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Sample records for nonequilibrium charge carriers

  1. Nonequilibrium population of charge carriers in structures with InGaN deep quantum dots

    SciTech Connect

    Sizov, D. S. Zavarin, E. E.; Ledentsov, N. N.; Lundin, V. V.; Musikhin, Yu. G.; Sizov, V. S.; Suris, R. A.; Tsatsul'nikov, A. F.

    2007-05-15

    Electronic and optical properties of ensembles of quantum dots with various energies of activation from the ground-state level to the continuous-spectrum region were studied theoretically and experimentally with the InGaN quantum dots as an example. It is shown that, depending on the activation energy, both the quasi-equilibrium statistic of charge carriers at the levels of quantum dots and nonequilibrium statistic at room temperature are possible. In the latter case, the position of the maximum in the emission spectrum is governed by the value of the demarcation transition: the quantum dots with the transition energy higher than this value feature the quasi-equilibrium population of charge carriers, while the quantum dots with the transition energy lower than the demarcation-transition energy feature the nonequilibrium population. A model based on kinetic equations was used in the theoretical analysis. The key parameters determining the statistic are the parameters of thermal ejection of charge carriers; these parameters depend exponentially on the activation energy. It is shown experimentally that the use of stimulated phase decomposition makes it possible to appreciably increase the activation energy. In this case, the thermal-activation time is found to be much longer than the recombination time for an electron-hole pair, which suppresses the redistribution of charge carriers between the quantum dots and gives rise to the nonequilibrium population. The effect of nonequilibrium population on the luminescent properties of the structures with quantum dots is studied in detail.

  2. Effect of annealing on the nonequilibrium carrier lifetime in GaAs grown at low temperatures

    SciTech Connect

    Pastor, A. A.; Prokhorova, U. V.; Serdobintsev, P. Yu.; Chaldyshev, V. V. Yagovkina, M. A.

    2013-08-15

    GaAs samples grown by molecular-beam epitaxy at low (230 Degree-Sign C) temperatures are investigated. One of the samples is subjected to aftergrowth annealing at 600 Degree-Sign C. Using an unconventional pump-probe scheme for measuring the dynamic variation in the light refractive index, the nonequilibrium charge-carrier lifetime (275 {+-} 30 fs before annealing) is determined. Such a short carrier lifetime in the unannealed material is due to the high concentration of point defects, mainly As{sub Ga} antisite defects. According to X-ray diffraction and steady-state optical absorption data, the As{sub Ga} concentration in the samples is 3 Multiplication-Sign 10{sup 19} cm{sup -3}, which corresponds to an arsenic excess of 0.26 at %. Upon annealing at 600 Degree-Sign C, the superstoichiometric As defects self-organize and form As nanoinclusions in the GaAs crystal matrix. It is shown that in this case the nonequilibrium charge-carrier lifetime increases to 452 {+-} 5 fs. This lifetime is apparently ensured by the capture of non-equilibrium charge carriers at metal As nanoinclusions.

  3. Non-equilibrium hot carrier dynamics in plasmonic nanostructures

    NASA Astrophysics Data System (ADS)

    Narang, Prineha; Sundararaman, Ravishankar; Jermyn, Adam; Cortes, Emiliano; Maier, Stefan A.; Goddard, William A., III

    Decay of surface plasmons to hot carriers is a new direction that has attracted considerable fundamental and application interest, yet a fundamental understanding of ultrafast plasmon decay processes and the underlying microscopic mechanisms remain incomplete. Ultrafast experiments provide insights into the relaxation of non-equilibrium carriers at the tens and hundreds of femtoseconds time scales, but do not yet directly probe shorter times with nanometer spatial resolution. Here we report the first ab initio calculations of non equilibrium transport of plasmonic hot carriers in metals and experimental observation of the injection of these carriers into molecules tethered to the metal surface. Specifically, metallic nanoantennas functionalized with a molecular monolayer allow for the direct probing of electron injection via surface enhanced Raman spectroscopy of the original and reduced molecular species. We combine first principles calculations of electron-electron and electron-phonon scattering rates with Boltzmann transport simulations to predict the ultrafast dynamics and transport of carriers in real materials. We also predict and compare the evolution of electron distributions in ultrafast experiments on noble metal nanoparticles.

  4. Nonequilibrium spin polarization induced charge Hall effect

    NASA Astrophysics Data System (ADS)

    Hou, Dazhi; Qiu, Z.; Iguchi, R.; Sato, K.; Uchida, K.; Bauer, G. W.; Saitoh, Eiji

    2015-03-01

    The nonequilibrium spin polarization lies at the heart of information processing in spin-based devices. The generation and manipulation of the spin polarization have been realized by various approaches, however, the spin polarization is usually considered to have negligible effect on the electric transport property, especially for systems of high electron concentration like metals (ɛF ~ eV). Here we show that the nonequilibrium spin polarization can cause a novel Hall voltage in a conventional metallic alloy at room temperature, which is due to a new mechanism and closely related to the spin Nernst effect.

  5. Calculations of heavy ion charge state distributions for nonequilibrium conditions

    NASA Technical Reports Server (NTRS)

    Luhn, A.; Hovestadt, D.

    1985-01-01

    Numerical calculations of the charge state distributions of test ions in a hot plasma under nonequilibrium conditions are presented. The mean ionic charges of heavy ions for finite residence times in an instantaneously heated plasma and for a non-Maxwellian electron distribution function are derived. The results are compared with measurements of the charge states of solar energetic particles, and it is found that neither of the two simple cases considered can explain the observations.

  6. Tunneling Measurements of Charge Imbalance of Non-Equilibrium Superconductors

    NASA Astrophysics Data System (ADS)

    Yagi, R.; Utsunomiya, K.; Tsuboi, K.; Kubota, T.; Terao, Y.; Ikebuchi, Y.

    2008-10-01

    We have observed excess current due to charge imbalance in the voltage-current characteristics of a superconductor-insulator-normal (SIN) tunnel junction connected to a non-equilibrium superconductor. It was found that that the excess current was unchanged against the bias voltage as expected from the theory of charge imbalance. The estimated excess current approximately agreed with the estimation from one-dimensional diffusion model of charge imbalance transport.

  7. Preface: Special issue featuring papers from the International Conference on Nonequilibrium Carrier Dynamics in Semiconductors

    NASA Astrophysics Data System (ADS)

    Reggiani, L.; Bordone, P.; Brunetti, R.

    2004-02-01

    The International Conference on Nonequilibrium Carrier Dynamics in Semiconductors (HCIS-13) celebrates 30 years since it first took place in Modena. Nonequilibrium dynamics of charge carriers, pioneered by the hot-electron concept, is an important issue for understanding electro-optic transport properties in semiconductor materials and structures. In these 30 years several topics have matured, and new ones have emerged thus fertilizing the field with a variety of physical problems and new ideas. The history of the conference is summarized in the opening paper `30 years of HCIS'. The future of the conference seems secure considering the continued lively interest of the participants. The conference addressed eleven major topics which constitute the backbone of the proceedings and are summarized as follows: carrier transport in low dimensional and nanostructure systems, nonequilibrium carriers in superlattices and devices, small devices and related phenomena, carrier dynamics and fluctuations, carrier quantum dynamics, coherent/incoherent carrier dynamics of optical excitations and ultra-fast optical phenomena, nonlinear optical effects, transport in organic matter, semiconductor-based spintronics, coherent dynamics in solid state systems for quantum processing and communication, novel materials and devices. Nanometric space scale and femtosecond time scale represent the ultimate domains of theoretical, experimental and practical interest. Traditional fields such as bulk properties, quantum transport, fluctuations and chaotic phenomena, etc, have received thorough and continuous attention. Emerging fields from previous conferences, such as quantum processing and communication, have been better assessed. New fields, such as spintronics and electron transport in organic matter, have appeared for the first time. One plenary talk, 11 invited talks, 230 submitted abstracts covering all these topics constituted a single-session conference. Following scientific selection

  8. Charge carrier thermalization in organic diodes

    PubMed Central

    van der Kaap, N. J.; Koster, L. J. A.

    2016-01-01

    Charge carrier mobilities of organic semiconductors are often characterized using steady-state measurements of space charge limited diodes. These measurements assume that charge carriers are in a steady-state equilibrium. In reality, however, energetically hot carriers are introduces by photo-excitation and injection into highly energetic sites from the electrodes. These carriers perturb the equilibrium density of occupied states, and therefore change the overall charge transport properties. In this paper, we look into the effect of energetically hot carriers on the charge transport in organic semiconductors using steady state kinetic Monte Carlo simulations. For injected hot carriers in a typical organic semiconductor, rapid energetic relaxation occurs in the order of tens of nanoseconds, which is much faster than the typical transit time of a charge carrier throught the device. Furthermore, we investigate the impact of photo-generated carriers on the steady-state mobility. For a typical organic voltaic material, an increase in mobility of a factor of 1.1 is found. Therefore, we conclude that the impact of energetically hot carriers on normal device operation is limited. PMID:26791095

  9. Ultrafast Lateral Photo-Dember Effect in Graphene Induced by Nonequilibrium Hot Carrier Dynamics.

    PubMed

    Liu, Chang-Hua; Chang, You-Chia; Lee, Seunghyun; Zhang, Yaozhong; Zhang, Yafei; Norris, Theodore B; Zhong, Zhaohui

    2015-06-10

    The photo-Dember effect arises from the asymmetric diffusivity of photoexcited electrons and holes, which creates a transient spatial charge distribution and hence the buildup of a voltage. Conventionally, a strong photo-Dember effect is only observed in semiconductors with a large asymmetry between the electron and hole mobilities, such as in GaAs or InAs, and is considered negligible in graphene due to its electron-hole symmetry. Here, we report the observation of a strong lateral photo-Dember effect induced by nonequilibrium hot carrier dynamics when exciting a graphene-metal interface with a femtosecond laser. Scanning photocurrent measurements reveal the extraction of photoexcited hot carriers is driven by the transient photo-Dember field, and the polarity of the photocurrent is determined by the device's mobility asymmetry. Furthermore, ultrafast pump-probe measurements indicate the magnitude of photocurrent is related to the hot carrier cooling rate. Our simulations also suggest that the lateral photo-Dember effect originates from graphene's 2D nature combined with its unique electrical and optical properties. Taken together, these results not only reveal a new ultrafast photocurrent generation mechanism in graphene but also suggest new types of terahertz sources based on 2D nanomaterials.

  10. Theoretical description of nonequilibrium behavior in charge density wave systems

    NASA Astrophysics Data System (ADS)

    Shen, Wen

    The fast development of time resolved photoemission (TRPES) techniques allow us to discover the rich features of nonequilibrium phenomena which may not appear in equilibrium. One of the most explored topics is the nonequilibrium behavior of a charge density wave (CDW) material. Being an ordered phase at low temperature, the CDW state provides a fertile ground to study electron-electron and electron-ion interactions. By driving this material out of equilibrium and taking ultrafast time resolution snapshots of its behavior, TRPES helps us understand these interactions and sheds light on the mechanisms behind these and other complex material properties, such as metal-insulator transitions, high temperature superconductivity, and magnetic phenomena. Recent experiments on TRPES in CDW materials show an ultrafast CDW gap closure in systems such as 1T--TaS2 and TbTe3 and the subsequent separation of time scales for the electron-electron interaction and the electron-lattice interaction. But it is still not clear what happens during the ultrashort period (in first 100 femtosecond). In this dissertation, we solve a two band model describing this ultrafast process in a CDW system. By fixing the lattice distortion effect in the CDW, we studied the nonequilibrium excitations of the electrons under a strong electric field. This research is performed by calculating nonequilibrium Green's functions (NGF) along the Kadanoff-Baym-Keldysh contour. We solved this nonequilibrium problem exactly. We show non-perturbative results and explore the nonlinear electronic behavior under an ultrashort light pulses. In addition to the TRPES problem, we also examined the behavior of Bloch oscillations under a large DC field, the response to an AC electric field, high harmonic generation from solids, and the crossover between frequency-driven excitation and amplitude-driven excitation.

  11. Effective Charge Carrier Utilization in Photocatalytic Conversions.

    PubMed

    Zhang, Peng; Wang, Tuo; Chang, Xiaoxia; Gong, Jinlong

    2016-05-17

    Continuous efforts have been devoted to searching for sustainable energy resources to alleviate the upcoming energy crises. Among various types of new energy resources, solar energy has been considered as one of the most promising choices, since it is clean, sustainable, and safe. Moreover, solar energy is the most abundant renewable energy, with a total power of 173 000 terawatts striking Earth continuously. Conversion of solar energy into chemical energy, which could potentially provide continuous and flexible energy supplies, has been investigated extensively. However, the conversion efficiency is still relatively low since complicated physical, electrical, and chemical processes are involved. Therefore, carefully designed photocatalysts with a wide absorption range of solar illumination, a high conductivity for charge carriers, a small number of recombination centers, and fast surface reaction kinetics are required to achieve a high activity. This Account describes our recent efforts to enhance the utilization of charge carriers for semiconductor photocatalysts toward efficient solar-to-chemical energy conversion. During photocatalytic reactions, photogenerated electrons and holes are involved in complex processes to convert solar energy into chemical energy. The initial step is the generation of charge carriers in semiconductor photocatalysts, which could be enhanced by extending the light absorption range. Integration of plasmonic materials and introduction of self-dopants have been proved to be effective methods to improve the light absorption ability of photocatalysts to produce larger amounts of photogenerated charge carriers. Subsequently, the photogenerated electrons and holes migrate to the surface. Therefore, acceleration of the transport process can result in enhanced solar energy conversion efficiency. Different strategies such as morphology control and conductivity improvement have been demonstrated to achieve this goal. Fine-tuning of the

  12. Effective Charge Carrier Utilization in Photocatalytic Conversions.

    PubMed

    Zhang, Peng; Wang, Tuo; Chang, Xiaoxia; Gong, Jinlong

    2016-05-17

    Continuous efforts have been devoted to searching for sustainable energy resources to alleviate the upcoming energy crises. Among various types of new energy resources, solar energy has been considered as one of the most promising choices, since it is clean, sustainable, and safe. Moreover, solar energy is the most abundant renewable energy, with a total power of 173 000 terawatts striking Earth continuously. Conversion of solar energy into chemical energy, which could potentially provide continuous and flexible energy supplies, has been investigated extensively. However, the conversion efficiency is still relatively low since complicated physical, electrical, and chemical processes are involved. Therefore, carefully designed photocatalysts with a wide absorption range of solar illumination, a high conductivity for charge carriers, a small number of recombination centers, and fast surface reaction kinetics are required to achieve a high activity. This Account describes our recent efforts to enhance the utilization of charge carriers for semiconductor photocatalysts toward efficient solar-to-chemical energy conversion. During photocatalytic reactions, photogenerated electrons and holes are involved in complex processes to convert solar energy into chemical energy. The initial step is the generation of charge carriers in semiconductor photocatalysts, which could be enhanced by extending the light absorption range. Integration of plasmonic materials and introduction of self-dopants have been proved to be effective methods to improve the light absorption ability of photocatalysts to produce larger amounts of photogenerated charge carriers. Subsequently, the photogenerated electrons and holes migrate to the surface. Therefore, acceleration of the transport process can result in enhanced solar energy conversion efficiency. Different strategies such as morphology control and conductivity improvement have been demonstrated to achieve this goal. Fine-tuning of the

  13. Nonequilibrium carrier dynamics in transition metal dichalcogenide semiconductors

    NASA Astrophysics Data System (ADS)

    Steinhoff, A.; Florian, M.; Rösner, M.; Lorke, M.; Wehling, T. O.; Gies, C.; Jahnke, F.

    2016-09-01

    When exploring new materials for their potential in (opto)electronic device applications, it is important to understand the role of various carrier interaction and scattering processes. In atomically thin transition metal dichalcogenide semiconductors, the Coulomb interaction is known to be much stronger than in quantum wells of conventional semiconductors like GaAs, as witnessed by the 50 times larger exciton binding energy. The question arises, whether this directly translates into equivalently faster carrier-carrier Coulomb scattering of excited carriers. Here we show that a combination of ab initio band-structure and many-body theory predicts Coulomb-mediated carrier relaxation on a sub-100 fs time scale for a wide range of excitation densities, which is less than an order of magnitude faster than in quantum wells.

  14. Nonequilibrium carrier dynamics in transition metal dichalcogenide semiconductors

    NASA Astrophysics Data System (ADS)

    Steinhoff, A.; Florian, M.; Rösner, M.; Lorke, M.; Wehling, T. O.; Gies, C.; Jahnke, F.

    2016-09-01

    When exploring new materials for their potential in (opto)electronic device applications, it is important to understand the role of various carrier interaction and scattering processes. In atomically thin transition metal dichalcogenide semiconductors, the Coulomb interaction is known to be much stronger than in quantum wells of conventional semiconductors like GaAs, as witnessed by the 50 times larger exciton binding energy. The question arises, whether this directly translates into equivalently faster carrier–carrier Coulomb scattering of excited carriers. Here we show that a combination of ab initio band-structure and many-body theory predicts Coulomb-mediated carrier relaxation on a sub-100 fs time scale for a wide range of excitation densities, which is less than an order of magnitude faster than in quantum wells.

  15. Solid state cloaking for electrical charge carrier mobility control

    DOEpatents

    Zebarjadi, Mona; Liao, Bolin; Esfarjani, Keivan; Chen, Gang

    2015-07-07

    An electrical mobility-controlled material includes a solid state host material having a controllable Fermi energy level and electrical charge carriers with a charge carrier mobility. At least one Fermi level energy at which a peak in charge carrier mobility is to occur is prespecified for the host material. A plurality of particles are distributed in the host material, with at least one particle disposed with an effective mass and a radius that minimize scattering of the electrical charge carriers for the at least one prespecified Fermi level energy of peak charge carrier mobility. The minimized scattering of electrical charge carriers produces the peak charge carrier mobility only at the at least one prespecified Fermi level energy, set by the particle effective mass and radius, the charge carrier mobility being less than the peak charge carrier mobility at Fermi level energies other than the at least one prespecified Fermi level energy.

  16. Mobility of charge carriers in disordered dielectrics

    NASA Astrophysics Data System (ADS)

    Tiotnev, A. P.; Boev, S. G.; Sadovnichii, D. N.

    1994-07-01

    We compare experimental data on the mobility of holes (the majority charge carriers) in polyepoxy-propylcarbazole, measured using the time-of-flight technique (drift mobility) and the nonsteady-state radiation-induced electrical conductivity method (effective mobility). We show that these two quantities are quite different in the dispersive transport regime; and while the second quantity is a characteristic of the material, the first quantity depends in a complicated fashion on the ratio of the electric field strength to the sample thickness. The “untreated” data on drift mobility measurements using the time-of-flight technique do not have direct physical meaning and cannot be compared with the conclusions of modern microscopic theories of the mobility of charge carriers in disordered matrices.

  17. Localized charge carriers in graphene nanodevices

    SciTech Connect

    Bischoff, D. Varlet, A.; Simonet, P.; Eich, M.; Overweg, H. C.; Ihn, T.; Ensslin, K.

    2015-09-15

    Graphene—two-dimensional carbon—is a material with unique mechanical, optical, chemical, and electronic properties. Its use in a wide range of applications was therefore suggested. From an electronic point of view, nanostructured graphene is of great interest due to the potential opening of a band gap, applications in quantum devices, and investigations of physical phenomena. Narrow graphene stripes called “nanoribbons” show clearly different electronical transport properties than micron-sized graphene devices. The conductivity is generally reduced and around the charge neutrality point, the conductance is nearly completely suppressed. While various mechanisms can lead to this observed suppression of conductance, disordered edges resulting in localized charge carriers are likely the main cause in a large number of experiments. Localized charge carriers manifest themselves in transport experiments by the appearance of Coulomb blockade diamonds. This review focuses on the mechanisms responsible for this charge localization, on interpreting the transport details, and on discussing the consequences for physics and applications. Effects such as multiple coupled sites of localized charge, cotunneling processes, and excited states are discussed. Also, different geometries of quantum devices are compared. Finally, an outlook is provided, where open questions are addressed.

  18. Localized charge carriers in graphene nanodevices

    NASA Astrophysics Data System (ADS)

    Bischoff, D.; Varlet, A.; Simonet, P.; Eich, M.; Overweg, H. C.; Ihn, T.; Ensslin, K.

    2015-09-01

    Graphene—two-dimensional carbon—is a material with unique mechanical, optical, chemical, and electronic properties. Its use in a wide range of applications was therefore suggested. From an electronic point of view, nanostructured graphene is of great interest due to the potential opening of a band gap, applications in quantum devices, and investigations of physical phenomena. Narrow graphene stripes called "nanoribbons" show clearly different electronical transport properties than micron-sized graphene devices. The conductivity is generally reduced and around the charge neutrality point, the conductance is nearly completely suppressed. While various mechanisms can lead to this observed suppression of conductance, disordered edges resulting in localized charge carriers are likely the main cause in a large number of experiments. Localized charge carriers manifest themselves in transport experiments by the appearance of Coulomb blockade diamonds. This review focuses on the mechanisms responsible for this charge localization, on interpreting the transport details, and on discussing the consequences for physics and applications. Effects such as multiple coupled sites of localized charge, cotunneling processes, and excited states are discussed. Also, different geometries of quantum devices are compared. Finally, an outlook is provided, where open questions are addressed.

  19. Nonequilibrium carrier dynamics in ultrathin Si-on-glass films

    NASA Astrophysics Data System (ADS)

    Serafini, J.; Akbas, Y.; Crandall, L.; Bellman, R.; Kosik Williams, C.; Sobolewski, Roman

    2015-10-01

    We present a femtosecond pump-probe spectroscopy approach for characterization of amorphous and microcrystalline silicon films grown on glass substrates. Such films are presently being considered as absorbers in tandem-type, Si-based photovoltaic cells. Our experiments consisted of time-resolved, two-colour femtosecond optical measurements, performed in the transmission mode in a wide range of delay times. Depending on the sample growth process, collected normalized transmissivity change (ΔT/T) waveforms exhibited a bi-exponential relaxation dynamics with the characteristic times varying from picoseconds to nanoseconds. Experimental data were interpreted using a three-rate-equation models, and the relaxation was identified as, depending on the Si film type, being dominated by either carrier trapping or electron-phonon cooling and followed by electron-hole recombination. An excellent fit between the model and the ΔT/T transients was obtained and a correlation between the Si film growth process, its hydrogen content, and the associated trap concentration was demonstrated.

  20. Dynamics of the phase transitions in the system of nonequilibrium charge carriers in quantum-dimensional Si{sub 1−x}Ge{sub x}/Si structures

    SciTech Connect

    Bagaev, V. S.; Krivobok, V. S. Nikolaev, S. N.; Onishchenko, E. E.; Pruchkina, A. A.; Aminev, D. F.; Skorikov, M. L.; Lobanov, D. N.; Novikov, A. V.

    2013-11-15

    The dynamics of the phase transition from an electron-hole plasma to an exciton gas is studied during pulsed excitation of heterostructures with Si{sub 1−x}Ge{sub x}/Si quantum wells. The scenario of the phase transition is shown to depend radically on the germanium content in the Si{sub 1−x}Ge{sub x} layer. The electron-hole system decomposes into a rarefied exciton and a dense plasma phases for quantum wells with a germanium content x = 3.5% in the time range 100–500 ns after an excitation pulse. In this case, the electron-hole plasma existing in quantum wells has all signs of an electron-hole liquid. A qualitatively different picture of the phase transition is observed for quantum wells with x = 9.5%, where no separation into phases with different electronic spectra is detected. The carrier recombination in the electron-hole plasma leads a gradual weakening of screening and the appearance of exciton states. For a germanium content of 5–7%, the scenario of the phase transition is complex: 20–250 ns after an excitation pulse, the properties of the electron-hole system are described in terms of a homogeneous electron-hole plasma, whereas its separation into an electron-hole liquid and an exciton gas is detected after 350 ns. It is shown that, for the electron-hole liquid to exist in quantum wells with x = 5–7% Ge, the exciton gas should have a substantially higher density than in quantum wells with x = 3.5% Ge. This finding agrees with a decrease in the depth of the local minimum of the electron-hole plasma energy with increasing germanium concentration in the SiGe layer. An increase in the density of the exciton gas coexisting with the electron-hole liquid is shown to enhance the role of multiparticle states, which are likely to be represented by trions T{sup +} and biexcitons, in the exciton gas.

  1. Charge carrier trapping at passivated silicon surfaces

    NASA Astrophysics Data System (ADS)

    Seiffe, Johannes; Hofmann, Marc; Rentsch, Jochen; Preu, Ralf

    2011-03-01

    Surface passivation has become an essential factor for translating high-efficiency crystalline silicon solar cell concepts into industrial production schemes. In photovoltaics, a widespread method to determine the surface recombination is to measure the effective charge carrier lifetime from the photoconductance of symmetrically passivated silicon wafers in transient or quasi-static mode. In this work, it is shown how the injection history at the surface influences the transient effective lifetime measurement for several passivation layers. This dependence leads to systematic differences between quasi-static and transient measurements. The influence can be explained by charge trapping in slow surface states at the surface passivation layer. A model including slow surface states is used in a fit procedure to evaluate the capture cross sections of these traps. The observed effect is well-pronounced for silicon-rich passivation layers like a-Si:H, a-SiCx:H or silicon-rich a-SiOxNy:H. For PECVD-AlOx layers and for thermally grown SiO2 layers as well, however, the effective lifetime measurement could be influenced.

  2. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... period lines less revenues recovered through the End User Common Line charge established under § 69.152... charge revenues. (b) If an end-user customer does not have a presubscribed interexchange carrier, the local exchange carrier may collect the PICC directly from the end user. (c) (d) Local exchange...

  3. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... period lines less revenues recovered through the End User Common Line charge established under § 69.152... charge revenues. (b) If an end-user customer does not have a presubscribed interexchange carrier, the local exchange carrier may collect the PICC directly from the end user. (c) (d) Local exchange...

  4. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... period lines less revenues recovered through the End User Common Line charge established under § 69.152... charge revenues. (b) If an end-user customer does not have a presubscribed interexchange carrier, the local exchange carrier may collect the PICC directly from the end user. (c) (d) Local exchange...

  5. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... period lines less revenues recovered through the End User Common Line charge established under § 69.152... charge revenues. (b) If an end-user customer does not have a presubscribed interexchange carrier, the local exchange carrier may collect the PICC directly from the end user. (c) (d) Local exchange...

  6. Charge carrier mobility in hybrid halide perovskites

    PubMed Central

    Motta, Carlo; El-Mellouhi, Fedwa; Sanvito, Stefano

    2015-01-01

    The charge transport properties of hybrid halide perovskites are investigated with a combination of density functional theory including van der Waals interaction and the Boltzmann theory for diffusive transport in the relaxation time approximation. We find the mobility of electrons to be in the range 5–10 cm2V−1s−1 and that for holes within 1–5 cm2V−1s−1, where the variations depend on the crystal structure investigated and the level of doping. Such results, in good agreement with recent experiments, set the relaxation time to about 1 ps, which is the time-scale for the molecular rotation at room temperature. For the room temperature tetragonal phase we explore two possible orientations of the organic cations and find that the mobility has a significant asymmetry depending on the direction of the current with respect to the molecular axis. This is due mostly to the way the PbI3 octahedral symmetry is broken. Interestingly we find that substituting I with Cl has minor effects on the mobilities. Our analysis suggests that the carrier mobility is probably not a key factor in determining the high solar-harvesting efficiency of this class of materials. PMID:26235910

  7. Anisotropic charged impurity-limited carrier mobility in monolayer phosphorene

    SciTech Connect

    Ong, Zhun-Yong; Zhang, Gang; Zhang, Yong Wei

    2014-12-07

    The room temperature carrier mobility in atomically thin 2D materials is usually far below the intrinsic limit imposed by phonon scattering as a result of scattering by remote charged impurities in its environment. We simulate the charged impurity-limited carrier mobility μ in bare and encapsulated monolayer phosphorene. We find a significant temperature dependence in the carrier mobilities (μ ∝ T{sup −γ}) that results from the temperature variability of the charge screening and varies with the crystal orientation. The anisotropy in the effective mass leads to an anisotropic carrier mobility, with the mobility in the armchair direction about one order of magnitude larger than in the zigzag direction. In particular, this mobility anisotropy is enhanced at low temperatures and high carrier densities. Under encapsulation with a high-κ overlayer, the mobility increases by up to an order of magnitude although its temperature dependence and its anisotropy are reduced.

  8. Image charge effects in the nonequilibrium Anderson-Holstein model

    NASA Astrophysics Data System (ADS)

    Perfetto, E.; Stefanucci, G.

    2013-12-01

    Image charge effects in nanoscale junctions with strong electron-phonon coupling open the way to unexplored physical scenarios. We propose a simple and still accurate many-body approach to deal with the simultaneous occurrence of the Franck-Condon blockade and the screening-induced enhancement of the polaron mobility. A transparent analytic expression for the polaron decay rate is derived and the dependence on the strength and range of the screening is highlighted. This allows us to interpret and explain several transient and steady-state features of the electrical current. Remarkably, we find that the competition between the charge blocking due to the electron-phonon interaction and the charge deblocking due to the image charges gives rise to a novel mechanism of negative differential conductance. An experimental setup to observe this phenomenon is discussed.

  9. Time-resolved, nonequilibrium carrier dynamics in Si-on-glass thin films for photovoltaic cells

    DOE PAGES

    Serafini, John; Akbas, Yunus; Crandall, Lucas; Bellman, Robert; Williams, Carlo Kosik; Sobolewski, Robert

    2016-03-02

    Here, a femtosecond pump–probe spectroscopy method was used to characterize the growth process and transport properties of amorphous silicon-on-glass, thin films, intended as absorbers for photovoltaic cells. We collected normalized transmissivity change (ΔT/T) waveforms and interpreted them using a comprehensive three-rate equation electron trapping and recombination model. Optically excited ~300–500 nm thick Si films exhibited a bi-exponential carrier relaxation with the characteristic times varying from picoseconds to nanoseconds depending on the film growth process. From our comprehensive trapping model, we could determine that for doped and intrinsic films with very low hydrogen dilution the dominant relaxation mode was carrier trapping;more » while for intrinsic films with large hydrogen content and some texture, it was the standard electron–phonon cooling. In both cases, the initial nonequilibrium relaxation was followed by Shockley–Read–Hall recombination. An excellent fit between the model and the ΔT/T experimental transients was obtained and a correlation between the Si film growth process, its hydrogen content, and the associated trap concentration was demonstrated.« less

  10. Time-resolved, nonequilibrium carrier dynamics in Si-on-glass thin films for photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Serafini, John; Akbas, Yunus; Crandall, Lucas; Bellman, Robert; Kosik Williams, Carlo; Sobolewski, Roman

    2016-04-01

    A femtosecond pump-probe spectroscopy method was used to characterize the growth process and transport properties of amorphous silicon-on-glass, thin films, intended as absorbers for photovoltaic cells. We collected normalized transmissivity change (ΔT/T) waveforms and interpreted them using a comprehensive three-rate equation electron trapping and recombination model. Optically excited ˜300-500 nm thick Si films exhibited a bi-exponential carrier relaxation with the characteristic times varying from picoseconds to nanoseconds depending on the film growth process. From our comprehensive trapping model, we could determine that for doped and intrinsic films with very low hydrogen dilution the dominant relaxation mode was carrier trapping; while for intrinsic films with large hydrogen content and some texture, it was the standard electron-phonon cooling. In both cases, the initial nonequilibrium relaxation was followed by Shockley-Read-Hall recombination. An excellent fit between the model and the ΔT/T experimental transients was obtained and a correlation between the Si film growth process, its hydrogen content, and the associated trap concentration was demonstrated.

  11. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... (PICC). 69.153 Section 69.153 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON... § 69.153 Presubscribed interexchange carrier charge (PICC). (a) A charge expressed in dollars and cents... maximum of $4.31 per line per month. In the event the ceilings on the PICC prevent the PICC...

  12. Charge states of energetic tellurium ions: Equilibrium and non-equilibrium calculations

    NASA Astrophysics Data System (ADS)

    Kartavykh, Y.; Droege, W.; Klecker, B.; Kocharov, L.; Moebius, E.

    2007-12-01

    Recently, very high abundances of ultraheavy ions were observed in impulsive SEP events, compared to coronal abundances with enrichment factors of >100 for atomic mass > 100 amu. Because wave/particle interaction processes, as discussed for heavy ion enrichment and acceleration, depend critically on the mass per charge (M/Q) of the ions, an estimate of the ionic charge is very important for model calculations. In any realistic acceleration model one would have to use the ionization and recombination rates of these ions as a function of energy, because charge changing processes in the solar corona are inevitable and energy dependent. As an example of high mass ions, we calculate the equilibrium and non-equilibrium charge states for tellurium ions (Te, nuclear charge 52), and present a method to estimate the cross sections and rates for ionization and recombination of ions with arbitrary nuclear charge Z and atomic mass number A.

  13. Space charge corrected electron emission from an aluminum surface under non-equilibrium conditions

    SciTech Connect

    Wendelen, W.; Bogaerts, A.; Mueller, B. Y.; Rethfeld, B.; Autrique, D.

    2012-06-01

    A theoretical study has been conducted of ultrashort pulsed laser induced electron emission from an aluminum surface. Electron emission fluxes retrieved from the commonly employed Fowler-DuBridge theory were compared to fluxes based on a laser-induced non-equilibrium electron distribution. As a result, the two- and three-photon photoelectron emission parameters for the Fowler-DuBridge theory have been approximated. We observe that at regimes where photoemission is important, laser-induced electron emission evolves in a more smooth manner than predicted by the Fowler-DuBridge theory. The importance of the actual electron distribution decreases at higher laser fluences, whereas the contribution of thermionic emission increases. Furthermore, the influence of a space charge effect on electron emission was evaluated by a one dimensional particle-in-cell model. Depending on the fluences, the space charge reduces the electron emission by several orders of magnitude. The influence of the electron emission flux profiles on the effective electron emission was found to be negligible. However, a non-equilibrium electron velocity distribution increases the effective electron emission significantly. Our results show that it is essential to consider the non-equilibrium electron distribution as well as the space charge effect for the description of laser-induced photoemission.

  14. The Influence of Trapped Ions and Non-equilibrium EDF on Dust Particle Charging

    SciTech Connect

    Sukhinin, G. I.; Fedoseev, A. V.; Antipov, S. N.; Petrov, O. F.; Fortov, V. E.

    2008-09-07

    Dust particles charging in a low-pressure glow discharge was investigated theoretically with the help of model for trapped and free ions coupled with the self-consistent solution of Poisson equation for electric potential. Non-equilibrium (non-Maxwellian) character of electron energy distribution function depending on gas pressure and electric field was also taken into account on the basis of the solution of kinetic Boltzmann equation. The results were compared with the experimental measurements of dust particle charge depending on gas pressure. It was shown that the calculated effective charge, i.e. the difference of the dust particle charge and trapped ion charge, is in a fairly good agreement with the experimental data.

  15. Shielding of a Moving Charged Dust Particle in the Nonequilibrium Plasma

    SciTech Connect

    Filippov, A. V.; Pal, A. F.; Starostin, A. N.; Momot, A. I.; Zagorodny, A. G.

    2008-09-07

    Study of shielding of a moving charged dust particle in the nonequilibrium plasma was performed. It is known that in the collisionless so-called Vlasov plasma the electric field of a slowly moving charged particle at high distances corresponds to quadrupole [1, 2, 3]. It was found that in the collisional plasma the electric field of a moving dust particle had the dipole component and the long distance behavior of the electric fields was defined by this component. Therefore the interaction of dust particles in plasma flow became dependent on the relative orientation of the interpaticle radius-vector and the flow velocity vector.

  16. Charge carrier coherence and Hall effect in organic semiconductors

    PubMed Central

    Yi, H. T.; Gartstein, Y. N.; Podzorov, V.

    2016-01-01

    Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor. PMID:27025354

  17. Columnar mesophases of hexabenzocoronene derivatives. II. Charge carrier mobility

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, James; Marcon, Valentina; Kremer, Kurt; Nelson, Jenny; Andrienko, Denis

    2008-09-01

    Combining atomistic molecular dynamic simulations, Marcus-Hush theory description of charge transport rates, and master equation description of charge dynamics, we correlate the temperature-driven change of the mesophase structure with the change of charge carrier mobilities in columnar phases of hexabenzocoronene derivatives. The time dependence of fluctuations in transfer integrals shows that static disorder is predominant in determining charge transport characteristics. Both site energies and transfer integrals are distributed because of disorder in the molecular arrangement. It is shown that the contributions to the site energies from polarization and electrostatic effects are of opposite sign for positive charges. We look at three mesophases of hexabenzocoronene: herringbone, discotic, and columnar disordered. All results are compared to time resolved microwave conductivity data and show excellent agreement with no fitting parameters.

  18. Non-equilibrium energy loss for very highly charged ions in insulators

    SciTech Connect

    Briere, M.A.; Schenkel, T.; Bauer, P.; Amau, A.

    1996-12-31

    The energy loss of 144 keV Ar{sup +16} ions on a bilayer structure of C-CaF{sub 2} has been measured. An asymmetry in the results is found depending on which layer is passed by the ion first: the energy loss is about four times larger when the CaF{sub 2} layer is traversed by the ion first. We interpret this as an indication of the existence of a nonequilibrium charge state of the Ar ions inside the solid in the case of the insulator.

  19. Nonequilibrium Dynamical Mean-Field Theory for the Charge-Density-Wave Phase of the Falicov-Kimball Model

    SciTech Connect

    Matveev, O. P.; Shvaika, A. M.; Devereaux, T. P.; Freericks, J. K.

    2015-12-08

    Nonequilibrium dynamical mean-field theory (DMFT) is developed for the case of the charge-density-wave ordered phase. We consider the spinless Falicov-Kimball model which can be solved exactly. This strongly correlated system is then placed in an uniform external dc electric field. We present a complete derivation for nonequilibrium dynamical mean-field theory Green’s functions defined on the Keldysh-Schwinger time contour. We also discuss numerical issues involved in solving the coupled equations.

  20. Identification of the Charge Carriers in Cerium Phosphate Ceramics

    SciTech Connect

    Ray, Hannah L.; Jonghe, Lutgard C. De

    2010-06-02

    The total conductivity of Sr-doped cerium orthophosphate changes by nearly two orders of magnitude depending on the oxygen and hydrogen content of the atmosphere. The defect model for the system suggests that this is because the identity of the dominant charge carrier can change from electron holes to protons when the sample is in equilibrium with air vs. humidified hydrogen. In this work are presented some preliminary measurements that can help to clarify this exchange between carriers. The conduction behavior of a 2percent Sr-doped CePO4 sample under symmetric atmospheric conditions is investigated using several techniques, including AC impedance, H/D isotope effects, and chronoamperometry.

  1. Unique characteristics of nonequilibrium carrier transport dynamics in an undoped GaAs/n-type GaAs epitaxial structure

    NASA Astrophysics Data System (ADS)

    Hasegawa, Takayuki; Nakayama, Masaaki

    2016-07-01

    We have investigated nonequilibrium carrier dynamics in an undoped GaAs/n-type GaAs epitaxial structure at room temperature using reflection-type pump–probe spectroscopy at different pump photon energies and Monte Carlo simulation. It was found that the transport process of photogenerated electrons in the undoped layer is characterized by the valance between the quasiballistic motion passing through the undoped layer and the intervalley scattering from the Γ valley to the L one as a function of the excess energy of photogenerated electrons. The Γ–L scattering component exhibits threshold-like appearance and then gradually increases with increasing excess energy.

  2. Electrical Conductivity of Rocks and Dominant Charge Carriers. Part 1; Thermally Activated Positive Holes

    NASA Technical Reports Server (NTRS)

    Freund, Friedemann T.; Freund, Minoru M.

    2012-01-01

    The prevailing view in the geophysics community is that the electrical conductivity structure of the Earth's continental crust over the 5-35 km depth range can best be understood by assuming the presence of intergranular fluids and/or of intragranular carbon films. Based on single crystal studies of melt-grown MgO, magma-derived sanidine and anorthosite feldspars and upper mantle olivine, we present evidence for the presence of electronic charge carriers, which derive from peroxy defects that are introduced during cooling, under non-equilibrium conditions, through a redox conversion of pairs of solute hydroxyl arising from dissolution of H2O.The peroxy defects become thermally activated in a 2-step process, leading to the release of defect electrons in the oxygen anion sublattice. Known as positive holes and symbolized by h(dot), these electronic charge carriers are highly mobile. Chemically equivalent to O(-) in a matrix of O(2-) they are highly oxidizing. Being metastable they can exist in the matrix of minerals, which crystallized in highly reduced environments. The h(dot) are highly mobile. They appear to control the electrical conductivity of crustal rocks in much of the 5-35 km depth range.

  3. Nanofaceting as a stamp for periodic graphene charge carrier modulations

    NASA Astrophysics Data System (ADS)

    Vondráček, M.; Kalita, D.; Kučera, M.; Fekete, L.; Kopeček, J.; Lančok, J.; Coraux, J.; Bouchiat, V.; Honolka, J.

    2016-04-01

    The exceptional electronic properties of monatomic thin graphene sheets triggered numerous original transport concepts, pushing quantum physics into the realm of device technology for electronics, optoelectronics and thermoelectrics. At the conceptual pivot point is the particular two-dimensional massless Dirac fermion character of graphene charge carriers and its volitional modification by intrinsic or extrinsic means. Here, interfaces between different electronic and structural graphene modifications promise exciting physics and functionality, in particular when fabricated with atomic precision. In this study we show that quasiperiodic modulations of doping levels can be imprinted down to the nanoscale in monolayer graphene sheets. Vicinal copper surfaces allow to alternate graphene carrier densities by several 1013 carriers per cm2 along a specific copper high-symmetry direction. The process is triggered by a self-assembled copper faceting process during high-temperature graphene chemical vapor deposition, which defines interfaces between different graphene doping levels at the atomic level.

  4. Nanofaceting as a stamp for periodic graphene charge carrier modulations

    PubMed Central

    Vondráček, M.; Kalita, D.; Kučera, M.; Fekete, L.; Kopeček, J.; Lančok, J.; Coraux, J.; Bouchiat, V.; Honolka, J.

    2016-01-01

    The exceptional electronic properties of monatomic thin graphene sheets triggered numerous original transport concepts, pushing quantum physics into the realm of device technology for electronics, optoelectronics and thermoelectrics. At the conceptual pivot point is the particular two-dimensional massless Dirac fermion character of graphene charge carriers and its volitional modification by intrinsic or extrinsic means. Here, interfaces between different electronic and structural graphene modifications promise exciting physics and functionality, in particular when fabricated with atomic precision. In this study we show that quasiperiodic modulations of doping levels can be imprinted down to the nanoscale in monolayer graphene sheets. Vicinal copper surfaces allow to alternate graphene carrier densities by several 1013 carriers per cm2 along a specific copper high-symmetry direction. The process is triggered by a self-assembled copper faceting process during high-temperature graphene chemical vapor deposition, which defines interfaces between different graphene doping levels at the atomic level. PMID:27040365

  5. Charge carrier separation in modulation doped coaxial semiconductor nanowires.

    PubMed

    Nduwimana, A; Wang, Xiao-Qian

    2009-01-01

    Complementary doped donor and acceptor dipoles effectively generate confinement potentials for carriers across a p-type/intrinsic/n-type coaxial nanowire due to the lineup of charge neutrality level. In order to verify this physical picture, we employ first-principles density functional theory to study the confinement of electrons and holes in complementary boron (p-type) and phosphorus (n-type) doped coaxial silicon nanowires. An analysis of the charge density distributions reveals that the electrons and holes are spatially separated in core and outer shell regions, respectively, in conformity with a type-II lineup of band structures.

  6. Giant Reduction of Charge Carrier Mobility in Strained Graphene

    NASA Astrophysics Data System (ADS)

    Shah, Raheel; Mohiuddin, Tariq M. G.; Singh, Ram N.

    2013-01-01

    Impact of induced strain on charge carrier mobility is investigated for a monolayer graphene sheet. The unsymmetrical hopping parameters between nearest neighbor atoms which emanate from induced strain are included in the density of states description. Mobility is then computed within the Born approximation by including three scattering mechanisms; charged impurity, surface roughness and lattice phonons interaction. Unlike its strained silicon counterpart, simulations reveal a significant drop in mobility for graphene with increasing strain. Additionally, mobility anisotropy is observed along the zigzag and armchair orientations. The prime reason for the drop in mobility can be attributed to the change in Fermi velocity due to strain induced distortions in the graphene honeycomb lattice.

  7. Spontaneous Charge Carrier Localization in Extended One-Dimensional Systems

    NASA Astrophysics Data System (ADS)

    Vlček, Vojtěch; Eisenberg, Helen R.; Steinle-Neumann, Gerd; Neuhauser, Daniel; Rabani, Eran; Baer, Roi

    2016-05-01

    Charge carrier localization in extended atomic systems has been described previously as being driven by disorder, point defects, or distortions of the ionic lattice. Here we show for the first time by means of first-principles computations that charge carriers can spontaneously localize due to a purely electronic effect in otherwise perfectly ordered structures. Optimally tuned range-separated density functional theory and many-body perturbation calculations within the G W approximation reveal that in trans-polyacetylene and polythiophene the hole density localizes on a length scale of several nanometers. This is due to exchange-induced translational symmetry breaking of the charge density. Ionization potentials, optical absorption peaks, excitonic binding energies, and the optimally tuned range parameter itself all become independent of polymer length as it exceeds the critical localization length. Moreover, we find that lattice disorder and the formation of a polaron result from the charge localization in contrast to the traditional view that lattice distortions precede charge localization. Our results can explain experimental findings that polarons in conjugated polymers form instantaneously after exposure to ultrafast light pulses.

  8. Charge-carrier transport in smectic mesophases of biphenyls

    NASA Astrophysics Data System (ADS)

    Ohno, Akira; Haruyama, Akihide; Kurotaki, Kensuke; Hanna, Jun-ichi

    2007-10-01

    The charge-transport properties of ω ,ω'-alkylalkoxylbiphenyls, one of the simplest calamitic (rodlike) liquid crystals exhibiting smectic mesophases, were investigated using the time-of-flight experiments. A mobility of ˜10-3 cm2/V s was determined for holes in both smectic B (SmB) and smectic E (SmE) phases. This high electronic mobility, comparable to the highest mobilities in amorphous organic semiconductors, indicates that the self-organization of such simple molecules including small aromatic compounds is quite effective in enhancing the charge transport in organic materials. The mobilities of both smectic mesophases, however, depend on temperatures, which is not the case for other typical smectic liquid crystals reported previously. Interestingly, the mobility in the SmE phase exhibits a Poole-Frenkel type of field dependence. Detailed experimental studies have shown that this field dependence is not due to the trapping effect of carriers caused by chemical contaminants or structural defects such as domain boundaries and dislocation, but arises from the widely distributed density of states with a distribution width of 0.11-0.13 eV for the SmE phase, as estimated based on a two-dimensional Gaussian disorder model. The phase-specific carrier transport in biphenyls may provide us with unique insights leading to a more complete understanding of the charge carrier transport in the mesophase materials.

  9. Charge carrier coherence and Hall effect in organic semiconductors

    DOE PAGES

    Yi, H. T.; Gartstein, Y. N.; Podzorov, V.

    2016-03-30

    Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force actingmore » on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Lastly, our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor.« less

  10. Nonequilibrium phenomena in charge recombination of excited donor-acceptor complexes and free energy gap law.

    PubMed

    Yudanov, Vladislav V; Mikhailova, Valentina A; Ivanov, Anatoly I

    2010-12-23

    The charge recombination dynamics of excited donor-acceptor complexes in polar solvents has been investigated within the framework of the stochastic approach. The model involves the excited state formation by the pump pulse and accounts for the reorganization of a number of intramolecular high-frequency vibrational modes, for their relaxation as well as for the solvent reorganization following nonexponential relaxation. The hot transitions accelerate the charge recombination in the low exergonic region and suppress it in the region of moderate exothermicity. This straightens the dependence of the logarithm of the charge recombination rate constant on the free energy gap to the form that can be fitted to the experimental data. The free energy dependence of the charge recombination rate constant can be well fitted to the multichannel stochastic model if the donor-acceptor complexes are separated into a few groups with different values of the electronic coupling. The model provides correct description of the nonexponential charge recombination dynamics in excited donor-acceptor complexes, in particular, nearly exponential recombination in perylene-tetracyanoethylene complex in acetonitrile. It appears that majority of the initially excited donor-acceptor complexes recombines in a nonthermal (hot) stage when the nonequilibrium wave packet passes through a number of term crossings corresponding to transitions toward vibrational excited states of the electronic ground state in the area of the low and moderate exothermicity.

  11. Morphology and charge carrier transport in eumelanin thin films

    NASA Astrophysics Data System (ADS)

    Santato, Clara; Wuensche, Julia; Rosei, Federico

    2012-02-01

    Eumelanin is a biomolecule with important functions in the human body, animals, and plants. However, several fundamental properties of eumelanin, such as the mechanism of charge carrier transport and the supramolecular structure, are still a matter of debate. This work is the first step of a study with the long-term goal to characterize structure and charge carrier transport of eumelanin in thin film form. We compared the most common synthesis routes and processing solvents for eumelanin observing the morphology (AFM) and chemical composition (XPS) of the prepared films. Eumelanin synthesized from tyrosine by oxidation with H2O2 and deposited from dimethyl sulfoxide yielded films with a RMS roughness below 0.4 nm and an elementary composition in agreement with the eumelanin building blocks suggested in literature. A more detailed AFM study revealed a layer-by-layer growth mode for solution-processed eumelanin films. The first electrical characterization of these films in a planar two-electrode configuration and a high-humidity environment demonstrated the high complexity of charge transport in eumelanin films. The planar device geometry permits imaging the changes in the optical or morphological properties of the eumelanin film by optical microscopy and AFM. Our measurements suggest that several processes, including electrochromism and electropolymerization, contribute to determine the electroactivity of eumelanin films, depending on the applied electrical bias. Current transients over several hours support the hypothesis that ions are involved in charge transport.

  12. Mobility of Charge Carriers in Polymer and Mica Electrets

    NASA Astrophysics Data System (ADS)

    Novikov, G. K.; Fedchishin, V. V.

    2015-04-01

    Ionizing radiation of an electric corona gas discharge (ECGD) and electric barrier gas discharge (EBGD) creates a radiation thickness gradient of recombination center concentration N rec = f(h) near the surface of polymer and mica electrets. The mobility of charge carriers in polymer and mica electrets and the stability of the electret potential difference U el = f(t) are obtained by the method of experimental measurements of the x-ray radiation half-absorption depth δ 1/2ECGD, EBGD .

  13. Two carrier temperatures non-equilibrium generalized Planck law for semiconductors

    NASA Astrophysics Data System (ADS)

    Gibelli, François; Lombez, Laurent; Guillemoles, Jean-François

    2016-10-01

    Planck's law of radiation describes the light emitted by a blackbody. This law has been generalized in the past for the case of a non-blackbody material having a quasi Fermi-level splitting: the lattice of the material and the carriers are then considered in an isothermal regime. Hot carrier spectroscopy deals with carriers out of the isothermal regime, as their respective temperatures (THe ≠ THh) are considered to be different than that of the lattice (TL). Here we show that Fermi-Dirac distribution temperature for each type of carrier still determine an effective radiation temperature: an explicit relationship is given involving the effective masses. Moreover, we show how to determine, in principle with an additional approximation, the carrier temperatures (THe, THh) and the corresponding absolute electrochemical potentials from photoluminescence measurements.

  14. Dynamics of charge carriers on hexagonal nanoribbons with vacancy defects

    NASA Astrophysics Data System (ADS)

    Ferreira da Cunha, Wiliam; de Oliveira Neto, Pedro Henrique; Terai, Akira; Magela e Silva, Geraldo

    2016-07-01

    We develop a general model to investigate the dynamics of charge carriers in vacancy endowed honeycomb two-dimensional nanolattices. As a fundamental application, results concerning the influence of vacancies placed on different sites of semiconducting armchair graphene nanoribbons (AGNR) over the transport of polarons are presented. It is observed that the positioning of vacancies plays a major role over the scattering of the charge carriers, in the sense that their overall mobility is determined by where the defect is allocated. By considering different structural configurations of the system, the arising polaron can either move freely or be reflected. Therefore, our work provides a phenomenological understanding of the underlying mechanism responsible for the change of conductivity experienced by systems in which structural defects are present, a fact that has been reported for different nanostructures of the same symmetry. Because vacancies are one of the most common kinds of defects and are, in practice, unavoidable, the kind of description proposed in the present paper is crucial to correctly address transport and electronic properties in more realistic electronic devices based on two-dimensional nanolattices.

  15. Polaron mass of charge carriers in semiconductor quantum wells

    SciTech Connect

    Maslov, A. Yu. Proshina, O. V.

    2015-10-15

    A theory of the interaction of charge carriers with optical phonons in a quantum well is developed with consideration for interface optical phonons. The dependence of the polaron effective mass on the quantum-well dimensions and dielectric characteristics of barriers is analyzed in detail. It is shown that, in narrow quantum wells, a quasi-two-dimensional polaron can be formed. In this case, however, the interaction parameters are defined by the charge-carrier effective mass in the quantum well and by the frequencies of interface optical phonons. If barriers are made of a nonpolar material, the polaron effective mass depends on the quantum-well width. As the quantum-well width is increased, a new mechanism of enhancement of the electron–phonon interaction develops. The mechanism is implemented, if the optical phonon energy is equal to the energy of one of the electronic transitions. This condition yields an unsteady dependence of the polaron effective mass on the quantum-well width.

  16. Charge-carrier relaxation dynamics in highly ordered poly( p -phenylene vinylene): Effects of carrier bimolecular recombination and trapping

    NASA Astrophysics Data System (ADS)

    Soci, Cesare; Moses, Daniel; Xu, Qing-Hua; Heeger, Alan J.

    2005-12-01

    We have studied the charge-carrier relaxation dynamics in highly ordered poly( p -phenylene vinylene) over a broad time range using fast (t>100ps) transient photoconductivity measurements. The carrier density was also monitored (t>100fs) by means of photoinduced absorption probed at the infrared active vibrational modes. We find that promptly upon charge-carrier photogeneration, the initial polaron dynamics is governed by bimolecular recombination, while later in the subnanosecond time regime carrier trapping gives rise to an exponential decay of the photocurrent. The more sensitive transient photocurrent measurements indicate that in the low excitation regime, when the density of photocarriers is comparable to that of the trapping states (˜1016cm-3) , carrier hopping between traps along with transport via extended states determines the carrier relaxation, a mechanism that is manifested by a long-lived photocurrent “tail.” This photocurrent tail is reduced by lowering the temperature and/or by increasing the excitation density. Based on these data, we develop a comprehensive kinetic model that takes into account the bipolar charge transport, the free-carrier bimolecular recombination, the carrier trapping, and the carrier recombination involving free and trapped carriers.

  17. Spontaneous charge carrier localization in extended one-dimensional systems

    NASA Astrophysics Data System (ADS)

    Vlček, Vojtěch; Eisenberg, Helen; Steinle-Neumann, Gerd; Baer, Roi

    Charge carrier localization in extended atomic systems can be driven by disorder, point defects or distortions of the ionic lattice. Herein we give first-principles theoretical computational evidence that it can also appear as a purely electronic effect in otherwise perfectly ordered periodic structures and we show that electronic eigenstates can spontaneously localize upon excitation. Optimally-tuned range separated density functional calculations reveal that in trans-polyacetylene and polythiophene the hole density localizes on a length scale of several nanometers. This is due to exchange induced translational symmetry breaking of the charge density. Ionization potentials, optical absorption peaks, excitonic binding energies and the optimally-tuned range parameter itself all become independent of polymer length when it exceeds the critical localization length scale. These first-principles findings show, for the first time, that charge localization is not caused by lattice distortion but rather it is their cause, changing the physical models of polaron formation and dynamics, helping to explain experimental findings that polarons in conjugated polymers form instantaneously after exposure to ultrafast light pulses. Secondary affiliation: Bayerisches Geoinstitut, Universität Bayreuth, Germany.

  18. Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics.

    PubMed

    Bazant, Martin Z

    2013-05-21

    the past 7 years, which is capable of answering these questions. The reaction rate is a nonlinear function of the thermodynamic driving force, the free energy of reaction, expressed in terms of variational chemical potentials. The theory unifies and extends the Cahn-Hilliard and Allen-Cahn equations through a master equation for nonequilibrium chemical thermodynamics. For electrochemistry, I have also generalized both Marcus and Butler-Volmer kinetics for concentrated solutions and ionic solids. This new theory provides a quantitative description of LFP phase behavior. Concentration gradients and elastic coherency strain enhance the intercalation rate. At low currents, the charge-transfer rate is focused on exposed phase boundaries, which propagate as "intercalation waves", nucleated by surface wetting. Unexpectedly, homogeneous reactions are favored above a critical current and below a critical size, which helps to explain the rate capability of LFP nanoparticles. Contrary to other mechanisms, elevated temperatures and currents may enhance battery performance and lifetime by suppressing phase separation. The theory has also been extended to porous electrodes and could be used for battery engineering with multiphase active materials. More broadly, the theory describes nonequilibrium chemical systems at mesoscopic length and time scales, beyond the reach of molecular simulations and bulk continuum models. The reaction rate is consistently defined for inhomogeneous, nonequilibrium states, for example, with phase separation, large electric fields, or mechanical stresses. This research is also potentially applicable to fluid extraction from nanoporous solids, pattern formation in electrophoretic deposition, and electrochemical dynamics in biological cells. PMID:23520980

  19. Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics.

    PubMed

    Bazant, Martin Z

    2013-05-21

    the past 7 years, which is capable of answering these questions. The reaction rate is a nonlinear function of the thermodynamic driving force, the free energy of reaction, expressed in terms of variational chemical potentials. The theory unifies and extends the Cahn-Hilliard and Allen-Cahn equations through a master equation for nonequilibrium chemical thermodynamics. For electrochemistry, I have also generalized both Marcus and Butler-Volmer kinetics for concentrated solutions and ionic solids. This new theory provides a quantitative description of LFP phase behavior. Concentration gradients and elastic coherency strain enhance the intercalation rate. At low currents, the charge-transfer rate is focused on exposed phase boundaries, which propagate as "intercalation waves", nucleated by surface wetting. Unexpectedly, homogeneous reactions are favored above a critical current and below a critical size, which helps to explain the rate capability of LFP nanoparticles. Contrary to other mechanisms, elevated temperatures and currents may enhance battery performance and lifetime by suppressing phase separation. The theory has also been extended to porous electrodes and could be used for battery engineering with multiphase active materials. More broadly, the theory describes nonequilibrium chemical systems at mesoscopic length and time scales, beyond the reach of molecular simulations and bulk continuum models. The reaction rate is consistently defined for inhomogeneous, nonequilibrium states, for example, with phase separation, large electric fields, or mechanical stresses. This research is also potentially applicable to fluid extraction from nanoporous solids, pattern formation in electrophoretic deposition, and electrochemical dynamics in biological cells.

  20. Intrinsic Charge Carrier Mobility in Single-Layer Black Phosphorus.

    PubMed

    Rudenko, A N; Brener, S; Katsnelson, M I

    2016-06-17

    We present a theory for single- and two-phonon charge carrier scattering in anisotropic two-dimensional semiconductors applied to single-layer black phosphorus (BP). We show that in contrast to graphene, where two-phonon processes due to the scattering by flexural phonons dominate at any practically relevant temperatures and are independent of the carrier concentration n, two-phonon scattering in BP is less important and can be considered negligible at n≳10^{13}  cm^{-2}. At smaller n, however, phonons enter in the essentially anharmonic regime. Compared to the hole mobility, which does not exhibit strong anisotropy between the principal directions of BP (μ_{xx}/μ_{yy}∼1.4 at n=10^{13} cm^{-2} and T=300  K), the electron mobility is found to be significantly more anisotropic (μ_{xx}/μ_{yy}∼6.2). Absolute values of μ_{xx} do not exceed 250 (700)  cm^{2} V^{-1} s^{-1} for holes (electrons), which can be considered as an upper limit for the mobility in BP at room temperature. PMID:27367397

  1. Intrinsic Charge Carrier Mobility in Single-Layer Black Phosphorus

    NASA Astrophysics Data System (ADS)

    Rudenko, A. N.; Brener, S.; Katsnelson, M. I.

    2016-06-01

    We present a theory for single- and two-phonon charge carrier scattering in anisotropic two-dimensional semiconductors applied to single-layer black phosphorus (BP). We show that in contrast to graphene, where two-phonon processes due to the scattering by flexural phonons dominate at any practically relevant temperatures and are independent of the carrier concentration n , two-phonon scattering in BP is less important and can be considered negligible at n ≳1013 cm-2 . At smaller n , however, phonons enter in the essentially anharmonic regime. Compared to the hole mobility, which does not exhibit strong anisotropy between the principal directions of BP (μx x/μy y˜1.4 at n =1013 cm-2 and T =300 K ), the electron mobility is found to be significantly more anisotropic (μx x/μy y˜6.2 ). Absolute values of μx x do not exceed 250 (700 ) cm2 V-1 s-1 for holes (electrons), which can be considered as an upper limit for the mobility in BP at room temperature.

  2. Thermal detection of trapped charge carriers in organic transport materials

    NASA Astrophysics Data System (ADS)

    von Malm, Norwin; Steiger, Juergen; Finnberg, Torsten; Schmechel, Roland; von Seggern, Heinz

    2003-03-01

    The effect of trap states on the transport and luminescence properties of organic light emitting diodes (OLEDs) is studied. For trap level detection energy resolved thermally stimulated current (TSC) measurements known as fractional glow are utilized to determine the density of occupied states (DOOS) in various organic semiconductors such as the small molecule systems Alq3 [aluminum tris(8-hydroxyquinoline)], 1-NaphDATA {4,4',4"-tris-[N-(1-naphtyl)-N-phenylamino]-triphenylamine} and α-NPD [N,N'-di-(1-naphthyl)-N,N'-diphenylbenzidine] and the polymeric semiconductor MDMO-PPV {poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene]}. Characteristic differences in the trap spectra are obtained and interpreted in terms of possible structural and compositional origins of the investigated materials. In order to judge the formation process of traps and their practical consequences on the charge carrier transport I-V and L-V characteristics of 1-NaphDATA doped α-NPD devices and α-NPD doped 1-NaphDATA devices were compared to respective non-doped samples. A clearly reduced current and luminescence was found only in the former case. It was possible to conclude that the detected electronic trap states either act as hole traps or as scattering centers. Furthermore, pulsed transport studies on ITO/α-NPD/Alq3/Al devices show thte critical influence of traps on the dynamical performance of the charge transport. In a two-pulse experiment the carrier injection and trap depletion can be separated.

  3. The effect of carrier gas contaminants on the charging probability of aerosols under bipolar charging conditions.

    PubMed

    Steiner, Gerhard; Reischl, Georg P

    2012-12-01

    This work concentrates on the experimental determination of the properties of ionic molecular clusters that are produced in the bipolar ionic atmosphere of a radioactivity based (241)Am charger. The main scope of this study was to investigate the dependency of the ions' properties on carrier gas contaminants caused by the evaporation of trace gases from different kinds of frequently encountered tubing materials. A recently developed high resolution mobility spectrometer allows the precise determination of the ions' electrical mobility; an empirical mass-mobility relationship was used to approximate the corresponding ion masses. It was found that impurities in the carrier gas dramatically change the pattern of the ion mobility/size distribution, resulting in very different ion properties that strongly depend on the carrier gas composition. Since the ion properties control the charging process of aerosols, it was further investigated how the different ion properties affect the calculation of the charging probabilities of aerosols. The results show that despite large variations of the ions' properties, only a minor effect on the calculated charging probabilities can be found.

  4. Charge carrier transport properties in layer structured hexagonal boron nitride

    SciTech Connect

    Doan, T. C.; Li, J.; Lin, J. Y.; Jiang, H. X.

    2014-10-15

    Due to its large in-plane thermal conductivity, high temperature and chemical stability, large energy band gap (~ 6.4 eV), hexagonal boron nitride (hBN) has emerged as an important material for applications in deep ultraviolet photonic devices. Among the members of the III-nitride material system, hBN is the least studied and understood. The study of the electrical transport properties of hBN is of utmost importance with a view to realizing practical device applications. Wafer-scale hBN epilayers have been successfully synthesized by metal organic chemical deposition and their electrical transport properties have been probed by variable temperature Hall effect measurements. The results demonstrate that undoped hBN is a semiconductor exhibiting weak p-type at high temperatures (> 700 °K). The measured acceptor energy level is about 0.68 eV above the valence band. In contrast to the electrical transport properties of traditional III-nitride wide bandgap semiconductors, the temperature dependence of the hole mobility in hBN can be described by the form of μ ∝ (T/T{sub 0}){sup −α} with α = 3.02, satisfying the two-dimensional (2D) carrier transport limit dominated by the polar optical phonon scattering. This behavior is a direct consequence of the fact that hBN is a layer structured material. The optical phonon energy deduced from the temperature dependence of the hole mobility is ħω = 192 meV (or 1546 cm{sup -1}), which is consistent with values previously obtained using other techniques. The present results extend our understanding of the charge carrier transport properties beyond the traditional III-nitride semiconductors.

  5. Ultrafast charge carrier dynamics in Au/semiconductor nanoheterostructures

    NASA Astrophysics Data System (ADS)

    Lambright, Scott

    The charge carrier dynamics in several Au/semiconductor core/shell heterostructures were examined. Firstly, Au/CdS core/shell nanocomposites were synthesized in a four step procedure culminating in a cation exchange performed on the shell. Previous studies of the ultrafast carrier dynamics in Au/CdS nanocomposites with epitaxial boundary regions reported the suppression of plasmon character in transient absorption spectra accompanied by broadband photoinduced absorption. The coupling of electron wavefunctions with lattice defects at the boundary of the two domains has been blamed for these phenomena. In the current study, transmission electron micrographs of Au/CdS synthesized using cation exchange showed no evidence of strain on the lattice of either component, while femtosecond transient absorption data show the retention of bleach regions attributed to CdS's 1S(e)-1S3/2(h) transition and Au's plasmon resonance. Accelerated rates of bleach recovery for both excitations ( tauexiton ≈ 300 ps, tauplasmon ≈ .7 ps) indicated that the interaction of Au and CdS domains leads to faster relaxation to their respective photoexcitations when compared to relaxation times in isolated Au and CdS nanoparticles. It was believed that the Au/CdS boundary was non-epitaxial in the presented core/shell nanocomposites. Secondly, these non-epitaxial Au/CdS core/shells were subsequently used to demonstrate near-field energy transfer from 5 nm diameter Au cores to CdS-encapsulated CdSe quantum dots. To this end, Au/CdS and CdSe/CdS nanocrystals were embedded in semiconductor-matrix-encapsulated-nanocrystal-arrays (SMENA) together. The encapsulation of both domains in the high band-gap semiconductor CdS was a means to suppress charge transfer between the two nanoparticles. The fluorescence intensity in these films was enhanced 6-fold in some cases as a result of the presence of Au domains. It was also demonstrated that the fluorescence enhancement was independent of the potential

  6. Ballistic-Charge-Carrier Spectroscopy Of CoSi(2)/Si Interfaces

    NASA Technical Reports Server (NTRS)

    Hecht, Michael H.; Kaiser, William J.; Fathauer, Robert W.; Bell, Lloyd D.; Lee, Edwin Y.

    1993-01-01

    Report discusses experiments in which ballistic-electron-emission microscopy (BEEM) and related ballistic-hole and charge-carrier-scattering spectroscopies used to investigate transport of electric-charge carriers (electrons and holes) in epitaxial CoSi2/Si system.

  7. Electric Properties of Obsidian: Evidence for Positive Hole Charge Carriers

    NASA Astrophysics Data System (ADS)

    Nordvik, R.; Freund, F. T.

    2012-12-01

    The blackness of obsidian is due to the presence of oxygen anions in the valence state 1-, creating broad energy levels at the upper edge of the valence band, which absorb visible light over a wide spectral range. These energy states are associated with defect electrons in the oxygen anion sublattice, well-known from "smoky quartz", where Al substituting for Si captures a defect electron in the oxygen anion sublattice for charge compensation [1]. Such defect electrons, also known as positive holes, are responsible for the increase in electrical conductivity in igneous rocks when uniaxial stresses are applied, causing the break-up of pre-existing peroxy defects, Si-OO-Si [2]. Peroxy defects in obsidian cannot be so easily activated by mechanical stress because the glassy matrix will break before sufficiently high stress levels can be reached. If peroxy defects do exist, however, they can be studied by activating them thermally [3]. We describe experiments with rectangular slabs of obsidian with Au electrodes at both ends. Upon heating one end, we observe (i) a thermopotential and (ii) a thermocurrent developing at distinct temperatures around 250°C and 450°C, marking the 2-step break-up of peroxy bonds. [1] Schnadt, R., and Schneider, J.: The electronic structure of the trapped-hole center in smoky quartz, Zeitschrift Physik B Condensed Matter 11, 19-42, 1970. [2] Freund, F. T., Takeuchi, A., and Lau, B. W.: Electric currents streaming out of stressed igneous rocks - A step towards understanding pre-earthquake low frequency EM emissions, Physics and Chemistry of the Earth, 31, 389-396, 2006. [3] Freund, F., and Masuda, M. M.: Highly mobile oxygen hole-type charge carriers in fused silica, Journal Material Research, 8, 1619-1622, 1991.

  8. Measuring charge carrier mobility in photovoltaic devices with micron-scale resolution

    SciTech Connect

    Ashraf, A.; Dissanayake, D. M. N. M.; Eisaman, M. D.

    2015-03-16

    We present a charge-extraction technique, micron-scale charge extraction by linearly increasing voltage, which enables simultaneous spatially resolved measurements of charge carrier mobility and photocurrent in thin-film photovoltaic devices with micron-scale resolution. An intensity-modulated laser with beam diameter near the optical diffraction limit is scanned over the device, while a linear voltage ramp in reverse bias is applied at each position of illumination. We calculate the majority carrier mobility, photocurrent, and number of photogenerated charge carriers from the resulting current transient. We demonstrate this technique on an organic photovoltaic device, but it is applicable to a wide range of photovoltaic materials.

  9. Where are the charge carriers along a closed circuit? A relativistic description

    NASA Astrophysics Data System (ADS)

    Fautrat, Sylvain

    2016-03-01

    We present relativistic transformations of charge densities for a closed electric circuit consisting of straight sections of finite length wires. The study of charge carrier movement is made in the rest frame of carriers, and with only basic relativistic kinematics, we follow a group of charge carriers along the different segments of the circuit. From the change in inter-particle distances when moving from one wire segment to another, expressions for the charge densities are deduced. This approach aims to provide a deeper understanding of the relativistic motion of objects around a closed loop.

  10. Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon

    SciTech Connect

    Astakhov, Oleksandr; Carius, Reinhard; Finger, Friedhelm; Petrusenko, Yuri; Borysenko, Valery; Barankov, Dmytro

    2009-03-01

    The influence of dangling-bond defects and the position of the Fermi level on the charge carrier transport properties in undoped and phosphorous doped thin-film silicon with structure compositions all the way from highly crystalline to amorphous is investigated. The dangling-bond density is varied reproducibly over several orders of magnitude by electron bombardment and subsequent annealing. The defects are investigated by electron-spin-resonance and photoconductivity spectroscopies. Comparing intrinsic amorphous and microcrystalline silicon, it is found that the relationship between defect density and photoconductivity is different in both undoped materials, while a similar strong influence of the position of the Fermi level on photoconductivity via the charge carrier lifetime is found in the doped materials. The latter allows a quantitative determination of the value of the transport gap energy in microcrystalline silicon. The photoconductivity in intrinsic microcrystalline silicon is, on one hand, considerably less affected by the bombardment but, on the other hand, does not generally recover with annealing of the defects and is independent from the spin density which itself can be annealed back to the as-deposited level. For amorphous silicon and material prepared close to the crystalline growth regime, the results for nonequilibrium transport fit perfectly to a recombination model based on direct capture into neutral dangling bonds over a wide range of defect densities. For the heterogeneous microcrystalline silicon, this model fails completely. The application of photoconductivity spectroscopy in the constant photocurrent mode (CPM) is explored for the entire structure composition range over a wide variation in defect densities. For amorphous silicon previously reported linear correlation between the spin density and the subgap absorption is confirmed for defect densities below 10{sup 18} cm{sup -3}. Beyond this defect level, a sublinear relation is found i

  11. The impact of hot charge carrier mobility on photocurrent losses in polymer-based solar cells.

    PubMed

    Philippa, Bronson; Stolterfoht, Martin; Burn, Paul L; Juška, Gytis; Meredith, Paul; White, Ronald D; Pivrikas, Almantas

    2014-07-22

    A typical signature of charge extraction in disordered organic systems is dispersive transport, which implies a distribution of charge carrier mobilities that negatively impact on device performance. Dispersive transport has been commonly understood to originate from a time-dependent mobility of hot charge carriers that reduces as excess energy is lost during relaxation in the density of states. In contrast, we show via photon energy, electric field and film thickness independence of carrier mobilities that the dispersive photocurrent in organic solar cells originates not from the loss of excess energy during hot carrier thermalization, but rather from the loss of carrier density to trap states during transport. Our results emphasize that further efforts should be directed to minimizing the density of trap states, rather than controlling energetic relaxation of hot carriers within the density of states.

  12. Secondary electron emissions and dust charging currents in the nonequilibrium dusty plasma with power-law distributions

    SciTech Connect

    Gong Jingyu; Du Jiulin

    2012-06-15

    We study the secondary electron emissions induced by the impact of electrons on dust grains and the resulting dust charging processes in the nonequilibrium dusty plasma with power-law distributions. We derive new expressions of the secondary emitted electron flux and the dust charging currents that are generalized by the power-law q-distributions, where the nonlinear core functions are numerically studied for the nonextensive parameter q. Our numerical analyses show that the power-law q-distribution of the primary electrons has a significant effect on both the secondary emitted electron flux and the dust charging currents, and this effect depends strongly on the ratio of the electrostatic potential energy of the primary electrons at the dust grain's surface to the thermodynamic energy, implying that a competition in the dusty plasma between these two energies plays a crucial role in this novel effect.

  13. Spectroscopy of Charge Carriers and Traps in Field-Doped Single Crystal Organic Semiconductors

    SciTech Connect

    Zhu, Xiaoyang

    2014-12-10

    The proposed research aims to achieve quantitative, molecular level understanding of charge carriers and traps in field-doped crystalline organic semiconductors via in situ linear and nonlinear optical spectroscopy, in conjunction with transport measurements and molecular/crystal engineering. Organic semiconductors are emerging as viable materials for low-cost electronics and optoelectronics, such as organic photovoltaics (OPV), organic field effect transistors (OFETs), and organic light emitting diodes (OLEDs). Despite extensive studies spanning many decades, a clear understanding of the nature of charge carriers in organic semiconductors is still lacking. It is generally appreciated that polaron formation and charge carrier trapping are two hallmarks associated with electrical transport in organic semiconductors; the former results from the low dielectric constants and weak intermolecular electronic overlap while the latter can be attributed to the prevalence of structural disorder. These properties have lead to the common observation of low charge carrier mobilities, e.g., in the range of 10-5 - 10-3 cm2/Vs, particularly at low carrier concentrations. However, there is also growing evidence that charge carrier mobility approaching those of inorganic semiconductors and metals can exist in some crystalline organic semiconductors, such as pentacene, tetracene and rubrene. A particularly striking example is single crystal rubrene (Figure 1), in which hole mobilities well above 10 cm2/Vs have been observed in OFETs operating at room temperature. Temperature dependent transport and spectroscopic measurements both revealed evidence of free carriers in rubrene. Outstanding questions are: what are the structural features and physical properties that make rubrene so unique? How do we establish fundamental design principles for the development of other organic semiconductors of high mobility? These questions are critically important but not comprehensive, as the nature of

  14. Ultrafast charge carrier relaxation and charge transfer processes in CdS/CdTe thin films.

    PubMed

    Pandit, Bill; Dharmadasa, Ruvini; Dharmadasa, I M; Druffel, Thad; Liu, Jinjun

    2015-07-14

    Ultrafast transient absorption pump-probe spectroscopy (TAPPS) has been employed to investigate charge carrier relaxation in cadmium sulfide/cadmium telluride (CdS/CdTe) nanoparticle (NP)-based thin films and electron transfer (ET) processes between CdTe and CdS. Effects of post-growth annealing treatments to ET processes have been investigated by carrying out TAPPS experiments on three CdS/CdTe samples: as deposited, heat treated, and CdCl2 treated. Clear evidence of ET process in the treated thin films has been observed by comparing transient absorption (TA) spectra of CdS/CdTe thin films to those of CdS and CdTe. Quantitative comparison between ultrafast kinetics at different probe wavelengths unravels the ET processes and enables determination of its rate constants. Implication of the photoinduced dynamics to photovoltaic devices is discussed. PMID:26033446

  15. Charge carrier transport in polycrystalline organic thin film based field effect transistors

    NASA Astrophysics Data System (ADS)

    Rani, Varsha; Sharma, Akanksha; Ghosh, Subhasis

    2016-05-01

    The charge carrier transport mechanism in polycrystalline thin film based organic field effect transistors (OFETs) has been explained using two competing models, multiple trapping and releases (MTR) model and percolation model. It has been shown that MTR model is most suitable for explaining charge carrier transport in grainy polycrystalline organic thin films. The energetic distribution of traps determined independently using Mayer-Neldel rule (MNR) is in excellent agreement with the values obtained by MTR model for copper phthalocyanine and pentacene based OFETs.

  16. Single Charge Current in a Normal Mesoscopic Region Attached to Superconductor Leads via a Coupled Poisson Nonequilibrium Green Function Formalism

    PubMed Central

    Marin, F. P.

    2014-01-01

    We study the I-V characteristic of mesoscopic systems or quantum dot (QD) attached to a pair of superconducting leads. Interaction effects in the QD are considered through the charging energy of the QD; that is, the treatment of current transport under a voltage bias is performed within a coupled Poisson nonequilibrium Green function (PNEGF) formalism. We derive the expression for the current in full generality but consider only the regime where transport occurs only via a single particle current. We show for this case and for various charging energies values U 0 and associated capacitances of the QD the effect on the I-V characteristic. Also the influence of the coupling constants on the I-V characteristic is investigated. Our approach puts forward a novel interpretation of experiments in the strong Coulomb regime. PMID:24977220

  17. Single charge current in a normal mesoscopic region attached to superconductor leads via a coupled poisson nonequilibrium green function formalism.

    PubMed

    Verrilli, David; Marin, F P; Rangel, Rafael

    2014-01-01

    We study the I-V characteristic of mesoscopic systems or quantum dot (QD) attached to a pair of superconducting leads. Interaction effects in the QD are considered through the charging energy of the QD; that is, the treatment of current transport under a voltage bias is performed within a coupled Poisson nonequilibrium Green function (PNEGF) formalism. We derive the expression for the current in full generality but consider only the regime where transport occurs only via a single particle current. We show for this case and for various charging energies values U 0 and associated capacitances of the QD the effect on the I-V characteristic. Also the influence of the coupling constants on the I-V characteristic is investigated. Our approach puts forward a novel interpretation of experiments in the strong Coulomb regime.

  18. Earthquake lights and the stress-activation of positive hole charge carriers in rocks

    USGS Publications Warehouse

    St-Laurent, F.; Derr, J.S.; Freund, F.T.

    2006-01-01

    Earthquake-related luminous phenomena (also known as earthquake lights) may arise from (1) the stress-activation of positive hole (p-hole) charge carriers in igneous rocks and (2) the accumulation of high charge carrier concentrations at asperities in the crust where the stress rates increase very rapidly as an earthquake approaches. It is proposed that, when a critical charge carrier concentration is reached, the p-holes form a degenerated solid state plasma that can break out of the confined rock volume and propagate as a rapidly expanding charge cloud. Upon reaching the surface the charge cloud causes dielectric breakdown at the air-rock interface, i.e. corona discharges, accompanied by the emission of light and high frequency electromagnetic radiation. ?? 2006 Elsevier Ltd. All rights reserved.

  19. Curl flux, coherence, and population landscape of molecular systems: Nonequilibrium quantum steady state, energy (charge) transport, and thermodynamics

    SciTech Connect

    Zhang, Z. D.; Wang, J.

    2014-06-28

    We established a theoretical framework in terms of the curl flux, population landscape, and coherence for non-equilibrium quantum systems at steady state, through exploring the energy and charge transport in molecular processes. The curl quantum flux plays the key role in determining transport properties and the system reaches equilibrium when flux vanishes. The novel curl quantum flux reflects the degree of non-equilibriumness and the time-irreversibility. We found an analytical expression for the quantum flux and its relationship to the environmental pumping (non-equilibriumness quantified by the voltage away from the equilibrium) and the quantum tunneling. Furthermore, we investigated another quantum signature, the coherence, quantitatively measured by the non-zero off diagonal element of the density matrix. Populations of states give the probabilities of individual states and therefore quantify the population landscape. Both curl flux and coherence depend on steady state population landscape. Besides the environment-assistance which can give dramatic enhancement of coherence and quantum flux with high voltage at a fixed tunneling strength, the quantum flux is promoted by the coherence in the regime of small tunneling while reduced by the coherence in the regime of large tunneling, due to the non-monotonic relationship between the coherence and tunneling. This is in contrast to the previously found linear relationship. For the systems coupled to bosonic (photonic and phononic) reservoirs the flux is significantly promoted at large voltage while for fermionic (electronic) reservoirs the flux reaches a saturation after a significant enhancement at large voltage due to the Pauli exclusion principle. In view of the system as a quantum heat engine, we studied the non-equilibrium thermodynamics and established the analytical connections of curl quantum flux to the transport quantities such as energy (charge) transfer efficiency, chemical reaction efficiency, energy

  20. Curl flux, coherence, and population landscape of molecular systems: nonequilibrium quantum steady state, energy (charge) transport, and thermodynamics.

    PubMed

    Zhang, Zhedong; Wang, Jin; Zhang, Z D; Wang, J

    2014-06-28

    We established a theoretical framework in terms of the curl flux, population landscape, and coherence for non-equilibrium quantum systems at steady state, through exploring the energy and charge transport in molecular processes. The curl quantum flux plays the key role in determining transport properties and the system reaches equilibrium when flux vanishes. The novel curl quantum flux reflects the degree of non-equilibriumness and the time-irreversibility. We found an analytical expression for the quantum flux and its relationship to the environmental pumping (non-equilibriumness quantified by the voltage away from the equilibrium) and the quantum tunneling. Furthermore, we investigated another quantum signature, the coherence, quantitatively measured by the non-zero off diagonal element of the density matrix. Populations of states give the probabilities of individual states and therefore quantify the population landscape. Both curl flux and coherence depend on steady state population landscape. Besides the environment-assistance which can give dramatic enhancement of coherence and quantum flux with high voltage at a fixed tunneling strength, the quantum flux is promoted by the coherence in the regime of small tunneling while reduced by the coherence in the regime of large tunneling, due to the non-monotonic relationship between the coherence and tunneling. This is in contrast to the previously found linear relationship. For the systems coupled to bosonic (photonic and phononic) reservoirs the flux is significantly promoted at large voltage while for fermionic (electronic) reservoirs the flux reaches a saturation after a significant enhancement at large voltage due to the Pauli exclusion principle. In view of the system as a quantum heat engine, we studied the non-equilibrium thermodynamics and established the analytical connections of curl quantum flux to the transport quantities such as energy (charge) transfer efficiency, chemical reaction efficiency, energy

  1. Direct observation of charge-carrier heating at WZ-ZB InP nanowire heterojunctions.

    PubMed

    Yong, Chaw Keong; Wong-Leung, Jennifer; Joyce, Hannah J; Lloyd-Hughes, James; Gao, Qiang; Tan, H Hoe; Jagadish, Chennupati; Johnston, Michael B; Herz, Laura M

    2013-09-11

    We have investigated the dynamics of hot charge carriers in InP nanowire ensembles containing a range of densities of zinc-blende inclusions along the otherwise wurtzite nanowires. From time-dependent photoluminescence spectra, we extract the temperature of the charge carriers as a function of time after nonresonant excitation. We find that charge-carrier temperature initially decreases rapidly with time in accordance with efficient heat transfer to lattice vibrations. However, cooling rates are subsequently slowed and are significantly lower for nanowires containing a higher density of stacking faults. We conclude that the transfer of charges across the type II interface is followed by release of additional energy to the lattice, which raises the phonon bath temperature above equilibrium and impedes the carrier cooling occurring through interaction with such phonons. These results demonstrate that type II heterointerfaces in semiconductor nanowires can sustain a hot charge-carrier distribution over an extended time period. In photovoltaic applications, such heterointerfaces may hence both reduce recombination rates and limit energy losses by allowing hot-carrier harvesting.

  2. Strong Asymmetric Charge Carrier Dependence in Inelastic Electron Tunneling Spectroscopy of Graphene Phonons.

    PubMed

    Natterer, Fabian D; Zhao, Yue; Wyrick, Jonathan; Chan, Yang-Hao; Ruan, Wen-Ying; Chou, Mei-Yin; Watanabe, Kenji; Taniguchi, Takashi; Zhitenev, Nikolai B; Stroscio, Joseph A

    2015-06-19

    The observation of phonons in graphene by inelastic electron tunneling spectroscopy has been met with limited success in previous measurements arising from weak signals and other spectral features which inhibit a clear distinction between phonons and miscellaneous excitations. Utilizing a back-gated graphene device that allows adjusting the global charge carrier density, we introduce an averaging method where individual tunneling spectra at varying charge carrier density are combined into one representative spectrum. This method improves the signal for inelastic transitions while it suppresses dispersive spectral features. We thereby map the total graphene phonon density of states, in good agreement with density functional calculations. Unexpectedly, an abrupt change in the phonon intensity is observed when the graphene charge carrier type is switched through a variation of the back-gate electrode potential. This sudden variation in phonon intensity is asymmetric in the carrier type, depending on the sign of the tunneling bias.

  3. 75 FR 18255 - Passenger Facility Charge Database System for Air Carrier Reporting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-09

    ... Federal Aviation Administration Passenger Facility Charge Database System for Air Carrier Reporting AGENCY... interested parties of the availability of the Passenger Facility Charge (PFC) database system to report PFC... public agency. The FAA has developed a national PFC database system in order to more easily track the...

  4. Charge-reversal nanoparticles: novel targeted drug delivery carriers.

    PubMed

    Chen, Xinli; Liu, Lisha; Jiang, Chen

    2016-07-01

    Spurred by significant progress in materials chemistry and drug delivery, charge-reversal nanocarriers are being developed to deliver anticancer formulations in spatial-, temporal- and dosage-controlled approaches. Charge-reversal nanoparticles can release their drug payload in response to specific stimuli that alter the charge on their surface. They can elude clearance from the circulation and be activated by protonation, enzymatic cleavage, or a molecular conformational change. In this review, we discuss the physiological basis for, and recent advances in the design of charge-reversal nanoparticles that are able to control drug biodistribution in response to specific stimuli, endogenous factors (changes in pH, redox gradients, or enzyme concentration) or exogenous factors (light or thermos-stimulation). PMID:27471667

  5. Controlling the screening process of a nanoscaled space charge region by minority carriers

    PubMed Central

    Kloth, Philipp; Kaiser, Katharina; Wenderoth, Martin

    2016-01-01

    The miniaturization of future electronic devices is intimately connected to the ability to control electric fields on the atomic scale. In a nanoscopic system defined by a limited number of charges, the combined dynamics of bound and free charges become important. Here we present a model system based on the electrostatic interaction between a metallic tip of a scanning tunnelling microscope and a GaAs(110) semiconductor surface. The system is driven out of equilibrium by optical excitation, which provides ambipolar free charge carriers, and by an optically induced unipolar tunnel current. This combination enables the active control of the density and spatial distribution of free and bound charge in the space-charge region, that is, modifying the screening processes. Temporal fluctuations of single dopants are modified, meaning we are able to control the noise of the system. It is found that free charge carriers suppress the noise level in field-controlled, nanoscopic systems. PMID:26728867

  6. Slower carriers limit charge generation in organic semiconductor light-harvesting systems

    PubMed Central

    Stolterfoht, Martin; Armin, Ardalan; Shoaee, Safa; Kassal, Ivan; Burn, Paul; Meredith, Paul

    2016-01-01

    Blends of electron-donating and -accepting organic semiconductors are widely used as photoactive materials in next-generation solar cells and photodetectors. The yield of free charges in these systems is often determined by the separation of interfacial electron–hole pairs, which is expected to depend on the ability of the faster carrier to escape the Coulomb potential. Here we show, by measuring geminate and non-geminate losses and key transport parameters in a series of bulk-heterojunction solar cells, that the charge-generation yield increases with increasing slower carrier mobility. This is in direct contrast with the well-established Braun model where the dissociation rate is proportional to the mobility sum, and recent models that underscore the importance of fullerene aggregation for coherent electron propagation. The behaviour is attributed to the restriction of opposite charges to different phases, and to an entropic contribution that favours the joint separation of both charge carriers. PMID:27324720

  7. Slower carriers limit charge generation in organic semiconductor light-harvesting systems.

    PubMed

    Stolterfoht, Martin; Armin, Ardalan; Shoaee, Safa; Kassal, Ivan; Burn, Paul; Meredith, Paul

    2016-01-01

    Blends of electron-donating and -accepting organic semiconductors are widely used as photoactive materials in next-generation solar cells and photodetectors. The yield of free charges in these systems is often determined by the separation of interfacial electron-hole pairs, which is expected to depend on the ability of the faster carrier to escape the Coulomb potential. Here we show, by measuring geminate and non-geminate losses and key transport parameters in a series of bulk-heterojunction solar cells, that the charge-generation yield increases with increasing slower carrier mobility. This is in direct contrast with the well-established Braun model where the dissociation rate is proportional to the mobility sum, and recent models that underscore the importance of fullerene aggregation for coherent electron propagation. The behaviour is attributed to the restriction of opposite charges to different phases, and to an entropic contribution that favours the joint separation of both charge carriers. PMID:27324720

  8. Comprehensive approach to intrinsic charge carrier mobility in conjugated organic molecules, macromolecules, and supramolecular architectures.

    PubMed

    Saeki, Akinori; Koizumi, Yoshiko; Aida, Takuzo; Seki, Shu

    2012-08-21

    Si-based inorganic electronics have long dominated the semiconductor industry. However, in recent years conjugated polymers have attracted increasing attention because such systems are flexible and offer the potential for low-cost, large-area production via roll-to-roll processing. The state-of-the-art organic conjugated molecular crystals can exhibit charge carrier mobilities (μ) that nearly match or even exceed that of amorphous silicon (1-10 cm(2) V(-1) s(-1)). The mean free path of the charge carriers estimated from these mobilities corresponds to the typical intersite (intermolecular) hopping distances in conjugated organic materials, which strongly suggests that the conduction model for the electronic band structure only applies to μ > 1 cm(2) V(-1) s(-1) for the translational motion of the charge carriers. However, to analyze the transport mechanism in organic electronics, researchers conventionally use a disorder formalism, where μ is usually less than 1 cm(2) V(-1) s(-1) and dominated by impurities, disorders, or defects that disturb the long-range translational motion. In this Account, we discuss the relationship between the alternating-current and direct-current mobilities of charge carriers, using time-resolved microwave conductivity (TRMC) and other techniques including field-effect transistor, time-of-flight, and space-charge limited current. TRMC measures the nanometer-scale mobility of charge carriers under an oscillating microwave electric field with no contact between the semiconductors and the metals. This separation allows us to evaluate the intrinsic charge carrier mobility with minimal trapping effects. We review a wide variety of organic electronics in terms of their charge carrier mobilities, and we describe recent studies of macromolecules, molecular crystals, and supramolecular architecture. For example, a rigid poly(phenylene-co-ethynylene) included in permethylated cyclodextrin shows a high intramolecular hole mobility of 0.5 cm(2) V

  9. Picosecond charge transport in rutile at high carrier densities studied by transient terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Zajac, V.; Němec, H.; Kužel, P.

    2016-09-01

    We study terahertz photoconductivity of a rutile single crystal between 10 and 300 K under strong photoexcitation by femtosecond pulses at 266 nm. A marked dependence of the carrier mobility on the carrier density is observed leading to highly complex transport phenomena on a picosecond time scale. We develop a general model of carrier photoconductive response in the case of time dependent inhomogeneous distribution of carrier density and mobility. This allows us to assess an important role of both electrons and holes in the response of photoexcited rutile. At low temperatures, the carrier mobility is initially reduced due to the electron-hole scattering and increases by one order of magnitude upon ambipolar diffusion of the carriers into deeper regions of the sample. At room temperature, contributions of transient hot optical phonons and/or of midinfrared polaron excitations with charge-density-dependent dielectric strength emerge in the photoconductivity spectra.

  10. Stabilization of Charge Carriers in Picket-Fence Polythiophenes Using Dielectric Side Chains.

    PubMed

    Zhao, Chunhui; Sakurai, Tsuneaki; Yoneda, Satoru; Seki, Shu; Sugimoto, Manabu; Oki, Choji; Takeuchi, Masayuki; Sugiyasu, Kazunori

    2016-08-19

    Insulated molecular wires (IMWs) are π-conjugated polymers that are molecularly sheathed with an insulating layer and are structurally analogous to electric power cords at the nanoscale. Such unique architectures are expected in molecular electronics and organic devices. Herein, we propose a new molecular design concept of IMWs, in which the sheaths can be customized, thereby enabling the modulation of the electronic properties of the interior π-conjugated systems. To this end, we focused our attention on the dielectric constant of the sheaths, as it governs the electrostatic interaction between charges. Upon doping, charge carriers, such as polaron and bipolaron, were generated regardless of the dielectric properties of the sheaths. Flash-photolysis time-resolved microwave conductivity measurements revealed that intrawire charge carrier mobility was independent of the sheaths. However, we found that the charge carriers could be stabilized by the sheaths with a high dielectric constant owing to the charge screening effect. We expect that IMWs designed in this way will be useful in a variety of applications, where the nature of charge carriers plays an important role, and particularly when redox switching is required (e.g., electrochromic, magnetic, and memory applications). PMID:27503254

  11. Dynamics of charge transfer: Rate processes formulated with nonequilibrium Green's functions

    SciTech Connect

    Yeganeh, Sina; Ratner, Mark A.; Mujica, Vladimiro

    2007-04-28

    The authors examine the connection between electron transport under bias in a junction and nonadiabatic intramolecular electron transfer (ET). It is shown that under certain assumptions it is possible to define a stationary current that allows the computation of the intramolecular transfer rate using the same formalism that is employed in the description of transport. They show that the nonequilibrium Green's function formalism of quantum transport can be used to calculate the ET rate. The formal connection between electron transport and electron transfer is made, and they work out the simple case of an electronic level coupled to a vibrational mode representing a thermal bath and show that the result is the same as expected from a Fermi golden rule treatment, and in the high-temperature limit yields the Marcus electron transfer theory. The usefulness of this alternative formulation of rates is discussed.

  12. Probing charge transfer and hot carrier dynamics in organic solar cells with terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Cunningham, Paul D.; Lane, Paul A.; Melinger, Joseph S.; Esenturk, Okan; Heilweil, Edwin J.

    2016-04-01

    Time-resolved terahertz spectroscopy (TRTS) was used to explore charge generation, transfer, and the role of hot carriers in organic solar cell materials. Two model molecular photovoltaic systems were investigated: with zinc phthalocyanine (ZnPc) or alpha-sexathiophene (α-6T) as the electron donors and buckminsterfullerene (C60) as the electron acceptor. TRTS provides charge carrier conductivity dynamics comprised of changes in both population and mobility. By using time-resolved optical spectroscopy in conjunction with TRTS, these two contributions can be disentangled. The sub-picosecond photo-induced conductivity decay dynamics of C60 were revealed to be caused by auto-ionization: the intrinsic process by which charge is generated in molecular solids. In donor-acceptor blends, the long-lived photo-induced conductivity is used for weight fraction optimization of the constituents. In nanoscale multilayer films, the photo-induced conductivity identifies optimal layer thicknesses. In films of ZnPc/C60, electron transfer from ZnPc yields hot charges that localize and become less mobile as they thermalize. Excitation of high-lying Franck Condon states in C60 followed by hole-transfer to ZnPc similarly produces hot charge carriers that self-localize; charge transfer clearly precedes carrier cooling. This picture is contrasted to charge transfer in α-6T/C60, where hole transfer takes place from a thermalized state and produces equilibrium carriers that do not show characteristic signs of cooling and self-localization. These results illustrate the value of terahertz spectroscopic methods for probing charge transfer reactions.

  13. Unraveling Charge Carriers Generation, Diffusion, and Recombination in Formamidinium Lead Triiodide Perovskite Polycrystalline Thin Film.

    PubMed

    Piatkowski, Piotr; Cohen, Boiko; Ponseca, Carlito S; Salado, Manuel; Kazim, Samrana; Ahmad, Shahzada; Sundström, Villy; Douhal, Abderrazzak

    2016-01-01

    We report on studies of the formamidinium lead triiodide (FAPbI3) perovskite film using time-resolved terahertz (THz) spectroscopy (TRTS) and flash photolysis to explore charge carriers generation, migration, and recombination. The TRTS results show that upon femtosecond excitation above the absorption edge, the initial high photoconductivity (∼75 cm(2) V(-1) s(-1)) remains constant at least up to 8 ns, which corresponds to a diffusion length of 25 μm. Pumping below the absorption edge results in a mobility of 40 cm(2) V(-1) s(-1) suggesting lower mobility of charge carriers located at the bottom of the conduction band or shallow sub-bandgap states. Furthermore, analysis of the THz kinetics reveals rising components of <1 and 20 ps, reflecting dissociation of excitons having different binding energies. Flash photolysis experiments indicate that trapped charge carriers persist for milliseconds. PMID:26703885

  14. Assessing charge carrier trapping in silicon nanowires using picosecond conductivity measurements.

    PubMed

    Ulbricht, Ronald; Kurstjens, Rufi; Bonn, Mischa

    2012-07-11

    Free-standing semiconductor nanowires on bulk substrates are increasingly being explored as building blocks for novel optoelectronic devices such as tandem solar cells. Although carrier transport properties, such as mobility and trap densities, are essential for such applications, it has remained challenging to quantify these properties. Here, we report on a method that permits the direct, contact-free quantification of nanowire carrier diffusivity and trap densities in thin (∼25 nm wide) silicon nanowires-without any additional processing steps such as transfer of wires onto a substrate. The approach relies on the very different terahertz (THz) conductivity response of photoinjected carriers within the silicon nanowires from those in the silicon substrate. This allows quantifying both the picosecond dynamics and the efficiency of charge carrier transport from the silicon nanowires into the silicon substrate. Varying the excitation density allows for quantification of nanowire trap densities: for sufficiently low excitation fluences the diffusion process stalls because the majority of charge carriers become trapped at nanowire surface defects. Using a model that includes these effects, we determine both the diffusion constant and the nanowire trap density. The trap density is found to be orders of magnitude larger than the charge carrier density that would be generated by AM1.5 sunlight.

  15. Charge-Carrier Dynamics and Mobilities in Formamidinium Lead Mixed-Halide Perovskites.

    PubMed

    Rehman, Waqaas; Milot, Rebecca L; Eperon, Giles E; Wehrenfennig, Christian; Boland, Jessica L; Snaith, Henry J; Johnston, Michael B; Herz, Laura M

    2015-12-22

    The mixed-halide perovskite FAPb(Bry I1-y )3 is attractive for color-tunable and tandem solar cells. Bimolecular and Auger charge-carrier recombination rate constants strongly correlate with the Br content, y, suggesting a link with electronic structure. FAPbBr3 and FAPbI3 exhibit charge-carrier mobilities of 14 and 27 cm(2) V(-1) s(-1) and diffusion lengths exceeding 1 μm, while mobilities across the mixed Br/I system depend on crystalline phase disorder.

  16. Ferrocene-decorated nanocrystalline cellulose with charge carrier mobility.

    PubMed

    Eyley, Samuel; Shariki, Sara; Dale, Sara E C; Bending, Simon; Marken, Frank; Thielemans, Wim

    2012-04-24

    Ferrocene-decorated cellulose nanowhiskers were prepared by the grafting of ethynylferrocene onto azide functionalized cotton-derived cellulose nanowhiskers using azide-alkyne cycloaddition. Successful surface modification and retention of the crystalline morphology of the nanocrystals was confirmed by elemental analysis, inductively coupled plasma-atomic emission spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The coverage with ferrocenyl is high (approximately 1.14 × 10(-3) mol g(-1) or 4.6 × 10(13) mol cm(-2) corresponding to a specific area of 61 Å(2) per ferrocene). Cyclic voltammetry measurements of films formed by deposition of ferrocene-decorated nanowhiskers showed that this small spacing of redox centers along the nanowhisker surface allowed conduction hopping of electrons. The apparent diffusion coefficient for electron (or hole) hopping via Fe(III/II) surface sites is estimated as Dapp = 10(-19) m(2)s(-1) via impedance methods, a value significantly less than nonsolvated ferrocene polymers, which would be expected as the 1,2,3-triazole ring forms a rigid linker tethering the ferrocene to the nanowhisker surface. In part, this is believed to be also due to "bottleneck" diffusion of charges across contact points where individual cellulose nanowhiskers contact each other. However, the charge-communication across the nanocrystal surface opens up the potential for use of cellulose nanocrystals as a charge percolation template for the preparation of conducting films via covalent surface modification (with applications similar to those using adsorbed conducting polymers), for use in bioelectrochemical devices to gently transfer and remove electrons without the need for a solution-soluble redox mediator, or for the fabrication of three-dimensional self-assembled conducting networks.

  17. Niosomal carriers enhance oral bioavailability of carvedilol: effects of bile salt-enriched vesicles and carrier surface charge

    PubMed Central

    Arzani, Gelareh; Haeri, Azadeh; Daeihamed, Marjan; Bakhtiari-Kaboutaraki, Hamid; Dadashzadeh, Simin

    2015-01-01

    Carvedilol (CRV) is an antihypertensive drug with both alpha and beta receptor blocking activity used to preclude angina and cardiac arrhythmias. To overcome the low, variable oral bioavailability of CRV, niosomal formulations were prepared and characterized: plain niosomes (without bile salts), bile salt-enriched niosomes (bilosomes containing various percentages of sodium cholate or sodium taurocholate), and charged niosomes (negative, containing dicetyl phosphate and positive, containing hexadecyl trimethyl ammonium bromide). All formulations were characterized in terms of encapsulation efficiency, size, zeta potential, release profile, stability, and morphology. Various formulations were administered orally to ten groups of Wistar rats (n=6 per group). The plasma levels of CRV were measured by a validated high-performance liquid chromatography (HPLC) method and pharmacokinetic properties of different formulations were characterized. Contribution of lymphatic transport to the oral bioavailability of niosomes was also investigated using a chylomicron flow-blocking approach. Of the bile salt-enriched vesicles examined, bilosomes containing 20% sodium cholate (F2) and 30% sodium taurocholate (F5) appeared to give the greatest enhancement of intestinal absorption. The relative bioavailability of F2 and F5 formulations to the suspension was estimated to be 1.84 and 1.64, respectively. With regard to charged niosomes, the peak plasma concentrations (Cmax) of CRV for positively (F7) and negatively charged formulations (F10) were approximately 2.3- and 1.7-fold higher than after a suspension. Bioavailability studies also revealed a significant increase in extent of drug absorption from charged vesicles. Tissue histology revealed no signs of inflammation or damage. The study proved that the type and concentration of bile salts as well as carrier surface charge had great influences on oral bioavailability of niosomes. Blocking the lymphatic absorption pathway

  18. Finite-size scaling of charge carrier mobility in disordered organic semiconductors

    NASA Astrophysics Data System (ADS)

    Kordt, Pascal; Speck, Thomas; Andrienko, Denis

    2016-07-01

    Simulations of charge transport in amorphous semiconductors are often performed in microscopically sized systems. As a result, charge carrier mobilities become system-size dependent. We propose a simple method for extrapolating a macroscopic, nondispersive mobility from the system-size dependence of a microscopic one. The method is validated against a temperature-based extrapolation [A. Lukyanov and D. Andrienko, Phys. Rev. B 82, 193202 (2010), 10.1103/PhysRevB.82.193202]. In addition, we provide an analytic estimate of system sizes required to perform nondispersive charge transport simulations in systems with finite charge carrier density, derived from a truncated Gaussian distribution. This estimate is not limited to lattice models or specific rate expressions.

  19. Charge transfer polarisation wave and carrier pairing in the high T(sub c) copper oxides

    NASA Technical Reports Server (NTRS)

    Chakraverty, B. K.

    1990-01-01

    The High T(sub c) oxides are highly polarizable materials and are charge transfer insulators. The charge transfer polarization wave formalism is developed in these oxides. The dispersion relationships due to long range dipole-dipole interaction of a charge transfer dipole lattice are obtained in 3-D and 2-D. These are high frequency bosons and their coupling with carriers is weak and antiadiabatic in nature. As a result, the mass renormalization of the carriers is negligible in complete contrast to conventional electron-phonon interaction, that give polarons and bipolarons. Both bound and superconducting pairing is discussed for a model Hamiltonian valid in the antiadiabatic regime, both in 3-D and 2-D. The stability of the charge transfer dipole lattice has interesting consequences that are discussed.

  20. Spin-orbit-coupling induced torque in ballistic domain walls: Equivalence of charge-pumping and nonequilibrium magnetization formalisms

    NASA Astrophysics Data System (ADS)

    Yuan, Zhe; Kelly, Paul J.

    2016-06-01

    To study the effect of spin-orbit coupling (SOC) on spin-transfer torque in magnetic materials, we have implemented two theoretical formalisms that can accommodate SOC. Using the "charge-pumping" formalism, we find two contributions to the out-of-plane spin-transfer torque parameter β in ballistic Ni domain walls (DWs). For short DWs, the nonadiabatic reflection of conduction electrons caused by the rapid spatial variation of the exchange potential results in an out-of-plane torque that increases rapidly with decreasing DW length. For long DWs, the Fermi level conduction channel anisotropy that gives rise to an intrinsic DW resistance in the presence of SOC leads to a linear dependence of β on the DW length. To understand this counterintuitive divergence of β in the long DW limit, we use the "nonequilibrium magnetization" formalism to examine the spatially resolved spin-transfer torque. The SOC-induced out-of-plane torque in ballistic DWs is found to be quantitatively consistent with the values obtained using the charge-pumping calculations, indicating the equivalence of the two theoretical methods.

  1. Recombination in liquid filled ionisation chambers with multiple charge carrier species: Theoretical and numerical results

    NASA Astrophysics Data System (ADS)

    Aguiar, P.; González-Castaño, D. M.; Gómez, F.; Pardo-Montero, J.

    2014-10-01

    Liquid-filled ionisation chambers (LICs) are used in radiotherapy for dosimetry and quality assurance. Volume recombination can be quite important in LICs for moderate dose rates, causing non-linearities in the dose rate response of these detectors, and needs to be corrected for. This effect is usually described with Greening and Boag models for continuous and pulsed radiation respectively. Such models assume that the charge is carried by two different species, positive and negative ions, each of those species with a given mobility. However, LICs operating in non-ultrapure mode can contain different types of electronegative impurities with different mobilities, thus increasing the number of different charge carriers. If this is the case, Greening and Boag models can be no longer valid and need to be reformulated. In this work we present a theoretical and numerical study of volume recombination in parallel-plate LICs with multiple charge carrier species, extending Boag and Greening models. Results from a recent publication that reported three different mobilities in an isooctane-filled LIC have been used to study the effect of extra carrier species on recombination. We have found that in pulsed beams the inclusion of extra mobilities does not affect volume recombination much, a behaviour that was expected because Boag formula for charge collection efficiency does not depend on the mobilities of the charge carriers if the Debye relationship between mobilities and recombination constant holds. This is not the case in continuous radiation, where the presence of extra charge carrier species significantly affects the amount of volume recombination.

  2. Hybrid Perovskites for Photovoltaics: Charge-Carrier Recombination, Diffusion, and Radiative Efficiencies.

    PubMed

    Johnston, Michael B; Herz, Laura M

    2016-01-19

    Photovoltaic (PV) devices that harvest the energy provided by the sun have great potential as renewable energy sources, yet uptake has been hampered by the increased cost of solar electricity compared with fossil fuels. Hybrid metal halide perovskites have recently emerged as low-cost active materials in PV cells with power conversion efficiencies now exceeding 20%. Rapid progress has been achieved over only a few years through improvements in materials processing and device design. In addition, hybrid perovskites appear to be good light emitters under certain conditions, raising the prospect of applications in low-cost light-emitting diodes and lasers. Further optimization of such hybrid perovskite devices now needs to be supported by a better understanding of how light is converted into electrical currents and vice versa. This Account provides an overview of charge-carrier recombination and mobility mechanisms encountered in such materials. Optical-pump-terahertz-probe (OPTP) photoconductivity spectroscopy is an ideal tool here, because it allows the dynamics of mobile charge carriers inside the perovskite to be monitored following excitation with a short laser pulse whose photon energy falls into the range of the solar spectrum. We first review our insights gained from transient OPTP and photoluminescence spectroscopy on the mechanisms dominating charge-carrier recombination in these materials. We discuss that mono-molecular charge-recombination predominantly originates from trapping of charges, with trap depths being relatively shallow (tens of millielectronvolts) for hybrid lead iodide perovskites. Bimolecular recombination arises from direct band-to-band electron-hole recombination and is found to be in significant violation of the simple Langevin model. Auger recombination exhibits links with electronic band structure, in accordance with its requirement for energy and momentum conservation for all charges involved. We further discuss charge-carrier mobility

  3. Origin and distribution of charge carriers in LaAlO3-SrTiO3 oxide heterostructures in the high carrier density limit

    NASA Astrophysics Data System (ADS)

    Mukherjee, Sumanta; Pal, Banabir; Choudhury, Debraj; Sarkar, Indranil; Drube, Wolfgang; Gorgoi, Mihaela; Karis, Olof; Takagi, H.; Matsuno, Jobu; Sarma, D. D.

    2016-06-01

    Using hard x-ray photoelectron spectroscopy with variable photon energy (2-8 keV), we address the distribution of charge carriers in the prototypical LaAlO3 (LAO) and SrTiO3 (STO) oxide heterostructures with high carrier densities (1017cm-2 ). Our results demonstrate the presence of two distinct charge distributions in this system: one tied to the interface with a ˜1 -nm width and ˜2 -5 × 1014-cm-2 carrier concentration, while the other appears distributed nearly homogeneously through the bulk of STO corresponding to a much larger carrier contribution. Our results also establish bimodal oxygen vacancies, namely on top of LAO and throughout STO, quantitatively establishing these as the origin of the observed bimodal depth distribution of charge carriers in these highly doped sample.

  4. Mapping the spatial distribution of charge carriers in quantum-confined heterostructures

    PubMed Central

    Smith, Andrew M.; Lane, Lucas A.; Nie, Shuming

    2014-01-01

    Quantum-confined nanostructures are considered ‘artificial atoms’ because the wavefunctions of their charge carriers resemble those of atomic orbitals. For multiple-domain heterostructures, however, carrier wavefunctions are more complex and still not well understood. We have prepared a unique series of cation-exchanged HgxCd1−xTe quantum dots (QDs) and seven epitaxial core–shell QDs and measured their first and second exciton peak oscillator strengths as a function of size and chemical composition. A major finding is that carrier locations can be quantitatively mapped and visualized during shell growth or cation exchange simply using absorption transition strengths. These results reveal that a broad range of quantum heterostructures with different internal structures and band alignments exhibit distinct carrier localization patterns that can be used to further improve the performance of optoelectronic devices and enhance the brightness of QD probes for bioimaging. PMID:25080298

  5. Ab initio charge-carrier mobility model for amorphous molecular semiconductors

    NASA Astrophysics Data System (ADS)

    Massé, Andrea; Friederich, Pascal; Symalla, Franz; Liu, Feilong; Nitsche, Robert; Coehoorn, Reinder; Wenzel, Wolfgang; Bobbert, Peter A.

    2016-05-01

    Accurate charge-carrier mobility models of amorphous organic molecular semiconductors are essential to describe the electrical properties of devices based on these materials. The disordered nature of these semiconductors leads to percolative charge transport with a large characteristic length scale, posing a challenge to the development of such models from ab initio simulations. Here, we develop an ab initio mobility model using a four-step procedure. First, the amorphous morphology together with its energy disorder and intermolecular charge-transfer integrals are obtained from ab initio simulations in a small box. Next, the ab initio information is used to set up a stochastic model for the morphology and transfer integrals. This stochastic model is then employed to generate a large simulation box with modeled morphology and transfer integrals, which can fully capture the percolative charge transport. Finally, the charge-carrier mobility in this simulation box is calculated by solving a master equation, yielding a mobility function depending on temperature, carrier concentration, and electric field. We demonstrate the procedure for hole transport in two important molecular semiconductors, α -NPD and TCTA. In contrast to a previous study, we conclude that spatial correlations in the energy disorder are unimportant for α -NPD. We apply our mobility model to two types of hole-only α -NPD devices and find that the experimental temperature-dependent current density-voltage characteristics of all devices can be well described by only slightly decreasing the simulated energy disorder strength.

  6. Strain engineering the charged-impurity-limited carrier mobility in phosphorene

    NASA Astrophysics Data System (ADS)

    Mohammadi, Yawar; Nia, Borhan Arghavani

    2016-01-01

    We investigate, based on the tight-binding model and in the linear deformation regime, the strain dependence of the electronic band structure of phosphorene, exposed to a uniaxial strain in one of its principle directions, the normal, the armchair and the zigzag directions. We show that the electronic band structure of strained phosphorene, for the experimentally accessible carrier densities and the uniaxial strains, is well described by a strain-dependent decoupled electron-hole Hamiltonian. Then, employing the decoupled Hamiltonian, we consider the strain dependence of the charged-impurity-limited carrier mobility in phosphorene, for both types of carriers, arbitrary carrier densities and in both armchair and zigzag directions. We show that a uniaxial tensile (compressive) strain in the normal direction enhances (weakens) the anisotropy of the carrier mobility, while a uniaxial strain in the zigzag direction acts inversely. Moreover applying a uniaxial strain in the armchair direction is shown to be ineffective on the anisotropy of the carrier mobility. These will be explained based on the effects of the strains on the carrier effective masses.

  7. Implicit Water Simulations of Non-Equilibrium Charge Transport in Ion Channels

    NASA Astrophysics Data System (ADS)

    Ravaioli, U.; van der Straaten, T. A.; Kathawala, G.

    Ion channels are natural nano-channels found in the membranes of all living cells, which exhibit a broad range of specific device-like functions to help regulate cell physiology. The study of charge transport in ion channels is imperative to understand how charge regulation is accomplished at the molecular level if one is to develop nanoscale artificial systems that mimic biological function and detection. Although Molecular Dynamics is the most popular approach to simulate ion channel behavior, the computational cost of representing all water molecules and ions in the system is prohibitive to study the timescales required to resolve ionic current and lead to structure design. A hierarchy of models of decreasing complexity is needed to address simulation of different time and space scales, similar to the set of models developed to study transport in semiconductors. This paper discusses the application of Monte Carlo and Drift-diffusion methods to simulate transport in ion channels, using the ompF porin channel as a prototype.

  8. Determination of charge carrier concentration in doped nonpolar liquids by impedance spectroscopy in the presence of charge adsorption.

    PubMed

    Yezer, Benjamin A; Khair, Aditya S; Sides, Paul J; Prieve, Dennis C

    2016-05-01

    The impedance of dodecane doped with sorbitan trioleate (Span 85), sorbitan monooleate (Span 80) and sorbitan monolaurate (Span 20) was measured as a function of frequency using a 10 mV amplitude sinusoidal voltage applied across a parallel plate cell with a 10 μm spacing. The tested solutions varied in concentration from 1 mM to 100 mM and the frequency range was 10(-2)-10(4) Hz. Nyquist plots of all three surfactants showed the high frequency semicircle characteristic of parallel resistance and capacitance but often exhibited a second semicircle at low frequencies which was attributed to charge adsorption and desorption. The electrical conductivity of each surfactant was proportional to surfactant concentration for concentrations above 10mM. Fitting the data to models for charge migration, differential capacitance, and adsorption allowed extraction of both charge concentration and two kinetic parameters that characterize the rate of adsorption and desorption. Above 10 mM the ratio of charge carriers per surfactant molecule was 22 ppm for Span 20, 3 ppm for Span 80, and 0.2 ppm for Span 85. A higher number of charge carriers per molecule of surfactant was associated with larger micelles. The adsorption rate constants were independent of surfactant concentration while the desorption rate constants were proportional to the surfactant concentration. This dependence indicated that uncharged surfactant, whether in micelles or not, participated in the desorption of charge. Predictions of the adsorption/desorption model for large constant electric fields agreed qualitatively with data from the literature (Karvar et al., 2014).

  9. On the nature of charge carrier scattering in Ag{sub 2}Se at low temperatures

    SciTech Connect

    Jafarov, M. B.

    2010-10-15

    The electric and thermoelectric properties of silver selenide in the temperature range of 4.2-300 K have been studied. The data obtained are interpreted within the theory of one-type carriers and Kane dispersion relation, with allowance for the character of electron-electron interaction. It is established that, for the concentrations n {<=} 7.8 x 10{sup 18} cm{sup -3}, charge carriers are scattered by impurity ions at T {<=} 30 K and by acoustic and optical phonons and point defects at T {>=} 30 K. Electron-electron interactions are found to be elastic at T < 30 K.

  10. Electrode configuration and signal subtraction technique for single polarity charge carrier sensing in ionization detectors

    DOEpatents

    Luke, P.

    1996-06-25

    An ionization detector electrode and signal subtraction apparatus and method provide at least one first conductive trace formed onto the first surface of an ionization detector. The first surface opposes a second surface of the ionization detector. At least one second conductive trace is also formed on the first surface of the ionization detector in a substantially interlaced and symmetrical pattern with the at least one first conductive trace. Both of the traces are held at a voltage potential of a first polarity type. By forming the traces in a substantially interlaced and symmetric pattern, signals generated by a charge carrier are substantially of equal strength with respect to both of the traces. The only significant difference in measured signal strength occurs when the charge carrier moves to within close proximity of the traces and is received at the collecting trace. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge and to determine the position at which the charge carrier originated within the ionization detector. 9 figs.

  11. Electrode configuration and signal subtraction technique for single polarity charge carrier sensing in ionization detectors

    DOEpatents

    Luke, Paul

    1996-01-01

    An ionization detector electrode and signal subtraction apparatus and method provides at least one first conductive trace formed onto the first surface of an ionization detector. The first surface opposes a second surface of the ionization detector. At least one second conductive trace is also formed on the first surface of the ionization detector in a substantially interlaced and symmetrical pattern with the at least one first conductive trace. Both of the traces are held at a voltage potential of a first polarity type. By forming the traces in a substantially interlaced and symmetric pattern, signals generated by a charge carrier are substantially of equal strength with respect to both of the traces. The only significant difference in measured signal strength occurs when the charge carrier moves to within close proximity of the traces and is received at the collecting trace. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge and to determine the position at which the charge carrier originated within the ionization detector.

  12. 41 CFR 302-7.103 - How are the charges calculated when a carrier charges a minimum weight, but the actual weight of...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 41 Public Contracts and Property Management 4 2010-07-01 2010-07-01 false How are the charges calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? 302-7.103 Section 302-7.103 Public Contracts and...

  13. 41 CFR 302-7.103 - How are the charges calculated when a carrier charges a minimum weight, but the actual weight of...

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 41 Public Contracts and Property Management 4 2011-07-01 2011-07-01 false How are the charges calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? 302-7.103 Section 302-7.103 Public Contracts and...

  14. 41 CFR 302-7.103 - How are the charges calculated when a carrier charges a minimum weight, but the actual weight of...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 41 Public Contracts and Property Management 4 2013-07-01 2012-07-01 true How are the charges calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? 302-7.103 Section 302-7.103 Public Contracts and...

  15. 41 CFR 302-7.103 - How are the charges calculated when a carrier charges a minimum weight, but the actual weight of...

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 41 Public Contracts and Property Management 4 2012-07-01 2012-07-01 false How are the charges calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? 302-7.103 Section 302-7.103 Public Contracts and...

  16. The non-random walk of chiral magnetic charge carriers in artificial spin ice

    PubMed Central

    Zeissler, K.; Walton, S. K.; Ladak, S.; Read, D. E.; Tyliszczak, T.; Cohen, L. F.; Branford, W. R.

    2013-01-01

    The flow of magnetic charge carriers (dubbed magnetic monopoles) through frustrated spin ice lattices, governed simply by Coulombic forces, represents a new direction in electromagnetism. Artificial spin ice nanoarrays realise this effect at room temperature, where the magnetic charge is carried by domain walls. Control of domain wall path is one important element of utilizing this new medium. By imaging the transit of domain walls across different connected 2D honeycomb structures we contribute an important aspect which will enable that control to be realized. Although apparently equivalent paths are presented to a domain wall as it approaches a Y-shaped vertex from a bar parallel to the field, we observe a stark non-random path distribution, which we attribute to the chirality of the magnetic charges. These observations are supported by detailed statistical modelling and micromagnetic simulations. The identification of chiral control to magnetic charge path selectivity invites analogy with spintronics. PMID:23409243

  17. Flexible cobalt-phthalocyanine thin films with high charge carrier mobility

    SciTech Connect

    Singh, Ajay; Kumar, Arvind; Kumar, Ashwini; Samanta, Soumen; Debnath, Anil K.; Jha, Purushottam; Prasad, Rajeshwar; Aswal, Dinesh K.; Gupta, Shiv K.; Salmi, Zakaria; Nowak, Sophie; Chehimi, Mohamed M.

    2012-11-26

    The structural and charge transport characteristics of cobalt phthalocyanine (CoPc) films deposited on flexible bi-axially oriented polyethylene terephthalate (BOPET) substrates are investigated. CoPc films exhibited a preferential (200) orientation with charge carrier mobility of {approx}118 cm{sup 2} V{sup -1} s{sup -1} (at 300 K). These films exhibited a reversible resistance changes upon bending them to different radius of curvature. The charge transport in CoPc films is governed by a bias dependent crossover from ohmic (J-V) to trap-free space-charge limited conduction (J-V{sup 2}). These results demonstrate that CoPc films on flexible BOPET having high mobility and high mechanical flexibility are a potential candidate for flexible electronic devices.

  18. Spectroscopy of Charge Carriers and Traps in Field-Doped Organic Semiconductors

    SciTech Connect

    Zhu, Xiaoyang; Frisbie, C Daniel

    2012-08-13

    This research project aims to achieve quantitative and molecular level understanding of charge carriers and traps in field-doped organic semiconductors via in situ optical absorption spectroscopy, in conjunction with time-resolved electrical measurements. During the funding period, we have made major progress in three general areas: (1) probed charge injection at the interface between a polymeric semiconductor and a polymer electrolyte dielectric and developed a thermodynamic model to quantitatively describe the transition from electrostatic to electrochemical doping; (2) developed vibrational Stark effect to probe electric field at buried organic semiconductor interfaces; (3) used displacement current measurement (DCM) to study charge transport at organic/dielectric interfaces and charge injection at metal/organic interfaces.

  19. Theoretical modeling of the terahertz response of ultrafast photoexcited charge carriers in graphene

    NASA Astrophysics Data System (ADS)

    Rustagi, Avinash; Stanton, Christopher J.

    2014-03-01

    We have formulated a semi-classical model to capture the terahertz response of photoexcited charge carriers in graphene. The model involves the time evolution of the initial carrier distribution function excited by a femtosecond laser pulse by solving the Boltzmann equation within the relaxation time approximation in presence of an in-plane DC electric field. We solve for the time dependent average velocity using the distribution function obtained from the Boltzmann equation. The time derivative of this average velocity is proportional to the terahertz signal measured in experiments. We also consider the contribution of virtual carriers to the terahertz signal. This model can also be applied to systems with a gapped graphene-like dispersion. Supported by NSF through grant OISE-0968405.

  20. Molecular ion battery: a rechargeable system without using any elemental ions as a charge carrier.

    PubMed

    Yao, Masaru; Sano, Hikaru; Ando, Hisanori; Kiyobayashi, Tetsu

    2015-06-04

    Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based "rocking chair" type battery.

  1. Molecular ion battery: a rechargeable system without using any elemental ions as a charge carrier

    PubMed Central

    Yao, Masaru; Sano, Hikaru; Ando, Hisanori; Kiyobayashi, Tetsu

    2015-01-01

    Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based “rocking chair” type battery. PMID:26043147

  2. Molecular ion battery: a rechargeable system without using any elemental ions as a charge carrier

    NASA Astrophysics Data System (ADS)

    Yao, Masaru; Sano, Hikaru; Ando, Hisanori; Kiyobayashi, Tetsu

    2015-06-01

    Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based “rocking chair” type battery.

  3. Plasmon-enhanced charge carrier generation in organic photovoltaic films using silver nanoprisms.

    PubMed

    Kulkarni, Abhishek P; Noone, Kevin M; Munechika, Keiko; Guyer, Samuel R; Ginger, David S

    2010-04-14

    We use photoinduced absorption spectroscopy to measure long-lived photogenerated charge carriers in optically thin donor/acceptor conjugated polymer blend films near plasmon-resonant silver nanoprisms. We measure up to 3 times more charge generation, as judged by the magnitude of the polaron absorption signal, in 35 nm thin blend films of poly(3-hexylthiophene)/phenyl-C(61)-butyric acid methyl ester on top of films of silver nanoprisms (approximately 40-100 nm edge length). We find that the polaron yields increase linearly with the total sample extinction. These excitation enhancements could in principle be used to increase photocurrents in thin organic solar cells.

  4. Charge carrier transport and photogeneration in P3HT:PCBM photovoltaic blends.

    PubMed

    Laquai, Frédéric; Andrienko, Denis; Mauer, Ralf; Blom, Paul W M

    2015-06-01

    This article reviews the charge transport and photogeneration in bulk-heterojunction solar cells made from blend films of regioregular poly(3-hexylthiophene) (RR-P3HT) and methano-fullerene (PCBM). The charge transport, specifically the hole mobility in the RR-P3HT phase of the polymer:fullerene photovoltaic blend, is dramatically affected by thermal annealing. The hole mobility increases more than three orders of magnitude and reaches a value of up to 2 × 10(-4) cm(2) V(-1) s(-1) after the thermal annealing process as a result of an improved semi-crystallinity of the film. This significant increase of the hole mobility balances the electron and hole mobilities in a photovoltaic blend in turn reducing space-charge formation, and this is the most important factor for the strong enhancement of the photovoltaic efficiency compared to an as cast, that is, non-annealed device. In fact, the balanced charge carrier mobility in RR-P3HT:PCBM blends in combination with a field- and temperature-independent charge carrier generation and greatly reduced non-geminate recombination explains the large quantum efficiencies mea-sured in P3HT:PCBM photovoltaic devices.

  5. Migration of excited charge carriers in arrays of phosphorus-doped silicon nanocrystals

    SciTech Connect

    Belyakov, V. A. Konakov, A. A.; Burdov, V. A.

    2010-11-15

    The rate of tunnel migration of excited charge carriers (electrons and holes) in the array of silicon nanocrystals doped with phosphorus is calculated. It is shown that, starting from certain phosphorus concentrations dependent on the relation between the dimensions of the emitting and accepting nanocrystals, the rate of tunneling of electrons sharply decreases (by several orders of magnitude) and becomes lower than the rate of interband radiative recombination

  6. Structural influences on charge carrier dynamics for small-molecule organic photovoltaics

    SciTech Connect

    Wang, Zhiping Shibata, Yosei; Yamanari, Toshihiro; Matsubara, Koji; Yoshida, Yuji; Miyadera, Tetsuhiko; Saeki, Akinori; Seki, Shu; Zhou, Ying

    2014-07-07

    We investigated the structural influences on the charge carrier dynamics in zinc phthalocyanine/fullerene (ZnPc/C{sub 60}) photovoltaic cells by introducing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and 2,5-bis(4-biphenylyl)-bithiophene (BP2T) between indium tin oxide and ZnPc layers. ZnPc films can be tuned to be round, long fiber-like, and short fiber-like structure, respectively. Time-resolved microwave conductivity measurements reveal that charge carrier lifetime in ZnPc/C{sub 60} bilayer films is considerably affected by the intra-grain properties. Transient photocurrent of ZnPc single films indicated that the charge carriers can transport for a longer distance in the long fiber-like grains than that in the round grains, due to the greatly lessened grain boundaries. By carefully controlling the structure of ZnPc films, the short-circuit current and fill factor of a ZnPc/C{sub 60} heterojunction solar cell with BP2T are significantly improved and the power conversion efficiency is increased to 2.6%, which is 120% larger than the conventional cell without BP2T.

  7. Structural influences on charge carrier dynamics for small-molecule organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Wang, Zhiping; Miyadera, Tetsuhiko; Saeki, Akinori; Zhou, Ying; Seki, Shu; Shibata, Yosei; Yamanari, Toshihiro; Matsubara, Koji; Yoshida, Yuji

    2014-07-01

    We investigated the structural influences on the charge carrier dynamics in zinc phthalocyanine/fullerene (ZnPc/C60) photovoltaic cells by introducing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and 2,5-bis(4-biphenylyl)-bithiophene (BP2T) between indium tin oxide and ZnPc layers. ZnPc films can be tuned to be round, long fiber-like, and short fiber-like structure, respectively. Time-resolved microwave conductivity measurements reveal that charge carrier lifetime in ZnPc/C60 bilayer films is considerably affected by the intra-grain properties. Transient photocurrent of ZnPc single films indicated that the charge carriers can transport for a longer distance in the long fiber-like grains than that in the round grains, due to the greatly lessened grain boundaries. By carefully controlling the structure of ZnPc films, the short-circuit current and fill factor of a ZnPc/C60 heterojunction solar cell with BP2T are significantly improved and the power conversion efficiency is increased to 2.6%, which is 120% larger than the conventional cell without BP2T.

  8. Optical generation of free charge carriers in thin films of tin oxide

    SciTech Connect

    Zhurbina, I. A. Tsetlin, O. I.; Timoshenko, V. Yu.

    2011-02-15

    The methods of infrared absorption spectroscopy and Raman spectroscopy are used to study nanocrystalline SnO{sub x} films (1 {<=} x {<=} 2) prepared by thermal oxidation of metallic tin layers. A monotonic decrease in the transmittance of films in the infrared region has been observed as a result of exposure of the films to light with the wavelength of 380 nm at room temperature. The effect is at a maximum for the samples with x Almost-Equal-To 2 and is observed for {approx}10 min after switching off of illumination. The mentioned variations in optical properties, similarly to those observed in the case of heating of the samples in the dark, are accounted for by an increase in the concentration of free charge carriers (electrons) in nanocrystals of tin dioxide. The data of infrared spectroscopy and the Drude model are used to calculate the concentrations of photogenerated charge carriers ({approx}10{sup 19} cm{sup -3}); variations in these concentrations in the course of illumination and after switching off of illumination are determined. Mechanisms of observed photogeneration of charge carriers in SnO{sub x} films and possible applications of this effect to gas sensors are discussed.

  9. Electrochemical characteristics of ideal polarizable interfaces with limited number of charge carriers

    NASA Astrophysics Data System (ADS)

    Přibyl, Michal; Slouka, Zdeněk

    2015-11-01

    Recent progress in material chemistry and surface engineering has led to emergence of new electrode materials with unique physical and electrochemical properties. Here, we introduce a physical model describing charging of ideal polarizable electrode-electrolyte interface where the electrode is characterized by a limited capacity to store charge. The analytical model treats the electrode and electrolyte phases as independent nonlinear capacitors that are eventually coupled through the condition of equality of the total stored electrical charge opposite in sign. Gouy-Chapman and condensed layer theories applied to a general 1 :n valent electrolyte are used to predict dependencies of differential capacitance of the electrolyte phase and surface concentration of the electrical charge on the applied potential. The model of the nonlinear capacitor for the electrode phase is described by a theory of electron donors and acceptors present in conductive solids as a result of thermal fluctuations. Both the differential capacitance and the surface concentration of the electrical charge in the electrode are evaluated as functions of the applied potential and related to the capacity of the electrode phase to accumulate charge and its ability to form electron donors and acceptors. The knowledge of capacitive properties of both phases allows to predict electrochemical characteristics of ideal polarizable interfaces, e.g., current responses in linear sweep voltammetry. The coupled model also shows significant potential drops in the electrode comparable to those in the electrolyte phase for materials with low charge carrier concentrations.

  10. In-situ imaging of charge carriers in an electrochemical cell.

    SciTech Connect

    Gerald, R. E. II

    1998-01-30

    A toroid cavity nuclear magnetic resonance (NMR) detector capable of quantitatively recording radial concentration profiles, diffusion constants, displacements of charge carriers, and radial profiles of spin-lattice relaxation time constants was employed to investigate the charge/discharge cycle of a solid-state electrochemical cell. One-dimensional radial concentration profiles (1D-images) of ions solvated in a polyethylene oxide matrix were recorded by {sup 19}F and {sup 7}Li NMR for several cells. A sequence of {sup 19}F NMR images, recorded at different stages of cell polarization, revealed the evolution of a region of the polymer depleted of charge carriers. From these images it is possible to extract the transference number for the Li{sup +} ion. Spatially localized diffusion coefficients and spin-lattice relaxation time constants can be measured simultaneously for the ions in the polymer electrolyte by a spin-labeling method that employs the radial B{sub 1}-field gradient of the toroid cavity. A spatial resolution of 7 {micro}m near the working electrode was achieved with a gradient strength of 800 gauss/cm. With this apparatus, it is also possible to investigate novel intercalation anode materials for lithium ion storage. These materials are coated onto the working electrode in a thin film. The penetration depth of lithium cations in these films can be imaged at different times in the charge/discharge cycle of the battery.

  11. Charge carrier trapping into mobile, ionic defects in nanoporous ultra-low-k dielectric materials

    NASA Astrophysics Data System (ADS)

    Plawsky, Joel; Borja, Juan; Lu, Toh-Ming; Gill, William

    2014-03-01

    Reliability and robustness of low-k materials for advanced interconnects has become a major challenge for the continuous down-scaling of silicon semiconductor devices. Metal catalyzed time dependent breakdown (TDDB) is a major force preventing the integration of sub-32nm process technology nodes. We investigate how ionic species can become trapping centers (mobile defects) for charge carriers. A mechanism for describing and quantifying the trapping of charge carriers into mobile ions under bias and temperature stress is presented and experimentally investigated. The dynamics of trapping into ionic centers are severely impacted by temperature and species mass transport. After extended bias and temperature stress, the magnitude of charge trapping into ionic centers decreases asymptotically. Various processes such as the reduction of ionic species, moisture outgassing, and the inhibition of ionic drift via the distortion of local fields were investigated as possible cause for the reduction in charge trapping. Simulations suggest that built-in fields reduce the effect of an externally applied field in directing ionic drift, which can lead to the inhibition of the trapping mechanism. In addition, conduction mechanisms are investigated for reactive and inert electrodes. Seimconductor Research Corporation.

  12. Revealing the ultrafast charge carrier dynamics in organo metal halide perovskite solar cell materials using time resolved THz spectroscopy.

    PubMed

    Ponseca, C S; Sundström, V

    2016-03-28

    Ultrafast charge carrier dynamics in organo metal halide perovskite has been probed using time resolved terahertz (THz) spectroscopy (TRTS). Current literature on its early time characteristics is unanimous: sub-ps charge carrier generation, highly mobile charges and very slow recombination rationalizing the exceptionally high power conversion efficiency for a solution processed solar cell material. Electron injection from MAPbI3 to nanoparticles (NP) of TiO2 is found to be sub-ps while Al2O3 NPs do not alter charge dynamics. Charge transfer to organic electrodes, Spiro-OMeTAD and PCBM, is sub-ps and few hundreds of ps respectively, which is influenced by the alignment of energy bands. It is surmised that minimizing defects/trap states is key in optimizing charge carrier extraction from these materials.

  13. Nature and the Sign of Stress-Activated Electronic Charge Carriers in Rocks

    NASA Astrophysics Data System (ADS)

    Freund, F.

    2013-12-01

    When rocks are subjected to increasing uniaxial stress, highly mobile charge carriers become activated, which have the remarkable ability to flow out of the stressed rock volume, spreading into and through adjacent less stressed or unstressed rocks. Two basic questions arise: (i) What is the nature - and the sign - of these charge carriers and (ii) How do they exist in the rocks before being activated by stress? A large body of evidence is available that points to a positive sign, consistent with defect electrons, which (in semiconductor parlance) are called 'holes'. Holes that reside in the oxygen anion sublattice, associated with O 2sp-type energy states at the upper edge of the valence band, are called 'positive holes'. The positive holes exist in rocks in form of dormant, electrically inactive peroxy defects. Ever so slight deformation, leading to grain-grain sliding, can break the peroxy bonds and activate positive holes. Electrons that are co-activated by the same process cannot flow out of the stressed rock volume into the unstressed rocks. This leads to charge separation and, hence, to a potential difference similar to a battery voltage. In order to experimentally confirm the positive sign of the positive hole charge carriers flowing out of a given stressed rock volume, certain rules have to be obeyed. If not, unreliable results may be obtained, even negative outflow currents, seemingly inconsistent with the postulated positive sign of the positive hole charge carriers. Such errors can be avoided by taking into account that the charge outflow occurs in response to a 'battery potential', V, rapidly evolving between stressed and unstressed or less stressed parts of the rock. The current I given by Ohm's Law, I=V/R, is then limited by the internal resistance R. A second complicating factor arises from the fact that, as the positive holes are stress-activated and begin to flow out, they simultaneously recombine, returning to the dormant state. The ensuing

  14. Subsurface Imaging and Sensing of Charge Carrier Movements in the Earth’s Crust

    NASA Astrophysics Data System (ADS)

    Dahlgren, R.; Freund, F. T.; Lazarus, M.; Wang, J. S.; Rekenthaler, D.; Peters, R. D.; Duma, G.

    2009-12-01

    The DUSEL facility will enable unique opportunities for field experiments that would otherwise not be possible at surface facilities (Lesko, K.T., TAUP, 2007) and support a host of undergraduate and graduate educational projects. In this presentation, some of the proposed geophysics experiments will be described as part of the subsurface Imaging and Sensing (SIS) project to study charge carrier movement in crustal rock as a function of various perturbations. The electric conductivity of the Earth’s crust is dominated by positive hole charge carriers, e.g. mobile electron vacancy defects (EVD) in the oxygen anion sublattice of minerals that make up the bulk of crustal rocks. We are interested in (i) coupling of fundamental processes linked to the activation of additional EVDs in rocks deep in the crust subjected to tectonic stresses and the outflow of these charge carriers into the surrounding rocks, (ii) their manifestation across the electromagnetic spectrum and other measuands, (iii) induced forces that arise when these charge carriers are subjected to the episodic or daily magnetic field variations coming from geomagnetic storms or from the ionospheric current vortex, and (iv) in the movement of positive holes in the shallow crust when a thunderstorm system drifts overhead, dragging along a charge cloud in the ground. We propose to conduct active rock stressing experiments in situ using expanding grout technique (performing electrical, electromagnetic, and VolksMeter tilt measurements) and to monitor the electric and magnetic field variations penetrating into the Earth’s crust. Additionally optical phenomena will be investigated (anomalous infrared signatures, visible light arising from atomic oxygen and corona discharge, and infrared imaging). If budget permits, measurement of changes of acoustic velocity, evolution of chemical species (H2, O*, Rn, etc) and radar reflectivity as a function of stresses will also be attempted. We propose to study the charge

  15. Order induced charge carrier mobility enhancement in columnar liquid crystal diodes.

    PubMed

    Eccher, Juliana; Faria, Gregório C; Bock, Harald; von Seggern, Heinz; Bechtold, Ivan H

    2013-11-27

    Discotic molecules comprising a rigid aromatic core and flexible side chains have been promisingly applied in OLEDs as self-organizing organic semiconductors. Due to their potentially high charge carrier mobility along the columns, device performance can be readily improved by proper alignment of columns throughout the bulk. In the present work, the charge mobility was increased by 5 orders of magnitude due to homeotropic columnar ordering induced by the boundary interfaces during thermal annealing in the mesophase. State-of-the-art diodes were fabricated using spin-coated films whose homeotropic alignment with formation of hexagonal germs was observed by polarizing optical microscopy. The photophysical properties showed drastic changes at the mesophase-isotropic transition, which is supported by the gain of order observed by X-ray diffraction. The electrical properties were investigated by modeling the current-voltage characteristics by a space-charge-limited current transport with a field dependent mobility. PMID:24191748

  16. Charge carrier mobility of zigzag carbon nanotubes with monovacancy defects from a first-principle crystal orbital view

    NASA Astrophysics Data System (ADS)

    Ma, Yujia; Yin, Bing; Bai, Hongcun; Ding, Xin; Cao, Yu; Li, Qiang; Ji, Yongqaing

    2016-05-01

    This work presents first-principle investigations into the charge carrier mobility of carbon nanotubes containing monovacancy or related defects. The pristine and defective zigzag (10, 0) tubes were selected to explore the role of defects on the charge carrier mobility. It was found that the electron mobility of one defective structure was unexpectedly increased, while most others were decreased upon the appearance of the defect. To further understand the modification of the carrier mobility induced by monovacancy or related defects, crystal orbital analysis was performed. It was observed that the vacancy defect plays an important role in the case of both increased and decreased mobility. The unusual increased carrier mobility was mainly derived from the weaker acoustic scattering due to the modified wave-function induced by the defect. As for the decreased carrier mobilities, the heavier carrier determined by localized wave-functions, caused by the defects, is the most important factor.

  17. Charge Carrier Conduction Mechanism in PbS Quantum Dot Solar Cells: Electrochemical Impedance Spectroscopy Study.

    PubMed

    Wang, Haowei; Wang, Yishan; He, Bo; Li, Weile; Sulaman, Muhammad; Xu, Junfeng; Yang, Shengyi; Tang, Yi; Zou, Bingsuo

    2016-07-20

    With its properties of bandgap tunability, low cost, and substrate compatibility, colloidal quantum dots (CQDs) are becoming promising materials for optoelectronic applications. Additionally, solution-processed organic, inorganic, and hybrid ligand-exchange technologies have been widely used in PbS CQDs solar cells, and currently the maximum certified power conversion efficiency of 9.9% has been reported by passivation treatment of molecular iodine. Presently, there are still some challenges, and the basic physical mechanism of charge carriers in CQDs-based solar cells is not clear. Electrochemical impedance spectroscopy is a monitoring technology for current by changing the frequency of applied alternating current voltage, and it provides an insight into its electrical properties that cannot be measured by direct current testing facilities. In this work, we used EIS to analyze the recombination resistance, carrier lifetime, capacitance, and conductivity of two typical PbS CQD solar cells Au/PbS-TBAl/ZnO/ITO and Au/PbS-EDT/PbS-TBAl/ZnO/ITO, in this way, to better understand the charge carriers conduction mechanism behind in PbS CQD solar cells, and it provides a guide to design high-performance quantum-dots solar cells. PMID:27176547

  18. Charge carrier trapping and acoustic phonon modes in single CdTe nanowires.

    PubMed

    Lo, Shun Shang; Major, Todd A; Petchsang, Nattasamon; Huang, Libai; Kuno, Masaru K; Hartland, Gregory V

    2012-06-26

    Semiconductor nanostructures produced by wet chemical synthesis are extremely heterogeneous, which makes single particle techniques a useful way to interrogate their properties. In this paper the ultrafast dynamics of single CdTe nanowires are studied by transient absorption microscopy. The wires have lengths of several micrometers and lateral dimensions on the order of 30 nm. The transient absorption traces show very fast decays, which are assigned to charge carrier trapping into surface defects. The time constants vary for different wires due to differences in the energetics and/or density of surface trap sites. Measurements performed at the band edge compared to the near-IR give slightly different time constants, implying that the dynamics for electron and hole trapping are different. The rate of charge carrier trapping was observed to slow down at high carrier densities, which was attributed to trap-state filling. Modulations due to the fundamental and first overtone of the acoustic breathing mode were also observed in the transient absorption traces. The quality factors for these modes were similar to those measured for metal nanostructures, and indicate a complex interaction with the environment.

  19. Charge Carrier Conduction Mechanism in PbS Quantum Dot Solar Cells: Electrochemical Impedance Spectroscopy Study.

    PubMed

    Wang, Haowei; Wang, Yishan; He, Bo; Li, Weile; Sulaman, Muhammad; Xu, Junfeng; Yang, Shengyi; Tang, Yi; Zou, Bingsuo

    2016-07-20

    With its properties of bandgap tunability, low cost, and substrate compatibility, colloidal quantum dots (CQDs) are becoming promising materials for optoelectronic applications. Additionally, solution-processed organic, inorganic, and hybrid ligand-exchange technologies have been widely used in PbS CQDs solar cells, and currently the maximum certified power conversion efficiency of 9.9% has been reported by passivation treatment of molecular iodine. Presently, there are still some challenges, and the basic physical mechanism of charge carriers in CQDs-based solar cells is not clear. Electrochemical impedance spectroscopy is a monitoring technology for current by changing the frequency of applied alternating current voltage, and it provides an insight into its electrical properties that cannot be measured by direct current testing facilities. In this work, we used EIS to analyze the recombination resistance, carrier lifetime, capacitance, and conductivity of two typical PbS CQD solar cells Au/PbS-TBAl/ZnO/ITO and Au/PbS-EDT/PbS-TBAl/ZnO/ITO, in this way, to better understand the charge carriers conduction mechanism behind in PbS CQD solar cells, and it provides a guide to design high-performance quantum-dots solar cells.

  20. Generating free charges by carrier multiplication in quantum dots for highly efficient photovoltaics.

    PubMed

    Ten Cate, Sybren; Sandeep, C S Suchand; Liu, Yao; Law, Matt; Kinge, Sachin; Houtepen, Arjan J; Schins, Juleon M; Siebbeles, Laurens D A

    2015-02-17

    CONSPECTUS: In a conventional photovoltaic device (solar cell or photodiode) photons are absorbed in a bulk semiconductor layer, leading to excitation of an electron from a valence band to a conduction band. Directly after photoexcitation, the hole in the valence band and the electron in the conduction band have excess energy given by the difference between the photon energy and the semiconductor band gap. In a bulk semiconductor, the initially hot charges rapidly lose their excess energy as heat. This heat loss is the main reason that the theoretical efficiency of a conventional solar cell is limited to the Shockley-Queisser limit of ∼33%. The efficiency of a photovoltaic device can be increased if the excess energy is utilized to excite additional electrons across the band gap. A sufficiently hot charge can produce an electron-hole pair by Coulomb scattering on a valence electron. This process of carrier multiplication (CM) leads to formation of two or more electron-hole pairs for the absorption of one photon. In bulk semiconductors such as silicon, the energetic threshold for CM is too high to be of practical use. However, CM in nanometer sized semiconductor quantum dots (QDs) offers prospects for exploitation in photovoltaics. CM leads to formation of two or more electron-hole pairs that are initially in close proximity. For photovoltaic applications, these charges must escape from recombination. This Account outlines our recent progress in the generation of free mobile charges that result from CM in QDs. Studies of charge carrier photogeneration and mobility were carried out using (ultrafast) time-resolved laser techniques with optical or ac conductivity detection. We found that charges can be extracted from photoexcited PbS QDs by bringing them into contact with organic electron and hole accepting materials. However, charge localization on the QD produces a strong Coulomb attraction to its counter charge in the organic material. This limits the production

  1. Generating free charges by carrier multiplication in quantum dots for highly efficient photovoltaics.

    PubMed

    Ten Cate, Sybren; Sandeep, C S Suchand; Liu, Yao; Law, Matt; Kinge, Sachin; Houtepen, Arjan J; Schins, Juleon M; Siebbeles, Laurens D A

    2015-02-17

    CONSPECTUS: In a conventional photovoltaic device (solar cell or photodiode) photons are absorbed in a bulk semiconductor layer, leading to excitation of an electron from a valence band to a conduction band. Directly after photoexcitation, the hole in the valence band and the electron in the conduction band have excess energy given by the difference between the photon energy and the semiconductor band gap. In a bulk semiconductor, the initially hot charges rapidly lose their excess energy as heat. This heat loss is the main reason that the theoretical efficiency of a conventional solar cell is limited to the Shockley-Queisser limit of ∼33%. The efficiency of a photovoltaic device can be increased if the excess energy is utilized to excite additional electrons across the band gap. A sufficiently hot charge can produce an electron-hole pair by Coulomb scattering on a valence electron. This process of carrier multiplication (CM) leads to formation of two or more electron-hole pairs for the absorption of one photon. In bulk semiconductors such as silicon, the energetic threshold for CM is too high to be of practical use. However, CM in nanometer sized semiconductor quantum dots (QDs) offers prospects for exploitation in photovoltaics. CM leads to formation of two or more electron-hole pairs that are initially in close proximity. For photovoltaic applications, these charges must escape from recombination. This Account outlines our recent progress in the generation of free mobile charges that result from CM in QDs. Studies of charge carrier photogeneration and mobility were carried out using (ultrafast) time-resolved laser techniques with optical or ac conductivity detection. We found that charges can be extracted from photoexcited PbS QDs by bringing them into contact with organic electron and hole accepting materials. However, charge localization on the QD produces a strong Coulomb attraction to its counter charge in the organic material. This limits the production

  2. Kinetics of photo-activated charge carriers in Sn:CdS

    NASA Astrophysics Data System (ADS)

    Patidar, Manju Mishra; Panda, Richa; Gorli, V. R.; Gangrade, Mohan; Nath, R.; Ganesan, V.

    2016-05-01

    Kinetics of the photo-activated charge carriers has been investigated in Tin substituted Cadmium Sulphide, Cd1-xSnxS (x=0, 0.05, 0.10 and 0.15), thin films prepared by spray pyrolysis. X-Ray Diffraction shows an increase in strain that resulted in the decreased crystallite size upon Sn substitution. At the first sight, the photo current characteristics show a quenching effect on Sn substitution. However, survival of persistent photocurrents is seen even up to 15% of Sn substitution. Transient photo current decay could be explained with a 2τ relaxation model. CdS normally has an n-type character and the Sn doping expected to inject hole carriers. The two fold increase in τ1, increase in activation energy and the decrease in photocurrents upon Sn substitution point towards a band gap cleaning scenario that include compensation and associated carrier injection dynamics. In addition Atomic Force Microscopy shows a drastic change in microstructure that modulates the carrier dynamics as a whole.

  3. Charge-Carrier Dynamics in Organic-Inorganic Metal Halide Perovskites

    NASA Astrophysics Data System (ADS)

    Herz, Laura M.

    2016-05-01

    Hybrid organic-inorganic metal halide perovskites have recently emerged as exciting new light-harvesting and charge-transporting materials for efficient photovoltaic devices. Yet knowledge of the nature of the photogenerated excitations and their subsequent dynamics is only just emerging. This article reviews the current state of the field, focusing first on a description of the crystal and electronic band structure that give rise to the strong optical transitions that enable light harvesting. An overview is presented of the numerous experimental approaches toward determining values for exciton binding energies, which appear to be small (a few milli-electron volts to a few tens of milli-electron volts) and depend significantly on temperature because of associated changes in the dielectric function. Experimental evidence for charge-carrier relaxation dynamics within the first few picoseconds after excitation is discussed in terms of thermalization, cooling, and many-body effects. Charge-carrier recombination mechanisms are reviewed, encompassing trap-assisted nonradiative recombination that is highly specific to processing conditions, radiative bimolecular (electron-hole) recombination, and nonradiative many-body (Auger) mechanisms.

  4. Charge-Carrier Dynamics in Organic-Inorganic Metal Halide Perovskites.

    PubMed

    Herz, Laura M

    2016-05-27

    Hybrid organic-inorganic metal halide perovskites have recently emerged as exciting new light-harvesting and charge-transporting materials for efficient photovoltaic devices. Yet knowledge of the nature of the photogenerated excitations and their subsequent dynamics is only just emerging. This article reviews the current state of the field, focusing first on a description of the crystal and electronic band structure that give rise to the strong optical transitions that enable light harvesting. An overview is presented of the numerous experimental approaches toward determining values for exciton binding energies, which appear to be small (a few milli-electron volts to a few tens of milli-electron volts) and depend significantly on temperature because of associated changes in the dielectric function. Experimental evidence for charge-carrier relaxation dynamics within the first few picoseconds after excitation is discussed in terms of thermalization, cooling, and many-body effects. Charge-carrier recombination mechanisms are reviewed, encompassing trap-assisted nonradiative recombination that is highly specific to processing conditions, radiative bimolecular (electron-hole) recombination, and nonradiative many-body (Auger) mechanisms.

  5. Temporary Charge Carrier Separation Dominates the Photoluminescence Decay Dynamics of Colloidal CdSe Nanoplatelets.

    PubMed

    Rabouw, Freddy T; van der Bok, Johanna C; Spinicelli, Piernicola; Mahler, Benoît; Nasilowski, Michel; Pedetti, Silvia; Dubertret, Benoît; Vanmaekelbergh, Daniël

    2016-03-01

    Luminescent colloidal CdSe nanoplatelets with atomically defined thicknesses have recently been developed, and their potential for various applications has been shown. To understand their special properties, experiments have until now focused on the relatively short time scales of at most a few nanoseconds. Here, we measure the photoluminescence decay dynamics of colloidal nanoplatelets on time scales up to tens of microseconds. The excited state dynamics are found to be dominated by the slow (∼μs) dynamics of temporary exciton storage in a charge-separated state, previously overlooked. We study the processes of charge carrier separation and exciton recovery in pure CdSe nanoplatelets as well as in core-crown and core-shell CdSe/CdS nanoplatelets with high ensemble quantum yields of 50%, and discuss the implications. Our work highlights the importance of reversible charge carrier trapping and experiments over a wide range of time scales for the understanding of colloidal nanoemitters in general and nanoplatelets in particular. PMID:26863992

  6. Bimodal behaviour of charge carriers in graphene induced by electric double layer

    NASA Astrophysics Data System (ADS)

    Tsai, Sing-Jyun; Yang, Ruey-Jen

    2016-07-01

    A theoretical investigation is performed into the electronic properties of graphene in the presence of liquid as a function of the contact area ratio. It is shown that the electric double layer (EDL) formed at the interface of the graphene and the liquid causes an overlap of the conduction bands and valance bands and increases the density of state (DOS) at the Fermi energy (EF). In other words, a greater number of charge carriers are induced for transport and the graphene changes from a semiconductor to a semimetal. In addition, it is shown that the dependence of the DOS at EF on the contact area ratio has a bimodal distribution which responses to the experimental observation, a pinnacle curve. The maximum number of induced carriers is expected to occur at contact area ratios of 40% and 60%. In general, the present results indicate that modulating the EDL provides an effective means of tuning the electronic properties of graphene in the presence of liquid.

  7. Light-emitting quantum dot transistors: emission at high charge carrier densities.

    PubMed

    Schornbaum, Julia; Zakharko, Yuriy; Held, Martin; Thiemann, Stefan; Gannott, Florentina; Zaumseil, Jana

    2015-03-11

    For the application of colloidal semiconductor quantum dots in optoelectronic devices, for example, solar cells and light-emitting diodes, it is crucial to understand and control their charge transport and recombination dynamics at high carrier densities. Both can be studied in ambipolar, light-emitting field-effect transistors (LEFETs). Here, we report the first quantum dot light-emitting transistor. Electrolyte-gated PbS quantum dot LEFETs exhibit near-infrared electroluminescence from a confined region within the channel, which proves true ambipolar transport in ligand-exchanged quantum dot solids. Unexpectedly, the external quantum efficiencies improve significantly with current density. This effect correlates with the unusual increase of photoluminescence quantum yield and longer average lifetimes at higher electron and hole concentrations in PbS quantum dot thin films. We attribute the initially low emission efficiencies to nonradiative losses through trap states. At higher carrier densities, these trap states are deactivated and emission is dominated by trions.

  8. Contactless Spectral-dependent Charge Carrier Lifetime Measurements in Silicon Photovoltaic Materials

    NASA Astrophysics Data System (ADS)

    Roller, John; Hamadani, Behrang; Dagenais, Mario

    Charge carrier lifetime measurements in bulk or unfinished photovoltaic (PV) materials allow for a more accurate estimate of power conversion efficiency in completed solar cells. In this work, carrier lifetimes in PV-grade silicon wafers are obtained by way of quasi-steady state photoconductance measurements. These measurements use a contactless RF system coupled with varying narrow spectrum input LEDs, ranging in wavelength from 460 nm to 1030 nm. Spectral dependent lifetime measurements allow for determination of bulk and surface properties of the material, including the intrinsic bulk lifetime and the surface recombination velocity. The effective lifetimes are fit to an analytical physics-based model to determine the desired parameters. Passivated and non-passivated samples are both studied and are shown to have good agreement with the theoretical model.

  9. Charge Carrier Dynamics of Quantum Confined Semiconductor Nanoparticles Analyzed via Transient Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Thibert, Arthur Joseph, III

    Semiconductor nanoparticles are tiny crystalline structures (typically range from 1 - 100 nm) whose shape in many cases can be dictated through tailored chemical synthesis with atomic scale precision. The small size of these nanoparticles often results in quantum confinement (spatial confinement of wave functions), which imparts the ability to manipulate band-gap energies thus allowing them to be optimally engineered for different applications (i.e., photovoltaics, photocatalysis, imaging). However, charge carriers excited within these nanoparticles are often involved in many different processes: trapping, trap migration, Auger recombination, non-radiative relaxation, radiative relaxation, oxidation / reduction, or multiple exciton generation. Broadband ultrafast transient absorption laser spectroscopy is used to spectrally resolve the fate of excited charge carriers in both wavelength and time, providing insight as to what synthetic developments or operating conditions will be necessary to optimize their efficiency for certain applications. This thesis outlines the effort of resolving the dynamics of excited charge carriers for several Cd and Si based nanoparticle systems using this experimental technique. The thesis is organized into five chapters and two appendices as indicated below. Chapter 1 provides a brief introduction to the photophysics of semiconductor nanoparticles. It begins by defining what nanoparticles, semiconductors, charge carriers, and quantum confinement are. From there it details how the study of charge carrier dynamics within nanoparticles can lead to increased efficiency in applications such as photocatalysis. Finally, the experimental methodology associated with ultrafast transient absorption spectroscopy is introduced and its power in mapping charge carrier dynamics is established. Chapter 2 (JPCC, 19647, 2011) introduces the first of the studied samples: water-solubilized 2D CdSe nanoribbons (NRs), which were synthesized in the Osterloh

  10. Experimental measurements of charge carrier mobility: lifetime products for large sample of pixilated CZT detectors

    NASA Astrophysics Data System (ADS)

    Vadawale, S. V.; Shanmugam, M.; Purohit, Shishir; Acharya, Y. B.; Sudhakar, Manju

    2012-07-01

    Cadmium-Zinc-Telluride (CZT) is thought to be a primary work horse for hard X-ray astronomy in future. Due to the relatively large band-gap, it offers near room temperature operation while maintaining much better energy resolution then scintillator detectors operating in similar energy range. Further, CZT detectors are available in the form of pixilated detectors with area up to few cm2 and hence it is possible to realize very large detector area by having an array of such pixilated CZT detectors. However, it is well known that the energy spectrum of mono-energetic X-ray measured by CZT detectors does not have a Gaussian shape but has significant low-energy tail. This is mainly due to relatively poor mobility and small life time of the charge carriers, particularly of holes, in the CZT crystals. Thus, in order to understand spectral response for a large array of CZT detectors consisting of multiple elements / pixels, it is essential to characterize the mobility-lifetime products of charge carriers for each individual elements / pixels. Here we present experimental measurements of charge carrier mobility-lifetime products for large sample of multi-pixel CZT detectors. The mobility-lifetime products are measured by simultaneously fitting a ‘CZT line’ model to pixel wise spectra of 122 keV X-rays from 57Co at three different bias voltages. These were carried out as a part of selection of CZT detector modules for the “High Energy X-ray spectrometer (HEX)” onboard Indian moon mission - Chandrayaan-1.

  11. Plasma wave instabilities in nonequilibrium graphene

    NASA Astrophysics Data System (ADS)

    Aryal, Chinta M.; Hu, Ben Yu-Kuang; Jauho, Antti-Pekka

    2016-09-01

    We study two-stream instabilities in a nonequilibrium system in which a stream of electrons is injected into doped graphene. As with equivalent nonequilibrium parabolic band systems, we find that the graphene systems can support unstable charge-density waves whose amplitudes grow with time. We determine the range of wave vectors q that are unstable, and their growth rates. We find no instability for waves with wave vectors parallel or perpendicular to the direction of the injected carriers. We find that, within the small-wave-vector approximation, the angle between q and the direction of the injected electrons that maximizes the growth rate increases with increasing |q | . We compare the range and strength of the instability in graphene to that of two- and three-dimensional parabolic band systems.

  12. Charge-carrier dynamics in TiO sub 2 powders

    SciTech Connect

    Schindler, K.; Kunst, M. )

    1990-10-18

    Contactless transient photoconductivity measurements in TiO{sub 2} powder are presented. Large differences between the modifications anatase and rutile are observed with anatase exhibiting higher yields and longer lifetimes of photoinduced excess charge carriers. It is shown that surface modification drastically changes the electron decay kinetics, where adsorption of 2-propanol and of tetranitromethane leads to a lower and a higher decay rate, respectively. Platinization opens an additional fast decay channel. The results are discussed in view of their relevance for photocatalysis.

  13. Effective of the q-deformed pseudoscalar magnetic field on the charge carriers in graphene

    NASA Astrophysics Data System (ADS)

    Eshghi, M.; Mehraban, H.

    2016-08-01

    In this paper, we have obtained exact analytical solutions of the time-independent Dirac-Weyl equation for the charge carriers with q-deformed pseudoscalar magnetic barrier (PMB) in graphene by using the ansatz method. We have also found a solution that describes the left propagating wave function to calculation of the reflection and transmission coefficients using the Riemann's equation. This allows us to conclude about the Dirac-Weyl equation with PMB and to understand quantum behavior of the Dirac fermions. Finally, some of the numerical results are shown, too.

  14. Long-lived charge carrier dynamics in polymer/quantum dot blends and organometal halide perovskites

    NASA Astrophysics Data System (ADS)

    Nagaoka, Hirokazu

    Solution-processable semiconductors offer a potential route to deploy solar panels on a wide scale, based on the possibility of reduced manufacturing costs by using earth-abundant materials and inexpensive production technologies, such as inkjet or roll-to-roll printing. Understanding the fundamental physics underlying device operation is important to realize this goal. This dissertation describes studies of two kinds of solar cells: hybrid polymer/PbS quantum dot solar cells and organometal halide perovskite solar cells. Chapter two discusses details of the experimental techniques. Chapter three and four explore the mechanisms of charge transfer and energy transfer spectroscopically, and find that both processes contribute to the device photocurrent. Chapter four investigates the important question of how the energy level alignment of quantum dot acceptors affects the operation of hybrid polymer/quantum dot solar cells, by making use of the size-tunable energy levels of PbS quantum dots. We observe that long-lived charge transfer yield is diminished at larger dot sizes as the energy level offset at the polymer/quantum dot interface is changed through decreasing quantum confinement using a combination of spectroscopy and device studies. Chapter five discusses the effects of TiO2 surface chemistry on the performance of organometal halide perovskite solar cells. Specifically, chapter five studies the effect of replacing the conventional TiO2 electrode with Zr-doped TiO2 (Zr-TiO2). We aim to explore the correlation between charge carrier dynamics and device studies by incorporating zirconium into TiO2. We find that, compared to Zr-free controls, solar cells employing Zr-TiO2 give rise to an increase in overall power conversion efficiency, and a decrease in hysteresis. We also observe longer carrier lifetimes and higher charge carrier densities in devices on Zr-TiO2 electrodes at microsecond times in transient photovoltage experiments, as well as at longer persistent

  15. Influence of Exciton Lifetime on Charge Carrier Dynamics in an Organic Heterostructure

    SciTech Connect

    Agrawal, Kanika L.; Sykes, Matthew E.; An, Kwang Hyup; Frieberg, Bradley; Green, P. F.; Shtein, Max

    2013-03-18

    Interactions between charge carriers and excitons, as well as between excitons and optical cavity modes in organic optoelectronic devices are fundamental to their operational limits and chief in preventing the realization of certain phenomena, such as electrically pumped organic lasing. We uncovered a previously unreported phenomenon, wherein optical cavity-modulated exciton decay rate leads to a concomitant modulation in the electrical current of an archetypal NPD/Alq₃ organic light emitting device operated in forward bias. The magnitude of this variation is sensitive to the local dielectric environment of the device and is found to be as large as 15%.

  16. Influence of defects on excess charge carrier kinetics studied by transient PC and transient PA

    SciTech Connect

    Feist, H.; Kunst, M.; Swiatkowski, C.

    1997-07-01

    By comparison of transient photoconductivity (TPC) and transient photoinduced absorption (PA) the influence of the density of states in the bandgap on excess charge carrier kinetics is studied for a-Si:H films deposited at different temperatures and for state of the art a-Si:H films in two different states of light soaking. In both series the rising deep defect density leads to an enhancement of electron trapping rather than recombination via deep defects. The samples deposited at temperatures lower than 250 C additionally show a lower effective electron mobility, i.e., a broader conduction band tail.

  17. A new approach to calculate charge carrier transport mobility in organic molecular crystals from imaginary time path integral simulations

    SciTech Connect

    Song, Linze; Shi, Qiang

    2015-05-07

    We present a new non-perturbative method to calculate the charge carrier mobility using the imaginary time path integral approach, which is based on the Kubo formula for the conductivity, and a saddle point approximation to perform the analytic continuation. The new method is first tested using a benchmark calculation from the numerical exact hierarchical equations of motion method. Imaginary time path integral Monte Carlo simulations are then performed to explore the temperature dependence of charge carrier delocalization and mobility in organic molecular crystals (OMCs) within the Holstein and Holstein-Peierls models. The effects of nonlocal electron-phonon interaction on mobility in different charge transport regimes are also investigated.

  18. Charge carrier transport in molecularly doped polycarbonate as a test case for the dipolar glass model.

    PubMed

    Novikov, S V; Tyutnev, A P

    2013-03-14

    We present the results of Monte Carlo simulations of the charge carrier transport in a disordered molecular system containing spatial and energetic disorders using the dipolar glass model. Model parameters of the material were chosen to fit a typical polar organic photoconductor polycarbonate doped with 30% of aromatic hydrazone, whose transport properties are well documented in literature. Simulated carrier mobility demonstrates a usual Poole-Frenkel field dependence and its slope is very close to the experimental value without using any adjustable parameter. At room temperature transients are universal with respect to the electric field and transport layer thickness. At the same time, carrier mobility does not depend on the layer thickness and transients develop a well-defined plateau where the current does not depend on time, thus demonstrating a non-dispersive transport regime. Tails of the transients decay as power law with the exponent close to -2. This particular feature indicates that transients are close to the boundary between dispersive and non-dispersive transport regimes. Shapes of the simulated transients are in very good agreement with the experimental ones. In summary, we provide a first verification of a self-consistency of the dipolar glass transport model, where major transport parameters, extracted from the experimental transport data, are then used in the transport simulation, and the resulting mobility field dependence and transients are in very good agreement with the initial experimental data.

  19. Charge carrier transport in molecularly doped polycarbonate as a test case for the dipolar glass model

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Tyutnev, A. P.

    2013-03-01

    We present the results of Monte Carlo simulations of the charge carrier transport in a disordered molecular system containing spatial and energetic disorders using the dipolar glass model. Model parameters of the material were chosen to fit a typical polar organic photoconductor polycarbonate doped with 30% of aromatic hydrazone, whose transport properties are well documented in literature. Simulated carrier mobility demonstrates a usual Poole-Frenkel field dependence and its slope is very close to the experimental value without using any adjustable parameter. At room temperature transients are universal with respect to the electric field and transport layer thickness. At the same time, carrier mobility does not depend on the layer thickness and transients develop a well-defined plateau where the current does not depend on time, thus demonstrating a non-dispersive transport regime. Tails of the transients decay as power law with the exponent close to -2. This particular feature indicates that transients are close to the boundary between dispersive and non-dispersive transport regimes. Shapes of the simulated transients are in very good agreement with the experimental ones. In summary, we provide a first verification of a self-consistency of the dipolar glass transport model, where major transport parameters, extracted from the experimental transport data, are then used in the transport simulation, and the resulting mobility field dependence and transients are in very good agreement with the initial experimental data.

  20. Charge carrier concentration dependence of encounter-limited bimolecular recombination in phase-separated organic semiconductor blends

    NASA Astrophysics Data System (ADS)

    Heiber, Michael C.; Nguyen, Thuc-Quyen; Deibel, Carsten

    2016-05-01

    Understanding how the complex intermolecular configurations and nanostructure present in organic semiconductor donor-acceptor blends impacts charge carrier motion, interactions, and recombination behavior is a critical fundamental issue with a particularly major impact on organic photovoltaic applications. In this study, kinetic Monte Carlo (KMC) simulations are used to numerically quantify the complex bimolecular charge carrier recombination behavior in idealized phase-separated blends. Recent KMC simulations have identified how the encounter-limited bimolecular recombination rate in these blends deviates from the often used Langevin model and have been used to construct the new power mean mobility model. Here, we make a challenging but crucial expansion to this work by determining the charge carrier concentration dependence of the encounter-limited bimolecular recombination coefficient. In doing so, we find that an accurate treatment of the long-range electrostatic interactions between charge carriers is critical, and we further argue that many previous KMC simulation studies have used a Coulomb cutoff radius that is too small, which causes a significant overestimation of the recombination rate. To shed more light on this issue, we determine the minimum cutoff radius required to reach an accuracy of less than ±10 % as a function of the domain size and the charge carrier concentration and then use this knowledge to accurately quantify the charge carrier concentration dependence of the recombination rate. Using these rigorous methods, we finally show that the parameters of the power mean mobility model are determined by a newly identified dimensionless ratio of the domain size to the average charge carrier separation distance.

  1. Ultrafast dynamics of charge carrier photogeneration and geminate recombination in conjugated polymer:fullerene solar cells

    NASA Astrophysics Data System (ADS)

    Müller, J. G.; Lupton, J. M.; Feldmann, J.; Lemmer, U.; Scharber, M. C.; Sariciftci, N. S.; Brabec, C. J.; Scherf, U.

    2005-11-01

    We investigate the nature of ultrafast exciton dissociation and carrier generation in acceptor-doped conjugated polymers. Using a combination of two-pulse femtosecond spectroscopy with photocurrent detection, we compare the exciton dissociation and geminate charge recombination dynamics in blends of two conjugated polymers, MeLPPP [methyl-substituted ladder-type poly( p -phenylene)] and MDMO-PPV [poly(2-methoxy,5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene], with the electron accepting fullerene derivative PCBM [1-(3-methoxycarbonyl)-propyl-1-phenyl- (6,6)C61 ]. This technique allows us to distinguish between free charge carriers and Coulombically bound polaron pairs. Our results highlight the importance of geminate pair recombination in photovoltaic devices, which limits the device performance. The comparison of different materials allows us to address the dependence of geminate recombination on the film morphology directly at the polymer:fullerene interface. We find that in the MeLPPP:PCBM blend exciton dissociation generates Coulombically bound geminate polaron pairs with a high probability for recombination, which explains the low photocurrent yield found in these samples. In contrast, in the highly efficient MDMO-PPV:PCBM blend the electron transfer leads to the formation of free carriers. The anisotropy dynamics of electronic transitions from neutral and charged states indicate that polarons in MDMO-PPV relax to delocalized states in ordered domains within 500fs . The results suggest that this relaxation enlarges the distance of carrier separation within the geminate pair, lowering its binding energy and favoring full dissociation. The difference in geminate pair recombination concurs with distinct dissociation dynamics. The electron transfer is preceded by exciton migration towards the PCBM sites. In MeLPPP:PCBM the exciton migration time decays smoothly with increasing PCBM concentration, indicating a trap-free exciton hopping. In MDMO-PPV:PCBM, however

  2. Temperature dependence of exciton and charge carrier dynamics in organic thin films

    NASA Astrophysics Data System (ADS)

    Platt, A. D.; Kendrick, M. J.; Loth, M.; Anthony, J. E.; Ostroverkhova, O.

    2011-12-01

    We report on physical mechanisms behind the temperature-dependent optical absorption, photoluminescence (PL), and photoconductivity in spin-coated films of a functionalized anthradithiophene (ADT) derivative, ADT-triethylsilylethynyl (TES)-F, and its composites with C60 and another ADT derivative, ADT-TIPS-CN. Measurements of absorption and PL spectra, PL lifetimes, and transient photocurrent were performed at temperatures between 98 and 300 K as a function of applied electric field. In pristine ADT-TES-F films, absorptive and emissive species were identified to be disordered H aggregates whose properties are affected by static and dynamic disorder. The exciton bandwidths were ≤0.06 and ˜0.115 eV for absorptive and emissive aggregates, respectively, indicative of higher disorder in the emissive species. The exciton in the latter was found to be delocalized over approximately four to five molecules. The PL properties were significantly modified upon adding a guest molecule to the ADT-TES-F host. In ADT-TES-F/C60 composites, the PL was considerably quenched due to photoinduced electron transfer from ADT-TES-F to C60, while in ADT-TES-F/ADT-TIPS-CN blends, the PL was dominated by emission from an exciplex formed between ADT-TES-F and ADT-TIPS-CN molecules. In all materials, the PL quantum yield dramatically decreased as the temperature increased due to thermally activated nonradiative recombination. Considerable electric-field-induced PL quenching was observed at low temperatures at electric fields above ˜105 V/cm due to tunneling into dark states. No significant contribution of ADT-TES-F emissive exciton dissociation to transient photocurrent was observed. In all materials, charge carriers were photogenerated at sub-500-ps time scales, limited by the laser pulse width, with temperature- and electric-field-independent photogeneration efficiency. In ADT-TES-F/C60 (2%) composites, the photogeneration efficiency was a factor of 2-3 higher than that in pristine ADT

  3. Effect of gamma irradiation on transport of charge carriers in Cu nanowires

    NASA Astrophysics Data System (ADS)

    Gehlawat, Devender; Chauhan, R. P.; Sonkawade, R. G.; Chakarvarti, S. K.

    2012-01-01

    In this paper, we report the effect of gamma ray photons on the electrical conductivity of 100 nm Cu nanowires prepared by the technique of electrodeposition using track-etched membranes. Different fluences of photons have been used to observe the effect and in each case of post-irradiation, electrical conductivity is found to increase in a linear manner with increase in applied potential difference; however the rate of increase of conductivity is different in different cases of radiation fluence. Grain boundary scattering is of significance for the post-irradiation parabolic nature of the I-V characteristics (IVC), which are of a linear pattern following Ohm's law before irradiation. Increase or decrease in the number of charge carriers during their transport through the nanowires is the result of two competitive processes—specular and diffusive scattering of charge carriers (electrons) from grain boundaries, which are itself a region of high resistance rather than inter-grain regions. The results have been discussed in light of the Mayadas and Shatzkes (MS) model with a slight modification for irradiated nanowires.

  4. Photo-excited charge carriers suppress sub-terahertz phonon mode in silicon at room temperature

    NASA Astrophysics Data System (ADS)

    Liao, Bolin; Maznev, A. A.; Nelson, Keith A.; Chen, Gang

    2016-10-01

    There is a growing interest in the mode-by-mode understanding of electron and phonon transport for improving energy conversion technologies, such as thermoelectrics and photovoltaics. Whereas remarkable progress has been made in probing phonon-phonon interactions, it has been a challenge to directly measure electron-phonon interactions at the single-mode level, especially their effect on phonon transport above cryogenic temperatures. Here we use three-pulse photoacoustic spectroscopy to investigate the damping of a single sub-terahertz coherent phonon mode by free charge carriers in silicon at room temperature. Building on conventional pump-probe photoacoustic spectroscopy, we introduce an additional laser pulse to optically generate charge carriers, and carefully design temporal sequence of the three pulses to unambiguously quantify the scattering rate of a single-phonon mode due to the electron-phonon interaction. Our results confirm predictions from first-principles simulations and indicate the importance of the often-neglected effect of electron-phonon interaction on phonon transport in doped semiconductors.

  5. Photo-excited charge carriers suppress sub-terahertz phonon mode in silicon at room temperature

    PubMed Central

    Liao, Bolin; Maznev, A. A.; Nelson, Keith A.; Chen, Gang

    2016-01-01

    There is a growing interest in the mode-by-mode understanding of electron and phonon transport for improving energy conversion technologies, such as thermoelectrics and photovoltaics. Whereas remarkable progress has been made in probing phonon–phonon interactions, it has been a challenge to directly measure electron–phonon interactions at the single-mode level, especially their effect on phonon transport above cryogenic temperatures. Here we use three-pulse photoacoustic spectroscopy to investigate the damping of a single sub-terahertz coherent phonon mode by free charge carriers in silicon at room temperature. Building on conventional pump–probe photoacoustic spectroscopy, we introduce an additional laser pulse to optically generate charge carriers, and carefully design temporal sequence of the three pulses to unambiguously quantify the scattering rate of a single-phonon mode due to the electron–phonon interaction. Our results confirm predictions from first-principles simulations and indicate the importance of the often-neglected effect of electron–phonon interaction on phonon transport in doped semiconductors. PMID:27731406

  6. Doped GaN nanowires on diamond: Structural properties and charge carrier distribution

    NASA Astrophysics Data System (ADS)

    Schuster, Fabian; Winnerl, Andrea; Weiszer, Saskia; Hetzl, Martin; Garrido, Jose A.; Stutzmann, Martin

    2015-01-01

    In this work, we present a detailed study on GaN nanowire doping, which is vital for device fabrication. The nanowires (NWs) are grown by means of molecular beam epitaxy on diamond (111) substrates. Dopant atoms are found to facilitate nucleation, thus an increasing NW density is observed for increasing dopant fluxes. While maintaining nanowire morphology, we demonstrate the incorporation of Si and Mg up to concentrations of 9 × 1020cm-3 and 1 × 1020cm-3 , respectively. The dopant concentration in the nanowire cores is determined by the thermodynamic solubility limit, whereas excess dopants are found to segregate to the nanowire surface. The strain state of the NWs is investigated by X-ray diffraction, which confirms a negligible strain compared to planar thin films. Doping-related emissions are identified in low-temperature photoluminescence spectroscopy and the temperature quenching yields ionization energies of Si donors and Mg acceptors of 17 meV and 167 meV, respectively. At room temperature, luminescence and absorption spectra are found to coincide and the sub-band gap absorption is suppressed in n-type NWs. The charge carrier distribution in doped GaN nanowires is simulated under consideration of surface states at the non-polar side facets. For doping concentrations below 1017cm-3 , the nanowires are depleted of charge carriers, whereas they become highly conductive above 1019cm-3 .

  7. An autonomous photosynthetic device in which all charge carriers derive from surface plasmons.

    PubMed

    Mubeen, Syed; Lee, Joun; Singh, Nirala; Krämer, Stephan; Stucky, Galen D; Moskovits, Martin

    2013-04-01

    Solar conversion to electricity or to fuels based on electron-hole pair production in semiconductors is a highly evolved scientific and commercial enterprise. Recently, it has been posited that charge carriers either directly transferred from the plasmonic structure to a neighbouring semiconductor (such as TiO₂) or to a photocatalyst, or induced by energy transfer in a neighbouring medium, could augment photoconversion processes, potentially leading to an entire new paradigm in harvesting photons for practical use. The strong dependence of the wavelength at which the local surface plasmon can be excited on the nanostructure makes it possible, in principle, to design plasmonic devices that can harvest photons over the entire solar spectrum and beyond. So far, however, most such systems show rather small photocatalytic activity in the visible as compared with the ultraviolet. Here, we report an efficient, autonomous solar water-splitting device based on a gold nanorod array in which essentially all charge carriers involved in the oxidation and reduction steps arise from the hot electrons resulting from the excitation of surface plasmons in the nanostructured gold. Each nanorod functions without external wiring, producing 5 × 10(13) H₂ molecules per cm(2) per s under 1 sun illumination (AM 1.5 and 100 mW cm(-2)), with unprecedented long-term operational stability. PMID:23435280

  8. Proton intercalated two-dimensional WO3 nano-flakes with enhanced charge-carrier mobility at room temperature

    NASA Astrophysics Data System (ADS)

    Zhuiykov, Serge; Kats, Eugene; Carey, Benjamin; Balendhran, Sivacarendran

    2014-11-01

    Quasi two-dimensional (Q2D) semiconducting metal oxides with enhanced charge carrier mobility hold tremendous promise for nano-electronics, photonics, catalysis, nano-sensors and electrochromic applications. In addition to graphene and metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te), 2D sub-stoichiometric WO3-x is gaining importance as a promising semiconductor material for field-effect-transistor (FET) based devices. A combination of high permittivity, suppression of the Coulomb effects, and their stratified structure enhances the carrier mobility in such a material. Additionally, the sub-stoichiometry of this semiconductor oxide allows the reduction of the bandgap and increase of the free charge carriers at the same time. Here, we report for the first time H+ intercalated WO3 FETs, made of Q2D nano-flakes, with enhanced charge-carrier mobility exceeding 319 cm2 V-1 s-1 comparable with the charge-carrier mobility of Q2D dichalcogenides MoS2 and WSe2. Analyses indicate that the enhanced electrical properties of the sub-stoichiometric WO3-x depend on the oxygen vacancies in the intercalated nano-flakes. These findings confirmed that Q2D sub-stoichiometric WO3-x is a promising material for various functional FET devices.Quasi two-dimensional (Q2D) semiconducting metal oxides with enhanced charge carrier mobility hold tremendous promise for nano-electronics, photonics, catalysis, nano-sensors and electrochromic applications. In addition to graphene and metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te), 2D sub-stoichiometric WO3-x is gaining importance as a promising semiconductor material for field-effect-transistor (FET) based devices. A combination of high permittivity, suppression of the Coulomb effects, and their stratified structure enhances the carrier mobility in such a material. Additionally, the sub-stoichiometry of this semiconductor oxide allows the reduction of the bandgap and increase of the free charge carriers at the same time. Here, we report

  9. Effects of Stress Activated Positive-Hole Charge Carriers on Radar Reflectance of Gabbro-Diorite

    NASA Astrophysics Data System (ADS)

    Williams, C.; Vanderbilt, V. C.; Dahlgren, R.; Cherukupally, A.; Freund, F. T.

    2011-12-01

    When load is applied to igneous or high-grade metamorphic rocks, trapped electron vacancy defects are activated and become mobile positive-hole charge carriers. These mobile charge carriers repel each other through Coulomb interactions and move outward from the stressed region. As large numbers of positive-holes reach the surface of the rock, this surface charge may cause an observable change in radar reflectance. In this experiment, a series of holes is drilled into a large gabbro-diorite boulder from the A.R. Wilson Quarry in Aromas, CA. Bustar, an expansive, non-explosive demolition agent, is poured into the holes while a 1.2 GHz radar system measures the amplitude of radar waves reflected from the rock's surface. Over the course of the experiment, the radar antenna is swept repeatedly across one face of the rock, pausing in one of twelve positions to collect data before moving to the next position. At the end of each sweep, the radar is calibrated against both a corner reflector and a flat-plate reflector. This sampling method is employed to detect and assign a cause to transient effects observed at any one location. An initial analysis of the radar data shows a high level of agreement between readings from the flat-plate and corner reflectors, supporting the use of flat-plate reflectors as a calibration source for this omnidirectional radar system. Fitting a trend to the amplitude of the wave reflected from the rock's surface is complicated by the presence of unexpected outliers and noise artifacts from the radar system itself. It appears that such a trend, if present, would likely indicate a change in amplitude of the reflected signal of less than 5 percent over the course of the experiment.

  10. Bulk charge carrier transport in push-pull type organic semiconductor.

    PubMed

    Karak, Supravat; Liu, Feng; Russell, Thomas P; Duzhko, Volodimyr V

    2014-12-10

    Operation of organic electronic and optoelectronic devices relies on charge transport properties of active layer materials. The magnitude of charge carrier mobility, a key efficiency metrics of charge transport properties, is determined by the chemical structure of molecular units and their crystallographic packing motifs, as well as strongly depends on the film fabrication approaches that produce films with different degrees of anisotropy and structural order. Probed by the time-of-flight and grazing incidence X-ray diffraction techniques, bulk charge carrier transport, molecular packing, and film morphology in different structural phases of push-pull type organic semiconductor, 7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl)bis(6-fluoro-4-(5'-hexyl-[2,2'-bithiophen]-5yl)benzo[c][1,2,5] thiadiazole), one of the most efficient small-molecule photovoltaic materials to-date, are described herein. In the isotropic phase, the material is ambipolar with high mobilities for a fluid state. The electron and hole mobilities at the phase onset at 210.78 °C are 1.0 × 10(-3) cm(2)/(V s) and 6.5 × 10(-4) cm(2)/(V s), respectively. Analysis of the temperature and electric field dependences of the mobilities in the framework of Gaussian disorder formalism suggests larger energetic and positional disorder for electron transport sites. Below 210 °C, crystallization into a polycrystalline film with a triclinic unit cell symmetry and high degree of anisotropy leads to a 10-fold increase of hole mobility. The mobility is limited by the charge transfer along the direction of branched alkyl side chains. Below 90 °C, faster cooling rates produce even higher hole mobilities up to 2 × 10(-2) cm(2)/(V s) at 25 °C because of the more isotropic orientations of crystalline domains. These properties facilitate in understanding efficient material performance in photovoltaic devices and will guide further development of materials and devices.

  11. Self-Trapping of Charge Carriers in Semiconducting Carbon Nanotubes: Structural Analysis.

    PubMed

    Adamska, Lyudmyla; Nazin, George V; Doorn, Stephen K; Tretiak, Sergei

    2015-10-01

    The spatial extent of charged electronic states in semiconducting carbon nanotubes with indices (6,5) and (7,6) was evaluated using density functional theory. It was observed that electrons and holes self-trap along the nanotube axis on length scales of about 4 and 8 nm, respectively, which localize cations and anions on comparable length scales. Self-trapping is accompanied by local structural distortions showing periodic bond-length alternation. The average lengthening (shortening) of the bonds for anions (cations) is expected to shift the G-mode frequency to lower (higher) values. The smaller-diameter nanotube has reduced structural relaxation due to higher carbon-carbon bond strain. The reorganization energy due to charge-induced deformations in both nanotubes is found to be in the 30-60 meV range. Our results represent the first theoretical simulation of self-trapping of charge carriers in semiconducting nanotubes, and agree with available experimental data. PMID:26722885

  12. Correlation of Crystalline and Structural Properties of C60 Thin Films Grown at Various Temperature with Charge Carrier Mobility

    SciTech Connect

    Singh,T.; Sarciftci, N.; Yang, H.; Yang, L.; Plochberger, B.; Sitter, H.

    2007-01-01

    Transistors fabricated from C{sub 60} films grown by hot wall epitaxy at higher substrate temperature, showed an order of magnitude increased charge carrier mobility up to 6 cm{sup 2}/V s. In this letter, the authors present an extensive study of morphology and crystallinity of the fullerene films using atomic force microscopy and grazing-incidence x-ray diffraction. A clear correlation of crystalline quality of the C{sub 60} film and charge carrier mobility was found. A higher substrate temperature leads to a single crystal-like faceted fullerene crystals. The high crystalline quality solely brings a drastic improvement in the charge carrier mobility. A gate voltage independent mobility is also observed in these devices which can be attributed to the highly conjugated nature of the C{sub 60} thin film.

  13. Charge carrier loss mechanisms in CuInS2/ZnO nanocrystal solar cells.

    PubMed

    Scheunemann, Dorothea; Wilken, Sebastian; Parisi, Jürgen; Borchert, Holger

    2016-06-28

    Heterojunction solar cells based on colloidal nanocrystals (NCs) have shown remarkable improvements in performance in the last decade, but this progress is limited to merely two materials, PbS and PbSe. However, solar cells based on other material systems such as copper-based compounds show lower power conversion efficiencies and much less effort has been made to develop a better understanding of factors limiting their performance. Here, we study charge carrier loss mechanisms in solution-processed CuInS2/ZnO NC solar cells by combining steady-state measurements with transient photocurrent and photovoltage measurements. We demonstrate the presence of an extraction barrier at the CuInS2/ZnO interface, which can be reduced upon illumination with UV light. However, trap-assisted recombination in the CuInS2 layer is shown to be the dominant decay process in these devices. PMID:27250665

  14. Charge carrier dynamics in nanocrystalline Dy substituted ceria based oxygen ion conductors

    NASA Astrophysics Data System (ADS)

    Anirban, Sk.; Dutta, A.

    2016-05-01

    Nano-crystalline Ce1-xDyxO2-δ (x = 0.1-0.5) materials were prepared using the low temperature citrate auto-ignition method. The Rietveld analysis of the XRD data confirmed the single phase cubic fluorite structure. The particle sizes of the sintered samples are in nano range and lattice parameter increases with Dy concentration. Polydispersed and agglomerated particles are observed by SEM. The EDAX spectra show good stoichiometry of the different atoms in the samples. The conductivity is found to have both grain and grain boundary contribution and shows highest value at x= 0.2. The frequency dependence of dielectric permittivity has been analyzed using Havrilliak-Negami formalism. The variation in different electrical properties has been explained by formation defect associates and their interaction with charge carriers.

  15. Quantifying charge carrier concentration in ZnO thin films by Scanning Kelvin Probe Microscopy

    PubMed Central

    Maragliano, C.; Lilliu, S.; Dahlem, M. S.; Chiesa, M.; Souier, T.; Stefancich, M.

    2014-01-01

    In the last years there has been a renewed interest for zinc oxide semiconductor, mainly triggered by its prospects in optoelectronic applications. In particular, zinc oxide thin films are being widely used for photovoltaic applications, in which the determination of the electrical conductivity is of great importance. Being an intrinsically doped material, the quantification of its doping concentration has always been challenging. Here we show how to probe the charge carrier density of zinc oxide thin films by Scanning Kelvin Probe Microscopy, a technique that allows measuring the contact potential difference between the tip and the sample surface with high spatial resolution. A simple electronic energy model is used for correlating the contact potential difference with the doping concentration in the material. Limitations of this technique are discussed in details and some experimental solutions are proposed. Two-dimensional doping concentration images acquired on radio frequency-sputtered intrinsic zinc oxide thin films with different thickness and deposited under different conditions are reported. We show that results inferred with this technique are in accordance with carrier concentration expected for zinc oxide thin films deposited under different conditions and obtained from resistivity and mobility measurements. PMID:24569599

  16. Bimodal behaviour of charge carriers in graphene induced by electric double layer

    PubMed Central

    Tsai, Sing-Jyun; Yang, Ruey-Jen

    2016-01-01

    A theoretical investigation is performed into the electronic properties of graphene in the presence of liquid as a function of the contact area ratio. It is shown that the electric double layer (EDL) formed at the interface of the graphene and the liquid causes an overlap of the conduction bands and valance bands and increases the density of state (DOS) at the Fermi energy (EF). In other words, a greater number of charge carriers are induced for transport and the graphene changes from a semiconductor to a semimetal. In addition, it is shown that the dependence of the DOS at EF on the contact area ratio has a bimodal distribution which responses to the experimental observation, a pinnacle curve. The maximum number of induced carriers is expected to occur at contact area ratios of 40% and 60%. In general, the present results indicate that modulating the EDL provides an effective means of tuning the electronic properties of graphene in the presence of liquid. PMID:27464986

  17. Proton intercalated two-dimensional WO3 nano-flakes with enhanced charge-carrier mobility at room temperature.

    PubMed

    Zhuiykov, Serge; Kats, Eugene; Carey, Benjamin; Balendhran, Sivacarendran

    2014-12-21

    Quasi two-dimensional (Q2D) semiconducting metal oxides with enhanced charge carrier mobility hold tremendous promise for nano-electronics, photonics, catalysis, nano-sensors and electrochromic applications. In addition to graphene and metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te), 2D sub-stoichiometric WO(3-x) is gaining importance as a promising semiconductor material for field-effect-transistor (FET) based devices. A combination of high permittivity, suppression of the Coulomb effects, and their stratified structure enhances the carrier mobility in such a material. Additionally, the sub-stoichiometry of this semiconductor oxide allows the reduction of the bandgap and increase of the free charge carriers at the same time. Here, we report for the first time H(+) intercalated WO(3) FETs, made of Q2D nano-flakes, with enhanced charge-carrier mobility exceeding 319 cm(2) V(-1) s(-1) comparable with the charge-carrier mobility of Q2D dichalcogenides MoS(2) and WSe(2). Analyses indicate that the enhanced electrical properties of the sub-stoichiometric WO(3-x) depend on the oxygen vacancies in the intercalated nano-flakes. These findings confirmed that Q2D sub-stoichiometric WO(3-x) is a promising material for various functional FET devices. PMID:25367432

  18. Doped GaN nanowires on diamond: Structural properties and charge carrier distribution

    SciTech Connect

    Schuster, Fabian Winnerl, Andrea; Weiszer, Saskia; Hetzl, Martin; Garrido, Jose A.; Stutzmann, Martin

    2015-01-28

    In this work, we present a detailed study on GaN nanowire doping, which is vital for device fabrication. The nanowires (NWs) are grown by means of molecular beam epitaxy on diamond (111) substrates. Dopant atoms are found to facilitate nucleation, thus an increasing NW density is observed for increasing dopant fluxes. While maintaining nanowire morphology, we demonstrate the incorporation of Si and Mg up to concentrations of 9× 10{sup 20}cm{sup −3} and 1 × 10{sup 20}cm{sup −3}, respectively. The dopant concentration in the nanowire cores is determined by the thermodynamic solubility limit, whereas excess dopants are found to segregate to the nanowire surface. The strain state of the NWs is investigated by X-ray diffraction, which confirms a negligible strain compared to planar thin films. Doping-related emissions are identified in low-temperature photoluminescence spectroscopy and the temperature quenching yields ionization energies of Si donors and Mg acceptors of 17 meV and 167 meV, respectively. At room temperature, luminescence and absorption spectra are found to coincide and the sub-band gap absorption is suppressed in n-type NWs. The charge carrier distribution in doped GaN nanowires is simulated under consideration of surface states at the non-polar side facets. For doping concentrations below 10{sup 17}cm{sup −3}, the nanowires are depleted of charge carriers, whereas they become highly conductive above 10{sup 19}cm{sup −3}.

  19. Temperature dependent charge transport in organic field-effect transistors with the variation of both carrier concentration and electric field

    NASA Astrophysics Data System (ADS)

    Abbas, Mamatimin; Pivrikas, Almantas; Arici, Elif; Tekin, Nalan; Ullah, Mujeeb; Sitter, Helmut; Sariciftci, Niyazi Serdar

    2013-12-01

    We present experimental evidence of combined effects of temperature, carrier concentration, electric field as well as disorder on charge transport in an organic field-effect transistor (OFET). Transfer characteristics of an OFET based on sexithiophene active layer were measured from 80 to 300 K. Thermally activated carrier mobility followed Arrhenius law with two activation energies. Carrier density variation led to finite extrapolated Meyer-Neldel (MN) temperature (780 K) at low fields. Negative electric field-dependent mobility was observed in available field range. MN temperature shifted towards higher temperature when the electric field increased, and did not retain its finite character above the field of 4 × 103 V cm-1.

  20. Time-resolved HAXPES using a microfocused XFEL beam: From vacuum space-charge effects to intrinsic charge-carrier recombination dynamics

    NASA Astrophysics Data System (ADS)

    Oloff, Lars-Philip; Chainani, Ashish; Matsunami, Masaharu; Takahashi, Kazutoshi; Togashi, Tadashi; Osawa, Hitoshi; Hanff, Kerstin; Quer, Arndt; Matsushita, Ryuki; Shiraishi, Ryutaro; Nagashima, Maki; Kimura, Ayato; Matsuishi, Kotaro; Yabashi, Makina; Tanaka, Yoshihito; Rossi, Giorgio; Ishikawa, Tetsuya; Rossnagel, Kai; Oura, Masaki

    2016-10-01

    Time-resolved hard X-ray photoelectron spectroscopy (trHAXPES) using microfocused X-ray free-electron laser (XFEL, hν = 8 keV) pulses as a probe and infrared laser pulses (hν = 1.55 eV) as a pump is employed to determine intrinsic charge-carrier recombination dynamics in La:SrTiO3. By means of a combination of experiments and numerical N-body simulations, we first develop a simple approach to characterize and decrease XFEL-induced vacuum space-charge effects, which otherwise pose a serious limitation to spectroscopy experiments. We then show that, using an analytical mean-field model, vacuum space-charge effects can be counteracted by pump laser-induced photoholes at high excitation densities. This provides us a method to separate vacuum space-charge effects from the intrinsic charge-carrier recombination dynamics in the time domain. Our trHAXPES results thus open a route to studies of intrinsic charge-carrier dynamics on picosecond time scales with lateral spatial resolution on the micrometer scale.

  1. Time-resolved HAXPES using a microfocused XFEL beam: From vacuum space-charge effects to intrinsic charge-carrier recombination dynamics

    PubMed Central

    Oloff, Lars-Philip; Chainani, Ashish; Matsunami, Masaharu; Takahashi, Kazutoshi; Togashi, Tadashi; Osawa, Hitoshi; Hanff, Kerstin; Quer, Arndt; Matsushita, Ryuki; Shiraishi, Ryutaro; Nagashima, Maki; Kimura, Ayato; Matsuishi, Kotaro; Yabashi, Makina; Tanaka, Yoshihito; Rossi, Giorgio; Ishikawa, Tetsuya; Rossnagel, Kai; Oura, Masaki

    2016-01-01

    Time-resolved hard X-ray photoelectron spectroscopy (trHAXPES) using microfocused X-ray free-electron laser (XFEL, hν = 8 keV) pulses as a probe and infrared laser pulses (hν = 1.55 eV) as a pump is employed to determine intrinsic charge-carrier recombination dynamics in La:SrTiO3. By means of a combination of experiments and numerical N-body simulations, we first develop a simple approach to characterize and decrease XFEL-induced vacuum space-charge effects, which otherwise pose a serious limitation to spectroscopy experiments. We then show that, using an analytical mean-field model, vacuum space-charge effects can be counteracted by pump laser-induced photoholes at high excitation densities. This provides us a method to separate vacuum space-charge effects from the intrinsic charge-carrier recombination dynamics in the time domain. Our trHAXPES results thus open a route to studies of intrinsic charge-carrier dynamics on picosecond time scales with lateral spatial resolution on the micrometer scale. PMID:27731408

  2. Long-lived charge carrier generation in ordered films of a covalent perylenediimide–diketopyrrolopyrrole–perylenediimide molecule

    DOE PAGES

    Hartnett, Patrick E.; Dyar, Scott M.; Margulies, Eric A.; Shoer, Leah E.; Cook, Andrew W.; Eaton, Samuel W.; Marks, Tobin J.; Wasielewski, Michael R.

    2015-07-31

    The photophysics of a covalently linked perylenediimide–diketopyrrolopyrrole–perylenediimide acceptor–donor–acceptor molecule (PDI–DPP–PDI, 1) were investigated and found to be markedly different in solution versus in unannealed and solvent annealed films. Photoexcitation of 1 in toluene results in quantitative charge separation in τ = 3.1 ± 0.2 ps, with charge recombination in τ = 340 ± 10 ps, while in unannealed/disordered films of 1, charge separation occurs in τ < 250 fs, while charge recombination displays a multiexponential decay in ~6 ns. The absence of long-lived, charge separation in the disordered film suggests that few free charge carriers are generated. In contrast, uponmore » CH₂Cl₂ vapor annealing films of 1, grazing-incidence X-ray scattering shows that the molecules form a more ordered structure. Photoexcitation of the ordered films results in initial formation of a spin-correlated radical ion pair (electron–hole pair) as indicated by magnetic field effects on the formation of free charge carriers which live for ~4 μs. This result has significant implications for the design of organic solar cells based on covalent donor–acceptor systems and shows that long-lived, charge-separated states can be achieved by controlling intramolecular charge separation dynamics in well-ordered systems.« less

  3. Long-lived charge carrier generation in ordered films of a covalent perylenediimide–diketopyrrolopyrrole–perylenediimide molecule

    SciTech Connect

    Hartnett, Patrick E.; Dyar, Scott M.; Margulies, Eric A.; Shoer, Leah E.; Cook, Andrew W.; Eaton, Samuel W.; Marks, Tobin J.; Wasielewski, Michael R.

    2015-07-31

    The photophysics of a covalently linked perylenediimide–diketopyrrolopyrrole–perylenediimide acceptor–donor–acceptor molecule (PDI–DPP–PDI, 1) were investigated and found to be markedly different in solution versus in unannealed and solvent annealed films. Photoexcitation of 1 in toluene results in quantitative charge separation in τ = 3.1 ± 0.2 ps, with charge recombination in τ = 340 ± 10 ps, while in unannealed/disordered films of 1, charge separation occurs in τ < 250 fs, while charge recombination displays a multiexponential decay in ~6 ns. The absence of long-lived, charge separation in the disordered film suggests that few free charge carriers are generated. In contrast, upon CH₂Cl₂ vapor annealing films of 1, grazing-incidence X-ray scattering shows that the molecules form a more ordered structure. Photoexcitation of the ordered films results in initial formation of a spin-correlated radical ion pair (electron–hole pair) as indicated by magnetic field effects on the formation of free charge carriers which live for ~4 μs. This result has significant implications for the design of organic solar cells based on covalent donor–acceptor systems and shows that long-lived, charge-separated states can be achieved by controlling intramolecular charge separation dynamics in well-ordered systems.

  4. Charge carrier dynamics and surface plasmon interaction in gold nanorod-blended organic solar cell

    NASA Astrophysics Data System (ADS)

    Rana, Aniket; Gupta, Neeraj; Lochan, Abhiram; Sharma, G. D.; Chand, Suresh; Kumar, Mahesh; Singh, Rajiv K.

    2016-08-01

    The inclusion of plasmonic nanoparticles into organic solar cell enhances the light harvesting properties that lead to higher power conversion efficiency without altering the device configuration. This work defines the consequences of the nanoparticle overloading amount and energy transfer process between gold nanorod and polymer (active matrix) in organic solar cells. We have studied the hole population decay dynamics coupled with gold nanorods loading amount which provides better understanding about device performance limiting factors. The exciton and plasmon together act as an interacting dipole; however, the energy exchange between these two has been elucidated via plasmon resonance energy transfer (PRET) mechanism. Further, the charge species have been identified specifically with respect to their energy levels appearing in ultrafast time domain. The specific interaction of these charge species with respective surface plasmon resonance mode, i.e., exciton to transverse mode of oscillation and polaron pair to longitudinal mode of oscillations, has been explained. Thus, our analysis reveals that PRET enhances the carrier population density in polymer via non-radiative process beyond the concurrence of a particular plasmon resonance oscillation mode and polymer absorption range. These findings give new insight and reveal specifically the factors that enhance and control the performance of gold nanorods blended organic solar cells. This work would lead in the emergence of future plasmon based efficient organic electronic devices.

  5. Initiating and imaging the coherent surface dynamics of charge carriers in real space

    PubMed Central

    Rusimova, K. R.; Bannister, N.; Harrison, P.; Lock, D.; Crampin, S.; Palmer, R. E.; Sloan, P. A.

    2016-01-01

    The tip of a scanning tunnelling microscope is an atomic-scale source of electrons and holes. As the injected charge spreads out, it can induce adsorbed molecules to react. By comparing large-scale ‘before' and ‘after' images of an adsorbate covered surface, the spatial extent of the nonlocal manipulation is revealed. Here, we measure the nonlocal manipulation of toluene molecules on the Si(111)-7 × 7 surface at room temperature. Both the range and probability of nonlocal manipulation have a voltage dependence. A region within 5–15 nm of the injection site shows a marked reduction in manipulation. We propose that this region marks the extent of the initial coherent (that is, ballistic) time-dependent evolution of the injected charge carrier. Using scanning tunnelling spectroscopy, we develop a model of this time-dependent expansion of the initially localized hole wavepacket within a particular surface state and deduce a quantum coherence (ballistic) lifetime of ∼10 fs. PMID:27677938

  6. Spiro-OMeTAD single crystals: Remarkably enhanced charge-carrier transport via mesoscale ordering

    PubMed Central

    Shi, Dong; Qin, Xiang; Li, Yuan; He, Yao; Zhong, Cheng; Pan, Jun; Dong, Huanli; Xu, Wei; Li, Tao; Hu, Wenping; Brédas, Jean-Luc; Bakr, Osman M.

    2016-01-01

    We report the crystal structure and hole-transport mechanism in spiro-OMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene], the dominant hole-transporting material in perovskite and solid-state dye-sensitized solar cells. Despite spiro-OMeTAD’s paramount role in such devices, its crystal structure was unknown because of highly disordered solution-processed films; the hole-transport pathways remained ill-defined and the charge carrier mobilities were low, posing a major bottleneck for advancing cell efficiencies. We devised an antisolvent crystallization strategy to grow single crystals of spiro-OMeTAD, which allowed us to experimentally elucidate its molecular packing and transport properties. Electronic structure calculations enabled us to map spiro-OMeTAD’s intermolecular charge-hopping pathways. Promisingly, single-crystal mobilities were found to exceed their thin-film counterparts by three orders of magnitude. Our findings underscore mesoscale ordering as a key strategy to achieving breakthroughs in hole-transport material engineering of solar cells. PMID:27152342

  7. Non-Abelian states in Fractional Quantum Hall effect in charge carrier hole systems

    NASA Astrophysics Data System (ADS)

    Simion, George; Lyanda-Geller, Yuli

    Quasiparticle excitations obeying non-Abelian statistics represent the key element of topological quantum computing. Crossing of levels and strong coupling between angular momentum and orbital motion, described by Luttinger Hamiltonian, make properties of charge carrier holes different from those of electrons. Peculiarities of hole spectrum in magnetic field provide an opportunity for controlling Landau level mixing in charge carier hole systems. In order to describe Fractional Quantum Hall effect for holes, we propose a method to map hole spectrum and wavefunctions using a spherical shell. We investigate the experimentally observed ν = 1 / 2 state in spherical geometry. Haldane pseudopotentials are computed and the effect of Landau level mixing is evaluated. Exact diagonalization of Coulomb interaction in systems with eight to fourteen holes is performed. We determine that the ground state superposition with Abelian 331 state is very small and the overlap with Moore-Read state is significant. The quasihole and quasielectron excitations are discussed. Research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0010544.

  8. Charge carrier mobility and electronic properties of Al(Op)3: impact of excimer formation

    PubMed Central

    Friederich, Pascal; Schäfer, Bernhard; Fattori, Valeria; Sun, Xiangnan; Strunk, Timo; Meded, Velimir; Hueso, Luis E; Wenzel, Wolfgang; Ruben, Mario

    2015-01-01

    Summary We have studied the electronic properties and the charge carrier mobility of the organic semiconductor tris(1-oxo-1H-phenalen-9-olate)aluminium(III) (Al(Op)3) both experimentally and theoretically. We experimentally estimated the HOMO and LUMO energy levels to be −5.93 and −3.26 eV, respectively, which were close to the corresponding calculated values. Al(Op)3 was successfully evaporated onto quartz substrates and was clearly identified in the absorption spectra of both the solution and the thin film. A structured steady state fluorescence emission was detected in solution, whereas a broad, red-shifted emission was observed in the thin film. This indicates the formation of excimers in the solid state, which is crucial for the transport properties. The incorporation of Al(Op)3 into organic thin film transistors (TFTs) was performed in order to measure the charge carrier mobility. The experimental setup detected no electron mobility, while a hole mobility between 0.6 × 10−6 and 2.1 × 10−6 cm2·V−1·s−1 was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10−6 cm2·V−1·s−1 and a hole mobility of 1.4 × 10−4 cm2·V−1·s−1. The theoretical simulation for the hole mobility predicted an approximately one order of magnitude higher hole mobility than was observed in the experiment, which is considered to be in good agreement. The result for the electron mobility was, on the other hand, unexpected, as both the calculated electron mobility and chemical common sense (based on the capability of extended aromatic structures to efficiently accept and delocalize additional electrons) suggest more robust electron charge transport properties. This discrepancy is explained by the excimer formation, whose inclusion in the multiscale simulation workflow is expected to bring the theoretical simulation and experiment into agreement. PMID:26171287

  9. Charge carrier mobility and electronic properties of Al(Op)3: impact of excimer formation.

    PubMed

    Magri, Andrea; Friederich, Pascal; Schäfer, Bernhard; Fattori, Valeria; Sun, Xiangnan; Strunk, Timo; Meded, Velimir; Hueso, Luis E; Wenzel, Wolfgang; Ruben, Mario

    2015-01-01

    We have studied the electronic properties and the charge carrier mobility of the organic semiconductor tris(1-oxo-1H-phenalen-9-olate)aluminium(III) (Al(Op)3) both experimentally and theoretically. We experimentally estimated the HOMO and LUMO energy levels to be -5.93 and -3.26 eV, respectively, which were close to the corresponding calculated values. Al(Op)3 was successfully evaporated onto quartz substrates and was clearly identified in the absorption spectra of both the solution and the thin film. A structured steady state fluorescence emission was detected in solution, whereas a broad, red-shifted emission was observed in the thin film. This indicates the formation of excimers in the solid state, which is crucial for the transport properties. The incorporation of Al(Op)3 into organic thin film transistors (TFTs) was performed in order to measure the charge carrier mobility. The experimental setup detected no electron mobility, while a hole mobility between 0.6 × 10(-6) and 2.1 × 10(-6) cm(2)·V(-1)·s(-1) was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10(-6) cm(2)·V(-1)·s(-1) and a hole mobility of 1.4 × 10(-4) cm(2)·V(-1)·s(-1). The theoretical simulation for the hole mobility predicted an approximately one order of magnitude higher hole mobility than was observed in the experiment, which is considered to be in good agreement. The result for the electron mobility was, on the other hand, unexpected, as both the calculated electron mobility and chemical common sense (based on the capability of extended aromatic structures to efficiently accept and delocalize additional electrons) suggest more robust electron charge transport properties. This discrepancy is explained by the excimer formation, whose inclusion in the multiscale simulation workflow is expected to bring the theoretical simulation and experiment into agreement. PMID:26171287

  10. Influence of Surface Mobility of Charge Carriers on Cdx Hg1-x Te (x=0,2-0,3) Photoconductivity

    NASA Astrophysics Data System (ADS)

    Salaev, Eldar; Guseýnov, Emil; Ýsmaýlov, Namýk; Tezer, Ateþ

    1997-10-01

    Experimental data on the photoconductivity of CdxHg1-xTe with different surface states are presented. The results are interpreted by he influence of surface mobility of charge carriers on photoeffect phenomena and the value of surface mobility for chemically treated, for polished surface and for aluminium covered surfaces of CdxHg1-xTe crystals are given.

  11. 14 CFR 382.31 - May carriers impose special charges on passengers with a disability for providing services and...

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 4 2010-01-01 2010-01-01 false May carriers impose special charges on... 382.31 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL...

  12. Charge Density and Molecular Weight of Polyphosphoramidate Gene Carrier Are Key Parameters Influencing Its DNA Compaction Ability and Transfection Efficiency

    PubMed Central

    Ren, Yong; Jiang, Xuan; Pan, Deng; Mao, Hai-Quan

    2011-01-01

    A series of polyphosphoramidates (PPA) with different molecular weights (MWs) and charge densities were synthesized and examined for their DNA compaction ability and transfection efficiency. A strong correlation was observed between the transfection efficiency of PPA/DNA nanoparticles and the MW and net positive charge density of the PPA gene carriers in three different cell lines (HeLa, HEK293 and HepG2 cells). An increase in MW and/or net positive charge density of PPA carrier yielded higher DNA compaction capacity, smaller nanoparticles with higher surface charges and higher complex stability against challenges by salt and polyanions. These favorable physicochemical properties of nanoparticles led to enhanced transfection efficiency. PPA/DNA nanoparticles with the highest complex stability showed comparable transfection efficiency as PEI/DNA nanoparticles likely by compensating the low buffering capacity with higher cellular uptake and affording higher level of protection to DNA in endolysosomal compartment. The differences in transfection efficiency were not attributed by any difference in cytotoxicity among the carriers, as all nanoparticles showed minimal level of cytotoxicity under the transfection conditions. Using PPA as a model system, we demonstrated the structural dependence of transfection efficiency of polymer gene carrier. These results offer more insights into nanoparticle engineering for non-viral gene delivery. PMID:21067136

  13. 14 CFR 382.31 - May carriers impose special charges on passengers with a disability for providing services and...

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 4 2014-01-01 2014-01-01 false May carriers impose special charges on... 382.31 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL...

  14. 14 CFR 382.31 - May carriers impose special charges on passengers with a disability for providing services and...

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 4 2013-01-01 2013-01-01 false May carriers impose special charges on... 382.31 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL...

  15. 14 CFR 382.31 - May carriers impose special charges on passengers with a disability for providing services and...

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 4 2011-01-01 2011-01-01 false May carriers impose special charges on... 382.31 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL...

  16. 14 CFR 382.31 - May carriers impose special charges on passengers with a disability for providing services and...

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 4 2012-01-01 2012-01-01 false May carriers impose special charges on... 382.31 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL...

  17. The Moving Lines on Electron Spectra as Charge Reflexes on Non-equilibrium States of Nanostructured Surfaces.

    PubMed

    Mishchuk, Oleg A

    2016-12-01

    The experimental results present the phenomenon of moving lines on electron spectra which are linked spatially and in time with the localization and durability of the processes of new surface producing in folds and grain boundaries. This effect was also realized for a thin-layer composite "organic on metal films on dielectric substrate" in modeling non-equilibrium conditions which are created by the intensive electron beam pulse impact. It was found that the nature of the inceptive adsorption layer, in addition to the metal film, determines the initial positions of moving lines on the spectra. The main accents in these investigations were in observations of appearance of the moving lines, dynamics of their displacements on the spectra, final stages when these lines vanished, and finding the general regularities between the spontaneous and induced events.

  18. The Moving Lines on Electron Spectra as Charge Reflexes on Non-equilibrium States of Nanostructured Surfaces

    NASA Astrophysics Data System (ADS)

    Mishchuk, Oleg A.

    2016-04-01

    The experimental results present the phenomenon of moving lines on electron spectra which are linked spatially and in time with the localization and durability of the processes of new surface producing in folds and grain boundaries. This effect was also realized for a thin-layer composite "organic on metal films on dielectric substrate" in modeling non-equilibrium conditions which are created by the intensive electron beam pulse impact. It was found that the nature of the inceptive adsorption layer, in addition to the metal film, determines the initial positions of moving lines on the spectra. The main accents in these investigations were in observations of appearance of the moving lines, dynamics of their displacements on the spectra, final stages when these lines vanished, and finding the general regularities between the spontaneous and induced events.

  19. The Moving Lines on Electron Spectra as Charge Reflexes on Non-equilibrium States of Nanostructured Surfaces.

    PubMed

    Mishchuk, Oleg A

    2016-12-01

    The experimental results present the phenomenon of moving lines on electron spectra which are linked spatially and in time with the localization and durability of the processes of new surface producing in folds and grain boundaries. This effect was also realized for a thin-layer composite "organic on metal films on dielectric substrate" in modeling non-equilibrium conditions which are created by the intensive electron beam pulse impact. It was found that the nature of the inceptive adsorption layer, in addition to the metal film, determines the initial positions of moving lines on the spectra. The main accents in these investigations were in observations of appearance of the moving lines, dynamics of their displacements on the spectra, final stages when these lines vanished, and finding the general regularities between the spontaneous and induced events. PMID:27083583

  20. On the generation of charge-carrier recombination centers in the sapphire substrates of silicon-on-sapphire structures

    SciTech Connect

    Aleksandrov, P. A. Belova, N. E.; Demakov, K. D.; Shemardov, S. G.

    2015-08-15

    A method for the production of high-quality radiation-resistant silicon-on-sapphire structures through the fabrication of a layer of nanopores in sapphire by helium ion implantation, i.e., by creating charge-carrier recombination centers, is proposed. In this case, the quality of the silicon layer is simultaneously improved. The problem of the thermal stability of the pores is discussed with the aim of analyzing the possibility of producing a microcircuit on the resultant modified silicon-on-sapphire sample. The layer of pores possesses a large total surface area and, hence, decreases the lifetime of charge carriers generated during irradiation of the operating microcircuit. This effect reduces the charge at the silicon-sapphire interface and improves radiation resistance.

  1. A new approach to calculate charge carrier transport mobility in organic molecular crystals from imaginary time path integral simulations.

    PubMed

    Song, Linze; Shi, Qiang

    2015-05-01

    We present a new non-perturbative method to calculate the charge carrier mobility using the imaginary time path integral approach, which is based on the Kubo formula for the conductivity, and a saddle point approximation to perform the analytic continuation. The new method is first tested using a benchmark calculation from the numerical exact hierarchical equations of motion method. Imaginary time path integral Monte Carlo simulations are then performed to explore the temperature dependence of charge carrier delocalization and mobility in organic molecular crystals (OMCs) within the Holstein and Holstein-Peierls models. The effects of nonlocal electron-phonon interaction on mobility in different charge transport regimes are also investigated. PMID:25956086

  2. Space charge memory effect in a-Si:H at low temperatures

    SciTech Connect

    Heck, S.; Stradins, P.; Fritzsche, H.

    1997-07-01

    Space charges build up near one or both electrodes of a photoconductor unless the thermoionic current balances the photocurrent. Space charges built up also when a voltage U is applied at low T to a semiconductor containing a nonequilibrium distribution of carriers. The presence of a space charge is observed as a relaxation-current transient when the sample is illuminated at zero bias. If one type of carrier is immobile the steady state photocurrent becomes zero.

  3. Charge carrier mobility in CBP films doped with Ir(ppy) 3

    NASA Astrophysics Data System (ADS)

    Parshin, Mikhail A.; Ollevier, Jeroen; Van der Auweraer, Mark

    2006-04-01

    We present the systematic study of charge carrier mobility in 4,4'-N,N'-dicarbazole-biphenyl (CBP) films doped with a triplet-emitter material tris(2-phenylpyridine) iridium (Ir(ppy) 3) - 1 wt% and 10 wt%. The hole mobility was investigated with the time-of-flight (TOF) technique, as a function of electric field in the range 10 5 - 2 × 10 6 V/cm. For a CBP film doped with 1% of Ir(ppy)3 the hole mobility was also measured as a function of temperature from 20° C to 70° C. The obtained hole mobilities in CBP film doped with 1% of Ir(ppy) 3 are in the range 5 × 10-10 - 3 × 10-7 cm2/Vs. The measured dependence of the hole mobility on temperature and electric field is explained in the framework of the Gaussian disorder model of Bassler. Calculated values for the effective energetic and the positional disorder are 162 meV and 4.2, respectively. The activation energy at zero field is 0.58 eV. The mobility extrapolated to zero field and infinite temperature amounts to 6 × 10-4 cm2/Vs. In CBP film doped with 10% of Ir(ppy) 3 the hole mobilities are in the range 2 × 10-8 - 3 × 10-7 cm2/Vs. The observed increase of the hole mobility in Ir(ppy) 3-doped CBP films with increasing doping concentration can be attributed to hopping transport of charge carries via dopant molecules.

  4. Universal crossover of the charge carrier fluctuation mechanism in different polymer/carbon nanotubes composites

    SciTech Connect

    Barone, C. Mauro, C.; Pagano, S.; Landi, G.; Neitzert, H. C.

    2015-10-05

    Carbon nanotubes added to polymer and epoxy matrices are compounds of interest for applications in electronics and aerospace. The realization of high-performance devices based on these materials can profit from the investigation of their electric noise properties, as this gives a more detailed insight of the basic charge carriers transport mechanisms at work. The dc and electrical noise characteristics of different polymer/carbon nanotubes composites have been analyzed from 10 to 300 K. The results suggest that all these systems can be regarded as random resistive networks of tunnel junctions formed by adjacent carbon nanotubes. However, in the high-temperature regime, contributions deriving from other possible mechanisms cannot be separated using dc information alone. A transition from a fluctuation-induced tunneling process to a thermally activated regime is instead revealed by electric noise spectroscopy. In particular, a crossover is found from a two-level tunneling mechanism, operating at low temperatures, to resistance fluctuations of a percolative network, in the high-temperature region. The observed behavior of 1/f noise seems to be a general feature for highly conductive samples, independent on the type of polymer matrix and on the nanotube density.

  5. Spatial localization of excitons and charge carriers in hybrid perovskite thin films

    DOE PAGES

    Simpson, Mary Jane; Doughty, Benjamin; Yang, Bin; Xiao, Kai; Ma, Ying -Zhong

    2015-07-21

    The fundamental photophysics underlying the remarkably high power conversion efficiency of organic-inorganic hybrid perovskite-based solar cells has been increasingly studied using complementary spectroscopic techniques. The spatially heterogeneous polycrystalline morphology of the photoactive layers owing to the presence of distinct crystalline grains has been generally neglected in optical measurements and therefore the reported results are typically averaged over hundreds or even thousands of such grains. Here, we apply femtosecond transient absorption microscopy to spatially and temporally probe ultrafast electronic excited-state dynamics in pristine methylammonium lead tri-iodide (CH3NH3PbI3) thin films and composite structures. We found that the electronic excited-state relaxation kinetics aremore » extremely sensitive to the sample location probed, which was manifested by position-dependent decay timescales and transient signals. As a result, analysis of transient absorption kinetics acquired at distinct spatial positions enabled us to identify contributions of excitons and free charge carriers.« less

  6. Spatial localization of excitons and charge carriers in hybrid perovskite thin films

    SciTech Connect

    Simpson, Mary Jane; Doughty, Benjamin; Yang, Bin; Xiao, Kai; Ma, Ying -Zhong

    2015-07-21

    The fundamental photophysics underlying the remarkably high power conversion efficiency of organic-inorganic hybrid perovskite-based solar cells has been increasingly studied using complementary spectroscopic techniques. The spatially heterogeneous polycrystalline morphology of the photoactive layers owing to the presence of distinct crystalline grains has been generally neglected in optical measurements and therefore the reported results are typically averaged over hundreds or even thousands of such grains. Here, we apply femtosecond transient absorption microscopy to spatially and temporally probe ultrafast electronic excited-state dynamics in pristine methylammonium lead tri-iodide (CH3NH3PbI3) thin films and composite structures. We found that the electronic excited-state relaxation kinetics are extremely sensitive to the sample location probed, which was manifested by position-dependent decay timescales and transient signals. As a result, analysis of transient absorption kinetics acquired at distinct spatial positions enabled us to identify contributions of excitons and free charge carriers.

  7. Ruthenium cation substitutional doping for efficient charge carrier transfer in organic/inorganic hybrid solar cells

    NASA Astrophysics Data System (ADS)

    Kong, Degui; Jin, Xiao; Sun, Weifu; Du, Jiaxing; Tong, Jifeng; Chen, Changyong; Yang, Xuwei; Cheng, Yuanyuan; Li, Qinghua

    2015-01-01

    Solution-processed organic/inorganic hybrid solar cells have emerged as a new platform for low-cost optoelectronics. At the heart of photovoltaic devices lies the matching of a junction, which requires the suitable energy level alignment of n-type and p-type semiconductors. Incorporating foreign ions into bulk semiconductors has been largely employed for many decades, yet electronically active doping in energy level control of the hybrid bulk heterojunctions has been rarely involved and the demonstration of robust functional optoelectronic devices had thus far been elusive. Herein, we introduce Ru ions into TiO2 to decorate the energy level of the acceptor to gain better energy level alignment between the donor and acceptor. By reducing the 'excess' energy offset between the n-type and p-type semiconductors, the electron transfer becomes faster, thus leading to a notable enhancement in power conversion efficiency, i.e., from 2.20% to 2.89%. The results demonstrate that the energy level can be controlled effectively by the versatile Ru dopants. This work opens an effective route for accelerating the charge carrier transfer at the interface and achieving high-performance organic/inorganic hybrid optoelectronic devices.

  8. Computational Confirmation of the Carrier for the "XCN" Interstellar Ice Bank: OCN(-) Charge Transfer Complexes

    NASA Technical Reports Server (NTRS)

    Park, J.-Y.; Woon, D. E.

    2004-01-01

    Recent experimental studies provide evidence that carrier for the so-called XCN feature at 2165 cm(exp -1) (4.62 micron) in young stellar objects is an OCN(-)/NH4(+) charge transfer (CT) complex that forms in energetically processed interstellar icy grain mantles. Although other RCN nitriles and RCN iosonitriles have been considered, Greenberg's conjecture that OCN(-) is associated with the XCN feature has persisted for over 15 years. In this work we report a computational investigation that thoroughly confirms the hypothesis that the XCN feature observed in laboratory studies can result from OCN(-)/NH4(+) CT complexes arising from HNCO and NH3, in a water ice environment. Density functional theory calculations with theory calculations with HNCO, NH3, and up to 12 waters reproduce seven spectroscopic measurements associated with XCN: the band origin of the asymmetric stretching mode of OCN(-), shifts due to isotopic substitutions of C, N, O, and H, and two weak features. However, very similar values are also found for the OCN(-)/NH4(+) CT complex arising from HOCN and NH3. In both cases, the complex forms by barrierless proton transfer from HNCO or HOCN to NH3 during the optimization of the solvated system. Scaled B3LYP/6-31+G** harmonic frequencies for HNCO and HOCN cases are 2181 and 2202 cm(exp -1), respectively.

  9. Heterodimensional charge-carrier confinement in stacked submonolayer InAs in GaAs

    NASA Astrophysics Data System (ADS)

    Harrison, S.; Young, M. P.; Hodgson, P. D.; Young, R. J.; Hayne, M.; Danos, L.; Schliwa, A.; Strittmatter, A.; Lenz, A.; Eisele, H.; Pohl, U. W.; Bimberg, D.

    2016-02-01

    Charge-carrier confinement in nanoscale In-rich agglomerations within a lateral InGaAs quantum well (QW) formed from stacked submonolayers (SMLs) of InAs in GaAs is studied. Low-temperature photoluminescence (PL) and magneto-PL clearly demonstrate strong vertical and weak lateral confinement, yielding two-dimensional (2D) excitons. In contrast, high-temperature (400 K) magneto-PL reveals excited states that fit a Fock-Darwin spectrum, characteristic of a zero-dimensional (0D) system in a magnetic field. This paradox is resolved by concluding that the system is heterodimensional: the light electrons extend over several In-rich agglomerations and see only the lateral InGaAs QW, i.e., are 2D, while the heavier holes are confined within the In-rich agglomerations, i.e., are 0D. This description is supported by single-particle effective-mass and eight-band k .p calculations. We suggest that the heterodimensional nature of nanoscale SML inclusions is fundamental to the ability of respective optoelectronic devices to operate efficiently and at high speed.

  10. Storage of charge carriers on emitter molecules in organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Weichsel, Caroline; Burtone, Lorenzo; Reineke, Sebastian; Hintschich, Susanne I.; Gather, Malte C.; Leo, Karl; Lüssem, Björn

    2012-08-01

    Organic light-emitting diodes (OLEDs) using the red phosphorescent emitter iridium(III)bis(2-methyldibenzo[f,h]quinoxaline) (acetylacetonate) [Ir(MDQ)2(acac)] are studied by time-resolved electroluminescence measurements. A transient overshoot after voltage turn-off is found, which is attributed to electron accumulation on Ir(MDQ)2(acac) molecules. The mechanism is verified via impedance spectroscopy and by application of positive and negative off-voltages. We calculate the density of accumulated electrons and find that it scales linearly with the doping concentration of the emitter. Using thin quenching layers, we locate the position of the emission zone during normal OLED operation and after voltage turn-off. In addition, the transient overshoot is also observed in three-color white-emitting OLEDs. By time- and spectrally resolved measurements using a streak camera, we directly attribute the overshoot to electron accumulation on Ir(MDQ)2(acac). We propose that similar processes are present in many state-of-the-art OLEDs and believe that the quantification of charge carrier storage will help to improve the efficiency of OLEDs.

  11. Thickness dependent charge transfer states and dark carriers density in vacuum deposited small molecule organic photocell

    NASA Astrophysics Data System (ADS)

    Shekhar, Himanshu; Tzabari, Lior; Solomeshch, Olga; Tessler, Nir

    2016-10-01

    We have investigated the influence of the active layer thickness on the balance of the internal mechanisms affecting the efficiency of copper phthalocyanine - fullerene (C60) based vacuum deposited bulk heterojunction organic photocell. We fabricated a range of devices for which we varied the thickness of the active layer from 40 to 120 nm and assessed their performance using optical and electrical characterization techniques. As reported previously for phthalocyanine:C60, the performance of the device is highly dependent on the active layer thickness and of all the thicknesses we tried, the 40 nm thin active layer device showed the best solar cell characteristic parameters. Using the transfer matrix based optical model, which includes interference effects, we calculated the optical power absorbed in the active layers for the entire absorption band, and we found that this cannot explain the trend with thickness. Measurement of the cell quantum efficiency as a function of light intensity showed that the relative weight of the device internal processes changes when going from 40 nm to 120 nm thick active layer. Electrical modeling of the device, which takes different internal processes into account, allowed to quantify the changes in the processes affecting the generation - recombination balance. Sub gap external quantum efficiency and morphological analysis of the surface of the films agree with the model's result. We found that as the thickness grows the density of charge transfer states and of dark carriers goes up and the uniformity in the vertical direction is reduced.

  12. Charge-carrier transport and recombination in heteroepitaxial CdTe

    SciTech Connect

    Kuciauskas, Darius Farrell, Stuart; Dippo, Pat; Moseley, John; Moutinho, Helio; Li, Jian V.; Allende Motz, A. M.; Kanevce, Ana; Zaunbrecher, Katherine; Gessert, Timothy A.; Levi, Dean H.; Metzger, Wyatt K.; Colegrove, Eric; Sivananthan, S.

    2014-09-28

    We analyze charge-carrier dynamics using time-resolved spectroscopy and varying epitaxial CdTe thickness in undoped heteroepitaxial CdTe/ZnTe/Si. By employing one-photon and nonlinear two-photon excitation, we assess surface, interface, and bulk recombination. Two-photon excitation with a focused laser beam enables characterization of recombination velocity at the buried epilayer/substrate interface, 17.5 μm from the sample surface. Measurements with a focused two-photon excitation beam also indicate a fast diffusion component, from which we estimate an electron mobility of 650 cm² (Vs)⁻¹ and diffusion coefficient D of 17 cm² s⁻¹. We find limiting recombination at the epitaxial film surface (surface recombination velocity Ssurface = (2.8 ± 0.3) × 10⁵cm s ⁻¹) and at the heteroepitaxial interface (interface recombination velocity Sinterface = (4.8 ± 0.5) × 10⁵ cm s⁻¹). The results demonstrate that reducing surface and interface recombination velocity is critical for photovoltaic solar cells and electronic devices that employ epitaxial CdTe.

  13. Modulation of phase behaviors and charge carrier mobilities by linkage length in discotic liquid crystal dimers.

    PubMed

    Wang, Yi-Fei; Zhang, Chun-Xiu; Wu, Hao; Zhang, Ao; Wang, Jian-Chuang; Zhang, Shuai-Feng; Pu, Jia-Ling

    2015-01-28

    A clear structure-property relationship was revealed in a series of triphenylene-based dimers, which contained two triphenylene nuclei each bearing five β-OC4H9 substituents and are linked through a flexible O(CH2)nO polymethylene chain (n=6-12). Dimers with the linkage close to twice the length of the free side chains (n=8, 9) exhibited a single Colhp phase, while others with the linkage shorter (n=6, 7) or longer (n=10, 11, 12) showed multiphase behaviors with a transition from the Colhp phase to Colh phase; hole mobilities of Colhp phases reached 1.4×10(-2) cm2 V(-1) s(-1) in the dimer for which the linkage is exactly twice the length of the free side chains (n=8), and decreased regularly both with linkage length becoming shorter or longer. This modulation of phase behaviors and charge carrier mobilities was demonstrated to be generated by various steric perturbations introduced by linkages with different lengths, which result in different degrees of lateral fluctuations of discotic moieties in the columns. PMID:25467212

  14. Universal crossover of the charge carrier fluctuation mechanism in different polymer/carbon nanotubes composites

    NASA Astrophysics Data System (ADS)

    Barone, C.; Landi, G.; Mauro, C.; Neitzert, H. C.; Pagano, S.

    2015-10-01

    Carbon nanotubes added to polymer and epoxy matrices are compounds of interest for applications in electronics and aerospace. The realization of high-performance devices based on these materials can profit from the investigation of their electric noise properties, as this gives a more detailed insight of the basic charge carriers transport mechanisms at work. The dc and electrical noise characteristics of different polymer/carbon nanotubes composites have been analyzed from 10 to 300 K. The results suggest that all these systems can be regarded as random resistive networks of tunnel junctions formed by adjacent carbon nanotubes. However, in the high-temperature regime, contributions deriving from other possible mechanisms cannot be separated using dc information alone. A transition from a fluctuation-induced tunneling process to a thermally activated regime is instead revealed by electric noise spectroscopy. In particular, a crossover is found from a two-level tunneling mechanism, operating at low temperatures, to resistance fluctuations of a percolative network, in the high-temperature region. The observed behavior of 1/f noise seems to be a general feature for highly conductive samples, independent on the type of polymer matrix and on the nanotube density.

  15. On the advancement of quantum dot solar cell performance through enhanced charge carrier dynamics

    NASA Astrophysics Data System (ADS)

    Baker, David R.

    The quantum dot solar cell is one of the few solar technologies which promises to compete with fossil fuels, but work is still needed to increase its performance. Electron transfer kinetics at interfaces and limitations of the redox couple within the cell, are responsible for lowering power conversion efficiency. Several techniques which are able to increase electron transfer within the working electrode and at the counter electrode/electrolyte interface are discussed in this dissertation. Trap sites on the surface of CdSe quantum dots are created when mercaptopropionic acid (MPA) is added to the suspension. The trap sites are emissive creating a loss pathway for photogenerated charges which will manifest as reduced photocurrent. MPA displaces amines on the surface of CdSe creating Se vacancies. Emission properties are controlled by the concentration of MPA. Because trap sites are generated, a more successful method to sensitize TiO2 films is the SILAR technique which directly grows quantum dots on the desired surface. Anodically etched TiO2 nanotubes yield photocurrents 20% greater than TiO2 nanoparticles because of longer electron diffusion lengths. Peak incident photon to charge carrier efficiencies of TiO2 nanotube samples show a doubling of photocurrent in the visible region compared to nanoparticles. The TiO2 substrates are sensitized with CdS by the SILAR process which is found to utilize both the inside and outside surfaces of the TiO2 nanotubes. Etched TiO2 nanotubes are removed from the underlying titanium foil in order to use spectroscopic techniques. Ultrafast transient absorption shows the extremely fast nature of charge injection from SILAR CdS into TiO 2 nanotubes. Surface area analysis of TiO2 nanotube powder gives an area of 77m2/g, a value 1.5 times larger than traditional TiO2 nanoparticles. By isolating the counter electrode with a salt bridge the effect of the polysulfide electrolyte is found to act as an electron scavenger on the working

  16. Effect of charge trapping on effective carrier lifetime in compound semiconductors: High resistivity CdZnTe

    SciTech Connect

    Kamieniecki, Emil

    2014-11-21

    The dominant problem limiting the energy resolution of compound semiconductor based radiation detectors is the trapping of charge carriers. The charge trapping affects energy resolution through the carrier lifetime more than through the mobility. Conventionally, the effective carrier lifetime is determined using a 2-step process based on measurement of the mobility-lifetime product (μτ) and determining drift mobility using time-of-flight measurements. This approach requires fabrication of contacts on the sample. A new RF-based pulse rise-time method, which replaces this 2-step process with a single non-contact direct measurement, is discussed. The application of the RF method is illustrated with high-resistivity detector-grade CdZnTe crystals. The carrier lifetime in the measured CdZnTe, depending on the quality of the crystals, was between about 5 μs and 8 μs. These values are in good agreement with the results obtained using conventional 2-step approach. While the effective carrier lifetime determined from the initial portion of the photoresponse transient combines both recombination and trapping in a manner similar to the conventional 2-step approach, both the conventional and the non-contact RF methods offer only indirect evaluation of the effect of charge trapping in the semiconductors used in radiation detectors. Since degradation of detector resolution is associated not with trapping but essentially with detrapping of carriers, and, in particular, detrapping of holes in n-type semiconductors, it is concluded that evaluation of recombination and detrapping during photoresponse decay is better suited for evaluation of compound semiconductors used in radiation detectors. Furthermore, based on previously reported data, it is concluded that photoresponse decay in high resistivity CdZnTe at room temperature is dominated by detrapping of carriers from the states associated with one type of point defect and by recombination of carriers at one type of

  17. Kinetics of optically excited charge carriers at the GaN surface: Influence of catalytic Pt nanostructures

    SciTech Connect

    Winnerl, Andrea Pereira, Rui N.; Stutzmann, Martin

    2015-10-21

    In this work, we use GaN with different deposited Pt nanostructures as a controllable model system to investigate the kinetics of photo-generated charge carriers in hybrid photocatalysts. We combine conductance and contact potential difference measurements to investigate the influence of Pt on the processes involved in the capture and decay of photo-generated charge carriers at and close to the GaN surface. We found that in the presence of Pt nanostructures the photo-excitation processes are similar to those found in Pt free GaN. However, in GaN with Pt nanostructures, photo-generated holes are preferentially trapped in surface states of the GaN covered with Pt and/or in electronic states of the Pt and lead to an accumulation of positive charge there, whereas negative charge is accumulated in localized states in a shallow defect band of the GaN covered with Pt. This preferential accumulation of photo-generated electrons close to the surface is responsible for a dramatic acceleration of the turn-off charge transfer kinetics and a stronger dependence of the surface photovoltage on light intensity when compared to a Pt free GaN surface. Our study shows that in hybrid photocatalysts, the metal nanostructures induce a spatially inhomogeneous surface band bending of the semiconductor that promotes a lateral drift of photogenerated charges towards the catalytic nanostructures.

  18. Characteristics of tissue distribution of various polysaccharides as drug carriers: influences of molecular weight and anionic charge on tumor targeting.

    PubMed

    Sugahara, S; Okuno, S; Yano, T; Hamana, H; Inoue, K

    2001-05-01

    Using the Walker 256 model for carcinosarcoma-bearing rats, we intravenously administered 5 polysaccharide carriers with various molecular weights (MWs) and electric charges and tested for their plasma and tissue distribution. Two carriers, carboxymethylated-D-manno-D-glucan (CMMG) and CMdextran (CMDex), showed higher plasma AUC than the other carriers tested, namely, CMchitin (CMCh), N-desulfated N-acetylated heparin (DSH), and hyaluronic acid (HA). This was consistently found to be true over the range of MWs tested. For CMDex, the maximum value of plasma AUC was obtained when the MW exceeded 150 kDa. As for the anionic charge, CMDex (110-180 kDa) with a degree of substitution (DS) of the CM groups ranging from 0.2 to 0.6, showed maximum plasma AUC values. Twenty-four hours after administration, the concentration of CMDex (180-250 kDa; DS: 0.6-1.2) in tumors was more than 3% of dose/g--approximately 10-fold higher than those observed with CMCh, DSH and HA. Doxorubicin (DXR) was bound to these carriers via a peptide spacer, GlyGlyPheGly (GGFG), to give carrier-GGFG-DXR conjugates (DXR content: 4.2-7.0 (w/w)%), and the antitumor effects of these conjugates were tested with Walker 256 carcinosarcoma-bearing rats by monitoring the tumor weights after a single intravenous injection. Compared with free DXR, CMDex-GGFG-DXR and CMMG-GGFG-DXR conjugates significantly suppressed tumor growth, while the CMCh-GGFG-DXR, DSH-GGFG-DXR, and HA-GGFG-DXR conjugates in a similar comparison showed weak tumor growth inhibition. These findings suggest that the antitumor effect of the carrier-DXR conjugates was related to the extent with which the carriers accumulated in the tumors.

  19. Remarkable enhancement of charge carrier mobility of conjugated polymer field-effect transistors upon incorporating an ionic additive

    PubMed Central

    Luo, Hewei; Yu, Chenmin; Liu, Zitong; Zhang, Guanxin; Geng, Hua; Yi, Yuanping; Broch, Katharina; Hu, Yuanyuan; Sadhanala, Aditya; Jiang, Lang; Qi, Penglin; Cai, Zhengxu; Sirringhaus, Henning; Zhang, Deqing

    2016-01-01

    Organic semiconductors with high charge carrier mobilities are crucial for flexible electronic applications. Apart from designing new conjugated frameworks, different strategies have been explored to increase charge carrier mobilities. We report a new and simple approach to enhancing the charge carrier mobility of DPP-thieno[3,2-b]thiophene–conjugated polymer by incorporating an ionic additive, tetramethylammonium iodide, without extra treatments into the polymer. The resulting thin films exhibit a very high hole mobility, which is higher by a factor of 24 than that of thin films without the ionic additive under the same conditions. On the basis of spectroscopic grazing incidence wide-angle x-ray scattering and atomic force microscopy studies as well as theoretical calculations, the remarkable enhancement of charge mobility upon addition of tetramethylammonium iodide is attributed primarily to an inhibition of the torsion of the alkyl side chains by the presence of the ionic species, facilitating a more ordered lamellar packing of the alkyl side chains and interchain π-π interactions. PMID:27386541

  20. Remarkable enhancement of charge carrier mobility of conjugated polymer field-effect transistors upon incorporating an ionic additive.

    PubMed

    Luo, Hewei; Yu, Chenmin; Liu, Zitong; Zhang, Guanxin; Geng, Hua; Yi, Yuanping; Broch, Katharina; Hu, Yuanyuan; Sadhanala, Aditya; Jiang, Lang; Qi, Penglin; Cai, Zhengxu; Sirringhaus, Henning; Zhang, Deqing

    2016-05-01

    Organic semiconductors with high charge carrier mobilities are crucial for flexible electronic applications. Apart from designing new conjugated frameworks, different strategies have been explored to increase charge carrier mobilities. We report a new and simple approach to enhancing the charge carrier mobility of DPP-thieno[3,2-b]thiophene-conjugated polymer by incorporating an ionic additive, tetramethylammonium iodide, without extra treatments into the polymer. The resulting thin films exhibit a very high hole mobility, which is higher by a factor of 24 than that of thin films without the ionic additive under the same conditions. On the basis of spectroscopic grazing incidence wide-angle x-ray scattering and atomic force microscopy studies as well as theoretical calculations, the remarkable enhancement of charge mobility upon addition of tetramethylammonium iodide is attributed primarily to an inhibition of the torsion of the alkyl side chains by the presence of the ionic species, facilitating a more ordered lamellar packing of the alkyl side chains and interchain π-π interactions.

  1. Remarkable enhancement of charge carrier mobility of conjugated polymer field-effect transistors upon incorporating an ionic additive.

    PubMed

    Luo, Hewei; Yu, Chenmin; Liu, Zitong; Zhang, Guanxin; Geng, Hua; Yi, Yuanping; Broch, Katharina; Hu, Yuanyuan; Sadhanala, Aditya; Jiang, Lang; Qi, Penglin; Cai, Zhengxu; Sirringhaus, Henning; Zhang, Deqing

    2016-05-01

    Organic semiconductors with high charge carrier mobilities are crucial for flexible electronic applications. Apart from designing new conjugated frameworks, different strategies have been explored to increase charge carrier mobilities. We report a new and simple approach to enhancing the charge carrier mobility of DPP-thieno[3,2-b]thiophene-conjugated polymer by incorporating an ionic additive, tetramethylammonium iodide, without extra treatments into the polymer. The resulting thin films exhibit a very high hole mobility, which is higher by a factor of 24 than that of thin films without the ionic additive under the same conditions. On the basis of spectroscopic grazing incidence wide-angle x-ray scattering and atomic force microscopy studies as well as theoretical calculations, the remarkable enhancement of charge mobility upon addition of tetramethylammonium iodide is attributed primarily to an inhibition of the torsion of the alkyl side chains by the presence of the ionic species, facilitating a more ordered lamellar packing of the alkyl side chains and interchain π-π interactions. PMID:27386541

  2. Retrieval of Electronic Spectra of Charge Carriers in Organic Field-Effect Transistors from Charge Modulation Reflectance Spectra Distorted by Optical Interference

    NASA Astrophysics Data System (ADS)

    Miyata, Kiyoshi; Ishino, Yuta; Watanabe, Kazuya; Miwa, Kazumoto; Uemura, Takafumi; Takeya, Jun; Matsumoto, Yoshiyasu

    2013-06-01

    Charge modulation (CM) spectroscopy is useful for detecting and characterizing the electronic structure of charge carriers accumulated in organic field-effect transistors (OFETs). However, CM spectra are distorted by optical interference due to multiple reflections in OFETs particularly when reflection configurations are used. In this study, we demonstrated a method for retrieving the spectra of complex refractive indices of carriers from the distorted CM spectra by using a 4×4 matrix algorithm with general transition matrices. We tested this method by applying it to the CM spectra of a rubrene single-crystal FET measured at several incident angles of light. In spite of the strong distortion of the CM spectra, we could retrieve the spectrum of the imaginary part of refractive indices, which is similar to that observed in the transmission configuration. This method extends the applicability of CM spectroscopy to OFETs with opaque electrodes, where transmission configurations cannot possibly be applied.

  3. Numerical Analysis on Non-Equilibrium Mechanism of Laser-Supported Detonation Wave Using Multiply-Charged Ionization

    SciTech Connect

    Shiraishi, Hiroyuki

    2006-05-02

    Laser-Supported Detonation (LSD), one type of Laser-Supported Plasma (LSP), is considered as the most important phenomena because it can generate high pressure and high temperature for laser absorption. In this study, I have numerically simulated the 1-D LSD waves propagating through a helium gas, in which Multiply-charged ionization model is considered for describing an accurate ionization process.

  4. FOB-SH: Fragment orbital-based surface hopping for charge carrier transport in organic and biological molecules and materials

    NASA Astrophysics Data System (ADS)

    Spencer, J.; Gajdos, F.; Blumberger, J.

    2016-08-01

    We introduce a fragment orbital-based fewest switches surface hopping method, FOB-SH, designed to efficiently simulate charge carrier transport in strongly fluctuating condensed phase systems such as organic semiconductors and biomolecules. The charge carrier wavefunction is expanded and the electronic Hamiltonian constructed in a set of singly occupied molecular orbitals of the molecular sites that mediate the charge transfer. Diagonal elements of the electronic Hamiltonian (site energies) are obtained from a force field, whereas the off-diagonal or electronic coupling matrix elements are obtained using our recently developed analytic overlap method. We derive a general expression for the exact forces on the adiabatic ground and excited electronic state surfaces from the nuclear gradients of the charge localized electronic states. Applications to electron hole transfer in a model ethylene dimer and through a chain of ten model ethylenes validate our implementation and demonstrate its computational efficiency. On the larger system, we calculate the qualitative behaviour of charge mobility with change in temperature T for different regimes of the intermolecular electronic coupling. For small couplings, FOB-SH predicts a crossover from a thermally activated regime at low temperatures to a band-like transport regime at higher temperatures. For higher electronic couplings, the thermally activated regime disappears and the mobility decreases according to a power law. This is interpreted by a gradual loss in probability for resonance between the sites as the temperature increases. The polaron hopping model solved for the same system gives a qualitatively different result and underestimates the mobility decay at higher temperatures. Taken together, the FOB-SH methodology introduced here shows promise for a realistic investigation of charge carrier transport in complex organic, aqueous, and biological systems.

  5. Carrier separation and charge transport characteristics of reduced graphene oxide supported visible-light active photocatalysts.

    PubMed

    Vinoth, Ramalingam; Karthik, Peramaiah; Muthamizhchelvan, Chellamuthu; Neppolian, Bernaurdshaw; Ashokkumar, Muthupandian

    2016-02-21

    Extending the absorption to the visible region by tuning the optical band-gap of semiconductors and preventing charge carrier recombination are important parameters to achieve a higher efficiency in the field of photocatalysis. The inclusion of reduced graphene oxide (rGO) support in photocatalysts is one of the key strategies to address the above-mentioned issues. In this study, rGO supported AgI-mesoTiO2 photocatalysts were synthesized using a sonochemical approach. The physical effects of ultrasound not only improved the crystallinity of AgI-mesoTiO2 but also increased the surface area and loading of the AgI-mesoTiO2 nanocomposite on rGO sheets. The low intense oxygen functionalities (C-O-C and COOH groups) peak observed in the high resolution C1s spectrum of a hybrid AgI-mesoTiO2-rGO photocatalyst clearly confirmed the successful reduction of graphene oxide (GO) to rGO. The interfacial charge transfer between the rGO and the p-n junction of heterostructured photocatalysts has decreased the band-gap of the photocatalyst from 2.80 to 2.65 eV. Importantly, the integration of rGO into AgI-mesoTiO2 composites serves as a carrier separation centre and provides further insight into the electron transfer pathways of heterostructured nanocomposites. The individual effects of photo-generated electrons and holes over rGO on the photocatalytic degradation efficiency of rhodamine (RhB) and methyl orange (MO) using AgI-mesoTiO2-rGO photocatalysts were also studied. Our experimental results revealed that photo-generated superoxide (O2(-)˙) radicals are the main reactive species for the degradation of MO, whereas photo-generated holes (h(+)) are responsible for the degradation of RhB. As a result, 60% enhancement in MO degradation was observed in the presence of rGO in comparison to that of the pure AgI-mesoTiO2 photocatalyst. This is due to the good electron acceptor and the ultrafast electron transfer properties of rGO that can effectively reduce the molecular oxygen to

  6. Effect of temperature and rare-earth doping on charge-carrier mobility in indium-monoselenide crystals

    SciTech Connect

    Abdinov, A. Sh.; Babayeva, R. F.; Amirova, S. I.; Rzayev, R. M.

    2013-08-15

    In the temperature range T = 77-600 K, the dependence of the charge-carrier mobility ({mu}) on the initial dark resistivity is experimentally investigated at 77 K ({rho}d{sub 0}), as well as on the temperature and the level (N) of rare-earth doping with such elements as gadolinium (Gd), holmium (Ho), and dysprosium (Dy) in n-type indium-monoselenide (InSe) crystals. It is established that the anomalous behavior of the dependences {mu}(T), {mu}({rho}d{sub 0}), and {mu}(N) found from the viewpoint of the theory of charge-carrier mobility in crystalline semiconductors is related, first of all, to partial disorder in indium-monoselenide crystals and can be attributed to the presence of random drift barriers in the free energy bands.

  7. Comparison of majority carrier charge transfer velocities at Si/polymer and Si/metal photovoltaic heterojunctions

    SciTech Connect

    Price, Michelle J.; Foley, Justin M.; May, Robert A.; Maldonado, Stephen

    2010-08-23

    Two sets of silicon (Si) heterojunctions with either Au or PEDOT:PSS contacts have been prepared to compare interfacial majority carrier charge transfer processes at Si/metal and Si/polymer heterojunctions. Current-voltage (J-V) responses at a range of temperatures, wavelength-dependent internal quantum yields, and steady-state J-V responses under illumination for these devices are reported. The cumulative data suggest that the velocity of majority carrier charge transfer, v{sub n}, is several orders of magnitude smaller at n-Si/PEDOT:PSS contacts than at n-Si/Au junctions, resulting in superior photoresponse characteristics for these inorganic/organic heterojunctions.

  8. Classical two-dimensional numerical algorithm for ?-Induced charge carrier advection-diffusion in Medipix-3 silicon pixel detectors

    NASA Astrophysics Data System (ADS)

    Biamonte, Mason; Idarraga, John

    2013-04-01

    A classical hybrid alternating-direction implicit difference scheme is used to simulate two-dimensional charge carrier advection-diffusion induced by alpha particles incident upon silicon pixel detectors at room temperature in vacuum. A mapping between the results of the simulation and a projection of the cluster size for each incident alpha is constructed. The error between the simulation and the experimental data diminishes with the increase in the applied voltage for the pixels in the central region of the cluster. Simulated peripheral pixel TOT values do not match the data for any value of applied voltage, suggesting possible modifications to the current algorithm from first principles. Coulomb repulsion between charge carriers is built into the algorithm using the Barnes-Hut tree algorithm. The plasma effect arising from the initial presence of holes in the silicon is incorporated into the simulation. The error between the simulation and the data helps identify physics not accounted for in standard literature simulation techniques.

  9. The Study Of Charge Carrier Transport On The Calamitic Liquid Crystals `` 5, 5'-Di-(Alkyl-Pyridin-Yl) - 2' Bithiophenes''

    NASA Astrophysics Data System (ADS)

    Shakya, Naresh; Pokhrel, Chandra; Ellman, Brett; Getmanenko, Yulia; Twieg, Robert

    2010-03-01

    The hole and electron mobilities in both types of calamitic liquid crystals C9 [5,5'-Di-(5-n-nonyl-pyridin-2-yl)-2,2'-bithiophenes] and C10 [5,5'-Di-(5-n-decyl-pyridin-2-yl)-2,2'-bithiophenes] were studied. The charge carrier mobilities were strongly electric field dependent. The mobilities decreased continuously with increase in the electric field up to a certain value, after which it became constant. Both types of charge carrier mobilities are independent of the temperature over our temperature range. The qualitative feature of our results could be tentatively explained by the Monte--Carlo modeling proposed by H Bassler. However, the results require further study for better understanding.

  10. Photogeneration of charge carrier correlated with amplified spontaneous emission in single crystals of a thiophene/phenylene co-oligomer.

    PubMed

    Saeki, Akinori; Seki, Shu; Shimizu, Yasuhiro; Yamao, Takeshi; Hotta, Shu

    2010-04-01

    Thiophene/phenylene co-oligomers have substantial promise for the use of not only organic electronics but also organic optical devices. However, considerably less is known about the correlation between their optical and optoelectronic properties. We have investigated the charge carrier generation in 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5) single crystals by flash-photolysis time-resolved microwave conductivity (TRMC) and transient absorption spectroscopy (TAS). It was found that the dependence of photocarrier generation efficiency on excitation photon density differed from that of emission efficiency once amplified spontaneous emission (ASE) and resultant spectrally narrowed emission occur upon exposure to 355 nm. In contrast, the dependences of emission and photocarrier generation efficiencies were identical when ASE was not involved at a different excitation wavelength (193 nm). An approximated analytical solution of rate equation considering ASE or singlet-singlet annihilation was applied to the experiments, exhibiting good agreement. On the basis of TRMC, TAS, and extinction coefficient of radical cation assessed by pulse radiolysis, the minimum charge carrier mobility was estimated, without electrodes, to be 0.12 cm(2) V(-1) s(-1). The dynamics of charge carrier and triplet excited state is discussed, accompanying with examination by time-dependent density functional theory. The present work would open the way to a deeper understanding of the fate of excited state in optically robust organic semiconducting crystals.

  11. Charge carrier transport and collection enhancement of copper indium diselenide photoactive nanoparticle-ink by laser crystallization

    SciTech Connect

    Nian, Qiong; Cheng, Gary J.; Zhang, Martin Y.; Wang, Yuefeng; Das, Suprem R.; Bhat, Venkataprasad S.; Huang, Fuqiang

    2014-09-15

    There has been increasing needs for cost-effective and high performance thin film deposition techniques for photovoltaics. Among all deposition techniques, roll-to-roll printing of nanomaterials has been a promising method. However, the printed thin film contains many internal imperfections, which reduce the charge-collection performance. Here, direct pulse laser crystallization (DPLC) of photoactive nanoparticles-inks is studied to meet this challenge. In this study, copper indium selenite (CIS) nanoparticle-inks is applied as an example. Enhanced crystallinity, densified structure in the thin film is resulted after DLPC under optimal conditions. It is found that the decreased film internal imperfections after DPLC results in reducing scattering and multi-trapping effects. Both of them contribute to better charge-collection performance of CIS absorber material by increasing extended state mobility and carrier lifetime, when carrier transport and kinetics are coupled. Charge carrier transport was characterized after DPLC, showing mobility increased by 2 orders of magnitude. Photocurrent under AM1.5 illumination was measured and shown 10 times enhancement of integrated power density after DPLC, which may lead to higher efficiency in photo-electric energy conversion.

  12. Insights from transport modeling of unusual charge carrier behavior of PDTSiTzTz:PC71BM bulk heterojunction materials

    NASA Astrophysics Data System (ADS)

    Slobodyan, Oleksiy; Moench, Sarah; Liang, Kelly; Danielson, Eric; Holliday, Bradley; Dodabalapur, Ananth

    2015-03-01

    Development of hole-transporting copolymers for use in bulk heterojunctions (BHJs) has significantly improved organic solar cell performance. Despite advances on the materials side, the physics of charge carrier transport remains unsettled. Intrigued by its ability to maintain high fill factors in thick active layers, we studied the copolymer poly[2-(5-(4,4-dioctyl-4H-silolo[3,2-b:4,5-b’]dithiophen-2-yl)-3-tetradecylthiophen-2-yl)- 5-(3-tetradecylthiophen-2-yl)thiazolo[5,4-d]thiazole] (PDTSiTzTz) blended with PC71BM. Results show mobilities which are carrier-concentration-dependent and characterized by a negative Poole-Frenkel effect. Such behavior is not described by current carrier transport models. Established transport mechanisms like multiple-trap-and-release or variable range hopping yield dependence of mobility on carrier concentration. However, a more basic model like Gaussian distribution model (GDM) is needed to produce the negative Poole-Frenkel effect, though GDM cannot describe carrier-concentration-dependent mobility. We have combined key aspects of existing models to create a unified transport model capable of describing phenomena observed in PDTSiTzTz:PC71BM. This model can be used to address open questions about transport physics of organic BHJ materials. U.S. Department of Energy, Award Number DE-SC0001091.

  13. Formation of polaron pairs and time-resolved photogeneration of free charge carriers in π-conjugated polymers

    NASA Astrophysics Data System (ADS)

    Frankevich, Eugene; Ishii, Hisao; Hamanaka, Yasushi; Yokoyama, Takahiro; Fuji, Akihiko; Li, Sergey; Yoshino, Katsumi; Nakamura, Arao; Seki, Kazuhiko

    2000-07-01

    We have performed in the present work time-resolved experiments on poly(3-dodecyl-thiophene) (P3DDT) and poly(2,5-dioctyloxy-p-phenylene vinylene) (OO-PPV) films by directly probing the formation of charge carriers responsible for the cw photoconductivity within the time domain of -10 ps to 1 ns. Laser light pulses of 400 nm wavelength, 150 fs width, induced photoconductivity in a sample with a frequency 1 kHz. Red 800 nm light pulses delayed in respect to blue ones were revealed to affect the photoconductivity. The effect of the second pulses increased with the delay time. Red light induced changes of the photoconductivity were positive in OO-PPV, and negative in P3DDT. These results are rationalized as an evidence of delayed not immediate formation of free charge carriers. The carriers seem to be formed within 10 ps after the pumping pulse. A mechanism of formation of free polarons from polaron pair is suggested, which has permitted to explain main feature of the results including different signs of the effect of the red light in different polymers.

  14. Electron spin resonance study of Er-concentration effect in GaAs;Er,O containing charge carriers

    SciTech Connect

    Elmasry, F.; Okubo, S.; Ohta, H.; Fujiwara, Y.

    2014-05-21

    Er-concentration effect in GaAs;Er,O containing charge carriers (n-type, high resistance, p-type) has been studied by X-band Electron spin resonance (ESR) at low temperature (4.7 K < T < 18 K). Observed A, B, and C types of ESR signals were identical to those observed previously in GaAs:Er,O without carrier. The local structure around Er-2O centers is not affected by carriers because similar angular dependence of g-values was observed in both cases (with/without carrier). For temperature dependence, linewidth and lineshape analysis suggested the existence of Er dimers with antiferromagnetic exchange interaction of about 7 K. Moreover, drastic decrease of ESR intensity for C signal in p-type sample was observed and it correlates with the decrease of photoluminescence (PL) intensity. Possible model for the Er-2O trap level in GaAs:Er,O is discussed from the ESR and PL experimental results.

  15. Investigation of free charge carrier dynamics in single-crystalline CVD diamond by two-photon absorption

    SciTech Connect

    Ivakin, E V; Kisialiou, I G; Ralchenko, V G; Bolshakov, A P; Ashkinazi, E E; Sharonov, G V

    2014-11-30

    By using the methods of transient gratings (TGs) and induced absorption, we have studied the kinetics of plasma of free charge carriers (FCCs) created by the action of a picosecond laser pulse in two high-purity diamond single crystals synthesised from the gas phase. The gratings with different spatial periods have been excited at the wavelengths of 266 or 213 nm (above and below the fundamental absorption edge in diamond) and probed with continuous-wave radiation in the visible region. At the moderate FCC concentrations (∼7 × 10{sup 17} cm{sup -3}), the coefficient of ambipolar diffusion and the carrier recombination time of two crystals are 20.3 and 18.9 cm{sup 2} s{sup -1} and 30 and 190 ns, respectively. The increase in the carrier concentration up to 5 × 10{sup 19} cm{sup -3} reduces the TG lifetime. We have determined the conditions under which the relaxation of the grating of carriers leads to the formation of a thermal grating, with the amplitude sufficient for its experimental observation. (interaction of laser radiation with matter. laser plasma)

  16. Analysis of carrier transport and carrier trapping in organic diodes with polyimide-6,13-Bis(triisopropylsilylethynyl)pentacene double-layer by charge modulation spectroscopy and optical second harmonic generation measurement

    SciTech Connect

    Lim, Eunju E-mail: taguchi.d.aa@m.titech.ac.jp; Taguchi, Dai E-mail: taguchi.d.aa@m.titech.ac.jp Iwamoto, Mitsumasa E-mail: taguchi.d.aa@m.titech.ac.jp

    2014-08-18

    We studied the carrier transport and carrier trapping in indium tin oxide/polyimide (PI)/6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)/Au diodes by using charge modulation spectroscopy (CMS) and time-resolved electric field induced optical second harmonic generation (TR-EFISHG) measurements. TR-EFISHG directly probes the spatial carrier behaviors in the diodes, and CMS is useful in explaining the carrier motion with respect to energy. The results clearly indicate that the injected carriers move across TIPS-pentacene thorough the molecular energy states of TIPS-pentacene and accumulate at the PI/TIPS-pentacene interface. However, some carriers are trapped in the PI layers. These findings take into account the capacitance-voltage and current-voltage characteristics of the diodes.

  17. Effect of Mg doping on the structural and free-charge carrier properties of InN films

    SciTech Connect

    Xie, M.-Y.; Ben Sedrine, N.; Hung, L.; Monemar, B.; Darakchieva, V.; Schöche, S.; Hofmann, T.; Schubert, M.; Wang, X.; Yoshikawa, A.; Wang, K.; Araki, T.; Nanishi, Y.

    2014-04-28

    We present a comprehensive study of free-charge carrier and structural properties of two sets of InN films grown by molecular beam epitaxy and systematically doped with Mg from 1.0 × 10{sup 18} cm{sup −3} to 3.9 × 10{sup 21} cm{sup −3}. The free electron and hole concentration, mobility, and plasmon broadening parameters are determined by infrared spectroscopic ellipsometry. The lattice parameters, microstructure, and surface morphology are determined by high-resolution X-ray diffraction and atomic force microscopy. Consistent results on the free-charge carrier type are found in the two sets of InN films and it is inferred that p-type conductivity could be achieved for 1.0 × 10{sup 18} cm{sup −3} ≲ [Mg] ≲ 9.0 × 10{sup 19} cm{sup −3}. The systematic change of free-charge carrier properties with Mg concentration is discussed in relation to the evolution of extended defect density and growth mode. A comparison between the structural characteristics and free electron concentrations in the films provides insights in the role of extended and point defects for the n-type conductivity in InN. It further allows to suggest pathways for achieving compensated InN material with relatively high electron mobility and low defect densities. The critical values of Mg concentration for which polarity inversion and formation of zinc-blende InN occurred are determined. Finally, the effect of Mg doping on the lattice parameters is established and different contributions to the strain in the films are discussed.

  18. Charge carrier motion in disordered conjugated polymers: a multiscale ab-initio study

    SciTech Connect

    Vukmirovic, Nenad; Wang, Lin-Wang

    2009-11-10

    We developed an ab-initio multiscale method for simulation of carrier transport in large disordered systems, based on direct calculation of electronic states and electron-phonon coupling constants. It enabled us to obtain the never seen before rich microscopic details of carrier motion in conjugated polymers, which led us to question several assumptions of phenomenological models, widely used in such systems. The macroscopic mobility of disordered poly(3- hexylthiophene) (P3HT) polymer, extracted from our simulation, is in agreement with experimental results from the literature.

  19. Two-dimensional semimetal in wide HgTe quantum wells: Charge-carrier energy spectrum and magnetotransport

    SciTech Connect

    Germanenko, A. V.; Minkov, G. M.; Rut, O. E.; Sherstobitov, A. A.; Dvoretsky, S. A.; Mikhailov, N. N.

    2013-12-15

    The magnetoresistivity and the Hall and Shubnikov-de Haas effects in heterostructures with a single 20.2-nm-wide quantum well made from the gapless semiconductor HgTe are studied experimentally. The measurements are performed on gated samples over a wide range of electron and hole densities. The data obtained are used to reconstruct the energy spectrum of electrons and holes in the vicinity of the extrema of the quantum-confinement subbands. It is shown that the charge-carrier dispersion relation in the investigated systems differs from that calculated within the framework of the conventional kp model.

  20. Combined impact of entropy and carrier delocalization on charge transfer exciton dissociation at the donor-acceptor interface

    NASA Astrophysics Data System (ADS)

    Ono, Shota; Ohno, Kaoru

    2016-08-01

    Several models of the charge transfer exciton (CTE) have been proposed to explain its dissociation at the donor-acceptor (DA) interface. However, the underlying physics is still under debate. Here, we derive a temperature (T ) dependent tight-binding model for an electron-hole pair at the DA interface. The main finding is the existence of the localization-delocalization transition at a critical T , which can explain the CTE dissociation. The present study highlights the combined effect of entropy (finite T ) and carrier delocalization in the CTE dissociation.

  1. 47 CFR 51.907 - Transition of price cap carrier access charges.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... “trunking basket” as described in 47 CFR 61.42(d)(2) and (3) to the extent that such rate elements are not... or intrastate tariff revisions increasing such rates. (e) Step 4. Beginning July 1, 2015...) Each Price Cap Carrier shall calculate its 2015 Target Composite Terminating End Office Access...

  2. Influence of the charge carrier tunneling processes on the recombination dynamics in single lateral quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Hermannstädter, C.; Beirne, G. J.; Witzany, M.; Heldmaier, M.; Peng, J.; Bester, G.; Wang, L.; Rastelli, A.; Schmidt, O. G.; Michler, P.

    2010-08-01

    We report on the charge carrier dynamics in single lateral quantum dot molecules and the effect of an applied electric field on the molecular states. Controllable electron tunneling manifests itself in a deviation from the typical excitonic decay behavior in dot molecules. It results in a faster population decay and can be strongly influenced by the tuning electric field and intermolecular Coulomb energies. A rate equation model is developed and compared to the experimental data to gain more insight into the charge transfer and tunneling mechanisms. Nonresonant (phonon-mediated) electron tunneling which changes the molecular exciton character from direct to indirect, and vice versa, is found to be the dominant tunable decay mechanism of excitons besides radiative recombination.

  3. Charge carrier dynamics of methylammonium lead iodide: from PbI₂-rich to low-dimensional broadly emitting perovskites.

    PubMed

    Klein, Johannes R; Flender, Oliver; Scholz, Mirko; Oum, Kawon; Lenzer, Thomas

    2016-04-28

    We provide an investigation of the charge carrier dynamics of the (MAI)(x)(PbI2)(1-x) system in the range x = 0.32-0.90 following the recently published "pseudobinary phase-composition processing diagram" of Song et al. (Chem. Mater., 2015, 27, 4612). The dynamics were studied using ultrafast pump-supercontinuum probe spectroscopy over the pump fluence range 2-50 μJ cm(-2), allowing for a wide variation of the initial carrier density. At high MAI excess (x = 0.90), low-dimensional perovskites (LDPs) are formed, and their luminescence spectra are significantly blue-shifted by ca. 50 nm and broadened compared to the 3D perovskite. The shift is due to quantum confinement effects, and the inhomogeneous broadening arises from different low-dimensional structures (predominantly 2D, but presumably also 1D and 0D). Accurate transient carrier temperatures are extracted from the transient absorption spectra. The regimes of carrier-carrier, carrier-optical phonon and acoustic phonon scattering are clearly distinguished. Perovskites with mole fractions x ≤ 0.71 exhibit extremely fast carrier cooling (ca. 300 fs) at low fluence of 2 μJ cm(-2), however cooling slows down significantly at high fluence of 50 μJ cm(-2) due to the "hot phonon effect" (ca. 2.8 ps). A kinetic analysis of the electron-hole recombination dynamics provides second-order recombination rate constants k2 which decrease from 5.3 to 1.5 × 10(-9) cm(3) s(-1) in the range x = 0.32-0.71. In contrast, recombination in the LDPs (x = 0.90) is more than one order of magnitude faster, 6.4 × 10(-8) cm(3) s(-1), which is related to the confined perovskite structure. Recombination in these LDPs should be however still slow enough for their potential application as efficient broadband emitters or solar light-harvesting materials. PMID:26972104

  4. Charge carrier photogeneration and recombination in ladder-type poly(para-phenylene): Interplay between impurities and external electric field

    NASA Astrophysics Data System (ADS)

    Gulbinas, V.; Hertel, D.; Yartsev, A.; Sundström, V.

    2007-12-01

    Charge carrier generation and decay in m -LPPP polymer films were examined by means of femtosecond transient absorption spectroscopy in the time window of 100fs-15ns . Two modes of polaron formation with distinct behavior were identified, impurity induced in the absence of an external electric field and electric field induced in pristine film. While field induced charge generation is relatively slow, occurring throughout the excited state lifetime, the rate of impurity induced charge generation is much faster and depends on excitation wavelength; it occurs on the several hundred femtosecond time scale under excitation within the main absorption band, but excitation into the red wing of the absorption band results in charge generation within less than 100fs . Polaron decay through geminate electron-hole recombination occurs with widely distributed lifetimes, from ˜0.8ns to microseconds; the polarons characterized by the shortest decay time have a redshifted absorption spectrum (as compared to more long-lived polarons) and are attributed to tightly bound polaron pairs.

  5. Determination of Effective Stability Constants of Ion-Carrier Complexes in Ion Selective Nanospheres with Charged Solvatochromic Dyes.

    PubMed

    Xie, Xiaojiang; Bakker, Eric

    2015-11-17

    Ionophores are widely used ion carriers in ion selective sensors. The effective stability constant (β) is a key physical parameter providing valuable guidelines to the design of ionophores and carrier-based ion selective sensors. The β value of ion-carrier complex in plasticized poly(vinyl chloride) (PVC) membranes and solutions have been determined in the past by various techniques, but most of them are difficult to implement at the nanoscale owing to the ultrasmall sample volume. A new methodology based on charged solvatochromic dyes is introduced here for the first time to determine β values directly within ion selective nanospheres. Four ionophores with different selectivities toward Na(+), K(+), Ca(2+), and H(+), respectively, are successfully characterized in nanospheres composed of triblock copolymer Pluronic F-127 and bis(2-ethylhexyl) sebacate. The values determined in the nanospheres are smaller compared with those in plasticized PVC membranes, indicating a more polar nanosphere microenvironment and possible uneven distribution of the sensing components in the interfacial region. PMID:26502342

  6. Absorption of Light by Free Charge Carriers in the Crystalline CdS Under Intense Electron Irradiation

    NASA Astrophysics Data System (ADS)

    Kulikov, V. D.; Yakovlev, V. Yu.

    2016-09-01

    The process of light absorption by free electrons in the crystalline cadmium sulfide under irradiation by a nanosecond electron beam with the current density of 8-100 A/cm2 is studied. A superlinear increase in optical absorption is observed if the beam current density is increased from ~8 to 12 A/cm2. The nature of light absorption by thermalized electrons corresponds to the scattering on lattice defects. An increase in the exponent of the power dependence of light absorption on the wavelength with increasing beam current density is associated with the single and double ionization of donors and acceptors. It is concluded that accumulation of charge carriers occurs without capture by traps due to their impact ionization by secondary electrons, whose energy in the thermalization stage is comparable with the band gap of the crystal. According to the results of calculations, the capture cross section of electrons by holes at quadratic recombination is ~10-20 cm2, the Auger recombination coefficient is ~10-31 cm6•s-1, and the charge carrier concentration is ~1.3•1018-1.5•1019 cm-3.

  7. The Effect of Diiodooctane on the Charge Carrier Generation in Organic Solar Cells Based on the Copolymer PBDTTT-C

    PubMed Central

    Zusan, Andreas; Gieseking, Björn; Zerson, Mario; Dyakonov, Vladimir; Magerle, Robert; Deibel, Carsten

    2015-01-01

    Microstructural changes and the understanding of their effect on photocurrent generation are key aspects for improving the efficiency of organic photovoltaic devices. We analyze the impact of a systematically increased amount of the solvent additive diiodooctane (DIO) on the morphology of PBDTTT-C:PC71BM blends and related changes in free carrier formation and recombination by combining surface imaging, photophysical and charge extraction techniques. We identify agglomerates visible in AFM images of the 0% DIO blend as PC71BM domains embedded in an intermixed matrix phase. With the addition of DIO, a decrease in the size of fullerene domains along with a demixing of the matrix phase appears for 0.6% and 1% DIO. Surprisingly, transient absorption spectroscopy reveals an efficient photogeneration already for the smallest amount of DIO, although the largest efficiency is found for 3% DIO. It is ascribed to a fine-tuning of the blend morphology in terms of the formation of interpenetrating donor and acceptor phases minimizing geminate and nongeminate recombination as indicated by charge extraction experiments. An increase in the DIO content to 10% adversely affects the photovoltaic performance, most probably due to an inefficient free carrier formation and trapping in a less interconnected donor-acceptor network. PMID:25655785

  8. The effect of diiodooctane on the charge carrier generation in organic solar cells based on the copolymer PBDTTT-C.

    PubMed

    Zusan, Andreas; Gieseking, Björn; Zerson, Mario; Dyakonov, Vladimir; Magerle, Robert; Deibel, Carsten

    2015-02-06

    Microstructural changes and the understanding of their effect on photocurrent generation are key aspects for improving the efficiency of organic photovoltaic devices. We analyze the impact of a systematically increased amount of the solvent additive diiodooctane (DIO) on the morphology of PBDTTT-C:PC71BM blends and related changes in free carrier formation and recombination by combining surface imaging, photophysical and charge extraction techniques. We identify agglomerates visible in AFM images of the 0% DIO blend as PC71BM domains embedded in an intermixed matrix phase. With the addition of DIO, a decrease in the size of fullerene domains along with a demixing of the matrix phase appears for 0.6% and 1% DIO. Surprisingly, transient absorption spectroscopy reveals an efficient photogeneration already for the smallest amount of DIO, although the largest efficiency is found for 3% DIO. It is ascribed to a fine-tuning of the blend morphology in terms of the formation of interpenetrating donor and acceptor phases minimizing geminate and nongeminate recombination as indicated by charge extraction experiments. An increase in the DIO content to 10% adversely affects the photovoltaic performance, most probably due to an inefficient free carrier formation and trapping in a less interconnected donor-acceptor network.

  9. Dynamics and relaxation of charge carriers in poly(methylmethacrylate)-lithium salt based polymer electrolytes plasticized with ethylene carbonate

    NASA Astrophysics Data System (ADS)

    Pal, P.; Ghosh, A.

    2016-07-01

    In this paper, we have studied the dynamics and relaxation of charge carriers in poly(methylmethacrylate)-lithium salt based polymer electrolytes plasticized with ethylene carbonate. Structural and thermal properties have been examined using X-ray diffraction and differential scanning calorimetry, respectively. We have analyzed the complex conductivity spectra by using power law model coupled with the contribution of electrode polarization at low frequencies and high temperatures. The temperature dependence of the ionic conductivity and crossover frequency exhibits Vogel-Tammann-Fulcher type behavior indicating a strong coupling between the ionic and the polymer chain segmental motions. The scaling of the ac conductivity indicates that relaxation dynamics of charge carriers follows a common mechanism for all temperatures and ethylene carbonate concentrations. The analysis of the ac conductivity also shows the existence of a nearly constant loss in these polymer electrolytes at low temperatures and high frequencies. The fraction of free anions and ion pairs in polymer electrolyte have been obtained from the analysis of Fourier transform infrared spectra. It is observed that these quantities influence the behavior of the composition dependence of the ionic conductivity.

  10. Charge Carrier Transport Through the Interface Between Hybrid Electrodes and Organic Materials in Flexible Organic Light Emitting Diodes.

    PubMed

    Zhou, Huanyu; Cheong, Hahn-Gil; Park, Jin-Woo

    2016-05-01

    We investigated the electronic properties of composite-type hybrid transparent conductive electrodes (h-TCEs) based on Ag nanowire networks (AgNWs) and indium tin oxide (ITO). These h-TCEs were developed to replace ITO, and their mechanical flexibility is superior to that of ITO. However, the characteristics of charge carriers and the mechanism of charge-carrier transport through the interface between the h-TCE and an organic material are not well understood when the h-TCE is used as the anode in a flexible organic light-emitting diode (f-OLED). AgNWs were spin coated onto polymer substrates, and ITO was sputtered atop the AgNWs. The electronic energy structures of h-TCEs were investigated by ultraviolet photoelectron spectroscopy. f-OLEDs were fabricated on both h-TCEs and ITO for comparison. The chemical bond formation at the interface between the h-TCE and the organic layer in f-OLEDs was investigated by X-ray photoelectron spectroscopy. The performances of f-OLEDs were compared based on the analysis results. PMID:27483896

  11. Tungsten-based nanomaterials (WO3 & Bi2WO6): Modifications related to charge carrier transfer mechanisms and photocatalytic applications

    NASA Astrophysics Data System (ADS)

    Girish Kumar, S.; Koteswara Rao, K. S. R.

    2015-11-01

    Heterogeneous photocatalysis is an ideal green energy technology for the purification of wastewater. Although titania dominates as the reference photocatalyst, its wide band gap is a bottleneck for extended utility. Thus, search for non-TiO2 based nanomaterials has become an active area of research in recent years. In this regard, visible light absorbing polycrystalline WO3 (2.4-2.8 eV) and Bi2WO6 (2.8 eV) with versatile structure-electronic properties has gained considerable interest to promote the photocatalytic reactions. These materials are also explored in selective functional group transformation in organic reactions, because of low reduction and oxidation potential of WO3 CB and Bi2WO6 VB, respectively. In this focused review, various strategies such as foreign ion doping, noble metal deposition and heterostructuring with other semiconductors designed for efficient photocatalysis is discussed. These modifications not only extend the optical response to longer wavelengths, but also prolong the life-time of the charge carriers and strengthen the photocatalyst stability. The changes in the surface-bulk properties and the charge carrier transfer dynamics associated with each modification correlating to the high activity are emphasized. The presence of oxidizing agents, surface modification with Cu2+ ions and synthesis of exposed facets to promote the degradation rate is highlighted. In depth study on these nanomaterials is likely to sustain interest in wastewater remediation and envisaged to signify in various green energy applications.

  12. Fullerene-Free Polymer Solar Cells with Highly Reduced Bimolecular Recombination and Field-Independent Charge Carrier Generation.

    PubMed

    Roland, Steffen; Schubert, Marcel; Collins, Brian A; Kurpiers, Jona; Chen, Zhihua; Facchetti, Antonio; Ade, Harald; Neher, Dieter

    2014-08-21

    Photogeneration, recombination, and transport of free charge carriers in all-polymer bulk heterojunction solar cells incorporating poly(3-hexylthiophene) (P3HT) as donor and poly([N,N'-bis(2-octyldodecyl)-naphthelene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)) (P(NDI2OD-T2)) as acceptor polymer have been investigated by the use of time delayed collection field (TDCF) and time-of-flight (TOF) measurements. Depending on the preparation procedure used to dry the active layers, these solar cells comprise high fill factors (FFs) of up to 67%. A strongly reduced bimolecular recombination (BMR), as well as a field-independent free charge carrier generation are observed, features that are common to high performance fullerene-based solar cells. Resonant soft X-ray measurements (R-SoXS) and photoluminescence quenching experiments (PQE) reveal that the BMR is related to domain purity. Our results elucidate the similarities of this polymeric acceptor with the superior recombination properties of fullerene acceptors. PMID:26278084

  13. A quantitative model for charge carrier transport, trapping and recombination in nanocrystal-based solar cells

    PubMed Central

    Bozyigit, Deniz; Lin, Weyde M. M.; Yazdani, Nuri; Yarema, Olesya; Wood, Vanessa

    2015-01-01

    Improving devices incorporating solution-processed nanocrystal-based semiconductors requires a better understanding of charge transport in these complex, inorganic–organic materials. Here we perform a systematic study on PbS nanocrystal-based diodes using temperature-dependent current–voltage characterization and thermal admittance spectroscopy to develop a model for charge transport that is applicable to different nanocrystal-solids and device architectures. Our analysis confirms that charge transport occurs in states that derive from the quantum-confined electronic levels of the individual nanocrystals and is governed by diffusion-controlled trap-assisted recombination. The current is limited not by the Schottky effect, but by Fermi-level pinning because of trap states that is independent of the electrode–nanocrystal interface. Our model successfully explains the non-trivial trends in charge transport as a function of nanocrystal size and the origins of the trade-offs facing the optimization of nanocrystal-based solar cells. We use the insights from our charge transport model to formulate design guidelines for engineering higher-performance nanocrystal-based devices. PMID:25625647

  14. A quantitative model for charge carrier transport, trapping and recombination in nanocrystal-based solar cells

    NASA Astrophysics Data System (ADS)

    Bozyigit, Deniz; Lin, Weyde M. M.; Yazdani, Nuri; Yarema, Olesya; Wood, Vanessa

    2015-01-01

    Improving devices incorporating solution-processed nanocrystal-based semiconductors requires a better understanding of charge transport in these complex, inorganic-organic materials. Here we perform a systematic study on PbS nanocrystal-based diodes using temperature-dependent current-voltage characterization and thermal admittance spectroscopy to develop a model for charge transport that is applicable to different nanocrystal-solids and device architectures. Our analysis confirms that charge transport occurs in states that derive from the quantum-confined electronic levels of the individual nanocrystals and is governed by diffusion-controlled trap-assisted recombination. The current is limited not by the Schottky effect, but by Fermi-level pinning because of trap states that is independent of the electrode-nanocrystal interface. Our model successfully explains the non-trivial trends in charge transport as a function of nanocrystal size and the origins of the trade-offs facing the optimization of nanocrystal-based solar cells. We use the insights from our charge transport model to formulate design guidelines for engineering higher-performance nanocrystal-based devices.

  15. Ionic liquid based lithium battery electrolytes: charge carriers and interactions derived by density functional theory calculations.

    PubMed

    Angenendt, Knut; Johansson, Patrik

    2011-06-23

    The solvation of lithium salts in ionic liquids (ILs) leads to the creation of a lithium ion carrying species quite different from those found in traditional nonaqueous lithium battery electrolytes. The most striking differences are that these species are composed only of ions and in general negatively charged. In many IL-based electrolytes, the dominant species are triplets, and the charge, stability, and size of the triplets have a large impact on the total ion conductivity, the lithium ion mobility, and also the lithium ion delivery at the electrode. As an inherent advantage, the triplets can be altered by selecting lithium salts and ionic liquids with different anions. Thus, within certain limits, the lithium ion carrying species can even be tailored toward distinct important properties for battery application. Here, we show by DFT calculations that the resulting charge carrying species from combinations of ionic liquids and lithium salts and also some resulting electrolyte properties can be predicted. PMID:21591707

  16. Exciton and charge carrier dynamics in few-layer WS2

    NASA Astrophysics Data System (ADS)

    Vega-Mayoral, Victor; Vella, Daniele; Borzda, Tetiana; Prijatelj, Matej; Tempra, Iacopo; Pogna, Eva A. A.; Dal Conte, Stefano; Topolovsek, Peter; Vujicic, Natasa; Cerullo, Giulio; Mihailovic, Dragan; Gadermaier, Christoph

    2016-03-01

    Semiconducting transition metal dichalcogenides (TMDs) have been applied as the active layer in photodetectors and solar cells, displaying substantial charge photogeneration yields. However, their large exciton binding energy, which increases with decreasing thickness (number of layers), as well as the strong resonance peaks in the absorption spectra suggest that excitons are the primary photoexcited states. Detailed time-domain studies of the photoexcitation dynamics in TMDs exist mostly for MoS2. Here, we use femtosecond optical spectroscopy to study the exciton and charge dynamics following impulsive photoexcitation in few-layer WS2. We confirm excitons as the primary photoexcitation species and find that they dissociate into charge pairs with a time constant of about 1.3 ps. The better separation of the spectral features compared to MoS2 allows us to resolve a previously undetected process: these charges diffuse through the samples and get trapped at defects, such as flake edges or grain boundaries, causing an appreciable change of their transient absorption spectra. This finding opens the way to further studies of traps in TMD samples with different defect contents.Semiconducting transition metal dichalcogenides (TMDs) have been applied as the active layer in photodetectors and solar cells, displaying substantial charge photogeneration yields. However, their large exciton binding energy, which increases with decreasing thickness (number of layers), as well as the strong resonance peaks in the absorption spectra suggest that excitons are the primary photoexcited states. Detailed time-domain studies of the photoexcitation dynamics in TMDs exist mostly for MoS2. Here, we use femtosecond optical spectroscopy to study the exciton and charge dynamics following impulsive photoexcitation in few-layer WS2. We confirm excitons as the primary photoexcitation species and find that they dissociate into charge pairs with a time constant of about 1.3 ps. The better

  17. A planarized triphenylborane mesogen: discotic liquid crystals with ambipolar charge-carrier transport properties.

    PubMed

    Kushida, Tomokatsu; Shuto, Ayumi; Yoshio, Masafumi; Kato, Takashi; Yamaguchi, Shigehiro

    2015-06-01

    A discotic liquid-crystalline (LC) material, consisting of a planarized triphenylborane mesogen, was synthesized. X-ray diffraction analysis confirmed that this compound forms a hexagonal columnar LC phase with an interfacial distance of 3.57 Å between the discs. At ambient temperature, this boron-centered discotic liquid crystal exhibited ambipolar carrier transport properties with electron and hole mobility values of approximately 10(-3) and 3×10(-5)  cm(2)  V(-1)  s(-1), respectively.

  18. Transient luminescence induced by electrical refilling of charge carrier traps of dislocation network at hydrophilically bonded Si wafers interface

    SciTech Connect

    Bondarenko, Anton; Vyvenko, Oleg

    2014-02-21

    Dislocation network (DN) at hydrophilically bonded Si wafers interface is placed in space charge region (SCR) of a Schottky diode at a depth of about 150 nm from Schottky electrode for simultaneous investigation of its electrical and luminescent properties. Our recently proposed pulsed traps refilling enhanced luminescence (Pulsed-TREL) technique based on the effect of transient luminescence induced by refilling of charge carrier traps with electrical pulses is further developed and used as a tool to establish DN energy levels responsible for D1 band of dislocation-related luminescence in Si (DRL). In present work we do theoretical analysis and simulation of traps refilling kinetics dependence on refilling pulse magnitude (Vp) in two levels model: shallow and deep. The influence of initial charge state of deep level on shallow level occupation-Vp dependence is discussed. Characteristic features predicted by simulations are used for Pulsed-TREL experimental results interpretation. We conclude that only shallow (∼0.1 eV from conduction and valence band) energetic levels in the band gap participate in D1 DRL.

  19. Theoretical predictions on the electronic structure and charge carrier mobility in 2D Phosphorus sheets

    PubMed Central

    Xiao, Jin; Long, Mengqiu; Zhang, Xiaojiao; Ouyang, Jun; Xu, Hui; Gao, Yongli

    2015-01-01

    We have investigated the electronic structure and carrier mobility of four types of phosphorous monolayer sheet (α-P, β-P,γ-P and δ-P) using density functional theory combined with Boltzmann transport method and relaxation time approximation. It is shown that α-P, β-P and γ-P are indirect gap semiconductors, while δ-P is a direct one. All four sheets have ultrahigh carrier mobility and show anisotropy in-plane. The highest mobility value is ~3 × 105 cm2V−1s−1, which is comparable to that of graphene. Because of the huge difference between the hole and electron mobilities, α-P, γ-P and δ-P sheets can be considered as n-type semiconductors, and β-P sheet can be considered as a p-type semiconductor. Our results suggest that phosphorous monolayer sheets can be considered as a new type of two dimensional materials for applications in optoelectronics and nanoelectronic devices. PMID:26035176

  20. Massively parallel kinetic Monte Carlo simulations of charge carrier transport in organic semiconductors

    NASA Astrophysics Data System (ADS)

    van der Kaap, N. J.; Koster, L. J. A.

    2016-02-01

    A parallel, lattice based Kinetic Monte Carlo simulation is developed that runs on a GPGPU board and includes Coulomb like particle-particle interactions. The performance of this computationally expensive problem is improved by modifying the interaction potential due to nearby particle moves, instead of fully recalculating it. This modification is achieved by adding dipole correction terms that represent the particle move. Exact evaluation of these terms is guaranteed by representing all interactions as 32-bit floating numbers, where only the integers between -222 and 222 are used. We validate our method by modelling the charge transport in disordered organic semiconductors, including Coulomb interactions between charges. Performance is mainly governed by the particle density in the simulation volume, and improves for increasing densities. Our method allows calculations on large volumes including particle-particle interactions, which is important in the field of organic semiconductors.

  1. Impact of speciation on the electron charge transfer properties of nanodiamond drug carriers

    NASA Astrophysics Data System (ADS)

    Sun, Baichuan; Barnard, Amanda S.

    2016-07-01

    Unpassivated diamond nanoparticles (bucky-diamonds) exhibit a unique surface reconstruction involving graphitization of certain crystal facets, giving rise to hybrid core-shell particles containing both aromatic and aliphatic carbon. Considerable effort is directed toward eliminating the aromatic shell, but persistent graphitization of subsequent subsurface-layers makes perdurable purification a challenge. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the impact of different fractions of aromatic and aliphatic carbon on the charge transfer properties of the ensembles of bucky-diamonds. By predicting quality factors for a variety of cases, we find that perfect purification is not necessary to preserve selectivity, and there is a clear motivation for purifying samples to improve the sensitivity of charge transfer reactions. This may prove useful in designing drug delivery systems where the release of (selected) drugs needs to be sensitive to specific conditions at the point of delivery.Unpassivated diamond nanoparticles (bucky-diamonds) exhibit a unique surface reconstruction involving graphitization of certain crystal facets, giving rise to hybrid core-shell particles containing both aromatic and aliphatic carbon. Considerable effort is directed toward eliminating the aromatic shell, but persistent graphitization of subsequent subsurface-layers makes perdurable purification a challenge. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the impact of different fractions of aromatic and aliphatic carbon on the charge transfer properties of the ensembles of bucky-diamonds. By predicting quality factors for a variety of cases, we find that perfect purification is not necessary to preserve selectivity, and there is a clear motivation for purifying samples to improve the sensitivity of charge transfer reactions. This may prove

  2. Signatures of electron-magnon interaction in charge and spin currents through magnetic tunnel junctions: A nonequilibrium many-body perturbation theory approach

    NASA Astrophysics Data System (ADS)

    Mahfouzi, Farzad; Nikolić, Branislav K.

    2014-07-01

    We develop a numerically exact scheme for resumming certain classes of Feynman diagrams in the self-consistent perturbative expansion for the electron and magnon self-energies in the nonequilibrium Green function formalism applied to a coupled electron-magnon (e-m) system driven out of equilibrium by the applied finite bias voltage. Our scheme operates with the electronic and magnonic GFs and the corresponding self-energies viewed as matrices in the Keldysh space, rather than conventionally extracting their retarded and lesser components, which greatly simplifies translation of diagrams into compact mathematical expressions and their computational implementation. This is employed to understand the effect of inelastic e-m scattering on charge and spin current vs bias voltage Vb in F/I/F (F-ferromagnet; I-insulating barrier) magnetic tunnel junctions (MTJs), which are modeled on a quasi-one-dimensional (quasi-1D) tight-binding lattice for the electronic subsystem and quasi-1D Heisenberg model for the magnonic subsystem. For this purpose, we evaluate the Fock diagram for the electronic self-energy and the electron-hole polarization bubble diagram for the magnonic self-energy. The respective electronic and magnonic GF lines within these diagrams are the fully interacting ones, thereby requiring to solve the ensuing coupled system of nonlinear integral equations self-consistently. Despite using the quasi-1D model and treating e-m interaction in many-body fashion only within a small active region consisting of few lattice sites around the F/I interface, our analysis captures essential features of the so-called zero-bias anomaly observed [V. Drewello, J. Schmalhorst, A. Thomas, and G. Reiss, Phys. Rev. B 77, 014440 (2008), 10.1103/PhysRevB.77.014440] in both MgO- and AlOx-based realistic 3D MTJs where the second derivative d2I /dVb2 (i.e., inelastic electron tunneling spectrum) of charge current exhibits sharp peaks of opposite sign on either side Vb=0. We show that this

  3. Diffusion length of photo-generated charge carriers in layers and powders of CH3NH3PbI3 perovskite

    NASA Astrophysics Data System (ADS)

    Dittrich, Th.; Lang, F.; Shargaieva, O.; Rappich, J.; Nickel, N. H.; Unger, E.; Rech, B.

    2016-08-01

    The diffusion or transport lengths of photo-generated charge carriers in CH3NH3PbI3 layers (thickness up to 1 μm) and powders have been directly measured with high accuracy by modulated surface photovoltage after Goodman. The values of the diffusion lengths of photo-generated charge carriers ranged from 200 nm to tenths of μm. In thin CH3NH3PbI3 layers, the transport lengths corresponded to the layer thickness whereas in thicker layers and in crystallites of CH3NH3PbI3 powders the grain size limited the diffusion length. For grains, the diffusion length of photo-generated charge carriers depended on the measurement conditions.

  4. Redox-active charge carriers of conducting polymers as a tuner of conductivity and its potential window.

    PubMed

    Park, Han-Saem; Ko, Seo-Jin; Park, Jeong-Seok; Kim, Jin Young; Song, Hyun-Kon

    2013-01-01

    Electric conductivity of conducting polymers has been steadily enhanced towards a level worthy of being called its alias, "synthetic metal". PEDOT:PSS (poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate)), as a representative conducting polymer, recently reached around 3,000 S cm(-1), the value to open the possibility to replace transparent conductive oxides. The leading strategy to drive the conductivity increase is solvent annealing in which aqueous solution of PEDOT:PSS is treated with an assistant solvent such as DMSO (dimethyl sulfoxide). In addition to the conductivity enhancement, we found that the potential range in which PEDOT:PSS is conductive is tuned wider into a negative potential direction by the DMSO-annealing. Also, the increase in a redox-active fraction of charge carriers is proposed to be responsible for the enhancement of conductivity in the solvent annealing process. PMID:23949091

  5. Redox-active charge carriers of conducting polymers as a tuner of conductivity and its potential window

    PubMed Central

    Park, Han-Saem; Ko, Seo-Jin; Park, Jeong-Seok; Kim, Jin Young; Song, Hyun-Kon

    2013-01-01

    Electric conductivity of conducting polymers has been steadily enhanced towards a level worthy of being called its alias, “synthetic metal”. PEDOT:PSS (poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate)), as a representative conducting polymer, recently reached around 3,000 S cm−1, the value to open the possibility to replace transparent conductive oxides. The leading strategy to drive the conductivity increase is solvent annealing in which aqueous solution of PEDOT:PSS is treated with an assistant solvent such as DMSO (dimethyl sulfoxide). In addition to the conductivity enhancement, we found that the potential range in which PEDOT:PSS is conductive is tuned wider into a negative potential direction by the DMSO-annealing. Also, the increase in a redox-active fraction of charge carriers is proposed to be responsible for the enhancement of conductivity in the solvent annealing process. PMID:23949091

  6. Dynamics and relaxation of charge carriers in poly(methylmethacrylate)-based polymer electrolytes embedded with ionic liquid

    NASA Astrophysics Data System (ADS)

    Pal, P.; Ghosh, A.

    2015-12-01

    In the present paper, we have studied dynamics and relaxation of the charge carriers in polymethylmethacrylate-lithium bis(trifluoromethane sulfonyl)imide polymer electrolytes embedded with 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid. We have analyzed the frequency dependent conductivity spectra using the random free-energy barrier model coupled with the contribution of electrode polarization in the low frequency region. The temperature dependence of ionic conductivity, and relaxation time obtained from the analysis of the spectra exhibits Vogel-Tammann-Fulcher type behavior. The Barton-Nakajima-Namikawa relation is consistent with the results obtained from the random free-energy barrier model. The scaling of ac conductivity spectra has been performed to understand the effect of temperature as well as the composition on the relaxation mechanism. The analysis of the ac conductivity also clearly indicates the existence of a nearly constant loss phenomenon at low temperatures or at high frequencies.

  7. Solar-induced direct biomass-to-electricity hybrid fuel cell using polyoxometalates as photocatalyst and charge carrier

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Mu, Wei; Liu, Mengjie; Zhang, Xiaodan; Cai, Hongli; Deng, Yulin

    2014-02-01

    The current polymer-exchange membrane fuel cell technology cannot directly use biomass as fuel. Here we present a solar-induced hybrid fuel cell that is directly powered with natural polymeric biomasses, such as starch, cellulose, lignin, and even switchgrass and wood powders. The fuel cell uses polyoxometalates as the photocatalyst and charge carrier to generate electricity at low temperature. This solar-induced hybrid fuel cell combines some features of solar cells, fuel cells and redox flow batteries. The power density of the solar-induced hybrid fuel cell powered by cellulose reaches 0.72 mW cm-2, which is almost 100 times higher than cellulose-based microbial fuel cells and is close to that of the best microbial fuel cells reported in literature. Unlike most cell technologies that are sensitive to impurities, the cell reported in this study is inert to most organic and inorganic contaminants present in the fuels.

  8. Solar-induced direct biomass-to-electricity hybrid fuel cell using polyoxometalates as photocatalyst and charge carrier.

    PubMed

    Liu, Wei; Mu, Wei; Liu, Mengjie; Zhang, Xiaodan; Cai, Hongli; Deng, Yulin

    2014-01-01

    The current polymer-exchange membrane fuel cell technology cannot directly use biomass as fuel. Here we present a solar-induced hybrid fuel cell that is directly powered with natural polymeric biomasses, such as starch, cellulose, lignin, and even switchgrass and wood powders. The fuel cell uses polyoxometalates as the photocatalyst and charge carrier to generate electricity at low temperature. This solar-induced hybrid fuel cell combines some features of solar cells, fuel cells and redox flow batteries. The power density of the solar-induced hybrid fuel cell powered by cellulose reaches 0.72 mW cm(-2), which is almost 100 times higher than cellulose-based microbial fuel cells and is close to that of the best microbial fuel cells reported in literature. Unlike most cell technologies that are sensitive to impurities, the cell reported in this study is inert to most organic and inorganic contaminants present in the fuels.

  9. Eigen function and corresponding eigen values of charge carriers in V-grooves quantum wires with variable width

    NASA Astrophysics Data System (ADS)

    Zaheri, Ali Hossein Mohammad

    2016-06-01

    In this work, we have calculated analytically the energy spectra of electrons and holes in V-grooves quantum wires. To modify wire structure, we have used the equations which suggested in the work of Inoshita et al. We introduce a new effective potential scheme which is applicable and matchable with actual interface geometry of this groove of ridge quantum wires. By applying this effective potential and considering a suitable transformed coordinate that allows the decoupling of the two-dimensional wave functions, we have calculated eigen values of the charge carriers in three states as well as the wave functions. We found that by increasing the curvature at the top of quantum wire (b) the energy eigen value decreases. Our results are in good agreement with the earlier investigations.

  10. The Effect of Dynamical Image Forces on The Transport Properties of Charge Carriers and Excitons in Metal-Semiconductor Nanostructures

    NASA Astrophysics Data System (ADS)

    Cherqui, Charles

    We examine coupled metal nanoparticle/semiconductor hybrid nano-stuctures and analyze the effect that the surface response metal nanoparticles (MNP) has on the transport properties of the system. This analysis is accomplished by treating surface plasmons as quantum oscillators. We find that charge carriers traveling in the nearby semiconductors experience a repulsion due to the ground state energy of the quantum SP (QSP). This effect is shown to be the quantum analogue of the ponderomotive effect found in plasma physics. We then extend the theory to examine the transport properties of carbon nano-tube excitons in the presence of localized SPs and show that this system maps onto a Fano-Anderson Hamiltonian. Through numerical simulation, we show that the emission patterns of the system are severely modified by the presence of localized surface plasmons.

  11. Eigen function and corresponding eigen values of charge carriers in V-grooves quantum wires with variable width

    NASA Astrophysics Data System (ADS)

    Zaheri, Ali Hossein Mohammad

    2016-06-01

    In this work, we have calculated analytically the energy spectra of electrons and holes in V-grooves quantum wires. To modify wire structure, we have used the equations which suggested in the work of Inoshita et al. We introduce a new effective potential scheme which is applicable and matchable with actual interface geometry of this groove of ridge quantum wires. By applying this effective potential and considering a suitable transformed coordinate that allows the decoupling of the two-dimensional wave functions, we have calculated eigen values of the charge carriers in three states as well as the wave functions. We found that by increasing the curvature at the top of quantum wire (b) the energy eigen value decreases. Our results are in good agreement with the earlier investigations.

  12. Empirical in operando analysis of the charge carrier dynamics in hematite photoanodes by PEIS, IMPS and IMVS.

    PubMed

    Klotz, Dino; Ellis, David Shai; Dotan, Hen; Rothschild, Avner

    2016-09-14

    In this Perspective, we introduce intensity modulated photocurrent/voltage spectroscopy (IMPS and IMVS) as powerful tools for the analysis of charge carrier dynamics in photoelectrochemical (PEC) cells for solar water splitting, taking hematite (α-Fe2O3) photoanodes as a case study. We complete the picture by including photoelectrochemical impedance spectroscopy (PEIS) and linking the trio of PEIS, IMPS and IMVS, introduced here as photoelectrochemical immittance triplets (PIT), both mathematically and phenomenologically, demonstrating what conclusions can be extracted from these measurements. A novel way of analyzing the results by an empirical approach with minimal presumptions is introduced, using the distribution of relaxation times (DRT) function. The DRT approach is compared to conventional analysis approaches that are based on physical models and therefore come with model presumptions. This work uses a thin film hematite photoanode as a model system, but the approach can be applied to other PEC systems as well. PMID:27524381

  13. Structural features of the photogeneration mechanism of free charge carriers in element-containing polydisalicylidene azomethine series

    SciTech Connect

    Aleksandrova, E. L.; Ivanov, A. G. Geller, N. M. Shamanin, V. V.

    2010-05-15

    Photophysical properties of new polytetra- and polydisalicylidene azomethines (PSAMs) with chains containing Si, Ge, Sn, or transition metal atoms and atoms of a number of other divalent metals are studied. Based on data on ultraviolet and infrared spectra, it was found that the noncovalent transannular donor-acceptor interaction N M (M is semimetal or metal) occurs in polymers, which leads to the formation of a polymer chain of six-membered cycles. As a result, polyconjugations arise in PSAMs by a 'non-classical' mechanism. Due to multiple donor-acceptor interactions of unshared electron pairs of azomethine groups with vacant d-orbitals in metals, polymers feature conductive, photosensitive, and photoconductive properties. The photosensitivity and quantum yield of photogeneration of free charge carriers for PSAMs are close to the values characteristic of classical conducting polymers. It was shown that the PSAM properties are controlled by the azomethine fragment structure and acceptor properties of metal. A mechanism of free carrier photogeneration was suggested.

  14. Overall current-voltage characteristics of space charge controlled currents for thin films by a single carrier species

    NASA Astrophysics Data System (ADS)

    Seki, Kazuhiko

    2014-08-01

    The Mott-Gurney equation (Child's law) has been frequently applied to measure the mobility of carrier transport layers. One of the main assumption in the Mott-Gurney theory is ignoring the diffusive currents. It was not obvious, however, whether the diffusive currents can be ignored for thin carrier transport layers. We obtained the current-voltage relation using analytical solutions of drift-diffusion equation coupled with the Poisson's equation. The integration constants were numerically determined using nonlinear equations obtained from boundary conditions. A simple analytical relation between the voltage and current was also derived. The analytical equation improved over the Mott-Gurney equation when the voltage is between 0.1 and 2 (V) at room temperature. By using published data, we show that both the mobility and the layer thickness can be simultaneously obtained by applying the analytical expression. The effect of diffusion on the current-voltage relation is explained by the movement of the virtual electrode formed by space charge accumulation.

  15. Molecular weight dependent charge carrier mobility in poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene).

    PubMed

    Verilhac, Jean-Marie; Pokrop, Rafal; LeBlevennec, Gilles; Kulszewicz-Bajer, Irena; Buga, Katarzyna; Zagorska, Malgorzata; Sadki, Said; Pron, Adam

    2006-07-13

    Poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene), a polymer recently used for the fabrication of organic field effect transistors, has been fractionated into five fractions distinctly differing in their molecular weights (Mn), with the goal of determining the influence of the degree of polymerization (DPn) on its principal physicochemical parameters. It has been demonstrated that within the Mn range studied (from 1.5 kDa to 10.5 kDa by SEC), corresponding to DPn from 10 to 38, the polymer band gap steadily decreases with growing molecular weight, which is clearly manifested by an increasing bathochromic shift of the band originating from the pi-pi* transition. The same trend is observed for the HOMO level, determined from the onset of the p-doping in cyclic voltammetry, which shifts from -5.10 eV to -4.90 eV for the lowest and the highest molecular weight fractions, respectively. The most pronounced influence of DPn has been found for the charge carriers' mobility-one of the most important parameters of field effect transistors (FETs) fabricated from this polymer. A fourfold increase in DPn results in an increase of the carriers' mobility by more than 3 orders of magnitude. Comparison of these results with those obtained for fractionated regioregular poly(3-hexylthiophene) shows a strikingly similar behavior of both polymers with respect to the molecular weight.

  16. Low Exciton-Phonon Coupling, High Charge Carrier Mobilities, and Multiexciton Properties in Two-Dimensional Lead, Silver, Cadmium, and Copper Chalcogenide Nanostructures.

    PubMed

    Ding, Yuchen; Singh, Vivek; Goodman, Samuel M; Nagpal, Prashant

    2014-12-18

    The development of two-dimensional (2D) nanomaterials has revealed novel physical properties, like high carrier mobilities and the tunable coupling of charge carriers with phonons, which can enable wide-ranging applications in optoelectronic and thermoelectric devices. While mechanical exfoliation of graphene and some transition metal dichalcogenides (e.g., MoS2, WSe2) has enabled their fabrication as 2D semiconductors and integration into devices, lack of similar syntheses for other 2D semiconductor materials has hindered further progress. Here, we report measurements of fundamental charge carrier interactions and optoelectronic properties of 2D nanomaterials made from two-monolayers-thick PbX, CdX, Cu2X, and Ag2X (X = S, Se) using colloidal syntheses. Extremely low coupling of charge carriers with phonons (2-6-fold lower than bulk and other low-dimensional semiconductors), high carrier mobilities (0.2-1.2 cm(2) V(-1) s(-1), without dielectric screening), observation of infrared surface plasmons in ultrathin 2D semiconductor nanostructures, strong quantum-confinement, and other multiexcitonic properties (different phonon coupling and photon-to-charge collection efficiencies for band-edge and higher-energy excitons) can pave the way for efficient solution-processed devices made from these 2D nanostructured semiconductors. PMID:26273976

  17. Photoinduced Charge Carrier Generation and Decay in Sequentially Deposited Polymer/Fullerene Layers: Bulk Heterojunction vs. Planar Interface

    SciTech Connect

    Nardes, A.; Ayzner, A.; Hammond, S.; Ferguson, A.; Schwartz, B.; Kopidakis, N.

    2012-04-05

    In this work, we use the time-resolved microwave conductivity (TRMC) technique to study the dynamics of charge carrier generation in sequentially deposited conjugated polymer/fullerene layers. These layers are either fully solution-processed, using orthogonal solvents for the layers of the polymer poly(3-hexylthiophene) (P3HT) and the fullerene phenyl-C{sup 61}-butyric acid methyl ester (PCBM), or prepared by thermally evaporating a C{sup 60} layer onto P3HT films. Our work is motivated by the remarkable efficiency of organic photovoltaic (OPV) devices using a sequentially processed P3HT/PCBM active layer. Here we use an electrodeless photoconductivity probe, so we can photoexcite the sample either through the polymer or the fullerene layer. We use samples with extremely thick P3HT films (2.4 {micro}m) and show that excitation from either side of both as-cast and thermally annealed sample yields virtually identical results, consistent with mixing of the PCBM into the polymer film. We also compare solution-deposited samples to samples made by thermally evaporating C{sup 60} on P3HT, and find that we can distinguish between charge generation in bulk-P3HT and at the polymer/fullerene interface. We show that, despite their morphological differences, the carrier dynamics in the sequentially processed samples resemble those of mixed, bulk heterojunction (BHJ) systems. All of this is consistent with the idea that PCBM readily mixes into the P3HT film in sequentially deposited P3HT/PCBM samples, although the total amount of fullerene mixed into the P3HT appears to be less than that typically used in an optimized BHJ. Finally, we discuss the implications for OPV device architectures prepared by sequential deposition from solution.

  18. Concentration and mobility of charge carriers in thin polymers at high temperature determined by electrode polarization modeling

    NASA Astrophysics Data System (ADS)

    Diaham, Sombel; Locatelli, Marie-Laure

    2012-07-01

    Charge carrier concentration (n0) and effective mobility (μeff) are reported in two polymer films (<10 μm) and in a very high temperature range (from 200 to 400 °C). This was possible thanks to an electrode polarization modeling of broadband dielectric spectroscopy data. It is shown that the glass transition temperature (Tg) occurrence has a strong influence on the temperature dependence of n0 and μeff. We carry out that n0 presents two distinct Arrhenius-like behaviors below and above Tg, while μeff exhibits a Vogel-Fulcher-Tamman behavior only above Tg whatever the polymer under study. For polyimide films, n0 varies from 1 × 1014 to 4 × 1016 cm-3 and μeff from 1 × 10-8 to 2 × 10-6 cm2 V-1 s-1 between 200 °C to 400 °C. Poly(amide-imide) films show n0 values between 6 × 1016 and 4 × 1018 cm-3 from 270 °C to 400 °C, while μeff varies between 1 × 10-10 and 2 × 10-7 cm2 V-1 s-1. Considering the activation energies of these physical parameters in the temperature range of investigation, n0 and μeff values appear as coherent with those reported in the literature at lower temperature (<80 °C). Surface charge carrier concentrations (nS) are reported and discussed for potential passivation (i.e., surface electrical insulation) applications. Polyimide films appear as good candidates due to nS values less than 1011 cm-2 up to 300 °C.

  19. Optical conductivity of charge carriers interacting with a two-level systems reservoir

    NASA Astrophysics Data System (ADS)

    Villares Ferrer, A.; Caldeira, A. O.; Smith, C. Morais

    2006-11-01

    Using the functional-integral method we investigate the effective dynamics of a charged particle coupled to a set of two-level systems as a function of temperature and external electric field. The optical conductivity and the direct current (dc) resistivity induced by the reservoir are computed. Three different regimes are found depending on the two-level system spectral function, which may lead to a non-Drude optical conductivity in a certain range of parameters. Our results contrast to the behavior found when considering the usual bath of harmonic oscillators which we are able to recover in the limit of very low temperatures.

  20. Pectin and charge modified pectin hydrogel beads as a colon-targeted drug delivery carrier.

    PubMed

    Jung, Jiyoung; Arnold, Robert D; Wicker, Louise

    2013-04-01

    The physical and chemical properties of commercial low methoxyl citrus pectins, CP 28 and CP 55, and a pectinmethylesterase (PME) charge modified citrus pectin (MP 38) were compared, and the differences in ability to encapsulate indomethacin in hydrogel beads was determined at 0.5 or 1.0% (w/v) indomethacin ratio, and 100, 200 or 300 mM CaCl(2) solution. In order to investigate the drug release characteristics, indomethacin loaded dried hydrogel beads were immersed in simulated gastric fluids (pH 1.2) for 2h, followed by immersing in simulated intestinal fluids (pH 7.4) for 3h. Pectin type was highly significant (p<0.0001) for encapsulation efficiency and in vitro release assay. Encapsulation efficiency was also highly affected (p<0.0001) by indomethacin ratio and CaCl(2) concentration. The accumulative release rate of indomethacin from pectin hydrogel bead was less than 15% in simulated gastro-intestinal fluids. MP 38 beads showed significantly higher entrapment efficiency and lower release rate than beads formed from CP 28 or CP 55. MP 38 hydrogel formulated with 300 mM CaCl(2) and 0.5% indomethacin ratio showed the highest entrapment efficiency. These studies suggest that charge modification of pectin improves encapsulation efficiency of drugs for colon targeted drug delivery system through oral administration.

  1. Scaling dependence of memory windows and different carrier charging behaviors in Si nanocrystal nonvolatile memory devices

    NASA Astrophysics Data System (ADS)

    Yu, Jie; Chen, Kun-ji; Ma, Zhong-yuan; Zhang, Xin-xin; Jiang, Xiao-fan; Wu, Yang-qing; Huang, Xin-fan; Oda, Shunri

    2016-09-01

    Based on the charge storage mode, it is important to investigate the scaling dependence of memory performance in silicon nanocrystal (Si-NC) nonvolatile memory (NVM) devices for its scaling down limit. In this work, we made eight kinds of test key cells with different gate widths and lengths by 0.13-μm node complementary metal oxide semiconductor (CMOS) technology. It is found that the memory windows of eight kinds of test key cells are almost the same of about 1.64 V @ ± 7 V/1 ms, which are independent of the gate area, but mainly determined by the average size (12 nm) and areal density (1.8 × 1011/cm2) of Si-NCs. The program/erase (P/E) speed characteristics are almost independent of gate widths and lengths. However, the erase speed is faster than the program speed of test key cells, which is due to the different charging behaviors between electrons and holes during the operation processes. Furthermore, the data retention characteristic is also independent of the gate area. Our findings are useful for further scaling down of Si-NC NVM devices to improve the performance and on-chip integration. Project supported by the State Key Development Program for Basic Research of China (Grant No. 2010CB934402) and the National Natural Science Foundation of China (Grant Nos. 11374153, 61571221, and 61071008).

  2. Thermal influence on charge carrier transport in solar cells based on GaAs PN junctions

    SciTech Connect

    Osses-Márquez, Juan; Calderón-Muñoz, Williams R.

    2014-10-21

    The electron and hole one-dimensional transport in a solar cell based on a Gallium Arsenide (GaAs) PN junction and its dependency with electron and lattice temperatures are studied here. Electrons and heat transport are treated on an equal footing, and a cell operating at high temperatures using concentrators is considered. The equations of a two-temperature hydrodynamic model are written in terms of asymptotic expansions for the dependent variables with the electron Reynolds number as a perturbation parameter. The dependency of the electron and hole densities through the junction with the temperature is analyzed solving the steady-state model at low Reynolds numbers. Lattice temperature distribution throughout the device is obtained considering the change of kinetic energy of electrons due to interactions with the lattice and heat absorbed from sunlight. In terms of performance, higher values of power output are obtained with low lattice temperature and hot energy carriers. This modeling contributes to improve the design of heat exchange devices and thermal management strategies in photovoltaic technologies.

  3. Reversible chemical tuning of charge carriers for enhanced photoelectrochemical conversion and probing of living cells.

    PubMed

    Wang, Yongcheng; Tang, Jing; Zhou, Tong; Da, Peimei; Li, Jun; Kong, Biao; Yang, Zhongqin; Zheng, Gengfeng

    2014-12-10

    A facile, solution method for reversible tuning of oxygen vacancies inside TiO2 nanowires, in which the reducing treatment of TiO2 by NaBH4 leads to 2.4-fold increase of photocurrent density, compared to pristine TiO2 nanowires, is reported. Subsequent oxidizing treatment using KMnO4 or annealing in air can reset the photocurrent density to the original values. The incident photo-to-current conversion efficiency measurement exhibits that the reduced TiO2 nanowires present both enhanced photoactivity in both UV and visible regions. Density functional theory calculations reveal that the oxygen vacancies in the reduced TiO2 cause defect states in the band structure and result in enhanced carrier density and conductivity. In addition, the enhanced solar energy-driven photoelectrochemical conversion allows real-time, sensitive chemical probing of living cells that are directly grown on the TiO2 nanowire photoanodes. As proofs-of-concept, after functionalized with horseradish peroxidase (HRP) on the surface, the reduced TiO2 NWs demonstrate sensitive, real-time monitoring of the H2O2 levels in several distinctive living cell lines, with the lowest detectable H2O2 concentration of 7.7 nM. This reversible tuning of oxygen vacancies suggests a facile means for transition metal oxides, with enhanced photoconversion activity and electrochemical sensitivity. PMID:25044916

  4. Arginine side chain interactions and the role of arginine as a gating charge carrier in voltage sensitive ion channels

    NASA Astrophysics Data System (ADS)

    Armstrong, Craig T.; Mason, Philip E.; Anderson, J. L. Ross; Dempsey, Christopher E.

    2016-02-01

    Gating charges in voltage-sensing domains (VSD) of voltage-sensitive ion channels and enzymes are carried on arginine side chains rather than lysine. This arginine preference may result from the unique hydration properties of the side chain guanidinium group which facilitates its movement through a hydrophobic plug that seals the center of the VSD, as suggested by molecular dynamics simulations. To test for side chain interactions implicit in this model we inspected interactions of the side chains of arginine and lysine with each of the 19 non-glycine amino acids in proteins in the protein data bank. The arginine guanidinium interacts with non-polar aromatic and aliphatic side chains above and below the guanidinium plane while hydrogen bonding with polar side chains is restricted to in-plane positions. In contrast, non-polar side chains interact largely with the aliphatic part of the lysine side chain. The hydration properties of arginine and lysine are strongly reflected in their respective interactions with non-polar and polar side chains as observed in protein structures and in molecular dynamics simulations, and likely underlie the preference for arginine as a mobile charge carrier in VSD.

  5. Arginine side chain interactions and the role of arginine as a gating charge carrier in voltage sensitive ion channels.

    PubMed

    Armstrong, Craig T; Mason, Philip E; Anderson, J L Ross; Dempsey, Christopher E

    2016-01-01

    Gating charges in voltage-sensing domains (VSD) of voltage-sensitive ion channels and enzymes are carried on arginine side chains rather than lysine. This arginine preference may result from the unique hydration properties of the side chain guanidinium group which facilitates its movement through a hydrophobic plug that seals the center of the VSD, as suggested by molecular dynamics simulations. To test for side chain interactions implicit in this model we inspected interactions of the side chains of arginine and lysine with each of the 19 non-glycine amino acids in proteins in the protein data bank. The arginine guanidinium interacts with non-polar aromatic and aliphatic side chains above and below the guanidinium plane while hydrogen bonding with polar side chains is restricted to in-plane positions. In contrast, non-polar side chains interact largely with the aliphatic part of the lysine side chain. The hydration properties of arginine and lysine are strongly reflected in their respective interactions with non-polar and polar side chains as observed in protein structures and in molecular dynamics simulations, and likely underlie the preference for arginine as a mobile charge carrier in VSD. PMID:26899474

  6. Arginine side chain interactions and the role of arginine as a gating charge carrier in voltage sensitive ion channels

    PubMed Central

    Armstrong, Craig T.; Mason, Philip E.; Anderson, J. L. Ross; Dempsey, Christopher E.

    2016-01-01

    Gating charges in voltage-sensing domains (VSD) of voltage-sensitive ion channels and enzymes are carried on arginine side chains rather than lysine. This arginine preference may result from the unique hydration properties of the side chain guanidinium group which facilitates its movement through a hydrophobic plug that seals the center of the VSD, as suggested by molecular dynamics simulations. To test for side chain interactions implicit in this model we inspected interactions of the side chains of arginine and lysine with each of the 19 non-glycine amino acids in proteins in the protein data bank. The arginine guanidinium interacts with non-polar aromatic and aliphatic side chains above and below the guanidinium plane while hydrogen bonding with polar side chains is restricted to in-plane positions. In contrast, non-polar side chains interact largely with the aliphatic part of the lysine side chain. The hydration properties of arginine and lysine are strongly reflected in their respective interactions with non-polar and polar side chains as observed in protein structures and in molecular dynamics simulations, and likely underlie the preference for arginine as a mobile charge carrier in VSD. PMID:26899474

  7. Efficient charge-carrier extraction from Ag2S quantum dots prepared by the SILAR method for utilization of multiple exciton generation

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoliang; Liu, Jianhua; Johansson, Erik M. J.

    2015-01-01

    The utilization of electron-hole pairs (EHPs) generated from multiple excitons in quantum dots (QDs) is of great interest toward efficient photovoltaic devices and other optoelectronic devices; however, extraction of charge carriers remains difficult. Herein, we extract photocharges from Ag2S QDs and investigate the dependence of the electric field on the extraction of charges from multiple exciton generation (MEG). Low toxic Ag2S QDs are directly grown on TiO2 mesoporous substrates by employing the successive ionic layer adsorption and reaction (SILAR) method. The contact between QDs is important for the initial charge separation after MEG and for the carrier transport, and the space between neighbor QDs decreases with more SILAR cycles, resulting in better charge extraction. At the optimal electric field for extraction of photocharges, the results suggest that the threshold energy (hνth) for MEG is 2.41Eg. The results reveal that Ag2S QD is a promising material for efficient extraction of charges from MEG and that QDs prepared by SILAR have an advantageous electrical contact facilitating charge separation and extraction.The utilization of electron-hole pairs (EHPs) generated from multiple excitons in quantum dots (QDs) is of great interest toward efficient photovoltaic devices and other optoelectronic devices; however, extraction of charge carriers remains difficult. Herein, we extract photocharges from Ag2S QDs and investigate the dependence of the electric field on the extraction of charges from multiple exciton generation (MEG). Low toxic Ag2S QDs are directly grown on TiO2 mesoporous substrates by employing the successive ionic layer adsorption and reaction (SILAR) method. The contact between QDs is important for the initial charge separation after MEG and for the carrier transport, and the space between neighbor QDs decreases with more SILAR cycles, resulting in better charge extraction. At the optimal electric field for extraction of photocharges, the

  8. Photocurrent microscopy of contact resistance and charge carrier traps in organic field-effect transistors

    NASA Astrophysics Data System (ADS)

    Liewald, C.; Reiser, D.; Westermeier, C.; Nickel, B.

    2016-08-01

    We use a pentacene transistor with asymmetric source drain contacts to test the sensitivity of scanning photocurrent microscopy (SPCM) for contact resistance and charge traps. The drain current of the device strongly depends on the choice of the drain electrode. In one case, more than 94% of the source drain voltage is lost due to contact resistance. Here, SPCM maps show an enhanced photocurrent signal at the hole-injecting contact. For the other bias condition, i.e., for ohmic contacts, the SPCM signal peaks heterogeneously along the channel. We argue from basic transport models that bright areas in SPCM maps indicate areas of large voltage gradients or high electric field strength caused by injection barriers or traps. Thus, SPCM allows us to identify and image the dominant voltage loss mechanism in organic field-effect transistors.

  9. Nonequilibrium green function approach to elastic and inelastic spin-charge transport in topological insulator-based heterostructures and magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Mahfouzi, Farzad

    Current and future technological needs increasingly motivate the intensive scientific research of the properties of materials at the nano-scale. One of the most important domains in this respect at present concerns nano-electronics and its diverse applications. The great interest in this domain arises from the potential reduction of the size of the circuit components, maintaining their quality and functionality, and aiming at greater efficiency, economy, and storage characteristics for the corresponding physical devices. The aim of this thesis is to present a contribution to the analysis of the electronic charge and spin transport phenomena that occur at the quantum level in nano-structures. This thesis spans the areas of quantum transport theory through time-dependent systems, electron-boson interacting systems and systems of interest to spintronics. A common thread in the thesis is to develop the theoretical foundations and computational algorithms to numerically simulate such systems. In order to optimize the numerical calculations I resort to different techniques (such as graph theory in finding inverse of a sparse matrix, adaptive grids for integrations and programming languages (e.g., MATLAB and C++) and distributed computing tools (MPI, CUDA). Outline of the Thesis: After giving an introduction to the topics covered in this thesis in Chapter 1, I present the theoretical foundations to the field of non-equilibrium quantum statistics in Chapter 2. The applications of this formalism and the results are covered in the subsequent chapters as follows: Spin and charge quantum pumping in time-dependent systems: Covered in Chapters 3, 4 and 5, this topics was initially motivated by experiments on measuring voltage signal from a magnetic tunnel junction (MTJ) exposed to a microwave radiation in ferromagnetic resonance (FMR) condition. In Chapter 3 we found a possible explanation for the finite voltage signal measured from a tunnel junction consisting of only a single

  10. Nonequilibrium green function approach to elastic and inelastic spin-charge transport in topological insulator-based heterostructures and magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Mahfouzi, Farzad

    Current and future technological needs increasingly motivate the intensive scientific research of the properties of materials at the nano-scale. One of the most important domains in this respect at present concerns nano-electronics and its diverse applications. The great interest in this domain arises from the potential reduction of the size of the circuit components, maintaining their quality and functionality, and aiming at greater efficiency, economy, and storage characteristics for the corresponding physical devices. The aim of this thesis is to present a contribution to the analysis of the electronic charge and spin transport phenomena that occur at the quantum level in nano-structures. This thesis spans the areas of quantum transport theory through time-dependent systems, electron-boson interacting systems and systems of interest to spintronics. A common thread in the thesis is to develop the theoretical foundations and computational algorithms to numerically simulate such systems. In order to optimize the numerical calculations I resort to different techniques (such as graph theory in finding inverse of a sparse matrix, adaptive grids for integrations and programming languages (e.g., MATLAB and C++) and distributed computing tools (MPI, CUDA). Outline of the Thesis: After giving an introduction to the topics covered in this thesis in Chapter 1, I present the theoretical foundations to the field of non-equilibrium quantum statistics in Chapter 2. The applications of this formalism and the results are covered in the subsequent chapters as follows: Spin and charge quantum pumping in time-dependent systems: Covered in Chapters 3, 4 and 5, this topics was initially motivated by experiments on measuring voltage signal from a magnetic tunnel junction (MTJ) exposed to a microwave radiation in ferromagnetic resonance (FMR) condition. In Chapter 3 we found a possible explanation for the finite voltage signal measured from a tunnel junction consisting of only a single

  11. Effective numbers of charge carriers in doped graphene: Generalized Fermi liquid approach

    NASA Astrophysics Data System (ADS)

    Kupčić, I.; Nikšić, G.; Rukelj, Z.; Pelc, D.

    2016-08-01

    The single-band current-dipole Kubo formula for the dynamical conductivity of heavily doped graphene from Kupčić [Phys. Rev. B 91, 205428 (2015), 10.1103/PhysRevB.91.205428] is extended to a two-band model for conduction π electrons in lightly doped graphene. Using a posteriori relaxation-time approximation in the two-band quantum transport equations, with two different relaxation rates and one quasiparticle lifetime, we explain a seemingly inconsistent dependence of the dc conductivity of ultraclean and dirty lightly doped graphene samples on electron doping, in a way consistent with the charge continuity equation. It is also shown that the intraband contribution to the effective number of conduction electrons in the dc conductivity vanishes at T =0 K in the ultraclean regime, but it remains finite in the dirty regime. The present model is shown to be consistent with a picture in which the intraband and interband contributions to the dc conductivity are characterized by two different mobilities of conduction electrons, the values of which are well below the widely accepted value of mobility in ultraclean graphene. The dispersions of Dirac and π plasmon resonances are reexamined to show that the present, relatively simple expression for the dynamical conductivity tensor can be used to study simultaneously single-particle excitations in the dc and optical conductivity and collective excitations in energy loss spectroscopy experiments.

  12. Ultrasonic coupling to optically generated charge carriers in CdS: Physical phenomena and applications. Ph.D. Thesis - Washington Univ., Saint Louis, Mo.

    NASA Technical Reports Server (NTRS)

    Heyman, J. S.

    1975-01-01

    Phonon-charge carrier interactions are studied as well as ultrasonic resonators. Sensitivity enhancement factors predicted by one dimensional resonator theory are verified and several sensitive ultrasonic experimental techniques are developed. Measurements are reported of an anomalous sign reversal of the acoustoelectric voltage in a CdS resonator. Applications of CdS as an ultrasonic power detector are described.

  13. Efficiency of extrinsic and intrinsic charge-carrier photogeneration processes obtained from the steady-state photocurrent action spectra of poly( p-phenylene vinylene) derivatives

    NASA Astrophysics Data System (ADS)

    Cazati, T.; Santos, L. F.; Reis, F. T.; Faria, R. M.

    2012-09-01

    The efficiency of the charge-carrier photogeneration processes in poly(2,5-bis(3',7'-dimethyl-octyloxy)-1,4-phenylene vinylene) (OC1OC10-PPV) has been analyzed by the spectral response of the photocurrent of devices in ITO/polymer/Al structures. The symbatic response of the photocurrent action spectra of the OC1OC10-PPV devices, obtained for light-excitation through the ITO electrode and for forward bias, has been fitted using a phenomenological model which considers that the predominant transport mechanism under external applied electric field is the drift of photogenerated charge-carriers, neglecting charge-carrier diffusion. The proposed model takes into account that charge-carrier photogeneration occurs via intermediate stages of bounded pairs (excitonic states), followed by dissociation processes. Such processes result in two different contributions to the photoconductivity: The first one, associated to direct creation of unbound polaron pairs due to intrinsic photoionization; and the second one is associated to secondary processes like extrinsic photoinjection at the metallic electrodes. The results obtained from the model have shown that the intrinsic component of the photoconductivity at higher excitation energies has a considerably higher efficiency than the extrinsic one, suggesting a dependence on the photon energy for the efficiency of the photogeneration process.

  14. Dynamics of charge carrier recombination and capture in laser nanostructures with InGaAsSb/AlGaAsSb quantum wells

    SciTech Connect

    Vinnichenko, Maxim Ya.; Vorobjev, Leonid E.; Firsov, Dmitry A.; Mashko, Marina O.; Sofronov, Anton N.; Shterengas, Leon; Belenky, Gregory

    2013-12-04

    Time dynamics of photoluminescence intensity was studied in InGaAsSb/AlGaAsSb quantum wells with different compositions of the barrier solid solution and with different width of the quantum wells. The time of charge carrier capture in quantum wells, the energy relaxation times, lifetime related to resonant Auger recombination were estimated.

  15. Quadrimolecular recombination kinetics of photogenerated charge carriers in the composites of regioregular polythiophene derivatives and soluble fullerene

    NASA Astrophysics Data System (ADS)

    Tanaka, Hisaaki; Yokoi, Yuki; Hasegawa, Naoki; Kuroda, Shin-ichi; Iijima, Takayuki; Sato, Takao; Yamamoto, Takakazu

    2010-04-01

    Light-induced electron spin resonance (LESR) measurements have been performed on the composites of regioregular polythiophene derivatives and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in order to study the recombination kinetics of photogenerated charge carriers. We adopt two regioregular polymers with different side chains; head-to-tail poly(3-hexylthiophene) (RR-P3HT) and head-to-head poly(3-dodecynylthiophene-2,5-diyl) [HH-P3(C≡CDec)Th]. In both systems, two LESR signals due to positive polarons on the polymer (g ˜2.002) and fullerene radical anions (g ˜2.000) have been observed. Quadrimolecular recombination (QR) kinetics, previously reported for RR-P3HT/C60 composites, where two positive polarons and two radical anions recombine simultaneously, has been confirmed in both systems by the observation of Iex0.25 dependence of the LESR intensity on the excitation light intensity (Iex) and the decay curve of the LESR intensity. This process implies the formation of doubly-charged states such as bipolarons or polaron pairs on the polymer to attract two radical anions. Temperature dependence of the QR rate constant, γ, in both systems has exhibited a crossover of the transport mechanism from low temperature tunneling to high temperature hopping process, as in the case of RR-P3HT/C60 composites. In the RR-P3HT/PCBM composites, γ has exhibited marked dependencies on the PCBM concentration or annealing, which may be related to the change of the crystallinity of the phase-separated polymer and fullerene domains as well as their interface structures, affecting the carrier mobilities or the trap states at the interface. Associated change of the molecular orientation of RR-P3HT crystalline domains with the lamellar structure has been further confirmed from the anisotropic LESR signals of the cast films on the substrates, exhibiting a qualitative agreement with the reported x-ray or optical analyses. In the HH-P3(C≡CDec)Th/PCBM composite, γ has been smaller

  16. Spatial Separation of Charge Carriers in In2O3-x(OH)y Nanocrystal Superstructures for Enhanced Gas-Phase Photocatalytic Activity.

    PubMed

    He, Le; Wood, Thomas E; Wu, Bo; Dong, Yuchan; Hoch, Laura B; Reyes, Laura M; Wang, Di; Kübel, Christian; Qian, Chenxi; Jia, Jia; Liao, Kristine; O'Brien, Paul G; Sandhel, Amit; Loh, Joel Y Y; Szymanski, Paul; Kherani, Nazir P; Sum, Tze Chien; Mims, Charles A; Ozin, Geoffrey A

    2016-05-24

    The development of strategies for increasing the lifetime of photoexcited charge carriers in nanostructured metal oxide semiconductors is important for enhancing their photocatalytic activity. Intensive efforts have been made in tailoring the properties of the nanostructured photocatalysts through different ways, mainly including band-structure engineering, doping, catalyst-support interaction, and loading cocatalysts. In liquid-phase photocatalytic dye degradation and water splitting, it was recently found that nanocrystal superstructure based semiconductors exhibited improved spatial separation of photoexcited charge carriers and enhanced photocatalytic performance. Nevertheless, it remains unknown whether this strategy is applicable in gas-phase photocatalysis. Using porous indium oxide nanorods in catalyzing the reverse water-gas shift reaction as a model system, we demonstrate here that assembling semiconductor nanocrystals into superstructures can also promote gas-phase photocatalytic processes. Transient absorption studies prove that the improved activity is a result of prolonged photoexcited charge carrier lifetimes due to the charge transfer within the nanocrystal network comprising the nanorods. Our study reveals that the spatial charge separation within the nanocrystal networks could also benefit gas-phase photocatalysis and sheds light on the design principles of efficient nanocrystal superstructure based photocatalysts. PMID:27159793

  17. Mean carrier transport properties and charge collection dynamics of single-crystal, natural type IIa diamonds from ion-induced conductivity measurements

    SciTech Connect

    Han, S.S.

    1993-09-01

    Ion-induced conductivity has been used to investigate the detector characteristics of diamond detectors. Both integrated-charge, and time-resolved current measurements were performed to examine the mean carrier transport properties of diamond and the dynamics of charge collection under highly-localized and high-density excitation conditions. The integrated-charge measurements were conducted with a standard pulse-counting system with {sup 241}Am radioactivity as the excitation source for the detectors. The time-resolved current measurements were performed using a 70 GHz random sampling oscilloscope with the detectors incorporated into high-speed microstrip transmission lines and the excitation source for these measurements was an ion beam of either 5-MeV He{sup +} or 10-MeV Si{sup 3+}. The detectors used in both experiments can be described as metal-semiconductor-metal (MSM) devices where a volume of the detector material is sandwiched between two metal plates. A charge collection model was developed to interpret the integrated-charge measurements which enabled estimation of the energy required to produce an electron-hole pair ({epsilon}{sub di}) and the mean carrier transport properties in diamond, such as carrier mobility and lifetime, and the behavior of the electrical contacts to diamond.

  18. Charge carrier recombination channels in the low-temperature phase of organic-inorganic lead halide perovskite thin films

    NASA Astrophysics Data System (ADS)

    Wehrenfennig, Christian; Liu, Mingzhen; Snaith, Henry J.; Johnston, Michael B.; Herz, Laura M.

    2014-08-01

    The optoelectronic properties of the mixed hybrid lead halide perovskite CH3NH3PbI3-xClx have been subject to numerous recent studies related to its extraordinary capabilities as an absorber material in thin film solar cells. While the greatest part of the current research concentrates on the behavior of the perovskite at room temperature, the observed influence of phonon-coupling and excitonic effects on charge carrier dynamics suggests that low-temperature phenomena can give valuable additional insights into the underlying physics. Here, we present a temperature-dependent study of optical absorption and photoluminescence (PL) emission of vapor-deposited CH3NH3PbI3-xClx exploring the nature of recombination channels in the room- and the low-temperature phase of the material. On cooling, we identify an up-shift of the absorption onset by about 0.1 eV at about 100 K, which is likely to correspond to the known tetragonal-to-orthorhombic transition of the pure halide CH3NH3PbI3. With further decreasing temperature, a second PL emission peak emerges in addition to the peak from the room-temperature phase. The transition on heating is found to occur at about 140 K, i.e., revealing significant hysteresis in the system. While PL decay lifetimes are found to be independent of temperature above the transition, significantly accelerated recombination is observed in the low-temperature phase. Our data suggest that small inclusions of domains adopting the room-temperature phase are responsible for this behavior rather than a spontaneous increase in the intrinsic rate constants. These observations show that even sparse lower-energy sites can have a strong impact on material performance, acting as charge recombination centres that may detrimentally affect photovoltaic performance but that may also prove useful for optoelectronic applications such as lasing by enhancing population inversion.

  19. Ohm's Law for a Bipolar Semiconductor: The Role of Carrier Concentration and Energy Nonequilibria

    NASA Astrophysics Data System (ADS)

    Lashkevych, Igor; Titov, Oleg Yu.; Gurevich, Yuri G.

    2016-09-01

    The effective linear electrical conductivity of a nondegenerate bipolar semiconductor, sandwiched between two metals, is investigated taking into account both its nonequilibrium charge carriers (both electrons and holes) and nonequilibrium temperature. We stress that even in the linear perturbative approximation both carrier concentration and energy nonequilbria arise automatically when an electrical current flows. The expression for the effective electrical conductivity is obtained and shown to depend on the electron and hole electrical conductivity, the thermal conductivity, the bandgap, charge carriers lifetimes, and both bulk and surface recombination rates. The effective electrical conductivity is equal to the classical result, i.e., the sum of the electron and hole electrical conductivities, only if the surface recombination rate at the interface is sufficiently strong or the charge carrier lifetime is sufficiently small. In this article, partial cases are considered, specifically, semiconductors with small and large thermal conductivities, semiconductors with monopolar electron and monopolar holes, strong and weak surface recombination rates, and small and large charge carrier lifetimes. Expressions for the effective electrical conductivity are obtained in all partial cases.

  20. Photogenerated charge carriers and reactive oxygen species in ZnO/Au hybrid nanostructures with enhanced photocatalytic and antibacterial activity.

    PubMed

    He, Weiwei; Kim, Hyun-Kyung; Wamer, Wayne G; Melka, David; Callahan, John H; Yin, Jun-Jie

    2014-01-15

    Semiconductor nanostructures with photocatalytic activity have the potential for many applications including remediation of environmental pollutants and use in antibacterial products. An effective way for promoting photocatalytic activity is depositing noble metal nanoparticles (NPs) on a semiconductor. In this paper, we demonstrated the successful deposition of Au NPs, having sizes smaller than 3 nm, onto ZnO NPs. ZnO/Au hybrid nanostructures having different molar ratios of Au to ZnO were synthesized. It was found that Au nanocomponents even at a very low Au/ZnO molar ratio of 0.2% can greatly enhance the photocatalytic and antibacterial activity of ZnO. Electron spin resonance spectroscopy with spin trapping and spin labeling was used to investigate the enhancing effect of Au NPs on the generation of reactive oxygen species and photoinduced charge carriers. Deposition of Au NPs onto ZnO resulted in a dramatic increase in light-induced generation of hydroxyl radical, superoxide and singlet oxygen, and production of holes and electrons. The enhancing effect of Au was dependent on the molar ratio of Au present in the ZnO/Au nanostructures. Consistent with these results from ESR measurements, ZnO/Au nanostructures also exhibited enhanced photocatalytic and antibacterial activity. These results unveiled the enhanced mechanism of Au on ZnO and these materials have great potential for use in water purification and antibacterial products.

  1. Probing molecular packing at engineered interfaces in organic field effect transistor and its correlation with charge carrier mobility.

    PubMed

    Maheshwari, Priya; Mukherjee, Saurabh; Bhattacharya, Debarati; Sen, Shashwati; Tokas, Raj Bahadur; Honda, Yoshihide; Basu, Saibal; Padma, Narayanan; Pujari, Pradeep Kumar

    2015-05-20

    Surface engineering of SiO2 dielectric using different self-assembled monolayer (SAM) has been carried out, and its effect on the molecular packing and growth behavior of copper phthalocyanine (CuPc) has been studied. A correlation between the growth behavior and performance of organic field effect transistors is examined. Depth profiling using positron annihilation and X-ray reflectivity techniques has been employed to characterize the interface between CuPc and the modified and/or unmodified dielectric. We observe the presence of structural defects or disorder due to disorientation of CuPc molecules on the unmodified dielectric and ordered arrangement on the modified dielectrics, consistent with the high charge carrier mobility in organic field effect transistors in the latter. The study also highlights the sensitivity of these techniques to the packing of CuPc molecules on SiO2 modified using different SAMs. Our study also signifies the sensitivity and utility of these two techniques in the characterization of buried interfaces in organic devices. PMID:25922969

  2. Charge carriers and small-polaron migration as the origin of intrinsic dielectric anomalies in multiferroic TbMnO3 polycrystals.

    PubMed

    Silveira, L G D; Dias, G S; Cótica, L F; Eiras, J A; Garcia, D; Sampaio, J A; Yokaichiya, F; Santos, I A

    2013-11-27

    Temperature-dependent and frequency-dependent dielectric investigations have been performed in TbMnO3 polycrystals sintered in either oxidative or reductive atmospheres. The results revealed the occurrence of two dielectric anomalies above 100 K, which are caused by the thermal activation of charge carriers and their motion in grain cores and grain boundaries. The temperature dependence of the bulk dc conductivity was also analysed and indicates that charge carriers move between inequivalent sites according to a variable-range-hopping mechanism. Also, a strong correlation between dielectric properties and crystalline structure was observed. Furthermore, a low-temperature dielectric relaxation, commonly reported in rare-earth manganite crystals, was observed in both samples. This relaxation follows the empirical Cole-Cole model and was attributed to small-polaron tunnelling. Polaron motion was observed to be affected by the magnetic transitions, structural properties and intrinsic anisotropies in TbMnO3. It is also worth mentioning that the dielectric anomaly due to motion of charge carriers in grain boundaries is the only one of extrinsic origin, while the anomalies related to carrier motion in grain cores and small-polaron tunnelling are intrinsic to TbMnO3.

  3. Investigation of non-equilibrium electron-hole plasma in nanowires by THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Cirlin, G. E.; Buyskih, A. C.; Bouravlev, A. D.; Samsonenko, Yu. B.; Kaliteevski, M. A.; Gallant, A. J.; Zeze, D.

    2016-05-01

    Efficient emission of THz radiation by AlGaAs nanowires via excitation of photocurrent by femtosecond optical pulses in nanowires was observed. Dynamics of photoinduced charge carrier was studied via influence of electron-hole plasma on THz radiation by optical pump THz probe method. It was found that characteristic time of screening of contact field is about 15 ps. Recombination of non-equilibrium occurs in two stages: fast recombination of free electron and holes (with relaxation time about 700 ps), and slow recombination (with relaxation time about 15 ns), which involves a capture of electrons and holes on the defects of crystalline structure of nanowires.

  4. Ultrafast terahertz probe of photoexcited free charge carriers in organometal CH3NH3PbI3 perovskite thin film

    NASA Astrophysics Data System (ADS)

    Yan, Huijie; An, Baoli; Fan, Zhengfu; Zhu, Xiaoya; Lin, Xian; Jin, Zuanming; Ma, Guohong

    2016-04-01

    By using optical pump-terahertz probe (OPTP) experiments, we study the free charge carrier dynamics in photoexcited drop-cast CH3NH3PbI3-based perovskite thin film at room temperature. Compared with the pump photon energy at 1.55 eV, the measured OPTP signal following excitation of 3.1 eV shows an additional fast decay channel of the photoconductivity. Our experimental results demonstrate that effective carrier lifetime can be strongly modulated by surface recombination. In addition, the Drude-Smith-like transient terahertz photoconductivity spectra suggest that photogenerated free carriers experience backscattering at grain boundaries in our solution-processed perovskite films studied here.

  5. Photoconductivity of CdTe Nanocrystal-Based Thin Films. Te2- Ligands Lead To Charge Carrier Diffusion Lengths Over 2 Micrometers

    SciTech Connect

    Crisp, Ryan W.; Callahan, Rebecca; Reid, Obadiah G.; Dolzhnikov, Dmitriy S.; Talapin, Dmitri V.; Rumbles, Garry; Luther, Joseph M.; Kopidakis, Nikos

    2015-11-16

    We report on photoconductivity of films of CdTe nanocrystals (NCs) using time-resolved microwave photoconductivity (TRMC). Spherical and tetrapodal CdTe NCs with tunable size-dependent properties are studied as a function of surface ligand (including inorganic molecular chalcogenide species) and annealing temperature. Relatively high carrier mobility is measured for films of sintered tetrapod NCs (4 cm2/(V s)). Our TRMC findings show that Te2- capped CdTe NCs show a marked improvement in carrier mobility (11 cm2/(V s)), indicating that NC surface termination can be altered to play a crucial role in charge-carrier mobility even after the NC solids are sintered into bulk films.

  6. Singular effect of crystallite size on the charge carrier generation and photocatalytic activity of nano-TiO2

    NASA Astrophysics Data System (ADS)

    Strauss, Mathias; Pastorello, Murilo; Sigoli, Fernando A.; Silva, Juliana M. de Souza e.; Mazali, Italo O.

    2014-11-01

    Photocatalytic processes on nanometric titanium oxide have been extensively studied from the standpoint of solar energy utilization and remediation of water and gas streams polluted with organic molecules. It is accepted that TiO2 crystallite size and crystalline phase are among the parameters involved in the control of the photocatalytic activity. However, while changing the catalyst nanoparticle size, other attributes important to assess photocatalytic activity may be modified, making thus difficult to define to which extension the photoactivity changes are related only to size differences. Therefore, aiming at studying exclusively the size effect and the parameters directly related to size on the photocatalytic activity of nanometric TiO2, in this work it was explored a method to synthesize TiO2 nanoparticles with controlled size, highly similar morphology and comparable phase and degree of crystallinity. A set composed of four samples of nano-TiO2 loaded porous Vycor glass, each sample having a specific TiO2 nanoparticle size, was tested on the photoactivated process of depollution of solutions of salicylic acid and methylene blue. The photocatalytic activity observed for the organic compounds tested was inversely proportional to the TiO2 nanoparticle size. An opposite tendency was observed for the generation of OH radicals during photocatalyst illumination, as more radicals are formed on the material containing the larger TiO2 nanoparticles. Results of this study suggest that photocatalytic activity of nano-TiO2 is less favored by the enhanced light absorption response and the higher generation of oxidative species observed for the larger nanoparticles. Better catalysts were obtained when nano-TiO2 exhibited high surface-to-volume ratio and had small recombination volumes, which respectively favors pollutant adsorption-desorption on catalyst surface and reduce the number of recombined charge carriers.

  7. Charge-carrier mobilities in Cd(0.8)Zn(0.2)Te single crystals used as nuclear radiation detectors

    NASA Technical Reports Server (NTRS)

    Burshtein, Z.; Jayatirtha, H. N.; Burger, A.; Butler, J. F.; Apotovsky, B.; Doty, F. P.

    1993-01-01

    Charge-carrier mobilities were measured for the first time in Cd(0.8)Zn(0.2)Te single crystals using time-of-flight measurements of charge carriers produced by short (10 ns) light pulses from a frequency-doubled Nd:YAG laser (532 nm). The electron mobility displayed a T exp -1.1 dependence on the absolute temperature T in the range 200-320 K, with a room-temperature mobility of 1350 sq cm/V s. The hole mobility displayed a T exp -2.0 dependence in the same temperature range, with a room-temperature mobility of 120 sq cm/V s. Cd(0.8)Zn(0.2)Te appears to be a very favorable material for a room-temperature electronic nuclear radiation detector.

  8. Photoinduced Charge-Carrier Generation in Epitaxial MOF Thin Films: High Efficiency as a Result of an Indirect Electronic Band Gap?

    PubMed

    Liu, Jinxuan; Zhou, Wencai; Liu, Jianxi; Howard, Ian; Kilibarda, Goran; Schlabach, Sabine; Coupry, Damien; Addicoat, Matthew; Yoneda, Satoru; Tsutsui, Yusuke; Sakurai, Tsuneaki; Seki, Shu; Wang, Zhengbang; Lindemann, Peter; Redel, Engelbert; Heine, Thomas; Wöll, Christof

    2015-06-15

    For inorganic semiconductors crystalline order leads to a band structure which gives rise to drastic differences to the disordered material. An example is the presence of an indirect band gap. For organic semiconductors such effects are typically not considered, since the bands are normally flat, and the band-gap therefore is direct. Herein we show results from electronic structure calculations demonstrating that ordered arrays of porphyrins reveal a small dispersion of occupied and unoccupied bands leading to the formation of a small indirect band gap. We demonstrate herein that such ordered structures can be fabricated by liquid-phase epitaxy and that the corresponding crystalline organic semiconductors exhibit superior photophysical properties, including large charge-carrier mobility and an unusually large charge-carrier generation efficiency. We have fabricated a prototype organic photovoltaic device based on this novel material exhibiting a remarkable efficiency. PMID:25960115

  9. Photoinduced Charge-Carrier Generation in Epitaxial MOF Thin Films: High Efficiency as a Result of an Indirect Electronic Band Gap?

    PubMed

    Liu, Jinxuan; Zhou, Wencai; Liu, Jianxi; Howard, Ian; Kilibarda, Goran; Schlabach, Sabine; Coupry, Damien; Addicoat, Matthew; Yoneda, Satoru; Tsutsui, Yusuke; Sakurai, Tsuneaki; Seki, Shu; Wang, Zhengbang; Lindemann, Peter; Redel, Engelbert; Heine, Thomas; Wöll, Christof

    2015-06-15

    For inorganic semiconductors crystalline order leads to a band structure which gives rise to drastic differences to the disordered material. An example is the presence of an indirect band gap. For organic semiconductors such effects are typically not considered, since the bands are normally flat, and the band-gap therefore is direct. Herein we show results from electronic structure calculations demonstrating that ordered arrays of porphyrins reveal a small dispersion of occupied and unoccupied bands leading to the formation of a small indirect band gap. We demonstrate herein that such ordered structures can be fabricated by liquid-phase epitaxy and that the corresponding crystalline organic semiconductors exhibit superior photophysical properties, including large charge-carrier mobility and an unusually large charge-carrier generation efficiency. We have fabricated a prototype organic photovoltaic device based on this novel material exhibiting a remarkable efficiency.

  10. The role of charge-transfer integral in determining and engineering the carrier mobilities of 9,10-di(2-naphthyl)anthracene compounds

    NASA Astrophysics Data System (ADS)

    Tse, S. C.; So, S. K.; Yeung, M. Y.; Lo, C. F.; Wen, S. W.; Chen, C. H.

    2006-05-01

    The charge transporting properties of t-butylated 9,10-di(2-naphthyl)anthracene (ADN) compounds have been investigated experimentally and computationally in relation to their molecular structures. The ADN compounds are found to be ambipolar with both electron and hole mobilities in the range of 1-4 × 10 -7 cm 2 V -1 s -1 (electric field 0.5-0.8 MV/cm). As the degree of t-butylation increases, the carrier mobility decreases progressively. The mobility reduction was examined by Marcus theory of reorganization energies. All ADN compounds possess similar reorganization energies of ˜0.3 eV. The reduction of carrier mobilities with increasing t-butylation can be attributed to a decrease in the charge-transfer integral or the wavefunction overlap.

  11. Thermal, transport, and magnetotransport properties of free charge carriers in Mn-doped structures with a GaAs/InGaAs/GaAs quantum well

    SciTech Connect

    Kulbachinskii, V. A.; Shchurova, L. Yu.

    2009-07-15

    The results of investigation of the magnetic and transport properties of a GaAs/InGaAs/GaAs quantum well delta-doped with carbon and manganese from different sides and containing a ferromagnetic phase are analyzed. A thermodynamic model is formulated and the composition of a system consisting of neutral Mn atoms, Mn ions, and holes in the quantum well is calculated for determining the concentration of free charge carriers. The contributions to the resistance from different mechanisms of hole scattering are calculated, and good agreement with the experimental temperature dependences of the resistance is attained. The calculated and experimental values of the negative magnetoresistance associated with variation in the contribution of scattering from magnetic ions of the spin-polarized system of charge carriers are found to be in quantitative agreement.

  12. Generation of charge carriers in C60 films by 100-fs laser pulses with photon energies above and below the mobility edge

    SciTech Connect

    Chekalin, Sergei V; Yartsev, A P; Sundstroem, V

    2001-05-31

    Primary stages of photoinduced processes are studied in C60 films excited by 100-fs laser pulses at wavelengths of 645 and 367 nm, the fraction of excited molecules being no more than several percent. Probing in the broad spectral range from 400 to 1100 nm showed that both charged (cations and electrons) and neutral (excited molecules) components were produced upon irradiation by the laser pulse. For both excitation wavelengths, charge carriers were produced due to direct optical excitation rather than due to singlet-singlet annihilation. Anions were produced with a delay of 10{sup -13} - 10{sup -11} s through electron trapping by C60 molecules. (femtosecond technologies)

  13. Determination of charge-carrier diffusion length in the photosensing layer of HgCdTe n-on-p photovoltaic infrared focal plane array detectors

    SciTech Connect

    Vishnyakov, A. V.; Stuchinsky, V. A. Brunev, D. V.; Zverev, A. V.; Dvoretsky, S. A.

    2014-03-03

    In the present paper, we propose a method for evaluating the bulk diffusion length of minority charge carriers in the photosensing layer of photovoltaic focal plane array (FPA) photodetectors. The method is based on scanning a strip-shaped illumination spot with one of the detector diodes at a low level of photocurrents j{sub ph} being registered; such scanning provides data for subsequent analysis of measured spot-scan profiles within a simple diffusion model. The asymptotic behavior of the effective (at j{sub ph} ≠ 0) charge-carrier diffusion length l{sub d} {sub eff} as a function of j{sub ph} for j{sub ph} → 0 inferred from our experimental data proved to be consistent with the behavior of l{sub d} {sub eff} vs j{sub ph} as predicted by the model, while the obtained values of the bulk diffusion length of minority carriers (electrons) in the p-HgCdTe film of investigated HgCdTe n-on-p FPA photodetectors were found to be in a good agreement with the previously reported carrier diffusion-length values for HgCdTe.

  14. Surfactant free fabrication and improved charge carrier separation induced enhanced photocatalytic activity of {001} facet exposed unique octagonal BiOCl nanosheets.

    PubMed

    Haider, Zeeshan; Zheng, Jin You; Kang, Young Soo

    2016-07-20

    Unique octagonal shaped BiOCl nanosheets (NS) dominantly exposed with high energy {001} crystal facets have been fabricated via a simple hydrothermal route without using organic surfactants. The dynamics of photogenerated charge carriers have been studied by time-resolved photoluminescence spectroscopy. The fitting parameters of the decay kinetics were used to calculate both the intensity weighted average lifetime (〈τ〉int.), as well as the amplitude weighted average lifetime (〈τ〉amp.) of the photogenerated charge carriers. The 〈τ〉int. and 〈τ〉amp. values for {001} BiOCl NS, i.e., 17.23 ns and 1.94 ns, respectively, were observed to be significantly higher than the corresponding values obtained for pristine BiOCl such as 2.52 ns and 1.07 ns, respectively. Significant quenching of the PL emission intensity of {001} BiOCl NS reflected the enhanced separation of the photogenerated charge carriers. Reduced thickness and in situ iodine doping was favorable to minimize the recombination tendency. The photocatalytic activity was monitored via the photodegradation of RhB under visible light illumination (λ > 400 nm). {001} BiOCl NS exhibited superior performance when compared to pristine BiOCl in terms of the rapid degradation kinetics and higher photonic efficiency. The photocatalytic efficiency of {001} BiOCl NS was 2.8 times higher than pristine BiOCl. Iodine doping induced extended the optical absorption in the visible region and improved the separation of the photogenerated charge carriers, which played an important role to enhance the photocatalytic activity. The photodegradation mechanism was systematically studied using various radical quenchers and it was revealed that photogenerated holes (h(+)) and superoxide radicals (˙O(2-)) actively participated whereas hydroxyl (OH˙) radicals had a negligible contribution in the photodegradation of RhB. {001} BiOCl NS has shown a higher photocurrent density and lower charge transfer resistance analyzed

  15. Surfactant free fabrication and improved charge carrier separation induced enhanced photocatalytic activity of {001} facet exposed unique octagonal BiOCl nanosheets.

    PubMed

    Haider, Zeeshan; Zheng, Jin You; Kang, Young Soo

    2016-07-20

    Unique octagonal shaped BiOCl nanosheets (NS) dominantly exposed with high energy {001} crystal facets have been fabricated via a simple hydrothermal route without using organic surfactants. The dynamics of photogenerated charge carriers have been studied by time-resolved photoluminescence spectroscopy. The fitting parameters of the decay kinetics were used to calculate both the intensity weighted average lifetime (〈τ〉int.), as well as the amplitude weighted average lifetime (〈τ〉amp.) of the photogenerated charge carriers. The 〈τ〉int. and 〈τ〉amp. values for {001} BiOCl NS, i.e., 17.23 ns and 1.94 ns, respectively, were observed to be significantly higher than the corresponding values obtained for pristine BiOCl such as 2.52 ns and 1.07 ns, respectively. Significant quenching of the PL emission intensity of {001} BiOCl NS reflected the enhanced separation of the photogenerated charge carriers. Reduced thickness and in situ iodine doping was favorable to minimize the recombination tendency. The photocatalytic activity was monitored via the photodegradation of RhB under visible light illumination (λ > 400 nm). {001} BiOCl NS exhibited superior performance when compared to pristine BiOCl in terms of the rapid degradation kinetics and higher photonic efficiency. The photocatalytic efficiency of {001} BiOCl NS was 2.8 times higher than pristine BiOCl. Iodine doping induced extended the optical absorption in the visible region and improved the separation of the photogenerated charge carriers, which played an important role to enhance the photocatalytic activity. The photodegradation mechanism was systematically studied using various radical quenchers and it was revealed that photogenerated holes (h(+)) and superoxide radicals (˙O(2-)) actively participated whereas hydroxyl (OH˙) radicals had a negligible contribution in the photodegradation of RhB. {001} BiOCl NS has shown a higher photocurrent density and lower charge transfer resistance analyzed

  16. 47 CFR 1.1154 - Schedule of annual regulatory charges and filing locations for common carrier services.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... facilities Fee amount Address 1. Microwave (Domestic Public Fixed) (Electronic Filing) (FCC Form 601 & 159) $25.00 FCC, P.O. Box 979097, St. Louis, MO 63197-9000 Carriers 1. Interstate Telephone Service Providers (per interstate and international end-user revenues (see FCC Form 499-A) .00349 FCC, Carriers,...

  17. Shapiro step at nonequilibrium conditions

    NASA Astrophysics Data System (ADS)

    Shukrinov, Yu. M.; Nashaat, M.; Kulikov, K. V.; Dawood, R.; El Samman, H.; El Sherbini, Th. M.

    2016-07-01

    Detailed numerical simulations of intrinsic Josephson junctions of high-temperature superconductors under external electromagnetic radiation are performed taking into account a charge imbalance effect. We demonstrate that the charge imbalance is responsible for a slope in the Shapiro step in the IV-characteristic. The value of slope increases with a nonequilibrium parameter. Coupling between junctions leads to the distribution of the slope's values along the stack. The nonperiodic boundary conditions shift the Shapiro step from the canonical position determined by Vss=\\hbar f /(2e) , where f is a frequency of external radiation. This fact makes the interpretation of the experimentally found Shapiro step shift by the charge imbalance effect ambiguous.

  18. Charge-carrier dynamics in polycrystalline thin-film CuIn{sub 1−x}Ga{sub x}Se{sub 2} photovoltaic devices after pulsed laser excitation: Interface and space-charge region analysis

    SciTech Connect

    Kuciauskas, Darius; Li, Jian V.; Kanevce, Ana; Guthrey, Harvey; Contreras, Miguel; Pankow, Joel; Dippo, Pat; Ramanathan, Kannan

    2015-05-14

    We used time-resolved photoluminescence (TRPL) spectroscopy to analyze time-domain and spectral-domain charge-carrier dynamics in CuIn{sub 1−x}Ga{sub x}Se{sub 2} (CIGS) photovoltaic (PV) devices. This new approach allowed detailed characterization for the CIGS/CdS buffer interface and for the space-charge region. We find that dynamics at the interface is dominated by diffusion, where the diffusion rate is several times greater than the thermionic emission or interface recombination rate. In the space-charge region, the electric field of the pn junction has the largest effect on the carrier dynamics. Based on the minority-carrier (electron) drift-rate dependence on the electric field strength, we estimated drift mobility in compensated CuIn{sub 1−x}Ga{sub x}Se{sub 2} (with x ≈ 0.3) as 22 ± 2 cm{sup 2}(Vs){sup −1}. Analysis developed in this study could be applied to evaluate interface and junction properties of PV and other electronic devices. For CIGS PV devices, TRPL spectroscopy could contribute to understanding effects due to absorber compositional grading, which is one of the focus areas in developing record-efficiency CIGS solar cells.

  19. Nonequilibrium is different

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, T. R.; Dorfman, J. R.

    2015-08-01

    Nonequilibrium and equilibrium fluid systems differ due to the existence of long-range correlations in nonequilibrium that are not present in equilibrium, except at critical points. Here we examine fluctuations of the temperature, of the pressure tensor, and of the heat current in a fluid maintained in a nonequilibrium stationary state (NESS) with a fixed temperature gradient, a system in which the nonequilibrium correlations are especially long-ranged. For this particular NESS, our results show that (i) the mean-squared fluctuations in nonequilibrium differ markedly in their system-size scaling compared to their equilibrium counterparts, and (ii) there are large, nonlocal correlations of the normal stress in this NESS. These terms provide important corrections to the fluctuating normal stress in linearized Landau-Lifshitz fluctuating hydrodynamics.

  20. Charge carrier effective mass and concentration derived from combination of Seebeck coefficient and Te125 NMR measurements in complex tellurides

    DOE PAGES

    Levin, E. M.

    2016-06-27

    Thermoelectric materials utilize the Seebeck effect to convert heat to electrical energy. The Seebeck coefficient (thermopower), S, depends on the free (mobile) carrier concentration, n, and effective mass, m*, as S ~ m*/n2/3. The carrier concentration in tellurides can be derived from 125Te nuclear magnetic resonance (NMR) spin-lattice relaxation measurements. The NMR spin-lattice relaxation rate, 1/T1, depends on both n and m* as 1/T1~(m*)3/2n (within classical Maxwell-Boltzmann statistics) or as 1/T1~(m*)2n2/3 (within quantum Fermi-Dirac statistics), which challenges the correct determination of the carrier concentration in some materials by NMR. Here it is shown that the combination of the Seebeck coefficientmore » and 125Te NMR spin-lattice relaxation measurements in complex tellurides provides a unique opportunity to derive the carrier effective mass and then to calculate the carrier concentration. This approach was used to study AgxSbxGe50–2xTe50, well-known GeTe-based high-efficiency tellurium-antimony-germanium-silver thermoelectric materials, where the replacement of Ge by [Ag+Sb] results in significant enhancement of the Seebeck coefficient. Thus, values of both m* and n derived using this combination show that the enhancement of thermopower can be attributed primarily to an increase of the carrier effective mass and partially to a decrease of the carrier concentration when the [Ag+Sb] content increases.« less

  1. Generation-dependent charge carrier transport in Cu(In,Ga)Se2/CdS/ZnO thin-film solar-cells

    NASA Astrophysics Data System (ADS)

    Nichterwitz, Melanie; Caballero, Raquel; Kaufmann, Christian A.; Schock, Hans-Werner; Unold, Thomas

    2013-01-01

    Cross section electron-beam induced current (EBIC) and illumination-dependent current voltage (IV) measurements show that charge carrier transport in Cu(In,Ga)Se2 (CIGSe)/CdS/ZnO solar-cells is generation-dependent. We perform a detailed analysis of CIGSe solar cells with different CdS layer thicknesses and varying Ga-content in the absorber layer. In conjunction with numerical simulations, EBIC and IV data are used to develop a consistent model for charge and defect distributions with a focus on the heterojunction region. The best model to explain our experimental data is based on a p+ layer at the CIGSe/CdS interface leading to generation-dependent transport in EBIC at room temperature. Acceptor-type defect states at the CdS/ZnO interface cause a significant reduction of the photocurrent in the red-light illuminated IV characteristics at low temperatures (red kink effect). Shallow donor-type defect states at the p+ layer/CdS interface of some grains of the absorber layer are responsible for grain specific, i.e., spatially inhomogeneous, charge carrier transport observed in EBIC.

  2. Negative differential mobility for negative carriers as revealed by space charge measurements on crosslinked polyethylene insulated model cables

    NASA Astrophysics Data System (ADS)

    Teyssedre, G.; Vu, T. T. N.; Laurent, C.

    2015-12-01

    Among features observed in polyethylene materials under relatively high field, space charge packets, consisting in a pulse of net charge that remains in the form of a pulse as it crosses the insulation, are repeatedly observed but without complete theory explaining their formation and propagation. Positive charge packets are more often reported, and the models based on negative differential mobility(NDM) for the transport of holes could account for some charge packets phenomenology. Conversely, NDM for electrons transport has never been reported so far. The present contribution reports space charge measurements by pulsed electroacoustic method on miniature cables that are model of HVDC cables. The measurements were realized at room temperature or with a temperature gradient of 10 °C through the insulation under DC fields on the order 30-60 kV/mm. Space charge results reveal systematic occurrence of a negative front of charges generated at the inner electrode that moves toward the outer electrode at the beginning of the polarization step. It is observed that the transit time of the front of negative charge increases, and therefore the mobility decreases, with the applied voltage. Further, the estimated mobility, in the range 10-14-10-13 m2 V-1 s-1 for the present results, increases when the temperature increases for the same condition of applied voltage. The features substantiate the hypothesis of negative differential mobility used for modelling space charge packets.

  3. Balance between light trapping and charge carrier collection: Electro-photonic optimization of organic photovoltaics with ridge-patterned back electrodes

    NASA Astrophysics Data System (ADS)

    Liu, Yingchi; Tippets, Cary A.; Kirsch, Christoph; Mitran, Sorin; Samulski, Edward T.; Lopez, Rene

    2013-06-01

    Light trapping strategies are frequently suggested to improve organic photovoltaic (OPV) cell efficiencies. However, one cannot overlook the side-effects to charge carrier collection which are introduced when seeking optical enhancements. A comprehensive electro-photonic model is utilized to study the optical and electrical effects of patterning poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl

  4. Temperature effects on the energy bandgap and conductivity effective masses of charge carriers in lead telluride from first-principles calculations

    SciTech Connect

    Venkatapathi, S. Dong, B.; Hin, C.

    2014-07-07

    We determined the temperature effects on the electronic properties of lead telluride (PbTe) such as the energy bandgap and the effective masses of charge carriers by incorporating the structural changes of the material with temperature using ab-initio density functional theory (DFT) calculations. Though the first-principles DFT calculations are done at absolute zero temperatures, by incorporating the lattice thermal expansion and the distortion of Pb{sup 2+} ions from the equilibrium positions, we could determine the stable structural configuration of the PbTe system at different temperatures.

  5. Negative differential mobility for negative carriers as revealed by space charge measurements on crosslinked polyethylene insulated model cables

    SciTech Connect

    Teyssedre, G. Laurent, C.; Vu, T. T. N.

    2015-12-21

    Among features observed in polyethylene materials under relatively high field, space charge packets, consisting in a pulse of net charge that remains in the form of a pulse as it crosses the insulation, are repeatedly observed but without complete theory explaining their formation and propagation. Positive charge packets are more often reported, and the models based on negative differential mobility(NDM) for the transport of holes could account for some charge packets phenomenology. Conversely, NDM for electrons transport has never been reported so far. The present contribution reports space charge measurements by pulsed electroacoustic method on miniature cables that are model of HVDC cables. The measurements were realized at room temperature or with a temperature gradient of 10 °C through the insulation under DC fields on the order 30–60 kV/mm. Space charge results reveal systematic occurrence of a negative front of charges generated at the inner electrode that moves toward the outer electrode at the beginning of the polarization step. It is observed that the transit time of the front of negative charge increases, and therefore the mobility decreases, with the applied voltage. Further, the estimated mobility, in the range 10{sup −14}–10{sup −13} m{sup 2} V{sup −1} s{sup −1} for the present results, increases when the temperature increases for the same condition of applied voltage. The features substantiate the hypothesis of negative differential mobility used for modelling space charge packets.

  6. Graded morphology in bulk-heterojunction solar cells based on colloidal semiconductor nanostructures: Directed charge-separation and facile carrier transport

    NASA Astrophysics Data System (ADS)

    Dasgupta, Uttiya; Pal, Amlan J.

    2016-08-01

    We introduce density gradient of p- and n-type compound semiconductor nanostructures in bulk-heterojunction (BHJ) solar cells. The graded BHJs (GBHJs) were formed with the p-type copper-zinc-tin-sulfide (Cu2ZnSnS4) nanoparticles and n-type Bi2S3 nanorods, both of which were based on nontoxic and earth-abundant elements and were grown at a moderate reaction temperature (180 °C). The concentration gradient of the nanostructures in the GBHJs provided a preferred directionality of nano-depletion regions for directed charge separation and also a controlled vertical segregation for ever-increasing carrier-transport pathways during the charge-extraction process. A comparison of solar cell characteristics having a bilayer, a BHJ, and a GBHJ structure is being presented. The performance of the thickness-optimized devices for highest efficiency shows that the GBHJ offered an improved short-circuit current as compared to the bilayer and the BHJ structures and a higher fill-factor as compared to the BHJ device. The overall energy conversion efficiency (η) of GBHJ exceeded that of the other two heterojunctions. The advantages of GBHJ structures in yielding an improved η have been explained through an increased exciton dissociation process along with a lower carrier recombination as compared to the bilayer and the BHJ structures, respectively. Series and shunt resistances, which were derived from current-voltage characteristics and impedance spectroscopy, supported such analyses.

  7. Role of Sub-Nanometer Dielectric Roughness on Microstructure and Charge Carrier Transport in α,ω-Dihexylsexithiophene Field-Effect Transistors.

    PubMed

    Li, Mengmeng; Marszalek, Tomasz; Müllen, Klaus; Pisula, Wojciech

    2016-06-29

    The effect of dielectric roughness on the microstructure evolution of thermally evaporated α,ω-dihexylsexithiophene (α,ω-DH6T) thin films from a single molecular layer to tens of monolayers (ML) is studied. Thereby, the surface roughness of dielectrics is controlled within a sub-nanometer range. It is found that the grain size of an α,ω-DH6T ML is affected by dielectric roughness, especially for 1.5 ML, whereby the transistor performance is barely influenced. This can be attributed to a domain interconnection in the second layer over a long-range formed on the rough surface. With deposition of more layers, both microstructure and charge carrier transport exhibit a roughness-independent behavior. The structural characterization of α,ω-DH6T 10 ML by grazing-incidence wide-angle X-ray scattering reveals that the interlayer distance is slightly decreased from 3.30 to 3.15 nm due to a higher roughness, while an unchanged π-stacking distance is in excellent agreement with the roughness-independent hole mobility. This study excludes the influence of molecular-solvent interaction and preaggregation taking place during solution deposition, and provides further evidence that the microstructure of the interfacial layer of organic semiconductors has only minor impact on the bulk charge carrier transport in thicker films.

  8. Optimization of charge carrier transport balance for performance improvement of PDPP3T-based polymer solar cells prepared using a hot solution.

    PubMed

    Wang, Jian; Zhang, Fujun; Zhang, Miao; Wang, Wenbin; An, Qiaoshi; Li, Lingliang; Sun, Qianqian; Tang, Weihua; Zhang, Jian

    2015-04-21

    Polymer solar cells (PSCs), with poly(diketopyrrolopyrrole-terthiophene) (PDPP3T):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the active layers, were fabricated using solutions of different temperatures. The best power conversion efficiency (PCE) of the PSCs prepared using a hot solution was about 6.22%, which is better than 5.54% for PSCs prepared using cool (room temperature) solutions and 5.85% for PSCs prepared using cool solutions with a 1,8-diiodooctane (DIO) solvent additive. The underlying reasons for the improved PCE of the PSCs prepared using a hot solution could be attributed to the more dispersive donor and acceptor distribution in the active layer, resulting in a better bi-continuous interpenetrating network for exciton dissociation and charge carrier transport. An enhanced and more balanced charge carrier transport in the active layer is obtained for the PSCs prepared using a hot solution, which can be determined from the J-V curves of the related hole-only and electron-only devices.

  9. Long-Lived Hot Carriers in III-V Nanowires.

    PubMed

    Tedeschi, D; De Luca, M; Fonseka, H A; Gao, Q; Mura, F; Tan, H H; Rubini, S; Martelli, F; Jagadish, C; Capizzi, M; Polimeni, A

    2016-05-11

    Heat management mechanisms play a pivotal role in driving the design of nanowire (NW)-based devices. In particular, the rate at which charge carriers cool down after an external excitation is crucial for the efficiency of solar cells, lasers, and high-speed transistors. Here, we investigate the thermalization properties of photogenerated carriers by continuous-wave (cw) photoluminescence (PL) in InP and GaAs NWs. A quantitative analysis of the PL spectra recorded up to 310 K shows that carriers can thermalize at a temperature much higher than that of the lattice. We find that the mismatch between carrier and lattice temperature, ΔT, increases exponentially with lattice temperature and depends inversely on the NW diameter. ΔT is instead independent of other NW characteristics, such as crystal structure (wurtzite vs zincblende), chemical composition (InP vs GaAs), shape (tapered vs columnar NWs), and growth method (vapor-liquid-solid vs selective-area growth). Remarkably, carrier temperatures as high as 500 K are reached at the lattice temperature of 310 K in NWs with ∼70 nm diameter. While a population of nonequilibrium carriers, usually referred to as "hot carriers", is routinely generated by high-power laser pulses and detected by ultrafast spectroscopy, it is quite remarkable that it can be observed in cw PL measurements, when a steady-state population of carriers is established. Time-resolved PL measurements show that even in the thinnest NWs carriers have enough time (∼1 ns) after photoexcitation to interact with phonons and thus to release their excess energy. Nevertheless, the inability of carriers to reach a full thermal equilibrium with the lattice points to inhibited phonon emission primarily caused by the large surface-to-volume ratio of small diameter NWs.

  10. Long-Lived Hot Carriers in III-V Nanowires.

    PubMed

    Tedeschi, D; De Luca, M; Fonseka, H A; Gao, Q; Mura, F; Tan, H H; Rubini, S; Martelli, F; Jagadish, C; Capizzi, M; Polimeni, A

    2016-05-11

    Heat management mechanisms play a pivotal role in driving the design of nanowire (NW)-based devices. In particular, the rate at which charge carriers cool down after an external excitation is crucial for the efficiency of solar cells, lasers, and high-speed transistors. Here, we investigate the thermalization properties of photogenerated carriers by continuous-wave (cw) photoluminescence (PL) in InP and GaAs NWs. A quantitative analysis of the PL spectra recorded up to 310 K shows that carriers can thermalize at a temperature much higher than that of the lattice. We find that the mismatch between carrier and lattice temperature, ΔT, increases exponentially with lattice temperature and depends inversely on the NW diameter. ΔT is instead independent of other NW characteristics, such as crystal structure (wurtzite vs zincblende), chemical composition (InP vs GaAs), shape (tapered vs columnar NWs), and growth method (vapor-liquid-solid vs selective-area growth). Remarkably, carrier temperatures as high as 500 K are reached at the lattice temperature of 310 K in NWs with ∼70 nm diameter. While a population of nonequilibrium carriers, usually referred to as "hot carriers", is routinely generated by high-power laser pulses and detected by ultrafast spectroscopy, it is quite remarkable that it can be observed in cw PL measurements, when a steady-state population of carriers is established. Time-resolved PL measurements show that even in the thinnest NWs carriers have enough time (∼1 ns) after photoexcitation to interact with phonons and thus to release their excess energy. Nevertheless, the inability of carriers to reach a full thermal equilibrium with the lattice points to inhibited phonon emission primarily caused by the large surface-to-volume ratio of small diameter NWs. PMID:27104870

  11. Coupled optical absorption, charge carrier separation, and surface electrochemistry in surface disordered/hydrogenated TiO2 for enhanced PEC water splitting reaction.

    PubMed

    Behara, Dilip Kumar; Ummireddi, Ashok Kumar; Aragonda, Vidyasagar; Gupta, Prashant Kumar; Pala, Raj Ganesh S; Sivakumar, Sri

    2016-03-28

    The central governing factors that influence the efficiency of photoelectrochemical (PEC) water splitting reaction are photon absorption, effective charge-carrier separation, and surface electrochemistry. Attempts to improve one of the three factors may debilitate other factors and we explore such issues in hydrogenated TiO2, wherein a significant increase in optical absorption has not resulted in a significant increase in PEC performance, which we attribute to the enhanced recombination rate due to the formation of amorphization/disorderness in the bulk during the hydrogenation process. To this end, we report a methodology to increase the charge-carrier separation with enhanced optical absorption of hydrogenated TiO2. Current methodology involves hydrogenation of non-metal (N and S) doped TiO2 which comprises (1) lowering of the band gap through shifting of the valence band via less electronegative non-metal N, S-doping, (2) lowering of the conduction band level and the band gap via formation of the Ti(3+) state and oxygen vacancies by hydrogenation, and (3) material processing to obtain a disordered surface structure which favors higher electrocatalytic (EC) activity. This design strategy yields enhanced PEC activity (%ABPE = 0.38) for the N-S co-doped TiO2 sample hydrogenated at 800 °C for 24 h over possible combinations of N-S co-doped TiO2 samples hydrogenated at 500 °C/24 h, 650 °C/24 h and 800 °C/72 h. This suggests that hydrogenation at lower temperatures does not result in much increase in optical absorption and prolonged hydrogenation results in an increase in optical absorption but a decrease in charge carrier separation by forming disorderness/oxygen vacancies in the bulk. Furthermore, the difference in double layer capacitance (C(dl)) calculated from electrochemical impedance spectroscopy (EIS) measurements of these samples reflects the change in the electrochemical surface area (ECSA) and facilitates assessing the key role of surface

  12. Coupled optical absorption, charge carrier separation, and surface electrochemistry in surface disordered/hydrogenated TiO2 for enhanced PEC water splitting reaction.

    PubMed

    Behara, Dilip Kumar; Ummireddi, Ashok Kumar; Aragonda, Vidyasagar; Gupta, Prashant Kumar; Pala, Raj Ganesh S; Sivakumar, Sri

    2016-03-28

    The central governing factors that influence the efficiency of photoelectrochemical (PEC) water splitting reaction are photon absorption, effective charge-carrier separation, and surface electrochemistry. Attempts to improve one of the three factors may debilitate other factors and we explore such issues in hydrogenated TiO2, wherein a significant increase in optical absorption has not resulted in a significant increase in PEC performance, which we attribute to the enhanced recombination rate due to the formation of amorphization/disorderness in the bulk during the hydrogenation process. To this end, we report a methodology to increase the charge-carrier separation with enhanced optical absorption of hydrogenated TiO2. Current methodology involves hydrogenation of non-metal (N and S) doped TiO2 which comprises (1) lowering of the band gap through shifting of the valence band via less electronegative non-metal N, S-doping, (2) lowering of the conduction band level and the band gap via formation of the Ti(3+) state and oxygen vacancies by hydrogenation, and (3) material processing to obtain a disordered surface structure which favors higher electrocatalytic (EC) activity. This design strategy yields enhanced PEC activity (%ABPE = 0.38) for the N-S co-doped TiO2 sample hydrogenated at 800 °C for 24 h over possible combinations of N-S co-doped TiO2 samples hydrogenated at 500 °C/24 h, 650 °C/24 h and 800 °C/72 h. This suggests that hydrogenation at lower temperatures does not result in much increase in optical absorption and prolonged hydrogenation results in an increase in optical absorption but a decrease in charge carrier separation by forming disorderness/oxygen vacancies in the bulk. Furthermore, the difference in double layer capacitance (C(dl)) calculated from electrochemical impedance spectroscopy (EIS) measurements of these samples reflects the change in the electrochemical surface area (ECSA) and facilitates assessing the key role of surface

  13. Assessment of Hot-Carrier Effects on Charge Separation in Type-II CdS/CdTe Heterostructured Nanorods.

    PubMed

    Okano, Makoto; Sakamoto, Masanori; Teranishi, Toshiharu; Kanemitsu, Yoshihiko

    2014-09-01

    Charge separation in semiconducting materials is an essential process that determines the efficiency of photovoltaic devices and photocatalysts. Herein, we report the charge-separation dynamics in type-II CdS/CdTe heterostructured nanorods revealed by femtosecond transient-absorption (TA) measurements with a broad-band white-light probe. Under selective excitation of the CdTe segment, bleaching signals at the band gap energy of CdS were clearly observed with a rise component on a subpicosecond time scale, which indicates efficient electron transfer from CdTe to CdS. The pump-energy dependence of the TA dynamics shows that hot electrons rapidly relax to the bottom of the conduction band of CdTe, and then the electrons transfer to the CdS segment.

  14. Extended characterization of the damage by hot charge carriers in gate oxide by short channel MOS field effect transistors

    NASA Astrophysics Data System (ADS)

    Mahnkopf, Reinhard

    Transistors from several technologies are tested by measurements of the capacities and the characteristic curves. A model allows obtaining of the gate and substrate currents. The damages at the phase limit and in the oxide are characterized by macroscopic current and voltage variations and by generated charge densities. For p-MOS (Metal Oxide Semiconductor) transistors, the production of oxide charges is the most important fact, in relation to the injected hot electrons; for n-MOS transistors, the generation of phase limit states is the main phenomenon. It is proved that the damages are located at the chain contact in the lateral direction but appear in the transistor channel with increasing functioning time or voltage.

  15. Electron Spin Resonance Study of Interface Trap States and Charge Carrier Concentration in Rubrene Single-Crystal Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Tsuji, Masaki; Arai, Norimichi; Marumoto, Kazuhiro; Takeya, Jun; Shimoi, Yukihiro; Tanaka, Hisaaki; Kuroda, Shin-ichi; Takenobu, Taishi; Iwasa, Yoshihiro

    2011-08-01

    Field-induced charge carriers at the semiconductor/dielectric interface of rubrene single-crystal field-effect transistors (RSC-FETs) were studied by ESR. We fabricated bottom-contact RSC-FETs to be used for ESR measurements by laminating RSCs onto SiO2 and polymer/SiO2 gate dielectric surfaces. The observed ESR spectra depict a minimal dependence on gate voltage, whose result is in sharp contrast to those obtained using RSC-FETs fabricated by the deposition of a parylene C gate dielectric. This behavior indicates that few deep trap levels are generated by the lamination technique. The dependence of ESR intensity on drain voltage was also investigated using gradual channel approximation.

  16. Flux-pinning mechanism in silicone-oil-doped MgB2 : Evidence for charge-carrier mean free path fluctuation pinning

    NASA Astrophysics Data System (ADS)

    Ghorbani, S. R.; Wang, X. L.; Dou, S. X.; Lee, Sung-Ik; Hossain, M. S. A.

    2008-11-01

    Flux-pinning mechanism of MgB2 doped with 10wt% silicone-oil sintered at low and high temperatures has been investigated by magnetic measurements. The field dependence of the critical current density, jc(B) , was analyzed within the collective pinning model. A crossover field, Bsb , from the single vortex to the small vortex bundle-pinning regime was observed. For both types of sintered samples, the temperature dependence of Bsb(T) at low temperature is in good agreement with the δl pinning mechanism, i.e., pinning associated with charge-carrier mean free path fluctuation. At temperatures close to the critical temperature, however, there is evidence for δTc pinning, which is associated with spatial fluctuations of the transition temperature. These results provide strong evidence that the liquid precursor, silicone oil, produces very small pinning centers and enhances the jc(B) .

  17. Nonequilibrium heat capacity.

    PubMed

    Mandal, Dibyendu

    2013-12-01

    Development of steady state thermodynamics and statistical mechanics depends crucially on our ability to extend the notions of equilibrium thermodynamics to nonequilibrium steady states (NESS). The present paper considers the extension of heat capacity. A modified definition is proposed which continues to maintain the same relation to steady state Shannon entropy as in equilibrium, thus providing a thermodynamically consistent treatment of NESS heat capacity.

  18. Nonequilibrium Tuning of the Thermal Casimir Effect.

    PubMed

    Dean, David S; Lu, Bing-Sui; Maggs, A C; Podgornik, Rudolf

    2016-06-17

    In net-neutral systems correlations between charge fluctuations generate strong attractive thermal Casimir forces and engineering these forces to optimize nanodevice performance is an important challenge. We show how the normal and lateral thermal Casimir forces between two plates containing Brownian charges can be modulated by decorrelating the system through the application of an electric field, which generates a nonequilibrium steady state with a constant current in one or both plates, reducing the ensuing fluctuation-generated normal force while at the same time generating a lateral drag force. This hypothesis is confirmed by detailed numerical simulations as well as an analytical approach based on stochastic density functional theory. PMID:27367374

  19. Nonequilibrium Tuning of the Thermal Casimir Effect

    NASA Astrophysics Data System (ADS)

    Dean, David S.; Lu, Bing-Sui; Maggs, A. C.; Podgornik, Rudolf

    2016-06-01

    In net-neutral systems correlations between charge fluctuations generate strong attractive thermal Casimir forces and engineering these forces to optimize nanodevice performance is an important challenge. We show how the normal and lateral thermal Casimir forces between two plates containing Brownian charges can be modulated by decorrelating the system through the application of an electric field, which generates a nonequilibrium steady state with a constant current in one or both plates, reducing the ensuing fluctuation-generated normal force while at the same time generating a lateral drag force. This hypothesis is confirmed by detailed numerical simulations as well as an analytical approach based on stochastic density functional theory.

  20. Charge carrier mobility in conjugated organic polymers: simulation of an electron mobility in a carbazole-benzothiadiazole-based polymer

    NASA Astrophysics Data System (ADS)

    Li, Yaping; Lagowski, Jolanta B.

    2011-08-01

    Inorganic (mostly silicon based) solar cells are important devices that are used to solve the world energy and environmental needs. Now days, organic solar cells are attracting considerable attention in the field of photovoltaic cells because of their low cost and processing flexibility. Often conjugated polymers are used in the construction of the organic solar cells. We study the conjugated polymers' charge transport using computational approach that involves the use of the density functional theory (DFT), semiempirical (ZINDO), and Monte Carlo (MC) theoretical methods in order to determine their transfer integrals, reorganization energies, transfer rates (with the use of Marcus-Hush equation) and mobilities. We employ the experimentally determined three dimensional (3D) structure of poly(9,9'-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) to estimate the electron mobility in a similar co-alternating polymer consisting of carbazole and benzothiadiazole units (C8BT). In agreement with our previous work, we found that including an orientational disorder in the crystal reduces the electron mobility in C8BT. We hope that the proposed computational approach can be used to predict charge mobility in organic materials that are used in solar cells.

  1. Time Evolution of Charge Carriers & Phonons after Photo-Excitation by an Ultra-Short Light Pulse in Bulk Germanium

    NASA Astrophysics Data System (ADS)

    Fahy, Stephen; Murphy-Armando, Felipe; Trigo, Mariano; Savic, Ivana; Murray, Eamonn; Reis, David

    We have calculated the time-evolution of carriers and generated phonons in Ge after ultrafast photo-excitation above the direct band-gap. The relevant electron-phonon and anharmonic phonon scattering rates are obtained from first-principles electronic structure calculations. Measurements of the x-ray diffuse scattering after excitation near the L point in the Brillouin zone find a relatively slow (5 ps, compared to the typical electron-phonon energy relaxation of the Gamma-L phonon) increase of the phonon population. We find this is due to emission caused by the scattering of electrons between the Delta and L valleys, after the initial depopulation of the Gamma valley. The relative slowness of this process is due to a combination of causes: (i) the finite time for the initial depopulation of the conduction Gamma valley; (ii) the associated electron-phonon coupling is relatively weaker (compared to Gamma-L, Gamma-Delta and Delta-Delta couplings) ; (iii) the TA associated phonon has a long lifetime and (iv) the depopulation of the Delta valley suppresses the phonon emission. Supported by Science Foundation Ireland, Grant 12/1A/1601.

  2. Light-Induced ESR Studies of Quadrimolecular Recombination Kinetics of Photogenerated Charge Carriers in Regioregular Poly(3-alkylthiophene)/C60 Composites: Alkyl Chain Dependence

    NASA Astrophysics Data System (ADS)

    Tanaka, Hisaaki; Hasegawa, Naoki; Sakamoto, Tomotaka; Marumoto, Kazuhiro; Kuroda, Shin-ichi

    2007-08-01

    Light-induced ESR (LESR) measurements have been performed on the composites of regioregular poly(3-alkylthiophene) (RR-P3AT) and C60 by using polymers having different alkyl chains (CmH2m+1 with m=6, 8, 10, 12). The quadrimolecular recombination (QR) kinetics of photogenerated charge carriers, previously reported, have been confirmed for all the composites from the excitation power (Iex) dependence of the LESR intensity showing an ˜Iex0.25 dependence. The time decay of LESR intensity is also consistent with the QR model. Considering that only bimolecular recombination is observed in regiorandom polymer composites, the occurrence of QR strongly suggests the formation of doubly charged states, either bipolarons or polaron pairs on the regioregular polymer chains. On the other hand, the QR rate constant γ has been found to exhibit weak alkyl chain dependence, contrary to the case of the field-effect mobility of pure regioregular polymers with systematic alkyl chain dependence. This implies the significant contribution of the polymer and fullerene interface in determining γ.

  3. Absence of carrier separation in ambipolar charge and spin drift in p{sup +}-GaAs

    SciTech Connect

    Cadiz, F.; Paget, D.; Rowe, A. C. H.; Martinelli, L.; Arscott, S.

    2015-10-19

    The electric field-induced modifications of the spatial distribution of photoelectrons, photoholes, and electronic spins in optically pumped p{sup +} GaAs are investigated using a polarized luminescence imaging microscopy. At low pump intensity, application of an electric field reveals the tail of charge and spin density of drifting electrons. These tails disappear when the pump intensity is increased since a slight differential drift of photoelectrons and photoholes causes the buildup of a strong internal electric field. Spatial separation of photoholes and photoelectrons is very weak so that photoholes drift in the same direction as photoelectrons, thus exhibiting a negative effective mobility. In contrast, for a zero electric field, no significant ambipolar diffusive effects are found in the same sample.

  4. Common Carrier Services.

    ERIC Educational Resources Information Center

    Federal Communications Commission, Washington, DC.

    After outlining the Federal Communications Commission's (FCC) responsibility for regulating interstate common carrier communication (non-broadcast communication whose carriers are required by law to furnish service at reasonable charges upon request), this information bulletin reviews the history, technological development, and current…

  5. Ultrafast Response of the Hubbard Model: Non-adiabatic TDDFT + DMFT versus Non-equilibrium DMFT Solution

    NASA Astrophysics Data System (ADS)

    Acharya, Shree Ram; Turkowski, Volodymyr; Rahman, Talat S.

    We study the ultrafast response of electrons in the one-band Hubbard model to an external laser-pulse perturbation by using the Non-adiabatic Time-Dependent Density Functional Theory + Dynamical Mean-Field Theory (TDDFT +DMFT) approach. The corresponding exchange-correlation kernel (XC) is obtained from the DMFT charge susceptibility by using the Quantum Monte Carlo solver for the impurity problem. Detailed analysis of the time-dependent excited charge density, the Fermi distribution function, and the spatially nonhomogeneous response (metallic domain growth), is performed for different values for the carrier density and local Coulomb repulsion. We compare the results with the corresponding non-equilibrium DMFT solutions, and demonstrate that non-adiabaticity (frequency-dependence) of the XC kernel is important in order to reproduce the non-equilibrium DMFT solution. Also, from the numerical results for the charge susceptibility, we obtain an approximate analytical expression for the XC kernel. Using this kernel, we reveal possible types of ''elementary'' excitations and the dynamics of metallic domain growth in the case of the one-band Hubbard model. Possible generalization of the approach to the multi-orbital case is discussed. Work supported in part by DOE Grant No. DOE-DE-FG02-07ER46354.

  6. A novel research approach on the dynamic properties of photogenerated charge carriers at Ag{sub 2}S quantum-dots-sensitized TiO{sub 2} films by a frequency-modulated surface photovoltage technology

    SciTech Connect

    Zhang, Yu; Zhang, Wei; Xie, Tengfeng; Wang, Dejun; Song, Xi-Ming

    2013-09-01

    Graphical abstract: The changed SPV with chopping frequencies indicate the separation speeds of photogenerated charge carriers in different films. - Highlights: • Ag{sub 2}S-sensitized TiO{sub 2} films show good photoelectric responses in visible-light region. • Frequency-modulated SPV give dynamic information and evidence of Ag{sub 2}S QDSSCs’ performance. • Frequency-modulated SPV can supply complementary information in the study of Ag{sub 2}S ODSSCs. - Abstract: Ag{sub 2}S quantum-dots-sensitized TiO{sub 2} films with different amount of Ag{sub 2}S were fabricated by a successive ionic layer adsorption and reaction (SILAR) method. The separation and transport of photogenerated charge carriers at different spectral regions were studied by the frequency-modulated surface photovoltage technology. Some novel dynamic information of photogenerated charge carriers in a wide spectral range is found. The results indicate that the rate and direction of separation (diffusion) for photogenerated charge carriers are closely related to the performance of quantum-dots-sensitized solar cells (QDSSCs) based on the Ag{sub 2}S/TiO{sub 2} nano-structure.

  7. Three-Dimensional Imaging of Lipid Gene-Carriers: Membrane Charge Density Controls Universal Transfection Behavior in Lamellar Cationic Liposome-DNA Complexes

    PubMed Central

    Lin, Alison J.; Slack, Nelle L.; Ahmad, Ayesha; George, Cyril X.; Samuel, Charles E.; Safinya, Cyrus R.

    2003-01-01

    Cationic liposomes (CLs) are used worldwide as gene vectors (carriers) in nonviral clinical applications of gene delivery, albeit with unacceptably low transfection efficiencies (TE). We present three-dimensional laser scanning confocal microscopy studies revealing distinct interactions between CL-DNA complexes, for both lamellar LαC and inverted hexagonal HIIC nanostructures, and mouse fibroblast cells. Confocal images of LαC complexes in cells identified two regimes. For low membrane charge density (σM), DNA remained trapped in CL-vectors. By contrast, for high σM, released DNA was observed in the cytoplasm, indicative of escape from endosomes through fusion. Remarkably, firefly luciferase reporter gene studies in the highly complex LαC-mammalian cell system revealed an unexpected simplicity where, at a constant cationic to anionic charge ratio, TE data for univalent and multivalent cationic lipids merged into a single curve as a function of σM, identifying it as a key universal parameter. The universal curve for transfection by LαC complexes climbs exponentially over ≈ four decades with increasing σM below an optimal charge density (σM*), and saturates for \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\sigma}_{{\\mathrm{M}}}>{\\sigma}_{M}^{{^\\ast}}\\end{equation*}\\end{document} at a value rivaling the high transfection efficiency of HIIC complexes. In contrast, the transfection efficiency of HIIC complexes is independent of σM. The exponential dependence of TE on σM for LαC complexes, suggests the existence of a kinetic barrier against endosomal fusion, where an increase in σM lowers the barrier. In the saturated TE regime, for both LαC complexes and HIIC, confocal microscopy reveals the dissociation of lipid and DNA. However, the lipid-released DNA is

  8. Giant THz photoconductivity and possible non-equilibrium superconductivity in metallic K3C60

    PubMed Central

    Mitrano, M.; Cantaluppi, A.; Nicoletti, D.; Kaiser, S.; Perucchi, A.; Lupi, S.; Di Pietro, P.; Pontiroli, D.; Riccò, M.; Clark, S. R.; Jaksch, D.; Cavalleri, A.

    2015-01-01

    The non-equilibrium control of emergent phenomena in solids is an important research frontier, encompassing effects like the optical enhancement of superconductivity 1 . Recently, nonlinear excitation 2 , 3 of certain phonons in bilayer cuprates was shown to induce superconducting-like optical properties at temperatures far above Tc 4,5,6. This effect was accompanied by the disruption of competing charge-density-wave correlations7,8, which explained some but not all of the experimental results. Here, we report a similar phenomenon in a very different compound. By exciting metallic K3C60 with mid-infrared optical pulses, we induce a large increase in carrier mobility, accompanied by the opening of a gap in the optical conductivity. Strikingly, these same signatures are observed at equilibrium when cooling metallic K3C60 below the superconducting transition temperature (Tc = 20 K). Although optical techniques alone cannot unequivocally identify non-equilibrium high-temperature superconductivity, we propose this scenario as a possible explanation of our results. PMID:26855424

  9. Separation of Contributions from the Ion Core and Free Charge Carriers to the Magnetic Susceptibility of an Anisotropic Semiconductor Bi2Te3-Sb2Te3 Crystal

    NASA Astrophysics Data System (ADS)

    Stepanov, N. P.; Nalivkin, V. Yu.

    2016-05-01

    A technique is presented, by which the magnetic susceptibility χ | G of the ion core of an anisotropic semiconductor Bi2Te3-Sb2Te3 crystal is determined from experimental data on the magnetic susceptibility χ ∥ and χ ⊥ obtained with allowance for the orientation of the magnetic field vector H with respect to the trigonal C3 axis of the crystal in accordance with the expression χ ∥/ χ ⊥ = ( χ ∥ eh + χ G )/( χ ⊥ eh + χ G ).In this expression, the value of the magnetic susceptibility of free charge carriers χ ∥ eh and χ ⊥ eh depending on their effective masses m ∥ * and m ⊥ * known from the experiment is calculated within the framework of the Pauli and Landau- Peierls approaches. The found value of χ | G for Bi2Te3-Sb2Te3 crystals is in good agreement with experimental data, as well as with the estimates obtained in the framework of the Larmor approach explaining, in particular, a linear dependence of the molar magnetic susceptibility on the number of electrons in the molecule observed for a large number of compounds. The proposed technique can be extended to other anisotropic semiconductors.

  10. Time-resolved optical study on the charge carrier dynamics in a TiO{sub 2}/AgI sandwich colloid

    SciTech Connect

    Fitzmaurice, D.; Frei, H.; Rabani, J. |

    1995-06-01

    Preparation of a sandwich colloid involving TiO{sub 2} and AgI (hexagonal) particles in alkaline aqueous solution is described. Time-resolved optical absorption experiments are reported that involve pulsed laser excitation at 355 nm (TiO{sub 2} bandgap) and at 410 nm (AgI bandgap). Charge carrier dynamics was probed directly by transient absorption measurements in the near-infrared and by reaction with methyl viologen (MV{sup 2+}). Reduction of MV{sup 2+} was observed to occur over a period of 100-200 {mu}s. MV{sup +} so produced reduced AgI to silver. By contrast, MV{sup 2+} reduction upon bandgap excitation of neat alkaline TiO{sub 2} colloid was complete within 1 {mu}s. These observations signal a prolonged electron-hole separation in the case of the AgI/TiO{sub 2} sol and indicate the formation of sandwich particles. 33 refs., 5 figs.

  11. Heterogeneous Charge Carrier Dynamics in Organic-Inorganic Hybrid Materials: Nanoscale Lateral and Depth-Dependent Variation of Recombination Rates in Methylammonium Lead Halide Perovskite Thin Films.

    PubMed

    Bischak, Connor G; Sanehira, Erin M; Precht, Jake T; Luther, Joseph M; Ginsberg, Naomi S

    2015-07-01

    We reveal substantial luminescence yield heterogeneity among individual subdiffraction grains of high-performing methylammonium lead halide perovskite films by using high-resolution cathodoluminescence microscopy. Using considerably lower accelerating voltages than is conventional in scanning electron microscopy, we image the electron beam-induced luminescence of the films and statistically characterize the depth-dependent role of defects that promote nonradiative recombination losses. The highest variability in the luminescence intensity is observed at the exposed grain surfaces, which we attribute to surface defects. By probing deeper into the film, it appears that bulk defects are more homogeneously distributed. By identifying the origin and variability of a surface-specific loss mechanism that deleteriously impacts device efficiency, we suggest that producing films homogeneously composed of the highest-luminescence grains found in this study could result in a dramatic improvement of overall device efficiency. We also show that although cathodoluminescence microscopy is generally used only to image inorganic materials it can be a powerful tool to investigate radiative and nonradiative charge carrier recombination on the nanoscale in organic-inorganic hybrid materials.

  12. Evaluation of the intrinsic charge carrier transporting properties of linear- and bent-shaped π-extended benzo-fused thieno[3,2-b]thiophenes.

    PubMed

    Tsutsui, Yusuke; Sakurai, Tsuneaki; Minami, Sojiro; Hirano, Koji; Satoh, Tetsuya; Matsuda, Wakana; Kato, Kenichi; Takata, Masaki; Miura, Masahiro; Seki, Shu

    2015-04-21

    The intrinsic charge carrier transporting properties of two isomeric linear- and bent-shaped 7-ring benzo-fused thieno[3,2-b] thiophenes and their octyl-substituted analogues were newly investigated using flash-photolysis (FP-) and field-induced (FI-) time-resolved microwave conductivity (TRMC) techniques. FP-TRMC study in the solid state revealed that octyl-substitution potentially improved the photoconductivity due to the enhanced crystalline lamellar packing. After this screening process, local-scale hole mobilities at the thienoacene-poly(methylmethacrylate) insulator interfaces were precisely recorded using FI-TRMC, reaching up to 4.5 cm(2) V(-1) s(-1) for the linear-shaped non-alkylated thienoacene. The combination of FP- and FI-TRMC measurements provides a rapid and quantitative evaluation scheme even for a variety of compounds with some issues in the processing conditions, leading to the optimized structure of the compounds used as active (interfacial) layers in practical electronic devices.

  13. Design of suitable carrier buffer for free-flow zone electrophoresis by charge-to-mass ratio and band broadening analysis.

    PubMed

    Kong, Fan-Zhi; Yang, Ying; He, Yu-Chen; Zhang, Qiang; Li, Guo-Qing; Fan, Liu-Yin; Xiao, Hua; Li, Shan; Cao, Cheng-Xi

    2016-09-01

    In this work, charge-to-mass ratio (C/M) and band broadening analyses were combined to provide better guidance for the design of free-flow zone electrophoresis carrier buffer (CB). First, the C/M analyses of hemoglobin and C-phycocyanin (C-PC) under different pH were performed by CLC Protein Workbench software. Second, band dispersion due to the initial bandwidth, diffusion, and hydrodynamic broadening were discussed, respectively. Based on the analyses of the C/M and band broadening, a better guidance for preparation of free-flow zone electrophoresis CB was obtained. Series of experiments were performed to validate the proposed method. The experimental data showed high accordance with our prediction allowing the CB to be prepared easily with our proposed method. To further evaluate this method, C-PC was purified from crude extracts of Spirulina platensis with the selected separation condition. Results showed that C-PC was well separated from other phycobiliproteins that have similar physicochemical properties, and analytical grade product with purity up to 4.5 (A620/A280) was obtained. PMID:27465345

  14. Ferromagnetism and the effect of free charge carriers on electric polarization in the double perovskite Y2NiMnO6

    NASA Astrophysics Data System (ADS)

    Nhalil, Hariharan; Nair, Harikrishnan S.; Kumar, C. M. N.; Strydom, André M.; Elizabeth, Suja

    2015-12-01

    The double perovskite Y2NiMnO6 displays ferromagnetic transition at Tc≈81 K. The ferromagnetic order at low temperature is confirmed by the saturation value of magnetization (Ms) and also validated by the refined ordered magnetic moment values extracted from neutron powder diffraction data at 10 K. This way, the dominant Mn+4 and Ni+2 cationic ordering is confirmed. The cation-ordered P 21/n nuclear structure is revealed by neutron powder diffraction studies at 300 and 10 K. Analysis of the frequency-dependent dielectric constant and equivalent circuit analysis of impedance data take into account the bulk contribution to the total dielectric constant. This reveals an anomaly which coincides with the ferromagnetic transition temperature (Tc) . Pyrocurrent measurements register a current flow with onset near Tc and a peak at 57 K that shifts with temperature ramp rate. The extrinsic nature of the observed pyrocurrent is established by employing a special protocol measurement. It is realized that the origin is due to reorientation of electric dipoles created by the free charge carriers and not by spontaneous electric polarization at variance with recently reported magnetism-driven ferroelectricity in this material.

  15. Theory of nonequilibrium superconductivity in cuprates

    NASA Astrophysics Data System (ADS)

    Oka, Takashi; Pietilä, Ville

    2013-03-01

    Recently, nonequilibrium properties of Hi Tc superconductors are attracting much interest. This is because new experimental methods such as time resolved ARPES has been applied to cuprates and succeeded in observing the dynamics of photo-excited quasiparticles as well as the temporal evolution of the d-wave superconducting order parameter (e.g.,). One can also realize nonequilibrium states in interfaces between cuprates and metal electrodes and control the superconducting order by changing the applied bias. In order to study the dynamics of superconductivity in strongly correlated systems, we developed a novel numerical method by combining the quantum kinetic equation with the fluctuation exchange approximation (FLEX, self-consistent T-matrix approximation). This method enables us to study the interplay between pair mediating fluctuations, e.g., antiferromagnetic and charge fluctuations, and the dynamics of quasiparticles and superconducting order parameter. In the presentation, we explain the physical insights we obtain by applying this method to nonequilibrium dynamics in d-wave superconductors.

  16. Nonequilibrium superconducting detectors

    NASA Astrophysics Data System (ADS)

    Cristiano, R.; Ejrnaes, M.; Esposito, E.; Lisitskyi, M. P.; Nappi, C.; Pagano, S.; Perez de Lara, D.

    2006-03-01

    Nonequilibrium superconducting detectors exploit the early stages of the energy down cascade which occur after the absorption of radiation. They operate on a short temporal scale ranging from few microseconds down to tens of picoseconds. In such a way they provide fast counting capability, high time discrimination and also, for some devices, energy sensitivity. Nonequilibrium superconducting detectors are developed for their use both in basic science and in practical applications for detection of single photons or single ionized macromolecules. In this paper we consider two devices: distributed readout imaging detectors (DROIDs) based on superconducting tunnel junctions (STJs), which are typically used for high-speed energy spectroscopy applications, and hot-electron superconductive detectors (HESDs), which are typically used as fast counters and time discriminators. Implementation of the DROID geometry to use a single superconductor is discussed. Progress in the fabrication technology of NbN nanostructured HESDs is presented. The two detectors share the high sensitivity that makes them able to efficiently detect even single photons down to infrared energy.

  17. Effect of Dual Cathode Buffer Layer on the Charge Carrier Dynamics of rrP3HT:PCBM Based Bulk Heterojunction Solar Cell.

    PubMed

    Singh, Ashish; Dey, Anamika; Das, Dipjyoti; Iyer, Parameswar Krishnan

    2016-05-01

    In bulk heterojunction (BHJ) solar cells, the buffer layer plays a vital role in enhancing the power conversion efficiency (PCE) by improving the charge carrier dynamics. A comprehensive understanding of the contacts is especially essential in order to optimize the performance of organic solar cells (OSCs). Although there are several fundamental reports on this subject, a proper correlation of the physical processes with experimental evidence at the photoactive layer and contact materials is essential. In this work, we incorporated three different additional buffer layers, namely, tris(8-hydroxyquinolinato) aluminum (Alq3), bathophenanthroline (BPhen) or bathocuproine (BCP) with LiF/Al as conventional cathode contact in both rrP3HT:PC61BM and rrP3HT:PC71BM blend BHJ solar cells and their corresponding photovoltaic performances were systematically correlated with their energy level diagram. The device with dual cathode buffer layer having ITO/PEDOT:PSS/blend polymer/BCP/LiF/Al configuration showed the best device performance with PCE, η = 4.96%, Jsc = 13.53 mA/cm(2), Voc = 0.60 V and FF= 61% for rrP3HT:PC71BM and PCE, η = 4.5% with Jsc = 13.3 mA/cm(2), Voc = 0.59 V and FF = 59% for rrP3HT:PC61BM. This drastic improvement in PCE in both the device configurations are due to the combined effects of better hole-blocking capacity of BCP and low work function provided by LiF/Al with the blend polymer. These results successfully explain the role of dual cathode buffer layers and their contribution to the PCE improvement and overall device performance with rrP3HT:PCBM based BHJ solar cell. PMID:27075007

  18. Effect of Dual Cathode Buffer Layer on the Charge Carrier Dynamics of rrP3HT:PCBM Based Bulk Heterojunction Solar Cell.

    PubMed

    Singh, Ashish; Dey, Anamika; Das, Dipjyoti; Iyer, Parameswar Krishnan

    2016-05-01

    In bulk heterojunction (BHJ) solar cells, the buffer layer plays a vital role in enhancing the power conversion efficiency (PCE) by improving the charge carrier dynamics. A comprehensive understanding of the contacts is especially essential in order to optimize the performance of organic solar cells (OSCs). Although there are several fundamental reports on this subject, a proper correlation of the physical processes with experimental evidence at the photoactive layer and contact materials is essential. In this work, we incorporated three different additional buffer layers, namely, tris(8-hydroxyquinolinato) aluminum (Alq3), bathophenanthroline (BPhen) or bathocuproine (BCP) with LiF/Al as conventional cathode contact in both rrP3HT:PC61BM and rrP3HT:PC71BM blend BHJ solar cells and their corresponding photovoltaic performances were systematically correlated with their energy level diagram. The device with dual cathode buffer layer having ITO/PEDOT:PSS/blend polymer/BCP/LiF/Al configuration showed the best device performance with PCE, η = 4.96%, Jsc = 13.53 mA/cm(2), Voc = 0.60 V and FF= 61% for rrP3HT:PC71BM and PCE, η = 4.5% with Jsc = 13.3 mA/cm(2), Voc = 0.59 V and FF = 59% for rrP3HT:PC61BM. This drastic improvement in PCE in both the device configurations are due to the combined effects of better hole-blocking capacity of BCP and low work function provided by LiF/Al with the blend polymer. These results successfully explain the role of dual cathode buffer layers and their contribution to the PCE improvement and overall device performance with rrP3HT:PCBM based BHJ solar cell.

  19. Delayed recombination of detrapped space-charge carriers in poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene]-based light-emitting diode

    NASA Astrophysics Data System (ADS)

    Sinha, S.; Monkman, A. P.

    2005-06-01

    We report the observation of a spectroscopically resolved delayed electrofluorescence (DEF) in the time domain of nanosecond to microsecond (depending on temperature, in the range of 30-290 K, as well as bias) from light-emitting diodes based on poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene]. The decay kinetics of this DEF are always found to be biexponential in nature. The fast decaying component with a lifetime of ˜40ns is attributed to the back transfer of nonemissive (or very weakly emissive) interchain excited singlets (partially charge-transfer states) to emissive intrachain excited singlets (this component is called DEFCT). The relatively slower decaying component with a lifetime of ˜0.2-6.2μs (depending on temperature as well as bias) is attributed to the recombination of detrapped space-charge carriers at the polymer-electrode interfaces (this component is called DEFSC). The intensity of DEFSC increases as the temperature is increased from 30 to 290 K, although it is weak at low temperature (<100K). The temperature dependence of the recombination rate of the detrapped space-charge carriers yields two activation energies of 2.2 and 40 meV below and above ˜130K, respectively. The existence of these two activation energies is explained on the assumption of electrons being in shallow traps and holes in deep traps. Also, our data indicate that the space-charge carriers generally act as major quenching sites (especially at 290 K) for triplet excitons in polymer light-emitting diodes.

  20. Nonequilibrium thermodynamics of nucleation

    SciTech Connect

    Schweizer, M.; Sagis, L. M. C.

    2014-12-14

    We present a novel approach to nucleation processes based on the GENERIC framework (general equation for the nonequilibrium reversible-irreversible coupling). Solely based on the GENERIC structure of time-evolution equations and thermodynamic consistency arguments of exchange processes between a metastable phase and a nucleating phase, we derive the fundamental dynamics for this phenomenon, based on continuous Fokker-Planck equations. We are readily able to treat non-isothermal nucleation even when the nucleating cores cannot be attributed intensive thermodynamic properties. In addition, we capture the dynamics of the time-dependent metastable phase being continuously expelled from the nucleating phase, and keep rigorous track of the volume corrections to the dynamics. Within our framework the definition of a thermodynamic nuclei temperature is manifest. For the special case of nucleation of a gas phase towards its vapor-liquid coexistence, we illustrate that our approach is capable of reproducing recent literature results obtained by more microscopic considerations for the suppression of the nucleation rate due to nonisothermal effects.

  1. Hall effect measurements on thermoelectric Ca{sub 3}Co{sub 4}O{sub 9}: On how to determine the charge carrier concentration in strongly correlated misfit cobaltites

    SciTech Connect

    Schrade, Matthias; Norby, Truls; Finstad, Terje G.

    2015-05-28

    The Hall coefficient R{sub H} and electrical conductivity of misfit calcium cobalt oxide (Ca{sub 2}CoO{sub 3−δ}){sub q}(CoO{sub 2}) (CCO) were measured at room temperature for different oxygen vacancy concentrations δ. Based on these and numerous previous results, it is shown that the charge carrier concentrations n obtained by the classical formula R{sub H} = 1/ne are between 3 and 6 × 10{sup 20} cm{sup −3} and thereby much lower than those derived by other experimental techniques and fail to explain the observed electric properties of CCO. We show that the experimental results are well described using an earlier proposed t–J-model for strongly correlated electrons on a triangular lattice. The hopping parameter t for CCO was found to be ≈ −20 K and the charge carrier concentration of fully oxidized CCO to be 5.7 × 10{sup 21} cm{sup −3} (0.41 hole type carriers per formula unit), in agreement with other experimental techniques.

  2. Charge carrier effective mass and concentration derived from combination of Seebeck coefficient and 125Te NMR measurements in complex tellurides

    NASA Astrophysics Data System (ADS)

    Levin, E. M.

    2016-06-01

    Thermoelectric materials utilize the Seebeck effect to convert heat to electrical energy. The Seebeck coefficient (thermopower), S , depends on the free (mobile) carrier concentration, n , and effective mass, m*, as S ˜m*/n2 /3 . The carrier concentration in tellurides can be derived from 125Te nuclear magnetic resonance (NMR) spin-lattice relaxation measurements. The NMR spin-lattice relaxation rate, 1 /T1 , depends on both n and m* as 1 /T1˜(m*)3/2n (within classical Maxwell-Boltzmann statistics) or as 1 /T1˜(m*)2n2 /3 (within quantum Fermi-Dirac statistics), which challenges the correct determination of the carrier concentration in some materials by NMR. Here it is shown that the combination of the Seebeck coefficient and 125Te NMR spin-lattice relaxation measurements in complex tellurides provides a unique opportunity to derive the carrier effective mass and then to calculate the carrier concentration. This approach was used to study A gxS bxG e50-2xT e50 , well-known GeTe-based high-efficiency tellurium-antimony-germanium-silver thermoelectric materials, where the replacement of Ge by [Ag+Sb] results in significant enhancement of the Seebeck coefficient. Values of both m* and n derived using this combination show that the enhancement of thermopower can be attributed primarily to an increase of the carrier effective mass and partially to a decrease of the carrier concentration when the [Ag+Sb] content increases.

  3. Effective cytoplasmic release of siRNA from liposomal carriers by controlling the electrostatic interaction of siRNA with a charge-invertible peptide, in response to cytoplasmic pH

    NASA Astrophysics Data System (ADS)

    Itakura, Shoko; Hama, Susumu; Matsui, Ryo; Kogure, Kentaro

    2016-05-01

    Condensing siRNA with cationic polymers is a major strategy used in the development of siRNA carriers that can avoid degradation by nucleases and achieve effective delivery of siRNA into the cytoplasm. However, ineffective release of siRNA from such condensed forms into the cytoplasm is a limiting step for induction of RNAi effects, and can be attributed to tight condensation of siRNA with the cationic polymers, due to potent electrostatic interactions. Here, we report that siRNA condensed with a slightly acidic pH-sensitive peptide (SAPSP), whose total charge is inverted from positive to negative in response to cytoplasmic pH, is effectively released via electrostatic repulsion of siRNA with negatively charged SAPSP at cytoplasmic pH (7.4). The condensed complex of siRNA and positively-charged SAPSP at acidic pH (siRNA/SAPSP) was found to result in almost complete release of siRNA upon charge inversion of SAPSP at pH 7.4, with the resultant negatively-charged SAPSP having no undesirable interactions with endogenous mRNA. Moreover, liposomes encapsulating siRNA/SAPSP demonstrated knockdown efficiencies comparable to those of commercially available siRNA carriers. Taken together, SAPSP may be very useful as a siRNA condenser, as it facilitates effective cytoplasmic release of siRNA, and subsequent induction of specific RNAi effects.Condensing siRNA with cationic polymers is a major strategy used in the development of siRNA carriers that can avoid degradation by nucleases and achieve effective delivery of siRNA into the cytoplasm. However, ineffective release of siRNA from such condensed forms into the cytoplasm is a limiting step for induction of RNAi effects, and can be attributed to tight condensation of siRNA with the cationic polymers, due to potent electrostatic interactions. Here, we report that siRNA condensed with a slightly acidic pH-sensitive peptide (SAPSP), whose total charge is inverted from positive to negative in response to cytoplasmic pH, is

  4. Nonequilibrium fluctuation-dissipation inequality and nonequilibrium uncertainty principle.

    PubMed

    Fleming, C H; Hu, B L; Roura, Albert

    2013-07-01

    The fluctuation-dissipation relation is usually formulated for a system interacting with a heat bath at finite temperature, and often in the context of linear response theory, where only small deviations from the mean are considered. We show that for an open quantum system interacting with a nonequilibrium environment, where temperature is no longer a valid notion, a fluctuation-dissipation inequality exists. Instead of being proportional, quantum fluctuations are bounded below by quantum dissipation, whereas classically the fluctuations vanish at zero temperature. The lower bound of this inequality is exactly satisfied by (zero-temperature) quantum noise and is in accord with the Heisenberg uncertainty principle, in both its microscopic origins and its influence upon systems. Moreover, it is shown that there is a coupling-dependent nonequilibrium fluctuation-dissipation relation that determines the nonequilibrium uncertainty relation of linear systems in the weak-damping limit.

  5. Phonon and free-charge carrier properties in group-III nitride heterostructures investigated by spectroscopic ellipsometry and optical Hall effect

    NASA Astrophysics Data System (ADS)

    Schoeche, Stefan

    The material class of group-III nitrides gained tremendous technological importance for optoelectronic and high-power/high-frequency amplification devices. Tunability of the direct band gap from 0.65 eV (InN) to 6.2 eV (AlN) by alloying, high breakthrough voltages and intrinsic mobilities, as well as the formation of highly mobile 2d electron gases (2DEG) at heterointerfaces make these compounds ideal for many applications. GaN and Ga-rich alloys are well studied and current research is mainly device-oriented. For example, choice and quality of the gate dielectric significantly influence device performance in high-electron mobility transistors (HEMT) which utilize highly mobile 2DEGs at heterointerfaces. Experimental access to the 2DEG channel properties without influence from parasitic currents or contact properties are desirable. In- and Al-rich ternary alloys are less explored than Ga-rich compounds. For InN and In-rich alloys, while many material parameters such as stiffness constants or effective mass values are largely unknown, reliable p-type doping is a major challenge, also because p-type conducting channels are buried within highly conductive n-type material formed at the surface and interfaces preventing electrical characterization. For AlN and high-Al content alloys, doping mechanisms are not understood and reliable fabrication of material with high free-charge carrier (FCC) concentrations was achieved just recently. Difficulties to form ohmic contacts impair electrical measurements and optical characterization is impeded by lack of high-energy excitation sources. In this work, spectroscopic ellipsometry over the wide spectral range from the THz to VUV in combination with optical Hall effect (generalized ellipsometry with applied magnetic field) from THz to MIR are applied in order to investigate the phonon modes and FCC properties in group-III nitride heterostructures. Adequate model descriptions and analysis strategies are introduced which allow

  6. Carrier Transport and Related Effects in Detectors of the Cryogenic Dark Matter Search

    SciTech Connect

    Sundqvist, Kyle Michael

    2012-01-01

    The Cryogenic Dark Matter Search (CDMS) is searching for weakly-interacting massive particles (WIMPS), which could explain the dark matter problem in cosmology and particle physics. By simultaneously measuring signals from deposited charge and the energy in nonequilibrium phonons created by particle interactions in intrinsic germanium crystals at a temperature of 40 mK, a signature response for each event is produced. This response, combined with phonon pulse-shape information, allows CDMS to actively discriminate candidate WIMP interactions with nuclei from electromagnetic radioactive background which interacts with electrons. The challenges associated with these techniques are unique. Carrier scattering is dominated by the spontaneous emission of Luke-Neganov phonons due to zeropoint fluctuations of the lattice ions. Drift fields are maintained at only a few V/cm, else these emitted phonons would dominate the phonons of the original interaction. The dominant systematic issues with CDMS detectors are due to the effects of space charge accumulation. It has been an open question how space charge accrues, and by which of several potential recombination and ionization processes. In this work, we have simulated the transport of electrons and holes in germanium under CDMS conditions. We have implemented both a traditional Monte Carlo technique based on carrier energy, followed later by a novel Monte Carlo algorithm with scattering rates defined and sampled by vector momentum. This vector-based method provides for a full anisotropic simulation of carrier transport including free-fight acceleration with an anisotropic mass, and anisotropic scattering rates. With knowledge of steady state carrier dynamics as a function of applied field, the results of our Monte Carlo simulations allow us to make a wide variety of predictions for energy dependent processes for both electrons and holes. Such processes include carrier capture by charged impurities, neutral impurities, static

  7. Elucidating the band structure and free charge carrier dynamics of pure and impurities doped CH3NH3PbI(3-x)Cl(x) perovskite thin films.

    PubMed

    Zhang, Zhen-Yu; Chen, Xin; Wang, Hai-Yu; Xu, Ming; Gao, Bing-Rong; Chen, Qi-Dai; Sun, Hong-Bo

    2015-11-28

    CH3NH3PbI3-xClx perovskite material has been commonly used as the free charge generator and reservoir in highly efficient perovskite-based solid-state solar photovoltaic devices. However, many of the underlying fundamental photophysical mechanisms in this material such as the perovskite transition band structure as well as the dependent relationship between the carrier properties and lattice properties still lack sufficient understanding. Here, we elucidated the fundamental band structure of the pure CH3NH3PbI3-xClx pervoskite lattice, and then reported about the dependent relationship between the free charge carrier characteristic and the different CH3NH3PbI3-xClx pervoskite lattice thin films utilizing femtosecond time-resolved pump-probe technologies. The data demonstrated that the pure perovskite crystal band structure should only have one conduction and one valence band rather than dual valences, and the pure perovskite lattice could trigger more free charge carriers with a slower recombination rate under an identical pump intensity compared with the impurities doped perovskite crystal. We also investigated the perovskite film performance when exposed to moisture and water, the corresponding results gave us a dip in the optimization of the performance of perovskite based devices, and so as a priority this material should be isolated from moisture (water). This work may propose a deeper perspective on the comprehension for this material and it is useful for future optimization of applications in photovoltaic and light emission devices. PMID:26497219

  8. Nonequilibrium mechanisms of weak electrolyte electrification under the action of constant voltage

    NASA Astrophysics Data System (ADS)

    Stishkov, Yu. K.; Chirkov, V. A.

    2016-07-01

    The formation of space charge in weak electrolytes, specifically in liquid dielectrics, has been considered. An analytical solution is given to a simplified set of Nernst-Planck equations that describe the formation of nonequilibrium recombination layers in weak electrolytes. This approximate analytical solution is compared with computer simulation data for a complete set of Poisson-Nernst-Planck equations. It has been shown that the current passage in weak electrolytes can be described by a single dimensionless parameter that equals the length of a near-electrode recombination layer divided by the width of the interelectrode gap. The formation mechanism and the structure of charged nonequilibrium near-electrode layers in the nonstationary regime have been analyzed for different injection-to-conduction current ratios. It has been found that almost all charge structures encountered in weak dielectrics can be accounted for by the nonequilibrium dissociation-recombination mechanism of space charge formation.

  9. Nonequilibrium Growth Processes

    NASA Astrophysics Data System (ADS)

    Ramanlal, Pradipkumar

    A number of issues in nonequilibrium aggregation and pattern formation are addressed. Using analytical, numerical, and computer simulation methods, an attempt is made to infer or conclude on a number of aspects of compact, fractal and dendritic growth. Using the ballistic aggregation model, we develop a mean-field continuum theory that successfully predicts the morphology of thin films formed by vapor deposition and aggregation on a seed. In addition, by relating the evolution of the surface of ballistic deposits to a problem of spin dynamics, we develop a theory for the roughness of the interface, showing it to be a self-affine fractal, and at the same time having a bounded interface length. We also develop a deterministic continuum model for the fractal growth of diffusion-limited aggregation (DLA), related to the problem of two-dimensional viscous fluid flow in a hele-shaw cell. With the introduction of a real-space renormalization scheme we solve the equations numerically to produce fractal growth and patterns reminiscent of real fluid flow experiments. In addition, we show the fractal patterns to have the same metric properties of DLA, with a prediction for the asymptotic value for the fractal dimension; D = 1.65. An important consequence of these results is that DLA is sufficiently unstable and sensitive to initial conditions to produce fractal growth in the absence of external noise present in computer simulation results. Further, we examine the effect of an underlying lattice on the growth process in both the discrete and continuum deterministic formulations of DLA. In both cases, the lattice anisotropy destroys the fractal characteristics and this is confirmed by studying large on-lattice DLA simulations. And finally, we infer a relationship between the lattice anisotropy and the phenomenological formulations of the interfacial anisotropy, and examine the nature of the transition between fractal and dendritic growth as a function of the interfacial

  10. Nonequilibrium thermodynamics of an interface

    NASA Astrophysics Data System (ADS)

    Schweizer, Marco; Öttinger, Hans Christian; Savin, Thierry

    2016-05-01

    Interfacial thermodynamics has deep ramifications in understanding the boundary conditions of transport theories. We present a formulation of local equilibrium for interfaces that extends the thermodynamics of the "dividing surface," as introduced by Gibbs, to nonequilibrium settings such as evaporation or condensation. By identifying the precise position of the dividing surface in the interfacial region with a gauge degree of freedom, we exploit gauge-invariance requirements to consistently define the intensive variables for the interface. The model is verified under stringent conditions by employing high-precision nonequilibrium molecular-dynamics simulations of a coexisting vapor-liquid Lennard-Jones fluid. We conclude that the interfacial temperature is determined using the surface tension as a "thermometer," and it can be significantly different from the temperatures of the adjacent phases. Our findings lay foundations for nonequilibrium interfacial thermodynamics.

  11. Nonequilibrium thermodynamics of an interface.

    PubMed

    Schweizer, Marco; Öttinger, Hans Christian; Savin, Thierry

    2016-05-01

    Interfacial thermodynamics has deep ramifications in understanding the boundary conditions of transport theories. We present a formulation of local equilibrium for interfaces that extends the thermodynamics of the "dividing surface," as introduced by Gibbs, to nonequilibrium settings such as evaporation or condensation. By identifying the precise position of the dividing surface in the interfacial region with a gauge degree of freedom, we exploit gauge-invariance requirements to consistently define the intensive variables for the interface. The model is verified under stringent conditions by employing high-precision nonequilibrium molecular-dynamics simulations of a coexisting vapor-liquid Lennard-Jones fluid. We conclude that the interfacial temperature is determined using the surface tension as a "thermometer," and it can be significantly different from the temperatures of the adjacent phases. Our findings lay foundations for nonequilibrium interfacial thermodynamics.

  12. Nonequilibrium thermodynamics of an interface.

    PubMed

    Schweizer, Marco; Öttinger, Hans Christian; Savin, Thierry

    2016-05-01

    Interfacial thermodynamics has deep ramifications in understanding the boundary conditions of transport theories. We present a formulation of local equilibrium for interfaces that extends the thermodynamics of the "dividing surface," as introduced by Gibbs, to nonequilibrium settings such as evaporation or condensation. By identifying the precise position of the dividing surface in the interfacial region with a gauge degree of freedom, we exploit gauge-invariance requirements to consistently define the intensive variables for the interface. The model is verified under stringent conditions by employing high-precision nonequilibrium molecular-dynamics simulations of a coexisting vapor-liquid Lennard-Jones fluid. We conclude that the interfacial temperature is determined using the surface tension as a "thermometer," and it can be significantly different from the temperatures of the adjacent phases. Our findings lay foundations for nonequilibrium interfacial thermodynamics. PMID:27300960

  13. Nonequilibrium spin crossover in copper phthalocyanine

    NASA Astrophysics Data System (ADS)

    Siegert, Benjamin; Donarini, Andrea; Grifoni, Milena

    2016-03-01

    We demonstrate the nonequilibrium tip induced control of the spin state of copper phthalocyanine on an insulator coated substrate. We find that, under the condition of energetic proximity of many-body neutral excited states to the anionic ground state, the system can undergo a population inversion towards these excited states. The resulting state of the system is accompanied by a change in the total spin quantum number. Experimental signatures of the crossover are the appearance of additional nodal planes in the topographical scanning tunneling microscopy images as well as a strong suppression of the current near the center of the molecule. The robustness of the effect against moderate charge conserving relaxation processes has also been tested.

  14. Nonequilibrium phase transitions in cuprates observed by ultrafast electron crystallography.

    PubMed

    Gedik, Nuh; Yang, Ding-Shyue; Logvenov, Gennady; Bozovic, Ivan; Zewail, Ahmed H

    2007-04-20

    Nonequilibrium phase transitions, which are defined by the formation of macroscopic transient domains, are optically dark and cannot be observed through conventional temperature- or pressure-change studies. We have directly determined the structural dynamics of such a nonequilibrium phase transition in a cuprate superconductor. Ultrafast electron crystallography with the use of a tilted optical geometry technique afforded the necessary atomic-scale spatial and temporal resolutions. The observed transient behavior displays a notable "structural isosbestic" point and a threshold effect for the dependence of c-axis expansion (Deltac) on fluence (F), with Deltac/F = 0.02 angstrom/(millijoule per square centimeter). This threshold for photon doping occurs at approximately 0.12 photons per copper site, which is unexpectedly close to the density (per site) of chemically doped carriers needed to induce superconductivity. PMID:17446397

  15. Nonequilibrium drift-diffusion model for organic semiconductor devices

    NASA Astrophysics Data System (ADS)

    Felekidis, Nikolaos; Melianas, Armantas; Kemerink, Martijn

    2016-07-01

    Two prevailing formalisms are currently used to model charge transport in organic semiconductor devices. Drift-diffusion calculations, on the one hand, are time effective but assume local thermodynamic equilibrium, which is not always realistic. Kinetic Monte Carlo models, on the other hand, do not require this assumption but are computationally expensive. Here, we present a nonequilibrium drift-diffusion model that bridges this gap by fusing the established multiple trap and release formalism with the drift-diffusion transport equation. For a prototypical photovoltaic system the model is shown to quantitatively describe, with a single set of parameters, experiments probing (1) temperature-dependent steady-state charge transport—space-charge limited currents, and (2) time-resolved charge transport and relaxation of nonequilibrated photocreated charges. Moreover, the outputs of the developed kinetic drift-diffusion model are an order of magnitude, or more, faster to compute and in good agreement with kinetic Monte Carlo calculations.

  16. a Nonequilibrium Plasmadynamics Model for Nitrogen/hydrogen Arcjets

    NASA Astrophysics Data System (ADS)

    Megli, Thomas W.

    Electrothermal arcjets offer significant cost advantage over conventional satellite propulsion systems. In these devices, the propellant is electrically heated, allowing for higher temperatures and specific impulse than chemical rockets. Despite the relative simplicity of the basic design, many complex physical processes are poorly understood. Less than 50% of the electrical power is converted to thrust kinetic power. A numerical model is developed to study arcjet plasma flowfields. The model employs a modified set of Navier-Stokes equations, which includes separate energy equations for the electrons and heavy species. A thermal nonequilibrium, chemical equilibrium model is first developed, and then generalized to chemical nonequilibrium. A seven -species plasma of molecules, atoms, and ions is assumed for a variable mixture ratio of nitrogen and hydrogen. This permits simulation of various propellants, including hydrogen, ammonia, and hydrazine. Equations for charge continuity and Ohm's Law are employed to predict the arc current distribution. A thermal model for the nozzle is also included. The combined features of thermal nonequilibrium, chemical nonequilibrium, and propellant flexibility distinguish this model from previous research efforts. Model calculations are presented for 1-2 kW-class arcjets operating with hydrogen and hydrazine propellants. Thermal equilibrium is predicted in the highly ionized arc core, while electron temperatures near the electrodes are an order of magnitude greater than heavy species temperatures. The thermal nonequilibrium enhances ionization and electrical conductivity, and thus governs the current attachment to the nozzle. A comparison of chemical equilibrium and nonequilibrium simulations indicates that ambipolar diffusion of electrons and ions also controls the current conduction. The model is compared with experimental measurements. Respective calculations for specific impulse and exhaust velocities are within approximately 5

  17. Open problems in non-equilibrium physics

    SciTech Connect

    Kusnezov, D.

    1997-09-22

    The report contains viewgraphs on the following: approaches to non-equilibrium statistical mechanics; classical and quantum processes in chaotic environments; classical fields in non-equilibrium situations: real time dynamics at finite temperature; and phase transitions in non-equilibrium conditions.

  18. Nonequilibrium diagnostics of plasma thrusters

    SciTech Connect

    Eddy, T.L.; Grandy, J.D.

    1990-01-01

    This paper describes possible techniques by which the state of plasma thruster operation for space propulsion can be determined from a minimum set of experimental data in the laboratory. The kinetic properties of the nonequilibrium plasma plume usually can not be directly related to the observed radiation; hence, appropriate nonequilibrium diagnostic techniques must be employed. A newly developed multithermal, multichemical equilibrium method is discussed that uses measured line emission intensities and N equations to solve for N unknowns. The effect of arbitrarily changing the number of selected N unknowns and how one determines the optimum (minimum) number to be used for a given composition is also presented. The chemical nonequilibrium aspects and the application to molecular species have not yet been published. The important conclusions are that (1) complete thermodynamic systems in nonequilibrium can be described by relatively few variables if appropriate choices and filtering methods are used, (2) a few radiation measurements can yield valid kinetic properties, and (3) the major question in the relations to be used is in the form of the law of mass action. The results are substantiated in the laboratory by additional alternative methods of measurement of some of the kinetic properties. 13 refs., 1 fig.

  19. Computer simulation of nonequilibrium processes

    SciTech Connect

    Hoover, W.G.; Moran, B.; Holian, B.L.; Posch, H.A.; Bestiale, S.

    1987-01-01

    Recent atomistic simulations of irreversible macroscopic hydrodynamic flows are illustrated. An extension of Nose's reversible atomistic mechanics makes it possible to simulate such non-equilibrium systems with completely reversible equations of motion. The new techniques show that macroscopic irreversibility is a natural inevitable consequence of time-reversible Lyapunov-unstable microscopic equations of motion.

  20. 49 CFR 1139.21 - Study carriers.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 8 2013-10-01 2013-10-01 false Study carriers. 1139.21 Section 1139.21... Industry § 1139.21 Study carriers. (a) For the purposes of this proceeding the “study carriers” shall... and/or charges. (b) To corroborate the selection of the above study carriers, and to provide a...

  1. 49 CFR 1139.21 - Study carriers.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 8 2012-10-01 2012-10-01 false Study carriers. 1139.21 Section 1139.21... Industry § 1139.21 Study carriers. (a) For the purposes of this proceeding the “study carriers” shall... and/or charges. (b) To corroborate the selection of the above study carriers, and to provide a...

  2. Carrier transport and collection in fully depleted semiconductors by a combined action of the space charge field and the field due to electrode voltages

    DOEpatents

    Rehak, P.; Gatti, E.

    1987-08-18

    A semiconductor charge transport device and method for making same are disclosed, characterized by providing a thin semiconductor wafer having rectifying junctions on its opposing major surfaces and including a small capacitance ohmic contact, in combination with bias voltage means and associated circuit means for applying a predetermined voltage to effectively deplete the wafer in regions thereof between the rectifying junctions and the ohmic contact. A charge transport device of the invention is usable as a drift chamber, a low capacitance detector, or a charge coupled device each constructed according to the methods of the invention for making such devices. Detectors constructed according to the principles of the invention are characterized by having significantly higher particle position indicating resolution than is attainable with prior art detectors, while at the same time requiring substantially fewer readout channels to realize such high resolution. 16 figs.

  3. Carrier transport and collection in fully depleted semiconductors by a combined action of the space charge field and the field due to electrode voltages

    DOEpatents

    Rehak, P.; Gatti, E.

    1984-02-24

    A semiconductor charge transport device and method for making same, characterized by providing a thin semiconductor wafer having rectifying functions on its opposing major surfaces and including a small capacitance ohmic contact, in combination with bias voltage means and associated circuit means for applying a predetermined voltage to effectively deplete the wafer in regions thereof between the rectifying junctions and the ohmic contact. A charge transport device of the invention is usable as a drift chamber, a low capacitance detector, or a charge coupled device each constructed according to the methods of the invention for making such devices. Detectors constructed according to the principles of the invention are characterized by having significantly higher particle position indicating resolution than is attainable with prior art detectors, while at the same time requiring substantially fewer readout channels to realize such high resolution.

  4. Carrier transport and collection in fully depleted semiconductors by a combined action of the space charge field and the field due to electrode voltages

    DOEpatents

    Rehak, Pavel; Gatti, Emilio

    1987-01-01

    A semiconductor charge transport device and method for making same, characterized by providing a thin semiconductor wafer having rectifying junctions on its opposing major surfaces and including a small capacitance ohmic contact, in combination with bias voltage means and associated circuit means for applying a predetermined voltage to effectively deplete the wafer in regions thereof between the rectifying junctions and the ohmic contact. A charge transport device of the invention is usable as a drift chamber, a low capacitance detector, or a charge coupled device each constructed according to the methods of the invention for making such devices. Detectors constructed according to the principles of the invention are characterized by having significantly higher particle position indicating resolution than is attainable with prior art detectors, while at the same time requiring substantially fewer readout channels to realize such high resolution.

  5. A comparative study on charge carrier recombination across the junction region of Cu2ZnSn(S,Se)4 and Cu(In,Ga)Se2 thin film solar cells

    NASA Astrophysics Data System (ADS)

    Halim, Mohammad Abdul; Islam, Muhammad Monirul; Luo, Xianjia; Sakurai, Takeaki; Sakai, Noriyuki; Kato, Takuya; Sugimoto, Hiroki; Tampo, Hitoshi; Shibata, Hajime; Niki, Shigeru; Akimoto, Katsuhiro

    2016-03-01

    A comparative study with focusing on carrier recombination properties in Cu2ZnSn(S,Se)4 (CZTSSe) and the CuInGaSe2 (CIGS) solar cells has been carried out. For this purpose, electroluminescence (EL) and also bias-dependent time resolved photoluminescence (TRPL) using femtosecond (fs) laser source were performed. For the similar forward current density, the EL-intensity of the CZTSSe sample was obtained significantly lower than that of the CIGS sample. Primarily, it can be attributed to the existence of excess amount of non-radiative recombination center in the CZTSSe, and/or CZTSSe/CdS interface comparing to that of CIGS sample. In case of CIGS sample, TRPL decay time was found to increase with the application of forward-bias. This can be attributed to the reduced charge separation rate resulting from the reduced electric-field at the junction. However, in CZTSSe sample, TRPL decay time has been found almost independent under the forward and reverse-bias conditions. This phenomenon indicates that the charge recombination rate strongly dominates over the charge separation rate across the junction of the CZTSSe sample. Finally, temperature dependent VOC suggests that interface related recombination in the CZTSSe solar cell structure might be one of the major factors that affect EL-intensity and also, TRPL decay curves.

  6. Ti-Doped Indium Tin Oxide Thin Films for Transparent Field-Effect Transistors: Control of Charge-Carrier Density and Crystalline Structure

    SciTech Connect

    J Kim; K Ji; M Jang; H Yang; R Choi; J Jeong

    2011-12-31

    Indium tin oxide (ITO) films are representative transparent conducting oxide media for organic light-emitting diodes, liquid crystal displays, and solar cell applications. Extending the utility of ITO films from passive electrodes to active channel layers in transparent field-effect transistors (FETs), however, has been largely limited because of the materials' high carrier density (>1 x 10{sup 20} cm{sup 03}), wide band gap, and polycrystalline structure. Here, we demonstrate that control over the cation composition in ITO-based oxide films via solid doping of titanium (Ti) can optimize the carrier concentration and suppress film crystallization. On 120 nm thick SiO{sub 2}/Mo (200 nm)/glass substrates, transparent n-type FETs prepared with 4 at % Ti-doped ITO films and fabricated via the cosputtering of ITO and TiO{sub 2} exhibited high electron mobilities of 13.4 cm{sup 2} V{sup -1} s{sup -1}, a low subthreshold gate swing of 0.25 V decade{sup -1}, and a high I{sub on}/I{sub off} ratio of >1 x 10{sup 8}.

  7. Nonequilibrium mesoscopic transport: a genealogy

    NASA Astrophysics Data System (ADS)

    Das, Mukunda P.; Green, Frederick

    2012-05-01

    Models of nonequilibrium quantum transport underpin all modern electronic devices, from the largest scales to the smallest. Past simplifications such as coarse graining and bulk self-averaging served well to understand electronic materials. Such particular notions become inapplicable at mesoscopic dimensions, edging towards the truly quantum regime. Nevertheless a unifying thread continues to run through transport physics, animating the design of small-scale electronic technology: microscopic conservation and nonequilibrium dissipation. These fundamentals are inherent in quantum transport and gain even greater and more explicit experimental meaning in the passage to atomic-sized devices. We review their genesis, their theoretical context, and their governing role in the electronic response of meso- and nanoscopic systems.

  8. Computer simulation of nonequilibrium processes

    SciTech Connect

    Wallace, D.C.

    1985-07-01

    The underlying concepts of nonequilibrium statistical mechanics, and of irreversible thermodynamics, will be described. The question at hand is then, how are these concepts to be realize in computer simulations of many-particle systems. The answer will be given for dissipative deformation processes in solids, on three hierarchical levels: heterogeneous plastic flow, dislocation dynamics, an molecular dynamics. Aplication to the shock process will be discussed.

  9. Charge-collection efficiency and long-term stability of single-crystal CVD diamond detector under different carrier-drift conditions

    NASA Astrophysics Data System (ADS)

    Sato, Yuki; Murakami, Hiroyuki; Shimaoka, Takehiro; Tsubota, Masakatsu; Kaneko, Junichi H.

    2016-04-01

    We investigate the performance of a charged-particle detector fabricated using single-crystal diamond grown by chemical vapor deposition. The detector identified four different 241Am α-particle energies (5.389, 5.443, 5.486, and 5.545 MeV) thanks to its superior energy resolution of 0.407 ± 0.004% for electron drift and 0.418 ± 0.004% for hole drift (full width at half maximum). The charge-collection efficiency inside the diamond crystal was above 97.0% for both electrons and holes. The diamond detector also exhibited no significant degradation in terms of pulse-height spectra and energy resolution during operation for more than 100 h under electron-drift conditions. In contrast, the pulse-height spectra obtained under hole-drift conditions deteriorated because of the polarization phenomenon.

  10. Plasma instabilities in a steady-state nonequilibrium one-dimensional solid-state plasma of finite length

    SciTech Connect

    Kempa, K.; Bakshi, P.; Gornik, E.

    1996-09-01

    We show theoretically that strong plasma mode generation is possible in a nonequilibrium steady-state quasi-one-dimensional bounded solid-state plasma, in which a nonequilibrium distribution is maintained by appropriate injection/extraction of carriers. We calculate the density response of realistic model systems using the random-phase approximation, determine the normal modes of the bounded carrier plasma, and show that strong plasma instabilities can be generated under suitable conditions. Such stimulated plasma oscillations could lead to sources of terahertz electromagnetic radiation. {copyright} {ital 1996 The American Physical Society.}

  11. Charge carrier transport and lifetimes in n-type and p-type phosphorene as 2D device active materials: an ab initio study

    NASA Astrophysics Data System (ADS)

    Tea, E.; Hin, C.

    In this work, we provide a detailed analysis of phosphorene performance as n-type and p-type active materials. The study is based on first principles calculation of phosphorene electronic structure, and resulting electron and hole scattering rates and lifetimes. Emphasis is put on extreme regimes commonly found in semiconductor devices, i.e. high electric fields and heavy doping, where impact ionization and Auger recombination can occur. We found that electron-initiated impact ionization is weaker than the hole-initiated process, when compared to carrier-phonon interaction rates, suggesting resilience to impact ionization initiated breakdown. Moreover, calculated minority electron lifetimes are limited by radiative recombination only, not by Auger processes, suggesting that phosphorene could achieve good quantum efficiencies in optoelectronic devices. The provided scattering rates and lifetimes are critical input data for the modeling and understanding of phosphorene-based device physics.

  12. Charge carrier transport and lifetimes in n-type and p-type phosphorene as 2D device active materials: an ab initio study.

    PubMed

    Tea, E; Hin, C

    2016-08-10

    In this work, we provide a detailed analysis of phosphorene's performance as an n-type and p-type active material. This study is based on first principles calculations of the phosphorene electronic structure, and the resulting electron and hole scattering rates and lifetimes. Emphasis is put on extreme regimes commonly found in semiconductor devices, i.e. high electric fields and heavy doping, where impact ionization and Auger recombination can occur. We found that electron-initiated impact ionization is weaker than the hole-initiated process, when compared to carrier-phonon interaction rates, suggesting resilience to impact ionization initiated breakdown. Moreover, calculated minority electron lifetimes are limited by radiative recombination only, not by Auger processes, suggesting that phosphorene could achieve good quantum efficiencies in optoelectronic devices. The provided scattering rates and lifetimes are critical input data for the modeling and understanding of phosphorene-based device physics.

  13. Charge carrier transport and lifetimes in n-type and p-type phosphorene as 2D device active materials: an ab initio study.

    PubMed

    Tea, E; Hin, C

    2016-08-10

    In this work, we provide a detailed analysis of phosphorene's performance as an n-type and p-type active material. This study is based on first principles calculations of the phosphorene electronic structure, and the resulting electron and hole scattering rates and lifetimes. Emphasis is put on extreme regimes commonly found in semiconductor devices, i.e. high electric fields and heavy doping, where impact ionization and Auger recombination can occur. We found that electron-initiated impact ionization is weaker than the hole-initiated process, when compared to carrier-phonon interaction rates, suggesting resilience to impact ionization initiated breakdown. Moreover, calculated minority electron lifetimes are limited by radiative recombination only, not by Auger processes, suggesting that phosphorene could achieve good quantum efficiencies in optoelectronic devices. The provided scattering rates and lifetimes are critical input data for the modeling and understanding of phosphorene-based device physics. PMID:27479904

  14. Nonequilibrium chemistry boundary layer integral matrix procedure

    NASA Technical Reports Server (NTRS)

    Tong, H.; Buckingham, A. C.; Morse, H. L.

    1973-01-01

    The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general boundary condition features built into the original code. For particular application to the pitch-plane of shuttle type vehicles, an approximate procedure was developed to estimate the nonequilibrium and nonisentropic state at the edge of the boundary layer.

  15. Nonequilibrium volumetric response of shocked polymers

    SciTech Connect

    Clements, B E

    2009-01-01

    Polymers are well known for their non-equilibrium deviatoric behavior. However, investigations involving both high rate shock experiments and equilibrium measured thermodynamic quantities remind us that the volumetric behavior also exhibits a non-equilibrium response. Experiments supporting the notion of a non-equilibrium volumetric behavior will be summarized. Following that discussion, a continuum-level theory is proposed that will account for both the equilibrium and non-equilibrium response. Upon finding agreement with experiment, the theory is used to study the relaxation of a shocked polymer back towards its shocked equilibrium state.

  16. 14 CFR 389.24 - Foreign air carriers.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 4 2011-01-01 2011-01-01 false Foreign air carriers. 389.24 Section 389.24...) ORGANIZATION FEES AND CHARGES FOR SPECIAL SERVICES Filing and Processing License Fees § 389.24 Foreign air carriers. A foreign air carrier, or such carriers, if from the same country, acting jointly, may apply...

  17. 14 CFR 389.24 - Foreign air carriers.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 4 2014-01-01 2014-01-01 false Foreign air carriers. 389.24 Section 389.24...) ORGANIZATION FEES AND CHARGES FOR SPECIAL SERVICES Filing and Processing License Fees § 389.24 Foreign air carriers. A foreign air carrier, or such carriers, if from the same country, acting jointly, may apply...

  18. 14 CFR 389.24 - Foreign air carriers.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 4 2010-01-01 2010-01-01 false Foreign air carriers. 389.24 Section 389.24...) ORGANIZATION FEES AND CHARGES FOR SPECIAL SERVICES Filing and Processing License Fees § 389.24 Foreign air carriers. A foreign air carrier, or such carriers, if from the same country, acting jointly, may apply...

  19. 47 CFR 64.1140 - Carrier liability for slamming.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 3 2010-10-01 2010-10-01 false Carrier liability for slamming. 64.1140 Section 64.1140 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES... Providers § 64.1140 Carrier liability for slamming. (a) Carrier Liability for Charges. Any...

  20. First-principles hybrid functional study of the electronic structure and charge carrier mobility in perovskite CH3NH3SnI3

    NASA Astrophysics Data System (ADS)

    Wu, Li-Juan; Zhao, Yu-Qing; Chen, Chang-Wen; Wang, Lin-Zhi; Liu, Biao; Cai, Meng-Qiu

    2016-10-01

    We calculate the electronic properties and carrier mobility of perovskite CH3NH3SnI3 as a solar cell absorber by using the hybrid functional method. The calculated result shows that the electron and hole mobilities have anisotropies with a large magnitude of 1.4 × 104 cm2·V-1·s-1 along the y direction. In view of the huge difference between hole and electron mobilities, the perovskite CH3NH3SnI3 can be considered as a p-type semiconductor. We also discover a relationship between the effective mass anisotropy and electronic occupation anisotropy. The above results can provide reliable guidance for its experimental applications in electronics and optoelectronics. Project supported by the National Natural Science Foundation of China (Grant No. 51172067), the Hunan Provincial Natural Science Fund for Distinguished Young Scholars, China (Grant No. 13JJ1013), the Specialized Research Fund for the Doctoral Program of Higher Education, China (Grant No. 20130161110036), and the New Century Excellent Talents in University, China (Grant No. NCET-12-0171.D).

  1. Enhanced spin-orbit coupling and charge carrier density suppression in LaAl1-xCrxO3/SrTiO3 hetero-interfaces

    NASA Astrophysics Data System (ADS)

    Kumar, Pramod; Dogra, Anjana; Bhadauria, P. P. S.; Gupta, Anurag; Maurya, K. K.; Budhani, R. C.

    2015-04-01

    We report a gradual suppression of the two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface on substitution of chromium at the Al sites. The sheet carrier density at the interface (n□) drops monotonically from ˜2.2 × 1014 cm-2 to ˜2.5 × 1013 cm-2 on replacing ≈60% of the Al sites by Cr and the sheet resistance (R□) exceeds the quantum limit for localization (h/2e2) in the concentrating range 40-60% of Cr. The samples with Cr ⩽40% show a distinct minimum (Tm) in metallic R□(T) whose position shifts to higher temperatures on increasing the substitution. Distinct signatures of Rashba spin-orbit interaction (SOI) induced magnetoresistance (MR) are seen in R□ measured in out of plane field (H⊥) geometry at T ⩽ 8 K. Analysis of these data in the framework of Maekawa-Fukuyama theory allows extraction of the SOI critical field (HSO) and time scale (τSO) whose evolution with Cr concentration is similar as with the increasing negative gate voltage in LAO/STO interface. The MR in the temperature range 8 K ⩽ T ⩽ Tm is quadratic in the field with a +ve sign for H⊥ and -ve sign for H∥. The behaviour of H∥ MR is consistent with Kondo theory which in the present case is renormalized by the strong Rashba SOI at T < 8 K.

  2. Sudden slowing down of charge carrier dynamics at the Mott metal-insulator transition in kappa-(D{sub 8}-BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br.

    SciTech Connect

    Brandenburg, J.; Muller, J.; Schlueter, J. A.

    2012-02-01

    We investigate the dynamics of correlated charge carriers in the vicinity of the Mott metal-insulator (MI) transition in the quasi-two-dimensional organic charge-transfer salt {kappa}-(D{sub 8}-BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br by means of fluctuation (noise) spectroscopy. The observed 1/f-type fluctuations are quantitatively very well described by a phenomenological model based on the concept of non-exponential kinetics. The main result is a correlation-induced enhancement of the fluctuations accompanied by a substantial shift of spectral weight to low frequencies in the vicinity of the Mott critical endpoint. This sudden slowing down of the electron dynamics, observed here in a pure Mott system, may be a universal feature of MI transitions. Our findings are compatible with an electronic phase separation in the critical region of the phase diagram and offer an explanation for the not yet understood absence of effective mass enhancement when crossing the Mott transition.

  3. Dopant selection for control of charge carrier density and mobility in amorphous indium oxide thin-film transistors: Comparison between Si- and W-dopants

    SciTech Connect

    Mitoma, Nobuhiko E-mail: TSUKAGOSHI.Kazuhito@nims.go.jp; Kizu, Takio; Lin, Meng-Fang; Tsukagoshi, Kazuhito E-mail: TSUKAGOSHI.Kazuhito@nims.go.jp; Aikawa, Shinya; Ou-Yang, Wei; Gao, Xu; Fujiwara, Akihiko

    2015-01-26

    The dependence of oxygen vacancy suppression on dopant species in amorphous indium oxide (a-InO{sub x}) thin film transistors (TFTs) is reported. In a-InO{sub x} TFTs incorporating equivalent atom densities of Si- and W-dopants, absorption of oxygen in the host a-InO{sub x} matrix was found to depend on difference of Gibbs free energy of the dopants for oxidation. For fully oxidized films, the extracted channel conductivity was higher in the a-InO{sub x} TFTs containing dopants of small ionic radius. This can be explained by a reduction in the ionic scattering cross sectional area caused by charge screening effects.

  4. Nonequilibrium transport in superconducting filaments

    NASA Technical Reports Server (NTRS)

    Arutyunov, K. YU.; Danilova, N. P.; Nikolaeva, A. A.

    1995-01-01

    The step-like current-voltage characteristics of highly homogeneous single-crystalline tin and indium thin filaments has been measured. The length of the samples L approximately 1 cm was much greater than the nonequilibrium quasiparticle relaxation length Lambda. It was found that the activation of a successive i-th voltage step occurs at current significantly greater than the one derived with the assumption that the phase slip centers are weakly interacting on a scale L much greater than Lambda. The observation of 'subharmonic' fine structure on the voltage-current characteristics of tin filaments confirms the hypothesis of the long-range phase slip centers interaction.

  5. Electron beam induced and microemulsion templated synthesis of CdSe quantum dots: tunable broadband emission and charge carrier recombination dynamics

    NASA Astrophysics Data System (ADS)

    Guleria, Apurav; Singh, Ajay K.; Rath, Madhab C.; Adhikari, Soumyakanti

    2015-04-01

    CdSe quantum dots (QDs) were synthesized by a rapid and one step templated approach inside the water pool of AOT (sodium bis(2-ethylhexyl) sulfosuccinate) based water-in-oil microemulsions (MEs) via electron beam (EB) irradiation technique with high dose rate, which favours high nucleation rate. The interplay of different experimental parameters such as precursor concentration, absorbed dose and {{W}0} values (aqueous phase to surfactant molar ratio) of MEs were found to have interesting consequences on the morphology, photoluminescence (PL), surface composition and carrier recombination dynamics of as-grown QDs. For instance, highly stable ultrasmall (∼1.7 nm) bluish-white light emitting QDs were obtained with quantum efficiency (η) of ∼9%. Furthermore, QDs were found to exhibit tunable broadband light emission extending from 450 to 750 nm (maximum FWHM ∼180 nm). This could be realized from the CIE (Commission Internationale d’Eclairage) chromaticity co-ordinates, which varied across the blue region to the orange region thereby, conferring their potential application in white light emitting diodes. Additionally, the average PL lifetime ≤ft( ≤ft< τ \\right> \\right) values could be varied from 18 ns to as high as 74 ns, which reflect the role of surface states in terms of their density and distribution. Another interesting revelation was the self-assembling of the initially formed QDs into nanorods with high aspect ratios ranging from 7 to 20, in correspondence with the {{W}0} values. Besides, the fundamental roles of the chemical nature of water pool and the interfacial fluidity of AOT MEs in influencing the photophysical properties of QDs were investigated by carrying out a similar study in CTAB (cetyltrimethylammonium bromide; cationic surfactant) based MEs. Surprisingly, very profound and contrasting results were observed wherein ≤ft< τ \\right> and η of the QDs in case of CTAB MEs were found to be at least three times lower as compared to

  6. Scientific Affairs Division of NATO Advanced Study Institute: abstracts for nonequilibrium superconductivity, phonons and Kapitza boundaries

    SciTech Connect

    1980-05-01

    Abstracts of papers presented at the meeting are given. Topics covered include: Kapitza resistance; superconducting tunneling; energy gap enhancement in superconductors; instabilities in nonequilibrium superconducting states; exchange of charge between superconducting pairs and quasiparticles; motion of magnetic flux (flux flow); and other new phenomena. (GHT)

  7. Full counting statistics for a single-electron transistor: nonequilibrium effects at intermediate conductance.

    PubMed

    Utsumi, Yasuhiro; Golubev, Dmitri S; Schön, Gerd

    2006-03-01

    We evaluate the current distribution for a single-electron transistor with intermediate strength tunnel conductance. Using the Schwinger-Keldysh approach and the drone (Majorana) fermion representation, we account for the renormalization of system parameters. Nonequilibrium effects induce a lifetime broadening of the charge-state levels, which suppress large current fluctuations.

  8. INTRODUCTION: Nonequilibrium Processes in Plasmas

    NASA Astrophysics Data System (ADS)

    Petrović, Zoran; Marić, Dragana; Malović, Gordana

    2009-07-01

    This book aims to give a cross section from a wide range of phenomena that, to different degrees, fall under the heading of non-equilibrium phenomenology. The selection is, of course, biased by the interests of the members of the scientific committee and of the FP6 Project 026328 IPB-CNP Reinforcing Experimental Centre for Non-equilibrium Studies with Application in Nano-technologies, Etching of Integrated Circuits and Environmental Research. Some of the papers included here are texts based on selected lectures presented at the Second International Workshop on Non-equilibrium Processes in Plasmas and Environmental Science. However, this volume is not just the proceedings of that conference as it contains a number of papers from authors that did not attend the conference. The goal was to put together a volume that would cover the interests of the project and support further work. It is published in the Institute of Physics journal Journal of Physics: Conference Series to ensure a wide accessibility of the articles. The texts presented here range from in-depth reviews of the current status and past achievements to progress reports of currently developed experimental devices and recently obtained still unpublished results. All papers have been refereed twice, first when speakers were selected based on their reputation and recently published results, and second after the paper was submitted both by the editorial board and individual assigned referees according to the standards of the conference and of the journal. Nevertheless, we still leave the responsibility (and honours) for the contents of the papers to the authors. The papers in this book are review articles that give a summary of the already published work or present the work in progress that will be published in full at a later date (or both). In the introduction to the first volume, in order to show how far reaching, ubiquitous and important non-equilibrium phenomena are, we claimed that ever since the early

  9. Non-equilibrium phase transitions

    SciTech Connect

    Mottola, E.; Cooper, F.M.; Bishop, A.R.; Habib, S.; Kluger, Y.; Jensen, N.G.

    1998-12-31

    This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Non-equilibrium phase transitions play a central role in a very broad range of scientific areas, ranging from nuclear, particle, and astrophysics to condensed matter physics and the material and biological sciences. The aim of this project was to explore the path to a deeper and more fundamental understanding of the common physical principles underlying the complex real time dynamics of phase transitions. The main emphasis was on the development of general theoretical tools to deal with non-equilibrium processes, and of numerical methods robust enough to capture the time-evolving structures that occur in actual experimental situations. Specific applications to Laboratory multidivisional efforts in relativistic heavy-ion physics (transition to a new phase of nuclear matter consisting of a quark-gluon plasma) and layered high-temperature superconductors (critical currents and flux flow at the National High Magnetic Field Laboratory) were undertaken.

  10. Disparities in voltage-sensor charge and electromotility imply slow chloride-driven state transitions in the solute carrier SLC26a5.

    PubMed

    Song, Lei; Santos-Sacchi, Joseph

    2013-03-01

    Outer hair cells (OHCs) drive cochlear amplification that enhances our ability to detect and discriminate sounds. The motor protein, prestin, which evolved from the SLC26 anion transporter family, underlies the OHC's voltage-dependent mechanical activity (eM). Here we report on simultaneous measures of prestin's voltage-sensor charge movement (nonlinear capacitance, NLC) and eM that evidence disparities in their voltage dependence and magnitude as a function of intracellular chloride, challenging decades' old dogma that NLC reports on eM steady-state behavior. A very simple kinetic model, possessing fast anion-binding transitions and fast voltage-dependent transitions, coupled together by a much slower transition recapitulates these disparities and other biophysical observations on the OHC. The intermediary slow transition probably relates to the transporter legacy of prestin, and this intermediary gateway, which shuttles anion-bound molecules into the voltage-enabled pool of motors, provides molecular delays that present as phase lags between membrane voltage and eM. Such phase lags may help to effectively inject energy at the appropriate moment to enhance basilar membrane motion. PMID:23431177

  11. Thermodynamics of Stability of Nonequilibrium Steady States.

    ERIC Educational Resources Information Center

    Rastogi, R. P.; Shabd, Ram

    1983-01-01

    Presented is a concise and critical account of developments in nonequilibrium thermodynamics. The criterion for stability of nonequilibrium steady states is critically examined for consecutive and monomolecular triangular reactions, autocatalytic reactions, auto-inhibited reactions, and the Lotka-Volterra model. (JN)

  12. Carrier rockets

    NASA Astrophysics Data System (ADS)

    Aleksandrov, V. A.; Vladimirov, V. V.; Dmitriev, R. D.; Osipov, S. O.

    This book takes into consideration domestic and foreign developments related to launch vehicles. General information concerning launch vehicle systems is presented, taking into account details of rocket structure, basic design considerations, and a number of specific Soviet and American launch vehicles. The basic theory of reaction propulsion is discussed, giving attention to physical foundations, the various types of forces acting on a rocket in flight, basic parameters characterizing rocket motion, the effectiveness of various approaches to obtain the desired velocity, and rocket propellants. Basic questions concerning the classification of launch vehicles are considered along with construction and design considerations, aspects of vehicle control, reliability, construction technology, and details of structural design. Attention is also given to details of rocket motor design, the basic systems of the carrier rocket, and questions of carrier rocket development.

  13. INTRODUCTION: Nonequilibrium Processes in Plasmas

    NASA Astrophysics Data System (ADS)

    Petrović, Zoran; Marić, Dragana; Malović, Gordana

    2009-07-01

    This book aims to give a cross section from a wide range of phenomena that, to different degrees, fall under the heading of non-equilibrium phenomenology. The selection is, of course, biased by the interests of the members of the scientific committee and of the FP6 Project 026328 IPB-CNP Reinforcing Experimental Centre for Non-equilibrium Studies with Application in Nano-technologies, Etching of Integrated Circuits and Environmental Research. Some of the papers included here are texts based on selected lectures presented at the Second International Workshop on Non-equilibrium Processes in Plasmas and Environmental Science. However, this volume is not just the proceedings of that conference as it contains a number of papers from authors that did not attend the conference. The goal was to put together a volume that would cover the interests of the project and support further work. It is published in the Institute of Physics journal Journal of Physics: Conference Series to ensure a wide accessibility of the articles. The texts presented here range from in-depth reviews of the current status and past achievements to progress reports of currently developed experimental devices and recently obtained still unpublished results. All papers have been refereed twice, first when speakers were selected based on their reputation and recently published results, and second after the paper was submitted both by the editorial board and individual assigned referees according to the standards of the conference and of the journal. Nevertheless, we still leave the responsibility (and honours) for the contents of the papers to the authors. The papers in this book are review articles that give a summary of the already published work or present the work in progress that will be published in full at a later date (or both). In the introduction to the first volume, in order to show how far reaching, ubiquitous and important non-equilibrium phenomena are, we claimed that ever since the early

  14. Nonequilibrium solvent effects in Born-Oppenheimer molecular dynamics for ground and excited electronic states.

    PubMed

    Bjorgaard, J A; Velizhanin, K A; Tretiak, S

    2016-04-21

    The effects of solvent on molecular processes such as excited state relaxation and photochemical reaction often occurs in a nonequilibrium regime. Dynamic processes such as these can be simulated using excited statemolecular dynamics. In this work, we describe methods of simulating nonequilibrium solvent effects in excited statemolecular dynamics using linear-response time-dependent density functional theory and apparent surface charge methods. These developments include a propagation method for solvent degrees of freedom and analytical energy gradients for the calculation of forces. Molecular dynamics of acetaldehyde in water or acetonitrile are demonstrated where the solute-solvent system is out of equilibrium due to photoexcitation and emission. PMID:27389206

  15. Nonequilibrium solvent effects in Born-Oppenheimer molecular dynamics for ground and excited electronic states

    NASA Astrophysics Data System (ADS)

    Bjorgaard, J. A.; Velizhanin, K. A.; Tretiak, S.

    2016-04-01

    The effects of solvent on molecular processes such as excited state relaxation and photochemical reaction often occurs in a nonequilibrium regime. Dynamic processes such as these can be simulated using excited state molecular dynamics. In this work, we describe methods of simulating nonequilibrium solvent effects in excited state molecular dynamics using linear-response time-dependent density functional theory and apparent surface charge methods. These developments include a propagation method for solvent degrees of freedom and analytical energy gradients for the calculation of forces. Molecular dynamics of acetaldehyde in water or acetonitrile are demonstrated where the solute-solvent system is out of equilibrium due to photoexcitation and emission.

  16. Nonequilibrium structure in sequential assembly

    NASA Astrophysics Data System (ADS)

    Popov, Alexander V.; Craven, Galen T.; Hernandez, Rigoberto

    2015-11-01

    The assembly of monomeric constituents into molecular superstructures through sequential-arrival processes has been simulated and theoretically characterized. When the energetic interactions allow for complete overlap of the particles, the model is equivalent to that of the sequential absorption of soft particles on a surface. In the present work, we consider more general cases by including arbitrary aggregating geometries and varying prescriptions of the connectivity network. The resulting theory accounts for the evolution and final-state configurations through a system of equations governing structural generation. We find that particle geometries differ significantly from those in equilibrium. In particular, variations of structural rigidity and morphology tune particle energetics and result in significant variation in the nonequilibrium distributions of the assembly in comparison to the corresponding equilibrium case.

  17. Nonequilibrium migration in human history.

    PubMed Central

    Wakeley, J

    1999-01-01

    A nonequilibrium migration model is proposed and applied to genetic data from humans. The model assumes symmetric migration among all possible pairs of demes and that the number of demes is large. With these assumptions it is straightforward to allow for changes in demography, and here a single abrupt change is considered. Under the model this change is identical to a change in the ancestral effective population size and might be caused by changes in deme size, in the number of demes, or in the migration rate. Expressions for the expected numbers of sites segregating at particular frequencies in a multideme sample are derived. A maximum-likelihood analysis of independent polymorphic restriction sites in humans reveals a decrease in effective size. This is consistent with a change in the rates of migration among human subpopulations from ancient low levels to present high ones. PMID:10581291

  18. Nonequilibrium interfaces in colloidal fluids

    NASA Astrophysics Data System (ADS)

    Bier, Markus; Arnold, Daniel

    2013-12-01

    The time-dependent structure, interfacial tension, and evaporation of an oversaturated colloid-rich (liquid) phase in contact with an undersaturated colloid-poor (vapor) phase of a colloidal dispersion is investigated theoretically during the early-stage relaxation, where the interface is relaxing towards a local equilibrium state while the bulk phases are still out of equilibrium. Since systems of this type exhibit a clear separation of colloidal and solvent relaxation time scales with typical times of interfacial tension measurements in between, they can be expected to be suitable for analogous experimental studies, too. The major finding is that, irrespective of how much the bulk phases differ from two-phase coexistence, the interfacial structure and the interfacial tension approach those at two-phase coexistence during the early-stage relaxation process. This is a surprising observation since it implies that the relaxation towards global equilibrium of the interface is not following but preceding that of the bulk phases. Scaling forms for the local chemical potential, the flux, and the dissipation rate exhibit qualitatively different leading order contributions depending on whether an equilibrium or a nonequilibrium system is considered. The degree of nonquilibrium between the bulk phases is found to not influence the qualitative relaxation behavior (i.e., the values of power-law exponents), but to determine the quantitative deviation of the observed quantities from their values at two-phase coexistence. Whereas the underlying dynamics differs between colloidal and molecular fluids, the behavior of quantities such as the interfacial tension approaching the equilibrium values during the early-stage relaxation process, during which nonequilibrium conditions of the bulk phases are not changed, can be expected to occur for both types of systems.

  19. 49 CFR 1139.21 - Study carriers.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Industry § 1139.21 Study carriers. (a) For the purposes of this proceeding the “study carriers” shall... charges, derived $500,000 or more in annual operating revenues from the issue traffic, or 1 percent or more of the total annual operating revenues received by all Class I carriers from the issue...

  20. Nonequilibrium molecular dynamics: The first 25 years

    SciTech Connect

    Hoover, W.G. |

    1992-08-01

    Equilibrium Molecular Dynamics has been generalized to simulate Nonequilibrium systems by adding sources of thermodynamic heat and work. This generalization incorporates microscopic mechanical definitions of macroscopic thermodynamic and hydrodynamic variables, such as temperature and stress, and augments atomistic forces with special boundary, constraint, and driving forces capable of doing work on, and exchanging heat with, an otherwise Newtonian system. The underlying Lyapunov instability of these nonequilibrium equations of motion links microscopic time-reversible deterministic trajectories to macroscopic time-irreversible hydrodynamic behavior as described by the Second Law of Thermodynamics. Green-Kubo linear-response theory has been checked. Nonlinear plastic deformation, intense heat conduction, shockwave propagation, and nonequilibrium phase transformation have all been simulated. The nonequilibrium techniques, coupled with qualitative improvements in parallel computer hardware, are enabling simulations to approximate real-world microscale and nanoscale experiments.

  1. A unified approach to modelling the charge state of monatomic hydrogen and other defects in crystalline silicon

    NASA Astrophysics Data System (ADS)

    Sun, Chang; Rougieux, Fiacre E.; Macdonald, Daniel

    2015-01-01

    There are a number of existing models for estimating the charge states of defects in silicon. In order of increasing complexity, these are (a) the Fermi-Dirac distribution, (b) the Shockley-Last model, (c) the Shockley-Read-Hall model, and (d) the Sah-Shockley model. In this work, we demonstrate their consistency with the general occupancy ratio α, and show that this parameter can be universally applied to predict the charge states of both monovalent and multivalent deep levels, under either thermal equilibrium or steady-state conditions with carrier injection. The capture cross section ratio is shown to play an important role in determining the charge state under non-equilibrium conditions. The application of the general occupancy ratio is compared with the quasi-Fermi levels, which are sometimes used to predict the charge states in the literature, and the conditions where the latter can be a good approximation are identified. The general approach is then applied to the prediction of the temperature- and injection level-dependent charge states for the technologically important case of multivalent monatomic hydrogen, and several other key monovalent deep levels including Fe, Cr, and the boron-oxygen complex in silicon solar cells. For the case of hydrogen, we adapt the model of Herring et al., which describes the charge states of hydrogen in thermal equilibrium, and generalize it for non-equilibrium conditions via the inclusion of the general occupancy ratio, while retaining the pre-factors which make the model more complete. Based on these results, the impact of temperature and injection on the hydrogenation of the key monovalent defects, and other pairing reactions, are discussed, demonstrating that the presented model provides a rigorous methodology for understanding the impact of charge states.

  2. A unified approach to modelling the charge state of monatomic hydrogen and other defects in crystalline silicon

    SciTech Connect

    Sun, Chang Rougieux, Fiacre E.; Macdonald, Daniel

    2015-01-28

    There are a number of existing models for estimating the charge states of defects in silicon. In order of increasing complexity, these are (a) the Fermi-Dirac distribution, (b) the Shockley-Last model, (c) the Shockley-Read-Hall model, and (d) the Sah-Shockley model. In this work, we demonstrate their consistency with the general occupancy ratio α, and show that this parameter can be universally applied to predict the charge states of both monovalent and multivalent deep levels, under either thermal equilibrium or steady-state conditions with carrier injection. The capture cross section ratio is shown to play an important role in determining the charge state under non-equilibrium conditions. The application of the general occupancy ratio is compared with the quasi-Fermi levels, which are sometimes used to predict the charge states in the literature, and the conditions where the latter can be a good approximation are identified. The general approach is then applied to the prediction of the temperature- and injection level-dependent charge states for the technologically important case of multivalent monatomic hydrogen, and several other key monovalent deep levels including Fe, Cr, and the boron-oxygen complex in silicon solar cells. For the case of hydrogen, we adapt the model of Herring et al., which describes the charge states of hydrogen in thermal equilibrium, and generalize it for non-equilibrium conditions via the inclusion of the general occupancy ratio, while retaining the pre-factors which make the model more complete. Based on these results, the impact of temperature and injection on the hydrogenation of the key monovalent defects, and other pairing reactions, are discussed, demonstrating that the presented model provides a rigorous methodology for understanding the impact of charge states.

  3. Renormalisation of Nonequilibrium Phonons Under Strong Perturbative Influences.

    NASA Astrophysics Data System (ADS)

    Mehta, Sushrut Madhukar

    Effects of strong perturbative influences, namely the presence of a narrow distribution of acoustic phonons, and the presence of an electron plasma, on the dynamics of nonequilibrium, near zone center, longitudinal optical phonons in GaP have been investigated in two separate experiments. The study of the effects of the interaction between the LO phonons and a heavily populated, narrow distribution of acoustic phonons lead to the observation of a new optically driven nonequilibrium phonon state. Time Resolved Coherent Antistokes Raman Scattering (TR-CARS), with picosecond resolution, was used to investigate the new mode. In order to achieve high occupation numbers in the acoustic branch, the picosecond laser pulses used were amplified up to 1.0 GW/cm^2 peak power per laser beam. An important characteristic property of the new state which differentiates it from the well known LO phonon state is the fact that rather than having the single decay rate observed under thermal equilibrium, the new state has two decay rates. Moreover, these two decay rates depend strongly on the distribution of the acoustic phonon occupation number. The coupling of the LO phonons with an electron plasma, on the other hand, was investigated by measurements of the shape of the Raman scattered line associated with the phonon-plasmon coupled mode. The plasma was generated by thermal excitation of carriers in doped samples. It was possible to study a large variety of plasma excitations by controlling the concentration of the dopant and the ambient temperature. A complete, self consistant model based on standard dielectric response theory is presented, and applied to the measurements of the phonon-plasmon coupled mode. It is possible to recover, via this model, the effective coupled mode damping rate, the plasma damping rate, and the plasma frequency as functions of ambient temperature, or the carrier concentration.

  4. Contact resistances in trigate and FinFET devices in a non-equilibrium Green's functions approach

    NASA Astrophysics Data System (ADS)

    Bourdet, Léo; Li, Jing; Pelloux-Prayer, Johan; Triozon, François; Cassé, Mikaël; Barraud, Sylvain; Martinie, Sébastien; Rideau, Denis; Niquet, Yann-Michel

    2016-02-01

    We compute the contact resistances Rc in trigate and FinFET devices with widths and heights in the 4-24 nm range using a Non-Equilibrium Green's Functions approach. Electron-phonon, surface roughness, and Coulomb scattering are taken into account. We show that Rc represents a significant part of the total resistance of devices with sub-30 nm gate lengths. The analysis of the quasi-Fermi level profile reveals that the spacers between the heavily doped source/drain and the gate are major contributors to the contact resistance. The conductance is indeed limited by the poor electrostatic control over the carrier density under the spacers. We then disentangle the ballistic and diffusive components of Rc and analyze the impact of different design parameters (cross section and doping profile in the contacts) on the electrical performances of the devices. The contact resistance and variability rapidly increase when the cross sectional area of the channel goes below ≃50 nm2. We also highlight the role of the charges trapped at the interface between silicon and the spacer material.

  5. Quantum thermodynamics: a nonequilibrium Green's function approach.

    PubMed

    Esposito, Massimiliano; Ochoa, Maicol A; Galperin, Michael

    2015-02-27

    We establish the foundations of a nonequilibrium theory of quantum thermodynamics for noninteracting open quantum systems strongly coupled to their reservoirs within the framework of the nonequilibrium Green's functions. The energy of the system and its coupling to the reservoirs are controlled by a slow external time-dependent force treated to first order beyond the quasistatic limit. We derive the four basic laws of thermodynamics and characterize reversible transformations. Stochastic thermodynamics is recovered in the weak coupling limit. PMID:25768745

  6. The nonequilibrium thermodynamics of small systems

    NASA Astrophysics Data System (ADS)

    Ritort, Felix

    2007-03-01

    Nonequilibrium behavior is widespread and rich in nature. Yet our understanding of the fundamental principles underlying nonequilibrium behavior is still poor as shown by the fact that non-equilibrium theories tend to be ad-hoc and specific (1). Recently there has been a lot of interest in applying single-molecule techniques to scrutinize nonequilibrium theories (2). The use of new micromanipulation tools in the exploration of the behavior of tiny objects (such as biomolecules and motors) embedded in a thermal environment opens the possibility to investigate how these systems exchange energy with their environment. The study of such questions, nowadays referred to as ``Nonequilibrium thermodynamics of small systems,'' is becoming quite popular among statistical physicists who recognize there new aspects of thermodynamics where large Brownian fluctuations are of pivotal importance as compared to fluctuations in macroscopic (or large) systems (3). Nonequilibrium small systems are characterized by large deviations in work/heat distributions that satisfy some relations called fluctuation theorems. In this talk I will discuss single-molecule experiments where some of these fluctuation theorems have been tested (4). REFERENCES: (1) F. Ritort, Nonequilibrium fluctuations in small sytems: From physics to biology, To be published in Advances in Chemical Physics, volume 137; (2) F. Ritort, Single molecule experiments in biological physics: methods and applications, Journal of Physics C (Condensed Matter),18 (2006) R531-R583; (3) C. Bustamante, J. Liphardt and F. Ritort, The nonequilibrium thermodynamics of small systems, Physics Today,58 (2005) 43-48; (4) D. Collin, F. Ritort, C. Jarzynski, S. B. Smith, I. Tinoco Jr and C. Bustamante, Verification of the Crooks fluctuation theorem and recovery of RNA folding free energies, Nature, 437 (2005) 231-234.

  7. Non-equilibrium Kinematics in Merging Galaxies

    NASA Astrophysics Data System (ADS)

    Mihos, J. C.

    Measurements of the kinematics of merging galaxies are often used to derive dynamical masses, study evolution onto the fundamental plane, or probe relaxation processes. These measurements are often compromised to some degree by strong non-equilibrium motions in the merging galaxies. This talk focuses on the evolution of the kinematics of merging galaxies, and highlights some pitfalls which occur when studying non-equilibrium systems.

  8. Nonequilibrium transport in superconducting tunneling structures.

    SciTech Connect

    Chtchelkatchev, N. M.; Vinokur, V. M.; Baturina, T. I.

    2010-12-01

    We derive the current-voltage (I-V) characteristics of far from equilibrium superconducting tunneling arrays and find that the energy relaxation ensuring the charge transfer occurs in two stages: (i) the energy exchange between charge carriers and the intermediate bosonic agent, environment, and (ii) relaxing the energy further to the (phonon) thermostat, the bath, provided the rate of the environmental modes-phonon interactions is slower than their energy exchange rate with the tunneling junction. For a single junction we find I {proportional_to} (V/R)ln({Lambda}/V), where R is the bare tunnel resistance of the junction and {Lambda} is the high energy cut-off of the electron-environment interaction. In large tunneling arrays comprised of macroscopic number of junctions, low-temperature transport is governed by the cotunneling processes losing energy to the electron-hole environment. Below some critical temperature, T*, the Coulomb interactions open a finite gap in the environment excitations spectrum blocking simultaneously Cooper pair and normal excitations currents through the array; this is the microscopic mechanism of the insulator-to-superinsulator transition.

  9. 47 CFR 64.1190 - Preferred carrier freezes.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... procedures necessary to lift a preferred carrier freeze; an explanation that these steps are in addition to... selection unless he or she lifts the freeze. (iii) An explanation of any charges associated with the... unable to make a change in carrier selection unless she or he lifts the preferred carrier freeze; and...

  10. 47 CFR 64.1190 - Preferred carrier freezes.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... procedures necessary to lift a preferred carrier freeze; an explanation that these steps are in addition to... selection unless he or she lifts the freeze. (iii) An explanation of any charges associated with the... unable to make a change in carrier selection unless she or he lifts the preferred carrier freeze; and...

  11. 47 CFR 69.601 - Exchange carrier association.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 3 2011-10-01 2011-10-01 false Exchange carrier association. 69.601 Section 69...) ACCESS CHARGES Exchange Carrier Association § 69.601 Exchange carrier association. (a) An association... Common Line revenue requirement, pay long term support to association Common Line tariff participants,...

  12. 47 CFR 69.601 - Exchange carrier association.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 3 2010-10-01 2010-10-01 false Exchange carrier association. 69.601 Section 69...) ACCESS CHARGES Exchange Carrier Association § 69.601 Exchange carrier association. (a) An association... Common Line revenue requirement, pay long term support to association Common Line tariff participants,...

  13. 14 CFR 158.23 - Consultation with air carriers and foreign air carriers.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 3 2014-01-01 2014-01-01 false Consultation with air carriers and foreign air carriers. 158.23 Section 158.23 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT... funding by PFC's; (2) The PFC level for each project, the proposed charge effective date, the...

  14. Femtosecond carrier dynamics in graphite

    NASA Astrophysics Data System (ADS)

    Seibert, K.; Cho, G. C.; Kütt, W.; Kurz, H.; Reitze, D. H.; Dadap, J. I.; Ahn, H.; Downer, M. C.; Malvezzi, A. M.

    1990-08-01

    We present a comprehensive report of pump-probe reflectivity and transmission measurements on highly oriented pyrolytic graphite with 50 fs time resolution. The experiments trace the generation, relaxation, and recombination of nonequilibrium carriers in a quasi-two-dimensional semimetallic solid over a wide range of experimental parameters. The fluence of excitation at hν=2.0 eV was varied between 10-6 and 10-2 J/cm2, below the threshold for optical damage, while probe pulses in the photon energy range 1.5carriers cool and recombine in less than 1 ps. Later dynamics reflect the generation and diffusion of heat in the lattice, and are consistent with previous picosecond reflectivity measurements.

  15. Ultrafast carriers dynamics in filled-skutterudites

    NASA Astrophysics Data System (ADS)

    Guo, Liang; Xu, Xianfan; Salvador, James R.

    2015-06-01

    Carrier dynamics of filled-skutterudites, an important class of thermoelectric materials, is investigated using ultrafast optical spectroscopy. By tuning the wavelength of the probe laser, charge transfers at different electronic energy levels are interrogated. Analysis based on the Kramers-Kronig relation explains the complex spectroscopy data, which is mainly due to band filling caused by photo-excited carriers and free carrier absorption. The relaxation time of hot carriers is found to be about 0.4-0.6 ps, depending on the electronic energy level, and the characteristic time for carrier-phonon equilibrium is about 0.95 ps. These studies of carrier dynamics, which fundamentally determines the transport properties of thermoelectric material, can provide guidance for the design of materials.

  16. Ultrafast carriers dynamics in filled-skutterudites

    SciTech Connect

    Guo, Liang; Xu, Xianfan; Salvador, James R.

    2015-06-08

    Carrier dynamics of filled-skutterudites, an important class of thermoelectric materials, is investigated using ultrafast optical spectroscopy. By tuning the wavelength of the probe laser, charge transfers at different electronic energy levels are interrogated. Analysis based on the Kramers-Kronig relation explains the complex spectroscopy data, which is mainly due to band filling caused by photo-excited carriers and free carrier absorption. The relaxation time of hot carriers is found to be about 0.4–0.6 ps, depending on the electronic energy level, and the characteristic time for carrier-phonon equilibrium is about 0.95 ps. These studies of carrier dynamics, which fundamentally determines the transport properties of thermoelectric material, can provide guidance for the design of materials.

  17. Equilibrium sampling by reweighting nonequilibrium simulation trajectories.

    PubMed

    Yang, Cheng; Wan, Biao; Xu, Shun; Wang, Yanting; Zhou, Xin

    2016-03-01

    Based on equilibrium molecular simulations, it is usually difficult to efficiently visit the whole conformational space of complex systems, which are separated into some metastable regions by high free energy barriers. Nonequilibrium simulations could enhance transitions among these metastable regions and then be applied to sample equilibrium distributions in complex systems, since the associated nonequilibrium effects can be removed by employing the Jarzynski equality (JE). Here we present such a systematical method, named reweighted nonequilibrium ensemble dynamics (RNED), to efficiently sample equilibrium conformations. The RNED is a combination of the JE and our previous reweighted ensemble dynamics (RED) method. The original JE reproduces equilibrium from lots of nonequilibrium trajectories but requires that the initial distribution of these trajectories is equilibrium. The RED reweights many equilibrium trajectories from an arbitrary initial distribution to get the equilibrium distribution, whereas the RNED has both advantages of the two methods, reproducing equilibrium from lots of nonequilibrium simulation trajectories with an arbitrary initial conformational distribution. We illustrated the application of the RNED in a toy model and in a Lennard-Jones fluid to detect its liquid-solid phase coexistence. The results indicate that the RNED sufficiently extends the application of both the original JE and the RED in equilibrium sampling of complex systems. PMID:27078486

  18. Equilibrium sampling by reweighting nonequilibrium simulation trajectories.

    PubMed

    Yang, Cheng; Wan, Biao; Xu, Shun; Wang, Yanting; Zhou, Xin

    2016-03-01

    Based on equilibrium molecular simulations, it is usually difficult to efficiently visit the whole conformational space of complex systems, which are separated into some metastable regions by high free energy barriers. Nonequilibrium simulations could enhance transitions among these metastable regions and then be applied to sample equilibrium distributions in complex systems, since the associated nonequilibrium effects can be removed by employing the Jarzynski equality (JE). Here we present such a systematical method, named reweighted nonequilibrium ensemble dynamics (RNED), to efficiently sample equilibrium conformations. The RNED is a combination of the JE and our previous reweighted ensemble dynamics (RED) method. The original JE reproduces equilibrium from lots of nonequilibrium trajectories but requires that the initial distribution of these trajectories is equilibrium. The RED reweights many equilibrium trajectories from an arbitrary initial distribution to get the equilibrium distribution, whereas the RNED has both advantages of the two methods, reproducing equilibrium from lots of nonequilibrium simulation trajectories with an arbitrary initial conformational distribution. We illustrated the application of the RNED in a toy model and in a Lennard-Jones fluid to detect its liquid-solid phase coexistence. The results indicate that the RNED sufficiently extends the application of both the original JE and the RED in equilibrium sampling of complex systems.

  19. Equilibrium sampling by reweighting nonequilibrium simulation trajectories

    NASA Astrophysics Data System (ADS)

    Yang, Cheng; Wan, Biao; Xu, Shun; Wang, Yanting; Zhou, Xin

    2016-03-01

    Based on equilibrium molecular simulations, it is usually difficult to efficiently visit the whole conformational space of complex systems, which are separated into some metastable regions by high free energy barriers. Nonequilibrium simulations could enhance transitions among these metastable regions and then be applied to sample equilibrium distributions in complex systems, since the associated nonequilibrium effects can be removed by employing the Jarzynski equality (JE). Here we present such a systematical method, named reweighted nonequilibrium ensemble dynamics (RNED), to efficiently sample equilibrium conformations. The RNED is a combination of the JE and our previous reweighted ensemble dynamics (RED) method. The original JE reproduces equilibrium from lots of nonequilibrium trajectories but requires that the initial distribution of these trajectories is equilibrium. The RED reweights many equilibrium trajectories from an arbitrary initial distribution to get the equilibrium distribution, whereas the RNED has both advantages of the two methods, reproducing equilibrium from lots of nonequilibrium simulation trajectories with an arbitrary initial conformational distribution. We illustrated the application of the RNED in a toy model and in a Lennard-Jones fluid to detect its liquid-solid phase coexistence. The results indicate that the RNED sufficiently extends the application of both the original JE and the RED in equilibrium sampling of complex systems.

  20. What Is Carrier Screening?

    MedlinePlus

    ... you want to learn. Search form Search Carrier screening You are here Home Testing & Services Testing for ... help you make the decision. What Is Carrier Screening? Carrier screening checks if a person is a " ...

  1. Thermal response of nonequilibrium R C circuits

    NASA Astrophysics Data System (ADS)

    Baiesi, Marco; Ciliberto, Sergio; Falasco, Gianmaria; Yolcu, Cem

    2016-08-01

    We analyze experimental data obtained from an electrical circuit having components at different temperatures, showing how to predict its response to temperature variations. This illustrates in detail how to utilize a recent linear response theory for nonequilibrium overdamped stochastic systems. To validate these results, we introduce a reweighting procedure that mimics the actual realization of the perturbation and allows extracting the susceptibility of the system from steady-state data. This procedure is closely related to other fluctuation-response relations based on the knowledge of the steady-state probability distribution. As an example, we show that the nonequilibrium heat capacity in general does not correspond to the correlation between the energy of the system and the heat flowing into it. Rather, also nondissipative aspects are relevant in the nonequilibrium fluctuation-response relations.

  2. Thermal response of nonequilibrium RC circuits.

    PubMed

    Baiesi, Marco; Ciliberto, Sergio; Falasco, Gianmaria; Yolcu, Cem

    2016-08-01

    We analyze experimental data obtained from an electrical circuit having components at different temperatures, showing how to predict its response to temperature variations. This illustrates in detail how to utilize a recent linear response theory for nonequilibrium overdamped stochastic systems. To validate these results, we introduce a reweighting procedure that mimics the actual realization of the perturbation and allows extracting the susceptibility of the system from steady-state data. This procedure is closely related to other fluctuation-response relations based on the knowledge of the steady-state probability distribution. As an example, we show that the nonequilibrium heat capacity in general does not correspond to the correlation between the energy of the system and the heat flowing into it. Rather, also nondissipative aspects are relevant in the nonequilibrium fluctuation-response relations. PMID:27627283

  3. Nonequilibrium combustion effects in supersonic streams

    NASA Technical Reports Server (NTRS)

    Jensen, R. M.; Bryce, C. A.; Reese, B. A.

    1972-01-01

    This research program is a theoretical and experimental investigation of the effect of nonequilibrium conditions upon the performance of combustors employing supersonic flows. Calculations and experiments are made regarding the effects on the ignition of hydrogen of the nonequilibrium species (free radicals, atoms, water vapor, etc.) obtained using vitiated air. Results of this investigation show that the nonequilibrium free-radical content from a supersonic vitiated air source will cause early ignition of the hydrogen. An analysis of heated air expended from a high temperature source to test section conditions also indicates that there is sufficient free radical content in the incoming flow to cause early ignition. Water vapor, an inherent contaminant in the generation of vitiated air, was found to reduce the ignition delay period under the experimental conditions considered.

  4. Nonequilibrium Ablation of Phenolic Impregnated Carbon Ablator

    NASA Technical Reports Server (NTRS)

    Milos, Frank S.; Chen, Yih K.; Gokcen, Tahir

    2012-01-01

    In previous work, an equilibrium ablation and thermal response model for Phenolic Impregnated Carbon Ablator was developed. In general, over a wide range of test conditions, model predictions compared well with arcjet data for surface recession, surface temperature, in-depth temperature at multiple thermocouples, and char depth. In this work, additional arcjet tests were conducted at stagnation conditions down to 40 W/sq cm and 1.6 kPa. The new data suggest that nonequilibrium effects become important for ablation predictions at heat flux or pressure below about 80 W/sq cm or 10 kPa, respectively. Modifications to the ablation model to account for nonequilibrium effects are investigated. Predictions of the equilibrium and nonequilibrium models are compared with the arcjet data.

  5. Plasma diagnostics of non-equilibrium atmospheric plasma jets

    NASA Astrophysics Data System (ADS)

    Shashurin, Alexey; Scott, David; Keidar, Michael; Shneider, Mikhail

    2014-10-01

    Intensive development and biomedical application of non-equilibrium atmospheric plasma jet (NEAPJ) facilitates rapid growth of the plasma medicine field. The NEAPJ facility utilized at the George Washington University (GWU) demonstrated efficacy for treatment of various cancer types (lung, bladder, breast, head, neck, brain and skin). In this work we review recent advances of the research conducted at GWU concerned with the development of NEAPJ diagnostics including Rayleigh Microwave Scattering setup, method of streamer scattering on DC potential, Rogowski coils, ICCD camera and optical emission spectroscopy. These tools allow conducting temporally-resolved measurements of plasma density, electrical potential, charge and size of the streamer head, electrical currents flowing though the jet, ionization front propagation speed etc. Transient dynamics of plasma and discharge parameters will be considered and physical processes involved in the discharge will be analyzed including streamer breakdown, electrical coupling of the streamer tip with discharge electrodes, factors determining NEAPJ length, cross-sectional shape and propagation path etc.

  6. Nonequilibrium air radiation (Nequair) program: User's manual

    NASA Astrophysics Data System (ADS)

    Park, C.

    1985-07-01

    A supplement to the data relating to the calculation of nonequilibrium radiation in flight regimes of aeroassisted orbital transfer vehicles contains the listings of the computer code NEQAIR (Nonequilibrium Air Radiation), its primary input data, and explanation of the user-supplied input variables. The user-supplied input variables are the thermodynamic variables of air at a given point, i.e., number densities of various chemical species, translational temperatures of heavy particles and electrons, and vibrational temperature. These thermodynamic variables do not necessarily have to be in thermodynamic equilibrium. The code calculates emission and absorption characteristics of air under these given conditions.

  7. Mesoscopic virial equation for nonequilibrium statistical mechanics

    NASA Astrophysics Data System (ADS)

    Falasco, G.; Baldovin, F.; Kroy, K.; Baiesi, M.

    2016-09-01

    We derive a class of mesoscopic virial equations governing energy partition between conjugate position and momentum variables of individual degrees of freedom. They are shown to apply to a wide range of nonequilibrium steady states with stochastic (Langevin) and deterministic (Nosé-Hoover) dynamics, and to extend to collective modes for models of heat-conducting lattices. A macroscopic virial theorem ensues upon summation over all degrees of freedom. It allows for the derivation of generalised (nonequilibrium) equations of state that involve average dissipative heat flows besides genuine state variables, as exemplified for inertial Brownian motion with solid friction and overdamped active Brownian particles subject to inhomogeneous pressure.

  8. Fluctuation theorem for partially masked nonequilibrium dynamics.

    PubMed

    Shiraishi, Naoto; Sagawa, Takahiro

    2015-01-01

    We establish a generalization of the fluctuation theorem for partially masked nonequilibrium dynamics. We introduce a partial entropy production with a subset of all possible transitions, and show that the partial entropy production satisfies the integral fluctuation theorem. Our result reveals the fundamental properties of a broad class of autonomous as well as nonautonomous nanomachines. In particular, our result gives a unified fluctuation theorem for both autonomous and nonautonomous Maxwell's demons, where mutual information plays a crucial role. Furthermore, we derive a fluctuation-dissipation theorem that relates nonequilibrium stationary current to two kinds of equilibrium fluctuations. PMID:25679593

  9. Fluctuation theorem for partially masked nonequilibrium dynamics

    NASA Astrophysics Data System (ADS)

    Shiraishi, Naoto; Sagawa, Takahiro

    2015-01-01

    We establish a generalization of the fluctuation theorem for partially masked nonequilibrium dynamics. We introduce a partial entropy production with a subset of all possible transitions, and show that the partial entropy production satisfies the integral fluctuation theorem. Our result reveals the fundamental properties of a broad class of autonomous as well as nonautonomous nanomachines. In particular, our result gives a unified fluctuation theorem for both autonomous and nonautonomous Maxwell's demons, where mutual information plays a crucial role. Furthermore, we derive a fluctuation-dissipation theorem that relates nonequilibrium stationary current to two kinds of equilibrium fluctuations.

  10. Nonequilibrium air radiation (Nequair) program: User's manual

    NASA Technical Reports Server (NTRS)

    Park, C.

    1985-01-01

    A supplement to the data relating to the calculation of nonequilibrium radiation in flight regimes of aeroassisted orbital transfer vehicles contains the listings of the computer code NEQAIR (Nonequilibrium Air Radiation), its primary input data, and explanation of the user-supplied input variables. The user-supplied input variables are the thermodynamic variables of air at a given point, i.e., number densities of various chemical species, translational temperatures of heavy particles and electrons, and vibrational temperature. These thermodynamic variables do not necessarily have to be in thermodynamic equilibrium. The code calculates emission and absorption characteristics of air under these given conditions.

  11. Nonequilibrium temperature response for stochastic overdamped systems

    NASA Astrophysics Data System (ADS)

    Falasco, G.; Baiesi, M.

    2016-04-01

    The thermal response of nonequilibrium systems requires the knowledge of concepts that go beyond entropy production. This is showed for systems obeying overdamped Langevin dynamics, either in steady states or going through a relaxation process. Namely, we derive the linear response to perturbations of the noise intensity, mapping it onto the quadratic response to a constant small force. The latter, displaying divergent terms, is explicitly regularised with a novel path-integral method. The nonequilibrium equivalents of heat capacity and thermal expansion coefficient are two applications of this approach, as we show with numerical examples.

  12. Thermodynamic model of nonequilibrium phase transitions.

    PubMed

    Martyushev, L M; Konovalov, M S

    2011-07-01

    Within the scope of a thermodynamic description using the maximum entropy production principle, transitions from one nonequilibrium (kinetic) regime to another are considered. It is shown that in the case when power-law dependencies of thermodynamic flux on force are similar for two regimes, only a transition accompanied by a positive jump of thermodynamic flux is possible between them. It is found that the difference in powers of the dependencies of thermodynamic fluxes on forces results in a number of interesting nonequilibrium transitions between kinetic regimes, including the reentrant one with a negative jump of thermodynamic flux. PMID:21867119

  13. 47 CFR 69.124 - Interconnection charge.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 3 2010-10-01 2010-10-01 false Interconnection charge. 69.124 Section 69.124... Computation of Charges § 69.124 Interconnection charge. (a) Until December 31, 2001, local exchange carriers not subject to price cap regulation shall assess an interconnection charge expressed in dollars...

  14. Stacking dependence of carrier transport properties in multilayered black phosphorous.

    PubMed

    Sengupta, A; Audiffred, M; Heine, T; Niehaus, T A

    2016-02-24

    We present the effect of different stacking orders on carrier transport properties of multi-layer black phosphorous. We consider three different stacking orders AAA, ABA and ACA, with increasing number of layers (from 2 to 6 layers). We employ a hierarchical approach in density functional theory (DFT), with structural simulations performed with generalized gradient approximation (GGA) and the bandstructure, carrier effective masses and optical properties evaluated with the meta-generalized gradient approximation (MGGA). The carrier transmission in the various black phosphorous sheets was carried out with the non-equilibrium green's function (NEGF) approach. The results show that ACA stacking has the highest electron and hole transmission probabilities. The results show tunability for a wide range of band-gaps, carrier effective masses and transmission with a great promise for lattice engineering (stacking order and layers) in black phosphorous. PMID:26809017

  15. Stacking dependence of carrier transport properties in multilayered black phosphorous

    NASA Astrophysics Data System (ADS)

    Sengupta, A.; Audiffred, M.; Heine, T.; Niehaus, T. A.

    2016-02-01

    We present the effect of different stacking orders on carrier transport properties of multi-layer black phosphorous. We consider three different stacking orders AAA, ABA and ACA, with increasing number of layers (from 2 to 6 layers). We employ a hierarchical approach in density functional theory (DFT), with structural simulations performed with generalized gradient approximation (GGA) and the bandstructure, carrier effective masses and optical properties evaluated with the meta-generalized gradient approximation (MGGA). The carrier transmission in the various black phosphorous sheets was carried out with the non-equilibrium green’s function (NEGF) approach. The results show that ACA stacking has the highest electron and hole transmission probabilities. The results show tunability for a wide range of band-gaps, carrier effective masses and transmission with a great promise for lattice engineering (stacking order and layers) in black phosphorous.

  16. Stacking dependence of carrier transport properties in multilayered black phosphorous.

    PubMed

    Sengupta, A; Audiffred, M; Heine, T; Niehaus, T A

    2016-02-24

    We present the effect of different stacking orders on carrier transport properties of multi-layer black phosphorous. We consider three different stacking orders AAA, ABA and ACA, with increasing number of layers (from 2 to 6 layers). We employ a hierarchical approach in density functional theory (DFT), with structural simulations performed with generalized gradient approximation (GGA) and the bandstructure, carrier effective masses and optical properties evaluated with the meta-generalized gradient approximation (MGGA). The carrier transmission in the various black phosphorous sheets was carried out with the non-equilibrium green's function (NEGF) approach. The results show that ACA stacking has the highest electron and hole transmission probabilities. The results show tunability for a wide range of band-gaps, carrier effective masses and transmission with a great promise for lattice engineering (stacking order and layers) in black phosphorous.

  17. Ergodicity: a historical perspective. Equilibrium and Nonequilibrium

    NASA Astrophysics Data System (ADS)

    Gallavotti, Giovanni

    2016-10-01

    A view on the physical meaning of the so called ergodic hypothesis: its role on the foundations of equilibrium statistical mechanics in mid '1800, its interpretations and hints at its relevance for modern nonequilibrium statistical mechanics. Followed by appendices with detailed comments on the original papers.

  18. Axisymmetric reacting gas nonequilibrium performance program

    NASA Technical Reports Server (NTRS)

    Kliegel, J. R.; Melde, J. E.; Nickerson, G. R.; Quan, V.

    1968-01-01

    Computer program calculates the inviscid one-dimensional equilibrium, frozen, and nonequilibrium nozzle expansion of propellant exhaust mixtures containing these six elements - carbon, hydrogen, oxygen, nitrogen, fluorine, and chlorine plus either aluminum, beryllium, boron or lithium. This program will perform calculations for contoured and conical nozzles.

  19. Boundary stability under nonequilibrium conditions. Final report

    SciTech Connect

    Hackney, S.A.; Lee, J.K.; Plichta, M.R.

    1999-08-01

    Summaries of research accomplished are given for the following areas: Morphological (Diffusional) Stability; A New Algorithm for Numerical Modeling of Non-equilibrium Materials Behavior; A Unified Treatment of Single and Microcrystalline Film Edge Instabilities; and Validation of the Structure Based Grain Boundary Diffusion/Migration Model.

  20. Ergodicity: a historical perspective. Equilibrium and Nonequilibrium

    NASA Astrophysics Data System (ADS)

    Gallavotti, Giovanni

    2016-09-01

    A view on the physical meaning of the so called ergodic hypothesis: its role on the foundations of equilibrium statistical mechanics in mid '1800, its interpretations and hints at its relevance for modern nonequilibrium statistical mechanics. Followed by appendices with detailed comments on the original papers.

  1. Universality of non-equilibrium fluctuations in strongly correlated quantum liquids

    NASA Astrophysics Data System (ADS)

    Ferrier, Meydi; Arakawa, Tomonori; Hata, Tokuro; Fujiwara, Ryo; Delagrange, Raphaëlle; Weil, Raphaël; Deblock, Richard; Sakano, Rui; Oguri, Akira; Kobayashi, Kensuke

    2016-03-01

    Interacting quantum many-body systems constitute a fascinating research field because they form quantum liquids with remarkable properties and universal behaviour. In fermionic systems, such quantum liquids are realized in helium-3 liquid, heavy fermion systems, neutron stars and cold gases. Their properties in the linear-response regime have been successfully described by the theory of Fermi liquids. The idea is that they behave as an ensemble of non-interacting `quasi-particles’. However, non-equilibrium properties have still to be established and remain a key issue of many-body physics. Here, we show a precise experimental demonstration of Landau Fermi liquid theory extended to the non-equilibrium regime in a zero-dimensional system. Combining transport and ultra-sensitive current noise measurements, we have unambiguously identified the SU(2) (ref. ) and SU(4) (refs ,,,,) symmetries of a quantum liquid in a carbon nanotube tuned in the universal Kondo regime. Whereas the free quasi-particle picture is found valid around equilibrium, an enhancement of the current fluctuations is detected out of equilibrium and perfectly explained by an effective charge induced by the residual interaction between quasi-particles. Moreover, an as-yet-unknown scaling law for the effective charge is discovered, suggesting a new non-equilibrium universality. Our method paves a new way to explore the exotic nature of quantum liquids out of equilibrium through their fluctuations in a wide variety of physical systems.

  2. 49 CFR 375.221 - May I use a charge or credit card plan for payments?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS TRANSPORTATION OF HOUSEHOLD GOODS IN INTERSTATE COMMERCE; CONSUMER PROTECTION REGULATIONS Before... for the payment of freight charges. Accepting charge or credit card payments is different...

  3. 49 CFR 375.221 - May I use a charge or credit card plan for payments?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ...) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS TRANSPORTATION OF HOUSEHOLD GOODS IN INTERSTATE COMMERCE; CONSUMER PROTECTION REGULATIONS Before... for the payment of freight charges. Accepting charge or credit card payments is different...

  4. Non-Condon nonequilibrium Fermi's golden rule rates from the linearized semiclassical method

    NASA Astrophysics Data System (ADS)

    Sun, Xiang; Geva, Eitan

    2016-08-01

    The nonequilibrium Fermi's golden rule describes the transition between a photoexcited bright donor electronic state and a dark acceptor electronic state, when the nuclear degrees of freedom start out in a nonequilibrium state. In a previous paper [X. Sun and E. Geva, J. Chem. Theory Comput. 12, 2926 (2016)], we proposed a new expression for the nonequilibrium Fermi's golden rule within the framework of the linearized semiclassical approximation and based on the Condon approximation, according to which the electronic coupling between donor and acceptor is assumed constant. In this paper we propose a more general expression, which is applicable to the case of non-Condon electronic coupling. We test the accuracy of the new non-Condon nonequilibrium Fermi's golden rule linearized semiclassical expression on a model where the donor and acceptor potential energy surfaces are parabolic and identical except for shifts in the equilibrium energy and geometry, and the coupling between them is linear in the nuclear coordinates. Since non-Condon effects may or may not give rise to conical intersections, both possibilities are examined by considering the following: (1) A modified Garg-Onuchic-Ambegaokar model for charge transfer in the condensed phase, where the donor-acceptor coupling is linear in the primary-mode coordinate, and for which non-Condon effects do not give rise to a conical intersection; (2) the linear vibronic coupling model for electronic transitions in gas phase molecules, where non-Condon effects give rise to conical intersections. We also present a comprehensive comparison between the linearized semiclassical expression and a progression of more approximate expressions, in both normal and inverted regions, and over a wide range of initial nonequilibrium states, temperatures, and frictions.

  5. Non-equilibrium dynamics of glass-forming liquid mixtures

    NASA Astrophysics Data System (ADS)

    Sánchez-Díaz, Luis Enrique; Lázaro-Lázaro, Edilio; Olais-Govea, José Manuel; Medina-Noyola, Magdaleno

    2014-06-01

    The non-equilibrium self-consistent generalized Langevin equation theory of irreversible processes in glass-forming liquids [P. Ramírez-González and M. Medina-Noyola, Phys. Rev. E 82, 061503 (2010)] is extended here to multi-component systems. The resulting theory describes the statistical properties of the instantaneous local particle concentration profiles nα(r, t) of species α in terms of the coupled time-evolution equations for the mean value overline{n}_α ({r},t) and for the covariance σ _{α β }({r},{r}^' };t)equiv overline{δ n_α ({r},t)δ n_β ({r}^' },t)} of the fluctuations δ n_α ({r},t) = n_α ({r},t)- overline{n}_α ({r},t). As in the monocomponent case, these two coarse-grained equations involve a local mobility function bα(r, t) for each species, written in terms of the memory function of the two-time correlation function C_{α β }({r},{r}^' };t,t^' }) equiv overline{δ n_α ({r},t)δ n_β ({r}^' },t^' })}. If the system is constrained to remain spatially uniform and subjected to a non-equilibrium preparation protocol described by a given temperature and composition change program T(t) and overline{n}_α (t), these equations predict the irreversible structural relaxation of the partial static structure factors Sαβ(k; t) and of the (collective and self) intermediate scattering functions Fαβ(k, τ; t) and F^S_{α β }(k,τ ;t). We illustrate the applicability of the resulting theory with two examples involving simple model mixtures subjected to an instantaneous temperature quench: an electroneutral binary mixture of equally sized and oppositely charged hard-spheres, and a binary mixture of soft-spheres of moderate size-asymmetry.

  6. Nonequilibrium solvation for vertical photoemission and photoabsorption processes using the symmetry-adapted cluster-configuration interaction method in the polarizable continuum model

    NASA Astrophysics Data System (ADS)

    Fukuda, Ryoichi; Ehara, Masahiro; Nakatsuji, Hiroshi; Cammi, Roberto

    2011-03-01

    In this paper, we present the theory and implementation of a nonequilibrium solvation model for the symmetry-adapted cluster (SAC) and symmetry-adapted cluster-configuration interaction (SAC-CI) method in the polarizable continuum model. For nonequilibrium solvation, we adopted the Pekar partition scheme in which solvent charges are divided into dynamical and inertial components. With this nonequilibrium solvation scheme, a vertical transition from an initial state to a final state may be described as follows: the initial state is described by equilibrium solvation, while in the final state, the inertial component remains in the solvation for the initial state; the dynamical component will be calculated self-consistently for the final state. The present method was applied to the vertical photoemission and absorption of s-trans acrolein and methylenecyclopropene. The effect of nonequilibrium solvation was significant for a polar solvent.

  7. Non-equilibrium Transport in Carbon based Adsorbate Systems

    NASA Astrophysics Data System (ADS)

    Fürst, Joachim; Brandbyge, Mads; Stokbro, Kurt; Jauho, Antti-Pekka

    2007-03-01

    We have used the Atomistix Tool Kit(ATK) and TranSIESTA[1] packages to investigate adsorption of iron atoms on a graphene sheet. The technique of both codes is based on density functional theory using local basis sets[2], and non-equilibrium Green's functions (NEGF) to calculate the charge distribution under external bias. Spin dependent electronic structure calculations are performed for different iron coverages. These reveal adsorption site dependent charge transfer from iron to graphene leading to screening effects. Transport calculations show spin dependent scattering of the transmission which is analysed obtaining the transmission eigenchannels for each spin type. The phenomena of electromigration of iron in these systems at finite bias will be discussed, estimating the so-called wind force from the reflection[3]. [1] M. Brandbyge, J.-L. Mozos, P. Ordejon, J. Taylor, and K. Stokbro. Physical Review B (Condensed Matter and Materials Physics), 65(16):165401/11-7, 2002. [2] Jose M. Soler, Emilio Artacho, Julian D. Gale, Alberto Garcia, Javier Junquera, Pablo Ordejon, and Daniel Sanchez-Portal. Journal of Physics Condensed Matter, 14(11):2745-2779, 2002. [3] Sorbello. Theory of electromigration. Solid State Physics, 1997.

  8. Nonequilibrium spin-polarized thermal transport in ferromagnetic-quantum dot-metal system

    NASA Astrophysics Data System (ADS)

    Xu, Li; Li, Zhi-Jian; Niu, Pengbin; Nie, Yi-Hang

    2016-10-01

    We use nonequilibrium Green function to analyze the nonequilibrium spin-polarized thermal transport through the ferromagnetic-quantum dot-metal system, in which a quantum dot (QD) is coupled to the ferromagnetic and metal electrodes with the voltage bias and the temperature shift. The differential thermoelectric conductance L (θ) is always zero and has no relation with the temperature shift when ε is equal to the Fermi level. The positive and negative values of L (θ) manifest the thermoelectric characteristic of electron-like (or hole-like) carrier when the temperature shift is nonzero. The electrostatic potential U becomes spin-dependent, and makes the dot level renormalization when the ferromagnetic-quantum dot-metal system is driven by the voltage bias and the temperature shift. We define that the spin polarization of the currents between the spin current Is and the electric current Ic is denoted as Is /Ic. The spin polarization Is /Ic shows novel and unique physical phenomenon when the voltage bias and the temperature shift are changed in the nonequilibrium state. Another interesting phenomenon is that we can obtain the pure spin current and a zero point of the thermocurrent Ith by adjusting the voltage bias and the temperature shift.

  9. Long-lived nonequilibrium states in the Hubbard model with an electric field

    NASA Astrophysics Data System (ADS)

    Joura, Alexander V.; Freericks, J. K.; Lichtenstein, Alexander I.

    2015-06-01

    We study the single-band Hubbard model in the presence of a large spatially uniform electric field out of equilibrium. Using the Keldysh nonequilibrium formalism, we solve the problem using perturbation theory in the Coulomb interaction U . We present numerical results for the charge current, the total energy of the system, and the double occupancy on an infinite-dimensional hypercubic lattice with nearest-neighbor hopping. The system is isolated from an external bath and is in the paramagnetic state. We show that an electric field pulse can drive the system to a steady nonequilibrium state, which does not evolve into a thermal state. We compare results obtained within second-order perturbation theory (SOPT), self-consistent SOPT, and iterated perturbation theory (IPT). We also discuss the importance of initial conditions for a system which is not coupled to an external bath.

  10. Nonlinear nonequilibrium quasiparticle relaxation in Josephson junctions.

    PubMed

    Krasnov, V M

    2009-11-27

    I solve numerically a full set of nonlinear kinetic balance equations for stacked Josephson junctions, which allows analysis of strongly nonequilibrium phenomena. It is shown that nonlinearity becomes significant already at very small disequilibrium. The following new, nonlinear effects are obtained: (i) At even-gap voltages V = 2nDelta/e (n = 2, 3, ...) nonequilibrium bosonic bands overlap. This leads to enhanced emission of Omega = 2Delta bosons and to the appearance of dips in tunnel conductance. (ii) A new type of radiative solution is found at strong disequilibrium. It is characterized by the fast stimulated relaxation of quasiparticles. A stack in this state behaves as a light emitting diode and directly converts electric power to boson emission, without utilization of the ac-Josephson effect. The phenomenon can be used for realization of a new type of superconducting cascade laser in the THz frequency range.

  11. Dynamic many-body and nonequilibrium effects in a quantum dot microcavity laser

    NASA Astrophysics Data System (ADS)

    Lingnau, Benjamin; Lüdge, Kathy; Schöll, Eckehard; Chow, Weng W.

    2010-04-01

    An interesting aspect of semiconductor quantum dot lasers is their potential for fast dynamical response. Since carrier relaxation is slowed down for discrete energy levels, it is generally agreed that nonequilibrium effects will have strong influence on dynamical behavior in quantum dot lasers. In this paper, we show that, furthermore, many-body effects should be taken into account. The reason is that the interplay of bandgap renormalization, population-hole burning and inhomogeneous broadening is crucial for understanding quantum dot laser dynamics. For example, when operating with a microcavity, the interplay gives rise to modifications of relaxation oscillation behavior that is beyond what can be described by the usual 2-variable rate equation treatment. The theory used in the simulations is based on a semiclassical approach, where the laser field and active medium are described by the Maxwell-semiconductor-Bloch equations. Many-body Coulomb effects are described in the screened Hartree-Fock approximation. Carrier-carrier and carrier-phonon collisions are treated within the effective relaxation rate approximation, with the effective rates estimated from a quantum mechanical approach. Current injection and carrier capture, details of the electronic structure, as well as influences of spectral-hole burning and state-filling in an inhomogeneously broadened quantum dot distribution are taken into account. This theory provides a microscopically consistent description of a quantum dot laser and allows one to perform parametric studies on time scales ranging from subpicosecond to nanoseconds.

  12. Design and Synthesis of Nonequilibrium Systems.

    PubMed

    Cheng, Chuyang; McGonigal, Paul R; Stoddart, J Fraser; Astumian, R Dean

    2015-09-22

    The active transport of ions and molecules across cell membranes is essential to creating the concentration gradients that sustain life in all living organisms, be they bacteria, fungi, plants, animals or Homo sapiens. Nature uses active transport everywhere for everything. Molecular biologists have long been attracted to the study of active transport and continue to this day to investigate and elucidate the tertiary structures of the complex motor proteins that sustain it, while physicists, interested in nonequilibrium statistical mechanics, have developed theoretical models to describe the driven ratcheting motions that are crucial to its function. The increasingly detailed understanding that contemporary science has acquired relating to active transport, however, has yet to lead to the design and construction of artificial molecular motors capable of employing ratchet-driven motions that can also perform work against concentration gradients. Mechanically interlocked molecules (MIMs) in the form of pseudo- and semirotaxanes are showing some encouraging signs in meeting these goals. This review summarizes recent progress in making artificial molecular motors that can perform work by "pumping" tetracationic rings into high-energy states. The launching pad is a bistable [2]rotaxane whose dumbbell component contains two electron-donating recognition sites, one, a tetrathiafulvalene (TTF) unit, which interacts more strongly with the ring component, cyclobis(paraquat-p-phenylene) (CBPQT(4+)), containing two electron-accepting bipyridinium units, than does the other 1,5-dioxynaphthalene (DNP) unit. Switching can be induced electrochemically by oxidizing the TTF unit to a TTF(•+) radical cation, whereupon Coulombic repulsion takes care of moving the ring to the DNP unit. Reduction of the radical cation resets the switch. Molecular switches operate at, or close to, equilibrium. Any work done during one switching event is undone during the reset. Molecular motors, on the

  13. Nonequilibrium diagrammatic technique for nanoscale devices

    NASA Astrophysics Data System (ADS)

    Zebrev, G. I.

    2006-05-01

    A general approach based on gauge invariance requirements has been developed for automatic construction of quantum kinetic equation in electron systems, far for equilibrium. Proposed theoretical scheme has high generality and automatism and capable to treat nonequilibrium effects of electron transport, quantum interference and energy dissipation. Dissipative and quantum-interference effects can be consequentially incorporated in the computational scheme through solution of dynamic Dyson equation for self-energies in the framework of conventional diagrammatic technique.

  14. Efficiency bounds for nonequilibrium heat engines

    SciTech Connect

    Mehta, Pankaj; Polkovnikov, Anatoli

    2013-05-15

    We analyze the efficiency of thermal engines (either quantum or classical) working with a single heat reservoir like an atmosphere. The engine first gets an energy intake, which can be done in an arbitrary nonequilibrium way e.g. combustion of fuel. Then the engine performs the work and returns to the initial state. We distinguish two general classes of engines where the working body first equilibrates within itself and then performs the work (ergodic engine) or when it performs the work before equilibrating (non-ergodic engine). We show that in both cases the second law of thermodynamics limits their efficiency. For ergodic engines we find a rigorous upper bound for the efficiency, which is strictly smaller than the equivalent Carnot efficiency. I.e. the Carnot efficiency can be never achieved in single reservoir heat engines. For non-ergodic engines the efficiency can be higher and can exceed the equilibrium Carnot bound. By extending the fundamental thermodynamic relation to nonequilibrium processes, we find a rigorous thermodynamic bound for the efficiency of both ergodic and non-ergodic engines and show that it is given by the relative entropy of the nonequilibrium and initial equilibrium distributions. These results suggest a new general strategy for designing more efficient engines. We illustrate our ideas by using simple examples. -- Highlights: ► Derived efficiency bounds for heat engines working with a single reservoir. ► Analyzed both ergodic and non-ergodic engines. ► Showed that non-ergodic engines can be more efficient. ► Extended fundamental thermodynamic relation to arbitrary nonequilibrium processes.

  15. Nonequilibrium self-energy functional theory

    NASA Astrophysics Data System (ADS)

    Hofmann, Felix; Eckstein, Martin; Arrigoni, Enrico; Potthoff, Michael

    2013-10-01

    The self-energy functional theory (SFT) is generalized to describe the real-time dynamics of correlated lattice-fermion models far from thermal equilibrium. This is achieved by starting from a reformulation of the original equilibrium theory in terms of double-time Green's functions on the Keldysh-Matsubara contour. With the help of a generalized Luttinger-Ward functional, we construct a functional Ω̂[Σ] which is stationary at the physical (nonequilibrium) self-energy Σ and which yields the grand potential of the initial thermal state Ω at the physical point. Nonperturbative approximations can be defined by specifying a reference system that serves to generate trial self-energies. These self-energies are varied by varying the reference system's one-particle parameters on the Keldysh-Matsubara contour. In the case of thermal equilibrium, this approach reduces to the conventional SFT. Contrary to the equilibrium theory, however, “unphysical” variations, i.e., variations that are different on the upper and the lower branches of the Keldysh contour, must be considered to fix the time dependence of the optimal physical parameters via the variational principle. Functional derivatives in the nonequilibrium SFT Euler equation are carried out analytically to derive conditional equations for the variational parameters that are accessible to a numerical evaluation via a time-propagation scheme. Approximations constructed by means of the nonequilibrium SFT are shown to be inherently causal, internally consistent, and to respect macroscopic conservation laws resulting from gauge symmetries of the Hamiltonian. This comprises the nonequilibrium dynamical mean-field theory but also dynamical-impurity and variational-cluster approximations that are specified by reference systems with a finite number of degrees of freedom. In this way, nonperturbative and consistent approximations can be set up, the numerical evaluation of which is accessible to an exact

  16. Effective equilibrium theory of nonequilibrium quantum transport

    SciTech Connect

    Dutt, Prasenjit; Koch, Jens; Han, Jong; Le Hur, Karyn

    2011-12-15

    The theoretical description of strongly correlated quantum systems out of equilibrium presents several challenges and a number of open questions persist. Here, we focus on nonlinear electronic transport through an interacting quantum dot maintained at finite bias using a concept introduced by Hershfield [S. Hershfield, Phys. Rev. Lett. 70 2134 (1993)] whereby one can express such nonequilibrium quantum impurity models in terms of the system's Lippmann-Schwinger operators. These scattering operators allow one to reformulate the nonequilibrium problem as an effective equilibrium problem associated with a modified Hamiltonian. In this paper, we provide a pedagogical analysis of the core concepts of the effective equilibrium theory. First, we demonstrate the equivalence between observables computed using the Schwinger-Keldysh framework and the effective equilibrium approach, and relate Green's functions in the two theoretical frameworks. Second, we expound some applications of this method in the context of interacting quantum impurity models. We introduce a novel framework to treat effects of interactions perturbatively while capturing the entire dependence on the bias voltage. For the sake of concreteness, we employ the Anderson model as a prototype for this scheme. Working at the particle-hole symmetric point, we investigate the fate of the Abrikosov-Suhl resonance as a function of bias voltage and magnetic field. - Highlights: > Reformulation of steady-state nonequilibrium quantum transport, following Hershfield. > Derivation of effective equilibrium density operator using the 'open-system' approach. > Equivalence with the Keldysh description and formulas relating the two approaches. > Novel framework to treat interactions perturbatively. > Application to nonequilibrium Anderson model and fate of Abrikosov-Suhl resonance.

  17. Nonequilibrium invariant measure under heat flow.

    PubMed

    Delfini, Luca; Lepri, Stefano; Livi, Roberto; Politi, Antonio

    2008-09-19

    We provide an explicit representation of the nonequilibrium invariant measure for a chain of harmonic oscillators with conservative noise in the presence of stationary heat flow. By first determining the covariance matrix, we are able to express the measure as the product of Gaussian distributions aligned along some collective modes that are spatially localized with power-law tails. Numerical studies show that such a representation applies also to a purely deterministic model, the quartic Fermi-Pasta-Ulam chain.

  18. Nonequilibrium quantum dynamics in optomechanical systems

    NASA Astrophysics Data System (ADS)

    Patil, Yogesh Sharad; Cheung, Hil F. H.; Shaffer, Airlia; Wang, Ke; Vengalattore, Mukund

    2016-05-01

    The thermalization dynamics of isolated quantum systems has so far been explored in the context of cold atomic systems containing a large number of particles and modes. Quantum optomechanical systems offer prospects of studying such dynamics in a qualitatively different regime - with few individually addressable modes amenable to continuous quantum measurement and thermalization times that vastly exceed those observed in cold atomic systems. We have experimentally realized a dynamical continuous phase transition in a quantum compatible nondegenerate mechanical parametric oscillator. This system is formally equivalent to the optical parametric amplifiers whose dynamics have been a subject of intense theoretical study. We experimentally verify its phase diagram and observe nonequilibrium behavior that was only theorized, but never directly observed, in the context of optical parametric amplifiers. We discuss prospects of using nonequilibrium protocols such as quenches in optomechanical systems to amplify weak nonclassical correlations and to realize macroscopic nonclassical states. This work was supported by the DARPA QuASAR program through a Grant from the ARO and the ARO MURI on non-equilibrium manybody dynamics.

  19. Separation of Spin and Charge Currents in a Superconductor

    NASA Astrophysics Data System (ADS)

    Hershfield, Selman

    1998-03-01

    Injecting electrons from a ferromagnet to a superconductor creates a nonequilibrium spin density. This is the spin analog to the well studied charge imbalance problem in superconductor-normal-metal tunnel junctions. We calculate the charge and spin imbalance in a unified manner.(Hui Lin Zhao and Selman Hershfield, Phys. Rev. B) 52, 3632 (1995). If one measures the charge and spin imbalance with a ferromagnetic voltage probe which has two possible spin configurations, 1 and 2, then the sum of the two voltages, V1 and V_2, measures the nonequilibrium charge density and the difference of the two voltages, V1 - V_2, measures the nonequilibrium spin density. One can use this technique to see the spatial separation of spin and charge currents in a superconductor: In a superconductor the charge current is carried by the condensate within a penetration length of the surface, and the spin current, which is carried by the the quasiparticles, can exist in the bulk. By placing a detection voltage probe within a few spin diffusion lengths of the injected electrons, but much further than the penetration length, one can see a nonequilibrium magnetization (and magnetic current) with no electrical current. We discuss the different spin relaxation rates and present explicit calculations of the spatial dependence of the spin and charge currents.

  20. 49 CFR 375.401 - Must I estimate charges?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Transportation Other Regulations Relating to Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS TRANSPORTATION OF HOUSEHOLD GOODS IN INTERSTATE COMMERCE; CONSUMER PROTECTION REGULATIONS Estimating Charges § 375.401 Must...

  1. 49 CFR 375.401 - Must I estimate charges?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Transportation Other Regulations Relating to Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS TRANSPORTATION OF HOUSEHOLD GOODS IN INTERSTATE COMMERCE; CONSUMER PROTECTION REGULATIONS Estimating Charges § 375.401 Must...

  2. Impact of nonequilibrium particle temperature considerations on seeded coal combustion plasma properties. Quarterly report, quarter No. 12, July 1, 1993--September 30, 1993

    SciTech Connect

    Oni, A.A.

    1995-04-01

    The first of the three tasks of this research activity is to develop a model that represents steady, nonequilibrium energy interactions between post-combustion entrained particles and carrier gases, under typical coal-fired MHD operating conditions. The second task is to use the developed model to evaluate, for both the MHD linear channel and disk configurations, the impact of nonequilibrium particle temperatures on predicted gasdynamic and electrical property values that depend, at times critically, on plasma temperatures, and on which the overall MHD system performance depends. The third task is to evaluate the relative impact of gas-particle temperature differences on generator slag phenomena and consequently on MHD channel performance.

  3. PREFACE: Progress in Nonequilibrium Green's Functions IV

    NASA Astrophysics Data System (ADS)

    Bonitz, Michael; Balzer, Karsten

    2010-04-01

    This is the fourth volume1 of articles on the theory of Nonequilibrium Green's functions (NEGF) and their modern application in various fields such as plasma physics, semiconductor physics, molecular electronics and high energy physics. It contains 23 articles written by experts in many-body theory and quantum transport who summarize recent progress in their respective area of research. The articles are based on talks given at the interdisciplinary conference Progress in Nonequilibrium Green's functions IV which was held 17-21 August 2009 at the University of Glasgow, Scotland. This conference continues the tradition of the previous meetings which started in 1999 and which aimed at an informal exchange across field boundaries. The previous meetings and the earlier proceedings proved to be very stimulating not only for young researchers but also for experienced scientists, and we are convinced that this fourth volume will be as successful as the previous ones. As before, this volume includes only extended review-type papers which are written in a way that they are understandable to a broad interdisciplinary audience. All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administrated by the Editors assuring highest scientific standards. In the review process some papers were substantially revised and improved and some were rejected. This conference would not have been possible without the remarkable work of the local organizing team around John Barker and Scott Roy and the generous financial support from the University of Glasgow and the Deutsche Forschungsgemeinschaft via SFB-Transregio 24. Michael Bonitz and Karsten Balzer Kiel, February 2010 1 The first two volumes are Progress in Nonequilibrium Green's functions, M Bonitz (ed) and Progress in Nonequilibrium Green's functions II, M Bonitz and D Semkat (eds), which were published by World Scientific (Singapore), in 2000 and 2003, respectively (ISBN

  4. 48 CFR 52.247-38 - F.o.b. Inland Carrier, Point of Exportation.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... absence of specifications, prepare the shipment for ocean transportation in conformance with carrier requirements to protect the goods and to ensure assessment of the lowest applicable transportation charge;...

  5. Long-lived non-equilibrium states in a quantum-Hall Tomonaga-Luttinger liquid

    NASA Astrophysics Data System (ADS)

    Fujisawa, Toshimasa; Washio, Kazuhisa; Nakazawa, Ryo; Hashisaka, Masayuki; Muraki, Koji; Tokura, Yasuhiro

    The existence of long-lived non-equilibrium states without showing thermalization, which has previously been demonstrated in time evolution of ultracold atoms (quantum quench), suggests the possibility of their spatial analogue in transport behavior of interacting electrons in solid-state systems. Here we report long-lived non-equilibrium states in one-dimensional edge channels in the integer quantum Hall regime. For this purpose, non-trivial binary spectrum composed of hot and cold carriers is prepared by an indirect heating scheme using weakly coupled counterpropagating edge channels in an AlGaAs/GaAs heterostructure. Quantum dot spectroscopy clearly reveals that the carriers with the non-trivial binary spectrum propagate over a long distance (5 - 10 um), much longer than the length required for electronic relaxation (about 0.1 um), without thermalization into a trivial Fermi distribution. This observation is consistent with the integrable model of Tomonaga-Luttinger liquid. The long-lived spectrum implies that the system is well described by non-interacting plasmons, which are attractive for carrying information for a long distance. This work was supported by the JSPS 26247051 and 15H05854, and Nanotechnology Platform Program of MEXT.

  6. Nonequilibrium Bose-Einstein condensation of hot magnons

    SciTech Connect

    Vannucchi, Fabio Stucchi; Vasconcellos, Aurea Rosas; Luzzi, Roberto

    2010-10-01

    We present an analysis of the emergence of a nonequilibrium Bose-Einstein-type condensation of magnons in radio-frequency pumped magnetic thin films, which has recently been experimentally observed. A complete description of all the nonequilibrium processes involved is given. It is demonstrated that the phenomenon is another example of the emergence of Bose-Einstein-type condensation in nonequilibrium many-boson systems embedded in a thermal bath, a phenomenon evidenced decades ago by the renowned late Herbert Froehlich.

  7. Nonequilibrium Phase Chemistry in High Temperature Structure Alloys

    NASA Technical Reports Server (NTRS)

    Wang, R.

    1991-01-01

    Titanium and nickel aluminides of nonequilibrium microstructures and in thin gauge thickness were identified, characterized and produced for potential high temperature applications. A high rate sputter deposition technique for rapid surveillance of the microstructures and nonequilibrium phase is demonstrated. Alloys with specific compositions were synthesized with extended solid solutions, stable dispersoids, and specific phase boundaries associated with different heat treatments. Phase stability and mechanical behavior of these nonequilibrium alloys were investigated and compared.

  8. Free carrier absorption in self-activated PbWO4 and Ce-doped Y3(Al0.25Ga0.75)3O12 and Gd3Al2Ga3O12 garnet scintillators

    NASA Astrophysics Data System (ADS)

    Auffray, E.; Korjik, M.; Lucchini, M. T.; Nargelas, S.; Sidletskiy, O.; Tamulaitis, G.; Tratsiak, Y.; Vaitkevičius, A.

    2016-08-01

    Nonequilibrium carrier dynamics in the scintillators prospective for fast timing in high energy physics and medical imaging applications was studied. The time-resolved free carrier absorption investigation was carried out to study the dynamics of nonequilibrium carriers in wide-band-gap scintillation materials: self-activated led tungstate (PbWO4, PWO) ant two garnet crystals, GAGG:Ce and YAGG:Ce. It was shown that free electrons appear in the conduction band of PWO and YAGG:Ce crystals within a sub-picosecond time scale, while the free holes in GAGG:Ce appear due to delocalization from Gd3+ ground states to the valence band within a few picoseconds after short-pulse excitation. The influence of Gd ions on the nonequilibrium carrier dynamics is discussed on the base of comparison the results of the free carrier absorption in GAGG:Ce containing gadolinium and in YAGG without Gd in the host lattice.

  9. Slowing hot-carrier relaxation in graphene using a magnetic field

    NASA Astrophysics Data System (ADS)

    Plochocka, P.; Kossacki, P.; Golnik, A.; Kazimierczuk, T.; Berger, C.; de Heer, W. A.; Potemski, M.

    2009-12-01

    A degenerate pump-probe technique is used to investigate the nonequilibrium carrier dynamics in multilayer graphene. Two distinctly different dynamics of the carrier relaxation are observed. A fast relaxation (˜50fs) of the carriers after the initial effect of phase-space filling followed by a slower relaxation (˜4ps) due to thermalization. Both relaxation processes are less efficient when a magnetic field is applied at low temperatures which is attributed to the suppression of the electron-electron Auger scattering due to the nonequidistant Landau-level spacing of the Dirac fermions in graphene.

  10. Non-equilibrium diffusion combustion of a fuel droplet

    NASA Astrophysics Data System (ADS)

    Tyurenkova, Veronika V.

    2012-06-01

    A mathematical model for the non-equilibrium combustion of droplets in rocket engines is developed. This model allows to determine the divergence of combustion rate for the equilibrium and non-equilibrium model. Criterion for droplet combustion deviation from equilibrium is introduced. It grows decreasing droplet radius, accommodation coefficient, temperature and decreases on decreasing diffusion coefficient. Also divergence from equilibrium increases on reduction of droplet radius. Droplet burning time essentially increases under non-equilibrium conditions. Comparison of theoretical and experimental data shows that to have adequate solution for small droplets it is necessary to use the non-equilibrium model.

  11. Fork truck battery charging system

    SciTech Connect

    Ducharme, R.L.; Taylor, R.

    1983-11-01

    A battery charging system includes a highrise storage rack system for holding a plurality of battery chargers and defining a plurality of battery locations. Each battery to be charged is placed on a pallet which has a connection block with a cable connectable to the battery and a male connector. A load carrier carries the pallet and the battery to a selected battery location in the rack and deposits it thereat in a charging position, thereby connecting the male connector to a female connector on the rack connected to one of the chargers. The load carrier also retrieves charged batteries on their pallets from the rack, the retrieval motion effecting disconnection of the pallet from the charger. Each pallet has a fluid receiving trough provided with a drain which cooperates with fluid inlets of a fluid collection system on the rack for collecting fluids emitted during the charging process.

  12. Non-equilibrium Dynamics of DNA Nanotubes

    NASA Astrophysics Data System (ADS)

    Hariadi, Rizal Fajar

    Can the fundamental processes that underlie molecular biology be understood and simulated by DNA nanotechnology? The early development of DNA nanotechnology by Ned Seeman was driven by the desire to find a solution to the protein crystallization problem. Much of the later development of the field was also driven by envisioned applications in computing and nanofabrication. While the DNA nanotechnology community has assembled a versatile tool kit with which DNA nanostructures of considerable complexity can be assembled, the application of this tool kit to other areas of science and technology is still in its infancy. This dissertation reports on the construction of non-equilibrium DNA nanotube dynamic to probe molecular processes in the areas of hydrodynamics and cytoskeletal behavior. As the first example, we used DNA nanotubes as a molecular probe for elongational flow measurement in different micro-scale flow settings. The hydrodynamic flow in the vicinity of simple geometrical objects, such as a rigid DNA nanotube, is amenable to rigorous theoretical investigation. We measured the distribution of elongational flows produced in progressively more complex settings, ranging from the vicinity of an orifice in a microfluidic chamber to within a bursting bubble of Pacific ocean water. This information can be used to constrain theories on the origin of life in which replication involves a hydrodynamically driven fission process, such as the coacervate fission proposed by Oparin. A second theme of this dissertation is the bottom-up construction of a de novo artificial cytoskeleton with DNA nanotubes. The work reported here encompasses structural, locomotion, and control aspects of non-equilibrium cytoskeletal behavior. We first measured the kinetic parameters of DNA nanotube assembly and tested the accuracy of the existing polymerization models in the literature. Toward recapitulation of non-equilibrium cytoskeletal dynamics, we coupled the polymerization of DNA

  13. Nonequilibrium Kinetics of Rydberg Atomic States

    SciTech Connect

    Bureyeva, L. A.; Kadomtsev, M. B.; Levashova, M. G.; Lisitsa, V. S.

    2008-10-22

    Two-dimensional quasi-classical model of the radiative-collisional cascade for hydrogen-like systems is developed. The model establishes the correspondence between the quantum and classical approaches. Our calculations of the two-dimensional populations of highly excited atomic hydrogen states for three-body and photorecombination sources of population allow the data of one-dimensional kinetic models to be refined. The calculated intensities of recombination lines demonstrate the degree of nonequilibrium of the Rydberg state populations under typical astrophysical plasma conditions.

  14. Adaptive Implicit Non-Equilibrium Radiation Diffusion

    SciTech Connect

    Philip, Bobby; Wang, Zhen; Berrill, Mark A; Rodriguez Rodriguez, Manuel; Pernice, Michael

    2013-01-01

    We describe methods for accurate and efficient long term time integra- tion of non-equilibrium radiation diffusion systems: implicit time integration for effi- cient long term time integration of stiff multiphysics systems, local control theory based step size control to minimize the required global number of time steps while control- ling accuracy, dynamic 3D adaptive mesh refinement (AMR) to minimize memory and computational costs, Jacobian Free Newton-Krylov methods on AMR grids for efficient nonlinear solution, and optimal multilevel preconditioner components that provide level independent solver convergence.

  15. Non-equilibrium processes in interstellar molecules

    NASA Technical Reports Server (NTRS)

    Strelnitskiy, V. S.

    1979-01-01

    The types of nonequilibrium emission and absorption by interstellar molecules are summarized. The observed brightness emission temperatures of compact OH and H2O sources are discussed using the concept of maser amplification. A single thermodynamic approach was used in which masers and anti-masers are considered as heat engines for the theoretical interpretation of the cosmic maser and anti-maser phenomena. The requirements for different models of pumping are formulated and a classification is suggested for the mechanisms of pumping, according to the source and discharge of energy.

  16. Conserved moments in nonequilibrium field dynamics

    SciTech Connect

    Mineev-Weinstein, M.B.; Alexander, F.J.

    1995-06-01

    We demonstrate with the example of Cahn-Hilliard dynamics that the macroscopic kinetics of first-order phase transitions exhibits an infinite number of constants of motion. Moreover, this results holds in any space dimension for a broad class of nonequilibrium processes whose macroscopic behavior is governed by equations of the form {partial_derivative}{phi}/{partial_derivative}t = LW({phi}), where {phi} is an {open_quotes}order parameter,{close_quotes} W is an arbitrary function of {phi}, and L is a linear Hermitian operator. We speculate on the implications of this result.

  17. Non-Equilibrium Transitions of Heliospheric plasma

    NASA Astrophysics Data System (ADS)

    Livadiotis, G.; McComas, D. J.

    2011-12-01

    Recent advances in Space Physics theory have established the connection between non-extensive Statistical Mechanics and space plasmas by providing a theoretical basis for the empirically derived kappa distributions commonly used to describe the phase space distribution functions of these systems [1]. The non-equilibrium temperature and the kappa index that govern these distributions are the two independent controlling parameters of non-equilibrium systems [1-3]. The significance of the kappa index is primarily given by its role in identifying the non-equilibrium stationary states, and measuring their "thermodynamic distance" from thermal equilibrium [4], while its physical meaning is connected to the correlation between the system's particles [5]. For example, analysis of the IBEX high Energetic Neutral Atom spectra [6] showed that the vast majority of measured kappa indices are between ~1.5 and ~2.5, consistent with the far-equilibrium "cavity" of minimum entropy discovered by Livadiotis & McComas [2]. Spontaneous procedures that can increase the entropy, move the system gradually toward equilibrium, that is the state with the maximum (infinite) kappa index. Other external factors that may decrease the entropy, move the system back to states further from equilibrium where the kappa indices are smaller. Newly formed pick-up ions can play this critical role in the solar wind and other space plasmas. We have analytically shown that their highly ordered motion can reduce the average entropy in the plasma beyond the termination shock, inside the inner heliosheath [7]. Non-equilibrium transitions have a key role in understanding the governing thermodynamical processes of space plasmas. References 1. Livadiotis, G., & McComas, D. J. 2009, JGR, 114, 11105. 2. Livadiotis, G., & McComas, D. J. 2010a, ApJ, 714, 971. 3. Livadiotis, G., & McComas, D. J. 2010c, in AIP Conf. Proc. 9, Pickup Ions Throughout the Heliosphere and Beyond, ed. J. LeRoux, V. Florinski, G. P. Zank, & A

  18. Nonequilibrium Interlayer Transport in Pulsed Laser Deposition

    SciTech Connect

    Tischler, Jonathan Zachary; Eres, Gyula; Larson, Ben C; Rouleau, Christopher M; Zschack, P.; Lowndes, Douglas H

    2006-01-01

    We use time-resolved surface x-ray diffraction measurements with microsecond range resolution to study the growth kinetics of pulsed laser deposited SrTiO3. Time-dependent surface coverages corresponding to single laser shots were determined directly from crystal truncation rod intensity transients. Analysis of surface coverage evolution shows that extremely fast nonequilibrium interlayer transport, which occurs concurrently with the arrival of the laser plume, dominates the deposition process. A much smaller fraction of material, which is governed by the dwell time between successive laser shots, is transferred by slow, thermally driven interlayer transport processes.

  19. Nonlinear and nonequilibrium dynamics in geomaterials.

    PubMed

    TenCate, James A; Pasqualini, Donatella; Habib, Salman; Heitmann, Katrin; Higdon, David; Johnson, Paul A

    2004-08-01

    The transition from linear to nonlinear dynamical elasticity in rocks is of considerable interest in seismic wave propagation as well as in understanding the basic dynamical processes in consolidated granular materials. We have carried out a careful experimental investigation of this transition for Berea and Fontainebleau sandstones. Below a well-characterized strain, the materials behave linearly, transitioning beyond that point to a nonlinear behavior which can be accurately captured by a simple macroscopic dynamical model. At even higher strains, effects due to a driven nonequilibrium state, and relaxation from it, complicate the characterization of the nonlinear behavior.

  20. Non-equilibrium slave bosons approach to quantum pumping in interacting quantum dots

    NASA Astrophysics Data System (ADS)

    Citro, Roberta; Romeo, Francesco

    2016-03-01

    We review a time-dependent slave bosons approach within the non-equilibrium Green's function technique to analyze the charge and spin pumping in a strongly interacting quantum dot. We study the pumped current as a function of the pumping phase and of the dot energy level and show that a parasitic current arises, beyond the pure pumping one, as an effect of the dynamical constraints. We finally illustrate an all-electrical mean for spin-pumping and discuss its relevance for spintronics applications.