Electron-beam induced conduction in some polymers

International Nuclear Information System (INIS)

Suzuoki, Yasuo; Mizutani, Teruyoshi; Ieda, Masayuki

1976-01-01

The charge signal induced by pulsed electron beam consists of two components, i.e. the fast and the slow components. The slow component which corresponds to carrier transport via shallow traps exhibited an asymmetry with respect to the bias field polarity. The asymmetry revealed that the main carriers which drifted via shallow traps were electrons in PET, both electrons and holes in PEN, and holes in PS. TSC spectra of electron-beam induced electrets proved directly the existence of electron shallow traps in PET and both electron and hole traps in PEN. Their trap energies were 0.1 to 0.2 eV. (auth.)

Beam-induced heat loads on the beam screens of the inner triplets for the HL-LHC

CERN Document Server

Skripka, Galina; CERN. Geneva. ATS Department

2018-01-01

The expected heat load induced on the beam screens has been evaluated for the triplet assemblies in the four experimental Insertion Regions (IRs) of the HL-LHC. The contribution from electron cloud effects has been estimated using PyECLOUD macroparticle simulations. The presence of a surface treatment for the reduction of the Secondary Electron Yield has been taken into account. The contribution from the impedance of the beam screen has been evaluated taking into account the impact of the temperature and of the magnetic field on the resistivity of the surface.

Definition and determination of the triplet-triplet energy transfer reaction coordinate.

Science.gov (United States)

Zapata, Felipe; Marazzi, Marco; Castaño, Obis; Acuña, A Ulises; Frutos, Luis Manuel

2014-01-21

A definition of the triplet-triplet energy transfer reaction coordinate within the very weak electronic coupling limit is proposed, and a novel theoretical formalism is developed for its quantitative determination in terms of internal coordinates The present formalism permits (i) the separation of donor and acceptor contributions to the reaction coordinate, (ii) the identification of the intrinsic role of donor and acceptor in the triplet energy transfer process, and (iii) the quantification of the effect of every internal coordinate on the transfer process. This formalism is general and can be applied to classical as well as to nonvertical triplet energy transfer processes. The utility of the novel formalism is demonstrated here by its application to the paradigm of nonvertical triplet-triplet energy transfer involving cis-stilbene as acceptor molecule. In this way the effect of each internal molecular coordinate in promoting the transfer rate, from triplet donors in the low and high-energy limit, could be analyzed in detail.

Effect of Förster-mediated triplet-polaron quenching and triplet-triplet annihilation on the efficiency roll-off of organic light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Eersel, H. van [Simbeyond B.V., P.O. Box 513, NL-5600 MB Eindhoven (Netherlands); Bobbert, P. A.; Janssen, R. A. J.; Coehoorn, R., E-mail: r.coehoorn@tue.nl [Department of Applied Physics and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, NL-5600 MB Eindhoven (Netherlands)

2016-04-28

We report the results of a systematic study of the interplay of triplet-polaron quenching (TPQ) and triplet-triplet annihilation (TTA) on the efficiency roll-off of organic light-emitting diodes (OLEDs) with increasing current density. First, we focus on OLEDs based on the green phosphorescent emitter tris[2-phenylpyridine]iridium(III) (Ir(ppy){sub 3}) and the red phosphorescent dye platinum octaethylporphyrin. It is found that the experimental data can be reproduced using kinetic Monte Carlo (kMC) simulations within which TPQ and TTA are due to a nearest-neighbor (NN) interaction, or due to a more long-range Förster-type process. Furthermore, we find a subtle interplay between TPQ and TTA: decreasing the contribution of one process can increase the contribution of the other process, so that the roll-off is not significantly reduced. Furthermore, we find that just analyzing the shape of the roll-off is insufficient for determining the relative role of TPQ and TTA. Subsequently, we investigate the wider validity of this picture using kMC simulations for idealized but realistic symmetric OLEDs, with an emissive layer containing a small concentration of phosphorescent dye molecules in a matrix material. Whereas for NN-interactions the roll-off can be reduced when the dye molecules act as shallow hole and electron traps, we find that such an approach becomes counterproductive for long-range TTA and TPQ. Developing well-founded OLED design rules will thus require that more quantitative information is available on the rate and detailed mechanism of the TPQ and TTA processes.

Formation and Coalescence of Electron Solitary Holes

DEFF Research Database (Denmark)

Saeki, K.; Michelsen, Poul; Pécseli, H. L.

1979-01-01

Electron solitary holes were observed in a magnetized collisionless plasma. These holes were identified as Bernstein-Green-Kruskal equilibria, thus being purely kinetic phenomena. The electron hole does not damp even though its velocity is close to the electron thermal velocity. Two holes attract...

Triplet exciton dissociation and electron extraction in graphene-templated pentacene observed with ultrafast spectroscopy.

Science.gov (United States)

McDonough, Thomas J; Zhang, Lushuai; Roy, Susmit Singha; Kearns, Nicholas M; Arnold, Michael S; Zanni, Martin T; Andrew, Trisha L

2017-02-08

We compare the ultrafast dynamics of singlet fission and charge generation in pentacene films grown on glass and graphene. Pentacene grown on graphene is interesting because it forms large crystals with the long axis of the molecules "lying-down" (parallel to the surface). At low excitation fluence, spectra for pentacene on graphene contain triplet absorptions at 507 and 545 nm and no bleaching at 630 nm, which we show is due to the orientation of the pentacene molecules. We perform the first transient absorption anisotropy measurements on pentacene, observing negative anisotropy of the 507 and 545 nm peaks, consistent with triplet absorption. A broad feature at 853 nm, observed on both glass and graphene, is isotropic, suggesting hole absorption. At high fluence, there are additional features, whose kinetics and anisotropies are not explained by heating, that we assign to charge generation; we propose a polaron pair absorption at 614 nm. The lifetimes are shorter at high fluence for both pentacene on glass and graphene, indicative of triplet-triplet annihilation that likely enhances charge generation. The anisotropy decays more slowly for pentacene on graphene than on glass, in keeping with the smaller domain size observed via atomic force microscopy. Coherent acoustic phonons are observed for pentacene on graphene, which is a consequence of more homogeneous domains. Measuring the ultrafast dynamics of pentacene as a function of molecular orientation, fluence, and polarization provides new insight to previous spectral assignments.

Can the ''doublet-triplet splitting'' problem be solved without doublet-triplet splitting?

International Nuclear Information System (INIS)

Dvali, G.R.

1992-03-01

We consider a new possible mechanism for the natural solution of the doublet-triplet splitting problem in SUSY GUTs. In contrast to the usually discussed scenarios, in our case the GUT symmetry breaking does not provide any splitting between the Higgs doublet and the triplet masses. The weak doublet and its colour triplet partner both remain light, but the triplet automatically occurs decoupled from the quark and lepton superfields and cannot induce proton decay. The advantage of the above scenarios is the absence at the GUT scale of the baryon number violating the tree level d = 5 and d = 6 operators via the colour-triple exchange. It is shown that in flipped SU(5) GUT they do not appear at any scale. In the SO(10) model, such operators can be induced after SUSY breaking but are strongly suppressed. (author). 22 refs, 2 figs

Tricritical behaviour in the phase transition induced by electron-hole pairing

International Nuclear Information System (INIS)

Crisan, M.

1980-01-01

The electron-hole pairing, which is possible in metals or semiconductors, can give condensed phases with two order parameters. If the coupling between the two order parameters is considered, the free energy functional is similar with the free energy of a n-component spin system with cubic anisotropy. Using the Wagner hypothesis (tricritical scaling) the non-linear scaling fields have been calculated. In order to perform the calculation of the nonlinear fields we used the method given by Rudnick and Nelson to solve the recursion relations for the 4-epsilon-dimensional system with n=6 components. The present calculation in the frame-work of the renormalization-group approach confirms the result obtained in the mean-field theory that the coupling of the two order parameters induces a first order phase transition. (author)

Electron Hole Plasma in Solids Induced by Ultrashort XUV Laser Pulses

International Nuclear Information System (INIS)

Rethfeld, B.; Medvedev, N.

2013-01-01

Irradiation of solids with ultrashort XUV laser pulses leads to an excitation of electrons from the valence band and deeper shells to the conduction band leading to a nonequilibrium highly energetic electron hole plasma. We investigate the transient electron dynamics in a solid semiconductor and metal (silicon and aluminum, respectively) under irradiation with a femtosecond VUV to XUV laser pulse as used in experiments with the Free Electron Laser FLASH at DESY in Hamburg, Germany. Applying the Asymptotical Trajectory Monte-Carlo technique, we obtain the transient energy distribution of the excited and ionized electrons within the solid. Photon absorption by electrons in different bands and secondary excitation and ionization processes are simulated event by event. The method was extended in order to take into account the electronic band structure and Pauli's principle for electrons in the conduction band. In this talk we review our results on the dynamics of the transient electron-hole plasma, in particular its transient density and energy distribution in dependence on laser and material parameters. For semiconductors we introduce the concept of an ''effective energy gap'' for collective electronic excitation, which can be applied to estimate the free electron density after high-intensity ultrashort XUV laser pulse irradiation. For aluminum we demonstrate that the electronic spectra depend on the relaxation kinetics of the excited electronic subsystem. Experimentally observed spectra of emitted photons from irradiated aluminum can be explained well with our results. (author)

Excitonic and electron-hole mechanisms of the creation of Frenkel defect in alkali halides

International Nuclear Information System (INIS)

Lushchik, A.; Kirm, M.; Lushchik, Ch.; Vasil'chenko, E.

2000-01-01

Excitonic and electron-hole (e-h) mechanisms of stable F centre creation by VUV radiation in alkali halide crystals are discussed. In KCl at 4.2 K, the efficiency of stable F-H pair creation is especially high at the direct optical formation of triplet excitons with n=1. At 200-400 K, the creation processes of stable F centres in KCl are especially efficient at the formation of one-halide exciton in the Urbach tail of an exciton absorption. In KCl and KBr, the decay of a cation exciton (∼20 eV) causes the formation of two e-h pairs, while in NaCl a cation exciton (33.5 eV) decays into two e-h and an anion exciton. An elastic uniaxial stress of a crystal excited by VUV radiation decreases the mean free path of excitons before their self-trapping (KI) and increases the mean free path of hot holes before self-trapping (NaCl)

Compact quadrupole triplet for the S-DALINAC polarized electron injector SPIN

Energy Technology Data Exchange (ETDEWEB)

Eckardt, C.; Eichhorn, R.; Enders, J.; Hessler, C.; Poltoratska, Y. [Inst. fuer Kernphysik, Technische Univ. Darmstadt (Germany); Ackermann, W.; Mueller, W.F.O.; Steiner, B.; Weiland, T. [Inst. fuer Theorie Elektromagnetischer Felder, Technische Univ. Darmstadt (Germany)

2007-07-01

An ultra compact quadrupole triplet for the S-DALINAC Polarized Electron Injector SPIN has been developed. This development is due to limiting spatial restrictions. Each individual quadrupole has a length of 8 mm, affixed by two 2 mm aluminum plates, resulting in a length of only 12 mm per quadrupole. The gaps between each quadrupole are set to 18 mm, therefore the complete triplet has a total length of only 72 mm. The quadrupole design includes a large aperture, suitable for CF 35 beam pipes. As fringe fields reach far info neighboring yokes, the assembly requires simulation by a beam dynamics tool for optimal weighting of the current excitation. Measurement of the magnetic field distribution is compared to numerical values and the quadrupole strength is calculated. (orig.)

Plasma electron hole kinematics. I. Momentum conservation

Energy Technology Data Exchange (ETDEWEB)

Hutchinson, I. H.; Zhou, C. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2016-08-15

We analyse the kinematic properties of a plasma electron hole: a non-linear self-sustained localized positive electric potential perturbation, trapping electrons, which behaves as a coherent entity. When a hole accelerates or grows in depth, ion and electron plasma momentum is changed both within the hole and outside, by an energization process we call jetting. We present a comprehensive analytic calculation of the momentum changes of an isolated general one-dimensional hole. The conservation of the total momentum gives the hole's kinematics, determining its velocity evolution. Our results explain many features of the behavior of hole speed observed in numerical simulations, including self-acceleration at formation, and hole pushing and trapping by ion streams.

Analysis of thermal detrapping of holes created by electron irradiation in high purity amorphous SiO_2 using the induced and secondary current measurements

International Nuclear Information System (INIS)

Said, K.; Moya, G.; Si Ahmed, A.; Damamme, G.; Kallel, A.

2016-01-01

Graphical abstract: - Highlights: • Positive charging of high purity amorphous SiO_2 achieved by electron irradiation in a specially equipped scanning electron microscope. • Quantity of detrapped holes evaluated via measurements of induced and secondary electron currents. • Study of isothermal detrapping for different temperatures (300–663 K). • Analysis of the hole detrapping via a first order kinetics. • Evaluation of the hole detrapping parameters (activation energy and frequency factor). - Abstract: Isothermal detrapping of holes after electron irradiation (using a SEM) in high purity amorphous SiO_2 is evaluated at different temperatures (in the range 300–663 K) by means of the induced and secondary current measurements. In order to single out the hole detrapping, the specific charging conditions (1 keV defocused electron beam of low density) leading to positive charging are adopted. The thermal detrapping, which stems from a single trap, begins at 523 K and is completed at 663 K. After annealing in air at 973 K during 48 h, two detrapping stages are revealed: the former is connected with an additional shallow trap, while the latter requires temperatures above 663 K for a complete detrapping. The first order kinetics describes reasonably well the detrapping process. The frequency factors (near 10"1"0 s"−"1) and the activation energies (about 1.6 eV) deduced from this analysis could be assigned, respectively, to the relaxation connected to detrapping and to the trap energy level of the charged oxygen vacancy.

Ultrafast Charge and Triplet State Formation in Diketopyrrolopyrrole Low Band Gap Polymer/Fullerene Blends: Influence of Nanoscale Morphology of Organic Photovoltaic Materials on Charge Recombination to the Triplet State

Directory of Open Access Journals (Sweden)

René M. Williams

2017-01-01

Full Text Available Femtosecond transient absorption spectroscopy of thin films of two types of morphologies of diketopyrrolopyrrole low band gap polymer/fullerene-adduct blends is presented and indicates triplet state formation by charge recombination, an important loss channel in organic photovoltaic materials. At low laser fluence (approaching solar intensity charge formation characterized by a 1350 nm band (in ~250 fs dominates in the two PDPP-PCBM blends with different nanoscale morphologies and these charges recombine to form a local polymer-based triplet state on the sub-ns timescale (in ~300 and ~900 ps indicated by an 1100 nm absorption band. The rate of triplet state formation is influenced by the morphology. The slower rate of charge recombination to the triplet state (in ~900 ps belongs to a morphology that results in a higher power conversion efficiency in the corresponding device. Nanoscale morphology not only influences interfacial area and conduction of holes and electrons but also influences the mechanism of intersystem crossing (ISC. We present a model that correlates morphology to the exchange integral and fast and slow mechanisms for ISC (SOCT-ISC and H-HFI-ISC. For the pristine polymer, a flat and unstructured singlet-singlet absorption spectrum (between 900 and 1400 nm and a very minor triplet state formation (5% are observed at low laser fluence.

High-frequency two-electron photoionization cross section of triplet states

International Nuclear Information System (INIS)

Krivec, R.; Amusia, M.Ya.; Mandelzweig, V.B.

2003-01-01

Using high precision wave functions describing the triplet ground and excited 3 S states of the He atom and heliumlike ions, the cross sections of single- and double-electron photoionization are calculated. The dependence of the ratio R of the double and single ionization cross sections on the nuclear charge Z and the principal quantum number of excitation n is studied. The results obtained are compared to those for previously studied singlet states

Analysis of thermal detrapping of holes created by electron irradiation in high purity amorphous SiO{sub 2} using the induced and secondary current measurements

Energy Technology Data Exchange (ETDEWEB)

Said, K., E-mail: kamel.said@fss.rnu.tn [LaMaCoP, Université de Sfax, BP 1171, 3000 Sfax (Tunisia); Moya, G.; Si Ahmed, A. [Im2np, UMR 7334 CNRS, Aix-Marseille Université, 13397 Marseille Cedex 20 (France); Damamme, G. [CEA, DAM, GRAMAT, 46500 Gramat (France); Kallel, A. [LaMaCoP, Université de Sfax, BP 1171, 3000 Sfax (Tunisia)

2016-01-15

Graphical abstract: - Highlights: • Positive charging of high purity amorphous SiO{sub 2} achieved by electron irradiation in a specially equipped scanning electron microscope. • Quantity of detrapped holes evaluated via measurements of induced and secondary electron currents. • Study of isothermal detrapping for different temperatures (300–663 K). • Analysis of the hole detrapping via a first order kinetics. • Evaluation of the hole detrapping parameters (activation energy and frequency factor). - Abstract: Isothermal detrapping of holes after electron irradiation (using a SEM) in high purity amorphous SiO{sub 2} is evaluated at different temperatures (in the range 300–663 K) by means of the induced and secondary current measurements. In order to single out the hole detrapping, the specific charging conditions (1 keV defocused electron beam of low density) leading to positive charging are adopted. The thermal detrapping, which stems from a single trap, begins at 523 K and is completed at 663 K. After annealing in air at 973 K during 48 h, two detrapping stages are revealed: the former is connected with an additional shallow trap, while the latter requires temperatures above 663 K for a complete detrapping. The first order kinetics describes reasonably well the detrapping process. The frequency factors (near 10{sup 10} s{sup −1}) and the activation energies (about 1.6 eV) deduced from this analysis could be assigned, respectively, to the relaxation connected to detrapping and to the trap energy level of the charged oxygen vacancy.

Desorption by Femtosecond Laser Pulses : An Electron-Hole Effect?

OpenAIRE

D. M., NEWNS; T. F., HEINZ; J. A., MISEWICH; IBM Research Division, T. J. Watson Research Center; IBM Research Division, T. J. Watson Research Center; IBM Research Division, T. J. Watson Research Center

1992-01-01

Desorption of molecules from metal surfaces induced by femtosecond visible laser pulses has been reported. Since the lattice temperature rise is insufficient to explain desorption, an electronic mechanism is clearly responsible. It is shown that a theory based on direct coupling between the center-of-mass degree of freedom of the adsorbate and the electron-hole excitations of the substrate provides a satisfactory explanation of the various experimental findings.

The triplet excited state of Bodipy: formation, modulation and application.

Science.gov (United States)

Zhao, Jianzhang; Xu, Kejing; Yang, Wenbo; Wang, Zhijia; Zhong, Fangfang

2015-12-21

Boron dipyrromethene (Bodipy) is one of the most extensively investigated organic chromophores. Most of the investigations are focused on the singlet excited state of Bodipy, such as fluorescence. In stark contrast, the study of the triplet excited state of Bodipy is limited, but it is an emerging area, since the triplet state of Bodipy is tremendously important for several areas, such as the fundamental photochemistry study, photodynamic therapy (PDT), photocatalysis and triplet-triplet annihilation (TTA) upconversion. The recent developments in the study of the production, modulation and application of the triplet excited state of Bodipy are discussed in this review article. The formation of the triplet state of Bodipy upon photoexcitation, via the well known approach such as the heavy atom effect (including I, Br, Ru, Ir, etc.), and the new methods, such as using a spin converter (e.g. C60), charge recombination, exciton coupling and the doubly substituted excited state, are summarized. All the Bodipy-based triplet photosensitizers show strong absorption of visible or near IR light and the long-lived triplet excited state, which are important for the application of the triplet excited state in PDT or photocatalysis. Moreover, the methods for switching (or modulation) of the triplet excited state of Bodipy were discussed, such as those based on the photo-induced electron transfer (PET), by controlling the competing Förster-resonance-energy-transfer (FRET), or the intermolecular charge transfer (ICT). Controlling the triplet excited state will give functional molecules such as activatable PDT reagents or molecular devices. It is worth noting that switching of the singlet excited state and the triplet state of Bodipy may follow different principles. Application of the triplet excited state of Bodipy in PDT, hydrogen (H2) production, photoredox catalytic organic reactions and TTA upconversion were discussed. The challenges and the opportunities in these areas were

Electron-hole pair effects in methane dissociative chemisorption on Ni(111)

Energy Technology Data Exchange (ETDEWEB)

Luo, Xuan; Jiang, Bin, E-mail: bjiangch@ustc.edu.cn [Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Juaristi, J. Iñaki [Centro de Física de Materiales CFM/MPC(CSIC-UPV/EHU), P. Manuel de Lardizabal 5, 20018 San Sebastián (Spain); Donostia International Physics Center DIPC, P. Manuel de Lardizabal 4, 20018 San Sebastián (Spain); Departamento de Física de Materiales, Facultad de Químicas, Universidad del País Vasco (UPV/EHU), Apartado 1072, 20080 San Sebastián (Spain); Alducin, Maite [Centro de Física de Materiales CFM/MPC(CSIC-UPV/EHU), P. Manuel de Lardizabal 5, 20018 San Sebastián (Spain); Donostia International Physics Center DIPC, P. Manuel de Lardizabal 4, 20018 San Sebastián (Spain); Guo, Hua [Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131 (United States)

2016-07-28

The dissociative chemisorption of methane on metal surfaces has attracted much attention in recent years as a prototype of gas-surface reactions in understanding the mode specific and bond selective chemistry. In this work, we systematically investigate the influence of electron-hole pair excitations on the dissociative chemisorption of CH{sub 4}/CH{sub 3}D/CHD{sub 3} on Ni(111). The energy dissipation induced by surface electron-hole pair excitations is modeled as a friction force introduced in the generalized Langevin equation, in which the independent atomic friction coefficients are determined within the local-density friction approximation. Quasi-classical trajectory calculations for CH{sub 4}/CH{sub 3}D/CHD{sub 3} have been carried out on a recently developed twelve-dimensional potential energy surface. Comparing the dissociation probabilities obtained with and without friction, our results clearly indicate that the electron-hole pair effects are generally small, both on absolute reactivity of each vibrational state and on the mode specificity and bond selectivity. Given similar observations in both water and methane dissociation processes, we conclude that electron-hole pair excitations would not play an important role as long as the reaction is direct and the interaction time between the molecule and metal electrons is relatively short.

Native and induced triplet nitrogen-vacancy centers in nano- and micro-diamonds: Half-field electron paramagnetic resonance fingerprint

Energy Technology Data Exchange (ETDEWEB)

Shames, A. I., E-mail: sham@bgu.ac.il [Department of Physics, Ben-Gurion University of the Negev, Be' er-Sheva 84105 (Israel); Osipov, V. Yu.; Vul’, A. Ya. [Ioffe Physical-Technical Institute, Polytechnicheskaya 26, 194021 St. Petersburg (Russian Federation); Bardeleben, H.-J. von [Institut des Nano Sciences de Paris-INSP, Université Pierre et Marie Curie/UMR 7588 au CNRS, 7500 Paris (France); Boudou, J.-P.; Treussart, F. [Laboratoire Aimé Cotton, CNRS, Université Paris-Sud and ENS Cachan, 91405 Orsay (France)

2014-02-10

Multiple frequency electron paramagnetic resonance (EPR) study of small (4–25 nm) nanodiamonds obtained by various dynamic synthesis techniques reveals systematic presence in the half-field (HF) region a distinctive doublet fingerprint consisting of resolved g{sub HF1} = 4.26 and g{sub HF2} = 4.00 signals. This feature is attributed to “forbidden” ΔM{sub S} = 2 transitions in EPR spectra of two native paramagnetic centers of triplet (S = 1) origin designated as TR1 and TR2, characterized by zero field splitting values D{sub 1} = 0.0950 ± 0.002 cm{sup −1} and D{sub 2} = 0.030 ± 0.005 cm{sup −1}. Nanodiamonds of ∼50 nm particle size, obtained by crushing of Ib type nitrogen rich synthetic diamonds, show only HF TR2 signal whereas the same sample undergone high energy (20 MeV) electron irradiation and thermal annealing demonstrates rise of HF TR1 signal. The same HF TR1 signals appear in the process of fabrication of fluorescent nanodiamonds from micron-size synthetic diamond precursors. Results obtained allow unambiguous attribution of the half-field TR1 EPR signals with g{sub HF1} = 4.26, observed in nano- and micron-diamond powders, to triplet negatively charged nitrogen-vacancy centers. These signals are proposed as reliable and convenient fingerprints in both qualitative and quantitative study of fluorescent nano- and micron-diamonds.

Native and induced triplet nitrogen-vacancy centers in nano- and micro-diamonds: Half-field electron paramagnetic resonance fingerprint

International Nuclear Information System (INIS)

Shames, A. I.; Osipov, V. Yu.; Vul’, A. Ya.; Bardeleben, H.-J. von; Boudou, J.-P.; Treussart, F.

2014-01-01

Multiple frequency electron paramagnetic resonance (EPR) study of small (4–25 nm) nanodiamonds obtained by various dynamic synthesis techniques reveals systematic presence in the half-field (HF) region a distinctive doublet fingerprint consisting of resolved g HF1  = 4.26 and g HF2  = 4.00 signals. This feature is attributed to “forbidden” ΔM S  = 2 transitions in EPR spectra of two native paramagnetic centers of triplet (S = 1) origin designated as TR1 and TR2, characterized by zero field splitting values D 1  = 0.0950 ± 0.002 cm −1 and D 2  = 0.030 ± 0.005 cm −1 . Nanodiamonds of ∼50 nm particle size, obtained by crushing of Ib type nitrogen rich synthetic diamonds, show only HF TR2 signal whereas the same sample undergone high energy (20 MeV) electron irradiation and thermal annealing demonstrates rise of HF TR1 signal. The same HF TR1 signals appear in the process of fabrication of fluorescent nanodiamonds from micron-size synthetic diamond precursors. Results obtained allow unambiguous attribution of the half-field TR1 EPR signals with g HF1  = 4.26, observed in nano- and micron-diamond powders, to triplet negatively charged nitrogen-vacancy centers. These signals are proposed as reliable and convenient fingerprints in both qualitative and quantitative study of fluorescent nano- and micron-diamonds

The dynamics of electron and ion holes in a collisionless plasma

Directory of Open Access Journals (Sweden)

B. Eliasson

2005-01-01

Full Text Available We present a review of recent analytical and numerical studies of the dynamics of electron and ion holes in a collisionless plasma. The new results are based on the class of analytic solutions which were found by Schamel more than three decades ago, and which here work as initial conditions to numerical simulations of the dynamics of ion and electron holes and their interaction with radiation and the background plasma. Our analytic and numerical studies reveal that ion holes in an electron-ion plasma can trap Langmuir waves, due the local electron density depletion associated with the negative ion hole potential. Since the scale-length of the ion holes are on a relatively small Debye scale, the trapped Langmuir waves are Landau damped. We also find that colliding ion holes accelerate electron streams by the negative ion hole potentials, and that these streams of electrons excite Langmuir waves due to a streaming instability. In our Vlasov simulation of two colliding ion holes, the holes survive the collision and after the collision, the electron distribution becomes flat-topped between the two ion holes due to the ion hole potentials which work as potential barriers for low-energy electrons. Our study of the dynamics between electron holes and the ion background reveals that standing electron holes can be accelerated by the self-created ion cavity owing to the positive electron hole potential. Vlasov simulations show that electron holes are repelled by ion density minima and attracted by ion density maxima. We also present an extension of Schamel's theory to relativistically hot plasmas, where the relativistic mass increase of the accelerated electrons have a dramatic effect on the electron hole, with an increase in the electron hole potential and in the width of the electron hole. A study of the interaction between electromagnetic waves with relativistic electron holes shows that electromagnetic waves can be both linearly and nonlinearly

Auger electron emission initiated by the creation of valence-band holes in graphene by positron annihilation.

Science.gov (United States)

Chirayath, V A; Callewaert, V; Fairchild, A J; Chrysler, M D; Gladen, R W; Mcdonald, A D; Imam, S K; Shastry, K; Koymen, A R; Saniz, R; Barbiellini, B; Rajeshwar, K; Partoens, B; Weiss, A H

2017-07-13

Auger processes involving the filling of holes in the valence band are thought to make important contributions to the low-energy photoelectron and secondary electron spectrum from many solids. However, measurements of the energy spectrum and the efficiency with which electrons are emitted in this process remain elusive due to a large unrelated background resulting from primary beam-induced secondary electrons. Here, we report the direct measurement of the energy spectra of electrons emitted from single layer graphene as a result of the decay of deep holes in the valence band. These measurements were made possible by eliminating competing backgrounds by employing low-energy positrons (holes by annihilation. Our experimental results, supported by theoretical calculations, indicate that between 80 and 100% of the deep valence-band holes in graphene are filled via an Auger transition.

Landau damping effects on collision-induced quantum interference in electron-hole plasmas

International Nuclear Information System (INIS)

Hwa-Min, Kim; Young-Dae, Jung

2007-01-01

The Landau damping effects on the quantum interference in electron collisions are investigated in a quantum plasma composed of electrons and holes. The Born method and the total spin states are considered to obtain the scattering cross-section by using the effective screened potential model. It is found that the Landau damping effects enhance the scattering cross-section, especially, near the scattering angle θ L = π/4. (authors)

Landau damping effects on collision-induced quantum interference in electron-hole plasmas

Energy Technology Data Exchange (ETDEWEB)

Hwa-Min, Kim [Daegu Univ. Catholic, Dept. of Electronics Engineering (Korea, Republic of); Young-Dae, Jung [Hanyang Univ., Dept. of Applied Physics, Seoul (Korea, Republic of)

2007-07-15

The Landau damping effects on the quantum interference in electron collisions are investigated in a quantum plasma composed of electrons and holes. The Born method and the total spin states are considered to obtain the scattering cross-section by using the effective screened potential model. It is found that the Landau damping effects enhance the scattering cross-section, especially, near the scattering angle {theta}{sub L} = {pi}/4. (authors)

Confinement sensitivity in quantum dot singlet-triplet relaxation

Science.gov (United States)

Wesslén, C. J.; Lindroth, E.

2017-11-01

Spin-orbit mediated phonon relaxation in a two-dimensional quantum dot is investigated using different confining potentials. Elliptical harmonic oscillator and cylindrical well results are compared to each other in the case of a two-electron GaAs quantum dot subjected to a tilted magnetic field. The lowest energy set of two-body singlet and triplet states are calculated including spin-orbit and magnetic effects. These are used to calculate the phonon induced transition rate from the excited triplet to the ground state singlet for magnetic fields up to where the states cross. The roll of the cubic Dresselhaus effect, which is found to be much more important than previously assumed, and the positioning of ‘spin hot-spots’ are discussed and relaxation rates for a few different systems are exhibited.

Theory of Transient Excited State Absorptions in Pentacene and Derivatives: Triplet-Triplet Biexciton versus Free Triplets.

Science.gov (United States)

Khan, Souratosh; Mazumdar, Sumit

2017-12-07

Recent experiments in several singlet-fission materials have found that the triplet-triplet biexciton either is the primary product of photoexcitation or has a much longer lifetime than believed until now. It thus becomes essential to determine the difference in the spectroscopic signatures of the bound triplet-triplet and free triplets to distinguish between them optically. We report calculations of excited state absorptions (ESAs) from the singlet and triplet excitons and from the triplet-triplet biexciton for a pentacene crystal with the herringbone structure and for nanocrystals of bis(triisopropylsilylethynyl) (TIPS)-pentacene. The triplet-triplet biexciton absorbs in both the visible and the near-infrared (NIR), while the monomer free triplet absorbs only in the visible. The intensity of the NIR absorption depends on the extent of intermolecular coupling, in agreement with observations in TIPS-pentacene nanocrystals. We predict additional weak ESA from the triplet-triplet but not from the triplet, at still lower energy.

Structure analysis of photo-induced triplet phenylnitrene using synchrotron radiation

CERN Document Server

Kawano, M; Uekusa, H; Ohashi, Y; Ozawa, Y; Matsubara, K; Imabayashi, H; Mitsumi, M; Toriumi, K

2003-01-01

The crystal structures of [(PhCH sub 2) sub 2 NH sub 2] sup + [m-C sub 6 H sub 4 (N sub 3)-(COO)] sup - before and after UV-irradiation were analyzed at 25 K by using an X-ray vacuum camera set up at the synchrotron laboratory (SPring-8). The C-N (nitrene) bond distance in the triplet state of the photo-induced m-carboxyphenylnitrene is determined to be 1.34(4) A.

Real-time observation of intersystem crossing induced by charge recombination during bimolecular electron transfer reactions

KAUST Repository

Alsam, Amani Abdu

2016-09-21

Real-time probing of intersystem crossing (ISC) and triplet-state formation after photoinduced electron transfer (ET) is a particularly challenging task that can be achieved by time-resolved spectroscopy with broadband capability. Here, we examine the mechanism of charge separation (CS), charge recombination (CR) and ISC of bimolecular photoinduced electron transfer (PET) between poly[(9,9-di(3,3′-N,N’-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9-dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and dicyanobenzene (DCB) using time-resolved spectroscopy. PET from PFN to DCB is confirmed by monitoring the transient absorption (TA) and infrared spectroscopic signatures for the radical ion pair (DCB─•-PFN+•). In addition, our time-resolved results clearly demonstrate that CS takes place within picoseconds followed by CR within nanoseconds. The ns-TA data exhibit the clear spectroscopic signature of PFN triplet-triplet absorption, induced by the CR of the radical ion pairs (DCB─•-PFN+•). As a result, the triplet state of PFN (3PFN*) forms and subsequently, the ground singlet state is replenished within microseconds. © 2016

Threshold law for the triplet state for electron-impact ionization in the Temkin-Poet model

International Nuclear Information System (INIS)

Ihra, W.; Mota-Furtado, F.; OMahony, P.F.; Macek, J.H.

1997-01-01

We derive the analytical threshold behavior for the triplet cross section for electron-impact ionization in the Temkin-Poet model. The analytical results indicate that the most recent numerical calculations may fail to reproduce the correct threshold behavior in an energy regime below about E=0.1 a.u. We also present an analytical expression for the energy distribution of the two electrons near threshold. copyright 1997 The American Physical Society

Systematic design of active spaces for multi-reference calculations of singlet-triplet gaps of organic diradicals, with benchmarks against doubly electron-attached coupled-cluster data

Science.gov (United States)

Stoneburner, Samuel J.; Shen, Jun; Ajala, Adeayo O.; Piecuch, Piotr; Truhlar, Donald G.; Gagliardi, Laura

2017-10-01

Singlet-triplet gaps in diradical organic π-systems are of interest in many applications. In this study, we calculate them in a series of molecules, including cyclobutadiene and its derivatives and cyclopentadienyl cation, by using correlated participating orbitals within the complete active space (CAS) and restricted active space (RAS) self-consistent field frameworks, followed by second-order perturbation theory (CASPT2 and RASPT2). These calculations are evaluated by comparison with the results of doubly electron-attached (DEA) equation-of-motion (EOM) coupled-cluster (CC) calculations with up to 4-particle-2-hole (4p-2h) excitations. We find active spaces that can accurately reproduce the DEA-EOMCC(4p-2h) data while being small enough to be applicable to larger organic diradicals.

Superconductivity switch from spin-singlet to -triplet pairing in a topological superconducting junction

Science.gov (United States)

Tao, Ze; Chen, F. J.; Zhou, L. Y.; Li, Bin; Tao, Y. C.; Wang, J.

2018-06-01

The interedge coupling is the cardinal characteristic of the narrow quantum spin Hall (QSH) insulator, and thus could bring about exotic transport phenomena. Herein, we present a theoretical investigation of the spin-resolved Andreev reflection (AR) in a QSH insulator strip touching on two neighbouring ferromagnetic insulators and one s-wave superconductor. It is demonstrated that, due to the interplay of the interedge coupling and ferromagnetic configuration, there could be not only usual local ARs leading to the spin-singlet pairing with the incident electron and Andreev-reflected hole from different spin subbands, but also novel local ARs giving rise to the spin-triplet pairing from the same spin subband. However, only the latter exists in the absence of the interedge coupling, and therefore the two pairings in turn testify the helical spin texture of the edge states. By proper tuning of the band structures of the ferromagnetic layers, under the resonance bias voltage, the usual and novel local ARs of can be all exhibited, resulting in fully spin-polarized pure spin-singlet superconductivity and pure spin-triplet superconductivity, respectively, which suggests a superconductivity switch from spin-singlet to -triplet pairing by electrical control. The results can be experimentally confirmed by the tunneling conductance and the noise power.

Post-Newtonian evolution of massive black hole triplets in galactic nuclei - II. Survey of the parameter space

Science.gov (United States)

Bonetti, Matteo; Haardt, Francesco; Sesana, Alberto; Barausse, Enrico

2018-04-01

Massive black hole binaries (MBHBs) are expected to form at the centre of merging galaxies during the hierarchical assembly of the cosmic structure, and are expected to be the loudest sources of gravitational waves (GWs) in the low frequency domain. However, because of the dearth of energy exchanges with background stars and gas, many of these MBHBs may stall at separations too large for GW emission to drive them to coalescence in less than a Hubble time. Triple MBH systems are then bound to form after a further galaxy merger, triggering a complex and rich dynamics that can eventually lead to MBH coalescence. Here we report on the results of a large set of numerical simulations, where MBH triplets are set in spherical stellar potentials and MBH dynamics is followed through 2.5 post-Newtonian order in the equations of motion. From our full suite of simulated systems we find that a fraction ≃ 20 - 30 % of the MBH binaries that would otherwise stall are led to coalesce within a Hubble time. The corresponding coalescence timescale peaks around 300 Myr, while the eccentricity close to the plunge, albeit small, is non-negligible (≲ 0.1). We construct and discuss marginalised probability distributions of the main parameters involved and, in a companion paper of the series, we will use the results presented here to forecast the contribution of MBH triplets to the GW signal in the nHz regime probed by Pulsar Timing Array experiments.

Energy of ground state of laminar electron-hole liquid

International Nuclear Information System (INIS)

Andryushin, E.A.

1976-01-01

The problem of a possible existence of metal electron-hole liquid in semiconductors is considered. The calculation has been carried out for the following model: two parallel planes are separated with the distance on one of the planes electrons moving, on the other holes doing. Transitions between the planes are forbidden. The density of particles for both planes is the same. The energy of the ground state and correlation functions for such electron-and hole system are calculated. It is shown that the state of a metal liquid is more advantageous against the exciton gas. For the mass ratio of electrons and holes, msub(e)/msub(h) → 0 a smooth rearrangement of the system into a state with ordered heavy particles is observed

Thermoelectric performance of electron and hole doped PtSb2

KAUST Repository

Saeed, Yasir; Singh, Nirpendra; Parker, D.; Schwingenschlö gl, Udo

2013-01-01

We investigate the thermoelectric properties of electron and hole doped PtSb2. Our results show that for doping of 0.04 holes per unit cell ( 1.5×1020 cm−3 ) PtSb2 shows a high Seebeck coefficient at room temperature, which can also be achieved at other temperatures by controlling the carrier concentration (both electron and hole). The electrical conductivity becomes temperature independent when the doping exceeds some 0.2 electrons/holes per unit cell. The figure of merit at 800 K in electron and hole doped PtSb2 is comparatively low at 0.13 and 0.21, respectively, but may increase significantly with As alloying due to the likely opening of a band gap and reduction of the lattice thermal conductivity.

Thermoelectric performance of electron and hole doped PtSb2

KAUST Repository

Saeed, Yasir

2013-04-30

We investigate the thermoelectric properties of electron and hole doped PtSb2. Our results show that for doping of 0.04 holes per unit cell ( 1.5×1020 cm−3 ) PtSb2 shows a high Seebeck coefficient at room temperature, which can also be achieved at other temperatures by controlling the carrier concentration (both electron and hole). The electrical conductivity becomes temperature independent when the doping exceeds some 0.2 electrons/holes per unit cell. The figure of merit at 800 K in electron and hole doped PtSb2 is comparatively low at 0.13 and 0.21, respectively, but may increase significantly with As alloying due to the likely opening of a band gap and reduction of the lattice thermal conductivity.

Analysis and simulation of BGK electron holes

Directory of Open Access Journals (Sweden)

L. Muschietti

1999-01-01

Full Text Available Recent observations from satellites crossing regions of magnetic-field-aligned electron streams reveal solitary potential structures that move at speeds much greater than the ion acoustic/thermal velocity. The structures appear as positive potential pulses rapidly drifting along the magnetic field, and are electrostatic in their rest frame. We interpret them as BGK electron holes supported by a drifting population of trapped electrons. Using Laplace transforms, we analyse the behavior of one phase-space electron hole. The resulting potential shapes and electron distribution functions are self-consistent and compatible with the field and particle data associated with the observed pulses. In particular, the spatial width increases with increasing amplitude. The stability of the analytic solution is tested by means of a two-dimensional particle-in-cell simulation code with open boundaries. We consider a strongly magnetized parameter regime in which the bounce frequency of the trapped electrons is much less than their gyrofrequency. Our investigation includes the influence of the ions, which in the frame of the hole appear as an incident beam, and impinge on the BGK potential with considerable energy. The nonlinear structure is remarkably resilient

Electrically induced spontaneous emission in open electronic system

Science.gov (United States)

Wang, Rulin; Zhang, Yu; Yam, Chiyung; Computation Algorithms Division (CSRC) Team; Theoretical; Computational Chemistry (HKU) Collaboration

A quantum mechanical approach is formulated for simulation of electroluminescence process in open electronic system. Based on nonequilibrium Green's function quantum transport equations and combining with photon-electron interaction, this method is used to describe electrically induced spontaneous emission caused by electron-hole recombination. The accuracy and reliability of simulation depends critically on correct description of the electronic band structure and the electron occupancy in the system. In this work, instead of considering electron-hole recombination in discrete states in the previous work, we take continuous states into account to simulate the spontaneous emission in open electronic system, and discover that the polarization of emitted photon is closely related to its propagation direction. Numerical studies have been performed to silicon nanowire-based P-N junction with different bias voltage.

Electron and hole transport in ambipolar, thin film pentacene transistors

International Nuclear Information System (INIS)

Saudari, Sangameshwar R.; Kagan, Cherie R.

2015-01-01

Solution-processed, ambipolar, thin-film pentacene field-effect transistors were employed to study both electron and hole transport simultaneously in a single, organic solid-state device. Electron and hole mobilities were extracted from the respective unipolar saturation regimes and show thermally activated behavior and gate voltage dependence. We fit the gate voltage dependent saturation mobility to a power law to extract the characteristic Meyer-Neldel (MN) energy, a measure of the width of the exponential distribution of localized states extending into the energy gap of the organic semiconductor. The MN energy is ∼78 and ∼28 meV for electrons and holes, respectively, which reflects a greater density of localized tail states for electrons than holes. This is consistent with the lower measured electron than hole mobility. For holes, the well-behaved linear regime allows for four-point probe measurement of the contact resistance independent mobility and separate characterization of the width of the localized density of states, yielding a consistent MN energy of 28 meV

Electron and hole transport in ambipolar, thin film pentacene transistors

Energy Technology Data Exchange (ETDEWEB)

Saudari, Sangameshwar R. [Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States); Kagan, Cherie R. [Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States); Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States); Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States)

2015-01-21

Solution-processed, ambipolar, thin-film pentacene field-effect transistors were employed to study both electron and hole transport simultaneously in a single, organic solid-state device. Electron and hole mobilities were extracted from the respective unipolar saturation regimes and show thermally activated behavior and gate voltage dependence. We fit the gate voltage dependent saturation mobility to a power law to extract the characteristic Meyer-Neldel (MN) energy, a measure of the width of the exponential distribution of localized states extending into the energy gap of the organic semiconductor. The MN energy is ∼78 and ∼28 meV for electrons and holes, respectively, which reflects a greater density of localized tail states for electrons than holes. This is consistent with the lower measured electron than hole mobility. For holes, the well-behaved linear regime allows for four-point probe measurement of the contact resistance independent mobility and separate characterization of the width of the localized density of states, yielding a consistent MN energy of 28 meV.

Magnetic holes in the dipolarized magnetotail: ion and electron anisotropies

Science.gov (United States)

Shustov, P.; Artemyev, A.; Zhang, X. J.; Yushkov, E.; Petrukovich, A. A.

2017-12-01

We conduct statistics on magnetic holes observed by THEMIS spacecraft in the near-Earth magnetotail. Groups of holes are detected after dipolarizations in the quiet, equatorial plasma sheet. Magnetic holes are characterized by significant magnetic field depressions (up to 50%) and strong electron currents ( 10-50 nA/m2), with spatial scales much smaller than the ion gyroradius. These magnetic holes are populated by hot (>10 keV), transversely anisotropic electrons supporting the pressure balance. We present statistical properties of these sub-ion scale magnetic holes and discuss possible mechanisms on the hole formation.

Electron holes observed in the Moon Plasma Wake

Science.gov (United States)

Hutchinson, I. H.; Malaspina, D.; Zhou, C.

2017-10-01

Electrostatic instabilities are predicted in the magnetized wake of plasma flowing past a non-magnetic absorbing object such as a probe or the moon. Analysis of the data from the Artemis satellites, now orbiting the moon at distances ten moon radii and less, shows very clear evidence of fast-moving isolated solitary potential structures causing bipolar electric field excursions as they pass the satellite's probes. These structures have all the hallmarks of electron holes: BGK solitons typically a few Debye-lengths in size, self-sustaining by a deficit of phase-space density on trapped orbits. Electron holes are now observed to be widespread in space plasmas. They have been observed in PIC simulations of the moon wake to be the non-linear consequence of the predicted electron instabilities. Simulations document hole prevalence, speed, length, and depth; and theory can explain many of these features from kinetic analysis. The solar wind wake is certainly the cause of the overwhelming majority of the holes observed by Artemis, because we observe almost all holes to be in or very near to the wake. We compare theory and simulation of the hole generation, lifetime, and transport mechanisms with observations. Work partially supported by NASA Grant NNX16AG82G.

Two types of fundamental luminescence of ionization-passive electrons and holes in optical dielectrics—Intraband-electron and interband-hole luminescence (theoretical calculation and comparison with experiment)

Science.gov (United States)

Vaisburd, D. I.; Kharitonova, S. V.

1997-11-01

A short high-power pulse of ionizing radiation creates a high concentration of nonequilibrium electrons and holes in a dielectric. They quickly lose their energy, generating a multiplicity of secondary quasiparticles: electron—hole pairs, excitons, plasmons, phonons of all types, and others. When the kinetic energy of an electron becomes less that some value EΔ≈(1.3-2)Eg it loses the ability to perform collisional ionization and electron excitations of the dielectric medium. Such an electron is said to be ionization-passive. It relaxes to the bottom of the lower conduction band by emitting phonons. Similarly a hole becomes ionization-passive when it “floats up” above some level EH and loses the ability for Auger ionization of the dielectric medium. It continues to float upward to the ceiling of the upper valance band only by emitting phonons. The concentrations of ionization-passive electrons and holes are larger by several orders of magnitude than those of the active electrons and holes and consequently make of a far larger contribution to many kinetic processes such as luminescence. Intraband and interband quantum transitions make the greatest contribution to the fundamental (independent of impurities and intrinsic defects) electromagnetic radiation of ionization-passive electrons and holes. Consequently the brightest types of purely fundamental luminescence of strongly nonequilibrium electrons and holes are intraband and interband luminescence. These forms of luminescence, discovered relatively recently, carry valuable information on the high-energy states of the electrons in the conduction band and of the holes in the valence band of a dielectric. Experimental investigations of these types of luminescence were made, mainly on alkali halide crystals which were excited by nanoseconal pulses of high-current-density electrons and by two-photon absorption of the ultraviolet harmonics of pulsed laser radiation beams of nanosecond and picosecond duration. The

Laboratory Observation of Electron Phase-Space Holes during Magnetic Reconnection

International Nuclear Information System (INIS)

Fox, W.; Porkolab, M.; Egedal, J.; Katz, N.; Le, A.

2008-01-01

We report the observation of large-amplitude, nonlinear electrostatic structures, identified as electron phase-space holes, during magnetic reconnection experiments on the Versatile Toroidal Facility at MIT. The holes are positive electric potential spikes, observed on high-bandwidth (∼2 GHz) Langmuir probes. Investigations with multiple probes establish that the holes travel at or above the electron thermal speed and have a three-dimensional, approximately spherical shape, with a scale size ∼2 mm. This corresponds to a few electron gyroradii, or many tens of Debye lengths, which is large compared to holes considered in simulations and observed by satellites, whose length scale is typically only a few Debye lengths. Finally, a statistical study over many discharges confirms that the holes appear in conjunction with the large inductive electric fields and the creation of energetic electrons associated with the magnetic energy release

Hole-capture properties of the electron-irradiation-induced deep-level H5 in p-type InP: A charge-controlled bistable model

International Nuclear Information System (INIS)

Bretagnon, T.; Bastide, G.; Rouzeyre, M.

1989-01-01

The electron-induced irradiated defect H 5 in Zn-doped p-type InP is an unusual hole trap, since its temperature-independent weak-hole capture cross section, σ c ∼10 -21 cm 2 , is 6 orders of magnitude lower than the value obtained from thermal-emission rates. We present a charge-controlled bistable configuration-coordinate diagram that explains this large difference and accounts for the optical-absorption properties. In addition, a microscopic D In n+ -Zn - defect, made by pairing under electrostatic attraction of the ionized acceptor Zn - and of a positively charged primitive defect D In n+ of the In sublattice, is tentatively proposed as a plausible complex at the origin of H 5

Coherent electron - hole state and femtosecond cooperative emission in bulk GaAs

International Nuclear Information System (INIS)

Vasil'ev, Petr P; Kan, H; Ohta, H; Hiruma, T

2002-01-01

The conditions for obtaining a collective coherent electron - hole state in semiconductors are discussed. The results of the experimental study of the regime of cooperative recombination of high-density electrons and holes (more than 3 x 10 18 cm -3 ) in bulk GaAs at room temperature are presented. It is shown that the collective pairing of electrons and holes and their condensation cause the formation of a short-living coherent electron - hole BCS-like state, which exhibits radiative recombination in the form of high-power femtosecond optical pulses. It is experimentally demonstrated that almost all of the electrons and holes available are condensed at the very bottoms of the bands and are at the cooperative state. The average lifetime of this state is measured to be of about 300 fs. The dependences of the order parameter (the energy gap of the spectrum of electrons and holes) and the Fermi energy of the coherent BCS state on the electron - hole concentration are obtained. (special issue devoted to the 80th anniversary of academician n g basov's birth)

Electron irradiation-induced defects in {beta}-SiC

Energy Technology Data Exchange (ETDEWEB)

Oshima, Ryuichiro [Osaka Prefectural Univ., Sakai (Japan). Reseach Inst. for Advanced Science and Technology

1996-04-01

To add information of point defects in cubic crystal SiC, polycrystal {beta}-SiC on the market was used as sample and irradiated by neutron and electron. In situ observation of neutron and electron irradiation-induced defects in {beta}-SiC were carried out by ultra high-voltage electronic microscope (UHVEM) and ordinary electronic microscope. The obtained results show that the electron irradiation-induced secondary defects are micro defects less than 20 nm at about 1273K, the density of defects is from 2x10{sup 17} to 1x10{sup 18}/cc, the secondary defects may be hole type at high temperature and the preexistant defects control nuclear formation of irradiation-induced defects, effective sink. (S.Y.)

Interaction between Electron Holes in a Strongly Magnetized Plasma

DEFF Research Database (Denmark)

Lynov, Jens-Peter; Michelsen, Poul; Pécseli, Hans

1980-01-01

The interaction between electron holes in a strongly magnetized, plasma-filled waveguide is investigated by means of computer simulation. Two holes may or may not coalesce, depending on their amplitudes and velocities. The interaction between holes and Trivelpiece-Gould solitons is demonstrated...

Triplet--Triplet Absorption Spectra of Organic Molecules in Condensed Phases

International Nuclear Information System (INIS)

Carmichael, I.; Hug, G.L.

1986-01-01

We present a compilation of spectral parameters associated with triplet--triplet absorption of organic molecules in condensed media. The wavelengths of maximum absorbance and the corresponding extinction coefficients, where known, have been critically evaluated. Other data, for example, lifetimes, energies and energy transfer rates, relevant to the triplet states of these molecules are included by way of comments but have not been subjected to a similar scrutiny. Work in the gas phase has been omitted, as have theoretical studies. We provide an introduction to triplet state processes in solution and solids, developing the conceptual background and offering an historical perspective on the detection and measurement of triplet state absorption. Techniques employed to populate the triplet state are reviewed and the various approaches to the estimation of the extinction coefficient of triplet--triplet absorption are critically discussed. A statistical analysis of the available data is presented and recommendations for a hierarchical choice of extinction coefficients are made. Data collection is expected to be complete through the end of 1984. Compound name, molecular formula and author indexes are appended

Electron Dynamics in a Subproton-Gyroscale Magnetic Hole

Science.gov (United States)

Gershman, Daniel J.; Dorelli, John C.; Vinas, Adolfo F.; Avanov, Levon A.; Gliese, Ulrik B.; Barrie, Alexander C.; Coffey, Victoria; Chandler, Michael; Dickson, Charles; MacDonald, Elizabeth A.;

Studying electron-PAG interactions using electron-induced fluorescence

Science.gov (United States)

Narasimhan, Amrit; Grzeskowiak, Steven; Ostrander, Jonathan; Schad, Jonathon; Rebeyev, Eliran; Neisser, Mark; Ocola, Leonidas E.; Denbeaux, Gregory; Brainard, Robert L.

2016-03-01

In extreme ultraviolet (EUV) lithography, 92 eV photons are used to expose photoresists. Typical EUV resists are organic-based and chemically amplified using photoacid generators (PAGs). Upon exposure, PAGs produce acids which catalyze reactions that result in changes in solubility. In EUV lithography, photo- and secondary electrons (energies of 10- 80 eV) play a large role in PAG acid-production. Several mechanisms for electron-PAG interactions (e.g. electron trapping, and hole-initiated chemistry) have been proposed. The aim of this study is to explore another mechanism - internal excitation - in which a bound PAG electron can be excited by receiving energy from another energetic electron, causing a reaction that produces acid. This paper explores the mechanism of internal excitation through the analogous process of electron-induced fluorescence, in which an electron loses energy by transferring that energy to a molecule and that molecule emits a photon rather than decomposing. We will show and quantify electron-induced fluorescence of several fluorophores in polymer films to mimic resist materials, and use this information to refine our proposed mechanism. Relationships between the molecular structure of fluorophores and fluorescent quantum yield may aid in the development of novel PAGs for EUV lithography.

Assessment of pseudo-bilayer structures in the heterogate germanium electron-hole bilayer tunnel field-effect transistor

International Nuclear Information System (INIS)

Padilla, J. L.; Alper, C.; Ionescu, A. M.; Medina-Bailón, C.; Gámiz, F.

2015-01-01

We investigate the effect of pseudo-bilayer configurations at low operating voltages (≤0.5 V) in the heterogate germanium electron-hole bilayer tunnel field-effect transistor (HG-EHBTFET) compared to the traditional bilayer structures of EHBTFETs arising from semiclassical simulations where the inversion layers for electrons and holes featured very symmetric profiles with similar concentration levels at the ON-state. Pseudo-bilayer layouts are attained by inducing a certain asymmetry between the top and the bottom gates so that even though the hole inversion layer is formed at the bottom of the channel, the top gate voltage remains below the required value to trigger the formation of the inversion layer for electrons. Resulting benefits from this setup are improved electrostatic control on the channel, enhanced gate-to-gate efficiency, and higher I ON levels. Furthermore, pseudo-bilayer configurations alleviate the difficulties derived from confining very high opposite carrier concentrations in very thin structures

Assessment of pseudo-bilayer structures in the heterogate germanium electron-hole bilayer tunnel field-effect transistor

Energy Technology Data Exchange (ETDEWEB)

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

2015-06-29

We investigate the effect of pseudo-bilayer configurations at low operating voltages (≤0.5 V) in the heterogate germanium electron-hole bilayer tunnel field-effect transistor (HG-EHBTFET) compared to the traditional bilayer structures of EHBTFETs arising from semiclassical simulations where the inversion layers for electrons and holes featured very symmetric profiles with similar concentration levels at the ON-state. Pseudo-bilayer layouts are attained by inducing a certain asymmetry between the top and the bottom gates so that even though the hole inversion layer is formed at the bottom of the channel, the top gate voltage remains below the required value to trigger the formation of the inversion layer for electrons. Resulting benefits from this setup are improved electrostatic control on the channel, enhanced gate-to-gate efficiency, and higher I{sub ON} levels. Furthermore, pseudo-bilayer configurations alleviate the difficulties derived from confining very high opposite carrier concentrations in very thin structures.

Observations of electron vortex magnetic holes and related wave-particle interactions in the turbulent magnetosheath

Science.gov (United States)

Huang, S.; Sahraoui, F.; Yuan, Z.; He, J.; Zhao, J.; Du, J.; Le Contel, O.; Wang, X.; Deng, X.; Fu, H.; Zhou, M.; Shi, Q.; Breuillard, H.; Pang, Y.; Yu, X.; Wang, D.

2017-12-01

Magnetic hole is characterized by a magnetic depression, a density peak, a total electron temperature increase (with a parallel temperature decrease but a perpendicular temperature increase), and strong currents carried by the electrons. The current has a dip in the core region of the magnetic hole and a peak in the outer region of the magnetic hole. There is an enhancement in the perpendicular electron fluxes at 90° pitch angles inside the magnetic hole, implying that the electrons are trapped within it. The variations of the electron velocity components Vem and Ven suggest that an electron vortex is formed by trapping electrons inside the magnetic hole in the circular cross-section. These observations demonstrate the existence of a new type of coherent structures behaving as an electron vortex magnetic hole in turbulent space plasmas as predicted by recent kinetic simulations. We perform a statistically study using high time solution data from the MMS mission. The magnetic holes with short duration (i.e., < 0.5 s) have their cross section smaller than the ion gyro-radius. Superposed epoch analysis of all events reveals that an increase in the electron density and total temperature, significantly increase (resp. decrease) the electron perpendicular (resp. parallel) temperature, and an electron vortex inside the holes. Electron fluxes at 90° pitch angles with selective energies increase in the KSMHs, are trapped inside KSMHs and form the electron vortex due to their collective motion. All these features are consistent with the electron vortex magnetic holes obtained in 2D and 3D particle-in-cell simulations, indicating that the observed the magnetic holes seem to be best explained as electron vortex magnetic holes. It is furthermore shown that the magnetic holes are likely to heat and accelerate the electrons. We also investigate the coupling between whistler waves and electron vortex magnetic holes. These whistler waves can be locally generated inside electron

Spin-triplet supercurrent in Co-based Josephson junctions

International Nuclear Information System (INIS)

Khasawneh, Mazin A; Khaire, Trupti S; Klose, Carolin; Pratt, William P Jr; Birge, Norman O

2011-01-01

In the past year several groups have reported experimental evidence for spin-triplet supercurrents in Josephson junctions containing strong ferromagnetic materials. In this paper we present several new experimental results that follow up on our previous work. We study Josephson junctions of the form S/X/N/SAF/N/X/S, where S is a superconductor (Nb), N is a normal metal, SAF is a synthetic antiferromagnet of the form Co/Ru/Co and X is an ferromagnetic layer necessary to induce spin-triplet correlations in the structure. Our work is distinguished by the fact that the generation of spin-triplet correlations is tuned by the type and thickness of the X layers. The most important new result reported here is the discovery that a conventional, strong ferromagnetic material, Ni, performs well as the X layer, if it is sufficiently thin. This discovery rules out our earlier hypothesis that out-of-plane magnetocrystalline anisotropy is an important attribute of the X layers. These results suggest that the spin-triplet correlations are most likely induced by noncollinear magnetization between the X layers and adjacent Co layers.

Theory of triplet-triplet annihilation in optically detected magnetic resonance

Science.gov (United States)

Keevers, T. L.; McCamey, D. R.

2016-01-01

Triplet-triplet annihilation allows two low-energy photons to be upconverted into a single high-energy photon. By essentially engineering the solar spectrum, this allows solar cells to be made more efficient and even exceed the Shockley-Quiesser limit. Unfortunately, optimizing the reaction pathway is difficult, especially with limited access to the microscopic time scales and states involved in the process. Optical measurements can provide detailed information: triplet-triplet annihilation is intrinsically spin dependent and exhibits substantial magnetoluminescence in the presence of a static magnetic field. Pulsed optically detected magnetic resonance is especially suitable, since it combines high spin sensitivity with coherent manipulation. In this paper, we develop a time-domain theory of triplet-triplet annihilation for complexes with arbitrary spin-spin coupling. We identify unique "Rabi fingerprints" for each coupling regime and show that this can be used to characterize the microscopic Hamiltonian.

Triplet formation in the ion recombination in irradiated liquids

International Nuclear Information System (INIS)

Bartczak, W.M.; Tachiya, M.; Hummel, A.

1990-01-01

The formation of singlet and triplet excited stages in the ion recombination in groups of oppositely charged ions (or positive ions and electrons) in nonpolar liquids, as occurs in the tracks of high energy electrons, is considered. Theoretical studies on triplet formation in groups of ion pairs have thus far concentrated on the case where recombination of the negative ions with any of the positive ions in the group is equally probable (random recombination). In this paper the probability for geminate recombination (electron and parent positive ion) vs cross-recombination (an electron with a positive ion other than its parent ion) in multiple ion pair groups is calculated by computer simulation and the effect of the initial spatial configuration of the charged species is investigated. It is also shown explicitly that the probability for singlet formation as a result of cross recombination is equal to 1/4, when spin relaxation by magnetic interaction with the medium and by exchange interaction can be neglected. The effect of the preferential recombination on the singlet formation probability is illustrated and recent experimental results on singlet to triplet ratios are discussed. (author)

Theory of magnetostriction of electron-hole drops in Ge

International Nuclear Information System (INIS)

Markiewicz, R.S.

1978-01-01

A large mass of electron-hole liquid (γ drop) formed in a strain-induced potential well in Ge is known to distort its shape significantly in a magnetic field B > or approx. = 1 kG. It is shown in this paper that the shape change can be understood in detail as due to a ''recombination current'' of electron-hole pairs needed to replace those pairs which recombine in the drop volume. The Lorentz force deflects this current and produces a macroscopic dipole current loop inside the drop. The drop then changes shape to minimize its total energy, including magnetic, strain, and surface energies. While the drop usually flattens along the field direction, both para- and diamagnetic effects (elongated drops) are found to be possible, depending on excitation conditions, in accord with experiment. Similar effects are predicted to occur in small drops in unstrained Ge. This paper presents a magnetohydrodynamic theory of the magnetostriction which takes into account density variations which occur in the strain well and in high magnetic fields. A simpler theory is given for the special case in which the drop may be considered incompressible (small drops and moderate fields). Effects of carrier mass anisotropy and fluid viscosity are taken into consideration

Electron holes in phase space: What they are and why they matter

Science.gov (United States)

Hutchinson, I. H.

2017-05-01

This is a tutorial and selective review explaining the fundamental concepts and some currently open questions concerning the plasma phenomenon of the electron hole. The widespread occurrence of electron holes in numerical simulations, space-craft observations, and laboratory experiments is illustrated. The elementary underlying theory is developed of a one-dimensional electron hole as a localized potential maximum, self-consistently sustained by a deficit of trapped electron phase-space density. The spatial extent of a hole is typically a few Debye lengths; what determines the minimum and maximum possible lengths is explained, addressing the key aspects of the as yet unsettled dispute between the integral and differential approaches to hole structure. In multiple dimensions, holes tend to form less readily; they generally require a magnetic field and distribution-function anisotropy. The mechanisms by which they break up are explained, noting that this transverse instability is not fully understood. Examples are given of plasma circumstances where holes play an important role, and of recent progress on understanding their holistic kinematics and self-acceleration.

Magnetospheric Multiscale Observations of Electron Vortex Magnetic Hole in the Turbulent Magnetosheath Plasma

Energy Technology Data Exchange (ETDEWEB)

Huang, S. Y.; Yuan, Z. G.; Wang, D. D.; Yu, X. D. [School of Electronic Information, Wuhan University, Wuhan (China); Sahraoui, F.; Contel, O. Le [Laboratoire de Physique des Plasmas, CNRS-Ecole Polytechnique-UPMC, Palaiseau (France); He, J. S. [School of Earth and Space Sciences, Peking University, Beijing (China); Zhao, J. S. [Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing (China); Deng, X. H.; Pang, Y.; Li, H. M. [Institute of Space Science and Technology, Nanchang University, Nanchang (China); Zhou, M. [Department of Physics and Astronomy, University of California, Los Angeles, CA (United States); Fu, H. S.; Yang, J. [School of Space and Environment, Beihang University, Beijing (China); Shi, Q. Q. [Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai (China); Lavraud, B. [Institut de Recherche and Astrophysique et Planétologie, Université de Toulouse (UPS), Toulouse (France); Pollock, C. J.; Giles, B. L. [NASA, Goddard Space Flight Center, Greenbelt, MD (United States); Torbert, R. B. [University of New Hampshire, Durham, NH (United States); Russell, C. T., E-mail: shiyonghuang@whu.edu.cn [Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA (United States); and others

2017-02-20

We report on the observations of an electron vortex magnetic hole corresponding to a new type of coherent structure in the turbulent magnetosheath plasma using the Magnetospheric Multiscale mission data. The magnetic hole is characterized by a magnetic depression, a density peak, a total electron temperature increase (with a parallel temperature decrease but a perpendicular temperature increase), and strong currents carried by the electrons. The current has a dip in the core region and a peak in the outer region of the magnetic hole. The estimated size of the magnetic hole is about 0.23 ρ {sub i} (∼30 ρ {sub e}) in the quasi-circular cross-section perpendicular to its axis, where ρ {sub i} and ρ {sub e} are respectively the proton and electron gyroradius. There are no clear enhancements seen in high-energy electron fluxes. However, there is an enhancement in the perpendicular electron fluxes at 90° pitch angle inside the magnetic hole, implying that the electrons are trapped within it. The variations of the electron velocity components V {sub em} and V {sub en} suggest that an electron vortex is formed by trapping electrons inside the magnetic hole in the cross-section in the M – N plane. These observations demonstrate the existence of a new type of coherent structures behaving as an electron vortex magnetic hole in turbulent space plasmas as predicted by recent kinetic simulations.

Probing odd-triplet contributions to the long-ranged proximity effect by scanning tunneling spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Diesch, Simon; Machon, Peter; Belzig, Wolfgang; Scheer, Elke [Universitaet Konstanz, Konstanz (Germany); Suergers, Christoph; Beckmann, Detlef [Karlsruhe Institute of Technology, Karlsruhe (Germany)

2015-07-01

In conventional superconductors, electrons are bound in singlet Cooper pairs, i.e. with opposite spin. More recently, experiments on superconductor-ferromagnet-systems have shown Cooper pairs tunneling through ferromagnetic layers, indicating Cooper pairs of equal spin, thus corresponding to a long-range triplet proximity effect. Most experimental evidence for triplet superconductivity comes from observations of the thickness dependence of the Josephson current through a ferromagnetic barrier, but there is an increasing interest in obtaining direct spectroscopic evidence. This project aims at analyzing the electronic density of states of a thin diffusive normal metal layer (Ag) coupled to a superconductor (Al) across a ferromagnetic insulator (EuS) using a scanning tunneling microscope in spectroscopy mode at 280 mK. For this purpose, we fabricated EuS films of different thicknesses and acquired spectroscopic data at different magnetic fields. We observe significant broadening of the superconductive energy gap and a variety of sub-gap structures including zero-bias conductance peaks induced by the presence of the ferromagnet.

Migration of O vacancies in α-quartz: The effect of excitons and electron holes

International Nuclear Information System (INIS)

Song, Jakyoung; Corrales, L. Rene; Kresse, Georg; Jonsson, Hannes

2001-01-01

We have used density-functional theory and the nudged elastic-band method to calculate migration pathways and estimated the activation energy for the diffusion of oxygen vacancies in α-quartz. While the energy barrier for the diffusion of a neutral vacancy is very high, 4.1 eV, the binding of a triplet-state exciton to the vacancy lowers the barrier to 1.7 eV and the attachment of a hole lowers the barrier to 1.9 eV, making the vacancy mobile at commonly used annealing temperatures

Electron, hole and exciton self-trapping in germanium doped silica glass from DFT calculations with self-interaction correction

International Nuclear Information System (INIS)

Du Jincheng; Rene Corrales, L.; Tsemekhman, Kiril; Bylaska, Eric J.

2007-01-01

Density functional theory (DFT) calculations were employed to understand the refractive index change in germanium doped silica glasses for the trapped states of electronic excitations induced by UV irradiation. Local structure relaxation and excess electron density distribution were calculated upon self-trapping of an excess electron, hole, and exciton in germanium doped silica glass. The results show that both the trapped exciton and excess electron are highly localized on germanium ion and, to some extent, on its oxygen neighbors. Exciton self-trapping is found to lead to the formation of a Ge E' center and a non-bridging hole center. Electron trapping changes the GeO 4 tetrahedron structure into trigonal bi-pyramid with the majority of the excess electron density located along the equatorial line. The self-trapped hole is localized on bridging oxygen ions that are not coordinated to germanium atoms that lead to elongation of the Si-O bonds and change of the Si-O-Si bond angles. We carried out a comparative study of standard DFT versus DFT with a hybrid PBE0 exchange and correlation functional. The results show that the two methods give qualitatively similar relaxed structure and charge distribution for electron and exciton trapping in germanium doped silica glass; however, only the PBE0 functional produces the self-trapped hole

Fine structure of excitons and electron-hole exchange energy in polymorphic CsPbBr3 single nanocrystals.

Science.gov (United States)

Ramade, Julien; Andriambariarijaona, Léon Marcel; Steinmetz, Violette; Goubet, Nicolas; Legrand, Laurent; Barisien, Thierry; Bernardot, Frédérick; Testelin, Christophe; Lhuillier, Emmanuel; Bramati, Alberto; Chamarro, Maria

2018-04-05

All inorganic CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) belong to the novel class of confined metal-halide perovskites which are currently arousing enthusiasm and stimulating huge activity across several fields of optoelectronics due to outstanding properties. A deep knowledge of the band-edge excitonic properties of these materials is thus crucial to further optimize their performances. Here, high-resolution photoluminescence (PL) spectroscopy of single bromide-based NCs reveals the exciton fine structure in the form of sharp peaks that are linearly polarized and grouped in doublets or triplets, which directly mirror the adopted crystalline structure, tetragonal (D4h symmetry) or orthorhombic (D2h symmetry). Intelligible equations are found that show how the fundamental parameters (spin-orbit coupling, ΔSO, crystal field term, T, and electron-hole exchange energy, J) rule the energy spacings in doublets and triplets. From experimental data, fine estimations of each parameter are obtained. The analysis of the absorption spectra of an ensemble of NCs with a "quasi-bulk" behavior leads to ΔSO = 1.20 ± 0.06 eV and T = -0.34 ± 0.05 eV in CsPbBr3. The study of individual luminescence responses of NCs having sizes comparable to the exciton Bohr diameter, 7 nm, allows us to estimate the value of J to be around ≈3 meV in both tetragonal and orthorhombic phases. This value is already enhanced by confinement.

Interlayer electron-hole pair multiplication by hot carriers in atomic layer semiconductor heterostructures

Science.gov (United States)

Barati, Fatemeh; Grossnickle, Max; Su, Shanshan; Lake, Roger; Aji, Vivek; Gabor, Nathaniel

Two-dimensional heterostructures composed of atomically thin transition metal dichalcogenides provide the opportunity to design novel devices for the study of electron-hole pair multiplication. We report on highly efficient multiplication of interlayer electron-hole pairs at the interface of a tungsten diselenide / molybdenum diselenide heterostructure. Electronic transport measurements of the interlayer current-voltage characteristics indicate that layer-indirect electron-hole pairs are generated by hot electron impact excitation. Our findings, which demonstrate an efficient energy relaxation pathway that competes with electron thermalization losses, make 2D semiconductor heterostructures viable for a new class of hot-carrier energy harvesting devices that exploit layer-indirect electron-hole excitations. SHINES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Air Force Office of Scientific Research.

Effects of density imbalance on the BCS-BEC crossover in semiconductor electron-hole bilayers

International Nuclear Information System (INIS)

Pieri, P.; Strinati, G. C.; Neilson, D.

2007-01-01

We study the occurrence of excitonic superfluidity in electron-hole bilayers at zero temperature. We not only identify the crossover in the phase diagram from the BCS limit of overlapping pairs to the BEC limit of nonoverlapping tightly bound pairs but also, by varying the electron and hole densities independently, we can analyze a number of phases that occur mainly in the crossover region. With different electron and hole effective masses, the phase diagram is asymmetric with respect to excess electron or hole densities. We propose, as the criterion for the onset of superfluidity, the jump of the electron and hole chemical potentials when their densities cross

Triplet Transport to and Trapping by Acceptor End Groups on Conjugated Polyfluorene Chains

Energy Technology Data Exchange (ETDEWEB)

Sreearunothai, P.; Miller, J.; Estrada, A.; Asaoka, S.; Kowalczyk, M.; Jang, S.; Cook, A.R.; Preses, J.M.

2011-08-31

Triplet excited states created in polyfluorene (pF) molecules having average lengths up to 170 repeat units were transported to and captured by trap groups at the ends in less {approx}40 ns. Almost all of the triplets attached to the chains reached the trap groups, ruling out the presence of substantial numbers of defects that prevent transport. The transport yields a diffusion coefficient D of at least 3 x 10{sup -4} cm{sup 2} s{sup -1}, which is 30 times typical molecular diffusion and close to a value for triplet transport reported by Keller (J. Am. Chem. Soc.2011, 133, 11289-11298). The triplet states were created in solution by pulse radiolysis; time resolution was limited by the rate of attachment of triplets to the pF chains. Naphthylimide (NI) or anthraquinone (AQ) groups attached to the ends of the chains acted as traps for the triplets, although AQ would not have been expected to serve as a trap on the basis of triplet energies of the separate molecules. The depths of the NI and AQ triplet traps were determined by intermolecular triplet transfer equilibria and temperature dependence. The trap depths are shallow, just a few times thermal energy for both, so a small fraction of the triplets reside in the pF chains in equilibrium with the end-trapped triplets. Trapping by AQ appears to arise from charge transfer interactions between the pF chains and the electron-accepting AQ groups. Absorption bands of the end-trapped triplet states are similar in peak wavelength (760 nm) and shape to the 760 nm bands of triplets in the pF chains but have reduced intensities. When an electron donor, N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), is added to the solution, it reacts with the end-trapped triplets to remove the 760 nm bands and to make the trapping irreversible. New bands created upon reaction with TMPD may be due to charge transfer states.

Effect of Temperature and Pressure on Correlation Energy in a Triplet State of a Two Electron Spherical Quantum Dot

Directory of Open Access Journals (Sweden)

A. Rejo Jeice

2013-09-01

Full Text Available The combined effect of hydrostatic pressure and temperature on correlation energy in a triplet state of two electron spherical quantum dot with square well potential is computed. The result is presented taking GaAs dot as an example. Our result shows the correlation energies are inegative in the triplet state contrast to the singlet state ii it increases with increase in pressure  iiifurther decreases due to the application  of temperature iv it approaches zero as dot size approaches infinity and v it contribute 10% decrement in total confined energy to the narrow dots. All the calculations have been carried out with finite models and the results are compared with existing literature.

Benchmarking triplet-triplet annihilation photon upconversion schemes.

Science.gov (United States)

Gertsen, Anders S; Koerstz, Mads; Mikkelsen, Kurt V

2018-05-07

Photon upconversion facilitated by triplet-triplet annihilation in molecular systems is a promising path toward utilization of sub bandgap photons in photovoltaic devices. Prior to the challenging synthesis of new molecules, quantum chemical computations can aid the design process and provide suggestions for new and optimal systems. Here, we benchmark time-dependent density functional methods by their ability to describe relevant photophysical quantities of a range of different types of sensitizer/annihilator pairs to provide guidelines for future computational studies of potential new pairs. Using meta-GGA, hybrid, and range-separated hybrid functionals, we find that the hybrid functionals B3LYP and PBE0 (incorporating low to medium fractions of exact exchange of 20% and 25%, respectively) describe singlet absorptions the best, while triplet energetics are best described by the meta-GGA functionals M06-L and M11-L (incorporating no exact exchange), respectively. Furthermore, we find that the Tamm-Dancoff approximation of time-dependent density functional theory in general does not improve the description of neither singlet nor triplet energies of sensitizer/annihilator pairs.

Photoswitching of triplet-triplet annihilation upconversion with photo-generated radical from hexaphenylbiimidazole

Energy Technology Data Exchange (ETDEWEB)

Mahmood, Zafar [State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024 (China); Toffoletti, Antonio [Dipartimento di Scienze Chimiche, Università degli Studi di Padova, Via Marzolo, 1, 35131 Padova (Italy); Zhao, Jianzhang, E-mail: zhaojzh@dlut.edu.cn [State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024 (China); Barbon, Antonio, E-mail: antonio.barbon@unipd.it [Dipartimento di Scienze Chimiche, Università degli Studi di Padova, Via Marzolo, 1, 35131 Padova (Italy)

2017-03-15

Photoirradiation generated radical from hexaphenyl-biimidazole (HPBI) was used for reversible switching of triplet-triplet annihilation (TTA) upconversion, based on quenching of the photosensitizer triplet state by radical-triplet pair mechanism. Upon 365 nm irradiation, the TTA upconversion in a system composed by a boron-dipyrromethene (BODIPY) derivative and perylene, was completely switched off due to quenching of triplet state of photosensitizer by photogenerated radical from HPBI. The upconversion was recovered after leaving the samples in darkness, due to regeneration of HPBI Dimer. The photophysical process involved in the photochromism and photoswitching of TTA upconversion were studied with steady-state UV–vis absorption spectroscopy, nanosecond transient absorption spectroscopy and EPR spectroscopy. - Graphical abstract: Radical-switched TTA upconversion was achieved with reversible quenching of the triplet state by photo-generated stable organic radical from photochromic hexaphenylbiimidazole.

Triplet states of carotenoids from photosynthetic bacteria studied by nanosecond ultraviolet and electron pulse irradiation

International Nuclear Information System (INIS)

Bensasson, R.; Land, E.J.; Maudinas, B.

1976-01-01

Absorptions of the triplet excited states of five carotenoids (15,15'-cis phytoene, all-trans phytoene, zeta-carotene, spheroidene and spirillox-anthin), extracted from the photosynthetic bacteria Rhodopseudomonas spheroides and Rhodospirillum rubrum, have been detected in solution using pulse radiolysis and laser flash photolysis. Triplet lifetimes, extinction coefficients, lowest energy levels and quantum efficiencies of formation have been determined. Comparison of the carotenoid triplet energy levels with that of O 2 ('Δsub(g)) suggests that spirilloxanthin, spheroidene and possibly also zeta-carotene, would be expected to protect against photodynamic action caused by O 2 ('Δsub(g)), but not cis or trans phytoene. The S → T intersystem crossing efficiencies of all five polyenes were found to be low, being a few per cent or less. In their protective role these triplet states can only therefore be effectively reached via energy transfer from another triplet, except in the case of O 2 (Δsub(g)). The low crossover efficiencies also mean that light absorbed in such carotenoids in their possible role as accessory pigments would not be wasted in crossing over to the triplet state. (author)

Linked-cluster formulation of electron-hole interaction kernel in real-space representation without using unoccupied states.

Science.gov (United States)

Bayne, Michael G; Scher, Jeremy A; Ellis, Benjamin H; Chakraborty, Arindam

2018-05-21

Electron-hole or quasiparticle representation plays a central role in describing electronic excitations in many-electron systems. For charge-neutral excitation, the electron-hole interaction kernel is the quantity of interest for calculating important excitation properties such as optical gap, optical spectra, electron-hole recombination and electron-hole binding energies. The electron-hole interaction kernel can be formally derived from the density-density correlation function using both Green's function and TDDFT formalism. The accurate determination of the electron-hole interaction kernel remains a significant challenge for precise calculations of optical properties in the GW+BSE formalism. From the TDDFT perspective, the electron-hole interaction kernel has been viewed as a path to systematic development of frequency-dependent exchange-correlation functionals. Traditional approaches, such as MBPT formalism, use unoccupied states (which are defined with respect to Fermi vacuum) to construct the electron-hole interaction kernel. However, the inclusion of unoccupied states has long been recognized as the leading computational bottleneck that limits the application of this approach for larger finite systems. In this work, an alternative derivation that avoids using unoccupied states to construct the electron-hole interaction kernel is presented. The central idea of this approach is to use explicitly correlated geminal functions for treating electron-electron correlation for both ground and excited state wave functions. Using this ansatz, it is derived using both diagrammatic and algebraic techniques that the electron-hole interaction kernel can be expressed only in terms of linked closed-loop diagrams. It is proved that the cancellation of unlinked diagrams is a consequence of linked-cluster theorem in real-space representation. The electron-hole interaction kernel derived in this work was used to calculate excitation energies in many-electron systems and results

Damages induced in lambda phage DNA by enzyme-generated triplet acetone

International Nuclear Information System (INIS)

Menck, C.F.; Cabral Neto, J.B.; Gomes, R.A.; Faljoni-Alario, A.

1985-01-01

Exposure of lambda phage to triplet acetone, generated during the aerobic oxidation of isobutanal by peroxidase, leads to genome lesions. The majority of these lesions are detected as DNA single-strand breaks only in alkaline conditions, so true breaks were not observed. Also, no sites sensitive to UV-endonuclease from Micrococcus luteus were found in DNA from treated phage. The participation of triplet acetone in the generation of such DNA damage is discussed. (Author) [pt

Heavy Atom Substituents as Molecular Probes for Solvent Effects on the Dynamics of Short-lived Triplet Exciplexes

OpenAIRE

Winter, Gerhard; Steiner, Ulrich

1980-01-01

The influence of heavy atom substituents (Br, I) in the electron donor aniline on the electron transfer reaction with thiopyronine triplet is investigated by flash spectroscopy in solvents of different viscosity and polarity. Triplet quenching constants and radical yields are determined. The results are analysed in terms of decay constants of an intermediate triplet exciplex where the heavy atom substituents significantly enhance the intersystem crossing process leading to singlet ground stat...

Electron vortex magnetic holes: A nonlinear coherent plasma structure

Energy Technology Data Exchange (ETDEWEB)

Haynes, Christopher T., E-mail: c.t.haynes@qmul.ac.uk; Burgess, David; Sundberg, Torbjorn [School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS (United Kingdom); Camporeale, Enrico [Multiscale Dynamics, Centrum Wiskunde and Informatica (CWI), Amsterdam (Netherlands)

2015-01-15

We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.

Negligible Electronic Interaction between Photoexcited Electron-Hole Pairs and Free Electrons in Phosphorus-Boron Co-Doped Silicon Nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Limpens, Rens [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Neale, Nathan R [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Fujii, Minoru [Kobe University; Gregorkiewicz, Tom [University of Amsterdam

2018-03-05

Phosphorus (P) and boron (B) co-doped Si nanocrystals (NCs) have raised interest in the optoelectronic industry due to their electronic tunability, optimal carrier multiplication properties, and straightforward dispersibility in polar solvents. Yet a basic understanding of the interaction of photoexcited electron-hole (e-h) pairs with new physical features that are introduced by the co-doping process (free carriers, defect states, and surface chemistry) is missing. Here, we present the first study of the ultrafast carrier dynamics in SiO2-embedded P-B co-doped Si NC ensembles using induced absorption spectroscopy through a two-step approach. First, the induced absorption data show that the large fraction of the dopants residing on the NC surface slows down carrier relaxation dynamics within the first 20 ps relative to intrinsic (undoped) Si NCs, which we interpret as enhanced surface passivation. On longer time-scales (picosecond to nanosecond regime), we observe a speeding up of the carrier relaxation dynamics and ascribe it to doping-induced trap states. This argument is deduced from the second part of the study, where we investigate multiexciton interactions. From a stochastic modeling approach we show that localized carriers, which are introduced by the P or B dopants, have minor electronic interactions with the photoexcited e-h pairs. This is understood in light of the strong localization of the introduced carriers on their original P- or B-dopant atoms, due to the strong quantum confinement regime in these relatively small NCs (<6 nm).

On measurement of photon polarization by triplet production differential cross sections

International Nuclear Information System (INIS)

Vinokurov, E.A.; Boldyshev, V.F.

1984-01-01

Dependence of triplet production by linearly polarized photon (the recoil electron momenta being p 1 >=p 10 ) upon the electron pair invariant mass Δ (in the ranges of 0.1 mc 10 2 2 ) is studied aiming to analyze possible use of triplet photoproduction to measure polarization of high-energy photon beams. It is shown that the regions 2m 2 and 2m 200 mc 2 are optimum and provide a 17-35% accuracy improvement for the photon beam polarization measurement, the number of events decreasing by a factor of 2.4-4.4

Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation

Science.gov (United States)

Ahmadi, N.; Wilder, F. D.; Usanova, M.; Ergun, R.; Argall, M. R.; Goodrich, K.; Eriksson, S.; Germaschewski, K.; Torbert, R. B.; Lindqvist, P. A.; Le Contel, O.; Khotyaintsev, Y. V.; Strangeway, R. J.; Schwartz, S. J.; Giles, B. L.; Burch, J.

2017-12-01

The Magnetospheric Multiscale (MMS) mission observed electron whistler waves at the center and at the gradients of magnetic holes on the dayside magnetosheath. The magnetic holes are nonlinear mirror structures which are anti-correlated with particle density. We used expanding box Particle-in-cell simulations and produced the mirror instability magnetic holes. We show that the electron whistler waves can be generated at the gradients and the center of magnetic holes in our simulations which is in agreement with MMS observations. At the nonlinear regime of mirror instability, the proton and electron temperature anisotropy are anti-correlated with the magnetic hole. The plasma is unstable to electron whistler waves at the minimum of the magnetic field structures. In the saturation regime of mirror instability, when magnetic holes are dominant, electron temperature anisotropy develops at the edges of the magnetic holes and electrons become isotropic at the magnetic field minimum. We investigate the possible mechanism for enhancing the electron temperature anisotropy and analyze the electron pitch angle distributions and electron distribution functions in our simulations and compare it with MMS observations.

Observation of preformed electron-hole Cooper pairs in highly excited ZnO

NARCIS (Netherlands)

Versteegh, M.A.M.; van Lange, A.J.; Stoof, H.T.C.; Dijkhuis, J.I.

2012-01-01

Electrons and holes in a semiconductor form hydrogen-atom-like bound states, called excitons. At high electron-hole densities the attractive Coulomb force becomes screened and excitons can no longer exist. Bardeen-Cooper-Schrieffer theory predicts that at such high densities co-operative many-body

Synthesis and properties of a spirobifluorene-based hole-transporting material containingtert-butyl group

Directory of Open Access Journals (Sweden)

DING Ning

2016-12-01

Full Text Available A spirobifluorene-based compound SPF-BMO was developed as hole transporters for green phosphorescent organic light-emitting diodes(PhOLEDs.The synthesized material showed sufficient HOMO/LUMO bandgap and triplet energy for green emitting bis［2-(2-pyridinyl-Nphenyl-C］ (acetylacetonato iridium(III ［Ir (ppy2(acac］.The addition of a thin layer of 4,4′,4″-tri(N-carbazolyltriphenylamine (TCTAwith a high triplet energy as an exciton-blockinglayer at hole transporter/emitter interface seems to be unnecessary.SPF-BMO showed high thermal stability due to its spiro-annulated structure.Compared with the standard green PhOLEDs,organic light-emitting diodes with SPF-BMO as the hole-transport material have improved performances such as enhanced device power efficiency andlonger stability.These results clearly demonstrate that SPF-BMO is among the best hole-transporting materials reported for green PhOLEDs and utilizing anappropriate hole transporter to construct a simplified device is a promising method to enhance the power efficiency of PhOLEDs.

Singlet and triplet polaron relaxation in doubly charged self-assembled quantum dots

International Nuclear Information System (INIS)

Grange, T; Zibik, E A; Ferreira, R; Bastard, G; Carpenter, B A; Phillips, P J; Stehr, D; Winnerl, S; Helm, M; Steer, M J; Hopkinson, M; Cockburn, J W; Skolnick, M S; Wilson, L R

2007-01-01

Polaron relaxation in self-assembled InAs/GaAs quantum dot samples containing 2 electrons per dot is studied using far-infrared, time-resolved pump-probe measurements for transitions between the s-like ground and p-like first excited conduction band states. Spin-flip transitions between singlet and triplet states are observed experimentally in the decay of the absorption bleaching, which shows a clear biexponential dependence. The initial fast decay (∼30 ps) is associated with the singlet polaron decay, while the decay component with the longer time constant (∼5 ns) corresponds to the excited state triplet lifetime. The results are explained by considering the intrinsic Dresselhaus spin-orbit interaction, which induces spin-flip transitions by acoustic phonon emission or phonon anharmonicity. We have calculated the spin-flip decay times, and good agreement is obtained between the experiment and the simulation of the pump-probe signal. Our results demonstrate the importance of spin-mixing effects for intraband energy relaxation in InAs/GaAs quantum dots

Electron-hole liquid in semiconductors and low-dimensional structures

Science.gov (United States)

Sibeldin, N. N.

2017-11-01

The condensation of excitons into an electron-hole liquid (EHL) and the main EHL properties in bulk semiconductors and low-dimensional structures are considered. The EHL properties in bulk materials are discussed primarily in qualitative terms based on the experimental results obtained for germanium and silicon. Some of the experiments in which the main EHL thermodynamic parameters (density and binding energy) have been obtained are described and the basic factors that determine these parameters are considered. Topics covered include the effect of external perturbations (uniaxial strain and magnetic field) on EHL stability; phase diagrams for a nonequilibrium exciton-gas-EHL system; information on the size and concentration of electron-hole drops (EHDs) under various experimental conditions; the kinetics of exciton condensation and of recombination in the exciton-gas-EHD system; dynamic EHD properties and the motion of EHDs under the action of external forces; the properties of giant EHDs that form in potential wells produced by applying an inhomogeneous strain to the crystal; and effects associated with the drag of EHDs by nonequilibrium phonons (phonon wind), including the dynamics and formation of an anisotropic spatial structure of the EHD cloud. In discussing EHLs in low-dimensional structures, a number of studies are reviewed on the observation and experimental investigation of phenomena such as spatially indirect (dipolar) electron-hole and exciton (dielectric) liquids in GaAs/AlGaAs structures with double quantum wells (QWs), EHDs containing only a few electron-hole pairs (dropletons), EHLs in type-I silicon QWs, and spatially direct and dipolar EHLs in type-II silicon-germanium heterostructures.

Observations of electron phase-space holes driven during magnetic reconnection in a laboratory plasma

Science.gov (United States)

Fox, W.; Porkolab, M.; Egedal, J.; Katz, N.; Le, A.

2012-03-01

This work presents detailed experimental observations of electron phase-space holes driven during magnetic reconnection events on the Versatile Toroidal Facility. The holes are observed to travel on the order of or faster than the electron thermal speed, and are of large size scale, with diameter of order 60 Debye lengths. In addition, they have 3D spheroidal structure with approximately unity aspect ratio. We estimate the direct anomalous resistivity due to ion interaction with the holes and find it to be too small to affect the reconnection rate; however, the holes may play a role in reining in a tail of accelerated electrons and they indicate the presence of other processes in the reconnection layer, such as electron energization and electron beam formation.

Electron-hole collision limited transport in charge-neutral bilayer graphene

Science.gov (United States)

Nam, Youngwoo; Ki, Dong-Keun; Soler-Delgado, David; Morpurgo, Alberto F.

2017-12-01

Ballistic transport occurs whenever electrons propagate without collisions deflecting their trajectory. It is normally observed in conductors with a negligible concentration of impurities, at low temperature, to avoid electron-phonon scattering. Here, we use suspended bilayer graphene devices to reveal a new regime, in which ballistic transport is not limited by scattering with phonons or impurities, but by electron-hole collisions. The phenomenon manifests itself in a negative four-terminal resistance that becomes visible when the density of holes (electrons) is suppressed by gate-shifting the Fermi level in the conduction (valence) band, above the thermal energy. For smaller densities, transport is diffusive, and the measured conductivity is reproduced quantitatively, with no fitting parameters, by including electron-hole scattering as the only process causing velocity relaxation. Experiments on a trilayer device show that the phenomenon is robust and that transport at charge neutrality is governed by the same physics. Our results provide a textbook illustration of a transport regime that had not been observed previously and clarify the nature of conduction through charge-neutral graphene under conditions in which carrier density inhomogeneity is immaterial. They also demonstrate that transport can be limited by a fully electronic mechanism, originating from the same microscopic processes that govern the physics of Dirac-like plasmas.

Simultaneous effects of electron-hole correlation, hydrostatic pressure, and temperature on the third harmonic generation in parabolic GaAs quantum dots

International Nuclear Information System (INIS)

Duque, C. M.; Mora-Ramos, M. E.; Duque, C. A.

2011-01-01

The combined effects of electron-hole correlation, hydrostatic pressure, and temperature on the third harmonic generation in disk-shaped parabolic GaAs quantum dots are studied under the density matrix formalism and the effective mass approximation. Two well-defined regimes are discussed: (1) the strong-confinement regime, where the Coulomb interaction between the electron and hole is neglected and (2) the weak-confinement regime where the parabolic confinement term is neglected and the system reaches the limit of a hydrogenic problem. The results show that the third harmonic-generation coefficient is strongly dependent on the localization of the electron-hole pair. Also, that by using external perturbations like hydrostatic pressure or by considering the temperature effects it is possible to induce a blue-shift and/or red-shift on the resonant peaks of the third harmonic generation coefficient.

Photoinduced electron transfer and persistent spectral hole-burning in natural emerald.

Science.gov (United States)

Riesen, Hans

2011-06-02

Wavelength-selective excited-state lifetime measurements and absorption, luminescence, and hole-burning spectra of a natural African emerald crystal are reported. The (2)E excited-state lifetime displays an extreme wavelength dependence, varying from 190 to 37 μs within 1.8 nm of the R(1)-line. Overall, the excited state is strongly quenched, in comparison to laboratory-created emerald (τ=1.3 ms), with an average quenching rate of ∼6 × 10(3) s(-1) at 2.5 K. This quenching is attributed to photoinduced electron transfer caused by a relatively high concentration of Fe(2+) ions. The forward electron-transfer rate, k(f), from the nearest possible Fe(2+) sites at around 5 Å is estimated to be ∼20 × 10(3) s(-1) at 2.5 K. The photoreductive quenching of the excited Cr(3+) ions by Fe(2+) is followed by rapid electron back-transfer in the ground state upon deactivation. The exchange interaction based quenching can be modeled by assuming a random quencher distribution within the possible Fe(2+) sites with the forward electron-transfer rate, k(f), given as a function of acceptor-donor separation R by exp[(R(f)-R)/a(f)]; R(f) and a(f) values of 13.5 and 2.7 Å are obtained at 2.5 K. The electron transfer/back-transfer reorganizes the local crystal lattice, occasionally leading to a minor variation of the short-range structure around the Cr(3+) ions. This provides a mechanism for spectral hole-burning for which a moderately high quantum efficiency of about ∼0.005% is observed. Spectral holes are subject to spontaneous hole-filling and spectral diffusion, and both effects can be quantified within the standard two-level systems for non-photochemical hole-burning. Importantly, the absorbance increases on both sides of broad spectral holes, and isosbestic points are observed, in accord with the expected distribution of the "photoproduct" in a non-photochemical hole-burning process. © 2011 American Chemical Society

Organic electronic devices using phthalimide compounds

Science.gov (United States)

Hassan, Azad M.; Thompson, Mark E.

2010-09-07

Organic electronic devices comprising a phthalimide compound. The phthalimide compounds disclosed herein are electron transporters with large HOMO-LUMO gaps, high triplet energies, large reduction potentials, and/or thermal and chemical stability. As such, these phthalimide compounds are suitable for use in any of various organic electronic devices, such as OLEDs and solar cells. In an OLED, the phthalimide compounds may serve various functions, such as a host in the emissive layer, as a hole blocking material, or as an electron transport material. In a solar cell, the phthalimide compounds may serve various functions, such as an exciton blocking material. Various examples of phthalimide compounds which may be suitable for use in the present invention are disclosed.

Deriving the coronal hole electron temperature: electron density dependent ionization / recombination considerations

International Nuclear Information System (INIS)

Doyle, John Gerard; Perez-Suarez, David; Singh, Avninda; Chapman, Steven; Bryans, Paul; Summers, Hugh; Savin, Daniel Wolf

2010-01-01

Comparison of appropriate theoretically derived line ratios with observational data can yield estimates of a plasma's physical parameters, such as electron density or temperature. The usual practice in the calculation of the line ratio is the assumption of excitation by electrons/protons followed by radiative decay. Furthermore, it is normal to use the so-called coronal approximation, i.e. one only considers ionization and recombination to and from the ground-state. A more accurate treatment is to include ionization/recombination to and from metastable levels. Here, we apply this to two lines from adjacent ionization stages, Mg IX 368 A and Mg X 625 A, which has been shown to be a very useful temperature diagnostic. At densities typical of coronal hole conditions, the difference between the electron temperature derived assuming the zero density limit compared with the electron density dependent ionization/recombination is small. This, however, is not the case for flares where the electron density is orders of magnitude larger. The derived temperature for the coronal hole at solar maximum is around 1.04 MK compared to just below 0.82 MK at solar minimum.

Exciplex-Sensitized Triplet-Triplet Annihilation in Heterojunction Organic Thin-Film.

Science.gov (United States)

Lin, Bo-Yen; Easley, Connor J; Chen, Chia-Hsun; Tseng, Po-Chen; Lee, Ming-Zer; Sher, Pin-Hao; Wang, Juen-Kai; Chiu, Tien-Lung; Lin, Chi-Feng; Bardeen, Christopher J; Lee, Jiun-Haw

2017-03-29

A new concept for organic light-emitting diodes (OLEDs) is presented, which is called exciplex-sensitized triplet-triplet annihilation (ESTTA). The exciplex formed at the organic heterojunction interface of 4,4',4″-tris(N-3-methyphenyl-N-phenyl-amino) triphenylamine and 9,10-bis(2'-naphthyl) anthracene (ADN) is used to sensitize the triplet-triplet annihilation (TTA) process on the ADN molecules. This results in a turn-on voltage (2.2 V) of the blue emission from the OLED below the bandgap (2.9 eV). From the transient electroluminescence measurement, blue emission totally came from the TTA process without direct recombination on the ADN molecules. The blue singlet exciton from the TTA process can be quenched by energy transfer to the exciplex, as revealed by transient photoluminescence measurements. This can be prevented by blocking the energy transfer path and improving the radiative recombination rate of blue emission. With the insertion of the "triplet diffusion and singlet blocking (TDSB)" layer and the incorporation of the dopant material, an ESTTA-OLED with external quantum efficiency of 5.1% was achieved, which consists of yellow and blue emission coming from the exciplex and ESTTA process, respectively.

Giant electron-hole transport asymmetry in ultra-short quantum transistors

Science.gov (United States)

McRae, A. C.; Tayari, V.; Porter, J. M.; Champagne, A. R.

2017-01-01

Making use of bipolar transport in single-wall carbon nanotube quantum transistors would permit a single device to operate as both a quantum dot and a ballistic conductor or as two quantum dots with different charging energies. Here we report ultra-clean 10 to 100 nm scale suspended nanotube transistors with a large electron-hole transport asymmetry. The devices consist of naked nanotube channels contacted with sections of tube under annealed gold. The annealed gold acts as an n-doping top gate, allowing coherent quantum transport, and can create nanometre-sharp barriers. These tunnel barriers define a single quantum dot whose charging energies to add an electron or a hole are vastly different (e−h charging energy asymmetry). We parameterize the e−h transport asymmetry by the ratio of the hole and electron charging energies ηe−h. This asymmetry is maximized for short channels and small band gap tubes. In a small band gap device, we demonstrate the fabrication of a dual functionality quantum device acting as a quantum dot for holes and a much longer quantum bus for electrons. In a 14 nm-long channel, ηe−h reaches up to 2.6 for a device with a band gap of 270 meV. The charging energies in this device exceed 100 meV. PMID:28561024

Electronic properties of electron and hole in type-II semiconductor nano-heterostructures

Science.gov (United States)

Rahul, K. Suseel; Souparnika, C.; Salini, K.; Mathew, Vincent

2016-05-01

In this project, we record the orbitals of electron and hole in type-II (CdTe/CdSe/CdTe/CdSe) semiconductor nanocrystal using effective mass approximation. In type-II the band edges of both valance and conduction band are higher than that of shell. So the electron and hole get confined in different layers of the hetero-structure. The energy eigen values and eigen functions are calculated by solving Schrodinger equation using finite difference matrix method. Based on this we investigate the effect of shell thickness and well width on energy and probability distribution of ground state (1s) and few excited states (1p,1d,etc). Our results predict that, type-II quantum dots have significant importance in photovoltaic applications.

Electronic properties of electron and hole in type-II semiconductor nano-heterostructures

Energy Technology Data Exchange (ETDEWEB)

Rahul, K. Suseel [Department of Physics, Central University of Kerala, Riverside Transit Campus, Kasaragod, Kerala. India (India); Department of Physics, Sri Vyasa NSS College, Wadakkancheri, Thrissur, Kerala, PIN:680623. India (India); Souparnika, C. [Department of Physics, Sri Vyasa NSS College, Wadakkancheri, Thrissur, Kerala, PIN:680623. India (India); Salini, K.; Mathew, Vincent, E-mail: vincent@cukerala.ac.in [Department of Physics, Central University of Kerala, Riverside Transit Campus, Kasaragod, Kerala. India (India)

2016-05-06

In this project, we record the orbitals of electron and hole in type-II (CdTe/CdSe/CdTe/CdSe) semiconductor nanocrystal using effective mass approximation. In type-II the band edges of both valance and conduction band are higher than that of shell. So the electron and hole get confined in different layers of the hetero-structure. The energy eigen values and eigen functions are calculated by solving Schrodinger equation using finite difference matrix method. Based on this we investigate the effect of shell thickness and well width on energy and probability distribution of ground state (1s) and few excited states (1p,1d,etc). Our results predict that, type-II quantum dots have significant importance in photovoltaic applications.

Biomimetic Interfacial Electron-Induced Electrochemiluminesence.

Science.gov (United States)

Pu, Guiqiang; Zhang, Dongxu; Mao, Xiang; Zhang, Zhen; Wang, Huan; Ning, Xingming; Lu, Xiaoquan

2018-04-17

We provide here, for the first time, a new interfacial electron-induced electrochemiluminescence (IEIECL) system, realizing bionic construction of bioluminescence (BL) by exploiting electrochemiluminescence (ECL) and ITIES (the interface between two immiscible electrolyte solutions). Significantly, the superiority of the IEIECL system is embodied with the solution of the two bottlenecks encountered in the conventional ECL innovation: that are (a) the applications of hydrophobic luminophores in more commonly used aqueous solution are inhibited tremendously due to the poor inherent solubility and the instability of radicals and (b) the analytes, insoluble in water, are hard to be discovered in an aqueous system because of too little content. More productive IEIECL radiation, analogous to BL, originates from the triplet excited state porphyrin in comparison to the homogeneous ECL. The mechanism of IEIECL, as well as the interaction mechanism between IEIECL and charge transfer (comprising electron transfer (ET), ion transfer (IT), and facilitated ion transfer (FIT)) at the ITIES, are explored in detail. Finally, we emphasize the actual application potential of the IEIECL system with the detection of cytochrome c (Cyt c); it is a key biomolecule in the electron transport chain in the process of biological oxidation and is also an intermediate species in apoptosis. Potentially, the IEIECL system permits ones to explore the lifetime and diffusion path of free radicals, as well as imparting a possibility for the construction of a bionic sensor.

Electron-phonon contribution to the phonon and excited electron (hole) linewidths in bulk Pd

International Nuclear Information System (INIS)

Sklyadneva, I Yu; Leonardo, A; Echenique, P M; Eremeev, S V; Chulkov, E V

2006-01-01

We present an ab initio study of the electron-phonon (e-ph) coupling and its contribution to the phonon linewidths and to the lifetime broadening of excited electron and hole states in bulk Pd. The calculations, based on density-functional theory, were carried out using a linear-response approach in the plane-wave pseudopotential representation. The obtained results for the Eliashberg spectral function α 2 F(ω), e-ph coupling constant λ, and the contribution to the lifetime broadening, Γ e-ph , show strong dependence on both the energy and momentum of an electron (hole) state. The calculation of phonon linewidths gives, in agreement with experimental observations, an anomalously large broadening for the transverse phonon mode T 1 in the Σ direction. In addition, this mode is found to contribute most strongly to the electron-phonon scattering processes on the Fermi surface

Spectral features of the tunneling-induced transparency and the Autler-Townes doublet and triplet in a triple quantum dot.

Science.gov (United States)

Luo, Xiao-Qing; Li, Zeng-Zhao; Jing, Jun; Xiong, Wei; Li, Tie-Fu; Yu, Ting

2018-02-15

We theoretically investigate the spectral features of tunneling-induced transparency (TIT) and Autler-Townes (AT) doublet and triplet in a triple-quantum-dot system. By analyzing the eigenenergy spectrum of the system Hamiltonian, we can discriminate TIT and double TIT from AT doublet and triplet, respectively. For the resonant case, the presence of the TIT does not exhibit distinguishable anticrossing in the eigenenergy spectrum in the weak-tunneling regime, while the occurrence of double anticrossings in the strong-tunneling regime shows that the TIT evolves to the AT doublet. For the off-resonance case, the appearance of a new detuning-dependent dip in the absorption spectrum leads to double TIT behavior in the weak-tunneling regime due to no distinguished anticrossing occurring in the eigenenergy spectrum. However, in the strong-tunneling regime, a new detuning-dependent dip in the absorption spectrum results in AT triplet owing to the presence of triple anticrossings in the eigenenergy spectrum. Our results can be applied to quantum measurement and quantum-optics devices in solid systems.

Triplet-triplet energy transfer from a UV-A absorber butylmethoxydibenzoylmethane to UV-B absorbers.

Science.gov (United States)

Kikuchi, Azusa; Oguchi-Fujiyama, Nozomi; Miyazawa, Kazuyuki; Yagi, Mikio

2014-01-01

The phosphorescence decay of a UV-A absorber, 4-tert-butyl-4'-methoxydibenzolymethane (BMDBM) has been observed following a 355 nm laser excitation in the absence and presence of UV-B absorbers, 2-ethylhexyl 4-methoxycinnamate (octyl methoxycinnamate, OMC) and octocrylene (OCR) in ethanol at 77 K. The lifetime of the lowest excited triplet (T1) state of BMDBM is significantly reduced in the presence of OMC and OCR. The observed quenching of BMDBM triplet by OMC and OCR suggests that the intermolecular triplet-triplet energy transfer occurs from BMDBM to OMC and OCR. The T1 state of OCR is nonphosphorescent or very weakly phosphorescent. However, we have shown that the energy level of the T1 state of OCR is lower than that of the enol form of BMDBM. Our methodology of energy-donor phosphorescence decay measurements can be applied to the study of the triplet-triplet energy transfer between UV absorbers even if the energy acceptor is nonphosphorescent. In addition, the delayed fluorescence of BMDBM due to triplet-triplet annihilation was observed in the BMDBM-OMC and BMDBM-OCR mixtures in ethanol at 77 K. Delayed fluorescence is one of the deactivation processes of the excited states of BMDBM under our experimental conditions. © 2013 The American Society of Photobiology.

Direct Observation of Electron-to-Hole Energy Transfer in CdSe Quantum Dots

NARCIS (Netherlands)

Hendry, E.; Koeberg, M.; Wang, F.; Zhang, H.; de Mello Donega, C.; Vanmaekelbergh, D.; Bonn, M.

2006-01-01

We independently determine the subpicosecond cooling rates for holes and electrons in CdSe quantum dots. Time-resolved luminescence and terahertz spectroscopy reveal that the rate of hole cooling, following photoexcitation of the quantum dots, depends critically on the electron excess energy. This

Balancing Hole and Electron Conduction in Ambipolar Split-Gate Thin-Film Transistors.

Science.gov (United States)

Yoo, Hocheon; Ghittorelli, Matteo; Lee, Dong-Kyu; Smits, Edsger C P; Gelinck, Gerwin H; Ahn, Hyungju; Lee, Han-Koo; Torricelli, Fabrizio; Kim, Jae-Joon

2017-07-10

Complementary organic electronics is a key enabling technology for the development of new applications including smart ubiquitous sensors, wearable electronics, and healthcare devices. High-performance, high-functionality and reliable complementary circuits require n- and p-type thin-film transistors with balanced characteristics. Recent advancements in ambipolar organic transistors in terms of semiconductor and device engineering demonstrate the great potential of this route but, unfortunately, the actual development of ambipolar organic complementary electronics is currently hampered by the uneven electron (n-type) and hole (p-type) conduction in ambipolar organic transistors. Here we show ambipolar organic thin-film transistors with balanced n-type and p-type operation. By manipulating air exposure and vacuum annealing conditions, we show that well-balanced electron and hole transport properties can be easily obtained. The method is used to control hole and electron conductions in split-gate transistors based on a solution-processed donor-acceptor semiconducting polymer. Complementary logic inverters with balanced charging and discharging characteristics are demonstrated. These findings may open up new opportunities for the rational design of complementary electronics based on ambipolar organic transistors.

Plasma phase transition in dense hydrogen and electron-hole plasmas

CERN Document Server

Filinov, V S; Levashov, P R; Fortov, V E; Ebeling, W; Schlanges, M; Koch, S W

2003-01-01

Plasma phase transitions in dense hydrogen and electron-hole plasmas are investigated by direct path integral Monte Carlo methods. The phase boundary of the electron-hole liquid in germanium is calculated and is found to agree reasonably well with the known experimental results. Analogous behaviour is found for high-density hydrogen. For a temperature of T = 10 000 K it is shown that the internal energy is lowered due to droplet formation for densities between 10 sup 2 sup 3 cm sup - sup 3 and 10 sup 2 sup 4 cm sup - sup 3.

A novel strategy to increase separated electron-hole dipoles in commercial Si based solar panel to assist photovoltaic effect

Science.gov (United States)

Feng, Yefeng; He, Cheng-En; Xu, Zhichao; Hu, Jianbing; Peng, Cheng

2018-01-01

Interface induced polarization has been found to have a significant impact on dielectric properties of 2-2 type polymer composites bearing Si based semi-conducting ceramic sheets. Inherent overall polarity of polymer layers in 2-2 composites has been verified to be closely connected with interface effect and achieved permittivity in composites. In present work, conducting performances of monocrystalline Si sheets coated by varied high polarity material layers were deeply researched. The positive results inspired us to propose a novel strategy to improve separated electron-hole dipoles in commercial Si based solar cell panel for assisting photovoltaic effect, based on strong interface induced polarization. Conducting features of solar panels coated by two different high polarity polymer layers were detected to be greatly elevated compared with solar panel standalone, thanks to interface induced polarization between panel and polymer. Polymer coating with higher polarity would lead to more separated electron-hole dipole pairs in solar panel contributing to higher conductivity of panel. Valid synergy of interface effect and photovoltaic effect was based on their unidirectional traits of electron transfer. Dielectric properties of solar panels in composites further confirmed that strategy. This work might provide a facile route to prepare promising Si based solar panels with higher photoelectric conversion efficiency by enhancing interface induced polarization between panel and polymer coating.

Quantum simulations of small electron-hole complexes

International Nuclear Information System (INIS)

Lee, M.A.; Kalia, R.K.; Vashishta, P.D.

1984-09-01

The Green's Function Monte Carlo method is applied to the calculation of the binding energies of electron-hole complexes in semiconductors. The quantum simulation method allows the unambiguous determination of the ground state energy and the effects of band anisotropy on the binding energy. 22 refs., 1 fig

Photoprotection and triplet energy transfer in higher plants: the role of electronic and nuclear fluctuations.

Science.gov (United States)

Cupellini, Lorenzo; Jurinovich, Sandro; Prandi, Ingrid G; Caprasecca, Stefano; Mennucci, Benedetta

2016-04-28

Photosynthetic organisms employ several photoprotection strategies to avoid damage due to the excess energy in high light conditions. Among these, quenching of triplet chlorophylls by neighboring carotenoids (Cars) is fundamental in preventing the formation of singlet oxygen. Cars are able to accept the triplets from chlorophylls by triplet energy transfer (TET). We have here studied TET rates in CP29, a minor light-harvesting complex (LHC) of the Photosystem II in plants. A fully atomistic strategy combining classical molecular dynamics of the LHC in its natural environment with a hybrid time-dependent density functional theory/polarizable MM description of the TET is used. We find that the structural fluctuations of the pigment-protein complex can largely enhance the transfer rates with respect to those predicted using the crystal structure, reducing the triplet quenching times in the subnanosecond scale. These findings add a new perspective for the interpretation of the photoprotection function and its relation with structural motions of the LHC.

Where do the doped holes go in La2-xSrxCuO4? A close look by XAFS

International Nuclear Information System (INIS)

Haskel, Daniel; Polinger, Victor; Stern, Edward A.

1999-01-01

Polarized x-ray absorption fine structure (XAFS) measurements at the La and Sr sites in La 2-x Sr x CuO 4 (0.075(less-or-similar sign)x(less-or-similar sign)0.35) indicate that doped holes introduced with Sr are not uniformly distributed in the CuO 2 planes but reside in impurity states with the majority of charge located on CuO 6 octahedra coupled to the Sr dopants by an apical oxygen (denoted as Sr octahedra). A model based on doped hole-induced Jahn Teller (JT) distortions of these Sr octahedra indicates the impurity states are overlapping singlet and triplet ones resulting from pairings of intrinsic and extrinsic holes. The more mobile singlet pairs reside in the CuO 2 planes, are bound by more than 0.1 eV and could Bose-condense into a superconducting state. The predominant appearance of (mostly) out-of plane triplet states at high x intimately related to the 2D-3D crossover in transport properties and could relate to the observed loss of high T c in the overdoped regime, as confinement of carriers to the CuO 2 planes is reduced. (c) 1999 American Institute of Physics

Generation of Triplet Excited States via Photoinduced Electron Transfer in meso-anthra-BODIPY: Fluorogenic Response toward Singlet Oxygen in Solution and in Vitro

KAUST Repository

Filatov, Mikhail A.; Karuthedath, Safakath; Polestshuk, Pavel M.; Savoie, Huguette; Flanagan, Keith J.; Sy, Cindy; Sitte, Elisabeth; Telitchko, Maxime; Laquai, Fré dé ric; Boyle, Ross W.; Senge, Mathias O.

2017-01-01

Heavy atom-free BODIPY-anthracene dyads (BADs) generate locally excited triplet states by way of photoinduced electron transfer (PeT), followed by recombination of the resulting charge-separated states (CSS). Subsequent quenching of the triplet states by molecular oxygen produces singlet oxygen (1O2), which reacts with the anthracene moiety yielding highly fluorescent species. The steric demand of the alkyl substituents in the BODIPY subunit defines the site of 1O2 addition. Novel bis- and tetraepoxides and bicyclic acetal products, arising from rearrangements of anthracene endoperoxides were isolated and characterized. 1O2 generation by BADs in living cells enables visualization of the dyads distribution, promising new imaging applications.

Generation of Triplet Excited States via Photoinduced Electron Transfer in meso-anthra-BODIPY: Fluorogenic Response toward Singlet Oxygen in Solution and in Vitro

KAUST Repository

Filatov, Mikhail A.

2017-04-14

Heavy atom-free BODIPY-anthracene dyads (BADs) generate locally excited triplet states by way of photoinduced electron transfer (PeT), followed by recombination of the resulting charge-separated states (CSS). Subsequent quenching of the triplet states by molecular oxygen produces singlet oxygen (1O2), which reacts with the anthracene moiety yielding highly fluorescent species. The steric demand of the alkyl substituents in the BODIPY subunit defines the site of 1O2 addition. Novel bis- and tetraepoxides and bicyclic acetal products, arising from rearrangements of anthracene endoperoxides were isolated and characterized. 1O2 generation by BADs in living cells enables visualization of the dyads distribution, promising new imaging applications.

Fermi-edge superfluorescence from a quantum-degenerate electron-hole gas

Science.gov (United States)

Kim, Ji-Hee; , G. Timothy Noe, II; McGill, Stephen A.; Wang, Yongrui; Wójcik, Aleksander K.; Belyanin, Alexey A.; Kono, Junichiro

2013-11-01

Nonequilibrium can be a source of order. This rather counterintuitive statement has been proven to be true through a variety of fluctuation-driven, self-organization behaviors exhibited by out-of-equilibrium, many-body systems in nature (physical, chemical, and biological), resulting in the spontaneous appearance of macroscopic coherence. Here, we report on the observation of spontaneous bursts of coherent radiation from a quantum-degenerate gas of nonequilibrium electron-hole pairs in semiconductor quantum wells. Unlike typical spontaneous emission from semiconductors, which occurs at the band edge, the observed emission occurs at the quasi-Fermi edge of the carrier distribution. As the carriers are consumed by recombination, the quasi-Fermi energy goes down toward the band edge, and we observe a continuously red-shifting streak. We interpret this emission as cooperative spontaneous recombination of electron-hole pairs, or superfluorescence (SF), which is enhanced by Coulomb interactions near the Fermi edge. This novel many-body enhancement allows the magnitude of the spontaneously developed macroscopic polarization to exceed the maximum value for ordinary SF, making electron-hole SF even more ``super'' than atomic SF.

Interacting Electrons and Holes in Quasi-2D Quantum Dots in Strong Magnetic Fields

Science.gov (United States)

Hawrylak, P.; Sheng, W.; Cheng, S.-J.

2004-09-01

Theory of optical properties of interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields is discussed. In two dimensions and the lowest Landau level, hidden symmetries control the interaction of the interacting system with light. By confining electrons and holes into quantum dots hidden symmetries can be removed and the excitation spectrum of electrons and excitons can be observed. We discuss a theory electronic and of excitonic quantum Hall droplets at a filling factorν=2. For an excitonic quantum Hall droplet the characteristic emission spectra are predicted to be related to the total spin of electron and hole configurations. For the electronic droplet the excitation spectrum of the droplet can be mapped out by measuring the emission for increasing number of electrons.

Interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields

International Nuclear Information System (INIS)

Hawrylak, P.; Sheng, W.; Cheng, S.-J.

2004-01-01

Theory of optical properties of interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields is discussed. In two dimensions and the lowest Landau level, hidden symmetries control the interaction of the interacting system with light. By confining electrons and holes into quantum dots hidden symmetries can be removed and the excitation spectrum of electrons and excitons can be observed. We discuss a theory electronic and excitonic quantum Hall droplets at a filling factor υ = 2. For an excitonic quantum Hall droplet the characteristic emission spectra are predicted to be related to the total spin of electron and hole configurations. For the electronic droplet the excitation spectrum of the droplet can be mapped out by measuring the emission for increasing number of electrons. (author)

Triplet energy transfer and triplet exciton recycling in singlet fission sensitized organic heterojunctions

Science.gov (United States)

Hamid, Tasnuva; Yambem, Soniya D.; Crawford, Ross; Roberts, Jonathan; Pandey, Ajay K.

2017-08-01

Singlet exciton fission is a process where an excited singlet state splits into two triplets, thus leading to generation of multiple excitons per absorbed photon in organic semiconductors. Herein, we report a detailed exciton management approach for multiexciton harvesting over a broadband region of the solar spectrum in singlet fission sensitized organic photodiodes. Through systematic studies on the model cascade of pentacene/rubrene/C60, we found that efficient photocurrent generation from pentacene can still occur despite the presence of a >10nm thick interlayer of rubrene in between the pentacene/C60 heterojunction. Our results show that thin rubrene interlayers of thickness pentacene despite having a reasonably thick rubrene interlayer, that too with higher triplet energy (T1=1.12 eV) than pentacene (T1= 0.86 eV), makes its operation a rather interesting result. We discuss the role of rubrene interlayer film discontinuity, triplet exciton reflection from rubrene interlayer and triplet energy transfer from rubrene to pentacene layer followed by diffusion of triplet excitons through rubrene as plausible mechanisms that would enable triplet excitons from pentacene to generate significant photocurrent in a multilayer organic heterojunction.

Doping Phosphorene with Holes and Electrons through Molecular Charge Transfer.

Science.gov (United States)

Vishnoi, Pratap; Rajesh, S; Manjunatha, S; Bandyopadhyay, Arkamita; Barua, Manaswee; Pati, Swapan K; Rao, C N R

2017-11-03

An important aspect of phosphorene, the novel two-dimensional semiconductor, is whether holes and electrons can both be doped in this material. Some reports found that only electrons can be preferentially doped into phosphorene. There are some theoretical calculations showing charge-transfer interaction with both tetrathiafulvalene (TTF) and tetracyanoethylene (TCNE). We have carried out an investigation of chemical doping of phosphorene by a variety of electron donor and acceptor molecules, employing both experiment and theory, Raman scattering being a crucial aspect of the study. We find that both electron acceptors and donors interact with phosphorene by charge-transfer, with the acceptors having more marked effects. All the three Raman bands of phosphorene soften and exhibit band broadening on interaction with both donor and acceptor molecules. First-principles calculations establish the occurrence of charge-transfer between phosphorene with donors as well as acceptors. The absence of electron-hole asymmetry is noteworthy. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Correlation effects on spin-polarized electron-hole quantum bilayer

Energy Technology Data Exchange (ETDEWEB)

Saini, L. K., E-mail: drlalitsaini75@gmail.com; Sharma, R. O., E-mail: sharmarajesh0387@gmail.com [Department of Applied Physics, S. V. National Institute of Technology, Surat – 395 007 (India); Nayak, Mukesh G. [Department of Physics, Silvassa College (Silvassa Institute of Higher Learning), Silvassa 396 230 (India)

2016-05-06

We present a numerical calculation for the intra- and interlayer pair-correlation functions, g{sub ll’}(r), of spin-polarized electron-hole quantum bilayers at zero temperature. The calculations of g{sub ll’}(r) are performed by including electron correlations within the dynamical version of the self-consistent mean-field approximation of Singwi, Tosi, Land and Sjölander (qSTLS). Our study reveals that the critical layer density decreases (increases) due to the inclusion of finite width (mass-asymmetry) effect during the phase-transition from charge-density wave to Wigner crystal ground-state by yielding the pronounced oscillatory behavior ing{sub ll}(r). The results are compared with recent findings of spin-polarized electron-hole quantum bilayers with mass-symmetry and zero width effects. To highlight the importance of dynamical character of correlations, we have also compared our results with the STLS results.

Optical and electron paramagnetic resonance studies of the excited triplet states of UV-B absorbers: 2-ethylhexyl salicylate and homomenthyl salicylate.

Science.gov (United States)

Sugiyama, Kazuto; Tsuchiya, Takumi; Kikuchi, Azusa; Yagi, Mikio

2015-09-26

The energy levels and lifetimes of the lowest excited triplet (T1) states of UV-B absorbers, 2-ethylhexyl salicylate (EHS) and homomenthyl salicylate (HMS), and their deprotonated anions (EHS(-) and HMS(-)) were determined through measurements of phosphorescence and electron paramagnetic resonance (EPR) spectra in rigid solutions at 77 K. The observed T1 energies of EHS and HMS are higher than those of butylmethoxydibenzoylmethane, the most widely used UV-A absorber, and octyl methoxycinnamate, the most widely used UV-B absorber. The T1 states of EHS, HMS, EHS(-) and HMS(-) were assigned to almost pure (3)ππ* state from the observed T1 lifetimes and zero-field splitting parameters. EHS and HMS with an intramolecular hydrogen bond show a photoinduced phosphorescence enhancement in ethanol at 77 K. The EPR signals of the T1 states of EHS and HMS also increase in intensity with UV-irradiation time (photoinduced EPR enhancement). The T1 lifetimes of EHS and HMS at room temperature were determined through triplet-triplet absorption measurements in ethanol. The quantum yields of singlet oxygen production by EHS and HMS were determined by using time-resolved near-IR phosphorescence.

Dynamics of electrons and holes at surfaces

International Nuclear Information System (INIS)

Chulkov, E.V.; Leonardo, A.; Sklyadneva, I.Yu.; Silkin, V.M.

2007-01-01

We present ab initio calculation results for electron-phonon (e-ph) contribution to hole lifetime broadening of the X-bar surface state on Al(0 0 1). We show that e-ph coupling in this state is significantly stronger than in bulk Al at the Fermi level. It makes the e-ph decay channel very important in the formation of the hole decay in the surface state at X-bar. We also present the results for e-e lifetime broadening in a quantum-well state in 1 ML K/Cu(1 1 1). We show that this contribution is not negligible and is much larger than that in a surface state on Ag(1 1 1)

Triplets pass their pressure test

CERN Multimedia

2007-01-01

All the LHC inner triplets have now been repaired and are in position. The first ones have passed their pressure tests with flying colours. The repaired inner triplet at LHC Point 1, right side (1R). Ranko Ostojic (on the right), who headed the team responsible for repairing the triplets, shows the magnet to Robert Zimmer, President of the University of Chicago and of Fermi Research Alliance, who visited CERN on 20th August.Three cheers for the triplets! All the LHC inner triplets have now been repaired and are in position in the tunnel. Thanks to the mobilisation of a multidisciplinary team from CERN and Fermilab, assisted by the KEK Laboratory and the Lawrence Berkeley National Laboratory (LBNL), a solution has been found, tested, validated and applied. At the end of March this year, one of the inner triplets at Point 5 failed to withstand a pressure test. A fault was identified in the supports of two out of the three quadruple magne...

The origin of efficient triplet state population in sulfur-substituted nucleobases

Science.gov (United States)

Mai, Sebastian; Pollum, Marvin; Martínez-Fernández, Lara; Dunn, Nicholas; Marquetand, Philipp; Corral, Inés; Crespo-Hernández, Carlos E.; González, Leticia

2016-10-01

Elucidating the photophysical mechanisms in sulfur-substituted nucleobases (thiobases) is essential for designing prospective drugs for photo- and chemotherapeutic applications. Although it has long been established that the phototherapeutic activity of thiobases is intimately linked to efficient intersystem crossing into reactive triplet states, the molecular factors underlying this efficiency are poorly understood. Herein we combine femtosecond transient absorption experiments with quantum chemistry and nonadiabatic dynamics simulations to investigate 2-thiocytosine as a necessary step to unravel the electronic and structural elements that lead to ultrafast and near-unity triplet-state population in thiobases in general. We show that different parts of the potential energy surfaces are stabilized to different extents via thionation, quenching the intrinsic photostability of canonical DNA and RNA nucleobases. These findings satisfactorily explain why thiobases exhibit the fastest intersystem crossing lifetimes measured to date among bio-organic molecules and have near-unity triplet yields, whereas the triplet yields of canonical nucleobases are nearly zero.

Formation of electrostatic double-layers and electron-holes in a low pressure mercury plasma column

International Nuclear Information System (INIS)

Petraconi, G; Maciel, Homero S

2003-01-01

Experimental studies of the formation of electrostatic double layers (DLs) and electron-holes (e-holes) are reported. The measurements were performed in the positive column of a mercury arc discharge operating in the low-pressure range of (2.0-14.0) x 10 -2 Pa with current density in the range of (3.0-8.0) x 10 3 A m -2 . Stable and unstable modes of the discharge were identified as the current was gradually increased, keeping constant the vapour pressure. The discharge remains stable until a critical current from which a slight increase of the current leads to an unstable regime characterized by high discharge impedance and strong oscillations. This mode ceased after a DL was formed in the plasma column. To induce the DL formation and to transport it smoothly along the discharge column, a low intensity B-field (7-10) x 10 -3 T produced by a movable single coil was used. The B-field locally increases the electron current density and makes the DL form at the centre of the magnetic constriction where it remained at rest. Electrostatic potential structures compatible with ordinary DLs and multiple-layers could be formed in the plasma column by dealing with the combined effects of the operational parameters of the discharge. It is noticeable that a pure e-hole, which is a symmetric triple-layer having a bell shape potential profile, could easily be formed by means of this experimental technique. A partial kinetic description, based on the space charge structure derived from an experimental e-hole, is presented in order to infer the charged particle populations that could contribute to the space charge of the e-hole. Evidence is shown that strong e-hole formation might be driven by an ion beam, therefore it could not be formed in isolation since its formation requires a nearby ion accelerating potential structure. Probe measurements of the plasma properties, at various radial positions of the stable positive column, are also presented. In the stable mode, prior to

Triplet exciton formation in organic photovoltaics

Energy Technology Data Exchange (ETDEWEB)

Yang, Xudong; Westenhoff, Sebastian; Howard, Ian; Ford, Thomas; Friend, Richard; Hodgkiss, Justin; Greenham, Neil [Cavendish Laboratory, University of Cambridge (United Kingdom)

2009-07-01

We have recently found that the formation of triplet excitons can be an important loss mechanism in organic photovoltaics, particularly in donor-acceptor blends designed to have high open-circuit voltages. This can occur when the intrachain triplet state lies lower in energy than the charge-transfer state formed at the heterojunction. We find that in a blend based on the polyfluorene derivatives F8BT and PFB, triplet excitons are formed after photoexcitation with much higher efficiency than in the component polymers. We use transient absorption spectroscopy to study the dynamics of charges and triplet excitons on timescales from picoseconds to microseconds. This allows us to determine a characteristic time of {proportional_to} 40 ns for intersystem crossing in the charge-separated state, and to estimate that as many as 75% of photoexcitations lead to the formation of triplet states. To avoid losses to triplet excitons in photovoltaic devices, it is necessary to separate charge pairs before intersystem crossing can occur. We also present photophysical measurements of saturation and relaxation of the triplet excited state absorption used to quantify triplet populations.

Long-Lived Correlated Triplet Pairs in a π-Stacked Crystalline Pentacene Derivative.

Science.gov (United States)

Folie, Brendan D; Haber, Jonah B; Refaely-Abramson, Sivan; Neaton, Jeffrey B; Ginsberg, Naomi S

2018-02-14

Singlet fission is the spin-conserving process by which a singlet exciton splits into two triplet excitons. Singlet fission occurs via a correlated triplet pair intermediate, but direct evidence of this state has been scant, and in films of TIPS-pentacene, a small molecule organic semiconductor, even the rate of fission has been unclear. We use polarization-resolved transient absorption microscopy on individual crystalline domains of TIPS-pentacene to establish the fission rate and demonstrate that the initially created triplets remain bound for a surprisingly long time, hundreds of picoseconds, before separating. Furthermore, using a broadband probe, we show that it is possible to determine absorbance spectra of individual excited species in a crystalline solid. We find that triplet interactions perturb the absorbance, and provide evidence that triplet interaction and binding could be caused by the π-stacked geometry. Elucidating the relationship between the lattice structure and the electronic structure and dynamics has important implications for the creation of photovoltaic devices that aim to boost efficiency via singlet fission.

Exchange electron-hole interaction of two-dimensional magnetoexcitons under the influence of the Rashba spin-orbit coupling

International Nuclear Information System (INIS)

Moskalenko, S.A.; Podlesny, I.V.; Lelyakov, I.A.; Novikov, B.V.; Kiselyova, E.S.; Gherciu, L.

2011-01-01

The Rashba spin-orbit coupling (RSOC) in the case of two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field was studied. The spinor-type wave functions are characterized by different numbers of Landau levels in different spin projections. For electrons they differ by 1 as was established earlier by Rashba, whereas for holes they differ by 3. Two lowest electron states and four lowest hole states of Landau quantization give rise to eight 2D magnetoexciton states. The exchange electron-hole interaction in the frame of these states is investigated.

Coulomb drag in electron-hole bilayer: Mass-asymmetry and exchange correlation effects

Science.gov (United States)

Arora, Priya; Singh, Gurvinder; Moudgil, R. K.

2018-04-01

Motivated by a recent experiment by Zheng et al. [App. Phys. Lett. 108, 062102 (2016)] on coulomb drag in electron-hole and hole-hole bilayers based on GaAs/AlGaAs semiconductor heterostructure, we investigate theoretically the influence of mass-asymmetry and temperature-dependence of correlations on the drag rate. The correlation effects are dealt with using the Vignale-Singwi effective inter-layer interaction model which includes correlations through local-field corrections to the bare coulomb interactions. However, in this work, we have incorporated only the intra-layer correlations using the temperature-dependent Hubbard approximation. Our results display a reasonably good agreement with the experimental data. However, it is crucial to include both the electron-hole mass-asymmetry and temperature-dependence of correlations. Mass-asymmetry and correlations are found to result in a substantial enhancement of drag resistivity.

Spin coherence in phosphorescent triplet states

International Nuclear Information System (INIS)

Hof, C.A. van 't

1977-01-01

The electron spin echo is studied on the dephasing mechanism in the photo-excited triplet state of quinoline in a durene host. First, a comparative investigation of the merits of the different spin echo techniques is presented. It turns out that the rotary echo generally yields a longer phase memory time than the two-pulse echo, whereas in the Carr-Purcell experiment, the dephasing can even be largely suppressed. Secondly, it is shown that the dephasing mechanism is determined by the nuclear spins of the guest molecules as well as those in the host material. A theoretical basis for interpreting the effect of vibronic relaxation on the decay rate of the rotary echo, as observed in parabenzoquinone, is given. Similar experiments in aniline reveal also that in this molecule, two close-lying triplet states exist, which is attributed to an inversion vibration analogous to the well-known example in ammonia

Heavy atoms as molecular probes in studying the solvent dependence of the dynamics of triplet exciplexes

International Nuclear Information System (INIS)

Steiner, U.; Winter, G.

1981-01-01

Electron transfer reactions between thiopyronine triplet (acceptor 3 A + ) and the electron donors (D), aniline, p-Br-aniline and p-I-aniline, are investigated by flash spectroscopy in solvents of different viscosity and polarity. Due to the heavy-atom effect the radical yield becomes very sensitive to the solvent influence, which can be explained by the dynamic properties of a triplet exciplex ( 3 (AD + )) formed as a primary product in the reaction between acceptor triplet and donor. Whereas on variation of solvent viscosity the solvent cage effect on the dissociation of 3 (AD + ) is observed, a change in solvent polarity is suggested to affect the radiationless deactivation of 3 (AD + ) to the ground state of the components. (author)

Excitons formed from spatially separated electrons and holes in Ge/Si geterostructures with Ge quantum dots

International Nuclear Information System (INIS)

Pokutnyj, S.I.

2016-01-01

The effect of a significant increase in the exciton binding energy of space-separated electrons and holes (hole moves in the volume of the quantum dot, and the electron is localized on a spherical surface section quantum dot-matrix) in nanosystems containing germanium quantum dots grown in a matrix of silicon by compared with the binding energy of an exciton in a silicon single crystal. It was found that in such nanosystems in the conduction band silicon matrix is first a zone of states of electron-hole pairs, which with increasing radius of the quantum dot becomes a zone of exciton states, located in the band gap of silicon matrix. It is shown that the mechanism of light absorption in nanosystems due to transitions between quantum-electron levels of the electron-hole pairs, as well as the electron transitions between quantum-exciton levels.

Observation of hole accumulation in Ge/Si core/shell nanowires using off-axis electron holography.

Science.gov (United States)

Li, Luying; Smith, David J; Dailey, Eric; Madras, Prashanth; Drucker, Jeff; McCartney, Martha R

2011-02-09

Hole accumulation in Ge/Si core/shell nanowires (NWs) has been observed and quantified using off-axis electron holography and other electron microscopy techniques. The epitaxial [110]-oriented Ge/Si core/shell NWs were grown on Si (111) substrates by chemical vapor deposition through the vapor-liquid-solid growth mechanism. High-angle annular-dark-field scanning transmission electron microscopy images and off-axis electron holograms were obtained from specific NWs. The excess phase shifts measured by electron holography across the NWs indicated the presence of holes inside the Ge cores. Calculations based on a simplified coaxial cylindrical model gave hole densities of (0.4 ± 0.2) /nm(3) in the core regions.

Electron-Rich 4-Substituted Spirobifluorenes: Toward a New Family of High Triplet Energy Host Materials for High-Efficiency Green and Sky Blue Phosphorescent OLEDs.

Science.gov (United States)

Quinton, Cassandre; Thiery, Sébastien; Jeannin, Olivier; Tondelier, Denis; Geffroy, Bernard; Jacques, Emmanuel; Rault-Berthelot, Joëlle; Poriel, Cyril

2017-02-22

We report herein a detailed structure-properties relationship study of the first examples of electron-rich 4-substituted spirobifluorenes for organic electronic applications, namely, 4-phenyl-N-carbazole-spirobifluorene (4-PhCz-SBF) and 4-(3,4,5-trimethoxyphenyl)-spirobifluorene (4-Ph(OMe) 3 -SBF). The incorporation of the electron-rich moieties in the ortho position of the biphenyl linkage (position C4) induces unique properties, very different from those previously described in the literature for this family of semiconductors. Both dyes can be readily synthesized, possess high triplet energies and excellent thermal stability, and their HOMO energy levels are highly increased compared to those of other 4-substituted SBFs. We also provide in this work the first rationalization of the peculiar fluorescence of 4-substituted SBFs. Finally, the present dyes have been successfully incorporated as host in green and blue phosphorescent organic light-emitting diodes with high performance either for the green (EQE of 20.2%) or the blue color (EQE of 9.6%). These performances are, to the best of our knowledge, among the highest reported to date for 4-substituted SBF derivatives.

Retinopathy of Prematurity in Triplets

Directory of Open Access Journals (Sweden)

Mehmet Ali Şekeroğlu

2016-06-01

Full Text Available Objectives: To investigate the incidence, severity and risk factors of retinopathy of prematurity (ROP in triplets. Materials and Methods: The medical records of consecutive premature triplets who had been screened for ROP in a single maternity hospital were analyzed and presence and severity of ROP; birth weight, gender, gestational age of the infant; route of delivery and the mode of conception were recorded. Results: A total of 54 triplets (40 males, 14 females who were screened for ROP between March 2010 and February 2013 were recruited for the study. All triplets were delivered by Caesarean section and 36 (66.7% were born following an assisted conception. During follow-up, seven (13% of the infants developed ROP of any stage and two (3.7% required laser photocoagulation. The mean gestational age of triplets with ROP was 27.6±1.5 (27-31 weeks whereas it was 32.0±1.5 (30-34 weeks in those without ROP (p=0.002. The mean birth weights of triplets with and without ROP were 1290.0±295.2 (970-1600 g and 1667.5±222.2 (1130-1960 g, respectively (p<0.001. The presence of ROP was not associated with gender (p=0.358 or mode of conception (p=0.674. Conclusion: ROP in triplets seems to be mainly related to low gestational age and low birth weight. Further prospective randomized studies are necessary to demonstrate risk factors of ROP in triplets and to determine if and how gemelarity plays a role in the development of ROP.

Electron-Hole Asymmetry of Spin Injection and Transport in Single-Layer Graphene

OpenAIRE

Han, Wei; Wang, W. H.; Pi, K.; McCreary, K. M.; Bao, W.; Li, Yan; Miao, F.; Lau, C. N.; Kawakami, R. K.

2009-01-01

Spin-dependent properties of single-layer graphene (SLG) have been studied by non-local spin valve measurements at room temperature. Gate voltage dependence shows that the non-local magnetoresistance (MR) is proportional to the conductivity of the SLG, which is the predicted behavior for transparent ferromagnetic/nonmagnetic contacts. While the electron and hole bands in SLG are symmetric, gate voltage and bias dependence of the non-local MR reveal an electron-hole asymmetry in which the non-...

Possible evidence for spin-transfer torque induced by spin-triplet supercurrent

KAUST Repository

Li, Lailai; Zhao, Yuelei; Zhang, Xixiang; Sun, Young

2017-01-01

Cooper pairs in superconductors are normally spin singlet. Nevertheless, recent studies suggest that spin-triplet Cooper pairs can be created at carefully engineered superconductor-ferromagnet interfaces. If Cooper pairs are spin

Bright triplet excitons in caesium lead halide perovskites

Science.gov (United States)

Becker, Michael A.; Vaxenburg, Roman; Nedelcu, Georgian; Sercel, Peter C.; Shabaev, Andrew; Mehl, Michael J.; Michopoulos, John G.; Lambrakos, Samuel G.; Bernstein, Noam; Lyons, John L.; Stöferle, Thilo; Mahrt, Rainer F.; Kovalenko, Maksym V.; Norris, David J.; Rainò, Gabriele; Efros, Alexander L.

2018-01-01

Nanostructured semiconductors emit light from electronic states known as excitons. For organic materials, Hund’s rules state that the lowest-energy exciton is a poorly emitting triplet state. For inorganic semiconductors, similar rules predict an analogue of this triplet state known as the ‘dark exciton’. Because dark excitons release photons slowly, hindering emission from inorganic nanostructures, materials that disobey these rules have been sought. However, despite considerable experimental and theoretical efforts, no inorganic semiconductors have been identified in which the lowest exciton is bright. Here we show that the lowest exciton in caesium lead halide perovskites (CsPbX3, with X = Cl, Br or I) involves a highly emissive triplet state. We first use an effective-mass model and group theory to demonstrate the possibility of such a state existing, which can occur when the strong spin-orbit coupling in the conduction band of a perovskite is combined with the Rashba effect. We then apply our model to CsPbX3 nanocrystals, and measure size- and composition-dependent fluorescence at the single-nanocrystal level. The bright triplet character of the lowest exciton explains the anomalous photon-emission rates of these materials, which emit about 20 and 1,000 times faster than any other semiconductor nanocrystal at room and cryogenic temperatures, respectively. The existence of this bright triplet exciton is further confirmed by analysis of the fine structure in low-temperature fluorescence spectra. For semiconductor nanocrystals, which are already used in lighting, lasers and displays, these excitons could lead to materials with brighter emission. More generally, our results provide criteria for identifying other semiconductors that exhibit bright excitons, with potential implications for optoelectronic devices.

On Electron Hole Evolution in Inhomogeneous Plasmas

Science.gov (United States)

Kuzichev, I.; Vasko, I.; Agapitov, O. V.; Mozer, F.; Artemyev, A.

2017-12-01

Electron holes (EHs) are the stationary localized non-linear structures in phase space existing due to an electron population trapped within EH electrostatic potential. EHs were found to be a common phenomenon in the Earth's magnetosphere. Such structures were observed in reconnecting current sheets, injection fronts in the outer radiation belt, and in many other situations. EHs usually propagate along magnetic field lines with velocities about electron thermal velocity, are localized on the scale of about 4-10 Debye lengths, and have the field amplitude up to hundreds of mV/m. Generation of these structures, evolution, and their role in relaxation of instabilities and energy dissipation, particle energization, supporting large-scale potential drops is under active investigation. In this report, we present the results of 1.5D gyrokinetic Vlasov-Maxwell simulations of the EH evolution in plasmas with inhomogeneous magnetic field and inhomogeneous density. Our calculations show that the inhomogeneity has a critical effect on the EH dynamics. EHs propagating into stronger (weaker) magnetic field are decelerated (accelerated) with deceleration (acceleration) rate dependent on the magnetic field gradient. During the deceleration of EH, the potential drop (weak double layer) along EH is generated. Such a potential drop might be experimentally observable even for single EH in the reconnecting current sheets. The same holds for the propagation in the plasma with inhomogeneous density. For some parameters of the system, the deceleration results in the turning of the hole. The interesting feature of this process is that the turning point depends only on the EH parameters, being independent of the average inhomogeneity scale. Our calculations also demonstrate the significant difference between "quasi-particle" concept and real evolution of the hole. Indeed, the EH is accelerated (decelerated) faster than it follows from a quasi-particle energy conservation law. It indicates

Triplet State Resonance Raman Spectrum of all-trans-diphenylbutadiene

DEFF Research Database (Denmark)

Wilbrandt, Robert Walter; Grossman, W.E.L.; Killough, P.M

1984-01-01

The resonance Raman spectrum of all-trans-diphenylbutadiene (DPB) in its ground state and the resonance Raman spectrum (RRS) of DPB in its short-lived electronically excited triplet state are reported. Transient spectra were obtained by a pump-probe technique using two pulsed lasers...

Triplet states at an O vacancy in alpha-quartz

DEFF Research Database (Denmark)

Lægsgaard, Jesper

2002-01-01

The energy landscape of an alpha-quartz O vacancy in the lowest triplet state is investigated. Four local minima are identified and geometries, total energies, and electron paramagnetic resonance (EPR) parameters are obtained. On the basis of calculated values for the magnetic dipole interaction...

Electrostatics of electron-hole interactions in van der Waals heterostructures

Science.gov (United States)

Cavalcante, L. S. R.; Chaves, A.; Van Duppen, B.; Peeters, F. M.; Reichman, D. R.

2018-03-01

The role of dielectric screening of electron-hole interaction in van der Waals heterostructures is theoretically investigated. A comparison between models available in the literature for describing these interactions is made and the limitations of these approaches are discussed. A simple numerical solution of Poisson's equation for a stack of dielectric slabs based on a transfer matrix method is developed, enabling the calculation of the electron-hole interaction potential at very low computational cost and with reasonable accuracy. Using different potential models, direct and indirect exciton binding energies in these systems are calculated within Wannier-Mott theory, and a comparison of theoretical results with recent experiments on excitons in two-dimensional materials is discussed.

Birth weight in a large series of triplets

Directory of Open Access Journals (Sweden)

van Beijsterveldt Catharina EM

2011-04-01

Full Text Available Abstract Background Triplets are often born premature and with a low birth weight. Because the incidence of triplet births is rare, there are relatively few studies describing triplet birth weight characteristics. Earlier studies are often characterized by small sample sizes and lack information on important background variables such as zygosity. The objective of this study is to examine factors associated with birth weight in a large, population-based sample of triplets registered with the Netherlands Twin Register (NTR. Methods In a sample of 1230 triplets from 410 families, the effects of assisted reproductive techniques, zygosity, birth order, gestational age, sex, maternal smoking and alcohol consumption during pregnancy on birth weight were assessed. The resemblance among triplets for birth weight was estimated as a function of zygosity. Birth weight discordance within families was studied by the pair-wise difference between triplets, expressed as a percentage of the birth weight of the heaviest child. We compare data from triplets registered with the NTR with data from population records, which include live births, stillbirths and children that have deceased within days after birth. Results There was no effect of assisted reproductive techniques on triplet birth weight. At gestational age 24 to 40 weeks triplets gained on average 130 grams per week; boys weighed 110 grams more than girls and triplets of smoking mothers weighted 104 grams less than children of non-smoking mothers. Monozygotic triplets had lower birth weights than di- and trizygotic triplets and birth weight discordance was smaller in monozygotic triplets than in di- and trizygotic triplets. The correlation in birth weight among monozygotic and dizygotic triplets was 0.42 and 0.32, respectively. In nearly two-thirds of the families, the heaviest and the lightest triplet had a birth weight discordance over 15%. The NTR sample is representative for the Dutch triplet

Harvesting multiple electron-hole pairs generated through plasmonic excitation of Au nanoparticles.

Science.gov (United States)

Kim, Youngsoo; Smith, Jeremy G; Jain, Prashant K

2018-05-07

Multi-electron redox reactions, although central to artificial photosynthesis, are kinetically sluggish. Amidst the search for synthetic catalysts for such processes, plasmonic nanoparticles have been found to catalyse multi-electron reduction of CO 2 under visible light. This example motivates the need for a general, insight-driven framework for plasmonic catalysis of such multi-electron chemistry. Here, we elucidate the principles underlying the extraction of multiple redox equivalents from a plasmonic photocatalyst. We measure the kinetics of electron harvesting from a gold nanoparticle photocatalyst as a function of photon flux. Our measurements, supported by theoretical modelling, reveal a regime where two-electron transfer from the excited gold nanoparticle becomes prevalent. Multiple electron harvesting becomes possible under continuous-wave, visible-light excitation of moderate intensity due to strong interband transitions in gold and electron-hole separation accomplished using a hole scavenger. These insights will help expand the utility of plasmonic photocatalysis beyond CO 2 reduction to other challenging multi-electron, multi-proton transformations such as N 2 fixation.

DNA Photosensitization by an "Insider": Photophysics and Triplet Energy Transfer of 5-Methyl-2-pyrimidone Deoxyribonucleoside.

Science.gov (United States)

Bignon, Emmanuelle; Gattuso, Hugo; Morell, Christophe; Dumont, Elise; Monari, Antonio

2015-08-03

The main chromophore of (6-4) photoproducts, namely, 5-methyl-2-pyrimidone (Pyo), is an artificial noncanonical nucleobase. This chromophore has recently been reported as a potential photosensitizer that induces triplet damage in thymine DNA. In this study, we investigate the spectroscopic properties of the Pyo unit embedded in DNA by means of explicit solvent molecular-dynamics simulations coupled to time-dependent DFT and quantum-mechanics/molecular-mechanics techniques. Triplet-state transfer from the Pyo to the thymine unit was monitored in B-DNA by probing the propensity of this photoactive pyrimidine analogue to induce a Dexter-type triplet photosensitization and subsequent DNA damage. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Diffusive scattering of electrons by electron holes around injection fronts

Science.gov (United States)

Vasko, I. Y.; Agapitov, O. V.; Mozer, F. S.; Artemyev, A. V.; Krasnoselskikh, V. V.; Bonnell, J. W.

2017-03-01

Van Allen Probes have detected nonlinear electrostatic spikes around injection fronts in the outer radiation belt. These spikes include electron holes (EH), double layers, and more complicated solitary waves. We show that EHs can efficiently scatter electrons due to their substantial transverse electric fields. Although the electron scattering driven by EHs is diffusive, it cannot be evaluated via the standard quasi-linear theory. We derive analytical formulas describing local electron scattering by a single EH and verify them via test particle simulations. We show that the most efficiently scattered are gyroresonant electrons (crossing EH on a time scale comparable to the local electron gyroperiod). We compute bounce-averaged diffusion coefficients and demonstrate their dependence on the EH spatial distribution (latitudinal extent and spatial filling factor) and individual EH parameters (amplitude of electrostatic potential, velocity, and spatial scales). We show that EHs can drive pitch angle scattering of ≲5 keV electrons at rates 10-2-10-4 s-1 and, hence, can contribute to electron losses and conjugated diffuse aurora brightenings. The momentum and pitch angle scattering rates can be comparable, so that EHs can also provide efficient electron heating. The scattering rates driven by EHs at L shells L ˜ 5-8 are comparable to those due to chorus waves and may exceed those due to electron cyclotron harmonics.

Stability of Sarma phases in density imbalanced electron-hole bilayer systems

International Nuclear Information System (INIS)

Subasi, A. L.; Tanatar, B.; Pieri, P.; Senatore, G.

2010-01-01

We study excitonic condensation in an electron-hole bilayer system with unequal layer densities at zero temperature. Using mean-field theory we solve the Bardeen-Cooper-Schrieffer (BCS) gap equations numerically and investigate the effects of intralayer interactions. The electron-hole system evolves from BCS in the weak coupling limit to Bose-Einstein condensation (BEC) in the strong coupling limit. We analyze the stability of the Sarma phase with k,-k pairing by calculating the superfluid mass density and also by checking the compressibility matrix. We find that with bare Coulomb interactions the superfluid density is always positive in the Sarma phase, due to a peculiar momentum structure of the gap function originating from the singular behavior of the Coulomb potential at zero momentum and the presence of a sharp Fermi surface. Introducing a simple model for screening, we find that the superfluid density becomes negative in some regions of the phase diagram, corresponding to an instability toward a Fulde-Ferrel-Larkin-Ovchinnikov-type superfluid phase. Thus, intralayer interaction and screening together can lead to a rich phase diagram in the BCS-BEC crossover regime in electron-hole bilayer systems.

Hole-induced d"0 ferromagnetism enhanced by Na-doping in GaN

International Nuclear Information System (INIS)

Zhang, Yong; Li, Feng

2017-01-01

The d"0 ferromagnetism in wurtzite GaN is investigated by the first-principle calculations. It is found that spontaneous magnetization occurs if sufficient holes are injected in GaN. Both Ga vacancy and Na doping can introduce holes into GaN. However, Ga vacancy has a high formation energy, and is thus unlikely to occur in a significant concentration. In contrast, Na doping has relatively low formation energy. Under N-rich growth condition, Na doping with a sufficient concentration can be achieved, which can induce half-metallic ferromagnetism in GaN. Moreover, the estimated Curie temperature of Na-doped GaN is well above the room temperature. - Highlights: • Hole-induced ferromagnetism in GaN is confirmed. • Both Ga Vacancy and Na-doping can introduce hole into GaN. • The concentration of Ga vacancy is too low to induce detectable ferromagnetism. • Na-doped GaN is a possible ferromagnet with a high curie-temperature.

Resonance fluorescence and electron spin in semiconductor quantum dots

Energy Technology Data Exchange (ETDEWEB)

Zhao, Yong

2009-11-18

The work presented in this dissertation contains the first observation of spin-resolved resonance fluorescence from a single quantum dot and its application of direct measurement of electron spin dynamics. The Mollow triplet and the Mollow quintuplet, which are the hallmarks of resonance fluorescence, are presented as the non-spin-resolved and spin-resolved resonance fluorescence spectrum, respectively. The negligible laser background contribution, the near pure radiative broadened spectrum and the anti-bunching photon statistics imply the sideband photons are background-free and near transform-limited single photons. This demonstration is a promising step towards the heralded single photon generation and electron spin readout. Instead of resolving spectrum, an alternative spin-readout scheme by counting resonance fluorescence photons under moderate laser power is demonstrated. The measurements of n-shot time-resolved resonance fluorescence readout are carried out to reveal electron spin dynamics of the measurement induced back action and the spin relaxation. Hyperfine interaction and heavy-light hole mixing are identified as the relevant mechanisms for the back action and phonon-assistant spin-orbit interaction dominates the spin relaxation. After a detailed discussion on charge-spin configurations in coupled quantum dots system, the single-shot readout on electron spin are proposed. (orig.)

Resonance fluorescence and electron spin in semiconductor quantum dots

International Nuclear Information System (INIS)

Zhao, Yong

2009-01-01

The work presented in this dissertation contains the first observation of spin-resolved resonance fluorescence from a single quantum dot and its application of direct measurement of electron spin dynamics. The Mollow triplet and the Mollow quintuplet, which are the hallmarks of resonance fluorescence, are presented as the non-spin-resolved and spin-resolved resonance fluorescence spectrum, respectively. The negligible laser background contribution, the near pure radiative broadened spectrum and the anti-bunching photon statistics imply the sideband photons are background-free and near transform-limited single photons. This demonstration is a promising step towards the heralded single photon generation and electron spin readout. Instead of resolving spectrum, an alternative spin-readout scheme by counting resonance fluorescence photons under moderate laser power is demonstrated. The measurements of n-shot time-resolved resonance fluorescence readout are carried out to reveal electron spin dynamics of the measurement induced back action and the spin relaxation. Hyperfine interaction and heavy-light hole mixing are identified as the relevant mechanisms for the back action and phonon-assistant spin-orbit interaction dominates the spin relaxation. After a detailed discussion on charge-spin configurations in coupled quantum dots system, the single-shot readout on electron spin are proposed. (orig.)

Light grand unified theory triplets and Yukawa splitting

International Nuclear Information System (INIS)

Rakshit, Subhendu; Shadmi, Yael; Raz, Guy; Roy, Sourov

2004-01-01

Triplet-mediated proton decay in grand unified theories (GUTs) is usually suppressed by arranging a large triplet mass. Here we explore instead a mechanism for suppressing the couplings of the triplets to the first and second generations compared to the Yukawa couplings, so that the triplets can be light. This mechanism is based on a 'triplet symmetry' in the context of product-group GUTs. We study two possibilities. The first possibility, which requires the top Yukawa coupling to arise from a nonrenormalizable operator at the GUT scale, is that all triplet couplings to matter are negligible, so that the triplets can be at the weak scale, giving new evidence for grand unification. The second possibility is that some triplet couplings, and in particular Ttb and Tt-barl-bar, are equal to the corresponding Yukawa couplings. This would give a distinct signature of grand unification if the triplets were sufficiently light. However, we derive a model-independent bound on the triplet mass in this case, which is at least 10 6 GeV. Finally, we construct an explicit viable GUT model based on Yukawa splitting, with the triplets at 10 14 GeV, as required for coupling unification to work. This model requires no additional thresholds below the GUT scale

Amorphous germanium as an electron or hole blocking contact on high-purity germanium detectors

International Nuclear Information System (INIS)

Hansen, W.L.; Haller, E.E.

1976-10-01

Experiments were performed in an attempt to make thin n + contacts on high-purity germanium by the solid phase/sup 1)/ epitaxial regrowth of arsenic doped amorphous germanium. After cleaning the crystal surface with argon sputtering and trying many combinations of layers, it was not found possible to induce recrystallization below 400 0 C. However, it was found that simple thermally evaporated amorphous Ge made fairly good electron or hole blocking contacts. Excellent spectrometers have been made with amorphous Ge replacing the n + contact. As presently produced, the amorphous Ge contact diodes show a large variation in high-voltage leakage current

Neutron induced electron radiography

International Nuclear Information System (INIS)

Andrade, Marcos Leandro Garcia

2008-01-01

In the present paper a new radiography technique, the 'Neutron Induced Electron Radiography' - NIER, to inspect low thickness samples on the order of micra, has been developed. This technique makes use of low energy electrons as penetrating radiation generated from metallic gadolinium screens when irradiated by thermal neutrons. The conditions to obtain the best image for the conventional X-ray film Kodak-AA were determined by using a digital system to quantify the darkening level of the film. The irradiations have been performed at a radiography equipment installed at the beam-hole no. 8 of the 5 MW IEA-R1 nuclear research reactor of IPEN-CNEN/SP. The irradiation time to obtain the best radiography was 100 seconds and for such condition the technique was able to discern 1 μm in 24 μm of aluminum at a resolution of 32 μm. By visual comparison the images obtained by the NIER shown a higher quality when compared with the ones from other usual techniques the make use of electrons a penetrating radiation and films for image registration. Furthermore the use of the digital system has provided a smaller time for data acquisition and data analysis as well as an improvement in the image visualization. (author)

Effects of model approximations for electron, hole, and photon transport in swift heavy ion tracks

Energy Technology Data Exchange (ETDEWEB)

Rymzhanov, R.A. [Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Moscow Region (Russian Federation); Medvedev, N.A., E-mail: nikita.medvedev@fzu.cz [Department of Radiation and Chemical Physics, Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 182 21 Prague 8 (Czech Republic); Laser Plasma Department, Institute of Plasma Physics, Czech Academy of Sciences, Za Slovankou 3, 182 00 Prague 8 (Czech Republic); Volkov, A.E. [Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Moscow Region (Russian Federation); National Research Centre ‘Kurchatov Institute’, Kurchatov Sq. 1, 123182 Moscow (Russian Federation); Lebedev Physical Institute of the Russian Academy of Sciences, Leninskij pr., 53,119991 Moscow (Russian Federation); National University of Science and Technology MISiS, Leninskij pr., 4, 119049 Moscow (Russian Federation); National Research Nuclear University MEPhI, Kashirskoye sh., 31, 115409 Moscow (Russian Federation)

2016-12-01

The event-by-event Monte Carlo code, TREKIS, was recently developed to describe excitation of the electron subsystems of solids in the nanometric vicinity of a trajectory of a nonrelativistic swift heavy ion (SHI) decelerated in the electronic stopping regime. The complex dielectric function (CDF) formalism was applied in the used cross sections to account for collective response of a matter to excitation. Using this model we investigate effects of the basic assumptions on the modeled kinetics of the electronic subsystem which ultimately determine parameters of an excited material in an SHI track. In particular, (a) effects of different momentum dependencies of the CDF on scattering of projectiles on the electron subsystem are investigated. The ‘effective one-band’ approximation for target electrons produces good coincidence of the calculated electron mean free paths with those obtained in experiments in metals. (b) Effects of collective response of a lattice appeared to dominate in randomization of electron motion. We study how sensitive these effects are to the target temperature. We also compare results of applications of different model forms of (quasi-) elastic cross sections in simulations of the ion track kinetics, e.g. those calculated taking into account optical phonons in the CDF form vs. Mott’s atomic cross sections. (c) It is demonstrated that the kinetics of valence holes significantly affects redistribution of the excess electronic energy in the vicinity of an SHI trajectory as well as its conversion into lattice excitation in dielectrics and semiconductors. (d) It is also shown that induced transport of photons originated from radiative decay of core holes brings the excess energy faster and farther away from the track core, however, the amount of this energy is relatively small.

Radiation-induced damage and recovery effects in GG17 glass irradiated by 1 MeV electrons

International Nuclear Information System (INIS)

Wang Qingyan; Zhang Zhonghua; Geng Hongbin; Sun Chengyue; Yang Dezhuang; He Shiyu; Hu Zhaochu

2012-01-01

The optical properties and microstructural damage of GG17 glasses, as well as their recovery during annealing at room temperature, are investigated after exposure to 1 MeV electrons with various fluences. Experimental results show that the electrons lead to severe optical degradation in the GG17 glass, and induce the formation of paramagnetic defects which can be mainly attributed to the boron–oxygen hole centers. With increasing annealing time at room temperature their decay serves as long-lived defects following first order kinetics. Except for the strong absorption bands located at 334–352 nm and 480 nm that corresponds to the boron–oxygen hole centers, weaker absorption bands appear at 780 nm or 794.6 nm after irradiation, inducing a decrease in transmittance by approximately 17% for a fluence of 1 × 10 16 cm −2 . It is shown that electron irradiation could cause a harmful effect on rubidium lamps when GG17 glass is used as the lamp envelope material.

Long-Lived Triplet Excited States of Bent-Shaped Pentacene Dimers by Intramolecular Singlet Fission.

Science.gov (United States)

Sakuma, Takao; Sakai, Hayato; Araki, Yasuyuki; Mori, Tadashi; Wada, Takehiko; Tkachenko, Nikolai V; Hasobe, Taku

2016-03-24

Intramolecular singlet fission (ISF) is a promising photophysical process to construct more efficient light energy conversion systems as one excited singlet state converts into two excited triplet states. Herein we synthesized and evaluated bent-shaped pentacene dimers as a prototype of ISF to reveal intrinsic characters of triplet states (e.g., lifetimes of triplet excited states). In this study, meta-phenylene-bridged TIPS-pentacene dimer (PcD-3Ph) and 2,2'-bipheynyl bridged TIPS-pentacene dimer (PcD-Biph) were newly synthesized as bent-shaped dimers. In the steady-state spectroscopy, absorption and emission bands of these dimers were fully characterized, suggesting the appropriate degree of electronic coupling between pentacene moieties in these dimers. In addition, the electrochemical measurements were also performed to check the electronic interaction between two pentacene moieties. Whereas the successive two oxidation peaks owing to the delocalization were observed in a directly linked-pentacene dimer (PcD) by a single bond, the cyclic voltammograms in PcD-Biph and PcD-3Ph implied the weaker interaction compared to that of p-phenylene-bridged TIPS-pentacene dimer (PcD-4Ph) and PcD. The femtosecond and nanosecond transient absorption spectra clearly revealed the slower ISF process in bent-shaped pentacene dimers (PcD-Biph and PcD-3Ph), more notably, the slower relaxation of the excited triplet states in PcD-Biph and PcD-3Ph. Namely, the quantum yields of triplet states (ΦT) by ISF approximately remain constant (ca. 180-200%) in all dimer systems, whereas the lifetimes of the triplet excited states became much longer (up to 360 ns) in PcD-Biph as compared to PcD-4Ph (15 ns). Additionally, the lifetimes of the corresponding triplet states in PcD-Biph and PcD-3Ph were sufficiently affected by solvent viscosity. In particular, the lifetimes of PcD-Biph triplet state in THF/paraffin (1.0 μs) increased up to approximately three times as compared to that in THF

Heats of Formation of Triplet Ethylene, Ethylidene, and Acetylene

Energy Technology Data Exchange (ETDEWEB)

Nguyen, M.T.; Matus, M.H.; Lester Jr, W.A.; Dixon, David A.

2007-06-28

Heats of formation of the lowest triplet state of ethylene and the ground triplet state of ethylidene have been predicted by high level electronic structure calculations. Total atomization energies obtained from coupled-cluster CCSD(T) energies extrapolated to the complete basis set limit using correlation consistent basis sets (CBS), plus additional corrections predict the following heats of formation in kcal/mol: Delta H0f(C2H4,3A1) = 80.1 at 0 K and 78.5 at 298 K, and Delta H0f(CH3CH,3A") = 86.8 at 0 K and 85.1 at 298 K, with an error of less than +-1.0 kcal/mol. The vertical and adiabatic singlet-triplet separation energies of ethylene were calculated as Delta ES-T,vert = 104.1 and Delta ES-T,adia = 65.8 kcal/mol. These results are in excellent agreement with recent quantum Monte Carlo (DMC) values of 103.5 +- 0.3 and 66.4 +- 0.3 kcal/mol. Both sets of computational values differ from the experimental estimate of 58 +- 3 kcal/mol for the adiabatic splitting. The computed singlet-triplet gap at 0 K for acetylene is Delta ES-T,adia(C2H2) = 90.5 kcal/mol, which is in notable disagreement with the experimental value of 82.6 kcal/mol. The heat of formation of the triplet is Delta H0f(C2H2,3B2) = 145.3 kcal/mol. There is a systematic underestimation of the singlet-triplet gaps in recent photodecomposition experiments by ~;;7 to 8 kcal/mol. For vinylidene, we predict Delta H0f(H2CC,1A1) = 98.8 kcal/mol at 298 K (exptl. 100.3 +- 4.0), Delta H0f(H2CC,3B2) = 146.2 at 298 K, and an energy gap Delta ES-T-adia(H2CC) = 47.7 kcal/mol.

Helical edge states and fractional quantum Hall effect in a graphene electron-hole bilayer.

Science.gov (United States)

Sanchez-Yamagishi, Javier D; Luo, Jason Y; Young, Andrea F; Hunt, Benjamin M; Watanabe, Kenji; Taniguchi, Takashi; Ashoori, Raymond C; Jarillo-Herrero, Pablo

2017-02-01

Helical 1D electronic systems are a promising route towards realizing circuits of topological quantum states that exhibit non-Abelian statistics. Here, we demonstrate a versatile platform to realize 1D systems made by combining quantum Hall (QH) edge states of opposite chiralities in a graphene electron-hole bilayer at moderate magnetic fields. Using this approach, we engineer helical 1D edge conductors where the counterpropagating modes are localized in separate electron and hole layers by a tunable electric field. These helical conductors exhibit strong non-local transport signals and suppressed backscattering due to the opposite spin polarizations of the counterpropagating modes. Unlike other approaches used for realizing helical states, the graphene electron-hole bilayer can be used to build new 1D systems incorporating fractional edge states. Indeed, we are able to tune the bilayer devices into a regime hosting fractional and integer edge states of opposite chiralities, paving the way towards 1D helical conductors with fractional quantum statistics.

Triplet ultrasound growth parameters.

Science.gov (United States)

Vora, Neeta L; Ruthazer, Robin; House, Michael; Chelmow, David

2006-03-01

To create ultrasound growth curves for normal growth of fetal triplets using statistical methodology that properly accounts for similarities of growth of fetuses within a mother as well as repeated measurements over time for each fetus. In this longitudinal study, all triplet pregnancies managed at a single tertiary center from 1992-2004 were reviewed. Fetuses with major anomalies, prior selective reduction, or fetal demise were excluded. Data from early and late gestation in which there were fewer than 30 fetal measurements available for analysis were excluded. We used multilevel models to account for variation in growth within a single fetus over time, variations in growth between multiple fetuses within a single mother, and variations in fetal growth between mothers. Medians (50th), 10th, and 90th percentiles were estimated by the creation of multiple quadratic growth models from bootstrap samples adapting a previously published method to compute prediction intervals. Estimated fetal weight was derived from Hadlock's formula. One hundred fifty triplet pregnancies were identified. Twenty-seven pregnancies were excluded for the following reasons: missing records (23), fetal demise (3), and fetal anomaly (1). The study group consisted of 123 pregnancies. The gestational age range was restricted to 14-34 weeks. Figures and tables were developed showing medians, 10th and 90th percentiles for estimated fetal weight, femur length, biparietal diameter, abdominal circumference, and head circumference. Growth curves for triplet pregnancies were derived. These may be useful for identification of abnormal growth in triplet fetuses. III.

Identification of electron and hole traps in KH2PO4 crystals

International Nuclear Information System (INIS)

Garces, N. Y.; Stevens, K. T.; Halliburton, L. E.; Demos, S. G.; Radousky, H. B.; Zaitseva, N. P.

2001-01-01

Electron paramagnetic resonance (EPR) has been used to characterize a hole trap and several electron traps in single crystals of potassium dihydrogen phosphate (KH 2 PO 4 or KDP). The paramagnetic charge states of these centers are produced by ionizing radiation (e.g., x rays or a 266 nm beam from a pulsed Nd:YAG laser) and are stable for days and even weeks at room temperature. One center consists of a hole trapped on an oxygen ion adjacent to a silicon impurity located on a phosphorus site. This defect has a small, but easily observed, hyperfine interaction with the adjacent substitutional proton. The other centers are formed when an electron is trapped at an oxygen vacancy. These latter defects are best described as (PO 3 ) 2- molecular ions, where the primary phosphorus nucleus is responsible for a large hyperfine splitting (500--800 G in magnitude). Five EPR spectra representing variations of these oxygen vacancy centers are observed, with the differences being attributed to the relative position of a nearby cation vacancy, either a missing proton or potassium. An angular study of the EPR spectra, conducted at room temperature, provided principal values and principal directions for the g matrices and hyperfine matrices for the hole center and two of the electron centers

Interplay between singlet and triplet excited states in a conformationally locked donor–acceptor dyad

KAUST Repository

Filatov, Mikhail A.

2015-10-13

The synthesis and photophysical characterization of a palladium(II) porphyrin – anthracene dyad bridged via short and conformationally rigid bicyclo[2.2.2]octadiene spacer were achieved. A spectroscopic investigation of the prepared molecule in solution has been undertaken to study electronic energy transfer in excited singlet and triplet states between the anthracene and porphyrin units. By using steady-state and time-resolved photoluminescence spectroscopy it was shown that excitation of the singlet excited state of the anthracene leads to energy transfer to the lower-lying singlet state of porphyrin. Alternatively, excitation of the porphyrin followed by intersystem crossing to the triplet state leads to very fast energy transfer to the triplet state of anthracene. The rate of this energy transfer has been determined by transient absorption spectroscopy. Comparative studies of the dynamics of triplet excited states of the dyad and reference palladium octaethylporphyrin (PdOEP) have been performed.

Interplay between singlet and triplet excited states in a conformationally locked donor–acceptor dyad

KAUST Repository

Filatov, Mikhail A.; Etzold, Fabian; Gehrig, Dominik; Laquai, Fré dé ric; Busko, Dmitri; Landfester, Katharina; Baluschev, Stanislav

2015-01-01

The synthesis and photophysical characterization of a palladium(II) porphyrin – anthracene dyad bridged via short and conformationally rigid bicyclo[2.2.2]octadiene spacer were achieved. A spectroscopic investigation of the prepared molecule in solution has been undertaken to study electronic energy transfer in excited singlet and triplet states between the anthracene and porphyrin units. By using steady-state and time-resolved photoluminescence spectroscopy it was shown that excitation of the singlet excited state of the anthracene leads to energy transfer to the lower-lying singlet state of porphyrin. Alternatively, excitation of the porphyrin followed by intersystem crossing to the triplet state leads to very fast energy transfer to the triplet state of anthracene. The rate of this energy transfer has been determined by transient absorption spectroscopy. Comparative studies of the dynamics of triplet excited states of the dyad and reference palladium octaethylporphyrin (PdOEP) have been performed.

Many-body correlation effects in the spatially separated electron and hole layers in the coupled quantum wells

Energy Technology Data Exchange (ETDEWEB)

Babichenko, V.S. [RRC Kurchatov Institute, Kurchatov Sq., 1, 123182 Moscow (Russian Federation); Polishchuk, I.Ya., E-mail: iyppolishchuk@gmail.com [RRC Kurchatov Institute, Kurchatov Sq., 1, 123182 Moscow (Russian Federation); Moscow Institute of Physics and Technology, 141700, 9, Institutskii per., Dolgoprudny, Moscow Region (Russian Federation)

2014-11-15

The many-body correlation effects in the spatially separated electron and hole layers in the coupled quantum wells are investigated. A special case of the many-component electron–hole system is considered. It is shown that if the hole mass is much greater than the electron mass, the negative correlation energy is mainly determined by the holes. The ground state of the system is found to be the 2D electron–hole liquid with the energy smaller than the exciton phase. It is shown that the system decays into the spatially separated neutral electron–hole drops if the initially created charge density in the layers is smaller than the certain critical value n{sub eq}.

The effects of electron-hole separation on the photoconductivity of individual metal oxide nanowires

International Nuclear Information System (INIS)

Prades, J D; Hernandez-Ramirez, F; Jimenez-Diaz, R; Manzanares, M; Andreu, T; Cirera, A; Romano-Rodriguez, A; Morante, J R

2008-01-01

The responses of individual ZnO nanowires to UV light demonstrate that the persistent photoconductivity (PPC) state is directly related to the electron-hole separation near the surface. Our results demonstrate that the electrical transport in these nanomaterials is influenced by the surface in two different ways. On the one hand, the effective mobility and the density of free carriers are determined by recombination mechanisms assisted by the oxidizing molecules in air. This phenomenon can also be blocked by surface passivation. On the other hand, the surface built-in potential separates the photogenerated electron-hole pairs and accumulates holes at the surface. After illumination, the charge separation makes the electron-hole recombination difficult and originates PPC. This effect is quickly reverted after increasing either the probing current (self-heating by Joule dissipation) or the oxygen content in air (favouring the surface recombination mechanisms). The model for PPC in individual nanowires presented here illustrates the intrinsic potential of metal oxide nanowires to develop optoelectronic devices or optochemical sensors with better and new performances.

Interaction of non-equilibrium phonons with electron-hole plasmas in germanium

International Nuclear Information System (INIS)

Kirch, S.J.

1985-01-01

This thesis presents results of experiments on the interaction of phonons and photo-excited electron-hole plasmas in Ge at low temperature. The first two studies involved the low-temperature fluid phase known as the electron-hole liquid (EHL). The third study involved a wider range of temperatures and includes the higher temperature electron-hole plasma (EHP). In the first experiment, superconducting tunnel junctions are used to produce quasi-monochromatic phonons, which propagate through the EHL. The magnitude of the absorption of these non-equilibrium phonons gives a direct measure of the coupling constant, the deformation potential. In the second experiment, the nonequilibrium phonons are generated by laser excitation of a metal film. An unusual sample geometry allows examination of the EHL-phonon interaction near the EHL excitation surface. This coupling is examined for both cw and pulsed EHL excitation. In the third experiment, the phonons are byproducts of the photo-excited carrier thermalization. The spatial, spectral and temporal dependence of the recombination luminescence is examined. A phonon wind force is observed to dominate the transport properties of the EHL and the EHP. These carriers are never observed to move faster than the phonon velocity even during the laser pulse

Ultrafast carrier dynamics in tetrahedral amorphous carbon: carrier trapping versus electron-hole recombination

International Nuclear Information System (INIS)

Carpene, E; Mancini, E; Dallera, C; Schwen, D; Ronning, C; Silvestri, S De

2007-01-01

We report the investigation of the ultrafast carrier dynamics in thin tetrahedral amorphous carbon films by means of femtosecond time-resolved reflectivity. We estimated the electron-phonon relaxation time of a few hundred femtoseconds and we observed that under low optical excitation photo-generated carriers decay according to two distinct mechanisms attributed to trapping by defect states and direct electron-hole recombination. With high excitation, when photo-carrier and trap densities are comparable, a unique temporal evolution develops, as the time dependence of the trapping process becomes degenerate with the electron-hole recombination. This experimental evidence highlights the role of defects in the ultrafast electronic dynamics and is not specific to this particular form of carbon, but has general validity for amorphous and disordered semiconductors

σ-holes and π-holes: Similarities and differences.

Science.gov (United States)

Politzer, Peter; Murray, Jane S

2018-04-05

σ-Holes and π-holes are regions of molecules with electronic densities lower than their surroundings. There are often positive electrostatic potentials associated with them. Through these potentials, the molecule can interact attractively with negative sites, such as lone pairs, π electrons, and anions. Such noncovalent interactions, "σ-hole bonding" and "π-hole bonding," are increasingly recognized as being important in a number of different areas. In this article, we discuss and compare the natures and characteristics of σ-holes and π-holes, and factors that influence the strengths and locations of the resulting electrostatic potentials. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Photochemical transformation of benzotriazole, relevant to sunlit surface waters: Assessing the possible role of triplet-sensitised processes

International Nuclear Information System (INIS)

Bianco, Angelica; Fabbri, Debora; Minella, Marco; Brigante, Marcello; Mailhot, Gilles; Maurino, Valter; Minero, Claudio; Vione, Davide

2016-01-01

The corrosion inhibitor 1H-benzotriazole (pK a = 8.4) can exist in two different forms in natural waters, and photochemical transformation is a potentially significant attenuation pathway for both of them. Depending on conditions, the modelled half-life times range from some days/weeks to several months. In sunlit water bodies, the acidic (neutral) form would undergo direct photolysis (accounting for up to 7% of total phototransformation) and, most notably, reaction with the hydroxyl radicals ( · OH) and the triplet states of chromophoric dissolved organic matter ( 3 CDOM*). The basic (anionic) form would undergo significant transformation with · OH and 3 CDOM*. The · OH reactions would be more important at low dissolved organic carbon (DOC) and the 3 CDOM* processes at high DOC. In the presence of highly reactive triplet-state model compounds, the two benzotriazole forms react with similar rate constants. In this case, they would show comparable half-life times in surface-water environments. With less reactive triplet states, the rate constant of the anionic form can be a couple of orders of magnitude higher than that of the neutral one. Under these circumstances, the neutral form could be considerably more photostable than the anionic one at high DOC. Therefore, depending on 3 CDOM* reactivity, the solution pH may or may not play an important role in the photoattenuation kinetics of 1H-benzotriazole in sunlit natural waters, especially at high DOC. Both forms of benzotriazole yield hydroxyderivatives as their main transformation intermediates under all the relevant photochemical reaction pathways. These intermediates could be formed via · OH-induced hydroxylation, or upon electron abstraction followed by reaction with water. Differently from UVC irradiation data reported in previous studies, the concentration of aniline upon excitation of 1H-benzotriazole under environmentally significant UV wavelengths was always below the detection limit of the analytical

Enhancing carrier injection in the active region of a 280nm emission wavelength LED using graded hole and electron blocking layers

KAUST Repository

Janjua, Bilal; Ng, Tien Khee; Alyamani, Ahmed Y.; El-Desouki, Munir M.; Ooi, Boon S.

2014-01-01

A theoretical investigation of AlGaN UV-LED with band engineering of hole and electron blocking layers (HBL and EBL, respectively) was conducted with an aim to improve injection efficiency and reduce efficiency droop in the UV LEDs. The analysis is based on energy band diagrams, carrier distribution and recombination rates (Shockley-Reed-Hall, Auger, and radiative recombination rates) in the quantum well, under equilibrium and forward bias conditions. Electron blocking layer is based on AlaGa1-aN / Al b → cGa1-b → 1-cN / AldGa 1-dN, where a < d < b < c. A graded layer sandwiched between large bandgap AlGaN materials was found to be effective in simultaneously blocking electrons and providing polarization field enhanced carrier injection. The graded interlayer reduces polarization induced band bending and mitigates the related drawback of impediment of holes injection. Similarly on the n-side, the Alx → yGa1-x → 1-yN / AlzGa 1-zN (x < z < y) barrier acts as a hole blocking layer. The reduced carrier leakage and enhanced carrier density in the active region results in significant improvement in radiative recombination rate compared to a structure with the conventional rectangular EBL layers. The improvement in device performance comes from meticulously designing the hole and electron blocking layers to increase carrier injection efficiency. The quantum well based UV-LED was designed to emit at 280nm, which is an effective wavelength for water disinfection application.

Enhancing carrier injection in the active region of a 280nm emission wavelength LED using graded hole and electron blocking layers

KAUST Repository

Janjua, Bilal

2014-02-27

A theoretical investigation of AlGaN UV-LED with band engineering of hole and electron blocking layers (HBL and EBL, respectively) was conducted with an aim to improve injection efficiency and reduce efficiency droop in the UV LEDs. The analysis is based on energy band diagrams, carrier distribution and recombination rates (Shockley-Reed-Hall, Auger, and radiative recombination rates) in the quantum well, under equilibrium and forward bias conditions. Electron blocking layer is based on AlaGa1-aN / Al b → cGa1-b → 1-cN / AldGa 1-dN, where a < d < b < c. A graded layer sandwiched between large bandgap AlGaN materials was found to be effective in simultaneously blocking electrons and providing polarization field enhanced carrier injection. The graded interlayer reduces polarization induced band bending and mitigates the related drawback of impediment of holes injection. Similarly on the n-side, the Alx → yGa1-x → 1-yN / AlzGa 1-zN (x < z < y) barrier acts as a hole blocking layer. The reduced carrier leakage and enhanced carrier density in the active region results in significant improvement in radiative recombination rate compared to a structure with the conventional rectangular EBL layers. The improvement in device performance comes from meticulously designing the hole and electron blocking layers to increase carrier injection efficiency. The quantum well based UV-LED was designed to emit at 280nm, which is an effective wavelength for water disinfection application.

Synthesis and Exciton Dynamics of Triplet Sensitized Conjugated Polymers

KAUST Repository

Andernach, Rolf

2015-07-22

We report the synthesis of a novel polythiophene-based host-guest copolymer incorporating a Pt-porphyrin complex (TTP-Pt) into the backbone for efficient singlet to triplet polymer exciton sensitization. We elucidated the exciton dynamics in thin films of the material by means of Transient Absorption Spectrosopcy (TAS) on multiple timescales and investigated the mechanism of triplet exciton formation. During sensitization, single exciton diffusion is followed by exciton transfer from the polymer backbone to the complex where it undergoes intersystem crossing to the triplet state of the complex. We directly monitored the triplet exciton back transfer from the Pt-porphyrin to the polymer and find that 60% of the complex triplet excitons are transferred with a time constant of 1087 ps. We propose an equilibrium between polymer and porphyrin triplet states as a result of the low triplet diffusion length in the polymer backbone and hence an increased local triplet population resulting in increased triplet-triplet annihilation. This novel system has significant implications for the design of novel materials for triplet sensitized solar cells and up-conversion layers.

Triplet exciton diffusion in organic semiconductors

Energy Technology Data Exchange (ETDEWEB)

Koehler, Anna [Department of Physics, University of Bayreuth (Germany)

2010-07-01

Efficient triplet exciton emission has allowed improved operation of organic light-emitting diodes (LEDs). To enhance the device performance, it is necessary to understand what governs the motion of triplet excitons through the organic semiconductor. We use a series of poly(p-phenylene)-type conjugated polymers and oligomers of variable degree of molecular distortion (i.e. polaron formation) and energetic disorder as model systems to study the Dexter-type triplet exciton diffusion in thin films. We show that triplet diffusion can be quantitatively described in the framework of a Holstein small polaron model (Marcus theory) that is extended to include contributions from energetic disorder. The model predicts a tunnelling process at low temperatures followed by a thermally activated hopping process above a transition temperature. In contrast to charge transfer, the activation energy required for triplet exciton transfer can be deduced from the optical spectra. We discuss the implications for device architecture.

Ultrafast Interfacial Electron and Hole Transfer from CsPbBr3 Perovskite Quantum Dots.

Science.gov (United States)

Wu, Kaifeng; Liang, Guijie; Shang, Qiongyi; Ren, Yueping; Kong, Degui; Lian, Tianquan

2015-10-14

Recently reported colloidal lead halide perovskite quantum dots (QDs) with tunable photoluminescence (PL) wavelengths covering the whole visible spectrum and exceptionally high PL quantum yields (QYs, 50-90%) constitute a new family of functional materials with potential applications in light-harvesting and -emitting devices. By transient absorption spectroscopy, we show that the high PL QYs (∼79%) can be attributed to negligible electron or hole trapping pathways in CsPbBr3 QDs: ∼94% of lowest excitonic states decayed with a single-exponential time constant of 4.5 ± 0.2 ns. Furthermore, excitons in CsPbBr3 QDs can be efficiently dissociated in the presence of electron or hole acceptors. The half-lives of electron transfer (ET) to benzoquinone and subsequent charge recombination are 65 ± 5 ps and 2.6 ± 0.4 ns, respectively. The half-lives for hole transfer (HT) to phenothiazine and the subsequent charge recombination are 49 ± 6 ps and 1.0 ± 0.2 ns, respectively. The lack of electron and hole traps and fast interfacial ET and HT rates are key properties that may enable the development of efficient lead halide perovskite QDs-based light-harvesting and -emitting devices.

Magnetic field enhanced electroluminescence in organic light emitting diodes based on electron donor-acceptor exciplex blends

Science.gov (United States)

Baniya, Sangita; Basel, Tek; Sun, Dali; McLaughlin, Ryan; Vardeny, Zeev Valy

2016-03-01

A useful process for light harvesting from injected electron-hole pairs in organic light emitting diodes (OLED) is the transfer from triplet excitons (T) to singlet excitons (S) via reverse intersystem crossing (RISC). This process adds a delayed electro-luminescence (EL) emission component that is known as thermally activated delayed fluorescence (TADF). We have studied electron donor (D)/acceptor(A) blends that form an exciplex manifold in which the energy difference, ΔEST between the lowest singlet (S1) and triplet (T1) levels is relatively small (exciplex blend is enhanced up to 40% by applying a relatively weak magnetic field of 50 mT at ambient. Moreover the MEL response is activated with activation energy similar that of the EL emission. This suggests that the large magneto-EL originates from an additional spin-mixing channel between singlet and triplet states of the generated exciplexes, which is due to TADF. We will report on the MEL dependencies on the temperature, bias voltage, and D-A materials for optimum OLED performance. Supported by SAMSUNG Global Research Outreach (GRO) program, and also by the NSF-Material Science & Engineering Center (MRSEC) program at the University of Utah (DMR-1121252).

Adaptive port-starboard beamforming of triplet arrays

NARCIS (Netherlands)

Beerens, S.P.; Been, R.; Groen, J.; Noutary, E.; Doisy, Y.

2000-01-01

Triplet arrays are single line arrays with three hydrophones on a circular section of the array. The triplet structure provides immediate port-starboard (PS) discrimination. This paper discusses the theoretical and experimental performance of triplet arrays. Results are obtained on detection gain

Quantum Monte Carlo study of the singlet-triplet transition in ethylene

International Nuclear Information System (INIS)

El Akramine, Ouafae; Kollias, Alexander C.; Lester, William A. Jr.

2003-01-01

A theoretical study is reported of the transition between the ground state ( 1 A g ) and the lowest triplet state (1 3 B 1u ) of ethylene based on the diffusion Monte Carlo (DMC) variant of the quantum Monte Carlo method. Using DMC trial functions constructed from Hartree-Fock, complete active space self-consistent field and multi-configuration self-consistent field wave functions, we have computed the atomization energy and the heat of formation of both states, and adiabatic and vertical energy differences between these states using both all-electron and effective core potential DMC. The ground state atomization energy and heat of formation are found to agree with experiment to within the error bounds of the computation and experiment. Predictions by DMC of the triplet state atomization energy and heat of formation are presented. The adiabatic singlet-triplet energy difference is found to differ by 5 kcal/mol from the value obtained in a recent photodissociation experiment

Delocalization of Coherent Triplet Excitons in Linear Rigid Rod Conjugated Oligomers.

Science.gov (United States)

Hintze, Christian; Korf, Patrick; Degen, Frank; Schütze, Friederike; Mecking, Stefan; Steiner, Ulrich E; Drescher, Malte

2017-02-02

In this work, the triplet state delocalization in a series of monodisperse oligo(p-phenyleneethynylene)s (OPEs) is studied by pulsed electron paramagnetic resonance (EPR) and pulsed electron nuclear double resonance (ENDOR) determining zero-field splitting, optical spin polarization, and proton hyperfine couplings. Neither the zero-field splitting parameters nor the optical spin polarization change significantly with OPE chain length, in contrast to the hyperfine coupling constants, which showed a systematic decrease with chain length n according to a 2/(1 + n) decay law. The results provide striking evidence for the Frenkel-type nature of the triplet excitons exhibiting full coherent delocalization in the OPEs under investigation with up to five OPE repeat units and with a spin density distribution described by a nodeless particle in the box wave function. The same model is successfully applied to recently published data on π-conjugated porphyrin oligomers.

Phase-space holes due to electron and ion beams accelerated by a current-driven potential ramp

Directory of Open Access Journals (Sweden)

M. V. Goldman

2003-01-01

Full Text Available One-dimensional open-boundary simulations have been carried out in a current-carrying plasma seeded with a neutral density depression and with no initial electric field. These simulations show the development of a variety of nonlinear localized electric field structures: double layers (unipolar localized fields, fast electron phase-space holes (bipolar fields moving in the direction of electrons accelerated by the double layer and trains of slow alternating electron and ion phase-space holes (wave-like fields moving in the direction of ions accelerated by the double layer. The principal new result in this paper is to show by means of a linear stability analysis that the slow-moving trains of electron and ion holes are likely to be the result of saturation via trapping of a kinetic-Buneman instability driven by the interaction of accelerated ions with unaccelerated electrons.

Efficient Algorithms for Computing the Triplet and Quartet Distance Between Trees of Arbitrary Degree

DEFF Research Database (Denmark)

Brodal, Gerth Stølting; Fagerberg, Rolf; Mailund, Thomas

2013-01-01

), respectively, and counting how often the induced topologies in the two input trees are different. In this paper we present efficient algorithms for computing these distances. We show how to compute the triplet distance in time O(n log n) and the quartet distance in time O(d n log n), where d is the maximal......The triplet and quartet distances are distance measures to compare two rooted and two unrooted trees, respectively. The leaves of the two trees should have the same set of n labels. The distances are defined by enumerating all subsets of three labels (triplets) and four labels (quartets...... degree of any node in the two trees. Within the same time bounds, our framework also allows us to compute the parameterized triplet and quartet distances, where a parameter is introduced to weight resolved (binary) topologies against unresolved (non-binary) topologies. The previous best algorithm...

First observation of liquid-xenon proportional electroluminescence in THGEM holes

International Nuclear Information System (INIS)

Arazi, L; Itay, R; Landsman, H; Levinson, L; Pasmantirer, B; Rappaport, M L; Vartsky, D; Breskin, A; Coimbra, A E C

2013-01-01

Radiation-induced proportional-electroluminescence UV signals, emitted from the holes of a Thick Gas Electron Multiplier (THGEM) electrode immersed in liquid xenon, were recorded with a PMT for the first time. Significant photon yields were observed with gamma photons and alpha particles using a 0.4 mm thick electrode with 0.3 mm diameter holes; at 2 kV across the THGEM the photon yield was estimated to be ∼ 600 UV photons/electron over 4π. This may pave the way towards the realization of novel single-phase noble-liquid radiation detectors incorporating liquid hole-multipliers (LHM); their concept is presented

Magnetic circular dichroism study of electron-irradiation induced defects in InP

International Nuclear Information System (INIS)

Gislason, H.P.

1989-01-01

A strong magnetic circular dichroism (MCD) absorption band centered at 1.07 eV in electron irradiated InP is reported. Temperature and magnetic field dependence of the signal reveal that the centre giving rise to this band is a spin triplet. By simulating neutral and reverse bias conditions of junction measurements through a careful choice of irradiation dose and starting material, the MCD band is shown to have an annealing behaviour closely resembling that of the majority carrier traps which control the Fermi level position in n- and p-type InP. The 1.07 eV MCD band represents the first magneto-optical signal connected with this family of complex irradiation-induced defects in InP. (author) 19 refs., 5 figs., 1 tab

Light-induced electronic non-equilibrium in plasmonic particles.

Science.gov (United States)

Kornbluth, Mordechai; Nitzan, Abraham; Seideman, Tamar

2013-05-07

We consider the transient non-equilibrium electronic distribution that is created in a metal nanoparticle upon plasmon excitation. Following light absorption, the created plasmons decohere within a few femtoseconds, producing uncorrelated electron-hole pairs. The corresponding non-thermal electronic distribution evolves in response to the photo-exciting pulse and to subsequent relaxation processes. First, on the femtosecond timescale, the electronic subsystem relaxes to a Fermi-Dirac distribution characterized by an electronic temperature. Next, within picoseconds, thermalization with the underlying lattice phonons leads to a hot particle in internal equilibrium that subsequently equilibrates with the environment. Here we focus on the early stage of this multistep relaxation process, and on the properties of the ensuing non-equilibrium electronic distribution. We consider the form of this distribution as derived from the balance between the optical absorption and the subsequent relaxation processes, and discuss its implication for (a) heating of illuminated plasmonic particles, (b) the possibility to optically induce current in junctions, and (c) the prospect for experimental observation of such light-driven transport phenomena.

Photoexcited riboflavin induces oxidative damage to human serum albumin

Science.gov (United States)

Hirakawa, Kazutaka; Yoshioka, Takuto

2015-08-01

Photoexcited riboflavin induced damage of human serum albumin (HSA), a water soluble protein, resulting in the diminishment of fluorescence from the tryptophan residue. Because riboflavin hardly photosensitized singlet oxygen generation and sodium azide, a singlet oxygen quencher, did not inhibit protein damage, electron transfer-mediated oxidation of HSA was speculated. Fluorescence lifetime of riboflavin was not affected by HSA, suggesting that the excited triplet state of riboflavin is responsible for protein damage through electron transfer. In addition, the preventive effect of xanthone derivatives, triplet quenchers, on photosensitized protein damage could be evaluated using this photosensitized reaction system of riboflavin and HSA.

Relation between bulk compressibility and surface energy of electron-hole liquids

International Nuclear Information System (INIS)

Singwi, K.S.; Tosi, M.P.

1979-08-01

Attention is drawn to the existence of an empirical relation chiσ/asup(*)sub(B) approximately 1 between the compressibility, the surface energy and the excitonic radius in electron-hole liquids. (author)

Dynamical effects of electron-hole correlation and giant quantum attenuation of ultrasound in semimetals

International Nuclear Information System (INIS)

Kuramoto, Y.

1982-01-01

The giant quantum attenuation of ultrasound in bismuth and other semimetals is noticeably enhanced when certain pair of Landau subbands of electrons and holes participate simultaneously in an attenuation peak. A theoretical analysis is presented which emphasizes importance of dynamical effects of the electron-hole correlation. In the temperature range between 1K and 4K covered by most experiments, the correlation effect is found to be weak on the real part of the relevant response function which gives change in sound velocity. This implies that equilibrium properties of the system are not much influenced by the correlation effect. Nonetheless, the electron-hole correlation is shown to have a drastic consequence on the imaginary part of the response function probed by the ultrasonic attenuation. Proposal for experiment is advanced to discriminate relative importance of this exciton-like correlation from that of repulsive correlation between carriers with the same charge. (orig.)

Triplet Focusing for Recirculating Linear Muon Accelerators

CERN Document Server

Keil, Eberhard

2001-01-01

Focusing by symmetrical triplets is studied for the linear accelerator lattices in recirculating muon accelerators with several passes where the ratio of final to initial muon energy is about four. Triplet and FODO lattices are compared. At similar acceptance, triplet lattices have straight sections for the RF cavities that are about twice as long as in FODO lat-tices. For the same energy gain, the total lengths of the linear accelerators with triplet lattices are about the same as of those with FODO lattices.

Fetomaternal outcome in triplet pregnancy

International Nuclear Information System (INIS)

Mazhar, S.B.; Furukh, T; Rahim, F.

2008-01-01

To determine maternal outcome as antenatal and postnatal complications and neonatal outcome as birth weight, morbidity and mortality in triplet gestation. All the patients with triplet pregnancy beyond 28 weeks gestation, who delivered at the study place during above period were included in the study. The primary outcome measures were frequency of maternal complications and neonatal birth, weight and morbidity. Secondary outcome measures included the frequency of assisted conception in the studied cohart. Eighteen women had triplet pregnancy beyond 28 weeks. Nine were booked, 6 non-booked and 3 of them were referred. Mean duration of gestation was 237.8 days (33.8 weeks). The antenatal complications were preterm delivery in 50%, hypertension in 50%, anemia in 44.4% and obstetric cholestasis in 5.6%. Eight patients (44.4%) suffered postpartum hemorrhage. One patient had peripartum hysterectomy and later expired in intensive care unit after three weeks. Maternal mortality ratio was 5.6%. Fifty five percent women had induction of ovulation with Clomiphene, while none had In Vitro Fertilization (IVF) or Intracytoplasmic Insemination (ICSI) or received gonadotrophins. Fifteen sets of triplets were delivered abdominally. Mean birth weights of 1st, 2nd and 3rd triplet were 1651, 1640 and 1443 grams respectively. Five sets of triplets (27.8%) had more than 25% discordance for birth weight. The mean Apgar scores of the babies at 1 and 10 minutes after birth were 6.0 and 8.0, 5.6 and 7.5; and 5.2 and 7.0 respectively. Of the 54 infants, 18 required Neonatal Intensive Care Unit (NICU) admission and 14 were admitted in nursery. Two died shortly after birth. Total perinatal mortalities were 13 including 4 cases of intra-uterine demise. Three babies suffered from jaundice, 7 had sepsis and 8 had respiratory distress syndrome. Triplet gestation had a high rate of fetomaternal complications. Majority had history of assisted conception. (author)

A topological extension of GR: Black holes induce dark energy

International Nuclear Information System (INIS)

Spaans, M

2013-01-01

A topological extension of general relativity is presented. The superposition principle of quantum mechanics, as formulated by the Feynman path integral, is taken as a starting point. It is argued that the trajectories that enter this path integral are distinct and thus that space-time topology is multiply connected. Specifically, space-time at the Planck scale consists of a lattice of three-tori that facilitates many distinct paths for particles to travel along. To add gravity, mini black holes are attached to this lattice. These mini black holes represent Wheeler's quantum foam and result from the fact that GR is not conformally invariant. The number of such mini black holes in any time-slice through four-space is found to be equal to the number of macroscopic (so long-lived) black holes in the entire universe. This connection, by which macroscopic black holes induce mini black holes, is a topological expression of Mach's principle. The proposed topological extension of GR can be tested because, if correct, the dark energy density of the universe should be proportional the total number of macroscopic black holes in the universe at any time. This prediction, although strange, agrees with current astrophysical observations.

Impact ionization coefficients for electrons and holes in In0.14Ga0.86As

International Nuclear Information System (INIS)

Pearsall, T.P.; Nahory, R.E.; Pollack, M.A.

1975-01-01

We report the measurement of impact ionization rates for electrons and holes in the direct band-gap semiconductor alloy In 0 . 14 Ga 0 . 86 As. Our results show clearly that the ionization rate for holes is greater than that for electrons. The measurments were made for electric fields between 2.6times10 5 and 3.4times10 5 V cm -1 . In this range, the ionization coefficients can be expressed as α=α/sub infinity/ exp(-A/E) for electrons and β=β/sub infinity/ exp(-B/E) for holes with α/sub infinity/=1.0times10 9 cm -1 , A=3.6times10 6 V cm -1 , and β/sub infinity/=1.3times10 8 cm -1 , B=2.7times10 6 V cm -1

Can black hole superradiance be induced by galactic plasmas?

Science.gov (United States)

Conlon, Joseph P.; Herdeiro, Carlos A. R.

2018-05-01

Highly spinning Kerr black holes with masses M = 1- 100M⊙ are subject to an efficient superradiant instability in the presence of bosons with masses μ ∼10-10-10-12eV. We observe that this matches the effective plasma-induced photon mass in diffuse galactic or intracluster environments (ωpl ∼10-10-10-12eV). This suggests that bare Kerr black holes within galactic or intracluster environments, possibly even including the ones produced in recently observed gravitational wave events, are unstable to formation of a photon cloud that may contain a significant fraction of the mass of the original black hole. At maximal efficiency, the instability timescale for a massive vector is milliseconds, potentially leading to a transient rate of energy extraction from a black hole in principle as large as ∼1055ergs-1. We discuss possible astrophysical effects this could give rise to, including a speculative connection to Fast Radio Bursts.

A study of the low-lying singlet and triplet electronic states of chlorophyll A and B

Directory of Open Access Journals (Sweden)

Etinski Mihajlo

2013-01-01

Full Text Available Chlorophylls have been extensively investigated both experimentally and theoretically owing to the fact that they are essential for photosynthesis. We have studied two forms of chlorophyll, chlorophyll a and chlorophyll b, by means of density functional theory. Optimization of S0, S1 and T1 states was performed with the B3-LYP functional. The computed fluorescence lifetimes show good agreement with the available experimental data. The electronic adiabatic energies of S1 and T1 states are 2.09/2.12 and 1.19/1.29 eV for chlorophyll a and chlorophyll b respectively. We discussed the implications of this results on the triplet formation. Also, the calculated vertical ionization potentials shows good agreement with the experimental results. [Projekat Ministarstva nauke Reoublike Srbije, br. 172040

Time-dependence hole and electron trapping effects in SIMOX buried oxides

International Nuclear Information System (INIS)

Boesch, H.E. Jr.; Taylor, T.L.; Hite, L.R.; Bailey, W.E.

1990-01-01

Back-channel threshold shift associated with the buried oxide layers of separation by implanted oxygen (SIMOX) and zone-melted recrystallization (ZMR) field-effect transistors (FETs) was measured following pulsed irradiation as a function of temperature and back-gate bias using a fast time-resolved I-V measurement technique. The SIMOX FETs showed large initial negative voltage shifts at 0.2 ms after irradiation followed by temperature- and bias-dependent additional negative shifts to 800s. Analysis and modeling of the results indicate efficient deep trapping of radiation-generated holes in the bulk of the oxide, substantial initial trapping of radiation-generated electrons in the oxide, and rapid removal of the trapped electrons by a thermal detrapping process. The ZMR FETs showed evidence of substantial trapping of holes alone in the oxide bulk

The alignment of the LHC low beta triplets. Review of instrumentation and methods

International Nuclear Information System (INIS)

Coosemans, W.; Mainaud Durand, H.; Marin, A.; Quesnel, J-P.

2003-01-01

Alignment tolerances for the LHC insertions are particularly stringent regarding the low beta quadrupoles, which induce strict positioning tolerances, in a severe environment (high radiation fluxes and magnetic fields): positioning of one inner triplet with respect to the other (left/right side): ±0.5 mm (3σ), stability of the positioning of one quadrupole inside its triplet: a few microns. We propose to continuously monitor the relative position of the quadrupoles of one inner triplet with respect to a reference frame materialized by a wire and a water surface, and to use common references to link a triplet on one side to the triplet on the other side of the experiment. When the offset between real and reference position becomes too great, the quadrupole will be moved using remote motorized jacks. Instrumentation (HLS, WPS, radial measuring system, etc.) and methods will be detailed as well as the first results obtained on a cryo-magnet prototype named TAP used as test facility. The TAP is equipped with HLS linked by two types of hydraulic networks (two pipes with air and water separated, one pipe half filled), WPS and one inclinometer. It is installed on three polyurethane motorized jacks in order to study and compare servo positioning using the different sensors. (author)

STM-Induced Hydrogen Desorption via a Hole Resonance

DEFF Research Database (Denmark)

Stokbro, Kurt; Thirstrup, C.; Sakurai, M.

1998-01-01

We report STM-induced desorption of H from Si(100)-H(2 X 1) at negative sample bias. The desorption rate exhibits a power-law dependence on current and a maximum desorption rate at -7 V. The desorption is explained by vibrational heating of H due to inelastic scattering of tunneling holes...... with the Si-H 5 sigma hole resonance. The dependence of desorption rate on current and bias is analyzed using a novel approach for calculating inelastic scattering, which includes the effect of the electric field between tip and sample. We show that the maximum desorption rate at -7 V is due to a maximum...

Electron-hole pairing and anomalous properties of layered high-Tc compounds

International Nuclear Information System (INIS)

Efetov, K.B.

1991-01-01

Band-structure pictures for layered high-T c materials available in the literature show that, besides the dispersive broad band responsible for metallic properties, there are at least two additional bands having minima and maxima near the Fermi surface. These additional bands belong to different planes (for example, CuO planes and BiO planes in Bi 2 Sr 2 CaCu 2 O 8 ) or to planes and chains (in YBa 2 Cu 3 O 7 ). Provided the Coulomb repulsion is not very weak, pairing of electrons and holes belonging to these additional bands in different planes or planes and chains is possible. It is shown that, if this possibility is realized, a transition in the additional bands into a state of an excitonic dielectric occurs. The spin of an electron-hole pair can be both 0 and 1. Due to the fact that the electron and the hole of the pair belong to different planes, there are no charge- or spin-density waves. This excitonic insulator can serve as a polarizing substance and give a strong attraction between electrons of the metallic band even if the bare interaction is repulsive. It is also shown that some interesting gapless excitations exist. Provided there are impurities in the system that scatter from plane to plane, these excitations are coupled to the electrons of the metallic band. This effective interaction can be described in terms of an effective mode P(ω) with ImP(ω)∼-sgnω. As a result, one can obtain such properties of the normal state as a linear dependence of the resistivity on temperature, linear dependence of the density of states on energy, constant background in the Raman-scattering intensity, large nuclear relaxation rate, etc., which are very well known from experiments

Monte Carlo studies of thermalization of electron-hole pairs in spin-polarized degenerate electron gas in monolayer graphene

Science.gov (United States)

Borowik, Piotr; Thobel, Jean-Luc; Adamowicz, Leszek

2018-02-01

Monte Carlo method is applied to the study of relaxation of excited electron-hole (e-h) pairs in graphene. The presence of background of spin-polarized electrons, with high density imposing degeneracy conditions, is assumed. To such system, a number of e-h pairs with spin polarization parallel or antiparallel to the background is injected. Two stages of relaxation: thermalization and cooling are clearly distinguished when average particles energy and its standard deviation σ _E are examined. At the very beginning of thermalization phase, holes loose energy to electrons, and after this process is substantially completed, particle distributions reorganize to take a Fermi-Dirac shape. To describe the evolution of and σ _E during thermalization, we define characteristic times τ _ {th} and values at the end of thermalization E_ {th} and σ _ {th}. The dependence of these parameters on various conditions, such as temperature and background density, is presented. It is shown that among the considered parameters, only the standard deviation of electrons energy allows to distinguish between different cases of relative spin polarizations of background and excited electrons.

Phage inactivation by triplet acetone

International Nuclear Information System (INIS)

Gomes, R.A.

1985-01-01

The exposure of lambda phage to triplet acetone is studied. The triplet acetone is obtained from aerobic oxidation of isobutanal catalysed by peroxidase. A decrease of lambda phage ability to infect Escherichia coli is reported, perhaps, partially due to the possible production of lesions in the phage genome. (M.A.C.) [pt

Optical and magneto-optical properties of the electron-doped and hole-doped C{sub 82} crystal

Energy Technology Data Exchange (ETDEWEB)

Rostampour, E., E-mail: el_rostampour@yahoo.com [Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of); Koohi, A. [Plasma Physics and Nuclear Fusion Research School, Nuclear Science and Technology Research Institute, AEOI, Tehran (Iran, Islamic Republic of)

2015-01-15

The optical and magnetic properties of the doped C{sub 82} crystal have been investigated by Su–Schrieffer–Heeger (SSH) model, which is based on the Ewald method. When the C{sub 82} molecule is doped with one electron (or hole), a single electron is remained in the energy level that affects the optical and magnetic properties of the C{sub 82} crystal. The lattice and electronic structures of C{sub 82} changed with doping electron (or hole) in the molecule of C{sub 82}. Therefore, polarons are predicted in doped fullerenes. The obtained results showed that the dielectric tensor of the C{sub 82} crystal increased with doping electron (or hole) in the molecule of C{sub 82}. The spectral shapes of the dielectric tensor, circular dichroism and birefringence coefficient of the C{sub 82} crystal turn out to be determined mainly by the geometrical distributions of the pentagons in the fullerene structures.

Mass-induced instability of SAdS black hole in Einstein-Ricci cubic gravity

Science.gov (United States)

Myung, Yun Soo

2018-05-01

We perform the stability analysis of Schwarzschild-AdS (SAdS) black hole in the Einstein-Ricci cubic gravity. It shows that the Ricci tensor perturbations exhibit unstable modes for small black holes. We call this the mass-induced instability of SAdS black hole because the instability of small black holes arises from the massiveness in the linearized Einstein-Ricci cubic gravity, but not a feature of higher-order derivative theory giving ghost states. Also, we point out that the correlated stability conjecture holds for the SAdS black hole by computing the Wald entropy of SAdS black hole in Einstein-Ricci cubic gravity.

Photoprotection in the antenna complexes of photosystem II: role of individual xanthophylls in chlorophyll triplet quenching.

Science.gov (United States)

Mozzo, Milena; Dall'Osto, Luca; Hienerwadel, Rainer; Bassi, Roberto; Croce, Roberta

2008-03-07

In this work the photoprotective role of all xanthophylls in LHCII, Lhcb4, and Lhcb5 is investigated by laser-induced Triplet-minus-Singlet (TmS) spectroscopy. The comparison of native LHCII trimeric complexes with different carotenoid composition shows that the xanthophylls in sites V1 and N1 do not directly contribute to the chlorophyll triplet quenching. The largest part of the triplets is quenched by the lutein bound in site L1, which is located in close proximity to the chlorophylls responsible for the low energy state of the complex. The lutein in the L2 site is also active in triplet quenching, and it shows a longer triplet lifetime than the lutein in the L1 site. This lifetime difference depends on the occupancy of the N1 binding site, where neoxanthin acts as an oxygen barrier, limiting the access of O(2) to the inner domain of the Lhc complex, thereby strongly contributing to the photostability. The carotenoid triplet decay of monomeric Lhcb1, Lhcb4, and Lhcb5 is mono-exponential, with shorter lifetimes than observed for trimeric LHCII, suggesting that their inner domains are more accessible for O(2). As for trimeric LHCII, only the xanthophylls in sites L1 and L2 are active in triplet quenching. Although the chlorophyll to carotenoid triplet transfer is efficient (95%) in all complexes, it is not perfect, leaving 5% of the chlorophyll triplets unquenched. This effect appears to be intrinsically related to the molecular organization of the Lhcb proteins.

Magnetoanisotropic spin-triplet Andreev reflection in ferromagnet-Ising superconductor junctions

Science.gov (United States)

Lv, Peng; Zhou, Yan-Feng; Yang, Ning-Xuan; Sun, Qing-Feng

2018-04-01

We theoretically study the electronic transport through a ferromagnet-Ising superconductor junction. A tight-binding Hamiltonian describing the Ising superconductor is presented. Then by combining the nonequilibrium Green's function method, the expressions of Andreev reflection coefficient and conductance are obtained. A strong magnetoanisotropic spin-triplet Andreev reflection is shown, and the magnetoanisotropic period is π instead of 2 π as in the conventional magnetoanisotropic system. We demonstrate a significant increase of the spin-triplet Andreev reflection for the single-band Ising superconductor. Furthermore, the dependence of the Andreev reflection on the incident energy and incident angle are also investigated. A complete Andreev reflection can occur when the incident energy is equal to the superconducting gap, regardless of the Fermi energy (spin polarization) of the ferromagnet. For the suitable oblique incidence, the spin-triplet Andreev reflection can be strongly enhanced. In addition, the conductance spectroscopies of both zero bias and finite bias are studied, and the influence of gate voltage, exchange energy, and spin-orbit coupling on the conductance spectroscopy are discussed in detail. The conductance exhibits a strong magnetoanisotropy with period π as the Andreev reflection coefficient. When the magnetization direction is parallel to the junction plane, a large conductance peak always emerges at the superconducting gap. This work offers a comprehensive and systematic study of the spin-triplet Andreev reflection and has an underlying application of π -periodic spin valve in spintronics.

The controlled fabrication of nanopores by focused electron-beam-induced etching

International Nuclear Information System (INIS)

Yemini, M; Ashkenasy, N; Hadad, B; Goldner, A; Liebes, Y

2009-01-01

The fabrication of nanometric holes within thin silicon-based membranes is of great importance for various nanotechnology applications. The preparation of such holes with accurate control over their size and shape is, thus, gaining a lot of interest. In this work we demonstrate the use of a focused electron-beam-induced etching (FEBIE) process as a promising tool for the fabrication of such nanopores in silicon nitride membranes and study the process parameters. The reduction of silicon nitride by the electron beam followed by chemical etching of the residual elemental silicon results in a linear dependence of pore diameter on electron beam exposure time, enabling accurate control of nanopore size in the range of 17-200 nm in diameter. An optimal pressure of 5.3 x 10 -6 Torr for the production of smaller pores with faster process rates, as a result of mass transport effects, was found. The pore formation process is also shown to be dependent on the details of the pulsed process cycle, which control the rate of the pore extension, and its minimal and maximal size. Our results suggest that the FEBIE process may play a key role in the fabrication of nanopores for future devices both in sensing and nano-electronics applications.

Electron-hole drop (EHD) stability in deformation potential well

International Nuclear Information System (INIS)

Makarov, A.G.; Tikhodeev, S.G.

1984-01-01

In heterogeneously-deformed Ge the stability of electron-hole droplets (EHD) being in a potential well is considered. It is shown that the potential well effect is equivalent to the decrease of effective density of phonon EHD charge. It is pointed out that heating EHD (for example, by IR radiation), can increase the phonon droplet charge and affect its stability

Morphology and physical properties of solar coronal holes

International Nuclear Information System (INIS)

Rozelot, J.P.

1983-01-01

By their peculiar characteristics, coronal holes induce on Earth climatic variations and cyclic effects, not well known nowadays. Because of low electronical density and very low temperature, study of these holes was neglected. The author presents the results of the observations from discovery in the fifteens. He gives some new results, a theoretical model and not well resolved questions which can conduct to new methods of searching [fr

Activity coefficients of electrons and holes in semiconductors

International Nuclear Information System (INIS)

Orazem, M.E.; Newman, J.

1984-01-01

Dilute-solution transport equations with constant activity coefficients are commonly used to model semiconductors. These equations are consistent with a Boltzmann distribution and are invalid in regions where the species concentration is close to the respective site concentration. A more rigorous treatment of transport in a semiconductor requires activity coefficients which are functions of concentration. Expressions are presented for activity coefficients of electrons and holes in semiconductors for which conduction- and valence-band energy levels are given by the respective bandedge energy levels. These activity coefficients are functions of concentration and are thermodynamically consistent. The use of activity coefficients in macroscopic transport relationships allows a description of electron transport in a manner consistent with the Fermi-Dirac distribution

Photochemical transformation of benzotriazole, relevant to sunlit surface waters: Assessing the possible role of triplet-sensitised processes

Energy Technology Data Exchange (ETDEWEB)

Bianco, Angelica [Clermont Université, Université Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP 10448, F-63000 Clermont-Ferrand (France); Fabbri, Debora; Minella, Marco [Università degli Studi di Torino, Dipartimento di Chimica, Via P. Giuria 5, 10125 Turin (Italy); Brigante, Marcello, E-mail: marcello.brigante@univ-bpclermont.fr [Clermont Université, Université Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR 6296, ICCF, BP 80026, F-63177 Aubière (France); Mailhot, Gilles [Clermont Université, Université Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR 6296, ICCF, BP 80026, F-63177 Aubière (France); Maurino, Valter; Minero, Claudio [Università degli Studi di Torino, Dipartimento di Chimica, Via P. Giuria 5, 10125 Turin (Italy); Vione, Davide, E-mail: davide.vione@unito.it [Università degli Studi di Torino, Dipartimento di Chimica, Via P. Giuria 5, 10125 Turin (Italy); Università degli Studi di Torino, Centro Interdipartimentale NatRisk, Via L. Da Vinci 44, 10095 Grugliasco (Italy)

2016-10-01

The corrosion inhibitor 1H-benzotriazole (pK{sub a} = 8.4) can exist in two different forms in natural waters, and photochemical transformation is a potentially significant attenuation pathway for both of them. Depending on conditions, the modelled half-life times range from some days/weeks to several months. In sunlit water bodies, the acidic (neutral) form would undergo direct photolysis (accounting for up to 7% of total phototransformation) and, most notably, reaction with the hydroxyl radicals ({sup ·}OH) and the triplet states of chromophoric dissolved organic matter ({sup 3}CDOM*). The basic (anionic) form would undergo significant transformation with {sup ·}OH and {sup 3}CDOM*. The {sup ·}OH reactions would be more important at low dissolved organic carbon (DOC) and the {sup 3}CDOM* processes at high DOC. In the presence of highly reactive triplet-state model compounds, the two benzotriazole forms react with similar rate constants. In this case, they would show comparable half-life times in surface-water environments. With less reactive triplet states, the rate constant of the anionic form can be a couple of orders of magnitude higher than that of the neutral one. Under these circumstances, the neutral form could be considerably more photostable than the anionic one at high DOC. Therefore, depending on {sup 3}CDOM* reactivity, the solution pH may or may not play an important role in the photoattenuation kinetics of 1H-benzotriazole in sunlit natural waters, especially at high DOC. Both forms of benzotriazole yield hydroxyderivatives as their main transformation intermediates under all the relevant photochemical reaction pathways. These intermediates could be formed via {sup ·}OH-induced hydroxylation, or upon electron abstraction followed by reaction with water. Differently from UVC irradiation data reported in previous studies, the concentration of aniline upon excitation of 1H-benzotriazole under environmentally significant UV wavelengths was always

Birth weight in a large series of triplets

NARCIS (Netherlands)

Ponsen-Lamb, D.J.; Middeldorp, C.M.; van Beijsterveldt, C.E.M.; Vink, J.M.; Haak, M.C.; Boomsma, D.I.

2011-01-01

Background: Triplets are often born premature and with a low birth weight. Because the incidence of triplet births is rare, there are relatively few studies describing triplet birth weight characteristics. Earlier studies are often characterized by small sample sizes and lack information on

Triplet leptogenesis in left–right symmetric seesaw models

International Nuclear Information System (INIS)

Hällgren, Tomas; Konstandin, Thomas; Ohlsson, Tommy

2008-01-01

We discuss scalar triplet leptogenesis in a specific left–right symmetric seesaw model. We show that the Majorana phases that are present in the model can be effectively used to saturate the existing upper limit on the CP-asymmetry of the triplets. We solve the relevant Boltzmann equations and analyze the viability of triplet leptogenesis. It is known for this kind of scenario that the efficiency of leptogenesis is maximal if there exists a hierarchy between the branching ratios of the triplet decays into leptons and Higgs particles. We show that triplet leptogenesis typically favors branching ratios with not too strong hierarchies, since maximal efficiency can only be obtained at the expense of suppressed CP-asymmetries

Birth weight in a large series of triplets

NARCIS (Netherlands)

Lamb, Diane J.; Middeldorp, Christel M.; van Beijsterveldt, Catharina E. M.; Vink, Jacqueline M.; Haak, Monique C.; Boomsma, Dorret I.

2011-01-01

Triplets are often born premature and with a low birth weight. Because the incidence of triplet births is rare, there are relatively few studies describing triplet birth weight characteristics. Earlier studies are often characterized by small sample sizes and lack information on important background

Tailoring of polarization in electron blocking layer for electron confinement and hole injection in ultraviolet light-emitting diodes

International Nuclear Information System (INIS)

Lu, Yu-Hsuan; Pilkuhn, Manfred H.; Fu, Yi-Keng; Chu, Mu-Tao; Huang, Shyh-Jer; Su, Yan-Kuin; Wang, Kang L.

2014-01-01

The influence of the AlGaN electron blocking layer (EBL) with graded aluminum composition on electron confinement and hole injection in AlGaN-based ultraviolet light-emitting diodes (LEDs) are investigated. The light output power of LED with graded AlGaN EBL was markedly improved, comparing to LED with conventional EBL. In experimental results, a high increment of 86.7% can be obtained in light output power. Simulation analysis shows that via proper modification of the barrier profile from the last barrier of the active region to EBL, not only the elimination of electron overflow to p-type layer can be achieved but also the hole injection into the active region can be enhanced, compared to a conventional LED structure. The dominant factor to the performance improvement is shown to be the modulation of polarization field by the graded Al composition in EBL

Tailoring of polarization in electron blocking layer for electron confinement and hole injection in ultraviolet light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Lu, Yu-Hsuan; Pilkuhn, Manfred H. [Department of Electrical Engineering, Institute of Microelectronics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan (China); Fu, Yi-Keng; Chu, Mu-Tao [Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute, Hsinchu 31040, Taiwan (China); Huang, Shyh-Jer, E-mail: yksu@mail.ncku.edu.tw, E-mail: totaljer48@gmail.com [Department of Electrical Engineering, Institute of Microelectronics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan (China); Department of Electrical Engineering, University of California at Los Angeles, Los Angeles, California 90095 (United States); Su, Yan-Kuin, E-mail: yksu@mail.ncku.edu.tw, E-mail: totaljer48@gmail.com [Department of Electrical Engineering, Institute of Microelectronics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan (China); Department of Electronic Engineering, Kun-Shan University, Tainan 71003, Taiwan (China); Wang, Kang L. [Department of Electrical Engineering, University of California at Los Angeles, Los Angeles, California 90095 (United States)

2014-03-21

The influence of the AlGaN electron blocking layer (EBL) with graded aluminum composition on electron confinement and hole injection in AlGaN-based ultraviolet light-emitting diodes (LEDs) are investigated. The light output power of LED with graded AlGaN EBL was markedly improved, comparing to LED with conventional EBL. In experimental results, a high increment of 86.7% can be obtained in light output power. Simulation analysis shows that via proper modification of the barrier profile from the last barrier of the active region to EBL, not only the elimination of electron overflow to p-type layer can be achieved but also the hole injection into the active region can be enhanced, compared to a conventional LED structure. The dominant factor to the performance improvement is shown to be the modulation of polarization field by the graded Al composition in EBL.

Triplet excited state properties in variable gap π-conjugated donor–acceptor–donor chromophores

KAUST Repository

Cekli, Seda; Winkel, Russell W.; Alarousu, Erkki; Mohammed, Omar F.; Schanze, Kirk S.

2016-01-01

A series of variable band-gap donor–acceptor–donor (DAD) chromophores capped with platinum(II) acetylide units has been synthesized and fully characterized by electrochemical and photophysical methods, with particular emphasis placed on probing triplet excited state properties. A counter-intuitive trend of increasing fluorescence quantum efficiency and lifetime with decreasing excited state energy (optical gap) is observed across the series of DAD chromophores. Careful study of the excited state dynamics, including triplet yields (as inferred from singlet oxygen sensitization), reveals that the underlying origin of the unusual trend in the fluorescence parameters is that the singlet–triplet intersystem crossing rate and yield decrease with decreasing optical gap. It is concluded that the rate of intersystem crossing decreases as the LUMO is increasingly localized on the acceptor unit in the DAD chromophore, and this result is interpreted as arising because the extent of spin–orbit coupling induced by the platinum heavy metal centers decreases as the LUMO is more localized on the acceptor. In addition to the trend in intersystem crossing, the results show that the triplet decay rates follow the Energy Gap Law correlation over a 1.8 eV range of triplet energy and 1000-fold range of triplet decay rates. Finally, femtosecond transient absorption studies for the DAD chromophores reveals a strong absorption in the near-infrared region which is attributed to the singlet excited state. This spectral band appears to be general for DAD chromophores, and may be a signature of the charge transfer (CT) singlet excited state.

Triplet excited state properties in variable gap π-conjugated donor–acceptor–donor chromophores

KAUST Repository

Cekli, Seda

2016-02-12

A series of variable band-gap donor–acceptor–donor (DAD) chromophores capped with platinum(II) acetylide units has been synthesized and fully characterized by electrochemical and photophysical methods, with particular emphasis placed on probing triplet excited state properties. A counter-intuitive trend of increasing fluorescence quantum efficiency and lifetime with decreasing excited state energy (optical gap) is observed across the series of DAD chromophores. Careful study of the excited state dynamics, including triplet yields (as inferred from singlet oxygen sensitization), reveals that the underlying origin of the unusual trend in the fluorescence parameters is that the singlet–triplet intersystem crossing rate and yield decrease with decreasing optical gap. It is concluded that the rate of intersystem crossing decreases as the LUMO is increasingly localized on the acceptor unit in the DAD chromophore, and this result is interpreted as arising because the extent of spin–orbit coupling induced by the platinum heavy metal centers decreases as the LUMO is more localized on the acceptor. In addition to the trend in intersystem crossing, the results show that the triplet decay rates follow the Energy Gap Law correlation over a 1.8 eV range of triplet energy and 1000-fold range of triplet decay rates. Finally, femtosecond transient absorption studies for the DAD chromophores reveals a strong absorption in the near-infrared region which is attributed to the singlet excited state. This spectral band appears to be general for DAD chromophores, and may be a signature of the charge transfer (CT) singlet excited state.

Coupled Simulations of the Synchrotron Radiation and Induced Desorption Pressure Profiles for the HL-LHC Triplet Area and Interaction Points

CERN Document Server

Kersevan, R; Bregliozzi, G

2014-01-01

The HiLumi-LHC machine upgrade has officially started as an approved LHC project (see dedicated presentations at this conference on the subject). One important feature of the upgrade is the installation of very high-gradient triplet magnets for focusing the beams at the collision points of the two high-luminosity detectors ATLAS and CMS. Other important topics are new superconducting D1 and D2 magnets, installation of crab cavities and new tertiary collimators, and re-shuffling of the dispersion suppression area. Based on the current magnetic lattice set-up and beam orbits, a detailed study of the emission of synchrotron radiation (SR) and related photon-induced desorption (PID) has been carried out. A significant amount of SR photons are generated by the two off-axis beams in the common vacuum chamber of the triplet area, about 57 m in length. Ray-tracing Montecarlo codes Synrad+ and Molflow+ have been employed in this study. The related PID pressure profiles are shown, together with simulations using the co...

Signal enhancement of neutral He emission lines by fast electron bombardment of laser-induced He plasma

Directory of Open Access Journals (Sweden)

Hery Suyanto

2016-08-01

Full Text Available A time-resolved spectroscopic study is performed on the enhancement signals of He gas plasma emission using nanosecond (ns and picosecond (ps lasers in an orthogonal configuration. The ns laser is used for the He gas plasma generation and the ps laser is employed for the ejection of fast electrons from a metal target, which serves to excite subsequently the He atoms in the plasma. The study is focused on the most dominant He I 587.6 nm and He I 667.8 nm emission lines suggested to be responsible for the He-assisted excitation (HAE mechanism. The time-dependent intensity enhancements induced by the fast electrons generated with a series of delayed ps laser ablations are deduced from the intensity time profiles of both He emission lines. The results clearly lead to the conclusion that the metastable excited triplet He atoms are actually the species overwhelmingly produced during the recombination process in the ns laser-induced He gas plasma. These metastable He atoms are believed to serve as the major energy source for the delayed excitation of analyte atoms in ns laser-induced breakdown spectroscopy (LIBS using He ambient gas.

Signal enhancement of neutral He emission lines by fast electron bombardment of laser-induced He plasma

Energy Technology Data Exchange (ETDEWEB)

Suyanto, Hery [Department of Physics, Faculty of Mathematics and Natural Sciences, Udayana University, Kampus Bukit Jimbaran, Denpasar 80361, Bali (Indonesia); Pardede, Marincan [Department of Electrical Engineering, University of Pelita Harapan, 1100 M.H. Thamrin Boulevard, Lippo Village, Tangerang 15811 (Indonesia); Hedwig, Rinda [Department of Computer Engineering, Bina Nusantara University, 9 K.H. Syahdan, Jakarta 14810 (Indonesia); Marpaung, Alion Mangasi [Department of Physics, Faculty of Mathematics and Natural Sciences, Jakarta State University, Rawamangun, Jakarta 12440 (Indonesia); Ramli, Muliadi [Department of Chemistry, Faculty of Mathematics and Natural Sciences, Syiah Kuala University, Darussalam, Banda Aceh 23111, NAD (Indonesia); Lie, Tjung Jie; Kurniawan, Koo Hendrik, E-mail: kurnia18@cbn.net.id [Research Center of Maju Makmur Mandiri Foundation, 40 Srengseng Raya, Kembangan, Jakarta Barat 11630 (Indonesia); Abdulmadjid, Syahrun Nur [Department of Physics, Faculty of Mathematics and Natural Sciences, Syiah Kuala University, Darussalam, Banda Aceh 23111, NAD (Indonesia); Tjia, May On [Research Center of Maju Makmur Mandiri Foundation, 40 Srengseng Raya, Kembangan, Jakarta Barat 11630 (Indonesia); Physics of Magnetism and Photonics Group, Faculty of Mathematics and Natural Sciences, Bandung Institute of Technology, 10 Ganesha,Bandung 40132 (Indonesia); Kagawa, Kiichiro [Research Center of Maju Makmur Mandiri Foundation, 40 Srengseng Raya, Kembangan, Jakarta Barat 11630 (Indonesia); Fukui Science Education Academy, Takagi Chuo 2 chome, Fukui 910-0804 (Japan)

2016-08-15

A time-resolved spectroscopic study is performed on the enhancement signals of He gas plasma emission using nanosecond (ns) and picosecond (ps) lasers in an orthogonal configuration. The ns laser is used for the He gas plasma generation and the ps laser is employed for the ejection of fast electrons from a metal target, which serves to excite subsequently the He atoms in the plasma. The study is focused on the most dominant He I 587.6 nm and He I 667.8 nm emission lines suggested to be responsible for the He-assisted excitation (HAE) mechanism. The time-dependent intensity enhancements induced by the fast electrons generated with a series of delayed ps laser ablations are deduced from the intensity time profiles of both He emission lines. The results clearly lead to the conclusion that the metastable excited triplet He atoms are actually the species overwhelmingly produced during the recombination process in the ns laser-induced He gas plasma. These metastable He atoms are believed to serve as the major energy source for the delayed excitation of analyte atoms in ns laser-induced breakdown spectroscopy (LIBS) using He ambient gas.

Dynamics and configurations of galaxy triplets

International Nuclear Information System (INIS)

Anosova, J.P.; Orlov, V.V.; Chernin, A.D.; Ivanov, A.V.; Kiseleva, L.G.

1990-01-01

The purpose is to infer the probable dynamical states of galaxy triplets by the observed data on their configurations. Two methods are proposed for describing the distributions of the triplet configuration parameters characterizing a tendency to alignment and hierarchy: (1) obtaining a representative sample of configurations and determining its statistical parameters (moments and percentages); and (2) dividing the region of possible configurations of triple systems (Agekian and Anosova, 1967) into a set of segments and finding the probabilities for the configurations to find themselves in each of them. Both these methods allow representation of the data by numerical simulations as well as observations. The effect of projection was studied. It rather overestimates the alignment and hierarchy of the triple systems. Among the parameters of interest there are found some parameters that are least sensitive to projection effects. The samples consist of simulated galaxy triplets (with hidden mass) as well as of 46 probably physical triple galaxies (Karachentseva et al., 1979). The observed triples as well as numerical models show a tendency to alignment. The triple galaxies do not show any tendency to hierarchy (formation of the temporary binaries), but this tendency may be present for simulated triplets without significant dark matter. The significant hidden mass (of order ten times the total mass of a triplet) decreases the probability of forming a binary and so weakens the hierarchy. Small galaxy groups consisting of 3 to 7 members are probably the most prevalent types of galaxy aggregate (Gorbatsky, 1987). Galaxy triplets are the simplest groups, but dynamically nontrivial ones

In situ investigation of ion-induced dewetting of a thin iron-oxide film on silicon by high resolution scanning electron microscopy

Energy Technology Data Exchange (ETDEWEB)

Amirthapandian, S. [Institut fuer Halbleiteroptik und Funktionelle Grenzflaechen, Universitaet Stuttgart, 70569 Stuttgart (Germany); Material Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India); Schuchart, F.; Garmatter, D.; Bolse, W. [Institut fuer Halbleiteroptik und Funktionelle Grenzflaechen, Universitaet Stuttgart, 70569 Stuttgart (Germany)

2012-11-15

Using our new in situ high resolution scanning electron microscope, which is integrated into the UNILAC ion beamline at the Helmholtzzentrum fuer Schwerionenforschung (GSI) in Darmstadt, Germany, we investigated the swift heavy ion induced dewetting of a thin iron oxide layer on Si. Besides heterogeneous hole nucleation at defects and spontaneous (homogeneous) hole nucleation, we could clearly identify a dewetting mechanism, which is similar to the spinodal dewetting observed for liquid films. Instead of being due to capillary waves, it is based on a stress induced surface instability. The latter results in the formation of a wavy surface with constant dominant wave-length and increasing amplitude during ion irradiation. Dewetting sets in as soon as the wave-troughs reach the film-substrate interface. Inspection of the hole radii and rim shapes indicates that removal of the material from the hole area occurs mainly by plastic deformation at the inner boundary and ion induced viscous flow in the peripheral zone due to surface tension.

Mechanism of the generation of black hole entropy in Sakharov's induced gravity

International Nuclear Information System (INIS)

Frolov, V.P.; Fursaev, D.V.

1997-01-01

The mechanism of the generation of Bekenstein-Hawking entropy S BH of a black hole in the Sakharov's induced gravity is proposed. It is suggested that the physical degrees of freedom, which explain the entropy S BH , form only a finite subset of the standard Rindler-like modes defined outside the black hole horizon. The entropy S R of the Rindler modes, or entanglement entropy, is always ultraviolet divergent, while the entropy of the physical modes is finite and coincides in the induced gravity with S BH . The two entropies S BH and S R differ by a surface integral Q interpreted as a Noether charge of nonminimally coupled scalar constituents of the model. We demonstrate that energy E and Hamiltonian H of the fields localized in a part of space-time, restricted by the Killing horizon Σ, differ by the quantity T H Q, where T H is the temperature of a black hole. The first law of black hole thermodynamics enables one to relate the probability distribution of fluctuations of the black hole mass, caused by the quantum fluctuations of the fields, to the probability distribution of physical modes over energy E. The latter turns out to be different from the distribution of the Rindler modes. We show that the probability distribution of the physical degrees of freedom has a sharp peak at E=0 with the width proportional to the Planck mass. The logarithm of number of physical states at the peak coincides exactly with the black hole entropy S BH . This enables us to argue that the energy distribution of the physical modes and distribution of the black hole mass are equivalent in induced gravity. Finally it is shown that the Noether charge Q is related to the entropy of the low-frequency modes propagating in the vicinity of the bifurcation surface Σ of the horizon. (Abstract Truncated)

Lead Monoxide: Two-Dimensional Ferromagnetic Semiconductor Induced by Hole-Doping

KAUST Repository

Wang, Yao

2017-04-12

We employ first-principles calculations to demonstrate ferromagnetic ground states for single- and multi-layer lead monoxide (PbO) under hole-doping, originating from a van Hove singularity at the valence band edge. Both the sample thickness and applied strain are found to have huge effects on the electronic and magnetic properties. Multi-layer PbO is an indirect band gap semiconductor, while a direct band gap is realized in the single-layer limit. In hole-doped single-layer PbO, biaxial tensile strain can enhance the stability of the ferromagnetic state.

Lead Monoxide: Two-Dimensional Ferromagnetic Semiconductor Induced by Hole-Doping

KAUST Repository

Wang, Yao; Zhang, Qingyun; Shen, Qian; Cheng, Yingchun; Schwingenschlö gl, Udo; Huang, Wei

2017-01-01

We employ first-principles calculations to demonstrate ferromagnetic ground states for single- and multi-layer lead monoxide (PbO) under hole-doping, originating from a van Hove singularity at the valence band edge. Both the sample thickness and applied strain are found to have huge effects on the electronic and magnetic properties. Multi-layer PbO is an indirect band gap semiconductor, while a direct band gap is realized in the single-layer limit. In hole-doped single-layer PbO, biaxial tensile strain can enhance the stability of the ferromagnetic state.

Psoralen phototherapy and the possible involvement of triplet excited states

International Nuclear Information System (INIS)

Bensasson, R.V.; Salet, E.J.; Land, E.J.

1979-01-01

Psoralens are important drugs used in the phototherapy of psoriasis and vitiligo. It has been predicted that the triplet excited state of psoralen is photoactive. The authors have employed pulse radiolysis and laser flash photolysis to determine the quantum yields of formation of the triplet states of psoralens and related molecules including 4'5' dihydropsoralen, a model for 4'5' psoralenpyrimidine mono-adducts. The triplet spectra were used to follow the reactions of the triplets with thymine and tryptophan. Such reactions may take place via a charge transfer mechanism. For 8-methoxy psoralen, in addition to triplet formation, photoionization was detected using high laser intensities. Although significant yields of psoralen triplets are formed, and some such triplets react with thymine, it is too early yet to say definitely whether or not the therapeutic action of psoralens is mediated via such triplet states. (Auth.)

Aggressive posterior retinopathy of prematurity in two of the triplets: a case report.

Science.gov (United States)

Wang, Dan; Zhang, Bo; Dong, Yu; Song, E

2015-02-01

Aggressive posterior retinopathy of prematurity is identified as a rare, rapidly progressing and severe form of retinopathy of prematurity (ROP). Here, we report the diagnosis and treatment of aggressive posterior retinopathy of prematurity (APROP) in two of the triplets born at low birth weight and small gestational age. A case concerning two triplets who were born at 31 weeks' gestational age with low birth weight and reached bilateral threshold APROP was reported. The ROP of triplets A and B had the characteristic features of aggressive diseases, which were posterior location, prominence of plus disease and rapid progression. Low birth weight and small gestational age, multiple pregnancies, pregnancy-induced hypertension and older age of the mother might account for the presentations of APROP. These cases demonstrate the importance of early screening and diagnosis in APROP infants. Prompt and adequate laser photocoagulation with a large number of high-intensity closely performed spots and early retreatment could be effective and safe for preventing the progression of APROP with plus disease in zone 1 or 2 in premature triplets. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Experimental confirmation of photon-induced spin-flip transitions in helium via triplet metastable yield spectra

International Nuclear Information System (INIS)

Rubensson, Jan-Erik; Moise, Angelica; Richter, Robert; Mihelic, Andrej; Bucar, Klemen; Zitnik, Matjaz

2010-01-01

Doubly excited states below the N=2 ionization threshold are populated by exciting helium atoms in a supersonic beam with monochromatized synchrotron radiation. The fluorescence decay of these states triggers a radiative cascade back to the ground state with large probability to populate long lived singlet and triplet helium metastable states. The yield of metastables is measured using a multichannel plate detector after the beam has passed a singlet-quenching discharge lamp. The variation of the yield observed with the lamp switched on or off is related to the triplet-singlet mixing of the doubly excited states.

Magnetization induced by odd-frequency spin-triplet Cooper pairs in a Josephson junction with metallic trilayers

Science.gov (United States)

Hikino, S.; Yunoki, S.

2015-07-01

We theoretically study the magnetization inside a normal metal induced in an s -wave superconductor/ferromagnetic metal/normal metal/ferromagnetic metal/s -wave superconductor (S /F 1 /N /F 2 /S ) Josephson junction. Using the quasiclassical Green's function method, we show that the magnetization becomes finite inside the N . The origin of this magnetization is due to odd-frequency spin-triplet Cooper pairs formed by electrons of equal and opposite spins, which are induced by the proximity effect in the S /F 1 /N /F 2 /S junction. We find that the magnetization M (d ,θ ) in the N can be decomposed into two parts, M (d ,θ ) =MI(d ) +MII(d ,θ ) , where θ is the superconducting phase difference between the two S s and d is the thickness of N . The θ -independent magnetization MI(d ) exists generally in S /F junctions, while MII(d ,θ ) carries all θ dependence and represents the fingerprint of the phase coherence between the two S s in Josephson junctions. The θ dependence thus allows us to control the magnetization in the N by tuning θ for a fixed d . We show that the θ -independent magnetization MI(d ) weakly decreases with increasing d , while the θ -dependent magnetization MII(d ,θ ) rapidly decays with d . Moreover, we find that the time-averaged magnetization exhibits a discontinuous peak at each resonance dc voltage Vn=n ℏ ωS/2 e (n : integer) when dc voltage V as well as ac voltage vac(t ) with frequency ωS are both applied to the S /F 1 /N /F 2 /S junction. This is because MII(d ,θ ) oscillates generally in time t (ac magnetization) with d θ /d t =2 e [V +vac(t ) ]/ℏ and thus =0 , but can be converted into the time-independent dc magnetization for the dc voltage at Vn. We also discuss that the magnetization induced in the N can be measurably large in realistic systems. Therefore, the measurement of the induced magnetization serves as an alternative way to detect the phase coherence between the two S s in Josephson junctions. Our results

The neonatal outcome in twin versus triplet and quadruplet pregnancies

Directory of Open Access Journals (Sweden)

Fatemeh Nasseri

2009-02-01

Full Text Available

• BACKGROUND: To assess the risk of neonatal mortality and morbidity in twin, triplet and quadruplet pregnancies.
• METHODS: In a retrospective study, the neonatal outcome of all twin, triplet and quadruplet gestations delivered from October 2001 to September 2006 was reviewed. The neonatal outcome of triples and quadruplets was compared with a matched group of twins for gestational age.
• RESULTS: During a 5-year period, 511 sets of twin pregnancies, 42 sets of triplet and 5 sets of quadruplet pregnancies were studied. The mean of gestational age for twins, triplets and quadruplets were 33.92 ± 3.5 weeks, 30.92 ± 3.8 weeks and 31.60 ± 2.0 weeks, respectively, (P = 0.0001. Triplets and quadruplets weighed less than twins, (P = 0.0001. Neonatal mortality was 13.5% for twins, 26.8% for triplets and 30% for quadruplets. In vitro fertilization, use of ovulation induction agents, and cesarean delivery in the women with triplet and quadruplet were significantly higher than in those with twin pregnancies, (P = 0.0001. The mean age of mothers with triplets and quadruplets was significantly higher than with twins (P = 0.026. There was not a significant difference in respiratory and non-respiratory short outcomes between triplets, quadruplets and twins when matched for gestational age. Apgar score at 1 and 5 minutes was significantly lower in triplets and quadruplets than twins. There was no influence of birth order on neonatal mortality of triplet pregnancy. Neonatal mortality of triplet births was significantly decreased over the 5 years of the study period.
• CONCLUSIONS: Triplets and quadruplets have a similar neonatal outcome as twins when matched for gestational age. There is no influence of birth on the neonatal mortality of triplet pregnancy. It appears that outcome is mainly dependent on gestational age.
• KEYWORDS: Neonatal

• Electronic correlations in hole- and electron-doped Fe-based superconductors

  Science.gov (United States)

  Hardy, Frederic; Boehmer, Anna; Schweiss, Peter; Wolf, Thomas; Heid, Rolf; Eder, Robert; Fisher, Robert A.; Meingast, Christoph

  2015-03-01

  High-temperature superconductivity in the cuprates occurs at the crossover from a highly-correlated Mott insulating state to a weaker correlated Fermi liquid as a function of hole doping. The iron pnictides were initially thought to be fairly weakly correlated. However, we have recently shown using transport and thermodynamic measurements that KFe2As2 is strongly correlated. Both the Sommerfeld coefficient and the Pauli susceptibility are strongly enhanced with respect to their bare DFT values. These correlations are even further enhanced in RbFe2As2andCsFe2As2. The temperature dependence of both the susceptibility and the thermal expansion provides strong experimental evidence for the existence of a coherence-incoherence crossover; similar to what is found in heavy-fermion compounds. Whereas the correlations in the cuprates result from a large value of the Hubbard U, recent works have stressed the particular relevance of Hund's coupling in the pnictides. Our data may be interpreted in terms of a close proximity of KFe2As2 to an orbital-selective Mott transition. We now have good thermodynamic data covering both the hole and electron sides of the BaFe2As2 system and we will discuss how these correlations are modified by doping.

• Molecular origin of differences in hole and electron mobility in amorphous Alq3--a multiscale simulation study.

  Science.gov (United States)

  Fuchs, Andreas; Steinbrecher, Thomas; Mommer, Mario S; Nagata, Yuki; Elstner, Marcus; Lennartz, Christian

  2012-03-28

  In order to determine the molecular origin of the difference in electron and hole mobilities of amorphous thin films of Alq(3) (meridional Alq(3) (tris(8-hydroxyquinoline) aluminium)) we performed multiscale simulations covering quantum mechanics, molecular mechanics and lattice models. The study includes realistic disordered morphologies, polarized site energies to describe diagonal disorder, quantum chemically calculated transfer integrals for the off-diagonal disorder, inner sphere reorganization energies and an approximative scheme for outer sphere reorganization energies. Intermolecular transfer rates were calculated via Marcus-theory and mobilities were simulated via kinetic Monte Carlo simulations and by a Master Equation approach. The difference in electron and hole mobility originates from the different localization of charge density in the radical anion (more delocalized) compared to the radical cation (more confined). This results in higher diagonal disorder for holes and less favourable overlap properties for the hole transfer integrals leading to an overall higher electron mobility.

• Analysis of radicals induced in irradiated cereal flour using ESR

  International Nuclear Information System (INIS)

  Kawamura, Shoei; Kishita, Keigo; Ukai, Mitsuko; Kikuchi, Masahiro; Kobayashi, Yasuhiko

  2013-01-01

  Using electron spin resonance (ESR) spectroscopy, we revealed radicals induced in cereal flour irradiated with gamma-ray or electron beam. Sample was wheat and rice. We detected a broad singlet signal at g = 2.0. It consists of a singlet signal and a triplet signal. It suggested that the singlet signal is originated from organic free radicals and the triplet signal is from 14 N. There were no differences of ESR spectra between irradiated wheat flour and rice flour. The signal intensity of radiation induced radical was tend to increase following with the increase of radiation dose level. After radiation treatment, relaxation time of radiation induced radical was changed during storage. T 1 was decreased and T 2 was increased. In this study, the relaxation time is calculated using the parameters obtained from the ESR signal. It is necessary to analyze the relaxation time directly with pulsed ESR spectroscopy in future. (author)

Triplet state photochemistry and the three-state crossing of acetophenone within time-dependent density-functional theory

Energy Technology Data Exchange (ETDEWEB)

Huix-Rotllant, Miquel, E-mail: miquel.huix@gmail.com; Ferré, Nicolas, E-mail: nicolas.ferre@univ-amu.fr [Institut de Chimie Radicalaire (UMR-7273), Aix-Marseille Université, CNRS, 13397 Marseille Cedex 20 (France)

2014-04-07

Even though time-dependent density-functional theory (TDDFT) works generally well for describing excited states energies and properties in the Franck-Condon region, it can dramatically fail in predicting photochemistry, notably when electronic state crossings occur. Here, we assess the ability of TDDFT to describe the photochemistry of an important class of triplet sensitizers, namely, aromatic ketones. We take acetophenone as a test molecule, for which accurate ab initio results exist in the literature. Triplet acetophenone is generated thanks to an exotic three-state crossing involving one singlet and two triplets states (i.e., a simultaneous intersystem crossing and triplet conical intersection), thus being a stringent test for approximate TDDFT. We show that most exchange-correlation functionals can only give a semi-qualitative picture of the overall photochemistry, in which the three-state crossing is rather represented as a triplet conical intersection separated from the intersystem crossing. The best result overall is given by the double hybrid functional mPW2PLYP, which is even able to reproduce quantitatively the three-state crossing region. We rationalize this results by noting that double hybrid functionals include a larger portion of double excitation character to the excited states.

Direct probing of electron and hole trapping into nano-floating-gate in organic field-effect transistor nonvolatile memories

Energy Technology Data Exchange (ETDEWEB)

Cui, Ze-Qun; Wang, Shun; Chen, Jian-Mei; Gao, Xu; Dong, Bin, E-mail: wangsd@suda.edu.cn, E-mail: chilf@suda.edu.cn, E-mail: bdong@suda.edu.cn; Chi, Li-Feng, E-mail: wangsd@suda.edu.cn, E-mail: chilf@suda.edu.cn, E-mail: bdong@suda.edu.cn; Wang, Sui-Dong, E-mail: wangsd@suda.edu.cn, E-mail: chilf@suda.edu.cn, E-mail: bdong@suda.edu.cn [Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, Suzhou, Jiangsu 215123 (China)

2015-03-23

Electron and hole trapping into the nano-floating-gate of a pentacene-based organic field-effect transistor nonvolatile memory is directly probed by Kelvin probe force microscopy. The probing is straightforward and non-destructive. The measured surface potential change can quantitatively profile the charge trapping, and the surface characterization results are in good accord with the corresponding device behavior. Both electrons and holes can be trapped into the nano-floating-gate, with a preference of electron trapping than hole trapping. The trapped charge quantity has an approximately linear relation with the programming/erasing gate bias, indicating that the charge trapping in the device is a field-controlled process.

Direct probing of electron and hole trapping into nano-floating-gate in organic field-effect transistor nonvolatile memories

International Nuclear Information System (INIS)

Cui, Ze-Qun; Wang, Shun; Chen, Jian-Mei; Gao, Xu; Dong, Bin; Chi, Li-Feng; Wang, Sui-Dong

2015-01-01

Electron and hole trapping into the nano-floating-gate of a pentacene-based organic field-effect transistor nonvolatile memory is directly probed by Kelvin probe force microscopy. The probing is straightforward and non-destructive. The measured surface potential change can quantitatively profile the charge trapping, and the surface characterization results are in good accord with the corresponding device behavior. Both electrons and holes can be trapped into the nano-floating-gate, with a preference of electron trapping than hole trapping. The trapped charge quantity has an approximately linear relation with the programming/erasing gate bias, indicating that the charge trapping in the device is a field-controlled process

Enhancement of tunnel conductivity by Cooper pair fluctuations in electron-hole bilayer

International Nuclear Information System (INIS)

Efimkin, D K; Lozovik, Yu E

2012-01-01

Influence of Cooper pair fluctuations that are precursor of pairing of electrons and holes located on opposite surfaces of topological insulator film on tunnel conductivity between the surfaces is investigated. Due to restrictions caused by momentum and energy conservation dependence of tunnel conductivity on external bias voltage has peak that becomes more prominent with decreasing of disorder and temperature. We have shown that Cooper pair fluctuations considerably enhance tunneling and height of the peak diverges in vicinity of critical temperature with critical index ν = 2. Width of the peak tends to zero in proximity of critical temperature. Pairing of electrons and holes can be suppressed by disorder and in vicinity of quantum critical point height of the peak also diverges as function of Cooper pair damping with critical index μ = 2.

Nearly Perfect Triplet-Triplet Energy Transfer from Wannier Excitons to Naphthalene in Organic-Inorganic Hybrid Quantum-Well Materials

Science.gov (United States)

Ema, K.; Inomata, M.; Kato, Y.; Kunugita, H.; Era, M.

2008-06-01

We report the observation of extremely efficient energy transfer (greater than 99%) in an organic-inorganic hybrid quantum-well structure consisting of perovskite-type lead bromide well layers and naphthalene-linked ammonium barrier layers. Time-resolved photoluminescence measurements confirm that the transfer is triplet-triplet Dexter-type energy transfer from Wannier excitons in the inorganic well to the triplet state of naphthalene molecules in the organic barrier. Using measurements in the 10 300 K temperature range, we also investigated the temperature dependence of the energy transfer.

Electron and hole drift mobility measurements on methylammonium lead iodide perovskite solar cells

Energy Technology Data Exchange (ETDEWEB)

Maynard, Brian; Long, Qi; Schiff, Eric A. [Department of Physics, Syracuse University, Syracuse, New York 13244 (United States); Yang, Mengjin; Zhu, Kai [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Kottokkaran, Ranjith; Abbas, Hisham; Dalal, Vikram L. [Iowa State University, Ames, Iowa 50011 (United States)

2016-04-25

We report nanosecond domain time-of-flight measurements of electron and hole photocarriers in methylammonium lead iodide perovskite solar cells. The mobilities ranged from 0.06 to 1.4 cm{sup 2}/Vs at room temperature, but there is little systematic difference between the two carriers. We also find that the drift mobilities are dispersive (time-dependent). The dispersion parameters are in the range of 0.4–0.7, and they imply that terahertz domain mobilities will be much larger than nanosecond domain mobilities. The temperature-dependences of the dispersion parameters are consistent with confinement of electron and hole transport to fractal-like spatial networks within nanoseconds of their photogeneration.

High-temperature electron-hole superfluidity with strong anisotropic gaps in double phosphorene monolayers

Science.gov (United States)

Saberi-Pouya, S.; Zarenia, M.; Perali, A.; Vazifehshenas, T.; Peeters, F. M.

2018-05-01

Excitonic superfluidity in double phosphorene monolayers is investigated using the BCS mean-field equations. Highly anisotropic superfluidity is predicted where we found that the maximum superfluid gap is in the Bose-Einstein condensate (BEC) regime along the armchair direction and in the BCS-BEC crossover regime along the zigzag direction. We estimate the highest Kosterlitz-Thouless transition temperature with maximum value up to ˜90 K with onset carrier densities as high as 4 ×1012cm-2 . This transition temperature is significantly larger than what is found in double electron-hole few-layers graphene. Our results can guide experimental research toward the realization of anisotropic condensate states in electron-hole phosphorene monolayers.

The effect of gold nanoparticles on exchange processes in collision complexes of triplet and singlet oxygen molecules with excited eosin molecules

Science.gov (United States)

Bryukhanov, V. V.; Minaev, B. M.; Tsibul'nikova, A. V.; Slezhkin, V. A.

2015-07-01

We have studied exchange processes in contact complexes of triplet eosin molecules with oxygen molecules in the triplet (3Σ{/g -}) and singlet (1Δ g ) states in thin polyvinylbutyral films in the presence of gold nanoparticles. Upon resonant excitation of surface plasmons in gold nanoparticles into the absorption band of eosin molecules-singlet oxygen sensitizers-we have obtained an increase in the intensity of the delayed fluorescence and an increase in the lifetime of the dye with simultaneous quenching of the luminescence of singlet oxygen. The kinetics of the delayed fluorescence of the dye as a result of singlet-triplet annihilation of triplet eosin molecules with singlet oxygen molecules has been investigated. To compare theoretical and experimental data, we have numerically simulated energy transfer processes. Rate constants of energy transfer and of singlet-triplet annihilation, as well as quenching constants of triplet states of the dye by molecular oxygen, have been calculated. Luminescence quantum yield 1Δ g of polyvinylbutyral has been estimated. We have analyzed quantum-chemically electronic mechanisms of singlet-triplet annihilation of oxygen and eosin.

Triplet-triplet annihilation photon-upconversion: towards solar energy applications.

Science.gov (United States)

Gray, Victor; Dzebo, Damir; Abrahamsson, Maria; Albinsson, Bo; Moth-Poulsen, Kasper

2014-06-14

Solar power production and solar energy storage are important research areas for development of technologies that can facilitate a transition to a future society independent of fossil fuel based energy sources. Devices for direct conversion of solar photons suffer from poor efficiencies due to spectrum losses, which are caused by energy mismatch between the optical absorption of the devices and the broadband irradiation provided by the sun. In this context, photon-upconversion technologies are becoming increasingly interesting since they might offer an efficient way of converting low energy solar energy photons into higher energy photons, ideal for solar power production and solar energy storage. This perspective discusses recent progress in triplet-triplet annihilation (TTA) photon-upconversion systems and devices for solar energy applications. Furthermore, challenges with evaluation of the efficiency of TTA-photon-upconversion systems are discussed and a general approach for evaluation and comparison of existing systems is suggested.

Ballistic hole magnetic microscopy

NARCIS (Netherlands)

Haq, E.; Banerjee, T.; Siekman, M.H.; Lodder, J.C.; Jansen, R.

2005-01-01

A technique to study nanoscale spin transport of holes is presented: ballistic hole magnetic microscopy. The tip of a scanning tunneling microscope is used to inject hot electrons into a ferromagnetic heterostructure, where inelastic decay creates a distribution of electron-hole pairs.

Transport Properties of an Electron-Hole Bilayer in Contact with a Superconductor Hybrid Junction

Science.gov (United States)

Bercioux, D.; Klapwijk, T. M.; Bergeret, F. S.

2017-08-01

We investigate the transport properties of a junction consisting of an electron-hole bilayer in contact with normal and superconducting leads. The electron-hole bilayer is considered as a semimetal with two electronic bands. We assume that in the region between the contacts the system hosts an exciton condensate described by a BCS-like model with a gap Γ in the quasiparticle density of states. We first discuss how the subgap electronic transport through the junction is mainly governed by the interplay between two kinds of reflection processes at the interfaces: the standard Andreev reflection at the interface between the superconductor and the exciton condensate, and a coherent crossed reflection at the semimetal-exciton-condensate interface that converts electrons from one layer into the other. We show that the differential conductance of the junction shows a minimum at voltages of the order of Γ /e . Such a minimum can be seen as a direct hallmark of the existence of the gapped excitonic state.

Spin-orbit coupling induced two-electron relaxation in silicon donor pairs

Science.gov (United States)

Song, Yang; Das Sarma, S.

2017-09-01

We unravel theoretically a key intrinsic relaxation mechanism among the low-lying singlet and triplet donor-pair states in silicon, an important element in the fast-developing field of spintronics and quantum computation. Despite the perceived weak spin-orbit coupling (SOC) in Si, we find that our discovered relaxation mechanism, combined with the electron-phonon and interdonor interactions, drives the transitions in the two-electron states over a large range of donor coupling regimes. The scaling of the relaxation rate with interdonor exchange interaction J goes from J5 to J4 at the low to high temperature limits. Our analytical study draws on the symmetry analysis over combined band, donor envelope, and valley configurations. It uncovers naturally the dependence on the donor-alignment direction and triplet spin orientation, and especially on the dominant SOC source from donor impurities. While a magnetic field is not necessary for this relaxation, unlike in the single-donor spin relaxation, we discuss the crossover behavior with increasing Zeeman energy in order to facilitate comparison with experiments.

Investigation of Triplet Exciplex Dynamics by Magnetic Field Effects due to the Triplet Mechanism

OpenAIRE

Ulrich, T.; Steiner, Ulrich; Föll, Rudolf E.

1983-01-01

A reaction scheme is described allowing for magnetic field effects on the chemical kinetics of triplet reactions due to the selective decay of triplet sublevels. The theoretical treatment of this scheme is outlined on the basis of a stochastic Liouville equation, taking into account the rotational diffusion of molecules in liquid solution. Whereas the exact solution of the general case is obtained by a numerical procedure as described by Pedersen and Freed, an approximate analytical expressio...

Triplet State Resonance Raman Spectroscopy

DEFF Research Database (Denmark)

Wilbrandt, Robert Walter; Jensen, N. H.; Pagsberg, Palle Bjørn

1978-01-01

Makes the first report on the resonance Raman spectrum of a molecule in its triplet state generated by pulse radiolysis. A solution of 0.01 mol dm-3 of p-terphenyl in benzene was studied......Makes the first report on the resonance Raman spectrum of a molecule in its triplet state generated by pulse radiolysis. A solution of 0.01 mol dm-3 of p-terphenyl in benzene was studied...

Adsorbate-induced modification of electronic band structure of epitaxial Bi(111) films

Energy Technology Data Exchange (ETDEWEB)

Matetskiy, A.V., E-mail: mateckij@iacp.dvo.ru [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); Bondarenko, L.V.; Tupchaya, A.Y.; Gruznev, D.V. [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); Eremeev, S.V. [Institute of Strength Physics and Materials Science, 634021 Tomsk (Russian Federation); Tomsk State University, 634050 Tomsk (Russian Federation); Zotov, A.V. [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); School of Natural Sciences, Far Eastern Federal University, 690950 Vladivostok (Russian Federation); Department of Electronics, Vladivostok State University of Economics and Service, 690600 Vladivostok (Russian Federation); Saranin, A.A. [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); School of Natural Sciences, Far Eastern Federal University, 690950 Vladivostok (Russian Federation)

2017-06-01

Highlights: • Modification of electronic properties of ultrathin Bi films by adsorbates is demonstrated. • Due to electron doping from Cs adatoms, surface-state bands shift to higher binding energies. • As a result, only electron pockets are left in the Fermi map. • Tin acts as an acceptor dopant for Bi, shifting Fermi level upward. • As a result, only hole pockets are left in the Fermi map. - Abstract: Changes of the electronic band structure of Bi(111) films on Si(111) induced by Cs and Sn adsorption have been studied using angle-resolved photoemission spectroscopy and density functional theory calculations. It has been found that small amounts of Cs when it presents at the surface in a form of the adatom gas leads to shifting of the surface and quantum well states to the higher binding energies due to the electron donation from adsorbate to the Bi film. In contrast, adsorbed Sn dissolves into the Bi film bulk upon heating and acts as an acceptor dopant, that results in shifting of the surface and quantum well states upward to the lower binding energies. These results pave the way to manipulate with the Bi thin film electron band structure allowing to achieve a certain type of conductivity (electron or hole) with a single spin channel at the Fermi level making the adsorbate-modified Bi a reliable base for prospective spintronics applications.

Numerical simulation of evolution of electron-hole avalanches and streamers in silicon in a uniform electric field

International Nuclear Information System (INIS)

Kyuregyan, A. S.

2010-01-01

Numerical simulation of origination and evolution of streamers in Si is performed for the first time. It is assumed that an external electric field E 0 is constant and uniform, the avalanche and streamer are axially symmetric, and background electrons and holes are absent. The calculations have been performed in the context of the diffusion-drift approximation with impact and tunneling ionization, Auger recombination, and electron-hole scattering taken into account. The most realistic values of the ionization and recombination rates, diffusion coefficients, and drift mobilities of electrons and holes have been used. It is shown that the features of evolution of avalanches and streamers are generally consistent with the result obtained previously for a hypothetic semiconductor with equal kinetic coefficients for electrons and holes. Asymmetry of these coefficients (mostly, the impact-ionization coefficients) manifests itself only at the initial stage of evolution. However, with time, two exponentially self-similar streamers are formed, differing only in the sign of charge of fronts and directions of their propagation. Empirical dependences of the main parameters of streamers on E 0 in the range of 0.34-0.75 MV/cm have been derived for this most important stage of evolution.

Constructing level-2 phylogenetic networks from triplets

OpenAIRE

Iersel, Leo; Keijsper, J.C.M.; Kelk, Steven; Stougie, Leen; Hagen, F.; Boekhout, T.; Vingron, M.; Wong, L.

2009-01-01

htmlabstractJansson and Sung showed that, given a dense set of input triplets T (representing hypotheses about the local evolutionary relationships of triplets of taxa), it is possible to determine in polynomial time whether there exists a level-1 network consistent with T, and if so to construct such a network (Inferring a Level-1 Phylogenetic Network from a Dense Set of Rooted Triplets, Theoretical Computer Science, 363, pp. 60-68 (2006)). Here we extend this work by showing that this probl...

Room temperature triplet state spectroscopy of organic semiconductors.

Science.gov (United States)

Reineke, Sebastian; Baldo, Marc A

2014-01-21

Organic light-emitting devices and solar cells are devices that create, manipulate, and convert excited states in organic semiconductors. It is crucial to characterize these excited states, or excitons, to optimize device performance in applications like displays and solar energy harvesting. This is complicated if the excited state is a triplet because the electronic transition is 'dark' with a vanishing oscillator strength. As a consequence, triplet state spectroscopy must usually be performed at cryogenic temperatures to reduce competition from non-radiative rates. Here, we control non-radiative rates by engineering a solid-state host matrix containing the target molecule, allowing the observation of phosphorescence at room temperature and alleviating constraints of cryogenic experiments. We test these techniques on a wide range of materials with functionalities spanning multi-exciton generation (singlet exciton fission), organic light emitting device host materials, and thermally activated delayed fluorescence type emitters. Control of non-radiative modes in the matrix surrounding a target molecule may also have broader applications in light-emitting and photovoltaic devices.

Crossover between the dense electron-hole phase and the BCS excitonic phase in quantum dots

International Nuclear Information System (INIS)

Rodriguez, B.A.; Gonzalez, A.; Quiroga, L.; Capote, R.; Rodriguez, F.J.

1999-09-01

Second order perturbation theory and a Lipkin-Nogami scheme combined with an exact Monte Carlo projection after variation are applied to compute the ground-state energy of 6 ≤ N ≤ 210 electron-hole pairs confined in a parabolic two-dimensional quantum dot. The energy shows nice scaling properties as N or the confinement strength is varied. A crossover from the high-density electron-hole phase to the BCS excitonic phase is found at a density which is roughly four times the close-packing density of excitons. (author)

Coexistence of spin-triplet superconductivity with magnetism within a single mechanism for orbitally degenerate correlated electrons: statistically consistent Gutzwiller approximation

International Nuclear Information System (INIS)

Zegrodnik, M; Spałek, J; Bünemann, J

2013-01-01

An orbitally degenerate two-band Hubbard model is analyzed with the inclusion of the Hund's rule-induced spin-triplet even-parity paired states and their coexistence with magnetic ordering. The so-called statistically consistent Gutzwiller approximation (SGA) has been applied to the case of a square lattice. The superconducting gaps, the magnetic moment and the free energy are analyzed as a function of the Hund's rule coupling strength and the band filling. Also, the influence of the intersite hybridization on the stability of paired phases is discussed. In order to examine the effect of correlations the results are compared with those calculated earlier within the Hartree–Fock (HF) approximation combined with the Bardeen–Cooper–Schrieffer (BCS) approach. Significant differences between the two methods used (HF + BCS versus SGA + real-space pairing) appear in the stability regions of the considered phases. Our results supplement the analysis of this canonical model used widely in the discussions of pure magnetic phases with the detailed elaboration of the stability of the spin-triplet superconducting states and the coexistent magnetic-superconducting states. At the end, we briefly discuss qualitatively the factors that need to be included for a detailed quantitative comparison with the corresponding experimental results. (paper)

Observation of Internal Photoinduced Electron and Hole Separation in Hybrid Two-Dimentional Perovskite Films.

Science.gov (United States)

Liu, Junxue; Leng, Jing; Wu, Kaifeng; Zhang, Jun; Jin, Shengye

2017-02-01

Two-dimensional (2D) organolead halide perovskites are promising for various optoelectronic applications. Here we report a unique spontaneous charge (electron/hole) separation property in multilayered (BA) 2 (MA) n-1 Pb n I 3n+1 (BA = CH 3 (CH 2 ) 3 NH 3 + , MA = CH 3 NH 3 + ) 2D perovskite films by studying the charge carrier dynamics using ultrafast transient absorption and photoluminescence spectroscopy. Surprisingly, the 2D perovskite films, although nominally prepared as "n = 4", are found to be mixture of multiple perovskite phases, with n = 2, 3, 4 and ≈ ∞, that naturally align in the order of n along the direction perpendicular to the substrate. Driven by the band alignment between 2D perovskites phases, we observe consecutive photoinduced electron transfer from small-n to large-n phases and hole transfer in the opposite direction on hundreds of picoseconds inside the 2D film of ∼358 nm thickness. This internal charge transfer efficiently separates electrons and holes to the upper and bottom surfaces of the films, which is a unique property beneficial for applications in photovoltaics and other optoelectronics devices.

Entanglement and Metrology with Singlet-Triplet Qubits

Science.gov (United States)

Shulman, Michael Dean

Electron spins confined in semiconductor quantum dots are emerging as a promising system to study quantum information science and to perform sensitive metrology. Their weak interaction with the environment leads to long coherence times and robust storage for quantum information, and the intrinsic tunability of semiconductors allows for controllable operations, initialization, and readout of their quantum state. These spin qubits are also promising candidates for the building block for a scalable quantum information processor due to their prospects for scalability and miniaturization. However, several obstacles limit the performance of quantum information experiments in these systems. For example, the weak coupling to the environment makes inter-qubit operations challenging, and a fluctuating nuclear magnetic field limits the performance of single-qubit operations. The focus of this thesis will be several experiments which address some of the outstanding problems in semiconductor spin qubits, in particular, singlet-triplet (S-T0) qubits. We use these qubits to probe both the electric field and magnetic field noise that limit the performance of these qubits. The magnetic noise bath is probed with high bandwidth and precision using novel techniques borrowed from the field of Hamiltonian learning, which are effective due to the rapid control and readout available in S-T 0 qubits. These findings allow us to effectively undo the undesired effects of the fluctuating nuclear magnetic field by tracking them in real-time, and we demonstrate a 30-fold improvement in the coherence time T2*. We probe the voltage noise environment of the qubit using coherent qubit oscillations, which is partially enabled by control of the nuclear magnetic field. We find that the voltage noise bath is frequency-dependent, even at frequencies as high as 1MHz, and it shows surprising and, as of yet, unexplained temperature dependence. We leverage this knowledge of the voltage noise environment, the

Direct observation of triplet energy transfer from semiconductor nanocrystals.

Science.gov (United States)

Mongin, Cédric; Garakyaraghi, Sofia; Razgoniaeva, Natalia; Zamkov, Mikhail; Castellano, Felix N

2016-01-22

Triplet excitons are pervasive in both organic and inorganic semiconductors but generally remain confined to the material in which they originate. We demonstrated by transient absorption spectroscopy that cadmium selenide semiconductor nanoparticles, selectively excited by green light, engage in interfacial Dexter-like triplet-triplet energy transfer with surface-anchored polyaromatic carboxylic acid acceptors, extending the excited-state lifetime by six orders of magnitude. Net triplet energy transfer also occurs from surface acceptors to freely diffusing molecular solutes, further extending the lifetime while sensitizing singlet oxygen in an aerated solution. The successful translation of triplet excitons from semiconductor nanoparticles to the bulk solution implies that such materials are generally effective surrogates for molecular triplets. The nanoparticles could thereby potentially sensitize a range of chemical transformations that are relevant for fields as diverse as optoelectronics, solar energy conversion, and photobiology. Copyright © 2016, American Association for the Advancement of Science.

Electron-hole pairs generated in ZrO2 nanoparticle resist upon exposure to extreme ultraviolet radiation

Science.gov (United States)

Kozawa, Takahiro; Santillan, Julius Joseph; Itani, Toshiro

2018-02-01

Metal oxide nanoparticle resists have attracted much attention as the next-generation resist used for the high-volume production of semiconductor devices. However, the sensitization mechanism of the metal oxide nanoparticle resists is unknown. Understanding the sensitization mechanism is important for the efficient development of resist materials. In this study, the energy deposition in a zirconium oxide (ZrO2) nanoparticle resist was investigated. The numbers of electron-hole pairs generated in a ZrO2 core and an methacrylic acid (MAA) ligand shell upon exposure to 1 mJ cm-2 (exposure dose) extreme ultraviolet (EUV) radiations were theoretically estimated to be 0.16 at most and 0.04-0.17 cm2 mJ-1, respectively. By comparing the calculated distribution of electron-hole pairs with the line-and-space patterns of the ZrO2 nanoparticle resist fabricated by an EUV exposure tool, the number of electron-hole pairs required for the solubility change of the resist films was estimated to be 1.3-2.2 per NP. NP denotes a nanoparticle consisting of a metal oxide core with a ligand shell. In the material design of metal oxide nanoparticle resists, it is important to efficiently use the electron-hole pairs generated in the metal oxide core for the chemical change of ligand molecules.

TRIO (Triplet Ionospheric Observatory) Mission

Science.gov (United States)

Lee, D.; Seon, J.; Jin, H.; Kim, K.; Lee, J.; Jang, M.; Pak, S.; Kim, K.; Lin, R. P.; Parks, G. K.; Halekas, J. S.; Larson, D. E.; Eastwood, J. P.; Roelof, E. C.; Horbury, T. S.

2009-12-01

Triplets of identical cubesats will be built to carry out the following scientific objectives: i) multi-observations of ionospheric ENA (Energetic Neutral Atom) imaging, ii) ionospheric signature of suprathermal electrons and ions associated with auroral acceleration as well as electron microbursts, and iii) complementary measurements of magnetic fields for particle data. Each satellite, a cubesat for ion, neutral, electron, and magnetic fields (CINEMA), is equipped with a suprathermal electron, ion, neutral (STEIN) instrument and a 3-axis magnetometer of magnetoresistive sensors. TRIO is developed by three institutes: i) two CINEMA by Kyung Hee University (KHU) under the WCU program, ii) one CINEMA by UC Berkeley under the NSF support, and iii) three magnetometers by Imperial College, respectively. Multi-spacecraft observations in the STEIN instruments will provide i) stereo ENA imaging with a wide angle in local times, which are sensitive to the evolution of ring current phase space distributions, ii) suprathermal electron measurements with narrow spacings, which reveal the differential signature of accelerated electrons driven by Alfven waves and/or double layer formation in the ionosphere between the acceleration region and the aurora, and iii) suprathermal ion precipitation when the storm-time ring current appears. In addition, multi-spacecraft magnetic field measurements in low earth orbits will allow the tracking of the phase fronts of ULF waves, FTEs, and quasi-periodic reconnection events between ground-based magnetometer data and upstream satellite data.

A code for optimising triplet layout

CERN Document Server

AUTHOR|(CDS)2141109; Seryi, Andrei; Abelleira, Jose; Cruz Alaniz, Emilia

2017-01-01

One of the main challenges when designing final focus systems of particle accelerators is maximising the beam stay clear in the strong quadrupole magnets of the inner triplet. Moreover it is desirable to keep the quadrupoles in the inner triplet as short as possible for space and costs reasons but also to reduce chromaticity and simplify corrections schemes. An algorithm that explores the triplet parameter space to optimise both these aspects was written. It uses thin lenses as a first approximation for a broad parameter scan and MADX for more precise calculations. The thin lens algorithm is significantly faster than a full scan using MADX and relatively precise at indicating the approximate area where the optimum solution lies.

Dynamical spin susceptibility of electron-doped high-Tc cuprates. Comparison with hole-doped systems

International Nuclear Information System (INIS)

Suzuki, Atsuo; Mutou, Tetsuya; Tanaka, Syunsuke; Hirashima, Dai S.

2010-01-01

The magnetic excitation spectrum of electron-doped copper oxide superconductors is studied by calculating the dynamical spin susceptibility of the two-dimensional Hubbard model in which a d x2-y2 -wave superconducting order parameter is assumed. The spectrum of electron-doped systems is compared with that of hole-doped systems, and the relationship between the frequency at which a peak grows in the spectrum and the superconducting energy gap at a hot spot is investigated. A peak may be observed even when the magnetic resonance condition is not exactly satisfied. We find that, in the electron-doped systems, the resonance condition is less likely to be satisfied than in the hole-doped systems because of the small density of states around the hot spots, and the peak frequency is close to twice the gap magnitude at the hot spots. (author)

Does interchain stacking morphology contribute to the singlet-triplet interconversion dynamics in polymer heterojunctions?

Energy Technology Data Exchange (ETDEWEB)

Bittner, Eric R. [Department of Chemistry and Texas Center for Superconductivity, University of Houston, Houston, TX 77204 (United States)], E-mail: bittner@uh.edu; Burghardt, Irene [Departement de Chimie, Ecole Normale Superieure, 24 rue Lhomond, F-75231 Paris cedex 05 (France); Friend, Richard H. [Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE (United Kingdom)

2009-02-23

Time-dependent density functional theory (TD-DFT) is used to examine the effect of stacking in a model semiconducting polymer hetrojunction system consisting of two co-facially stacked oligomers. We find that the excited electronic states are highly sensitive to the alignment of the monomer units of the two chains. In the system we examined, the exchange energy is nearly identical to both the and band off-set at the heterojunction and to the exciton binding energy. Our results indicate that the triplet excitonic states are nearly degenerate with the singlet exciplex states opening the possibility for the interconversion of singlet and triplet electronic states at the heterojunction interface via spin-orbit coupling localized on the heteroatoms. Using Russell-Saunders theory, we estimate this interconversion rate to be approximately 700-800 ps, roughly a 5-10-fold increase compared to isolated organic polymer chains.

Hybrid spin and valley quantum computing with singlet-triplet qubits.

Science.gov (United States)

Rohling, Niklas; Russ, Maximilian; Burkard, Guido

2014-10-24

The valley degree of freedom in the electronic band structure of silicon, graphene, and other materials is often considered to be an obstacle for quantum computing (QC) based on electron spins in quantum dots. Here we show that control over the valley state opens new possibilities for quantum information processing. Combining qubits encoded in the singlet-triplet subspace of spin and valley states allows for universal QC using a universal two-qubit gate directly provided by the exchange interaction. We show how spin and valley qubits can be separated in order to allow for single-qubit rotations.

Theory of the electronic structure and carrier dynamics of strain-induced (Ga, In)As quantum dots

International Nuclear Information System (INIS)

Boxberg, Fredrik; Tulkki, Jukka

2007-01-01

Strain-induced quantum dots (SIQD) confine electrons and holes to a lateral potential minimum within a near-surface quantum well (QW). The potential minimum is located in the QW below a nanometre-sized stressor crystal grown on top of the QW. SIQD exhibit well-resolved and prominently atomic-like optical spectra, making them ideal for experimental and theoretical studies of mesoscopic phenomena in semiconductor nanocrystals. In this report we review the theory of strain-induced confinement, electronic structure, photonics and carrier relaxation dynamics in SIQD. The theoretical results are compared with available experimental data. Electronic structure calculations are mainly performed using the multiband envelope function approach. Many-body effects are discussed using a direct diagonalization method, albeit, for the sake of computational feasibility, within a two-band model. The QD carrier dynamics are discussed in terms of a master equation model, which accounts for the details of the electronic structure as well as the leading photon, phonon and Coulomb interaction processes. We also discuss the quantum confined Stark effect, the Zeeman splitting and the formation of Landau levels in external fields. Finally, we review a recent theory of the cooling of radiative QD excitons by THz radiation. In particular we discuss the resonance charge transfer of holes between piezoelectric trap states and the deformation potential minima. The agreement between the theory and experiment is fair throughout, but calls for further investigations

Femtosecond-laser induced dynamics of CO on Ru(0001): Deep insights from a hot-electron friction model including surface motion

Science.gov (United States)

Scholz, Robert; Floß, Gereon; Saalfrank, Peter; Füchsel, Gernot; Lončarić, Ivor; Juaristi, J. I.

2016-10-01

A Langevin model accounting for all six molecular degrees of freedom is applied to femtosecond-laser induced, hot-electron driven dynamics of Ru(0001)(2 ×2 ):CO. In our molecular dynamics with electronic friction approach, a recently developed potential energy surface based on gradient-corrected density functional theory accounting for van der Waals interactions is adopted. Electronic friction due to the coupling of molecular degrees of freedom to electron-hole pairs in the metal are included via a local density friction approximation, and surface phonons by a generalized Langevin oscillator model. The action of ultrashort laser pulses enters through a substrate-mediated, hot-electron mechanism via a time-dependent electronic temperature (derived from a two-temperature model), causing random forces acting on the molecule. The model is applied to laser induced lateral diffusion of CO on the surface, "hot adsorbate" formation, and laser induced desorption. Reaction probabilities are strongly enhanced compared to purely thermal processes, both for diffusion and desorption. Reaction yields depend in a characteristic (nonlinear) fashion on the applied laser fluence, as well as branching ratios for various reaction channels. Computed two-pulse correlation traces for desorption and other indicators suggest that aside from electron-hole pairs, phonons play a non-negligible role for laser induced dynamics in this system, acting on a surprisingly short time scale. Our simulations on precomputed potentials allow for good statistics and the treatment of long-time dynamics (300 ps), giving insight into this system which hitherto has not been reached. We find generally good agreement with experimental data where available and make predictions in addition. A recently proposed laser induced population of physisorbed precursor states could not be observed with the present low-coverage model.

Many-particle correlations in quasi-two-dimensional electron-hole systems

International Nuclear Information System (INIS)

Nikolaev, Valentin

2002-01-01

This thesis reports a theoretical investigation of many-particle correlation effects in semiconductor heterostructures containing quantum wells. Particular attention is paid towards quasi-particle pair correlations. Using the Green's function technique and the ladder approximation as a basis, the generalized mass action law, which describes the redistribution of particles between correlated and uncorrelated states in quasi-two-dimensional systems for different temperatures and total densities, is derived. The expression is valid beyond the low-density limit, which allows us to investigate the transition of the system from a dilute exciton gas to a dense electron-hole plasma. A generalized Levinson theorem, which takes k-space filling into account, is formulated. Screening in quasi-two-dimensional systems is analyzed rigorously. Firstly, the qualitatively new mechanism of static local screening by indirect excitons is studied using the simple Thomas-Fermi approximation. Then, a detailed many-body description suitable for a proper account of dynamic screening by a quasi-2D electron-hole plasma, and consistent with the previously derived mass action law, is provided. The generalized Lindhard approximation and excitonic plasmon-pole approximations are also derived. The theory is applied to single and double quantum wells. A self-consistent procedure is developed for numerical investigation of the ionization degree of an electron-hole plasma at different values of temperature/exciton Rydberg ratios. This procedure accounts for screening, k-space filling (exciton bleaching), and the formation of excitons. An abrupt jump in the value of the ionization degree that happens with an increase of the carrier density or temperature (Mott transition) is found in a certain density-temperature region. It has been found that the critical density of the Mott transition for indirect excitons may be much smaller than that for direct excitons. A suggestion has been made that some of the

Prediction of ultraviolet-induced damage during plasma processes in dielectric films using on-wafer monitoring techniques

International Nuclear Information System (INIS)

Ishikawa, Yasushi; Katoh, Yuji; Okigawa, Mitsuru; Samukawa, Seiji

2005-01-01

We measured electron-hole pairs generated in dielectric film using our developed on-wafer monitoring technique to detect electrical currents in the film during the plasma etching processes. The electron-hole pairs were generated by plasma induced ultraviolet (UV) photons, and the number of electron-hole pairs depends on the UV wavelength. In SiO 2 film, UV light, which has a wavelength of less than 140 nm, generates electron-hole pairs, because the band gap energy of the film is 8.8 eV. On the other hand, in Si 3 N 4 film, which has a band gap energy level of 5.0 eV, UV light below 250 nm induces the electron-hole pairs. Additionally, we evaluated the fluorocarbon gas plasma process that induces UV radiation damage using multilayer sensors that consisted of both SiO 2 and Si 3 N 4 stacked films. In these cases, electron-hole pair generation depended on the dielectric film structure. There were more electron-hole pairs generated in the SiO 2 deposited on the Si 3 N 4 film than in the Si 3 N 4 deposited on the SiO 2 film. As a result, our developed on-wafer monitoring sensor was able to predict electron-hole pair generation and the device characteristics

Singlet-triplet annihilation in single LHCII complexes

NARCIS (Netherlands)

Gruber, J.M.; Chmeliov, J.; Kruger, T.P.J.; Valkunas, L.; van Grondelle, R.

2015-01-01

In light harvesting complex II (LHCII) of higher plants and green algae, carotenoids (Cars) have an important function to quench chlorophyll (Chl) triplet states and therefore avoid the production of harmful singlet oxygen. The resulting Car triplet states lead to a non-linear self-quenching

Mesoscopic chaos mediated by Drude electron-hole plasma in silicon optomechanical oscillators

Science.gov (United States)

Wu, Jiagui; Huang, Shu-Wei; Huang, Yongjun; Zhou, Hao; Yang, Jinghui; Liu, Jia-Ming; Yu, Mingbin; Lo, Guoqiang; Kwong, Dim-Lee; Duan, Shukai; Wei Wong, Chee

2017-01-01

Chaos has revolutionized the field of nonlinear science and stimulated foundational studies from neural networks, extreme event statistics, to physics of electron transport. Recent studies in cavity optomechanics provide a new platform to uncover quintessential architectures of chaos generation and the underlying physics. Here, we report the generation of dynamical chaos in silicon-based monolithic optomechanical oscillators, enabled by the strong and coupled nonlinearities of two-photon absorption induced Drude electron–hole plasma. Deterministic chaotic oscillation is achieved, and statistical and entropic characterization quantifies the chaos complexity at 60 fJ intracavity energies. The correlation dimension D2 is determined at 1.67 for the chaotic attractor, along with a maximal Lyapunov exponent rate of about 2.94 times the fundamental optomechanical oscillation for fast adjacent trajectory divergence. Nonlinear dynamical maps demonstrate the subharmonics, bifurcations and stable regimes, along with distinct transitional routes into chaos. This provides a CMOS-compatible and scalable architecture for understanding complex dynamics on the mesoscopic scale. PMID:28598426

Optimal weight gain in triplet pregnancies.

Science.gov (United States)

Johnston, Robert C; Erfani, Hadi; Shamshirsaz, Amir A; Spiel, Melissa; Ravangard, Sam F; Shaman, Majid; Allaf, M Baraa; Shamshirsaz, Alireza A; Haeri, Sina

2017-08-01

To identify appropriate weight gain in triplet gestations, which may aid in reducing the risk of perinatal morbidity within this high-risk cohort. This retrospective cohort study evaluated all non-anomalous triplet pregnancies between 23 and 40 weeks' gestation resulting in live births at five tertiary-care medical centers between 1991 and 2011. Subjects were divided by pre-pregnancy BMI into underweight, normal-weight, overweight, and obese groups, and then stratified by low (gain (≥1.5 lbs/week). Primary outcomes included spontaneous preterm birth and preeclampsia. We included 116 mothers and 348 corresponding neonates for final analysis. The incidence of preeclampsia and preterm delivery less than 32 weeks' gestation was 37% and 41%, respectively. The incidence of preeclampsia increased with weight gain per week, but was not statistically different from subjects who gained less weight. We found no statistical correlation between weight gain per week and preterm delivery. We found no association between preeclampsia or preterm delivery and increasing weight gain in triplet pregnancies. The association with increased risk for preeclampsia was predominantly due to BMI effect. Based on the current study, recommendations for optimal weight gain in mothers with triplet gestations could not be defined.

Can Baird's and Clar's Rules Combined Explain Triplet State Energies of Polycyclic Conjugated Hydrocarbons with Fused 4nπ- and (4n + 2)π-Rings?

Science.gov (United States)

Ayub, Rabia; Bakouri, Ouissam El; Jorner, Kjell; Solà, Miquel; Ottosson, Henrik

2017-06-16

Compounds that can be labeled as "aromatic chameleons" are π-conjugated compounds that are able to adjust their π-electron distributions so as to comply with the different rules of aromaticity in different electronic states. We used quantum chemical calculations to explore how the fusion of benzene rings onto aromatic chameleonic units represented by biphenylene, dibenzocyclooctatetraene, and dibenzo[a,e]pentalene modifies the first triplet excited states (T 1 ) of the compounds. Decreases in T 1 energies are observed when going from isomers with linear connectivity of the fused benzene rings to those with cis- or trans-bent connectivities. The T 1 energies decreased down to those of the parent (isolated) 4nπ-electron units. Simultaneously, we observe an increased influence of triplet state aromaticity of the central 4n ring as given by Baird's rule and evidenced by geometric, magnetic, and electron density based aromaticity indices (HOMA, NICS-XY, ACID, and FLU). Because of an influence of triplet state aromaticity in the central 4nπ-electron units, the most stabilized compounds retain the triplet excitation in Baird π-quartets or octets, enabling the outer benzene rings to adapt closed-shell singlet Clar π-sextet character. Interestingly, the T 1 energies go down as the total number of aromatic cycles within a molecule in the T 1 state increases.

On static triplet structures in fluids with quantum behavior

Science.gov (United States)

Sesé, Luis M.

2018-03-01

The problem of the equilibrium triplet structures in fluids with quantum behavior is discussed. Theoretical questions of interest to the real space structures are addressed by studying the three types of structures that can be determined via path integrals (instantaneous, centroid, and total thermalized-continuous linear response). The cases of liquid para-H2 and liquid neon on their crystallization lines are examined with path-integral Monte Carlo simulations, the focus being on the instantaneous and the centroid triplet functions (equilateral and isosceles configurations). To analyze the results further, two standard closures, Kirkwood superposition and Jackson-Feenberg convolution, are utilized. In addition, some pilot calculations with path integrals and closures of the instantaneous triplet structure factor of liquid para-H2 are also carried out for the equilateral components. Triplet structural regularities connected to the pair radial structures are identified, a remarkable usefulness of the closures employed is observed (e.g., triplet spatial functions for medium-long distances, triplet structure factors for medium k wave numbers), and physical insight into the role of pair correlations near quantum crystallization is gained.

Birth weight discordance and perinatal mortality among triplets

Directory of Open Access Journals (Sweden)

Egić Amira

2005-01-01

Full Text Available INTRODUCTION. The incidence of multiple births has increased in the last decade. Perinatal mortality in triplets is significantly greater than in twin and singleton births. OBJECTIVE. The objective of this study was to describe the extent of birth weight discordance among triplets and to identify its association with an increased risk of perinatal mortality. METHOD A retrospective analysis of triplet births, for the period 1993-2003, was conducted at the Gynaecological-Obstetric Clinic "Narodni Front" in Belgrade. Birth weight discordance was defined as the difference in birth weight between the largest and the smallest triplet's weight of more than 20%. RESULTS. The rate of triplets has increased by almost 75% between the first (7.7% and the last (29.6% 5-year period of the last decade. Triplets are becoming more common because of the frequent use of assisted reproductive technology as a treatment for infertility. In the period 1993-2003, there were a total of 40 triplet live births (24 weeks and greater with incidence of 0.06%. There was no clear association between maternal age, parity, method of conception, birth gestational age, and disorders complicating pregnancy with birth discordance more than 20%. Regarding birth weight groups, statistical significance occurred only in the <999 grams group for discordant and in the 2000-2499 grams group for concordant triplets. Overall, the perinatal mortality rate in the group was 10.8%, the foetal mortality rate was 1.7% (2/120, and the neonatal (0-28 days mortality rate was 9.1% (11/120. An odds ratio of 95% confidence interval shows 3 times greater risk for adverse perinatal outcome in the discordant group. However, the difference was not significant. CONCLUSION. Increasing birth weight discordance may increase the risk of adverse perinatal outcome. Triplet pregnancies, being high risk, require intensive antenatal care in order to prevent preterm delivery and ultrasound in order to diagnose foetal

Probing the singlet character of the two-hole states in cuprate superconductors

NARCIS (Netherlands)

Ghiringhelli, G; Brookes, NB; Tjeng, LH; Mizokawa, T; Tjernberg, O; Menovsky, AA; Steeneken, P.G.

Using spin-resolved resonant photoemission we have probed the singlet vs. triplet character of the two-hole state in the layered cuprates Bi2Sr2CaCu2O8+delta La2-xSrxCuO4 and Sr2CuO2Cl2. The combination of the photon circular polarization with the photoelectron spin detection gives access to the

Hole and electron extraction layers based on graphene oxide derivatives for high-performance bulk heterojunction solar cells.

Science.gov (United States)

Liu, Jun; Xue, Yuhua; Gao, Yunxiang; Yu, Dingshan; Durstock, Michael; Dai, Liming

2012-05-02

By charge neutralization of carboxylic acid groups in graphene oxide (GO) with Cs(2)CO(3) to afford Cesium-neutralized GO (GO-Cs), GO derivatives with appropriate modification are used as both hole- and electron-extraction layers for bulk heterojunction (BHJ) solar cells. The normal and inverted devices based on GO hole- and GO-Cs electron-extraction layers both outperform the corresponding standard BHJ solar cells. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetometry of low-dimensional electron and hole systems

Energy Technology Data Exchange (ETDEWEB)

Usher, A [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Elliott, M [School of Physics and Astronomy, Cardiff University, Queens Buildings, Cardiff CF24 3AA (United Kingdom)], E-mail: a.usher@exeter.ac.uk, E-mail: elliottm@cf.ac.uk

2009-03-11

The high-magnetic-field, low-temperature magnetic properties of low-dimensional electron and hole systems reveal a wealth of fundamental information. Quantum oscillations of the thermodynamic equilibrium magnetization yield the total density of states, a central quantity in understanding the quantum Hall effect in 2D systems. The magnetization arising from non-equilibrium circulating currents reveals details, not accessible with traditional measurements, of the vanishingly small longitudinal resistance in the quantum Hall regime. We review how the technique of magnetometry has been applied to these systems, the most important discoveries that have been made, and their theoretical significance. (topical review)

K-shell-hole production, multiple-hole production, charge transfer, and antisymmetry

International Nuclear Information System (INIS)

Reading, J.F.; Ford, A.L.

1980-01-01

In calculating K-shell-hole production when an ion collides with an atom, account must be taken of the fact that processes involving electrons other than the K-shell electron can occur. For example, after making a K-shell hole an L-shell electron may be knocked into it, or an L-shell vacancy may be produced and the K-shell electron promoted to that vacancy in the ''Fermi sea'' of the target-atom orbitals. In 1973 a theorem was proved by one of the present authors demonstrating that all these multielectron processes cancel in an independent-particle model for the target atom. In this paper it is shown that the same thing occurs for hole production by charge transfer to the ion. The authors demonstrate that multihole production does not obey this simple rule and that the probability for multihole production is not the product of independent single-electron probabilities. The correct expressions that should be used for these processes are given, together with new results for charge-transfer processes accompanied by hole production

Resonant third-harmonic generation of a short-pulse laser from electron-hole plasmas

Energy Technology Data Exchange (ETDEWEB)

Kant, Niti [Department of Physics, Lovely Professional University, Phagwara, Punjab 144 402 (India); Nandan Gupta, Devki [Department of Physics and Astrophysics, University of Delhi, Delhi 110 007 (India); Suk, Hyyong [Advanced Photonics Research Institute (APRI) and Graduate Program of Photonics and Applied Physics, Gwangju Institute of Science and Technology, Gwangju 500 712 (Korea, Republic of)

2012-01-15

In semiconductors, free carriers are created in pairs in inter-band transitions and consist of an electron and its corresponding hole. At very high carrier densities, carrier-carrier collisions dominate over carrier-lattice collisions and carriers begin to behave collectively to form plasma. Here, we apply a short-pulse laser to generate third-harmonic radiation from a semiconductor plasma (electron-hole plasma) in the presence of a transverse wiggler magnetic-field. The process of third-harmonic generation of an intense short-pulse laser is resonantly enhanced by the magnetic wiggler, i.e., wiggler magnetic field provides the necessary momentum to third-harmonic photons. In addition, a high-power laser radiation, propagating through a semiconductor imparts an oscillatory velocity to the electrons and exerts a ponderomotive force on electrons at the third-harmonic frequency of the laser. This oscillatory velocity produces a third-harmonic longitudinal current. And due to the beating of the longitudinal electron velocity and the wiggler magnetic field, a transverse third-harmonic current is produced that drives third-harmonic electromagnetic radiation. It is finally observed that for a specific wiggler wave number value, the phase-matching conditions for the process are satisfied, leading to resonant enhancement in the energy conversion efficiency.

Resonant third-harmonic generation of a short-pulse laser from electron-hole plasmas

International Nuclear Information System (INIS)

Kant, Niti; Nandan Gupta, Devki; Suk, Hyyong

2012-01-01

In semiconductors, free carriers are created in pairs in inter-band transitions and consist of an electron and its corresponding hole. At very high carrier densities, carrier-carrier collisions dominate over carrier-lattice collisions and carriers begin to behave collectively to form plasma. Here, we apply a short-pulse laser to generate third-harmonic radiation from a semiconductor plasma (electron-hole plasma) in the presence of a transverse wiggler magnetic-field. The process of third-harmonic generation of an intense short-pulse laser is resonantly enhanced by the magnetic wiggler, i.e., wiggler magnetic field provides the necessary momentum to third-harmonic photons. In addition, a high-power laser radiation, propagating through a semiconductor imparts an oscillatory velocity to the electrons and exerts a ponderomotive force on electrons at the third-harmonic frequency of the laser. This oscillatory velocity produces a third-harmonic longitudinal current. And due to the beating of the longitudinal electron velocity and the wiggler magnetic field, a transverse third-harmonic current is produced that drives third-harmonic electromagnetic radiation. It is finally observed that for a specific wiggler wave number value, the phase-matching conditions for the process are satisfied, leading to resonant enhancement in the energy conversion efficiency.

Observation of topological surface states and strong electron/hole imbalance in extreme magnetoresistance compound LaBi

Science.gov (United States)

Jiang, J.; Schröter, N. B. M.; Wu, S.-C.; Kumar, N.; Shekhar, C.; Peng, H.; Xu, X.; Chen, C.; Yang, H. F.; Hwang, C.-C.; Mo, S.-K.; Felser, C.; Yan, B. H.; Liu, Z. K.; Yang, L. X.; Chen, Y. L.

2018-02-01

The recent discovery of the extreme magnetoresistance (XMR) in the nonmagnetic rare-earth monopnictides La X (X = P, As, Sb, Bi,), a recently proposed new topological semimetal family, has inspired intensive research effort in the exploration of the correlation between the XMR and their electronic structures. In this work, using angle-resolved photoemission spectroscopy to investigate the three-dimensional band structure of LaBi, we unraveled its topologically nontrivial nature with the observation of multiple topological surface Dirac fermions, as supported by our ab initio calculations. Furthermore, we observed substantial imbalance between the volume of electron and hole pockets, which rules out the electron-hole compensation as the primary cause of the XMR in LaBi.

Colored triplets with integral quantum numbers

International Nuclear Information System (INIS)

Han, M.Y.

1974-01-01

The systematics of low-lying hadron spectra and the relations between mass, cross-section and magnetic moment in terms of ''constituent'' quarks on one hand, and abstraction of the properties of hadronic weak and electromagnetic current in terms of ''current'' quarks on the other hand have been extremely useful. In the category of three triplet models, there are several versions with the varying degree of similarity and difference among them. These include; (1) the paraquarks of order three, (2) the three triplets with SU(3)' x SU(3)'' symmetry, (3) SUB version by Cabibbo et al., and (4) perfect ''color'' symmetry by Gell-Mann. The physical difference among these various versions of the three triplet models and their consequence are discussed with respect to some of the current theoretical and experimental topics. (Iwase, T.)

Above-cutoff impedance measurements of pumping holes for the Collider Liner

International Nuclear Information System (INIS)

Walling, L.; Barts, T.; Ruiz, E.; Turner, W.; Spayd, N.

1994-04-01

A holed liner was considered for the Superconducting Super Collider (SSC) Collider Ring because of vacuum problems caused by photon-induced desorption. The liner would serve to shield the cold surface of the beam tube from the synchrotron radiation and the holes (or slots) would allow distributed pumping by gas-absorption material that could be placed between the liner and the beam tube. The impedance of holes and slots in a liner were studied by means of simulations using both MAFIA and HFSS, analytical modelling, wire measurements and electron beam measurements

Hole and electron extraction layers based on graphene oxide derivatives for high-performance bulk heterojunction solar cells

Energy Technology Data Exchange (ETDEWEB)

Liu, Jun; Gao, Yunxiang; Yu, Dingshan; Dai, Liming [Center of Advanced Science and Engineering for Carbon, Department of Macromolecular, Science and Engineering, Case School of Engineering, Case Western Reserve University, Cleveland, Ohio (United States); Xue, Yuhua [Center of Advanced Science and Engineering for Carbon, Department of Macromolecular, Science and Engineering, Case School of Engineering, Case Western Reserve University, Cleveland, Ohio (United States); Institute of Advanced Materials for Nano-Bio Applications, School of Ophthalmology and Optometry, Wenzhou Medical College, Zhejiang 325027 (China); Durstock, Michael [Materials and Manufacturing Directorate, Air Force Research Laboratory, RXBP, Wright-Patterson Air Force Base, Ohio 45433 (United States)

2012-05-02

By charge neutralization of carboxylic acid groups in graphene oxide (GO) with Cs{sub 2}CO{sub 3} to afford Cesium-neutralized GO (GO-Cs), GO derivatives with appropriate modification are used as both hole- and electron-extraction layers for bulk heterojunction (BHJ) solar cells. The normal and inverted devices based on GO hole- and GO-Cs electron-extraction layers both outperform the corresponding standard BHJ solar cells. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Electronic hole localization in rutile and anatase TiO2 - Self-interaction correction in Delta-SCF DFT

DEFF Research Database (Denmark)

Zawadzki, Pawel; Jacobsen, Karsten Wedel; Rossmeisl, Jan

2011-01-01

We study electronic hole localization in rutile and anatase titanium dioxide by means of Δ-Self-Consistent Field Density Functional Theory. In order to compare stabilities of the localized and the delocalized hole states we introduce a simple correction to the wrong description of the localizatio...

The effects of electron and hole transport layer with the electrode work function on perovskite solar cells

Science.gov (United States)

Deng, Quanrong; Li, Yiqi; Chen, Lian; Wang, Shenggao; Wang, Geming; Sheng, Yonglong; Shao, Guosheng

2016-09-01

The effects of electron and hole transport layer with the electrode work function on perovskite solar cells with the interface defects were simulated by using analysis of microelectronic and photonic structures-one-dimensional (AMPS-1D) software. The simulation results suggest that TiO2 electron transport layer provides best device performance with conversion efficiency of 25.9% compared with ZnO and CdS. The threshold value of back electrode work function for Spiro-OMeTAD, NiO, CuI and Cu2O hole transport layer are calculated to be 4.9, 4.8, 4.7 and 4.9 eV, respectively, to reach the highest conversion efficiency. The mechanisms of device physics with various electron and hole transport materials are discussed in details. The device performance deteriorates gradually as the increased density of interface defects located at ETM/absorber or absorber/HTM. This research results can provide helpful guidance for materials and metal electrode choice for perovskite solar cells.

Experimental Investigation of Triplet Correlation Approximations for Fluid Water.

Science.gov (United States)

Pallewela, Gayani N; Ploetz, Elizabeth A; Smith, Paul E

2018-08-25

Triplet correlations play a central role in our understanding of fluids and their properties. Of particular interest is the relationship between the pair and triplet correlations. Here we use a combination of Fluctuation Solution Theory and experimental pair radial distribution functions to investigate the accuracy of the Kirkwood Superposition Approximation (KSA), as given by integrals over the relevant pair and triplet correlation functions, at a series of state points for pure water using only experimental quantities. The KSA performs poorly, in agreement with a variety of other studies. Several additional approximate relationships between the pair and triplet correlations in fluids are also investigated and generally provide good agreement for the fluid thermodynamics for regions of the phase diagram where the compressibility is small. A simple power law relationship between the pair and triplet fluctuations is particularly successful for state points displaying low to moderately high compressibilities.

The Role of Electron Transport and Trapping in MOS Total-Dose Modeling

International Nuclear Information System (INIS)

Fleetwood, D.M.; Winokur, P.S.; Riewe, L.C.; Flament, O.; Paillet, P.; Leray, J.L.

1999-01-01

Radiation-induced hole and electron transport and trapping are fundamental to MOS total-dose models. Here we separate the effects of electron-hole annihilation and electron trapping on the neutralization of radiation-induced charge during switched-bias irradiation for hard and soft oxides, via combined thermally stimulated current (TSC) and capacitance-voltage measurements. We also show that present total-dose models cannot account for the thermal stability of deeply trapped electrons near the Si/SiO 2 interface, or the inability of electrons in deep or shallow traps to contribute to TSC at positive bias following (1) room-temperature, (2) high-temperature, or (3) switched-bias irradiation. These results require revisions of modeling parameters and boundary conditions for hole and electron transport in SiO 2 . The nature of deep and shallow electron traps in the near-interfacial SiO 2 is discussed

Modulating the Electron-Hole Interaction in a Hybrid Lead Halide Perovskite with an Electric Field.

Science.gov (United States)

Leijtens, Tomas; Srimath Kandada, Ajay Ram; Eperon, Giles E; Grancini, Giulia; D'Innocenzo, Valerio; Ball, James M; Stranks, Samuel D; Snaith, Henry J; Petrozza, Annamaria

2015-12-16

Despite rapid developments in both photovoltaic and light-emitting device performance, the understanding of the optoelectronic properties of hybrid lead halide perovskites is still incomplete. In particular, the polarizability of the material, the presence of molecular dipoles, and their influence on the dynamics of the photoexcitations remain an open issue to be clarified. Here, we investigate the effect of an applied external electric field on the photoexcited species of CH3NH3PbI3 thin films, both at room temperature and at low temperature, by monitoring the photoluminescence (PL) yield and PL decays. At room temperature we find evidence for electric-field-induced reduction of radiative bimolecular carrier recombination together with motion of charged defects that affects the nonradiative decay rate of the photoexcited species. At low temperature (190 K), we observe a field-induced enhancement of radiative free carrier recombination rates that lasts even after the removal of the field. We assign this to field-induced alignment of the molecular dipoles, which reduces the vibrational freedom of the lattice and the associated local screening and hence results in a stronger electron-hole interaction.

Measurement of heat treatment induced residual stresses by using ESPI combined with hole-drilling method

Directory of Open Access Journals (Sweden)

Jie Cheng

2010-08-01

Full Text Available In this study, residual stresses in heat treated specimen were measured by using ESPI (Electronic Speckle-Pattern Interferometry combined with the hole-drilling method. The specimen, made of SUS 304 austenitic stainless steel, was quenched and water cooled to room temperature. Numerical simulation using a hybrid FDM/FEM package was also carried out to simulate the heat treatment process. As a result, the thermal stress fields were obtained from both the experiment and the numerical simulation. By comparision of stress fields, results from the experimental method and numerical simulation well agreed to each other, therefore, it is proved that the presented experimental method is applicable and reliable for heat treatment induced residual stress measurement.

Uncorrelated electron-hole transition energy in GaN|InGaN|GaN spherical QDQW nanoparticles

International Nuclear Information System (INIS)

Haddou El Ghazi; Anouar Jorio and Izeddine Zorkani

2013-01-01

The electron (hole) energy and uncorrelated 1S e - 1S h electron-hole transition in Core(GaN)|well(In x Ga 1-x N)|shell(GaN) spherical QDQW nanoparticles is investigated as a function of the inner and the outer radii. The calculations are performed within the framework of the effective-mass approximation and the finite parabolic potential confinement barrier in which two confined parameters are taking account. The Indium composition effect is also investigated. A critical value of the outer and the inner ratio is obtained which constitutes the turning point of two indium composition behaviors. (author)

Brane holes

International Nuclear Information System (INIS)

Frolov, Valeri P.; Mukohyama, Shinji

2011-01-01

The aim of this paper is to demonstrate that in models with large extra dimensions under special conditions one can extract information from the interior of 4D black holes. For this purpose we study an induced geometry on a test brane in the background of a higher-dimensional static black string or a black brane. We show that, at the intersection surface of the test brane and the bulk black string or brane, the induced metric has an event horizon, so that the test brane contains a black hole. We call it a brane hole. When the test brane moves with a constant velocity V with respect to the bulk black object, it also has a brane hole, but its gravitational radius r e is greater than the size of the bulk black string or brane r 0 by the factor (1-V 2 ) -1 . We show that bulk ''photon'' emitted in the region between r 0 and r e can meet the test brane again at a point outside r e . From the point of view of observers on the test brane, the events of emission and capture of the bulk photon are connected by a spacelike curve in the induced geometry. This shows an example in which extra dimensions can be used to extract information from the interior of a lower-dimensional black object. Instead of the bulk black string or brane, one can also consider a bulk geometry without a horizon. We show that nevertheless the induced geometry on the moving test brane can include a brane hole. In such a case the extra dimensions can be used to extract information from the complete region of the brane-hole interior. We discuss thermodynamic properties of brane holes and interesting questions which arise when such an extra-dimensional channel for the information mining exists.

Motional spin relaxation in photoexcited triplet states

International Nuclear Information System (INIS)

Harryvan, D.; Faassen, E. van

1997-01-01

Transient EPR experiments were performed on photoexcited spin triplet states of the luminescent dye EOSIN-Y in diluted (order of 1 nMol) frozen propane-1-ol solutions at various temperatures. Photoexcitation was achieved by irradiation with intense, short laser pulses. The details of the spin relaxation, in particular the dependence on time, magnetic field and microwave field strength are all reproduced by a model which computes the total magnetization in a population of photoexcited triplet states undergoing random reorientational motion. Using this model, we estimated the motional correlation times to be around a microsecond. This timescale is two orders of magnitude slower than the phase memory time of the triplets. (author)

MTGAN: Speaker Verification through Multitasking Triplet Generative Adversarial Networks

OpenAIRE

Ding, Wenhao; He, Liang

2018-01-01

In this paper, we propose an enhanced triplet method that improves the encoding process of embeddings by jointly utilizing generative adversarial mechanism and multitasking optimization. We extend our triplet encoder with Generative Adversarial Networks (GANs) and softmax loss function. GAN is introduced for increasing the generality and diversity of samples, while softmax is for reinforcing features about speakers. For simplification, we term our method Multitasking Triplet Generative Advers...

'Blueberry' Triplets Born in Rock

Science.gov (United States)

2004-01-01

This microscopic image, taken at the outcrop region dubbed 'Berry Bowl' near the Mars Exploration Rover Opportunity's landing site, shows the sphere-like grains or 'blueberries' that fill Berry Bowl. Of particular interest is the blueberry triplet, which indicates that these geologic features grew in pre-existing wet sediments. Other sphere-like grains that form in the air, such as impact spherules or ejected volcanic material called lapilli, are unlikely to fuse along a line and form triplets. This image was taken by the rover's microscopic imager on the 46th martian day, or sol, of its mission.

Role of electronic nematicity in the interplay between s- and d-wave broken-symmetry states

International Nuclear Information System (INIS)

Kee, Hae-Young

2010-01-01

To understand the role of electronic nematic order in the interplay between s- and d-wave particle-particle or particle-hole condensate states, relations between various s- and d-wave order parameters are studied. We find that the nematic operator transforms two independent six-dimensional vectors. The d-wave superconducting, d-density wave, and antiferromagnetic orders are organized into one vector, and the s-wave superconducting, charge density wave, and spin-triplet d-density wave orders into the other vector. Each vector acts as a superspin and transforms under the action of SO(6) where charge, spin, η- and π-pairing, spin-triplet nematic operators satisfy the SO(6) Lie algebra. Electronic nematic order is not a part of the SO(6) group. It commutes with all 15 generators. Our findings imply that nematic order does not affect the competition among the order parameters within the same superspin, while it strongly interferes the interplay between two order parameters that belong to different superspins. For example, nematicity allows a linear coupling between d- and s-wave superconducting order parameters which modifies the superconducting transition temperature. A generalized Ginzburg-Landau theory and further physical implications are discussed.

Sensitized Triplet Formation of Chlorophyll-A and beta-Carotene

DEFF Research Database (Denmark)

Jensen, Nina Mejlhede; Wilbrandt, Robert Walter; Pagsberg, Palle Bjørn

1980-01-01

The naphthalene-sensitized formation of triplet excited chlorophyll-a (Chl-a) and all-transß-carotene has been studied by pulse radiolysis. The rate constants for transfer of triplet energy from naphthalene to Chl-a and all-transß-carotene in benzene at 25°C are (3.6 ± 0.6)·109M-1 s-1 and (10.7 ± 1.......2)·109M-1 s-1, respectively. The decays of the excited triplet states of naphthalene, Chl-a and all-transß-carotene all follow a mixed first-and second-order mechanism. The first-order rate constant for triplet decay is strongly dose dependent for naphthalene but only slightly dependent and independent...

Charge generation and trapping in bisphenol-A-polycarbonate/N-isopropylcarbazole mixture: A study by electron bombardment-induced conductivity

International Nuclear Information System (INIS)

Santos, S.; Caraballo, D.

2007-01-01

Electron bombardment-induced conductivity measurements were carried out on cast films of N-isopropylcarbazole (NIPC) dispersed into an amorphous matrix of bisphenol-A-polycarbonate. The charge generation was studied by estimating the hole yield (g), the fraction of charge escaping recombination, as a function of electric field and concentration of NIPC at room temperature. The hole yield, besides increasing by increasing the content of NIPC, was observed to increase with the electric field in the manner predicted by the Onsager theory of geminate recombination. Deep trapping levels were studied by filling under electron bombardment and observing transients. The deep traps were neutral in nature with a concentration on the order of 8.0x10 14 cm -3 , which was low enough not to degrade transport under normal conditions

BVRI SURFACE PHOTOMETRY OF ISOLATED GALAXY TRIPLETS

International Nuclear Information System (INIS)

Hernandez-Toledo, H. M.; Mendez-Hernandez, H.; Aceves, H.; OlguIn, L.

2011-01-01

Optical broadband BVRI observations of 54 galaxies selected from the Catalog of Isolated Triplets of Galaxies in the Northern Hemisphere have been carried out at San Pedro Martir National Observatory to evaluate their photometric and morphological properties. We complement our analysis with Two-Micron All Sky Survey (2MASS) and Sloan Digital Sky Survey (SDSS) images and look for signatures likely related to interactions/mergers. We report apparent/absolute BVRI magnitudes and colors for the 54 galaxies. The membership of these galaxies is re-evaluated by imposing a reasonable condition of concordant redshifts upon the original selection criteria, rendering a final sample of 34 galaxies in 13 triplets, 12 galaxies in close pairs, and 8 galaxy outliers. The triplets are spiral-dominated systems in different dynamical stages from loosely interacting to almost merged objects. The incidence fraction of features likely associated with interactions is ∼56%, similar to those found in northern and southern compact groups. The average fraction of bars is 35% with a mean value of maximum bar ellipticity ε max ∼ 0.4. Bars are hosted in the late-type triplet spirals, almost twice more than in early-type spirals. The global fraction of rings is 20%, all in the late-type components. The overdensity of triplets with respect to the background and their current dynamical status, as devised from our estimate of their dynamical parameters, namely the harmonic radius R H , velocity dispersion σ, dimensionless crossing time H 0 τ c , and virial mass M V , appear to be sufficient to favor galaxy transformations similar to those seen in dense groups and clusters. By contrast, the lower fraction of bonafide ellipticals and the relatively higher fraction of late-type spirals make these triplets essentially different from the Hickson Compact Groups and more representative of the field. A modest 1.6 enhancement factor in the optical luminosity of the late-type triplet components

Luminescence of high density electron-hole plasma in CdS and CdSe in a wide temperature range

International Nuclear Information System (INIS)

Yoshida, H.; Shionoya, S.

1983-01-01

Time-resolved spectra of the spontaneous luminescence of the high density electron-hole plasma (EHP) in CdS and CdSe are observed in a wide range of temperature which is surely higher than the calculated critical temperature for electron-hole liquid formation, in order to carry forward discussion on dynamic nature of the EHP previously observed in 4.2 K experiments. Spectra in the late stage are analyzed, and obtained values of the reduced bandgap energy and chemical potential are compared with those theoretically calculated for higher temperatures. The aspects of the change of the spectral shape in the late stage are hard to understand. Unfortunately no clear conclusion is drawn on the nature of the EHP produced at 4.2 K. The only thing one can say is that the condensed electron-hole liquid state, which is in equilibrium with the exciton state, is not realized. (author)

The xanthophylls in light-harvesting complex II of higher plants: light harvesting and triplet quenching.

NARCIS (Netherlands)

Peterman, E.J.G.; Gradinaru, C.C.; Calkoen, F.; Borst, J.C.; van Grondelle, R.; van Amerongen, H.

1997-01-01

A spectral and functional assignment of the xanthophylls in monomeric and trimeric light-harvesting complex II of green plants has been obtained using HPLC analysis of the pigment composition, laser-flash induced triplet- minus-singlet, fluorescence excitation, and absorption spectra. It is shown

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

Energy Technology Data Exchange (ETDEWEB)

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

2016-01-28

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

Polarization-induced hole doping in N-polar III-nitride LED grown by metalorganic chemical vapor deposition

KAUST Repository

Yan, Long

2018-05-03

Polarization-induced doping has been shown to be effective for wide-bandgap III-nitrides. In this work, we demonstrated a significantly enhanced hole concentration via linearly grading an N-polar AlxGa1-xN (x = 0–0.3) layer grown by metal-organic chemical vapor deposition. The hole concentration increased by ∼17 times compared to that of N-polar p-GaN at 300 K. The fitting results of temperature-dependent hole concentration indicated that the holes in the graded p-AlGaN layer comprised both polarization-induced and thermally activated ones. By optimizing the growth conditions, the hole concentration was further increased to 9.0 × 1017 cm−3 in the graded AlGaN layer. The N-polar blue-violet light-emitting device with the graded p-AlGaN shows stronger electroluminescence than the one with the conventional p-GaN. The study indicates the potential of the polarization doping technique in high-performance N-polar light-emitting devices.

Polarization-induced hole doping in N-polar III-nitride LED grown by metalorganic chemical vapor deposition

KAUST Repository

Yan, Long; Zhang, Yuantao; Han, Xu; Deng, Gaoqiang; Li, Pengchong; Yu, Ye; Chen, Liang; Li, Xiaohang; Song, Junfeng

2018-01-01

Polarization-induced doping has been shown to be effective for wide-bandgap III-nitrides. In this work, we demonstrated a significantly enhanced hole concentration via linearly grading an N-polar AlxGa1-xN (x = 0–0.3) layer grown by metal-organic chemical vapor deposition. The hole concentration increased by ∼17 times compared to that of N-polar p-GaN at 300 K. The fitting results of temperature-dependent hole concentration indicated that the holes in the graded p-AlGaN layer comprised both polarization-induced and thermally activated ones. By optimizing the growth conditions, the hole concentration was further increased to 9.0 × 1017 cm−3 in the graded AlGaN layer. The N-polar blue-violet light-emitting device with the graded p-AlGaN shows stronger electroluminescence than the one with the conventional p-GaN. The study indicates the potential of the polarization doping technique in high-performance N-polar light-emitting devices.

Electron Transfer from Triplet State of TIPS-Pentacene Generated by Singlet Fission Processes to CH3NH3PbI3 Perovskite.

Science.gov (United States)

Lee, Sangsu; Hwang, Daesub; Jung, Seok Il; Kim, Dongho

2017-02-16

To reveal the applicability of singlet fission processes in perovskite solar cell, we investigated electron transfer from TIPS-pentacene to CH 3 NH 3 PbI 3 (MAPbI 3 ) perovskite in film phase. Through the observation of the shorter fluorescence lifetime in TIPS-pentacene/MAPbI 3 perovskite bilayer film (5 ns) compared with pristine MAPbI 3 perovskite film (20 ns), we verified electron-transfer processes between TIPS-pentacene and MAPbI 3 perovskite. Furthermore, the observation of singlet fission processes, a faster decay rate, TIPS-pentacene cations, and the analysis of kinetic profiles of the intensity ratio between 500 and 525 nm in the TA spectra of the TIPS-pentacene/MAPbI 3 perovskite bilayer film indicate that electron transfer occurs from triplet state of TIPS-pentacene generated by singlet fission processes to MAPbI 3 perovskite conduction band. We believe that our results can provide useful information on the design of solar cells sensitized by singlet fission processes and pave the way for new types of perovskite solar cells.

Influence of relaxation processes in polymers on energy transfer by triplet levels

International Nuclear Information System (INIS)

Ibraev, N.Kh.; Zhunusbekov, A.M.

1996-01-01

Temperature influence on triplet-triplet (T-T) energy transfer between molecules of eosin and 3,4-benzopyrene is studied. Polyvenylbuteryl films have been used in capacity of polymer matrix. Calculation has being carried out on spectral-kinetic unit. It is revealed, that 3,4-benzopyrene triplets have been formed in polymer matrix after end of T-T energy transfer. These triplets join in a reaction of mixed triplet-triplet annihilation with non-blow out triplets of eosin and its sensitize slowed fluorescence (SF) of donor. This explains non-exponent character of eosin's dumping kinetics. Non-linear dependence of SF output ration to eosin phosphorescence output under presence of 3,4-benzopyrene molecules in film indicates on process of mixed annihilation. Fractal character of SF donor and acceptor has been evidenced about microscopical distribution of phosphor in polymer. 13 refs., 5 figs

Analysis of generic insertions made of two symmetric triplets

CERN Document Server

D'Amico, T E

1998-01-01

This paper reports on the study undertaken to explore the capabilities of a symmetric triplet to achieve the optics constraints required by the inner triplet of an insertion and more generally of a co mplete insertion made of two symmetric triplets to match a double focus to a FODO lattice. It is based on analytical treatment formulating a number of constraints equal to the parameters available. Th is thorough and systematic analysis made it possible to establish for an inner triplet as well as for a complete insertion the existence of solutions and to explicitly find out all the solutions, with out resorting to unguided numerical searches. As a by-product, a lattice transformer, made of a single triplet, that matches two different FODO cells has been singled out and studied in details. The r esults should be profitable in a number of cases. Here, the method is applied to an insertion of the type of an experimental LHC insertion in order to investigate its domain of validity and tunability .

Broadband Cooling Spectra of Hot Electrons and Holes in PbSe Quantum Dots

NARCIS (Netherlands)

Spoor, F.C.M.; Tomić, Stanko; Houtepen, A.J.; Siebbeles, L.D.A.

2017-01-01

Understanding cooling of hot charge carriers in semiconductor quantum dots (QDs) is of fundamental interest and useful to enhance the performance of QDs in photovoltaics. We study electron and hole cooling dynamics in PbSe QDs up to high energies where carrier multiplication occurs. We

Assessment of immunological properties of neurofilament triplet proteins.

Science.gov (United States)

Schlaepfer, W W; Lee, V; Wu, H L

1981-12-07

The relationship between mammalian neurofilament triplet proteins was studied immunologically using rabbit and guinea pig antibodies to bovine neurofilament triplet proteins. Neurofilament proteins were separated by preparative electrophoresis, each protein being isolated and re-electrophoresed to enhance purification. Antisera to 68,000 (P68), 150,000 (P150) and 200,000 (P200) dalton neurofilament proteins showed greatest activity with the corresponding protein immunogen but also revealed cross-reactivity with the other two neurofilament proteins when assessed by the ELISA method. The same antigenic inoculum elicited variable cross-reactivity, more in the guinea pig than in the rabbit. Rabbit antisera to P68 was specific in that it did not cross-react with P150 or P200. Rabbit antisera to P150 and to P200 were rendered specific by absorption with P200 and P150, respectively. By electron microscopy, isolated neurofilaments became decorated with an uniform coat of antibodies when exposed to specific antisera for each of the neurofilament proteins. By indirect immunofluorescence, each antisera showed identical patterns of tissue localization, corresponding to the distribution of neurofilaments in peripheral nerve, spinal ganglia, spinal cord, cerebellum and cerebrum. Neurofilament antigens were not detected in liver, kidney, spleen, lung, bladder, intestine, aorta, heart or tongue.

Higher-Spin Triplet Fields and String Theory

Directory of Open Access Journals (Sweden)

D. Sorokin

2010-01-01

Full Text Available We review basic properties of reducible higher-spin multiplets, called triplets, and demonstrate how they naturally appear as part of the spectrum of String Field Theory in the tensionless limit. We show how in the frame-like formulation the triplet fields are endowed with the geometrical meaning of being components of higher-spin vielbeins and connections and present actions describing their free dynamics.

Polarized fine structure in the excitation spectrum of a negatively charged quantum dot

OpenAIRE

Ware, M. E.; Stinaff, E. A.; Gammon, D.; Doty, M. F.; Bracker, A. S.; Gershoni, D.; Korenev, V. L.; Badescu, S. C.; Lyanda-Geller, Y.; Reinecke, T. L.

2005-01-01

We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of qua...

Rate constant of free electrons and holes recombination in thin films CdSe

International Nuclear Information System (INIS)

Radychev, N.A.; Novikov, G.F.

2006-01-01

Destruction kinetics of electrons generated in thin films CdSe by laser impulse (wave length is 337 nm, period of impulse - 8 nc) is studied by the method of microwave photoconductivity (36 GHz) at 295 K. Model of the process was suggested using the analysis of kinetics of photo-responses decay, and it allowed determination of rate constant of recombination of free electrons and holes in cadmium selenide - (4-6)x10 -11 cm 3 s -1 [ru

Electron trapping during irradiation in reoxidized nitrided oxide

International Nuclear Information System (INIS)

Mallik, A.; Vasi, J.; Chandorkar, A.N.

1993-01-01

Isochronal detrapping experiments have been performed following irradiation under different gate biases in reoxidized nitrided oxide (RNO) MOS capacitors. These show electron trapping by the nitridation-induced electron traps at low oxide fields during irradiation. A difference in the detrapping behavior of trapped holes and electrons is observed, with trapped holes being detrapped at relatively lower temperatures compared to trapped electrons. Electron trapping shows a strong dependence on tile magnitude of the applied gate bias during irradiation but is independent of its polarity. Conventional oxide devices, as expected, do not show any electron trapping during irradiation by the native electron traps. Finally, a comparison of the isochronal detrapping behavior following irradiation and following avalanche injection of electrons has been made to estimate the extent of electron trapping. The results show that electron trapping by the nitridation-induced electron traps does not play the dominant role in improving radiation performance of RNO, though its contribution cannot be completely neglected for low oxide field irradiations

Electron ejection from solids induced by fast highly-charged ions

Energy Technology Data Exchange (ETDEWEB)

Schiwietz, G. [Hahn-Meitner-Inst. GmbH, Berlin (Germany). Abt. FD; Xiao, G. [Hahn-Meitner-Inst. GmbH, Berlin (Germany). Abt. FD

1996-02-01

Total electron-ejection yields and Auger-electron spectra for highly-charged ions interacting with different foil targets have been investigated in this work. New experimental and theoretical data for normal incident 5 MeV/u heavy ions on graphite and polypropylene foils are presented and discussed. These two materials have been selected as model systems representing conductors and insulator targets. Our measured projectile nuclear-charge dependence of the total electron yield from carbon foils clearly deviates from results of some transport models that predict a proportionality with respect to the electronic stopping power of the projectiles. Possible reasons for this deviation are discussed. We have also extended our measurements on cascade-induced C-KLL Auger-electron production. The corresponding results for 5 MeV/u S ions on carbon were obtained with a new method and agree fairly well with previous data. Furthermore, we have performed an experimental and theoretical investigation on the nuclear-track potential in insulators. Comparison of experimental data with theoretical results for N{sup 7+}, Ne{sup 9+}, Ar{sup 16+} and Ni{sup 23+} ions allow for an estimate of the electron/hole pair recombination time at the center of the track in polypropylene. (orig.).

Mixed Inert scalar triplet dark matter, radiative neutrino masses and leptogenesis

Directory of Open Access Journals (Sweden)

Wen-Bin Lu

2017-11-01

Full Text Available The neutral component of an inert scalar multiplet with hypercharge can provide a stable dark matter particle when its real and imaginary parts have a splitting mass spectrum. Otherwise, a tree-level dark-matter-nucleon scattering mediated by the Z boson will be much above the experimental limit. In this paper we focus on a mixed inert scalar triplet dark matter scenario where a complex scalar triplet with hypercharge can mix with another real scalar triplet without hypercharge through their renormalizable coupling to the standard model Higgs doublet. We consider three specified cases that carry most of the relevant features of the full parameter space: (i the neutral component of the real triplet dominates the dark matter particle, (ii the neutral component of the complex triplet dominates the dark matter particle; and (iii the neutral components of the real and complex triplets equally constitute the dark matter particle. Subject to the dark matter relic abundance and direct detection constraint, we perform a systematic study on the allowed parameter space with particular emphasis on the interplay among triplet-doublet terms and gauge interactions. In the presence of these mixed inert scalar triplets, some heavy Dirac fermions composed of inert fermion doublets can be utilized to generate a tiny Majorana neutrino mass term at one-loop level and realize a successful leptogenesis for explaining the cosmic baryon asymmetry.

Black-holes-hedgehogs in the false vacuum and a new physics beyond the Standard Model

Science.gov (United States)

Das, C. R.; Laperashvili, L. V.; Sidharth, B. G.; Nielsen, H. B.

2017-12-01

In the present talk, we consider the existence of the two degenerate universal vacua: a) the first Electroweak vacuum at v = 246 GeV - “true vacuum”, and b) the second Planck scale “false vacuum” at v 2 ∼ 1018 GeV. In these vacua, we investigated the different topological defects. The main aim of this paper is an investigation of the hedgehog’s configurations as defects of the false vacuum. In the framework of the f(R) gravity, suggested by authors in their Gravi-Weak Unification model, we obtained a black hole solution, which corresponds to a “hedgehog” - global monopole, “swallowed” by a black-hole with mass ∼ 1019 GeV. These black-holes form a lattice-like structure of the vacuum at the Planck scale. Considering the results of the hedgehog lattice theory in the framework of the SU(2) Yang-Mills gauge-invariant theory with hedgehogs in the Wilson loops, we have used the critical value of temperature for the hedgehog’s confinement phase. This result gave us the possibility to conclude that there exist triplet Higgs fields which can contribute to the SM at the energy scale ≃ 104 ∼ 105 GeV. Showing a new physics at the scale 10÷100 TeV, these triplet Higgs particles can provide the stability of the EW-vacuum of the SM.

sl(2)-1/2 and the triplet model

International Nuclear Information System (INIS)

Ridout, David

2010-01-01

Conformal field theories with sl(2) -1/2 symmetry are studied with a view to investigating logarithmic structures. Applying the parafermionic coset construction to the non-logarithmic theory, a part of the structure of the triplet model is uncovered. In particular, the coset theory is shown to admit the triplet W-algebra as a chiral algebra. This motivates the introduction of an augmented sl(2) -1/2 -theory for which the corresponding coset theory is precisely the triplet model. This augmentation is envisaged to lead to a precise characterisation of the 'logarithmic lift' of the non-logarithmic sl(2) -1/2 -theory that has been proposed by Lesage et al.

Electron and hole spectrum in InAs quantum dot renormalized by InAs/GaAs heterostructure deformation

International Nuclear Information System (INIS)

Dan'kiv, O.O.; Peleshchak, R.M.

2005-01-01

Analytical expressions describing the energy spectrum of electrons and holes are obtained for a quantum dot occurring in a self-consistent strain field created by an array of coherently stressed quantum dots. A method of taking into account the lattice mismatch at the quantum dot-matrix interface is proposed that allows for the dependence of the mismatch parameter on the quantum dot size and the matrix layer thickness. It is shown that the internal elastic strain arising at the quantum dot-matrix interface influences the energy spectrum of electrons more significantly than the spectrum of holes [ru

The inversion layer of electric fields and electron phase-space-hole structure during two-dimensional collisionless magnetic reconnection

International Nuclear Information System (INIS)

Chen Lijen; Lefebvre, Bertrand; Torbert, Roy B.; Daughton, William S.

2011-01-01

Based on two-dimensional fully kinetic simulations that resolve the electron diffusion layer in undriven collisionless magnetic reconnection with zero guide field, this paper reports the existence and evolution of an inversion layer of bipolar electric fields, its corresponding phase-space structure (an electron-hole layer), and the implication to collisionless dissipation. The inversion electric field layer is embedded in the layer of bipolar Hall electric field and extends throughout the entire length of the electron diffusion layer. The electron phase-space hole structure spontaneously arises during the explosive growth phase when there exist significant inflows into the reconnection layer, and electrons perform meandering orbits across the layer while being cyclotron-turned toward the outflow directions. The cyclotron turning of meandering electrons by the magnetic field normal to the reconnection layer is shown to be a primary factor limiting the current density in the region where the reconnection electric field is balanced by the gradient (along the current sheet normal) of the off-diagonal electron pressure-tensor.

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

International Nuclear Information System (INIS)

Li, Wei; Zhang, Qin; Kirillov, Oleg A.; Levin, Igor; Richter, Curt A.; Gundlach, David J.; Nguyen, N. V.; Bijesh, R.; Datta, S.; Liang, Yiran; Peng, Lian-Mao; Liang, Xuelei

2014-01-01

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 2 O 3 /InAs/GaSb layer structure, the barrier height from the top of the InAs and GaSb valence bands to the bottom of the Al 2 O 3 conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of the Al 2 O 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

Spectral and spatial resolving of photoelectric property of femtosecond laser drilled holes of GaSb(1-x)Bi(x).

Science.gov (United States)

Pan, C B; Zha, F X; Song, Y X; Shao, J; Dai, Y; Chen, X R; Ye, J Y; Wang, S M

2015-07-15

Femtosecond laser drilled holes of GaSbBi were characterized by the joint measurements of photoconductivity (PC) spectroscopy and laser-beam-induced current (LBIC) mapping. The excitation light in PC was focused down to 60 μm presenting the spectral information of local electronic property of individual holes. A redshift of energy band edge of about 6-8 meV was observed by the PC measurement when the excitation light irradiated on the laser drilled holes. The spatial resolving of photoelectric property was achieved by the LBIC mapping which shows "pseudo-holes" with much larger dimensions than the geometric sizes of the holes. The reduced LBIC current with the pseudo-holes is associated with the redshift effect indicating that the electronic property of the rim areas of the holes is modified by the femtosecond laser drilling.

The effect of electron and hole doping on the thermoelectric properties of shandite-type Co3Sn2S2

Science.gov (United States)

Mangelis, Panagiotis; Vaqueiro, Paz; Jumas, Jean-Claude; da Silva, Ivan; Smith, Ronald I.; Powell, Anthony V.

2017-07-01

Electron and hole doping in Co3Sn2S2, through chemical substitution of cobalt by the neighbouring elements, nickel and iron, affects both the structure and thermoelectric properties. Electron doping to form Co3-xNixSn2S2 (0≤x≤3) results in an expansion of the kagome layer and materials become increasingly metallic as cobalt is substituted. Conversely, hole doping in Co3-xFexSn2S2 (0≤x≤0.6) leads to a transition from metallic to n-type semiconducting behaviour at x=0.5. Iron substitution induces a small increase in the separation between the kagome layers and improves the thermoelectric performance. Neutron diffraction data reveal that substitution occurs at the Co 9(d) site in a disordered fashion. Mössbauer spectroscopy reveals two iron environments with very different isomer shifts, which may be indicative of a mixed-valence state, while Sn exhibits an oxidation state close to zero in both series. Co2.6Fe0.4Sn2S2 exhibits a maximum figure-of-merit, ZT=0.2 at 523 K while Co2.4Fe0.6Sn2S2 reaches a power factor of 10.3 μW cm-1 K-2 close to room temperature.

The microjetting behavior from single laser-induced bubbles generated above a solid boundary with a through hole

Science.gov (United States)

Abboud, Jack E.; Oweis, Ghanem F.

2013-01-01

An inertial bubble collapsing near a solid boundary generates a fast impulsive microjet directed toward the boundary. The jet impacts the solid boundary at a high velocity, and this effect has been taken advantage of in industrial cleaning such as when tiny bubbles are driven ultrasonically to cavitate around machined parts to produce jets that are believed to induce the cleaning effect. In this experimental investigation, we are interested in the jetting from single cavities near a boundary. By introducing a through hole in the boundary beneath a laser-induced bubble, it is hypothesized that the forming jet, upon bubble implosion, will proceed to penetrate through the hole to the other side and that it may be utilized in useful applications such as precise surgeries. It was found that the growth of the bubble induced a fast flow through the hole and lead to the formation of secondary hydrodynamic cavitation. The experiments also showed the formation of a counter jet directed away from the hole and into the bubble. During the growth phase of the bubble, and near the point of maximum expansion, the bubble wall bulged out toward the hole in a `bulb' like formation, which sometimes resulted in the pinching-off of a secondary small bubble. This was ensued by the inward recoiling of the primary bubble wall near the pinch-off spot, which developed into a counter jet seen to move away from the hole and inward into the bubble.

Laser-induced grating in ZnO

DEFF Research Database (Denmark)

Ravn, Jesper N.

1992-01-01

A simple approach for the calculation of self-diffraction in a thin combined phase and amplitude grating is presented. The third order nonlinearity, the electron-hole recombination time, and the ambipolar diffusion coefficient in a ZnO crystal are measured by means of laser-induced self-diffracti......A simple approach for the calculation of self-diffraction in a thin combined phase and amplitude grating is presented. The third order nonlinearity, the electron-hole recombination time, and the ambipolar diffusion coefficient in a ZnO crystal are measured by means of laser-induced self...

Theory of Weak Bipolar Fields and Electron Holes with Applications to Space Plasmas

International Nuclear Information System (INIS)

Goldman, Martin V.; Newman, David L.; Mangeney, Andre

2007-01-01

A theoretical model of weak electron phase-space holes is used to interpret bipolar field structures observed in space. In the limit eφ max /T e max sech 4 (x/α), where φ max depends on the derivative of the trapped distribution at the separatrix, while α depends only on a screening integral over the untrapped distribution. Idealized trapped and passing electron distributions are inferred from the speed, amplitude, and shape of satellite waveform measurements of weak bipolar field structures

Electron and hole doping effects in Sr{sub 2}FeMoO{sub 6} double perovskites

Energy Technology Data Exchange (ETDEWEB)

Sanchez, D. E-mail: diana.sanchez@icmm.csic.es; Alonso, J.A.; Garcia-Hernandez, M.; Martinez-Lope, M.J.; Casais, M.T.; Martinez, J.L.; Fernandez-Diaz, M.T

2004-05-01

Electron and hole doping effects in the ferromagnetic and structural properties of the double perovskite Sr{sub 2}FeMoO{sub 6} are studied along the series Sr{sub 2-x}La{sub x}FeMoO{sub 6} (0{<=}x{<=}1) and Sr{sub 2-x}FeMoO{sub 6} (0{<=}x{<=}0.4) from neutron powder diffraction and magnetization data. Sr-deficient samples (hole doped) show moderate changes in the structure and both T{sub c} and M{sub s} rapidly decrease with x. On the contrary, a change from tetragonal to monoclinic symmetry and a non monotonic behaviour in T{sub c} is found in the La-substituted series (electron doped)

Correlated proton-electron hole dynamics in protonated water clusters upon extreme ultraviolet photoionization

Directory of Open Access Journals (Sweden)

Zheng Li

2016-07-01

Full Text Available The ultrafast nuclear and electronic dynamics of protonated water clusters H+(H2On after extreme ultraviolet photoionization is investigated. In particular, we focus on cluster cations with n = 3, 6, and 21. Upon ionization, two positive charges are present in the cluster related to the excess proton and the missing electron, respectively. A correlation is found between the cluster's geometrical conformation and initial electronic energy with the size of the final fragments produced. For situations in which the electron hole and proton are initially spatially close, the two entities become correlated and separate in a time-scale of 20 to 40 fs driven by strong non-adiabatic effects.

Correlated proton-electron hole dynamics in protonated water clusters upon extreme ultraviolet photoionization

Science.gov (United States)

Li, Zheng; Vendrell, Oriol

2016-01-01

The ultrafast nuclear and electronic dynamics of protonated water clusters H+(H2O)n after extreme ultraviolet photoionization is investigated. In particular, we focus on cluster cations with n = 3, 6, and 21. Upon ionization, two positive charges are present in the cluster related to the excess proton and the missing electron, respectively. A correlation is found between the cluster's geometrical conformation and initial electronic energy with the size of the final fragments produced. For situations in which the electron hole and proton are initially spatially close, the two entities become correlated and separate in a time-scale of 20 to 40 fs driven by strong non-adiabatic effects. PMID:26798842

Thermally Cross-Linkable Hole Transport Materials for Solution Processed Phosphorescent OLEDs

Science.gov (United States)

Kim, Beom Seok; Kim, Ohyoung; Chin, Byung Doo; Lee, Chil Won

2018-04-01

Materials for unique fabrication of a solution-processed, multi-layered organic light-emitting diode (OLED) were developed. Preparation of a hole transport layer with a thermally cross-linkable chemical structure, which can be processed to form a thin film and then transformed into an insoluble film by using an amine-alcohol condensation reaction with heat treatment, was investigated. Functional groups, such as triplenylamine linked with phenylcarbazole or biphenyl, were employed in the chemical structure of the hole transport layer in order to maintain high triplet energy properties. When phenylcarbazole or biphenyl compounds continuously react with triphenylamine under acid catalysis, a chemically stable thin film material with desirable energy-level properties for a blue OLED could be obtained. The prepared hole transport materials showed excellent surface roughness and thermal stability in comparison with the commercial reference material. On the solution-processed model hole transport layer, we fabricated a device with a blue phosphorescent OLED by using sequential vacuum deposition. The maximum external quantum, 19.3%, was improved by more than 40% over devices with the commercial reference material (11.4%).

Dark Matter from the Supersymmetric Custodial Triplet Model

CERN Document Server

Delgado, Antonio; Ostdiek, Bryan; Quiros, Mariano

2015-01-01

The Supersymmetric Custodial Triplet Model (SCTM) adds to the particle content of the MSSM three $SU(2)_L$ triplet chiral superfields with hypercharge $Y=(0,\\pm1)$. At the superpotential level the model respects a global $SU(2)_L \\otimes SU(2)_R$ symmetry only broken by the Yukawa interactions. The pattern of vacuum expectation values of the neutral doublet and triplet scalar fields depends on the symmetry pattern of the Higgs soft breaking masses. We study the cases where this symmetry is maintained in the Higgs sector, and when it is broken only by the two doublets attaining different vacuum expectation values. In the former case, the symmetry is spontaneously broken down to the vectorial subgroup $SU(2)_V$ and the $\\rho$ parameter is protected by the custodial symmetry. However in both situations the $\\rho$ parameter is protected at tree level, allowing for light triplet scalars with large vacuum expectation values. We find that over a large range of parameter space, a light neutralino can supply the corre...

Selectively Modulating Triplet Exciton Formation in Host Materials for Highly Efficient Blue Electrophosphorescence.

Science.gov (United States)

Li, Huanhuan; Bi, Ran; Chen, Ting; Yuan, Kai; Chen, Runfeng; Tao, Ye; Zhang, Hongmei; Zheng, Chao; Huang, Wei

2016-03-23

The concept of limiting the triplet exciton formation to fundamentally alleviate triplet-involved quenching effects is introduced to construct host materials for highly efficient and stable blue phosphorescent organic light-emitting diodes (PhOLEDs). The low triplet exciton formation is realized by small triplet exciton formation fraction and rate with high binding energy and high reorganization energy of triplet exciton. Demonstrated in two analogue molecules in conventional donor-acceptor molecule structure for bipolar charge injection and transport with nearly the same frontier orbital energy levels and triplet excited energies, the new concept host material shows significantly suppressed triplet exciton formation in the host to avoid quenching effects, leading to much improved device efficiencies and stabilities. The low-voltage-driving blue PhOLED devices exhibit maximum efficiencies of 43.7 cd A(-1) for current efficiency, 32.7 lm W(-1) for power efficiency, and 20.7% for external quantum efficiency with low roll-off and remarkable relative quenching effect reduction ratio up to 41%. Our fundamental solution for preventing quenching effects of long-lived triplet excitons provides exciting opportunities for fabricating high-performance devices using the advanced host materials with intrinsically small triplet exciton formation cross section.

Exploring Higgs triplet models via vector boson scattering at the LHC

International Nuclear Information System (INIS)

Godfrey, Stephen; Moats, Ken

2010-01-01

We present the results of a study of Higgs triplet boson production arising in the littlest Higgs, left-right symmetric, and Georgi-Machacek models in the W ± W ± , W ± Z, W + W - , and ZZ channels at the LHC. We focus on the ''gold-plated'' purely leptonic decay modes and consider the irreducible electroweak, QCD, and t-quark backgrounds, applying a combination of forward-jet tagging, central-jet vetoing, and stringent leptonic cuts to suppress the backgrounds. We find that, given the constraints on the triplet vacuum expectation value (vev), considerable luminosity is required to observe Higgs triplet bosons in vector boson scattering. Observing a Higgs triplet at the LHC is most promising in the Georgi-Machacek model due to a weaker constraint on the triplet vev. In this model, we find that a Higgs triplet boson with a mass of 1.0(1.5) TeV can be observed at the LHC with an integrated luminosity as low as 41(119) fb -1 in the W ± W ± channel and as low as 171(474) fb -1 in the W ± Z channel. Observation of Higgs triplet bosons in these channels would help identify the underlying theory.

Single-step electron transfer on the nanometer scale: ultra-fast charge shift in strongly coupled zinc porphyrin-gold porphyrin dyads.

Science.gov (United States)

Fortage, Jérôme; Boixel, Julien; Blart, Errol; Hammarström, Leif; Becker, Hans Christian; Odobel, Fabrice

2008-01-01

The synthesis, electrochemical properties, and photoinduced electron transfer processes of a series of three novel zinc(II)-gold(III) bisporphyrin dyads (ZnP--S--AuP(+)) are described. The systems studied consist of two trisaryl porphyrins connected directly in the meso position via an alkyne unit to tert-(phenylenethynylene) or penta(phenylenethynylene) spacers. In these dyads, the estimated center to center interporphyrin separation distance varies from 32 to 45 A. The absorption, emission, and electrochemical data indicate that there are strong electronic interactions between the linked elements, thanks to the direct attachment of the spacer on the porphyrin ring through the alkyne unit. At room temperature in toluene, light excitation of the zinc porphyrin results in almost quantitative formation of the charge shifted state (.+)ZnP--S--AuP(.), whose lifetime is in the order of hundreds of picoseconds. In this solvent, the charge-separated state decays to the ground state through the intermediate population of the zinc porphyrin triplet excited state. Excitation of the gold porphyrin leads instead to rapid energy transfer to the triplet ZnP. In dichloromethane the charge shift reactions are even faster, with time constants down to 2 ps, and may be induced also by excitation of the gold porphyrin. In this latter solvent, the longest charge-shifted lifetime (tau=2.3 ns) was obtained with the penta-(phenylenethynylene) spacer. The charge shift reactions are discussed in terms of bridge-mediated super-exchange mechanisms as electron or hole transfer. These new bis-porphyrin arrays, with strong electronic coupling, represent interesting molecular systems in which extremely fast and efficient long-range photoinduced charge shift occurs over a long distance. The rate constants are two to three orders of magnitude larger than for corresponding ZnP--AuP(+) dyads linked via meso-phenyl groups to oligo-phenyleneethynylene spacers. This study demonstrates the critical

Effects of irradiation and isochronal anneal temperature on hole and electron trapping in MOS devices

International Nuclear Information System (INIS)

Fleetwood, D.M.; Winokur, P.S.; Shaneyfelt, M.R.; Riewe, L.C.; Flament, O.; Paillet, P.; Leray, J.L.

1998-02-01

Capacitance-voltage and thermally-stimulated-current techniques are used to estimate trapped hole and electron densities in MOS oxides as functions of irradiation and isochronal anneal temperature. Trapped-charge annealing and compensation effects are discussed

Breakdown of the one-electron picture in XPS, XES and AES spectra involving 4s and 4p holes in Pd to Xe

International Nuclear Information System (INIS)

Ohno, M.; Wendin, G.

1981-01-01

Certain XES spectra of Pd to Xe have been calculated using diagrammatic many-body theory within the framework of a free atom calculation. Both XPS an XES spectra demonstrate breakdown of the one-electron picture of a 4p hole due to strong dynamical grant-Coster Kronig (gCK) fluctuation and decay processes. For a 4s hole, there is a large energy shift due to gCK fluctuation, but an effective one-electron model of the 4s hole is valid. For elements Cd to Te, gCK fluctuation and decay lead to broad continuance spectrum and breakdown of the 4p model. Breakdown of the one-electron, or even quasi-particle, model must occur when 4s and 4p holes are part of multiple vacancies

AN STIS ATLAS OF Ca II TRIPLET ABSORPTION LINE KINEMATICS IN GALACTIC NUCLEI

International Nuclear Information System (INIS)

Batcheldor, D.; Mandalou, J.; Axon, D.; Valluri, M.; Merritt, D.

2013-01-01

The relations observed between supermassive black holes and their host galaxies suggest a fundamental link in the processes that cause these two objects to evolve. A more comprehensive understanding of these relations could be gained by increasing the number of supermassive black hole mass (M . ) measurements. This can be achieved, in part, by continuing to model the stellar dynamics at the centers of galactic bulges using data of the highest possible spatial resolution. Consequently, we present here an atlas of galaxies in the Space Telescope Imaging Spectrograph (STIS) data archive that may have spectra suitable for new M . estimates. Archived STIS G750M data for all non-barred galactic bulges are co-aligned and combined, where appropriate, and the radial signal-to-noise ratios calculated. The line-of-sight velocity distributions from the Ca II triplet are then determined using a maximum penalized likelihood method. We find 19 out of 42 galaxies may provide useful new M . estimates since they are found to have data that is comparable in quality with data that has been used in the past to estimate M . . However, we find no relation between the signal-to-noise ratio in the previously analyzed spectra and the uncertainties of the black hole masses derived from the spectra. We also find that there is a very limited number of appropriately observed stellar templates in the archive from which to estimate the effects of template mismatching

Electron-positron pairs in physics and astrophysics: From heavy nuclei to black holes

Science.gov (United States)

Ruffini, Remo; Vereshchagin, Gregory; Xue, She-Sheng

2010-02-01

Due to the interaction of physics and astrophysics we are witnessing in these years a splendid synthesis of theoretical, experimental and observational results originating from three fundamental physical processes. They were originally proposed by Dirac, by Breit and Wheeler and by Sauter, Heisenberg, Euler and Schwinger. For almost seventy years they have all three been followed by a continued effort of experimental verification on Earth-based experiments. The Dirac process, e+e-→2γ, has been by far the most successful. It has obtained extremely accurate experimental verification and has led as well to an enormous number of new physics in possibly one of the most fruitful experimental avenues by introduction of storage rings in Frascati and followed by the largest accelerators worldwide: DESY, SLAC etc. The Breit-Wheeler process, 2γ→e+e-, although conceptually simple, being the inverse process of the Dirac one, has been by far one of the most difficult to be verified experimentally. Only recently, through the technology based on free electron X-ray laser and its numerous applications in Earth-based experiments, some first indications of its possible verification have been reached. The vacuum polarization process in strong electromagnetic field, pioneered by Sauter, Heisenberg, Euler and Schwinger, introduced the concept of critical electric field Ec=me2c3/(eħ). It has been searched without success for more than forty years by heavy-ion collisions in many of the leading particle accelerators worldwide. The novel situation today is that these same processes can be studied on a much more grandiose scale during the gravitational collapse leading to the formation of a black hole being observed in Gamma Ray Bursts (GRBs). This report is dedicated to the scientific race. The theoretical and experimental work developed in Earth-based laboratories is confronted with the theoretical interpretation of space-based observations of phenomena originating on cosmological

Optical conductivity calculation of a k.p model semiconductor GaAs incorporating first-order electron-hole vertex correction

Science.gov (United States)

Nurhuda, Maryam; Aziz Majidi, Muhammad

2018-04-01

The role of excitons in semiconducting materials carries potential applications. Experimental results show that excitonic signals also appear in optical absorption spectra of semiconductor system with narrow gap, such as Gallium Arsenide (GaAs). While on the theoretical side, calculation of optical spectra based purely on Density Functional Theory (DFT) without taking electron-hole (e-h) interactions into account does not lead to the appearance of any excitonic signal. Meanwhile, existing DFT-based algorithms that include a full vertex correction through Bethe-Salpeter equation may reveal an excitonic signal, but the algorithm has not provided a way to analyze the excitonic signal further. Motivated to provide a way to isolate the excitonic effect in the optical response theoretically, we develop a method of calculation for the optical conductivity of a narrow band-gap semiconductor GaAs within the 8-band k.p model that includes electron-hole interactions through first-order electron-hole vertex correction. Our calculation confirms that the first-order e-h vertex correction reveals excitonic signal around 1.5 eV (the band gap edge), consistent with the experimental data.

Atomistic Tight-Binding Theory of Electron-Hole Exchange Interaction in Morphological Evolution of CdSe/ZnS Core/Shell Nanodisk to CdSe/ZnS Core/Shell Nanorod

Directory of Open Access Journals (Sweden)

Worasak Sukkabot

2016-01-01

Full Text Available Based on the atomistic tight-binding theory (TB and a configuration interaction (CI description, the electron-hole exchange interaction in the morphological transformation of CdSe/ZnS core/shell nanodisk to CdSe/ZnS core/shell nanorod is described with the aim of understanding the impact of the structural shapes on the change of the electron-hole exchange interaction. Normally, the ground hole states confined in typical CdSe/ZnS core/shell nanocrystals are of heavy hole-like character. However, the atomistic tight-binding theory shows that a transition of the ground hole states from heavy hole-like to light hole-like contribution with the increasing aspect ratios of the CdSe/ZnS core/shell nanostructures is recognized. According to the change in the ground-state hole characters, the electron-hole exchange interaction is also significantly altered. To do so, optical band gaps, ground-state electron character, ground-state hole character, oscillation strengths, ground-state coulomb energies, ground-state exchange energies, and dark-bright (DB excitonic splitting (stoke shift are numerically demonstrated. These atomistic computations obviously show the sensitivity with the aspect ratios. Finally, the alteration in the hole character has a prominent effect on dark-bright (DB excitonic splitting.

Harvesting Triplet Excitons with Exciplex Thermally Activated Delayed Fluorescence Emitters toward High Performance Heterostructured Organic Light-Emitting Field Effect Transistors.

Science.gov (United States)

Song, Li; Hu, Yongsheng; Liu, Zheqin; Lv, Ying; Guo, Xiaoyang; Liu, Xingyuan

2017-01-25

The utilization of triplet excitons plays a key role in obtaining high emission efficiency for organic electroluminescent devices. However, to date, only phosphorescent materials have been implemented to harvest the triplet excitons in the organic light-emitting field effect transistors (OLEFETs). In this work, we report the first incorporation of exciplex thermally activated delayed fluorescence (TADF) emitters in heterostructured OLEFETs to harvest the triplet excitons. By developing a new kind of exciplex TADF emitter constituted by m-MTDATA (4,4',4″-tris(N-3-methylphenyl-N-phenylamino)triphenylamine) as the donor and OXD-7 (1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene) as the acceptor, an exciton utilization efficiency of 74.3% for the devices was achieved. It is found that the injection barrier between hole transport layer and emission layer as well as the ratio between donor and acceptor would influence the external quantum efficiency (EQE) significantly. Devices with a maximum EQE of 3.76% which is far exceeding the reported results for devices with conventional fluorescent emitters were successfully demonstrated. Moreover, the EQE at high brightness even outperformed the result for organic light-emitting diode based on the same emitter. Our results demonstrate that the exciplex TADF emitters can be promising candidates to develop OLEFETs with high performance.

Impact of Relativistic Electron Beam on Hole Acoustic Instability in Quantum Semiconductor Plasmas

Science.gov (United States)

Siddique, M.; Jamil, M.; Rasheed, A.; Areeb, F.; Javed, Asif; Sumera, P.

2018-01-01

We studied the influence of the classical relativistic beam of electrons on the hole acoustic wave (HAW) instability exciting in the semiconductor quantum plasmas. We conducted this study by using the quantum-hydrodynamic model of dense plasmas, incorporating the quantum effects of semiconductor plasma species which include degeneracy pressure, exchange-correlation potential and Bohm potential. Analysis of the quantum characteristics of semiconductor plasma species along with relativistic effect of beam electrons on the dispersion relation of the HAW is given in detail qualitatively and quantitatively by plotting them numerically. It is worth mentioning that the relativistic electron beam (REB) stabilises the HAWs exciting in semiconductor (GaAs) degenerate plasma.

Reactivating Catalytic Surface: Insights into the Role of Hot Holes in Plasmonic Catalysis.

Science.gov (United States)

Peng, Tianhuan; Miao, Junjian; Gao, Zhaoshuai; Zhang, Linjuan; Gao, Yi; Fan, Chunhai; Li, Di

2018-03-01

Surface plasmon resonance of coinage metal nanoparticles is extensively exploited to promote catalytic reactions via harvesting solar energy. Previous efforts on elucidating the mechanisms of enhanced catalysis are devoted to hot electron-induced photothermal conversion and direct charge transfer to the adsorbed reactants. However, little attention is paid to roles of hot holes that are generated concomitantly with hot electrons. In this work, 13 nm spherical Au nanoparticles with small absorption cross-section are employed to catalyze a well-studied glucose oxidation reaction. Density functional theory calculation and X-ray absorption spectrum analysis reveal that hot holes energetically favor transferring catalytic intermediates to product molecules and then desorbing from the surface of plasmonic catalysts, resulting in the recovery of their catalytic activities. The studies shed new light on the use of the synergy of hot holes and hot electrons for plasmon-promoted catalysis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Red-light-controllable liquid-crystal soft actuators via low-power excited upconversion based on triplet-triplet annihilation.

Science.gov (United States)

Jiang, Zhen; Xu, Ming; Li, Fuyou; Yu, Yanlei

2013-11-06

A red-light-controllable soft actuator has been achieved, driven by low-power excited triplet-triplet annihilation-based upconversion luminescence (TTA-UCL). First, a red-to-blue TTA-based upconversion system with a high absolute quantum yield of 9.3 ± 0.5% was prepared by utilizing platinum(II) tetraphenyltetrabenzoporphyrin (PtTPBP) as the sensitizer and 9,10-bis(diphenylphosphoryl)anthracene (BDPPA) as the annihilator. In order to be employed as a highly effective phototrigger of photodeformable cross-linked liquid-crystal polymers (CLCPs), the PtTPBP&BDPPA system was incorporated into a rubbery polyurethane film and then assembled with an azotolane-containing CLCP film. The generating assembly film bent toward the light source when irradiated with a 635 nm laser at low power density of 200 mW cm(-2) because the TTA-UCL was effectively utilized by the azotolane moieties in the CLCP film, inducing their trans-cis photoisomerization and an alignment change of the mesogens via an emission-reabsorption process. It is the first example of a soft actuator in which the TTA-UCL is trapped and utilized to create photomechanical effect. Such advantages of using this novel red-light-controllable soft actuator in potential biological applications have also been demonstrated as negligible thermal effect and its excellent penetration ability into tissues. This work not only provides a novel photomanipulated soft actuation material system based on the TTA-UCL technology but also introduces a new technological application of the TTA-based upconversion system in photonic devices.

Solution-processable ambipolar diketopyrrolopyrrole-selenophene polymer with unprecedentedly high hole and electron mobilities.

Science.gov (United States)

Lee, Junghoon; Han, A-Reum; Kim, Jonggi; Kim, Yiho; Oh, Joon Hak; Yang, Changduk

2012-12-26

There is a fast-growing demand for polymer-based ambipolar thin-film transistors (TFTs), in which both n-type and p-type transistor operations are realized in a single layer, while maintaining simplicity in processing. Research progress toward this end is essentially fueled by molecular engineering of the conjugated backbones of the polymers and the development of process architectures for device fabrication, which has recently led to hole and electron mobilities of more than 1.0 cm(2) V(-1) s(-1). However, ambipolar polymers with even higher performance are still required. By taking into account both the conjugated backbone and side chains of the polymer component, we have developed a dithienyl-diketopyrrolopyrrole (TDPP) and selenophene containing polymer with hybrid siloxane-solubilizing groups (PTDPPSe-Si). A synergistic combination of rational polymer backbone design, side-chain dynamics, and solution processing affords an enormous boost in ambipolar TFT performance, resulting in unprecedentedly high hole and electron mobilities of 3.97 and 2.20 cm(2) V(-1) s(-1), respectively.

The order parameter equations of superfluid Fermi-liquid with spin-triplet pairing near Tc in magnetic field

International Nuclear Information System (INIS)

Tarasov, A.N.

1995-01-01

The article is devoted to description of equilibrium properties of superfluid phases of 3 He in magnetic field at temperatures near the normal-superfluid point T c . The Landau Fermi-liquid (F-L) approach generalized to superfluid Fermi-liquids (SFLs) is used. Equations for the order parameter paramagnetic SFL with spin-triplet pairing in static and uniform (DC) moderately strong magnetic field are derived without taking into account strong-coupling (SC) effects. An integro-differential equation is deduced for the order parameter in the general case of spin-triplet pairing (spin of a pair is s = 1, orbital moment l of a pair is any odd number). It is valid in the approximation of small space inhomogeneities of the SFL for external DC magnetic field at temperatures near T c . In the case of spin-triplet p-wave pairing a Ginzburg-Landau (GL) equation is derived for the order parameter A αj (complex 3 x 3 matrix). Corrections to the coefficients in the GL eq. are resulted from taking into account the influence of moderately strong DC magnetic field and spin-exchange F-L interaction by the theory of permutations. In such fields these corrections can be of the same order of magnitude as the so-called > SC corrections to the GL eq. (or even exceed them) and are much higher than the particle-hole asymmetric contribution. The above corrections are connected with deformation of the order parameter in moderate magnetic fields and are of interest at description of 3 He - B at low pressures

Abnormal maternal echocardiographic findings in triplet pregnancies presenting with dyspnoea.

Science.gov (United States)

Elhenicky, Marie; Distelmaier, Klaus; Mailath-Pokorny, Mariella; Worda, Christof; Langer, Martin; Worda, Katharina

2016-03-01

The objective of our study was to evaluate the prevalence of abnormal maternal echocardiographic findings in triplet pregnancies presenting with dyspnoea. Between 2003 and 2013, patients' records of 96 triplet pregnancies at our department were analysed including maternal and fetal outcome, echocardiographic parameters and N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels. After exclusion of triplet pregnancies with fetal demise before 23 + 0 weeks, selective feticide or missing outcome data, the study population consisted of 60 triplet pregnancies. All women with dyspnoea underwent echocardiography and measurement of NT-proBNP. Dyspnoea towards the end of pregnancy was observed in 13.3% (8/60) of all women with triplet pregnancies, and all of these women underwent echocardiography. The prevalence of abnormal echocardiographic findings in women with dyspnoea was 37.5% (3/8) with peripartum cardiomyopathy in one woman. Median serum NT-proBNP was significantly higher in women with abnormal echocardiographic findings compared with those without (1779 ng/ml, range 1045-6076 ng/ml vs 172 ng/ml, range 50-311 ng/ml; p presenting with dyspnoea show a high prevalence of abnormal echocardiographic findings. Since dyspnoea is a common sign in triplet pregnancies and is associated with a high rate of cardiac involvement, echocardiography and evaluation of maternal NT-proBNP could be considered to improve early diagnosis and perinatal management.

Prediction and Observation of Electron Instabilities and Phase Space Holes Concentrated in the Lunar Plasma Wake

Science.gov (United States)

Hutchinson, Ian H.; Malaspina, David M.

2018-05-01

Recent theory and numerical simulation predicts that the wake of the solar wind flow past the Moon should be the site of electrostatic instabilities that give rise to electron holes. These play an important role in the eventual merging of the wake with the background solar wind. Analysis of measurements from the ARTEMIS satellites, orbiting the Moon at distances from 1.2 to 11 RM, detects holes highly concentrated in the wake, in agreement with prediction. The theory also predicts that the hole flux density observed should be hollow, peaking away from the wake axis. Observation statistics qualitatively confirm this hollowness, lending extra supporting evidence for the identification of their generation mechanism.

Pyridine-2,6-diyl dinitroxides as room-temperature triplet ligands

Energy Technology Data Exchange (ETDEWEB)

Kawakami, Hinako; Tonegawa, Asato; Ishida, Takayuki, E-mail: takayuki.ishida@uec.ac.jp [Department of Engineering Science, The University of Electro-Communications, Tokyo (Japan)

2016-02-01

We have proposed tert-butyl 2-pyridyl nitroxide radicals as a promising paramagnetic chelating ligand, where the direct radical-metal bond leads to strong magnetic interaction. We successfully synthesized and isolated PyBN derivatives (pyridine-2,6-diyl bis(tert-butyl nitroxides)). The molecular and crystal structures of the target biradicals, MesPyBN, AntPyBN and tBuOPyBN were determined from the X-ray crystal structure analysis, which possess mesityl, 9-anthryl and tert-butoxy groups at the 5-position of the pyridine ring, respectively. The ground triplet state was characterized by means of SQUID susceptometry for each compound. On heating, the χ{sub m}T values of all the PyBN derivatives increased and reached a plateau at ca. 1.0 cm{sup 3} K mol{sup −1} at 300 K. It implies that biradicals behaved as triplet molecules even at room temperature, or 2J/k{sub B} >> 300 K. From the decay monitored in solution electron-spin resonance spectroscopy, MesPyBN was the most persistent, while tBuOPyBN was the most reactive, of the three.

Phasic Triplet Markov Chains.

Science.gov (United States)

El Yazid Boudaren, Mohamed; Monfrini, Emmanuel; Pieczynski, Wojciech; Aïssani, Amar

2014-11-01

Hidden Markov chains have been shown to be inadequate for data modeling under some complex conditions. In this work, we address the problem of statistical modeling of phenomena involving two heterogeneous system states. Such phenomena may arise in biology or communications, among other fields. Namely, we consider that a sequence of meaningful words is to be searched within a whole observation that also contains arbitrary one-by-one symbols. Moreover, a word may be interrupted at some site to be carried on later. Applying plain hidden Markov chains to such data, while ignoring their specificity, yields unsatisfactory results. The Phasic triplet Markov chain, proposed in this paper, overcomes this difficulty by means of an auxiliary underlying process in accordance with the triplet Markov chains theory. Related Bayesian restoration techniques and parameters estimation procedures according to the new model are then described. Finally, to assess the performance of the proposed model against the conventional hidden Markov chain model, experiments are conducted on synthetic and real data.

Separation of electron and hole dynamics in the semimetal LaSb

Energy Technology Data Exchange (ETDEWEB)

Han, F.; Xu, J.; Botana, A. S.; Xiao, Z. L.; Wang, Y. L.; Yang, W. G.; Chung, D. Y.; Kanatzidis, M. G.; Norman, M. R.; Crabtree, G. W.; Kwok, W. K.

2017-09-01

We report investigations on the magnetotransport in LaSb, which exhibits extremely large magnetoresistance (XMR). Foremost, we demonstrate that the resistivity plateau can be explained without invoking topological protection. We then determine the Fermi surface from Shubnikov–de Haas (SdH) quantum oscillation measurements and find good agreement with the bulk Fermi pockets derived from first-principles calculations. Using a semiclassical theory and the experimentally determined Fermi pocket anisotropies, we quantitatively describe the orbital magnetoresistance, including its angle dependence.We show that the origin of XMR in LaSb lies in its high mobility with diminishing Hall effect, where the high mobility leads to a strong magnetic-field dependence of the longitudinal magnetoconductance. Unlike a one-band material, when a system has two or more bands (Fermi pockets) with electron and hole carriers, the added conductance arising from the Hall effect is reduced, hence revealing the latent XMR enabled by the longitudinal magnetoconductance. With diminishing Hall effect, the magnetoresistivity is simply the inverse of the longitudinal magnetoconductivity, enabling the differentiation of the electron and hole contributions to the XMR, which varies with the strength and orientation of the magnetic field. This work demonstrates a convenient way to separate the dynamics of the charge carriers and to uncover the origin of XMR in multiband materials with anisotropic Fermi surfaces. Our approach can be readily applied to other XMR materials.

Temperature-Dependent Mollow Triplet Spectra from a Single Quantum Dot: Rabi Frequency Renormalization and Sideband Linewidth Insensitivity

DEFF Research Database (Denmark)

Wei, Yu-Jia; He, Yu; He, Yu-Ming

2014-01-01

We investigate temperature-dependent resonance fluorescence spectra obtained from a single self- assembled quantum dot. A decrease of the Mollow triplet sideband splitting is observed with increasing temperature, an effect we attribute to a phonon-induced renormalization of the driven dot Rabi fr...

A practical O(n log2 n) time algorithm for computing the triplet distance on binary trees

DEFF Research Database (Denmark)

Sand, Andreas; Pedersen, Christian Nørgaard Storm; Mailund, Thomas

2013-01-01

rooted binary trees in time O (n log2 n). The algorithm is related to an algorithm for computing the quartet distance between two unrooted binary trees in time O (n log n). While the quartet distance algorithm has a very severe overhead in the asymptotic time complexity that makes it impractical compared......The triplet distance is a distance measure that compares two rooted trees on the same set of leaves by enumerating all sub-sets of three leaves and counting how often the induced topologies of the tree are equal or different. We present an algorithm that computes the triplet distance between two...

Precision spectroscopy with ultracold 87Rb2 triplet molecules

International Nuclear Information System (INIS)

Strauss, Christoph

2011-01-01

In this thesis I report precision spectroscopy with ultracold 87 Rb 2 triplet molecules where we use lasers to couple the states in different molecular potentials. We study in detail states of the a 3 sum + u and (1) 3 sum + g potentials. These states are of great importance for transferring weakly bound molecules to the ro-vibrational triplet ground state via states of the excited potential. As most experiments start from molecules in their X 1 sum + g ground state, the triplet states were hard to access via dipole transitions and remained largely unexplored. The measurements presented in this thesis are the first detailed study of diatomic 87 Rb 2 molecules in these states. Our experiments start with an ultracold cloud of 87 Rb atoms. We then load this cloud into an optical lattice where we use a magnetic Feshbach resonance at 1007.4 G to perform a Feshbach association. After we have removed all unbound atoms, we end up with a pure sample of weakly bound Feshbach molecules inside the optical lattice. The optical lattice prevents these molecules from colliding with each other which results in molecular lifetimes on the order of a few hundred milliseconds. In the first set of experiments, we use a laser coupling the Feshbach state to the excited (1) 3 sum + g triplet state to map out its low-lying vibrational (v = 0.. 15), rotational, hyperfine, and Zeeman structure. The experimental results are in good agreement with calculations done by Marius Lysebo and Prof. Leif Veseth. We then map out in detail the vibrational, rotational, hyperfine, and Zeeman structure of the a 3 sum + u triplet ground state using dark state spectroscopy with levels in the (1) 3 sum + g potential as an intermediate state. In this scheme we are able to access molecules in triplet states because our Feshbach state has strong triplet character. Interestingly, it happens that some deeply bound states which belong to the X 1 sum + g potential are close to levels in the a 3 sum + u potential. In

Design and Analysis of CMOS-Compatible III-V Compound Electron-Hole Bilayer Tunneling Field-Effect Transistor for Ultra-Low-Power Applications.

Science.gov (United States)

Kim, Sung Yoon; Seo, Jae Hwa; Yoon, Young Jun; Lee, Ho-Young; Lee, Seong Min; Cho, Seongjae; Kang, In Man

2015-10-01

In this work, we design and analyze complementary metal-oxide-semiconductor (CMOS)-compatible III-V compound electron-hole bilayer (EHB) tunneling field-effect transistors (TFETs) by using two-dimensional (2D) technology computer-aided design (TCAD) simulations. A recently proposed EHB TFET exploits a bias-induced band-to-band tunneling (BTBT) across the electron-hole bilayer by an electric field from the top and bottom gates. This is in contrast to conventional planar p(+)-p(-)-n TFETs, which utilize BTBT across the source-to-channel junction. We applied III-V compound semiconductor materials to the EHB TFETs in order to enhance the current drivability and switching performance. Devices based on various compound semiconductor materials have been designed and analyzed in terms of their primary DC characteristics. In addition, the operational principles were validated by close examination of the electron concentrations and energy-band diagrams under various operation conditions. The simulation results of the optimally designed In0.533Ga0.47As EHB TFET show outstanding performance, with an on-state current (Ion) of 249.5 μA/μm, subthreshold swing (S) of 11.4 mV/dec, and threshold voltage (Vth) of 50 mV at VDS = 0.5 V. Based on the DC-optimized InGaAs EHB TFET, the CMOS inverter circuit was simulated in views of static and dynamic behaviors of the p-channel device with exchanges between top and bottom gates or between source and drain electrodes maintaining the device structure.

G-factors and diamagnetic coefficients of electrons, holes, and excitons in InAs/InP quantum dots

NARCIS (Netherlands)

Bree, van J.; Silov, A.Yu.; Koenraad, P.M.; Flatté, M.E.; Pryor, C.E.

2012-01-01

The electron, hole, and exciton g factors and diamagnetic coefficients have been calculated using envelope-function theory for cylindrical InAs/InP quantum dots in the presence of a magnetic field parallel to the dot symmetry axis. A clear connection is established between the electron g factor and

Even-parity spin-triplet pairing by purely repulsive interactions for orbitally degenerate correlated fermions

International Nuclear Information System (INIS)

Zegrodnik, M; Bünemann, J; Spałek, J

2014-01-01

We demonstrate the stability of the spin-triplet paired s-wave (with an admixture of extended s-wave) state for the limit of purely repulsive interactions in a degenerate two-band Hubbard model of correlated fermions. The repulsive interactions limit represents an essential extension of our previous analysis (2013 New J. Phys. 15 073050), regarded here as I. We also show that near the half-filling the considered type of superconductivity can coexist with antiferromagnetism. The calculations have been carried out with the use of the so-called statistically consistent Gutzwiller approximation (SGA) for the case of a square lattice. We suggest that the electron correlations in conjunction with the Hund's rule exchange play the crucial role in stabilizing the real-space spin-triplet superconducting state. A sizable hybridization of the bands suppresses the homogeneous paired state. (paper)

DNA partitions into triplets under tension in the presence of organic cations, with sequence evolutionary age predicting the stability of the triplet phase

NARCIS (Netherlands)

Taghavi, Amirhossein; van der Schoot, Paul; Berryman, Joshua T

2017-01-01

Using atomistic simulations, we show the formation of stable triplet structure when particular GC-rich DNA duplexes are extended in solution over a timescale of hundreds of nanoseconds, in the presence of organic salt. We present planar-stacked triplet disproportionated DNA (Σ DNA) as a possible

Codon-triplet context unveils unique features of the Candida albicans protein coding genome

Directory of Open Access Journals (Sweden)

Oliveira José L

2007-11-01

Full Text Available Abstract Background The evolutionary forces that determine the arrangement of synonymous codons within open reading frames and fine tune mRNA translation efficiency are not yet understood. In order to tackle this question we have carried out a large scale study of codon-triplet contexts in 11 fungal species to unravel associations or relationships between codons present at the ribosome A-, P- and E-sites during each decoding cycle. Results Our analysis unveiled high bias within the context of codon-triplets, in particular strong preference for triplets of identical codons. We have also identified a surprisingly large number of codon-triplet combinations that vanished from fungal ORFeomes. Candida albicans exacerbated these features, showed an unbalanced tRNA population for decoding its pool of codons and used near-cognate decoding for a large set of codons, suggesting that unique evolutionary forces shaped the evolution of its ORFeome. Conclusion We have developed bioinformatics tools for large-scale analysis of codon-triplet contexts. These algorithms identified codon-triplets context biases, allowed for large scale comparative codon-triplet analysis, and identified rules governing codon-triplet context. They could also detect alterations to the standard genetic code.

Triplet pregnancies in a southeastern Nigerian Hospital: Before the ...

African Journals Online (AJOL)

of triplet pregnancy of 0.1% or 1 triplet pregnancy in 1051 deliveries. ... The babies had a weight range of 0.6–3.4 kg, with an average weight of 1.73 kg. ... outcome of these pregnancies, especially now that the incidence is bound to increase ...

Half-metallic superconducting triplet spin multivalves

Science.gov (United States)

Alidoust, Mohammad; Halterman, Klaus

2018-02-01

We study spin switching effects in finite-size superconducting multivalve structures. We examine F1F2SF3 and F1F2SF3F4 hybrids where a singlet superconductor (S) layer is sandwiched among ferromagnet (F) layers with differing thicknesses and magnetization orientations. Our results reveal a considerable number of experimentally viable spin-valve configurations that lead to on-off switching of the superconducting state. For S widths on the order of the superconducting coherence length ξ0, noncollinear magnetization orientations in adjacent F layers with multiple spin axes leads to a rich variety of triplet spin-valve effects. Motivated by recent experiments, we focus on samples where the magnetizations in the F1 and F4 layers exist in a fully spin-polarized half-metallic phase, and calculate the superconducting transition temperature, spatially and energy resolved density of states, and the spin-singlet and spin-triplet superconducting correlations. Our findings demonstrate that superconductivity in these devices can be completely switched on or off over a wide range of magnetization misalignment angles due to the generation of equal-spin and opposite-spin triplet pairings.

Suppressing Energy Loss due to Triplet Exciton Formation in Organic Solar Cells: The Role of Chemical Structures and Molecular Packing

KAUST Repository

Chen, Xiankai; Wang, Tonghui; Bredas, Jean-Luc

2017-01-01

In the most efficient solar cells based on blends of a conjugated polymer (electron donor) and a fullerene derivative (electron acceptor),ultrafast formation of charge-transfer (CT) electronic states at the donor-acceptor interfaces and efficient separation of these CT states into free charges, lead to internal quantum efficiencies near 100%. However, there occur substantial energy losses due to the non-radiative recombinations of the charges, mediated by the loweset-energy (singlet and triplet) CT states; for example, such recombinations can lead to the formation of triplet excited electronic states on the polymer chains, which do not generate free charges. This issue remains a major factor limiting the power conversion efficiencies (PCE) of these devices. The recombination rates are, however, difficult to quantify experimentally. To shed light on these issues, here, an integrated multi-scale theoretical approach that combines molecular dynamics simulations with quantum chemistry calculations is employed in order to establish the relationships among chemical structures, molecular packing, and non-radiative recombination losses mediated by the lowest-energy charge-transfer states.

Suppressing Energy Loss due to Triplet Exciton Formation in Organic Solar Cells: The Role of Chemical Structures and Molecular Packing

KAUST Repository

Chen, Xiankai

2017-04-21

In the most efficient solar cells based on blends of a conjugated polymer (electron donor) and a fullerene derivative (electron acceptor),ultrafast formation of charge-transfer (CT) electronic states at the donor-acceptor interfaces and efficient separation of these CT states into free charges, lead to internal quantum efficiencies near 100%. However, there occur substantial energy losses due to the non-radiative recombinations of the charges, mediated by the loweset-energy (singlet and triplet) CT states; for example, such recombinations can lead to the formation of triplet excited electronic states on the polymer chains, which do not generate free charges. This issue remains a major factor limiting the power conversion efficiencies (PCE) of these devices. The recombination rates are, however, difficult to quantify experimentally. To shed light on these issues, here, an integrated multi-scale theoretical approach that combines molecular dynamics simulations with quantum chemistry calculations is employed in order to establish the relationships among chemical structures, molecular packing, and non-radiative recombination losses mediated by the lowest-energy charge-transfer states.

Triplet Tellurophene-Based Acceptors for Organic Solar Cells.

Science.gov (United States)

Yang, Lei; Gu, Wenxing; Lv, Lei; Chen, Yusheng; Yang, Yufei; Ye, Pan; Wu, Jianfei; Hong, Ling; Peng, Aidong; Huang, Hui

2018-01-22

Triplet materials have been employed to achieve high-performing organic solar cells (OSCs) by extending the exciton lifetime and diffusion distances, while the triplet non-fullerene acceptor materials have never been reported for bulk heterojunction OSCs. Herein, for the first time, three triplet molecular acceptors based on tellurophene with different degrees of ring fusing were designed and synthesized for OSCs. Significantly, these molecules have long exciton lifetime and diffusion lengths, leading to efficient power conversion efficiency (7.52 %), which is the highest value for tellurophene-based OSCs. The influence of the extent of ring fusing on molecular geometry and OSCs performance was investigated to show the power conversion efficiencies (PCEs) continuously increased along with increasing the extent of ring fusing. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermal conductivity of graphene with defects induced by electron beam irradiation

Science.gov (United States)

Malekpour, Hoda; Ramnani, Pankaj; Srinivasan, Srilok; Balasubramanian, Ganesh; Nika, Denis L.; Mulchandani, Ashok; Lake, Roger K.; Balandin, Alexander A.

2016-07-01

We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is analyzed using the Boltzmann transport equation and molecular dynamics simulations. The results are important for understanding phonon - point defect scattering in two-dimensional systems and for practical applications of graphene in thermal management.We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is

Electromagnetic interactions in an electron-hole plasma

International Nuclear Information System (INIS)

1977-01-01

Certain problems electromagnetic interactions both of external SHF radiation with an electron-hole (eh) plasma and in the plasma itself are considered. The production and properties of a non-equilibrium eh plasma in semiconductors, pinch effect in a plasma of solids, strong electric fields in a plasma of inhomogeneous semiconductors and heat effects in a semiconductor plasma are discussed. The influence of a surface, kinetics of recombination processes in the semiconductor volume and the plasma statistics the spatial distribution of carriers, current characteristics and plasma recombination radiation under the conditions of pinch effect is described. The diagnostics methods of the phenomena are presented. The behaviour of diode structures with pn transitions in strong SHF fields is discussed. Special attention is paid to collective phenomena in the plasma of semiconductor devices and the variation of carrier density in strong fields. The appearance of electromotive force in inhomogeneous diode structures placed in strong SHF fields is considered

Photodegradation mechanism of sulfonamides with excited triplet state dissolved organic matter: A case of sulfadiazine with 4-carboxybenzophenone as a proxy

International Nuclear Information System (INIS)

Li, Yingjie; Wei, Xiaoxuan; Chen, Jingwen; Xie, Hongbin; Zhang, Ya-nan

2015-01-01

Highlights: • Excited triplet state of dissolved organic matter ( 3 DOM * ) is largely responsible for the enhanced photodegradation of sulfadiazine. • Electron followed by proton transfer is a major mechanism for the reactions of sulfadiazine with 3 DOM * proxies. • Two reaction sites (amino- or sulfonyl-N) and sulfadiazine radicals were identified in the reactions of sulfadiazine with 3 DOM * proxies. - Abstract: Excited triplet states of dissolved organic matter ( 3 DOM*) are important players for photodegradation sulfonamide antibiotics (SAs) in sunlit natural waters. However, the triplet-mediated reaction mechanism was poorly understood. In this study, we investigated the reaction adopting sulfadiazine as a representative SA and 4-carboxybenzophenone (CBBP)as a proxy of DOM. Results showed that the excited triplet state of CBBP ( 3 CBBP*) is responsible for the photodegradation of sulfadiazine. The reaction of 3 CBBP* with substructure model compounds verified there are two reaction sites (amino-or sulfonyl-N atoms) of sulfadiazine. Density functional theory calculations were performed, which unveiled that electrons transfer from the N reaction sites to the carbonyl oxygen atom of 3 CBBP* moiety, followed by proton transfers, leading to the formation of sulfadiazine radicals. Laser flash photolysis experiments were performed to confirm the mechanism. Thus, this study identified that the photodegradation mechanism of SAs initiated by 3 DOM*, which is important for understanding the photochemical fate, predicting the photoproducts, and assessing the ecological risks of SAs in the aquatic environment

Laser induced transient absorptions of the excited triplet state of 9,10-anthraquinone-2-sulfonate. A further study by 248 nm laser photolysis

International Nuclear Information System (INIS)

Ma Jianhua; Lin Weizheng; Wang Wenfen; Yao Side; Lin Nianyun

1999-01-01

Transient absorption spectrum of triplet state of 9,10-anthraquinone-2-sulfonate (AQS) in aqueous solution has been investigated using 248 nm (KrF) laser photolysis. A whole transient absorption spectrum with absorption maxim at 380 nm and 580 nm has been assigned to triple AQS from detailed kinetic analysis of decay of 380 nm and 580 nm signals, which is the neat characteristic absorption of triplet AQS reported for the first time. In addition, the difference in feature of the spectrum of triplet AQS in H 2 O and that in CH 3 CN was eliminated by further study using 248 nm laser pulses

Effect of strong correlations on the high energy anomaly in hole- and electron-doped high-Tc superconductors

International Nuclear Information System (INIS)

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

2009-01-01

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 by-product 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.

Vlasov simulations of electron hole dynamics in inhomogeneous magnetic field

Science.gov (United States)

Kuzichev, Ilya; Vasko, Ivan; Agapitov, Oleksiy; Mozer, Forrest; Artemyev, Anton

2017-04-01

Electron holes (EHs) or phase space vortices are solitary electrostatic waves existing due to electrons trapped within EH electrostatic potential. Since the first direct observation [1], EHs have been widely observed in the Earth's magnetosphere: in reconnecting current sheets [2], injection fronts [3], auroral region [4], and many other space plasma systems. EHs have typical spatial scales up to tens of Debye lengths, electric field amplitudes up to hundreds of mV/m and propagate along magnetic field lines with velocities of about electron thermal velocity [5]. The role of EHs in energy dissipation and supporting of large-scale potential drops is under active investigation. The accurate interpretation of spacecraft observations requires understanding of EH evolution in inhomogeneous plasma. The critical role of plasma density gradients in EH evolution was demonstrated in [6] using PIC simulations. Interestingly, up to date no studies have addressed a role of magnetic field gradients in EH evolution. In this report, we use 1.5D gyrokinetic Vlasov code to demonstrate the critical role of magnetic field gradients in EH dynamics. We show that EHs propagating into stronger (weaker) magnetic field are decelerated (accelerated) with deceleration (acceleration) rate dependent on the magnetic field gradient. Remarkably, the reflection points of decelerating EHs are independent of the average magnetic field gradient in the system and depend only on the EH parameters. EHs are decelerated (accelerated) faster than would follow from the "quasi-particle" concept assuming that EH is decelerated (accelerated) entirely due to the mirror force acting on electrons trapped within EH. We demonstrate that EH propagation in inhomogeneous magnetic fields results in development of a net potential drop along an EH, which depends on the magnetic field gradient. The revealed features will be helpful for interpreting spacecraft observations and results of advanced particle simulations. In

Electron-electron interaction in p-SiGe/Ge quantum wells

International Nuclear Information System (INIS)

Roessner, Benjamin; Kaenel, Hans von; Chrastina, Daniel; Isella, Giovanni; Batlogg, Bertram

2005-01-01

The temperature dependent magnetoresistance of high mobility p-SiGe/Ge quantum wells is studied with hole densities ranging from 1.7 to 5.9 x 10 11 cm -2 . At magnetic fields below the onset of quantum oscillations that reflect the high mobility values (up to 75000 cm 2 /Vs), we observe the clear signatures of electron-electron interaction. We compare our experiment with the theory of electron-electron interaction including the Zeeman band splitting. The observed magnetoresistance is well explained as a superposition of band structure induced positive magnetoresistance and the negative magntoresistance due to the electron-electron interaction effect

Spin polarized and density modulated phases in symmetric electron-electron and electron-hole bilayers.

Science.gov (United States)

Kumar, Krishan; Moudgil, R K

2012-10-17

We have studied symmetric electron-electron and electron-hole bilayers to explore the stable homogeneous spin phase and the feasibility of inhomogeneous charge-/spin-density ground states. The former is resolved by comparing the ground-state energies in states of different spin polarizations, while the latter is resolved by searching for a divergence in the wavevector-dependent static charge/spin susceptibility. For this endeavour, we have used the dielectric approach within the self-consistent mean-field theory of Singwi et al. We find that the inter-layer interactions tend to change an abrupt spin-polarization transition of an isolated layer into a nearly gradual one, even though the partially spin-polarized phases are not clearly stable within the accuracy of our calculation. The transition density is seen to decrease with a reduction in layer spacing, implying a suppression of spin polarization by inter-layer interactions. Indeed, the suppression shows up distinctly in the spin susceptibility computed from the spin-polarization dependence of the ground-state energy. However, below a critical layer spacing, the unpolarized liquid becomes unstable against a charge-density-wave (CDW) ground state at a density preceding full spin polarization, with the transition density for the CDW state increasing on further reduction in the layer spacing. Due to attractive e-h correlations, the CDW state is found to be more pronounced in the e-h bilayer. On the other hand, the static spin susceptibility diverges only in the long-wavelength limit, which simply represents a transition to the homogeneous spin-polarized phase.

Disappearance of electron-hole asymmetry in nanoparticles of Nd1−xCaxMnO3(x=0.6,0.4): magnetization and electron paramagnetic resonance evidence

International Nuclear Information System (INIS)

Bhagyashree, K. S.; Bhat, S. V.

2015-01-01

We study and compare magnetic and electron paramagnetic resonance behaviors of bulk and nanoparticles of Nd 1−x Ca x MnO 3 in hole doped (x=0.4;NCMOH) and electron doped (x=0.6;NCMOE) samples. NCMOH in bulk form shows a complex temperature dependence of magnetization M(T), with a charge ordering transition at ∼250 K, an antiferromagnetic (AFM) transition at ∼150 K, and a transition to a canted AFM phase/mixed phase at ∼80 K. Bulk NCMOE behaves quite differently with just a charge ordering transition at ∼280 K, thus providing a striking example of the so called electron-hole asymmetry. While our magnetization data on bulk samples are consistent with the earlier reports, the new results on the nanoparticles bring out drastic effects of size reduction. They show that M(T) behaviors of the two nanosamples are essentially similar in addition to the absence of the charge order in them thus providing strong evidence for vanishing of the electron-hole asymmetry in nanomanganites. This conclusion is further corroborated by electron paramagnetic resonance studies which show that the large difference in the “g” values and their temperature dependences found for the two bulk samples disappears as they approach a common behavior in the corresponding nanosamples

Improved organic light-emitting device with tris-(8-hydroxyquinoline) aluminium inserted between hole-injection layer and hole-transporting layer

Energy Technology Data Exchange (ETDEWEB)

Divayana, Y [School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore (Singapore); Sun, X W [School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore (Singapore); Chen, B J [School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore (Singapore); Sarma, K R [Aerospace Electronic Systems, Honeywell, 21111 N 19th Avenue, Phoenix, AZ 85027 (United States)

2007-01-07

A layer of tris-(8-hydroxyquinoline) aluminium (Alq{sub 3}), which is normally used as an electron-transporting and emissive layer, was incorporated between the hole-transporting layer and the hole-injection layer to balance the electron-hole injection. The Alq{sub 3} layer performed to block the hole current which is a majority carrier in a typical organic light-emitting device. An increase in current efficiency by almost 30%, from 3.1 to 4.0 cd A{sup -1}, with a minimum voltage shift was achieved with a 2 nm Alq{sub 3} layer as a hole-blocking layer. A reduction in HTL thickness was observed to reduce the efficiency due to electron leakage to the HIL, whereby an inefficient exciplex emission was observed.

Value and Anisotropy of the Electron and Hole Mass in Pure Wurtzite InP Nanowires.

Science.gov (United States)

Tedeschi, D; De Luca, M; Granados Del Águila, A; Gao, Q; Ambrosio, G; Capizzi, M; Tan, H H; Christianen, P C M; Jagadish, C; Polimeni, A

2016-10-12

The effective mass of electrons and holes in semiconductors is pivotal in determining the dynamics of carriers and their confinement energy in nanostructured materials. Surprisingly, this quantity is still unknown in wurtzite (WZ) nanowires (NWs) made of III-V compounds (e.g., GaAs, InAs, GaP, InP), where the WZ phase has no bulk counterpart. Here, we investigate the magneto-optical properties of InP WZ NWs grown by selective-area epitaxy that provides perfectly ordered NWs featuring high-crystalline quality. The combined analysis of the energy of free exciton states and impurity levels under magnetic field (B up to 29 T) allows us to disentangle the dynamics of oppositely charged carriers from the Coulomb interaction and thus to determine the values of the electron and hole effective mass. By application of B⃗ along different crystallographic directions, we also assess the dependence of the transport properties with respect to the NW growth axis (namely, the WZ ĉ axis). The effective mass of electrons along ĉ is m e ∥ = (0.078 ± 0.002) m 0 (m 0 is the electron mass in vacuum) and perpendicular to ĉ is m e ⊥ = (0.093 ± 0.001) m 0 , resulting in a 20% mass anisotropy. Holes exhibit a much larger (∼320%) and opposite mass anisotropy with their effective mass along and perpendicular to ĉ equal to m h ∥ = (0.81 ± 0.18) m 0 and m h ⊥ = (0.250 ± 0.016) m 0 , respectively. While no full consensus is found with current theoretical results on WZ InP, our findings show trends remarkably similar to the experimental data available in WZ bulk materials, such as InN, GaN, and ZnO.

Photoprotection in the antenna complexes of photosystem II : Role of individual xanthophylls in chlorophyll triplet quenching

NARCIS (Netherlands)

Mozzo, Milena; Dall'Osto, Luca; Hienerwadel, Rainer; Bassi, Roberto; Croce, Roberta

2008-01-01

In this work the photoprotective role of all xanthophylls in LHCII, Lhcb4, and Lhcb5 is investigated by laser-induced Triplet-minus-Singlet (TmS) spectroscopy. The comparison of native LHCII trimeric complexes with different carotenoid composition shows that the xanthophylls in sites V1 and N1 do

Photoprotection in the antenna complexes of photosystem II - Role of individual xanthophylls in chlorophyll triplet quenching

NARCIS (Netherlands)

Mozzo, Milena; Dall'Osto, Luca; Hienerwadel, Rainer; Bassi, Roberto; Croce, Roberta; Osto, Luca Dall’

2008-01-01

In this work the photoprotective role of all xanthophylls in LHCII, Lhcb4, and Lhcb5 is investigated by laser-induced Triplet-minus-Singlet (TmS) spectroscopy. The comparison of native LHCII trimeric complexes with different carotenoid composition shows that the xanthophylls in sites V1 and N1 do

Plasmon sidebands in the gain spectrum of an electron-hole plasma

International Nuclear Information System (INIS)

Hoang Ngoc Cam; Nguyen Van Hieu; Nguyen Ai Viet.

1987-06-01

The theory is represented for the recombination of the electron-hole pair into the photon with and without the emission of the plasmon-phonon coupled modes. In calculating the energies of the plasmon and the plasmon-phonon coupled modes as well as the vertices of their effective interactions the quantum field theory method has been applied. The theoretical prediction agrees well with the experimental result in the main part EHP 0 and the first sideband EHP - of the gain spectrum. (author). 6 refs, 9 figs

BEC-BCS-laser crossover in Coulomb-correlated electron-hole-photon systems

International Nuclear Information System (INIS)

Yamaguchi, M; Kamide, K; Ogawa, T; Yamamoto, Y

2012-01-01

Many-body features caused by Coulomb correlations are of great importance for understanding phenomena pertaining to polariton systems in semiconductor microcavities, i.e. electron-hole-photon systems. Remarkable many-body effects are shown to exist in both thermal-equilibrium phases and non-equilibrium lasing states. We then show a unified framework for connecting the thermal-equilibrium and the non-equilibrium steady states based on a non-equilibrium Green's function approach. Bose-Einstein condensate (BEC)-Bardeen-Cooper-Schrieffer (BCS)-laser crossovers are investigated by using this approach. (paper)

Bodipy–C60 triple hydrogen bonding assemblies as heavy atom-free triplet photosensitizers: preparation and study of the singlet/triplet energy transfer† †Electronic supplementary information (ESI) available: Syntheses, structure characterization data, and UV/vis absorption and emission spectra. See DOI: 10.1039/c4sc03865g

Science.gov (United States)

Guo, Song; Xu, Liang; Xu, Kejing; Küçüköz, Betül; Karatay, Ahmet; Yaglioglu, Halime Gul; Hayvali, Mustafa; Elmali, Ayhan

2015-01-01

Supramolecular triplet photosensitizers based on hydrogen bonding-mediated molecular assemblies were prepared. Three thymine-containing visible light-harvesting Bodipy derivatives (B-1, B-2 and B-3, which show absorption at 505 nm, 630 nm and 593 nm, respectively) were used as H-bonding modules, and 1,6-diaminopyridine-appended C60 was used as the complementary hydrogen bonding module (C-1), in which the C60 part acts as a spin converter for triplet formation. Visible light-harvesting antennae with methylated thymine were prepared as references (B-1-Me, B-2-Me and B-3-Me), which are unable to form strong H-bonds with C-1. Triple H-bonds are formed between each Bodipy antenna (B-1, B-2 and B-3) and the C60 module (C-1). The photophysical properties of the H-bonding assemblies and the reference non-hydrogen bond-forming mixtures were studied using steady state UV/vis absorption spectroscopy, fluorescence emission spectroscopy, electrochemical characterization, and nanosecond transient absorption spectroscopy. Singlet energy transfer from the Bodipy antenna to the C60 module was confirmed by fluorescence quenching studies. The intersystem crossing of the latter produced the triplet excited state. The nanosecond transient absorption spectroscopy showed that the triplet state is either localized on the C60 module (for assembly B-1·C-1), or on the styryl-Bodipy antenna (for assemblies B-2·C-1 and B-3·C-1). Intra-assembly forward–backward (ping-pong) singlet/triplet energy transfer was proposed. In contrast to the H-bonding assemblies, slow triplet energy transfer was observed for the non-hydrogen bonding mixtures. As a proof of concept, these supramolecular assemblies were used as triplet photosensitizers for triplet–triplet annihilation upconversion. PMID:29218142

Sensitive triplet exciton detection in polyfluorene using Pd-coordinated porphyrin

NARCIS (Netherlands)

Mikhnenko, O.V.; Blom, P.W.M.; Loi, M.A.

2011-01-01

We developed a sensitive spectroscopic method to probe triplet concentration in thin films of polyfluorene (PF) at room temperature. The energy of photoexcited triplet excitons is transferred to the guest metal-organic complex, meso-tetratolylporphyrin-Pd (PdTPP), and detected as phosphorescent

Polarized Fine Structure in the Photoluminescence Excitation Spectrum of a Negatively Charged Quantum Dot

Science.gov (United States)

Ware, M. E.; Stinaff, E. A.; Gammon, D.; Doty, M. F.; Bracker, A. S.; Gershoni, D.; Korenev, V. L.; Bădescu, Ş. C.; Lyanda-Geller, Y.; Reinecke, T. L.

2005-10-01

We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge-tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wave functions through asymmetric e-e and e-h exchange interactions.

Investigation of Spiral and Sweeping Holes

Science.gov (United States)

Thurman, Douglas; Poinsatte, Philip; Ameri, Ali; Culley, Dennis; Raghu, Surya; Shyam, Vikram

2015-01-01

Surface infrared thermography, hotwire anemometry, and thermocouple surveys were performed on two new film cooling hole geometries: spiral/rifled holes and fluidic sweeping holes. The spiral holes attempt to induce large-scale vorticity to the film cooling jet as it exits the hole to prevent the formation of the kidney shaped vortices commonly associated with film cooling jets. The fluidic sweeping hole uses a passive in-hole geometry to induce jet sweeping at frequencies that scale with blowing ratios. The spiral hole performance is compared to that of round holes with and without compound angles. The fluidic hole is of the diffusion class of holes and is therefore compared to a 777 hole and Square holes. A patent-pending spiral hole design showed the highest potential of the non-diffusion type hole configurations. Velocity contours and flow temperature were acquired at discreet cross-sections of the downstream flow field. The passive fluidic sweeping hole shows the most uniform cooling distribution but suffers from low span-averaged effectiveness levels due to enhanced mixing. The data was taken at a Reynolds number of 11,000 based on hole diameter and freestream velocity. Infrared thermography was taken for blowing rations of 1.0, 1.5, 2.0, and 2.5 at a density ration of 1.05. The flow inside the fluidic sweeping hole was studied using 3D unsteady RANS.

Effects of optical pumping in the photo-excitation of organic triplet states

International Nuclear Information System (INIS)

Lin, Tien-Sung; Yang, Tran-Chin; Sloop, David J.

2013-01-01

Highlights: • High electron spin polarization (ESP) was observed in pentacene triplets at room temperature. • The high ESP is transfer to the surrounding nuclear spin by optical pumping in zero-field (ZF). • The ZF transition frequencies and their line width depend on the laser pumping rate. • The spin–lattice relaxation times of the nuclear system are evaluated. - Abstract: Upon the application of laser and microwave pulses, non-zero magnetic moment of a photo-excited triplet state of organic molecules is generated in zero-field (ZF). The time evolution of the transient magnetic moments can be measured by free induction decay (FID) in ZF. The observed ZF spectra become broadened and ZF transition shifted to lower frequencies when the repetition rate of laser excitation is increased, which are attributed to the optical pumping of nuclear polarization (ONP) effect and the associated nuclear spin lattice relaxation processes. The observed ONP effect is discussed in terms of the local field effect and spin diffusion processes in optical pumping

Effects of optical pumping in the photo-excitation of organic triplet states

Energy Technology Data Exchange (ETDEWEB)

Lin, Tien-Sung, E-mail: lin@wustl.edu; Yang, Tran-Chin; Sloop, David J.

2013-08-30

Highlights: • High electron spin polarization (ESP) was observed in pentacene triplets at room temperature. • The high ESP is transfer to the surrounding nuclear spin by optical pumping in zero-field (ZF). • The ZF transition frequencies and their line width depend on the laser pumping rate. • The spin–lattice relaxation times of the nuclear system are evaluated. - Abstract: Upon the application of laser and microwave pulses, non-zero magnetic moment of a photo-excited triplet state of organic molecules is generated in zero-field (ZF). The time evolution of the transient magnetic moments can be measured by free induction decay (FID) in ZF. The observed ZF spectra become broadened and ZF transition shifted to lower frequencies when the repetition rate of laser excitation is increased, which are attributed to the optical pumping of nuclear polarization (ONP) effect and the associated nuclear spin lattice relaxation processes. The observed ONP effect is discussed in terms of the local field effect and spin diffusion processes in optical pumping.

Maternal and neonatal outcomes in twin and triplet gestations in Western Saudi Arabia

Directory of Open Access Journals (Sweden)

Samera F. AlBasri

2017-06-01

Full Text Available Objectives: Tocompare maternal and neonatal complications in twin and triplet gestations at King Abdulaziz University Hospital, Jeddah, Saudi Arabia. Methods: Retrospective medical records of 165 women with 144 twin and 21 triplet pregnancies from 2004 to 2011 were analyzed. Comparisons were carried out for maternal complications, gestational age at birth, neonatal birth weight, and neonatal intensive care admission. Results: Most common complications were preterm birth (49%, gestational diabetes mellitus (13.3%, and premature rupture of membrane (4.8%. All triplet pregnancies and 42% twin pregnancies terminated in preterm birth. Gestational length was longer (p less than 0.001 in twin births (36.0 ± 3.05 weeks than for triplet births (32 ± 3.81 weeks. Rates for in vitro fertilization, ovulation induction, and cesareans were higher in women with triplets than in those with twins. Neonatal intensive care unit (NICU admission was higher (p less than 0.001 for triplets (76.2% than for twins (23.6%. The mean weight of twins was 2333.83 ± 558.69 grams and triplets was 1553.41 ± 569.73 grams. Hyaline membrane disease, neonatal jaundice, and neonatal sepsis were most common neonatal complications. Conclusion: Neonates from triplet pregnancies were preterm, had low birth weight and needed more often NICU admission in comparison to those from twin pregnancies.

Electron and Hole Transport Layers: Their Use in Inverted Bulk Heterojunction Polymer Solar Cells

Directory of Open Access Journals (Sweden)

Sandro Lattante

2014-03-01

Full Text Available Bulk heterojunction polymer solar cells (BHJ PSCs are very promising organic-based devices for low-cost solar energy conversion, compatible with roll-to-roll or general printing methods for mass production. Nevertheless, to date, many issues should still be addressed, one of these being the poor stability in ambient conditions. One elegant way to overcome such an issue is the so-called “inverted” BHJ PSC, a device geometry in which the charge collection is reverted in comparison with the standard geometry device, i.e., the electrons are collected by the bottom electrode and the holes by the top electrode (in contact with air. This reverted geometry allows one to use a high work function top metal electrode, like silver or gold (thus avoiding its fast oxidation and degradation, and eliminates the need of a polymeric hole transport layer, typically of an acidic nature, on top of the transparent metal oxide bottom electrode. Moreover, this geometry is fully compatible with standard roll-to-roll manufacturing in air and is less demanding for a good post-production encapsulation process. To date, the external power conversion efficiencies of the inverted devices are generally comparable to their standard analogues, once both the electron transport layer and the hole transport layer are fully optimized for the particular device. Here, the most recent results on this particular optimization process will be reviewed, and a general outlook regarding the inverted BHJ PSC will be depicted.

TR-ESR Investigation on Reaction of Vitamin C with Excited Triplet of 9,10-phenanthrenequinone in Reversed Micelle Solutions

Science.gov (United States)

Xu, Xin-sheng; Shi, Lei; Liu, Yi; Ji, Xue-han; Cui, Zhi-feng

2011-04-01

Time-resolved electron spin resonance has been used to study quenching reactions between the antioxidant Vitamin C (VC) and the triplet excited states of 9,10-phenanthrenequinone (PAQ) in ethylene glycol-water (EG-H2O) homogeneous and inhomogeneous reversed micelle solutions. Reversed micelle solutions were used to be the models of physiological environment of biological cell and tissue. In PAQ/EG-H2O homogeneous solution, the excited triplet of PAQ (3PAQ*) abstracts hydrogen atom from solvent EG. In PAQ/VC/EG-H2O solution, 3PAQ* abstracts hydrogen atom not only from solvent EG but also from VC. The quenching rate constant of 3PAQ* by VC is close to the diffusion-controlled value of 1.41 × 108 L/(mol ·s). In hexadecyltrimethylammonium bromide (CTAB)/EG-H2O and aerosol OT (AOT)/EG-H2O reversed micelle solutions, 3PAQ* and VC react around the water-oil interface of the reversed micelle. Exit of 3PAQ* from the lipid phase slows down the quenching reaction. For Triton X-100 (TX-100)/EG-H2O reversed micelle solution, PAQ and VC coexist inside the hydrophilic polyethylene glycol core, and the quenching rate constant of 3PAQ* by VC is larger than those in AOT/EG-H2O and CTAB/EG-H2O reversed micelle solutions, even a little larger than that in EG-H2O homogeneous solution. The strong emissive chemically induced dynamic electron polarization of As.- resulted from the effective TM spin polarization transfer in hydrogen abstraction of 3PAQ* from VC.

Picosecond kinetics of the electron-hole layers formation in wide-bandgap II-VI type-II heterostructures

Energy Technology Data Exchange (ETDEWEB)

Filatov, E.V.; Zaitsev, S.V.; Tartakovskii, I.I.; Maksimov, A.A. [Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow region (Russian Federation); Yakovlev, D.R. [A.F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Experimentelle Physik II, Technische Universitaet Dortmund (Germany); Waag, A. [Institute of Semiconductor Technology, Braunschweig Technical University, 38106 Braunschweig (Germany)

2010-06-15

Considerable slowdown of luminescence kinetics of the direct optical transition was discovered in ZnSe/BeTe type-II heterostructures under high levels of optical pumping. The effect is attributed to forming of a potential barrier for holes in the ZnSe layer due to band bending at high densities of spatially separated carriers. That results in a longer time of the photoexcited holes energy relaxation to their ground state in the BeTe layer. The decrease of overlapping of electron and hole wavefunctions in the ZnSe layer in thick ZnSe/BeTe structures at high levels of optical excitation reveals an additional important effect, that leads to sufficient retardation of radiative recombination time for photoexcited carriers (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Electron-irradiation-induced phase transformation in alumina

International Nuclear Information System (INIS)

Chen, C.L.; Arakawa, K.; Lee, J.-G.; Mori, H.

2010-01-01

In this study, electron-irradiation-induced phase transformations between alumina polymorphs were investigated by high-resolution transmission electron microscopy. It was found that the electron-irradiation-induced α → κ' phase transformation occurred in the alumina under 100 keV electron irradiation. It is likely that the knock-on collision between incident electrons and Al 3+ cations is responsible for the occurrence of electron-irradiation-induced phase transformation from α-alumina to κ'-alumina.

High Power Efficiency Solution-Processed Blue Phosphorescent Organic Light-Emitting Diodes Using Exciplex-Type Host with a Turn-on Voltage Approaching the Theoretical Limit.

Science.gov (United States)

Ban, Xinxin; Sun, Kaiyong; Sun, Yueming; Huang, Bin; Ye, Shanghui; Yang, Min; Jiang, Wei

2015-11-18

Three solution-processable exciplex-type host materials were successfully designed and characterized by equal molar blending hole transporting molecules with a newly synthesized electron transporting material, which possesses high thermal stability and good film-forming ability through a spin-coating technique. The excited-state dynamics and the structure-property relationships were systematically investigated. By gradually deepening the highest occupied molecular orbital (HOMO) level of electron-donating components, the triplet energy of exciplex hosts were increased from 2.64 to 3.10 eV. Low temperature phosphorescence spectra demonstrated that the excessively high triplet energy of exciplex would induce a serious energy leakage from the complex state to the constituting molecule. Furthermore, the low energy electromer state, which only exists under the electroexcitation, was found as another possible channel for energy loss in exciplex-based phosphorescent organic light-emitting diodes (OLEDs). In particular, as quenching of the exciplex-state and the triplet exciton were largely eliminated, solution-processed blue phosphorescence OLEDs using the exciplex-type host achieved an extremely low turn-on voltage of 2.7 eV and record-high power efficiency of 22.5 lm W(-1), which were among the highest values in the devices with identical structure.

Local CC2 response method for triplet states based on Laplace transform: excitation energies and first-order properties.

Science.gov (United States)

Freundorfer, Katrin; Kats, Daniel; Korona, Tatiana; Schütz, Martin

2010-12-28

A new multistate local CC2 response method for calculating excitation energies and first-order properties of excited triplet states in extended molecular systems is presented. The Laplace transform technique is employed to partition the left/right local CC2 eigenvalue problems as well as the linear equations determining the Lagrange multipliers needed for the properties. The doubles part in the equations can then be inverted on-the-fly and only effective equations for the singles part must be solved iteratively. The local approximation presented here is adaptive and state-specific. The density-fitting method is utilized to approximate the electron-repulsion integrals. The accuracy of the new method is tested by comparison to canonical reference values for a set of 12 test molecules and 62 excited triplet states. As an illustrative application example, the lowest four triplet states of 3-(5-(5-(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)thiophene-2-yl)thiophene-2-yl)-2-cyanoacrylic acid, an organic sensitizer for solar-cell applications, are computed in the present work. No triplet charge-transfer states are detected among these states. This situation contrasts with the singlet states of this molecule, where the lowest singlet state has been recently found to correspond to an excited state with a pronounced charge-transfer character having a large transition strength.

Controllable behaviours of rogue wave triplets in the nonautonomous nonlinear and dispersive system

International Nuclear Information System (INIS)

Dai Chaoqing; Tian Qing; Zhu Shiqun

2012-01-01

A similarity transformation connecting the variable coefficient nonlinear Schrödinger equation with the standard nonlinear Schrödinger equation is constructed. The self-similar rogue wave triplet solutions (rational solutions) are analytically obtained for the nonautonomous nonlinear and dispersive system. The controllable behaviours of rogue wave triplets in two typical soliton management systems are discussed. In the exponential dispersion decreasing fibre, three kinds of rogue wave triplets with controllable behaviours are analysed. In the periodic distributed system, the rogue wave triplets recur periodically in the form of a cluster. (paper)

Favorable performance of the DFT methods in predicting the minimum-energy structure of the lowest triplet state of WF4

International Nuclear Information System (INIS)

Gutowski, M.; Univ. of Utah, Salt Lake City, UT

1999-01-01

The tetrahedral structure of the lowest triplet state of the WF 4 complex was examined using different variants of the density functional theory (DFT) and conventional ab initio methods. The low-level, conventional, ab initio methods, such as SCF, MP2, MP3, and CISD, predict the tetrahedral structure to be a minimum, whereas the DFT schemes predict an imaginary frequency for the e vibrational mode. Only after recovering electron correlation effects at the MP4 and higher levels, the conventional electronic structure methods also predict the T d structure to be a second-order stationary point. This is not the correlation but the exchange part of the DFT functionals which is responsible for the discrepancy between the DFT and low-level, conventional, ab initio predictions. The lowering of symmetry to C 2v leads to a minimum on the lowest triplet potential energy surface and the electronic energy difference between the T d and C 2v stationary points amounts to 0.85 and 0.96 kcal/mol at the B3LYP and CCSD(T) levels, respectively

Vitrectomy with internal limiting membrane peeling vs no peeling for Macular Hole-induced Retinal Detachment (MHRD): a meta-analysis.

Science.gov (United States)

Su, Jing; Liu, Xinquan; Zheng, Lijun; Cui, Hongping

2015-06-20

we conducted our meta-analysis of published studies to assess existing evidence about the efficacy and safety of vitrectomy with ILM peeling vs. that of vitrectomy with no ILM peeling for Macular hole-induced retinal detachment. Databases, including Pubmed, Cochrane Library, Ovid, Web of Science, Wanfang and CNKI, were searched to identify studies comparing outcomes following vitrectomy with ILM peeling and that with no ILM peeling for macular hole-induced retinal detachment. The meta-analysis was performed by RevMan 5.1. Six comparative studies comprising 180 eyes were identified. It was indicated that the rate of retinal reattachment (Odds ratio (OR) = 3.03, 95 % Confidence interval (CI):1.35 to 6.78; P = 0.007) and macular hole closure (OR = 6.74, 95 % CI:3.26 to 13.93; P peeling than that in the group of vitrectomy with no ILM peeling. However, the improved BCVA (Weighted mean difference (WMD) = 0.14, 95 % CI: -0.20 to 0.47; P = 0.42) and the rate of postoperative complications were similar between the two groups. Vitrectomy with internal limiting membrane peeling is an efficient and safe procedure for macular hole-induced retinal detachment.

Sirenomelia in a Nigerian triplet: a case report.

Science.gov (United States)

Ugwu, Rosemary O; Eneh, Augusta U; Wonodi, Woroma

2011-09-02

Sirenomelia, also known as mermaid syndrome, is a very rare fatal congenital abnormality in which the legs are fused together, giving them the appearance of a mermaid's tail. It is commonly associated with abnormal kidney development, genital and rectal abnormalities. A handful of cases have been reported in other parts of the world, however, no cases have previously been reported in a Nigerian neonate. To the best of our knowledge, we believe that this is the first case reported from West Africa and in a triplet. A 16-hour-old baby boy, the second of a set of Nigerian triplets, presented to our facility with fusion of the entire lower limbs, imperforate anus, indiscernible genital structures, single umbilical artery and a neural tube defect. His parents were from the Hausa ethnic group and not related. Sirenomelia has not been previously described in a set of triplets, and it is hoped that this report from West Africa will give information about the non-racial predilection of this condition.

Three-dimensional triplet tracking for LHC and future high rate experiments

International Nuclear Information System (INIS)

Schöning, A

2014-01-01

The hit combinatorial problem is a main challenge for track reconstruction and triggering at high rate experiments. At hadron colliders the dominant fraction of hits is due to low momentum tracks for which multiple scattering (MS) effects dominate the hit resolution. MS is also the dominating source for hit confusion and track uncertainties in low energy precision experiments. In all such environments, where MS dominates, track reconstruction and fitting can be largely simplified by using three-dimensional (3D) hit-triplets as provided by pixel detectors. This simplification is possible since track uncertainties are solely determined by MS if high precision spatial information is provided. Fitting of hit-triplets is especially simple for tracking detectors in solenoidal magnetic fields. The over-constrained 3D-triplet method provides a complete set of track parameters and is robust against fake hit combinations. Full tracks can be reconstructed step-wise by connecting hit triplet combinations from different layers, thus heavily reducing the combinatorial problem and accelerating track linking. The triplet method is ideally suited for pixel detectors where hits can be treated as 3D-space points. With the advent of relatively cheap and industrially available CMOS-sensors the construction of highly granular full scale pixel tracking detectors seems to be possible also for experiments at LHC or future high energy (hadron) colliders. In this paper tracking performance studies for full-scale pixel detectors, including their optimisation for 3D-triplet tracking, are presented. The results obtained for different types of tracker geometries and different reconstruction methods are compared. The potential of reducing the number of tracking layers and - along with that - the material budget using this new tracking concept is discussed. The possibility of using 3D-triplet tracking for triggering and fast online reconstruction is highlighted

Migration of CT triplet excitons in TCNB-biphenyl and TCNB-HMB crystals

Science.gov (United States)

Kozankiewicz, BolesAw

1994-01-01

Delayed fluorescence decay curves of charge transfer (CT) crystals of tetracyanobenzene with biphenyl (TCNB-B) and with hexamethylbenzene (TCNB-HMB) have been studied over a wide temperature range (5-200 K). The decay curves have been adequately described by decay expressions derived for different mechanisms of triplet-triplet annihilation. This analysis points to one-dimensional, thermally activated motion of CT triplet excitons. The estimated activation energies for the exciton hopping are 360±60 and 650±100 cm -1 (or 550±150 cm -1 depending on the applied model) for the TCNB-B and TCNB-HMB crystals, respectively. The results seem to confirm the self-trapping of triplet CT excitons.

Triplet excited States as a source of relevant (bio)chemical information.

Science.gov (United States)

Jiménez, M Consuelo; Miranda, Miguel A

2014-01-01

The properties of triplet excited states are markedly medium-dependent, which turns this species into valuable tools for investigating the microenvironments existing in protein binding pockets. Monitoring of the triplet excited state behavior of drugs within transport proteins (serum albumins and α1-acid glycoproteins) by laser flash photolysis constitutes a valuable source of information on the strength of interaction, conformational freedom and protection from oxygen or other external quenchers. With proteins, formation of spatially confined triplet excited states is favored over competitive processes affording ionic species. Remarkably, under aerobic atmosphere, the triplet decay of drug@protein complexes is dramatically longer than in bulk solution. This offers a convenient dynamic range for assignment of different triplet populations or for stereochemical discrimination. In this review, selected examples of the application of the laser flash photolysis technique are described, including drug distribution between the bulk solution and the protein cavities, or between two types of proteins, detection of drug-drug interactions inside proteins, and enzyme-like activity processes mediated by proteins. Finally, protein encapsulation can also modify the photoreactivity of the guest. This is illustrated by presenting an example of retarded photooxidation.

Combined UMC- DFT prediction of electron-hole coupling in unit cells of pentacene crystals.

Science.gov (United States)

Leal, Luciano Almeida; de Souza Júnior, Rafael Timóteo; de Almeida Fonseca, Antonio Luciano; Ribeiro Junior, Luiz Antonio; Blawid, Stefan; da Silva Filho, Demetrio Antonio; da Cunha, Wiliam Ferreira

2017-05-01

Pentacene is an organic semiconductor that draws special attention from the scientific community due to the high mobility of its charge carriers. As electron-hole interactions are important aspects in the regard of such property, a computationally inexpensive method to predict the coupling between these quasi-particles is highly desired. In this work, we propose a hybrid methodology of combining Uncoupled Monte Carlo Simulations (UMC) and Density functional Theory (DFT) methodologies to obtain a good compromise between computational feasibility and accuracy. As a first step in considering a Pentacene crystal, we describe its unit cell: the Pentacene Dimer. Because many conformations can be encountered for the dimer and considering the complexity of the system, we make use of UMC in order to find the most probable structures and relative orientations for the Pentacene-Pentacene complex. Following, we carry out electronic structure calculations in the scope of DFT with the goal of describing the electron-hole coupling on the most probable configurations obtained by UMC. The comparison of our results with previously reported data on the literature suggests that the methodology is well suited for describing transfer integrals of organic semiconductors. The observed accuracy together with the smaller computational cost required by our approach allows us to conclude that such methodology might be an important tool towards the description of systems with higher complexity.

Electron-hole transition in spherical QD-QW nanoparticles based on GaN∣(In,Ga)N∣GaN under hydrostatic pressure

International Nuclear Information System (INIS)

El Ghazi, Haddou; Jorio, Anouar

2013-01-01

Within the framework of effective-mass approximation and finite parabolic potential confinement barrier in which two confinement parameters are taking account, the electron (hole) energy and the ground-state electron-hole (e−h) transition in Core∣well∣shell (GaN|In x Ga 1−x N|GaN) spherical QD-QW nanoparticles are investigated as a function of the inner and the outer radii under externally applied hydrostatic pressure. The pressure dependencies of the effective-mass and the QD radius are taking into account. The results we obtained are in quite good agreement with the theoretical and the experimental findings

Electron-hole transition in spherical QD-QW nanoparticles based on GaN∣(In,Ga)N∣GaN under hydrostatic pressure

Energy Technology Data Exchange (ETDEWEB)

El Ghazi, Haddou, E-mail: hadghazi@gmail.com [LPS, Faculty of Science, Dhar EL Mehrez, BP 1796 Fes-Atlas (Morocco); Special Mathematics, CPGE Kénitra, Chakib Arsalane Street (Morocco); Jorio, Anouar [LPS, Faculty of Science, Dhar EL Mehrez, BP 1796 Fes-Atlas (Morocco)

2013-11-15

Within the framework of effective-mass approximation and finite parabolic potential confinement barrier in which two confinement parameters are taking account, the electron (hole) energy and the ground-state electron-hole (e−h) transition in Core∣well∣shell (GaN|In{sub x}Ga{sub 1−x}N|GaN) spherical QD-QW nanoparticles are investigated as a function of the inner and the outer radii under externally applied hydrostatic pressure. The pressure dependencies of the effective-mass and the QD radius are taking into account. The results we obtained are in quite good agreement with the theoretical and the experimental findings.

The effect of electron and hole doping on the thermoelectric properties of shandite-type Co3Sn2S2

OpenAIRE

Mangelis, Panagiotis; Vaqueiro, Paz; Jumas, Jean-Claude; da Silva, Ivan; Smith, Ronald I; Powell, Anthony V

2017-01-01

Electron and hole doping in Co3Sn2S2, through chemical substitution of cobalt by the neighbouring elements, nickel and iron, affects both the structure and thermoelectric properties. Electron doping to form Co3-xNixSn2S2 (0 ≤ x ≤ 3) results in an expansion of the kagome layer and materials become increasingly metallic as cobalt is substituted. Conversely, hole doping in Co3-xFexSn2S2 (0 ≤ x ≤ 0.6) leads to a transition from metallic to n-type semiconducting behaviour at x = 0.5. Iron substitu...

Phosphate Changes Effect of Humic Acids on TiO2 Photocatalysis: From Inhibition to Mitigation of Electron-Hole Recombination.

Science.gov (United States)

Long, Mingce; Brame, Jonathon; Qin, Fan; Bao, Jiming; Li, Qilin; Alvarez, Pedro J J

2017-01-03

A major challenge for photocatalytic water purification with TiO 2 is the strong inhibitory effect of natural organic matter (NOM), which can scavenge photogenerated holes and radicals and occlude ROS generation sites upon adsorption. This study shows that phosphate counteracts the inhibitory effect of humic acids (HA) by decreasing HA adsorption and mitigating electron-hole recombination. As a measure of the inhibitory effect of HA, the ratios of first-order reaction rate constants between photocatalytic phenol degradation in the absence versus presence of HA were calculated. This ratio was very high, up to 5.72 at 30 mg/L HA and pH 4.8 without phosphate, but was decreased to 0.76 (5 mg/L HA, pH 8.4) with 2 mM phosphate. The latter ratio indicates a surprising favorable effect of HA on TiO 2 photocatalysis. FTIR analyses suggest that this favorable effect is likely due to a change in the conformation of adsorbed HA, from a multiligand exchange arrangement to a complexation predominantly between COOH groups in HA and the TiO 2 surface in the presence of phosphate. This configuration can reduce hole consumption and facilitate electron transfer to O 2 by the adsorbed HA (indicated by linear sweep voltammetry), which mitigates electron-hole recombination and enhances contaminant degradation. A decrease in HA surface adsorption and hole scavenging (the predominant inhibitory mechanisms of HA) by phosphate (2 mM) was indicated by a 50% decrease in the photocatalytic degradation rate of HA and 80% decrease in the decay rate coefficient of interfacial-related photooxidation in photocurrent transients. These results, which were validated with other compounds (FFA and cimetidine), indicate that anchoring phosphate - or anions that exert similar effects on the TiO 2 surface - might be a feasible strategy to counteract the inhibitory effect of NOM during photocatalytic water treatment.

Neutron induced electron radiography; Radiografia com eletrons induzida por neutrons

Energy Technology Data Exchange (ETDEWEB)

Andrade, Marcos Leandro Garcia

2008-07-01

In the present paper a new radiography technique, the 'Neutron Induced Electron Radiography' - NIER, to inspect low thickness samples on the order of micra, has been developed. This technique makes use of low energy electrons as penetrating radiation generated from metallic gadolinium screens when irradiated by thermal neutrons. The conditions to obtain the best image for the conventional X-ray film Kodak-AA were determined by using a digital system to quantify the darkening level of the film. The irradiations have been performed at a radiography equipment installed at the beam-hole no. 8 of the 5 MW IEA-R1 nuclear research reactor of IPEN-CNEN/SP. The irradiation time to obtain the best radiography was 100 seconds and for such condition the technique was able to discern 1 {mu}m in 24 {mu}m of aluminum at a resolution of 32 {mu}m. By visual comparison the images obtained by the NIER shown a higher quality when compared with the ones from other usual techniques the make use of electrons a penetrating radiation and films for image registration. Furthermore the use of the digital system has provided a smaller time for data acquisition and data analysis as well as an improvement in the image visualization. (author)

Reactive carbon-chain molecules: synthesis of 1-diazo-2,4-pentadiyne and spectroscopic characterization of triplet pentadiynylidene (H-C[triple bond]C-:C-C[triple bond]C-H).

Science.gov (United States)

Bowling, Nathan P; Halter, Robert J; Hodges, Jonathan A; Seburg, Randal A; Thomas, Phillip S; Simmons, Christopher S; Stanton, John F; McMahon, Robert J

2006-03-15

1-Diazo-2,4-pentadiyne (6a), along with both monodeuterio isotopomers 6b and 6c, has been synthesized via a route that proceeds through diacetylene, 2,4-pentadiynal, and 2,4-pentadiynal tosylhydrazone. Photolysis of diazo compounds 6a-c (lambda > 444 nm; Ar or N2, 10 K) generates triplet carbenes HC5H (1) and HC5D (1-d), which have been characterized by IR, EPR, and UV/vis spectroscopy. Although many resonance structures contribute to the resonance hybrid for this highly unsaturated carbon-chain molecule, experiment and theory reveal that the structure is best depicted in terms of the dominant resonance contributor of penta-1,4-diyn-3-ylidene (diethynylcarbene, H-C[triple bond]C-:C-C[triple bond]C-H). Theory predicts an axially symmetric (D(infinity h)) structure and a triplet electronic ground state for 1 (CCSD(T)/ANO). Experimental IR frequencies and isotope shifts are in good agreement with computed values. The triplet EPR spectrum of 1 (absolute value(D/hc) = 0.6157 cm(-1), absolute value(E/hc) = 0.0006 cm(-1)) is consistent with an axially symmetric structure, and the Curie law behavior confirms that the triplet state is the ground state. The electronic absorption spectrum of 1 exhibits a weak transition near 400 nm with extensive vibronic coupling. Chemical trapping of triplet HC5H (1) in an O2-doped matrix affords the carbonyl oxide 16 derived exclusively from attack at the central carbon.

The triplet excited state of bilirubin

International Nuclear Information System (INIS)

Land, E.J.

1976-01-01

Pulse radiolysis of benzene solutions of 40 μM bilirubin alone or with 0.1 M biphenyl has yielded evidence for the formation of the triplet excited state of bilirubin. Measurements were made of a number of properties, including the absorption spectrum (lambdasub(max)500nm), lifetime 9μs), extinction coefficient (8800 M -1 cm -1 ), energy level (approximately 150 kJ mol -1 ) and the rate of quenching by oxygen (rate constant, 8.2 x 10 8 M -1 s -1 ). An upper limit of 0.1 has also been obtained for the singlet to triplet crossover efficiency of bilirubin following excitation by 353 nm radiation. Consideration is given to the relevance of these data to the mechanism of bilirubin photo-destruction, both in vivo and in vitro. (U.K.)

Classical and quantum 'EPR'-spin correlations in the triplet state

International Nuclear Information System (INIS)

Barut, A.O.; Bozic, M.

1987-01-01

Quantum correlations and joint probabilities in the triplet state as well as the correlations of components of two correlated classical spin vectors, are evaluated. Correlations in the states with |S tot z |=1 are different from correlations in the state with S tot z =0 which may serve to distinguish different states of the triplet. As in the singlet case, we can reproduce quantum correlations by correlated classical spin vectors which also provide a precision of the notion of ''parallel spins''. Triplet state correlations could in principle be measured, for example, in the decay reaction J/ψ → e + e - for which there is a sufficiently large branching ratio. (author). 12 refs

Triplet superconductors as the basis for solid-state quantum computing

International Nuclear Information System (INIS)

Gulian, A M; Wood, K S

2003-01-01

We propose triplet superconductors, such as ruthenates, as prospective materials for qubit construction. The vectorial nature of the order parameter in triplet superconductors makes it conceptually easy to estimate the performance of the qubits. The Cooper condensate of pairs in triplet superconductors has all the attributes of Bose-Einstein condensates and should facilitate long decoherence times for these qubits, relative to other vectorial schemes for qubits, such as small ferromagnets. There are other benefits, which the superconducting state provides for requirements such as entanglement between qubits via the proximity effect, etc. We consider these benefits in detail, although our consideration is only preliminary and further experimental and theoretical research will undoubtedly introduce correctives

Terahertz properties of Dirac electrons and holes in HgTe films with critical thickness

Energy Technology Data Exchange (ETDEWEB)

Dziom, Uladzislau; Shuvaev, Alexey; Pimenov, Andrei [Institute of Solid State Physics, Vienna University of Technology, 1040 Vienna (Austria); Mikhailov, Nikolai; Kvon, Ze Don [Novosibirsk State University, Novosibirsk 630090 (Russian Federation)

2016-07-01

We present and discuss properties of mercury telluride (HgTe) films with critical thickness in far-infrared (THz) spectral range. Density of charge carriers is controlled, using contact-free optical gating by visible light. Transmission measurements in applied magnetic field demonstrate switching from hole to electron-like behavior, as illumination time increases. The cyclotron mass of the electrons, extracted from the data, shows a square root dependence upon the charge concentration in a broad range of parameters. This can be interpreted as a clear proof of a linear dispersion relations, i.e. Dirac-type charge carriers.

Blue and white phosphorescent organic light emitting diode performance improvement by confining electrons and holes inside double emitting layers

Energy Technology Data Exchange (ETDEWEB)

Tsai, Yu-Sheng; Hong, Lin-Ann; Juang, Fuh-Shyang; Chen, Cheng-Yin

2014-09-15

In this research, complex emitting layers (EML) were fabricated using TCTA doping hole-transport material in the front half of a bipolar 26DCzPPy as well as PPT doping electron-transport material in the back half of 26DCzPPy. Blue dopant FIrpic was also mixed inside the complex emitting layer to produce a highly efficient blue phosphorescent organic light emitting diode (OLED). The hole and electron injection and carrier recombination rate were effectively increased. The fabricated complex emitting layers exhibited current efficiency of 42 cd/A and power efficiency of 30 lm/W when the luminance was 1000 cd/m{sup 2}, driving voltage was 4.4 V, and current density was 2.4 mA/cm{sup 2}. A white OLED component was then manufactured by doping red dopant [Os(bpftz){sub 2}(PPh{sub 2}Me){sub 2}] (Os) in proper locations. When the Os dopant was doped in between the complex emitting layers, excitons were effectively confined within, increasing the recombination rate and therefore reducing the color shift. The resulting Commission Internationale de L’Eclairage (CIE) coordinates shifted from 4 to 10 V is (Δx=−0.04, Δy=+0.01). The component had a current efficiency of 35.7 cd/A, a power efficiency of 24 lm/W, driving voltage of 4.6 V and a CIE{sub x,y} of (0.31,0.35) at a luminance of 1000 cd/m{sup 2}, with a maximum luminance of 15,600 cd/m{sup 2} at 10 V. Attaching an outcoupling enhancement film was applied to increase the luminance efficiency to 30 lm/W. - Highlights: • Used the complex double emitting layers. • Respectively doped hole and electron transport material in the bipolar host. • Electrons and holes are effectively confined within EMLs to produce excitons.

Blue and white phosphorescent organic light emitting diode performance improvement by confining electrons and holes inside double emitting layers

International Nuclear Information System (INIS)

Tsai, Yu-Sheng; Hong, Lin-Ann; Juang, Fuh-Shyang; Chen, Cheng-Yin

2014-01-01

In this research, complex emitting layers (EML) were fabricated using TCTA doping hole-transport material in the front half of a bipolar 26DCzPPy as well as PPT doping electron-transport material in the back half of 26DCzPPy. Blue dopant FIrpic was also mixed inside the complex emitting layer to produce a highly efficient blue phosphorescent organic light emitting diode (OLED). The hole and electron injection and carrier recombination rate were effectively increased. The fabricated complex emitting layers exhibited current efficiency of 42 cd/A and power efficiency of 30 lm/W when the luminance was 1000 cd/m 2 , driving voltage was 4.4 V, and current density was 2.4 mA/cm 2 . A white OLED component was then manufactured by doping red dopant [Os(bpftz) 2 (PPh 2 Me) 2 ] (Os) in proper locations. When the Os dopant was doped in between the complex emitting layers, excitons were effectively confined within, increasing the recombination rate and therefore reducing the color shift. The resulting Commission Internationale de L’Eclairage (CIE) coordinates shifted from 4 to 10 V is (Δx=−0.04, Δy=+0.01). The component had a current efficiency of 35.7 cd/A, a power efficiency of 24 lm/W, driving voltage of 4.6 V and a CIE x,y of (0.31,0.35) at a luminance of 1000 cd/m 2 , with a maximum luminance of 15,600 cd/m 2 at 10 V. Attaching an outcoupling enhancement film was applied to increase the luminance efficiency to 30 lm/W. - Highlights: • Used the complex double emitting layers. • Respectively doped hole and electron transport material in the bipolar host. • Electrons and holes are effectively confined within EMLs to produce excitons

Exciton fine structure in CdSe nanoclusters

International Nuclear Information System (INIS)

Leung, K.; Pokrant, S.; Whaley, K.B.

1998-01-01

The fine structure in the CdSe nanocrystal absorption spectrum is computed by incorporating two-particle electron-hole interactions and spin-orbit coupling into a tight-binding model, with an expansion in electron-hole single-particle states. The exchange interaction and spin-orbit coupling give rise to dark, low-lying states that are predominantly triplet in character, as well as to a manifold of exciton states that are sensitive to the nanocrystal shape. Near the band gap, the exciton degeneracies are in qualitative agreement with the effective mass approximation (EMA). However, instead of the infinite lifetimes for dark states characteristic of the EMA, we obtain finite radiative lifetimes for the dark states. In particular, for the lowest, predominantly triplet, states we obtain radiative lifetimes of microseconds, in qualitative agreement with the experimental measured lifetimes. The resonant Stokes shifts obtained from the splitting between the lowest dark and bright states are also in good agreement with experimental values for larger crystallites. Higher-lying states exhibit significantly more complex behavior than predicted by EMA, due to extensive mixing of electron-hole pair states. copyright 1998 The American Physical Society

The effect of electron-electron interaction induced dephasing on electronic transport in graphene nanoribbons

Energy Technology Data Exchange (ETDEWEB)

Kahnoj, Sina Soleimani; Touski, Shoeib Babaee [School of Electrical and Computer Engineering, University of Tehran, P.O. Box 14395-515, Tehran (Iran, Islamic Republic of); Pourfath, Mahdi, E-mail: pourfath@ut.ac.ir, E-mail: pourfath@iue.tuwien.ac.at [School of Electrical and Computer Engineering, University of Tehran, P.O. Box 14395-515, Tehran (Iran, Islamic Republic of); Institute for Microelectronics, TU Wien, Gusshausstrasse 27–29/E360, 1040 Vienna (Austria)

2014-09-08

The effect of dephasing induced by electron-electron interaction on electronic transport in graphene nanoribbons is theoretically investigated. In the presence of disorder in graphene nanoribbons, wavefunction of electrons can set up standing waves along the channel and the conductance exponentially decreases with the ribbon's length. Employing the non-equilibrium Green's function formalism along with an accurate model for describing the dephasing induced by electron-electron interaction, we show that this kind of interaction prevents localization and transport of electrons remains in the diffusive regime where the conductance is inversely proportional to the ribbon's length.

Generation of fluorescence quenchers from the triplet states of chlorophylls in the major light-harvesting complex II from green plants

NARCIS (Netherlands)

Barzda, V.; Vengris, M.; Valkunas, L.; van Amerongen, H.; van Grondelle, R.

2000-01-01

Laser flash-induced changes of the fluorescence yield were studied in aggregates of light-harvesting complex II (LHCII) on a time scale ranging from microseconds to seconds. Carotenoid (Car) and chlorophyll (Chl) triplet states, decaying with lifetimes of several microseconds and hundreds of

Accurate simulation of geometry, singlet-singlet and triplet-singlet excitation of cyclometalated iridium(III) complex.

Science.gov (United States)

Wang, Jian; Bai, Fu-Quan; Xia, Bao-Hui; Zhang, Hong-Xing; Cui, Tian

2014-03-01

In the current contribution, we present a critical study of the theoretical protocol used for the determination of the electronic spectra properties of luminescent cyclometalated iridium(III) complex, [Ir(III)(ppy)₂H₂dcbpy]⁺ (where, ppy = 2-phenylpyridine, H₂dcbpy = 2,2'-bipyridine-4,4'-dicarboxylic acid), considered as a representative example of the various problems related to the prediction of electronic spectra of transition metal complex. The choice of the exchange-correlation functional is crucial for the validity of the conclusions that would be drawn from the numerical results. The influence of the exchange-correlation on geometry parameter and absorption/emission band, the role of solvent effects on time-dependent density function theory (TD-DFT) calculations, as well as the importance of the chosen proper procedure to optimize triplet excited geometry, have been thus examined in detail. From the obtained results, some general conclusions and guidelines are presented: i) PBE0 functional is the most accurate in prediction of ground state geometry; ii) the well-established B3LYP, B3P86, PBE0, and X3LYP have similar accuracy in calculation of absorption spectrum; and iii) the hybrid approach TD-DFT//CIS gives out excellent agreement in the evaluation of triplet excitation energy.

Running with triplets: How slepton masses change with doubly-charged Higgs bosons

International Nuclear Information System (INIS)

Setzer, N.; Spinner, S.

2007-01-01

We examine the slepton masses of SUSYLR models and how they change due to the presence of light doubly-charged Higgs bosons. We discover that the measurement of the slepton masses could bound and even predict the value of the third generation Yukawa coupling of leptons to the SU(2) R triplets. We also consider the unification prospects for this model with the addition of left-handed, B-L=0 triplets--a model we call the triplet extended supersymmetric standard model (TESSM)

Zn induced in-gap electronic states in La214 probed by uniform magnetic susceptibility: relevance to the suppression of superconducting T c

Science.gov (United States)

Islam, R. S.; Naqib, S. H.

2018-02-01

Substitution of isovalent non-magnetic defects, such as Zn, in the CuO2 plane strongly modifies the magnetic properties of strongly electron correlated hole doped cuprate superconductors. The reason for enhanced uniform magnetic susceptibility, χ, in Zn substituted cuprates is debatable. Generally the defect induced magnetic behavior has been analyzed mainly in terms of two somewhat contrasting scenarios. The first one is due to independent localized moments appearing in the vicinity of Zn arising because of the strong electronic/magnetic correlations present in the host compound and the second one is due to transfer of quasiparticle (QP) spectral weight and creation of weakly localized low-energy electronic states associated with each Zn atom in place of an in-plane Cu. If the second scenario is correct, one should expect a direct correspondence between Zn induced suppression of the superconducting transition temperature, T c, and the extent of the enhanced magnetic susceptibility at low temperature. In this case, the low-T enhancement of χ would be due to weakly localized QP states at low energy and these electronic states will be precluded from taking part in Cooper pairing. We explore this second possibility by analyzing the χ(T) data for La2-x Sr x Cu1-y Zn y O4 with different hole contents, p (=x), and Zn concentrations (y) in this paper. The results of our analysis support this scenario.

Triplet-triplet energy transfer from chlorophylls to carotenoids in two antenna complexes from dinoflagellate Amphidinium carterae

Czech Academy of Sciences Publication Activity Database

Kvíčalová, Z.; Alster, J.; Hofmann, E.; Khoroshyy, P.; Litvín, Radek; Bína, David; Polívka, Tomáš; Pšenčík, J.

2016-01-01

Roč. 1857, č. 4 (2016), s. 341-349 ISSN 0005-2728 R&D Projects: GA ČR GBP501/12/G055 Institutional support: RVO:60077344 Keywords : Dinoflagellate * Chlorophyll * Carotenoid * Triplet state Subject RIV: BO - Biophysics Impact factor: 4.932, year: 2016

Quenching of chlorophyll a singlets and triplets by carotenoids in light-harvesting complex of photosystem II: comparison of aggregates with trimers

Science.gov (United States)

Naqvi, K. Razi; Melø, T. B.; Raju, B. Bangar; Jávorfi, Tamás; Simidjiev, Ilian; Garab, Gyözö

1997-12-01

Laser-induced changes in the absorption spectra of isolated light-harvesting chlorophyll a/ b complex (LHC II) associated with photosystem II of higher plants have been recorded under anaerobic conditions and at ambient temperature by using multichannel detection with sub-microsecond time resolution. Difference spectra (Δ A) of LHC II aggregates have been found to differ from the corresponding spectra of trimers on two counts: (i) in the aggregates, the carotenoid (Car) triplet-triplet absorption band (Δ A>0) is red-shifted and broader; and (ii) the features attributable to the perturbation of the Qy band of a chlorophyll a (Chl a) by a nearby Car triplet are more pronounced, than in trimers. Aggregation, which is known to be accompanied by a reduction in the fluorescence yield of Chl a, is shown to cause a parallel decline in the triplet formation yield of Chl a; on the other hand, the efficiency (100%) of Chl a-to-Car transfer of triplet energy and the lifetime (9.3 μs) of Car triplets are not affected by aggregation. These findings are rationalized by postulating that the antenna Cars transact, besides light-harvesting and photoprotection, a third process: energy dissipation within the antenna. The suggestion is advanced that luteins, which are buried inside the LHC II monomers, as well as the other, peripheral, xanthophylls (neoxanthin and violaxanthin) quench the excited singlet state of Chl a by catalyzing internal conversion, a decay channel that competes with fluorescence and intersystem crossing; support for this explanation is presented by recalling reports of similar behaviour in bichromophoric model compounds in which one moiety is a Car and the other a porphyrin or a pyropheophorbide.

Three-Dimensional Triplet Tracking for LHC and Future High Rate Experiments

CERN Document Server

Schöning, Andre

2014-10-20

The hit combinatorial problem is a main challenge for track reconstruction and triggering at high rate experiments. At hadron colliders the dominant fraction of hits is due to low momentum tracks for which multiple scattering (MS) effects dominate the hit resolution. MS is also the dominating source for hit confusion and track uncertainties in low energy precision experiments. In all such environments, where MS dominates, track reconstruction and fitting can be largely simplified by using three-dimensional (3D) hit-triplets as provided by pixel detectors. This simplification is possible since track uncertainties are solely determined by MS if high precision spatial information is provided. Fitting of hit-triplets is especially simple for tracking detectors in solenoidal magnetic fields. The over-constrained 3D-triplet method provides a complete set of track parameters and is robust against fake hit combinations. The triplet method is ideally suited for pixel detectors where hits can be treated as 3D-space poi...

Sirenomelia in a Nigerian triplet: a case report

Science.gov (United States)

2011-01-01

Introduction Sirenomelia, also known as mermaid syndrome, is a very rare fatal congenital abnormality in which the legs are fused together, giving them the appearance of a mermaid's tail. It is commonly associated with abnormal kidney development, genital and rectal abnormalities. A handful of cases have been reported in other parts of the world, however, no cases have previously been reported in a Nigerian neonate. To the best of our knowledge, we believe that this is the first case reported from West Africa and in a triplet. Case presentation A 16-hour-old baby boy, the second of a set of Nigerian triplets, presented to our facility with fusion of the entire lower limbs, imperforate anus, indiscernible genital structures, single umbilical artery and a neural tube defect. His parents were from the Hausa ethnic group and not related. Conclusion Sirenomelia has not been previously described in a set of triplets, and it is hoped that this report from West Africa will give information about the non-racial predilection of this condition. PMID:21888626

Sirenomelia in a Nigerian triplet: a case report

Directory of Open Access Journals (Sweden)

Wonodi Woroma

2011-09-01

Full Text Available Abstract Introduction Sirenomelia, also known as mermaid syndrome, is a very rare fatal congenital abnormality in which the legs are fused together, giving them the appearance of a mermaid's tail. It is commonly associated with abnormal kidney development, genital and rectal abnormalities. A handful of cases have been reported in other parts of the world, however, no cases have previously been reported in a Nigerian neonate. To the best of our knowledge, we believe that this is the first case reported from West Africa and in a triplet. Case presentation A 16-hour-old baby boy, the second of a set of Nigerian triplets, presented to our facility with fusion of the entire lower limbs, imperforate anus, indiscernible genital structures, single umbilical artery and a neural tube defect. His parents were from the Hausa ethnic group and not related. Conclusion Sirenomelia has not been previously described in a set of triplets, and it is hoped that this report from West Africa will give information about the non-racial predilection of this condition.

Minimum triplet covers of binary phylogenetic X-trees.

Science.gov (United States)

Huber, K T; Moulton, V; Steel, M

2017-12-01

Trees with labelled leaves and with all other vertices of degree three play an important role in systematic biology and other areas of classification. A classical combinatorial result ensures that such trees can be uniquely reconstructed from the distances between the leaves (when the edges are given any strictly positive lengths). Moreover, a linear number of these pairwise distance values suffices to determine both the tree and its edge lengths. A natural set of pairs of leaves is provided by any 'triplet cover' of the tree (based on the fact that each non-leaf vertex is the median vertex of three leaves). In this paper we describe a number of new results concerning triplet covers of minimum size. In particular, we characterize such covers in terms of an associated graph being a 2-tree. Also, we show that minimum triplet covers are 'shellable' and thereby provide a set of pairs for which the inter-leaf distance values will uniquely determine the underlying tree and its associated branch lengths.

Proximity effects and Josephson currents in ferromagnet. Spin-triplet superconductors junctions

International Nuclear Information System (INIS)

Terrade, Damien

2015-01-01

Spin-triplet superconductivity, first attached to the description of 3 He, is now generally considered to also occur in heavy-fermions compounds and in perovskite ruthenium oxide Sr 2 RuO 4 . The latter material is especially interesting since many experiments show strong evidences for a unitary chiral spin-triplet state. Moreover, the recent fabrication of thin heterostructures made of ferromagnetic SrRuO 3 on the top of Sr 2 RuO 4 strongly encourages new theoretical studies on the interplay between spin-triplet superconductor and ferromagnet in similar fashion to spin-singlet superconductors. Using an extended tight-binding Hamiltonian to model the superconductor, we discuss in this thesis the specific proximity effects of such interface by solving self-consistently the Bogoliubov-De Gennes equations on two- and three-dimensional lattices in the ballistic limit. We obtain the spatial profile of the superconducting order parameters at the interface as well as the spin-polarisation and the current across the Josephson junctions. In contrast to heterostructures made of spin-singlet superconductor, we show that the physical properties at the interface are not only controlled by the strength of the magnetization inside the ferromagnet but also by its orientation due to the existence of a finite pair spin projection of the spin-triplet Cooper pairs. We analyse in the first part the spin-polarisation and the Gibbs free energy at the three-dimensional ferromagnet-chiral spin-triplet superconductor interface. Then, the second part of the thesis is dedicated to the study of the Josephson junctions made of a chiral spin-triplet superconductor and a ferromagnetic barrier. More precisely, we analyse the existence of 0-π state transitions in two- and three-dimensional junctions with respect to the strength and the orientation of the magnetization. Finally, we study the proximity effects at the interface of helical spin-triplet superconductors. They differ from the chiral

New Gauss-Bonnet Black Holes with Curvature-Induced Scalarization in Extended Scalar-Tensor Theories.

Science.gov (United States)

Doneva, Daniela D; Yazadjiev, Stoytcho S

2018-03-30

In the present Letter, we consider a class of extended scalar-tensor-Gauss-Bonnet (ESTGB) theories for which the scalar degree of freedom is excited only in the extreme curvature regime. We show that in the mentioned class of ESTGB theories there exist new black-hole solutions that are formed by spontaneous scalarization of the Schwarzschild black holes in the extreme curvature regime. In this regime, below certain mass, the Schwarzschild solution becomes unstable and a new branch of solutions with a nontrivial scalar field bifurcates from the Schwarzschild one. As a matter of fact, more than one branch with a nontrivial scalar field can bifurcate at different masses, but only the first one is supposed to be stable. This effect is quite similar to the spontaneous scalarization of neutron stars. In contrast to the standard spontaneous scalarization of neutron stars, which is induced by the presence of matter, in our case, the scalarization is induced by the curvature of the spacetime.

Stable micron-scale holes are a general feature of canonical holins.

Science.gov (United States)

Savva, Christos G; Dewey, Jill S; Moussa, Samir H; To, Kam H; Holzenburg, Andreas; Young, Ry

2014-01-01

At a programmed time in phage infection cycles, canonical holins suddenly trigger to cause lethal damage to the cytoplasmic membrane, resulting in the cessation of respiration and the non-specific release of pre-folded, fully active endolysins to the periplasm. For the paradigm holin S105 of lambda, triggering is correlated with the formation of micron-scale membrane holes, visible as interruptions in the bilayer in cryo-electron microscopic images and tomographic reconstructions. Here we report that the size distribution of the holes is stable for long periods after triggering. Moreover, early triggering caused by an early lysis allele of S105 formed approximately the same number of holes, but the lesions were significantly smaller. In contrast, early triggering prematurely induced by energy poisons resulted in many fewer visible holes, consistent with previous sizing studies. Importantly, the unrelated canonical holins P2 Y and T4 T were found to cause the formation of holes of approximately the same size and number as for lambda. In contrast, no such lesions were visible after triggering of the pinholin S(21) 68. These results generalize the hole formation phenomenon for canonical holins. A model is presented suggesting the unprecedentedly large size of these holes is related to the timing mechanism. © 2013 John Wiley & Sons Ltd.

Superluminescence from an optically pumped molecular tunneling junction by injection of plasmon induced hot electrons

Directory of Open Access Journals (Sweden)

Kai Braun

2015-05-01

Full Text Available Here, we demonstrate a bias-driven superluminescent point light-source based on an optically pumped molecular junction (gold substrate/self-assembled molecular monolayer/gold tip of a scanning tunneling microscope, operating at ambient conditions and providing almost three orders of magnitude higher electron-to-photon conversion efficiency than electroluminescence induced by inelastic tunneling without optical pumping. A positive, steadily increasing bias voltage induces a step-like rise of the Stokes shifted optical signal emitted from the junction. This emission is strongly attenuated by reversing the applied bias voltage. At high bias voltage, the emission intensity depends non-linearly on the optical pump power. The enhanced emission can be modelled by rate equations taking into account hole injection from the tip (anode into the highest occupied orbital of the closest substrate-bound molecule (lower level and radiative recombination with an electron from above the Fermi level (upper level, hence feeding photons back by stimulated emission resonant with the gap mode. The system reflects many essential features of a superluminescent light emitting diode.

Surgical treatment and optical coherence tomographic evaluation for accidental laser-induced full-thickness macular holes.

Science.gov (United States)

Qi, Y; Wang, Y; You, Q; Tsai, F; Liu, W

2017-07-01

PurposeTo report OCT appearance and surgical outcomes of full-thickness macular holes (MHs) accidentally caused by laser devices.Patients and methodsThis retrospective case series included 11 eyes of 11 patients with laser-induced MHs treated by pars plana vitrectomy, internal limiting membrane (ILM) peeling, and gas or silicone oil tamponade. Evaluations included a full ophthalmic examination, macular spectral-domain optical coherence tomography (SD-OCT), and fundus photography. Main outcome measures is MH closure and final visual acuity; the secondary outcome was the changes of retinal pigment epithelium and photoreceptor layer evaluated by sequential post-operative SD-OCT images.ResultsFive patients were accidentally injured by a yttrium aluminum garnet (YAG) laser and six patients by handheld laser. MH diameters ranged from 272 to 815 μm (mean, 505.5±163.0 μm) preoperatively. Best-corrected visual acuity (BCVA) improved from a mean of 0.90 logMAR (range, counting finger-8/20) preoperatively to a mean of 0.34 logMAR (range, a counting finger-20/20) postoperatively (P=0.001, t=4.521). Seven of 11 patients (63.6%) achieved a BCVA better than 10/20. Ten patients had a subfoveal hyperreflectivity and four patients had a focal choroidal depression subfoveal preoperatively. At the last follow-up, all 11 eyes demonstrated the following: closure of the macular hole, variable degrees of disruption of external limiting membrane (ELM) and outer photoreceptor ellipsoid and interdigitation bands. In 10 eyes, the disruption was in the form of focal defects in the outer retina. After surgery, the subfoveal hyperreflectivity and focal choroidal depression remained.ConclusionAccidental laser-induced full-thickness macular holes can be successfully closed with surgery. Inadvertent retinal injury from laser devices, especially handheld laser injury has occurred with increasing frequency in recent years. However, there is a paucity of data regarding these types of injuries

Origin of Hund's multiplicity rule in quasi-two-dimensional two-electron quantum dots

International Nuclear Information System (INIS)

Sako, Tokuei; Paldus, Josef; Diercksen, Geerd H. F.

2010-01-01

The origin of Hund's multiplicity rules has been studied for a system of two electrons confined by a quasi-two-dimensional harmonic-oscillator potential by relying on a full configuration interaction wave function and Cartesian anisotropic Gaussian basis sets. In terms of appropriate normal-mode coordinates the wave function factors into a product of the center-of-mass and the internal components. The 1 Π u singlet state and the 3 Π u triplet state represent the energetically lowest pair of states to which Hund's multiplicity rule applies. They are shown to involve excitations into different degrees of freedom, namely, into the center-of-mass angular mode and the internal angular mode for the singlet and triplet states, respectively. The presence of an angular nodal line in the internal space allows then the triplet state to avoid the singularity in the electron-electron interaction potential, leading to the energy lowering of the triplet state relative to its counterpart singlet state.

Photochemical reactions of triplet benzophenone and anthraquinone molecules with amines in the gas phase

International Nuclear Information System (INIS)

Zalesskaya, G.A.; Sambor, E.G.; Belyi, N.N.

2004-01-01

The intermolecular photoinduced reactions between triplet ketone molecules and aliphatic amines and pyridine are studied by the quenching of delayed fluorescence of anthraquinone and benzophenone vapors by diethylamine, dibutylamine, cyclohexylamine, triethylamine, and pyridine. In the temperature range 423-573 K, the delayed fluorescence quenching rate constants k q are estimated from changes in the decay rate constant and the intensity of delayed fluorescence upon increasing pressure of bath gases. It is ascertained that, in the gas phase, the mixtures under study exhibit both a negative and a positive dependence of k q on temperature, which indicates that some photoinduced reactions do not have activation barriers. The rate constant k q is shown to increase with decreasing ionization potential of the electron donors. This points to the importance of interactions with charge transfer in the photoreaction of triplet ketone molecules with aliphatic amines and pyridine in the gas phase. The relationship between k q and the change in the free energy ΔG upon the photoinduced intermolecular electron transfer, which is the primary stage of the photochemical reaction, is studied. It is shown that the dependence k q (ΔG) for the donor-acceptor pairs under study is described well by the Marcus equation, in which the average vibrational energies of the donor and acceptor are taken into account for the estimate of ΔG

Direct determination of triplet phases and enantiomorphs of non-centrosymmetric structures. Pt. 2

International Nuclear Information System (INIS)

Huemmer, K.; Weckert, E.; Bondza, H.

1989-01-01

Direct measurements of triplet phase relationships for non-centrosymmetric light-atom organic structures with medium-size unit cells are reported. The phase information can be extracted from the three-beam profiles of a Renninger ψ-scan experiment. The measurements were carried out with a special ψ-circle diffractometer installed on a rotating Cu-anode generator. The incident-beam divergence is reduced to 0.02 0 . The experimental results confirm the theoretical considerations of paper I of this work. As triplet phases of ±90 0 can be distinguished, the absolute structure can be determined unambiguously. The measurements show that the triplet-phase-dependent interference effects may be superposed on phase-independent Umweganregung or Aufhellung effects. By a comparison of the ψ-scan profiles of two centrosymmetrically related three-beam cases, the triplet phases of which have opposite signs, it is possible to evaluate the phase-independent effects and to determine the value of the triplet phase with an accuracy of at least 90 0 . (orig.)

Reduction of charge trapping and electron tunneling in SIMOX by supplemental implantation of oxygen

International Nuclear Information System (INIS)

Stahlbush, R.E.; Hughes, H.L.; Krull, W.A.

1993-01-01

Silicon-on-insulator, SOI, technologies are being aggressively pursued to produce high density, high speed, radiation tolerant electronics. The dielectric isolation of the buried oxide makes it possible to design integrated circuits that greatly minimize single event upset and eliminate dose-rate induced latchup and upset. The reduction of excess-silicon related defects in SIMOX by the supplemental implantation of oxygen has been examined. The supplemental implant is 6% of the oxygen dose used to form the buried oxide, and is followed by a 1,000 C anneal, in contrast to the >1,300 C anneal used to form the buried oxide layer of SIMOX. The defects examined include shallow electron traps, deep hole traps, and silicon clusters. The radiation-induced shallow electron and deep hole trapping are measured by cryogenic detrapping and isothermal annealing techniques. The low-field (3 to 6 MV/cm) electron tunneling is interpreted as due to a two phase mixture of stoichiometric SiO 2 and Si clusters a few nm in size. Single and triple SIMOS samples have been examined. All of the defects are reduced by the supplemental oxygen processing. Shallow electron trapping is reduced by an order of magnitude. Because of the larger capture cross section for hole trapping, hole trapping is not reduced as much. The low-field electron tunneling due to Si clusters is also significantly reduced. Both uniform and nonuniform electron tunneling have been observed in SIMOX samples without supplement processing. In samples exhibiting only uniform tunneling, electron capture at holes has been observed. The nonuniform tunneling is superimposed upon the uniform tunneling and is characterized by current spiking

Energy relaxation and separation of a hot electron-hole pair in organic aggregates from a time-dependent wavepacket diffusion method

International Nuclear Information System (INIS)

Han, Lu; Liang, WanZhen; Zhao, Yi; Zhong, Xinxin

2014-01-01

The time-dependent wavepacket diffusive method [X. Zhong and Y. Zhao, J. Chem. Phys. 138, 014111 (2013)] is extended to investigate the energy relaxation and separation of a hot electron-hole pair in organic aggregates with incorporation of Coulomb interaction and electron-phonon coupling. The pair initial condition generated by laser pulse is represented by a Gaussian wavepacket with a central momentum. The results reveal that the hot electron energy relaxation is very well described by two rate processes with the fast rate much larger than the slow one, consistent with experimental observations, and an efficient electron-hole separation is accomplished accompanying the fast energy relaxation. Furthermore, although the extra energy indeed helps the separation by overcoming the Coulomb interaction, the width of initial wavepacket is much sensitive to the separation efficiency and the narrower wavepacket generates the more separated charges. This behavior may be useful to understand the experimental controversy of the hot carrier effect on charge separation

Reconstructing neutrino properties from collider experiments in a Higgs triplet neutrino mass model

International Nuclear Information System (INIS)

Aristizabal Sierra, D.; Hirsch, M.; Valle, J. W. F.; Villanova del Moral, A.

2003-01-01

We extend the minimal supersymmetric standard model with bilinear R-parity violation to include a pair of Higgs triplet superfields. The neutral components of the Higgs triplets develop small vacuum expectation values (VEVs) quadratic in the bilinear R-parity breaking parameters. In this scheme the atmospheric neutrino mass scale arises from bilinear R-parity breaking while for reasonable values of parameters the solar neutrino mass scale is generated from the small Higgs triplet VEVs. We calculate neutrino masses and mixing angles in this model and show how the model can be tested at future colliders. The branching ratios of the doubly charged triplet decays are related to the solar neutrino angle via a simple formula

Hot phonon generation by split-off hole band electrons in AlxGa1-xAs alloys investigated by picosecond Raman scattering

International Nuclear Information System (INIS)

Jacob, J.M.; Kim, D.S.; Zhou, J.F.; Song, J.J.

1992-01-01

The initial generation of hot LO phonons by the relaxation of hot carriers in GaAs and Al x Ga 1-x As alloy semiconductors is studied. Within the initial 2ps of photoexcitation, only those electrons originating from the split-off hole bands are found to generate a significant number of I-valley hot phonons when photon energies of 2.33eV are used. A picosecond Raman scattering technique is used to determine the hot phonon occupation number in a series of MBE grown Al x Ga 1-x As samples with 0≤x≤0.39. The Stokes and anti-Stokes lines were measured for both GaAs-like and AlAs-like LO phonon modes to determine their occupation numbers. The authors observe a rapid decrease in the phonon occupation numbers as the aluminum concentration increases beyond x = 0.2. This rapid decrease is explained by considering only those electrons photoexcited from the split-off hole band. Almost all of the electrons originating from the heavy and light-hole bands are shown to quickly transfer and remain in the X and L valleys without generating significant numbers of hot LO phonons during the initial 2ps and at a carrier density of 10 17 cm -3 . A model based upon the instantaneous thermalization of hot electrons photoexcited from the split-off hole bands is used to fit the data. They have obtained very good agreement between experiment and theory. This work provides a clear understanding to the relaxation of Γ valley hot electrons by the generation of hot phonons on subpicosecond and picosecond time scales, which has long standing implications to previous time resolved Raman experiments