above 20 GeV for each year of observation. Precise spectral reconstruction with high statistics presents us with a unique opportunity to investigate several important problems such as studying galactic models of IC radiation, revealing the signatures of nearby sources such as high energy cutoff in the electron spectrum, testing the propagation model, and searching for KKDM particles decay through their contribution to the electron spectrum.

  6. The source of multi spectral energy of solar energetic electron

    SciTech Connect

    Herdiwijaya, Dhani

    2015-04-16

    We study the solar energetic electron distribution obtained from ACE and GOES satellites which have different altitudes and electron spectral energy during the year 1997 to 2011. The electron spectral energies were 0.038–0.315 MeV from EPAM instrument onboard ACE satellite and >2 MeV from GOES satellite. We found that the low electron energy has no correlation with high energy. In spite of we have corrected to the altitude differences. It implied that they originated from time dependent events with different sources and physical processes at the solar atmosphere. The sources of multi spectral energetic electron were related to flare and CME phenomena. However, we also found that high energetic electron comes from coronal hole.

  7. Clinical implementation of electron energy changes of varian linear accelerators.

    PubMed

    Zhang, Sean; Liengsawangwong, Praimakorn; Lindsay, Patricia; Prado, Karl; Sun, Tzouh-Liang; Steadham, Roy; Wang, Xiaochun; Salehpour, Mohammad; Gillin, Michael

    2009-10-27

    Modern dual photon energy linear accelerators often come with a few megavoltage electron beams. The megavoltage electron beam has limited range and relative sharp distal falloff in its depth dose curve compared to that of megavoltage photon beam. Its radiation dose is often delivered appositionally to cover the target volume to its distal 90% depth dose (d90), while avoiding the normal--sometimes critical--structure immediately distal to the target. Varian linear accelerators currently offer selected electron beams of 4, 6, 9, 12, 16 and 20 MeV electron beam energies. However, intermediate electron energy is often needed for optimal dose distribution. In this study we investigated electron beam characteristics and implemented two intermediate 7 and 11 MeV electron beams on Varian linear accelerators. Comprehensive tests and measurements indicated the new electron beams met all dosimetry parameter criteria and operational safety standards. Between the two new electron beams and the existing electron beams we were able to provide a choice of electron beams of 4, 6, 7, 9, 11, 12, 16 and 20 MeV electron energies, which had d90 depth between 1.5 cm and 6.0 cm (from 1.5 cm to 4.0 cm in 0.5 cm increments) to meet our clinical needs.

  8. Quantitative operando visualization of the energy band depth profile in solar cells

    PubMed Central

    Chen, Qi; Mao, Lin; Li, Yaowen; Kong, Tao; Wu, Na; Ma, Changqi; Bai, Sai; Jin, Yizheng; Wu, Dan; Lu, Wei; Wang, Bing; Chen, Liwei

    2015-01-01

    The energy band alignment in solar cell devices is critically important because it largely governs elementary photovoltaic processes, such as the generation, separation, transport, recombination and collection of charge carriers. Despite the expenditure of considerable effort, the measurement of energy band depth profiles across multiple layers has been extremely challenging, especially for operando devices. Here we present direct visualization of the surface potential depth profile over the cross-sections of operando organic photovoltaic devices using scanning Kelvin probe microscopy. The convolution effect due to finite tip size and cantilever beam crosstalk has previously prohibited quantitative interpretation of scanning Kelvin probe microscopy-measured surface potential depth profiles. We develop a bias voltage-compensation method to address this critical problem and obtain quantitatively accurate measurements of the open-circuit voltage, built-in potential and electrode potential difference. PMID:26166580

  9. Quantitative operando visualization of the energy band depth profile in solar cells.

    PubMed

    Chen, Qi; Mao, Lin; Li, Yaowen; Kong, Tao; Wu, Na; Ma, Changqi; Bai, Sai; Jin, Yizheng; Wu, Dan; Lu, Wei; Wang, Bing; Chen, Liwei

    2015-07-13

    The energy band alignment in solar cell devices is critically important because it largely governs elementary photovoltaic processes, such as the generation, separation, transport, recombination and collection of charge carriers. Despite the expenditure of considerable effort, the measurement of energy band depth profiles across multiple layers has been extremely challenging, especially for operando devices. Here we present direct visualization of the surface potential depth profile over the cross-sections of operando organic photovoltaic devices using scanning Kelvin probe microscopy. The convolution effect due to finite tip size and cantilever beam crosstalk has previously prohibited quantitative interpretation of scanning Kelvin probe microscopy-measured surface potential depth profiles. We develop a bias voltage-compensation method to address this critical problem and obtain quantitatively accurate measurements of the open-circuit voltage, built-in potential and electrode potential difference.

  10. SHEEBA: A spatial high energy electron beam analyzer

    NASA Astrophysics Data System (ADS)

    Galimberti, Marco; Giulietti, Antonio; Giulietti, Danilo; Gizzi, Leonida A.

    2005-05-01

    Electron bunches with large energy and angle spread are not easy to be analyzed with conventional spectrometers. In this article, a device for the detection of high energy electrons is presented. This detector, based on the traces left by electrons on a stack of dosimetric films, together with an original numerical algorithm for traces deconvolution, is able to characterize both angularly and spectrally (up to some mega-electron-volts) a broad-spectrum electron bunch. A numerical test was successfully performed with a virtual electron beam, which was in turn reconstructed using a Montecarlo code (based on the CERN library GEANT4). Due to its simplicity and small size, the spatial high energy electron beam analyzer (SHEEBA) detector is particularly suitable to be used in laser plasma acceleration experiments.

  11. Electrothermal energy conversion using electron gas volumetric change inside semiconductors

    NASA Astrophysics Data System (ADS)

    Yazawa, K.; Shakouri, A.

    2016-07-01

    We propose and analyze an electrothermal energy converter using volumetric changes in non-equilibrium electron gas inside semiconductors. The geometric concentration of electron gas under an electric field increases the effective pressure of the electrons, and then a barrier filters out cold electrons, acting like a valve. Nano- and micro-scale features enable hot electrons to arrive at the contact in a short enough time to avoid thermalization with the lattice. Key length and time scales, preliminary device geometry, and anticipated efficiency are estimated for electronic analogs of Otto and Brayton power generators and Joule-Thomson micro refrigerators on a chip. The power generators convert the energy of incident photons from the heat source to electrical current, and the refrigerator can reduce the temperature of electrons in a semiconductor device. The analytic calculations show that a large energy conversion efficiency or coefficient of performance may be possible.

  12. Electron-helium and electron-neon scattering cross sections at low electron energies using a photoelectron source

    NASA Technical Reports Server (NTRS)

    Kumar, Vijay; Subramanian, K. P.; Krishnakumar, E.

    1987-01-01

    Absolute electron-helium and electron-neon scattering cross sections have been measured at low electron energies using the powerful technique of photoelectron spectroscopy. The measurements have been carried out at 17 electron energies varying from 0.7 to 10 eV with an accuracy of + or - 2.7 percent. The results obtained in the present work have been compared with other recent measurement and calculations.

  13. Tensile-strain effect of inducing the indirect-to-direct band-gap transition and reducing the band-gap energy of Ge

    SciTech Connect

    Inaoka, Takeshi Furukawa, Takuro; Toma, Ryo; Yanagisawa, Susumu

    2015-09-14

    By means of a hybrid density-functional method, we investigate the tensile-strain effect of inducing the indirect-to-direct band-gap transition and reducing the band-gap energy of Ge. We consider [001], [111], and [110] uniaxial tensility and (001), (111), and (110) biaxial tensility. Under the condition of no normal stress, we determine both normal compression and internal strain, namely, relative displacement of two atoms in the primitive unit cell, by minimizing the total energy. We identify those strain types which can induce the band-gap transition, and evaluate the critical strain coefficient where the gap transition occurs. Either normal compression or internal strain operates unfavorably to induce the gap transition, which raises the critical strain coefficient or even blocks the transition. We also examine how each type of tensile strain decreases the band-gap energy, depending on its orientation. Our analysis clearly shows that synergistic operation of strain orientation and band anisotropy has a great influence on the gap transition and the gap energy.

  14. Coulomb energy differences in analog rotational bands of f7/2-shell nuclei

    NASA Astrophysics Data System (ADS)

    Lenzi, S. M.; Mǎrginean, N.; Napoli, D. R.; Ur, C. A.; Zuker, A. P.; Axiotis, M.; Brandolini, F.; de Angelis, G.; Farnea, E.; Gadea, A.; Martínez-Pinedo, G.; Poves, A.; Sánchez-Solano, J.

    2002-04-01

    Recent experimental and shell model studies of isospin symmetry along the ground state rotational bands in the mirror nuclei 50Fe and 50Cr are presented. This is the heaviest T=1 mirror pair studied so far at high spin. It is shown that the Coulomb energy differences provide a good tool to probe the alignment mechanism at the backbending and that they also give information about the evolution of yrast radii as a function of the angular momentum. .

  15. Electron energy-loss spectra in molecular fluorine

    NASA Technical Reports Server (NTRS)

    Nishimura, H.; Cartwright, D. C.; Trajmar, S.

    1979-01-01

    Electron energy-loss spectra in molecular fluorine, for energy losses from 0 to 17.0 eV, have been taken at incident electron energies of 30, 50, and 90 eV and scattering angles from 5 to 140 deg. Features in the spectra above 11.5 eV energy loss agree well with the assignments recently made from optical spectroscopy. Excitations of many of the eleven repulsive valence excited electronic states are observed and their location correlates reasonably well with recent theoretical results. Several of these excitations have been observed for the first time and four features, for which there are no identifications, appear in the spectra.

  16. 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.

  17. 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

  18. On the influence of nonlinearities on vibrational energy transduction under band-limited noise excitations

    NASA Astrophysics Data System (ADS)

    Nakano, K.; Su, D.; Zheng, R.; Cartmell, M.

    2016-09-01

    Vibrational energy harvesters are often excited by band-limited noise excitations. In this paper, the influence of the stiffness nonlinearity on the transduction of the energy harvester and the relative performance of linear, monostable hardening-type and bistable energy harvesters are compared and investigated. The performance is experimentally compared under band-limited noise excitations of different levels, bandwidths, and centre frequencies at first. The rms output power delivered to the same load resistance is measured and compared under the same excitation levels, which indicts the constant electrical damping level. It is shown that the effect of nonlinearities is strongly dependent on the excitation parameters. Under a moderate excitation level it is shown that the monostable hardening-type oscillator performs worse than its linear counterpart under band-limited excitation. However, the results also illustrate that for the most part of the frequency and bandwidth range considered, the bistable harvester can outperforms the linear variant but for around the peak output area. Moreover, the comparison is also numerically conducted with the consideration of the optimised electrical damping level and the displacement constraint of the device. General conclusions are drawn based on the experimental observations.

  19. Engineering of optical polarization based on electronic band structures of A-plane ZnO layers under biaxial strains

    SciTech Connect

    Matsui, Hiroaki Tabata, Hitoshi; Hasuike, Noriyuki; Harima, Hiroshi

    2014-09-21

    In-plane anisotropic strains in A-plane layers on the electronic band structure of ZnO were investigated from the viewpoint of optical polarization anisotropy. Investigations utilizing k·p perturbation theory revealed that energy transitions and associated oscillation strengths were dependent on in-plane strains. The theoretical correlation between optical polarizations and in-plane strains was experimentally demonstrated using A-plane ZnO layers with different in-plane strains. Finally, optical polarization anisotropy and its implications for in-plane optical properties are discussed in relation to the energy shift between two orthogonal directions. Higher polarization rotations were obtained in an A-plane ZnO layer with in-plane biaxially compressive strains as compared to strain-free ZnO. This study provides detailed information concerning the role played by in-plane strains in optically polarized applications based on nonpolar ZnO in the ultra-violet region.

  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. Enhanced Water Splitting by Fe2O3-TiO2-FTO Photoanode with Modified Energy Band Structure

    PubMed Central

    Noh, Eul; Noh, Kyung-Jong; Yun, Kang-Seop; Kim, Bo-Ra; Jeong, Hee-June; Oh, Hyo-Jin; Kang, Woo-Seung

    2013-01-01

    The effect of TiO2 layer applied to the conventional Fe2O3/FTO photoanode to improve the photoelectrochemical performance was assessed from the viewpoint of the microstructure and energy band structure. Regardless of the location of the TiO2 layer in the photoanodes, that is, Fe2O3/TiO2/FTO or TiO2/Fe2O3/FTO, high performance was obtained when α-Fe2O3 and H-TiNT/anatase-TiO2 phases existed in the constituent Fe2O3 and TiO2 layers after optimized heat treatments. The presence of the Fe2O3 nanoparticles with high uniformity in the each layer of the Fe2O3/TiO2/FTO photoanode achieved by a simple dipping process seemed to positively affect the performance improvement by modifying the energy band structure to a more favorable one for efficient electrons transfer. Our current study suggests that the application of the TiO2 interlayer, together with α-Fe2O3 nanoparticles present in the each constituent layers, could significantly contribute to the performance improvement of the conventional Fe2O3 photoanode. PMID:24501585

  5. Band structure engineering for solar energy applications: Zinc oxide(1-x) selenium(x) films and devices

    NASA Astrophysics Data System (ADS)

    Mayer, Marie Annette

    New technologies motivate the development of new semiconducting materials, for which structural, electrical and chemical properties are not well understood. In addition to new materials systems, there are huge opportunities for new applications, especially in solar energy conversion. In this dissertation I explore the role of band structure engineering of semiconducting oxides for solar energy. Due to the abundance and electrochemical stability of oxides, the appropriate modification could make them appealing for applications in both photovoltaics and photoelectrochemical hydrogen production. This dissertation describes the design, synthesis and evaluation of the alloy ZnO1-xSe x for these purposes. I review several methods of band structure engineering including strain, quantum confinement and alloying. A detailed description of the band anticrossing (BAC) model for highly mismatched alloys is provided, including the derivation of the BAC model as well as recent work and potential applications. Thin film ZnOxSe1-x samples are grown by pulsed laser deposition (PLD). I describe in detail the effect of growth conditions (temperature, pressure and laser fluence) on the chemistry, structure and optoelectronic properties of ZnOxSe1-x. The films are grown using different combinations of PLD conditions and characterized with a variety of techniques. Phase pure films with low roughness and high crystallinity were obtained at temperatures below 450¢ªC, pressures less than 10-4 Torr and laser fluences on the order of 1.5 J/cm 2. Electrical conduction was still observed despite heavy concentrations of grain boundaries. The band structure of ZnO1-xSex is then examined in detail. The bulk electron affinity of a ZnO thin film was measured to be 4.5 eV by pinning the Fermi level with native defects. This is explained in the framework of the amphoteric defect model. A shift in the ZnO1-xSe x valence band edge with x is observed using synchrotron x-ray absorption and emission

  6. Electron cooling for low-energy RHIC program

    SciTech Connect

    Fedotov, A.; Ben-Zvi, I.; Chang, X.; Kayran, D.; Litvinenko, V.N.; Pendzick, A.; Satogata, T.

    2009-08-31

    Electron cooling was proposed to increase luminosity of the RHIC collider for heavy ion beam energies below 10 GeV/nucleon. Providing collisions at such energies, termed RHIC 'low-energy' operation, will help to answer one of the key questions in the field of QCD about existence and location of critical point on the QCD phase diagram. The electron cooling system should deliver electron beam of required good quality over energies of 0.9-5 MeV. Several approaches to provide such cooling were considered. The baseline approach was chosen and design work started. Here we describe the main features of the cooling system and its expected performance. We have started design work on a low-energy RHIC electron cooler which will operate with kinetic electron energy range 0.86-2.8 (4.9) MeV. Several approaches to an electron cooling system in this energy range are being investigated. At present, our preferred scheme is to transfer the Fermilab Pelletron to BNL after Tevatron shutdown, and to use it for DC non-magnetized cooling in RHIC. Such electron cooling system can significantly increase RHIC luminosities at low-energy operation.

  7. OPTIMAL ELECTRON ENERGIES FOR DRIVING CHROMOSPHERIC EVAPORATION IN SOLAR FLARES

    SciTech Connect

    Reep, J. W.; Bradshaw, S. J.; Alexander, D. E-mail: stephen.bradshaw@rice.edu

    2015-08-01

    In the standard model of solar flares, energy deposition by a beam of electrons drives strong chromospheric evaporation leading to a significantly denser corona and much brighter emission across the spectrum. Chromospheric evaporation was examined in great detail by Fisher et al., who described a distinction between two different regimes, termed explosive and gentle evaporation. In this work, we examine the importance of electron energy and stopping depths on the two regimes and on the atmospheric response. We find that with explosive evaporation, the atmospheric response does not depend strongly on electron energy. In the case of gentle evaporation, lower energy electrons are significantly more efficient at heating the atmosphere and driving up-flows sooner than higher energy electrons. We also find that the threshold between explosive and gentle evaporation is not fixed at a given beam energy flux, but also depends strongly on the electron energy and duration of heating. Further, at low electron energies, a much weaker beam flux is required to drive explosive evaporation.

  8. Energy-filtered Electron Transport Structures for Low-power Low-noise 2-D Electronics

    PubMed Central

    Pan, Xuan; Qiu, Wanzhi; Skafidas, Efstratios

    2016-01-01

    In addition to cryogenic techniques, energy filtering has the potential to achieve high-performance low-noise 2-D electronic systems. Assemblies based on graphene quantum dots (GQDs) have been demonstrated to exhibit interesting transport properties, including resonant tunnelling. In this paper, we investigate GQDs based structures with the goal of producing energy filters for next generation lower-power lower-noise 2-D electronic systems. We evaluate the electron transport properties of the proposed GQD device structures to demonstrate electron energy filtering and the ability to control the position and magnitude of the energy passband by appropriate device dimensioning. We also show that the signal-to-thermal noise ratio performance of the proposed nanoscale device can be modified according to device geometry. The tunability of two-dimensional GQD structures indicates a promising route for the design of electron energy filters to produce low-power and low-noise electronics. PMID:27796343

  9. Energy-filtered Electron Transport Structures for Low-power Low-noise 2-D Electronics.

    PubMed

    Pan, Xuan; Qiu, Wanzhi; Skafidas, Efstratios

    2016-10-31

    In addition to cryogenic techniques, energy filtering has the potential to achieve high-performance low-noise 2-D electronic systems. Assemblies based on graphene quantum dots (GQDs) have been demonstrated to exhibit interesting transport properties, including resonant tunnelling. In this paper, we investigate GQDs based structures with the goal of producing energy filters for next generation lower-power lower-noise 2-D electronic systems. We evaluate the electron transport properties of the proposed GQD device structures to demonstrate electron energy filtering and the ability to control the position and magnitude of the energy passband by appropriate device dimensioning. We also show that the signal-to-thermal noise ratio performance of the proposed nanoscale device can be modified according to device geometry. The tunability of two-dimensional GQD structures indicates a promising route for the design of electron energy filters to produce low-power and low-noise electronics.

  10. Energy-filtered Electron Transport Structures for Low-power Low-noise 2-D Electronics

    NASA Astrophysics Data System (ADS)

    Pan, Xuan; Qiu, Wanzhi; Skafidas, Efstratios

    2016-10-01

    In addition to cryogenic techniques, energy filtering has the potential to achieve high-performance low-noise 2-D electronic systems. Assemblies based on graphene quantum dots (GQDs) have been demonstrated to exhibit interesting transport properties, including resonant tunnelling. In this paper, we investigate GQDs based structures with the goal of producing energy filters for next generation lower-power lower-noise 2-D electronic systems. We evaluate the electron transport properties of the proposed GQD device structures to demonstrate electron energy filtering and the ability to control the position and magnitude of the energy passband by appropriate device dimensioning. We also show that the signal-to-thermal noise ratio performance of the proposed nanoscale device can be modified according to device geometry. The tunability of two-dimensional GQD structures indicates a promising route for the design of electron energy filters to produce low-power and low-noise electronics.

  11. First-principles calculation of defect formation energies and electronic properties in stannate pyrochlores

    NASA Astrophysics Data System (ADS)

    Chen, Z. J.; Xiao, H. Y.; Zu, X. T.; Gao, F.

    2008-11-01

    The electronic structures and defect formation energies for a series of stannate pyrochlores Ln2Sn2O7 (Ln=La, Pr, Nd, Sm, Gd, Tb, Ho, Er, Lu, and Y) have been investigated using the first-principles total energy calculations. The calculated results show that Ln-site cation ionic radius, x-O48f, lattice constant and the covalency of the ⟨Sn-O48f⟩ bond have a significant affect on the defect formation energies. The cation-antisite defect has the lowest formation energy, as compared with that of other defects, indicating that cation disorder causes local oxygen disordering. The present studies suggest that Lu2Sn2O7 is the most resistant to ion beam-induced amorphization. The electronic structure calculations reveal that Ln2Sn2O7 compounds have direct band gaps of 2.64-2.95 eV at the Γ point in the Brillouin zone.

  12. Energy transport in weakly nonlinear wave systems with narrow frequency band excitation.

    PubMed

    Kartashova, Elena

    2012-10-01

    A novel discrete model (D model) is presented describing nonlinear wave interactions in systems with small and moderate nonlinearity under narrow frequency band excitation. It integrates in a single theoretical frame two mechanisms of energy transport between modes, namely, intermittency and energy cascade, and gives the conditions under which each regime will take place. Conditions for the formation of a cascade, cascade direction, conditions for cascade termination, etc., are given and depend strongly on the choice of excitation parameters. The energy spectra of a cascade may be computed, yielding discrete and continuous energy spectra. The model does not require statistical assumptions, as all effects are derived from the interaction of distinct modes. In the example given-surface water waves with dispersion function ω(2)=gk and small nonlinearity-the D model predicts asymmetrical growth of side-bands for Benjamin-Feir instability, while the transition from discrete to continuous energy spectrum, excitation parameters properly chosen, yields the saturated Phillips' power spectrum ~g(2)ω(-5). The D model can be applied to the experimental and theoretical study of numerous wave systems appearing in hydrodynamics, nonlinear optics, electrodynamics, plasma, convection theory, etc.

  13. Relation between fine structure of energy spectra for pulsating aurora electrons and frequency spectra of whistler mode chorus waves

    NASA Astrophysics Data System (ADS)

    Miyoshi, Y.; Saito, S.; Seki, K.; Nishiyama, T.; Kataoka, R.; Asamura, K.; Katoh, Y.; Ebihara, Y.; Sakanoi, T.; Hirahara, M.; Oyama, S.; Kurita, S.; Santolik, O.

    2015-09-01

    We investigate the origin of the fine structure of the energy spectrum of precipitating electrons for the pulsating aurora (PsA) observed by the low-altitude Reimei satellite. The Reimei satellite achieved simultaneous observations of the optical images and precipitating electrons of the PsA from satellite altitude (~620 km) with resolution of 40 ms. The main modulation of precipitation, with a few seconds, and the internal modulations, with a few hertz, that are embedded inside the main modulations are identified above ~3 keV. Moreover, stable precipitations at ~1 keV are found for the PsA. A "precipitation gap" is discovered between two energy bands. We identify the origin of the fine structure of the energy spectrum for the precipitating electrons using the computer simulation on the wave-particle interaction between electrons and chorus waves. The lower band chorus (LBC) bursts cause the main modulation of energetic electrons, and the generation and collapse of the LBC bursts determines on-off switching of the PsA. A train of rising tone elements embedded in the LBC bursts drives the internal modulations. A close set of upper band chorus (UBC) waves causes the stable precipitations at ~1 keV. We show that a wave power gap around the half gyrofrequency at the equatorial plane in the magnetosphere between LBC and UBC reduces the loss rate of electrons at the intermediate energy range, forming a gap of precipitating electrons in the ionosphere.

  14. The electron energy loss rate due to radiative recombination

    NASA Astrophysics Data System (ADS)

    Mao, Junjie; Kaastra, Jelle; Badnell, N. R.

    2017-02-01

    Context. For photoionized plasmas, electron energy loss rates due to radiative recombination (RR) are required for thermal equilibrium calculations, which assume a local balance between the energy gain and loss. While many calculations of total and/or partial RR rates are available from the literature, specific calculations of associated RR electron energy loss rates are lacking. Aims: Here we focus on electron energy loss rates due to radiative recombination of H-like to Ne-like ions for all the elements up to and including zinc (Z = 30), over a wide temperature range. Methods: We used the AUTOSTRUCTURE code to calculate the level-resolved photoionization cross section and modify the ADASRR code so that we can simultaneously obtain level-resolved RR rate coefficients and associated RR electron energy loss rate coefficients. We compared the total RR rates and electron energy loss rates of H i and He i with those found in the literature. Furthermore, we utilized and parameterized the weighted electron energy loss factors (dimensionless) to characterize total electron energy loss rates due to RR. Results: The RR electron energy loss data are archived according to the Atomic Data and Analysis Structure (ADAS) data class adf48. The RR electron energy loss data are also incorporated into the SPEX code for detailed modeling of photoionized plamsas. Full Tables 1 and 2 are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A10

  15. Pulsars in the Mid-Energy Gamma-Ray Band - Implications for ComPair

    NASA Astrophysics Data System (ADS)

    Ferrara, Elizabeth; Harding, Alice; ComPair Team

    2017-01-01

    The investigation of the high-energy gamma-ray band by Fermi has revolutionized our understanding of the populations of pulsars - and by extension neutron starts - in the Galactic field. However, there exist a number of pulsars with energy output that peaks below 500 GeV, and whose gamma-ray characteristics are not well constrained by Fermi. The Compton-Pair Telescope (ComPair) is a proposed wide-field medium-energy gamma-ray mission (0.2 keV to > 500 MeV), re-opening an energy regime that was last investigated by COMPTEL on the Compton Gamma-Ray Observatory. The increased sensitivity and spatial resolution of the proposed instrument may lead to a similar knowledge revolution for these MeV-peaked pulsars. Here we discuss the properties of the MeV-peaked pulsar population, and speculate on the potential new science that ComPair may provide.

  16. Energy conversion within infrared plasmonic absorption metamaterials for multi-band resonance

    NASA Astrophysics Data System (ADS)

    Li, Yongqian; Su, Lei; Xu, Xiaolun; Zhang, Chenglin; Wang, Binbin

    2015-05-01

    The energy conversion within the cross-shaped plasmonic absorber metamaterials (PAM) was investigated theoretically and numerically in the infrared range based on the Poynting's theorem of electromagnetic energy. From the microscopic details, the heat generation owing to the electric current accounts for the majority of the energy conversion, while the magnetic resonance plays a negligible role. The PAMs possess three distinct resonant peaks standing independently, which are attributed to the polarization sensitive excitation of plasmonic resonance. Field redistribution and enhancement associated with multiplex resonant electromagnetic wave passing through the PAM medium provided insight into the energy conversion processes inside the nanostructure. The research results will assist the design of novel plasmon enhanced infrared detectors with multiple-band detection.

  17. The energy-band alignment at molybdenum disulphide and high-k dielectrics interfaces

    SciTech Connect

    Tao, Junguang; Chai, J. W.; Zhang, Z.; Pan, J. S.; Wang, S. J.

    2014-06-09

    Energy-band alignments for molybdenum disulphide (MoS{sub 2}) films on high-k dielectric oxides have been studied using photoemission spectroscopy. The valence band offset (VBO) at monolayer MoS{sub 2}/Al{sub 2}O{sub 3} (ZrO{sub 2}) interface was measured to be 3.31 eV (2.76 eV), while the conduction-band offset (CBO) was 3.56 eV (1.22 eV). For bulk MoS{sub 2}/Al{sub 2}O{sub 3} interface, both VBO and CBO increase by ∼0.3 eV, due to the upwards shift of Mo 4d{sub z{sup 2}} band. The symmetric change of VBO and CBO implies Fermi level pinning by interfacial states. Our finding ensures the practical application of both p-type and n-type MoS{sub 2} based complementary metal-oxide semiconductor and other transistor devices using Al{sub 2}O{sub 3} and ZrO{sub 2} as gate materials.

  18. CHEER, Canadian high energy electron ring

    NASA Astrophysics Data System (ADS)

    Hemingway, R. J.

    The Institute of Particle Physics (IPP) in Canada have received funds from the Natural Sciences and Engineering Research Council (NSERC) to pursue a study which looks at the feasibility of adding an external electron storage ring at one of the long straight sections of the Tevatron. The machine, as currently configured, has a 300 MeV Linac injector, a 300 MeV accumulator ring, a 2 GeV booster synchrotron, and a 10 GeV storage ring holding 120 mA of either electrons or positrons. Particular attention has been paid to beam polarisation and the design of the interaction region.

  19. Low electron beam energy CIVA analysis of passivated ICs

    SciTech Connect

    Cole, E.I. Jr.; Soden, J.M.; Dodd, B.A.; Henderson, C.L.

    1994-08-01

    Low Energy Charge-Induced Voltage Alteration (LECIVA) is a new scanning electron microscopy technique developed to localize open conductors in passivated ICs. LECIVA takes advantage of recent experimental work showing that the dielectric surface equilibrium voltage has an electron flux density dependence at low electron beam energies ({le}1.0 keV). The equilibrium voltage changes from positive to negative as the electron flux density is increased. Like Charge-Induced Voltage Alteration (CIVA), LECIVA images are produced from the voltage fluctuations of a constant current power supply as an electron beam is scanned over the IC surface. LECIVA image contrast is generated only by the electrically open part of a conductor, yielding, the same high selectivity demonstrated by CIVA. Because LECIVA is performed at low beam energies, radiation damage by the primary electrons and x-rays to MOS structures is far less than that caused by CIVA. LECIVA may also be performed on commercial electron beam test systems that do not have high primary electron beam energy capabilities. The physics of LECIVA signal generation are described. LECIVA imaging examples illustrate its utility on both a standard scanning electron microscope (SEM) and a commercial electron beam test system.

  20. Energy landscape and band-structure tuning in realistic MoS2/MoSe2 heterostructures

    NASA Astrophysics Data System (ADS)

    Constantinescu, Gabriel C.; Hine, Nicholas D. M.

    2015-05-01

    While monolayer forms of two-dimensional materials are well characterized both experimentally and theoretically, properties of bilayer heterostructures are not nearly so well known. We employ high-accuracy linear-scaling density functional theory calculations utilizing nonlocal van der Waals functionals to explore the possible constructions of the MoS2/MoSe2 interface. Utilizing large supercells, we vary rotation, translation, and separation of the layers without introducing unrealistic strain. The energy landscape shows very low variations under rotation, with no strongly preferred alignments. By unfolding the spectral function into the primitive cells, we show that the monolayers are more independent than in homo-bilayers and that the electronic band structure of each layer is tunable through rotation, thus influencing hole effective masses.

  1. Enhanced Spontaneous Emission of Bloch Oscillation Radiation from a Single Energy Band

    DTIC Science & Technology

    2006-06-30

    electron becomes BPe s =4.3 10−6 meV, and since there are a total of n=5 109 electrons in the active region of the SL, the generated energy achievable...is estimated to be P=n BPe s =21.7 eV, which corresponds to an approximate power generation of W= B /NP0.1 W. In this power estimate, it is noted

  2. Satellite observations of energy-banded ions during large geomagnetic storms: Event studies, statistics, and comparisons to source models

    NASA Astrophysics Data System (ADS)

    Colpitts, C. A.; Cattell, C. A.; Kozyra, J. U.; Thomsen, M. F.; Lavraud, B.

    2016-07-01

    Energy-banded ions from tens to ten thousands of eV are observed in the low-latitude auroral and subauroral zones during every large (minimum Dst < -150 nT) geomagnetic storm encountered by the FAST satellite. The banded ions persist for many FAST orbits, lasting up to 12 h, in both the northern and southern hemispheres. The energy-banded ions often have more than six distinct bands, and the O+, He+, and H+ bands are often observed at the same energies. The bands are extensive in latitude (~50-75° on the dayside, often extending to 45°) and magnetic local time, covering all magnetic local time over the data set of storms. The distributions are peaked in the perpendicular direction at the altitudes of the FAST satellite (~350-4175 km), although in some cases the precipitating component dominates for the lowest energy bands. At the same time, for some of the events studied in detail, long-lasting intervals of field-aligned energy dispersed ions from ~100 eV to 40 keV are seen in Los Alamos National Laboratory geosynchronous observations, primarily on the dayside and after magnetosheath encounters (i.e., highly compressed magnetosphere). We present both case and statistical studies of the banded ions. These bands are a new phenomenon associated with all large storms, which are distinctly different from other banded populations, and are not readily interpreted using previous models for particle sources, transport, and loss. The energy-banded ions are an energetically important component of the inner magnetosphere during the most intense magnetic storms.

  3. The transfer between electron bulk kinetic energy and thermal energy in collisionless magnetic reconnection

    SciTech Connect

    Lu, San; Lu, Quanming; Huang, Can; Wang, Shui

    2013-06-15

    By performing two-dimensional particle-in-cell simulations, we investigate the transfer between electron bulk kinetic and electron thermal energy in collisionless magnetic reconnection. In the vicinity of the X line, the electron bulk kinetic energy density is much larger than the electron thermal energy density. The evolution of the electron bulk kinetic energy is mainly determined by the work done by the electric field force and electron pressure gradient force. The work done by the electron gradient pressure force in the vicinity of the X line is changed to the electron enthalpy flux. In the magnetic island, the electron enthalpy flux is transferred to the electron thermal energy due to the compressibility of the plasma in the magnetic island. The compression of the plasma in the magnetic island is the consequence of the electromagnetic force acting on the plasma as the magnetic field lines release their tension after being reconnected. Therefore, we can observe that in the magnetic island the electron thermal energy density is much larger than the electron bulk kinetic energy density.

  4. Energy Spread Reduction of Electron Beams Produced via Laser Wake

    SciTech Connect

    Pollock, Bradley Bolt

    2012-01-01

    Laser wakefield acceleration of electrons holds great promise for producing ultra-compact stages of GeV scale, high quality electron beams for applications such as x-ray free electron lasers and high energy colliders. Ultra-high intensity laser pulses can be self-guided by relativistic plasma waves over tens of vacuum diffraction lengths, to give >1 GeV energy in cm-scale low density plasma using ionization-induced injection to inject charge into the wake at low densities. This thesis describes a series of experiments which investigates the physics of LWFA in the self-guided blowout regime. Beginning with high density gas jet experiments the scaling of the LWFA-produced electron beam energy with plasma electron density is found to be in excellent agreement with both phenomenological theory and with 3-D PIC simulations. It is also determined that self-trapping of background electrons into the wake exhibits a threshold as a function of the electron density, and at the densities required to produce electron beams with energies exceeding 1 GeV a different mechanism is required to trap charge into low density wakes. By introducing small concentrations of high-Z gas to the nominal He background the ionization-induced injection mechanism is enabled. Electron trapping is observed at densities as low as 1.3 x 1018 cm-3 in a gas cell target, and 1.45 GeV electrons are demonstrated for the first time from LWFA. This is currently the highest electron energy ever produced from LWFA. The ionization-induced trapping mechanism is also shown to generate quasi-continuous electron beam energies, which is undesirable for accelerator applications. By limiting the region over which ionization-induced trapping occurs, the energy spread of the electron beams can be controlled. The development of a novel two-stage gas cell target provides the capability to tailor the gas composition in the longitudinal direction, and confine the trapping process to occur only in a

  5. Electron energy recovery system for negative ion sources

    DOEpatents

    Dagenhart, William K.; Stirling, William L.

    1982-01-01

    An electron energy recovery system for negative ion sources is provided. The system, employs crossed electric and magnetic fields to separate the electrons from ions as they are extracted from a negative ion source plasma generator and before the ions are accelerated to their full kinetic energy. With the electric and magnetic fields oriented 90.degree. to each other, the electrons are separated from the plasma and remain at approximately the electrical potential of the generator in which they were generated. The electrons migrate from the ion beam path in a precessing motion out of the ion accelerating field region into an electron recovery region provided by a specially designed electron collector electrode. The electron collector electrode is uniformly spaced from a surface of the ion generator which is transverse to the direction of migration of the electrons and the two surfaces are contoured in a matching relationship which departs from a planar configuration to provide an electric field component in the recovery region which is parallel to the magnetic field thereby forcing the electrons to be directed into and collected by the electron collector electrode. The collector electrode is maintained at a potential slightly positive with respect to the ion generator so that the electrons are collected at a small fraction of the full accelerating supply voltage energy.

  6. Microbunched electron cooling for high-energy hadron beams.

    PubMed

    Ratner, D

    2013-08-23

    Electron and stochastic cooling are proven methods for cooling low-energy hadron beams, but at present there is no way of cooling hadrons as they near the TeV scale. In the 1980s, Derbenev suggested that electron instabilities, such as free-electron lasers, could create collective space charge fields strong enough to correct the hadron energies. This Letter presents a variation on Derbenev's electron cooling scheme using the microbunching instability as the amplifier. The large bandwidth of the instability allows for faster cooling of high-density beams. A simple analytical model illustrates the cooling mechanism, and simulations show cooling rates for realistic parameters of the Large Hadron Collider.

  7. Study on electron beam in a low energy plasma focus

    SciTech Connect

    Khan, Muhammad Zubair; Ling, Yap Seong; San, Wong Chiow

    2014-03-05

    Electron beam emission was investigated in a low energy plasma focus device (2.2 kJ) using copper hollow anode. Faraday cup was used to estimate the energy of the electron beam. XR100CR X-ray spectrometer was used to explore the impact of the electron beam on the target observed from top-on and side-on position. Experiments were carried out at optimized pressure of argon gas. The impact of electron beam is exceptionally notable with two different approaches using lead target inside hollow anode in our plasma focus device.

  8. 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.

  9. Substituent effect on electronic transition energy of dichlorobenzyl radicals

    NASA Astrophysics Data System (ADS)

    Yoon, Young Wook; Chae, Sang Youl; Lee, Sang Kuk

    2016-01-01

    Ring-substituted benzyl radicals exhibit electronic energies of the D1 ⿿ D0 transition being shifted to red region with respect to the benzyl radical. The red-shifts of disubstituted benzyl radicals are highly dependent on the substitution positions irrespective of substituents. By analyzing the red-shifts of dichlorobenzyl radicals observed, we found that the substituent effect on electronic transition energy is attributed to the molecular plane shape of delocalized Ͽ electrons. We will discuss the influences of locations of Cl substituents on the D1 ⿿ D0 transition energies of dichlorobenzyl radicals using Hückel's molecular orbital theory.

  10. 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.

  11. Can low-energy electrons affect high-energy physics accelerators?

    SciTech Connect

    Cimino, R.; Collins, I.R.; Furman, M.A.; Pivi, M.; Ruggiero, F.; Rumolo, G.; Zimmermann, F.

    2004-02-09

    Present and future accelerators performances may be limited by the electron cloud (EC) effect. The EC formation and evolution are determined by the wall-surface properties of the accelerator vacuum chamber.We present measurements of the total secondary electron yield (SEY) and the related energy distribution curves of the secondary electrons as a function of incident-electron energy. Particular attention has been paid to the emission process due to very low-energy primary electrons (<20 eV). It is shown that the SEY approaches unity and the reflected electron component is predominant in the limit of zero primary incident electron energy. Motivated by these measurements, we have used state-of-the-art EC simulation codes to predict how these results may impact the production of the electron cloud in the Large Hadron Collider, under construction at CERN, and the related surface heat load.

  12. Binding energy of excitons formed from spatially separated electrons and holes in insulating quantum dots

    SciTech Connect

    Pokutnyi, S. I.; Kulchin, Yu. N.; Dzyuba, V. P.

    2015-10-15

    It is found that the binding energy of the ground state of an exciton formed from an electron and a hole spatially separated from each other (the hole is moving within a quantum dot, and the electron is localized above the spherical (quantum dot)–(insulating matrix) interface) in a nanosystem containing insulating Al{sub 2}O{sub 3} quantum dots is substantially increased (by nearly two orders of magnitude) compared to the exciton binding energy in an Al{sub 2}O{sub 3} single crystal. It is established that, in the band gap of an Al{sub 2}O{sub 3} nanoparticle, a band of exciton states (formed from spatially separated electrons and holes) appears. It is shown that there exists the possibility of experimentally detecting the ground and excited exciton states in the band gap of Al{sub 2}O{sub 3} nanoparticles at room temperature from the absorption spectrum of the nanosystem.

  13. High-Current Energy-Recovering Electron Linacs

    SciTech Connect

    Nikolitsa Merminga; David Douglas; Geoffrey Krafft

    2003-12-01

    The use of energy recovery provides a potentially powerful new paradigm for generation of the charged particle beams used in synchrotron radiation sources, high-energy electron cooling devices, electron-ion colliders, and other applications in photon science and nuclear and high-energy physics. Energy-recovering electron linear accelerators (called energy-recovering linacs, or ERLs) share many characteristics with ordinary linacs, as their six-dimensional beam phase space is largely determined by electron source properties. However, in common with classic storage rings, ERLs possess a high average-current-carrying capability enabled by the energy recovery process, and thus promise similar efficiencies. The authors discuss the concept of energy recovery and its technical challenges and describe the Jefferson Lab (JLab) Infrared Demonstration Free-Electron Laser (IR Demo FEL), originally driven by a 3548-MeV, 5-mA superconducting radiofrequency (srf) ERL, which provided the most substantial demonstration of energy recovery to date: a beam of 250 kW average power. They present an overview of envisioned ERL applications and a development path to achieving the required performance. They use experimental data obtained at the JLab IR Demo FEL and recent experimental results from CEBAF-ERL GeV-scale, comparatively low-current energy-recovery demonstration at JLab to evaluate the feasibility of the new applications of high-current ERLs, as well as ERLs' limitations and ultimate performance.

  14. HIGH-ENERGY ELECTRON COOLING BASED ON REALISTIC SIX-DIMENSIONAL DISTRIBUTION OF ELECTRONS

    SciTech Connect

    FEDOTOV,A.; BEN-ZVI, I.; ET AL.

    2007-06-25

    The high-energy electron cooling system for RHIC-II is unique compared to standard coolers. It requires bunched electron beam. Electron bunches are produced by an Energy Recovery Linac (ERL), and cooling is planned without longitudinal magnetic field. To address unique features of the RHIC cooler, a generalized treatment of cooling force was introduced in BETACOOE code which allows us to calculate friction force for an arbitrary distribution of electrons. Simulations for RHIC cooler based on electron distribution from ERL are presented.

  15. Ligand reorganization and activation energies in nonadiabatic electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Zhu, Jianjun; Wang, Jianji; Stell, George

    2006-10-01

    The activation energy and ligand reorganization energy for nonadiabatic electron transfer reactions in chemical and biological systems are investigated in this paper. The free energy surfaces and the activation energy are derived exactly in the general case in which the ligand vibration frequencies are not equal. The activation energy is derived by free energy minimization at the transition state. Our formulation leads to the Marcus-Hush [J. Chem. Phys. 24, 979 (1956); 98, 7170 (1994); 28, 962 (1958)] results in the equal-frequency limit and also generalizes the Marcus-Sumi [J. Chem. Phys. 84, 4894 (1986)] model in the context of studying the solvent dynamic effect on electron transfer reactions. It is found that when the ligand vibration frequencies are different, the activation energy derived from the Marcus-Hush formula deviates by 5%-10% from the exact value. If the reduced reorganization energy approximation is introduced in the Marcus-Hush formula, the result is almost exact.

  16. The Number of High-Energy Bands in the Photoelectron Spectrum of Alkanes

    NASA Astrophysics Data System (ADS)

    Merris, Russell; Gutman, Ivan

    2000-12-01

    It was observed that within the Bieri-Dill-Heilbronner-Schmelzer model for the calculation of the ion-ization energies of alkanes CnH2n+2, there are exactly n C2s -electron energy levels lying below the degenerate α-ß manifold. We now show that, indeed, this regularity is obeyed by practically all alkane species. Exceptions do exist, but they must possess a (chemically infeasible) group of more than six mutually connected quaternary carbon atoms.

  17. Synthesis and energy band characterization of hybrid molecular materials based on organic–polyoxometalate charge-transfer salts

    SciTech Connect

    Tan, Chunxia; Bu, Weifeng

    2014-11-15

    A cationic amphiphilic molecule was synthesized and employed to encapsulate Lindqvist ([M{sub 6}O{sub 19}]{sup 2−}) and Keggin polyoxometalates ([SiM{sub 12}O{sub 40}]{sup 4−}, M=Mo, W) to form hybrid molecules through electrostatic interaction. The X-ray diffraction results illustrate that the former hybrids possess lamellar nanostructures in their solid states, while the latter hybrids show a cubic Im3m packing model with low intensities and poor long-range order. These hybrids have clear charge-transfer characters as shown in their deeper colors and UV–vis diffuse reflectance spectra. According to the reported reduction potentials of the POM acceptors and the band gaps deduced from their diffuse reflectance spectra, we have calculated the theoretical values of the lowest unoccupied molecular orbital (LUMO) position similar to the electron affinity (E{sub A}) of solid materials. Such energy level parameters are comparable to those of electroluminescence and electron-transport materials commonly used in organic electroluminescence devices. These organic–polyoxometalate charge-transfer salts have more advantages, such as higher decomposition temperatures, easier film fabrication and better electron affinities, which presumably would be used for electron-transport materials in the area of the electroluminescence. - Graphical abstract: Hybrid molecular materials with charge-transfer characters formed by a positively charged donor L and acceptors of the Lindqvist-type and Keggin-type POMs have lamellar and cubic structures in their solid state. - Highlights: • Charge-transfer salts are obtained by self-assembling POMs with an anthracene cation. • Their energy parameters are comparable to those of optoelectronic materials in OLEDs. • These POM-based hybrids could be applied in the area of optoelectronic devices.

  18. 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.

  19. Intermediate-band photosensitive device with quantum dots embedded in energy fence barrier

    DOEpatents

    Forrest, Stephen R.; Wei, Guodan

    2010-07-06

    A plurality of layers of a first semiconductor material and a plurality of dots-in-a-fence barriers disposed in a stack between a first electrode and a second electrode. Each dots-in-a-fence barrier consists essentially of a plurality of quantum dots of a second semiconductor material embedded between and in direct contact with two layers of a third semiconductor material. Wave functions of the quantum dots overlap as at least one intermediate band. The layers of the third semiconductor material are arranged as tunneling barriers to require a first electron and/or a first hole in a layer of the first material to perform quantum mechanical tunneling to reach the second material within a respective quantum dot, and to require a second electron and/or a second hole in a layer of the first semiconductor material to perform quantum mechanical tunneling to reach another layer of the first semiconductor material.

  20. Monte Carlo simulation of energy deposition by low-energy electrons in molecular hydrogen

    NASA Technical Reports Server (NTRS)

    Heaps, M. G.; Furman, D. R.; Green, A. E. S.

    1975-01-01

    A set of detailed atomic cross sections has been used to obtain the spatial deposition of energy by 1-20-eV electrons in molecular hydrogen by a Monte Carlo simulation of the actual trajectories. The energy deposition curve (energy per distance traversed) is quite peaked in the forward direction about the entry point for electrons with energies above the threshold of the electronic states, but the peak decreases and broadens noticeably as the electron energy decreases below 10 eV (threshold for the lowest excitable electronic state of H2). The curve also assumes a very symmetrical shape for energies below 10 eV, indicating the increasing importance of elastic collisions in determining the shape of the curve, although not the mode of energy deposition.

  1. Enhanced production of low energy electrons by alpha particle impact.

    PubMed

    Kim, Hong-Keun; Titze, Jasmin; Schöffler, Markus; Trinter, Florian; Waitz, Markus; Voigtsberger, Jörg; Sann, Hendrik; Meckel, Moritz; Stuck, Christian; Lenz, Ute; Odenweller, Matthias; Neumann, Nadine; Schössler, Sven; Ullmann-Pfleger, Klaus; Ulrich, Birte; Fraga, Rui Costa; Petridis, Nikos; Metz, Daniel; Jung, Annika; Grisenti, Robert; Czasch, Achim; Jagutzki, Ottmar; Schmidt, Lothar; Jahnke, Till; Schmidt-Böcking, Horst; Dörner, Reinhard

    2011-07-19

    Radiation damage to living tissue stems not only from primary ionizing particles but to a substantial fraction from the dissociative attachment of secondary electrons with energies below the ionization threshold. We show that the emission yield of those low energy electrons increases dramatically in ion-atom collisions depending on whether or not the target atoms are isolated or embedded in an environment. Only when the atom that has been ionized and excited by the primary particle impact is in immediate proximity of another atom is a fragmentation route known as interatomic Coulombic decay (ICD) enabled. This leads to the emission of a low energy electron. Over the past decade ICD was explored in several experiments following photoionization. Most recent results show its observation even in water clusters. Here we show the quantitative role of ICD for the production of low energy electrons by ion impact, thus approaching a scenario closer to that of radiation damage by alpha particles: We choose ion energies on the maximum of the Bragg peak where energy is most efficiently deposited in tissue. We compare the electron production after colliding He(+) ions on isolated Ne atoms and on Ne dimers (Ne(2)). In the latter case the Ne atom impacted is surrounded by a most simple environment already opening ICD as a deexcitation channel. As a consequence, we find a dramatically enhanced low energy electron yield. The results suggest that ICD may have a significant influence on cell survival after exposure to ionizing radiation.

  2. Nudged-elastic band used to find reaction coordinates based on the free energy.

    PubMed

    Bohner, Matthias U; Zeman, Johannes; Smiatek, Jens; Arnold, Axel; Kästner, Johannes

    2014-02-21

    Transition paths characterize chemical reaction mechanisms. In this paper, we present a new method to find mean reaction paths based on the free energy. A nudged elastic band (NEB) is optimized using gradients and Hessians of the free energy, which are obtained from umbrella integration. The transition state can be refined by a Newton-Raphson search starting from the highest point of the NEB path. All optimizations are done using Cartesian coordinates. Independent molecular dynamics (MD) runs are performed at each image used to discretize the path. This makes the method intrinsically parallel. In contrast to other free energy methods, the algorithm does not become more expensive when including more degrees of freedom in the active space. The method is applied to the alanine-dipeptide as a test case and compared to pathways that have been derived from metadynamics and forward flux sampling.

  3. Nudged-elastic band method with two climbing images: Finding transition states in complex energy landscapes

    SciTech Connect

    Zarkevich, Nikolai A.; Johnson, Duane D.

    2015-01-09

    The nudged-elastic band (NEB) method is modified with concomitant two climbing images (C2-NEB) to find a transition state (TS) in complex energy landscapes, such as those with a serpentine minimal energy path (MEP). If a single climbing image (C1-NEB) successfully finds the TS, then C2-NEB finds it too. Improved stability of C2-NEB makes it suitable for more complex cases, where C1-NEB misses the TS because the MEP and NEB directions near the saddle point are different. Generally, C2-NEB not only finds the TS, but guarantees, by construction, that the climbing images approach it from the opposite sides along the MEP. In addition, C2-NEB provides an accuracy estimate from the three images: the highest-energy one and its climbing neighbors. C2-NEB is suitable for fixed-cell NEB and the generalized solid-state NEB.

  4. Nudged-elastic band method with two climbing images: Finding transition states in complex energy landscapes

    DOE PAGES

    Zarkevich, Nikolai A.; Johnson, Duane D.

    2015-01-09

    The nudged-elastic band (NEB) method is modified with concomitant two climbing images (C2-NEB) to find a transition state (TS) in complex energy landscapes, such as those with a serpentine minimal energy path (MEP). If a single climbing image (C1-NEB) successfully finds the TS, then C2-NEB finds it too. Improved stability of C2-NEB makes it suitable for more complex cases, where C1-NEB misses the TS because the MEP and NEB directions near the saddle point are different. Generally, C2-NEB not only finds the TS, but guarantees, by construction, that the climbing images approach it from the opposite sides along the MEP.more » In addition, C2-NEB provides an accuracy estimate from the three images: the highest-energy one and its climbing neighbors. C2-NEB is suitable for fixed-cell NEB and the generalized solid-state NEB.« less

  5. 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).

  6. 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.

  7. 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…

  8. Electron, photons, and molecules: Storing energy from light

    SciTech Connect

    Miller, J.R.

    1996-09-01

    Molecular charge separation has important potential for photochemical energy storage. Its efficiency can be enhanced by principals which maximize the rates of the electron transfer steps which separate charge and minimize those which recombine high-energy charge pairs to lose stored energy. Dramatic scientific progress in understanding these principals has occurred since the founding of DOE and its predecessor agency ERDA. While additional knowledge in needed in broad areas of molecular electron transfer, some key areas of knowledge hold particular promise for the possibility of moving this area from science toward technology capable of contributing to the nation`s energy economy.

  9. Diagnostics of Rotational Temperature and Mean Electron Energy Distribution of DC Glow Discharge Using Spectral Image Processing

    NASA Astrophysics Data System (ADS)

    Shimizu, Daisuke; Sasamoto, Ryo; Matsumoto, Takao; Izawa, Yasuji; Nishijima, Kiyoto

    2014-10-01

    The non-thermal plasma has been used in various application fields of manufacturing industry such as surface reforming, plasma etching, deposited film forming. The gas temperature and electron energy in non-thermal plasma play a key role of production of active species. Therefore, it is essential to understand the properties of non-thermal plasma for effective plasma applications. In this study, the two-dimensional rotational temperature and mean electron energy distribution of DC glow discharge plasma under various air pressures were observed using spectral image processing. Rotational temperature distribution was estimated from the emission intensity ratio of head and tail of 2nd positive system band of N2 (0, 2). On the other hand, mean electron energy was estimated from the emission intensity ratio of 2nd positive system band of N2 (0, 2) and 1st negative system band of N2+ (0, 0). The each spectral images were taken by an ICCD camera with narrow band-path filters respectively. As a result, the dependences of rotational temperature and mean electron energy distribution in DC glow discharge on ambient air pressure were clearly observed using spectral image processing.

  10. Electron energy distribution produced by beam-plasma discharge

    NASA Technical Reports Server (NTRS)

    Anderson, H. R.; Gordeuk, J.; Jost, R. J.

    1982-01-01

    In an investigation of a beam-plasma discharge (BPD), the electron energy distribution of an electron beam moving through a partially ionized gas is analyzed. Among other results, it is found that the occurrence of BPD heats the initially cold electron beam from the accelerator. The directional intensity of electrons measured outside the beam core indicates that most particles suffer a single scattering in energy and pitch angle. At low currents this result is expected as beam particles collide with the neutral atmosphere, while in BPD the majority of particles is determined to still undergo a single scattering near the original beam core. The extended energy spectra at various beam currents show two rather distinct plasma populations, one centered at the initial beam energy (approximately 1500 eV) and the other at approximately 150 eV.

  11. Ultra High Energy Electrons Powered by Pulsar Rotation

    NASA Astrophysics Data System (ADS)

    Mahajan, Swadesh; Machabeli, George; Osmanov, Zaza; Chkheidze, Nino

    2013-02-01

    A new mechanism of particle acceleration, driven by the rotational slow down of the Crab pulsar, is explored. The rotation, through the time dependent centrifugal force, can efficiently excite unstable Langmuir waves in the electron-positron (hereafter e+/-) plasma of the star magnetosphere. These waves, then, Landau damp on electrons accelerating them in the process. The net transfer of energy is optimal when the wave growth and the Landau damping times are comparable and are both very short compared to the star rotation time. We show, by detailed calculations, that these are precisely the conditions for the parameters of the Crab pulsar. This highly efficient route for energy transfer allows the electrons in the primary beam to be catapulted to multiple TeV (~ 100 TeV) and even PeV energy domain. It is expected that the proposed mechanism may, unravel the puzzle of the origin of ultra high energy cosmic ray electrons.

  12. Ultra high energy electrons powered by pulsar rotation.

    PubMed

    Mahajan, Swadesh; Machabeli, George; Osmanov, Zaza; Chkheidze, Nino

    2013-01-01

    A new mechanism of particle acceleration, driven by the rotational slow down of the Crab pulsar, is explored. The rotation, through the time dependent centrifugal force, can efficiently excite unstable Langmuir waves in the electron-positron (hereafter e(±)) plasma of the star magnetosphere. These waves, then, Landau damp on electrons accelerating them in the process. The net transfer of energy is optimal when the wave growth and the Landau damping times are comparable and are both very short compared to the star rotation time. We show, by detailed calculations, that these are precisely the conditions for the parameters of the Crab pulsar. This highly efficient route for energy transfer allows the electrons in the primary beam to be catapulted to multiple TeV (~ 100 TeV) and even PeV energy domain. It is expected that the proposed mechanism may, unravel the puzzle of the origin of ultra high energy cosmic ray electrons.

  13. Ultra High Energy Electrons Powered by Pulsar Rotation

    PubMed Central

    Mahajan, Swadesh; Machabeli, George; Osmanov, Zaza; Chkheidze, Nino

    2013-01-01

    A new mechanism of particle acceleration, driven by the rotational slow down of the Crab pulsar, is explored. The rotation, through the time dependent centrifugal force, can efficiently excite unstable Langmuir waves in the electron-positron (hereafter e±) plasma of the star magnetosphere. These waves, then, Landau damp on electrons accelerating them in the process. The net transfer of energy is optimal when the wave growth and the Landau damping times are comparable and are both very short compared to the star rotation time. We show, by detailed calculations, that these are precisely the conditions for the parameters of the Crab pulsar. This highly efficient route for energy transfer allows the electrons in the primary beam to be catapulted to multiple TeV (~ 100 TeV) and even PeV energy domain. It is expected that the proposed mechanism may, unravel the puzzle of the origin of ultra high energy cosmic ray electrons. PMID:23405276

  14. The Analysis of Hand Movement Distinction Based on Relative Frequency Band Energy Method

    PubMed Central

    Zhang, Yanyan; Teng, Chaolin; Sun, Zhongjiang; Wang, Jue

    2014-01-01

    For the purpose of successfully developing a prosthetic control system, many attempts have been made to improve the classification accuracy of surface electromyographic (SEMG) signals. Nevertheless, the effective feature extraction is still a paramount challenge for the classification of SEMG signals. The relative frequency band energy (RFBE) method based on wavelet packet decomposition was proposed for the prosthetic pattern recognition of multichannel SEMG signals. Firstly, the wavelet packet energy of SEMG signals in each subspace was calculated by using wavelet packet decomposition and the RFBE of each frequency band was obtained by the wavelet packet energy. Then, the principal component analysis (PCA) and the Davies-Bouldin (DB) index were used to perform the feature selection. Lastly, the support vector machine (SVM) was applied for the classification of SEMG signals. Our results demonstrated that the RFBE approach was suitable for identifying different types of forearm movements. By comparing with other classification methods, the proposed method achieved higher classification accuracy in terms of the classification of SEMG signals. PMID:25431766

  15. Radial Distribution of Electron Spectra from High-Energy Ions

    NASA Technical Reports Server (NTRS)

    Cucinotta, Francis A.; Katz, Robert; Wilson, John W.

    1998-01-01

    The average track model describes the response of physical and biological systems using radial dose distribution as the key physical descriptor. We report on an extension of this model to describe the average distribution of electron spectra as a function of radial distance from an ion. We present calculations of these spectra for ions of identical linear energy transfer (LET), but dissimilar charge and velocity to evaluate the differences in electron spectra from these ions. To illustrate the usefulness of the radial electron spectra for describing effects that are not described by electron dose, we consider the evaluation of the indirect events in microdosimetric distributions for ions. We show that folding our average electron spectra model with experimentally determined frequency distributions for photons or electrons provides a good representation of radial event spectra from high-energy ions in 0.5-2 micrometer sites.

  16. Multi-shell spherical GaAs /AlxGa1-x As quantum dot shells-size distribution as a mechanism to generate intermediate band energy levels

    NASA Astrophysics Data System (ADS)

    Rodríguez-Magdaleno, K. A.; Pérez-Álvarez, R.; Martínez-Orozco, J. C.; Pernas-Salomón, R.

    2017-04-01

    In this work the generation of an intermediate band of energy levels from multi-shell spherical GaAs /AlxGa1-x As quantum dot shells-size distribution is reported. Within the effective mass approximation the electronic structure of a GaAs spherical quantum-dot surrounded by one, two and three shells is studied in detail using a numerically stable transfer matrix method. We found that a shells-size distribution characterized by continuously wider GaAs domains is a suitable mechanism to generate the intermediate band whose width is also dependent on the Aluminium concentration x. Our results suggest that this effective mechanism can be used for the design of wider intermediate band than reported in other quantum systems with possible solar cells enhanced performance.

  17. Diffraction of electrons at intermediate energies: The role of phonons

    NASA Astrophysics Data System (ADS)

    Ascolani, H.; Zampieri, G.

    1996-07-01

    The intensity of electrons reflected ``elastically'' from crystalline surfaces presents two regimes: the low-energy or LEED regime (<500 eV), in which the electrons are reflected along the Bragg directions, and the intermediate-energy or XPD/AED regime (>500 eV), in which the maxima of intensity are along the main crystallographic axes. We present a model which explains this transition in terms of the excitation/absorption of phonons during the scattering.

  18. Evaluation of Miscellaneous and Electronic Device Energy Use in Hospitals

    SciTech Connect

    Black, Douglas R.; Lanzisera, Steven M.; Lai, Judy; Brown, Richard E.; Singer, Brett C.

    2012-09-01

    Miscellaneous and electronic loads (MELs) consume about one-thirdof the primary energy used in US buildings, and their energy use is increasing faster than other end-uses. In healthcare facilities, 30percent of the annual electricity was used by MELs in 2008. This paper presents methods and challenges for estimating medical MELs energy consumption along with estimates of energy use in a hospital by combining device-level metered data with inventories and usage information. An important finding is that common, small devices consume large amounts of energy in aggregate and should not be ignored when trying to address hospital energy use.

  19. High energy Compton spectroscopy and electronic structure of Laves phase ZrFe2

    NASA Astrophysics Data System (ADS)

    Bhatt, Samir; Kumar, Kishor; Arora, Gunjan; Bapna, Komal; Ahuja, B. L.

    2016-08-01

    We present the first-ever experimental Compton profile of Laves phase ZrFe2 using indigenous 20 Ci 137Cs Compton spectrometer. To annotate the experimental electron momentum density, we have calculated the theoretical Compton profiles using density functional theory (DFT) and hybridization of Hartree-Fock and DFT within linear combination of atomic orbitals (LCAO) method. The spin-polarized energy bands and density of states are computed using LCAO and full potential-linearized augmented plane wave methods. The revised Perdew-Burke-Ernzerhof functional (for solids) based theoretical profile gives a marginally better agreement with the experimental profile as compared to other approximations considered in the present work. The Fermi surface topology of ZrFe2 is explained in terms of majority- and minority-spin energy bands.

  20. Anomalous electron-ion energy coupling in electron drift wave turbulence

    NASA Astrophysics Data System (ADS)

    Zhao, Lei

    Turbulence is a ubiquitous phenomenon in nature, and it is well known that turbulence couples energy input to dissipation by cascade processes. Plasma turbulence play a critical role in tokamak confinement. Magnetized plasma turbulence is quasi 2D, anisotropic, wave like and two fluid (i.e. electrons and ions) in structure. Thus, weakly collisional plasma turbulence can mediate electron and ion energy transfer. The issue of anomalous electron and ion energy coupling is particularly important for low collisionality, electron heated plasmas, such as ITER. In this work, we reconsider the classic problem of turbulent heating and energy transfer pathways in drift wave turbulence. The total turbulent heating, composed of quasilinear electron cooling, quasilinear ion heating, nonlinear ion heating and zonal flow frictional heating, is analyzed. In Chapter 2, the electron and ion energy exchange via linear wave and particle resonance will be computed. To address net heating, we show the turbulent heating in an annulus arises due to a wave energy flux differential across this region. We show this net heating is proportional to the Reynolds work on the zonal flow. Zonal flow friction heats ions, thus the turbulence and zonal flow interaction enters as an important energy transfer channel. Since zonal flows are nonlinearly generated, it follows that we should apply weak turbulence theory to calculate the nonlinear ion turbulent heating via the virtual mode resonance in the electron drift wave turbulence, which will be discussed in Chapter 3. We defines a new collisionless turbulent energy transfer channel through nonlinear Landau damping in the electron and ion energy coupling process. The result shows that nonlinear ion heating can exceed quasilinear ion heating, so that nonlinear heating becomes the principal collisionless wave energy dissipation channel in electron drift wave turbulence. This follows since the beat mode resonates with the bulk of the ion distribution, in

  1. Non-locality, adiabaticity, thermodynamics and electron energy probability functions

    NASA Astrophysics Data System (ADS)

    Boswell, Roderick; Zhang, Yunchao; Charles, Christine; Takahashi, Kazunori

    2016-09-01

    Thermodynamic properties are revisited for electrons that are governed by nonlocal electron energy probability functions in a plasma of low collisionality. Measurements in a laboratory helicon double layer experiment have shown that the effective electron temperature and density show a polytropic correlation with an index of γe = 1 . 17 +/- 0 . 02 along the divergent magnetic field, implying a nearly isothermal plasma (γe = 1) with heat being brought into the system. However, the evolution of electrons along the divergent magnetic field is essentially an adiabatic process, which should have a γe = 5 / 3 . The reason for this apparent contradiction is that the nearly collisionless plasma is very far from local thermodynamic equilibrium and the electrons behave nonlocally. The corresponding effective electron enthalpy has a conservation relation with the potential energy, which verifies that there is no heat transferred into the system during the electron evolution. The electrons are shown in nonlocal momentum equilibrium under the electric field and the gradient of the effective electron pressure. The convective momentum of ions, which can be assumed as a cold species, is determined by the effective electron pressure and the effective electron enthalpy is shown to be the source for ion acceleration. For these nearly collisionless plasmas, the use of traditional thermodynamic concepts can lead to very erroneous conclusions regarding the thermal conductivity.

  2. High-energy-resolution monochromator for aberration-corrected scanning transmission electron microscopy/electron energy-loss spectroscopy.

    PubMed

    Krivanek, Ondrej L; Ursin, Jonathan P; Bacon, Neil J; Corbin, George J; Dellby, Niklas; Hrncirik, Petr; Murfitt, Matthew F; Own, Christopher S; Szilagyi, Zoltan S

    2009-09-28

    An all-magnetic monochromator/spectrometer system for sub-30 meV energy-resolution electron energy-loss spectroscopy in the scanning transmission electron microscope is described. It will link the energy being selected by the monochromator to the energy being analysed by the spectrometer, without resorting to decelerating the electron beam. This will allow it to attain spectral energy stability comparable to systems using monochromators and spectrometers that are raised to near the high voltage of the instrument. It will also be able to correct the chromatic aberration of the probe-forming column. It should be able to provide variable energy resolution down to approximately 10 meV and spatial resolution less than 1 A.

  3. Energy measurement of electron beams by Compton scattering

    NASA Technical Reports Server (NTRS)

    Keppel, Cynthia

    1995-01-01

    A method has been proposed to utilize the well-known Compton scattering process as a tool to measure the centroid energy of a high energy electron beam at the 0.01% level. It is suggested to use the Compton scattering of an infrared laser off the electron beam, and then to measure the energy of the scattered gamma-rays very precisely using solid-state detectors. The technique proposed is applicable for electron beams with energies from 200 MeV to 16 GeV using presently available lasers. This technique was judged to be the most viable of all those proposed for beam energy measurements at the nearby Continuous Electron Beam Accelerator Facility (CEBAF). Plans for a prototype test of the technique are underway, where the main issues are the possible photon backgrounds associated with an electron accelerator and the electron and laser beam stabilities and diagnostics. The bulk of my ASEE summer research has been spent utilizing the expertise of the staff at the Aerospace Electronics Systems Division at LaRC to assist in the design of the test. Investigations were made regarding window and mirror transmission and radiation damage issues, remote movement of elements in ultra-high vacuum conditions, etc. The prototype test of the proposed laser backscattering method is planned for this December.

  4. Magnetosphere-Ionosphere Energy Interchange in the Electron Diffuse Aurora

    NASA Technical Reports Server (NTRS)

    Khazanov, George V.; Glocer, Alex; Himwich, E. W.

    2014-01-01

    The diffuse aurora has recently been shown to be a major contributor of energy flux into the Earth's ionosphere. Therefore, a comprehensive theoretical analysis is required to understand its role in energy redistribution in the coupled ionosphere-magnetosphere system. In previous theoretical descriptions of precipitated magnetospheric electrons (E is approximately 1 keV), the major focus has been the ionization and excitation rates of the neutral atmosphere and the energy deposition rate to thermal ionospheric electrons. However, these precipitating electrons will also produce secondary electrons via impact ionization of the neutral atmosphere. This paper presents the solution of the Boltzman-Landau kinetic equation that uniformly describes the entire electron distribution function in the diffuse aurora, including the affiliated production of secondary electrons (E greater than 600 eV) and their ionosphere-magnetosphere coupling processes. In this article, we discuss for the first time how diffuse electron precipitation into the atmosphere and the associated secondary electron production participate in ionosphere-magnetosphere energy redistribution.

  5. Weighting mean timers for high energy physics electronics

    SciTech Connect

    J. Wu

    1998-11-01

    A new family of electronics circuits, weighting mean timer, is presented in this technical memo. Weighting mean timers can be used in high energy physics experiment electronics to implement the \\concurrence" condition in hardware trigger stage. Several possible architectures of weighting mean timers have been discussed.

  6. Monolithic electronics for nuclear and high-energy physics experiments

    SciTech Connect

    Young, G.R.

    1994-12-31

    Electronic instrumentation for large fixed-target and collider experiments is rapidly moving to the use of highly integrated electronics wherever it is cost effective. This trend is aided by the development of circuit building blocks useful for nuclear and high-energy physics instrumentation and has accelerated recently with the development of monolithic silicon chips with multiple functions on one substrate. Examples of recent developments are given, together with remarks on the rationale for use of monolithic electronics and economic considerations.

  7. Relativistically parametrized extended Hueckel calculations. 11. Energy bands for elemental tellurium and polonium

    SciTech Connect

    Lohr, L.L.

    1987-06-17

    An extension of the REX relativistically parametrized extended Hueckel LCAO molecular orbital method to periodic solids is outlined. The method provides a simple and systematic approach to the description of the spin-orbit splitting of energy bands. The method is illustrated with results for the main-group elements tellurium and polonium, with trigonal-helical and simple-cubic structures, respectively. The helical structure of tellurium is described as a distortion of a simple-cubic structure, with the distortion being quenched in the case of polonium by its very large spin-orbit coupling. 36 references, 10 figures, 1 table.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  9. Efficiency enhancement using electron energy detuning in a laser seeded free electron laser amplifier

    SciTech Connect

    Wang, X. J.; Watanabe, T.; Shen, Y.; Li, R. K.; Murphy, J. B.; Tsang, T.; Freund, H. P.

    2007-10-29

    We report the experimental characterization of efficiency enhancement in a single-pass seeded free-electron laser (FEL) where the electron energy is detuned from resonance. Experiments show a doubling of the efficiency for beam energies above the resonant energy. Measurements of the FEL spectra versus energy detuning shows that the wavelength is governed by the seed laser. The variation in the gain length with beam energy was also observed. Good agreement is found between the experiment and numerical simulations using the MEDUSA simulation code.

  10. Continuous Electron--Energy Variation of the Eindhoven Racetrack Microtron.

    NASA Astrophysics Data System (ADS)

    Theuws, W. H. C.; Botman, J. I. M.; Hagedoorn, H. L.

    1997-05-01

    Energy variation of the Eindhoven racetrack microtron, which has been designed as a fixed--energy electron accelerator at 75 MeV, is considered in this paper. By taking the orbit pattern in the RTM as constant and varying certain parameters continuous energy variation can be obtained. The microtron injector is a linac producing electrons between 6 and 12 MeV. The microtron cavity potential and the magnetic guide fields must be adapted to the injection energy in order to fulfil the synchronism condition. The transverse and longitudinal acceptance of the RTM are effected by deviations of the electron velocity from the speed of light, which are different for each parameter setting. An account of these effects is presented together with the energy--setting measurements by using one of the microtron magnets as a spectrometer.

  11. 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

  12. Low and High Energy Electron Velocity Distributions During Wave-Particle Interaction Events

    NASA Astrophysics Data System (ADS)

    Roeder, J. L.; Fennell, J. F.; Claudepierre, S. G.; Blake, J. B.; Spence, H. E.; Friedel, R. H.

    2015-12-01

    Several wave-particle interaction events have been detected by the Magnetic Electron Ion Spectrometer (MagEIS) instrument on the Van Allen Probes. Most of these occur during the recovery of electron injections by substorm activity. One example reported by Fennell et al [2014] occurred on January 13, 2013. The high resolution mode on MagEIS, with up to 1000 samples per spacecraft spin, provided very detailed pitch angle data for a few energy channels. This data showed quasiperiodic bursts of 30-40 keV electrons at oblique pitch angles that correlate with simultaneously detected emissions of whistler-mode, upper-band chorus. The electron bursts were superimposed on a pre-existing trapped electron distributions at that energy that were of the form sinn α, where α is the pitch angle and the exponent n is approximately 0.8. The data from the Helium, Oxygen, Proton and Electron (HOPE) instrument was investigated to determine if the electron distributions at lower energy were anisotropic. An electron population with high perpendicular anisotropy could provide free energy for the generation of the observed waves. In this case, only small amounts of anisotropy were observed by HOPE. This could indicate that the wave-particle interaction could be some distance away from the Van Allen Probes. But this conclusion appears inconsistent with the electron and the waves arriving simultaneously at the spacecraft for several bursts, despite traveling at different speeds. The result will be discussed and compared with theories and models of such interactions.

  13. Mn Doping Effects on the Electronic Band Structure of PbS Quantum Dot Thin Films: A Scanning Tunneling Microscopy Analysis

    NASA Astrophysics Data System (ADS)

    Yost, Andrew J.; Rimal, Gaurab; Tang, Jinke; Chien, Teyu

    A thorough understanding of the phenomena associated with doping of transition metals in semiconductors is important for the development of semiconducting electronic technologies such as semiconducting quantum dot sensitized solar cells (QDSSC). Manganese doping is of particular interest in a PbS QD as it is potentially capable of increasing overall QDSSC performance. Here we present scanning tunneling microscopy and spectroscopy studies about the effects of Manganese doping on the energy band structures of PbS semiconducting QD thin films, grown using pulsed laser deposition. As a result of Manganese doping in the PbS QD thin films, a widening of the electronic band gap was observed, which is responsible for the observed increase in resistivity. Furthermore, a loss of long range periodicity observed by XRD, upon incorporation of Manganese, indicates that the Manganese dopants also induce a large amount of grain boundaries. This work was supported by the following: U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering, DEFG02-10ER46728 and the National Science Foundation Grant #0948027.

  14. Absence of a {open_quote}{open_quote}Threshold Effect{close_quote}{close_quote} in the Energy Loss of Slow Protons Traversing Large-Band-Gap Insulators

    SciTech Connect

    Eder, K.; Semrad, D.; Bauer, P.; Golser, R.; Maier-Komor, P.; Aumayr, F.; Penalba, M.; Arnau, A.; Ugalde, J.M.; Echenique, P.M.

    1997-11-01

    The electronic stopping cross section {var_epsilon} of slow hydrogen projectiles in large-band-gap insulators has been measured at energies of a few keV. Even at velocities as low as v{sub 0}/3 (v{sub 0}=c/137) , we find no influence of the band gap on the velocity dependence of {var_epsilon} , contrary to the case of gaseous targets with similar minimum excitation energy. The magnitude of {var_epsilon} and its essentially linear velocity dependence allow us to arrive at the following conclusion: Electron promotion processes contribute substantially to stopping due to formation of molecular orbitals. This points towards the existence of a bound electron state at a proton that moves slowly in an insulator. A simple model based on the calculation of molecular orbital correlation diagrams for the H/LiF collision system supports the idea of local reduction of the band gap of an insulating target. {copyright} {ital 1997} {ital The American Physical Society}

  15. Properties of the electron cloud in a high-energy positron and electron storage ring

    DOE PAGES

    Harkay, K. C.; Rosenberg, R. A.

    2003-03-20

    Low-energy, background electrons are ubiquitous in high-energy particle accelerators. Under certain conditions, interactions between this electron cloud and the high-energy beam can give rise to numerous effects that can seriously degrade the accelerator performance. These effects range from vacuum degradation to collective beam instabilities and emittance blowup. Although electron-cloud effects were first observed two decades ago in a few proton storage rings, they have in recent years been widely observed and intensely studied in positron and proton rings. Electron-cloud diagnostics developed at the Advanced Photon Source enabled for the first time detailed, direct characterization of the electron-cloud properties in amore » positron and electron storage ring. From in situ measurements of the electron flux and energy distribution at the vacuum chamber wall, electron-cloud production mechanisms and details of the beam-cloud interaction can be inferred. A significant longitudinal variation of the electron cloud is also observed, due primarily to geometrical details of the vacuum chamber. Furthermore, such experimental data can be used to provide realistic limits on key input parameters in modeling efforts, leading ultimately to greater confidence in predicting electron-cloud effects in future accelerators.« less

  16. Properties of the electron cloud in a high-energy positron and electron storage ring

    SciTech Connect

    Harkay, K. C.; Rosenberg, R. A.

    2003-03-20

    Low-energy, background electrons are ubiquitous in high-energy particle accelerators. Under certain conditions, interactions between this electron cloud and the high-energy beam can give rise to numerous effects that can seriously degrade the accelerator performance. These effects range from vacuum degradation to collective beam instabilities and emittance blowup. Although electron-cloud effects were first observed two decades ago in a few proton storage rings, they have in recent years been widely observed and intensely studied in positron and proton rings. Electron-cloud diagnostics developed at the Advanced Photon Source enabled for the first time detailed, direct characterization of the electron-cloud properties in a positron and electron storage ring. From in situ measurements of the electron flux and energy distribution at the vacuum chamber wall, electron-cloud production mechanisms and details of the beam-cloud interaction can be inferred. A significant longitudinal variation of the electron cloud is also observed, due primarily to geometrical details of the vacuum chamber. Furthermore, such experimental data can be used to provide realistic limits on key input parameters in modeling efforts, leading ultimately to greater confidence in predicting electron-cloud effects in future accelerators.

  17. Relative spins and excitation energies of superdeformed bands in {sup 190}Hg: Further evidence for octupole vibration

    SciTech Connect

    Crowell, B.; Carpenter, M.; Janssens, R.; Blumenthal, D.; Timar, J.; Wilson, A.; Sharpey-Schafer, J. |; Nakatsukasa, T.; Ahmad, I.; Astier, A.; Azaiez, F.; du Croux, L.; Gall, B.; Hannachi, F.; Khoo, T.; Korichi, A.; Lauritsen, T.; Lopez-Martens, A.

    1995-04-01

    An experiment using the Eurogam phase II {gamma}-ray spectrometer confirms the existence of an excited superdeformed (SD) band in {sup 190}Hg and its very unusual decay into the lowest SD band over 3--4 transitions. The energies of the transitions linking the two SD bands have been firmly established, and their angular distributions are consistent with a dipole character. Comparisons with calculations using random-phase approximation indicate that the excited SD band can be interpreted as an octupole-vibrational structure.

  18. 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.

  19. 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.

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

    PubMed

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

    2014-12-15

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